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Re: [PATCH] mudflap: remove usage of builtin_frame_address

Andrew Pinski <> wrote on 01/13/2005 03:32:39 AM:
> On Jan 12, 2005, at 9:22 PM, Ulrich Weigand wrote:
> > When -fomit-frame-pointer is true, and the function doesn't otherwise
> > require a frame pointer, the hard register hard_frame_pointer_rtx is
> > not set up as frame pointer, and basically contains a random value ...
> But in reload/greg, it gets replaced with the stack based frame pointer.
> At least it does on rs6000 and most likely every other target.

It may happen to work on rs6000 because that doesn't even define
HARD_FRAME_POINTER_REGNUM in the first place, so hard_frame_pointer_rtx
is actually frame_pointer_rtx, which of course works.

But on all platforms that *do* define a HARD_FRAME_POINTER_REGNUM,
including i386, alpha, sparc, ... it is just the other way around:
reload replaces *frame_pointer_rtx* with either hard_frame_pointer_rtx
or stack_pointer_rtx, depending on whether a hard frame pointer is
needed or not.

B.t.w. building

void *test (void)
  return __builtin_frame_address (0);

on i386 with -fomit-frame-pointer results in

        pushl   %ebp
        movl    %ebp, %eax
        popl    %ebp

which doesn't strike me as exactly correct either; this is the very
same problem I'm seeing on s390.

Mit freundlichen Gruessen / Best Regards

Ulrich Weigand

  Dr. Ulrich Weigand
  Linux for S/390 Design & Development
  IBM Deutschland Entwicklung GmbH, Schoenaicher Str. 220, 71032 Boeblingen
  Phone: +49-7031/16-3727   ---   Email:

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