1 \input texinfo @c -*-texinfo-*-
2 @c Copyright 1988 1989 1990 1991 1992 1993 1994 1995
3 @c Free Software Foundation, Inc.
6 @c makeinfo ignores cmds prev to setfilename, so its arg cannot make use
7 @c of @set vars. However, you can override filename with makeinfo -o.
13 @settitle Debugging with @value{GDBN}
16 @settitle Debugging with @value{GDBN} (@value{TARGET})
19 @setchapternewpage odd
30 @c readline appendices use @vindex
33 @c !!set GDB manual's edition---not the same as GDB version!
36 @c !!set GDB manual's revision date
37 @set DATE January 1994
39 @c GDB CHANGELOG CONSULTED BETWEEN:
40 @c Fri Oct 11 23:27:06 1991 John Gilmore (gnu at cygnus.com)
41 @c Sat Dec 22 02:51:40 1990 John Gilmore (gnu at cygint)
43 @c THIS MANUAL REQUIRES TEXINFO-2 macros and info-makers to format properly.
46 @c This is a dir.info fragment to support semi-automated addition of
47 @c manuals to an info tree. zoo@cygnus.com is developing this facility.
50 * Gdb: (gdb). The @sc{gnu} debugger.
57 This file documents the @sc{gnu} debugger @value{GDBN}.
60 This is Edition @value{EDITION}, @value{DATE},
61 of @cite{Debugging with @value{GDBN}: the @sc{gnu} Source-Level Debugger}
62 for @value{GDBN} Version @value{GDBVN}.
64 Copyright (C) 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995
65 Free Software Foundation, Inc.
67 Permission is granted to make and distribute verbatim copies of
68 this manual provided the copyright notice and this permission notice
69 are preserved on all copies.
72 Permission is granted to process this file through TeX and print the
73 results, provided the printed document carries copying permission
74 notice identical to this one except for the removal of this paragraph
75 (this paragraph not being relevant to the printed manual).
78 Permission is granted to copy and distribute modified versions of this
79 manual under the conditions for verbatim copying, provided also that the
80 entire resulting derived work is distributed under the terms of a
81 permission notice identical to this one.
83 Permission is granted to copy and distribute translations of this manual
84 into another language, under the above conditions for modified versions.
88 @title Debugging with @value{GDBN}
89 @subtitle The @sc{gnu} Source-Level Debugger
91 @subtitle (@value{TARGET})
94 @subtitle Edition @value{EDITION}, for @value{GDBN} version @value{GDBVN}
95 @subtitle @value{DATE}
96 @author Richard M. Stallman and Roland H. Pesch
100 \hfill (Send bugs and comments on @value{GDBN} to bug-gdb\@prep.ai.mit.edu.)\par
101 \hfill {\it Debugging with @value{GDBN}}\par
102 \hfill \TeX{}info \texinfoversion\par
103 \hfill doc\@cygnus.com\par
107 @vskip 0pt plus 1filll
108 Copyright @copyright{} 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995
109 Free Software Foundation, Inc.
111 Published by the Free Software Foundation @*
112 675 Massachusetts Avenue, @*
113 Cambridge, MA 02139 USA @*
114 Printed copies are available for $20 each. @*
115 ISBN 1-882114-11-6 @*
117 Permission is granted to make and distribute verbatim copies of
118 this manual provided the copyright notice and this permission notice
119 are preserved on all copies.
121 Permission is granted to copy and distribute modified versions of this
122 manual under the conditions for verbatim copying, provided also that the
123 entire resulting derived work is distributed under the terms of a
124 permission notice identical to this one.
126 Permission is granted to copy and distribute translations of this manual
127 into another language, under the above conditions for modified versions.
133 @top Debugging with @value{GDBN}
135 This file describes @value{GDBN}, the @sc{gnu} symbolic debugger.
137 This is Edition @value{EDITION}, @value{DATE}, for @value{GDBN} Version
141 * Summary:: Summary of @value{GDBN}
143 * Sample Session:: A sample @value{GDBN} session
146 * Invocation:: Getting in and out of @value{GDBN}
147 * Commands:: @value{GDBN} commands
148 * Running:: Running programs under @value{GDBN}
149 * Stopping:: Stopping and continuing
150 * Stack:: Examining the stack
151 * Source:: Examining source files
152 * Data:: Examining data
154 * Languages:: Using @value{GDBN} with different languages
157 * C:: C language support
159 @c remnant makeinfo bug, blank line needed after two end-ifs?
161 * Symbols:: Examining the symbol table
162 * Altering:: Altering execution
163 * GDB Files:: @value{GDBN} files
164 * Targets:: Specifying a debugging target
165 * Controlling GDB:: Controlling @value{GDBN}
166 * Sequences:: Canned sequences of commands
168 * Emacs:: Using @value{GDBN} under @sc{gnu} Emacs
171 * GDB Bugs:: Reporting bugs in @value{GDBN}
172 * Command Line Editing:: Facilities of the readline library
173 * Using History Interactively::
175 @c * Renamed Commands::
177 @ifclear PRECONFIGURED
178 * Formatting Documentation:: How to format and print @value{GDBN} documentation
179 * Installing GDB:: Installing GDB
187 @unnumbered Summary of @value{GDBN}
189 The purpose of a debugger such as @value{GDBN} is to allow you to see what is
190 going on ``inside'' another program while it executes---or what another
191 program was doing at the moment it crashed.
193 @value{GDBN} can do four main kinds of things (plus other things in support of
194 these) to help you catch bugs in the act:
198 Start your program, specifying anything that might affect its behavior.
201 Make your program stop on specified conditions.
204 Examine what has happened, when your program has stopped.
207 Change things in your program, so you can experiment with correcting the
208 effects of one bug and go on to learn about another.
212 You can use @value{GDBN} to debug programs written in C or C++.
213 @c "MOD2" used as a "miscellaneous languages" flag here.
214 @c This is acceptable while there is no real doc for Chill and Pascal.
216 For more information, see @ref{Support,,Supported languages}.
219 For more information, see @ref{C,,C and C++}.
221 Support for Modula-2 and Chill is partial. For information on Modula-2,
222 see @ref{Modula-2,,Modula-2}. There is no further documentation on Chill yet.
224 Debugging Pascal programs which use sets, subranges, file variables, or nested
225 functions does not currently work. @value{GDBN} does not support
226 entering expressions, printing values, or similar features using Pascal syntax.
231 @value{GDBN} can be used to debug programs written in Fortran, although
232 it does not yet support entering expressions, printing values, or
233 similar features using Fortran syntax. It may be necessary to refer to
234 some variables with a trailing underscore.
239 * Free Software:: Freely redistributable software
240 * Contributors:: Contributors to GDB
244 @unnumberedsec Free software
246 @value{GDBN} is @dfn{free software}, protected by the @sc{gnu}
247 General Public License
248 (GPL). The GPL gives you the freedom to copy or adapt a licensed
249 program---but every person getting a copy also gets with it the
250 freedom to modify that copy (which means that they must get access to
251 the source code), and the freedom to distribute further copies.
252 Typical software companies use copyrights to limit your freedoms; the
253 Free Software Foundation uses the GPL to preserve these freedoms.
255 Fundamentally, the General Public License is a license which says that
256 you have these freedoms and that you cannot take these freedoms away
260 @unnumberedsec Contributors to GDB
262 Richard Stallman was the original author of GDB, and of many other @sc{gnu}
263 programs. Many others have contributed to its development. This
264 section attempts to credit major contributors. One of the virtues of
265 free software is that everyone is free to contribute to it; with
266 regret, we cannot actually acknowledge everyone here. The file
267 @file{ChangeLog} in the @value{GDBN} distribution approximates a blow-by-blow
270 Changes much prior to version 2.0 are lost in the mists of time.
273 @emph{Plea:} Additions to this section are particularly welcome. If you
274 or your friends (or enemies, to be evenhanded) have been unfairly
275 omitted from this list, we would like to add your names!
278 So that they may not regard their long labor as thankless, we
279 particularly thank those who shepherded GDB through major releases:
280 Stan Shebs (release 4.14),
281 Fred Fish (releases 4.13, 4.12, 4.11, 4.10, and 4.9),
282 Stu Grossman and John Gilmore (releases 4.8, 4.7, 4.6, 4.5, and 4.4),
283 John Gilmore (releases 4.3, 4.2, 4.1, 4.0, and 3.9);
284 Jim Kingdon (releases 3.5, 3.4, and 3.3);
285 and Randy Smith (releases 3.2, 3.1, and 3.0).
286 As major maintainer of @value{GDBN} for some period, each
287 contributed significantly to the structure, stability, and capabilities
288 of the entire debugger.
290 Richard Stallman, assisted at various times by Peter TerMaat, Chris
291 Hanson, and Richard Mlynarik, handled releases through 2.8.
294 Michael Tiemann is the author of most of the @sc{gnu} C++ support in GDB,
295 with significant additional contributions from Per Bothner. James
296 Clark wrote the @sc{gnu} C++ demangler. Early work on C++ was by Peter
297 TerMaat (who also did much general update work leading to release 3.0).
300 @value{GDBN} 4 uses the BFD subroutine library to examine multiple
301 object-file formats; BFD was a joint project of David V.
302 Henkel-Wallace, Rich Pixley, Steve Chamberlain, and John Gilmore.
304 David Johnson wrote the original COFF support; Pace Willison did
305 the original support for encapsulated COFF.
307 Adam de Boor and Bradley Davis contributed the ISI Optimum V support.
308 Per Bothner, Noboyuki Hikichi, and Alessandro Forin contributed MIPS
310 Jean-Daniel Fekete contributed Sun 386i support.
311 Chris Hanson improved the HP9000 support.
312 Noboyuki Hikichi and Tomoyuki Hasei contributed Sony/News OS 3 support.
313 David Johnson contributed Encore Umax support.
314 Jyrki Kuoppala contributed Altos 3068 support.
315 Jeff Law contributed HP PA and SOM support.
316 Keith Packard contributed NS32K support.
317 Doug Rabson contributed Acorn Risc Machine support.
318 Bob Rusk contributed Harris Nighthawk CX-UX support.
319 Chris Smith contributed Convex support (and Fortran debugging).
320 Jonathan Stone contributed Pyramid support.
321 Michael Tiemann contributed SPARC support.
322 Tim Tucker contributed support for the Gould NP1 and Gould Powernode.
323 Pace Willison contributed Intel 386 support.
324 Jay Vosburgh contributed Symmetry support.
326 Rich Schaefer and Peter Schauer helped with support of SunOS shared
329 Jay Fenlason and Roland McGrath ensured that @value{GDBN} and GAS agree about
330 several machine instruction sets.
332 Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped
333 develop remote debugging. Intel Corporation and Wind River Systems
334 contributed remote debugging modules for their products.
336 Brian Fox is the author of the readline libraries providing
337 command-line editing and command history.
339 Andrew Beers of SUNY Buffalo wrote the language-switching code,
341 the Modula-2 support,
343 and contributed the Languages chapter of this manual.
345 Fred Fish wrote most of the support for Unix System Vr4.
347 He also enhanced the command-completion support to cover C++ overloaded
351 Hitachi America, Ltd. sponsored the support for Hitachi microprocessors.
353 Kung Hsu, Jeff Law, and Rick Sladkey added support for hardware
356 Stu Grossman wrote gdbserver.
358 Jim Kingdon, Peter Schauer, Ian Taylor, and Stu Grossman made
359 nearly innumerable bug fixes and cleanups throughout GDB.
363 @chapter A Sample @value{GDBN} Session
365 You can use this manual at your leisure to read all about @value{GDBN}.
366 However, a handful of commands are enough to get started using the
367 debugger. This chapter illustrates those commands.
370 In this sample session, we emphasize user input like this: @b{input},
371 to make it easier to pick out from the surrounding output.
374 @c FIXME: this example may not be appropriate for some configs, where
375 @c FIXME...primary interest is in remote use.
377 One of the preliminary versions of @sc{gnu} @code{m4} (a generic macro
378 processor) exhibits the following bug: sometimes, when we change its
379 quote strings from the default, the commands used to capture one macro
380 definition within another stop working. In the following short @code{m4}
381 session, we define a macro @code{foo} which expands to @code{0000}; we
382 then use the @code{m4} built-in @code{defn} to define @code{bar} as the
383 same thing. However, when we change the open quote string to
384 @code{<QUOTE>} and the close quote string to @code{<UNQUOTE>}, the same
385 procedure fails to define a new synonym @code{baz}:
394 @b{define(bar,defn(`foo'))}
398 @b{changequote(<QUOTE>,<UNQUOTE>)}
400 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
403 m4: End of input: 0: fatal error: EOF in string
407 Let us use @value{GDBN} to try to see what is going on.
410 $ @b{@value{GDBP} m4}
411 @c FIXME: this falsifies the exact text played out, to permit smallbook
412 @c FIXME... format to come out better.
413 @value{GDBN} is free software and you are welcome to distribute copies
414 of it under certain conditions; type "show copying" to see
416 There is absolutely no warranty for @value{GDBN}; type "show warranty"
419 @value{GDBN} @value{GDBVN}, Copyright 1995 Free Software Foundation, Inc...
424 @value{GDBN} reads only enough symbol data to know where to find the
425 rest when needed; as a result, the first prompt comes up very quickly.
426 We now tell @value{GDBN} to use a narrower display width than usual, so
427 that examples fit in this manual.
430 (@value{GDBP}) @b{set width 70}
434 We need to see how the @code{m4} built-in @code{changequote} works.
435 Having looked at the source, we know the relevant subroutine is
436 @code{m4_changequote}, so we set a breakpoint there with the @value{GDBN}
437 @code{break} command.
440 (@value{GDBP}) @b{break m4_changequote}
441 Breakpoint 1 at 0x62f4: file builtin.c, line 879.
445 Using the @code{run} command, we start @code{m4} running under @value{GDBN}
446 control; as long as control does not reach the @code{m4_changequote}
447 subroutine, the program runs as usual:
450 (@value{GDBP}) @b{run}
451 Starting program: /work/Editorial/gdb/gnu/m4/m4
459 To trigger the breakpoint, we call @code{changequote}. @value{GDBN}
460 suspends execution of @code{m4}, displaying information about the
461 context where it stops.
464 @b{changequote(<QUOTE>,<UNQUOTE>)}
466 Breakpoint 1, m4_changequote (argc=3, argv=0x33c70)
468 879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]),argc,1,3))
472 Now we use the command @code{n} (@code{next}) to advance execution to
473 the next line of the current function.
477 882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\
482 @code{set_quotes} looks like a promising subroutine. We can go into it
483 by using the command @code{s} (@code{step}) instead of @code{next}.
484 @code{step} goes to the next line to be executed in @emph{any}
485 subroutine, so it steps into @code{set_quotes}.
489 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
491 530 if (lquote != def_lquote)
495 The display that shows the subroutine where @code{m4} is now
496 suspended (and its arguments) is called a stack frame display. It
497 shows a summary of the stack. We can use the @code{backtrace}
498 command (which can also be spelled @code{bt}), to see where we are
499 in the stack as a whole: the @code{backtrace} command displays a
500 stack frame for each active subroutine.
503 (@value{GDBP}) @b{bt}
504 #0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
506 #1 0x6344 in m4_changequote (argc=3, argv=0x33c70)
508 #2 0x8174 in expand_macro (sym=0x33320) at macro.c:242
509 #3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30)
511 #4 0x79dc in expand_input () at macro.c:40
512 #5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195
516 We step through a few more lines to see what happens. The first two
517 times, we can use @samp{s}; the next two times we use @code{n} to avoid
518 falling into the @code{xstrdup} subroutine.
522 0x3b5c 532 if (rquote != def_rquote)
524 0x3b80 535 lquote = (lq == nil || *lq == '\0') ? \
525 def_lquote : xstrdup(lq);
527 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
530 538 len_lquote = strlen(rquote);
534 The last line displayed looks a little odd; we can examine the variables
535 @code{lquote} and @code{rquote} to see if they are in fact the new left
536 and right quotes we specified. We use the command @code{p}
537 (@code{print}) to see their values.
540 (@value{GDBP}) @b{p lquote}
541 $1 = 0x35d40 "<QUOTE>"
542 (@value{GDBP}) @b{p rquote}
543 $2 = 0x35d50 "<UNQUOTE>"
547 @code{lquote} and @code{rquote} are indeed the new left and right quotes.
548 To look at some context, we can display ten lines of source
549 surrounding the current line with the @code{l} (@code{list}) command.
555 535 lquote = (lq == nil || *lq == '\0') ? def_lquote\
557 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
560 538 len_lquote = strlen(rquote);
561 539 len_rquote = strlen(lquote);
568 Let us step past the two lines that set @code{len_lquote} and
569 @code{len_rquote}, and then examine the values of those variables.
573 539 len_rquote = strlen(lquote);
576 (@value{GDBP}) @b{p len_lquote}
578 (@value{GDBP}) @b{p len_rquote}
583 That certainly looks wrong, assuming @code{len_lquote} and
584 @code{len_rquote} are meant to be the lengths of @code{lquote} and
585 @code{rquote} respectively. We can set them to better values using
586 the @code{p} command, since it can print the value of
587 any expression---and that expression can include subroutine calls and
591 (@value{GDBP}) @b{p len_lquote=strlen(lquote)}
593 (@value{GDBP}) @b{p len_rquote=strlen(rquote)}
598 Is that enough to fix the problem of using the new quotes with the
599 @code{m4} built-in @code{defn}? We can allow @code{m4} to continue
600 executing with the @code{c} (@code{continue}) command, and then try the
601 example that caused trouble initially:
607 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
614 Success! The new quotes now work just as well as the default ones. The
615 problem seems to have been just the two typos defining the wrong
616 lengths. We allow @code{m4} exit by giving it an EOF as input:
620 Program exited normally.
624 The message @samp{Program exited normally.} is from @value{GDBN}; it
625 indicates @code{m4} has finished executing. We can end our @value{GDBN}
626 session with the @value{GDBN} @code{quit} command.
629 (@value{GDBP}) @b{quit}
634 @chapter Getting In and Out of @value{GDBN}
636 This chapter discusses how to start @value{GDBN}, and how to get out of it.
640 type @samp{@value{GDBP}} to start GDB.
642 type @kbd{quit} or @kbd{C-d} to exit.
646 * Invoking GDB:: How to start @value{GDBN}
647 * Quitting GDB:: How to quit @value{GDBN}
648 * Shell Commands:: How to use shell commands inside @value{GDBN}
652 @section Invoking @value{GDBN}
655 For details on starting up @value{GDBP} as a
656 remote debugger attached to a Hitachi microprocessor, see @ref{Hitachi
657 Remote,,@value{GDBN} and Hitachi Microprocessors}.
660 Invoke @value{GDBN} by running the program @code{@value{GDBP}}. Once started,
661 @value{GDBN} reads commands from the terminal until you tell it to exit.
663 You can also run @code{@value{GDBP}} with a variety of arguments and options,
664 to specify more of your debugging environment at the outset.
667 The command-line options described here are designed
668 to cover a variety of situations; in some environments, some of these
669 options may effectively be unavailable.
672 The most usual way to start @value{GDBN} is with one argument,
673 specifying an executable program:
676 @value{GDBP} @var{program}
681 You can also start with both an executable program and a core file
685 @value{GDBP} @var{program} @var{core}
688 You can, instead, specify a process ID as a second argument, if you want
689 to debug a running process:
692 @value{GDBP} @var{program} 1234
696 would attach @value{GDBN} to process @code{1234} (unless you also have a file
697 named @file{1234}; @value{GDBN} does check for a core file first).
699 Taking advantage of the second command-line argument requires a fairly
700 complete operating system; when you use @value{GDBN} as a remote debugger
701 attached to a bare board, there may not be any notion of ``process'',
702 and there is often no way to get a core dump.
705 You can run @code{gdb} without printing the front material, which describes
706 @value{GDBN}'s non-warranty, by specifying @code{-silent}:
709 @value{GDBP} @var{-silent}
713 You can further control how @value{GDBN} starts up by using command-line
714 options. @value{GDBN} itself can remind you of the options available.
724 to display all available options and briefly describe their use
725 (@samp{@value{GDBP} -h} is a shorter equivalent).
727 All options and command line arguments you give are processed
728 in sequential order. The order makes a difference when the
729 @samp{-x} option is used.
735 * Remote Serial:: @value{GDBN} remote serial protocol
738 * i960-Nindy Remote:: @value{GDBN} with a remote i960 (Nindy)
741 * UDI29K Remote:: The UDI protocol for AMD29K
742 * EB29K Remote:: The EBMON protocol for AMD29K
745 * VxWorks Remote:: @value{GDBN} and VxWorks
748 * ST2000 Remote:: @value{GDBN} with a Tandem ST2000
751 * Hitachi Remote:: @value{GDBN} and Hitachi Microprocessors
754 * MIPS Remote:: @value{GDBN} and MIPS boards
757 * Simulator:: Simulated CPU target
760 @c remnant makeinfo bug requires this blank line after *two* end-ifblahs:
762 * File Options:: Choosing files
763 * Mode Options:: Choosing modes
771 @subsection Choosing files
774 When @value{GDBN} starts, it reads any arguments other than options as
775 specifying an executable file and core file (or process ID). This is
776 the same as if the arguments were specified by the @samp{-se} and
777 @samp{-c} options respectively. (@value{GDBN} reads the first argument
778 that does not have an associated option flag as equivalent to the
779 @samp{-se} option followed by that argument; and the second argument
780 that does not have an associated option flag, if any, as equivalent to
781 the @samp{-c} option followed by that argument.)
784 When @value{GDBN} starts, it reads any argument other than options as
785 specifying an executable file. This is the same as if the argument was
786 specified by the @samp{-se} option.
789 Many options have both long and short forms; both are shown in the
790 following list. @value{GDBN} also recognizes the long forms if you truncate
791 them, so long as enough of the option is present to be unambiguous.
792 (If you prefer, you can flag option arguments with @samp{--} rather
793 than @samp{-}, though we illustrate the more usual convention.)
796 @item -symbols @var{file}
798 Read symbol table from file @var{file}.
800 @item -exec @var{file}
802 Use file @var{file} as the executable file to execute when
807 appropriate, and for examining pure data in conjunction with a core
812 Read symbol table from file @var{file} and use it as the executable
816 @item -core @var{file}
818 Use file @var{file} as a core dump to examine.
820 @item -c @var{number}
821 Connect to process ID @var{number}, as with the @code{attach} command
822 (unless there is a file in core-dump format named @var{number}, in which
823 case @samp{-c} specifies that file as a core dump to read).
826 @item -command @var{file}
828 Execute @value{GDBN} commands from file @var{file}. @xref{Command
829 Files,, Command files}.
831 @item -directory @var{directory}
832 @itemx -d @var{directory}
833 Add @var{directory} to the path to search for source files.
838 @emph{Warning: this option depends on operating system facilities that are not
839 supported on all systems.}@*
840 If memory-mapped files are available on your system through the @code{mmap}
841 system call, you can use this option
842 to have @value{GDBN} write the symbols from your
843 program into a reusable file in the current directory. If the program you are debugging is
844 called @file{/tmp/fred}, the mapped symbol file is @file{./fred.syms}.
845 Future @value{GDBN} debugging sessions notice the presence of this file,
846 and can quickly map in symbol information from it, rather than reading
847 the symbol table from the executable program.
849 The @file{.syms} file is specific to the host machine where @value{GDBN}
850 is run. It holds an exact image of the internal @value{GDBN} symbol
851 table. It cannot be shared across multiple host platforms.
856 Read each symbol file's entire symbol table immediately, rather than
857 the default, which is to read it incrementally as it is needed.
858 This makes startup slower, but makes future operations faster.
862 The @code{-mapped} and @code{-readnow} options are typically combined in
863 order to build a @file{.syms} file that contains complete symbol
864 information. (@xref{Files,,Commands to specify files}, for information
866 a @file{.syms} file for future use is:
869 gdb -batch -nx -mapped -readnow programname
874 @subsection Choosing modes
876 You can run @value{GDBN} in various alternative modes---for example, in
877 batch mode or quiet mode.
882 Do not execute commands from any initialization files (normally called
883 @file{@value{GDBINIT}}). Normally, the commands in these files are
884 executed after all the command options and arguments have been
885 processed. @xref{Command Files,,Command files}.
889 ``Quiet''. Do not print the introductory and copyright messages. These
890 messages are also suppressed in batch mode.
893 Run in batch mode. Exit with status @code{0} after processing all the
894 command files specified with @samp{-x} (and all commands from
895 initialization files, if not inhibited with @samp{-n}). Exit with
896 nonzero status if an error occurs in executing the @value{GDBN} commands
897 in the command files.
899 Batch mode may be useful for running @value{GDBN} as a filter, for example to
900 download and run a program on another computer; in order to make this
901 more useful, the message
904 Program exited normally.
908 (which is ordinarily issued whenever a program running under @value{GDBN} control
909 terminates) is not issued when running in batch mode.
911 @item -cd @var{directory}
912 Run @value{GDBN} using @var{directory} as its working directory,
913 instead of the current directory.
916 @item -context @var{authentication}
917 When the Energize programming system starts up @value{GDBN}, it uses this
918 option to trigger an alternate mode of interaction.
919 @var{authentication} is a pair of numeric codes that identify @value{GDBN}
920 as a client in the Energize environment. Avoid this option when you run
921 @value{GDBN} directly from the command line. See @ref{Energize,,Using
922 @value{GDBN} with Energize} for more discussion of using @value{GDBN} with Energize.
928 @sc{gnu} Emacs sets this option when it runs @value{GDBN} as a subprocess. It tells @value{GDBN}
929 to output the full file name and line number in a standard,
930 recognizable fashion each time a stack frame is displayed (which
931 includes each time your program stops). This recognizable format looks
932 like two @samp{\032} characters, followed by the file name, line number
933 and character position separated by colons, and a newline. The
934 Emacs-to-@value{GDBN} interface program uses the two @samp{\032} characters as
935 a signal to display the source code for the frame.
940 Set the line speed (baud rate or bits per second) of any serial
941 interface used by @value{GDBN} for remote debugging.
943 @item -tty @var{device}
944 Run using @var{device} for your program's standard input and output.
945 @c FIXME: kingdon thinks there is more to -tty. Investigate.
950 @section Quitting @value{GDBN}
951 @cindex exiting @value{GDBN}
952 @cindex leaving @value{GDBN}
958 To exit @value{GDBN}, use the @code{quit} command (abbreviated @code{q}), or
959 type an end-of-file character (usually @kbd{C-d}).
963 An interrupt (often @kbd{C-c}) does not exit from @value{GDBN}, but rather
964 terminates the action of any @value{GDBN} command that is in progress and
965 returns to @value{GDBN} command level. It is safe to type the interrupt
966 character at any time because @value{GDBN} does not allow it to take effect
967 until a time when it is safe.
970 If you have been using @value{GDBN} to control an attached process or
971 device, you can release it with the @code{detach} command
972 (@pxref{Attach, ,Debugging an already-running process}).
976 @section Shell commands
978 If you need to execute occasional shell commands during your
979 debugging session, there is no need to leave or suspend @value{GDBN}; you can
980 just use the @code{shell} command.
985 @item shell @var{command string}
986 Invoke a the standard shell to execute @var{command string}.
988 If it exists, the environment variable @code{SHELL} determines which
989 shell to run. Otherwise @value{GDBN} uses @code{/bin/sh}.
993 The utility @code{make} is often needed in development environments.
994 You do not have to use the @code{shell} command for this purpose in
1000 @item make @var{make-args}
1001 Execute the @code{make} program with the specified
1002 arguments. This is equivalent to @samp{shell make @var{make-args}}.
1006 @chapter @value{GDBN} Commands
1008 You can abbreviate a @value{GDBN} command to the first few letters of the command
1009 name, if that abbreviation is unambiguous; and you can repeat certain
1010 @value{GDBN} commands by typing just @key{RET}. You can also use the @key{TAB}
1011 key to get @value{GDBN} to fill out the rest of a word in a command (or to
1012 show you the alternatives available, if there is more than one possibility).
1015 * Command Syntax:: How to give commands to @value{GDBN}
1016 * Completion:: Command completion
1017 * Help:: How to ask @value{GDBN} for help
1020 @node Command Syntax
1021 @section Command syntax
1023 A @value{GDBN} command is a single line of input. There is no limit on
1024 how long it can be. It starts with a command name, which is followed by
1025 arguments whose meaning depends on the command name. For example, the
1026 command @code{step} accepts an argument which is the number of times to
1027 step, as in @samp{step 5}. You can also use the @code{step} command
1028 with no arguments. Some command names do not allow any arguments.
1030 @cindex abbreviation
1031 @value{GDBN} command names may always be truncated if that abbreviation is
1032 unambiguous. Other possible command abbreviations are listed in the
1033 documentation for individual commands. In some cases, even ambiguous
1034 abbreviations are allowed; for example, @code{s} is specially defined as
1035 equivalent to @code{step} even though there are other commands whose
1036 names start with @code{s}. You can test abbreviations by using them as
1037 arguments to the @code{help} command.
1039 @cindex repeating commands
1041 A blank line as input to @value{GDBN} (typing just @key{RET}) means to
1042 repeat the previous command. Certain commands (for example, @code{run})
1043 will not repeat this way; these are commands whose unintentional
1044 repetition might cause trouble and which you are unlikely to want to
1047 The @code{list} and @code{x} commands, when you repeat them with
1048 @key{RET}, construct new arguments rather than repeating
1049 exactly as typed. This permits easy scanning of source or memory.
1051 @value{GDBN} can also use @key{RET} in another way: to partition lengthy
1052 output, in a way similar to the common utility @code{more}
1053 (@pxref{Screen Size,,Screen size}). Since it is easy to press one
1054 @key{RET} too many in this situation, @value{GDBN} disables command
1055 repetition after any command that generates this sort of display.
1059 Any text from a @kbd{#} to the end of the line is a comment; it does
1060 nothing. This is useful mainly in command files (@pxref{Command
1061 Files,,Command files}).
1064 @section Command completion
1067 @cindex word completion
1068 @value{GDBN} can fill in the rest of a word in a command for you, if there is
1069 only one possibility; it can also show you what the valid possibilities
1070 are for the next word in a command, at any time. This works for @value{GDBN}
1071 commands, @value{GDBN} subcommands, and the names of symbols in your program.
1073 Press the @key{TAB} key whenever you want @value{GDBN} to fill out the rest
1074 of a word. If there is only one possibility, @value{GDBN} fills in the
1075 word, and waits for you to finish the command (or press @key{RET} to
1076 enter it). For example, if you type
1078 @c FIXME "@key" does not distinguish its argument sufficiently to permit
1079 @c complete accuracy in these examples; space introduced for clarity.
1080 @c If texinfo enhancements make it unnecessary, it would be nice to
1081 @c replace " @key" by "@key" in the following...
1083 (@value{GDBP}) info bre @key{TAB}
1087 @value{GDBN} fills in the rest of the word @samp{breakpoints}, since that is
1088 the only @code{info} subcommand beginning with @samp{bre}:
1091 (@value{GDBP}) info breakpoints
1095 You can either press @key{RET} at this point, to run the @code{info
1096 breakpoints} command, or backspace and enter something else, if
1097 @samp{breakpoints} does not look like the command you expected. (If you
1098 were sure you wanted @code{info breakpoints} in the first place, you
1099 might as well just type @key{RET} immediately after @samp{info bre},
1100 to exploit command abbreviations rather than command completion).
1102 If there is more than one possibility for the next word when you press
1103 @key{TAB}, @value{GDBN} sounds a bell. You can either supply more
1104 characters and try again, or just press @key{TAB} a second time;
1105 @value{GDBN} displays all the possible completions for that word. For
1106 example, you might want to set a breakpoint on a subroutine whose name
1107 begins with @samp{make_}, but when you type @kbd{b make_@key{TAB}} @value{GDBN}
1108 just sounds the bell. Typing @key{TAB} again displays all the
1109 function names in your program that begin with those characters, for
1113 (@value{GDBP}) b make_ @key{TAB}
1114 @exdent @value{GDBN} sounds bell; press @key{TAB} again, to see:
1115 make_a_section_from_file make_environ
1116 make_abs_section make_function_type
1117 make_blockvector make_pointer_type
1118 make_cleanup make_reference_type
1119 make_command make_symbol_completion_list
1120 (@value{GDBP}) b make_
1124 After displaying the available possibilities, @value{GDBN} copies your
1125 partial input (@samp{b make_} in the example) so you can finish the
1128 If you just want to see the list of alternatives in the first place, you
1129 can press @kbd{M-?} rather than pressing @key{TAB} twice. @kbd{M-?}
1130 means @kbd{@key{META} ?}. You can type this
1132 either by holding down a
1133 key designated as the @key{META} shift on your keyboard (if there is
1134 one) while typing @kbd{?}, or
1136 as @key{ESC} followed by @kbd{?}.
1138 @cindex quotes in commands
1139 @cindex completion of quoted strings
1140 Sometimes the string you need, while logically a ``word'', may contain
1141 parentheses or other characters that @value{GDBN} normally excludes from its
1142 notion of a word. To permit word completion to work in this situation,
1143 you may enclose words in @code{'} (single quote marks) in @value{GDBN} commands.
1146 The most likely situation where you might need this is in typing the
1147 name of a C++ function. This is because C++ allows function overloading
1148 (multiple definitions of the same function, distinguished by argument
1149 type). For example, when you want to set a breakpoint you may need to
1150 distinguish whether you mean the version of @code{name} that takes an
1151 @code{int} parameter, @code{name(int)}, or the version that takes a
1152 @code{float} parameter, @code{name(float)}. To use the word-completion
1153 facilities in this situation, type a single quote @code{'} at the
1154 beginning of the function name. This alerts @value{GDBN} that it may need to
1155 consider more information than usual when you press @key{TAB} or
1156 @kbd{M-?} to request word completion:
1159 (@value{GDBP}) b 'bubble( @key{M-?}
1160 bubble(double,double) bubble(int,int)
1161 (@value{GDBP}) b 'bubble(
1164 In some cases, @value{GDBN} can tell that completing a name requires using
1165 quotes. When this happens, @value{GDBN} inserts the quote for you (while
1166 completing as much as it can) if you do not type the quote in the first
1170 (@value{GDBP}) b bub @key{TAB}
1171 @exdent @value{GDBN} alters your input line to the following, and rings a bell:
1172 (@value{GDBP}) b 'bubble(
1176 In general, @value{GDBN} can tell that a quote is needed (and inserts it) if
1177 you have not yet started typing the argument list when you ask for
1178 completion on an overloaded symbol.
1183 @section Getting help
1184 @cindex online documentation
1187 You can always ask @value{GDBN} itself for information on its commands,
1188 using the command @code{help}.
1194 You can use @code{help} (abbreviated @code{h}) with no arguments to
1195 display a short list of named classes of commands:
1199 List of classes of commands:
1201 running -- Running the program
1202 stack -- Examining the stack
1203 data -- Examining data
1204 breakpoints -- Making program stop at certain points
1205 files -- Specifying and examining files
1206 status -- Status inquiries
1207 support -- Support facilities
1208 user-defined -- User-defined commands
1209 aliases -- Aliases of other commands
1210 obscure -- Obscure features
1212 Type "help" followed by a class name for a list of
1213 commands in that class.
1214 Type "help" followed by command name for full
1216 Command name abbreviations are allowed if unambiguous.
1220 @item help @var{class}
1221 Using one of the general help classes as an argument, you can get a
1222 list of the individual commands in that class. For example, here is the
1223 help display for the class @code{status}:
1226 (@value{GDBP}) help status
1231 @c Line break in "show" line falsifies real output, but needed
1232 @c to fit in smallbook page size.
1233 show -- Generic command for showing things set
1235 info -- Generic command for printing status
1237 Type "help" followed by command name for full
1239 Command name abbreviations are allowed if unambiguous.
1243 @item help @var{command}
1244 With a command name as @code{help} argument, @value{GDBN} displays a
1245 short paragraph on how to use that command.
1248 @item complete @var{args}
1249 The @code{complete @var{args}} command lists all the possible completions
1250 for the beginning of a command. Use @var{args} to specify the beginning of the
1251 command you want completed. For example:
1257 @noindent results in:
1265 @noindent This is intended for use by @sc{gnu} Emacs.
1268 In addition to @code{help}, you can use the @value{GDBN} commands @code{info}
1269 and @code{show} to inquire about the state of your program, or the state
1270 of @value{GDBN} itself. Each command supports many topics of inquiry; this
1271 manual introduces each of them in the appropriate context. The listings
1272 under @code{info} and under @code{show} in the Index point to
1273 all the sub-commands. @xref{Index}.
