1 \input texinfo @c -*-texinfo-*-
2 @c Copyright 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999
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
38 @set DATE January 1999
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, 1999
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, 1999
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 Interactively:: 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
271 * Breakpoints:: Breakpoints, watchpoints, and catchpoints
272 * Continuing and Stepping:: Resuming execution
277 * Thread Stops:: Stopping and starting multi-thread programs
280 Breakpoints and watchpoints
282 * Set Breaks:: Setting breakpoints
283 * Set Watchpoints:: Setting watchpoints
284 * Set Catchpoints:: Setting catchpoints
285 * Delete Breaks:: Deleting breakpoints
286 * Disabling:: Disabling breakpoints
287 * Conditions:: Break conditions
288 * Break Commands:: Breakpoint command lists
290 * Breakpoint Menus:: Breakpoint menus
295 * Frames:: Stack frames
296 * Backtrace:: Backtraces
297 * Selection:: Selecting a frame
298 * Frame Info:: Information on a frame
300 * MIPS Stack:: MIPS machines and the function stack
303 Examining Source Files
305 * List:: Printing source lines
307 * Search:: Searching source files
309 * Source Path:: Specifying source directories
310 * Machine Code:: Source and machine code
314 * Expressions:: Expressions
315 * Variables:: Program variables
316 * Arrays:: Artificial arrays
317 * Output Formats:: Output formats
318 * Memory:: Examining memory
319 * Auto Display:: Automatic display
320 * Print Settings:: Print settings
321 * Value History:: Value history
322 * Convenience Vars:: Convenience variables
323 * Registers:: Registers
325 * Floating Point Hardware:: Floating point hardware
328 Using @value{GDBN} with Different Languages
330 * Setting:: Switching between source languages
331 * Show:: Displaying the language
333 * Checks:: Type and range checks
336 * Support:: Supported languages
338 Switching between source languages
340 * Filenames:: Filename extensions and languages.
341 * Manually:: Setting the working language manually
342 * Automatically:: Having @value{GDBN} infer the source language
345 Type and range checking
347 * Type Checking:: An overview of type checking
348 * Range Checking:: An overview of range checking
358 * C Operators:: C operators
363 * C Operators:: C and C++ operators
364 * C Constants:: C and C++ constants
365 * Cplus expressions:: C++ expressions
366 * C Defaults:: Default settings for C and C++
368 * C Checks:: C and C++ type and range checks
370 * Debugging C:: @value{GDBN} and C
371 * Debugging C plus plus:: @value{GDBN} features for C++
376 * M2 Operators:: Built-in operators
377 * Built-In Func/Proc:: Built-in functions and procedures
378 * M2 Constants:: Modula-2 constants
379 * M2 Defaults:: Default settings for Modula-2
380 * Deviations:: Deviations from standard Modula-2
381 * M2 Checks:: Modula-2 type and range checks
382 * M2 Scope:: The scope operators @code{::} and @code{.}
383 * GDB/M2:: @value{GDBN} and Modula-2
388 * Assignment:: Assignment to variables
389 * Jumping:: Continuing at a different address
391 * Signaling:: Giving your program a signal
393 * Returning:: Returning from a function
394 * Calling:: Calling your program's functions
395 * Patching:: Patching your program
399 * Files:: Commands to specify files
400 * Symbol Errors:: Errors reading symbol files
402 Specifying a Debugging Target
404 * Active Targets:: Active targets
405 * Target Commands:: Commands for managing targets
407 * Byte Order:: Choosing target byte order
408 * Remote:: Remote debugging
414 * Remote Serial:: @value{GDBN} remote serial protocol
418 * i960-Nindy Remote:: @value{GDBN} with a remote i960 (Nindy)
422 * UDI29K Remote:: The UDI protocol for AMD29K
423 * EB29K Remote:: The EBMON protocol for AMD29K
427 * VxWorks Remote:: @value{GDBN} and VxWorks
431 * ST2000 Remote:: @value{GDBN} with a Tandem ST2000
435 * Hitachi Remote:: @value{GDBN} and Hitachi Microprocessors
439 * MIPS Remote:: @value{GDBN} and MIPS boards
443 * Simulator:: Simulated CPU target
446 Controlling @value{GDBN}
449 * Editing:: Command editing
450 * History:: Command history
451 * Screen Size:: Screen size
453 * Messages/Warnings:: Optional warnings and messages
455 Canned Sequences of Commands
457 * Define:: User-defined commands
458 * Hooks:: User-defined command hooks
459 * Command Files:: Command files
460 * Output:: Commands for controlled output
462 Reporting Bugs in @value{GDBN}
464 * Bug Criteria:: Have you found a bug?
465 * Bug Reporting:: How to report bugs
467 Installing @value{GDBN}
469 * Separate Objdir:: Compiling @value{GDBN} in another directory
470 * Config Names:: Specifying names for hosts and targets
471 * Configure Options:: Summary of options for configure
476 @node Summary, Sample Session, Top, Top
477 @unnumbered Summary of @value{GDBN}
479 The purpose of a debugger such as @value{GDBN} is to allow you to see what is
480 going on ``inside'' another program while it executes---or what another
481 program was doing at the moment it crashed.
483 @value{GDBN} can do four main kinds of things (plus other things in support of
484 these) to help you catch bugs in the act:
488 Start your program, specifying anything that might affect its behavior.
491 Make your program stop on specified conditions.
494 Examine what has happened, when your program has stopped.
497 Change things in your program, so you can experiment with correcting the
498 effects of one bug and go on to learn about another.
502 You can use @value{GDBN} to debug programs written in C or C++.
503 @c "MOD2" used as a "miscellaneous languages" flag here.
504 @c This is acceptable while there is no real doc for Chill and Pascal.
506 For more information, see @ref{Support,,Supported languages}.
509 For more information, see @ref{C,,C and C++}.
511 Support for Modula-2 and Chill is partial. For information on Modula-2,
512 see @ref{Modula-2,,Modula-2}. There is no further documentation on Chill yet.
514 Debugging Pascal programs which use sets, subranges, file variables, or nested
515 functions does not currently work. @value{GDBN} does not support
516 entering expressions, printing values, or similar features using Pascal syntax.
521 @value{GDBN} can be used to debug programs written in Fortran, although
522 it does not yet support entering expressions, printing values, or
523 similar features using Fortran syntax. It may be necessary to refer to
524 some variables with a trailing underscore.
529 This version of the manual documents HP Wildebeest (WDB) Version 0.75,
530 implemented on HP 9000 systems running Release 10.20, 10.30, or 11.0 of
531 the HP-UX operating system. HP WDB 0.75 can be used to debug code
532 generated by the HP ANSI C and HP ANSI C++ compilers as well as the
533 @sc{gnu} C and C++ compilers. It does not support the debugging of
534 Fortran, Modula-2, or Chill programs.
538 * Free Software:: Freely redistributable software
539 * Contributors:: Contributors to GDB
542 @node Free Software, Contributors, Summary, Summary
543 @unnumberedsec Free software
545 @value{GDBN} is @dfn{free software}, protected by the @sc{gnu}
546 General Public License
547 (GPL). The GPL gives you the freedom to copy or adapt a licensed
548 program---but every person getting a copy also gets with it the
549 freedom to modify that copy (which means that they must get access to
550 the source code), and the freedom to distribute further copies.
551 Typical software companies use copyrights to limit your freedoms; the
552 Free Software Foundation uses the GPL to preserve these freedoms.
554 Fundamentally, the General Public License is a license which says that
555 you have these freedoms and that you cannot take these freedoms away
558 @node Contributors, , Free Software, Summary
559 @unnumberedsec Contributors to GDB
561 Richard Stallman was the original author of GDB, and of many other @sc{gnu}
562 programs. Many others have contributed to its development. This
563 section attempts to credit major contributors. One of the virtues of
564 free software is that everyone is free to contribute to it; with
565 regret, we cannot actually acknowledge everyone here. The file
566 @file{ChangeLog} in the @value{GDBN} distribution approximates a blow-by-blow
569 Changes much prior to version 2.0 are lost in the mists of time.
572 @emph{Plea:} Additions to this section are particularly welcome. If you
573 or your friends (or enemies, to be evenhanded) have been unfairly
574 omitted from this list, we would like to add your names!
577 So that they may not regard their long labor as thankless, we
578 particularly thank those who shepherded GDB through major releases:
579 Stan Shebs (release 4.14),
580 Fred Fish (releases 4.13, 4.12, 4.11, 4.10, and 4.9),
581 Stu Grossman and John Gilmore (releases 4.8, 4.7, 4.6, 4.5, and 4.4),
582 John Gilmore (releases 4.3, 4.2, 4.1, 4.0, and 3.9);
583 Jim Kingdon (releases 3.5, 3.4, and 3.3);
584 and Randy Smith (releases 3.2, 3.1, and 3.0).
585 As major maintainer of @value{GDBN} for some period, each
586 contributed significantly to the structure, stability, and capabilities
587 of the entire debugger.
589 Richard Stallman, assisted at various times by Peter TerMaat, Chris
590 Hanson, and Richard Mlynarik, handled releases through 2.8.
593 Michael Tiemann is the author of most of the @sc{gnu} C++ support in GDB,
594 with significant additional contributions from Per Bothner. James
595 Clark wrote the @sc{gnu} C++ demangler. Early work on C++ was by Peter
596 TerMaat (who also did much general update work leading to release 3.0).
599 @value{GDBN} 4 uses the BFD subroutine library to examine multiple
600 object-file formats; BFD was a joint project of David V.
601 Henkel-Wallace, Rich Pixley, Steve Chamberlain, and John Gilmore.
603 David Johnson wrote the original COFF support; Pace Willison did
604 the original support for encapsulated COFF.
606 Brent Benson of Harris Computer Systems contributed DWARF 2 support.
608 Adam de Boor and Bradley Davis contributed the ISI Optimum V support.
609 Per Bothner, Noboyuki Hikichi, and Alessandro Forin contributed MIPS
611 Jean-Daniel Fekete contributed Sun 386i support.
612 Chris Hanson improved the HP9000 support.
613 Noboyuki Hikichi and Tomoyuki Hasei contributed Sony/News OS 3 support.
614 David Johnson contributed Encore Umax support.
615 Jyrki Kuoppala contributed Altos 3068 support.
616 Jeff Law contributed HP PA and SOM support.
617 Keith Packard contributed NS32K support.
618 Doug Rabson contributed Acorn Risc Machine support.
619 Bob Rusk contributed Harris Nighthawk CX-UX support.
620 Chris Smith contributed Convex support (and Fortran debugging).
621 Jonathan Stone contributed Pyramid support.
622 Michael Tiemann contributed SPARC support.
623 Tim Tucker contributed support for the Gould NP1 and Gould Powernode.
624 Pace Willison contributed Intel 386 support.
625 Jay Vosburgh contributed Symmetry support.
627 Rich Schaefer and Peter Schauer helped with support of SunOS shared
630 Jay Fenlason and Roland McGrath ensured that @value{GDBN} and GAS agree about
631 several machine instruction sets.
633 Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped develop
634 remote debugging. Intel Corporation, Wind River Systems, AMD, and ARM
635 contributed remote debugging modules for the i960, VxWorks, A29K UDI,
636 and RDI targets, respectively.
638 Brian Fox is the author of the readline libraries providing
639 command-line editing and command history.
641 Andrew Beers of SUNY Buffalo wrote the language-switching code,
643 the Modula-2 support,
645 and contributed the Languages chapter of this manual.
647 Fred Fish wrote most of the support for Unix System Vr4.
649 He also enhanced the command-completion support to cover C++ overloaded
653 Hitachi America, Ltd. sponsored the support for Hitachi microprocessors.
655 Kung Hsu, Jeff Law, and Rick Sladkey added support for hardware
658 Michael Snyder added support for tracepoints.
660 Stu Grossman wrote gdbserver.
662 Jim Kingdon, Peter Schauer, Ian Taylor, and Stu Grossman made
663 nearly innumerable bug fixes and cleanups throughout GDB.
665 The following people at the Hewlett-Packard Company contributed
666 support for the PA-RISC 2.0 architecture, HP-UX 10.20, 10.30, and 11.0
667 (narrow mode), HP's implementation of kernel threads, HP's aC++
668 compiler, and the terminal user interface: Ben Krepp, Richard Title,
669 John Bishop, Susan Macchia, Kathy Mann, Satish Pai, India Paul, Steve
670 Rehrauer, and Elena Zannoni. Kim Haase provided HP-specific
671 information in this manual.
673 Cygnus Solutions has sponsored GDB maintenance and much of its
674 development since 1991.
677 @node Sample Session, Invocation, Summary, Top
678 @chapter A Sample @value{GDBN} Session
680 You can use this manual at your leisure to read all about @value{GDBN}.
681 However, a handful of commands are enough to get started using the
682 debugger. This chapter illustrates those commands.
685 In this sample session, we emphasize user input like this: @b{input},
686 to make it easier to pick out from the surrounding output.
689 @c FIXME: this example may not be appropriate for some configs, where
690 @c FIXME...primary interest is in remote use.
692 One of the preliminary versions of @sc{gnu} @code{m4} (a generic macro
693 processor) exhibits the following bug: sometimes, when we change its
694 quote strings from the default, the commands used to capture one macro
695 definition within another stop working. In the following short @code{m4}
696 session, we define a macro @code{foo} which expands to @code{0000}; we
697 then use the @code{m4} built-in @code{defn} to define @code{bar} as the
698 same thing. However, when we change the open quote string to
699 @code{<QUOTE>} and the close quote string to @code{<UNQUOTE>}, the same
700 procedure fails to define a new synonym @code{baz}:
709 @b{define(bar,defn(`foo'))}
713 @b{changequote(<QUOTE>,<UNQUOTE>)}
715 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
718 m4: End of input: 0: fatal error: EOF in string
722 Let us use @value{GDBN} to try to see what is going on.
726 $ @b{@value{GDBP} m4}
727 @c FIXME: this falsifies the exact text played out, to permit smallbook
728 @c FIXME... format to come out better.
729 @value{GDBN} is free software and you are welcome to distribute copies
730 of it under certain conditions; type "show copying" to see
732 There is absolutely no warranty for @value{GDBN}; type "show warranty"
735 @value{GDBN} @value{GDBVN}, Copyright 1995 Free Software Foundation, Inc...
741 $ @b{@value{GDBP} m4}
742 Wildebeest is free software and you are welcome to distribute copies of
743 it under certain conditions; type "show copying" to see the conditions.
744 There is absolutely no warranty for Wildebeest; type "show warranty"
747 Hewlett-Packard Wildebeest 0.75 (based on GDB 4.16)
748 (built for PA-RISC 1.1 or 2.0, HP-UX 10.20)
749 Copyright 1996, 1997 Free Software Foundation, Inc.
755 @value{GDBN} reads only enough symbol data to know where to find the
756 rest when needed; as a result, the first prompt comes up very quickly.
757 We now tell @value{GDBN} to use a narrower display width than usual, so
758 that examples fit in this manual.
761 (@value{GDBP}) @b{set width 70}
765 We need to see how the @code{m4} built-in @code{changequote} works.
766 Having looked at the source, we know the relevant subroutine is
767 @code{m4_changequote}, so we set a breakpoint there with the @value{GDBN}
768 @code{break} command.
771 (@value{GDBP}) @b{break m4_changequote}
772 Breakpoint 1 at 0x62f4: file builtin.c, line 879.
776 Using the @code{run} command, we start @code{m4} running under @value{GDBN}
777 control; as long as control does not reach the @code{m4_changequote}
778 subroutine, the program runs as usual:
781 (@value{GDBP}) @b{run}
782 Starting program: /work/Editorial/gdb/gnu/m4/m4
790 To trigger the breakpoint, we call @code{changequote}. @value{GDBN}
791 suspends execution of @code{m4}, displaying information about the
792 context where it stops.
795 @b{changequote(<QUOTE>,<UNQUOTE>)}
797 Breakpoint 1, m4_changequote (argc=3, argv=0x33c70)
799 879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]),argc,1,3))
803 Now we use the command @code{n} (@code{next}) to advance execution to
804 the next line of the current function.
808 882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\
813 @code{set_quotes} looks like a promising subroutine. We can go into it
814 by using the command @code{s} (@code{step}) instead of @code{next}.
815 @code{step} goes to the next line to be executed in @emph{any}
816 subroutine, so it steps into @code{set_quotes}.
820 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
822 530 if (lquote != def_lquote)
826 The display that shows the subroutine where @code{m4} is now
827 suspended (and its arguments) is called a stack frame display. It
828 shows a summary of the stack. We can use the @code{backtrace}
829 command (which can also be spelled @code{bt}), to see where we are
830 in the stack as a whole: the @code{backtrace} command displays a
831 stack frame for each active subroutine.
834 (@value{GDBP}) @b{bt}
835 #0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
837 #1 0x6344 in m4_changequote (argc=3, argv=0x33c70)
839 #2 0x8174 in expand_macro (sym=0x33320) at macro.c:242
840 #3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30)
842 #4 0x79dc in expand_input () at macro.c:40
843 #5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195
847 We step through a few more lines to see what happens. The first two
848 times, we can use @samp{s}; the next two times we use @code{n} to avoid
849 falling into the @code{xstrdup} subroutine.
853 0x3b5c 532 if (rquote != def_rquote)
855 0x3b80 535 lquote = (lq == nil || *lq == '\0') ? \
856 def_lquote : xstrdup(lq);
858 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
861 538 len_lquote = strlen(rquote);
865 The last line displayed looks a little odd; we can examine the variables
866 @code{lquote} and @code{rquote} to see if they are in fact the new left
867 and right quotes we specified. We use the command @code{p}
868 (@code{print}) to see their values.
871 (@value{GDBP}) @b{p lquote}
872 $1 = 0x35d40 "<QUOTE>"
873 (@value{GDBP}) @b{p rquote}
874 $2 = 0x35d50 "<UNQUOTE>"
878 @code{lquote} and @code{rquote} are indeed the new left and right quotes.
879 To look at some context, we can display ten lines of source
880 surrounding the current line with the @code{l} (@code{list}) command.
886 535 lquote = (lq == nil || *lq == '\0') ? def_lquote\
888 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
891 538 len_lquote = strlen(rquote);
892 539 len_rquote = strlen(lquote);
899 Let us step past the two lines that set @code{len_lquote} and
900 @code{len_rquote}, and then examine the values of those variables.
904 539 len_rquote = strlen(lquote);
907 (@value{GDBP}) @b{p len_lquote}
909 (@value{GDBP}) @b{p len_rquote}
914 That certainly looks wrong, assuming @code{len_lquote} and
915 @code{len_rquote} are meant to be the lengths of @code{lquote} and
916 @code{rquote} respectively. We can set them to better values using
917 the @code{p} command, since it can print the value of
918 any expression---and that expression can include subroutine calls and
922 (@value{GDBP}) @b{p len_lquote=strlen(lquote)}
924 (@value{GDBP}) @b{p len_rquote=strlen(rquote)}
929 Is that enough to fix the problem of using the new quotes with the
930 @code{m4} built-in @code{defn}? We can allow @code{m4} to continue
931 executing with the @code{c} (@code{continue}) command, and then try the
932 example that caused trouble initially:
938 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
945 Success! The new quotes now work just as well as the default ones. The
946 problem seems to have been just the two typos defining the wrong
947 lengths. We allow @code{m4} exit by giving it an EOF as input:
951 Program exited normally.
955 The message @samp{Program exited normally.} is from @value{GDBN}; it
956 indicates @code{m4} has finished executing. We can end our @value{GDBN}
957 session with the @value{GDBN} @code{quit} command.
960 (@value{GDBP}) @b{quit}
964 @node Invocation, Commands, Sample Session, Top
965 @chapter Getting In and Out of @value{GDBN}
967 This chapter discusses how to start @value{GDBN}, and how to get out of it.
971 type @samp{@value{GDBP}} to start GDB.
973 type @kbd{quit} or @kbd{C-d} to exit.
977 * Invoking GDB:: How to start @value{GDBN}
978 * Quitting GDB:: How to quit @value{GDBN}
979 * Shell Commands:: How to use shell commands inside @value{GDBN}
982 @node Invoking GDB, Quitting GDB, Invocation, Invocation
983 @section Invoking @value{GDBN}
986 For details on starting up @value{GDBP} as a
987 remote debugger attached to a Hitachi microprocessor, see @ref{Hitachi
988 Remote,,@value{GDBN} and Hitachi Microprocessors}.
991 Invoke @value{GDBN} by running the program @code{@value{GDBP}}. Once started,
992 @value{GDBN} reads commands from the terminal until you tell it to exit.
994 You can also run @code{@value{GDBP}} with a variety of arguments and options,
995 to specify more of your debugging environment at the outset.
998 The command-line options described here are designed
999 to cover a variety of situations; in some environments, some of these
1000 options may effectively be unavailable.
1003 The most usual way to start @value{GDBN} is with one argument,
1004 specifying an executable program:
1007 @value{GDBP} @var{program}
1012 You can also start with both an executable program and a core file
1016 @value{GDBP} @var{program} @var{core}
1019 You can, instead, specify a process ID as a second argument, if you want
1020 to debug a running process:
1023 @value{GDBP} @var{program} 1234
1027 would attach @value{GDBN} to process @code{1234} (unless you also have a file
1028 named @file{1234}; @value{GDBN} does check for a core file first).
1031 Taking advantage of the second command-line argument requires a fairly
1032 complete operating system; when you use @value{GDBN} as a remote debugger
1033 attached to a bare board, there may not be any notion of ``process'',
1034 and there is often no way to get a core dump.
1038 You can run @code{gdb} without printing the front material, which describes
1039 @value{GDBN}'s non-warranty, by specifying @code{-silent}:
1042 @value{GDBP} -silent
1046 You can further control how @value{GDBN} starts up by using command-line
1047 options. @value{GDBN} itself can remind you of the options available.
1057 to display all available options and briefly describe their use
1058 (@samp{@value{GDBP} -h} is a shorter equivalent).
1060 All options and command line arguments you give are processed
1061 in sequential order. The order makes a difference when the
1062 @samp{-x} option is used.
1068 * Remote Serial:: @value{GDBN} remote serial protocol
1071 * i960-Nindy Remote:: @value{GDBN} with a remote i960 (Nindy)
1074 * UDI29K Remote:: The UDI protocol for AMD29K
1075 * EB29K Remote:: The EBMON protocol for AMD29K
1078 * VxWorks Remote:: @value{GDBN} and VxWorks
1081 * ST2000 Remote:: @value{GDBN} with a Tandem ST2000
1084 * Hitachi Remote:: @value{GDBN} and Hitachi Microprocessors
1087 * MIPS Remote:: @value{GDBN} and MIPS boards
1090 * Sparclet Remote:: @value{GDBN} and Sparclet boards
1093 * Simulator:: Simulated CPU target
1096 @c remnant makeinfo bug requires this blank line after *two* end-ifblahs:
1098 * File Options:: Choosing files
1099 * Mode Options:: Choosing modes
1104 @include remote.texi
1109 @subsection Choosing files
1112 When @value{GDBN} starts, it reads any arguments other than options as
1113 specifying an executable file and core file (or process ID). This is
1114 the same as if the arguments were specified by the @samp{-se} and
1115 @samp{-c} options respectively. (@value{GDBN} reads the first argument
1116 that does not have an associated option flag as equivalent to the
1117 @samp{-se} option followed by that argument; and the second argument
1118 that does not have an associated option flag, if any, as equivalent to
1119 the @samp{-c} option followed by that argument.)
1122 When @value{GDBN} starts, it reads any argument other than options as
1123 specifying an executable file. This is the same as if the argument was
1124 specified by the @samp{-se} option.
1127 Many options have both long and short forms; both are shown in the
1128 following list. @value{GDBN} also recognizes the long forms if you truncate
1129 them, so long as enough of the option is present to be unambiguous.
1130 (If you prefer, you can flag option arguments with @samp{--} rather
1131 than @samp{-}, though we illustrate the more usual convention.)
1134 @item -symbols @var{file}
1135 @itemx -s @var{file}
1136 Read symbol table from file @var{file}.
1138 @item -exec @var{file}
1139 @itemx -e @var{file}
1140 Use file @var{file} as the executable file to execute when
1145 appropriate, and for examining pure data in conjunction with a core
1149 @item -se @var{file}
1150 Read symbol table from file @var{file} and use it as the executable
1154 @item -core @var{file}
1155 @itemx -c @var{file}
1156 Use file @var{file} as a core dump to examine.
1158 @item -c @var{number}
1159 Connect to process ID @var{number}, as with the @code{attach} command
1160 (unless there is a file in core-dump format named @var{number}, in which
1161 case @samp{-c} specifies that file as a core dump to read).
1164 @item -command @var{file}
1165 @itemx -x @var{file}
1166 Execute @value{GDBN} commands from file @var{file}. @xref{Command
1167 Files,, Command files}.
1169 @item -directory @var{directory}
1170 @itemx -d @var{directory}
1171 Add @var{directory} to the path to search for source files.
1177 @emph{Warning: this option depends on operating system facilities that are not
1178 supported on all systems.}@*
1179 If memory-mapped files are available on your system through the @code{mmap}
1180 system call, you can use this option
1181 to have @value{GDBN} write the symbols from your
1182 program into a reusable file in the current directory. If the program you are debugging is
1183 called @file{/tmp/fred}, the mapped symbol file is @file{./fred.syms}.
1184 Future @value{GDBN} debugging sessions notice the presence of this file,
1185 and can quickly map in symbol information from it, rather than reading
1186 the symbol table from the executable program.
1188 The @file{.syms} file is specific to the host machine where @value{GDBN}
1189 is run. It holds an exact image of the internal @value{GDBN} symbol
1190 table. It cannot be shared across multiple host platforms.
1197 Read each symbol file's entire symbol table immediately, rather than
1198 the default, which is to read it incrementally as it is needed.
1199 This makes startup slower, but makes future operations faster.
1205 The @code{-mapped} and @code{-readnow} options are typically combined in
1206 order to build a @file{.syms} file that contains complete symbol
1207 information. (@xref{Files,,Commands to specify files}, for
1208 information on @file{.syms} files.) A simple GDB invocation to do
1209 nothing but build a @file{.syms} file for future use is:
1212 gdb -batch -nx -mapped -readnow programname
1217 @node Mode Options, , File Options, Invoking GDB
1218 @subsection Choosing modes
1220 You can run @value{GDBN} in various alternative modes---for example, in
1221 batch mode or quiet mode.
1226 Do not execute commands from any initialization files (normally called
1227 @file{@value{GDBINIT}}). Normally, the commands in these files are
1228 executed after all the command options and arguments have been
1229 processed. @xref{Command Files,,Command files}.
1233 ``Quiet''. Do not print the introductory and copyright messages. These
1234 messages are also suppressed in batch mode.
1237 Run in batch mode. Exit with status @code{0} after processing all the
1238 command files specified with @samp{-x} (and all commands from
1239 initialization files, if not inhibited with @samp{-n}). Exit with
1240 nonzero status if an error occurs in executing the @value{GDBN} commands
1241 in the command files.
1243 Batch mode may be useful for running @value{GDBN} as a filter, for example to
1244 download and run a program on another computer; in order to make this
1245 more useful, the message
1248 Program exited normally.
1252 (which is ordinarily issued whenever a program running under @value{GDBN} control
1253 terminates) is not issued when running in batch mode.
1255 @item -cd @var{directory}
1256 Run @value{GDBN} using @var{directory} as its working directory,
1257 instead of the current directory.
1260 @item -context @var{authentication}
1261 When the Energize programming system starts up @value{GDBN}, it uses this
1262 option to trigger an alternate mode of interaction.
1263 @var{authentication} is a pair of numeric codes that identify @value{GDBN}
1264 as a client in the Energize environment. Avoid this option when you run
1265 @value{GDBN} directly from the command line. See @ref{Energize,,Using
1266 @value{GDBN} with Energize} for more discussion of using @value{GDBN} with Energize.
1272 @sc{gnu} Emacs sets this option when it runs @value{GDBN} as a subprocess. It tells @value{GDBN}
1273 to output the full file name and line number in a standard,
1274 recognizable fashion each time a stack frame is displayed (which
1275 includes each time your program stops). This recognizable format looks
1276 like two @samp{\032} characters, followed by the file name, line number
1277 and character position separated by colons, and a newline. The
1278 Emacs-to-@value{GDBN} interface program uses the two @samp{\032} characters as
1279 a signal to display the source code for the frame.
1285 Set the line speed (baud rate or bits per second) of any serial
1286 interface used by @value{GDBN} for remote debugging.
1289 @item -tty @var{device}
1290 Run using @var{device} for your program's standard input and output.
1291 @c FIXME: kingdon thinks there is more to -tty. Investigate.
1296 Use a Terminal User Interface. For information, use your Web browser to
1297 read the file @file{TUI.html}, which is usually installed in the
1298 directory @code{/opt/langtools/wdb/doc} on HP-UX systems. Do not use
1299 this option if you run @value{GDBN} from Emacs (see @pxref{Emacs, ,Using
1300 @value{GDBN} under @sc{gnu} Emacs}).
1303 Run in XDB compatibility mode, allowing the use of certain XDB commands.
1304 For information, see the file @file{xdb_trans.html}, which is usually
1305 installed in the directory @code{/opt/langtools/wdb/doc} on HP-UX
1310 @node Quitting GDB, Shell Commands, Invoking GDB, Invocation
1311 @section Quitting @value{GDBN}
1312 @cindex exiting @value{GDBN}
1313 @cindex leaving @value{GDBN}
1316 @kindex quit @r{[}@var{expression}@r{]}
1319 To exit @value{GDBN}, use the @code{quit} command (abbreviated @code{q}), or
1320 type an end-of-file character (usually @kbd{C-d}). If you do not supply
1321 @var{expression}, @value{GDBN} will terminate normally; otherwise it will
1322 terminate using the result of @var{expression} as the error code.
1326 An interrupt (often @kbd{C-c}) does not exit from @value{GDBN}, but rather
1327 terminates the action of any @value{GDBN} command that is in progress and
1328 returns to @value{GDBN} command level. It is safe to type the interrupt
1329 character at any time because @value{GDBN} does not allow it to take effect
1330 until a time when it is safe.
1333 If you have been using @value{GDBN} to control an attached process or
1334 device, you can release it with the @code{detach} command
1335 (@pxref{Attach, ,Debugging an already-running process}).
1338 @node Shell Commands, , Quitting GDB, Invocation
1339 @section Shell commands
1341 If you need to execute occasional shell commands during your
1342 debugging session, there is no need to leave or suspend @value{GDBN}; you can
1343 just use the @code{shell} command.
1347 @cindex shell escape
1348 @item shell @var{command string}
1349 Invoke a standard shell to execute @var{command string}.
1351 If it exists, the environment variable @code{SHELL} determines which
1352 shell to run. Otherwise @value{GDBN} uses @code{/bin/sh}.
1356 The utility @code{make} is often needed in development environments.
1357 You do not have to use the @code{shell} command for this purpose in
1362 @cindex calling make
1363 @item make @var{make-args}
1364 Execute the @code{make} program with the specified
1365 arguments. This is equivalent to @samp{shell make @var{make-args}}.
1368 @node Commands, Running, Invocation, Top
1369 @chapter @value{GDBN} Commands
1371 You can abbreviate a @value{GDBN} command to the first few letters of the command
1372 name, if that abbreviation is unambiguous; and you can repeat certain
1373 @value{GDBN} commands by typing just @key{RET}. You can also use the @key{TAB}
1374 key to get @value{GDBN} to fill out the rest of a word in a command (or to
1375 show you the alternatives available, if there is more than one possibility).
1378 * Command Syntax:: How to give commands to @value{GDBN}
1379 * Completion:: Command completion
1380 * Help:: How to ask @value{GDBN} for help
1383 @node Command Syntax, Completion, Commands, Commands
1384 @section Command syntax
1386 A @value{GDBN} command is a single line of input. There is no limit on
1387 how long it can be. It starts with a command name, which is followed by
1388 arguments whose meaning depends on the command name. For example, the
1389 command @code{step} accepts an argument which is the number of times to
1390 step, as in @samp{step 5}. You can also use the @code{step} command
1391 with no arguments. Some command names do not allow any arguments.
1393 @cindex abbreviation
1394 @value{GDBN} command names may always be truncated if that abbreviation is
1395 unambiguous. Other possible command abbreviations are listed in the
1396 documentation for individual commands. In some cases, even ambiguous
1397 abbreviations are allowed; for example, @code{s} is specially defined as
1398 equivalent to @code{step} even though there are other commands whose
1399 names start with @code{s}. You can test abbreviations by using them as
1400 arguments to the @code{help} command.
1402 @cindex repeating commands
1404 A blank line as input to @value{GDBN} (typing just @key{RET}) means to
1405 repeat the previous command. Certain commands (for example, @code{run})
1406 will not repeat this way; these are commands whose unintentional
1407 repetition might cause trouble and which you are unlikely to want to
1410 The @code{list} and @code{x} commands, when you repeat them with
1411 @key{RET}, construct new arguments rather than repeating
1412 exactly as typed. This permits easy scanning of source or memory.
1414 @value{GDBN} can also use @key{RET} in another way: to partition lengthy
1415 output, in a way similar to the common utility @code{more}
1416 (@pxref{Screen Size,,Screen size}). Since it is easy to press one
1417 @key{RET} too many in this situation, @value{GDBN} disables command
1418 repetition after any command that generates this sort of display.
1422 Any text from a @kbd{#} to the end of the line is a comment; it does
1423 nothing. This is useful mainly in command files (@pxref{Command
1424 Files,,Command files}).
1426 @node Completion, Help, Command Syntax, Commands
1427 @section Command completion
1430 @cindex word completion
1431 @value{GDBN} can fill in the rest of a word in a command for you, if there is
1432 only one possibility; it can also show you what the valid possibilities
1433 are for the next word in a command, at any time. This works for @value{GDBN}
1434 commands, @value{GDBN} subcommands, and the names of symbols in your program.
1436 Press the @key{TAB} key whenever you want @value{GDBN} to fill out the rest
1437 of a word. If there is only one possibility, @value{GDBN} fills in the
1438 word, and waits for you to finish the command (or press @key{RET} to
1439 enter it). For example, if you type
1441 @c FIXME "@key" does not distinguish its argument sufficiently to permit
1442 @c complete accuracy in these examples; space introduced for clarity.
1443 @c If texinfo enhancements make it unnecessary, it would be nice to
1444 @c replace " @key" by "@key" in the following...
1446 (@value{GDBP}) info bre @key{TAB}
1450 @value{GDBN} fills in the rest of the word @samp{breakpoints}, since that is
1451 the only @code{info} subcommand beginning with @samp{bre}:
1454 (@value{GDBP}) info breakpoints
1458 You can either press @key{RET} at this point, to run the @code{info
1459 breakpoints} command, or backspace and enter something else, if
1460 @samp{breakpoints} does not look like the command you expected. (If you
1461 were sure you wanted @code{info breakpoints} in the first place, you
1462 might as well just type @key{RET} immediately after @samp{info bre},
1463 to exploit command abbreviations rather than command completion).
1465 If there is more than one possibility for the next word when you press
1466 @key{TAB}, @value{GDBN} sounds a bell. You can either supply more
1467 characters and try again, or just press @key{TAB} a second time;
1468 @value{GDBN} displays all the possible completions for that word. For
1469 example, you might want to set a breakpoint on a subroutine whose name
1470 begins with @samp{make_}, but when you type @kbd{b make_@key{TAB}} @value{GDBN}
1471 just sounds the bell. Typing @key{TAB} again displays all the
1472 function names in your program that begin with those characters, for
1476 (@value{GDBP}) b make_ @key{TAB}
1477 @exdent @value{GDBN} sounds bell; press @key{TAB} again, to see:
1478 make_a_section_from_file make_environ
1479 make_abs_section make_function_type
1480 make_blockvector make_pointer_type
1481 make_cleanup make_reference_type
1482 make_command make_symbol_completion_list
1483 (@value{GDBP}) b make_
1487 After displaying the available possibilities, @value{GDBN} copies your
1488 partial input (@samp{b make_} in the example) so you can finish the
1491 If you just want to see the list of alternatives in the first place, you
1492 can press @kbd{M-?} rather than pressing @key{TAB} twice. @kbd{M-?}
1493 means @kbd{@key{META} ?}. You can type this
1495 either by holding down a
1496 key designated as the @key{META} shift on your keyboard (if there is
1497 one) while typing @kbd{?}, or
1499 as @key{ESC} followed by @kbd{?}.
1501 @cindex quotes in commands
1502 @cindex completion of quoted strings
1503 Sometimes the string you need, while logically a ``word'', may contain
1504 parentheses or other characters that @value{GDBN} normally excludes from its
1505 notion of a word. To permit word completion to work in this situation,
1506 you may enclose words in @code{'} (single quote marks) in @value{GDBN} commands.
1509 The most likely situation where you might need this is in typing the
1510 name of a C++ function. This is because C++ allows function overloading
1511 (multiple definitions of the same function, distinguished by argument
1512 type). For example, when you want to set a breakpoint you may need to
1513 distinguish whether you mean the version of @code{name} that takes an
1514 @code{int} parameter, @code{name(int)}, or the version that takes a
1515 @code{float} parameter, @code{name(float)}. To use the word-completion
1516 facilities in this situation, type a single quote @code{'} at the
1517 beginning of the function name. This alerts @value{GDBN} that it may need to
1518 consider more information than usual when you press @key{TAB} or
1519 @kbd{M-?} to request word completion:
1522 (@value{GDBP}) b 'bubble( @key{M-?}
1523 bubble(double,double) bubble(int,int)
1524 (@value{GDBP}) b 'bubble(
1527 In some cases, @value{GDBN} can tell that completing a name requires using
1528 quotes. When this happens, @value{GDBN} inserts the quote for you (while
1529 completing as much as it can) if you do not type the quote in the first
1533 (@value{GDBP}) b bub @key{TAB}
1534 @exdent @value{GDBN} alters your input line to the following, and rings a bell:
1535 (@value{GDBP}) b 'bubble(
1539 In general, @value{GDBN} can tell that a quote is needed (and inserts it) if
1540 you have not yet started typing the argument list when you ask for
1541 completion on an overloaded symbol.
1543 For more information about overloaded functions, @pxref{Cplus
1544 expressions, ,C++ expressions}. You can use the command @code{set
1545 overload-resolution off} to disable overload resolution;
1546 @pxref{Debugging C plus plus, ,@value{GDBN} features for C++}.
1550 @node Help, , Completion, Commands
1551 @section Getting help
1552 @cindex online documentation
1555 You can always ask @value{GDBN} itself for information on its commands,
1556 using the command @code{help}.
1562 You can use @code{help} (abbreviated @code{h}) with no arguments to
1563 display a short list of named classes of commands:
1567 List of classes of commands:
1569 running -- Running the program
1570 stack -- Examining the stack
1571 data -- Examining data
1572 breakpoints -- Making program stop at certain points
1573 files -- Specifying and examining files
1574 status -- Status inquiries
1575 support -- Support facilities
1576 user-defined -- User-defined commands
1577 aliases -- Aliases of other commands
1578 obscure -- Obscure features
1580 Type "help" followed by a class name for a list of
1581 commands in that class.
1582 Type "help" followed by command name for full
1584 Command name abbreviations are allowed if unambiguous.
1588 @item help @var{class}
1589 Using one of the general help classes as an argument, you can get a
1590 list of the individual commands in that class. For example, here is the
1591 help display for the class @code{status}:
1594 (@value{GDBP}) help status
1599 @c Line break in "show" line falsifies real output, but needed
1600 @c to fit in smallbook page size.
1601 show -- Generic command for showing things set
1603 info -- Generic command for printing status
1605 Type "help" followed by command name for full
1607 Command name abbreviations are allowed if unambiguous.
1611 @item help @var{command}
1612 With a command name as @code{help} argument, @value{GDBN} displays a
1613 short paragraph on how to use that command.
1616 @item complete @var{args}
1617 The @code{complete @var{args}} command lists all the possible completions
1618 for the beginning of a command. Use @var{args} to specify the beginning of the
1619 command you want completed. For example:
1625 @noindent results in:
1635 @noindent This is intended for use by @sc{gnu} Emacs.
