RFC: Support for separate debug info files

[Nick Clifton <nickc at redhat dot com>]

Hi Guys,

  OK, here is a heavily revised patch to implement support for
  generating separate debuginfo files in binutils.  The highlights of
  this version are:

    * Adds a new switch to objcopy "--add-gnu-debuglink=<file>", which
      creates a .gnu_debuglink section in the output file which points
      to the specified <file>.

    * It no longer adds a "--strip-nondebug" or "--only-keep-debug" switch
      to strip and objcopy - it is not needed.  (Although this is open
      to debate, see below).

    * Exports the CRC32 computing function that was already in BFD so
      that it can be used by other tools.  This would allow the
      version in GDB to be made obsolete...

  Here is an example of the patch in action:

    % cat hello.c
    int main (void) { return printf ("hello world\n"); }

    % gcc hello.c -g -o hello
    % strip --strip-all hello hello.stripped.all
    % strip --strip-debug hello hello.stripped.debug
    % objcopy --add-gnu-debuglink=hello hello.stripped.all hello.stripped.all.with-link
    % ls -l
    -rwxrwx---    12031 Jun 11 10:09 hello*
    -rw-rw----       54 Jun 11 10:09 hello.c
    -rwxrwx---     2804 Jun 11 10:10 hello.stripped.all*
    -rwxrwx---     4382 Jun 11 10:10 hello.stripped.debug*
    -rwxrwx---     2872 Jun 11 10:11 hello.stripped.all.with-link*

    % gdb hello.stripped.all.with-link
    GNU gdb 2003-06-09-cvs
    Copyright 2003 Free Software Foundation, Inc.
    (gdb) break main
    Breakpoint 1 at 0x8048364: file hello.c, line 1.
    (gdb) run
    Starting program: /builds/FSF/native/tests/debug-info-test/hello.stripped.with-link
 
    Breakpoint 1, main () at hello.c:1
    1       int main (void) { return printf ("hello world\n"); }

  So the fully stripped executable "hello.stripped.all.with-link" is
  only 2872 bytes long, but it can be fully debugged when accompanied
  by the original, unstripped executable "hello".  (Which at 12031
  bytes is 4 times the size of the stripped version).

  This leads me to my main point.  Do we need the ability to create
  stripped debuginfo files ?  The original patch did this, but it
  turns out to be problematical since the debuginfo files need to
  contain dummy versions of the .text, .data, etc sections.  Doing
  this, rather than just stripping them out, looked non-trivial, so I
  decided to skip it for this version.

  My theory is that the only benefit gained by being able to ship a
  stripped debuginfo file as opposed to an unstripped one is that it
  reduces the shipping size, making a distribution smaller.  I am
  assuming that hard disk space is not really an issue, just the size
  of the shipped binaries.

  Any comments ?

Cheers
        Nick

bfd/ChangeLog
2003-06-11  Nick Clifton  <nickc@redhat.com>

	* opncls.c (calc_crc32): Rename to
	bfd_calc_gnu_debuglink_crc32 and export.
        (GNU_DEBUGLINK): Define and use to replace occurrences of
	hard-coded ".gnu_debuglink" in the code.
        (get_debug_link_info): Prevent aborts by replacing call to
	xmalloc with a call to malloc.
        (find_separate_debug_file): Prevent aborts by replacing calls
	to xmalloc and xstrdup with calls to malloc and strdup.
        (bfd_add_gnu_debuglink): New function.  Add a .gnu_debuglink
	section to a bfd.
	* bfd-in2.h: Regenerate.

binutils/ChangeLog
2003-06-11  Nick Clifton  <nickc@redhat.com>

	* objcopy.c (gnu_debuglink_filename): New variable.
        (OPTION_ADD_GNU_DEBUGLINK): New switch
        (copy_options): Describe --add-gnu-debuglink switch.
        Mention that --strip-debug removes sections as well.
        (is_strip_section): Process the sections removed and kept
        lists before checking for debugging sections.
        (add_redefine_syms_file): Make function static.
        (copy_object): Use is_strip_section.
        Check to see if a .gnu_debuglink section should be added.  If
        so, call bfd_add_gnu_debuglink.
        (setup_section): Use is_strip_section.
        (copy_section): Use is_strip_section.
        (copy_main): Handle OPTION_ADD_GNU_DEBUGLINK.
	* NEWS: Mention new objcopy switch.
        * doc/binutils.texi: Document new switch.

Attachment: gnu-debuglink.patch.2.bz2
Description: Patch to add support for --add-gnu-debuglink switch to objcopy