Re: [PATCH v4 3/6] arm64: ftrace: fix a stack tracer's output under function graph tracer

Jungseok Lee
2015-11-01T08:00:57Z

On Oct 30, 2015, at 2:25 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 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..631c49d 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>
>
> @@ -78,6 +79,9 @@ 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 +90,20 @@ 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 */
> +

This hunk would be affected as the commit, "ARM64: unwind: Fix PC calculation",
e306dfd0, has been reverted.

Best Regards
Jungseok Lee