Debugging with GDB Manual
The GNU Source-Level Debugger
HP Part Number: 5992-4701
Published: February 2009
Edition: 19
Table of Contents
Summary of GDB........................................................................................................................15
1 A Sample GDB Session.............................................................................................................19
2 Getting In and Out of GDB.......................................................................................................25
3 GDB Commands......................................................................................................................33
4 Running Programs Under GDB...................................................................................................39
Table of Contents
3
5 Stopping and Continuing..........................................................................................................51
6 Examining the Stack.................................................................................................................71
7 Examining Source Files.............................................................................................................77
8 Examining Data.......................................................................................................................83
4
Table of Contents
9 Using GDB with Different Languages........................................................................................101
10 Examining the Symbol Table..................................................................................................115
11 Altering Execution.................................................................................................................119
12 GDB Files.............................................................................................................................125
Table of Contents
5
14.10.10.2 info heap arena...............................................................................179
14.10.10.4 info moduleADDRESS.....................................................................179
14.10.10.5 info heap process..........................................................................179
14.11.6 Thread Debugging in +checkMode..............................................................193
Table of Contents
7
14.25.3 Support for _ _fpregdata type on IPF.........................................................222
14.29.1.1 +O0and +O1............................................................................................229
14.29.1.2 +O2/+O3/+O4/-ipo..............................................................................229
14.31.6 Changing the size of the source or debugger pane.........................................236
14.32 Support for ddd.......................................................................................................238
14.33.1 stop in/at dbxcommands........................................................................238
Table of Contents
9
17 Controlling GDB...................................................................................................................281
18 Canned Sequences of Commands..........................................................................................287
19 Using GDB under gnu Emacs.................................................................................................293
20 GDB Annotations.................................................................................................................297
Table of Contents
11
21 The GDB/MI Interface...........................................................................................................307
21.1 GDB/MICommand Syntax........................................................................................307
21.1.1 GDB/MIInput syntax.........................................................................................307
21.1.2 GDB/MIOutput syntax......................................................................................308
21.1.3 Simple examples of GDB/MIinteraction...........................................................310
21.2 GDB/MIcompatibility with CLI................................................................................310
21.3 GDB/MIoutput records.............................................................................................311
21.3.1 GDB/MIresult records.......................................................................................311
21.3.2 GDB/MIstream records.....................................................................................311
21.3.3 GDB/MIout-of-band records.............................................................................311
21.4 GDB/MIcommand description format......................................................................311
21.5 GDB/MIbreakpoint table commands........................................................................312
21.6 GDB/MIData manipulation.......................................................................................320
21.7 GDB/MIprogram control...........................................................................................330
21.8 Miscellaneous GDB commands in GDB/MI..............................................................339
21.9 GDB/MIStack Manipulation Commands..................................................................341
21.10 GDB/MISymbol query commands..........................................................................346
21.11 GDB/MITarget Manipulation Commands..............................................................349
21.12 GDB/MIthread commands......................................................................................353
21.13 GDB/MItracepoint commands................................................................................355
21.14 GDB/MIvariable objects..........................................................................................355
22 Reporting Bugs in GDB.........................................................................................................361
A Installing GDB.......................................................................................................................365
A.3 configureoptions...................................................................................................368
12
Table of Contents
List of Tables
16-10 Breakpoint creation commands.................................................................................261
16-11 Overall breakpoint commands..................................................................................262
16-12 Global breakpoint commands...................................................................................263
16-13 Macro facility commands..........................................................................................265
16-14 Signal control commands..........................................................................................265
16-15 Miscellaneous commands.........................................................................................265
16-16 Data format commands.............................................................................................266
16-17 Macro facility commands..........................................................................................268
16-18 Special language operators........................................................................................269
16-19 Special variables........................................................................................................269
16-20 Variable Identifiers....................................................................................................270
16-23 C through D...............................................................................................................272
16-24 F through K...............................................................................................................273
16-26 M through P..............................................................................................................274
16-27 Q through S...............................................................................................................275
16-29 U through Z...............................................................................................................276
21-1 GDB/MI Operations...................................................................................................356
13
Summary of GDB
The purpose of a debugger such as GDB is to allow you to see what is going on “inside”
another program while it executes―or what another program was doing at the moment
it crashed.
GDB allows you to do the following:
•
•
•
•
Load the executable along with any required arguments.
Stop your program on specified blocks of code.
Examine your program when it has stopped running due to an error.
Change things in your program, so you can experiment with correcting the effects
of one bug and go on to learn about another.
You can use GDB to debug programs written in C, C++, and Fortran. For more
GDB can be used to debug programs written in Fortran, although it may be necessary
This version of the manual documents WDB, implemented on HP 9000 or HP Integrity
systems running Release 11.x of the HP-UX operating system. WDB can be used to
debug code generated by the HP ANSI C, HP ANSI aC++ and HP Fortran compilers
as well as the GNUC and C++ compilers. It does not support the debugging of Pascal,
Modula-2 or Chill programs.
Free Software
GDB is free software, protected by the GNUGeneral Public License (GPL). The GPL gives
you the freedom to copy or adapt a licensed program―but every person getting a copy
also gets with it the freedom to modify that copy (which means that they must get
access to the source code), and the freedom to distribute further copies. Typical software
companies use copyrights to limit your freedoms; the Free Software Foundation uses
the GPL to preserve these freedoms.
Fundamentally, the General Public License is a license which says that you have these
freedoms and that you cannot take these freedoms away from anyone else.
Contributors to GDB
Richard Stallman was the original author of GDB, and of many other GNUprograms.
Many others have contributed to its development. This section attempts to credit major
contributors. One of the virtues of free software is that everyone is free to contribute
to it; with regret, we cannot actually acknowledge everyone here. The file 'ChangeLog'
in the GDB distribution approximates a blow-by-blow account.
Changes much prior to version 2.0 are lost in the mists of time.
Free Software
15
Plea: Additions to this section are particularly welcome. If you or your friends (or
enemies, to be evenhanded) have been unfairly omitted from this list, we would like
to add your names!
So that they may not regard their many labors as thankless, we particularly thank those
who shepherded GDB through major releases: Andrew Cagney (release 5.0); Jim Blandy
(release 4.18); Jason Molenda (release 4.17); Stan Shebs (release 4.14); Fred Fish (releases
4.16, 4.15, 4.13, 4.12, 4.11, 4.10, and 4.9); Stu Grossman and John Gilmore (releases 4.8,
4.7, 4.6, 4.5, and 4.4); John Gilmore (releases 4.3, 4.2, 4.1, 4.0, and 3.9); Jim Kingdon
(releases 3.5, 3.4, and 3.3); and Randy Smith (releases 3.2, 3.1, and 3.0).
Richard Stallman, assisted at various times by Peter TerMaat, Chris Hanson, and Richard
Mlynarik, handled releases through 2.8.
Michael Tiemann is the author of most of the GNUC++ support in GDB, with significant
additional contributions from Per Bothner. James Clark wrote the GNUC++ demangler.
Early work on C++ was by Peter TerMaat (who also did much general update work
leading to release 3.0).
GDB 4 uses the BFD subroutine library to examine multiple object-file formats; BFD
was a joint project of David V. Henkel-Wallace, Rich Pixley, Steve Chamberlain, and
John Gilmore.
David Johnson wrote the original COFF support; Pace Willison did the original support
for encapsulated COFF.
Brent Benson of Harris Computer Systems contributed DWARF 2 support.
Adam de Boor and Bradley Davis contributed the ISI Optimum V support. Per Bothner,
Noboyuki Hikichi, and Alessandro Forin contributed MIPS support. Jean-Daniel Fekete
contributed Sun 386i support. Chris Hanson improved the HP 9000 support. Noboyuki
Hikichi and Tomoyuki Hasei contributed Sony/News OS 3 support. David Johnson
contributed Encore Umax support. Jyrki Kuoppala contributed Altos 3068 support. Jeff
Law contributed HP PA and SOM support. Keith Packard contributed NS32K support.
Doug Rabson contributed Acorn Risc Machine support. Bob Rusk contributed Harris
Nighthawk CX-UX support. Chris Smith contributed Convex support (and Fortran
debugging). Jonathan Stone contributed Pyramid support. Michael Tiemann contributed
SPARC support. Tim Tucker contributed support for the Gould NP1 and Gould
Powernode. Pace Willison contributed Intel 386 support. Jay Vosburgh contributed
Symmetry support.
Andreas Schwab contributed M68K Linux support.
Rich Schaefer and Peter Schauer helped with support of SunOS shared libraries.
Jay Fenlason and Roland McGrath ensured that GDB and GAS agree about several
machine instruction sets.
Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped develop remote
debugging. Intel Corporation, Wind River Systems, AMD, and ARM contributed remote
debugging modules for the i960, VxWorks, A29K UDI, and RDI targets, respectively.
16
Brian Fox is the author of the readline libraries providing command-line editing and
command history.
Andrew Beers of SUNY Buffalo wrote the language-switching code, the Modula-2
support, and contributed the Languages chapter of this manual.
Fred Fish wrote most of the support for Unix System Vr4. He also enhanced the
command-completion support to cover C++ overloaded symbols.
Hitachi America, Ltd. sponsored the support for H8/300, H8/500, and Super-H
processors.
NEC sponsored the support for the v850, Vr4xxx, and Vr5xxx processors.
Mitsubishi sponsored the support for D10V, D30V, and M32R/D processors.
Toshiba sponsored the support for the TX39 Mips processor.
Matsushita sponsored the support for the MN10200 and MN10300 processors.
Fujitsu sponsored the support for SPARClite and FR30 processors.
Kung Hsu, Je Law, and Rick Sladkey added support for hardware watchpoints.
Michael Snyder added support for tracepoints.
Stu Grossman wrote gdbserver.
Jim Kingdon, Peter Schauer, Ian Taylor, and Stu Grossman made nearly innumerable
bug fixes and cleanups throughout GDB.
The following people at the Hewlett-Packard Company contributed support for the
PA-RISC 2.0 architecture, HP-UX 10.20, 10.30, and 11.x (narrow mode), HP's
implementation of kernel threads, HP's aC++ compiler, and the terminal user interface:
Ben Krepp, Richard Title, John Bishop, Susan Macchia, Kathy Mann, Satish Pai, India
Paul, Steve Rehrauer, and Elena Zannoni. Kim Haase, Rosario de la Torre, Alex McKale,
Michael Coulter, Carl Burch, Bharath Chndramohan, Diwakar Nag, Muthuswami,
Dennis Handly, Subash Babu and Dipshikha Basu provided HP-specific information
in this manual.
Cygnus Solutions has sponsored GDB maintenance and much of its development since
1991. Cygnus engineers who have worked on GDB full time include Mark Alexander,
Jim Blandy, Per Bothner, Kevin Buettner, Edith Epstein, Chris Faylor, Fred Fish, Martin
Hunt, Jim Ingham, John Gilmore, Stu Grossman, Kung Hsu, Jim Kingdon, John Metzler,
Fernando Nasser, Georey Noer, Dawn Perchik, Rich Pixley, Zdenek Radouch, Keith
Seitz, Stan Shebs, David Taylor, and Elena Zannoni. In addition, Dave Brolley, Ian
Carmichael, Steve Chamberlain, Nick Clifton, JT Conklin, Stan Cox, DJ Delorie, Ulrich
Drepper, Frank Eigler, Doug Evans, Sean Fagan, David Henkel-Wallace, Richard
Henderson, Jeff Holcomb, Jeff Law, Jim Lemke, Tom Lord, Bob Manson, Michael
Meissner, Jason Merrill, Catherine Moore, Drew Moseley, Ken Raeburn, Gavin
Romig-Koch, Rob Savoye, Jamie Smith, Mike Stump, Ian Taylor, Angela Thomas,
Michael Tiemann, Tom Tromey, Ron Unrau, Jim Wilson, and David Zuhn have made
contributions both large and small.
Contributors to GDB
17
18
1 A Sample GDB Session
This chapter describes the most common GDB commands with the help of an example.
The following topics are discussed:
•
•
•
•
•
•
•
•
•
•
Loading the Executable
Setting the Display Width
Setting Breakpoints
Running the Executable under GDB
Stepping to the next line
Stepping into a Subroutine
Examining the Stack
Printing Variable Values
Listing the Source Code
Setting Variable Values During a Debug Session
In this sample session, we emphasize user input like this: input, to make it easier to
pick out from the surrounding output.
One of the preliminary versions of GNUm4(a generic macro processor) exhibits the
following bug: sometimes, when we change its quote strings from the default, the
commands used to capture one macro definition within another stop working. In the
following short m4session, we define a macro foowhich expands to 0000; we then
use the m4 built-indefnto define baras the same thing. However, when we
change the open quote string to <QUOTE>and the close quote string to <UNQUOTE>,
the same procedure fails to define a new synonym baz:
$ cd gnu/m4 //change your current directory to the location where the m4 executable is stored.
$ ./m4 //run the m4 application
define(foo,0000)
foo
0000
define (bar,defn('foo'))
bar
0000
changequote(<QUOTE>,<UNQUOTE>)
define(baz,defn(<QUOTE>foo<UNQUOTE>))
baz
C-d
m4: End of input: 0: fatal error: EOF in string
1.1 Loading the Executable
Let us use GDB to try to see what is going on.
1.1 Loading the Executable
19
$ (gdb) m4
HP gdb 3.0 for PA-RISC 1.1 or 2.0 (narrow), HP-UX 11.00.
Copyright 1986 - 2001 Free Software Foundation, Inc.
Hewlett-Packard Wildebeest 3.0 (based on GDB ) is covered by the
GNU General Public License. Type "show copying" to see the conditions to
change it and/or distribute copies. Type "show warranty" for warranty/support.
GDB reads only enough symbol data to know where to find the rest when needed; as
a result, the first prompt comes up very quickly.
1.2 Setting Display width
We now tell GDB to use a narrower display width than usual, so that examples fit in
this manual.
((gdb)) set width 70
We need to see how the m4 built-inchangequoteworks. Having looked at the
source, we know the relevant subroutine is m4_changequote, so we set a breakpoint
there with the GDB break command.
1.3 Setting Breakpoints
Here we describe how to set a breakpoint.
((gdb)) break m4 changequote
Breakpoint 1 at 0x62f4: file builtin.c, line 879.
1.4 Running the executable under GDB
Using the runcommand, we start m4under GDB control. As long as the control does
not reach the m4_changequotesubroutine, the program runs as usual.
((gdb)) run
Starting program: /work/Editorial/gdb/gnu/m4/m4
define(foo,0000)
foo
0000
To trigger the breakpoint, we call changequote. GDB suspends execution of m4,
displaying information about the context where it stops.
changequote(<QUOTE>,<UNQUOTE>)
Breakpoint 1, m4_changequote (argc=3, argv=0x33c70)
at builtin.c:879
879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]),argc,1,3))
1.5 Stepping to the next line in the source program
Now we use the command n(next) to advance execution to the next line of the current
function.
20
A Sample GDB Session
((gdb)) n
882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\
: nil,
1.6 Stepping into a subroutine
The set_quoteslooks like a promising subroutine. We can go into it by using the
command s(step) instead of next. stepgoes to the next line to be executed in any
subroutine, so it steps into set_quotes.
((gdb)) s
set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
at input.c:530
530 if (lquote != def_lquote)
1.7 Examining the Stack
The display that shows the subroutine where m4is now suspended (and its arguments)
is called a stack frame display. It shows a summary of the stack. We can use the
backtracecommand (which can also be spelled bt), to see where we are in the stack
as a whole: the backtracecommand displays a stack frame for each active subroutine.
((gdb)) bt
#0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
at input.c:530
#1 0x6344 in m4_changequote (argc=3, argv=0x33c70)
at builtin.c:882
#2 0x8174 in expand_macro (sym=0x33320) at macro.c:242
#3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30)
at macro.c:71
#4 0x79dc in expand_input () at macro.c:40
#5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195
We step through a few more lines to see what happens. The first two times, we can use
's'; the next two times we use nto avoid falling into the xstrdupsubroutine.
((gdb)) s
0x3b5c 532 if (rquote != def_rquote)
((gdb)) s
0x3b80 535 lquote = (lq == nil || *lq == '\0') ? \
def_lquote : xstrdup(lq);
((gdb)) n
536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
: xstrdup(rq);
((gdb)) n
538 len_lquote = strlen(rquote);
1.8 Printing Variable Values
The last line displayed looks a little odd in the listing above; we can examine the
variables lquoteand rquoteto see if they are in fact the new left and right quotes
we specified. We use the command p(print) to view their values.
1.6 Stepping into a subroutine
21
((gdb)) p lquote
$1 = 0x35d40 "<QUOTE>"
((gdb)) p rquote
$2 = 0x35d50 "<UNQUOTE>"
1.9 Listing Source Code
lquoteand rquoteare indeed the new left and right quotes. To look at some context,
we can display ten lines of source surrounding the current line with the l(list)
command.
((gdb)) l
533 xfree(rquote);
534
535 lquote = (lq == nil || *lq == '\0') ? def_lquote\
: xstrdup (lq);
536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
: xstrdup (rq);
537
538 len_lquote = strlen(rquote);
539 len_rquote = strlen(lquote);
540 }
541
542 void
Let us step past the two lines that set len_lquoteand len_rquote, and then examine
the values of those variables.
((gdb)) n
539 len_rquote = strlen(lquote);
((gdb)) n
540 }
((gdb)) p len_lquote
$3 = 9
((gdb)) p len_rquote
$4 = 7
1.10 Setting Variable Values During a Session
That certainly looks wrong, assuming len_lquoteand len_rquoteare meant to be
the lengths of lquoteand rquoterespectively. We can set them to better values using
the pcommand, since it can print the value of any expression―and that expression
can include subroutine calls and assignments.
((gdb)) p len_lquote=strlen(lquote)
$5 = 7
((gdb)) p len_rquote=strlen(rquote)
$6 = 9
Is that enough to fix the problem of using the new quotes with the m4 built-in
defn? We can allow m4to continue executing with the c(continue) command, and
then try the example that caused trouble initially:
22
A Sample GDB Session
((gdb)) c
Continuing.
define(baz,defn(<QUOTE>foo<UNQUOTE>))
baz
0000
Success! The new quotes now work just as well as the default ones. The problem seems
to have been just the two typos defining the wrong lengths. We allow m4to exit by
giving it an EOF as input:
C-d
Program exited normally.
The message `Program exited normally.' is from GDB; it indicates m4has finished
executing. We can end our GDB session with the GDB quitcommand.
((gdb)) quit
1.10 Setting Variable Values During a Session
23
24
2 Getting In and Out of GDB
This chapter discusses how to start GDB, and exit out of it. The essentials are:
•
•
type '(gdb)' to start GDB.
type quit or C-d to exit.
2.1 Invoking GDB
Invoke GDB by running the program (gdb). Once started, GDB reads commands from
the terminal until you tell it to exit.
You can also run (gdb) with a variety of arguments and options, to specify more of
your debugging environment at the outset.
The command-line options described here are designed to cover a variety of situations;
in some environments, some of these options may effectively be unavailable.
The most usual way to start GDB is with one argument, specifying an executable
program:
(gdb) program
You can also start with both an executable program and a core file specified:
(gdb) program core
You can, instead, specify a process ID as a second argument, if you want to debug a
running process:
(gdb) program 1234
would attach GDB to process 1234(unless you also have a file named '1234'; GDB
does check for a core file first).
Taking advantage of the second command-line argument requires a fairly complete
operating system; when you use GDB as a remote debugger attached to a bare board,
there may not be any notion of “process”, and there is often no way to get a core dump.
GDB will warn you if it is unable to attach or to read core dumps.
You can run (gdb) without printing the front material, which describes GDB's
non-warranty, by specifying -silent:
gdb -silent
You can further control how GDB starts up by using command-line options. GDB itself
can remind you of the options available.
Type
(gdb) -help
to display all available options and briefly describe their use ('(gdb)-h' is a shorter
equivalent).
2.1 Invoking GDB
25
All options and command-line arguments you give are processed in sequential order.
The order makes a difference when the `-x' option is used.
2.1.1 Choosing files
When GDB starts, it reads any arguments other than options as specifying an executable
file and core file (or process ID). This is the same as if the arguments were specified by
the '-se' and '-c' options respectively. (GDB reads the first argument that does not
have an associated option flag as equivalent to the '-se' option followed by that
argument; and the second argument that does not have an associated option flag, if
any, as equivalent to the '-c' option followed by that argument.)
If GDB has not been configured to included core file support, such as for most embedded
targets, then it will complain about a second argument and ignore it.
Many options have both long and short forms; both are shown in the following list.
GDB also recognizes the long forms if you truncate them, so long as enough of the
option is present to be unambiguous. (If you prefer, you can flag option arguments
with `--' rather than `-', though we illustrate the more usual convention.)
-symbols file
-s file
Read symbol table from file file.
-exec file
-e file
Use file file as the executable file to execute when
appropriate, and for examining pure data in
conjunction with a core dump.
-se file
Read symbol table from file file and use it as the
executable file.
-core file
-c file
Use file file as a core dump to examine.
-c number
Connect to process ID number, as with the attach
command (unless there is a file in core-dump format
named number, in which case `-c' specifies that file as
a core dump to read).
-command file
-x file
-directory directory
-d directory
Add directory to the path to search for source files.
26
Getting In and Out of GDB
-m, -mapped
Warning: this option depends on operating system facilities
that are not supported on all systems.
If memory-mapped files are available on your system
through the mmapsystem call, you can use this option
to have GDB write the symbols from your program
into a reusable file in the current directory. If the
program you are debugging is called '/tmp/fred', the
mapped symbol file is '/tmp/fred.syms'. Future GDB
debugging sessions notice the presence of this file, and
can quickly map in symbol information from it, rather
than reading the symbol table from the executable
program.
The '.syms' file is specific to the host machine where
GDB is run. It holds an exact image of the internal GDB
symbol table. It cannot be shared across multiple host
platforms.
-r, -readnow
Read each symbol file's entire symbol table
immediately, rather than the default, which is to read
it incrementally as it is needed. This makes startup
slower, but makes future operations faster.
You typically combine the -mappedand -readnowoptions in order to build a '.syms'
file that contains complete symbol information. (See “Commands to specify files”
but build a '.syms' file for future use is:
gdb -batch -nx -mapped -readnow programname
2.1.2 Choosing modes
You can run GDB in various alternative modes―for example, in batch mode or quiet
mode.
-nx, -n
Do not execute commands found in any initialization
files (normally called '.gdbinit', or 'gdb.ini' on PCs).
Normally, GDB executes the commands in these files
after all the command options and arguments have been
-quiet, -silent, -q
“Quiet”. Do not print the introductory and copyright
messages. These messages are also suppressed in batch
mode.
-batch
Run in batch mode. Exit with status 0after processing
all the command files specified with '-x' (and all
commands from initialization files, if not inhibited with
2.1 Invoking GDB
27
'-n'). Exit with nonzero status if an error occurs in
executing the GDB commands in the command files.
Batch mode may be useful for running GDB as a filter,
for example to download and run a program on another
computer; in order to make this more useful, the message
Program exited normally.
(which is ordinarily issued whenever a program running
under GDB control terminates) is not issued when
running in batch mode.
-nowindows, -nw
“No windows”. If GDB comes with a graphical user
interface (GUI) built in, then this option tells GDB to
only use the command-line interface. If no GUI is
available, this option has no effect.
-windows, -w
If GDB includes a GUI, then this option requires it to be
used if possible.
Run GDB using directory as its working directory, instead
of the current directory.
-cd directory
-dbx
Support additional dbxcommands, including:
• use
• status(in dbxmode, status has a different
meaning than in default GDB mode.)
• whereis
• func
• file
• assign
• call
• stop
-fullname, -f
GNUEmacs sets this option when it runs GDB as a
subprocess. It tells GDB to output the full file name and
line number in a standard, recognizable fashion each
time a stack frame is displayed (which includes each
time your program stops). This recognizable format looks
like two `\032' characters, followed by the file name,
line number, and character position separated by colons,
and a newline. The Emacs-to-GDB interface program
uses the two '\032' characters as a signal to display the
source code for the frame.
-epoch
The Epoch Emacs-GDB interface sets this option when
it runs GDB as a subprocess. It tells GDB to modify its
28
Getting In and Out of GDB
print routines so as to allow Epoch to display values of
expressions in a separate window.
-annotate level
This option sets the annotation level inside GDB. Its effect
Annotations” (page 297)). Annotation level controls how
much information does GDB print together with its
prompt, values of expressions, source lines, and other
types of output. Level 0 is the normal, level 1 is for use
when GDB is run as a subprocess of GNUEmacs, level 2
is the maximum annotation suitable for programs that
control GDB.
-async
Use the asynchronous event loop for the command-line
1
interface. GDB processes all events, such as user
keyboard input, via a special event loop. This allows
GDB to accept and process user commands in parallel
1
with the debugged process being run , so you do not
need to wait for control to return to GDB before you type
the next command.
NOTE: As of version 5.0, the target side of the
asynchronous operation is not yet in place, so '-async'
does not work fully yet.
When the standard input is connected to a terminal
device, GDB uses the asynchronous event loop by
default, unless disabled by the '-noasync' option.
-noasync
Disable the asynchronous event loop for the
command-line interface.
-baud bps, -b bps
Set the line speed (baud rate or bits per second) of any
serial interface used by GDB for remote debugging.
-tty device, -t device Run using device for your program's standard input and
output.
-tui
Use a Terminal User Interface. For information, use your
Web browser to read the file 'tui.html', which is
usually installed in the directory /opt/langtools/
wdb/docon HP-UX systems. Do not use this option if
you run GDB from Emacs (see “Using GDB under gnu
-xdb
Run in XDB compatibility mode, allowing the use of
certain XDB commands. For information, see the file
1. GDB built with DJGPP tools for MS-DOS/MS-Windows supports this mode of operation, but the event
loop is suspended when the debug target runs.
2.1 Invoking GDB
29
'xdb_trans.html', which is usually installed in the
directory /opt/langtools/wdb/docon HP-UX
systems.
-interpreter interp
Use the interpreter interp for interface with the
controlling program or device. This option is meant to
be set by programs which communicate with GDB using
it as a back end. For example, '--interpreter=mi'
-write
Open the executable and core files for both reading and
writing. This is equivalent to the 'set write on'
command inside GDB (see “Patching programs”
-statistics
-version
This option causes GDB to print statistics about time and
memory usage after it completes each command and
returns to the prompt.
This option causes GDB to print its version number and
no-warranty blurb, and exit.
-pid
This option causes GDB to attach to a running process.
-inline
This option causes the debugger to start with the inline
debugging on.
-src_no_g
This option is used to set the limited source level
debugging without compiling.
2.1.3 Redirecting WDB input and output to a file
To redirect WDB input and output to a file, use either of these commands to start the
debugger:
$ script log1
$ gdb
or
$ gdb | tee log1
2.2 Quitting GDB
quit [expression], q To exit GDB, use the quitcommand (abbreviated q), or
type an end-of-file character (usually C-d). If you do not
supply expression, GDB will terminate normally; otherwise
it will terminate using the result of expression as the error
code.
An interrupt (often C-c) does not exit from GDB, but rather terminates the action of
any GDB command that is in progress and returns to GDB command level. It is safe to
30
Getting In and Out of GDB
type the interrupt character at any time because GDB does not allow it to take effect
until a time when it is safe.
You can use the detachcommand to release an attached process or device.
2.3 Shell commands
If you need to execute occasional shell commands during your debugging session,
there is no need to leave or suspend GDB; you can just use the shellcommand.
shell command string
Invoke a standard shell to execute command string. If it
exists, the environment variable SHELLdetermines
which shell to run. Otherwise GDB uses the default
shell ('/bin/sh' on UNIX systems, 'COMMAND.COM' on
MS-DOS, and so on.).
The utility makeis often needed in development environments. You do not have to
use the shellcommand for this purpose in GDB:
make make-args
Execute the makeprogram with the specified arguments. This
is equivalent to 'shell make make-args'.
2.3 Shell commands
31
32
3 GDB Commands
You can abbreviate a GDB command to the first few letters of the command name, if
that abbreviation is unambiguous; and you can repeat certain GDB commands by
typing just RET ). You can also use the TAB key to get GDB to fill out the rest of a
word in a command (or to show you the alternatives available, if there is more than
one possibility).
3.1 Command syntax
•
•
A GDB command is a single line of input. There is no limit on how long it can be.
It starts with a command name, and is followed by arguments whose meaning
depends on the command name.
•
GDB command names can be truncated if that abbreviation is unambiguous. The
possible command abbreviations are listed in the documentation for individual
commands. In some cases, even ambiguous abbreviations are allowed; for example,
sis specially defined as equivalent to stepeven though there are other commands
whose names start with s. You can test abbreviations by using them as arguments
to the help command.
•
A blank line as input to GDB (typing just RET) means to repeat the previous
command. Some commands (for example, run) do not repeat this way. These are
commands whose unintentional repetition might cause trouble and which you are
unlikely to want to repeat. The listand xcommands, when you repeat them
with RET, construct new arguments rather than repeating exactly as typed. This
permits easy scanning of source or memory.
•
•
GDB can also use RET in another way: to partition lengthy output, in a way similar
it is easy to press one RET too many in this situation, GDB disables command
repetition after any command that generates this sort of display.
Any text from a # to the end of the line is a comment; it does nothing. This is useful
3.2 Command completion
GDB can fill in the rest of a word in a command for you, if there is only one possibility;
it can also show you what the valid possibilities are for the next word in a command,
at any time. This works for GDB commands, GDB subcommands, and the names of
symbols in your program.
Press the TAB key whenever you want GDB to fill out the rest of a word. If there is
only one possibility, GDB fills in the word, and waits for you to finish the command
(or press RET to enter it). For example, if you type
((gdb)) info bre TAB
3.1 Command syntax
33
GDB fills in the rest of the word 'breakpoints', since that is the only info
subcommand beginning with 'bre':
((gdb)) info breakpoints
You can either press RET at this point, to run the info breakpointscommand, or
backspace and enter something else, if 'breakpoints' does not look like the command
you expected. (If you were sure you wanted info breakpointsin the first place,
you might as well just type RET immediately after 'info bre', to exploit command
abbreviations rather than command completion.)
If there is more than one possibility for the next word when you press TAB , GDB
sounds a bell. You can either supply more characters and try again, or just press TAB
a second time; GDB displays all the possible completions for that word. For example,
you might want to set a breakpoint on a subroutine whose name begins with 'make_',
but when you type b make_TAB GDBjust sounds the bell. Typing TAB again displays
all the function names in your program that begin with those characters, for example:
((gdb)) b make_TAB
GDB sounds bell; press TAB again, to see:
make_a_section_from_file make_environ
make_abs_section make_function_type
make_blockvector make_pointer_type
make_cleanup make_reference_type
make_command make_symbol_completion_list
((gdb)) b make_
After displaying the available possibilities, GDB copies your partial input ('b make_'
in the example) so you can finish the command.
If you just want to see the list of alternatives in the first place, you can press M-? rather
than pressing TAB twice. M-? means META?. You can type this either by holding down
a key designated as the META shift on your keyboard (if there is one) while typing ?,
or as ESC followed by ?.
Sometimes the string you need, while logically a “word”, may contain parentheses or
other characters that GDB normally excludes from its notion of a word. To permit word
completion to work in this situation, you may enclose words in ' (single quote marks)
in GDB commands.
The most likely situation where you might need this is in typing the name of a C++
function. This is because C++ allows function overloading (multiple definitions of the
same function, distinguished by argument type). For example, when you want to set
a breakpoint you may need to distinguish whether you mean the version of name that
takes an int parameter, name(int), or the version that takes a float parameter, name(float).
To use the word-completion facilities in this situation, type a single quote ' at the
beginning of the function name. This alerts GDB that it may need to consider more
information than usual when you press TAB or M-? to request word completion:
((gdb)) b 'bubble( M-?
34
GDB Commands
bubble(double,double) bubble(int,int)
((gdb)) b 'bubble(
In some cases, GDB can tell that completing a name requires using quotes. When this
happens, GDB inserts the quote for you (while completing as much as it can) if you do
not type the quote in the first place:
((gdb)) b bub TAB
GDB alters your input line to the following, and rings a bell:
((gdb)) b 'bubble(
In general, GDB can tell that a quote is needed (and inserts it) if you have not yet started
typing the argument list when you ask for completion on an overloaded symbol.
You can use the command set overload-resolution offto disable overload
3.3 Getting help
You can always ask GDB itself for information on its commands, using the command
help.
help, h
You can use help(abbreviated h) with no arguments to display
a short list of named classes of commands:
((gdb)) help
List of classes of commands:
aliases -- Aliases of other commands
breakpoints -- Making program stop at certain points
data -- Examining data
files -- Specifying and examining files
internals -- Maintenance commands
obscure -- Obscure features
running -- Running the program
stack -- Examining the stack
status -- Status inquiries
support -- Support facilities
tracepoints -- Tracing of program execution without
stopping the program
user-defined -- User-defined commands
Type "help" followed by a class name for a list of
commands in that class.
Type "help" followed by command name for full
documentation.
Command name abbreviations are allowed if unambiguous.
((gdb))
3.3 Getting help
35
help class
Using one of the general help classes as an argument, you can
get a list of the individual commands in that class. For example,
here is the help display for the class status:
((gdb)) help status
Status inquiries.
List of commands:
info -- Generic command for showing things
about the program being debugged
show -- Generic command for showing things
about the debugger
Type "help" followed by command name for full
documentation.
Command name abbreviations are allowed if unambiguous.
((gdb))
help command
With a command name as helpargument, GDB displays a short
paragraph on how to use that command.
apropos args
The apropos args command searches through all of the GDB
commands, and their documentation, for the regular expression
specified in args. It prints out all matches found. For example:
apropos reload
results in:
set symbol-reloading -- Set dynamic symbol table
reloading
multiple times in one run
show symbol-reloading -- Show dynamic symbol table
reloading
multiple times in one run
complete args
The complete args command lists all the possible completions
for the beginning of a command. Use args to specify the
beginning of the command you want completed. For example:
complete i
results in:
if
ignore
info
inspect
This is intended for use by GNU Emacs.
In addition to help, you can use the GDB commands infoand showto inquire about
the state of your program, or the state of GDB itself. Each command supports many
topics of inquiry; this manual introduces each of them in the appropriate context. The
36
GDB Commands
listings under infoand under showin the Index point to all the sub-commands. See
???.
info This command (abbreviated i) is for describing the state of your program. For
example, you can list the arguments given to your program with info args,
list the registers currently in use with info registers, or list the breakpoints
you have set with info breakpoints. You can get a complete list of the
infosub-commands with help info.
set
You can assign the result of an expression to an environment variable with
set. For example, you can set the GDB prompt to a $-signwith set prompt
$.
show In contrast to info, showis for describing the state of GDB itself. You can
change most of the things you can show, by using the related command set;
for example, you can control what number system is used for displays with
set radix, or simply inquire which is currently in use with show radix.
To display all the settable parameters and their current values, you can use
showwith no arguments; you may also use info set. Both commands
produce the same display.
Here are three miscellaneous showsubcommands, all of which are exceptional in
lacking corresponding setcommands:
show version
Show what version of GDB is running. You should include this
information in GDB bug-reports. If multiple versions of GDB are
in use at your site, you may need to determine which version of
GDB you are running; as GDB evolves, new commands are
introduced, and old ones may wither away. Also, many system
vendors ship variant versions of GDB, and there are variant
versions of GDB in GNU/Linux distributions as well. The version
number is the same as the one announced when you start GDB.
show copying
show warranty
Display information about permission for copying GDB.
Display the GNU “NO WARRANTY” statement, or a warranty,
if your version of GDB comes with one.
3.3 Getting help
37
38
4 Running Programs Under GDB
When you run a program under GDB, you must first generate debugging information
when you compile it using compiler option cc -g -O.
You may start GDB with its arguments, if any, in an environment of your choice. If
you are doing native debugging, you may redirect your program's input and output,
debug an already running process, or kill a child process.
4.1 Compiling for debugging
Following points are noteable while compiling programs for debugging:
•
•
Compile your program with the -g-Ooption to generate debugging information.
The -g-Ooption is supported by HP ANSI C and HP aC++ compilers and GNU
gcc compiler.
•
•
Some compilers do not support the -g-Ooptions together.
The -g-Ooptions do not work on machines with instruction scheduling.
NOTE: Older versions of the GNU C compiler permitted a variant option '-gg' for
debugging information. GDB no longer supports this format; if your GNU C compiler
has this option, do not use it.
4.2 Starting your program
run, Use the runcommand to start your program under GDB. You must first specify
r
the program name (except on VxWorks) with an argument to GDB (see Chapter 2
NOTE: If you are running your program in an execution environment that supports
processes, run creates an inferior process and makes that process run your program.
(In environments without processes, run jumps to the start of your program.)
The execution of a program is affected by the information it receives from the parent
process. You must provide GDB the information before starting the program. (You can
change the information after starting your program, but such changes only affect your
program the next time you start it.) The information that must be passed to GDB can
be categorized into four categories:
arguments.
Specify the arguments to give your program as
the arguments of the runcommand. If a shell is
available on your target, the shell is used to pass
the arguments, so that you may use normal
conventions (such as wildcard expansion or
4.1 Compiling for debugging
39
variable substitution) in describing the
arguments. On Unix systems, you can control
which shell is used with the SHELLenvironment
variable. GDB uses the C shell (/usr/bin/csh).
environment.
Your program inherits its environment from
GDB. However, you can use the GDB commands
set environmentand unset environment
to change parts of the environment that affect
your program. See“Program Environment”
working directory.
Your program inherits its working directory from
GDB. You can set the GDB working directory
standard input and output. Your program as default uses the same device
for standard input and standard output as GDB
is using. You can redirect input and output in
the runcommand line, or you can use the tty
command to set a different device for your
40
Running Programs Under GDB
program. See “Program Input and Output”
WARNING! You can redirect input and output,
but you cannot use pipes to pass the output of
the program you are debugging to another
program; if you attempt this, GDB is likely to
wind up debugging the wrong program.
NOTE:
•
When you issue the runcommand, your program begins to execute immediately.
stop. Once your program has stopped, you may call functions in your program,
•
If the modification time of your symbol file has changed since the last time GDB
read its symbols, GDB discards its symbol table, and reads it again. When it does
this, GDB tries to retain your current breakpoints.
4.3 Arguments To Your Program
The arguments to your program can be specified by the arguments of the runcommand.
On HP-UX, they are passed to the C shell (/usr/bin/csh), which expands wildcard
characters and performs redirection of I/O, and then to your program.
On non-Unix systems, the program is usually invoked directly by GDB, which emulates
I/O redirection via the appropriate system calls, and the wildcard characters are
expanded by the startup code of the program, not by the shell.
The runcommand used with no arguments uses the same arguments used by the
previous run, or those set by the set argscommand.
Following commands are used to pass the argument values to your program:
set args
Specify the arguments to be used the next time your program is run. If
set argshas no arguments, runexecutes your program with no
arguments. Once you have run your program with arguments, using
set args before the next runis the only way to run it again without
arguments.
show args Show the arguments to give your program when it is started.
4.4 Program Environment
The environment consists of a set of environment variables and their values. Environment
variables conventionally record information such as your user name, your home
directory, your terminal type, and your search path for programs to run. Usually you
set up environment variables with the shell and they are inherited by all the other
4.3 Arguments To Your Program
41
programs you run. When debugging, it can be useful to try running your program
with a modified environment without having to start GDB over again.
show envvar
List all the environment variables used by GDB.
show paths
Display the list of search paths for executables
(the PATHenvironment variable).
show environment [varname] Print the value of environment variable varname
to be given to your program when it starts. If you
do not supply varname, print the names and
values of all environment variables to be given
to your program. You can abbreviate
environmentas env.
set environment varname
[=value]
Set environment variable varname to value.
The value changes for your program only, not
for GDB itself. The value may be any string; the
values of environment variables are just strings,
and any interpretation is supplied by your
program itself. The value parameter is optional;
if it is eliminated, the variable is set to a null
value.
For example, this command:
set env USER = foo
tells the debugged program, when subsequently
run, that its user is named 'foo'. (The spaces
around '=' are used for clarity here; they are not
actually required.)
unset environment varname
Remove variable varname from the environment
to be passed to your program. This is different
from 'set env varname ='; unset
environmentremoves the variable from the
environment, rather than assigning it an empty
value.
path directory
Add directory to the front of the PATH
environment variable (the search path for
executables), for both GDB and your program.
You may specify several directory names,
separated by whitespace or by a
system-dependent separator character (`:' on
Unix, `;' on MS-DOS and MS-Windows). If
directory is already in the path, it is moved
to the front, so it is searched sooner.
42
Running Programs Under GDB
You can use the string '$cwd' to refer to whatever is the current working directory at
the time GDB searches the path. If you use '.' instead, it refers to the directory where
you executed the pathcommand. GDB replaces '.' in the directory argument (with the
current path) before adding directory to the search path.
4.5 Working directory
Each time you start your program with run, it inherits its working directory from the
current working directory of GDB. The GDB working directory is initially whatever it
inherited from its parent process (typically the shell), but you can specify a new working
directory in GDB with the cdcommand.
The GDB working directory also serves as a default for the commands that specify files
Following commands are used to set the working directory for your program:
cd directory
Set the GDB working directory to directory.
pwd
Print the GDB working directory.
4.6 Program Input and Output
By default, the program you run under GDB does input and output to the same terminal
that GDB uses. GDB switches the terminal to its own terminal modes to interact with
you, but it records the terminal modes your program was using and switches back to
them when you continue running your program.
Following commands are used for redirecting the input and output:
info terminal
Displays information recorded by GDB about the terminal modes
your program is using.
tty
Another way to specify where your program should do input
and output is with the ttycommand. This command accepts a
file name as argument, and causes this file to be the default for
future runcommands. It also resets the controlling terminal for
the child process, for future runcommands. For example,
tty /dev/ttyb
directs that processes started with subsequent runcommands
default to do input and output on the terminal '/dev/ttyb' and
have that as their controlling terminal.
4.5 Working directory
43
NOTE:
•
You can redirect your program input and output using shell redirection with the
runcommand. For example,
run > outfile
starts your program, diverting its output to the file 'outfile'.
•
•
An explicit redirection in runoverrides the ttycommand's effect on the
input/output device, but not its effect on the controlling terminal.
When you use the ttycommand or redirect input in the runcommand, only the
input for your program is affected. The input for GDB still comes from your terminal.
4.7 Debugging a Running Process
You can use GDB to debug a running process by specifying the process ID. Following
commands are used to debug a running process:
attach process-id
This command attaches to a running process―one that was
started outside GDB. (info filesshows your active
targets.) The command takes as argument a process ID. The
usual way to find out the process-id of a Unix process is
with the psutility, or with the 'jobs -l' shell command.
attachdoes not repeat if you press RET a second time
after executing the command.
44
Running Programs Under GDB
NOTE:
•
To use attach, your program must be running in an environment which supports
processes; for example, attachdoes not work for programs on bare-board targets
that lack an operating system.
•
•
You must also have permission to send the process a signal.
When you use attach, the debugger finds the program running in the process
first by looking in the current working directory, then (if the program is not found)
•
GDB stops the process being attached for debugging. You can examine and modify
an attached process with the GDB commands that are available when you start
processes with run. You can insert breakpoints; you can step and continue; you
continue running, you can use the continuecommand after attaching GDB to
the process.
detach When you have finished debugging the attached process, you can use the
detachcommand to release it from GDB control. The process continues
its execution after being detached. After the detachcommand, that process
and GDB become completely independent once more, and you are ready
to attachanother process or start one with run. detachdoes not repeat
if you press RET again after executing the command.
If you exit GDB or use the runcommand while you have an attached process, you kill
that process. By default, GDB asks for confirmation if you try to do either of these
things; you can control whether or not you need to confirm by using the set confirm
NOTE: When GDB attaches to a running program you may get a message saying
"Attaching to process #nnnnn failed."
The most likely cause for this message is that you have attached to a process that was
started across an NFS mount. Versions of the HP-UX kernel before 11.x have a restriction
that prevents a debugger from attaching to a process started from an NFS mount, unless
the mount was made non-interruptible with the -nointrflag, see mount(1).
4.8 Killing the child process
Following command is used to kill the child process:
kill Kill the child process in which your program is running under GDB.
The killcommand is useful if you wish to debug a core dump instead of a running
process. GDB ignores any core dump file while your program is running.
4.8 Killing the child process
45
On some operating systems, a program cannot be executed outside GDB while you
have breakpoints set on it inside GDB. You can use the killcommand in this situation
to permit running your program outside the debugger.
The killcommand is also useful if you wish to recompile and relink your program,
since on many systems it is impossible to modify an executable file while it is running
in a process. In this case, when you next type run, GDB notices that the file has changed,
and reads the symbol table again (while trying to preserve your current breakpoint
settings).
4.9 Debugging programs with multiple threads
In some operating systems, such as HP-UX and Solaris, a single program may have
more than one thread of execution. The precise semantics of threads differ from one
operating system to another, but in general the threads of a single program are akin to
multiple processes―except that they share one address space (that is, they can all
examine and modify the same variables). On the other hand, each thread has its own
registers and execution stack, and private memory.
GDB provides these facilities for debugging multi-thread programs:
•
•
automatic notification of new threads
thread-specific breakpoints
WARNING! These facilities are not yet available on every GDB configuration where
the operating system supports threads. If your GDB does not support threads, these
commands have no effect. For example, a system without thread support shows no
output from 'info threads', and always rejects the threadcommand, like this:
((gdb)) info threads
((gdb)) thread 1
Thread ID 1 not known. Use the "info threads" command to
see the IDs of currently known threads.
Following commands are used to debug multi-threaded programs:
•
•
•
'thread threadno', a command to switch among threads
'info threads', a command to inquire about existing threads
'thread apply [threadno] [all] args', a command to apply a command
to a list of threads
The GDB thread debugging facility allows you to observe all threads while your
program runs―but whenever GDB takes control, one thread in particular is always
the focus of debugging. This thread is called the current thread. Debugging commands
show program information from the perspective of the current thread.
Whenever GDB detects a new thread in your program, it displays the target system's
identification for the thread with a message in the form '[New systag]'. systag is a
46
Running Programs Under GDB
thread identifier whose form varies depending on the particular system. For example,
on LynxOS, you might see
[New process 35 thread 27]
when GDB notices a new thread. In contrast, on an SGI system, the systag is simply
something like 'process 368', with no further qualifier.
For debugging purposes, GDB associates its own thread number―always a single
integer―with each thread in your program.
info threads
Display a summary of all threads currently in your program. GDB
displays for each thread (in this order):
1. the thread number assigned by GDB
2. the target system's thread identifier (systag)
3. the current stack frame summary for that thread
An asterisk '*' to the left of the GDB thread number indicates the
current thread.
For example,
((gdb)) info threads
3 process 35 thread 27 0x34e5 in sigpause ()
2 process 35 thread 23 0x34e5 in sigpause ()
* 1 process 35 thread 13 main (argc=1, argv=0x7ffffff8)
at threadtest.c:68
On HP-UX systems:
For debugging purposes, GDB associates its own thread number―a small integer
assigned in thread-creation order―with each thread in your program.
Whenever GDB detects a new thread in your program, it displays both GDB's thread
number and the target system's identification for the thread with a message in the form
'[New systag]'. systag is a thread identifier whose form varies depending on the
particular system. For example, on HP-UX, you see
[New thread 2 (system thread 26594)]
when GDB notices a new thread.
On HP-UX systems, you can control the display of thread creation messages. Following
commands are used to control the display of thread creation:
set threadverbose on
Enable the output of informational messages
regarding thread creation. The default setting is on.
You can set it to offto stop displaying of messages.
set threadverbose off
Disable the output of informational messages
regarding thread creation. The default setting is on.
You can set it to onto display messages.
4.9 Debugging programs with multiple threads
47
show threadverbose
Display whether set threadverboseis onor
off.
Here are commands to get more information about threads:
info threads
Display a summary of all threads currently in
your program. GDB displays for each thread (in
this order):
1. the thread number assigned by GDB
2. the target system's thread identifier (systag)
3. the current stack frame summary for that
thread
4. the priority of a thread
An asterisk '*' to the left of the GDB thread
number indicates the current thread.
For example,
((gdb)) info threads
* 3 system thread 26607 worker
(wptr=0x7b09c318 "@") \
at quicksort.c:137
2 system thread 26606 0x7b0030d8 in
__ksleep () \
from /usr/lib/libc.2
1 system thread 27905 0x7b003498 in _brk
() \
from /usr/lib/libc.2
thread threadno
Make thread number threadno the current
thread. The command argument threadno is
the internal GDB thread number, as shown in
the first field of the 'info threads' display.
GDB responds by displaying the system identifier
of the thread you selected, and its current stack
frame summary:
((gdb)) thread 2
[Switching to thread 2 (system thread
26594)]
0x34e5 in sigpause ()
As with the '[New ...]' message, the form of
the text after 'Switching to' depends on your
system's conventions for identifying threads.
thread apply [threadno]
[all] args
The thread applycommand allows you to
apply a command to one or more threads. Specify
the numbers of the threads that you want affected
with the command argument threadno.
48
Running Programs Under GDB
threadno is the internal GDB thread number,
as shown in the first field of the 'info threads'
display. To apply a command to all threads, use
thread apply allargs.
Whenever GDB stops your program, due to a breakpoint or a signal, it automatically
selects the thread where that breakpoint or signal happened. GDB alerts you to the
context switch with a message of the form '[Switching to systag]' to identify the
thread.
about how GDB behaves when you stop and start programs with multiple threads.
with multiple threads.
NOTE: On HP-UX 11.x, debugging a multi-thread process can cause a deadlock if
the process is waiting for an NFS-server response. A thread can be stopped while asleep
in this state, and NFS holds a lock on the rnode while asleep.
To prevent the thread from being interrupted while holding the rnode lock, make the
NFS mount non-interruptible with the '-nointr' flag. See mount(1).
4.10 Debugging programs with multiple processes
On most systems, GDB has no special support for debugging programs which create
additional processes using the forkfunction. When a program forks, GDB will continue
to debug the parent process and the child process will run unimpeded. If you have set
a breakpoint in any code which the child then executes, the child will get a SIGTRAP
signal which (unless it catches the signal) will cause it to terminate.
However, if you want to debug the child process there is a workaround which isn't too
painful. Put a call to sleepin the code which the child process executes after the fork.
It may be useful to sleep only if a certain environment variable is set, or a certain file
exists, so that the delay need not occur when you do not want to run GDB on the child.
While the child is sleeping, use the psprogram to get its process ID. Then tell GDB (a
new invocation of GDB if you are also debugging the parent process) to attach to the
can debug the child process just like any other process which you attached to.
On HP-UX (11.x and later only), GDB provides support for debugging programs that
create additional processes using the forkor vforkfunction.
By default, when a program forks, GDB will continue to debug the parent process and
the child process will run unimpeded.
If you want to follow the child process instead of the parent process, use the command
set follow-fork-mode.
4.10 Debugging programs with multiple processes
49
set follow-fork-mode mode
Set the debugger response to a program call of
forkor vfork. A call to forkor vforkcreates
a new process. The mode can be:
parent The original process is debugged after
a fork. The child process runs
unimpeded. This is the default.
child
The new process is debugged after a
fork. The parent process runs
unimpeded.
show follow-fork-mode
Display the current debugger response to a fork
or vforkcall.
If you ask to debug a child process and a vforkis followed by an exec, GDB executes
the new target up to the first breakpoint in the new target. If you have a breakpoint set
on mainin your original program, the breakpoint will also be set on the child process's
main.
When a child process is spawned by vfork, you cannot debug the child or parent until
an execcall completes.
If you issue a runcommand to GDB after an execcall executes, the new target restarts.
To restart the parent process, use the filecommand with the parent executable name
as its argument.
You can use the catchcommand to make GDB stop whenever a fork, vfork, or
50
Running Programs Under GDB
5 Stopping and Continuing
The principal purpose of a debugger is to let you stop your program before it terminates
abnormally or runs into trouble, so that you can investigate and determine the reason.
Inside GDB, your program can stop for several reasons, such as a signal, a breakpoint,
or reaching a new line after a GDB command such as step. You can then examine and
change variables, set new breakpoints or remove old ones, and then continue execution.
Usually, the messages shown by GDB provide information on the status of your
program―but you can also explicitly request this information at any time.
info program
Display information about the status of your program: whether it
is running or not, what process it is, and why it stopped.
5.1 Breakpoints
A breakpoint makes your program stop whenever a certain point in the program is
reached. For each breakpoint, you can add conditions to control in finer detail whether
your program stops. You can set breakpoints with the breakcommand and its variants.
function name or an address in the program.
You can arrange to have values from your program displayed automatically whenever
In HP-UX, SunOS 4.x, SVR4, and Alpha OSF/1 configurations, you can set breakpoints
in shared libraries before the executable is run. See “Debugging support for shared
A catchpoint is another special breakpoint that stops your program when a certain kind
of event occurs, such as the throwing of a C++ exception or the loading of a library. As
with watchpoints, you use a different command to set a catchpoint (see “Setting
catchpoints” (page 56)), but apart from that, you can manage a catchpoint like any
other breakpoint. (To stop when your program receives a signal, use the handle
GDB assigns a number to each breakpoint, watchpoint, or catchpoint when you create
it; these numbers are successive integers starting with one. In many of the commands
for controlling various features of breakpoints you use the breakpoint number to say
which breakpoint you want to change. Each breakpoint may be enabled or disabled;
if disabled, it has no effect on your program until you enable it again.
Some GDB commands accept a range of breakpoints on which to operate. A breakpoint
range is either a single breakpoint number, like '5', or two such numbers, in increasing
order, separated by a hyphen, like '5-7'. When a breakpoint range is given to a
command, all breakpoint in that range are operated on.
5.1 Breakpoints
51
5.1.1 Setting breakpoints
Breakpoints are set with the breakcommand (abbreviated b). The debugger
convenience variable '$bpnum' records the number of the breakpoint you have set most
with convenience variables.
You have several ways to say where the breakpoint should go.
break function
Set a breakpoint at entry to function function. When
using source languages that permit overloading
of symbols, such as C++, function may refer to more
than one possible place to break. See “Breakpoint
menus” (page 62), for a discussion of that
situation.
break +offset, break
-offset
Set a breakpoint some number of lines forward or
back from the position at which execution stopped
frames” (page 71), for a description of stack
frames.)
break linenum
Set a breakpoint at line linenum in the current
source file. The current source file is the last file
whose source text was printed. The breakpoint
will stop your program just before it executes any
of the code on that line.
break filename:linenum
Set a breakpoint at line linenum in source file
filename.
break filename:function
Set a breakpoint at entry to function function
found in file filename. Specifying a fie name as
well as a function name is superfluous except
when multiple files contain similarly named
functions.
break *address
Set a breakpoint at address address. You can use
this to set breakpoints in parts of your program
which do not have debugging information or
source files.
break
When called without any arguments, breaksets
a breakpoint at the next instruction to be executed
in the selected stack frame (see Chapter 6
(page 71)). In any selected frame but the
innermost, this makes your program stop as soon
as control returns to that frame. This is similar to
the effect of a finishcommand in the frame
inside the selected frame―except that finish
52
Stopping and Continuing
does not leave an active breakpoint. If you use
breakwithout an argument in the innermost
frame, GDB stops the next time it reaches the
current location; this may be useful inside loops.
GDB normally ignores breakpoints when it
resumes execution, until at least one instruction
has been executed. If it did not do this, you would
be unable to proceed past a breakpoint without
first disabling the breakpoint. This rule applies
whether or not the breakpoint already existed
when your program stopped.
break ... if cond
Set a breakpoint with condition cond; evaluate
the expression cond each time the breakpoint is
reached, and stop only if the value is
nonzero―that is, if cond evaluates as true. '...'
stands for one of the possible arguments described
above (or no argument) specifying where to break.
information on breakpoint conditions.
tbreak args
Set a breakpoint enabled only for one stop. args
are the same as for the breakcommand, and the
breakpoint is set in the same way, but the
breakpoint is automatically deleted after the first
time your program stops there. See “Disabling
hbreak args
Set a hardware-assisted breakpoint. args are the
same as for the breakcommand and the
breakpoint is set in the same way, but the
breakpoint requires hardware support and some
target hardware may not have this support. The
main purpose of this is EPROM/ROM code
debugging, so you can set a breakpoint at an
instruction without changing the instruction. This
can be used with the new trap-generation provided
by SPARClite DSU and some x86-based targets.
These targets will generate traps when a program
accesses some data or instruction address that is
assigned to the debug registers. However, the
hardware breakpoint registers can take a limited
number of breakpoints. For example, on the DSU,
only two data breakpoints can be set at a time, and
GDB will reject this command if more than two
5.1 Breakpoints
53
are used. Delete or disable unused hardware
breakpoints before setting new ones (see
thbreak args
Set a hardware-assisted breakpoint enabled only
for one stop. args are the same as for the hbreak
command and the breakpoint is set in the same
way. However, like the tbreakcommand, the
breakpoint is automatically deleted after the first
time your program stops there. Also, like the
hbreakcommand, the breakpoint requires
hardware support and some target hardware may
not have this support. See “Disabling breakpoints”
rbreak regex
Set breakpoints on all functions matching the
regular expression regex. This command sets an
unconditional breakpoint on all matches, printing
a list of all breakpoints it set. Once these
breakpoints are set, they are treated just like the
breakpoints set with the breakcommand. You
can delete them, disable them, or make them
conditional the same way as any other breakpoint.
The syntax of the regular expression is the
standard one used with tools like 'grep'. Note that
this is different from the syntax used by shells, so
for instance foo*matches all functions that
include an fofollowed by zero or more os. There
is an implicit .* leading and trailing the regular
expression you supply, so to match only functions
that begin with foo, use ^foo.
When debugging C++ programs, rbreakis useful
for setting breakpoints on overloaded functions
that are not members of any special classes.
info breakpoints [n], info Print a table of all breakpoints, watchpoints, and
catchpoints set and not deleted, with the following
columns for each breakpoint:
break [n], info watchpoints
[n]
Breakpoint Numbers,
Type
Breakpoint,
watchpoint, or
catchpoint.
Disposition
Whether the
breakpoint is
54
Stopping and Continuing
marked to be
disabled or deleted
when hit.
Enabled or Disabled
Enabled
breakpoints are
marked with 'y'. 'n'
marks breakpoints
that are not
enabled.
Address
What
Where the
breakpoint is in
your program, as a
memory address.
Where the
breakpoint is in the
source for your
program, as a file
and line number.
If a breakpoint is conditional, info breakshows
the condition on the line following the affected
breakpoint; breakpoint commands, if any, are
listed after that.
info break with a breakpoint number n as
argument lists only that breakpoint. The
convenience variable $_and the default
examining-address for the x command are set to
the address of the last breakpoint listed (see
info break displays a count of the number of
times the breakpoint has been hit. This is especially
useful in conjunction with the ignorecommand.
You can ignore a large number of breakpoint hits,
look at the breakpoint info to see how many times
the breakpoint was hit, and then run again,
ignoring one less than that number. This will get
you quickly to the last hit of that breakpoint.
GDB allows you to set any number of breakpoints at the same place in your program.
There is nothing silly or meaningless about this. When the breakpoints are conditional,
5.1 Breakpoints
55
GDB itself sometimes sets breakpoints in your program for special purposes, such as
proper handling of longjmp(in C programs). These internal breakpoints are assigned
negative numbers, starting with -1; 'info breakpoints' does not display them.
You can see these breakpoints with the GDB maintenance command 'maint info
breakpoints'.
maint info breakpoints
Using the same format as 'info breakpoints',
display both the breakpoints you have set explicitly,
and those GDB is using for internal purposes.
Internal breakpoints are shown with negative
breakpoint numbers. The type column identifies
what kind of breakpoint is shown:
breakpoint
watchpoint
longjmp
Normal, explicitly set
breakpoint.
Normal, explicitly set
watchpoint.
Internal breakpoint, used to
handle correctly stepping
through longjmpcalls.
longjmp resume
until
Internal breakpoint at the
target of a longjmp.
Temporary internal
breakpoint used by the GDB
untilcommand.
finish
Temporary internal
breakpoint used by the GDB
finishcommand.
shlib events
Shared library events.
5.1.2 Setting catchpoints
You can use catchpoints to cause the debugger to stop for certain kinds of program
events, such as C++ exceptions or the loading of a shared library. Use the catch
command to set a catchpoint.
catch event
Stop when event occurs. event can be any of the following:
throw
catch
exec
The throwing of a C++ exception.
The catching of a C++ exception.
A call to exec. This is currently only
available for HP-UX.
fork
A call to fork. This is currently only
available for HP-UX.
56
Stopping and Continuing
vfork
A call to vfork. This is currently only
available for HP-UX.
load, load
libname
The dynamic loading of any shared library,
or the loading of the library libname. This
is currently only available for HP-UX.
unload, unload
libname
The unloading of any dynamically loaded
shared library, or the unloading of the
library libname. This is currently only
available for HP-UX.
tcatch event
Set a catchpoint that is enabled only for one stop. The catchpoint
is automatically deleted after the first time the event is caught.
Use the info breakcommand to list the current catchpoints.
There are currently some limitations to C++ exception handling (catch throwand
catch catch) in GDB:
•
If you call a function interactively, GDB normally returns control to you when the
function has finished executing. If the call raises an exception, however, the call
may bypass the mechanism that returns control to you and cause your program
either to abort or to simply continue running until it hits a breakpoint, catches a
signal that GDB is listening for, or exits. This is the case even if you set a catchpoint
for the exception; catchpoints on exceptions are disabled within interactive calls.
•
•
You cannot raise an exception interactively.
You cannot install an exception handler interactively.
Sometimes catchis not the best way to debug exception handling: if you need to know
exactly where an exception is raised, it is better to stop before the exception handler is
called, since that way you can see the stack before any unwinding takes place. If you
set a breakpoint in an exception handler instead, it may not be easy to find out where
the exception was raised.
To stop just before an exception handler is called, you need some knowledge of the
implementation. In the case of GNU C++, exceptions are raised by calling a library
function named _ _raise_exceptionwhich has the following ANSI C interface:
/* addr is where the exception identifier is stored.
id is the exception identifier. */
void __raise_exception (void **addr, void *id);
To make the debugger catch all exceptions before any stack unwinding takes place, set
value of id, you can stop your program when a specific exception is raised. You can
use multiple conditional breakpoints to stop your program when any of a number of
exceptions are raised.
5.1 Breakpoints
57
5.1.3 Deleting breakpoints
It is often necessary to eliminate a breakpoint, watchpoint, or catchpoint once it has
done its job and you no longer want your program to stop there. This is called deleting
the breakpoint. A breakpoint that has been deleted no longer exists; it is forgotten.
With the clearcommand you can delete breakpoints according to where they are in
your program. With the deletecommand you can delete individual breakpoints,
watchpoints, or catchpoints by specifying their breakpoint numbers.
It is not necessary to delete a breakpoint to proceed past it. GDB automatically ignores
breakpoints on the first instruction to be executed when you continue execution without
changing the execution address.
clear
Delete any breakpoints at the next instruction to
be executed in the selected stack frame (see
“Selecting a frame” (page 73)). When the
innermost frame is selected, this is a good way
to delete a breakpoint where your program just
stopped.
clear function, clear
filename:function
Delete any breakpoints set at entry to the function
function.
clear linenum, clear
filename:linenum
Delete any breakpoints set at or within the code
of the specified line.
delete [breakpoints]
[range...]
