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Re: BUG: GCC-4.4.x changes the function frame on some functions
- From: Andrew Haley <aph at redhat dot com>
- To: Thomas Gleixner <tglx at linutronix dot de>
- Cc: 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>, Steven Rostedt <rostedt at goodmis dot org>, Peter Zijlstra <peterz at infradead dot org>, jakub at redhat dot com, gcc at gcc dot gnu dot org
- Date: Thu, 19 Nov 2009 15:44:32 +0000
- 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>
Thomas Gleixner wrote:
> On Thu, 19 Nov 2009, Thomas Gleixner wrote:
>
> Can the GCC folks please shed some light on this:
>
> standard function start:
>
> push %ebp
> mov %esp, %ebp
> ....
> call mcount
>
> modified function start on a handful of functions only seen with gcc
> 4.4.x on x86 32 bit:
>
> push %edi
> lea 0x8(%esp),%edi
> and $0xfffffff0,%esp
> pushl -0x4(%edi)
> push %ebp
> mov %esp,%ebp
> ...
> call mcount
>
> This modification leads to a hard to solve problem in the kernel
> function graph tracer which assumes that the stack looks like:
>
> return address
> saved ebp
>
> With the modified function start sequence this is not longer true and
> the manipulation of the return address on the stack fails silently.
>
> Neither gcc 4.3 nor gcc 3.4 are generating such function frames, so it
> looks like a gcc 4.4.x feature.
>
> There is no real obvious reason why the edi magic needs to be done
> _before_
>
> push %ebp
> mov %esp,%ebp
Sure there is: unless you do the adjustment first %ebp won't be 16-aligned.
We're aligning the stack properly, as per the ABI requirements. Can't
you just fix the tracer?
Andrew.