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: <6dc9ffc80911221530t38d83cf6je739743c8d756667@mail.gmail.com>
Date:	Sun, 22 Nov 2009 15:30:44 -0800
From:	"H.J. Lu" <hjl.tools@...il.com>
To:	Andrew Haley <aph@...hat.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

On Sun, Nov 22, 2009 at 9:20 AM, Andrew Haley <aph@...hat.com> wrote:
> 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.
>

Why not, there is

static const unsigned int x86_accumulate_outgoing_args
  = m_AMD_MULTIPLE | m_ATOM | m_PENT4 | m_NOCONA | m_PPRO | m_CORE2
    | m_GENERIC;

-mtune=generic turns on -maccumulate-outgoing-args.


-- 
H.J.
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