Delete the breakpoints, watchpoints, or
catchpoints of the breakpoint ranges specified as
arguments. If no argument is specified, delete all
breakpoints (GDB asks confirmation, unless you
have set confirm off). You can abbreviate
this command as d.
5.1.4 Disabling breakpoints
Rather than deleting a breakpoint, watchpoint, or catchpoint, you might prefer to disable
it. This makes the breakpoint inoperative as if it had been deleted, but remembers the
information on the breakpoint so that you can enable it again later.
You disable and enable breakpoints, watchpoints, and catchpoints with the enable
and disablecommands, optionally specifying one or more breakpoint numbers as
arguments. Use info break or info watchto print a list of breakpoints,
watchpoints, and catchpoints if you do not know which numbers to use.
A breakpoint, watchpoint, or catchpoint can have any of four different states of
enablement:
•
Enabled. The breakpoint stops your program. A breakpoint set with the break
command starts out in this state.
•
Disabled. The breakpoint has no effect on your program.
58
Stopping and Continuing
•
•
Enabled once. The breakpoint stops your program, but then becomes disabled.
Enabled for deletion. The breakpoint stops your program, but immediately after
it does so it is deleted permanently. A breakpoint set with the tbreakcommand
starts out in this state.
You can use the following commands to enable or disable breakpoints, watchpoints,
and catchpoints:
disable [breakpoints]
[range...]
Disable the specified breakpoints―or all
breakpoints, if none are listed. A disabled
breakpoint has no effect but is not forgotten. All
options such as ignore-counts, conditions, and
commands are remembered in case the
breakpoint is enabled again later. You may
abbreviate disableas dis.
enable [breakpoints]
[range...]
Enable the specified breakpoints (or all defined
breakpoints). They become effective once again
in stopping your program.
enable [breakpoints] once
range...
Enable the specified breakpoints temporarily.
GDB disables any of these breakpoints
immediately after stopping your program.
enable [breakpoints] delete Enable the specified breakpoints to work once,
then die. GDB deletes any of these breakpoints
as soon as your program stops there.
range...
breakpoints that you set are initially enabled; subsequently, they become disabled or
enabled only when you use one of the commands above. (The command untilcan
set and delete a breakpoint of its own, but it does not change the state of your other
5.1.5 Break conditions
The simplest sort of breakpoint breaks every time your program reaches a specified
place. You can also specify a condition for a breakpoint. A condition is just a Boolean
with a condition evaluates the expression each time your program reaches it, and your
program stops only if the condition is true.
This is the converse of using assertions for program validation; in that situation, you
want to stop when the assertion is violated―that is, when the condition is false. In C,
if you want to test an assertion expressed by the condition assert, you should set the
condition '! assert' on the appropriate breakpoint.
Conditions are also accepted for watchpoints; you may not need them, since a
watchpoint is inspecting the value of an expression anyhow―but it might be simpler,
5.1 Breakpoints
59
say, to just set a watchpoint on a variable name, and specify a condition that tests
whether the new value is an interesting one.
Break conditions can have side effects, and may even call functions in your program.
This can be useful, for example, to activate functions that log program progress, or to
use your own print functions to format special data structures. The effects are completely
predictable unless there is another enabled breakpoint at the same address. (In that
case, GDB might see the other breakpoint first and stop your program without checking
the condition of this one.) Note that breakpoint commands are usually more convenient
and flexible than break conditions for the purpose of performing side effects when a
Break conditions can be specified when a breakpoint is set, by using 'if' in the arguments
at any time with the conditioncommand.
You can also use the if keyword with the watchcommand. The catchcommand does
not recognize the if keyword; conditionis the only way to impose a further condition
on a catchpoint.
condition bnum expression
Specify expression as the break condition for
breakpoint, watchpoint, or catchpoint number
bnum. After you set a condition, breakpoint bnum
stops your program only if the value of
expression is true (nonzero, in C). When you
use condition, GDB checks expression
immediately for syntactic correctness, and to
determine whether symbols in it have referents
in the context of your breakpoint. If expression
uses symbols not referenced in the context of the
breakpoint, GDB prints an error message:
No symbol "foo" in current context.
GDB does not actually evaluate expression at the
time the conditioncommand (or a command
that sets a breakpoint with a condition, like break
condition bnum
Remove the condition from breakpoint number
bnum. It becomes an ordinary unconditional
breakpoint.
A special case of a breakpoint condition is to stop only when the breakpoint has been
reached a certain number of times. This is so useful that there is a special way to do it,
using the ignore count of the breakpoint. Every breakpoint has an ignore count,
which is an integer. Most of the time, the ignore count is zero, and therefore has no
effect. But if your program reaches a breakpoint whose ignore count is positive, then
60
Stopping and Continuing
instead of stopping, it just decrements the ignore count by one and continues. As a
result, if the ignore count value is n, the breakpoint does not stop the next n times your
program reaches it.
ignore bnum count
Set the ignore count of breakpoint number bnum to count.
The next count times the breakpoint is reached, your
program's execution does not stop; other than to decrement
the ignore count, GDB takes no action.
To make the breakpoint stop the next time it is reached,
specify a count of zero.
When you use continueto resume execution of your
program from a breakpoint, you can specify an ignore count
directly as an argument to continue, rather than using
If a breakpoint has a positive ignore count and a condition,
the condition is not checked. Once the ignore count reaches
zero, GDB resumes checking the condition.
You could achieve the effect of the ignore count with a
condition such as '$foo-- <= 0' using a debugger
convenience variable that is decremented each time. See
Ignore counts apply to breakpoints, watchpoints, and catchpoints.
5.1.6 Breakpoint command lists
You can give any breakpoint (or watchpoint or catchpoint) a series of commands to
execute when your program stops due to that breakpoint. For example, you might
want to print the values of certain expressions, or enable other breakpoints.
commands [bnum], ...
command-list ..., end
Specify a list of commands for breakpoint number
bnum. The commands themselves appear on the
following lines. Type a line containing just endto
terminate the commands.
To remove all commands from a breakpoint, type
commandsand follow it immediately with end; that
is, give no commands.
With no bnum argument, commandsrefers to the last
breakpoint, watchpoint, or catchpoint set (not to the
breakpoint most recently encountered).
Pressing RET as a means of repeating the last GDB command is disabled within a
command-list.
5.1 Breakpoints
61
You can use breakpoint commands to start your program up again. Simply use the
continuecommand, or step, or any other command that resumes execution.
Any other commands in the command list, after a command that resumes execution,
are ignored. This is because any time you resume execution (even with a simple next
or step), you may encounter another breakpoint―which could have its own command
list, leading to ambiguities about which list to execute.
If the first command you specify in a command list is silent, the usual message about
stopping at a breakpoint is not printed. This may be desirable for breakpoints that are
to print a specific message and then continue. If none of the remaining commands print
anything, you see no sign that the breakpoint was reached. silentis meaningful only
at the beginning of a breakpoint command list.
The commands echo, output, and printfallow you to print precisely controlled
output, and are often useful in silent breakpoints. See “Commands for controlled
For example, here is how you could use breakpoint commands to print the value of
x at entry to foowhenever xis positive.
break foo if x>0
commands
silent
printf "x is %d\n",x
cont
end
One application for breakpoint commands is to compensate for one bug so you can
test for another. Put a breakpoint just after the erroneous line of code, give it a condition
to detect the case in which something erroneous has been done, and give it commands
to assign correct values to any variables that need them. End with the continue
command so that your program does not stop, and start with the silentcommand
so that no output is produced. Here is an example:
break 403
commands
silent
set x = y + 4
cont
end
5.1.7 Breakpoint menus
Some programming languages (notably C++) permit a single function name to be
defined several times, for application in different contexts. This is called overloading.
When a function name is overloaded, 'break function' is not enough to tell GDB
where you want a breakpoint. If you realize this is a problem, you can use something
like 'break function(types)' to specify which particular version of the function
you want. Otherwise, GDB offers you a menu of numbered choices for different possible
breakpoints, and waits for your selection with the prompt '>'. The first two options are
62
Stopping and Continuing
always '[0] cancel' and '[1] all'. Typing 1 sets a breakpoint at each definition of
function, and typing 0 aborts the breakcommand without setting any new breakpoints.
For example, the following session excerpt shows an attempt to set a breakpoint at the
overloaded symbol String::after. We choose three particular definitions of that function
name:
((gdb)) b String::after
[0] cancel
[1] all
[2] file:String.cc; line number:867
[3] file:String.cc; line number:860
[4] file:String.cc; line number:875
[5] file:String.cc; line number:853
[6] file:String.cc; line number:846
[7] file:String.cc; line number:735
> 2 4 6
Breakpoint 1 at 0xb26c: file String.cc, line 867.
Breakpoint 2 at 0xb344: file String.cc, line 875.
Breakpoint 3 at 0xafcc: file String.cc, line 846.
Multiple breakpoints were set.
Use the "delete" command to delete unwanted
breakpoints.
((gdb))
5.1.8 “Cannot insert breakpoints”
Under some operating systems, breakpoints cannot be used in a program if any other
process is running that program. In this situation, attempting to run or continue a
program with a breakpoint causes GDB to print an error message:
Cannot insert breakpoints.
The same program may be running in another process.
When this happens, you have three ways to proceed:
1. Remove or disable the breakpoints, then continue.
2. Suspend GDB, and copy the file containing your program to a new name. Resume
GDB and use the exec-filecommand to specify that GDB should run your
program under that name. Then start your program again.
3. Relink your program so that the text segment is nonsharable, using the linker
option '-N'. The operating system limitation may not apply to nonsharable
executables.
A similar message can be printed if you request too many active hardware-assisted
breakpoints and watchpoints:
Stopped; cannot insert breakpoints.
You may have requested too many hardware breakpoints and watchpoints.
This message is printed when you attempt to resume the program, since only then
GDB knows exactly how many hardware breakpoints and watchpoints it needs to
insert.
5.1 Breakpoints
63
When this message is printed, you need to disable or remove some of the
hardware-assisted breakpoints and watchpoints, and then continue.
5.2 Continuing and stepping
Continuing means resuming program execution until your program completes normally.
In contrast, stepping means executing just one more “step” of your program, where
“step” may mean either one line of source code, or one machine instruction (depending
on what particular command you use). Either when continuing or when stepping, your
program may stop even sooner, due to a breakpoint or a signal. (If it stops due to a
signal, you may want to use handle, or use 'signal 0' to resume execution. See
continue [ignore-count], c Resume program execution, at the address where
your program last stopped; any breakpoints set at
that address are bypassed. The optional argument
ignore-count allows you to specify a further
number of times to ignore a breakpoint at this
[ignore-count], fg
[ignore-count]
The argument ignore-count is meaningful only
when your program stopped due to a breakpoint.
At other times, the argument to continueis
ignored.
The synonyms cand fg (for foreground, as the
debugged program is deemed to be the foreground
program) are provided purely for convenience,
and have exactly the same behavior as continue.
different address” (page 120)) to go to an arbitrary location in your program.
A typical technique for using stepping is to set a breakpoint (see “Breakpoints”
(page 51)) at the beginning of the function or the section of your program where a
problem is believed to lie, run your program until it stops at that breakpoint, and then
step through the suspect area, examining the variables that are interesting, until you
see the problem happen.
64
Stopping and Continuing
step
Continue running your program until control reaches a different
source line, then stop it and return control to GDB. This
command is abbreviated s.
WARNING! If you use the stepcommand while control is
within a function that was compiled without debugging
information, execution proceeds until control reaches a function
that does have debugging information. Likewise, it will not step
into a function which is compiled without debugging
information. To stepthrough functions without debugging
information, use the stepicommand, described below.
The stepcommand only stops at the first instruction of a source
line. This prevents the multiple stops that could otherwise occur
in switch statements, for loops, and so on. stepcontinues to
stop if a function that has debugging information is called within
the line. In other words, stepsteps inside any functions called
within the line.
Also, the stepcommand only enters a function if there is line
number information for the function. Otherwise it acts like the
nextcommand. This avoids problems when using cc -gl
on MIPS machines. Previously, step entered subroutines if there
was any debugging information about the routine.
step count
Continue running as in step, but do so count times. If a
breakpoint is reached, or a signal not related to stepping occurs
before count steps, stepping stops right away.
next [count]
Continue to the next source line in the current (innermost) stack
frame. This is similar to step, but function calls that appear
within the line of code are executed without stopping. Execution
stops when control reaches a different line of code at the original
stack level that was executing when you gave the next
command. This command is abbreviated n.
An argument count is a repeat count, as for step.
The nextcommand only stops at the first instruction of a source
line. This prevents multiple stops that could otherwise occur in
switch statements, for loops, and so on.
finish
Continue running until just after function in the selected stack
frame returns. Print the returned value (if any).
5.2 Continuing and stepping
65
until, u
Continue running until a source line past the current line, in the
current stack frame, is reached. This command is used to avoid
single stepping through a loop more than once. It is like the
nextcommand, except that when untilencounters a jump,
it automatically continues execution until the program counter
is greater than the address of the jump.
This means that when you reach the end of a loop after single
stepping though it, untilmakes your program continue
execution until it exits the loop. In contrast, a nextcommand
at the end of a loop simply steps back to the beginning of the
loop, which forces you to step through the next iteration.
untilalways stops your program if it attempts to exit the
current stack frame.
untilmay produce somewhat counterintuitive results if the
order of machine code does not match the order of the source
lines. For example, in the following excerpt from a debugging
session, the f(frame) command shows that execution is stopped
at line 206; yet when we use until, we get to line 195:
((gdb)) f
#0 main (argc=4, argv=0xf7fffae8) at m4.c:206
206 expand_input();
((gdb)) until
195 for ( ; argc > 0; NEXTARG) {
This happened because, for execution efficiency, the compiler
had generated code for the loop closure test at the end, rather
than the start, of the loop―even though the test in a C for-loop
is written before the body of the loop. The untilcommand
appeared to step back to the beginning of the loop when it
advanced to this expression; however, it has not really gone to
an earlier statement―not in terms of the actual machine code.
untilwith no argument works by means of single instruction
stepping, and hence is slower than untilwith an argument.
until location, Continue running your program until either the specified
location is reached, or the current stack frame returns. location
is any of the forms of argument acceptable to break(see
“Setting breakpoints” (page 52)). This form of the command
uses breakpoints, and hence is quicker than untilwithout an
argument.
u location
66
Stopping and Continuing
stepi, stepi arg, Execute one machine instruction, then stop and return to the
debugger.
si
It is often useful to do 'display/i $pc' when stepping by
machine instructions. This makes GDB automatically display
the next instruction to be executed, each time your program
An argument is a repeat count, as in step.
nexti, nexti arg, Execute one machine instruction, but if it is a function call,
proceed until the function returns.
ni
An argument is a repeat count, as in next.
5.3 Signals
A signal is an asynchronous event that can happen in a program. The operating system
defines the possible kinds of signals, and gives each kind a name and a number. For
example, in Unix SIGINTis the signal a program gets when you type an interrupt
character (often C- c); SIGSEGVis the signal a program gets from referencing a place
in memory far away from all the areas in use; SIGALRMoccurs when the alarm clock
timer goes off (which happens only if your program has requested an alarm).
Some signals, including SIGALRM, are a normal part of the functioning of your program.
Others, such as SIGSEGV, indicate errors; these signals are fatal (they kill your program
immediately) if the program has not specified in advance some other way to handle
the signal. SIGINTdoes not indicate an error in your program, but it is normally fatal
so it can carry out the purpose of the interrupt: to kill the program.
GDB has the ability to detect any occurrence of a signal in your program. You can tell
GDB in advance what to do for each kind of signal.
Normally, GDB is set up to ignore non-erroneous signals like SIGALRM(so as not to
interfere with their role in the functioning of your program) but to stop your program
immediately whenever an error signal happens. You can change these settings with
the handlecommand.
5.3 Signals
67
NOTE: Use caution if you disable all signals from certain processes. Disabling
'SIGTRAP' in your program may cause your program to hang.
HP-UX uses 'SIGTRAP' to communicate with the debugger. If you disable all signals
from certain processes so that signals will be delivered to the right process, your
program may hang when you try to debug it. This behavior occurs because if you
disable 'SIGTRAP', the debugger no longer receives notification of events such as
breakpoint hits and loading or unloading of shared libraries.
To prevent this problem:
Make certain you set this flag:
(gdb) set complain-if-sigtrap-disabled on
Also make certain the following warning was not emitted by the debugger before your
program hung:
Warning: Thread %d (in process %d) has disabled SIGTRAPs.
Debugging this thread is probably impossible.
If you do not want to see this message again, use:
"set complain-if-sigtrap-disabled 0"
info signals, info handle
Print a table of all the kinds of signals and how
GDB has been told to handle each one. You can
use this to see the signal numbers of all the
defined types of signals.
info handleis an alias for info signals.
handle signal keywords...
Change the way GDB handles signal signal.
signal can be the number of a signal or its name
(with or without the 'SIG' at the beginning). The
keywords say what change to make.
The keywords allowed by the handlecommand can be abbreviated. Their full names
are:
nostop
GDB should not stop your program when this signal happens. It may still
print a message telling you that the signal has come in.
stop
GDB should stop your program when this signal happens. This implies
the print keyword as well.
print
GDB should print a message when this signal happens.
noprint GDB should not mention the occurrence of the signal at all. This implies
the nostop keyword as well.
68
Stopping and Continuing
pass
GDB should allow your program to see this signal; your program can
handle the signal, or else it may terminate if the signal is fatal and not
handled.
nopass
GDB should not allow your program to see this signal.
When a signal stops your program, the signal is not visible to the program until you
continue. Your program sees the signal then, if passis in effect for the signal in question
at that time. In other words, after GDB reports a signal, you can use the handle
command with passor nopassto control whether your program sees that signal
when you continue.
You can also use the signalcommand to prevent your program from seeing a signal,
or cause it to see a signal it normally would not see, or to give it any signal at any time.
For example, if your program stopped due to some sort of memory reference error,
you might store correct values into the erroneous variables and continue, hoping to
see more execution; but your program would probably terminate immediately as a
result of the fatal signal once it saw the signal. To prevent this, you can continue with
5.4 Stopping and starting multi-thread programs
When your program has multiple threads (see “Debugging programs with multiple
threads” (page 46)), you can choose whether to set breakpoints on all threads, or on a
particular thread.
break linespec thread
threadno, break linespec
thread threadno if ...
linespec specifies source lines; there are several
ways of writing them, but the effect is always to
specify some source line.
Use the qualifier 'thread threadno' with a
breakpoint command to specify that you only
want GDB to stop the program when a particular
thread reaches this breakpoint. threadno is one
of the numeric thread identifiers assigned by
GDB, shown in the first column of the 'info
threads' display.
If you do not specify 'thread threadno' when
you set a breakpoint, the breakpoint applies to
all threads of your program.
You can use the threadqualifier on conditional
breakpoints as well; in this case, place 'thread
threadno' before the breakpoint condition, like
this:
((gdb)) break frik.c:13 thread 28 if
bartab > lim
5.4 Stopping and starting multi-thread programs
69
Whenever your program stops under GDB for any reason, all threads of execution stop,
not just the current thread. This allows you to examine the overall state of the program,
including switching between threads, without worrying that things may change
underfoot.
Conversely, whenever you restart the program, all threads start executing. This is true
even when single-stepping with commands like stepor next.
In particular, GDB cannot single-step all threads in lockstep. Since thread scheduling
is up to your debugging target's operating system (not controlled by GDB), other threads
may execute more than one statement while the current thread completes a single step.
Moreover, in general other threads stop in the middle of a statement, rather than at a
clean statement boundary, when the program stops.
You might even find your program stopped in another thread after continuing or even
single-stepping. This happens whenever some other thread runs into a breakpoint, a
signal, or an exception before the first thread completes whatever you requested.
On some OSes, you can lock the OS scheduler and thus allow only a single thread to
run.
set scheduler-locking mode Set the scheduler locking mode. If it is off, then
there is no locking and any thread may run at
any time. If on, then only the current thread may
run when the inferior is resumed. The step
mode optimizes for single-stepping. It stops other
threads from “seizing the prompt” by
preempting the current thread while you are
stepping. Other threads will only rarely (or
never) get a chance to run when you step. They
are more likely to run when you 'next' over a
function call, and they are completely free to run
when you use commands like 'continue',
'until', or 'finish'. However, unless another
thread hits a breakpoint during its timeslice, they
will never steal the GDB prompt away from the
thread that you are debugging.
show scheduler-locking
Display the current scheduler locking mode.
70
Stopping and Continuing
6 Examining the Stack
When your program has stopped, the first thing you need to know is where it stopped
and how it got there.
Each time your program performs a function call, information about the call is generated.
The information includes the location of the call in your program, the arguments of
the call, and the local variables of the function being called. The information is saved
in a block of data called a stack frame. The stack frames are allocated in a region of
memory called the call stack.
The GDB commands for examining the stack allow you to view all of this information.
6.1 Stack frames
The call stack is divided up into contiguous pieces called stack frames, or frames for short;
each frame is the data associated with one call to one function. The frame contains the
arguments given to the function, the local variables, and the address at which the
function is executing.
When your program is started, the stack has only one frame, that of the function main.
This is called the initial frame or the outermost frame. Each time a function is called, a
new frame is made. Each time a function returns, the frame for that function invocation
is eliminated. If a function is recursive, there can be many frames for the same function.
The frame for the function in which execution is actually occurring is called the innermost
frame. This is the most recently created of all the stack frames that still exist.
Inside your program, stack frames are identified by their addresses. A stack frame
consists of many bytes, each of which has its own address; each kind of computer has
a convention for choosing one byte whose address serves as the address of the frame.
Usually this address is kept in a register called the frame pointer register while execution
is going on in that frame.
GDB assigns numbers to all existing stack frames, starting with zero for the innermost
frame, one for the frame that called it, and so on upward. These numbers do not really
exist in your program; they are assigned by GDB to give you a way of designating stack
frames in GDB commands.
One of the stack frames is selected by GDB and the GDB commands refer implicitly to
the selected frame. In particular, whenever you ask GDB for the value of a variable in
your program, the value is found in the selected frame. There are special GDB
commands to select whichever frame you are interested in. See “Selecting a frame”
When your program stops, GDB automatically selects the currently executing frame
6.1 Stack frames
71
6.2 Stacks Without frames
Some compilers provide a way to compile functions so that they operate without stack
frames. (For example, the gcc option
'-fomit-frame-pointer'
generates functions without a frame.) This is occasionally done with heavily used
library functions to save the frame setup time. GDB has limited facilities for dealing
with these function invocations. If the innermost function invocation has no stack frame,
GDB nevertheless regards it as though it had a separate frame, which is numbered zero
as usual, allowing correct tracing of the function call chain. However, GDB has no
provision for frameless functions elsewhere in the stack.
6.3 Commands for Examining the Stack
The following commands are used for examining the stack:
frame args
Select and print a stack frame. With no argument, prints the selected
stack frame. An argument specifies the frame to select. It can be a
stack frame number or the address of the frame. With argument,
nothing is printed if input is coming from a command file or a
user-defined command.
select-frame
The select-framecommand allows you to move from one stack
frame to another without printing the frame. This is the silent
version of frame.
6.4 Backtraces
A backtrace is a report of the active stack frames instantiated by the execution of a
program. It shows one line per frame, for all the active frames, starting with the currently
executing frame (frame zero), followed by its caller (frame one), and on up the stack.
The following commands are used for backtrace:
backtrace, bt
Print a backtrace of the entire stack: one line per
frame for all frames in the stack.
You can stop the backtrace at any time by typing
the system interrupt character, normally C-c.
backtrace n, bt n
Similar, but print only the innermost n frames.
backtrace -n, bt -n
backtrace-other-thread
Similar, but print only the outermost n frames.
Print backtrace of all stack frames for a thread with
stack pointer SP and program counter PC. This
command is useful in cases where the debugger
does not support a user thread package fully.
72
Examining the Stack
The names whereand info stack(abbreviated info s) are additional aliases for
backtrace.
Each line in the backtrace shows the frame number and the function name. The program
counter value is also shown―unless you use set print address off. The backtrace
also shows the source file name and line number, as well as the arguments to the
function. The program counter value is omitted if it is at the beginning of the code for
that line number.
Here is an example of a backtrace. It was made with the command 'bt 3', so it shows
the innermost three frames.
#0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
at builtin.c:993
#1 0x6e38 in expand_macro (sym=0x2b600) at macro.c:242
#2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08)
at macro.c:71
(More stack frames follow...)
The display for frame zero does not begin with a program counter value, indicating
that your program has stopped at the beginning of the code for line 993 of builtin.c.
6.5 Selecting a frame
Most commands for examining the stack and other data in your program work on
whichever stack frame is selected at the moment.
The following commands are used for selecting a stack frame; all of them finish by
printing a brief description of the stack frame selected.
frame n, f n Select frame number n. Recall that frame zero is the innermost
(currently executing) frame, frame one is the frame that called the
innermost one, and so on. The highest-numbered frame is the one for
main.
frame addr, Select the frame at address addr. This is useful mainly if the chaining
f addr
of stack frames has been damaged by a bug, making it impossible for
GDB to assign numbers properly to all frames. In addition, this can
be useful when your program has multiple stacks and switches
between them.
6.5 Selecting a frame
73
NOTE:
•
•
•
On the SPARC architecture, frameneeds two addresses to select
an arbitrary frame: a frame pointer and a stack pointer.
On the MIPS and Alpha architecture, it needs two addresses: a
stack pointer and a program counter.
On the 29k architecture, it needs three addresses: a register stack
pointer, a program counter, and a memory stack pointer.
up n
Move n frames up the stack. For positive numbers n, this advances
toward the outermost frame, to higher frame numbers, to frames that
have existed longer. n defaults to one.
down n
Move n frames down the stack. For positive numbers n, this advances
toward the innermost frame, to lower frame numbers, to frames that
were created more recently. n defaults to one. You may abbreviate
downas do.
All of these commands end by printing two lines of output describing the frame. The
first line shows the frame number, the function name, the arguments, and the source
file and line number of execution in that frame. The second line shows the text of that
source line.
For example:
((gdb)) up
#1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
at env.c:10
10 read_input_file (argv[i]);
After such a printout, the listcommand with no arguments prints ten lines centered
up-silently n,
down-silently n
These two commands are variants of upand down,
respectively; they differ in that they do their work silently,
without causing display of the new frame. They are intended
primarily for use in GDB command scripts, where the output
might be unnecessary and distracting.
6.6 Information about a frame
The following commands are used to print information about the selected stack frame:
frame, f
When used without any argument, this command does not
change which frame is selected, but prints a brief description
of the currently selected stack frame. It can be abbreviated f.
With an argument, this command is used to select a stack
74
Examining the Stack
info frame, info
f
This command prints a verbose description of the selected
stack frame, including:
•
•
•
•
the address of the frame
the address of the next frame down (called by this frame)
the address of the next frame up (caller of this frame)
the language in which the source code corresponding to
this frame is written
•
•
•
the address of the frame's arguments
the address of the frame's local variables
the program counter saved in it (the address of execution
in the caller frame)
•
which registers were saved in the frame
The verbose description is useful when something has gone
wrong that has made the stack format fail to fit the usual
conventions.
info frame addr,
info f addr
Print a verbose description of the frame at address addr,
without selecting that frame. The selected frame remains
unchanged by this command. This requires the same kind of
address (more than one for some architectures) that you specify
info args
Print the arguments of the selected frame, each on a separate
line.
info locals
Print the local variables of the selected frame, each on a
separate line. These are all variables (declared either static or
automatic) accessible at the point of execution of the selected
frame.
info catch
Print a list of all the exception handlers that are active in the
current stack frame at the current point of execution. To see
other exception handlers, visit the associated frame (using the
up, down, or framecommands); then type info catch. See
6.6 Information about a frame
75
76
7 Examining Source Files
GDB can print parts of the source code of your program, since the debugging
information recorded in the program tells GDB what source files were used to build
it. When your program stops, GDB spontaneously prints the line where it stopped.
the line where execution in that frame has stopped. You can print other portions of
source files by explicit command.
You can invoke GDB from its GNU Emacs interface to view the source code see
7.1 Printing source lines
To print lines from a source file, use the listcommand (abbreviated l). By default,
ten lines are printed. There are several ways to specify what part of the file you want
to print.
The following forms of the listcommand are used:
list linenum
Prints lines centered around line number linenum in the current
source file.
list function
Prints lines centered around the beginning of function function.
list
Prints more lines. The listcommand prints lines following the
lines printed by a previously executed listcommand. If the
command prior to executing a listjust printed the stack frame,
then the listcommand only prints the lines around that line.
list-
Prints lines just before the lines last printed.
By default, GDB prints ten source lines with any of these forms of the listcommand.
The number of lines printed by GDB can be set by the set listsizecommand. The
following two forms are supported:
set listsize count
Makes the listcommand display count source lines
(unless the listargument explicitly specifies some other
number).
show listsize
Displays the number of lines that listprints.
Repeating a listcommand with RET discards the argument, so it is equivalent to
typing just list. This is more useful than listing the same lines again. An exception
is made for an argument of '-'; that argument is preserved in repetition so that each
repetition moves up in the source file.
In general, the listcommand expects you to supply zero, one or two linespecs.
Linespecs specify source lines. There are several ways of writing them, but the most
common way is to specify some source line.
7.1 Printing source lines
77
The following arguments can be given to the listcommand:
list linespec
Print lines centered around the line specified by linespec.
list first,last
Print lines from first to last. Both arguments must be
linespecs.
list, last
list first,
list +
Print lines ending with last.
Print lines starting with first.
Print lines just after the lines last printed.
Print lines just before the lines last printed.
As described in the preceding table.
list -
list
A single source line can be specified in the following ways:
number
Specifies line number of the current source file. When a
listcommand has two linespecs, this refers to the same
source file as the first linespec.
+offset
Specifies the line offset lines after the last line printed.
When used as the second linespec in a listcommand that
has two, this specifies the line offset lines down from the
first linespec.
-offset
Specifies the line offset lines before the last line printed.
filename:number
function
Specifies line number in the source file filename.
Specifies the line that begins the body of the function
function. For example: in C, this is the line with the open
brace.
filename:function
Specifies the line of the open-brace that begins the body of
the function function in the file filename. You only
need the file name with a function name to avoid ambiguity
when there are identically named functions in different
source files.
*address
Specifies the line containing the program address address.
address may be any expression.
7.2 Searching source files
There are two commands for searching through the current source file for a regular
expression.
forward-search regexp,
search regexp
The command 'forward-search regexp' checks
each line, starting with one of the following in the
last line listed, for a match of the regexp. It lists the
line that is found. You can use the synonym 'search
regexp' or abbreviate the command name as fo.
78
Examining Source Files
reverse-search regexp
The command 'reverse-search regexp' checks
each line, starting with the one before the last line
listed and going backward, for a match for the
regexp. It lists the line(s) that is found. You can
abbreviate this command as rev.
7.3 Specifying source directories
Executable programs sometimes do not record the directories of the source files from
which they were compiled. Even when they do, the directories can be moved between
the compilation and your debugging session. GDB has a list of directories to search for
source files; this is called the source path. Each time GDB looks for a source file, it tries
all the directories in the list, in the order they are present in the list, until it finds a file
with the desired name. Note that the executable search path is not used for this purpose.
Neither is the current working directory, unless it happens to be in the source path.
If GDB cannot find a source file in the source path, and the object program records a
directory, GDB tries that directory too. If the source path is empty, and there is no
record of the compilation directory, GDB looks in the current directory as a last resort.
Whenever you reset or rearrange the source path, GDB clears out any information it
has cached about where the source files are located and where each line is in the
respective file.
When you start GDB, its source path includes only 'cdir' and 'cwd', in that order.
To add other directories, you can use the directorycommand.
directory dirname ...,
dir dirname ...
Add directory dirname to the front of the source
path. Several directory names may be given to this
command, separated by ':' (';' on MS-DOS and
MS-Windows, where ':' usually appears as part of
absolute file names) or a whitespace. You can specify
a directory that is already in the source path; this
moves it forward, so GDB searches it sooner.
You can use the string '$cdir' to refer to the
compilation directory (if one is recorded), and '$cwd'
to refer to the current working directory. '$cwd' is
not the same as '.'. The former tracks the current
working directory as it changes during your GDB
session, while the latter is immediately expanded to
the current directory at the time you add an entry to
the source path.
directory
Reset the source path to empty again. This requires
confirmation from the user.
7.3 Specifying source directories
79
show directories
Print the source path and display the directories it
contains.
If your source path is cluttered with directories that are no longer of interest, GDB can
end up detecting the wrong version of the source. To correct this situation, follow these
steps:
1. Use directorywith no arguments to reset the source path to empty.
2. Use directorywith suitable arguments to reinstall the directories you want in
the source path. You can add all the directories in one command.
7.4 Source and machine code
You can use the command info lineto map source lines to program addresses (and
vice versa), and the command disassembleto display a range of addresses as machine
instructions. When run under GNU Emacs mode, the info linecommand causes
the arrow to point to the line specified. Also, info lineprints addresses in symbolic
form as well as hex.
info line linespec
Print the starting and ending addresses of the compiled
code for source line linespec. You can specify source
lines in any of the ways understood by the listcommand
For example, we can use info lineto discover the location of the object code for the
first line of function.
m4_changequote:
((gdb)) info line m4_changequote
Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350.
We can also inquire (using *addr as the form for linespec) what source line covers
a particular address. For example,
((gdb)) info line *0x63ff
Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404.
After info line, the default address for the xcommand is changed to the starting
address of the line, so that 'x/i' is sufficient to begin examining the machine code (see
Section 8.5 (page 87)). Also, this address is saved as the value of the convenience
disassemble
This specialized command dumps a range of memory as machine
instructions. The default memory range is the function surrounding
the program counter of the selected frame. A single argument to this
command is a program counter value; GDB dumps the function
surrounding this value. Two arguments specify a range of addresses
(first inclusive, second exclusive) to dump.
80
Examining Source Files
The following example shows the disassembly of a range of addresses of HP PA-RISC
2.0 code:
((gdb)) disas 0x32c4 0x32e4
Dump of assembler code from 0x32c4 to 0x32e4:
0x32c4 <main+204>: addil 0,dp
0x32c8 <main+208>: ldw 0x22c(sr0,r1),r26
0x32cc <main+212>: ldil 0x3000,r31
0x32d0 <main+216>: ble 0x3f8(sr4,r31)
0x32d4 <main+220>: ldo 0(r31),rp
0x32d8 <main+224>: addil -0x800,dp
0x32dc <main+228>: ldo 0x588(r1),r26
0x32e0 <main+232>: ldil 0x3000,r31
End of assembler dump.
Some architectures have more than one commonly-used set of instruction mnemonics
or other syntax.
set disassembly-flavor
instruction-set
Select the instruction set to use when
disassembling the program via the
disassembleor x/icommands.
Currently this command is only defined for the
Intel x86 family. You can set instruction-set
to either intelor att. The default is att, the
AT&T flavor used by default by Unix assemblers
for x86-based targets.
7.4 Source and machine code
81
82
8 Examining Data
The usual way to examine data in your program is with the printcommand
(abbreviated p), or its synonym inspect. It evaluates and prints the value of an
The following forms of printcommand are supported:
print expr,
print /f expr
expr is an expression (in the source language). By default, the
value of expr is printed in a format appropriate to its data type;
you can choose a different format by specifying '/f', where f is
print, print /f If you omit expr, GDB displays the last value again (from the
conveniently inspect the same value in an alternative format.
A more low-level way of examining data is with the xcommand. It examines data in
memory at a specified address and prints it in a specified format. See “Examining
If you are interested in information about types, or about how the fields of a struct or
8.1 Expressions
printand many other GDB commands accept an expression and compute its value.
Any kind of constant, variable or operator defined by the programming language you
are using is valid in an expression in GDB. This includes conditional expressions,
function calls, casts, and string constants. It unfortunately does not include symbols
defined by preprocessor #definecommands.
GDB supports array constants in expressions input by the user. The syntax is
{element, element. . .}. For example, you can use the command print {1,
2, 3}to build up an array in memory that calls mallocin the target program.
Because C is so widespread, most of the expressions shown in examples in this manual
languages.
In this section, we discuss operators that you can use in GDB expressions regardless
of your programming language.
Casts are supported in all languages, not just in C, because it is so useful to cast a
number into a pointer in order to examine a structure at that address in memory.
GDB supports these operators, in addition to those common to programming languages:
@
'@' is a binary operator for treating parts of memory as arrays. Refer
8.1 Expressions
83
::
'::' allows you to specify a variable in terms of the file or function
{type} addr
Refers to an object of type type stored at address addr in memory.
addr may be any expression whose value is an integer or pointer
(but parentheses are required around binary operators, just as in a
cast). This construct is allowed regardless of what kind of data is
normally supposed to reside at addr.
8.2 Program variables
The most common kind of expression to use is the name of a variable in your program.
Variables in expressions are understood in the selected stack frame (see “Selecting a
frame” (page 73); they must be either:
•
global (or file-static)
or
•
visible according to the scope rules of the programming language from the point
of execution in that frame
This means that in the function
foo (a)
int a;
{
bar (a);
{
int b = test ();
bar (b);
}
}
you can examine and use the variable awhenever your program is executing within
the function foo, but you can only use or examine the variable bwhile your program
is executing inside the block where bis declared.
However, you can refer to a variable or function whose scope is a single source file
even if the current execution point is not in this file. But it is possible to have more than
one such variable or function with the same name (in different source files). If that
happens, referring to that name has unpredictable effects. If you wish, you can specify
a static variable in a particular function or file, using the colon-colon notation:
file::variable
function::variable
Here file or function is the name of the context for the static variable. In the case
of file names, you can use quotes to make sure GDB parses the file name as a single
word. For example, to print a global value of xdefined in 'f2.c':
((gdb)) p 'f2.c'::x
84
Examining Data
This use of '::' is very rarely in conflict with the very similar use of the same notation
in C++. GDB also supports use of the C++ scope resolution operator in GDB expressions.
WARNING! Occasionally, a local variable may appear to have the wrong value at
certain points in a function just after entry to a new scope, and just before exit.
You may see this problem when you are stepping by machine instructions. This is
because, on most machines, it takes more than one instruction to set up a stack frame
(including local variable definitions); if you are stepping by machine instructions,
variables may appear to have the wrong values until the stack frame is completely
built. On exit, it usually also takes more than one machine instruction to destroy a stack
frame; after you begin stepping through that group of instructions, local variable
definitions may be gone.
This may also happen when the compiler does significant optimizations. To be sure of
always seeing accurate values, turn o all optimization when compiling.
Another possible effect of compiler optimizations is to optimize unused variables out
of existence, or assign variables to registers (as opposed to memory addresses).
Depending on the support for such cases offered by the debug info format used by the
compiler, GDB might not be able to display values for such local variables. If that
happens, GDB will print a message like this:
No symbol "foo" in current context.
To solve such problems, either recompile without optimizations, or use a different
debug info format, if the compiler supports several such formats. For example, GCC,
the GNU C/C++ compiler usually supports the '-gstabs' option. The '-gstabs'
produces debug information in a format that is superior to formats such as COFF. You
may be able to use DWARF-2('-gdwarf-2'), which is also an effective form for debug
8.3 Artificial arrays
It is often useful to print out several successive objects of the same type in memory; a
section of an array, or an array of dynamically determined size for which only a pointer
exists in the program.
You can do this by referring to a contiguous span of memory as an artificial array, using
the binary operator '@'. The left operand of '@' should be the first element of the desired
array and be an individual object. The right operand should be the desired length of
the array. The result is an array value whose elements are all of the type of the left
argument. The first element is actually the left argument; the second element comes
from bytes of memory immediately following those that hold the first element, and so
on. Here is an example. If a program says
int *array = (int *) malloc (len * sizeof (int));
you can print the contents of arraywith
8.3 Artificial arrays
85
p *array@len
The left operand of '@' must reside in memory. Array values made with '@' in this way
behave just like other arrays in terms of subscripting, and are coerced to pointers when
used in expressions. Artificial arrays most often appear in expressions via the value
Another way to create an artificial array is to use a cast. This re-interprets a value as if
it were an array. The value need not be in memory:
((gdb)) p/x (short[2])0x12345678
$1 = {0x1234, 0x5678}
As a convenience, if you leave the array length out (as in '(type[])value'), GDB
calculates the size to fill the value (as 'sizeof(value)/sizeof(type)':
((gdb)) p/x (short[])0x12345678
$2 = {0x1234, 0x5678}
Sometimes the artificial array mechanism is not quite enough; in moderately complex
data structures, the elements of interest may not actually be adjacent―for example, if
you are interested in the values of pointers in an array. One useful work-around in this
a counter in an expression that prints the first interesting value, and then repeat that
expression via RET. For instance, suppose you have an array dtabof pointers to
structures, and you are interested in the values of a field fvin each structure. Here is
an example of what you might type:
set $i = 0
p dtab[$i++]->fv
<RET>
<RET>
...
8.4 Output formats
By default, GDB prints a value according to its data type. Sometimes this is not what
you want. For example, you might want to print a number in hex, or a pointer in
decimal. Or you might want to view data in memory at a certain address as a character
string or as an instruction. To do these things, specify an output format when you print
a value.
The simplest use of output formats is to say how to print a value already computed.
This is done by starting the arguments of the printcommand with a slash and a format
letter. The format letters supported are:
x
d
u
o
Regard the bits of the value as an integer, and print the integer in hexadecimal.
Print as integer in signed decimal.
Print as integer in unsigned decimal.
Print as integer in octal.
86
Examining Data
2
2
t
a
Print as integer in binary. The letter 't' stands for “two” .
Print as an address, both absolute in hexadecimal and as an offset from the nearest
preceding symbol. You can use this format used to discover where (in what function)
an unknown address is located:
((gdb)) p/a 0x54320
$3 = 0x54320 <_initialize_vx+396>
c
f
Regard as an integer and print it as a character constant.
Regard the bits of the value as a floating point number and print using typical
floating point syntax.
p/x $pc
Note that no space is required before the slash; this is because command names in GDB
cannot contain a slash.
To reprint the last value in the value history with a different format, you can use the
printcommand with just a format and no expression. For example, 'p/x' reprints the
last value in hex.
8.5 Examining memory
You can use the command x(for “examine”) to examine memory in any of several
formats, independent of your program data types.
x/nfu addr, Use the xcommand to examine memory.
x addr, x
[n],[ f], and [u] are all optional parameters that specify how much memory to display
and how to format it; addr is an expression giving the address where you want to start
displaying memory. If you use defaults for nfu, you need not type the slash '/'. Several
commands set convenient defaults for addr.
[n], the repeat count
The repeat count is a decimal integer and the
default is 1. It specifies how much memory
(counting by units u) to display.
[f], the display format
The display format is one of the formats used by
print, 's' (null-terminated string), or 'i'
(machine instruction). The default is 'x'
(hexadecimal) initially. The default changes each
time you use either xor print.
[u], the unit size
The unit size is any of
b
Bytes.
h
Halfwords (two bytes).
2. 'b' cannot be used because these format letters are also used with the x command, where 'b' stands for
8.5 Examining memory
87
w
g
Words (four bytes). This is the initial default.
Giant words (eight bytes).
Each time you specify a unit size with x, that
size becomes the default unit the next time
you use x. (For the 's' and 'i' formats, the
unit size is ignored and is normally not
written.)
addr, starting display address
addr is the address where you want GDB to
begin displaying memory. The expression need
not have a pointer value (though it may); it is
always interpreted as an integer address of a byte
for more information on expressions. The default
for addr is usually just after the last address
examined―but several other commands also set
the default address: info breakpoints(to the
address of the last breakpoint listed), info line
(to the starting address of a line), and print(if
you use it to display a value from memory).
For example, 'x/3uh 0x54320' is a request to display three halfwords (h) of memory,
formatted as unsigned decimal integers ('u'), starting at address 0x54320. 'x/4xw $sp'
(page 98)) in hexadecimal ('x').
Since the letters indicating unit sizes are all distinct from the letters specifying output
formats, you do not have to remember whether unit size or format comes first; either
order works. The output specifications '4xw' and '4wx' mean exactly the same thing.
(However, the count n must come first; 'wx4' does not work.)
Even though the unit size u is ignored for the formats 's' and 'i', you might still want
to use a count n; for example, '3i' specifies that you want to see three machine
instructions, including any operands. The command disassemblegives an alternative
All the defaults for the arguments to xare designed to make it easy to continue scanning
memory with minimal specifications each time you use x. For example, after you have
inspected three machine instructions with 'x/3i addr', you can inspect the next seven
with just 'x/7'. If you use RET to repeat the xcommand, the repeat count n is used
again; the other arguments default as for successive uses of x.
The addresses and contents printed by the xcommand are not saved in the value
history because there is often too much of them and they would get in the way. Instead,
GDB makes these values available for subsequent use in expressions as values of the
convenience variables $_and $__. After an xcommand, the last address examined is
88
Examining Data
available for use in expressions in the convenience variable $_. The contents of that
address, as examined, are available in the convenience variable $__.
If the xcommand has a repeat count, the address and contents saved are from the last
memory unit printed; this is not the same as the last address printed if several units
were printed on the last line of output.
8.6 Automatic display
If you find that you want to print the value of an expression frequently (to see how it
changes), you might want to add it to the automatic display list so that GDB prints its
value each time your program stops. Each expression added to the list is given a number
to identify it; to remove an expression from the list, you specify that number. The
automatic display looks like this:
2: foo = 38
3: bar[5] = (struct hack *) 0x3804
This display shows item numbers, expressions, and their current values. As with
displays you request manually using xor print, you can specify the output format
you prefer; in fact, displaydecides whether to use printor xdepending on how
elaborate your format specification is―it uses xif you specify a unit size, or one of the
two formats ('i' and 's') that are only supported by x; otherwise it uses print.
display expr
Add the expression expr to the list of expressions to display
displaydoes not repeat if you press RET again after using
it.
display/fmt expr
For fmt specifying only a display format and not a size or
count, add the expression expr to the auto-display list but
arrange to display it each time in the specified format fmt.
display/fmt addr
For fmt 'i' or 's', or including a unit-size or a number of
units, add the expression addr as a memory address to be
examined each time your program stops. Examining means
For example, `display/i $pc' can be helpful, to view the machine instruction about
to be executed each time execution stops (`$pc' is a common name for the program
undisplay dnums..., delete
display dnums...
Remove item numbers dnums from the list of
expressions to display. undisplaydoes not
repeat if you press RET after using it. (Otherwise
you would just get the error 'No display number
...'.)
8.6 Automatic display
89
disable display dnums...
Disable the display of item numbers dnums. A
disabled display item is not printed
automatically, but is not forgotten. It may be
enabled again later.
enable display dnums...
Enable display of item numbers dnums. It
becomes effective once again in auto display of
its expression, until you specify otherwise.
display
Display the current values of the expressions on
the list, just as is done when your program stops.
info display
Print the list of expressions previously set up to
display automatically, each one with its item
number, but without showing the values. This
includes disabled expressions, which are marked
as such. It also includes expressions which would
not be displayed right now because they refer to
automatic variables not currently available.
If a display expression refers to local variables, then it does not make sense outside the
lexical context for which it was set up. Such an expression is disabled when execution
enters a context where one of its variables is not defined. For example, if you give the
command display last_charwhile inside a function with an argument last_char,
GDB displays this argument while your program continues to stop inside that function.
When it stops elsewhere, where there is no variable last_char, the display is disabled
automatically. The next time your program stops where last_charis meaningful,
you can enable the display expression again.
8.7 Print settings
GDB provides the following ways to control how arrays, structures, and symbols are
printed.
These settings are useful for debugging programs in any language:
set print address, set
print address on
GDB prints memory addresses showing the location
of stack traces, structure values, pointer values,
breakpoints, and so forth, even when it also displays
the contents of those addresses. The default is on. For
example, this is what a stack frame display looks like
with set print address on:
((gdb)) f
#0 set_quotes (lq=0x34c78 "<<", rq=0x34c88
">>")
at input.c:530
530 if (lquote != def_lquote)
90
Examining Data
set print address off
Do not print addresses when displaying their
contents. For example, this is the same stack frame
displayed with set print address off:
((gdb)) set print addr off
((gdb)) f
#0 set_quotes (lq="<<", rq=">>") at
input.c:530
530 if (lquote != def_lquote)
You can use 'set print address off' to eliminate
all machine dependent displays from the GDB
interface. For example, with print address off,
you should get the same text for backtraces on all
machines―whether or not they involve pointer
arguments.
show print address
Show whether or not addresses are to be printed.
When GDB prints a symbolic address, it normally prints the closest previous symbol
plus an offset. If that symbol does not uniquely identify the address (for example, it is
a name whose scope is a single source file), you may need to clarify it. One way to do
this is with info line. For example 'info line *0x4537'. Alternately, you can
set GDB to print the source file and the line number when it prints a symbolic address:
set print symbol-filename
on
Tell GDB to print the source file name and line
number of a symbol in the symbolic form of an
address.
set print symbol-filename
off
Do not print source file name and line number
of a symbol. This is the default.
show print symbol-filename Show whether or not GDB will print the source
file name and line number of a symbol in the
symbolic form of an address.
Another situation where it is helpful to show symbol filenames and line numbers is
when disassembling code. GDB shows you the line number and source file that
corresponds to each instruction.
Also, you may wish to see the symbolic form only if the address being printed is
reasonably close to the closest earlier symbol:
set print
max-symbolic-offset
max-offset
Tell GDB to only display the symbolic form of
an address if the offset between the closest
symbol and the address is less than
max-offset. The default is 0, which tells GDB
to always print the symbolic form of an address
if any symbol precedes it.
show print
max-symbolic-offset
Ask how large the maximum offset is that GDB
prints in a symbolic address.
8.7 Print settings
91
If you have a pointer and you are not sure where it points, try 'set print
symbol-filename on'. Then you can determine the name and source file location
of the variable where it points, using 'p/a pointer'. This interprets the address in
symbolic form. For example, here GDB shows that a variable pttpoints at another
variable t, defined in 'hi2.c':
((gdb)) set print symbol-filename on
((gdb)) p/a ptt
$4 = 0xe008 <t in hi2.c>
WARNING! For pointers that point to a local variable, 'p/a' does not show the symbol
name and filename of the referent, even with the appropriate set printoptions
turned on.
Other settings to control how different kinds of objects are printed:
set print array, set print
array on
Pretty print arrays. This format is more
convenient to read, but uses more space. The
default is off.
set print array off
show print array
Return to compressed format for arrays.
Show whether compressed or pretty format is
selected for displaying arrays.
set print elements
number-of-elements
Set a limit on how many elements of an array
GDB will print. If GDB is printing a large array,
it stops printing after it has printed the number
of elements set by the set print elements
command. This limit also applies to the display
of strings. When GDB starts, this limit is set to
200. Setting number-of-elements to zero
means that the printing is unlimited.
show print elements
set print null-stop
Display the number of elements of a large array
that GDB will print. If the number is 0, then the
printing is unlimited.
Cause GDB to stop printing the characters of an
array when the first NULLis encountered. This
is useful when large arrays actually contain only
short strings. The default is off.
set print pretty on
Cause GDB to print structures in an indented
format with one member per line, like this:
$1 = {
next = 0x0,
flags = {
sweet = 1,
sour = 1
92
Examining Data
},
meat = 0x54 "Pork"
}
set print pretty off
Cause GDB to print structures in a compact
format, like this:
$1 = {next = 0x0, flags = {sweet = 1,
sour = 1}, \
meat = 0x54 "Pork"}
This is the default format.
show print pretty
Show which format GDB is using to print
structures.
set print sevenbit-strings Print using only seven-bit characters; if this
option is set, GDB displays any eight-bit
characters (in strings or character values) using
the notation \nnn. This setting is best if you are
working in English (ASCII) and you use the
high-order bit of characters as a marker or “meta”
bit.
on
set print sevenbit-strings Print full eight-bit characters. This allows the use
of more international character sets, and is the
default.
off
show print sevenbit-strings Show whether or not GDB is printing only
seven-bit characters.
set print union on
set print union off
show print union
Tell GDB to print unions which are contained in
structures. This is the default setting.
Tell GDB not to print unions which are contained
in structures.
Ask GDB whether or not it will print unions
which are contained in structures.
For example, given the declarations
typedef enum {Tree, Bug} Species;
typedef enum {Big_tree, Acorn, Seedling}
Tree_forms;
typedef enum {Caterpillar, Cocoon,
Butterfly}
Bug_forms;
struct thing {
Species it;
union {
Tree_forms tree;
Bug_forms bug;
8.7 Print settings
93
} form;
};
struct thing foo = {Tree, {Acorn}};
with set print union onin effect 'p foo'
would print
$1 = {it = Tree, form = {tree = Acorn,
bug = Cocoon}}
and with set print union offin effect it
would print
$1 = {it = Tree, form = {...}}
These settings are of interest when debugging C++ programs:
set print demangle, set
print demangle on
Print C++ names in their source form rather than
in the encoded (“mangled”) form passed to the
assembler and linker for type-safe linkage. The
default is on.
show print demangle
Show whether C++ names are printed in mangled
or demangled form.
set print asm-demangle, set Print C++ names in their source form rather than
their mangled form, even in assembler code
printouts such as instruction disassemblies. The
default is off.
print asm-demangle on
show print asm-demangle
Show whether C++ names in assembly listings
are printed in mangled or demangled form.
set demangle-style style
Choose among several encoding schemes used
by different compilers to represent C++ names.
On HP-UX, WDB automatically chooses the
appropriate style.
The choices for style currently supported are:
auto
gnu
hp
Allow GDB to choose a decoding style
by inspecting your program.
Decode based on the GNU C++
compiler (g++) encoding algorithm.
Decode based on the HP ANSI C++
(aCC) encoding algorithm.
lucid Decode based on the Lucid C++
compiler (lcc) encoding algorithm.
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Examining Data
arm
Decode using the algorithm in the C++
Annotated Reference Manual.
WARNING! This setting alone is not
sufficient to allow debugging cfront
generated executables. GDB would
require further enhancement to permit
that.
If you omit style, you will see a list
of possible formats.
show demangle-style
Display the encoding style currently in use for
decoding C++ symbols.
set print object, set print When displaying a pointer to an object, identify
the actual (derived) type of the object rather than
the declared type, using the virtual function
table.
object on
set print object off
show print object
Display only the declared type of objects, without
reference to the virtual function table. This is the
default setting.
Show whether actual or declared object types are
displayed.
set print static-members,
set print static-members
on
Print static members when displaying a C++
object. The default is on.
set print static-members
off
Do not print static members when displaying a
C++ object.
show print static-members
Show whether C++ static members are printed,
or not.
set print vtbl, set print
vtbl on
Pretty print C++ virtual function tables. The
default is off. (The vtblcommands do not work
on programs compiled with the HP ANSI C++
compiler (aCC).)
set print vtbl off
show print vtbl
Do not pretty print C++ virtual function tables.
Show whether C++ virtual function tables are
pretty printed, or not.
8.8 Value history
Values printed by the printcommand are saved in the GDB value history. This allows
you to refer to them in other expressions. Values are kept until the symbol table is
8.8 Value history
95
re-read or discarded (for example with the fileor symbol-filecommands). When
the symbol table changes, the value history is discarded, since the values may contain
pointers back to the types defined in the symbol table.
The values printed are given history numbers by which you can refer to them. These are
a range of integers starting with one. printshows you the history number assigned
to a value by printing '$num = ' before the value; here num is the history number.
To refer to any previous value, use '$' followed by the history number of the value. The
way printlabels its output is designed to remind you of this. Just $ refers to the most
recent value in the history, and $$ refers to the value before that. $$n refers to the nth
value from the end; $$2 is the value just prior to $$, $$1 is equivalent to $$, and $$0 is
equivalent to $.
For example, suppose you have just printed a pointer to a structure and want to see
the contents of the structure. It suffices to type
p *$
If you have a chain of structures where the component nextpoints to the next one,
you can print the contents of the next one with this:
p *$.next
You can print successive links in the chain by repeating this command using the RET
key.
Note that the history records values, not expressions. If the value of xis 4 and you type
these commands:
print x
set x=5
then the value recorded in the value history by the printcommand remains 4 even
though the value of xhas changed.
show values
Print the last ten values in the value history, with their item
numbers. This is like 'p $$9' repeated ten times, except that show
valuesdoes not change the history.
show values n
Print ten history values centered on history item number n.
show values +
Print ten history values following the values last printed. If no
more values are available, show values +produces no display.
Pressing RET to repeat show values n has exactly the same effect as 'show values
+'.
8.9 Convenience variables
GDB provides convenience variables that you can use within GDB to hold on to a value
and refer to it later. These variables exist entirely within GDB. They are not part of your
program, and setting a convenience variable has no direct effect on further execution
of your program. That is why you can use them freely.
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Examining Data
Convenience variables are prefixed with '$'. Any name preceded by '$' can be used for
a convenience variable, unless it is one of the predefined machine-specific register
You can save a value in a convenience variable with an assignment expression, just as
you would set a variable in your program. For example:
set $foo = *object_ptr
would save in $foothe value contained in the object pointed to by object_ptr.
Using a convenience variable for the first time creates it, but its value is voiduntil you
assign a new value. You can alter the value with another assignment at any time.
Convenience variables have no fixed types. You can assign a convenience variable any
type of value, including structures and arrays, even if that variable already has a value
of a different type. The convenience variable, when used as an expression, has the type
of its current value.
show convenience
Print a list of convenience variables used so far, and their
values. Abbreviated show conv.
A convenient variable can be used as a counter to be incremented or a pointer to be
advanced. For example, to print a field from successive elements of an array of
structures:
set $i = 0
print bar[$i++]->contents
Repeat that command by typing RET.
Some convenience variables are created automatically by GDB and assigned values.
$_
The variable $_is automatically set by the xcommand to the last
commands which provide a default address for xto examine, also set
$_to that address. These commands include info lineand info
breakpoint. The type of $_is void *except when set by the x
command, in which case it is a pointer to the type of $__.
$__
The variable $__is automatically set by the xcommand to the value
found in the last address examined. Its type is chosen to match the
format in which the data was printed.
$_exitcode
The variable $_exitcodeis automatically set to the exit code when
the program being debugged terminates.
On HP-UX systems, if you refer to a function or variable name that begins with a dollar
sign, GDB searches for a user or system name first, before it searches for a convenience
variable.
8.9 Convenience variables
97
8.10 Registers
You can refer to machine register contents, in expressions, as variables with names
starting with '$'. The names of registers are different for each machine. Use info
registersto view the names used on your machine.
info registers
Print the names and values of all registers except
floating-point registers (in the selected stack
frame).
info all-registers
Print the names and values of all registers,
including floating-point registers.
info registers regname ... Print the relativized value of each specified
register regname. As discussed in detail below,
register values are normally relative to the
selected stack frame. regname may be any
register name valid on the machine you are
using, with or without the initial '$'.
GDB has four standard register names that are available (in expressions) on most
machines―whenever they do not conflict with an architecture's canonical mnemonics
for registers. The register names $pcand $spare used for the program counter register
and the stack pointer. $fpis used for a register that contains a pointer to the current
stack frame, and $psis used for a register that contains the processor status. For
example, you could print the program counter in hex with
p/x $pc
or print the instruction to be executed next with
x/i $pc
3
3
or add four to the stack pointer with with
set $sp += 4
Whenever possible, these four standard register names are available on your machine
even though the machine has different canonical mnemonics, so long as there is no
conflict. The info registerscommand shows the canonical names. For example,
on the SPARC, info registersdisplays the processor status register as $psrbut
you can also refer to it as $ps; and on x86-based machines $psis an alias for the EFLAGS
register.
GDB always considers the contents of an ordinary register as an integer when the
register is examined in this way. Some machines have special registers which can hold
nothing but floating point; these registers are considered to have floating point values.
There is no way to refer to the contents of an ordinary register as floating point value
(although you can print it as a floating point value with 'print/f $regname').
3. This is a way of removing one word from the stack, on machines where stacks grow downward in memory
(most machines, nowadays). This assumes that the innermost stack frame is selected; setting $spis not
allowed when other stack frames are selected. To pop entire frames off the stack, regardless of machine
98
Examining Data
Some registers have distinct raw and virtual data formats. This means that the data
format in which the register contents are saved by the operating system is not the same
one that your program normally sees. For example, the registers of the 68881 floating
point coprocessor are always saved in “extended” (raw) format, but all C programs
expect to work with “double” (virtual) format. In such cases, GDB normally works
with the virtual format only (the format that makes sense for your program), but the
info registerscommand prints the data in both formats.
(page 73)). This means that you get the value that the register would contain if all stack
frames farther in were exited and their saved registers restored. In order to see the true
contents of hardware registers, you must select the innermost frame (with 'frame 0').
However, GDB must deduce where registers are saved, from the machine code generated
by your compiler. If some registers are not saved, or if GDB is unable to locate the saved
registers, the selected stack frame makes no difference.
8.11 Printing Floating Point Values
You can print the values of floating-point registers in different formats.
To print both single and double-precision values:
(gdb) info reg $fr5
fr5 (single precision) 10.1444092
fr5
To get the bit pattern, try the following macro:
define pbits
set *((float *) $sp)=$arg0
p/x *((int *) $sp)
end
This is what the macro produces:
(gdb) pbits $fr6
$1 = 0x4082852d
8.12 Floating point hardware
Depending on the configuration, GDB may be able to give you more information about
the status of the floating point hardware.
info float
Display hardware-dependent information about the floating point
unit. The exact contents and layout vary depending on the floating
point chip. Currently, 'info float' is supported on the ARM and
x86 machines.
8.11 Printing Floating Point Values
99
100
9 Using GDB with Different Languages
Although programming languages generally have common aspects, they are rarely
expressed in the same manner. For instance, in ANSI C, dereferencing a pointer pis
accomplished by *p, but in Modula-2, it is accomplished by p^. Values can also be
represented (and displayed) differently. Hex numbers in C appear as '0x1ae', while
in Modula-2 they appear as '1AEH'.
Language-specific information is built into GDB for some languages, allowing you to
express operations like the above in the native language of your program, and allowing
GDB to output values in a manner consistent with the syntax of the native language.
The language you use to build expressions is called the working language.
9.1 Switching between source languages
There are two ways to control the working language. You can have GDB set it
automatically, or you can select it manually. You can use the set languagecommand
for either purpose. On startup, GDB sets the default language automatically. The
working language is used to determine how expressions are interpreted, how values
are printed, and so on.
In addition to the working language, every source file that GDB knows about has its
own working language. For some object file formats, the compiler might indicate which
language a particular source file is in. However, most of the time GDB infers the
language from the name of the file. The language of a source file controls whether C++
names are demangled―this way backtracecan show each frame appropriately for
its own language. There is no way to set the language of a source file from within GDB,
but you can set the language associated with a filename extension. See “Displaying the
This is a common problem when you use a program, such as cfrontor f2c, that
generates C but is written in another language. In that case, make the program use
#linedirectives in its C output; that way GDB will know the correct language of the
source code of the original program, and will display that source code, not the generated
C code.
9.1.1 List of filename extensions and languages
If a source file name ends in one of the following extensions, then GDB infers that its
language is the one indicated.
'.c'
C source file
'.C',
C++ source file
'.cc',
'.cp',
'.cpp',
9.1 Switching between source languages 101
'.cxx',
'.c++'
'.f', '.F', Fortran source file. GDB does not distinguish between Fortran 77 and Fortran
90 files.
