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diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo new file mode 100644 index 00000000000..fc920bb0c57 --- /dev/null +++ b/gdb/doc/gdb.texinfo @@ -0,0 +1,10316 @@ +\input texinfo @c -*-texinfo-*- +@c Copyright 1988-1999 +@c Free Software Foundation, Inc. +@c +@c %**start of header +@c makeinfo ignores cmds prev to setfilename, so its arg cannot make use +@c of @set vars. However, you can override filename with makeinfo -o. +@setfilename gdb.info +@c +@include gdb-cfg.texi +@c +@ifset GENERIC +@settitle Debugging with @value{GDBN} +@end ifset +@ifclear GENERIC +@settitle Debugging with @value{GDBN} (@value{TARGET}) +@end ifclear +@setchapternewpage odd +@c %**end of header + +@iftex +@c @smallbook +@c @cropmarks +@end iftex + +@finalout +@syncodeindex ky cp + +@c readline appendices use @vindex +@syncodeindex vr cp + +@c !!set GDB manual's edition---not the same as GDB version! +@set EDITION Seventh + +@c !!set GDB manual's revision date +@set DATE February 1999 + +@c THIS MANUAL REQUIRES TEXINFO-2 macros and info-makers to format properly. + +@ifinfo +@c This is a dir.info fragment to support semi-automated addition of +@c manuals to an info tree. zoo@cygnus.com is developing this facility. +@format +START-INFO-DIR-ENTRY +* Gdb: (gdb). The @sc{gnu} debugger. +END-INFO-DIR-ENTRY +@end format +@end ifinfo +@c +@c +@ifinfo +This file documents the @sc{gnu} debugger @value{GDBN}. + + +This is the @value{EDITION} Edition, @value{DATE}, +of @cite{Debugging with @value{GDBN}: the @sc{gnu} Source-Level Debugger} +for @value{GDBN} Version @value{GDBVN}. + +Copyright (C) 1988-1999 Free Software Foundation, Inc. + +Permission is granted to make and distribute verbatim copies of +this manual provided the copyright notice and this permission notice +are preserved on all copies. + +@ignore +Permission is granted to process this file through TeX and print the +results, provided the printed document carries copying permission +notice identical to this one except for the removal of this paragraph +(this paragraph not being relevant to the printed manual). + +@end ignore +Permission is granted to copy and distribute modified versions of this +manual under the conditions for verbatim copying, provided also that the +entire resulting derived work is distributed under the terms of a +permission notice identical to this one. + +Permission is granted to copy and distribute translations of this manual +into another language, under the above conditions for modified versions. +@end ifinfo + +@titlepage +@title Debugging with @value{GDBN} +@subtitle The @sc{gnu} Source-Level Debugger +@ifclear GENERIC +@subtitle (@value{TARGET}) +@end ifclear +@sp 1 +@ifclear HPPA +@subtitle @value{EDITION} Edition, for @value{GDBN} version @value{GDBVN} +@subtitle @value{DATE} +@author Richard M. Stallman and Roland H. Pesch +@end ifclear +@ifset HPPA +@subtitle Edition @value{EDITION}, for @value{HPVER} (based on @value{GDBN} @value{GDBVN}) +@subtitle @value{DATE} +@author Richard M. Stallman and Roland H. Pesch (modified by HP) +@end ifset +@page +@ifclear HPPA +@tex +{\parskip=0pt +\hfill (Send bugs and comments on @value{GDBN} to bug-gdb\@prep.ai.mit.edu.)\par +\hfill {\it Debugging with @value{GDBN}}\par +\hfill \TeX{}info \texinfoversion\par +} +@end tex +@end ifclear +@ifset HPPA +@tex +{\parskip=0pt +\hfill {\it Debugging with @value{GDBN}}\par +\hfill \TeX{}info \texinfoversion\par +} +@end tex +@end ifset + +@vskip 0pt plus 1filll +Copyright @copyright{} 1988-1999 Free Software Foundation, Inc. +@sp 2 +@ifclear HPPA +Published by the Free Software Foundation @* +59 Temple Place - Suite 330, @* +Boston, MA 02111-1307 USA @* +Printed copies are available for $20 each. @* +ISBN 1-882114-11-6 @* +@end ifclear + +Permission is granted to make and distribute verbatim copies of +this manual provided the copyright notice and this permission notice +are preserved on all copies. + +Permission is granted to copy and distribute modified versions of this +manual under the conditions for verbatim copying, provided also that the +entire resulting derived work is distributed under the terms of a +permission notice identical to this one. + +Permission is granted to copy and distribute translations of this manual +into another language, under the above conditions for modified versions. +@end titlepage +@page + +@ifinfo +@node Top, Summary, (dir), (dir) +@top Debugging with @value{GDBN} + +This file describes @value{GDBN}, the @sc{gnu} symbolic debugger. + +This is the @value{EDITION} Edition, @value{DATE}, for @value{GDBN} Version +@value{GDBVN}. + +Copyright (C) 1988-1999 Free Software Foundation, Inc. +@menu +* Summary:: Summary of @value{GDBN} +@ifclear BARETARGET +* Sample Session:: A sample @value{GDBN} session +@end ifclear + +* Invocation:: Getting in and out of @value{GDBN} +* Commands:: @value{GDBN} commands +* Running:: Running programs under @value{GDBN} +* Stopping:: Stopping and continuing +* Stack:: Examining the stack +* Source:: Examining source files +* Data:: Examining data +@ifclear CONLY +* Languages:: Using @value{GDBN} with different languages +@end ifclear + +@ifset CONLY +* C:: C language support +@end ifset + +* Symbols:: Examining the symbol table +* Altering:: Altering execution +* GDB Files:: @value{GDBN} files +* Targets:: Specifying a debugging target +* Controlling GDB:: Controlling @value{GDBN} +* Sequences:: Canned sequences of commands +@ifclear DOSHOST +* Emacs:: Using @value{GDBN} under @sc{gnu} Emacs +@end ifclear + +* GDB Bugs:: Reporting bugs in @value{GDBN} + +@ifclear PRECONFIGURED +@ifclear HPPA +* Formatting Documentation:: How to format and print @value{GDBN} documentation +@end ifclear + +@end ifclear + +* Command Line Editing:: Command Line Editing +* Using History Interactively:: Using History Interactively +* Installing GDB:: Installing GDB +* Index:: Index + + --- The Detailed Node Listing --- + +Summary of @value{GDBN} + +* Free Software:: Freely redistributable software +* Contributors:: Contributors to GDB + +Getting In and Out of @value{GDBN} + +* Invoking GDB:: How to start @value{GDBN} +* Quitting GDB:: How to quit @value{GDBN} +* Shell Commands:: How to use shell commands inside @value{GDBN} + +Invoking @value{GDBN} + +* File Options:: Choosing files +* Mode Options:: Choosing modes + +@value{GDBN} Commands + +* Command Syntax:: How to give commands to @value{GDBN} +* Completion:: Command completion +* Help:: How to ask @value{GDBN} for help + +Running Programs Under @value{GDBN} + +* Compilation:: Compiling for debugging +* Starting:: Starting your program +@ifclear BARETARGET +* Arguments:: Your program's arguments +* Environment:: Your program's environment +@end ifclear + +* Working Directory:: Your program's working directory +* Input/Output:: Your program's input and output +* Attach:: Debugging an already-running process +* Kill Process:: Killing the child process +@ifclear HPPA +* Process Information:: Additional process information +@end ifclear + +* Threads:: Debugging programs with multiple threads +* Processes:: Debugging programs with multiple processes + +Stopping and Continuing + +* Breakpoints:: Breakpoints, watchpoints, and catchpoints +* Continuing and Stepping:: Resuming execution +@ifset POSIX +* Signals:: Signals +@end ifset +@ifclear BARETARGET +* Thread Stops:: Stopping and starting multi-thread programs +@end ifclear + +Breakpoints and watchpoints + +* Set Breaks:: Setting breakpoints +* Set Watchpoints:: Setting watchpoints +* Set Catchpoints:: Setting catchpoints +* Delete Breaks:: Deleting breakpoints +* Disabling:: Disabling breakpoints +* Conditions:: Break conditions +* Break Commands:: Breakpoint command lists +@ifclear CONLY +* Breakpoint Menus:: Breakpoint menus +@end ifclear + +Examining the Stack + +* Frames:: Stack frames +* Backtrace:: Backtraces +* Selection:: Selecting a frame +* Frame Info:: Information on a frame +* Alpha/MIPS Stack:: Alpha and MIPS machines and the function stack + +Examining Source Files + +* List:: Printing source lines +@ifclear DOSHOST +* Search:: Searching source files +@end ifclear +* Source Path:: Specifying source directories +* Machine Code:: Source and machine code + +Examining Data + +* Expressions:: Expressions +* Variables:: Program variables +* Arrays:: Artificial arrays +* Output Formats:: Output formats +* Memory:: Examining memory +* Auto Display:: Automatic display +* Print Settings:: Print settings +* Value History:: Value history +* Convenience Vars:: Convenience variables +* Registers:: Registers +@ifclear HAVE-FLOAT +* Floating Point Hardware:: Floating point hardware +@end ifclear + +Using @value{GDBN} with Different Languages + +* Setting:: Switching between source languages +* Show:: Displaying the language +@ifset MOD2 +* Checks:: Type and range checks +@end ifset + +* Support:: Supported languages + +Switching between source languages + +* Filenames:: Filename extensions and languages. +* Manually:: Setting the working language manually +* Automatically:: Having @value{GDBN} infer the source language + +@ifset MOD2 +Type and range checking + +* Type Checking:: An overview of type checking +* Range Checking:: An overview of range checking +@end ifset + +Supported languages + +@ifset MOD2 +* C:: C and C++ + +C Language Support + +* C Operators:: C operators + +C Language Support +@end ifset + +* C Operators:: C and C++ operators +* C Constants:: C and C++ constants +* Cplus expressions:: C++ expressions +* C Defaults:: Default settings for C and C++ +@ifset MOD2 +* C Checks:: C and C++ type and range checks +@end ifset +* Debugging C:: @value{GDBN} and C +* Debugging C plus plus:: @value{GDBN} features for C++ + +@ifset MOD2 +Modula-2 + +* M2 Operators:: Built-in operators +* Built-In Func/Proc:: Built-in functions and procedures +* M2 Constants:: Modula-2 constants +* M2 Defaults:: Default settings for Modula-2 +* Deviations:: Deviations from standard Modula-2 +* M2 Checks:: Modula-2 type and range checks +* M2 Scope:: The scope operators @code{::} and @code{.} +* GDB/M2:: @value{GDBN} and Modula-2 +@end ifset + +Altering Execution + +* Assignment:: Assignment to variables +* Jumping:: Continuing at a different address +@ifclear BARETARGET +* Signaling:: Giving your program a signal +@end ifclear +* Returning:: Returning from a function +* Calling:: Calling your program's functions +* Patching:: Patching your program + +@value{GDBN} Files + +* Files:: Commands to specify files +* Symbol Errors:: Errors reading symbol files + +Specifying a Debugging Target + +* Active Targets:: Active targets +* Target Commands:: Commands for managing targets +@ifclear HPPA +* Byte Order:: Choosing target byte order +* Remote:: Remote debugging + +Remote debugging +@end ifclear + +@ifset REMOTESTUB +* Remote Serial:: @value{GDBN} remote serial protocol +@end ifset + +@ifset I960 +* i960-Nindy Remote:: @value{GDBN} with a remote i960 (Nindy) +@end ifset + +@ifset AMD29K +* UDI29K Remote:: The UDI protocol for AMD29K +* EB29K Remote:: The EBMON protocol for AMD29K +@end ifset + +@ifset VXWORKS +* VxWorks Remote:: @value{GDBN} and VxWorks +@end ifset + +@ifset ST2000 +* ST2000 Remote:: @value{GDBN} with a Tandem ST2000 +@end ifset + +@ifset H8 +* Hitachi Remote:: @value{GDBN} and Hitachi Microprocessors +@end ifset + +@ifset MIPS +* MIPS Remote:: @value{GDBN} and MIPS boards +@end ifset + +@ifset SIMS +* Simulator:: Simulated CPU target +@end ifset + +Controlling @value{GDBN} + +* Prompt:: Prompt +* Editing:: Command editing +* History:: Command history +* Screen Size:: Screen size +* Numbers:: Numbers +* Messages/Warnings:: Optional warnings and messages + +Canned Sequences of Commands + +* Define:: User-defined commands +* Hooks:: User-defined command hooks +* Command Files:: Command files +* Output:: Commands for controlled output + +Reporting Bugs in @value{GDBN} + +* Bug Criteria:: Have you found a bug? +* Bug Reporting:: How to report bugs + +Installing @value{GDBN} + +* Separate Objdir:: Compiling @value{GDBN} in another directory +* Config Names:: Specifying names for hosts and targets +* Configure Options:: Summary of options for configure +@end menu + +@end ifinfo + +@node Summary, Sample Session, Top, Top +@unnumbered Summary of @value{GDBN} + +The purpose of a debugger such as @value{GDBN} is to allow you to see what is +going on ``inside'' another program while it executes---or what another +program was doing at the moment it crashed. + +@value{GDBN} can do four main kinds of things (plus other things in support of +these) to help you catch bugs in the act: + +@itemize @bullet +@item +Start your program, specifying anything that might affect its behavior. + +@item +Make your program stop on specified conditions. + +@item +Examine what has happened, when your program has stopped. + +@item +Change things in your program, so you can experiment with correcting the +effects of one bug and go on to learn about another. +@end itemize + +@ifclear CONLY +You can use @value{GDBN} to debug programs written in C or C++. +@c "MOD2" used as a "miscellaneous languages" flag here. +@c This is acceptable while there is no real doc for Chill and Pascal. +@ifclear MOD2 +For more information, see @ref{Support,,Supported languages}. +@end ifclear +@ifset MOD2 +For more information, see @ref{C,,C and C++}. + +Support for Modula-2 and Chill is partial. For information on Modula-2, +see @ref{Modula-2,,Modula-2}. There is no further documentation on Chill yet. + +Debugging Pascal programs which use sets, subranges, file variables, or nested +functions does not currently work. @value{GDBN} does not support +entering expressions, printing values, or similar features using Pascal syntax. +@end ifset + +@ifset FORTRAN +@cindex Fortran +@value{GDBN} can be used to debug programs written in Fortran, although +it does not yet support entering expressions, printing values, or +similar features using Fortran syntax. It may be necessary to refer to +some variables with a trailing underscore. +@end ifset +@end ifclear + +@ifset HPPA +This version of the manual documents HP Wildebeest (WDB) Version 0.75, +implemented on HP 9000 systems running Release 10.20, 10.30, or 11.0 of +the HP-UX operating system. HP WDB 0.75 can be used to debug code +generated by the HP ANSI C and HP ANSI C++ compilers as well as the +@sc{gnu} C and C++ compilers. It does not support the debugging of +Fortran, Modula-2, or Chill programs. +@end ifset + +@menu +* Free Software:: Freely redistributable software +* Contributors:: Contributors to GDB +@end menu + +@node Free Software, Contributors, Summary, Summary +@unnumberedsec Free software + +@value{GDBN} is @dfn{free software}, protected by the @sc{gnu} +General Public License +(GPL). The GPL gives you the freedom to copy or adapt a licensed +program---but every person getting a copy also gets with it the +freedom to modify that copy (which means that they must get access to +the source code), and the freedom to distribute further copies. +Typical software companies use copyrights to limit your freedoms; the +Free Software Foundation uses the GPL to preserve these freedoms. + +Fundamentally, the General Public License is a license which says that +you have these freedoms and that you cannot take these freedoms away +from anyone else. + +@node Contributors, , Free Software, Summary +@unnumberedsec Contributors to GDB + +Richard Stallman was the original author of GDB, and of many other +@sc{gnu} programs. Many others have contributed to its development. +This section attempts to credit major contributors. One of the virtues +of free software is that everyone is free to contribute to it; with +regret, we cannot actually acknowledge everyone here. The file +@file{ChangeLog} in the @value{GDBN} distribution approximates a +blow-by-blow account. + +Changes much prior to version 2.0 are lost in the mists of time. + +@quotation +@emph{Plea:} Additions to this section are particularly welcome. If you +or your friends (or enemies, to be evenhanded) have been unfairly +omitted from this list, we would like to add your names! +@end quotation + +So that they may not regard their many labors as thankless, we +particularly thank those who shepherded @value{GDBN} through major +releases: +Jim Blandy (release 4.18); +Jason Molenda (release 4.17); +Stan Shebs (release 4.14); +Fred Fish (releases 4.16, 4.15, 4.13, 4.12, 4.11, 4.10, and 4.9); +Stu Grossman and John Gilmore (releases 4.8, 4.7, 4.6, 4.5, and 4.4); +John Gilmore (releases 4.3, 4.2, 4.1, 4.0, and 3.9); +Jim Kingdon (releases 3.5, 3.4, and 3.3); +and Randy Smith (releases 3.2, 3.1, and 3.0). + +Richard Stallman, assisted at various times by Peter TerMaat, Chris +Hanson, and Richard Mlynarik, handled releases through 2.8. + +@ifclear CONLY +Michael Tiemann is the author of most of the @sc{gnu} C++ support in GDB, +with significant additional contributions from Per Bothner. James +Clark wrote the @sc{gnu} C++ demangler. Early work on C++ was by Peter +TerMaat (who also did much general update work leading to release 3.0). +@end ifclear + +@value{GDBN} 4 uses the BFD subroutine library to examine multiple +object-file formats; BFD was a joint project of David V. +Henkel-Wallace, Rich Pixley, Steve Chamberlain, and John Gilmore. + +David Johnson wrote the original COFF support; Pace Willison did +the original support for encapsulated COFF. + +Brent Benson of Harris Computer Systems contributed DWARF 2 support. + +Adam de Boor and Bradley Davis contributed the ISI Optimum V support. +Per Bothner, Noboyuki Hikichi, and Alessandro Forin contributed MIPS +support. +Jean-Daniel Fekete contributed Sun 386i support. +Chris Hanson improved the HP9000 support. +Noboyuki Hikichi and Tomoyuki Hasei contributed Sony/News OS 3 support. +David Johnson contributed Encore Umax support. +Jyrki Kuoppala contributed Altos 3068 support. +Jeff Law contributed HP PA and SOM support. +Keith Packard contributed NS32K support. +Doug Rabson contributed Acorn Risc Machine support. +Bob Rusk contributed Harris Nighthawk CX-UX support. +Chris Smith contributed Convex support (and Fortran debugging). +Jonathan Stone contributed Pyramid support. +Michael Tiemann contributed SPARC support. +Tim Tucker contributed support for the Gould NP1 and Gould Powernode. +Pace Willison contributed Intel 386 support. +Jay Vosburgh contributed Symmetry support. + +Andreas Schwab contributed M68K Linux support. + +Rich Schaefer and Peter Schauer helped with support of SunOS shared +libraries. + +Jay Fenlason and Roland McGrath ensured that @value{GDBN} and GAS agree +about several machine instruction sets. + +Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped develop +remote debugging. Intel Corporation, Wind River Systems, AMD, and ARM +contributed remote debugging modules for the i960, VxWorks, A29K UDI, +and RDI targets, respectively. + +Brian Fox is the author of the readline libraries providing +command-line editing and command history. + +Andrew Beers of SUNY Buffalo wrote the language-switching code, +@ifset MOD2 +the Modula-2 support, +@end ifset +and contributed the Languages chapter of this manual. + +Fred Fish wrote most of the support for Unix System Vr4. +@ifclear CONLY +He also enhanced the command-completion support to cover C++ overloaded +symbols. +@end ifclear + +Hitachi America, Ltd. sponsored the support for H8/300, H8/500, and +Super-H processors. + +NEC sponsored the support for the v850, Vr4xxx, and Vr5xxx processors. + +Mitsubishi sponsored the support for D10V, D30V, and M32R/D processors. + +Toshiba sponsored the support for the TX39 Mips processor. + +Matsushita sponsored the support for the MN10200 and MN10300 processors. + +Fujitsu sponsored the support for SPARClite and FR30 processors + +Kung Hsu, Jeff Law, and Rick Sladkey added support for hardware +watchpoints. + +Michael Snyder added support for tracepoints. + +Stu Grossman wrote gdbserver. + +Jim Kingdon, Peter Schauer, Ian Taylor, and Stu Grossman made +nearly innumerable bug fixes and cleanups throughout GDB. + +The following people at the Hewlett-Packard Company contributed +support for the PA-RISC 2.0 architecture, HP-UX 10.20, 10.30, and 11.0 +(narrow mode), HP's implementation of kernel threads, HP's aC++ +compiler, and the terminal user interface: Ben Krepp, Richard Title, +John Bishop, Susan Macchia, Kathy Mann, Satish Pai, India Paul, Steve +Rehrauer, and Elena Zannoni. Kim Haase provided HP-specific +information in this manual. + +Cygnus Solutions has sponsored GDB maintenance and much of its +development since 1991. Cygnus engineers who have worked on GDB +fulltime include Mark Alexander, Jim Blandy, Per Bothner, Edith Epstein, +Chris Faylor, Fred Fish, Martin Hunt, Jim Ingham, John Gilmore, Stu +Grossman, Kung Hsu, Jim Kingdon, John Metzler, Fernando Nasser, Geoffrey +Noer, Dawn Perchik, Rich Pixley, Zdenek Radouch, Keith Seitz, Stan +Shebs, David Taylor, and Elena Zannoni. In addition, Dave Brolley, Ian +Carmichael, Steve Chamberlain, Nick Clifton, JT Conklin, Stan Cox, DJ +Delorie, Ulrich Drepper, Frank Eigler, Doug Evans, Sean Fagan, David +Henkel-Wallace, Richard Henderson, Jeff Holcomb, Jeff Law, Jim Lemke, +Tom Lord, Bob Manson, Michael Meissner, Jason Merrill, Catherine Moore, +Drew Moseley, Ken Raeburn, Gavin Romig-Koch, Rob Savoye, Jamie Smith, +Mike Stump, Ian Taylor, Angela Thomas, Michael Tiemann, Tom Tromey, Ron +Unrau, Jim Wilson, and David Zuhn have made contributions both large +and small. + + +@ifclear BARETARGET +@node Sample Session, Invocation, Summary, Top +@chapter A Sample @value{GDBN} Session + +You can use this manual at your leisure to read all about @value{GDBN}. +However, a handful of commands are enough to get started using the +debugger. This chapter illustrates those commands. + +@iftex +In this sample session, we emphasize user input like this: @b{input}, +to make it easier to pick out from the surrounding output. +@end iftex + +@c FIXME: this example may not be appropriate for some configs, where +@c FIXME...primary interest is in remote use. + +One of the preliminary versions of @sc{gnu} @code{m4} (a generic macro +processor) exhibits the following bug: sometimes, when we change its +quote strings from the default, the commands used to capture one macro +definition within another stop working. In the following short @code{m4} +session, we define a macro @code{foo} which expands to @code{0000}; we +then use the @code{m4} built-in @code{defn} to define @code{bar} as the +same thing. However, when we change the open quote string to +@code{<QUOTE>} and the close quote string to @code{<UNQUOTE>}, the same +procedure fails to define a new synonym @code{baz}: + +@smallexample +$ @b{cd gnu/m4} +$ @b{./m4} +@b{define(foo,0000)} + +@b{foo} +0000 +@b{define(bar,defn(`foo'))} + +@b{bar} +0000 +@b{changequote(<QUOTE>,<UNQUOTE>)} + +@b{define(baz,defn(<QUOTE>foo<UNQUOTE>))} +@b{baz} +@b{C-d} +m4: End of input: 0: fatal error: EOF in string +@end smallexample + +@noindent +Let us use @value{GDBN} to try to see what is going on. + +@ifclear HPPA +@smallexample +$ @b{@value{GDBP} m4} +@c FIXME: this falsifies the exact text played out, to permit smallbook +@c FIXME... format to come out better. +@value{GDBN} is free software and you are welcome to distribute copies + of it under certain conditions; type "show copying" to see + the conditions. +There is absolutely no warranty for @value{GDBN}; type "show warranty" + for details. + +@value{GDBN} @value{GDBVN}, Copyright 1999 Free Software Foundation, Inc... +(@value{GDBP}) +@end smallexample +@end ifclear +@ifset HPPA +@smallexample +$ @b{@value{GDBP} m4} +Wildebeest is free software and you are welcome to distribute copies of +it under certain conditions; type "show copying" to see the conditions. +There is absolutely no warranty for Wildebeest; type "show warranty" +for details. + +Hewlett-Packard Wildebeest 0.75 (based on GDB 4.16) +(built for PA-RISC 1.1 or 2.0, HP-UX 10.20) +Copyright 1996, 1997 Free Software Foundation, Inc. +(@value{GDBP}) +@end smallexample +@end ifset + +@noindent +@value{GDBN} reads only enough symbol data to know where to find the +rest when needed; as a result, the first prompt comes up very quickly. +We now tell @value{GDBN} to use a narrower display width than usual, so +that examples fit in this manual. + +@smallexample +(@value{GDBP}) @b{set width 70} +@end smallexample + +@noindent +We need to see how the @code{m4} built-in @code{changequote} works. +Having looked at the source, we know the relevant subroutine is +@code{m4_changequote}, so we set a breakpoint there with the @value{GDBN} +@code{break} command. + +@smallexample +(@value{GDBP}) @b{break m4_changequote} +Breakpoint 1 at 0x62f4: file builtin.c, line 879. +@end smallexample + +@noindent +Using the @code{run} command, we start @code{m4} running under @value{GDBN} +control; as long as control does not reach the @code{m4_changequote} +subroutine, the program runs as usual: + +@smallexample +(@value{GDBP}) @b{run} +Starting program: /work/Editorial/gdb/gnu/m4/m4 +@b{define(foo,0000)} + +@b{foo} +0000 +@end smallexample + +@noindent +To trigger the breakpoint, we call @code{changequote}. @value{GDBN} +suspends execution of @code{m4}, displaying information about the +context where it stops. + +@smallexample +@b{changequote(<QUOTE>,<UNQUOTE>)} + +Breakpoint 1, m4_changequote (argc=3, argv=0x33c70) + at builtin.c:879 +879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]),argc,1,3)) +@end smallexample + +@noindent +Now we use the command @code{n} (@code{next}) to advance execution to +the next line of the current function. + +@smallexample +(@value{GDBP}) @b{n} +882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\ + : nil, +@end smallexample + +@noindent +@code{set_quotes} looks like a promising subroutine. We can go into it +by using the command @code{s} (@code{step}) instead of @code{next}. +@code{step} goes to the next line to be executed in @emph{any} +subroutine, so it steps into @code{set_quotes}. + +@smallexample +(@value{GDBP}) @b{s} +set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>") + at input.c:530 +530 if (lquote != def_lquote) +@end smallexample + +@noindent +The display that shows the subroutine where @code{m4} is now +suspended (and its arguments) is called a stack frame display. It +shows a summary of the stack. We can use the @code{backtrace} +command (which can also be spelled @code{bt}), to see where we are +in the stack as a whole: the @code{backtrace} command displays a +stack frame for each active subroutine. + +@smallexample +(@value{GDBP}) @b{bt} +#0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>") + at input.c:530 +#1 0x6344 in m4_changequote (argc=3, argv=0x33c70) + at builtin.c:882 +#2 0x8174 in expand_macro (sym=0x33320) at macro.c:242 +#3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30) + at macro.c:71 +#4 0x79dc in expand_input () at macro.c:40 +#5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195 +@end smallexample + +@noindent +We step through a few more lines to see what happens. The first two +times, we can use @samp{s}; the next two times we use @code{n} to avoid +falling into the @code{xstrdup} subroutine. + +@smallexample +(@value{GDBP}) @b{s} +0x3b5c 532 if (rquote != def_rquote) +(@value{GDBP}) @b{s} +0x3b80 535 lquote = (lq == nil || *lq == '\0') ? \ +def_lquote : xstrdup(lq); +(@value{GDBP}) @b{n} +536 rquote = (rq == nil || *rq == '\0') ? def_rquote\ + : xstrdup(rq); +(@value{GDBP}) @b{n} +538 len_lquote = strlen(rquote); +@end smallexample + +@noindent +The last line displayed looks a little odd; we can examine the variables +@code{lquote} and @code{rquote} to see if they are in fact the new left +and right quotes we specified. We use the command @code{p} +(@code{print}) to see their values. + +@smallexample +(@value{GDBP}) @b{p lquote} +$1 = 0x35d40 "<QUOTE>" +(@value{GDBP}) @b{p rquote} +$2 = 0x35d50 "<UNQUOTE>" +@end smallexample + +@noindent +@code{lquote} and @code{rquote} are indeed the new left and right quotes. +To look at some context, we can display ten lines of source +surrounding the current line with the @code{l} (@code{list}) command. + +@smallexample +(@value{GDBP}) @b{l} +533 xfree(rquote); +534 +535 lquote = (lq == nil || *lq == '\0') ? def_lquote\ + : xstrdup (lq); +536 rquote = (rq == nil || *rq == '\0') ? def_rquote\ + : xstrdup (rq); +537 +538 len_lquote = strlen(rquote); +539 len_rquote = strlen(lquote); +540 @} +541 +542 void +@end smallexample + +@noindent +Let us step past the two lines that set @code{len_lquote} and +@code{len_rquote}, and then examine the values of those variables. + +@smallexample +(@value{GDBP}) @b{n} +539 len_rquote = strlen(lquote); +(@value{GDBP}) @b{n} +540 @} +(@value{GDBP}) @b{p len_lquote} +$3 = 9 +(@value{GDBP}) @b{p len_rquote} +$4 = 7 +@end smallexample + +@noindent +That certainly looks wrong, assuming @code{len_lquote} and +@code{len_rquote} are meant to be the lengths of @code{lquote} and +@code{rquote} respectively. We can set them to better values using +the @code{p} command, since it can print the value of +any expression---and that expression can include subroutine calls and +assignments. + +@smallexample +(@value{GDBP}) @b{p len_lquote=strlen(lquote)} +$5 = 7 +(@value{GDBP}) @b{p len_rquote=strlen(rquote)} +$6 = 9 +@end smallexample + +@noindent +Is that enough to fix the problem of using the new quotes with the +@code{m4} built-in @code{defn}? We can allow @code{m4} to continue +executing with the @code{c} (@code{continue}) command, and then try the +example that caused trouble initially: + +@smallexample +(@value{GDBP}) @b{c} +Continuing. + +@b{define(baz,defn(<QUOTE>foo<UNQUOTE>))} + +baz +0000 +@end smallexample + +@noindent +Success! The new quotes now work just as well as the default ones. The +problem seems to have been just the two typos defining the wrong +lengths. We allow @code{m4} exit by giving it an EOF as input: + +@smallexample +@b{C-d} +Program exited normally. +@end smallexample + +@noindent +The message @samp{Program exited normally.} is from @value{GDBN}; it +indicates @code{m4} has finished executing. We can end our @value{GDBN} +session with the @value{GDBN} @code{quit} command. + +@smallexample +(@value{GDBP}) @b{quit} +@end smallexample +@end ifclear + +@node Invocation, Commands, Sample Session, Top +@chapter Getting In and Out of @value{GDBN} + +This chapter discusses how to start @value{GDBN}, and how to get out of it. +The essentials are: +@itemize @bullet +@item +type @samp{@value{GDBP}} to start GDB. +@item +type @kbd{quit} or @kbd{C-d} to exit. +@end itemize + +@menu +* Invoking GDB:: How to start @value{GDBN} +* Quitting GDB:: How to quit @value{GDBN} +* Shell Commands:: How to use shell commands inside @value{GDBN} +@end menu + +@node Invoking GDB, Quitting GDB, Invocation, Invocation +@section Invoking @value{GDBN} + +@ifset H8EXCLUSIVE +For details on starting up @value{GDBP} as a +remote debugger attached to a Hitachi microprocessor, see @ref{Hitachi +Remote,,@value{GDBN} and Hitachi Microprocessors}. +@end ifset + +Invoke @value{GDBN} by running the program @code{@value{GDBP}}. Once started, +@value{GDBN} reads commands from the terminal until you tell it to exit. + +You can also run @code{@value{GDBP}} with a variety of arguments and options, +to specify more of your debugging environment at the outset. + +@ifset GENERIC +The command-line options described here are designed +to cover a variety of situations; in some environments, some of these +options may effectively be unavailable. +@end ifset + +The most usual way to start @value{GDBN} is with one argument, +specifying an executable program: + +@example +@value{GDBP} @var{program} +@end example + +@ifclear BARETARGET +@noindent +You can also start with both an executable program and a core file +specified: + +@example +@value{GDBP} @var{program} @var{core} +@end example + +You can, instead, specify a process ID as a second argument, if you want +to debug a running process: + +@example +@value{GDBP} @var{program} 1234 +@end example + +@noindent +would attach @value{GDBN} to process @code{1234} (unless you also have a file +named @file{1234}; @value{GDBN} does check for a core file first). + +@ifclear HPPA +Taking advantage of the second command-line argument requires a fairly +complete operating system; when you use @value{GDBN} as a remote debugger +attached to a bare board, there may not be any notion of ``process'', +and there is often no way to get a core dump. +@end ifclear +@end ifclear + +You can run @code{gdb} without printing the front material, which describes +@value{GDBN}'s non-warranty, by specifying @code{-silent}: + +@smallexample +@value{GDBP} -silent +@end smallexample + +@noindent +You can further control how @value{GDBN} starts up by using command-line +options. @value{GDBN} itself can remind you of the options available. + +@noindent +Type + +@example +@value{GDBP} -help +@end example + +@noindent +to display all available options and briefly describe their use +(@samp{@value{GDBP} -h} is a shorter equivalent). + +All options and command line arguments you give are processed +in sequential order. The order makes a difference when the +@samp{-x} option is used. + + +@menu +@ifclear GENERIC +@ifset REMOTESTUB +* Remote Serial:: @value{GDBN} remote serial protocol +@end ifset +@ifset I960 +* i960-Nindy Remote:: @value{GDBN} with a remote i960 (Nindy) +@end ifset +@ifset AMD29K +* UDI29K Remote:: The UDI protocol for AMD29K +* EB29K Remote:: The EBMON protocol for AMD29K +@end ifset +@ifset VXWORKS +* VxWorks Remote:: @value{GDBN} and VxWorks +@end ifset +@ifset ST2000 +* ST2000 Remote:: @value{GDBN} with a Tandem ST2000 +@end ifset +@ifset H8 +* Hitachi Remote:: @value{GDBN} and Hitachi Microprocessors +@end ifset +@ifset MIPS +* MIPS Remote:: @value{GDBN} and MIPS boards +@end ifset +@ifset SPARCLET +* Sparclet Remote:: @value{GDBN} and Sparclet boards +@end ifset +@ifset SIMS +* Simulator:: Simulated CPU target +@end ifset +@end ifclear +@c remnant makeinfo bug requires this blank line after *two* end-ifblahs: + +* File Options:: Choosing files +* Mode Options:: Choosing modes +@end menu + +@ifclear GENERIC +@ifclear HPPA +@include remote.texi +@end ifclear +@end ifclear + +@node File Options +@subsection Choosing files + +@ifclear BARETARGET +When @value{GDBN} starts, it reads any arguments other than options as +specifying an executable file and core file (or process ID). This is +the same as if the arguments were specified by the @samp{-se} and +@samp{-c} options respectively. (@value{GDBN} reads the first argument +that does not have an associated option flag as equivalent to the +@samp{-se} option followed by that argument; and the second argument +that does not have an associated option flag, if any, as equivalent to +the @samp{-c} option followed by that argument.) +@end ifclear +@ifset BARETARGET +When @value{GDBN} starts, it reads any argument other than options as +specifying an executable file. This is the same as if the argument was +specified by the @samp{-se} option. +@end ifset + +Many options have both long and short forms; both are shown in the +following list. @value{GDBN} also recognizes the long forms if you truncate +them, so long as enough of the option is present to be unambiguous. +(If you prefer, you can flag option arguments with @samp{--} rather +than @samp{-}, though we illustrate the more usual convention.) + +@table @code +@item -symbols @var{file} +@itemx -s @var{file} +Read symbol table from file @var{file}. + +@item -exec @var{file} +@itemx -e @var{file} +Use file @var{file} as the executable file to execute when +@ifset BARETARGET +appropriate. +@end ifset +@ifclear BARETARGET +appropriate, and for examining pure data in conjunction with a core +dump. +@end ifclear + +@item -se @var{file} +Read symbol table from file @var{file} and use it as the executable +file. + +@ifclear BARETARGET +@item -core @var{file} +@itemx -c @var{file} +Use file @var{file} as a core dump to examine. + +@item -c @var{number} +Connect to process ID @var{number}, as with the @code{attach} command +(unless there is a file in core-dump format named @var{number}, in which +case @samp{-c} specifies that file as a core dump to read). +@end ifclear + +@item -command @var{file} +@itemx -x @var{file} +Execute @value{GDBN} commands from file @var{file}. @xref{Command +Files,, Command files}. + +@item -directory @var{directory} +@itemx -d @var{directory} +Add @var{directory} to the path to search for source files. + +@ifclear BARETARGET +@ifclear HPPA +@item -m +@itemx -mapped +@emph{Warning: this option depends on operating system facilities that are not +supported on all systems.}@* +If memory-mapped files are available on your system through the @code{mmap} +system call, you can use this option +to have @value{GDBN} write the symbols from your +program into a reusable file in the current directory. If the program you are debugging is +called @file{/tmp/fred}, the mapped symbol file is @file{./fred.syms}. +Future @value{GDBN} debugging sessions notice the presence of this file, +and can quickly map in symbol information from it, rather than reading +the symbol table from the executable program. + +The @file{.syms} file is specific to the host machine where @value{GDBN} +is run. It holds an exact image of the internal @value{GDBN} symbol +table. It cannot be shared across multiple host platforms. +@end ifclear +@end ifclear + +@ifclear HPPA +@item -r +@itemx -readnow +Read each symbol file's entire symbol table immediately, rather than +the default, which is to read it incrementally as it is needed. +This makes startup slower, but makes future operations faster. +@end ifclear +@end table + +@ifclear BARETARGET +@ifclear HPPA +The @code{-mapped} and @code{-readnow} options are typically combined in +order to build a @file{.syms} file that contains complete symbol +information. (@xref{Files,,Commands to specify files}, for +information on @file{.syms} files.) A simple GDB invocation to do +nothing but build a @file{.syms} file for future use is: + +@example + gdb -batch -nx -mapped -readnow programname +@end example +@end ifclear +@end ifclear + +@node Mode Options, , File Options, Invoking GDB +@subsection Choosing modes + +You can run @value{GDBN} in various alternative modes---for example, in +batch mode or quiet mode. + +@table @code +@item -nx +@itemx -n +Do not execute commands from any initialization files (normally called +@file{.gdbinit}, or @file{gdb.ini} on PCs). Normally, the commands in +these files are executed after all the command options and arguments +have been processed. @xref{Command Files,,Command files}. + +@item -quiet +@itemx -q +``Quiet''. Do not print the introductory and copyright messages. These +messages are also suppressed in batch mode. + +@item -batch +Run in batch mode. Exit with status @code{0} after processing all the +command files specified with @samp{-x} (and all commands from +initialization files, if not inhibited with @samp{-n}). Exit with +nonzero status if an error occurs in executing the @value{GDBN} commands +in the command files. + +Batch mode may be useful for running @value{GDBN} as a filter, for example to +download and run a program on another computer; in order to make this +more useful, the message + +@example +Program exited normally. +@end example + +@noindent +(which is ordinarily issued whenever a program running under @value{GDBN} control +terminates) is not issued when running in batch mode. + +@item -cd @var{directory} +Run @value{GDBN} using @var{directory} as its working directory, +instead of the current directory. + +@ifclear DOSHOST +@item -fullname +@itemx -f +@sc{gnu} Emacs sets this option when it runs @value{GDBN} as a subprocess. It tells @value{GDBN} +to output the full file name and line number in a standard, +recognizable fashion each time a stack frame is displayed (which +includes each time your program stops). This recognizable format looks +like two @samp{\032} characters, followed by the file name, line number +and character position separated by colons, and a newline. The +Emacs-to-@value{GDBN} interface program uses the two @samp{\032} characters as +a signal to display the source code for the frame. +@end ifclear + +@ifset SERIAL +@ifclear HPPA +@item -b @var{bps} +Set the line speed (baud rate or bits per second) of any serial +interface used by @value{GDBN} for remote debugging. +@end ifclear + +@item -tty @var{device} +Run using @var{device} for your program's standard input and output. +@c FIXME: kingdon thinks there is more to -tty. Investigate. +@end ifset + +@ifset HPPA +@item -tui +Use a Terminal User Interface. For information, use your Web browser to +read the file @file{TUI.html}, which is usually installed in the +directory @code{/opt/langtools/wdb/doc} on HP-UX systems. Do not use +this option if you run @value{GDBN} from Emacs (see @pxref{Emacs, ,Using +@value{GDBN} under @sc{gnu} Emacs}). + +@item -xdb +Run in XDB compatibility mode, allowing the use of certain XDB commands. +For information, see the file @file{xdb_trans.html}, which is usually +installed in the directory @code{/opt/langtools/wdb/doc} on HP-UX +systems. +@end ifset +@end table + +@node Quitting GDB, Shell Commands, Invoking GDB, Invocation +@section Quitting @value{GDBN} +@cindex exiting @value{GDBN} +@cindex leaving @value{GDBN} + +@table @code +@kindex quit @r{[}@var{expression}@r{]} +@kindex q +@item quit +To exit @value{GDBN}, use the @code{quit} command (abbreviated @code{q}), or +type an end-of-file character (usually @kbd{C-d}). If you do not supply +@var{expression}, @value{GDBN} will terminate normally; otherwise it will +terminate using the result of @var{expression} as the error code. +@end table + +@cindex interrupt +An interrupt (often @kbd{C-c}) does not exit from @value{GDBN}, but rather +terminates the action of any @value{GDBN} command that is in progress and +returns to @value{GDBN} command level. It is safe to type the interrupt +character at any time because @value{GDBN} does not allow it to take effect +until a time when it is safe. + +@ifclear BARETARGET +If you have been using @value{GDBN} to control an attached process or +device, you can release it with the @code{detach} command +(@pxref{Attach, ,Debugging an already-running process}). +@end ifclear + +@node Shell Commands, , Quitting GDB, Invocation +@section Shell commands + +If you need to execute occasional shell commands during your +debugging session, there is no need to leave or suspend @value{GDBN}; you can +just use the @code{shell} command. + +@table @code +@kindex shell +@cindex shell escape +@item shell @var{command string} +Invoke a standard shell to execute @var{command string}. +@ifclear DOSHOST +If it exists, the environment variable @code{SHELL} determines which +shell to run. Otherwise @value{GDBN} uses @code{/bin/sh}. +@end ifclear +@end table + +The utility @code{make} is often needed in development environments. +You do not have to use the @code{shell} command for this purpose in +@value{GDBN}: + +@table @code +@kindex make +@cindex calling make +@item make @var{make-args} +Execute the @code{make} program with the specified +arguments. This is equivalent to @samp{shell make @var{make-args}}. +@end table + +@node Commands, Running, Invocation, Top +@chapter @value{GDBN} Commands + +You can abbreviate a @value{GDBN} command to the first few letters of the command +name, if that abbreviation is unambiguous; and you can repeat certain +@value{GDBN} commands by typing just @key{RET}. You can also use the @key{TAB} +key to get @value{GDBN} to fill out the rest of a word in a command (or to +show you the alternatives available, if there is more than one possibility). + +@menu +* Command Syntax:: How to give commands to @value{GDBN} +* Completion:: Command completion +* Help:: How to ask @value{GDBN} for help +@end menu + +@node Command Syntax, Completion, Commands, Commands +@section Command syntax + +A @value{GDBN} command is a single line of input. There is no limit on +how long it can be. It starts with a command name, which is followed by +arguments whose meaning depends on the command name. For example, the +command @code{step} accepts an argument which is the number of times to +step, as in @samp{step 5}. You can also use the @code{step} command +with no arguments. Some command names do not allow any arguments. + +@cindex abbreviation +@value{GDBN} command names may always be truncated if that abbreviation is +unambiguous. Other possible command abbreviations are listed in the +documentation for individual commands. In some cases, even ambiguous +abbreviations are allowed; for example, @code{s} is specially defined as +equivalent to @code{step} even though there are other commands whose +names start with @code{s}. You can test abbreviations by using them as +arguments to the @code{help} command. + +@cindex repeating commands +@kindex RET +A blank line as input to @value{GDBN} (typing just @key{RET}) means to +repeat the previous command. Certain commands (for example, @code{run}) +will not repeat this way; these are commands whose unintentional +repetition might cause trouble and which you are unlikely to want to +repeat. + +The @code{list} and @code{x} commands, when you repeat them with +@key{RET}, construct new arguments rather than repeating +exactly as typed. This permits easy scanning of source or memory. + +@value{GDBN} can also use @key{RET} in another way: to partition lengthy +output, in a way similar to the common utility @code{more} +(@pxref{Screen Size,,Screen size}). Since it is easy to press one +@key{RET} too many in this situation, @value{GDBN} disables command +repetition after any command that generates this sort of display. + +@kindex # +@cindex comment +Any text from a @kbd{#} to the end of the line is a comment; it does +nothing. This is useful mainly in command files (@pxref{Command +Files,,Command files}). + +@node Completion, Help, Command Syntax, Commands +@section Command completion + +@cindex completion +@cindex word completion +@value{GDBN} can fill in the rest of a word in a command for you, if there is +only one possibility; it can also show you what the valid possibilities +are for the next word in a command, at any time. This works for @value{GDBN} +commands, @value{GDBN} subcommands, and the names of symbols in your program. + +Press the @key{TAB} key whenever you want @value{GDBN} to fill out the rest +of a word. If there is only one possibility, @value{GDBN} fills in the +word, and waits for you to finish the command (or press @key{RET} to +enter it). For example, if you type + +@c FIXME "@key" does not distinguish its argument sufficiently to permit +@c complete accuracy in these examples; space introduced for clarity. +@c If texinfo enhancements make it unnecessary, it would be nice to +@c replace " @key" by "@key" in the following... +@example +(@value{GDBP}) info bre @key{TAB} +@end example + +@noindent +@value{GDBN} fills in the rest of the word @samp{breakpoints}, since that is +the only @code{info} subcommand beginning with @samp{bre}: + +@example +(@value{GDBP}) info breakpoints +@end example + +@noindent +You can either press @key{RET} at this point, to run the @code{info +breakpoints} command, or backspace and enter something else, if +@samp{breakpoints} does not look like the command you expected. (If you +were sure you wanted @code{info breakpoints} in the first place, you +might as well just type @key{RET} immediately after @samp{info bre}, +to exploit command abbreviations rather than command completion). + +If there is more than one possibility for the next word when you press +@key{TAB}, @value{GDBN} sounds a bell. You can either supply more +characters and try again, or just press @key{TAB} a second time; +@value{GDBN} displays all the possible completions for that word. For +example, you might want to set a breakpoint on a subroutine whose name +begins with @samp{make_}, but when you type @kbd{b make_@key{TAB}} @value{GDBN} +just sounds the bell. Typing @key{TAB} again displays all the +function names in your program that begin with those characters, for +example: + +@example +(@value{GDBP}) b make_ @key{TAB} +@exdent @value{GDBN} sounds bell; press @key{TAB} again, to see: +make_a_section_from_file make_environ +make_abs_section make_function_type +make_blockvector make_pointer_type +make_cleanup make_reference_type +make_command make_symbol_completion_list +(@value{GDBP}) b make_ +@end example + +@noindent +After displaying the available possibilities, @value{GDBN} copies your +partial input (@samp{b make_} in the example) so you can finish the +command. + +If you just want to see the list of alternatives in the first place, you +can press @kbd{M-?