linux-kernel - Re: [Xen-devel] Re: [PATCH] xen: Disable stack protector for irq helper

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Date:	Mon, 05 Oct 2009 17:36:02 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Bastian Blank <bastian@...di.eu.org>,
	Ingo Molnar <mingo@...hat.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	Stable Kernel <stable@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Xen-devel <xen-devel@...ts.xensource.com>
Subject: Re: [Xen-devel] Re: [PATCH] xen: Disable stack protector for irq
 helper

On 10/05/09 15:43, Bastian Blank wrote:
> On Mon, Oct 05, 2009 at 10:21:01AM -0700, Jeremy Fitzhardinge wrote:
>   
>>> Save all caller-saved registers on x86_32 for the paravirt callee saved
>>> registers.
>>>       
>> That looks better, but it is still overkill.  We only need to save the
>> set of registers the ABI requires the callee to preserve.  What
>> additional register(s) gets clobbered by stack-protector that need to be
>> saved?
>>     
> Well, exactly the two, ecx and edx. eax is still clobbered by the return
> value. Anyway, it works in praxis.

I'm confused.  It already saves ecx, so what else needs saving?

Besides, most of the code in that file isn't used unless you're using a
very old version of Xen; it will generally prefer to use the ones in
xen-asm_X.S.

I have the feeling we haven't really found the root cause of your
problem yet.

Thanks,
    J

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