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.aka...@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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