1280 This command (abbreviated @code{i}) is for describing the state of your
1281 program. For example, you can list the arguments given to your program
1282 with @code{info args}, list the registers currently in use with @code{info
1283 registers}, or list the breakpoints you have set with @code{info breakpoints}.
1284 You can get a complete list of the @code{info} sub-commands with
1285 @w{@code{help info}}.
1289 You can assign the result of an expresson to an environment variable with
1290 @code{set}. For example, you can set the @value{GDBN} prompt to a $-sign with
1291 @code{set prompt $}.
1295 In contrast to @code{info}, @code{show} is for describing the state of
1296 @value{GDBN} itself.
1297 You can change most of the things you can @code{show}, by using the
1298 related command @code{set}; for example, you can control what number
1299 system is used for displays with @code{set radix}, or simply inquire
1300 which is currently in use with @code{show radix}.
1303 To display all the settable parameters and their current
1304 values, you can use @code{show} with no arguments; you may also use
1305 @code{info set}. Both commands produce the same display.
1306 @c FIXME: "info set" violates the rule that "info" is for state of
1307 @c FIXME...program. Ck w/ GNU: "info set" to be called something else,
1308 @c FIXME...or change desc of rule---eg "state of prog and debugging session"?
1312 Here are three miscellaneous @code{show} subcommands, all of which are
1313 exceptional in lacking corresponding @code{set} commands:
1316 @kindex show version
1317 @cindex version number
1319 Show what version of @value{GDBN} is running. You should include this
1320 information in @value{GDBN} bug-reports. If multiple versions of @value{GDBN} are in
1321 use at your site, you may occasionally want to determine which version
1322 of @value{GDBN} you are running; as @value{GDBN} evolves, new commands are introduced,
1323 and old ones may wither away. The version number is also announced
1324 when you start @value{GDBN}.
1326 @kindex show copying
1328 Display information about permission for copying @value{GDBN}.
1330 @kindex show warranty
1332 Display the @sc{gnu} ``NO WARRANTY'' statement.
1336 @chapter Running Programs Under @value{GDBN}
1338 When you run a program under @value{GDBN}, you must first generate
1339 debugging information when you compile it.
1341 You may start @value{GDBN} with its arguments, if any, in an environment
1342 of your choice. You may redirect your program's input and output, debug an
1343 already running process, or kill a child process.
1347 * Compilation:: Compiling for debugging
1348 * Starting:: Starting your program
1350 * Arguments:: Your program's arguments
1351 * Environment:: Your program's environment
1352 * Working Directory:: Your program's working directory
1353 * Input/Output:: Your program's input and output
1354 * Attach:: Debugging an already-running process
1355 * Kill Process:: Killing the child process
1356 * Process Information:: Additional process information
1357 * Threads:: Debugging programs with multiple threads
1358 * Processes:: Debugging programs with multiple processes
1363 @section Compiling for debugging
1365 In order to debug a program effectively, you need to generate
1366 debugging information when you compile it. This debugging information
1367 is stored in the object file; it describes the data type of each
1368 variable or function and the correspondence between source line numbers
1369 and addresses in the executable code.
1371 To request debugging information, specify the @samp{-g} option when you run
1374 Many C compilers are unable to handle the @samp{-g} and @samp{-O}
1375 options together. Using those compilers, you cannot generate optimized
1376 executables containing debugging information.
1378 @value{NGCC}, the @sc{gnu} C compiler, supports @samp{-g} with or without
1379 @samp{-O}, making it possible to debug optimized code. We recommend
1380 that you @emph{always} use @samp{-g} whenever you compile a program.
1381 You may think your program is correct, but there is no sense in pushing
1384 @cindex optimized code, debugging
1385 @cindex debugging optimized code
1386 When you debug a program compiled with @samp{-g -O}, remember that the
1387 optimizer is rearranging your code; the debugger shows you what is
1388 really there. Do not be too surprised when the execution path does not
1389 exactly match your source file! An extreme example: if you define a
1390 variable, but never use it, @value{GDBN} never sees that
1391 variable---because the compiler optimizes it out of existence.
1393 Some things do not work as well with @samp{-g -O} as with just
1394 @samp{-g}, particularly on machines with instruction scheduling. If in
1395 doubt, recompile with @samp{-g} alone, and if this fixes the problem,
1396 please report it to us as a bug (including a test case!).
1398 Older versions of the @sc{gnu} C compiler permitted a variant option
1399 @w{@samp{-gg}} for debugging information. @value{GDBN} no longer supports this
1400 format; if your @sc{gnu} C compiler has this option, do not use it.
1404 @section Starting your program
1412 Use the @code{run} command to start your program under @value{GDBN}. You must
1413 first specify the program name
1417 with an argument to @value{GDBN} (@pxref{Invocation, ,Getting In and
1418 Out of @value{GDBN}}), or by using the @code{file} or @code{exec-file}
1419 command (@pxref{Files, ,Commands to specify files}).
1424 If you are running your program in an execution environment that
1425 supports processes, @code{run} creates an inferior process and makes
1426 that process run your program. (In environments without processes,
1427 @code{run} jumps to the start of your program.)
1429 The execution of a program is affected by certain information it
1430 receives from its superior. @value{GDBN} provides ways to specify this
1431 information, which you must do @emph{before} starting your program. (You
1432 can change it after starting your program, but such changes only affect
1433 your program the next time you start it.) This information may be
1434 divided into four categories:
1437 @item The @emph{arguments.}
1438 Specify the arguments to give your program as the arguments of the
1439 @code{run} command. If a shell is available on your target, the shell
1440 is used to pass the arguments, so that you may use normal conventions
1441 (such as wildcard expansion or variable substitution) in describing
1442 the arguments. In Unix systems, you can control which shell is used
1443 with the @code{SHELL} environment variable. @xref{Arguments, ,Your
1444 program's arguments}.
1446 @item The @emph{environment.}
1447 Your program normally inherits its environment from @value{GDBN}, but you can
1448 use the @value{GDBN} commands @code{set environment} and @code{unset
1449 environment} to change parts of the environment that affect
1450 your program. @xref{Environment, ,Your program's environment}.
1452 @item The @emph{working directory.}
1453 Your program inherits its working directory from @value{GDBN}. You can set
1454 the @value{GDBN} working directory with the @code{cd} command in @value{GDBN}.
1455 @xref{Working Directory, ,Your program's working directory}.
1457 @item The @emph{standard input and output.}
1458 Your program normally uses the same device for standard input and
1459 standard output as @value{GDBN} is using. You can redirect input and output
1460 in the @code{run} command line, or you can use the @code{tty} command to
1461 set a different device for your program.
1462 @xref{Input/Output, ,Your program's input and output}.
1465 @emph{Warning:} While input and output redirection work, you cannot use
1466 pipes to pass the output of the program you are debugging to another
1467 program; if you attempt this, @value{GDBN} is likely to wind up debugging the
1472 When you issue the @code{run} command, your program begins to execute
1473 immediately. @xref{Stopping, ,Stopping and continuing}, for discussion
1474 of how to arrange for your program to stop. Once your program has
1475 stopped, you may call functions in your program, using the @code{print}
1476 or @code{call} commands. @xref{Data, ,Examining Data}.
1478 If the modification time of your symbol file has changed since the last
1479 time @value{GDBN} read its symbols, @value{GDBN} discards its symbol
1480 table, and reads it again. When it does this, @value{GDBN} tries to retain
1481 your current breakpoints.
1485 @section Your program's arguments
1487 @cindex arguments (to your program)
1488 The arguments to your program can be specified by the arguments of the
1489 @code{run} command. They are passed to a shell, which expands wildcard
1490 characters and performs redirection of I/O, and thence to your program.
1491 Your @code{SHELL} environment variable (if it exists) specifies what
1492 shell @value{GDBN} uses. If you do not define @code{SHELL},
1493 @value{GDBN} uses @code{/bin/sh}.
1495 @code{run} with no arguments uses the same arguments used by the previous
1496 @code{run}, or those set by the @code{set args} command.
1501 Specify the arguments to be used the next time your program is run. If
1502 @code{set args} has no arguments, @code{run} executes your program
1503 with no arguments. Once you have run your program with arguments,
1504 using @code{set args} before the next @code{run} is the only way to run
1505 it again without arguments.
1509 Show the arguments to give your program when it is started.
1513 @section Your program's environment
1515 @cindex environment (of your program)
1516 The @dfn{environment} consists of a set of environment variables and
1517 their values. Environment variables conventionally record such things as
1518 your user name, your home directory, your terminal type, and your search
1519 path for programs to run. Usually you set up environment variables with
1520 the shell and they are inherited by all the other programs you run. When
1521 debugging, it can be useful to try running your program with a modified
1522 environment without having to start @value{GDBN} over again.
1526 @item path @var{directory}
1527 Add @var{directory} to the front of the @code{PATH} environment variable
1528 (the search path for executables), for both @value{GDBN} and your program.
1529 You may specify several directory names, separated by @samp{:} or
1530 whitespace. If @var{directory} is already in the path, it is moved to
1531 the front, so it is searched sooner.
1533 You can use the string @samp{$cwd} to refer to whatever is the current
1534 working directory at the time @value{GDBN} searches the path. If you
1535 use @samp{.} instead, it refers to the directory where you executed the
1536 @code{path} command. @value{GDBN} replaces @samp{.} in the
1537 @var{directory} argument (with the current path) before adding
1538 @var{directory} to the search path.
1539 @c 'path' is explicitly nonrepeatable, but RMS points out it is silly to
1540 @c document that, since repeating it would be a no-op.
1544 Display the list of search paths for executables (the @code{PATH}
1545 environment variable).
1547 @kindex show environment
1548 @item show environment @r{[}@var{varname}@r{]}
1549 Print the value of environment variable @var{varname} to be given to
1550 your program when it starts. If you do not supply @var{varname},
1551 print the names and values of all environment variables to be given to
1552 your program. You can abbreviate @code{environment} as @code{env}.
1554 @kindex set environment
1555 @item set environment @var{varname} @r{[}=@r{]} @var{value}
1556 Set environment variable @var{varname} to @var{value}. The value
1557 changes for your program only, not for @value{GDBN} itself. @var{value} may
1558 be any string; the values of environment variables are just strings, and
1559 any interpretation is supplied by your program itself. The @var{value}
1560 parameter is optional; if it is eliminated, the variable is set to a
1562 @c "any string" here does not include leading, trailing
1563 @c blanks. Gnu asks: does anyone care?
1565 For example, this command:
1572 tells a Unix program, when subsequently run, that its user is named
1573 @samp{foo}. (The spaces around @samp{=} are used for clarity here; they
1574 are not actually required.)
1576 @kindex unset environment
1577 @item unset environment @var{varname}
1578 Remove variable @var{varname} from the environment to be passed to your
1579 program. This is different from @samp{set env @var{varname} =};
1580 @code{unset environment} removes the variable from the environment,
1581 rather than assigning it an empty value.
1584 @emph{Warning:} @value{GDBN} runs your program using the shell indicated
1585 by your @code{SHELL} environment variable if it exists (or
1586 @code{/bin/sh} if not). If your @code{SHELL} variable names a shell
1587 that runs an initialization file---such as @file{.cshrc} for C-shell, or
1588 @file{.bashrc} for BASH---any variables you set in that file affect
1589 your program. You may wish to move setting of environment variables to
1590 files that are only run when you sign on, such as @file{.login} or
1593 @node Working Directory
1594 @section Your program's working directory
1596 @cindex working directory (of your program)
1597 Each time you start your program with @code{run}, it inherits its
1598 working directory from the current working directory of @value{GDBN}.
1599 The @value{GDBN} working directory is initially whatever it inherited
1600 from its parent process (typically the shell), but you can specify a new
1601 working directory in @value{GDBN} with the @code{cd} command.
1603 The @value{GDBN} working directory also serves as a default for the commands
1604 that specify files for @value{GDBN} to operate on. @xref{Files, ,Commands to
1609 @item cd @var{directory}
1610 Set the @value{GDBN} working directory to @var{directory}.
1614 Print the @value{GDBN} working directory.
1618 @section Your program's input and output
1623 By default, the program you run under @value{GDBN} does input and output to
1624 the same terminal that @value{GDBN} uses. @value{GDBN} switches the terminal
1625 to its own terminal modes to interact with you, but it records the terminal
1626 modes your program was using and switches back to them when you continue
1627 running your program.
1630 @kindex info terminal
1632 Displays information recorded by @value{GDBN} about the terminal modes your
1636 You can redirect your program's input and/or output using shell
1637 redirection with the @code{run} command. For example,
1644 starts your program, diverting its output to the file @file{outfile}.
1647 @cindex controlling terminal
1648 Another way to specify where your program should do input and output is
1649 with the @code{tty} command. This command accepts a file name as
1650 argument, and causes this file to be the default for future @code{run}
1651 commands. It also resets the controlling terminal for the child
1652 process, for future @code{run} commands. For example,
1659 directs that processes started with subsequent @code{run} commands
1660 default to do input and output on the terminal @file{/dev/ttyb} and have
1661 that as their controlling terminal.
1663 An explicit redirection in @code{run} overrides the @code{tty} command's
1664 effect on the input/output device, but not its effect on the controlling
1667 When you use the @code{tty} command or redirect input in the @code{run}
1668 command, only the input @emph{for your program} is affected. The input
1669 for @value{GDBN} still comes from your terminal.
1672 @section Debugging an already-running process
1677 @item attach @var{process-id}
1678 This command attaches to a running process---one that was started
1679 outside @value{GDBN}. (@code{info files} shows your active
1680 targets.) The command takes as argument a process ID. The usual way to
1681 find out the process-id of a Unix process is with the @code{ps} utility,
1682 or with the @samp{jobs -l} shell command.
1684 @code{attach} does not repeat if you press @key{RET} a second time after
1685 executing the command.
1688 To use @code{attach}, your program must be running in an environment
1689 which supports processes; for example, @code{attach} does not work for
1690 programs on bare-board targets that lack an operating system. You must
1691 also have permission to send the process a signal.
1693 When using @code{attach}, you should first use the @code{file} command
1694 to specify the program running in the process and load its symbol table.
1695 @xref{Files, ,Commands to Specify Files}.
1697 The first thing @value{GDBN} does after arranging to debug the specified
1698 process is to stop it. You can examine and modify an attached process
1699 with all the @value{GDBN} commands that are ordinarily available when you start
1700 processes with @code{run}. You can insert breakpoints; you can step and
1701 continue; you can modify storage. If you would rather the process
1702 continue running, you may use the @code{continue} command after
1703 attaching @value{GDBN} to the process.
1708 When you have finished debugging the attached process, you can use the
1709 @code{detach} command to release it from @value{GDBN} control. Detaching
1710 the process continues its execution. After the @code{detach} command,
1711 that process and @value{GDBN} become completely independent once more, and you
1712 are ready to @code{attach} another process or start one with @code{run}.
1713 @code{detach} does not repeat if you press @key{RET} again after
1714 executing the command.
1717 If you exit @value{GDBN} or use the @code{run} command while you have an
1718 attached process, you kill that process. By default, @value{GDBN} asks
1719 for confirmation if you try to do either of these things; you can
1720 control whether or not you need to confirm by using the @code{set
1721 confirm} command (@pxref{Messages/Warnings, ,Optional warnings and
1726 @section Killing the child process
1731 Kill the child process in which your program is running under @value{GDBN}.
1734 This command is useful if you wish to debug a core dump instead of a
1735 running process. @value{GDBN} ignores any core dump file while your program
1739 On some operating systems, a program cannot be executed outside @value{GDBN}
1740 while you have breakpoints set on it inside @value{GDBN}. You can use the
1741 @code{kill} command in this situation to permit running your program
1742 outside the debugger.
1744 The @code{kill} command is also useful if you wish to recompile and
1745 relink your program, since on many systems it is impossible to modify an
1746 executable file while it is running in a process. In this case, when you
1747 next type @code{run}, @value{GDBN} notices that the file has changed, and
1748 reads the symbol table again (while trying to preserve your current
1749 breakpoint settings).
1751 @node Process Information
1752 @section Additional process information
1755 @cindex process image
1756 Some operating systems provide a facility called @samp{/proc} that can
1757 be used to examine the image of a running process using file-system
1758 subroutines. If @value{GDBN} is configured for an operating system with this
1759 facility, the command @code{info proc} is available to report on several
1760 kinds of information about the process running your program.
1761 @code{info proc} works only on SVR4 systems that support @code{procfs}.
1766 Summarize available information about the process.
1768 @kindex info proc mappings
1769 @item info proc mappings
1770 Report on the address ranges accessible in the program, with information
1771 on whether your program may read, write, or execute each range.
1773 @kindex info proc times
1774 @item info proc times
1775 Starting time, user CPU time, and system CPU time for your program and
1778 @kindex info proc id
1780 Report on the process IDs related to your program: its own process ID,
1781 the ID of its parent, the process group ID, and the session ID.
1783 @kindex info proc status
1784 @item info proc status
1785 General information on the state of the process. If the process is
1786 stopped, this report includes the reason for stopping, and any signal
1790 Show all the above information about the process.
1794 @section Debugging programs with multiple threads
1796 @cindex threads of execution
1797 @cindex multiple threads
1798 @cindex switching threads
1799 In some operating systems, a single program may have more than one
1800 @dfn{thread} of execution. The precise semantics of threads differ from
1801 one operating system to another, but in general the threads of a single
1802 program are akin to multiple processes---except that they share one
1803 address space (that is, they can all examine and modify the same
1804 variables). On the other hand, each thread has its own registers and
1805 execution stack, and perhaps private memory.
1807 @value{GDBN} provides these facilities for debugging multi-thread
1811 @item automatic notification of new threads
1812 @item @samp{thread @var{threadno}}, a command to switch among threads
1813 @item @samp{info threads}, a command to inquire about existing threads
1814 @item @samp{thread apply [@var{threadno}] [@var{all}] @var{args}},
1815 a command to apply a command to a list of threads
1816 @item thread-specific breakpoints
1820 @emph{Warning:} These facilities are not yet available on every
1821 @value{GDBN} configuration where the operating system supports threads.
1822 If your @value{GDBN} does not support threads, these commands have no
1823 effect. For example, a system without thread support shows no output
1824 from @samp{info threads}, and always rejects the @code{thread} command,
1828 (@value{GDBP}) info threads
1829 (@value{GDBP}) thread 1
1830 Thread ID 1 not known. Use the "info threads" command to
1831 see the IDs of currently known threads.
1833 @c FIXME to implementors: how hard would it be to say "sorry, this GDB
1834 @c doesn't support threads"?
1837 @cindex focus of debugging
1838 @cindex current thread
1839 The @value{GDBN} thread debugging facility allows you to observe all
1840 threads while your program runs---but whenever @value{GDBN} takes
1841 control, one thread in particular is always the focus of debugging.
1842 This thread is called the @dfn{current thread}. Debugging commands show
1843 program information from the perspective of the current thread.
1845 @kindex New @var{systag}
1846 @cindex thread identifier (system)
1847 @c FIXME-implementors!! It would be more helpful if the [New...] message
1848 @c included GDB's numeric thread handle, so you could just go to that
1849 @c thread without first checking `info threads'.
1850 Whenever @value{GDBN} detects a new thread in your program, it displays
1851 the target system's identification for the thread with a message in the
1852 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
1853 whose form varies depending on the particular system. For example, on
1854 LynxOS, you might see
1857 [New process 35 thread 27]
1861 when @value{GDBN} notices a new thread. In contrast, on an SGI system,
1862 the @var{systag} is simply something like @samp{process 368}, with no
1865 @c FIXME!! (1) Does the [New...] message appear even for the very first
1866 @c thread of a program, or does it only appear for the
1867 @c second---i.e., when it becomes obvious we have a multithread
1869 @c (2) *Is* there necessarily a first thread always? Or do some
1870 @c multithread systems permit starting a program with multiple
1871 @c threads ab initio?
1873 @cindex thread number
1874 @cindex thread identifier (GDB)
1875 For debugging purposes, @value{GDBN} associates its own thread
1876 number---always a single integer---with each thread in your program.
1879 @kindex info threads
1881 Display a summary of all threads currently in your
1882 program. @value{GDBN} displays for each thread (in this order):
1885 @item the thread number assigned by @value{GDBN}
1887 @item the target system's thread identifier (@var{systag})
1889 @item the current stack frame summary for that thread
1893 An asterisk @samp{*} to the left of the @value{GDBN} thread number
1894 indicates the current thread.
1898 @c end table here to get a little more width for example
1901 (@value{GDBP}) info threads
1902 3 process 35 thread 27 0x34e5 in sigpause ()
1903 2 process 35 thread 23 0x34e5 in sigpause ()
1904 * 1 process 35 thread 13 main (argc=1, argv=0x7ffffff8)
1909 @kindex thread @var{threadno}
1910 @item thread @var{threadno}
1911 Make thread number @var{threadno} the current thread. The command
1912 argument @var{threadno} is the internal @value{GDBN} thread number, as
1913 shown in the first field of the @samp{info threads} display.
1914 @value{GDBN} responds by displaying the system identifier of the thread
1915 you selected, and its current stack frame summary:
1918 @c FIXME!! This example made up; find a @value{GDBN} w/threads and get real one
1919 (@value{GDBP}) thread 2
1920 [Switching to process 35 thread 23]
1921 0x34e5 in sigpause ()
1925 As with the @samp{[New @dots{}]} message, the form of the text after
1926 @samp{Switching to} depends on your system's conventions for identifying
1929 @kindex thread apply
1930 @item thread apply [@var{threadno}] [@var{all}] @var{args}
1931 The @code{thread apply} command allows you to apply a command to one or
1932 more threads. Specify the numbers of the threads that you want affected
1933 with the command argument @var{threadno}. @var{threadno} is the internal
1934 @value{GDBN} thread number, as shown in the first field of the @samp{info
1935 threads} display. To apply a command to all threads, use
1936 @code{thread apply all} @var{args}.
1939 @cindex automatic thread selection
1940 @cindex switching threads automatically
1941 @cindex threads, automatic switching
1942 Whenever @value{GDBN} stops your program, due to a breakpoint or a
1943 signal, it automatically selects the thread where that breakpoint or
1944 signal happened. @value{GDBN} alerts you to the context switch with a
1945 message of the form @samp{[Switching to @var{systag}]} to identify the
1948 @xref{Thread Stops,,Stopping and starting multi-thread programs}, for
1949 more information about how @value{GDBN} behaves when you stop and start
1950 programs with multiple threads.
1952 @xref{Set Watchpoints,,Setting watchpoints}, for information about
1953 watchpoints in programs with multiple threads.
1957 @section Debugging programs with multiple processes
1959 @cindex fork, debugging programs which call
1960 @cindex multiple processes
1961 @cindex processes, multiple
1962 @value{GDBN} has no special support for debugging programs which create
1963 additional processes using the @code{fork} function. When a program
1964 forks, @value{GDBN} will continue to debug the parent process and the
1965 child process will run unimpeded. If you have set a breakpoint in any
1966 code which the child then executes, the child will get a @code{SIGTRAP}
1967 signal which (unless it catches the signal) will cause it to terminate.
1969 However, if you want to debug the child process there is a workaround
1970 which isn't too painful. Put a call to @code{sleep} in the code which
1971 the child process executes after the fork. It may be useful to sleep
1972 only if a certain environment variable is set, or a certain file exists,
1973 so that the delay need not occur when you don't want to run @value{GDBN}
1974 on the child. While the child is sleeping, use the @code{ps} program to
1975 get its process ID. Then tell @value{GDBN} (a new invocation of
1976 @value{GDBN} if you are also debugging the parent process) to attach to
1977 the child process (see @ref{Attach}). From that point on you can debug
1978 the child process just like any other process which you attached to.
1981 @chapter Stopping and Continuing
1983 The principal purposes of using a debugger are so that you can stop your
1984 program before it terminates; or so that, if your program runs into
1985 trouble, you can investigate and find out why.
1987 Inside @value{GDBN}, your program may stop for any of several reasons, such
1992 a breakpoint, or reaching a new line after a @value{GDBN}
1993 command such as @code{step}. You may then examine and change
1994 variables, set new breakpoints or remove old ones, and then continue
1995 execution. Usually, the messages shown by @value{GDBN} provide ample
1996 explanation of the status of your program---but you can also explicitly
1997 request this information at any time.
2000 @kindex info program
2002 Display information about the status of your program: whether it is
2012 * Breakpoints:: Breakpoints, watchpoints, and exceptions
2015 * Breakpoints:: Breakpoints and watchpoints
2017 @c Remnant makeinfo bug requires blank line after *successful* end-if in menu:
2019 * Continuing and Stepping:: Resuming execution
2024 * Thread Stops:: Stopping and starting multi-thread programs
2028 @c makeinfo node-defaulting requires adjacency of @node and sectioning cmds
2029 @c ...hence distribute @node Breakpoints over two possible @if expansions.
2033 @section Breakpoints, watchpoints, and exceptions
2037 @section Breakpoints and watchpoints
2041 A @dfn{breakpoint} makes your program stop whenever a certain point in
2042 the program is reached. For each breakpoint, you can add
2043 conditions to control in finer detail whether your program stops.
2044 You can set breakpoints with the @code{break} command and its variants
2045 (@pxref{Set Breaks, ,Setting breakpoints}), to specify the place where
2046 your program should stop by line number, function name or exact address
2049 In languages with exception handling (such as @sc{gnu} C++), you can also set
2050 breakpoints where an exception is raised (@pxref{Exception Handling,,
2051 Breakpoints and exceptions}).
2054 In SunOS 4.x, SVR4, and Alpha OSF/1 configurations, you can now set
2055 breakpoints in shared libraries before the executable is run.
2058 @cindex memory tracing
2059 @cindex breakpoint on memory address
2060 @cindex breakpoint on variable modification
2061 A @dfn{watchpoint} is a special breakpoint that stops your program
2062 when the value of an expression changes. You must use a different
2063 command to set watchpoints (@pxref{Set Watchpoints, ,Setting
2064 watchpoints}), but aside from that, you can manage a watchpoint like
2065 any other breakpoint: you enable, disable, and delete both breakpoints
2066 and watchpoints using the same commands.
2068 You can arrange to have values from your program displayed automatically
2069 whenever @value{GDBN} stops at a breakpoint. @xref{Auto Display,,
2072 @cindex breakpoint numbers
2073 @cindex numbers for breakpoints
2074 @value{GDBN} assigns a number to each breakpoint or watchpoint when you
2075 create it; these numbers are successive integers starting with one. In
2076 many of the commands for controlling various features of breakpoints you
2077 use the breakpoint number to say which breakpoint you want to change.
2078 Each breakpoint may be @dfn{enabled} or @dfn{disabled}; if disabled, it has
2079 no effect on your program until you enable it again.
2082 * Set Breaks:: Setting breakpoints
2083 * Set Watchpoints:: Setting watchpoints
2085 * Exception Handling:: Breakpoints and exceptions
2088 * Delete Breaks:: Deleting breakpoints
2089 * Disabling:: Disabling breakpoints
2090 * Conditions:: Break conditions
2091 * Break Commands:: Breakpoint command lists
2093 * Breakpoint Menus:: Breakpoint menus
2095 @c @ifclear BARETARGET
2096 @c * Error in Breakpoints:: ``Cannot insert breakpoints''
2101 @subsection Setting breakpoints
2103 @c FIXME LMB what does GDB do if no code on line of breakpt?
2104 @c consider in particular declaration with/without initialization.
2106 @c FIXME 2 is there stuff on this already? break at fun start, already init?
2111 @cindex latest breakpoint
2112 Breakpoints are set with the @code{break} command (abbreviated
2113 @code{b}). The debugger convenience variable @samp{$bpnum} records the
2114 number of the breakpoints you've set most recently; see @ref{Convenience
2115 Vars,, Convenience variables}, for a discussion of what you can do with
2116 convenience variables.
2118 You have several ways to say where the breakpoint should go.
2121 @item break @var{function}
2122 Set a breakpoint at entry to function @var{function}.
2124 When using source languages that permit overloading of symbols, such as
2125 C++, @var{function} may refer to more than one possible place to break.
2126 @xref{Breakpoint Menus,,Breakpoint menus}, for a discussion of that situation.
2129 @item break +@var{offset}
2130 @itemx break -@var{offset}
2131 Set a breakpoint some number of lines forward or back from the position
2132 at which execution stopped in the currently selected frame.
2134 @item break @var{linenum}
2135 Set a breakpoint at line @var{linenum} in the current source file.
2136 That file is the last file whose source text was printed. This
2137 breakpoint stops your program just before it executes any of the
2140 @item break @var{filename}:@var{linenum}
2141 Set a breakpoint at line @var{linenum} in source file @var{filename}.
2143 @item break @var{filename}:@var{function}
2144 Set a breakpoint at entry to function @var{function} found in file
2145 @var{filename}. Specifying a file name as well as a function name is
2146 superfluous except when multiple files contain similarly named
2149 @item break *@var{address}
2150 Set a breakpoint at address @var{address}. You can use this to set
2151 breakpoints in parts of your program which do not have debugging
2152 information or source files.
2155 When called without any arguments, @code{break} sets a breakpoint at
2156 the next instruction to be executed in the selected stack frame
2157 (@pxref{Stack, ,Examining the Stack}). In any selected frame but the
2158 innermost, this makes your program stop as soon as control
2159 returns to that frame. This is similar to the effect of a
2160 @code{finish} command in the frame inside the selected frame---except
2161 that @code{finish} does not leave an active breakpoint. If you use
2162 @code{break} without an argument in the innermost frame, @value{GDBN} stops
2163 the next time it reaches the current location; this may be useful
2166 @value{GDBN} normally ignores breakpoints when it resumes execution, until at
2167 least one instruction has been executed. If it did not do this, you
2168 would be unable to proceed past a breakpoint without first disabling the
2169 breakpoint. This rule applies whether or not the breakpoint already
2170 existed when your program stopped.
2172 @item break @dots{} if @var{cond}
2173 Set a breakpoint with condition @var{cond}; evaluate the expression
2174 @var{cond} each time the breakpoint is reached, and stop only if the
2175 value is nonzero---that is, if @var{cond} evaluates as true.
2176 @samp{@dots{}} stands for one of the possible arguments described
2177 above (or no argument) specifying where to break. @xref{Conditions,
2178 ,Break conditions}, for more information on breakpoint conditions.
2181 @item tbreak @var{args}
2182 Set a breakpoint enabled only for one stop. @var{args} are the
2183 same as for the @code{break} command, and the breakpoint is set in the same
2184 way, but the breakpoint is automatically deleted after the first time your
2185 program stops there. @xref{Disabling, ,Disabling breakpoints}.
2188 @item hbreak @var{args}
2189 Set a hardware-assisted breakpoint. @var{args} are the same as for the
2190 @code{break} command and the breakpoint is set in the same way, but the
2191 breakpoint requires hardware support and some target hardware may not
2192 have this support. The main purpose of this is EPROM/ROM code
2193 debugging, so you can set a breakpoint at an instruction without
2194 changing the instruction. This can be used with the new trap-generation
2195 provided by SPARClite DSU. DSU will generate traps when a program accesses
2196 some date or instruction address that is assigned to the debug registers.
2197 However the hardware breakpoint registers can only take two data breakpoints,
2198 and @value{GDBN} will reject this command if more than two are used.
2199 Delete or disable usused hardware breakpoints before setting
2200 new ones. @xref{Conditions, ,Break conditions}.
2203 @item thbreak @var{args}
2204 Set a hardware-assisted breakpoint enabled only for one stop. @var{args}
2205 are the same as for the @code{hbreak} command and the breakpoint is set in
2206 the same way. However, like the @code{tbreak} command,
2207 the breakpoint is automatically deleted after the
2208 first time your program stops there. Also, like the @code{hbreak}
2209 command, the breakpoint requires hardware support and some target hardware
2210 may not have this support. @xref{Disabling, ,Disabling breakpoints}.
2211 Also @xref{Conditions, ,Break conditions}.
2214 @cindex regular expression
2215 @item rbreak @var{regex}
2216 @c FIXME what kind of regexp?
2217 Set breakpoints on all functions matching the regular expression
2218 @var{regex}. This command
2219 sets an unconditional breakpoint on all matches, printing a list of all
2220 breakpoints it set. Once these breakpoints are set, they are treated
2221 just like the breakpoints set with the @code{break} command. You can
2222 delete them, disable them, or make them conditional the same way as any
2226 When debugging C++ programs, @code{rbreak} is useful for setting
2227 breakpoints on overloaded functions that are not members of any special
2231 @kindex info breakpoints
2232 @cindex @code{$_} and @code{info breakpoints}
2233 @item info breakpoints @r{[}@var{n}@r{]}
2234 @itemx info break @r{[}@var{n}@r{]}
2235 @itemx info watchpoints @r{[}@var{n}@r{]}
2236 Print a table of all breakpoints and watchpoints set and not
2237 deleted, with the following columns for each breakpoint:
2240 @item Breakpoint Numbers
2242 Breakpoint or watchpoint.
2244 Whether the breakpoint is marked to be disabled or deleted when hit.
2245 @item Enabled or Disabled
2246 Enabled breakpoints are marked with @samp{y}. @samp{n} marks breakpoints
2247 that are not enabled.
2249 Where the breakpoint is in your program, as a memory address
2251 Where the breakpoint is in the source for your program, as a file and
2256 If a breakpoint is conditional, @code{info break} shows the condition on
2257 the line following the affected breakpoint; breakpoint commands, if any,
2258 are listed after that.
2261 @code{info break} with a breakpoint
2262 number @var{n} as argument lists only that breakpoint. The
2263 convenience variable @code{$_} and the default examining-address for
2264 the @code{x} command are set to the address of the last breakpoint
2265 listed (@pxref{Memory, ,Examining memory}).
2268 @code{info break} now displays a count of the number of times the
2269 breakpoint has been hit. This is especially useful in conjunction with
2270 the @code{ignore} command. You can ignore a large number of breakpoint
2271 hits, look at the breakpoint info to see how many times the
2272 breakpoint was hit, and then run again, ignoring one less than that
2273 number. This will get you quickly to the last hit of that breakpoint.
2276 @value{GDBN} allows you to set any number of breakpoints at the same place in
2277 your program. There is nothing silly or meaningless about this. When
2278 the breakpoints are conditional, this is even useful
2279 (@pxref{Conditions, ,Break conditions}).
2281 @cindex negative breakpoint numbers
2282 @cindex internal @value{GDBN} breakpoints
2283 @value{GDBN} itself sometimes sets breakpoints in your program for special
2284 purposes, such as proper handling of @code{longjmp} (in C programs).
2285 These internal breakpoints are assigned negative numbers, starting with
2286 @code{-1}; @samp{info breakpoints} does not display them.
2288 You can see these breakpoints with the @value{GDBN} maintenance command
2289 @samp{maint info breakpoints}.
2292 @kindex maint info breakpoints
2293 @item maint info breakpoints
2294 Using the same format as @samp{info breakpoints}, display both the
2295 breakpoints you've set explicitly, and those @value{GDBN} is using for
2296 internal purposes. Internal breakpoints are shown with negative
2297 breakpoint numbers. The type column identifies what kind of breakpoint
2302 Normal, explicitly set breakpoint.
2305 Normal, explicitly set watchpoint.
2308 Internal breakpoint, used to handle correctly stepping through
2309 @code{longjmp} calls.
2311 @item longjmp resume
2312 Internal breakpoint at the target of a @code{longjmp}.
2315 Temporary internal breakpoint used by the @value{GDBN} @code{until} command.
2318 Temporary internal breakpoint used by the @value{GDBN} @code{finish} command.
2324 @node Set Watchpoints
2325 @subsection Setting watchpoints
2326 @cindex setting watchpoints
2328 You can use a watchpoint to stop execution whenever the value of an
2329 expression changes, without having to predict a particular place
2330 where this may happen.
2332 Watchpoints currently execute two orders of magnitude more slowly than
2333 other breakpoints, but this can be well worth it to catch errors where
2334 you have no clue what part of your program is the culprit.
2336 @c FIXME - did Stan mean to @ignore this out?
2338 Some processors provide special hardware to support watchpoint
2339 evaluation; @value{GDBN} will use such hardware if it is available,
2340 and if the support code has been added for that configuration.
2345 @item watch @var{expr}
2346 Set a watchpoint for an expression. @value{GDBN} will break when @var{expr}
2347 is written into by the program and its value changes.
2348 This can be used with the new trap-generation provided by
2349 SPARClite DSU. DSU will generate traps when a program accesses
2350 some date or instruction address that is assigned to the debug registers.
