On Wed, 15 Jul 2015 20:41:34 +0900
AKASHI Takahiro <[email protected]> wrote:
> Thank you for the explanation. But what I don't really understand here
> is why we need to add the "current function" to the stack dump list
> returned by save_stack_trace():
>
> In check_stack(),
> > /*
> > * Add the passed in ip from the function tracer.
> > * Searching for this on the stack will skip over
> > * most of the overhead from the stack tracer itself.
> > */
> > stack_dump_trace[0] = ip;
> > max_stack_trace.nr_entries++;
>
> I think that "ip" here is the "return address for func" in your
Ah, you are correct (for fentry).
> ascii art, and it should be already in the list if a frame is made
> by mcount (or func_call).
>
> In fact, stack tracer on arm64 works OK even without the patch[3/3]
> if the code quoted above is commented out.
> Even on x86, the code is conditional and not activated if the kernel
> is compiled without -mfentry before the following commit:
> commit 4df297129f62 ("tracing: Remove most or all of stack tracer stack
> size from stack_max_size")
>
> So what do I misunderstand here?
>
Hmm, I haven't touched the stack trace code in a while. With the added
stack frame for fentry, the hacks there are probably not needed.
I'll take a look at it and try to clean up the code.
Thanks,
-- Steve
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