1638 In addition to @code{help}, you can use the @value{GDBN} commands @code{info}
1639 and @code{show} to inquire about the state of your program, or the state
1640 of @value{GDBN} itself. Each command supports many topics of inquiry; this
1641 manual introduces each of them in the appropriate context. The listings
1642 under @code{info} and under @code{show} in the Index point to
1643 all the sub-commands. @xref{Index}.
1650 This command (abbreviated @code{i}) is for describing the state of your
1651 program. For example, you can list the arguments given to your program
1652 with @code{info args}, list the registers currently in use with @code{info
1653 registers}, or list the breakpoints you have set with @code{info breakpoints}.
1654 You can get a complete list of the @code{info} sub-commands with
1655 @w{@code{help info}}.
1659 You can assign the result of an expresson to an environment variable with
1660 @code{set}. For example, you can set the @value{GDBN} prompt to a $-sign with
1661 @code{set prompt $}.
1665 In contrast to @code{info}, @code{show} is for describing the state of
1666 @value{GDBN} itself.
1667 You can change most of the things you can @code{show}, by using the
1668 related command @code{set}; for example, you can control what number
1669 system is used for displays with @code{set radix}, or simply inquire
1670 which is currently in use with @code{show radix}.
1673 To display all the settable parameters and their current
1674 values, you can use @code{show} with no arguments; you may also use
1675 @code{info set}. Both commands produce the same display.
1676 @c FIXME: "info set" violates the rule that "info" is for state of
1677 @c FIXME...program. Ck w/ GNU: "info set" to be called something else,
1678 @c FIXME...or change desc of rule---eg "state of prog and debugging session"?
1682 Here are three miscellaneous @code{show} subcommands, all of which are
1683 exceptional in lacking corresponding @code{set} commands:
1686 @kindex show version
1687 @cindex version number
1689 Show what version of @value{GDBN} is running. You should include this
1690 information in @value{GDBN} bug-reports. If multiple versions of @value{GDBN} are in
1691 use at your site, you may occasionally want to determine which version
1692 of @value{GDBN} you are running; as @value{GDBN} evolves, new commands are introduced,
1693 and old ones may wither away. The version number is also announced
1694 when you start @value{GDBN}.
1696 @kindex show copying
1698 Display information about permission for copying @value{GDBN}.
1700 @kindex show warranty
1702 Display the @sc{gnu} ``NO WARRANTY'' statement.
1705 @node Running, Stopping, Commands, Top
1706 @chapter Running Programs Under @value{GDBN}
1708 When you run a program under @value{GDBN}, you must first generate
1709 debugging information when you compile it.
1711 You may start @value{GDBN} with its arguments, if any, in an environment
1712 of your choice. You may redirect your program's input and output, debug an
1713 already running process, or kill a child process.
1717 * Compilation:: Compiling for debugging
1718 * Starting:: Starting your program
1720 * Arguments:: Your program's arguments
1721 * Environment:: Your program's environment
1724 * Working Directory:: Your program's working directory
1725 * Input/Output:: Your program's input and output
1726 * Attach:: Debugging an already-running process
1727 * Kill Process:: Killing the child process
1729 * Process Information:: Additional process information
1732 * Threads:: Debugging programs with multiple threads
1733 * Processes:: Debugging programs with multiple processes
1736 @node Compilation, Starting, Running, Running
1737 @section Compiling for debugging
1739 In order to debug a program effectively, you need to generate
1740 debugging information when you compile it. This debugging information
1741 is stored in the object file; it describes the data type of each
1742 variable or function and the correspondence between source line numbers
1743 and addresses in the executable code.
1745 To request debugging information, specify the @samp{-g} option when you run
1748 Many C compilers are unable to handle the @samp{-g} and @samp{-O}
1749 options together. Using those compilers, you cannot generate optimized
1750 executables containing debugging information.
1753 @value{NGCC}, the @sc{gnu} C compiler, supports @samp{-g} with or without
1756 The HP ANSI C and C++ compilers, as well as @value{NGCC}, the @sc{gnu} C
1757 compiler, support @samp{-g} with or without
1759 @samp{-O}, making it possible to debug optimized code. We recommend
1760 that you @emph{always} use @samp{-g} whenever you compile a program.
1761 You may think your program is correct, but there is no sense in pushing
1764 @cindex optimized code, debugging
1765 @cindex debugging optimized code
1766 When you debug a program compiled with @samp{-g -O}, remember that the
1767 optimizer is rearranging your code; the debugger shows you what is
1768 really there. Do not be too surprised when the execution path does not
1769 exactly match your source file! An extreme example: if you define a
1770 variable, but never use it, @value{GDBN} never sees that
1771 variable---because the compiler optimizes it out of existence.
1773 Some things do not work as well with @samp{-g -O} as with just
1774 @samp{-g}, particularly on machines with instruction scheduling. If in
1775 doubt, recompile with @samp{-g} alone, and if this fixes the problem,
1776 please report it to us as a bug (including a test case!).
1778 Older versions of the @sc{gnu} C compiler permitted a variant option
1779 @w{@samp{-gg}} for debugging information. @value{GDBN} no longer supports this
1780 format; if your @sc{gnu} C compiler has this option, do not use it.
1783 @node Starting, Arguments, Compilation, Running
1784 @section Starting your program
1792 Use the @code{run} command to start your program under @value{GDBN}. You must
1793 first specify the program name
1797 with an argument to @value{GDBN} (@pxref{Invocation, ,Getting In and
1798 Out of @value{GDBN}}), or by using the @code{file} or @code{exec-file}
1799 command (@pxref{Files, ,Commands to specify files}).
1804 If you are running your program in an execution environment that
1805 supports processes, @code{run} creates an inferior process and makes
1806 that process run your program. (In environments without processes,
1807 @code{run} jumps to the start of your program.)
1809 The execution of a program is affected by certain information it
1810 receives from its superior. @value{GDBN} provides ways to specify this
1811 information, which you must do @emph{before} starting your program. (You
1812 can change it after starting your program, but such changes only affect
1813 your program the next time you start it.) This information may be
1814 divided into four categories:
1817 @item The @emph{arguments.}
1818 Specify the arguments to give your program as the arguments of the
1819 @code{run} command. If a shell is available on your target, the shell
1820 is used to pass the arguments, so that you may use normal conventions
1821 (such as wildcard expansion or variable substitution) in describing
1823 In Unix systems, you can control which shell is used with the
1824 @code{SHELL} environment variable.
1825 @xref{Arguments, ,Your program's arguments}.
1827 @item The @emph{environment.}
1828 Your program normally inherits its environment from @value{GDBN}, but you can
1829 use the @value{GDBN} commands @code{set environment} and @code{unset
1830 environment} to change parts of the environment that affect
1831 your program. @xref{Environment, ,Your program's environment}.
1833 @item The @emph{working directory.}
1834 Your program inherits its working directory from @value{GDBN}. You can set
1835 the @value{GDBN} working directory with the @code{cd} command in @value{GDBN}.
1836 @xref{Working Directory, ,Your program's working directory}.
1838 @item The @emph{standard input and output.}
1839 Your program normally uses the same device for standard input and
1840 standard output as @value{GDBN} is using. You can redirect input and output
1841 in the @code{run} command line, or you can use the @code{tty} command to
1842 set a different device for your program.
1843 @xref{Input/Output, ,Your program's input and output}.
1846 @emph{Warning:} While input and output redirection work, you cannot use
1847 pipes to pass the output of the program you are debugging to another
1848 program; if you attempt this, @value{GDBN} is likely to wind up debugging the
1853 When you issue the @code{run} command, your program begins to execute
1854 immediately. @xref{Stopping, ,Stopping and continuing}, for discussion
1855 of how to arrange for your program to stop. Once your program has
1856 stopped, you may call functions in your program, using the @code{print}
1857 or @code{call} commands. @xref{Data, ,Examining Data}.
1859 If the modification time of your symbol file has changed since the last
1860 time @value{GDBN} read its symbols, @value{GDBN} discards its symbol
1861 table, and reads it again. When it does this, @value{GDBN} tries to retain
1862 your current breakpoints.
1865 @node Arguments, Environment, Starting, Running
1866 @section Your program's arguments
1868 @cindex arguments (to your program)
1869 The arguments to your program can be specified by the arguments of the
1871 They are passed to a shell, which expands wildcard characters and
1872 performs redirection of I/O, and thence to your program. Your
1873 @code{SHELL} environment variable (if it exists) specifies what shell
1874 @value{GDBN} uses. If you do not define @code{SHELL}, @value{GDBN} uses
1877 @code{run} with no arguments uses the same arguments used by the previous
1878 @code{run}, or those set by the @code{set args} command.
1883 Specify the arguments to be used the next time your program is run. If
1884 @code{set args} has no arguments, @code{run} executes your program
1885 with no arguments. Once you have run your program with arguments,
1886 using @code{set args} before the next @code{run} is the only way to run
1887 it again without arguments.
1891 Show the arguments to give your program when it is started.
1894 @node Environment, Working Directory, Arguments, Running
1895 @section Your program's environment
1897 @cindex environment (of your program)
1898 The @dfn{environment} consists of a set of environment variables and
1899 their values. Environment variables conventionally record such things as
1900 your user name, your home directory, your terminal type, and your search
1901 path for programs to run. Usually you set up environment variables with
1902 the shell and they are inherited by all the other programs you run. When
1903 debugging, it can be useful to try running your program with a modified
1904 environment without having to start @value{GDBN} over again.
1908 @item path @var{directory}
1909 Add @var{directory} to the front of the @code{PATH} environment variable
1910 (the search path for executables), for both @value{GDBN} and your program.
1911 You may specify several directory names, separated by @samp{:} or
1912 whitespace. If @var{directory} is already in the path, it is moved to
1913 the front, so it is searched sooner.
1915 You can use the string @samp{$cwd} to refer to whatever is the current
1916 working directory at the time @value{GDBN} searches the path. If you
1917 use @samp{.} instead, it refers to the directory where you executed the
1918 @code{path} command. @value{GDBN} replaces @samp{.} in the
1919 @var{directory} argument (with the current path) before adding
1920 @var{directory} to the search path.
1921 @c 'path' is explicitly nonrepeatable, but RMS points out it is silly to
1922 @c document that, since repeating it would be a no-op.
1926 Display the list of search paths for executables (the @code{PATH}
1927 environment variable).
1929 @kindex show environment
1930 @item show environment @r{[}@var{varname}@r{]}
1931 Print the value of environment variable @var{varname} to be given to
1932 your program when it starts. If you do not supply @var{varname},
1933 print the names and values of all environment variables to be given to
1934 your program. You can abbreviate @code{environment} as @code{env}.
1936 @kindex set environment
1937 @item set environment @var{varname} @r{[}=@r{]} @var{value}
1938 Set environment variable @var{varname} to @var{value}. The value
1939 changes for your program only, not for @value{GDBN} itself. @var{value} may
1940 be any string; the values of environment variables are just strings, and
1941 any interpretation is supplied by your program itself. The @var{value}
1942 parameter is optional; if it is eliminated, the variable is set to a
1944 @c "any string" here does not include leading, trailing
1945 @c blanks. Gnu asks: does anyone care?
1947 For example, this command:
1954 tells a Unix program, when subsequently run, that its user is named
1955 @samp{foo}. (The spaces around @samp{=} are used for clarity here; they
1956 are not actually required.)
1958 @kindex unset environment
1959 @item unset environment @var{varname}
1960 Remove variable @var{varname} from the environment to be passed to your
1961 program. This is different from @samp{set env @var{varname} =};
1962 @code{unset environment} removes the variable from the environment,
1963 rather than assigning it an empty value.
1966 @emph{Warning:} @value{GDBN} runs your program using the shell indicated
1967 by your @code{SHELL} environment variable if it exists (or
1968 @code{/bin/sh} if not). If your @code{SHELL} variable names a shell
1969 that runs an initialization file---such as @file{.cshrc} for C-shell, or
1970 @file{.bashrc} for BASH---any variables you set in that file affect
1971 your program. You may wish to move setting of environment variables to
1972 files that are only run when you sign on, such as @file{.login} or
1975 @node Working Directory, Input/Output, Environment, Running
1976 @section Your program's working directory
1978 @cindex working directory (of your program)
1979 Each time you start your program with @code{run}, it inherits its
1980 working directory from the current working directory of @value{GDBN}.
1981 The @value{GDBN} working directory is initially whatever it inherited
1982 from its parent process (typically the shell), but you can specify a new
1983 working directory in @value{GDBN} with the @code{cd} command.
1985 The @value{GDBN} working directory also serves as a default for the commands
1986 that specify files for @value{GDBN} to operate on. @xref{Files, ,Commands to
1991 @item cd @var{directory}
1992 Set the @value{GDBN} working directory to @var{directory}.
1996 Print the @value{GDBN} working directory.
1999 @node Input/Output, Attach, Working Directory, Running
2000 @section Your program's input and output
2005 By default, the program you run under @value{GDBN} does input and output to
2006 the same terminal that @value{GDBN} uses. @value{GDBN} switches the terminal
2007 to its own terminal modes to interact with you, but it records the terminal
2008 modes your program was using and switches back to them when you continue
2009 running your program.
2012 @kindex info terminal
2014 Displays information recorded by @value{GDBN} about the terminal modes your
2018 You can redirect your program's input and/or output using shell
2019 redirection with the @code{run} command. For example,
2026 starts your program, diverting its output to the file @file{outfile}.
2029 @cindex controlling terminal
2030 Another way to specify where your program should do input and output is
2031 with the @code{tty} command. This command accepts a file name as
2032 argument, and causes this file to be the default for future @code{run}
2033 commands. It also resets the controlling terminal for the child
2034 process, for future @code{run} commands. For example,
2041 directs that processes started with subsequent @code{run} commands
2042 default to do input and output on the terminal @file{/dev/ttyb} and have
2043 that as their controlling terminal.
2045 An explicit redirection in @code{run} overrides the @code{tty} command's
2046 effect on the input/output device, but not its effect on the controlling
2049 When you use the @code{tty} command or redirect input in the @code{run}
2050 command, only the input @emph{for your program} is affected. The input
2051 for @value{GDBN} still comes from your terminal.
2053 @node Attach, Kill Process, Input/Output, Running
2054 @section Debugging an already-running process
2059 @item attach @var{process-id}
2060 This command attaches to a running process---one that was started
2061 outside @value{GDBN}. (@code{info files} shows your active
2062 targets.) The command takes as argument a process ID. The usual way to
2063 find out the process-id of a Unix process is with the @code{ps} utility,
2064 or with the @samp{jobs -l} shell command.
2066 @code{attach} does not repeat if you press @key{RET} a second time after
2067 executing the command.
2070 To use @code{attach}, your program must be running in an environment
2071 which supports processes; for example, @code{attach} does not work for
2072 programs on bare-board targets that lack an operating system. You must
2073 also have permission to send the process a signal.
2075 When you use @code{attach}, the debugger finds the program running in
2076 the process first by looking in the current working directory, then (if
2077 the program is not found) by using the source file search path
2078 (@pxref{Source Path, ,Specifying source directories}). You can also use
2079 the @code{file} command to load the program. @xref{Files, ,Commands to
2082 The first thing @value{GDBN} does after arranging to debug the specified
2083 process is to stop it. You can examine and modify an attached process
2084 with all the @value{GDBN} commands that are ordinarily available when you start
2086 processes with @code{run}. You can insert breakpoints; you can step and
2089 processes with @code{run}. You can insert breakpoints (except in shared
2090 libraries); you can step and
2092 continue; you can modify storage. If you would rather the process
2093 continue running, you may use the @code{continue} command after
2094 attaching @value{GDBN} to the process.
2099 When you have finished debugging the attached process, you can use the
2100 @code{detach} command to release it from @value{GDBN} control. Detaching
2101 the process continues its execution. After the @code{detach} command,
2102 that process and @value{GDBN} become completely independent once more, and you
2103 are ready to @code{attach} another process or start one with @code{run}.
2104 @code{detach} does not repeat if you press @key{RET} again after
2105 executing the command.
2108 If you exit @value{GDBN} or use the @code{run} command while you have an
2109 attached process, you kill that process. By default, @value{GDBN} asks
2110 for confirmation if you try to do either of these things; you can
2111 control whether or not you need to confirm by using the @code{set
2112 confirm} command (@pxref{Messages/Warnings, ,Optional warnings and
2116 @node Kill Process, Threads, Attach, Running
2117 @section Killing the child process
2120 @node Kill Process, Process Information, Attach, Running
2121 @section Killing the child process
2127 Kill the child process in which your program is running under @value{GDBN}.
2130 This command is useful if you wish to debug a core dump instead of a
2131 running process. @value{GDBN} ignores any core dump file while your program
2134 On some operating systems, a program cannot be executed outside @value{GDBN}
2135 while you have breakpoints set on it inside @value{GDBN}. You can use the
2136 @code{kill} command in this situation to permit running your program
2137 outside the debugger.
2139 The @code{kill} command is also useful if you wish to recompile and
2140 relink your program, since on many systems it is impossible to modify an
2141 executable file while it is running in a process. In this case, when you
2142 next type @code{run}, @value{GDBN} notices that the file has changed, and
2143 reads the symbol table again (while trying to preserve your current
2144 breakpoint settings).
2147 @node Process Information, Threads, Kill Process, Running
2148 @section Additional process information
2151 @cindex process image
2152 Some operating systems provide a facility called @samp{/proc} that can
2153 be used to examine the image of a running process using file-system
2154 subroutines. If @value{GDBN} is configured for an operating system with this
2155 facility, the command @code{info proc} is available to report on several
2156 kinds of information about the process running your program.
2157 @code{info proc} works only on SVR4 systems that support @code{procfs}.
2162 Summarize available information about the process.
2164 @kindex info proc mappings
2165 @item info proc mappings
2166 Report on the address ranges accessible in the program, with information
2167 on whether your program may read, write, or execute each range.
2169 @kindex info proc times
2170 @item info proc times
2171 Starting time, user CPU time, and system CPU time for your program and
2174 @kindex info proc id
2176 Report on the process IDs related to your program: its own process ID,
2177 the ID of its parent, the process group ID, and the session ID.
2179 @kindex info proc status
2180 @item info proc status
2181 General information on the state of the process. If the process is
2182 stopped, this report includes the reason for stopping, and any signal
2186 Show all the above information about the process.
2191 @node Threads, Processes, Kill Process, Running
2192 @section Debugging programs with multiple threads
2195 @node Threads, Processes, Process Information, Running
2196 @section Debugging programs with multiple threads
2199 @cindex threads of execution
2200 @cindex multiple threads
2201 @cindex switching threads
2202 In some operating systems,
2206 a single program may have more than one
2207 @dfn{thread} of execution. The precise semantics of threads differ from
2208 one operating system to another, but in general the threads of a single
2209 program are akin to multiple processes---except that they share one
2210 address space (that is, they can all examine and modify the same
2211 variables). On the other hand, each thread has its own registers and
2212 execution stack, and perhaps private memory.
2214 @value{GDBN} provides these facilities for debugging multi-thread
2218 @item automatic notification of new threads
2219 @item @samp{thread @var{threadno}}, a command to switch among threads
2220 @item @samp{info threads}, a command to inquire about existing threads
2221 @item @samp{thread apply [@var{threadno}] [@var{all}] @var{args}},
2222 a command to apply a command to a list of threads
2223 @item thread-specific breakpoints
2228 @emph{Warning:} These facilities are not yet available on every
2229 @value{GDBN} configuration where the operating system supports threads.
2230 If your @value{GDBN} does not support threads, these commands have no
2231 effect. For example, a system without thread support shows no output
2232 from @samp{info threads}, and always rejects the @code{thread} command,
2236 (@value{GDBP}) info threads
2237 (@value{GDBP}) thread 1
2238 Thread ID 1 not known. Use the "info threads" command to
2239 see the IDs of currently known threads.
2241 @c FIXME to implementors: how hard would it be to say "sorry, this GDB
2242 @c doesn't support threads"?
2246 @cindex focus of debugging
2247 @cindex current thread
2248 The @value{GDBN} thread debugging facility allows you to observe all
2249 threads while your program runs---but whenever @value{GDBN} takes
2250 control, one thread in particular is always the focus of debugging.
2251 This thread is called the @dfn{current thread}. Debugging commands show
2252 program information from the perspective of the current thread.
2255 @kindex New @var{systag}
2256 @cindex thread identifier (system)
2257 @c FIXME-implementors!! It would be more helpful if the [New...] message
2258 @c included GDB's numeric thread handle, so you could just go to that
2259 @c thread without first checking `info threads'.
2260 Whenever @value{GDBN} detects a new thread in your program, it displays
2261 the target system's identification for the thread with a message in the
2262 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
2263 whose form varies depending on the particular system. For example, on
2264 LynxOS, you might see
2267 [New process 35 thread 27]
2271 when @value{GDBN} notices a new thread. In contrast, on an SGI system,
2272 the @var{systag} is simply something like @samp{process 368}, with no
2275 @c FIXME!! (1) Does the [New...] message appear even for the very first
2276 @c thread of a program, or does it only appear for the
2277 @c second---i.e., when it becomes obvious we have a multithread
2279 @c (2) *Is* there necessarily a first thread always? Or do some
2280 @c multithread systems permit starting a program with multiple
2281 @c threads ab initio?
2283 @cindex thread number
2284 @cindex thread identifier (GDB)
2285 For debugging purposes, @value{GDBN} associates its own thread
2286 number---always a single integer---with each thread in your program.
2289 @kindex info threads
2291 Display a summary of all threads currently in your
2292 program. @value{GDBN} displays for each thread (in this order):
2295 @item the thread number assigned by @value{GDBN}
2297 @item the target system's thread identifier (@var{systag})
2299 @item the current stack frame summary for that thread
2303 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2304 indicates the current thread.
2308 @c end table here to get a little more width for example
2311 (@value{GDBP}) info threads
2312 3 process 35 thread 27 0x34e5 in sigpause ()
2313 2 process 35 thread 23 0x34e5 in sigpause ()
2314 * 1 process 35 thread 13 main (argc=1, argv=0x7ffffff8)
2320 @cindex thread number
2321 @cindex thread identifier (GDB)
2322 For debugging purposes, @value{GDBN} associates its own thread
2323 number---a small integer assigned in thread-creation order---with each
2324 thread in your program.
2326 @kindex New @var{systag}
2327 @cindex thread identifier (system)
2328 @c FIXME-implementors!! It would be more helpful if the [New...] message
2329 @c included GDB's numeric thread handle, so you could just go to that
2330 @c thread without first checking `info threads'.
2331 Whenever @value{GDBN} detects a new thread in your program, it displays
2332 both @value{GDBN}'s thread number and the target system's identification for the thread with a message in the
2333 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
2334 whose form varies depending on the particular system. For example, on
2338 [New thread 2 (system thread 26594)]
2342 when @value{GDBN} notices a new thread.
2345 @kindex info threads
2347 Display a summary of all threads currently in your
2348 program. @value{GDBN} displays for each thread (in this order):
2351 @item the thread number assigned by @value{GDBN}
2353 @item the target system's thread identifier (@var{systag})
2355 @item the current stack frame summary for that thread
2359 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2360 indicates the current thread.
2364 @c end table here to get a little more width for example
2367 (@value{GDBP}) info threads
2368 * 3 system thread 26607 worker (wptr=0x7b09c318 "@@") at quicksort.c:137
2369 2 system thread 26606 0x7b0030d8 in __ksleep () from /usr/lib/libc.2
2370 1 system thread 27905 0x7b003498 in _brk () from /usr/lib/libc.2
2375 @kindex thread @var{threadno}
2376 @item thread @var{threadno}
2377 Make thread number @var{threadno} the current thread. The command
2378 argument @var{threadno} is the internal @value{GDBN} thread number, as
2379 shown in the first field of the @samp{info threads} display.
2380 @value{GDBN} responds by displaying the system identifier of the thread
2381 you selected, and its current stack frame summary:
2384 @c FIXME!! This example made up; find a @value{GDBN} w/threads and get real one
2385 (@value{GDBP}) thread 2
2387 [Switching to process 35 thread 23]
2390 [Switching to thread 2 (system thread 26594)]
2392 0x34e5 in sigpause ()
2396 As with the @samp{[New @dots{}]} message, the form of the text after
2397 @samp{Switching to} depends on your system's conventions for identifying
2400 @kindex thread apply
2401 @item thread apply [@var{threadno}] [@var{all}] @var{args}
2402 The @code{thread apply} command allows you to apply a command to one or
2403 more threads. Specify the numbers of the threads that you want affected
2404 with the command argument @var{threadno}. @var{threadno} is the internal
2405 @value{GDBN} thread number, as shown in the first field of the @samp{info
2406 threads} display. To apply a command to all threads, use
2407 @code{thread apply all} @var{args}.
2410 @cindex automatic thread selection
2411 @cindex switching threads automatically
2412 @cindex threads, automatic switching
2413 Whenever @value{GDBN} stops your program, due to a breakpoint or a
2414 signal, it automatically selects the thread where that breakpoint or
2415 signal happened. @value{GDBN} alerts you to the context switch with a
2416 message of the form @samp{[Switching to @var{systag}]} to identify the
2419 @xref{Thread Stops,,Stopping and starting multi-thread programs}, for
2420 more information about how @value{GDBN} behaves when you stop and start
2421 programs with multiple threads.
2423 @xref{Set Watchpoints,,Setting watchpoints}, for information about
2424 watchpoints in programs with multiple threads.
2428 @node Processes, , Threads, Running
2429 @section Debugging programs with multiple processes
2431 @cindex fork, debugging programs which call
2432 @cindex multiple processes
2433 @cindex processes, multiple
2434 @value{GDBN} has no special support for debugging programs which create
2435 additional processes using the @code{fork} function. When a program
2436 forks, @value{GDBN} will continue to debug the parent process and the
2437 child process will run unimpeded. If you have set a breakpoint in any
2438 code which the child then executes, the child will get a @code{SIGTRAP}
2439 signal which (unless it catches the signal) will cause it to terminate.
2441 However, if you want to debug the child process there is a workaround
2442 which isn't too painful. Put a call to @code{sleep} in the code which
2443 the child process executes after the fork. It may be useful to sleep
2444 only if a certain environment variable is set, or a certain file exists,
2445 so that the delay need not occur when you don't want to run @value{GDBN}
2446 on the child. While the child is sleeping, use the @code{ps} program to
2447 get its process ID. Then tell @value{GDBN} (a new invocation of
2448 @value{GDBN} if you are also debugging the parent process) to attach to
2449 the child process (see @ref{Attach}). From that point on you can debug
2450 the child process just like any other process which you attached to.
2453 @node Processes, , Threads, Running
2454 @section Debugging programs with multiple processes
2456 @cindex fork, debugging programs which call
2457 @cindex multiple processes
2458 @cindex processes, multiple
2460 @value{GDBN} provides support for debugging programs that create
2461 additional processes using the @code{fork} or @code{vfork} function.
2463 By default, when a program forks, @value{GDBN} will continue to debug
2464 the parent process and the child process will run unimpeded.
2466 If you want to follow the child process instead of the parent process,
2467 use the command @w{@code{set follow-fork-mode}}.
2470 @kindex set follow-fork-mode
2471 @item set follow-fork-mode @var{mode}
2472 Set the debugger response to a program call of @code{fork} or
2473 @code{vfork}. A call to @code{fork} or @code{vfork} creates a new
2474 process. The @var{mode} can be:
2478 The original process is debugged after a fork. The child process runs
2482 The new process is debugged after a fork. The parent process runs
2486 The debugger will ask for one of the above choices.
2489 @item show follow-fork-mode
2490 Display the current debugger response to a fork or vfork call.
2493 If you ask to debug a child process and a @code{vfork} is followed by an
2494 @code{exec}, @value{GDBN} executes the new target up to the first
2495 breakpoint in the new target. If you have a breakpoint set on
2496 @code{main} in your original program, the breakpoint will also be set on
2497 the child process's @code{main}.
2499 When a child process is spawned by @code{vfork}, you cannot debug the
2500 child or parent until an @code{exec} call completes.
2502 If you issue a @code{run} command to @value{GDBN} after an @code{exec}
2503 call executes, the new target restarts. To restart the parent process,
2504 use the @code{file} command with the parent executable name as its
2507 You can use the @code{catch} command to make @value{GDBN} stop whenever
2508 a @code{fork}, @code{vfork}, or @code{exec} call is made. @xref{Set
2509 Catchpoints, ,Setting catchpoints}.
2512 @node Stopping, Stack, Running, Top
2513 @chapter Stopping and Continuing
2515 The principal purposes of using a debugger are so that you can stop your
2516 program before it terminates; or so that, if your program runs into
2517 trouble, you can investigate and find out why.
2519 Inside @value{GDBN}, your program may stop for any of several reasons, such
2524 a breakpoint, or reaching a new line after a @value{GDBN}
2525 command such as @code{step}. You may then examine and change
2526 variables, set new breakpoints or remove old ones, and then continue
2527 execution. Usually, the messages shown by @value{GDBN} provide ample
2528 explanation of the status of your program---but you can also explicitly
2529 request this information at any time.
2532 @kindex info program
2534 Display information about the status of your program: whether it is
2543 * Breakpoints:: Breakpoints, watchpoints, and catchpoints
2544 * Continuing and Stepping:: Resuming execution
2550 * Thread Stops:: Stopping and starting multi-thread programs
2555 @node Breakpoints, Continuing and Stepping, Stopping, Stopping
2556 @section Breakpoints, watchpoints, and catchpoints
2559 A @dfn{breakpoint} makes your program stop whenever a certain point in
2560 the program is reached. For each breakpoint, you can add
2561 conditions to control in finer detail whether your program stops.
2562 You can set breakpoints with the @code{break} command and its variants
2563 (@pxref{Set Breaks, ,Setting breakpoints}), to specify the place where
2564 your program should stop by line number, function name or exact address
2568 In languages with exception handling (such as @sc{gnu} C++), you can
2569 also set catchpoints where an exception is raised (@pxref{Set
2570 Catchpoints, , Setting catchpoints}).
2574 In HP-UX, SunOS 4.x, SVR4, and Alpha OSF/1 configurations, you can set
2575 breakpoints in shared libraries before the executable is run.
2576 There is a minor limitation on HP-UX systems: you must wait until the
2577 executable is run in order to set breakpoints in shared library routines
2578 that are not called directly by the program (for example, routines that
2579 are arguments in a @code{pthread_create} call).
2582 @cindex memory tracing
2583 @cindex breakpoint on memory address
2584 @cindex breakpoint on variable modification
2585 A @dfn{watchpoint} is a special breakpoint that stops your program
2586 when the value of an expression changes. You must use a different
2587 command to set watchpoints (@pxref{Set Watchpoints, ,Setting
2588 watchpoints}), but aside from that, you can manage a watchpoint like
2589 any other breakpoint: you enable, disable, and delete both breakpoints
2590 and watchpoints using the same commands.
2592 You can arrange to have values from your program displayed automatically
2593 whenever @value{GDBN} stops at a breakpoint. @xref{Auto Display,,
2597 @cindex breakpoint on events
2598 A @dfn{catchpoint} is another special breakpoint that stops your program
2599 when a certain kind of event occurs, such as the throwing of a C++
2600 exception or the loading of a library. As with watchpoints, you use a
2601 different command to set a catchpoint (@pxref{Set Catchpoints, ,Setting
2602 catchpoints}), but aside from that, you can manage a catchpoint like any
2603 other breakpoint. (To stop when your program receives a signal, use the
2604 @code{handle} command; @pxref{Signals, ,Signals}.)
2606 @cindex breakpoint numbers
2607 @cindex numbers for breakpoints
2608 @value{GDBN} assigns a number to each breakpoint, watchpoint, or
2609 catchpoint when you create it; these numbers are successive integers
2610 starting with one. In many of the commands for controlling various
2611 features of breakpoints you use the breakpoint number to say which
2612 breakpoint you want to change. Each breakpoint may be @dfn{enabled} or
2613 @dfn{disabled}; if disabled, it has no effect on your program until you
2617 * Set Breaks:: Setting breakpoints
2618 * Set Watchpoints:: Setting watchpoints
2619 * Set Catchpoints:: Setting catchpoints
2620 * Delete Breaks:: Deleting breakpoints
2621 * Disabling:: Disabling breakpoints
2622 * Conditions:: Break conditions
2623 * Break Commands:: Breakpoint command lists
2625 * Breakpoint Menus:: Breakpoint menus
2628 @c @ifclear BARETARGET
2629 @c * Error in Breakpoints:: ``Cannot insert breakpoints''
2633 @node Set Breaks, Set Watchpoints, Breakpoints, Breakpoints
2634 @subsection Setting breakpoints
2636 @c FIXME LMB what does GDB do if no code on line of breakpt?
2637 @c consider in particular declaration with/without initialization.
2639 @c FIXME 2 is there stuff on this already? break at fun start, already init?
2644 @cindex latest breakpoint
2645 Breakpoints are set with the @code{break} command (abbreviated
2646 @code{b}). The debugger convenience variable @samp{$bpnum} records the
2647 number of the breakpoints you've set most recently; see @ref{Convenience
2648 Vars,, Convenience variables}, for a discussion of what you can do with
2649 convenience variables.
2651 You have several ways to say where the breakpoint should go.
2654 @item break @var{function}
2655 Set a breakpoint at entry to function @var{function}.
2657 When using source languages that permit overloading of symbols, such as
2658 C++, @var{function} may refer to more than one possible place to break.
2659 @xref{Breakpoint Menus,,Breakpoint menus}, for a discussion of that situation.
2662 @item break +@var{offset}
2663 @itemx break -@var{offset}
2664 Set a breakpoint some number of lines forward or back from the position
2665 at which execution stopped in the currently selected frame.
2667 @item break @var{linenum}
2668 Set a breakpoint at line @var{linenum} in the current source file.
2669 That file is the last file whose source text was printed. This
2670 breakpoint stops your program just before it executes any of the
2673 @item break @var{filename}:@var{linenum}
2674 Set a breakpoint at line @var{linenum} in source file @var{filename}.
2676 @item break @var{filename}:@var{function}
2677 Set a breakpoint at entry to function @var{function} found in file
2678 @var{filename}. Specifying a file name as well as a function name is
2679 superfluous except when multiple files contain similarly named
2682 @item break *@var{address}
2683 Set a breakpoint at address @var{address}. You can use this to set
2684 breakpoints in parts of your program which do not have debugging
2685 information or source files.
2688 When called without any arguments, @code{break} sets a breakpoint at
2689 the next instruction to be executed in the selected stack frame
2690 (@pxref{Stack, ,Examining the Stack}). In any selected frame but the
2691 innermost, this makes your program stop as soon as control
2692 returns to that frame. This is similar to the effect of a
2693 @code{finish} command in the frame inside the selected frame---except
2694 that @code{finish} does not leave an active breakpoint. If you use
2695 @code{break} without an argument in the innermost frame, @value{GDBN} stops
2696 the next time it reaches the current location; this may be useful
2699 @value{GDBN} normally ignores breakpoints when it resumes execution, until at
2700 least one instruction has been executed. If it did not do this, you
2701 would be unable to proceed past a breakpoint without first disabling the
2702 breakpoint. This rule applies whether or not the breakpoint already
2703 existed when your program stopped.
2705 @item break @dots{} if @var{cond}
2706 Set a breakpoint with condition @var{cond}; evaluate the expression
2707 @var{cond} each time the breakpoint is reached, and stop only if the
2708 value is nonzero---that is, if @var{cond} evaluates as true.
2709 @samp{@dots{}} stands for one of the possible arguments described
2710 above (or no argument) specifying where to break. @xref{Conditions,
2711 ,Break conditions}, for more information on breakpoint conditions.
2714 @item tbreak @var{args}
2715 Set a breakpoint enabled only for one stop. @var{args} are the
2716 same as for the @code{break} command, and the breakpoint is set in the same
2717 way, but the breakpoint is automatically deleted after the first time your
2718 program stops there. @xref{Disabling, ,Disabling breakpoints}.
2722 @item hbreak @var{args}
2723 Set a hardware-assisted breakpoint. @var{args} are the same as for the
2724 @code{break} command and the breakpoint is set in the same way, but the
2725 breakpoint requires hardware support and some target hardware may not
2726 have this support. The main purpose of this is EPROM/ROM code
2727 debugging, so you can set a breakpoint at an instruction without
2728 changing the instruction. This can be used with the new trap-generation
2729 provided by SPARClite DSU. DSU will generate traps when a program accesses
2730 some data or instruction address that is assigned to the debug registers.
2731 However the hardware breakpoint registers can only take two data breakpoints,
2732 and @value{GDBN} will reject this command if more than two are used.
2733 Delete or disable usused hardware breakpoints before setting
2734 new ones. @xref{Conditions, ,Break conditions}.
2737 @item thbreak @var{args}
2738 Set a hardware-assisted breakpoint enabled only for one stop. @var{args}
2739 are the same as for the @code{hbreak} command and the breakpoint is set in
2740 the same way. However, like the @code{tbreak} command,
2741 the breakpoint is automatically deleted after the
2742 first time your program stops there. Also, like the @code{hbreak}
2743 command, the breakpoint requires hardware support and some target hardware
2744 may not have this support. @xref{Disabling, ,Disabling breakpoints}.
2745 Also @xref{Conditions, ,Break conditions}.
2749 @cindex regular expression
2750 @item rbreak @var{regex}
2751 @c FIXME what kind of regexp?
2752 Set breakpoints on all functions matching the regular expression
2753 @var{regex}. This command
2754 sets an unconditional breakpoint on all matches, printing a list of all
2755 breakpoints it set. Once these breakpoints are set, they are treated
2756 just like the breakpoints set with the @code{break} command. You can
2757 delete them, disable them, or make them conditional the same way as any
2761 When debugging C++ programs, @code{rbreak} is useful for setting
2762 breakpoints on overloaded functions that are not members of any special
2766 @kindex info breakpoints
2767 @cindex @code{$_} and @code{info breakpoints}
2768 @item info breakpoints @r{[}@var{n}@r{]}
2769 @itemx info break @r{[}@var{n}@r{]}
2770 @itemx info watchpoints @r{[}@var{n}@r{]}
2771 Print a table of all breakpoints, watchpoints, and catchpoints set and
2772 not deleted, with the following columns for each breakpoint:
2775 @item Breakpoint Numbers
2777 Breakpoint, watchpoint, or catchpoint.
2779 Whether the breakpoint is marked to be disabled or deleted when hit.
2780 @item Enabled or Disabled
2781 Enabled breakpoints are marked with @samp{y}. @samp{n} marks breakpoints
2782 that are not enabled.
2784 Where the breakpoint is in your program, as a memory address
2786 Where the breakpoint is in the source for your program, as a file and
2791 If a breakpoint is conditional, @code{info break} shows the condition on
2792 the line following the affected breakpoint; breakpoint commands, if any,
2793 are listed after that.
2796 @code{info break} with a breakpoint
2797 number @var{n} as argument lists only that breakpoint. The
2798 convenience variable @code{$_} and the default examining-address for
2799 the @code{x} command are set to the address of the last breakpoint
2800 listed (@pxref{Memory, ,Examining memory}).
2803 @code{info break} displays a count of the number of times the breakpoint
2804 has been hit. This is especially useful in conjunction with the
2805 @code{ignore} command. You can ignore a large number of breakpoint
2806 hits, look at the breakpoint info to see how many times the breakpoint
2807 was hit, and then run again, ignoring one less than that number. This
2808 will get you quickly to the last hit of that breakpoint.
2811 @value{GDBN} allows you to set any number of breakpoints at the same place in
2812 your program. There is nothing silly or meaningless about this. When
2813 the breakpoints are conditional, this is even useful
2814 (@pxref{Conditions, ,Break conditions}).
2816 @cindex negative breakpoint numbers
2817 @cindex internal @value{GDBN} breakpoints
2818 @value{GDBN} itself sometimes sets breakpoints in your program for special
2819 purposes, such as proper handling of @code{longjmp} (in C programs).
2820 These internal breakpoints are assigned negative numbers, starting with
2821 @code{-1}; @samp{info breakpoints} does not display them.
2823 You can see these breakpoints with the @value{GDBN} maintenance command
2824 @samp{maint info breakpoints}.
