[ARM] 5382/1: unwind: Reorganise the stacktrace support

This patch changes the walk_stacktrace and its callers for easier
integration of stack unwinding. The arch/arm/kernel/stacktrace.h file is
also moved to arch/arm/include/asm/stacktrace.h.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 60 insertions, 28 deletions

diff --git a/arch/arm/kernel/stacktrace.c b/arch/arm/kernel/stacktrace.c
index fc650f64df43..9f444e5cc165 100644
--- a/arch/arm/kernel/stacktrace.c
+++ b/arch/arm/kernel/stacktrace.c
@@ -2,35 +2,60 @@
 #include <linux/sched.h>
 #include <linux/stacktrace.h>
 
-#include "stacktrace.h"
-
-int walk_stackframe(unsigned long fp, unsigned long low, unsigned long high,
-                    int (*fn)(struct stackframe *, void *), void *data)
+#include <asm/stacktrace.h>
+
+#if defined(CONFIG_FRAME_POINTER) && !defined(CONFIG_ARM_UNWIND)
+/*
+ * Unwind the current stack frame and store the new register values in the
+ * structure passed as argument. Unwinding is equivalent to a function return,
+ * hence the new PC value rather than LR should be used for backtrace.
+ *
+ * With framepointer enabled, a simple function prologue looks like this:
+ *      mov     ip, sp
+ *      stmdb   sp!, {fp, ip, lr, pc}
+ *      sub     fp, ip, #4
+ *
+ * A simple function epilogue looks like this:
+ *      ldm     sp, {fp, sp, pc}
+ *
+ * Note that with framepointer enabled, even the leaf functions have the same
+ * prologue and epilogue, therefore we can ignore the LR value in this case.
+ */
+int unwind_frame(struct stackframe *frame)
 {
-        struct stackframe *frame;
-
-        do {
-                /*
-                 * Check current frame pointer is within bounds
-                 */
-                if (fp < (low + 12) || fp + 4 >= high)
-                        break;
+        unsigned long high, low;
+        unsigned long fp = frame->fp;
 
-                frame = (struct stackframe *)(fp - 12);
+        /* only go to a higher address on the stack */
+        low = frame->sp;
+        high = ALIGN(low, THREAD_SIZE) + THREAD_SIZE;
 
-                if (fn(frame, data))
-                        break;
+        /* check current frame pointer is within bounds */
+        if (fp < (low + 12) || fp + 4 >= high)
+                return -EINVAL;
 
-                /*
-                 * Update the low bound - the next frame must always
-                 * be at a higher address than the current frame.
-                 */
-                low = fp + 4;
-                fp = frame->fp;
-        } while (fp);
+        /* restore the registers from the stack frame */
+        frame->fp = *(unsigned long *)(fp - 12);
+        frame->sp = *(unsigned long *)(fp - 8);
+        frame->pc = *(unsigned long *)(fp - 4);
 
         return 0;
 }
+#endif
+
+void walk_stackframe(struct stackframe *frame,
+                     int (*fn)(struct stackframe *, void *), void *data)
+{
+        while (1) {
+                int ret;
+
+                if (fn(frame, data))
+                        break;
+                ret = unwind_frame(frame);
+                if (ret < 0)
+                        break;
+        }
+}
 EXPORT_SYMBOL(walk_stackframe);
 
 #ifdef CONFIG_STACKTRACE
@@ -44,7 +69,7 @@ static int save_trace(struct stackframe *frame, void *d)
 {
         struct stack_trace_data *data = d;
         struct stack_trace *trace = data->trace;
-        unsigned long addr = frame->lr;
+        unsigned long addr = frame->pc;
 
         if (data->no_sched_functions && in_sched_functions(addr))
                 return 0;
@@ -61,11 +86,10 @@ static int save_trace(struct stackframe *frame, void *d)
 void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
 {
         struct stack_trace_data data;
-        unsigned long fp, base;
+        struct stackframe frame;
 
         data.trace = trace;
         data.skip = trace->skip;
-        base = (unsigned long)task_stack_page(tsk);
 
         if (tsk != current) {
 #ifdef CONFIG_SMP
@@ -76,14 +100,22 @@ void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
                 BUG();
 #else
                 data.no_sched_functions = 1;
-                fp = thread_saved_fp(tsk);
+                frame.fp = thread_saved_fp(tsk);
+                frame.sp = thread_saved_sp(tsk);
+                frame.lr = 0;           /* recovered from the stack */
+                frame.pc = thread_saved_pc(tsk);
 #endif
         } else {
+                register unsigned long current_sp asm ("sp");
+
                 data.no_sched_functions = 0;
-                asm("mov %0, fp" : "=r" (fp));
+                frame.fp = (unsigned long)__builtin_frame_address(0);
+                frame.sp = current_sp;
+                frame.lr = (unsigned long)__builtin_return_address(0);
+                frame.pc = (unsigned long)save_stack_trace_tsk;
         }
 
-        walk_stackframe(fp, base, base + THREAD_SIZE, save_trace, &data);
+        walk_stackframe(&frame, save_trace, &data);
         if (trace->nr_entries < trace->max_entries)
                 trace->entries[trace->nr_entries++] = ULONG_MAX;
 }