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Date: Fri, 20 Nov 2009 03:14:12 +0100 (CET)
From: Thomas Gleixner <tglx@linutronix.de>
To: Linus Torvalds <torvalds@linux-foundation.org>
cc: Jeff Law <law@redhat.com>, rostedt@goodmis.org,
       "H. Peter Anvin" <hpa@zytor.com>,
       David Daney <ddaney@caviumnetworks.com>, Andrew Haley <aph@redhat.com>,
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       Fr??d??ric Weisbecker <fweisbec@gmail.com>,
       Peter Zijlstra <peterz@infradead.org>, jakub@redhat.com,
       gcc@gcc.gnu.org
Subject: Re: BUG: GCC-4.4.x changes the function frame on some functions
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On Fri, 20 Nov 2009, Thomas Gleixner wrote:

> On Thu, 19 Nov 2009, Linus Torvalds wrote:
> > On Fri, 20 Nov 2009, Thomas Gleixner wrote:
> > > 
> > > While testing various kernel configs we found out that the problem
> > > comes and goes. Finally I started to compare the gcc command line
> > > options and after some fiddling it turned out that the following
> > > minimal deltas change the code generator behaviour:
> > > 
> > > Bad:  -march=pentium-mmx                -Wa,-mtune=generic32
> > > Good: -march=i686        -mtune=generic -Wa,-mtune=generic32
> > > Good: -march=pentium-mmx -mtune-generic -Wa,-mtune=generic32

Found some more:

Bad:  -march=k6                   -Wa,-mtune=generic32
Bad:  -march=geode                -Wa,-mtune=generic32
Bad:  -march=c3                   -Wa,-mtune=generic32

That seems every thing which has MMX support but no SSE and is somehow
compatible to the pentium-mmx.

Looks like the code generator optimization for those was done after
consuming the secret gcc-shrooms.

Thanks,

	tglx