1 \input texinfo @c -*-texinfo-*-
2 @c Copyright 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998
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
34 @c !!set GDB manual's edition---not the same as GDB version!
37 @c !!set GDB manual's revision date
41 @c THIS MANUAL REQUIRES TEXINFO-2 macros and info-makers to format properly.
44 @c !!set GDB manual's edition---not the same as GDB version!
47 @c !!set GDB manual's revision date
48 @set DATE November 1997
51 @set HPVER HP WDB Version 0.75
55 @c This is a dir.info fragment to support semi-automated addition of
56 @c manuals to an info tree. zoo@cygnus.com is developing this facility.
59 * Gdb: (gdb). The @sc{gnu} debugger.
66 This file documents the @sc{gnu} debugger @value{GDBN}.
69 This is the @value{EDITION} Edition, @value{DATE},
70 of @cite{Debugging with @value{GDBN}: the @sc{gnu} Source-Level Debugger}
71 for @value{GDBN} Version @value{GDBVN}.
73 Copyright (C) 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998
74 Free Software Foundation, Inc.
76 Permission is granted to make and distribute verbatim copies of
77 this manual provided the copyright notice and this permission notice
78 are preserved on all copies.
81 Permission is granted to process this file through TeX and print the
82 results, provided the printed document carries copying permission
83 notice identical to this one except for the removal of this paragraph
84 (this paragraph not being relevant to the printed manual).
87 Permission is granted to copy and distribute modified versions of this
88 manual under the conditions for verbatim copying, provided also that the
89 entire resulting derived work is distributed under the terms of a
90 permission notice identical to this one.
92 Permission is granted to copy and distribute translations of this manual
93 into another language, under the above conditions for modified versions.
97 @title Debugging with @value{GDBN}
98 @subtitle The @sc{gnu} Source-Level Debugger
100 @subtitle (@value{TARGET})
104 @subtitle @value{EDITION} Edition, for @value{GDBN} version @value{GDBVN}
105 @subtitle @value{DATE}
106 @author Richard M. Stallman and Roland H. Pesch
109 @subtitle Edition @value{EDITION}, for @value{HPVER} (based on @value{GDBN} @value{GDBVN})
110 @subtitle @value{DATE}
111 @author Richard M. Stallman and Roland H. Pesch (modified by HP)
117 \hfill (Send bugs and comments on @value{GDBN} to bug-gdb\@prep.ai.mit.edu.)\par
118 \hfill {\it Debugging with @value{GDBN}}\par
119 \hfill \TeX{}info \texinfoversion\par
120 \hfill doc\@cygnus.com\par
127 \hfill {\it Debugging with @value{GDBN}}\par
128 \hfill \TeX{}info \texinfoversion\par
133 @vskip 0pt plus 1filll
134 Copyright @copyright{} 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998
135 Free Software Foundation, Inc.
138 Published by the Free Software Foundation @*
139 59 Temple Place - Suite 330, @*
140 Boston, MA 02111-1307 USA @*
141 Printed copies are available for $20 each. @*
142 ISBN 1-882114-11-6 @*
145 Permission is granted to make and distribute verbatim copies of
146 this manual provided the copyright notice and this permission notice
147 are preserved on all copies.
149 Permission is granted to copy and distribute modified versions of this
150 manual under the conditions for verbatim copying, provided also that the
151 entire resulting derived work is distributed under the terms of a
152 permission notice identical to this one.
154 Permission is granted to copy and distribute translations of this manual
155 into another language, under the above conditions for modified versions.
160 @node Top, Summary, (dir), (dir)
161 @top Debugging with @value{GDBN}
163 This file describes @value{GDBN}, the @sc{gnu} symbolic debugger.
165 This is the @value{EDITION} Edition, @value{DATE}, for @value{GDBN} Version
168 Copyright (C) 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1997
169 Free Software Foundation, Inc.
171 * Summary:: Summary of @value{GDBN}
173 * Sample Session:: A sample @value{GDBN} session
176 * Invocation:: Getting in and out of @value{GDBN}
177 * Commands:: @value{GDBN} commands
178 * Running:: Running programs under @value{GDBN}
179 * Stopping:: Stopping and continuing
180 * Stack:: Examining the stack
181 * Source:: Examining source files
182 * Data:: Examining data
184 * Languages:: Using @value{GDBN} with different languages
188 * C:: C language support
191 * Symbols:: Examining the symbol table
192 * Altering:: Altering execution
193 * GDB Files:: @value{GDBN} files
194 * Targets:: Specifying a debugging target
195 * Controlling GDB:: Controlling @value{GDBN}
196 * Sequences:: Canned sequences of commands
198 * Emacs:: Using @value{GDBN} under @sc{gnu} Emacs
205 * GDB Bugs:: Reporting bugs in @value{GDBN}
208 * Renamed Commands:: @c @end ifset
213 @ifclear PRECONFIGURED
215 * Formatting Documentation:: How to format and print @value{GDBN} documentation
220 * Command Line Editing:: Command Line Editing
221 * Using History:: Using History Interactively
222 * Installing GDB:: Installing GDB
225 --- The Detailed Node Listing ---
227 Summary of @value{GDBN}
229 * Free Software:: Freely redistributable software
230 * Contributors:: Contributors to GDB
232 Getting In and Out of @value{GDBN}
234 * Invoking GDB:: How to start @value{GDBN}
235 * Quitting GDB:: How to quit @value{GDBN}
236 * Shell Commands:: How to use shell commands inside @value{GDBN}
238 Invoking @value{GDBN}
240 * File Options:: Choosing files
241 * Mode Options:: Choosing modes
243 @value{GDBN} Commands
245 * Command Syntax:: How to give commands to @value{GDBN}
246 * Completion:: Command completion
247 * Help:: How to ask @value{GDBN} for help
249 Running Programs Under @value{GDBN}
251 * Compilation:: Compiling for debugging
252 * Starting:: Starting your program
254 * Arguments:: Your program's arguments
255 * Environment:: Your program's environment
258 * Working Directory:: Your program's working directory
259 * Input/Output:: Your program's input and output
260 * Attach:: Debugging an already-running process
261 * Kill Process:: Killing the child process
263 * Process Information:: Additional process information
266 * Threads:: Debugging programs with multiple threads
267 * Processes:: Debugging programs with multiple processes
269 Stopping and Continuing
273 * Breakpoints:: Breakpoints, watchpoints, and exceptions
277 * Breakpoints:: Breakpoints, watchpoints, and catchpoints
283 * Breakpoints:: Breakpoints and watchpoints
286 * Continuing and Stepping:: Resuming execution
292 * Thread Stops:: Stopping and starting multi-thread programs
295 Breakpoints and watchpoints
297 * Set Breaks:: Setting breakpoints
298 * Set Watchpoints:: Setting watchpoints
301 * Exception Handling:: Breakpoints and exceptions
305 * Set Catchpoints:: Setting catchpoints
310 * Delete Breaks:: Deleting breakpoints
311 * Disabling:: Disabling breakpoints
312 * Conditions:: Break conditions
313 * Break Commands:: Breakpoint command lists
315 * Breakpoint Menus:: Breakpoint menus
320 * Frames:: Stack frames
321 * Backtrace:: Backtraces
322 * Selection:: Selecting a frame
323 * Frame Info:: Information on a frame
325 * MIPS Stack:: MIPS machines and the function stack
328 Examining Source Files
330 * List:: Printing source lines
332 * Search:: Searching source files
335 * Source Path:: Specifying source directories
336 * Machine Code:: Source and machine code
340 * Expressions:: Expressions
341 * Variables:: Program variables
342 * Arrays:: Artificial arrays
343 * Output Formats:: Output formats
344 * Memory:: Examining memory
345 * Auto Display:: Automatic display
346 * Print Settings:: Print settings
347 * Value History:: Value history
348 * Convenience Vars:: Convenience variables
349 * Registers:: Registers
351 * Floating Point Hardware:: Floating point hardware
354 Using @value{GDBN} with Different Languages
356 * Setting:: Switching between source languages
357 * Show:: Displaying the language
359 * Checks:: Type and range checks
362 * Support:: Supported languages
364 Switching between source languages
366 * Filenames:: Filename extensions and languages.
367 * Manually:: Setting the working language manually
368 * Automatically:: Having @value{GDBN} infer the source language
371 Type and range checking
373 * Type Checking:: An overview of type checking
374 * Range Checking:: An overview of range checking
384 * C Operators:: C operators
389 * C Operators:: C and C++ operators
390 * C Constants:: C and C++ constants
391 * Cplus expressions:: C++ expressions
392 * C Defaults:: Default settings for C and C++
394 * C Checks:: C and C++ type and range checks
396 * Debugging C:: @value{GDBN} and C
397 * Debugging C plus plus:: @value{GDBN} features for C++
402 * M2 Operators:: Built-in operators
403 * Built-In Func/Proc:: Built-in functions and procedures
404 * M2 Constants:: Modula-2 constants
405 * M2 Defaults:: Default settings for Modula-2
406 * Deviations:: Deviations from standard Modula-2
407 * M2 Checks:: Modula-2 type and range checks
408 * M2 Scope:: The scope operators @code{::} and @code{.}
409 * GDB/M2:: @value{GDBN} and Modula-2
414 * Assignment:: Assignment to variables
415 * Jumping:: Continuing at a different address
417 * Signaling:: Giving your program a signal
420 * Returning:: Returning from a function
421 * Calling:: Calling your program's functions
422 * Patching:: Patching your program
426 * Files:: Commands to specify files
427 * Symbol Errors:: Errors reading symbol files
429 Specifying a Debugging Target
431 * Active Targets:: Active targets
432 * Target Commands:: Commands for managing targets
434 * Byte Order:: Choosing target byte order
435 * Remote:: Remote debugging
441 * Remote Serial:: @value{GDBN} remote serial protocol
445 * i960-Nindy Remote:: @value{GDBN} with a remote i960 (Nindy)
449 * UDI29K Remote:: The UDI protocol for AMD29K
450 * EB29K Remote:: The EBMON protocol for AMD29K
454 * VxWorks Remote:: @value{GDBN} and VxWorks
458 * ST2000 Remote:: @value{GDBN} with a Tandem ST2000
462 * Hitachi Remote:: @value{GDBN} and Hitachi Microprocessors
466 * MIPS Remote:: @value{GDBN} and MIPS boards
470 * Simulator:: Simulated CPU target
473 Controlling @value{GDBN}
476 * Editing:: Command editing
477 * History:: Command history
478 * Screen Size:: Screen size
480 * Messages/Warnings:: Optional warnings and messages
482 Canned Sequences of Commands
484 * Define:: User-defined commands
485 * Hooks:: User-defined command hooks
486 * Command Files:: Command files
487 * Output:: Commands for controlled output
489 Reporting Bugs in @value{GDBN}
491 * Bug Criteria:: Have you found a bug?
492 * Bug Reporting:: How to report bugs
494 Installing @value{GDBN}
496 * Separate Objdir:: Compiling @value{GDBN} in another directory
497 * Config Names:: Specifying names for hosts and targets
498 * Configure Options:: Summary of options for configure
503 @node Summary, Sample Session, Top, Top
504 @unnumbered Summary of @value{GDBN}
506 The purpose of a debugger such as @value{GDBN} is to allow you to see what is
507 going on ``inside'' another program while it executes---or what another
508 program was doing at the moment it crashed.
510 @value{GDBN} can do four main kinds of things (plus other things in support of
511 these) to help you catch bugs in the act:
515 Start your program, specifying anything that might affect its behavior.
518 Make your program stop on specified conditions.
521 Examine what has happened, when your program has stopped.
524 Change things in your program, so you can experiment with correcting the
525 effects of one bug and go on to learn about another.
529 You can use @value{GDBN} to debug programs written in C or C++.
530 @c "MOD2" used as a "miscellaneous languages" flag here.
531 @c This is acceptable while there is no real doc for Chill and Pascal.
533 For more information, see @ref{Support,,Supported languages}.
536 For more information, see @ref{C,,C and C++}.
538 Support for Modula-2 and Chill is partial. For information on Modula-2,
539 see @ref{Modula-2,,Modula-2}. There is no further documentation on Chill yet.
541 Debugging Pascal programs which use sets, subranges, file variables, or nested
542 functions does not currently work. @value{GDBN} does not support
543 entering expressions, printing values, or similar features using Pascal syntax.
548 @value{GDBN} can be used to debug programs written in Fortran, although
549 it does not yet support entering expressions, printing values, or
550 similar features using Fortran syntax. It may be necessary to refer to
551 some variables with a trailing underscore.
556 This version of the manual documents HP Wildebeest (WDB) Version 0.75,
557 implemented on HP 9000 systems running Release 10.20, 10.30, or 11.0 of
558 the HP-UX operating system. HP WDB 0.75 can be used to debug code
559 generated by the HP ANSI C and HP ANSI C++ compilers as well as the
560 @sc{gnu} C and C++ compilers. It does not support the debugging of
561 Fortran, Modula-2, or Chill programs.
565 * Free Software:: Freely redistributable software
566 * Contributors:: Contributors to GDB
569 @node Free Software, Contributors, Summary, Summary
570 @unnumberedsec Free software
572 @value{GDBN} is @dfn{free software}, protected by the @sc{gnu}
573 General Public License
574 (GPL). The GPL gives you the freedom to copy or adapt a licensed
575 program---but every person getting a copy also gets with it the
576 freedom to modify that copy (which means that they must get access to
577 the source code), and the freedom to distribute further copies.
578 Typical software companies use copyrights to limit your freedoms; the
579 Free Software Foundation uses the GPL to preserve these freedoms.
581 Fundamentally, the General Public License is a license which says that
582 you have these freedoms and that you cannot take these freedoms away
585 @node Contributors, , Free Software, Summary
586 @unnumberedsec Contributors to GDB
588 Richard Stallman was the original author of GDB, and of many other @sc{gnu}
589 programs. Many others have contributed to its development. This
590 section attempts to credit major contributors. One of the virtues of
591 free software is that everyone is free to contribute to it; with
592 regret, we cannot actually acknowledge everyone here. The file
593 @file{ChangeLog} in the @value{GDBN} distribution approximates a blow-by-blow
596 Changes much prior to version 2.0 are lost in the mists of time.
599 @emph{Plea:} Additions to this section are particularly welcome. If you
600 or your friends (or enemies, to be evenhanded) have been unfairly
601 omitted from this list, we would like to add your names!
604 So that they may not regard their long labor as thankless, we
605 particularly thank those who shepherded GDB through major releases:
606 Stan Shebs (release 4.14),
607 Fred Fish (releases 4.13, 4.12, 4.11, 4.10, and 4.9),
608 Stu Grossman and John Gilmore (releases 4.8, 4.7, 4.6, 4.5, and 4.4),
609 John Gilmore (releases 4.3, 4.2, 4.1, 4.0, and 3.9);
610 Jim Kingdon (releases 3.5, 3.4, and 3.3);
611 and Randy Smith (releases 3.2, 3.1, and 3.0).
612 As major maintainer of @value{GDBN} for some period, each
613 contributed significantly to the structure, stability, and capabilities
614 of the entire debugger.
616 Richard Stallman, assisted at various times by Peter TerMaat, Chris
617 Hanson, and Richard Mlynarik, handled releases through 2.8.
620 Michael Tiemann is the author of most of the @sc{gnu} C++ support in GDB,
621 with significant additional contributions from Per Bothner. James
622 Clark wrote the @sc{gnu} C++ demangler. Early work on C++ was by Peter
623 TerMaat (who also did much general update work leading to release 3.0).
626 @value{GDBN} 4 uses the BFD subroutine library to examine multiple
627 object-file formats; BFD was a joint project of David V.
628 Henkel-Wallace, Rich Pixley, Steve Chamberlain, and John Gilmore.
630 David Johnson wrote the original COFF support; Pace Willison did
631 the original support for encapsulated COFF.
633 Brent Benson of Harris Computer Systems contributed DWARF 2 support.
635 Adam de Boor and Bradley Davis contributed the ISI Optimum V support.
636 Per Bothner, Noboyuki Hikichi, and Alessandro Forin contributed MIPS
638 Jean-Daniel Fekete contributed Sun 386i support.
639 Chris Hanson improved the HP9000 support.
640 Noboyuki Hikichi and Tomoyuki Hasei contributed Sony/News OS 3 support.
641 David Johnson contributed Encore Umax support.
642 Jyrki Kuoppala contributed Altos 3068 support.
643 Jeff Law contributed HP PA and SOM support.
644 Keith Packard contributed NS32K support.
645 Doug Rabson contributed Acorn Risc Machine support.
646 Bob Rusk contributed Harris Nighthawk CX-UX support.
647 Chris Smith contributed Convex support (and Fortran debugging).
648 Jonathan Stone contributed Pyramid support.
649 Michael Tiemann contributed SPARC support.
650 Tim Tucker contributed support for the Gould NP1 and Gould Powernode.
651 Pace Willison contributed Intel 386 support.
652 Jay Vosburgh contributed Symmetry support.
654 Rich Schaefer and Peter Schauer helped with support of SunOS shared
657 Jay Fenlason and Roland McGrath ensured that @value{GDBN} and GAS agree about
658 several machine instruction sets.
660 Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped develop
661 remote debugging. Intel Corporation, Wind River Systems, AMD, and ARM
662 contributed remote debugging modules for the i960, VxWorks, A29K UDI,
663 and RDI targets, respectively.
665 Brian Fox is the author of the readline libraries providing
666 command-line editing and command history.
668 Andrew Beers of SUNY Buffalo wrote the language-switching code,
670 the Modula-2 support,
672 and contributed the Languages chapter of this manual.
674 Fred Fish wrote most of the support for Unix System Vr4.
676 He also enhanced the command-completion support to cover C++ overloaded
680 Hitachi America, Ltd. sponsored the support for Hitachi microprocessors.
682 Kung Hsu, Jeff Law, and Rick Sladkey added support for hardware
685 Michael Snyder added support for tracepoints.
687 Stu Grossman wrote gdbserver.
689 Jim Kingdon, Peter Schauer, Ian Taylor, and Stu Grossman made
690 nearly innumerable bug fixes and cleanups throughout GDB.
692 Cygnus Solutions has sponsored GDB maintenance and much of its
693 development since 1991.
696 The following people at the Hewlett-Packard Company contributed
697 support for the PA-RISC 2.0 architecture, HP-UX 10.20, 10.30, and 11.0
698 (narrow mode), HP's implementation of kernel threads, HP's aC++
699 compiler, and the terminal user interface: Ben Krepp, Richard Title,
700 John Bishop, Susan Macchia, Kathy Mann, Satish Pai, India Paul, Steve
701 Rehrauer, and Elena Zannoni. Kim Haase provided HP-specific
702 information in this manual.
706 @node Sample Session, Invocation, Summary, Top
707 @chapter A Sample @value{GDBN} Session
709 You can use this manual at your leisure to read all about @value{GDBN}.
710 However, a handful of commands are enough to get started using the
711 debugger. This chapter illustrates those commands.
714 In this sample session, we emphasize user input like this: @b{input},
715 to make it easier to pick out from the surrounding output.
718 @c FIXME: this example may not be appropriate for some configs, where
719 @c FIXME...primary interest is in remote use.
721 One of the preliminary versions of @sc{gnu} @code{m4} (a generic macro
722 processor) exhibits the following bug: sometimes, when we change its
723 quote strings from the default, the commands used to capture one macro
724 definition within another stop working. In the following short @code{m4}
725 session, we define a macro @code{foo} which expands to @code{0000}; we
726 then use the @code{m4} built-in @code{defn} to define @code{bar} as the
727 same thing. However, when we change the open quote string to
728 @code{<QUOTE>} and the close quote string to @code{<UNQUOTE>}, the same
729 procedure fails to define a new synonym @code{baz}:
738 @b{define(bar,defn(`foo'))}
742 @b{changequote(<QUOTE>,<UNQUOTE>)}
744 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
747 m4: End of input: 0: fatal error: EOF in string
751 Let us use @value{GDBN} to try to see what is going on.
755 $ @b{@value{GDBP} m4}
756 @c FIXME: this falsifies the exact text played out, to permit smallbook
757 @c FIXME... format to come out better.
758 @value{GDBN} is free software and you are welcome to distribute copies
759 of it under certain conditions; type "show copying" to see
761 There is absolutely no warranty for @value{GDBN}; type "show warranty"
764 @value{GDBN} @value{GDBVN}, Copyright 1995 Free Software Foundation, Inc...
770 $ @b{@value{GDBP} m4}
771 Wildebeest is free software and you are welcome to distribute copies of
772 it under certain conditions; type "show copying" to see the conditions.
773 There is absolutely no warranty for Wildebeest; type "show warranty"
776 Hewlett-Packard Wildebeest 0.75 (based on GDB 4.16)
777 (built for PA-RISC 1.1 or 2.0, HP-UX 10.20)
778 Copyright 1996, 1997 Free Software Foundation, Inc.
784 @value{GDBN} reads only enough symbol data to know where to find the
785 rest when needed; as a result, the first prompt comes up very quickly.
786 We now tell @value{GDBN} to use a narrower display width than usual, so
787 that examples fit in this manual.
790 (@value{GDBP}) @b{set width 70}
794 We need to see how the @code{m4} built-in @code{changequote} works.
795 Having looked at the source, we know the relevant subroutine is
796 @code{m4_changequote}, so we set a breakpoint there with the @value{GDBN}
797 @code{break} command.
800 (@value{GDBP}) @b{break m4_changequote}
801 Breakpoint 1 at 0x62f4: file builtin.c, line 879.
805 Using the @code{run} command, we start @code{m4} running under @value{GDBN}
806 control; as long as control does not reach the @code{m4_changequote}
807 subroutine, the program runs as usual:
810 (@value{GDBP}) @b{run}
811 Starting program: /work/Editorial/gdb/gnu/m4/m4
819 To trigger the breakpoint, we call @code{changequote}. @value{GDBN}
820 suspends execution of @code{m4}, displaying information about the
821 context where it stops.
824 @b{changequote(<QUOTE>,<UNQUOTE>)}
826 Breakpoint 1, m4_changequote (argc=3, argv=0x33c70)
828 879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]),argc,1,3))
832 Now we use the command @code{n} (@code{next}) to advance execution to
833 the next line of the current function.
837 882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\
842 @code{set_quotes} looks like a promising subroutine. We can go into it
843 by using the command @code{s} (@code{step}) instead of @code{next}.
844 @code{step} goes to the next line to be executed in @emph{any}
845 subroutine, so it steps into @code{set_quotes}.
849 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
851 530 if (lquote != def_lquote)
855 The display that shows the subroutine where @code{m4} is now
856 suspended (and its arguments) is called a stack frame display. It
857 shows a summary of the stack. We can use the @code{backtrace}
858 command (which can also be spelled @code{bt}), to see where we are
859 in the stack as a whole: the @code{backtrace} command displays a
860 stack frame for each active subroutine.
863 (@value{GDBP}) @b{bt}
864 #0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
866 #1 0x6344 in m4_changequote (argc=3, argv=0x33c70)
868 #2 0x8174 in expand_macro (sym=0x33320) at macro.c:242
869 #3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30)
871 #4 0x79dc in expand_input () at macro.c:40
872 #5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195
876 We step through a few more lines to see what happens. The first two
877 times, we can use @samp{s}; the next two times we use @code{n} to avoid
878 falling into the @code{xstrdup} subroutine.
882 0x3b5c 532 if (rquote != def_rquote)
884 0x3b80 535 lquote = (lq == nil || *lq == '\0') ? \
885 def_lquote : xstrdup(lq);
887 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
890 538 len_lquote = strlen(rquote);
894 The last line displayed looks a little odd; we can examine the variables
895 @code{lquote} and @code{rquote} to see if they are in fact the new left
896 and right quotes we specified. We use the command @code{p}
897 (@code{print}) to see their values.
900 (@value{GDBP}) @b{p lquote}
901 $1 = 0x35d40 "<QUOTE>"
902 (@value{GDBP}) @b{p rquote}
903 $2 = 0x35d50 "<UNQUOTE>"
907 @code{lquote} and @code{rquote} are indeed the new left and right quotes.
908 To look at some context, we can display ten lines of source
909 surrounding the current line with the @code{l} (@code{list}) command.
915 535 lquote = (lq == nil || *lq == '\0') ? def_lquote\
917 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
920 538 len_lquote = strlen(rquote);
921 539 len_rquote = strlen(lquote);
928 Let us step past the two lines that set @code{len_lquote} and
929 @code{len_rquote}, and then examine the values of those variables.
933 539 len_rquote = strlen(lquote);
936 (@value{GDBP}) @b{p len_lquote}
938 (@value{GDBP}) @b{p len_rquote}
943 That certainly looks wrong, assuming @code{len_lquote} and
944 @code{len_rquote} are meant to be the lengths of @code{lquote} and
945 @code{rquote} respectively. We can set them to better values using
946 the @code{p} command, since it can print the value of
947 any expression---and that expression can include subroutine calls and
951 (@value{GDBP}) @b{p len_lquote=strlen(lquote)}
953 (@value{GDBP}) @b{p len_rquote=strlen(rquote)}
958 Is that enough to fix the problem of using the new quotes with the
959 @code{m4} built-in @code{defn}? We can allow @code{m4} to continue
960 executing with the @code{c} (@code{continue}) command, and then try the
961 example that caused trouble initially:
967 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
974 Success! The new quotes now work just as well as the default ones. The
975 problem seems to have been just the two typos defining the wrong
976 lengths. We allow @code{m4} exit by giving it an EOF as input:
980 Program exited normally.
984 The message @samp{Program exited normally.} is from @value{GDBN}; it
985 indicates @code{m4} has finished executing. We can end our @value{GDBN}
986 session with the @value{GDBN} @code{quit} command.
989 (@value{GDBP}) @b{quit}
993 @node Invocation, Commands, Sample Session, Top
994 @chapter Getting In and Out of @value{GDBN}
996 This chapter discusses how to start @value{GDBN}, and how to get out of it.
1000 type @samp{@value{GDBP}} to start GDB.
1002 type @kbd{quit} or @kbd{C-d} to exit.
1006 * Invoking GDB:: How to start @value{GDBN}
1007 * Quitting GDB:: How to quit @value{GDBN}
1008 * Shell Commands:: How to use shell commands inside @value{GDBN}
1011 @node Invoking GDB, Quitting GDB, Invocation, Invocation
1012 @section Invoking @value{GDBN}
1015 For details on starting up @value{GDBP} as a
1016 remote debugger attached to a Hitachi microprocessor, see @ref{Hitachi
1017 Remote,,@value{GDBN} and Hitachi Microprocessors}.
1020 Invoke @value{GDBN} by running the program @code{@value{GDBP}}. Once started,
1021 @value{GDBN} reads commands from the terminal until you tell it to exit.
1023 You can also run @code{@value{GDBP}} with a variety of arguments and options,
1024 to specify more of your debugging environment at the outset.
1027 The command-line options described here are designed
1028 to cover a variety of situations; in some environments, some of these
1029 options may effectively be unavailable.
1032 The most usual way to start @value{GDBN} is with one argument,
1033 specifying an executable program:
1036 @value{GDBP} @var{program}
1041 You can also start with both an executable program and a core file
1045 @value{GDBP} @var{program} @var{core}
1048 You can, instead, specify a process ID as a second argument, if you want
1049 to debug a running process:
1052 @value{GDBP} @var{program} 1234
1056 would attach @value{GDBN} to process @code{1234} (unless you also have a file
1057 named @file{1234}; @value{GDBN} does check for a core file first).
1060 Taking advantage of the second command-line argument requires a fairly
1061 complete operating system; when you use @value{GDBN} as a remote debugger
1062 attached to a bare board, there may not be any notion of ``process'',
1063 and there is often no way to get a core dump.
1067 You can run @code{gdb} without printing the front material, which describes
1068 @value{GDBN}'s non-warranty, by specifying @code{-silent}:
1071 @value{GDBP} -silent
1075 You can further control how @value{GDBN} starts up by using command-line
1076 options. @value{GDBN} itself can remind you of the options available.
1086 to display all available options and briefly describe their use
1087 (@samp{@value{GDBP} -h} is a shorter equivalent).
1089 All options and command line arguments you give are processed
1090 in sequential order. The order makes a difference when the
1091 @samp{-x} option is used.
1097 * Remote Serial:: @value{GDBN} remote serial protocol
1100 * i960-Nindy Remote:: @value{GDBN} with a remote i960 (Nindy)
1103 * UDI29K Remote:: The UDI protocol for AMD29K
1104 * EB29K Remote:: The EBMON protocol for AMD29K
1107 * VxWorks Remote:: @value{GDBN} and VxWorks
1110 * ST2000 Remote:: @value{GDBN} with a Tandem ST2000
1113 * Hitachi Remote:: @value{GDBN} and Hitachi Microprocessors
1116 * MIPS Remote:: @value{GDBN} and MIPS boards
1119 * Sparclet Remote:: @value{GDBN} and Sparclet boards
1122 * Simulator:: Simulated CPU target
1125 @c remnant makeinfo bug requires this blank line after *two* end-ifblahs:
1127 * File Options:: Choosing files
1128 * Mode Options:: Choosing modes
1133 @include remote.texi
1138 @subsection Choosing files
1141 When @value{GDBN} starts, it reads any arguments other than options as
1142 specifying an executable file and core file (or process ID). This is
1143 the same as if the arguments were specified by the @samp{-se} and
1144 @samp{-c} options respectively. (@value{GDBN} reads the first argument
1145 that does not have an associated option flag as equivalent to the
1146 @samp{-se} option followed by that argument; and the second argument
1147 that does not have an associated option flag, if any, as equivalent to
1148 the @samp{-c} option followed by that argument.)
1151 When @value{GDBN} starts, it reads any argument other than options as
1152 specifying an executable file. This is the same as if the argument was
1153 specified by the @samp{-se} option.
1156 Many options have both long and short forms; both are shown in the
1157 following list. @value{GDBN} also recognizes the long forms if you truncate
1158 them, so long as enough of the option is present to be unambiguous.
1159 (If you prefer, you can flag option arguments with @samp{--} rather
1160 than @samp{-}, though we illustrate the more usual convention.)
1163 @item -symbols @var{file}
1164 @itemx -s @var{file}
1165 Read symbol table from file @var{file}.
1167 @item -exec @var{file}
1168 @itemx -e @var{file}
1169 Use file @var{file} as the executable file to execute when
1174 appropriate, and for examining pure data in conjunction with a core
1178 @item -se @var{file}
1179 Read symbol table from file @var{file} and use it as the executable
1183 @item -core @var{file}
1184 @itemx -c @var{file}
1185 Use file @var{file} as a core dump to examine.
1187 @item -c @var{number}
1188 Connect to process ID @var{number}, as with the @code{attach} command
1189 (unless there is a file in core-dump format named @var{number}, in which
1190 case @samp{-c} specifies that file as a core dump to read).
1193 @item -command @var{file}
1194 @itemx -x @var{file}
1195 Execute @value{GDBN} commands from file @var{file}. @xref{Command
1196 Files,, Command files}.
1198 @item -directory @var{directory}
1199 @itemx -d @var{directory}
1200 Add @var{directory} to the path to search for source files.
1206 @emph{Warning: this option depends on operating system facilities that are not
1207 supported on all systems.}@*
1208 If memory-mapped files are available on your system through the @code{mmap}
1209 system call, you can use this option
1210 to have @value{GDBN} write the symbols from your
1211 program into a reusable file in the current directory. If the program you are debugging is
1212 called @file{/tmp/fred}, the mapped symbol file is @file{./fred.syms}.
1213 Future @value{GDBN} debugging sessions notice the presence of this file,
1214 and can quickly map in symbol information from it, rather than reading
1215 the symbol table from the executable program.
1217 The @file{.syms} file is specific to the host machine where @value{GDBN}
1218 is run. It holds an exact image of the internal @value{GDBN} symbol
1219 table. It cannot be shared across multiple host platforms.
1226 Read each symbol file's entire symbol table immediately, rather than
1227 the default, which is to read it incrementally as it is needed.
1228 This makes startup slower, but makes future operations faster.
1234 The @code{-mapped} and @code{-readnow} options are typically combined in
1235 order to build a @file{.syms} file that contains complete symbol
1236 information. (@xref{Files,,Commands to specify files}, for
1237 information on @file{.syms} files.) A simple GDB invocation to do
1238 nothing but build a @file{.syms} file for future use is:
1241 gdb -batch -nx -mapped -readnow programname
1246 @node Mode Options, , File Options, Invoking GDB
1247 @subsection Choosing modes
1249 You can run @value{GDBN} in various alternative modes---for example, in
1250 batch mode or quiet mode.
1255 Do not execute commands from any initialization files (normally called
1256 @file{@value{GDBINIT}}). Normally, the commands in these files are
1257 executed after all the command options and arguments have been
1258 processed. @xref{Command Files,,Command files}.
1262 ``Quiet''. Do not print the introductory and copyright messages. These
1263 messages are also suppressed in batch mode.
1266 Run in batch mode. Exit with status @code{0} after processing all the
1267 command files specified with @samp{-x} (and all commands from
1268 initialization files, if not inhibited with @samp{-n}). Exit with
1269 nonzero status if an error occurs in executing the @value{GDBN} commands
1270 in the command files.
1272 Batch mode may be useful for running @value{GDBN} as a filter, for example to
1273 download and run a program on another computer; in order to make this
1274 more useful, the message
1277 Program exited normally.
1281 (which is ordinarily issued whenever a program running under @value{GDBN} control
1282 terminates) is not issued when running in batch mode.
1284 @item -cd @var{directory}
1285 Run @value{GDBN} using @var{directory} as its working directory,
1286 instead of the current directory.
1289 @item -context @var{authentication}
1290 When the Energize programming system starts up @value{GDBN}, it uses this
1291 option to trigger an alternate mode of interaction.
1292 @var{authentication} is a pair of numeric codes that identify @value{GDBN}
1293 as a client in the Energize environment. Avoid this option when you run
1294 @value{GDBN} directly from the command line. See @ref{Energize,,Using
1295 @value{GDBN} with Energize} for more discussion of using @value{GDBN} with Energize.
1301 @sc{gnu} Emacs sets this option when it runs @value{GDBN} as a subprocess. It tells @value{GDBN}
1302 to output the full file name and line number in a standard,
1303 recognizable fashion each time a stack frame is displayed (which
1304 includes each time your program stops). This recognizable format looks
1305 like two @samp{\032} characters, followed by the file name, line number
1306 and character position separated by colons, and a newline. The
1307 Emacs-to-@value{GDBN} interface program uses the two @samp{\032} characters as
1308 a signal to display the source code for the frame.
1314 Set the line speed (baud rate or bits per second) of any serial
1315 interface used by @value{GDBN} for remote debugging.
1318 @item -tty @var{device}
1319 Run using @var{device} for your program's standard input and output.
1320 @c FIXME: kingdon thinks there is more to -tty. Investigate.
1325 Use a Terminal User Interface. For information, use your Web browser to
1326 read the file @file{TUI.html}, which is usually installed in the
1327 directory @code{/opt/langtools/wdb/doc} on HP-UX systems. Do not use
1328 this option if you run @value{GDBN} from Emacs (see @pxref{Emacs, ,Using
1329 @value{GDBN} under @sc{gnu} Emacs}).
1332 Run in XDB compatibility mode, allowing the use of certain XDB commands.
1333 For information, see the file @file{xdb_trans.html}, which is usually
1334 installed in the directory @code{/opt/langtools/wdb/doc} on HP-UX
1339 @node Quitting GDB, Shell Commands, Invoking GDB, Invocation
1340 @section Quitting @value{GDBN}
1341 @cindex exiting @value{GDBN}
1342 @cindex leaving @value{GDBN}
1345 @kindex quit @r{[}@var{expression}@r{]}
1348 To exit @value{GDBN}, use the @code{quit} command (abbreviated @code{q}), or
1349 type an end-of-file character (usually @kbd{C-d}). If you do not supply
1350 @var{expression}, @value{GDBN} will terminate normally; otherwise it will
1351 terminate using the result of @var{expression} as the error code.
1355 An interrupt (often @kbd{C-c}) does not exit from @value{GDBN}, but rather
1356 terminates the action of any @value{GDBN} command that is in progress and
1357 returns to @value{GDBN} command level. It is safe to type the interrupt
1358 character at any time because @value{GDBN} does not allow it to take effect
1359 until a time when it is safe.
1362 If you have been using @value{GDBN} to control an attached process or
1363 device, you can release it with the @code{detach} command
1364 (@pxref{Attach, ,Debugging an already-running process}).
1367 @node Shell Commands, , Quitting GDB, Invocation
1368 @section Shell commands
1370 If you need to execute occasional shell commands during your
1371 debugging session, there is no need to leave or suspend @value{GDBN}; you can
1372 just use the @code{shell} command.
1376 @cindex shell escape
1377 @item shell @var{command string}
1378 Invoke a standard shell to execute @var{command string}.
1380 If it exists, the environment variable @code{SHELL} determines which
1381 shell to run. Otherwise @value{GDBN} uses @code{/bin/sh}.
1385 The utility @code{make} is often needed in development environments.
1386 You do not have to use the @code{shell} command for this purpose in
1391 @cindex calling make
1392 @item make @var{make-args}
1393 Execute the @code{make} program with the specified
1394 arguments. This is equivalent to @samp{shell make @var{make-args}}.
1397 @node Commands, Running, Invocation, Top
1398 @chapter @value{GDBN} Commands
1400 You can abbreviate a @value{GDBN} command to the first few letters of the command
1401 name, if that abbreviation is unambiguous; and you can repeat certain
1402 @value{GDBN} commands by typing just @key{RET}. You can also use the @key{TAB}
1403 key to get @value{GDBN} to fill out the rest of a word in a command (or to
1404 show you the alternatives available, if there is more than one possibility).
1407 * Command Syntax:: How to give commands to @value{GDBN}
1408 * Completion:: Command completion
1409 * Help:: How to ask @value{GDBN} for help
1412 @node Command Syntax, Completion, Commands, Commands
1413 @section Command syntax
1415 A @value{GDBN} command is a single line of input. There is no limit on
1416 how long it can be. It starts with a command name, which is followed by
1417 arguments whose meaning depends on the command name. For example, the
1418 command @code{step} accepts an argument which is the number of times to
1419 step, as in @samp{step 5}. You can also use the @code{step} command
1420 with no arguments. Some command names do not allow any arguments.
1422 @cindex abbreviation
1423 @value{GDBN} command names may always be truncated if that abbreviation is
1424 unambiguous. Other possible command abbreviations are listed in the
1425 documentation for individual commands. In some cases, even ambiguous
1426 abbreviations are allowed; for example, @code{s} is specially defined as
1427 equivalent to @code{step} even though there are other commands whose
1428 names start with @code{s}. You can test abbreviations by using them as
1429 arguments to the @code{help} command.
1431 @cindex repeating commands
1433 A blank line as input to @value{GDBN} (typing just @key{RET}) means to
1434 repeat the previous command. Certain commands (for example, @code{run})
1435 will not repeat this way; these are commands whose unintentional
1436 repetition might cause trouble and which you are unlikely to want to
1439 The @code{list} and @code{x} commands, when you repeat them with
1440 @key{RET}, construct new arguments rather than repeating
1441 exactly as typed. This permits easy scanning of source or memory.
1443 @value{GDBN} can also use @key{RET} in another way: to partition lengthy
1444 output, in a way similar to the common utility @code{more}
1445 (@pxref{Screen Size,,Screen size}). Since it is easy to press one
1446 @key{RET} too many in this situation, @value{GDBN} disables command
1447 repetition after any command that generates this sort of display.
1451 Any text from a @kbd{#} to the end of the line is a comment; it does
1452 nothing. This is useful mainly in command files (@pxref{Command
1453 Files,,Command files}).
1455 @node Completion, Help, Command Syntax, Commands
1456 @section Command completion
1459 @cindex word completion
1460 @value{GDBN} can fill in the rest of a word in a command for you, if there is
1461 only one possibility; it can also show you what the valid possibilities
1462 are for the next word in a command, at any time. This works for @value{GDBN}
1463 commands, @value{GDBN} subcommands, and the names of symbols in your program.
1465 Press the @key{TAB} key whenever you want @value{GDBN} to fill out the rest
1466 of a word. If there is only one possibility, @value{GDBN} fills in the
1467 word, and waits for you to finish the command (or press @key{RET} to
1468 enter it). For example, if you type
1470 @c FIXME "@key" does not distinguish its argument sufficiently to permit
1471 @c complete accuracy in these examples; space introduced for clarity.
1472 @c If texinfo enhancements make it unnecessary, it would be nice to
1473 @c replace " @key" by "@key" in the following...
1475 (@value{GDBP}) info bre @key{TAB}
1479 @value{GDBN} fills in the rest of the word @samp{breakpoints}, since that is
1480 the only @code{info} subcommand beginning with @samp{bre}:
1483 (@value{GDBP}) info breakpoints
1487 You can either press @key{RET} at this point, to run the @code{info
1488 breakpoints} command, or backspace and enter something else, if
1489 @samp{breakpoints} does not look like the command you expected. (If you
1490 were sure you wanted @code{info breakpoints} in the first place, you
1491 might as well just type @key{RET} immediately after @samp{info bre},
1492 to exploit command abbreviations rather than command completion).