2351 For the data addresses, DSU facilitates the @code{watch} command.
2352 However the hardware breakpoint registers can only take two data watchpoints,
2353 and both watchpoints must be the same kind. For example, you can set two
2354 watchpoints with @code{watch} commands, two with @code{rwatch}
2355 commands, @strong{or} two with @code{awatch} commands, but you cannot set one
2356 watchpoint with one command and the other with a different command.
2357 @value{GBDN} will reject the command if you try to mix watchpoints.
2358 Delete or disable unused watchpoint commands before setting new ones.
2361 @item rwatch @var{expr}
2362 Set a watchpoint that will break when watch @var{args} is read by the program.
2363 If you use both watchpoints, both must be set with the @code{rwatch}
2367 @item awatch @var{expr}
2368 Set a watchpoint that will break when @var{args} is read and written into
2369 by the program. If you use both watchpoints, both must be set with the
2370 @code{awatch} command.
2372 @kindex info watchpoints
2373 @item info watchpoints
2374 This command prints a list of watchpoints and breakpoints; it is the
2375 same as @code{info break}.
2380 @cindex watchpoints and threads
2381 @cindex threads and watchpoints
2382 @emph{Warning:} in multi-thread programs, watchpoints have only limited
2383 usefulness. With the current watchpoint implementation, @value{GDBN}
2384 can only watch the value of an expression @emph{in a single thread}. If
2385 you are confident that the expression can only change due to the current
2386 thread's activity (and if you are also confident that no other thread
2387 can become current), then you can use watchpoints as usual. However,
2388 @value{GDBN} may not notice when a non-current thread's activity changes
2394 @node Exception Handling
2395 @subsection Breakpoints and exceptions
2396 @cindex exception handlers
2398 Some languages, such as @sc{gnu} C++, implement exception handling. You can
2399 use @value{GDBN} to examine what caused your program to raise an exception,
2400 and to list the exceptions your program is prepared to handle at a
2401 given point in time.
2405 @item catch @var{exceptions}
2406 You can set breakpoints at active exception handlers by using the
2407 @code{catch} command. @var{exceptions} is a list of names of exceptions
2411 You can use @code{info catch} to list active exception handlers.
2412 @xref{Frame Info, ,Information about a frame}.
2414 There are currently some limitations to exception handling in @value{GDBN}:
2418 If you call a function interactively, @value{GDBN} normally returns
2419 control to you when the function has finished executing. If the call
2420 raises an exception, however, the call may bypass the mechanism that
2421 returns control to you and cause your program to simply continue
2422 running until it hits a breakpoint, catches a signal that @value{GDBN} is
2423 listening for, or exits.
2426 You cannot raise an exception interactively.
2429 You cannot install an exception handler interactively.
2432 @cindex raise exceptions
2433 Sometimes @code{catch} is not the best way to debug exception handling:
2434 if you need to know exactly where an exception is raised, it is better to
2435 stop @emph{before} the exception handler is called, since that way you
2436 can see the stack before any unwinding takes place. If you set a
2437 breakpoint in an exception handler instead, it may not be easy to find
2438 out where the exception was raised.
2440 To stop just before an exception handler is called, you need some
2441 knowledge of the implementation. In the case of @sc{gnu} C++, exceptions are
2442 raised by calling a library function named @code{__raise_exception}
2443 which has the following ANSI C interface:
2446 /* @var{addr} is where the exception identifier is stored.
2447 ID is the exception identifier. */
2448 void __raise_exception (void **@var{addr}, void *@var{id});
2452 To make the debugger catch all exceptions before any stack
2453 unwinding takes place, set a breakpoint on @code{__raise_exception}
2454 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and exceptions}).
2456 With a conditional breakpoint (@pxref{Conditions, ,Break conditions})
2457 that depends on the value of @var{id}, you can stop your program when
2458 a specific exception is raised. You can use multiple conditional
2459 breakpoints to stop your program when any of a number of exceptions are
2464 @subsection Deleting breakpoints
2466 @cindex clearing breakpoints, watchpoints
2467 @cindex deleting breakpoints, watchpoints
2468 It is often necessary to eliminate a breakpoint or watchpoint once it
2469 has done its job and you no longer want your program to stop there. This
2470 is called @dfn{deleting} the breakpoint. A breakpoint that has been
2471 deleted no longer exists; it is forgotten.
2473 With the @code{clear} command you can delete breakpoints according to
2474 where they are in your program. With the @code{delete} command you can
2475 delete individual breakpoints or watchpoints by specifying their
2478 It is not necessary to delete a breakpoint to proceed past it. @value{GDBN}
2479 automatically ignores breakpoints on the first instruction to be executed
2480 when you continue execution without changing the execution address.
2485 Delete any breakpoints at the next instruction to be executed in the
2486 selected stack frame (@pxref{Selection, ,Selecting a frame}). When
2487 the innermost frame is selected, this is a good way to delete a
2488 breakpoint where your program just stopped.
2490 @item clear @var{function}
2491 @itemx clear @var{filename}:@var{function}
2492 Delete any breakpoints set at entry to the function @var{function}.
2494 @item clear @var{linenum}
2495 @itemx clear @var{filename}:@var{linenum}
2496 Delete any breakpoints set at or within the code of the specified line.
2498 @cindex delete breakpoints
2501 @item delete @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]}
2502 Delete the breakpoints or watchpoints of the numbers specified as
2503 arguments. If no argument is specified, delete all breakpoints (@value{GDBN}
2504 asks confirmation, unless you have @code{set confirm off}). You
2505 can abbreviate this command as @code{d}.
2509 @subsection Disabling breakpoints
2511 @kindex disable breakpoints
2512 @kindex enable breakpoints
2513 Rather than deleting a breakpoint or watchpoint, you might prefer to
2514 @dfn{disable} it. This makes the breakpoint inoperative as if it had
2515 been deleted, but remembers the information on the breakpoint so that
2516 you can @dfn{enable} it again later.
2518 You disable and enable breakpoints and watchpoints with the
2519 @code{enable} and @code{disable} commands, optionally specifying one or
2520 more breakpoint numbers as arguments. Use @code{info break} or
2521 @code{info watch} to print a list of breakpoints or watchpoints if you
2522 do not know which numbers to use.
2524 A breakpoint or watchpoint can have any of four different states of
2529 Enabled. The breakpoint stops your program. A breakpoint set
2530 with the @code{break} command starts out in this state.
2532 Disabled. The breakpoint has no effect on your program.
2534 Enabled once. The breakpoint stops your program, but then becomes
2535 disabled. A breakpoint set with the @code{tbreak} command starts out in
2538 Enabled for deletion. The breakpoint stops your program, but
2539 immediately after it does so it is deleted permanently.
2542 You can use the following commands to enable or disable breakpoints and
2546 @kindex disable breakpoints
2549 @item disable @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]}
2550 Disable the specified breakpoints---or all breakpoints, if none are
2551 listed. A disabled breakpoint has no effect but is not forgotten. All
2552 options such as ignore-counts, conditions and commands are remembered in
2553 case the breakpoint is enabled again later. You may abbreviate
2554 @code{disable} as @code{dis}.
2556 @kindex enable breakpoints
2558 @item enable @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]}
2559 Enable the specified breakpoints (or all defined breakpoints). They
2560 become effective once again in stopping your program.
2562 @item enable @r{[}breakpoints@r{]} once @var{bnums}@dots{}
2563 Enable the specified breakpoints temporarily. @value{GDBN} disables any
2564 of these breakpoints immediately after stopping your program.
2566 @item enable @r{[}breakpoints@r{]} delete @var{bnums}@dots{}
2567 Enable the specified breakpoints to work once, then die. @value{GDBN}
2568 deletes any of these breakpoints as soon as your program stops there.
2571 Except for a breakpoint set with @code{tbreak} (@pxref{Set Breaks,
2572 ,Setting breakpoints}), breakpoints that you set are initially enabled;
2573 subsequently, they become disabled or enabled only when you use one of
2574 the commands above. (The command @code{until} can set and delete a
2575 breakpoint of its own, but it does not change the state of your other
2576 breakpoints; see @ref{Continuing and Stepping, ,Continuing and
2580 @subsection Break conditions
2581 @cindex conditional breakpoints
2582 @cindex breakpoint conditions
2584 @c FIXME what is scope of break condition expr? Context where wanted?
2585 @c in particular for a watchpoint?
2586 The simplest sort of breakpoint breaks every time your program reaches a
2587 specified place. You can also specify a @dfn{condition} for a
2588 breakpoint. A condition is just a Boolean expression in your
2589 programming language (@pxref{Expressions, ,Expressions}). A breakpoint with
2590 a condition evaluates the expression each time your program reaches it,
2591 and your program stops only if the condition is @emph{true}.
2593 This is the converse of using assertions for program validation; in that
2594 situation, you want to stop when the assertion is violated---that is,
2595 when the condition is false. In C, if you want to test an assertion expressed
2596 by the condition @var{assert}, you should set the condition
2597 @samp{! @var{assert}} on the appropriate breakpoint.
2599 Conditions are also accepted for watchpoints; you may not need them,
2600 since a watchpoint is inspecting the value of an expression anyhow---but
2601 it might be simpler, say, to just set a watchpoint on a variable name,
2602 and specify a condition that tests whether the new value is an interesting
2605 Break conditions can have side effects, and may even call functions in
2606 your program. This can be useful, for example, to activate functions
2607 that log program progress, or to use your own print functions to
2608 format special data structures. The effects are completely predictable
2609 unless there is another enabled breakpoint at the same address. (In
2610 that case, @value{GDBN} might see the other breakpoint first and stop your
2611 program without checking the condition of this one.) Note that
2612 breakpoint commands are usually more convenient and flexible for the
2613 purpose of performing side effects when a breakpoint is reached
2614 (@pxref{Break Commands, ,Breakpoint command lists}).
2616 Break conditions can be specified when a breakpoint is set, by using
2617 @samp{if} in the arguments to the @code{break} command. @xref{Set
2618 Breaks, ,Setting breakpoints}. They can also be changed at any time
2619 with the @code{condition} command. The @code{watch} command does not
2620 recognize the @code{if} keyword; @code{condition} is the only way to
2621 impose a further condition on a watchpoint.
2625 @item condition @var{bnum} @var{expression}
2626 Specify @var{expression} as the break condition for breakpoint or
2627 watchpoint number @var{bnum}. After you set a condition, breakpoint
2628 @var{bnum} stops your program only if the value of @var{expression} is
2629 true (nonzero, in C). When you use @code{condition}, @value{GDBN}
2630 checks @var{expression} immediately for syntactic correctness, and to
2631 determine whether symbols in it have referents in the context of your
2633 @c FIXME so what does GDB do if there is no referent? Moreover, what
2634 @c about watchpoints?
2636 not actually evaluate @var{expression} at the time the @code{condition}
2637 command is given, however. @xref{Expressions, ,Expressions}.
2639 @item condition @var{bnum}
2640 Remove the condition from breakpoint number @var{bnum}. It becomes
2641 an ordinary unconditional breakpoint.
2644 @cindex ignore count (of breakpoint)
2645 A special case of a breakpoint condition is to stop only when the
2646 breakpoint has been reached a certain number of times. This is so
2647 useful that there is a special way to do it, using the @dfn{ignore
2648 count} of the breakpoint. Every breakpoint has an ignore count, which
2649 is an integer. Most of the time, the ignore count is zero, and
2650 therefore has no effect. But if your program reaches a breakpoint whose
2651 ignore count is positive, then instead of stopping, it just decrements
2652 the ignore count by one and continues. As a result, if the ignore count
2653 value is @var{n}, the breakpoint does not stop the next @var{n} times
2654 your program reaches it.
2658 @item ignore @var{bnum} @var{count}
2659 Set the ignore count of breakpoint number @var{bnum} to @var{count}.
2660 The next @var{count} times the breakpoint is reached, your program's
2661 execution does not stop; other than to decrement the ignore count, @value{GDBN}
2664 To make the breakpoint stop the next time it is reached, specify
2667 When you use @code{continue} to resume execution of your program from a
2668 breakpoint, you can specify an ignore count directly as an argument to
2669 @code{continue}, rather than using @code{ignore}. @xref{Continuing and
2670 Stepping,,Continuing and stepping}.
2672 If a breakpoint has a positive ignore count and a condition, the
2673 condition is not checked. Once the ignore count reaches zero,
2674 @value{GDBN} resumes checking the condition.
2676 You could achieve the effect of the ignore count with a condition such
2677 as @w{@samp{$foo-- <= 0}} using a debugger convenience variable that
2678 is decremented each time. @xref{Convenience Vars, ,Convenience
2682 @node Break Commands
2683 @subsection Breakpoint command lists
2685 @cindex breakpoint commands
2686 You can give any breakpoint (or watchpoint) a series of commands to
2687 execute when your program stops due to that breakpoint. For example, you
2688 might want to print the values of certain expressions, or enable other
2694 @item commands @r{[}@var{bnum}@r{]}
2695 @itemx @dots{} @var{command-list} @dots{}
2697 Specify a list of commands for breakpoint number @var{bnum}. The commands
2698 themselves appear on the following lines. Type a line containing just
2699 @code{end} to terminate the commands.
2701 To remove all commands from a breakpoint, type @code{commands} and
2702 follow it immediately with @code{end}; that is, give no commands.
2704 With no @var{bnum} argument, @code{commands} refers to the last
2705 breakpoint or watchpoint set (not to the breakpoint most recently
2709 Pressing @key{RET} as a means of repeating the last @value{GDBN} command is
2710 disabled within a @var{command-list}.
2712 You can use breakpoint commands to start your program up again. Simply
2713 use the @code{continue} command, or @code{step}, or any other command
2714 that resumes execution.
2716 Any other commands in the command list, after a command that resumes
2717 execution, are ignored. This is because any time you resume execution
2718 (even with a simple @code{next} or @code{step}), you may encounter
2719 another breakpoint---which could have its own command list, leading to
2720 ambiguities about which list to execute.
2723 If the first command you specify in a command list is @code{silent}, the
2724 usual message about stopping at a breakpoint is not printed. This may
2725 be desirable for breakpoints that are to print a specific message and
2726 then continue. If none of the remaining commands print anything, you
2727 see no sign that the breakpoint was reached. @code{silent} is
2728 meaningful only at the beginning of a breakpoint command list.
2730 The commands @code{echo}, @code{output}, and @code{printf} allow you to
2731 print precisely controlled output, and are often useful in silent
2732 breakpoints. @xref{Output, ,Commands for controlled output}.
2734 For example, here is how you could use breakpoint commands to print the
2735 value of @code{x} at entry to @code{foo} whenever @code{x} is positive.
2741 printf "x is %d\n",x
2746 One application for breakpoint commands is to compensate for one bug so
2747 you can test for another. Put a breakpoint just after the erroneous line
2748 of code, give it a condition to detect the case in which something
2749 erroneous has been done, and give it commands to assign correct values
2750 to any variables that need them. End with the @code{continue} command
2751 so that your program does not stop, and start with the @code{silent}
2752 command so that no output is produced. Here is an example:
2764 @node Breakpoint Menus
2765 @subsection Breakpoint menus
2767 @cindex symbol overloading
2769 Some programming languages (notably C++) permit a single function name
2770 to be defined several times, for application in different contexts.
2771 This is called @dfn{overloading}. When a function name is overloaded,
2772 @samp{break @var{function}} is not enough to tell @value{GDBN} where you want
2773 a breakpoint. If you realize this is a problem, you can use
2774 something like @samp{break @var{function}(@var{types})} to specify which
2775 particular version of the function you want. Otherwise, @value{GDBN} offers
2776 you a menu of numbered choices for different possible breakpoints, and
2777 waits for your selection with the prompt @samp{>}. The first two
2778 options are always @samp{[0] cancel} and @samp{[1] all}. Typing @kbd{1}
2779 sets a breakpoint at each definition of @var{function}, and typing
2780 @kbd{0} aborts the @code{break} command without setting any new
2783 For example, the following session excerpt shows an attempt to set a
2784 breakpoint at the overloaded symbol @code{String::after}.
2785 We choose three particular definitions of that function name:
2787 @c FIXME! This is likely to change to show arg type lists, at least
2789 (@value{GDBP}) b String::after
2792 [2] file:String.cc; line number:867
2793 [3] file:String.cc; line number:860
2794 [4] file:String.cc; line number:875
2795 [5] file:String.cc; line number:853
2796 [6] file:String.cc; line number:846
2797 [7] file:String.cc; line number:735
2799 Breakpoint 1 at 0xb26c: file String.cc, line 867.
2800 Breakpoint 2 at 0xb344: file String.cc, line 875.
2801 Breakpoint 3 at 0xafcc: file String.cc, line 846.
2802 Multiple breakpoints were set.
2803 Use the "delete" command to delete unwanted
2809 @c @ifclear BARETARGET
2810 @c @node Error in Breakpoints
2811 @c @subsection ``Cannot insert breakpoints''
2813 @c FIXME!! 14/6/95 Is there a real example of this? Let's use it.
2815 @c Under some operating systems, breakpoints cannot be used in a program if
2816 @c any other process is running that program. In this situation,
2817 @c attempting to run or continue a program with a breakpoint causes
2818 @c @value{GDBN} to stop the other process.
2820 @c When this happens, you have three ways to proceed:
2824 @c Remove or disable the breakpoints, then continue.
2827 @c Suspend @value{GDBN}, and copy the file containing your program to a new
2828 @c name. Resume @value{GDBN} and use the @code{exec-file} command to specify
2829 @c that @value{GDBN} should run your program under that name.
2830 @c Then start your program again.
2833 @c Relink your program so that the text segment is nonsharable, using the
2834 @c linker option @samp{-N}. The operating system limitation may not apply
2835 @c to nonsharable executables.
2839 @node Continuing and Stepping
2840 @section Continuing and stepping
2844 @cindex resuming execution
2845 @dfn{Continuing} means resuming program execution until your program
2846 completes normally. In contrast, @dfn{stepping} means executing just
2847 one more ``step'' of your program, where ``step'' may mean either one
2848 line of source code, or one machine instruction (depending on what
2849 particular command you use). Either when continuing
2850 or when stepping, your program may stop even sooner, due to
2855 a breakpoint or a signal. (If due to a signal, you may want to use
2856 @code{handle}, or use @samp{signal 0} to resume execution.
2857 @xref{Signals, ,Signals}.)
2864 @item continue @r{[}@var{ignore-count}@r{]}
2865 @itemx c @r{[}@var{ignore-count}@r{]}
2866 @itemx fg @r{[}@var{ignore-count}@r{]}
2867 Resume program execution, at the address where your program last stopped;
2868 any breakpoints set at that address are bypassed. The optional argument
2869 @var{ignore-count} allows you to specify a further number of times to
2870 ignore a breakpoint at this location; its effect is like that of
2871 @code{ignore} (@pxref{Conditions, ,Break conditions}).
2873 The argument @var{ignore-count} is meaningful only when your program
2874 stopped due to a breakpoint. At other times, the argument to
2875 @code{continue} is ignored.
2877 The synonyms @code{c} and @code{fg} are provided purely for convenience,
2878 and have exactly the same behavior as @code{continue}.
2881 To resume execution at a different place, you can use @code{return}
2882 (@pxref{Returning, ,Returning from a function}) to go back to the
2883 calling function; or @code{jump} (@pxref{Jumping, ,Continuing at a
2884 different address}) to go to an arbitrary location in your program.
2886 A typical technique for using stepping is to set a breakpoint
2888 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and exceptions})
2891 (@pxref{Breakpoints, ,Breakpoints and watchpoints})
2894 beginning of the function or the section of your program where a
2895 problem is believed to lie, run your program until it stops at that
2896 breakpoint, and then step through the suspect area, examining the
2897 variables that are interesting, until you see the problem happen.
2903 Continue running your program until control reaches a different source
2904 line, then stop it and return control to @value{GDBN}. This command is
2905 abbreviated @code{s}.
2908 @c "without debugging information" is imprecise; actually "without line
2909 @c numbers in the debugging information". (gcc -g1 has debugging info but
2910 @c not line numbers). But it seems complex to try to make that
2911 @c distinction here.
2912 @emph{Warning:} If you use the @code{step} command while control is
2913 within a function that was compiled without debugging information,
2914 execution proceeds until control reaches a function that does have
2915 debugging information. Likewise, it will not step into a function which
2916 is compiled without debugging information. To step through functions
2917 without debugging information, use the @code{stepi} command, described
2921 The @code{step} command now only stops at the first instruction of a
2922 source line. This prevents the multiple stops that used to occur in
2923 switch statements, for loops, etc. @code{step} continues to stop if a
2924 function that has debugging information is called within the line.
2926 Also, the @code{step} command now only enters a subroutine if there is line
2927 number information for the subroutine. Otherwise it acts like the
2928 @code{next} command. This avoids problems when using @code{cc -gl}
2929 on MIPS machines. Previously, @code{step} entered subroutines if there
2930 was any debugging information about the routine.
2932 @item step @var{count}
2933 Continue running as in @code{step}, but do so @var{count} times. If a
2934 breakpoint is reached,
2936 or a signal not related to stepping occurs before @var{count} steps,
2938 stepping stops right away.
2942 @item next @r{[}@var{count}@r{]}
2943 Continue to the next source line in the current (innermost) stack frame.
2944 This is similar to @code{step}, but function calls that appear within the line
2945 of code are executed without stopping. Execution stops when control
2946 reaches a different line of code at the original stack level that was
2947 executing when you gave the @code{next} command. This command is abbreviated
2950 An argument @var{count} is a repeat count, as for @code{step}.
2953 @c FIX ME!! Do we delete this, or is there a way it fits in with
2954 @c the following paragraph? --- Vctoria
2956 @c @code{next} within a function that lacks debugging information acts like
2957 @c @code{step}, but any function calls appearing within the code of the
2958 @c function are executed without stopping.
2960 The @code{next} command now only stops at the first instruction of a
2961 source line. This prevents the multiple stops that used to occur in
2962 swtch statements, for loops, etc.
2966 Continue running until just after function in the selected stack frame
2967 returns. Print the returned value (if any).
2969 Contrast this with the @code{return} command (@pxref{Returning,
2970 ,Returning from a function}).
2976 Continue running until a source line past the current line, in the
2977 current stack frame, is reached. This command is used to avoid single
2978 stepping through a loop more than once. It is like the @code{next}
2979 command, except that when @code{until} encounters a jump, it
2980 automatically continues execution until the program counter is greater
2981 than the address of the jump.
2983 This means that when you reach the end of a loop after single stepping
2984 though it, @code{until} makes your program continue execution until it
2985 exits the loop. In contrast, a @code{next} command at the end of a loop
2986 simply steps back to the beginning of the loop, which forces you to step
2987 through the next iteration.
2989 @code{until} always stops your program if it attempts to exit the current
2992 @code{until} may produce somewhat counterintuitive results if the order
2993 of machine code does not match the order of the source lines. For
2994 example, in the following excerpt from a debugging session, the @code{f}
2995 (@code{frame}) command shows that execution is stopped at line
2996 @code{206}; yet when we use @code{until}, we get to line @code{195}:
3000 #0 main (argc=4, argv=0xf7fffae8) at m4.c:206
3002 (@value{GDBP}) until
3003 195 for ( ; argc > 0; NEXTARG) @{
3006 This happened because, for execution efficiency, the compiler had
3007 generated code for the loop closure test at the end, rather than the
3008 start, of the loop---even though the test in a C @code{for}-loop is
3009 written before the body of the loop. The @code{until} command appeared
3010 to step back to the beginning of the loop when it advanced to this
3011 expression; however, it has not really gone to an earlier
3012 statement---not in terms of the actual machine code.
3014 @code{until} with no argument works by means of single
3015 instruction stepping, and hence is slower than @code{until} with an
3018 @item until @var{location}
3019 @itemx u @var{location}
3020 Continue running your program until either the specified location is
3021 reached, or the current stack frame returns. @var{location} is any of
3022 the forms of argument acceptable to @code{break} (@pxref{Set Breaks,
3023 ,Setting breakpoints}). This form of the command uses breakpoints,
3024 and hence is quicker than @code{until} without an argument.
3030 Execute one machine instruction, then stop and return to the debugger.
3032 It is often useful to do @samp{display/i $pc} when stepping by machine
3033 instructions. This makes @value{GDBN} automatically display the next
3034 instruction to be executed, each time your program stops. @xref{Auto
3035 Display,, Automatic display}.
3037 An argument is a repeat count, as in @code{step}.
3044 Execute one machine instruction, but if it is a function call,
3045 proceed until the function returns.
3047 An argument is a repeat count, as in @code{next}.
3055 A signal is an asynchronous event that can happen in a program. The
3056 operating system defines the possible kinds of signals, and gives each
3057 kind a name and a number. For example, in Unix @code{SIGINT} is the
3058 signal a program gets when you type an interrupt (often @kbd{C-c});
3059 @code{SIGSEGV} is the signal a program gets from referencing a place in
3060 memory far away from all the areas in use; @code{SIGALRM} occurs when
3061 the alarm clock timer goes off (which happens only if your program has
3062 requested an alarm).
3064 @cindex fatal signals
3065 Some signals, including @code{SIGALRM}, are a normal part of the
3066 functioning of your program. Others, such as @code{SIGSEGV}, indicate
3067 errors; these signals are @dfn{fatal} (kill your program immediately) if the
3068 program has not specified in advance some other way to handle the signal.
3069 @code{SIGINT} does not indicate an error in your program, but it is normally
3070 fatal so it can carry out the purpose of the interrupt: to kill the program.
3072 @value{GDBN} has the ability to detect any occurrence of a signal in your
3073 program. You can tell @value{GDBN} in advance what to do for each kind of
3076 @cindex handling signals
3077 Normally, @value{GDBN} is set up to ignore non-erroneous signals like @code{SIGALRM}
3078 (so as not to interfere with their role in the functioning of your program)
3079 but to stop your program immediately whenever an error signal happens.
3080 You can change these settings with the @code{handle} command.
3083 @kindex info signals
3085 Print a table of all the kinds of signals and how @value{GDBN} has been told to
3086 handle each one. You can use this to see the signal numbers of all
3087 the defined types of signals.
3089 @code{info handle} is the new alias for @code{info signals}.
3092 @item handle @var{signal} @var{keywords}@dots{}
3093 Change the way @value{GDBN} handles signal @var{signal}. @var{signal} can
3094 be the number of a signal or its name (with or without the @samp{SIG} at the
3095 beginning). The @var{keywords} say what change to make.
3099 The keywords allowed by the @code{handle} command can be abbreviated.
3100 Their full names are:
3104 @value{GDBN} should not stop your program when this signal happens. It may
3105 still print a message telling you that the signal has come in.
3108 @value{GDBN} should stop your program when this signal happens. This implies
3109 the @code{print} keyword as well.
3112 @value{GDBN} should print a message when this signal happens.
3115 @value{GDBN} should not mention the occurrence of the signal at all. This
3116 implies the @code{nostop} keyword as well.
3119 @value{GDBN} should allow your program to see this signal; your program
3120 can handle the signal, or else it may terminate if the signal is fatal
3124 @value{GDBN} should not allow your program to see this signal.
3128 When a signal stops your program, the signal is not visible until you
3129 continue. Your program sees the signal then, if @code{pass} is in
3130 effect for the signal in question @emph{at that time}. In other words,
3131 after @value{GDBN} reports a signal, you can use the @code{handle}
3132 command with @code{pass} or @code{nopass} to control whether your
3133 program sees that signal when you continue.
3135 You can also use the @code{signal} command to prevent your program from
3136 seeing a signal, or cause it to see a signal it normally would not see,
3137 or to give it any signal at any time. For example, if your program stopped
3138 due to some sort of memory reference error, you might store correct
3139 values into the erroneous variables and continue, hoping to see more
3140 execution; but your program would probably terminate immediately as
3141 a result of the fatal signal once it saw the signal. To prevent this,
3142 you can continue with @samp{signal 0}. @xref{Signaling, ,Giving your
3148 @section Stopping and starting multi-thread programs
3150 When your program has multiple threads (@pxref{Threads,, Debugging
3151 programs with multiple threads}), you can choose whether to set
3152 breakpoints on all threads, or on a particular thread.
3155 @cindex breakpoints and threads
3156 @cindex thread breakpoints
3157 @kindex break @dots{} thread @var{threadno}
3158 @item break @var{linespec} thread @var{threadno}
3159 @itemx break @var{linespec} thread @var{threadno} if @dots{}
3160 @var{linespec} specifies source lines; there are several ways of
3161 writing them, but the effect is always to specify some source line.
3163 Use the qualifier @samp{thread @var{threadno}} with a breakpoint command
3164 to specify that you only want @value{GDBN} to stop the program when a
3165 particular thread reaches this breakpoint. @var{threadno} is one of the
3166 numeric thread identifiers assigned by @value{GDBN}, shown in the first
3167 column of the @samp{info threads} display.
3169 If you do not specify @samp{thread @var{threadno}} when you set a
3170 breakpoint, the breakpoint applies to @emph{all} threads of your
3173 You can use the @code{thread} qualifier on conditional breakpoints as
3174 well; in this case, place @samp{thread @var{threadno}} before the
3175 breakpoint condition, like this:
3178 (gdb) break frik.c:13 thread 28 if bartab > lim
3183 @cindex stopped threads
3184 @cindex threads, stopped
3185 Whenever your program stops under @value{GDBN} for any reason,
3186 @emph{all} threads of execution stop, not just the current thread. This
3187 allows you to examine the overall state of the program, including
3188 switching between threads, without worrying that things may change
3191 @cindex continuing threads
3192 @cindex threads, continuing
3193 Conversely, whenever you restart the program, @emph{all} threads start
3194 executing. @emph{This is true even when single-stepping} with commands
3195 like @code{step} or @code{next}.
3197 In particular, @value{GDBN} cannot single-step all threads in lockstep.
3198 Since thread scheduling is up to your debugging target's operating
3199 system (not controlled by @value{GDBN}), other threads may
3200 execute more than one statement while the current thread completes a
3201 single step. Moreover, in general other threads stop in the middle of a
3202 statement, rather than at a clean statement boundary, when the program
3205 You might even find your program stopped in another thread after
3206 continuing or even single-stepping. This happens whenever some other
3207 thread runs into a breakpoint, a signal, or an exception before the
3208 first thread completes whatever you requested.
3212 @chapter Examining the Stack
3214 When your program has stopped, the first thing you need to know is where it
3215 stopped and how it got there.
3218 Each time your program performs a function call, information about the call
3220 That information includes the location of the call in your program,
3221 the arguments of the call,
3222 and the local variables of the function being called.
3223 The information is saved in a block of data called a @dfn{stack frame}.
3224 The stack frames are allocated in a region of memory called the @dfn{call
3227 When your program stops, the @value{GDBN} commands for examining the
3228 stack allow you to see all of this information.
3230 @cindex selected frame
3231 One of the stack frames is @dfn{selected} by @value{GDBN} and many
3232 @value{GDBN} commands refer implicitly to the selected frame. In
3233 particular, whenever you ask @value{GDBN} for the value of a variable in
3234 your program, the value is found in the selected frame. There are
3235 special @value{GDBN} commands to select whichever frame you are
3236 interested in. @xref{Selection, ,Selecting a frame}.
3238 When your program stops, @value{GDBN} automatically selects the
3239 currently executing frame and describes it briefly, similar to the
3240 @code{frame} command (@pxref{Frame Info, ,Information about a frame}).
3243 * Frames:: Stack frames
3244 * Backtrace:: Backtraces
3245 * Selection:: Selecting a frame
3246 * Frame Info:: Information on a frame
3248 * MIPS Stack:: MIPS machines and the function stack
3253 @section Stack frames
3257 The call stack is divided up into contiguous pieces called @dfn{stack
3258 frames}, or @dfn{frames} for short; each frame is the data associated
3259 with one call to one function. The frame contains the arguments given
3260 to the function, the function's local variables, and the address at
3261 which the function is executing.
3263 @cindex initial frame
3264 @cindex outermost frame
3265 @cindex innermost frame
3266 When your program is started, the stack has only one frame, that of the
3267 function @code{main}. This is called the @dfn{initial} frame or the
3268 @dfn{outermost} frame. Each time a function is called, a new frame is
3269 made. Each time a function returns, the frame for that function invocation
3270 is eliminated. If a function is recursive, there can be many frames for
3271 the same function. The frame for the function in which execution is
3272 actually occurring is called the @dfn{innermost} frame. This is the most
3273 recently created of all the stack frames that still exist.
3275 @cindex frame pointer
3276 Inside your program, stack frames are identified by their addresses. A
3277 stack frame consists of many bytes, each of which has its own address; each
3278 kind of computer has a convention for choosing one byte whose
3279 address serves as the address of the frame. Usually this address is kept
3280 in a register called the @dfn{frame pointer register} while execution is
3281 going on in that frame.
3283 @cindex frame number
3284 @value{GDBN} assigns numbers to all existing stack frames, starting with
3285 zero for the innermost frame, one for the frame that called it,
3286 and so on upward. These numbers do not really exist in your program;
3287 they are assigned by @value{GDBN} to give you a way of designating stack
3288 frames in @value{GDBN} commands.
3290 @c below produces an acceptable overful hbox. --mew 13aug1993
3291 @cindex frameless execution
3292 Some compilers provide a way to compile functions so that they operate
3293 without stack frames. (For example, the @code{@value{GCC}} option
3294 @samp{-fomit-frame-pointer} generates functions without a frame.)
3295 This is occasionally done with heavily used library functions to save
3296 the frame setup time. @value{GDBN} has limited facilities for dealing
3297 with these function invocations. If the innermost function invocation
3298 has no stack frame, @value{GDBN} nevertheless regards it as though
3299 it had a separate frame, which is numbered zero as usual, allowing
3300 correct tracing of the function call chain. However, @value{GDBN} has
3301 no provision for frameless functions elsewhere in the stack.
3305 @item frame @var{args}
3306 The @code{frame} command allows you to move from one stack frame to another,
3307 and to print the stack frame you select. @var{args} may be either the
3308 address of the frame of the stack frame number. Without an argument,
3309 @code{frame} prints the current stack frame.
3311 @kindex select-frame
3313 The @code{select-frame} command allows you to move from one stack frame
3314 to another without printing the frame. This is the silent version of
3321 A backtrace is a summary of how your program got where it is. It shows one
3322 line per frame, for many frames, starting with the currently executing
3323 frame (frame zero), followed by its caller (frame one), and on up the
3331 Print a backtrace of the entire stack: one line per frame for all
3332 frames in the stack.
3334 You can stop the backtrace at any time by typing the system interrupt
3335 character, normally @kbd{C-c}.
3337 @item backtrace @var{n}
3339 Similar, but print only the innermost @var{n} frames.
3341 @item backtrace -@var{n}
3343 Similar, but print only the outermost @var{n} frames.
3349 The names @code{where} and @code{info stack} (abbreviated @code{info s})
3350 are additional aliases for @code{backtrace}.
3352 Each line in the backtrace shows the frame number and the function name.
3353 The program counter value is also shown---unless you use @code{set
3354 print address off}. The backtrace also shows the source file name and
3355 line number, as well as the arguments to the function. The program
3356 counter value is omitted if it is at the beginning of the code for that
3359 Here is an example of a backtrace. It was made with the command
3360 @samp{bt 3}, so it shows the innermost three frames.
3364 #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
3366 #1 0x6e38 in expand_macro (sym=0x2b600) at macro.c:242
3367 #2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08)
3369 (More stack frames follow...)
3374 The display for frame zero does not begin with a program counter
3375 value, indicating that your program has stopped at the beginning of the
3376 code for line @code{993} of @code{builtin.c}.
3379 @section Selecting a frame
3381 Most commands for examining the stack and other data in your program work on
3382 whichever stack frame is selected at the moment. Here are the commands for
3383 selecting a stack frame; all of them finish by printing a brief description
3384 of the stack frame just selected.
3391 Select frame number @var{n}. Recall that frame zero is the innermost
3392 (currently executing) frame, frame one is the frame that called the
3393 innermost one, and so on. The highest-numbered frame is the one for
3396 @item frame @var{addr}
3398 Select the frame at address @var{addr}. This is useful mainly if the
3399 chaining of stack frames has been damaged by a bug, making it
3400 impossible for @value{GDBN} to assign numbers properly to all frames. In
3401 addition, this can be useful when your program has multiple stacks and
3402 switches between them.
3404 @ifclear H8EXCLUSIVE
3405 On the SPARC architecture, @code{frame} needs two addresses to
3406 select an arbitrary frame: a frame pointer and a stack pointer.
3408 On the MIPS and Alpha architecture, it needs two addresses: a stack
3409 pointer and a program counter.