} rather than pressing @key{TAB} twice. @kbd{M-?} +means @kbd{@key{META} ?}. You can type this +@ifclear DOSHOST +either by holding down a +key designated as the @key{META} shift on your keyboard (if there is +one) while typing @kbd{?}, or +@end ifclear +as @key{ESC} followed by @kbd{?}. + +@cindex quotes in commands +@cindex completion of quoted strings +Sometimes the string you need, while logically a ``word'', may contain +parentheses or other characters that @value{GDBN} normally excludes from its +notion of a word. To permit word completion to work in this situation, +you may enclose words in @code{'} (single quote marks) in @value{GDBN} commands. + +@ifclear CONLY +The most likely situation where you might need this is in typing the +name of a C++ function. This is because C++ allows function overloading +(multiple definitions of the same function, distinguished by argument +type). For example, when you want to set a breakpoint you may need to +distinguish whether you mean the version of @code{name} that takes an +@code{int} parameter, @code{name(int)}, or the version that takes a +@code{float} parameter, @code{name(float)}. To use the word-completion +facilities in this situation, type a single quote @code{'} at the +beginning of the function name. This alerts @value{GDBN} that it may need to +consider more information than usual when you press @key{TAB} or +@kbd{M-?} to request word completion: + +@example +(@value{GDBP}) b 'bubble( @key{M-?} +bubble(double,double) bubble(int,int) +(@value{GDBP}) b 'bubble( +@end example + +In some cases, @value{GDBN} can tell that completing a name requires using +quotes. When this happens, @value{GDBN} inserts the quote for you (while +completing as much as it can) if you do not type the quote in the first +place: + +@example +(@value{GDBP}) b bub @key{TAB} +@exdent @value{GDBN} alters your input line to the following, and rings a bell: +(@value{GDBP}) b 'bubble( +@end example + +@noindent +In general, @value{GDBN} can tell that a quote is needed (and inserts it) if +you have not yet started typing the argument list when you ask for +completion on an overloaded symbol. + +For more information about overloaded functions, @pxref{Cplus +expressions, ,C++ expressions}. You can use the command @code{set +overload-resolution off} to disable overload resolution; +@pxref{Debugging C plus plus, ,@value{GDBN} features for C++}. +@end ifclear + + +@node Help, , Completion, Commands +@section Getting help +@cindex online documentation +@kindex help + +You can always ask @value{GDBN} itself for information on its commands, +using the command @code{help}. + +@table @code +@kindex h +@item help +@itemx h +You can use @code{help} (abbreviated @code{h}) with no arguments to +display a short list of named classes of commands: + +@smallexample +(@value{GDBP}) help +List of classes of commands: + +running -- Running the program +stack -- Examining the stack +data -- Examining data +breakpoints -- Making program stop at certain points +files -- Specifying and examining files +status -- Status inquiries +support -- Support facilities +user-defined -- User-defined commands +aliases -- Aliases of other commands +obscure -- Obscure features + +Type "help" followed by a class name for a list of +commands in that class. +Type "help" followed by command name for full +documentation. +Command name abbreviations are allowed if unambiguous. +(@value{GDBP}) +@end smallexample + +@item help @var{class} +Using one of the general help classes as an argument, you can get a +list of the individual commands in that class. For example, here is the +help display for the class @code{status}: + +@smallexample +(@value{GDBP}) help status +Status inquiries. + +List of commands: + +@c Line break in "show" line falsifies real output, but needed +@c to fit in smallbook page size. +show -- Generic command for showing things set + with "set" +info -- Generic command for printing status + +Type "help" followed by command name for full +documentation. +Command name abbreviations are allowed if unambiguous. +(@value{GDBP}) +@end smallexample + +@item help @var{command} +With a command name as @code{help} argument, @value{GDBN} displays a +short paragraph on how to use that command. + +@kindex complete +@item complete @var{args} +The @code{complete @var{args}} command lists all the possible completions +for the beginning of a command. Use @var{args} to specify the beginning of the +command you want completed. For example: + +@smallexample +complete i +@end smallexample + +@noindent results in: + +@smallexample +@group +info +inspect +ignore +@end group +@end smallexample + +@noindent This is intended for use by @sc{gnu} Emacs. +@end table + +In addition to @code{help}, you can use the @value{GDBN} commands @code{info} +and @code{show} to inquire about the state of your program, or the state +of @value{GDBN} itself. Each command supports many topics of inquiry; this +manual introduces each of them in the appropriate context. The listings +under @code{info} and under @code{show} in the Index point to +all the sub-commands. @xref{Index}. + +@c @group +@table @code +@kindex info +@kindex i +@item info +This command (abbreviated @code{i}) is for describing the state of your +program. For example, you can list the arguments given to your program +with @code{info args}, list the registers currently in use with @code{info +registers}, or list the breakpoints you have set with @code{info breakpoints}. +You can get a complete list of the @code{info} sub-commands with +@w{@code{help info}}. + +@kindex set +@item set +You can assign the result of an expression to an environment variable with +@code{set}. For example, you can set the @value{GDBN} prompt to a $-sign with +@code{set prompt $}. + +@kindex show +@item show +In contrast to @code{info}, @code{show} is for describing the state of +@value{GDBN} itself. +You can change most of the things you can @code{show}, by using the +related command @code{set}; for example, you can control what number +system is used for displays with @code{set radix}, or simply inquire +which is currently in use with @code{show radix}. + +@kindex info set +To display all the settable parameters and their current +values, you can use @code{show} with no arguments; you may also use +@code{info set}. Both commands produce the same display. +@c FIXME: "info set" violates the rule that "info" is for state of +@c FIXME...program. Ck w/ GNU: "info set" to be called something else, +@c FIXME...or change desc of rule---eg "state of prog and debugging session"? +@end table +@c @end group + +Here are three miscellaneous @code{show} subcommands, all of which are +exceptional in lacking corresponding @code{set} commands: + +@table @code +@kindex show version +@cindex version number +@item show version +Show what version of @value{GDBN} is running. You should include this +information in @value{GDBN} bug-reports. If multiple versions of @value{GDBN} are in +use at your site, you may occasionally want to determine which version +of @value{GDBN} you are running; as @value{GDBN} evolves, new commands are introduced, +and old ones may wither away. The version number is also announced +when you start @value{GDBN}. + +@kindex show copying +@item show copying +Display information about permission for copying @value{GDBN}. + +@kindex show warranty +@item show warranty +Display the @sc{gnu} ``NO WARRANTY'' statement. +@end table + +@node Running, Stopping, Commands, Top +@chapter Running Programs Under @value{GDBN} + +When you run a program under @value{GDBN}, you must first generate +debugging information when you compile it. +@ifclear BARETARGET +You may start @value{GDBN} with its arguments, if any, in an environment +of your choice. You may redirect your program's input and output, debug an +already running process, or kill a child process. +@end ifclear + +@menu +* Compilation:: Compiling for debugging +* Starting:: Starting your program +@ifclear BARETARGET +* Arguments:: Your program's arguments +* Environment:: Your program's environment +@end ifclear + +* Working Directory:: Your program's working directory +* Input/Output:: Your program's input and output +* Attach:: Debugging an already-running process +* Kill Process:: Killing the child process +@ifclear HPPA +* Process Information:: Additional process information +@end ifclear + +* Threads:: Debugging programs with multiple threads +* Processes:: Debugging programs with multiple processes +@end menu + +@node Compilation, Starting, Running, Running +@section Compiling for debugging + +In order to debug a program effectively, you need to generate +debugging information when you compile it. This debugging information +is stored in the object file; it describes the data type of each +variable or function and the correspondence between source line numbers +and addresses in the executable code. + +To request debugging information, specify the @samp{-g} option when you run +the compiler. + +Many C compilers are unable to handle the @samp{-g} and @samp{-O} +options together. Using those compilers, you cannot generate optimized +executables containing debugging information. + +@ifclear HPPA +@value{NGCC}, the @sc{gnu} C compiler, supports @samp{-g} with or without +@end ifclear +@ifset HPPA +The HP ANSI C and C++ compilers, as well as @value{NGCC}, the @sc{gnu} C +compiler, support @samp{-g} with or without +@end ifset +@samp{-O}, making it possible to debug optimized code. We recommend +that you @emph{always} use @samp{-g} whenever you compile a program. +You may think your program is correct, but there is no sense in pushing +your luck. + +@cindex optimized code, debugging +@cindex debugging optimized code +When you debug a program compiled with @samp{-g -O}, remember that the +optimizer is rearranging your code; the debugger shows you what is +really there. Do not be too surprised when the execution path does not +exactly match your source file! An extreme example: if you define a +variable, but never use it, @value{GDBN} never sees that +variable---because the compiler optimizes it out of existence. + +Some things do not work as well with @samp{-g -O} as with just +@samp{-g}, particularly on machines with instruction scheduling. If in +doubt, recompile with @samp{-g} alone, and if this fixes the problem, +please report it to us as a bug (including a test case!). + +Older versions of the @sc{gnu} C compiler permitted a variant option +@w{@samp{-gg}} for debugging information. @value{GDBN} no longer supports this +format; if your @sc{gnu} C compiler has this option, do not use it. + +@need 2000 +@node Starting, Arguments, Compilation, Running +@section Starting your program +@cindex starting +@cindex running + +@table @code +@kindex run +@item run +@itemx r +Use the @code{run} command to start your program under @value{GDBN}. You must +first specify the program name +@ifset VXWORKS +(except on VxWorks) +@end ifset +with an argument to @value{GDBN} (@pxref{Invocation, ,Getting In and +Out of @value{GDBN}}), or by using the @code{file} or @code{exec-file} +command (@pxref{Files, ,Commands to specify files}). + +@end table + +@ifclear BARETARGET +If you are running your program in an execution environment that +supports processes, @code{run} creates an inferior process and makes +that process run your program. (In environments without processes, +@code{run} jumps to the start of your program.) + +The execution of a program is affected by certain information it +receives from its superior. @value{GDBN} provides ways to specify this +information, which you must do @emph{before} starting your program. (You +can change it after starting your program, but such changes only affect +your program the next time you start it.) This information may be +divided into four categories: + +@table @asis +@item The @emph{arguments.} +Specify the arguments to give your program as the arguments of the +@code{run} command. If a shell is available on your target, the shell +is used to pass the arguments, so that you may use normal conventions +(such as wildcard expansion or variable substitution) in describing +the arguments. +In Unix systems, you can control which shell is used with the +@code{SHELL} environment variable. +@xref{Arguments, ,Your program's arguments}. + +@item The @emph{environment.} +Your program normally inherits its environment from @value{GDBN}, but you can +use the @value{GDBN} commands @code{set environment} and @code{unset +environment} to change parts of the environment that affect +your program. @xref{Environment, ,Your program's environment}. + +@item The @emph{working directory.} +Your program inherits its working directory from @value{GDBN}. You can set +the @value{GDBN} working directory with the @code{cd} command in @value{GDBN}. +@xref{Working Directory, ,Your program's working directory}. + +@item The @emph{standard input and output.} +Your program normally uses the same device for standard input and +standard output as @value{GDBN} is using. You can redirect input and output +in the @code{run} command line, or you can use the @code{tty} command to +set a different device for your program. +@xref{Input/Output, ,Your program's input and output}. + +@cindex pipes +@emph{Warning:} While input and output redirection work, you cannot use +pipes to pass the output of the program you are debugging to another +program; if you attempt this, @value{GDBN} is likely to wind up debugging the +wrong program. +@end table +@end ifclear + +When you issue the @code{run} command, your program begins to execute +immediately. @xref{Stopping, ,Stopping and continuing}, for discussion +of how to arrange for your program to stop. Once your program has +stopped, you may call functions in your program, using the @code{print} +or @code{call} commands. @xref{Data, ,Examining Data}. + +If the modification time of your symbol file has changed since the last +time @value{GDBN} read its symbols, @value{GDBN} discards its symbol +table, and reads it again. When it does this, @value{GDBN} tries to retain +your current breakpoints. + +@ifclear BARETARGET +@node Arguments, Environment, Starting, Running +@section Your program's arguments + +@cindex arguments (to your program) +The arguments to your program can be specified by the arguments of the +@code{run} command. +They are passed to a shell, which expands wildcard characters and +performs redirection of I/O, and thence to your program. Your +@code{SHELL} environment variable (if it exists) specifies what shell +@value{GDBN} uses. If you do not define @code{SHELL}, @value{GDBN} uses +@code{/bin/sh}. + +@code{run} with no arguments uses the same arguments used by the previous +@code{run}, or those set by the @code{set args} command. + +@kindex set args +@table @code +@item set args +Specify the arguments to be used the next time your program is run. If +@code{set args} has no arguments, @code{run} executes your program +with no arguments. Once you have run your program with arguments, +using @code{set args} before the next @code{run} is the only way to run +it again without arguments. + +@kindex show args +@item show args +Show the arguments to give your program when it is started. +@end table + +@node Environment, Working Directory, Arguments, Running +@section Your program's environment + +@cindex environment (of your program) +The @dfn{environment} consists of a set of environment variables and +their values. Environment variables conventionally record such things as +your user name, your home directory, your terminal type, and your search +path for programs to run. Usually you set up environment variables with +the shell and they are inherited by all the other programs you run. When +debugging, it can be useful to try running your program with a modified +environment without having to start @value{GDBN} over again. + +@table @code +@kindex path +@item path @var{directory} +Add @var{directory} to the front of the @code{PATH} environment variable +(the search path for executables), for both @value{GDBN} and your program. +You may specify several directory names, separated by @samp{:} or +whitespace. If @var{directory} is already in the path, it is moved to +the front, so it is searched sooner. + +You can use the string @samp{$cwd} to refer to whatever is the current +working directory at the time @value{GDBN} searches the path. If you +use @samp{.} instead, it refers to the directory where you executed the +@code{path} command. @value{GDBN} replaces @samp{.} in the +@var{directory} argument (with the current path) before adding +@var{directory} to the search path. +@c 'path' is explicitly nonrepeatable, but RMS points out it is silly to +@c document that, since repeating it would be a no-op. + +@kindex show paths +@item show paths +Display the list of search paths for executables (the @code{PATH} +environment variable). + +@kindex show environment +@item show environment @r{[}@var{varname}@r{]} +Print the value of environment variable @var{varname} to be given to +your program when it starts. If you do not supply @var{varname}, +print the names and values of all environment variables to be given to +your program. You can abbreviate @code{environment} as @code{env}. + +@kindex set environment +@item set environment @var{varname} @r{[}=@r{]} @var{value} +Set environment variable @var{varname} to @var{value}. The value +changes for your program only, not for @value{GDBN} itself. @var{value} may +be any string; the values of environment variables are just strings, and +any interpretation is supplied by your program itself. The @var{value} +parameter is optional; if it is eliminated, the variable is set to a +null value. +@c "any string" here does not include leading, trailing +@c blanks. Gnu asks: does anyone care? + +For example, this command: + +@example +set env USER = foo +@end example + +@noindent +tells a Unix program, when subsequently run, that its user is named +@samp{foo}. (The spaces around @samp{=} are used for clarity here; they +are not actually required.) + +@kindex unset environment +@item unset environment @var{varname} +Remove variable @var{varname} from the environment to be passed to your +program. This is different from @samp{set env @var{varname} =}; +@code{unset environment} removes the variable from the environment, +rather than assigning it an empty value. +@end table + +@emph{Warning:} @value{GDBN} runs your program using the shell indicated +by your @code{SHELL} environment variable if it exists (or +@code{/bin/sh} if not). If your @code{SHELL} variable names a shell +that runs an initialization file---such as @file{.cshrc} for C-shell, or +@file{.bashrc} for BASH---any variables you set in that file affect +your program. You may wish to move setting of environment variables to +files that are only run when you sign on, such as @file{.login} or +@file{.profile}. + +@node Working Directory, Input/Output, Environment, Running +@section Your program's working directory + +@cindex working directory (of your program) +Each time you start your program with @code{run}, it inherits its +working directory from the current working directory of @value{GDBN}. +The @value{GDBN} working directory is initially whatever it inherited +from its parent process (typically the shell), but you can specify a new +working directory in @value{GDBN} with the @code{cd} command. + +The @value{GDBN} working directory also serves as a default for the commands +that specify files for @value{GDBN} to operate on. @xref{Files, ,Commands to +specify files}. + +@table @code +@kindex cd +@item cd @var{directory} +Set the @value{GDBN} working directory to @var{directory}. + +@kindex pwd +@item pwd +Print the @value{GDBN} working directory. +@end table + +@node Input/Output, Attach, Working Directory, Running +@section Your program's input and output + +@cindex redirection +@cindex i/o +@cindex terminal +By default, the program you run under @value{GDBN} does input and output to +the same terminal that @value{GDBN} uses. @value{GDBN} switches the terminal +to its own terminal modes to interact with you, but it records the terminal +modes your program was using and switches back to them when you continue +running your program. + +@table @code +@kindex info terminal +@item info terminal +Displays information recorded by @value{GDBN} about the terminal modes your +program is using. +@end table + +You can redirect your program's input and/or output using shell +redirection with the @code{run} command. For example, + +@example +run > outfile +@end example + +@noindent +starts your program, diverting its output to the file @file{outfile}. + +@kindex tty +@cindex controlling terminal +Another way to specify where your program should do input and output is +with the @code{tty} command. This command accepts a file name as +argument, and causes this file to be the default for future @code{run} +commands. It also resets the controlling terminal for the child +process, for future @code{run} commands. For example, + +@example +tty /dev/ttyb +@end example + +@noindent +directs that processes started with subsequent @code{run} commands +default to do input and output on the terminal @file{/dev/ttyb} and have +that as their controlling terminal. + +An explicit redirection in @code{run} overrides the @code{tty} command's +effect on the input/output device, but not its effect on the controlling +terminal. + +When you use the @code{tty} command or redirect input in the @code{run} +command, only the input @emph{for your program} is affected. The input +for @value{GDBN} still comes from your terminal. + +@node Attach, Kill Process, Input/Output, Running +@section Debugging an already-running process +@kindex attach +@cindex attach + +@table @code +@item attach @var{process-id} +This command attaches to a running process---one that was started +outside @value{GDBN}. (@code{info files} shows your active +targets.) The command takes as argument a process ID. The usual way to +find out the process-id of a Unix process is with the @code{ps} utility, +or with the @samp{jobs -l} shell command. + +@code{attach} does not repeat if you press @key{RET} a second time after +executing the command. +@end table + +To use @code{attach}, your program must be running in an environment +which supports processes; for example, @code{attach} does not work for +programs on bare-board targets that lack an operating system. You must +also have permission to send the process a signal. + +When you use @code{attach}, the debugger finds the program running in +the process first by looking in the current working directory, then (if +the program is not found) by using the source file search path +(@pxref{Source Path, ,Specifying source directories}). You can also use +the @code{file} command to load the program. @xref{Files, ,Commands to +Specify Files}. + +The first thing @value{GDBN} does after arranging to debug the specified +process is to stop it. You can examine and modify an attached process +with all the @value{GDBN} commands that are ordinarily available when you start +@ifclear HPPA +processes with @code{run}. You can insert breakpoints; you can step and +@end ifclear +@ifset HPPA +processes with @code{run}. You can insert breakpoints (except in shared +libraries); you can step and +@end ifset +continue; you can modify storage. If you would rather the process +continue running, you may use the @code{continue} command after +attaching @value{GDBN} to the process. + +@table @code +@kindex detach +@item detach +When you have finished debugging the attached process, you can use the +@code{detach} command to release it from @value{GDBN} control. Detaching +the process continues its execution. After the @code{detach} command, +that process and @value{GDBN} become completely independent once more, and you +are ready to @code{attach} another process or start one with @code{run}. +@code{detach} does not repeat if you press @key{RET} again after +executing the command. +@end table + +If you exit @value{GDBN} or use the @code{run} command while you have an +attached process, you kill that process. By default, @value{GDBN} asks +for confirmation if you try to do either of these things; you can +control whether or not you need to confirm by using the @code{set +confirm} command (@pxref{Messages/Warnings, ,Optional warnings and +messages}). + +@ifset HPPA +@node Kill Process, Threads, Attach, Running +@section Killing the child process +@end ifset +@ifclear HPPA +@node Kill Process, Process Information, Attach, Running +@section Killing the child process +@end ifclear + +@table @code +@kindex kill +@item kill +Kill the child process in which your program is running under @value{GDBN}. +@end table + +This command is useful if you wish to debug a core dump instead of a +running process. @value{GDBN} ignores any core dump file while your program +is running. + +On some operating systems, a program cannot be executed outside @value{GDBN} +while you have breakpoints set on it inside @value{GDBN}. You can use the +@code{kill} command in this situation to permit running your program +outside the debugger. + +The @code{kill} command is also useful if you wish to recompile and +relink your program, since on many systems it is impossible to modify an +executable file while it is running in a process. In this case, when you +next type @code{run}, @value{GDBN} notices that the file has changed, and +reads the symbol table again (while trying to preserve your current +breakpoint settings). + +@ifclear HPPA +@node Process Information, Threads, Kill Process, Running +@section Additional process information + +@kindex /proc +@cindex process image +Some operating systems provide a facility called @samp{/proc} that can +be used to examine the image of a running process using file-system +subroutines. If @value{GDBN} is configured for an operating system with this +facility, the command @code{info proc} is available to report on several +kinds of information about the process running your program. +@code{info proc} works only on SVR4 systems that support @code{procfs}. + +@table @code +@kindex info proc +@item info proc +Summarize available information about the process. + +@kindex info proc mappings +@item info proc mappings +Report on the address ranges accessible in the program, with information +on whether your program may read, write, or execute each range. + +@kindex info proc times +@item info proc times +Starting time, user CPU time, and system CPU time for your program and +its children. + +@kindex info proc id +@item info proc id +Report on the process IDs related to your program: its own process ID, +the ID of its parent, the process group ID, and the session ID. + +@kindex info proc status +@item info proc status +General information on the state of the process. If the process is +stopped, this report includes the reason for stopping, and any signal +received. + +@item info proc all +Show all the above information about the process. +@end table +@end ifclear + +@ifset HPPA +@node Threads, Processes, Kill Process, Running +@section Debugging programs with multiple threads +@end ifset +@ifclear HPPA +@node Threads, Processes, Process Information, Running +@section Debugging programs with multiple threads +@end ifclear + +@cindex threads of execution +@cindex multiple threads +@cindex switching threads +In some operating systems, such as HP-UX and Solaris, a single program +may have more than one @dfn{thread} of execution. The precise semantics +of threads differ from one operating system to another, but in general +the threads of a single program are akin to multiple processes---except +that they share one address space (that is, they can all examine and +modify the same variables). On the other hand, each thread has its own +registers and execution stack, and perhaps private memory. + +@value{GDBN} provides these facilities for debugging multi-thread +programs: + +@itemize @bullet +@item automatic notification of new threads +@item @samp{thread @var{threadno}}, a command to switch among threads +@item @samp{info threads}, a command to inquire about existing threads +@item @samp{thread apply [@var{threadno}] [@var{all}] @var{args}}, +a command to apply a command to a list of threads +@item thread-specific breakpoints +@end itemize + +@ifclear HPPA +@quotation +@emph{Warning:} These facilities are not yet available on every +@value{GDBN} configuration where the operating system supports threads. +If your @value{GDBN} does not support threads, these commands have no +effect. For example, a system without thread support shows no output +from @samp{info threads}, and always rejects the @code{thread} command, +like this: + +@smallexample +(@value{GDBP}) info threads +(@value{GDBP}) thread 1 +Thread ID 1 not known. Use the "info threads" command to +see the IDs of currently known threads. +@end smallexample +@c FIXME to implementors: how hard would it be to say "sorry, this GDB +@c doesn't support threads"? +@end quotation +@end ifclear + +@cindex focus of debugging +@cindex current thread +The @value{GDBN} thread debugging facility allows you to observe all +threads while your program runs---but whenever @value{GDBN} takes +control, one thread in particular is always the focus of debugging. +This thread is called the @dfn{current thread}. Debugging commands show +program information from the perspective of the current thread. + +@ifclear HPPA +@kindex New @var{systag} +@cindex thread identifier (system) +@c FIXME-implementors!! It would be more helpful if the [New...] message +@c included GDB's numeric thread handle, so you could just go to that +@c thread without first checking `info threads'. +Whenever @value{GDBN} detects a new thread in your program, it displays +the target system's identification for the thread with a message in the +form @samp{[New @var{systag}]}. @var{systag} is a thread identifier +whose form varies depending on the particular system. For example, on +LynxOS, you might see + +@example +[New process 35 thread 27] +@end example + +@noindent +when @value{GDBN} notices a new thread. In contrast, on an SGI system, +the @var{systag} is simply something like @samp{process 368}, with no +further qualifier. + +@c FIXME!! (1) Does the [New...] message appear even for the very first +@c thread of a program, or does it only appear for the +@c second---i.e., when it becomes obvious we have a multithread +@c program? +@c (2) *Is* there necessarily a first thread always? Or do some +@c multithread systems permit starting a program with multiple +@c threads ab initio? + +@cindex thread number +@cindex thread identifier (GDB) +For debugging purposes, @value{GDBN} associates its own thread +number---always a single integer---with each thread in your program. + +@table @code +@kindex info threads +@item info threads +Display a summary of all threads currently in your +program. @value{GDBN} displays for each thread (in this order): + +@enumerate +@item the thread number assigned by @value{GDBN} + +@item the target system's thread identifier (@var{systag}) + +@item the current stack frame summary for that thread +@end enumerate + +@noindent +An asterisk @samp{*} to the left of the @value{GDBN} thread number +indicates the current thread. + +For example, +@end table +@c end table here to get a little more width for example + +@smallexample +(@value{GDBP}) info threads + 3 process 35 thread 27 0x34e5 in sigpause () + 2 process 35 thread 23 0x34e5 in sigpause () +* 1 process 35 thread 13 main (argc=1, argv=0x7ffffff8) + at threadtest.c:68 +@end smallexample +@end ifclear +@ifset HPPA + +@cindex thread number +@cindex thread identifier (GDB) +For debugging purposes, @value{GDBN} associates its own thread +number---a small integer assigned in thread-creation order---with each +thread in your program. + +@kindex New @var{systag} +@cindex thread identifier (system) +@c FIXME-implementors!! It would be more helpful if the [New...] message +@c included GDB's numeric thread handle, so you could just go to that +@c thread without first checking `info threads'. +Whenever @value{GDBN} detects a new thread in your program, it displays +both @value{GDBN}'s thread number and the target system's identification for the thread with a message in the +form @samp{[New @var{systag}]}. @var{systag} is a thread identifier +whose form varies depending on the particular system. For example, on +HP-UX, you see + +@example +[New thread 2 (system thread 26594)] +@end example + +@noindent +when @value{GDBN} notices a new thread. + +@table @code +@kindex info threads +@item info threads +Display a summary of all threads currently in your +program. @value{GDBN} displays for each thread (in this order): + +@enumerate +@item the thread number assigned by @value{GDBN} + +@item the target system's thread identifier (@var{systag}) + +@item the current stack frame summary for that thread +@end enumerate + +@noindent +An asterisk @samp{*} to the left of the @value{GDBN} thread number +indicates the current thread. + +For example, +@end table +@c end table here to get a little more width for example + +@example +(@value{GDBP}) info threads + * 3 system thread 26607 worker (wptr=0x7b09c318 "@@") at quicksort.c:137 + 2 system thread 26606 0x7b0030d8 in __ksleep () from /usr/lib/libc.2 + 1 system thread 27905 0x7b003498 in _brk () from /usr/lib/libc.2 +@end example +@end ifset + +@table @code +@kindex thread @var{threadno} +@item thread @var{threadno} +Make thread number @var{threadno} the current thread. The command +argument @var{threadno} is the internal @value{GDBN} thread number, as +shown in the first field of the @samp{info threads} display. +@value{GDBN} responds by displaying the system identifier of the thread +you selected, and its current stack frame summary: + +@smallexample +@c FIXME!! This example made up; find a @value{GDBN} w/threads and get real one +(@value{GDBP}) thread 2 +@ifclear HPPA +[Switching to process 35 thread 23] +@end ifclear +@ifset HPPA +[Switching to thread 2 (system thread 26594)] +@end ifset +0x34e5 in sigpause () +@end smallexample + +@noindent +As with the @samp{[New @dots{}]} message, the form of the text after +@samp{Switching to} depends on your system's conventions for identifying +threads. + +@kindex thread apply +@item thread apply [@var{threadno}] [@var{all}] @var{args} +The @code{thread apply} command allows you to apply a command to one or +more threads. Specify the numbers of the threads that you want affected +with the command argument @var{threadno}. @var{threadno} is the internal +@value{GDBN} thread number, as shown in the first field of the @samp{info +threads} display. To apply a command to all threads, use +@code{thread apply all} @var{args}. +@end table + +@cindex automatic thread selection +@cindex switching threads automatically +@cindex threads, automatic switching +Whenever @value{GDBN} stops your program, due to a breakpoint or a +signal, it automatically selects the thread where that breakpoint or +signal happened. @value{GDBN} alerts you to the context switch with a +message of the form @samp{[Switching to @var{systag}]} to identify the +thread. + +@xref{Thread Stops,,Stopping and starting multi-thread programs}, for +more information about how @value{GDBN} behaves when you stop and start +programs with multiple threads. + +@xref{Set Watchpoints,,Setting watchpoints}, for information about +watchpoints in programs with multiple threads. +@end ifclear + +@ifclear HPPA +@node Processes, , Threads, Running +@section Debugging programs with multiple processes + +@cindex fork, debugging programs which call +@cindex multiple processes +@cindex processes, multiple +@value{GDBN} has no special support for debugging programs which create +additional processes using the @code{fork} function. When a program +forks, @value{GDBN} will continue to debug the parent process and the +child process will run unimpeded. If you have set a breakpoint in any +code which the child then executes, the child will get a @code{SIGTRAP} +signal which (unless it catches the signal) will cause it to terminate. + +However, if you want to debug the child process there is a workaround +which isn't too painful. Put a call to @code{sleep} in the code which +the child process executes after the fork. It may be useful to sleep +only if a certain environment variable is set, or a certain file exists, +so that the delay need not occur when you don't want to run @value{GDBN} +on the child. While the child is sleeping, use the @code{ps} program to +get its process ID. Then tell @value{GDBN} (a new invocation of +@value{GDBN} if you are also debugging the parent process) to attach to +the child process (see @ref{Attach}). From that point on you can debug +the child process just like any other process which you attached to. +@end ifclear +@ifset HPPA +@node Processes, , Threads, Running +@section Debugging programs with multiple processes + +@cindex fork, debugging programs which call +@cindex multiple processes +@cindex processes, multiple + +@value{GDBN} provides support for debugging programs that create +additional processes using the @code{fork} or @code{vfork} function. + +By default, when a program forks, @value{GDBN} will continue to debug +the parent process and the child process will run unimpeded. + +If you want to follow the child process instead of the parent process, +use the command @w{@code{set follow-fork-mode}}. + +@table @code +@kindex set follow-fork-mode +@item set follow-fork-mode @var{mode} +Set the debugger response to a program call of @code{fork} or +@code{vfork}. A call to @code{fork} or @code{vfork} creates a new +process. The @var{mode} can be: + +@table @code +@item parent +The original process is debugged after a fork. The child process runs +unimpeded. + +@item child +The new process is debugged after a fork. The parent process runs +unimpeded. + +@item ask +The debugger will ask for one of the above choices. +@end table + +@item show follow-fork-mode +Display the current debugger response to a fork or vfork call. +@end table + +If you ask to debug a child process and a @code{vfork} is followed by an +@code{exec}, @value{GDBN} executes the new target up to the first +breakpoint in the new target. If you have a breakpoint set on +@code{main} in your original program, the breakpoint will also be set on +the child process's @code{main}. + +When a child process is spawned by @code{vfork}, you cannot debug the +child or parent until an @code{exec} call completes. + +If you issue a @code{run} command to @value{GDBN} after an @code{exec} +call executes, the new target restarts. To restart the parent process, +use the @code{file} command with the parent executable name as its +argument. + +You can use the @code{catch} command to make @value{GDBN} stop whenever +a @code{fork}, @code{vfork}, or @code{exec} call is made. @xref{Set +Catchpoints, ,Setting catchpoints}. +@end ifset + +@node Stopping, Stack, Running, Top +@chapter Stopping and Continuing + +The principal purposes of using a debugger are so that you can stop your +program before it terminates; or so that, if your program runs into +trouble, you can investigate and find out why. + +Inside @value{GDBN}, your program may stop for any of several reasons, such +as +@ifclear BARETARGET +a signal, +@end ifclear +a breakpoint, or reaching a new line after a @value{GDBN} +command such as @code{step}. You may then examine and change +variables, set new breakpoints or remove old ones, and then continue +execution. Usually, the messages shown by @value{GDBN} provide ample +explanation of the status of your program---but you can also explicitly +request this information at any time. + +@table @code +@kindex info program +@item info program +Display information about the status of your program: whether it is +running or not, +@ifclear BARETARGET +what process it is, +@end ifclear +and why it stopped. +@end table + +@menu +* Breakpoints:: Breakpoints, watchpoints, and catchpoints +* Continuing and Stepping:: Resuming execution +@ifset POSIX +* Signals:: Signals +@end ifset + +@ifclear BARETARGET +* Thread Stops:: Stopping and starting multi-thread programs +@end ifclear + +@end menu + +@node Breakpoints, Continuing and Stepping, Stopping, Stopping +@section Breakpoints, watchpoints, and catchpoints + +@cindex breakpoints +A @dfn{breakpoint} makes your program stop whenever a certain point in +the program is reached. For each breakpoint, you can add conditions to +control in finer detail whether your program stops. You can set +breakpoints with the @code{break} command and its variants (@pxref{Set +Breaks, ,Setting breakpoints}), to specify the place where your program +should stop by line number, function name or exact address in the +program. + +In HP-UX, SunOS 4.x, SVR4, and Alpha OSF/1 configurations, you can set +breakpoints in shared libraries before the executable is run. There is +a minor limitation on HP-UX systems: you must wait until the executable +is run in order to set breakpoints in shared library routines that are +not called directly by the program (for example, routines that are +arguments in a @code{pthread_create} call). + +@cindex watchpoints +@cindex memory tracing +@cindex breakpoint on memory address +@cindex breakpoint on variable modification +A @dfn{watchpoint} is a special breakpoint that stops your program +when the value of an expression changes. You must use a different +command to set watchpoints (@pxref{Set Watchpoints, ,Setting +watchpoints}), but aside from that, you can manage a watchpoint like +any other breakpoint: you enable, disable, and delete both breakpoints +and watchpoints using the same commands. + +You can arrange to have values from your program displayed automatically +whenever @value{GDBN} stops at a breakpoint. @xref{Auto Display,, +Automatic display}. + +@cindex catchpoints +@cindex breakpoint on events +A @dfn{catchpoint} is another special breakpoint that stops your program +when a certain kind of event occurs, such as the throwing of a C++ +exception or the loading of a library. As with watchpoints, you use a +different command to set a catchpoint (@pxref{Set Catchpoints, ,Setting +catchpoints}), but aside from that, you can manage a catchpoint like any +other breakpoint. (To stop when your program receives a signal, use the +@code{handle} command; @pxref{Signals, ,Signals}.) + +@cindex breakpoint numbers +@cindex numbers for breakpoints +@value{GDBN} assigns a number to each breakpoint, watchpoint, or +catchpoint when you create it; these numbers are successive integers +starting with one. In many of the commands for controlling various +features of breakpoints you use the breakpoint number to say which +breakpoint you want to change. Each breakpoint may be @dfn{enabled} or +@dfn{disabled}; if disabled, it has no effect on your program until you +enable it again. + +@menu +* Set Breaks:: Setting breakpoints +* Set Watchpoints:: Setting watchpoints +* Set Catchpoints:: Setting catchpoints +* Delete Breaks:: Deleting breakpoints +* Disabling:: Disabling breakpoints +* Conditions:: Break conditions +* Break Commands:: Breakpoint command lists +@ifclear CONLY +* Breakpoint Menus:: Breakpoint menus +@end ifclear + +@c @ifclear BARETARGET +@c * Error in Breakpoints:: ``Cannot insert breakpoints'' +@c @end ifclear +@end menu + +@node Set Breaks, Set Watchpoints, Breakpoints, Breakpoints +@subsection Setting breakpoints + +@c FIXME LMB what does GDB do if no code on line of breakpt? +@c consider in particular declaration with/without initialization. +@c +@c FIXME 2 is there stuff on this already? break at fun start, already init? + +@kindex break +@kindex b +@kindex $bpnum +@cindex latest breakpoint +Breakpoints are set with the @code{break} command (abbreviated +@code{b}). The debugger convenience variable @samp{$bpnum} records the +number of the breakpoints you've set most recently; see @ref{Convenience +Vars,, Convenience variables}, for a discussion of what you can do with +convenience variables. + +You have several ways to say where the breakpoint should go. + +@table @code +@item break @var{function} +Set a breakpoint at entry to function @var{function}. +@ifclear CONLY +When using source languages that permit overloading of symbols, such as +C++, @var{function} may refer to more than one possible place to break. +@xref{Breakpoint Menus,,Breakpoint menus}, for a discussion of that situation. +@end ifclear + +@item break +@var{offset} +@itemx break -@var{offset} +Set a breakpoint some number of lines forward or back from the position +at which execution stopped in the currently selected frame. + +@item break @var{linenum} +Set a breakpoint at line @var{linenum} in the current source file. +That file is the last file whose source text was printed. This +breakpoint stops your program just before it executes any of the +code on that line. + +@item break @var{filename}:@var{linenum} +Set a breakpoint at line @var{linenum} in source file @var{filename}. + +@item break @var{filename}:@var{function} +Set a breakpoint at entry to function @var{function} found in file +@var{filename}. Specifying a file name as well as a function name is +superfluous except when multiple files contain similarly named +functions. + +@item break *@var{address} +Set a breakpoint at address @var{address}. You can use this to set +breakpoints in parts of your program which do not have debugging +information or source files. + +@item break +When called without any arguments, @code{break} sets a breakpoint at +the next instruction to be executed in the selected stack frame +(@pxref{Stack, ,Examining the Stack}). In any selected frame but the +innermost, this makes your program stop as soon