2827 @kindex maint info breakpoints
2828 @item maint info breakpoints
2829 Using the same format as @samp{info breakpoints}, display both the
2830 breakpoints you've set explicitly, and those @value{GDBN} is using for
2831 internal purposes. Internal breakpoints are shown with negative
2832 breakpoint numbers. The type column identifies what kind of breakpoint
2837 Normal, explicitly set breakpoint.
2840 Normal, explicitly set watchpoint.
2843 Internal breakpoint, used to handle correctly stepping through
2844 @code{longjmp} calls.
2846 @item longjmp resume
2847 Internal breakpoint at the target of a @code{longjmp}.
2850 Temporary internal breakpoint used by the @value{GDBN} @code{until} command.
2853 Temporary internal breakpoint used by the @value{GDBN} @code{finish} command.
2857 Shared library events.
2863 @node Set Watchpoints, Set Catchpoints, Set Breaks, Breakpoints
2864 @subsection Setting watchpoints
2866 @cindex setting watchpoints
2867 You can use a watchpoint to stop execution whenever the value of an
2868 expression changes, without having to predict a particular place where
2872 Watchpoints currently execute two orders of magnitude more slowly than
2873 other breakpoints, but this can be well worth it to catch errors where
2874 you have no clue what part of your program is the culprit.
2877 @c FIXME - did Stan mean to @ignore this out?
2879 Some processors provide special hardware to support watchpoint
2880 evaluation; @value{GDBN} will use such hardware if it is available,
2881 and if the support code has been added for that configuration.
2886 @item watch @var{expr}
2887 Set a watchpoint for an expression. @value{GDBN} will break when @var{expr}
2888 is written into by the program and its value changes.
2890 This can be used with the new trap-generation provided by
2891 SPARClite DSU. DSU will generate traps when a program accesses
2892 some data or instruction address that is assigned to the debug registers.
2893 For the data addresses, DSU facilitates the @code{watch} command.
2894 However the hardware breakpoint registers can only take two data watchpoints,
2895 and both watchpoints must be the same kind. For example, you can set two
2896 watchpoints with @code{watch} commands, two with @code{rwatch}
2897 commands, @strong{or} two with @code{awatch} commands, but you cannot set one
2898 watchpoint with one command and the other with a different command.
2899 @value{GDBN} will reject the command if you try to mix watchpoints.
2900 Delete or disable unused watchpoint commands before setting new ones.
2903 @item rwatch @var{expr}
2904 Set a watchpoint that will break when watch @var{expr} is read by the program.
2905 If you use both watchpoints, both must be set with the @code{rwatch}
2909 @item awatch @var{expr}
2910 Set a watchpoint that will break when @var{args} is read and written into
2911 by the program. If you use both watchpoints, both must be set with the
2912 @code{awatch} command.
2915 @kindex info watchpoints
2916 @item info watchpoints
2917 This command prints a list of watchpoints, breakpoints, and catchpoints;
2918 it is the same as @code{info break}.
2922 @value{GDBN} sets a @dfn{hardware watchpoint} if possible. Hardware
2923 watchpoints execute very quickly, and the debugger reports a change in
2924 value at the exact instruction where the change occurs. If @value{GDBN}
2925 cannot set a hardware watchpoint, it sets a software watchpoint, which
2926 executes more slowly and reports the change in value at the next
2927 statement, not the instruction, after the change occurs.
2929 When you issue the @code{watch} command, @value{GDBN} reports
2932 Hardware watchpoint @var{num}: @var{expr}
2936 if it was able to set a hardware watchpoint.
2939 If you call a function interactively using @code{print} or @code{call},
2940 any watchpoints you have set will be inactive until GDB reaches another
2941 kind of breakpoint or the call completes.
2945 @cindex watchpoints and threads
2946 @cindex threads and watchpoints
2948 @emph{Warning:} In multi-thread programs, watchpoints have only limited
2949 usefulness. With the current watchpoint implementation, @value{GDBN}
2950 can only watch the value of an expression @emph{in a single thread}. If
2951 you are confident that the expression can only change due to the current
2952 thread's activity (and if you are also confident that no other thread
2953 can become current), then you can use watchpoints as usual. However,
2954 @value{GDBN} may not notice when a non-current thread's activity changes
2958 @emph{Warning:} In multi-thread programs, software watchpoints have only
2959 limited usefulness. If @value{GDBN} creates a software watchpoint, it
2960 can only watch the value of an expression @emph{in a single thread}. If
2961 you are confident that the expression can only change due to the current
2962 thread's activity (and if you are also confident that no other thread
2963 can become current), then you can use software watchpoints as usual.
2964 However, @value{GDBN} may not notice when a non-current thread's
2965 activity changes the expression. (Hardware watchpoints, in contrast,
2966 watch an expression in all threads.)
2971 @node Set Catchpoints, Delete Breaks, Set Watchpoints, Breakpoints
2972 @subsection Setting catchpoints
2974 @cindex exception handlers
2975 @cindex event handling
2977 You can use @dfn{catchpoints} to cause the debugger to stop for certain
2978 kinds of program events, such as C++ exceptions or the loading of a
2979 shared library. Use the @code{catch} command to set a catchpoint.
2983 @item catch @var{event}
2984 Stop when @var{event} occurs. @var{event} can be any of the following:
2988 The throwing of a C++ exception.
2992 The catching of a C++ exception.
2996 A call to @code{exec}.
3000 A call to @code{fork}.
3004 A call to @code{vfork}.
3007 @itemx load @var{libname}
3009 The dynamic loading of any shared library, or the loading of the library
3013 @itemx unload @var{libname}
3014 @kindex catch unload
3015 The unloading of any dynamically loaded shared library, or the unloading
3016 of the library @var{libname}.
3019 @item tcatch @var{event}
3020 Set a catchpoint that is enabled only for one stop. The catchpoint is
3021 automatically deleted after the first time the event is caught.
3025 Use the @code{info break} command to list the current catchpoints.
3027 There are currently some limitations to C++ exception handling
3028 (@code{catch throw} and @code{catch catch}) in @value{GDBN}:
3032 If you call a function interactively, @value{GDBN} normally returns
3033 control to you when the function has finished executing. If the call
3034 raises an exception, however, the call may bypass the mechanism that
3035 returns control to you and cause your program either to abort or to
3036 simply continue running until it hits a breakpoint, catches a signal
3037 that @value{GDBN} is listening for, or exits. This is the case even if
3038 you set a catchpoint for the exception; catchpoints on exceptions are
3039 disabled within interactive calls.
3042 You cannot raise an exception interactively.
3045 You cannot install an exception handler interactively.
3048 @cindex raise exceptions
3049 Sometimes @code{catch} is not the best way to debug exception handling:
3050 if you need to know exactly where an exception is raised, it is better to
3051 stop @emph{before} the exception handler is called, since that way you
3052 can see the stack before any unwinding takes place. If you set a
3053 breakpoint in an exception handler instead, it may not be easy to find
3054 out where the exception was raised.
3056 To stop just before an exception handler is called, you need some
3057 knowledge of the implementation. In the case of @sc{gnu} C++, exceptions are
3058 raised by calling a library function named @code{__raise_exception}
3059 which has the following ANSI C interface:
3062 /* @var{addr} is where the exception identifier is stored.
3063 ID is the exception identifier. */
3064 void __raise_exception (void **@var{addr}, void *@var{id});
3068 To make the debugger catch all exceptions before any stack
3069 unwinding takes place, set a breakpoint on @code{__raise_exception}
3070 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and exceptions}).
3072 With a conditional breakpoint (@pxref{Conditions, ,Break conditions})
3073 that depends on the value of @var{id}, you can stop your program when
3074 a specific exception is raised. You can use multiple conditional
3075 breakpoints to stop your program when any of a number of exceptions are
3079 @node Delete Breaks, Disabling, Set Catchpoints, Breakpoints
3080 @subsection Deleting breakpoints
3082 @cindex clearing breakpoints, watchpoints, catchpoints
3083 @cindex deleting breakpoints, watchpoints, catchpoints
3084 It is often necessary to eliminate a breakpoint, watchpoint, or
3085 catchpoint once it has done its job and you no longer want your program
3086 to stop there. This is called @dfn{deleting} the breakpoint. A
3087 breakpoint that has been deleted no longer exists; it is forgotten.
3089 With the @code{clear} command you can delete breakpoints according to
3090 where they are in your program. With the @code{delete} command you can
3091 delete individual breakpoints, watchpoints, or catchpoints by specifying
3092 their breakpoint numbers.
3094 It is not necessary to delete a breakpoint to proceed past it. @value{GDBN}
3095 automatically ignores breakpoints on the first instruction to be executed
3096 when you continue execution without changing the execution address.
3101 Delete any breakpoints at the next instruction to be executed in the
3102 selected stack frame (@pxref{Selection, ,Selecting a frame}). When
3103 the innermost frame is selected, this is a good way to delete a
3104 breakpoint where your program just stopped.
3106 @item clear @var{function}
3107 @itemx clear @var{filename}:@var{function}
3108 Delete any breakpoints set at entry to the function @var{function}.
3110 @item clear @var{linenum}
3111 @itemx clear @var{filename}:@var{linenum}
3112 Delete any breakpoints set at or within the code of the specified line.
3114 @cindex delete breakpoints
3117 @item delete @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]}
3118 Delete the breakpoints, watchpoints, or catchpoints of the numbers
3119 specified as arguments. If no argument is specified, delete all
3120 breakpoints (@value{GDBN} asks confirmation, unless you have @code{set
3121 confirm off}). You can abbreviate this command as @code{d}.
3124 @node Disabling, Conditions, Delete Breaks, Breakpoints
3125 @subsection Disabling breakpoints
3127 @kindex disable breakpoints
3128 @kindex enable breakpoints
3129 Rather than deleting a breakpoint, watchpoint, or catchpoint, you might
3130 prefer to @dfn{disable} it. This makes the breakpoint inoperative as if
3131 it had been deleted, but remembers the information on the breakpoint so
3132 that you can @dfn{enable} it again later.
3134 You disable and enable breakpoints, watchpoints, and catchpoints with
3135 the @code{enable} and @code{disable} commands, optionally specifying one
3136 or more breakpoint numbers as arguments. Use @code{info break} or
3137 @code{info watch} to print a list of breakpoints, watchpoints, and
3138 catchpoints if you do not know which numbers to use.
3140 A breakpoint, watchpoint, or catchpoint can have any of four different
3141 states of enablement:
3145 Enabled. The breakpoint stops your program. A breakpoint set
3146 with the @code{break} command starts out in this state.
3148 Disabled. The breakpoint has no effect on your program.
3150 Enabled once. The breakpoint stops your program, but then becomes
3151 disabled. A breakpoint set with the @code{tbreak} command starts out in
3154 Enabled for deletion. The breakpoint stops your program, but
3155 immediately after it does so it is deleted permanently.
3158 You can use the following commands to enable or disable breakpoints,
3159 watchpoints, and catchpoints:
3162 @kindex disable breakpoints
3165 @item disable @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]}
3166 Disable the specified breakpoints---or all breakpoints, if none are
3167 listed. A disabled breakpoint has no effect but is not forgotten. All
3168 options such as ignore-counts, conditions and commands are remembered in
3169 case the breakpoint is enabled again later. You may abbreviate
3170 @code{disable} as @code{dis}.
3172 @kindex enable breakpoints
3174 @item enable @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]}
3175 Enable the specified breakpoints (or all defined breakpoints). They
3176 become effective once again in stopping your program.
3178 @item enable @r{[}breakpoints@r{]} once @var{bnums}@dots{}
3179 Enable the specified breakpoints temporarily. @value{GDBN} disables any
3180 of these breakpoints immediately after stopping your program.
3182 @item enable @r{[}breakpoints@r{]} delete @var{bnums}@dots{}
3183 Enable the specified breakpoints to work once, then die. @value{GDBN}
3184 deletes any of these breakpoints as soon as your program stops there.
3187 Except for a breakpoint set with @code{tbreak} (@pxref{Set Breaks,
3188 ,Setting breakpoints}), breakpoints that you set are initially enabled;
3189 subsequently, they become disabled or enabled only when you use one of
3190 the commands above. (The command @code{until} can set and delete a
3191 breakpoint of its own, but it does not change the state of your other
3192 breakpoints; see @ref{Continuing and Stepping, ,Continuing and
3195 @node Conditions, Break Commands, Disabling, Breakpoints
3196 @subsection Break conditions
3197 @cindex conditional breakpoints
3198 @cindex breakpoint conditions
3200 @c FIXME what is scope of break condition expr? Context where wanted?
3201 @c in particular for a watchpoint?
3202 The simplest sort of breakpoint breaks every time your program reaches a
3203 specified place. You can also specify a @dfn{condition} for a
3204 breakpoint. A condition is just a Boolean expression in your
3205 programming language (@pxref{Expressions, ,Expressions}). A breakpoint with
3206 a condition evaluates the expression each time your program reaches it,
3207 and your program stops only if the condition is @emph{true}.
3209 This is the converse of using assertions for program validation; in that
3210 situation, you want to stop when the assertion is violated---that is,
3211 when the condition is false. In C, if you want to test an assertion expressed
3212 by the condition @var{assert}, you should set the condition
3213 @samp{! @var{assert}} on the appropriate breakpoint.
3215 Conditions are also accepted for watchpoints; you may not need them,
3216 since a watchpoint is inspecting the value of an expression anyhow---but
3217 it might be simpler, say, to just set a watchpoint on a variable name,
3218 and specify a condition that tests whether the new value is an interesting
3221 Break conditions can have side effects, and may even call functions in
3222 your program. This can be useful, for example, to activate functions
3223 that log program progress, or to use your own print functions to
3224 format special data structures. The effects are completely predictable
3225 unless there is another enabled breakpoint at the same address. (In
3226 that case, @value{GDBN} might see the other breakpoint first and stop your
3227 program without checking the condition of this one.) Note that
3228 breakpoint commands are usually more convenient and flexible for the
3229 purpose of performing side effects when a breakpoint is reached
3230 (@pxref{Break Commands, ,Breakpoint command lists}).
3232 Break conditions can be specified when a breakpoint is set, by using
3233 @samp{if} in the arguments to the @code{break} command. @xref{Set
3234 Breaks, ,Setting breakpoints}. They can also be changed at any time
3235 with the @code{condition} command.
3237 @c The watch command now seems to recognize the if keyword.
3238 @c catch doesn't, though.
3239 The @code{watch} command does not recognize the @code{if} keyword;
3240 @code{condition} is the only way to impose a further condition on a
3244 You can also use the @code{if} keyword with the @code{watch} command.
3245 The @code{catch} command does not recognize the @code{if} keyword;
3246 @code{condition} is the only way to impose a further condition on a
3252 @item condition @var{bnum} @var{expression}
3253 Specify @var{expression} as the break condition for breakpoint,
3254 watchpoint, or catchpoint number @var{bnum}. After you set a condition,
3255 breakpoint @var{bnum} stops your program only if the value of
3256 @var{expression} is true (nonzero, in C). When you use
3257 @code{condition}, @value{GDBN} checks @var{expression} immediately for
3258 syntactic correctness, and to determine whether symbols in it have
3259 referents in the context of your breakpoint.
3260 @c FIXME so what does GDB do if there is no referent? Moreover, what
3261 @c about watchpoints?
3263 not actually evaluate @var{expression} at the time the @code{condition}
3264 command is given, however. @xref{Expressions, ,Expressions}.
3266 @item condition @var{bnum}
3267 Remove the condition from breakpoint number @var{bnum}. It becomes
3268 an ordinary unconditional breakpoint.
3271 @cindex ignore count (of breakpoint)
3272 A special case of a breakpoint condition is to stop only when the
3273 breakpoint has been reached a certain number of times. This is so
3274 useful that there is a special way to do it, using the @dfn{ignore
3275 count} of the breakpoint. Every breakpoint has an ignore count, which
3276 is an integer. Most of the time, the ignore count is zero, and
3277 therefore has no effect. But if your program reaches a breakpoint whose
3278 ignore count is positive, then instead of stopping, it just decrements
3279 the ignore count by one and continues. As a result, if the ignore count
3280 value is @var{n}, the breakpoint does not stop the next @var{n} times
3281 your program reaches it.
3285 @item ignore @var{bnum} @var{count}
3286 Set the ignore count of breakpoint number @var{bnum} to @var{count}.
3287 The next @var{count} times the breakpoint is reached, your program's
3288 execution does not stop; other than to decrement the ignore count, @value{GDBN}
3291 To make the breakpoint stop the next time it is reached, specify
3294 When you use @code{continue} to resume execution of your program from a
3295 breakpoint, you can specify an ignore count directly as an argument to
3296 @code{continue}, rather than using @code{ignore}. @xref{Continuing and
3297 Stepping,,Continuing and stepping}.
3299 If a breakpoint has a positive ignore count and a condition, the
3300 condition is not checked. Once the ignore count reaches zero,
3301 @value{GDBN} resumes checking the condition.
3303 You could achieve the effect of the ignore count with a condition such
3304 as @w{@samp{$foo-- <= 0}} using a debugger convenience variable that
3305 is decremented each time. @xref{Convenience Vars, ,Convenience
3309 Ignore counts apply to breakpoints, watchpoints, and catchpoints.
3312 @node Break Commands, Breakpoint Menus, Conditions, Breakpoints
3313 @subsection Breakpoint command lists
3315 @cindex breakpoint commands
3316 You can give any breakpoint (or watchpoint or catchpoint) a series of
3317 commands to execute when your program stops due to that breakpoint. For
3318 example, you might want to print the values of certain expressions, or
3319 enable other breakpoints.
3324 @item commands @r{[}@var{bnum}@r{]}
3325 @itemx @dots{} @var{command-list} @dots{}
3327 Specify a list of commands for breakpoint number @var{bnum}. The commands
3328 themselves appear on the following lines. Type a line containing just
3329 @code{end} to terminate the commands.
3331 To remove all commands from a breakpoint, type @code{commands} and
3332 follow it immediately with @code{end}; that is, give no commands.
3334 With no @var{bnum} argument, @code{commands} refers to the last
3335 breakpoint, watchpoint, or catchpoint set (not to the breakpoint most
3336 recently encountered).
3339 Pressing @key{RET} as a means of repeating the last @value{GDBN} command is
3340 disabled within a @var{command-list}.
3342 You can use breakpoint commands to start your program up again. Simply
3343 use the @code{continue} command, or @code{step}, or any other command
3344 that resumes execution.
3346 Any other commands in the command list, after a command that resumes
3347 execution, are ignored. This is because any time you resume execution
3348 (even with a simple @code{next} or @code{step}), you may encounter
3349 another breakpoint---which could have its own command list, leading to
3350 ambiguities about which list to execute.
3353 If the first command you specify in a command list is @code{silent}, the
3354 usual message about stopping at a breakpoint is not printed. This may
3355 be desirable for breakpoints that are to print a specific message and
3356 then continue. If none of the remaining commands print anything, you
3357 see no sign that the breakpoint was reached. @code{silent} is
3358 meaningful only at the beginning of a breakpoint command list.
3360 The commands @code{echo}, @code{output}, and @code{printf} allow you to
3361 print precisely controlled output, and are often useful in silent
3362 breakpoints. @xref{Output, ,Commands for controlled output}.
3364 For example, here is how you could use breakpoint commands to print the
3365 value of @code{x} at entry to @code{foo} whenever @code{x} is positive.
3371 printf "x is %d\n",x
3376 One application for breakpoint commands is to compensate for one bug so
3377 you can test for another. Put a breakpoint just after the erroneous line
3378 of code, give it a condition to detect the case in which something
3379 erroneous has been done, and give it commands to assign correct values
3380 to any variables that need them. End with the @code{continue} command
3381 so that your program does not stop, and start with the @code{silent}
3382 command so that no output is produced. Here is an example:
3394 @node Breakpoint Menus, , Break Commands, Breakpoints
3395 @subsection Breakpoint menus
3397 @cindex symbol overloading
3399 Some programming languages (notably C++) permit a single function name
3400 to be defined several times, for application in different contexts.
3401 This is called @dfn{overloading}. When a function name is overloaded,
3402 @samp{break @var{function}} is not enough to tell @value{GDBN} where you want
3403 a breakpoint. If you realize this is a problem, you can use
3404 something like @samp{break @var{function}(@var{types})} to specify which
3405 particular version of the function you want. Otherwise, @value{GDBN} offers
3406 you a menu of numbered choices for different possible breakpoints, and
3407 waits for your selection with the prompt @samp{>}. The first two
3408 options are always @samp{[0] cancel} and @samp{[1] all}. Typing @kbd{1}
3409 sets a breakpoint at each definition of @var{function}, and typing
3410 @kbd{0} aborts the @code{break} command without setting any new
3413 For example, the following session excerpt shows an attempt to set a
3414 breakpoint at the overloaded symbol @code{String::after}.
3415 We choose three particular definitions of that function name:
3417 @c FIXME! This is likely to change to show arg type lists, at least
3420 (@value{GDBP}) b String::after
3423 [2] file:String.cc; line number:867
3424 [3] file:String.cc; line number:860
3425 [4] file:String.cc; line number:875
3426 [5] file:String.cc; line number:853
3427 [6] file:String.cc; line number:846
3428 [7] file:String.cc; line number:735
3430 Breakpoint 1 at 0xb26c: file String.cc, line 867.
3431 Breakpoint 2 at 0xb344: file String.cc, line 875.
3432 Breakpoint 3 at 0xafcc: file String.cc, line 846.
3433 Multiple breakpoints were set.
3434 Use the "delete" command to delete unwanted
3441 @c @ifclear BARETARGET
3442 @c @node Error in Breakpoints
3443 @c @subsection ``Cannot insert breakpoints''
3445 @c FIXME!! 14/6/95 Is there a real example of this? Let's use it.
3447 @c Under some operating systems, breakpoints cannot be used in a program if
3448 @c any other process is running that program. In this situation,
3449 @c attempting to run or continue a program with a breakpoint causes
3450 @c @value{GDBN} to stop the other process.
3452 @c When this happens, you have three ways to proceed:
3456 @c Remove or disable the breakpoints, then continue.
3459 @c Suspend @value{GDBN}, and copy the file containing your program to a new
3460 @c name. Resume @value{GDBN} and use the @code{exec-file} command to specify
3461 @c that @value{GDBN} should run your program under that name.
3462 @c Then start your program again.
3465 @c Relink your program so that the text segment is nonsharable, using the
3466 @c linker option @samp{-N}. The operating system limitation may not apply
3467 @c to nonsharable executables.
3471 @node Continuing and Stepping, Signals, Breakpoints, Stopping
3472 @section Continuing and stepping
3476 @cindex resuming execution
3477 @dfn{Continuing} means resuming program execution until your program
3478 completes normally. In contrast, @dfn{stepping} means executing just
3479 one more ``step'' of your program, where ``step'' may mean either one
3480 line of source code, or one machine instruction (depending on what
3481 particular command you use). Either when continuing
3482 or when stepping, your program may stop even sooner, due to
3487 a breakpoint or a signal. (If due to a signal, you may want to use
3488 @code{handle}, or use @samp{signal 0} to resume execution.
3489 @xref{Signals, ,Signals}.)
3496 @item continue @r{[}@var{ignore-count}@r{]}
3497 @itemx c @r{[}@var{ignore-count}@r{]}
3498 @itemx fg @r{[}@var{ignore-count}@r{]}
3499 Resume program execution, at the address where your program last stopped;
3500 any breakpoints set at that address are bypassed. The optional argument
3501 @var{ignore-count} allows you to specify a further number of times to
3502 ignore a breakpoint at this location; its effect is like that of
3503 @code{ignore} (@pxref{Conditions, ,Break conditions}).
3505 The argument @var{ignore-count} is meaningful only when your program
3506 stopped due to a breakpoint. At other times, the argument to
3507 @code{continue} is ignored.
3509 The synonyms @code{c} and @code{fg} are provided purely for convenience,
3510 and have exactly the same behavior as @code{continue}.
3513 To resume execution at a different place, you can use @code{return}
3514 (@pxref{Returning, ,Returning from a function}) to go back to the
3515 calling function; or @code{jump} (@pxref{Jumping, ,Continuing at a
3516 different address}) to go to an arbitrary location in your program.
3518 A typical technique for using stepping is to set a breakpoint
3519 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and catchpoints}) at the
3520 beginning of the function or the section of your program where a problem
3521 is believed to lie, run your program until it stops at that breakpoint,
3522 and then step through the suspect area, examining the variables that are
3523 interesting, until you see the problem happen.
3529 Continue running your program until control reaches a different source
3530 line, then stop it and return control to @value{GDBN}. This command is
3531 abbreviated @code{s}.
3534 @c "without debugging information" is imprecise; actually "without line
3535 @c numbers in the debugging information". (gcc -g1 has debugging info but
3536 @c not line numbers). But it seems complex to try to make that
3537 @c distinction here.
3538 @emph{Warning:} If you use the @code{step} command while control is
3539 within a function that was compiled without debugging information,
3540 execution proceeds until control reaches a function that does have
3541 debugging information. Likewise, it will not step into a function which
3542 is compiled without debugging information. To step through functions
3543 without debugging information, use the @code{stepi} command, described
3547 The @code{step} command now only stops at the first instruction of a
3548 source line. This prevents the multiple stops that used to occur in
3549 switch statements, for loops, etc. @code{step} continues to stop if a
3550 function that has debugging information is called within the line.
3552 Also, the @code{step} command now only enters a subroutine if there is line
3553 number information for the subroutine. Otherwise it acts like the
3554 @code{next} command. This avoids problems when using @code{cc -gl}
3555 on MIPS machines. Previously, @code{step} entered subroutines if there
3556 was any debugging information about the routine.
3558 @item step @var{count}
3559 Continue running as in @code{step}, but do so @var{count} times. If a
3560 breakpoint is reached,
3562 or a signal not related to stepping occurs before @var{count} steps,
3564 stepping stops right away.
3568 @item next @r{[}@var{count}@r{]}
3569 Continue to the next source line in the current (innermost) stack frame.
3570 This is similar to @code{step}, but function calls that appear within the line
3571 of code are executed without stopping. Execution stops when control
3572 reaches a different line of code at the original stack level that was
3573 executing when you gave the @code{next} command. This command is abbreviated
3576 An argument @var{count} is a repeat count, as for @code{step}.
3579 @c FIX ME!! Do we delete this, or is there a way it fits in with
3580 @c the following paragraph? --- Vctoria
3582 @c @code{next} within a function that lacks debugging information acts like
3583 @c @code{step}, but any function calls appearing within the code of the
3584 @c function are executed without stopping.
3586 The @code{next} command now only stops at the first instruction of a
3587 source line. This prevents the multiple stops that used to occur in
3588 switch statements, for loops, etc.
3592 Continue running until just after function in the selected stack frame
3593 returns. Print the returned value (if any).
3595 Contrast this with the @code{return} command (@pxref{Returning,
3596 ,Returning from a function}).
3602 Continue running until a source line past the current line, in the
3603 current stack frame, is reached. This command is used to avoid single
3604 stepping through a loop more than once. It is like the @code{next}
3605 command, except that when @code{until} encounters a jump, it
3606 automatically continues execution until the program counter is greater
3607 than the address of the jump.
3609 This means that when you reach the end of a loop after single stepping
3610 though it, @code{until} makes your program continue execution until it
3611 exits the loop. In contrast, a @code{next} command at the end of a loop
3612 simply steps back to the beginning of the loop, which forces you to step
3613 through the next iteration.
3615 @code{until} always stops your program if it attempts to exit the current
3618 @code{until} may produce somewhat counterintuitive results if the order
3619 of machine code does not match the order of the source lines. For
3620 example, in the following excerpt from a debugging session, the @code{f}
3621 (@code{frame}) command shows that execution is stopped at line
3622 @code{206}; yet when we use @code{until}, we get to line @code{195}:
3626 #0 main (argc=4, argv=0xf7fffae8) at m4.c:206
3628 (@value{GDBP}) until
3629 195 for ( ; argc > 0; NEXTARG) @{
3632 This happened because, for execution efficiency, the compiler had
3633 generated code for the loop closure test at the end, rather than the
3634 start, of the loop---even though the test in a C @code{for}-loop is
3635 written before the body of the loop. The @code{until} command appeared
3636 to step back to the beginning of the loop when it advanced to this
3637 expression; however, it has not really gone to an earlier
3638 statement---not in terms of the actual machine code.
3640 @code{until} with no argument works by means of single
3641 instruction stepping, and hence is slower than @code{until} with an
3644 @item until @var{location}
3645 @itemx u @var{location}
3646 Continue running your program until either the specified location is
3647 reached, or the current stack frame returns. @var{location} is any of
3648 the forms of argument acceptable to @code{break} (@pxref{Set Breaks,
3649 ,Setting breakpoints}). This form of the command uses breakpoints,
3650 and hence is quicker than @code{until} without an argument.
3656 Execute one machine instruction, then stop and return to the debugger.
3658 It is often useful to do @samp{display/i $pc} when stepping by machine
3659 instructions. This makes @value{GDBN} automatically display the next
3660 instruction to be executed, each time your program stops. @xref{Auto
3661 Display,, Automatic display}.
3663 An argument is a repeat count, as in @code{step}.
3670 Execute one machine instruction, but if it is a function call,
3671 proceed until the function returns.
3673 An argument is a repeat count, as in @code{next}.
3677 @node Signals, Thread Stops, Continuing and Stepping, Stopping
3681 A signal is an asynchronous event that can happen in a program. The
3682 operating system defines the possible kinds of signals, and gives each
3683 kind a name and a number. For example, in Unix @code{SIGINT} is the
3684 signal a program gets when you type an interrupt (often @kbd{C-c});
3685 @code{SIGSEGV} is the signal a program gets from referencing a place in
3686 memory far away from all the areas in use; @code{SIGALRM} occurs when
3687 the alarm clock timer goes off (which happens only if your program has
3688 requested an alarm).
3690 @cindex fatal signals
3691 Some signals, including @code{SIGALRM}, are a normal part of the
3692 functioning of your program. Others, such as @code{SIGSEGV}, indicate
3693 errors; these signals are @dfn{fatal} (kill your program immediately) if the
3694 program has not specified in advance some other way to handle the signal.
3695 @code{SIGINT} does not indicate an error in your program, but it is normally
3696 fatal so it can carry out the purpose of the interrupt: to kill the program.
3698 @value{GDBN} has the ability to detect any occurrence of a signal in your
3699 program. You can tell @value{GDBN} in advance what to do for each kind of
3702 @cindex handling signals
3703 Normally, @value{GDBN} is set up to ignore non-erroneous signals like @code{SIGALRM}
3704 (so as not to interfere with their role in the functioning of your program)
3705 but to stop your program immediately whenever an error signal happens.
3706 You can change these settings with the @code{handle} command.
3709 @kindex info signals
3711 Print a table of all the kinds of signals and how @value{GDBN} has been told to
3712 handle each one. You can use this to see the signal numbers of all
3713 the defined types of signals.
3715 @code{info handle} is the new alias for @code{info signals}.
3718 @item handle @var{signal} @var{keywords}@dots{}
3719 Change the way @value{GDBN} handles signal @var{signal}. @var{signal} can
3720 be the number of a signal or its name (with or without the @samp{SIG} at the
3721 beginning). The @var{keywords} say what change to make.
3725 The keywords allowed by the @code{handle} command can be abbreviated.
3726 Their full names are:
3730 @value{GDBN} should not stop your program when this signal happens. It may
3731 still print a message telling you that the signal has come in.
3734 @value{GDBN} should stop your program when this signal happens. This implies
3735 the @code{print} keyword as well.
3738 @value{GDBN} should print a message when this signal happens.
3741 @value{GDBN} should not mention the occurrence of the signal at all. This
3742 implies the @code{nostop} keyword as well.
3745 @value{GDBN} should allow your program to see this signal; your program
3746 can handle the signal, or else it may terminate if the signal is fatal
3750 @value{GDBN} should not allow your program to see this signal.
3754 When a signal stops your program, the signal is not visible until you
3755 continue. Your program sees the signal then, if @code{pass} is in
3756 effect for the signal in question @emph{at that time}. In other words,
3757 after @value{GDBN} reports a signal, you can use the @code{handle}
3758 command with @code{pass} or @code{nopass} to control whether your
3759 program sees that signal when you continue.
3761 You can also use the @code{signal} command to prevent your program from
3762 seeing a signal, or cause it to see a signal it normally would not see,
3763 or to give it any signal at any time. For example, if your program stopped
3764 due to some sort of memory reference error, you might store correct
3765 values into the erroneous variables and continue, hoping to see more
3766 execution; but your program would probably terminate immediately as
3767 a result of the fatal signal once it saw the signal. To prevent this,
3768 you can continue with @samp{signal 0}. @xref{Signaling, ,Giving your
3773 @node Thread Stops, , Signals, Stopping
3774 @section Stopping and starting multi-thread programs
3776 When your program has multiple threads (@pxref{Threads,, Debugging
3777 programs with multiple threads}), you can choose whether to set
3778 breakpoints on all threads, or on a particular thread.
3781 @cindex breakpoints and threads
3782 @cindex thread breakpoints
3783 @kindex break @dots{} thread @var{threadno}
3784 @item break @var{linespec} thread @var{threadno}
3785 @itemx break @var{linespec} thread @var{threadno} if @dots{}
3786 @var{linespec} specifies source lines; there are several ways of
3787 writing them, but the effect is always to specify some source line.
3789 Use the qualifier @samp{thread @var{threadno}} with a breakpoint command
3790 to specify that you only want @value{GDBN} to stop the program when a
3791 particular thread reaches this breakpoint. @var{threadno} is one of the
3792 numeric thread identifiers assigned by @value{GDBN}, shown in the first
3793 column of the @samp{info threads} display.
3795 If you do not specify @samp{thread @var{threadno}} when you set a
3796 breakpoint, the breakpoint applies to @emph{all} threads of your
3799 You can use the @code{thread} qualifier on conditional breakpoints as
3800 well; in this case, place @samp{thread @var{threadno}} before the
3801 breakpoint condition, like this:
3804 (gdb) break frik.c:13 thread 28 if bartab > lim
3809 @cindex stopped threads
3810 @cindex threads, stopped
3811 Whenever your program stops under @value{GDBN} for any reason,
3812 @emph{all} threads of execution stop, not just the current thread. This
3813 allows you to examine the overall state of the program, including
3814 switching between threads, without worrying that things may change
3817 @cindex continuing threads
3818 @cindex threads, continuing
3819 Conversely, whenever you restart the program, @emph{all} threads start
3820 executing. @emph{This is true even when single-stepping} with commands
3821 like @code{step} or @code{next}.
3823 In particular, @value{GDBN} cannot single-step all threads in lockstep.
3824 Since thread scheduling is up to your debugging target's operating
3825 system (not controlled by @value{GDBN}), other threads may
3826 execute more than one statement while the current thread completes a
3827 single step. Moreover, in general other threads stop in the middle of a
3828 statement, rather than at a clean statement boundary, when the program
3831 You might even find your program stopped in another thread after
3832 continuing or even single-stepping. This happens whenever some other
3833 thread runs into a breakpoint, a signal, or an exception before the
3834 first thread completes whatever you requested.
3837 @node Stack, Source, Stopping, Top
3838 @chapter Examining the Stack
3840 When your program has stopped, the first thing you need to know is where it
3841 stopped and how it got there.
3844 Each time your program performs a function call, information about the call
3846 That information includes the location of the call in your program,
3847 the arguments of the call,
3848 and the local variables of the function being called.
3849 The information is saved in a block of data called a @dfn{stack frame}.
3850 The stack frames are allocated in a region of memory called the @dfn{call
3853 When your program stops, the @value{GDBN} commands for examining the
3854 stack allow you to see all of this information.
3856 @cindex selected frame
3857 One of the stack frames is @dfn{selected} by @value{GDBN} and many
3858 @value{GDBN} commands refer implicitly to the selected frame. In
3859 particular, whenever you ask @value{GDBN} for the value of a variable in
3860 your program, the value is found in the selected frame. There are
3861 special @value{GDBN} commands to select whichever frame you are
3862 interested in. @xref{Selection, ,Selecting a frame}.
3864 When your program stops, @value{GDBN} automatically selects the
3865 currently executing frame and describes it briefly, similar to the
3866 @code{frame} command (@pxref{Frame Info, ,Information about a frame}).
3869 * Frames:: Stack frames
3870 * Backtrace:: Backtraces
3871 * Selection:: Selecting a frame
3872 * Frame Info:: Information on a frame
3874 * MIPS Stack:: MIPS machines and the function stack
3879 @node Frames, Backtrace, Stack, Stack
3880 @section Stack frames
3884 The call stack is divided up into contiguous pieces called @dfn{stack
3885 frames}, or @dfn{frames} for short; each frame is the data associated
3886 with one call to one function. The frame contains the arguments given
3887 to the function, the function's local variables, and the address at
3888 which the function is executing.
3890 @cindex initial frame
3891 @cindex outermost frame
3892 @cindex innermost frame
3893 When your program is started, the stack has only one frame, that of the
3894 function @code{main}. This is called the @dfn{initial} frame or the
3895 @dfn{outermost} frame. Each time a function is called, a new frame is
3896 made. Each time a function returns, the frame for that function invocation
3897 is eliminated. If a function is recursive, there can be many frames for
3898 the same function. The frame for the function in which execution is
3899 actually occurring is called the @dfn{innermost} frame. This is the most
3900 recently created of all the stack frames that still exist.
3902 @cindex frame pointer
3903 Inside your program, stack frames are identified by their addresses. A
3904 stack frame consists of many bytes, each of which has its own address; each
3905 kind of computer has a convention for choosing one byte whose
3906 address serves as the address of the frame. Usually this address is kept
3907 in a register called the @dfn{frame pointer register} while execution is
3908 going on in that frame.
3910 @cindex frame number
3911 @value{GDBN} assigns numbers to all existing stack frames, starting with
3912 zero for the innermost frame, one for the frame that called it,
3913 and so on upward. These numbers do not really exist in your program;
3914 they are assigned by @value{GDBN} to give you a way of designating stack
3915 frames in @value{GDBN} commands.
3917 @c below produces an acceptable overful hbox. --mew 13aug1993
3918 @cindex frameless execution
3919 Some compilers provide a way to compile functions so that they operate
3920 without stack frames. (For example, the @code{@value{GCC}} option
3921 @samp{-fomit-frame-pointer} generates functions without a frame.)
3922 This is occasionally done with heavily used library functions to save
3923 the frame setup time. @value{GDBN} has limited facilities for dealing
3924 with these function invocations. If the innermost function invocation
3925 has no stack frame, @value{GDBN} nevertheless regards it as though
3926 it had a separate frame, which is numbered zero as usual, allowing
3927 correct tracing of the function call chain. However, @value{GDBN} has
3928 no provision for frameless functions elsewhere in the stack.
3932 @item frame @var{args}
3933 The @code{frame} command allows you to move from one stack frame to another,
3934 and to print the stack frame you select. @var{args} may be either the
3935 address of the frame or the stack frame number. Without an argument,
3936 @code{frame} prints the current stack frame.
3938 @kindex select-frame
3940 The @code{select-frame} command allows you to move from one stack frame
3941 to another without printing the frame. This is the silent version of
3945 @node Backtrace, Selection, Frames, Stack
3950 @cindex stack traces
3951 A backtrace is a summary of how your program got where it is. It shows one
3952 line per frame, for many frames, starting with the currently executing
3953 frame (frame zero), followed by its caller (frame one), and on up the
3961 Print a backtrace of the entire stack: one line per frame for all
3962 frames in the stack.
3964 You can stop the backtrace at any time by typing the system interrupt
3965 character, normally @kbd{C-c}.
3967 @item backtrace @var{n}
3969 Similar, but print only the innermost @var{n} frames.
3971 @item backtrace -@var{n}
3973 Similar, but print only the outermost @var{n} frames.
3979 The names @code{where} and @code{info stack} (abbreviated @code{info s})
3980 are additional aliases for @code{backtrace}.
3982 Each line in the backtrace shows the frame number and the function name.
3983 The program counter value is also shown---unless you use @code{set
3984 print address off}. The backtrace also shows the source file name and
3985 line number, as well as the arguments to the function. The program
3986 counter value is omitted if it is at the beginning of the code for that
3989 Here is an example of a backtrace. It was made with the command
3990 @samp{bt 3}, so it shows the innermost three frames.
