Messages in this thread | | | Subject | Re: [PATCH v5 2/6] arm64: ftrace: fix a stack tracer's output under function graph tracer | From | AKASHI Takahiro <> | Date | Tue, 10 Nov 2015 11:42:31 +0900 |
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On 11/09/2015 11:04 PM, Jungseok Lee wrote: > 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?
You're right! I thought I had tested the patches, but...
>> + } >> +#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?
Thanks for pointing this out. Will fix it although it works without a change since save_stack_trace_sp() is called only in a 'current task' context.
-Takahiro AKASHI
> Best Regards > Jungseok Lee >
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