[PATCH] i386/x86-64: Work around gcc bug with noreturn functions in unwinder

Current gcc generates calls not jumps to noreturn functions. When that happens the
return address can point to the next function, which confuses the unwinder.

This patch works around it by marking asynchronous exception
frames in contrast normal call frames in the unwind information.  Then teach
the unwinder to decode this.

For normal call frames the unwinder now subtracts one from the address which avoids
this problem.  The standard libgcc unwinder uses the same trick.

It doesn't include adjustment of the printed address (i.e. for the original
example, it'd still be kernel_math_error+0 that gets displayed, but the
unwinder wouldn't get confused anymore.

This only works with binutils 2.6.17+ and some versions of H.J.Lu's 2.6.16
unfortunately because earlier binutils don't support .cfi_signal_frame

[AK: added automatic detection of the new binutils and wrote description]

Signed-off-by: Jan Beulich <jbeulich@novell.com>
Signed-off-by: Andi Kleen <ak@suse.de>

1 files changed, 4 insertions, 0 deletions

diff --git a/arch/i386/kernel/entry.S b/arch/i386/kernel/entry.S
index 284f2e908ad0..5a63d6fdb70e 100644
--- a/arch/i386/kernel/entry.S
+++ b/arch/i386/kernel/entry.S
@@ -183,18 +183,21 @@ VM_MASK		= 0x00020000
 
 #define RING0_INT_FRAME \
         CFI_STARTPROC simple;\
+        CFI_SIGNAL_FRAME;\
         CFI_DEF_CFA esp, 3*4;\
         /*CFI_OFFSET cs, -2*4;*/\
         CFI_OFFSET eip, -3*4
 
 #define RING0_EC_FRAME \
         CFI_STARTPROC simple;\
+        CFI_SIGNAL_FRAME;\
         CFI_DEF_CFA esp, 4*4;\
         /*CFI_OFFSET cs, -2*4;*/\
         CFI_OFFSET eip, -3*4
 
 #define RING0_PTREGS_FRAME \
         CFI_STARTPROC simple;\
+        CFI_SIGNAL_FRAME;\
         CFI_DEF_CFA esp, OLDESP-EBX;\
         /*CFI_OFFSET cs, CS-OLDESP;*/\
         CFI_OFFSET eip, EIP-OLDESP;\
@@ -275,6 +278,7 @@ need_resched:
         # sysenter call handler stub
 ENTRY(sysenter_entry)
         CFI_STARTPROC simple
+        CFI_SIGNAL_FRAME
         CFI_DEF_CFA esp, 0
         CFI_REGISTER esp, ebp
         movl TSS_sysenter_esp0(%esp),%esp