3411 On the 29k architecture, it needs three addresses: a register stack
3412 pointer, a program counter, and a memory stack pointer.
3413 @c note to future updaters: this is conditioned on a flag
3414 @c SETUP_ARBITRARY_FRAME in the tm-*.h files. The above is up to date
3415 @c as of 27 Jan 1994.
3420 Move @var{n} frames up the stack. For positive numbers @var{n}, this
3421 advances toward the outermost frame, to higher frame numbers, to frames
3422 that have existed longer. @var{n} defaults to one.
3427 Move @var{n} frames down the stack. For positive numbers @var{n}, this
3428 advances toward the innermost frame, to lower frame numbers, to frames
3429 that were created more recently. @var{n} defaults to one. You may
3430 abbreviate @code{down} as @code{do}.
3433 All of these commands end by printing two lines of output describing the
3434 frame. The first line shows the frame number, the function name, the
3435 arguments, and the source file and line number of execution in that
3436 frame. The second line shows the text of that source line.
3444 #1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
3446 10 read_input_file (argv[i]);
3450 After such a printout, the @code{list} command with no arguments
3451 prints ten lines centered on the point of execution in the frame.
3452 @xref{List, ,Printing source lines}.
3455 @kindex down-silently
3457 @item up-silently @var{n}
3458 @itemx down-silently @var{n}
3459 These two commands are variants of @code{up} and @code{down},
3460 respectively; they differ in that they do their work silently, without
3461 causing display of the new frame. They are intended primarily for use
3462 in @value{GDBN} command scripts, where the output might be unnecessary and
3467 @section Information about a frame
3469 There are several other commands to print information about the selected
3475 When used without any argument, this command does not change which
3476 frame is selected, but prints a brief description of the currently
3477 selected stack frame. It can be abbreviated @code{f}. With an
3478 argument, this command is used to select a stack frame.
3479 @xref{Selection, ,Selecting a frame}.
3485 This command prints a verbose description of the selected stack frame,
3490 the address of the frame
3492 the address of the next frame down (called by this frame)
3494 the address of the next frame up (caller of this frame)
3496 the language in which the source code corresponding to this frame is written
3498 the address of the frame's arguments
3500 the program counter saved in it (the address of execution in the caller frame)
3502 which registers were saved in the frame
3505 @noindent The verbose description is useful when
3506 something has gone wrong that has made the stack format fail to fit
3507 the usual conventions.
3509 @item info frame @var{addr}
3510 @itemx info f @var{addr}
3511 Print a verbose description of the frame at address @var{addr}, without
3512 selecting that frame. The selected frame remains unchanged by this
3513 command. This requires the same kind of address (more than one for some
3514 architectures) that you specify in the @code{frame} command.
3515 @xref{Selection, ,Selecting a frame}.
3519 Print the arguments of the selected frame, each on a separate line.
3523 Print the local variables of the selected frame, each on a separate
3524 line. These are all variables (declared either static or automatic)
3525 accessible at the point of execution of the selected frame.
3529 @cindex catch exceptions
3530 @cindex exception handlers
3532 Print a list of all the exception handlers that are active in the
3533 current stack frame at the current point of execution. To see other
3534 exception handlers, visit the associated frame (using the @code{up},
3535 @code{down}, or @code{frame} commands); then type @code{info catch}.
3536 @xref{Exception Handling, ,Breakpoints and exceptions}.
3542 @section MIPS machines and the function stack
3544 @cindex stack on MIPS
3546 MIPS based computers use an unusual stack frame, which sometimes
3547 requires @value{GDBN} to search backward in the object code to find the
3548 beginning of a function.
3550 @cindex response time, MIPS debugging
3551 To improve response time (especially for embedded applications, where
3552 @value{GDBN} may be restricted to a slow serial line for this search)
3553 you may want to limit the size of this search, using one of these
3557 @cindex @code{heuristic-fence-post} (MIPS)
3558 @item set heuristic-fence-post @var{limit}
3559 Restrict @value{GDBN} to examining at most @var{limit} bytes in its search
3560 for the beginning of a function. A value of @var{0} (the default)
3561 means there is no limit. However, except for @var{0}, the larger the
3562 limit the more bytes @code{heuristic-fence-post} must search and
3563 therefore the longer it takes to run.
3565 @item show heuristic-fence-post
3566 Display the current limit.
3570 These commands are available @emph{only} when @value{GDBN} is configured
3571 for debugging programs on MIPS processors.
3575 @chapter Examining Source Files
3577 @value{GDBN} can print parts of your program's source, since the debugging
3578 information recorded in the program tells @value{GDBN} what source files were
3579 used to build it. When your program stops, @value{GDBN} spontaneously prints
3580 the line where it stopped. Likewise, when you select a stack frame
3581 (@pxref{Selection, ,Selecting a frame}), @value{GDBN} prints the line where
3582 execution in that frame has stopped. You can print other portions of
3583 source files by explicit command.
3586 If you use @value{GDBN} through its @sc{gnu} Emacs interface, you may prefer
3588 Emacs facilities to view source; @pxref{Emacs, ,Using @value{GDBN} under @sc{gnu} Emacs}.
3592 * List:: Printing source lines
3594 * Search:: Searching source files
3597 * Source Path:: Specifying source directories
3598 * Machine Code:: Source and machine code
3602 @section Printing source lines
3606 To print lines from a source file, use the @code{list} command
3607 (abbreviated @code{l}). By default, ten lines are printed.
3608 There are several ways to specify what part of the file you want to print.
3610 Here are the forms of the @code{list} command most commonly used:
3613 @item list @var{linenum}
3614 Print lines centered around line number @var{linenum} in the
3615 current source file.
3617 @item list @var{function}
3618 Print lines centered around the beginning of function
3622 Print more lines. If the last lines printed were printed with a
3623 @code{list} command, this prints lines following the last lines
3624 printed; however, if the last line printed was a solitary line printed
3625 as part of displaying a stack frame (@pxref{Stack, ,Examining the
3626 Stack}), this prints lines centered around that line.
3629 Print lines just before the lines last printed.
3632 By default, @value{GDBN} prints ten source lines with any of these forms of
3633 the @code{list} command. You can change this using @code{set listsize}:
3636 @kindex set listsize
3637 @item set listsize @var{count}
3638 Make the @code{list} command display @var{count} source lines (unless
3639 the @code{list} argument explicitly specifies some other number).
3641 @kindex show listsize
3643 Display the number of lines that @code{list} prints.
3646 Repeating a @code{list} command with @key{RET} discards the argument,
3647 so it is equivalent to typing just @code{list}. This is more useful
3648 than listing the same lines again. An exception is made for an
3649 argument of @samp{-}; that argument is preserved in repetition so that
3650 each repetition moves up in the source file.
3653 In general, the @code{list} command expects you to supply zero, one or two
3654 @dfn{linespecs}. Linespecs specify source lines; there are several ways
3655 of writing them but the effect is always to specify some source line.
3656 Here is a complete description of the possible arguments for @code{list}:
3659 @item list @var{linespec}
3660 Print lines centered around the line specified by @var{linespec}.
3662 @item list @var{first},@var{last}
3663 Print lines from @var{first} to @var{last}. Both arguments are
3666 @item list ,@var{last}
3667 Print lines ending with @var{last}.
3669 @item list @var{first},
3670 Print lines starting with @var{first}.
3673 Print lines just after the lines last printed.
3676 Print lines just before the lines last printed.
3679 As described in the preceding table.
3682 Here are the ways of specifying a single source line---all the
3687 Specifies line @var{number} of the current source file.
3688 When a @code{list} command has two linespecs, this refers to
3689 the same source file as the first linespec.
3692 Specifies the line @var{offset} lines after the last line printed.
3693 When used as the second linespec in a @code{list} command that has
3694 two, this specifies the line @var{offset} lines down from the
3698 Specifies the line @var{offset} lines before the last line printed.
3700 @item @var{filename}:@var{number}
3701 Specifies line @var{number} in the source file @var{filename}.
3703 @item @var{function}
3704 Specifies the line that begins the body of the function @var{function}.
3705 For example: in C, this is the line with the open brace.
3707 @item @var{filename}:@var{function}
3708 Specifies the line of the open-brace that begins the body of the
3709 function @var{function} in the file @var{filename}. You only need the
3710 file name with a function name to avoid ambiguity when there are
3711 identically named functions in different source files.
3713 @item *@var{address}
3714 Specifies the line containing the program address @var{address}.
3715 @var{address} may be any expression.
3720 @section Searching source files
3722 @kindex reverse-search
3724 There are two commands for searching through the current source file for a
3729 @kindex forward-search
3730 @item forward-search @var{regexp}
3731 @itemx search @var{regexp}
3732 The command @samp{forward-search @var{regexp}} checks each line,
3733 starting with the one following the last line listed, for a match for
3734 @var{regexp}. It lists the line that is found. You can use the
3735 synonym @samp{search @var{regexp}} or abbreviate the command name as
3738 @item reverse-search @var{regexp}
3739 The command @samp{reverse-search @var{regexp}} checks each line, starting
3740 with the one before the last line listed and going backward, for a match
3741 for @var{regexp}. It lists the line that is found. You can abbreviate
3742 this command as @code{rev}.
3747 @section Specifying source directories
3750 @cindex directories for source files
3751 Executable programs sometimes do not record the directories of the source
3752 files from which they were compiled, just the names. Even when they do,
3753 the directories could be moved between the compilation and your debugging
3754 session. @value{GDBN} has a list of directories to search for source files;
3755 this is called the @dfn{source path}. Each time @value{GDBN} wants a source file,
3756 it tries all the directories in the list, in the order they are present
3757 in the list, until it finds a file with the desired name. Note that
3758 the executable search path is @emph{not} used for this purpose. Neither is
3759 the current working directory, unless it happens to be in the source
3762 If @value{GDBN} cannot find a source file in the source path, and the
3763 object program records a directory, @value{GDBN} tries that directory
3764 too. If the source path is empty, and there is no record of the
3765 compilation directory, @value{GDBN} looks in the current directory as a
3768 Whenever you reset or rearrange the source path, @value{GDBN} clears out
3769 any information it has cached about where source files are found and where
3770 each line is in the file.
3774 When you start @value{GDBN}, its source path is empty.
3775 To add other directories, use the @code{directory} command.
3778 @item directory @var{dirname} @dots{}
3779 @item dir @var{dirname} @dots{}
3780 Add directory @var{dirname} to the front of the source path. Several
3781 directory names may be given to this command, separated by @samp{:} or
3782 whitespace. You may specify a directory that is already in the source
3783 path; this moves it forward, so @value{GDBN} searches it sooner.
3789 @cindex compilation directory
3790 @cindex current directory
3791 @cindex working directory
3792 @cindex directory, current
3793 @cindex directory, compilation
3794 You can use the string @samp{$cdir} to refer to the compilation
3795 directory (if one is recorded), and @samp{$cwd} to refer to the current
3796 working directory. @samp{$cwd} is not the same as @samp{.}---the former
3797 tracks the current working directory as it changes during your @value{GDBN}
3798 session, while the latter is immediately expanded to the current
3799 directory at the time you add an entry to the source path.
3802 Reset the source path to empty again. This requires confirmation.
3804 @c RET-repeat for @code{directory} is explicitly disabled, but since
3805 @c repeating it would be a no-op we do not say that. (thanks to RMS)
3807 @item show directories
3808 @kindex show directories
3809 Print the source path: show which directories it contains.
3812 If your source path is cluttered with directories that are no longer of
3813 interest, @value{GDBN} may sometimes cause confusion by finding the wrong
3814 versions of source. You can correct the situation as follows:
3818 Use @code{directory} with no argument to reset the source path to empty.
3821 Use @code{directory} with suitable arguments to reinstall the
3822 directories you want in the source path. You can add all the
3823 directories in one command.
3827 @section Source and machine code
3829 You can use the command @code{info line} to map source lines to program
3830 addresses (and vice versa), and the command @code{disassemble} to display
3831 a range of addresses as machine instructions. When run under @sc{gnu} Emacs
3832 mode, the @code{info line} command now causes the arrow to point to the
3833 line specified. Also, @code{info line} prints addresses in symbolic form as
3838 @item info line @var{linespec}
3839 Print the starting and ending addresses of the compiled code for
3840 source line @var{linespec}. You can specify source lines in any of
3841 the ways understood by the @code{list} command (@pxref{List, ,Printing
3845 For example, we can use @code{info line} to discover the location of
3846 the object code for the first line of function
3847 @code{m4_changequote}:
3850 (@value{GDBP}) info line m4_changecom
3851 Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350.
3855 We can also inquire (using @code{*@var{addr}} as the form for
3856 @var{linespec}) what source line covers a particular address:
3858 (@value{GDBP}) info line *0x63ff
3859 Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404.
3862 @cindex @code{$_} and @code{info line}
3863 After @code{info line}, the default address for the @code{x} command
3864 is changed to the starting address of the line, so that @samp{x/i} is
3865 sufficient to begin examining the machine code (@pxref{Memory,
3866 ,Examining memory}). Also, this address is saved as the value of the
3867 convenience variable @code{$_} (@pxref{Convenience Vars, ,Convenience
3872 @cindex assembly instructions
3873 @cindex instructions, assembly
3874 @cindex machine instructions
3875 @cindex listing machine instructions
3877 This specialized command dumps a range of memory as machine
3878 instructions. The default memory range is the function surrounding the
3879 program counter of the selected frame. A single argument to this
3880 command is a program counter value; @value{GDBN} dumps the function
3881 surrounding this value. Two arguments specify a range of addresses
3882 (first inclusive, second exclusive) to dump.
3885 @ifclear H8EXCLUSIVE
3886 We can use @code{disassemble} to inspect the object code
3887 range shown in the last @code{info line} example (the example
3888 shows SPARC machine instructions):
3892 (@value{GDBP}) disas 0x63e4 0x6404
3893 Dump of assembler code from 0x63e4 to 0x6404:
3894 0x63e4 <builtin_init+5340>: ble 0x63f8 <builtin_init+5360>
3895 0x63e8 <builtin_init+5344>: sethi %hi(0x4c00), %o0
3896 0x63ec <builtin_init+5348>: ld [%i1+4], %o0
3897 0x63f0 <builtin_init+5352>: b 0x63fc <builtin_init+5364>
3898 0x63f4 <builtin_init+5356>: ld [%o0+4], %o0
3899 0x63f8 <builtin_init+5360>: or %o0, 0x1a4, %o0
3900 0x63fc <builtin_init+5364>: call 0x9288 <path_search>
3901 0x6400 <builtin_init+5368>: nop
3902 End of assembler dump.
3907 For example, here is the beginning of the output for the
3908 disassembly of a function @code{fact}:
3912 (@value{GDBP}) disas fact
3913 Dump of assembler code for function fact:
3915 0x802c <fact>: 6d f2 mov.w r2,@@-r7
3916 0x802e <fact+2>: 6d f3 mov.w r3,@@-r7
3917 0x8030 <fact+4>: 6d f6 mov.w r6,@@-r7
3918 0x8032 <fact+6>: 0d 76 mov.w r7,r6
3919 0x8034 <fact+8>: 6f 70 00 08 mov.w @@(0x8,r7),r0
3920 0x8038 <fact+12> 19 11 sub.w r1,r1
3928 @chapter Examining Data
3930 @cindex printing data
3931 @cindex examining data
3934 @c "inspect" is not quite a synonym if you are using Epoch, which we do not
3935 @c document because it is nonstandard... Under Epoch it displays in a
3936 @c different window or something like that.
3937 The usual way to examine data in your program is with the @code{print}
3938 command (abbreviated @code{p}), or its synonym @code{inspect}.
3940 It evaluates and prints the value of an expression of the language your
3941 program is written in (@pxref{Languages, ,Using @value{GDBN} with Different
3946 @item print @var{exp}
3947 @itemx print /@var{f} @var{exp}
3948 @var{exp} is an expression (in the source language). By default the
3949 value of @var{exp} is printed in a format appropriate to its data type;
3950 you can choose a different format by specifying @samp{/@var{f}}, where
3951 @var{f} is a letter specifying the format; @pxref{Output Formats,,Output
3955 @itemx print /@var{f}
3956 If you omit @var{exp}, @value{GDBN} displays the last value again (from the
3957 @dfn{value history}; @pxref{Value History, ,Value history}). This allows you to
3958 conveniently inspect the same value in an alternative format.
3961 A more low-level way of examining data is with the @code{x} command.
3962 It examines data in memory at a specified address and prints it in a
3963 specified format. @xref{Memory, ,Examining memory}.
3965 If you are interested in information about types, or about how the fields
3970 are declared, use the @code{ptype @var{exp}}
3971 command rather than @code{print}. @xref{Symbols, ,Examining the Symbol Table}.
3974 * Expressions:: Expressions
3975 * Variables:: Program variables
3976 * Arrays:: Artificial arrays
3977 * Output Formats:: Output formats
3978 * Memory:: Examining memory
3979 * Auto Display:: Automatic display
3980 * Print Settings:: Print settings
3981 * Value History:: Value history
3982 * Convenience Vars:: Convenience variables
3983 * Registers:: Registers
3985 * Floating Point Hardware:: Floating point hardware
3990 @section Expressions
3993 @code{print} and many other @value{GDBN} commands accept an expression and
3994 compute its value. Any kind of constant, variable or operator defined
3995 by the programming language you are using is valid in an expression in
3996 @value{GDBN}. This includes conditional expressions, function calls, casts
3997 and string constants. It unfortunately does not include symbols defined
3998 by preprocessor @code{#define} commands.
4000 @value{GDBN} now supports array constants in expressions input by
4001 the user. The syntax is @var{element, element@dots{}}. For example,
4002 you can now use the command @code{print @{1 2 3@}} to build up an array in
4003 memory that is malloc'd in the target program.
4006 Because C is so widespread, most of the expressions shown in examples in
4007 this manual are in C. @xref{Languages, , Using @value{GDBN} with Different
4008 Languages}, for information on how to use expressions in other
4011 In this section, we discuss operators that you can use in @value{GDBN}
4012 expressions regardless of your programming language.
4014 Casts are supported in all languages, not just in C, because it is so
4015 useful to cast a number into a pointer in order to examine a structure
4016 at that address in memory.
4017 @c FIXME: casts supported---Mod2 true?
4020 @value{GDBN} supports these operators, in addition to those common
4021 to programming languages:
4025 @samp{@@} is a binary operator for treating parts of memory as arrays.
4026 @xref{Arrays, ,Artificial arrays}, for more information.
4029 @samp{::} allows you to specify a variable in terms of the file or
4030 function where it is defined. @xref{Variables, ,Program variables}.
4032 @cindex @{@var{type}@}
4033 @cindex type casting memory
4034 @cindex memory, viewing as typed object
4035 @cindex casts, to view memory
4036 @item @{@var{type}@} @var{addr}
4037 Refers to an object of type @var{type} stored at address @var{addr} in
4038 memory. @var{addr} may be any expression whose value is an integer or
4039 pointer (but parentheses are required around binary operators, just as in
4040 a cast). This construct is allowed regardless of what kind of data is
4041 normally supposed to reside at @var{addr}.
4045 @section Program variables
4047 The most common kind of expression to use is the name of a variable
4050 Variables in expressions are understood in the selected stack frame
4051 (@pxref{Selection, ,Selecting a frame}); they must be either:
4062 visible according to the scope rules of the
4063 programming language from the point of execution in that frame
4066 @noindent This means that in the function
4081 you can examine and use the variable @code{a} whenever your program is
4082 executing within the function @code{foo}, but you can only use or
4083 examine the variable @code{b} while your program is executing inside
4084 the block where @code{b} is declared.
4086 @cindex variable name conflict
4087 There is an exception: you can refer to a variable or function whose
4088 scope is a single source file even if the current execution point is not
4089 in this file. But it is possible to have more than one such variable or
4090 function with the same name (in different source files). If that
4091 happens, referring to that name has unpredictable effects. If you wish,
4092 you can specify a static variable in a particular function or file,
4093 using the colon-colon notation:
4097 @c info cannot cope with a :: index entry, but why deprive hard copy readers?
4101 @var{file}::@var{variable}
4102 @var{function}::@var{variable}
4106 Here @var{file} or @var{function} is the name of the context for the
4107 static @var{variable}. In the case of file names, you can use quotes to
4108 make sure @value{GDBN} parses the file name as a single word---for example,
4109 to print a global value of @code{x} defined in @file{f2.c}:
4112 (@value{GDBP}) p 'f2.c'::x
4116 @cindex C++ scope resolution
4117 This use of @samp{::} is very rarely in conflict with the very similar
4118 use of the same notation in C++. @value{GDBN} also supports use of the C++
4119 scope resolution operator in @value{GDBN} expressions.
4120 @c FIXME: Um, so what happens in one of those rare cases where it's in
4124 @cindex wrong values
4125 @cindex variable values, wrong
4127 @emph{Warning:} Occasionally, a local variable may appear to have the
4128 wrong value at certain points in a function---just after entry to a new
4129 scope, and just before exit.
4131 You may see this problem when you are stepping by machine instructions.
4132 This is because, on most machines, it takes more than one instruction to
4133 set up a stack frame (including local variable definitions); if you are
4134 stepping by machine instructions, variables may appear to have the wrong
4135 values until the stack frame is completely built. On exit, it usually
4136 also takes more than one machine instruction to destroy a stack frame;
4137 after you begin stepping through that group of instructions, local
4138 variable definitions may be gone.
4141 @section Artificial arrays
4143 @cindex artificial array
4145 It is often useful to print out several successive objects of the
4146 same type in memory; a section of an array, or an array of
4147 dynamically determined size for which only a pointer exists in the
4150 You can do this by referring to a contiguous span of memory as an
4151 @dfn{artificial array}, using the binary operator @samp{@@}. The left
4152 operand of @samp{@@} should be the first element of the desired array
4153 and be an individual object. The right operand should be the desired length
4154 of the array. The result is an array value whose elements are all of
4155 the type of the left argument. The first element is actually the left
4156 argument; the second element comes from bytes of memory immediately
4157 following those that hold the first element, and so on. Here is an
4158 example. If a program says
4161 int *array = (int *) malloc (len * sizeof (int));
4165 you can print the contents of @code{array} with
4171 The left operand of @samp{@@} must reside in memory. Array values made
4172 with @samp{@@} in this way behave just like other arrays in terms of
4173 subscripting, and are coerced to pointers when used in expressions.
4174 Artificial arrays most often appear in expressions via the value history
4175 (@pxref{Value History, ,Value history}), after printing one out.
4177 Another way to create an artificial array is to use a cast.
4178 This re-interprets a value as if it were an array.
4179 The value need not be in memory:
4181 (@value{GDBP}) p/x (short[2])0x12345678
4182 $1 = @{0x1234, 0x5678@}
4185 As a convenience, if you leave the array length out (as in
4186 @samp{(@var{type})[])@var{value}}) gdb calculates the size to fill
4187 the value (as @samp{sizeof(@var{value})/sizeof(@var{type})}:
4189 (@value{GDBP}) p/x (short[])0x12345678
4190 $2 = @{0x1234, 0x5678@}
4193 Sometimes the artificial array mechanism is not quite enough; in
4194 moderately complex data structures, the elements of interest may not
4195 actually be adjacent---for example, if you are interested in the values
4196 of pointers in an array. One useful work-around in this situation is
4197 to use a convenience variable (@pxref{Convenience Vars, ,Convenience
4198 variables}) as a counter in an expression that prints the first
4199 interesting value, and then repeat that expression via @key{RET}. For
4200 instance, suppose you have an array @code{dtab} of pointers to
4201 structures, and you are interested in the values of a field @code{fv}
4202 in each structure. Here is an example of what you might type:
4212 @node Output Formats
4213 @section Output formats
4215 @cindex formatted output
4216 @cindex output formats
4217 By default, @value{GDBN} prints a value according to its data type. Sometimes
4218 this is not what you want. For example, you might want to print a number
4219 in hex, or a pointer in decimal. Or you might want to view data in memory
4220 at a certain address as a character string or as an instruction. To do
4221 these things, specify an @dfn{output format} when you print a value.
4223 The simplest use of output formats is to say how to print a value
4224 already computed. This is done by starting the arguments of the
4225 @code{print} command with a slash and a format letter. The format
4226 letters supported are:
4230 Regard the bits of the value as an integer, and print the integer in
4234 Print as integer in signed decimal.
4237 Print as integer in unsigned decimal.
4240 Print as integer in octal.
4243 Print as integer in binary. The letter @samp{t} stands for ``two''.
4244 @footnote{@samp{b} cannot be used because these format letters are also
4245 used with the @code{x} command, where @samp{b} stands for ``byte'';
4246 @pxref{Memory,,Examining memory}.}
4249 @cindex unknown address, locating
4250 Print as an address, both absolute in hexadecimal and as an offset from
4251 the nearest preceding symbol. You can use this format used to discover
4252 where (in what function) an unknown address is located:
4255 (@value{GDBP}) p/a 0x54320
4256 $3 = 0x54320 <_initialize_vx+396>
4260 Regard as an integer and print it as a character constant.
4263 Regard the bits of the value as a floating point number and print
4264 using typical floating point syntax.
4267 For example, to print the program counter in hex (@pxref{Registers}), type
4274 Note that no space is required before the slash; this is because command
4275 names in @value{GDBN} cannot contain a slash.
4277 To reprint the last value in the value history with a different format,
4278 you can use the @code{print} command with just a format and no
4279 expression. For example, @samp{p/x} reprints the last value in hex.
4282 @section Examining memory
4284 You can use the command @code{x} (for ``examine'') to examine memory in
4285 any of several formats, independently of your program's data types.
4287 @cindex examining memory
4290 @item x/@var{nfu} @var{addr}
4293 Use the @code{x} command to examine memory.
4296 @var{n}, @var{f}, and @var{u} are all optional parameters that specify how
4297 much memory to display and how to format it; @var{addr} is an
4298 expression giving the address where you want to start displaying memory.
4299 If you use defaults for @var{nfu}, you need not type the slash @samp{/}.
4300 Several commands set convenient defaults for @var{addr}.
4303 @item @var{n}, the repeat count
4304 The repeat count is a decimal integer; the default is 1. It specifies
4305 how much memory (counting by units @var{u}) to display.
4306 @c This really is **decimal**; unaffected by 'set radix' as of GDB
4309 @item @var{f}, the display format
4310 The display format is one of the formats used by @code{print},
4311 @samp{s} (null-terminated string), or @samp{i} (machine instruction).
4312 The default is @samp{x} (hexadecimal) initially.
4313 The default changes each time you use either @code{x} or @code{print}.
4315 @item @var{u}, the unit size
4316 The unit size is any of
4322 Halfwords (two bytes).
4324 Words (four bytes). This is the initial default.
4326 Giant words (eight bytes).
4329 Each time you specify a unit size with @code{x}, that size becomes the
4330 default unit the next time you use @code{x}. (For the @samp{s} and
4331 @samp{i} formats, the unit size is ignored and is normally not written.)
4333 @item @var{addr}, starting display address
4334 @var{addr} is the address where you want @value{GDBN} to begin displaying
4335 memory. The expression need not have a pointer value (though it may);
4336 it is always interpreted as an integer address of a byte of memory.
4337 @xref{Expressions, ,Expressions}, for more information on expressions. The default for
4338 @var{addr} is usually just after the last address examined---but several
4339 other commands also set the default address: @code{info breakpoints} (to
4340 the address of the last breakpoint listed), @code{info line} (to the
4341 starting address of a line), and @code{print} (if you use it to display
4342 a value from memory).
4345 For example, @samp{x/3uh 0x54320} is a request to display three halfwords
4346 (@code{h}) of memory, formatted as unsigned decimal integers (@samp{u}),
4347 starting at address @code{0x54320}. @samp{x/4xw $sp} prints the four
4348 words (@samp{w}) of memory above the stack pointer (here, @samp{$sp};
4349 @pxref{Registers}) in hexadecimal (@samp{x}).
4351 Since the letters indicating unit sizes are all distinct from the
4352 letters specifying output formats, you do not have to remember whether
4353 unit size or format comes first; either order works. The output
4354 specifications @samp{4xw} and @samp{4wx} mean exactly the same thing.
4355 (However, the count @var{n} must come first; @samp{wx4} does not work.)
4357 Even though the unit size @var{u} is ignored for the formats @samp{s}
4358 and @samp{i}, you might still want to use a count @var{n}; for example,
4359 @samp{3i} specifies that you want to see three machine instructions,
4360 including any operands. The command @code{disassemble} gives an
4361 alternative way of inspecting machine instructions; @pxref{Machine
4362 Code,,Source and machine code}.
4364 All the defaults for the arguments to @code{x} are designed to make it
4365 easy to continue scanning memory with minimal specifications each time
4366 you use @code{x}. For example, after you have inspected three machine
4367 instructions with @samp{x/3i @var{addr}}, you can inspect the next seven
4368 with just @samp{x/7}. If you use @key{RET} to repeat the @code{x} command,
4369 the repeat count @var{n} is used again; the other arguments default as
4370 for successive uses of @code{x}.
4372 @cindex @code{$_}, @code{$__}, and value history
4373 The addresses and contents printed by the @code{x} command are not saved
4374 in the value history because there is often too much of them and they
4375 would get in the way. Instead, @value{GDBN} makes these values available for
4376 subsequent use in expressions as values of the convenience variables
4377 @code{$_} and @code{$__}. After an @code{x} command, the last address
4378 examined is available for use in expressions in the convenience variable
4379 @code{$_}. The contents of that address, as examined, are available in
4380 the convenience variable @code{$__}.
4382 If the @code{x} command has a repeat count, the address and contents saved
4383 are from the last memory unit printed; this is not the same as the last
4384 address printed if several units were printed on the last line of output.
4387 @section Automatic display
4388 @cindex automatic display
4389 @cindex display of expressions
4391 If you find that you want to print the value of an expression frequently
4392 (to see how it changes), you might want to add it to the @dfn{automatic
4393 display list} so that @value{GDBN} prints its value each time your program stops.
4394 Each expression added to the list is given a number to identify it;
4395 to remove an expression from the list, you specify that number.
4396 The automatic display looks like this:
4400 3: bar[5] = (struct hack *) 0x3804
4404 This display shows item numbers, expressions and their current values. As with
4405 displays you request manually using @code{x} or @code{print}, you can
4406 specify the output format you prefer; in fact, @code{display} decides
4407 whether to use @code{print} or @code{x} depending on how elaborate your
4408 format specification is---it uses @code{x} if you specify a unit size,
4409 or one of the two formats (@samp{i} and @samp{s}) that are only
4410 supported by @code{x}; otherwise it uses @code{print}.
4414 @item display @var{exp}
4415 Add the expression @var{exp} to the list of expressions to display
4416 each time your program stops. @xref{Expressions, ,Expressions}.
4418 @code{display} does not repeat if you press @key{RET} again after using it.
4420 @item display/@var{fmt} @var{exp}
4421 For @var{fmt} specifying only a display format and not a size or
4422 count, add the expression @var{exp} to the auto-display list but
4423 arrange to display it each time in the specified format @var{fmt}.
4424 @xref{Output Formats,,Output formats}.
4426 @item display/@var{fmt} @var{addr}
4427 For @var{fmt} @samp{i} or @samp{s}, or including a unit-size or a
4428 number of units, add the expression @var{addr} as a memory address to
4429 be examined each time your program stops. Examining means in effect
4430 doing @samp{x/@var{fmt} @var{addr}}. @xref{Memory, ,Examining memory}.
4433 For example, @samp{display/i $pc} can be helpful, to see the machine
4434 instruction about to be executed each time execution stops (@samp{$pc}
4435 is a common name for the program counter; @pxref{Registers}).
4438 @kindex delete display
4440 @item undisplay @var{dnums}@dots{}
4441 @itemx delete display @var{dnums}@dots{}
4442 Remove item numbers @var{dnums} from the list of expressions to display.
4444 @code{undisplay} does not repeat if you press @key{RET} after using it.
4445 (Otherwise you would just get the error @samp{No display number @dots{}}.)
4447 @kindex disable display
4448 @item disable display @var{dnums}@dots{}
4449 Disable the display of item numbers @var{dnums}. A disabled display
4450 item is not printed automatically, but is not forgotten. It may be
4451 enabled again later.
4453 @kindex enable display
4454 @item enable display @var{dnums}@dots{}
4455 Enable display of item numbers @var{dnums}. It becomes effective once
4456 again in auto display of its expression, until you specify otherwise.
4459 Display the current values of the expressions on the list, just as is
4460 done when your program stops.
4462 @kindex info display
4464 Print the list of expressions previously set up to display
4465 automatically, each one with its item number, but without showing the
4466 values. This includes disabled expressions, which are marked as such.
4467 It also includes expressions which would not be displayed right now
4468 because they refer to automatic variables not currently available.
4471 If a display expression refers to local variables, then it does not make
4472 sense outside the lexical context for which it was set up. Such an
4473 expression is disabled when execution enters a context where one of its
4474 variables is not defined. For example, if you give the command
4475 @code{display last_char} while inside a function with an argument
4476 @code{last_char}, @value{GDBN} displays this argument while your program
4477 continues to stop inside that function. When it stops elsewhere---where
4478 there is no variable @code{last_char}---the display is disabled
4479 automatically. The next time your program stops where @code{last_char}
4480 is meaningful, you can enable the display expression once again.
4482 @node Print Settings
4483 @section Print settings
4485 @cindex format options
4486 @cindex print settings
4487 @value{GDBN} provides the following ways to control how arrays, structures,
4488 and symbols are printed.
4491 These settings are useful for debugging programs in any language:
4494 @kindex set print address
4495 @item set print address
4496 @itemx set print address on
4497 @value{GDBN} prints memory addresses showing the location of stack
4498 traces, structure values, pointer values, breakpoints, and so forth,
4499 even when it also displays the contents of those addresses. The default
4500 is @code{on}. For example, this is what a stack frame display looks like with
4501 @code{set print address on}:
4506 #0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>")
4508 530 if (lquote != def_lquote)
4512 @item set print address off
4513 Do not print addresses when displaying their contents. For example,
4514 this is the same stack frame displayed with @code{set print address off}:
4518 (@value{GDBP}) set print addr off
4520 #0 set_quotes (lq="<<", rq=">>") at input.c:530
4521 530 if (lquote != def_lquote)
4525 You can use @samp{set print address off} to eliminate all machine
4526 dependent displays from the @value{GDBN} interface. For example, with
4527 @code{print address off}, you should get the same text for backtraces on
4528 all machines---whether or not they involve pointer arguments.
4530 @kindex show print address
4531 @item show print address
4532 Show whether or not addresses are to be printed.
4535 When @value{GDBN} prints a symbolic address, it normally prints the
4536 closest earlier symbol plus an offset. If that symbol does not uniquely
4537 identify the address (for example, it is a name whose scope is a single
4538 source file), you may need to clarify. One way to do this is with
4539 @code{info line}, for example @samp{info line *0x4537}. Alternately,
4540 you can set @value{GDBN} to print the source file and line number when
4541 it prints a symbolic address:
4544 @kindex set print symbol-filename
4545 @item set print symbol-filename on
4546 Tell @value{GDBN} to print the source file name and line number of a
4547 symbol in the symbolic form of an address.
4549 @item set print symbol-filename off
4550 Do not print source file name and line number of a symbol. This is the
4553 @kindex show print symbol-filename
4554 @item show print symbol-filename
4555 Show whether or not @value{GDBN} will print the source file name and
4556 line number of a symbol in the symbolic form of an address.
4559 Another situation where it is helpful to show symbol filenames and line
4560 numbers is when disassembling code; @value{GDBN} shows you the line
4561 number and source file that corresponds to each instruction.
4563 Also, you may wish to see the symbolic form only if the address being
4564 printed is reasonably close to the closest earlier symbol:
4567 @kindex set print max-symbolic-offset
4568 @item set print max-symbolic-offset @var{max-offset}
4569 Tell @value{GDBN} to only display the symbolic form of an address if the
4570 offset between the closest earlier symbol and the address is less than
4571 @var{max-offset}. The default is 0, which tells @value{GDBN}
4572 to always print the symbolic form of an address if any symbol precedes it.
4574 @kindex show print max-symbolic-offset
4575 @item show print max-symbolic-offset
4576 Ask how large the maximum offset is that @value{GDBN} prints in a
4580 @cindex wild pointer, interpreting
4581 @cindex pointer, finding referent
4582 If you have a pointer and you are not sure where it points, try
4583 @samp{set print symbol-filename on}. Then you can determine the name
4584 and source file location of the variable where it points, using
4585 @samp{p/a @var{pointer}}. This interprets the address in symbolic form.
