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SubjectRe: [PATCH][GIT PULL][v2.6.32] tracing/x86: Add check to detect GCC messing with mcount prologue
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On Tue, 2009-11-24 at 17:12 +0000, Andrew Haley wrote:
> H. Peter Anvin wrote:
> > If we're changing gcc anyway, then let's add the option of intercepting
> > the function at the point where the machine state is well-defined by
> > ABI, which is before the function stack frame is set up.
>
> Hmm. On the x86 I suppose we could just inject a naked call instruction,
> but not all aeches allow us to call anything before we've saved the return
> address. Or are you talking x86 only?

Earlier in the GCC BUG thread we talked about this. Adding a __fentry__
call at the beginning of the function. This could be done for other
archs as well, but yes, the return address must be stored. For x86 it is
the easiest because it automatically stores the return address on the
stack (Andi already has a working patch I believe).

For other archs, Linus showed some examples:

http://lkml.org/lkml/2009/11/19/349

-- Steve




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