1494 If there is more than one possibility for the next word when you press
1495 @key{TAB}, @value{GDBN} sounds a bell. You can either supply more
1496 characters and try again, or just press @key{TAB} a second time;
1497 @value{GDBN} displays all the possible completions for that word. For
1498 example, you might want to set a breakpoint on a subroutine whose name
1499 begins with @samp{make_}, but when you type @kbd{b make_@key{TAB}} @value{GDBN}
1500 just sounds the bell. Typing @key{TAB} again displays all the
1501 function names in your program that begin with those characters, for
1505 (@value{GDBP}) b make_ @key{TAB}
1506 @exdent @value{GDBN} sounds bell; press @key{TAB} again, to see:
1507 make_a_section_from_file make_environ
1508 make_abs_section make_function_type
1509 make_blockvector make_pointer_type
1510 make_cleanup make_reference_type
1511 make_command make_symbol_completion_list
1512 (@value{GDBP}) b make_
1516 After displaying the available possibilities, @value{GDBN} copies your
1517 partial input (@samp{b make_} in the example) so you can finish the
1520 If you just want to see the list of alternatives in the first place, you
1521 can press @kbd{M-?} rather than pressing @key{TAB} twice. @kbd{M-?}
1522 means @kbd{@key{META} ?}. You can type this
1524 either by holding down a
1525 key designated as the @key{META} shift on your keyboard (if there is
1526 one) while typing @kbd{?}, or
1528 as @key{ESC} followed by @kbd{?}.
1530 @cindex quotes in commands
1531 @cindex completion of quoted strings
1532 Sometimes the string you need, while logically a ``word'', may contain
1533 parentheses or other characters that @value{GDBN} normally excludes from its
1534 notion of a word. To permit word completion to work in this situation,
1535 you may enclose words in @code{'} (single quote marks) in @value{GDBN} commands.
1538 The most likely situation where you might need this is in typing the
1539 name of a C++ function. This is because C++ allows function overloading
1540 (multiple definitions of the same function, distinguished by argument
1541 type). For example, when you want to set a breakpoint you may need to
1542 distinguish whether you mean the version of @code{name} that takes an
1543 @code{int} parameter, @code{name(int)}, or the version that takes a
1544 @code{float} parameter, @code{name(float)}. To use the word-completion
1545 facilities in this situation, type a single quote @code{'} at the
1546 beginning of the function name. This alerts @value{GDBN} that it may need to
1547 consider more information than usual when you press @key{TAB} or
1548 @kbd{M-?} to request word completion:
1551 (@value{GDBP}) b 'bubble( @key{M-?}
1552 bubble(double,double) bubble(int,int)
1553 (@value{GDBP}) b 'bubble(
1556 In some cases, @value{GDBN} can tell that completing a name requires using
1557 quotes. When this happens, @value{GDBN} inserts the quote for you (while
1558 completing as much as it can) if you do not type the quote in the first
1562 (@value{GDBP}) b bub @key{TAB}
1563 @exdent @value{GDBN} alters your input line to the following, and rings a bell:
1564 (@value{GDBP}) b 'bubble(
1568 In general, @value{GDBN} can tell that a quote is needed (and inserts it) if
1569 you have not yet started typing the argument list when you ask for
1570 completion on an overloaded symbol.
1572 For more information about overloaded functions, @pxref{Cplus
1573 expressions, ,C++ expressions}. You can use the command @code{set
1574 overload-resolution off} to disable overload resolution;
1575 @pxref{Debugging C plus plus, ,@value{GDBN} features for C++}.
1579 @node Help, , Completion, Commands
1580 @section Getting help
1581 @cindex online documentation
1584 You can always ask @value{GDBN} itself for information on its commands,
1585 using the command @code{help}.
1591 You can use @code{help} (abbreviated @code{h}) with no arguments to
1592 display a short list of named classes of commands:
1596 List of classes of commands:
1598 running -- Running the program
1599 stack -- Examining the stack
1600 data -- Examining data
1601 breakpoints -- Making program stop at certain points
1602 files -- Specifying and examining files
1603 status -- Status inquiries
1604 support -- Support facilities
1605 user-defined -- User-defined commands
1606 aliases -- Aliases of other commands
1607 obscure -- Obscure features
1609 Type "help" followed by a class name for a list of
1610 commands in that class.
1611 Type "help" followed by command name for full
1613 Command name abbreviations are allowed if unambiguous.
1617 @item help @var{class}
1618 Using one of the general help classes as an argument, you can get a
1619 list of the individual commands in that class. For example, here is the
1620 help display for the class @code{status}:
1623 (@value{GDBP}) help status
1628 @c Line break in "show" line falsifies real output, but needed
1629 @c to fit in smallbook page size.
1630 show -- Generic command for showing things set
1632 info -- Generic command for printing status
1634 Type "help" followed by command name for full
1636 Command name abbreviations are allowed if unambiguous.
1640 @item help @var{command}
1641 With a command name as @code{help} argument, @value{GDBN} displays a
1642 short paragraph on how to use that command.
1645 @item complete @var{args}
1646 The @code{complete @var{args}} command lists all the possible completions
1647 for the beginning of a command. Use @var{args} to specify the beginning of the
1648 command you want completed. For example:
1654 @noindent results in:
1664 @noindent This is intended for use by @sc{gnu} Emacs.
1667 In addition to @code{help}, you can use the @value{GDBN} commands @code{info}
1668 and @code{show} to inquire about the state of your program, or the state
1669 of @value{GDBN} itself. Each command supports many topics of inquiry; this
1670 manual introduces each of them in the appropriate context. The listings
1671 under @code{info} and under @code{show} in the Index point to
1672 all the sub-commands. @xref{Index}.
1679 This command (abbreviated @code{i}) is for describing the state of your
1680 program. For example, you can list the arguments given to your program
1681 with @code{info args}, list the registers currently in use with @code{info
1682 registers}, or list the breakpoints you have set with @code{info breakpoints}.
1683 You can get a complete list of the @code{info} sub-commands with
1684 @w{@code{help info}}.
1688 You can assign the result of an expresson to an environment variable with
1689 @code{set}. For example, you can set the @value{GDBN} prompt to a $-sign with
1690 @code{set prompt $}.
1694 In contrast to @code{info}, @code{show} is for describing the state of
1695 @value{GDBN} itself.
1696 You can change most of the things you can @code{show}, by using the
1697 related command @code{set}; for example, you can control what number
1698 system is used for displays with @code{set radix}, or simply inquire
1699 which is currently in use with @code{show radix}.
1702 To display all the settable parameters and their current
1703 values, you can use @code{show} with no arguments; you may also use
1704 @code{info set}. Both commands produce the same display.
1705 @c FIXME: "info set" violates the rule that "info" is for state of
1706 @c FIXME...program. Ck w/ GNU: "info set" to be called something else,
1707 @c FIXME...or change desc of rule---eg "state of prog and debugging session"?
1711 Here are three miscellaneous @code{show} subcommands, all of which are
1712 exceptional in lacking corresponding @code{set} commands:
1715 @kindex show version
1716 @cindex version number
1718 Show what version of @value{GDBN} is running. You should include this
1719 information in @value{GDBN} bug-reports. If multiple versions of @value{GDBN} are in
1720 use at your site, you may occasionally want to determine which version
1721 of @value{GDBN} you are running; as @value{GDBN} evolves, new commands are introduced,
1722 and old ones may wither away. The version number is also announced
1723 when you start @value{GDBN}.
1725 @kindex show copying
1727 Display information about permission for copying @value{GDBN}.
1729 @kindex show warranty
1731 Display the @sc{gnu} ``NO WARRANTY'' statement.
1734 @node Running, Stopping, Commands, Top
1735 @chapter Running Programs Under @value{GDBN}
1737 When you run a program under @value{GDBN}, you must first generate
1738 debugging information when you compile it.
1740 You may start @value{GDBN} with its arguments, if any, in an environment
1741 of your choice. You may redirect your program's input and output, debug an
1742 already running process, or kill a child process.
1746 * Compilation:: Compiling for debugging
1747 * Starting:: Starting your program
1749 * Arguments:: Your program's arguments
1750 * Environment:: Your program's environment
1753 * Working Directory:: Your program's working directory
1754 * Input/Output:: Your program's input and output
1755 * Attach:: Debugging an already-running process
1756 * Kill Process:: Killing the child process
1758 * Process Information:: Additional process information
1761 * Threads:: Debugging programs with multiple threads
1762 * Processes:: Debugging programs with multiple processes
1765 @node Compilation, Starting, Running, Running
1766 @section Compiling for debugging
1768 In order to debug a program effectively, you need to generate
1769 debugging information when you compile it. This debugging information
1770 is stored in the object file; it describes the data type of each
1771 variable or function and the correspondence between source line numbers
1772 and addresses in the executable code.
1774 To request debugging information, specify the @samp{-g} option when you run
1777 Many C compilers are unable to handle the @samp{-g} and @samp{-O}
1778 options together. Using those compilers, you cannot generate optimized
1779 executables containing debugging information.
1782 @value{NGCC}, the @sc{gnu} C compiler, supports @samp{-g} with or without
1785 The HP ANSI C and C++ compilers, as well as @value{NGCC}, the @sc{gnu} C
1786 compiler, support @samp{-g} with or without
1788 @samp{-O}, making it possible to debug optimized code. We recommend
1789 that you @emph{always} use @samp{-g} whenever you compile a program.
1790 You may think your program is correct, but there is no sense in pushing
1793 @cindex optimized code, debugging
1794 @cindex debugging optimized code
1795 When you debug a program compiled with @samp{-g -O}, remember that the
1796 optimizer is rearranging your code; the debugger shows you what is
1797 really there. Do not be too surprised when the execution path does not
1798 exactly match your source file! An extreme example: if you define a
1799 variable, but never use it, @value{GDBN} never sees that
1800 variable---because the compiler optimizes it out of existence.
1802 Some things do not work as well with @samp{-g -O} as with just
1803 @samp{-g}, particularly on machines with instruction scheduling. If in
1804 doubt, recompile with @samp{-g} alone, and if this fixes the problem,
1805 please report it to us as a bug (including a test case!).
1807 Older versions of the @sc{gnu} C compiler permitted a variant option
1808 @w{@samp{-gg}} for debugging information. @value{GDBN} no longer supports this
1809 format; if your @sc{gnu} C compiler has this option, do not use it.
1812 @node Starting, Arguments, Compilation, Running
1813 @section Starting your program
1821 Use the @code{run} command to start your program under @value{GDBN}. You must
1822 first specify the program name
1826 with an argument to @value{GDBN} (@pxref{Invocation, ,Getting In and
1827 Out of @value{GDBN}}), or by using the @code{file} or @code{exec-file}
1828 command (@pxref{Files, ,Commands to specify files}).
1833 If you are running your program in an execution environment that
1834 supports processes, @code{run} creates an inferior process and makes
1835 that process run your program. (In environments without processes,
1836 @code{run} jumps to the start of your program.)
1838 The execution of a program is affected by certain information it
1839 receives from its superior. @value{GDBN} provides ways to specify this
1840 information, which you must do @emph{before} starting your program. (You
1841 can change it after starting your program, but such changes only affect
1842 your program the next time you start it.) This information may be
1843 divided into four categories:
1846 @item The @emph{arguments.}
1847 Specify the arguments to give your program as the arguments of the
1848 @code{run} command. If a shell is available on your target, the shell
1849 is used to pass the arguments, so that you may use normal conventions
1850 (such as wildcard expansion or variable substitution) in describing
1852 In Unix systems, you can control which shell is used with the
1853 @code{SHELL} environment variable.
1854 @xref{Arguments, ,Your program's arguments}.
1856 @item The @emph{environment.}
1857 Your program normally inherits its environment from @value{GDBN}, but you can
1858 use the @value{GDBN} commands @code{set environment} and @code{unset
1859 environment} to change parts of the environment that affect
1860 your program. @xref{Environment, ,Your program's environment}.
1862 @item The @emph{working directory.}
1863 Your program inherits its working directory from @value{GDBN}. You can set
1864 the @value{GDBN} working directory with the @code{cd} command in @value{GDBN}.
1865 @xref{Working Directory, ,Your program's working directory}.
1867 @item The @emph{standard input and output.}
1868 Your program normally uses the same device for standard input and
1869 standard output as @value{GDBN} is using. You can redirect input and output
1870 in the @code{run} command line, or you can use the @code{tty} command to
1871 set a different device for your program.
1872 @xref{Input/Output, ,Your program's input and output}.
1875 @emph{Warning:} While input and output redirection work, you cannot use
1876 pipes to pass the output of the program you are debugging to another
1877 program; if you attempt this, @value{GDBN} is likely to wind up debugging the
1882 When you issue the @code{run} command, your program begins to execute
1883 immediately. @xref{Stopping, ,Stopping and continuing}, for discussion
1884 of how to arrange for your program to stop. Once your program has
1885 stopped, you may call functions in your program, using the @code{print}
1886 or @code{call} commands. @xref{Data, ,Examining Data}.
1888 If the modification time of your symbol file has changed since the last
1889 time @value{GDBN} read its symbols, @value{GDBN} discards its symbol
1890 table, and reads it again. When it does this, @value{GDBN} tries to retain
1891 your current breakpoints.
1894 @node Arguments, Environment, Starting, Running
1895 @section Your program's arguments
1897 @cindex arguments (to your program)
1898 The arguments to your program can be specified by the arguments of the
1900 They are passed to a shell, which expands wildcard characters and
1901 performs redirection of I/O, and thence to your program. Your
1902 @code{SHELL} environment variable (if it exists) specifies what shell
1903 @value{GDBN} uses. If you do not define @code{SHELL}, @value{GDBN} uses
1906 @code{run} with no arguments uses the same arguments used by the previous
1907 @code{run}, or those set by the @code{set args} command.
1912 Specify the arguments to be used the next time your program is run. If
1913 @code{set args} has no arguments, @code{run} executes your program
1914 with no arguments. Once you have run your program with arguments,
1915 using @code{set args} before the next @code{run} is the only way to run
1916 it again without arguments.
1920 Show the arguments to give your program when it is started.
1923 @node Environment, Working Directory, Arguments, Running
1924 @section Your program's environment
1926 @cindex environment (of your program)
1927 The @dfn{environment} consists of a set of environment variables and
1928 their values. Environment variables conventionally record such things as
1929 your user name, your home directory, your terminal type, and your search
1930 path for programs to run. Usually you set up environment variables with
1931 the shell and they are inherited by all the other programs you run. When
1932 debugging, it can be useful to try running your program with a modified
1933 environment without having to start @value{GDBN} over again.
1937 @item path @var{directory}
1938 Add @var{directory} to the front of the @code{PATH} environment variable
1939 (the search path for executables), for both @value{GDBN} and your program.
1940 You may specify several directory names, separated by @samp{:} or
1941 whitespace. If @var{directory} is already in the path, it is moved to
1942 the front, so it is searched sooner.
1944 You can use the string @samp{$cwd} to refer to whatever is the current
1945 working directory at the time @value{GDBN} searches the path. If you
1946 use @samp{.} instead, it refers to the directory where you executed the
1947 @code{path} command. @value{GDBN} replaces @samp{.} in the
1948 @var{directory} argument (with the current path) before adding
1949 @var{directory} to the search path.
1950 @c 'path' is explicitly nonrepeatable, but RMS points out it is silly to
1951 @c document that, since repeating it would be a no-op.
1955 Display the list of search paths for executables (the @code{PATH}
1956 environment variable).
1958 @kindex show environment
1959 @item show environment @r{[}@var{varname}@r{]}
1960 Print the value of environment variable @var{varname} to be given to
1961 your program when it starts. If you do not supply @var{varname},
1962 print the names and values of all environment variables to be given to
1963 your program. You can abbreviate @code{environment} as @code{env}.
1965 @kindex set environment
1966 @item set environment @var{varname} @r{[}=@r{]} @var{value}
1967 Set environment variable @var{varname} to @var{value}. The value
1968 changes for your program only, not for @value{GDBN} itself. @var{value} may
1969 be any string; the values of environment variables are just strings, and
1970 any interpretation is supplied by your program itself. The @var{value}
1971 parameter is optional; if it is eliminated, the variable is set to a
1973 @c "any string" here does not include leading, trailing
1974 @c blanks. Gnu asks: does anyone care?
1976 For example, this command:
1983 tells a Unix program, when subsequently run, that its user is named
1984 @samp{foo}. (The spaces around @samp{=} are used for clarity here; they
1985 are not actually required.)
1987 @kindex unset environment
1988 @item unset environment @var{varname}
1989 Remove variable @var{varname} from the environment to be passed to your
1990 program. This is different from @samp{set env @var{varname} =};
1991 @code{unset environment} removes the variable from the environment,
1992 rather than assigning it an empty value.
1995 @emph{Warning:} @value{GDBN} runs your program using the shell indicated
1996 by your @code{SHELL} environment variable if it exists (or
1997 @code{/bin/sh} if not). If your @code{SHELL} variable names a shell
1998 that runs an initialization file---such as @file{.cshrc} for C-shell, or
1999 @file{.bashrc} for BASH---any variables you set in that file affect
2000 your program. You may wish to move setting of environment variables to
2001 files that are only run when you sign on, such as @file{.login} or
2004 @node Working Directory, Input/Output, Environment, Running
2005 @section Your program's working directory
2007 @cindex working directory (of your program)
2008 Each time you start your program with @code{run}, it inherits its
2009 working directory from the current working directory of @value{GDBN}.
2010 The @value{GDBN} working directory is initially whatever it inherited
2011 from its parent process (typically the shell), but you can specify a new
2012 working directory in @value{GDBN} with the @code{cd} command.
2014 The @value{GDBN} working directory also serves as a default for the commands
2015 that specify files for @value{GDBN} to operate on. @xref{Files, ,Commands to
2020 @item cd @var{directory}
2021 Set the @value{GDBN} working directory to @var{directory}.
2025 Print the @value{GDBN} working directory.
2028 @node Input/Output, Attach, Working Directory, Running
2029 @section Your program's input and output
2034 By default, the program you run under @value{GDBN} does input and output to
2035 the same terminal that @value{GDBN} uses. @value{GDBN} switches the terminal
2036 to its own terminal modes to interact with you, but it records the terminal
2037 modes your program was using and switches back to them when you continue
2038 running your program.
2041 @kindex info terminal
2043 Displays information recorded by @value{GDBN} about the terminal modes your
2047 You can redirect your program's input and/or output using shell
2048 redirection with the @code{run} command. For example,
2055 starts your program, diverting its output to the file @file{outfile}.
2058 @cindex controlling terminal
2059 Another way to specify where your program should do input and output is
2060 with the @code{tty} command. This command accepts a file name as
2061 argument, and causes this file to be the default for future @code{run}
2062 commands. It also resets the controlling terminal for the child
2063 process, for future @code{run} commands. For example,
2070 directs that processes started with subsequent @code{run} commands
2071 default to do input and output on the terminal @file{/dev/ttyb} and have
2072 that as their controlling terminal.
2074 An explicit redirection in @code{run} overrides the @code{tty} command's
2075 effect on the input/output device, but not its effect on the controlling
2078 When you use the @code{tty} command or redirect input in the @code{run}
2079 command, only the input @emph{for your program} is affected. The input
2080 for @value{GDBN} still comes from your terminal.
2082 @node Attach, Kill Process, Input/Output, Running
2083 @section Debugging an already-running process
2088 @item attach @var{process-id}
2089 This command attaches to a running process---one that was started
2090 outside @value{GDBN}. (@code{info files} shows your active
2091 targets.) The command takes as argument a process ID. The usual way to
2092 find out the process-id of a Unix process is with the @code{ps} utility,
2093 or with the @samp{jobs -l} shell command.
2095 @code{attach} does not repeat if you press @key{RET} a second time after
2096 executing the command.
2099 To use @code{attach}, your program must be running in an environment
2100 which supports processes; for example, @code{attach} does not work for
2101 programs on bare-board targets that lack an operating system. You must
2102 also have permission to send the process a signal.
2104 When you use @code{attach}, the debugger finds the program running in
2105 the process first by looking in the current working directory, then (if
2106 the program is not found) by using the source file search path
2107 (@pxref{Source Path, ,Specifying source directories}). You can also use
2108 the @code{file} command to load the program. @xref{Files, ,Commands to
2111 The first thing @value{GDBN} does after arranging to debug the specified
2112 process is to stop it. You can examine and modify an attached process
2113 with all the @value{GDBN} commands that are ordinarily available when you start
2115 processes with @code{run}. You can insert breakpoints; you can step and
2118 processes with @code{run}. You can insert breakpoints (except in shared
2119 libraries); you can step and
2121 continue; you can modify storage. If you would rather the process
2122 continue running, you may use the @code{continue} command after
2123 attaching @value{GDBN} to the process.
2128 When you have finished debugging the attached process, you can use the
2129 @code{detach} command to release it from @value{GDBN} control. Detaching
2130 the process continues its execution. After the @code{detach} command,
2131 that process and @value{GDBN} become completely independent once more, and you
2132 are ready to @code{attach} another process or start one with @code{run}.
2133 @code{detach} does not repeat if you press @key{RET} again after
2134 executing the command.
2137 If you exit @value{GDBN} or use the @code{run} command while you have an
2138 attached process, you kill that process. By default, @value{GDBN} asks
2139 for confirmation if you try to do either of these things; you can
2140 control whether or not you need to confirm by using the @code{set
2141 confirm} command (@pxref{Messages/Warnings, ,Optional warnings and
2145 @node Kill Process, Threads, Attach, Running
2146 @section Killing the child process
2149 @node Kill Process, Process Information, Attach, Running
2150 @section Killing the child process
2156 Kill the child process in which your program is running under @value{GDBN}.
2159 This command is useful if you wish to debug a core dump instead of a
2160 running process. @value{GDBN} ignores any core dump file while your program
2163 On some operating systems, a program cannot be executed outside @value{GDBN}
2164 while you have breakpoints set on it inside @value{GDBN}. You can use the
2165 @code{kill} command in this situation to permit running your program
2166 outside the debugger.
2168 The @code{kill} command is also useful if you wish to recompile and
2169 relink your program, since on many systems it is impossible to modify an
2170 executable file while it is running in a process. In this case, when you
2171 next type @code{run}, @value{GDBN} notices that the file has changed, and
2172 reads the symbol table again (while trying to preserve your current
2173 breakpoint settings).
2176 @node Process Information, Threads, Kill Process, Running
2177 @section Additional process information
2180 @cindex process image
2181 Some operating systems provide a facility called @samp{/proc} that can
2182 be used to examine the image of a running process using file-system
2183 subroutines. If @value{GDBN} is configured for an operating system with this
2184 facility, the command @code{info proc} is available to report on several
2185 kinds of information about the process running your program.
2186 @code{info proc} works only on SVR4 systems that support @code{procfs}.
2191 Summarize available information about the process.
2193 @kindex info proc mappings
2194 @item info proc mappings
2195 Report on the address ranges accessible in the program, with information
2196 on whether your program may read, write, or execute each range.
2198 @kindex info proc times
2199 @item info proc times
2200 Starting time, user CPU time, and system CPU time for your program and
2203 @kindex info proc id
2205 Report on the process IDs related to your program: its own process ID,
2206 the ID of its parent, the process group ID, and the session ID.
2208 @kindex info proc status
2209 @item info proc status
2210 General information on the state of the process. If the process is
2211 stopped, this report includes the reason for stopping, and any signal
2215 Show all the above information about the process.
2220 @node Threads, Processes, Kill Process, Running
2221 @section Debugging programs with multiple threads
2224 @node Threads, Processes, Process Information, Running
2225 @section Debugging programs with multiple threads
2228 @cindex threads of execution
2229 @cindex multiple threads
2230 @cindex switching threads
2231 In some operating systems,
2235 a single program may have more than one
2236 @dfn{thread} of execution. The precise semantics of threads differ from
2237 one operating system to another, but in general the threads of a single
2238 program are akin to multiple processes---except that they share one
2239 address space (that is, they can all examine and modify the same
2240 variables). On the other hand, each thread has its own registers and
2241 execution stack, and perhaps private memory.
2243 @value{GDBN} provides these facilities for debugging multi-thread
2247 @item automatic notification of new threads
2248 @item @samp{thread @var{threadno}}, a command to switch among threads
2249 @item @samp{info threads}, a command to inquire about existing threads
2250 @item @samp{thread apply [@var{threadno}] [@var{all}] @var{args}},
2251 a command to apply a command to a list of threads
2252 @item thread-specific breakpoints
2257 @emph{Warning:} These facilities are not yet available on every
2258 @value{GDBN} configuration where the operating system supports threads.
2259 If your @value{GDBN} does not support threads, these commands have no
2260 effect. For example, a system without thread support shows no output
2261 from @samp{info threads}, and always rejects the @code{thread} command,
2265 (@value{GDBP}) info threads
2266 (@value{GDBP}) thread 1
2267 Thread ID 1 not known. Use the "info threads" command to
2268 see the IDs of currently known threads.
2270 @c FIXME to implementors: how hard would it be to say "sorry, this GDB
2271 @c doesn't support threads"?
2275 @cindex focus of debugging
2276 @cindex current thread
2277 The @value{GDBN} thread debugging facility allows you to observe all
2278 threads while your program runs---but whenever @value{GDBN} takes
2279 control, one thread in particular is always the focus of debugging.
2280 This thread is called the @dfn{current thread}. Debugging commands show
2281 program information from the perspective of the current thread.
2284 @kindex New @var{systag}
2285 @cindex thread identifier (system)
2286 @c FIXME-implementors!! It would be more helpful if the [New...] message
2287 @c included GDB's numeric thread handle, so you could just go to that
2288 @c thread without first checking `info threads'.
2289 Whenever @value{GDBN} detects a new thread in your program, it displays
2290 the target system's identification for the thread with a message in the
2291 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
2292 whose form varies depending on the particular system. For example, on
2293 LynxOS, you might see
2296 [New process 35 thread 27]
2300 when @value{GDBN} notices a new thread. In contrast, on an SGI system,
2301 the @var{systag} is simply something like @samp{process 368}, with no
2304 @c FIXME!! (1) Does the [New...] message appear even for the very first
2305 @c thread of a program, or does it only appear for the
2306 @c second---i.e., when it becomes obvious we have a multithread
2308 @c (2) *Is* there necessarily a first thread always? Or do some
2309 @c multithread systems permit starting a program with multiple
2310 @c threads ab initio?
2312 @cindex thread number
2313 @cindex thread identifier (GDB)
2314 For debugging purposes, @value{GDBN} associates its own thread
2315 number---always a single integer---with each thread in your program.
2318 @kindex info threads
2320 Display a summary of all threads currently in your
2321 program. @value{GDBN} displays for each thread (in this order):
2324 @item the thread number assigned by @value{GDBN}
2326 @item the target system's thread identifier (@var{systag})
2328 @item the current stack frame summary for that thread
2332 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2333 indicates the current thread.
2337 @c end table here to get a little more width for example
2340 (@value{GDBP}) info threads
2341 3 process 35 thread 27 0x34e5 in sigpause ()
2342 2 process 35 thread 23 0x34e5 in sigpause ()
2343 * 1 process 35 thread 13 main (argc=1, argv=0x7ffffff8)
2349 @cindex thread number
2350 @cindex thread identifier (GDB)
2351 For debugging purposes, @value{GDBN} associates its own thread
2352 number---a small integer assigned in thread-creation order---with each
2353 thread in your program.
2355 @kindex New @var{systag}
2356 @cindex thread identifier (system)
2357 @c FIXME-implementors!! It would be more helpful if the [New...] message
2358 @c included GDB's numeric thread handle, so you could just go to that
2359 @c thread without first checking `info threads'.
2360 Whenever @value{GDBN} detects a new thread in your program, it displays
2361 both @value{GDBN}'s thread number and the target system's identification for the thread with a message in the
2362 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
2363 whose form varies depending on the particular system. For example, on
2367 [New thread 2 (system thread 26594)]
2371 when @value{GDBN} notices a new thread.
2374 @kindex info threads
2376 Display a summary of all threads currently in your
2377 program. @value{GDBN} displays for each thread (in this order):
2380 @item the thread number assigned by @value{GDBN}
2382 @item the target system's thread identifier (@var{systag})
2384 @item the current stack frame summary for that thread
2388 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2389 indicates the current thread.
2393 @c end table here to get a little more width for example
2396 (@value{GDBP}) info threads
2397 * 3 system thread 26607 worker (wptr=0x7b09c318 "@@") at quicksort.c:137
2398 2 system thread 26606 0x7b0030d8 in __ksleep () from /usr/lib/libc.2
2399 1 system thread 27905 0x7b003498 in _brk () from /usr/lib/libc.2
2404 @kindex thread @var{threadno}
2405 @item thread @var{threadno}
2406 Make thread number @var{threadno} the current thread. The command
2407 argument @var{threadno} is the internal @value{GDBN} thread number, as
2408 shown in the first field of the @samp{info threads} display.
2409 @value{GDBN} responds by displaying the system identifier of the thread
2410 you selected, and its current stack frame summary:
2413 @c FIXME!! This example made up; find a @value{GDBN} w/threads and get real one
2414 (@value{GDBP}) thread 2
2416 [Switching to process 35 thread 23]
2419 [Switching to thread 2 (system thread 26594)]
2421 0x34e5 in sigpause ()
2425 As with the @samp{[New @dots{}]} message, the form of the text after
2426 @samp{Switching to} depends on your system's conventions for identifying
2429 @kindex thread apply
2430 @item thread apply [@var{threadno}] [@var{all}] @var{args}
2431 The @code{thread apply} command allows you to apply a command to one or
2432 more threads. Specify the numbers of the threads that you want affected
2433 with the command argument @var{threadno}. @var{threadno} is the internal
2434 @value{GDBN} thread number, as shown in the first field of the @samp{info
2435 threads} display. To apply a command to all threads, use
2436 @code{thread apply all} @var{args}.
2439 @cindex automatic thread selection
2440 @cindex switching threads automatically
2441 @cindex threads, automatic switching
2442 Whenever @value{GDBN} stops your program, due to a breakpoint or a
2443 signal, it automatically selects the thread where that breakpoint or
2444 signal happened. @value{GDBN} alerts you to the context switch with a
2445 message of the form @samp{[Switching to @var{systag}]} to identify the
2448 @xref{Thread Stops,,Stopping and starting multi-thread programs}, for
2449 more information about how @value{GDBN} behaves when you stop and start
2450 programs with multiple threads.
2452 @xref{Set Watchpoints,,Setting watchpoints}, for information about
2453 watchpoints in programs with multiple threads.
2457 @node Processes, , Threads, Running
2458 @section Debugging programs with multiple processes
2460 @cindex fork, debugging programs which call
2461 @cindex multiple processes
2462 @cindex processes, multiple
2463 @value{GDBN} has no special support for debugging programs which create
2464 additional processes using the @code{fork} function. When a program
2465 forks, @value{GDBN} will continue to debug the parent process and the
2466 child process will run unimpeded. If you have set a breakpoint in any
2467 code which the child then executes, the child will get a @code{SIGTRAP}
2468 signal which (unless it catches the signal) will cause it to terminate.
2470 However, if you want to debug the child process there is a workaround
2471 which isn't too painful. Put a call to @code{sleep} in the code which
2472 the child process executes after the fork. It may be useful to sleep
2473 only if a certain environment variable is set, or a certain file exists,
2474 so that the delay need not occur when you don't want to run @value{GDBN}
2475 on the child. While the child is sleeping, use the @code{ps} program to
2476 get its process ID. Then tell @value{GDBN} (a new invocation of
2477 @value{GDBN} if you are also debugging the parent process) to attach to
2478 the child process (see @ref{Attach}). From that point on you can debug
2479 the child process just like any other process which you attached to.
2482 @node Processes, , Threads, Running
2483 @section Debugging programs with multiple processes
2485 @cindex fork, debugging programs which call
2486 @cindex multiple processes
2487 @cindex processes, multiple
2489 @value{GDBN} provides support for debugging programs that create
2490 additional processes using the @code{fork} or @code{vfork} function.
2492 By default, when a program forks, @value{GDBN} will continue to debug
2493 the parent process and the child process will run unimpeded.
2495 If you want to follow the child process instead of the parent process,
2496 use the command @w{@code{set follow-fork-mode}}.
2499 @kindex set follow-fork-mode
2500 @item set follow-fork-mode @var{mode}
2501 Set the debugger response to a program call of @code{fork} or
2502 @code{vfork}. A call to @code{fork} or @code{vfork} creates a new
2503 process. The @var{mode} can be:
2507 The original process is debugged after a fork. The child process runs
2511 The new process is debugged after a fork. The parent process runs
2515 The debugger will ask for one of the above choices.
2518 @item show follow-fork-mode
2519 Display the current debugger response to a fork or vfork call.
2522 If you ask to debug a child process and a @code{vfork} is followed by an
2523 @code{exec}, @value{GDBN} executes the new target up to the first
2524 breakpoint in the new target. If you have a breakpoint set on
2525 @code{main} in your original program, the breakpoint will also be set on
2526 the child process's @code{main}.
2528 When a child process is spawned by @code{vfork}, you cannot debug the
2529 child or parent until an @code{exec} call completes.
2531 If you issue a @code{run} command to @value{GDBN} after an @code{exec}
2532 call executes, the new target restarts. To restart the parent process,
2533 use the @code{file} command with the parent executable name as its
2536 You can use the @code{catch} command to make @value{GDBN} stop whenever
2537 a @code{fork}, @code{vfork}, or @code{exec} call is made. @xref{Set
2538 Catchpoints, ,Setting catchpoints}.
2541 @node Stopping, Stack, Running, Top
2542 @chapter Stopping and Continuing
2544 The principal purposes of using a debugger are so that you can stop your
2545 program before it terminates; or so that, if your program runs into
2546 trouble, you can investigate and find out why.
2548 Inside @value{GDBN}, your program may stop for any of several reasons, such
2553 a breakpoint, or reaching a new line after a @value{GDBN}
2554 command such as @code{step}. You may then examine and change
2555 variables, set new breakpoints or remove old ones, and then continue
2556 execution. Usually, the messages shown by @value{GDBN} provide ample
2557 explanation of the status of your program---but you can also explicitly
2558 request this information at any time.
2561 @kindex info program
2563 Display information about the status of your program: whether it is
2574 * Breakpoints:: Breakpoints, watchpoints, and exceptions
2578 * Breakpoints:: Breakpoints, watchpoints, and catchpoints
2584 * Breakpoints:: Breakpoints and watchpoints
2587 * Continuing and Stepping:: Resuming execution
2593 * Thread Stops:: Stopping and starting multi-thread programs
2598 @c makeinfo node-defaulting requires adjacency of @node and sectioning cmds
2599 @c ...hence distribute @node Breakpoints over two possible @if expansions.
2603 @node Breakpoints, Continuing and Stepping, Stopping, Stopping
2604 @section Breakpoints, watchpoints, and exceptions
2607 @node Breakpoints, Continuing and Stepping, Stopping, Stopping
2608 @section Breakpoints, watchpoints, and catchpoints
2612 @node Breakpoints, Continuing and Stepping, Stopping, Stopping
2613 @section Breakpoints and watchpoints
2617 A @dfn{breakpoint} makes your program stop whenever a certain point in
2618 the program is reached. For each breakpoint, you can add
2619 conditions to control in finer detail whether your program stops.
2620 You can set breakpoints with the @code{break} command and its variants
2621 (@pxref{Set Breaks, ,Setting breakpoints}), to specify the place where
2622 your program should stop by line number, function name or exact address
2626 In languages with exception handling (such as @sc{gnu} C++), you can also set
2627 breakpoints where an exception is raised (@pxref{Exception Handling,,
2628 Breakpoints and exceptions}).
2632 In HP-UX, SunOS 4.x, SVR4, and Alpha OSF/1 configurations, you can set
2633 breakpoints in shared libraries before the executable is run.
2635 There is a minor limitation on HP-UX systems: you must wait until the
2636 executable is run in order to set breakpoints in shared library routines
2637 that are not called directly by the program (for example, routines that
2638 are arguments in a @code{pthread_create} call).
2642 @cindex memory tracing
2643 @cindex breakpoint on memory address
2644 @cindex breakpoint on variable modification
2645 A @dfn{watchpoint} is a special breakpoint that stops your program
2646 when the value of an expression changes. You must use a different
2647 command to set watchpoints (@pxref{Set Watchpoints, ,Setting
2648 watchpoints}), but aside from that, you can manage a watchpoint like
2649 any other breakpoint: you enable, disable, and delete both breakpoints
2650 and watchpoints using the same commands.
2652 You can arrange to have values from your program displayed automatically
2653 whenever @value{GDBN} stops at a breakpoint. @xref{Auto Display,,
2657 @cindex breakpoint on events
2658 A @dfn{catchpoint} is another special breakpoint that stops your program
2659 when a certain kind of event occurs, such as the throwing of a C++
2660 exception or the loading of a library. As with watchpoints, you use a
2661 different command to set a catchpoint (@pxref{Set Catchpoints, ,Setting
2662 catchpoints}), but aside from that, you can manage a catchpoint like any
2663 other breakpoint. (To stop when your program receives a signal, use the
2664 @code{handle} command; @pxref{Signals, ,Signals}.)
2666 @cindex breakpoint numbers
2667 @cindex numbers for breakpoints
2669 @value{GDBN} assigns a number to each breakpoint or watchpoint when you
2672 @value{GDBN} assigns a number to each breakpoint, watchpoint, or
2675 create it; these numbers are successive integers starting with one. In
2676 many of the commands for controlling various features of breakpoints you
2677 use the breakpoint number to say which breakpoint you want to change.
2678 Each breakpoint may be @dfn{enabled} or @dfn{disabled}; if disabled, it has
2679 no effect on your program until you enable it again.
2682 * Set Breaks:: Setting breakpoints
2683 * Set Watchpoints:: Setting watchpoints
2686 * Exception Handling:: Breakpoints and exceptions
2690 * Set Catchpoints:: Setting catchpoints
2695 * Delete Breaks:: Deleting breakpoints
2696 * Disabling:: Disabling breakpoints
2697 * Conditions:: Break conditions
2698 * Break Commands:: Breakpoint command lists
2700 * Breakpoint Menus:: Breakpoint menus
2703 @c @ifclear BARETARGET
2704 @c * Error in Breakpoints:: ``Cannot insert breakpoints''
2708 @node Set Breaks, Set Watchpoints, Breakpoints, Breakpoints
2709 @subsection Setting breakpoints
2711 @c FIXME LMB what does GDB do if no code on line of breakpt?
2712 @c consider in particular declaration with/without initialization.
2714 @c FIXME 2 is there stuff on this already? break at fun start, already init?
2719 @cindex latest breakpoint
2720 Breakpoints are set with the @code{break} command (abbreviated
2721 @code{b}). The debugger convenience variable @samp{$bpnum} records the
2722 number of the breakpoints you've set most recently; see @ref{Convenience
2723 Vars,, Convenience variables}, for a discussion of what you can do with
2724 convenience variables.
2726 You have several ways to say where the breakpoint should go.
2729 @item break @var{function}
2730 Set a breakpoint at entry to function @var{function}.
2732 When using source languages that permit overloading of symbols, such as
2733 C++, @var{function} may refer to more than one possible place to break.
2734 @xref{Breakpoint Menus,,Breakpoint menus}, for a discussion of that situation.
2737 @item break +@var{offset}
2738 @itemx break -@var{offset}
2739 Set a breakpoint some number of lines forward or back from the position
2740 at which execution stopped in the currently selected frame.
2742 @item break @var{linenum}
2743 Set a breakpoint at line @var{linenum} in the current source file.
2744 That file is the last file whose source text was printed. This
2745 breakpoint stops your program just before it executes any of the
2748 @item break @var{filename}:@var{linenum}
2749 Set a breakpoint at line @var{linenum} in source file @var{filename}.
2751 @item break @var{filename}:@var{function}
2752 Set a breakpoint at entry to function @var{function} found in file
2753 @var{filename}. Specifying a file name as well as a function name is
2754 superfluous except when multiple files contain similarly named
2757 @item break *@var{address}
2758 Set a breakpoint at address @var{address}. You can use this to set
2759 breakpoints in parts of your program which do not have debugging
2760 information or source files.
2763 When called without any arguments, @code{break} sets a breakpoint at
2764 the next instruction to be executed in the selected stack frame
2765 (@pxref{Stack, ,Examining the Stack}). In any selected frame but the
2766 innermost, this makes your program stop as soon as control
2767 returns to that frame. This is similar to the effect of a
2768 @code{finish} command in the frame inside the selected frame---except
2769 that @code{finish} does not leave an active breakpoint. If you use
2770 @code{break} without an argument in the innermost frame, @value{GDBN} stops
2771 the next time it reaches the current location; this may be useful
2774 @value{GDBN} normally ignores breakpoints when it resumes execution, until at
2775 least one instruction has been executed. If it did not do this, you
2776 would be unable to proceed past a breakpoint without first disabling the
2777 breakpoint. This rule applies whether or not the breakpoint already
2778 existed when your program stopped.
2780 @item break @dots{} if @var{cond}
2781 Set a breakpoint with condition @var{cond}; evaluate the expression
2782 @var{cond} each time the breakpoint is reached, and stop only if the
2783 value is nonzero---that is, if @var{cond} evaluates as true.
2784 @samp{@dots{}} stands for one of the possible arguments described
2785 above (or no argument) specifying where to break. @xref{Conditions,
2786 ,Break conditions}, for more information on breakpoint conditions.
2789 @item tbreak @var{args}
2790 Set a breakpoint enabled only for one stop. @var{args} are the
2791 same as for the @code{break} command, and the breakpoint is set in the same
2792 way, but the breakpoint is automatically deleted after the first time your
2793 program stops there. @xref{Disabling, ,Disabling breakpoints}.
