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Re: BUG: GCC-4.4.x changes the function frame on some functions
- From: Thomas Gleixner <tglx at linutronix dot de>
- To: Linus Torvalds <torvalds at linux-foundation dot org>
- Cc: Andrew Haley <aph at redhat dot com>, Richard Guenther <richard dot guenther at gmail dot com>, rostedt at goodmis dot org, Ingo Molnar <mingo at elte dot hu>, "H. Peter Anvin" <hpa at zytor dot com>, LKML <linux-kernel at vger dot kernel dot org>, Andrew Morton <akpm at linux-foundation dot org>, Heiko Carstens <heiko dot carstens at de dot ibm dot com>, feng dot tang at intel dot com, Fr??d??ric Weisbecker <fweisbec at gmail dot com>, Peter Zijlstra <peterz at infradead dot org>, jakub at redhat dot com, gcc at gcc dot gnu dot org
- Date: Thu, 19 Nov 2009 20:01:57 +0100 (CET)
- Subject: Re: BUG: GCC-4.4.x changes the function frame on some functions
- References: <alpine.LFD.2.00.0911181933540.24119@localhost.localdomain> <tip-887a29f59b93cf54e21814869a4ab6e80b6fa623@git.kernel.org> <20091119072040.GA23579@elte.hu> <alpine.LFD.2.00.0911191053390.24119@localhost.localdomain> <alpine.LFD.2.00.0911191423190.24119@localhost.localdomain> <alpine.LFD.2.00.0911191607440.24119@localhost.localdomain> <alpine.LFD.2.00.0911190934070.2793@localhost.localdomain> <1258653562.22249.682.camel@gandalf.stny.rr.com> <84fc9c000911191003t244eb864o3d5b355ab5485f@mail.gmail.com> <4B058CCD.8050605@redhat.com> <alpine.LFD.2.00.0911191039470.2793@localhost.localdomain> <alpine.LFD.2.00.0911191041471.2793@localhost.localdomain> <alpine.LFD.2.00.0911191047350.2793@localhost.localdomain>
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