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


Mark Kettenis wrote:
> > 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.

In my tests XLC (version 12.1 on Linux) seems to consistently use the
GCC register numbering in both .eh_frame and .dwarf_frame.  LLVM also
consistently uses the GCC register numbering.  Looks like this would
be another argument for variant 3 ...

Bye,
Ulrich

-- 
  Dr. Ulrich Weigand
  GNU Toolchain for Linux on System z and Cell BE
  Ulrich.Weigand@de.ibm.com


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