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[PATCH v3 3/7] arm64: ftrace: fix a stack tracer's output under function graph tracer

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  [PATCH v3 3/7] arm64: ftrace: fix a stack tracer's output under function graph tracer AKASHI Takahiro <takahiro.akashi@linaro.org> - 2015-10-08 12:10 +0200
    Re: [PATCH v3 3/7] arm64: ftrace: fix a stack tracer's output under function graph tracer Jungseok Lee <jungseoklee85@gmail.com> - 2015-10-13 17:30 +0200
      Re: [PATCH v3 3/7] arm64: ftrace: fix a stack tracer's output under  function graph tracer AKASHI Takahiro <takahiro.akashi@linaro.org> - 2015-10-14 07:10 +0200

#1242147 — [PATCH v3 3/7] arm64: ftrace: fix a stack tracer's output under function graph tracer

Function graph tracer modifies a return address (LR) in a stack frame
to hook a function return. This will result in many useless entries
(return_to_handler) showing up in a stack tracer's output.

This patch replaces such entries with originals values preserved in
current->ret_stack[].

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
---
 arch/arm64/include/asm/ftrace.h |    2 ++
 arch/arm64/kernel/stacktrace.c  |   20 ++++++++++++++++++++
 2 files changed, 22 insertions(+)

diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h
index 2b43e20..b7d597c 100644
--- a/arch/arm64/include/asm/ftrace.h
+++ b/arch/arm64/include/asm/ftrace.h
@@ -29,6 +29,8 @@ struct dyn_arch_ftrace {
 
 extern unsigned long ftrace_graph_call;
 
+extern void return_to_handler(void);
+
 static inline unsigned long ftrace_call_adjust(unsigned long addr)
 {
 	/*
diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
index bc0689a..1555a8b 100644
--- a/arch/arm64/kernel/stacktrace.c
+++ b/arch/arm64/kernel/stacktrace.c
@@ -78,6 +78,9 @@ struct stack_trace_data {
 	struct stack_trace *trace;
 	unsigned int no_sched_functions;
 	unsigned int skip;
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+	unsigned int ret_stack_index;
+#endif
 };
 
 static int save_trace(struct stackframe *frame, void *d)
@@ -86,6 +89,20 @@ static int save_trace(struct stackframe *frame, void *d)
 	struct stack_trace *trace = data->trace;
 	unsigned long addr = frame->pc;
 
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+	if (addr == (unsigned long)return_to_handler - AARCH64_INSN_SIZE) {
+		/*
+		 * This is a case where function graph tracer has
+		 * modified a return address (LR) in a stack frame
+		 * to hook a function return.
+		 * So replace it to an original value.
+		 */
+		frame->pc = addr =
+			current->ret_stack[data->ret_stack_index--].ret
+							- AARCH64_INSN_SIZE;
+	}
+#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
+
 	if (data->no_sched_functions && in_sched_functions(addr))
 		return 0;
 	if (data->skip) {
@@ -105,6 +122,9 @@ void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
 
 	data.trace = trace;
 	data.skip = trace->skip;
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+	data.ret_stack_index = current->curr_ret_stack;
+#endif
 
 	if (tsk != current) {
 		data.no_sched_functions = 1;
-- 
1.7.9.5

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#1245838

On Oct 8, 2015, at 7:01 PM, AKASHI Takahiro wrote:

Hi Akashi,

> Function graph tracer modifies a return address (LR) in a stack frame
> to hook a function return. This will result in many useless entries
> (return_to_handler) showing up in a stack tracer's output.
> 
> This patch replaces such entries with originals values preserved in
> current->ret_stack[].
> 
> Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>

The following diff should be folded into this patch, not [7/7] one, to
address build breakage.

----8<----
diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
index 407991b..7126d4d 100644
--- a/arch/arm64/kernel/stacktrace.c
+++ b/arch/arm64/kernel/stacktrace.c
@@ -17,6 +17,7 @@
  */
 #include <linux/kernel.h>
 #include <linux/export.h>
+#include <linux/ftrace.h>
 #include <linux/sched.h>
 #include <linux/stacktrace.h>
----8<----

Best Regards
Jungseok Lee
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#1246303 — Re: [PATCH v3 3/7] arm64: ftrace: fix a stack tracer's output under function graph tracer

On 10/14/2015 12:24 AM, Jungseok Lee wrote:
> On Oct 8, 2015, at 7:01 PM, AKASHI Takahiro wrote:
>
> Hi Akashi,
>
>> Function graph tracer modifies a return address (LR) in a stack frame
>> to hook a function return. This will result in many useless entries
>> (return_to_handler) showing up in a stack tracer's output.
>>
>> This patch replaces such entries with originals values preserved in
>> current->ret_stack[].
>>
>> Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
>
> The following diff should be folded into this patch, not [7/7] one, to
> address build breakage.

Thanks.
I fixed all the build errors reported by kbuild test robot.

-Takahiro AKASHI

> ----8<----
> diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
> index 407991b..7126d4d 100644
> --- a/arch/arm64/kernel/stacktrace.c
> +++ b/arch/arm64/kernel/stacktrace.c
> @@ -17,6 +17,7 @@
>    */
>   #include <linux/kernel.h>
>   #include <linux/export.h>
> +#include <linux/ftrace.h>
>   #include <linux/sched.h>
>   #include <linux/stacktrace.h>
> ----8<----
>
> Best Regards
> Jungseok Lee
>
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