[PATCH] fix profiling

[Dave Korn]

Brian Dessent wrote on 05 August 2008 06:28:

> Brian Dessent wrote:
> 
>> Since this code is lifted from the BSDs I did check that this change was
>> made there as well, e.g.
>>
<http://www.openbsd.org/cgi-bin/cvsweb/src/sys/arch/i386/include/profile.h?r
ev=1.10&content-type=text/x-cvsweb-markup>.

  Adding 'volatile' to asms that didn't need it could never do any harm,
anyway, apart from the minor missed-optimisation opportunities it implies,
but correctness is more important here!
 
> Actually, I also missed that the above version uses +r instead of =r for
> the second constraint.  I guess we should make that change too.

  I think that change is wrong.  The register is written, not read; the
input value is not used.  (The fact it is used as a source operand in the
second instruction doesn't matter, because it's not the input value being
used there but the previously-written value that just clobbered the input
value).  It looks like a misunderstanding of what read-write means in terms
of gcc constraints.


    cheers,
      DaveK
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