NAME

       gdb - The GNU Debugger

SYNOPSIS

       gdb [-help] [-nh] [-nx] [-q] [-batch] [-cd=dir] [-f] [-b bps]
           [-tty=dev] [-s symfile] [-e prog] [-se prog] [-c core] [-p procID]
           [-x cmds] [-d dir] [prog|prog procID|prog core]

DESCRIPTION

       The purpose of a debugger such as GDB is to allow you to see what is going on "inside"
       another program while it executes -- or what another program was doing at the moment it
       crashed.

       GDB can do four main kinds of things (plus other things in support of these) to help you
       catch bugs in the act:

       •   Start your program, specifying anything that might affect its behavior.

       •   Make your program stop on specified conditions.

       •   Examine what has happened, when your program has stopped.

       •   Change things in your program, so you can experiment with correcting the effects of
           one bug and go on to learn about another.

       You can use GDB to debug programs written in C, C@t{++}, Fortran and Modula-2.

       GDB is invoked with the shell command "gdb".  Once started, it reads commands from the
       terminal until you tell it to exit with the GDB command "quit".  You can get online help
       from GDB itself by using the command "help".

       You can run "gdb" with no arguments or options; but the most usual way to start GDB is
       with one argument or two, specifying an executable program as the argument:

               gdb program

       You can also start with both an executable program and a core file specified:

               gdb program core

       You can, instead, specify a process ID as a second argument or use option "-p", if you
       want to debug a running process:

               gdb program 1234
               gdb -p 1234

       would attach GDB to process 1234.  With option -p you can omit the program filename.

       Here are some of the most frequently needed GDB commands:

       break [file:]function
           Set a breakpoint at function (in file).

       run [arglist]
           Start your program (with arglist, if specified).

       bt  Backtrace: display the program stack.

       print expr
           Display the value of an expression.

       c   Continue running your program (after stopping, e.g. at a breakpoint).

       next
           Execute next program line (after stopping); step over any function calls in the line.

       edit [file:]function
           look at the program line where it is presently stopped.

       list [file:]function
           type the text of the program in the vicinity of where it is presently stopped.

       step
           Execute next program line (after stopping); step into any function calls in the line.

       help [name]
           Show information about GDB command name, or general information about using GDB.

       quit
           Exit from GDB.

       For full details on GDB, see Using GDB: A Guide to the GNU Source-Level Debugger, by
       Richard M. Stallman and Roland H. Pesch.  The same text is available online as the "gdb"
       entry in the "info" program.

OPTIONS

       Any arguments other than options specify an executable file and core file (or process ID);
       that is, the first argument encountered with no associated option flag is equivalent to a
       -se option, and the second, if any, is equivalent to a -c option if it's the name of a
       file.  Many options have both long and short forms; both are shown here.  The long forms
       are also recognized if you truncate them, so long as enough of the option is present to be
       unambiguous.  (If you prefer, you can flag option arguments with + rather than -, though
       we illustrate the more usual convention.)

       All the options and command line arguments you give are processed in sequential order.
       The order makes a difference when the -x option is used.

       -help
       -h  List all options, with brief explanations.

       -symbols=file
       -s file
           Read symbol table from file file.

       -write
           Enable writing into executable and core files.

       -exec=file
       -e file
           Use file file as the executable file to execute when appropriate, and for examining
           pure data in conjunction with a core dump.

       -se=file
           Read symbol table from file file and use it as the executable file.

       -core=file
       -c file
           Use file file as a core dump to examine.

       -command=file
       -x file
           Execute GDB commands from file file.

       -ex command
           Execute given GDB command.

       -directory=directory
       -d directory
           Add directory to the path to search for source files.

       -nh Do not execute commands from ~/.gdbinit.

       -nx
       -n  Do not execute commands from any .gdbinit initialization files.

       -quiet
       -q  "Quiet".  Do not print the introductory and copyright messages.  These messages are
           also suppressed in batch mode.

       -batch
           Run in batch mode.  Exit with status 0 after processing all the command files
           specified with -x (and .gdbinit, if not inhibited).  Exit with nonzero status if an
           error occurs in executing the GDB commands in the command files.

           Batch mode may be useful for running GDB as a filter, for example to download and run
           a program on another computer; in order to make this more useful, the message

                   Program exited normally.

           (which is ordinarily issued whenever a program running under GDB control terminates)
           is not issued when running in batch mode.

       -cd=directory
           Run GDB using directory as its working directory, instead of the current directory.

       -fullname
       -f  Emacs sets this option when it runs GDB as a subprocess.  It tells GDB to output the
           full file name and line number in a standard, recognizable fashion each time a stack
           frame is displayed (which includes each time the program stops).  This recognizable
           format looks like two \032 characters, followed by the file name, line number and
           character position separated by colons, and a newline.  The Emacs-to-GDB interface
           program uses the two \032 characters as a signal to display the source code for the
           frame.

       -b bps
           Set the line speed (baud rate or bits per second) of any serial interface used by GDB
           for remote debugging.

       -tty=device
           Run using device for your program's standard input and output.

SEE ALSO

       The full documentation for GDB is maintained as a Texinfo manual.  If the "info" and "gdb"
       programs and GDB's Texinfo documentation are properly installed at your site, the command

               info gdb

       should give you access to the complete manual.

       Using GDB: A Guide to the GNU Source-Level Debugger, Richard M. Stallman and Roland H.
       Pesch, July 1991.

COPYRIGHT

       Copyright (c) 1988-2020 Free Software Foundation, Inc.

       Permission is granted to copy, distribute and/or modify this document under the terms of
       the GNU Free Documentation License, Version 1.3 or any later version published by the Free
       Software Foundation; with the Invariant Sections being "Free Software" and "Free Software
       Needs Free Documentation", with the Front-Cover Texts being "A GNU Manual," and with the
       Back-Cover Texts as in (a) below.

       (a) The FSF's Back-Cover Text is: "You are free to copy and modify this GNU Manual.
       Buying copies from GNU Press supports the FSF in developing GNU and promoting software
       freedom."