as control +returns to that frame. This is similar to the effect of a +@code{finish} command in the frame inside the selected frame---except +that @code{finish} does not leave an active breakpoint. If you use +@code{break} without an argument in the innermost frame, @value{GDBN} stops +the next time it reaches the current location; this may be useful +inside loops. + +@value{GDBN} normally ignores breakpoints when it resumes execution, until at +least one instruction has been executed. If it did not do this, you +would be unable to proceed past a breakpoint without first disabling the +breakpoint. This rule applies whether or not the breakpoint already +existed when your program stopped. + +@item break @dots{} if @var{cond} +Set a breakpoint with condition @var{cond}; evaluate the expression +@var{cond} each time the breakpoint is reached, and stop only if the +value is nonzero---that is, if @var{cond} evaluates as true. +@samp{@dots{}} stands for one of the possible arguments described +above (or no argument) specifying where to break. @xref{Conditions, +,Break conditions}, for more information on breakpoint conditions. + +@kindex tbreak +@item tbreak @var{args} +Set a breakpoint enabled only for one stop. @var{args} are the +same as for the @code{break} command, and the breakpoint is set in the same +way, but the breakpoint is automatically deleted after the first time your +program stops there. @xref{Disabling, ,Disabling breakpoints}. + +@ifclear HPPA +@kindex hbreak +@item hbreak @var{args} +Set a hardware-assisted breakpoint. @var{args} are the same as for the +@code{break} command and the breakpoint is set in the same way, but the +breakpoint requires hardware support and some target hardware may not +have this support. The main purpose of this is EPROM/ROM code +debugging, so you can set a breakpoint at an instruction without +changing the instruction. This can be used with the new trap-generation +provided by SPARClite DSU. DSU will generate traps when a program accesses +some data or instruction address that is assigned to the debug registers. +However the hardware breakpoint registers can only take two data breakpoints, +and @value{GDBN} will reject this command if more than two are used. +Delete or disable unused hardware breakpoints before setting +new ones. @xref{Conditions, ,Break conditions}. + +@kindex thbreak +@item thbreak @var{args} +Set a hardware-assisted breakpoint enabled only for one stop. @var{args} +are the same as for the @code{hbreak} command and the breakpoint is set in +the same way. However, like the @code{tbreak} command, +the breakpoint is automatically deleted after the +first time your program stops there. Also, like the @code{hbreak} +command, the breakpoint requires hardware support and some target hardware +may not have this support. @xref{Disabling, ,Disabling breakpoints}. +Also @xref{Conditions, ,Break conditions}. +@end ifclear + +@kindex rbreak +@cindex regular expression +@item rbreak @var{regex} +@c FIXME what kind of regexp? +Set breakpoints on all functions matching the regular expression +@var{regex}. This command +sets an unconditional breakpoint on all matches, printing a list of all +breakpoints it set. Once these breakpoints are set, they are treated +just like the breakpoints set with the @code{break} command. You can +delete them, disable them, or make them conditional the same way as any +other breakpoint. + +@ifclear CONLY +When debugging C++ programs, @code{rbreak} is useful for setting +breakpoints on overloaded functions that are not members of any special +classes. +@end ifclear + +@kindex info breakpoints +@cindex @code{$_} and @code{info breakpoints} +@item info breakpoints @r{[}@var{n}@r{]} +@itemx info break @r{[}@var{n}@r{]} +@itemx info watchpoints @r{[}@var{n}@r{]} +Print a table of all breakpoints, watchpoints, and catchpoints set and +not deleted, with the following columns for each breakpoint: + +@table @emph +@item Breakpoint Numbers +@item Type +Breakpoint, watchpoint, or catchpoint. +@item Disposition +Whether the breakpoint is marked to be disabled or deleted when hit. +@item Enabled or Disabled +Enabled breakpoints are marked with @samp{y}. @samp{n} marks breakpoints +that are not enabled. +@item Address +Where the breakpoint is in your program, as a memory address +@item What +Where the breakpoint is in the source for your program, as a file and +line number. +@end table + +@noindent +If a breakpoint is conditional, @code{info break} shows the condition on +the line following the affected breakpoint; breakpoint commands, if any, +are listed after that. + +@noindent +@code{info break} with a breakpoint +number @var{n} as argument lists only that breakpoint. The +convenience variable @code{$_} and the default examining-address for +the @code{x} command are set to the address of the last breakpoint +listed (@pxref{Memory, ,Examining memory}). + +@noindent +@code{info break} displays a count of the number of times the breakpoint +has been hit. This is especially useful in conjunction with the +@code{ignore} command. You can ignore a large number of breakpoint +hits, look at the breakpoint info to see how many times the breakpoint +was hit, and then run again, ignoring one less than that number. This +will get you quickly to the last hit of that breakpoint. +@end table + +@value{GDBN} allows you to set any number of breakpoints at the same place in +your program. There is nothing silly or meaningless about this. When +the breakpoints are conditional, this is even useful +(@pxref{Conditions, ,Break conditions}). + +@cindex negative breakpoint numbers +@cindex internal @value{GDBN} breakpoints +@value{GDBN} itself sometimes sets breakpoints in your program for special +purposes, such as proper handling of @code{longjmp} (in C programs). +These internal breakpoints are assigned negative numbers, starting with +@code{-1}; @samp{info breakpoints} does not display them. + +You can see these breakpoints with the @value{GDBN} maintenance command +@samp{maint info breakpoints}. + +@table @code +@kindex maint info breakpoints +@item maint info breakpoints +Using the same format as @samp{info breakpoints}, display both the +breakpoints you've set explicitly, and those @value{GDBN} is using for +internal purposes. Internal breakpoints are shown with negative +breakpoint numbers. The type column identifies what kind of breakpoint +is shown: + +@table @code +@item breakpoint +Normal, explicitly set breakpoint. + +@item watchpoint +Normal, explicitly set watchpoint. + +@item longjmp +Internal breakpoint, used to handle correctly stepping through +@code{longjmp} calls. + +@item longjmp resume +Internal breakpoint at the target of a @code{longjmp}. + +@item until +Temporary internal breakpoint used by the @value{GDBN} @code{until} command. + +@item finish +Temporary internal breakpoint used by the @value{GDBN} @code{finish} command. + +@ifset HPPA +@item shlib events +Shared library events. +@end ifset +@end table +@end table + + +@node Set Watchpoints, Set Catchpoints, Set Breaks, Breakpoints +@subsection Setting watchpoints + +@cindex setting watchpoints +@cindex software watchpoints +@cindex hardware watchpoints +You can use a watchpoint to stop execution whenever the value of an +expression changes, without having to predict a particular place where +this may happen. + +Depending on your system, watchpoints may be implemented in software or +hardware. GDB does software watchpointing by single-stepping your +program and testing the variable's value each time, which is hundreds of +times slower than normal execution. (But this may still be worth it, to +catch errors where you have no clue what part of your program is the +culprit.) + +On some systems, such as HP-UX and Linux, GDB includes support for +hardware watchpoints, which do not slow down the running of your +program. + +@table @code +@kindex watch +@item watch @var{expr} +Set a watchpoint for an expression. @value{GDBN} will break when @var{expr} +is written into by the program and its value changes. + +@kindex rwatch +@item rwatch @var{expr} +Set a watchpoint that will break when watch @var{expr} is read by the program. +If you use both watchpoints, both must be set with the @code{rwatch} +command. + +@kindex awatch +@item awatch @var{expr} +Set a watchpoint that will break when @var{args} is read and written into +by the program. If you use both watchpoints, both must be set with the +@code{awatch} command. + +@kindex info watchpoints +@item info watchpoints +This command prints a list of watchpoints, breakpoints, and catchpoints; +it is the same as @code{info break}. +@end table + +@value{GDBN} sets a @dfn{hardware watchpoint} if possible. Hardware +watchpoints execute very quickly, and the debugger reports a change in +value at the exact instruction where the change occurs. If @value{GDBN} +cannot set a hardware watchpoint, it sets a software watchpoint, which +executes more slowly and reports the change in value at the next +statement, not the instruction, after the change occurs. + +When you issue the @code{watch} command, @value{GDBN} reports + +@example +Hardware watchpoint @var{num}: @var{expr} +@end example + +@noindent +if it was able to set a hardware watchpoint. + +The SPARClite DSU will generate traps when a program accesses +some data or instruction address that is assigned to the debug registers. +For the data addresses, DSU facilitates the @code{watch} command. +However the hardware breakpoint registers can only take two data watchpoints, +and both watchpoints must be the same kind. For example, you can set two +watchpoints with @code{watch} commands, two with @code{rwatch} +commands, @strong{or} two with @code{awatch} commands, but you cannot set one +watchpoint with one command and the other with a different command. +@value{GDBN} will reject the command if you try to mix watchpoints. +Delete or disable unused watchpoint commands before setting new ones. + +If you call a function interactively using @code{print} or @code{call}, +any watchpoints you have set will be inactive until GDB reaches another +kind of breakpoint or the call completes. + +@ifclear BARETARGET +@quotation +@cindex watchpoints and threads +@cindex threads and watchpoints +@ifclear HPPA +@emph{Warning:} In multi-thread programs, watchpoints have only limited +usefulness. With the current watchpoint implementation, @value{GDBN} +can only watch the value of an expression @emph{in a single thread}. If +you are confident that the expression can only change due to the current +thread's activity (and if you are also confident that no other thread +can become current), then you can use watchpoints as usual. However, +@value{GDBN} may not notice when a non-current thread's activity changes +the expression. +@end ifclear +@ifset HPPA +@emph{Warning:} In multi-thread programs, software watchpoints have only +limited usefulness. If @value{GDBN} creates a software watchpoint, it +can only watch the value of an expression @emph{in a single thread}. If +you are confident that the expression can only change due to the current +thread's activity (and if you are also confident that no other thread +can become current), then you can use software watchpoints as usual. +However, @value{GDBN} may not notice when a non-current thread's +activity changes the expression. (Hardware watchpoints, in contrast, +watch an expression in all threads.) +@end ifset +@end quotation +@end ifclear + +@node Set Catchpoints, Delete Breaks, Set Watchpoints, Breakpoints +@subsection Setting catchpoints +@cindex catchpoints +@cindex exception handlers +@cindex event handling + +You can use @dfn{catchpoints} to cause the debugger to stop for certain +kinds of program events, such as C++ exceptions or the loading of a +shared library. Use the @code{catch} command to set a catchpoint. + +@table @code +@kindex catch +@item catch @var{event} +Stop when @var{event} occurs. @var{event} can be any of the following: +@table @code +@item throw +@kindex catch throw +The throwing of a C++ exception. + +@item catch +@kindex catch catch +The catching of a C++ exception. + +@item exec +@kindex catch exec +A call to @code{exec}. This is currently only available for HP-UX. + +@item fork +@kindex catch fork +A call to @code{fork}. This is currently only available for HP-UX. + +@item vfork +@kindex catch vfork +A call to @code{vfork}. This is currently only available for HP-UX. + +@item load +@itemx load @var{libname} +@kindex catch load +The dynamic loading of any shared library, or the loading of the library +@var{libname}. This is currently only available for HP-UX. + +@item unload +@itemx unload @var{libname} +@kindex catch unload +The unloading of any dynamically loaded shared library, or the unloading +of the library @var{libname}. This is currently only available for HP-UX. +@end table + +@item tcatch @var{event} +Set a catchpoint that is enabled only for one stop. The catchpoint is +automatically deleted after the first time the event is caught. + +@end table + +Use the @code{info break} command to list the current catchpoints. + +There are currently some limitations to C++ exception handling +(@code{catch throw} and @code{catch catch}) in @value{GDBN}: + +@itemize @bullet +@item +If you call a function interactively, @value{GDBN} normally returns +control to you when the function has finished executing. If the call +raises an exception, however, the call may bypass the mechanism that +returns control to you and cause your program either to abort or to +simply continue running until it hits a breakpoint, catches a signal +that @value{GDBN} is listening for, or exits. This is the case even if +you set a catchpoint for the exception; catchpoints on exceptions are +disabled within interactive calls. + +@item +You cannot raise an exception interactively. + +@item +You cannot install an exception handler interactively. +@end itemize + +@cindex raise exceptions +Sometimes @code{catch} is not the best way to debug exception handling: +if you need to know exactly where an exception is raised, it is better to +stop @emph{before} the exception handler is called, since that way you +can see the stack before any unwinding takes place. If you set a +breakpoint in an exception handler instead, it may not be easy to find +out where the exception was raised. + +To stop just before an exception handler is called, you need some +knowledge of the implementation. In the case of @sc{gnu} C++, exceptions are +raised by calling a library function named @code{__raise_exception} +which has the following ANSI C interface: + +@example + /* @var{addr} is where the exception identifier is stored. + ID is the exception identifier. */ + void __raise_exception (void **@var{addr}, void *@var{id}); +@end example + +@noindent +To make the debugger catch all exceptions before any stack +unwinding takes place, set a breakpoint on @code{__raise_exception} +(@pxref{Breakpoints, ,Breakpoints; watchpoints; and exceptions}). + +With a conditional breakpoint (@pxref{Conditions, ,Break conditions}) +that depends on the value of @var{id}, you can stop your program when +a specific exception is raised. You can use multiple conditional +breakpoints to stop your program when any of a number of exceptions are +raised. + + +@node Delete Breaks, Disabling, Set Catchpoints, Breakpoints +@subsection Deleting breakpoints + +@cindex clearing breakpoints, watchpoints, catchpoints +@cindex deleting breakpoints, watchpoints, catchpoints +It is often necessary to eliminate a breakpoint, watchpoint, or +catchpoint once it has done its job and you no longer want your program +to stop there. This is called @dfn{deleting} the breakpoint. A +breakpoint that has been deleted no longer exists; it is forgotten. + +With the @code{clear} command you can delete breakpoints according to +where they are in your program. With the @code{delete} command you can +delete individual breakpoints, watchpoints, or catchpoints by specifying +their breakpoint numbers. + +It is not necessary to delete a breakpoint to proceed past it. @value{GDBN} +automatically ignores breakpoints on the first instruction to be executed +when you continue execution without changing the execution address. + +@table @code +@kindex clear +@item clear +Delete any breakpoints at the next instruction to be executed in the +selected stack frame (@pxref{Selection, ,Selecting a frame}). When +the innermost frame is selected, this is a good way to delete a +breakpoint where your program just stopped. + +@item clear @var{function} +@itemx clear @var{filename}:@var{function} +Delete any breakpoints set at entry to the function @var{function}. + +@item clear @var{linenum} +@itemx clear @var{filename}:@var{linenum} +Delete any breakpoints set at or within the code of the specified line. + +@cindex delete breakpoints +@kindex delete +@kindex d +@item delete @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]} +Delete the breakpoints, watchpoints, or catchpoints of the numbers +specified as arguments. If no argument is specified, delete all +breakpoints (@value{GDBN} asks confirmation, unless you have @code{set +confirm off}). You can abbreviate this command as @code{d}. +@end table + +@node Disabling, Conditions, Delete Breaks, Breakpoints +@subsection Disabling breakpoints + +@kindex disable breakpoints +@kindex enable breakpoints +Rather than deleting a breakpoint, watchpoint, or catchpoint, you might +prefer to @dfn{disable} it. This makes the breakpoint inoperative as if +it had been deleted, but remembers the information on the breakpoint so +that you can @dfn{enable} it again later. + +You disable and enable breakpoints, watchpoints, and catchpoints with +the @code{enable} and @code{disable} commands, optionally specifying one +or more breakpoint numbers as arguments. Use @code{info break} or +@code{info watch} to print a list of breakpoints, watchpoints, and +catchpoints if you do not know which numbers to use. + +A breakpoint, watchpoint, or catchpoint can have any of four different +states of enablement: + +@itemize @bullet +@item +Enabled. The breakpoint stops your program. A breakpoint set +with the @code{break} command starts out in this state. +@item +Disabled. The breakpoint has no effect on your program. +@item +Enabled once. The breakpoint stops your program, but then becomes +disabled. A breakpoint set with the @code{tbreak} command starts out in +this state. +@item +Enabled for deletion. The breakpoint stops your program, but +immediately after it does so it is deleted permanently. +@end itemize + +You can use the following commands to enable or disable breakpoints, +watchpoints, and catchpoints: + +@table @code +@kindex disable breakpoints +@kindex disable +@kindex dis +@item disable @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]} +Disable the specified breakpoints---or all breakpoints, if none are +listed. A disabled breakpoint has no effect but is not forgotten. All +options such as ignore-counts, conditions and commands are remembered in +case the breakpoint is enabled again later. You may abbreviate +@code{disable} as @code{dis}. + +@kindex enable breakpoints +@kindex enable +@item enable @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]} +Enable the specified breakpoints (or all defined breakpoints). They +become effective once again in stopping your program. + +@item enable @r{[}breakpoints@r{]} once @var{bnums}@dots{} +Enable the specified breakpoints temporarily. @value{GDBN} disables any +of these breakpoints immediately after stopping your program. + +@item enable @r{[}breakpoints@r{]} delete @var{bnums}@dots{} +Enable the specified breakpoints to work once, then die. @value{GDBN} +deletes any of these breakpoints as soon as your program stops there. +@end table + +Except for a breakpoint set with @code{tbreak} (@pxref{Set Breaks, +,Setting breakpoints}), breakpoints that you set are initially enabled; +subsequently, they become disabled or enabled only when you use one of +the commands above. (The command @code{until} can set and delete a +breakpoint of its own, but it does not change the state of your other +breakpoints; see @ref{Continuing and Stepping, ,Continuing and +stepping}.) + +@node Conditions, Break Commands, Disabling, Breakpoints +@subsection Break conditions +@cindex conditional breakpoints +@cindex breakpoint conditions + +@c FIXME what is scope of break condition expr? Context where wanted? +@c in particular for a watchpoint? +The simplest sort of breakpoint breaks every time your program reaches a +specified place. You can also specify a @dfn{condition} for a +breakpoint. A condition is just a Boolean expression in your +programming language (@pxref{Expressions, ,Expressions}). A breakpoint with +a condition evaluates the expression each time your program reaches it, +and your program stops only if the condition is @emph{true}. + +This is the converse of using assertions for program validation; in that +situation, you want to stop when the assertion is violated---that is, +when the condition is false. In C, if you want to test an assertion expressed +by the condition @var{assert}, you should set the condition +@samp{! @var{assert}} on the appropriate breakpoint. + +Conditions are also accepted for watchpoints; you may not need them, +since a watchpoint is inspecting the value of an expression anyhow---but +it might be simpler, say, to just set a watchpoint on a variable name, +and specify a condition that tests whether the new value is an interesting +one. + +Break conditions can have side effects, and may even call functions in +your program. This can be useful, for example, to activate functions +that log program progress, or to use your own print functions to +format special data structures. The effects are completely predictable +unless there is another enabled breakpoint at the same address. (In +that case, @value{GDBN} might see the other breakpoint first and stop your +program without checking the condition of this one.) Note that +breakpoint commands are usually more convenient and flexible for the +purpose of performing side effects when a breakpoint is reached +(@pxref{Break Commands, ,Breakpoint command lists}). + +Break conditions can be specified when a breakpoint is set, by using +@samp{if} in the arguments to the @code{break} command. @xref{Set +Breaks, ,Setting breakpoints}. They can also be changed at any time +with the @code{condition} command. +@ifclear HPPA +@c The watch command now seems to recognize the if keyword. +@c catch doesn't, though. +The @code{watch} command does not recognize the @code{if} keyword; +@code{condition} is the only way to impose a further condition on a +watchpoint. +@end ifclear +@ifset HPPA +You can also use the @code{if} keyword with the @code{watch} command. +The @code{catch} command does not recognize the @code{if} keyword; +@code{condition} is the only way to impose a further condition on a +catchpoint. +@end ifset + +@table @code +@kindex condition +@item condition @var{bnum} @var{expression} +Specify @var{expression} as the break condition for breakpoint, +watchpoint, or catchpoint number @var{bnum}. After you set a condition, +breakpoint @var{bnum} stops your program only if the value of +@var{expression} is true (nonzero, in C). When you use +@code{condition}, @value{GDBN} checks @var{expression} immediately for +syntactic correctness, and to determine whether symbols in it have +referents in the context of your breakpoint. +@c FIXME so what does GDB do if there is no referent? Moreover, what +@c about watchpoints? +@value{GDBN} does +not actually evaluate @var{expression} at the time the @code{condition} +command is given, however. @xref{Expressions, ,Expressions}. + +@item condition @var{bnum} +Remove the condition from breakpoint number @var{bnum}. It becomes +an ordinary unconditional breakpoint. +@end table + +@cindex ignore count (of breakpoint) +A special case of a breakpoint condition is to stop only when the +breakpoint has been reached a certain number of times. This is so +useful that there is a special way to do it, using the @dfn{ignore +count} of the breakpoint. Every breakpoint has an ignore count, which +is an integer. Most of the time, the ignore count is zero, and +therefore has no effect. But if your program reaches a breakpoint whose +ignore count is positive, then instead of stopping, it just decrements +the ignore count by one and continues. As a result, if the ignore count +value is @var{n}, the breakpoint does not stop the next @var{n} times +your program reaches it. + +@table @code +@kindex ignore +@item ignore @var{bnum} @var{count} +Set the ignore count of breakpoint number @var{bnum} to @var{count}. +The next @var{count} times the breakpoint is reached, your program's +execution does not stop; other than to decrement the ignore count, @value{GDBN} +takes no action. + +To make the breakpoint stop the next time it is reached, specify +a count of zero. + +When you use @code{continue} to resume execution of your program from a +breakpoint, you can specify an ignore count directly as an argument to +@code{continue}, rather than using @code{ignore}. @xref{Continuing and +Stepping,,Continuing and stepping}. + +If a breakpoint has a positive ignore count and a condition, the +condition is not checked. Once the ignore count reaches zero, +@value{GDBN} resumes checking the condition. + +You could achieve the effect of the ignore count with a condition such +as @w{@samp{$foo-- <= 0}} using a debugger convenience variable that +is decremented each time. @xref{Convenience Vars, ,Convenience +variables}. +@end table + +Ignore counts apply to breakpoints, watchpoints, and catchpoints. + + +@node Break Commands, Breakpoint Menus, Conditions, Breakpoints +@subsection Breakpoint command lists + +@cindex breakpoint commands +You can give any breakpoint (or watchpoint or catchpoint) a series of +commands to execute when your program stops due to that breakpoint. For +example, you might want to print the values of certain expressions, or +enable other breakpoints. + +@table @code +@kindex commands +@kindex end +@item commands @r{[}@var{bnum}@r{]} +@itemx @dots{} @var{command-list} @dots{} +@itemx end +Specify a list of commands for breakpoint number @var{bnum}. The commands +themselves appear on the following lines. Type a line containing just +@code{end} to terminate the commands. + +To remove all commands from a breakpoint, type @code{commands} and +follow it immediately with @code{end}; that is, give no commands. + +With no @var{bnum} argument, @code{commands} refers to the last +breakpoint, watchpoint, or catchpoint set (not to the breakpoint most +recently encountered). +@end table + +Pressing @key{RET} as a means of repeating the last @value{GDBN} command is +disabled within a @var{command-list}. + +You can use breakpoint commands to start your program up again. Simply +use the @code{continue} command, or @code{step}, or any other command +that resumes execution. + +Any other commands in the command list, after a command that resumes +execution, are ignored. This is because any time you resume execution +(even with a simple @code{next} or @code{step}), you may encounter +another breakpoint---which could have its own command list, leading to +ambiguities about which list to execute. + +@kindex silent +If the first command you specify in a command list is @code{silent}, the +usual message about stopping at a breakpoint is not printed. This may +be desirable for breakpoints that are to print a specific message and +then continue. If none of the remaining commands print anything, you +see no sign that the breakpoint was reached. @code{silent} is +meaningful only at the beginning of a breakpoint command list. + +The commands @code{echo}, @code{output}, and @code{printf} allow you to +print precisely controlled output, and are often useful in silent +breakpoints. @xref{Output, ,Commands for controlled output}. + +For example, here is how you could use breakpoint commands to print the +value of @code{x} at entry to @code{foo} whenever @code{x} is positive. + +@example +break foo if x>0 +commands +silent +printf "x is %d\n",x +cont +end +@end example + +One application for breakpoint commands is to compensate for one bug so +you can test for another. Put a breakpoint just after the erroneous line +of code, give it a condition to detect the case in which something +erroneous has been done, and give it commands to assign correct values +to any variables that need them. End with the @code{continue} command +so that your program does not stop, and start with the @code{silent} +command so that no output is produced. Here is an example: + +@example +break 403 +commands +silent +set x = y + 4 +cont +end +@end example + +@ifclear CONLY +@node Breakpoint Menus, , Break Commands, Breakpoints +@subsection Breakpoint menus +@cindex overloading +@cindex symbol overloading + +Some programming languages (notably C++) permit a single function name +to be defined several times, for application in different contexts. +This is called @dfn{overloading}. When a function name is overloaded, +@samp{break @var{function}} is not enough to tell @value{GDBN} where you want +a breakpoint. If you realize this is a problem, you can use +something like @samp{break @var{function}(@var{types})} to specify which +particular version of the function you want. Otherwise, @value{GDBN} offers +you a menu of numbered choices for different possible breakpoints, and +waits for your selection with the prompt @samp{>}. The first two +options are always @samp{[0] cancel} and @samp{[1] all}. Typing @kbd{1} +sets a breakpoint at each definition of @var{function}, and typing +@kbd{0} aborts the @code{break} command without setting any new +breakpoints. + +For example, the following session excerpt shows an attempt to set a +breakpoint at the overloaded symbol @code{String::after}. +We choose three particular definitions of that function name: + +@c FIXME! This is likely to change to show arg type lists, at least +@smallexample +@group +(@value{GDBP}) b String::after +[0] cancel +[1] all +[2] file:String.cc; line number:867 +[3] file:String.cc; line number:860 +[4] file:String.cc; line number:875 +[5] file:String.cc; line number:853 +[6] file:String.cc; line number:846 +[7] file:String.cc; line number:735 +> 2 4 6 +Breakpoint 1 at 0xb26c: file String.cc, line 867. +Breakpoint 2 at 0xb344: file String.cc, line 875. +Breakpoint 3 at 0xafcc: file String.cc, line 846. +Multiple breakpoints were set. +Use the "delete" command to delete unwanted + breakpoints. +(@value{GDBP}) +@end group +@end smallexample +@end ifclear + +@c @ifclear BARETARGET +@c @node Error in Breakpoints +@c @subsection ``Cannot insert breakpoints'' +@c +@c FIXME!! 14/6/95 Is there a real example of this? Let's use it. +@c +@c Under some operating systems, breakpoints cannot be used in a program if +@c any other process is running that program. In this situation, +@c attempting to run or continue a program with a breakpoint causes +@c @value{GDBN} to stop the other process. +@c +@c When this happens, you have three ways to proceed: +@c +@c @enumerate +@c @item +@c Remove or disable the breakpoints, then continue. +@c +@c @item +@c Suspend @value{GDBN}, and copy the file containing your program to a new +@c name. Resume @value{GDBN} and use the @code{exec-file} command to specify +@c that @value{GDBN} should run your program under that name. +@c Then start your program again. +@c +@c @item +@c Relink your program so that the text segment is nonsharable, using the +@c linker option @samp{-N}. The operating system limitation may not apply +@c to nonsharable executables. +@c @end enumerate +@c @end ifclear + +@node Continuing and Stepping, Signals, Breakpoints, Stopping +@section Continuing and stepping + +@cindex stepping +@cindex continuing +@cindex resuming execution +@dfn{Continuing} means resuming program execution until your program +completes normally. In contrast, @dfn{stepping} means executing just +one more ``step'' of your program, where ``step'' may mean either one +line of source code, or one machine instruction (depending on what +particular command you use). Either when continuing +or when stepping, your program may stop even sooner, due to +@ifset BARETARGET +a breakpoint. +@end ifset +@ifclear BARETARGET +a breakpoint or a signal. (If due to a signal, you may want to use +@code{handle}, or use @samp{signal 0} to resume execution. +@xref{Signals, ,Signals}.) +@end ifclear + +@table @code +@kindex continue +@kindex c +@kindex fg +@item continue @r{[}@var{ignore-count}@r{]} +@itemx c @r{[}@var{ignore-count}@r{]} +@itemx fg @r{[}@var{ignore-count}@r{]} +Resume program execution, at the address where your program last stopped; +any breakpoints set at that address are bypassed. The optional argument +@var{ignore-count} allows you to specify a further number of times to +ignore a breakpoint at this location; its effect is like that of +@code{ignore} (@pxref{Conditions, ,Break conditions}). + +The argument @var{ignore-count} is meaningful only when your program +stopped due to a breakpoint. At other times, the argument to +@code{continue} is ignored. + +The synonyms @code{c} and @code{fg} are provided purely for convenience, +and have exactly the same behavior as @code{continue}. +@end table + +To resume execution at a different place, you can use @code{return} +(@pxref{Returning, ,Returning from a function}) to go back to the +calling function; or @code{jump} (@pxref{Jumping, ,Continuing at a +different address}) to go to an arbitrary location in your program. + +A typical technique for using stepping is to set a breakpoint +(@pxref{Breakpoints, ,Breakpoints; watchpoints; and catchpoints}) at the +beginning of the function or the section of your program where a problem +is believed to lie, run your program until it stops at that breakpoint, +and then step through the suspect area, examining the variables that are +interesting, until you see the problem happen. + +@table @code +@kindex step +@kindex s +@item step +Continue running your program until control reaches a different source +line, then stop it and return control to @value{GDBN}. This command is +abbreviated @code{s}. + +@quotation +@c "without debugging information" is imprecise; actually "without line +@c numbers in the debugging information". (gcc -g1 has debugging info but +@c not line numbers). But it seems complex to try to make that +@c distinction here. +@emph{Warning:} If you use the @code{step} command while control is +within a function that was compiled without debugging information, +execution proceeds until control reaches a function that does have +debugging information. Likewise, it will not step into a function which +is compiled without debugging information. To step through functions +without debugging information, use the @code{stepi} command, described +below. +@end quotation + +The @code{step} command now only stops at the first instruction of a +source line. This prevents the multiple stops that used to occur in +switch statements, for loops, etc. @code{step} continues to stop if a +function that has debugging information is called within the line. + +Also, the @code{step} command now only enters a subroutine if there is line +number information for the subroutine. Otherwise it acts like the +@code{next} command. This avoids problems when using @code{cc -gl} +on MIPS machines. Previously, @code{step} entered subroutines if there +was any debugging information about the routine. + +@item step @var{count} +Continue running as in @code{step}, but do so @var{count} times. If a +breakpoint is reached, +@ifclear BARETARGET +or a signal not related to stepping occurs before @var{count} steps, +@end ifclear +stepping stops right away. + +@kindex next +@kindex n +@item next @r{[}@var{count}@r{]} +Continue to the next source line in the current (innermost) stack frame. +This is similar to @code{step}, but function calls that appear within the line +of code are executed without stopping. Execution stops when control +reaches a different line of code at the original stack level that was +executing when you gave the @code{next} command. This command is abbreviated +@code{n}. + +An argument @var{count} is a repeat count, as for @code{step}. + + +@c FIX ME!! Do we delete this, or is there a way it fits in with +@c the following paragraph? --- Vctoria +@c +@c @code{next} within a function that lacks debugging information acts like +@c @code{step}, but any function calls appearing within the code of the +@c function are executed without stopping. + +The @code{next} command now only stops at the first instruction of a +source line. This prevents the multiple stops that used to occur in +switch statements, for loops, etc. + +@kindex finish +@item finish +Continue running until just after function in the selected stack frame +returns. Print the returned value (if any). + +Contrast this with the @code{return} command (@pxref{Returning, +,Returning from a function}). + +@kindex until +@kindex u +@item until +@itemx u +Continue running until a source line past the current line, in the +current stack frame, is reached. This command is used to avoid single +stepping through a loop more than once. It is like the @code{next} +command, except that when @code{until} encounters a jump, it +automatically continues execution until the program counter is greater +than the address of the jump. + +This means that when you reach the end of a loop after single stepping +though it, @code{until} makes your program continue execution until it +exits the loop. In contrast, a @code{next} command at the end of a loop +simply steps back to the beginning of the loop, which forces you to step +through the next iteration. + +@code{until} always stops your program if it attempts to exit the current +stack frame. + +@code{until} may produce somewhat counterintuitive results if the order +of machine code does not match the order of the source lines. For +example, in the following excerpt from a debugging session, the @code{f} +(@code{frame}) command shows that execution is stopped at line +@code{206}; yet when we use @code{until}, we get to line @code{195}: + +@example +(@value{GDBP}) f +#0 main (argc=4, argv=0xf7fffae8) at m4.c:206 +206 expand_input(); +(@value{GDBP}) until +195 for ( ; argc > 0; NEXTARG) @{ +@end example + +This happened because, for execution efficiency, the compiler had +generated code for the loop closure test at the end, rather than the +start, of the loop---even though the test in a C @code{for}-loop is +written before the body of the loop. The @code{until} command appeared +to step back to the beginning of the loop when it advanced to this +expression; however, it has not really gone to an earlier +statement---not in terms of the actual machine code. + +@code{until} with no argument works by means of single +instruction stepping, and hence is slower than @code{until} with an +argument. + +@item until @var{location} +@itemx u @var{location} +Continue running your program until either the specified location is +reached, or the current stack frame returns. @var{location} is any of +the forms of argument acceptable to @code{break} (@pxref{Set Breaks, +,Setting breakpoints}). This form of the command uses breakpoints, +and hence is quicker than @code{until} without an argument. + +@kindex stepi +@kindex si +@item stepi +@itemx si +Execute one machine instruction, then stop and return to the debugger. + +It is often useful to do @samp{display/i $pc} when stepping by machine +instructions. This makes @value{GDBN} automatically display the next +instruction to be executed, each time your program stops. @xref{Auto +Display,, Automatic display}. + +An argument is a repeat count, as in @code{step}. + +@need 750 +@kindex nexti +@kindex ni +@item nexti +@itemx ni +Execute one machine instruction, but if it is a function call, +proceed until the function returns. + +An argument is a repeat count, as in @code{next}. +@end table + +@ifset POSIX +@node Signals, Thread Stops, Continuing and Stepping, Stopping +@section Signals +@cindex signals + +A signal is an asynchronous event that can happen in a program. The +operating system defines the possible kinds of signals, and gives each +kind a name and a number. For example, in Unix @code{SIGINT} is the +signal a program gets when you type an interrupt (often @kbd{C-c}); +@code{SIGSEGV} is the signal a program gets from referencing a place in +memory far away from all the areas in use; @code{SIGALRM} occurs when +the alarm clock timer goes off (which happens only if your program has +requested an alarm). + +@cindex fatal signals +Some signals, including @code{SIGALRM}, are a normal part of the +functioning of your program. Others, such as @code{SIGSEGV}, indicate +errors; these signals are @dfn{fatal} (kill your program immediately) if the +program has not specified in advance some other way to handle the signal. +@code{SIGINT} does not indicate an error in your program, but it is normally +fatal so it can carry out the purpose of the interrupt: to kill the program. + +@value{GDBN} has the ability to detect any occurrence of a signal in your +program. You can tell @value{GDBN} in advance what to do for each kind of +signal. + +@cindex handling signals +Normally, @value{GDBN} is set up to ignore non-erroneous signals like @code{SIGALRM} +(so as not to interfere with their role in the functioning of your program) +but to stop your program immediately whenever an error signal happens. +You can change these settings with the @code{handle} command. + +@table @code +@kindex info signals +@item info signals +Print a table of all the kinds of signals and how @value{GDBN} has been told to +handle each one. You can use this to see the signal numbers of all +the defined types of signals. + +@code{info handle} is the new alias for @code{info signals}. + +@kindex handle +@item handle @var{signal} @var{keywords}@dots{} +Change the way @value{GDBN} handles signal @var{signal}. @var{signal} can +be the number of a signal or its name (with or without the @samp{SIG} at the +beginning). The @var{keywords} say what change to make. +@end table + +@c @group +The keywords allowed by the @code{handle} command can be abbreviated. +Their full names are: + +@table @code +@item nostop +@value{GDBN} should not stop your program when this signal happens. It may +still print a message telling you that the signal has come in. + +@item stop +@value{GDBN} should stop your program when this signal happens. This implies +the @code{print} keyword as well. + +@item print +@value{GDBN} should print a message when this signal happens. + +@item noprint +@value{GDBN} should not mention the occurrence of the signal at all. This +implies the @code{nostop} keyword as well. + +@item pass +@value{GDBN} should allow your program to see this signal; your program +can handle the signal, or else it may terminate if the signal is fatal +and not handled. + +@item nopass +@value{GDBN} should not allow your program to see this signal. +@end table +@c @end group + +When a signal stops your program, the signal is not visible until you +continue. Your program sees the signal then, if @code{pass} is in +effect for the signal in question @emph{at that time}. In other words, +after @value{GDBN} reports a signal, you can use the @code{handle} +command with @code{pass} or @code{nopass} to control whether your +program sees that signal when you continue. + +You can also use the @code{signal} command to prevent your program from +seeing a signal, or cause it to see a signal it normally would not see, +or to give it any signal at any time. For example, if your program stopped +due to some sort of memory reference error, you might store correct +values into the erroneous variables and continue, hoping to see more +execution; but your program would probably terminate immediately as +a result of the fatal signal once it saw the signal. To prevent this, +you can continue with @samp{signal 0}. @xref{Signaling, ,Giving your +program a signal}. +@end ifset + +@ifclear BARETARGET +@node Thread Stops, , Signals, Stopping +@section Stopping and starting multi-thread programs + +When your program has multiple threads (@pxref{Threads,, Debugging +programs with multiple threads}), you can choose whether to set +breakpoints on all threads, or on a particular thread. + +@table @code +@cindex breakpoints and threads +@cindex thread breakpoints +@kindex break @dots{} thread @var{threadno} +@item break @var{linespec} thread @var{threadno} +@itemx break @var{linespec} thread @var{threadno} if @dots{} +@var{linespec} specifies source lines; there are several ways of +writing them, but the effect is always to specify some source line. + +Use the qualifier @samp{thread @var{threadno}} with a breakpoint command +to specify that you only want @value{GDBN} to stop the program when a +particular thread reaches this breakpoint. @var{threadno} is one of the +numeric thread identifiers assigned by @value{GDBN}, shown in the first +column of the @samp{info threads} display. + +If you do not specify @samp{thread @var{threadno}} when you set a +breakpoint, the breakpoint applies to @emph{all} threads of your +program. + +You can use the @code{thread} qualifier on conditional breakpoints as +well; in this case, place @samp{thread @var{threadno}} before the +breakpoint condition, like this: + +@smallexample +(gdb) break frik.c:13 thread 28 if bartab > lim +@end smallexample + +@end table + +@cindex stopped threads +@cindex threads, stopped +Whenever your program stops under @value{GDBN} for any reason, +@emph{all} threads of execution stop, not just the current thread. This +allows you to examine the overall state of the program, including +switching between threads, without worrying that things may change +underfoot. + +@cindex continuing threads +@cindex threads, continuing +Conversely, whenever you restart the program, @emph{all} threads start +executing. @emph{This is true even when single-stepping} with commands +like @code{step} or @code{next}. + +In particular, @value{GDBN} cannot single-step all threads in lockstep. +Since thread scheduling is up to your debugging target's operating +system (not controlled by @value{GDBN}), other threads may +execute more than one statement while the current thread completes a +single step. Moreover, in general other threads stop in the middle of a +statement, rather than at a clean statement boundary, when the program +stops. + +You might even find your program stopped in another thread after +continuing or even single-stepping. This happens whenever some other +thread runs into a breakpoint, a signal, or an exception before the +first thread completes whatever you requested. + +On some OSes, you can lock the OS scheduler and thus allow only a single +thread to run. + +@table @code +@item set scheduler-locking @var{mode} +Set the scheduler locking mode. If it is @code{off}, then there is no +locking and any thread may run at any time. If @code{on}, then only the +current thread may run when the inferior is resumed. The @code{step} +mode optimizes for single-stepping. It stops other threads from +``seizing the prompt'' by preempting the current