linux-kernel - Re: [PATCH][GIT PULL][v2.6.32] tracing/x86: Add check to detect GCC messing with mcount prologue

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Message-ID: <4B0D8FC1.1010608@zytor.com>
Date:	Wed, 25 Nov 2009 12:12:49 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jakub Jelinek <jakub@...hat.com>
CC:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	Andrew Haley <aph@...hat.com>, "H.J. Lu" <hjl.tools@...il.com>,
	rostedt@...dmis.org, LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	feng.tang@...el.com, Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	David Daney <ddaney@...iumnetworks.com>,
	Richard Guenther <richard.guenther@...il.com>,
	gcc <gcc@....gnu.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH][GIT PULL][v2.6.32] tracing/x86: Add check to detect GCC
 messing with mcount prologue

On 11/25/2009 08:44 AM, Jakub Jelinek wrote:
> 
> If you compile kernels 90%+ people out there run with -p on i?86/x86_64,
> then certainly coming up with a new gcc switch and new profiling ABI is
> desirable.  -p on i?86/x86_64 e.g. forces -fno-omit-frame-pointer, which
> makes code on these register starved arches significantly worse.
> Making GCC output profiling call before prologue instead of after prologue
> is a 4 liner in generic code and a few lines in target specific code.
> The important thing is that we shouldn't have 100 different profiling ABIs,
> so it is desirable to agree on something that will be generally useful not
> just for the kernel, but perhaps for other purposes.
> 

There is really just one that makes sense, which is providing the
ABI-defined entry state, which means intercepting at the point of entry.

Anything else is/was a mistake.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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