[PATCH] x86_64: Fix backtracing for interrupt stacks

Re-add backlink for old style unwinder to stack switching.  Add proper
stack frame and CFI annotations to call_softirq

This prevents a oops when backtracing with fallback through the
interrupt stack top.

Suggested by Jan Beulich and Herbert Xu wanted it in 2.6.18.

Cc: jbeulich@novell.com
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 11 insertions, 7 deletions

diff --git a/arch/x86_64/kernel/entry.S b/arch/x86_64/kernel/entry.S
index d464dded68c0..6f810424df44 100644
--- a/arch/x86_64/kernel/entry.S
+++ b/arch/x86_64/kernel/entry.S
@@ -513,6 +513,7 @@ END(stub_rt_sigreturn)
         swapgs  
 1:      incl    %gs:pda_irqcount        # RED-PEN should check preempt count
         cmoveq %gs:pda_irqstackptr,%rsp
+        push    %rbp                    # backlink for old unwinder
         /*
          * We entered an interrupt context - irqs are off:
          */
@@ -1139,18 +1140,21 @@ ENTRY(machine_check)
 END(machine_check)
 #endif
 
+/* Call softirq on interrupt stack. Interrupts are off. */
 ENTRY(call_softirq)
         CFI_STARTPROC
-        movq %gs:pda_irqstackptr,%rax
-        movq %rsp,%rdx
-        CFI_DEF_CFA_REGISTER    rdx
+        push %rbp
+        CFI_ADJUST_CFA_OFFSET   8
+        CFI_REL_OFFSET rbp,0
+        mov  %rsp,%rbp
+        CFI_DEF_CFA_REGISTER rbp
         incl %gs:pda_irqcount
-        cmove %rax,%rsp
-        pushq %rdx
-        /*todo CFI_DEF_CFA_EXPRESSION ...*/
+        cmove %gs:pda_irqstackptr,%rsp
+        push  %rbp                      # backlink for old unwinder
         call __do_softirq
-        popq %rsp
+        leaveq
         CFI_DEF_CFA_REGISTER    rsp
+        CFI_ADJUST_CFA_OFFSET   -8
         decl %gs:pda_irqcount
         ret
         CFI_ENDPROC