3994 #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
3996 #1 0x6e38 in expand_macro (sym=0x2b600) at macro.c:242
3997 #2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08)
3999 (More stack frames follow...)
4004 The display for frame zero does not begin with a program counter
4005 value, indicating that your program has stopped at the beginning of the
4006 code for line @code{993} of @code{builtin.c}.
4008 @node Selection, Frame Info, Backtrace, Stack
4009 @section Selecting a frame
4011 Most commands for examining the stack and other data in your program work on
4012 whichever stack frame is selected at the moment. Here are the commands for
4013 selecting a stack frame; all of them finish by printing a brief description
4014 of the stack frame just selected.
4021 Select frame number @var{n}. Recall that frame zero is the innermost
4022 (currently executing) frame, frame one is the frame that called the
4023 innermost one, and so on. The highest-numbered frame is the one for
4026 @item frame @var{addr}
4028 Select the frame at address @var{addr}. This is useful mainly if the
4029 chaining of stack frames has been damaged by a bug, making it
4030 impossible for @value{GDBN} to assign numbers properly to all frames. In
4031 addition, this can be useful when your program has multiple stacks and
4032 switches between them.
4034 @ifclear H8EXCLUSIVE
4036 On the SPARC architecture, @code{frame} needs two addresses to
4037 select an arbitrary frame: a frame pointer and a stack pointer.
4039 On the MIPS and Alpha architecture, it needs two addresses: a stack
4040 pointer and a program counter.
4042 On the 29k architecture, it needs three addresses: a register stack
4043 pointer, a program counter, and a memory stack pointer.
4044 @c note to future updaters: this is conditioned on a flag
4045 @c SETUP_ARBITRARY_FRAME in the tm-*.h files. The above is up to date
4046 @c as of 27 Jan 1994.
4052 Move @var{n} frames up the stack. For positive numbers @var{n}, this
4053 advances toward the outermost frame, to higher frame numbers, to frames
4054 that have existed longer. @var{n} defaults to one.
4059 Move @var{n} frames down the stack. For positive numbers @var{n}, this
4060 advances toward the innermost frame, to lower frame numbers, to frames
4061 that were created more recently. @var{n} defaults to one. You may
4062 abbreviate @code{down} as @code{do}.
4065 All of these commands end by printing two lines of output describing the
4066 frame. The first line shows the frame number, the function name, the
4067 arguments, and the source file and line number of execution in that
4068 frame. The second line shows the text of that source line.
4076 #1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
4078 10 read_input_file (argv[i]);
4082 After such a printout, the @code{list} command with no arguments
4083 prints ten lines centered on the point of execution in the frame.
4084 @xref{List, ,Printing source lines}.
4087 @kindex down-silently
4089 @item up-silently @var{n}
4090 @itemx down-silently @var{n}
4091 These two commands are variants of @code{up} and @code{down},
4092 respectively; they differ in that they do their work silently, without
4093 causing display of the new frame. They are intended primarily for use
4094 in @value{GDBN} command scripts, where the output might be unnecessary and
4099 @node Frame Info, MIPS Stack, Selection, Stack
4100 @section Information about a frame
4103 @node Frame Info, , Selection, Stack
4104 @section Information about a frame
4107 There are several other commands to print information about the selected
4113 When used without any argument, this command does not change which
4114 frame is selected, but prints a brief description of the currently
4115 selected stack frame. It can be abbreviated @code{f}. With an
4116 argument, this command is used to select a stack frame.
4117 @xref{Selection, ,Selecting a frame}.
4123 This command prints a verbose description of the selected stack frame,
4128 the address of the frame
4130 the address of the next frame down (called by this frame)
4132 the address of the next frame up (caller of this frame)
4134 the language in which the source code corresponding to this frame is written
4136 the address of the frame's arguments
4138 the program counter saved in it (the address of execution in the caller frame)
4140 which registers were saved in the frame
4143 @noindent The verbose description is useful when
4144 something has gone wrong that has made the stack format fail to fit
4145 the usual conventions.
4147 @item info frame @var{addr}
4148 @itemx info f @var{addr}
4149 Print a verbose description of the frame at address @var{addr}, without
4150 selecting that frame. The selected frame remains unchanged by this
4151 command. This requires the same kind of address (more than one for some
4152 architectures) that you specify in the @code{frame} command.
4153 @xref{Selection, ,Selecting a frame}.
4157 Print the arguments of the selected frame, each on a separate line.
4161 Print the local variables of the selected frame, each on a separate
4162 line. These are all variables (declared either static or automatic)
4163 accessible at the point of execution of the selected frame.
4168 @cindex catch exceptions
4169 @cindex exception handlers
4171 Print a list of all the exception handlers that are active in the
4172 current stack frame at the current point of execution. To see other
4173 exception handlers, visit the associated frame (using the @code{up},
4174 @code{down}, or @code{frame} commands); then type @code{info catch}.
4175 @xref{Set Catchpoints, , Setting catchpoints}.
4181 @node MIPS Stack, , Frame Info, Stack
4182 @section MIPS machines and the function stack
4184 @cindex stack on MIPS
4186 MIPS based computers use an unusual stack frame, which sometimes
4187 requires @value{GDBN} to search backward in the object code to find the
4188 beginning of a function.
4190 @cindex response time, MIPS debugging
4191 To improve response time (especially for embedded applications, where
4192 @value{GDBN} may be restricted to a slow serial line for this search)
4193 you may want to limit the size of this search, using one of these
4197 @cindex @code{heuristic-fence-post} (MIPS)
4198 @item set heuristic-fence-post @var{limit}
4199 Restrict @value{GDBN} to examining at most @var{limit} bytes in its search
4200 for the beginning of a function. A value of @var{0} (the default)
4201 means there is no limit. However, except for @var{0}, the larger the
4202 limit the more bytes @code{heuristic-fence-post} must search and
4203 therefore the longer it takes to run.
4205 @item show heuristic-fence-post
4206 Display the current limit.
4210 These commands are available @emph{only} when @value{GDBN} is configured
4211 for debugging programs on MIPS processors.
4214 @node Source, Data, Stack, Top
4215 @chapter Examining Source Files
4217 @value{GDBN} can print parts of your program's source, since the debugging
4218 information recorded in the program tells @value{GDBN} what source files were
4219 used to build it. When your program stops, @value{GDBN} spontaneously prints
4220 the line where it stopped. Likewise, when you select a stack frame
4221 (@pxref{Selection, ,Selecting a frame}), @value{GDBN} prints the line where
4222 execution in that frame has stopped. You can print other portions of
4223 source files by explicit command.
4226 If you use @value{GDBN} through its @sc{gnu} Emacs interface, you may prefer
4228 Emacs facilities to view source; @pxref{Emacs, ,Using @value{GDBN} under @sc{gnu} Emacs}.
4232 * List:: Printing source lines
4234 * Search:: Searching source files
4237 * Source Path:: Specifying source directories
4238 * Machine Code:: Source and machine code
4241 @node List, Search, Source, Source
4242 @section Printing source lines
4246 To print lines from a source file, use the @code{list} command
4247 (abbreviated @code{l}). By default, ten lines are printed.
4248 There are several ways to specify what part of the file you want to print.
4250 Here are the forms of the @code{list} command most commonly used:
4253 @item list @var{linenum}
4254 Print lines centered around line number @var{linenum} in the
4255 current source file.
4257 @item list @var{function}
4258 Print lines centered around the beginning of function
4262 Print more lines. If the last lines printed were printed with a
4263 @code{list} command, this prints lines following the last lines
4264 printed; however, if the last line printed was a solitary line printed
4265 as part of displaying a stack frame (@pxref{Stack, ,Examining the
4266 Stack}), this prints lines centered around that line.
4269 Print lines just before the lines last printed.
4272 By default, @value{GDBN} prints ten source lines with any of these forms of
4273 the @code{list} command. You can change this using @code{set listsize}:
4276 @kindex set listsize
4277 @item set listsize @var{count}
4278 Make the @code{list} command display @var{count} source lines (unless
4279 the @code{list} argument explicitly specifies some other number).
4281 @kindex show listsize
4283 Display the number of lines that @code{list} prints.
4286 Repeating a @code{list} command with @key{RET} discards the argument,
4287 so it is equivalent to typing just @code{list}. This is more useful
4288 than listing the same lines again. An exception is made for an
4289 argument of @samp{-}; that argument is preserved in repetition so that
4290 each repetition moves up in the source file.
4293 In general, the @code{list} command expects you to supply zero, one or two
4294 @dfn{linespecs}. Linespecs specify source lines; there are several ways
4295 of writing them but the effect is always to specify some source line.
4296 Here is a complete description of the possible arguments for @code{list}:
4299 @item list @var{linespec}
4300 Print lines centered around the line specified by @var{linespec}.
4302 @item list @var{first},@var{last}
4303 Print lines from @var{first} to @var{last}. Both arguments are
4306 @item list ,@var{last}
4307 Print lines ending with @var{last}.
4309 @item list @var{first},
4310 Print lines starting with @var{first}.
4313 Print lines just after the lines last printed.
4316 Print lines just before the lines last printed.
4319 As described in the preceding table.
4322 Here are the ways of specifying a single source line---all the
4327 Specifies line @var{number} of the current source file.
4328 When a @code{list} command has two linespecs, this refers to
4329 the same source file as the first linespec.
4332 Specifies the line @var{offset} lines after the last line printed.
4333 When used as the second linespec in a @code{list} command that has
4334 two, this specifies the line @var{offset} lines down from the
4338 Specifies the line @var{offset} lines before the last line printed.
4340 @item @var{filename}:@var{number}
4341 Specifies line @var{number} in the source file @var{filename}.
4343 @item @var{function}
4344 Specifies the line that begins the body of the function @var{function}.
4345 For example: in C, this is the line with the open brace.
4347 @item @var{filename}:@var{function}
4348 Specifies the line of the open-brace that begins the body of the
4349 function @var{function} in the file @var{filename}. You only need the
4350 file name with a function name to avoid ambiguity when there are
4351 identically named functions in different source files.
4353 @item *@var{address}
4354 Specifies the line containing the program address @var{address}.
4355 @var{address} may be any expression.
4359 @node Search, Source Path, List, Source
4360 @section Searching source files
4362 @kindex reverse-search
4364 There are two commands for searching through the current source file for a
4369 @kindex forward-search
4370 @item forward-search @var{regexp}
4371 @itemx search @var{regexp}
4372 The command @samp{forward-search @var{regexp}} checks each line,
4373 starting with the one following the last line listed, for a match for
4374 @var{regexp}. It lists the line that is found. You can use the
4375 synonym @samp{search @var{regexp}} or abbreviate the command name as
4378 @item reverse-search @var{regexp}
4379 The command @samp{reverse-search @var{regexp}} checks each line, starting
4380 with the one before the last line listed and going backward, for a match
4381 for @var{regexp}. It lists the line that is found. You can abbreviate
4382 this command as @code{rev}.
4386 @node Source Path, Machine Code, Search, Source
4387 @section Specifying source directories
4390 @cindex directories for source files
4391 Executable programs sometimes do not record the directories of the source
4392 files from which they were compiled, just the names. Even when they do,
4393 the directories could be moved between the compilation and your debugging
4394 session. @value{GDBN} has a list of directories to search for source files;
4395 this is called the @dfn{source path}. Each time @value{GDBN} wants a source file,
4396 it tries all the directories in the list, in the order they are present
4397 in the list, until it finds a file with the desired name. Note that
4398 the executable search path is @emph{not} used for this purpose. Neither is
4399 the current working directory, unless it happens to be in the source
4402 If @value{GDBN} cannot find a source file in the source path, and the
4403 object program records a directory, @value{GDBN} tries that directory
4404 too. If the source path is empty, and there is no record of the
4405 compilation directory, @value{GDBN} looks in the current directory as a
4408 Whenever you reset or rearrange the source path, @value{GDBN} clears out
4409 any information it has cached about where source files are found and where
4410 each line is in the file.
4414 When you start @value{GDBN}, its source path is empty.
4415 To add other directories, use the @code{directory} command.
4418 @item directory @var{dirname} @dots{}
4419 @item dir @var{dirname} @dots{}
4420 Add directory @var{dirname} to the front of the source path. Several
4421 directory names may be given to this command, separated by @samp{:} or
4422 whitespace. You may specify a directory that is already in the source
4423 path; this moves it forward, so @value{GDBN} searches it sooner.
4429 @cindex compilation directory
4430 @cindex current directory
4431 @cindex working directory
4432 @cindex directory, current
4433 @cindex directory, compilation
4434 You can use the string @samp{$cdir} to refer to the compilation
4435 directory (if one is recorded), and @samp{$cwd} to refer to the current
4436 working directory. @samp{$cwd} is not the same as @samp{.}---the former
4437 tracks the current working directory as it changes during your @value{GDBN}
4438 session, while the latter is immediately expanded to the current
4439 directory at the time you add an entry to the source path.
4442 Reset the source path to empty again. This requires confirmation.
4444 @c RET-repeat for @code{directory} is explicitly disabled, but since
4445 @c repeating it would be a no-op we do not say that. (thanks to RMS)
4447 @item show directories
4448 @kindex show directories
4449 Print the source path: show which directories it contains.
4452 If your source path is cluttered with directories that are no longer of
4453 interest, @value{GDBN} may sometimes cause confusion by finding the wrong
4454 versions of source. You can correct the situation as follows:
4458 Use @code{directory} with no argument to reset the source path to empty.
4461 Use @code{directory} with suitable arguments to reinstall the
4462 directories you want in the source path. You can add all the
4463 directories in one command.
4466 @node Machine Code, , Source Path, Source
4467 @section Source and machine code
4469 You can use the command @code{info line} to map source lines to program
4470 addresses (and vice versa), and the command @code{disassemble} to display
4471 a range of addresses as machine instructions. When run under @sc{gnu} Emacs
4472 mode, the @code{info line} command now causes the arrow to point to the
4473 line specified. Also, @code{info line} prints addresses in symbolic form as
4478 @item info line @var{linespec}
4479 Print the starting and ending addresses of the compiled code for
4480 source line @var{linespec}. You can specify source lines in any of
4481 the ways understood by the @code{list} command (@pxref{List, ,Printing
4485 For example, we can use @code{info line} to discover the location of
4486 the object code for the first line of function
4487 @code{m4_changequote}:
4490 (@value{GDBP}) info line m4_changecom
4491 Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350.
4495 We can also inquire (using @code{*@var{addr}} as the form for
4496 @var{linespec}) what source line covers a particular address:
4498 (@value{GDBP}) info line *0x63ff
4499 Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404.
4502 @cindex @code{$_} and @code{info line}
4503 After @code{info line}, the default address for the @code{x} command
4504 is changed to the starting address of the line, so that @samp{x/i} is
4505 sufficient to begin examining the machine code (@pxref{Memory,
4506 ,Examining memory}). Also, this address is saved as the value of the
4507 convenience variable @code{$_} (@pxref{Convenience Vars, ,Convenience
4512 @cindex assembly instructions
4513 @cindex instructions, assembly
4514 @cindex machine instructions
4515 @cindex listing machine instructions
4517 This specialized command dumps a range of memory as machine
4518 instructions. The default memory range is the function surrounding the
4519 program counter of the selected frame. A single argument to this
4520 command is a program counter value; @value{GDBN} dumps the function
4521 surrounding this value. Two arguments specify a range of addresses
4522 (first inclusive, second exclusive) to dump.
4525 @ifclear H8EXCLUSIVE
4526 The following example shows the disassembly of a range of addresses of
4527 HP PA-RISC 2.0 code:
4530 (@value{GDBP}) disas 0x32c4 0x32e4
4531 Dump of assembler code from 0x32c4 to 0x32e4:
4532 0x32c4 <main+204>: addil 0,dp
4533 0x32c8 <main+208>: ldw 0x22c(sr0,r1),r26
4534 0x32cc <main+212>: ldil 0x3000,r31
4535 0x32d0 <main+216>: ble 0x3f8(sr4,r31)
4536 0x32d4 <main+220>: ldo 0(r31),rp
4537 0x32d8 <main+224>: addil -0x800,dp
4538 0x32dc <main+228>: ldo 0x588(r1),r26
4539 0x32e0 <main+232>: ldil 0x3000,r31
4540 End of assembler dump.
4545 For example, here is the beginning of the output for the
4546 disassembly of a function @code{fact}:
4550 (@value{GDBP}) disas fact
4551 Dump of assembler code for function fact:
4553 0x802c <fact>: 6d f2 mov.w r2,@@-r7
4554 0x802e <fact+2>: 6d f3 mov.w r3,@@-r7
4555 0x8030 <fact+4>: 6d f6 mov.w r6,@@-r7
4556 0x8032 <fact+6>: 0d 76 mov.w r7,r6
4557 0x8034 <fact+8>: 6f 70 00 08 mov.w @@(0x8,r7),r0
4558 0x8038 <fact+12> 19 11 sub.w r1,r1
4566 @kindex set assembly-language
4567 @cindex assembly instructions
4568 @cindex instructions, assembly
4569 @cindex machine instructions
4570 @cindex listing machine instructions
4571 @item set assembly-language @var{instruction-set}
4572 This command selects the instruction set to use when disassembling the program via the
4573 @code{disassemble} or @code{x/i} commands. It is useful for architectures that
4574 have more than one native instruction set.
4576 Currently it is only defined for the Intel x86 family. You can set @var{instruction-set}
4577 to either @code{i386} or @code{i8086}. The default is @code{i386}.
4581 @node Data, Languages, Source, Top
4582 @chapter Examining Data
4584 @cindex printing data
4585 @cindex examining data
4588 @c "inspect" is not quite a synonym if you are using Epoch, which we do not
4589 @c document because it is nonstandard... Under Epoch it displays in a
4590 @c different window or something like that.
4591 The usual way to examine data in your program is with the @code{print}
4592 command (abbreviated @code{p}), or its synonym @code{inspect}.
4594 It evaluates and prints the value of an expression of the language your
4595 program is written in (@pxref{Languages, ,Using @value{GDBN} with Different
4600 @item print @var{exp}
4601 @itemx print /@var{f} @var{exp}
4602 @var{exp} is an expression (in the source language). By default the
4603 value of @var{exp} is printed in a format appropriate to its data type;
4604 you can choose a different format by specifying @samp{/@var{f}}, where
4605 @var{f} is a letter specifying the format; @pxref{Output Formats,,Output
4609 @itemx print /@var{f}
4610 If you omit @var{exp}, @value{GDBN} displays the last value again (from the
4611 @dfn{value history}; @pxref{Value History, ,Value history}). This allows you to
4612 conveniently inspect the same value in an alternative format.
4615 A more low-level way of examining data is with the @code{x} command.
4616 It examines data in memory at a specified address and prints it in a
4617 specified format. @xref{Memory, ,Examining memory}.
4619 If you are interested in information about types, or about how the fields
4624 are declared, use the @code{ptype @var{exp}}
4625 command rather than @code{print}. @xref{Symbols, ,Examining the Symbol Table}.
4628 * Expressions:: Expressions
4629 * Variables:: Program variables
4630 * Arrays:: Artificial arrays
4631 * Output Formats:: Output formats
4632 * Memory:: Examining memory
4633 * Auto Display:: Automatic display
4634 * Print Settings:: Print settings
4635 * Value History:: Value history
4636 * Convenience Vars:: Convenience variables
4637 * Registers:: Registers
4639 * Floating Point Hardware:: Floating point hardware
4644 @node Expressions, Variables, Data, Data
4645 @section Expressions
4648 @code{print} and many other @value{GDBN} commands accept an expression and
4649 compute its value. Any kind of constant, variable or operator defined
4650 by the programming language you are using is valid in an expression in
4651 @value{GDBN}. This includes conditional expressions, function calls, casts
4652 and string constants. It unfortunately does not include symbols defined
4653 by preprocessor @code{#define} commands.
4655 @value{GDBN} now supports array constants in expressions input by
4656 the user. The syntax is @var{@{element, element@dots{}@}}. For example,
4657 you can now use the command @code{print @{1, 2, 3@}} to build up an array in
4658 memory that is malloc'd in the target program.
4661 Because C is so widespread, most of the expressions shown in examples in
4662 this manual are in C. @xref{Languages, , Using @value{GDBN} with Different
4663 Languages}, for information on how to use expressions in other
4666 In this section, we discuss operators that you can use in @value{GDBN}
4667 expressions regardless of your programming language.
4669 Casts are supported in all languages, not just in C, because it is so
4670 useful to cast a number into a pointer in order to examine a structure
4671 at that address in memory.
4672 @c FIXME: casts supported---Mod2 true?
4675 @value{GDBN} supports these operators, in addition to those common
4676 to programming languages:
4680 @samp{@@} is a binary operator for treating parts of memory as arrays.
4681 @xref{Arrays, ,Artificial arrays}, for more information.
4684 @samp{::} allows you to specify a variable in terms of the file or
4685 function where it is defined. @xref{Variables, ,Program variables}.
4687 @cindex @{@var{type}@}
4688 @cindex type casting memory
4689 @cindex memory, viewing as typed object
4690 @cindex casts, to view memory
4691 @item @{@var{type}@} @var{addr}
4692 Refers to an object of type @var{type} stored at address @var{addr} in
4693 memory. @var{addr} may be any expression whose value is an integer or
4694 pointer (but parentheses are required around binary operators, just as in
4695 a cast). This construct is allowed regardless of what kind of data is
4696 normally supposed to reside at @var{addr}.
4699 @node Variables, Arrays, Expressions, Data
4700 @section Program variables
4702 The most common kind of expression to use is the name of a variable
4705 Variables in expressions are understood in the selected stack frame
4706 (@pxref{Selection, ,Selecting a frame}); they must be either:
4710 global (or file-static)
4717 visible according to the scope rules of the
4718 programming language from the point of execution in that frame
4721 @noindent This means that in the function
4736 you can examine and use the variable @code{a} whenever your program is
4737 executing within the function @code{foo}, but you can only use or
4738 examine the variable @code{b} while your program is executing inside
4739 the block where @code{b} is declared.
4741 @cindex variable name conflict
4742 There is an exception: you can refer to a variable or function whose
4743 scope is a single source file even if the current execution point is not
4744 in this file. But it is possible to have more than one such variable or
4745 function with the same name (in different source files). If that
4746 happens, referring to that name has unpredictable effects. If you wish,
4747 you can specify a static variable in a particular function or file,
4748 using the colon-colon notation:
4752 @c info cannot cope with a :: index entry, but why deprive hard copy readers?
4756 @var{file}::@var{variable}
4757 @var{function}::@var{variable}
4761 Here @var{file} or @var{function} is the name of the context for the
4762 static @var{variable}. In the case of file names, you can use quotes to
4763 make sure @value{GDBN} parses the file name as a single word---for example,
4764 to print a global value of @code{x} defined in @file{f2.c}:
4767 (@value{GDBP}) p 'f2.c'::x
4771 @cindex C++ scope resolution
4772 This use of @samp{::} is very rarely in conflict with the very similar
4773 use of the same notation in C++. @value{GDBN} also supports use of the C++
4774 scope resolution operator in @value{GDBN} expressions.
4775 @c FIXME: Um, so what happens in one of those rare cases where it's in
4779 @cindex wrong values
4780 @cindex variable values, wrong
4782 @emph{Warning:} Occasionally, a local variable may appear to have the
4783 wrong value at certain points in a function---just after entry to a new
4784 scope, and just before exit.
4786 You may see this problem when you are stepping by machine instructions.
4787 This is because, on most machines, it takes more than one instruction to
4788 set up a stack frame (including local variable definitions); if you are
4789 stepping by machine instructions, variables may appear to have the wrong
4790 values until the stack frame is completely built. On exit, it usually
4791 also takes more than one machine instruction to destroy a stack frame;
4792 after you begin stepping through that group of instructions, local
4793 variable definitions may be gone.
4795 @node Arrays, Output Formats, Variables, Data
4796 @section Artificial arrays
4798 @cindex artificial array
4800 It is often useful to print out several successive objects of the
4801 same type in memory; a section of an array, or an array of
4802 dynamically determined size for which only a pointer exists in the
4805 You can do this by referring to a contiguous span of memory as an
4806 @dfn{artificial array}, using the binary operator @samp{@@}. The left
4807 operand of @samp{@@} should be the first element of the desired array
4808 and be an individual object. The right operand should be the desired length
4809 of the array. The result is an array value whose elements are all of
4810 the type of the left argument. The first element is actually the left
4811 argument; the second element comes from bytes of memory immediately
4812 following those that hold the first element, and so on. Here is an
4813 example. If a program says
4816 int *array = (int *) malloc (len * sizeof (int));
4820 you can print the contents of @code{array} with
4826 The left operand of @samp{@@} must reside in memory. Array values made
4827 with @samp{@@} in this way behave just like other arrays in terms of
4828 subscripting, and are coerced to pointers when used in expressions.
4829 Artificial arrays most often appear in expressions via the value history
4830 (@pxref{Value History, ,Value history}), after printing one out.
4832 Another way to create an artificial array is to use a cast.
4833 This re-interprets a value as if it were an array.
4834 The value need not be in memory:
4836 (@value{GDBP}) p/x (short[2])0x12345678
4837 $1 = @{0x1234, 0x5678@}
4840 As a convenience, if you leave the array length out (as in
4841 @samp{(@var{type})[])@var{value}}) gdb calculates the size to fill
4842 the value (as @samp{sizeof(@var{value})/sizeof(@var{type})}:
4844 (@value{GDBP}) p/x (short[])0x12345678
4845 $2 = @{0x1234, 0x5678@}
4848 Sometimes the artificial array mechanism is not quite enough; in
4849 moderately complex data structures, the elements of interest may not
4850 actually be adjacent---for example, if you are interested in the values
4851 of pointers in an array. One useful work-around in this situation is
4852 to use a convenience variable (@pxref{Convenience Vars, ,Convenience
4853 variables}) as a counter in an expression that prints the first
4854 interesting value, and then repeat that expression via @key{RET}. For
4855 instance, suppose you have an array @code{dtab} of pointers to
4856 structures, and you are interested in the values of a field @code{fv}
4857 in each structure. Here is an example of what you might type:
4867 @node Output Formats, Memory, Arrays, Data
4868 @section Output formats
4870 @cindex formatted output
4871 @cindex output formats
4872 By default, @value{GDBN} prints a value according to its data type. Sometimes
4873 this is not what you want. For example, you might want to print a number
4874 in hex, or a pointer in decimal. Or you might want to view data in memory
4875 at a certain address as a character string or as an instruction. To do
4876 these things, specify an @dfn{output format} when you print a value.
4878 The simplest use of output formats is to say how to print a value
4879 already computed. This is done by starting the arguments of the
4880 @code{print} command with a slash and a format letter. The format
4881 letters supported are:
4885 Regard the bits of the value as an integer, and print the integer in
4889 Print as integer in signed decimal.
4892 Print as integer in unsigned decimal.
4895 Print as integer in octal.
4898 Print as integer in binary. The letter @samp{t} stands for ``two''.
4899 @footnote{@samp{b} cannot be used because these format letters are also
4900 used with the @code{x} command, where @samp{b} stands for ``byte'';
4901 @pxref{Memory,,Examining memory}.}
4904 @cindex unknown address, locating
4905 Print as an address, both absolute in hexadecimal and as an offset from
4906 the nearest preceding symbol. You can use this format used to discover
4907 where (in what function) an unknown address is located:
4910 (@value{GDBP}) p/a 0x54320
4911 $3 = 0x54320 <_initialize_vx+396>
4915 Regard as an integer and print it as a character constant.
4918 Regard the bits of the value as a floating point number and print
4919 using typical floating point syntax.
4922 For example, to print the program counter in hex (@pxref{Registers}), type
4929 Note that no space is required before the slash; this is because command
4930 names in @value{GDBN} cannot contain a slash.
4932 To reprint the last value in the value history with a different format,
4933 you can use the @code{print} command with just a format and no
4934 expression. For example, @samp{p/x} reprints the last value in hex.
4936 @node Memory, Auto Display, Output Formats, Data
4937 @section Examining memory
4939 You can use the command @code{x} (for ``examine'') to examine memory in
4940 any of several formats, independently of your program's data types.
4942 @cindex examining memory
4945 @item x/@var{nfu} @var{addr}
4948 Use the @code{x} command to examine memory.
4951 @var{n}, @var{f}, and @var{u} are all optional parameters that specify how
4952 much memory to display and how to format it; @var{addr} is an
4953 expression giving the address where you want to start displaying memory.
4954 If you use defaults for @var{nfu}, you need not type the slash @samp{/}.
4955 Several commands set convenient defaults for @var{addr}.
4958 @item @var{n}, the repeat count
4959 The repeat count is a decimal integer; the default is 1. It specifies
4960 how much memory (counting by units @var{u}) to display.
4961 @c This really is **decimal**; unaffected by 'set radix' as of GDB
4964 @item @var{f}, the display format
4965 The display format is one of the formats used by @code{print},
4966 @samp{s} (null-terminated string), or @samp{i} (machine instruction).
4967 The default is @samp{x} (hexadecimal) initially.
4968 The default changes each time you use either @code{x} or @code{print}.
4970 @item @var{u}, the unit size
4971 The unit size is any of
4977 Halfwords (two bytes).
4979 Words (four bytes). This is the initial default.
4981 Giant words (eight bytes).
4984 Each time you specify a unit size with @code{x}, that size becomes the
4985 default unit the next time you use @code{x}. (For the @samp{s} and
4986 @samp{i} formats, the unit size is ignored and is normally not written.)
4988 @item @var{addr}, starting display address
4989 @var{addr} is the address where you want @value{GDBN} to begin displaying
4990 memory. The expression need not have a pointer value (though it may);
4991 it is always interpreted as an integer address of a byte of memory.
4992 @xref{Expressions, ,Expressions}, for more information on expressions. The default for
4993 @var{addr} is usually just after the last address examined---but several
4994 other commands also set the default address: @code{info breakpoints} (to
4995 the address of the last breakpoint listed), @code{info line} (to the
4996 starting address of a line), and @code{print} (if you use it to display
4997 a value from memory).
5000 For example, @samp{x/3uh 0x54320} is a request to display three halfwords
5001 (@code{h}) of memory, formatted as unsigned decimal integers (@samp{u}),
5002 starting at address @code{0x54320}. @samp{x/4xw $sp} prints the four
5003 words (@samp{w}) of memory above the stack pointer (here, @samp{$sp};
5004 @pxref{Registers}) in hexadecimal (@samp{x}).
5006 Since the letters indicating unit sizes are all distinct from the
5007 letters specifying output formats, you do not have to remember whether
5008 unit size or format comes first; either order works. The output
5009 specifications @samp{4xw} and @samp{4wx} mean exactly the same thing.
5010 (However, the count @var{n} must come first; @samp{wx4} does not work.)
5012 Even though the unit size @var{u} is ignored for the formats @samp{s}
5013 and @samp{i}, you might still want to use a count @var{n}; for example,
5014 @samp{3i} specifies that you want to see three machine instructions,
5015 including any operands. The command @code{disassemble} gives an
5016 alternative way of inspecting machine instructions; @pxref{Machine
5017 Code,,Source and machine code}.
5019 All the defaults for the arguments to @code{x} are designed to make it
5020 easy to continue scanning memory with minimal specifications each time
5021 you use @code{x}. For example, after you have inspected three machine
5022 instructions with @samp{x/3i @var{addr}}, you can inspect the next seven
5023 with just @samp{x/7}. If you use @key{RET} to repeat the @code{x} command,
5024 the repeat count @var{n} is used again; the other arguments default as
5025 for successive uses of @code{x}.
5027 @cindex @code{$_}, @code{$__}, and value history
5028 The addresses and contents printed by the @code{x} command are not saved
5029 in the value history because there is often too much of them and they
5030 would get in the way. Instead, @value{GDBN} makes these values available for
5031 subsequent use in expressions as values of the convenience variables
5032 @code{$_} and @code{$__}. After an @code{x} command, the last address
5033 examined is available for use in expressions in the convenience variable
5034 @code{$_}. The contents of that address, as examined, are available in
5035 the convenience variable @code{$__}.
5037 If the @code{x} command has a repeat count, the address and contents saved
5038 are from the last memory unit printed; this is not the same as the last
5039 address printed if several units were printed on the last line of output.
5041 @node Auto Display, Print Settings, Memory, Data
5042 @section Automatic display
5043 @cindex automatic display
5044 @cindex display of expressions
5046 If you find that you want to print the value of an expression frequently
5047 (to see how it changes), you might want to add it to the @dfn{automatic
5048 display list} so that @value{GDBN} prints its value each time your program stops.
5049 Each expression added to the list is given a number to identify it;
5050 to remove an expression from the list, you specify that number.
5051 The automatic display looks like this:
5055 3: bar[5] = (struct hack *) 0x3804
5059 This display shows item numbers, expressions and their current values. As with
5060 displays you request manually using @code{x} or @code{print}, you can
5061 specify the output format you prefer; in fact, @code{display} decides
5062 whether to use @code{print} or @code{x} depending on how elaborate your
5063 format specification is---it uses @code{x} if you specify a unit size,
5064 or one of the two formats (@samp{i} and @samp{s}) that are only
5065 supported by @code{x}; otherwise it uses @code{print}.
5069 @item display @var{exp}
5070 Add the expression @var{exp} to the list of expressions to display
5071 each time your program stops. @xref{Expressions, ,Expressions}.
5073 @code{display} does not repeat if you press @key{RET} again after using it.
5075 @item display/@var{fmt} @var{exp}
5076 For @var{fmt} specifying only a display format and not a size or
5077 count, add the expression @var{exp} to the auto-display list but
5078 arrange to display it each time in the specified format @var{fmt}.
5079 @xref{Output Formats,,Output formats}.
5081 @item display/@var{fmt} @var{addr}
5082 For @var{fmt} @samp{i} or @samp{s}, or including a unit-size or a
5083 number of units, add the expression @var{addr} as a memory address to
5084 be examined each time your program stops. Examining means in effect
5085 doing @samp{x/@var{fmt} @var{addr}}. @xref{Memory, ,Examining memory}.
5088 For example, @samp{display/i $pc} can be helpful, to see the machine
5089 instruction about to be executed each time execution stops (@samp{$pc}
5090 is a common name for the program counter; @pxref{Registers}).
5093 @kindex delete display
5095 @item undisplay @var{dnums}@dots{}
5096 @itemx delete display @var{dnums}@dots{}
5097 Remove item numbers @var{dnums} from the list of expressions to display.
5099 @code{undisplay} does not repeat if you press @key{RET} after using it.
5100 (Otherwise you would just get the error @samp{No display number @dots{}}.)
5102 @kindex disable display
5103 @item disable display @var{dnums}@dots{}
5104 Disable the display of item numbers @var{dnums}. A disabled display
5105 item is not printed automatically, but is not forgotten. It may be
5106 enabled again later.
5108 @kindex enable display
5109 @item enable display @var{dnums}@dots{}
5110 Enable display of item numbers @var{dnums}. It becomes effective once
5111 again in auto display of its expression, until you specify otherwise.
5114 Display the current values of the expressions on the list, just as is
5115 done when your program stops.
5117 @kindex info display
5119 Print the list of expressions previously set up to display
5120 automatically, each one with its item number, but without showing the
5121 values. This includes disabled expressions, which are marked as such.
5122 It also includes expressions which would not be displayed right now
5123 because they refer to automatic variables not currently available.
5126 If a display expression refers to local variables, then it does not make
5127 sense outside the lexical context for which it was set up. Such an
5128 expression is disabled when execution enters a context where one of its
5129 variables is not defined. For example, if you give the command
5130 @code{display last_char} while inside a function with an argument
5131 @code{last_char}, @value{GDBN} displays this argument while your program
5132 continues to stop inside that function. When it stops elsewhere---where
5133 there is no variable @code{last_char}---the display is disabled
5134 automatically. The next time your program stops where @code{last_char}
5135 is meaningful, you can enable the display expression once again.
5137 @node Print Settings, Value History, Auto Display, Data
5138 @section Print settings
5140 @cindex format options
5141 @cindex print settings
5142 @value{GDBN} provides the following ways to control how arrays, structures,
5143 and symbols are printed.
5146 These settings are useful for debugging programs in any language:
5149 @kindex set print address
5150 @item set print address
5151 @itemx set print address on
5152 @value{GDBN} prints memory addresses showing the location of stack
5153 traces, structure values, pointer values, breakpoints, and so forth,
5154 even when it also displays the contents of those addresses. The default
5155 is @code{on}. For example, this is what a stack frame display looks like with
5156 @code{set print address on}:
5161 #0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>")
5163 530 if (lquote != def_lquote)
5167 @item set print address off
5168 Do not print addresses when displaying their contents. For example,
5169 this is the same stack frame displayed with @code{set print address off}:
5173 (@value{GDBP}) set print addr off
5175 #0 set_quotes (lq="<<", rq=">>") at input.c:530
5176 530 if (lquote != def_lquote)
5180 You can use @samp{set print address off} to eliminate all machine
5181 dependent displays from the @value{GDBN} interface. For example, with
5182 @code{print address off}, you should get the same text for backtraces on
5183 all machines---whether or not they involve pointer arguments.
5185 @kindex show print address
5186 @item show print address
5187 Show whether or not addresses are to be printed.
5190 When @value{GDBN} prints a symbolic address, it normally prints the
5191 closest earlier symbol plus an offset. If that symbol does not uniquely
5192 identify the address (for example, it is a name whose scope is a single
5193 source file), you may need to clarify. One way to do this is with
5194 @code{info line}, for example @samp{info line *0x4537}. Alternately,
5195 you can set @value{GDBN} to print the source file and line number when
5196 it prints a symbolic address:
5199 @kindex set print symbol-filename
5200 @item set print symbol-filename on
5201 Tell @value{GDBN} to print the source file name and line number of a
5202 symbol in the symbolic form of an address.
5204 @item set print symbol-filename off
5205 Do not print source file name and line number of a symbol. This is the
5208 @kindex show print symbol-filename
5209 @item show print symbol-filename
5210 Show whether or not @value{GDBN} will print the source file name and
5211 line number of a symbol in the symbolic form of an address.
5214 Another situation where it is helpful to show symbol filenames and line
5215 numbers is when disassembling code; @value{GDBN} shows you the line
5216 number and source file that corresponds to each instruction.
5218 Also, you may wish to see the symbolic form only if the address being
5219 printed is reasonably close to the closest earlier symbol:
5222 @kindex set print max-symbolic-offset
5223 @item set print max-symbolic-offset @var{max-offset}
5224 Tell @value{GDBN} to only display the symbolic form of an address if the
5225 offset between the closest earlier symbol and the address is less than
5226 @var{max-offset}. The default is 0, which tells @value{GDBN}
5227 to always print the symbolic form of an address if any symbol precedes it.
5229 @kindex show print max-symbolic-offset
5230 @item show print max-symbolic-offset
5231 Ask how large the maximum offset is that @value{GDBN} prints in a
5235 @cindex wild pointer, interpreting
5236 @cindex pointer, finding referent
5237 If you have a pointer and you are not sure where it points, try
5238 @samp{set print symbol-filename on}. Then you can determine the name
5239 and source file location of the variable where it points, using
5240 @samp{p/a @var{pointer}}. This interprets the address in symbolic form.
5241 For example, here @value{GDBN} shows that a variable @code{ptt} points
5242 at another variable @code{t}, defined in @file{hi2.c}:
5245 (@value{GDBP}) set print symbol-filename on
5246 (@value{GDBP}) p/a ptt
5247 $4 = 0xe008 <t in hi2.c>
5251 @emph{Warning:} For pointers that point to a local variable, @samp{p/a}
5252 does not show the symbol name and filename of the referent, even with
5253 the appropriate @code{set print} options turned on.
5256 Other settings control how different kinds of objects are printed:
5259 @kindex set print array
5260 @item set print array
5261 @itemx set print array on
5262 Pretty print arrays. This format is more convenient to read,
5263 but uses more space. The default is off.