2797 @item hbreak @var{args}
2798 Set a hardware-assisted breakpoint. @var{args} are the same as for the
2799 @code{break} command and the breakpoint is set in the same way, but the
2800 breakpoint requires hardware support and some target hardware may not
2801 have this support. The main purpose of this is EPROM/ROM code
2802 debugging, so you can set a breakpoint at an instruction without
2803 changing the instruction. This can be used with the new trap-generation
2804 provided by SPARClite DSU. DSU will generate traps when a program accesses
2805 some data or instruction address that is assigned to the debug registers.
2806 However the hardware breakpoint registers can only take two data breakpoints,
2807 and @value{GDBN} will reject this command if more than two are used.
2808 Delete or disable usused hardware breakpoints before setting
2809 new ones. @xref{Conditions, ,Break conditions}.
2812 @item thbreak @var{args}
2813 Set a hardware-assisted breakpoint enabled only for one stop. @var{args}
2814 are the same as for the @code{hbreak} command and the breakpoint is set in
2815 the same way. However, like the @code{tbreak} command,
2816 the breakpoint is automatically deleted after the
2817 first time your program stops there. Also, like the @code{hbreak}
2818 command, the breakpoint requires hardware support and some target hardware
2819 may not have this support. @xref{Disabling, ,Disabling breakpoints}.
2820 Also @xref{Conditions, ,Break conditions}.
2824 @cindex regular expression
2825 @item rbreak @var{regex}
2826 @c FIXME what kind of regexp?
2827 Set breakpoints on all functions matching the regular expression
2828 @var{regex}. This command
2829 sets an unconditional breakpoint on all matches, printing a list of all
2830 breakpoints it set. Once these breakpoints are set, they are treated
2831 just like the breakpoints set with the @code{break} command. You can
2832 delete them, disable them, or make them conditional the same way as any
2836 When debugging C++ programs, @code{rbreak} is useful for setting
2837 breakpoints on overloaded functions that are not members of any special
2841 @kindex info breakpoints
2842 @cindex @code{$_} and @code{info breakpoints}
2843 @item info breakpoints @r{[}@var{n}@r{]}
2844 @itemx info break @r{[}@var{n}@r{]}
2845 @itemx info watchpoints @r{[}@var{n}@r{]}
2847 Print a table of all breakpoints and watchpoints set and not
2848 deleted, with the following columns for each breakpoint:
2851 Print a table of all breakpoints, watchpoints, and catchpoints set and
2852 not deleted, with the following columns for each breakpoint:
2856 @item Breakpoint Numbers
2859 Breakpoint or watchpoint.
2862 Breakpoint, watchpoint, or catchpoint.
2865 Whether the breakpoint is marked to be disabled or deleted when hit.
2866 @item Enabled or Disabled
2867 Enabled breakpoints are marked with @samp{y}. @samp{n} marks breakpoints
2868 that are not enabled.
2870 Where the breakpoint is in your program, as a memory address
2872 Where the breakpoint is in the source for your program, as a file and
2877 If a breakpoint is conditional, @code{info break} shows the condition on
2878 the line following the affected breakpoint; breakpoint commands, if any,
2879 are listed after that.
2882 @code{info break} with a breakpoint
2883 number @var{n} as argument lists only that breakpoint. The
2884 convenience variable @code{$_} and the default examining-address for
2885 the @code{x} command are set to the address of the last breakpoint
2886 listed (@pxref{Memory, ,Examining memory}).
2889 @code{info break} displays a count of the number of times the breakpoint
2890 has been hit. This is especially useful in conjunction with the
2891 @code{ignore} command. You can ignore a large number of breakpoint
2892 hits, look at the breakpoint info to see how many times the breakpoint
2893 was hit, and then run again, ignoring one less than that number. This
2894 will get you quickly to the last hit of that breakpoint.
2897 @value{GDBN} allows you to set any number of breakpoints at the same place in
2898 your program. There is nothing silly or meaningless about this. When
2899 the breakpoints are conditional, this is even useful
2900 (@pxref{Conditions, ,Break conditions}).
2902 @cindex negative breakpoint numbers
2903 @cindex internal @value{GDBN} breakpoints
2904 @value{GDBN} itself sometimes sets breakpoints in your program for special
2905 purposes, such as proper handling of @code{longjmp} (in C programs).
2906 These internal breakpoints are assigned negative numbers, starting with
2907 @code{-1}; @samp{info breakpoints} does not display them.
2909 You can see these breakpoints with the @value{GDBN} maintenance command
2910 @samp{maint info breakpoints}.
2913 @kindex maint info breakpoints
2914 @item maint info breakpoints
2915 Using the same format as @samp{info breakpoints}, display both the
2916 breakpoints you've set explicitly, and those @value{GDBN} is using for
2917 internal purposes. Internal breakpoints are shown with negative
2918 breakpoint numbers. The type column identifies what kind of breakpoint
2923 Normal, explicitly set breakpoint.
2926 Normal, explicitly set watchpoint.
2929 Internal breakpoint, used to handle correctly stepping through
2930 @code{longjmp} calls.
2932 @item longjmp resume
2933 Internal breakpoint at the target of a @code{longjmp}.
2936 Temporary internal breakpoint used by the @value{GDBN} @code{until} command.
2939 Temporary internal breakpoint used by the @value{GDBN} @code{finish} command.
2943 Shared library events.
2950 @node Set Watchpoints, Exception Handling, Set Breaks, Breakpoints
2951 @subsection Setting watchpoints
2954 @node Set Watchpoints, Set Catchpoints, Set Breaks, Breakpoints
2955 @subsection Setting watchpoints
2957 @cindex setting watchpoints
2959 You can use a watchpoint to stop execution whenever the value of an
2960 expression changes, without having to predict a particular place
2961 where this may happen.
2964 Watchpoints currently execute two orders of magnitude more slowly than
2965 other breakpoints, but this can be well worth it to catch errors where
2966 you have no clue what part of your program is the culprit.
2969 @c FIXME - did Stan mean to @ignore this out?
2971 Some processors provide special hardware to support watchpoint
2972 evaluation; @value{GDBN} will use such hardware if it is available,
2973 and if the support code has been added for that configuration.
2978 @item watch @var{expr}
2979 Set a watchpoint for an expression. @value{GDBN} will break when @var{expr}
2980 is written into by the program and its value changes.
2982 This can be used with the new trap-generation provided by
2983 SPARClite DSU. DSU will generate traps when a program accesses
2984 some data or instruction address that is assigned to the debug registers.
2985 For the data addresses, DSU facilitates the @code{watch} command.
2986 However the hardware breakpoint registers can only take two data watchpoints,
2987 and both watchpoints must be the same kind. For example, you can set two
2988 watchpoints with @code{watch} commands, two with @code{rwatch}
2989 commands, @strong{or} two with @code{awatch} commands, but you cannot set one
2990 watchpoint with one command and the other with a different command.
2991 @value{GDBN} will reject the command if you try to mix watchpoints.
2992 Delete or disable unused watchpoint commands before setting new ones.
2995 @item rwatch @var{expr}
2996 Set a watchpoint that will break when watch @var{expr} is read by the program.
2997 If you use both watchpoints, both must be set with the @code{rwatch}
3001 @item awatch @var{expr}
3002 Set a watchpoint that will break when @var{args} is read and written into
3003 by the program. If you use both watchpoints, both must be set with the
3004 @code{awatch} command.
3007 @kindex info watchpoints
3008 @item info watchpoints
3010 This command prints a list of watchpoints and breakpoints; it is the
3011 same as @code{info break}.
3014 This command prints a list of watchpoints, breakpoints, and catchpoints;
3015 it is the same as @code{info break}.
3020 @value{GDBN} sets a @dfn{hardware watchpoint} if possible. Hardware
3021 watchpoints execute very quickly, and the debugger reports a change in
3022 value at the exact instruction where the change occurs. If @value{GDBN}
3023 cannot set a hardware watchpoint, it sets a software watchpoint, which
3024 executes more slowly and reports the change in value at the next
3025 statement, not the instruction, after the change occurs.
3027 When you issue the @code{watch} command, @value{GDBN} reports
3030 Hardware watchpoint @var{num}: @var{expr}
3034 if it was able to set a hardware watchpoint.
3037 If you call a function interactively using @code{print} or @code{call},
3038 any watchpoints you have set will be inactive until GDB reaches another
3039 kind of breakpoint or the call completes.
3043 @cindex watchpoints and threads
3044 @cindex threads and watchpoints
3046 @emph{Warning:} In multi-thread programs, watchpoints have only limited
3047 usefulness. With the current watchpoint implementation, @value{GDBN}
3048 can only watch the value of an expression @emph{in a single thread}. If
3049 you are confident that the expression can only change due to the current
3050 thread's activity (and if you are also confident that no other thread
3051 can become current), then you can use watchpoints as usual. However,
3052 @value{GDBN} may not notice when a non-current thread's activity changes
3056 @emph{Warning:} In multi-thread programs, software watchpoints have only
3057 limited usefulness. If @value{GDBN} creates a software watchpoint, it
3058 can only watch the value of an expression @emph{in a single thread}. If
3059 you are confident that the expression can only change due to the current
3060 thread's activity (and if you are also confident that no other thread
3061 can become current), then you can use software watchpoints as usual.
3062 However, @value{GDBN} may not notice when a non-current thread's
3063 activity changes the expression. (Hardware watchpoints, in contrast,
3064 watch an expression in all threads.)
3071 @node Exception Handling, Delete Breaks, Set Watchpoints, Breakpoints
3072 @subsection Breakpoints and exceptions
3073 @cindex exception handlers
3075 Some languages, such as @sc{gnu} C++, implement exception handling. You can
3076 use @value{GDBN} to examine what caused your program to raise an exception,
3077 and to list the exceptions your program is prepared to handle at a
3078 given point in time.
3082 @item catch @var{exceptions}
3083 You can set breakpoints at active exception handlers by using the
3084 @code{catch} command. @var{exceptions} is a list of names of exceptions
3088 You can use @code{info catch} to list active exception handlers.
3089 @xref{Frame Info, ,Information about a frame}.
3091 There are currently some limitations to exception handling in @value{GDBN}:
3095 If you call a function interactively, @value{GDBN} normally returns
3096 control to you when the function has finished executing. If the call
3097 raises an exception, however, the call may bypass the mechanism that
3098 returns control to you and cause your program to simply continue
3099 running until it hits a breakpoint, catches a signal that @value{GDBN} is
3100 listening for, or exits.
3103 You cannot raise an exception interactively.
3106 You cannot install an exception handler interactively.
3109 @cindex raise exceptions
3110 Sometimes @code{catch} is not the best way to debug exception handling:
3111 if you need to know exactly where an exception is raised, it is better to
3112 stop @emph{before} the exception handler is called, since that way you
3113 can see the stack before any unwinding takes place. If you set a
3114 breakpoint in an exception handler instead, it may not be easy to find
3115 out where the exception was raised.
3117 To stop just before an exception handler is called, you need some
3118 knowledge of the implementation. In the case of @sc{gnu} C++, exceptions are
3119 raised by calling a library function named @code{__raise_exception}
3120 which has the following ANSI C interface:
3123 /* @var{addr} is where the exception identifier is stored.
3124 ID is the exception identifier. */
3125 void __raise_exception (void **@var{addr}, void *@var{id});
3129 To make the debugger catch all exceptions before any stack
3130 unwinding takes place, set a breakpoint on @code{__raise_exception}
3131 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and exceptions}).
3133 With a conditional breakpoint (@pxref{Conditions, ,Break conditions})
3134 that depends on the value of @var{id}, you can stop your program when
3135 a specific exception is raised. You can use multiple conditional
3136 breakpoints to stop your program when any of a number of exceptions are
3141 @node Set Catchpoints, Delete Breaks, Set Watchpoints, Breakpoints
3142 @subsection Setting catchpoints
3144 @cindex exception handlers
3145 @cindex event handling
3147 You can use @dfn{catchpoints} to cause the debugger to stop for certain
3148 kinds of program events, such as C++ exceptions or the loading of a
3149 shared library. Use the @code{catch} command to set a catchpoint.
3153 @item catch @var{event}
3154 Stop when @var{event} occurs. @var{event} can be any of the following:
3158 The throwing of a C++ exception.
3162 The catching of a C++ exception.
3166 A call to @code{exec}.
3170 A call to @code{fork}.
3174 A call to @code{vfork}.
3177 @itemx load @var{libname}
3179 The dynamic loading of any shared library, or the loading of the library
3183 @itemx unload @var{libname}
3184 @kindex catch unload
3185 The unloading of any dynamically loaded shared library, or the unloading
3186 of the library @var{libname}.
3189 @item tcatch @var{event}
3190 Set a catchpoint that is enabled only for one stop. The catchpoint is
3191 automatically deleted after the first time the event is caught.
3195 Use the @code{info break} command to list the current catchpoints.
3197 There are currently some limitations to C++ exception handling
3198 (@code{catch throw} and @code{catch catch}) in @value{GDBN}:
3202 If you call a function interactively, @value{GDBN} normally returns
3203 control to you when the function has finished executing. If the call
3204 raises an exception, however, the call may bypass the mechanism that
3205 returns control to you and cause your program either to abort or to
3206 simply continue running until it hits a breakpoint, catches a signal
3207 that @value{GDBN} is listening for, or exits. This is the case even if
3208 you set a catchpoint for the exception; catchpoints on exceptions are
3209 disabled within interactive calls.
3212 You cannot raise an exception interactively.
3215 You cannot install an exception handler interactively.
3220 @node Delete Breaks, Disabling, Set Catchpoints, Breakpoints
3221 @subsection Deleting breakpoints
3224 @cindex clearing breakpoints, watchpoints
3225 @cindex deleting breakpoints, watchpoints
3226 It is often necessary to eliminate a breakpoint or watchpoint once it
3229 @cindex clearing breakpoints, watchpoints, catchpoints
3230 @cindex deleting breakpoints, watchpoints, catchpoints
3231 It is often necessary to eliminate a breakpoint, watchpoint, or
3234 has done its job and you no longer want your program to stop there. This
3235 is called @dfn{deleting} the breakpoint. A breakpoint that has been
3236 deleted no longer exists; it is forgotten.
3238 With the @code{clear} command you can delete breakpoints according to
3239 where they are in your program. With the @code{delete} command you can
3241 delete individual breakpoints or watchpoints by specifying their
3244 delete individual breakpoints, watchpoints, or catchpoints by specifying
3249 It is not necessary to delete a breakpoint to proceed past it. @value{GDBN}
3250 automatically ignores breakpoints on the first instruction to be executed
3251 when you continue execution without changing the execution address.
3256 Delete any breakpoints at the next instruction to be executed in the
3257 selected stack frame (@pxref{Selection, ,Selecting a frame}). When
3258 the innermost frame is selected, this is a good way to delete a
3259 breakpoint where your program just stopped.
3261 @item clear @var{function}
3262 @itemx clear @var{filename}:@var{function}
3263 Delete any breakpoints set at entry to the function @var{function}.
3265 @item clear @var{linenum}
3266 @itemx clear @var{filename}:@var{linenum}
3267 Delete any breakpoints set at or within the code of the specified line.
3269 @cindex delete breakpoints
3272 @item delete @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]}
3274 Delete the breakpoints or watchpoints of the numbers specified as
3277 Delete the breakpoints, watchpoints, or catchpoints of the numbers
3280 arguments. If no argument is specified, delete all breakpoints (@value{GDBN}
3281 asks confirmation, unless you have @code{set confirm off}). You
3282 can abbreviate this command as @code{d}.
3285 @node Disabling, Conditions, Delete Breaks, Breakpoints
3286 @subsection Disabling breakpoints
3288 @kindex disable breakpoints
3289 @kindex enable breakpoints
3291 Rather than deleting a breakpoint or watchpoint, you might prefer to
3294 Rather than deleting a breakpoint, watchpoint, or catchpoint, you might
3297 @dfn{disable} it. This makes the breakpoint inoperative as if it had
3298 been deleted, but remembers the information on the breakpoint so that
3299 you can @dfn{enable} it again later.
3302 You disable and enable breakpoints and watchpoints with the
3305 You disable and enable breakpoints, watchpoints, and catchpoints with
3308 @code{enable} and @code{disable} commands, optionally specifying one or
3309 more breakpoint numbers as arguments. Use @code{info break} or
3311 @code{info watch} to print a list of breakpoints or watchpoints if you
3314 @code{info watch} to print a list of breakpoints, watchpoints, and
3317 do not know which numbers to use.
3320 A breakpoint or watchpoint can have any of four different states of
3323 A breakpoint, watchpoint, or catchpoint can have any of four different
3330 Enabled. The breakpoint stops your program. A breakpoint set
3331 with the @code{break} command starts out in this state.
3333 Disabled. The breakpoint has no effect on your program.
3335 Enabled once. The breakpoint stops your program, but then becomes
3336 disabled. A breakpoint set with the @code{tbreak} command starts out in
3339 Enabled for deletion. The breakpoint stops your program, but
3340 immediately after it does so it is deleted permanently.
3344 You can use the following commands to enable or disable breakpoints and
3348 You can use the following commands to enable or disable breakpoints,
3349 watchpoints, and catchpoints:
3353 @kindex disable breakpoints
3356 @item disable @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]}
3357 Disable the specified breakpoints---or all breakpoints, if none are
3358 listed. A disabled breakpoint has no effect but is not forgotten. All
3359 options such as ignore-counts, conditions and commands are remembered in
3360 case the breakpoint is enabled again later. You may abbreviate
3361 @code{disable} as @code{dis}.
3363 @kindex enable breakpoints
3365 @item enable @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]}
3366 Enable the specified breakpoints (or all defined breakpoints). They
3367 become effective once again in stopping your program.
3369 @item enable @r{[}breakpoints@r{]} once @var{bnums}@dots{}
3370 Enable the specified breakpoints temporarily. @value{GDBN} disables any
3371 of these breakpoints immediately after stopping your program.
3373 @item enable @r{[}breakpoints@r{]} delete @var{bnums}@dots{}
3374 Enable the specified breakpoints to work once, then die. @value{GDBN}
3375 deletes any of these breakpoints as soon as your program stops there.
3378 Except for a breakpoint set with @code{tbreak} (@pxref{Set Breaks,
3379 ,Setting breakpoints}), breakpoints that you set are initially enabled;
3380 subsequently, they become disabled or enabled only when you use one of
3381 the commands above. (The command @code{until} can set and delete a
3382 breakpoint of its own, but it does not change the state of your other
3383 breakpoints; see @ref{Continuing and Stepping, ,Continuing and
3386 @node Conditions, Break Commands, Disabling, Breakpoints
3387 @subsection Break conditions
3388 @cindex conditional breakpoints
3389 @cindex breakpoint conditions
3391 @c FIXME what is scope of break condition expr? Context where wanted?
3392 @c in particular for a watchpoint?
3393 The simplest sort of breakpoint breaks every time your program reaches a
3394 specified place. You can also specify a @dfn{condition} for a
3395 breakpoint. A condition is just a Boolean expression in your
3396 programming language (@pxref{Expressions, ,Expressions}). A breakpoint with
3397 a condition evaluates the expression each time your program reaches it,
3398 and your program stops only if the condition is @emph{true}.
3400 This is the converse of using assertions for program validation; in that
3401 situation, you want to stop when the assertion is violated---that is,
3402 when the condition is false. In C, if you want to test an assertion expressed
3403 by the condition @var{assert}, you should set the condition
3404 @samp{! @var{assert}} on the appropriate breakpoint.
3406 Conditions are also accepted for watchpoints; you may not need them,
3407 since a watchpoint is inspecting the value of an expression anyhow---but
3408 it might be simpler, say, to just set a watchpoint on a variable name,
3409 and specify a condition that tests whether the new value is an interesting
3412 Break conditions can have side effects, and may even call functions in
3413 your program. This can be useful, for example, to activate functions
3414 that log program progress, or to use your own print functions to
3415 format special data structures. The effects are completely predictable
3416 unless there is another enabled breakpoint at the same address. (In
3417 that case, @value{GDBN} might see the other breakpoint first and stop your
3418 program without checking the condition of this one.) Note that
3419 breakpoint commands are usually more convenient and flexible for the
3420 purpose of performing side effects when a breakpoint is reached
3421 (@pxref{Break Commands, ,Breakpoint command lists}).
3423 Break conditions can be specified when a breakpoint is set, by using
3424 @samp{if} in the arguments to the @code{break} command. @xref{Set
3425 Breaks, ,Setting breakpoints}. They can also be changed at any time
3426 with the @code{condition} command.
3428 @c The watch command now seems to recognize the if keyword.
3429 @c catch doesn't, though.
3430 The @code{watch} command does not recognize the @code{if} keyword;
3431 @code{condition} is the only way to impose a further condition on a
3435 You can also use the @code{if} keyword with the @code{watch} command.
3436 The @code{catch} command does not recognize the @code{if} keyword;
3437 @code{condition} is the only way to impose a further condition on a
3443 @item condition @var{bnum} @var{expression}
3445 Specify @var{expression} as the break condition for breakpoint or
3446 watchpoint number @var{bnum}. After you set a condition, breakpoint
3449 Specify @var{expression} as the break condition for breakpoint,
3450 watchpoint, or catchpoint number @var{bnum}. After you set a condition,
3453 @var{bnum} stops your program only if the value of @var{expression} is
3454 true (nonzero, in C). When you use @code{condition}, @value{GDBN}
3455 checks @var{expression} immediately for syntactic correctness, and to
3456 determine whether symbols in it have referents in the context of your
3458 @c FIXME so what does GDB do if there is no referent? Moreover, what
3459 @c about watchpoints?
3461 not actually evaluate @var{expression} at the time the @code{condition}
3462 command is given, however. @xref{Expressions, ,Expressions}.
3464 @item condition @var{bnum}
3465 Remove the condition from breakpoint number @var{bnum}. It becomes
3466 an ordinary unconditional breakpoint.
3469 @cindex ignore count (of breakpoint)
3470 A special case of a breakpoint condition is to stop only when the
3471 breakpoint has been reached a certain number of times. This is so
3472 useful that there is a special way to do it, using the @dfn{ignore
3473 count} of the breakpoint. Every breakpoint has an ignore count, which
3474 is an integer. Most of the time, the ignore count is zero, and
3475 therefore has no effect. But if your program reaches a breakpoint whose
3476 ignore count is positive, then instead of stopping, it just decrements
3477 the ignore count by one and continues. As a result, if the ignore count
3478 value is @var{n}, the breakpoint does not stop the next @var{n} times
3479 your program reaches it.
3483 @item ignore @var{bnum} @var{count}
3484 Set the ignore count of breakpoint number @var{bnum} to @var{count}.
3485 The next @var{count} times the breakpoint is reached, your program's
3486 execution does not stop; other than to decrement the ignore count, @value{GDBN}
3489 To make the breakpoint stop the next time it is reached, specify
3492 When you use @code{continue} to resume execution of your program from a
3493 breakpoint, you can specify an ignore count directly as an argument to
3494 @code{continue}, rather than using @code{ignore}. @xref{Continuing and
3495 Stepping,,Continuing and stepping}.
3497 If a breakpoint has a positive ignore count and a condition, the
3498 condition is not checked. Once the ignore count reaches zero,
3499 @value{GDBN} resumes checking the condition.
3501 You could achieve the effect of the ignore count with a condition such
3502 as @w{@samp{$foo-- <= 0}} using a debugger convenience variable that
3503 is decremented each time. @xref{Convenience Vars, ,Convenience
3508 Ignore counts apply to breakpoints, watchpoints, and catchpoints.
3512 @node Break Commands, Breakpoint Menus, Conditions, Breakpoints
3513 @subsection Breakpoint command lists
3515 @cindex breakpoint commands
3517 You can give any breakpoint (or watchpoint) a series of commands to
3520 You can give any breakpoint (or watchpoint or catchpoint) a series of
3523 execute when your program stops due to that breakpoint. For example, you
3524 might want to print the values of certain expressions, or enable other
3530 @item commands @r{[}@var{bnum}@r{]}
3531 @itemx @dots{} @var{command-list} @dots{}
3533 Specify a list of commands for breakpoint number @var{bnum}. The commands
3534 themselves appear on the following lines. Type a line containing just
3535 @code{end} to terminate the commands.
3537 To remove all commands from a breakpoint, type @code{commands} and
3538 follow it immediately with @code{end}; that is, give no commands.
3540 With no @var{bnum} argument, @code{commands} refers to the last
3542 breakpoint or watchpoint set (not to the breakpoint most recently
3545 breakpoint, watchpoint, or catchpoint set (not to the breakpoint most
3551 Pressing @key{RET} as a means of repeating the last @value{GDBN} command is
3552 disabled within a @var{command-list}.
3554 You can use breakpoint commands to start your program up again. Simply
3555 use the @code{continue} command, or @code{step}, or any other command
3556 that resumes execution.
3558 Any other commands in the command list, after a command that resumes
3559 execution, are ignored. This is because any time you resume execution
3560 (even with a simple @code{next} or @code{step}), you may encounter
3561 another breakpoint---which could have its own command list, leading to
3562 ambiguities about which list to execute.
3565 If the first command you specify in a command list is @code{silent}, the
3566 usual message about stopping at a breakpoint is not printed. This may
3567 be desirable for breakpoints that are to print a specific message and
3568 then continue. If none of the remaining commands print anything, you
3569 see no sign that the breakpoint was reached. @code{silent} is
3570 meaningful only at the beginning of a breakpoint command list.
3572 The commands @code{echo}, @code{output}, and @code{printf} allow you to
3573 print precisely controlled output, and are often useful in silent
3574 breakpoints. @xref{Output, ,Commands for controlled output}.
3576 For example, here is how you could use breakpoint commands to print the
3577 value of @code{x} at entry to @code{foo} whenever @code{x} is positive.
3583 printf "x is %d\n",x
3588 One application for breakpoint commands is to compensate for one bug so
3589 you can test for another. Put a breakpoint just after the erroneous line
3590 of code, give it a condition to detect the case in which something
3591 erroneous has been done, and give it commands to assign correct values
3592 to any variables that need them. End with the @code{continue} command
3593 so that your program does not stop, and start with the @code{silent}
3594 command so that no output is produced. Here is an example:
3606 @node Breakpoint Menus, , Break Commands, Breakpoints
3607 @subsection Breakpoint menus
3609 @cindex symbol overloading
3611 Some programming languages (notably C++) permit a single function name
3612 to be defined several times, for application in different contexts.
3613 This is called @dfn{overloading}. When a function name is overloaded,
3614 @samp{break @var{function}} is not enough to tell @value{GDBN} where you want
3615 a breakpoint. If you realize this is a problem, you can use
3616 something like @samp{break @var{function}(@var{types})} to specify which
3617 particular version of the function you want. Otherwise, @value{GDBN} offers
3618 you a menu of numbered choices for different possible breakpoints, and
3619 waits for your selection with the prompt @samp{>}. The first two
3620 options are always @samp{[0] cancel} and @samp{[1] all}. Typing @kbd{1}
3621 sets a breakpoint at each definition of @var{function}, and typing
3622 @kbd{0} aborts the @code{break} command without setting any new
3625 For example, the following session excerpt shows an attempt to set a
3626 breakpoint at the overloaded symbol @code{String::after}.
3627 We choose three particular definitions of that function name:
3629 @c FIXME! This is likely to change to show arg type lists, at least
3632 (@value{GDBP}) b String::after
3635 [2] file:String.cc; line number:867
3636 [3] file:String.cc; line number:860
3637 [4] file:String.cc; line number:875
3638 [5] file:String.cc; line number:853
3639 [6] file:String.cc; line number:846
3640 [7] file:String.cc; line number:735
3642 Breakpoint 1 at 0xb26c: file String.cc, line 867.
3643 Breakpoint 2 at 0xb344: file String.cc, line 875.
3644 Breakpoint 3 at 0xafcc: file String.cc, line 846.
3645 Multiple breakpoints were set.
3646 Use the "delete" command to delete unwanted
3653 @c @ifclear BARETARGET
3654 @c @node Error in Breakpoints
3655 @c @subsection ``Cannot insert breakpoints''
3657 @c FIXME!! 14/6/95 Is there a real example of this? Let's use it.
3659 @c Under some operating systems, breakpoints cannot be used in a program if
3660 @c any other process is running that program. In this situation,
3661 @c attempting to run or continue a program with a breakpoint causes
3662 @c @value{GDBN} to stop the other process.
3664 @c When this happens, you have three ways to proceed:
3668 @c Remove or disable the breakpoints, then continue.
3671 @c Suspend @value{GDBN}, and copy the file containing your program to a new
3672 @c name. Resume @value{GDBN} and use the @code{exec-file} command to specify
3673 @c that @value{GDBN} should run your program under that name.
3674 @c Then start your program again.
3677 @c Relink your program so that the text segment is nonsharable, using the
3678 @c linker option @samp{-N}. The operating system limitation may not apply
3679 @c to nonsharable executables.
3683 @node Continuing and Stepping, Signals, Breakpoints, Stopping
3684 @section Continuing and stepping
3688 @cindex resuming execution
3689 @dfn{Continuing} means resuming program execution until your program
3690 completes normally. In contrast, @dfn{stepping} means executing just
3691 one more ``step'' of your program, where ``step'' may mean either one
3692 line of source code, or one machine instruction (depending on what
3693 particular command you use). Either when continuing
3694 or when stepping, your program may stop even sooner, due to
3699 a breakpoint or a signal. (If due to a signal, you may want to use
3700 @code{handle}, or use @samp{signal 0} to resume execution.
3701 @xref{Signals, ,Signals}.)
3708 @item continue @r{[}@var{ignore-count}@r{]}
3709 @itemx c @r{[}@var{ignore-count}@r{]}
3710 @itemx fg @r{[}@var{ignore-count}@r{]}
3711 Resume program execution, at the address where your program last stopped;
3712 any breakpoints set at that address are bypassed. The optional argument
3713 @var{ignore-count} allows you to specify a further number of times to
3714 ignore a breakpoint at this location; its effect is like that of
3715 @code{ignore} (@pxref{Conditions, ,Break conditions}).
3717 The argument @var{ignore-count} is meaningful only when your program
3718 stopped due to a breakpoint. At other times, the argument to
3719 @code{continue} is ignored.
3721 The synonyms @code{c} and @code{fg} are provided purely for convenience,
3722 and have exactly the same behavior as @code{continue}.
3725 To resume execution at a different place, you can use @code{return}
3726 (@pxref{Returning, ,Returning from a function}) to go back to the
3727 calling function; or @code{jump} (@pxref{Jumping, ,Continuing at a
3728 different address}) to go to an arbitrary location in your program.
3730 A typical technique for using stepping is to set a breakpoint
3733 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and exceptions})
3736 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and catchpoints})
3740 (@pxref{Breakpoints, ,Breakpoints and watchpoints})
3743 beginning of the function or the section of your program where a
3744 problem is believed to lie, run your program until it stops at that
3745 breakpoint, and then step through the suspect area, examining the
3746 variables that are interesting, until you see the problem happen.
3752 Continue running your program until control reaches a different source
3753 line, then stop it and return control to @value{GDBN}. This command is
3754 abbreviated @code{s}.
3757 @c "without debugging information" is imprecise; actually "without line
3758 @c numbers in the debugging information". (gcc -g1 has debugging info but
3759 @c not line numbers). But it seems complex to try to make that
3760 @c distinction here.
3761 @emph{Warning:} If you use the @code{step} command while control is
3762 within a function that was compiled without debugging information,
3763 execution proceeds until control reaches a function that does have
3764 debugging information. Likewise, it will not step into a function which
3765 is compiled without debugging information. To step through functions
3766 without debugging information, use the @code{stepi} command, described
3770 The @code{step} command now only stops at the first instruction of a
3771 source line. This prevents the multiple stops that used to occur in
3772 switch statements, for loops, etc. @code{step} continues to stop if a
3773 function that has debugging information is called within the line.
3775 Also, the @code{step} command now only enters a subroutine if there is line
3776 number information for the subroutine. Otherwise it acts like the
3777 @code{next} command. This avoids problems when using @code{cc -gl}
3778 on MIPS machines. Previously, @code{step} entered subroutines if there
3779 was any debugging information about the routine.
3781 @item step @var{count}
3782 Continue running as in @code{step}, but do so @var{count} times. If a
3783 breakpoint is reached,
3785 or a signal not related to stepping occurs before @var{count} steps,
3787 stepping stops right away.
3791 @item next @r{[}@var{count}@r{]}
3792 Continue to the next source line in the current (innermost) stack frame.
3793 This is similar to @code{step}, but function calls that appear within the line
3794 of code are executed without stopping. Execution stops when control
3795 reaches a different line of code at the original stack level that was
3796 executing when you gave the @code{next} command. This command is abbreviated
3799 An argument @var{count} is a repeat count, as for @code{step}.
3802 @c FIX ME!! Do we delete this, or is there a way it fits in with
3803 @c the following paragraph? --- Vctoria
3805 @c @code{next} within a function that lacks debugging information acts like
3806 @c @code{step}, but any function calls appearing within the code of the
3807 @c function are executed without stopping.
3809 The @code{next} command now only stops at the first instruction of a
3810 source line. This prevents the multiple stops that used to occur in
3811 switch statements, for loops, etc.
3815 Continue running until just after function in the selected stack frame
3816 returns. Print the returned value (if any).
3818 Contrast this with the @code{return} command (@pxref{Returning,
3819 ,Returning from a function}).
3825 Continue running until a source line past the current line, in the
3826 current stack frame, is reached. This command is used to avoid single
3827 stepping through a loop more than once. It is like the @code{next}
3828 command, except that when @code{until} encounters a jump, it
3829 automatically continues execution until the program counter is greater
3830 than the address of the jump.
3832 This means that when you reach the end of a loop after single stepping
3833 though it, @code{until} makes your program continue execution until it
3834 exits the loop. In contrast, a @code{next} command at the end of a loop
3835 simply steps back to the beginning of the loop, which forces you to step
3836 through the next iteration.
3838 @code{until} always stops your program if it attempts to exit the current
3841 @code{until} may produce somewhat counterintuitive results if the order
3842 of machine code does not match the order of the source lines. For
3843 example, in the following excerpt from a debugging session, the @code{f}
3844 (@code{frame}) command shows that execution is stopped at line
3845 @code{206}; yet when we use @code{until}, we get to line @code{195}:
3849 #0 main (argc=4, argv=0xf7fffae8) at m4.c:206
3851 (@value{GDBP}) until
3852 195 for ( ; argc > 0; NEXTARG) @{
3855 This happened because, for execution efficiency, the compiler had
3856 generated code for the loop closure test at the end, rather than the
3857 start, of the loop---even though the test in a C @code{for}-loop is
3858 written before the body of the loop. The @code{until} command appeared
3859 to step back to the beginning of the loop when it advanced to this
3860 expression; however, it has not really gone to an earlier
3861 statement---not in terms of the actual machine code.
3863 @code{until} with no argument works by means of single
3864 instruction stepping, and hence is slower than @code{until} with an
3867 @item until @var{location}
3868 @itemx u @var{location}
3869 Continue running your program until either the specified location is
3870 reached, or the current stack frame returns. @var{location} is any of
3871 the forms of argument acceptable to @code{break} (@pxref{Set Breaks,
3872 ,Setting breakpoints}). This form of the command uses breakpoints,
3873 and hence is quicker than @code{until} without an argument.
3879 Execute one machine instruction, then stop and return to the debugger.
3881 It is often useful to do @samp{display/i $pc} when stepping by machine
3882 instructions. This makes @value{GDBN} automatically display the next
3883 instruction to be executed, each time your program stops. @xref{Auto
3884 Display,, Automatic display}.
3886 An argument is a repeat count, as in @code{step}.
3893 Execute one machine instruction, but if it is a function call,
3894 proceed until the function returns.
3896 An argument is a repeat count, as in @code{next}.
3900 @node Signals, Thread Stops, Continuing and Stepping, Stopping
3904 A signal is an asynchronous event that can happen in a program. The
3905 operating system defines the possible kinds of signals, and gives each
3906 kind a name and a number. For example, in Unix @code{SIGINT} is the
3907 signal a program gets when you type an interrupt (often @kbd{C-c});
3908 @code{SIGSEGV} is the signal a program gets from referencing a place in
3909 memory far away from all the areas in use; @code{SIGALRM} occurs when
3910 the alarm clock timer goes off (which happens only if your program has
3911 requested an alarm).
3913 @cindex fatal signals
3914 Some signals, including @code{SIGALRM}, are a normal part of the
3915 functioning of your program. Others, such as @code{SIGSEGV}, indicate
3916 errors; these signals are @dfn{fatal} (kill your program immediately) if the
3917 program has not specified in advance some other way to handle the signal.
3918 @code{SIGINT} does not indicate an error in your program, but it is normally
3919 fatal so it can carry out the purpose of the interrupt: to kill the program.
3921 @value{GDBN} has the ability to detect any occurrence of a signal in your
3922 program. You can tell @value{GDBN} in advance what to do for each kind of
3925 @cindex handling signals
3926 Normally, @value{GDBN} is set up to ignore non-erroneous signals like @code{SIGALRM}
3927 (so as not to interfere with their role in the functioning of your program)
3928 but to stop your program immediately whenever an error signal happens.
3929 You can change these settings with the @code{handle} command.
3932 @kindex info signals
3934 Print a table of all the kinds of signals and how @value{GDBN} has been told to
3935 handle each one. You can use this to see the signal numbers of all
3936 the defined types of signals.
3938 @code{info handle} is the new alias for @code{info signals}.
3941 @item handle @var{signal} @var{keywords}@dots{}
3942 Change the way @value{GDBN} handles signal @var{signal}. @var{signal} can
3943 be the number of a signal or its name (with or without the @samp{SIG} at the
3944 beginning). The @var{keywords} say what change to make.
3948 The keywords allowed by the @code{handle} command can be abbreviated.
3949 Their full names are:
3953 @value{GDBN} should not stop your program when this signal happens. It may
3954 still print a message telling you that the signal has come in.
3957 @value{GDBN} should stop your program when this signal happens. This implies
3958 the @code{print} keyword as well.
3961 @value{GDBN} should print a message when this signal happens.
3964 @value{GDBN} should not mention the occurrence of the signal at all. This
3965 implies the @code{nostop} keyword as well.
3968 @value{GDBN} should allow your program to see this signal; your program
3969 can handle the signal, or else it may terminate if the signal is fatal
3973 @value{GDBN} should not allow your program to see this signal.
3977 When a signal stops your program, the signal is not visible until you
3978 continue. Your program sees the signal then, if @code{pass} is in
3979 effect for the signal in question @emph{at that time}. In other words,
3980 after @value{GDBN} reports a signal, you can use the @code{handle}
3981 command with @code{pass} or @code{nopass} to control whether your
3982 program sees that signal when you continue.
3984 You can also use the @code{signal} command to prevent your program from
3985 seeing a signal, or cause it to see a signal it normally would not see,
3986 or to give it any signal at any time. For example, if your program stopped
3987 due to some sort of memory reference error, you might store correct
3988 values into the erroneous variables and continue, hoping to see more
3989 execution; but your program would probably terminate immediately as
3990 a result of the fatal signal once it saw the signal. To prevent this,
3991 you can continue with @samp{signal 0}. @xref{Signaling, ,Giving your
3996 @node Thread Stops, , Signals, Stopping
3997 @section Stopping and starting multi-thread programs
3999 When your program has multiple threads (@pxref{Threads,, Debugging
4000 programs with multiple threads}), you can choose whether to set
4001 breakpoints on all threads, or on a particular thread.
4004 @cindex breakpoints and threads
4005 @cindex thread breakpoints
4006 @kindex break @dots{} thread @var{threadno}
4007 @item break @var{linespec} thread @var{threadno}
4008 @itemx break @var{linespec} thread @var{threadno} if @dots{}
4009 @var{linespec} specifies source lines; there are several ways of
4010 writing them, but the effect is always to specify some source line.
4012 Use the qualifier @samp{thread @var{threadno}} with a breakpoint command
4013 to specify that you only want @value{GDBN} to stop the program when a
4014 particular thread reaches this breakpoint. @var{threadno} is one of the
4015 numeric thread identifiers assigned by @value{GDBN}, shown in the first
4016 column of the @samp{info threads} display.
4018 If you do not specify @samp{thread @var{threadno}} when you set a
4019 breakpoint, the breakpoint applies to @emph{all} threads of your
4022 You can use the @code{thread} qualifier on conditional breakpoints as
4023 well; in this case, place @samp{thread @var{threadno}} before the
4024 breakpoint condition, like this:
4027 (gdb) break frik.c:13 thread 28 if bartab > lim
4032 @cindex stopped threads
4033 @cindex threads, stopped
4034 Whenever your program stops under @value{GDBN} for any reason,
4035 @emph{all} threads of execution stop, not just the current thread. This
4036 allows you to examine the overall state of the program, including
4037 switching between threads, without worrying that things may change
4040 @cindex continuing threads
4041 @cindex threads, continuing
4042 Conversely, whenever you restart the program, @emph{all} threads start
4043 executing. @emph{This is true even when single-stepping} with commands
4044 like @code{step} or @code{next}.
4046 In particular, @value{GDBN} cannot single-step all threads in lockstep.
4047 Since thread scheduling is up to your debugging target's operating
4048 system (not controlled by @value{GDBN}), other threads may
4049 execute more than one statement while the current thread completes a
4050 single step. Moreover, in general other threads stop in the middle of a
4051 statement, rather than at a clean statement boundary, when the program
4054 You might even find your program stopped in another thread after
4055 continuing or even single-stepping. This happens whenever some other
4056 thread runs into a breakpoint, a signal, or an exception before the
4057 first thread completes whatever you requested.
