From: Vegard Nossum <vegard.nossum@gmail.com>
Date: Fri, 27 Jun 2008 15:22:17 +0000 (+0200)
Subject: x86: don't destroy %rbp on kernel-mode faults
X-Git-Tag: v2.6.27-rc1~1106^2~249^5~1
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=9d8ad5d6c7fce31fd2c0fd4fe9977bda3e92e340;p=pandora-kernel.git

x86: don't destroy %rbp on kernel-mode faults

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.

Signed-off-by: Vegard Nossum <vegard.nossum@gmail.com>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
Acked-by: Arjan van de Ven <arjan@linux.intel.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Pekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---

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