'.f90'
'.s', '.S' Assembler source file. This actually behaves almost like C, but GDB does
not skip over function prologues when stepping.
In addition, you may set the language associated with a filename extension. See
9.1.2 Setting the working language
If you allow GDB to set the language automatically, expressions are interpreted the
same way in your debugging session and your program.
If you wish, you may set the language manually. To do this, issue the command 'set
language lang', where langis the name of a language, such as c. For a list of the
supported languages, type 'set language'.
Setting the language manually prevents GDB from updating the working language
automatically. This can lead to confusion if you try to debug a program when the
working language is not the same as the source language, when an expression is
acceptable to both languages―but means different things. For instance, if the current
source file was written in C, and GDB was parsing Modula-2, a command such as:
print a = b + c
might not have the effect you intended. In C, this means to add band cand place the
result in a. The result printed would be the value of a. In Modula-2, this means to
compare ato the result of b+c, yielding a BOOLEAN value.
9.1.3 Having GDB infer the source language
To have GDB set the working language automatically, use 'set language local'
or 'set language auto'. GDB then infers the working language. That is, when your
program stops in a frame (usually by encountering a breakpoint), GDB sets the working
language to the language recorded for the function in that frame. If the language for a
frame is unknown (that is, if the function or block corresponding to the frame was
defined in a source file that does not have a recognized extension), the current working
language is not changed, and GDB issues a warning.
This may not seem necessary for most programs, which are written entirely in one
source language. However, program modules and libraries written in one source
language can be used by a main program written in a different source language. Using
'set language auto' in this case frees you from having to set the working language
manually.
102 Using GDB with Different Languages
9.2 Displaying the language
The following commands help you find out which language is the working language,
and also what language source files were written in.
show language
info frame
Display the current working language. This is the language you
can use with commands such as printto build and compute
expressions that may involve variables in your program.
Display the source language for this frame. This language becomes
the working language if you use an identifier from this frame.
information listed here.
info source
Display the source language of this source file. Refer to See
Chapter 10 (page 115), to identify the other information listed here.
In unusual circumstances, you may have source files with extensions not in the standard
list. You can then set the extension associated with a language explicitly:
set extension-language .ext Set source files with extension .extto be
language
assumed to be in the source language language.
However, this is not valid on Unix systems.
info extensions
List all the filename extensions and the associated
languages. Not valid on Unix systems.
9.3 Type and range checking
Some languages are designed to guard you against making seemingly common errors
through a series of compile and run-time checks. These include checking the type of
arguments to functions and operators, and making sure mathematical overflows are
caught at run time. Checks such as these help to ensure the correctness of the program
once it has been compiled by eliminating type mismatches, and providing active checks
for range errors when your program is running.
GDB can check for conditions like the above if you wish. Although GDB does not check
the statements in your program, it can check expressions entered directly into GDB for
evaluation via the printcommand, for example. As with the working language, GDB
can also decide whether or not to check automatically based on your source language.
9.3.1 An overview of type checking
Some languages are strongly typed, meaning that the arguments to operators and
functions have to be of the correct type, otherwise an error occurs. These checks prevent
type mismatch errors from causing run-time problems. For example,
1 + 2 3
but
9.2 Displaying the language 103
error 1 + 2.3
The second example fails because the CARDINAL1 is not type-compatible with the
REAL2.3.
For the expressions you use in GDB commands, you can tell the GDB type checker to
skip checking; to treat any mismatches as errors and abandon the expression; or to only
issue warnings when type mismatches occur, and evaluate the expression anyway.
When you choose the last of these, GDB evaluates expressions like the second example
above, but also issues a warning.
Even if you turn type checking off, there may be other reasons related to type that
prevent GDB from evaluating an expression. For instance, GDB does not know how
to add an intand a struct foo. These particular type errors have nothing to do
with the language in use, and usually arise from expressions, such as the one described
above, which make little sense to evaluate anyway.
Each language defines to what degree it is strict about type. For instance C requires
the arguments to arithmetical operators to be numbers. In C, enumerated types and
pointers can be represented as numbers, so that they are valid arguments to
specific languages.
GDB provides some additional commands for controlling the type checker:
set check type auto
Set type checking on or off based on the current working
default settings for each language.
set check type on, set Set type checking on or off, overriding the default setting
for the current working language. Issue a warning if the
setting does not match the language default. If any type
mismatches occur in evaluating an expression while type
checking is on, GDB prints a message and aborts
evaluation of the expression.
check type off
set check type warn
Cause the type checker to issue warnings, but to always
attempt to evaluate the expression. Evaluating the
expression may still be impossible for other reasons. For
example, GDB cannot add numbers and structures.
show type
Show the current setting of the type checker, and
whether or not GDB is setting it automatically.
9.3.2 An overview of range checking
In some languages it is an error to exceed the bounds of a type; this is enforced with
run-time checks. Such range checking is meant to ensure program correctness by making
sure computations do not overflow, or indices on an array element access do not exceed
the bounds of the array.
104 Using GDB with Different Languages
For expressions you use in GDB commands, you can tell GDB to treat range errors in
one of three ways: ignore them, always treat them as errors and abandon the expression,
or issue warnings but evaluate the expression anyway.
A range error can result from numerical overflow, from exceeding an array index
bound, or when you type a constant that is not a member of any type. Some languages,
however, do not treat overflows as an error. In many implementations of C,
mathematical overflow causes the result to “wrap around” to lower values―for example,
if mis the largest integer value, and sis the smallest, then
m + 1 s
This, too, is specific to individual languages, and in some cases specific to individual
details on specific languages.
GDB provides the following additional commands for controlling the range checker:
set check range auto
Set range checking on or off based on the current
working language. See “Supported languages”
(page 105), for the default settings for each language.
set check range on, set Set range checking on or off, overriding the default
setting for the current working language. A warning
is issued if the setting does not match the default
language. If a range error occurs and range checking
is on, then a message is printed and evaluation of the
expression is aborted.
check range off
set check range warn
Output messages when the GDB range checker detects
a range error, but attempt to evaluate the expression
anyway. Evaluating the expression may still be
impossible for other reasons, such as accessing memory
that the process does not own (a typical example from
many Unix systems).
show range
Show the current setting of the range checker, and
whether or not it is being set automatically by GDB.
9.4 Supported languages
GDB supports C, C++, and Fortran. Refer to for specific information about Fortran.
Some GDB features may be used in expressions regardless of the language you use:
(page 83)) can be used with the constructs of any supported language.
The following section discusses GDB support for each source language. These sections
are not meant to be language tutorials or references, but serve only as a reference guide
to what the GDB expression parser accepts, and what input and output formats should
look like for different languages.
9.4 Supported languages 105
9.4.1 C and C++
Since C and C++ are so closely related, many features of GDB apply to both languages.
Whenever this is the case, we discuss those languages together.
The C++ debugging facilities are jointly implemented by the C++ compiler and GDB.
Therefore, to debug your C++ code effectively, you must compile your C++ programs
with a supported C++ compiler, such as GNU g++, or the HP ANSI C++ compiler (aCC).
For best results when using GNU C++, use the stabs debugging format. You can select
that format explicitly with the g++ command-line options '-gstabs' or '-gstabs+'.
Refer to section “Options for Debugging Your Program or GNU CC” in Using GNU
CC, for more information.
9.4.1.1 C and C++ operators
Operators must be defined on values of specific types. For instance, + is defined on
numbers, but not on structures. Operators are often defined on groups of types.
For the purposes of C and C++, the following definitions hold:
•
Integral types include intwith any of its storage-class specifiers; char; enum; and,
for C++, bool.
•
Floating-point types include float, double, and long double(if supported by
the target platform).
•
•
Pointer types include all types defined as (type *).
Scalar types include all of the above.
The following operators are supported. They are listed here in order of increasing
precedence:
,
The comma or sequencing operator. Expressions in a
comma-separated list are evaluated from left to right, with the
result of the entire expression being the last expression evaluated.
=
Assignment. The value of an assignment expression is the value
assigned. Defined on scalar types.
op=
Used in an expression of the form a op= b, and translated to a = a
op b. op= and = have the same precedence. op is any one of the
operators |, ^, &, <<, >>, +, -, *, /, %.
?:
The ternary operator. a ? b : c can be thought of as: if a then b else
c. a should be of an integral type.
||
&&
|
Logical OR. Defined on integral types.
Logical AND. Defined on integral types.
Bitwise OR. Defined on integral types.
Bitwise exclusive-OR. Defined on integral types.
Bitwise AND. Defined on integral types.
^
&
106 Using GDB with Different Languages
==, !=
Equality and inequality. Defined on scalar types. The value of these
expressions is 0 for false and non-zero for true.
<, >, <=, >=
Less than, greater than, less than or equal, greater than or equal.
Defined on scalar types. The value of these expressions is 0 for false
and non-zero for true.
<<, >>
@
left shift, and right shift. Defined on integral types.
+, -
Addition and subtraction. Defined on integral types, floating-point
types and pointer types.
*, /, %
++, --
Multiplication, division, and modulus. Multiplication and division
are defined on integral and floating-point types. Modulus is defined
on integral types.
Increment and decrement. When appearing before a variable, the
operation is performed before the variable is used in an expression;
when appearing after it, the value of the variable is used before
the operation takes place.
*
&
Pointer dereferencing. Defined on pointer types. Same precedence
as ++.
Address operator. Defined on variables. Same precedence as ++.
For debugging C++, GDB implements a use of '&' beyond what is
allowed in the C++ language itself: you can use '&(&ref)' (or, if
you prefer, simply '&&ref') to examine the address where a C++
reference variable (declared with '&ref') is stored.
-
Negative. Defined on integral and floating-point types. Same
precedence as ++.
!
Logical negation. Defined on integral types. Same precedence as
++.
~
Bitwise complement operator. Defined on integral types. Same
precedence as ++.
., ->
Structure member, and pointer-to-structure member. For
convenience, GDB regards the two as equivalent, choosing whether
to dereference a pointer based on the stored type information.
Defined on structand uniondata.
.*, ->*
[]
Dereferences pointers to members.
Array indexing. a[i]is defined as *(a+i). Same precedence as
->.
()
Function parameter list. Same precedence as ->.
9.4 Supported languages 107
::
::
C++ scope resolution operator. Defined on struct, union, and
classtypes.
Double colons also represent the GDB scope operator (see
If an operator is redefined in the user code, GDB usually attempts to invoke the
redefined version instead of using the original meaning.
9.4.1.2 C and C++ constants
GDB allows you to express the constants of C and C++ in the following ways:
•
Integer constants are a sequence of digits. Octal constants are specified by a leading
'0' (that is zero), and hexadecimal constants by a leading '0x' or '0X'. Constants can
also end with a letter 'l', specifying that the constant should be treated as a long
value.
•
Floating point constants are a sequence of digits, followed by a decimal point,
followed by a sequence of digits, and optionally followed by an exponent. An
exponent is of the form: 'e[[+]|-]nnn', where nnnis a sequence of digits. The
'+' is optional for positive exponents. A floating-point constant may also end with
a letter 'f' or 'F', specifying that the constant should be treated as being of the
float(as opposed to the default double) type; or with a letter 'l' or `L', which
specifies a long doubleconstant.
•
•
Enumerated constants consist of enumerated identifiers, or their integral
equivalents.
Character constants are a single character surrounded by single quotes ('), or a
number or the ordinal value of the corresponding character (usually its ASCII
value). Within quotes, the single character may be represented by a letter or by
escape sequences, which are of the form '\nnn', where nnnis the octal representation
of the character's ordinal value; or of the form '\x', where 'x' is a predefined special
character―for example, '\n' for newline.
•
String constants are a sequence of character constants surrounded by double quotes
("). Any valid character constant (as described above) may appear. Double quotes
within the string must be preceded by a backslash, so for instance '"a\"b'c"' is
a string of five characters.
•
•
Pointer constants are an integral value. You can also write pointers to constants
using the C operator '&'.
Array constants are comma-separated lists surrounded by braces '{' and '}'; for
example, '{1,2,3}' is a three-element array of integers, '{{1,2}, {3,4},
{5,6}}' is a three-by-two array, and '{&"hi", &"there", &"fred"}' is a
three-element array of pointers.
108 Using GDB with Different Languages
9.4.1.3 C++ expressions
GDB expression handling can interpret most C++ expressions.
WARNING! GDB can only debug C++ code if you use the proper compiler. Typically,
C++ debugging depends on the use of additional debugging information in the symbol
table, and thus requires special support. In particular, if your compiler generates a.out,
MIPS ECOFF, RS/6000 XCOFF, or ELF with stabs extensions to the symbol table, these
facilities are all available. (With GNU CC, you can use the '-gstabs' option to request
stabs debugging extensions explicitly.) Where the object code format is standard COFF
or DWARF in ELF, on the other hand, most of the C++ support in GDB does not work.
1. Member function calls are allowed; you can use expressions like
count = aml->GetOriginal(x, y)
2. While a member function is active (in the selected stack frame), your expressions
have the same namespace available as the member function; that is, GDB allows
implicit references to the class instance pointer thisfollowing the same rules as
C++.
3. You can call overloaded functions; GDB resolves the function call to the right
definition, with some restrictions. GDB does not perform overload resolution
involving user-defined type conversions, calls to constructors, or instantiations of
templates that do not exist in the program. It also cannot handle ellipsis argument
lists or default arguments.
It does perform integral conversions and promotions, floating-point promotions,
arithmetic conversions, pointer conversions, conversions of class objects to base
classes, and standard conversions such as those of functions or arrays to pointers;
it requires an exact match on the number of function arguments.
Overload resolution is always performed, unless you have specified set
You must specify set overload-resolution offin order to use an explicit
function signature to call an overloaded function, as in
p 'foo(char,int)'('x', 13)
The GDB command-completion facility can simplify this. Refer to “Command
4. GDB understands variables declared as C++ references; you can use them in
expressions just as you do in C++ source―they are automatically dereferenced.
In the parameter list shown when GDB displays a frame, the values of reference
variables are not displayed (unlike other variables); this avoids clutter, since
9.4 Supported languages 109
references are often used for large structures. The address of a reference variable
is always shown, unless you have specified 'set print address off'.
5. GDB supports the C++ name resolution operator ::―your expressions can use it
just as expressions in your program do. Since one scope may be defined in another,
you can use ::repeatedly if necessary, for example in an expression like
'scope1::scope2::name'. GDB also allows resolving name scope by reference
In addition, when used with the HP aC++ compiler, GDB supports calling virtual
functions correctly, printing out virtual bases of objects, calling functions in a base
subobject, casting objects, and invoking user-defined operators.
NOTE: GDB cannot display debugging information for classes or functions defined
in a shared library that is not compiled for debugging (with the -g0 option). GDB
displays the function with the message <no data fields>.
For example, after 'd3' is created by the following line:
`RWCollectableDate d3(15,5,2001);'
printing the variable or class returns:
(gdb) p d3
$3 = {<No data fields>}
(gdb) ptype RWCollectableDate
type = class RWCollectableDate {
<no data fields>
9.4.1.4 C and C++ defaults
If you allow GDB to set type and range checking automatically, they both default to
offwhenever the working language changes to C or C++. This happens regardless of
whether you or GDB selects the working language.
If you allow GDB to set the language automatically, it recognizes source files whose
names end with '.c', '.C', or '.cc', and so on, and when GDB enters code compiled
from one of these files, it sets the working language to C or C++. Refer to See “Having
GDB infer the source language” (page 102), for further details.
9.4.1.5 C and C++ type and range checks
By default, when GDB parses C or C++ expressions, type checking is not used. However,
if you turn type checking on, GDB considers two variable types equivalent if:
•
The two variables are structured and have the same structure, union, or enumerated
tag.
•
The two variables have the same type name, or types that have been declared
equivalent through typedef.
110 Using GDB with Different Languages
Range checking, if turned on, is done on mathematical operations. Array indices are
not checked, since they are often used to index a pointer that is not itself an array.
9.4.1.6 GDB and C
The set print unionand show print unioncommands apply to the union
type. When set to 'on', any unionthat is inside a structor classis also printed.
Otherwise, it appears as '{...}'.
The @operator aids in the debugging of dynamic arrays, formed with pointers and a
9.4.1.7 GDB features for C++
Some GDB commands are particularly useful with C++, and some are designed
specifically for use with C++. Here is a summary:
breakpoint menus
When you want a breakpoint in a function whose
name is overloaded, GDB breakpoint menus help
you specify which function definition you want.
rbreak regex
Setting breakpoints using regular expressions is
helpful for setting breakpoints on overloaded
functions that are not members of any special
catch throw, catch catch
Debug C++ exception handling using these
ptype typename
Print inheritance relationships as well as other
set print demangle, show
print demangle, set print
asm-demangle, show print
asm-demangle
Control whether C++ symbols display in their
source form, both when displaying code as C++
source and when displaying disassemblies. See
set print object, show print Choose whether to print derived (actual) or
declared types of objects. See “Print settings”
object
set print vtbl, show print
vtbl
Control the format for printing virtual function
commands do not work on programs compiled
with the HP ANSI C++ compiler (aCC).)
set overload-resolution on Enable overload resolution for C++ expression
evaluation. The default is on. For overloaded
functions, GDB evaluates the arguments and
9.4 Supported languages 111
searches for a function whose signature matches
the argument types, using the standard C++
conversion rules (see “C++ expressions”
(page 109), for details). If it cannot find a match,
it emits a message.
set overload-resolution off Disable overload resolution for C++ expression
evaluation. For overloaded functions that are not
class member functions, GDB chooses the first
function of the specified name that it finds in the
symbol table, whether or not its arguments are
of the correct type. For overloaded functions that
are class member functions, GDB searches for a
function whose signature exactly matches the
argument types.
show overload-resolution
Display current overload resolution setting for
C++ expression evaluation.
Overloaded symbolnames
You can specify a particular definition of an
overloaded symbol, using the same notation that
is used to declare such symbols in C++: type
symbol(types)rather than just symbol. You
can also use the GDB command-line word
completion facilities to list the available choices,
or to finish the type list for you. See “Command
completion” (page 33), for details on how to do
this.
9.4.2 Fortran
You can use WDB to debug programs written in Fortran. WDB does not distinguish
between Fortran 77 and Fortran 90 files.
WDB provides the following command to control case sensitivity:
case-sensitive [on | off]
The default for Fortran is off while for other
languages the default is on.
Other supported features are:
•
•
•
•
Fortran 90 pointers
Structures and unions
Calling functions with integer, logical, real, complex arguments
Intrinsic support
9.4.2.1 Fortran types
Fortran types supported:
112 Using GDB with Different Languages
integer*1, integer*2,
integer*4, integer*8
logical*1, logical*2,
logical*4, logical*8 byte,
real*4, real*8, real*16
complex*8, complex*16
character*len,
•
•
•
•
•
•
allocatable
assumed-size
assumed-shape
adjustable
automatic
explicit-shape
Array elements are displayed in column-major
order. Use () for array member access (for
example, arr(i) instead of arr[i]). Use set print
elementsto control the number of elements
printed out when specifying a whole array. The
default is 200 elements or the number of elements
of the array, whichever is smaller.
character*(*) [len is a
user supplied length]
arrays
9.4.2.2 Fortran operators
The following Fortran operators are listed here in the order of increasing precedence:
=
Assignment
*, -, *, /
+, -
Binary operators
Unary operators
Exponentiation
Equal
Not equal, or concatenation
Less than
Less than or equal to
Greater than
Greater than or equal to
Concatenation
**
.EQ., =
.NE., /=
.LT., <
.LE., <=
.GT., >
.GE., >=
//
.NOT.
Logical negation
Logical AND
.AND.
.OR.
Logical OR
.EQV.
Logical equivalence
Logical non-equivalence
.NEQV., .XOR.
Logical constants are represented as .TRUE. or .FALSE.
GDB includes support for viewing Fortran common blocks.
info common
Lists common blocks visible in the current frame.
9.4 Supported languages 113
info common
<common_block_name>
Lists values of variables in the named common
block.
Fortran entry points are supported.
You can set a break point specifying an entry point name.
9.4.2.3 Fortran special issues
Fortran allows main to be a non-main procedure; therefore, to set a breakpoint in the
main program, use break _MAIN_or break <program_name>.
Do not use break mainunless it is the name of a non-main procedure.
114 Using GDB with Different Languages
10 Examining the Symbol Table
The commands described in this chapter allow you to inquire about the symbols (names
of variables, functions, and types) defined in your program. This information is inherent
in the text of your program and does not change as your program executes. GDB finds
it in your program's symbol table, in the file indicated when you started GDB (see
“Choosing files” (page 26)), or by one of the file-management commands (see
Occasionally, you may need to refer to symbols that contain unusual characters, which
GDB ordinarily treats as word delimiters. The most frequent case is in referring to static
recorded in object files as debugging symbols, but GDB would ordinarily parse a typical
file name, like 'foo.c', as the three words 'foo' '.' 'c'. To allow GDB to recognize
'foo.c' as a single symbol, enclose it in single quotes; for example,
p 'foo.c'::x
looks up the value of xin the scope of the file 'foo.c'.
info address symbol
Describe where the data for symbolis stored.
For a register variable, this says which register
it is kept in. For a non-register local variable, this
prints the stack-frame offset at which the variable
is always stored.
Note the contrast with 'print &symbol', which
does not work at all for a register variable, and
for a stack local variable prints the exact address
of the current instantiation of the variable.
whatis expr
Print the data type of expression expr. expris
not actually evaluated, and any side-effecting
operations (such as assignments or function calls)
inside it do not take place. See “Expressions”
whatis
Print the data type of $, the last value in the value
history.
ptype typename
Print a description of data type typename.
typenamemay be the name of a type, or for C
code it may have the form 'class class-name',
'struct struct-tag', 'union union-tag'
or 'enum enum-tag'.
ptype expr, ptype
Print a description of the type of expression
expr. ptypediffers from whatisby printing a
115
detailed description, instead of just the name of
the type.
For example, for this variable declaration:
struct complex {double real; double
imag;} v;
the two commands give this output:
((gdb)) whatis v
type = struct complex
((gdb)) ptype v
type = struct complex {
double real;
double imag;
}
As with whatis, using ptypewithout an
argument refers to the type of $, the last value
in the value history.
info types regexp, info
types
Print a brief description of all types whose names
match regexp(or all types in your program, if
you supply no argument). Each complete
typename is matched as though it were a
complete line; thus, 'i type value' gives
information on all types in your program whose
names include the string value, but 'i type
^value$' gives information only on types whose
complete name is value.
This command differs from ptypein two ways:
first, like whatis, it does not print a detailed
description; second, it lists all source files where
a type is defined.
info source
info sources
Show the name of the current source file―that
is, the source file for the function containing the
current point of execution―and the language it
was written in.
Print the names of all source files in your
program for which there is debugging
information, organized into two lists: files whose
symbols have already been read, and files whose
symbols will be read when needed.
info functions
Print the names and data types of all defined
functions.
116 Examining the Symbol Table
info functions regexp
Print the names and data types of all defined
functions whose names contain a match for
regular expression regexp. Thus, 'info fun
step' finds all functions whose names include
step; 'info fun ^step' finds those whose
names start with step.
info variables
Print the names and data types of all variables
that are declared outside of functions (that is,
excluding local variables).
info variables regexp
Print the names and data types of all variables
(except for local variables) whose names contain
a match for regular expression regexp.
Some systems allow individual object files that
make up your program to be replaced without
stopping and restarting your program. For
example, in VxWorks you can simply recompile
a defective object file and keep on running. If you
are running on one of these systems, you can
allow GDB to reload the symbols for
automatically relinked modules:
set
Replace symbol definitions
for the corresponding source
file when an object file with
a particular name is seen
again.
symbol-reloading
on
set
Do not replace symbol
definitions when
symbol-reloading
off
encountering object files of
the same name more than
once. This is the default
state; if you are not running
on a system that permits
automatic relinking of
modules, you should leave
symbol-reloading off,
since otherwise GDB may
discard symbols when
linking large programs, that
may contain several
modules (from different
directories or libraries) with
the same name.
117
show
Show the current onor off
symbol-reloading setting.
set opaque-type-resolution Tell GDB to resolve opaque types. An opaque
on
type is a type declared as a pointer to a struct,
class, or union―for example, struct
MyType *―that is used in one source file
although the full declaration of struct MyType
is in another source file. The default is on.
A change in the setting of this subcommand will
not take effect until the next time symbols for a
file are loaded.
set opaque-type-resolution Tell GDB not to resolve opaque types. In this
case, the type is printed as follows:
off
{<no data fields>}
show opaque-type-resolution Show whether opaque types are resolved or not.
maint print symbols
Write a dump of debugging symbol data into the
file filename. These commands are used to
debug the GDB symbol-reading code. Only
symbols with debugging data are included. If
you use 'maint print symbols', GDB
includes all the symbols for which it has already
collected full details: that is, filenamereflects
symbols for only those files whose symbols GDB
has read. You can use the command info
sourcesto find out which files these are. If you
use 'maint print psymbols' instead, the
dump shows information about symbols that
GDB only knows partially―that is, symbols
defined in files that GDB has skimmed, but not
yet read completely. Finally, 'maint print
msymbols' dumps just the minimal symbol
information required for each object file from
which GDB has read some symbols. See
filename, maint print
psymbols filename, maint
print msymbols filename
discussion of how GDB reads symbols (in the
description of symbol-file).
118 Examining the Symbol Table
11 Altering Execution
Once you think you have found an error in your program, you might want to find out
for certain whether correcting the apparent error would lead to correct results in the
rest of the run. You can find the answer by experiment, using the GDB features for
altering execution of the program.
For example, you can store new values into variables or memory locations, give your
program a signal, restart it at a different address, or even return prematurely from a
function.
11.1 Assignment to variables
To alter the value of a variable, evaluate an assignment expression. See “Expressions”
(page 83). For example,
print x=4
stores the value 4 into the variable x, and then prints the value of the assignment
supported languages.
If you are not interested in seeing the value of the assignment, use the setcommand
instead of the printcommand. setis really the same as printexcept that the
expression's value is not printed and is not put in the value history (see “Value history”
(page 95)). The expression is evaluated only for its effects.
The setcommand has a number of subcommands that conflict with the names of
program variables. The set variablecommand is a better alternative for setting
program variables. The following two examples illustrate the same:
•
Example 1
((gdb)) whatis width
type = double
((gdb)) p width
$4 = 13
((gdb)) set width=47
Invalid syntax in expression.
The invalid expression, of course, is '=47'. In order to actually set the program's
variable width, use
•
Example 2
((gdb)) set var width=47
if your program has a variable g, you run into problems if you try to set a new
value with just 'set g=4', because GDB has the command set gnutarget,
abbreviated set g:
((gdb)) whatis g
type = double
11.1 Assignment to variables 119
((gdb)) p g
$1 = 1
((gdb)) set g=4
((gdb)) p g
$2 = 1
((gdb)) r
The program being debugged has been started already.
Start it from the beginning? (y or n) y
Starting program: /home/smith/cc_progs/a.out
"/home/smith/cc_progs/a.out": can't open to read symbols:
Invalid bfd target.
((gdb)) show g
The current BFD target is "=4".
The steps shown above sets the gnutargetto an invalid value in place of the program
variable g.
In order to set the variable g, use
((gdb)) set var g=4
GDB allows more implicit conversions in assignments than C; you can freely store an
integer value into a pointer variable or vice versa, and you can convert any structure
to any other structure that is the same length or shorter.
To store values into arbitrary places in memory, use the '{...}' construct to generate
example, {int}0x83040refers to memory location 0x83040as an integer (which
implies a certain size and representation in memory), and
set {int}0x83040 = 4
stores the value 4 into that memory location.
11.2 Continuing at a different address
Ordinarily, when you continue your program, you do so at the place where it stopped,
with the continuecommand. You can continue at a selected address using one of the
following commands:
jump linespec
Resume execution at line linespec. Execution stops again
immediately if there is a breakpoint there. See “Printing source
lines” (page 77), for a description of the different forms of
linespec. It is common practice to use the tbreakcommand
The jumpcommand does not change the current stack frame, the
stack pointer, the contents of any memory location or any register
other than the program counter. If line linespecis in a different
function from the one currently executing, the results may be
bizarre if the two functions expect different patterns of arguments
120 Altering Execution
or of local variables. For this reason, the jumpcommand requests
confirmation if the specified line is not in the function currently
executing. However, even bizarre results are predictable if you
are well acquainted with the machine-language code of your
program.
jump *address
Resume execution at the instruction at address address.
On many systems, you can get much the same effect as the jumpcommand by storing
a new value into the register $pc. This does not start the execution of your program
at the specified address, instead only changes the program counter.
For example,
set $pc = 0x485
makes the next continuecommand or stepping command execute at address 0x485,
rather than at the address where your program stopped. See “Continuing and stepping”
The most common occasion to use the jumpcommand is to back up―perhaps with
more breakpoints set―over a portion of a program that has already executed, in order
to examine its execution in more detail.
11.3 Giving your program a signal
You can use the following command to send signals to your program:
signal signal
Resume execution where your program stopped, but immediately
give it the signal signal. signalcan be the name or the number
of a signal. For example, on many systems signal 2and signal
SIGINTare both ways of sending an interrupt signal.
Alternatively, if signalis zero, continue execution without
giving a signal. This is useful when your program stopped on
account of a signal and would ordinary see the signal when
resumed with the continuecommand; 'signal 0' causes it to
resume without a signal.
signaldoes not repeat when you press RET a second time after
executing the command.
Invoking the signalcommand is not the same as invoking the killutility from the
shell. Sending a signal with killcauses GDB to decide what to do with the signal
command passes the signal directly to your program.
11.4 Returning from a function
You can use the following command to return from a function:
11.3 Giving your program a signal 121
return, return
expression
You can cancel execution of a function call with the return
command. If you give an expressionargument, its value
is used as the return value from the function value.
When you use return, GDB discards the selected stack frame (and all frames within
it). You can think of this as making the discarded frame return prematurely. If you
wish to specify a value to be returned, give that value as the argument to return.
frames inside of it, leaving its caller as the innermost remaining frame. That frame
becomes selected. The specified value is stored in the registers used for returning values
of functions.
The returncommand does not resume execution; it leaves the program stopped in
the state that would exist if the function had just returned. In contrast, the finish
selected stack frame returns naturally.
11.5 Calling program functions
call expr Evaluate the expression exprwithout displaying voidreturned values.
You can use this variant of the printcommand if you want to execute a function from
your program, but without cluttering the output with voidreturned values. If the
result is not void, it is printed and saved in the value history.
For the A29K, a user-controlled variable call_scratch_addressspecifies the location
of a scratch area to be used when GDB calls a function in the target. This is necessary
because the usual method of putting the scratch area on the stack does not work in
systems that have separate instruction and data spaces.
11.6 Patching programs
By default, GDB opens the file containing the executable code of your program (or the
corefile) as read-only. This prevents accidental alteration to machine code; and it also
prevents you from intentionally patching your program binary.
If you would like to be able to patch the binary, you can specify that explicitly with the
set writecommand. For example, you might want to turn on internal debugging
flags, or even to make emergency repairs.
set write on,
set write off
If you specify 'set write on', GDB opens executable and core
files for both reading and writing; if you specify 'set write
off' (the default), GDB opens them as read-only.
If you have already loaded a file, you must load it again (using
the exec-fileor core-filecommand) after changing set
write, for your new setting to take effect.
122 Altering Execution
show write
Display whether executable files and core files are opened for
writing as well as reading.
11.6 Patching programs 123
124
12 GDB Files
GDB needs to know the file name of the program to be debugged, both in order to read
its symbol table and in order to start your program. To debug a core dump of a previous
run, you must also tell GDB the name of the core dump file.
12.1 Commands to specify files
You can specify executable and core dump file names as arguments to the GDB start-up
Occasionally it is necessary to change to a different file during a GDB session. In these
situations the GDB commands to specify new files are useful.
file filename
Use filename as the program to be debugged. It
is read for its symbols and for the contents of
pure memory. It is also the program executed
when you use the run command. If you do not
specify a directory and the file is not found in
the GDB working directory, GDB uses the
environment variable PATH as a list of
directories to search, just as the shell does when
looking for a program to run. You can change
the value of this variable, for both GDB and your
program, using the path command.
On systems with memory-mapped files, an
auxiliary file named filename.symsmay hold
symbol table information for filename. If so, GDB
maps in the symbol table from `filename.syms',
starting up more quickly. See the descriptions of
the file options -mappedand -readnow
(available on the command line, and with the
commands file, symbol-file, or
add-symbol-file, described below) for more
information.
file
file with no argument makes GDB discard any
information it has on both executable file and the
symbol table.
exec-file[ filename]
Specify that the program to be run (but not the
symbol table) is found in file- name. GDB
searches the environment variable PATH if
necessary to locate your program. Omitting
12.1 Commands to specify files 125
filename means to discard information on the
executable file.
symbol-file[ filename ]
Read symbol table information from file filename.
PATH is searched when necessary. Use the file
command to get both symbol table and program
to run from the same file.
symbol-file with no argument clears out GDB
information on the symbol table of your program.
The symbol-file command causes GDB to forget
the contents of its convenience variables, the
value history, and all breakpoints and
auto-display expressions. This is because they
may contain pointers to the internal data
recording symbols and data types, which are part
of the old symbol table data being discarded
inside GDB.
symbol-file does not repeat if you press RET
again after executing it once. When GDB is
configured for a particular environment, it
understands debugging information in whatever
format is the standard generated for that
environment; you may use either a gnu compiler,
or other compilers that adhere to the local
conventions.
For most kinds of object files, the symbol-file
command does not normally read the symbol
table in full right away. Instead, it scans the
symbol table quickly to nd which source files
and which symbols are present. The details are
read later, one source file at a time, as they are
needed.
The purpose of this two-stage reading strategy
is to make GDB start up faster. For the most part,
it is invisible except for occasional pauses while
the symbol table details for a particular source
file are being read. (The set verbosecommand
can turn these pauses into messages if desired.
symbol-filefilename[
-readnow] [ -mapped], file
You can override the GDB two-stage strategy for
reading symbol tables by using the `-readnow'
126 GDB Files
filename[ -readnow ] [
-mapped]
option with any of the commands that load
symbol table information, if you want to be sure
GDB has the entire symbol table available.
If memory-mapped files are available on your
system through the mmapsystem call, you can
use another option, `-mapped', to cause GDB to
write the symbols for your program into a
reusable file. Future GDB debugging sessions
map in symbol information from this auxiliary
symbol file (if the program has not changed),
rather than spending time reading the symbol
table from the executable program. Using the
`-mapped' option has the same effect as starting
GDB with the `-mapped' command-line option.
You can use both options together, to make sure
the auxiliary symbol file has all the symbol
information for your program.
The auxiliary symbol file for a program called
myprogis called myprog.syms. Once this file
exists (so long as it is newer than the
corresponding executable), GDB always attempts
to use it when you debug myprog; no special
options or commands are needed.
The `.syms' file is specific to the host machine
where you run GDB. It holds an exact image of
the internal GDB symbol table. It cannot be
shared across multiple host platforms.
core-file[ filename]
Specify the whereabouts of a core dump file to
be used as the contents of memory.
Traditionally, core files contain only some parts
of the address space of the process that generated
them; GDB can access the executable file itself
for other parts.
core-file with no argument specifies that no core
file is to be used.
Note that the core file is ignored when your
program is actually running under GDB. So, if
you have been running your program and you
wish to debug a core file instead, you must kill
the subprocess in which the program is running.
12.1 Commands to specify files 127
To do this, use the kill command (see “Killing
add-symbol-filefilename
address, add-symbol-file
filenameaddress[ -readnow]
[ -mapped], add-symbol-file
filenameaddress
data_address bss_address,
add-symbol-filefilename
-section address
The add-symbol-file command reads additional
symbol table information from the file filename.
You would use this command when filename
has been dynamically loaded (by some other
means) into the program that is running.
addressshould be the memory address at
which the file has been loaded; GDB cannot
figure this out for itself. You can specify up to
three addresses, in which case they are taken to
be the addresses of the text, data, and bss
segments respectively. For complicated cases,
you can specify an arbitrary number of
-ssectionaddress pairs, to give an explicit
section name and base address for that section.
You can specify any address as an expression.
The symbol table of the file filename is added to
the symbol table originally read with the
symbol-file command. You can use the
add-symbol-file command any number of times;
the new symbol data thus read keeps adding to
the old. To discard all old symbol data instead,
use the symbol-file command without any
arguments.
add-symbol-file does not repeat if you press RET
after using it.
You can use the `-mapped' and `-readnow'
options just as with the symbol- file command,
to change how GDB manages the symbol table
information for filename.
section
The sectioncommand changes the base
address of section SECTION of the exec file to
ADDR. This can be used if the exec file does not
contain section addresses, (such as in the a.out
format), or when the addresses specified in the
file itself are wrong. Each section must be
changed separately. The infofiles command,
described below, lists all the sections and their
addresses.
128 GDB Files
infofiles, infotarget
info filesand info targetare
synonymous; both commands print the current
names of the executable and core dump files
currently in use by GDB, and the files from which
symbols were loaded. Both the commands list
all possible targets rather than the current targets.
All file-specifying commands allow both absolute and relative file names as arguments.
GDB always converts the file name to an absolute file name and remembers it that way.
GDB automatically loads symbol definitions from shared libraries when you use the
run command, or when you examine a core file. (Before you issue the run command,
GDB does not understand references to a function in a shared library, however ―
unless you are debugging a core file).
On HP-UX, if the program loads a library explicitly, GDB automatically loads the
information.
infoshare, info
sharedlibrary
Print the names of the shared libraries which are
currently loaded.
sharedlibrary regex, share Load shared object library symbols for files matching a
Unix regular expression. As with files loaded
automatically, it only loads shared libraries required by
your program for a core file or after typing run. If regex
is omitted all shared libraries required by your program
are loaded.
regex
On HP-UX systems, GDB detects the loading of a shared library and automatically
reads in symbols from the newly loaded library, up to a threshold that is initially set
but that you can modify if you wish.
Beyond that threshold, symbols from shared libraries must be explicitly loaded. To
load these symbols, use the command sharedlibraryfilename. The base address
of the shared library is determined automatically by GDB and need not be specified.
To display or set the threshold, use the commands:
set auto-solib-add
threshold
Set the autoloading size threshold, in megabytes.
If thresholdis nonzero, symbols from all
shared object libraries will be loaded
automatically when the inferior begins execution
or when the dynamic linker informs GDB that a
new library has been loaded, until the symbol
table of the program and libraries exceeds this
threshold. Otherwise, symbols must be loaded
manually, using the sharedlibrarycommand.
The default threshold is 100 megabytes.
12.1 Commands to specify files 129
show auto-solib-add
Display the current autoloading size threshold,
in megabytes.
12.2 Specifying shared library locations
On HP-UX, when the shared libraries your program uses are in a different directory
than the path specified in the source or object files, specify the correct files to use with
one of two environment variables.
`GDB_SHLIB_PATH'
Set this variable to a colon-separated list of directory path
names where the desired shared libraries reside. GDB
searches specified list of directories for shared libraries before
searching the default system directories.
`GDB_SHLIB_ROOT'
Set this variable to point to the root of the library in which
the desired libraries reside.
NOTE: If you set both the `GDB_SHLIB_PATH'and `GDB_SHLIB_ROOT'
environment variables, the `GDB_SHLIB_PATH'behavior overrides
`GDB_SHLIB_ROOT'.
These environment variables are useful when you are analyzing core files on a system
other than the one that produced the core file.
For example, if you want GDB to search for libraries in /home/debugger/liband
/tmp/libbefore searching the default system directories for libraries, you can use
this setting:
GDB_SHLIB_PATH=/home/debugger/lib:/tmp/lib
With this setting, GDB searches the directories in the order specified until it finds a
library with the correct name.
In this example, if GDB encounters a library by the name of /usr/lib/libsubs.sl,
GDB searches first for /home/debugger/lib/libsubs.sland then for /tmp/lib/
libsubs.sl. If neither of these exists, then GDB searches the default system directories
and finds /usr/lib/libsubs.sl.
In most cases, GDB_SHLIB_PATHallows more flexibility than GDB_SHLIB_ROOT'
because it allows you to specify more than one path. However, there are some cases in
which you may want to choose to use GDB_SHLIB_ROOT.
For example, if you have more than one shared library with the same name but different
path names, you may want to use GDB_SHLIB_ROOTbecause GDB searches for libraries
based on the full path name.
Note that GDB_SHLIB_PATHmay not give you the results you expect because GDB
searches for libraries that match only the name, regardless of the path, and always
accepts the first library that matches the name.
130 GDB Files
For example, if you want to use /tmp/usr/lib/libsubs.sland /tmp/usr/share/
lib/libsubs.sl, you can set GDB_SHLIB_ROOT' to /tmp. Now whenever GDB
encounters a library with the name /usr/lib/libsubs.sland /usr/share/lib/
libsubs.sl, GDB looks at /tmp/usr/lib/libsubs.sland /tmp/usr/share/
lib/libsubs.slrespectively.
12.3 Errors reading symbol files
While reading a symbol file, GDB occasionally encounters problems, such as symbol
types it does not recognize, or known bugs in compiler output. By default, GDB does
not notify you of such problems, since they are relatively common and primarily of
interest to people debugging compilers. If you are interested in seeing information
about ill-constructed symbol tables, you can either ask GDB to print only one message
about each such type of problem, no matter how many times the problem occurs; or
you can ask GDB to print more messages, to see how many times the problems occur,
The messages currently printed, and their meanings, include:
inner block not inside outer block in The symbol information shows where symbol
symbol
scopes begin and end (such as at the start of a
function or a block of statements). This error
indicates that an inner scope block is not fully
contained in its outer scope blocks.
GDB circumvents the problem by treating the
inner block as if it had the same scope as the
outer block. In the error message, symbol may be
shown as "(don't know)"if the outer block
is not a function.
block at address out of order
The symbol information for symbol scope blocks
should occur in order of in- creasing addresses.
This error indicates that it does not do so.
GDB does not circumvent this problem, and has
trouble locating symbols in the source file whose
symbols it is reading. (You can often determine
what source file is affected by specifying set
bad block start address patched
The symbol information for a symbol scope block
has a start address smaller than the address of
12.3 Errors reading symbol files 131
the preceding source line. This is known to occur
in the SunOS 4.1.1 (and earlier) C compiler.
GDB circumvents the problem by treating the
symbol scope block as starting on the previous
source line.
bad string table offset in symbol n
Symbol number n contains a pointer into the
string table which is larger than the size of the
string table.
GDB circumvents the problem by considering
the symbol to have the name foo, which may
cause other problems if many symbols end up
with this name.
unknown symbol type 0xnn
The symbol information contains new data types
that GDB does not yet know how to read. 0xnn
is the symbol type of the uncomprehended
information, in hexadecimal.
GDB circumvents the error by ignoring this
symbol information. This usually allows you to
debug your program, though certain symbols
are not accessible. If you encounter such a
problem and feel like debugging it, you can
debug (gdb) with itself, breakpoint on
complain, then go up to the function
read_dbx_ symtaband examine *bufpto see
the symbol.
stub type has NULL name
GDB could not nd the full definition for a struct
or class.
const/volatile indicator missing (ok The symbol information for a C++ member
if using g++ v1.x), got...
function is missing some information that recent
versions of the compiler should have output for
it.
info mismatch between compiler
and debugger
GDB could not parse a type specification output
by the compiler.
132 GDB Files
13 Specifying a Debugging Target
A targetis the execution environment occupied by your program.
Often, GDB runs in the same host environment as your program; in that case, the
debugging target is specified as a side effect when you use the fileor corecommands.
For HP-UX specific information, see undefined [HP-UX Targets], page undefined.
When you need more flexibility, for example, running GDB on a physically separate
host, or controlling a standalone system over a serial port or a realtime system over a
TCP/IP connection you can use the targetcommand to specify one of the target types
13.1 Active targets
There are three classes of targets: processes, core files, and executable files. GDB can
work concurrently on up to three active targets, one in each class. This allows you, for
example, to start a process and inspect its activity without abandoning your work on
a core file.
For example, if you execute `gdb a.out', then the executable file a.out is the only active
target. If you designate a core file as well presumably from a prior run that crashed
and coredumped, then GDB has two active targets and uses them in tandem, looking
first in the corefile target, then in the executable file, to satisfy requests for memory
addresses. (Typically, these two classes of target are complementary, since core files
contain only the contents of the program read-write memory, variables, machine status
etc. While the executable files contain only the program text and initialized data.)
When you type run, your executable file becomes an active process target as well. When
a process target is active, all GDB commands requesting memory addresses refer to
that target; addresses in an active core file or executable file target are obscured while
the process target is active.
Use the core-file and exec-file commands to select a new core file or executable target
already running, use the attach command (see “Debugging a Running Process”
13.2 Commands for managing targets
target type parameters
Connects the GDB host environment to a target
machine or process. A target is typically a protocol
for talking to debugging facilities. You use the
argument type to specify the type or protocol of the
target machine.
Further parameters are interpreted by the target
protocol, but typically include things like device
13.1 Active targets 133
names or host names to connect with, process
numbers, and baud rates.
The targetcommand does not repeat if you press
RET again after executing the command.
help target
Displays the names of all targets available. To
display targets currently selected, use either info
target or info files (see “Commands to specify files”
help targetname
Describe a particular target, including any
parameters necessary to select it.
set gnutarget args
GDB uses its own library BFD to read your files.
GDB knows whether it is reading an executable, a
core, or a .ofile; however, you can specify the file
format with the set gnutargetcommand. Unlike
most targetcommands, with gnutargetthe
targetrefers to a program, not a machine.
Warning: To specify a file format with set gnutarget,
you must know the actual BFD name.
show gnutarget
Use the show gnutargetcommand to display
what file format gnutargetis set to read. If you
have not set gnutarget, GDB will determine the
file format for each file automatically, and show
gnutargetdisplays `The current BDF target is
"auto"'.
Here are some common targets (available, or not, depending on the GDB configuration):
target execprogram
target corefilename
target remotedev
An executable file. target exec programis the
same as exec-file program.
A core dump file. target core filenameis the
same as core-file filename.
Remote serial target in GDB-specific protocol. The
argument dev specifies what serial device to use for the
connection (for example, /dev/ttya). targetremote
supports the loadcommand. This is only useful if you
have some other way of getting the stub to the target
system, and you can put it somewhere in memory
where it will not get clobbered by the download.
134 Specifying a Debugging Target
target sim
Builtin CPU simulator. GDB includes simulators for
most architectures. In general,the following commands
work:
target sim
load
run
However, you cannot assume that a specific memory
map, device drivers, or even basic I/O is available,
although some simulators do provide these.
Some configurations may include these targets as well:
target nromdev
NetROM ROM emulator. This
target only supports
downloading.
Different targets are available on different configurations of GDB; your configuration
may have more or fewer targets.
Many remote targets require you to download the executable code once you have
successfully established a connection.
loadfilename
Depending on what remote debugging facilities are configured
into GDB, the load command may be available. Where it exists,
it is meant to make filename (an executable) available for
debugging on the remote system|by downloading, or dynamic
linking, for example. loadalso records the filenamesymbol
table in GDB, like the add-symbol-filecommand.
If your GDB does not have a loadcommand, attempting to
execute it gets the error message "You can't do that when your
target is ...".
The file is loaded at whatever address is specified in the
executable. For some object file formats, you can specify the load
address when you link the program; for other formats, like a.out,
the object file format specifies a fixed address. loaddoes not
repeat if you press RET again after using it.
loaddoes not repeat if you press RET again after using it.
13.3 Choosing target byte order
Some types of processors, such as the MIPS, PowerPC, and Hitachi SH, offer the ability
to run either big-endian or little-endian byte orders. Usually the executable or symbol
will include a bit to designate the endian-ness, and you will not need to worry about
which to use. However, you can adjust the processor byte order manually using one
of the following commands:
13.3 Choosing target byte order 135
set endianbig
set endianlittle
set endianauto
Instruct GDB to assume the target is big-endian.
Instruct GDB to assume the target is little-endian.
Instruct GDB to use the byte order associated with the
executable.
show endian
Display GDB's current idea of the target byte order.
Note that these commands merely adjust interpretation of symbolic data on the host,
and that they have absolutely no effect on the target system.
136 Specifying a Debugging Target
14 HP-UX Configuration-Specific Information
While nearly all GDB commands are available for all native and cross versions of the
debugger, there are some exceptions. This chapter describes features, commands and,
enhancements available only on HP-UX.
14.1 Summary of HP Enhancements to GDB
WDB provides the following features in addition to the standard GDB features:
•
•
•
Support for debugging memory problems.
Support for heap usage reporting
The min-heap-size <num> option for set heap-check command reports
the heap allocations that exceed the specified number <num>of bytes based on
the cumulative number of bytes that are allocated at each call-site, which is inclusive
of multiple calls to mallocat a particular call site.
•
Heap checking commands info heap high-memand set heap-check
high-mem-count X_number.
•
•
Commands which, exit, info heap processand, info heap arena.
WDB supports the +check compiler option on Integrity systems to invoke batch
RTC, to determine runtime memory problems.
•
•
•
Enhanced batch RTC support, for better reporting, and options have replaced old
ones.
RTC heap corruption checks for calls to strcpy(), memset(), and memcpy()
have been added.
Support for memory checking analysis for user defined memory management
routines.
•
•
•
•
•
•
•
High water mark records the number of times the brk()value changes.
Heap analysis on programs with pending signals using the info leakcommand.
Commands info module ADDRESS, show envvars, and info corruption.
Command line option (-pid or -p) to attach to an existing process.
Support for debugging kernel threads and user threads.
Support for enabling and disabling threads.
Thread debugging commands set thread-check on/off, info thread
[thread-id], info mutex [mutex- id], info condvar [condvar-id],
and info rwlock [rwlock- id].
•
Enhanced thread debugging options for set thread-checkcommand such as
recursive-relock, num-waiter, stack-util,
thread-exit-no-join-detach, thread-exit-own-mutex,
cv-wait-no-mx, cv-multiple-mxs, mixed-sched- policy, and
unlock-not-own.
14.1 Summary of HP Enhancements to GDB 137
•
•
Serial debugging of a parent and child process.
Support for Parallel Processing limited to pthreadparallelism, but not the compiler
generated parallelism, for example, with directives.
•
•
•
Implementation of ask mode for set follow-fork-mode.
Support for setting breakpoints using shared library name.
Support for core file commands packcore, unpackcore, getcore, dumpcore
and info rtti address.
•
On PA-RISC systems, sanity check for core files dumped by hardware generated
signals can be performed. HP WDB can detect and warn the user about certain
cases of corrupted core files.
•
•
•
Inline support is on by default on Integrity systems. On PA-RISC, the inline support
is still off by default.
For PA 64-bit applications, WDB can step into shared library bind-on-reference
calls. This support is available for PA 32-bit as well.
Interception of synchronous signals used by sigwait(), sigwaitinfo()and
sigtimedwait()functions. These signals are displayed by WDB just like
asynchronous signals but are always passed to the debugger whether [nopass]
is set or not.
•
•
Support for debugging hardware watchpoints and shared libraries.
For PA 64-bit applications, WDB can step into shared library bind-on-reference
calls. This support is available for PA 32-bit as well.
•
•
Implementation of -mapsharedoption to suppress mapping all the shared libraries
in a process private.
Support for deferred breakpoints on dlopenedand shl_loadedlibraries with
stripped main program.
•
•
Additional support for procedural breakpoints.
C99 variable arrays implemented on Integrity systems. This support is available
on PA-RISC as well.
•
The show envvarscommand can be used to print information on environment
variables supported by WDB.
•
•
Support for handling __fpregdata type.
Support for making changes to the program when debugging without having to
re- compile or re-link it.
•
•
•
Hardware breakpoints on Integrity systems.
Support for debugging PA-RISC Applications on Integrity systems.
Unwinding Java stack frames on Integrity systems. The 64-bit version of gdb can
unwind through Java stack frames using the shared library in the Java product.
The 64-bit library is part of the JDK 1.4.2.10 and JDK 1.5.0.03 products.
•
Enhanced nextiand stepicommands. The WDB nextiand stepicommands,
prints the assembly instruction along with the next source line.
138 HP-UX Configuration-Specific Information
•
Enhanced info symbol ADDRESScommand. The info symbol ADDRESS
command has been enhanced to search for a symbol at the given address.
Previously, the info symbolcommand could be used only to search the global
namespace.
•
•
•
•
•
Enhanced Java debugging support.
Support for debugging C++ programs running under Linux Runtime Environment.
Support for stop in/at dbx commands.
Support for GNU GDB logging commands.
Support for persistent display of expressions across re-runs. The user does not
need to re-initiate the display settings for every run.
•
•
•
Viewing wide character and wide-character strings of type wchar_t using the
type printcommand.
Support for debugging of executables with method and expressions involving
covariant return types
Support for commands, catch throw, catch catch, and info catch, for
debugging exception handlers in C++ on Integrity systems, with the aCC compiler
A.06.00 and later.
•
Support for the steplastcommand for C and C++. However, steplast
command is not supported.
•
•
•
•
•
Support for dumping an array into an ASCII file.
Support for the Fortran array slices.
Source level debugging of Fortran applications that contain nested routines.
Support for making command line calls in a stripped executable.
Support for a terminal user interface that provides view of source while debugging
at the WDB command line.
•
support for debugging 32-bit and 64-bit PA-RISC programs as well as 64-bit Itanium
programs .
•
•
•
Support for assembly-level debugging.
Support for a subset of xdbcommands, enabled with -xdbmode.
Support for Java/C/aCC++ stack unwinding with Java SDK version 1.3.1.02 or later
for HP-UX.
•
•
•
•
Visual Interface for HP WDB -tuimode supports output logging
Command line calls for 64-bit PA-RISC applications that are not linked with end.o.
Command watch_target.
Command line option set display-full-paththat displays the full pathname
of the source file name while printing the frame information.
•
•
Command line option set dereference [on |off]when off, WDB does
not dereference char *variables by default.
Support for show macro, macro expand to view, and expand macro
expressions.
14.1 Summary of HP Enhancements to GDB 139
•
•
•
•
•
•
•
•
•
•
Support for evaluating macros.
Support for printing the execution path entries in the current frame, or thread.
New Command for Searching a Pattern in the Memory Address Space
New Option to Limit the Number of Frames Unwound
Updated Procedure to Process the Initialization File
Enhancement to the info sharedCommand
Enhancement to the info targetCommand
Support for automatic debugging of shared libraries
Attaching a PA-RISC debugger to a PA-RISC process
Improvement in the performance of memory debugging for the stringoption
14.2 HP-UX dependencies
14.2.1 Linker Dependencies
Several features available in WDB depend on specific versions of the linker or the
compiler.
•
Linker patch required for +objdebug
For releases prior to HP-UX 11i v2 (for IA) and HP-UX 11i v1 (for PA-RISC), you
must install the latest linker patch to generate object modules that enable faster
linking and smaller executable file sizes for large applications. See your compiler
release notes for more details.
•
•
Support for debugging incrementally linked 64-bit programs
This feature requires linker version B.11.18 or later on HP-UX 11i v1.
Support to automatically preload librtc.slwith chatr +mem_checkoption.
This feature requires linker version B.11.61 and later on HP 9000 systems, and
linker version B.12.46 and later on Integrity systems. +mem_checkoption is used
only for memory debugging.
•
Support to automatically preload librtc.slwith chatr +rtcoption.
This feature requires linker version B.11.66 and later on HP 9000 systems, and
linker version B.12.51 and later on Integrity systems. However, +mem_check
option is retained with the latest Linker version.
14.2.2 Dependent Standard Library Routines for Run Time Checking
The Run Time Checking feature (Interactive and Batch Mode) of WDB cannot be used
with applications that re-define or over-ride the default system-supplied versions of
140 HP-UX Configuration-Specific Information
the standard library routines under libc.soand libdld.so. The following standard
libraries are dependencies for runtime checking:
abort()
unlink()
atoi()
chdir()
uwx_register_callbacks()
lseek()
dlsym()
open()
strstr()
strcat()
ctime()
sprintf()
strcmp()
printf()
dlclose()
memchr()
strrchr()
dlgetname()
dlget()
pthread_self()
putenv()
shmctl()
strchr()
rand()
clock_gettime()
strlen()
dlhook()
dlmodinfo()
environ()
getenv()
strlen()
execl()
uwx_self_lookupip()
shl_get()
shl_unload()
shl_findsym ()
strtok_r()
time()
uwx_get_reg()
shl_get_r()
perror()
exit()
fclose()
fork()
strdup()
fopen()
uwx_init()
uwx_self_copyin()
creat()
uwx_step()
fprintf()
fscanf()
sscanf()
strcasecmp()
getcwd()
getpagesize()
getpid()
srand()
write()
uwx_self_init_context()
pthread_getschedparam()
uwx_self_init_info()
uwx_register_alloc_cb()
U_STACK_TRACE()
close()
strchr()
The runtime checking (of dynamic memory, libraries, and pthreads) in the debugger
relies on the semantic and standard behavior of these library routines. Run Time
Checking results in unexpected and unpredictable behavior when used with applications
that substitute or re-define these library routines.
Before enabling the Run Time Checking feature in WDB, use the nm(1) command to
determine if the application or the dependent libraries in the application redefine or
substitute these standard library routines.
14.2 HP-UX dependencies 141
14.3 Supported Platforms and Modes
•
Supported Platforms
HP WDB supports source-level debugging of programs written in HP C, HP aC++,
and Fortran 90 on Integrity systems running on HP-UX 11i v2 or later and PA-
RISC systems running HP-UX 11i v1 and later.
•
•
Support for assembly-level debugging
HP WDB provides support for assembly-level debugging.
Support for automatic loading of debug information
Debug information is automatically loaded from modules when an application is
com- piled with the +objdebugoption.
•
Support for debugging PA-RISC programs on Itanium-based systems
You can debug PA-RISC applications and core files on Itanium-based systems.
When you start HP WDB, if the debug target is a PA-RISC binary program, the
debugger automatically loads PA-RISC WDB. The PA-RISC version of HP WDB
is provided as part of the HP-UX operating system.
•
•
Support for debugging large core files (> 2GB)
HP WDB supports debugging of core files with sizes more than 2 GB.
Support co-variant type
HP WDB can step into a co-variant function. The compiler-generated function
called thunks, which is used internally by the compiler to support co-variant return
type, is not shown when you do a backtrace or switch from one frame to another
frame. Similarly, using a finishor returncommand at a co-variant callee
function directly returns the control back to the caller of thunks.
•
New attach command line options and handling (-pid or -p)
HP WDB accepts -pidor -pfollowed by a process ID to attach a running process
to the debugger.
142 HP-UX Configuration-Specific Information
NOTE: HP WDB cannot be attached to a process that is traced by tools which use
ttrace, such as Caliper, adb, and tusc. The debugger displays the following error message
on attempting to attach to such a process:
Attaching to process <pid> failed.
Hint: Check if this process is already being traced by another gdb or
other trace tools like caliper and tusc.
Hint: Check whether program is on an NFS-mounted file-system.
If so, you will need to mount the file system with the "nointr" option
with mount(1) or make a local copy of the program to resolve this problem.
14.4 HP-UX targets
On HP-UX systems, GDB has been configured to support debugging of processes
running on the PA-RISC and Itanium architectures. This means that the only possible
targets are:
•
•
•
An executable that has been compiled and linked to run on HP-UX. This includes
binaries that have been marked as SHMEM_MAGIC.
A live HP-UX process, either started by WDB (with the runcommand) or started
outside of WDB and attached to (with the attachcommand).
A core file generated by an HP-UX process that previously aborted execution.
GDB on HP-UX has not been configured to support remote debugging, or to support
programs running on other platforms.
WDB can only debug C++ programs compiled with HP aC++, the ANSI-compatible
C++ compiler.
14.5 Support for Alternate root
HP WDB supports alternate root functionality, which is helpful when you do not want
to use the system-installed HP WDB or its components.
The environment variable WDB_ROOTspecifies the alternate root for HP WDB. You
must specify a structure similar to the default /opt/langtoolsused for HP WDB.
You can use the environment variable GDB_ROOTto specify an alternate root for GDB.
If you specify both WDB_ROOTand GDB_ROOT, the value for GDB_ROOTis ignored.
HP WDB supports these environment variables to override the location of different
component of HP WDB.
Defined Variable /opt/langtools/ GDB_ROOT
$GDB_SERVER
bin
WDB Location
GDB location
/opt/langtools/ n/a
n/a
lib
WDB_ROOT
$GDB_ROOT/bin LIBRTC_SERVER
14.4 HP-UX targets 143
librtc.sllocation $WDB_ROOT/bin /opt/langtools/ n/a
bin
None
$WDB_ROOT/bin GDB_SERVER
n/a
/opt/langtools/ $WDB_ROOT/lib
bin
n/a
$LIBRTC_SERVER
NOTE: If you define WDB_ROOTor GDB_ROOTbut do not create the correct directory
structure below it, the debugger may fail.
14.6 Specifying object file directories
GDB enables automatic loading of debug information from object modules when an
application is compiled with the +objdebugoption.
GDB uses the full path name to the object module files and searches the same directories
for source files.
Although this behavior is transparent, you can control when and how object files are
loaded with three commands:
objectdirpath
Specifies a colon (:) separated list of directories in which
GDB searches for object files. These directories are added
to the beginning of the existing objectdirpath. If you
specify a directory that is already in the objectdirpath,
the specified directory is moved up in the objectdir
path so that it is searched earlier.
GDB recognizes two special directory names: $cdir,
which refers to the compilation directory (if available) and
$cwd, which tracks GDB's current working directory.
objectloadfile.c
Causes GDB to load the debug information for file.c
immediately. The default is to load debug information
from object modules on demand.
objectretryfile.c
Forces GDB to retry loading an object file if GDB
encounters a file error while reading an object module.
File errors that might cause this include incorrect
permissions, file not found, or if the objectdirpath
changes. By default, GDB does not try to read an object
file after an error.
pathmap
Enables you to define a list of substitution rules to be
applied to path names to identify object files and the
corresponding source files. The pathmapcommand,
144 HP-UX Configuration-Specific Information
however, may not find source files if the object files are
not available.
This minimizes or eliminates the need to specify multiple
objectdircommands when object files are moved from
the compilation directories or when compilation
directories are mounted over NFS.
To use this feature, the program must be compiled with
the +objdebugoption. For information on how pathmap
works type help pathmapat the HP WDB prompt.
If the debugger cannot find the source files, perform the following steps:
1. Make certain the files were compiled with the -gswitch. Type info sources to nd
the list of files that the debugger knows were compiled with -g.
2. Make certain that the debugger can find the source file. Type show dirto find
the list of directories the debugger uses to search for source files and type set
dirto change that path.
On HP-UX, the debug information does not contain the full path name to the source
file, only the relative path name that was recorded at compile time. Consequently,
you may need several dircommands for a complex application with multiple
source directories. One way to do this is to place them in a .gdbinitfile placed
in the directory used to debug the application.
A sample of the .gdbinitfile might look like the following:
dir /home/fred/appx/system
dir /home/fred/appx/display
dir /home/fred/appx/actor
dir /home/fred/appx/actor/sys
...
When you compile the program with the +objdebugoption, the debugger may
nd the source files without using the dircommand. This happens because the
debugger stores the full path name to the object files and searches for source files
in the same directories.
14.7 Fix and continue debugging
Fix and continue enables you to see the result of changes you make to a program you
are debugging without having to re-compile and re-link the entire program.