4060 @node Stack, Source, Stopping, Top
4061 @chapter Examining the Stack
4063 When your program has stopped, the first thing you need to know is where it
4064 stopped and how it got there.
4067 Each time your program performs a function call, information about the call
4069 That information includes the location of the call in your program,
4070 the arguments of the call,
4071 and the local variables of the function being called.
4072 The information is saved in a block of data called a @dfn{stack frame}.
4073 The stack frames are allocated in a region of memory called the @dfn{call
4076 When your program stops, the @value{GDBN} commands for examining the
4077 stack allow you to see all of this information.
4079 @cindex selected frame
4080 One of the stack frames is @dfn{selected} by @value{GDBN} and many
4081 @value{GDBN} commands refer implicitly to the selected frame. In
4082 particular, whenever you ask @value{GDBN} for the value of a variable in
4083 your program, the value is found in the selected frame. There are
4084 special @value{GDBN} commands to select whichever frame you are
4085 interested in. @xref{Selection, ,Selecting a frame}.
4087 When your program stops, @value{GDBN} automatically selects the
4088 currently executing frame and describes it briefly, similar to the
4089 @code{frame} command (@pxref{Frame Info, ,Information about a frame}).
4092 * Frames:: Stack frames
4093 * Backtrace:: Backtraces
4094 * Selection:: Selecting a frame
4095 * Frame Info:: Information on a frame
4097 * MIPS Stack:: MIPS machines and the function stack
4102 @node Frames, Backtrace, Stack, Stack
4103 @section Stack frames
4107 The call stack is divided up into contiguous pieces called @dfn{stack
4108 frames}, or @dfn{frames} for short; each frame is the data associated
4109 with one call to one function. The frame contains the arguments given
4110 to the function, the function's local variables, and the address at
4111 which the function is executing.
4113 @cindex initial frame
4114 @cindex outermost frame
4115 @cindex innermost frame
4116 When your program is started, the stack has only one frame, that of the
4117 function @code{main}. This is called the @dfn{initial} frame or the
4118 @dfn{outermost} frame. Each time a function is called, a new frame is
4119 made. Each time a function returns, the frame for that function invocation
4120 is eliminated. If a function is recursive, there can be many frames for
4121 the same function. The frame for the function in which execution is
4122 actually occurring is called the @dfn{innermost} frame. This is the most
4123 recently created of all the stack frames that still exist.
4125 @cindex frame pointer
4126 Inside your program, stack frames are identified by their addresses. A
4127 stack frame consists of many bytes, each of which has its own address; each
4128 kind of computer has a convention for choosing one byte whose
4129 address serves as the address of the frame. Usually this address is kept
4130 in a register called the @dfn{frame pointer register} while execution is
4131 going on in that frame.
4133 @cindex frame number
4134 @value{GDBN} assigns numbers to all existing stack frames, starting with
4135 zero for the innermost frame, one for the frame that called it,
4136 and so on upward. These numbers do not really exist in your program;
4137 they are assigned by @value{GDBN} to give you a way of designating stack
4138 frames in @value{GDBN} commands.
4140 @c below produces an acceptable overful hbox. --mew 13aug1993
4141 @cindex frameless execution
4142 Some compilers provide a way to compile functions so that they operate
4143 without stack frames. (For example, the @code{@value{GCC}} option
4144 @samp{-fomit-frame-pointer} generates functions without a frame.)
4145 This is occasionally done with heavily used library functions to save
4146 the frame setup time. @value{GDBN} has limited facilities for dealing
4147 with these function invocations. If the innermost function invocation
4148 has no stack frame, @value{GDBN} nevertheless regards it as though
4149 it had a separate frame, which is numbered zero as usual, allowing
4150 correct tracing of the function call chain. However, @value{GDBN} has
4151 no provision for frameless functions elsewhere in the stack.
4155 @item frame @var{args}
4156 The @code{frame} command allows you to move from one stack frame to another,
4157 and to print the stack frame you select. @var{args} may be either the
4158 address of the frame or the stack frame number. Without an argument,
4159 @code{frame} prints the current stack frame.
4161 @kindex select-frame
4163 The @code{select-frame} command allows you to move from one stack frame
4164 to another without printing the frame. This is the silent version of
4168 @node Backtrace, Selection, Frames, Stack
4173 @cindex stack traces
4174 A backtrace is a summary of how your program got where it is. It shows one
4175 line per frame, for many frames, starting with the currently executing
4176 frame (frame zero), followed by its caller (frame one), and on up the
4184 Print a backtrace of the entire stack: one line per frame for all
4185 frames in the stack.
4187 You can stop the backtrace at any time by typing the system interrupt
4188 character, normally @kbd{C-c}.
4190 @item backtrace @var{n}
4192 Similar, but print only the innermost @var{n} frames.
4194 @item backtrace -@var{n}
4196 Similar, but print only the outermost @var{n} frames.
4202 The names @code{where} and @code{info stack} (abbreviated @code{info s})
4203 are additional aliases for @code{backtrace}.
4205 Each line in the backtrace shows the frame number and the function name.
4206 The program counter value is also shown---unless you use @code{set
4207 print address off}. The backtrace also shows the source file name and
4208 line number, as well as the arguments to the function. The program
4209 counter value is omitted if it is at the beginning of the code for that
4212 Here is an example of a backtrace. It was made with the command
4213 @samp{bt 3}, so it shows the innermost three frames.
4217 #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
4219 #1 0x6e38 in expand_macro (sym=0x2b600) at macro.c:242
4220 #2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08)
4222 (More stack frames follow...)
4227 The display for frame zero does not begin with a program counter
4228 value, indicating that your program has stopped at the beginning of the
4229 code for line @code{993} of @code{builtin.c}.
4231 @node Selection, Frame Info, Backtrace, Stack
4232 @section Selecting a frame
4234 Most commands for examining the stack and other data in your program work on
4235 whichever stack frame is selected at the moment. Here are the commands for
4236 selecting a stack frame; all of them finish by printing a brief description
4237 of the stack frame just selected.
4244 Select frame number @var{n}. Recall that frame zero is the innermost
4245 (currently executing) frame, frame one is the frame that called the
4246 innermost one, and so on. The highest-numbered frame is the one for
4249 @item frame @var{addr}
4251 Select the frame at address @var{addr}. This is useful mainly if the
4252 chaining of stack frames has been damaged by a bug, making it
4253 impossible for @value{GDBN} to assign numbers properly to all frames. In
4254 addition, this can be useful when your program has multiple stacks and
4255 switches between them.
4257 @ifclear H8EXCLUSIVE
4259 On the SPARC architecture, @code{frame} needs two addresses to
4260 select an arbitrary frame: a frame pointer and a stack pointer.
4262 On the MIPS and Alpha architecture, it needs two addresses: a stack
4263 pointer and a program counter.
4265 On the 29k architecture, it needs three addresses: a register stack
4266 pointer, a program counter, and a memory stack pointer.
4267 @c note to future updaters: this is conditioned on a flag
4268 @c SETUP_ARBITRARY_FRAME in the tm-*.h files. The above is up to date
4269 @c as of 27 Jan 1994.
4275 Move @var{n} frames up the stack. For positive numbers @var{n}, this
4276 advances toward the outermost frame, to higher frame numbers, to frames
4277 that have existed longer. @var{n} defaults to one.
4282 Move @var{n} frames down the stack. For positive numbers @var{n}, this
4283 advances toward the innermost frame, to lower frame numbers, to frames
4284 that were created more recently. @var{n} defaults to one. You may
4285 abbreviate @code{down} as @code{do}.
4288 All of these commands end by printing two lines of output describing the
4289 frame. The first line shows the frame number, the function name, the
4290 arguments, and the source file and line number of execution in that
4291 frame. The second line shows the text of that source line.
4299 #1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
4301 10 read_input_file (argv[i]);
4305 After such a printout, the @code{list} command with no arguments
4306 prints ten lines centered on the point of execution in the frame.
4307 @xref{List, ,Printing source lines}.
4310 @kindex down-silently
4312 @item up-silently @var{n}
4313 @itemx down-silently @var{n}
4314 These two commands are variants of @code{up} and @code{down},
4315 respectively; they differ in that they do their work silently, without
4316 causing display of the new frame. They are intended primarily for use
4317 in @value{GDBN} command scripts, where the output might be unnecessary and
4322 @node Frame Info, MIPS Stack, Selection, Stack
4323 @section Information about a frame
4326 @node Frame Info, , Selection, Stack
4327 @section Information about a frame
4330 There are several other commands to print information about the selected
4336 When used without any argument, this command does not change which
4337 frame is selected, but prints a brief description of the currently
4338 selected stack frame. It can be abbreviated @code{f}. With an
4339 argument, this command is used to select a stack frame.
4340 @xref{Selection, ,Selecting a frame}.
4346 This command prints a verbose description of the selected stack frame,
4351 the address of the frame
4353 the address of the next frame down (called by this frame)
4355 the address of the next frame up (caller of this frame)
4357 the language in which the source code corresponding to this frame is written
4359 the address of the frame's arguments
4361 the program counter saved in it (the address of execution in the caller frame)
4363 which registers were saved in the frame
4366 @noindent The verbose description is useful when
4367 something has gone wrong that has made the stack format fail to fit
4368 the usual conventions.
4370 @item info frame @var{addr}
4371 @itemx info f @var{addr}
4372 Print a verbose description of the frame at address @var{addr}, without
4373 selecting that frame. The selected frame remains unchanged by this
4374 command. This requires the same kind of address (more than one for some
4375 architectures) that you specify in the @code{frame} command.
4376 @xref{Selection, ,Selecting a frame}.
4380 Print the arguments of the selected frame, each on a separate line.
4384 Print the local variables of the selected frame, each on a separate
4385 line. These are all variables (declared either static or automatic)
4386 accessible at the point of execution of the selected frame.
4391 @cindex catch exceptions
4392 @cindex exception handlers
4394 Print a list of all the exception handlers that are active in the
4395 current stack frame at the current point of execution. To see other
4396 exception handlers, visit the associated frame (using the @code{up},
4397 @code{down}, or @code{frame} commands); then type @code{info catch}.
4398 @xref{Exception Handling, ,Breakpoints and exceptions}.
4404 @node MIPS Stack, , Frame Info, Stack
4405 @section MIPS machines and the function stack
4407 @cindex stack on MIPS
4409 MIPS based computers use an unusual stack frame, which sometimes
4410 requires @value{GDBN} to search backward in the object code to find the
4411 beginning of a function.
4413 @cindex response time, MIPS debugging
4414 To improve response time (especially for embedded applications, where
4415 @value{GDBN} may be restricted to a slow serial line for this search)
4416 you may want to limit the size of this search, using one of these
4420 @cindex @code{heuristic-fence-post} (MIPS)
4421 @item set heuristic-fence-post @var{limit}
4422 Restrict @value{GDBN} to examining at most @var{limit} bytes in its search
4423 for the beginning of a function. A value of @var{0} (the default)
4424 means there is no limit. However, except for @var{0}, the larger the
4425 limit the more bytes @code{heuristic-fence-post} must search and
4426 therefore the longer it takes to run.
4428 @item show heuristic-fence-post
4429 Display the current limit.
4433 These commands are available @emph{only} when @value{GDBN} is configured
4434 for debugging programs on MIPS processors.
4437 @node Source, Data, Stack, Top
4438 @chapter Examining Source Files
4440 @value{GDBN} can print parts of your program's source, since the debugging
4441 information recorded in the program tells @value{GDBN} what source files were
4442 used to build it. When your program stops, @value{GDBN} spontaneously prints
4443 the line where it stopped. Likewise, when you select a stack frame
4444 (@pxref{Selection, ,Selecting a frame}), @value{GDBN} prints the line where
4445 execution in that frame has stopped. You can print other portions of
4446 source files by explicit command.
4449 If you use @value{GDBN} through its @sc{gnu} Emacs interface, you may prefer
4451 Emacs facilities to view source; @pxref{Emacs, ,Using @value{GDBN} under @sc{gnu} Emacs}.
4455 * List:: Printing source lines
4457 * Search:: Searching source files
4460 * Source Path:: Specifying source directories
4461 * Machine Code:: Source and machine code
4464 @node List, Search, Source, Source
4465 @section Printing source lines
4469 To print lines from a source file, use the @code{list} command
4470 (abbreviated @code{l}). By default, ten lines are printed.
4471 There are several ways to specify what part of the file you want to print.
4473 Here are the forms of the @code{list} command most commonly used:
4476 @item list @var{linenum}
4477 Print lines centered around line number @var{linenum} in the
4478 current source file.
4480 @item list @var{function}
4481 Print lines centered around the beginning of function
4485 Print more lines. If the last lines printed were printed with a
4486 @code{list} command, this prints lines following the last lines
4487 printed; however, if the last line printed was a solitary line printed
4488 as part of displaying a stack frame (@pxref{Stack, ,Examining the
4489 Stack}), this prints lines centered around that line.
4492 Print lines just before the lines last printed.
4495 By default, @value{GDBN} prints ten source lines with any of these forms of
4496 the @code{list} command. You can change this using @code{set listsize}:
4499 @kindex set listsize
4500 @item set listsize @var{count}
4501 Make the @code{list} command display @var{count} source lines (unless
4502 the @code{list} argument explicitly specifies some other number).
4504 @kindex show listsize
4506 Display the number of lines that @code{list} prints.
4509 Repeating a @code{list} command with @key{RET} discards the argument,
4510 so it is equivalent to typing just @code{list}. This is more useful
4511 than listing the same lines again. An exception is made for an
4512 argument of @samp{-}; that argument is preserved in repetition so that
4513 each repetition moves up in the source file.
4516 In general, the @code{list} command expects you to supply zero, one or two
4517 @dfn{linespecs}. Linespecs specify source lines; there are several ways
4518 of writing them but the effect is always to specify some source line.
4519 Here is a complete description of the possible arguments for @code{list}:
4522 @item list @var{linespec}
4523 Print lines centered around the line specified by @var{linespec}.
4525 @item list @var{first},@var{last}
4526 Print lines from @var{first} to @var{last}. Both arguments are
4529 @item list ,@var{last}
4530 Print lines ending with @var{last}.
4532 @item list @var{first},
4533 Print lines starting with @var{first}.
4536 Print lines just after the lines last printed.
4539 Print lines just before the lines last printed.
4542 As described in the preceding table.
4545 Here are the ways of specifying a single source line---all the
4550 Specifies line @var{number} of the current source file.
4551 When a @code{list} command has two linespecs, this refers to
4552 the same source file as the first linespec.
4555 Specifies the line @var{offset} lines after the last line printed.
4556 When used as the second linespec in a @code{list} command that has
4557 two, this specifies the line @var{offset} lines down from the
4561 Specifies the line @var{offset} lines before the last line printed.
4563 @item @var{filename}:@var{number}
4564 Specifies line @var{number} in the source file @var{filename}.
4566 @item @var{function}
4567 Specifies the line that begins the body of the function @var{function}.
4568 For example: in C, this is the line with the open brace.
4570 @item @var{filename}:@var{function}
4571 Specifies the line of the open-brace that begins the body of the
4572 function @var{function} in the file @var{filename}. You only need the
4573 file name with a function name to avoid ambiguity when there are
4574 identically named functions in different source files.
4576 @item *@var{address}
4577 Specifies the line containing the program address @var{address}.
4578 @var{address} may be any expression.
4582 @node Search, Source Path, List, Source
4583 @section Searching source files
4585 @kindex reverse-search
4587 There are two commands for searching through the current source file for a
4592 @kindex forward-search
4593 @item forward-search @var{regexp}
4594 @itemx search @var{regexp}
4595 The command @samp{forward-search @var{regexp}} checks each line,
4596 starting with the one following the last line listed, for a match for
4597 @var{regexp}. It lists the line that is found. You can use the
4598 synonym @samp{search @var{regexp}} or abbreviate the command name as
4601 @item reverse-search @var{regexp}
4602 The command @samp{reverse-search @var{regexp}} checks each line, starting
4603 with the one before the last line listed and going backward, for a match
4604 for @var{regexp}. It lists the line that is found. You can abbreviate
4605 this command as @code{rev}.
4609 @node Source Path, Machine Code, Search, Source
4610 @section Specifying source directories
4613 @cindex directories for source files
4614 Executable programs sometimes do not record the directories of the source
4615 files from which they were compiled, just the names. Even when they do,
4616 the directories could be moved between the compilation and your debugging
4617 session. @value{GDBN} has a list of directories to search for source files;
4618 this is called the @dfn{source path}. Each time @value{GDBN} wants a source file,
4619 it tries all the directories in the list, in the order they are present
4620 in the list, until it finds a file with the desired name. Note that
4621 the executable search path is @emph{not} used for this purpose. Neither is
4622 the current working directory, unless it happens to be in the source
4625 If @value{GDBN} cannot find a source file in the source path, and the
4626 object program records a directory, @value{GDBN} tries that directory
4627 too. If the source path is empty, and there is no record of the
4628 compilation directory, @value{GDBN} looks in the current directory as a
4631 Whenever you reset or rearrange the source path, @value{GDBN} clears out
4632 any information it has cached about where source files are found and where
4633 each line is in the file.
4637 When you start @value{GDBN}, its source path is empty.
4638 To add other directories, use the @code{directory} command.
4641 @item directory @var{dirname} @dots{}
4642 @item dir @var{dirname} @dots{}
4643 Add directory @var{dirname} to the front of the source path. Several
4644 directory names may be given to this command, separated by @samp{:} or
4645 whitespace. You may specify a directory that is already in the source
4646 path; this moves it forward, so @value{GDBN} searches it sooner.
4652 @cindex compilation directory
4653 @cindex current directory
4654 @cindex working directory
4655 @cindex directory, current
4656 @cindex directory, compilation
4657 You can use the string @samp{$cdir} to refer to the compilation
4658 directory (if one is recorded), and @samp{$cwd} to refer to the current
4659 working directory. @samp{$cwd} is not the same as @samp{.}---the former
4660 tracks the current working directory as it changes during your @value{GDBN}
4661 session, while the latter is immediately expanded to the current
4662 directory at the time you add an entry to the source path.
4665 Reset the source path to empty again. This requires confirmation.
4667 @c RET-repeat for @code{directory} is explicitly disabled, but since
4668 @c repeating it would be a no-op we do not say that. (thanks to RMS)
4670 @item show directories
4671 @kindex show directories
4672 Print the source path: show which directories it contains.
4675 If your source path is cluttered with directories that are no longer of
4676 interest, @value{GDBN} may sometimes cause confusion by finding the wrong
4677 versions of source. You can correct the situation as follows:
4681 Use @code{directory} with no argument to reset the source path to empty.
4684 Use @code{directory} with suitable arguments to reinstall the
4685 directories you want in the source path. You can add all the
4686 directories in one command.
4689 @node Machine Code, , Source Path, Source
4690 @section Source and machine code
4692 You can use the command @code{info line} to map source lines to program
4693 addresses (and vice versa), and the command @code{disassemble} to display
4694 a range of addresses as machine instructions. When run under @sc{gnu} Emacs
4695 mode, the @code{info line} command now causes the arrow to point to the
4696 line specified. Also, @code{info line} prints addresses in symbolic form as
4701 @item info line @var{linespec}
4702 Print the starting and ending addresses of the compiled code for
4703 source line @var{linespec}. You can specify source lines in any of
4704 the ways understood by the @code{list} command (@pxref{List, ,Printing
4708 For example, we can use @code{info line} to discover the location of
4709 the object code for the first line of function
4710 @code{m4_changequote}:
4713 (@value{GDBP}) info line m4_changecom
4714 Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350.
4718 We can also inquire (using @code{*@var{addr}} as the form for
4719 @var{linespec}) what source line covers a particular address:
4721 (@value{GDBP}) info line *0x63ff
4722 Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404.
4725 @cindex @code{$_} and @code{info line}
4726 After @code{info line}, the default address for the @code{x} command
4727 is changed to the starting address of the line, so that @samp{x/i} is
4728 sufficient to begin examining the machine code (@pxref{Memory,
4729 ,Examining memory}). Also, this address is saved as the value of the
4730 convenience variable @code{$_} (@pxref{Convenience Vars, ,Convenience
4735 @cindex assembly instructions
4736 @cindex instructions, assembly
4737 @cindex machine instructions
4738 @cindex listing machine instructions
4740 This specialized command dumps a range of memory as machine
4741 instructions. The default memory range is the function surrounding the
4742 program counter of the selected frame. A single argument to this
4743 command is a program counter value; @value{GDBN} dumps the function
4744 surrounding this value. Two arguments specify a range of addresses
4745 (first inclusive, second exclusive) to dump.
4748 @ifclear H8EXCLUSIVE
4750 We can use @code{disassemble} to inspect the object code
4751 range shown in the last @code{info line} example (the example
4752 shows SPARC machine instructions):
4756 (@value{GDBP}) disas 0x63e4 0x6404
4757 Dump of assembler code from 0x63e4 to 0x6404:
4758 0x63e4 <builtin_init+5340>: ble 0x63f8 <builtin_init+5360>
4759 0x63e8 <builtin_init+5344>: sethi %hi(0x4c00), %o0
4760 0x63ec <builtin_init+5348>: ld [%i1+4], %o0
4761 0x63f0 <builtin_init+5352>: b 0x63fc <builtin_init+5364>
4762 0x63f4 <builtin_init+5356>: ld [%o0+4], %o0
4763 0x63f8 <builtin_init+5360>: or %o0, 0x1a4, %o0
4764 0x63fc <builtin_init+5364>: call 0x9288 <path_search>
4765 0x6400 <builtin_init+5368>: nop
4766 End of assembler dump.
4772 For example, here is the beginning of the output for the
4773 disassembly of a function @code{fact}:
4777 (@value{GDBP}) disas fact
4778 Dump of assembler code for function fact:
4780 0x802c <fact>: 6d f2 mov.w r2,@@-r7
4781 0x802e <fact+2>: 6d f3 mov.w r3,@@-r7
4782 0x8030 <fact+4>: 6d f6 mov.w r6,@@-r7
4783 0x8032 <fact+6>: 0d 76 mov.w r7,r6
4784 0x8034 <fact+8>: 6f 70 00 08 mov.w @@(0x8,r7),r0
4785 0x8038 <fact+12> 19 11 sub.w r1,r1
4793 @kindex set assembly-language
4794 @cindex assembly instructions
4795 @cindex instructions, assembly
4796 @cindex machine instructions
4797 @cindex listing machine instructions
4798 @item set assembly-language @var{instruction-set}
4799 This command selects the instruction set to use when disassembling the program via the
4800 @code{disassemble} or @code{x/i} commands. It is useful for architectures that
4801 have more than one native instruction set.
4803 Currently it is only defined for the Intel x86 family. You can set @var{instruction-set}
4804 to either @code{i386} or @code{i8086}. The default is @code{i386}.
4809 The following example shows the disassembly of a range of addresses of
4810 HP PA-RISC 2.0 code:
4813 (@value{GDBP}) disas 0x32c4 0x32e4
4814 Dump of assembler code from 0x32c4 to 0x32e4:
4815 0x32c4 <main+204>: addil 0,dp
4816 0x32c8 <main+208>: ldw 0x22c(sr0,r1),r26
4817 0x32cc <main+212>: ldil 0x3000,r31
4818 0x32d0 <main+216>: ble 0x3f8(sr4,r31)
4819 0x32d4 <main+220>: ldo 0(r31),rp
4820 0x32d8 <main+224>: addil -0x800,dp
4821 0x32dc <main+228>: ldo 0x588(r1),r26
4822 0x32e0 <main+232>: ldil 0x3000,r31
4823 End of assembler dump.
4827 @node Data, Languages, Source, Top
4828 @chapter Examining Data
4830 @cindex printing data
4831 @cindex examining data
4834 @c "inspect" is not quite a synonym if you are using Epoch, which we do not
4835 @c document because it is nonstandard... Under Epoch it displays in a
4836 @c different window or something like that.
4837 The usual way to examine data in your program is with the @code{print}
4838 command (abbreviated @code{p}), or its synonym @code{inspect}.
4840 It evaluates and prints the value of an expression of the language your
4841 program is written in (@pxref{Languages, ,Using @value{GDBN} with Different
4846 @item print @var{exp}
4847 @itemx print /@var{f} @var{exp}
4848 @var{exp} is an expression (in the source language). By default the
4849 value of @var{exp} is printed in a format appropriate to its data type;
4850 you can choose a different format by specifying @samp{/@var{f}}, where
4851 @var{f} is a letter specifying the format; @pxref{Output Formats,,Output
4855 @itemx print /@var{f}
4856 If you omit @var{exp}, @value{GDBN} displays the last value again (from the
4857 @dfn{value history}; @pxref{Value History, ,Value history}). This allows you to
4858 conveniently inspect the same value in an alternative format.
4861 A more low-level way of examining data is with the @code{x} command.
4862 It examines data in memory at a specified address and prints it in a
4863 specified format. @xref{Memory, ,Examining memory}.
4865 If you are interested in information about types, or about how the fields
4870 are declared, use the @code{ptype @var{exp}}
4871 command rather than @code{print}. @xref{Symbols, ,Examining the Symbol Table}.
4874 * Expressions:: Expressions
4875 * Variables:: Program variables
4876 * Arrays:: Artificial arrays
4877 * Output Formats:: Output formats
4878 * Memory:: Examining memory
4879 * Auto Display:: Automatic display
4880 * Print Settings:: Print settings
4881 * Value History:: Value history
4882 * Convenience Vars:: Convenience variables
4883 * Registers:: Registers
4885 * Floating Point Hardware:: Floating point hardware
4890 @node Expressions, Variables, Data, Data
4891 @section Expressions
4894 @code{print} and many other @value{GDBN} commands accept an expression and
4895 compute its value. Any kind of constant, variable or operator defined
4896 by the programming language you are using is valid in an expression in
4897 @value{GDBN}. This includes conditional expressions, function calls, casts
4898 and string constants. It unfortunately does not include symbols defined
4899 by preprocessor @code{#define} commands.
4901 @value{GDBN} now supports array constants in expressions input by
4902 the user. The syntax is @var{@{element, element@dots{}@}}. For example,
4903 you can now use the command @code{print @{1, 2, 3@}} to build up an array in
4904 memory that is malloc'd in the target program.
4907 Because C is so widespread, most of the expressions shown in examples in
4908 this manual are in C. @xref{Languages, , Using @value{GDBN} with Different
4909 Languages}, for information on how to use expressions in other
4912 In this section, we discuss operators that you can use in @value{GDBN}
4913 expressions regardless of your programming language.
4915 Casts are supported in all languages, not just in C, because it is so
4916 useful to cast a number into a pointer in order to examine a structure
4917 at that address in memory.
4918 @c FIXME: casts supported---Mod2 true?
4921 @value{GDBN} supports these operators, in addition to those common
4922 to programming languages:
4926 @samp{@@} is a binary operator for treating parts of memory as arrays.
4927 @xref{Arrays, ,Artificial arrays}, for more information.
4930 @samp{::} allows you to specify a variable in terms of the file or
4931 function where it is defined. @xref{Variables, ,Program variables}.
4933 @cindex @{@var{type}@}
4934 @cindex type casting memory
4935 @cindex memory, viewing as typed object
4936 @cindex casts, to view memory
4937 @item @{@var{type}@} @var{addr}
4938 Refers to an object of type @var{type} stored at address @var{addr} in
4939 memory. @var{addr} may be any expression whose value is an integer or
4940 pointer (but parentheses are required around binary operators, just as in
4941 a cast). This construct is allowed regardless of what kind of data is
4942 normally supposed to reside at @var{addr}.
4945 @node Variables, Arrays, Expressions, Data
4946 @section Program variables
4948 The most common kind of expression to use is the name of a variable
4951 Variables in expressions are understood in the selected stack frame
4952 (@pxref{Selection, ,Selecting a frame}); they must be either:
4956 global (or file-static)
4963 visible according to the scope rules of the
4964 programming language from the point of execution in that frame
4967 @noindent This means that in the function
4982 you can examine and use the variable @code{a} whenever your program is
4983 executing within the function @code{foo}, but you can only use or
4984 examine the variable @code{b} while your program is executing inside
4985 the block where @code{b} is declared.
4987 @cindex variable name conflict
4988 There is an exception: you can refer to a variable or function whose
4989 scope is a single source file even if the current execution point is not
4990 in this file. But it is possible to have more than one such variable or
4991 function with the same name (in different source files). If that
4992 happens, referring to that name has unpredictable effects. If you wish,
4993 you can specify a static variable in a particular function or file,
4994 using the colon-colon notation:
4998 @c info cannot cope with a :: index entry, but why deprive hard copy readers?
5002 @var{file}::@var{variable}
5003 @var{function}::@var{variable}
5007 Here @var{file} or @var{function} is the name of the context for the
5008 static @var{variable}. In the case of file names, you can use quotes to
5009 make sure @value{GDBN} parses the file name as a single word---for example,
5010 to print a global value of @code{x} defined in @file{f2.c}:
5013 (@value{GDBP}) p 'f2.c'::x
5017 @cindex C++ scope resolution
5018 This use of @samp{::} is very rarely in conflict with the very similar
5019 use of the same notation in C++. @value{GDBN} also supports use of the C++
5020 scope resolution operator in @value{GDBN} expressions.
5021 @c FIXME: Um, so what happens in one of those rare cases where it's in
5025 @cindex wrong values
5026 @cindex variable values, wrong
5028 @emph{Warning:} Occasionally, a local variable may appear to have the
5029 wrong value at certain points in a function---just after entry to a new
5030 scope, and just before exit.
5032 You may see this problem when you are stepping by machine instructions.
5033 This is because, on most machines, it takes more than one instruction to
5034 set up a stack frame (including local variable definitions); if you are
5035 stepping by machine instructions, variables may appear to have the wrong
5036 values until the stack frame is completely built. On exit, it usually
5037 also takes more than one machine instruction to destroy a stack frame;
5038 after you begin stepping through that group of instructions, local
5039 variable definitions may be gone.
5041 @node Arrays, Output Formats, Variables, Data
5042 @section Artificial arrays
5044 @cindex artificial array
5046 It is often useful to print out several successive objects of the
5047 same type in memory; a section of an array, or an array of
5048 dynamically determined size for which only a pointer exists in the
5051 You can do this by referring to a contiguous span of memory as an
5052 @dfn{artificial array}, using the binary operator @samp{@@}. The left
5053 operand of @samp{@@} should be the first element of the desired array
5054 and be an individual object. The right operand should be the desired length
5055 of the array. The result is an array value whose elements are all of
5056 the type of the left argument. The first element is actually the left
5057 argument; the second element comes from bytes of memory immediately
5058 following those that hold the first element, and so on. Here is an
5059 example. If a program says
5062 int *array = (int *) malloc (len * sizeof (int));
5066 you can print the contents of @code{array} with
5072 The left operand of @samp{@@} must reside in memory. Array values made
5073 with @samp{@@} in this way behave just like other arrays in terms of
5074 subscripting, and are coerced to pointers when used in expressions.
5075 Artificial arrays most often appear in expressions via the value history
5076 (@pxref{Value History, ,Value history}), after printing one out.
5078 Another way to create an artificial array is to use a cast.
5079 This re-interprets a value as if it were an array.
5080 The value need not be in memory:
5082 (@value{GDBP}) p/x (short[2])0x12345678
5083 $1 = @{0x1234, 0x5678@}
5086 As a convenience, if you leave the array length out (as in
5087 @samp{(@var{type})[])@var{value}}) gdb calculates the size to fill
5088 the value (as @samp{sizeof(@var{value})/sizeof(@var{type})}:
5090 (@value{GDBP}) p/x (short[])0x12345678
5091 $2 = @{0x1234, 0x5678@}
5094 Sometimes the artificial array mechanism is not quite enough; in
5095 moderately complex data structures, the elements of interest may not
5096 actually be adjacent---for example, if you are interested in the values
5097 of pointers in an array. One useful work-around in this situation is
5098 to use a convenience variable (@pxref{Convenience Vars, ,Convenience
5099 variables}) as a counter in an expression that prints the first
5100 interesting value, and then repeat that expression via @key{RET}. For
5101 instance, suppose you have an array @code{dtab} of pointers to
5102 structures, and you are interested in the values of a field @code{fv}
5103 in each structure. Here is an example of what you might type:
5113 @node Output Formats, Memory, Arrays, Data
5114 @section Output formats
5116 @cindex formatted output
5117 @cindex output formats
5118 By default, @value{GDBN} prints a value according to its data type. Sometimes
5119 this is not what you want. For example, you might want to print a number
5120 in hex, or a pointer in decimal. Or you might want to view data in memory
5121 at a certain address as a character string or as an instruction. To do
5122 these things, specify an @dfn{output format} when you print a value.
5124 The simplest use of output formats is to say how to print a value
5125 already computed. This is done by starting the arguments of the
5126 @code{print} command with a slash and a format letter. The format
5127 letters supported are:
5131 Regard the bits of the value as an integer, and print the integer in
5135 Print as integer in signed decimal.
5138 Print as integer in unsigned decimal.
5141 Print as integer in octal.
5144 Print as integer in binary. The letter @samp{t} stands for ``two''.
5145 @footnote{@samp{b} cannot be used because these format letters are also
5146 used with the @code{x} command, where @samp{b} stands for ``byte'';
5147 @pxref{Memory,,Examining memory}.}
5150 @cindex unknown address, locating
5151 Print as an address, both absolute in hexadecimal and as an offset from
5152 the nearest preceding symbol. You can use this format used to discover
5153 where (in what function) an unknown address is located:
5156 (@value{GDBP}) p/a 0x54320
5157 $3 = 0x54320 <_initialize_vx+396>
5161 Regard as an integer and print it as a character constant.
5164 Regard the bits of the value as a floating point number and print
5165 using typical floating point syntax.
5168 For example, to print the program counter in hex (@pxref{Registers}), type
5175 Note that no space is required before the slash; this is because command
5176 names in @value{GDBN} cannot contain a slash.
5178 To reprint the last value in the value history with a different format,
5179 you can use the @code{print} command with just a format and no
5180 expression. For example, @samp{p/x} reprints the last value in hex.
5182 @node Memory, Auto Display, Output Formats, Data
5183 @section Examining memory
5185 You can use the command @code{x} (for ``examine'') to examine memory in
5186 any of several formats, independently of your program's data types.
5188 @cindex examining memory
5191 @item x/@var{nfu} @var{addr}
5194 Use the @code{x} command to examine memory.
5197 @var{n}, @var{f}, and @var{u} are all optional parameters that specify how
5198 much memory to display and how to format it; @var{addr} is an
5199 expression giving the address where you want to start displaying memory.
5200 If you use defaults for @var{nfu}, you need not type the slash @samp{/}.
5201 Several commands set convenient defaults for @var{addr}.
5204 @item @var{n}, the repeat count
5205 The repeat count is a decimal integer; the default is 1. It specifies
5206 how much memory (counting by units @var{u}) to display.
5207 @c This really is **decimal**; unaffected by 'set radix' as of GDB
5210 @item @var{f}, the display format
5211 The display format is one of the formats used by @code{print},
5212 @samp{s} (null-terminated string), or @samp{i} (machine instruction).
5213 The default is @samp{x} (hexadecimal) initially.
5214 The default changes each time you use either @code{x} or @code{print}.
5216 @item @var{u}, the unit size
5217 The unit size is any of
5223 Halfwords (two bytes).
5225 Words (four bytes). This is the initial default.
5227 Giant words (eight bytes).
5230 Each time you specify a unit size with @code{x}, that size becomes the
5231 default unit the next time you use @code{x}. (For the @samp{s} and
5232 @samp{i} formats, the unit size is ignored and is normally not written.)
5234 @item @var{addr}, starting display address
5235 @var{addr} is the address where you want @value{GDBN} to begin displaying
5236 memory. The expression need not have a pointer value (though it may);
5237 it is always interpreted as an integer address of a byte of memory.
5238 @xref{Expressions, ,Expressions}, for more information on expressions. The default for
5239 @var{addr} is usually just after the last address examined---but several
5240 other commands also set the default address: @code{info breakpoints} (to
5241 the address of the last breakpoint listed), @code{info line} (to the
5242 starting address of a line), and @code{print} (if you use it to display
5243 a value from memory).
5246 For example, @samp{x/3uh 0x54320} is a request to display three halfwords
5247 (@code{h}) of memory, formatted as unsigned decimal integers (@samp{u}),
5248 starting at address @code{0x54320}. @samp{x/4xw $sp} prints the four
5249 words (@samp{w}) of memory above the stack pointer (here, @samp{$sp};
5250 @pxref{Registers}) in hexadecimal (@samp{x}).
5252 Since the letters indicating unit sizes are all distinct from the
5253 letters specifying output formats, you do not have to remember whether
5254 unit size or format comes first; either order works. The output
5255 specifications @samp{4xw} and @samp{4wx} mean exactly the same thing.
5256 (However, the count @var{n} must come first; @samp{wx4} does not work.)
5258 Even though the unit size @var{u} is ignored for the formats @samp{s}
5259 and @samp{i}, you might still want to use a count @var{n}; for example,
5260 @samp{3i} specifies that you want to see three machine instructions,
5261 including any operands. The command @code{disassemble} gives an
5262 alternative way of inspecting machine instructions; @pxref{Machine
5263 Code,,Source and machine code}.
5265 All the defaults for the arguments to @code{x} are designed to make it
5266 easy to continue scanning memory with minimal specifications each time
5267 you use @code{x}. For example, after you have inspected three machine
5268 instructions with @samp{x/3i @var{addr}}, you can inspect the next seven
5269 with just @samp{x/7}. If you use @key{RET} to repeat the @code{x} command,
5270 the repeat count @var{n} is used again; the other arguments default as
5271 for successive uses of @code{x}.
5273 @cindex @code{$_}, @code{$__}, and value history
5274 The addresses and contents printed by the @code{x} command are not saved
5275 in the value history because there is often too much of them and they
5276 would get in the way. Instead, @value{GDBN} makes these values available for
5277 subsequent use in expressions as values of the convenience variables
5278 @code{$_} and @code{$__}. After an @code{x} command, the last address
5279 examined is available for use in expressions in the convenience variable
5280 @code{$_}. The contents of that address, as examined, are available in
5281 the convenience variable @code{$__}.
5283 If the @code{x} command has a repeat count, the address and contents saved
5284 are from the last memory unit printed; this is not the same as the last
5285 address printed if several units were printed on the last line of output.
5287 @node Auto Display, Print Settings, Memory, Data
5288 @section Automatic display
5289 @cindex automatic display
5290 @cindex display of expressions
5292 If you find that you want to print the value of an expression frequently
5293 (to see how it changes), you might want to add it to the @dfn{automatic
5294 display list} so that @value{GDBN} prints its value each time your program stops.
5295 Each expression added to the list is given a number to identify it;
5296 to remove an expression from the list, you specify that number.
5297 The automatic display looks like this:
5301 3: bar[5] = (struct hack *) 0x3804
5305 This display shows item numbers, expressions and their current values. As with
5306 displays you request manually using @code{x} or @code{print}, you can
5307 specify the output format you prefer; in fact, @code{display} decides
5308 whether to use @code{print} or @code{x} depending on how elaborate your
5309 format specification is---it uses @code{x} if you specify a unit size,
5310 or one of the two formats (@samp{i} and @samp{s}) that are only
5311 supported by @code{x}; otherwise it uses @code{print}.
5315 @item display @var{exp}
5316 Add the expression @var{exp} to the list of expressions to display
5317 each time your program stops. @xref{Expressions, ,Expressions}.
5319 @code{display} does not repeat if you press @key{RET} again after using it.
5321 @item display/@var{fmt} @var{exp}
5322 For @var{fmt} specifying only a display format and not a size or
5323 count, add the expression @var{exp} to the auto-display list but
5324 arrange to display it each time in the specified format @var{fmt}.
5325 @xref{Output Formats,,Output formats}.
5327 @item display/@var{fmt} @var{addr}
5328 For @var{fmt} @samp{i} or @samp{s}, or including a unit-size or a
5329 number of units, add the expression @var{addr} as a memory address to
5330 be examined each time your program stops. Examining means in effect
5331 doing @samp{x/@var{fmt} @var{addr}}. @xref{Memory, ,Examining memory}.
5334 For example, @samp{display/i $pc} can be helpful, to see the machine
5335 instruction about to be executed each time execution stops (@samp{$pc}
5336 is a common name for the program counter; @pxref{Registers}).
5339 @kindex delete display
5341 @item undisplay @var{dnums}@dots{}
5342 @itemx delete display @var{dnums}@dots{}
5343 Remove item numbers @var{dnums} from the list of expressions to display.
5345 @code{undisplay} does not repeat if you press @key{RET} after using it.
5346 (Otherwise you would just get the error @samp{No display number @dots{}}.)
5348 @kindex disable display
5349 @item disable display @var{dnums}@dots{}
5350 Disable the display of item numbers @var{dnums}. A disabled display
5351 item is not printed automatically, but is not forgotten. It may be
5352 enabled again later.
5354 @kindex enable display
5355 @item enable display @var{dnums}@dots{}
5356 Enable display of item numbers @var{dnums}. It becomes effective once
5357 again in auto display of its expression, until you specify otherwise.
5360 Display the current values of the expressions on the list, just as is
5361 done when your program stops.
