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

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Date:	Sun, 22 Nov 2009 17:20:09 +0000
From:	Andrew Haley <aph@...hat.com>
To:	"H.J. Lu" <hjl.tools@...il.com>
CC:	rostedt@...dmis.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	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>,
	jakub@...hat.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

H.J. Lu wrote:
> On Fri, Nov 20, 2009 at 11:35 AM, Andrew Haley <aph@...hat.com> wrote:
>> Steven Rostedt wrote:
>>> Ingo, Thomas and Linus,
>>>
>>> I know Thomas did a patch to force the -mtune=generic, but just in case
>>> gcc decides to do something crazy again, this patch will catch it.
>>>
>>> Should we try to get this in now?
>> I'm sure this makes sense, but a gcc test case would be even better.
>> If this can be detected in the gcc test suite it'll be found and
>> fixed long before y'all in kernel land get to see it.  That's the
>> only way to guarantee this never bothers you again.
>>
>> H.J., who wrote the code in question, is hopefully looking at why
>> this odd code is being generated.  Once he's done I can put a
>> suitable test case in the gcc test suite.
>>
> 
> See:
> 
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42109#c7

I saw that, but does it mean you're going to investigate?  There is
no obvious reason why -mtune=generic should affect code generation
in this way, but it does.

Andrew.
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