[PATCH] x86: Get bp from the IRQ regs instead of directly from the CPU

[Soeren Sandmann <sandmann@daimi.au.dk>]

Passing 0 for bp causes dump_trace() to get bp directly from the
hardware register. This leads to the IRQ stack being included in the
generated call chains, which means the stack looks something like
this:

	[ ip ] [ IRQ stack ] [ rest of stack trace ]

which is incorrect and confusing to user space.

Getting bp from the IRQ regs instead makes the tracing start after the
IRQ stack:

	[ ip ] [ rest of stack trace ]

Signed-off-by: Søren Sandmann Pedersen <sandmann@redhat.com>
---
 arch/x86/kernel/cpu/perf_event.c |   10 +++++++++-
 1 files changed, 9 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index b5801c3..39b1d0c 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -2177,10 +2177,18 @@ static const struct stacktrace_ops backtrace_ops = {
 static void
 perf_callchain_kernel(struct pt_regs *regs, struct perf_callchain_entry *entry)
 {
+	unsigned long bp;
+    
 	callchain_store(entry, PERF_CONTEXT_KERNEL);
 	callchain_store(entry, regs->ip);
 
-	dump_trace(NULL, regs, NULL, 0, &backtrace_ops, entry);
+#ifdef CONFIG_FRAME_POINTER
+	bp = regs->bp;
+#else
+	bp = 0;
+#endif
+	
+	dump_trace(NULL, regs, NULL, bp, &backtrace_ops, entry);
 }
 
 /*
-- 
1.6.5.rc2