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Re: [PATCH v5 2/6] arm64: ftrace: fix a stack tracer's output under function graph tracer

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On Nov 6, 2015, at 3:44 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>
> ---
> arch/arm64/include/asm/ftrace.h |    2 ++
> arch/arm64/kernel/stacktrace.c  |   21 +++++++++++++++++++++
> 2 files changed, 23 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h
> index c5534fa..3c60f37 100644
> --- a/arch/arm64/include/asm/ftrace.h
> +++ b/arch/arm64/include/asm/ftrace.h
> @@ -28,6 +28,8 @@ 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 ccb6078..5fd3477 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>
> 
> @@ -73,6 +74,9 @@ 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)
> @@ -81,6 +85,20 @@ 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) {

not if (adds == (unsigned long)return_to_handler)?

> +		/*
> +		 * 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;

Ditto. not without AARCH64_INSN_SIZE?

I've observed many return_to_handler without the changes.
Am I missing something?

> +	}
> +#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
> +
> 	if (data->no_sched_functions && in_sched_functions(addr))
> 		return 0;
> 	if (data->skip) {
> @@ -100,6 +118,9 @@ 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;

Can I get an idea on why current->curr_ret_stack is used instead of
tsk->curr_ret_stack?

Best Regards
Jungseok Lee--
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[PATCH v5 0/6] arm64: ftrace: fix incorrect output from stack tracer AKASHI Takahiro <takahiro.akashi@linaro.org> - 2015-11-06 07:50 +0100
  [PATCH v5 5/6] arm64: ftrace: add arch-specific stack tracer AKASHI Takahiro <takahiro.akashi@linaro.org> - 2015-11-06 07:50 +0100
    Re: [PATCH v5 5/6] arm64: ftrace: add arch-specific stack tracer Jungseok Lee <jungseoklee85@gmail.com> - 2015-11-10 15:10 +0100
      Re: [PATCH v5 5/6] arm64: ftrace: add arch-specific stack tracer AKASHI Takahiro <takahiro.akashi@linaro.org> - 2015-11-11 06:10 +0100
        Re: [PATCH v5 5/6] arm64: ftrace: add arch-specific stack tracer Jungseok Lee <jungseoklee85@gmail.com> - 2015-11-12 00:00 +0100
  [PATCH v5 4/6] arm64: insn: add instruction decoders for ldp/stp and add/sub AKASHI Takahiro <takahiro.akashi@linaro.org> - 2015-11-06 07:50 +0100
    Re: [PATCH v5 4/6] arm64: insn: add instruction decoders for ldp/stp and add/sub Jungseok Lee <jungseoklee85@gmail.com> - 2015-11-10 14:50 +0100
      Re: [PATCH v5 4/6] arm64: insn: add instruction decoders for ldp/stp  and add/sub AKASHI Takahiro <takahiro.akashi@linaro.org> - 2015-11-11 06:00 +0100
  [PATCH v5 1/6] arm64: ftrace: modify a stack frame in a safe way AKASHI Takahiro <takahiro.akashi@linaro.org> - 2015-11-06 07:50 +0100
  [PATCH v5 2/6] arm64: ftrace: fix a stack tracer's output under function graph tracer AKASHI Takahiro <takahiro.akashi@linaro.org> - 2015-11-06 07:50 +0100
    Re: [PATCH v5 2/6] arm64: ftrace: fix a stack tracer's output under function graph tracer Jungseok Lee <jungseoklee85@gmail.com> - 2015-11-09 15:10 +0100
      Re: [PATCH v5 2/6] arm64: ftrace: fix a stack tracer's output under  function graph tracer AKASHI Takahiro <takahiro.akashi@linaro.org> - 2015-11-10 03:50 +0100
        Re: [PATCH v5 2/6] arm64: ftrace: fix a stack tracer's output under function graph tracer Jungseok Lee <jungseoklee85@gmail.com> - 2015-11-13 16:10 +0100
          Re: [PATCH v5 2/6] arm64: ftrace: fix a stack tracer's output under  function graph tracer AKASHI Takahiro <takahiro.akashi@linaro.org> - 2015-11-16 10:30 +0100
  [PATCH v5 3/6] ftrace: allow arch-specific stack tracer AKASHI Takahiro <takahiro.akashi@linaro.org> - 2015-11-06 07:50 +0100
    Re: [PATCH v5 3/6] ftrace: allow arch-specific stack tracer Steven Rostedt <rostedt@goodmis.org> - 2015-11-06 14:40 +0100
  [PATCH v5 6/6] arm64: ftrace: add a test of function prologue analyzer AKASHI Takahiro <takahiro.akashi@linaro.org> - 2015-11-06 07:50 +0100
  Re: [PATCH v5 0/6] arm64: ftrace: fix incorrect output from stack tracer Jungseok Lee <jungseoklee85@gmail.com> - 2015-11-09 15:30 +0100
    Re: [PATCH v5 0/6] arm64: ftrace: fix incorrect output from stack  tracer AKASHI Takahiro <takahiro.akashi@linaro.org> - 2015-11-10 04:00 +0100
      Re: [PATCH v5 0/6] arm64: ftrace: fix incorrect output from stack tracer Jungseok Lee <jungseoklee85@gmail.com> - 2015-11-10 14:40 +0100

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