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Re: Fix PR debug/24444: incorrect frame base in IA64 prologues
rOn Sat, Feb 04, 2006 at 04:54:11PM -0200, Alexandre Oliva wrote:
> On Feb 3, 2006, Richard Henderson <rth@redhat.com> wrote:
>
> > It looks ok to me. Be prepared to help the arm folk if
> > they report problems.
>
> As it turned out, testing revealed that stack unwinding was thoroughly
> broken, because of the fix to the definition of the CFA location from
> past the red zone to the literal SP value. This broke unwind-ia64.c's
> uw_init_context_1, that used to compensate for the incorrect CFA
> value. Since you'd confirmed in private that the CFA fix was correct,
> I'll proceed to check in this patch without further approval, unless
> retesting reveals any remaining regressions.
Just a general note: once a platform has defined the CFA with or
without a particular bias to the caller's SP, you can't change it.
It's an ABI break of a peculiar sort for debuggers.
For instance, GDB may know about it. All the unwinders for a target
need to agree about the interpretation of the CFA, or else frames will
appear to be on the stack in a bogus order. And if you've got some
code compiled with the old CFA for dwarf and some with the new...
It looks to me like ia64-tdep.c does know about the magic +16, but
I'm not familiar enough with ia64 to work that out for sure.
--
Daniel Jacobowitz
CodeSourcery