5265 @item set print array off
5266 Return to compressed format for arrays.
5268 @kindex show print array
5269 @item show print array
5270 Show whether compressed or pretty format is selected for displaying
5273 @kindex set print elements
5274 @item set print elements @var{number-of-elements}
5275 Set a limit on how many elements of an array @value{GDBN} will print.
5276 If @value{GDBN} is printing a large array, it stops printing after it has
5277 printed the number of elements set by the @code{set print elements} command.
5278 This limit also applies to the display of strings.
5279 Setting @var{number-of-elements} to zero means that the printing is unlimited.
5281 @kindex show print elements
5282 @item show print elements
5283 Display the number of elements of a large array that @value{GDBN} will print.
5284 If the number is 0, then the printing is unlimited.
5286 @kindex set print null-stop
5287 @item set print null-stop
5288 Cause @value{GDBN} to stop printing the characters of an array when the first
5289 @sc{NULL} is encountered. This is useful when large arrays actually
5290 contain only short strings.
5292 @kindex set print pretty
5293 @item set print pretty on
5294 Cause @value{GDBN} to print structures in an indented format with one member
5295 per line, like this:
5310 @item set print pretty off
5311 Cause @value{GDBN} to print structures in a compact format, like this:
5315 $1 = @{next = 0x0, flags = @{sweet = 1, sour = 1@}, \
5316 meat = 0x54 "Pork"@}
5321 This is the default format.
5323 @kindex show print pretty
5324 @item show print pretty
5325 Show which format @value{GDBN} is using to print structures.
5327 @kindex set print sevenbit-strings
5328 @item set print sevenbit-strings on
5329 Print using only seven-bit characters; if this option is set,
5330 @value{GDBN} displays any eight-bit characters (in strings or
5331 character values) using the notation @code{\}@var{nnn}. This setting is
5332 best if you are working in English (@sc{ascii}) and you use the
5333 high-order bit of characters as a marker or ``meta'' bit.
5335 @item set print sevenbit-strings off
5336 Print full eight-bit characters. This allows the use of more
5337 international character sets, and is the default.
5339 @kindex show print sevenbit-strings
5340 @item show print sevenbit-strings
5341 Show whether or not @value{GDBN} is printing only seven-bit characters.
5343 @kindex set print union
5344 @item set print union on
5345 Tell @value{GDBN} to print unions which are contained in structures. This
5346 is the default setting.
5348 @item set print union off
5349 Tell @value{GDBN} not to print unions which are contained in structures.
5351 @kindex show print union
5352 @item show print union
5353 Ask @value{GDBN} whether or not it will print unions which are contained in
5356 For example, given the declarations
5359 typedef enum @{Tree, Bug@} Species;
5360 typedef enum @{Big_tree, Acorn, Seedling@} Tree_forms;
5361 typedef enum @{Caterpillar, Cocoon, Butterfly@}
5372 struct thing foo = @{Tree, @{Acorn@}@};
5376 with @code{set print union on} in effect @samp{p foo} would print
5379 $1 = @{it = Tree, form = @{tree = Acorn, bug = Cocoon@}@}
5383 and with @code{set print union off} in effect it would print
5386 $1 = @{it = Tree, form = @{...@}@}
5393 These settings are of interest when debugging C++ programs:
5397 @kindex set print demangle
5398 @item set print demangle
5399 @itemx set print demangle on
5400 Print C++ names in their source form rather than in the encoded
5401 (``mangled'') form passed to the assembler and linker for type-safe
5402 linkage. The default is @samp{on}.
5404 @kindex show print demangle
5405 @item show print demangle
5406 Show whether C++ names are printed in mangled or demangled form.
5408 @kindex set print asm-demangle
5409 @item set print asm-demangle
5410 @itemx set print asm-demangle on
5411 Print C++ names in their source form rather than their mangled form, even
5412 in assembler code printouts such as instruction disassemblies.
5415 @kindex show print asm-demangle
5416 @item show print asm-demangle
5417 Show whether C++ names in assembly listings are printed in mangled
5420 @kindex set demangle-style
5421 @cindex C++ symbol decoding style
5422 @cindex symbol decoding style, C++
5423 @item set demangle-style @var{style}
5424 Choose among several encoding schemes used by different compilers to
5425 represent C++ names. The choices for @var{style} are currently:
5429 Allow @value{GDBN} to choose a decoding style by inspecting your program.
5432 Decode based on the @sc{gnu} C++ compiler (@code{g++}) encoding algorithm.
5434 This is the default.
5438 Decode based on the HP ANSI C++ (@code{aCC}) encoding algorithm.
5441 Decode based on the Lucid C++ compiler (@code{lcc}) encoding algorithm.
5444 Decode using the algorithm in the @cite{C++ Annotated Reference Manual}.
5445 @strong{Warning:} this setting alone is not sufficient to allow
5446 debugging @code{cfront}-generated executables. @value{GDBN} would
5447 require further enhancement to permit that.
5450 Show the list of formats.
5453 @kindex show demangle-style
5454 @item show demangle-style
5455 Display the encoding style currently in use for decoding C++ symbols.
5457 @kindex set print object
5458 @item set print object
5459 @itemx set print object on
5460 When displaying a pointer to an object, identify the @emph{actual}
5461 (derived) type of the object rather than the @emph{declared} type, using
5462 the virtual function table.
5464 @item set print object off
5465 Display only the declared type of objects, without reference to the
5466 virtual function table. This is the default setting.
5468 @kindex show print object
5469 @item show print object
5470 Show whether actual, or declared, object types are displayed.
5472 @kindex set print static-members
5473 @item set print static-members
5474 @itemx set print static-members on
5475 Print static members when displaying a C++ object. The default is on.
5477 @item set print static-members off
5478 Do not print static members when displaying a C++ object.
5480 @kindex show print static-members
5481 @item show print static-members
5482 Show whether C++ static members are printed, or not.
5484 @c These don't work with HP ANSI C++ yet.
5485 @kindex set print vtbl
5486 @item set print vtbl
5487 @itemx set print vtbl on
5488 Pretty print C++ virtual function tables. The default is off.
5490 (The @code{vtbl} commands do not work on programs compiled with the HP
5491 ANSI C++ compiler (@code{aCC}).)
5494 @item set print vtbl off
5495 Do not pretty print C++ virtual function tables.
5497 @kindex show print vtbl
5498 @item show print vtbl
5499 Show whether C++ virtual function tables are pretty printed, or not.
5503 @node Value History, Convenience Vars, Print Settings, Data
5504 @section Value history
5506 @cindex value history
5507 Values printed by the @code{print} command are saved in the @value{GDBN}
5508 @dfn{value history}. This allows you to refer to them in other expressions.
5509 Values are kept until the symbol table is re-read or discarded
5510 (for example with the @code{file} or @code{symbol-file} commands).
5511 When the symbol table changes, the value history is discarded,
5512 since the values may contain pointers back to the types defined in the
5517 @cindex history number
5518 The values printed are given @dfn{history numbers} by which you can
5519 refer to them. These are successive integers starting with one.
5520 @code{print} shows you the history number assigned to a value by
5521 printing @samp{$@var{num} = } before the value; here @var{num} is the
5524 To refer to any previous value, use @samp{$} followed by the value's
5525 history number. The way @code{print} labels its output is designed to
5526 remind you of this. Just @code{$} refers to the most recent value in
5527 the history, and @code{$$} refers to the value before that.
5528 @code{$$@var{n}} refers to the @var{n}th value from the end; @code{$$2}
5529 is the value just prior to @code{$$}, @code{$$1} is equivalent to
5530 @code{$$}, and @code{$$0} is equivalent to @code{$}.
5532 For example, suppose you have just printed a pointer to a structure and
5533 want to see the contents of the structure. It suffices to type
5539 If you have a chain of structures where the component @code{next} points
5540 to the next one, you can print the contents of the next one with this:
5547 You can print successive links in the chain by repeating this
5548 command---which you can do by just typing @key{RET}.
5550 Note that the history records values, not expressions. If the value of
5551 @code{x} is 4 and you type these commands:
5559 then the value recorded in the value history by the @code{print} command
5560 remains 4 even though the value of @code{x} has changed.
5565 Print the last ten values in the value history, with their item numbers.
5566 This is like @samp{p@ $$9} repeated ten times, except that @code{show
5567 values} does not change the history.
5569 @item show values @var{n}
5570 Print ten history values centered on history item number @var{n}.
5573 Print ten history values just after the values last printed. If no more
5574 values are available, @code{show values +} produces no display.
5577 Pressing @key{RET} to repeat @code{show values @var{n}} has exactly the
5578 same effect as @samp{show values +}.
5580 @node Convenience Vars, Registers, Value History, Data
5581 @section Convenience variables
5583 @cindex convenience variables
5584 @value{GDBN} provides @dfn{convenience variables} that you can use within
5585 @value{GDBN} to hold on to a value and refer to it later. These variables
5586 exist entirely within @value{GDBN}; they are not part of your program, and
5587 setting a convenience variable has no direct effect on further execution
5588 of your program. That is why you can use them freely.
5590 Convenience variables are prefixed with @samp{$}. Any name preceded by
5591 @samp{$} can be used for a convenience variable, unless it is one of
5592 the predefined machine-specific register names (@pxref{Registers}).
5593 (Value history references, in contrast, are @emph{numbers} preceded
5594 by @samp{$}. @xref{Value History, ,Value history}.)
5596 You can save a value in a convenience variable with an assignment
5597 expression, just as you would set a variable in your program.
5601 set $foo = *object_ptr
5605 would save in @code{$foo} the value contained in the object pointed to by
5608 Using a convenience variable for the first time creates it, but its
5609 value is @code{void} until you assign a new value. You can alter the
5610 value with another assignment at any time.
5612 Convenience variables have no fixed types. You can assign a convenience
5613 variable any type of value, including structures and arrays, even if
5614 that variable already has a value of a different type. The convenience
5615 variable, when used as an expression, has the type of its current value.
5618 @kindex show convenience
5619 @item show convenience
5620 Print a list of convenience variables used so far, and their values.
5621 Abbreviated @code{show con}.
5624 One of the ways to use a convenience variable is as a counter to be
5625 incremented or a pointer to be advanced. For example, to print
5626 a field from successive elements of an array of structures:
5630 print bar[$i++]->contents
5633 @noindent Repeat that command by typing @key{RET}.
5635 Some convenience variables are created automatically by @value{GDBN} and given
5636 values likely to be useful.
5641 The variable @code{$_} is automatically set by the @code{x} command to
5642 the last address examined (@pxref{Memory, ,Examining memory}). Other
5643 commands which provide a default address for @code{x} to examine also
5644 set @code{$_} to that address; these commands include @code{info line}
5645 and @code{info breakpoint}. The type of @code{$_} is @code{void *}
5646 except when set by the @code{x} command, in which case it is a pointer
5647 to the type of @code{$__}.
5651 The variable @code{$__} is automatically set by the @code{x} command
5652 to the value found in the last address examined. Its type is chosen
5653 to match the format in which the data was printed.
5657 The variable @code{$_exitcode} is automatically set to the exit code when
5658 the program being debugged terminates.
5662 If you refer to a function or variable name that begins with a dollar
5663 sign, @value{GDBN} searches for a user or system name first, before it
5664 searches for a convenience variable.
5667 @node Registers, Floating Point Hardware, Convenience Vars, Data
5671 You can refer to machine register contents, in expressions, as variables
5672 with names starting with @samp{$}. The names of registers are different
5673 for each machine; use @code{info registers} to see the names used on
5677 @kindex info registers
5678 @item info registers
5679 Print the names and values of all registers except floating-point
5680 registers (in the selected stack frame).
5682 @kindex info all-registers
5683 @cindex floating point registers
5684 @item info all-registers
5685 Print the names and values of all registers, including floating-point
5688 @item info registers @var{regname} @dots{}
5689 Print the @dfn{relativized} value of each specified register @var{regname}.
5690 As discussed in detail below, register values are normally relative to
5691 the selected stack frame. @var{regname} may be any register name valid on
5692 the machine you are using, with or without the initial @samp{$}.
5695 @value{GDBN} has four ``standard'' register names that are available (in
5696 expressions) on most machines---whenever they do not conflict with an
5697 architecture's canonical mnemonics for registers. The register names
5698 @code{$pc} and @code{$sp} are used for the program counter register and
5699 the stack pointer. @code{$fp} is used for a register that contains a
5700 pointer to the current stack frame, and @code{$ps} is used for a
5701 register that contains the processor status. For example,
5702 you could print the program counter in hex with
5709 or print the instruction to be executed next with
5716 or add four to the stack pointer@footnote{This is a way of removing
5717 one word from the stack, on machines where stacks grow downward in
5718 memory (most machines, nowadays). This assumes that the innermost
5719 stack frame is selected; setting @code{$sp} is not allowed when other
5720 stack frames are selected. To pop entire frames off the stack,
5721 regardless of machine architecture, use @code{return};
5722 @pxref{Returning, ,Returning from a function}.} with
5728 Whenever possible, these four standard register names are available on
5729 your machine even though the machine has different canonical mnemonics,
5730 so long as there is no conflict. The @code{info registers} command
5731 shows the canonical names. For example, on the SPARC, @code{info
5732 registers} displays the processor status register as @code{$psr} but you
5733 can also refer to it as @code{$ps}.
5735 @value{GDBN} always considers the contents of an ordinary register as an
5736 integer when the register is examined in this way. Some machines have
5737 special registers which can hold nothing but floating point; these
5738 registers are considered to have floating point values. There is no way
5739 to refer to the contents of an ordinary register as floating point value
5740 (although you can @emph{print} it as a floating point value with
5741 @samp{print/f $@var{regname}}).
5743 Some registers have distinct ``raw'' and ``virtual'' data formats. This
5744 means that the data format in which the register contents are saved by
5745 the operating system is not the same one that your program normally
5746 sees. For example, the registers of the 68881 floating point
5747 coprocessor are always saved in ``extended'' (raw) format, but all C
5748 programs expect to work with ``double'' (virtual) format. In such
5749 cases, @value{GDBN} normally works with the virtual format only (the format
5750 that makes sense for your program), but the @code{info registers} command
5751 prints the data in both formats.
5753 Normally, register values are relative to the selected stack frame
5754 (@pxref{Selection, ,Selecting a frame}). This means that you get the
5755 value that the register would contain if all stack frames farther in
5756 were exited and their saved registers restored. In order to see the
5757 true contents of hardware registers, you must select the innermost
5758 frame (with @samp{frame 0}).
5760 However, @value{GDBN} must deduce where registers are saved, from the machine
5761 code generated by your compiler. If some registers are not saved, or if
5762 @value{GDBN} is unable to locate the saved registers, the selected stack
5763 frame makes no difference.
5767 @kindex set rstack_high_address
5768 @cindex AMD 29K register stack
5769 @cindex register stack, AMD29K
5770 @item set rstack_high_address @var{address}
5771 On AMD 29000 family processors, registers are saved in a separate
5772 ``register stack''. There is no way for @value{GDBN} to determine the extent
5773 of this stack. Normally, @value{GDBN} just assumes that the stack is ``large
5774 enough''. This may result in @value{GDBN} referencing memory locations that
5775 do not exist. If necessary, you can get around this problem by
5776 specifying the ending address of the register stack with the @code{set
5777 rstack_high_address} command. The argument should be an address, which
5778 you probably want to precede with @samp{0x} to specify in
5781 @kindex show rstack_high_address
5782 @item show rstack_high_address
5783 Display the current limit of the register stack, on AMD 29000 family
5789 @node Floating Point Hardware, , Registers, Data
5790 @section Floating point hardware
5791 @cindex floating point
5793 Depending on the configuration, @value{GDBN} may be able to give
5794 you more information about the status of the floating point hardware.
5799 Display hardware-dependent information about the floating
5800 point unit. The exact contents and layout vary depending on the
5801 floating point chip. Currently, @samp{info float} is supported on
5802 the ARM and x86 machines.
5807 @node Languages, Symbols, Data, Top
5808 @chapter Using @value{GDBN} with Different Languages
5812 Although programming languages generally have common aspects, they are
5813 rarely expressed in the same manner. For instance, in ANSI C,
5814 dereferencing a pointer @code{p} is accomplished by @code{*p}, but in
5815 Modula-2, it is accomplished by @code{p^}. Values can also be
5816 represented (and displayed) differently. Hex numbers in C appear as
5817 @samp{0x1ae}, while in Modula-2 they appear as @samp{1AEH}.
5820 @cindex working language
5821 Language-specific information is built into @value{GDBN} for some languages,
5822 allowing you to express operations like the above in your program's
5823 native language, and allowing @value{GDBN} to output values in a manner
5824 consistent with the syntax of your program's native language. The
5825 language you use to build expressions is called the @dfn{working
5829 * Setting:: Switching between source languages
5830 * Show:: Displaying the language
5832 * Checks:: Type and range checks
5835 * Support:: Supported languages
5838 @node Setting, Show, Languages, Languages
5839 @section Switching between source languages
5841 There are two ways to control the working language---either have @value{GDBN}
5842 set it automatically, or select it manually yourself. You can use the
5843 @code{set language} command for either purpose. On startup, @value{GDBN}
5844 defaults to setting the language automatically. The working language is
5845 used to determine how expressions you type are interpreted, how values
5848 In addition to the working language, every source file that
5849 @value{GDBN} knows about has its own working language. For some object
5850 file formats, the compiler might indicate which language a particular
5851 source file is in. However, most of the time @value{GDBN} infers the
5852 language from the name of the file. The language of a source file
5853 controls whether C++ names are demangled---this way @code{backtrace} can
5854 show each frame appropriately for its own language. There is no way to
5855 set the language of a source file from within @value{GDBN}.
5857 This is most commonly a problem when you use a program, such
5858 as @code{cfront} or @code{f2c}, that generates C but is written in
5859 another language. In that case, make the
5860 program use @code{#line} directives in its C output; that way
5861 @value{GDBN} will know the correct language of the source code of the original
5862 program, and will display that source code, not the generated C code.
5865 * Filenames:: Filename extensions and languages.
5866 * Manually:: Setting the working language manually
5867 * Automatically:: Having @value{GDBN} infer the source language
5870 @node Filenames, Manually, Setting, Setting
5871 @subsection List of filename extensions and languages
5873 If a source file name ends in one of the following extensions, then
5874 @value{GDBN} infers that its language is the one indicated.
5879 Modula-2 source file
5902 Assembler source file. This actually behaves almost like C, but
5903 @value{GDBN} does not skip over function prologues when stepping.
5906 @node Manually, Automatically, Filenames, Setting
5907 @subsection Setting the working language
5909 If you allow @value{GDBN} to set the language automatically,
5910 expressions are interpreted the same way in your debugging session and
5913 @kindex set language
5914 If you wish, you may set the language manually. To do this, issue the
5915 command @samp{set language @var{lang}}, where @var{lang} is the name of
5921 @code{c} or @code{modula-2}.
5923 For a list of the supported languages, type @samp{set language}.
5926 Setting the language manually prevents @value{GDBN} from updating the
5927 working language automatically. For example, if you used the @code{c}
5928 setting to debug a C++ program, names might not be demangled properly,
5929 overload resolution would not work, user-defined operators might not be
5930 interpreted correctly, and so on.
5933 Setting the language manually prevents @value{GDBN} from updating the working
5934 language automatically. This can lead to confusion if you try
5935 to debug a program when the working language is not the same as the
5936 source language, when an expression is acceptable to both
5937 languages---but means different things. For instance, if the current
5938 source file were written in C, and @value{GDBN} was parsing Modula-2, a
5946 might not have the effect you intended. In C, this means to add
5947 @code{b} and @code{c} and place the result in @code{a}. The result
5948 printed would be the value of @code{a}. In Modula-2, this means to compare
5949 @code{a} to the result of @code{b+c}, yielding a @code{BOOLEAN} value.
5952 @node Automatically, , Manually, Setting
5953 @subsection Having @value{GDBN} infer the source language
5955 To have @value{GDBN} set the working language automatically, use
5956 @samp{set language local} or @samp{set language auto}. @value{GDBN}
5957 then infers the working language. That is, when your program stops in a
5958 frame (usually by encountering a breakpoint), @value{GDBN} sets the
5959 working language to the language recorded for the function in that
5960 frame. If the language for a frame is unknown (that is, if the function
5961 or block corresponding to the frame was defined in a source file that
5962 does not have a recognized extension), the current working language is
5963 not changed, and @value{GDBN} issues a warning.
5965 This may not seem necessary for most programs, which are written
5966 entirely in one source language. However, program modules and libraries
5967 written in one source language can be used by a main program written in
5968 a different source language. Using @samp{set language auto} in this
5969 case frees you from having to set the working language manually.
5972 @node Show, Checks, Setting, Languages
5973 @section Displaying the language
5976 @node Show, Support, Setting, Languages
5977 @section Displaying the language
5980 The following commands help you find out which language is the
5981 working language, and also what language source files were written in.
5983 @kindex show language
5988 Display the current working language. This is the
5989 language you can use with commands such as @code{print} to
5990 build and compute expressions that may involve variables in your program.
5993 Display the source language for this frame. This language becomes the
5994 working language if you use an identifier from this frame.
5995 @xref{Frame Info, ,Information about a frame}, to identify the other
5996 information listed here.
5999 Display the source language of this source file.
6000 @xref{Symbols, ,Examining the Symbol Table}, to identify the other
6001 information listed here.
6005 @node Checks, Support, Show, Languages
6006 @section Type and range checking
6009 @emph{Warning:} In this release, the @value{GDBN} commands for type and range
6010 checking are included, but they do not yet have any effect. This
6011 section documents the intended facilities.
6013 @c FIXME remove warning when type/range code added
6015 Some languages are designed to guard you against making seemingly common
6016 errors through a series of compile- and run-time checks. These include
6017 checking the type of arguments to functions and operators, and making
6018 sure mathematical overflows are caught at run time. Checks such as
6019 these help to ensure a program's correctness once it has been compiled
6020 by eliminating type mismatches, and providing active checks for range
6021 errors when your program is running.
6023 @value{GDBN} can check for conditions like the above if you wish.
6024 Although @value{GDBN} does not check the statements in your program, it
6025 can check expressions entered directly into @value{GDBN} for evaluation via
6026 the @code{print} command, for example. As with the working language,
6027 @value{GDBN} can also decide whether or not to check automatically based on
6028 your program's source language. @xref{Support, ,Supported languages},
6029 for the default settings of supported languages.
6032 * Type Checking:: An overview of type checking
6033 * Range Checking:: An overview of range checking
6036 @cindex type checking
6037 @cindex checks, type
6038 @node Type Checking, Range Checking, Checks, Checks
6039 @subsection An overview of type checking
6041 Some languages, such as Modula-2, are strongly typed, meaning that the
6042 arguments to operators and functions have to be of the correct type,
6043 otherwise an error occurs. These checks prevent type mismatch
6044 errors from ever causing any run-time problems. For example,
6052 The second example fails because the @code{CARDINAL} 1 is not
6053 type-compatible with the @code{REAL} 2.3.
6055 For the expressions you use in @value{GDBN} commands, you can tell the
6056 @value{GDBN} type checker to skip checking;
6057 to treat any mismatches as errors and abandon the expression;
6058 or to only issue warnings when type mismatches occur,
6059 but evaluate the expression anyway. When you choose the last of
6060 these, @value{GDBN} evaluates expressions like the second example above, but
6061 also issues a warning.
6063 Even if you turn type checking off, there may be other reasons
6064 related to type that prevent @value{GDBN} from evaluating an expression.
6065 For instance, @value{GDBN} does not know how to add an @code{int} and
6066 a @code{struct foo}. These particular type errors have nothing to do
6067 with the language in use, and usually arise from expressions, such as
6068 the one described above, which make little sense to evaluate anyway.
6070 Each language defines to what degree it is strict about type. For
6071 instance, both Modula-2 and C require the arguments to arithmetical
6072 operators to be numbers. In C, enumerated types and pointers can be
6073 represented as numbers, so that they are valid arguments to mathematical
6074 operators. @xref{Support, ,Supported languages}, for further
6075 details on specific languages.
6077 @value{GDBN} provides some additional commands for controlling the type checker:
6080 @kindex set check type
6081 @kindex show check type
6083 @item set check type auto
6084 Set type checking on or off based on the current working language.
6085 @xref{Support, ,Supported languages}, for the default settings for
6088 @item set check type on
6089 @itemx set check type off
6090 Set type checking on or off, overriding the default setting for the
6091 current working language. Issue a warning if the setting does not
6092 match the language default. If any type mismatches occur in
6093 evaluating an expression while typechecking is on, @value{GDBN} prints a
6094 message and aborts evaluation of the expression.
6096 @item set check type warn
6097 Cause the type checker to issue warnings, but to always attempt to
6098 evaluate the expression. Evaluating the expression may still
6099 be impossible for other reasons. For example, @value{GDBN} cannot add
6100 numbers and structures.
6103 Show the current setting of the type checker, and whether or not @value{GDBN}
6104 is setting it automatically.
6107 @cindex range checking
6108 @cindex checks, range
6109 @node Range Checking, , Type Checking, Checks
6110 @subsection An overview of range checking
6112 In some languages (such as Modula-2), it is an error to exceed the
6113 bounds of a type; this is enforced with run-time checks. Such range
6114 checking is meant to ensure program correctness by making sure
6115 computations do not overflow, or indices on an array element access do
6116 not exceed the bounds of the array.
6118 For expressions you use in @value{GDBN} commands, you can tell
6119 @value{GDBN} to treat range errors in one of three ways: ignore them,
6120 always treat them as errors and abandon the expression, or issue
6121 warnings but evaluate the expression anyway.
6123 A range error can result from numerical overflow, from exceeding an
6124 array index bound, or when you type a constant that is not a member
6125 of any type. Some languages, however, do not treat overflows as an
6126 error. In many implementations of C, mathematical overflow causes the
6127 result to ``wrap around'' to lower values---for example, if @var{m} is
6128 the largest integer value, and @var{s} is the smallest, then
6131 @var{m} + 1 @result{} @var{s}
6134 This, too, is specific to individual languages, and in some cases
6135 specific to individual compilers or machines. @xref{Support, ,
6136 Supported languages}, for further details on specific languages.
6138 @value{GDBN} provides some additional commands for controlling the range checker:
6141 @kindex set check range
6142 @kindex show check range
6144 @item set check range auto
6145 Set range checking on or off based on the current working language.
6146 @xref{Support, ,Supported languages}, for the default settings for
6149 @item set check range on
6150 @itemx set check range off
6151 Set range checking on or off, overriding the default setting for the
6152 current working language. A warning is issued if the setting does not
6153 match the language default. If a range error occurs, then a message
6154 is printed and evaluation of the expression is aborted.
6156 @item set check range warn
6157 Output messages when the @value{GDBN} range checker detects a range error,
6158 but attempt to evaluate the expression anyway. Evaluating the
6159 expression may still be impossible for other reasons, such as accessing
6160 memory that the process does not own (a typical example from many Unix
6164 Show the current setting of the range checker, and whether or not it is
6165 being set automatically by @value{GDBN}.
6170 @node Support, , Checks, Languages
6171 @section Supported languages
6174 @node Support, , Show, Languages
6175 @section Supported languages
6179 @value{GDBN} 4 supports C, C++, and Modula-2.
6182 @value{GDBN} 4 supports C and C++.
6184 Some @value{GDBN} features may be used in expressions regardless of the
6185 language you use: the @value{GDBN} @code{@@} and @code{::} operators,
6186 and the @samp{@{type@}addr} construct (@pxref{Expressions,
6187 ,Expressions}) can be used with the constructs of any supported
6190 The following sections detail to what degree each source language is
6191 supported by @value{GDBN}. These sections are not meant to be language
6192 tutorials or references, but serve only as a reference guide to what the
6193 @value{GDBN} expression parser accepts, and what input and output
6194 formats should look like for different languages. There are many good
6195 books written on each of these languages; please look to these for a
6196 language reference or tutorial.
6201 * Modula-2:: Modula-2
6204 @node C, Modula-2, , Support
6205 @subsection C and C++
6207 @cindex expressions in C or C++
6210 Since C and C++ are so closely related, many features of @value{GDBN} apply
6211 to both languages. Whenever this is the case, we discuss those languages
6215 @c Cancel this below, under same condition, at end of this chapter!
6222 @cindex @sc{gnu} C++
6223 The C++ debugging facilities are jointly implemented by the @sc{gnu} C++
6224 compiler and @value{GDBN}. Therefore, to debug your C++ code
6225 effectively, you must compile your C++ programs with the @sc{gnu} C++
6226 compiler, @code{g++}.
6228 For best results when debugging C++ programs, use the stabs debugging
6229 format. You can select that format explicitly with the @code{g++}
6230 command-line options @samp{-gstabs} or @samp{-gstabs+}. See
6231 @ref{Debugging Options,,Options for Debugging Your Program or @sc{gnu} CC,
6232 gcc.info, Using @sc{gnu} CC}, for more information.
6237 @cindex @sc{gnu} C++
6238 You can use @value{GDBN} to debug C programs compiled with either the HP
6239 C compiler (@code{cc}) or the GNU C compiler (@code{gcc}), and to debug
6240 programs compiled with either the HP ANSI C++ compiler (@code{aCC}) or
6241 the @sc{gnu} C++ compiler (@code{g++}).
6243 If you compile with the @sc{gnu} C++ compiler, use the stabs debugging
6244 format for best results when debugging. You can select that format
6245 explicitly with the @code{g++} command-line options @samp{-gstabs} or
6246 @samp{-gstabs+}. See @ref{Debugging Options,,Options for Debugging Your
6247 Program or @sc{gnu} CC, gcc.info, Using @sc{gnu} CC}, for more
6253 @node C, Symbols, Data, Top
6254 @chapter C Language Support
6256 @cindex expressions in C
6258 Information specific to the C language is built into @value{GDBN} so that you
6259 can use C expressions while degugging. This also permits @value{GDBN} to
6260 output values in a manner consistent with C conventions.
6263 * C Operators:: C operators
6269 * C Operators:: C and C++ operators
6270 * C Constants:: C and C++ constants
6271 * Cplus expressions:: C++ expressions
6272 * C Defaults:: Default settings for C and C++
6274 * C Checks:: C and C++ type and range checks
6277 * Debugging C:: @value{GDBN} and C
6278 * Debugging C plus plus:: @value{GDBN} features for C++
6283 @cindex C and C++ operators
6284 @node C Operators, C Constants, , C
6285 @subsubsection C and C++ operators
6289 @node C Operators, C Constants, C, C
6290 @section C operators
6293 Operators must be defined on values of specific types. For instance,
6294 @code{+} is defined on numbers, but not on structures. Operators are
6295 often defined on groups of types.
6298 For the purposes of C and C++, the following definitions hold:
6304 @emph{Integral types} include @code{int} with any of its storage-class
6305 specifiers; @code{char}; and @code{enum}.
6308 @emph{Integral types} include @code{int} with any of its storage-class
6309 specifiers; @code{char}; @code{enum}; and, for C++, @code{bool}.
6313 @emph{Floating-point types} include @code{float} and @code{double}.
6316 @emph{Pointer types} include all types defined as @code{(@var{type}
6320 @emph{Scalar types} include all of the above.
6324 The following operators are supported. They are listed here
6325 in order of increasing precedence:
6329 The comma or sequencing operator. Expressions in a comma-separated list
6330 are evaluated from left to right, with the result of the entire
6331 expression being the last expression evaluated.
6334 Assignment. The value of an assignment expression is the value
6335 assigned. Defined on scalar types.
6338 Used in an expression of the form @w{@code{@var{a} @var{op}= @var{b}}},
6339 and translated to @w{@code{@var{a} = @var{a op b}}}.
6340 @w{@code{@var{op}=}} and @code{=} have the same precendence.
6341 @var{op} is any one of the operators @code{|}, @code{^}, @code{&},
6342 @code{<<}, @code{>>}, @code{+}, @code{-}, @code{*}, @code{/}, @code{%}.
6345 The ternary operator. @code{@var{a} ? @var{b} : @var{c}} can be thought
6346 of as: if @var{a} then @var{b} else @var{c}. @var{a} should be of an
6350 Logical @sc{or}. Defined on integral types.
6353 Logical @sc{and}. Defined on integral types.
6356 Bitwise @sc{or}. Defined on integral types.
6359 Bitwise exclusive-@sc{or}. Defined on integral types.
6362 Bitwise @sc{and}. Defined on integral types.
6365 Equality and inequality. Defined on scalar types. The value of these
6366 expressions is 0 for false and non-zero for true.
6368 @item <@r{, }>@r{, }<=@r{, }>=
6369 Less than, greater than, less than or equal, greater than or equal.
6370 Defined on scalar types. The value of these expressions is 0 for false
6371 and non-zero for true.
6374 left shift, and right shift. Defined on integral types.
6377 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
6380 Addition and subtraction. Defined on integral types, floating-point types and
6383 @item *@r{, }/@r{, }%
6384 Multiplication, division, and modulus. Multiplication and division are
6385 defined on integral and floating-point types. Modulus is defined on
6389 Increment and decrement. When appearing before a variable, the
6390 operation is performed before the variable is used in an expression;
6391 when appearing after it, the variable's value is used before the
6392 operation takes place.
6395 Pointer dereferencing. Defined on pointer types. Same precedence as
6399 Address operator. Defined on variables. Same precedence as @code{++}.
6402 For debugging C++, @value{GDBN} implements a use of @samp{&} beyond what is
6403 allowed in the C++ language itself: you can use @samp{&(&@var{ref})}
6404 (or, if you prefer, simply @samp{&&@var{ref}}) to examine the address
6405 where a C++ reference variable (declared with @samp{&@var{ref}}) is
6410 Negative. Defined on integral and floating-point types. Same
6411 precedence as @code{++}.
6414 Logical negation. Defined on integral types. Same precedence as
6418 Bitwise complement operator. Defined on integral types. Same precedence as
6423 Structure member, and pointer-to-structure member. For convenience,
6424 @value{GDBN} regards the two as equivalent, choosing whether to dereference a
6425 pointer based on the stored type information.
6426 Defined on @code{struct} and @code{union} data.
6430 Dereferences of pointers to members.
6434 Array indexing. @code{@var{a}[@var{i}]} is defined as
6435 @code{*(@var{a}+@var{i})}. Same precedence as @code{->}.
6438 Function parameter list. Same precedence as @code{->}.
6442 C++ scope resolution operator. Defined on
6443 @code{struct}, @code{union}, and @code{class} types.
6451 represent the @value{GDBN} scope operator (@pxref{Expressions,
6454 Same precedence as @code{::}, above.
6459 If an operator is redefined in the user code, @value{GDBN} usually
6460 attempts to invoke the redefined version instead of using the operator's
6470 @node C Constants, Cplus expressions, C Operators, C
6471 @subsubsection C and C++ constants
6474 @node C Constants, Cplus expressions, C Operators, Support
6475 @subsubsection C and C++ constants
6478 @cindex C and C++ constants
6479 @value{GDBN} allows you to express the constants of C and C++ in the
6484 @node C Constants, Debugging C, C Operators, C
6485 @section C constants
6487 @value{GDBN} allows you to express the constants of C in the
6493 Integer constants are a sequence of digits. Octal constants are
6494 specified by a leading @samp{0} (i.e. zero), and hexadecimal constants by
6495 a leading @samp{0x} or @samp{0X}. Constants may also end with a letter
6496 @samp{l}, specifying that the constant should be treated as a
6500 Floating point constants are a sequence of digits, followed by a decimal
6501 point, followed by a sequence of digits, and optionally followed by an
6502 exponent. An exponent is of the form:
6503 @samp{@w{e@r{[[}+@r{]|}-@r{]}@var{nnn}}}, where @var{nnn} is another
6504 sequence of digits. The @samp{+} is optional for positive exponents.
6507 Enumerated constants consist of enumerated identifiers, or their
6508 integral equivalents.
6511 Character constants are a single character surrounded by single quotes
6512 (@code{'}), or a number---the ordinal value of the corresponding character
6513 (usually its @sc{ASCII} value). Within quotes, the single character may
6514 be represented by a letter or by @dfn{escape sequences}, which are of
6515 the form @samp{\@var{nnn}}, where @var{nnn} is the octal representation
6516 of the character's ordinal value; or of the form @samp{\@var{x}}, where
6517 @samp{@var{x}} is a predefined special character---for example,
6518 @samp{\n} for newline.
6521 String constants are a sequence of character constants surrounded
6522 by double quotes (@code{"}).
6525 Pointer constants are an integral value. You can also write pointers
6526 to constants using the C operator @samp{&}.
6529 Array constants are comma-separated lists surrounded by braces @samp{@{}
6530 and @samp{@}}; for example, @samp{@{1,2,3@}} is a three-element array of
6531 integers, @samp{@{@{1,2@}, @{3,4@}, @{5,6@}@}} is a three-by-two array,
6532 and @samp{@{&"hi", &"there", &"fred"@}} is a three-element array of pointers.
6537 * Cplus expressions::
6547 @node Cplus expressions, C Defaults, C Constants, C
6548 @subsubsection C++ expressions
6551 @node Cplus expressions, C Defaults, C Constants, Support
6552 @subsubsection C++ expressions
6555 @cindex expressions in C++
6556 @value{GDBN} expression handling can interpret most C++ expressions.
6559 @cindex C++ support, not in @sc{coff}
6560 @cindex @sc{coff} versus C++
6561 @cindex C++ and object formats
6562 @cindex object formats and C++
6563 @cindex a.out and C++
6564 @cindex @sc{ecoff} and C++
6565 @cindex @sc{xcoff} and C++
6566 @cindex @sc{elf}/stabs and C++
6567 @cindex @sc{elf}/@sc{dwarf} and C++
6568 @c FIXME!! GDB may eventually be able to debug C++ using DWARF; check
6569 @c periodically whether this has happened...
6571 @emph{Warning:} @value{GDBN} can only debug C++ code if you compile with
6572 the @sc{gnu} C++ compiler. Moreover, C++ debugging depends on the use of
6573 additional debugging information in the symbol table, and thus requires
6574 special support. @value{GDBN} has this support @emph{only} with the
6575 stabs debug format. In particular, if your compiler generates a.out,
6576 MIPS @sc{ecoff}, RS/6000 @sc{xcoff}, or @sc{elf} with stabs extensions
6577 to the symbol table, these facilities are all available. (With @sc{gnu} CC,
6578 you can use the @samp{-gstabs} option to request stabs debugging
6579 extensions explicitly.) Where the object code format is standard
6580 @sc{coff} or @sc{dwarf} in @sc{elf}, on the other hand, most of the C++
6581 support in @value{GDBN} does @emph{not} work.
6587 @cindex member functions
6589 Member function calls are allowed; you can use expressions like
6592 count = aml->GetOriginal(x, y)
6596 @cindex namespace in C++
6598 While a member function is active (in the selected stack frame), your
6599 expressions have the same namespace available as the member function;
6600 that is, @value{GDBN} allows implicit references to the class instance
6601 pointer @code{this} following the same rules as C++.
6604 @cindex call overloaded functions
6605 @cindex type conversions in C++
6607 You can call overloaded functions; @value{GDBN} resolves the function
6608 call to the right definition, with one restriction---you must use
6609 arguments of the type required by the function that you want to call.
6610 @value{GDBN} does not perform conversions requiring constructors or
6611 user-defined type operators.
6614 @cindex call overloaded functions
6615 @cindex overloaded functions
6616 @cindex type conversions in C++
6618 You can call overloaded functions; @value{GDBN} resolves the function
6619 call to the right definition, with some restrictions. GDB does not
6620 perform overload resolution involving user-defined type conversions,
6621 calls to constructors, or instantiations of templates that do not exist
6622 in the program. It also cannot handle ellipsis argument lists or
6625 It does perform integral conversions and promotions, floating-point
6626 promotions, arithmetic conversions, pointer conversions, conversions of
6627 class objects to base classes, and standard conversions such as those of
6628 functions or arrays to pointers; it requires an exact match on the
6629 number of function arguments.
6631 Overload resolution is always performed, unless you have specified
6632 @code{set overload-resolution off}. @xref{Debugging C plus plus,
6633 ,@value{GDBN} features for C++}.
6635 You must specify@code{set overload-resolution off} in order to use an
6636 explicit function signature to call an overloaded function, as in
6638 p 'foo(char,int)'('x', 13)
6640 The @value{GDBN} command-completion facility can simplify this;
6641 @pxref{Completion, ,Command completion}.