5363 @kindex info display
5365 Print the list of expressions previously set up to display
5366 automatically, each one with its item number, but without showing the
5367 values. This includes disabled expressions, which are marked as such.
5368 It also includes expressions which would not be displayed right now
5369 because they refer to automatic variables not currently available.
5372 If a display expression refers to local variables, then it does not make
5373 sense outside the lexical context for which it was set up. Such an
5374 expression is disabled when execution enters a context where one of its
5375 variables is not defined. For example, if you give the command
5376 @code{display last_char} while inside a function with an argument
5377 @code{last_char}, @value{GDBN} displays this argument while your program
5378 continues to stop inside that function. When it stops elsewhere---where
5379 there is no variable @code{last_char}---the display is disabled
5380 automatically. The next time your program stops where @code{last_char}
5381 is meaningful, you can enable the display expression once again.
5383 @node Print Settings, Value History, Auto Display, Data
5384 @section Print settings
5386 @cindex format options
5387 @cindex print settings
5388 @value{GDBN} provides the following ways to control how arrays, structures,
5389 and symbols are printed.
5392 These settings are useful for debugging programs in any language:
5395 @kindex set print address
5396 @item set print address
5397 @itemx set print address on
5398 @value{GDBN} prints memory addresses showing the location of stack
5399 traces, structure values, pointer values, breakpoints, and so forth,
5400 even when it also displays the contents of those addresses. The default
5401 is @code{on}. For example, this is what a stack frame display looks like with
5402 @code{set print address on}:
5407 #0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>")
5409 530 if (lquote != def_lquote)
5413 @item set print address off
5414 Do not print addresses when displaying their contents. For example,
5415 this is the same stack frame displayed with @code{set print address off}:
5419 (@value{GDBP}) set print addr off
5421 #0 set_quotes (lq="<<", rq=">>") at input.c:530
5422 530 if (lquote != def_lquote)
5426 You can use @samp{set print address off} to eliminate all machine
5427 dependent displays from the @value{GDBN} interface. For example, with
5428 @code{print address off}, you should get the same text for backtraces on
5429 all machines---whether or not they involve pointer arguments.
5431 @kindex show print address
5432 @item show print address
5433 Show whether or not addresses are to be printed.
5436 When @value{GDBN} prints a symbolic address, it normally prints the
5437 closest earlier symbol plus an offset. If that symbol does not uniquely
5438 identify the address (for example, it is a name whose scope is a single
5439 source file), you may need to clarify. One way to do this is with
5440 @code{info line}, for example @samp{info line *0x4537}. Alternately,
5441 you can set @value{GDBN} to print the source file and line number when
5442 it prints a symbolic address:
5445 @kindex set print symbol-filename
5446 @item set print symbol-filename on
5447 Tell @value{GDBN} to print the source file name and line number of a
5448 symbol in the symbolic form of an address.
5450 @item set print symbol-filename off
5451 Do not print source file name and line number of a symbol. This is the
5454 @kindex show print symbol-filename
5455 @item show print symbol-filename
5456 Show whether or not @value{GDBN} will print the source file name and
5457 line number of a symbol in the symbolic form of an address.
5460 Another situation where it is helpful to show symbol filenames and line
5461 numbers is when disassembling code; @value{GDBN} shows you the line
5462 number and source file that corresponds to each instruction.
5464 Also, you may wish to see the symbolic form only if the address being
5465 printed is reasonably close to the closest earlier symbol:
5468 @kindex set print max-symbolic-offset
5469 @item set print max-symbolic-offset @var{max-offset}
5470 Tell @value{GDBN} to only display the symbolic form of an address if the
5471 offset between the closest earlier symbol and the address is less than
5472 @var{max-offset}. The default is 0, which tells @value{GDBN}
5473 to always print the symbolic form of an address if any symbol precedes it.
5475 @kindex show print max-symbolic-offset
5476 @item show print max-symbolic-offset
5477 Ask how large the maximum offset is that @value{GDBN} prints in a
5481 @cindex wild pointer, interpreting
5482 @cindex pointer, finding referent
5483 If you have a pointer and you are not sure where it points, try
5484 @samp{set print symbol-filename on}. Then you can determine the name
5485 and source file location of the variable where it points, using
5486 @samp{p/a @var{pointer}}. This interprets the address in symbolic form.
5487 For example, here @value{GDBN} shows that a variable @code{ptt} points
5488 at another variable @code{t}, defined in @file{hi2.c}:
5491 (@value{GDBP}) set print symbol-filename on
5492 (@value{GDBP}) p/a ptt
5493 $4 = 0xe008 <t in hi2.c>
5497 @emph{Warning:} For pointers that point to a local variable, @samp{p/a}
5498 does not show the symbol name and filename of the referent, even with
5499 the appropriate @code{set print} options turned on.
5502 Other settings control how different kinds of objects are printed:
5505 @kindex set print array
5506 @item set print array
5507 @itemx set print array on
5508 Pretty print arrays. This format is more convenient to read,
5509 but uses more space. The default is off.
5511 @item set print array off
5512 Return to compressed format for arrays.
5514 @kindex show print array
5515 @item show print array
5516 Show whether compressed or pretty format is selected for displaying
5519 @kindex set print elements
5520 @item set print elements @var{number-of-elements}
5521 Set a limit on how many elements of an array @value{GDBN} will print.
5522 If @value{GDBN} is printing a large array, it stops printing after it has
5523 printed the number of elements set by the @code{set print elements} command.
5524 This limit also applies to the display of strings.
5525 Setting @var{number-of-elements} to zero means that the printing is unlimited.
5527 @kindex show print elements
5528 @item show print elements
5529 Display the number of elements of a large array that @value{GDBN} will print.
5530 If the number is 0, then the printing is unlimited.
5532 @kindex set print null-stop
5533 @item set print null-stop
5534 Cause @value{GDBN} to stop printing the characters of an array when the first
5535 @sc{NULL} is encountered. This is useful when large arrays actually
5536 contain only short strings.
5538 @kindex set print pretty
5539 @item set print pretty on
5540 Cause @value{GDBN} to print structures in an indented format with one member
5541 per line, like this:
5556 @item set print pretty off
5557 Cause @value{GDBN} to print structures in a compact format, like this:
5561 $1 = @{next = 0x0, flags = @{sweet = 1, sour = 1@}, \
5562 meat = 0x54 "Pork"@}
5567 This is the default format.
5569 @kindex show print pretty
5570 @item show print pretty
5571 Show which format @value{GDBN} is using to print structures.
5573 @kindex set print sevenbit-strings
5574 @item set print sevenbit-strings on
5575 Print using only seven-bit characters; if this option is set,
5576 @value{GDBN} displays any eight-bit characters (in strings or
5577 character values) using the notation @code{\}@var{nnn}. This setting is
5578 best if you are working in English (@sc{ascii}) and you use the
5579 high-order bit of characters as a marker or ``meta'' bit.
5581 @item set print sevenbit-strings off
5582 Print full eight-bit characters. This allows the use of more
5583 international character sets, and is the default.
5585 @kindex show print sevenbit-strings
5586 @item show print sevenbit-strings
5587 Show whether or not @value{GDBN} is printing only seven-bit characters.
5589 @kindex set print union
5590 @item set print union on
5591 Tell @value{GDBN} to print unions which are contained in structures. This
5592 is the default setting.
5594 @item set print union off
5595 Tell @value{GDBN} not to print unions which are contained in structures.
5597 @kindex show print union
5598 @item show print union
5599 Ask @value{GDBN} whether or not it will print unions which are contained in
5602 For example, given the declarations
5605 typedef enum @{Tree, Bug@} Species;
5606 typedef enum @{Big_tree, Acorn, Seedling@} Tree_forms;
5607 typedef enum @{Caterpillar, Cocoon, Butterfly@}
5618 struct thing foo = @{Tree, @{Acorn@}@};
5622 with @code{set print union on} in effect @samp{p foo} would print
5625 $1 = @{it = Tree, form = @{tree = Acorn, bug = Cocoon@}@}
5629 and with @code{set print union off} in effect it would print
5632 $1 = @{it = Tree, form = @{...@}@}
5639 These settings are of interest when debugging C++ programs:
5643 @kindex set print demangle
5644 @item set print demangle
5645 @itemx set print demangle on
5646 Print C++ names in their source form rather than in the encoded
5647 (``mangled'') form passed to the assembler and linker for type-safe
5648 linkage. The default is @samp{on}.
5650 @kindex show print demangle
5651 @item show print demangle
5652 Show whether C++ names are printed in mangled or demangled form.
5654 @kindex set print asm-demangle
5655 @item set print asm-demangle
5656 @itemx set print asm-demangle on
5657 Print C++ names in their source form rather than their mangled form, even
5658 in assembler code printouts such as instruction disassemblies.
5661 @kindex show print asm-demangle
5662 @item show print asm-demangle
5663 Show whether C++ names in assembly listings are printed in mangled
5666 @kindex set demangle-style
5667 @cindex C++ symbol decoding style
5668 @cindex symbol decoding style, C++
5669 @item set demangle-style @var{style}
5670 Choose among several encoding schemes used by different compilers to
5671 represent C++ names. The choices for @var{style} are currently:
5675 Allow @value{GDBN} to choose a decoding style by inspecting your program.
5678 Decode based on the @sc{gnu} C++ compiler (@code{g++}) encoding algorithm.
5680 This is the default.
5685 Decode based on the HP ANSI C++ (@code{aCC}) encoding algorithm.
5689 Decode based on the Lucid C++ compiler (@code{lcc}) encoding algorithm.
5692 Decode using the algorithm in the @cite{C++ Annotated Reference Manual}.
5693 @strong{Warning:} this setting alone is not sufficient to allow
5694 debugging @code{cfront}-generated executables. @value{GDBN} would
5695 require further enhancement to permit that.
5698 Show the list of formats.
5701 @kindex show demangle-style
5702 @item show demangle-style
5703 Display the encoding style currently in use for decoding C++ symbols.
5705 @kindex set print object
5706 @item set print object
5707 @itemx set print object on
5708 When displaying a pointer to an object, identify the @emph{actual}
5709 (derived) type of the object rather than the @emph{declared} type, using
5710 the virtual function table.
5712 @item set print object off
5713 Display only the declared type of objects, without reference to the
5714 virtual function table. This is the default setting.
5716 @kindex show print object
5717 @item show print object
5718 Show whether actual, or declared, object types are displayed.
5720 @kindex set print static-members
5721 @item set print static-members
5722 @itemx set print static-members on
5723 Print static members when displaying a C++ object. The default is on.
5725 @item set print static-members off
5726 Do not print static members when displaying a C++ object.
5728 @kindex show print static-members
5729 @item show print static-members
5730 Show whether C++ static members are printed, or not.
5732 @c These don't work with HP ANSI C++ yet.
5733 @kindex set print vtbl
5734 @item set print vtbl
5735 @itemx set print vtbl on
5736 Pretty print C++ virtual function tables. The default is off.
5738 (The @code{vtbl} commands do not work on programs compiled with the HP
5739 ANSI C++ compiler (@code{aCC}).)
5742 @item set print vtbl off
5743 Do not pretty print C++ virtual function tables.
5745 @kindex show print vtbl
5746 @item show print vtbl
5747 Show whether C++ virtual function tables are pretty printed, or not.
5751 @node Value History, Convenience Vars, Print Settings, Data
5752 @section Value history
5754 @cindex value history
5755 Values printed by the @code{print} command are saved in the @value{GDBN}
5756 @dfn{value history}. This allows you to refer to them in other expressions.
5757 Values are kept until the symbol table is re-read or discarded
5758 (for example with the @code{file} or @code{symbol-file} commands).
5759 When the symbol table changes, the value history is discarded,
5760 since the values may contain pointers back to the types defined in the
5765 @cindex history number
5766 The values printed are given @dfn{history numbers} by which you can
5767 refer to them. These are successive integers starting with one.
5768 @code{print} shows you the history number assigned to a value by
5769 printing @samp{$@var{num} = } before the value; here @var{num} is the
5772 To refer to any previous value, use @samp{$} followed by the value's
5773 history number. The way @code{print} labels its output is designed to
5774 remind you of this. Just @code{$} refers to the most recent value in
5775 the history, and @code{$$} refers to the value before that.
5776 @code{$$@var{n}} refers to the @var{n}th value from the end; @code{$$2}
5777 is the value just prior to @code{$$}, @code{$$1} is equivalent to
5778 @code{$$}, and @code{$$0} is equivalent to @code{$}.
5780 For example, suppose you have just printed a pointer to a structure and
5781 want to see the contents of the structure. It suffices to type
5787 If you have a chain of structures where the component @code{next} points
5788 to the next one, you can print the contents of the next one with this:
5795 You can print successive links in the chain by repeating this
5796 command---which you can do by just typing @key{RET}.
5798 Note that the history records values, not expressions. If the value of
5799 @code{x} is 4 and you type these commands:
5807 then the value recorded in the value history by the @code{print} command
5808 remains 4 even though the value of @code{x} has changed.
5813 Print the last ten values in the value history, with their item numbers.
5814 This is like @samp{p@ $$9} repeated ten times, except that @code{show
5815 values} does not change the history.
5817 @item show values @var{n}
5818 Print ten history values centered on history item number @var{n}.
5821 Print ten history values just after the values last printed. If no more
5822 values are available, @code{show values +} produces no display.
5825 Pressing @key{RET} to repeat @code{show values @var{n}} has exactly the
5826 same effect as @samp{show values +}.
5828 @node Convenience Vars, Registers, Value History, Data
5829 @section Convenience variables
5831 @cindex convenience variables
5832 @value{GDBN} provides @dfn{convenience variables} that you can use within
5833 @value{GDBN} to hold on to a value and refer to it later. These variables
5834 exist entirely within @value{GDBN}; they are not part of your program, and
5835 setting a convenience variable has no direct effect on further execution
5836 of your program. That is why you can use them freely.
5838 Convenience variables are prefixed with @samp{$}. Any name preceded by
5839 @samp{$} can be used for a convenience variable, unless it is one of
5840 the predefined machine-specific register names (@pxref{Registers}).
5841 (Value history references, in contrast, are @emph{numbers} preceded
5842 by @samp{$}. @xref{Value History, ,Value history}.)
5844 You can save a value in a convenience variable with an assignment
5845 expression, just as you would set a variable in your program.
5849 set $foo = *object_ptr
5853 would save in @code{$foo} the value contained in the object pointed to by
5856 Using a convenience variable for the first time creates it, but its
5857 value is @code{void} until you assign a new value. You can alter the
5858 value with another assignment at any time.
5860 Convenience variables have no fixed types. You can assign a convenience
5861 variable any type of value, including structures and arrays, even if
5862 that variable already has a value of a different type. The convenience
5863 variable, when used as an expression, has the type of its current value.
5866 @kindex show convenience
5867 @item show convenience
5868 Print a list of convenience variables used so far, and their values.
5869 Abbreviated @code{show con}.
5872 One of the ways to use a convenience variable is as a counter to be
5873 incremented or a pointer to be advanced. For example, to print
5874 a field from successive elements of an array of structures:
5878 print bar[$i++]->contents
5881 @noindent Repeat that command by typing @key{RET}.
5883 Some convenience variables are created automatically by @value{GDBN} and given
5884 values likely to be useful.
5889 The variable @code{$_} is automatically set by the @code{x} command to
5890 the last address examined (@pxref{Memory, ,Examining memory}). Other
5891 commands which provide a default address for @code{x} to examine also
5892 set @code{$_} to that address; these commands include @code{info line}
5893 and @code{info breakpoint}. The type of @code{$_} is @code{void *}
5894 except when set by the @code{x} command, in which case it is a pointer
5895 to the type of @code{$__}.
5899 The variable @code{$__} is automatically set by the @code{x} command
5900 to the value found in the last address examined. Its type is chosen
5901 to match the format in which the data was printed.
5905 The variable @code{$_exitcode} is automatically set to the exit code when
5906 the program being debugged terminates.
5910 If you refer to a function or variable name that begins with a dollar
5911 sign, @value{GDBN} searches for a user or system name first, before it
5912 searches for a convenience variable.
5915 @node Registers, Floating Point Hardware, Convenience Vars, Data
5919 You can refer to machine register contents, in expressions, as variables
5920 with names starting with @samp{$}. The names of registers are different
5921 for each machine; use @code{info registers} to see the names used on
5925 @kindex info registers
5926 @item info registers
5927 Print the names and values of all registers except floating-point
5928 registers (in the selected stack frame).
5930 @kindex info all-registers
5931 @cindex floating point registers
5932 @item info all-registers
5933 Print the names and values of all registers, including floating-point
5936 @item info registers @var{regname} @dots{}
5937 Print the @dfn{relativized} value of each specified register @var{regname}.
5938 As discussed in detail below, register values are normally relative to
5939 the selected stack frame. @var{regname} may be any register name valid on
5940 the machine you are using, with or without the initial @samp{$}.
5943 @value{GDBN} has four ``standard'' register names that are available (in
5944 expressions) on most machines---whenever they do not conflict with an
5945 architecture's canonical mnemonics for registers. The register names
5946 @code{$pc} and @code{$sp} are used for the program counter register and
5947 the stack pointer. @code{$fp} is used for a register that contains a
5948 pointer to the current stack frame, and @code{$ps} is used for a
5949 register that contains the processor status. For example,
5950 you could print the program counter in hex with
5957 or print the instruction to be executed next with
5964 or add four to the stack pointer@footnote{This is a way of removing
5965 one word from the stack, on machines where stacks grow downward in
5966 memory (most machines, nowadays). This assumes that the innermost
5967 stack frame is selected; setting @code{$sp} is not allowed when other
5968 stack frames are selected. To pop entire frames off the stack,
5969 regardless of machine architecture, use @code{return};
5970 @pxref{Returning, ,Returning from a function}.} with
5976 Whenever possible, these four standard register names are available on
5977 your machine even though the machine has different canonical mnemonics,
5978 so long as there is no conflict. The @code{info registers} command
5979 shows the canonical names. For example, on the SPARC, @code{info
5980 registers} displays the processor status register as @code{$psr} but you
5981 can also refer to it as @code{$ps}.
5983 @value{GDBN} always considers the contents of an ordinary register as an
5984 integer when the register is examined in this way. Some machines have
5985 special registers which can hold nothing but floating point; these
5986 registers are considered to have floating point values. There is no way
5987 to refer to the contents of an ordinary register as floating point value
5988 (although you can @emph{print} it as a floating point value with
5989 @samp{print/f $@var{regname}}).
5991 Some registers have distinct ``raw'' and ``virtual'' data formats. This
5992 means that the data format in which the register contents are saved by
5993 the operating system is not the same one that your program normally
5994 sees. For example, the registers of the 68881 floating point
5995 coprocessor are always saved in ``extended'' (raw) format, but all C
5996 programs expect to work with ``double'' (virtual) format. In such
5997 cases, @value{GDBN} normally works with the virtual format only (the format
5998 that makes sense for your program), but the @code{info registers} command
5999 prints the data in both formats.
6001 Normally, register values are relative to the selected stack frame
6002 (@pxref{Selection, ,Selecting a frame}). This means that you get the
6003 value that the register would contain if all stack frames farther in
6004 were exited and their saved registers restored. In order to see the
6005 true contents of hardware registers, you must select the innermost
6006 frame (with @samp{frame 0}).
6008 However, @value{GDBN} must deduce where registers are saved, from the machine
6009 code generated by your compiler. If some registers are not saved, or if
6010 @value{GDBN} is unable to locate the saved registers, the selected stack
6011 frame makes no difference.
6015 @kindex set rstack_high_address
6016 @cindex AMD 29K register stack
6017 @cindex register stack, AMD29K
6018 @item set rstack_high_address @var{address}
6019 On AMD 29000 family processors, registers are saved in a separate
6020 ``register stack''. There is no way for @value{GDBN} to determine the extent
6021 of this stack. Normally, @value{GDBN} just assumes that the stack is ``large
6022 enough''. This may result in @value{GDBN} referencing memory locations that
6023 do not exist. If necessary, you can get around this problem by
6024 specifying the ending address of the register stack with the @code{set
6025 rstack_high_address} command. The argument should be an address, which
6026 you probably want to precede with @samp{0x} to specify in
6029 @kindex show rstack_high_address
6030 @item show rstack_high_address
6031 Display the current limit of the register stack, on AMD 29000 family
6037 @node Floating Point Hardware, , Registers, Data
6038 @section Floating point hardware
6039 @cindex floating point
6041 Depending on the configuration, @value{GDBN} may be able to give
6042 you more information about the status of the floating point hardware.
6047 Display hardware-dependent information about the floating
6048 point unit. The exact contents and layout vary depending on the
6049 floating point chip. Currently, @samp{info float} is supported on
6050 the ARM and x86 machines.
6055 @node Languages, Symbols, Data, Top
6056 @chapter Using @value{GDBN} with Different Languages
6060 Although programming languages generally have common aspects, they are
6061 rarely expressed in the same manner. For instance, in ANSI C,
6062 dereferencing a pointer @code{p} is accomplished by @code{*p}, but in
6063 Modula-2, it is accomplished by @code{p^}. Values can also be
6064 represented (and displayed) differently. Hex numbers in C appear as
6065 @samp{0x1ae}, while in Modula-2 they appear as @samp{1AEH}.
6068 @cindex working language
6069 Language-specific information is built into @value{GDBN} for some languages,
6070 allowing you to express operations like the above in your program's
6071 native language, and allowing @value{GDBN} to output values in a manner
6072 consistent with the syntax of your program's native language. The
6073 language you use to build expressions is called the @dfn{working
6077 * Setting:: Switching between source languages
6078 * Show:: Displaying the language
6080 * Checks:: Type and range checks
6083 * Support:: Supported languages
6086 @node Setting, Show, Languages, Languages
6087 @section Switching between source languages
6089 There are two ways to control the working language---either have @value{GDBN}
6090 set it automatically, or select it manually yourself. You can use the
6091 @code{set language} command for either purpose. On startup, @value{GDBN}
6092 defaults to setting the language automatically. The working language is
6093 used to determine how expressions you type are interpreted, how values
6096 In addition to the working language, every source file that
6097 @value{GDBN} knows about has its own working language. For some object
6098 file formats, the compiler might indicate which language a particular
6099 source file is in. However, most of the time @value{GDBN} infers the
6100 language from the name of the file. The language of a source file
6101 controls whether C++ names are demangled---this way @code{backtrace} can
6102 show each frame appropriately for its own language. There is no way to
6103 set the language of a source file from within @value{GDBN}.
6105 This is most commonly a problem when you use a program, such
6106 as @code{cfront} or @code{f2c}, that generates C but is written in
6107 another language. In that case, make the
6108 program use @code{#line} directives in its C output; that way
6109 @value{GDBN} will know the correct language of the source code of the original
6110 program, and will display that source code, not the generated C code.
6113 * Filenames:: Filename extensions and languages.
6114 * Manually:: Setting the working language manually
6115 * Automatically:: Having @value{GDBN} infer the source language
6118 @node Filenames, Manually, Setting, Setting
6119 @subsection List of filename extensions and languages
6121 If a source file name ends in one of the following extensions, then
6122 @value{GDBN} infers that its language is the one indicated.
6127 Modula-2 source file
6150 Assembler source file. This actually behaves almost like C, but
6151 @value{GDBN} does not skip over function prologues when stepping.
6154 @node Manually, Automatically, Filenames, Setting
6155 @subsection Setting the working language
6157 If you allow @value{GDBN} to set the language automatically,
6158 expressions are interpreted the same way in your debugging session and
6161 @kindex set language
6162 If you wish, you may set the language manually. To do this, issue the
6163 command @samp{set language @var{lang}}, where @var{lang} is the name of
6169 @code{c} or @code{modula-2}.
6171 For a list of the supported languages, type @samp{set language}.
6174 Setting the language manually prevents @value{GDBN} from updating the
6175 working language automatically. For example, if you used the @code{c}
6176 setting to debug a C++ program, names might not be demangled properly,
6177 overload resolution would not work, user-defined operators might not be
6178 interpreted correctly, and so on.
6181 Setting the language manually prevents @value{GDBN} from updating the working
6182 language automatically. This can lead to confusion if you try
6183 to debug a program when the working language is not the same as the
6184 source language, when an expression is acceptable to both
6185 languages---but means different things. For instance, if the current
6186 source file were written in C, and @value{GDBN} was parsing Modula-2, a
6194 might not have the effect you intended. In C, this means to add
6195 @code{b} and @code{c} and place the result in @code{a}. The result
6196 printed would be the value of @code{a}. In Modula-2, this means to compare
6197 @code{a} to the result of @code{b+c}, yielding a @code{BOOLEAN} value.
6200 @node Automatically, , Manually, Setting
6201 @subsection Having @value{GDBN} infer the source language
6203 To have @value{GDBN} set the working language automatically, use
6204 @samp{set language local} or @samp{set language auto}. @value{GDBN}
6205 then infers the working language. That is, when your program stops in a
6206 frame (usually by encountering a breakpoint), @value{GDBN} sets the
6207 working language to the language recorded for the function in that
6208 frame. If the language for a frame is unknown (that is, if the function
6209 or block corresponding to the frame was defined in a source file that
6210 does not have a recognized extension), the current working language is
6211 not changed, and @value{GDBN} issues a warning.
6213 This may not seem necessary for most programs, which are written
6214 entirely in one source language. However, program modules and libraries
6215 written in one source language can be used by a main program written in
6216 a different source language. Using @samp{set language auto} in this
6217 case frees you from having to set the working language manually.
6220 @node Show, Checks, Setting, Languages
6221 @section Displaying the language
6224 @node Show, Support, Setting, Languages
6225 @section Displaying the language
6228 The following commands help you find out which language is the
6229 working language, and also what language source files were written in.
6231 @kindex show language
6236 Display the current working language. This is the
6237 language you can use with commands such as @code{print} to
6238 build and compute expressions that may involve variables in your program.
6241 Display the source language for this frame. This language becomes the
6242 working language if you use an identifier from this frame.
6243 @xref{Frame Info, ,Information about a frame}, to identify the other
6244 information listed here.
6247 Display the source language of this source file.
6248 @xref{Symbols, ,Examining the Symbol Table}, to identify the other
6249 information listed here.
6253 @node Checks, Support, Show, Languages
6254 @section Type and range checking
6257 @emph{Warning:} In this release, the @value{GDBN} commands for type and range
6258 checking are included, but they do not yet have any effect. This
6259 section documents the intended facilities.
6261 @c FIXME remove warning when type/range code added
6263 Some languages are designed to guard you against making seemingly common
6264 errors through a series of compile- and run-time checks. These include
6265 checking the type of arguments to functions and operators, and making
6266 sure mathematical overflows are caught at run time. Checks such as
6267 these help to ensure a program's correctness once it has been compiled
6268 by eliminating type mismatches, and providing active checks for range
6269 errors when your program is running.
6271 @value{GDBN} can check for conditions like the above if you wish.
6272 Although @value{GDBN} does not check the statements in your program, it
6273 can check expressions entered directly into @value{GDBN} for evaluation via
6274 the @code{print} command, for example. As with the working language,
6275 @value{GDBN} can also decide whether or not to check automatically based on
6276 your program's source language. @xref{Support, ,Supported languages},
6277 for the default settings of supported languages.
6280 * Type Checking:: An overview of type checking
6281 * Range Checking:: An overview of range checking
6284 @cindex type checking
6285 @cindex checks, type
6286 @node Type Checking, Range Checking, Checks, Checks
6287 @subsection An overview of type checking
6289 Some languages, such as Modula-2, are strongly typed, meaning that the
6290 arguments to operators and functions have to be of the correct type,
6291 otherwise an error occurs. These checks prevent type mismatch
6292 errors from ever causing any run-time problems. For example,
6300 The second example fails because the @code{CARDINAL} 1 is not
6301 type-compatible with the @code{REAL} 2.3.
6303 For the expressions you use in @value{GDBN} commands, you can tell the
6304 @value{GDBN} type checker to skip checking;
6305 to treat any mismatches as errors and abandon the expression;
6306 or to only issue warnings when type mismatches occur,
6307 but evaluate the expression anyway. When you choose the last of
6308 these, @value{GDBN} evaluates expressions like the second example above, but
6309 also issues a warning.
6311 Even if you turn type checking off, there may be other reasons
6312 related to type that prevent @value{GDBN} from evaluating an expression.
6313 For instance, @value{GDBN} does not know how to add an @code{int} and
6314 a @code{struct foo}. These particular type errors have nothing to do
6315 with the language in use, and usually arise from expressions, such as
6316 the one described above, which make little sense to evaluate anyway.
6318 Each language defines to what degree it is strict about type. For
6319 instance, both Modula-2 and C require the arguments to arithmetical
6320 operators to be numbers. In C, enumerated types and pointers can be
6321 represented as numbers, so that they are valid arguments to mathematical
6322 operators. @xref{Support, ,Supported languages}, for further
6323 details on specific languages.
6325 @value{GDBN} provides some additional commands for controlling the type checker:
6328 @kindex set check type
6329 @kindex show check type
6331 @item set check type auto
6332 Set type checking on or off based on the current working language.
6333 @xref{Support, ,Supported languages}, for the default settings for
6336 @item set check type on
6337 @itemx set check type off
6338 Set type checking on or off, overriding the default setting for the
6339 current working language. Issue a warning if the setting does not
6340 match the language default. If any type mismatches occur in
6341 evaluating an expression while typechecking is on, @value{GDBN} prints a
6342 message and aborts evaluation of the expression.
6344 @item set check type warn
6345 Cause the type checker to issue warnings, but to always attempt to
6346 evaluate the expression. Evaluating the expression may still
6347 be impossible for other reasons. For example, @value{GDBN} cannot add
6348 numbers and structures.
6351 Show the current setting of the type checker, and whether or not @value{GDBN}
6352 is setting it automatically.
6355 @cindex range checking
6356 @cindex checks, range
6357 @node Range Checking, , Type Checking, Checks
6358 @subsection An overview of range checking
6360 In some languages (such as Modula-2), it is an error to exceed the
6361 bounds of a type; this is enforced with run-time checks. Such range
6362 checking is meant to ensure program correctness by making sure
6363 computations do not overflow, or indices on an array element access do
6364 not exceed the bounds of the array.
6366 For expressions you use in @value{GDBN} commands, you can tell
6367 @value{GDBN} to treat range errors in one of three ways: ignore them,
6368 always treat them as errors and abandon the expression, or issue
6369 warnings but evaluate the expression anyway.
6371 A range error can result from numerical overflow, from exceeding an
6372 array index bound, or when you type a constant that is not a member
6373 of any type. Some languages, however, do not treat overflows as an
6374 error. In many implementations of C, mathematical overflow causes the
6375 result to ``wrap around'' to lower values---for example, if @var{m} is
6376 the largest integer value, and @var{s} is the smallest, then
6379 @var{m} + 1 @result{} @var{s}
6382 This, too, is specific to individual languages, and in some cases
6383 specific to individual compilers or machines. @xref{Support, ,
6384 Supported languages}, for further details on specific languages.
6386 @value{GDBN} provides some additional commands for controlling the range checker:
6389 @kindex set check range
6390 @kindex show check range
6392 @item set check range auto
6393 Set range checking on or off based on the current working language.
6394 @xref{Support, ,Supported languages}, for the default settings for
6397 @item set check range on
6398 @itemx set check range off
6399 Set range checking on or off, overriding the default setting for the
6400 current working language. A warning is issued if the setting does not
6401 match the language default. If a range error occurs, then a message
6402 is printed and evaluation of the expression is aborted.
6404 @item set check range warn
6405 Output messages when the @value{GDBN} range checker detects a range error,
6406 but attempt to evaluate the expression anyway. Evaluating the
6407 expression may still be impossible for other reasons, such as accessing
6408 memory that the process does not own (a typical example from many Unix
6412 Show the current setting of the range checker, and whether or not it is
6413 being set automatically by @value{GDBN}.
6418 @node Support, , Checks, Languages
6419 @section Supported languages
6422 @node Support, , Show, Languages
6423 @section Supported languages
6427 @value{GDBN} 4 supports C, C++, and Modula-2.
6430 @value{GDBN} 4 supports C and C++.
6432 Some @value{GDBN} features may be used in expressions regardless of the
6433 language you use: the @value{GDBN} @code{@@} and @code{::} operators,
6434 and the @samp{@{type@}addr} construct (@pxref{Expressions,
6435 ,Expressions}) can be used with the constructs of any supported
6438 The following sections detail to what degree each source language is
6439 supported by @value{GDBN}. These sections are not meant to be language
6440 tutorials or references, but serve only as a reference guide to what the
6441 @value{GDBN} expression parser accepts, and what input and output
6442 formats should look like for different languages. There are many good
6443 books written on each of these languages; please look to these for a
6444 language reference or tutorial.
6449 * Modula-2:: Modula-2
6452 @node C, Modula-2, , Support
6453 @subsection C and C++
6455 @cindex expressions in C or C++
6458 Since C and C++ are so closely related, many features of @value{GDBN} apply
6459 to both languages. Whenever this is the case, we discuss those languages
6463 @c Cancel this below, under same condition, at end of this chapter!
6470 @cindex @sc{gnu} C++
6471 The C++ debugging facilities are jointly implemented by the @sc{gnu} C++
6472 compiler and @value{GDBN}. Therefore, to debug your C++ code
6473 effectively, you must compile your C++ programs with the @sc{gnu} C++
6474 compiler, @code{g++}.
6476 For best results when debugging C++ programs, use the stabs debugging
6477 format. You can select that format explicitly with the @code{g++}
6478 command-line options @samp{-gstabs} or @samp{-gstabs+}. See
6479 @ref{Debugging Options,,Options for Debugging Your Program or @sc{gnu} CC,
6480 gcc.info, Using @sc{gnu} CC}, for more information.
6485 @cindex @sc{gnu} C++
6486 You can use @value{GDBN} to debug C programs compiled with either the HP
6487 C compiler (@code{cc}) or the GNU C compiler (@code{gcc}), and to debug
6488 programs compiled with either the HP ANSI C++ compiler (@code{aCC}) or
6489 the @sc{gnu} C++ compiler (@code{g++}).
6491 If you compile with the @sc{gnu} C++ compiler, use the stabs debugging
6492 format for best results when debugging. You can select that format
6493 explicitly with the @code{g++} command-line options @samp{-gstabs} or
6494 @samp{-gstabs+}. See @ref{Debugging Options,,Options for Debugging Your
6495 Program or @sc{gnu} CC, gcc.info, Using @sc{gnu} CC}, for more
6501 @node C, Symbols, Data, Top
6502 @chapter C Language Support
6504 @cindex expressions in C
6506 Information specific to the C language is built into @value{GDBN} so that you
6507 can use C expressions while degugging. This also permits @value{GDBN} to
6508 output values in a manner consistent with C conventions.
6511 * C Operators:: C operators
6517 * C Operators:: C and C++ operators
6518 * C Constants:: C and C++ constants
6519 * Cplus expressions:: C++ expressions
6520 * C Defaults:: Default settings for C and C++
6522 * C Checks:: C and C++ type and range checks
6525 * Debugging C:: @value{GDBN} and C
6526 * Debugging C plus plus:: @value{GDBN} features for C++
6531 @cindex C and C++ operators
6532 @node C Operators, C Constants, , C
6533 @subsubsection C and C++ operators
6537 @node C Operators, C Constants, C, C
6538 @section C operators
6541 Operators must be defined on values of specific types. For instance,
6542 @code{+} is defined on numbers, but not on structures. Operators are
6543 often defined on groups of types.
6546 For the purposes of C and C++, the following definitions hold:
6552 @emph{Integral types} include @code{int} with any of its storage-class
6553 specifiers; @code{char}; and @code{enum}.
6556 @emph{Integral types} include @code{int} with any of its storage-class
6557 specifiers; @code{char}; @code{enum}; and, for C++, @code{bool}.
6561 @emph{Floating-point types} include @code{float} and @code{double}.
6564 @emph{Pointer types} include all types defined as @code{(@var{type}
6568 @emph{Scalar types} include all of the above.
6572 The following operators are supported. They are listed here
6573 in order of increasing precedence:
6577 The comma or sequencing operator. Expressions in a comma-separated list
6578 are evaluated from left to right, with the result of the entire
6579 expression being the last expression evaluated.
6582 Assignment. The value of an assignment expression is the value
6583 assigned. Defined on scalar types.
6586 Used in an expression of the form @w{@code{@var{a} @var{op}= @var{b}}},
6587 and translated to @w{@code{@var{a} = @var{a op b}}}.
6588 @w{@code{@var{op}=}} and @code{=} have the same precendence.
6589 @var{op} is any one of the operators @code{|}, @code{^}, @code{&},
6590 @code{<<}, @code{>>}, @code{+}, @code{-}, @code{*}, @code{/}, @code{%}.
6593 The ternary operator. @code{@var{a} ? @var{b} : @var{c}} can be thought
6594 of as: if @var{a} then @var{b} else @var{c}. @var{a} should be of an
6598 Logical @sc{or}. Defined on integral types.
6601 Logical @sc{and}. Defined on integral types.
6604 Bitwise @sc{or}. Defined on integral types.
6607 Bitwise exclusive-@sc{or}. Defined on integral types.
6610 Bitwise @sc{and}. Defined on integral types.
6613 Equality and inequality. Defined on scalar types. The value of these
6614 expressions is 0 for false and non-zero for true.
6616 @item <@r{, }>@r{, }<=@r{, }>=
6617 Less than, greater than, less than or equal, greater than or equal.
6618 Defined on scalar types. The value of these expressions is 0 for false
6619 and non-zero for true.
6622 left shift, and right shift. Defined on integral types.
6625 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
6628 Addition and subtraction. Defined on integral types, floating-point types and
6631 @item *@r{, }/@r{, }%
6632 Multiplication, division, and modulus. Multiplication and division are
6633 defined on integral and floating-point types. Modulus is defined on
6637 Increment and decrement. When appearing before a variable, the
6638 operation is performed before the variable is used in an expression;
6639 when appearing after it, the variable's value is used before the
6640 operation takes place.
6643 Pointer dereferencing. Defined on pointer types. Same precedence as
6647 Address operator. Defined on variables. Same precedence as @code{++}.
6650 For debugging C++, @value{GDBN} implements a use of @samp{&} beyond what is
6651 allowed in the C++ language itself: you can use @samp{&(&@var{ref})}
6652 (or, if you prefer, simply @samp{&&@var{ref}}) to examine the address
6653 where a C++ reference variable (declared with @samp{&@var{ref}}) is
6658 Negative. Defined on integral and floating-point types. Same
6659 precedence as @code{++}.
6662 Logical negation. Defined on integral types. Same precedence as
6666 Bitwise complement operator. Defined on integral types. Same precedence as
6671 Structure member, and pointer-to-structure member. For convenience,
6672 @value{GDBN} regards the two as equivalent, choosing whether to dereference a
6673 pointer based on the stored type information.
6674 Defined on @code{struct} and @code{union} data.
6678 Dereferences of pointers to members.
6682 Array indexing. @code{@var{a}[@var{i}]} is defined as
6683 @code{*(@var{a}+@var{i})}. Same precedence as @code{->}.
6686 Function parameter list. Same precedence as @code{->}.
6690 C++ scope resolution operator. Defined on
6691 @code{struct}, @code{union}, and @code{class} types.
6699 represent the @value{GDBN} scope operator (@pxref{Expressions,
6702 Same precedence as @code{::}, above.
6707 If an operator is redefined in the user code, @value{GDBN} usually
6708 attempts to invoke the redefined version instead of using the operator's
6718 @node C Constants, Cplus expressions, C Operators, C
6719 @subsubsection C and C++ constants
6722 @node C Constants, Cplus expressions, C Operators, Support
6723 @subsubsection C and C++ constants
6726 @cindex C and C++ constants
6727 @value{GDBN} allows you to express the constants of C and C++ in the
6732 @node C Constants, Debugging C, C Operators, C
6733 @section C constants
6735 @value{GDBN} allows you to express the constants of C in the
6741 Integer constants are a sequence of digits. Octal constants are
6742 specified by a leading @samp{0} (i.e. zero), and hexadecimal constants by
6743 a leading @samp{0x} or @samp{0X}. Constants may also end with a letter
6744 @samp{l}, specifying that the constant should be treated as a
6748 Floating point constants are a sequence of digits, followed by a decimal
6749 point, followed by a sequence of digits, and optionally followed by an
6750 exponent. An exponent is of the form:
6751 @samp{@w{e@r{[[}+@r{]|}-@r{]}@var{nnn}}}, where @var{nnn} is another
6752 sequence of digits. The @samp{+} is optional for positive exponents.
6755 Enumerated constants consist of enumerated identifiers, or their
6756 integral equivalents.
6759 Character constants are a single character surrounded by single quotes
6760 (@code{'}), or a number---the ordinal value of the corresponding character
6761 (usually its @sc{ASCII} value). Within quotes, the single character may
6762 be represented by a letter or by @dfn{escape sequences}, which are of
6763 the form @samp{\@var{nnn}}, where @var{nnn} is the octal representation
6764 of the character's ordinal value; or of the form @samp{\@var{x}}, where
6765 @samp{@var{x}} is a predefined special character---for example,
6766 @samp{\n} for newline.
6769 String constants are a sequence of character constants surrounded
6770 by double quotes (@code{"}).
6773 Pointer constants are an integral value. You can also write pointers
6774 to constants using the C operator @samp{&}.