thread while you are +stepping. Other threads will only rarely (or never) get a chance to run +when you step. They are more likely to run when you ``next'' over a +function call, and they are completely free to run when you use commands +like ``continue'', ``until'', or ``finish''. However, unless another +thread hits a breakpoint during its timeslice, they will never steal the +GDB prompt away from the thread that you are debugging. + +@item show scheduler-locking +Display the current scheduler locking mode. +@end table + +@end ifclear + + +@node Stack, Source, Stopping, Top +@chapter Examining the Stack + +When your program has stopped, the first thing you need to know is where it +stopped and how it got there. + +@cindex call stack +Each time your program performs a function call, information about the call +is generated. +That information includes the location of the call in your program, +the arguments of the call, +and the local variables of the function being called. +The information is saved in a block of data called a @dfn{stack frame}. +The stack frames are allocated in a region of memory called the @dfn{call +stack}. + +When your program stops, the @value{GDBN} commands for examining the +stack allow you to see all of this information. + +@cindex selected frame +One of the stack frames is @dfn{selected} by @value{GDBN} and many +@value{GDBN} commands refer implicitly to the selected frame. In +particular, whenever you ask @value{GDBN} for the value of a variable in +your program, the value is found in the selected frame. There are +special @value{GDBN} commands to select whichever frame you are +interested in. @xref{Selection, ,Selecting a frame}. + +When your program stops, @value{GDBN} automatically selects the +currently executing frame and describes it briefly, similar to the +@code{frame} command (@pxref{Frame Info, ,Information about a frame}). + +@menu +* Frames:: Stack frames +* Backtrace:: Backtraces +* Selection:: Selecting a frame +* Frame Info:: Information on a frame +* Alpha/MIPS Stack:: Alpha and MIPS machines and the function stack + +@end menu + +@node Frames, Backtrace, Stack, Stack +@section Stack frames + +@cindex frame +@cindex stack frame +The call stack is divided up into contiguous pieces called @dfn{stack +frames}, or @dfn{frames} for short; each frame is the data associated +with one call to one function. The frame contains the arguments given +to the function, the function's local variables, and the address at +which the function is executing. + +@cindex initial frame +@cindex outermost frame +@cindex innermost frame +When your program is started, the stack has only one frame, that of the +function @code{main}. This is called the @dfn{initial} frame or the +@dfn{outermost} frame. Each time a function is called, a new frame is +made. Each time a function returns, the frame for that function invocation +is eliminated. If a function is recursive, there can be many frames for +the same function. The frame for the function in which execution is +actually occurring is called the @dfn{innermost} frame. This is the most +recently created of all the stack frames that still exist. + +@cindex frame pointer +Inside your program, stack frames are identified by their addresses. A +stack frame consists of many bytes, each of which has its own address; each +kind of computer has a convention for choosing one byte whose +address serves as the address of the frame. Usually this address is kept +in a register called the @dfn{frame pointer register} while execution is +going on in that frame. + +@cindex frame number +@value{GDBN} assigns numbers to all existing stack frames, starting with +zero for the innermost frame, one for the frame that called it, +and so on upward. These numbers do not really exist in your program; +they are assigned by @value{GDBN} to give you a way of designating stack +frames in @value{GDBN} commands. + +@c below produces an acceptable overful hbox. --mew 13aug1993 +@cindex frameless execution +Some compilers provide a way to compile functions so that they operate +without stack frames. (For example, the @code{@value{GCC}} option +@samp{-fomit-frame-pointer} generates functions without a frame.) +This is occasionally done with heavily used library functions to save +the frame setup time. @value{GDBN} has limited facilities for dealing +with these function invocations. If the innermost function invocation +has no stack frame, @value{GDBN} nevertheless regards it as though +it had a separate frame, which is numbered zero as usual, allowing +correct tracing of the function call chain. However, @value{GDBN} has +no provision for frameless functions elsewhere in the stack. + +@table @code +@kindex frame +@item frame @var{args} +The @code{frame} command allows you to move from one stack frame to another, +and to print the stack frame you select. @var{args} may be either the +address of the frame or the stack frame number. Without an argument, +@code{frame} prints the current stack frame. + +@kindex select-frame +@item select-frame +The @code{select-frame} command allows you to move from one stack frame +to another without printing the frame. This is the silent version of +@code{frame}. +@end table + +@node Backtrace, Selection, Frames, Stack +@section Backtraces + +@cindex backtraces +@cindex tracebacks +@cindex stack traces +A backtrace is a summary of how your program got where it is. It shows one +line per frame, for many frames, starting with the currently executing +frame (frame zero), followed by its caller (frame one), and on up the +stack. + +@table @code +@kindex backtrace +@kindex bt +@item backtrace +@itemx bt +Print a backtrace of the entire stack: one line per frame for all +frames in the stack. + +You can stop the backtrace at any time by typing the system interrupt +character, normally @kbd{C-c}. + +@item backtrace @var{n} +@itemx bt @var{n} +Similar, but print only the innermost @var{n} frames. + +@item backtrace -@var{n} +@itemx bt -@var{n} +Similar, but print only the outermost @var{n} frames. +@end table + +@kindex where +@kindex info stack +@kindex info s +The names @code{where} and @code{info stack} (abbreviated @code{info s}) +are additional aliases for @code{backtrace}. + +Each line in the backtrace shows the frame number and the function name. +The program counter value is also shown---unless you use @code{set +print address off}. The backtrace also shows the source file name and +line number, as well as the arguments to the function. The program +counter value is omitted if it is at the beginning of the code for that +line number. + +Here is an example of a backtrace. It was made with the command +@samp{bt 3}, so it shows the innermost three frames. + +@smallexample +@group +#0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8) + at builtin.c:993 +#1 0x6e38 in expand_macro (sym=0x2b600) at macro.c:242 +#2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08) + at macro.c:71 +(More stack frames follow...) +@end group +@end smallexample + +@noindent +The display for frame zero does not begin with a program counter +value, indicating that your program has stopped at the beginning of the +code for line @code{993} of @code{builtin.c}. + +@node Selection, Frame Info, Backtrace, Stack +@section Selecting a frame + +Most commands for examining the stack and other data in your program work on +whichever stack frame is selected at the moment. Here are the commands for +selecting a stack frame; all of them finish by printing a brief description +of the stack frame just selected. + +@table @code +@kindex frame +@kindex f +@item frame @var{n} +@itemx f @var{n} +Select frame number @var{n}. Recall that frame zero is the innermost +(currently executing) frame, frame one is the frame that called the +innermost one, and so on. The highest-numbered frame is the one for +@code{main}. + +@item frame @var{addr} +@itemx f @var{addr} +Select the frame at address @var{addr}. This is useful mainly if the +chaining of stack frames has been damaged by a bug, making it +impossible for @value{GDBN} to assign numbers properly to all frames. In +addition, this can be useful when your program has multiple stacks and +switches between them. + +@ifclear H8EXCLUSIVE +@ifclear HPPA +On the SPARC architecture, @code{frame} needs two addresses to +select an arbitrary frame: a frame pointer and a stack pointer. + +On the MIPS and Alpha architecture, it needs two addresses: a stack +pointer and a program counter. + +On the 29k architecture, it needs three addresses: a register stack +pointer, a program counter, and a memory stack pointer. +@c note to future updaters: this is conditioned on a flag +@c SETUP_ARBITRARY_FRAME in the tm-*.h files. The above is up to date +@c as of 27 Jan 1994. +@end ifclear +@end ifclear + +@kindex up +@item up @var{n} +Move @var{n} frames up the stack. For positive numbers @var{n}, this +advances toward the outermost frame, to higher frame numbers, to frames +that have existed longer. @var{n} defaults to one. + +@kindex down +@kindex do +@item down @var{n} +Move @var{n} frames down the stack. For positive numbers @var{n}, this +advances toward the innermost frame, to lower frame numbers, to frames +that were created more recently. @var{n} defaults to one. You may +abbreviate @code{down} as @code{do}. +@end table + +All of these commands end by printing two lines of output describing the +frame. The first line shows the frame number, the function name, the +arguments, and the source file and line number of execution in that +frame. The second line shows the text of that source line. + +@need 1000 +For example: + +@smallexample +@group +(@value{GDBP}) up +#1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc) + at env.c:10 +10 read_input_file (argv[i]); +@end group +@end smallexample + +After such a printout, the @code{list} command with no arguments +prints ten lines centered on the point of execution in the frame. +@xref{List, ,Printing source lines}. + +@table @code +@kindex down-silently +@kindex up-silently +@item up-silently @var{n} +@itemx down-silently @var{n} +These two commands are variants of @code{up} and @code{down}, +respectively; they differ in that they do their work silently, without +causing display of the new frame. They are intended primarily for use +in @value{GDBN} command scripts, where the output might be unnecessary and +distracting. +@end table + +@node Frame Info, Alpha/MIPS Stack, Selection, Stack +@section Information about a frame + +There are several other commands to print information about the selected +stack frame. + +@table @code +@item frame +@itemx f +When used without any argument, this command does not change which +frame is selected, but prints a brief description of the currently +selected stack frame. It can be abbreviated @code{f}. With an +argument, this command is used to select a stack frame. +@xref{Selection, ,Selecting a frame}. + +@kindex info frame +@kindex info f +@item info frame +@itemx info f +This command prints a verbose description of the selected stack frame, +including: + +@itemize @bullet +@item +the address of the frame +@item +the address of the next frame down (called by this frame) +@item +the address of the next frame up (caller of this frame) +@item +the language in which the source code corresponding to this frame is written +@item +the address of the frame's arguments +@item +the program counter saved in it (the address of execution in the caller frame) +@item +which registers were saved in the frame +@end itemize + +@noindent The verbose description is useful when +something has gone wrong that has made the stack format fail to fit +the usual conventions. + +@item info frame @var{addr} +@itemx info f @var{addr} +Print a verbose description of the frame at address @var{addr}, without +selecting that frame. The selected frame remains unchanged by this +command. This requires the same kind of address (more than one for some +architectures) that you specify in the @code{frame} command. +@xref{Selection, ,Selecting a frame}. + +@kindex info args +@item info args +Print the arguments of the selected frame, each on a separate line. + +@item info locals +@kindex info locals +Print the local variables of the selected frame, each on a separate +line. These are all variables (declared either static or automatic) +accessible at the point of execution of the selected frame. + +@ifclear CONLY +@ifclear HPPA +@kindex info catch +@cindex catch exceptions +@cindex exception handlers +@item info catch +Print a list of all the exception handlers that are active in the +current stack frame at the current point of execution. To see other +exception handlers, visit the associated frame (using the @code{up}, +@code{down}, or @code{frame} commands); then type @code{info catch}. +@xref{Set Catchpoints, , Setting catchpoints}. +@end ifclear +@end ifclear +@end table + +@node Alpha/MIPS Stack, , Frame Info, Stack +@section MIPS/Alpha machines and the function stack + +@cindex stack on Alpha +@cindex stack on MIPS +@cindex Alpha stack +@cindex MIPS stack +Alpha- and MIPS-based computers use an unusual stack frame, which +sometimes requires @value{GDBN} to search backward in the object code to +find the beginning of a function. + +@cindex response time, MIPS debugging +To improve response time (especially for embedded applications, where +@value{GDBN} may be restricted to a slow serial line for this search) +you may want to limit the size of this search, using one of these +commands: + +@table @code +@cindex @code{heuristic-fence-post} (Alpha,MIPS) +@item set heuristic-fence-post @var{limit} +Restrict @value{GDBN} to examining at most @var{limit} bytes in its search +for the beginning of a function. A value of @var{0} (the default) +means there is no limit. However, except for @var{0}, the larger the +limit the more bytes @code{heuristic-fence-post} must search and +therefore the longer it takes to run. + +@item show heuristic-fence-post +Display the current limit. +@end table + +@noindent +These commands are available @emph{only} when @value{GDBN} is configured +for debugging programs on Alpha or MIPS processors. + + +@node Source, Data, Stack, Top +@chapter Examining Source Files + +@value{GDBN} can print parts of your program's source, since the debugging +information recorded in the program tells @value{GDBN} what source files were +used to build it. When your program stops, @value{GDBN} spontaneously prints +the line where it stopped. Likewise, when you select a stack frame +(@pxref{Selection, ,Selecting a frame}), @value{GDBN} prints the line where +execution in that frame has stopped. You can print other portions of +source files by explicit command. + +@ifclear DOSHOST +If you use @value{GDBN} through its @sc{gnu} Emacs interface, you may prefer +to use +Emacs facilities to view source; @pxref{Emacs, ,Using @value{GDBN} under @sc{gnu} Emacs}. +@end ifclear + +@menu +* List:: Printing source lines +@ifclear DOSHOST +* Search:: Searching source files +@end ifclear + +* Source Path:: Specifying source directories +* Machine Code:: Source and machine code +@end menu + +@node List, Search, Source, Source +@section Printing source lines + +@kindex list +@kindex l +To print lines from a source file, use the @code{list} command +(abbreviated @code{l}). By default, ten lines are printed. +There are several ways to specify what part of the file you want to print. + +Here are the forms of the @code{list} command most commonly used: + +@table @code +@item list @var{linenum} +Print lines centered around line number @var{linenum} in the +current source file. + +@item list @var{function} +Print lines centered around the beginning of function +@var{function}. + +@item list +Print more lines. If the last lines printed were printed with a +@code{list} command, this prints lines following the last lines +printed; however, if the last line printed was a solitary line printed +as part of displaying a stack frame (@pxref{Stack, ,Examining the +Stack}), this prints lines centered around that line. + +@item list - +Print lines just before the lines last printed. +@end table + +By default, @value{GDBN} prints ten source lines with any of these forms of +the @code{list} command. You can change this using @code{set listsize}: + +@table @code +@kindex set listsize +@item set listsize @var{count} +Make the @code{list} command display @var{count} source lines (unless +the @code{list} argument explicitly specifies some other number). + +@kindex show listsize +@item show listsize +Display the number of lines that @code{list} prints. +@end table + +Repeating a @code{list} command with @key{RET} discards the argument, +so it is equivalent to typing just @code{list}. This is more useful +than listing the same lines again. An exception is made for an +argument of @samp{-}; that argument is preserved in repetition so that +each repetition moves up in the source file. + +@cindex linespec +In general, the @code{list} command expects you to supply zero, one or two +@dfn{linespecs}. Linespecs specify source lines; there are several ways +of writing them but the effect is always to specify some source line. +Here is a complete description of the possible arguments for @code{list}: + +@table @code +@item list @var{linespec} +Print lines centered around the line specified by @var{linespec}. + +@item list @var{first},@var{last} +Print lines from @var{first} to @var{last}. Both arguments are +linespecs. + +@item list ,@var{last} +Print lines ending with @var{last}. + +@item list @var{first}, +Print lines starting with @var{first}. + +@item list + +Print lines just after the lines last printed. + +@item list - +Print lines just before the lines last printed. + +@item list +As described in the preceding table. +@end table + +Here are the ways of specifying a single source line---all the +kinds of linespec. + +@table @code +@item @var{number} +Specifies line @var{number} of the current source file. +When a @code{list} command has two linespecs, this refers to +the same source file as the first linespec. + +@item +@var{offset} +Specifies the line @var{offset} lines after the last line printed. +When used as the second linespec in a @code{list} command that has +two, this specifies the line @var{offset} lines down from the +first linespec. + +@item -@var{offset} +Specifies the line @var{offset} lines before the last line printed. + +@item @var{filename}:@var{number} +Specifies line @var{number} in the source file @var{filename}. + +@item @var{function} +Specifies the line that begins the body of the function @var{function}. +For example: in C, this is the line with the open brace. + +@item @var{filename}:@var{function} +Specifies the line of the open-brace that begins the body of the +function @var{function} in the file @var{filename}. You only need the +file name with a function name to avoid ambiguity when there are +identically named functions in different source files. + +@item *@var{address} +Specifies the line containing the program address @var{address}. +@var{address} may be any expression. +@end table + +@ifclear DOSHOST +@node Search, Source Path, List, Source +@section Searching source files +@cindex searching +@kindex reverse-search + +There are two commands for searching through the current source file for a +regular expression. + +@table @code +@kindex search +@kindex forward-search +@item forward-search @var{regexp} +@itemx search @var{regexp} +The command @samp{forward-search @var{regexp}} checks each line, +starting with the one following the last line listed, for a match for +@var{regexp}. It lists the line that is found. You can use the +synonym @samp{search @var{regexp}} or abbreviate the command name as +@code{fo}. + +@item reverse-search @var{regexp} +The command @samp{reverse-search @var{regexp}} checks each line, starting +with the one before the last line listed and going backward, for a match +for @var{regexp}. It lists the line that is found. You can abbreviate +this command as @code{rev}. +@end table +@end ifclear + +@node Source Path, Machine Code, Search, Source +@section Specifying source directories + +@cindex source path +@cindex directories for source files +Executable programs sometimes do not record the directories of the source +files from which they were compiled, just the names. Even when they do, +the directories could be moved between the compilation and your debugging +session. @value{GDBN} has a list of directories to search for source files; +this is called the @dfn{source path}. Each time @value{GDBN} wants a source file, +it tries all the directories in the list, in the order they are present +in the list, until it finds a file with the desired name. Note that +the executable search path is @emph{not} used for this purpose. Neither is +the current working directory, unless it happens to be in the source +path. + +If @value{GDBN} cannot find a source file in the source path, and the +object program records a directory, @value{GDBN} tries that directory +too. If the source path is empty, and there is no record of the +compilation directory, @value{GDBN} looks in the current directory as a +last resort. + +Whenever you reset or rearrange the source path, @value{GDBN} clears out +any information it has cached about where source files are found and where +each line is in the file. + +@kindex directory +@kindex dir +When you start @value{GDBN}, its source path is empty. +To add other directories, use the @code{directory} command. + +@table @code +@item directory @var{dirname} @dots{} +@item dir @var{dirname} @dots{} +Add directory @var{dirname} to the front of the source path. Several +directory names may be given to this command, separated by @samp{:} or +whitespace. You may specify a directory that is already in the source +path; this moves it forward, so @value{GDBN} searches it sooner. + +@kindex cdir +@kindex cwd +@kindex $cdir +@kindex $cwd +@cindex compilation directory +@cindex current directory +@cindex working directory +@cindex directory, current +@cindex directory, compilation +You can use the string @samp{$cdir} to refer to the compilation +directory (if one is recorded), and @samp{$cwd} to refer to the current +working directory. @samp{$cwd} is not the same as @samp{.}---the former +tracks the current working directory as it changes during your @value{GDBN} +session, while the latter is immediately expanded to the current +directory at the time you add an entry to the source path. + +@item directory +Reset the source path to empty again. This requires confirmation. + +@c RET-repeat for @code{directory} is explicitly disabled, but since +@c repeating it would be a no-op we do not say that. (thanks to RMS) + +@item show directories +@kindex show directories +Print the source path: show which directories it contains. +@end table + +If your source path is cluttered with directories that are no longer of +interest, @value{GDBN} may sometimes cause confusion by finding the wrong +versions of source. You can correct the situation as follows: + +@enumerate +@item +Use @code{directory} with no argument to reset the source path to empty. + +@item +Use @code{directory} with suitable arguments to reinstall the +directories you want in the source path. You can add all the +directories in one command. +@end enumerate + +@node Machine Code, , Source Path, Source +@section Source and machine code + +You can use the command @code{info line} to map source lines to program +addresses (and vice versa), and the command @code{disassemble} to display +a range of addresses as machine instructions. When run under @sc{gnu} Emacs +mode, the @code{info line} command now causes the arrow to point to the +line specified. Also, @code{info line} prints addresses in symbolic form as +well as hex. + +@table @code +@kindex info line +@item info line @var{linespec} +Print the starting and ending addresses of the compiled code for +source line @var{linespec}. You can specify source lines in any of +the ways understood by the @code{list} command (@pxref{List, ,Printing +source lines}). +@end table + +For example, we can use @code{info line} to discover the location of +the object code for the first line of function +@code{m4_changequote}: + +@smallexample +(@value{GDBP}) info line m4_changecom +Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350. +@end smallexample + +@noindent +We can also inquire (using @code{*@var{addr}} as the form for +@var{linespec}) what source line covers a particular address: +@smallexample +(@value{GDBP}) info line *0x63ff +Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404. +@end smallexample + +@cindex @code{$_} and @code{info line} +After @code{info line}, the default address for the @code{x} command +is changed to the starting address of the line, so that @samp{x/i} is +sufficient to begin examining the machine code (@pxref{Memory, +,Examining memory}). Also, this address is saved as the value of the +convenience variable @code{$_} (@pxref{Convenience Vars, ,Convenience +variables}). + +@table @code +@kindex disassemble +@cindex assembly instructions +@cindex instructions, assembly +@cindex machine instructions +@cindex listing machine instructions +@item disassemble +This specialized command dumps a range of memory as machine +instructions. The default memory range is the function surrounding the +program counter of the selected frame. A single argument to this +command is a program counter value; @value{GDBN} dumps the function +surrounding this value. Two arguments specify a range of addresses +(first inclusive, second exclusive) to dump. +@end table + +@ifclear H8EXCLUSIVE +The following example shows the disassembly of a range of addresses of +HP PA-RISC 2.0 code: + +@smallexample +(@value{GDBP}) disas 0x32c4 0x32e4 +Dump of assembler code from 0x32c4 to 0x32e4: +0x32c4 <main+204>: addil 0,dp +0x32c8 <main+208>: ldw 0x22c(sr0,r1),r26 +0x32cc <main+212>: ldil 0x3000,r31 +0x32d0 <main+216>: ble 0x3f8(sr4,r31) +0x32d4 <main+220>: ldo 0(r31),rp +0x32d8 <main+224>: addil -0x800,dp +0x32dc <main+228>: ldo 0x588(r1),r26 +0x32e0 <main+232>: ldil 0x3000,r31 +End of assembler dump. +@end smallexample +@end ifclear + +@ifset H8EXCLUSIVE +For example, here is the beginning of the output for the +disassembly of a function @code{fact}: + + +@smallexample +(@value{GDBP}) disas fact +Dump of assembler code for function fact: +to 0x808c: +0x802c <fact>: 6d f2 mov.w r2,@@-r7 +0x802e <fact+2>: 6d f3 mov.w r3,@@-r7 +0x8030 <fact+4>: 6d f6 mov.w r6,@@-r7 +0x8032 <fact+6>: 0d 76 mov.w r7,r6 +0x8034 <fact+8>: 6f 70 00 08 mov.w @@(0x8,r7),r0 +0x8038 <fact+12> 19 11 sub.w r1,r1 + . + . + . +@end smallexample +@end ifset + +Some architectures have more than one commonly-used set of instruction +mnemonics or other syntax. + +@table @code +@kindex set assembly-language +@cindex assembly instructions +@cindex instructions, assembly +@cindex machine instructions +@cindex listing machine instructions +@item set assembly-language @var{instruction-set} +Select the instruction set to use when disassembling the +program via the @code{disassemble} or @code{x/i} commands. + +Currently this command is only defined for the Intel x86 family. You +can set @var{instruction-set} to either @code{i386} or @code{i8086}. +The default is @code{i386}. +@end table + + +@node Data, Languages, Source, Top +@chapter Examining Data + +@cindex printing data +@cindex examining data +@kindex print +@kindex inspect +@c "inspect" is not quite a synonym if you are using Epoch, which we do not +@c document because it is nonstandard... Under Epoch it displays in a +@c different window or something like that. +The usual way to examine data in your program is with the @code{print} +command (abbreviated @code{p}), or its synonym @code{inspect}. +@ifclear CONLY +It evaluates and prints the value of an expression of the language your +program is written in (@pxref{Languages, ,Using @value{GDBN} with Different +Languages}). +@end ifclear + +@table @code +@item print @var{exp} +@itemx print /@var{f} @var{exp} +@var{exp} is an expression (in the source language). By default the +value of @var{exp} is printed in a format appropriate to its data type; +you can choose a different format by specifying @samp{/@var{f}}, where +@var{f} is a letter specifying the format; @pxref{Output Formats,,Output +formats}. + +@item print +@itemx print /@var{f} +If you omit @var{exp}, @value{GDBN} displays the last value again (from the +@dfn{value history}; @pxref{Value History, ,Value history}). This allows you to +conveniently inspect the same value in an alternative format. +@end table + +A more low-level way of examining data is with the @code{x} command. +It examines data in memory at a specified address and prints it in a +specified format. @xref{Memory, ,Examining memory}. + +If you are interested in information about types, or about how the fields +of a struct +@ifclear CONLY +or class +@end ifclear +are declared, use the @code{ptype @var{exp}} +command rather than @code{print}. @xref{Symbols, ,Examining the Symbol Table}. + +@menu +* Expressions:: Expressions +* Variables:: Program variables +* Arrays:: Artificial arrays +* Output Formats:: Output formats +* Memory:: Examining memory +* Auto Display:: Automatic display +* Print Settings:: Print settings +* Value History:: Value history +* Convenience Vars:: Convenience variables +* Registers:: Registers +@ifclear HAVE-FLOAT +* Floating Point Hardware:: Floating point hardware +@end ifclear + +@end menu + +@node Expressions, Variables, Data, Data +@section Expressions + +@cindex expressions +@code{print} and many other @value{GDBN} commands accept an expression and +compute its value. Any kind of constant, variable or operator defined +by the programming language you are using is valid in an expression in +@value{GDBN}. This includes conditional expressions, function calls, casts +and string constants. It unfortunately does not include symbols defined +by preprocessor @code{#define} commands. + +@value{GDBN} now supports array constants in expressions input by +the user. The syntax is @var{@{element, element@dots{}@}}. For example, +you can now use the command @code{print @{1, 2, 3@}} to build up an array in +memory that is malloc'd in the target program. + +@ifclear CONLY +Because C is so widespread, most of the expressions shown in examples in +this manual are in C. @xref{Languages, , Using @value{GDBN} with Different +Languages}, for information on how to use expressions in other +languages. + +In this section, we discuss operators that you can use in @value{GDBN} +expressions regardless of your programming language. + +Casts are supported in all languages, not just in C, because it is so +useful to cast a number into a pointer in order to examine a structure +at that address in memory. +@c FIXME: casts supported---Mod2 true? +@end ifclear + +@value{GDBN} supports these operators, in addition to those common +to programming languages: + +@table @code +@item @@ +@samp{@@} is a binary operator for treating parts of memory as arrays. +@xref{Arrays, ,Artificial arrays}, for more information. + +@item :: +@samp{::} allows you to specify a variable in terms of the file or +function where it is defined. @xref{Variables, ,Program variables}. + +@cindex @{@var{type}@} +@cindex type casting memory +@cindex memory, viewing as typed object +@cindex casts, to view memory +@item @{@var{type}@} @var{addr} +Refers to an object of type @var{type} stored at address @var{addr} in +memory. @var{addr} may be any expression whose value is an integer or +pointer (but parentheses are required around binary operators, just as in +a cast). This construct is allowed regardless of what kind of data is +normally supposed to reside at @var{addr}. +@end table + +@node Variables, Arrays, Expressions, Data +@section Program variables + +The most common kind of expression to use is the name of a variable +in your program. + +Variables in expressions are understood in the selected stack frame +(@pxref{Selection, ,Selecting a frame}); they must be either: + +@itemize @bullet +@item +global (or file-static) +@end itemize + +@noindent or + +@itemize @bullet +@item +visible according to the scope rules of the +programming language from the point of execution in that frame +@end itemize + +@noindent This means that in the function + +@example +foo (a) + int a; +@{ + bar (a); + @{ + int b = test (); + bar (b); + @} +@} +@end example + +@noindent +you can examine and use the variable @code{a} whenever your program is +executing within the function @code{foo}, but you can only use or +examine the variable @code{b} while your program is executing inside +the block where @code{b} is declared. + +@cindex variable name conflict +There is an exception: you can refer to a variable or function whose +scope is a single source file even if the current execution point is not +in this file. But it is possible to have more than one such variable or +function with the same name (in different source files). If that +happens, referring to that name has unpredictable effects. If you wish, +you can specify a static variable in a particular function or file, +using the colon-colon notation: + +@cindex colon-colon +@iftex +@c info cannot cope with a :: index entry, but why deprive hard copy readers? +@kindex :: +@end iftex +@example +@var{file}::@var{variable} +@var{function}::@var{variable} +@end example + +@noindent +Here @var{file} or @var{function} is the name of the context for the +static @var{variable}. In the case of file names, you can use quotes to +make sure @value{GDBN} parses the file name as a single word---for example, +to print a global value of @code{x} defined in @file{f2.c}: + +@example +(@value{GDBP}) p 'f2.c'::x +@end example + +@ifclear CONLY +@cindex C++ scope resolution +This use of @samp{::} is very rarely in conflict with the very similar +use of the same notation in C++. @value{GDBN} also supports use of the C++ +scope resolution operator in @value{GDBN} expressions. +@c FIXME: Um, so what happens in one of those rare cases where it's in +@c conflict?? --mew +@end ifclear + +@cindex wrong values +@cindex variable values, wrong +@quotation +@emph{Warning:} Occasionally, a local variable may appear to have the +wrong value at certain points in a function---just after entry to a new +scope, and just before exit. +@end quotation +You may see this problem when you are stepping by machine instructions. +This is because, on most machines, it takes more than one instruction to +set up a stack frame (including local variable definitions); if you are +stepping by machine instructions, variables may appear to have the wrong +values until the stack frame is completely built. On exit, it usually +also takes more than one machine instruction to destroy a stack frame; +after you begin stepping through that group of instructions, local +variable definitions may be gone. + +This may also happen when the compiler does significant optimizations. +To be sure of always seeing accurate values, turn off all optimization +when compiling. + +@node Arrays, Output Formats, Variables, Data +@section Artificial arrays + +@cindex artificial array +@kindex @@ +It is often useful to print out several successive objects of the +same type in memory; a section of an array, or an array of +dynamically determined size for which only a pointer exists in the +program. + +You can do this by referring to a contiguous span of memory as an +@dfn{artificial array}, using the binary operator @samp{@@}. The left +operand of @samp{@@} should be the first element of the desired array +and be an individual object. The right operand should be the desired length +of the array. The result is an array value whose elements are all of +the type of the left argument. The first element is actually the left +argument; the second element comes from bytes of memory immediately +following those that hold the first element, and so on. Here is an +example. If a program says + +@example +int *array = (int *) malloc (len * sizeof (int)); +@end example + +@noindent +you can print the contents of @code{array} with + +@example +p *array@@len +@end example + +The left operand of @samp{@@} must reside in memory. Array values made +with @samp{@@} in this way behave just like other arrays in terms of +subscripting, and are coerced to pointers when used in expressions. +Artificial arrays most often appear in expressions via the value history +(@pxref{Value History, ,Value history}), after printing one out. + +Another way to create an artificial array is to use a cast. +This re-interprets a value as if it were an array. +The value need not be in memory: +@example +(@value{GDBP}) p/x (short[2])0x12345678 +$1 = @{0x1234, 0x5678@} +@end example + +As a convenience, if you leave the array length out (as in +@samp{(@var{type})[])@var{value}}) gdb calculates the size to fill +the value (as @samp{sizeof(@var{value})/sizeof(@var{type})}: +@example +(@value{GDBP}) p/x (short[])0x12345678 +$2 = @{0x1234, 0x5678@} +@end example + +Sometimes the artificial array mechanism is not quite enough; in +moderately complex data structures, the elements of interest may not +actually be adjacent---for example, if you are interested in the values +of pointers in an array. One useful work-around in this situation is +to use a convenience variable (@pxref{Convenience Vars, ,Convenience +variables}) as a counter in an expression that prints the first +interesting value, and then repeat that expression via @key{RET}. For +instance, suppose you have an array @code{dtab} of pointers to +structures, and you are interested in the values of a field @code{fv} +in each structure. Here is an example of what you might type: + +@example +set $i = 0 +p dtab[$i++]->fv +@key{RET} +@key{RET} +@dots{} +@end example + +@node Output Formats, Memory, Arrays, Data +@section Output formats + +@cindex formatted output +@cindex output formats +By default, @value{GDBN} prints a value according to its data type. Sometimes +this is not what you want. For example, you might want to print a number +in hex, or a pointer in decimal. Or you might want to view data in memory +at a certain address as a character string or as an instruction. To do +these things, specify an @dfn{output format} when you print a value. + +The simplest use of output formats is to say how to print a value +already computed. This is done by starting the arguments of the +@code{print} command with a slash and a format letter. The format +letters supported are: + +@table @code +@item x +Regard the bits of the value as an integer, and print the integer in +hexadecimal. + +@item d +Print as integer in signed decimal. + +@item u +Print as integer in unsigned decimal. + +@item o +Print as integer in octal. + +@item t +Print as integer in binary. The letter @samp{t} stands for ``two''. +@footnote{@samp{b} cannot be used because these format letters are also +used with the @code{x} command, where @samp{b} stands for ``byte''; +@pxref{Memory,,Examining memory}.} + +@item a +@cindex unknown address, locating +Print as an address, both absolute in hexadecimal and as an offset from +the nearest preceding symbol. You can use this format used to discover +where (in what function) an unknown address is located: + +@example +(@value{GDBP}) p/a 0x54320 +$3 = 0x54320 <_initialize_vx+396> +@end example + +@item c +Regard as an integer and print it as a character constant. + +@item f +Regard the bits of the value as a floating point number and print +using typical floating point syntax. +@end table + +For example, to print the program counter in hex (@pxref{Registers}), type + +@example +p/x $pc +@end example + +@noindent +Note that no space is required before the slash; this is because command +names in @value{GDBN} cannot contain a slash. + +To reprint the last value in the value history with a different format, +you can use the @code{print} command with just a format and no +expression. For example, @samp{p/x} reprints the last value in hex. + +@node Memory, Auto Display, Output Formats, Data +@section Examining memory + +You can use the command @code{x} (for ``examine'') to examine memory in +any of several formats, independently of your program's data types. + +@cindex examining memory +@table @code +@kindex x +@item x/@var{nfu} @var{addr} +@itemx x @var{addr} +@itemx x +Use the @code{x} command to examine memory. +@end table + +@var{n}, @var{f}, and @var{u} are all optional parameters that specify how +much memory to display and how to format it; @var{addr} is an +expression giving the address where you want to start displaying memory. +If you use defaults for @var{nfu}, you need not type the slash @samp{/}. +Several commands set convenient defaults for @var{addr}. + +@table @r +@item @var{n}, the repeat count +The repeat count is a decimal integer; the default is 1. It specifies +how much memory (counting by units @var{u}) to display. +@c This really is **decimal**; unaffected by 'set radix' as of GDB +@c 4.1.2. + +@item @var{f}, the display format +The display format is one of the formats used by @code{print}, +@samp{s} (null-terminated string), or @samp{i} (machine instruction). +The default is @samp{x} (hexadecimal) initially. +The default changes each time you use either @code{x} or @code{print}. + +@item @var{u}, the unit size +The unit size is any of + +@table @code +@item b +Bytes. +@item h +Halfwords (two bytes). +@item w +Words (four bytes). This is the initial default. +@item g +Giant words (eight bytes). +@end table + +Each time you specify a unit size with @code{x}, that size becomes the +default unit the next time you use @code{x}. (For the @samp{s} and +@samp{i} formats, the unit size is ignored and is normally not written.) + +@item @var{addr}, starting display address +@var{addr} is the address where you want @value{GDBN} to begin displaying +memory. The expression need not have a pointer value (though it may); +it is always interpreted as an integer address of a byte of memory. +@xref{Expressions, ,Expressions}, for more information on expressions. The default for +@var{addr} is usually just after the last address examined---but several +other commands also set the default address: @code{info breakpoints} (to +the address of the last breakpoint listed), @code{info line} (to the +starting address of a line), and @code{print} (if you use it to display +a value from memory). +@end table + +For example, @samp{x/3uh 0x54320} is a request to display three halfwords +(@code{h}) of memory, formatted as unsigned decimal integers (@samp{u}), +starting at address @code{0x54320}. @samp{x/4xw $sp} prints the four +words (@samp{w}) of memory above the stack pointer (here, @samp{$sp}; +@pxref{Registers}) in hexadecimal (@samp{x}). + +Since the letters indicating unit sizes are all distinct from the +letters specifying output formats, you do not have to remember whether +unit size or format comes first; either order works. The output +specifications @samp{4xw} and @samp{4wx} mean exactly the same thing. +(However, the count @var{n} must come first; @samp{wx4} does not work.) + +Even though the unit size @var{u} is ignored for the formats @samp{s} +and @samp{i}, you might still want to use a count @var{n}; for example, +@samp{3i} specifies that you want to see three machine instructions, +including any operands. The command @code{disassemble} gives an +alternative way of inspecting machine instructions; @pxref{Machine +Code,,Source and machine code}. + +All the defaults for the arguments to @code{x} are designed to make it +easy to continue scanning memory with minimal specifications each time +you use @code{x}. For example, after you have inspected three machine +instructions with @samp{x/3i @var{addr}}, you can inspect the next seven +with just @samp{x/7}. If you use @key{RET} to repeat the @code{x} command, +the repeat count @var{n} is used again; the other arguments default as +for successive uses of @code{x}. + +@cindex @code{$_}, @code{$__}, and value history +The addresses and contents printed by the @code{x} command are not saved +in the value history because there is often too much of them and they +would get in the way. Instead, @value{GDBN} makes these values available for +subsequent use in expressions as values of the convenience variables +@code{$_} and @code{$__}. After an @code{x} command, the last address +examined is available for use in expressions in the convenience variable +@code{$_}. The contents of that address, as examined, are available in +the convenience variable @code{$__}. + +If the @code{x} command has a repeat count, the address and contents saved +are from the last memory unit printed; this is not the same as the last +address printed if several units were printed on the last line of output. + +@node Auto Display, Print Settings, Memory, Data +@section Automatic display +@cindex automatic display +@cindex display of expressions + +If you find that you want to print the value of an expression frequently +(to see how it changes), you might want to add it to the @dfn{automatic +display list} so that @value{GDBN} prints its value each time your program stops. +Each expression added to the list is given a number to identify it; +to remove an expression from the list, you specify that number. +The automatic display looks like this: + +@example +2: foo = 38 +3: bar[5] = (struct hack *) 0x3804 +@end example + +@noindent +This display shows item numbers, expressions and their current values. As with +displays you request manually using @code{x} or @code{print}, you can +specify the output format you prefer; in fact, @code{display} decides +whether to use @code{print} or @code{x} depending on how elaborate your +format specification is---it uses @code{x} if you specify a unit size, +or one of the two formats (@samp{i} and @samp{s}) that are only +supported by @code{x}; otherwise it uses @code{print}. + +@table @code +@kindex display +@item display @var{exp} +Add the expression @var{exp} to the list of expressions to display +each time your program stops. @xref{Expressions, ,Expressions}. + +@code{display} does not repeat if you press @key{RET} again after using it. + +@item display/@var{fmt} @var{exp} +For @var{fmt} specifying only a display format and not a size or +count, add the expression @var{exp} to the auto-display list but +arrange to display it each time in the specified format @var{fmt}. +@xref{Output Formats,,Output formats}. + +@item display/@var{fmt} @var{addr} +For @var{fmt} @samp{i} or @samp{s}, or including a unit-size or a +number of units, add the expression @var{addr} as a memory address to +be examined each time your program stops. Examining means in effect +doing @samp{x/@var{fmt} @var{addr}}. @xref{Memory, ,Examining memory}. +@end table + +For example, @samp{display/i $pc} can be helpful, to see the machine +instruction about to be executed each time execution stops (@samp{$pc} +is a common name for the program counter; @pxref{Registers}). + +@table @code +@kindex delete display +@kindex undisplay +@item undisplay @var{dnums}@dots{} +@itemx delete display @var{dnums}@dots{} +Remove item numbers @var{dnums} from the list of expressions to display. + +@code{undisplay} does not repeat if you press @key{RET} after using it. +(Otherwise