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

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Date:	Thu, 19 Nov 2009 13:14:18 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jeff Law <law@...hat.com>
CC:	rostedt@...dmis.org, David Daney <ddaney@...iumnetworks.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Haley <aph@...hat.com>,
	Richard Guenther <richard.guenther@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	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

Hence a new unconstrained option...

"Jeff Law" <law@...hat.com> wrote:

>On 11/19/09 12:50, H. Peter Anvin wrote:
>>
>> Calling the profiler immediately at the entry point is clearly the more
>> sane option.  It means the ABI is well-defined, stable, and independent
>> of what the actual function contents are.  It means that ABI isn't the
>> normal C ABI (the __fentry__ function would have to preserve all
>> registers), but that's fine...
>>    
>Note there are targets (even some old x86 variants) that required the 
>profiling calls to occur after the prologue.  Unfortunately, nobody 
>documented *why* that  was the case.   Sigh.
>
>Jeff

--
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