linux-kernel - Re: [RESEND][PATCH] x86: don't destroy %rbp on kernel-mode faults

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Date:	Fri, 27 Jun 2008 17:46:07 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Vegard Nossum <vegard.nossum@...il.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Andi Kleen <andi@...stfloor.org>,
	Pekka Enberg <penberg@...helsinki.fi>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RESEND][PATCH] x86: don't destroy %rbp on kernel-mode faults


* Vegard Nossum <vegard.nossum@...il.com> wrote:

> >From the code:
> 
>     "B stepping K8s sometimes report an truncated RIP for IRET exceptions
>     returning to compat mode. Check for these here too."
> 
> The code then proceeds to truncate the upper 32 bits of %rbp. This means
> that when do_page_fault() is finally called, its prologue,
> 
>     do_page_fault:
>         push %rbp
>         movl %rsp, %rbp
> 
> will put the truncated base pointer on the stack. This means that the
> stack tracer will not be able to follow the base-pointer changes and
> will see all subsequent stack frames as unreliable.
> 
> This patch changes the code to use a different register (%rcx) for the
> checking and leaves %rbp untouched.

applied to tip/x86/debug - thanks Vegard!

	Ingo
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