For example, you can edit a function and use the fixcommand, which automatically
re-compiles the code, links it into a shared library, and continues execution of the
program, without leaving the debugger.
With Fix and Continue, you can experiment with various ways of fixing problems until
you are satisfied with the correction, before you exit the debugger.
14.7 Fix and continue debugging 145
The advantages include:
•
•
•
•
You do not have to recompile and relink the entire program.
You do not have to reload the program into the debugger.
You can resume execution of the program from the x location.
You can speed up the development cycle.
NOTE: Fix and Continue is only supported with the most recent versions of HP C
and HP aC++ on PA-RISC systems.
In command-line mode, you use the editcommand before invoking the fixcommand.
The editcommand has the following syntax:
edit file1 file2
where
file represents one or more source files for the current executable. If you do not specify
a file name, WDB edits the currently open source file.
When you edit a file with the editcommand and save the changes, the original source
file contains the changes, even if you do not use the fixcommand to recompile the
program in the debugger.
14.7.1 Fix and Continue compiler dependencies
Fix and Continue is supported only for PA-RISC on HP-UX 11.x with these compilers:
•
•
•
HP C/ANSI C A.11.01.20, or later
HP aC++ A.03.25, or later
HP Fortran 90 2.4, or later
14.7.2 Fix and Continue restrictions
Fix and Continue has the following restrictions and behaviors:
•
•
You cannot recompile code that has been optimized.
You cannot add, delete, or reorder the local variables and parameters in a function
currently active on the stack.
•
•
If you x a routine in a file that contains function pointers, those function pointers
become invalid and will likely cause the program to receive a SIGSEGV error if
the pointers are used.
You cannot change the type of a local variable, file static, global variable, or
parameter of a function.
•
•
You cannot add any function calls that increase the size of the parameter area.
You cannot change a local or file static or global variable to be a register variable,
and vice-versa.
146 HP-UX Configuration-Specific Information
•
•
You cannot add an alloca()function to a frame that did not previously use
alloca().
New structure fields can be added at the end of a structure object, not in the middle
of a structure. New fields are only accessible by the modified files. Old structure
fields remain intact; no swapping of them is permitted.
•
If the redefined function is in the call stack but not on the top of the call stack, the
modified code will not be executed when the execution resumes.
The modified function will be executed when it is called next time, or a rerun.
•
•
Breakpoints in the original source file are moved to the modified fie. Breakpoints
in the already instantiated functions on the call stack in the original file are lost.
If you change the name of a function and there was a breakpoint set to the old
function, WDB does not move the breakpoint to the new function. The old
breakpoint is still valid.
•
•
If the number of lines of the modified file is different from that of the original file,
the placement of breakpoints may not be correct.
When the program resumes, the program counter is moved to the beginning of
the same line in the modified function. The program counter may be at the wrong
line.
14.7.3 Using Fix and Continue
When WDB recompiles a fixed source file, it uses the same compiler and the same
options that were used to create the original executable. If the compiler generates any
syntax errors or it encounters any of the restrictions, WDB does not patch the changes
into the executable image being debugged.
After you successfully recompile the changes, WDB uses the fixed version of the code
when you use any of the execution commands such as step, run, or continue.
When you use the editcommand, WDB then monitors any edited source files for
additional changes. After you enter the initial fixcommand, WDB checks for additional
saved changes to a source file each time you enter a program execution command. If
a saved source file has been changed, WDB asks if you want to fix the changed source,
allowing you to apply repeated fixes without explicitly entering the fixcommand.
The Fix and Continue facility enables you to make the following changes:
•
•
•
•
•
Change existing function definitions.
Disable, reenable, save, and delete redefinitions
Adding global and file static variables.
Add new structure fields to the end of a structure type object.
Set breakpoints in and single-step within redefined code.
14.7 Fix and continue debugging 147
NOTE: You must rebuild the program after you use the fixcommand because the
changes you make are temporarily patched into the executable image. The changes are
lost if you load a different executable and are not re ected in the original executable
when you exit the debugger.
14.7.4 Example Fix and Continue session
This example shows how you can make and test changes to a function without leaving
the debugger session.
Here is a short sample C program with an error:
int sum (num) int num;
{
int j, total = 0;
for (j = 0; j <= num; j++)
total += num;
}
main()
{
int num = 10;
printf("The sum from 1 to %d is = %d\n", num, sum(num));
}
1. Compile the program.
cc sum.c -g -o mysum
/usr/ccs/bin/ld: (Warning) At least one PA 2.0 object file
(sum.o) was detected.
The linked output may not run on a PA 1.x system.
2. Run the program.
./mysum
The sum from 1 to 10 is = 0
This result is obviously wrong. We need to debug the program.
3. Run the debugger:
gdb mysum
HP gdb 3.0 for PA-RISC 1.1 or 2.0 (narrow), HP-UX 11.00.
Copyright 1986 - 2001 Free Software Foundation, Inc.
Hewlett-Packard Wildebeest 3.0 (based on GDB ) is covered by the
GNU General Public License. Type "show copying" to see the
conditions to change it and/or distribute copies. Type
"show warranty" for warranty/support.
If the TERMenvironment variable is not set to hpterm, start the debugger and set
the terminal type for editing in WDB with this command (kshshell):
TERM=hpterm gdb mysum
148 HP-UX Configuration-Specific Information
The problem might be that there is no return for the num function. You can correct
this without leaving the debugger.
4. Set a break point at main:
(gdb) b main
Breakpoint 1 at 0x23f8: file sum.c, line 11.
5. Run the program:
(gdb) run
Starting program: /tmp/hmc/mysum
Breakpoint 1, main () at sum.c:11
11 int num = 10;
6. When the program stops at the break point, use the editcommand to make
changes to the source file.
Because you are going to edit the current file, you do not need to specify a source
file name.
(gdb) edit
The editcommand opens a new terminal session using your environment variable
settings for terminal and editor. The debugger automatically loads the source file.
7. Make the necessary changes. In this case, add:
return total;
to the function named num.
8. Save the edited source file and exit the editor. This saves the changes in the actual
source file for the program.
9. Use the fixcommand to recompile the program to see the results of the changes:
(gdb) fix
Compiling /dev/src/sum.c...
Linking...
Applying code changes to sum.c.
Fix succeeded.
The fixcommand creates a new executable that includes the changes you made
to the source file.
The debugger automatically uses the new executable and picks up the debugging
session where you stopped before using the editcommand.
For example, you can continue stepping through the program and you will nd the
new return total; statement in the source view. You can print the value of
total, and see that the result is 110.
14.7 Fix and continue debugging 149
10. When you finish with the debugging session, you can exit the debugger normally:
(gdb) q
The following modules in /dev/src/mysum have been fixed:
/dev/src/sum.c
Remember to remake the program.
The debugger message lists the source files that you have changed during the
debugging session.
NOTE: You must rebuild the program after you use the fixcommand because
the changes you make are temporarily patched into the executable image. The
changes are lost when you exit the debugger or you load a different executable.
14.8 Inline Support
HP WDB enables you to debug inline functions in applications compiled with -goption.
To enable inline debugging in HP 9000 systems, the applications must be compiled
with the +inline_debugoption (introduced in the A.03.65 and later versions of the
HP aC++ compiler). In Integrity systems, the applications that are compiled with -g
option support inline debugging by default and require no additional options. Compiler
versions A.06.02 and later support the inline debugging feature in Integrity systems.
14.8.1 Inline Debugging in HP 9000 Systems
To debug inline functions in HP 9000 systems, complete the following steps:
1. Compile the source files with the +inline_debugoption.
For example:
/opt/aCC/bin/aCC -g +inline_debug test.c
2. Inline debugging is enabled by default. To explicitly enable or disable inline de-
bugging, complete either of the following steps before loading the application to
the debugger:
$ gdb --inline=<on/off> a.out
or
(gdb) set inline-debug <on/off>
150 HP-UX Configuration-Specific Information
3. You can use the following commands for debugging inline functions in HP 9000
systems:
step
next
list
backtrace
frame <n>
info locals
info args
The following commands are not available for debugging inline functions in HP
9000 systems:
breakpoint
info frame
disassembly
NOTE: Inline debugging commands are not available for inlined template
functions and inlined functions which are defined after the call site.
14.8.2 Inline Debugging in Integrity Systems
In Integrity systems, applications that are compiled with -g option support inline
debugging by default. Compiler versions A.06.02 and later support the inline debugging
feature in Integrity systems and require no additional options.
WDB 5.6 and later versions enable you to set and modify breakpoints in inline functions
for programs compiled with optimization level less than +O2. The breakpoint features
for inline functions are introduced as additional options in the set inline-debug
command.
You can toggle the options for inline debugging by entering either of the following
commands:
(gdb) set inline-debug <option>
or
$ gdb --inline= <option>
The following options available for the set inline-debugcommand:
• on
• off
• inline_bp_all
• inline_bp_individual
The set inline-debugon command enables the inline debugging feature without
the inline breakpoints options in Integrity systems. This command is enabled by default.
14.8 Inline Support 151
The set inline-debug offcommand disables the inline debugging feature. You
can disable inline debugging by entering this command before attaching the debugger
to the application.
The set inline-debug inline_bp_allcommand enables you to set and modify
break- points on all instances of a particular inline function. It also enables the inline
debugging feature. A single instance of the specified inline function is displayed as a
representative in- stance for all the instances of the specified inline function. This creates
a single-breakpoint illusion for multiple instances of the inline function. You can set
and modify breakpoints on all the instances of the inline functions by setting and
modifying breakpoints on the displayed instance of the inline function. You must enter
this command before attaching the debugger to the application.
The set inline-debug inline_bp_individualcommand enables you to set
and modify breakpoints on a specific instance of an inline function. It also enables the
inline debugging feature. All instances of the inline function are displayed separately
with individual breakpoint occurrences. You can set or delete individual breakpoints
on a specific instance of an inline function without modifying the breakpoints on other
instances of the inline function. You must enter this command before attaching the
debugger to the application.
Limitations:
•
The inline breakpoint features are not available for programs that are com- piled
with +O2 optimization level and above.
•
The inline breakpoint features can degrade performance of the application that is
being debugged. You can explicitly disable the breakpoint features when the
features are not required and continue to use other inline debugging features, such
as stepand next.
14.8.2.1 Debugging Inline Functions in Integrity Systems
To debug inline functions in Integrity systems, complete the following steps:
1. The application must be compiled with the -g option for inline debugging. No
additional options are required. For example:
/opt/aCC/bin/aCC -g test.c
2. Inline debugging without the breakpoint feature is enabled by default. You can
modify the inline debugging settings by toggling the options for the set inline-
debugcommand.
•
To enable inline debugging without inline breakpoint support, enter either
of the following commands:
(gdb) set inline-debug on
or
$ gdb --inline = on
•
To set and modify breakpoints collectively on all instances of inline functions
and enable inline debugging, enter either of the following commands:
152 HP-UX Configuration-Specific Information
(gdb) set inline-debug inline_bp_all
or
$ gdb --inline = inline_bp_all
•
•
To set and modify individual breakpoints on specific instances of inline
functions and enable inline debugging, enter either of the following commands
be- fore debugging the application:
(gdb) set inline-debug inline_bp_individual
or
$ gdb --inline = inline_bp_individual
To disable inline debugging, enter either of the following commands be- fore
debugging the application:
(gdb) set inline-debug off
or
$ gdb --inline= off
3. You can use the following commands for debugging inline functions in Integrity
systems:
step
next
list
backtrace
frame <n>
info locals
info args
breakpoint
The following commands are not available for debugging inline functions in
Integrity systems:
info frame
disassembly
14.9 Debugging Macros
HP WDB 5.7 and later versions of the debugger enable you to display and evaluate
macro definitions for programs running on Integrity systems. This feature is available
only for compiler versions A.06.15 and later.
14.9.1 Viewing and Evaluating Macro Definitions
HP WDB 5.7 and later versions of the debugger provide the following support for de-
bugging macros:
•
Displaying Macro Definitions
Displaying Macro Definitions HP WDB provides the following commands to
display macro definitions:
14.9 Debugging Macros 153
- show macro [macro-name] or info macro [macro-name]
Displays the macro definition, source file name, and the line number. For example:
(gdb) info macro VAR2
Defined at scope.c:21
#define VAR2 201
- macro expand [macro-name]
Expands the macro and the parameters in the macro. If there are any parameters
in the macro, they are substituted in the macro definition when the definition is
displayed.
For example:
#define YY 6
#define MAC (67 + YY)
...
$ gdb
...
(gdb) macro expand MAC
expands to: (67 + 6)
•
Evaluating Macros
HP WDB enables you to evaluate a macro and display the output. You can evaluate
the macro by using the commonly used gdb commands for evaluating and
displaying expressions, such as print. HP WDB supports the evaluation of macros
with variables, constants, complex algebraic expressions involving variables, nested
macros, and function calls. HP WDB does not support the evaluation of macros
with multiple statements in the macro definitions, or the evaluation of macros
with stringifying and pasting tokens in the macro definitions.
14.9.1.1 Compiler Options to Enable Macro Debugging
To enable macro debugging, the program must be compiled with the
+macro_debug=[all|none|ref]compiler option.
Additionally, the program must be compiled with one of the -goptions (-g, -g0, or
-g1) to enable macro debugging. For example:
cc -g +macro_debug=all -o sample sample.c
The following options are available for the +macro_debug compiler option:
all
To view and evaluate all the macro expressions in the program, you must
compile the program with +macro_debug=all. This option can cause a
significant increase in object file size.
ref
To view and evaluate only the reference macros in the program, you must
compile the program with +macro_debug=ref. This is the default for -g,
-g0, or -g1.
none To disable macro debugging, you must compile the program with +macro_
debug=none
154 HP-UX Configuration-Specific Information
The macro debugging features are supported for +objdebugand +noobjdebug
compiler options.
14.9.2 Examples for Macro Debugging
The following example illustrates the use of the macro debugging:
Sample Program:
$ cat scope.c
1
2 #include <stdio.h>
3
4 #define USED1 100
5 #define USED2 200
6 #define UNUSED1 0
7 #define UNUSED2 0
8 #define DUMMY1
9 #define DUMMY2
10
11 int
12 main ()
13 {
14
15 int val = USED1;
16
17 #undef UNUSED1
18 #undef USED2
19 #undef USED1
20 #define USED1 101
21 #define USED2 201
22
23 val = USED1 + USED2;
24
25 #undef USED1
26 #undef UNUSED2
27 #undef USED2
28 #define USED1 102
29
30 val = USED1;
31
32 return 0;
33 }
Sample Debugging Session
•
The following debugging session illustrates macro debugging when the program
is com- piled with +macro_debug=alloption:
$ cc -g +macro_debug=all -o sc scope.c
$ gdb sc
HP gdb for HP Itanium (32 or 64 bit) and target HP-UX 11.2x.
Copyright 1986 - 2001 Free Software Foundation, Inc.
...
14.9 Debugging Macros 155
(gdb) b 13
Breakpoint 1 at 0x40007d0:0: file scope.c, line 13 from sc.
(gdb) b 23
Breakpoint 2 at 0x40007d0:2: file scope.c, line 23 from sc.
(gdb) b 30
Breakpoint 3 at 0x40007e0:0: file scope.c, line 30 from sc.
(gdb) r
Starting program: sc
Breakpoint 1, main () at scope.c:13
13 {
(gdb) print USED1
100
(gdb) print USED1+10
110
(gdb) info macro USED1
Defined at scope.c:4
#define USED1 100
(gdb) info macro USED2
Defined at scope.c:5
#define USED2 200
(gdb) c
Continuing.
Breakpoint 2, main () at scope.c:23
23 val = USED1 + USED2;
(gdb) info macro USED1
Defined at scope.c:20
#define USED1 101
(gdb) info macro USED2
Defined at scope.c:21
#define USED2 201
(gdb) c
Continuing.
Breakpoint 3, main () at scope.c:30
30 val = USED1;
(gdb) info macro USED1
Defined at scope.c:28
#define USED1 102
(gdb) info macro USED2
The macro `USED2' has no definition in the current scope.
(gdb)
•
The following debugging session illustrates macro debugging when the program
is com- piled with +macro_debug=referencedoption:
$ cc -g +macro_debug=referenced -o sc1 scope.c
$ gdb sc1
HP gdb for HP Itanium (32 or 64 bit) and target HP-UX 11.2x.
Copyright 1986 - 2001 Free Software Foundation, Inc.
...
(gdb) b 13
Breakpoint 1 at 0x40007d0:0: file scope.c, line 13 from sc1.
(gdb) b 23
156 HP-UX Configuration-Specific Information
Breakpoint 2 at 0x40007d0:2: file scope.c, line 23 from sc1.
(gdb) b 30
Breakpoint 3 at 0x40007e0:0: file scope.c, line 30 from sc1.
(gdb) r
Starting program: sc1
Breakpoint 1, main () at scope.c:13
13 {
(gdb) print USED1
100
(gdb) print USED1+10
110
(gdb) info macro USED1
Defined at scope.c:4
#define USED1 100
(gdb) info macro USED2
The macro `USED2' has no definition in the current scope.
(gdb) c
Continuing.
Breakpoint 2, main () at scope.c:23
23 val = USED1 + USED2;
(gdb) info macro USED1
Defined at scope.c:20
#define USED1 101
(gdb) info macro USED2
Defined at scope.c:21
#define USED2 201
(gdb) c
Continuing.
Breakpoint 3, main () at scope.c:30
30 val = USED1;
(gdb) info macro USED1
Defined at scope.c:28
#define USED1 102
(gdb) info macro USED2
The macro `USED2' has no definition in the current scope.
(gdb) q
The program is running. Exit anyway? (y or n) y.
14.10 Debugging Memory Problems
You can use WDB to nd leaks, profile heap usage and detect other heap-related errors
in HP C, HP aC++, and HP Fortran programs written for HP-UX 11.x systems. (Both
32-bit and 64-bit programs are supported.)
On HP-UX 11.x, the memory debugging features of WDB work with both
single-threaded and multi-threaded programs that use POSIX threads.
14.10 Debugging Memory Problems 157
For more information on memory debugging with WDB, see the Debugging Dynamic
Memory Usage Errors Using HP WDB whitepaper at the HP WDB Documentation
14.10.1 When to suspect a memory leak
You should suspect a memory leak in the code when you notice that the system is
running out of swap space or running slower, or both.
Applications or non-kernel code (including daemons) that have memory leaks can
eventually use up all swap space. You can run top(1)to verify whether the process
data space (SIZE, RES) is growing more than you expect.
If the system is running out of swap space, programs will fail with out-of-memory
(ENOMEM) errors or SIGBUSsignals. In addition, the system might run slower and
slower until it comes to a stop; all processes requiring swap to continue running will
wait for it indefinitely. GDB allows you to catch out-of-memory conditions through
runtime memory checking. Use the command catch nomemto detect out-of-memory
conditions. GDB will stop whenever malloc returns NULLand allows you to look at
the current context.
14.10.2 Memory debugging restrictions
Programs with these attributes are not supported:
•
•
CMA or DCE threaded programs on 11.x (32-bit and 64-bit)
Memory checking features. These features work only in programs that directly or
indirectly call malloc, realloc, free, mmap, or munmap from the standard C library
libc.sl.
•
•
Programs that link the archive version of the standard C library, libc.a, or the
core library, libcl.a, on HP-UX 11.x
NOTE: Linker with version number B.11.19 or higher is required for debugging
memory problems.
From HP WDB 5.7 onwards, the archive version of the run time check library,
librtc.a, is not available. You must use the shared version of the library,
librtc.[sl|so], instead.
14.10.3 Memory Debugging Methodologies
WDB enables you to debug memory problems in applications written for HP-UX 11.x
or later using C, aC++, FORTRAN 77, and Fortran 90.
WDB provides several commands that help expose memory-related problems.
158 HP-UX Configuration-Specific Information
HP WDB offers the following memory-debugging capabilities:
•
•
•
Reports memory leaks
Reports heap allocation profile
Stops program execution if bad writes occur with string operations such as strcpy
and memcpy
•
•
Stops program execution when freeing unallocated or de-allocated blocks
Stops program execution when freeing a block if bad writes occur outside block
boundary
•
Stops program execution conditionally based on whether a specified block address
is allocated or de-allocated
•
•
•
•
•
•
Scrambles previous memory contents at malloc()and free()calls
Simulates and detects out-of-memory event errors
Detects dangling pointers and dangling blocks
Detects in-blockcorruption of freed blocks
Specifies the amount of guard bytes for every block of allocated memory
Displays the run time type information for C++ polymorphic objects
You can use any of the following methods to identify memory problems:
•
•
•
14.10.4 Debugging Memory in Interactive Mode
This section describes the various commands which help in debugging memory
problems when the debugger is used in the interactive mode.
14.10.4.1 Commands for interactive memory debugging
To debug memory problems, use these commands:
set heap-check [on|off]
This toggles the capability for detection of leaks,
heap profiles, bounds checking, and checking for
double free.
info heap
Displays a heap report, listing information such
as the start of heap, end of heap, heap size, heap
allocations, size of blocks, and number of
instances. The report shows heap usage at the
point you use the info heapcommand. The
report does not show allocations that have
already been freed. For example, if you make
several allocations, free them all, and then you
14.10 Debugging Memory Problems 159
use info heap, the result does not show any
allocations.
info heapfilename
Writes heap report output to the specified file.
info heapidnumber
Produces detailed information on the specified
heap allocation including the allocation call stack.
show heap-check
Displays all current settings for memory
checking.
set heap-check interval <
nn >
This command starts incremental heap growth
profile. All allocations prior to the execution of
this command are ignored from report. If
incremental heap growth profile is already on,
executing this command will reset the counters
and start a fresh collection. Interval is specified
in seconds.
set heap-check repeat < nn This allows user to specify the number of
intervals GDB should collect the incremental
heap growth. The default value is 100. Every
repeat of the interval tracks heap allocation
during that interval.
>
Example:
< gdb > set heap-check interval 10
< gdb > set heap-check repeat 100
Here WDB will create 100 incremental apart heap
profiles which are 10 seconds apart.
set heap-check reset
GDB stores incremental heap growth data in an
internal file. During one session data is appended
to this file. If the session is very long, it is possible
that this file may become very large. This
command discards the data existing in the file
and creates a new data file. Once this command
is executed, the user cannot see the old data.
info heap-interval < file
name >
This command creates the report of heap growth.
The data for each interval has the start and end
time of the interval. If file name is mentioned a
detailed report is written in the file.
set heap-check leaks [on | Controls WDB memory leak checking.
off]
info leaks
Displays a leak report, listing information such
as the leaks, size of blocks, and number of
instances.
160 HP-UX Configuration-Specific Information
info leaksfilename
Writes the complete leak report output to the
specified file.
info leakleaknumber
Produces detailed information on the specified
leak including the allocation call stack.
set heap-check block-size
num-bytes
Instructs WDB to stop the program whenever it
tries to allocate a block larger than num-bytes in
size.
set heap-check heap-size
num-size
Instructs WDB to stop the program whenever it
tries to increase the program heap by at least
num-bytes.
min-heap-size
This option reports the heap allocations that
exceed the specified number <num> of bytes
based on the cumulative number of bytes that
are allocated at each call-site, which is inclusive
of multiple calls to mallocat a particular call
site.
set heap-check watch
address
Stops the program whenever a block at a
specified address is allocated or deal- located.
set heap-check null-check
[N | random]
Force mallocto return NULLafter N or random
number of invocations of malloc. Use set
heap-check random-range Nand set
heap-check seed-value Nto define the seed
value and range for random number calculation.
Useful for simulating out-of-memory situations.
set heap-check
null-check-size N
Force mallocto return NULLafter N bytes have
been allocated by the program.
catch nomem
Allows the user to get control of an
out-of-memory event. The user can step through
once the nomemevent is caught to see whether
the out-of-memory event is handled correctly.
set heap-check free [on |
off]
When set to on, forces WDB to stop the program
when it detects a call to free()with an
improper argument, a call to realloc()that
does not point to a valid currently allocated heap
block, or a call to free a block of memory, which
has been corrupted. Refer set heap-check
boundsfor details on detecting memory
corruption.
set heap-check string [on
| off]
Toggles validation of calls to strcpy, strncpy,
memcpy, memccpy, memset, memmove, bzero,
14.10 Debugging Memory Problems 161
and, bcopy. WDB 5.6 and later versions of the
debugger also validates calls to strcatand
strncat.
NOTE: HP WDB 6.0 and later versions of the
debugger improves performance of memory
debugging when the stringoption is set for
32-bit applications on HP-UX 11i v2 and later on
Itanium systems. However, the performance
degrades for 64-bit applications on HP-UX 11i
v2 and later on Itanium systems.
set heap-check bounds [on
| off]
Allocates extra space at the beginning and end
of a heap block during allocation and fills it with
a specific pattern. When blocks are freed, WDB
verifies whether these patterns are intact. If they
are corrupted, an under flow or over- flow must
have occurred and WDB reports the problem.
This option increases the program's memory
requirements.
set heap-check scramble [on Scrambles a memory block and overwrites it with
a specific pattern when it is allocated or
deallocated. This change to the memory contents
increases the chance that erroneous behaviors,
such as attempting to access space that is freed
or depending on initial values of malloc()
blocks, cause the program to fail.
| off]
info dangling
Displays a list of all the dangling pointers and
dangling blocks that are potential sources of
memory corruption( may have false positives).
info corruption
Checks for corruption in the currently allocated
heap blocks.In addition, it lists the potential
in-blockcorruptions in all the freed blocks.
set heap-check
min-leak-sizenum
Collects a stack trace only when the size of the
leak exceeds the number of bytes you specify for
this value. Larger values improve run-time
performance. The default value is zero (0) bytes.
set heap-check frame-count Controls the depth of the call stack collected.
Larger values increase run time. The default
value is four (4) stack frames.
num
set heap-check header-size Sets the Header guard for each block of the
allocated memory. The default number of bytes
num of bytes
162 HP-UX Configuration-Specific Information
for the footer is 16 bytes if this option is not used.
If the user specifies a value less than 16 for the
number of bytes, the debugger ignores it and
takes the default of 16 bytes. If the user specifies
more than 16 bytes, then the debugger considers
the largest and closest 16 byte integral from the
user-specified value.
Example:
If the user specifies 60 bytes, the debugger takes
it as 48 bytes. If the user specifies 65, the
debugger considers 64 bytes.
set heap-check footer-size Sets the Footer guard for each block of the
allocated memory. The default number of bytes
for the footer is one byte if this option is not used.
num of bytes
14.10.4.2 Example for interactive debugging session
This example describes checking a program running on HP-UX 11.x using linker version
B.11.19 or later:
1. Link the program with /usr/lib/libc.slinstead of libc.a.
2. Run the debugger and load the program:
> gdb a.out
3. Turn on leak checking:
(gdb) set heap-check leaks on
4. Set one or more breakpoints in the code where you want to examine cumulative
leaks:
(gdb) b myfunction
5. Run the program in the debugger:
(gdb) run
6. Use the infocommand to show list of memory leaks:
(gdb) info leaks
Scanning for memory leaks...done
2439 bytes leaked in 25 blocks
No. Total bytes Blocks Address Function
0 1234 1 0x40419710 foo()
1 333 1 0x40410bf8 main()
2 245 8 0x40410838 strdup()
[...]
14.10 Debugging Memory Problems 163
The debugger assigns each leak a numeric identifier.
7. To display a stack trace for a specific leak, use the info leakcommand and
specify the number from the list associated with a leak:
(gdb) infoleak 2
245 bytes leaked in 8 blocks (10.05% of all bytes leaked)
These range in size from 26 to 36 bytes and are allocated
in strdup ()
in link_the_list () at test.c:55
in main () at test.c:13
in _start ()
14.10.5 Debugging Memory in Batch Mode
HP WDB supports batch mode memory leak detection, also called batch Run Time
Checking (Batch RTC). Most of the memory debugging features supported in interactive
mode are also supported in batch mode.
NOTE: The batch mode commands may not always work when invoked through a
shell script.
14.10.5.1 Setting Configuration Options for Batch Mode
You can specify the batch mode configuration through a configuration file called
rtcconfig. The configuration file supports these variables:
check_free=on|off(or) set
heap-check free <on/off>
Enables detection of multiple incorrect free of
memory
check_heap|heap=on|off (or) Enables heap profiling.
set heap-check <on/off>
check_leaks|leaks=on|off
(or) set heap-check leaks
<on/off>
Enables leak detection.
check_string=on|off (or)
set heap-check string
<on/off>
Enables detection for writing out of boundary
for strcpy, strncpy, memcpy, memccpy,
memset, memmove, bzero, bcopy.
check_bounds|bounds=on|off Enables checking of bounds corruption.
(or) set heap-check bounds
<on/off>
files=<file1:file2:...|fileN> Specifies the executables for which memory leak
detection is enabled. If files option is not
specified, after setting BATCH_RTC=on, RTC will
instrument ALL executables.
164 HP-UX Configuration-Specific Information
frame_count=no_frames (or) Sets the number of frames to be printed for leak
context.
set heap-check frame-count
<no_frames>
min_heap_size=block_size
(or) set heap-check
min-heap-size <block_size>
Sets the minimum block size to use for heap
reporting.
min_leak_size=block_size
(or) set heap-check
min-leak-size <block_size>
Sets the minimum block size to use for leak
detection.
output_dir=output_data_dir Specifies the name of the output data directory.
scramble_blocks=on|off (or) Enables block scrambling.
set heap-check scramble
<on/off>
Batch mode leak detection stops the application at the end, when libraries are being
unloaded, and invokes HP WDB to print the leak or heap data.
NOTE: It is incorrect usage to use spaces before or after the '=' symbol in the batch
mode configuration options in the configuration file, rtcconfig. Additionally, it is
incorrect usage to use spaces before the batch mode configuration options.
For example:
Correct Usage:
$ cat rtcconfig
check_leaks=on
check_heap=on
files=batchrtc4
$
Incorrect Usage:
$ cat rtcconfig
check_leaks=on
check_heap = on
files=batchrtc4
$
Steps for Batch Mode Memory Debugging
To use batch memory debugging, complete the following steps:
1. Compile the source files.
2. Create an rtcconfigfile in the current directory.
3. Dene an environment variable BATCH_RTC. If you are using the Korn or Posix
shell, enter the following command at the HP-UX prompt:
export BATCH_RTC=on
14.10 Debugging Memory Problems 165
4. Complete one of the following steps to preload the librtcruntime library:
•
Set the target application to preload librtc by using the +rtcoption for the
chatrcommand. In addition to automatically loading the librtclibrary,
the +rtcoption for the chatrcommand also maps the shared libraries as
private. To enable or disable the target application to preload the librtc runtime
library, enter the following command at the HP-UX prompt:
$ chatr +rtc <enable|disable> <executable>
NOTE: The chatr+rtcoption preloads the librtc runtime library from the
following default paths:
– For 32 bit IPF applications,
/opt/langtools/lib/hpux32/librtc.so
– For 64 bit IPF applications,
/opt/langtools/lib/hpux64/librtc.so
– For 32 bit PA applications,
opt/langtools/lib/librtc.sl
– For 64 bit PA applications,
/opt/langtools/lib/pa20_64/librtc.sl
To preload the librtc runtime library from a path that is different from the
default paths, you must use the LD_PRELOADenvironment variable.
•
Instead of automatically preloading librtc and mapping the shared libraries,
you can explicitly preload the required librtc library after mapping the shared
libraries private.
In the case of HP 9000 systems, you must explicitly map the share libraries as
private by using the +dbg enableoption for the chatrcommand, as follows:
$ chatr +dbg enable ./<executable>
(This step is not required on Integrity systems.)
To explicitly preload the librtcruntime library and start the target
application, enter one of the following commands:
– For 32-bit IPF applications,
LD_PRELOAD=/opt/langtools/lib/hpux32/librtc.so <executable>
– For 64-bit IPF applications,
LD_PRELOAD=/opt/langtools/lib/hpux64/librtc.so <executable>
– For 32-bit PA applications,
166 HP-UX Configuration-Specific Information
LD_PRELOAD=/opt/langtools/lib/librtc.sl <executable>
– For 64-bit IPF applications,
LD_PRELOAD=/opt/langtools/lib/pa20_64/librtc.sl <executable>
If LD_PRELOADand chatr +rtcare used to preload the librtc runtime library
, the librtcruntime library is loaded from the path specified by
LD_PRELOAD.
NOTE: Batch Mode RTC displays one of the following errors and causes the
program to temporarily hang if the version of WDB and librtc.[sl|so]
do not match, or if WDB is not available on the system:
"/opt/langtools/bin/gdb: unrecognized option `-brtc'
Use `/opt/langtools/bin/gdb --help' for a complete list of options."
OR
"execl failed. Cannot print RTC info: No such file or directory"
This error does not occur under normal usage where WDB or
librtc.[sl|so] is used from the default location at /opt/langtools/
...However, this error occurs if GDB_SERVERand/or LIBRTC_SERVERare
set to a mismatched version of WDB or librtc.[sl|so]respectively.
5. At the end of the run, output data file is created in output_data_dir, if defined
in rtcconfig, or the current directory. HP WDB creates output data file for each
run. It creates a separate file for leak detection and heap information. The naming
convention for output files is as follows:
<file_name>.<pid>.<suffix>
where, <pid>is the process id and the value for <sux>can be either leaks, heap,
or mem.
NOTE: During operations such as system(3s)and popen(), which invoke a
new shell, librtc.sl|somust not be loaded to the invoked shell. You must use
LD_PRELOAD_ONCE, instead of LD_PRELOAD, to exclusively load the
librtc.sl|sofile to the calling process only. Following is the syntax for using
LD_PRELOAD_ONCE:
LD_PRELOAD_ONCE= /opt/langtools/lib/librtc.sl
14.10.5.2 Environment variable setting for Batch mode debugging
Batch mode memory leak detection uses the following environment variables:
• GDBRTC_CONFIGspecifies the location of rtcconfiguration file. If this option is
not specified, the configuration file is assumed to be in the current location, and
14.10 Debugging Memory Problems 167
has the filename rtcconfig. If user prefers to set this option, it must include the
filename.
◦
Incorrect usage:
export GDBRTC_CONFIG=./
export GDBRTC_CONFIG=/tmp
◦
Correct usage:
export GDBRTC_CONFIG=/tmp/yet_another_config
export GDBRTC_CONFIG=/tmp/rtcconfig
• BATCH_RTCenables or disables batch memory leak detection.
• GDB_SERVERis used to override the default path from where the gdb executable
is used to provide the information on memory leak. By default, /opt/langtools/
bin/gdbis used to print the output. This can be overridden by setting
GDB_SERVERappropriately.
• RTC_MALLOC_CONFIGis used to override the default configand rtcconfig
file settings. This variable can be set as follows:
export RTC_MALLOC_CONFIG=config_string1[;config_strings].
◦
◦
The config_strings are separated by a semi-colon(;).
The following config_strings options exist for RTC_MALLOC_CONFIG:
abort_on_bounds=[01]
abort_on_bad_free=[01]
abort_on_nomem=[01]
Aborts execution when heap objects
bounds check fail, value is 1, and the
environment variable RTC_NO_ABORT
is not set.
Aborts execution when free or realloc is
trying to free a heap object which is not
valid, value is 1, and environment
variable RTC_NO_ABORTis not set.
Aborts execution when out of memory
if value is 1, and environment variable
RTC_NO_ABORTis not set.
leak_logfile=stderr[+]filename The log file for batch mode must be
specified.
stderr: error message goes to stderr
[+]filename: error message goes to
filename, + means output is appended to
the file.
168 HP-UX Configuration-Specific Information
mem_logfile=stderr[+]filename
heap_logfile=stderr[+]filename
◦
Specify config_stringsfor +check=mallocon Itanium or WDB memory
check batch mode on Integrity systems.
• RTC_PROCESS_GDBINITis an optional environment variable used to enable
processing of the .gdbinitfile. You can use the .gdbinitfile to specify path
settings such as dir, objectdir, and pathmap to set the path of the source and object
files in case the source or object paths are different than the current directory, so
that the generated RTC reports display the symbol names and line numbers
correctly. This feature is optionally enabled only when the RTC_PROCESS_GDBINIT
environment variable is set to 1.
There are limitations on whatcommands in the .gdbinitfile. If there are erroneous
commands in the .gdbinitfile, the batch RTC session can possibly hang and not
produce the expected RTC reports. Following are some examples:
1. If the 'q' (quit) command is used, the session would hang and finally terminate
after approximately 10 mins, and not generate any RTC reports. It would print
the error message "Broken synchronization between child/parent process".
2. If any gdb command that would take more processing time is used, this would
interfere with the assumptions of RTC and the session may hang and print
the error message "Broken synchronization between child/parent process".
14.10.5.3 Example for Batch Mode RTC
This section illustrates examples of batch mode RTC on HP 9000 and Integrity Systems.
•
Example for Batch Mode RTC of a PA-RISC 32 bit Executable
1. Compile the source files.
2. The rtcconfigfile must contain entries, such as the following:
check_heap=on
check_leaks=on
check_free=on
files=executable_name
output_dir=/tmp/results
3. Set the following environment variables as follows:
export BATCH_RTC=on
14.10 Debugging Memory Problems 169
4. Complete one of the following steps:
– Map the shared libraries privately using chatr, as follows:
chatr +dbg enable <executable>
On HP-UX 11i v3 Integrity systems, WDB enables automatic debugging
of shared libraries without them being mapped private while attaching to
a running program. For enabling automatic debugging of shared libraries,
you must install the kernel patches PHKL_38651 and PHKL_38778.
Explicitly preload the librtcruntime library and start the target
application, as follows:
LD_PRELOAD=/opt/langtools/lib//librtc.sl <executable>
<arguments>
OR
– Set the target application to preload librtcby using the +rtcoption for
the chatrcommand. In addition to automatically loading the librtc
library, the +rtcoption for the chatrcommand also maps the shared
libraries as private.
To set the target application to preload the librtcruntime library, enter
the following command at the HP-UX prompt:
$ chatr +rtc enable <executable>
•
Example for Batch Mode RTC on Integrity Systems: Example-1
1. Compile the source files.
2. The rtcconfigfile must contain entries such as the following:
check_heap=on
check_leaks=on
check_free=on
files=executable_name
output_dir=/tmp/results
3. Set the following environment variables as follows:
export BATCH_RTC=on
4. Complete one of the following steps:
– Preload the librtcruntime library, as follows:
PRELOAD=/opt/langtools/lib/hpux32/librtc.so <executable>
<arguments if any>
OR
– Preload the librtcruntime library, as follows:
$ chatr +rtc enable <executable>
•
Example from Integrity Systems: Example-2
1. Compile the source files.
170 HP-UX Configuration-Specific Information
2. The rtcconfig file should contain entries such as the following:
check_heap=on
check_leaks=on
check_free=on
files=exec1:exec2:exec3
output_dir=/tmp/results
3. Set the following environment variables as follows:
export BATCH_RTC=on
4. Complete one of the following steps:
— Use the +rtcoption for the chatrcommand on each of the required
executable files that must be instrumented, as follows:
$ chatr +rtc enable exec1 exec2 exec3
OR
— Preload the librtclibrary as follows:
export LD_PRELOAD /opt/langtools/lib/hpux32/librtc.so
5. Run the program as follows:
./exec1
Suppose exec1eventually spawns exec2, exec3, exec4, exec5, only
exec1, exec2, exec3will be instrumented based on the settings in the
rtcconfigfile.
14.10.6 Debugging Memory Interactively After Attaching to a Running Process
HP WDB accepts -pidor -pfollowed by a process ID to attach a running process to
the debugger.
To use Batch RTC after attaching GDB to a running process, complete the following
steps:
14.10 Debugging Memory Problems 171
1. Complete one of the following steps to preload the librtc runtime library:
–
Set the target application to preload librtcby using the +rtcoption for the
chatrcommand.In addition to automatically loading the librtc library, the
+rtcoption for the chatrcommand also maps the shared libraries as private.
To enable or disable the target application to preload the librtcruntime
library, enter the following command at the HP-UX prompt:
$ chatr +rtc <enable|disable> <executable>
NOTE: To attach and nd leaks for PA-32 applications from the startup, the
environment variable RTC_INIT should be set to on in addition to preloading
the librtc.[sl|so]library before starting the application, as follows:
$ RTC_INIT=on <executable>
OR
–
Instead of automatically preloading librtcand mapping the shared libraries,
you can explicitly preload the required librtc library.
In the case of HP 9000 systems, you must explicitly map the share libraries as
private by using the +dbgenable option for the chatrcommand, as follows:
$ chatr +dbg enable ./<executable>
(This step is not required on Integrity systems.)
To explicitly preload the librtcruntime library and start the target
application, enter one of the following commands:
◦
◦
◦
◦
For 32 bit IPF applications:
LD_PRELOAD=/opt/langtools/lib/hpux32/librtc.so <executable>
For 64 bit IPF applications:
LD_PRELOAD=/opt/langtools/lib/hpux64/librtc.so <executable>
For 32 bit PA applications:
LD_PRELOAD=/opt/langtools/lib/librtc.sl <executable>
For 64 bit PA applications:
LD_PRELOAD=/opt/langtools/lib/pa20_64/librtc.sl <executable>
NOTE: To attach and nd leaks for PA-32 applications from the startup, the
environment variable RTC_INITshould be set to onin addition to preloading
the librtc.[sl|so]library before starting the application, as follows:
$ LD_PRELOAD=/opt/langtools/lib/librtc.sl RTC_INIT=on <application>
If RTC_INITis turned on, librtc starts recording heap information for PA32
process, by default. Hence, you must set this environment variable only when
it is required, and you must not export this environment variable for shell.
172 HP-UX Configuration-Specific Information
2. Run the program.
3. Start a debugging session as follows:
gdb -leaks <executable-name> <process-id>
4. Use info heapand info leakscommands to obtain a memory analysis report
of the application.
NOTE: From HP WDB 5.7 onwards, the archive version of the run time check library,
librtc.a, is not available. You must use the shared version of the library,
librtc.[sl|so], instead.
14.10.7 Configuring memory debugging settings
The following configuration settings are supported to control the level of details of
information required to be displayed when debugging memory leaks.
14.10.7.1 Specifying the stack depth
Memory debugging reduces the performance of an application by 20-40% because of
stack unwinding. To provide a clear profile of every allocation in the program, the
debugger collects the stack trace information for every allocation in the debugged
application. Reducing the stack depth (the number of stack frames that the debugger
collects for each allocation) reduces the performance degradation.
The set heap-check frame-count command enables you to control the depth
of the stack frames that are collected by WDB for each allocation. By default, four stack
frames are displayed from the allocating call stack.
To set the depth of the stack frames that is collected by WDB, enter the following
command at the gdb prompt:
$ set heap-check frame-count [num]
The stack depth, [num], is the number of stack frames that WDB collects for each
allocation.
You can specify a higher value for [num] to view more stack frames for each reported
allocation. However, the performance of the application is reduced because of the
increased stack depth.
14.10.7.2 Specifying minimum leak size
WDB enables you to specify the minimum leak size for stack trace collection to improve
the program's performance.
Stack trace collection slows down the program because it occurs on every allocation
call. Therefore, if the program is allocation-intensive, WDB can spend a substantial
amount of time collecting stack traces.
You can improve performance by using the command:
14.10 Debugging Memory Problems 173
set heap-check min-leak-size num
For example, if you use,
set heap-check min-leak-size 100
WDB does not collect stack traces for allocations smaller than 100 bytes. HP WDB still
reports leaks smaller than this size, but does not include a stack trace.
14.10.7.3 Specifying minimum block size
The min-heap-sizeoption reports the heap allocations that exceed the specified
number <num> of bytes based on the cumulative number of bytes that are allocated at
each call-site, which is inclusive of multiple calls to malloc at a particular call site. For
example:
set heap-check min-heap-size 100
When the option min-heap-sizeis set to 100, GDB reports all the cumulative block
allocations that 100 bytes at each call-site.
14.10.8 Scenarios in memory debugging
14.10.8.1 Stop when freeing unallocated or deallocated blocks
WDB enables you to locate improper calls to free()and realloc(), with the
command:
–
–
In interactive debugging mode: set heap-check free [on | off].
In batch mode debugging: check_free [on | off].
With this setting on, whenever the program calls free()or realloc()WDB inspects
the parameters to verify that they are pointing to valid currently allocated heap blocks.
If WDB detects an erroneous call to free(), it stops the program and reports this
condition. You can then look at the stack trace to understand where and how the
problem occurred.
14.10.8.2 Stop when freeing a block if bad writes occurred outside block boundary
WDB enables you to locate problems caused by heap block over flow or underflow
with the command
–
–
In Interactive debugging mode: set heap-check bounds [on | off]
In batch mode debugging: check_bounds [on | off]
When bounds checking is turned on, WDB allocates extra space at the beginning and
end of a block during allocation and fills it up with a specific pattern. When blocks are
freed, WDB verifies whether these patterns are intact. If they are corrupted, an under
flow or over flow must have occurred and WDB reports the problem. If you want to
nd corruption at any time, use the info corruptioncommand.
The info corruptioncommand can detect memory corruption in an application.
That is, it reports all the memory blocks that have over-writes and under-writes.
174 HP-UX Configuration-Specific Information
Syntax:
info corruption [<file name>]
The run time memory checking must be enabled before using the info corruption
command to detect memory corruption. The corruption information is written to a file
specified in the .filename argument if provided. Otherwise, it is printed to the
stdout.
NOTE: Turning on bounds checking increases the program's memory requirements
because the extra guard bytes must be allocated at the beginning and end of each block.
14.10.8.3 Stop when a specified block address is allocated or deallocated
To stop a program whenever a block at a specified address is allocated or deallocated,
use the command:
set heap-check watch address
You can use this to debug situations such as multiple free() calls to the same block.
Limitation : This is not supported in batch mode debugging.
14.10.8.4 Scramble previous memory contents at malloc/free calls
WDB enables you to potentially expose latent memory access defects with the command:
–
–
In Interactive debugging mode: set heap-check scramble [on | off]
In batch mode debugging: scramble_blocks [on | off].
When this setting is turned on, any time a memory block is allocated or deallocated,
WDB scrambles the space and overwrites it with a specific pattern.
This change to the memory contents increases the chance that erroneous behaviors will
cause the program to fail. Examples of such behavior include attempting to access space
that is freed or depending on initial values of malloc()blocks.
You can now look at the stack trace to understand where and how the problem occurred.
NOTE: Turning on scrambling slows down the program slightly, because at every
malloc()and free()call, the space involved must be overwritten.
14.10.8.5 Detect dangling pointers and dangling blocks
A pointer is a Dangling pointer if the block of memory it points to, has been freed by
the application. The block is called Dangling Block.
The same freed block could be subsequently allocated to the application in response
to another memory allocation request. In this scenario, if the application incorrectly
tries to write into the freed memory block using the dangling pointer, it could result
in incorrect or an undefined program behavior, as the new owner or function owning
the same allocated block would nd different values in the heap block.
14.10 Debugging Memory Problems 175
NOTE: Software literature names this concept as premature free or Reading/writing freed
memory using a pointer.
WDB tracks the dangling pointers and dangling blocks using a modified version of
Garbage collection. The enabler for doing this is by retaining all the freed blocks
internally within RTC without actually freeing it as long as possible. It displays all the
potential pointers to the freed dangling blocks, in the application data space.
The pointers are potential because the pointers need not be actual pointers and could
be a datum value and hence there are chances of false positives in the dangling report.
NOTE: WDB tries to help as much as possible to detect if these pointers are of type
datum or real pointers. In a -g compiled binary, WDB performs a look-up on a symbol
table to nd the symbol name and type to nd the symbol name of the potential pointer
and if its of pointer type, then the corresponding dangling block is really dangling(not
a false positive).
WDB turns on these checks, only when you specify set heap-check
retain-freed- blocks on.
14.10.8.6 Detect in-block corruption of freed blocks
HP WDB detects all the attempts of a program to write to the freed dangling blocks
using dangling pointers. We detect such in-block corruptions and are reported as part
of the existing info corruptioncommand output.
14.10.8.7 Specify the amount of guard bytes for every block of allocated memory
HP WDB enables you to programmatically control the size of guard bytes for every
block of the allocated memory. You can use these guard bytes to spot very rare and
non-trivial boundary (buffer over-run and buffer under-run) corruptions. This again
is available optionally when the user specifies set heap-check
retain-freed-blocks <on>.
14.10.9 Comparison of Memory Debugging Commands in Interactive Mode and Batch
Mode
HP WDB 5.6 and later versions provide consistency in format for the batch mode options
and the interactive mode commands.
The following table lists the memory debugging commands available in batch and
interactive mode:
176 HP-UX Configuration-Specific Information
Table 14-1 Memory Debugging Commands in Interactive and Batch Mode
Command Description
Interactive mode
Batch mode
Toggles heap profiling and detection set heap-check [on check_heap= [on | off] (or)
of leaks, bounds, and double free
| off]
set heap-check [on | off]
Toggle the leak detection capability set heap-check leaks [on check_leaks =[on | off](or)
|off]
set heap-check leaks [on
|off]
Toggle validation of calls to strcpy, set heap-check
check_string= [on |off] (or)
set heap-check string [on |
off]
strncpy, memcpy, memccpy,
memset, memmove, bzero, and
bcopy
string [on | off]
Toggle validation of calls to free() set heap-check free check_free = [on |off](or)
[on |off]
set heap-check free [on |
off]
Specify whether freed blocks should set heap-check
scramble_blocks=[on| off](or)
scramble [on |off] set heap-check scramble [on
|off]
be scrambled
Toggle bounds check on heap blocks set heap-check
check_bounds = [on | off]
(or) set heap-check bounds
[on| off]
bounds [on| off]
Specify the minimum size of a block set heap-check
min_heap_size = <num>(or) set
min-heap-size <num> heap-check min-heap-size
<num>
for stack trace collection. GDB will
report blocks of size greater than or
equal to <num>at each call-site.
Specify the minimum size of a block set heap-check
min_leak_size = <num>(or) set
min-leak-size <num> heap-check min-leak-size
<num>
for stack trace collection. GDB report
leaks of blocks, smaller than this
value. However, no stack trace is
provided.
Specify the depth of call stack to be set heap-check
captured
frame_count = <num>(or) set
heap-check frame-count <num>
frame-count <num>
Instruct GDB to stop, whenever a set heap-check watch Not supported in batch mode
block at the given address gets
allocated or deallocated.
address
Instructs mallocto return null after set heap-check
<num>invocations of malloc. null-check <num>
Not supported in batch mode
Not supported in batch mode
Instructs mallocto return null after set heap-check
<num>bytes have been allocated by null-check-size
malloc.
<size>
Specifies the seed value to be used set heap-check
Not supported in batch mode
for generating random
seed-value <num>
null-check-count.
14.10 Debugging Memory Problems 177
Table 14-1 Memory Debugging Commands in Interactive and Batch Mode (continued)
Command Description
Interactive mode
Batch mode
Specifies the random range to be
used by random-range.
set heap-check
random-range <num>
Not supported in batch mode
Specifies the time interval to be used set heap-check
Not supported in batch mode
Not supported in batch mode
for incremental memory profile.
interval <num>
Perform incremental profile for
set heap-check
<num>interval periods where each repeat <num>
period duration is defined by set
heap-check interval command. The
default value is 100.
NULL pointer return by memory catch nomem
allocators; used with set
heap-check on, with/without
null-checkenabled.
Not supported in batch mode
NOTE: The files=<executable-name>and output_dir=<path>options are
exclusive to batch mode debugging.
14.10.10 Heap Profiling
The heap profile is useful for identifying how memory is being used by the program.
You can use WDB to profile an application's current heap usage.
14.10.10.1 Commands for heap profiling
info heap
Displays a heap report, listing information such
as the start of the heap, end of the heap, heap
allocations, size of blocks, and number of
instances. The report shows heap usage at the
point you use the info heapcommand.
The report does not show allocations that have
already been freed. For example, if you make
several allocations, free them all, and then you
use info heap, the result does not show any
allocations.
info heapfilename
Writes heap report output to the specified file.
info heapidnumber
Produces detailed information on the specified
heap allocation including the allocation call stack.
set heap-check frame-count Controls the depth of the call stack collected.
Larger values increase run time. The default
value is four (4) stack frames.
num
178 HP-UX Configuration-Specific Information
show heap-check
Displays all current settings for memory
checking.
14.10.10.2 info heap arena
The info heap arenacommand enables the user to view high level memory usage
details of each arena. The info heap arenais not supported in batch mode. This
command is available only for applications running on 11i v3 or later.
14.10.10.3 info heap arena [0 |1|2|..]blocks stacks
Displays the memory profile report for block level and overall memory usage with
stack trace where applicable. This command is available only for applications running
on 11i v3 or later.
14.10.10.4 info moduleADDRESS
The info modulecommand identifies load modules, and determines whether it lies
in the text or data region for a given address. This command is available only for
applications running on 11i v3 or later.
Syntax:
info module ADDRESS
14.10.10.5 info heap process
The info heap process command enables the user to view a high level memory usage
report of a process. This command is available only for applications running on 11i v3
or later.
14.10.10.6 Example for heap profiling
This example shows how to use this feature on HP-UX 11.x:
1. If the linker version is earlier than B.11.19, link with /opt/langtools/lib/
pa20_ 64/librtc.slfor PA-64 programs. For a 32-bit program, you must link
with /opt/langtools/lib/librtc.sl.
If the dynamic linker version is B.11.19 or later, skip this step because WDB
automatically loads the librtc.sl library.
2. Turn on profiling with the set heap-check on command:
(gdb) set heap-check on
3. Set a breakpoint:
(gdb) b myfunction
14.10 Debugging Memory Problems 179
4. When the program is stopped at a breakpoint, use the info heapcommand:
(gdb) info heap
Analyzing heap ...done
Actual Heap Usage:
Heap Start = 0x40408000
Heap End = 0x4041a900
Heap Size = 76288 bytes
Outstanding Allocations:
41558 bytes allocated in 28 blocks
No. Total bytes Blocks Address Function
0 34567 1 0x40411000 foo()
1 4096 1 0x7bd63000 bar()
2 1234 1 0x40419710 baz()
3 245 8 0x404108b0 boo()
[...]
The display shows the currently allocated heap blocks. Any blocks that have been
allocated and already freed are not listed.
To look at a specific allocation, specify the allocation number with the info heap
command:
(gdb) info heap 1
4096 bytes at 0x7bd63000 (9.86% of all bytes allocated)
in bar () at test.c:108
in main () at test.c:17
in _start ()
in $START$ ()
14.10.11 Memory Checking Analysis for User Defined Memory Management Routines
Many user applications have their own memory management routines. These custom
allocator routines are either user defined or sometimes wrappers to the default memory
management routines. Memory checking features has been extended for user defined
memory management routines. Memory leak, profile of heap memory or memory
errors can be obtained for user defined memory management routines.
Limitations:
•
This feature routes to default memory routines instead of calling user defined
memory management routines to obtain memory analysis.
•
This feature is not supported in batch mode and attach mode debugging.
14.10.12 Commands to track the change in data segment value
The high water mark records the number of times the brk()value changes. The
following commands are supported:
info heap high-mem
Displays the number of times brk()value
changes for a given run.
180 HP-UX Configuration-Specific Information
set heap-check high-mem-count
X_number
Stops when brk()value has moved X_number
of times.
Limitations:
•
This feature assumes that an application has a deterministic memory allocation
pattern from one run to another.
•
The high_memfeature is not supported in batch mode debugging.
14.11 Thread Debugging Support
HP WDB provides thread-debugging support for kernel, user, and MxN threads. You
can exclusively disable or enable specific thread execution. Advanced thread debugging
support in HP WDB enables you to view information on pthread primitives and detect
certain thread-related conditions.
NOTE: WDB supports pthreadparallelism, but it does not support
compiler-generated parallelism such as parallelism with directives.
14.11.1 Support for Enabling and Disabling Specific Threads
When you suspect that a specific thread is causing a problem while debugging a multi-
threaded application, you can suspend the execution of other threads in the application
and debug the doubtful thread exclusively. HP WDB 3.2 and later versions provide
the following commands to disable and enable specific thread execution:
thread disable
This command prevents the specified threads from running
until they are enabled again using the thread enable
command.
thread enable
This command enables the specified thread to run when you
issue the continueor stepcommand. By default, all threads
are in the enabled state. You can use the thread enable
command to reactivate a disabled thread.
Consider the following example:
(gdb) info threadsystem thread 4189 0x7f666da8
in __pthread_create_system+0x3d8 () from /usr/lib/libpthread.1
2 system thread 4188 worker (wptr=0x40004640 ") at quicksort.c:135
1 system thread 4184 0x7f66f728 in _lwp_create+0x10 () from /usr/lib/libpthread.1
To disable a thread, execute the following command:
(gdb) thread disable 1
warning: ATTENTION!! Disabling threads may result in
deadlocks in the program.Disabling thread 1
To enable a thread, execute the following command:
(gdb) thread enable 1
Enabling thread 1
14.11 Thread Debugging Support 181
14.11.2 Backtrace Support for Thread Debugging
The following commands are available as backtrace support for thread debugging:
bt
The btcommand provides the stack trace of the
current thread that is being executed or the thread
that accepts the signal in case of a core file.
thread apply all bt
You can use the thread apply all btcommand
to display the backtrace of all threads. The bt
command only provides the stack trace of the
current thread under execution.
backtrace_other_thread
The backtrace_other_threadcommand prints
the backtrace of all stack frames for a thread with
stack pointer SP, program counter PC and address
of gr32in the backing store BSP. This command
enables you to view the stack trace when the stack
is corrupted. When using this command, you must
ensure that the SP, PC, and BSP values are valid.
The syntax for the backtrace_other_thread
command is as follows:
backtrace_other_thread SP PC BSP
14.11.3 Advanced Thread Debugging Support
Advanced thread debugging support is available for multi-threaded applications
running on HP-UX 11iv2, or HP-UX 11iv3.
HP WDB 5.5 and later versions provide advanced thread debugging features to display
extended information on the state of pthreadprimitives such as mutexes, read-write
locks and conditional variables.
HP WDB 5.6 and later versions provide advanced thread-debugging options to detect
the following thread-related conditions:
•
•
The thread attempts to acquire a non-recursive mutex that it currently holds.
The thread attempts to unlock a mutex or a read-write lock that it has not ac-
quired.
•
•
•
•
The thread waits (blocked) on a mutex or read-write lock that is held by a thread
with a different scheduling policy.
Different threads non-concurrently wait on the same condition variable, but with
different associated mutexes.
The thread terminates execution without unlocking the associated mutexes or
read-write locks.
The thread waits on a condition variable for which the associated mutex is not
locked.
182 HP-UX Configuration-Specific Information
•
The thread terminates execution, and the resources associated with the terminated
thread continues to exist in the application because the thread has not been joined
or detached.
•
•
The thread uses more than the specified percentage of the stack allocated to the
thread.
The number of threads waiting on any pthread object exceeds the specified thresh-
old number.
14.11.3.1 Pre-requisites for Advanced Thread Debugging
The following pre-requisites apply for advanced thread debugging:
•
The advanced thread debugging features are supported only on HP-UX 11i v2
and later on both PA-RISC and Integrity systems.
•
The tracing pthreadlibrary is required for advanced thread-debugging. The
pthreadtracer library is available by default on systems running on HP-UX 11i
v2 or later. You must install HP WDB 5.5 or later versions of the debugger to
support enhanced thread debugging. The installation scripts for HP WDB 5.5 and
later versions of the debugger automatically add links at /opt/langtools/lib/
to replace the standard libpthreadlibrary with libpthread tracer library
at run time.
•
•
The thread debugging feature in HP WDB is dependent on the availability of the
dynamic Linker Version B.11.19.
HP WDB uses librtc.slto enable thread debugging support. If the debugger
is installed in a directory other than the default /opt/langtools/bindirectory,
you must use the environment variable, LIBRTC_SERVER, to export the path of
the appropriate version of librtc.sl.
•
HP WDB does not support debugging of programs that link with the archive
version of the standard C library libc.aor the core library libcl.a. The
programs must be linked with libc.sl.
•
•
The advanced thread debugging commands work only if set thread-check
is set to on.
For PA-RISC 32-bit applications, the dynamic library path look-up must be enabled
for advanced thread debugging. To enable dynamic library path look-up for
advanced thread debugging, enter the following command at HP-UX prompt:
# chatr +s enable <PA32-bitApp>
This command automatically enables dynamic library path look-up. No additional
environmental variables are required to be set.
14.11.3.2 Enabling and Disabling Advanced Thread Debugging Features
HP WDB 5.6 and later versions of the debugger provide advanced thread debugging
features for debugging multi-threaded applications running on 11i v2, or 11i v3. These
14.11 Thread Debugging Support 183
features are available as options to the set thread-checkcommand. The syntax for
the set thread-checkcommand is as follows:
set thread check { [on|off]| [option] [on|off] |[option] [num]}
The set thread-check [on|off] command enables or disables advanced thread
debugging. This feature is off by default. The set thread-check [on|off]
command must be enabled prior to running the application under the debugger, to
force the underlying runtime system to collect information on pthreadprimitives.
The advanced thread debugging features can be enabled only if the set
thread-check [on]command is enabled. The following advanced thread debugging
options are available for the set thread-checkcommand:
recursive-relock [on|off]
This set thread-check recursive-relock
[on|off]command checks if a thread has
attempted to acquire a non-recursive mutex that
it currently holds. Re-locking a non-recursive
mutex results in a deadlock. At run-time, the
debugger keeps track of each mutex in the
application and the thread that currently holds
each mutex. When a thread attempts to acquire
a lock on a non-recursive mutex, the debugger
checks if the thread currently holds the lock
object for the mutex. The debugger transfers the
execution control to the user and prints a
warning message when this condition is detected.
unlock-not-own [on|off]
The set thread-check unlock-not-own
[on|off]command checks if a thread has
attempted to unlock a mutex or a read-write lock
that it has not acquired. The debugger transfers
the execution control to the user and prints a
warning message when this condition is detected.
mixed-sched-policy [on|off] The set thread-check
mixed-sched-policy [on|off]command
checks if a thread is waiting (blocked) on a mutex
or a read-write lock that is held by a thread with
a different scheduling policy. This is not an
application error and does not always result in
deadlock. However, it degrades the application
performance. The debugger transfers the
execution control to the user and prints a
warning message when this condition is detected.
cv-multiple-mxs [on|off]
The set thread-check cv-multiple-mxs
[on|off]command checks if an application
184 HP-UX Configuration-Specific Information
uses the same condition variable in multiple calls,
by different threads to pthread_cond_wait()
or pthread_cond_timedwait(), but specifies
different mutexes. The debugger transfers the
execution control to the user and prints a
warning message when this condition is detected.
All threads that concurrently wait on any single
condition variable must specify the same
associated mutex. For example,the pthread
implementation does not allow thread 1to
wait on condition variable Aby specifying
mutex A, while thread 2waits on the same
condition variable Aby specifying mutex
B. This returns an EINVALerror to the
application. In contrast to this obvious EINVAL
error, the cv-multiple-mxsoption detects the
less-obvious and non-concurrent use of multiple
mutexes with the same condition variable by
different threads. This option detects potential
EINVALerrors that exist as a result of different
timings or execution paths.
