linux-kernel - Re: BUG: GCC-4.4.x changes the function frame on some functions

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Date:	Fri, 20 Nov 2009 03:14:12 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
cc:	Jeff Law <law@...hat.com>, rostedt@...dmis.org,
	"H. Peter Anvin" <hpa@...or.com>,
	David Daney <ddaney@...iumnetworks.com>,
	Andrew Haley <aph@...hat.com>,
	Richard Guenther <richard.guenther@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	feng.tang@...el.com, Fr??d??ric Weisbecker <fweisbec@...il.com>,
	Peter Zijlstra <peterz@...radead.org>, jakub@...hat.com,
	gcc@....gnu.org
Subject: Re: BUG: GCC-4.4.x changes the function frame on some functions

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
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