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

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Message-ID: <4831EE48.5050908@firstfloor.org>
Date:	Mon, 19 May 2008 23:16:56 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Vegard Nossum <vegard.nossum@...il.com>
CC:	Ingo Molnar <mingo@...e.hu>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH] x86: don't destroy %rbp on kernel-mode faults

Vegard Nossum wrote:
> Hi,
> 
> The RFC part of this patch is: Does anybody see why touching %rcx would
> be bad? It certainly looks like %ecx is free. This fixes the stacktrace
> problem I was seeing, and Pekka tested a bootup to userspace. (Pekka also
> did half of the debugging. When will git allow multiple authors for a
> patch? :-))

The patch is ok, but I'm sure there's lots of other assembler code that
destroys %rbp when it was saved elsewhere.

When I wrote all the assembler the assumption was always that a real
unwinder would be used for backtraces, not frame pointer.

-Andi
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