Subject: [RFC 2/3] arm64: refactor save_stack_trace()

From: [email-masked] (AKASHI Takahiro)
Date: Thu, 16 Jul 2015 10:08:03 +0900

On 07/16/2015 09:27 AM, AKASHI Takahiro wrote:
> On 07/16/2015 01:13 AM, Steven Rostedt wrote:
>> On Wed, 15 Jul 2015 10:55:36 -0400
>> Steven Rostedt <[email-masked]> wrote:
>>
>>
>>> I'll take a look at it and try to clean up the code.
>>
>> Does the  following patch make sense for you?
>
> Looks nice. The patch greatly simplifies changes on arm64 side.

As follows:

- Takahiro AKASHI

diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h
index c5534fa..868d6f1 100644
--- a/arch/arm64/include/asm/ftrace.h
+++ b/arch/arm64/include/asm/ftrace.h
@@ -15,6 +15,7 @@

  #define MCOUNT_ADDR		((unsigned long)_mcount)
  #define MCOUNT_INSN_SIZE	AARCH64_INSN_SIZE
+#define FTRACE_STACK_FRAME_OFFSET 4 /* sync it up with stacktrace.c */

  #ifndef __ASSEMBLY__
  #include <linux/compat.h>
diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index 1da6029..2c1bf7d 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -260,6 +260,13 @@ static inline void ftrace_kill(void) { }
  #endif /* CONFIG_FUNCTION_TRACER */

  #ifdef CONFIG_STACK_TRACER
+/*
+ * the offset value to add to return address from save_stack_trace()
+ */
+#ifndef FTRACE_STACK_FRAME_OFFSET
+#define FTRACE_STACK_FRAME_OFFSET 0
+#endif
+
  extern int stack_tracer_enabled;
  int
  stack_trace_sysctl(struct ctl_table *table, int write,
diff --git a/kernel/trace/trace_stack.c b/kernel/trace/trace_stack.c
index 9384647..c5b9748 100644
--- a/kernel/trace/trace_stack.c
+++ b/kernel/trace/trace_stack.c
@@ -105,7 +105,7 @@ check_stack(unsigned long ip, unsigned long *stack)

  	/* Skip over the overhead of the stack tracer itself */
  	for (i = 0; i < max_stack_trace.nr_entries; i++) {
-		if (stack_dump_trace[i] == ip)
+		if ((stack_dump_trace[i] + FTRACE_STACK_FRAME_OFFSET) == ip)
  			break;
  	}

@@ -131,7 +131,8 @@ check_stack(unsigned long ip, unsigned long *stack)
  		p = start;

  		for (; p < top && i < max_stack_trace.nr_entries; p++) {
-			if (*p == stack_dump_trace[i]) {
+			if (*p == (stack_dump_trace[i]
+					+ FTRACE_STACK_FRAME_OFFSET)) {
  				stack_dump_trace[x] = stack_dump_trace[i++];
  				this_size = stack_dump_index[x++] =
  					(top - p) * sizeof(unsigned long);
-- 
1.7.9.5