This option is used to detect unintentional use
of multiple mutexes with the same condition
variable by different threads. In the case of
applications that use a dynamic pool of mutexes,
the cv-multiple-mxs option is not required
because this usage is normal and expected
application behavior.
cv-wait-no-mx [on|off]
The set thread-check cv-wait-no-mx
[on|off]checks if the associated mutex of a
condition variable is locked when the thread calls
the pthread_cond_wait()routine. The
debugger transfers the execution control to the
user and prints a warning message when this
condition is detected. This check is not a POSIX.1
standard requirement for the
pthread_cond_wait()routine. It is an
additional check provided by WDB.
thread-exit-own-mutex
[on|off]
The set thread-check
thread-exit-own-mutex [on|off]
command checks if any thread has terminated
execution without unlocking the mutexes or
14.11 Thread Debugging Support 185
read-write locks that are associated with the
thread. The debugger transfers the execution
control to the user and prints a warning message
when this condition is detected. This situation
can result in deadlocks if other threads are
waiting to acquire the locked mutexes or
read-write locks.
thread-exit-no-join-detach The set thread-check
[on|off]
thread-exit-no-join-detach [on|off]
command checks if a thread has terminated
execution (either successfully or because of an
exception or a cancel) without joining or
detaching the thread. The debugger transfers the
execution control to the user and prints a
warning message when this condition is detected.
The resources associated with a terminated
thread continue to exist in the application if the
thread is not joined or detached. The thread must
be explicitly joined or detached, or it must be
created with the detach attribute. When an
application repeatedly creates threads without
a join or detach operation, the application leaks
resources. This may result in application failure.
stack-util [num]
The set thread-check stack-util [num]
command checks if any thread has used more
than the specified percentage [num]of the stack
allocation. The debugger transfers the execution
control to the user and prints a warning message
when this condition is detected. You can use this
option to verify if there is a margin of safety in
stack utilization by the threads. The application
must ensure that the thread stack size is sufficient
for all the operations of the thread. Each thread
is assigned a stack allocation when it is created.
If the stack allocation is not specified for a thread,
the default value is used. The stack allocation
cannot be modified after a thread is created. If a
thread attempts to use more stack space than the
allocated stack space, it results in a stack
overflow. Stack over flow can result in memory
access violations, bus errors, or segmentation
faults.
186 HP-UX Configuration-Specific Information
num-waiters [num]
The set thread-check num-waiters
[num]command checks if the number of threads
waiting on any pthread object exceeds the
specified threshold number [num]. The debugger
transfers the execution control to the user and
prints a warning message when this condition is
detected.
14.11.3.3 Commands to view information on pthread primitives
WDB 5.5 and later versions of the debugger display extended information on pthread
primitives for multi-threaded applications running on HP-UX 11i v2, or 11i v3. This
feature is available only if the set thread-check [on|off]command is enabled.
The following commands enable you to view extended information on threads, mutexes,
read-write locks and conditional variables in multi-threaded applications:
info thread [thread-id]
info mutex [mutex-id]
info condvar [condvar-id]
The info thread [thread-id]command
displays a list of known threads. If a thread-id is
provided, the command displays extended
information on the specified thread.
The info mutex [mutex-id]command
displays a list of known mutexes. If a mutex-id
is provided, the command displays extended
information on the specified mutex.
The info condvar [condvar-id]command
displays a list of known condition variables. If
condvar-id is provided, the command displays
extended information on the specified condition
variable.
info rwlock [rwlock-id]
The info rwlock [rwlock-id]command
displays a list of known read-write locks. If
rwlock-id is provided, the command displays
extended information on the specified read-write
lock.
14.11.4 Debugging Threads Interactively After Attaching to a Process
HP WDB provides support to attach a running process to the debugger. To use thread
debugging commands after attaching GDB to a running process, complete the following
steps:
14.11 Thread Debugging Support 187
1. Set LD_LIBRARY_PATH to include the appropriate directory, by entering one of
the following commands:
•
•
•
•
For 32 bit IPF applications,
LD_LIBRARY_PATH=/opt/langtools/wdb/lib/hpux32
For 64 bit IPF applications,
LD_LIBRARY_PATH=/opt/langtools/wdb/lib/hpux64
For 32 bit PA applications,
LD_LIBRARY_PATH=/opt/langtools/wdb/lib
For 64-bit PA applications,
LD_LIBRARY_PATH=/opt/langtools/wdb/lib/pa20_64
2. Complete one of the following steps to preload the librtcruntime library:
•
Set the target application to preload librtc by using the +rtcoption for the
chatrcommand. In addition to automatically loading the librtclibrary,
the +rtcoption for the chatrcommand also maps the shared libraries as
private. To enable or disable the target application to preload the librtc
runtime library, enter the following command at the HP-UX prompt:
$ chatr +rtc <enable|disable> <executable>
NOTE: The chatr+rtcoption preloads the librtcruntime library from
the following default paths:
— For 32 bit IPF applications,
/opt/langtools/lib/hpux32/librtc.so
— For 64 bit IPF applications,
/opt/langtools/lib/hpux64/librtc.so
— For 32 bit PA applications,
opt/langtools/lib/librtc.sl
— For 64-bit PA applications,
/opt/langtools/lib/pa20_64/librtc.sl
To preload the librtcruntime library from a path that is different from the
default paths, you must use the LD_PRELOADenvironment variable.
OR
•
Instead of automatically preloading librtcand mapping the shared libraries,
you can explicitly preload the required librtclibrary after mapping the
shared libraries private.
In the case of HP 9000 systems, you must explicitly map the share libraries as
private by using the +dbg enableoption for the chatrcommand, as follows:
188 HP-UX Configuration-Specific Information
$ chatr +dbg enable ./<executable>
(This step is not required on Integrity systems.)
To explicitly preload the librtc runtime library and start the target application,
enter one of the following commands:
— For 32 bit IPF applications,
LD_PRELOAD=/opt/langtools/lib/hpux32/librtc.so <executable>
— For 64 bit IPF applications,
LD_PRELOAD=/opt/langtools/lib/hpux64/librtc.so <executable>
— For 32 bit PA applications,
LD_PRELOAD=/opt/langtools/lib/librtc.sl <executable>
— For 64-bit PA applications,
LD_PRELOAD=/opt/langtools/lib/pa20_64/librtc.sl <executable>
If LD_PRELOADand chatr+rtcare used to preload the librtc runtime library
, the librtcruntime library is loaded from the path specified by
LD_PRELOAD.
3. Complete one of the following steps:
•
Attach the debugger to the required process and enable thread debugging,
as follows:
gdb -thread -p <pid>
or
gdb -thread <executable> <pid>
•
Alternately, you can attach the process to the debugger and consequently
invoke thread debugging, as follows:
$ gdb <executable> <pid>
...
(gdb)set thread-check on
14.11.5 Thread Debugging in Batch Mode
HP WDB supports batch mode of debugging threads for HP-UX 11iv2 and later, on
Integrity systems and on HP-UX 11i v3 in PA-RISC systems for 64 bit applications. The
debugger provides a log file with the list of thread-related errors that occur in the
application.
In batch mode, the debugger detects the all the thread-conditions that are detected
during an interactive debugging session.
The debugger reports extended information such as variable address, name, id and
other specifications related to the involved pthread objects. In addition, it displays the
stack trace of the executing thread at the point of error.
14.11 Thread Debugging Support 189
NOTE: Use the set frame-countsetting in the rtconfigfile to control the depth
of the stack trace file. This command controls the depth of the call stack collected. Larger
values increase the run time.
14.11.5.1 Pre-requisites for Batch mode of Thread Debugging
The various prerequisites for Batch mode of Thread Debugging are as follows:
•
The thread-debugging feature in HP WDB is dependent on the availability of the
dynamic linker version B.11.19.
•
Advanced thread-debugging feature requires the pthread tracer library which is
available by default on systems running HP-UX 11i v2 or later.
Steps to debug threads in batch mode
1. Compile the source files.
Set the LD_LIBRARY_PATH environment variable, based on the platform as
follows:
•
•
•
For 32 bit IPF applications, set
LD_LIBRARY_PATH=/opt/langtools/wdb/lib/hpux32
For 64 bit IPF applications, set
LD_LIBRARY_PATH=/opt/langtools/wdb/lib/hpux64
For 64-bit PA applications, set
LD_LIBRARY_PATH=/opt/langtools/wdb/lib/pa20_64
2. Map the share libraries as private for HP 9000 systems using the following
command:
$ chatr +dbg enable ./<executable>
NOTE: This step is not applicable for Integrity systems.
3. Create a configuration file, rtcconfigto specify the various thread conditions
that you want the debugger to detect.
190 HP-UX Configuration-Specific Information
NOTE: The configuration file contains lines of the following form:
set thread-check [on|off] | [option] [on|off] | [option] [num]
And/Or
set frame-count [num]
And/Or
files=<name of the executable on which the thread checking is to be
done>
For more information, see “Enabling and Disabling Advanced Thread Debugging
4. Set the environment variable BATCH_RTCto on as:
Set BATCH_RTC=on
14.11 Thread Debugging Support 191
5. Complete one of the following steps to preload the librtcruntime library:
•
Set the target application to preload librtcby using the +rtcoption for the
chatrcommand. In addition to automatically loading the librtclibrary,
the +rtcoption for the chatrcommand also maps the shared libraries as
private.
To enable or disable the target application to preload the librtcruntime
library, enter the following command at the HP-UX prompt:
$ chatr +rtc <enable|disable> <executable>
NOTE: The chatr+rtcoption preloads the librtcruntime library from
the following default paths:
— For 32 bit IPF applications,
/opt/langtools/lib/hpux32/librtc.so
— For 64 bit IPF applications,
/opt/langtools/lib/hpux64/librtc.so
— For 64-bit PA applications,
/opt/langtools/lib/pa20_64/librtc.sl
To preload the librtc runtime library from a path that is different from the
default paths, you must use the LD_PRELOADenvironment variable.
OR
•
Instead of automatically preloading librtcand mapping the shared libraries,
you can explicitly preload the required librtclibrary after mapping the
shared libraries private.
In the case of HP 9000 systems, you must explicitly map the share libraries as
private by using the +dbg enable option for the chatrcommand, as follows:
$ chatr +dbg enable ./<executable>
(This step is not required on Integrity systems.)
To explicitly preload the librtc runtime library and start the target application,
enter one of the following commands:
— For 32 bit IPF applications,
LD_PRELOAD=/opt/langtools/lib/hpux32/librtc.so <executable>
— For 64 bit IPF applications,
LD_PRELOAD=/opt/langtools/lib/hpux64/librtc.so <executable>
— For 64-bit PA applications,
LD_PRELOAD=/opt/langtools/lib/pa20_64/librtc.sl <executable>
192 HP-UX Configuration-Specific Information
If LD_PRELOADand chatr+rtcare used to preload the librtcruntime
library , the librtcruntime library is loaded from the path specified by
LD_PRELOAD.
If HP WDB detects any thread error condition during the application run, the error
log is output to a file in the current working directory. The output file has the
following naming convention:
<executable name>.<pid>.threads
where,
<pid>is the process id.
14.11.5.2 Limitations in Batch mode of thread debugging
The feature does not obtain the thread-error information in batch mode for forked
process in a multiprocessing application. However, if the librtc.sllibrary is
preloaded, the debugger obtains the thread-error information in the batch mode for
exec-edapplication.
You cannot specify an alternate output directory for the thread-error log. The thread-
error log file is output into the current working directory only.
HP WDB cannot execute both batch mode thread check and batch mode heap check
together. If the rtcconfigfile has both entries, then batch heap check overrides the
batch thread check.
14.11.6 Thread Debugging in +checkMode
A new compiler option +check=threadenables batch mode thread debugging features
of HP WDB.
NOTE: This feature is available only for compiler versions A.06.20 and later.
It is a convenient way of launching the batch mode advanced thread checking features
without setting any other environment variables at runtime. In other words, batch
mode thread checking has two modes of invocation. The first method is to use the run-
time environment variables LD_LIBRARY_PATH, LD_PRELOAD, and BATCH_RTCon
existing precompiled applications. The second method is to use the +check=thread
option at the compile time.
+check=threadmust only be used with multithreaded programs. It is not enabled
by +check=all. This functionality requires HP WDB 5.9 or later.
The default configuration used by +check=threadoption is as follows:
thread-check=1;recursive-relock=1;unlock-not-own=1;
mix-sched-policy=1;cv-multiple-mxs=1;cv-wait-no-mx=1;
thread-exit-own-mutex=1;thread-exit-no-join-detach=1;stack-util=80;
num-waiters=0;frame_count=4;output_dir=.;
14.11 Thread Debugging Support 193
Behavior of the +check=threadoption can be changed by users by providing their
own rtcconfigfile. The user specified rtcconfigfile can be in the current directory
or in a directory specified by the GDBRTC_CONFIGenvironment variable.
If any thread error condition is detected during the application run, the error log will
be output to a file in the current working directory. The output file will have the
following naming convention:
<executable name>.<pid>.threads,
where <pid>is the process identifier.
14.11.7 Known issues with Thread Debugging for Interactive and Batch mode
Issue 1:
During the execution of advanced thread checking for applications that fork, in the
interactive mode, the following message appears if the GDB follows the child:
Pthread analysis file missing!
This error message appears because the thread-error information for the forked process
is not available.
However, if the forked process exec()s another binary, the thread-error information
is available for the exec-ed binary.
Issue 2
In both interactive and batch modes, if the applications exceed their thread stack
utilization, the following error message appears:
Error accessing memory address
This occurs when GDB attempts a command line call on an already overflowing thread
stack.
14.12 Debugging MPI Programs
You can attach the debugger to Message Passing Interface (MPI) programs for
debugging. You must set the one of the following environment variables before you
launch the MPI process:
set MPI_FLAGS= egdb for invoking GDB
or
set MPI_FLAGS= ewdb for invoking WDB
For more information, see the mpidebug(1)and mpienv(1)manpages.
Attaching the debugger to an MPI process (or to any other process that has not been
compiled for debugging) can result in the following warning:
warning: reading 'r3' register: No data
194 HP-UX Configuration-Specific Information
14.13 Debugging multiple processes ( programs with forkand vfork
calls)
14.13.1 Ask mode for set follow-fork-mode
The ask command prompts the user to select between parent and child as the debugger
response to a program call of fork/vfork. Based on the user selection, the parent or
the child process is debugged.
For example,
(gdb) set follow-fork-mode ask (gdb) show follow-fork-mode
The debugger response to a program call to forkor vforkis ask.
(gdb) run Starting program: sample [New process 4941] Select follow-fork-
mode: [0] parent [1] child
14.13.2 Serial mode for set follow-fork-mode
The option serial, for the follow-fork-modecommand, enables debugging of a
parent and child process within a debugger session. During a debug session, if the
parent process forks a child, the debugger starts debugging the child process. When
the child process exits, the debugger switches back to the parent process. The
follow-fork-modewill work only if there is a wait() call by the parent process. This
feature is enabled by setting the follow-fork-modeflag to serial, as specified in the
following example:
(gdb) set follow-fork-mode serial
The follow-fork-modeis not supported under following conditions:
•
•
MxN threaded programs
Parent process is 32-bit and child process is 64-bit and vice versa. For the follow-
fork-modeto work both parent and child process must be of the same mode.
14.13.3 Support for showing unwind info
The maint info unwindcommand prints the unwind information for the regions
unwinded at the given address expression. Usage:
maint info unwind exp
where, expis an address expression.
For example,
(gdb) maint info unwind $pc
modsched:
0x4000930 .. 0x4000a20, end_prologue@0x4000970
Info block version:0x0, flags:0x0, length:4 * 4 == 16
0x40172b20: (0c) R1prologue rlen=12
0x40172b21: (e8) P7preds_when t=11
0x40172b23: (b1) P3preds_gr gr=41
0x40172b25: (ea) P7lc_when t=7
14.13 Debugging multiple processes ( programs with fork and vfork calls) 195
0x40172b27: (b2) P3lc_gr gr=40
0x40172b29: (61) R3body rlen=33
0x40172b2b: (81) B1label_state label=1
0x40172b2c: (c0) B2epilogue t=44
0x40172b2e: (00) R1prologue rlen=0
0x40172b2f: (00) R1prologue rlen=0
14.13.4 Printing CFM and PFS registers
On Integrity systems, HP WDB prints Current Frame Marker (CFM) and Previous
Frame State (PFS) ar64registers in two different formats:
•
•
raw values
special formats identifying the size of rotating registers, frame and locals.
For example,
ar64: 0xc00000000000050c (sor:0, sol:10, sof:12)
cfm: 0x800000000000450a (sor:1, sol:10, sof:10)
14.14 Command to Search for a Pattern in the Memory Address Space
The HP WDB findcommand searches for a pattern in the given memory address
range for both live and corefile debugging. Following is the syntax for the find
command:
find [/size-char] [/max-count] start-address, end-address, expr1
[, expr2 ...]
find [/size-char] [/max-count] start-address, +length, expr1 [,
expr2 ...]
where:
/size-char
Specifies the size of the pattern. It can be b, h, w, or gfor
8-, 16-, 32-, 64-bit values, respectively. It is applicable only
for hexadecimal patterns.
If /size-charis not specified, the size is obtained from
the type of the expression in the current programming
language.
This is an optional parameter.
/max-count
Specifies the maximum number of matching patterns to
be displayed. This is an optional parameter.
start-address
end-address
Specifies the start address in the given memory address
range. This parameter is mandatory.
Specifies the end address in the given memory address
range. This parameter is mandatory.
196 HP-UX Configuration-Specific Information
+length
Specifies the length of the memory address range. This
parameter is mandatory when end-addressis not
specified.
expr1, expr2, ....
Specifies a variable or pattern to be searched. The pattern
can be a variable, hexadecimal character, a character, or
a string value. The character pattern must be enclosed
within single quotes. The string pattern must be enclosed
within double quotes. This parameter is mandatory.
The $numfoundvariable contains the number of patterns matched within the given
memory address range.
14.14 Command to Search for a Pattern in the Memory Address Space 197
Example 14-1 Sample Output for the findcommand
$ cat example.c
#include <stdio.h>
#include <stdlib.h>
int main()
{
char *str;
str = (char *) malloc (15);
strcpy(str,"hihi-hikh");
return 0;
}
(gdb) find &str[0], &str[15], "hi"
0x400123e0
0x400123e2
0x400123e5
3 patterns found.
(gdb) find/2 &str[0], &str[15], "hi"
0x400123e0
0x400123e2
2 patterns found.
(gdb) find/2b &str[0], &str[15], 0x68
0x400123e0
0x400123e2
2 patterns found.
(gdb) find/2b &str[0], +10, 0x68
0x400123e0
0x400123e2
2 patterns found.
(gdb) find/2b &str[0], +10, 0x68, 0x69
0x400123e0
0x400123e2
2 patterns found.
(gdb) find &str[0], &str[15], "hi", "hi"
0x400123e0
1 pattern found.
The following examples provide sample usages of the different parameters in the find
command:
•
Using the start address (start-address), end address (end-address), and
patterns (expr1, expr2)
(gdb) find &a[0], &a[10], "el",'l'
2 patterns found.
198 HP-UX Configuration-Specific Information
where:
&a[0]
&a[10]
“el”, 'l'
Specifies the start address of the memory address range.
Specifies the end address of the memory address range.
Specifies the pattern.
•
•
Using the start address (start-address), length (+length) parameter, and a
pattern (expr1)
find &str[0], +11, "hihi"
&str[0] Specifies the starting address.
+11
Specifies the length of the memory address range, starting from
&str[0].
"hihi"
Specifies the pattern (expr1).
Using the /max-countparameter
(gdb) find /1 &int8_search_buf[0], +sizeof(int8_search_buf), 'a', 'a', 'a'
where:
/1
Specifies the findcommand to display only
one matching pattern.
&int8_search_buf[0]
+sizeof(int8_search_buf)
'a', 'a', 'a'
Specifies the starting address.
Specifies the ending address.
Specifies the pattern (expr1, expr2,
expr3).
•
Using the /size-charparameter
(gdb) find /b &int8_search_buf[0], &int8_search_buf[0]+sizeof(int8_search_buf),
0x61, 0x61, 0x61, 0x61
where:
/b
Specifies that the size of the pattern is 8 bits.
Specifies the starting address.
&int8_search_buf[0]
&int8_search_buf[0]
+sizeof(int8_search_buf)
Specifies the ending address.
0x61, 0x61, 0x61, 0x61
Specifies the pattern (expr1, expr2, expr3,
exp4).
14.14 Command to Search for a Pattern in the Memory Address Space 199
NOTE: Following are different ways of representing the /size-charand
/max-countparameters:
/1b
/b1
/b /1
/1 /b
where:
1
Specifies that findmust display 1 matching pattern.
b
Specifies that the size of the pattern is 8 bits.
14.15 Debugging Core Files
14.15.1 Generating core files with packcore/unpackcore/getcore
The contents of a core file can be viewed only on a system which has all the shared
libraries that were in use on the system on which the core file was generated. If you
want to view the content of the core file on a system which does not have the shared
libraries, you have to set the environment variables GDB_SHLIB_PATHor GDB_SHLIB_
ROOTto make it search for the desired libraries. The commands packcore, unpackcore,
and core simplify the process of examining the contents of a core file on a system other
than the one in which it was generated.
The packcorecommand is used on the system which generated the core file. When
you are examining the core file on the original system, you can execute packcoreto
make a packcore.tar.Zfile. This is a compressed tar file which contains the core
file, the executable, and all the shared libraries that were used by the program when
it generated the core file. The core file is removed after it is added to the
packcore.tar.Z file.
The packcorecommand has one optional argument, basename, which can be used
instead of packcoreto make packcore.tar.Z.
The packcore.tar.Zfile can be copied to a different system and the gdb command
unpackcoreunpacks the packcore.tar.Zfile in the current directory, creating a
new packcore directory. After unpacking the packcore file, the unpackcorecommand
invokes getcoreto load the executable and the core file from the packcore directory,
and sets GDB_SHLIB_PATH to the modules directory in the packcore directory. The
modules directory holds all of the shared libraries that were used when the core file
was generated.
The unpackcorecommand has two optional arguments. The first defaults to
packcore.tar.Zand is the name of the packcore file to be unpacked. The second
argument is given if the core file is too large to fit in the packcore file. It is the path to
200 HP-UX Configuration-Specific Information
the core file to be used if the packcore directory does not contain a core file. If used,
this second argument causes a symbolic link to be created in the packcore directory in
place of the missing core file.
The getcorecommand can be used to examine a packcore directory which was
previously created by unpackcore. It takes one optional argument, the name of the
packcore directory, which defaults to packcore.
14.15.2 Support for the info targetCommand
The info targetcommand is enhanced to display the memory segments for the
corefile. The output also displays other details, such as system name, node name,
operating system release name, license level, and machine model, for the core file. The
enhancement is available for HP-UX 11i v2 and later versions of Itanium systems.
Following is the sample output for the enhanced info targetcommand:
(gdb) file info_target
Reading symbols from info_target...done.
(gdb) core core
Core was generated by `info_target'.
Program terminated with signal 6, Aborted.
#0 0xc00000000032c5b0:0 in kill+0x30 () from /usr/lib/hpux64/libc.so.1
(gdb) info target
Operating System Information:
sysname : HP-UX
nodename : test1
release : B.11.23
version : U (128-user, 256-user or Unlimited-user system)
machine : ia64
idnumber : 0735747273
Symbols from "/tmp/info_target".
Local core dump file:
`/tmp/core',
file type elf64-big.
0x6000000000000000 - 0x6000000000010000 is segment4 (PT_HP_CORE_LOADABLE)
0x9ffffffffb7d9000 - 0x9ffffffffb7da000 is segment5 (PT_HP_CORE_MMF)
0x9ffffffffb7da000 - 0x9ffffffffb7dc000 is segment6 (PT_HP_CORE_MMF)
0x9ffffffffb7dc000 - 0x9ffffffffb7e0000 is segment7 (PT_HP_CORE_MMF)
0x9ffffffffb7e0000 - 0x9ffffffffb7e8000 is segment8 (PT_HP_CORE_MMF)
0x9ffffffffb7e8000 - 0x9ffffffffb7f3000 is segment9 (PT_HP_CORE_MMF)
0x9ffffffffb7f3000 - 0x9ffffffffb7f4000 is segment10 (PT_HP_CORE_MMF)
0x9ffffffffb7f4000 - 0x9ffffffffb7f6000 is segment11 (PT_HP_CORE_MMF)
0x9ffffffffb7f6000 - 0x9ffffffffb7fa000 is segment12 (PT_HP_CORE_MMF)
0x9ffffffffb7fa000 - 0x9ffffffffb7fc000 is segment13 (PT_HP_CORE_MMF)
0x9ffffffffb7fc000 - 0x9ffffffffb7fe000 is segment14 (PT_HP_CORE_MMF)
0x9ffffffffb7fe000 - 0x9ffffffffb7ff000 is segment15 (PT_HP_CORE_MMF)
0x9ffffffffb7ff000 - 0x9ffffffffb800000 is segment16 (PT_HP_CORE_STACK - RSE)
0x9fffffffffffa000 - 0xa000000000000000 is segment17 (PT_HP_CORE_STACK)
0x6000000000000058 - 0x600000000000d000 is heap segment
0x9fffffff7b7f6270 - 0x9fffffff7b7f62e8 is .note.hpux_options in /usr/lib/hpux64/dld.so
0x9fffffff7b7f62e8 - 0x9fffffff7b7f6458 is .dynamic in /usr/lib/hpux64/dld.so
............
...........
14.15 Debugging Core Files 201
NOTE: Limitations for the enhanced info targetcommand on corefile are as
follows:
•
The enhanced info targetcommand is not supported when the
expanded_node_host_names kernel parameter is set. It is supported only for the
default utsname.
•
The heap segment listed in the memory segment does not contain mmapped
memory for the given core file.
14.15.3 Support for the dumpcorecommand
HP WDB provides the command, dumpcore to generate a core image file for a process
running under the debugger during execution.
The dumpcore command does not require any argument. It saves the core image for
the current process being debugged in the file named core.<pid>, where <pid> is the
process ID number.
To dump the core for a live process, you must pass the following commands:
(gdb) run Starting program: sample Breakpoint 3, main () at sample.c:1010 b
= foo(a); (gdb) dumpcore Dumping core to the core file core.24091(gdb)
When starting from the HP WDB command line:
(gdb) file sample
Reading
symbols from sample...done
(gdb) set live-core 1
(gdb) core-file core.24091
Core was generated by 'sample'.#0 main () at sample.c:1010 b = foo(a);
(gdb) backtrace#0 main () at sample.c:10
(gdb)
When starting from the shell prompt:
% gdb --lcore a.out core.<pid>
For example:
% ./gdb --lcore sample core.24091
HP gdb...
Type "show warranty" for warranty/support....
Core was generated by 'sample'.#0 main () at sample.c:10
(gdb)
14.15.3.1 Enhancements to the dumpcorecommand
HP WDB provides an option for the dumpcore command, to specify a <core-
filename>, to generate a core image file of a process running under the debugger in
the middle of execution and saves it in the file named <core-filename>.
The dumpcorecommand with no arguments saves the core image for the current
process being debugged in the file named core.<pid>, where pidis the process ID
number.
202 HP-UX Configuration-Specific Information
To analyze this core file with HP WDB on HP-UX 11i version 2, you must do the
following:
•
When starting from HP WDB command line:
(gdb) core-file [core.pid | core-filename]
•
When starting from shell prompt:
$ gdb -core a.out [core.pid | core-filename]
14.15.4 Support for display of run time type information
HP WDB enables you to view the run time type information for C++ polymorphic
object.
info rtti address
This command displays run time type information for C++ polymorphic object. The
input to this command is addressof the C++ polymorphic object. GDB displays the
demangled type name as output.
NOTE: This command is supported only on Integrity systems.
Sample Output
(gdb) info rtti <address>
RTTI: <run time type/class name>
14.16 Printing the Execution Path Entries for the Current Frame or Thread
HP WDB 5.7 and later versions of the debugger enable you to print the execution path
entries in the current frame, or the current thread for programs running on Integrity
systems. This feature enables the display of the execution path taken across branched
modules. The first instruction in each block associated with the executed branch is
displayed.
This feature is supported only for compiler versions A.06.15 and later.
HP WDB supports the following commands to print the execution path entries in the
current frame, or in the current thread:
• info exec-path [start_index] [end_index] (aliased to info
ep)
Lists all the local execution path entries in the current frame. The [start_index]
and [end_index]indicate the range of table indexes (execution path entries)
that must be displayed.
If [end_index]is not specified, the debugger displays the complete table of
execution path entries, starting from [start_index].
If [start_index]and [end_index]are not specified, the complete table of
execution path entries is displayed.
14.16 Printing the Execution Path Entries for the Current Frame or Thread 203
For example,
(gdb) i ep 4 10
• info exec-path summary
Prints the summary information about all the local execution path entries in the
current frame. This command displays the total number of branches for the frame,
the number of branches executed in this frame in the last iteration, and the last
executed branch number.
• info global-exec-path [start_index] [end_index](aliased to
info gep)
Lists all the global execution path entries for the current thread.
The [start_index]and [end_index]indicate the range of table indexes
(execution path entries) that must be displayed.
If [end_index]is not specified, the debugger displays the complete table of
execution path entries, starting from [start_index].
If [start_index]and [end_index]are not specified, the complete table of
execution path entries is displayed.
• info global-exec-path summary
Prints the summary information about all the global execution path entries in the
current frame. This command displays the total number of global execution path
entries that can be stored, the number of global execution path entries in this frame
in the last iteration, and the last executed global execution path number.
• exec-path [up][down][path_index] (aliased to ep)
Enables you to select, print, and navigate through the execution path entries. When
no arguments are specified, it prints the selected execution path entry. You can
specify the argument as an execution path index from the info exec-pathor
the info global-exec-pathcommands. Alternately, you can use the up or down
command to navigate through the execution path entries.
14.16.1 Compiler Dependencies for Printing the Execution Path Entries
The +pathtracecompiler option provides a mechanism to record program execution
control flow into global path tables, local path tables, or both. This saved information
enables the debugger to print the execution path entries in the current thread or frame.
To print the execution path entries in the current thread or frame for programs running
on Integrity systems, you can set the required sub-options for the +pathtracecompiler
option.
You must set the following +pathtracecompiler option to enable the debugger to
print the execution path entries:
+pathtrace= [<global|global_fixed_size>:<local>]
204 HP-UX Configuration-Specific Information
For more information on this feature, see the following example.
14.16.2 Example Illustrating Execution Path Recovery
The following example illustrates the use of the execution path recovery feature in HP
WDB:
Sample Program:
$cat execpath.c
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int main()
{
int a = 3, b = 0, c = 4;
if (a)
printf("Value of a greater than 0\n");
if (b)
printf("Value of b greater than 0\n");
if (c)
printf("Value of c greater than 0\n");
printf("All condition checking done\n");
return 0;
}
Sample Debugging Session:
$cc +pathtrace -g execpath.c
$gdb a.out
HP gdb ...
Type "show warranty" for warranty/support.
...
(gdb) b main
Breakpoint 1 at 0x4000a60:0: file execpath.c, line 7 from a.out.
(gdb) r
Starting program: a.out
Breakpoint 1, main () at execpath.c:7
7 int a = 3, b = 0, c = 4;
(gdb) n
9 if (a)
(gdb) i ep
Local execution path table for main():
empty
(gdb) i gep
Global execution path table:
empty
(gdb) n
10 printf("Value of a greater than 0\n");
(gdb) n
Value of a greater than 0
12 if (b)
14.16 Printing the Execution Path Entries for the Current Frame or Thread 205
(gdb) i ep
Local execution path table for main():
0 0x4000a80:2 (execpath.c:10)
(gdb) i gep
Global execution path table:
G0 0x4000a80:2 main (execpath.c:10)
(gdb) n
15 if (c)
(gdb) i ep
Local execution path table for main():
0 0x4000a80:2 (execpath.c:10)
(gdb) i gep
Global execution path table:
G0 0x4000a80:2 main (execpath.c:10)
(gdb) n
16 printf("Value of c greater than 0\n");
(gdb) n
Value of c greater than 0
18 printf("All condition checking done\n");
(gdb) i ep
Local execution path table for main():
0 0x4000a80:2 (execpath.c:10)
2 0x4000bd0:2 (execpath.c:16)
(gdb) i ep summary
Summary for local execution path table for main()
Size: 3 \*Total Number of Branch Paths in Current Function
Effective entries: 2 \*Number of Branches executed till this instant
Current entry: 2 \* Last executed branch number
(gdb) i gep
Global execution path table:
G0 0x4000a80:2 main (execpath.c:10)
G1 0x4000bd0:2 main (execpath.c:16)
(gdb) i gep summary
Summary for global execution path table
Size: 65536 \*Maximum execution path entries to be stored
Effective entries: 2 \*Number of global execution path entries
Current entry: 1 \*The last Global Path ID executed
(gdb)
14.17 Command to Unwind Beyond 10000 Frames
The number of frames to be unwound by default is set to 10000 so that HP WDB does
not run out-of-memory. To enable unwinding beyond 10000 frames, HP WDB supports
the set unwind-all-framescommand at the gdbprompt.
Following is the syntax for the unwind-all-framescommand:
set unwind-all-frames [on|off]
where:
on
Enables WDB to unwind beyond 10000 frames.
off Disables the limitation on the number of frames.
206 HP-UX Configuration-Specific Information
14.18 Invoking GDB Before a Program Aborts
This -crashdebugoption enables GDB to monitor the execution of a process or a
program. It invokes GDB when the program execution is about to abort. Once the
debugger is invoked, you can debug the application using the normal debugger
commands. This option enables you to debug a live process instead of getting a core
dump if the program is about to abort.
You can examine the state of the process, make changes to the state and continue
program execution, force a core dump, or terminate execution. It enables you to control
program execution under the debugger if the program is about to abort. You can load
a new process or attach to a running process for monitoring.
To monitor a new process, enter the following command:
gdb -crashdebug <command> <options>
To monitor a running process, attach to the process using the following command:
gdb -crashdebug -pid <pid>
14.19 Aborting a Command Line Call
When a command line call is issued and it is interrupted by a breakpoint or a signal
before completing the program execution, the abort command enables the user to abort
the command line call without allowing the signal to modify the state of the debugged
process.
When a signal interrupts program execution, it can modify the process state of the de-
bugged program and result in an abrupt termination of the program (due to addressing
errors from a call that is not a part of the source program). In such cases, the abort
command is particularly useful in exiting the command line call without modifying
the process state of the debugged program.
The following example illustrates the use of the abort command:
(gdb) break main
Breakpoint 1 at 0x2c74: file .../address_error.c, line 41.
(gdb) run
Starting program: ./address_error
Breakpoint 1, main () at ./address_error.c:41
41 fun (count, count*1.1);
(gdb) p fun(10, 1.1)
Program received signal SIGBUS, Bus error
si_code: 0 - BUS_UNKNOWN - Unknown Error.
0x2c38 in fun (i=10, f=0) at ./address_error.c:37
37 count = *p;
The program being debugged was signaled while in a function called from GDB.
GDB remains in the frame where the signal was received.
To change this behavior use "set unwindonsignal on"
Evaluation of the expression containing the function (fun) will be abandoned.
(gdb) bt
#0 0x2c38 in fun (i=10, f=0) at ../address_error.c:37
#1 0x1920 in _sr4export+0x8 ()
#2 <function called from gdb>
#3 0x2c74 in main () at ./address_error.c:40
(gdb) abort
14.18 Invoking GDB Before a Program Aborts 207
Abort gdb command line call? (y or n) y
#0 main () at ./address_error.c:41
41 fun (count, count*1.1);
(gdb) bt
#0 main () at ./address_error.c:41
(gdb) quit
The program is running. Exit anyway? (y or n) y
14.20 Instruction Level Stepping
During instruction level stepping with nexti and stepi, WDB prints the assembly
instruction along with the next source line.
(gdb) stepi 0x101530:0 st4 [r9]=r34 1337 args.argc = argc;
It also prints DOC line information, which includes actual line number and the column
number, when debugging a binary with -g -O.
(gdb) stepi ;;; [8, 1] 0x4000820:1 nop.m 0x0
GDB cannot step into a function with no debug information. GDB cannot do a next
over a line when there is not debug information. However, the continuecommand
works in such situations.
14.21 Enhanced support for watchpoints and breakpoints
14.21.1 Deferred watchpoints
When you try to set a watchpoint in an expression, HP WDB places a deferred watch-
point if HP WDB cannot evaluate the expression. The watchpoint is automatically
enabled whenever the expression can be evaluated during the programs execution.
This is especially useful when placing the watchpoints on unallocated addresses.
14.21.2 Hardware watchpoints
HP WDB provides support for hardware watchpoints on HP-UX 11.x.
14.21.3 Hardware breakpoints
The hbreakcommand sets hardware assisted breakpoints.
hbreak args
The arguments (args) is same as that for the break command and the breakpoint is set
in the same way. However, the breakpoint uses hardware assisted breakpoint registers.
There are only two hardware breakpoints that can be set on Integrity systems. This is
useful in ROM code debugging and shared library debugging for libraries, including
dld, that are not loaded private.
The normal breakpoints are converted to a hardware breakpoint when WDB cannot
set a normal breakpoint in the shared library.
208 HP-UX Configuration-Specific Information
14.21.3.1 Setting breakpoints in unstripped shared library
GDB will not be able to put breakpoints using symbolic names(of the symbols not in
export list) or line numbers in the stripped modules.
GDB will be able to place breakpoints using symbol names in the unstripped shared
libraries loaded into the stripped executable.
14.21.4 Support for procedural breakpoints
HP WDB enables you to set breakpoints at the beginning (first executable line) of every
function that can be debugged. In addition, you can specify a set of commands to be
performed when the breakpoint is reached. These breakpoints work like procedural
breakpoints in the xdb debugger.
The breakpoint commands are rbpand rdp.
• rbp
Sets breakpoints at the first executable statement in all the functions that can be
debugged, including any shared libraries that are already loaded. The rbp
command sets breakpoints in all the functions, which can be debugged, in all the
source files. After you set these breakpoints, you can manage them like any
standard breakpoints. You can delete them, disable them, or make them conditional.
Each time you use the rbpcommand, HP WDB adds an additional breakpoint at
the beginning of each function that performs the commands you specify, if any.
• rdp
Deletes all the breakpoints set by the rbpcommand.
This example shows how to set a breakpoint at the start of each procedure that displays
information at the breakpoint:
(gdb) file a.out
Reading symbols from a.out...done.
(gdb) rbp
Breakpoints set from 170 to 211
Type commands to execute when the breakpoint is hit (one command per line).
End with a line saying just "end".
>info break
>end
(gdb)
14.21.5 Support for template breakpoints
With HP WDB 5.0, you can set breakpoints on all instantiations of the template class
by just specifying the template name with member function name.
For example:
(gdb) break ::
It is not necessary to specify the instantiation type.
14.21 Enhanced support for watchpoints and breakpoints 209
Setting a breakpoint on a template method with multiple instantiations displays a menu
showing all instantiations and the user can choose to set breakpoints on all or any one
or none.
For example,
(gdb) file test
Reading symbols from test...done.
(gdb) b MyClass::MyMember
[0] cancel
[1] all
[2] MyClass::MyMember(int, int) at test.C:14
[3] MyClass::MyMember(int, float) at test.C:14
[4] MyClass::MyMember(int, double) at test.C:14
14.22 Debugging support for shared libraries
On HP-UX, shared libraries are special. Until the library is loaded, GDB does not know
the names of symbols. However, GDB gives you two ways to set breakpoints in shared
libraries:
•
•
deferred breakpoints
catch load command
14.22.1 Using shared library as main program
If the main program is in a shared library and you try to load it as follows:
(gdb) symbol-file main.sl
Load new symbol table from "main.sl"? (y or n) y
Reading symbols from main.sl
done.
Things don't appear to work.
This command is not the correct thing to do. This command assumes that main.slis
loaded at its link time address. This is not true for shared libraries.
Do not use symbol-file with shared libraries.
Instead, what you should do is to use the deferred breakpoint feature to set breakpoints
on any functions necessary before the program starts running.
(gdb) b main
Breakpoint 1 (deferred) at "main" ("main" was not found).
Breakpoint deferred until a shared library containing "main" is loaded.
(gdb) r
Once the program has started running, it will hit the breakpoint. In addition, the de-
bugger will then already know about the sources for main, since it gets this information
when the shared library is loaded.
210 HP-UX Configuration-Specific Information
14.22.2 Setting Deferred Breakpoints in Shared Library
On HP-UX, GDB automatically loads symbol definitions from shared libraries when
you use the run command, or when you examine a core file. (Before you issue the run
command, GDB does not understand references to a function in a shared library| unless
you are debugging a core file.)
When you specify a breakpoint using a name that GDB does not recognize, the debugger
warns you with a message that it is setting a deferred breakpoint on the name you
specified. If any shared library is loaded with a matching name, then GDB sets the
breakpoint.
For example, if you type:
`break foo'
the debugger does not know whether foois a misspelled name or whether it is the
name of a routine that has not yet been loaded from a shared library. The debugger
displays a warning message that it is setting a deferred breakpoint on foo. If any shared
library is loaded that contains a foo, then GDB sets the breakpoint.
If this is not what you want (for example, if the name was mistyped), then you can
delete the breakpoint.
14.22.3 Using catch load
The `catch load <libname>' command causes the debugger to stop when the
particular library is loaded. This gives you a chance to set breakpoints before routines
are executed.
14.22.4 Privately mapping shared libraries
In cases where you attach to a running program and you try to set a breakpoint in a
shared library, GDB may generate the following message:
The shared libraries were not privately mapped; setting a breakpoint
in a shared library will not work until you rerun the program.
GDB generates this message because the debugger sets breakpoints by replacing an
instruction with a BREAK instruction. The debugger cannot set a breakpoint in a shared
library because doing so can affect other processes on the system in addition to the
process being debugged.
14.22 Debugging support for shared libraries 211
To set the breakpoint you must kill the program and then rerun it so that the dynamic
linker maps a copy of the shared library privately. There are two ways to run the
program:
•
Rerun the program under GDB to have the debugger cause dld to map all shared
libraries as private, enabling breakpoint debugging.
•
On PA-RISC systems, use the following command on an executable:
/opt/langtools/bin/pxdb -s on executable-name
The pxdb -son command marks the executable so that dldmaps shared libraries
as private when the program starts up.
You can verify the status of the shared library with this command:
/opt/langtools/bin/pxdb -s status executable-name
•
On both PA-RISC and IA64 systems, use the following command on an executable:
chatr +dbg enable executable-name
This is similar to the pxdb command described above wherein it directs the dldto load
the shared libraries as private when the program starts up.
On HP-UX 11i v3 Integrity systems, WDB enables automatic debugging of shared
libraries without them being mapped private while attaching to a running program.
For enabling automatic debugging of shared libraries, you must install the kernel
patches PHKL_38651 and PHKL_38778.
14.22.5 Selectively Mapping Shared Libraries As Private
The -mapsharedoption suppresses mapping all shared libraries in a process private.
This option enables new functions in the dynamic loader (patch PHSSS_33110 or later)
to designate individual shared libraries for debugging. By default, HP WDB instructs
the shared library dynamic loader, dld.sl(5), to map shared libraries in a process
private, regardless of whether the chatrcommand is run for a particular shlib with
+dbgor not.
The -mapsharedoption is used to save virtual memory for debugging applications
with large amounts of code in shared libraries on machines with simultaneous debug
sessions. The chatr +dbgoption, and the _HP_DLDOPTSenvironment variable are
used to identify shared libraries for debugging. The -mapsharedoption ensures that
the text segments of all other shared libraries is shared across the system. The shared
libraries are not mapped private and cannot have breakpoints set in them.
The set mapshared oncommand can be used to change modes from the (gdb)
prompt.
(gdb) set mapshared on
The set mapshared offcommand can be used to load shared libraries after the
current point is mapped private.
(gdb) set mapshared off
212 HP-UX Configuration-Specific Information
The -mapsharedoption is implemented on both PA-RISC and Itanium platforms in
HP WDB 5.2. This option is provided in the WDB GUI and HP WDB. The default
behavior does not change if the -mapsharedoption for all shared libraries in processes
started under the debugger, or dynamically loaded after an attach, are mapped private.
14.22.6 Setting breakpoints in shared library
Breakpoints can be set on functions in a shared library, by specifying the library name
with the function name.
(gdb) b libutil.sl:fun Breakpoint 1 at 0x79a86228: file simple.c,
line 13 from /CLO/Components/WDB/build/hppa1.1-hp-hpux11.00/gdb/
simple_shared/lib.sl
14.22.7 Enhancement to the info sharedCommand
HP WDB 6.0 and later versions provide the enhanced info sharedcommand to
display the global pointer (gp) values along with text start, text end, data start, and
data end values of the shared library. Following is a sample output of the info shared
command with the gpvalues:
tstart
tend
dstart
dend
gp
/usr/lib/hpux32/dld.so
0x2000000065858000 0x20000000658fb080 0x2000000065853000 0x2000000065857a38 0x2000000065855720
/usr/lib/hpux32/libstd_v2.so.1
0x20000000656ab000 0x200000006584bfc0 0x200000006569d000 0x20000000656aac28 0x20000000656a6d78
14.23 Debugging support for Decimal Floating Point data type
HP WDB versions 5.9 and above enable you to print and evaluate decimal floating
point data types for programs running on the September 2008 release of HP-UX 11i
v3, Integrity systems. This feature is available only for compiler versions A.06.20 and
later.
The various features supported for decimal floating point data types are as follows:
•
Printing Decimal Floating point data types
— Printing Decimal floating point constant
— Printing Decimal floating point variable
•
•
Handling Decimal Floating Point data types
Evaluating Decimal Floating Point data types
— Printing Type of Decimal floating point data type.
14.23.1 Printing Decimal Floating point data types
HP WDB versions 5.9 and above enable you to print a decimal floating point data type
constant or variable. It handles and prints decimal floating point constant or variable
when you use common GDB commands such as stack trace and command-line calls.
14.23 Debugging support for Decimal Floating Point data type 213
14.23.1.1 Printing Decimal floating point constant
(gdb) print <num><df/dd/dl/DF/DD/DL>
df, DF - _Decimal32
dd, DD - _Decimal64
dl, DL - _Decimal128
This prints the decimal floating point constant based on the data type.
14.23.1.2 Printing Decimal floating point variable
(gdb) print/<fmt> <var-name>
<fmt> = df, dd, dl
<var-name> - variable name
This prints the decimal floating point variable. If you specify format <fmt>then it
prints the variable based on its data type.
14.23.2 Printing NaT Registers
On Integrity systems, following is the command to print the NaT bit corresponding to
a register:
print $natr<reg_nbr>
where, reg_nbrrepresents the NaT bit corresponding to a register.
Example 14-2 Sample Commands to Print NaT Registers
Following are sample commands to print NaT registers:
(gdb) p $natr32
$1 = 0 '\000'
(gdb) p $natr33
$2 = 0 '\000'
(gdb) p $natr39
$3 = 0 '\000'
14.23.3 Handling Decimal Floating Point Data types
GDB supports decimal floating point values in command line call of functions that
contain decimal floating point arguments and which return decimal floating point
arguments.
(gdb) print func1(1.2dd)
14.23.4 Evaluating Decimal Floating Point data types
HP WDB versions 5.9 and above enable you to evaluate the decimal floating point
variable and displays the output. Use the commonly used GDB commands for evaluating
and displaying expressions, such as print to evaluate the decimal floating point variable.
214 HP-UX Configuration-Specific Information
HP WDB supports:
•
•
•
Evaluation of expressions with decimal floating point constants and variables.
Setting or assignment of decimal floating point constant or variable.
Arithmetic operations such as addition, subtraction, multiplication, division, and
negation with decimal floating point constants or variables.
•
•
Comparison operations such as ==,!=, >, >=, <, <= with decimal floating point
constants or variables.
Conversion between data types during assignment, arithmetic and comparison
operations and while printing values in specified format.
Assignment of Decimal floating point value to variable:
(gdb) print <variable> = <dfp-const>/<dfp-var>
<dfp-const> = decimal floating point constant
<dfp-var> = decimal floating point variable
This assigns decimal floating point value to the variable according to its data type.
Arithmetic Operations:
(gdb) print a(op1)b
(gdb) print (op2)a
op1 = addition, subtraction, multiplication and division.
op2 = negation
This performs arithmetic operation with decimal floating point data types.
Comparison Operations:
(gdb) p <dfp-val> (op) <dfp-val>
where,
op = ==, !=, >, >=, <, <=
If expression contains comparison operation, then GDB compares the decimal floating
point data types accordingly.
(gdb) p 1.2dd == 1.2dd
(gdb) 2.4
14.23.4.1 Printing type of Decimal Floating Point variable
(gdb) ptype <dfp-const>/<dfp-var>
This prints the type of the Decimal floating point variable or constant.
(gdb) ptype 1.22dd
type = _Decimal64
14.23 Debugging support for Decimal Floating Point data type 215
Conversion of types:
GDB handles conversion of data types during assignment, printing, and arithmetic
and comparison operation.
(gdb) p 1.2df +1.2dd
This converts double data type (1.2) to _Decimal64data type and performs addition
operation with _Decimal64data type (1.2dd) and prints value in _Decimal64type.
HP WDB handles exceptions such as overflow, infinity and division by zero for Decimal
Floating Point data type.
(gdb) print 1.2dd / 0
(gdb) inf
HP WDB handles finite, infinite and NaN(Not a Number) values of decimal floating
point data type.
NOTE: HP WDB will not support:
•
Command line calls of intrinsic functions(Mathematical functions like cos, sin, log
etc)
•
•
Decimal Floating Point data type support for Fortran and C++
HP-UX 11iv2 Integrity and HP 9000 systems
14.24 Additional Support for binary floating point data type
14.24.1 Support for Binary Floating Point constants f, l
If the binary floating point constant contains the letter f or l then HP WDB recognizes
it as float or long double binary floating point constant. Generally a floating point
constant without f or l is considered as double binary floating point constant.
(gdb) p <num><f/l>
This prints the binary floating point constant depending upon its data type.
14.24.2 Support Binary Floating Point variables with format specifier
HP WDB versions 5.9 and later provide the following format specifiers for binary
floating point variables, which print the variables in the specified binary floating point
format:
(gdb) p/f <var-name>
This prints the binary floating point value as oat.
(gdb) p/db <var-name>
This prints the binary floating point value as double.
(gdb) p/l <var-name>
This prints the binary floating point value as long double.
216 HP-UX Configuration-Specific Information
14.25 Language support
14.25.1 Enhanced Java Debugging Support
HP WDB shows stack traces of mixed Java, C, and C++ programs. It supports unwinding
across Java frames and provides an effective way to examine stack traces containing
mixed language frames (Java and C/C++) of both live Java processes and core files. This
has been implemented by adding subcommands for Java VM debugging to gdb. The
stack trace functionality requires Java SDK version 1.3.1.02 or later versions, for HP-UX.
To nd the availability of Java SDK version 1.3.1.02 or later, go to the HP web site for
features are available in gdb version 4.5 and later versions. From gdb version 5.3 and
later versions, it requires SDK 1.4.2.10 and later versions, or JDK 1.5.0.03 and later
versions in order to use the Java VM debugging features.
In order to use this functionality, the GDB_JAVA_UNWINDLIBenvironment variable
must be set to the path name of the Java unwind library. This environment variable
must be set for normal java debugging and java corefile debugging. The default location
of the Java unwind library on various systems is shown following. The examples are
for SDK 1.4; if you are using JDK 1.5, substitute /opt/java1.5for /opt/java1.4.
•
•
•
•
For 32 bit IPF applications,
export GDB_JAVA_UNWINDLIB = /opt/java1.4/jre/lib/IA64N/server/libjunwind.so
For 64 bit IPF applications,
export GDB_JAVA_UNWINDLIB = /opt/java1.4/jre/lib/IA64W/server/libjunwind.so
For 32 bit PA applications,
export GDB_JAVA_UNWINDLIB = /opt/java1.4/jre/lib/PA_RISC/server/libjunwind.sl
For 64-bit PA applications,
export GDB_JAVA_UNWINDLIB = /opt/java1.4/jre/lib/PA_RISC2.0/server/libjunwind.sl
export GDB_JAVA_UNWINDLIB = /opt/java1.4/jre/lib/PA_RISC2.0W/server/libjunwind.sl
If the SDK is installed in a location other than the default, substitute the non-default
location for /opt/java1.4in the previous commands.
14.25.1.1 Java Stack Unwind Features
The Java stack unwind features are useful for troubleshooting problems in the Java
VM. Following is a list of the Java stack unwind features:
•
•
•
View mixed language frames information, including Java frames and C/C++ native
frames, in a gdb backtrace.
Distinguish various Java frame types including interpreted, compiled, and adapter
frames.
View Java method name, signature, and class package name for Java method
frames.
14.25 Language support 217
Additional stack unwind features are available starting with SDK 1.4.2. These features
fall into three categories: Java stack unwind enhancements, Java heap support, and
Java threads support.
These additional features are available as part of the Java stack unwind enhancements:
•
•
•
•
•
View Java compiled frame inlined methods.
View Java interpreted or compiled frame specific information.
View Java interpreted or compiled frame arguments and local variables.
Disassemble Java method bytecodes.
Print out the Java unwind table.
These additional features are available as part of Java heap support:
•
•
•
•
•
•
View Java heap parameters.
Dump Java object.
Print Java heap histogram.
Find all the instances of a given Java class.
Find all the references to a given object in the Java heap.
Find out the object OOP (object-oriented pointer) of the given field address.
These additional features are available as part of Java threads support:
•
•
•
View Java threads state information.
View current Java thread information.
View Java interpreted frame monitors information.
14.25.1.2 gdb Subcommands for Java VM Debugging
Commands for Examining Java Virtual Machine(JVM) internals
To view the gdb commands that support Java VM debugging, type help java at the
gdb prompt.
(gdb) help java
Java and JVM debugging commands.
List of java subcommands:
java args -- Show the current or specified Java frame arguments info
java bytecodes -- Disassemble the given Java method's bytecodes
java heap-histogram -- Show the Java heap object histogram
java instances -- Find all the instances of the given klassOop in the Java heap
java jvm-state -- Show Java virtual machine's current internal states
java locals -- Show the current or specified Java frame locals info
java mutex-info -- Print out details of the static mutexes
java object -- Print out the given Java object's fields info
java oop -- Find the Java object oop of the given Java heap address
java references -- Find all the references to the given Java object in the Java heap
java unwind-info -- Show the unwind info of the code where the given pc is located
java unwind-table -- Print out the dynamically generated Java Unwind Table
Type help javafollowed by java subcommand name for full documentation.
Command name abbreviations are allowed if unambiguous.
218 HP-UX Configuration-Specific Information
Java VM Debugging Commands
The following commands have been added to enhance Java debugging support:
brbacktrace
Prints backtrace of mixed Java and native frames. Standard
backtrace command of GDB has been enhanced to work with mixed
Java and native stack frames.
info frame
Prints Java frame specific information for a Java frame. Standard
frame command of GDB has been enhanced to interpret a Java
stack frame.
info threads
thread
Prints state information for Java threads.
Prints detailed state information for the current Java thread.
Java subcommands
The following Java subcommands have been added:
java args <frame-number>
Prints the current or specified Java frame
arguments information
java bytecodes <methodOop>
java heap-histogram
Disassembles the given Java method bytecode
Displays the Java heap object histogram
java instances <klassOop>
Locates the instances of the given klassOop in
the Java heap.
java jvm-state
java locals
Prints current status of JVM internal states
Prints the current or specified Java frame locals
information
java mutex-info
Prints details of static mutexes
java object <object-ptr>
Prints the given Java object field information
java oop <Java_heap_address> Locates Java object oop of the given Java heap
address
java references <oop>
java unwind-info <pc>
java unwind-table
Locates references to the given Java object in the
Java heap
Prints unwind information of the code where the
PC is located
Prints the dynamically generated Java Unwind
Table
Type help javafollowed by the subcommand name for full documentation. Command
name abbreviations are allowed if they are unambiguous.
14.25 Language support 219
14.25.1.3 Java corefile debugging support
HP WDB shows stack traces of mixed Java, C, and C++ programs for java corefile.
GDB_JAVA_UNWINDLIBenvironment variable must be set to the path name of the Java
unwind library as explained above.
Following are examples that illustrate the gdb command-line options for invoking gdb
on a core file:
1. Invoke gdb on a core file generated when running a 32-bit Java application on an
Integrity system with /opt/java1.4/bin/java:
$ gdb /opt/java1.4/bin/IA64N/java core.java
2. Invoke gdb on a core file generated when running a 64-bit Java application on an
Integrity system with /opt/java1.4/bin/java -d64:
$ gdb /opt/java1.4/bin/IA64W/java core.java
3. Invoke gdb on a core file generated when running a 32-bit Java application on
PA-RISC using /opt/java1.4/bin/java:
$ gdb /opt/java1.4/bin/PA_RISC2.0/java core.java
4. Invoke gdb on a core file generated when running a 64-bit Java application on
PA-RISC using /opt/java1.4/bin/java:
$ gdb /opt/java1.4/bin/PA_RISC2.0W/java core.java
When debugging a core file, it is good practice to rename the file from core to another
name to avoid accidentally overwriting it.
If the Java and system libraries used by the failed application reside in non-standard
locations, then the GDB_SHLIB_PATHenvironment variable must be set to specify the
location of the libraries.
14.25.1.4 Java attach mode debugging support
HP WDB supports java debugging in attach mode also. GDB_JAVA_UNWINDLIB
environment variable must be set to the path name of the Java unwind library. From
gdb version 5.6 and later versions, GDB JAVA UNWINDLIBenvironment variable need
not be set to the path name of the Java unwind library. HP WDB uses the
libjunwind.slspecified by the Java Virtual Machine.
The following examples illustrate how to invoke gdb on a hung process:
1. Determine the process id:
$ ps -u user1 | grep java
23989 pts/9 8:52 java
220 HP-UX Configuration-Specific Information
2. Attach gdb to the running process:
$ gdb -p 23989
HP gdb 5.0 for HP Itanium (32 or 64 bit) and target HP-UX 11.2x.
Copyright 1986 - 2001 Free Software Foundation, Inc.
Hewlett-Packard Wildebeest 5.0 (based on GDB) is covered by the
GNU General Public License.Type "show copying" to see the con-
ditions to
change it and/or distribute copies. Type "show warranty" for
warranty/support.
Reading symbols from /opt/java1.4/bin/IA64N/java...
(no debugging symbols found)...done.
Attaching to program: /opt/java1.4/bin/IA64N/java, process 23989
(no debugging symbols found)...
Reading symbols from /usr/lib/hpux32/libpthread.so.1...
(no debugging symbols found)...done.
Reading symbols from /usr/lib/hpux32/libdl.so.1...
...
NOTE: If the version of gdb on the system is older than version 4.5, it will be necessary
to specify the full path of the Java executable in order to use the gdb subcommands.
For example: gdb /opt/java1.4/bin/PA_RISC2.0/java p 23989
14.25.2 Enhanced support for C++ templates
This version of HP WDB includes these features to support C++ templates:
•
Setting breakpoints in template class functions and template functions without
having to specify details about the instantiation.
•
The ptypecommand shows any one of the class instantiations.
A option -vin ptype command will now display the field offset and size information
of a struct/union/classin addition to the default type information.
Syntax:
(gdb) ptype -v struct info
type = struct info /* off 0 bits, len 512 bits */
int i;
/* off 0 bits, len 32 bits */
char a[20];
/* off 32 bits, len 160 bits */
struct details d;
/* off 192 bits, len 256 bits */
int b : 2;
/* off 448 bits, len 2 bits */
int c : 3;
/* off 450 bits, len 3 bits */
< filler >
14.25 Language support 221
/* off 453 bits, len 27 bits */
float f;
/* off 480 bits, len 32 bits */
14.25.3 Support for _ _fpregdata type on IPF
WDB internally converts __fpregdata type to long double data type to evaluate an
expression or to print the value of the expression. Since long double data type has only
15 bit exponent as opposed to 17 bit exponent of __fpreg, some precision is lost when
the exponent is larger than that can t in 15 bits.
14.25.4 Support for _Complex variables in HP C
HP C on Itanium systems supports a _Complexdata type built from any of the floating
point types.
A _Complexnumber holds a pair of floating point numbers; the first is the “real part”
and the second is the “imaginary part”.
Here are examples of declarations and initializations using _Complexnumbers:
float _Complex glob_float_complex;
double _Complex glob_double_complex = 6;
long double _Complex glob_long_double_complex = _Imaginary_I;
__float80 _Complex glob_float80_complex = 8 + 9 * _Imaginary_I;
_Imaginary_I is a keyword which represents the square root of -1.
The debugger has limited support for _Complexvariables. No arithmetic operations
are allowed with _Complexnumbers. A _Complexnumber may be cast or assigned
to any numeric data type and vice versa.
A _Complexvariable can be initialized with an expression of the form:
A + B * _Imaginary_I
where, A and B are ordinary numeric expressions, perhaps in parentheses.
This is also the format in which the debugger displays a Complex value.
Imaginary values cannot be assigned to variables because there is no imaginary data
type. You can take a normal number and multiply it by an imaginary number and get
another imaginary number. You can take a normal number and add it to an imaginary
number to get a complex number.
Complex numbers cannot be used in arithmetic expressions in the debugger.
For more information of _Complex type, refer to the HP C/ANSI C documentation.
14.25.5 Support for debugging namespaces
This release of HP WDB provides full support for debugging namespaces.
222 HP-UX Configuration-Specific Information
You do not need to use fully qualified names to access symbols within a namespace.
The debugger can compile a list of namespaces active in the scope that you are in and,
when possible, choose an appropriate symbol.
The debugger recognizes using declarations, using directives, namespace aliases, nested
namespaces, and unqualified lookup within a namespace. It also recognizes using
directives and aliases, and using declarations within namespaces.
When the debugger has a list of possible resolutions for a given symbol, it displays a
menu that shows all names fully qualified whenever namespaces are involved. You
can choose the appropriate symbol from the list.
For example, if you stop the debugger in a function that contains an int i using directive
for a namespace such as:
using namespace A::AB::ABC::ABCD
You can use the command print i and if the only possible resolution for i is
A::AB::ABC::ABCD::i the debugger prints out the name of the symbol and its value. If,
however, a global i exists, the debugger displays a menu from which to choose:
(1) i
(2) A::AB::ABC::ABCD::i
>
Setting breakpoints on functions works in the same way.
The debugger also allows semi-qualified names. For example, if you stop in a function
in namespace B, which is nested in namespace A, and namespace A has an int i, you
can use print B::i to display the value of A::B::i.
To disable namespace support, use the command:
(gdb) set namespaces-enabled off
14.25.6 Command for evaluating the address of an expression
The watch_targetcommand takes an expression as an argument, evaluates it to an
address, and watches the target of that address.
For example:
(gdb) watch_target current_frame
This is equivalent to executing:
(gdb) print current_frame $1 = (struct frame_info *) 0x7fdf78 (gdb) watch
*(struct frame_info *) 0x7fdf78
14.26 Viewing Wide Character Strings
HP WDB printcommand can print wide characters and wide-character strings of the
type wchar_t. The user must use the /Woption of the print command to print wide
characters and wide-character strings.
print /W <wide-char-symbol-name>
14.26 Viewing Wide Character Strings 223
14.27 Support for output logging
The Visual Interface for HP WDB terminal user interface (TUI) mode supports the
command, log logfile_name, that saves the content of a session to the specified log
file.
