[patch 3/8] x86: Improve the 32 bit Frame Pointer backtracer to also use the traditional backtrace

Arjan van de Ven
2008-01-12T05:31:03Z

Subject: x86: Improve the 32 bit Frame Pointer backtracer to also use the traditional backtrace
From: Arjan van de Ven <arjan@linux.intel.com>

The 32 bit Frame Pointer backtracer code checks if the EBP is valid
to do a backtrace; however currently on a failure it just gives up
and prints nothing. That's not very nice; we can do better and still
print a decent backtrace.

This patch changes the backtracer to use the regular backtracing algorithm
at the same time as the EBP backtracer; the EBP backtracer is basically
used to figure out which part of the backtrace are reliable vs those
which are likely to be noise.

Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>

---
arch/x86/kernel/traps_32.c | 44 ++++++++++++++++++++------------------------
1 file changed, 20 insertions(+), 24 deletions(-)

Index: linux-2.6.24-rc7/arch/x86/kernel/traps_32.c
===================================================================
--- linux-2.6.24-rc7.orig/arch/x86/kernel/traps_32.c
+++ linux-2.6.24-rc7/arch/x86/kernel/traps_32.c
@@ -117,36 +117,32 @@ static inline unsigned long print_contex
unsigned long *stack, unsigned long ebp,
const struct stacktrace_ops *ops, void *data)
{
-#ifdef CONFIG_FRAME_POINTER
struct stack_frame *frame = (struct stack_frame *)ebp;
- while (valid_stack_ptr(tinfo, frame, sizeof(*frame))) {
- struct stack_frame *next;
- unsigned long addr;

- addr = frame->return_address;
- if (__kernel_text_address(addr))
- ops->address(data, addr, 1);
- /*
- * break out of recursive entries (such as
- * end_of_stack_stop_unwind_function). Also,
- * we can never allow a frame pointer to
- * move downwards!
- */
- next = frame->next_frame;
- ebp = (unsigned long) next;
- if (next <= frame)
- break;
- frame = next;
- }
-#else
+ /*
+ * if EBP is "deeper" into the stack than the actual stack pointer,
+ * we need to rewind the stack pointer a little to start at the
+ * first stack frame, but only if EBP is in this stack frame.
+ */
+ if (stack > (unsigned long *) ebp
+ && valid_stack_ptr(tinfo, frame, sizeof(*frame)))
+ stack = (unsigned long *) ebp;
+
while (valid_stack_ptr(tinfo, stack, sizeof(*stack))) {
unsigned long addr;

- addr = *stack++;
- if (__kernel_text_address(addr))
- ops->address(data, addr, 1);
+ addr = *stack;
+ if (__kernel_text_address(addr)) {
+ if ((unsigned long) stack == ebp + 4) {
+ ops->address(data, addr, 1);
+ frame = frame->next_frame;
+ ebp = (unsigned long) frame;
+ } else {
+ ops->address(data, addr, 0);
+ }
+ }
+ stack++;
}
-#endif
return ebp;