[Bug binutils/23947] objcopy refuses to copy !(SEC_LOAD|SEC_ALLOC) sections

[nickc at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=23947

Nick Clifton <nickc at redhat dot com> changed:

           What    |Removed                     |Added
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                 CC|                            |nickc at redhat dot com

--- Comment #1 from Nick Clifton <nickc at redhat dot com> ---
(In reply to Paul Pluzhnikov from comment #0)
Hi Paul,

> On Fedora, /usr/bin/ls has a mini-symbols .gnu_debugdata section:
> I wanted to examine the contents of this section, so I did the usual:
> 
>   objcopy -O binary -j.gnu_debuglink /usr/bin/ls /tmp/ls.mini.xz

Did you know that you can dump the contents of the .gnu.debuglink section
using readelf ?  For example:

  % readelf --debug-dump=links /usr/bin/ls
  Contents of the .gnu_debuglink section:

    Separate debug info file: ls-8.30-6.fc29.x86_64.debug
    CRC value: 0x98ccdd5c

> but that produced an empty file.
> AFAICT, this is happening because of the following check in bfd/binary.c:
> 
> 284     /* We don't want to output anything for a section that is neither
> 285        loaded nor allocated.  The contents of such a section are not
> 286        meaningful in the binary format.  */
> 287     if ((sec->flags & (SEC_LOAD | SEC_ALLOC)) == 0)
> 288       return TRUE;


> The statement that "contents is not meaningful in binary format" seems to be
> patently false (or rather, assumes that "binary" is going to be used for a
> specific purpose different from mine).
> 
> This appears to have been broken since forever:

Yeah - it has been this way for a very long time.  You can work around the 
problem however, by adding a section flag.  For example:

  % objcopy -j.gnu_debuglink --set-section-flags .gnu_debuglink=A /usr/bin/ls
fred
  % od fred
  0000000 071554 034055 031456 026460 027066 061546 034462 074056
  0000020 033070 033137 027064 062544 072542 000147 156534 114314
  0000040

Cheers
  Nick

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