When you use the logcommand, the debugger saves a snapshot of the current session,
from the start of the session to the point where you issued the logcommand. Each
time you use the logcommand, HP WDB overwrites the specified log file with a new
snapshot from the start of the session.
To run the Visual Interface for HP WDB, use the following command:
$vdb -tui
To redirect HP WDB output to a log file named mylogfile, use the logcommand in
the following manner:
(gdb) log mylogfile
The Visual Interface for HP WDB stores the log file, mylogfile, in the current directory.
To view the log file from Visual Interface for HP WDB, start a shell process and use
the following command:
(gdb) shell vi mylogfile
14.27.1 Support for dumping array in an ASCII file
HP WDBN supports dumping an array into an ASCII file.
The array elements are stored in Array format of Matrix Market in a predefined
(column-major order for Fortran arrays) order. The objective is to provide a simple
mechanism to facilitate the exchange of matrix data and to enable easier parsing of the
array elements. For common file formats, see
http://math.nist.gov/MatrixMarket/formats.html.
To dump an array, ARRAY, to a file named DUMPFILE, use the following command:
(gdb) dump2file ARRAY DUMPFILE
The entries of ARRAY are dumped into an ASCII file named DUMPFILEin the array
format. The file is created in the current working directory. The content of the file has
the following format:
%%ArrayBrowsing matrix array ARRAY
% A 5x5 matrix
5 5
0
2
4
6
8
2
..
..
224 HP-UX Configuration-Specific Information
where, ARRAYis the name of the array, and its size is 5x5.
The first two lines are comments about this file and the array. The third line denotes
the array coordinates. From the fourth line, the elements of the array are listed. Note:
This feature is not supported for the Fortran array slices.
14.27.2 Support for Fortran array slices
HP WDB prints Fortran array slices if you specify a range of elements by the Fortran
90 array section syntax. For instance, for an array Xdeclared by REAL, DIMENSION(-
1:1, 2:10) :: X, you could print all five even-numbered elements of the row with
the first dimension equal to 0 by typing the WDB command print X(0,2:10:2).
14.27.3 Displaying enumerators
You can display the union of several enumeration elements by specifying a value if the
elements of the enumeration type are the powers of 2 and the given value is a sum of
any given combination of the enumeration elements.
For example, assume you have an enumerated type named color in the program, with
these elements: RED=0, ORANGE=1, YELLOW=2, GREEN=8, and BLUE=16. If you
use the command printf 3, the debugger displays ORANGE|YELLOW, the elements
corresponding to 1 and 2. If you print 5, you will get the value, 5, because it does not
form the sum of any combination in the set. However, if you wanted to print 25, you
will get Orange|Green|Blue.
Values that do not form the sum of any combination of the elements will be displayed
as integers while the values that form the sum of any combination of the elements will
be printed as unions.
14.27.4 Support for debugging typedefs
When you have a typedef class as a template parameter, you can set a breakpoint on
a member function by using the command:
break Class<typedef_classB>::memfunc
14.27.5 Support for steplast command for C and C++
Typically, if a function call has arguments that make further function calls, executing
a simple stepcommand in GDB steps into the argument evaluation call. HP WDB
includes the steplastcommand, which helps to step into a function, and not into
the calls for evaluating the arguments. However, the steplastcommand is not
available on Integrity systems. The following example illustrates how GDB behaves
when you execute the steplastcommand:
(gdb) 16 foo (bar ()); ---> bar() will return 10 (gdb) steplast foo (x=10) at
foo.c:4 4 int k = 10;
If the steplastcommand is not meaningful for the current line, GDB displays the
following error message:
14.27 Support for output logging 225
"Steplast is not meaningful for the current line."
For example,
(gdb) 4 int k = 10; (gdb) sl ---> alias to "steplast" command error: Steplast
is not meaningful for the current line
To execute the steplastcommand in C++ compiled applications, you must compile
the application using the HP aC++ version A.03.50 or later with the -g0 option.
In C++, the steplastcommand is helpful while debugging heavy templated functions,
because it directly steps into the call, thus skipping the constructor calls, if any. This
behavior is unlike the stepcommand that steps into the constructor itself.
Consider the following example:
void call_me ( string s ) ... (gdb)
10
call_me ( "hello" );
(gdb) steplast call_me (s=static npos = 4294967295,
static nullref = ref_hdr = mutex_= dummy1 = 0x7f4f79e0, dummy2 = 2136325568,
refs_ = 2136327612,
capacity_ = 2136327468, nchars_ = 2136327464, eos_char = 64 '@',
alloc_ = <No data fields>,
value_allocator = alloc_ = 0x7f7f133c,
data_ = 0x40003a64 "hello") at str.C:55
printf ("Will just print the value of \n");
If there are multiple top-level calls, the steplastcommand enables you to step into
each top-level call. For example, for the following line, the steplastcommand takes
you to the first top-level call, (foo()):
foo(bar()) + bar(foo());
Debug foo(), use the finishcommand to exit from the first top-level call, (foo()),
execute the steplastcommand to step into the next top-level call, (bar()). The
following example illustrates the use of steplast command:
(gdb)10 foo( bar() ) + bar( foo() ) (gdb) sl Use the steplast (sl) command to step
14.28 Getting information from a non-debug executable
You can get some information about the arguments passed to the functions displayed
in the stack trace in a non-debug, optimized executable.
When GDB has no debug information; it does not know where the arguments are
located or even the type of the arguments. GDB cannot infer this in an optimized,
non-debug executable.
However, for integer arguments you can nd the first few parameters for the top-of-
stack frame by looking at the registers. On PA-RISC systems, the first parameter will
be in $r26, the second in $r25, and so on. On IPF systems, the first few parameters will
be in $gr32 and $gr33.
226 HP-UX Configuration-Specific Information
14.29 Debugging optimized code
HP WDB supports debugging of optimized code (compiled with both -g and -O) for
HP aC++, HP ANSI C and HP WDB for HP Itanium.
The following commands evaluate the name of a function and hence are affected by
the optimization level of the program being debugged (in particular, due to inlining):
• break
• call
• clear
• disassem
• list
The following commands evaluate an expression referring to variables in the user pro-
gram and hence, are affected by the optimization level of the program being debugged:
• break
• call
• cond
• jump
• return
• print
• set <var>
• watch
• whatis x
NOTE: The breakand callcommands involve evaluation of both the name of a
function and an expression.
The following commands are also affected by the optimization level of the program
being debugged:
• backtrace
• display
• down
• finish
• frame
• info *
• next
• step
• tbreak
• rbreak
• up
14.29 Debugging optimized code 227
The following commands are not affected by the optimization level of the program
being debugged:
• attach
• catch
• commands
• continue
• core
• delete
• define
• detach
• disable
• enable *
• file
• forw
• handle *
• help *
• ignore
• kill
• load
• nexti
• path
• quit
• rev
• run
• set args, set env, set <param>
• show args, show <param>
• signal
• source
• stepi
• symbol
• target
• tty
• undisplay
• unset env
• until
228 HP-UX Configuration-Specific Information
14.29.1 Debugging Optimized Code at Various Optimization Levels
The following sections describe debugging optimized code support at each optimization
level.
14.29.1.1 +O0and +O1
At +O1level, optimizations that affect the user visible state of a program are avoided.
Line numbers are accurately associated with each machine instruction. Global or local
variables may be examined, except for unused variables (which may be eliminated).
New values may be assigned to a global and a local variable (set <var> =
<expression>) when stepping by line (step/next/break <line>). However,
while stepping by instruction (stepi/nexti) at optimization level +O1, assign a value to
a variable only if stopped at the very first instruction. This is a must as local
optimizations are performed within a statement.
Backtrace commands (backtrace) may be used to display the current nest of function
calls, including for calls that are inlined. Note that even at +O1, C++ methods that are
defined within a class and Fortran arithmetic statement functions are implicitly inlinable
and are inlined. Other functions are not inlined, regardless of the inline pragmas or
keywords.
14.29.1.2 +O2/+O3/+O4/-ipo
Stepping by line number (step/next) and running to a breakpoint(break) moves the
state of a program forward. However, the program execution does not necessarily stop
at the given line.
You can set breakpoints (break) at the entry to a routine that is not inlined and examine
the values of parameters when the program execution stops at the entry of a routine.
The local variables can be examined within a function. However, the values of the local
variables may not be available at all code locations in the function. Assignment of new
values to formal parameters or local variables is NOT supported in code compiled with
optimization above +O1.
Optimization of code results in the reordering of the instructions and the source line-
numbers. Hence, the value of the variable, which is printed by the debugger may not
correspond to the reported source code location. The debugger may print the value of
the variable at a source code location either before or after the reported source code
location.(If the printed value is not current with respect to the current source line, the
printed value will be the immediately previous or immediately later value for the
variable.)
Backtrace commands (backtrace) can be used to display the current nest of function
calls, including calls that are inlined. When stopped within the code for an inlined call,
the parameters and the local variables of the inlined routine are not reported or available.
The disassemcommand does not work for functions that have no code (because all
calls to these functions are inlined or these functions are not called at all). HP WDB 5.7
14.29 Debugging optimized code 229
and later versions provide support to prevent the debugged program from stopping
at instructions that are predicated false. The program execution can be stopped by a
software breakpoint, a hardware breakpoint, or an asynchronous signal. In the case of
optimizations such as if-conversion, the predicated false instructions indicate that an
alternate source path is executed. Hence, stopping the program at a predicated false
instruction results in the misleading conclusion that the path corresponding to the
predicated false instruction is executed. To prevent this ambiguity, HP WDB does not
stop at predicated false instructions.
The predicated false instructions are equated to NOPs(No OPeration), because these
instructions do not modify the processor state. The exception to this rule is the use of
certain instructions, such as wtop, wexit, and frcpa, which modify the processor
state even when predicated false. In such cases, the debugger stops at the instructions
irrespective of the predicate value of the instructions. Assembly and low-level
programmers, who require the old behavior of the debugger to stop at the instructions
irrespective of the predicate value of these instructions, can explicitly turn o this feature.
To explicitly turn o this feature, enter the following command at the gdb prompt:
(gdb) set no-predication-handling
The following limitations apply when debugging optimized code:
•
Support for high-level loop transformations such as modulo-scheduled loops, or
LNO-optimized loop nests is limited. (This limited support includes all loop
optimizations that are enabled at +O3and above, and some loop optimizations at
+O2or -O.)
•
•
•
Debug support for local aggregates and arrays is limited.
Complete debug support for inlined subroutines is not available.
Values that are not at the current code location will be reported as being
unavailable, even if these values can be computed from some other values that
are available.
•
•
Step operations may include occasional "backwards" steps, because of the re-
ordered code during optimization.
The program stops at asynchronous signal stops even if the reported instruction
is predicated false.
Complete support is available for debugging at the assembly language level. Stepping
by instructions (stepi/nexti) steps as expected and reports the associated source line
numbers for each instruction.
NOTE: The -ipocompilation implies the +noobjdebugoption because the -ipo
object files do not store executable code or debug info.
14.30 Debugging with ARIES
The ARIES fast interpreter emulates a complete set of non-privileged PA-RISC
instructions with no user intervention. During interpretation, it monitors the applications
230 HP-UX Configuration-Specific Information
execution pattern and translates only the frequently executed code into native Itanium
(R)code at runtime.
14.30.1 Debugging the application using GDB under ARIES
ARIES supports debugging of HP 9000 HP-UX applications on HP-UX 11i Integrity
servers using the HP 9000 HP-UX GDB.
•
•
•
•
Both the GDB and the application run under ARIES.
No change in GDB user interface (including WDB GUI).
Negligible loss of performance in interactive mode.
The HP 9000 GDB is included by default as part of the Integrity HP-UX WDB/GDB
package.
•
All GDB commands work just like they would on an HP 9000 server.
Use the following steps to debug HP 9000 HP-UX applications on HP-UX 11i Integrity
servers using GDB:
1. Set the environment variable PA_DEBUG to 1.
2. Set the environment variable SHELL to point to an HP 9000 shell, copied from an
HP 9000 HP-UX system from /usr/bin path.
3. Add /usr/ccs/binto the PATH environment variable.
4. Invoke GDB as:
gdb PA-RISC_executable
After the debugging is finished, perform the following steps:
1. Unset the environment variable PA_DEBUG.
2. Restore the original value of the SHELL environment variable.
3. The rest of the debugging operations are the same as that on the HP 9000 HP-UX
platform.
NOTE: Make sure that the user has write permission on /tmpdirectory and that
there is enough space to create a temporary file of one page size as obtained by
sysconf(_SC_PAGE_SIZE)system call.
14.30.1.1 Limitations of GDB Support under ARIES
•
No support for debuggers other than HP 9000 HP-UX GDB for debugging HP
9000 applications under ARIES on HP-UX 11i Integrity servers.
•
No support for old GDB versions (of HP-UX 10.20 and earlier). However, debugging
of HP-UX 10.20 applications using a HP-UX 11.0 (and newer) HP 9000 GDB is
supported.
•
HP 9000 GDB behaves differently for child processes created using fork()and
vfork()system calls. ARIES emulates fork()and vfork()system calls
14.30 Debugging with ARIES 231
identically. The exact behavior shown by HP 9000 GDB under ARIES may differ
from that on a HP 9000 HP-UX server.
•
•
If the debugged process is blocking in a system call, any attempt to get to the GDB
command prompt by pressing ctrl-C does not work. The process needs to be killed
from a different shell.
ARIES does not provide true emulation of MxN threads, and thus does not support
debugging of HP 9000 applications that are linked with pthreads library and create
threads in MxN model.
NOTE: The HP 9000 applications linked with MxN pthreads library are emulated
under ARIES as traditional 1x1 threads, and thus can only be debugged under
ARIES as any other non-MxN multi-threaded application.
•
ARIES supports debugging of 32-bit and 64-bit HP 9000 HP-UX applications using
32-bit HP 9000 HP-UX GDB. 64-bit HP 9000 HP-UX gdb is not supported under
ARIES.
14.30.2 Attaching GDB to an already running emulated process
You can attach GDB to an already running HP 9000 application process on HP-UX 11i
for HP Integrity servers to debug the application. After a successful attach, all of the
GDB commands work in exactly the same manner as they do on an HP 9000 HP-UX
server.
Use the steps below to attach GDB to HP 9000 application process under ARIES on
HP-UX 11i Integrity servers:
•
Perform the same preparatory steps as required for debugging an HP 9000 HP-UX
application using GDB under ARIES on HP-UX 11i Integrity server.
•
Invoke GDB as follows:
gdb <pa_process_name> <pa_process_name>
You can also invoke GDB through any of the attach modes supported by GDB
using the -pid <pa_pid>option or by issuing the attach <pa_pid>command
at the gdbprompt
After the debugging, the process can continue or abort, as specified by the user. This
feature is especially useful when triaging problems in an environment with a large
number of processes and a mix of Integrity native and HP 9000 processes.
14.30.3 Detecting memory leaks using GDB under ARIES
Applications cannot leak memory under ARIES unless they do so on HP 9000 servers.
HP GDB can be used to detect memory leaks of HP 9000 applications under ARIES.
Refer to HP GDB documentation for more details.
232 HP-UX Configuration-Specific Information
14.31 Visual Interface for WDB
WDB includes an HP-supported Visual Interface for WDB with both graphical and
terminal modes. The interface is based on Vim 5.7 and WDB. This interface replaces
the -tuimode on Itanium-based systems.
When you use the interface you are actually using vim, which is a vi-compatible editor.
With the interface you can use vi commands to browse in the WDB display.
Most of Visual Interface for WDB functionality is also available for emacs users. Visual
Interface for WDB does not require knowledge of vi commands.
Visual Interface for WDB identifies you as an emacs user by looking at the environment
variable `$EDITOR'. If this variable has a value that matches emacs, or gmacs, or xemacs,
then Visual Interface for WDB starts in emacs mode automatically.
NOTE: If the program expects unbuffered input or uses curses, termcap, or terminfo,
or otherwise transmits escape or control sequences to the terminal, you must use one
of the following methods to run Visual Interface for WDB:
•
•
Start the process in one terminal and attach to it with Visual Interface for WDB.
Use the ttycommand at the debugger prompt so the program's input and output
are directed to another terminal.
NOTE: If the underlying GDB terminates abnormally when you are using Visual
Interface for WDB, do not close the Visual Interface for WDB window. Wait for a minute
or two. Visual Interface for WDB captures the stack trace and the debugging session
details and sends you an email. You can then forward this to HP when you report the
problem. This is helpful to HP in reconstructing the crash scenario.
14.31.1 Starting and stopping Visual Interface for WDB
You can use Visual Interface for WDB in either of two modes:
•
•
X-window-based graphical interface: Supports mouse and keyboard commands.
Terminal interface: Supports keyboard commands only.
Visual Interface for WDB accepts the same command line arguments as GDB so you
can add options to the startup command. See the man page for GDB for the list of
arguments.
•
•
•
To start Visual Interface for WDB in graphical mode with mouse support, run
Visual Interface for WDB with the command:
/opt/langtools/bin/vdb
To start Visual Interface for WDB in terminal user interface mode, run Visual
Interface for WDB with the command:
/opt/langtools/bin/vdb -tui
To stop Visual Interface for WDB, type quiton the WDB command line:
14.31 Visual Interface for WDB 233
(wdb) quit
14.31.2 Navigating the Visual Interface for WDB display
The Visual Interface for WDB window consists of two areas:
•
•
Source pane at the top
Debugger pane at the bottom
You can use the arrow and pagination keys on the keyboard to move the cursor:
•
Pagination keys move the cursor in the source window, at the top, above the status
line.
•
Holding the shift key down while using the pagination keys moves the cursor in
the debugger window.
•
•
The up and down arrow keys move the cursor in the source window.
Holding the shift key down while using the up and down arrow keys move the
cursor in the debugger window.
•
•
The left and right arrow keys move the cursor in the debugger window.
Two rows of labeled softkeys at the bottom of the display give you quick access
to common commands.
Visual Interface for WDB GUI display
33 #include <stdlib.h>
34 #include "Deck.h"
35 #include "Player.h"
36 #include "House.h"
37
38 int main ()
39 {
*> 40 srand ((int) time(0));
41
42 Deck theDeck;
43 Player thePlayer (100);
44 House theHouse (16);
45
46 theHouse.Instructions();
47 }
File: BlackJack.C
Function: main Line: 40
Pc: 0x3ea0
(wdb) b main
Breakpoint 1 at 0x3ea0: file BlackJack.C, line 40.
(wdb) run
Starting program: /work/wdb/blackjack/blackjack
Breakpoint 1, main () at BlackJack.C:40
40 srand ((int) time(0));
(wdb)
234 HP-UX Configuration-Specific Information
Run
Faq
Resume Stop Up Visual
Interface for
WDB
Finish Print Type List
Stop
Next Down
Prompt Print* Edit Credits
You can click the softkey or press a function key on the keyboard to invoke the
command.
The function keys F1 through F8 correspond to the bottom row of softkeys. The function
keys F9 and up correspond to the top row.
14.31.3 Specifying foreground and background colors
To change the foreground and background colors, update the `.Xdefaults' file in the
home directory. The resources are the same as for `hpterm'.
Here is a sample entry:
HPterm*foreground: white
HPterm*background: rgb:68/90/C4
14.31.4 Using the X-window graphical interface
To start Visual Interface for WDB in graphical mode with mouse support, run Visual
Interface for WDB with the command:
/opt/langtools/bin/vdb
Visual Interface for WDB opens an `hpterm' window, ignoring the value of the TERM
environment variable, for debugging a program.
With a mouse you can do the following:
•
•
Left-click the line number to insert or remove breakpoints.
Left-click an identifier to select the identifier as an operand for the Print, Print*,
Type, and List softkeys.
•
•
Where necessary, manually select an expression by dragging the cursor over it.
Right-click the line number to activate a pop-up menu with several useful
commands.
•
•
Right-click an identifier to automatically select it and use the selection as an operand
for the pop-up window that appears.
Right-click an empty region for a third pop-up menu with several useful actions.
•
•
•
Left-click the command softkeys at the bottom of Visual Interface for WDB window.
Click the middle button to paste the selection.
Drag the status bar with the mouse to resize the debugger window relative to the
source window.
14.31 Visual Interface for WDB 235
14.31.5 Using the TUI mode
To start Visual Interface for WDB in terminal user interface (TUI) mode, run Visual
Interface for WDB with the command:
/opt/langtools/bin/vdb -tui
This mode works well with hptermand xtermand fairly well with dttermand VT100
(telnet) terminals.
NOTE: A defect in dttermmay truncate the display of lines that do not t within the
window. To work around this defect, refresh the display with CTRL-L or widen the
terminal window so source lines do not wrap.
If you use xtermand dtterm, update the `.Xdefaults' file with keyboard translations
to get the shifted arrows and shifted paging keys to work.
For xterm, use the following:
XTerm*vt100.translations: #override \
Shift <Key>Prior: string(0x2) \n \
Shift <Key>Next: string(0x6) \n \
Shift <Key>Up: string(0x5) \n \
Shift <Key>Down: string(0x19) \n \
Shift <Key>Left: string(0x1b) string(i) \n \
Shift <Key>Right: string(0x1b) string(la)
For dterm, use the following:
*DtTerm*Translations: #override\n \
Shift <Key>osfPageUp: string(0x2) \n \
Shift <Key>osfPageDown: string(0x6) \n \
Shift <Key>osfUp: string(0x5) \n \
Shift <Key>osfDown: string(0x19) \n \
Shift <Key>osfLeft: string(0x1b) string(i) \n \
Shift <Key>osfRight: string(0x1b) string(la)
Mouse operations are not supported in the -tuimode. Also the paging and shift keys
do not work well with VT100.
14.31.6 Changing the size of the source or debugger pane
1. Escape to vicommand mode first.
2. Drag the status bar using the mouse.
If you are using -tuimode, use these commands to change the size of the current
window:
CTRL-W +
to increase
CTRL-W -
to decrease
In Visual Interface for WDB, the current window is usually the debugger window.
236 HP-UX Configuration-Specific Information
14.31.7 Using commands to browse through source files
browse. For example, CTRL-B, CTRL-F, CTRL-D, CTRL-Uare useful for browsing the
debugger window. These commands work whether or not you escape to `vi' mode.
These `vim' commands require you to escape to `vi' mode. For example:
`/'
Search forward
`?'
`n' `N'
`%'
Search backward
Repeat search
Match braces
`[[', `]]'
`:line number'
Skip to the next procedure
Go to any line number
All these commands require you to escape to `vi' command mode first. When you are
done, type a for append or i for insert or other `vi' commands to return to text insertion
mode.
Or you can simply click the Prompt softkey.
14.31.8 Loading source files
Escape to `vi' command mode and use the :e command to load a source file.
:e filename
When the source files are located in multiple directories, you can simply specify the
base name alone as long as file names are unique and the appropriate dir commands
have been executed.
Pressing the Prompt softkey takes you to the command prompt and also updates the
source window so that the cursor remains where the program is stopped.
14.31.9 Editing source files
To edit a file, kill the process then click the Edit button. If you do not kill the process,
the source file and binaries can get out of sync.
14.31.10 Editing the command line and command-line history
Visual Interface for WDB preserves the entire session's transactions so you can browse
through these at any time.
To edit the command line, press ESC to enter vi mode and then use vi commands. You
can recall previous commands in history by using [jk^P^N]. Complete command
lines using TAB.
14.31.11 Saving the contents of a debugging session to a file
You can save the contents of the current debugging session, including debugger
input/output and program input/output to a file.
14.31 Visual Interface for WDB 237
To save a session to a file:
1. Right-click an empty region of the source or debugger pane.
2. Choose "Save Session to vdb.pid" from the pop-up menu.
The debugger writes the input and output to a file whose name ends in the pid of the
debugger. If you save the session more than once, the new transactions are appended
to the file.
14.32 Support for ddd
GDB works with ddd, the free GDB GUI shell available at http://mumm.ibr.cs.tu-bs.de/.
While this is not formally supported by Hewlett-Packard, these two do work together.
Note however if you have dddissues, you'll need to report them to the dddsupport
channel.
14.33 Support for XDB commands
HP WDB provides support for a subset of XDB commands, enabled with the -xdb
option.
14.33.1 stop in/at dbxcommands
The commands <stop in function/address>and <stop at line>are
equivalent of dbx <break function/address /line>command. WDB supports
the <stop in/at>command in non-dbx mode.
For example:
$ gdb a.out (gdb) stop in main Breakpoint 1 at 0x2a34: file list.c, line 18
from /tmp/a.out (gdb) stop at 25 Breakpoint 2 at 0x2a6c: file list.c, line
25 from /tmp/a.out (gdb)
14.34 GNU GDB Logging Commands
The following commands control GDB logging activities:
• set logging file: Set the current log file
• set logging off: Set logging off
• set logging on: Set logging on
• set logging overwrite[on|off]: Set whether logging overwrites or appends
to the log file.
• set logging redirect [on|off]: Set the logging output mode
14.35 Support for command line calls in a stripped executable
HP WDB enables you to perform command line calls in a stripped executable.
238 HP-UX Configuration-Specific Information
14.35.1 Support for command line calls in a stripped executable on PA-RISC systems
In WDB, to perform command line calls in a shared library without the help of dynamic
linker (using end.o), you must execute the following command:
chatr -B immediate <executable>
In addition, modify all the calls to shl_load()to specify BIND_IMMEDIATE.
To perform command line calls after attaching a running process to GDB, you must
execute one of the following commands:
• /opt/langtools/bin/pxdb -s on <executable>
• chatr +dbg enable <executable>
14.35.2 Additional support for command line calls in a stripped executable
HP WDB enables you to perform command line calls in a stripped executable. The
various scenarios in which you can make command line calls in a stripped executable
are as follows:
14.35.2.1 For 32-bit applications:
To perform command line calls in a shared library, without the help of dynamic linker
(using end.o), you must perform the following operations:
•
•
Execute the chatr -B immediate <executable>command.
Modify all the calls to shl_load()to specify BIND_IMMEDIATE, if any.
To perform command line calls after attaching GDB to a running process, without the
help of dynamic linker (using end.o), you must do the following for the program:
•
•
•
Execute the chatr -B immediate <executable>command
Modify all the calls to shl_load()to specify BIND_IMMEDIATE, if any.
Execute the /opt/langtools/bin/pxdb -s on <executable>or chatr
+dbg enable <executable>command.
On HP-UX 11i v3 Integrity systems, WDB enables automatic debugging of shared
libraries without them being mapped private while attaching to a running program.
For enabling automatic debugging of shared libraries, you must install the kernel
patches PHKL_38651 and PHKL_38778.
To avoid changing of the run-time binding behavior of a program to BIND_IMMEDIATE,
to perform command line call, do the following:
•
•
•
Use the linker option, +ea, to export symbols from an object file.
Install the linker patch, PHSS 28870 (for 11.0) or PHSS 28871 (for 11i).
Execute the following commands:
cc -c file.c cc file.o -Wl,+ea,/opt/langtools/lib/end.o -s
14.35 Support for command line calls in a stripped executable 239
14.35.2.2 For 64-bit applications
To perform command line calls in a stripped executable, linked with end.o, you need
to do the following:
•
In the +stdlink mode, GDB supports this feature without any changes. You must
export the __wdb_call_dummysymbol as shown in the next line.
•
In the +compatlink mode, execute the following command:
cc +DD64-g file.c -Wl,+ee,__wdb_call_dummy -s
14.35.3 Support for debugging stripped binaries
HP WDB provides limited support for debugging stripped binaries.
14.35.3.1 Printing of locals and globals in a stripped module
GDB will not be able to print the locals and statics declared in a module which has
been stripped. GDB will be able to print the exported symbols since exported symbols
are not stripped with strip command (they stay in .dynsym).
GDB will be able to access the globals or locals defined in other unstripped shared
libraries loaded into the stripped executable when you are in the right scope.
14.35.3.2 Backtrace on stripped frames
GDB should be able to backtrace properly stripped frames. Arguments will not be
displayed (as in the case of non -gbinary). If it is a fully archived stripped binary,
function names will not be displayed (but PCs will be).
14.35.3.3 Command line calls to non-stripped library
Command line calls to the functions (exported symbols) in the stripped binary work
fine. Command line calls to the non-stripped library work normally regardless where
the process is stopped.
14.35.3.4 Setting breakpoints in unstripped shared library
GDB will not be able to put breakpoints using symbolic names(of the symbols not in
export list) or line numbers in the stripped modules.
GDB will be able to place breakpoints using symbol names in the unstripped shared
libraries loaded into the stripped executable.
240 HP-UX Configuration-Specific Information
14.36 Displaying the current block scope information
The whichcommand takes a symbol as an argument and prints the information on a
given symbol. It prints the following information:
•
•
•
current block scope addresses
line information of the definition of the symbol
filename in which the definition of the symbol occurs
The whichcommand does not work for global and type symbols since they do not
contain line information.
Syntax:
which <symbol>
For example :
(gdb) which i Line 4 of "example.c" block starts at address 0x29a8 <main> and ends at 0x29e4
<main+0x3c>
14.37 Linux support
Linux Runtime Environment (LRE) on HP-UX Itanium enables users to execute Intel
Itanium Linux applications on HP-UX. HP WDB provides a prototype for LRE
debugging, which allows you to debug applications ported from Linux that run under
LRE. This provides a minimal debugging capability for LRE.
14.36 Displaying the current block scope information 241
242
15 The HP-UX Terminal User Interface
By default, GDB runs in line mode. For users who prefer an interface similar (though
not identical) to that of the XDB debugger, HP provides a terminal user interface (TUI),
which appears when you invoke the gdb command with the -tui option.
15.1 Starting the TUI
Invoke the debugger using a command like the following:
gdb -xdb -tui a.out
These examples use the default terminal screen size of 24 by 80 characters. Following
is a sample terminal screen window:
|----------------------------------------------------------------------|
|30
|31
|32
|33
|34
|35
|36
|37
|38
|39
|40
|41
|42
{
|
|
|
|
|
|
|
|
|
|
|
|
|
/* Try two test cases. */
print_average (my_list, first, last);
print_average (my_list, first, last - 3);
}
|----------------------------------------------------------------------|
File: average.c Procedure: ?? Line: ?? pc: ??
Wildebeest is free software, covered by the GNU General Public License, and
you are welcome to change it and/or distribute copies of it under certain
conditions. Type "show copying" to see the conditions. There is
absolutely no warranty for Wildebeest. Type "show warranty" for details.
---Type <return> to continue, or q <return> to quit---
Wildebeest was built for PA-RISC 1.1 or 2.0 (narrow), HP-UX 11.00.
..
(gdb)
The terminal window is divided into two panes: a Source pane at the top and a
Command pane at the bottom. In the middle is a locator barthat shows the current
file, procedure, line, and program counter (PC) address, when they are known to the
debugger.
When you set a breakpoint on the main program by issuing the command
b main
an asterisk (*) appears opposite the first executable line of the program.
15.1 Starting the TUI 243
When you execute the program up to the first breakpoint by issuing the command
run
a right angle bracket (>) points to the current location. So after you issue those
commands, the window looks something like this:
|----------------------------------------------------------------------|
|27
|28
|29
|30
|31
}
|
|
|
|
|
|
|
|
|
|
|
|
|
int main(void)
{
/* Try two test cases. */
print_average (my_list, first, last);
print_average (my_list, first, last - 3);
*>|32
|33
|34
|35
|36
|37
|38
|39
}
|----------------------------------------------------------------------|
File: average.c
..
Procedure: main
Line: 32
pc: 0x3524
(gdb) b main
Breakpoint 1 at 0x3524: file average.c, line 32.
(gdb) run
Starting program: /home/work/wdb/a.out
Breakpoint 1, main () at average.c:32
(gdb)
15.2 Automatically running a program at startup
WDB does not start running the target executable at startup as do `xdb' and HP DDE.
This makes it easy to set break points before the target program's main function.
To make WDB automatically start running the target program add these lines to your
startup file, .gdbinit:
break main
run
15.3 Screen Layouts
The TUI supports four panes within the terminal window, in various combinations:
•
•
•
•
Command
Source
Disassembly
Register
244 The HP-UX Terminal User Interface
The Command pane is always present. The possible configurations of the other panes
are:
•
•
•
•
•
Source
Disassembly
Source/Disassembly
Disassembly/Register
Source/Register
The layoutcommand (abbreviated la) enables you to change from one window
configuration to another.
NOTE: You can abbreviate any command to its shortest unambiguous form.
15.3.1 Source pane
The Source pane, Figure 1, appears by default when you invoke the debugger. You can
also make it appear by issuing the command
la src
15.3.2 Disassembly pane
The Disassembly pane appears when you issue the command
la asm
The pane looks like this:
|----------------------------------------------------------------------|
|;;;
print_average (my_list, first, last);
|
|
|
|
|
|
|
|
|
|
|
|
|
*>|0x3524 <main+8> addil L'-0x800,%dp,%r1
|0x3528 <main+12>
|0x352c <main+16>
|0x3530 <main+20>
|0x3534 <main+24>
|0x3538 <main+28>
|0x353c <main+32>
ldo 0x730(%r1),%r26
ldi 9,%r24
ldi 0,%r25
ldil L'0x3000,%r31
be,l 0x498(%sr4,%r31)
copy %r31,%rp
|;;; print_average (my_list, first, last - 3);
|0x3540 <main+36>
|0x3544 <main+40>
|0x3548 <main+44>
|0x354c <main+48>
addil L'-0x800,%dp,%r1
ldo 0x730(%r1),%r26
ldi 6,%r24
ldi 0,%r25
|----------------------------------------------------------------------|
File: average.c
(gdb) b main
Procedure: main
Line: 32
pc: 0x3524
Breakpoint 1 at 0x3524: file average.c, line 32.
(gdb) r
Starting program: /home/work/wdb/a.out
Breakpoint 1, main () at average.c:32
(gdb) la asm
(gdb)
15.3 Screen Layouts 245
15.3.3 Source/Disassembly pane
The Source/Disassembly pane appears when you issue the command:
la split
You can also reach this pane from the Source pane with the XDB command:
td
The window looks like this:
:......................................................................:
*>:32
:33
print_average (my_list, first, last);
print_average (my_list, first, last - 3);
:
:
:
:
:
:
:34
:35
:36
:37
}
:......................................................................:
|;;;
print_average (my_list, first, last);
|
|
|
|
|
|
*>|0x3524 <main+8> addil L'-0x800,%dp,%r1
|0x3528 <main+12>
|0x352c <main+16>
|0x3530 <main+20>
|0x3534 <main+24>
ldo 0x730(%r1),%r26
ldi 9,%r24
ldi 0,%r25
ldil L'0x3000,%r31
|----------------------------------------------------------------------|
File: average.c Procedure: main Line: 32 pc: 0x3524
Breakpoint 1 at 0x3524: file average.c, line 32.
(gdb) r
Starting program: /home/work/wdb/a.out
Breakpoint 1, main () at average.c:32
(gdb) la asm
(gdb) la split
(gdb)
15.3.4 Disassembly/Register pane
The Disassembly/Register pane appears when you issue the command
la regs
when the current pane is the Source/Disassembly pane. By default, the debugger
displays the general registers.
The window looks like this:
:.........................................................................:
:flags 29000041
:r3 7f7f0000
:r6 7f7f06fc
:r9 40006b10
:r12 1
r1 51a800
r4 1
r7 7f7f0800
r10 0
r13 0
r16 40003fb8
rp 7f6ce597
r5 7f7f06f4
r8 7f7f0800
r11 40004b78
r14 0
:
:
:
:
:
:
:r15 0
r17 4
:.........................................................................:
246 The HP-UX Terminal User Interface
|;;;
print_average (my_list, first, last);
|
|
|
|
|
|
*> |0x3524 <main+8> addil L'-0x800,%dp,%r1
|0x3528 <main+12>
|0x352c <main+16>
|0x3530 <main+20>
|0x3534 <main+24>
ldo 0x730(%r1),%r26
ldi 9,%r24
ldi 0,%r25
ldil L'0x3000,%r31
|----------------------------------------------------------------------|
File: average.c
(gdb) r
Procedure: main
Line: 32
pc: 0x3524
Starting program: /home/work/wdb/a.out
Breakpoint 1, main () at average.c:32
(gdb) la asm
(gdb) la split
(gdb) la regs
(gdb)
15.3.5 Source/Register pane
The Source/Register pane appears when you issue the command:
la regs
when the current pane is the Source pane.
The screen looks like this:
:.........................................................................:
:flags 29000041
:r3 7f7f0000
:r6 7f7f06fc
:r9 40006b10
:r12 1
r1 51a800
r4 1
r7 7f7f0800
r10 0
r13 0
r16 40003fb8
rp 7f6ce597
r5 7f7f06f4
r8 7f7f0800
r11 40004b78
r14 0
:
:
:
:
:
:
:r15 0
r17 4
:.........................................................................:
*>|32
|33
print_average (my_list, first, last);
print_average (my_list, first, last - 3);
|
|
|
|
|
|
|34
|35
|36
|37
}
|----------------------------------------------------------------------|
File: average.c
Procedure: main
Line: 32
pc: 0x3524
Breakpoint 1, main () at average.c:32
(gdb) la asm
(gdb) la split
(gdb) la regs
(gdb) la src
(gdb) la regs
(gdb)
15.3 Screen Layouts 247
15.4 Cycling through the panes
Use the commands
la next
and
la prev
to move from one pane to another without specifying a window name. If you specify
la nextrepeatedly, the order the debugger uses is:
•
•
•
•
•
Source (src)
Disassembly (asm)
Source/Disassembly (split)
Source/Register
Disassembly/Register
If you invoked the gdb command with the -xdboption as well as the -tuioption,
you can also use the following commands:
td Toggle between Source and Disassembly/Register panes.
td Toggle split-screen mode.
15.5 Changing pane focus
The command pane always has keyboard focus, so that you can enter debugger
commands. If there is only one other pane (Source or Disassembly), the other pane has
the logical focus, so that you can scroll within that pane by using the arrow keys or the
Page Up and Page Down keys (on some keyboards these are Prev and Next).
NOTE: In the command pane, the scrolling behavior only works for an `hpterm' and
not for an `xterm' or `dtterm'.
If you are in split-screen mode, you may want to change the logical focus of the pane.
To do so, use the command focus
{win_name | prev | next}
where win name can be src, asm, regs, or cmd.
Remember, if you change the focus to a pane other than the command pane, you need
to use focus cmdto switch back to the command pane to enter or scroll through
commands.
For example, with the sequence of commands just issued, you are in split-screen mode
with the focus in the Source pane.
The pane with logical focus has a border constructed from "|" and "-".
A pane that does not have logical focus has a border constructed from ":"vand ".":
248 The HP-UX Terminal User Interface
:.........................................................................:
:flags 29000041
:r3 7f7f0000
:r6 7f7f06fc
:r9 40006b10
:r12 1
r1 51a800
r4 1
r7 7f7f0800
r10 0
r13 0
r16 40003fb8
rp 7f6ce597
r5 7f7f06f4
r8 7f7f0800
r11 40004b78
r14 0
:
:
:
:
:
:
:r15 0
r17 4
:.........................................................................:
*>|32
|33
print_average (my_list, first, last);
print_average (my_list, first, last - 3);
|
|
|
|
|
|
|34
|35
|36
|37
}
|----------------------------------------------------------------------|
File: average.c Procedure: main Line: 32 pc: 0x3524
Breakpoint 1, main () at average.c:32
(gdb) la asm
(gdb) la split
(gdb) la regs
(gdb) la src
(gdb) la regs
(gdb)
By default, the Source pane can scroll. To change the focus so that you can scroll in the
Register pane, use the focuscommand (abbreviated focor fs):
fs regs
or
foc next
If you then use the Page Down key to scroll in the Register pane, the window looks
like this:
|-------------------------------------------------------------------------|
|flags 29000041
|r3 7f7f0000
|r6 7f7f06fc
|r9 40006b10
|r12 1
r1 51a800
r4 1
r7 7f7f0800
r10 0
r13 0
r16 40003fb8
rp 7f6ce597
r5 7f7f06f4
r8 7f7f0800
r11 40004b78
r14 0
|
|
|
|
|
|
|r15 0
r17 4
|-------------------------------------------------------------------------|
*>:32
:33
print_average (my_list, first, last);
print_average (my_list, first, last - 3);
:
:
:
:
:
:
:34
:35
:36
:37
}
:.......................................................................:
File: average.c
(gdb) la asm
Procedure: main
Line: 32
pc: 0x3524
15.5 Changing pane focus 249
(gdb) la split
(gdb) la regs
(gdb) la src
(gdb) la regs
(gdb) foc next
Focus set to REGS window.
(gdb)
15.6 Scrolling panes
To scroll within a pane, you can use the arrow keys or the Page Up and Page Down
keys (on some keyboards these are Prev and Next). You can also use the following
commands:
{+ | -} [num_lines]
[win_name]
Vertically scroll the pane forward (+) or backward
(-). + or - with no arguments scrolls the pane
forward or backward one page. Use num_lines
to specify how many lines to scroll the pane. Use
win_name to specify a pane other than the one
with logical focus.
{< | >} [num_char]
[win_name]
Horizontally scroll the pane left (<) or right (>)
the specified number of characters. If you do not
specify num_char, the pane is scrolled one
character.
Note that a space is required between the +, -, <, or > and the number.
To scroll the command pane, use the scroll bars on the terminal pane.
15.7 Changing the register display
To look at the floating-point or special registers instead of the general registers, and
then to return to the general registers, you can use the following XDB commands:
fr, display $fregs
sr, display $sregs
gr, display $gregs
Display the floating-point registers.
Display the special registers.
Display the general registers.
For example, if you use the frcommand, the window looks like this:
|-------------------------------------------------------------------------|
|flags 29000041
|r3 7f7f0000
|r6 7f7f06fc
|r9 40006b10
|r12 1
r1 51a800
r4 1
r7 7f7f0800
r10 0
r13 0
r16 40003fb8
rp 7f6ce597
r5 7f7f06f4
r8 7f7f0800
r11 40004b78
r14 0
|
|
|
|
|
|
|r15 0
r17 4
:......................................................................:
:30
:31
{
:
:
/* Try two test cases. */
250 The HP-UX Terminal User Interface
*>:32
:33
print_average (my_list, first, last);
print_average (my_list, first, last - 3);
:
:
:
:
:34
:35
}
:......................................................................:
File: average.c
(gdb) la regs
(gdb) la src
Procedure: main
Line: 32
pc: 0x3524
(gdb) la regs
(gdb) foc next
Focus set to REGS window.
(gdb) fr
#0 main () at average.c:32
(gdb)
The default floating-point register display is single-precision. To change the register
display to double-precision and then back again, use the XDB toggle float
command:
toggle $fregs
The window looks like this:
|-------------------------------------------------------------------------|
|fpsr 0
|fpe2 0
|fpe4 0
|fpe6 0
|fr4
fpe1 0
fpe3 0
fpe5 0
fpe7 0
fr4R
|
|
|
|
|
|
0
0
|fr5
1.0000000000000011
fr5R
7.00649232e-45
|-------------------------------------------------------------------------|
*>:32
:33
print_average (my_list, first, last);
print_average (my_list, first, last - 3);
:
:
:
:
:
:
:34
:35
:36
:37
}
:......................................................................:
File: average.c
(gdb) la regs
(gdb) la src
Procedure: main
Line: 32
pc: 0x3524
(gdb) la regs
(gdb) foc next
Focus set to REGS window.
(gdb) fr
(gdb) tf
(gdb)
15.8 Changing the pane size
To specify a new height for a pane or to increase or decrease the current height, use
the winheightcommand (abbreviated winhor wh).
The syntax is:
15.8 Changing the pane size 251
winheight [win_name] [+ | -] num_lines
If you omit win_name, the pane with logical focus is resized. When you increase the
height of a pane, the height of the Command pane is decreased by the same amount,
and vice versa. The height of any other panes remains unchanged.
For example, the command
wh src +3
increases the size of the source pane, and decreases the size of the command pane, by
3 lines.
To nd out the current sizes of all panes, use the info win command. For example, if you
have a split-screen layout, the command output might be as follows:
(gdb) i win
SRC (8 lines)
REGS (8 lines)
CMD (8 lines)
If you use the mouse or window menus to resize the terminal window during a
debugging session, the window remains the same size it was when you started. To
change the window size, you must exit the debugger and restart it.
15.9 Refreshing and updating the window
If the screen display is disrupted for some reason, use the refreshcommand (ref) to
restore the windows to their previous state:
ref
If you use stack-navigation commands such as up, down, and frameto change your
source location, and you want to return the display to the current point of execution,
use the update command (upd):
upd
252 The HP-UX Terminal User Interface
16 XDB to WDB Transition Guide
This transition aid is designed for XDB users who are learning WDB, an HP-supported
version of the industry-standard GDB debugger. Select one of these lists for a table that
shows WDB equivalents for many common XDB commands and other features.
Invoke WDB with the command gdb -tuito obtain a terminal user interface (TUI)
similar to that provided by XDB. Commands marked "(with -tui)" are valid when
you use the -tuioption.
Invoke WDB with the command gdb -xdbto turn on XDB compatibility mode, which
enables you to use many XDB commands as synonyms for GDB commands. Commands
marked "(with -xdb)" are valid when you use the -xdboption.
You may use both -xdband -tuiat the same time. Some commands are valid only
when you use both options.
For a tutorial introduction to WDB, refer to the Getting Started with WDB.
•
•
•
•
•
•
•
•
16.1 By-function lists of XDB commands and HP WDB equivalents
•
•
•
•
•
•
•
•
•
•
•
•
•
16.1 By-function lists of XDB commands and HP WDB equivalents 253
•
•
•
•
•
16.1.1 Invocation commands
By default, HP WDB runs in line mode. To run it with a terminal user interface similar
to that of XDB, use the -tuioption.
The following table lists the XDB and the equivalent WDB commands for invoking the
terminal user interface:
Table 16-1 Invocation commands
XDB Command
xdb program
WDB Equivalent
Meaning
gdb -xdb program, gdb -xdb Debug program
-tui program
xdb program corefile
xdb -d dir
gdb -xdb program -c
corefile
Debug core file
gdb -xdb -d dir
Specify alternate directory to
search for source files
xdb -P pid program
gdb -xdb program pid
Attach to running pro- gram at
invocation
xdb -i
xdb -o
(after starting) run < file
Specify input to target program
(after starting) run > file
Specify output from target
program
16.1.2 Window mode commands
The following commands are TUI mode or XDB compatibility mode commands. They
are available when you invoke WDB by using the -tuior -xdbor both options.
Table 16-2 Window mode commands
XDB Command
{+ | -}r
WDB Equivalent
Meaning
{+ | -}r (with -xdb
Scroll floating-point registers
-tui), {+ | -} data (with forward or backward (src, cmd,
-tui), gdb -xdb -tui
program
and asmare also valid window
names)
fr
fr (with -xdb -tui),
display $fregs (with
-tui)
Display floating-point registers
254 XDB to WDB Transition Guide
Table 16-2 Window mode commands (continued)
XDB Command
WDB Equivalent
Meaning
gr
sr
gr (with -xdb -tui),
display $regs (with -tui)
Display general registers
sr (with -xdb -tui),
display $sregs (with
-tui)
Display special registers
td
tf
td (with -xdb -tui)
Toggle disassembly mode
tf (with -xdb -tui),
toggle $fregs (with -tui)
Toggle float register display
precision
ts
u
ts (with -xdb -tui)
Toggle split-screen mode
u (with -xdb -tui),
update (with -tui)
Update screen to current execution
point
V
U (with -xdb -tui),
refresh (with -tui)
Refresh all windows
w number
w number (with -xdb
-tui), winheight src
number (with -tui)
Set size of source window
16.1.3 File viewing commands
The following table lists the XDB and the equivalent WDB commands for viewing
source files:
Table 16-3 File viewing commands
XDB Command
WDB Equivalent
Meaning
{+ | -}[number]
{+ | -}[ number] (with
-tui; note that a space
is required between + or
- and the number)
Move view location forward or
backward in source file number
lines
/[string]
/[string] (with -xdb),
search regexp, forw
regexp
Search source forward for [last]
string
?[string]
D "dir"
L
?[string] (with -xdb),
rev regexp
Search source backward for [last]
string
D "dir" (with -xdb), dir Add a directory search path for
source files
pathname
L (with -xdb)
Show current viewing location or
current point of execution
16.1 By-function lists of XDB commands and HP WDB equivalents 255
Table 16-3 File viewing commands (continued)
XDB Command
WDB Equivalent
Meaning
ld
lf
ld (with -xdb), show
directories
List source directory search path
(list all directories)
lf (with -xdb), info
sources
List all source files
lf [string]
No equivalent
fo or rev
fo or rev
List matching files
n
N
Repeat previous search
Repeat previous search in opposite
direction
v
v (with -xdb), list
Show one source window forward
from current
v location
va address
va label
v location (with -xdb), View source at locationin
list location
source window
va address (with -xdb), View addressin disassembly
disas address
window
va label (with -xdb),
disas label
View labelin disassembly
window (labelis a location)
va label + offset
va label + offset (with View label+ offset in
-xdb), disas label +
disassembly window
offset
16.1.4 Source directory mapping commands
Use the D or dir command to add new directories to be searched for source files. See
GDB does not provide a source directory mapping capability and therefore does not
have any equivalent of the apm, dpm, and lpmcommands.
16.1.5 Data Viewing and modification commands
There are many info commands in addition to those shown here. Use help info to get
a list.
The following table lists the XDB and equivalent WDB commands for viewing and
modifying the program data:
256 XDB to WDB Transition Guide
Table 16-4 Data viewing and modification commands
XDB Command
WDB Equivalent
Meaning
l
l (with -xdb), info args Move view location forward or
backward in source file number
lines
followed by info locals
lc [string]
lg [string]
ll [string]
lc [string] (with -xdb), Search source forward for [last]
string
info common string
lg [string] (with -xdb), Search source backward for [last]
string
info variables [string]
info functions [string], Add a directory search path for
source files
info variables [string],
maint print msymbols file
lm
show user
Show current viewing location or
current point of execution
lm string
show user string
List source directory search path
(list all directories)
lo [[class]::][string]
lp
info func
[[class]::][string]
List all source files
info functions
Show current scope, list program
blocks, list names (symbols)
lp [[class]::]string
info func
[[class]::]string info
addr [[class]::]string
List all (or matching) procedures
lr
lr (with -xdb), info
all-reg
List all registers
lr [string]
ls [string]
mm
lr string (with -xdb),
info reg string
List matching registers
No equivalent
List all (or matching) special
variables
info sharedlibrary
No equivalent
Show memory map of all loaded
shared libraries
mm string
p expr[\format
Show memory map of matching
loaded shared libraries
p[/format expr[Note: The
count and size portions of
formats are not allowed in the p
(print)command. They are
allowed in the xcommand
(examine memory).]
Print value using the specified
format
16.1 By-function lists of XDB commands and HP WDB equivalents 257
Table 16-4 Data viewing and modification commands (continued)
XDB Command
p expr?format
WDB Equivalent
Meaning
p/format &expr
Print address using specified for-
mat
p class::
No equivalent
show language
Print static members of class
Inquire what language is used
p $lang
p {+ | -}[\format
Use x/format command to
obtain initial value, then use x
with no argument to obtain value
of next memory location. To
obtain value of previous memory
location, use "x $_ - 1".
Print value of next/previous
memory location using format
pq expr
set expr, set var expr
Evaluate using the specified
format
pq expr?format
No equivalent
Determine address using specified
format
pq class::
No equivalent
No equivalent
Evaluate static members of class
pq {+ | -}[\format
Evaluate next/previous memory
location using format
16.1.6 Stack viewing commands
The GDB concept of the top and bottom of the stack is the opposite of XDB, so the XDB
up is GDBdown.
The following table lists the XDBand equivalent WDBcommands for viewing the stack
contents:
Table 16-5 Stack viewing commands
XDB Command
WDB Equivalent
Meaning
down
up
View procedure one level nearer
outermost frame of stack (higher
number)
down number
t [depth]
T [depth]
top
up number
View procedure number levels
nearer outermost frame of stack
t [depth] (with -xdb), bt Print stack trace to depth
[depth]
T [depth] (with -xdb),
bt full [depth]
Print stack trace and show local
vars
frame 0
View procedure at innermost
frame of stack
258 XDB to WDB Transition Guide
Table 16-5 Stack viewing commands (continued)
XDB Command
WDB Equivalent
Meaning
up
down
View procedure one level nearer
innermost frame of stack (lower
number)
up number
down number
View procedure number levels
nearer innermost frame of stack
V [depth]
V [depth] (with -xdb),
frame [depth]
Display text for current active
procedure or at specified depth on
stack
16.1.7 Status-viewing command
Type the showcommand with no arguments to get a list of current debugger settings.
Table 16-6 Status viewing commands
XDB Command
WDB Equivalent
Meaning
I
info(many kinds), show(many Display state of debugger and
kinds)
program
16.1.8 Job control commands
The following table lists the XDB and equivalent WDB commands for controlling
program execution:
Table 16-7 Job control commands
XDB Command
WDB Equivalent
c, continue
Meaning
c
Continue from breakpoint,
ignoring any pending signal
c location
until location
Continue from breakpoint,
ignoring any pending signal, set
temporary breakpoint at
location
C
c, continue
Continue, allowing any pending
signal
C [location]
until location
Continue, allowing any pending
signal, set temporary breakpoint
at location
g line
g line (with -xdb), go
line, tb line followed by
jump line
Go to linein current procedure
g #label
No equivalent
Go to labelin current procedure
16.1 By-function lists of XDB commands and HP WDB equivalents 259
Table 16-7 Job control commands (continued)
XDB Command
g {+ | -}lines
WDB Equivalent
Meaning
g {+ | -}lines (with
-xdb), go {+ | -}lines, tb
{+ | -}linesfollowed by
jump {+ | -}lines
Go forward or back given # lines
g {+ | -}
g {+ | -} (with -xdb), go Go forward or back 1 line
{+ | -}1, tb {+ | -}1
followed by jump {+ | -}1
k
k
Detach and terminate target
r [arguments]
r [arguments]
Run with last arguments [or with
new arguments]
R
s
R (with -xdb), r
Rerun with no arguments
s, si
Single step (into procedures) (si:
step by instruction)
s number
s number, si number
Single step number steps (into
procedures) (si: step by
instruction)
S
S (with -xdb), n, ni
Step over (ni: step over by
instruction)
S number
S number (with -xdb), n
number, ninumber
Step over by numberstatements
or instructions (ni: step over by
instruction)
16.2 Overall breakpoint commands
The following table lists the XDB and equivalent WDB commands for setting additional
breakpoints:
Table 16-8 Overall breakpoint commands
XDB Command
WDB Equivalent
lb (with -xdb), ib
No equivalent
Meaning
List breakpoints
Toggle overall breakpoint state
lb
tb
16.2.1 Auxiliary breakpoint commands
The following table lists the XDB and equivalent WDB auxiliary breakpoint related
commands:
260 XDB to WDB Transition Guide
Table 16-9 Auxillary breakpoint commands
XDB Command
any_string
WDB Equivalent
p "any string"
Meaning
Print any string
if expr {cmds} [{cmds}] if expr cmds [else cmds] Conditionally execute cmds
end
Q
Q (with -xdb), silent(must Quiet breakpoints
be first command in a commands
list)
16.2.2 Breakpoint creation commands
The GDB equivalent of the countand cmdsarguments is to use the commandsbnum
command to set an ignore count and/or to specify commands to be executed for that
breakpoint.
For C++ programs, you can use the regular-expression breakpoint command rbreak
to set breakpoints on all the member functions of a class or on overloaded functions
outside a class.
The following table lists the XDB and equivalent WDB commands for creating
breakpoints:
Table 16-10 Breakpoint creation commands
XDB Command
WDB Equivalent
Meaning
b loc
b loc
Set a breakpoint at the specified
location.
b
b
Set a breakpoint at the current line.
ba address
bb [depth]
bi expr.proc
bi -c expr
ba address (with -xdb), b Set breakpoint at a code address.
*address
No equivalent (use bproc)
Set breakpoint at procedure
beginning.
b class::proc cond bnum Set an instance breakpoint at the
first executable line of expr.proc.
(this == expr)
No Equivalent
Set an instance breakpoint at first
executable line. No equivalent of
all non-static member functions of
the instance of a class (no base
classes).
bi -C expr
No equivalent
Set an instance breakpoint at first
executable line of all non- static
member functions of the instance's
class (base classes included).
16.2 Overall breakpoint commands 261
Table 16-10 Breakpoint creation commands (continued)
XDB Command
bpc -c class
WDB Equivalent
rb ^class::*
Meaning
Set a class breakpoint at first
executable line of all member
functions of the instance's class (no
base classes).
bpc -C class
Use rb ^class::*for base
classes also
Set a class breakpoint at first ex-
ecutableUse rb ^class::* for base
classes also line of all member
functions of the class (base classes
included).
bpo proc
rbproc
Set breakpoints on overloaded
functions outside a class.
bpo class::proc
bt [depth]
b class::proc
No equivalent
Set breakpoints on overloaded
functions in a class.
Set trace breakpoint at procedure
at specified depth on program
stack.
bt proc
b proccommands bnum
finish c end
Set trace breakpoint at proc.
bu [depth]
bu [depth] (with -xdb).
The finishcommand is
equivalent to the sequence bu,
c, db(to continue out of the
current routine).
Set up-level breakpoint.
bx [depth]
bx [depth] (with -xdb)
Set a breakpoint at procedure exit.
16.2.3 Breakpoint status commands
The following table lists the XDB and equivalent WDB commands for changing the
breakpoint status:
Table 16-11 Overall breakpoint commands
XDB Command
ab number
WDB Equivalent
enable number
Meaning
Activate suspended breakpoint of
the given number
ab *
enable
Activate all suspended break-
points
ab @shared- library
No equivalent
Activate suspended breakpoints
in named shared library
262 XDB to WDB Transition Guide
Table 16-11 Overall breakpoint commands (continued)
XDB Command
bc number expr
WDB Equivalent
Meaning
bc number expr(with -xdb), Set a breakpoint count
ignorenumber expr(within a
commands list)
db
clear
Delete breakpoint at current line
db number
delete number
Delete breakpoint of the given
number
db *
delete
Delete all breakpoints
sb number
disable number
Suspend breakpoint of the given
number
sb *
disable
Suspend all breakpoints
sb @shared- library
No equivalent
Suspend breakpoints in named
shared library
16.2.4 All-procedures breakpoint commands
GDB does not provide the ability to set breakpoints on all procedures with a single
command. Therefore, it does not have any equivalent of the following commands:
bp
bpt
bpx
dp
Dpt
Dpx
16.2.5 Global breakpoint commands
The following table lists the XDB and equivalent WDB commands for setting global
breakpoints:
Table 16-12 Global breakpoint commands
XDB Command
abc cmds
WDB Equivalent
Meaning
No exact equivalent, but
Set or delete cmdsto execute at
display expris equivalent to every stop
abc print expr
dbc
undisplay
Stop displaying values at each stop
16.2 Overall breakpoint commands 263
16.2.6 Assertion control commands
GDB does not provide the ability to trace by instruction. Watchpoints, however, provide
similar functionality to xdbassertions.
For example, watchpoints can be:
•
•
•
•
Enabled (corresponds to aa)
Disabled (corresponds to da)
Listed (corresponds to info watch)
Added (corresponds to x)
WDB does not have explicit equivalents for the following commands:
a
aa
da
la
sa
ta
x
16.2.7 Record and playback commands
Use the source command to read commands from a file. GDB does not provide a
recording capability like XDB's, but you can use the set history savecommand
to record all GDB commands in the file ./.gdb_history(similar to the $HOME/
.xdbhistfile). The history file is not saved until the end of your debugging session.
To change the name of the history file, use set history filename.
To stop recording, use set history save off.
To display the current history status, use show history. For an equivalent of the
XDB record-all facility, pipe the output of the gdbcommand to the tee(1)command.
For example:
gdb a.out | tee mylogfile
This solution works with the default line-mode user interface, not with the terminal
user interface.
The following table lists the XDB and the equivalent WDB commands for handling
macros:
16.2.8 Macro facility commands
Use the show user or help user-defined command to obtain a list of all user-defined
commands.
264 XDB to WDB Transition Guide
Table 16-13 Macro facility commands
XDB Command
WDB Equivalent
Meaning
def name replacement-text def name[GDB prompts for
Define a user-defined command
commands]
tm
No equivalent
Toggle the macro substitution
mechanism
undef name
undef *
def name[follow with empty
Remove the macro definition for
name
command list]
No equivalent
Remove all macro definitions
16.2.9 Signal control commands
The following table lists the XDB and equivalent WDB commands for signal control:
Table 16-14 Signal control commands
XDB Command
WDB Equivalent
Meaning
lz
lz(with -xdb), info signals List signal handling
z number s
z number i
z number s(with -xdb),
handle numberstop, handle
number nostop
Toggle stop flag for signal number
z number i(with -xdb),
handle numbernopass,
handle number pass
Toggle ignore flag for signal
number
z number r
z number r(with -xdb),
handle number print,
handle number noprint
Toggle report flag for signal
number
z number Q
z number Q(with -xdb),
handle number noprint
Do not print the new state of the
signal
16.2.10 Miscellaneous commands
Some of the additional XDB and the equivalent WDB commands are discussed below:
Table 16-15 Miscellaneous commands
XDB Command
WDB Equivalent
Meaning
Return
Return
Return
Repeat previous command
Repeat previous command
~
;
No equivalent (one command per Separate commands in command
line in command list)
list
16.2 Overall breakpoint commands 265
Table 16-15 Miscellaneous commands (continued)
XDB Command
! cmd line
WDB Equivalent
Meaning
! cmd line(with -xdb), she Invoke a shell
cmd line
{cmd list}
commands [number]... end
Execute command list (group
commands)
Control-C
# [text]
am
Control-C
Interrupt the program
A comment
# [text]
am(with -xdb), set height
num
Activate more (turn on pagination)
f ["printf-style- fmt"] No equivalent
Set address printing format
Help
h
h
M[{t | c} [expr[;
expr...]]]
No equivalent
Print object or corefile map
q
q
Quit debugger
sm
sm(with -xdb), set height 0 Suspend more (turn o pagination)
ss file
No equivalent
Save (breakpoint, macro, assertion)
state
tc
No equivalent
Toggle case sensitivity in searches
16.3 XDB data formats and HP WDB equivalents
The format of the printcommand is different in XDB and GDB:
XDB: p expr\fmt
GDB: p/fmt expr
Use the set print prettycommand to obtain a structured display similar to the
default XDB display.
The following table lists the XDB and equivalent WDB commands for setting data
display formats:
Table 16-16 Data format commands
XDB Command
WDB Equivalent
Meaning
Byte in decimal
b
d
d
c
B (1)
c
Byte in decimal
Character
C (1)
c
Wide character
266 XDB to WDB Transition Guide
Table 16-16 Data format commands (continued)
XDB Command
WDB Equivalent
Meaning
Decimal integer
d
d
d
D (1)
Long decimal integer
e
No equivalent
No equivalent
No equivalent
No equivalent
f
e Floating-point notation as float
e Foating-point notation as double
f floating-point notation as float
f floating-point notation as double
g floating-point notation as float
g floating-point notation as double
Machine instruction (disassembly)
Formatted structure display
E (1)
f
F (1)
g
G (1)
f
i
Use x/i command
No equivalent
No equivalent
k
K (1)
Formatted structure display with
base classes
n
print
Normal (default) format, based on
type
o
o
o
a
Expression in octal as integer
O (1)
P
Expression in octal as long integer
Print name of procedure
containing address
s
No equivalent
No equivalent
whatis, ptype
ptype
String
S
Formatted structure display
Show type of the expression
t
T (1)
Show type of expression, including
base class information
u
u
u
Expression in unsigned decimal
format
U (1)
Expression in long unsigned
decimal format
w
No equivalent
Wide character string
W (1)
x
No equivalent
Address of wide character string
Print in hexadecimal
x
x
X (1)
Print in long hexadecimal
16.3 XDB data formats and HP WDB equivalents 267
Table 16-16 Data format commands (continued)
XDB Command
WDB Equivalent
Meaning
Print in binary
Print in long binary
z
t
t
Z (1)
(1) HP WDB will display data in the size appropriate for the data. It will not extend
the length displayed in response to one of the uppercase formchars (for example, O,
D, F).
