MIPS: oprofile: Backtrace: don't fail on leaf functions

Continue the backtrace if we cannot find SP adjustment and RA save. In
that case, just assume the current RA. This allows us to get samples of
frequent callers of e.g. GLIBC memset().
Signed-off-by: NAaro Koskinen <aaro.koskinen@nsn.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/8109/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

arch/mips/oprofile/backtrace.c

@@ -65,7 +65,7 @@ static inline int is_end_of_function_marker(union mips_instruction *ip)
  * - handle cases where the stack is adjusted inside a function
  *     (generally doesn't happen)
  * - find optimal value for max_instr_check
- * - try to find a way to handle leaf functions
+ * - try to find a better way to handle leaf functions
  */
 
 static inline int unwind_user_frame(struct stackframe *old_frame,
@@ -104,7 +104,7 @@ static inline int unwind_user_frame(struct stackframe *old_frame,
 	}
 
 	if (!ra_offset || !stack_size)
-		return -1;
+		goto done;
 
 	if (ra_offset) {
 		new_frame.ra = old_frame->sp + ra_offset;
@@ -121,6 +121,7 @@ static inline int unwind_user_frame(struct stackframe *old_frame,
 	if (new_frame.sp > old_frame->sp)
 		return -2;
 
+done:
 	new_frame.pc = old_frame->ra;
 	*old_frame = new_frame;