4586 For example, here @value{GDBN} shows that a variable @code{ptt} points
4587 at another variable @code{t}, defined in @file{hi2.c}:
4590 (@value{GDBP}) set print symbol-filename on
4591 (@value{GDBP}) p/a ptt
4592 $4 = 0xe008 <t in hi2.c>
4596 @emph{Warning:} For pointers that point to a local variable, @samp{p/a}
4597 does not show the symbol name and filename of the referent, even with
4598 the appropriate @code{set print} options turned on.
4601 Other settings control how different kinds of objects are printed:
4604 @kindex set print array
4605 @item set print array
4606 @itemx set print array on
4607 Pretty print arrays. This format is more convenient to read,
4608 but uses more space. The default is off.
4610 @item set print array off
4611 Return to compressed format for arrays.
4613 @kindex show print array
4614 @item show print array
4615 Show whether compressed or pretty format is selected for displaying
4618 @kindex set print elements
4619 @item set print elements @var{number-of-elements}
4620 Set a limit on how many elements of an array @value{GDBN} will print.
4621 If @value{GDBN} is printing a large array, it stops printing after it has
4622 printed the number of elements set by the @code{set print elements} command.
4623 This limit also applies to the display of strings.
4624 Setting @var{number-of-elements} to zero means that the printing is unlimited.
4626 @kindex show print elements
4627 @item show print elements
4628 Display the number of elements of a large array that @value{GDBN} will print.
4629 If the number is 0, then the printing is unlimited.
4631 @kindex set print null-stop
4632 @item set print null-stop
4633 Cause @value{GDBN} to stop printing the characters of an array when the first
4634 @sc{NULL} is encountered. This is useful when large arrays actually
4635 contain only short strings.
4637 @kindex set print pretty
4638 @item set print pretty on
4639 Cause @value{GDBN} to print structures in an indented format with one member
4640 per line, like this:
4655 @item set print pretty off
4656 Cause @value{GDBN} to print structures in a compact format, like this:
4660 $1 = @{next = 0x0, flags = @{sweet = 1, sour = 1@}, \
4661 meat = 0x54 "Pork"@}
4666 This is the default format.
4668 @kindex show print pretty
4669 @item show print pretty
4670 Show which format @value{GDBN} is using to print structures.
4672 @kindex set print sevenbit-strings
4673 @item set print sevenbit-strings on
4674 Print using only seven-bit characters; if this option is set,
4675 @value{GDBN} displays any eight-bit characters (in strings or
4676 character values) using the notation @code{\}@var{nnn}. This setting is
4677 best if you are working in English (@sc{ascii}) and you use the
4678 high-order bit of characters as a marker or ``meta'' bit.
4680 @item set print sevenbit-strings off
4681 Print full eight-bit characters. This allows the use of more
4682 international character sets, and is the default.
4684 @kindex show print sevenbit-strings
4685 @item show print sevenbit-strings
4686 Show whether or not @value{GDBN} is printing only seven-bit characters.
4688 @kindex set print union
4689 @item set print union on
4690 Tell @value{GDBN} to print unions which are contained in structures. This
4691 is the default setting.
4693 @item set print union off
4694 Tell @value{GDBN} not to print unions which are contained in structures.
4696 @kindex show print union
4697 @item show print union
4698 Ask @value{GDBN} whether or not it will print unions which are contained in
4701 For example, given the declarations
4704 typedef enum @{Tree, Bug@} Species;
4705 typedef enum @{Big_tree, Acorn, Seedling@} Tree_forms;
4706 typedef enum @{Caterpillar, Cocoon, Butterfly@}
4717 struct thing foo = @{Tree, @{Acorn@}@};
4721 with @code{set print union on} in effect @samp{p foo} would print
4724 $1 = @{it = Tree, form = @{tree = Acorn, bug = Cocoon@}@}
4728 and with @code{set print union off} in effect it would print
4731 $1 = @{it = Tree, form = @{...@}@}
4738 These settings are of interest when debugging C++ programs:
4742 @kindex set print demangle
4743 @item set print demangle
4744 @itemx set print demangle on
4745 Print C++ names in their source form rather than in the encoded
4746 (``mangled'') form passed to the assembler and linker for type-safe
4747 linkage. The default is @samp{on}.
4749 @kindex show print demangle
4750 @item show print demangle
4751 Show whether C++ names are printed in mangled or demangled form.
4753 @kindex set print asm-demangle
4754 @item set print asm-demangle
4755 @itemx set print asm-demangle on
4756 Print C++ names in their source form rather than their mangled form, even
4757 in assembler code printouts such as instruction disassemblies.
4760 @kindex show print asm-demangle
4761 @item show print asm-demangle
4762 Show whether C++ names in assembly listings are printed in mangled
4765 @kindex set demangle-style
4766 @cindex C++ symbol decoding style
4767 @cindex symbol decoding style, C++
4768 @item set demangle-style @var{style}
4769 Choose among several encoding schemes used by different compilers to
4770 represent C++ names. The choices for @var{style} are currently:
4774 Allow @value{GDBN} to choose a decoding style by inspecting your program.
4777 Decode based on the @sc{gnu} C++ compiler (@code{g++}) encoding algorithm.
4778 This is the default.
4781 Decode based on the Lucid C++ compiler (@code{lcc}) encoding algorithm.
4784 Decode using the algorithm in the @cite{C++ Annotated Reference Manual}.
4785 @strong{Warning:} this setting alone is not sufficient to allow
4786 debugging @code{cfront}-generated executables. @value{GDBN} would
4787 require further enhancement to permit that.
4790 Show the list of formats.
4793 @kindex show demangle-style
4794 @item show demangle-style
4795 Display the encoding style currently in use for decoding C++ symbols.
4797 @kindex set print object
4798 @item set print object
4799 @itemx set print object on
4800 When displaying a pointer to an object, identify the @emph{actual}
4801 (derived) type of the object rather than the @emph{declared} type, using
4802 the virtual function table.
4804 @item set print object off
4805 Display only the declared type of objects, without reference to the
4806 virtual function table. This is the default setting.
4808 @kindex show print object
4809 @item show print object
4810 Show whether actual, or declared, object types are displayed.
4812 @kindex set print vtbl
4813 @item set print vtbl
4814 @itemx set print vtbl on
4815 Pretty print C++ virtual function tables. The default is off.
4817 @item set print vtbl off
4818 Do not pretty print C++ virtual function tables.
4820 @kindex show print vtbl
4821 @item show print vtbl
4822 Show whether C++ virtual function tables are pretty printed, or not.
4827 @section Value history
4829 @cindex value history
4830 Values printed by the @code{print} command are saved in the @value{GDBN}
4831 @dfn{value history}. This allows you to refer to them in other expressions.
4832 Values are kept until the symbol table is re-read or discarded
4833 (for example with the @code{file} or @code{symbol-file} commands).
4834 When the symbol table changes, the value history is discarded,
4835 since the values may contain pointers back to the types defined in the
4840 @cindex history number
4841 The values printed are given @dfn{history numbers} by which you can
4842 refer to them. These are successive integers starting with one.
4843 @code{print} shows you the history number assigned to a value by
4844 printing @samp{$@var{num} = } before the value; here @var{num} is the
4847 To refer to any previous value, use @samp{$} followed by the value's
4848 history number. The way @code{print} labels its output is designed to
4849 remind you of this. Just @code{$} refers to the most recent value in
4850 the history, and @code{$$} refers to the value before that.
4851 @code{$$@var{n}} refers to the @var{n}th value from the end; @code{$$2}
4852 is the value just prior to @code{$$}, @code{$$1} is equivalent to
4853 @code{$$}, and @code{$$0} is equivalent to @code{$}.
4855 For example, suppose you have just printed a pointer to a structure and
4856 want to see the contents of the structure. It suffices to type
4862 If you have a chain of structures where the component @code{next} points
4863 to the next one, you can print the contents of the next one with this:
4870 You can print successive links in the chain by repeating this
4871 command---which you can do by just typing @key{RET}.
4873 Note that the history records values, not expressions. If the value of
4874 @code{x} is 4 and you type these commands:
4882 then the value recorded in the value history by the @code{print} command
4883 remains 4 even though the value of @code{x} has changed.
4888 Print the last ten values in the value history, with their item numbers.
4889 This is like @samp{p@ $$9} repeated ten times, except that @code{show
4890 values} does not change the history.
4892 @item show values @var{n}
4893 Print ten history values centered on history item number @var{n}.
4896 Print ten history values just after the values last printed. If no more
4897 values are available, @code{show values +} produces no display.
4900 Pressing @key{RET} to repeat @code{show values @var{n}} has exactly the
4901 same effect as @samp{show values +}.
4903 @node Convenience Vars
4904 @section Convenience variables
4906 @cindex convenience variables
4907 @value{GDBN} provides @dfn{convenience variables} that you can use within
4908 @value{GDBN} to hold on to a value and refer to it later. These variables
4909 exist entirely within @value{GDBN}; they are not part of your program, and
4910 setting a convenience variable has no direct effect on further execution
4911 of your program. That is why you can use them freely.
4913 Convenience variables are prefixed with @samp{$}. Any name preceded by
4914 @samp{$} can be used for a convenience variable, unless it is one of
4915 the predefined machine-specific register names (@pxref{Registers}).
4916 (Value history references, in contrast, are @emph{numbers} preceded
4917 by @samp{$}. @xref{Value History, ,Value history}.)
4919 You can save a value in a convenience variable with an assignment
4920 expression, just as you would set a variable in your program.
4924 set $foo = *object_ptr
4928 would save in @code{$foo} the value contained in the object pointed to by
4931 Using a convenience variable for the first time creates it, but its
4932 value is @code{void} until you assign a new value. You can alter the
4933 value with another assignment at any time.
4935 Convenience variables have no fixed types. You can assign a convenience
4936 variable any type of value, including structures and arrays, even if
4937 that variable already has a value of a different type. The convenience
4938 variable, when used as an expression, has the type of its current value.
4941 @kindex show convenience
4942 @item show convenience
4943 Print a list of convenience variables used so far, and their values.
4944 Abbreviated @code{show con}.
4947 One of the ways to use a convenience variable is as a counter to be
4948 incremented or a pointer to be advanced. For example, to print
4949 a field from successive elements of an array of structures:
4953 print bar[$i++]->contents
4956 @noindent Repeat that command by typing @key{RET}.
4958 Some convenience variables are created automatically by @value{GDBN} and given
4959 values likely to be useful.
4964 The variable @code{$_} is automatically set by the @code{x} command to
4965 the last address examined (@pxref{Memory, ,Examining memory}). Other
4966 commands which provide a default address for @code{x} to examine also
4967 set @code{$_} to that address; these commands include @code{info line}
4968 and @code{info breakpoint}. The type of @code{$_} is @code{void *}
4969 except when set by the @code{x} command, in which case it is a pointer
4970 to the type of @code{$__}.
4974 The variable @code{$__} is automatically set by the @code{x} command
4975 to the value found in the last address examined. Its type is chosen
4976 to match the format in which the data was printed.
4983 You can refer to machine register contents, in expressions, as variables
4984 with names starting with @samp{$}. The names of registers are different
4985 for each machine; use @code{info registers} to see the names used on
4989 @kindex info registers
4990 @item info registers
4991 Print the names and values of all registers except floating-point
4992 registers (in the selected stack frame).
4994 @kindex info all-registers
4995 @cindex floating point registers
4996 @item info all-registers
4997 Print the names and values of all registers, including floating-point
5000 @item info registers @var{regname} @dots{}
5001 Print the @dfn{relativized} value of each specified register @var{regname}.
5002 As discussed in detail below, register values are normally relative to
5003 the selected stack frame. @var{regname} may be any register name valid on
5004 the machine you are using, with or without the initial @samp{$}.
5007 @value{GDBN} has four ``standard'' register names that are available (in
5008 expressions) on most machines---whenever they do not conflict with an
5009 architecture's canonical mnemonics for registers. The register names
5010 @code{$pc} and @code{$sp} are used for the program counter register and
5011 the stack pointer. @code{$fp} is used for a register that contains a
5012 pointer to the current stack frame, and @code{$ps} is used for a
5013 register that contains the processor status. For example,
5014 you could print the program counter in hex with
5021 or print the instruction to be executed next with
5028 or add four to the stack pointer@footnote{This is a way of removing
5029 one word from the stack, on machines where stacks grow downward in
5030 memory (most machines, nowadays). This assumes that the innermost
5031 stack frame is selected; setting @code{$sp} is not allowed when other
5032 stack frames are selected. To pop entire frames off the stack,
5033 regardless of machine architecture, use @code{return};
5034 @pxref{Returning, ,Returning from a function}.} with
5040 Whenever possible, these four standard register names are available on
5041 your machine even though the machine has different canonical mnemonics,
5042 so long as there is no conflict. The @code{info registers} command
5043 shows the canonical names. For example, on the SPARC, @code{info
5044 registers} displays the processor status register as @code{$psr} but you
5045 can also refer to it as @code{$ps}.
5047 @value{GDBN} always considers the contents of an ordinary register as an
5048 integer when the register is examined in this way. Some machines have
5049 special registers which can hold nothing but floating point; these
5050 registers are considered to have floating point values. There is no way
5051 to refer to the contents of an ordinary register as floating point value
5052 (although you can @emph{print} it as a floating point value with
5053 @samp{print/f $@var{regname}}).
5055 Some registers have distinct ``raw'' and ``virtual'' data formats. This
5056 means that the data format in which the register contents are saved by
5057 the operating system is not the same one that your program normally
5058 sees. For example, the registers of the 68881 floating point
5059 coprocessor are always saved in ``extended'' (raw) format, but all C
5060 programs expect to work with ``double'' (virtual) format. In such
5061 cases, @value{GDBN} normally works with the virtual format only (the format
5062 that makes sense for your program), but the @code{info registers} command
5063 prints the data in both formats.
5065 Normally, register values are relative to the selected stack frame
5066 (@pxref{Selection, ,Selecting a frame}). This means that you get the
5067 value that the register would contain if all stack frames farther in
5068 were exited and their saved registers restored. In order to see the
5069 true contents of hardware registers, you must select the innermost
5070 frame (with @samp{frame 0}).
5072 However, @value{GDBN} must deduce where registers are saved, from the machine
5073 code generated by your compiler. If some registers are not saved, or if
5074 @value{GDBN} is unable to locate the saved registers, the selected stack
5075 frame makes no difference.
5079 @kindex set rstack_high_address
5080 @cindex AMD 29K register stack
5081 @cindex register stack, AMD29K
5082 @item set rstack_high_address @var{address}
5083 On AMD 29000 family processors, registers are saved in a separate
5084 ``register stack''. There is no way for @value{GDBN} to determine the extent
5085 of this stack. Normally, @value{GDBN} just assumes that the stack is ``large
5086 enough''. This may result in @value{GDBN} referencing memory locations that
5087 do not exist. If necessary, you can get around this problem by
5088 specifying the ending address of the register stack with the @code{set
5089 rstack_high_address} command. The argument should be an address, which
5090 you probably want to precede with @samp{0x} to specify in
5093 @kindex show rstack_high_address
5094 @item show rstack_high_address
5095 Display the current limit of the register stack, on AMD 29000 family
5101 @node Floating Point Hardware
5102 @section Floating point hardware
5103 @cindex floating point
5105 Depending on the configuration, @value{GDBN} may be able to give
5106 you more information about the status of the floating point hardware.
5111 Display hardware-dependent information about the floating
5112 point unit. The exact contents and layout vary depending on the
5113 floating point chip. Currently, @samp{info float} is supported on
5114 the ARM and x86 machines.
5120 @chapter Using @value{GDBN} with Different Languages
5124 Although programming languages generally have common aspects, they are
5125 rarely expressed in the same manner. For instance, in ANSI C,
5126 dereferencing a pointer @code{p} is accomplished by @code{*p}, but in
5127 Modula-2, it is accomplished by @code{p^}. Values can also be
5128 represented (and displayed) differently. Hex numbers in C appear as
5129 @samp{0x1ae}, while in Modula-2 they appear as @samp{1AEH}.
5132 @cindex working language
5133 Language-specific information is built into @value{GDBN} for some languages,
5134 allowing you to express operations like the above in your program's
5135 native language, and allowing @value{GDBN} to output values in a manner
5136 consistent with the syntax of your program's native language. The
5137 language you use to build expressions is called the @dfn{working
5141 * Setting:: Switching between source languages
5142 * Show:: Displaying the language
5144 * Checks:: Type and range checks
5147 * Support:: Supported languages
5151 @section Switching between source languages
5153 There are two ways to control the working language---either have @value{GDBN}
5154 set it automatically, or select it manually yourself. You can use the
5155 @code{set language} command for either purpose. On startup, @value{GDBN}
5156 defaults to setting the language automatically. The working language is
5157 used to determine how expressions you type are interpreted, how values
5160 In addition to the working language, every source file that
5161 @value{GDBN} knows about has its own working language. For some object
5162 file formats, the compiler might indicate which language a particular
5163 source file is in. However, most of the time @value{GDBN} infers the
5164 language from the name of the file. The language of a source file
5165 controls whether C++ names are demangled---this way @code{backtrace} can
5166 show each frame appropriately for its own language. There is no way to
5167 set the language of a source file from within @value{GDBN}.
5169 This is most commonly a problem when you use a program, such
5170 as @code{cfront} or @code{f2c}, that generates C but is written in
5171 another language. In that case, make the
5172 program use @code{#line} directives in its C output; that way
5173 @value{GDBN} will know the correct language of the source code of the original
5174 program, and will display that source code, not the generated C code.
5177 * Filenames:: Filename extensions and languages.
5178 * Manually:: Setting the working language manually
5179 * Automatically:: Having @value{GDBN} infer the source language
5183 @subsection List of filename extensions and languages
5185 If a source file name ends in one of the following extensions, then
5186 @value{GDBN} infers that its language is the one indicated.
5191 Modula-2 source file
5212 Assembler source file. This actually behaves almost like C, but
5213 @value{GDBN} does not skip over function prologues when stepping.
5217 @subsection Setting the working language
5219 If you allow @value{GDBN} to set the language automatically,
5220 expressions are interpreted the same way in your debugging session and
5223 @kindex set language
5224 If you wish, you may set the language manually. To do this, issue the
5225 command @samp{set language @var{lang}}, where @var{lang} is the name of
5231 @code{c} or @code{modula-2}.
5233 For a list of the supported languages, type @samp{set language}.
5236 Setting the language manually prevents @value{GDBN} from updating the working
5237 language automatically. This can lead to confusion if you try
5238 to debug a program when the working language is not the same as the
5239 source language, when an expression is acceptable to both
5240 languages---but means different things. For instance, if the current
5241 source file were written in C, and @value{GDBN} was parsing Modula-2, a
5249 might not have the effect you intended. In C, this means to add
5250 @code{b} and @code{c} and place the result in @code{a}. The result
5251 printed would be the value of @code{a}. In Modula-2, this means to compare
5252 @code{a} to the result of @code{b+c}, yielding a @code{BOOLEAN} value.
5256 @subsection Having @value{GDBN} infer the source language
5258 To have @value{GDBN} set the working language automatically, use
5259 @samp{set language local} or @samp{set language auto}. @value{GDBN}
5260 then infers the working language. That is, when your program stops in a
5261 frame (usually by encountering a breakpoint), @value{GDBN} sets the
5262 working language to the language recorded for the function in that
5263 frame. If the language for a frame is unknown (that is, if the function
5264 or block corresponding to the frame was defined in a source file that
5265 does not have a recognized extension), the current working language is
5266 not changed, and @value{GDBN} issues a warning.
5268 This may not seem necessary for most programs, which are written
5269 entirely in one source language. However, program modules and libraries
5270 written in one source language can be used by a main program written in
5271 a different source language. Using @samp{set language auto} in this
5272 case frees you from having to set the working language manually.
5275 @section Displaying the language
5277 The following commands help you find out which language is the
5278 working language, and also what language source files were written in.
5280 @kindex show language
5285 Display the current working language. This is the
5286 language you can use with commands such as @code{print} to
5287 build and compute expressions that may involve variables in your program.
5290 Display the source language for this frame. This language becomes the
5291 working language if you use an identifier from this frame.
5292 @xref{Frame Info, ,Information about a frame}, to identify the other
5293 information listed here.
5296 Display the source language of this source file.
5297 @xref{Symbols, ,Examining the Symbol Table}, to identify the other
5298 information listed here.
5303 @section Type and range checking
5306 @emph{Warning:} In this release, the @value{GDBN} commands for type and range
5307 checking are included, but they do not yet have any effect. This
5308 section documents the intended facilities.
5310 @c FIXME remove warning when type/range code added
5312 Some languages are designed to guard you against making seemingly common
5313 errors through a series of compile- and run-time checks. These include
5314 checking the type of arguments to functions and operators, and making
5315 sure mathematical overflows are caught at run time. Checks such as
5316 these help to ensure a program's correctness once it has been compiled
5317 by eliminating type mismatches, and providing active checks for range
5318 errors when your program is running.
5320 @value{GDBN} can check for conditions like the above if you wish.
5321 Although @value{GDBN} does not check the statements in your program, it
5322 can check expressions entered directly into @value{GDBN} for evaluation via
5323 the @code{print} command, for example. As with the working language,
5324 @value{GDBN} can also decide whether or not to check automatically based on
5325 your program's source language. @xref{Support, ,Supported languages},
5326 for the default settings of supported languages.
5329 * Type Checking:: An overview of type checking
5330 * Range Checking:: An overview of range checking
5333 @cindex type checking
5334 @cindex checks, type
5336 @subsection An overview of type checking
5338 Some languages, such as Modula-2, are strongly typed, meaning that the
5339 arguments to operators and functions have to be of the correct type,
5340 otherwise an error occurs. These checks prevent type mismatch
5341 errors from ever causing any run-time problems. For example,
5349 The second example fails because the @code{CARDINAL} 1 is not
5350 type-compatible with the @code{REAL} 2.3.
5352 For the expressions you use in @value{GDBN} commands, you can tell the
5353 @value{GDBN} type checker to skip checking;
5354 to treat any mismatches as errors and abandon the expression;
5355 or to only issue warnings when type mismatches occur,
5356 but evaluate the expression anyway. When you choose the last of
5357 these, @value{GDBN} evaluates expressions like the second example above, but
5358 also issues a warning.
5360 Even if you turn type checking off, there may be other reasons
5361 related to type that prevent @value{GDBN} from evaluating an expression.
5362 For instance, @value{GDBN} does not know how to add an @code{int} and
5363 a @code{struct foo}. These particular type errors have nothing to do
5364 with the language in use, and usually arise from expressions, such as
5365 the one described above, which make little sense to evaluate anyway.
5367 Each language defines to what degree it is strict about type. For
5368 instance, both Modula-2 and C require the arguments to arithmetical
5369 operators to be numbers. In C, enumerated types and pointers can be
5370 represented as numbers, so that they are valid arguments to mathematical
5371 operators. @xref{Support, ,Supported languages}, for further
5372 details on specific languages.
5374 @value{GDBN} provides some additional commands for controlling the type checker:
5377 @kindex set check type
5378 @kindex show check type
5380 @item set check type auto
5381 Set type checking on or off based on the current working language.
5382 @xref{Support, ,Supported languages}, for the default settings for
5385 @item set check type on
5386 @itemx set check type off
5387 Set type checking on or off, overriding the default setting for the
5388 current working language. Issue a warning if the setting does not
5389 match the language default. If any type mismatches occur in
5390 evaluating an expression while typechecking is on, @value{GDBN} prints a
5391 message and aborts evaluation of the expression.
5393 @item set check type warn
5394 Cause the type checker to issue warnings, but to always attempt to
5395 evaluate the expression. Evaluating the expression may still
5396 be impossible for other reasons. For example, @value{GDBN} cannot add
5397 numbers and structures.
5400 Show the current setting of the type checker, and whether or not @value{GDBN}
5401 is setting it automatically.
5404 @cindex range checking
5405 @cindex checks, range
5406 @node Range Checking
5407 @subsection An overview of range checking
5409 In some languages (such as Modula-2), it is an error to exceed the
5410 bounds of a type; this is enforced with run-time checks. Such range
5411 checking is meant to ensure program correctness by making sure
5412 computations do not overflow, or indices on an array element access do
5413 not exceed the bounds of the array.
5415 For expressions you use in @value{GDBN} commands, you can tell
5416 @value{GDBN} to treat range errors in one of three ways: ignore them,
5417 always treat them as errors and abandon the expression, or issue
5418 warnings but evaluate the expression anyway.
5420 A range error can result from numerical overflow, from exceeding an
5421 array index bound, or when you type a constant that is not a member
5422 of any type. Some languages, however, do not treat overflows as an
5423 error. In many implementations of C, mathematical overflow causes the
5424 result to ``wrap around'' to lower values---for example, if @var{m} is
5425 the largest integer value, and @var{s} is the smallest, then
5428 @var{m} + 1 @result{} @var{s}
5431 This, too, is specific to individual languages, and in some cases
5432 specific to individual compilers or machines. @xref{Support, ,
5433 Supported languages}, for further details on specific languages.
5435 @value{GDBN} provides some additional commands for controlling the range checker:
5438 @kindex set check range
5439 @kindex show check range
5441 @item set check range auto
5442 Set range checking on or off based on the current working language.
5443 @xref{Support, ,Supported languages}, for the default settings for
5446 @item set check range on
5447 @itemx set check range off
5448 Set range checking on or off, overriding the default setting for the
5449 current working language. A warning is issued if the setting does not
5450 match the language default. If a range error occurs, then a message
5451 is printed and evaluation of the expression is aborted.
5453 @item set check range warn
5454 Output messages when the @value{GDBN} range checker detects a range error,
5455 but attempt to evaluate the expression anyway. Evaluating the
5456 expression may still be impossible for other reasons, such as accessing
5457 memory that the process does not own (a typical example from many Unix
5461 Show the current setting of the range checker, and whether or not it is
5462 being set automatically by @value{GDBN}.
5467 @section Supported languages
5470 @value{GDBN} 4 supports C, C++, and Modula-2.
5473 @value{GDBN} 4 supports C, and C++.
5475 Some @value{GDBN} features may be used in expressions regardless of the
5476 language you use: the @value{GDBN} @code{@@} and @code{::} operators,
5477 and the @samp{@{type@}addr} construct (@pxref{Expressions,
5478 ,Expressions}) can be used with the constructs of any supported
5481 The following sections detail to what degree each source language is
5482 supported by @value{GDBN}. These sections are not meant to be language
5483 tutorials or references, but serve only as a reference guide to what the
5484 @value{GDBN} expression parser accepts, and what input and output
5485 formats should look like for different languages. There are many good
5486 books written on each of these languages; please look to these for a
5487 language reference or tutorial.
5492 * Modula-2:: Modula-2
5496 @subsection C and C++
5498 @cindex expressions in C or C++
5500 Since C and C++ are so closely related, many features of @value{GDBN} apply
5501 to both languages. Whenever this is the case, we discuss those languages
5505 @c Cancel this below, under same condition, at end of this chapter!
5511 @cindex @sc{gnu} C++
5512 The C++ debugging facilities are jointly implemented by the @sc{gnu} C++
5513 compiler and @value{GDBN}. Therefore, to debug your C++ code
5514 effectively, you must compile your C++ programs with the @sc{gnu} C++
5515 compiler, @code{g++}.
5517 For best results when debugging C++ programs, use the stabs debugging
5518 format. You can select that format explicitly with the @code{g++}
5519 command-line options @samp{-gstabs} or @samp{-gstabs+}. See
5520 @ref{Debugging Options,,Options for Debugging Your Program or @sc{gnu} CC,
5521 gcc.info, Using @sc{gnu} CC}, for more information.
5525 @chapter C Language Support
5527 @cindex expressions in C
5529 Information specific to the C language is built into @value{GDBN} so that you
5530 can use C expressions while degugging. This also permits @value{GDBN} to
5531 output values in a manner consistent with C conventions.
5534 * C Operators:: C operators
5535 * C Constants:: C constants
5536 * Debugging C:: @value{GDBN} and C
5541 * C Operators:: C and C++ operators
5542 * C Constants:: C and C++ constants
5543 * Cplus expressions:: C++ expressions
5544 * C Defaults:: Default settings for C and C++
5546 * C Checks:: C and C++ type and range checks
5549 * Debugging C:: @value{GDBN} and C
5550 * Debugging C plus plus:: Special features for C++
5555 @cindex C and C++ operators
5557 @subsubsection C and C++ operators
5562 @section C operators
5565 Operators must be defined on values of specific types. For instance,
5566 @code{+} is defined on numbers, but not on structures. Operators are
5567 often defined on groups of types.
5570 For the purposes of C and C++, the following definitions hold:
5575 @emph{Integral types} include @code{int} with any of its storage-class
5576 specifiers; @code{char}; and @code{enum}.
5579 @emph{Floating-point types} include @code{float} and @code{double}.
5582 @emph{Pointer types} include all types defined as @code{(@var{type}
5586 @emph{Scalar types} include all of the above.
5590 The following operators are supported. They are listed here
5591 in order of increasing precedence:
5595 The comma or sequencing operator. Expressions in a comma-separated list
5596 are evaluated from left to right, with the result of the entire
5597 expression being the last expression evaluated.
5600 Assignment. The value of an assignment expression is the value
5601 assigned. Defined on scalar types.
5604 Used in an expression of the form @w{@code{@var{a} @var{op}= @var{b}}},
5605 and translated to @w{@code{@var{a} = @var{a op b}}}.
5606 @w{@code{@var{op}=}} and @code{=} have the same precendence.
5607 @var{op} is any one of the operators @code{|}, @code{^}, @code{&},
5608 @code{<<}, @code{>>}, @code{+}, @code{-}, @code{*}, @code{/}, @code{%}.
5611 The ternary operator. @code{@var{a} ? @var{b} : @var{c}} can be thought
5612 of as: if @var{a} then @var{b} else @var{c}. @var{a} should be of an
5616 Logical @sc{or}. Defined on integral types.
5619 Logical @sc{and}. Defined on integral types.
5622 Bitwise @sc{or}. Defined on integral types.
5625 Bitwise exclusive-@sc{or}. Defined on integral types.
5628 Bitwise @sc{and}. Defined on integral types.
5631 Equality and inequality. Defined on scalar types. The value of these
5632 expressions is 0 for false and non-zero for true.
5634 @item <@r{, }>@r{, }<=@r{, }>=
5635 Less than, greater than, less than or equal, greater than or equal.
5636 Defined on scalar types. The value of these expressions is 0 for false
5637 and non-zero for true.
5640 left shift, and right shift. Defined on integral types.
5643 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
5646 Addition and subtraction. Defined on integral types, floating-point types and
5649 @item *@r{, }/@r{, }%
5650 Multiplication, division, and modulus. Multiplication and division are
5651 defined on integral and floating-point types. Modulus is defined on
5655 Increment and decrement. When appearing before a variable, the
5656 operation is performed before the variable is used in an expression;
5657 when appearing after it, the variable's value is used before the
5658 operation takes place.
5661 Pointer dereferencing. Defined on pointer types. Same precedence as
5665 Address operator. Defined on variables. Same precedence as @code{++}.
5668 For debugging C++, @value{GDBN} implements a use of @samp{&} beyond what is
5669 allowed in the C++ language itself: you can use @samp{&(&@var{ref})}
5670 (or, if you prefer, simply @samp{&&@var{ref}}) to examine the address
5671 where a C++ reference variable (declared with @samp{&@var{ref}}) is
5676 Negative. Defined on integral and floating-point types. Same
5677 precedence as @code{++}.
5680 Logical negation. Defined on integral types. Same precedence as
5684 Bitwise complement operator. Defined on integral types. Same precedence as
5689 Structure member, and pointer-to-structure member. For convenience,
5690 @value{GDBN} regards the two as equivalent, choosing whether to dereference a
5691 pointer based on the stored type information.
5692 Defined on @code{struct} and @code{union} data.
5695 Array indexing. @code{@var{a}[@var{i}]} is defined as
5696 @code{*(@var{a}+@var{i})}. Same precedence as @code{->}.
5699 Function parameter list. Same precedence as @code{->}.
5703 C++ scope resolution operator. Defined on
5704 @code{struct}, @code{union}, and @code{class} types.
5712 represent the @value{GDBN} scope operator (@pxref{Expressions,
5715 Same precedence as @code{::}, above.
5720 @cindex C and C++ constants
5722 @subsubsection C and C++ constants
5724 @value{GDBN} allows you to express the constants of C and C++ in the
5730 @section C constants
5732 @value{GDBN} allows you to express the constants of C in the
5738 Integer constants are a sequence of digits. Octal constants are
5739 specified by a leading @samp{0} (i.e. zero), and hexadecimal constants by
5740 a leading @samp{0x} or @samp{0X}. Constants may also end with a letter
5741 @samp{l}, specifying that the constant should be treated as a
5745 Floating point constants are a sequence of digits, followed by a decimal
5746 point, followed by a sequence of digits, and optionally followed by an
5747 exponent. An exponent is of the form:
5748 @samp{@w{e@r{[[}+@r{]|}-@r{]}@var{nnn}}}, where @var{nnn} is another
5749 sequence of digits. The @samp{+} is optional for positive exponents.
5752 Enumerated constants consist of enumerated identifiers, or their
5753 integral equivalents.
5756 Character constants are a single character surrounded by single quotes
5757 (@code{'}), or a number---the ordinal value of the corresponding character
5758 (usually its @sc{ASCII} value). Within quotes, the single character may
5759 be represented by a letter or by @dfn{escape sequences}, which are of
5760 the form @samp{\@var{nnn}}, where @var{nnn} is the octal representation
5761 of the character's ordinal value; or of the form @samp{\@var{x}}, where
5762 @samp{@var{x}} is a predefined special character---for example,
5763 @samp{\n} for newline.
5766 String constants are a sequence of character constants surrounded
5767 by double quotes (@code{"}).
5770 Pointer constants are an integral value. You can also write pointers
5771 to constants using the C operator @samp{&}.
5774 Array constants are comma-separated lists surrounded by braces @samp{@{}
5775 and @samp{@}}; for example, @samp{@{1,2,3@}} is a three-element array of
5776 integers, @samp{@{@{1,2@}, @{3,4@}, @{5,6@}@}} is a three-by-two array,
5777 and @samp{@{&"hi", &"there", &"fred"@}} is a three-element array of pointers.
5781 @node Cplus expressions
5782 @subsubsection C++ expressions
5784 @cindex expressions in C++
5785 @value{GDBN} expression handling has a number of extensions to
5786 interpret a significant subset of C++ expressions.
5788 @cindex C++ support, not in @sc{coff}
5789 @cindex @sc{coff} versus C++
5790 @cindex C++ and object formats
5791 @cindex object formats and C++
5792 @cindex a.out and C++
5793 @cindex @sc{ecoff} and C++
5794 @cindex @sc{xcoff} and C++
5795 @cindex @sc{elf}/stabs and C++
5796 @cindex @sc{elf}/@sc{dwarf} and C++
5797 @c FIXME!! GDB may eventually be able to debug C++ using DWARF; check
5798 @c periodically whether this has happened...
5800 @emph{Warning:} @value{GDBN} can only debug C++ code if you compile with
5801 the @sc{gnu} C++ compiler. Moreover, C++ debugging depends on the use of
5802 additional debugging information in the symbol table, and thus requires
5803 special support. @value{GDBN} has this support @emph{only} with the
5804 stabs debug format. In particular, if your compiler generates a.out,
5805 MIPS @sc{ecoff}, RS/6000 @sc{xcoff}, or @sc{elf} with stabs extensions
5806 to the symbol table, these facilities are all available. (With @sc{gnu} CC,
5807 you can use the @samp{-gstabs} option to request stabs debugging
5808 extensions explicitly.) Where the object code format is standard
5809 @sc{coff} or @sc{dwarf} in @sc{elf}, on the other hand, most of the C++
5810 support in @value{GDBN} does @emph{not} work.
5815 @cindex member functions
5817 Member function calls are allowed; you can use expressions like
5820 count = aml->GetOriginal(x, y)
5824 @cindex namespace in C++
5826 While a member function is active (in the selected stack frame), your
5827 expressions have the same namespace available as the member function;
5828 that is, @value{GDBN} allows implicit references to the class instance
5829 pointer @code{this} following the same rules as C++.
5831 @cindex call overloaded functions
5832 @cindex type conversions in C++
5834 You can call overloaded functions; @value{GDBN} resolves the function
5835 call to the right definition, with one restriction---you must use
5836 arguments of the type required by the function that you want to call.
5837 @value{GDBN} does not perform conversions requiring constructors or
5838 user-defined type operators.