you would just get the error @samp{No display number @dots{}}.) + +@kindex disable display +@item disable display @var{dnums}@dots{} +Disable the display of item numbers @var{dnums}. A disabled display +item is not printed automatically, but is not forgotten. It may be +enabled again later. + +@kindex enable display +@item enable display @var{dnums}@dots{} +Enable display of item numbers @var{dnums}. It becomes effective once +again in auto display of its expression, until you specify otherwise. + +@item display +Display the current values of the expressions on the list, just as is +done when your program stops. + +@kindex info display +@item info display +Print the list of expressions previously set up to display +automatically, each one with its item number, but without showing the +values. This includes disabled expressions, which are marked as such. +It also includes expressions which would not be displayed right now +because they refer to automatic variables not currently available. +@end table + +If a display expression refers to local variables, then it does not make +sense outside the lexical context for which it was set up. Such an +expression is disabled when execution enters a context where one of its +variables is not defined. For example, if you give the command +@code{display last_char} while inside a function with an argument +@code{last_char}, @value{GDBN} displays this argument while your program +continues to stop inside that function. When it stops elsewhere---where +there is no variable @code{last_char}---the display is disabled +automatically. The next time your program stops where @code{last_char} +is meaningful, you can enable the display expression once again. + +@node Print Settings, Value History, Auto Display, Data +@section Print settings + +@cindex format options +@cindex print settings +@value{GDBN} provides the following ways to control how arrays, structures, +and symbols are printed. + +@noindent +These settings are useful for debugging programs in any language: + +@table @code +@kindex set print address +@item set print address +@itemx set print address on +@value{GDBN} prints memory addresses showing the location of stack +traces, structure values, pointer values, breakpoints, and so forth, +even when it also displays the contents of those addresses. The default +is @code{on}. For example, this is what a stack frame display looks like with +@code{set print address on}: + +@smallexample +@group +(@value{GDBP}) f +#0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>") + at input.c:530 +530 if (lquote != def_lquote) +@end group +@end smallexample + +@item set print address off +Do not print addresses when displaying their contents. For example, +this is the same stack frame displayed with @code{set print address off}: + +@smallexample +@group +(@value{GDBP}) set print addr off +(@value{GDBP}) f +#0 set_quotes (lq="<<", rq=">>") at input.c:530 +530 if (lquote != def_lquote) +@end group +@end smallexample + +You can use @samp{set print address off} to eliminate all machine +dependent displays from the @value{GDBN} interface. For example, with +@code{print address off}, you should get the same text for backtraces on +all machines---whether or not they involve pointer arguments. + +@kindex show print address +@item show print address +Show whether or not addresses are to be printed. +@end table + +When @value{GDBN} prints a symbolic address, it normally prints the +closest earlier symbol plus an offset. If that symbol does not uniquely +identify the address (for example, it is a name whose scope is a single +source file), you may need to clarify. One way to do this is with +@code{info line}, for example @samp{info line *0x4537}. Alternately, +you can set @value{GDBN} to print the source file and line number when +it prints a symbolic address: + +@table @code +@kindex set print symbol-filename +@item set print symbol-filename on +Tell @value{GDBN} to print the source file name and line number of a +symbol in the symbolic form of an address. + +@item set print symbol-filename off +Do not print source file name and line number of a symbol. This is the +default. + +@kindex show print symbol-filename +@item show print symbol-filename +Show whether or not @value{GDBN} will print the source file name and +line number of a symbol in the symbolic form of an address. +@end table + +Another situation where it is helpful to show symbol filenames and line +numbers is when disassembling code; @value{GDBN} shows you the line +number and source file that corresponds to each instruction. + +Also, you may wish to see the symbolic form only if the address being +printed is reasonably close to the closest earlier symbol: + +@table @code +@kindex set print max-symbolic-offset +@item set print max-symbolic-offset @var{max-offset} +Tell @value{GDBN} to only display the symbolic form of an address if the +offset between the closest earlier symbol and the address is less than +@var{max-offset}. The default is 0, which tells @value{GDBN} +to always print the symbolic form of an address if any symbol precedes it. + +@kindex show print max-symbolic-offset +@item show print max-symbolic-offset +Ask how large the maximum offset is that @value{GDBN} prints in a +symbolic address. +@end table + +@cindex wild pointer, interpreting +@cindex pointer, finding referent +If you have a pointer and you are not sure where it points, try +@samp{set print symbol-filename on}. Then you can determine the name +and source file location of the variable where it points, using +@samp{p/a @var{pointer}}. This interprets the address in symbolic form. +For example, here @value{GDBN} shows that a variable @code{ptt} points +at another variable @code{t}, defined in @file{hi2.c}: + +@example +(@value{GDBP}) set print symbol-filename on +(@value{GDBP}) p/a ptt +$4 = 0xe008 <t in hi2.c> +@end example + +@quotation +@emph{Warning:} For pointers that point to a local variable, @samp{p/a} +does not show the symbol name and filename of the referent, even with +the appropriate @code{set print} options turned on. +@end quotation + +Other settings control how different kinds of objects are printed: + +@table @code +@kindex set print array +@item set print array +@itemx set print array on +Pretty print arrays. This format is more convenient to read, +but uses more space. The default is off. + +@item set print array off +Return to compressed format for arrays. + +@kindex show print array +@item show print array +Show whether compressed or pretty format is selected for displaying +arrays. + +@kindex set print elements +@item set print elements @var{number-of-elements} +Set a limit on how many elements of an array @value{GDBN} will print. +If @value{GDBN} is printing a large array, it stops printing after it has +printed the number of elements set by the @code{set print elements} command. +This limit also applies to the display of strings. +Setting @var{number-of-elements} to zero means that the printing is unlimited. + +@kindex show print elements +@item show print elements +Display the number of elements of a large array that @value{GDBN} will print. +If the number is 0, then the printing is unlimited. + +@kindex set print null-stop +@item set print null-stop +Cause @value{GDBN} to stop printing the characters of an array when the first +@sc{NULL} is encountered. This is useful when large arrays actually +contain only short strings. + +@kindex set print pretty +@item set print pretty on +Cause @value{GDBN} to print structures in an indented format with one member +per line, like this: + +@smallexample +@group +$1 = @{ + next = 0x0, + flags = @{ + sweet = 1, + sour = 1 + @}, + meat = 0x54 "Pork" +@} +@end group +@end smallexample + +@item set print pretty off +Cause @value{GDBN} to print structures in a compact format, like this: + +@smallexample +@group +$1 = @{next = 0x0, flags = @{sweet = 1, sour = 1@}, \ +meat = 0x54 "Pork"@} +@end group +@end smallexample + +@noindent +This is the default format. + +@kindex show print pretty +@item show print pretty +Show which format @value{GDBN} is using to print structures. + +@kindex set print sevenbit-strings +@item set print sevenbit-strings on +Print using only seven-bit characters; if this option is set, +@value{GDBN} displays any eight-bit characters (in strings or +character values) using the notation @code{\}@var{nnn}. This setting is +best if you are working in English (@sc{ascii}) and you use the +high-order bit of characters as a marker or ``meta'' bit. + +@item set print sevenbit-strings off +Print full eight-bit characters. This allows the use of more +international character sets, and is the default. + +@kindex show print sevenbit-strings +@item show print sevenbit-strings +Show whether or not @value{GDBN} is printing only seven-bit characters. + +@kindex set print union +@item set print union on +Tell @value{GDBN} to print unions which are contained in structures. This +is the default setting. + +@item set print union off +Tell @value{GDBN} not to print unions which are contained in structures. + +@kindex show print union +@item show print union +Ask @value{GDBN} whether or not it will print unions which are contained in +structures. + +For example, given the declarations + +@smallexample +typedef enum @{Tree, Bug@} Species; +typedef enum @{Big_tree, Acorn, Seedling@} Tree_forms; +typedef enum @{Caterpillar, Cocoon, Butterfly@} + Bug_forms; + +struct thing @{ + Species it; + union @{ + Tree_forms tree; + Bug_forms bug; + @} form; +@}; + +struct thing foo = @{Tree, @{Acorn@}@}; +@end smallexample + +@noindent +with @code{set print union on} in effect @samp{p foo} would print + +@smallexample +$1 = @{it = Tree, form = @{tree = Acorn, bug = Cocoon@}@} +@end smallexample + +@noindent +and with @code{set print union off} in effect it would print + +@smallexample +$1 = @{it = Tree, form = @{...@}@} +@end smallexample +@end table + +@ifclear CONLY +@need 1000 +@noindent +These settings are of interest when debugging C++ programs: + +@table @code +@cindex demangling +@kindex set print demangle +@item set print demangle +@itemx set print demangle on +Print C++ names in their source form rather than in the encoded +(``mangled'') form passed to the assembler and linker for type-safe +linkage. The default is @samp{on}. + +@kindex show print demangle +@item show print demangle +Show whether C++ names are printed in mangled or demangled form. + +@kindex set print asm-demangle +@item set print asm-demangle +@itemx set print asm-demangle on +Print C++ names in their source form rather than their mangled form, even +in assembler code printouts such as instruction disassemblies. +The default is off. + +@kindex show print asm-demangle +@item show print asm-demangle +Show whether C++ names in assembly listings are printed in mangled +or demangled form. + +@kindex set demangle-style +@cindex C++ symbol decoding style +@cindex symbol decoding style, C++ +@item set demangle-style @var{style} +Choose among several encoding schemes used by different compilers to +represent C++ names. The choices for @var{style} are currently: + +@table @code +@item auto +Allow @value{GDBN} to choose a decoding style by inspecting your program. + +@item gnu +Decode based on the @sc{gnu} C++ compiler (@code{g++}) encoding algorithm. +@ifclear HPPA +This is the default. +@end ifclear + +@item hp +Decode based on the HP ANSI C++ (@code{aCC}) encoding algorithm. + +@item lucid +Decode based on the Lucid C++ compiler (@code{lcc}) encoding algorithm. + +@item arm +Decode using the algorithm in the @cite{C++ Annotated Reference Manual}. +@strong{Warning:} this setting alone is not sufficient to allow +debugging @code{cfront}-generated executables. @value{GDBN} would +require further enhancement to permit that. + +@end table +If you omit @var{style}, you will see a list of possible formats. + +@kindex show demangle-style +@item show demangle-style +Display the encoding style currently in use for decoding C++ symbols. + +@kindex set print object +@item set print object +@itemx set print object on +When displaying a pointer to an object, identify the @emph{actual} +(derived) type of the object rather than the @emph{declared} type, using +the virtual function table. + +@item set print object off +Display only the declared type of objects, without reference to the +virtual function table. This is the default setting. + +@kindex show print object +@item show print object +Show whether actual, or declared, object types are displayed. + +@kindex set print static-members +@item set print static-members +@itemx set print static-members on +Print static members when displaying a C++ object. The default is on. + +@item set print static-members off +Do not print static members when displaying a C++ object. + +@kindex show print static-members +@item show print static-members +Show whether C++ static members are printed, or not. + +@c These don't work with HP ANSI C++ yet. +@kindex set print vtbl +@item set print vtbl +@itemx set print vtbl on +Pretty print C++ virtual function tables. The default is off. +@ifset HPPA +(The @code{vtbl} commands do not work on programs compiled with the HP +ANSI C++ compiler (@code{aCC}).) +@end ifset + +@item set print vtbl off +Do not pretty print C++ virtual function tables. + +@kindex show print vtbl +@item show print vtbl +Show whether C++ virtual function tables are pretty printed, or not. +@end table +@end ifclear + +@node Value History, Convenience Vars, Print Settings, Data +@section Value history + +@cindex value history +Values printed by the @code{print} command are saved in the @value{GDBN} +@dfn{value history}. This allows you to refer to them in other expressions. +Values are kept until the symbol table is re-read or discarded +(for example with the @code{file} or @code{symbol-file} commands). +When the symbol table changes, the value history is discarded, +since the values may contain pointers back to the types defined in the +symbol table. + +@cindex @code{$} +@cindex @code{$$} +@cindex history number +The values printed are given @dfn{history numbers} by which you can +refer to them. These are successive integers starting with one. +@code{print} shows you the history number assigned to a value by +printing @samp{$@var{num} = } before the value; here @var{num} is the +history number. + +To refer to any previous value, use @samp{$} followed by the value's +history number. The way @code{print} labels its output is designed to +remind you of this. Just @code{$} refers to the most recent value in +the history, and @code{$$} refers to the value before that. +@code{$$@var{n}} refers to the @var{n}th value from the end; @code{$$2} +is the value just prior to @code{$$}, @code{$$1} is equivalent to +@code{$$}, and @code{$$0} is equivalent to @code{$}. + +For example, suppose you have just printed a pointer to a structure and +want to see the contents of the structure. It suffices to type + +@example +p *$ +@end example + +If you have a chain of structures where the component @code{next} points +to the next one, you can print the contents of the next one with this: + +@example +p *$.next +@end example + +@noindent +You can print successive links in the chain by repeating this +command---which you can do by just typing @key{RET}. + +Note that the history records values, not expressions. If the value of +@code{x} is 4 and you type these commands: + +@example +print x +set x=5 +@end example + +@noindent +then the value recorded in the value history by the @code{print} command +remains 4 even though the value of @code{x} has changed. + +@table @code +@kindex show values +@item show values +Print the last ten values in the value history, with their item numbers. +This is like @samp{p@ $$9} repeated ten times, except that @code{show +values} does not change the history. + +@item show values @var{n} +Print ten history values centered on history item number @var{n}. + +@item show values + +Print ten history values just after the values last printed. If no more +values are available, @code{show values +} produces no display. +@end table + +Pressing @key{RET} to repeat @code{show values @var{n}} has exactly the +same effect as @samp{show values +}. + +@node Convenience Vars, Registers, Value History, Data +@section Convenience variables + +@cindex convenience variables +@value{GDBN} provides @dfn{convenience variables} that you can use within +@value{GDBN} to hold on to a value and refer to it later. These variables +exist entirely within @value{GDBN}; they are not part of your program, and +setting a convenience variable has no direct effect on further execution +of your program. That is why you can use them freely. + +Convenience variables are prefixed with @samp{$}. Any name preceded by +@samp{$} can be used for a convenience variable, unless it is one of +the predefined machine-specific register names (@pxref{Registers}). +(Value history references, in contrast, are @emph{numbers} preceded +by @samp{$}. @xref{Value History, ,Value history}.) + +You can save a value in a convenience variable with an assignment +expression, just as you would set a variable in your program. +For example: + +@example +set $foo = *object_ptr +@end example + +@noindent +would save in @code{$foo} the value contained in the object pointed to by +@code{object_ptr}. + +Using a convenience variable for the first time creates it, but its +value is @code{void} until you assign a new value. You can alter the +value with another assignment at any time. + +Convenience variables have no fixed types. You can assign a convenience +variable any type of value, including structures and arrays, even if +that variable already has a value of a different type. The convenience +variable, when used as an expression, has the type of its current value. + +@table @code +@kindex show convenience +@item show convenience +Print a list of convenience variables used so far, and their values. +Abbreviated @code{show con}. +@end table + +One of the ways to use a convenience variable is as a counter to be +incremented or a pointer to be advanced. For example, to print +a field from successive elements of an array of structures: + +@example +set $i = 0 +print bar[$i++]->contents +@end example + +@noindent Repeat that command by typing @key{RET}. + +Some convenience variables are created automatically by @value{GDBN} and given +values likely to be useful. + +@table @code +@kindex $_ +@item $_ +The variable @code{$_} is automatically set by the @code{x} command to +the last address examined (@pxref{Memory, ,Examining memory}). Other +commands which provide a default address for @code{x} to examine also +set @code{$_} to that address; these commands include @code{info line} +and @code{info breakpoint}. The type of @code{$_} is @code{void *} +except when set by the @code{x} command, in which case it is a pointer +to the type of @code{$__}. + +@kindex $__ +@item $__ +The variable @code{$__} is automatically set by the @code{x} command +to the value found in the last address examined. Its type is chosen +to match the format in which the data was printed. + +@item $_exitcode +@kindex $_exitcode +The variable @code{$_exitcode} is automatically set to the exit code when +the program being debugged terminates. +@end table + +@ifset HPPA +If you refer to a function or variable name that begins with a dollar +sign, @value{GDBN} searches for a user or system name first, before it +searches for a convenience variable. +@end ifset + +@node Registers, Floating Point Hardware, Convenience Vars, Data +@section Registers + +@cindex registers +You can refer to machine register contents, in expressions, as variables +with names starting with @samp{$}. The names of registers are different +for each machine; use @code{info registers} to see the names used on +your machine. + +@table @code +@kindex info registers +@item info registers +Print the names and values of all registers except floating-point +registers (in the selected stack frame). + +@kindex info all-registers +@cindex floating point registers +@item info all-registers +Print the names and values of all registers, including floating-point +registers. + +@item info registers @var{regname} @dots{} +Print the @dfn{relativized} value of each specified register @var{regname}. +As discussed in detail below, register values are normally relative to +the selected stack frame. @var{regname} may be any register name valid on +the machine you are using, with or without the initial @samp{$}. +@end table + +@value{GDBN} has four ``standard'' register names that are available (in +expressions) on most machines---whenever they do not conflict with an +architecture's canonical mnemonics for registers. The register names +@code{$pc} and @code{$sp} are used for the program counter register and +the stack pointer. @code{$fp} is used for a register that contains a +pointer to the current stack frame, and @code{$ps} is used for a +register that contains the processor status. For example, +you could print the program counter in hex with + +@example +p/x $pc +@end example + +@noindent +or print the instruction to be executed next with + +@example +x/i $pc +@end example + +@noindent +or add four to the stack pointer@footnote{This is a way of removing +one word from the stack, on machines where stacks grow downward in +memory (most machines, nowadays). This assumes that the innermost +stack frame is selected; setting @code{$sp} is not allowed when other +stack frames are selected. To pop entire frames off the stack, +regardless of machine architecture, use @code{return}; +@pxref{Returning, ,Returning from a function}.} with + +@example +set $sp += 4 +@end example + +Whenever possible, these four standard register names are available on +your machine even though the machine has different canonical mnemonics, +so long as there is no conflict. The @code{info registers} command +shows the canonical names. For example, on the SPARC, @code{info +registers} displays the processor status register as @code{$psr} but you +can also refer to it as @code{$ps}. + +@value{GDBN} always considers the contents of an ordinary register as an +integer when the register is examined in this way. Some machines have +special registers which can hold nothing but floating point; these +registers are considered to have floating point values. There is no way +to refer to the contents of an ordinary register as floating point value +(although you can @emph{print} it as a floating point value with +@samp{print/f $@var{regname}}). + +Some registers have distinct ``raw'' and ``virtual'' data formats. This +means that the data format in which the register contents are saved by +the operating system is not the same one that your program normally +sees. For example, the registers of the 68881 floating point +coprocessor are always saved in ``extended'' (raw) format, but all C +programs expect to work with ``double'' (virtual) format. In such +cases, @value{GDBN} normally works with the virtual format only (the format +that makes sense for your program), but the @code{info registers} command +prints the data in both formats. + +Normally, register values are relative to the selected stack frame +(@pxref{Selection, ,Selecting a frame}). This means that you get the +value that the register would contain if all stack frames farther in +were exited and their saved registers restored. In order to see the +true contents of hardware registers, you must select the innermost +frame (with @samp{frame 0}). + +However, @value{GDBN} must deduce where registers are saved, from the machine +code generated by your compiler. If some registers are not saved, or if +@value{GDBN} is unable to locate the saved registers, the selected stack +frame makes no difference. + +@ifset AMD29K +@table @code +@kindex set rstack_high_address +@cindex AMD 29K register stack +@cindex register stack, AMD29K +@item set rstack_high_address @var{address} +On AMD 29000 family processors, registers are saved in a separate +``register stack''. There is no way for @value{GDBN} to determine the extent +of this stack. Normally, @value{GDBN} just assumes that the stack is ``large +enough''. This may result in @value{GDBN} referencing memory locations that +do not exist. If necessary, you can get around this problem by +specifying the ending address of the register stack with the @code{set +rstack_high_address} command. The argument should be an address, which +you probably want to precede with @samp{0x} to specify in +hexadecimal. + +@kindex show rstack_high_address +@item show rstack_high_address +Display the current limit of the register stack, on AMD 29000 family +processors. +@end table +@end ifset + +@ifclear HAVE-FLOAT +@node Floating Point Hardware, , Registers, Data +@section Floating point hardware +@cindex floating point + +Depending on the configuration, @value{GDBN} may be able to give +you more information about the status of the floating point hardware. + +@table @code +@kindex info float +@item info float +Display hardware-dependent information about the floating +point unit. The exact contents and layout vary depending on the +floating point chip. Currently, @samp{info float} is supported on +the ARM and x86 machines. +@end table +@end ifclear + +@ifclear CONLY +@node Languages, Symbols, Data, Top +@chapter Using @value{GDBN} with Different Languages +@cindex languages + +@ifset MOD2 +Although programming languages generally have common aspects, they are +rarely expressed in the same manner. For instance, in ANSI C, +dereferencing a pointer @code{p} is accomplished by @code{*p}, but in +Modula-2, it is accomplished by @code{p^}. Values can also be +represented (and displayed) differently. Hex numbers in C appear as +@samp{0x1ae}, while in Modula-2 they appear as @samp{1AEH}. +@end ifset + +@cindex working language +Language-specific information is built into @value{GDBN} for some languages, +allowing you to express operations like the above in your program's +native language, and allowing @value{GDBN} to output values in a manner +consistent with the syntax of your program's native language. The +language you use to build expressions is called the @dfn{working +language}. + +@menu +* Setting:: Switching between source languages +* Show:: Displaying the language +@ifset MOD2 +* Checks:: Type and range checks +@end ifset + +* Support:: Supported languages +@end menu + +@node Setting, Show, Languages, Languages +@section Switching between source languages + +There are two ways to control the working language---either have @value{GDBN} +set it automatically, or select it manually yourself. You can use the +@code{set language} command for either purpose. On startup, @value{GDBN} +defaults to setting the language automatically. The working language is +used to determine how expressions you type are interpreted, how values +are printed, etc. + +In addition to the working language, every source file that +@value{GDBN} knows about has its own working language. For some object +file formats, the compiler might indicate which language a particular +source file is in. However, most of the time @value{GDBN} infers the +language from the name of the file. The language of a source file +controls whether C++ names are demangled---this way @code{backtrace} can +show each frame appropriately for its own language. There is no way to +set the language of a source file from within @value{GDBN}. + +This is most commonly a problem when you use a program, such +as @code{cfront} or @code{f2c}, that generates C but is written in +another language. In that case, make the +program use @code{#line} directives in its C output; that way +@value{GDBN} will know the correct language of the source code of the original +program, and will display that source code, not the generated C code. + +@menu +* Filenames:: Filename extensions and languages. +* Manually:: Setting the working language manually +* Automatically:: Having @value{GDBN} infer the source language +@end menu + +@node Filenames, Manually, Setting, Setting +@subsection List of filename extensions and languages + +If a source file name ends in one of the following extensions, then +@value{GDBN} infers that its language is the one indicated. + +@table @file + +@item .c +C source file + +@item .C +@itemx .cc +@itemx .cp +@itemx .cpp +@itemx .cxx +@itemx .c++ +C++ source file + +@item .f +@itemx .F +Fortran source file + +@ifclear HPPA +@item .ch +@itemx .c186 +@itemx .c286 +CHILL source file. +@end ifclear + +@ifset MOD2 +@item .mod +Modula-2 source file +@end ifset + +@item .s +@itemx .S +Assembler source file. This actually behaves almost like C, but +@value{GDBN} does not skip over function prologues when stepping. +@end table + +In addition, you may set the language associated with a filename +extension. @xref{Show, , Displaying the language}. + +@node Manually, Automatically, Filenames, Setting +@subsection Setting the working language + +If you allow @value{GDBN} to set the language automatically, +expressions are interpreted the same way in your debugging session and +your program. + +@kindex set language +If you wish, you may set the language manually. To do this, issue the +command @samp{set language @var{lang}}, where @var{lang} is the name of +a language, such as +@ifclear MOD2 +@code{c}. +@end ifclear +@ifset MOD2 +@code{c} or @code{modula-2}. +@end ifset +For a list of the supported languages, type @samp{set language}. + +@ifclear MOD2 +Setting the language manually prevents @value{GDBN} from updating the +working language automatically. For example, if you used the @code{c} +setting to debug a C++ program, names might not be demangled properly, +overload resolution would not work, user-defined operators might not be +interpreted correctly, and so on. +@end ifclear +@ifset MOD2 +Setting the language manually prevents @value{GDBN} from updating the working +language automatically. This can lead to confusion if you try +to debug a program when the working language is not the same as the +source language, when an expression is acceptable to both +languages---but means different things. For instance, if the current +source file were written in C, and @value{GDBN} was parsing Modula-2, a +command such as: + +@example +print a = b + c +@end example + +@noindent +might not have the effect you intended. In C, this means to add +@code{b} and @code{c} and place the result in @code{a}. The result +printed would be the value of @code{a}. In Modula-2, this means to compare +@code{a} to the result of @code{b+c}, yielding a @code{BOOLEAN} value. +@end ifset + +@node Automatically, , Manually, Setting +@subsection Having @value{GDBN} infer the source language + +To have @value{GDBN} set the working language automatically, use +@samp{set language local} or @samp{set language auto}. @value{GDBN} +then infers the working language. That is, when your program stops in a +frame (usually by encountering a breakpoint), @value{GDBN} sets the +working language to the language recorded for the function in that +frame. If the language for a frame is unknown (that is, if the function +or block corresponding to the frame was defined in a source file that +does not have a recognized extension), the current working language is +not changed, and @value{GDBN} issues a warning. + +This may not seem necessary for most programs, which are written +entirely in one source language. However, program modules and libraries +written in one source language can be used by a main program written in +a different source language. Using @samp{set language auto} in this +case frees you from having to set the working language manually. + +@ifset MOD2 +@node Show, Checks, Setting, Languages +@section Displaying the language +@end ifset +@ifclear MOD2 +@node Show, Support, Setting, Languages +@section Displaying the language +@end ifclear + +The following commands help you find out which language is the +working language, and also what language source files were written in. + +@kindex show language +@kindex info frame +@kindex info source +@table @code +@item show language +Display the current working language. This is the +language you can use with commands such as @code{print} to +build and compute expressions that may involve variables in your program. + +@item info frame +Display the source language for this frame. This language becomes the +working language if you use an identifier from this frame. +@xref{Frame Info, ,Information about a frame}, to identify the other +information listed here. + +@item info source +Display the source language of this source file. +@xref{Symbols, ,Examining the Symbol Table}, to identify the other +information listed here. +@end table + +In unusual circumstances, you may have source files with extensions +not in the standard list. You can then set the extension associated +with a language explicitly: + +@kindex set extension-language +@kindex info extensions +@table @code +@item set extension-language @var{.ext} @var{language} +Set source files with extension @var{.ext} to be assumed to be in +the source language @var{language}. + +@item info extensions +List all the filename extensions and the associated languages. +@end table + +@ifset MOD2 +@node Checks, Support, Show, Languages +@section Type and range checking + +@quotation +@emph{Warning:} In this release, the @value{GDBN} commands for type and range +checking are included, but they do not yet have any effect. This +section documents the intended facilities. +@end quotation +@c FIXME remove warning when type/range code added + +Some languages are designed to guard you against making seemingly common +errors through a series of compile- and run-time checks. These include +checking the type of arguments to functions and operators, and making +sure mathematical overflows are caught at run time. Checks such as +these help to ensure a program's correctness once it has been compiled +by eliminating type mismatches, and providing active checks for range +errors when your program is running. + +@value{GDBN} can check for conditions like the above if you wish. +Although @value{GDBN} does not check the statements in your program, it +can check expressions entered directly into @value{GDBN} for evaluation via +the @code{print} command, for example. As with the working language, +@value{GDBN} can also decide whether or not to check automatically based on +your program's source language. @xref{Support, ,Supported languages}, +for the default settings of supported languages. + +@menu +* Type Checking:: An overview of type checking +* Range Checking:: An overview of range checking +@end menu + +@cindex type checking +@cindex checks, type +@node Type Checking, Range Checking, Checks, Checks +@subsection An overview of type checking + +Some languages, such as Modula-2, are strongly typed, meaning that the +arguments to operators and functions have to be of the correct type, +otherwise an error occurs. These checks prevent type mismatch +errors from ever causing any run-time problems. For example, + +@smallexample +1 + 2 @result{} 3 +@exdent but +@error{} 1 + 2.3 +@end smallexample + +The second example fails because the @code{CARDINAL} 1 is not +type-compatible with the @code{REAL} 2.3. + +For the expressions you use in @value{GDBN} commands, you can tell the +@value{GDBN} type checker to skip checking; +to treat any mismatches as errors and abandon the expression; +or to only issue warnings when type mismatches occur, +but evaluate the expression anyway. When you choose the last of +these, @value{GDBN} evaluates expressions like the second example above, but +also issues a warning. + +Even if you turn type checking off, there may be other reasons +related to type that prevent @value{GDBN} from evaluating an expression. +For instance, @value{GDBN} does not know how to add an @code{int} and +a @code{struct foo}. These particular type errors have nothing to do +with the language in use, and usually arise from expressions, such as +the one described above, which make little sense to evaluate anyway. + +Each language defines to what degree it is strict about type. For +instance, both Modula-2 and C require the arguments to arithmetical +operators to be numbers. In C, enumerated types and pointers can be +represented as numbers, so that they are valid arguments to mathematical +operators. @xref{Support, ,Supported languages}, for further +details on specific languages. + +@value{GDBN} provides some additional commands for controlling the type checker: + +@kindex set check +@kindex set check type +@kindex show check type +@table @code +@item set check type auto +Set type checking on or off based on the current working language. +@xref{Support, ,Supported languages}, for the default settings for +each language. + +@item set check type on +@itemx set check type off +Set type checking on or off, overriding the default setting for the +current working language. Issue a warning if the setting does not +match the language default. If any type mismatches occur in +evaluating an expression while typechecking is on, @value{GDBN} prints a +message and aborts evaluation of the expression. + +@item set check type warn +Cause the type checker to issue warnings, but to always attempt to +evaluate the expression. Evaluating the expression may still +be impossible for other reasons. For example, @value{GDBN} cannot add +numbers and structures. + +@item show type +Show the current setting of the type checker, and whether or not @value{GDBN} +is setting it automatically. +@end table + +@cindex range checking +@cindex checks, range +@node Range Checking, , Type Checking, Checks +@subsection An overview of range checking + +In some languages (such as Modula-2), it is an error to exceed the +bounds of a type; this is enforced with run-time checks. Such range +checking is meant to ensure program correctness by making sure +computations do not overflow, or indices on an array element access do +not exceed the bounds of the array. + +For expressions you use in @value{GDBN} commands, you can tell +@value{GDBN} to treat range errors in one of three ways: ignore them, +always treat them as errors and abandon the expression, or issue +warnings but evaluate the expression anyway. + +A range error can result from numerical overflow, from exceeding an +array index bound, or when you type a constant that is not a member +of any type. Some languages, however, do not treat overflows as an +error. In many implementations of C, mathematical overflow causes the +result to ``wrap around'' to lower values---for example, if @var{m} is +the largest integer value, and @var{s} is the smallest, then + +@example +@var{m} + 1 @result{} @var{s} +@end example + +This, too, is specific to individual languages, and in some cases +specific to individual compilers or machines. @xref{Support, , +Supported languages}, for further details on specific languages. + +@value{GDBN} provides some additional commands for controlling the range checker: + +@kindex set check +@kindex set check range +@kindex show check range +@table @code +@item set check range auto +Set range checking on or off based on the current working language. +@xref{Support, ,Supported languages}, for the default settings for +each language. + +@item set check range on +@itemx set check range off +Set range checking on or off, overriding the default setting for the +current working language. A warning is issued if the setting does not +match the language default. If a range error occurs, then a message +is printed and evaluation of the expression is aborted. + +@item set check range warn +Output messages when the @value{GDBN} range checker detects a range error, +but attempt to evaluate the expression anyway. Evaluating the +expression may still be impossible for other reasons, such as accessing +memory that the process does not own (a typical example from many Unix +systems). + +@item show range +Show the current setting of the range checker, and whether or not it is +being set automatically by @value{GDBN}. +@end table +@end ifset + +@ifset MOD2 +@node Support, , Checks, Languages +@section Supported languages +@end ifset +@ifclear MOD2 +@node Support, , Show, Languages +@section Supported languages +@end ifclear + +@ifset MOD2 +@value{GDBN} supports C, C++, Fortran, Chill, assembly, and Modula-2. +@end ifset +@ifclear MOD2 +@value{GDBN} supports C, C++, Fortran, Chill, and assembly. +@end ifclear +Some @value{GDBN} features may be used in expressions regardless of the +language you use: the @value{GDBN} @code{@@} and @code{::} operators, +and the @samp{@{type@}addr} construct (@pxref{Expressions, +,Expressions}) can be used with the constructs of any supported +language. + +The following sections detail to what degree each source language is +supported by @value{GDBN}. These sections are not meant to be language +tutorials or references, but serve only as a reference guide to what the +@value{GDBN} expression parser accepts, and what input and output +formats should look like for different languages. There are many good +books written on each of these languages; please look to these for a +language reference or tutorial. + +@ifset MOD2 +@menu +* C:: C and C++ +* Modula-2:: Modula-2 +@end menu + +@node C, Modula-2, , Support +@subsection C and C++ +@cindex C and C++ +@cindex expressions in C or C++ +@end ifset + +Since C and C++ are so closely related, many features of @value{GDBN} apply +to both languages. Whenever this is the case, we discuss those languages +together. + +@ifclear MOD2 +@c Cancel this below, under same condition, at end of this chapter! +@raisesections +@end ifclear + +@ifclear HPPA +@cindex C++ +@kindex g++ +@cindex @sc{gnu} C++ +The C++ debugging facilities are jointly implemented by the C++ +compiler and @value{GDBN}. Therefore, to debug your C++ code +effectively, you must compile your C++ programs with a supported +C++ compiler, such as @sc{gnu} @code{g++}, or the HP ANSI C++ +compiler (@code{aCC}). + +For best results when using @sc{gnu} C++, use the stabs debugging +format. You can select that format explicitly with the @code{g++} +command-line options @samp{-gstabs} or @samp{-gstabs+}. See +@ref{Debugging Options,,Options for Debugging Your Program or @sc{gnu} +CC, gcc.info, Using @sc{gnu} CC}, for more information. +@end ifclear +@ifset HPPA +@cindex C++ +@kindex g++ +@cindex @sc{gnu} C++ +You can use @value{GDBN} to debug C programs compiled with either the HP +C compiler (@code{cc}) or the GNU C compiler (@code{gcc}), and to debug +programs compiled with either the HP ANSI C++ compiler (@code{aCC}) or +the @sc{gnu} C++ compiler (@code{g++}). + +If you compile with the @sc{gnu} C++ compiler, use the stabs debugging +format for best results when debugging. You can select that format +explicitly with the @code{g++} command-line options @samp{-gstabs} or +@samp{-gstabs+}. See @ref{Debugging Options,,Options for Debugging Your +Program or @sc{gnu} CC, gcc.info, Using @sc{gnu} CC}, for more +information. +@end ifset +@end ifclear + +@ifset CONLY +@node C, Symbols, Data, Top +@chapter C Language Support +@cindex C language +@cindex expressions in C + +Information specific to the C language is built into @value{GDBN} so that you +can use C expressions while debugging. This also permits @value{GDBN} to +output values in a manner consistent with C conventions. + +@menu +* C Operators:: C operators +@end menu +@end ifset + +@ifclear CONLY +@menu +* C Operators:: C and C++ operators +* C Constants:: C and C++ constants +* Cplus expressions:: C++ expressions +* C Defaults:: Default settings for C and C++ +@ifset MOD2 +* C Checks:: C and C++ type and range checks +@end ifset + +* Debugging C:: @value{GDBN} and C +* Debugging C plus plus:: @value{GDBN} features for C++ +@end menu +@end ifclear + +@ifclear CONLY +@cindex C and C++ operators +@node C Operators, C Constants, , C +@subsubsection C and C++ operators +@end ifclear +@ifset CONLY +@cindex C operators +@node C Operators, C Constants, C, C +@section C operators +@end ifset + +Operators must be defined on values of specific types. For instance, +@code{+} is defined on numbers, but not on structures. Operators are +often defined on groups of types. + +@ifclear CONLY +For the purposes of C and C++, the following definitions hold: +@end ifclear + +@itemize @bullet +@item +@ifclear HPPA +@emph{Integral types} include @code{int} with any of its storage-class +specifiers; @code{char}; and @code{enum}. +@end ifclear +@ifset HPPA +@emph{Integral types} include @code{int} with any of its storage-class +specifiers; @code{char}; @code{enum}; and, for C++, @code{bool}. +@end ifset + +@item +@emph{Floating-point types} include @code{float} and @code{double}. + +@item +@emph{Pointer types} include all types defined as @code{(@var{type} +*)}. + +@item +@emph{Scalar types} include all of the above. +@end itemize + +@noindent +The following operators are supported. They are listed here +in order of increasing precedence: + +@table @code +@item , +The comma or sequencing operator. Expressions in a comma-separated list +are evaluated from left to right, with the result of the entire +expression being the last expression evaluated. + +@item = +Assignment. The value of an assignment expression is the value +assigned. Defined on scalar types. + +@item @var{op}= +Used in an expression of the form @w{@code{@var{a} @var{op}= @var{b}}}, +and translated to @w{@code{@var{a} = @var{a op b}}}. +@w{@code{@var{op}=}} and @code{=} have the same precendence. +@var{op} is any one of the operators @code{|}, @code{^}, @code{&}, +@code{<<}, @code{>>}, @code{+}, @code{-}, @code{*}, @code{/}, @code{%}. + +@item ?: +The ternary operator. @code{@var{a} ? @var{b} : @var{c}} can be thought +of as: if @var{a} then @var{b} else @var{c}. @var{a} should be of an +integral type. + +@item || +Logical @sc{or}. Defined on integral types. + +@item && +Logical @sc{and}. Defined on integral types. + +@item | +Bitwise @sc{or}. Defined on integral types. + +@item ^ +Bitwise exclusive-@sc{or}. Defined on integral types. + +@item & +Bitwise @sc{and}. Defined on integral types. + +@item ==@r{, }!= +Equality and inequality. Defined on scalar types. The value of these +expressions is 0 for false and non-zero for true. + +@item <@r{, }>@r{, }<=@r{, }>= +Less than, greater than, less than or equal, greater than or equal. +Defined on scalar types. The value of these expressions is 0 for false +and non-zero for true. + +@item <<@r{, }>> +left shift, and right shift. Defined on integral types. + +@item @@ +The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}). + +@item +@r{, }- +Addition and subtraction. Defined on integral types, floating-point types and +pointer types. + +@item *@r{, }/@r{, }% +Multiplication, division, and modulus. Multiplication and division are +defined on integral and floating-point types. Modulus is defined on +integral types. + +@item ++@r{, }-- +Increment and decrement. When appearing before a variable, the +operation is performed before the variable is used in an expression; +when appearing after it, the variable's value is used before the +operation takes place. + +@item * +Pointer dereferencing. Defined on pointer types. Same precedence as +@code{++}. + +@item & +Address operator. Defined on variables. Same precedence as @code{++}. + +@ifclear CONLY +For debugging C++, @value{GDBN} implements a use of @samp{&} beyond what is +allowed in the C++ language itself: you can use @samp{&(&@var{ref})} +(or, if you prefer, simply @samp{&&@var{ref}}) to examine the address +where a C++ reference variable (declared with @samp{&@var{ref}}) is +stored. +@end ifclear + +@item - +Negative. Defined on integral and floating-point types. Same +precedence as @code{++}. + +@item ! +Logical negation. Defined on integral types. Same precedence as +@code{++}. + +@item ~ +Bitwise complement operator. Defined on integral types. Same precedence as +@code{++}. + + +@item .