6645 @cindex reference declarations
6647 @value{GDBN} understands variables declared as C++ references; you can use
6648 them in expressions just as you do in C++ source---they are automatically
6651 In the parameter list shown when @value{GDBN} displays a frame, the values of
6652 reference variables are not displayed (unlike other variables); this
6653 avoids clutter, since references are often used for large structures.
6654 The @emph{address} of a reference variable is always shown, unless
6655 you have specified @samp{set print address off}.
6658 @value{GDBN} supports the C++ name resolution operator @code{::}---your
6659 expressions can use it just as expressions in your program do. Since
6660 one scope may be defined in another, you can use @code{::} repeatedly if
6661 necessary, for example in an expression like
6662 @samp{@var{scope1}::@var{scope2}::@var{name}}. @value{GDBN} also allows
6663 resolving name scope by reference to source files, in both C and C++
6664 debugging (@pxref{Variables, ,Program variables}).
6668 In addition, @value{GDBN} supports calling virtual functions correctly,
6669 printing out virtual bases of objects, calling functions in a base
6670 subobject, casting objects, and invoking user-defined operators.
6674 @node C Defaults, C Checks, Cplus expressions, C
6675 @subsubsection C and C++ defaults
6678 @node C Defaults, Debugging C, Cplus expressions, Support
6679 @subsubsection C and C++ defaults
6681 @cindex C and C++ defaults
6684 If you allow @value{GDBN} to set type and range checking automatically, they
6685 both default to @code{off} whenever the working language changes to
6686 C or C++. This happens regardless of whether you or @value{GDBN}
6687 selects the working language.
6690 If you allow @value{GDBN} to set the language automatically, it recognizes
6691 source files whose names end with @file{.c}, @file{.C}, or @file{.cc}, and
6692 when @value{GDBN} enters code compiled from one of these files,
6693 it sets the working language to C or C++.
6694 @xref{Automatically, ,Having @value{GDBN} infer the source language}, for
6698 @c Type checking is (a) primarily motivated by Modula-2, and (b)
6699 @c unimplemented. If (b) changes, it might make sense to let this node
6700 @c appear even if Mod-2 does not, but meanwhile ignore it. roland 16jul93.
6701 @node C Checks, Debugging C, C Defaults, C Constants
6702 @subsubsection C and C++ type and range checks
6703 @cindex C and C++ checks
6705 By default, when @value{GDBN} parses C or C++ expressions, type checking
6706 is not used. However, if you turn type checking on, @value{GDBN}
6707 considers two variables type equivalent if:
6711 The two variables are structured and have the same structure, union, or
6715 The two variables have the same type name, or types that have been
6716 declared equivalent through @code{typedef}.
6719 @c leaving this out because neither J Gilmore nor R Pesch understand it.
6722 The two @code{struct}, @code{union}, or @code{enum} variables are
6723 declared in the same declaration. (Note: this may not be true for all C
6728 Range checking, if turned on, is done on mathematical operations. Array
6729 indices are not checked, since they are often used to index a pointer
6730 that is not itself an array.
6736 @node Debugging C, Debugging C plus plus, C Checks, C
6737 @subsubsection @value{GDBN} and C
6740 @node Debugging C, Debugging C plus plus, C Defaults, Support
6741 @subsubsection @value{GDBN} and C
6745 @node Debugging C, , C Constants, C
6746 @section @value{GDBN} and C
6749 The @code{set print union} and @code{show print union} commands apply to
6750 the @code{union} type. When set to @samp{on}, any @code{union} that is
6751 inside a @code{struct}
6756 Otherwise, it appears as @samp{@{...@}}.
6758 The @code{@@} operator aids in the debugging of dynamic arrays, formed
6759 with pointers and a memory allocation function. @xref{Expressions,
6764 * Debugging C plus plus::
6768 @node Debugging C plus plus, , Debugging C, C
6769 @subsubsection @value{GDBN} features for C++
6772 @node Debugging C plus plus, , Debugging C, Support
6773 @subsubsection @value{GDBN} features for C++
6776 @cindex commands for C++
6777 Some @value{GDBN} commands are particularly useful with C++, and some are
6778 designed specifically for use with C++. Here is a summary:
6781 @cindex break in overloaded functions
6782 @item @r{breakpoint menus}
6783 When you want a breakpoint in a function whose name is overloaded,
6784 @value{GDBN} breakpoint menus help you specify which function definition
6785 you want. @xref{Breakpoint Menus,,Breakpoint menus}.
6787 @cindex overloading in C++
6788 @item rbreak @var{regex}
6789 Setting breakpoints using regular expressions is helpful for setting
6790 breakpoints on overloaded functions that are not members of any special
6792 @xref{Set Breaks, ,Setting breakpoints}.
6794 @cindex C++ exception handling
6797 Debug C++ exception handling using these commands. @xref{Set
6798 Catchpoints, , Setting catchpoints}.
6801 @item ptype @var{typename}
6802 Print inheritance relationships as well as other information for type
6804 @xref{Symbols, ,Examining the Symbol Table}.
6806 @cindex C++ symbol display
6807 @item set print demangle
6808 @itemx show print demangle
6809 @itemx set print asm-demangle
6810 @itemx show print asm-demangle
6811 Control whether C++ symbols display in their source form, both when
6812 displaying code as C++ source and when displaying disassemblies.
6813 @xref{Print Settings, ,Print settings}.
6815 @item set print object
6816 @itemx show print object
6817 Choose whether to print derived (actual) or declared types of objects.
6818 @xref{Print Settings, ,Print settings}.
6820 @item set print vtbl
6821 @itemx show print vtbl
6822 Control the format for printing virtual function tables.
6823 @xref{Print Settings, ,Print settings}.
6825 (The @code{vtbl} commands do not work on programs compiled with the HP
6826 ANSI C++ compiler (@code{aCC}).)
6828 @kindex set overload-resolution
6829 @cindex overloaded functions
6830 @item set overload-resolution on
6831 Enable overload resolution for C++ expression evaluation. The default
6832 is on. For overloaded functions, @value{GDBN} evaluates the arguments
6833 and searches for a function whose signature matches the argument types,
6834 using the standard C++ conversion rules (@pxref{Cplus expressions, ,C++
6835 expressions} for details). If it cannot find a match, it emits a
6838 @item set overload-resolution off
6839 Disable overload resolution for C++ expression evaluation. For
6840 overloaded functions that are not class member functions, @value{GDBN}
6841 chooses the first function of the specified name that it finds in the
6842 symbol table, whether or not its arguments are of the correct type. For
6843 overloaded functions that are class member functions, @value{GDBN}
6844 searches for a function whose signature @emph{exactly} matches the
6848 @item @r{Overloaded symbol names}
6849 You can specify a particular definition of an overloaded symbol, using
6850 the same notation that is used to declare such symbols in C++: type
6851 @code{@var{symbol}(@var{types})} rather than just @var{symbol}. You can
6852 also use the @value{GDBN} command-line word completion facilities to list the
6853 available choices, or to finish the type list for you.
6854 @xref{Completion,, Command completion}, for details on how to do this.
6857 @c cancels "raisesections" under same conditions near bgn of chapter
6862 @node Modula-2, ,C , Support
6863 @subsection Modula-2
6866 The extensions made to @value{GDBN} to support Modula-2 only support
6867 output from the @sc{gnu} Modula-2 compiler (which is currently being
6868 developed). Other Modula-2 compilers are not currently supported, and
6869 attempting to debug executables produced by them is most likely
6870 to give an error as @value{GDBN} reads in the executable's symbol
6873 @cindex expressions in Modula-2
6875 * M2 Operators:: Built-in operators
6876 * Built-In Func/Proc:: Built-in functions and procedures
6877 * M2 Constants:: Modula-2 constants
6878 * M2 Defaults:: Default settings for Modula-2
6879 * Deviations:: Deviations from standard Modula-2
6880 * M2 Checks:: Modula-2 type and range checks
6881 * M2 Scope:: The scope operators @code{::} and @code{.}
6882 * GDB/M2:: @value{GDBN} and Modula-2
6885 @node M2 Operators, Built-In Func/Proc, Modula-2, Modula-2
6886 @subsubsection Operators
6887 @cindex Modula-2 operators
6889 Operators must be defined on values of specific types. For instance,
6890 @code{+} is defined on numbers, but not on structures. Operators are
6891 often defined on groups of types. For the purposes of Modula-2, the
6892 following definitions hold:
6897 @emph{Integral types} consist of @code{INTEGER}, @code{CARDINAL}, and
6901 @emph{Character types} consist of @code{CHAR} and its subranges.
6904 @emph{Floating-point types} consist of @code{REAL}.
6907 @emph{Pointer types} consist of anything declared as @code{POINTER TO
6911 @emph{Scalar types} consist of all of the above.
6914 @emph{Set types} consist of @code{SET} and @code{BITSET} types.
6917 @emph{Boolean types} consist of @code{BOOLEAN}.
6921 The following operators are supported, and appear in order of
6922 increasing precedence:
6926 Function argument or array index separator.
6929 Assignment. The value of @var{var} @code{:=} @var{value} is
6933 Less than, greater than on integral, floating-point, or enumerated
6937 Less than, greater than, less than or equal to, greater than or equal to
6938 on integral, floating-point and enumerated types, or set inclusion on
6939 set types. Same precedence as @code{<}.
6941 @item =@r{, }<>@r{, }#
6942 Equality and two ways of expressing inequality, valid on scalar types.
6943 Same precedence as @code{<}. In @value{GDBN} scripts, only @code{<>} is
6944 available for inequality, since @code{#} conflicts with the script
6948 Set membership. Defined on set types and the types of their members.
6949 Same precedence as @code{<}.
6952 Boolean disjunction. Defined on boolean types.
6955 Boolean conjuction. Defined on boolean types.
6958 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
6961 Addition and subtraction on integral and floating-point types, or union
6962 and difference on set types.
6965 Multiplication on integral and floating-point types, or set intersection
6969 Division on floating-point types, or symmetric set difference on set
6970 types. Same precedence as @code{*}.
6973 Integer division and remainder. Defined on integral types. Same
6974 precedence as @code{*}.
6977 Negative. Defined on @code{INTEGER} and @code{REAL} data.
6980 Pointer dereferencing. Defined on pointer types.
6983 Boolean negation. Defined on boolean types. Same precedence as
6987 @code{RECORD} field selector. Defined on @code{RECORD} data. Same
6988 precedence as @code{^}.
6991 Array indexing. Defined on @code{ARRAY} data. Same precedence as @code{^}.
6994 Procedure argument list. Defined on @code{PROCEDURE} objects. Same precedence
6998 @value{GDBN} and Modula-2 scope operators.
7002 @emph{Warning:} Sets and their operations are not yet supported, so @value{GDBN}
7003 treats the use of the operator @code{IN}, or the use of operators
7004 @code{+}, @code{-}, @code{*}, @code{/}, @code{=}, , @code{<>}, @code{#},
7005 @code{<=}, and @code{>=} on sets as an error.
7008 @cindex Modula-2 built-ins
7009 @node Built-In Func/Proc, M2 Constants, M2 Operators, Modula-2
7010 @subsubsection Built-in functions and procedures
7012 Modula-2 also makes available several built-in procedures and functions.
7013 In describing these, the following metavariables are used:
7018 represents an @code{ARRAY} variable.
7021 represents a @code{CHAR} constant or variable.
7024 represents a variable or constant of integral type.
7027 represents an identifier that belongs to a set. Generally used in the
7028 same function with the metavariable @var{s}. The type of @var{s} should
7029 be @code{SET OF @var{mtype}} (where @var{mtype} is the type of @var{m}).
7032 represents a variable or constant of integral or floating-point type.
7035 represents a variable or constant of floating-point type.
7041 represents a variable.
7044 represents a variable or constant of one of many types. See the
7045 explanation of the function for details.
7048 All Modula-2 built-in procedures also return a result, described below.
7052 Returns the absolute value of @var{n}.
7055 If @var{c} is a lower case letter, it returns its upper case
7056 equivalent, otherwise it returns its argument
7059 Returns the character whose ordinal value is @var{i}.
7062 Decrements the value in the variable @var{v}. Returns the new value.
7064 @item DEC(@var{v},@var{i})
7065 Decrements the value in the variable @var{v} by @var{i}. Returns the
7068 @item EXCL(@var{m},@var{s})
7069 Removes the element @var{m} from the set @var{s}. Returns the new
7072 @item FLOAT(@var{i})
7073 Returns the floating point equivalent of the integer @var{i}.
7076 Returns the index of the last member of @var{a}.
7079 Increments the value in the variable @var{v}. Returns the new value.
7081 @item INC(@var{v},@var{i})
7082 Increments the value in the variable @var{v} by @var{i}. Returns the
7085 @item INCL(@var{m},@var{s})
7086 Adds the element @var{m} to the set @var{s} if it is not already
7087 there. Returns the new set.
7090 Returns the maximum value of the type @var{t}.
7093 Returns the minimum value of the type @var{t}.
7096 Returns boolean TRUE if @var{i} is an odd number.
7099 Returns the ordinal value of its argument. For example, the ordinal
7100 value of a character is its ASCII value (on machines supporting the
7101 ASCII character set). @var{x} must be of an ordered type, which include
7102 integral, character and enumerated types.
7105 Returns the size of its argument. @var{x} can be a variable or a type.
7107 @item TRUNC(@var{r})
7108 Returns the integral part of @var{r}.
7110 @item VAL(@var{t},@var{i})
7111 Returns the member of the type @var{t} whose ordinal value is @var{i}.
7115 @emph{Warning:} Sets and their operations are not yet supported, so
7116 @value{GDBN} treats the use of procedures @code{INCL} and @code{EXCL} as
7120 @cindex Modula-2 constants
7121 @node M2 Constants, M2 Defaults, Built-In Func/Proc, Modula-2
7122 @subsubsection Constants
7124 @value{GDBN} allows you to express the constants of Modula-2 in the following
7130 Integer constants are simply a sequence of digits. When used in an
7131 expression, a constant is interpreted to be type-compatible with the
7132 rest of the expression. Hexadecimal integers are specified by a
7133 trailing @samp{H}, and octal integers by a trailing @samp{B}.
7136 Floating point constants appear as a sequence of digits, followed by a
7137 decimal point and another sequence of digits. An optional exponent can
7138 then be specified, in the form @samp{E@r{[}+@r{|}-@r{]}@var{nnn}}, where
7139 @samp{@r{[}+@r{|}-@r{]}@var{nnn}} is the desired exponent. All of the
7140 digits of the floating point constant must be valid decimal (base 10)
7144 Character constants consist of a single character enclosed by a pair of
7145 like quotes, either single (@code{'}) or double (@code{"}). They may
7146 also be expressed by their ordinal value (their ASCII value, usually)
7147 followed by a @samp{C}.
7150 String constants consist of a sequence of characters enclosed by a
7151 pair of like quotes, either single (@code{'}) or double (@code{"}).
7152 Escape sequences in the style of C are also allowed. @xref{C
7153 Constants, ,C and C++ constants}, for a brief explanation of escape
7157 Enumerated constants consist of an enumerated identifier.
7160 Boolean constants consist of the identifiers @code{TRUE} and
7164 Pointer constants consist of integral values only.
7167 Set constants are not yet supported.
7170 @node M2 Defaults, Deviations, M2 Constants, Modula-2
7171 @subsubsection Modula-2 defaults
7172 @cindex Modula-2 defaults
7174 If type and range checking are set automatically by @value{GDBN}, they
7175 both default to @code{on} whenever the working language changes to
7176 Modula-2. This happens regardless of whether you, or @value{GDBN},
7177 selected the working language.
7179 If you allow @value{GDBN} to set the language automatically, then entering
7180 code compiled from a file whose name ends with @file{.mod} sets the
7181 working language to Modula-2. @xref{Automatically, ,Having @value{GDBN} set
7182 the language automatically}, for further details.
7184 @node Deviations, M2 Checks, M2 Defaults, Modula-2
7185 @subsubsection Deviations from standard Modula-2
7186 @cindex Modula-2, deviations from
7188 A few changes have been made to make Modula-2 programs easier to debug.
7189 This is done primarily via loosening its type strictness:
7193 Unlike in standard Modula-2, pointer constants can be formed by
7194 integers. This allows you to modify pointer variables during
7195 debugging. (In standard Modula-2, the actual address contained in a
7196 pointer variable is hidden from you; it can only be modified
7197 through direct assignment to another pointer variable or expression that
7198 returned a pointer.)
7201 C escape sequences can be used in strings and characters to represent
7202 non-printable characters. @value{GDBN} prints out strings with these
7203 escape sequences embedded. Single non-printable characters are
7204 printed using the @samp{CHR(@var{nnn})} format.
7207 The assignment operator (@code{:=}) returns the value of its right-hand
7211 All built-in procedures both modify @emph{and} return their argument.
7214 @node M2 Checks, M2 Scope, Deviations, Modula-2
7215 @subsubsection Modula-2 type and range checks
7216 @cindex Modula-2 checks
7219 @emph{Warning:} in this release, @value{GDBN} does not yet perform type or
7222 @c FIXME remove warning when type/range checks added
7224 @value{GDBN} considers two Modula-2 variables type equivalent if:
7228 They are of types that have been declared equivalent via a @code{TYPE
7229 @var{t1} = @var{t2}} statement
7232 They have been declared on the same line. (Note: This is true of the
7233 @sc{gnu} Modula-2 compiler, but it may not be true of other compilers.)
7236 As long as type checking is enabled, any attempt to combine variables
7237 whose types are not equivalent is an error.
7239 Range checking is done on all mathematical operations, assignment, array
7240 index bounds, and all built-in functions and procedures.
7242 @node M2 Scope, GDB/M2, M2 Checks, Modula-2
7243 @subsubsection The scope operators @code{::} and @code{.}
7246 @cindex colon, doubled as scope operator
7249 @c Info cannot handle :: but TeX can.
7255 There are a few subtle differences between the Modula-2 scope operator
7256 (@code{.}) and the @value{GDBN} scope operator (@code{::}). The two have
7261 @var{module} . @var{id}
7262 @var{scope} :: @var{id}
7266 where @var{scope} is the name of a module or a procedure,
7267 @var{module} the name of a module, and @var{id} is any declared
7268 identifier within your program, except another module.
7270 Using the @code{::} operator makes @value{GDBN} search the scope
7271 specified by @var{scope} for the identifier @var{id}. If it is not
7272 found in the specified scope, then @value{GDBN} searches all scopes
7273 enclosing the one specified by @var{scope}.
7275 Using the @code{.} operator makes @value{GDBN} search the current scope for
7276 the identifier specified by @var{id} that was imported from the
7277 definition module specified by @var{module}. With this operator, it is
7278 an error if the identifier @var{id} was not imported from definition
7279 module @var{module}, or if @var{id} is not an identifier in
7282 @node GDB/M2, , M2 Scope, Modula-2
7283 @subsubsection @value{GDBN} and Modula-2
7285 Some @value{GDBN} commands have little use when debugging Modula-2 programs.
7286 Five subcommands of @code{set print} and @code{show print} apply
7287 specifically to C and C++: @samp{vtbl}, @samp{demangle},
7288 @samp{asm-demangle}, @samp{object}, and @samp{union}. The first four
7289 apply to C++, and the last to the C @code{union} type, which has no direct
7290 analogue in Modula-2.
7292 The @code{@@} operator (@pxref{Expressions, ,Expressions}), while available
7293 while using any language, is not useful with Modula-2. Its
7294 intent is to aid the debugging of @dfn{dynamic arrays}, which cannot be
7295 created in Modula-2 as they can in C or C++. However, because an
7296 address can be specified by an integral constant, the construct
7297 @samp{@{@var{type}@}@var{adrexp}} is still useful. (@pxref{Expressions, ,Expressions})
7299 @cindex @code{#} in Modula-2
7300 In @value{GDBN} scripts, the Modula-2 inequality operator @code{#} is
7301 interpreted as the beginning of a comment. Use @code{<>} instead.
7305 @node Symbols, Altering, Languages, Top
7306 @chapter Examining the Symbol Table
7308 The commands described in this section allow you to inquire about the
7309 symbols (names of variables, functions and types) defined in your
7310 program. This information is inherent in the text of your program and
7311 does not change as your program executes. @value{GDBN} finds it in your
7312 program's symbol table, in the file indicated when you started @value{GDBN}
7313 (@pxref{File Options, ,Choosing files}), or by one of the
7314 file-management commands (@pxref{Files, ,Commands to specify files}).
7316 @cindex symbol names
7317 @cindex names of symbols
7318 @cindex quoting names
7319 Occasionally, you may need to refer to symbols that contain unusual
7320 characters, which @value{GDBN} ordinarily treats as word delimiters. The
7321 most frequent case is in referring to static variables in other
7322 source files (@pxref{Variables,,Program variables}). File names
7323 are recorded in object files as debugging symbols, but @value{GDBN} would
7324 ordinarily parse a typical file name, like @file{foo.c}, as the three words
7325 @samp{foo} @samp{.} @samp{c}. To allow @value{GDBN} to recognize
7326 @samp{foo.c} as a single symbol, enclose it in single quotes; for example,
7333 looks up the value of @code{x} in the scope of the file @file{foo.c}.
7336 @kindex info address
7337 @item info address @var{symbol}
7338 Describe where the data for @var{symbol} is stored. For a register
7339 variable, this says which register it is kept in. For a non-register
7340 local variable, this prints the stack-frame offset at which the variable
7343 Note the contrast with @samp{print &@var{symbol}}, which does not work
7344 at all for a register variable, and for a stack local variable prints
7345 the exact address of the current instantiation of the variable.
7348 @item whatis @var{exp}
7349 Print the data type of expression @var{exp}. @var{exp} is not
7350 actually evaluated, and any side-effecting operations (such as
7351 assignments or function calls) inside it do not take place.
7352 @xref{Expressions, ,Expressions}.
7355 Print the data type of @code{$}, the last value in the value history.
7358 @item ptype @var{typename}
7359 Print a description of data type @var{typename}. @var{typename} may be
7360 the name of a type, or for C code it may have the form
7362 @samp{class @var{class-name}},
7364 @samp{struct @var{struct-tag}}, @samp{union @var{union-tag}} or
7365 @samp{enum @var{enum-tag}}.
7367 @item ptype @var{exp}
7369 Print a description of the type of expression @var{exp}. @code{ptype}
7370 differs from @code{whatis} by printing a detailed description, instead
7371 of just the name of the type.
7373 For example, for this variable declaration:
7376 struct complex @{double real; double imag;@} v;
7380 the two commands give this output:
7384 (@value{GDBP}) whatis v
7385 type = struct complex
7386 (@value{GDBP}) ptype v
7387 type = struct complex @{
7395 As with @code{whatis}, using @code{ptype} without an argument refers to
7396 the type of @code{$}, the last value in the value history.
7399 @item info types @var{regexp}
7401 Print a brief description of all types whose name matches @var{regexp}
7402 (or all types in your program, if you supply no argument). Each
7403 complete typename is matched as though it were a complete line; thus,
7404 @samp{i type value} gives information on all types in your program whose
7405 name includes the string @code{value}, but @samp{i type ^value$} gives
7406 information only on types whose complete name is @code{value}.
7408 This command differs from @code{ptype} in two ways: first, like
7409 @code{whatis}, it does not print a detailed description; second, it
7410 lists all source files where a type is defined.
7414 Show the name of the current source file---that is, the source file for
7415 the function containing the current point of execution---and the language
7418 @kindex info sources
7420 Print the names of all source files in your program for which there is
7421 debugging information, organized into two lists: files whose symbols
7422 have already been read, and files whose symbols will be read when needed.
7424 @kindex info functions
7425 @item info functions
7426 Print the names and data types of all defined functions.
7428 @item info functions @var{regexp}
7429 Print the names and data types of all defined functions
7430 whose names contain a match for regular expression @var{regexp}.
7431 Thus, @samp{info fun step} finds all functions whose names
7432 include @code{step}; @samp{info fun ^step} finds those whose names
7433 start with @code{step}.
7435 @kindex info variables
7436 @item info variables
7437 Print the names and data types of all variables that are declared
7438 outside of functions (i.e., excluding local variables).
7440 @item info variables @var{regexp}
7441 Print the names and data types of all variables (except for local
7442 variables) whose names contain a match for regular expression
7446 This was never implemented.
7447 @kindex info methods
7449 @itemx info methods @var{regexp}
7450 The @code{info methods} command permits the user to examine all defined
7451 methods within C++ program, or (with the @var{regexp} argument) a
7452 specific set of methods found in the various C++ classes. Many
7453 C++ classes provide a large number of methods. Thus, the output
7454 from the @code{ptype} command can be overwhelming and hard to use. The
7455 @code{info-methods} command filters the methods, printing only those
7456 which match the regular-expression @var{regexp}.
7460 @cindex reloading symbols
7461 Some systems allow individual object files that make up your program to
7462 be replaced without stopping and restarting your program.
7464 For example, in VxWorks you can simply recompile a defective object file
7465 and keep on running.
7467 If you are running on one of these systems, you can allow @value{GDBN} to
7468 reload the symbols for automatically relinked modules:
7471 @kindex set symbol-reloading
7472 @item set symbol-reloading on
7473 Replace symbol definitions for the corresponding source file when an
7474 object file with a particular name is seen again.
7476 @item set symbol-reloading off
7477 Do not replace symbol definitions when re-encountering object files of
7478 the same name. This is the default state; if you are not running on a
7479 system that permits automatically relinking modules, you should leave
7480 @code{symbol-reloading} off, since otherwise @value{GDBN} may discard symbols
7481 when linking large programs, that may contain several modules (from
7482 different directories or libraries) with the same name.
7484 @kindex show symbol-reloading
7485 @item show symbol-reloading
7486 Show the current @code{on} or @code{off} setting.
7491 @kindex set opaque-type-resolution
7492 @item set opaque-type-resolution on
7493 Tell @value{GDBN} to resolve opaque types. An opaque type is a type
7494 declared as a pointer to a @code{struct}, @code{class}, or
7495 @code{union}---for example, @code{struct MyType *}---that is used in one
7496 source file although the full declaration of @code{struct MyType} is in
7497 another source file. The default is on.
7499 A change in the setting of this subcommand will not take effect until
7500 the next time symbols for a file are loaded.
7502 @item set opaque-type-resolution off
7503 Tell @value{GDBN} not to resolve opaque types. In this case, the type
7504 is printed as follows:
7506 @{<no data fields>@}
7509 @kindex show opaque-type-resolution
7510 @item show opaque-type-resolution
7511 Show whether opaque types are resolved or not.
7514 @kindex maint print symbols
7516 @kindex maint print psymbols
7517 @cindex partial symbol dump
7518 @item maint print symbols @var{filename}
7519 @itemx maint print psymbols @var{filename}
7520 @itemx maint print msymbols @var{filename}
7521 Write a dump of debugging symbol data into the file @var{filename}.
7522 These commands are used to debug the @value{GDBN} symbol-reading code. Only
7523 symbols with debugging data are included. If you use @samp{maint print
7524 symbols}, @value{GDBN} includes all the symbols for which it has already
7525 collected full details: that is, @var{filename} reflects symbols for
7526 only those files whose symbols @value{GDBN} has read. You can use the
7527 command @code{info sources} to find out which files these are. If you
7528 use @samp{maint print psymbols} instead, the dump shows information about
7529 symbols that @value{GDBN} only knows partially---that is, symbols defined in
7530 files that @value{GDBN} has skimmed, but not yet read completely. Finally,
7531 @samp{maint print msymbols} dumps just the minimal symbol information
7532 required for each object file from which @value{GDBN} has read some symbols.
7533 @xref{Files, ,Commands to specify files}, for a discussion of how
7534 @value{GDBN} reads symbols (in the description of @code{symbol-file}).
7537 @node Altering, GDB Files, Symbols, Top
7538 @chapter Altering Execution
7540 Once you think you have found an error in your program, you might want to
7541 find out for certain whether correcting the apparent error would lead to
7542 correct results in the rest of the run. You can find the answer by
7543 experiment, using the @value{GDBN} features for altering execution of the
7546 For example, you can store new values into variables or memory
7549 give your program a signal, restart it
7552 restart your program
7554 at a different address, or even return prematurely from a function.
7557 * Assignment:: Assignment to variables
7558 * Jumping:: Continuing at a different address
7560 * Signaling:: Giving your program a signal
7563 * Returning:: Returning from a function
7564 * Calling:: Calling your program's functions
7565 * Patching:: Patching your program
7568 @node Assignment, Jumping, Altering, Altering
7569 @section Assignment to variables
7572 @cindex setting variables
7573 To alter the value of a variable, evaluate an assignment expression.
7574 @xref{Expressions, ,Expressions}. For example,
7581 stores the value 4 into the variable @code{x}, and then prints the
7582 value of the assignment expression (which is 4).
7584 @xref{Languages, ,Using @value{GDBN} with Different Languages}, for more
7585 information on operators in supported languages.
7588 @kindex set variable
7589 @cindex variables, setting
7590 If you are not interested in seeing the value of the assignment, use the
7591 @code{set} command instead of the @code{print} command. @code{set} is
7592 really the same as @code{print} except that the expression's value is
7593 not printed and is not put in the value history (@pxref{Value History,
7594 ,Value history}). The expression is evaluated only for its effects.
7597 If the beginning of the argument string of the @code{set} command
7598 appears identical to a @code{set} subcommand, use the @code{set
7599 variable} command instead of just @code{set}. This command is identical
7600 to @code{set} except for its lack of subcommands. For example, if your
7601 program has a variable @code{width}, you get an error if you try to set
7602 a new value with just @samp{set width=13}, because @value{GDBN} has the
7603 command @code{set width}:
7606 (@value{GDBP}) whatis width
7608 (@value{GDBP}) p width
7610 (@value{GDBP}) set width=47
7611 Invalid syntax in expression.
7615 The invalid expression, of course, is @samp{=47}. In
7616 order to actually set the program's variable @code{width}, use
7619 (@value{GDBP}) set var width=47
7623 Because the @code{set} command has many subcommands that can conflict
7624 with the names of program variables, it is a good idea to use the
7625 @code{set variable} command instead of just @code{set}. For example, if
7626 your program has a variable @code{g}, you run into problems if you try
7627 to set a new value with just @samp{set g=4}, because @value{GDBN} has
7628 the command @code{set gnutarget}, abbreviated @code{set g}:
7632 (@value{GDBP}) whatis g
7636 (@value{GDBP}) set g=4
7640 The program being debugged has been started already.
7641 Start it from the beginning? (y or n) y
7642 Starting program: /home/smith/cc_progs/a.out
7643 "/home/smith/cc_progs/a.out": can't open to read symbols: Invalid bfd target.
7644 (@value{GDBP}) show g
7645 The current BFD target is "=4".
7650 The program variable @code{g} did not change, and you silently set the
7651 @code{gnutarget} to an invalid value. In order to set the variable
7655 (@value{GDBP}) set var g=4
7659 @value{GDBN} allows more implicit conversions in assignments than C; you can
7660 freely store an integer value into a pointer variable or vice versa,
7661 and you can convert any structure to any other structure that is the
7662 same length or shorter.
7663 @comment FIXME: how do structs align/pad in these conversions?
7664 @comment /doc@cygnus.com 18dec1990
7666 To store values into arbitrary places in memory, use the @samp{@{@dots{}@}}
7667 construct to generate a value of specified type at a specified address
7668 (@pxref{Expressions, ,Expressions}). For example, @code{@{int@}0x83040} refers
7669 to memory location @code{0x83040} as an integer (which implies a certain size
7670 and representation in memory), and
7673 set @{int@}0x83040 = 4
7677 stores the value 4 into that memory location.
7679 @node Jumping, Signaling, Assignment, Altering
7680 @section Continuing at a different address
7682 Ordinarily, when you continue your program, you do so at the place where
7683 it stopped, with the @code{continue} command. You can instead continue at
7684 an address of your own choosing, with the following commands:
7688 @item jump @var{linespec}
7689 Resume execution at line @var{linespec}. Execution stops again
7690 immediately if there is a breakpoint there. @xref{List, ,Printing
7691 source lines}, for a description of the different forms of
7692 @var{linespec}. It is common practice to use the @code{tbreak} command
7693 in conjunction with @code{jump}. @xref{Set Breaks, ,Setting
7696 The @code{jump} command does not change the current stack frame, or
7697 the stack pointer, or the contents of any memory location or any
7698 register other than the program counter. If line @var{linespec} is in
7699 a different function from the one currently executing, the results may
7700 be bizarre if the two functions expect different patterns of arguments or
7701 of local variables. For this reason, the @code{jump} command requests
7702 confirmation if the specified line is not in the function currently
7703 executing. However, even bizarre results are predictable if you are
7704 well acquainted with the machine-language code of your program.
7706 @item jump *@var{address}
7707 Resume execution at the instruction at address @var{address}.
7711 @c Doesn't work on HP-UX; have to set $pcoqh and $pcoqt.
7712 You can get much the same effect as the @code{jump} command by storing a
7713 new value into the register @code{$pc}. The difference is that this
7714 does not start your program running; it only changes the address of where it
7715 @emph{will} run when you continue. For example,
7722 makes the next @code{continue} command or stepping command execute at
7723 address @code{0x485}, rather than at the address where your program stopped.
7724 @xref{Continuing and Stepping, ,Continuing and stepping}.
7727 The most common occasion to use the @code{jump} command is to back
7728 up---perhaps with more breakpoints set---over a portion of a program
7729 that has already executed, in order to examine its execution in more
7734 @node Signaling, Returning, Jumping, Altering
7735 @section Giving your program a signal
7739 @item signal @var{signal}
7740 Resume execution where your program stopped, but immediately give it the
7741 signal @var{signal}. @var{signal} can be the name or the number of a
7742 signal. For example, on many systems @code{signal 2} and @code{signal
7743 SIGINT} are both ways of sending an interrupt signal.
7745 Alternatively, if @var{signal} is zero, continue execution without
7746 giving a signal. This is useful when your program stopped on account of
7747 a signal and would ordinary see the signal when resumed with the
7748 @code{continue} command; @samp{signal 0} causes it to resume without a
7751 @code{signal} does not repeat when you press @key{RET} a second time
7752 after executing the command.
7756 Invoking the @code{signal} command is not the same as invoking the
7757 @code{kill} utility from the shell. Sending a signal with @code{kill}
7758 causes @value{GDBN} to decide what to do with the signal depending on
7759 the signal handling tables (@pxref{Signals}). The @code{signal} command
7760 passes the signal directly to your program.
7764 @node Returning, Calling, Signaling, Altering
7765 @section Returning from a function
7768 @cindex returning from a function
7771 @itemx return @var{expression}
7772 You can cancel execution of a function call with the @code{return}
7773 command. If you give an
7774 @var{expression} argument, its value is used as the function's return
7778 When you use @code{return}, @value{GDBN} discards the selected stack frame
7779 (and all frames within it). You can think of this as making the
7780 discarded frame return prematurely. If you wish to specify a value to
7781 be returned, give that value as the argument to @code{return}.
7783 This pops the selected stack frame (@pxref{Selection, ,Selecting a
7784 frame}), and any other frames inside of it, leaving its caller as the
7785 innermost remaining frame. That frame becomes selected. The
7786 specified value is stored in the registers used for returning values
7789 The @code{return} command does not resume execution; it leaves the
7790 program stopped in the state that would exist if the function had just
7791 returned. In contrast, the @code{finish} command (@pxref{Continuing
7792 and Stepping, ,Continuing and stepping}) resumes execution until the
7793 selected stack frame returns naturally.
7795 @node Calling, Patching, Returning, Altering
7796 @section Calling program functions
7798 @cindex calling functions
7801 @item call @var{expr}
7802 Evaluate the expression @var{expr} without displaying @code{void}
7806 You can use this variant of the @code{print} command if you want to
7807 execute a function from your program, but without cluttering the output
7808 with @code{void} returned values. If the result is not void, it
7809 is printed and saved in the value history.
7812 A new user-controlled variable, @var{call_scratch_address}, specifies
7813 the location of a scratch area to be used when @value{GDBN} calls a
7814 function in the target. This is necessary because the usual method
7815 of putting the scratch area on the stack does not work in systems that
7816 have separate instruction and data spaces.
7819 @node Patching, , Calling, Altering
7820 @section Patching programs
7821 @cindex patching binaries
7822 @cindex writing into executables
7824 @cindex writing into corefiles
7827 By default, @value{GDBN} opens the file containing your program's executable
7832 read-only. This prevents accidental alterations
7833 to machine code; but it also prevents you from intentionally patching
7834 your program's binary.
7836 If you'd like to be able to patch the binary, you can specify that
7837 explicitly with the @code{set write} command. For example, you might
7838 want to turn on internal debugging flags, or even to make emergency
7844 @itemx set write off
7845 If you specify @samp{set write on}, @value{GDBN} opens executable
7849 files for both reading and writing; if you specify @samp{set write
7850 off} (the default), @value{GDBN} opens them read-only.
7852 If you have already loaded a file, you must load it again (using the
7857 command) after changing @code{set write}, for your new setting to take
7862 Display whether executable files
7866 are opened for writing as well as reading.
7869 @node GDB Files, Targets, Altering, Top
7870 @chapter @value{GDBN} Files
7872 @value{GDBN} needs to know the file name of the program to be debugged, both in
7873 order to read its symbol table and in order to start your program.
7875 To debug a core dump of a previous run, you must also tell @value{GDBN}
7876 the name of the core dump file.
7880 * Files:: Commands to specify files
7881 * Symbol Errors:: Errors reading symbol files
7884 @node Files, Symbol Errors, GDB Files, GDB Files
7885 @section Commands to specify files
7886 @cindex symbol table
7889 @cindex core dump file
7890 You may want to specify executable and core dump file names.
7891 The usual way to do this is at start-up time, using the arguments to
7892 @value{GDBN}'s start-up commands (@pxref{Invocation, ,
7893 Getting In and Out of @value{GDBN}}).
7896 The usual way to specify an executable file name is with
7897 the command argument given when you start @value{GDBN}, (@pxref{Invocation,
7898 ,Getting In and Out of @value{GDBN}}.
7901 Occasionally it is necessary to change to a different file during a
7902 @value{GDBN} session. Or you may run @value{GDBN} and forget to specify
7903 a file you want to use. In these situations the @value{GDBN} commands
7904 to specify new files are useful.
7907 @cindex executable file
7909 @item file @var{filename}
7910 Use @var{filename} as the program to be debugged. It is read for its
7911 symbols and for the contents of pure memory. It is also the program
7912 executed when you use the @code{run} command. If you do not specify a
7913 directory and the file is not found in the @value{GDBN} working directory,
7914 @value{GDBN} uses the environment variable @code{PATH} as a list of
7915 directories to search, just as the shell does when looking for a program
7916 to run. You can change the value of this variable, for both @value{GDBN}
7917 and your program, using the @code{path} command.
7920 On systems with memory-mapped files, an auxiliary file
7921 @file{@var{filename}.syms} may hold symbol table information for
7922 @var{filename}. If so, @value{GDBN} maps in the symbol table from
7923 @file{@var{filename}.syms}, starting up more quickly. See the
7924 descriptions of the file options @samp{-mapped} and @samp{-readnow}
7925 (available on the command line, and with the commands @code{file},
7926 @code{symbol-file}, or @code{add-symbol-file}, described below),
7927 for more information.
7931 @code{file} with no argument makes @value{GDBN} discard any information it
7932 has on both executable file and the symbol table.
7935 @item exec-file @r{[} @var{filename} @r{]}
7936 Specify that the program to be run (but not the symbol table) is found
7937 in @var{filename}. @value{GDBN} searches the environment variable @code{PATH}
7938 if necessary to locate your program. Omitting @var{filename} means to
7939 discard information on the executable file.
7942 @item symbol-file @r{[} @var{filename} @r{]}
7943 Read symbol table information from file @var{filename}. @code{PATH} is
7944 searched when necessary. Use the @code{file} command to get both symbol
7945 table and program to run from the same file.
7947 @code{symbol-file} with no argument clears out @value{GDBN} information on your
7948 program's symbol table.
7950 The @code{symbol-file} command causes @value{GDBN} to forget the contents
7951 of its convenience variables, the value history, and all breakpoints and
7952 auto-display expressions. This is because they may contain pointers to
7953 the internal data recording symbols and data types, which are part of
7954 the old symbol table data being discarded inside @value{GDBN}.