6777 Array constants are comma-separated lists surrounded by braces @samp{@{}
6778 and @samp{@}}; for example, @samp{@{1,2,3@}} is a three-element array of
6779 integers, @samp{@{@{1,2@}, @{3,4@}, @{5,6@}@}} is a three-by-two array,
6780 and @samp{@{&"hi", &"there", &"fred"@}} is a three-element array of pointers.
6785 * Cplus expressions::
6795 @node Cplus expressions, C Defaults, C Constants, C
6796 @subsubsection C++ expressions
6799 @node Cplus expressions, C Defaults, C Constants, Support
6800 @subsubsection C++ expressions
6803 @cindex expressions in C++
6804 @value{GDBN} expression handling can interpret most C++ expressions.
6807 @cindex C++ support, not in @sc{coff}
6808 @cindex @sc{coff} versus C++
6809 @cindex C++ and object formats
6810 @cindex object formats and C++
6811 @cindex a.out and C++
6812 @cindex @sc{ecoff} and C++
6813 @cindex @sc{xcoff} and C++
6814 @cindex @sc{elf}/stabs and C++
6815 @cindex @sc{elf}/@sc{dwarf} and C++
6816 @c FIXME!! GDB may eventually be able to debug C++ using DWARF; check
6817 @c periodically whether this has happened...
6819 @emph{Warning:} @value{GDBN} can only debug C++ code if you compile with
6820 the @sc{gnu} C++ compiler. Moreover, C++ debugging depends on the use of
6821 additional debugging information in the symbol table, and thus requires
6822 special support. @value{GDBN} has this support @emph{only} with the
6823 stabs debug format. In particular, if your compiler generates a.out,
6824 MIPS @sc{ecoff}, RS/6000 @sc{xcoff}, or @sc{elf} with stabs extensions
6825 to the symbol table, these facilities are all available. (With @sc{gnu} CC,
6826 you can use the @samp{-gstabs} option to request stabs debugging
6827 extensions explicitly.) Where the object code format is standard
6828 @sc{coff} or @sc{dwarf} in @sc{elf}, on the other hand, most of the C++
6829 support in @value{GDBN} does @emph{not} work.
6835 @cindex member functions
6837 Member function calls are allowed; you can use expressions like
6840 count = aml->GetOriginal(x, y)
6844 @cindex namespace in C++
6846 While a member function is active (in the selected stack frame), your
6847 expressions have the same namespace available as the member function;
6848 that is, @value{GDBN} allows implicit references to the class instance
6849 pointer @code{this} following the same rules as C++.
6852 @cindex call overloaded functions
6853 @cindex type conversions in C++
6855 You can call overloaded functions; @value{GDBN} resolves the function
6856 call to the right definition, with one restriction---you must use
6857 arguments of the type required by the function that you want to call.
6858 @value{GDBN} does not perform conversions requiring constructors or
6859 user-defined type operators.
6862 @cindex call overloaded functions
6863 @cindex overloaded functions
6864 @cindex type conversions in C++
6866 You can call overloaded functions; @value{GDBN} resolves the function
6867 call to the right definition, with some restrictions. GDB does not
6868 perform overload resolution involving user-defined type conversions,
6869 calls to constructors, or instantiations of templates that do not exist
6870 in the program. It also cannot handle ellipsis argument lists or
6873 It does perform integral conversions and promotions, floating-point
6874 promotions, arithmetic conversions, pointer conversions, conversions of
6875 class objects to base classes, and standard conversions such as those of
6876 functions or arrays to pointers; it requires an exact match on the
6877 number of function arguments.
6879 Overload resolution is always performed, unless you have specified
6880 @code{set overload-resolution off}. @xref{Debugging C plus plus,
6881 ,@value{GDBN} features for C++}.
6883 You must specify@code{set overload-resolution off} in order to use an
6884 explicit function signature to call an overloaded function, as in
6886 p 'foo(char,int)'('x', 13)
6888 The @value{GDBN} command-completion facility can simplify this;
6889 @pxref{Completion, ,Command completion}.
6893 @cindex reference declarations
6895 @value{GDBN} understands variables declared as C++ references; you can use
6896 them in expressions just as you do in C++ source---they are automatically
6899 In the parameter list shown when @value{GDBN} displays a frame, the values of
6900 reference variables are not displayed (unlike other variables); this
6901 avoids clutter, since references are often used for large structures.
6902 The @emph{address} of a reference variable is always shown, unless
6903 you have specified @samp{set print address off}.
6906 @value{GDBN} supports the C++ name resolution operator @code{::}---your
6907 expressions can use it just as expressions in your program do. Since
6908 one scope may be defined in another, you can use @code{::} repeatedly if
6909 necessary, for example in an expression like
6910 @samp{@var{scope1}::@var{scope2}::@var{name}}. @value{GDBN} also allows
6911 resolving name scope by reference to source files, in both C and C++
6912 debugging (@pxref{Variables, ,Program variables}).
6916 In addition, @value{GDBN} supports calling virtual functions correctly,
6917 printing out virtual bases of objects, calling functions in a base
6918 subobject, casting objects, and invoking user-defined operators.
6922 @node C Defaults, C Checks, Cplus expressions, C
6923 @subsubsection C and C++ defaults
6926 @node C Defaults, Debugging C, Cplus expressions, Support
6927 @subsubsection C and C++ defaults
6929 @cindex C and C++ defaults
6932 If you allow @value{GDBN} to set type and range checking automatically, they
6933 both default to @code{off} whenever the working language changes to
6934 C or C++. This happens regardless of whether you or @value{GDBN}
6935 selects the working language.
6938 If you allow @value{GDBN} to set the language automatically, it recognizes
6939 source files whose names end with @file{.c}, @file{.C}, or @file{.cc}, and
6940 when @value{GDBN} enters code compiled from one of these files,
6941 it sets the working language to C or C++.
6942 @xref{Automatically, ,Having @value{GDBN} infer the source language}, for
6946 @c Type checking is (a) primarily motivated by Modula-2, and (b)
6947 @c unimplemented. If (b) changes, it might make sense to let this node
6948 @c appear even if Mod-2 does not, but meanwhile ignore it. roland 16jul93.
6949 @node C Checks, Debugging C, C Defaults, C Constants
6950 @subsubsection C and C++ type and range checks
6951 @cindex C and C++ checks
6953 By default, when @value{GDBN} parses C or C++ expressions, type checking
6954 is not used. However, if you turn type checking on, @value{GDBN}
6955 considers two variables type equivalent if:
6959 The two variables are structured and have the same structure, union, or
6963 The two variables have the same type name, or types that have been
6964 declared equivalent through @code{typedef}.
6967 @c leaving this out because neither J Gilmore nor R Pesch understand it.
6970 The two @code{struct}, @code{union}, or @code{enum} variables are
6971 declared in the same declaration. (Note: this may not be true for all C
6976 Range checking, if turned on, is done on mathematical operations. Array
6977 indices are not checked, since they are often used to index a pointer
6978 that is not itself an array.
6984 @node Debugging C, Debugging C plus plus, C Checks, C
6985 @subsubsection @value{GDBN} and C
6988 @node Debugging C, Debugging C plus plus, C Defaults, Support
6989 @subsubsection @value{GDBN} and C
6993 @node Debugging C, , C Constants, C
6994 @section @value{GDBN} and C
6997 The @code{set print union} and @code{show print union} commands apply to
6998 the @code{union} type. When set to @samp{on}, any @code{union} that is
6999 inside a @code{struct}
7004 Otherwise, it appears as @samp{@{...@}}.
7006 The @code{@@} operator aids in the debugging of dynamic arrays, formed
7007 with pointers and a memory allocation function. @xref{Expressions,
7012 * Debugging C plus plus::
7016 @node Debugging C plus plus, , Debugging C, C
7017 @subsubsection @value{GDBN} features for C++
7020 @node Debugging C plus plus, , Debugging C, Support
7021 @subsubsection @value{GDBN} features for C++
7024 @cindex commands for C++
7025 Some @value{GDBN} commands are particularly useful with C++, and some are
7026 designed specifically for use with C++. Here is a summary:
7029 @cindex break in overloaded functions
7030 @item @r{breakpoint menus}
7031 When you want a breakpoint in a function whose name is overloaded,
7032 @value{GDBN} breakpoint menus help you specify which function definition
7033 you want. @xref{Breakpoint Menus,,Breakpoint menus}.
7035 @cindex overloading in C++
7036 @item rbreak @var{regex}
7037 Setting breakpoints using regular expressions is helpful for setting
7038 breakpoints on overloaded functions that are not members of any special
7040 @xref{Set Breaks, ,Setting breakpoints}.
7043 @cindex C++ exception handling
7044 @item catch @var{exceptions}
7046 Debug C++ exception handling using these commands. @xref{Exception
7047 Handling, ,Breakpoints and exceptions}.
7050 @cindex C++ exception handling
7053 Debug C++ exception handling using these commands. @xref{Set
7054 Catchpoints, ,Setting catchpoints}.
7058 @item ptype @var{typename}
7059 Print inheritance relationships as well as other information for type
7061 @xref{Symbols, ,Examining the Symbol Table}.
7063 @cindex C++ symbol display
7064 @item set print demangle
7065 @itemx show print demangle
7066 @itemx set print asm-demangle
7067 @itemx show print asm-demangle
7068 Control whether C++ symbols display in their source form, both when
7069 displaying code as C++ source and when displaying disassemblies.
7070 @xref{Print Settings, ,Print settings}.
7072 @item set print object
7073 @itemx show print object
7074 Choose whether to print derived (actual) or declared types of objects.
7075 @xref{Print Settings, ,Print settings}.
7077 @item set print vtbl
7078 @itemx show print vtbl
7079 Control the format for printing virtual function tables.
7080 @xref{Print Settings, ,Print settings}.
7082 (The @code{vtbl} commands do not work on programs compiled with the HP
7083 ANSI C++ compiler (@code{aCC}).)
7085 @kindex set overload-resolution
7086 @cindex overloaded functions
7087 @item set overload-resolution on
7088 Enable overload resolution for C++ expression evaluation. The default
7089 is on. For overloaded functions, @value{GDBN} evaluates the arguments
7090 and searches for a function whose signature matches the argument types,
7091 using the standard C++ conversion rules (@pxref{Cplus expressions, ,C++
7092 expressions} for details). If it cannot find a match, it emits a
7095 @item set overload-resolution off
7096 Disable overload resolution for C++ expression evaluation. For
7097 overloaded functions that are not class member functions, @value{GDBN}
7098 chooses the first function of the specified name that it finds in the
7099 symbol table, whether or not its arguments are of the correct type. For
7100 overloaded functions that are class member functions, @value{GDBN}
7101 searches for a function whose signature @emph{exactly} matches the
7105 @item @r{Overloaded symbol names}
7106 You can specify a particular definition of an overloaded symbol, using
7107 the same notation that is used to declare such symbols in C++: type
7108 @code{@var{symbol}(@var{types})} rather than just @var{symbol}. You can
7109 also use the @value{GDBN} command-line word completion facilities to list the
7110 available choices, or to finish the type list for you.
7111 @xref{Completion,, Command completion}, for details on how to do this.
7114 @c cancels "raisesections" under same conditions near bgn of chapter
7119 @node Modula-2, ,C , Support
7120 @subsection Modula-2
7123 The extensions made to @value{GDBN} to support Modula-2 only support
7124 output from the @sc{gnu} Modula-2 compiler (which is currently being
7125 developed). Other Modula-2 compilers are not currently supported, and
7126 attempting to debug executables produced by them is most likely
7127 to give an error as @value{GDBN} reads in the executable's symbol
7130 @cindex expressions in Modula-2
7132 * M2 Operators:: Built-in operators
7133 * Built-In Func/Proc:: Built-in functions and procedures
7134 * M2 Constants:: Modula-2 constants
7135 * M2 Defaults:: Default settings for Modula-2
7136 * Deviations:: Deviations from standard Modula-2
7137 * M2 Checks:: Modula-2 type and range checks
7138 * M2 Scope:: The scope operators @code{::} and @code{.}
7139 * GDB/M2:: @value{GDBN} and Modula-2
7142 @node M2 Operators, Built-In Func/Proc, Modula-2, Modula-2
7143 @subsubsection Operators
7144 @cindex Modula-2 operators
7146 Operators must be defined on values of specific types. For instance,
7147 @code{+} is defined on numbers, but not on structures. Operators are
7148 often defined on groups of types. For the purposes of Modula-2, the
7149 following definitions hold:
7154 @emph{Integral types} consist of @code{INTEGER}, @code{CARDINAL}, and
7158 @emph{Character types} consist of @code{CHAR} and its subranges.
7161 @emph{Floating-point types} consist of @code{REAL}.
7164 @emph{Pointer types} consist of anything declared as @code{POINTER TO
7168 @emph{Scalar types} consist of all of the above.
7171 @emph{Set types} consist of @code{SET} and @code{BITSET} types.
7174 @emph{Boolean types} consist of @code{BOOLEAN}.
7178 The following operators are supported, and appear in order of
7179 increasing precedence:
7183 Function argument or array index separator.
7186 Assignment. The value of @var{var} @code{:=} @var{value} is
7190 Less than, greater than on integral, floating-point, or enumerated
7194 Less than, greater than, less than or equal to, greater than or equal to
7195 on integral, floating-point and enumerated types, or set inclusion on
7196 set types. Same precedence as @code{<}.
7198 @item =@r{, }<>@r{, }#
7199 Equality and two ways of expressing inequality, valid on scalar types.
7200 Same precedence as @code{<}. In @value{GDBN} scripts, only @code{<>} is
7201 available for inequality, since @code{#} conflicts with the script
7205 Set membership. Defined on set types and the types of their members.
7206 Same precedence as @code{<}.
7209 Boolean disjunction. Defined on boolean types.
7212 Boolean conjuction. Defined on boolean types.
7215 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
7218 Addition and subtraction on integral and floating-point types, or union
7219 and difference on set types.
7222 Multiplication on integral and floating-point types, or set intersection
7226 Division on floating-point types, or symmetric set difference on set
7227 types. Same precedence as @code{*}.
7230 Integer division and remainder. Defined on integral types. Same
7231 precedence as @code{*}.
7234 Negative. Defined on @code{INTEGER} and @code{REAL} data.
7237 Pointer dereferencing. Defined on pointer types.
7240 Boolean negation. Defined on boolean types. Same precedence as
7244 @code{RECORD} field selector. Defined on @code{RECORD} data. Same
7245 precedence as @code{^}.
7248 Array indexing. Defined on @code{ARRAY} data. Same precedence as @code{^}.
7251 Procedure argument list. Defined on @code{PROCEDURE} objects. Same precedence
7255 @value{GDBN} and Modula-2 scope operators.
7259 @emph{Warning:} Sets and their operations are not yet supported, so @value{GDBN}
7260 treats the use of the operator @code{IN}, or the use of operators
7261 @code{+}, @code{-}, @code{*}, @code{/}, @code{=}, , @code{<>}, @code{#},
7262 @code{<=}, and @code{>=} on sets as an error.
7265 @cindex Modula-2 built-ins
7266 @node Built-In Func/Proc, M2 Constants, M2 Operators, Modula-2
7267 @subsubsection Built-in functions and procedures
7269 Modula-2 also makes available several built-in procedures and functions.
7270 In describing these, the following metavariables are used:
7275 represents an @code{ARRAY} variable.
7278 represents a @code{CHAR} constant or variable.
7281 represents a variable or constant of integral type.
7284 represents an identifier that belongs to a set. Generally used in the
7285 same function with the metavariable @var{s}. The type of @var{s} should
7286 be @code{SET OF @var{mtype}} (where @var{mtype} is the type of @var{m}).
7289 represents a variable or constant of integral or floating-point type.
7292 represents a variable or constant of floating-point type.
7298 represents a variable.
7301 represents a variable or constant of one of many types. See the
7302 explanation of the function for details.
7305 All Modula-2 built-in procedures also return a result, described below.
7309 Returns the absolute value of @var{n}.
7312 If @var{c} is a lower case letter, it returns its upper case
7313 equivalent, otherwise it returns its argument
7316 Returns the character whose ordinal value is @var{i}.
7319 Decrements the value in the variable @var{v}. Returns the new value.
7321 @item DEC(@var{v},@var{i})
7322 Decrements the value in the variable @var{v} by @var{i}. Returns the
7325 @item EXCL(@var{m},@var{s})
7326 Removes the element @var{m} from the set @var{s}. Returns the new
7329 @item FLOAT(@var{i})
7330 Returns the floating point equivalent of the integer @var{i}.
7333 Returns the index of the last member of @var{a}.
7336 Increments the value in the variable @var{v}. Returns the new value.
7338 @item INC(@var{v},@var{i})
7339 Increments the value in the variable @var{v} by @var{i}. Returns the
7342 @item INCL(@var{m},@var{s})
7343 Adds the element @var{m} to the set @var{s} if it is not already
7344 there. Returns the new set.
7347 Returns the maximum value of the type @var{t}.
7350 Returns the minimum value of the type @var{t}.
7353 Returns boolean TRUE if @var{i} is an odd number.
7356 Returns the ordinal value of its argument. For example, the ordinal
7357 value of a character is its ASCII value (on machines supporting the
7358 ASCII character set). @var{x} must be of an ordered type, which include
7359 integral, character and enumerated types.
7362 Returns the size of its argument. @var{x} can be a variable or a type.
7364 @item TRUNC(@var{r})
7365 Returns the integral part of @var{r}.
7367 @item VAL(@var{t},@var{i})
7368 Returns the member of the type @var{t} whose ordinal value is @var{i}.
7372 @emph{Warning:} Sets and their operations are not yet supported, so
7373 @value{GDBN} treats the use of procedures @code{INCL} and @code{EXCL} as
7377 @cindex Modula-2 constants
7378 @node M2 Constants, M2 Defaults, Built-In Func/Proc, Modula-2
7379 @subsubsection Constants
7381 @value{GDBN} allows you to express the constants of Modula-2 in the following
7387 Integer constants are simply a sequence of digits. When used in an
7388 expression, a constant is interpreted to be type-compatible with the
7389 rest of the expression. Hexadecimal integers are specified by a
7390 trailing @samp{H}, and octal integers by a trailing @samp{B}.
7393 Floating point constants appear as a sequence of digits, followed by a
7394 decimal point and another sequence of digits. An optional exponent can
7395 then be specified, in the form @samp{E@r{[}+@r{|}-@r{]}@var{nnn}}, where
7396 @samp{@r{[}+@r{|}-@r{]}@var{nnn}} is the desired exponent. All of the
7397 digits of the floating point constant must be valid decimal (base 10)
7401 Character constants consist of a single character enclosed by a pair of
7402 like quotes, either single (@code{'}) or double (@code{"}). They may
7403 also be expressed by their ordinal value (their ASCII value, usually)
7404 followed by a @samp{C}.
7407 String constants consist of a sequence of characters enclosed by a
7408 pair of like quotes, either single (@code{'}) or double (@code{"}).
7409 Escape sequences in the style of C are also allowed. @xref{C
7410 Constants, ,C and C++ constants}, for a brief explanation of escape
7414 Enumerated constants consist of an enumerated identifier.
7417 Boolean constants consist of the identifiers @code{TRUE} and
7421 Pointer constants consist of integral values only.
7424 Set constants are not yet supported.
7427 @node M2 Defaults, Deviations, M2 Constants, Modula-2
7428 @subsubsection Modula-2 defaults
7429 @cindex Modula-2 defaults
7431 If type and range checking are set automatically by @value{GDBN}, they
7432 both default to @code{on} whenever the working language changes to
7433 Modula-2. This happens regardless of whether you, or @value{GDBN},
7434 selected the working language.
7436 If you allow @value{GDBN} to set the language automatically, then entering
7437 code compiled from a file whose name ends with @file{.mod} sets the
7438 working language to Modula-2. @xref{Automatically, ,Having @value{GDBN} set
7439 the language automatically}, for further details.
7441 @node Deviations, M2 Checks, M2 Defaults, Modula-2
7442 @subsubsection Deviations from standard Modula-2
7443 @cindex Modula-2, deviations from
7445 A few changes have been made to make Modula-2 programs easier to debug.
7446 This is done primarily via loosening its type strictness:
7450 Unlike in standard Modula-2, pointer constants can be formed by
7451 integers. This allows you to modify pointer variables during
7452 debugging. (In standard Modula-2, the actual address contained in a
7453 pointer variable is hidden from you; it can only be modified
7454 through direct assignment to another pointer variable or expression that
7455 returned a pointer.)
7458 C escape sequences can be used in strings and characters to represent
7459 non-printable characters. @value{GDBN} prints out strings with these
7460 escape sequences embedded. Single non-printable characters are
7461 printed using the @samp{CHR(@var{nnn})} format.
7464 The assignment operator (@code{:=}) returns the value of its right-hand
7468 All built-in procedures both modify @emph{and} return their argument.
7471 @node M2 Checks, M2 Scope, Deviations, Modula-2
7472 @subsubsection Modula-2 type and range checks
7473 @cindex Modula-2 checks
7476 @emph{Warning:} in this release, @value{GDBN} does not yet perform type or
7479 @c FIXME remove warning when type/range checks added
7481 @value{GDBN} considers two Modula-2 variables type equivalent if:
7485 They are of types that have been declared equivalent via a @code{TYPE
7486 @var{t1} = @var{t2}} statement
7489 They have been declared on the same line. (Note: This is true of the
7490 @sc{gnu} Modula-2 compiler, but it may not be true of other compilers.)
7493 As long as type checking is enabled, any attempt to combine variables
7494 whose types are not equivalent is an error.
7496 Range checking is done on all mathematical operations, assignment, array
7497 index bounds, and all built-in functions and procedures.
7499 @node M2 Scope, GDB/M2, M2 Checks, Modula-2
7500 @subsubsection The scope operators @code{::} and @code{.}
7503 @cindex colon, doubled as scope operator
7506 @c Info cannot handle :: but TeX can.
7512 There are a few subtle differences between the Modula-2 scope operator
7513 (@code{.}) and the @value{GDBN} scope operator (@code{::}). The two have
7518 @var{module} . @var{id}
7519 @var{scope} :: @var{id}
7523 where @var{scope} is the name of a module or a procedure,
7524 @var{module} the name of a module, and @var{id} is any declared
7525 identifier within your program, except another module.
7527 Using the @code{::} operator makes @value{GDBN} search the scope
7528 specified by @var{scope} for the identifier @var{id}. If it is not
7529 found in the specified scope, then @value{GDBN} searches all scopes
7530 enclosing the one specified by @var{scope}.
7532 Using the @code{.} operator makes @value{GDBN} search the current scope for
7533 the identifier specified by @var{id} that was imported from the
7534 definition module specified by @var{module}. With this operator, it is
7535 an error if the identifier @var{id} was not imported from definition
7536 module @var{module}, or if @var{id} is not an identifier in
7539 @node GDB/M2, , M2 Scope, Modula-2
7540 @subsubsection @value{GDBN} and Modula-2
7542 Some @value{GDBN} commands have little use when debugging Modula-2 programs.
7543 Five subcommands of @code{set print} and @code{show print} apply
7544 specifically to C and C++: @samp{vtbl}, @samp{demangle},
7545 @samp{asm-demangle}, @samp{object}, and @samp{union}. The first four
7546 apply to C++, and the last to the C @code{union} type, which has no direct
7547 analogue in Modula-2.
7549 The @code{@@} operator (@pxref{Expressions, ,Expressions}), while available
7550 while using any language, is not useful with Modula-2. Its
7551 intent is to aid the debugging of @dfn{dynamic arrays}, which cannot be
7552 created in Modula-2 as they can in C or C++. However, because an
7553 address can be specified by an integral constant, the construct
7554 @samp{@{@var{type}@}@var{adrexp}} is still useful. (@pxref{Expressions, ,Expressions})
7556 @cindex @code{#} in Modula-2
7557 In @value{GDBN} scripts, the Modula-2 inequality operator @code{#} is
7558 interpreted as the beginning of a comment. Use @code{<>} instead.
7562 @node Symbols, Altering, Languages, Top
7563 @chapter Examining the Symbol Table
7565 The commands described in this section allow you to inquire about the
7566 symbols (names of variables, functions and types) defined in your
7567 program. This information is inherent in the text of your program and
7568 does not change as your program executes. @value{GDBN} finds it in your
7569 program's symbol table, in the file indicated when you started @value{GDBN}
7570 (@pxref{File Options, ,Choosing files}), or by one of the
7571 file-management commands (@pxref{Files, ,Commands to specify files}).
7573 @cindex symbol names
7574 @cindex names of symbols
7575 @cindex quoting names
7576 Occasionally, you may need to refer to symbols that contain unusual
7577 characters, which @value{GDBN} ordinarily treats as word delimiters. The
7578 most frequent case is in referring to static variables in other
7579 source files (@pxref{Variables,,Program variables}). File names
7580 are recorded in object files as debugging symbols, but @value{GDBN} would
7581 ordinarily parse a typical file name, like @file{foo.c}, as the three words
7582 @samp{foo} @samp{.} @samp{c}. To allow @value{GDBN} to recognize
7583 @samp{foo.c} as a single symbol, enclose it in single quotes; for example,
7590 looks up the value of @code{x} in the scope of the file @file{foo.c}.
7593 @kindex info address
7594 @item info address @var{symbol}
7595 Describe where the data for @var{symbol} is stored. For a register
7596 variable, this says which register it is kept in. For a non-register
7597 local variable, this prints the stack-frame offset at which the variable
7600 Note the contrast with @samp{print &@var{symbol}}, which does not work
7601 at all for a register variable, and for a stack local variable prints
7602 the exact address of the current instantiation of the variable.
7605 @item whatis @var{exp}
7606 Print the data type of expression @var{exp}. @var{exp} is not
7607 actually evaluated, and any side-effecting operations (such as
7608 assignments or function calls) inside it do not take place.
7609 @xref{Expressions, ,Expressions}.
7612 Print the data type of @code{$}, the last value in the value history.
7615 @item ptype @var{typename}
7616 Print a description of data type @var{typename}. @var{typename} may be
7617 the name of a type, or for C code it may have the form
7619 @samp{class @var{class-name}},
7621 @samp{struct @var{struct-tag}}, @samp{union @var{union-tag}} or
7622 @samp{enum @var{enum-tag}}.
7624 @item ptype @var{exp}
7626 Print a description of the type of expression @var{exp}. @code{ptype}
7627 differs from @code{whatis} by printing a detailed description, instead
7628 of just the name of the type.
7630 For example, for this variable declaration:
7633 struct complex @{double real; double imag;@} v;
7637 the two commands give this output:
7641 (@value{GDBP}) whatis v
7642 type = struct complex
7643 (@value{GDBP}) ptype v
7644 type = struct complex @{
7652 As with @code{whatis}, using @code{ptype} without an argument refers to
7653 the type of @code{$}, the last value in the value history.
7656 @item info types @var{regexp}
7658 Print a brief description of all types whose name matches @var{regexp}
7659 (or all types in your program, if you supply no argument). Each
7660 complete typename is matched as though it were a complete line; thus,
7661 @samp{i type value} gives information on all types in your program whose
7662 name includes the string @code{value}, but @samp{i type ^value$} gives
7663 information only on types whose complete name is @code{value}.
7665 This command differs from @code{ptype} in two ways: first, like
7666 @code{whatis}, it does not print a detailed description; second, it
7667 lists all source files where a type is defined.
7671 Show the name of the current source file---that is, the source file for
7672 the function containing the current point of execution---and the language
7675 @kindex info sources
7677 Print the names of all source files in your program for which there is
7678 debugging information, organized into two lists: files whose symbols
7679 have already been read, and files whose symbols will be read when needed.
7681 @kindex info functions
7682 @item info functions
7683 Print the names and data types of all defined functions.
7685 @item info functions @var{regexp}
7686 Print the names and data types of all defined functions
7687 whose names contain a match for regular expression @var{regexp}.
7688 Thus, @samp{info fun step} finds all functions whose names
7689 include @code{step}; @samp{info fun ^step} finds those whose names
7690 start with @code{step}.
7692 @kindex info variables
7693 @item info variables
7694 Print the names and data types of all variables that are declared
7695 outside of functions (i.e., excluding local variables).
7697 @item info variables @var{regexp}
7698 Print the names and data types of all variables (except for local
7699 variables) whose names contain a match for regular expression
7703 This was never implemented.
7704 @kindex info methods
7706 @itemx info methods @var{regexp}
7707 The @code{info methods} command permits the user to examine all defined
7708 methods within C++ program, or (with the @var{regexp} argument) a
7709 specific set of methods found in the various C++ classes. Many
7710 C++ classes provide a large number of methods. Thus, the output
7711 from the @code{ptype} command can be overwhelming and hard to use. The
7712 @code{info-methods} command filters the methods, printing only those
7713 which match the regular-expression @var{regexp}.
7717 @cindex reloading symbols
7718 Some systems allow individual object files that make up your program to
7719 be replaced without stopping and restarting your program.
7721 For example, in VxWorks you can simply recompile a defective object file
7722 and keep on running.
7724 If you are running on one of these systems, you can allow @value{GDBN} to
7725 reload the symbols for automatically relinked modules:
7728 @kindex set symbol-reloading
7729 @item set symbol-reloading on
7730 Replace symbol definitions for the corresponding source file when an
7731 object file with a particular name is seen again.
7733 @item set symbol-reloading off
7734 Do not replace symbol definitions when re-encountering object files of
7735 the same name. This is the default state; if you are not running on a
7736 system that permits automatically relinking modules, you should leave
7737 @code{symbol-reloading} off, since otherwise @value{GDBN} may discard symbols
7738 when linking large programs, that may contain several modules (from
7739 different directories or libraries) with the same name.
7741 @kindex show symbol-reloading
7742 @item show symbol-reloading
7743 Show the current @code{on} or @code{off} setting.
7748 @kindex set opaque-type-resolution
7749 @item set opaque-type-resolution on
7750 Tell @value{GDBN} to resolve opaque types. An opaque type is a type
7751 declared as a pointer to a @code{struct}, @code{class}, or
7752 @code{union}---for example, @code{struct MyType *}---that is used in one
7753 source file although the full declaration of @code{struct MyType} is in
7754 another source file. The default is on.
7756 A change in the setting of this subcommand will not take effect until
7757 the next time symbols for a file are loaded.
7759 @item set opaque-type-resolution off
7760 Tell @value{GDBN} not to resolve opaque types. In this case, the type
7761 is printed as follows:
7763 @{<no data fields>@}
7766 @kindex show opaque-type-resolution
7767 @item show opaque-type-resolution
7768 Show whether opaque types are resolved or not.
7771 @kindex maint print symbols
7773 @kindex maint print psymbols
7774 @cindex partial symbol dump
7775 @item maint print symbols @var{filename}
7776 @itemx maint print psymbols @var{filename}
7777 @itemx maint print msymbols @var{filename}
7778 Write a dump of debugging symbol data into the file @var{filename}.
7779 These commands are used to debug the @value{GDBN} symbol-reading code. Only
7780 symbols with debugging data are included. If you use @samp{maint print
7781 symbols}, @value{GDBN} includes all the symbols for which it has already
7782 collected full details: that is, @var{filename} reflects symbols for
7783 only those files whose symbols @value{GDBN} has read. You can use the
7784 command @code{info sources} to find out which files these are. If you
7785 use @samp{maint print psymbols} instead, the dump shows information about
7786 symbols that @value{GDBN} only knows partially---that is, symbols defined in
7787 files that @value{GDBN} has skimmed, but not yet read completely. Finally,
7788 @samp{maint print msymbols} dumps just the minimal symbol information
7789 required for each object file from which @value{GDBN} has read some symbols.
7790 @xref{Files, ,Commands to specify files}, for a discussion of how
7791 @value{GDBN} reads symbols (in the description of @code{symbol-file}).
7794 @node Altering, GDB Files, Symbols, Top
7795 @chapter Altering Execution
7797 Once you think you have found an error in your program, you might want to
7798 find out for certain whether correcting the apparent error would lead to
7799 correct results in the rest of the run. You can find the answer by
7800 experiment, using the @value{GDBN} features for altering execution of the
7803 For example, you can store new values into variables or memory
7806 give your program a signal, restart it
7809 restart your program
7811 at a different address, or even return prematurely from a function.
7814 * Assignment:: Assignment to variables
7815 * Jumping:: Continuing at a different address
7817 * Signaling:: Giving your program a signal
7820 * Returning:: Returning from a function
7821 * Calling:: Calling your program's functions
7822 * Patching:: Patching your program
7825 @node Assignment, Jumping, Altering, Altering
7826 @section Assignment to variables
7829 @cindex setting variables
7830 To alter the value of a variable, evaluate an assignment expression.
7831 @xref{Expressions, ,Expressions}. For example,
7838 stores the value 4 into the variable @code{x}, and then prints the
7839 value of the assignment expression (which is 4).
7841 @xref{Languages, ,Using @value{GDBN} with Different Languages}, for more
7842 information on operators in supported languages.
7845 @kindex set variable
7846 @cindex variables, setting
7847 If you are not interested in seeing the value of the assignment, use the
7848 @code{set} command instead of the @code{print} command. @code{set} is
7849 really the same as @code{print} except that the expression's value is
7850 not printed and is not put in the value history (@pxref{Value History,
7851 ,Value history}). The expression is evaluated only for its effects.
7854 If the beginning of the argument string of the @code{set} command
7855 appears identical to a @code{set} subcommand, use the @code{set
7856 variable} command instead of just @code{set}. This command is identical
7857 to @code{set} except for its lack of subcommands. For example, if your
7858 program has a variable @code{width}, you get an error if you try to set
7859 a new value with just @samp{set width=13}, because @value{GDBN} has the
7860 command @code{set width}:
7863 (@value{GDBP}) whatis width
7865 (@value{GDBP}) p width
7867 (@value{GDBP}) set width=47
7868 Invalid syntax in expression.
7872 The invalid expression, of course, is @samp{=47}. In
7873 order to actually set the program's variable @code{width}, use
7876 (@value{GDBP}) set var width=47
7880 Because the @code{set} command has many subcommands that can conflict
7881 with the names of program variables, it is a good idea to use the
7882 @code{set variable} command instead of just @code{set}. For example, if
7883 your program has a variable @code{g}, you run into problems if you try
7884 to set a new value with just @samp{set g=4}, because @value{GDBN} has
7885 the command @code{set gnutarget}, abbreviated @code{set g}:
7889 (@value{GDBP}) whatis g
7893 (@value{GDBP}) set g=4
7897 The program being debugged has been started already.
7898 Start it from the beginning? (y or n) y
7899 Starting program: /home/smith/cc_progs/a.out
7900 "/home/smith/cc_progs/a.out": can't open to read symbols: Invalid bfd target.
7901 (@value{GDBP}) show g
7902 The current BFD target is "=4".
7907 The program variable @code{g} did not change, and you silently set the
7908 @code{gnutarget} to an invalid value. In order to set the variable
7912 (@value{GDBP}) set var g=4
7916 @value{GDBN} allows more implicit conversions in assignments than C; you can
7917 freely store an integer value into a pointer variable or vice versa,
7918 and you can convert any structure to any other structure that is the
7919 same length or shorter.
7920 @comment FIXME: how do structs align/pad in these conversions?
7921 @comment /doc@cygnus.com 18dec1990
7923 To store values into arbitrary places in memory, use the @samp{@{@dots{}@}}
7924 construct to generate a value of specified type at a specified address
7925 (@pxref{Expressions, ,Expressions}). For example, @code{@{int@}0x83040} refers
7926 to memory location @code{0x83040} as an integer (which implies a certain size
7927 and representation in memory), and
7930 set @{int@}0x83040 = 4
7934 stores the value 4 into that memory location.
7936 @node Jumping, Signaling, Assignment, Altering
7937 @section Continuing at a different address
7939 Ordinarily, when you continue your program, you do so at the place where
7940 it stopped, with the @code{continue} command. You can instead continue at
7941 an address of your own choosing, with the following commands:
7945 @item jump @var{linespec}
7946 Resume execution at line @var{linespec}. Execution stops again
7947 immediately if there is a breakpoint there. @xref{List, ,Printing
7948 source lines}, for a description of the different forms of
7951 It is common practice to use the @code{tbreak} command in conjunction
7952 with @code{jump}. @xref{Set Breaks, ,Setting breakpoints}.
7955 The @code{jump} command does not change the current stack frame, or
7956 the stack pointer, or the contents of any memory location or any
7957 register other than the program counter. If line @var{linespec} is in
7958 a different function from the one currently executing, the results may
7959 be bizarre if the two functions expect different patterns of arguments or
7960 of local variables. For this reason, the @code{jump} command requests
7961 confirmation if the specified line is not in the function currently
7962 executing. However, even bizarre results are predictable if you are
7963 well acquainted with the machine-language code of your program.
7965 @item jump *@var{address}
7966 Resume execution at the instruction at address @var{address}.
7970 @c Doesn't work on HP-UX; have to set $pcoqh and $pcoqt.
7971 You can get much the same effect as the @code{jump} command by storing a
7972 new value into the register @code{$pc}. The difference is that this
7973 does not start your program running; it only changes the address of where it
7974 @emph{will} run when you continue. For example,
7981 makes the next @code{continue} command or stepping command execute at
7982 address @code{0x485}, rather than at the address where your program stopped.
7983 @xref{Continuing and Stepping, ,Continuing and stepping}.
7986 The most common occasion to use the @code{jump} command is to back
7987 up---perhaps with more breakpoints set---over a portion of a program
7988 that has already executed, in order to examine its execution in more
7993 @node Signaling, Returning, Jumping, Altering
7994 @section Giving your program a signal
7998 @item signal @var{signal}
7999 Resume execution where your program stopped, but immediately give it the
8000 signal @var{signal}. @var{signal} can be the name or the number of a
8001 signal. For example, on many systems @code{signal 2} and @code{signal
8002 SIGINT} are both ways of sending an interrupt signal.
8004 Alternatively, if @var{signal} is zero, continue execution without
8005 giving a signal. This is useful when your program stopped on account of
8006 a signal and would ordinary see the signal when resumed with the
8007 @code{continue} command; @samp{signal 0} causes it to resume without a
8010 @code{signal} does not repeat when you press @key{RET} a second time
8011 after executing the command.
8015 Invoking the @code{signal} command is not the same as invoking the
8016 @code{kill} utility from the shell. Sending a signal with @code{kill}
8017 causes @value{GDBN} to decide what to do with the signal depending on
8018 the signal handling tables (@pxref{Signals}). The @code{signal} command
8019 passes the signal directly to your program.
8023 @node Returning, Calling, Signaling, Altering
8024 @section Returning from a function
8027 @cindex returning from a function
8030 @itemx return @var{expression}
8031 You can cancel execution of a function call with the @code{return}
8032 command. If you give an
8033 @var{expression} argument, its value is used as the function's return
8037 When you use @code{return}, @value{GDBN} discards the selected stack frame
8038 (and all frames within it). You can think of this as making the
8039 discarded frame return prematurely. If you wish to specify a value to
8040 be returned, give that value as the argument to @code{return}.
8042 This pops the selected stack frame (@pxref{Selection, ,Selecting a
8043 frame}), and any other frames inside of it, leaving its caller as the
8044 innermost remaining frame. That frame becomes selected. The
8045 specified value is stored in the registers used for returning values
8048 The @code{return} command does not resume execution; it leaves the
8049 program stopped in the state that would exist if the function had just
8050 returned. In contrast, the @code{finish} command (@pxref{Continuing
8051 and Stepping, ,Continuing and stepping}) resumes execution until the
8052 selected stack frame returns naturally.
8054 @node Calling, Patching, Returning, Altering
8055 @section Calling program functions
8057 @cindex calling functions
8060 @item call @var{expr}
8061 Evaluate the expression @var{expr} without displaying @code{void}
8065 You can use this variant of the @code{print} command if you want to
8066 execute a function from your program, but without cluttering the output
8067 with @code{void} returned values. If the result is not void, it
8068 is printed and saved in the value history.
8071 A new user-controlled variable, @var{call_scratch_address}, specifies
8072 the location of a scratch area to be used when @value{GDBN} calls a
8073 function in the target. This is necessary because the usual method
8074 of putting the scratch area on the stack does not work in systems that
8075 have separate instruction and data spaces.
8078 @node Patching, , Calling, Altering
8079 @section Patching programs
8080 @cindex patching binaries
8081 @cindex writing into executables
8083 @cindex writing into corefiles
8086 By default, @value{GDBN} opens the file containing your program's executable
8091 read-only. This prevents accidental alterations
8092 to machine code; but it also prevents you from intentionally patching
8093 your program's binary.
8095 If you'd like to be able to patch the binary, you can specify that
8096 explicitly with the @code{set write} command. For example, you might
8097 want to turn on internal debugging flags, or even to make emergency
8103 @itemx set write off
8104 If you specify @samp{set write on}, @value{GDBN} opens executable
8108 files for both reading and writing; if you specify @samp{set write
8109 off} (the default), @value{GDBN} opens them read-only.
8111 If you have already loaded a file, you must load it again (using the
8116 command) after changing @code{set write}, for your new setting to take
8121 Display whether executable files
8125 are opened for writing as well as reading.
8128 @node GDB Files, Targets, Altering, Top
8129 @chapter @value{GDBN} Files
8131 @value{GDBN} needs to know the file name of the program to be debugged, both in
8132 order to read its symbol table and in order to start your program.
8134 To debug a core dump of a previous run, you must also tell @value{GDBN}
8135 the name of the core dump file.
