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

AKASHI Takahiro
2015-11-04T07:50:05Z

On 11/01/2015 05:00 PM, Jungseok Lee wrote:
> 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.

Yeah, we don't need apply this patch any more.
The other patches in the series will not be affected.

Thanks,
-Takahiro AKASHI

> Best Regards
> Jungseok Lee
>