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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: mjw at redhat dot com (Mark Wielaard)
- 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 19:49:12 +0100 (CET)
- Subject: Re: [RFC] Wrong register numbers in .dwarf_frame on Linux/PowerPC
Mark Wielaard wrote:
> Which other unwinders are out there, that might rely on the current
Well, runtime unwinders using .eh_frame should be fine, since this
uses (and has always used) consistently the GCC numbering. I don't
know if there are other unwinders using .dwarf_frame ...
> The Systemtap runtime unwinder (*) currently is incomplete
> (and in one case wrong since the numbering overlaps), so it doesn't
> really matter much which solution you pick (we will just have to watch
> out and fix things to be as consistent as possible when your change goes
> through). If you do change the numbering it would be ideal if there was
> a way to detect which one was in place (although it is probably hopeless
> because depending on which GCC version is in use there can already be
> different numberings).
The change will most likely be to consistently use GCC numbering in
.dwarf_frame as well, which changes only the encoding of the condition
code register. Since you're not using that at all in systemtap, you
shouldn't be affected.
> BTW. The reason the systemtap runtime unwinder is
> a little wrong here is because on all other architectures we assume
> eh_frame and debug_frame DWARF register numberings are equal, is ppc
> really the only architecture for which that isn't true, or were we just
As far as Linux goes, yes, ppc was the only architecture with a
different encoding between .eh_frame and .dwarf_frame. The only
other such platforms I'm aware of are Darwin on 32-bit i386, and
some other operating systems on ppc (AIX, Darwin, BSD).
Dr. Ulrich Weigand
GNU Toolchain for Linux on System z and Cell BE