16.4 XDB location syntax and HP WDB equivalents
The following command lists the XDB and the equivalent WDB commands for locating
source lines:
Table 16-17 Macro facility commands
XDB location syntax
WDB Equivalent
Meaning
line
line
Source line and code address
Source line and code address
Procedure name
file[:line]
proc
file[:line]
proc
[file:]proc[:proc[...]][:line] No equivalent
Source line and code address
Source line and code address
Source line and code address
Source line and code address
Source line and code address
Code address
[file:]proc[:proc[...]][:#label] No equivalent
[class]::proc
[class]::proc
[class]::proc[:line]
[class]::proc[#label]
proc#line
No equivalent
No equivalent
No equivalent
No equivalent
No equivalent
No equivalent
[class]::proc#line
#label
Code address
Source line and code address
name@shared-library
Address of name in shared library
shared-library
16.5 XDB special language operators and HP WDB equivalents
The following table lists the XDB and the equivalent WDB commands for language
operators:
268 XDB to WDB Transition Guide
Table 16-18 Special language operators
XDB Language Operator
$addr
WDB Equivalent
Meaning
Depends on language
No equivalent
Unary operator, address of object
$in
Unary Boolean operator, execution
in procedure
$sizeof
sizeof
Unary operator, size of object
16.6 XDB special variables and HP WDB equivalents
GDB does not provide special variables of the kind that XDB has, but you can use show
and set to display and modify many debugger settings.
Table 16-19 Special variables
XDB Special Variable
$cplusplus
WDB Equivalent
No equivalent
Meaning
C++ feature control flags
$depth
No equivalent
No equivalent
No equivalent
show language
Default stack depth for local
variables
$fpa
Treat FPA sequence as one
instruction
$fpa_reg
$lang
Address register for FPA
sequences
Current language for expression
evaluation
$line
No equivalent
No equivalent
Current source line number
$malloc
Debugger memory allocation
(bytes)
$print
No equivalent
Display mode for character data
Hardware registers
$regname
$result
$regname
Use $n(value history number
assigned to the desired result)
Return value of last command line
procedure call
$signal
$step
No equivalent
No equivalent
Current child procedure signal
number
Number of instructions debugger
will step in non-debuggable
procedures before free-running
$var
$var
Dene or use special variable
(convenience variable)
16.6 XDB special variables and HP WDB equivalents 269
16.7 XDB variable identifiers and HP WDB equivalents
Table 16-20 Variable Identifiers
XDB Variable Identifier
WDB Equivalent
Meaning
Search for var
var
class::
var
class::
Search class for var(bug: not yet)
[[class]::]proc:[class::]var proc::var
Search proc for var(static
variables only)
[[class]::]proc:depth:[class::] No equivalent
Search proc for depth on stack
. (dot)
Empty string; for example, p is
the equivalent of p .
Shorthand for last thing you
looked at
:var or ::var
::varto distinguish a global from Search for global variable only
a local variable with same name
16.8 Alphabetical lists of XDB commands and HP WDB equivalents
•
•
•
•
•
•
•
•
•
•
16.8.1 A
Table 16-21 A
XDB Command
Equivalent WDB Command
No equivalent
a [cmds]
aa number
aa *
No equivalent
No equivalent
enable number
enable
ab number
ab *
ab @shared-library
No equivalent
270 XDB to WDB Transition Guide
Table 16-21 A (continued)
XDB Command
Equivalent WDB Command
abc cmds
No exact equivalent, but display expris equivalent
to abc print expr
am
am (with -xdb), set height num
No equivalent
apm oldpath [newpath]
apm "" [newpath]
No equivalent
16.8.2 B
Table 16-22 B
XDB Command
Equivalent WDB Command
b loc
b loc
b
b
ba address
bb [depth]
ba address(with -xdb), b *address
No equivalent (use b proc)
bc number expr
bc number expr(with -xdb), ignore number expr
(within a commands list)
bi expr.proc
bi -c expr
bi -C expr
bp
b class::proccond bnum (this == expr)
No equivalent
No equivalent
No equivalent
bp cmds
No equivalent
bpc -c class
bpc -C class
bpo proc
bpo class::proc
bpt
rb ^class::*
Use rb ^class::* for base classesalso
rb proc
b class::proc
No equivalent
bpt cmds
bpx
No equivalent
No equivalent
bpx cmds
bt proc
No equivalent
b proc commands bnum finish c end
16.8 Alphabetical lists of XDB commands and HP WDB equivalents 271
Table 16-22 B (continued)
XDB Command
Equivalent WDB Command
bu [depth]
bu [depth] (with -xdb). The finish command is
equivalent to the sequence bu, c, db (to continue
out of the current routine).
bx [depth]
bx [depth] (with -xdb)
16.8.3 C through D
Table 16-23 C through D
XDB Command
Equivalent WDB Command
c, continue
c
c location
until location
C
c, continue
C location
until location
D "dir"
D "dir" (with -xdb), dir pathname
No equivalent
No equivalent
clear
da number
da *
db
db number
delete number
delete
db *
dbc
undisplay
def name replacement-text
def name [GDB prompts for commands]
up
down
down number
dp
up number
No equivalent
No equivalent
No equivalent
No equivalent
No equivalent
dpm index
dpm *
Dpt
Dpx
272 XDB to WDB Transition Guide
16.8.4 F through K
Table 16-24 F through K
XDB Command
Equivalent WDB Command
No equivalent
f ["printf-style-fmt"]
fr
fr (with -xdb -tui), display $fregs (with -tui)
g line
g line (with -xdb), go line, tb line followed by jump
line
g #label
No equivalent
g {+ | -}lines
g {+ | -}lines (with -xdb), go {+ | -}lines tb {+ | -}lines
followed by jump {+ | -}lines
g {+ | -}
g {+ | -} (with -xdb), go {+ | -}1, tb {+ | -}1 followed
by jump {+ | -}1
gr
gr (with -xdb -tui), display $regs (with -tui)
h
h
if expr {cmds} [{cmds}]
if expr cmds [else cmds] end
I
k
info (many kinds), show (many kinds)
k
16.8.5 L
Table 16-25 L
XDB Command
Equivalent WDB Command
l (with -xdb), info args followed by info locals
L (with -xdb)
l
L
la
No equivalent
lb
lb (with -xdb), i b
lc [string]
ld
lc [string] (with -xdb), info common string
ld (with -xdb), show directories
lf (with -xdb), info sources
No equivalent
lf
lf [string]
lg [string]
ll [string]
lg [string] (with -xdb), info variables [string]
info functions [string], info variables [string], maint
print msymbolsfile
16.8 Alphabetical lists of XDB commands and HP WDB equivalents 273
Table 16-25 L (continued)
XDB Command
Equivalent WDB Command
show user [string]
lm [string]
lo [[class]::][string]
info func [[class]::][string]
info functions
lp
lp [[class]::]string
info func [[class]::]string info addr [[class]::]string
No equivalent
lpm
lr
lr (with -xdb), info all-reg
lr string (with -xdb), info reg string
No equivalent
lr string
ls [string]
lz
lz (with -xdb), info signals
16.8.6 M through P
Table 16-26 M through P
XDB Command
Equivalent WDB Command
No equivalent
M[{t | c} [expr[; expr...]]]
mm
info sharedlibrary
No equivalent
mm string
N
fo or rev
n
fo or rev
p expr[\format]
p[/format] expr [Note: The count and size portions
of formats are not allowed in the p (print) command.
They are allowed in the x command (examine
memory).]
p expr?format
p class::
p/format &expr
No equivalent
p $lang
show language
p {+ | -}[\format
Use x/format command to obtain initial value, then
use x with no argument to obtain value of next
memory location. To obtain value of previous
memory location, use "x $_ - 1".
pq expr
set expr, set var expr
No equivalent
pq expr?format
274 XDB to WDB Transition Guide
Table 16-26 M through P (continued)
XDB Command
pq class::
Equivalent WDB Command
No equivalent
No equivalent
pq [+ | -][\format
16.8.7 Q through S
Table 16-27 Q through S
XDB Command
Equivalent WDB Command
q
q
Q
Q (with -xdb), silent (must be first command in a
commands list)
r [arguments]
r [arguments]
R
R (with -xdb), r
s
s, si
s number
s number, si number
S (with -xdb), n, ni
S number (with -xdb), n number, ninumber
No equivalent
S
S number
sa number
sa *
No equivalent
sb number
disable number
sb *
disable
sb @shared-library
No equivalent
sm
sm (with -xdb), set height 0
sr (with -xdb -tui), display $sregs (with -tui)
No equivalent
sr
ss file
16.8.8 T
Table 16-28 T
XDB Command
Equivalent WDB Command
t [depth] (with -xdb), bt [depth]
t [depth]
T [depth]
T [depth] (with -xdb), bt full [depth]
16.8 Alphabetical lists of XDB commands and HP WDB equivalents 275
Table 16-28 T (continued)
XDB Command
Equivalent WDB Command
No equivalent
ta
tb
No equivalent
tc
No equivalent
td
td (with -xdb -tui)
tf (with -xdb -tui), toggle $fregs (with -tui)
No equivalent
tf
tm
top
tr [@]
ts
frame 0
No equivalent
ts (with -xdb -tui)
16.8.9 U through Z
Table 16-29 U through Z
XDB Command
Equivalent WDB Command
u (with -xdb -tui), update (with -tui)
U (with -xdb -tui), refresh (with -tui)
def name [follow with empty command list]
No equivalent
u
U
undef name
undef *
up
down
up number
v
down number
v (with -xdb), list
v location
V [depth]
va address
va label
va label + offset
w number
v location (with -xdb), list location
V [depth] (with -xdb), frame [depth]
va address (with -xdb), disas address
va label (with -xdb), disas label
va label + offset (with -xdb), disas label + offset
w number (with -xdb -tui), winheight src number
(with - tui)
x [expr]
No equivalent
xdb program
gdb -xdb program, gdb -xdb -tui program
276 XDB to WDB Transition Guide
Table 16-29 U through Z (continued)
XDB Command
xdb program corefile
xdb -d dir
Equivalent WDB Command
gdb -xdb program -c corefile
gdb -xdb -d dir
xdb -P pid program
xdb -i
gdb -xdb program pid
(after starting) run < file
(after starting) run > file
xdb -o
z number s
z number s (with -xdb), handle number stop, handle
number nostop
z number i
z number r
z number Q
z number i (with -xdb), handle number nopass,
handle number pass
z number r (with -xdb), handle number print,
handle number noprint
z number Q (with -xdb), handle number noprint
16.8.10 Symbols
Table 16-30 Symbols
XDB Command
Equivalent WDB Command
line
line
file[:line]
file[:line]
proc
proc
[file:]proc[:proc[...]][:line]
[file:]proc[:proc[...]][:#label]
[class]::proc
No equivalent
No equivalent
[class]::proc
No equivalent
[class]::proc[:line]
[class]::proc[#label]
proc#line
No equivalent
No equivalent
name@shared-library
var
No equivalent
var
class::var
class::var (bug: not yet)
proc::var (static variables only)
No equivalent
[[class]::]proc:[class::]var
[[class]::]proc:depth:[class::]var
16.8 Alphabetical lists of XDB commands and HP WDB equivalents 277
Table 16-30 Symbols (continued)
XDB Command
Return
Equivalent WDB Command
Return
"any string"
. (dot)
p "any string"
Empty string; for example, p is the equivalent
of p .
-
Return
{+ | -}r
{+ | -}r (with -xdb -tui), {+ | -} data
(with -tui)
{+ | -}[number]
{+ | -}[ number](with -tui; note that a space
is required between + or - and the number)
/[string]
/[string] (with -xdb), search regexp,
forw regexp
?[string]
?[string] (with -xdb), rev regexp
;
No equivalent (one command per line in command
list)
:var or ::var
::var
! cmd_line
{cmd_list}
<file
<<file
>
! cmd line (with -xdb), she cmd line
commands [number]... end
source file
No equivalent
No equivalent
>file
>c
No equivalent
No equivalent
>f
No equivalent
>t
No equivalent
>@[c | f | t]
>@file
>>
No equivalent
No equivalent
No equivalent
>>file
>>@
No equivalent
No equivalent
>>@file
No equivalent
278 XDB to WDB Transition Guide
Table 16-30 Symbols (continued)
XDB Command
Control-C
Equivalent WDB Command
Control-C
# [text]
# [text]
#label
No equivalent
16.8 Alphabetical lists of XDB commands and HP WDB equivalents 279
280
17 Controlling GDB
You can alter the way GDB interacts with you by using the set command. For commands
described here.
17.1 Setting the GDB Prompt
GDB indicates its readiness to read a command by printing a string called the prompt.
This string is normally `((gdb))'. You can change the prompt string with the set prompt
command. For instance, when debugging GDB with GDB, it is useful to change the
prompt in one of the GDB sessions so that you can always tell which one you are talking
to.
NOTE: set prompt does not add a space for you after the prompt you set. This allows
you to set a prompt which ends in a space or a prompt that does not.
set prompt newprompt
Directs GDB to use newpromptas its prompt string
henceforth.
show prompt
Prints a line of the form: “Gdb's prompt is:
your-prompt”
17.2 Setting Command Editing Options in GDB
GDB reads its input commands via the readline interface. This gnu library provides
consistent behavior for programs which provide a command line interface to the user.
Ad- vantages are gnu Emacs-style or vi-style inline editing of commands, csh-like
history substitution, and a storage and recall of command history across debugging
sessions.
You may control the behavior of command line editing in GDB with the command set.
set editing, set editing Enable command line editing (enabled by default).
on
set editing off
show editing
Disable command line editing.
Show whether command line editing is enabled.
17.3 Setting Command History Feature in GDB
GDB can keep track of the commands you type during your debugging sessions, so
that you can be certain of precisely what happened. Use these commands to manage
the GDB command history facility.
To make command history understand your vi key bindings you need to create a ~/
.inputrcfile with the following contents:
17.1 Setting the GDB Prompt 281
set editing-mode vi
The readline interface uses the .inputrcfile to
control the settings.
set history filename fname
Set the name of the GDB command history file
to fname. This is the file where GDB reads an
initial command history list, and where it writes
the command history from this session when it
exits. You can access this list through history
expansion or through the history command
editing characters listed below. This file defaults
to the value of the environment variable
GDBHISTFILE, or to ./.gdb_history(./
_gdb_historyon MS-DOS) if this variable is
not set.
set history save, set history save on Record command history in a file, whose name
may be specified with the set history
filenamecommand. By default, this option is
disabled.
set history save off
Stop recording command history in a file.
set history size size
Set the number of commands which GDB keeps
in its history list. This defaults to the value of the
environment variable HISTSIZE, or to 256 if this
variable is not set.
History expansion assigns special meaning to the character !.
Since !is also the logical not operator in C, history expansion is o by default. If you
decide to enable history expansion with the set history expansion on command, you
may sometimes need to follow !(when it is used as logical not, in an expression) with
a space or a tab to prevent it from being expanded. The readline history facilities do
not attempt substitution on the strings !=and !(, even when history expansion is
enabled.
The commands to control history expansion are:
set history expansion on, set history Enable history expansion. History expansion is
expansion
o by default.
set history expansion off
Disable history expansion.
The readline code comes with more complete
documentation of editing and history expansion
features. Users unfamiliar with GNUEmacs or vi
may wish to read it.
show history, show history filename, These commands display the state of the GDB
show history save, show history
size, show history expansion
history parameters. show historyby itself
displays all four states.
282 Controlling GDB
show commands
show commands n
show commands +
Display the last ten commands in the command
history.
Print ten commands centered on command
number n.
Print ten commands just after the commands last
printed.
17.4 Setting the GDB Screen Size
Certain commands to GDB may produce large amounts of information output to the
screen. To help you read all of it, GDB pauses and asks you for input at the end of each
page of output. Type RET when you want to continue the output, or qto discard the
remaining output. Also, the screen width setting determines when to wrap lines of
output. Depending on what is being printed, GDB tries to break the line at a readable
place, rather than simply letting it over flow onto the following line.
Normally GDB knows the size of the screen from the terminal driver software. For
example, on Unix, GDB uses the termcap data base together with the value of the TERM
environment variable and the sttyrows and sttycols settings. If this is not correct,
you can override it with the set heightand set widthcommands:
set height lpp, show These setcommands specify a screen height of lpplines and
height se, set width a screen width of cplcharacters. The associated show
cpl, show width
commands display the current settings.
If you specify a height of zero lines, GDB does not pause during
output no matter how long the output is. This is useful if output
is to a file or to an editor buffer.
Likewise, you can specify set width 0to prevent GDB from
wrapping its output.
17.5 Supported Number Formats
You can always enter numbers in octal, decimal, or hexadecimal in GDB by the usual
conventions: octal numbers begin with `0', decimal numbers end with `.', and
hexadecimal numbers begin with `0x'. Numbers that begin with none of these are, by
default, entered in base 10; likewise, the default display for numbers|when no particular
format is specified| is base 10. You can change the default base for both input and
output with the set radix command.
set input-radix base
Set the default base for numeric input. Supported
choices for base are decimal 8, 10, or 16. basemust
itself be specified either unambiguously or using the
current default radix; for example, any of
set radix 012
set radix 10
17.4 Setting the GDB Screen Size 283
set radix 0xa
sets the base to decimal. On the other hand, set
radix 10leaves the radix unchanged no matter
what it was.
set output-radix base
Set the default base for numeric display. Supported
choices for baseare decimal 8, 10, or 16. basemust
itself be specified either unambiguously or using the
current default radix.
show input-radix
show output-radix
Display the current default base for numeric input.
Display the current default base for numeric display.
17.6 Optional warnings and messages
By default, GDB is silent about its inner workings. If you are running on a slow machine,
you may want to use the set verbosecommand. This makes GDB tell you when it
does a lengthy internal operation, so you will not think it has crashed.
Currently, the messages controlled by set verbose are those which announce that the
symbol table for a source file is being read; see symbol-file in “Commands to specify
set verbose on
set verbose off
show verbose
Enables GDB output of certain informational messages.
Disables GDB output of certain informational messages.
Displays whether set verbose is on or o.
By default, if GDB encounters bugs in the symbol table of an object file, it is silent; but
if you are debugging a compiler, you may nd this information useful (see “Specifying
set complaints limit
Permits GDB to output limitcomplaints about each
type of unusual symbols before becoming silent about
the problem. Set limitto zero to suppress all
complaints; set it to a large number to prevent
complaints from being suppressed.
show complaints
Displays how many symbol complaints GDB is
permitted to produce.
By default, GDB is cautious, and asks the user to confirm on certain commands. For
example, if you try to run a program which is already running:
((gdb)) run
The program being debugged has been started already.
Start it from the beginning? (y or n)
If you are willing to unflinchingly face the consequences of your own commands, you
can disable this feature:
set confirm off
Disables confirmation requests.
284 Controlling GDB
set confirm on
show confirm
Enables confirmation requests (the default).
Displays state of confirmation requests.
17.7 Optional messages about internal happenings
set debug arch
Turns on or off display of gdbarchdebugging info.
The default is off
show debug arch
set debug event
Displays the current state of displaying gdbarch
debugging information.
Turns on or o display of GDB event debugging
information. The default is o.
show debug event
set debug expression
show debug expression
set debug overload
Displays the current state of displaying GDB event
debugging info.
Turns on or off display of GDB expression debugging
information. The default is o.
Displays the current state of displaying GDB
expression debugging info.
Turns on or o display of GDB C++ overload
debugging info. This includes info such as ranking
of functions, etc. The default is o.
show debug overload
set debug remote
Displays the current state of displaying GDB C++
overload debugging info.
Turns on or o display of reports on all packets sent
back and forth across the serial line to the remote
machine. The info is printed on the GDB standard
output stream. The default is o.
show debug remote
set debug serial
Displays the state of display of remote packets.
Turns on or o display of GDB serial debugging info.
The default is o.
show debug serial
set debug target
Displays the current state of displaying GDB serial
debugging info.
Turns on or o display of GDB target debugging info.
This info includes what is going on at the target level
of GDB, as it happens. The default is o.
show debug target
set debug varobj
Displays the current state of displaying GDB target
debugging info.
Turns on or o display of GDB variable object
debugging info. The default is o.
17.7 Optional messages about internal happenings 285
show debug varobj
Displays the current state of displaying GDB variable
object debugging info.
286 Controlling GDB
18 Canned Sequences of Commands
provides the following two ways to store sequence of commands for execution as a
unit:
•
•
user-defined commands
command files
18.1 User-defined commands
A user-defined command is a sequence of GDB commands to which you assign a new
name as a command. This is done with the definecommand. User commands may
accept up to 10 arguments separated by whitespace. Arguments are accessed within
the user command via $arg0. . . $arg9. The following example illustrates the use
of canned sequence of commands:
define adder
print $arg0 + $arg1 + $arg2
To execute the command use:
adder 1 2 3
This defines the command adder, which prints the sum of its three arguments. Note
the arguments are text substitutions, so they may reference variables, use complex
expressions, or even perform further functions calls.
The following constructs can be used to create canned sequence of commands:
define commandname
Define a command named commandname. If there is
already a command by that name, you are asked to
confirm that you want to redefine it. The definition
of the command is made up of other GDB command
lines, which are given following the define
command. The end of these commands is marked by
a line containing end.
if
Takes a single argument, which is an expression to
evaluate. It is followed by a series of commands that
are executed only if the expression is true (nonzero).
The ifclause can be followed by an optional else
clause. You can add a list of commands to the else
clause which get executed only if the expression is
false.
while
The syntax is similar to if:the command takes a
single argument, which is an expression to evaluate,
and must be followed by the commands to execute,
one per line, terminated by an end. The commands
18.1 User-defined commands 287
are executed repeatedly as long as the expression
evaluates to true.
document commandname
Document the user-defined command commandname,
so that it can be accessed by help. The command
commandnamemust already be defined. This
command reads lines of documentation just as define
reads the lines of the command definition, ending
with end. After the document command is finished,
help on command commandnamedisplays the
documentation you have written.
You may use the document command again to change
the documentation of a command. Redefining the
command with define does not change the
documentation.
help user-defined
List all user-defined commands, with the first line of
the documentation (if any) for each.
show user, show user
commandname
Display the GDB commands used to define
commandname(but not its documentation). If no
commandnameis given, display the definitions for
all user- defined commands.
When user-defined commands are executed, the commands of the definition are not
printed. An error in any command stops execution of the user-defined command.
If used interactively, commands that would ask for confirmation proceed without
asking when used inside a user-defined command. Many GDB commands that normally
print messages to say what they are doing omit the messages when used in a
user-defined command.
18.2 User-defined command hooks
You may define hooks, which are a special kind of user-defined command. Whenever
you run the command foo, if the user-defined command hook-fooexists, it is executed
(with no arguments) before that command.
In addition, a pseudo-command, stopexists. Defining (hook-stop) makes the
associated commands execute every time execution stops in your program: before
breakpoint commands are run, displays are printed, or the stack frame is printed.
For example, to ignore SIGALRMsignals while single-stepping, and treat them normally
during normal execution, you could define:
define hook-stop
handle SIGALRM nopass
end
define hook-run
handle SIGALRM pass
288 Canned Sequences of Commands
end
define hook-continue
handle SIGLARM pass
end
You can define a hook for any single-word command in GDB, and not for command
aliases; Also you should define a hook for the basic command name, for example,
backtracerather than bt. If an error occurs during the execution of your hook,
execution of GDB commands stops and GDB issues a prompt (before the command
that you actually typed had a chance to run).
If you try to define a hook which does not match any known command, GDB issues a
warning from the definecommand.
18.3 Command files
A command file for GDB is a file of lines that are GDB commands. Comments (lines
starting with #) may also be included. An empty line in a command file does nothing;
it does not mean to repeat the last command, as it would from the terminal.
When you start GDB, it executes commands from its initfiles. These are files named
.gdbiniton UNIX. During startup, GDB does the following:
4
1. Read the init file (if any) in your home directory.
2. Process command-line options and operands.
3. Read the init file (if any) in the current working directory,
4. Read the init file (if any) in the /tmpdirectory if the GDB_PROCESS_TMP_GDBINIT
environment variable is set.
5. Read command files specified by the `-x' option.
The init file in your home directory can set options (such as `set complaints') that affect
subsequent processing of command line options and operands. Init files are not executed
It can be useful to create a `.gdbinit' file in the directory where you are debugging an
application. This file will set the actions that apply for this application.
For example, one might add lines like:
dir /usr/src/path/to/source/files
to add source directories or:
break fatal
to set breakpoints on fatal error routines or diagnostic routines.
On some configurations of GDB, the initfile is known by a different name (these are
typically environments where a specialized form of GDB may need to coexist with
other forms, hence a different name for the specialized version's initfile). These are
the environments with special initfile names:
18.3 Command files 289
•
•
•
VxWorks (Wind River Systems real-time OS): .vxgdbinit
OS68K (Enea Data Systems real-time OS): .os68gdbinit
ES-1800 (Ericsson Telecom AB M68000 emulator): .esgdbinit
You can also request the execution of a command file with the sourcecommand:
source filename Execute the command file filename.
The lines in a command file are executed sequentially. They are not printed as they are
executed. An error in any command terminates execution of the command file.
Commands that would ask for confirmation if used interactively proceed without
asking when used in a command file. Many GDB commands that normally print
messages to say what they are doing omit the messages when called from command
4
files.
18.4 Commands for controlled output
During the execution of a command file or a user-defined command, normal GDB
output is suppressed; the only output that appears is what is explicitly printed by the
commands in the definition. This section describes three commands useful for generating
exactly the output you want.
echo text
Print text. Nonprinting characters can be
included in textusing C escape sequences, such
as \n to print a newline. No newline is printed
unless you specify one. In addition to the
standard C escape sequences, a backslash
followed by a space stands for a space. This is
useful for displaying a string with spaces at the
beginning or the end, since leading and trailing
spaces are otherwise trimmed from all
arguments. To print and foo =, use the
command echo \and foo = \.
A backslash at the end of text can be used, as in
C, to continue the command onto subsequent
lines. For example,
echo This is some text\n\
which is continued\n\
onto several lines.\n
produces the same output as
echo This is some text\n
echo which is continued\n
echo onto several lines.\n
output expression
Print the value of expression and nothing but
that value: no newlines, no `$nn = '. The value is
4. On DOS/Windows systems, the home directory is the one pointed to by the HOME environment variable.
290 Canned Sequences of Commands
not entered in the value history either. See
output/fmt expression
Print the value of expression in format fmt. You
can use the same formats as for print. See
printf string, expressions...
Print the values of the expressionsunder the
control of string. The expressionsare
separated by commas and may be either numbers
or pointers. Their values are printed as specified
by string, exactly as if your program were to
execute the C subroutine
printf (string, expressions...);
For example, you can print two values in hex like
this:
printf "foo, bar-foo = 0x%x, 0x%x\n",
foo, bar-foo
The only backslash-escape sequences that you
can use in the format string are the simple ones
that consist of backslash followed by a letter.
18.4 Commands for controlled output 291
292
19 Using GDB under gnu Emacs
A special interface allows you to use gnu Emacs to view (and edit) the source files for
the program you are debugging with GDB.
To use this interface, use the command M-x gdb in Emacs. Give the executable file you
want to debug as an argument. This command starts GDB as a subprocess of Emacs,
with input and output through a newly created Emacs buffer.
Using GDB under Emacs is just like using GDB normally except for two things:
•
All terminalinput and output goes through the Emacs buffer.
This applies both to GDB commands and their output, and to the input and output
done by the program you are debugging.
This is useful because it means that you can copy the text of previous commands
and input them again; you can even use parts of the output in this way.
All the facilities of Emacs' Shell mode are available for interacting with your
program. In particular, you can send signals the usual way|for example, C-c
C-cfor an interrupt, C-c C-zfor a stop.
•
GDB displays source code through Emacs.
Each time GDB displays a stack frame, Emacs automatically finds the source file
for that frame and puts an arrow (`=>') at the left margin of the current line. Emacs
uses a separate buffer for source display, and splits the screen to show both your
GDB session and the source.
Explicit GDB list or search commands still produce output as usual, but you
probably have no reason to use them from Emacs.
Warning: If the directory where your program resides is not your current di-
rectory, it can be easy to confuse Emacs about the location of the source files,
in which case the auxiliary display buffer does not appear to show your source.
GDB can nd programs by searching your environment's PATH variable, so the
GDB input and output session proceeds normally; but Emacs does not get
enough information back from GDB to locate the source files in this situation.
To avoid this problem, either start GDB mode from the directory where your
program resides, or specify an absolute file name when prompted for the M-x
gdb argument.
A similar confusion can result if you use the GDB file command to switch to
debugging a program in some other location, from an existing GDB buffer in
Emacs.
By default, M-x gdb calls the program called `gdb'. If you need to call GDB by a
different name (for example, if you keep several configurations around, with
different names) you can set the Emacs variable gdb-command-name; for example,
(setq gdb-command-name "mygdb")
(preceded by M-:or ESC:, or typed in the *scratch* buffer, or in your .emacs
file) makes Emacs call the program named mygdbinstead.
293
In the GDB I/O buffer, you can use these special Emacs commands in addition to the
standard Shell mode commands:
C-h m
Describe the features of Emacs' GDB Mode.
M-s
Execute to another source line, like the GDB step command; also
update the display window to show the current file and location.
M-n
Execute to next source line in this function, skipping all function
calls, like the GDB nextcommand. Then update the display
window to show the current file and location.
M-i
Execute one instruction, like the GDB stepicommand; update
display window accordingly.
M-x gdb-nexti
C-c C-f
Execute to next instruction, using the GDB nexticommand;
update display window accordingly.
Execute until exit from the selected stack frame, like the GDB
finishcommand.
M-c
Continue execution of your program, like the GDB continue
command.
WARNING! In Emacs v19, this command is C-c C-p.
M-u
Go up the number of frames indicated by the numeric argument
(see section "Numeric Arguments" in The gnu Emacs Manual), like
the GDB upcommand.
WARNING! In Emacs v19, this command is C-c C-u.
M-d
Go down the number of frames indicated by the numeric
argument, like the GDB downcommand.
WARNING! In Emacs v19, this command is C-c C-d.
C-x &
Read the number where the cursor is positioned, and insert it at
the end of the GDB I/O buffer. For example, if you wish to
disassemble code around an address that was displayed earlier,
type disassemble; then move the cursor to the address display,
and pick up the argument for disassemble by typing C-x &.
You can customize this further by defining elements of the list
gdb-print- command; once it is defined, you can format or
otherwise process numbers picked up by C-x &before they are
inserted. A numeric argument to C-x &indicates that you wish
special formatting, and also acts as an index to pick an element
of the list. If the list element is a string, the number to be inserted
294 Using GDB under gnu Emacs
is formatted using the Emacs function format; otherwise the
number is passed as an argument to the corresponding list
element.
In any source file, the Emacs command C-x SPC (gdb-break)tells GDB to set a
break- point on the source line point is on.
If you accidentally delete the source-display buffer, an easy way to get it back is to type
the command fin the GDB buffer, to request a frame display; when you run under
Emacs, this recreates the source buffer if necessary to show you the context of the
current frame.
The source files displayed in Emacs are in ordinary Emacs buffers which are visiting
the source files in the usual way. You can edit the files with these buffers if you wish;
but keep in mind that GDB communicates with Emacs in terms of line numbers. If you
add or delete lines from the text, the line numbers that GDB knows cease to correspond
properly with the code.
295
296
20 GDB Annotations
This chapter describes annotations in GDB. Annotations are designed to interface GDB
to graphical user interfaces or other similar programs which want to interact with GDB
at a relatively high level.
20.1 What is an annotation?
To produce annotations, start GDB with the --annotate=2option.
Annotations start with a newline character, two control-zcharacters, and the name
of the annotation. If there is no additional information associated with this annotation,
the name of the annotation is followed immediately by a newline. If there is additional
information, the name of the annotation is followed by a space, the additional
information, and a newline. The additional information cannot contain newline
characters.
Any output not beginning with a newline and two control-z characters denotes
literal output from GDB. Currently there is no need for GDB to output a newline
followed by two control-zcharacters, but if there was such a need, the annotations
could be extended with an `escape' annotation which means those three characters as
output.
A simple example of starting up GDB with annotations is:
$ gdb --annotate=2
GNU GDB 5.0
Copyright 2000 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License,
and you are welcome to change it and/or distribute copies of it
under certain conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB. Type "show warranty"
for details.
This GDB was configured as "sparc-sun-sunos4.1.3"
^Z^Zpre-prompt
(gdb)
^Z^Zprompt
quit
^Z^Zpost-prompt
$
Here quitis input to GDB; the rest is output from GDB. The three lines beginning
`^Z^Z' (where `^Z' denotes a control-zcharacter) are annotations; the rest is output
from GDB.
20.2 The server prefix
To issue a command to GDB without affecting certain aspects of the state which is seen
by users, prefix it with server. This means that this command will not affect the
20.1 What is an annotation? 297
command history, nor will it affect GDB's notion of which command to repeat if RET
is pressed on a line by itself.
The server prefix does not affect the recording of values into the value history; to print
a value without recording it into the value history, use the outputcommand instead
of the printcommand.
20.3 Values
When a value is printed in various contexts, GDB uses annotations to delimit the value
from the surrounding text.
If a value is printed using print and added to the value history, the annotation looks
like:
^Z^Zvalue-history-begin history-number value-flags
history-string
^Z^Zvalue-history-value
the-value
^Z^Zvalue-history-end
where history-numberis the number it is getting in the value history,
history-stringis a string, such as $5 = , which introduces the value to the user,
the-valueis the output corresponding to the value itself, and value- flagsis `*'
for a value which can be dereferenced and `-' for a value which cannot.
If the value is not added to the value history (it is an invalid float or it is printed with
the outputcommand), the annotation is similar:
^Z^Zvalue-begin value-flags
the-value
^Z^Zvalue-end
When GDB prints an argument to a function (for example, in the output from the
backtracecommand), it annotates it as follows:
^Z^Zarg-begin
argument-name
^Z^Zarg-name-end
separator-string
^Z^Zarg-value value-flags
the-value
^Z^Zarg-end
where argument-nameis the name of the argument, separator-stringis text
which separates the name from the value for the user's benefit (such as =), and
value-flagsand the-valuehave the same meanings as in a
value-history-beginannotation.
When printing a structure, GDB annotates it as follows:
^Z^Zfield-begin value-flags
field-name
^Z^Zfield-name-end
separator-string
298 GDB Annotations
^Z^Zfield-value
the-value
^Z^Zfield-end
where field-nameis the name of the field, separator-stringis text which
separates the name from the value for the user's benefit (such as `='), and value-flags
and the-valuehave the same meanings as in a value-history-beginannotation.
When printing an array, GDB annotates it as follows:
^Z^Zarray-section-begin array-index value-flags
where array-indexis the index of the first element being annotated and
value-flagshas the same meaning as in a value-history-beginannotation.
This is followed by any number of elements, where the element can be either a single
element or a repeated element as shown in the examples below:
`,' whitespace ; omitted for the first element
the-value
^Z^Zelt
`,' whitespace ; omitted for the first element
the-value
^Z^Zelt-rep number-of-repititions
repetition-string
^Z^Zelt-rep-end
In both cases, the-valueis the output for the value of the element and whitespace
can contain spaces, tabs, and newlines. In the repeated case, number-of-repititons
is the number of consecutive array elements which contain that value, and
repetition-stringis a string which is designed to convey to the user that repetition
is being depicted.
Once all the array elements have been output, the array annotation is ended with:
^Z^Zarray-section-end
20.4 Frames
Whenever GDB prints a frame, it annotates it. For example, this applies to frames
printed when GDB stops, output from commands such as backtrace or up, etc.
The frame annotation begins with:
^Z^Zframe-begin level address
level-string
where levelis the number of the frame (0 is the innermost frame, and other frames
have positive numbers), addressis the address of the code executing in that frame,
and level-stringis a string designed to convey the level to the user. addressis
in the form `0x' followed by one or more lowercase hex digits (note that this does not
depend on the language). The frame ends with:
^Z^Zframe-end
Between these annotations is the main body of the frame, which can consist of:
20.4 Frames 299
• ^Z^Zfunction-call
function-call-string
where function-call-stringis text designed to convey to the user that this
frame is associated with a function call made by GDB to a function in the program
being debugged.
• ^Z^Zsignal-handler-caller
signal-handler-caller-string
where signal-handler-caller-stringis text designed to convey to the user
that this frame is associated with whatever mechanism is used by this operating
system to call a signal handler (it is the frame which calls the signal handler, not
the frame for the signal handler itself).
•
A normal frame.
This can optionally (depending on whether this is thought of as interesting
information for the user to see) begin with
^Z^Zframe-address
address
^Z^Zframe-address-end
separator-string
where addressis the address executing in the frame (the same address as in the
frame-beginannotation, but printed in a form which is intended for user
consumption|in particular, the syntax varies depending on the language), and
separator-stringis a string intended to separate this address from what
follows for the user's benefit.
Then comes
^Z^Zframe-function-name
function-name
^Z^Zframe-args
arguments
where function-nameis the name of the function executing in the frame, or `??'
if not known, and argumentsare the arguments to the frame, with parentheses
around them (each argument is annotated individually as well, see “Values”
If source information is available, a reference to it is then printed:
^Z^Zframe-source-begin
source-intro-string
^Z^Zframe-source-file
filename
^Z^Zframe-source-file-end
:
^Z^Zframe-source-line
line-number
^Z^Zframe-source-end
300 GDB Annotations
where source-intro-stringseparates for the user's benefit the reference from
the text which precedes it, filenameis the name of the source file, and
line-numberis the line number within that file (the first line is line 1).
If GDB prints some information about where the frame is from (which library,
which load segment, etc.; currently only done on the RS/6000), it is annotated with
^Z^Zframe-where
information
Then, if source is to be actually displayed for this frame (for example, this is not
true for output from the backtrace command), then a source annotation (see
“Displaying source” (page 304)) is displayed. Unlike most annotations, this is output
instead of the normal text which would be output, not in addition.
20.5 Displays
When GDB is told to display something using the displaycommand, the results of
the display are annotated:
^Z^Zdisplay-begin
number
^Z^Zdisplay-number-end
number-separator
^Z^Zdisplay-format
format
^Z^Zdisplay-expression
expression
^Z^Zdisplay-expression-end
expression-separator
^Z^Zdisplay-value
value
^Z^Zdisplay-end
where numberis the number of the display, number-separatoris intended to
separate the number from what follows for the user, formatincludes information
such as the size, format, or other informationabout how the value is being displayed,
expressionis the expression being displayed, expression-separatoris intended
to separate the expression from the text that follows for the user,and valueis the actual
value being displayed.
20.6 Annotation for GDB input
When GDB prompts for input, it annotates this fact so it is possible to know when to
send output, when the output from a given command is over, etc.
Different kinds of input each have a different input type. Each input type has three
annotations: a preannotation, which denotes the beginning of any prompt which is
being output, a plain annotation, which denotes the end of the prompt, and then a post-
annotation which denotes the end of any echo which may (or may not) be associated
with the input. For example, the prompt input type features the following annotations:
20.5 Displays 301
^Z^Zpre-prompt
^Z^Zprompt
^Z^Zpost-prompt
The input types are:
prompt
When GDB is prompting for a command (the main GDB
prompt).
commands
When GDB prompts for a set of commands, like in the
commands command. The annotations are repeated for
each command which is input.
overload-choice
query
When GDB wants the user to select between various
overloaded functions.
When GDB wants the user to confirm a potentially
dangerous operation.
prompt-for-continue
When GDB is asking the user to press return to continue.
Note: Don't expect this to work well; instead use set
height 0to disable prompting. This is because the
counting of lines is buggy in the presence of annotations.
20.7 Errors
^Z^Zquit
This annotation occurs right before GDB responds to an interrupt.
^Z^Zerror
This annotation occurs right before GDB responds to an error.
Quit and error annotations indicate that any annotations which GDB was in the middle
of may end abruptly. For example, if a value-history-beginannotation is followed
by a error, one cannot expect to receive the matching value-history-end. One
cannot expect not to receive it either; however, an error annotation does not necessarily
mean that GDB is immediately returning all the way to the top level.
A quit or error annotation may be preceded by:
^Z^Zerror-begin
Any output between that and the quit or error annotation is the error message.
Warning messages are not yet annotated.
20.8 Information on breakpoints
The output from the info breakpoints command is annotated as follows:
^Z^Zbreakpoints-headers
header-entry
^Z^Zbreakpoints-table
302 GDB Annotations
where header-entryhas the same syntax as an entry (see below) but instead of
containing data, it contains strings which are intended to convey the meaning of each
field to the user. This is followed by any number of entries. If a field does not apply
for this entry, it is omitted. Fields may contain trailing whitespace. Each entry consists
of:
^Z^Zrecord
^Z^Zfield 0
number
^Z^Zfield 1
type
^Z^Zfield 2
disposition
^Z^Zfield 3
enable
^Z^Zfield 4
address
^Z^Zfield 5
what
^Z^Zfield 6
frame
^Z^Zfield 7
condition
^Z^Zfield 8
ignore-count
^Z^Zfield 9
commands
Note that addressis intended for user consumption|the syntax varies depending on
the language.
The output ends with:
^Z^Zbreakpoints-table-end
20.9 Invalidation notices
The following annotations say that certain pieces of state may have changed:
^Z^Zframes-invalid
The frames (for example, output from the
backtrace command) may have changed.
^Z^Zbreakpoints-invalid
The breakpoints may have changed. For example,
the user just added or deleted a breakpoint.
20.10 Running the program
When the program starts executing due to a GDB command such as stepor continue,
^Z^Zstarting
is output. When the program stops,
^Z^Zstopped
20.9 Invalidation notices 303
is output. Before the stoppedannotation, a variety of annotations describe how the
program stopped.
^Z^Zexited exit-status
The program exited, and exit-statusis the exit
status (zero for successful exit, otherwise nonzero).
^Z^Zsignalled
The program exited with a signal. After the
^Z^Zsignalled, the annotation continues:
intro-text
^Z^Zsignal-name
name
^Z^Zsignal-name-end
middle-text
^Z^Zsignal-string
string
^Z^Zsignal-string-end
end-text
where nameis the name of the signal, such as
SIGILL or SIGSEGV, and stringis the explanation
of the signal, such as Illegal Instructionor
Segmentation fault. intro-text,
middle-text, and end-textare for the user's
benefit and have no particular format.
^Z^Zsignal
The syntax of this annotation is just like signalled,
but GDB is just saying that the program received
the signal, not that it was terminated with it.
^Z^Zbreakpoint number
The program hit breakpoint number number.
^Z^Zwatchpoint number
The program hit watchpoint number number.
20.11 Displaying source
The following annotation is used instead of displaying source code:
^Z^Zsource filename:line:character:middle:addr
where filenameis an absolute file name indicating which source file, lineis the line
number within that file (where 1 is the first line in the file), characteris the character
position within the file (where 0 is the first character in the file, for most debug formats
this will necessarily point to the beginning of a line), middleis `middle' if addris in
the middle of the line, or `beg' if addris at the beginning of the line, and addris the
address in the target program associated with the source which is being displayed.
addris in the form `0x' followed by one or more lowercase hex digits (note that this
does not depend on the language).
304 GDB Annotations
20.12 Annotations We Might Want in the Future
•
target-invalid
the target might have changed (registers, heap contents, or execution status). For
performance, we might eventually want to hit registers-invalidand
all-registers-invalidwith greater precision
•
•
systematic annotation for set/show parameters (including invalidation notices).
similarly, `info' returns a list of candidates for invalidation notices.
20.12 Annotations We Might Want in the Future 305
306
21 The GDB/MIInterface
Function and purpose
GDB/MIis a line based machine oriented text interface to GDB. It is specifically intended
to support the development of systems which use the debugger as just one small
component of a larger system.
This chapter is a specification of the GDB/MIinterface. It is written in the form of a
reference manual.
Notation and terminology
This chapter uses the following notation:
• |separates two alternatives.
•
•
[ something] indicates that somethingis optional: it may or may not be given.
( group)* means that groupinside the parentheses may repeat zero or more
times.
•
•
( group)+ means that groupinside the parentheses may repeat one or more times.
“string” means a literal string.
Acknowledgments
In alphabetic order: Andrew Cagney, Fernando Nasser, Stan Shebs and Elena Zannoni.
21.1 GDB/MICommand Syntax
21.1.1 GDB/MIInput syntax
command
cli-command| mi-command
cli-command
[ token] cli-command nl, where cli-commandis
any existing GDB CLI command.
mi-command
[ token] "-" operation( " " option)* [ " --" ] ( "
" parameter)* nl
token
"any sequence of digits"
option
"-" parameter[ " " parameter]
non-blank-sequence| c-string
any of the operations described in this chapter
anything, provided it does not contain special
characters such as “-”, nl, """ and of course “”
parameter
operation
non-blank-sequence
c-string
nl
""" seven-bit-iso-c-string-content"""
CR | CR-LF
21.1 GDB/MI Command Syntax 307
Notes:
•
The CLI commands are still handled by the MIinterpreter; their output is described
below.
•
•
The token, when present, is passed back when the command finishes.
Some MIcommands accept optional arguments as part of the parameter list. Each
option is identified by a leading `-' (dash) and may be followed by an optional
argument parameter. Options occur first in the parameter list and can be delimited
from normal parameters using `--' (this is useful when some parameters begin
with a dash).
Pragmatics:
•
•
We want easy access to the existing CLI syntax (for debugging).
We want it to be easy to spot a MIoperation.
21.1.2 GDB/MIOutput syntax
The output from GDB/MIconsists of zero or more out-of-band records followed,
optionally, by a single result record. This result record is for the most recent command.
The sequence of output records is terminated by '(gdb)'.
If an input command was prefixed with a token then the corresponding output for that
command will also be prefixed by that same token.
output →
( out-of-band-record )* [
result-record ] "(gdb)" nl
result-record
[ token ] "^" result-class ( ","
result )* nl
out-of-band-record →
async-record | stream-record
async-record
exec-async-output |
status-async-output |
notify-async-output
exec-async-output
status-async-output
notify-async-output
async-output
[ token ] "*" async-output
[ token ] "+" async-output
[ token ] "=" async-output
async-class ( "," result )* nl
result-class
"done" | "running" | "connected" |
"error" | "exit"
async-class
"stopped" | others(where otherswill be
added depending on the needs―this is still in
development).
result
variable "=" value
variable
string
308 The GDB/MIInterface
value
const
tuple→
list
const | tuple | list
c-string
"{}" | "{" result ( "," result )* "}"
"[]" | "[" value ( "," value )* "]"
| "[" result ( "," result )* "]"
stream-record
console-stream-output |
target-stream-output |
log-stream-output
console-stream-output
"~" c-string
target-stream-output
"@" c-string
log-stream-output
"&" c-string
nl
CR | CR-LF
token
any sequence of digits.
Notes:
•
•
All output sequences end in a single line containing a period.
The tokenis from the corresponding request. If an execution command is
interrupted by the '-exec-interrupt' command, the tokenassociated with the
'*stopped' message is the one of the original execution command, not the one of
the interrupt command.
• status-async-outputcontains on-going status information about the progress
of a slow operation. It can be discarded. All status output is prefixed by '+'.
• exec-async-outputcontains asynchronous state change on the target (stopped,
started, disappeared). All async output is prefixed by '*'.
• notify-async-outputcontains supplementary information that the client
should handle (for example, a new breakpoint information). All notify output is
prefixed by '='.
• console-stream-outputis output that should be displayed as is in the console.
It is the textual response to a CLI command. All the console output is prefixed by
'~'.
• target-stream-outputis the output produced by the target program. All the
target output is prefixed by '@'.
• log-stream-outputis output text coming from GDB's internals, for instance
messages that should be displayed as part of an error log. All the log output is
prefixed by '&'.
•
New GDB/MIcommands should only output lists containing values.
records.
21.1 GDB/MI Command Syntax 309
21.1.3 Simple examples of GDB/MIinteraction
This subsection presents several simple examples of interaction using the GDB/MI
interface. In these examples, '->' means that the following line is passed to GDB/MIas
input, while '<-' means the output received from GDB/MI.
Evaluate expression
Here is an example to evaluate an expression:
-> -data-evaluate-expression 2+3
<- (gdb)
<- ^done,value="5"
<- (gdb)
and later:
<- *stop,reason="stop",address="0x123",source="a.c:123"
<- (gdb)
Simple CLI command
Here is an example of a simple CLI command being passed through GDB/MIand on
to the CLI.
-> print 1+2
<- &"print 1+2\n"
<- ~"$1 = 3\n"
<- ^done
<- (gdb)
A bad command
Here is what happens if you pass a bad command:
-> -rubbish
<- ^error,msg="Undefined MI command: rubbish"
<- (gdb)
21.2 GDB/MIcompatibility with CLI
To help users get familiar with GDB CLI, GDB/MIaccepts existing CLI commands. As
specified by the syntax, such commands can be directly entered into the GDB/MI
interface and GDB will respond.
This mechanism is provided as an aid to developers of GDB/MIclients and not as a
reliable interface into the CLI. Since the command is being interpreted in an environment
that assumes GDB/MIbehaviour, the exact output of such commands is likely to end
up being an un-supported hybrid of GDB/MIand CLI output.
310 The GDB/MIInterface
21.3 GDB/MIoutput records
21.3.1 GDB/MIresult records
In addition to a number of out-of-band notifications, the response to a GDB/MIcommand
includes one of the following result indications:
"^done" [ "," results ]
The synchronous operation was successful,
resultsare the return values.
"^running"
The asynchronous operation was successfully
started. The target is running.
"^error" "," c-string
The operation failed. The c-stringcontains the
corresponding error message.
21.3.2 GDB/MIstream records
GDB internally maintains a number of output streams: the console, the target, and the
log. The output intended for each of these streams is funneled through the gdb/mi
interface using stream records.
Each stream record begins with a unique prefix character which identifies its stream (see
contains a string-output. This is either raw text (with an implicit new line) or a
quoted C string (which does not contain an implicit new line).
"~" string-output
The console output stream contains text that should be
displayed in the CLI console window. It contains the textual
responses to CLI commands.
"@" string-output
The target output stream contains any textual output from
the running target.
"&" string-output
The log stream contains internal debugging messages being
produced by GDB.
21.3.3 GDB/MIout-of-band records
Out-of-band records are used to notify the GDB/MIclient of additional changes that
have occurred. Those changes can either be a consequence of GDB/MI(for example, a
breakpoint modified) or a result of target activity (for example, target stopped).
The following is a preliminary list of possible out-of-band records.
"*" "stop"
21.4 GDB/MIcommand description format
The remaining sections describe blocks of commands. Each block of commands is laid
out in a fashion similar to this section.
21.3 GDB/MI output records 311
Note the line breaks shown in the examples are here only for readability. They do not
appear in the real output. Also note that the commands with a non-available example
(N.A.) are not yet implemented.
Motivation
The motivation for this collection of commands.
Introduction
A brief introduction to this collection of commands as a whole.
Commands
For each command in the block, the following is described:
Synopsis
-command args...
GDB command
The corresponding GDB CLI command.
Result
Out-of-band
Notes
Example
21.5 GDB/MIbreakpoint table commands
This section documents GDB/MIcommands for manipulating breakpoints.
The -break-afterCommand
Synopsis
-break-after number count
The breakpoint number numberis not in effect until it has been hit counttimes. To
see how this is reflected in the output of the '-break-list' command, see the
description of the '-break-list' command below.
GDB command
The corresponding GDB command is 'ignore'.
312 The GDB/MIInterface
Example
(gdb)
-break-insert main
^done,bkpt=number="1",type="breakpoint",disp="keep",enabled="y",
addr="0x000100d0",func="main",file="hello.c",line="5",times="0"(gdb)
-break-after 1 3
~
^done
(gdb)
-break-list
^done,BreakpointTable={nr_rows="1",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},
{width="14",alignment="-1",col_name="type",colhdr="Type"},
{width="4",alignment="-1",col_name="disp",colhdr="Disp"},
{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},
{width="10",alignment="-1",col_name="addr",colhdr="Address"},
{width="40",alignment="2",col_name="what",colhdr="What"}],
body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y",
addr="0x000100d0",func="main",file="hello.c",line="5",times="0",
ignore="3"}]}
(gdb)
The -break-conditioncommand
Synopsis
-break-condition number expr
Breakpoint numberwill stop the program only if the condition in expris true. The
condition becomes part of the '-break-list' output (see the description of the
'-break-list' command below).
GDB command
The corresponding GDB command is 'condition'.
Example
(gdb)
-break-condition 1 1
^done
(gdb)
-break-list
^done,BreakpointTable={nr_rows="1",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},
{width="14",alignment="-1",col_name="type",colhdr="Type"},
{width="4",alignment="-1",col_name="disp",colhdr="Disp"},
{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},
{width="10",alignment="-1",col_name="addr",colhdr="Address"},
{width="40",alignment="2",col_name="what",colhdr="What"}],
body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y",
21.5 GDB/MI breakpoint table commands 313
addr="0x000100d0",func="main",file="hello.c",line="5",cond="1",
times="0",ignore="3"}]}
(gdb)
The -break-deletecommand
Synopsis
-break-delete ( breakpoint )+
Delete the breakpoint(s) whose number(s) are specified in the argument list. This is
obviously reflected in the breakpoint list.
GDB command
The corresponding GDB command is 'delete'.
Example
(gdb)
-break-delete 1
^done
(gdb)
-break-list
^done,BreakpointTable={nr_rows="0",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},
{width="14",alignment="-1",col_name="type",colhdr="Type"},
{width="4",alignment="-1",col_name="disp",colhdr="Disp"},
{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},
{width="10",alignment="-1",col_name="addr",colhdr="Address"},
{width="40",alignment="2",col_name="what",colhdr="What"}],
body=[]}
(gdb)
The -break-disablecommand
Synopsis
-break-disable ( breakpoint )+
Disable the named breakpoint(s). The field 'enabled' in the break list is now set to
'n' for the named breakpoint(s).
GDB command
The corresponding GDB command is 'disable'.
Example
(gdb)
-break-disable 2
^done
(gdb)
314 The GDB/MIInterface
-break-list
^done,BreakpointTable={nr_rows="1",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},
{width="14",alignment="-1",col_name="type",colhdr="Type"},
{width="4",alignment="-1",col_name="disp",colhdr="Disp"},
{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},
{width="10",alignment="-1",col_name="addr",colhdr="Address"},
{width="40",alignment="2",col_name="what",colhdr="What"}],
body=[bkpt={number="2",type="breakpoint",disp="keep",enabled="n",
addr="0x000100d0",func="main",file="hello.c",line="5",times="0"}]}
(gdb)
The -break-enablecommand
Synopsis
-break-enable ( breakpoint )+
Enable (previously disabled) breakpoint(s).
GDB command
The corresponding GDB command is 'enable'.
Example
(gdb)
-break-enable 2
^done
(gdb)
-break-list
^done,BreakpointTable={nr_rows="1",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},
{width="14",alignment="-1",col_name="type",colhdr="Type"},
{width="4",alignment="-1",col_name="disp",colhdr="Disp"},
{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},
{width="10",alignment="-1",col_name="addr",colhdr="Address"},
{width="40",alignment="2",col_name="what",colhdr="What"}],
body=[bkpt={number="2",type="breakpoint",disp="keep",enabled="y",
addr="0x000100d0",func="main",file="hello.c",line="5",times="0"}]}
(gdb)
The -break-infoCommand
Synopsis
-break-info breakpoint
Get information about a single breakpoint.
GDB command
The corresponding GDB command is 'info break breakpoint'.
21.5 GDB/MI breakpoint table commands 315
Example
N.A.
The -break-insertcommand
Synopsis
-break-insert [ -t ] [ -h ] [ -r ]
[ -c condition ] [ -i ignore-count ]
[ -p thread ] [ line | addr ]
If specified, line, can be one of:
•
•
•
•
function
filename:linenum
filename:function
*address
The possible optional parameters of this command are:
'-t'
Insert a temporary breakpoint.
'[-h]'
Insert a hardware breakpoint.
'[-c condition]'
'[-i ignore-count]'
`-r'
Make the breakpoint conditional on condition.
Initialize the ignore-count.
Insert a regular breakpoint in all the functions whose
names match the given regular expression. Other flags
are not applicable to regular expression.
Result
The result is in the form:
^done,bkptno="number",func="funcname",
file="filename",line="lineno"
where numberis the GDB number for this breakpoint, funcnameis the name of the
function where the breakpoint was inserted, filenameis the name of the source file
which contains this function, and linenois the source line number within that file.
NOTE: This format is open to change.
GDB command
The corresponding GDB commands are 'break', 'tbreak', 'hbreak', 'thbreak', and
'rbreak'.
Example
(gdb)
-break-insert main
316 The GDB/MIInterface
^done,bkpt=number="1",type="breakpoint",disp="keep",enabled="y",addr="0x0001072c",
file="recursive2.c",line="4",times="0"
(gdb)
-break-insert -t foo
^done,bkpt=number="2",type="breakpoint",disp="keep",enabled="y",addr="0x00010774",
file="recursive2.c",line="11",times="0"(gdb)
-break-list
^done,BreakpointTable={nr_rows="2",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},
{width="14",alignment="-1",col_name="type",colhdr="Type"},
{width="4",alignment="-1",col_name="disp",colhdr="Disp"},
{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},
{width="10",alignment="-1",col_name="addr",colhdr="Address"},
{width="40",alignment="2",col_name="what",colhdr="What"}],
body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y",
addr="0x0001072c", func="main",file="recursive2.c",line="4",times="0"},
bkpt={number="2",type="breakpoint",disp="del",enabled="y",
addr="0x00010774",func="foo",file="recursive2.c",line="11",times="0"}]}
(gdb)
-break-insert -r foo.*
~int foo(int, int);
^done,bkpt={number="3",addr="0x00010774",file="recursive2.c",line="11"}
(gdb)
The -break-listcommand
Synopsis
-break-list
Displays the list of inserted breakpoints, showing the following fields:
'Number'
number of the breakpoint
'Type'
type of the breakpoint: 'breakpoint' or 'watchpoint'
'Disposition'
should the breakpoint be deleted or disabled when it is hit: 'keep'
or 'nokeep'
'Enabled'
'Address'
'What'
is the breakpoint enabled or no: 'y' or 'n'
memory location at which the breakpoint is set
logical location of the breakpoint, expressed by function name,
file name, line number
'Times'
number of times the breakpoint has been hit
If there are no breakpoints or watchpoints, the BreakpointTable bodyfield is an
empty list.
GDB command
The corresponding GDB command is 'info break'.
Example
(gdb)
-break-list
^done,BreakpointTable={nr_rows="2",nr_cols="6",
21.5 GDB/MI breakpoint table commands 317
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},
{width="14",alignment="-1",col_name="type",colhdr="Type"},
{width="4",alignment="-1",col_name="disp",colhdr="Disp"},
{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},
{width="10",alignment="-1",col_name="addr",colhdr="Address"},
{width="40",alignment="2",col_name="what",colhdr="What"}],
body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y",
addr="0x000100d0",func="main",file="hello.c",line="5",times="0"},
bkpt={number="2",type="breakpoint",disp="keep",enabled="y",
addr="0x00010114",func="foo",file="hello.c",line="13",times="0"}]}
(gdb)
Here is an example of the result when there are no breakpoints:
(gdb)
-break-list
^done,BreakpointTable={nr_rows="0",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},
{width="14",alignment="-1",col_name="type",colhdr="Type"},
{width="4",alignment="-1",col_name="disp",colhdr="Disp"},
{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},
{width="10",alignment="-1",col_name="addr",colhdr="Address"},
{width="40",alignment="2",col_name="what",colhdr="What"}],
body=[]}
(gdb)
The -break-watchcommand
Synopsis
-break-watch [ -a | -r ]
Create a watchpoint. With the '-a' option it will create an access watchpoint, that is a
watchpoint that triggers either on a read from or on a write to the memory location.
With the '-r' option, the watchpoint created is a read watchpoint, that is it will trigger
only when the memory location is accessed for reading. Without either of the options,
the watchpoint created is a regular watchpoint, that is it will trigger when the memory
location is accessed for writing. See “Enhanced support for watchpoints and
Note that '-break-list' will report a single list of watchpoints and breakpoints
inserted.
GDB command
The corresponding GDB commands are 'watch', 'awatch', and 'rwatch'.
Example
Setting a watchpoint on a variable in the mainfunction:
(gdb)
-break-watch i
^done,wpt=number="2",exp="i"
318 The GDB/MIInterface
(gdb)
-exec-continue
^running
(gdb)
*stopped,reason="watchpoint-trigger",wpt=number="2",exp="i",value=old="0",new="7"
,thread-id="1",frame=addr="0x000029c4",func="main",args=[],file="hello.c",line="8"
(gdb)
Setting a watchpoint on a variable local to a function. GDB will stop the program
execution twice: first for the variable changing value, then for the watchpoint going
out of scope.
(gdb)
-break-watch j
^done,wpt=number="2",exp="j"
(gdb)
-exec-continue
^running
(gdb)
*stopped,reason="watchpoint-trigger",wpt=number="2",exp="j",value=old="0",new="17",
thread-id="1",frame=addr="0x000029bc",func="call",args=[],file="hello.c",line="10"
(gdb)
-exec-continue
^running
(gdb)
*stopped,reason="watchpoint-scope",wpnum="2",thread-id="1",frame=addr="0x000029ec",
func="main",args=[],file="hello.c",line="18"
(gdb)
Listing breakpoints and watchpoints, at different points in the program execution. Note
that once the watchpoint goes out of scope, it is deleted.
