Messages in this thread | | | Date | Mon, 19 May 2008 13:22:37 -0700 | From | Arjan van de Ven <> | Subject | Re: [RFC][PATCH] x86: don't destroy %rbp on kernel-mode faults |
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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? :-)) > > > Vegard > > > From b1cbf24fcd05aa5ed2e610c80c06bc519d3188f7 Mon Sep 17 00:00:00 2001 > From: Vegard Nossum <vegard.nossum@gmail.com> > Date: Mon, 19 May 2008 21:39:44 +0200 > Subject: [PATCH] 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. > > Cc: Andi Kleen <andi@firstfloor.org> > Cc: Ingo Molnar <mingo@elte.hu> > Cc: Arjan van de Ven <arjan@linux.intel.com> > Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi> > Signed-off-by: Vegard Nossum <vegard.nossum@gmail.com>
looks good to me; good debugging!
Acked-by: Arjan van de Ven <arjan@linux.intel.com>
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