5840 @cindex reference declarations
5842 @value{GDBN} understands variables declared as C++ references; you can use
5843 them in expressions just as you do in C++ source---they are automatically
5846 In the parameter list shown when @value{GDBN} displays a frame, the values of
5847 reference variables are not displayed (unlike other variables); this
5848 avoids clutter, since references are often used for large structures.
5849 The @emph{address} of a reference variable is always shown, unless
5850 you have specified @samp{set print address off}.
5853 @value{GDBN} supports the C++ name resolution operator @code{::}---your
5854 expressions can use it just as expressions in your program do. Since
5855 one scope may be defined in another, you can use @code{::} repeatedly if
5856 necessary, for example in an expression like
5857 @samp{@var{scope1}::@var{scope2}::@var{name}}. @value{GDBN} also allows
5858 resolving name scope by reference to source files, in both C and C++
5859 debugging (@pxref{Variables, ,Program variables}).
5863 @subsubsection C and C++ defaults
5864 @cindex C and C++ defaults
5866 If you allow @value{GDBN} to set type and range checking automatically, they
5867 both default to @code{off} whenever the working language changes to
5868 C or C++. This happens regardless of whether you or @value{GDBN}
5869 selects the working language.
5871 If you allow @value{GDBN} to set the language automatically, it recognizes
5872 source files whose names end with @file{.c}, @file{.C}, or @file{.cc}, and
5873 when @value{GDBN} enters code compiled from one of these files,
5874 it sets the working language to C or C++.
5875 @xref{Automatically, ,Having @value{GDBN} infer the source language}, for
5879 @c Type checking is (a) primarily motivated by Modula-2, and (b)
5880 @c unimplemented. If (b) changes, it might make sense to let this node
5881 @c appear even if Mod-2 does not, but meanwhile ignore it. pesch 16jul93.
5883 @subsubsection C and C++ type and range checks
5884 @cindex C and C++ checks
5886 By default, when @value{GDBN} parses C or C++ expressions, type checking
5887 is not used. However, if you turn type checking on, @value{GDBN}
5888 considers two variables type equivalent if:
5892 The two variables are structured and have the same structure, union, or
5896 The two variables have the same type name, or types that have been
5897 declared equivalent through @code{typedef}.
5900 @c leaving this out because neither J Gilmore nor R Pesch understand it.
5903 The two @code{struct}, @code{union}, or @code{enum} variables are
5904 declared in the same declaration. (Note: this may not be true for all C
5909 Range checking, if turned on, is done on mathematical operations. Array
5910 indices are not checked, since they are often used to index a pointer
5911 that is not itself an array.
5917 @subsubsection @value{GDBN} and C
5921 @section @value{GDBN} and C
5924 The @code{set print union} and @code{show print union} commands apply to
5925 the @code{union} type. When set to @samp{on}, any @code{union} that is
5926 inside a @code{struct}
5931 Otherwise, it appears as @samp{@{...@}}.
5933 The @code{@@} operator aids in the debugging of dynamic arrays, formed
5934 with pointers and a memory allocation function. @xref{Expressions,
5938 @node Debugging C plus plus
5939 @subsubsection @value{GDBN} features for C++
5941 @cindex commands for C++
5942 Some @value{GDBN} commands are particularly useful with C++, and some are
5943 designed specifically for use with C++. Here is a summary:
5946 @cindex break in overloaded functions
5947 @item @r{breakpoint menus}
5948 When you want a breakpoint in a function whose name is overloaded,
5949 @value{GDBN} breakpoint menus help you specify which function definition
5950 you want. @xref{Breakpoint Menus,,Breakpoint menus}.
5952 @cindex overloading in C++
5953 @item rbreak @var{regex}
5954 Setting breakpoints using regular expressions is helpful for setting
5955 breakpoints on overloaded functions that are not members of any special
5957 @xref{Set Breaks, ,Setting breakpoints}.
5959 @cindex C++ exception handling
5960 @item catch @var{exceptions}
5962 Debug C++ exception handling using these commands. @xref{Exception
5963 Handling, ,Breakpoints and exceptions}.
5966 @item ptype @var{typename}
5967 Print inheritance relationships as well as other information for type
5969 @xref{Symbols, ,Examining the Symbol Table}.
5971 @cindex C++ symbol display
5972 @item set print demangle
5973 @itemx show print demangle
5974 @itemx set print asm-demangle
5975 @itemx show print asm-demangle
5976 Control whether C++ symbols display in their source form, both when
5977 displaying code as C++ source and when displaying disassemblies.
5978 @xref{Print Settings, ,Print settings}.
5980 @item set print object
5981 @itemx show print object
5982 Choose whether to print derived (actual) or declared types of objects.
5983 @xref{Print Settings, ,Print settings}.
5985 @item set print vtbl
5986 @itemx show print vtbl
5987 Control the format for printing virtual function tables.
5988 @xref{Print Settings, ,Print settings}.
5990 @item @r{Overloaded symbol names}
5991 You can specify a particular definition of an overloaded symbol, using
5992 the same notation that is used to declare such symbols in C++: type
5993 @code{@var{symbol}(@var{types})} rather than just @var{symbol}. You can
5994 also use the @value{GDBN} command-line word completion facilities to list the
5995 available choices, or to finish the type list for you.
5996 @xref{Completion,, Command completion}, for details on how to do this.
5999 @c cancels "raisesections" under same conditions near bgn of chapter
6005 @subsection Modula-2
6008 The extensions made to @value{GDBN} to support Modula-2 only support
6009 output from the @sc{gnu} Modula-2 compiler (which is currently being
6010 developed). Other Modula-2 compilers are not currently supported, and
6011 attempting to debug executables produced by them is most likely
6012 to give an error as @value{GDBN} reads in the executable's symbol
6015 @cindex expressions in Modula-2
6017 * M2 Operators:: Built-in operators
6018 * Built-In Func/Proc:: Built-in functions and procedures
6019 * M2 Constants:: Modula-2 constants
6020 * M2 Defaults:: Default settings for Modula-2
6021 * Deviations:: Deviations from standard Modula-2
6022 * M2 Checks:: Modula-2 type and range checks
6023 * M2 Scope:: The scope operators @code{::} and @code{.}
6024 * GDB/M2:: @value{GDBN} and Modula-2
6028 @subsubsection Operators
6029 @cindex Modula-2 operators
6031 Operators must be defined on values of specific types. For instance,
6032 @code{+} is defined on numbers, but not on structures. Operators are
6033 often defined on groups of types. For the purposes of Modula-2, the
6034 following definitions hold:
6039 @emph{Integral types} consist of @code{INTEGER}, @code{CARDINAL}, and
6043 @emph{Character types} consist of @code{CHAR} and its subranges.
6046 @emph{Floating-point types} consist of @code{REAL}.
6049 @emph{Pointer types} consist of anything declared as @code{POINTER TO
6053 @emph{Scalar types} consist of all of the above.
6056 @emph{Set types} consist of @code{SET} and @code{BITSET} types.
6059 @emph{Boolean types} consist of @code{BOOLEAN}.
6063 The following operators are supported, and appear in order of
6064 increasing precedence:
6068 Function argument or array index separator.
6071 Assignment. The value of @var{var} @code{:=} @var{value} is
6075 Less than, greater than on integral, floating-point, or enumerated
6079 Less than, greater than, less than or equal to, greater than or equal to
6080 on integral, floating-point and enumerated types, or set inclusion on
6081 set types. Same precedence as @code{<}.
6083 @item =@r{, }<>@r{, }#
6084 Equality and two ways of expressing inequality, valid on scalar types.
6085 Same precedence as @code{<}. In @value{GDBN} scripts, only @code{<>} is
6086 available for inequality, since @code{#} conflicts with the script
6090 Set membership. Defined on set types and the types of their members.
6091 Same precedence as @code{<}.
6094 Boolean disjunction. Defined on boolean types.
6097 Boolean conjuction. Defined on boolean types.
6100 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
6103 Addition and subtraction on integral and floating-point types, or union
6104 and difference on set types.
6107 Multiplication on integral and floating-point types, or set intersection
6111 Division on floating-point types, or symmetric set difference on set
6112 types. Same precedence as @code{*}.
6115 Integer division and remainder. Defined on integral types. Same
6116 precedence as @code{*}.
6119 Negative. Defined on @code{INTEGER} and @code{REAL} data.
6122 Pointer dereferencing. Defined on pointer types.
6125 Boolean negation. Defined on boolean types. Same precedence as
6129 @code{RECORD} field selector. Defined on @code{RECORD} data. Same
6130 precedence as @code{^}.
6133 Array indexing. Defined on @code{ARRAY} data. Same precedence as @code{^}.
6136 Procedure argument list. Defined on @code{PROCEDURE} objects. Same precedence
6140 @value{GDBN} and Modula-2 scope operators.
6144 @emph{Warning:} Sets and their operations are not yet supported, so @value{GDBN}
6145 treats the use of the operator @code{IN}, or the use of operators
6146 @code{+}, @code{-}, @code{*}, @code{/}, @code{=}, , @code{<>}, @code{#},
6147 @code{<=}, and @code{>=} on sets as an error.
6150 @cindex Modula-2 built-ins
6151 @node Built-In Func/Proc
6152 @subsubsection Built-in functions and procedures
6154 Modula-2 also makes available several built-in procedures and functions.
6155 In describing these, the following metavariables are used:
6160 represents an @code{ARRAY} variable.
6163 represents a @code{CHAR} constant or variable.
6166 represents a variable or constant of integral type.
6169 represents an identifier that belongs to a set. Generally used in the
6170 same function with the metavariable @var{s}. The type of @var{s} should
6171 be @code{SET OF @var{mtype}} (where @var{mtype} is the type of @var{m}).
6174 represents a variable or constant of integral or floating-point type.
6177 represents a variable or constant of floating-point type.
6183 represents a variable.
6186 represents a variable or constant of one of many types. See the
6187 explanation of the function for details.
6190 All Modula-2 built-in procedures also return a result, described below.
6194 Returns the absolute value of @var{n}.
6197 If @var{c} is a lower case letter, it returns its upper case
6198 equivalent, otherwise it returns its argument
6201 Returns the character whose ordinal value is @var{i}.
6204 Decrements the value in the variable @var{v}. Returns the new value.
6206 @item DEC(@var{v},@var{i})
6207 Decrements the value in the variable @var{v} by @var{i}. Returns the
6210 @item EXCL(@var{m},@var{s})
6211 Removes the element @var{m} from the set @var{s}. Returns the new
6214 @item FLOAT(@var{i})
6215 Returns the floating point equivalent of the integer @var{i}.
6218 Returns the index of the last member of @var{a}.
6221 Increments the value in the variable @var{v}. Returns the new value.
6223 @item INC(@var{v},@var{i})
6224 Increments the value in the variable @var{v} by @var{i}. Returns the
6227 @item INCL(@var{m},@var{s})
6228 Adds the element @var{m} to the set @var{s} if it is not already
6229 there. Returns the new set.
6232 Returns the maximum value of the type @var{t}.
6235 Returns the minimum value of the type @var{t}.
6238 Returns boolean TRUE if @var{i} is an odd number.
6241 Returns the ordinal value of its argument. For example, the ordinal
6242 value of a character is its ASCII value (on machines supporting the
6243 ASCII character set). @var{x} must be of an ordered type, which include
6244 integral, character and enumerated types.
6247 Returns the size of its argument. @var{x} can be a variable or a type.
6249 @item TRUNC(@var{r})
6250 Returns the integral part of @var{r}.
6252 @item VAL(@var{t},@var{i})
6253 Returns the member of the type @var{t} whose ordinal value is @var{i}.
6257 @emph{Warning:} Sets and their operations are not yet supported, so
6258 @value{GDBN} treats the use of procedures @code{INCL} and @code{EXCL} as
6262 @cindex Modula-2 constants
6264 @subsubsection Constants
6266 @value{GDBN} allows you to express the constants of Modula-2 in the following
6272 Integer constants are simply a sequence of digits. When used in an
6273 expression, a constant is interpreted to be type-compatible with the
6274 rest of the expression. Hexadecimal integers are specified by a
6275 trailing @samp{H}, and octal integers by a trailing @samp{B}.
6278 Floating point constants appear as a sequence of digits, followed by a
6279 decimal point and another sequence of digits. An optional exponent can
6280 then be specified, in the form @samp{E@r{[}+@r{|}-@r{]}@var{nnn}}, where
6281 @samp{@r{[}+@r{|}-@r{]}@var{nnn}} is the desired exponent. All of the
6282 digits of the floating point constant must be valid decimal (base 10)
6286 Character constants consist of a single character enclosed by a pair of
6287 like quotes, either single (@code{'}) or double (@code{"}). They may
6288 also be expressed by their ordinal value (their ASCII value, usually)
6289 followed by a @samp{C}.
6292 String constants consist of a sequence of characters enclosed by a
6293 pair of like quotes, either single (@code{'}) or double (@code{"}).
6294 Escape sequences in the style of C are also allowed. @xref{C
6295 Constants, ,C and C++ constants}, for a brief explanation of escape
6299 Enumerated constants consist of an enumerated identifier.
6302 Boolean constants consist of the identifiers @code{TRUE} and
6306 Pointer constants consist of integral values only.
6309 Set constants are not yet supported.
6313 @subsubsection Modula-2 defaults
6314 @cindex Modula-2 defaults
6316 If type and range checking are set automatically by @value{GDBN}, they
6317 both default to @code{on} whenever the working language changes to
6318 Modula-2. This happens regardless of whether you, or @value{GDBN},
6319 selected the working language.
6321 If you allow @value{GDBN} to set the language automatically, then entering
6322 code compiled from a file whose name ends with @file{.mod} sets the
6323 working language to Modula-2. @xref{Automatically, ,Having @value{GDBN} set
6324 the language automatically}, for further details.
6327 @subsubsection Deviations from standard Modula-2
6328 @cindex Modula-2, deviations from
6330 A few changes have been made to make Modula-2 programs easier to debug.
6331 This is done primarily via loosening its type strictness:
6335 Unlike in standard Modula-2, pointer constants can be formed by
6336 integers. This allows you to modify pointer variables during
6337 debugging. (In standard Modula-2, the actual address contained in a
6338 pointer variable is hidden from you; it can only be modified
6339 through direct assignment to another pointer variable or expression that
6340 returned a pointer.)
6343 C escape sequences can be used in strings and characters to represent
6344 non-printable characters. @value{GDBN} prints out strings with these
6345 escape sequences embedded. Single non-printable characters are
6346 printed using the @samp{CHR(@var{nnn})} format.
6349 The assignment operator (@code{:=}) returns the value of its right-hand
6353 All built-in procedures both modify @emph{and} return their argument.
6357 @subsubsection Modula-2 type and range checks
6358 @cindex Modula-2 checks
6361 @emph{Warning:} in this release, @value{GDBN} does not yet perform type or
6364 @c FIXME remove warning when type/range checks added
6366 @value{GDBN} considers two Modula-2 variables type equivalent if:
6370 They are of types that have been declared equivalent via a @code{TYPE
6371 @var{t1} = @var{t2}} statement
6374 They have been declared on the same line. (Note: This is true of the
6375 @sc{gnu} Modula-2 compiler, but it may not be true of other compilers.)
6378 As long as type checking is enabled, any attempt to combine variables
6379 whose types are not equivalent is an error.
6381 Range checking is done on all mathematical operations, assignment, array
6382 index bounds, and all built-in functions and procedures.
6385 @subsubsection The scope operators @code{::} and @code{.}
6388 @cindex colon, doubled as scope operator
6391 @c Info cannot handle :: but TeX can.
6397 There are a few subtle differences between the Modula-2 scope operator
6398 (@code{.}) and the @value{GDBN} scope operator (@code{::}). The two have
6403 @var{module} . @var{id}
6404 @var{scope} :: @var{id}
6408 where @var{scope} is the name of a module or a procedure,
6409 @var{module} the name of a module, and @var{id} is any declared
6410 identifier within your program, except another module.
6412 Using the @code{::} operator makes @value{GDBN} search the scope
6413 specified by @var{scope} for the identifier @var{id}. If it is not
6414 found in the specified scope, then @value{GDBN} searches all scopes
6415 enclosing the one specified by @var{scope}.
6417 Using the @code{.} operator makes @value{GDBN} search the current scope for
6418 the identifier specified by @var{id} that was imported from the
6419 definition module specified by @var{module}. With this operator, it is
6420 an error if the identifier @var{id} was not imported from definition
6421 module @var{module}, or if @var{id} is not an identifier in
6425 @subsubsection @value{GDBN} and Modula-2
6427 Some @value{GDBN} commands have little use when debugging Modula-2 programs.
6428 Five subcommands of @code{set print} and @code{show print} apply
6429 specifically to C and C++: @samp{vtbl}, @samp{demangle},
6430 @samp{asm-demangle}, @samp{object}, and @samp{union}. The first four
6431 apply to C++, and the last to the C @code{union} type, which has no direct
6432 analogue in Modula-2.
6434 The @code{@@} operator (@pxref{Expressions, ,Expressions}), while available
6435 while using any language, is not useful with Modula-2. Its
6436 intent is to aid the debugging of @dfn{dynamic arrays}, which cannot be
6437 created in Modula-2 as they can in C or C++. However, because an
6438 address can be specified by an integral constant, the construct
6439 @samp{@{@var{type}@}@var{adrexp}} is still useful. (@pxref{Expressions, ,Expressions})
6441 @cindex @code{#} in Modula-2
6442 In @value{GDBN} scripts, the Modula-2 inequality operator @code{#} is
6443 interpreted as the beginning of a comment. Use @code{<>} instead.
6448 @chapter Examining the Symbol Table
6450 The commands described in this section allow you to inquire about the
6451 symbols (names of variables, functions and types) defined in your
6452 program. This information is inherent in the text of your program and
6453 does not change as your program executes. @value{GDBN} finds it in your
6454 program's symbol table, in the file indicated when you started @value{GDBN}
6455 (@pxref{File Options, ,Choosing files}), or by one of the
6456 file-management commands (@pxref{Files, ,Commands to specify files}).
6458 @cindex symbol names
6459 @cindex names of symbols
6460 @cindex quoting names
6461 Occasionally, you may need to refer to symbols that contain unusual
6462 characters, which @value{GDBN} ordinarily treats as word delimiters. The
6463 most frequent case is in referring to static variables in other
6464 source files (@pxref{Variables,,Program variables}). File names
6465 are recorded in object files as debugging symbols, but @value{GDBN} would
6466 ordinarily parse a typical file name, like @file{foo.c}, as the three words
6467 @samp{foo} @samp{.} @samp{c}. To allow @value{GDBN} to recognize
6468 @samp{foo.c} as a single symbol, enclose it in single quotes; for example,
6475 looks up the value of @code{x} in the scope of the file @file{foo.c}.
6478 @kindex info address
6479 @item info address @var{symbol}
6480 Describe where the data for @var{symbol} is stored. For a register
6481 variable, this says which register it is kept in. For a non-register
6482 local variable, this prints the stack-frame offset at which the variable
6485 Note the contrast with @samp{print &@var{symbol}}, which does not work
6486 at all for a register variable, and for a stack local variable prints
6487 the exact address of the current instantiation of the variable.
6490 @item whatis @var{exp}
6491 Print the data type of expression @var{exp}. @var{exp} is not
6492 actually evaluated, and any side-effecting operations (such as
6493 assignments or function calls) inside it do not take place.
6494 @xref{Expressions, ,Expressions}.
6497 Print the data type of @code{$}, the last value in the value history.
6500 @item ptype @var{typename}
6501 Print a description of data type @var{typename}. @var{typename} may be
6502 the name of a type, or for C code it may have the form
6504 @samp{class @var{class-name}},
6506 @samp{struct @var{struct-tag}}, @samp{union @var{union-tag}} or
6507 @samp{enum @var{enum-tag}}.
6509 @item ptype @var{exp}
6511 Print a description of the type of expression @var{exp}. @code{ptype}
6512 differs from @code{whatis} by printing a detailed description, instead
6513 of just the name of the type.
6515 For example, for this variable declaration:
6518 struct complex @{double real; double imag;@} v;
6522 the two commands give this output:
6526 (@value{GDBP}) whatis v
6527 type = struct complex
6528 (@value{GDBP}) ptype v
6529 type = struct complex @{
6537 As with @code{whatis}, using @code{ptype} without an argument refers to
6538 the type of @code{$}, the last value in the value history.
6541 @item info types @var{regexp}
6543 Print a brief description of all types whose name matches @var{regexp}
6544 (or all types in your program, if you supply no argument). Each
6545 complete typename is matched as though it were a complete line; thus,
6546 @samp{i type value} gives information on all types in your program whose
6547 name includes the string @code{value}, but @samp{i type ^value$} gives
6548 information only on types whose complete name is @code{value}.
6550 This command differs from @code{ptype} in two ways: first, like
6551 @code{whatis}, it does not print a detailed description; second, it
6552 lists all source files where a type is defined.
6556 Show the name of the current source file---that is, the source file for
6557 the function containing the current point of execution---and the language
6560 @kindex info sources
6562 Print the names of all source files in your program for which there is
6563 debugging information, organized into two lists: files whose symbols
6564 have already been read, and files whose symbols will be read when needed.
6566 @kindex info functions
6567 @item info functions
6568 Print the names and data types of all defined functions.
6570 @item info functions @var{regexp}
6571 Print the names and data types of all defined functions
6572 whose names contain a match for regular expression @var{regexp}.
6573 Thus, @samp{info fun step} finds all functions whose names
6574 include @code{step}; @samp{info fun ^step} finds those whose names
6575 start with @code{step}.
6577 @kindex info variables
6578 @item info variables
6579 Print the names and data types of all variables that are declared
6580 outside of functions (i.e., excluding local variables).
6582 @item info variables @var{regexp}
6583 Print the names and data types of all variables (except for local
6584 variables) whose names contain a match for regular expression
6588 This was never implemented.
6589 @kindex info methods
6591 @itemx info methods @var{regexp}
6592 The @code{info methods} command permits the user to examine all defined
6593 methods within C++ program, or (with the @var{regexp} argument) a
6594 specific set of methods found in the various C++ classes. Many
6595 C++ classes provide a large number of methods. Thus, the output
6596 from the @code{ptype} command can be overwhelming and hard to use. The
6597 @code{info-methods} command filters the methods, printing only those
6598 which match the regular-expression @var{regexp}.
6601 @cindex reloading symbols
6602 Some systems allow individual object files that make up your program to
6603 be replaced without stopping and restarting your program.
6605 For example, in VxWorks you can simply recompile a defective object file
6606 and keep on running.
6608 If you are running on one of these systems, you can allow @value{GDBN} to
6609 reload the symbols for automatically relinked modules:
6612 @kindex set symbol-reloading
6613 @item set symbol-reloading on
6614 Replace symbol definitions for the corresponding source file when an
6615 object file with a particular name is seen again.
6617 @item set symbol-reloading off
6618 Do not replace symbol definitions when re-encountering object files of
6619 the same name. This is the default state; if you are not running on a
6620 system that permits automatically relinking modules, you should leave
6621 @code{symbol-reloading} off, since otherwise @value{GDBN} may discard symbols
6622 when linking large programs, that may contain several modules (from
6623 different directories or libraries) with the same name.
6625 @kindex show symbol-reloading
6626 @item show symbol-reloading
6627 Show the current @code{on} or @code{off} setting.
6630 @kindex maint print symbols
6632 @kindex maint print psymbols
6633 @cindex partial symbol dump
6634 @item maint print symbols @var{filename}
6635 @itemx maint print psymbols @var{filename}
6636 @itemx maint print msymbols @var{filename}
6637 Write a dump of debugging symbol data into the file @var{filename}.
6638 These commands are used to debug the @value{GDBN} symbol-reading code. Only
6639 symbols with debugging data are included. If you use @samp{maint print
6640 symbols}, @value{GDBN} includes all the symbols for which it has already
6641 collected full details: that is, @var{filename} reflects symbols for
6642 only those files whose symbols @value{GDBN} has read. You can use the
6643 command @code{info sources} to find out which files these are. If you
6644 use @samp{maint print psymbols} instead, the dump shows information about
6645 symbols that @value{GDBN} only knows partially---that is, symbols defined in
6646 files that @value{GDBN} has skimmed, but not yet read completely. Finally,
6647 @samp{maint print msymbols} dumps just the minimal symbol information
6648 required for each object file from which @value{GDBN} has read some symbols.
6649 @xref{Files, ,Commands to specify files}, for a discussion of how
6650 @value{GDBN} reads symbols (in the description of @code{symbol-file}).
6654 @chapter Altering Execution
6656 Once you think you have found an error in your program, you might want to
6657 find out for certain whether correcting the apparent error would lead to
6658 correct results in the rest of the run. You can find the answer by
6659 experiment, using the @value{GDBN} features for altering execution of the
6662 For example, you can store new values into variables or memory
6665 give your program a signal, restart it
6668 restart your program
6670 at a different address, or even return prematurely from a function.
6673 * Assignment:: Assignment to variables
6674 * Jumping:: Continuing at a different address
6676 * Signaling:: Giving your program a signal
6679 * Returning:: Returning from a function
6680 * Calling:: Calling your program's functions
6681 * Patching:: Patching your program
6685 @section Assignment to variables
6688 @cindex setting variables
6689 To alter the value of a variable, evaluate an assignment expression.
6690 @xref{Expressions, ,Expressions}. For example,
6697 stores the value 4 into the variable @code{x}, and then prints the
6698 value of the assignment expression (which is 4).
6700 @xref{Languages, ,Using @value{GDBN} with Different Languages}, for more
6701 information on operators in supported languages.
6704 @kindex set variable
6705 @cindex variables, setting
6706 If you are not interested in seeing the value of the assignment, use the
6707 @code{set} command instead of the @code{print} command. @code{set} is
6708 really the same as @code{print} except that the expression's value is
6709 not printed and is not put in the value history (@pxref{Value History,
6710 ,Value history}). The expression is evaluated only for its effects.
6712 If the beginning of the argument string of the @code{set} command
6713 appears identical to a @code{set} subcommand, use the @code{set
6714 variable} command instead of just @code{set}. This command is identical
6715 to @code{set} except for its lack of subcommands. For example, if
6716 your program has a variable @code{width}, you get
6717 an error if you try to set a new value with just @samp{set width=13},
6718 because @value{GDBN} has the command @code{set width}:
6721 (@value{GDBP}) whatis width
6723 (@value{GDBP}) p width
6725 (@value{GDBP}) set width=47
6726 Invalid syntax in expression.
6730 The invalid expression, of course, is @samp{=47}. In
6731 order to actually set the program's variable @code{width}, use
6734 (@value{GDBP}) set var width=47
6737 @value{GDBN} allows more implicit conversions in assignments than C; you can
6738 freely store an integer value into a pointer variable or vice versa,
6739 and you can convert any structure to any other structure that is the
6740 same length or shorter.
6741 @comment FIXME: how do structs align/pad in these conversions?
6742 @comment /pesch@cygnus.com 18dec1990
6744 To store values into arbitrary places in memory, use the @samp{@{@dots{}@}}
6745 construct to generate a value of specified type at a specified address
6746 (@pxref{Expressions, ,Expressions}). For example, @code{@{int@}0x83040} refers
6747 to memory location @code{0x83040} as an integer (which implies a certain size
6748 and representation in memory), and
6751 set @{int@}0x83040 = 4
6755 stores the value 4 into that memory location.
6758 @section Continuing at a different address
6760 Ordinarily, when you continue your program, you do so at the place where
6761 it stopped, with the @code{continue} command. You can instead continue at
6762 an address of your own choosing, with the following commands:
6766 @item jump @var{linespec}
6767 Resume execution at line @var{linespec}. Execution stops again
6768 immediately if there is a breakpoint there. @xref{List, ,Printing
6769 source lines}, for a description of the different forms of
6772 The @code{jump} command does not change the current stack frame, or
6773 the stack pointer, or the contents of any memory location or any
6774 register other than the program counter. If line @var{linespec} is in
6775 a different function from the one currently executing, the results may
6776 be bizarre if the two functions expect different patterns of arguments or
6777 of local variables. For this reason, the @code{jump} command requests
6778 confirmation if the specified line is not in the function currently
6779 executing. However, even bizarre results are predictable if you are
6780 well acquainted with the machine-language code of your program.
6782 @item jump *@var{address}
6783 Resume execution at the instruction at address @var{address}.
6786 You can get much the same effect as the @code{jump} command by storing a
6787 new value into the register @code{$pc}. The difference is that this
6788 does not start your program running; it only changes the address of where it
6789 @emph{will} run when you continue. For example,
6796 makes the next @code{continue} command or stepping command execute at
6797 address @code{0x485}, rather than at the address where your program stopped.
6798 @xref{Continuing and Stepping, ,Continuing and stepping}.
6800 The most common occasion to use the @code{jump} command is to back up--
6801 perhaps with more breakpoints set--over a portion of a program that has
6802 already executed, in order to examine its execution in more detail.
6807 @section Giving your program a signal
6811 @item signal @var{signal}
6812 Resume execution where your program stopped, but immediately give it the
6813 signal @var{signal}. @var{signal} can be the name or the number of a
6814 signal. For example, on many systems @code{signal 2} and @code{signal
6815 SIGINT} are both ways of sending an interrupt signal.
6817 Alternatively, if @var{signal} is zero, continue execution without
6818 giving a signal. This is useful when your program stopped on account of
6819 a signal and would ordinary see the signal when resumed with the
6820 @code{continue} command; @samp{signal 0} causes it to resume without a
6823 @code{signal} does not repeat when you press @key{RET} a second time
6824 after executing the command.
6828 Invoking the @code{signal} command is not the same as invoking the
6829 @code{kill} utility from the shell. Sending a signal with @code{kill}
6830 causes @value{GDBN} to decide what to do with the signal depending on
6831 the signal handling tables (@pxref{Signals}). The @code{signal} command
6832 passes the signal directly to your program.
6837 @section Returning from a function
6840 @cindex returning from a function
6843 @itemx return @var{expression}
6844 You can cancel execution of a function call with the @code{return}
6845 command. If you give an
6846 @var{expression} argument, its value is used as the function's return
6850 When you use @code{return}, @value{GDBN} discards the selected stack frame
6851 (and all frames within it). You can think of this as making the
6852 discarded frame return prematurely. If you wish to specify a value to
6853 be returned, give that value as the argument to @code{return}.
6855 This pops the selected stack frame (@pxref{Selection, ,Selecting a
6856 frame}), and any other frames inside of it, leaving its caller as the
6857 innermost remaining frame. That frame becomes selected. The
6858 specified value is stored in the registers used for returning values
6861 The @code{return} command does not resume execution; it leaves the
6862 program stopped in the state that would exist if the function had just
6863 returned. In contrast, the @code{finish} command (@pxref{Continuing
6864 and Stepping, ,Continuing and stepping}) resumes execution until the
6865 selected stack frame returns naturally.
6868 @section Calling program functions
6870 @cindex calling functions
6873 @item call @var{expr}
6874 Evaluate the expression @var{expr} without displaying @code{void}
6878 You can use this variant of the @code{print} command if you want to
6879 execute a function from your program, but without cluttering the output
6880 with @code{void} returned values. If the result is not void, it
6881 is printed and saved in the value history.
6883 A new user-controlled variable, @var{call_scratch_address}, specifies
6884 the location of a scratch area to be used when @value{GDBN} calls a
6885 function in the target. This is necessary because the usual method
6886 of putting the scratch area on the stack does not work in systems that
6887 have separate instruction and data spaces.
6890 @section Patching programs
6891 @cindex patching binaries
6892 @cindex writing into executables
6894 @cindex writing into corefiles
6897 By default, @value{GDBN} opens the file containing your program's executable
6902 read-only. This prevents accidental alterations
6903 to machine code; but it also prevents you from intentionally patching
6904 your program's binary.
6906 If you'd like to be able to patch the binary, you can specify that
6907 explicitly with the @code{set write} command. For example, you might
6908 want to turn on internal debugging flags, or even to make emergency
6914 @itemx set write off
6915 If you specify @samp{set write on}, @value{GDBN} opens executable
6919 files for both reading and writing; if you specify @samp{set write
6920 off} (the default), @value{GDBN} opens them read-only.
6922 If you have already loaded a file, you must load it again (using the
6927 command) after changing @code{set write}, for your new setting to take
6932 Display whether executable files
6936 are opened for writing as well as reading.
6940 @chapter @value{GDBN} Files
6942 @value{GDBN} needs to know the file name of the program to be debugged, both in
6943 order to read its symbol table and in order to start your program.
6945 To debug a core dump of a previous run, you must also tell @value{GDBN}
6946 the name of the core dump file.
6950 * Files:: Commands to specify files
6951 * Symbol Errors:: Errors reading symbol files
6955 @section Commands to specify files
6956 @cindex symbol table
6959 @cindex core dump file
6960 You may want to specify executable and core dump file names.
6961 The usual way to do this is at start-up time, using the arguments to
6962 @value{GDBN}'s start-up commands (@pxref{Invocation, ,
6963 Getting In and Out of @value{GDBN}}).
6966 The usual way to specify an executable file name is with
6967 the command argument given when you start @value{GDBN}, (@pxref{Invocation,
6968 ,Getting In and Out of @value{GDBN}}.
6971 Occasionally it is necessary to change to a different file during a
6972 @value{GDBN} session. Or you may run @value{GDBN} and forget to specify
6973 a file you want to use. In these situations the @value{GDBN} commands
6974 to specify new files are useful.
6977 @cindex executable file
6979 @item file @var{filename}
6980 Use @var{filename} as the program to be debugged. It is read for its
6981 symbols and for the contents of pure memory. It is also the program
6982 executed when you use the @code{run} command. If you do not specify a
6983 directory and the file is not found in the @value{GDBN} working directory,
6984 @value{GDBN} uses the environment variable @code{PATH} as a list of
6985 directories to search, just as the shell does when looking for a program
6986 to run. You can change the value of this variable, for both @value{GDBN}
6987 and your program, using the @code{path} command.
6989 On systems with memory-mapped files, an auxiliary file
6990 @file{@var{filename}.syms} may hold symbol table information for
6991 @var{filename}. If so, @value{GDBN} maps in the symbol table from
6992 @file{@var{filename}.syms}, starting up more quickly. See the
6993 descriptions of the file options @samp{-mapped} and @samp{-readnow}
6994 (available on the command line, and with the commands @code{file},
6995 @code{symbol-file}, or @code{add-symbol-file}, described below),
6996 for more information.
6999 @code{file} with no argument makes @value{GDBN} discard any information it
7000 has on both executable file and the symbol table.
7003 @item exec-file @r{[} @var{filename} @r{]}
7004 Specify that the program to be run (but not the symbol table) is found
7005 in @var{filename}. @value{GDBN} searches the environment variable @code{PATH}
7006 if necessary to locate your program. Omitting @var{filename} means to
7007 discard information on the executable file.
7010 @item symbol-file @r{[} @var{filename} @r{]}
7011 Read symbol table information from file @var{filename}. @code{PATH} is
7012 searched when necessary. Use the @code{file} command to get both symbol
7013 table and program to run from the same file.
7015 @code{symbol-file} with no argument clears out @value{GDBN} information on your
7016 program's symbol table.
7018 The @code{symbol-file} command causes @value{GDBN} to forget the contents
7019 of its convenience variables, the value history, and all breakpoints and
7020 auto-display expressions. This is because they may contain pointers to
7021 the internal data recording symbols and data types, which are part of
7022 the old symbol table data being discarded inside @value{GDBN}.
7024 @code{symbol-file} does not repeat if you press @key{RET} again after
7027 When @value{GDBN} is configured for a particular environment, it
7028 understands debugging information in whatever format is the standard
7029 generated for that environment; you may use either a @sc{gnu} compiler, or
7030 other compilers that adhere to the local conventions. Best results are
7031 usually obtained from @sc{gnu} compilers; for example, using @code{@value{GCC}}
7032 you can generate debugging information for optimized code.
7034 On some kinds of object files, the @code{symbol-file} command does not
7035 normally read the symbol table in full right away. Instead, it scans
7036 the symbol table quickly to find which source files and which symbols
7037 are present. The details are read later, one source file at a time,
7040 The purpose of this two-stage reading strategy is to make @value{GDBN} start up
7041 faster. For the most part, it is invisible except for occasional
7042 pauses while the symbol table details for a particular source file are
7043 being read. (The @code{set verbose} command can turn these pauses
7044 into messages if desired. @xref{Messages/Warnings, ,Optional warnings
7047 We have not implemented the two-stage strategy for COFF yet. When the
7048 symbol table is stored in COFF format, @code{symbol-file} reads the
7049 symbol table data in full right away.
