[PATCH] x86_64: fix page fault from show_trace()

["Jan Beulich" <JBeulich@novell.com>]

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The introduction of call_softirq switching to the interrupt stack
several releases earlier resulted in a problem with the code in
show_trace, which assumes that it can pick the previous stack pointer
from the end of the interrupt stack.

From: Jan Beulich <jbeulich@novell.com>

(actual patch attached)

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The introduction of call_softirq switching to the interrupt stack
several releases earlier resulted in a problem with the code in
show_trace, which assumes that it can pick the previous stack pointer
from the end of the interrupt stack.

From: Jan Beulich <jbeulich@novell.com>

--- 2.6.14/arch/x86_64/kernel/entry.S	2005-10-28 02:02:08.000000000 +0200
+++ 2.6.14-nlkd/arch/x86_64/kernel/entry.S	2005-11-07 14:56:02.000000000 +0100
@@ -1024,17 +1024,15 @@ ENTRY(machine_check)
 ENTRY(call_softirq)
 	CFI_STARTPROC
 	movq %gs:pda_irqstackptr,%rax
-	pushq %r15
-	CFI_ADJUST_CFA_OFFSET 8
-	movq %rsp,%r15
-	CFI_DEF_CFA_REGISTER	r15
+	movq %rsp,%rdx
+	CFI_DEF_CFA_REGISTER	rdx
 	incl %gs:pda_irqcount
 	cmove %rax,%rsp
+	pushq %rdx
+	/*todo CFI_DEF_CFA_EXPRESSION ...*/
 	call __do_softirq
-	movq %r15,%rsp
+	popq %rsp
 	CFI_DEF_CFA_REGISTER	rsp
 	decl %gs:pda_irqcount
-	popq %r15
-	CFI_ADJUST_CFA_OFFSET -8
 	ret
 	CFI_ENDPROC