7956 @code{symbol-file} does not repeat if you press @key{RET} again after
7959 When @value{GDBN} is configured for a particular environment, it
7960 understands debugging information in whatever format is the standard
7961 generated for that environment; you may use either a @sc{gnu} compiler, or
7962 other compilers that adhere to the local conventions.
7964 Best results are usually obtained from @sc{gnu} compilers; for example,
7965 using @code{@value{GCC}} you can generate debugging information for
7970 On some kinds of object files, the @code{symbol-file} command does not
7973 The @code{symbol-file} command does not
7975 normally read the symbol table in full right away. Instead, it scans
7976 the symbol table quickly to find which source files and which symbols
7977 are present. The details are read later, one source file at a time,
7980 The purpose of this two-stage reading strategy is to make @value{GDBN} start up
7981 faster. For the most part, it is invisible except for occasional
7982 pauses while the symbol table details for a particular source file are
7983 being read. (The @code{set verbose} command can turn these pauses
7984 into messages if desired. @xref{Messages/Warnings, ,Optional warnings
7988 We have not implemented the two-stage strategy for COFF yet. When the
7989 symbol table is stored in COFF format, @code{symbol-file} reads the
7990 symbol table data in full right away.
7993 @cindex reading symbols immediately
7994 @cindex symbols, reading immediately
7996 @cindex memory-mapped symbol file
7997 @cindex saving symbol table
7998 @item symbol-file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
7999 @itemx file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
8000 You can override the @value{GDBN} two-stage strategy for reading symbol
8001 tables by using the @samp{-readnow} option with any of the commands that
8002 load symbol table information, if you want to be sure @value{GDBN} has the
8003 entire symbol table available.
8008 If memory-mapped files are available on your system through the
8009 @code{mmap} system call, you can use another option, @samp{-mapped}, to
8010 cause @value{GDBN} to write the symbols for your program into a reusable
8011 file. Future @value{GDBN} debugging sessions map in symbol information
8012 from this auxiliary symbol file (if the program has not changed), rather
8013 than spending time reading the symbol table from the executable
8014 program. Using the @samp{-mapped} option has the same effect as
8015 starting @value{GDBN} with the @samp{-mapped} command-line option.
8017 You can use both options together, to make sure the auxiliary symbol
8018 file has all the symbol information for your program.
8020 The auxiliary symbol file for a program called @var{myprog} is called
8021 @samp{@var{myprog}.syms}. Once this file exists (so long as it is newer
8022 than the corresponding executable), @value{GDBN} always attempts to use
8023 it when you debug @var{myprog}; no special options or commands are
8026 The @file{.syms} file is specific to the host machine where you run
8027 @value{GDBN}. It holds an exact image of the internal @value{GDBN}
8028 symbol table. It cannot be shared across multiple host platforms.
8031 @c FIXME: for now no mention of directories, since this seems to be in
8032 @c flux. 13mar1992 status is that in theory GDB would look either in
8033 @c current dir or in same dir as myprog; but issues like competing
8034 @c GDB's, or clutter in system dirs, mean that in practice right now
8035 @c only current dir is used. FFish says maybe a special GDB hierarchy
8036 @c (eg rooted in val of env var GDBSYMS) could exist for mappable symbol
8041 @item core-file @r{[} @var{filename} @r{]}
8042 Specify the whereabouts of a core dump file to be used as the ``contents
8043 of memory''. Traditionally, core files contain only some parts of the
8044 address space of the process that generated them; @value{GDBN} can access the
8045 executable file itself for other parts.
8047 @code{core-file} with no argument specifies that no core file is
8050 Note that the core file is ignored when your program is actually running
8051 under @value{GDBN}. So, if you have been running your program and you wish to
8052 debug a core file instead, you must kill the subprocess in which the
8053 program is running. To do this, use the @code{kill} command
8054 (@pxref{Kill Process, ,Killing the child process}).
8058 @kindex load @var{filename}
8059 @item load @var{filename}
8061 Depending on what remote debugging facilities are configured into
8062 @value{GDBN}, the @code{load} command may be available. Where it exists, it
8063 is meant to make @var{filename} (an executable) available for debugging
8064 on the remote system---by downloading, or dynamic linking, for example.
8065 @code{load} also records the @var{filename} symbol table in @value{GDBN}, like
8066 the @code{add-symbol-file} command.
8068 If your @value{GDBN} does not have a @code{load} command, attempting to
8069 execute it gets the error message ``@code{You can't do that when your
8070 target is @dots{}}''
8073 The file is loaded at whatever address is specified in the executable.
8074 For some object file formats, you can specify the load address when you
8075 link the program; for other formats, like a.out, the object file format
8076 specifies a fixed address.
8077 @c FIXME! This would be a good place for an xref to the GNU linker doc.
8080 On VxWorks, @code{load} links @var{filename} dynamically on the
8081 current target system as well as adding its symbols in @value{GDBN}.
8085 @cindex download to Nindy-960
8086 With the Nindy interface to an Intel 960 board, @code{load}
8087 downloads @var{filename} to the 960 as well as adding its symbols in
8092 @cindex download to H8/300 or H8/500
8093 @cindex H8/300 or H8/500 download
8094 @cindex download to Hitachi SH
8095 @cindex Hitachi SH download
8096 When you select remote debugging to a Hitachi SH, H8/300, or H8/500 board
8097 (@pxref{Hitachi Remote,,@value{GDBN} and Hitachi Microprocessors}),
8098 the @code{load} command downloads your program to the Hitachi board and also
8099 opens it as the current executable target for @value{GDBN} on your host
8100 (like the @code{file} command).
8103 @code{load} does not repeat if you press @key{RET} again after using it.
8108 @kindex add-symbol-file
8109 @cindex dynamic linking
8110 @item add-symbol-file @var{filename} @var{address}
8111 @itemx add-symbol-file @var{filename} @var{address} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
8112 The @code{add-symbol-file} command reads additional symbol table information
8113 from the file @var{filename}. You would use this command when @var{filename}
8114 has been dynamically loaded (by some other means) into the program that
8115 is running. @var{address} should be the memory address at which the
8116 file has been loaded; @value{GDBN} cannot figure this out for itself.
8117 You can specify @var{address} as an expression.
8119 The symbol table of the file @var{filename} is added to the symbol table
8120 originally read with the @code{symbol-file} command. You can use the
8121 @code{add-symbol-file} command any number of times; the new symbol data thus
8122 read keeps adding to the old. To discard all old symbol data instead,
8123 use the @code{symbol-file} command.
8125 @code{add-symbol-file} does not repeat if you press @key{RET} after using it.
8127 You can use the @samp{-mapped} and @samp{-readnow} options just as with
8128 the @code{symbol-file} command, to change how @value{GDBN} manages the symbol
8129 table information for @var{filename}.
8131 @kindex add-shared-symbol-file
8132 @item add-shared-symbol-file
8133 The @code{add-shared-symbol-file} command can be used only under Harris' CXUX
8134 operating system for the Motorola 88k. @value{GDBN} automatically looks for
8135 shared libraries, however if @value{GDBN} does not find yours, you can run
8136 @code{add-shared-symbol-file}. It takes no arguments.
8143 The @code{section} command changes the base address of section SECTION of
8144 the exec file to ADDR. This can be used if the exec file does not contain
8145 section addresses, (such as in the a.out format), or when the addresses
8146 specified in the file itself are wrong. Each section must be changed
8147 separately. The ``info files'' command lists all the sections and their
8155 @code{info files} and @code{info target} are synonymous; both print
8156 the current target (@pxref{Targets, ,Specifying a Debugging Target}),
8159 names of the executable and core dump files
8162 name of the executable file
8164 currently in use by @value{GDBN}, and the files from which symbols were
8165 loaded. The command @code{help target} lists all possible targets
8166 rather than current ones.
8169 All file-specifying commands allow both absolute and relative file names
8170 as arguments. @value{GDBN} always converts the file name to an absolute file
8171 name and remembers it that way.
8174 @cindex shared libraries
8176 @c added HP-UX -- Kim (HP writer)
8177 @value{GDBN} supports HP-UX, SunOS, SVr4, Irix 5, and IBM RS/6000 shared
8181 @value{GDBN} supports HP-UX shared libraries.
8183 @value{GDBN} automatically loads symbol definitions from shared libraries
8184 when you use the @code{run} command, or when you examine a core file.
8185 (Before you issue the @code{run} command, @value{GDBN} does not understand
8186 references to a function in a shared library, however---unless you are
8187 debugging a core file).
8189 If the program loads a library explicitly, @value{GDBN} automatically
8190 loads the symbols at the time of the @code{shl_load} call.
8192 @c FIXME: some @value{GDBN} release may permit some refs to undef
8193 @c FIXME...symbols---eg in a break cmd---assuming they are from a shared
8194 @c FIXME...lib; check this from time to time when updating manual
8197 @kindex info sharedlibrary
8200 @itemx info sharedlibrary
8201 Print the names of the shared libraries which are currently loaded.
8203 @kindex sharedlibrary
8205 @item sharedlibrary @var{regex}
8206 @itemx share @var{regex}
8208 Load shared object library symbols for files matching a
8209 Unix regular expression.
8210 As with files loaded automatically, it only loads shared libraries
8211 required by your program for a core file or after typing @code{run}. If
8212 @var{regex} is omitted all shared libraries required by your program are
8217 @value{GDBN} detects the loading of a shared library and automatically
8218 reads in symbols from the newly loaded library, up to a threshold that
8219 is initially set but that you can modify if you wish.
8221 Beyond that threshold, symbols from shared libraries must be explicitly
8222 loaded. To load these symbols, use the command @code{sharedlibrary}
8223 @var{filename}. The base address of the shared library is determined
8224 automatically by @value{GDBN} and need not be specified.
8226 To display or set the threshold, use the commands:
8229 @kindex set auto-solib-add
8230 @item set auto-solib-add @var{threshold}
8231 Set the autoloading size threshold, in megabytes. If @var{threshold} is
8232 nonzero, symbols from all shared object libraries will be loaded
8233 automatically when the inferior begins execution or when the dynamic
8234 linker informs @value{GDBN} that a new library has been loaded, until
8235 the symbol table of the program and libraries exceeds this threshold.
8236 Otherwise, symbols must be loaded manually, using the
8237 @code{sharedlibrary} command. The default threshold is 100 megabytes.
8239 @kindex show auto-solib-add
8240 @item show auto-solib-add
8241 Display the current autoloading size threshold, in megabytes.
8247 @node Symbol Errors, , Files, GDB Files
8248 @section Errors reading symbol files
8250 While reading a symbol file, @value{GDBN} occasionally encounters problems,
8251 such as symbol types it does not recognize, or known bugs in compiler
8252 output. By default, @value{GDBN} does not notify you of such problems, since
8253 they are relatively common and primarily of interest to people
8254 debugging compilers. If you are interested in seeing information
8255 about ill-constructed symbol tables, you can either ask @value{GDBN} to print
8256 only one message about each such type of problem, no matter how many
8257 times the problem occurs; or you can ask @value{GDBN} to print more messages,
8258 to see how many times the problems occur, with the @code{set
8259 complaints} command (@pxref{Messages/Warnings, ,Optional warnings and
8262 The messages currently printed, and their meanings, include:
8265 @item inner block not inside outer block in @var{symbol}
8267 The symbol information shows where symbol scopes begin and end
8268 (such as at the start of a function or a block of statements). This
8269 error indicates that an inner scope block is not fully contained
8270 in its outer scope blocks.
8272 @value{GDBN} circumvents the problem by treating the inner block as if it had
8273 the same scope as the outer block. In the error message, @var{symbol}
8274 may be shown as ``@code{(don't know)}'' if the outer block is not a
8277 @item block at @var{address} out of order
8279 The symbol information for symbol scope blocks should occur in
8280 order of increasing addresses. This error indicates that it does not
8283 @value{GDBN} does not circumvent this problem, and has trouble
8284 locating symbols in the source file whose symbols it is reading. (You
8285 can often determine what source file is affected by specifying
8286 @code{set verbose on}. @xref{Messages/Warnings, ,Optional warnings and
8289 @item bad block start address patched
8291 The symbol information for a symbol scope block has a start address
8292 smaller than the address of the preceding source line. This is known
8293 to occur in the SunOS 4.1.1 (and earlier) C compiler.
8295 @value{GDBN} circumvents the problem by treating the symbol scope block as
8296 starting on the previous source line.
8298 @item bad string table offset in symbol @var{n}
8301 Symbol number @var{n} contains a pointer into the string table which is
8302 larger than the size of the string table.
8304 @value{GDBN} circumvents the problem by considering the symbol to have the
8305 name @code{foo}, which may cause other problems if many symbols end up
8308 @item unknown symbol type @code{0x@var{nn}}
8310 The symbol information contains new data types that @value{GDBN} does not yet
8311 know how to read. @code{0x@var{nn}} is the symbol type of the misunderstood
8312 information, in hexadecimal.
8314 @value{GDBN} circumvents the error by ignoring this symbol information. This
8315 usually allows you to debug your program, though certain symbols
8316 are not accessible. If you encounter such a problem and feel like
8317 debugging it, you can debug @code{@value{GDBP}} with itself, breakpoint on
8318 @code{complain}, then go up to the function @code{read_dbx_symtab} and
8319 examine @code{*bufp} to see the symbol.
8321 @item stub type has NULL name
8322 @value{GDBN} could not find the full definition for
8331 @item const/volatile indicator missing (ok if using g++ v1.x), got@dots{}
8333 The symbol information for a C++ member function is missing some
8334 information that recent versions of the compiler should have output
8338 @item info mismatch between compiler and debugger
8340 @value{GDBN} could not parse a type specification output by the compiler.
8343 @node Targets, Controlling GDB, GDB Files, Top
8344 @chapter Specifying a Debugging Target
8345 @cindex debugging target
8348 A @dfn{target} is the execution environment occupied by your program.
8351 Often, @value{GDBN} runs in the same host environment as your program; in
8352 that case, the debugging target is specified as a side effect when you
8353 use the @code{file} or @code{core} commands. When you need more
8354 flexibility---for example, running @value{GDBN} on a physically separate
8355 host, or controlling a standalone system over a serial port or a
8356 realtime system over a TCP/IP connection---you
8360 On HP-UX systems, @value{GDBN} has been configured to support debugging
8361 of processes running on the PA-RISC architecture. This means that the
8362 only possible targets are:
8366 An executable that has been compiled and linked to run on HP-UX
8369 A live HP-UX process, either started by @value{GDBN} (with the
8370 @code{run} command) or started outside of @value{GDBN} and attached to
8371 (with the @code{attach} command)
8374 A core file generated by an HP-UX process that previously aborted
8378 @value{GDBN} on HP-UX has not been configured to support remote
8379 debugging, or to support programs running on other platforms. You
8384 can use the @code{target} command to specify one of the target types
8385 configured for @value{GDBN} (@pxref{Target Commands, ,Commands for managing
8389 * Active Targets:: Active targets
8390 * Target Commands:: Commands for managing targets
8392 * Byte Order:: Choosing target byte order
8393 * Remote:: Remote debugging
8398 @node Active Targets, Target Commands, Targets, Targets
8399 @section Active targets
8400 @cindex stacking targets
8401 @cindex active targets
8402 @cindex multiple targets
8405 There are three classes of targets: processes, core files, and
8406 executable files. @value{GDBN} can work concurrently on up to three active
8407 targets, one in each class. This allows you to (for example) start a
8408 process and inspect its activity without abandoning your work on a core
8411 For example, if you execute @samp{gdb a.out}, then the executable file
8412 @code{a.out} is the only active target. If you designate a core file as
8413 well---presumably from a prior run that crashed and coredumped---then
8414 @value{GDBN} has two active targets and uses them in tandem, looking
8415 first in the corefile target, then in the executable file, to satisfy
8416 requests for memory addresses. (Typically, these two classes of target
8417 are complementary, since core files contain only a program's
8418 read-write memory---variables and so on---plus machine status, while
8419 executable files contain only the program text and initialized data.)
8422 When you type @code{run}, your executable file becomes an active process
8423 target as well. When a process target is active, all @value{GDBN} commands
8424 requesting memory addresses refer to that target; addresses in an
8428 executable file target are obscured while the process
8432 Use the @code{exec-file} command to select a
8433 new executable target (@pxref{Files, ,Commands to specify
8437 Use the @code{core-file} and @code{exec-file} commands to select a
8438 new core file or executable target (@pxref{Files, ,Commands to specify
8439 files}). To specify as a target a process that is already running, use
8440 the @code{attach} command (@pxref{Attach, ,Debugging an
8441 already-running process}).
8444 @node Target Commands, Byte Order, Active Targets, Targets
8445 @section Commands for managing targets
8448 @item target @var{type} @var{parameters}
8449 Connects the @value{GDBN} host environment to a target
8454 machine or process. A target is typically a protocol for talking to
8455 debugging facilities. You use the argument @var{type} to specify the
8456 type or protocol of the target machine.
8458 Further @var{parameters} are interpreted by the target protocol, but
8459 typically include things like device names or host names to connect
8460 with, process numbers, and baud rates.
8463 The @code{target} command does not repeat if you press @key{RET} again
8464 after executing the command.
8468 Displays the names of all targets available. To display targets
8469 currently selected, use either @code{info target} or @code{info files}
8470 (@pxref{Files, ,Commands to specify files}).
8472 @item help target @var{name}
8473 Describe a particular target, including any parameters necessary to
8476 @kindex set gnutarget
8477 @item set gnutarget @var{args}
8478 @value{GDBN} uses its own library BFD to read your files. @value{GDBN}
8479 knows whether it is reading an @dfn{executable},
8480 a @dfn{core}, or a @dfn{.o} file; however, you can specify the file format
8481 with the @code{set gnutarget} command. Unlike most @code{target} commands,
8482 with @code{gnutarget} the @code{target} refers to a program, not a machine.
8484 @emph{Warning:} To specify a file format with @code{set gnutarget},
8485 you must know the actual BFD name.
8487 @noindent @xref{Files, , Commands to specify files}.
8489 @kindex show gnutarget
8490 @item show gnutarget
8491 Use the @code{show gnutarget} command to display what file format
8492 @code{gnutarget} is set to read. If you have not set @code{gnutarget},
8493 @value{GDBN} will determine the file format for each file automatically,
8494 and @code{show gnutarget} displays @samp{The current BDF target is "auto"}.
8498 Here are some common targets (available, or not, depending on the GDB
8502 These are the valid targets on HP-UX systems:
8507 @item target exec @var{program}
8508 An executable file. @samp{target exec @var{program}} is the same as
8509 @samp{exec-file @var{program}}.
8513 @item target core @var{filename}
8514 A core dump file. @samp{target core @var{filename}} is the same as
8515 @samp{core-file @var{filename}}.
8519 @kindex target remote
8520 @item target remote @var{dev}
8521 Remote serial target in GDB-specific protocol. The argument @var{dev}
8522 specifies what serial device to use for the connection (e.g.
8523 @file{/dev/ttya}). @xref{Remote, ,Remote debugging}. @code{target remote}
8524 now supports the @code{load} command. This is only useful if you have
8525 some other way of getting the stub to the target system, and you can put
8526 it somewhere in memory where it won't get clobbered by the download.
8532 CPU simulator. @xref{Simulator,,Simulated CPU Target}.
8537 @item target udi @var{keyword}
8538 Remote AMD29K target, using the AMD UDI protocol. The @var{keyword}
8539 argument specifies which 29K board or simulator to use. @xref{UDI29K
8540 Remote,,The UDI protocol for AMD29K}.
8542 @kindex target amd-eb
8543 @item target amd-eb @var{dev} @var{speed} @var{PROG}
8545 Remote PC-resident AMD EB29K board, attached over serial lines.
8546 @var{dev} is the serial device, as for @code{target remote};
8547 @var{speed} allows you to specify the linespeed; and @var{PROG} is the
8548 name of the program to be debugged, as it appears to DOS on the PC.
8549 @xref{EB29K Remote, ,The EBMON protocol for AMD29K}.
8554 @item target hms @var{dev}
8555 A Hitachi SH, H8/300, or H8/500 board, attached via serial line to your host.
8556 @ifclear H8EXCLUSIVE
8557 Use special commands @code{device} and @code{speed} to control the serial
8558 line and the communications speed used.
8560 @xref{Hitachi Remote,,@value{GDBN} and Hitachi Microprocessors}.
8564 @kindex target nindy
8565 @item target nindy @var{devicename}
8566 An Intel 960 board controlled by a Nindy Monitor. @var{devicename} is
8567 the name of the serial device to use for the connection, e.g.
8568 @file{/dev/ttya}. @xref{i960-Nindy Remote, ,@value{GDBN} with a remote i960 (Nindy)}.
8572 @kindex target st2000
8573 @item target st2000 @var{dev} @var{speed}
8574 A Tandem ST2000 phone switch, running Tandem's STDBUG protocol. @var{dev}
8575 is the name of the device attached to the ST2000 serial line;
8576 @var{speed} is the communication line speed. The arguments are not used
8577 if @value{GDBN} is configured to connect to the ST2000 using TCP or Telnet.
8578 @xref{ST2000 Remote,,@value{GDBN} with a Tandem ST2000}.
8582 @kindex target vxworks
8583 @item target vxworks @var{machinename}
8584 A VxWorks system, attached via TCP/IP. The argument @var{machinename}
8585 is the target system's machine name or IP address.
8586 @xref{VxWorks Remote, ,@value{GDBN} and VxWorks}.
8590 @item target bug @var{dev}
8591 BUG monitor, running on a MVME187 (m88k) board.
8594 @kindex target cpu32bug
8595 @item target cpu32bug @var{dev}
8596 CPU32BUG monitor, running on a CPU32 (M68K) board.
8598 @kindex target op50n
8599 @item target op50n @var{dev}
8600 OP50N monitor, running on an OKI HPPA board.
8603 @item target w89k @var{dev}
8604 W89K monitor, running on a Winbond HPPA board.
8607 @item target est @var{dev}
8608 EST-300 ICE monitor, running on a CPU32 (M68K) board.
8610 @kindex target rom68k
8611 @item target rom68k @var{dev}
8612 ROM 68K monitor, running on an IDP board.
8614 @kindex target array
8615 @item target array @var{dev}
8616 Array Tech LSI33K RAID controller board.
8618 @kindex target sparclite
8619 @item target sparclite @var{dev}
8620 Fujitsu sparclite boards, used only for the purpose of loading.
8621 You must use an additional command to debug the program.
8622 For example: target remote @var{dev} using @value{GDBN} standard
8628 Different targets are available on different configurations of @value{GDBN};
8629 your configuration may have more or fewer targets.
8633 @node Byte Order, Remote, Target Commands, Targets
8634 @section Choosing target byte order
8635 @cindex choosing target byte order
8636 @cindex target byte order
8637 @kindex set endian big
8638 @kindex set endian little
8639 @kindex set endian auto
8642 You can now choose which byte order to use with a target system.
8643 Use the @code{set endian big} and @code{set endian little} commands.
8644 Use the @code{set endian auto} command to instruct
8645 @value{GDBN} to use the byte order associated with the executable.
8646 You can see the current setting for byte order with the @code{show endian}
8649 @emph{Warning:} Currently, only embedded MIPS configurations support
8650 dynamic selection of target byte order.
8652 @node Remote, , Byte Order, Targets
8653 @section Remote debugging
8654 @cindex remote debugging
8656 If you are trying to debug a program running on a machine that cannot run
8657 @value{GDBN} in the usual way, it is often useful to use remote debugging.
8658 For example, you might use remote debugging on an operating system kernel,
8659 or on a small system which does not have a general purpose operating system
8660 powerful enough to run a full-featured debugger.
8662 Some configurations of @value{GDBN} have special serial or TCP/IP interfaces
8663 to make this work with particular debugging targets. In addition,
8664 @value{GDBN} comes with a generic serial protocol (specific to @value{GDBN},
8665 but not specific to any particular target system) which you can use if you
8666 write the remote stubs---the code that runs on the remote system to
8667 communicate with @value{GDBN}.
8669 Other remote targets may be available in your
8670 configuration of @value{GDBN}; use @code{help target} to list them.
8674 @c Text on starting up GDB in various specific cases; it goes up front
8675 @c in manuals configured for any of those particular situations, here
8679 * Remote Serial:: @value{GDBN} remote serial protocol
8682 * i960-Nindy Remote:: @value{GDBN} with a remote i960 (Nindy)
8685 * UDI29K Remote:: The UDI protocol for AMD29K
8686 * EB29K Remote:: The EBMON protocol for AMD29K
8689 * VxWorks Remote:: @value{GDBN} and VxWorks
8692 * ST2000 Remote:: @value{GDBN} with a Tandem ST2000
8695 * Hitachi Remote:: @value{GDBN} and Hitachi Microprocessors
8698 * MIPS Remote:: @value{GDBN} and MIPS boards
8701 * Sparclet Remote:: @value{GDBN} and Sparclet boards
8704 * Simulator:: Simulated CPU target
8708 @include remote.texi
8711 @node Controlling GDB
8712 @chapter Controlling @value{GDBN}
8714 You can alter the way @value{GDBN} interacts with you by using
8715 the @code{set} command. For commands controlling how @value{GDBN} displays
8716 data, @pxref{Print Settings, ,Print settings}; other settings are described
8721 * Editing:: Command editing
8722 * History:: Command history
8723 * Screen Size:: Screen size
8725 * Messages/Warnings:: Optional warnings and messages
8728 @node Prompt, Editing, Controlling GDB, Controlling GDB
8733 @value{GDBN} indicates its readiness to read a command by printing a string
8734 called the @dfn{prompt}. This string is normally @samp{(@value{GDBP})}. You
8735 can change the prompt string with the @code{set prompt} command. For
8736 instance, when debugging @value{GDBN} with @value{GDBN}, it is useful to change
8737 the prompt in one of the @value{GDBN} sessions so that you can always tell
8738 which one you are talking to.
8740 @emph{Note:} @code{set prompt} no longer adds a space for you after the
8741 prompt you set. This allows you to set a prompt which ends in a space
8742 or a prompt that does not.
8746 @item set prompt @var{newprompt}
8747 Directs @value{GDBN} to use @var{newprompt} as its prompt string henceforth.
8751 Prints a line of the form: @samp{Gdb's prompt is: @var{your-prompt}}
8754 @node Editing, History, Prompt, Controlling GDB
8755 @section Command editing
8757 @cindex command line editing
8759 @value{GDBN} reads its input commands via the @dfn{readline} interface. This
8760 @sc{gnu} library provides consistent behavior for programs which provide a
8761 command line interface to the user. Advantages are @sc{gnu} Emacs-style
8762 or @dfn{vi}-style inline editing of commands, @code{csh}-like history
8763 substitution, and a storage and recall of command history across
8766 You may control the behavior of command line editing in @value{GDBN} with the
8773 @itemx set editing on
8774 Enable command line editing (enabled by default).
8776 @item set editing off
8777 Disable command line editing.
8779 @kindex show editing
8781 Show whether command line editing is enabled.
8784 @node History, Screen Size, Editing, Controlling GDB
8785 @section Command history
8787 @value{GDBN} can keep track of the commands you type during your
8788 debugging sessions, so that you can be certain of precisely what
8789 happened. Use these commands to manage the @value{GDBN} command
8793 @cindex history substitution
8794 @cindex history file
8795 @kindex set history filename
8797 @item set history filename @var{fname}
8798 Set the name of the @value{GDBN} command history file to @var{fname}.
8799 This is the file where @value{GDBN} reads an initial command history
8800 list, and where it writes the command history from this session when it
8801 exits. You can access this list through history expansion or through
8802 the history command editing characters listed below. This file defaults
8803 to the value of the environment variable @code{GDBHISTFILE}, or to
8804 @file{./.gdb_history} if this variable is not set.
8806 @cindex history save
8807 @kindex set history save
8808 @item set history save
8809 @itemx set history save on
8810 Record command history in a file, whose name may be specified with the
8811 @code{set history filename} command. By default, this option is disabled.
8813 @item set history save off
8814 Stop recording command history in a file.
8816 @cindex history size
8817 @kindex set history size
8818 @item set history size @var{size}
8819 Set the number of commands which @value{GDBN} keeps in its history list.
8820 This defaults to the value of the environment variable
8821 @code{HISTSIZE}, or to 256 if this variable is not set.
8824 @cindex history expansion
8825 History expansion assigns special meaning to the character @kbd{!}.
8826 @ifset have-readline-appendices
8827 @xref{Event Designators}.
8830 Since @kbd{!} is also the logical not operator in C, history expansion
8831 is off by default. If you decide to enable history expansion with the
8832 @code{set history expansion on} command, you may sometimes need to
8833 follow @kbd{!} (when it is used as logical not, in an expression) with
8834 a space or a tab to prevent it from being expanded. The readline
8835 history facilities do not attempt substitution on the strings
8836 @kbd{!=} and @kbd{!(}, even when history expansion is enabled.
8838 The commands to control history expansion are:
8841 @kindex set history expansion
8842 @item set history expansion on
8843 @itemx set history expansion
8844 Enable history expansion. History expansion is off by default.
8846 @item set history expansion off
8847 Disable history expansion.
8849 The readline code comes with more complete documentation of
8850 editing and history expansion features. Users unfamiliar with @sc{gnu} Emacs
8851 or @code{vi} may wish to read it.
8852 @ifset have-readline-appendices
8853 @xref{Command Line Editing}.
8857 @kindex show history
8859 @itemx show history filename
8860 @itemx show history save
8861 @itemx show history size
8862 @itemx show history expansion
8863 These commands display the state of the @value{GDBN} history parameters.
8864 @code{show history} by itself displays all four states.
8869 @kindex show commands
8871 Display the last ten commands in the command history.
8873 @item show commands @var{n}
8874 Print ten commands centered on command number @var{n}.
8876 @item show commands +
8877 Print ten commands just after the commands last printed.
8880 @node Screen Size, Numbers, History, Controlling GDB
8881 @section Screen size
8882 @cindex size of screen
8883 @cindex pauses in output
8885 Certain commands to @value{GDBN} may produce large amounts of
8886 information output to the screen. To help you read all of it,
8887 @value{GDBN} pauses and asks you for input at the end of each page of
8888 output. Type @key{RET} when you want to continue the output, or @kbd{q}
8889 to discard the remaining output. Also, the screen width setting
8890 determines when to wrap lines of output. Depending on what is being
8891 printed, @value{GDBN} tries to break the line at a readable place,
8892 rather than simply letting it overflow onto the following line.
8894 Normally @value{GDBN} knows the size of the screen from the termcap data base
8895 together with the value of the @code{TERM} environment variable and the
8896 @code{stty rows} and @code{stty cols} settings. If this is not correct,
8897 you can override it with the @code{set height} and @code{set
8905 @item set height @var{lpp}
8907 @itemx set width @var{cpl}
8909 These @code{set} commands specify a screen height of @var{lpp} lines and
8910 a screen width of @var{cpl} characters. The associated @code{show}
8911 commands display the current settings.
8913 If you specify a height of zero lines, @value{GDBN} does not pause during
8914 output no matter how long the output is. This is useful if output is to a
8915 file or to an editor buffer.
8917 Likewise, you can specify @samp{set width 0} to prevent @value{GDBN}
8918 from wrapping its output.
8921 @node Numbers, Messages/Warnings, Screen Size, Controlling GDB
8923 @cindex number representation
8924 @cindex entering numbers
8926 You can always enter numbers in octal, decimal, or hexadecimal in @value{GDBN} by
8927 the usual conventions: octal numbers begin with @samp{0}, decimal
8928 numbers end with @samp{.}, and hexadecimal numbers begin with @samp{0x}.
8929 Numbers that begin with none of these are, by default, entered in base
8930 10; likewise, the default display for numbers---when no particular
8931 format is specified---is base 10. You can change the default base for
8932 both input and output with the @code{set radix} command.
8935 @kindex set input-radix
8936 @item set input-radix @var{base}
8937 Set the default base for numeric input. Supported choices
8938 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
8939 specified either unambiguously or using the current default radix; for
8949 sets the base to decimal. On the other hand, @samp{set radix 10}
8950 leaves the radix unchanged no matter what it was.
8952 @kindex set output-radix
8953 @item set output-radix @var{base}
8954 Set the default base for numeric display. Supported choices
8955 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
8956 specified either unambiguously or using the current default radix.
8958 @kindex show input-radix
8959 @item show input-radix
8960 Display the current default base for numeric input.
8962 @kindex show output-radix
8963 @item show output-radix
8964 Display the current default base for numeric display.
8967 @node Messages/Warnings, , Numbers, Controlling GDB
8968 @section Optional warnings and messages
8970 By default, @value{GDBN} is silent about its inner workings. If you are running
8971 on a slow machine, you may want to use the @code{set verbose} command.
8972 This makes @value{GDBN} tell you when it does a lengthy internal operation, so
8973 you will not think it has crashed.
8975 Currently, the messages controlled by @code{set verbose} are those
8976 which announce that the symbol table for a source file is being read;
8977 see @code{symbol-file} in @ref{Files, ,Commands to specify files}.
8981 @item set verbose on
8982 Enables @value{GDBN} output of certain informational messages.
8984 @item set verbose off
8985 Disables @value{GDBN} output of certain informational messages.
8987 @kindex show verbose
8989 Displays whether @code{set verbose} is on or off.
8992 By default, if @value{GDBN} encounters bugs in the symbol table of an object
8993 file, it is silent; but if you are debugging a compiler, you may find
8994 this information useful (@pxref{Symbol Errors, ,Errors reading symbol files}).
8997 @kindex set complaints
8998 @item set complaints @var{limit}
8999 Permits @value{GDBN} to output @var{limit} complaints about each type of unusual
9000 symbols before becoming silent about the problem. Set @var{limit} to
9001 zero to suppress all complaints; set it to a large number to prevent
9002 complaints from being suppressed.
9004 @kindex show complaints
9005 @item show complaints
9006 Displays how many symbol complaints @value{GDBN} is permitted to produce.
9009 By default, @value{GDBN} is cautious, and asks what sometimes seems to be a
9010 lot of stupid questions to confirm certain commands. For example, if
9011 you try to run a program which is already running:
9015 The program being debugged has been started already.
9016 Start it from the beginning? (y or n)
9019 If you are willing to unflinchingly face the consequences of your own
9020 commands, you can disable this ``feature'':
9025 @cindex confirmation
9026 @cindex stupid questions
9027 @item set confirm off
9028 Disables confirmation requests.
9030 @item set confirm on
9031 Enables confirmation requests (the default).
9033 @kindex show confirm
9035 Displays state of confirmation requests.
9038 @node Sequences, Emacs, Controlling GDB, Top
9039 @chapter Canned Sequences of Commands
9041 Aside from breakpoint commands (@pxref{Break Commands, ,Breakpoint
9042 command lists}), @value{GDBN} provides two ways to store sequences of commands
9043 for execution as a unit: user-defined commands and command files.
9046 * Define:: User-defined commands
9047 * Hooks:: User-defined command hooks
9048 * Command Files:: Command files
9049 * Output:: Commands for controlled output
9052 @node Define, Hooks, Sequences, Sequences
9053 @section User-defined commands
9055 @cindex user-defined command
9056 A @dfn{user-defined command} is a sequence of @value{GDBN} commands to which
9057 you assign a new name as a command. This is done with the @code{define}
9058 command. User commands may accept up to 10 arguments separated by whitespace.
9059 Arguments are accessed within the user command via @var{$arg0@dots{}$arg9}.
9064 print $arg0 + $arg1 + $arg2
9067 @noindent To execute the command use:
9073 @noindent This defines the command @code{adder}, which prints the sum of
9074 its three arguments. Note the arguments are text substitutions, so they may
9075 reference variables, use complex expressions, or even perform inferior
9080 @item define @var{commandname}
9081 Define a command named @var{commandname}. If there is already a command
9082 by that name, you are asked to confirm that you want to redefine it.
9084 The definition of the command is made up of other @value{GDBN} command lines,
9085 which are given following the @code{define} command. The end of these
9086 commands is marked by a line containing @code{end}.
9091 Takes a single argument, which is an expression to evaluate.
9092 It is followed by a series of commands that are executed
9093 only if the expression is true (nonzero).
9094 There can then optionally be a line @code{else}, followed
9095 by a series of commands that are only executed if the expression
9096 was false. The end of the list is marked by a line containing @code{end}.
9100 The syntax is similar to @code{if}: the command takes a single argument,
9101 which is an expression to evaluate, and must be followed by the commands to
9102 execute, one per line, terminated by an @code{end}.
9103 The commands are executed repeatedly as long as the expression
9107 @item document @var{commandname}
9108 Document the user-defined command @var{commandname}, so that it can be
9109 accessed by @code{help}. The command @var{commandname} must already be
9110 defined. This command reads lines of documentation just as @code{define}
9111 reads the lines of the command definition, ending with @code{end}.
9112 After the @code{document} command is finished, @code{help} on command
9113 @var{commandname} displays the documentation you have written.
9115 You may use the @code{document} command again to change the
9116 documentation of a command. Redefining the command with @code{define}
9117 does not change the documentation.
9119 @kindex help user-defined
9120 @item help user-defined
9121 List all user-defined commands, with the first line of the documentation
9126 @itemx show user @var{commandname}
9127 Display the @value{GDBN} commands used to define @var{commandname} (but not its
9128 documentation). If no @var{commandname} is given, display the
9129 definitions for all user-defined commands.
9132 When user-defined commands are executed, the
9133 commands of the definition are not printed. An error in any command
9134 stops execution of the user-defined command.
9136 If used interactively, commands that would ask for confirmation proceed
9137 without asking when used inside a user-defined command. Many @value{GDBN}
9138 commands that normally print messages to say what they are doing omit the
9139 messages when used in a user-defined command.
9141 @node Hooks, Command Files, Define, Sequences
9142 @section User-defined command hooks
9143 @cindex command files
9145 You may define @emph{hooks}, which are a special kind of user-defined
9146 command. Whenever you run the command @samp{foo}, if the user-defined
9147 command @samp{hook-foo} exists, it is executed (with no arguments)
9148 before that command.
9150 In addition, a pseudo-command, @samp{stop} exists. Defining
9151 (@samp{hook-stop}) makes the associated commands execute every time
9152 execution stops in your program: before breakpoint commands are run,
9153 displays are printed, or the stack frame is printed.
9156 For example, to ignore @code{SIGALRM} signals while
9157 single-stepping, but treat them normally during normal execution,
9162 handle SIGALRM nopass
9169 define hook-continue
9175 You can define a hook for any single-word command in @value{GDBN}, but
9176 not for command aliases; you should define a hook for the basic command
9177 name, e.g. @code{backtrace} rather than @code{bt}.
9178 @c FIXME! So how does Joe User discover whether a command is an alias
9180 If an error occurs during the execution of your hook, execution of
9181 @value{GDBN} commands stops and @value{GDBN} issues a prompt
9182 (before the command that you actually typed had a chance to run).
9184 If you try to define a hook which does not match any known command, you
9185 get a warning from the @code{define} command.
9187 @node Command Files, Output, Hooks, Sequences
9188 @section Command files
9190 @cindex command files
9191 A command file for @value{GDBN} is a file of lines that are @value{GDBN}
9192 commands. Comments (lines starting with @kbd{#}) may also be included.
9193 An empty line in a command file does nothing; it does not mean to repeat
9194 the last command, as it would from the terminal.
9197 @cindex @file{@value{GDBINIT}}
9198 When you start @value{GDBN}, it automatically executes commands from its
9199 @dfn{init files}. These are files named @file{@value{GDBINIT}}.
9200 @value{GDBN} reads the init file (if any) in your home directory, then
9201 processes command line options and operands, and then reads the init
9202 file (if any) in the current working directory. This is so the init
9203 file in your home directory can set options (such as @code{set
9204 complaints}) which affect the processing of the command line options and
9205 operands. The init files are not executed if you use the @samp{-nx}
9206 option; @pxref{Mode Options, ,Choosing modes}.