7052 @cindex reading symbols immediately
7053 @cindex symbols, reading immediately
7055 @cindex memory-mapped symbol file
7056 @cindex saving symbol table
7057 @item symbol-file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
7058 @itemx file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
7059 You can override the @value{GDBN} two-stage strategy for reading symbol
7060 tables by using the @samp{-readnow} option with any of the commands that
7061 load symbol table information, if you want to be sure @value{GDBN} has the
7062 entire symbol table available.
7065 If memory-mapped files are available on your system through the
7066 @code{mmap} system call, you can use another option, @samp{-mapped}, to
7067 cause @value{GDBN} to write the symbols for your program into a reusable
7068 file. Future @value{GDBN} debugging sessions map in symbol information
7069 from this auxiliary symbol file (if the program has not changed), rather
7070 than spending time reading the symbol table from the executable
7071 program. Using the @samp{-mapped} option has the same effect as
7072 starting @value{GDBN} with the @samp{-mapped} command-line option.
7074 You can use both options together, to make sure the auxiliary symbol
7075 file has all the symbol information for your program.
7077 The auxiliary symbol file for a program called @var{myprog} is called
7078 @samp{@var{myprog}.syms}. Once this file exists (so long as it is newer
7079 than the corresponding executable), @value{GDBN} always attempts to use
7080 it when you debug @var{myprog}; no special options or commands are
7083 The @file{.syms} file is specific to the host machine where you run
7084 @value{GDBN}. It holds an exact image of the internal @value{GDBN}
7085 symbol table. It cannot be shared across multiple host platforms.
7087 @c FIXME: for now no mention of directories, since this seems to be in
7088 @c flux. 13mar1992 status is that in theory GDB would look either in
7089 @c current dir or in same dir as myprog; but issues like competing
7090 @c GDB's, or clutter in system dirs, mean that in practice right now
7091 @c only current dir is used. FFish says maybe a special GDB hierarchy
7092 @c (eg rooted in val of env var GDBSYMS) could exist for mappable symbol
7097 @item core-file @r{[} @var{filename} @r{]}
7098 Specify the whereabouts of a core dump file to be used as the ``contents
7099 of memory''. Traditionally, core files contain only some parts of the
7100 address space of the process that generated them; @value{GDBN} can access the
7101 executable file itself for other parts.
7103 @code{core-file} with no argument specifies that no core file is
7106 Note that the core file is ignored when your program is actually running
7107 under @value{GDBN}. So, if you have been running your program and you wish to
7108 debug a core file instead, you must kill the subprocess in which the
7109 program is running. To do this, use the @code{kill} command
7110 (@pxref{Kill Process, ,Killing the child process}).
7113 @kindex load @var{filename}
7114 @item load @var{filename}
7116 Depending on what remote debugging facilities are configured into
7117 @value{GDBN}, the @code{load} command may be available. Where it exists, it
7118 is meant to make @var{filename} (an executable) available for debugging
7119 on the remote system---by downloading, or dynamic linking, for example.
7120 @code{load} also records the @var{filename} symbol table in @value{GDBN}, like
7121 the @code{add-symbol-file} command.
7123 If your @value{GDBN} does not have a @code{load} command, attempting to
7124 execute it gets the error message ``@code{You can't do that when your
7125 target is @dots{}}''
7128 The file is loaded at whatever address is specified in the executable.
7129 For some object file formats, you can specify the load address when you
7130 link the program; for other formats, like a.out, the object file format
7131 specifies a fixed address.
7132 @c FIXME! This would be a good place for an xref to the GNU linker doc.
7135 On VxWorks, @code{load} links @var{filename} dynamically on the
7136 current target system as well as adding its symbols in @value{GDBN}.
7140 @cindex download to Nindy-960
7141 With the Nindy interface to an Intel 960 board, @code{load}
7142 downloads @var{filename} to the 960 as well as adding its symbols in
7147 @cindex download to H8/300 or H8/500
7148 @cindex H8/300 or H8/500 download
7149 @cindex download to Hitachi SH
7150 @cindex Hitachi SH download
7151 When you select remote debugging to a Hitachi SH, H8/300, or H8/500 board
7152 (@pxref{Hitachi Remote,,@value{GDBN} and Hitachi Microprocessors}),
7153 the @code{load} command downloads your program to the Hitachi board and also
7154 opens it as the current executable target for @value{GDBN} on your host
7155 (like the @code{file} command).
7158 @code{load} does not repeat if you press @key{RET} again after using it.
7161 @kindex add-symbol-file
7162 @cindex dynamic linking
7163 @item add-symbol-file @var{filename} @var{address}
7164 @itemx add-symbol-file @var{filename} @var{address} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
7165 The @code{add-symbol-file} command reads additional symbol table information
7166 from the file @var{filename}. You would use this command when @var{filename}
7167 has been dynamically loaded (by some other means) into the program that
7168 is running. @var{address} should be the memory address at which the
7169 file has been loaded; @value{GDBN} cannot figure this out for itself.
7170 You can specify @var{address} as an expression.
7172 The symbol table of the file @var{filename} is added to the symbol table
7173 originally read with the @code{symbol-file} command. You can use the
7174 @code{add-symbol-file} command any number of times; the new symbol data thus
7175 read keeps adding to the old. To discard all old symbol data instead,
7176 use the @code{symbol-file} command.
7178 @code{add-symbol-file} does not repeat if you press @key{RET} after using it.
7180 You can use the @samp{-mapped} and @samp{-readnow} options just as with
7181 the @code{symbol-file} command, to change how @value{GDBN} manages the symbol
7182 table information for @var{filename}.
7184 @kindex add-shared-symbol-file
7185 @item add-shared-symbol-file
7186 The @code{add-shared-symbol-file} command can be used only under Harris' CXUX
7187 operating system for the Motorola 88k. @value{GDBN} automatically looks for
7188 shared libraries, however if @value{GDBN} does not find yours, you can run
7189 @code{add-shared-symbol-file}. It takes no arguments.
7194 The @code{section} command changes the base address of section SECTION of
7195 the exec file to ADDR. This can be used if the exec file does not contain
7196 section addresses, (such as in the a.out format), or when the addresses
7197 specified in the file itself are wrong. Each section must be changed
7198 separately. The ``info files'' command lists all the sections and their
7205 @code{info files} and @code{info target} are synonymous; both print
7206 the current target (@pxref{Targets, ,Specifying a Debugging Target}),
7209 names of the executable and core dump files
7212 name of the executable file
7214 currently in use by @value{GDBN}, and the files from which symbols were
7215 loaded. The command @code{help target} lists all possible targets
7216 rather than current ones.
7219 All file-specifying commands allow both absolute and relative file names
7220 as arguments. @value{GDBN} always converts the file name to an absolute file
7221 name and remembers it that way.
7224 @cindex shared libraries
7225 @value{GDBN} supports SunOS, SVr4, Irix 5, and IBM RS/6000 shared libraries.
7226 @value{GDBN} automatically loads symbol definitions from shared libraries
7227 when you use the @code{run} command, or when you examine a core file.
7228 (Before you issue the @code{run} command, @value{GDBN} does not understand
7229 references to a function in a shared library, however---unless you are
7230 debugging a core file).
7231 @c FIXME: some @value{GDBN} release may permit some refs to undef
7232 @c FIXME...symbols---eg in a break cmd---assuming they are from a shared
7233 @c FIXME...lib; check this from time to time when updating manual
7236 @kindex info sharedlibrary
7239 @itemx info sharedlibrary
7240 Print the names of the shared libraries which are currently loaded.
7242 @kindex sharedlibrary
7244 @item sharedlibrary @var{regex}
7245 @itemx share @var{regex}
7247 Load shared object library symbols for files matching a
7248 Unix regular expression.
7249 As with files loaded automatically, it only loads shared libraries
7250 required by your program for a core file or after typing @code{run}. If
7251 @var{regex} is omitted all shared libraries required by your program are
7257 @section Errors reading symbol files
7259 While reading a symbol file, @value{GDBN} occasionally encounters problems,
7260 such as symbol types it does not recognize, or known bugs in compiler
7261 output. By default, @value{GDBN} does not notify you of such problems, since
7262 they are relatively common and primarily of interest to people
7263 debugging compilers. If you are interested in seeing information
7264 about ill-constructed symbol tables, you can either ask @value{GDBN} to print
7265 only one message about each such type of problem, no matter how many
7266 times the problem occurs; or you can ask @value{GDBN} to print more messages,
7267 to see how many times the problems occur, with the @code{set
7268 complaints} command (@pxref{Messages/Warnings, ,Optional warnings and
7271 The messages currently printed, and their meanings, include:
7274 @item inner block not inside outer block in @var{symbol}
7276 The symbol information shows where symbol scopes begin and end
7277 (such as at the start of a function or a block of statements). This
7278 error indicates that an inner scope block is not fully contained
7279 in its outer scope blocks.
7281 @value{GDBN} circumvents the problem by treating the inner block as if it had
7282 the same scope as the outer block. In the error message, @var{symbol}
7283 may be shown as ``@code{(don't know)}'' if the outer block is not a
7286 @item block at @var{address} out of order
7288 The symbol information for symbol scope blocks should occur in
7289 order of increasing addresses. This error indicates that it does not
7292 @value{GDBN} does not circumvent this problem, and has trouble
7293 locating symbols in the source file whose symbols it is reading. (You
7294 can often determine what source file is affected by specifying
7295 @code{set verbose on}. @xref{Messages/Warnings, ,Optional warnings and
7298 @item bad block start address patched
7300 The symbol information for a symbol scope block has a start address
7301 smaller than the address of the preceding source line. This is known
7302 to occur in the SunOS 4.1.1 (and earlier) C compiler.
7304 @value{GDBN} circumvents the problem by treating the symbol scope block as
7305 starting on the previous source line.
7307 @item bad string table offset in symbol @var{n}
7310 Symbol number @var{n} contains a pointer into the string table which is
7311 larger than the size of the string table.
7313 @value{GDBN} circumvents the problem by considering the symbol to have the
7314 name @code{foo}, which may cause other problems if many symbols end up
7317 @item unknown symbol type @code{0x@var{nn}}
7319 The symbol information contains new data types that @value{GDBN} does not yet
7320 know how to read. @code{0x@var{nn}} is the symbol type of the misunderstood
7321 information, in hexadecimal.
7323 @value{GDBN} circumvents the error by ignoring this symbol information. This
7324 usually allows you to debug your program, though certain symbols
7325 are not accessible. If you encounter such a problem and feel like
7326 debugging it, you can debug @code{@value{GDBP}} with itself, breakpoint on
7327 @code{complain}, then go up to the function @code{read_dbx_symtab} and
7328 examine @code{*bufp} to see the symbol.
7330 @item stub type has NULL name
7331 @value{GDBN} could not find the full definition for
7340 @item const/volatile indicator missing (ok if using g++ v1.x), got@dots{}
7342 The symbol information for a C++ member function is missing some
7343 information that recent versions of the compiler should have output
7347 @item info mismatch between compiler and debugger
7349 @value{GDBN} could not parse a type specification output by the compiler.
7353 @chapter Specifying a Debugging Target
7354 @cindex debugging target
7357 A @dfn{target} is the execution environment occupied by your program.
7359 Often, @value{GDBN} runs in the same host environment as your program; in
7360 that case, the debugging target is specified as a side effect when you
7361 use the @code{file} or @code{core} commands. When you need more
7362 flexibility---for example, running @value{GDBN} on a physically separate
7363 host, or controlling a standalone system over a serial port or a
7364 realtime system over a TCP/IP connection---you
7369 can use the @code{target} command to specify one of the target types
7370 configured for @value{GDBN} (@pxref{Target Commands, ,Commands for managing
7374 * Active Targets:: Active targets
7375 * Target Commands:: Commands for managing targets
7376 * Remote:: Remote debugging
7379 @node Active Targets
7380 @section Active targets
7381 @cindex stacking targets
7382 @cindex active targets
7383 @cindex multiple targets
7386 There are three classes of targets: processes, core files, and
7387 executable files. @value{GDBN} can work concurrently on up to three active
7388 targets, one in each class. This allows you to (for example) start a
7389 process and inspect its activity without abandoning your work on a core
7392 For example, if you execute @samp{gdb a.out}, then the executable file
7393 @code{a.out} is the only active target. If you designate a core file as
7394 well---presumably from a prior run that crashed and coredumped---then
7395 @value{GDBN} has two active targets and uses them in tandem, looking
7396 first in the corefile target, then in the executable file, to satisfy
7397 requests for memory addresses. (Typically, these two classes of target
7398 are complementary, since core files contain only a program's
7399 read-write memory---variables and so on---plus machine status, while
7400 executable files contain only the program text and initialized data.)
7403 When you type @code{run}, your executable file becomes an active process
7404 target as well. When a process target is active, all @value{GDBN} commands
7405 requesting memory addresses refer to that target; addresses in an
7409 executable file target are obscured while the process
7413 Use the @code{exec-file} command to select a
7414 new executable target (@pxref{Files, ,Commands to specify
7418 Use the @code{core-file} and @code{exec-file} commands to select a
7419 new core file or executable target (@pxref{Files, ,Commands to specify
7420 files}). To specify as a target a process that is already running, use
7421 the @code{attach} command (@pxref{Attach, ,Debugging an
7422 already-running process}).
7425 @node Target Commands
7426 @section Commands for managing targets
7429 @item target @var{type} @var{parameters}
7430 Connects the @value{GDBN} host environment to a target
7435 machine or process. A target is typically a protocol for talking to
7436 debugging facilities. You use the argument @var{type} to specify the
7437 type or protocol of the target machine.
7439 Further @var{parameters} are interpreted by the target protocol, but
7440 typically include things like device names or host names to connect
7441 with, process numbers, and baud rates.
7444 The @code{target} command does not repeat if you press @key{RET} again
7445 after executing the command.
7449 Displays the names of all targets available. To display targets
7450 currently selected, use either @code{info target} or @code{info files}
7451 (@pxref{Files, ,Commands to specify files}).
7453 @item help target @var{name}
7454 Describe a particular target, including any parameters necessary to
7457 @kindex set gnutarget
7458 @item set gnutarget @var{args}
7459 @value{GDBN}uses its own library BFD to read your files. @value{GDBN}
7460 knows whether it is reading an @dfn{executable},
7461 a @dfn{core}, or a @dfn{.o} file, however you can specify the file format
7462 with the @code{set gnutarget} command. Unlike most @code{target} commands,
7463 with @code{gnutarget} the @code{target} refers to a program, not a machine.
7465 @emph{Warning:} To specify a file format with @code{set gnutarget},
7466 you must know the actual BFD name.
7468 @noindent @xref{Files, , Commands to specify files}.
7470 @kindex show gnutarget
7471 @item show gnutarget
7472 Use the @code{show gnutarget} command to display what file format
7473 @code{gnutarget} is set to read. If you have not set @code{gnutarget},
7474 @value{GDBN} will determine the file format for each file automatically
7475 and @code{show gnutarget} displays @code{The current BDF target is "auto"}.
7478 Here are some common targets (available, or not, depending on the GDB
7483 @item target exec @var{program}
7484 An executable file. @samp{target exec @var{program}} is the same as
7485 @samp{exec-file @var{program}}.
7489 @item target core @var{filename}
7490 A core dump file. @samp{target core @var{filename}} is the same as
7491 @samp{core-file @var{filename}}.
7495 @kindex target remote
7496 @item target remote @var{dev}
7497 Remote serial target in GDB-specific protocol. The argument @var{dev}
7498 specifies what serial device to use for the connection (e.g.
7499 @file{/dev/ttya}). @xref{Remote, ,Remote debugging}. @code{target remote}
7500 now supports the @code{load} command. This is only useful if you have
7501 some other way of getting the stub to the target system, and you can put
7502 it somewhere in memory where it won't get clobbered by the download.
7508 CPU simulator. @xref{Simulator,,Simulated CPU Target}.
7513 @item target udi @var{keyword}
7514 Remote AMD29K target, using the AMD UDI protocol. The @var{keyword}
7515 argument specifies which 29K board or simulator to use. @xref{UDI29K
7516 Remote,,The UDI protocol for AMD29K}.
7518 @kindex target amd-eb
7519 @item target amd-eb @var{dev} @var{speed} @var{PROG}
7521 Remote PC-resident AMD EB29K board, attached over serial lines.
7522 @var{dev} is the serial device, as for @code{target remote};
7523 @var{speed} allows you to specify the linespeed; and @var{PROG} is the
7524 name of the program to be debugged, as it appears to DOS on the PC.
7525 @xref{EB29K Remote, ,The EBMON protocol for AMD29K}.
7530 @item target hms @var{dev}
7531 A Hitachi SH, H8/300, or H8/500 board, attached via serial line to your host.
7532 @ifclear H8EXCLUSIVE
7533 Use special commands @code{device} and @code{speed} to control the serial
7534 line and the communications speed used.
7536 @xref{Hitachi Remote,,@value{GDBN} and Hitachi Microprocessors}.
7540 @kindex target nindy
7541 @item target nindy @var{devicename}
7542 An Intel 960 board controlled by a Nindy Monitor. @var{devicename} is
7543 the name of the serial device to use for the connection, e.g.
7544 @file{/dev/ttya}. @xref{i960-Nindy Remote, ,@value{GDBN} with a remote i960 (Nindy)}.
7548 @kindex target st2000
7549 @item target st2000 @var{dev} @var{speed}
7550 A Tandem ST2000 phone switch, running Tandem's STDBUG protocol. @var{dev}
7551 is the name of the device attached to the ST2000 serial line;
7552 @var{speed} is the communication line speed. The arguments are not used
7553 if @value{GDBN} is configured to connect to the ST2000 using TCP or Telnet.
7554 @xref{ST2000 Remote,,@value{GDBN} with a Tandem ST2000}.
7558 @kindex target vxworks
7559 @item target vxworks @var{machinename}
7560 A VxWorks system, attached via TCP/IP. The argument @var{machinename}
7561 is the target system's machine name or IP address.
7562 @xref{VxWorks Remote, ,@value{GDBN} and VxWorks}.
7565 @kindex target cpu32bug
7566 @item target cpu32bug @var{dev}
7567 CPU32BUG monitor, running on a CPU32 (M68K) board.
7569 @kindex target op50n
7570 @item target op50n @var{dev}
7571 OP50N monitor, running on an OKI HPPA board.
7574 @item target w89k @var{dev}
7575 W89K monitor, running on a Winbond HPPA board.
7578 @item target est @var{dev}
7579 EST-300 ICE monitor, running on a CPU32 (M68K) board.
7581 @kindex target rom68k
7582 @item target rom68k @var{dev}
7583 ROM 68K monitor, running on an IDP board.
7585 @kindex target array
7586 @item target array @var{dev}
7587 Array Tech LSI33K RAID controller board.
7589 @kindex target sparclite
7590 @item target sparclite @var{dev}
7591 Fujitsu sparclite boards, used only for the purpose of loading.
7592 You must use an additional command to debug the program.
7593 For example: target remote @var{dev} using @value{GDBN} standard
7598 Different targets are available on different configurations of @value{GDBN};
7599 your configuration may have more or fewer targets.
7602 @section Choosing target byte order
7603 @cindex choosing target byte order
7604 @cindex target byte order
7605 @kindex set endian big
7606 @kindex set endian little
7607 @kindex set endian auto
7610 You can now choose which byte order to use with a target system.
7611 Use the @code{set endian big} and @code{set endian little} commands.
7612 Use the @code{set endian auto} command to instruct
7613 @value{GDBN} to use the byte order associated with the executable.
7614 You can see the current setting for byte order with the @code{show endian}
7617 @emph{Warning:} Currently, only embedded MIPS configurations support
7618 dynamic selection of target byte order.
7621 @section Remote debugging
7622 @cindex remote debugging
7624 If you are trying to debug a program running on a machine that cannot run
7625 @value{GDBN} in the usual way, it is often useful to use remote debugging.
7626 For example, you might use remote debugging on an operating system kernel,
7627 or on a small system which does not have a general purpose operating system
7628 powerful enough to run a full-featured debugger.
7630 Some configurations of @value{GDBN} have special serial or TCP/IP interfaces
7631 to make this work with particular debugging targets. In addition,
7632 @value{GDBN} comes with a generic serial protocol (specific to @value{GDBN},
7633 but not specific to any particular target system) which you can use if you
7634 write the remote stubs---the code that runs on the remote system to
7635 communicate with @value{GDBN}.
7637 Other remote targets may be available in your
7638 configuration of @value{GDBN}; use @code{help target} to list them.
7641 @c Text on starting up GDB in various specific cases; it goes up front
7642 @c in manuals configured for any of those particular situations, here
7646 * Remote Serial:: @value{GDBN} remote serial protocol
7649 * i960-Nindy Remote:: @value{GDBN} with a remote i960 (Nindy)
7652 * UDI29K Remote:: The UDI protocol for AMD29K
7653 * EB29K Remote:: The EBMON protocol for AMD29K
7656 * VxWorks Remote:: @value{GDBN} and VxWorks
7659 * ST2000 Remote:: @value{GDBN} with a Tandem ST2000
7662 * Hitachi Remote:: @value{GDBN} and Hitachi Microprocessors
7665 * MIPS Remote:: @value{GDBN} and MIPS boards
7668 * Simulator:: Simulated CPU target
7672 @include remote.texi
7675 @node Controlling GDB
7676 @chapter Controlling @value{GDBN}
7678 You can alter the way @value{GDBN} interacts with you by using
7679 the @code{set} command. For commands controlling how @value{GDBN} displays
7680 data, @pxref{Print Settings, ,Print settings}; other settings are described
7685 * Editing:: Command editing
7686 * History:: Command history
7687 * Screen Size:: Screen size
7689 * Messages/Warnings:: Optional warnings and messages
7697 @value{GDBN} indicates its readiness to read a command by printing a string
7698 called the @dfn{prompt}. This string is normally @samp{(@value{GDBP})}. You
7699 can change the prompt string with the @code{set prompt} command. For
7700 instance, when debugging @value{GDBN} with @value{GDBN}, it is useful to change
7701 the prompt in one of the @value{GDBN} sessions so that you can always tell
7702 which one you are talking to.
7704 @emph{Note:} @code{set prompt} no longer adds a space for you after the
7705 prompt you set. This allows you to set a prompt which ends in a space
7706 or a prompt that does not.
7710 @item set prompt @var{newprompt}
7711 Directs @value{GDBN} to use @var{newprompt} as its prompt string henceforth.
7715 Prints a line of the form: @samp{Gdb's prompt is: @var{your-prompt}}
7719 @section Command editing
7721 @cindex command line editing
7723 @value{GDBN} reads its input commands via the @dfn{readline} interface. This
7724 @sc{gnu} library provides consistent behavior for programs which provide a
7725 command line interface to the user. Advantages are @sc{gnu} Emacs-style
7726 or @dfn{vi}-style inline editing of commands, @code{csh}-like history
7727 substitution, and a storage and recall of command history across
7730 You may control the behavior of command line editing in @value{GDBN} with the
7737 @itemx set editing on
7738 Enable command line editing (enabled by default).
7740 @item set editing off
7741 Disable command line editing.
7743 @kindex show editing
7745 Show whether command line editing is enabled.
7749 @section Command history
7751 @value{GDBN} can keep track of the commands you type during your
7752 debugging sessions, so that you can be certain of precisely what
7753 happened. Use these commands to manage the @value{GDBN} command
7757 @cindex history substitution
7758 @cindex history file
7759 @kindex set history filename
7761 @item set history filename @var{fname}
7762 Set the name of the @value{GDBN} command history file to @var{fname}.
7763 This is the file where @value{GDBN} reads an initial command history
7764 list, and where it writes the command history from this session when it
7765 exits. You can access this list through history expansion or through
7766 the history command editing characters listed below. This file defaults
7767 to the value of the environment variable @code{GDBHISTFILE}, or to
7768 @file{./.gdb_history} if this variable is not set.
7770 @cindex history save
7771 @kindex set history save
7772 @item set history save
7773 @itemx set history save on
7774 Record command history in a file, whose name may be specified with the
7775 @code{set history filename} command. By default, this option is disabled.
7777 @item set history save off
7778 Stop recording command history in a file.
7780 @cindex history size
7781 @kindex set history size
7782 @item set history size @var{size}
7783 Set the number of commands which @value{GDBN} keeps in its history list.
7784 This defaults to the value of the environment variable
7785 @code{HISTSIZE}, or to 256 if this variable is not set.
7788 @cindex history expansion
7789 History expansion assigns special meaning to the character @kbd{!}.
7790 @ifset have-readline-appendices
7791 @xref{Event Designators}.
7794 Since @kbd{!} is also the logical not operator in C, history expansion
7795 is off by default. If you decide to enable history expansion with the
7796 @code{set history expansion on} command, you may sometimes need to
7797 follow @kbd{!} (when it is used as logical not, in an expression) with
7798 a space or a tab to prevent it from being expanded. The readline
7799 history facilities do not attempt substitution on the strings
7800 @kbd{!=} and @kbd{!(}, even when history expansion is enabled.
7802 The commands to control history expansion are:
7805 @kindex set history expansion
7806 @item set history expansion on
7807 @itemx set history expansion
7808 Enable history expansion. History expansion is off by default.
7810 @item set history expansion off
7811 Disable history expansion.
7813 The readline code comes with more complete documentation of
7814 editing and history expansion features. Users unfamiliar with @sc{gnu} Emacs
7815 or @code{vi} may wish to read it.
7816 @ifset have-readline-appendices
7817 @xref{Command Line Editing}.
7821 @kindex show history
7823 @itemx show history filename
7824 @itemx show history save
7825 @itemx show history size
7826 @itemx show history expansion
7827 These commands display the state of the @value{GDBN} history parameters.
7828 @code{show history} by itself displays all four states.
7833 @kindex show commands
7835 Display the last ten commands in the command history.
7837 @item show commands @var{n}
7838 Print ten commands centered on command number @var{n}.
7840 @item show commands +
7841 Print ten commands just after the commands last printed.
7845 @section Screen size
7846 @cindex size of screen
7847 @cindex pauses in output
7849 Certain commands to @value{GDBN} may produce large amounts of
7850 information output to the screen. To help you read all of it,
7851 @value{GDBN} pauses and asks you for input at the end of each page of
7852 output. Type @key{RET} when you want to continue the output, or @kbd{q}
7853 to discard the remaining output. Also, the screen width setting
7854 determines when to wrap lines of output. Depending on what is being
7855 printed, @value{GDBN} tries to break the line at a readable place,
7856 rather than simply letting it overflow onto the following line.
7858 Normally @value{GDBN} knows the size of the screen from the termcap data base
7859 together with the value of the @code{TERM} environment variable and the
7860 @code{stty rows} and @code{stty cols} settings. If this is not correct,
7861 you can override it with the @code{set height} and @code{set
7869 @item set height @var{lpp}
7871 @itemx set width @var{cpl}
7873 These @code{set} commands specify a screen height of @var{lpp} lines and
7874 a screen width of @var{cpl} characters. The associated @code{show}
7875 commands display the current settings.
7877 If you specify a height of zero lines, @value{GDBN} does not pause during
7878 output no matter how long the output is. This is useful if output is to a
7879 file or to an editor buffer.
7881 Likewise, you can specify @samp{set width 0} to prevent @value{GDBN}
7882 from wrapping its output.
7887 @cindex number representation
7888 @cindex entering numbers
7890 You can always enter numbers in octal, decimal, or hexadecimal in @value{GDBN} by
7891 the usual conventions: octal numbers begin with @samp{0}, decimal
7892 numbers end with @samp{.}, and hexadecimal numbers begin with @samp{0x}.
7893 Numbers that begin with none of these are, by default, entered in base
7894 10; likewise, the default display for numbers---when no particular
7895 format is specified---is base 10. You can change the default base for
7896 both input and output with the @code{set radix} command.
7899 @kindex set input-radix
7900 @item set input-radix @var{base}
7901 Set the default base for numeric input. Supported choices
7902 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
7903 specified either unambiguously or using the current default radix; for
7913 sets the base to decimal. On the other hand, @samp{set radix 10}
7914 leaves the radix unchanged no matter what it was.
7916 @kindex set output-radix
7917 @item set output-radix @var{base}
7918 Set the default base for numeric display. Supported choices
7919 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
7920 specified either unambiguously or using the current default radix.
7922 @kindex show input-radix
7923 @item show input-radix
7924 Display the current default base for numeric input.
7926 @kindex show output-radix
7927 @item show output-radix
7928 Display the current default base for numeric display.
7931 @node Messages/Warnings
7932 @section Optional warnings and messages
7934 By default, @value{GDBN} is silent about its inner workings. If you are running
7935 on a slow machine, you may want to use the @code{set verbose} command.
7936 This makes @value{GDBN} tell you when it does a lengthy internal operation, so
7937 you will not think it has crashed.
7939 Currently, the messages controlled by @code{set verbose} are those
7940 which announce that the symbol table for a source file is being read;
7941 see @code{symbol-file} in @ref{Files, ,Commands to specify files}.
7945 @item set verbose on
7946 Enables @value{GDBN} output of certain informational messages.
7948 @item set verbose off
7949 Disables @value{GDBN} output of certain informational messages.
7951 @kindex show verbose
7953 Displays whether @code{set verbose} is on or off.
7956 By default, if @value{GDBN} encounters bugs in the symbol table of an object
7957 file, it is silent; but if you are debugging a compiler, you may find
7958 this information useful (@pxref{Symbol Errors, ,Errors reading symbol files}).
7961 @kindex set complaints
7962 @item set complaints @var{limit}
7963 Permits @value{GDBN} to output @var{limit} complaints about each type of unusual
7964 symbols before becoming silent about the problem. Set @var{limit} to
7965 zero to suppress all complaints; set it to a large number to prevent
7966 complaints from being suppressed.
7968 @kindex show complaints
7969 @item show complaints
7970 Displays how many symbol complaints @value{GDBN} is permitted to produce.
7973 By default, @value{GDBN} is cautious, and asks what sometimes seems to be a
7974 lot of stupid questions to confirm certain commands. For example, if
7975 you try to run a program which is already running:
7979 The program being debugged has been started already.
7980 Start it from the beginning? (y or n)
7983 If you are willing to unflinchingly face the consequences of your own
7984 commands, you can disable this ``feature'':
7989 @cindex confirmation
7990 @cindex stupid questions
7991 @item set confirm off
7992 Disables confirmation requests.
7994 @item set confirm on
7995 Enables confirmation requests (the default).
7997 @kindex show confirm
7999 Displays state of confirmation requests.
8003 @chapter Canned Sequences of Commands
8005 Aside from breakpoint commands (@pxref{Break Commands, ,Breakpoint
8006 command lists}), @value{GDBN} provides two ways to store sequences of commands
8007 for execution as a unit: user-defined commands and command files.
8010 * Define:: User-defined commands
8011 * Hooks:: User-defined command hooks
8012 * Command Files:: Command files
8013 * Output:: Commands for controlled output
8017 @section User-defined commands
8019 @cindex user-defined command
8020 A @dfn{user-defined command} is a sequence of @value{GDBN} commands to which
8021 you assign a new name as a command. This is done with the @code{define}
8022 command. User commands may accept up to 10 arguments separated by whitespace.
8023 Arguments are accessed within the user command via @var{$arg0@dots{}$arg9}.
8028 print $arg0 + $arg1 + $arg2
8031 @noindent To execute the command use:
8037 @noindent This defines the command @code{adder}, which prints the sum of
8038 its three arguments. Note the arguments are text substitutions, so they may
8039 reference variables, use complex expressions, or even perform inferior
8044 @item define @var{commandname}
8045 Define a command named @var{commandname}. If there is already a command
8046 by that name, you are asked to confirm that you want to redefine it.
8048 The definition of the command is made up of other @value{GDBN} command lines,
8049 which are given following the @code{define} command. The end of these
8050 commands is marked by a line containing @code{end}.
8055 Takes a single argument, which is an expression to evaluate.
8056 It is followed by a series of commands that are executed
8057 only if the expression is true (nonzero).
8058 There can then optionally be a line @code{else}, followed
8059 by a series of commands that are only executed if the expression
8060 was false. The end of the list is marked by a line containing @code{end}.
8064 The syntax is similar to @code{if}: the command takes a single argument,
8065 which is an expression to evaluate, and must be followed by the commands to
8066 execute, one per line, terminated by an @code{end}.
8067 The commands are executed repeatedly as long as the expression
8071 @item document @var{commandname}
8072 Document the user-defined command @var{commandname}, so that it can be
8073 accessed by @code{help}. The command @var{commandname} must already be
8074 defined. This command reads lines of documentation just as @code{define}
8075 reads the lines of the command definition, ending with @code{end}.
8076 After the @code{document} command is finished, @code{help} on command
8077 @var{commandname} displays the documentation you have written.
8079 You may use the @code{document} command again to change the
8080 documentation of a command. Redefining the command with @code{define}
8081 does not change the documentation.
8083 @kindex help user-defined
8084 @item help user-defined
8085 List all user-defined commands, with the first line of the documentation
8090 @itemx show user @var{commandname}
8091 Display the @value{GDBN} commands used to define @var{commandname} (but not its
8092 documentation). If no @var{commandname} is given, display the
8093 definitions for all user-defined commands.
8096 When user-defined commands are executed, the
8097 commands of the definition are not printed. An error in any command
8098 stops execution of the user-defined command.
8100 If used interactively, commands that would ask for confirmation proceed
8101 without asking when used inside a user-defined command. Many @value{GDBN}
8102 commands that normally print messages to say what they are doing omit the
8103 messages when used in a user-defined command.
8106 @section User-defined command hooks
8107 @cindex command files
8109 You may define @emph{hooks}, which are a special kind of user-defined
8110 command. Whenever you run the command @samp{foo}, if the user-defined
8111 command @samp{hook-foo} exists, it is executed (with no arguments)
8112 before that command.
8114 In addition, a pseudo-command, @samp{stop} exists. Defining
8115 (@samp{hook-stop}) makes the associated commands execute every time
8116 execution stops in your program: before breakpoint commands are run,
8117 displays are printed, or the stack frame is printed.
8120 For example, to ignore @code{SIGALRM} signals while
8121 single-stepping, but treat them normally during normal execution,
8126 handle SIGALRM nopass
8133 define hook-continue
8139 You can define a hook for any single-word command in @value{GDBN}, but
8140 not for command aliases; you should define a hook for the basic command
8141 name, e.g. @code{backtrace} rather than @code{bt}.
8142 @c FIXME! So how does Joe User discover whether a command is an alias
8144 If an error occurs during the execution of your hook, execution of
8145 @value{GDBN} commands stops and @value{GDBN} issues a prompt
8146 (before the command that you actually typed had a chance to run).
8148 If you try to define a hook which does not match any known command, you
8149 get a warning from the @code{define} command.
8152 @section Command files
8154 @cindex command files
8155 A command file for @value{GDBN} is a file of lines that are @value{GDBN}
8156 commands. Comments (lines starting with @kbd{#}) may also be included.
8157 An empty line in a command file does nothing; it does not mean to repeat
8158 the last command, as it would from the terminal.
8161 @cindex @file{@value{GDBINIT}}
8162 When you start @value{GDBN}, it automatically executes commands from its
8163 @dfn{init files}. These are files named @file{@value{GDBINIT}}.
8164 @value{GDBN} reads the init file (if any) in your home directory, then
8165 processes command line options and operands, and then reads the init
8166 file (if any) in the current working directory. This is so the init
8167 file in your home directory can set options (such as @code{set
8168 complaints}) which affect the processing of the command line options and
8169 operands. The init files are not executed if you use the @samp{-nx}
8170 option; @pxref{Mode Options, ,Choosing modes}.
8173 @cindex init file name
8174 On some configurations of @value{GDBN}, the init file is known by a
8175 different name (these are typically environments where a specialized
8176 form of @value{GDBN} may need to coexist with other forms,
8177 hence a different name
8178 for the specialized version's init file). These are the environments
8179 with special init file names:
8184 VxWorks (Wind River Systems real-time OS): @samp{.vxgdbinit}
8186 @kindex .os68gdbinit
8188 OS68K (Enea Data Systems real-time OS): @samp{.os68gdbinit}
8192 ES-1800 (Ericsson Telecom AB M68000 emulator): @samp{.esgdbinit}
8196 You can also request the execution of a command file with the
8197 @code{source} command:
8201 @item source @var{filename}
8202 Execute the command file @var{filename}.
8205 The lines in a command file are executed sequentially. They are not
8206 printed as they are executed. An error in any command terminates execution
8207 of the command file.
8209 Commands that would ask for confirmation if used interactively proceed
8210 without asking when used in a command file. Many @value{GDBN} commands that
8211 normally print messages to say what they are doing omit the messages
8212 when called from command files.
