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gdb: Core File Generation

 
 10.19 How to Produce a Core File from Your Program
 ==================================================
 
 A "core file" or "core dump" is a file that records the memory image of
 a running process and its process status (register values etc.).  Its
 primary use is post-mortem debugging of a program that crashed while it
 ran outside a debugger.  A program that crashes automatically produces a
 core file, unless this feature is disabled by the user.  Files,
 for information on invoking GDB in the post-mortem debugging mode.
 
    Occasionally, you may wish to produce a core file of the program you
 are debugging in order to preserve a snapshot of its state.  GDB has a
 special command for that.
 
 'generate-core-file [FILE]'
 'gcore [FILE]'
      Produce a core dump of the inferior process.  The optional argument
      FILE specifies the file name where to put the core dump.  If not
      specified, the file name defaults to 'core.PID', where PID is the
      inferior process ID.
 
      Note that this command is implemented only for some systems (as of
      this writing, GNU/Linux, FreeBSD, Solaris, and S390).
 
      On GNU/Linux, this command can take into account the value of the
      file '/proc/PID/coredump_filter' when generating the core dump
      (set use-coredump-filter), and by default honors the
      'VM_DONTDUMP' flag for mappings where it is present in the file
      '/proc/PID/smaps' (set dump-excluded-mappings).
 
 'set use-coredump-filter on'
 'set use-coredump-filter off'
      Enable or disable the use of the file '/proc/PID/coredump_filter'
      when generating core dump files.  This file is used by the Linux
      kernel to decide what types of memory mappings will be dumped or
      ignored when generating a core dump file.  PID is the process ID of
      a currently running process.
 
      To make use of this feature, you have to write in the
      '/proc/PID/coredump_filter' file a value, in hexadecimal, which is
      a bit mask representing the memory mapping types.  If a bit is set
      in the bit mask, then the memory mappings of the corresponding
      types will be dumped; otherwise, they will be ignored.  This
      configuration is inherited by child processes.  For more
      information about the bits that can be set in the
      '/proc/PID/coredump_filter' file, please refer to the manpage of
      'core(5)'.
 
      By default, this option is 'on'.  If this option is turned 'off',
      GDB does not read the 'coredump_filter' file and instead uses the
      same default value as the Linux kernel in order to decide which
      pages will be dumped in the core dump file.  This value is
      currently '0x33', which means that bits '0' (anonymous private
      mappings), '1' (anonymous shared mappings), '4' (ELF headers) and
      '5' (private huge pages) are active.  This will cause these memory
      mappings to be dumped automatically.
 
 'set dump-excluded-mappings on'
 'set dump-excluded-mappings off'
      If 'on' is specified, GDB will dump memory mappings marked with the
      'VM_DONTDUMP' flag.  This flag is represented in the file
      '/proc/PID/smaps' with the acronym 'dd'.
 
      The default value is 'off'.
 

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