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

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Date:	Thu, 19 Nov 2009 20:01:57 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
cc:	Andrew Haley <aph@...hat.com>,
	Richard Guenther <richard.guenther@...il.com>,
	rostedt@...dmis.org, 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, 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 Thu, 19 Nov 2009, Linus Torvalds wrote:
> > I bet other people than just the kernel use the mcount hook for subtler 
> > things than just doing profiles. And even if they don't, the quoted code 
> > generation is just crazy _crap_.
> 
> For the kernel, if the only case is that timer_stat.c thing that Thomas 
> pointed at, I guess we can at least work around it with something like the 
> appended. The kernel code is certainly ugly too, no question about that. 
> 
> It's just that we'd like to be able to depend on mcount code generation 
> not being insane even in the presense of ugly code..
> 
> The alternative would be to have some warning when this happens, so that 
> we can at least see it. "mcount won't work reliably"

There are at least 20 other random functions which have the same
problem. Have not looked at the details yet.

Just compiled with -mincoming-stack-boundary=4 and the problem goes
away as gcc now thinks that the incoming stack is already 16 byte
aligned. But that might break code which actually uses SSE

Thanks,

	tglx


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