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>

1 files changed, 20 insertions, 24 deletions

diff --git a/arch/x86/kernel/traps_32.c b/arch/x86/kernel/traps_32.c
index 8ef8a9ddfec..959d40edecd 100644
--- 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;
 }