8215 @section Commands for controlled output
8217 During the execution of a command file or a user-defined command, normal
8218 @value{GDBN} output is suppressed; the only output that appears is what is
8219 explicitly printed by the commands in the definition. This section
8220 describes three commands useful for generating exactly the output you
8225 @item echo @var{text}
8226 @c I do not consider backslash-space a standard C escape sequence
8227 @c because it is not in ANSI.
8228 Print @var{text}. Nonprinting characters can be included in
8229 @var{text} using C escape sequences, such as @samp{\n} to print a
8230 newline. @strong{No newline is printed unless you specify one.}
8231 In addition to the standard C escape sequences, a backslash followed
8232 by a space stands for a space. This is useful for displaying a
8233 string with spaces at the beginning or the end, since leading and
8234 trailing spaces are otherwise trimmed from all arguments.
8235 To print @samp{@w{ }and foo =@w{ }}, use the command
8236 @samp{echo \@w{ }and foo = \@w{ }}.
8238 A backslash at the end of @var{text} can be used, as in C, to continue
8239 the command onto subsequent lines. For example,
8242 echo This is some text\n\
8243 which is continued\n\
8244 onto several lines.\n
8247 produces the same output as
8250 echo This is some text\n
8251 echo which is continued\n
8252 echo onto several lines.\n
8256 @item output @var{expression}
8257 Print the value of @var{expression} and nothing but that value: no
8258 newlines, no @samp{$@var{nn} = }. The value is not entered in the
8259 value history either. @xref{Expressions, ,Expressions}, for more information
8262 @item output/@var{fmt} @var{expression}
8263 Print the value of @var{expression} in format @var{fmt}. You can use
8264 the same formats as for @code{print}. @xref{Output Formats,,Output
8265 formats}, for more information.
8268 @item printf @var{string}, @var{expressions}@dots{}
8269 Print the values of the @var{expressions} under the control of
8270 @var{string}. The @var{expressions} are separated by commas and may be
8271 either numbers or pointers. Their values are printed as specified by
8272 @var{string}, exactly as if your program were to execute the C
8276 printf (@var{string}, @var{expressions}@dots{});
8279 For example, you can print two values in hex like this:
8282 printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
8285 The only backslash-escape sequences that you can use in the format
8286 string are the simple ones that consist of backslash followed by a
8292 @chapter Using @value{GDBN} under @sc{gnu} Emacs
8295 @cindex @sc{gnu} Emacs
8296 A special interface allows you to use @sc{gnu} Emacs to view (and
8297 edit) the source files for the program you are debugging with
8300 To use this interface, use the command @kbd{M-x gdb} in Emacs. Give the
8301 executable file you want to debug as an argument. This command starts
8302 @value{GDBN} as a subprocess of Emacs, with input and output through a newly
8303 created Emacs buffer.
8305 Using @value{GDBN} under Emacs is just like using @value{GDBN} normally except for two
8310 All ``terminal'' input and output goes through the Emacs buffer.
8313 This applies both to @value{GDBN} commands and their output, and to the input
8314 and output done by the program you are debugging.
8316 This is useful because it means that you can copy the text of previous
8317 commands and input them again; you can even use parts of the output
8320 All the facilities of Emacs' Shell mode are available for interacting
8321 with your program. In particular, you can send signals the usual
8322 way---for example, @kbd{C-c C-c} for an interrupt, @kbd{C-c C-z} for a
8327 @value{GDBN} displays source code through Emacs.
8330 Each time @value{GDBN} displays a stack frame, Emacs automatically finds the
8331 source file for that frame and puts an arrow (@samp{=>}) at the
8332 left margin of the current line. Emacs uses a separate buffer for
8333 source display, and splits the screen to show both your @value{GDBN} session
8336 Explicit @value{GDBN} @code{list} or search commands still produce output as
8337 usual, but you probably have no reason to use them from Emacs.
8340 @emph{Warning:} If the directory where your program resides is not your
8341 current directory, it can be easy to confuse Emacs about the location of
8342 the source files, in which case the auxiliary display buffer does not
8343 appear to show your source. @value{GDBN} can find programs by searching your
8344 environment's @code{PATH} variable, so the @value{GDBN} input and output
8345 session proceeds normally; but Emacs does not get enough information
8346 back from @value{GDBN} to locate the source files in this situation. To
8347 avoid this problem, either start @value{GDBN} mode from the directory where
8348 your program resides, or specify an absolute file name when prompted for the
8349 @kbd{M-x gdb} argument.
8351 A similar confusion can result if you use the @value{GDBN} @code{file} command to
8352 switch to debugging a program in some other location, from an existing
8353 @value{GDBN} buffer in Emacs.
8356 By default, @kbd{M-x gdb} calls the program called @file{gdb}. If
8357 you need to call @value{GDBN} by a different name (for example, if you keep
8358 several configurations around, with different names) you can set the
8359 Emacs variable @code{gdb-command-name}; for example,
8362 (setq gdb-command-name "mygdb")
8366 (preceded by @kbd{ESC ESC}, or typed in the @code{*scratch*} buffer, or
8367 in your @file{.emacs} file) makes Emacs call the program named
8368 ``@code{mygdb}'' instead.
8370 In the @value{GDBN} I/O buffer, you can use these special Emacs commands in
8371 addition to the standard Shell mode commands:
8375 Describe the features of Emacs' @value{GDBN} Mode.
8378 Execute to another source line, like the @value{GDBN} @code{step} command; also
8379 update the display window to show the current file and location.
8382 Execute to next source line in this function, skipping all function
8383 calls, like the @value{GDBN} @code{next} command. Then update the display window
8384 to show the current file and location.
8387 Execute one instruction, like the @value{GDBN} @code{stepi} command; update
8388 display window accordingly.
8391 Execute to next instruction, using the @value{GDBN} @code{nexti} command; update
8392 display window accordingly.
8395 Execute until exit from the selected stack frame, like the @value{GDBN}
8396 @code{finish} command.
8399 Continue execution of your program, like the @value{GDBN} @code{continue}
8402 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-p}.
8405 Go up the number of frames indicated by the numeric argument
8406 (@pxref{Arguments, , Numeric Arguments, Emacs, The @sc{gnu} Emacs Manual}),
8407 like the @value{GDBN} @code{up} command.
8409 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-u}.
8412 Go down the number of frames indicated by the numeric argument, like the
8413 @value{GDBN} @code{down} command.
8415 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-d}.
8418 Read the number where the cursor is positioned, and insert it at the end
8419 of the @value{GDBN} I/O buffer. For example, if you wish to disassemble code
8420 around an address that was displayed earlier, type @kbd{disassemble};
8421 then move the cursor to the address display, and pick up the
8422 argument for @code{disassemble} by typing @kbd{C-x &}.
8424 You can customize this further by defining elements of the list
8425 @code{gdb-print-command}; once it is defined, you can format or
8426 otherwise process numbers picked up by @kbd{C-x &} before they are
8427 inserted. A numeric argument to @kbd{C-x &} indicates that you
8428 wish special formatting, and also acts as an index to pick an element of the
8429 list. If the list element is a string, the number to be inserted is
8430 formatted using the Emacs function @code{format}; otherwise the number
8431 is passed as an argument to the corresponding list element.
8434 In any source file, the Emacs command @kbd{C-x SPC} (@code{gdb-break})
8435 tells @value{GDBN} to set a breakpoint on the source line point is on.
8437 If you accidentally delete the source-display buffer, an easy way to get
8438 it back is to type the command @code{f} in the @value{GDBN} buffer, to
8439 request a frame display; when you run under Emacs, this recreates
8440 the source buffer if necessary to show you the context of the current
8443 The source files displayed in Emacs are in ordinary Emacs buffers
8444 which are visiting the source files in the usual way. You can edit
8445 the files with these buffers if you wish; but keep in mind that @value{GDBN}
8446 communicates with Emacs in terms of line numbers. If you add or
8447 delete lines from the text, the line numbers that @value{GDBN} knows cease
8448 to correspond properly with the code.
8450 @c The following dropped because Epoch is nonstandard. Reactivate
8451 @c if/when v19 does something similar. ---pesch@cygnus.com 19dec1990
8453 @kindex Emacs Epoch environment
8457 Version 18 of @sc{gnu} Emacs has a built-in window system
8458 called the @code{epoch}
8459 environment. Users of this environment can use a new command,
8460 @code{inspect} which performs identically to @code{print} except that
8461 each value is printed in its own window.
8467 @chapter Using @value{GDBN} with Energize
8470 The Energize Programming System is an integrated development environment
8471 that includes a point-and-click interface to many programming tools.
8472 When you use @value{GDBN} in this environment, you can use the standard
8473 Energize graphical interface to drive @value{GDBN}; you can also, if you
8474 choose, type @value{GDBN} commands as usual in a debugging window. Even if
8475 you use the graphical interface, the debugging window (which uses Emacs,
8476 and resembles the standard @sc{gnu} Emacs interface to
8477 @value{GDBN}) displays the
8478 equivalent commands, so that the history of your debugging session is
8481 When Energize starts up a @value{GDBN} session, it uses one of the
8482 command-line options @samp{-energize} or @samp{-cadillac} (``cadillac''
8483 is the name of the communications protocol used by the Energize system).
8484 This option makes @value{GDBN} run as one of the tools in the Energize Tool
8485 Set: it sends all output to the Energize kernel, and accept input from
8488 See the user manual for the Energize Programming System for
8489 information on how to use the Energize graphical interface and the other
8490 development tools that Energize integrates with @value{GDBN}.
8495 @chapter Reporting Bugs in @value{GDBN}
8496 @cindex bugs in @value{GDBN}
8497 @cindex reporting bugs in @value{GDBN}
8499 Your bug reports play an essential role in making @value{GDBN} reliable.
8501 Reporting a bug may help you by bringing a solution to your problem, or it
8502 may not. But in any case the principal function of a bug report is to help
8503 the entire community by making the next version of @value{GDBN} work better. Bug
8504 reports are your contribution to the maintenance of @value{GDBN}.
8506 In order for a bug report to serve its purpose, you must include the
8507 information that enables us to fix the bug.
8510 * Bug Criteria:: Have you found a bug?
8511 * Bug Reporting:: How to report bugs
8515 @section Have you found a bug?
8516 @cindex bug criteria
8518 If you are not sure whether you have found a bug, here are some guidelines:
8521 @cindex fatal signal
8522 @cindex debugger crash
8523 @cindex crash of debugger
8525 If the debugger gets a fatal signal, for any input whatever, that is a
8526 @value{GDBN} bug. Reliable debuggers never crash.
8528 @cindex error on valid input
8530 If @value{GDBN} produces an error message for valid input, that is a bug.
8532 @cindex invalid input
8534 If @value{GDBN} does not produce an error message for invalid input,
8535 that is a bug. However, you should note that your idea of
8536 ``invalid input'' might be our idea of ``an extension'' or ``support
8537 for traditional practice''.
8540 If you are an experienced user of debugging tools, your suggestions
8541 for improvement of @value{GDBN} are welcome in any case.
8545 @section How to report bugs
8547 @cindex @value{GDBN} bugs, reporting
8549 A number of companies and individuals offer support for @sc{gnu} products.
8550 If you obtained @value{GDBN} from a support organization, we recommend you
8551 contact that organization first.
8553 You can find contact information for many support companies and
8554 individuals in the file @file{etc/SERVICE} in the @sc{gnu} Emacs
8557 In any event, we also recommend that you send bug reports for @value{GDBN} to one
8561 bug-gdb@@prep.ai.mit.edu
8562 @{ucbvax|mit-eddie|uunet@}!prep.ai.mit.edu!bug-gdb
8565 @strong{Do not send bug reports to @samp{info-gdb}, or to
8566 @samp{help-gdb}, or to any newsgroups.} Most users of @value{GDBN} do not want to
8567 receive bug reports. Those that do have arranged to receive @samp{bug-gdb}.
8569 The mailing list @samp{bug-gdb} has a newsgroup @samp{gnu.gdb.bug} which
8570 serves as a repeater. The mailing list and the newsgroup carry exactly
8571 the same messages. Often people think of posting bug reports to the
8572 newsgroup instead of mailing them. This appears to work, but it has one
8573 problem which can be crucial: a newsgroup posting often lacks a mail
8574 path back to the sender. Thus, if we need to ask for more information,
8575 we may be unable to reach you. For this reason, it is better to send
8576 bug reports to the mailing list.
8578 As a last resort, send bug reports on paper to:
8581 @sc{gnu} Debugger Bugs
8582 Free Software Foundation
8587 The fundamental principle of reporting bugs usefully is this:
8588 @strong{report all the facts}. If you are not sure whether to state a
8589 fact or leave it out, state it!
8591 Often people omit facts because they think they know what causes the
8592 problem and assume that some details do not matter. Thus, you might
8593 assume that the name of the variable you use in an example does not matter.
8594 Well, probably it does not, but one cannot be sure. Perhaps the bug is a
8595 stray memory reference which happens to fetch from the location where that
8596 name is stored in memory; perhaps, if the name were different, the contents
8597 of that location would fool the debugger into doing the right thing despite
8598 the bug. Play it safe and give a specific, complete example. That is the
8599 easiest thing for you to do, and the most helpful.
8601 Keep in mind that the purpose of a bug report is to enable us to fix
8602 the bug if it is new to us.
8604 @c FIX ME!!--What the heck does the following sentence mean,
8605 @c in the context of the one above?
8607 @c It is not as important as what happens if the bug is already known.
8609 Therefore, always write your bug reports on
8610 the assumption that the bug has not been reported previously.
8612 Sometimes people give a few sketchy facts and ask, ``Does this ring a
8613 bell?'' Those bug reports are useless, and we urge everyone to
8614 @emph{refuse to respond to them} except to chide the sender to report
8617 To enable us to fix the bug, you should include all these things:
8621 The version of @value{GDBN}. @value{GDBN} announces it if you start with no
8622 arguments; you can also print it at any time using @code{show version}.
8624 Without this, we will not know whether there is any point in looking for
8625 the bug in the current version of @value{GDBN}.
8628 The type of machine you are using, and the operating system name and
8632 What compiler (and its version) was used to compile @value{GDBN}---e.g.
8633 ``@value{GCC}--2.0''.
8636 What compiler (and its version) was used to compile the program you
8637 are debugging---e.g. ``@value{GCC}--2.0''.
8640 The command arguments you gave the compiler to compile your example and
8641 observe the bug. For example, did you use @samp{-O}? To guarantee
8642 you will not omit something important, list them all. A copy of the
8643 Makefile (or the output from make) is sufficient.
8645 If we were to try to guess the arguments, we would probably guess wrong
8646 and then we might not encounter the bug.
8649 A complete input script, and all necessary source files, that will
8653 A description of what behavior you observe that you believe is
8654 incorrect. For example, ``It gets a fatal signal.''
8656 Of course, if the bug is that @value{GDBN} gets a fatal signal, then we will
8657 certainly notice it. But if the bug is incorrect output, we might not
8658 notice unless it is glaringly wrong. You might as well not give us a
8659 chance to make a mistake.
8661 Even if the problem you experience is a fatal signal, you should still
8662 say so explicitly. Suppose something strange is going on, such as,
8663 your copy of @value{GDBN} is out of synch, or you have encountered a
8664 bug in the C library on your system. (This has happened!) Your copy
8665 might crash and ours would not. If you told us to expect a crash,
8666 then when ours fails to crash, we would know that the bug was not
8667 happening for us. If you had not told us to expect a crash, then we
8668 would not be able to draw any conclusion from our observations.
8671 If you wish to suggest changes to the @value{GDBN} source, send us context
8672 diffs. If you even discuss something in the @value{GDBN} source, refer to
8673 it by context, not by line number.
8675 The line numbers in our development sources will not match those in your
8676 sources. Your line numbers would convey no useful information to us.
8679 Here are some things that are not necessary:
8683 A description of the envelope of the bug.
8685 Often people who encounter a bug spend a lot of time investigating
8686 which changes to the input file will make the bug go away and which
8687 changes will not affect it.
8689 This is often time consuming and not very useful, because the way we
8690 will find the bug is by running a single example under the debugger
8691 with breakpoints, not by pure deduction from a series of examples.
8692 We recommend that you save your time for something else.
8694 Of course, if you can find a simpler example to report @emph{instead}
8695 of the original one, that is a convenience for us. Errors in the
8696 output will be easier to spot, running under the debugger will take
8697 less time, and so on.
8699 However, simplification is not vital; if you do not want to do this,
8700 report the bug anyway and send us the entire test case you used.
8703 A patch for the bug.
8705 A patch for the bug does help us if it is a good one. But do not omit
8706 the necessary information, such as the test case, on the assumption that
8707 a patch is all we need. We might see problems with your patch and decide
8708 to fix the problem another way, or we might not understand it at all.
8710 Sometimes with a program as complicated as @value{GDBN} it is very hard to
8711 construct an example that will make the program follow a certain path
8712 through the code. If you do not send us the example, we will not be able
8713 to construct one, so we will not be able to verify that the bug is fixed.
8715 And if we cannot understand what bug you are trying to fix, or why your
8716 patch should be an improvement, we will not install it. A test case will
8717 help us to understand.
8720 A guess about what the bug is or what it depends on.
8722 Such guesses are usually wrong. Even we cannot guess right about such
8723 things without first using the debugger to find the facts.
8726 @c The readline documentation is distributed with the readline code
8727 @c and consists of the two following files:
8730 @c Use -I with makeinfo to point to the appropriate directory,
8731 @c environment var TEXINPUTS with TeX.
8732 @include rluser.texinfo
8733 @include inc-hist.texi
8737 @node Renamed Commands
8738 @appendix Renamed Commands
8740 The following commands were renamed in @value{GDBN} 4, in order to make the
8741 command set as a whole more consistent and easier to use and remember:
8744 @kindex delete environment
8745 @kindex info copying
8746 @kindex info convenience
8747 @kindex info directories
8748 @kindex info editing
8749 @kindex info history
8750 @kindex info targets
8752 @kindex info version
8753 @kindex info warranty
8754 @kindex set addressprint
8755 @kindex set arrayprint
8756 @kindex set prettyprint
8757 @kindex set screen-height
8758 @kindex set screen-width
8759 @kindex set unionprint
8760 @kindex set vtblprint
8761 @kindex set demangle
8762 @kindex set asm-demangle
8763 @kindex set sevenbit-strings
8764 @kindex set array-max
8766 @kindex set history write
8767 @kindex show addressprint
8768 @kindex show arrayprint
8769 @kindex show prettyprint
8770 @kindex show screen-height
8771 @kindex show screen-width
8772 @kindex show unionprint
8773 @kindex show vtblprint
8774 @kindex show demangle
8775 @kindex show asm-demangle
8776 @kindex show sevenbit-strings
8777 @kindex show array-max
8778 @kindex show caution
8779 @kindex show history write
8784 @c END TEXI2ROFF-KILL
8786 OLD COMMAND NEW COMMAND
8788 --------------- -------------------------------
8789 @c END TEXI2ROFF-KILL
8790 add-syms add-symbol-file
8791 delete environment unset environment
8792 info convenience show convenience
8793 info copying show copying
8794 info directories show directories
8795 info editing show commands
8796 info history show values
8797 info targets help target
8798 info values show values
8799 info version show version
8800 info warranty show warranty
8801 set/show addressprint set/show print address
8802 set/show array-max set/show print elements
8803 set/show arrayprint set/show print array
8804 set/show asm-demangle set/show print asm-demangle
8805 set/show caution set/show confirm
8806 set/show demangle set/show print demangle
8807 set/show history write set/show history save
8808 set/show prettyprint set/show print pretty
8809 set/show screen-height set/show height
8810 set/show screen-width set/show width
8811 set/show sevenbit-strings set/show print sevenbit-strings
8812 set/show unionprint set/show print union
8813 set/show vtblprint set/show print vtbl
8815 unset [No longer an alias for delete]
8821 \vskip \parskip\vskip \baselineskip
8822 \halign{\tt #\hfil &\qquad#&\tt #\hfil\cr
8823 {\bf Old Command} &&{\bf New Command}\cr
8824 add-syms &&add-symbol-file\cr
8825 delete environment &&unset environment\cr
8826 info convenience &&show convenience\cr
8827 info copying &&show copying\cr
8828 info directories &&show directories \cr
8829 info editing &&show commands\cr
8830 info history &&show values\cr
8831 info targets &&help target\cr
8832 info values &&show values\cr
8833 info version &&show version\cr
8834 info warranty &&show warranty\cr
8835 set{\rm / }show addressprint &&set{\rm / }show print address\cr
8836 set{\rm / }show array-max &&set{\rm / }show print elements\cr
8837 set{\rm / }show arrayprint &&set{\rm / }show print array\cr
8838 set{\rm / }show asm-demangle &&set{\rm / }show print asm-demangle\cr
8839 set{\rm / }show caution &&set{\rm / }show confirm\cr
8840 set{\rm / }show demangle &&set{\rm / }show print demangle\cr
8841 set{\rm / }show history write &&set{\rm / }show history save\cr
8842 set{\rm / }show prettyprint &&set{\rm / }show print pretty\cr
8843 set{\rm / }show screen-height &&set{\rm / }show height\cr
8844 set{\rm / }show screen-width &&set{\rm / }show width\cr
8845 set{\rm / }show sevenbit-strings &&set{\rm / }show print sevenbit-strings\cr
8846 set{\rm / }show unionprint &&set{\rm / }show print union\cr
8847 set{\rm / }show vtblprint &&set{\rm / }show print vtbl\cr
8849 unset &&\rm(No longer an alias for delete)\cr
8852 @c END TEXI2ROFF-KILL
8856 @ifclear PRECONFIGURED
8857 @node Formatting Documentation
8858 @appendix Formatting Documentation
8860 @cindex @value{GDBN} reference card
8861 @cindex reference card
8862 The @value{GDBN} 4 release includes an already-formatted reference card, ready
8863 for printing with PostScript or Ghostscript, in the @file{gdb}
8864 subdirectory of the main source directory@footnote{In
8865 @file{gdb-@value{GDBVN}/gdb/refcard.ps} of the version @value{GDBVN}
8866 release.}. If you can use PostScript or Ghostscript with your printer,
8867 you can print the reference card immediately with @file{refcard.ps}.
8869 The release also includes the source for the reference card. You
8870 can format it, using @TeX{}, by typing:
8876 The @value{GDBN} reference card is designed to print in @dfn{landscape}
8877 mode on US ``letter'' size paper;
8878 that is, on a sheet 11 inches wide by 8.5 inches
8879 high. You will need to specify this form of printing as an option to
8880 your @sc{dvi} output program.
8882 @cindex documentation
8884 All the documentation for @value{GDBN} comes as part of the machine-readable
8885 distribution. The documentation is written in Texinfo format, which is
8886 a documentation system that uses a single source file to produce both
8887 on-line information and a printed manual. You can use one of the Info
8888 formatting commands to create the on-line version of the documentation
8889 and @TeX{} (or @code{texi2roff}) to typeset the printed version.
8891 @value{GDBN} includes an already formatted copy of the on-line Info version of
8892 this manual in the @file{gdb} subdirectory. The main Info file is
8893 @file{gdb-@r{version-number}/gdb/gdb.info}, and it refers to
8894 subordinate files matching @samp{gdb.info*} in the same directory. If
8895 necessary, you can print out these files, or read them with any editor;
8896 but they are easier to read using the @code{info} subsystem in @sc{gnu} Emacs
8897 or the standalone @code{info} program, available as part of the @sc{gnu}
8898 Texinfo distribution.
8900 If you want to format these Info files yourself, you need one of the
8901 Info formatting programs, such as @code{texinfo-format-buffer} or
8904 If you have @code{makeinfo} installed, and are in the top level @value{GDBN}
8905 source directory (@file{gdb-@value{GDBVN}}, in the case of version @value{GDBVN}), you can
8906 make the Info file by typing:
8913 If you want to typeset and print copies of this manual, you need @TeX{},
8914 a program to print its @sc{dvi} output files, and @file{texinfo.tex}, the
8915 Texinfo definitions file.
8917 @TeX{} is a typesetting program; it does not print files directly, but
8918 produces output files called @sc{dvi} files. To print a typeset
8919 document, you need a program to print @sc{dvi} files. If your system
8920 has @TeX{} installed, chances are it has such a program. The precise
8921 command to use depends on your system; @kbd{lpr -d} is common; another
8922 (for PostScript devices) is @kbd{dvips}. The @sc{dvi} print command may
8923 require a file name without any extension or a @samp{.dvi} extension.
8925 @TeX{} also requires a macro definitions file called
8926 @file{texinfo.tex}. This file tells @TeX{} how to typeset a document
8927 written in Texinfo format. On its own, @TeX{} cannot either read or
8928 typeset a Texinfo file. @file{texinfo.tex} is distributed with GDB
8929 and is located in the @file{gdb-@var{version-number}/texinfo}
8932 If you have @TeX{} and a @sc{dvi} printer program installed, you can
8933 typeset and print this manual. First switch to the the @file{gdb}
8934 subdirectory of the main source directory (for example, to
8935 @file{gdb-@value{GDBVN}/gdb}) and then type:
8941 @node Installing GDB
8942 @appendix Installing @value{GDBN}
8943 @cindex configuring @value{GDBN}
8944 @cindex installation
8946 @value{GDBN} comes with a @code{configure} script that automates the process
8947 of preparing @value{GDBN} for installation; you can then use @code{make} to
8948 build the @code{gdb} program.
8950 @c irrelevant in info file; it's as current as the code it lives with.
8951 @footnote{If you have a more recent version of @value{GDBN} than @value{GDBVN},
8952 look at the @file{README} file in the sources; we may have improved the
8953 installation procedures since publishing this manual.}
8956 The @value{GDBN} distribution includes all the source code you need for
8957 @value{GDBN} in a single directory, whose name is usually composed by
8958 appending the version number to @samp{gdb}.
8960 For example, the @value{GDBN} version @value{GDBVN} distribution is in the
8961 @file{gdb-@value{GDBVN}} directory. That directory contains:
8964 @item gdb-@value{GDBVN}/configure @r{(and supporting files)}
8965 script for configuring @value{GDBN} and all its supporting libraries
8967 @item gdb-@value{GDBVN}/gdb
8968 the source specific to @value{GDBN} itself
8970 @item gdb-@value{GDBVN}/bfd
8971 source for the Binary File Descriptor library
8973 @item gdb-@value{GDBVN}/include
8974 @sc{gnu} include files
8976 @item gdb-@value{GDBVN}/libiberty
8977 source for the @samp{-liberty} free software library
8979 @item gdb-@value{GDBVN}/opcodes
8980 source for the library of opcode tables and disassemblers
8982 @item gdb-@value{GDBVN}/readline
8983 source for the @sc{gnu} command-line interface
8985 @item gdb-@value{GDBVN}/glob
8986 source for the @sc{gnu} filename pattern-matching subroutine
8988 @item gdb-@value{GDBVN}/mmalloc
8989 source for the @sc{gnu} memory-mapped malloc package
8992 The simplest way to configure and build @value{GDBN} is to run @code{configure}
8993 from the @file{gdb-@var{version-number}} source directory, which in
8994 this example is the @file{gdb-@value{GDBVN}} directory.
8996 First switch to the @file{gdb-@var{version-number}} source directory
8997 if you are not already in it; then run @code{configure}. Pass the
8998 identifier for the platform on which @value{GDBN} will run as an
9004 cd gdb-@value{GDBVN}
9005 ./configure @var{host}
9010 where @var{host} is an identifier such as @samp{sun4} or
9011 @samp{decstation}, that identifies the platform where @value{GDBN} will run.
9012 (You can often leave off @var{host}; @code{configure} tries to guess the
9013 correct value by examining your system.)
9015 Running @samp{configure @var{host}} and then running @code{make} builds the
9016 @file{bfd}, @file{readline}, @file{mmalloc}, and @file{libiberty}
9017 libraries, then @code{gdb} itself. The configured source files, and the
9018 binaries, are left in the corresponding source directories.
9021 @code{configure} is a Bourne-shell (@code{/bin/sh}) script; if your
9022 system does not recognize this automatically when you run a different
9023 shell, you may need to run @code{sh} on it explicitly:
9026 sh configure @var{host}
9029 If you run @code{configure} from a directory that contains source
9030 directories for multiple libraries or programs, such as the
9031 @file{gdb-@value{GDBVN}} source directory for version @value{GDBVN}, @code{configure}
9032 creates configuration files for every directory level underneath (unless
9033 you tell it not to, with the @samp{--norecursion} option).
9035 You can run the @code{configure} script from any of the
9036 subordinate directories in the @value{GDBN} distribution if you only want to
9037 configure that subdirectory, but be sure to specify a path to it.
9039 For example, with version @value{GDBVN}, type the following to configure only
9040 the @code{bfd} subdirectory:
9044 cd gdb-@value{GDBVN}/bfd
9045 ../configure @var{host}
9049 You can install @code{@value{GDBP}} anywhere; it has no hardwired paths.
9050 However, you should make sure that the shell on your path (named by
9051 the @samp{SHELL} environment variable) is publicly readable. Remember
9052 that @value{GDBN} uses the shell to start your program---some systems refuse to
9053 let @value{GDBN} debug child processes whose programs are not readable.
9056 * Separate Objdir:: Compiling @value{GDBN} in another directory
9057 * Config Names:: Specifying names for hosts and targets
9058 * configure Options:: Summary of options for configure
9061 @node Separate Objdir
9062 @section Compiling @value{GDBN} in another directory
9064 If you want to run @value{GDBN} versions for several host or target machines,
9065 you need a different @code{gdb} compiled for each combination of
9066 host and target. @code{configure} is designed to make this easy by
9067 allowing you to generate each configuration in a separate subdirectory,
9068 rather than in the source directory. If your @code{make} program
9069 handles the @samp{VPATH} feature (@sc{gnu} @code{make} does), running
9070 @code{make} in each of these directories builds the @code{gdb}
9071 program specified there.
9073 To build @code{gdb} in a separate directory, run @code{configure}
9074 with the @samp{--srcdir} option to specify where to find the source.
9075 (You also need to specify a path to find @code{configure}
9076 itself from your working directory. If the path to @code{configure}
9077 would be the same as the argument to @samp{--srcdir}, you can leave out
9078 the @samp{--srcdir} option; it is assumed.)
9080 For example, with version @value{GDBVN}, you can build @value{GDBN} in a
9081 separate directory for a Sun 4 like this:
9085 cd gdb-@value{GDBVN}
9088 ../gdb-@value{GDBVN}/configure sun4
9093 When @code{configure} builds a configuration using a remote source
9094 directory, it creates a tree for the binaries with the same structure
9095 (and using the same names) as the tree under the source directory. In
9096 the example, you'd find the Sun 4 library @file{libiberty.a} in the
9097 directory @file{gdb-sun4/libiberty}, and @value{GDBN} itself in
9098 @file{gdb-sun4/gdb}.
9100 One popular reason to build several @value{GDBN} configurations in separate
9101 directories is to configure @value{GDBN} for cross-compiling (where
9102 @value{GDBN} runs on one machine---the @dfn{host}---while debugging
9103 programs that run on another machine---the @dfn{target}).
9104 You specify a cross-debugging target by
9105 giving the @samp{--target=@var{target}} option to @code{configure}.
9107 When you run @code{make} to build a program or library, you must run
9108 it in a configured directory---whatever directory you were in when you
9109 called @code{configure} (or one of its subdirectories).
9111 The @code{Makefile} that @code{configure} generates in each source
9112 directory also runs recursively. If you type @code{make} in a source
9113 directory such as @file{gdb-@value{GDBVN}} (or in a separate configured
9114 directory configured with @samp{--srcdir=@var{dirname}/gdb-@value{GDBVN}}), you
9115 will build all the required libraries, and then build GDB.
9117 When you have multiple hosts or targets configured in separate
9118 directories, you can run @code{make} on them in parallel (for example,
9119 if they are NFS-mounted on each of the hosts); they will not interfere
9123 @section Specifying names for hosts and targets
9125 The specifications used for hosts and targets in the @code{configure}
9126 script are based on a three-part naming scheme, but some short predefined
9127 aliases are also supported. The full naming scheme encodes three pieces
9128 of information in the following pattern:
9131 @var{architecture}-@var{vendor}-@var{os}
9134 For example, you can use the alias @code{sun4} as a @var{host} argument,
9135 or as the value for @var{target} in a @code{--target=@var{target}}
9136 option. The equivalent full name is @samp{sparc-sun-sunos4}.
9138 The @code{configure} script accompanying @value{GDBN} does not provide
9139 any query facility to list all supported host and target names or
9140 aliases. @code{configure} calls the Bourne shell script
9141 @code{config.sub} to map abbreviations to full names; you can read the
9142 script, if you wish, or you can use it to test your guesses on
9143 abbreviations---for example:
9146 % sh config.sub sun4
9147 sparc-sun-sunos4.1.1
9148 % sh config.sub sun3
9150 % sh config.sub decstation
9152 % sh config.sub hp300bsd
9154 % sh config.sub i386v
9156 % sh config.sub i786v
9157 Invalid configuration `i786v': machine `i786v' not recognized
9161 @code{config.sub} is also distributed in the @value{GDBN} source
9162 directory (@file{gdb-@value{GDBVN}}, for version @value{GDBVN}).
9164 @node configure Options
9165 @section @code{configure} options
9167 Here is a summary of the @code{configure} options and arguments that
9168 are most often useful for building @value{GDBN}. @code{configure} also has
9169 several other options not listed here. @inforef{What Configure
9170 Does,,configure.info}, for a full explanation of @code{configure}.
9173 configure @r{[}--help@r{]}
9174 @r{[}--prefix=@var{dir}@r{]}
9175 @r{[}--srcdir=@var{dirname}@r{]}
9176 @r{[}--norecursion@r{]} @r{[}--rm@r{]}
9177 @r{[}--target=@var{target}@r{]} @var{host}
9181 You may introduce options with a single @samp{-} rather than
9182 @samp{--} if you prefer; but you may abbreviate option names if you use
9187 Display a quick summary of how to invoke @code{configure}.
9189 @item -prefix=@var{dir}
9190 Configure the source to install programs and files under directory
9193 @c avoid splitting the warning from the explanation:
9195 @item --srcdir=@var{dirname}
9196 @strong{Warning: using this option requires @sc{gnu} @code{make}, or another
9197 @code{make} that implements the @code{VPATH} feature.}@*
9198 Use this option to make configurations in directories separate from the
9199 @value{GDBN} source directories. Among other things, you can use this to
9200 build (or maintain) several configurations simultaneously, in separate
9201 directories. @code{configure} writes configuration specific files in
9202 the current directory, but arranges for them to use the source in the
9203 directory @var{dirname}. @code{configure} creates directories under
9204 the working directory in parallel to the source directories below
9208 Configure only the directory level where @code{configure} is executed; do not
9209 propagate configuration to subdirectories.
9212 @emph{Remove} files otherwise built during configuration.
9214 @c This does not work (yet if ever). FIXME.
9215 @c @item --parse=@var{lang} @dots{}
9216 @c Configure the @value{GDBN} expression parser to parse the listed languages.
9217 @c @samp{all} configures @value{GDBN} for all supported languages. To get a
9218 @c list of all supported languages, omit the argument. Without this
9219 @c option, @value{GDBN} is configured to parse all supported languages.
9221 @item --target=@var{target}
9222 Configure @value{GDBN} for cross-debugging programs running on the specified
9223 @var{target}. Without this option, @value{GDBN} is configured to debug
9224 programs that run on the same machine (@var{host}) as @value{GDBN} itself.
9226 There is no convenient way to generate a list of all available targets.
9228 @item @var{host} @dots{}
9229 Configure @value{GDBN} to run on the specified @var{host}.
9231 There is no convenient way to generate a list of all available hosts.
9235 @code{configure} accepts other options, for compatibility with
9236 configuring other @sc{gnu} tools recursively; but these are the only
9237 options that affect @value{GDBN} or its supporting libraries.
9246 % I think something like @colophon should be in texinfo. In the
9248 \long\def\colophon{\hbox to0pt{}\vfill
9249 \centerline{The body of this manual is set in}
9250 \centerline{\fontname\tenrm,}
9251 \centerline{with headings in {\bf\fontname\tenbf}}
9252 \centerline{and examples in {\tt\fontname\tentt}.}
9253 \centerline{{\it\fontname\tenit\/},}
9254 \centerline{{\bf\fontname\tenbf}, and}
9255 \centerline{{\sl\fontname\tensl\/}}
9256 \centerline{are used for emphasis.}\vfill}
9258 % Blame: pesch@cygnus.com, 1991.