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

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Date:	Tue, 6 Oct 2009 05:30:50 +0200
From:	Bastian Blank <bastian@...di.eu.org>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	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 Mon, Oct 05, 2009 at 05:36:02PM -0700, Jeremy Fitzhardinge wrote:
> 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?

The original version saves ecx, but not edx. Both are official
caller-saved registers.

> 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.

Well, my call stack say something different. It crashs during early
startup without a console. The modifications to the function pointers is
done much later.

Bastian

-- 
Vulcans never bluff.
		-- Spock, "The Doomsday Machine", stardate 4202.1
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