[RFC] Wrong register numbers in .dwarf_frame on Linux/PowerPC

Mark Kettenis mark.kettenis@xs4all.nl
Mon Nov 26 20:14:00 GMT 2012


> Date: Mon, 26 Nov 2012 20:10:06 +0100 (CET)
> From: "Ulrich Weigand" <uweigand@de.ibm.com>
> 
> Hello,
> 
> I noticed what appears to be a long-standing bug in generating .dwarf_frame
> sections with GCC on Linux on PowerPC.
> 
> ...
> 
> So I'm wondering where to go from here.  I guess we could:
> 
> 1. Bring GCC (and gas) behaviour in compliance with the documented ABI
>    by removing the #undef DBX_REGISTER_NUMBER and changing gas's
>    md_reg_eh_frame_to_debug_frame to the original implementation from
>    Jakub's patch.  That would make GDB work well on new files, but
>    there are a large number of binaries out there where we continue
>    to have the same behaviour as today ...
> 
> 2. Leave GCC and gas as-is and modify GDB to expect GCC numbering in
>    .dwarf_frame, except for the condition code register.  This would
>    break debugging of files built with GCC 4.0 and 4.1 unless we
>    want to add a special hack for that.
> 
> 3. Like 2., but remove the condition code hack: simply use identical
>    numbers in .eh_frame and .dwarf_frame.  This would make PowerPC
>    like other Linux platforms in that respect.
> 
> Thoughts?

What do other compilers (in particular XLC) do?  From a GDB standpoint
it would be a major PITA if different compilers would use different
encodings for .dwarf_frame.



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