8139 * Files:: Commands to specify files
8140 * Symbol Errors:: Errors reading symbol files
8143 @node Files, Symbol Errors, GDB Files, GDB Files
8144 @section Commands to specify files
8145 @cindex symbol table
8148 @cindex core dump file
8149 You may want to specify executable and core dump file names.
8150 The usual way to do this is at start-up time, using the arguments to
8151 @value{GDBN}'s start-up commands (@pxref{Invocation, ,
8152 Getting In and Out of @value{GDBN}}).
8155 The usual way to specify an executable file name is with
8156 the command argument given when you start @value{GDBN}, (@pxref{Invocation,
8157 ,Getting In and Out of @value{GDBN}}.
8160 Occasionally it is necessary to change to a different file during a
8161 @value{GDBN} session. Or you may run @value{GDBN} and forget to specify
8162 a file you want to use. In these situations the @value{GDBN} commands
8163 to specify new files are useful.
8166 @cindex executable file
8168 @item file @var{filename}
8169 Use @var{filename} as the program to be debugged. It is read for its
8170 symbols and for the contents of pure memory. It is also the program
8171 executed when you use the @code{run} command. If you do not specify a
8172 directory and the file is not found in the @value{GDBN} working directory,
8173 @value{GDBN} uses the environment variable @code{PATH} as a list of
8174 directories to search, just as the shell does when looking for a program
8175 to run. You can change the value of this variable, for both @value{GDBN}
8176 and your program, using the @code{path} command.
8179 On systems with memory-mapped files, an auxiliary file
8180 @file{@var{filename}.syms} may hold symbol table information for
8181 @var{filename}. If so, @value{GDBN} maps in the symbol table from
8182 @file{@var{filename}.syms}, starting up more quickly. See the
8183 descriptions of the file options @samp{-mapped} and @samp{-readnow}
8184 (available on the command line, and with the commands @code{file},
8185 @code{symbol-file}, or @code{add-symbol-file}, described below),
8186 for more information.
8190 @code{file} with no argument makes @value{GDBN} discard any information it
8191 has on both executable file and the symbol table.
8194 @item exec-file @r{[} @var{filename} @r{]}
8195 Specify that the program to be run (but not the symbol table) is found
8196 in @var{filename}. @value{GDBN} searches the environment variable @code{PATH}
8197 if necessary to locate your program. Omitting @var{filename} means to
8198 discard information on the executable file.
8201 @item symbol-file @r{[} @var{filename} @r{]}
8202 Read symbol table information from file @var{filename}. @code{PATH} is
8203 searched when necessary. Use the @code{file} command to get both symbol
8204 table and program to run from the same file.
8206 @code{symbol-file} with no argument clears out @value{GDBN} information on your
8207 program's symbol table.
8209 The @code{symbol-file} command causes @value{GDBN} to forget the contents
8210 of its convenience variables, the value history, and all breakpoints and
8211 auto-display expressions. This is because they may contain pointers to
8212 the internal data recording symbols and data types, which are part of
8213 the old symbol table data being discarded inside @value{GDBN}.
8215 @code{symbol-file} does not repeat if you press @key{RET} again after
8218 When @value{GDBN} is configured for a particular environment, it
8219 understands debugging information in whatever format is the standard
8220 generated for that environment; you may use either a @sc{gnu} compiler, or
8221 other compilers that adhere to the local conventions.
8223 Best results are usually obtained from @sc{gnu} compilers; for example,
8224 using @code{@value{GCC}} you can generate debugging information for
8229 On some kinds of object files, the @code{symbol-file} command does not
8232 The @code{symbol-file} command does not
8234 normally read the symbol table in full right away. Instead, it scans
8235 the symbol table quickly to find which source files and which symbols
8236 are present. The details are read later, one source file at a time,
8239 The purpose of this two-stage reading strategy is to make @value{GDBN} start up
8240 faster. For the most part, it is invisible except for occasional
8241 pauses while the symbol table details for a particular source file are
8242 being read. (The @code{set verbose} command can turn these pauses
8243 into messages if desired. @xref{Messages/Warnings, ,Optional warnings
8247 We have not implemented the two-stage strategy for COFF yet. When the
8248 symbol table is stored in COFF format, @code{symbol-file} reads the
8249 symbol table data in full right away.
8252 @cindex reading symbols immediately
8253 @cindex symbols, reading immediately
8255 @cindex memory-mapped symbol file
8256 @cindex saving symbol table
8257 @item symbol-file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
8258 @itemx file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
8259 You can override the @value{GDBN} two-stage strategy for reading symbol
8260 tables by using the @samp{-readnow} option with any of the commands that
8261 load symbol table information, if you want to be sure @value{GDBN} has the
8262 entire symbol table available.
8267 If memory-mapped files are available on your system through the
8268 @code{mmap} system call, you can use another option, @samp{-mapped}, to
8269 cause @value{GDBN} to write the symbols for your program into a reusable
8270 file. Future @value{GDBN} debugging sessions map in symbol information
8271 from this auxiliary symbol file (if the program has not changed), rather
8272 than spending time reading the symbol table from the executable
8273 program. Using the @samp{-mapped} option has the same effect as
8274 starting @value{GDBN} with the @samp{-mapped} command-line option.
8276 You can use both options together, to make sure the auxiliary symbol
8277 file has all the symbol information for your program.
8279 The auxiliary symbol file for a program called @var{myprog} is called
8280 @samp{@var{myprog}.syms}. Once this file exists (so long as it is newer
8281 than the corresponding executable), @value{GDBN} always attempts to use
8282 it when you debug @var{myprog}; no special options or commands are
8285 The @file{.syms} file is specific to the host machine where you run
8286 @value{GDBN}. It holds an exact image of the internal @value{GDBN}
8287 symbol table. It cannot be shared across multiple host platforms.
8290 @c FIXME: for now no mention of directories, since this seems to be in
8291 @c flux. 13mar1992 status is that in theory GDB would look either in
8292 @c current dir or in same dir as myprog; but issues like competing
8293 @c GDB's, or clutter in system dirs, mean that in practice right now
8294 @c only current dir is used. FFish says maybe a special GDB hierarchy
8295 @c (eg rooted in val of env var GDBSYMS) could exist for mappable symbol
8300 @item core-file @r{[} @var{filename} @r{]}
8301 Specify the whereabouts of a core dump file to be used as the ``contents
8302 of memory''. Traditionally, core files contain only some parts of the
8303 address space of the process that generated them; @value{GDBN} can access the
8304 executable file itself for other parts.
8306 @code{core-file} with no argument specifies that no core file is
8309 Note that the core file is ignored when your program is actually running
8310 under @value{GDBN}. So, if you have been running your program and you wish to
8311 debug a core file instead, you must kill the subprocess in which the
8312 program is running. To do this, use the @code{kill} command
8313 (@pxref{Kill Process, ,Killing the child process}).
8317 @kindex load @var{filename}
8318 @item load @var{filename}
8320 Depending on what remote debugging facilities are configured into
8321 @value{GDBN}, the @code{load} command may be available. Where it exists, it
8322 is meant to make @var{filename} (an executable) available for debugging
8323 on the remote system---by downloading, or dynamic linking, for example.
8324 @code{load} also records the @var{filename} symbol table in @value{GDBN}, like
8325 the @code{add-symbol-file} command.
8327 If your @value{GDBN} does not have a @code{load} command, attempting to
8328 execute it gets the error message ``@code{You can't do that when your
8329 target is @dots{}}''
8332 The file is loaded at whatever address is specified in the executable.
8333 For some object file formats, you can specify the load address when you
8334 link the program; for other formats, like a.out, the object file format
8335 specifies a fixed address.
8336 @c FIXME! This would be a good place for an xref to the GNU linker doc.
8339 On VxWorks, @code{load} links @var{filename} dynamically on the
8340 current target system as well as adding its symbols in @value{GDBN}.
8344 @cindex download to Nindy-960
8345 With the Nindy interface to an Intel 960 board, @code{load}
8346 downloads @var{filename} to the 960 as well as adding its symbols in
8351 @cindex download to H8/300 or H8/500
8352 @cindex H8/300 or H8/500 download
8353 @cindex download to Hitachi SH
8354 @cindex Hitachi SH download
8355 When you select remote debugging to a Hitachi SH, H8/300, or H8/500 board
8356 (@pxref{Hitachi Remote,,@value{GDBN} and Hitachi Microprocessors}),
8357 the @code{load} command downloads your program to the Hitachi board and also
8358 opens it as the current executable target for @value{GDBN} on your host
8359 (like the @code{file} command).
8362 @code{load} does not repeat if you press @key{RET} again after using it.
8367 @kindex add-symbol-file
8368 @cindex dynamic linking
8369 @item add-symbol-file @var{filename} @var{address}
8370 @itemx add-symbol-file @var{filename} @var{address} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
8371 The @code{add-symbol-file} command reads additional symbol table information
8372 from the file @var{filename}. You would use this command when @var{filename}
8373 has been dynamically loaded (by some other means) into the program that
8374 is running. @var{address} should be the memory address at which the
8375 file has been loaded; @value{GDBN} cannot figure this out for itself.
8376 You can specify @var{address} as an expression.
8378 The symbol table of the file @var{filename} is added to the symbol table
8379 originally read with the @code{symbol-file} command. You can use the
8380 @code{add-symbol-file} command any number of times; the new symbol data thus
8381 read keeps adding to the old. To discard all old symbol data instead,
8382 use the @code{symbol-file} command.
8384 @code{add-symbol-file} does not repeat if you press @key{RET} after using it.
8386 You can use the @samp{-mapped} and @samp{-readnow} options just as with
8387 the @code{symbol-file} command, to change how @value{GDBN} manages the symbol
8388 table information for @var{filename}.
8390 @kindex add-shared-symbol-file
8391 @item add-shared-symbol-file
8392 The @code{add-shared-symbol-file} command can be used only under Harris' CXUX
8393 operating system for the Motorola 88k. @value{GDBN} automatically looks for
8394 shared libraries, however if @value{GDBN} does not find yours, you can run
8395 @code{add-shared-symbol-file}. It takes no arguments.
8402 The @code{section} command changes the base address of section SECTION of
8403 the exec file to ADDR. This can be used if the exec file does not contain
8404 section addresses, (such as in the a.out format), or when the addresses
8405 specified in the file itself are wrong. Each section must be changed
8406 separately. The ``info files'' command lists all the sections and their
8414 @code{info files} and @code{info target} are synonymous; both print
8415 the current target (@pxref{Targets, ,Specifying a Debugging Target}),
8418 names of the executable and core dump files
8421 name of the executable file
8423 currently in use by @value{GDBN}, and the files from which symbols were
8424 loaded. The command @code{help target} lists all possible targets
8425 rather than current ones.
8428 All file-specifying commands allow both absolute and relative file names
8429 as arguments. @value{GDBN} always converts the file name to an absolute file
8430 name and remembers it that way.
8433 @cindex shared libraries
8435 @c added HP-UX -- Kim (HP writer)
8436 @value{GDBN} supports HP-UX, SunOS, SVr4, Irix 5, and IBM RS/6000 shared
8440 @value{GDBN} supports HP-UX shared libraries.
8442 @value{GDBN} automatically loads symbol definitions from shared libraries
8443 when you use the @code{run} command, or when you examine a core file.
8444 (Before you issue the @code{run} command, @value{GDBN} does not understand
8445 references to a function in a shared library, however---unless you are
8446 debugging a core file).
8448 If the program loads a library explicitly, @value{GDBN} automatically
8449 loads the symbols at the time of the @code{shl_load} call.
8451 @c FIXME: some @value{GDBN} release may permit some refs to undef
8452 @c FIXME...symbols---eg in a break cmd---assuming they are from a shared
8453 @c FIXME...lib; check this from time to time when updating manual
8456 @kindex info sharedlibrary
8459 @itemx info sharedlibrary
8460 Print the names of the shared libraries which are currently loaded.
8462 @kindex sharedlibrary
8464 @item sharedlibrary @var{regex}
8465 @itemx share @var{regex}
8467 Load shared object library symbols for files matching a
8468 Unix regular expression.
8469 As with files loaded automatically, it only loads shared libraries
8470 required by your program for a core file or after typing @code{run}. If
8471 @var{regex} is omitted all shared libraries required by your program are
8476 @value{GDBN} detects the loading of a shared library and automatically
8477 reads in symbols from the newly loaded library, up to a threshold that
8478 is initially set but that you can modify if you wish.
8480 Beyond that threshold, symbols from shared libraries must be explicitly
8481 loaded. To load these symbols, use the command @code{sharedlibrary}
8482 @var{filename}. The base address of the shared library is determined
8483 automatically by @value{GDBN} and need not be specified.
8485 To display or set the threshold, use the commands:
8488 @kindex set auto-solib-add
8489 @item set auto-solib-add @var{threshold}
8490 Set the autoloading size threshold, in megabytes. If @var{threshold} is
8491 nonzero, symbols from all shared object libraries will be loaded
8492 automatically when the inferior begins execution or when the dynamic
8493 linker informs @value{GDBN} that a new library has been loaded, until
8494 the symbol table of the program and libraries exceeds this threshold.
8495 Otherwise, symbols must be loaded manually, using the
8496 @code{sharedlibrary} command. The default threshold is 100 megabytes.
8498 @kindex show auto-solib-add
8499 @item show auto-solib-add
8500 Display the current autoloading size threshold, in megabytes.
8506 @node Symbol Errors, , Files, GDB Files
8507 @section Errors reading symbol files
8509 While reading a symbol file, @value{GDBN} occasionally encounters problems,
8510 such as symbol types it does not recognize, or known bugs in compiler
8511 output. By default, @value{GDBN} does not notify you of such problems, since
8512 they are relatively common and primarily of interest to people
8513 debugging compilers. If you are interested in seeing information
8514 about ill-constructed symbol tables, you can either ask @value{GDBN} to print
8515 only one message about each such type of problem, no matter how many
8516 times the problem occurs; or you can ask @value{GDBN} to print more messages,
8517 to see how many times the problems occur, with the @code{set
8518 complaints} command (@pxref{Messages/Warnings, ,Optional warnings and
8521 The messages currently printed, and their meanings, include:
8524 @item inner block not inside outer block in @var{symbol}
8526 The symbol information shows where symbol scopes begin and end
8527 (such as at the start of a function or a block of statements). This
8528 error indicates that an inner scope block is not fully contained
8529 in its outer scope blocks.
8531 @value{GDBN} circumvents the problem by treating the inner block as if it had
8532 the same scope as the outer block. In the error message, @var{symbol}
8533 may be shown as ``@code{(don't know)}'' if the outer block is not a
8536 @item block at @var{address} out of order
8538 The symbol information for symbol scope blocks should occur in
8539 order of increasing addresses. This error indicates that it does not
8542 @value{GDBN} does not circumvent this problem, and has trouble
8543 locating symbols in the source file whose symbols it is reading. (You
8544 can often determine what source file is affected by specifying
8545 @code{set verbose on}. @xref{Messages/Warnings, ,Optional warnings and
8548 @item bad block start address patched
8550 The symbol information for a symbol scope block has a start address
8551 smaller than the address of the preceding source line. This is known
8552 to occur in the SunOS 4.1.1 (and earlier) C compiler.
8554 @value{GDBN} circumvents the problem by treating the symbol scope block as
8555 starting on the previous source line.
8557 @item bad string table offset in symbol @var{n}
8560 Symbol number @var{n} contains a pointer into the string table which is
8561 larger than the size of the string table.
8563 @value{GDBN} circumvents the problem by considering the symbol to have the
8564 name @code{foo}, which may cause other problems if many symbols end up
8567 @item unknown symbol type @code{0x@var{nn}}
8569 The symbol information contains new data types that @value{GDBN} does not yet
8570 know how to read. @code{0x@var{nn}} is the symbol type of the misunderstood
8571 information, in hexadecimal.
8573 @value{GDBN} circumvents the error by ignoring this symbol information. This
8574 usually allows you to debug your program, though certain symbols
8575 are not accessible. If you encounter such a problem and feel like
8576 debugging it, you can debug @code{@value{GDBP}} with itself, breakpoint on
8577 @code{complain}, then go up to the function @code{read_dbx_symtab} and
8578 examine @code{*bufp} to see the symbol.
8580 @item stub type has NULL name
8581 @value{GDBN} could not find the full definition for
8590 @item const/volatile indicator missing (ok if using g++ v1.x), got@dots{}
8592 The symbol information for a C++ member function is missing some
8593 information that recent versions of the compiler should have output
8597 @item info mismatch between compiler and debugger
8599 @value{GDBN} could not parse a type specification output by the compiler.
8602 @node Targets, Controlling GDB, GDB Files, Top
8603 @chapter Specifying a Debugging Target
8604 @cindex debugging target
8607 A @dfn{target} is the execution environment occupied by your program.
8610 Often, @value{GDBN} runs in the same host environment as your program; in
8611 that case, the debugging target is specified as a side effect when you
8612 use the @code{file} or @code{core} commands. When you need more
8613 flexibility---for example, running @value{GDBN} on a physically separate
8614 host, or controlling a standalone system over a serial port or a
8615 realtime system over a TCP/IP connection---you
8619 On HP-UX systems, @value{GDBN} has been configured to support debugging
8620 of processes running on the PA-RISC architecture. This means that the
8621 only possible targets are:
8625 An executable that has been compiled and linked to run on HP-UX
8628 A live HP-UX process, either started by @value{GDBN} (with the
8629 @code{run} command) or started outside of @value{GDBN} and attached to
8630 (with the @code{attach} command)
8633 A core file generated by an HP-UX process that previously aborted
8637 @value{GDBN} on HP-UX has not been configured to support remote
8638 debugging, or to support programs running on other platforms. You
8643 can use the @code{target} command to specify one of the target types
8644 configured for @value{GDBN} (@pxref{Target Commands, ,Commands for managing
8648 * Active Targets:: Active targets
8649 * Target Commands:: Commands for managing targets
8651 * Byte Order:: Choosing target byte order
8652 * Remote:: Remote debugging
8657 @node Active Targets, Target Commands, Targets, Targets
8658 @section Active targets
8659 @cindex stacking targets
8660 @cindex active targets
8661 @cindex multiple targets
8664 There are three classes of targets: processes, core files, and
8665 executable files. @value{GDBN} can work concurrently on up to three active
8666 targets, one in each class. This allows you to (for example) start a
8667 process and inspect its activity without abandoning your work on a core
8670 For example, if you execute @samp{gdb a.out}, then the executable file
8671 @code{a.out} is the only active target. If you designate a core file as
8672 well---presumably from a prior run that crashed and coredumped---then
8673 @value{GDBN} has two active targets and uses them in tandem, looking
8674 first in the corefile target, then in the executable file, to satisfy
8675 requests for memory addresses. (Typically, these two classes of target
8676 are complementary, since core files contain only a program's
8677 read-write memory---variables and so on---plus machine status, while
8678 executable files contain only the program text and initialized data.)
8681 When you type @code{run}, your executable file becomes an active process
8682 target as well. When a process target is active, all @value{GDBN} commands
8683 requesting memory addresses refer to that target; addresses in an
8687 executable file target are obscured while the process
8691 Use the @code{exec-file} command to select a
8692 new executable target (@pxref{Files, ,Commands to specify
8696 Use the @code{core-file} and @code{exec-file} commands to select a
8697 new core file or executable target (@pxref{Files, ,Commands to specify
8698 files}). To specify as a target a process that is already running, use
8699 the @code{attach} command (@pxref{Attach, ,Debugging an
8700 already-running process}).
8703 @node Target Commands, Byte Order, Active Targets, Targets
8704 @section Commands for managing targets
8707 @item target @var{type} @var{parameters}
8708 Connects the @value{GDBN} host environment to a target
8713 machine or process. A target is typically a protocol for talking to
8714 debugging facilities. You use the argument @var{type} to specify the
8715 type or protocol of the target machine.
8717 Further @var{parameters} are interpreted by the target protocol, but
8718 typically include things like device names or host names to connect
8719 with, process numbers, and baud rates.
8722 The @code{target} command does not repeat if you press @key{RET} again
8723 after executing the command.
8727 Displays the names of all targets available. To display targets
8728 currently selected, use either @code{info target} or @code{info files}
8729 (@pxref{Files, ,Commands to specify files}).
8731 @item help target @var{name}
8732 Describe a particular target, including any parameters necessary to
8735 @kindex set gnutarget
8736 @item set gnutarget @var{args}
8737 @value{GDBN} uses its own library BFD to read your files. @value{GDBN}
8738 knows whether it is reading an @dfn{executable},
8739 a @dfn{core}, or a @dfn{.o} file; however, you can specify the file format
8740 with the @code{set gnutarget} command. Unlike most @code{target} commands,
8741 with @code{gnutarget} the @code{target} refers to a program, not a machine.
8743 @emph{Warning:} To specify a file format with @code{set gnutarget},
8744 you must know the actual BFD name.
8746 @noindent @xref{Files, , Commands to specify files}.
8748 @kindex show gnutarget
8749 @item show gnutarget
8750 Use the @code{show gnutarget} command to display what file format
8751 @code{gnutarget} is set to read. If you have not set @code{gnutarget},
8752 @value{GDBN} will determine the file format for each file automatically,
8753 and @code{show gnutarget} displays @samp{The current BDF target is "auto"}.
8757 Here are some common targets (available, or not, depending on the GDB
8761 These are the valid targets on HP-UX systems:
8766 @item target exec @var{program}
8767 An executable file. @samp{target exec @var{program}} is the same as
8768 @samp{exec-file @var{program}}.
8772 @item target core @var{filename}
8773 A core dump file. @samp{target core @var{filename}} is the same as
8774 @samp{core-file @var{filename}}.
8778 @kindex target remote
8779 @item target remote @var{dev}
8780 Remote serial target in GDB-specific protocol. The argument @var{dev}
8781 specifies what serial device to use for the connection (e.g.
8782 @file{/dev/ttya}). @xref{Remote, ,Remote debugging}. @code{target remote}
8783 now supports the @code{load} command. This is only useful if you have
8784 some other way of getting the stub to the target system, and you can put
8785 it somewhere in memory where it won't get clobbered by the download.
8791 CPU simulator. @xref{Simulator,,Simulated CPU Target}.
8796 @item target udi @var{keyword}
8797 Remote AMD29K target, using the AMD UDI protocol. The @var{keyword}
8798 argument specifies which 29K board or simulator to use. @xref{UDI29K
8799 Remote,,The UDI protocol for AMD29K}.
8801 @kindex target amd-eb
8802 @item target amd-eb @var{dev} @var{speed} @var{PROG}
8804 Remote PC-resident AMD EB29K board, attached over serial lines.
8805 @var{dev} is the serial device, as for @code{target remote};
8806 @var{speed} allows you to specify the linespeed; and @var{PROG} is the
8807 name of the program to be debugged, as it appears to DOS on the PC.
8808 @xref{EB29K Remote, ,The EBMON protocol for AMD29K}.
8813 @item target hms @var{dev}
8814 A Hitachi SH, H8/300, or H8/500 board, attached via serial line to your host.
8815 @ifclear H8EXCLUSIVE
8816 Use special commands @code{device} and @code{speed} to control the serial
8817 line and the communications speed used.
8819 @xref{Hitachi Remote,,@value{GDBN} and Hitachi Microprocessors}.
8823 @kindex target nindy
8824 @item target nindy @var{devicename}
8825 An Intel 960 board controlled by a Nindy Monitor. @var{devicename} is
8826 the name of the serial device to use for the connection, e.g.
8827 @file{/dev/ttya}. @xref{i960-Nindy Remote, ,@value{GDBN} with a remote i960 (Nindy)}.
8831 @kindex target st2000
8832 @item target st2000 @var{dev} @var{speed}
8833 A Tandem ST2000 phone switch, running Tandem's STDBUG protocol. @var{dev}
8834 is the name of the device attached to the ST2000 serial line;
8835 @var{speed} is the communication line speed. The arguments are not used
8836 if @value{GDBN} is configured to connect to the ST2000 using TCP or Telnet.
8837 @xref{ST2000 Remote,,@value{GDBN} with a Tandem ST2000}.
8841 @kindex target vxworks
8842 @item target vxworks @var{machinename}
8843 A VxWorks system, attached via TCP/IP. The argument @var{machinename}
8844 is the target system's machine name or IP address.
8845 @xref{VxWorks Remote, ,@value{GDBN} and VxWorks}.
8849 @item target bug @var{dev}
8850 BUG monitor, running on a MVME187 (m88k) board.
8853 @kindex target cpu32bug
8854 @item target cpu32bug @var{dev}
8855 CPU32BUG monitor, running on a CPU32 (M68K) board.
8857 @kindex target op50n
8858 @item target op50n @var{dev}
8859 OP50N monitor, running on an OKI HPPA board.
8862 @item target w89k @var{dev}
8863 W89K monitor, running on a Winbond HPPA board.
8866 @item target est @var{dev}
8867 EST-300 ICE monitor, running on a CPU32 (M68K) board.
8869 @kindex target rom68k
8870 @item target rom68k @var{dev}
8871 ROM 68K monitor, running on an IDP board.
8873 @kindex target array
8874 @item target array @var{dev}
8875 Array Tech LSI33K RAID controller board.
8877 @kindex target sparclite
8878 @item target sparclite @var{dev}
8879 Fujitsu sparclite boards, used only for the purpose of loading.
8880 You must use an additional command to debug the program.
8881 For example: target remote @var{dev} using @value{GDBN} standard
8887 Different targets are available on different configurations of @value{GDBN};
8888 your configuration may have more or fewer targets.
8892 @node Byte Order, Remote, Target Commands, Targets
8893 @section Choosing target byte order
8894 @cindex choosing target byte order
8895 @cindex target byte order
8896 @kindex set endian big
8897 @kindex set endian little
8898 @kindex set endian auto
8901 You can now choose which byte order to use with a target system.
8902 Use the @code{set endian big} and @code{set endian little} commands.
8903 Use the @code{set endian auto} command to instruct
8904 @value{GDBN} to use the byte order associated with the executable.
8905 You can see the current setting for byte order with the @code{show endian}
8908 @emph{Warning:} Currently, only embedded MIPS configurations support
8909 dynamic selection of target byte order.
8911 @node Remote, , Byte Order, Targets
8912 @section Remote debugging
8913 @cindex remote debugging
8915 If you are trying to debug a program running on a machine that cannot run
8916 @value{GDBN} in the usual way, it is often useful to use remote debugging.
8917 For example, you might use remote debugging on an operating system kernel,
8918 or on a small system which does not have a general purpose operating system
8919 powerful enough to run a full-featured debugger.
8921 Some configurations of @value{GDBN} have special serial or TCP/IP interfaces
8922 to make this work with particular debugging targets. In addition,
8923 @value{GDBN} comes with a generic serial protocol (specific to @value{GDBN},
8924 but not specific to any particular target system) which you can use if you
8925 write the remote stubs---the code that runs on the remote system to
8926 communicate with @value{GDBN}.
8928 Other remote targets may be available in your
8929 configuration of @value{GDBN}; use @code{help target} to list them.
8933 @c Text on starting up GDB in various specific cases; it goes up front
8934 @c in manuals configured for any of those particular situations, here
8938 * Remote Serial:: @value{GDBN} remote serial protocol
8941 * i960-Nindy Remote:: @value{GDBN} with a remote i960 (Nindy)
8944 * UDI29K Remote:: The UDI protocol for AMD29K
8945 * EB29K Remote:: The EBMON protocol for AMD29K
8948 * VxWorks Remote:: @value{GDBN} and VxWorks
8951 * ST2000 Remote:: @value{GDBN} with a Tandem ST2000
8954 * Hitachi Remote:: @value{GDBN} and Hitachi Microprocessors
8957 * MIPS Remote:: @value{GDBN} and MIPS boards
8960 * Sparclet Remote:: @value{GDBN} and Sparclet boards
8963 * Simulator:: Simulated CPU target
8967 @include remote.texi
8970 @node Controlling GDB
8971 @chapter Controlling @value{GDBN}
8973 You can alter the way @value{GDBN} interacts with you by using
8974 the @code{set} command. For commands controlling how @value{GDBN} displays
8975 data, @pxref{Print Settings, ,Print settings}; other settings are described
8980 * Editing:: Command editing
8981 * History:: Command history
8982 * Screen Size:: Screen size
8984 * Messages/Warnings:: Optional warnings and messages
8987 @node Prompt, Editing, Controlling GDB, Controlling GDB
8992 @value{GDBN} indicates its readiness to read a command by printing a string
8993 called the @dfn{prompt}. This string is normally @samp{(@value{GDBP})}. You
8994 can change the prompt string with the @code{set prompt} command. For
8995 instance, when debugging @value{GDBN} with @value{GDBN}, it is useful to change
8996 the prompt in one of the @value{GDBN} sessions so that you can always tell
8997 which one you are talking to.
8999 @emph{Note:} @code{set prompt} no longer adds a space for you after the
9000 prompt you set. This allows you to set a prompt which ends in a space
9001 or a prompt that does not.
9005 @item set prompt @var{newprompt}
9006 Directs @value{GDBN} to use @var{newprompt} as its prompt string henceforth.
9010 Prints a line of the form: @samp{Gdb's prompt is: @var{your-prompt}}
9013 @node Editing, History, Prompt, Controlling GDB
9014 @section Command editing
9016 @cindex command line editing
9018 @value{GDBN} reads its input commands via the @dfn{readline} interface. This
9019 @sc{gnu} library provides consistent behavior for programs which provide a
9020 command line interface to the user. Advantages are @sc{gnu} Emacs-style
9021 or @dfn{vi}-style inline editing of commands, @code{csh}-like history
9022 substitution, and a storage and recall of command history across
9025 You may control the behavior of command line editing in @value{GDBN} with the
9032 @itemx set editing on
9033 Enable command line editing (enabled by default).
9035 @item set editing off
9036 Disable command line editing.
9038 @kindex show editing
9040 Show whether command line editing is enabled.
9043 @node History, Screen Size, Editing, Controlling GDB
9044 @section Command history
9046 @value{GDBN} can keep track of the commands you type during your
9047 debugging sessions, so that you can be certain of precisely what
9048 happened. Use these commands to manage the @value{GDBN} command
9052 @cindex history substitution
9053 @cindex history file
9054 @kindex set history filename
9056 @item set history filename @var{fname}
9057 Set the name of the @value{GDBN} command history file to @var{fname}.
9058 This is the file where @value{GDBN} reads an initial command history
9059 list, and where it writes the command history from this session when it
9060 exits. You can access this list through history expansion or through
9061 the history command editing characters listed below. This file defaults
9062 to the value of the environment variable @code{GDBHISTFILE}, or to
9063 @file{./.gdb_history} if this variable is not set.
9065 @cindex history save
9066 @kindex set history save
9067 @item set history save
9068 @itemx set history save on
9069 Record command history in a file, whose name may be specified with the
9070 @code{set history filename} command. By default, this option is disabled.
9072 @item set history save off
9073 Stop recording command history in a file.
9075 @cindex history size
9076 @kindex set history size
9077 @item set history size @var{size}
9078 Set the number of commands which @value{GDBN} keeps in its history list.
9079 This defaults to the value of the environment variable
9080 @code{HISTSIZE}, or to 256 if this variable is not set.
9083 @cindex history expansion
9084 History expansion assigns special meaning to the character @kbd{!}.
9085 @ifset have-readline-appendices
9086 @xref{Event Designators}.
9089 Since @kbd{!} is also the logical not operator in C, history expansion
9090 is off by default. If you decide to enable history expansion with the
9091 @code{set history expansion on} command, you may sometimes need to
9092 follow @kbd{!} (when it is used as logical not, in an expression) with
9093 a space or a tab to prevent it from being expanded. The readline
9094 history facilities do not attempt substitution on the strings
9095 @kbd{!=} and @kbd{!(}, even when history expansion is enabled.
9097 The commands to control history expansion are:
9100 @kindex set history expansion
9101 @item set history expansion on
9102 @itemx set history expansion
9103 Enable history expansion. History expansion is off by default.
9105 @item set history expansion off
9106 Disable history expansion.
9108 The readline code comes with more complete documentation of
9109 editing and history expansion features. Users unfamiliar with @sc{gnu} Emacs
9110 or @code{vi} may wish to read it.
9111 @ifset have-readline-appendices
9112 @xref{Command Line Editing}.
9116 @kindex show history
9118 @itemx show history filename
9119 @itemx show history save
9120 @itemx show history size
9121 @itemx show history expansion
9122 These commands display the state of the @value{GDBN} history parameters.
9123 @code{show history} by itself displays all four states.
9128 @kindex show commands
9130 Display the last ten commands in the command history.
9132 @item show commands @var{n}
9133 Print ten commands centered on command number @var{n}.
9135 @item show commands +
9136 Print ten commands just after the commands last printed.
9139 @node Screen Size, Numbers, History, Controlling GDB
9140 @section Screen size
9141 @cindex size of screen
9142 @cindex pauses in output
9144 Certain commands to @value{GDBN} may produce large amounts of
9145 information output to the screen. To help you read all of it,
9146 @value{GDBN} pauses and asks you for input at the end of each page of
9147 output. Type @key{RET} when you want to continue the output, or @kbd{q}
9148 to discard the remaining output. Also, the screen width setting
9149 determines when to wrap lines of output. Depending on what is being
9150 printed, @value{GDBN} tries to break the line at a readable place,
9151 rather than simply letting it overflow onto the following line.
9153 Normally @value{GDBN} knows the size of the screen from the termcap data base
9154 together with the value of the @code{TERM} environment variable and the
9155 @code{stty rows} and @code{stty cols} settings. If this is not correct,
9156 you can override it with the @code{set height} and @code{set
9164 @item set height @var{lpp}
9166 @itemx set width @var{cpl}
9168 These @code{set} commands specify a screen height of @var{lpp} lines and
9169 a screen width of @var{cpl} characters. The associated @code{show}
9170 commands display the current settings.
9172 If you specify a height of zero lines, @value{GDBN} does not pause during
9173 output no matter how long the output is. This is useful if output is to a
9174 file or to an editor buffer.
9176 Likewise, you can specify @samp{set width 0} to prevent @value{GDBN}
9177 from wrapping its output.
9180 @node Numbers, Messages/Warnings, Screen Size, Controlling GDB
9182 @cindex number representation
9183 @cindex entering numbers
9185 You can always enter numbers in octal, decimal, or hexadecimal in @value{GDBN} by
9186 the usual conventions: octal numbers begin with @samp{0}, decimal
9187 numbers end with @samp{.}, and hexadecimal numbers begin with @samp{0x}.
9188 Numbers that begin with none of these are, by default, entered in base
9189 10; likewise, the default display for numbers---when no particular
9190 format is specified---is base 10. You can change the default base for
9191 both input and output with the @code{set radix} command.
9194 @kindex set input-radix
9195 @item set input-radix @var{base}
9196 Set the default base for numeric input. Supported choices
9197 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
9198 specified either unambiguously or using the current default radix; for
9208 sets the base to decimal. On the other hand, @samp{set radix 10}
9209 leaves the radix unchanged no matter what it was.
9211 @kindex set output-radix
9212 @item set output-radix @var{base}
9213 Set the default base for numeric display. Supported choices
9214 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
9215 specified either unambiguously or using the current default radix.
9217 @kindex show input-radix
9218 @item show input-radix
9219 Display the current default base for numeric input.
9221 @kindex show output-radix
9222 @item show output-radix
9223 Display the current default base for numeric display.
9226 @node Messages/Warnings, , Numbers, Controlling GDB
9227 @section Optional warnings and messages
9229 By default, @value{GDBN} is silent about its inner workings. If you are running
9230 on a slow machine, you may want to use the @code{set verbose} command.
9231 This makes @value{GDBN} tell you when it does a lengthy internal operation, so
9232 you will not think it has crashed.
9234 Currently, the messages controlled by @code{set verbose} are those
9235 which announce that the symbol table for a source file is being read;
9236 see @code{symbol-file} in @ref{Files, ,Commands to specify files}.
9240 @item set verbose on
9241 Enables @value{GDBN} output of certain informational messages.
9243 @item set verbose off
9244 Disables @value{GDBN} output of certain informational messages.
9246 @kindex show verbose
9248 Displays whether @code{set verbose} is on or off.
9251 By default, if @value{GDBN} encounters bugs in the symbol table of an object
9252 file, it is silent; but if you are debugging a compiler, you may find
9253 this information useful (@pxref{Symbol Errors, ,Errors reading symbol files}).
9256 @kindex set complaints
9257 @item set complaints @var{limit}
9258 Permits @value{GDBN} to output @var{limit} complaints about each type of unusual
9259 symbols before becoming silent about the problem. Set @var{limit} to
9260 zero to suppress all complaints; set it to a large number to prevent
9261 complaints from being suppressed.
9263 @kindex show complaints
9264 @item show complaints
9265 Displays how many symbol complaints @value{GDBN} is permitted to produce.
9268 By default, @value{GDBN} is cautious, and asks what sometimes seems to be a
9269 lot of stupid questions to confirm certain commands. For example, if
9270 you try to run a program which is already running:
9274 The program being debugged has been started already.
9275 Start it from the beginning? (y or n)
9278 If you are willing to unflinchingly face the consequences of your own
9279 commands, you can disable this ``feature'':
9284 @cindex confirmation
9285 @cindex stupid questions
9286 @item set confirm off
9287 Disables confirmation requests.
9289 @item set confirm on
9290 Enables confirmation requests (the default).
9292 @kindex show confirm
9294 Displays state of confirmation requests.
9297 @node Sequences, Emacs, Controlling GDB, Top
9298 @chapter Canned Sequences of Commands
9300 Aside from breakpoint commands (@pxref{Break Commands, ,Breakpoint
9301 command lists}), @value{GDBN} provides two ways to store sequences of commands
9302 for execution as a unit: user-defined commands and command files.
9305 * Define:: User-defined commands
9306 * Hooks:: User-defined command hooks
9307 * Command Files:: Command files
9308 * Output:: Commands for controlled output
9311 @node Define, Hooks, Sequences, Sequences
9312 @section User-defined commands
9314 @cindex user-defined command
9315 A @dfn{user-defined command} is a sequence of @value{GDBN} commands to which
9316 you assign a new name as a command. This is done with the @code{define}
9317 command. User commands may accept up to 10 arguments separated by whitespace.
9318 Arguments are accessed within the user command via @var{$arg0@dots{}$arg9}.
9323 print $arg0 + $arg1 + $arg2
9326 @noindent To execute the command use:
9332 @noindent This defines the command @code{adder}, which prints the sum of
9333 its three arguments. Note the arguments are text substitutions, so they may
9334 reference variables, use complex expressions, or even perform inferior
9339 @item define @var{commandname}
9340 Define a command named @var{commandname}. If there is already a command
9341 by that name, you are asked to confirm that you want to redefine it.
9343 The definition of the command is made up of other @value{GDBN} command lines,
9344 which are given following the @code{define} command. The end of these
9345 commands is marked by a line containing @code{end}.
9350 Takes a single argument, which is an expression to evaluate.
9351 It is followed by a series of commands that are executed
9352 only if the expression is true (nonzero).
9353 There can then optionally be a line @code{else}, followed
9354 by a series of commands that are only executed if the expression
9355 was false. The end of the list is marked by a line containing @code{end}.
9359 The syntax is similar to @code{if}: the command takes a single argument,
9360 which is an expression to evaluate, and must be followed by the commands to
9361 execute, one per line, terminated by an @code{end}.
9362 The commands are executed repeatedly as long as the expression
9366 @item document @var{commandname}
9367 Document the user-defined command @var{commandname}, so that it can be
9368 accessed by @code{help}. The command @var{commandname} must already be
9369 defined. This command reads lines of documentation just as @code{define}
9370 reads the lines of the command definition, ending with @code{end}.
9371 After the @code{document} command is finished, @code{help} on command
9372 @var{commandname} displays the documentation you have written.
9374 You may use the @code{document} command again to change the
9375 documentation of a command. Redefining the command with @code{define}
9376 does not change the documentation.
9378 @kindex help user-defined
9379 @item help user-defined
9380 List all user-defined commands, with the first line of the documentation
9385 @itemx show user @var{commandname}
9386 Display the @value{GDBN} commands used to define @var{commandname} (but not its
9387 documentation). If no @var{commandname} is given, display the
9388 definitions for all user-defined commands.
9391 When user-defined commands are executed, the
9392 commands of the definition are not printed. An error in any command
9393 stops execution of the user-defined command.
9395 If used interactively, commands that would ask for confirmation proceed
9396 without asking when used inside a user-defined command. Many @value{GDBN}
9397 commands that normally print messages to say what they are doing omit the
9398 messages when used in a user-defined command.
9400 @node Hooks, Command Files, Define, Sequences
9401 @section User-defined command hooks
9402 @cindex command files
9404 You may define @emph{hooks}, which are a special kind of user-defined
9405 command. Whenever you run the command @samp{foo}, if the user-defined
9406 command @samp{hook-foo} exists, it is executed (with no arguments)
9407 before that command.
9409 In addition, a pseudo-command, @samp{stop} exists. Defining
9410 (@samp{hook-stop}) makes the associated commands execute every time
9411 execution stops in your program: before breakpoint commands are run,
9412 displays are printed, or the stack frame is printed.
9415 For example, to ignore @code{SIGALRM} signals while
9416 single-stepping, but treat them normally during normal execution,
9421 handle SIGALRM nopass
9428 define hook-continue
9434 You can define a hook for any single-word command in @value{GDBN}, but
9435 not for command aliases; you should define a hook for the basic command
9436 name, e.g. @code{backtrace} rather than @code{bt}.
9437 @c FIXME! So how does Joe User discover whether a command is an alias
9439 If an error occurs during the execution of your hook, execution of
9440 @value{GDBN} commands stops and @value{GDBN} issues a prompt
9441 (before the command that you actually typed had a chance to run).
