x86: improve the 32 bit Frame Pointer backtracer to also use the traditional backtrace

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>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

diff --git a/arch/x86/kernel/traps_32.c b/arch/x86/kernel/traps_32.c
index 8ef8a9ddfec60aceee9b37f2fca29df45c4d7c3d..959d40edecd51a021f0d3f548fd88cc18a6f0104 100644 (file)
--- a/arch/x86/kernel/traps_32.c
+++ b/arch/x86/kernel/traps_32.c
@@ -118,36 +118,32 @@ static inline unsigned long print_context_stack(struct thread_info *tinfo,
                                unsigned long *stack, unsigned long bp,
                                const struct stacktrace_ops *ops, void *data)
 {
-#ifdef CONFIG_FRAME_POINTER
        struct stack_frame *frame = (struct stack_frame *)bp;
-       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;
-               bp = (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 *) bp
+                       && valid_stack_ptr(tinfo, frame, sizeof(*frame)))
+               stack = (unsigned long *) bp;
+
        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 == bp + 4) {
+                               ops->address(data, addr, 1);
+                               frame = frame->next_frame;
+                               bp = (unsigned long) frame;
+                       } else {
+                               ops->address(data, addr, 0);
+                       }
+               }
+               stack++;
        }
-#endif
        return bp;
 }