@r{, }-> +Structure member, and pointer-to-structure member. For convenience, +@value{GDBN} regards the two as equivalent, choosing whether to dereference a +pointer based on the stored type information. +Defined on @code{struct} and @code{union} data. + +@ifset HPPA +@item .*@r{, }->* +Dereferences of pointers to members. +@end ifset + +@item [] +Array indexing. @code{@var{a}[@var{i}]} is defined as +@code{*(@var{a}+@var{i})}. Same precedence as @code{->}. + +@item () +Function parameter list. Same precedence as @code{->}. + +@ifclear CONLY +@item :: +C++ scope resolution operator. Defined on +@code{struct}, @code{union}, and @code{class} types. +@end ifclear + +@item :: +Doubled colons +@ifclear CONLY +also +@end ifclear +represent the @value{GDBN} scope operator (@pxref{Expressions, +,Expressions}). +@ifclear CONLY +Same precedence as @code{::}, above. +@end ifclear +@end table + +@ifset HPPA +If an operator is redefined in the user code, @value{GDBN} usually +attempts to invoke the redefined version instead of using the operator's +predefined meaning. +@end ifset + +@ifclear CONLY +@menu +* C Constants:: +@end menu + +@ifset MOD2 +@node C Constants, Cplus expressions, C Operators, C +@subsubsection C and C++ constants +@end ifset +@ifclear MOD2 +@node C Constants, Cplus expressions, C Operators, Support +@subsubsection C and C++ constants +@end ifclear + +@cindex C and C++ constants +@value{GDBN} allows you to express the constants of C and C++ in the +following ways: +@end ifclear +@ifset CONLY +@cindex C constants +@node C Constants, Debugging C, C Operators, C +@section C constants + +@value{GDBN} allows you to express the constants of C in the +following ways: +@end ifset + +@itemize @bullet +@item +Integer constants are a sequence of digits. Octal constants are +specified by a leading @samp{0} (i.e. zero), and hexadecimal constants by +a leading @samp{0x} or @samp{0X}. Constants may also end with a letter +@samp{l}, specifying that the constant should be treated as a +@code{long} value. + +@item +Floating point constants are a sequence of digits, followed by a decimal +point, followed by a sequence of digits, and optionally followed by an +exponent. An exponent is of the form: +@samp{@w{e@r{[[}+@r{]|}-@r{]}@var{nnn}}}, where @var{nnn} is another +sequence of digits. The @samp{+} is optional for positive exponents. + +@item +Enumerated constants consist of enumerated identifiers, or their +integral equivalents. + +@item +Character constants are a single character surrounded by single quotes +(@code{'}), or a number---the ordinal value of the corresponding character +(usually its @sc{ASCII} value). Within quotes, the single character may +be represented by a letter or by @dfn{escape sequences}, which are of +the form @samp{\@var{nnn}}, where @var{nnn} is the octal representation +of the character's ordinal value; or of the form @samp{\@var{x}}, where +@samp{@var{x}} is a predefined special character---for example, +@samp{\n} for newline. + +@item +String constants are a sequence of character constants surrounded +by double quotes (@code{"}). + +@item +Pointer constants are an integral value. You can also write pointers +to constants using the C operator @samp{&}. + +@item +Array constants are comma-separated lists surrounded by braces @samp{@{} +and @samp{@}}; for example, @samp{@{1,2,3@}} is a three-element array of +integers, @samp{@{@{1,2@}, @{3,4@}, @{5,6@}@}} is a three-by-two array, +and @samp{@{&"hi", &"there", &"fred"@}} is a three-element array of pointers. +@end itemize + +@ifclear CONLY +@menu +* Cplus expressions:: +* C Defaults:: +@ifset MOD2 +* C Checks:: +@end ifset + +* Debugging C:: +@end menu + +@ifset MOD2 +@node Cplus expressions, C Defaults, C Constants, C +@subsubsection C++ expressions +@end ifset +@ifclear MOD2 +@node Cplus expressions, C Defaults, C Constants, Support +@subsubsection C++ expressions +@end ifclear + +@cindex expressions in C++ +@value{GDBN} expression handling can interpret most C++ expressions. + +@ifclear HPPA +@cindex C++ support, not in @sc{coff} +@cindex @sc{coff} versus C++ +@cindex C++ and object formats +@cindex object formats and C++ +@cindex a.out and C++ +@cindex @sc{ecoff} and C++ +@cindex @sc{xcoff} and C++ +@cindex @sc{elf}/stabs and C++ +@cindex @sc{elf}/@sc{dwarf} and C++ +@c FIXME!! GDB may eventually be able to debug C++ using DWARF; check +@c periodically whether this has happened... +@quotation +@emph{Warning:} @value{GDBN} can only debug C++ code if you use the +proper compiler. Typically, C++ debugging depends on the use of +additional debugging information in the symbol table, and thus requires +special support. In particular, if your compiler generates a.out, MIPS +@sc{ecoff}, RS/6000 @sc{xcoff}, or @sc{elf} with stabs extensions to the +symbol table, these facilities are all available. (With @sc{gnu} CC, +you can use the @samp{-gstabs} option to request stabs debugging +extensions explicitly.) Where the object code format is standard +@sc{coff} or @sc{dwarf} in @sc{elf}, on the other hand, most of the C++ +support in @value{GDBN} does @emph{not} work. +@end quotation +@end ifclear + +@enumerate + +@cindex member functions +@item +Member function calls are allowed; you can use expressions like + +@example +count = aml->GetOriginal(x, y) +@end example + +@kindex this +@cindex namespace in C++ +@item +While a member function is active (in the selected stack frame), your +expressions have the same namespace available as the member function; +that is, @value{GDBN} allows implicit references to the class instance +pointer @code{this} following the same rules as C++. + +@ifclear HPPA +@cindex call overloaded functions +@cindex type conversions in C++ +@item +You can call overloaded functions; @value{GDBN} resolves the function +call to the right definition, with one restriction---you must use +arguments of the type required by the function that you want to call. +@value{GDBN} does not perform conversions requiring constructors or +user-defined type operators. +@end ifclear +@ifset HPPA +@cindex call overloaded functions +@cindex overloaded functions +@cindex type conversions in C++ +@item +You can call overloaded functions; @value{GDBN} resolves the function +call to the right definition, with some restrictions. GDB does not +perform overload resolution involving user-defined type conversions, +calls to constructors, or instantiations of templates that do not exist +in the program. It also cannot handle ellipsis argument lists or +default arguments. + +It does perform integral conversions and promotions, floating-point +promotions, arithmetic conversions, pointer conversions, conversions of +class objects to base classes, and standard conversions such as those of +functions or arrays to pointers; it requires an exact match on the +number of function arguments. + +Overload resolution is always performed, unless you have specified +@code{set overload-resolution off}. @xref{Debugging C plus plus, +,@value{GDBN} features for C++}. + +You must specify@code{set overload-resolution off} in order to use an +explicit function signature to call an overloaded function, as in +@smallexample +p 'foo(char,int)'('x', 13) +@end smallexample +The @value{GDBN} command-completion facility can simplify this; +@pxref{Completion, ,Command completion}. + +@end ifset + +@cindex reference declarations +@item +@value{GDBN} understands variables declared as C++ references; you can use +them in expressions just as you do in C++ source---they are automatically +dereferenced. + +In the parameter list shown when @value{GDBN} displays a frame, the values of +reference variables are not displayed (unlike other variables); this +avoids clutter, since references are often used for large structures. +The @emph{address} of a reference variable is always shown, unless +you have specified @samp{set print address off}. + +@item +@value{GDBN} supports the C++ name resolution operator @code{::}---your +expressions can use it just as expressions in your program do. Since +one scope may be defined in another, you can use @code{::} repeatedly if +necessary, for example in an expression like +@samp{@var{scope1}::@var{scope2}::@var{name}}. @value{GDBN} also allows +resolving name scope by reference to source files, in both C and C++ +debugging (@pxref{Variables, ,Program variables}). +@end enumerate + +@ifset HPPA +In addition, @value{GDBN} supports calling virtual functions correctly, +printing out virtual bases of objects, calling functions in a base +subobject, casting objects, and invoking user-defined operators. +@end ifset + +@ifset MOD2 +@node C Defaults, C Checks, Cplus expressions, C +@subsubsection C and C++ defaults +@end ifset +@ifclear MOD2 +@node C Defaults, Debugging C, Cplus expressions, Support +@subsubsection C and C++ defaults +@end ifclear +@cindex C and C++ defaults + +@ifclear HPPA +If you allow @value{GDBN} to set type and range checking automatically, they +both default to @code{off} whenever the working language changes to +C or C++. This happens regardless of whether you or @value{GDBN} +selects the working language. +@end ifclear + +If you allow @value{GDBN} to set the language automatically, it +recognizes source files whose names end with @file{.c}, @file{.C}, or +@file{.cc}, etc, and when @value{GDBN} enters code compiled from one of +these files, it sets the working language to C or C++. +@xref{Automatically, ,Having @value{GDBN} infer the source language}, +for further details. + +@ifset MOD2 +@c Type checking is (a) primarily motivated by Modula-2, and (b) +@c unimplemented. If (b) changes, it might make sense to let this node +@c appear even if Mod-2 does not, but meanwhile ignore it. roland 16jul93. +@node C Checks, Debugging C, C Defaults, C Constants +@subsubsection C and C++ type and range checks +@cindex C and C++ checks + +By default, when @value{GDBN} parses C or C++ expressions, type checking +is not used. However, if you turn type checking on, @value{GDBN} +considers two variables type equivalent if: + +@itemize @bullet +@item +The two variables are structured and have the same structure, union, or +enumerated tag. + +@item +The two variables have the same type name, or types that have been +declared equivalent through @code{typedef}. + +@ignore +@c leaving this out because neither J Gilmore nor R Pesch understand it. +@c FIXME--beers? +@item +The two @code{struct}, @code{union}, or @code{enum} variables are +declared in the same declaration. (Note: this may not be true for all C +compilers.) +@end ignore +@end itemize + +Range checking, if turned on, is done on mathematical operations. Array +indices are not checked, since they are often used to index a pointer +that is not itself an array. +@end ifset +@end ifclear + +@ifclear CONLY +@ifset MOD2 +@node Debugging C, Debugging C plus plus, C Checks, C +@subsubsection @value{GDBN} and C +@end ifset +@ifclear MOD2 +@node Debugging C, Debugging C plus plus, C Defaults, Support +@subsubsection @value{GDBN} and C +@end ifclear +@end ifclear +@ifset CONLY +@node Debugging C, , C Constants, C +@section @value{GDBN} and C +@end ifset + +The @code{set print union} and @code{show print union} commands apply to +the @code{union} type. When set to @samp{on}, any @code{union} that is +inside a @code{struct} +@ifclear CONLY +or @code{class} +@end ifclear +is also printed. +Otherwise, it appears as @samp{@{...@}}. + +The @code{@@} operator aids in the debugging of dynamic arrays, formed +with pointers and a memory allocation function. @xref{Expressions, +,Expressions}. + +@ifclear CONLY +@menu +* Debugging C plus plus:: +@end menu + +@ifset MOD2 +@node Debugging C plus plus, , Debugging C, C +@subsubsection @value{GDBN} features for C++ +@end ifset +@ifclear MOD2 +@node Debugging C plus plus, , Debugging C, Support +@subsubsection @value{GDBN} features for C++ +@end ifclear + +@cindex commands for C++ +Some @value{GDBN} commands are particularly useful with C++, and some are +designed specifically for use with C++. Here is a summary: + +@table @code +@cindex break in overloaded functions +@item @r{breakpoint menus} +When you want a breakpoint in a function whose name is overloaded, +@value{GDBN} breakpoint menus help you specify which function definition +you want. @xref{Breakpoint Menus,,Breakpoint menus}. + +@cindex overloading in C++ +@item rbreak @var{regex} +Setting breakpoints using regular expressions is helpful for setting +breakpoints on overloaded functions that are not members of any special +classes. +@xref{Set Breaks, ,Setting breakpoints}. + +@cindex C++ exception handling +@item catch throw +@itemx catch catch +Debug C++ exception handling using these commands. @xref{Set +Catchpoints, , Setting catchpoints}. + +@cindex inheritance +@item ptype @var{typename} +Print inheritance relationships as well as other information for type +@var{typename}. +@xref{Symbols, ,Examining the Symbol Table}. + +@cindex C++ symbol display +@item set print demangle +@itemx show print demangle +@itemx set print asm-demangle +@itemx show print asm-demangle +Control whether C++ symbols display in their source form, both when +displaying code as C++ source and when displaying disassemblies. +@xref{Print Settings, ,Print settings}. + +@item set print object +@itemx show print object +Choose whether to print derived (actual) or declared types of objects. +@xref{Print Settings, ,Print settings}. + +@item set print vtbl +@itemx show print vtbl +Control the format for printing virtual function tables. +@xref{Print Settings, ,Print settings}. +@ifset HPPA +(The @code{vtbl} commands do not work on programs compiled with the HP +ANSI C++ compiler (@code{aCC}).) + +@kindex set overload-resolution +@cindex overloaded functions +@item set overload-resolution on +Enable overload resolution for C++ expression evaluation. The default +is on. For overloaded functions, @value{GDBN} evaluates the arguments +and searches for a function whose signature matches the argument types, +using the standard C++ conversion rules (@pxref{Cplus expressions, ,C++ +expressions} for details). If it cannot find a match, it emits a +message. + +@item set overload-resolution off +Disable overload resolution for C++ expression evaluation. For +overloaded functions that are not class member functions, @value{GDBN} +chooses the first function of the specified name that it finds in the +symbol table, whether or not its arguments are of the correct type. For +overloaded functions that are class member functions, @value{GDBN} +searches for a function whose signature @emph{exactly} matches the +argument types. +@end ifset + +@item @r{Overloaded symbol names} +You can specify a particular definition of an overloaded symbol, using +the same notation that is used to declare such symbols in C++: type +@code{@var{symbol}(@var{types})} rather than just @var{symbol}. You can +also use the @value{GDBN} command-line word completion facilities to list the +available choices, or to finish the type list for you. +@xref{Completion,, Command completion}, for details on how to do this. +@end table +@ifclear MOD2 +@c cancels "raisesections" under same conditions near bgn of chapter +@lowersections +@end ifclear + +@ifset MOD2 +@node Modula-2, ,C , Support +@subsection Modula-2 +@cindex Modula-2 + +The extensions made to @value{GDBN} to support Modula-2 only support +output from the @sc{gnu} Modula-2 compiler (which is currently being +developed). Other Modula-2 compilers are not currently supported, and +attempting to debug executables produced by them is most likely +to give an error as @value{GDBN} reads in the executable's symbol +table. + +@cindex expressions in Modula-2 +@menu +* M2 Operators:: Built-in operators +* Built-In Func/Proc:: Built-in functions and procedures +* M2 Constants:: Modula-2 constants +* M2 Defaults:: Default settings for Modula-2 +* Deviations:: Deviations from standard Modula-2 +* M2 Checks:: Modula-2 type and range checks +* M2 Scope:: The scope operators @code{::} and @code{.} +* GDB/M2:: @value{GDBN} and Modula-2 +@end menu + +@node M2 Operators, Built-In Func/Proc, Modula-2, Modula-2 +@subsubsection Operators +@cindex Modula-2 operators + +Operators must be defined on values of specific types. For instance, +@code{+} is defined on numbers, but not on structures. Operators are +often defined on groups of types. For the purposes of Modula-2, the +following definitions hold: + +@itemize @bullet + +@item +@emph{Integral types} consist of @code{INTEGER}, @code{CARDINAL}, and +their subranges. + +@item +@emph{Character types} consist of @code{CHAR} and its subranges. + +@item +@emph{Floating-point types} consist of @code{REAL}. + +@item +@emph{Pointer types} consist of anything declared as @code{POINTER TO +@var{type}}. + +@item +@emph{Scalar types} consist of all of the above. + +@item +@emph{Set types} consist of @code{SET} and @code{BITSET} types. + +@item +@emph{Boolean types} consist of @code{BOOLEAN}. +@end itemize + +@noindent +The following operators are supported, and appear in order of +increasing precedence: + +@table @code +@item , +Function argument or array index separator. + +@item := +Assignment. The value of @var{var} @code{:=} @var{value} is +@var{value}. + +@item <@r{, }> +Less than, greater than on integral, floating-point, or enumerated +types. + +@item <=@r{, }>= +Less than, greater than, less than or equal to, greater than or equal to +on integral, floating-point and enumerated types, or set inclusion on +set types. Same precedence as @code{<}. + +@item =@r{, }<>@r{, }# +Equality and two ways of expressing inequality, valid on scalar types. +Same precedence as @code{<}. In @value{GDBN} scripts, only @code{<>} is +available for inequality, since @code{#} conflicts with the script +comment character. + +@item IN +Set membership. Defined on set types and the types of their members. +Same precedence as @code{<}. + +@item OR +Boolean disjunction. Defined on boolean types. + +@item AND@r{, }& +Boolean conjuction. Defined on boolean types. + +@item @@ +The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}). + +@item +@r{, }- +Addition and subtraction on integral and floating-point types, or union +and difference on set types. + +@item * +Multiplication on integral and floating-point types, or set intersection +on set types. + +@item / +Division on floating-point types, or symmetric set difference on set +types. Same precedence as @code{*}. + +@item DIV@r{, }MOD +Integer division and remainder. Defined on integral types. Same +precedence as @code{*}. + +@item - +Negative. Defined on @code{INTEGER} and @code{REAL} data. + +@item ^ +Pointer dereferencing. Defined on pointer types. + +@item NOT +Boolean negation. Defined on boolean types. Same precedence as +@code{^}. + +@item . +@code{RECORD} field selector. Defined on @code{RECORD} data. Same +precedence as @code{^}. + +@item [] +Array indexing. Defined on @code{ARRAY} data. Same precedence as @code{^}. + +@item () +Procedure argument list. Defined on @code{PROCEDURE} objects. Same precedence +as @code{^}. + +@item ::@r{, }. +@value{GDBN} and Modula-2 scope operators. +@end table + +@quotation +@emph{Warning:} Sets and their operations are not yet supported, so @value{GDBN} +treats the use of the operator @code{IN}, or the use of operators +@code{+}, @code{-}, @code{*}, @code{/}, @code{=}, , @code{<>}, @code{#}, +@code{<=}, and @code{>=} on sets as an error. +@end quotation + +@cindex Modula-2 built-ins +@node Built-In Func/Proc, M2 Constants, M2 Operators, Modula-2 +@subsubsection Built-in functions and procedures + +Modula-2 also makes available several built-in procedures and functions. +In describing these, the following metavariables are used: + +@table @var + +@item a +represents an @code{ARRAY} variable. + +@item c +represents a @code{CHAR} constant or variable. + +@item i +represents a variable or constant of integral type. + +@item m +represents an identifier that belongs to a set. Generally used in the +same function with the metavariable @var{s}. The type of @var{s} should +be @code{SET OF @var{mtype}} (where @var{mtype} is the type of @var{m}). + +@item n +represents a variable or constant of integral or floating-point type. + +@item r +represents a variable or constant of floating-point type. + +@item t +represents a type. + +@item v +represents a variable. + +@item x +represents a variable or constant of one of many types. See the +explanation of the function for details. +@end table + +All Modula-2 built-in procedures also return a result, described below. + +@table @code +@item ABS(@var{n}) +Returns the absolute value of @var{n}. + +@item CAP(@var{c}) +If @var{c} is a lower case letter, it returns its upper case +equivalent, otherwise it returns its argument + +@item CHR(@var{i}) +Returns the character whose ordinal value is @var{i}. + +@item DEC(@var{v}) +Decrements the value in the variable @var{v}. Returns the new value. + +@item DEC(@var{v},@var{i}) +Decrements the value in the variable @var{v} by @var{i}. Returns the +new value. + +@item EXCL(@var{m},@var{s}) +Removes the element @var{m} from the set @var{s}. Returns the new +set. + +@item FLOAT(@var{i}) +Returns the floating point equivalent of the integer @var{i}. + +@item HIGH(@var{a}) +Returns the index of the last member of @var{a}. + +@item INC(@var{v}) +Increments the value in the variable @var{v}. Returns the new value. + +@item INC(@var{v},@var{i}) +Increments the value in the variable @var{v} by @var{i}. Returns the +new value. + +@item INCL(@var{m},@var{s}) +Adds the element @var{m} to the set @var{s} if it is not already +there. Returns the new set. + +@item MAX(@var{t}) +Returns the maximum value of the type @var{t}. + +@item MIN(@var{t}) +Returns the minimum value of the type @var{t}. + +@item ODD(@var{i}) +Returns boolean TRUE if @var{i} is an odd number. + +@item ORD(@var{x}) +Returns the ordinal value of its argument. For example, the ordinal +value of a character is its ASCII value (on machines supporting the +ASCII character set). @var{x} must be of an ordered type, which include +integral, character and enumerated types. + +@item SIZE(@var{x}) +Returns the size of its argument. @var{x} can be a variable or a type. + +@item TRUNC(@var{r}) +Returns the integral part of @var{r}. + +@item VAL(@var{t},@var{i}) +Returns the member of the type @var{t} whose ordinal value is @var{i}. +@end table + +@quotation +@emph{Warning:} Sets and their operations are not yet supported, so +@value{GDBN} treats the use of procedures @code{INCL} and @code{EXCL} as +an error. +@end quotation + +@cindex Modula-2 constants +@node M2 Constants, M2 Defaults, Built-In Func/Proc, Modula-2 +@subsubsection Constants + +@value{GDBN} allows you to express the constants of Modula-2 in the following +ways: + +@itemize @bullet + +@item +Integer constants are simply a sequence of digits. When used in an +expression, a constant is interpreted to be type-compatible with the +rest of the expression. Hexadecimal integers are specified by a +trailing @samp{H}, and octal integers by a trailing @samp{B}. + +@item +Floating point constants appear as a sequence of digits, followed by a +decimal point and another sequence of digits. An optional exponent can +then be specified, in the form @samp{E@r{[}+@r{|}-@r{]}@var{nnn}}, where +@samp{@r{[}+@r{|}-@r{]}@var{nnn}} is the desired exponent. All of the +digits of the floating point constant must be valid decimal (base 10) +digits. + +@item +Character constants consist of a single character enclosed by a pair of +like quotes, either single (@code{'}) or double (@code{"}). They may +also be expressed by their ordinal value (their ASCII value, usually) +followed by a @samp{C}. + +@item +String constants consist of a sequence of characters enclosed by a +pair of like quotes, either single (@code{'}) or double (@code{"}). +Escape sequences in the style of C are also allowed. @xref{C +Constants, ,C and C++ constants}, for a brief explanation of escape +sequences. + +@item +Enumerated constants consist of an enumerated identifier. + +@item +Boolean constants consist of the identifiers @code{TRUE} and +@code{FALSE}. + +@item +Pointer constants consist of integral values only. + +@item +Set constants are not yet supported. +@end itemize + +@node M2 Defaults, Deviations, M2 Constants, Modula-2 +@subsubsection Modula-2 defaults +@cindex Modula-2 defaults + +If type and range checking are set automatically by @value{GDBN}, they +both default to @code{on} whenever the working language changes to +Modula-2. This happens regardless of whether you, or @value{GDBN}, +selected the working language. + +If you allow @value{GDBN} to set the language automatically, then entering +code compiled from a file whose name ends with @file{.mod} sets the +working language to Modula-2. @xref{Automatically, ,Having @value{GDBN} set +the language automatically}, for further details. + +@node Deviations, M2 Checks, M2 Defaults, Modula-2 +@subsubsection Deviations from standard Modula-2 +@cindex Modula-2, deviations from + +A few changes have been made to make Modula-2 programs easier to debug. +This is done primarily via loosening its type strictness: + +@itemize @bullet +@item +Unlike in standard Modula-2, pointer constants can be formed by +integers. This allows you to modify pointer variables during +debugging. (In standard Modula-2, the actual address contained in a +pointer variable is hidden from you; it can only be modified +through direct assignment to another pointer variable or expression that +returned a pointer.) + +@item +C escape sequences can be used in strings and characters to represent +non-printable characters. @value{GDBN} prints out strings with these +escape sequences embedded. Single non-printable characters are +printed using the @samp{CHR(@var{nnn})} format. + +@item +The assignment operator (@code{:=}) returns the value of its right-hand +argument. + +@item +All built-in procedures both modify @emph{and} return their argument. +@end itemize + +@node M2 Checks, M2 Scope, Deviations, Modula-2 +@subsubsection Modula-2 type and range checks +@cindex Modula-2 checks + +@quotation +@emph{Warning:} in this release, @value{GDBN} does not yet perform type or +range checking. +@end quotation +@c FIXME remove warning when type/range checks added + +@value{GDBN} considers two Modula-2 variables type equivalent if: + +@itemize @bullet +@item +They are of types that have been declared equivalent via a @code{TYPE +@var{t1} = @var{t2}} statement + +@item +They have been declared on the same line. (Note: This is true of the +@sc{gnu} Modula-2 compiler, but it may not be true of other compilers.) +@end itemize + +As long as type checking is enabled, any attempt to combine variables +whose types are not equivalent is an error. + +Range checking is done on all mathematical operations, assignment, array +index bounds, and all built-in functions and procedures. + +@node M2 Scope, GDB/M2, M2 Checks, Modula-2 +@subsubsection The scope operators @code{::} and @code{.} +@cindex scope +@kindex . +@cindex colon, doubled as scope operator +@ifinfo +@kindex colon-colon +@c Info cannot handle :: but TeX can. +@end ifinfo +@iftex +@kindex :: +@end iftex + +There are a few subtle differences between the Modula-2 scope operator +(@code{.}) and the @value{GDBN} scope operator (@code{::}). The two have +similar syntax: + +@example + +@var{module} . @var{id} +@var{scope} :: @var{id} +@end example + +@noindent +where @var{scope} is the name of a module or a procedure, +@var{module} the name of a module, and @var{id} is any declared +identifier within your program, except another module. + +Using the @code{::} operator makes @value{GDBN} search the scope +specified by @var{scope} for the identifier @var{id}. If it is not +found in the specified scope, then @value{GDBN} searches all scopes +enclosing the one specified by @var{scope}. + +Using the @code{.} operator makes @value{GDBN} search the current scope for +the identifier specified by @var{id} that was imported from the +definition module specified by @var{module}. With this operator, it is +an error if the identifier @var{id} was not imported from definition +module @var{module}, or if @var{id} is not an identifier in +@var{module}. + +@node GDB/M2, , M2 Scope, Modula-2 +@subsubsection @value{GDBN} and Modula-2 + +Some @value{GDBN} commands have little use when debugging Modula-2 programs. +Five subcommands of @code{set print} and @code{show print} apply +specifically to C and C++: @samp{vtbl}, @samp{demangle}, +@samp{asm-demangle}, @samp{object}, and @samp{union}. The first four +apply to C++, and the last to the C @code{union} type, which has no direct +analogue in Modula-2. + +The @code{@@} operator (@pxref{Expressions, ,Expressions}), while available +while using any language, is not useful with Modula-2. Its +intent is to aid the debugging of @dfn{dynamic arrays}, which cannot be +created in Modula-2 as they can in C or C++. However, because an +address can be specified by an integral constant, the construct +@samp{@{@var{type}@}@var{adrexp}} is still useful. (@pxref{Expressions, ,Expressions}) + +@cindex @code{#} in Modula-2 +In @value{GDBN} scripts, the Modula-2 inequality operator @code{#} is +interpreted as the beginning of a comment. Use @code{<>} instead. +@end ifset +@end ifclear + +@node Symbols, Altering, Languages, Top +@chapter Examining the Symbol Table + +The commands described in this section allow you to inquire about the +symbols (names of variables, functions and types) defined in your +program. This information is inherent in the text of your program and +does not change as your program executes. @value{GDBN} finds it in your +program's symbol table, in the file indicated when you started @value{GDBN} +(@pxref{File Options, ,Choosing files}), or by one of the +file-management commands (@pxref{Files, ,Commands to specify files}). + +@cindex symbol names +@cindex names of symbols +@cindex quoting names +Occasionally, you may need to refer to symbols that contain unusual +characters, which @value{GDBN} ordinarily treats as word delimiters. The +most frequent case is in referring to static variables in other +source files (@pxref{Variables,,Program variables}). File names +are recorded in object files as debugging symbols, but @value{GDBN} would +ordinarily parse a typical file name, like @file{foo.c}, as the three words +@samp{foo} @samp{.} @samp{c}. To allow @value{GDBN} to recognize +@samp{foo.c} as a single symbol, enclose it in single quotes; for example, + +@example +p 'foo.c'::x +@end example + +@noindent +looks up the value of @code{x} in the scope of the file @file{foo.c}. + +@table @code +@kindex info address +@item info address @var{symbol} +Describe where the data for @var{symbol} is stored. For a register +variable, this says which register it is kept in. For a non-register +local variable, this prints the stack-frame offset at which the variable +is always stored. + +Note the contrast with @samp{print &@var{symbol}}, which does not work +at all for a register variable, and for a stack local variable prints +the exact address of the current instantiation of the variable. + +@kindex whatis +@item whatis @var{exp} +Print the data type of expression @var{exp}. @var{exp} is not +actually evaluated, and any side-effecting operations (such as +assignments or function calls) inside it do not take place. +@xref{Expressions, ,Expressions}. + +@item whatis +Print the data type of @code{$}, the last value in the value history. + +@kindex ptype +@item ptype @var{typename} +Print a description of data type @var{typename}. @var{typename} may be +the name of a type, or for C code it may have the form +@ifclear CONLY +@samp{class @var{class-name}}, +@end ifclear +@samp{struct @var{struct-tag}}, @samp{union @var{union-tag}} or +@samp{enum @var{enum-tag}}. + +@item ptype @var{exp} +@itemx ptype +Print a description of the type of expression @var{exp}. @code{ptype} +differs from @code{whatis} by printing a detailed description, instead +of just the name of the type. + +For example, for this variable declaration: + +@example +struct complex @{double real; double imag;@} v; +@end example + +@noindent +the two commands give this output: + +@example +@group +(@value{GDBP}) whatis v +type = struct complex +(@value{GDBP}) ptype v +type = struct complex @{ + double real; + double imag; +@} +@end group +@end example + +@noindent +As with @code{whatis}, using @code{ptype} without an argument refers to +the type of @code{$}, the last value in the value history. + +@kindex info types +@item info types @var{regexp} +@itemx info types +Print a brief description of all types whose name matches @var{regexp} +(or all types in your program, if you supply no argument). Each +complete typename is matched as though it were a complete line; thus, +@samp{i type value} gives information on all types in your program whose +name includes the string @code{value}, but @samp{i type ^value$} gives +information only on types whose complete name is @code{value}. + +This command differs from @code{ptype} in two ways: first, like +@code{whatis}, it does not print a detailed description; second, it +lists all source files where a type is defined. + +@kindex info source +@item info source +Show the name of the current source file---that is, the source file for +the function containing the current point of execution---and the language +it was written in. + +@kindex info sources +@item info sources +Print the names of all source files in your program for which there is +debugging information, organized into two lists: files whose symbols +have already been read, and files whose symbols will be read when needed. + +@kindex info functions +@item info functions +Print the names and data types of all defined functions. + +@item info functions @var{regexp} +Print the names and data types of all defined functions +whose names contain a match for regular expression @var{regexp}. +Thus, @samp{info fun step} finds all functions whose names +include @code{step}; @samp{info fun ^step} finds those whose names +start with @code{step}. + +@kindex info variables +@item info variables +Print the names and data types of all variables that are declared +outside of functions (i.e., excluding local variables). + +@item info variables @var{regexp} +Print the names and data types of all variables (except for local +variables) whose names contain a match for regular expression +@var{regexp}. + +@ignore +This was never implemented. +@kindex info methods +@item info methods +@itemx info methods @var{regexp} +The @code{info methods} command permits the user to examine all defined +methods within C++ program, or (with the @var{regexp} argument) a +specific set of methods found in the various C++ classes. Many +C++ classes provide a large number of methods. Thus, the output +from the @code{ptype} command can be overwhelming and hard to use. The +@code{info-methods} command filters the methods, printing only those +which match the regular-expression @var{regexp}. +@end ignore + +@ifclear HPPA +@cindex reloading symbols +Some systems allow individual object files that make up your program to +be replaced without stopping and restarting your program. +@ifset VXWORKS +For example, in VxWorks you can simply recompile a defective object file +and keep on running. +@end ifset +If you are running on one of these systems, you can allow @value{GDBN} to +reload the symbols for automatically relinked modules: + +@table @code +@kindex set symbol-reloading +@item set symbol-reloading on +Replace symbol definitions for the corresponding source file when an +object file with a particular name is seen again. + +@item set symbol-reloading off +Do not replace symbol definitions when re-encountering object files of +the same name. This is the default state; if you are not running on a +system that permits automatically relinking modules, you should leave +@code{symbol-reloading} off, since otherwise @value{GDBN} may discard symbols +when linking large programs, that may contain several modules (from +different directories or libraries) with the same name. + +@kindex show symbol-reloading +@item show symbol-reloading +Show the current @code{on} or @code{off} setting. +@end table +@end ifclear + +@ifset HPPA +@kindex set opaque-type-resolution +@item set opaque-type-resolution on +Tell @value{GDBN} to resolve opaque types. An opaque type is a type +declared as a pointer to a @code{struct}, @code{class}, or +@code{union}---for example, @code{struct MyType *}---that is used in one +source file although the full declaration of @code{struct MyType} is in +another source file. The default is on. + +A change in the setting of this subcommand will not take effect until +the next time symbols for a file are loaded. + +@item set opaque-type-resolution off +Tell @value{GDBN} not to resolve opaque types. In this case, the type +is printed as follows: +@smallexample +@{<no data fields>@} +@end smallexample + +@kindex show opaque-type-resolution +@item show opaque-type-resolution +Show whether opaque types are resolved or not. +@end ifset + +@kindex maint print symbols +@cindex symbol dump +@kindex maint print psymbols +@cindex partial symbol dump +@item maint print symbols @var{filename} +@itemx maint print psymbols @var{filename} +@itemx maint print msymbols @var{filename} +Write a dump of debugging symbol data into the file @var{filename}. +These commands are used to debug the @value{GDBN} symbol-reading code. Only +symbols with debugging data are included. If you use @samp{maint print +symbols}, @value{GDBN} includes all the symbols for which it has already +collected full details: that is, @var{filename} reflects symbols for +only those files whose symbols @value{GDBN} has read. You can use the +command @code{info sources} to find out which files these are. If you +use @samp{maint print psymbols} instead, the dump shows information about +symbols that @value{GDBN} only knows partially---that is, symbols defined in +files that @value{GDBN} has skimmed, but not yet read completely. Finally, +@samp{maint print msymbols} dumps just the minimal symbol information +required for each object file from which @value{GDBN} has read some symbols. +@xref{Files, ,Commands to specify files}, for a discussion of how +@value{GDBN} reads symbols (in the description of @code{symbol-file}). +@end table + +@node Altering, GDB Files, Symbols, Top +@chapter Altering Execution + +Once you think you have found an error in your program, you might want to +find out for certain whether correcting the apparent error would lead to +correct results in the rest of the run. You can find the answer by +experiment, using the @value{GDBN} features for altering execution of the +program. + +For example, you can store new values into variables or memory +locations, +@ifclear BARETARGET +give your program a signal, restart it +@end ifclear +@ifset BARETARGET +restart your program +@end ifset +at a different address, or even return prematurely from a function. + +@menu +* Assignment:: Assignment to variables +* Jumping:: Continuing at a different address +@ifclear BARETARGET +* Signaling:: Giving your program a signal +@end ifclear + +* Returning:: Returning from a function +* Calling:: Calling your program's functions +* Patching:: Patching your program +@end menu + +@node Assignment, Jumping, Altering, Altering +@section Assignment to variables + +@cindex assignment +@cindex setting variables +To alter the value of a variable, evaluate an assignment expression. +@xref{Expressions, ,Expressions}. For example, + +@example +print x=4 +@end example + +@noindent +stores the value 4 into the variable @code{x}, and then prints the +value of the assignment expression (which is 4). +@ifclear CONLY +@xref{Languages, ,Using @value{GDBN} with Different Languages}, for more +information on operators in supported languages. +@end ifclear + +@kindex set variable +@cindex variables, setting +If you are not interested in seeing the value of the assignment, use the +@code{set} command instead of the @code{print} command. @code{set} is +really the same as @code{print} except that the expression's value is +not printed and is not put in the value history (@pxref{Value History, +,Value history}). The expression is evaluated only for its effects. + +@ifclear HPPA +If the beginning of the argument string of the @code{set} command +appears identical to a @code{set} subcommand, use the @code{set +variable} command instead of just @code{set}. This command is identical +to @code{set} except for its lack of subcommands. For example, if your +program has a variable @code{width}, you get an error if you try to set +a new value with just @samp{set width=13}, because @value{GDBN} has the +command @code{set width}: + +@example +(@value{GDBP}) whatis width +type = double +(@value{GDBP}) p width +$4 = 13 +(@value{GDBP}) set width=47 +Invalid syntax in expression. +@end example + +@noindent +The invalid expression, of course, is @samp{=47}. In +order to actually set the program's variable @code{width}, use + +@example +(@value{GDBP}) set var width=47 +@end example +@end ifclear +@ifset HPPA +Because the @code{set} command has many subcommands that can conflict +with the names of program variables, it is a good idea to use the +@code{set variable} command instead of just @code{set}. For example, if +your program has a variable @code{g}, you run into problems if you try +to set a new value with just @samp{set g=4}, because @value{GDBN} has +the command @code{set gnutarget}, abbreviated @code{set g}: + +@example +@group +(@value{GDBP}) whatis g +type = double +(@value{GDBP}) p g +$1 = 1 +(@value{GDBP}) set g=4 +(gdb) p g +$2 = 1 +(@value{GDBP}) r +The program being debugged has been started already. +Start it from the beginning? (y or n) y +Starting program: /home/smith/cc_progs/a.out +"/home/smith/cc_progs/a.out": can't open to read symbols: Invalid bfd target. +(@value{GDBP}) show g +The current BFD target is "=4". +@end group +@end example + +@noindent +The program variable @code{g} did not change, and you silently set the +@code{gnutarget} to an invalid value. In order to set the variable +@code{g}, use + +@example +(@value{GDBP}) set var g=4 +@end example +@end ifset + +@value{GDBN} allows more implicit conversions in assignments than C; you can +freely store an integer value into a pointer variable or vice versa, +and you can convert any structure to any other structure that is the +same length or shorter. +@comment FIXME: how do structs align/pad in these conversions? +@comment /doc@cygnus.com 18dec1990 + +To store values into arbitrary places in memory, use the @samp{@{@dots{}@}} +construct to generate a value of specified type at a specified address +(@pxref{Expressions, ,Expressions}). For example, @code{@{int@}0x83040} refers +to memory location @code{0x83040} as an integer (which implies a certain size +and representation in memory), and + +@example +set @{int@}0x83040 = 4 +@end example + +@noindent +stores the value 4 into that memory location. + +@node Jumping, Signaling, Assignment, Altering +@section Continuing at a different address + +Ordinarily, when you continue your program, you do so at the place where +it stopped, with the @code{continue} command. You can instead continue at +an address of your own choosing, with the following commands: + +@table @code +@kindex jump +@item jump @var{linespec} +Resume execution at line @var{linespec}. Execution stops again +immediately if there is a breakpoint there. @xref{List, ,Printing +source lines}, for a description of the different forms of +@var{linespec}. It is common practice to use the @code{tbreak} command +in conjunction with @code{jump}. @xref{Set Breaks, ,Setting +breakpoints}. + +The @code{jump} command does not change the current stack frame, or +the stack pointer, or the contents of any memory location or any +register other than the program counter. If line @var{linespec} is in +a different function from the one currently executing, the results may +be bizarre if the two functions expect different patterns of arguments or +of local variables. For this reason, the @code{jump} command requests +confirmation if the specified line is not in the function currently +executing. However, even bizarre results are predictable if you are +well acquainted with the machine-language code of your program. + +@item jump *@var{address} +Resume execution at the instruction at address @var{address}. +@end table + +@ifclear HPPA +@c Doesn't work on HP-UX; have to set $pcoqh and $pcoqt. +You can get much the same effect as the @code{jump} command by storing a +new value into the register @code{$pc}. The difference is that this +does not start your program running; it only changes the address of where it +@emph{will} run when you continue. For example, + +@example +set $pc = 0x485 +@end example + +@noindent +makes the next @code{continue} command or stepping command execute at +address @code{0x485}, rather than at the address where your program stopped. +@xref{Continuing and Stepping, ,Continuing and stepping}. +@end ifclear + +The most common occasion to use the @code{jump} command is to back +up---perhaps with more breakpoints set---over a portion of a program +that has already executed, in order to examine its execution in more +detail. + +@ifclear BARETARGET +@c @group +@node Signaling, Returning, Jumping, Altering +@section Giving your program a signal + +@table @code +@kindex signal +@item signal @var{signal} +Resume execution where your program stopped, but immediately give it the +signal @var{signal}. @var{signal} can be the name or the number of a +signal. For example, on many systems @code{signal 2} and @code{signal +SIGINT} are both ways of sending an interrupt signal. + +Alternatively, if @var{signal} is zero, continue execution without +giving a signal. This is useful when your program stopped on account of +a signal and would ordinary see the signal when resumed with the +@code{continue} command; @samp{signal 0} causes it to resume without a +signal. + +@code{signal} does not repeat when you press @key{RET} a second time +after executing the command. +@end table +@c @end group + +Invoking the @code{signal} command is not the same as invoking the +@code{kill} utility from the shell. Sending a signal with @code{kill} +causes @value{GDBN} to decide what to do with the signal depending on +the signal handling tables (@pxref{Signals}). The @code{signal} command +passes the signal directly to your program. + +@end ifclear + +@node Returning, Calling, Signaling, Altering +@section Returning from a function + +@table @code +@cindex returning from a function +@kindex return +@item return +@itemx return @var{expression} +You can cancel execution of a function call with the @code{return} +command. If you give an +@var{expression} argument, its value is used as the function's return +value. +@end table + +When you use @code{return}, @value{GDBN} discards the selected stack frame +(and all frames within it). You can think of this as making the +discarded frame return prematurely. If you wish to specify a value to +be returned, give that value as the argument to @code{return}. + +This pops the selected stack frame (@pxref{Selection, ,Selecting a +frame}), and any other frames inside of it, leaving its caller as the +innermost remaining frame. That frame becomes selected. The +specified value is stored in the registers used for returning values +of functions. + +The @code{return} command does not resume execution; it leaves the +program stopped in the state that would exist if the function had just +returned. In contrast, the @code{finish} command (@pxref{Continuing +and Stepping, ,Continuing and stepping}) resumes execution until the +selected stack frame returns naturally. + +@node Calling, Patching, Returning, Altering +@section Calling program functions + +@cindex calling functions +@kindex call +@table @code +@item call @var{expr} +Evaluate the expression @var{expr} without displaying @code{void} +returned values. +@end table + +You can use this variant of the @code{print} command if you want to +execute a function from your program, but without cluttering the output +with @code{void} returned values. If the result is not void, it +is printed and saved in the value history. + +@ifclear HPPA +For the A29K, a user-controlled variable @code{call_scratch_address}, +specifies the location of a scratch area to be used when @value{GDBN} +calls a function in the target. This is necessary because the usual +method of putting the scratch area on the stack does not work in systems +that have separate instruction and data spaces. +@end ifclear + +@node Patching, , Calling, Altering +@section Patching programs +@cindex patching binaries +@cindex writing into executables +@ifclear BARETARGET +@cindex writing into corefiles +@end ifclear + +By default, @value{GDBN} opens the file containing your program's executable +code +@ifclear BARETARGET +(or the corefile) +@end ifclear +read-only. This prevents accidental alterations +to machine code; but it also prevents you from intentionally patching +your program's binary. + +If you'd like to be able to patch the binary, you can specify that +explicitly with the @code{set write} command. For example, you might +want to turn on internal debugging flags, or even to make emergency +repairs. + +@table @code +@kindex set write +@item set write on +@itemx set write off +If you specify @samp{set write on}, @value{GDBN} opens executable +@ifclear BARETARGET +and core +@end ifclear +files for both reading and writing; if you specify @samp{set write +off} (the default), @value{GDBN} opens them read-only. + +If you have already loaded a file, you must load it again (using the +@code{exec-file} +@ifclear BARETARGET +or @code{core-file} +@end ifclear +command) after changing @code{set write}, for your new setting to take +effect. + +@item show write +@kindex show write +Display whether executable files +@ifclear BARETARGET +and core files +@end ifclear +are opened for writing as well as reading. +@end table + +@node GDB Files, Targets, Altering, Top +@chapter @value{GDBN} Files + +@value{GDBN} needs to know the file name of the program to be debugged, both in +order to read its symbol table and in order to start your program. +@ifclear BARETARGET +To debug a core dump of a previous run, you must also tell @value{GDBN} +the name of the core dump file. +@end ifclear + +@menu +* Files:: Commands to specify files +* Symbol Errors:: Errors reading symbol files +@end menu + +@node Files, Symbol Errors, GDB Files, GDB Files +@section Commands to specify files +@cindex symbol table + +@ifclear BARETARGET +@cindex core dump file +You may want to specify executable and core dump file names. +The usual way to do this is at start-up time, using the arguments to +@value{GDBN}'s start-up commands (@pxref{Invocation, , +Getting In and Out of @value{GDBN}}). +@end ifclear +@ifset BARETARGET +The usual way to specify an executable file name is with +the command argument given when you start @value{GDBN}, (@pxref{Invocation, +,Getting In and Out of @value{GDBN}}. +@end ifset + +Occasionally it is necessary to change to a different file during a +@value{GDBN} session. Or you may run @value{GDBN} and forget to specify +a file you want to use. In these situations the @value{GDBN} commands +to specify new files are useful. + +@table @code +@cindex executable file +@kindex file +@item file @var{filename} +Use @var{filename} as the program to be debugged. It is read for its +symbols and for the contents of pure memory. It is also the program +executed when you use the @code{run} command. If you do not specify a +directory and the file is not found in the @value{GDBN} working directory, +@value{GDBN} uses the environment variable @code{PATH} as a list of +directories to search, just as the shell does when looking for a program +to run. You can change the value of this variable, for both @value{GDBN} +and your program, using the @code{path} command. + +@ifclear HPPA +On systems with memory-mapped files, an auxiliary file +@file{@var{filename}.syms} may hold symbol table information for +@var{filename}. If so, @value{GDBN} maps in the symbol table from +@file{@var{filename}.syms}, starting up more quickly. See the +descriptions of the file options @samp{-mapped} and @samp{-readnow} +(available on the command line, and with the commands @code{file}, +@code{symbol-file}, or @code{add-symbol-file}, described below), +for more information. +@end ifclear + +@item file +@code{file} with no argument makes @value{GDBN} discard any information it +has on both executable file and the symbol table. + +@kindex exec-file +@item exec-file @r{[} @var{filename} @r{]} +Specify that the program to be run (but not the symbol table) is found +in @var{filename}. @value{GDBN} searches the environment variable @code{PATH} +if necessary to locate your program. Omitting @var{filename} means to +discard information on the executable file. + +@kindex symbol-file +@item symbol-file @r{[} @var{filename} @r{]} +Read symbol table information from file @var{filename}. @code{PATH} is +searched when necessary. Use the @code{file} command to get both symbol +table and program to run from the same file. + +@code{symbol-file} with no argument clears out @value{GDBN} information on your +program's symbol table. + +The @code{symbol-file} command causes @value{GDBN} to forget the contents +of its convenience variables, the value history, and all breakpoints and +auto-display expressions. This is because they may contain pointers to +the internal data recording symbols and data types, which are part of +the old symbol table data being discarded inside @value{GDBN}. + +@code{symbol-file} does not repeat if you press @key{RET} again after +executing it once. + +When @value{GDBN} is configured for a particular environment, it +understands debugging information in whatever format is the standard +generated for that environment; you may use either a @sc{gnu} compiler, or +other compilers that adhere to the local conventions. +@ifclear HPPA +Best results are usually obtained from @sc{gnu} compilers; for example, +using @code{@value{GCC}} you can generate debugging information for +optimized code. +@end ifclear + +For most kinds of object files, with the exception of old SVR3 systems +using COFF, the @code{symbol-file} command does not normally read the +symbol table in full right away. Instead, it scans the symbol table +quickly to find which source files and which symbols are present. The +details are read later, one source file at a time, as they are needed. + +The purpose of this two-stage reading strategy is to make @value{GDBN} +start up faster. For the most part, it is invisible except for +occasional pauses while the symbol table details for a particular source +file are being read. (The @code{set verbose} command can turn these +pauses into messages if desired. @xref{Messages/Warnings, ,Optional +warnings and messages}.) + +@ifclear HPPA +We have not implemented the two-stage strategy for COFF yet. When the +symbol table is stored in COFF format, @code{symbol-file} reads the +symbol table data in full right away. Note that ``stabs-in-COFF'' +still does the two-stage strategy, since the debug info is actually +in stabs format. + +@kindex readnow +@cindex reading symbols immediately +@cindex symbols, reading immediately +@kindex mapped +@cindex memory-mapped symbol file +@cindex saving symbol table +@item symbol-file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]} +@itemx file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]} +You can override the @value{GDBN} two-stage strategy for reading symbol +tables by using the @samp{-readnow} option with any of the commands that +load symbol table information, if you want to be sure @value{GDBN} has the +entire symbol table available. +@end ifclear + +@ifclear BARETARGET +@ifclear HPPA +If memory-mapped files are available on your system through the +@code{mmap} system call, you can use another option, @samp{-mapped}, to +cause @value{GDBN} to write the symbols for your program into a reusable +file. Future @value{GDBN} debugging sessions map in symbol information +from this auxiliary symbol file (if the program has not changed), rather +than spending time reading the symbol table from the executable +program. Using the @samp{-mapped} option has the same effect as +starting @value{GDBN} with the @samp{-mapped} command-line option. + +You can use both options together, to make sure the auxiliary symbol +file has all the symbol information for your program. + +The auxiliary symbol file for a program called @var{myprog} is called +@samp{@var{myprog}.syms}. Once this file exists (so long as it is newer +than the corresponding executable), @value{GDBN} always attempts to use +it when you debug @var{myprog}; no special options or commands are +needed. + +The @file{.syms} file is specific to the host machine where you run +@value{GDBN}. It holds an exact image of the internal @value{GDBN} +symbol table. It cannot be shared across multiple host platforms. +@end ifclear + +@c FIXME: for now no mention of directories, since this seems to be in +@c flux. 13mar1992 status is that in theory GDB would look either in +@c current dir or in same dir as myprog; but issues like competing +@c GDB's, or clutter in system dirs, mean that in practice right now +@c only current dir is used. FFish says maybe a special GDB hierarchy +@c (eg rooted in val of env var GDBSYMS) could exist for mappable symbol +@c files. + +@kindex core +@kindex core-file +@item core-file @r{[} @var{filename} @r{]} +Specify the whereabouts of a core dump file to be used as the ``contents +of memory''. Traditionally, core files contain only some parts of the +address space of the process that generated them; @value{GDBN} can access the +executable file itself for other parts. + +@code{core-file} with no argument specifies that no core file is +to be used. + +Note that the core file is ignored when your program is actually running +under @value{GDBN}. So, if you have been running your program and you wish to +debug a core file instead, you must kill the subprocess in which the +program is running. To do this, use the @code{kill} command +(@pxref{Kill Process, ,Killing the child process}). +@end ifclear + +@ifclear BARETARGET +@ifclear HPPA +@kindex add-symbol-file +@cindex dynamic linking +@item add-symbol-file @var{filename} @var{address} +@itemx add-symbol-file @var{filename} @var{address} @r{[} -readnow @r{]} @r{[} -mapped @r{]} +The @code{add-symbol-file} command reads additional symbol table information +from the file @var{filename}. You would use this command when @var{filename} +has been dynamically loaded (by some other means) into the program that +is running. @var{address} should be the memory address at which the +file has been loaded; @value{GDBN} cannot figure this out for itself. +You can specify @var{address} as an expression. + +The symbol table of the file @var{filename} is added to the symbol table +originally read with the @code{symbol-file} command. You can use the +@code{add-symbol-file} command any number of times; the new symbol data thus +read keeps adding to the old. To discard all old symbol data instead, +use the @code{symbol-file} command. + +@code{add-symbol-file} does not repeat if you press @key{RET} after using it. + +You can use the @samp{-mapped} and @samp{-readnow} options just as with +the @code{symbol-file} command, to change how @value{GDBN} manages the symbol +table information for @var{filename}. + +@kindex add-shared-symbol-file +@item add-shared-symbol-file +The @code{add-shared-symbol-file} command can be used only under Harris' CXUX +operating system for the Motorola 88k. @value{GDBN} automatically looks for +shared libraries, however if @value{GDBN} does not find yours, you can run +@code{add-shared-symbol-file}. It takes no arguments. +@end ifclear +@end ifclear + +@ifclear HPPA +@kindex section +@item section +The @code{section} command changes the base address of section SECTION of +the exec file to ADDR. This can be used if the exec file does not contain +section addresses, (such as in the a.out format), or when the addresses +specified in the file itself are wrong. Each section must be changed +separately. The ``info files'' command lists all the sections and their +addresses. +@end ifclear + +@kindex info files +@kindex info target +@item info files +@itemx info target +@code{info files} and @code{info target} are synonymous; both print +the current target (@pxref{Targets, ,Specifying a Debugging Target}), +including the +@ifclear BARETARGET +names of the executable and core dump files +@end ifclear +@ifset BARETARGET +name of the executable file +@end ifset +currently in use by @value{GDBN}, and the files from which symbols were +loaded. The command @code{help target} lists all possible targets +rather than current ones. +@end table + +All file-specifying commands allow both absolute and relative file names +as arguments. @value{GDBN} always converts the file name to an absolute file +name and remembers it that way. + +@ifclear BARETARGET +@cindex shared libraries +@ifclear HPPA +@c added HP-UX -- Kim (HP writer) +@value{GDBN} supports HP-UX, SunOS, SVr4, Irix 5, and IBM RS/6000 shared +libraries. +@end ifclear +@ifset HPPA +@value{GDBN} supports HP-UX shared libraries. +@end ifset +@value{GDBN} automatically loads symbol definitions from shared libraries +when you use the @code{run} command, or when you examine a core file. +(Before you issue the @code{run} command, @value{GDBN} does not understand +references to a function in a shared library, however---unless you are +debugging a core file). +@ifset HPPA +If the program loads a library explicitly, @value{GDBN} automatically +loads the symbols at the time of the @code{shl_load} call. +@end ifset +@c FIXME: some @value{GDBN} release may permit some refs to undef +@c FIXME...symbols---eg in a break cmd---assuming they are from a shared +@c FIXME...lib; check this from time to time when updating manual + +@table @code +@kindex info sharedlibrary +@kindex info share +@item info share +@itemx info sharedlibrary +Print the names of the shared libraries which are currently loaded. + +@kindex sharedlibrary +@kindex share +@item sharedlibrary @var{regex} +@itemx share @var{regex} + +Load shared object library symbols for files matching a +Unix regular expression. +As with files loaded automatically, it only loads shared libraries +required by your program for a core file or after typing @code{run}. If +@var{regex} is omitted all shared libraries required by your program are +loaded. +@end table + +@ifset HPPA +@value{GDBN} detects the loading of a shared library and automatically +reads in symbols from the newly loaded library, up to a threshold that +is initially set but that you can modify if you wish. + +Beyond that threshold, symbols from shared libraries must be explicitly +loaded. To load these symbols, use the command @code{sharedlibrary} +@var{filename}. The base address of the shared library is determined +automatically by @value{GDBN} and need not be specified. + +To display or set the threshold, use the commands: + +@table @code +@kindex set auto-solib-add +@item set auto-solib-add @var{threshold} +Set the autoloading size threshold, in megabytes. If @var{threshold} is +nonzero, symbols from all shared object libraries will be loaded +automatically when the inferior begins execution or when the dynamic +linker informs @value{GDBN} that a new library has been loaded, until +the symbol table of the program and libraries exceeds this threshold. +Otherwise, symbols must be loaded manually, using the +@code{sharedlibrary} command. The default threshold is 100 megabytes. + +@kindex show auto-solib-add +@item show auto-solib-add +Display the current autoloading size threshold, in megabytes. +@end table +@end ifset + +@end ifclear + +@node Symbol Errors, , Files, GDB Files +@section Errors reading symbol files + +While reading a symbol file, @value{GDBN} occasionally encounters problems, +such as symbol types it does not recognize, or known bugs in compiler +output. By default, @value{GDBN} does not notify you of such problems, since +they are relatively common and primarily of interest to people +debugging compilers. If you are interested in seeing information +about ill-constructed symbol tables, you can either ask @value{GDBN} to print +only one message about each such type of problem, no matter how many +times the problem occurs; or you can ask @value{GDBN} to print more messages, +to see how many times the problems occur, with the @code{set +complaints} command (@pxref{Messages/Warnings, ,Optional warnings and +messages}). + +The messages currently printed, and their meanings, include: + +@table @code +@item inner block not inside outer block in @var{symbol} + +The symbol information shows where symbol scopes begin and end +(such as at the start of a function or a block of statements). This +error indicates that an inner scope block is not fully contained +in its outer scope blocks. + +@value{GDBN} circumvents the problem by treating the inner block as if it had +the same scope as the outer block. In the error message, @var{symbol} +may be shown as ``@code{(don't know)}'' if the outer block is not a +function. + +@item block at @var{address} out of order + +The symbol information for symbol scope blocks should occur in +order of increasing addresses. This error indicates that it does not +do so. + +@value{GDBN} does not circumvent this problem, and has trouble +locating symbols in the source file whose symbols it is reading. (You +can often determine what source file is affected by specifying +@code{set verbose on}. @xref{Messages/Warnings, ,Optional warnings and +messages}.) + +@item bad block start address patched + +The symbol information for a symbol scope block has a start address +smaller than the address of the preceding source line. This is known +to occur in the SunOS 4.1.1 (and earlier) C compiler. + +@value{GDBN} circumvents the problem by treating the symbol scope block as +starting on the previous source line. + +@item bad string table offset in symbol @var{n} + +@cindex foo +Symbol number @var{n} contains a pointer into the string table which is +larger than the size of the string table. + +@value{GDBN} circumvents the problem by considering the symbol to have the +name @code{foo}, which may cause other problems if many symbols end up +with this name. + +@item unknown symbol type @code{0x@var{nn}} + +The symbol information contains new data types that @value{GDBN} does not yet +know how to read. @code{0x@var{nn}} is the symbol type of the misunderstood +information, in hexadecimal. + +@value{GDBN} circumvents the error by ignoring this symbol information. This +usually allows you to debug your program, though certain symbols +are not accessible. If you encounter such a problem and feel like +debugging it, you can debug @code{@value{GDBP}} with itself, breakpoint on +@code{complain}, then go up to the function @code{read_dbx_symtab} and +examine @code{*bufp} to see the symbol. + +@item stub type has NULL name +@value{GDBN} could not find the full definition for +@ifclear CONLY +a struct or class. +@end ifclear +@ifset CONLY +a struct. +@end ifset + +@ifclear CONLY +@item const/volatile indicator missing (ok if using g++ v1.x), got@dots{} + +The symbol information for a C++ member function is missing some +information that recent versions of the compiler should have output +for it. +@end ifclear + +@item info mismatch between compiler and debugger + +@value{GDBN} could not parse a type specification output by the compiler. +@end table + +@node Targets, Controlling GDB, GDB Files, Top +@chapter Specifying a Debugging Target +@cindex debugging target +@kindex target + +A @dfn{target} is the execution environment occupied by your program. +@ifclear HPPA +@ifclear BARETARGET +Often, @value{GDBN} runs in the same host environment as your program; in +that case, the debugging target is specified as a side effect when you +use the @code{file} or @code{core} commands. When you need more +flexibility---for example, running @value{GDBN} on a physically separate +host, or controlling a standalone system over a serial port or a +realtime system over a TCP/IP connection---you +@end ifclear +@end ifclear +@ifset HPPA +On HP-UX systems, @value{GDBN} has been configured to support debugging +of processes running on the PA-RISC architecture. This means that the +only possible targets are: + +@itemize @bullet +@item +An executable that has been compiled and linked to run on HP-UX + +@item +A live HP-UX process, either started by @value{GDBN} (with the +@code{run} command) or started outside of @value{GDBN} and attached to +(with the @code{attach} command) + +@item +A core file generated by an HP-UX process that previously aborted +execution +@end itemize + +@value{GDBN} on HP-UX has not been configured to support remote +debugging, or to support programs running on other platforms. You +@end ifset +@ifset BARETARGET +You +@end ifset +can use the @code{target} command to specify one of the target types +configured for @value{GDBN} (@pxref{Target Commands, ,Commands for managing +targets}). + +@menu +* Active Targets:: Active targets +* Target Commands:: Commands for managing targets +@ifset REMOTESTUB +* Byte Order:: Choosing target byte order +* Remote:: Remote debugging +@end ifset + +@end menu + +@node Active Targets, Target Commands, Targets, Targets +@section Active targets +@cindex stacking targets +@cindex active targets +@cindex multiple targets + +@ifclear BARETARGET +There are three classes of targets: processes, core files, and +executable files. @value{GDBN} can work concurrently on up to three active +targets, one in each class. This allows you to (for example) start a +process and inspect its activity without abandoning your work on a core +file. + +For example, if you execute @samp{gdb a.out}, then the executable file +@code{a.out} is the only active target. If you designate a core file as +well---presumably from a prior run that crashed and coredumped---then +@value{GDBN} has two active targets and uses them in tandem, looking +first in the corefile target, then in the executable file, to satisfy +requests for memory addresses. (Typically, these two classes of target +are complementary, since core files contain only a program's +read-write memory---variables and so on---plus machine status, while +executable files contain only the program text and initialized data.) +@end ifclear + +When you type @code{run}, your executable file becomes an active process +target as well. When a process target is active, all @value{GDBN} commands +requesting memory addresses refer to that target; addresses in an +@ifclear BARETARGET +active core file or +@end ifclear +executable file target are obscured while the process +target is active. + +@ifset BARETARGET +Use the @code{exec-file} command to select a +new executable target (@pxref{Files, ,Commands to specify +files}). +@end ifset +@ifclear BARETARGET +Use the @code{core-file} and @code{exec-file} commands to select a +new core file or executable target (@pxref{Files, ,Commands to specify +files}). To specify as a target a process that is already running, use +the @code{attach} command (@pxref{Attach, ,Debugging an +already-running process}). +@end ifclear + +@node Target Commands, Byte Order, Active Targets, Targets +@section Commands for managing targets + +@table @code +@item target @var{type} @var{parameters} +Connects the @value{GDBN} host environment to a target +@ifset BARETARGET +machine. +@end ifset +@ifclear BARETARGET +machine or process. A target is typically a protocol for talking to +debugging facilities. You use the argument @var{type} to specify the +type or protocol of the target machine. + +Further @var{parameters} are interpreted by the target protocol, but +typically include things like device names or host names to connect +with, process numbers, and baud rates. +@end ifclear + +The @code{target} command does not repeat if you press @key{RET} again +after executing the command. + +@kindex help target +@item help target +Displays the names of all targets available. To display targets +currently selected, use either @code{info target} or @code{info files} +(@pxref{Files, ,Commands to specify files}). + +@item help target @var{name} +Describe a particular target, including any parameters necessary to +select it. + +@kindex set gnutarget +@item set gnutarget @var{args} +@value{GDBN} uses its own library BFD to read your files. @value{GDBN} +knows whether it is reading an @dfn{executable}, +a @dfn{core}, or a @dfn{.o} file; however, you can specify the file format +with the @code{set gnutarget} command. Unlike most @code{target} commands, +with @code{gnutarget} the @code{target} refers to a program, not a machine. + +@emph{Warning:} To specify a file format with @code{set gnutarget}, +you must know the actual BFD name. + +@noindent @xref{Files, , Commands to specify files}. + +@kindex show gnutarget +@item show gnutarget +Use the @code{show gnutarget} command to display what file format +@code{gnutarget} is set to read. If you have not set @code{gnutarget}, +@value{GDBN} will determine the file format for each file automatically, +and @code{show gnutarget} displays @samp{The current BDF target is "auto"}. +@end table + +@ifclear HPPA +Here are some common targets (available, or not, depending on the GDB +configuration): +@end ifclear +@ifset HPPA +These are the valid targets on HP-UX systems: +@end ifset + +@table @code +@kindex target exec +@item target exec @var{program} +An executable file. @samp{target exec @var{program}} is the same as +@samp{exec-file @var{program}}. + +@ifclear BARETARGET +@kindex target core +@item target core @var{filename} +A core dump file. @samp{target core @var{filename}} is the same as +@samp{core-file @var{filename}}. +@end ifclear + +@kindex target remote +@item target remote @var{dev} +Remote serial target in GDB-specific protocol. The argument @var{dev} +specifies what serial device to use for the connection (e.g. +@file{/dev/ttya}). @xref{Remote, ,Remote debugging}. @code{target remote} +now supports the @code{load} command. This is only useful if you have +some other way of getting the stub to the target system, and you can put +it somewhere in memory where it won't get clobbered by the download. + +@ifclear HPPA +@kindex target sim +@item target sim +CPU simulator. @xref{Simulator,,Simulated CPU Target}. +@end ifclear +@end table + +The following targets are all CPU-specific, and only available for +specific configurations. +@c should organize by CPU + +@table @code + +@kindex target abug +@item target abug @var{dev} +ABug ROM monitor for M68K. + +@kindex target adapt +@item target adapt @var{dev} +Adapt monitor for A29K. + +@kindex target amd-eb +@item target amd-eb @var{dev} @var{speed} @var{PROG} +@cindex AMD EB29K +Remote PC-resident AMD EB29K board, attached over serial lines. +@var{dev} is the serial device, as for @code{target remote}; +@var{speed} allows you to specify the linespeed; and @var{PROG} is the +name of the program to be debugged, as it appears to DOS on the PC. +@xref{EB29K Remote, ,The EBMON protocol for AMD29K}. + +@kindex target array +@item target array @var{dev} +Array Tech LSI33K RAID controller board. + +@kindex target bug +@item target bug @var{dev} +BUG monitor, running on a MVME187 (m88k) board. + +@kindex target cpu32bug +@item target cpu32bug @var{dev} +CPU32BUG monitor, running on a CPU32 (M68K) board. + +@kindex target dbug +@item target dbug @var{dev} +dBUG ROM monitor for Motorola ColdFire. + +@kindex target ddb +@item target ddb @var{dev} +NEC's DDB monitor for Mips Vr4300. + +@kindex target dink32 +@item target dink32 @var{dev} +DINK32 ROM monitor for PowerPC. + +@kindex target e7000 +@item target e7000 @var{dev} +E7000 emulator for Hitachi H8 and SH. + +@kindex target es1800 +@item target es1800 @var{dev} +ES-1800 emulator for M68K. + +@kindex target est +@item target est @var{dev} +EST-300 ICE monitor, running on a CPU32 (M68K) board. + +@kindex target hms +@item target hms @var{dev} +A Hitachi SH, H8/300, or H8/500 board, attached via serial line to your host. +@ifclear H8EXCLUSIVE +Use special commands @code{device} and @code{speed} to control the serial +line and the communications speed used. +@xref{Hitachi Remote,,@value{GDBN} and Hitachi Microprocessors}. + +@kindex target lsi +@item target lsi @var{dev} +LSI ROM monitor for Mips. + +@kindex target m32r +@item target m32r @var{dev} +Mitsubishi M32R/D ROM monitor. + +@kindex target mips +@item target mips @var{dev} +IDT/SIM ROM monitor for Mips. + +@kindex target mon960 +@item target mon960 @var{dev} +MON960 monitor for Intel i960. + +@kindex target nindy +@item target nindy @var{devicename} +An Intel 960 board controlled by a Nindy Monitor. @var{devicename} is +the name of the serial device to use for the connection, e.g. +@file{/dev/ttya}. @xref{i960-Nindy Remote, ,@value{GDBN} with a remote i960 (Nindy)}. + +@kindex target nrom +@item target nrom @var{dev} +NetROM ROM emulator. This target only supports downloading. + +@kindex target op50n +@item target op50n @var{dev} +OP50N monitor, running on an OKI HPPA board. + +@kindex target pmon +@item target pmon @var{dev} +PMON ROM monitor for Mips. + +@kindex target ppcbug +@item target ppcbug @var{dev} +@kindex target ppcbug1 +@item target ppcbug1 @var{dev} +PPCBUG ROM monitor for PowerPC. + +@kindex target r3900 +@item target r3900 @var{dev} +Densan DVE-R3900 ROM monitor for Toshiba R3900 Mips. + +@kindex target rdi +@item target rdi @var{dev} +ARM Angel monitor, via RDI library interface. + +@kindex target rdp +@item target rdp @var{dev} +ARM Demon monitor. + +@kindex target rom68k +@item target rom68k @var{dev} +ROM 68K monitor, running on an M68K IDP board. + +@kindex target rombug +@item target rombug @var{dev} +ROMBUG ROM monitor for OS/9000. + +@kindex target sds +@item target sds @var{dev} +SDS monitor, running on a PowerPC board (such as Motorola's ADS). + +@kindex target sparclite +@item target sparclite @var{dev} +Fujitsu sparclite boards, used only for the purpose of loading. +You must use an additional command to debug the program. +For example: target remote @var{dev} using @value{GDBN} standard +remote protocol. + +@kindex target sh3 +@kindex target sh3e +@item target sh3 @var{dev} +@item target sh3e @var{dev} +Hitachi SH-3 and SH-3E target systems. + +@kindex target st2000 +@item target st2000 @var{dev} @var{speed} +A Tandem ST2000 phone switch, running Tandem's STDBUG protocol. @var{dev} +is the name of the device attached to the ST2000 serial line; +@var{speed} is the communication line speed. The arguments are not used +if @value{GDBN} is configured to connect to the ST2000 using TCP or Telnet. +@xref{ST2000 Remote,,@value{GDBN} with a Tandem ST2000}. + +@kindex target udi +@item target udi @var{keyword} +Remote AMD29K target, using the AMD UDI protocol. The @var{keyword} +argument specifies which 29K board or simulator to use. @xref{UDI29K +Remote,,The UDI protocol for AMD29K}. + +@kindex target vxworks +@item target vxworks @var{machinename} +A VxWorks system, attached via TCP/IP. The argument @var{machinename} +is the target system's machine name or IP address. +@xref{VxWorks Remote, ,@value{GDBN} and VxWorks}. + +@kindex target w89k +@item target w89k @var{dev} +W89K monitor, running on a Winbond HPPA board. + +@end ifclear +@end table + +@ifset GENERIC +Different targets are available on different configurations of @value{GDBN}; +your configuration may have more or fewer targets. +@end ifset + +Many remote targets require you to download the executable's code +once you've successfully established a connection. + +@table @code + +@kindex load @var{filename} +@item load @var{filename} +@ifset GENERIC +Depending on what remote debugging facilities are configured into +@value{GDBN}, the @code{load} command may be available. Where it exists, it +is meant to make @var{filename} (an executable) available for debugging +on the remote system---by downloading, or dynamic linking, for example. +@code{load} also records the @var{filename} symbol table in @value{GDBN}, like +the @code{add-symbol-file} command. + +If your @value{GDBN} does not have a @code{load} command, attempting to +execute it gets the error message ``@code{You can't do that when your +target is @dots{}}'' +@end ifset + +The file is loaded at whatever address is specified in the executable. +For some object file formats, you can specify the load address when you +link the program; for other formats, like a.out, the object file format +specifies a fixed address. +@c FIXME! This would be a good place for an xref to the GNU linker doc. + +@ifset VXWORKS +On VxWorks, @code{load} links @var{filename} dynamically on the +current target system as well as adding its symbols in @value{GDBN}. +@end ifset + +@ifset I960 +@cindex download to Nindy-960 +With the Nindy interface to an Intel 960 board, @code{load} +downloads @var{filename} to the 960 as well as adding its symbols in +@value{GDBN}. +@end ifset + +@ifset H8 +@cindex download to H8/300 or H8/500 +@cindex H8/300 or H8/500 download +@cindex download to Hitachi SH +@cindex Hitachi SH download +When you select remote debugging to a Hitachi SH, H8/300, or H8/500 board +(@pxref{Hitachi Remote,,@value{GDBN} and Hitachi Microprocessors}), +the @code{load} command downloads your program to the Hitachi board and also +opens it as the current executable target for @value{GDBN} on your host +(like the @code{file} command). +@end ifset + +@code{load} does not repeat if you press @key{RET} again after using it. +@end table + +@ifset REMOTESTUB +@node Byte Order, Remote, Target Commands, Targets +@section Choosing target byte order +@cindex choosing target byte order +@cindex target byte order +@kindex set endian big +@kindex set endian little +@kindex set endian auto +@kindex show endian + +Some types of processors, such as the MIPS, PowerPC, and Hitachi SH, +offer the ability to run either big-endian or little-endian byte +orders. Usually the executable or symbol will include a bit to +designate the endian-ness, and you will not need to worry about +which to use. However, you may still find it useful to adjust +GDB's idea of processor endian-ness manually. + +@table @code +@kindex set endian big +@item set endian big +Instruct @value{GDBN} to assume the target is big-endian. + +@kindex set endian little +@item set endian little +Instruct @value{GDBN} to assume the target is little-endian. + +@kindex set endian auto +@item set endian auto +Instruct @value{GDBN} to use the byte order associated with the +executable. + +@item show endian +Display @value{GDBN}'s current idea of the target byte order. + +@end table + +Note that these commands merely adjust interpretation of symbolic +data on the host, and that they have absolutely no effect on the +target system. + +@node Remote, , Byte Order, Targets +@section Remote debugging +@cindex remote debugging + +If you are trying to debug a program running on a machine that cannot run +@value{GDBN} in the usual way, it is often useful to use remote debugging. +For example, you might use remote debugging on an operating system kernel, +or on a small system which does not have a general purpose operating system +powerful enough to run a full-featured debugger. + +Some configurations of @value{GDBN} have special serial or TCP/IP interfaces +to make this work with particular debugging targets. In addition, +@value{GDBN} comes with a generic serial protocol (specific to @value{GDBN}, +but not specific to any particular target system) which you can use if you +write the remote stubs---the code that runs on the remote system to +communicate with @value{GDBN}. + +Other remote targets may be available in your +configuration of @value{GDBN}; use @code{help target} to list them. +@end ifset + +@ifset GENERIC +@c Text on starting up GDB in various specific cases; it goes up front +@c in manuals configured for any of those particular situations, here +@c otherwise. +@menu +@ifset REMOTESTUB +* Remote Serial:: @value{GDBN} remote serial protocol +@end ifset +@ifset I960 +* i960-Nindy Remote:: @value{GDBN} with a remote i960 (Nindy) +@end ifset +@ifset AMD29K +* UDI29K Remote:: The UDI protocol for AMD29K +* EB29K Remote:: The EBMON protocol for AMD29K +@end ifset +@ifset VXWORKS +* VxWorks Remote:: @value{GDBN} and VxWorks +@end ifset +@ifset ST2000 +* ST2000 Remote:: @value{GDBN} with a Tandem ST2000 +@end ifset +@ifset H8 +* Hitachi Remote:: @value{GDBN} and Hitachi Microprocessors +@end ifset +@ifset MIPS +* MIPS Remote:: @value{GDBN} and MIPS boards +@end ifset +@ifset SPARCLET +* Sparclet Remote:: @value{GDBN} and Sparclet boards +@end ifset +@ifset SIMS +* Simulator:: Simulated CPU target +@end ifset +@end menu + +@include remote.texi +@end ifset + +@node Controlling GDB +@chapter Controlling @value{GDBN} + +You can alter the way @value{GDBN} interacts with you by using +the @code{set} command. For commands controlling how @value{GDBN} displays +data, @pxref{Print Settings, ,Print settings}; other settings are described +here. + +@menu +* Prompt:: Prompt +* Editing:: Command editing +* History:: Command history +* Screen Size:: Screen size +* Numbers:: Numbers +* Messages/Warnings:: Optional warnings and messages +@end menu + +@node Prompt, Editing, Controlling GDB, Controlling GDB +@section Prompt + +@cindex prompt + +@value{GDBN} indicates its readiness to read a command by printing a string +called the @dfn{prompt}. This string is normally @samp{(@value{GDBP})}. You +can change the prompt string with the @code{set prompt} command. For +instance, when debugging @value{GDBN} with @value{GDBN}, it is useful to change +the prompt in one of the @value{GDBN} sessions so that you can always tell +which one you are talking to. + +@emph{Note:} @code{set prompt} no longer adds a space for you after the +prompt you set. This allows you to set a prompt which ends in a space +or a prompt that does not. + +@table @code +@kindex set prompt +@item set prompt @var{newprompt} +Directs @value{GDBN} to use @var{newprompt} as its prompt string henceforth. + +@kindex show prompt +@item show prompt +Prints a line of the form: @samp{Gdb's prompt is: @var{your-prompt}} +@end table + +@node Editing, History, Prompt, Controlling GDB +@section Command editing +@cindex readline +@cindex command line editing + +@value{GDBN} reads its input commands via the @dfn{readline} interface. This +@sc{gnu} library provides consistent behavior for programs which provide a +command line interface to the user. Advantages are @sc{gnu} Emacs-style +or @dfn{vi}-style inline editing of commands, @code{csh}-like history +substitution, and a storage and recall of command history across +debugging sessions. + +You may control the behavior of command line editing in @value{GDBN} with the +command @code{set}. + +@table @code +@kindex set editing +@cindex editing +@item set editing +@itemx set editing on +Enable command line editing (enabled by default). + +@item set editing off +Disable command line editing. + +@kindex show editing +@item show editing +Show whether command line editing is enabled. +@end table + +@node History, Screen Size, Editing, Controlling GDB +@section Command history + +@value{GDBN} can keep track of the commands you type during your +debugging sessions, so that you can be certain of precisely what +happened. Use these commands to manage the @value{GDBN} command +history facility. + +@table @code +@cindex history substitution +@cindex history file +@kindex set history filename +@kindex GDBHISTFILE +@item set history filename @var{fname} +Set the name of the @value{GDBN} command history file to @var{fname}. +This is the file where @value{GDBN} reads an initial command history +list, and where it writes the command history from this session when it +exits. You can access this list through history expansion or through +the history command editing characters listed below. This file defaults +to the value of the environment variable @code{GDBHISTFILE}, or to +@file{./.gdb_history} if this variable is not set. + +@cindex history save +@kindex set history save +@item set history save +@itemx set history save on +Record command history in a file, whose name may be specified with the +@code{set history filename} command. By default, this option is disabled. + +@item set history save off +Stop recording command history in a file. + +@cindex history size +@kindex set history size +@item set history size @var{size} +Set the number of commands which @value{GDBN} keeps in its history list. +This defaults to the value of the environment variable +@code{HISTSIZE}, or to 256 if this variable is not set. +@end table + +@cindex history expansion +History expansion assigns special meaning to the character @kbd{!}. +@ifset have-readline-appendices +@xref{Event Designators}. +@end ifset + +Since @kbd{!} is also the logical not operator in C, history expansion +is off by default. If you decide to enable history expansion with the +@code{set history expansion on} command, you may sometimes need to +follow @kbd{!} (when it is used as logical not, in an expression) with +a space or a tab to prevent it from being expanded. The readline +history facilities do not attempt substitution on the strings +@kbd{!=} and @kbd{!(}, even when history expansion is enabled. + +The commands to control history expansion are: + +@table @code +@kindex set history expansion +@item set history expansion on +@itemx set history expansion +Enable history expansion. History expansion is off by default. + +@item set history expansion off +Disable history expansion. + +The readline code comes with more complete documentation of +editing and history expansion features. Users unfamiliar with @sc{gnu} Emacs +or @code{vi} may wish to read it. +@ifset have-readline-appendices +@xref{Command Line Editing}. +@end ifset + +@c @group +@kindex show history +@item show history +@itemx show history filename +@itemx show history save +@itemx show history size +@itemx show history expansion +These commands display the state of the @value{GDBN} history parameters. +@code{show history} by itself displays all four states. +@c @end group +@end table + +@table @code +@kindex show commands +@item show commands +Display the last ten commands in the command history. + +@item show commands @var{n} +Print ten commands centered on command number @var{n}. + +@item show commands + +Print ten commands just after the commands last printed. +@end table + +@node Screen Size, Numbers, History, Controlling GDB +@section Screen size +@cindex size of screen +@cindex pauses in output + +Certain commands to @value{GDBN} may produce large amounts of +information output to the screen. To help you read all of it, +@value{GDBN} pauses and asks you for input at the end of each page of +output. Type @key{RET} when you want to continue the output, or @kbd{q} +to discard the remaining output. Also, the screen width setting +determines when to wrap lines of output. Depending on what is being +printed, @value{GDBN} tries to break the line at a readable place, +rather than simply letting it overflow onto the following line. + +Normally @value{GDBN} knows the size of the screen from the termcap data base +together with the value of the @code{TERM} environment variable and the +@code{stty rows} and @code{stty cols} settings. If this is not correct, +you can override it with the @code{set height} and @code{set +width} commands: + +@table @code +@kindex set height +@kindex set width +@kindex show width +@kindex show height +@item set height @var{lpp} +@itemx show height +@itemx set width @var{cpl} +@itemx show width +These @code{set} commands specify a screen height of @var{lpp} lines and +a screen width of @var{cpl} characters. The associated @code{show} +commands display the current settings. + +If you specify a height of zero lines, @value{GDBN} does not pause during +output no matter how long the output is. This is useful if output is to a +file or to an editor buffer. + +Likewise, you can specify @samp{set width 0} to prevent @value{GDBN} +from wrapping its output. +@end table + +@node Numbers, Messages/Warnings, Screen Size, Controlling GDB +@section Numbers +@cindex number representation +@cindex entering numbers + +You can always enter numbers in octal, decimal, or hexadecimal in @value{GDBN} by +the usual conventions: octal numbers begin with @samp{0}, decimal +numbers end with @samp{.