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Re: [RFC] Wrong register numbers in .dwarf_frame on Linux/PowerPC
- From: "Ulrich Weigand" <uweigand at de dot ibm dot com>
- To: mark dot kettenis at xs4all dot nl (Mark Kettenis)
- Cc: dje dot gcc at gmail dot com, geoffk at geoffk dot org, jakub at redhat dot com, gcc-patches at gcc dot gnu dot org, binutils at sourceware dot org, gdb-patches at sourceware dot org
- Date: Tue, 27 Nov 2012 19:43:40 +0100 (CET)
- Subject: 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" <firstname.lastname@example.org>
> > 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 ...
Dr. Ulrich Weigand
GNU Toolchain for Linux on System z and Cell BE