9209 @cindex init file name
9210 On some configurations of @value{GDBN}, the init file is known by a
9211 different name (these are typically environments where a specialized
9212 form of @value{GDBN} may need to coexist with other forms,
9213 hence a different name
9214 for the specialized version's init file). These are the environments
9215 with special init file names:
9220 VxWorks (Wind River Systems real-time OS): @samp{.vxgdbinit}
9222 @kindex .os68gdbinit
9224 OS68K (Enea Data Systems real-time OS): @samp{.os68gdbinit}
9228 ES-1800 (Ericsson Telecom AB M68000 emulator): @samp{.esgdbinit}
9232 You can also request the execution of a command file with the
9233 @code{source} command:
9237 @item source @var{filename}
9238 Execute the command file @var{filename}.
9241 The lines in a command file are executed sequentially. They are not
9242 printed as they are executed. An error in any command terminates execution
9243 of the command file.
9245 Commands that would ask for confirmation if used interactively proceed
9246 without asking when used in a command file. Many @value{GDBN} commands that
9247 normally print messages to say what they are doing omit the messages
9248 when called from command files.
9250 @node Output, , Command Files, Sequences
9251 @section Commands for controlled output
9253 During the execution of a command file or a user-defined command, normal
9254 @value{GDBN} output is suppressed; the only output that appears is what is
9255 explicitly printed by the commands in the definition. This section
9256 describes three commands useful for generating exactly the output you
9261 @item echo @var{text}
9262 @c I do not consider backslash-space a standard C escape sequence
9263 @c because it is not in ANSI.
9264 Print @var{text}. Nonprinting characters can be included in
9265 @var{text} using C escape sequences, such as @samp{\n} to print a
9266 newline. @strong{No newline is printed unless you specify one.}
9267 In addition to the standard C escape sequences, a backslash followed
9268 by a space stands for a space. This is useful for displaying a
9269 string with spaces at the beginning or the end, since leading and
9270 trailing spaces are otherwise trimmed from all arguments.
9271 To print @samp{@w{ }and foo =@w{ }}, use the command
9272 @samp{echo \@w{ }and foo = \@w{ }}.
9274 A backslash at the end of @var{text} can be used, as in C, to continue
9275 the command onto subsequent lines. For example,
9278 echo This is some text\n\
9279 which is continued\n\
9280 onto several lines.\n
9283 produces the same output as
9286 echo This is some text\n
9287 echo which is continued\n
9288 echo onto several lines.\n
9292 @item output @var{expression}
9293 Print the value of @var{expression} and nothing but that value: no
9294 newlines, no @samp{$@var{nn} = }. The value is not entered in the
9295 value history either. @xref{Expressions, ,Expressions}, for more information
9298 @item output/@var{fmt} @var{expression}
9299 Print the value of @var{expression} in format @var{fmt}. You can use
9300 the same formats as for @code{print}. @xref{Output Formats,,Output
9301 formats}, for more information.
9304 @item printf @var{string}, @var{expressions}@dots{}
9305 Print the values of the @var{expressions} under the control of
9306 @var{string}. The @var{expressions} are separated by commas and may be
9307 either numbers or pointers. Their values are printed as specified by
9308 @var{string}, exactly as if your program were to execute the C
9312 printf (@var{string}, @var{expressions}@dots{});
9315 For example, you can print two values in hex like this:
9318 printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
9321 The only backslash-escape sequences that you can use in the format
9322 string are the simple ones that consist of backslash followed by a
9327 @node Emacs, GDB Bugs, Sequences, Top
9328 @chapter Using @value{GDBN} under @sc{gnu} Emacs
9331 @cindex @sc{gnu} Emacs
9332 A special interface allows you to use @sc{gnu} Emacs to view (and
9333 edit) the source files for the program you are debugging with
9336 To use this interface, use the command @kbd{M-x gdb} in Emacs. Give the
9337 executable file you want to debug as an argument. This command starts
9338 @value{GDBN} as a subprocess of Emacs, with input and output through a newly
9339 created Emacs buffer.
9341 (Do not use the @code{-tui} option to run @value{GDBN} from Emacs.)
9344 Using @value{GDBN} under Emacs is just like using @value{GDBN} normally except for two
9349 All ``terminal'' input and output goes through the Emacs buffer.
9352 This applies both to @value{GDBN} commands and their output, and to the input
9353 and output done by the program you are debugging.
9355 This is useful because it means that you can copy the text of previous
9356 commands and input them again; you can even use parts of the output
9359 All the facilities of Emacs' Shell mode are available for interacting
9360 with your program. In particular, you can send signals the usual
9361 way---for example, @kbd{C-c C-c} for an interrupt, @kbd{C-c C-z} for a
9366 @value{GDBN} displays source code through Emacs.
9369 Each time @value{GDBN} displays a stack frame, Emacs automatically finds the
9370 source file for that frame and puts an arrow (@samp{=>}) at the
9371 left margin of the current line. Emacs uses a separate buffer for
9372 source display, and splits the screen to show both your @value{GDBN} session
9375 Explicit @value{GDBN} @code{list} or search commands still produce output as
9376 usual, but you probably have no reason to use them from Emacs.
9379 @emph{Warning:} If the directory where your program resides is not your
9380 current directory, it can be easy to confuse Emacs about the location of
9381 the source files, in which case the auxiliary display buffer does not
9382 appear to show your source. @value{GDBN} can find programs by searching your
9383 environment's @code{PATH} variable, so the @value{GDBN} input and output
9384 session proceeds normally; but Emacs does not get enough information
9385 back from @value{GDBN} to locate the source files in this situation. To
9386 avoid this problem, either start @value{GDBN} mode from the directory where
9387 your program resides, or specify an absolute file name when prompted for the
9388 @kbd{M-x gdb} argument.
9390 A similar confusion can result if you use the @value{GDBN} @code{file} command to
9391 switch to debugging a program in some other location, from an existing
9392 @value{GDBN} buffer in Emacs.
9395 By default, @kbd{M-x gdb} calls the program called @file{gdb}. If
9396 you need to call @value{GDBN} by a different name (for example, if you keep
9397 several configurations around, with different names) you can set the
9398 Emacs variable @code{gdb-command-name}; for example,
9401 (setq gdb-command-name "mygdb")
9405 (preceded by @kbd{ESC ESC}, or typed in the @code{*scratch*} buffer, or
9406 in your @file{.emacs} file) makes Emacs call the program named
9407 ``@code{mygdb}'' instead.
9409 In the @value{GDBN} I/O buffer, you can use these special Emacs commands in
9410 addition to the standard Shell mode commands:
9414 Describe the features of Emacs' @value{GDBN} Mode.
9417 Execute to another source line, like the @value{GDBN} @code{step} command; also
9418 update the display window to show the current file and location.
9421 Execute to next source line in this function, skipping all function
9422 calls, like the @value{GDBN} @code{next} command. Then update the display window
9423 to show the current file and location.
9426 Execute one instruction, like the @value{GDBN} @code{stepi} command; update
9427 display window accordingly.
9430 Execute to next instruction, using the @value{GDBN} @code{nexti} command; update
9431 display window accordingly.
9434 Execute until exit from the selected stack frame, like the @value{GDBN}
9435 @code{finish} command.
9438 Continue execution of your program, like the @value{GDBN} @code{continue}
9441 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-p}.
9444 Go up the number of frames indicated by the numeric argument
9445 (@pxref{Arguments, , Numeric Arguments, Emacs, The @sc{gnu} Emacs Manual}),
9446 like the @value{GDBN} @code{up} command.
9448 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-u}.
9451 Go down the number of frames indicated by the numeric argument, like the
9452 @value{GDBN} @code{down} command.
9454 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-d}.
9457 Read the number where the cursor is positioned, and insert it at the end
9458 of the @value{GDBN} I/O buffer. For example, if you wish to disassemble code
9459 around an address that was displayed earlier, type @kbd{disassemble};
9460 then move the cursor to the address display, and pick up the
9461 argument for @code{disassemble} by typing @kbd{C-x &}.
9463 You can customize this further by defining elements of the list
9464 @code{gdb-print-command}; once it is defined, you can format or
9465 otherwise process numbers picked up by @kbd{C-x &} before they are
9466 inserted. A numeric argument to @kbd{C-x &} indicates that you
9467 wish special formatting, and also acts as an index to pick an element of the
9468 list. If the list element is a string, the number to be inserted is
9469 formatted using the Emacs function @code{format}; otherwise the number
9470 is passed as an argument to the corresponding list element.
9473 In any source file, the Emacs command @kbd{C-x SPC} (@code{gdb-break})
9474 tells @value{GDBN} to set a breakpoint on the source line point is on.
9476 If you accidentally delete the source-display buffer, an easy way to get
9477 it back is to type the command @code{f} in the @value{GDBN} buffer, to
9478 request a frame display; when you run under Emacs, this recreates
9479 the source buffer if necessary to show you the context of the current
9482 The source files displayed in Emacs are in ordinary Emacs buffers
9483 which are visiting the source files in the usual way. You can edit
9484 the files with these buffers if you wish; but keep in mind that @value{GDBN}
9485 communicates with Emacs in terms of line numbers. If you add or
9486 delete lines from the text, the line numbers that @value{GDBN} knows cease
9487 to correspond properly with the code.
9489 @c The following dropped because Epoch is nonstandard. Reactivate
9490 @c if/when v19 does something similar. ---doc@cygnus.com 19dec1990
9492 @kindex Emacs Epoch environment
9496 Version 18 of @sc{gnu} Emacs has a built-in window system
9497 called the @code{epoch}
9498 environment. Users of this environment can use a new command,
9499 @code{inspect} which performs identically to @code{print} except that
9500 each value is printed in its own window.
9505 @node Energize, GDB Bugs, Emacs, Top
9506 @chapter Using @value{GDBN} with Energize
9509 The Energize Programming System is an integrated development environment
9510 that includes a point-and-click interface to many programming tools.
9511 When you use @value{GDBN} in this environment, you can use the standard
9512 Energize graphical interface to drive @value{GDBN}; you can also, if you
9513 choose, type @value{GDBN} commands as usual in a debugging window. Even if
9514 you use the graphical interface, the debugging window (which uses Emacs,
9515 and resembles the standard @sc{gnu} Emacs interface to
9516 @value{GDBN}) displays the
9517 equivalent commands, so that the history of your debugging session is
9520 When Energize starts up a @value{GDBN} session, it uses one of the
9521 command-line options @samp{-energize} or @samp{-cadillac} (``cadillac''
9522 is the name of the communications protocol used by the Energize system).
9523 This option makes @value{GDBN} run as one of the tools in the Energize Tool
9524 Set: it sends all output to the Energize kernel, and accept input from
9527 See the user manual for the Energize Programming System for
9528 information on how to use the Energize graphical interface and the other
9529 development tools that Energize integrates with @value{GDBN}.
9534 @c links whacked to pacify makeinfo
9535 @c , Command Line Editing, Emacs, Top
9536 @chapter Reporting Bugs in @value{GDBN}
9537 @cindex bugs in @value{GDBN}
9538 @cindex reporting bugs in @value{GDBN}
9540 Your bug reports play an essential role in making @value{GDBN} reliable.
9542 Reporting a bug may help you by bringing a solution to your problem, or it
9543 may not. But in any case the principal function of a bug report is to help
9544 the entire community by making the next version of @value{GDBN} work better. Bug
9545 reports are your contribution to the maintenance of @value{GDBN}.
9547 In order for a bug report to serve its purpose, you must include the
9548 information that enables us to fix the bug.
9551 * Bug Criteria:: Have you found a bug?
9552 * Bug Reporting:: How to report bugs
9555 @node Bug Criteria, Bug Reporting, GDB Bugs, GDB Bugs
9556 @section Have you found a bug?
9557 @cindex bug criteria
9559 If you are not sure whether you have found a bug, here are some guidelines:
9562 @cindex fatal signal
9563 @cindex debugger crash
9564 @cindex crash of debugger
9566 If the debugger gets a fatal signal, for any input whatever, that is a
9567 @value{GDBN} bug. Reliable debuggers never crash.
9569 @cindex error on valid input
9571 If @value{GDBN} produces an error message for valid input, that is a bug.
9573 @cindex invalid input
9575 If @value{GDBN} does not produce an error message for invalid input,
9576 that is a bug. However, you should note that your idea of
9577 ``invalid input'' might be our idea of ``an extension'' or ``support
9578 for traditional practice''.
9581 If you are an experienced user of debugging tools, your suggestions
9582 for improvement of @value{GDBN} are welcome in any case.
9585 @node Bug Reporting, , Bug Criteria, GDB Bugs
9586 @section How to report bugs
9588 @cindex @value{GDBN} bugs, reporting
9591 A number of companies and individuals offer support for @sc{gnu} products.
9592 If you obtained @value{GDBN} from a support organization, we recommend you
9593 contact that organization first.
9595 You can find contact information for many support companies and
9596 individuals in the file @file{etc/SERVICE} in the @sc{gnu} Emacs
9599 In any event, we also recommend that you send bug reports for @value{GDBN} to one
9603 bug-gdb@@prep.ai.mit.edu
9604 @{ucbvax|mit-eddie|uunet@}!prep.ai.mit.edu!bug-gdb
9607 @strong{Do not send bug reports to @samp{info-gdb}, or to
9608 @samp{help-gdb}, or to any newsgroups.} Most users of @value{GDBN} do not want to
9609 receive bug reports. Those that do have arranged to receive @samp{bug-gdb}.
9611 The mailing list @samp{bug-gdb} has a newsgroup @samp{gnu.gdb.bug} which
9612 serves as a repeater. The mailing list and the newsgroup carry exactly
9613 the same messages. Often people think of posting bug reports to the
9614 newsgroup instead of mailing them. This appears to work, but it has one
9615 problem which can be crucial: a newsgroup posting often lacks a mail
9616 path back to the sender. Thus, if we need to ask for more information,
9617 we may be unable to reach you. For this reason, it is better to send
9618 bug reports to the mailing list.
9620 As a last resort, send bug reports on paper to:
9623 @sc{gnu} Debugger Bugs
9624 Free Software Foundation Inc.
9625 59 Temple Place - Suite 330
9626 Boston, MA 02111-1307
9632 If you obtained HP GDB as part of your HP ANSI C or HP ANSI C++ compiler
9633 kit, report problems to your HP Support Representative.
9635 If you obtained HP GDB from the Hewlett-Packard Web site, report
9636 problems by electronic mail to @code{wdb-www@@ch.hp.com}.
9639 The fundamental principle of reporting bugs usefully is this:
9640 @strong{report all the facts}. If you are not sure whether to state a
9641 fact or leave it out, state it!
9643 Often people omit facts because they think they know what causes the
9644 problem and assume that some details do not matter. Thus, you might
9645 assume that the name of the variable you use in an example does not matter.
9646 Well, probably it does not, but one cannot be sure. Perhaps the bug is a
9647 stray memory reference which happens to fetch from the location where that
9648 name is stored in memory; perhaps, if the name were different, the contents
9649 of that location would fool the debugger into doing the right thing despite
9650 the bug. Play it safe and give a specific, complete example. That is the
9651 easiest thing for you to do, and the most helpful.
9653 Keep in mind that the purpose of a bug report is to enable us to fix
9654 the bug if it is new to us.
9656 @c FIX ME!!--What the heck does the following sentence mean,
9657 @c in the context of the one above?
9659 @c It is not as important as what happens if the bug is already known.
9661 Therefore, always write your bug reports on
9662 the assumption that the bug has not been reported previously.
9664 Sometimes people give a few sketchy facts and ask, ``Does this ring a
9665 bell?'' Those bug reports are useless, and we urge everyone to
9666 @emph{refuse to respond to them} except to chide the sender to report
9669 To enable us to fix the bug, you should include all these things:
9673 The version of @value{GDBN}. @value{GDBN} announces it if you start with no
9674 arguments; you can also print it at any time using @code{show version}.
9676 Without this, we will not know whether there is any point in looking for
9677 the bug in the current version of @value{GDBN}.
9680 The type of machine you are using, and the operating system name and
9685 What compiler (and its version) was used to compile @value{GDBN}---e.g.
9686 ``@value{GCC}--2.0''.
9690 What compiler (and its version) was used to compile the program you
9692 are debugging---e.g. ``@value{GCC}--2.0''.
9695 are debugging---e.g. ``HP92453-01 A.10.32.03 HP C Compiler''. Use the
9696 @code{what} command with the pathname of the compile command
9697 (@file{what /opt/ansic/bin/cc}, for example) to obtain this information.
9701 The command arguments you gave the compiler to compile your example and
9702 observe the bug. For example, did you use @samp{-O}? To guarantee
9703 you will not omit something important, list them all. A copy of the
9704 Makefile (or the output from make) is sufficient.
9706 If we were to try to guess the arguments, we would probably guess wrong
9707 and then we might not encounter the bug.
9710 A complete input script, and all necessary source files, that will
9714 A description of what behavior you observe that you believe is
9715 incorrect. For example, ``It gets a fatal signal.''
9717 Of course, if the bug is that @value{GDBN} gets a fatal signal, then we will
9718 certainly notice it. But if the bug is incorrect output, we might not
9719 notice unless it is glaringly wrong. You might as well not give us a
9720 chance to make a mistake.
9722 Even if the problem you experience is a fatal signal, you should still
9723 say so explicitly. Suppose something strange is going on, such as,
9724 your copy of @value{GDBN} is out of synch, or you have encountered a
9725 bug in the C library on your system. (This has happened!) Your copy
9726 might crash and ours would not. If you told us to expect a crash,
9727 then when ours fails to crash, we would know that the bug was not
9728 happening for us. If you had not told us to expect a crash, then we
9729 would not be able to draw any conclusion from our observations.
9733 If you wish to suggest changes to the @value{GDBN} source, send us context
9734 diffs. If you even discuss something in the @value{GDBN} source, refer to
9735 it by context, not by line number.
9737 The line numbers in our development sources will not match those in your
9738 sources. Your line numbers would convey no useful information to us.
9742 Here are some things that are not necessary:
9746 A description of the envelope of the bug.
9748 Often people who encounter a bug spend a lot of time investigating
9749 which changes to the input file will make the bug go away and which
9750 changes will not affect it.
9752 This is often time consuming and not very useful, because the way we
9753 will find the bug is by running a single example under the debugger
9754 with breakpoints, not by pure deduction from a series of examples.
9755 We recommend that you save your time for something else.
9757 Of course, if you can find a simpler example to report @emph{instead}
9758 of the original one, that is a convenience for us. Errors in the
9759 output will be easier to spot, running under the debugger will take
9760 less time, and so on.
9762 However, simplification is not vital; if you do not want to do this,
9763 report the bug anyway and send us the entire test case you used.
9766 A patch for the bug.
9768 A patch for the bug does help us if it is a good one. But do not omit
9769 the necessary information, such as the test case, on the assumption that
9770 a patch is all we need. We might see problems with your patch and decide
9771 to fix the problem another way, or we might not understand it at all.
9773 Sometimes with a program as complicated as @value{GDBN} it is very hard to
9774 construct an example that will make the program follow a certain path
9775 through the code. If you do not send us the example, we will not be able
9776 to construct one, so we will not be able to verify that the bug is fixed.
9778 And if we cannot understand what bug you are trying to fix, or why your
9779 patch should be an improvement, we will not install it. A test case will
9780 help us to understand.
9783 A guess about what the bug is or what it depends on.
9785 Such guesses are usually wrong. Even we cannot guess right about such
9786 things without first using the debugger to find the facts.
9789 @c The readline documentation is distributed with the readline code
9790 @c and consists of the two following files:
9793 @c Use -I with makeinfo to point to the appropriate directory,
9794 @c environment var TEXINPUTS with TeX.
9795 @include rluser.texinfo
9796 @include inc-hist.texi
9800 @node Renamed Commands, Formatting Documentation, GDB Bugs, Top
9801 @appendix Renamed Commands
9803 The following commands were renamed in @value{GDBN} 4, in order to make the
9804 command set as a whole more consistent and easier to use and remember:
9807 @kindex delete environment
9808 @kindex info copying
9809 @kindex info convenience
9810 @kindex info directories
9811 @kindex info editing
9812 @kindex info history
9813 @kindex info targets
9815 @kindex info version
9816 @kindex info warranty
9817 @kindex set addressprint
9818 @kindex set arrayprint
9819 @kindex set prettyprint
9820 @kindex set screen-height
9821 @kindex set screen-width
9822 @kindex set unionprint
9823 @kindex set vtblprint
9824 @kindex set demangle
9825 @kindex set asm-demangle
9826 @kindex set sevenbit-strings
9827 @kindex set array-max
9829 @kindex set history write
9830 @kindex show addressprint
9831 @kindex show arrayprint
9832 @kindex show prettyprint
9833 @kindex show screen-height
9834 @kindex show screen-width
9835 @kindex show unionprint
9836 @kindex show vtblprint
9837 @kindex show demangle
9838 @kindex show asm-demangle
9839 @kindex show sevenbit-strings
9840 @kindex show array-max
9841 @kindex show caution
9842 @kindex show history write
9847 @c END TEXI2ROFF-KILL
9849 OLD COMMAND NEW COMMAND
9851 --------------- -------------------------------
9852 @c END TEXI2ROFF-KILL
9853 add-syms add-symbol-file
9854 delete environment unset environment
9855 info convenience show convenience
9856 info copying show copying
9857 info directories show directories
9858 info editing show commands
9859 info history show values
9860 info targets help target
9861 info values show values
9862 info version show version
9863 info warranty show warranty
9864 set/show addressprint set/show print address
9865 set/show array-max set/show print elements
9866 set/show arrayprint set/show print array
9867 set/show asm-demangle set/show print asm-demangle
9868 set/show caution set/show confirm
9869 set/show demangle set/show print demangle
9870 set/show history write set/show history save
9871 set/show prettyprint set/show print pretty
9872 set/show screen-height set/show height
9873 set/show screen-width set/show width
9874 set/show sevenbit-strings set/show print sevenbit-strings
9875 set/show unionprint set/show print union
9876 set/show vtblprint set/show print vtbl
9878 unset [No longer an alias for delete]
9884 \vskip \parskip\vskip \baselineskip
9885 \halign{\tt #\hfil &\qquad#&\tt #\hfil\cr
9886 {\bf Old Command} &&{\bf New Command}\cr
9887 add-syms &&add-symbol-file\cr
9888 delete environment &&unset environment\cr
9889 info convenience &&show convenience\cr
9890 info copying &&show copying\cr
9891 info directories &&show directories \cr
9892 info editing &&show commands\cr
9893 info history &&show values\cr
9894 info targets &&help target\cr
9895 info values &&show values\cr
9896 info version &&show version\cr
9897 info warranty &&show warranty\cr
9898 set{\rm / }show addressprint &&set{\rm / }show print address\cr
9899 set{\rm / }show array-max &&set{\rm / }show print elements\cr
9900 set{\rm / }show arrayprint &&set{\rm / }show print array\cr
9901 set{\rm / }show asm-demangle &&set{\rm / }show print asm-demangle\cr
9902 set{\rm / }show caution &&set{\rm / }show confirm\cr
9903 set{\rm / }show demangle &&set{\rm / }show print demangle\cr
9904 set{\rm / }show history write &&set{\rm / }show history save\cr
9905 set{\rm / }show prettyprint &&set{\rm / }show print pretty\cr
9906 set{\rm / }show screen-height &&set{\rm / }show height\cr
9907 set{\rm / }show screen-width &&set{\rm / }show width\cr
9908 set{\rm / }show sevenbit-strings &&set{\rm / }show print sevenbit-strings\cr
9909 set{\rm / }show unionprint &&set{\rm / }show print union\cr
9910 set{\rm / }show vtblprint &&set{\rm / }show print vtbl\cr
9912 unset &&\rm(No longer an alias for delete)\cr
9915 @c END TEXI2ROFF-KILL
9919 @ifclear PRECONFIGURED
9921 @node Formatting Documentation
9922 @c links whacked to pacify makeinfo
9923 @c , Installing GDB, Renamed Commands, Top
9924 @appendix Formatting Documentation
9926 @cindex @value{GDBN} reference card
9927 @cindex reference card
9928 The @value{GDBN} 4 release includes an already-formatted reference card, ready
9929 for printing with PostScript or Ghostscript, in the @file{gdb}
9930 subdirectory of the main source directory@footnote{In
9931 @file{gdb-@value{GDBVN}/gdb/refcard.ps} of the version @value{GDBVN}
9932 release.}. If you can use PostScript or Ghostscript with your printer,
9933 you can print the reference card immediately with @file{refcard.ps}.
9935 The release also includes the source for the reference card. You
9936 can format it, using @TeX{}, by typing:
9942 The @value{GDBN} reference card is designed to print in @dfn{landscape}
9943 mode on US ``letter'' size paper;
9944 that is, on a sheet 11 inches wide by 8.5 inches
9945 high. You will need to specify this form of printing as an option to
9946 your @sc{dvi} output program.
9948 @cindex documentation
9950 All the documentation for @value{GDBN} comes as part of the machine-readable
9951 distribution. The documentation is written in Texinfo format, which is
9952 a documentation system that uses a single source file to produce both
9953 on-line information and a printed manual. You can use one of the Info
9954 formatting commands to create the on-line version of the documentation
9955 and @TeX{} (or @code{texi2roff}) to typeset the printed version.
9957 @value{GDBN} includes an already formatted copy of the on-line Info version of
9958 this manual in the @file{gdb} subdirectory. The main Info file is
9959 @file{gdb-@r{version-number}/gdb/gdb.info}, and it refers to
9960 subordinate files matching @samp{gdb.info*} in the same directory. If
9961 necessary, you can print out these files, or read them with any editor;
9962 but they are easier to read using the @code{info} subsystem in @sc{gnu} Emacs
9963 or the standalone @code{info} program, available as part of the @sc{gnu}
9964 Texinfo distribution.
9966 If you want to format these Info files yourself, you need one of the
9967 Info formatting programs, such as @code{texinfo-format-buffer} or
9970 If you have @code{makeinfo} installed, and are in the top level @value{GDBN}
9971 source directory (@file{gdb-@value{GDBVN}}, in the case of version @value{GDBVN}), you can
9972 make the Info file by typing:
9979 If you want to typeset and print copies of this manual, you need @TeX{},
9980 a program to print its @sc{dvi} output files, and @file{texinfo.tex}, the
9981 Texinfo definitions file.
9983 @TeX{} is a typesetting program; it does not print files directly, but
9984 produces output files called @sc{dvi} files. To print a typeset
9985 document, you need a program to print @sc{dvi} files. If your system
9986 has @TeX{} installed, chances are it has such a program. The precise
9987 command to use depends on your system; @kbd{lpr -d} is common; another
9988 (for PostScript devices) is @kbd{dvips}. The @sc{dvi} print command may
9989 require a file name without any extension or a @samp{.dvi} extension.
9991 @TeX{} also requires a macro definitions file called
9992 @file{texinfo.tex}. This file tells @TeX{} how to typeset a document
9993 written in Texinfo format. On its own, @TeX{} cannot either read or
9994 typeset a Texinfo file. @file{texinfo.tex} is distributed with GDB
9995 and is located in the @file{gdb-@var{version-number}/texinfo}
9998 If you have @TeX{} and a @sc{dvi} printer program installed, you can
9999 typeset and print this manual. First switch to the the @file{gdb}
10000 subdirectory of the main source directory (for example, to
10001 @file{gdb-@value{GDBVN}/gdb}) and then type:
10008 @node Installing GDB, Index, Using History Interactively, Top
10009 @appendix Installing @value{GDBN}
10010 @cindex configuring @value{GDBN}
10011 @cindex installation
10014 If you obtain @value{GDBN} (HP WDB 0.75) as part of your HP ANSI C or
10015 HP ANSI C++ Developer's Kit at HP-UX Release 11.0, you do not have to
10016 take any special action to build or install @value{GDBN}.
10018 If you obtain @value{GDBN} (HP WDB 0.75) from an HP web site, you may
10019 download either a @code{swinstall}-able package or a source tree, or
10022 Most customers will want to install the @value{GDBN} binary that is part
10023 of the @code{swinstall}-able package. To do so, use a command of the
10027 /usr/sbin/swinstall -s @var{package-name} WDB
10030 Alternatively, it is possible to build @value{GDBN} from the source
10031 distribution. Sophisticated customers who want to modify the debugger
10032 sources to tailor @value{GDBN} to their their needs may wish to do this.
10033 The source distribution consists of a @code{tar}'ed source tree rooted
10034 at @file{gdb-4.16/...}. The instructions that follow describe how to
10035 build a @file{gdb} executable from this source tree. HP believes that
10036 these instructions apply to the WDB source tree that it distributes.
10037 However, HP does not explicitly support building a @file{gdb} for any
10038 non-HP platform from the WDB source tree. It may work, but HP has not
10039 tested it for any platforms other than those described in the WDB 0.75
10043 @value{GDBN} comes with a @code{configure} script that automates the process
10044 of preparing @value{GDBN} for installation; you can then use @code{make} to
10045 build the @code{gdb} program.
10047 @c irrelevant in info file; it's as current as the code it lives with.
10048 @footnote{If you have a more recent version of @value{GDBN} than @value{GDBVN},
10049 look at the @file{README} file in the sources; we may have improved the
10050 installation procedures since publishing this manual.}
10053 The @value{GDBN} distribution includes all the source code you need for
10054 @value{GDBN} in a single directory, whose name is usually composed by
10055 appending the version number to @samp{gdb}.
10057 For example, the @value{GDBN} version @value{GDBVN} distribution is in the
10058 @file{gdb-@value{GDBVN}} directory. That directory contains:
10061 @item gdb-@value{GDBVN}/configure @r{(and supporting files)}
10062 script for configuring @value{GDBN} and all its supporting libraries
10064 @item gdb-@value{GDBVN}/gdb
10065 the source specific to @value{GDBN} itself
10067 @item gdb-@value{GDBVN}/bfd
10068 source for the Binary File Descriptor library
10070 @item gdb-@value{GDBVN}/include
10071 @sc{gnu} include files
10073 @item gdb-@value{GDBVN}/libiberty
10074 source for the @samp{-liberty} free software library
10076 @item gdb-@value{GDBVN}/opcodes
10077 source for the library of opcode tables and disassemblers
10079 @item gdb-@value{GDBVN}/readline
10080 source for the @sc{gnu} command-line interface
10082 @item gdb-@value{GDBVN}/glob
10083 source for the @sc{gnu} filename pattern-matching subroutine
10085 @item gdb-@value{GDBVN}/mmalloc
10086 source for the @sc{gnu} memory-mapped malloc package
10089 The simplest way to configure and build @value{GDBN} is to run @code{configure}
10090 from the @file{gdb-@var{version-number}} source directory, which in
10091 this example is the @file{gdb-@value{GDBVN}} directory.
10093 First switch to the @file{gdb-@var{version-number}} source directory
10094 if you are not already in it; then run @code{configure}. Pass the
10095 identifier for the platform on which @value{GDBN} will run as an
10101 cd gdb-@value{GDBVN}
10102 ./configure @var{host}
10107 where @var{host} is an identifier such as @samp{sun4} or
10108 @samp{decstation}, that identifies the platform where @value{GDBN} will run.
10109 (You can often leave off @var{host}; @code{configure} tries to guess the
10110 correct value by examining your system.)
10112 Running @samp{configure @var{host}} and then running @code{make} builds the
10113 @file{bfd}, @file{readline}, @file{mmalloc}, and @file{libiberty}
10114 libraries, then @code{gdb} itself. The configured source files, and the
10115 binaries, are left in the corresponding source directories.
10118 @code{configure} is a Bourne-shell (@code{/bin/sh}) script; if your
10119 system does not recognize this automatically when you run a different
10120 shell, you may need to run @code{sh} on it explicitly:
10123 sh configure @var{host}
10126 If you run @code{configure} from a directory that contains source
10127 directories for multiple libraries or programs, such as the
10128 @file{gdb-@value{GDBVN}} source directory for version @value{GDBVN}, @code{configure}
10129 creates configuration files for every directory level underneath (unless
10130 you tell it not to, with the @samp{--norecursion} option).
10132 You can run the @code{configure} script from any of the
10133 subordinate directories in the @value{GDBN} distribution if you only want to
10134 configure that subdirectory, but be sure to specify a path to it.
10136 For example, with version @value{GDBVN}, type the following to configure only
10137 the @code{bfd} subdirectory:
10141 cd gdb-@value{GDBVN}/bfd
10142 ../configure @var{host}
10146 You can install @code{@value{GDBP}} anywhere; it has no hardwired paths.
10147 However, you should make sure that the shell on your path (named by
10148 the @samp{SHELL} environment variable) is publicly readable. Remember
10149 that @value{GDBN} uses the shell to start your program---some systems refuse to
10150 let @value{GDBN} debug child processes whose programs are not readable.
10153 * Separate Objdir:: Compiling @value{GDBN} in another directory
10154 * Config Names:: Specifying names for hosts and targets
10155 * Configure Options:: Summary of options for configure
10158 @node Separate Objdir, Config Names, Installing GDB, Installing GDB
10159 @section Compiling @value{GDBN} in another directory
10161 If you want to run @value{GDBN} versions for several host or target machines,
10162 you need a different @code{gdb} compiled for each combination of
10163 host and target. @code{configure} is designed to make this easy by
10164 allowing you to generate each configuration in a separate subdirectory,
10165 rather than in the source directory. If your @code{make} program
10166 handles the @samp{VPATH} feature (@sc{gnu} @code{make} does), running
10167 @code{make} in each of these directories builds the @code{gdb}
10168 program specified there.
10170 To build @code{gdb} in a separate directory, run @code{configure}
10171 with the @samp{--srcdir} option to specify where to find the source.
10172 (You also need to specify a path to find @code{configure}
10173 itself from your working directory. If the path to @code{configure}
10174 would be the same as the argument to @samp{--srcdir}, you can leave out
10175 the @samp{--srcdir} option; it is assumed.)
10177 For example, with version @value{GDBVN}, you can build @value{GDBN} in a
10178 separate directory for a Sun 4 like this:
10182 cd gdb-@value{GDBVN}
10185 ../gdb-@value{GDBVN}/configure sun4
10190 When @code{configure} builds a configuration using a remote source
10191 directory, it creates a tree for the binaries with the same structure
10192 (and using the same names) as the tree under the source directory. In
10193 the example, you'd find the Sun 4 library @file{libiberty.a} in the
10194 directory @file{gdb-sun4/libiberty}, and @value{GDBN} itself in
10195 @file{gdb-sun4/gdb}.
10197 One popular reason to build several @value{GDBN} configurations in separate
10198 directories is to configure @value{GDBN} for cross-compiling (where
10199 @value{GDBN} runs on one machine---the @dfn{host}---while debugging
10200 programs that run on another machine---the @dfn{target}).
10201 You specify a cross-debugging target by
10202 giving the @samp{--target=@var{target}} option to @code{configure}.
10204 When you run @code{make} to build a program or library, you must run
10205 it in a configured directory---whatever directory you were in when you
10206 called @code{configure} (or one of its subdirectories).
10208 The @code{Makefile} that @code{configure} generates in each source
10209 directory also runs recursively. If you type @code{make} in a source
10210 directory such as @file{gdb-@value{GDBVN}} (or in a separate configured
10211 directory configured with @samp{--srcdir=@var{dirname}/gdb-@value{GDBVN}}), you
10212 will build all the required libraries, and then build GDB.
10214 When you have multiple hosts or targets configured in separate
10215 directories, you can run @code{make} on them in parallel (for example,
10216 if they are NFS-mounted on each of the hosts); they will not interfere
10219 @node Config Names, Configure Options, Separate Objdir, Installing GDB
10220 @section Specifying names for hosts and targets
10222 The specifications used for hosts and targets in the @code{configure}
10223 script are based on a three-part naming scheme, but some short predefined
10224 aliases are also supported. The full naming scheme encodes three pieces
10225 of information in the following pattern:
10228 @var{architecture}-@var{vendor}-@var{os}
10231 For example, you can use the alias @code{sun4} as a @var{host} argument,
10232 or as the value for @var{target} in a @code{--target=@var{target}}
10233 option. The equivalent full name is @samp{sparc-sun-sunos4}.
10235 The @code{configure} script accompanying @value{GDBN} does not provide
10236 any query facility to list all supported host and target names or
10237 aliases. @code{configure} calls the Bourne shell script
10238 @code{config.sub} to map abbreviations to full names; you can read the
10239 script, if you wish, or you can use it to test your guesses on
10240 abbreviations---for example:
10243 % sh config.sub sun4
10244 sparc-sun-sunos4.1.1
10245 % sh config.sub sun3
10246 m68k-sun-sunos4.1.1
10247 % sh config.sub decstation
10249 % sh config.sub hp300bsd
10251 % sh config.sub i386v
10253 % sh config.sub i786v
10254 Invalid configuration `i786v': machine `i786v' not recognized
10258 @code{config.sub} is also distributed in the @value{GDBN} source
10259 directory (@file{gdb-@value{GDBVN}}, for version @value{GDBVN}).
10261 @node Configure Options, , Config Names, Installing GDB
10262 @section @code{configure} options
10264 Here is a summary of the @code{configure} options and arguments that
10265 are most often useful for building @value{GDBN}. @code{configure} also has
10266 several other options not listed here. @inforef{What Configure
10267 Does,,configure.info}, for a full explanation of @code{configure}.
10270 configure @r{[}--help@r{]}
10271 @r{[}--prefix=@var{dir}@r{]}
10272 @r{[}--srcdir=@var{dirname}@r{]}
10273 @r{[}--norecursion@r{]} @r{[}--rm@r{]}
10274 @r{[}--target=@var{target}@r{]} @var{host}
10278 You may introduce options with a single @samp{-} rather than
10279 @samp{--} if you prefer; but you may abbreviate option names if you use
10284 Display a quick summary of how to invoke @code{configure}.
10286 @item -prefix=@var{dir}
10287 Configure the source to install programs and files under directory
10290 @c avoid splitting the warning from the explanation:
10292 @item --srcdir=@var{dirname}
10293 @strong{Warning: using this option requires @sc{gnu} @code{make}, or another
10294 @code{make} that implements the @code{VPATH} feature.}@*
10295 Use this option to make configurations in directories separate from the
10296 @value{GDBN} source directories. Among other things, you can use this to
10297 build (or maintain) several configurations simultaneously, in separate
10298 directories. @code{configure} writes configuration specific files in
10299 the current directory, but arranges for them to use the source in the
10300 directory @var{dirname}. @code{configure} creates directories under
10301 the working directory in parallel to the source directories below
10304 @item --norecursion
10305 Configure only the directory level where @code{configure} is executed; do not
10306 propagate configuration to subdirectories.
10309 @emph{Remove} files otherwise built during configuration.
10311 @c This does not work (yet if ever). FIXME.
10312 @c @item --parse=@var{lang} @dots{}
10313 @c Configure the @value{GDBN} expression parser to parse the listed languages.
10314 @c @samp{all} configures @value{GDBN} for all supported languages. To get a
10315 @c list of all supported languages, omit the argument. Without this
10316 @c option, @value{GDBN} is configured to parse all supported languages.
10318 @item --target=@var{target}
10319 Configure @value{GDBN} for cross-debugging programs running on the specified
10320 @var{target}. Without this option, @value{GDBN} is configured to debug
10321 programs that run on the same machine (@var{host}) as @value{GDBN} itself.
10323 There is no convenient way to generate a list of all available targets.
10325 @item @var{host} @dots{}
10326 Configure @value{GDBN} to run on the specified @var{host}.
10328 There is no convenient way to generate a list of all available hosts.
10332 @code{configure} accepts other options, for compatibility with
10333 configuring other @sc{gnu} tools recursively; but these are the only
10334 options that affect @value{GDBN} or its supporting libraries.
10338 @node Index, , Installing GDB, Top
10344 % I think something like @colophon should be in texinfo. In the
10346 \long\def\colophon{\hbox to0pt{}\vfill
10347 \centerline{The body of this manual is set in}
10348 \centerline{\fontname\tenrm,}
10349 \centerline{with headings in {\bf\fontname\tenbf}}
10350 \centerline{and examples in {\tt\fontname\tentt}.}
10351 \centerline{{\it\fontname\tenit\/},}
10352 \centerline{{\bf\fontname\tenbf}, and}
10353 \centerline{{\sl\fontname\tensl\/}}
10354 \centerline{are used for emphasis.}\vfill}
10356 % Blame: doc@cygnus.com, 1991.