-break-watch j
^done,wpt=number="2",exp="j"
(gdb)
-break-list
^done,BreakpointTable=nr_rows="2",nr_cols="6",hdr=[width="3",
alignment="-1",col_name="number",colhdr="Num",width="14",alignment="-1",
col_name="type",colhdr"Type",width="4",alignment="-1",col_name="disp",
colhdr="Disp",width="3",alinment="-1",col_name="enabled",colhdr="Enb",
width="10",alignment="-1",col_name"addr",colhdr="Address",
width="40",alignment="2",col_name="what",colhdr="What],body=[bkpt=number="1",
type="breakpoint",disp="keep",enabled="y",addr="0x00029b4",func="call",
file="hello.c",line="9",times="1",bkpt=number="2",type="wathpoint",disp="keep",
enabled="y",addr="",what="j",times="0"]
(gdb)
-exec-continue
^running
(gdb)
*stopped,reason="watchpoint-trigger",wpt=number="2",exp="j",value=old="0",ne="17",
thread-id="1",frame=addr="0x000029bc",func="call",args=[],file="hello.c,line="10"
(gdb)
-break-list
^done,BreakpointTable=nr_rows="2",nr_cols="6",hdr=[width="3",alignment="-1",
col_name="number",colhdr="Num",width="14",alignment="-1",col_name="type",colhdr"Type",
width="4",alignment="-1",col_name="disp",colhdr="Disp",width="3",alinment="-1",
col_name="enabled",colhdr="Enb",width="10",alignment="-1",col_name"addr",colhdr="Address",
width="40",alignment="2",col_name="what",colhdr="What],body=[bkpt=number="1",
type="breakpoint",disp="keep",enabled="y",addr="0x00029b4",func="call",file="hello.c",
line="9",times="1",bkpt=number="2",type="wathpoint",disp="keep",enabled="y",addr="",
what="j",times="1"]
(gdb)
-exec-continue
^running
(gdb)
*stopped,reason="watchpoint-scope",wpnum="2",thread-id="1",frame=addr="0x000029ec",
func="main",args=[],file="hello.c",line="18"
(gdb)
-break-list
21.5 GDB/MI breakpoint table commands 319
^done,BreakpointTable=nr_rows="1",nr_cols="6",hdr=[width="3",alignment="-1",
col_name="number",colhdr="Num",width="14",alignment="-1",col_name="type",colhdr="Type",
width="4",alignment="-1",col_name="disp",colhdr="Disp",width="3",alignment="-1",
col_name="enabled",colhdr="Enb",width="10",alignment="-1",col_name="addr",
colhdr="Address",width="40",alignment="2",col_name="what",colhdr="What"],
body=[bkpt=number="1",type="breakpoint",disp="keep",enabled="y",addr="0x000029b4",
func="call",file="hello.c",line="9",times="1"]
(gdb)
21.6 GDB/MIData manipulation
This section describes the GDB/MIcommands that manipulate data: examine memory
and registers, evaluate expressions, and so on.
The -data-disassemblecommand
Synopsis
-data-disassemble
[ -s start-addr -e end-addr ]
| [ -f filename -l linenum [ -n lines ] ]
-- mode
Where:
'start-addr'
'end-addr'
'filename'
'linenum'
'lines'
is the beginning address (or $pc)
is the end address
is the name of the file to disassemble
is the line number to disassemble around
is the number of disassembly lines to be produced. If it is -1, the
whole function will be disassembled, in case no end-addris
specified. If end-addris specified as a non-zero value, and lines
is lower than the number of disassembly lines between
start-addrand end-addr, only lineslines are displayed; if
linesis higher than the number of lines between start-addr
and end-addr, only the lines up to end-addrare displayed.
'mode'
is either 0 (meaning only disassembly) or 1 (meaning mixed source
and disassembly).
Result
The output for each instruction is composed of four fields:
•
•
•
•
Address
Func-name
Offset
Instruction
Note that whatever included in the instruction field, is not manipulated directly by
GDB/MI, that is it is not possible to adjust its format.
320 The GDB/MIInterface
GDB command
There is no direct mapping from this command to the CLI.
Example
Disassemble from the current value of $pcto $pc + 20:
(gdb)
-data-disassemble -s $pc -e "$pc + 20" -- 0
^done,
asm_insns=[
{address="0x000107c0",func-name="main",offset="4",
inst="mov 2, %o0"},
{address="0x000107c4",func-name="main",offset="8",
inst="sethi %hi(0x11800), %o2"},
{address="0x000107c8",func-name="main",offset="12",
inst="or %o2, 0x140, %o1\t! 0x11940 <_lib_version+8>"},
{address="0x000107cc",func-name="main",offset="16",
inst="sethi %hi(0x11800), %o2"},
{address="0x000107d0",func-name="main",offset="20",
inst="or %o2, 0x168, %o4\t! 0x11968 <_lib_version+48>"}]
(gdb)
Disassemble the whole mainfunction. Line 32 is part of main.
-data-disassemble -f basics.c -l 32 -- 0
^done,asm_insns=[
{address="0x000107bc",func-name="main",offset="0",
inst="save %sp, -112, %sp"},
{address="0x000107c0",func-name="main",offset="4",
inst="mov 2, %o0"},
{address="0x000107c4",func-name="main",offset="8",
inst="sethi %hi(0x11800), %o2"},
[...]
{address="0x0001081c",func-name="main",offset="96",inst="ret "},
{address="0x00010820",func-name="main",offset="100",inst="restore "}]
(gdb)
Disassemble 3 instructions from the start of main:
(gdb)
-data-disassemble -f basics.c -l 32 -n 3 -- 0
^done,asm_insns=[
{address="0x000107bc",func-name="main",offset="0",
inst="save %sp, -112, %sp"},
{address="0x000107c0",func-name="main",offset="4",
inst="mov 2, %o0"},
{address="0x000107c4",func-name="main",offset="8",
inst="sethi %hi(0x11800), %o2"}]
(gdb)
Disassemble 3 instructions from the start of mainin mixed mode:
(gdb)
-data-disassemble -f basics.c -l 32 -n 3 -- 1
21.6 GDB/MI Data manipulation 321
^done,asm_insns=[
src_and_asm_line={line="31",
file="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb/ \
testsuite/gdb.mi/basics.c",line_asm_insn=[
{address="0x000107bc",func-name="main",offset="0",
inst="save %sp, -112, %sp"}]},
src_and_asm_line={line="32",
file="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb/ \
testsuite/gdb.mi/basics.c",line_asm_insn=[
{address="0x000107c0",func-name="main",offset="4",
inst="mov 2, %o0"},
{address="0x000107c4",func-name="main",offset="8",
inst="sethi %hi(0x11800), %o2"}]}]
(gdb)
The -data-evaluate-expressioncommand
Synopsis
-data-evaluate-expression expr
Evaluate expras an expression. The expression could contain an inferior function call.
The function call will execute synchronously. If the expression contains spaces, it must
be enclosed in double quotes.
GDB command
The corresponding GDB commands are 'print', 'output', and 'call'. In gdbtkonly,
there is a corresponding 'gdb_eval' command.
Example
In the following example, the numbers that precede the commands are the tokens
same tokens in its output.
211-data-evaluate-expression A
211^done,value="1"
(gdb)
311-data-evaluate-expression &A
311^done,value="0xefffeb7c"
(gdb)
411-data-evaluate-expression A+3
411^done,value="4"
(gdb)
511-data-evaluate-expression "A + 3"
511^done,value="4"
(gdb)
322 The GDB/MIInterface
The -data-list-changed-registersCommand
Synopsis
-data-list-changed-registers
Display a list of the registers that have changed.
GDB command
GDB does not have a direct analog for this command; gdbtkhas the corresponding
command 'gdb_changed_register_list'.
Example
On a PPC MBX board:
(gdb)
-exec-continue
^running
(gdb)
*stopped,reason="breakpoint-hit",bkptno="1",frame={func="main",
args=[],file="try.c",line="5"}
(gdb)
-data-list-changed-registers
^done,changed-registers=["0","1","2","4","5","6","7","8","9",
"10","11","13","14","15","16","17","18","19","20","21","22","23",
"24","25","26","27","28","30","31","64","65","66","67","69"]
(gdb)
The -data-list-register-namescommand
Synopsis
-data-list-register-names [ ( regno )+ ]
Show a list of register names for the current target. If no arguments are given, it shows
a list of the names of all the registers. If integer numbers are given as arguments, it will
print a list of the names of the registers corresponding to the arguments. To ensure
consistency between a register name and its number, the output list may include empty
register names.
GDB command
GDB does not have a command which corresponds to
'-data-list-register-names'. In gdbtkthere is a corresponding command
'gdb_regnames'.
Example
For the PPC MBX board:
21.6 GDB/MI Data manipulation 323
(gdb)
-data-list-register-names
^done,register-names=["r0","r1","r2","r3","r4","r5","r6","r7",
"r8","r9","r10","r11","r12","r13","r14","r15","r16","r17","r18",
"r19","r20","r21","r22","r23","r24","r25","r26","r27","r28","r29",
"r30","r31","f0","f1","f2","f3","f4","f5","f6","f7","f8","f9",
"f10","f11","f12","f13","f14","f15","f16","f17","f18","f19","f20",
"f21","f22","f23","f24","f25","f26","f27","f28","f29","f30","f31",
"", "pc","ps","cr","lr","ctr","xer"]
(gdb)
-data-list-register-names 1 2 3
^done,register-names=["r1","r2","r3"]
(gdb)
The -data-list-register-valuescommand
Synopsis
-data-list-register-values fmt [ ( regno )*]
Display the registers contents. fmtis the format according to which the registers'
contents are to be returned, followed by an optional list of numbers specifying the
registers to display. A missing list of numbers indicates that the contents of all the
registers must be returned.
Allowed formats for fmtare:
x
o
t
d
r
N
Hexadecimal
Octal
Binary
Decimal
Raw
Natural
GDB command
The corresponding GDB commands are 'info reg', 'info all-reg', and (in gdbtk)
'gdb_fetch_registers'.
Example
For a PPC MBX board (note: line breaks are for readability only, they do not appear in
the actual output):
(gdb)
-data-list-register-values r 64 65
^done,register-values=[{number="64",value="0xfe00a300"},
{number="65",value="0x00029002"}]
(gdb)
-data-list-register-values x
324 The GDB/MIInterface
^done,register-values=[{number="0",value="0xfe0043c8"},
{number="1",value="0x3fff88"},{number="2",value="0xfffffffe"},
{number="3",value="0x0"},{number="4",value="0xa"},
{number="5",value="0x3fff68"},{number="6",value="0x3fff58"},
{number="7",value="0xfe011e98"},{number="8",value="0x2"},
{number="9",value="0xfa202820"},{number="10",value="0xfa202808"},
{number="11",value="0x1"},{number="12",value="0x0"},
{number="13",value="0x4544"},{number="14",value="0xffdfffff"},
{number="15",value="0xffffffff"},{number="16",value="0xfffffeff"},
{number="17",value="0xefffffed"},{number="18",value="0xfffffffe"},
{number="19",value="0xffffffff"},{number="20",value="0xffffffff"},
{number="21",value="0xffffffff"},{number="22",value="0xfffffff7"},
{number="23",value="0xffffffff"},{number="24",value="0xffffffff"},
{number="25",value="0xffffffff"},{number="26",value="0xfffffffb"},
{number="27",value="0xffffffff"},{number="28",value="0xf7bfffff"},
{number="29",value="0x0"},{number="30",value="0xfe010000"},
{number="31",value="0x0"},{number="32",value="0x0"},
{number="33",value="0x0"},{number="34",value="0x0"},
{number="35",value="0x0"},{number="36",value="0x0"},
{number="37",value="0x0"},{number="38",value="0x0"},
{number="39",value="0x0"},{number="40",value="0x0"},
{number="41",value="0x0"},{number="42",value="0x0"},
{number="43",value="0x0"},{number="44",value="0x0"},
{number="45",value="0x0"},{number="46",value="0x0"},
{number="47",value="0x0"},{number="48",value="0x0"},
{number="49",value="0x0"},{number="50",value="0x0"},
{number="51",value="0x0"},{number="52",value="0x0"},
{number="53",value="0x0"},{number="54",value="0x0"},
{number="55",value="0x0"},{number="56",value="0x0"},
{number="57",value="0x0"},{number="58",value="0x0"},
{number="59",value="0x0"},{number="60",value="0x0"},
{number="61",value="0x0"},{number="62",value="0x0"},
{number="63",value="0x0"},{number="64",value="0xfe00a300"},
{number="65",value="0x29002"},{number="66",value="0x202f04b5"},
{number="67",value="0xfe0043b0"},{number="68",value="0xfe00b3e4"},
{number="69",value="0x20002b03"}]
(gdb)
The -data-read-memorycommand
Synopsis
-data-read-memory [ -o byte-offset ]
address word-format word-size
nr-rows nr-cols [ aschar ]
where:
'address'
An expression specifying the address of the first memory word
to be read. Complex expressions containing embedded white
space should be quoted using the C convention.
21.6 GDB/MI Data manipulation 325
'word-format'
The format to be used to print the memory words. The notation
'word-size'
'nr-rows'
'nr-cols'
'aschar'
The size of each memory word in bytes.
The number of rows in the output table.
The number of columns in the output table.
If present, indicates that each row should include an ASCII dump.
The value of ascharis used as a padding character when a byte
is not a member of the printable ASCII character set (printable
ASCII characters are those whose code is between 32 and 126,
inclusively).
'byte-offset'
An offset to add to the addressbefore fetching memory.
This command displays memory contents as a table of nr-rowsby nr-colswords,
each word being word-sizebytes. In total, nr-rows * nr-cols * word-size
bytesare read (returned as 'total-bytes'). Should less than the requested number
of bytes be returned by the target, the missing words are identified using 'N/A'. The
number of bytes read from the target is returned in 'nr-bytes' and the starting address
used to read memory in 'addr'.
The address of the next/previous row or page is available in 'next-row' and
'prev-row', 'next-page' and 'prev-page'.
GDB command
The corresponding GDB command is 'x'. gdbtkhas 'gdb_get_mem' memory read
command.
Example
Read six bytes of memory starting at bytes+6 but then offset by -6 bytes. Format as
three rows of two columns. One byte per word. Display each word in hex.
(gdb)
9-data-read-memory -o -6 -- bytes+6 x 1 3 2
9^done,addr="0x00001390",nr-bytes="6",total-bytes="6",
next-row="0x00001396",prev-row="0x0000138e",next-page="0x00001396",
prev-page="0x0000138a",memory=[
{addr="0x00001390",data=["0x00","0x01"]},
{addr="0x00001392",data=["0x02","0x03"]},
{addr="0x00001394",data=["0x04","0x05"]}]
(gdb)
Read two bytes of memory starting at address shorts+ 64 and display as a single
word formatted in decimal.
(gdb)
5-data-read-memory shorts+64 d 2 1 1
5^done,addr="0x00001510",nr-bytes="2",total-bytes="2",
326 The GDB/MIInterface
next-row="0x00001512",prev-row="0x0000150e",
next-page="0x00001512",prev-page="0x0000150e",memory=[
{addr="0x00001510",data=["128"]}]
(gdb)
Read thirty two bytes of memory starting at bytes+16 and format as eight rows of
four columns. Include a string encoding with 'x' used as the non-printable character.
(gdb)
4-data-read-memory bytes+16 x 1 8 4 x
4^done,addr="0x000013a0",nr-bytes="32",total-bytes="32",
next-row="0x000013c0",prev-row="0x0000139c",
next-page="0x000013c0",prev-page="0x00001380",memory=[
{addr="0x000013a0",data=["0x10","0x11","0x12","0x13"],ascii="xxxx"},
{addr="0x000013a4",data=["0x14","0x15","0x16","0x17"],ascii="xxxx"},
{addr="0x000013a8",data=["0x18","0x19","0x1a","0x1b"],ascii="xxxx"},
{addr="0x000013ac",data=["0x1c","0x1d","0x1e","0x1f"],ascii="xxxx"},
{addr="0x000013b0",data=["0x20","0x21","0x22","0x23"],ascii=" !\"#"},
{addr="0x000013b4",data=["0x24","0x25","0x26","0x27"],ascii="$%&'"},
{addr="0x000013b8",data=["0x28","0x29","0x2a","0x2b"],ascii="()*+"},
{addr="0x000013bc",data=["0x2c","0x2d","0x2e","0x2f"],ascii=",-./"}]
(gdb)
The -display-deletecommand
Synopsis
-display-delete number
Delete the display number.
GDB command
The corresponding GDB command is 'delete display'.
Example
N.A.
The -display-disableCommand
Synopsis
-display-disable number
Disable display number.
GDB command
The corresponding GDB command is 'disable display'.
Example
N.A.
21.6 GDB/MI Data manipulation 327
The -display-enablecommand
Synopsis
-display-enable number
Enable display number.
GDB command
The corresponding GDB command is 'enable display'.
Example
N.A.
The -display-insertCommand
Synopsis
-display-insert expression
Display expressionevery time the program stops.
GDB command
The corresponding GDB command is 'display'.
Example
N.A.
The -display-listcommand
Synopsis
-display-list
List the displays. Do not show the current values.
GDB command
The corresponding GDB command is 'info display'.
Example
N.A.
The -environment-cdcommand
Synopsis
-environment-cd pathdir
328 The GDB/MIInterface
Set the GDB working directory.
GDB command
The corresponding GDB command is 'cd'.
Example
(gdb)
-environment-cd /kwikemart/marge/ezannoni/flathead-dev/devo/gdb
^done
(gdb)
The -environment-directorycommand
Synopsis
-environment-directory pathdir
Add directory pathdirto the beginning of search path for source files.
GDB command
The corresponding GDB command is 'dir'.
Example
(gdb)
-environment-directory /kwikemart/marge/ezannoni/flathead-dev/devo/gdb
^done
(gdb)
The -environment-pathcommand
Synopsis
-environment-path ( pathdir )+
Add directories pathdirto beginning of search path for object files.
GDB command
The corresponding GDB command is 'path'.
Example
(gdb)
-environment-path /kwikemart/marge/ezannoni/flathead-dev/ppc-eabi/gdb
^done
(gdb)
21.6 GDB/MI Data manipulation 329
The -environment-pwdcommand
Synopsis
-environment-pwd
Show the current working directory.
GDB command
The corresponding GDB command is 'pwd'.
Example
(gdb)
-environment-pwd
~Working directory /kwikemart/marge/ezannoni/flathead-dev/devo/gdb.
^done
(gdb)
21.7 GDB/MIprogram control
Program termination As a result of execution, the inferior program can run to
completion, if it does not encounter any breakpoints. In this case the output will include
an exit code, if the program has exited exceptionally.
Examples Program exited normally:
(gdb)
-exec-run
^running
(gdb)
x = 55
*stopped,reason="exited-normally"
(gdb)
Program exited exceptionally:
(gdb)
-exec-run
^running
(gdb)
x = 55
*stopped,reason="exited",exit-code="01"
(gdb)
Another way the program can terminate is if it receives a signal such as SIGINT. In this
case, GDB/MIdisplays this:
(gdb)
*stopped,reason="exited-signalled",signal-name="SIGINT",
signal-meaning="Interrupt"
330 The GDB/MIInterface
The -exec-abortcommand
Synopsis
-exec-abort
Kill the inferior running program.
GDB command
The corresponding GDB command is 'kill'.
Example
N.A.
The -exec-argumentscommand
Synopsis
-exec-arguments args
Set the inferior program arguments, to be used in the next '-exec-run'.
GDB command
The corresponding GDB command is 'set args'.
Example
Do not have one around.
The -exec-continuecommand
Synopsis
-exec-continue
Asynchronous command. Resumes the execution of the inferior program until a
breakpoint is encountered, or until the inferior exits.
GDB command
The corresponding GDB is 'continue'.
Example
-exec-continue
^running
(gdb)
@Hello world
*stopped,reason="breakpoint-hit",bkptno="2",thread-id="1",frame=addr="0x000029d8",
func="foo",args=[],file="hello.c",line="16"file="hello.c",line="13"}
(gdb)
21.7 GDB/MI program control 331
The -exec-finishcommand
Synopsis
-exec-finish
Asynchronous command. Resumes the execution of the inferior program until the
current function is exited. Displays the results returned by the function.
GDB command
The corresponding GDB command is 'finish'.
Example
Function returning void.
-exec-finish
^running
(gdb)
@hello from foo
*stopped,reason="function-finished",thread-id="1",frame=addr="0x000029ec",
func="main",args=[],file="hello.c",line="7file="hello.c",line="7"}
(gdb)
Function returning other than void. The name of the internal GDB variable storing
the result is printed, together with the value itself.
-exec-finish
^running
(gdb)
*stopped,reason="function-finished",thread-id="1",
frame=addr="0x000107b0",func="foo",
args=[name="a"],name="b",
file="recursive2.c",line="14"},
gdb-result-var="$1",return-value="0"
(gdb)
The -exec-interruptcommand
Synopsis
-exec-interrupt
Asynchronous command. Interrupts the background execution of the target. Note how
the token associated with the stop message is the one for the execution command that
has been interrupted. The token for the interrupt itself only appears in the '^done'
output. If the user is trying to interrupt a non-running program, an error message will
be printed.
GDB command
The corresponding GDB command is 'interrupt'.
332 The GDB/MIInterface
Example
(gdb)
111-exec-continue
111^running
(gdb)
222-exec-interrupt
222^done
(gdb)
111*stopped,signal-name="SIGINT",signal-meaning="Interrupt",
frame={addr="0x00010140",func="foo",args=[],file="try.c",line="13"}
(gdb)
(gdb)
-exec-interrupt
^error,msg="mi_cmd_exec_interrupt: Inferior not executing."
(gdb)
The -exec-nextcommand
Synopsis
-exec-next
Asynchronous command. Resumes execution of the inferior program, stopping when
the beginning of the next source line is reached.
GDB command
The corresponding GDB command is 'next'.
Example
-exec-next
^running
(gdb)
*stopped,reason="end-stepping-range",thread-id="1",frame=addr="0x00002a10",
func="main",args=[],file="hello.c",line="24"(gdb)
The -exec-next-instructioncommand
Synopsis
-exec-next-instruction
Asynchronous command. Executes one machine instruction. If the instruction is a
function, call continues until the function returns. If the program stops at an instruction
in the middle of a source line, the address will be printed as well.
GDB command
The corresponding GDB command is 'nexti'.
21.7 GDB/MI program control 333
Example
(gdb)
-exec-next-instruction
^running
(gdb)
*stopped,reason="end-stepping-range",thread-
id="1",frame=addr="0x00002a14",func="main",args=[],file="hello.c",line="24"
(gdb)
The -exec-returncommand
Synopsis
-exec-return
Makes current function return immediately. Does not execute the inferior. Displays
the new current frame.
GDB command
The corresponding GDB command is return'.
Example
(gdb)
-break-insert call1
^done,bkpt=number="1",type="breakpoint",disp="keep",enabled="y",addr="0x000029ac",
func="call1",file="hello.c",line="9",times="0"
(gdb)
-exec-run
^running
(gdb)
~"3"
*stopped,reason="breakpoint-hit",bkptno="1",thread-id="1",frame=addr="0x000029ac",
func="call1",args=[name="a"],file="hello.c",line="9"
(gdb)
-exec-return
~"2"
~"3"
^done,frame=level="0 ",addr="0x000029e8",func="call",args=[name="a",name="b"],
file="hello.c",line="17"
(gdb)
The -exec-runcommand
Synopsis
-exec-run
Asynchronous command. Starts execution of the inferior from the beginning. The
inferior executes until either a breakpoint is encountered or the program exits.
GDB command
The corresponding GDB command is 'run'.
334 The GDB/MIInterface
Example
(gdb)
-break-insert main
^done,bkpt=number="1",type="breakpoint",disp="keep",enabled="y",addr="0x00002a08",
func="main",file="hello.c",line="23",times="0"
(gdb)
-exec-run
^running
(gdb)
*stopped,reason="breakpoint-hit",bkptno="1",thread-id="1",frame=addr="0x00002a08",
func="main",args=[],file="hello.c",line="23"
(gdb)
The -exec-show-arguments command
Synopsis
-exec-show-arguments
Prints the arguments of the program.
GDB command
The corresponding GDB command is 'show args'.
Example
N.A.
The -exec-stepCommand
Synopsis
-exec-step
Asynchronous command. Resumes execution of the inferior program, stopping when
the beginning of the next source line is reached, if the next source line is not a function
call. If it is, stop at the first instruction of the called function.
GDB command
The corresponding GDB command is 'step'.
Example
Stepping into a function:
-exec-step
^running
(gdb)
~"2"
~"3"
*stopped,reason="end-stepping-range",thread-id="1",frame=addr="0x000029d0",
func="call",args=[name="a",name="b"],file="hello.c",line="15"
(gdb)
21.7 GDB/MI program control 335
Regular stepping:
-exec-step
^running
(gdb)
~"2"
~"3"
*stopped,reason="end-stepping-range",thread-id="1",frame=addr="0x000029d8",
func="call",args=[name="a",name="b"],file="hello.c",line="16"
(gdb)
The -exec-step-instructioncommand
Synopsis
-exec-step-instruction
Asynchronous command. Resumes the inferior which executes one machine instruction.
The output, once GDB has stopped, will vary depending on whether we have stopped
in the middle of a source line or not. In the former case, the address at which the
program stopped will be printed as well.
GDB command
The corresponding GDB command is 'stepi'.
Example
(gdb)
-exec-step-instruction
^running
(gdb)
~"2"
~"3"
*stopped,reason="end-stepping-range",thread-id="1",frame=addr="0x000029dc",
func="call",args=[name="a",name="b"],file="hello.c",line="16"
(gdb)
-exec-step-instruction
^running
(gdb)
*stopped,reason="end-stepping-range",
frame={addr="0x000100f4",func="foo",args=[],file="try.c",line="10"}
(gdb)
The -exec-untilcommand
Synopsis
-exec-until [ location ]
Asynchronous command. Executes the inferior until the locationspecified in the
argument is reached. If there is no argument, the inferior executes until a source line
336 The GDB/MIInterface
greater than the current one is reached. The reason for stopping in this case will be
'location-reached'.
GDB command
The corresponding GDB command is 'until'.
Example
(gdb)
-exec-until recursive2.c:6
^running
(gdb)
x = 55
*stopped,reason="location-reached",thread-id="1",frame=addr="0x00002a24",func="main",args=[],
file="recursive2.c",line="6"
(gdb)
The -file-exec-and-symbolscommand
Synopsis
-file-exec-and-symbols file
Specify the executable file to be debugged. This file is the one from which the symbol
table is also read. If no file is specified, the command clears the executable and symbol
information. If breakpoints are set when using this command with no arguments, GDB
will produce error messages. Otherwise, no output is produced, except a completion
notification.
GDB command
The corresponding GDB command is 'file'.
Example
(gdb)
-file-exec-and-symbols /kwikemart/marge/ezannoni/TRUNK/mbx/hello.mbx
^done
(gdb)
The -file-exec-filecommand
Synopsis
-file-exec-file file
Specify the executable file to be debugged. Unlike '-file-exec-and-symbols', the
symbol table is not read from this file. If used without argument, GDB clears the
information about the executable file. No output is produced, except a completion
notification.
21.7 GDB/MI program control 337
GDB command
The corresponding GDB command is 'exec-file'.
Example
(gdb)
-file-exec-file /kwikemart/marge/ezannoni/TRUNK/mbx/hello.mbx
^done
(gdb)
The -file-list-exec-sectionscommand
Synopsis
-file-list-exec-sections
List the sections of the current executable file.
GDB command
The GDB command 'info file' shows, among the rest, the same information as this
command. gdbtkhas a corresponding command 'gdb_load_info'.
Example
N.A.
The -file-list-exec-source-filescommand
Synopsis
-file-list-exec-source-files
List the source files for the current executable.
GDB command
There is no GDB command which directly corresponds to this one. gdbtkhas an
analogous command 'gdb_listfiles'.
Example
N.A.
The -file-list-shared-librariescommand
Synopsis
-file-list-shared-libraries
List the shared libraries in the program.
338 The GDB/MIInterface
GDB command
The corresponding GDB command is info shared.
Example
N.A.
The -file-list-symbol-filescommand
Synopsis
-file-list-symbol-files
List symbol files.
GDB command
The corresponding GDB command is 'info file' (part of it).
Example
N.A.
The -file-symbol-filecommand
Synopsis
-file-symbol-file file
Read symbol table info from the specified fileargument. When used without
arguments, clears GDB's symbol table info. No output is produced, except for a
completion notification.
GDB command
The corresponding GDB command is 'symbol-file'.
Example
(gdb)
-file-symbol-file /kwikemart/marge/ezannoni/TRUNK/mbx/hello.mbx
^done
(gdb)
21.8 Miscellaneous GDB commands in GDB/MI
The -gdb-exitcommand
Synopsis
-gdb-exit
21.8 Miscellaneous GDB commands in GDB/MI 339
Exit GDB immediately.
GDB command
Approximately corresponds to 'quit'.
Example
(gdb)
-gdb-exit
The -gdb-setcommand
Synopsis
-gdb-set
Set an internal GDB variable.
GDB command
The corresponding GDB command is 'set'.
Example
(gdb)
-gdb-set $foo=3
^done
(gdb)
The -gdb-showcommand
Synopsis
-gdb-show
Show the current value of a GDB variable.
GDB command
The corresponding GDB command is 'show'.
Example
(gdb)
-gdb-show annotate
^done,value="0"
(gdb)
The -gdb-versioncommand
Synopsis
-gdb-version
340 The GDB/MIInterface
Show version information for GDB. Used mostly in testing.
GDB command
The corresponding GDB command is 'show version'.
Example
(gdb)
-gdb-version
~GNU gdb 5.2.1
~Copyright 2000 Free Software Foundation, Inc.
~GDB is free software, covered by the GNU General Public License, and
~you are welcome to change it and/or distribute copies of it under
~ certain conditions.
~Type "show copying" to see the conditions.
~There is absolutely no warranty for GDB. Type "show warranty" for
~ details.
~This GDB was configured as
"--host=sparc-sun-solaris2.5.1 --target=ppc-eabi".
^done
(gdb)
21.9 GDB/MIStack Manipulation Commands
The -stack-info-framecommand
Synopsis
-stack-info-frame
Get info on the current frame.
GDB command
The corresponding GDB command is 'info frame' or 'frame' (without arguments).
Example
N.A.
The -stack-info-depthcommand
Synopsis
-stack-info-depth [ max-depth ]
Return the depth of the stack. If the integer argument max-depthis specified, do not
count beyond max-depthframes.
GDB command
There is no equivalent GDB command.
21.9 GDB/MI Stack Manipulation Commands 341
Example
For a stack with frame levels 0 through 11:
(gdb)
-stack-info-depth
^done,depth="12"
(gdb)
-stack-info-depth 4
^done,depth="4"
(gdb)
-stack-info-depth 12
^done,depth="12"
(gdb)
-stack-info-depth 11
^done,depth="11"
(gdb)
-stack-info-depth 13
^done,depth="12"
(gdb)
The -stack-list-arguments command
Synopsis
-stack-list-arguments show-values
[ low-frame high-frame ]
Display a list of the arguments for the frames between low-frameand high-frame
(inclusive). If low-frameand high-frameare not provided, list the arguments for
the whole call stack.
The show-valuesargument must have a value of 0 or 1. A value of 0 means that only
the names of the arguments are listed, a value of 1 means that both names and values
of the arguments are printed.
GDB command
GDB does not have an equivalent command. gdbtkhas a 'gdb_get_args' command
which partially overlaps with the functionality of '-stack-list-arguments'.
Example
(gdb)
-stack-list-frames
^done,
stack=[
frame={level="0 ",addr="0x00010734",func="callee4",
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",line="8"},
frame={level="1 ",addr="0x0001076c",func="callee3",
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",line="17"},
frame={level="2 ",addr="0x0001078c",func="callee2",
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",line="22"},
frame={level="3 ",addr="0x000107b4",func="callee1",
342 The GDB/MIInterface
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",line="27"},
frame={level="4 ",addr="0x000107e0",func="main",
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",line="32"}]
(gdb)
-stack-list-arguments 0
^done,
stack-args=[
frame={level="0",args=[]},
frame={level="1",args=[name="strarg"]},
frame={level="2",args=[name="intarg",name="strarg"]},
frame={level="3",args=[name="intarg",name="strarg",name="fltarg"]},
frame={level="4",args=[]}]
(gdb)
-stack-list-arguments 1
^done,
stack-args=[
frame={level="0",args=[]},
frame={level="1",
args=[{name="strarg",value="0x11940 \"A string argument.\""}]},
frame={level="2",args=[
{name="intarg",value="2"},
{name="strarg",value="0x11940 \"A string argument.\""}]},
{frame={level="3",args=[
{name="intarg",value="2"},
{name="strarg",value="0x11940 \"A string argument.\""},
{name="fltarg",value="3.5"}]},
frame={level="4",args=[]}]
(gdb)
-stack-list-arguments 0 2 2
^done,stack-args=[frame={level="2",args=[name="intarg",name="strarg"]}]
(gdb)
-stack-list-arguments 1 2 2
^done,stack-args=[frame={level="2",
args=[{name="intarg",value="2"},
{name="strarg",value="0x11940 \"A string argument.\""}]}]
(gdb)
The -stack-list-framescommand
Synopsis
-stack-list-frames [ low-frame high-frame ]
List the frames currently on the stack. For each frame it displays the following info:
'level'
The frame number, 0 being the topmost frame, that is the innermost
function.
'addr'
'func'
'file'
'line'
The $pc value for that frame.
Function name.
File name of the source file where the function lives.
Line number corresponding to the $pc.
If invoked without arguments, this command prints a backtrace for the whole stack.
If given two integer arguments, it shows the frames whose levels are between the two
21.9 GDB/MI Stack Manipulation Commands 343
arguments (inclusive). If the two arguments are equal, it shows the single frame at the
corresponding level.
GDB command
The corresponding GDB commands are 'backtrace' and 'where'.
Example
Full stack backtrace:
(gdb)
-stack-list-frames
^done,stack=
[frame={level="0 ",addr="0x0001076c",func="foo",
file="recursive2.c",line="11"},
frame={level="1 ",addr="0x000107a4",func="foo",
file="recursive2.c",line="14"},
frame={level="2 ",addr="0x000107a4",func="foo",
file="recursive2.c",line="14"},
frame={level="3 ",addr="0x000107a4",func="foo",
file="recursive2.c",line="14"},
frame={level="4 ",addr="0x000107a4",func="foo",
file="recursive2.c",line="14"},
frame={level="5 ",addr="0x000107a4",func="foo",
file="recursive2.c",line="14"},
frame={level="6 ",addr="0x000107a4",func="foo",
file="recursive2.c",line="14"},
frame={level="7 ",addr="0x000107a4",func="foo",
file="recursive2.c",line="14"},
frame={level="8 ",addr="0x000107a4",func="foo",
file="recursive2.c",line="14"},
frame={level="9 ",addr="0x000107a4",func="foo",
file="recursive2.c",line="14"},
frame={level="10",addr="0x000107a4",func="foo",
file="recursive2.c",line="14"},
frame={level="11",addr="0x00010738",func="main",
file="recursive2.c",line="4"}]
(gdb)
Show frames between low_frameand high_frame:
(gdb)
-stack-list-frames 3 5
^done,stack=
[frame={level="3 ",addr="0x000107a4",func="foo",
file="recursive2.c",line="14"},
frame={level="4 ",addr="0x000107a4",func="foo",
file="recursive2.c",line="14"},
frame={level="5 ",addr="0x000107a4",func="foo",
file="recursive2.c",line="14"}]
(gdb)
Show a single frame:
344 The GDB/MIInterface
(gdb)
-stack-list-frames 3 3
^done,stack=
[frame={level="3 ",addr="0x000107a4",func="foo",
file="recursive2.c",line="14"}]
(gdb)
The -stack-list-localscommand
Synopsis
-stack-list-locals print-values
Display the local variable names for the current frame. With an argument of 0 prints
only the names of the variables, with argument of 1 prints also their values.
GDB command
'info locals' in GDB, 'gdb_get_locals' in gdbtk.
Example
(gdb)
-stack-list-locals 0
^done,locals=[name="A",name="B",name="C"]
(gdb)
-stack-list-locals 1
^done,locals=[{name="A",value="1"},{name="B",value="2"},
{name="C",value="3"}]
(gdb)
The -stack-select-framecommand
Synopsis
-stack-select-frame framenum
Change the current frame. Select a different frame framenumon the stack.
GDB command
The corresponding GDB commands are 'frame', 'up', 'down', 'select-frame',
'up-silent', and 'down-silent'.
Example
(gdb)
-stack-select-frame 2
^done
(gdb)
21.9 GDB/MI Stack Manipulation Commands 345
21.10 GDB/MISymbol query commands
The -symbol-info-addresscommand
Synopsis
-symbol-info-address symbol
Describe where symbolis stored.
GDB command
The corresponding GDB command is 'info address'.
Example
N.A.
The -symbol-info-filecommand
Synopsis
-symbol-info-file
Show the file for the symbol.
GDB command
There is no equivalent GDB command. gdbtkhas 'gdb_find_file'.
Example
N.A.
The -symbol-info-functioncommand
Synopsis
-symbol-info-function
Show which function the symbol lives in.
GDB command
'gdb_get_function' in gdbtk.
Example
N.A.
346 The GDB/MIInterface
The -symbol-info-linecommand
Synopsis
-symbol-info-line
Show the core addresses of the code for a source line.
GDB command
The corresponding GDB command is 'info line'. gdbtkhas the 'gdb_get_line'
and 'gdb_get_file' commands.
Example
N.A.
The -symbol-info-symbolcommand
Synopsis
-symbol-info-symbol addr
Describe what symbol is at location addr.
GDB command
The corresponding GDB command is 'info symbol'.
Example
N.A.
The -symbol-list-functionscommand
Synopsis
-symbol-list-functions
List the functions in the executable.
GDB command
'info functions' in GDB, 'gdb_listfunc' and 'gdb_search' in gdbtk.
Example
N.A.
The -symbol-list-typescommand
Synopsis
-symbol-list-types
21.10 GDB/MI Symbol query commands 347
List all the type names.
GDB command
The corresponding commands are 'info types' in GDB, 'gdb_search' in gdbtk.
Example
N.A.
The -symbol-list-variablescommand
Synopsis
-symbol-list-variables
List all the global and static variable names.
GDB command
'info variables' in GDB, 'gdb_search' in gdbtk.
Example
N.A.
The -symbol-locatecommand
Synopsis
-symbol-locate
GDB command
'gdb_loc' in gdbtk.
Example
N.A.
The -symbol-typecommand
Synopsis
-symbol-type variable
Show type of variable.
GDB command
The corresponding GDB command is 'ptype', gdbtkhas 'gdb_obj_variable'.
348 The GDB/MIInterface
Example
N.A.
21.11 GDB/MITarget Manipulation Commands
The -target-attachcommand
Synopsis
-target-attach pid | file
Attach to a process pidor a file fileoutside of GDB.
GDB command
The corresponding GDB command is 'attach'.
Example
N.A.
The -target-compare-sectionscommand
Synopsis
-target-compare-sections [ section ]
Compare data of section sectionon target to the exec file. Without the argument, all
sections are compared.
GDB command
The GDB equivalent is 'compare-sections'.
Example
N.A.
The -target-detachcommand
Synopsis
-target-detach
Disconnect from the remote target. There is no output.
GDB command
The corresponding GDB command is 'detach'.
21.11 GDB/MI Target Manipulation Commands 349
Example
(gdb)
-target-detach
^done
(gdb)
The -target-downloadcommand
Synopsis
-target-download
Loads the executable onto the remote target. It prints out an update message every half
second, which includes the fields:
'section'
The name of the section.
'section-sent'
'section-size'
'total-sent'
The size of what has been sent so far for that section.
The size of the section.
The total size of what was sent so far (the current and the
previous sections).
'total-size'
The size of the overall executable to download.
In addition, it prints the name and size of the sections, as they are downloaded. These
messages include the following fields:
'section'
The name of the section.
'section-size'
'total-size'
The size of the section.
The size of the overall executable to download.
At the end, a summary is printed.
GDB command
The corresponding GDB command is 'load'.
Example
NOTE: Each status message appears on a single line. Here the messages have been
broken down so that they can fit onto a page.
(gdb)
-target-download
+download,{section=".text",section-size="6668",total-size="9880"}
+download,{section=".text",section-sent="512",section-size="6668",
total-sent="512",total-size="9880"}
+download,{section=".text",section-sent="1024",section-size="6668",
total-sent="1024",total-size="9880"}
350 The GDB/MIInterface
+download,{section=".text",section-sent="1536",section-size="6668",
total-sent="1536",total-size="9880"}
+download,{section=".text",section-sent="2048",section-size="6668",
total-sent="2048",total-size="9880"}
+download,{section=".text",section-sent="2560",section-size="6668",
total-sent="2560",total-size="9880"}
+download,{section=".text",section-sent="3072",section-size="6668",
total-sent="3072",total-size="9880"}
+download,{section=".text",section-sent="3584",section-size="6668",
total-sent="3584",total-size="9880"}
+download,{section=".text",section-sent="4096",section-size="6668",
total-sent="4096",total-size="9880"}
+download,{section=".text",section-sent="4608",section-size="6668",
total-sent="4608",total-size="9880"}
+download,{section=".text",section-sent="5120",section-size="6668",
total-sent="5120",total-size="9880"}
+download,{section=".text",section-sent="5632",section-size="6668",
total-sent="5632",total-size="9880"}
+download,{section=".text",section-sent="6144",section-size="6668",
total-sent="6144",total-size="9880"}
+download,{section=".text",section-sent="6656",section-size="6668",
total-sent="6656",total-size="9880"}
+download,{section=".init",section-size="28",total-size="9880"}
+download,{section=".fini",section-size="28",total-size="9880"}
+download,{section=".data",section-size="3156",total-size="9880"}
+download,{section=".data",section-sent="512",section-size="3156",
total-sent="7236",total-size="9880"}
+download,{section=".data",section-sent="1024",section-size="3156",
total-sent="7748",total-size="9880"}
+download,{section=".data",section-sent="1536",section-size="3156",
total-sent="8260",total-size="9880"}
+download,{section=".data",section-sent="2048",section-size="3156",
total-sent="8772",total-size="9880"}
+download,{section=".data",section-sent="2560",section-size="3156",
total-sent="9284",total-size="9880"}
+download,{section=".data",section-sent="3072",section-size="3156",
total-sent="9796",total-size="9880"}
^done,address="0x10004",load-size="9880",transfer-rate="6586",
write-rate="429"
(gdb)
The -target-exec-statuscommand
Synopsis
-target-exec-status
Provide information on the state of the target (whether it is running or not, for instance).
GDB command
There is no equivalent GDB command.
21.11 GDB/MI Target Manipulation Commands 351
Example
N.A.
The -target-list-available-targetscommand
Synopsis
-target-list-available-targets
List the possible targets to connect to.
GDB command
The corresponding GDB command is 'help target'.
Example
N.A.
The -target-list-current-targetscommand
Synopsis
-target-list-current-targets
Describe the current target.
GDB command
The corresponding information is printed by 'info file' (among other things).
Example
N.A.
The -target-list-parameterscommand
Synopsis
-target-list-parameters
GDB command
No equivalent.
Example
N.A.
352 The GDB/MIInterface
The -target-selectcommand
Synopsis
-target-select type parameters ...
Connect GDB to the remote target. This command takes two args:
'type'
The type of target, for instance 'async', 'remote', and so on.
'parameters'
Device names, host names and the like. See “Commands for
managing targets” (page 133), for more details.
The output is a connection notification, followed by the address at which the target
program is, in the following form:
^connected,addr="address",func="function name",
args=[arg list]
GDB command
The corresponding GDB command is 'target'.
Example
(gdb)
-target-select async /dev/ttya
^connected,addr="0xfe00a300",func="??",args=[]
(gdb)
21.12 GDB/MIthread commands
The -thread-infocommand
Synopsis
-thread-info
GDB command
No equivalent.
Example
N.A.
The -thread-list-all-threadscommand
Synopsis
-thread-list-all-threads
21.12 GDB/MI thread commands 353
GDB command
The equivalent GDB command is 'info threads'.
Example
N.A.
The -thread-list-idscommand
Synopsis
-thread-list-ids
Produces a list of the currently known GDB thread ids. At the end of the list it also
prints the total number of such threads.
GDB command
Part of 'info threads' supplies the same information.
Example
No threads present, besides the main process:
(gdb)
-thread-list-ids
^done,thread-ids={},number-of-threads="0"
(gdb)
Several threads:
(gdb)
-thread-list-ids
^done,thread-ids={thread-id="3",thread-id="2",thread-id="1"},
number-of-threads="3"
(gdb)
The -thread-selectcommand
Synopsis
-thread-select threadnum
Make threadnumthe current thread. It prints the number of the new current thread,
and the topmost frame for that thread.
GDB command
The corresponding GDB command is 'thread'.
Example
(gdb)
-exec-next
354 The GDB/MIInterface
^running
(gdb)
~"0x7f7f0aec"
*stopped,reason="end-stepping-range",thread-id="2",frame=addr="0x00002ca4",func
="printme",args=[name="ip"],file="multithread.c",line="9"
(gdb)
-thread-list-ids
^done,thread-ids=thread-id="2",thread-id="1",number-of-threads="2"
(gdb)
-thread-select 1
^done,new-thread-id="1",frame=level="0 ",addr="0x7ad47d70",func="_lwp_create","
+0x10",args=[],from="/usr/lib/libpthread.1"
(gdb)
21.13 GDB/MItracepoint commands
The tracepoint commands are not yet implemented.
21.14 GDB/MIvariable objects
Motivation for variable objects in GDB/MI For the implementation of a variable
debugger window (locals, watched expressions, and so on.), we are proposing the
adaptation of the existing code used by Insight.
The two main reasons for that are:
1. It has been proven in practice (it is already on its second generation).
2. It will shorten development time (needless to say how important it is now).
The original interface was designed to be used by Tcl code, so it was slightly changed
so it could be used through GDB/MI. This section describes the GDB/MIoperations that
will be available and gives some hints about their use.
NOTE: In addition to the set of operations described here, we expect the GUI
implementation of a variable window to require, at least, the following operations:
• -gdb-show output-radix
• -stack-list-arguments
• -stack-list-locals
• -stack-select-frame
Introduction to variable objects in GDB/MI The basic idea behind variable objects is
the creation of a named object to represent a variable, an expression, a memory location
or even a CPU register. For each object created, a set of operations is available for
examining or changing its properties.
Furthermore, complex data types, such as C structures, are represented in a tree format.
For instance, the structtype variable is the root and the children will represent the
struct members. If a child is itself of a complex type, it will also have children of its
own. Appropriate language differences are handled for C, C++ and Java.
When returning the actual values of the objects, this facility allows for the individual
selection of the display format used in the result creation. It can be chosen among:
21.13 GDB/MI tracepoint commands 355
binary, decimal, hexadecimal, octal, and natural. Natural refers to a default format
automatically chosen based on the variable type (like decimal for an int, hex for
pointers, and so on.).
The following is the complete set of GDB/MIoperations defined to access this
functionality:
Table 21-1 GDB/MIOperations
Operation
Description
-var-create
create a variable object
-var-delete
delete the variable object and its children
set the display format of this variable
show the display format of this variable
tells how many children this object has
return a list of the object children
show the type of this variable object
print what this variable object represents
is this variable editable? does it exist here?
get the value of this variable
-var-set-format
-var-show-format
-var-info-num-children
-var-list-children
-var-info-type
-var-info-expression
-var-show-attributes
-var-evaluate-expression
-var-assign
set the value of this variable
-var-update
update the variable and its children
In the next subsection we describe each operation in detail and suggest how it can be
used.
Description and use of operations on variable objects
The -var-createcommand
Synopsis
-var-create {name | "-"}
{frame-addr | "*"} expression
This operation creates a variable object, which allows the monitoring of a variable, the
result of an expression, a memory cell or a CPU register.
The nameparameter is the string by which the object can be referenced. It must be
unique. If '-' is specified, the varobj system will generate a string “varNNNNNN”
automatically. It will be unique provided that one does not specify nameon that format.
The command fails if a duplicate name is found.
356 The GDB/MIInterface
The frame under which the expression should be evaluated can be specified by
frame-addr. A '*' indicates that the current frame should be used.
expressionis any expression valid on the current language set (must not begin with
a '*'), or one of the following:
•
•
•
'*addr', where addris the address of a memory cell
'*addr-addr' ― a memory address range (TBD)
'$regname' ― a CPU register name
Result
This operation returns the name, number of children and the type of the object created.
Type is returned as a string as the ones generated by the GDB CLI:
name="name",numchild="N",type="type"
The -var-deletecommand
Synopsis
-var-delete name
Deletes a previously created variable object and all of its children.
Returns an error if the object nameis not found.
The -var-set-formatcommand
Synopsis
-var-set-format name format-spec
Sets the output format for the value of the object nameto be format-spec.
The syntax for the format-specis as follows:
format-spec
{binary | decimal | hexadecimal | octal | natural}
The -var-show-formatcommand
Synopsis
-var-show-format name
Returns the format used to display the value of the object name.
format
format-spec
The -var-info-num-childrencommand
Synopsis
-var-info-num-children name
21.14 GDB/MI variable objects 357
Returns the number of children of a variable object name:
numchild=n
The -var-list-childrencommand
Synopsis
-var-list-children name
Returns a list of the children of the specified variable object:
numchild=n,children={{name=name,
numchild=n,type=type},(repeats N times)}
The -var-info-typecommand
Synopsis
-var-info-type name
Returns the type of the specified variable name. The type is returned as a string in the
same format as it is output by the GDB CLI:
type=typename
The -var-info-expressioncommand
Synopsis
-var-info-expression name
Returns what is represented by the variable object name:
lang=lang-spec,exp=expression
where lang-specis {"C" | "C++" | "Java"}.
The -var-show-attributescommand
Synopsis
-var-show-attributes name
List attributes of the specified variable object name:
status=attr [ ( ,attr )* ]
where attris { { editable | noneditable } | TBD }.
The -var-evaluate-expressioncommand
Synopsis
-var-evaluate-expression name
Evaluates the expression that is represented by the specified variable object and returns
its value as a string in the current format specified for the object:
358 The GDB/MIInterface
value=value
The -var-assigncommand
Synopsis
-var-assign name expression
Assigns the value of expressionto the variable object specified by name. The object
must be 'editable'.
The -var-updatecommand
Synopsis
-var-update {name | "*"}
Update the value of the variable object nameby evaluating its expression after fetching
all the new values from memory or registers. A '*' causes all existing variable objects
to be updated.
21.14 GDB/MI variable objects 359
360
22 Reporting Bugs in GDB
Your bug reports play an essential role in making GDB reliable.
Reporting a bug may help you by bringing a solution to your problem, or it may not.
But in any case the principal function of a bug report is to help the entire community
by making the next version of GDB work better. Bug reports are your contribution to
the maintenance of GDB.
In order for a bug report to serve its purpose, you must include the information that
enables us to x the bug.
22.1 Have you found a bug?
If you are not sure whether you have found a bug, here are some guidelines:
•
If the debugger gets a fatal signal, for any input whatever, that is a GDB bug.
Reliable debuggers never crash.
•
If GDB produces an error message for valid input, that is a bug. (Note that if you're
cross debugging, the problem may also be somewhere in the connection to the
target.)
•
•
If GDB does not produce an error message for invalid input, that is a bug. However,
you should note that your idea of \invalid input" might be our idea of \an
extension" or \support for traditional practice".
If you are an experienced user of debugging tools, your suggestions for
improvement of GDB are welcome in any case.
22.2 How to report bugs
If you obtained GDB (Hewlett-Packard Wildebeest (based on GDB 5.0-hpwdb-
20000516)) as part of your HP ANSI C, HP ANSI C++, or HP Fortran compiler kit, report
problems to your HP Support Representative.
If you obtained GDB (Hewlett-Packard Wildebeest (based on GDB 5.0-hpwdb-
20000516)) from the Hewlett-Packard Web site, report problems to your HP Support
Representative. Support is covered under the support contract for your HP compiler.
The fundamental principle of reporting bugs usefully is this: “report all the facts”. If
you are not sure whether to state a fact or leave it out, state it!
Often people omit facts because they think they know what causes the problem and
assume that some details do not matter. Thus, you might assume that the name of the
variable you use in an example does not matter. Well, probably it does not, but one
cannot be sure. Perhaps the bug is a stray memory reference which happens to fetch
from the location where that name is stored in memory; perhaps, if the name were
different, the contents of that location would fool the debugger into doing the right
thing despite the bug. Play it safe and give a specific, complete example. That is the
easiest thing for you to do, and the most helpful.
22.1 Have you found a bug? 361
Keep in mind that the purpose of a bug report is to enable us to x the bug. It may be
that the bug has been reported previously, but neither you nor we can know that unless
your bug report is complete and self-contained.
Sometimes people give a few sketchy facts and ask, \Does this ring a bell?" Those bug
reports are useless, and we urge everyone to refuse to respond to them except to chide
the sender to report bugs properly.
To enable us to x the bug, you should include all these things:
•
The version of GDB. GDB announces it if you start with no arguments; you can
also print it at any time using show version.
Without this, we will not know whether there is any point in looking for the bug
in the current version of GDB.
•
•
The type of machine you are using, and the operating system name and version
number.
What compiler (and its version) was used to compile the program you are
debugging| e.g. \HP92453-01 A.10.32.03 HP C Compiler". Use the whatcommand
with the pathname of the compile command (`what /opt/ansic/bin/cc', for example)
to obtain this information.
•
The command arguments you gave the compiler to compile your example and
observe the bug. For example, did you use `-O'? To guarantee you will not omit
something important, list them all. A copy of the Makefile (or the output from
make) is sufficient.
If we were to try to guess the arguments, we would probably guess wrong and
then we might not encounter the bug.
•
•
A complete input script, and all necessary source files, that will reproduce the bug
A description of what behavior you observe that you believe is incorrect. For
example, \It gets a fatal signal."
Of course, if the bug is that GDB gets a fatal signal, then we will certainly notice
it. But if the bug is incorrect output, we might not notice unless it is glaringly
wrong. You might as well not give us a chance to make a mistake.
Even if the problem you experience is a fatal signal, you should still say so explicitly.
Suppose something strange is going on, such as, your copy of GDB is out of synch,
or you have encountered a bug in the C library on your system. (This has
happened!) Your copy might crash and ours would not. If you told us to expect a
crash, then when ours fails to crash, we would know that the bug was not
happening for us. If you had not told us to expect a crash, then we would not be
able to draw any conclusion from our observations.
Here are some things that are not necessary:
362 Reporting Bugs in GDB
•
•
•
A description of the envelope of the bug.
Often people who encounter a bug spend a lot of time investigating which changes
to the input file will make the bug go away and which changes will not affect it.
This is often time consuming and not very useful, because the way we will nd the
bug is by running a single example under the debugger with breakpoints, not by
pure deduction from a series of examples. We recommend that you save your time
for something else.
Of course, if you can nd a simpler example to report instead of the original one,
that is a convenience for us. Errors in the output will be easier to spot, running
under the debugger will take less time, and so on.
However, simplification is not vital; if you do not want to do this, report the bug
anyway and send us the entire test case you used.
A patch for the bug.
A patch for the bug does help us if it is a good one. But do not omit the necessary
information, such as the test case, on the assumption that a patch is all we need.
We might see problems with your patch and decide to x the problem another way,
or we might not understand it at all.
Sometimes with a program as complicated as GDB it is very hard to construct an
example that will make the program follow a certain path through the code. If you
do not send us the example, we will not be able to construct one, so we will not
be able to verify that the bug is fixed.
And if we cannot understand what bug you are trying to x, or why your patch
should be an improvement, we will not install it. A test case will help us to
understand.
A guess about what the bug is or what it depends on.
Such guesses are usually wrong. Even we cannot guess right about such things
without first using the debugger to nd the facts.
22.2 How to report bugs 363
364
A Installing GDB
If you obtain GDB (WDB) as part of the HP ANSI C, HP ANSI C++ Developer's Kit for
HP-UX Release 11.x, or HP Fortran, you do not have to take any special action to build
or install GDB.
If you obtain GDB (WDB) from an HP web site, you may download either an swinstall
package or a source tree, or both.
Most customers will want to install the GDB binary that is part of the swinstall package.
To do so, use a command of the form:
/usr/sbin/swinstall -s package-name WDB
Alternatively, it is possible to build GDB from the source distribution. If you want to
modify the debugger sources to tailor GDB to your needs, you may wish to do this.
The source distribution consists of a tarfile containing the source tree rooted at
gdb-4.17/.... The instructions that follow describe how to build a `gdb' executable
from this source tree. HP believes that these instructions apply to the WDB source tree
that it distributes. However, HP does not explicitly support building a `gdb' for any
non-HP platform from the WDB source tree. It may work, but HP has not tested it for
any platforms other than those described in the WDB Release Notes.
You can nd additional information specific to Hewlett-Packard in the
`README.HP.WDB' file at the root of the source tree.
GDB comes with a configure script that automates the process of preparing GDB for
5
installation; you can then use make to build the gdb program.
The GDB distribution includes all the source code you need for GDB in a single
directory, whose name is usually composed by appending the version number to `gdb'.
For example, the GDB version gdb-199991101 distribution is in the `gdb-gdb-199991101'
directory. That directory contains:
gdb-gdb-199991101/configure (and script for configuring GDB and all its supporting
supporting files)
libraries
gdb-gdb-199991101/gdb
gdb-gdb-199991101/bfd
gdb-gdb-199991101/include
gdb-gdb-199991101/libiberty
gdb-gdb-199991101/opcodes
the source specific to GDB itself
source for the Binary File Descriptor library
gnu include files
source for the `-liberty' free software library
source for the library of opcode tables and
disassemblers
gdb-gdb-199991101/readline
5
source for the gnu command-line interface
gdb-gdb-199991101/glob
source for the gnu filename pattern-matching
subroutine
5. If you have a more recent version of GDB than gdb-199991101, look at the READMEfile in the sources; we
may have improved the installation procedures since publishing this manual.
365
gdb-gdb-199991101/mmalloc
source for the gnu memory-mapped malloc
package
The simplest way to configure and build GDB is to run configure from the
gdb-version-numbersource directory, which in this example is the
gdb-gdb-199991101directory.
First switch to the gdb-version-numbersource directory if you are not already in
it; then run configure. Pass the identifier for the platform on which GDB will run as an
argument.
For example:
cd gdb-gdb-199991101
./configure host
make
where host is an identifier such as sun4'or decstation, that identifies the platform
where GDB will run. (You can often leave off host; configuretries to guess the
correct value by examining your system.)
Running configurehostand then running make builds the `bfd', `readline',
`mmalloc', and `libiberty' libraries, then gdb itself. The configured source files, and
the binaries, are left in the corresponding source directories.
configureis a Bourne-shell (/bin/sh) script; if your system does not recognize this
automatically when you run a different shell, you may need to run sh on it explicitly:
sh configure host
If you run configure from a directory that contains source directories for multiple
libraries or programs, such as the gdb-gdb-199991101source directory for version
gdb-199991101, configurecreates configuration files for every directory level
underneath (unless you tell it not to, with the --norecursionoption).
You can run the configurescript from any of the subordinate directories in the GDB
distribution if you only want to configure that subdirectory, but be sure to specify a
pathto it.
For example, with version gdb-199991101, type the following to configure only the
bfd subdirectory:
cd gdb-gdb-199991101/bfd
../configure host
You can install (gdb) anywhere; it has no hardwired paths. However, you should make
sure that the shell on your path (named by the SHELLenvironment variable) is publicly
readable. Remember that GDB uses the shell to start your program|some systems
refuse to let GDB debug child processes whose programs are not readable.
A.1 Compiling GDB in another directory
If you want to run GDB versions for several host or target machines, you need a different
gdb compiled for each combination of host and target. configureis designed to make
this easy by allowing you to generate each configuration in a separate subdirectory,
rather than in the source directory. If your makeprogram handles the VPATHfeature
366 Installing GDB
(GNU makedoes), running makein each of these directories builds the gdb program
specified there.
To build gdb in a separate directory, run configurewith the --srcdiroption to
specify where to find the source. (You also need to specify a pathto find configure
itself from your working directory. If the path to configure would be the same as the
argument to --srcdir, you can leave out the --srcdiroption; it is assumed.)
For example, with version gdb-199991101, you can build GDB in a separate directory
for a Sun 4 like this:
cd gdb-gdb-199991101
mkdir ../gdb-sun4
cd ../gdb-sun4
../gdb-gdb-199991101/configure sun4
make
When configure builds a configuration using a remote source directory, it creates a tree
for the binaries with the same structure (and using the same names) as the tree under
the source directory. In the example, you'd nd the Sun 4 library `libiberty.a' in the
directory gdb-sun4/libiberty, and GDB itself in `gdb-sun4/gdb.
One popular reason to build several GDB configurations in separate directories is to
configure GDB for cross-compiling (where GDB runs on one machine — the host —
while debugging programs that run on another machine — the target). You specify a
cross-debugging target by giving the --target=targetoption to configure.
When you run maketo build a program or library, you must run it in a configured
directory — whatever directory you were in when you called configure(or one of
its subdirectories).
The Makefilethat configuregenerates in each source directory also runs recursively.
If you type makein a source directory such as gdb-gdb-199991101 (or in a separate
configured directory configured with `--srcdir=dirname/gdb-gdb-199991101),
you will build all the required libraries, and then build GDB.
When you have multiple hosts or targets configured in separate directories, you can
run makeon them in parallel (for example, if they are NFS-mounted on each of the
hosts); they will not interfere with each other.
A.2 Specifying names for hosts and targets
The specifications used for hosts and targets in the configurescript are based on a
three-part naming scheme, but some short predefined aliases are also supported. The
full naming scheme encodes three pieces of information in the following pattern:
architecture-vendor-os
For example, you can use the alias sun4 as a host argument, or as the value for target
in a --target=targetoption. The equivalent full name is sparc-sun-sunos4.
The configurescript accompanying GDB does not provide any query facility to list
all supported host and target names or aliases. configurecalls the Bourne shell script
config.subto map abbreviations to full names; you can read the script, if you wish,
or you can use it to test your guesses on abbreviations|for example:
A.2 Specifying names for hosts and targets 367
% sh config.sub i386-linux
i386-pc-linux-gnu
% sh config.sub alpha-linux
alpha-unknown-linux-gnu
% sh config.sub hp9k700
hppa1.1-hp-hpux
% sh config.sub sun4
sparc-sun-sunos4.1.1
% sh config.sub sun3
m68k-sun-sunos4.1.1
% sh config.sub i986v
Invalid configuration `i986v': machine `i986v' not recognized
config.subis also distributed in the GDB source directory (gdb-gdb-199991101,
for version gdb-199991101).
A.3 configureoptions
Here is a summary of the configureoptions and arguments that are most often useful
for building GDB. configurealso has several other options not listed here. See Info
file configure.info, or the node What Configure Does, for a full explanation of
configure.
configure [--help]
[--prefix=dir]
[--exec-prefix=dir]
[--srcdir=dirname]
[--norecursion] [--rm]
[--target=target]
host
You may introduce options with a single -rather than --if you prefer; but you may
abbreviate option names if you use --.
--help
Display a quick summary of how to invoke configure.
--prefix=dir
Configure the source to install programs and files under
directory `dir.
--exec-prefix=dir
Configure the source to install programs under directory
dir.
--srcdir=dirname
Warning: using this option requires gnu make, or another
make that implements the VPATHfeature. Use this option
to make configurations in directories separate from the GDB
source directories. Among other things, you can use this to
build (or maintain) several configurations simultaneously,
in separate directories. configurewrites configuration
specific files in the current directory, but arranges for them
to use the source in the directory dirname. configure
creates directories under the working directory in parallel
to the source directories below dirname.
368 Installing GDB
--norecursion
--target=target
Configure only the directory level where configureis
executed; do not propagate configuration to subdirectories.
Configure GDB for cross-debugging programs running on
the specified target. Without this option, GDB is configured
to debug programs that run on the same machine (host) as
GDB itself. There is no convenient way to generate a list of
all available targets.
host ...
Configure GDB to run on the specified host. There is no
convenient way to generate a list of all available hosts.
There are many other options available as well, but they are generally needed for special
purposes only.
A.3 configure options 369
|