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       gdb - The GNU Debugger


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


       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

          ·   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

       You  can  use  GDB  to  debug programs written in C, C++, and Modula-2.
       Fortran support will be added when a GNU Fortran compiler is ready.

       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

       gdb program core

       You can, instead, specify a process ID as a  second  argument,  if  you
       want to debug a running process:

       gdb program 1234

       would  attach  GDB  to  process 1234 (unless you also have a file named
       ‘1234’; GDB does check for a core file first).

       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

       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.


       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


       -h     List all options, with brief explanations.


       -s file
               Read symbol table from file file.

       -write Enable writing into executable and core files.


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

                Read  symbol table from file file and use it as the executable


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


       -x file
               Execute GDB commands from file file.


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


       -n     Do not  execute  commands  from  any  ‘.gdbinit’  initialization
              files.  Normally, the commands in these files are executed after
              all the command options and arguments have been processed.


       -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.

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


       -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 ‘ 32’ 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 ‘ 32’ 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.

                Run using device for your program’s standard input and output.


gdb’ entry in info;  Using  GDB:  A  Guide  to  the  GNU  Source-Level
       Debugger, Richard M. Stallman and Roland H. Pesch, July 1991.


       Copyright (c) 1991 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.

       Permission  is granted to copy and distribute modified versions of this
       manual under the conditions for verbatim  copying,  provided  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, except  that  this  permission  notice  may  be  included  in
       translations approved by the Free Software Foundation instead of in the
       original English.