9443 If you try to define a hook which does not match any known command, you
9444 get a warning from the @code{define} command.
9446 @node Command Files, Output, Hooks, Sequences
9447 @section Command files
9449 @cindex command files
9450 A command file for @value{GDBN} is a file of lines that are @value{GDBN}
9451 commands. Comments (lines starting with @kbd{#}) may also be included.
9452 An empty line in a command file does nothing; it does not mean to repeat
9453 the last command, as it would from the terminal.
9456 @cindex @file{@value{GDBINIT}}
9457 When you start @value{GDBN}, it automatically executes commands from its
9458 @dfn{init files}. These are files named @file{@value{GDBINIT}}.
9459 @value{GDBN} reads the init file (if any) in your home directory, then
9460 processes command line options and operands, and then reads the init
9461 file (if any) in the current working directory. This is so the init
9462 file in your home directory can set options (such as @code{set
9463 complaints}) which affect the processing of the command line options and
9464 operands. The init files are not executed if you use the @samp{-nx}
9465 option; @pxref{Mode Options, ,Choosing modes}.
9468 @cindex init file name
9469 On some configurations of @value{GDBN}, the init file is known by a
9470 different name (these are typically environments where a specialized
9471 form of @value{GDBN} may need to coexist with other forms,
9472 hence a different name
9473 for the specialized version's init file). These are the environments
9474 with special init file names:
9479 VxWorks (Wind River Systems real-time OS): @samp{.vxgdbinit}
9481 @kindex .os68gdbinit
9483 OS68K (Enea Data Systems real-time OS): @samp{.os68gdbinit}
9487 ES-1800 (Ericsson Telecom AB M68000 emulator): @samp{.esgdbinit}
9491 You can also request the execution of a command file with the
9492 @code{source} command:
9496 @item source @var{filename}
9497 Execute the command file @var{filename}.
9500 The lines in a command file are executed sequentially. They are not
9501 printed as they are executed. An error in any command terminates execution
9502 of the command file.
9504 Commands that would ask for confirmation if used interactively proceed
9505 without asking when used in a command file. Many @value{GDBN} commands that
9506 normally print messages to say what they are doing omit the messages
9507 when called from command files.
9509 @node Output, , Command Files, Sequences
9510 @section Commands for controlled output
9512 During the execution of a command file or a user-defined command, normal
9513 @value{GDBN} output is suppressed; the only output that appears is what is
9514 explicitly printed by the commands in the definition. This section
9515 describes three commands useful for generating exactly the output you
9520 @item echo @var{text}
9521 @c I do not consider backslash-space a standard C escape sequence
9522 @c because it is not in ANSI.
9523 Print @var{text}. Nonprinting characters can be included in
9524 @var{text} using C escape sequences, such as @samp{\n} to print a
9525 newline. @strong{No newline is printed unless you specify one.}
9526 In addition to the standard C escape sequences, a backslash followed
9527 by a space stands for a space. This is useful for displaying a
9528 string with spaces at the beginning or the end, since leading and
9529 trailing spaces are otherwise trimmed from all arguments.
9530 To print @samp{@w{ }and foo =@w{ }}, use the command
9531 @samp{echo \@w{ }and foo = \@w{ }}.
9533 A backslash at the end of @var{text} can be used, as in C, to continue
9534 the command onto subsequent lines. For example,
9537 echo This is some text\n\
9538 which is continued\n\
9539 onto several lines.\n
9542 produces the same output as
9545 echo This is some text\n
9546 echo which is continued\n
9547 echo onto several lines.\n
9551 @item output @var{expression}
9552 Print the value of @var{expression} and nothing but that value: no
9553 newlines, no @samp{$@var{nn} = }. The value is not entered in the
9554 value history either. @xref{Expressions, ,Expressions}, for more information
9557 @item output/@var{fmt} @var{expression}
9558 Print the value of @var{expression} in format @var{fmt}. You can use
9559 the same formats as for @code{print}. @xref{Output Formats,,Output
9560 formats}, for more information.
9563 @item printf @var{string}, @var{expressions}@dots{}
9564 Print the values of the @var{expressions} under the control of
9565 @var{string}. The @var{expressions} are separated by commas and may be
9566 either numbers or pointers. Their values are printed as specified by
9567 @var{string}, exactly as if your program were to execute the C
9571 printf (@var{string}, @var{expressions}@dots{});
9574 For example, you can print two values in hex like this:
9577 printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
9580 The only backslash-escape sequences that you can use in the format
9581 string are the simple ones that consist of backslash followed by a
9586 @node Emacs, GDB Bugs, Sequences, Top
9587 @chapter Using @value{GDBN} under @sc{gnu} Emacs
9590 @cindex @sc{gnu} Emacs
9591 A special interface allows you to use @sc{gnu} Emacs to view (and
9592 edit) the source files for the program you are debugging with
9595 To use this interface, use the command @kbd{M-x gdb} in Emacs. Give the
9596 executable file you want to debug as an argument. This command starts
9597 @value{GDBN} as a subprocess of Emacs, with input and output through a newly
9598 created Emacs buffer.
9600 (Do not use the @code{-tui} option to run @value{GDBN} from Emacs.)
9603 Using @value{GDBN} under Emacs is just like using @value{GDBN} normally except for two
9608 All ``terminal'' input and output goes through the Emacs buffer.
9611 This applies both to @value{GDBN} commands and their output, and to the input
9612 and output done by the program you are debugging.
9614 This is useful because it means that you can copy the text of previous
9615 commands and input them again; you can even use parts of the output
9618 All the facilities of Emacs' Shell mode are available for interacting
9619 with your program. In particular, you can send signals the usual
9620 way---for example, @kbd{C-c C-c} for an interrupt, @kbd{C-c C-z} for a
9625 @value{GDBN} displays source code through Emacs.
9628 Each time @value{GDBN} displays a stack frame, Emacs automatically finds the
9629 source file for that frame and puts an arrow (@samp{=>}) at the
9630 left margin of the current line. Emacs uses a separate buffer for
9631 source display, and splits the screen to show both your @value{GDBN} session
9634 Explicit @value{GDBN} @code{list} or search commands still produce output as
9635 usual, but you probably have no reason to use them from Emacs.
9638 @emph{Warning:} If the directory where your program resides is not your
9639 current directory, it can be easy to confuse Emacs about the location of
9640 the source files, in which case the auxiliary display buffer does not
9641 appear to show your source. @value{GDBN} can find programs by searching your
9642 environment's @code{PATH} variable, so the @value{GDBN} input and output
9643 session proceeds normally; but Emacs does not get enough information
9644 back from @value{GDBN} to locate the source files in this situation. To
9645 avoid this problem, either start @value{GDBN} mode from the directory where
9646 your program resides, or specify an absolute file name when prompted for the
9647 @kbd{M-x gdb} argument.
9649 A similar confusion can result if you use the @value{GDBN} @code{file} command to
9650 switch to debugging a program in some other location, from an existing
9651 @value{GDBN} buffer in Emacs.
9654 By default, @kbd{M-x gdb} calls the program called @file{gdb}. If
9655 you need to call @value{GDBN} by a different name (for example, if you keep
9656 several configurations around, with different names) you can set the
9657 Emacs variable @code{gdb-command-name}; for example,
9660 (setq gdb-command-name "mygdb")
9664 (preceded by @kbd{ESC ESC}, or typed in the @code{*scratch*} buffer, or
9665 in your @file{.emacs} file) makes Emacs call the program named
9666 ``@code{mygdb}'' instead.
9668 In the @value{GDBN} I/O buffer, you can use these special Emacs commands in
9669 addition to the standard Shell mode commands:
9673 Describe the features of Emacs' @value{GDBN} Mode.
9676 Execute to another source line, like the @value{GDBN} @code{step} command; also
9677 update the display window to show the current file and location.
9680 Execute to next source line in this function, skipping all function
9681 calls, like the @value{GDBN} @code{next} command. Then update the display window
9682 to show the current file and location.
9685 Execute one instruction, like the @value{GDBN} @code{stepi} command; update
9686 display window accordingly.
9689 Execute to next instruction, using the @value{GDBN} @code{nexti} command; update
9690 display window accordingly.
9693 Execute until exit from the selected stack frame, like the @value{GDBN}
9694 @code{finish} command.
9697 Continue execution of your program, like the @value{GDBN} @code{continue}
9700 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-p}.
9703 Go up the number of frames indicated by the numeric argument
9704 (@pxref{Arguments, , Numeric Arguments, Emacs, The @sc{gnu} Emacs Manual}),
9705 like the @value{GDBN} @code{up} command.
9707 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-u}.
9710 Go down the number of frames indicated by the numeric argument, like the
9711 @value{GDBN} @code{down} command.
9713 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-d}.
9716 Read the number where the cursor is positioned, and insert it at the end
9717 of the @value{GDBN} I/O buffer. For example, if you wish to disassemble code
9718 around an address that was displayed earlier, type @kbd{disassemble};
9719 then move the cursor to the address display, and pick up the
9720 argument for @code{disassemble} by typing @kbd{C-x &}.
9722 You can customize this further by defining elements of the list
9723 @code{gdb-print-command}; once it is defined, you can format or
9724 otherwise process numbers picked up by @kbd{C-x &} before they are
9725 inserted. A numeric argument to @kbd{C-x &} indicates that you
9726 wish special formatting, and also acts as an index to pick an element of the
9727 list. If the list element is a string, the number to be inserted is
9728 formatted using the Emacs function @code{format}; otherwise the number
9729 is passed as an argument to the corresponding list element.
9732 In any source file, the Emacs command @kbd{C-x SPC} (@code{gdb-break})
9733 tells @value{GDBN} to set a breakpoint on the source line point is on.
9735 If you accidentally delete the source-display buffer, an easy way to get
9736 it back is to type the command @code{f} in the @value{GDBN} buffer, to
9737 request a frame display; when you run under Emacs, this recreates
9738 the source buffer if necessary to show you the context of the current
9741 The source files displayed in Emacs are in ordinary Emacs buffers
9742 which are visiting the source files in the usual way. You can edit
9743 the files with these buffers if you wish; but keep in mind that @value{GDBN}
9744 communicates with Emacs in terms of line numbers. If you add or
9745 delete lines from the text, the line numbers that @value{GDBN} knows cease
9746 to correspond properly with the code.
9748 @c The following dropped because Epoch is nonstandard. Reactivate
9749 @c if/when v19 does something similar. ---doc@cygnus.com 19dec1990
9751 @kindex Emacs Epoch environment
9755 Version 18 of @sc{gnu} Emacs has a built-in window system
9756 called the @code{epoch}
9757 environment. Users of this environment can use a new command,
9758 @code{inspect} which performs identically to @code{print} except that
9759 each value is printed in its own window.
9764 @node Energize, GDB Bugs, Emacs, Top
9765 @chapter Using @value{GDBN} with Energize
9768 The Energize Programming System is an integrated development environment
9769 that includes a point-and-click interface to many programming tools.
9770 When you use @value{GDBN} in this environment, you can use the standard
9771 Energize graphical interface to drive @value{GDBN}; you can also, if you
9772 choose, type @value{GDBN} commands as usual in a debugging window. Even if
9773 you use the graphical interface, the debugging window (which uses Emacs,
9774 and resembles the standard @sc{gnu} Emacs interface to
9775 @value{GDBN}) displays the
9776 equivalent commands, so that the history of your debugging session is
9779 When Energize starts up a @value{GDBN} session, it uses one of the
9780 command-line options @samp{-energize} or @samp{-cadillac} (``cadillac''
9781 is the name of the communications protocol used by the Energize system).
9782 This option makes @value{GDBN} run as one of the tools in the Energize Tool
9783 Set: it sends all output to the Energize kernel, and accept input from
9786 See the user manual for the Energize Programming System for
9787 information on how to use the Energize graphical interface and the other
9788 development tools that Energize integrates with @value{GDBN}.
9792 @node GDB Bugs, Command Line Editing, Emacs, Top
9793 @chapter Reporting Bugs in @value{GDBN}
9794 @cindex bugs in @value{GDBN}
9795 @cindex reporting bugs in @value{GDBN}
9797 Your bug reports play an essential role in making @value{GDBN} reliable.
9799 Reporting a bug may help you by bringing a solution to your problem, or it
9800 may not. But in any case the principal function of a bug report is to help
9801 the entire community by making the next version of @value{GDBN} work better. Bug
9802 reports are your contribution to the maintenance of @value{GDBN}.
9804 In order for a bug report to serve its purpose, you must include the
9805 information that enables us to fix the bug.
9808 * Bug Criteria:: Have you found a bug?
9809 * Bug Reporting:: How to report bugs
9812 @node Bug Criteria, Bug Reporting, GDB Bugs, GDB Bugs
9813 @section Have you found a bug?
9814 @cindex bug criteria
9816 If you are not sure whether you have found a bug, here are some guidelines:
9819 @cindex fatal signal
9820 @cindex debugger crash
9821 @cindex crash of debugger
9823 If the debugger gets a fatal signal, for any input whatever, that is a
9824 @value{GDBN} bug. Reliable debuggers never crash.
9826 @cindex error on valid input
9828 If @value{GDBN} produces an error message for valid input, that is a bug.
9830 @cindex invalid input
9832 If @value{GDBN} does not produce an error message for invalid input,
9833 that is a bug. However, you should note that your idea of
9834 ``invalid input'' might be our idea of ``an extension'' or ``support
9835 for traditional practice''.
9838 If you are an experienced user of debugging tools, your suggestions
9839 for improvement of @value{GDBN} are welcome in any case.
9842 @node Bug Reporting, , Bug Criteria, GDB Bugs
9843 @section How to report bugs
9845 @cindex @value{GDBN} bugs, reporting
9848 A number of companies and individuals offer support for @sc{gnu} products.
9849 If you obtained @value{GDBN} from a support organization, we recommend you
9850 contact that organization first.
9852 You can find contact information for many support companies and
9853 individuals in the file @file{etc/SERVICE} in the @sc{gnu} Emacs
9856 In any event, we also recommend that you send bug reports for @value{GDBN} to one
9860 bug-gdb@@prep.ai.mit.edu
9861 @{ucbvax|mit-eddie|uunet@}!prep.ai.mit.edu!bug-gdb
9864 @strong{Do not send bug reports to @samp{info-gdb}, or to
9865 @samp{help-gdb}, or to any newsgroups.} Most users of @value{GDBN} do not want to
9866 receive bug reports. Those that do have arranged to receive @samp{bug-gdb}.
9868 The mailing list @samp{bug-gdb} has a newsgroup @samp{gnu.gdb.bug} which
9869 serves as a repeater. The mailing list and the newsgroup carry exactly
9870 the same messages. Often people think of posting bug reports to the
9871 newsgroup instead of mailing them. This appears to work, but it has one
9872 problem which can be crucial: a newsgroup posting often lacks a mail
9873 path back to the sender. Thus, if we need to ask for more information,
9874 we may be unable to reach you. For this reason, it is better to send
9875 bug reports to the mailing list.
9877 As a last resort, send bug reports on paper to:
9880 @sc{gnu} Debugger Bugs
9881 Free Software Foundation Inc.
9882 59 Temple Place - Suite 330
9883 Boston, MA 02111-1307
9889 If you obtained HP GDB as part of your HP ANSI C or HP ANSI C++ compiler
9890 kit, report problems to your HP Support Representative.
9892 If you obtained HP GDB from the Hewlett-Packard Web site, report
9893 problems by electronic mail to @code{wdb-www@@ch.hp.com}.
9896 The fundamental principle of reporting bugs usefully is this:
9897 @strong{report all the facts}. If you are not sure whether to state a
9898 fact or leave it out, state it!
9900 Often people omit facts because they think they know what causes the
9901 problem and assume that some details do not matter. Thus, you might
9902 assume that the name of the variable you use in an example does not matter.
9903 Well, probably it does not, but one cannot be sure. Perhaps the bug is a
9904 stray memory reference which happens to fetch from the location where that
9905 name is stored in memory; perhaps, if the name were different, the contents
9906 of that location would fool the debugger into doing the right thing despite
9907 the bug. Play it safe and give a specific, complete example. That is the
9908 easiest thing for you to do, and the most helpful.
9910 Keep in mind that the purpose of a bug report is to enable us to fix
9911 the bug if it is new to us.
9913 @c FIX ME!!--What the heck does the following sentence mean,
9914 @c in the context of the one above?
9916 @c It is not as important as what happens if the bug is already known.
9918 Therefore, always write your bug reports on
9919 the assumption that the bug has not been reported previously.
9921 Sometimes people give a few sketchy facts and ask, ``Does this ring a
9922 bell?'' Those bug reports are useless, and we urge everyone to
9923 @emph{refuse to respond to them} except to chide the sender to report
9926 To enable us to fix the bug, you should include all these things:
9930 The version of @value{GDBN}. @value{GDBN} announces it if you start with no
9931 arguments; you can also print it at any time using @code{show version}.
9933 Without this, we will not know whether there is any point in looking for
9934 the bug in the current version of @value{GDBN}.
9937 The type of machine you are using, and the operating system name and
9942 What compiler (and its version) was used to compile @value{GDBN}---e.g.
9943 ``@value{GCC}--2.0''.
9947 What compiler (and its version) was used to compile the program you
9949 are debugging---e.g. ``@value{GCC}--2.0''.
9952 are debugging---e.g. ``HP92453-01 A.10.32.03 HP C Compiler''. Use the
9953 @code{what} command with the pathname of the compile command
9954 (@file{what /opt/ansic/bin/cc}, for example) to obtain this information.
9958 The command arguments you gave the compiler to compile your example and
9959 observe the bug. For example, did you use @samp{-O}? To guarantee
9960 you will not omit something important, list them all. A copy of the
9961 Makefile (or the output from make) is sufficient.
9963 If we were to try to guess the arguments, we would probably guess wrong
9964 and then we might not encounter the bug.
9967 A complete input script, and all necessary source files, that will
9971 A description of what behavior you observe that you believe is
9972 incorrect. For example, ``It gets a fatal signal.''
9974 Of course, if the bug is that @value{GDBN} gets a fatal signal, then we will
9975 certainly notice it. But if the bug is incorrect output, we might not
9976 notice unless it is glaringly wrong. You might as well not give us a
9977 chance to make a mistake.
9979 Even if the problem you experience is a fatal signal, you should still
9980 say so explicitly. Suppose something strange is going on, such as,
9981 your copy of @value{GDBN} is out of synch, or you have encountered a
9982 bug in the C library on your system. (This has happened!) Your copy
9983 might crash and ours would not. If you told us to expect a crash,
9984 then when ours fails to crash, we would know that the bug was not
9985 happening for us. If you had not told us to expect a crash, then we
9986 would not be able to draw any conclusion from our observations.
9990 If you wish to suggest changes to the @value{GDBN} source, send us context
9991 diffs. If you even discuss something in the @value{GDBN} source, refer to
9992 it by context, not by line number.
9994 The line numbers in our development sources will not match those in your
9995 sources. Your line numbers would convey no useful information to us.
9999 Here are some things that are not necessary:
10003 A description of the envelope of the bug.
10005 Often people who encounter a bug spend a lot of time investigating
10006 which changes to the input file will make the bug go away and which
10007 changes will not affect it.
10009 This is often time consuming and not very useful, because the way we
10010 will find the bug is by running a single example under the debugger
10011 with breakpoints, not by pure deduction from a series of examples.
10012 We recommend that you save your time for something else.
10014 Of course, if you can find a simpler example to report @emph{instead}
10015 of the original one, that is a convenience for us. Errors in the
10016 output will be easier to spot, running under the debugger will take
10017 less time, and so on.
10019 However, simplification is not vital; if you do not want to do this,
10020 report the bug anyway and send us the entire test case you used.
10023 A patch for the bug.
10025 A patch for the bug does help us if it is a good one. But do not omit
10026 the necessary information, such as the test case, on the assumption that
10027 a patch is all we need. We might see problems with your patch and decide
10028 to fix the problem another way, or we might not understand it at all.
10030 Sometimes with a program as complicated as @value{GDBN} it is very hard to
10031 construct an example that will make the program follow a certain path
10032 through the code. If you do not send us the example, we will not be able
10033 to construct one, so we will not be able to verify that the bug is fixed.
10035 And if we cannot understand what bug you are trying to fix, or why your
10036 patch should be an improvement, we will not install it. A test case will
10037 help us to understand.
10040 A guess about what the bug is or what it depends on.
10042 Such guesses are usually wrong. Even we cannot guess right about such
10043 things without first using the debugger to find the facts.
10046 @c The readline documentation is distributed with the readline code
10047 @c and consists of the two following files:
10050 @c Use -I with makeinfo to point to the appropriate directory,
10051 @c environment var TEXINPUTS with TeX.
10052 @include rluser.texinfo
10053 @include inc-hist.texi
10057 @node Renamed Commands, Formatting Documentation, GDB Bugs, Top
10058 @appendix Renamed Commands
10060 The following commands were renamed in @value{GDBN} 4, in order to make the
10061 command set as a whole more consistent and easier to use and remember:
10064 @kindex delete environment
10065 @kindex info copying
10066 @kindex info convenience
10067 @kindex info directories
10068 @kindex info editing
10069 @kindex info history
10070 @kindex info targets
10071 @kindex info values
10072 @kindex info version
10073 @kindex info warranty
10074 @kindex set addressprint
10075 @kindex set arrayprint
10076 @kindex set prettyprint
10077 @kindex set screen-height
10078 @kindex set screen-width
10079 @kindex set unionprint
10080 @kindex set vtblprint
10081 @kindex set demangle
10082 @kindex set asm-demangle
10083 @kindex set sevenbit-strings
10084 @kindex set array-max
10085 @kindex set caution
10086 @kindex set history write
10087 @kindex show addressprint
10088 @kindex show arrayprint
10089 @kindex show prettyprint
10090 @kindex show screen-height
10091 @kindex show screen-width
10092 @kindex show unionprint
10093 @kindex show vtblprint
10094 @kindex show demangle
10095 @kindex show asm-demangle
10096 @kindex show sevenbit-strings
10097 @kindex show array-max
10098 @kindex show caution
10099 @kindex show history write
10104 @c END TEXI2ROFF-KILL
10106 OLD COMMAND NEW COMMAND
10108 --------------- -------------------------------
10109 @c END TEXI2ROFF-KILL
10110 add-syms add-symbol-file
10111 delete environment unset environment
10112 info convenience show convenience
10113 info copying show copying
10114 info directories show directories
10115 info editing show commands
10116 info history show values
10117 info targets help target
10118 info values show values
10119 info version show version
10120 info warranty show warranty
10121 set/show addressprint set/show print address
10122 set/show array-max set/show print elements
10123 set/show arrayprint set/show print array
10124 set/show asm-demangle set/show print asm-demangle
10125 set/show caution set/show confirm
10126 set/show demangle set/show print demangle
10127 set/show history write set/show history save
10128 set/show prettyprint set/show print pretty
10129 set/show screen-height set/show height
10130 set/show screen-width set/show width
10131 set/show sevenbit-strings set/show print sevenbit-strings
10132 set/show unionprint set/show print union
10133 set/show vtblprint set/show print vtbl
10135 unset [No longer an alias for delete]
10141 \vskip \parskip\vskip \baselineskip
10142 \halign{\tt #\hfil &\qquad#&\tt #\hfil\cr
10143 {\bf Old Command} &&{\bf New Command}\cr
10144 add-syms &&add-symbol-file\cr
10145 delete environment &&unset environment\cr
10146 info convenience &&show convenience\cr
10147 info copying &&show copying\cr
10148 info directories &&show directories \cr
10149 info editing &&show commands\cr
10150 info history &&show values\cr
10151 info targets &&help target\cr
10152 info values &&show values\cr
10153 info version &&show version\cr
10154 info warranty &&show warranty\cr
10155 set{\rm / }show addressprint &&set{\rm / }show print address\cr
10156 set{\rm / }show array-max &&set{\rm / }show print elements\cr
10157 set{\rm / }show arrayprint &&set{\rm / }show print array\cr
10158 set{\rm / }show asm-demangle &&set{\rm / }show print asm-demangle\cr
10159 set{\rm / }show caution &&set{\rm / }show confirm\cr
10160 set{\rm / }show demangle &&set{\rm / }show print demangle\cr
10161 set{\rm / }show history write &&set{\rm / }show history save\cr
10162 set{\rm / }show prettyprint &&set{\rm / }show print pretty\cr
10163 set{\rm / }show screen-height &&set{\rm / }show height\cr
10164 set{\rm / }show screen-width &&set{\rm / }show width\cr
10165 set{\rm / }show sevenbit-strings &&set{\rm / }show print sevenbit-strings\cr
10166 set{\rm / }show unionprint &&set{\rm / }show print union\cr
10167 set{\rm / }show vtblprint &&set{\rm / }show print vtbl\cr
10169 unset &&\rm(No longer an alias for delete)\cr
10172 @c END TEXI2ROFF-KILL
10176 @ifclear PRECONFIGURED
10178 @node Formatting Documentation, Installing GDB, Renamed Commands, Top
10179 @appendix Formatting Documentation
10181 @cindex @value{GDBN} reference card
10182 @cindex reference card
10183 The @value{GDBN} 4 release includes an already-formatted reference card, ready
10184 for printing with PostScript or Ghostscript, in the @file{gdb}
10185 subdirectory of the main source directory@footnote{In
10186 @file{gdb-@value{GDBVN}/gdb/refcard.ps} of the version @value{GDBVN}
10187 release.}. If you can use PostScript or Ghostscript with your printer,
10188 you can print the reference card immediately with @file{refcard.ps}.
10190 The release also includes the source for the reference card. You
10191 can format it, using @TeX{}, by typing:
10197 The @value{GDBN} reference card is designed to print in @dfn{landscape}
10198 mode on US ``letter'' size paper;
10199 that is, on a sheet 11 inches wide by 8.5 inches
10200 high. You will need to specify this form of printing as an option to
10201 your @sc{dvi} output program.
10203 @cindex documentation
10205 All the documentation for @value{GDBN} comes as part of the machine-readable
10206 distribution. The documentation is written in Texinfo format, which is
10207 a documentation system that uses a single source file to produce both
10208 on-line information and a printed manual. You can use one of the Info
10209 formatting commands to create the on-line version of the documentation
10210 and @TeX{} (or @code{texi2roff}) to typeset the printed version.
10212 @value{GDBN} includes an already formatted copy of the on-line Info version of
10213 this manual in the @file{gdb} subdirectory. The main Info file is
10214 @file{gdb-@r{version-number}/gdb/gdb.info}, and it refers to
10215 subordinate files matching @samp{gdb.info*} in the same directory. If
10216 necessary, you can print out these files, or read them with any editor;
10217 but they are easier to read using the @code{info} subsystem in @sc{gnu} Emacs
10218 or the standalone @code{info} program, available as part of the @sc{gnu}
10219 Texinfo distribution.
10221 If you want to format these Info files yourself, you need one of the
10222 Info formatting programs, such as @code{texinfo-format-buffer} or
10225 If you have @code{makeinfo} installed, and are in the top level @value{GDBN}
10226 source directory (@file{gdb-@value{GDBVN}}, in the case of version @value{GDBVN}), you can
10227 make the Info file by typing:
10234 If you want to typeset and print copies of this manual, you need @TeX{},
10235 a program to print its @sc{dvi} output files, and @file{texinfo.tex}, the
10236 Texinfo definitions file.
10238 @TeX{} is a typesetting program; it does not print files directly, but
10239 produces output files called @sc{dvi} files. To print a typeset
10240 document, you need a program to print @sc{dvi} files. If your system
10241 has @TeX{} installed, chances are it has such a program. The precise
10242 command to use depends on your system; @kbd{lpr -d} is common; another
10243 (for PostScript devices) is @kbd{dvips}. The @sc{dvi} print command may
10244 require a file name without any extension or a @samp{.dvi} extension.
10246 @TeX{} also requires a macro definitions file called
10247 @file{texinfo.tex}. This file tells @TeX{} how to typeset a document
10248 written in Texinfo format. On its own, @TeX{} cannot either read or
10249 typeset a Texinfo file. @file{texinfo.tex} is distributed with GDB
10250 and is located in the @file{gdb-@var{version-number}/texinfo}
10253 If you have @TeX{} and a @sc{dvi} printer program installed, you can
10254 typeset and print this manual. First switch to the the @file{gdb}
10255 subdirectory of the main source directory (for example, to
10256 @file{gdb-@value{GDBVN}/gdb}) and then type:
10263 @node Installing GDB, Index, Using History, Top
10264 @appendix Installing @value{GDBN}
10265 @cindex configuring @value{GDBN}
10266 @cindex installation
10269 If you obtain @value{GDBN} (HP WDB 0.75) as part of your HP ANSI C or
10270 HP ANSI C++ Developer's Kit at HP-UX Release 11.0, you do not have to
10271 take any special action to build or install @value{GDBN}.
10273 If you obtain @value{GDBN} (HP WDB 0.75) from an HP web site, you may
10274 download either a @code{swinstall}-able package or a source tree, or
10277 Most customers will want to install the @value{GDBN} binary that is part
10278 of the @code{swinstall}-able package. To do so, use a command of the
10282 /usr/sbin/swinstall -s @var{package-name} WDB
10285 Alternatively, it is possible to build @value{GDBN} from the source
10286 distribution. Sophisticated customers who want to modify the debugger
10287 sources to tailor @value{GDBN} to their their needs may wish to do this.
10288 The source distribution consists of a @code{tar}'ed source tree rooted
10289 at @file{gdb-4.16/...}. The instructions that follow describe how to
10290 build a @file{gdb} executable from this source tree. HP believes that
10291 these instructions apply to the WDB source tree that it distributes.
10292 However, HP does not explicitly support building a @file{gdb} for any
10293 non-HP platform from the WDB source tree. It may work, but HP has not
10294 tested it for any platforms other than those described in the WDB 0.75
10298 @value{GDBN} comes with a @code{configure} script that automates the process
10299 of preparing @value{GDBN} for installation; you can then use @code{make} to
10300 build the @code{gdb} program.
10302 @c irrelevant in info file; it's as current as the code it lives with.
10303 @footnote{If you have a more recent version of @value{GDBN} than @value{GDBVN},
10304 look at the @file{README} file in the sources; we may have improved the
10305 installation procedures since publishing this manual.}
10308 The @value{GDBN} distribution includes all the source code you need for
10309 @value{GDBN} in a single directory, whose name is usually composed by
10310 appending the version number to @samp{gdb}.
10312 For example, the @value{GDBN} version @value{GDBVN} distribution is in the
10313 @file{gdb-@value{GDBVN}} directory. That directory contains:
10316 @item gdb-@value{GDBVN}/configure @r{(and supporting files)}
10317 script for configuring @value{GDBN} and all its supporting libraries
10319 @item gdb-@value{GDBVN}/gdb
10320 the source specific to @value{GDBN} itself
10322 @item gdb-@value{GDBVN}/bfd
10323 source for the Binary File Descriptor library
10325 @item gdb-@value{GDBVN}/include
10326 @sc{gnu} include files
10328 @item gdb-@value{GDBVN}/libiberty
10329 source for the @samp{-liberty} free software library
10331 @item gdb-@value{GDBVN}/opcodes
10332 source for the library of opcode tables and disassemblers
10334 @item gdb-@value{GDBVN}/readline
10335 source for the @sc{gnu} command-line interface
10337 @item gdb-@value{GDBVN}/glob
10338 source for the @sc{gnu} filename pattern-matching subroutine
10340 @item gdb-@value{GDBVN}/mmalloc
10341 source for the @sc{gnu} memory-mapped malloc package
10344 The simplest way to configure and build @value{GDBN} is to run @code{configure}
10345 from the @file{gdb-@var{version-number}} source directory, which in
10346 this example is the @file{gdb-@value{GDBVN}} directory.
10348 First switch to the @file{gdb-@var{version-number}} source directory
10349 if you are not already in it; then run @code{configure}. Pass the
10350 identifier for the platform on which @value{GDBN} will run as an
10356 cd gdb-@value{GDBVN}
10357 ./configure @var{host}
10362 where @var{host} is an identifier such as @samp{sun4} or
10363 @samp{decstation}, that identifies the platform where @value{GDBN} will run.
10364 (You can often leave off @var{host}; @code{configure} tries to guess the
10365 correct value by examining your system.)
10367 Running @samp{configure @var{host}} and then running @code{make} builds the
10368 @file{bfd}, @file{readline}, @file{mmalloc}, and @file{libiberty}
10369 libraries, then @code{gdb} itself. The configured source files, and the
10370 binaries, are left in the corresponding source directories.
10373 @code{configure} is a Bourne-shell (@code{/bin/sh}) script; if your
10374 system does not recognize this automatically when you run a different
10375 shell, you may need to run @code{sh} on it explicitly:
10378 sh configure @var{host}
10381 If you run @code{configure} from a directory that contains source
10382 directories for multiple libraries or programs, such as the
10383 @file{gdb-@value{GDBVN}} source directory for version @value{GDBVN}, @code{configure}
10384 creates configuration files for every directory level underneath (unless
10385 you tell it not to, with the @samp{--norecursion} option).
10387 You can run the @code{configure} script from any of the
10388 subordinate directories in the @value{GDBN} distribution if you only want to
10389 configure that subdirectory, but be sure to specify a path to it.
10391 For example, with version @value{GDBVN}, type the following to configure only
10392 the @code{bfd} subdirectory:
10396 cd gdb-@value{GDBVN}/bfd
10397 ../configure @var{host}
10401 You can install @code{@value{GDBP}} anywhere; it has no hardwired paths.
10402 However, you should make sure that the shell on your path (named by
10403 the @samp{SHELL} environment variable) is publicly readable. Remember
10404 that @value{GDBN} uses the shell to start your program---some systems refuse to
10405 let @value{GDBN} debug child processes whose programs are not readable.
10408 * Separate Objdir:: Compiling @value{GDBN} in another directory
10409 * Config Names:: Specifying names for hosts and targets
10410 * Configure Options:: Summary of options for configure
10413 @node Separate Objdir, Config Names, Installing GDB, Installing GDB
10414 @section Compiling @value{GDBN} in another directory
10416 If you want to run @value{GDBN} versions for several host or target machines,
10417 you need a different @code{gdb} compiled for each combination of
10418 host and target. @code{configure} is designed to make this easy by
10419 allowing you to generate each configuration in a separate subdirectory,
10420 rather than in the source directory. If your @code{make} program
10421 handles the @samp{VPATH} feature (@sc{gnu} @code{make} does), running
10422 @code{make} in each of these directories builds the @code{gdb}
10423 program specified there.
10425 To build @code{gdb} in a separate directory, run @code{configure}
10426 with the @samp{--srcdir} option to specify where to find the source.
10427 (You also need to specify a path to find @code{configure}
10428 itself from your working directory. If the path to @code{configure}
10429 would be the same as the argument to @samp{--srcdir}, you can leave out
10430 the @samp{--srcdir} option; it is assumed.)
10432 For example, with version @value{GDBVN}, you can build @value{GDBN} in a
10433 separate directory for a Sun 4 like this:
10437 cd gdb-@value{GDBVN}
10440 ../gdb-@value{GDBVN}/configure sun4
10445 When @code{configure} builds a configuration using a remote source
10446 directory, it creates a tree for the binaries with the same structure
10447 (and using the same names) as the tree under the source directory. In
10448 the example, you'd find the Sun 4 library @file{libiberty.a} in the
10449 directory @file{gdb-sun4/libiberty}, and @value{GDBN} itself in
10450 @file{gdb-sun4/gdb}.
10452 One popular reason to build several @value{GDBN} configurations in separate
10453 directories is to configure @value{GDBN} for cross-compiling (where
10454 @value{GDBN} runs on one machine---the @dfn{host}---while debugging
10455 programs that run on another machine---the @dfn{target}).
10456 You specify a cross-debugging target by
10457 giving the @samp{--target=@var{target}} option to @code{configure}.
10459 When you run @code{make} to build a program or library, you must run
10460 it in a configured directory---whatever directory you were in when you
10461 called @code{configure} (or one of its subdirectories).
10463 The @code{Makefile} that @code{configure} generates in each source
10464 directory also runs recursively. If you type @code{make} in a source
10465 directory such as @file{gdb-@value{GDBVN}} (or in a separate configured
10466 directory configured with @samp{--srcdir=@var{dirname}/gdb-@value{GDBVN}}), you
10467 will build all the required libraries, and then build GDB.
10469 When you have multiple hosts or targets configured in separate
10470 directories, you can run @code{make} on them in parallel (for example,
10471 if they are NFS-mounted on each of the hosts); they will not interfere
10474 @node Config Names, Configure Options, Separate Objdir, Installing GDB
10475 @section Specifying names for hosts and targets
10477 The specifications used for hosts and targets in the @code{configure}
10478 script are based on a three-part naming scheme, but some short predefined
10479 aliases are also supported. The full naming scheme encodes three pieces
10480 of information in the following pattern:
10483 @var{architecture}-@var{vendor}-@var{os}
10486 For example, you can use the alias @code{sun4} as a @var{host} argument,
10487 or as the value for @var{target} in a @code{--target=@var{target}}
10488 option. The equivalent full name is @samp{sparc-sun-sunos4}.
10490 The @code{configure} script accompanying @value{GDBN} does not provide
10491 any query facility to list all supported host and target names or
10492 aliases. @code{configure} calls the Bourne shell script
10493 @code{config.sub} to map abbreviations to full names; you can read the
10494 script, if you wish, or you can use it to test your guesses on
10495 abbreviations---for example:
10498 % sh config.sub sun4
10499 sparc-sun-sunos4.1.1
10500 % sh config.sub sun3
10501 m68k-sun-sunos4.1.1
10502 % sh config.sub decstation
10504 % sh config.sub hp300bsd
10506 % sh config.sub i386v
10508 % sh config.sub i786v
10509 Invalid configuration `i786v': machine `i786v' not recognized
10513 @code{config.sub} is also distributed in the @value{GDBN} source
10514 directory (@file{gdb-@value{GDBVN}}, for version @value{GDBVN}).
10516 @node Configure Options, , Config Names, Installing GDB
10517 @section @code{configure} options
10519 Here is a summary of the @code{configure} options and arguments that
10520 are most often useful for building @value{GDBN}. @code{configure} also has
10521 several other options not listed here. @inforef{What Configure
10522 Does,,configure.info}, for a full explanation of @code{configure}.
10525 configure @r{[}--help@r{]}
10526 @r{[}--prefix=@var{dir}@r{]}
10527 @r{[}--srcdir=@var{dirname}@r{]}
10528 @r{[}--norecursion@r{]} @r{[}--rm@r{]}
10529 @r{[}--target=@var{target}@r{]} @var{host}
10533 You may introduce options with a single @samp{-} rather than
10534 @samp{--} if you prefer; but you may abbreviate option names if you use
10539 Display a quick summary of how to invoke @code{configure}.
10541 @item -prefix=@var{dir}
10542 Configure the source to install programs and files under directory
10545 @c avoid splitting the warning from the explanation:
10547 @item --srcdir=@var{dirname}
10548 @strong{Warning: using this option requires @sc{gnu} @code{make}, or another
10549 @code{make} that implements the @code{VPATH} feature.}@*
10550 Use this option to make configurations in directories separate from the
10551 @value{GDBN} source directories. Among other things, you can use this to
10552 build (or maintain) several configurations simultaneously, in separate
10553 directories. @code{configure} writes configuration specific files in
10554 the current directory, but arranges for them to use the source in the
10555 directory @var{dirname}. @code{configure} creates directories under
10556 the working directory in parallel to the source directories below
10559 @item --norecursion
10560 Configure only the directory level where @code{configure} is executed; do not
10561 propagate configuration to subdirectories.
10564 @emph{Remove} files otherwise built during configuration.
10566 @c This does not work (yet if ever). FIXME.
10567 @c @item --parse=@var{lang} @dots{}
10568 @c Configure the @value{GDBN} expression parser to parse the listed languages.
10569 @c @samp{all} configures @value{GDBN} for all supported languages. To get a
10570 @c list of all supported languages, omit the argument. Without this
10571 @c option, @value{GDBN} is configured to parse all supported languages.
10573 @item --target=@var{target}
10574 Configure @value{GDBN} for cross-debugging programs running on the specified
10575 @var{target}. Without this option, @value{GDBN} is configured to debug
10576 programs that run on the same machine (@var{host}) as @value{GDBN} itself.
10578 There is no convenient way to generate a list of all available targets.
10580 @item @var{host} @dots{}
10581 Configure @value{GDBN} to run on the specified @var{host}.
10583 There is no convenient way to generate a list of all available hosts.
10587 @code{configure} accepts other options, for compatibility with
10588 configuring other @sc{gnu} tools recursively; but these are the only
10589 options that affect @value{GDBN} or its supporting libraries.
10593 @node Index, , Installing GDB, Top
10599 % I think something like @colophon should be in texinfo. In the
10601 \long\def\colophon{\hbox to0pt{}\vfill
10602 \centerline{The body of this manual is set in}
10603 \centerline{\fontname\tenrm,}
10604 \centerline{with headings in {\bf\fontname\tenbf}}
10605 \centerline{and examples in {\tt\fontname\tentt}.}
10606 \centerline{{\it\fontname\tenit\/},}
10607 \centerline{{\bf\fontname\tenbf}, and}
10608 \centerline{{\sl\fontname\tensl\/}}
10609 \centerline{are used for emphasis.}\vfill}
10611 % Blame: doc@cygnus.com, 1991.