}, and hexadecimal numbers begin with @samp{0x}. +Numbers that begin with none of these are, by default, entered in base +10; likewise, the default display for numbers---when no particular +format is specified---is base 10. You can change the default base for +both input and output with the @code{set radix} command. + +@table @code +@kindex set input-radix +@item set input-radix @var{base} +Set the default base for numeric input. Supported choices +for @var{base} are decimal 8, 10, or 16. @var{base} must itself be +specified either unambiguously or using the current default radix; for +example, any of + +@smallexample +set radix 012 +set radix 10. +set radix 0xa +@end smallexample + +@noindent +sets the base to decimal. On the other hand, @samp{set radix 10} +leaves the radix unchanged no matter what it was. + +@kindex set output-radix +@item set output-radix @var{base} +Set the default base for numeric display. Supported choices +for @var{base} are decimal 8, 10, or 16. @var{base} must itself be +specified either unambiguously or using the current default radix. + +@kindex show input-radix +@item show input-radix +Display the current default base for numeric input. + +@kindex show output-radix +@item show output-radix +Display the current default base for numeric display. +@end table + +@node Messages/Warnings, , Numbers, Controlling GDB +@section Optional warnings and messages + +By default, @value{GDBN} is silent about its inner workings. If you are running +on a slow machine, you may want to use the @code{set verbose} command. +This makes @value{GDBN} tell you when it does a lengthy internal operation, so +you will not think it has crashed. + +Currently, the messages controlled by @code{set verbose} are those +which announce that the symbol table for a source file is being read; +see @code{symbol-file} in @ref{Files, ,Commands to specify files}. + +@table @code +@kindex set verbose +@item set verbose on +Enables @value{GDBN} output of certain informational messages. + +@item set verbose off +Disables @value{GDBN} output of certain informational messages. + +@kindex show verbose +@item show verbose +Displays whether @code{set verbose} is on or off. +@end table + +By default, if @value{GDBN} encounters bugs in the symbol table of an object +file, it is silent; but if you are debugging a compiler, you may find +this information useful (@pxref{Symbol Errors, ,Errors reading symbol files}). + +@table @code +@kindex set complaints +@item set complaints @var{limit} +Permits @value{GDBN} to output @var{limit} complaints about each type of unusual +symbols before becoming silent about the problem. Set @var{limit} to +zero to suppress all complaints; set it to a large number to prevent +complaints from being suppressed. + +@kindex show complaints +@item show complaints +Displays how many symbol complaints @value{GDBN} is permitted to produce. +@end table + +By default, @value{GDBN} is cautious, and asks what sometimes seems to be a +lot of stupid questions to confirm certain commands. For example, if +you try to run a program which is already running: + +@example +(@value{GDBP}) run +The program being debugged has been started already. +Start it from the beginning? (y or n) +@end example + +If you are willing to unflinchingly face the consequences of your own +commands, you can disable this ``feature'': + +@table @code +@kindex set confirm +@cindex flinching +@cindex confirmation +@cindex stupid questions +@item set confirm off +Disables confirmation requests. + +@item set confirm on +Enables confirmation requests (the default). + +@kindex show confirm +@item show confirm +Displays state of confirmation requests. +@end table + +@node Sequences, Emacs, Controlling GDB, Top +@chapter Canned Sequences of Commands + +Aside from breakpoint commands (@pxref{Break Commands, ,Breakpoint +command lists}), @value{GDBN} provides two ways to store sequences of commands +for execution as a unit: user-defined commands and command files. + +@menu +* Define:: User-defined commands +* Hooks:: User-defined command hooks +* Command Files:: Command files +* Output:: Commands for controlled output +@end menu + +@node Define, Hooks, Sequences, Sequences +@section User-defined commands + +@cindex user-defined command +A @dfn{user-defined command} is a sequence of @value{GDBN} commands to which +you assign a new name as a command. This is done with the @code{define} +command. User commands may accept up to 10 arguments separated by whitespace. +Arguments are accessed within the user command via @var{$arg0@dots{}$arg9}. +A trivial example: + +@smallexample +define adder + print $arg0 + $arg1 + $arg2 +@end smallexample + +@noindent To execute the command use: + +@smallexample +adder 1 2 3 +@end smallexample + +@noindent This defines the command @code{adder}, which prints the sum of +its three arguments. Note the arguments are text substitutions, so they may +reference variables, use complex expressions, or even perform inferior +functions calls. + +@table @code +@kindex define +@item define @var{commandname} +Define a command named @var{commandname}. If there is already a command +by that name, you are asked to confirm that you want to redefine it. + +The definition of the command is made up of other @value{GDBN} command lines, +which are given following the @code{define} command. The end of these +commands is marked by a line containing @code{end}. + +@kindex if +@kindex else +@item if +Takes a single argument, which is an expression to evaluate. +It is followed by a series of commands that are executed +only if the expression is true (nonzero). +There can then optionally be a line @code{else}, followed +by a series of commands that are only executed if the expression +was false. The end of the list is marked by a line containing @code{end}. + +@kindex while +@item while +The syntax is similar to @code{if}: the command takes a single argument, +which is an expression to evaluate, and must be followed by the commands to +execute, one per line, terminated by an @code{end}. +The commands are executed repeatedly as long as the expression +evaluates to true. + +@kindex document +@item document @var{commandname} +Document the user-defined command @var{commandname}, so that it can be +accessed by @code{help}. The command @var{commandname} must already be +defined. This command reads lines of documentation just as @code{define} +reads the lines of the command definition, ending with @code{end}. +After the @code{document} command is finished, @code{help} on command +@var{commandname} displays the documentation you have written. + +You may use the @code{document} command again to change the +documentation of a command. Redefining the command with @code{define} +does not change the documentation. + +@kindex help user-defined +@item help user-defined +List all user-defined commands, with the first line of the documentation +(if any) for each. + +@kindex show user +@item show user +@itemx show user @var{commandname} +Display the @value{GDBN} commands used to define @var{commandname} (but not its +documentation). If no @var{commandname} is given, display the +definitions for all user-defined commands. +@end table + +When user-defined commands are executed, the +commands of the definition are not printed. An error in any command +stops execution of the user-defined command. + +If used interactively, commands that would ask for confirmation proceed +without asking when used inside a user-defined command. Many @value{GDBN} +commands that normally print messages to say what they are doing omit the +messages when used in a user-defined command. + +@node Hooks, Command Files, Define, Sequences +@section User-defined command hooks +@cindex command files + +You may define @emph{hooks}, which are a special kind of user-defined +command. Whenever you run the command @samp{foo}, if the user-defined +command @samp{hook-foo} exists, it is executed (with no arguments) +before that command. + +In addition, a pseudo-command, @samp{stop} exists. Defining +(@samp{hook-stop}) makes the associated commands execute every time +execution stops in your program: before breakpoint commands are run, +displays are printed, or the stack frame is printed. + +@ifclear BARETARGET +For example, to ignore @code{SIGALRM} signals while +single-stepping, but treat them normally during normal execution, +you could define: + +@example +define hook-stop +handle SIGALRM nopass +end + +define hook-run +handle SIGALRM pass +end + +define hook-continue +handle SIGLARM pass +end +@end example +@end ifclear + +You can define a hook for any single-word command in @value{GDBN}, but +not for command aliases; you should define a hook for the basic command +name, e.g. @code{backtrace} rather than @code{bt}. +@c FIXME! So how does Joe User discover whether a command is an alias +@c or not? +If an error occurs during the execution of your hook, execution of +@value{GDBN} commands stops and @value{GDBN} issues a prompt +(before the command that you actually typed had a chance to run). + +If you try to define a hook which does not match any known command, you +get a warning from the @code{define} command. + +@node Command Files, Output, Hooks, Sequences +@section Command files + +@cindex command files +A command file for @value{GDBN} is a file of lines that are @value{GDBN} +commands. Comments (lines starting with @kbd{#}) may also be included. +An empty line in a command file does nothing; it does not mean to repeat +the last command, as it would from the terminal. + +@cindex init file +@cindex @file{.gdbinit} +When you start @value{GDBN}, it automatically executes commands from its +@dfn{init files}. These are files named @file{.gdbinit} on Unix, or +@file{gdb.ini} on DOS/Windows. @value{GDBN} reads the init file (if +any) in your home directory, then processes command line options and +operands, and then reads the init file (if any) in the current working +directory. This is so the init file in your home directory can set +options (such as @code{set complaints}) which affect the processing of +the command line options and operands. The init files are not executed +if you use the @samp{-nx} option; @pxref{Mode Options, ,Choosing modes}. + +@ifset GENERIC +@cindex init file name +On some configurations of @value{GDBN}, the init file is known by a +different name (these are typically environments where a specialized +form of @value{GDBN} may need to coexist with other forms, hence a +different name for the specialized version's init file). These are the +environments with special init file names: + +@kindex .vxgdbinit +@itemize @bullet +@item +VxWorks (Wind River Systems real-time OS): @samp{.vxgdbinit} + +@kindex .os68gdbinit +@item +OS68K (Enea Data Systems real-time OS): @samp{.os68gdbinit} + +@kindex .esgdbinit +@item +ES-1800 (Ericsson Telecom AB M68000 emulator): @samp{.esgdbinit} +@end itemize +@end ifset + +You can also request the execution of a command file with the +@code{source} command: + +@table @code +@kindex source +@item source @var{filename} +Execute the command file @var{filename}. +@end table + +The lines in a command file are executed sequentially. They are not +printed as they are executed. An error in any command terminates execution +of the command file. + +Commands that would ask for confirmation if used interactively proceed +without asking when used in a command file. Many @value{GDBN} commands that +normally print messages to say what they are doing omit the messages +when called from command files. + +@node Output, , Command Files, Sequences +@section Commands for controlled output + +During the execution of a command file or a user-defined command, normal +@value{GDBN} output is suppressed; the only output that appears is what is +explicitly printed by the commands in the definition. This section +describes three commands useful for generating exactly the output you +want. + +@table @code +@kindex echo +@item echo @var{text} +@c I do not consider backslash-space a standard C escape sequence +@c because it is not in ANSI. +Print @var{text}. Nonprinting characters can be included in +@var{text} using C escape sequences, such as @samp{\n} to print a +newline. @strong{No newline is printed unless you specify one.} +In addition to the standard C escape sequences, a backslash followed +by a space stands for a space. This is useful for displaying a +string with spaces at the beginning or the end, since leading and +trailing spaces are otherwise trimmed from all arguments. +To print @samp{@w{ }and foo =@w{ }}, use the command +@samp{echo \@w{ }and foo = \@w{ }}. + +A backslash at the end of @var{text} can be used, as in C, to continue +the command onto subsequent lines. For example, + +@example +echo This is some text\n\ +which is continued\n\ +onto several lines.\n +@end example + +produces the same output as + +@example +echo This is some text\n +echo which is continued\n +echo onto several lines.\n +@end example + +@kindex output +@item output @var{expression} +Print the value of @var{expression} and nothing but that value: no +newlines, no @samp{$@var{nn} = }. The value is not entered in the +value history either. @xref{Expressions, ,Expressions}, for more information +on expressions. + +@item output/@var{fmt} @var{expression} +Print the value of @var{expression} in format @var{fmt}. You can use +the same formats as for @code{print}. @xref{Output Formats,,Output +formats}, for more information. + +@kindex printf +@item printf @var{string}, @var{expressions}@dots{} +Print the values of the @var{expressions} under the control of +@var{string}. The @var{expressions} are separated by commas and may be +either numbers or pointers. Their values are printed as specified by +@var{string}, exactly as if your program were to execute the C +subroutine + +@example +printf (@var{string}, @var{expressions}@dots{}); +@end example + +For example, you can print two values in hex like this: + +@smallexample +printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo +@end smallexample + +The only backslash-escape sequences that you can use in the format +string are the simple ones that consist of backslash followed by a +letter. +@end table + +@ifclear DOSHOST +@node Emacs, GDB Bugs, Sequences, Top +@chapter Using @value{GDBN} under @sc{gnu} Emacs + +@cindex Emacs +@cindex @sc{gnu} Emacs +A special interface allows you to use @sc{gnu} Emacs to view (and +edit) the source files for the program you are debugging with +@value{GDBN}. + +To use this interface, use the command @kbd{M-x gdb} in Emacs. Give the +executable file you want to debug as an argument. This command starts +@value{GDBN} as a subprocess of Emacs, with input and output through a newly +created Emacs buffer. +@ifset HPPA +(Do not use the @code{-tui} option to run @value{GDBN} from Emacs.) +@end ifset + +Using @value{GDBN} under Emacs is just like using @value{GDBN} normally except for two +things: + +@itemize @bullet +@item +All ``terminal'' input and output goes through the Emacs buffer. +@end itemize + +This applies both to @value{GDBN} commands and their output, and to the input +and output done by the program you are debugging. + +This is useful because it means that you can copy the text of previous +commands and input them again; you can even use parts of the output +in this way. + +All the facilities of Emacs' Shell mode are available for interacting +with your program. In particular, you can send signals the usual +way---for example, @kbd{C-c C-c} for an interrupt, @kbd{C-c C-z} for a +stop. + +@itemize @bullet +@item +@value{GDBN} displays source code through Emacs. +@end itemize + +Each time @value{GDBN} displays a stack frame, Emacs automatically finds the +source file for that frame and puts an arrow (@samp{=>}) at the +left margin of the current line. Emacs uses a separate buffer for +source display, and splits the screen to show both your @value{GDBN} session +and the source. + +Explicit @value{GDBN} @code{list} or search commands still produce output as +usual, but you probably have no reason to use them from Emacs. + +@quotation +@emph{Warning:} If the directory where your program resides is not your +current directory, it can be easy to confuse Emacs about the location of +the source files, in which case the auxiliary display buffer does not +appear to show your source. @value{GDBN} can find programs by searching your +environment's @code{PATH} variable, so the @value{GDBN} input and output +session proceeds normally; but Emacs does not get enough information +back from @value{GDBN} to locate the source files in this situation. To +avoid this problem, either start @value{GDBN} mode from the directory where +your program resides, or specify an absolute file name when prompted for the +@kbd{M-x gdb} argument. + +A similar confusion can result if you use the @value{GDBN} @code{file} command to +switch to debugging a program in some other location, from an existing +@value{GDBN} buffer in Emacs. +@end quotation + +By default, @kbd{M-x gdb} calls the program called @file{gdb}. If +you need to call @value{GDBN} by a different name (for example, if you keep +several configurations around, with different names) you can set the +Emacs variable @code{gdb-command-name}; for example, + +@example +(setq gdb-command-name "mygdb") +@end example + +@noindent +(preceded by @kbd{ESC ESC}, or typed in the @code{*scratch*} buffer, or +in your @file{.emacs} file) makes Emacs call the program named +``@code{mygdb}'' instead. + +In the @value{GDBN} I/O buffer, you can use these special Emacs commands in +addition to the standard Shell mode commands: + +@table @kbd +@item C-h m +Describe the features of Emacs' @value{GDBN} Mode. + +@item M-s +Execute to another source line, like the @value{GDBN} @code{step} command; also +update the display window to show the current file and location. + +@item M-n +Execute to next source line in this function, skipping all function +calls, like the @value{GDBN} @code{next} command. Then update the display window +to show the current file and location. + +@item M-i +Execute one instruction, like the @value{GDBN} @code{stepi} command; update +display window accordingly. + +@item M-x gdb-nexti +Execute to next instruction, using the @value{GDBN} @code{nexti} command; update +display window accordingly. + +@item C-c C-f +Execute until exit from the selected stack frame, like the @value{GDBN} +@code{finish} command. + +@item M-c +Continue execution of your program, like the @value{GDBN} @code{continue} +command. + +@emph{Warning:} In Emacs v19, this command is @kbd{C-c C-p}. + +@item M-u +Go up the number of frames indicated by the numeric argument +(@pxref{Arguments, , Numeric Arguments, Emacs, The @sc{gnu} Emacs Manual}), +like the @value{GDBN} @code{up} command. + +@emph{Warning:} In Emacs v19, this command is @kbd{C-c C-u}. + +@item M-d +Go down the number of frames indicated by the numeric argument, like the +@value{GDBN} @code{down} command. + +@emph{Warning:} In Emacs v19, this command is @kbd{C-c C-d}. + +@item C-x & +Read the number where the cursor is positioned, and insert it at the end +of the @value{GDBN} I/O buffer. For example, if you wish to disassemble code +around an address that was displayed earlier, type @kbd{disassemble}; +then move the cursor to the address display, and pick up the +argument for @code{disassemble} by typing @kbd{C-x &}. + +You can customize this further by defining elements of the list +@code{gdb-print-command}; once it is defined, you can format or +otherwise process numbers picked up by @kbd{C-x &} before they are +inserted. A numeric argument to @kbd{C-x &} indicates that you +wish special formatting, and also acts as an index to pick an element of the +list. If the list element is a string, the number to be inserted is +formatted using the Emacs function @code{format}; otherwise the number +is passed as an argument to the corresponding list element. +@end table + +In any source file, the Emacs command @kbd{C-x SPC} (@code{gdb-break}) +tells @value{GDBN} to set a breakpoint on the source line point is on. + +If you accidentally delete the source-display buffer, an easy way to get +it back is to type the command @code{f} in the @value{GDBN} buffer, to +request a frame display; when you run under Emacs, this recreates +the source buffer if necessary to show you the context of the current +frame. + +The source files displayed in Emacs are in ordinary Emacs buffers +which are visiting the source files in the usual way. You can edit +the files with these buffers if you wish; but keep in mind that @value{GDBN} +communicates with Emacs in terms of line numbers. If you add or +delete lines from the text, the line numbers that @value{GDBN} knows cease +to correspond properly with the code. + +@c The following dropped because Epoch is nonstandard. Reactivate +@c if/when v19 does something similar. ---doc@cygnus.com 19dec1990 +@ignore +@kindex Emacs Epoch environment +@kindex Epoch +@kindex inspect + +Version 18 of @sc{gnu} Emacs has a built-in window system +called the @code{epoch} +environment. Users of this environment can use a new command, +@code{inspect} which performs identically to @code{print} except that +each value is printed in its own window. +@end ignore +@end ifclear + +@node GDB Bugs +@c links whacked to pacify makeinfo +@c , Command Line Editing, Emacs, Top +@chapter Reporting Bugs in @value{GDBN} +@cindex bugs in @value{GDBN} +@cindex reporting bugs in @value{GDBN} + +Your bug reports play an essential role in making @value{GDBN} reliable. + +Reporting a bug may help you by bringing a solution to your problem, or it +may not. But in any case the principal function of a bug report is to help +the entire community by making the next version of @value{GDBN} work better. Bug +reports are your contribution to the maintenance of @value{GDBN}. + +In order for a bug report to serve its purpose, you must include the +information that enables us to fix the bug. + +@menu +* Bug Criteria:: Have you found a bug? +* Bug Reporting:: How to report bugs +@end menu + +@node Bug Criteria, Bug Reporting, GDB Bugs, GDB Bugs +@section Have you found a bug? +@cindex bug criteria + +If you are not sure whether you have found a bug, here are some guidelines: + +@itemize @bullet +@cindex fatal signal +@cindex debugger crash +@cindex crash of debugger +@item +If the debugger gets a fatal signal, for any input whatever, that is a +@value{GDBN} bug. Reliable debuggers never crash. + +@cindex error on valid input +@item +If @value{GDBN} produces an error message for valid input, that is a +bug. (Note that if you're cross debugging, the problem may also be +somewhere in the connection to the target.) + +@cindex invalid input +@item +If @value{GDBN} does not produce an error message for invalid input, +that is a bug. However, you should note that your idea of +``invalid input'' might be our idea of ``an extension'' or ``support +for traditional practice''. + +@item +If you are an experienced user of debugging tools, your suggestions +for improvement of @value{GDBN} are welcome in any case. +@end itemize + +@node Bug Reporting, , Bug Criteria, GDB Bugs +@section How to report bugs +@cindex bug reports +@cindex @value{GDBN} bugs, reporting + +@ifclear HPPA +A number of companies and individuals offer support for @sc{gnu} products. +If you obtained @value{GDBN} from a support organization, we recommend you +contact that organization first. + +You can find contact information for many support companies and +individuals in the file @file{etc/SERVICE} in the @sc{gnu} Emacs +distribution. +@c should add a web page ref... + +In any event, we also recommend that you send bug reports for +@value{GDBN} to this addresses: + +@example +bug-gdb@@prep.ai.mit.edu +@end example + +@strong{Do not send bug reports to @samp{info-gdb}, or to +@samp{help-gdb}, or to any newsgroups.} Most users of @value{GDBN} do +not want to receive bug reports. Those that do have arranged to receive +@samp{bug-gdb}. + +The mailing list @samp{bug-gdb} has a newsgroup @samp{gnu.gdb.bug} which +serves as a repeater. The mailing list and the newsgroup carry exactly +the same messages. Often people think of posting bug reports to the +newsgroup instead of mailing them. This appears to work, but it has one +problem which can be crucial: a newsgroup posting often lacks a mail +path back to the sender. Thus, if we need to ask for more information, +we may be unable to reach you. For this reason, it is better to send +bug reports to the mailing list. + +As a last resort, send bug reports on paper to: + +@example +@sc{gnu} Debugger Bugs +Free Software Foundation Inc. +59 Temple Place - Suite 330 +Boston, MA 02111-1307 +USA +@end example +@end ifclear + +@ifset HPPA +If you obtained HP GDB as part of your HP ANSI C or HP ANSI C++ compiler +kit, report problems to your HP Support Representative. + +If you obtained HP GDB from the Hewlett-Packard Web site, report +problems by electronic mail to @code{wdb-www@@ch.hp.com}. +@end ifset + +The fundamental principle of reporting bugs usefully is this: +@strong{report all the facts}. If you are not sure whether to state a +fact or leave it out, state it! + +Often people omit facts because they think they know what causes the +problem and assume that some details do not matter. Thus, you might +assume that the name of the variable you use in an example does not matter. +Well, probably it does not, but one cannot be sure. Perhaps the bug is a +stray memory reference which happens to fetch from the location where that +name is stored in memory; perhaps, if the name were different, the contents +of that location would fool the debugger into doing the right thing despite +the bug. Play it safe and give a specific, complete example. That is the +easiest thing for you to do, and the most helpful. + +Keep in mind that the purpose of a bug report is to enable us to fix the +bug. It may be that the bug has been reported previously, but neither +you nor we can know that unless your bug report is complete and +self-contained. + +Sometimes people give a few sketchy facts and ask, ``Does this ring a +bell?'' Those bug reports are useless, and we urge everyone to +@emph{refuse to respond to them} except to chide the sender to report +bugs properly. + +To enable us to fix the bug, you should include all these things: + +@itemize @bullet +@item +The version of @value{GDBN}. @value{GDBN} announces it if you start +with no arguments; you can also print it at any time using @code{show +version}. + +Without this, we will not know whether there is any point in looking for +the bug in the current version of @value{GDBN}. + +@item +The type of machine you are using, and the operating system name and +version number. + +@ifclear HPPA +@item +What compiler (and its version) was used to compile @value{GDBN}---e.g. +``@value{GCC}--2.8.1''. +@end ifclear + +@item +What compiler (and its version) was used to compile the program you are +debugging---e.g. ``@value{GCC}--2.8.1'', or ``HP92453-01 A.10.32.03 HP +C Compiler''. For GCC, you can say @code{gcc --version} to get this +information; for other compilers, see the documentation for those +compilers. + +@item +The command arguments you gave the compiler to compile your example and +observe the bug. For example, did you use @samp{-O}? To guarantee +you will not omit something important, list them all. A copy of the +Makefile (or the output from make) is sufficient. + +If we were to try to guess the arguments, we would probably guess wrong +and then we might not encounter the bug. + +@item +A complete input script, and all necessary source files, that will +reproduce the bug. + +@item +A description of what behavior you observe that you believe is +incorrect. For example, ``It gets a fatal signal.'' + +Of course, if the bug is that @value{GDBN} gets a fatal signal, then we +will certainly notice it. But if the bug is incorrect output, we might +not notice unless it is glaringly wrong. You might as well not give us +a chance to make a mistake. + +Even if the problem you experience is a fatal signal, you should still +say so explicitly. Suppose something strange is going on, such as, your +copy of @value{GDBN} is out of synch, or you have encountered a bug in +the C library on your system. (This has happened!) Your copy might +crash and ours would not. If you told us to expect a crash, then when +ours fails to crash, we would know that the bug was not happening for +us. If you had not told us to expect a crash, then we would not be able +to draw any conclusion from our observations. + +@ifclear HPPA +@item +If you wish to suggest changes to the @value{GDBN} source, send us context +diffs. If you even discuss something in the @value{GDBN} source, refer to +it by context, not by line number. + +The line numbers in our development sources will not match those in your +sources. Your line numbers would convey no useful information to us. +@end ifclear +@end itemize + +Here are some things that are not necessary: + +@itemize @bullet +@item +A description of the envelope of the bug. + +Often people who encounter a bug spend a lot of time investigating +which changes to the input file will make the bug go away and which +changes will not affect it. + +This is often time consuming and not very useful, because the way we +will find the bug is by running a single example under the debugger +with breakpoints, not by pure deduction from a series of examples. +We recommend that you save your time for something else. + +Of course, if you can find a simpler example to report @emph{instead} +of the original one, that is a convenience for us. Errors in the +output will be easier to spot, running under the debugger will take +less time, and so on. + +However, simplification is not vital; if you do not want to do this, +report the bug anyway and send us the entire test case you used. + +@item +A patch for the bug. + +A patch for the bug does help us if it is a good one. But do not omit +the necessary information, such as the test case, on the assumption that +a patch is all we need. We might see problems with your patch and decide +to fix the problem another way, or we might not understand it at all. + +Sometimes with a program as complicated as @value{GDBN} it is very hard to +construct an example that will make the program follow a certain path +through the code. If you do not send us the example, we will not be able +to construct one, so we will not be able to verify that the bug is fixed. + +And if we cannot understand what bug you are trying to fix, or why your +patch should be an improvement, we will not install it. A test case will +help us to understand. + +@item +A guess about what the bug is or what it depends on. + +Such guesses are usually wrong. Even we cannot guess right about such +things without first using the debugger to find the facts. +@end itemize + +@c The readline documentation is distributed with the readline code +@c and consists of the two following files: +@c rluser.texinfo +@c inc-hist.texi +@c Use -I with makeinfo to point to the appropriate directory, +@c environment var TEXINPUTS with TeX. +@include rluser.texinfo +@include inc-hist.texi + + +@ifclear PRECONFIGURED +@ifclear HPPA +@node Formatting Documentation +@c links whacked to pacify makeinfo +@c , Installing GDB, Renamed Commands, Top +@appendix Formatting Documentation + +@cindex @value{GDBN} reference card +@cindex reference card +The @value{GDBN} 4 release includes an already-formatted reference card, ready +for printing with PostScript or Ghostscript, in the @file{gdb} +subdirectory of the main source directory@footnote{In +@file{gdb-@value{GDBVN}/gdb/refcard.ps} of the version @value{GDBVN} +release.}. If you can use PostScript or Ghostscript with your printer, +you can print the reference card immediately with @file{refcard.ps}. + +The release also includes the source for the reference card. You +can format it, using @TeX{}, by typing: + +@example +make refcard.dvi +@end example + +The @value{GDBN} reference card is designed to print in @dfn{landscape} +mode on US ``letter'' size paper; +that is, on a sheet 11 inches wide by 8.5 inches +high. You will need to specify this form of printing as an option to +your @sc{dvi} output program. + +@cindex documentation + +All the documentation for @value{GDBN} comes as part of the machine-readable +distribution. The documentation is written in Texinfo format, which is +a documentation system that uses a single source file to produce both +on-line information and a printed manual. You can use one of the Info +formatting commands to create the on-line version of the documentation +and @TeX{} (or @code{texi2roff}) to typeset the printed version. + +@value{GDBN} includes an already formatted copy of the on-line Info +version of this manual in the @file{gdb} subdirectory. The main Info +file is @file{gdb-@value{GDBVN}/gdb/gdb.info}, and it refers to +subordinate files matching @samp{gdb.info*} in the same directory. If +necessary, you can print out these files, or read them with any editor; +but they are easier to read using the @code{info} subsystem in @sc{gnu} +Emacs or the standalone @code{info} program, available as part of the +@sc{gnu} Texinfo distribution. + +If you want to format these Info files yourself, you need one of the +Info formatting programs, such as @code{texinfo-format-buffer} or +@code{makeinfo}. + +If you have @code{makeinfo} installed, and are in the top level +@value{GDBN} source directory (@file{gdb-@value{GDBVN}}, in the case of +version @value{GDBVN}), you can make the Info file by typing: + +@example +cd gdb +make gdb.info +@end example + +If you want to typeset and print copies of this manual, you need @TeX{}, +a program to print its @sc{dvi} output files, and @file{texinfo.tex}, the +Texinfo definitions file. + +@TeX{} is a typesetting program; it does not print files directly, but +produces output files called @sc{dvi} files. To print a typeset +document, you need a program to print @sc{dvi} files. If your system +has @TeX{} installed, chances are it has such a program. The precise +command to use depends on your system; @kbd{lpr -d} is common; another +(for PostScript devices) is @kbd{dvips}. The @sc{dvi} print command may +require a file name without any extension or a @samp{.dvi} extension. + +@TeX{} also requires a macro definitions file called +@file{texinfo.tex}. This file tells @TeX{} how to typeset a document +written in Texinfo format. On its own, @TeX{} cannot either read or +typeset a Texinfo file. @file{texinfo.tex} is distributed with GDB +and is located in the @file{gdb-@var{version-number}/texinfo} +directory. + +If you have @TeX{} and a @sc{dvi} printer program installed, you can +typeset and print this manual. First switch to the the @file{gdb} +subdirectory of the main source directory (for example, to +@file{gdb-@value{GDBVN}/gdb}) and type: + +@example +make gdb.dvi +@end example + +Then give @file{gdb.dvi} to your @sc{dvi} printing program. +@end ifclear + +@node Installing GDB, Index, Using History Interactively, Top +@appendix Installing @value{GDBN} +@cindex configuring @value{GDBN} +@cindex installation + +@ifset HPPA +If you obtain @value{GDBN} (HP WDB 0.75) as part of your HP ANSI C or +HP ANSI C++ Developer's Kit at HP-UX Release 11.0, you do not have to +take any special action to build or install @value{GDBN}. + +If you obtain @value{GDBN} (HP WDB 0.75) from an HP web site, you may +download either a @code{swinstall}-able package or a source tree, or +both. + +Most customers will want to install the @value{GDBN} binary that is part +of the @code{swinstall}-able package. To do so, use a command of the +form + +@smallexample +/usr/sbin/swinstall -s @var{package-name} WDB +@end smallexample + +Alternatively, it is possible to build @value{GDBN} from the source +distribution. Sophisticated customers who want to modify the debugger +sources to tailor @value{GDBN} to their their needs may wish to do this. +The source distribution consists of a @code{tar}'ed source tree rooted +at @file{gdb-4.16/...}. The instructions that follow describe how to +build a @file{gdb} executable from this source tree. HP believes that +these instructions apply to the WDB source tree that it distributes. +However, HP does not explicitly support building a @file{gdb} for any +non-HP platform from the WDB source tree. It may work, but HP has not +tested it for any platforms other than those described in the WDB 0.75 +Release Notes. +@end ifset + +@value{GDBN} comes with a @code{configure} script that automates the process +of preparing @value{GDBN} for installation; you can then use @code{make} to +build the @code{gdb} program. +@iftex +@c irrelevant in info file; it's as current as the code it lives with. +@footnote{If you have a more recent version of @value{GDBN} than @value{GDBVN}, +look at the @file{README} file in the sources; we may have improved the +installation procedures since publishing this manual.} +@end iftex + +The @value{GDBN} distribution includes all the source code you need for +@value{GDBN} in a single directory, whose name is usually composed by +appending the version number to @samp{gdb}. + +For example, the @value{GDBN} version @value{GDBVN} distribution is in the +@file{gdb-@value{GDBVN}} directory. That directory contains: + +@table @code +@item gdb-@value{GDBVN}/configure @r{(and supporting files)} +script for configuring @value{GDBN} and all its supporting libraries + +@item gdb-@value{GDBVN}/gdb +the source specific to @value{GDBN} itself + +@item gdb-@value{GDBVN}/bfd +source for the Binary File Descriptor library + +@item gdb-@value{GDBVN}/include +@sc{gnu} include files + +@item gdb-@value{GDBVN}/libiberty +source for the @samp{-liberty} free software library + +@item gdb-@value{GDBVN}/opcodes +source for the library of opcode tables and disassemblers + +@item gdb-@value{GDBVN}/readline +source for the @sc{gnu} command-line interface + +@item gdb-@value{GDBVN}/glob +source for the @sc{gnu} filename pattern-matching subroutine + +@item gdb-@value{GDBVN}/mmalloc +source for the @sc{gnu} memory-mapped malloc package +@end table + +The simplest way to configure and build @value{GDBN} is to run @code{configure} +from the @file{gdb-@var{version-number}} source directory, which in +this example is the @file{gdb-@value{GDBVN}} directory. + +First switch to the @file{gdb-@var{version-number}} source directory +if you are not already in it; then run @code{configure}. Pass the +identifier for the platform on which @value{GDBN} will run as an +argument. + +For example: + +@example +cd gdb-@value{GDBVN} +./configure @var{host} +make +@end example + +@noindent +where @var{host} is an identifier such as @samp{sun4} or +@samp{decstation}, that identifies the platform where @value{GDBN} will run. +(You can often leave off @var{host}; @code{configure} tries to guess the +correct value by examining your system.) + +Running @samp{configure @var{host}} and then running @code{make} builds the +@file{bfd}, @file{readline}, @file{mmalloc}, and @file{libiberty} +libraries, then @code{gdb} itself. The configured source files, and the +binaries, are left in the corresponding source directories. + +@need 750 +@code{configure} is a Bourne-shell (@code{/bin/sh}) script; if your +system does not recognize this automatically when you run a different +shell, you may need to run @code{sh} on it explicitly: + +@example +sh configure @var{host} +@end example + +If you run @code{configure} from a directory that contains source +directories for multiple libraries or programs, such as the +@file{gdb-@value{GDBVN}} source directory for version @value{GDBVN}, @code{configure} +creates configuration files for every directory level underneath (unless +you tell it not to, with the @samp{--norecursion} option). + +You can run the @code{configure} script from any of the +subordinate directories in the @value{GDBN} distribution if you only want to +configure that subdirectory, but be sure to specify a path to it. + +For example, with version @value{GDBVN}, type the following to configure only +the @code{bfd} subdirectory: + +@example +@group +cd gdb-@value{GDBVN}/bfd +../configure @var{host} +@end group +@end example + +You can install @code{@value{GDBP}} anywhere; it has no hardwired paths. +However, you should make sure that the shell on your path (named by +the @samp{SHELL} environment variable) is publicly readable. Remember +that @value{GDBN} uses the shell to start your program---some systems refuse to +let @value{GDBN} debug child processes whose programs are not readable. + +@menu +* Separate Objdir:: Compiling @value{GDBN} in another directory +* Config Names:: Specifying names for hosts and targets +* Configure Options:: Summary of options for configure +@end menu + +@node Separate Objdir, Config Names, Installing GDB, Installing GDB +@section Compiling @value{GDBN} in another directory + +If you want to run @value{GDBN} versions for several host or target machines, +you need a different @code{gdb} compiled for each combination of +host and target. @code{configure} is designed to make this easy by +allowing you to generate each configuration in a separate subdirectory, +rather than in the source directory. If your @code{make} program +handles the @samp{VPATH} feature (@sc{gnu} @code{make} does), running +@code{make} in each of these directories builds the @code{gdb} +program specified there. + +To build @code{gdb} in a separate directory, run @code{configure} +with the @samp{--srcdir} option to specify where to find the source. +(You also need to specify a path to find @code{configure} +itself from your working directory. If the path to @code{configure} +would be the same as the argument to @samp{--srcdir}, you can leave out +the @samp{--srcdir} option; it is assumed.) + +For example, with version @value{GDBVN}, you can build @value{GDBN} in a +separate directory for a Sun 4 like this: + +@example +@group +cd gdb-@value{GDBVN} +mkdir ../gdb-sun4 +cd ../gdb-sun4 +../gdb-@value{GDBVN}/configure sun4 +make +@end group +@end example + +When @code{configure} builds a configuration using a remote source +directory, it creates a tree for the binaries with the same structure +(and using the same names) as the tree under the source directory. In +the example, you'd find the Sun 4 library @file{libiberty.a} in the +directory @file{gdb-sun4/libiberty}, and @value{GDBN} itself in +@file{gdb-sun4/gdb}. + +One popular reason to build several @value{GDBN} configurations in separate +directories is to configure @value{GDBN} for cross-compiling (where +@value{GDBN} runs on one machine---the @dfn{host}---while debugging +programs that run on another machine---the @dfn{target}). +You specify a cross-debugging target by +giving the @samp{--target=@var{target}} option to @code{configure}. + +When you run @code{make} to build a program or library, you must run +it in a configured directory---whatever directory you were in when you +called @code{configure} (or one of its subdirectories). + +The @code{Makefile} that @code{configure} generates in each source +directory also runs recursively. If you type @code{make} in a source +directory such as @file{gdb-@value{GDBVN}} (or in a separate configured +directory configured with @samp{--srcdir=@var{dirname}/gdb-@value{GDBVN}}), you +will build all the required libraries, and then build GDB. + +When you have multiple hosts or targets configured in separate +directories, you can run @code{make} on them in parallel (for example, +if they are NFS-mounted on each of the hosts); they will not interfere +with each other. + +@node Config Names, Configure Options, Separate Objdir, Installing GDB +@section Specifying names for hosts and targets + +The specifications used for hosts and targets in the @code{configure} +script are based on a three-part naming scheme, but some short predefined +aliases are also supported. The full naming scheme encodes three pieces +of information in the following pattern: + +@example +@var{architecture}-@var{vendor}-@var{os} +@end example + +For example, you can use the alias @code{sun4} as a @var{host} argument, +or as the value for @var{target} in a @code{--target=@var{target}} +option. The equivalent full name is @samp{sparc-sun-sunos4}. + +The @code{configure} script accompanying @value{GDBN} does not provide +any query facility to list all supported host and target names or +aliases. @code{configure} calls the Bourne shell script +@code{config.sub} to map abbreviations to full names; you can read the +script, if you wish, or you can use it to test your guesses on +abbreviations---for example: + +@smallexample +% sh config.sub i386-linux +i386-pc-linux-gnu +% sh config.sub alpha-linux +alpha-unknown-linux-gnu +% sh config.sub hp9k700 +hppa1.1-hp-hpux +% sh config.sub sun4 +sparc-sun-sunos4.1.1 +% sh config.sub sun3 +m68k-sun-sunos4.1.1 +% sh config.sub i986v +Invalid configuration `i986v': machine `i986v' not recognized +@end smallexample + +@noindent +@code{config.sub} is also distributed in the @value{GDBN} source +directory (@file{gdb-@value{GDBVN}}, for version @value{GDBVN}). + +@node Configure Options, , Config Names, Installing GDB +@section @code{configure} options + +Here is a summary of the @code{configure} options and arguments that +are most often useful for building @value{GDBN}. @code{configure} also has +several other options not listed here. @inforef{What Configure +Does,,configure.info}, for a full explanation of @code{configure}. + +@example +configure @r{[}--help@r{]} + @r{[}--prefix=@var{dir}@r{]} + @r{[}--exec-prefix=@var{dir}@r{]} + @r{[}--srcdir=@var{dirname}@r{]} + @r{[}--norecursion@r{]} @r{[}--rm@r{]} + @r{[}--target=@var{target}@r{]} + @var{host} +@end example + +@noindent +You may introduce options with a single @samp{-} rather than +@samp{--} if you prefer; but you may abbreviate option names if you use +@samp{--}. + +@table @code +@item --help +Display a quick summary of how to invoke @code{configure}. + +@item --prefix=@var{dir} +Configure the source to install programs and files under directory +@file{@var{dir}}. + +@item --exec-prefix=@var{dir} +Configure the source to install programs under directory +@file{@var{dir}}. + +@c avoid splitting the warning from the explanation: +@need 2000 +@item --srcdir=@var{dirname} +@strong{Warning: using this option requires @sc{gnu} @code{make}, or another +@code{make} that implements the @code{VPATH} feature.}@* +Use this option to make configurations in directories separate from the +@value{GDBN} source directories. Among other things, you can use this to +build (or maintain) several configurations simultaneously, in separate +directories. @code{configure} writes configuration specific files in +the current directory, but arranges for them to use the source in the +directory @var{dirname}. @code{configure} creates directories under +the working directory in parallel to the source directories below +@var{dirname}. + +@item --norecursion +Configure only the directory level where @code{configure} is executed; do not +propagate configuration to subdirectories. + +@item --target=@var{target} +Configure @value{GDBN} for cross-debugging programs running on the specified +@var{target}. Without this option, @value{GDBN} is configured to debug +programs that run on the same machine (@var{host}) as @value{GDBN} itself. + +There is no convenient way to generate a list of all available targets. + +@item @var{host} @dots{} +Configure @value{GDBN} to run on the specified @var{host}. + +There is no convenient way to generate a list of all available hosts. +@end table + +There are many other options available as well, but they are generally +needed for special purposes only. +@end ifclear + + +@node Index, , Installing GDB, Top +@unnumbered Index + +@printindex cp + +@tex +% I think something like @colophon should be in texinfo. In the +% meantime: +\long\def\colophon{\hbox to0pt{}\vfill +\centerline{The body of this manual is set in} +\centerline{\fontname\tenrm,} +\centerline{with headings in {\bf\fontname\tenbf}} +\centerline{and examples in {\tt\fontname\tentt}.} +\centerline{{\it\fontname\tenit\/},} +\centerline{{\bf\fontname\tenbf}, and} +\centerline{{\sl\fontname\tensl\/}} +\centerline{are used for emphasis.}\vfill} +\page\colophon +% Blame: doc@cygnus.com, 1991. +@end tex + +@contents +@bye |