Re: [PATCH v2] perf: fix dwarf unwind using libunwind.

Jiri Olsa
2015-01-14T11:58:42Z

On Wed, Jan 14, 2015 at 10:36:47AM +0800, Wang Nan wrote:
> Perf tool fails to unwind user stack if the event raises in a shared

SNIP

> +
> __attribute__ ((noinline))
> static int krava_3(struct thread *thread)
> {
> - return unwind_thread(thread);
> + struct thread *array[2] = {thread, thread};
> + void *fp = &bsearch;
> + /*
> + * make _bsearch a volatile function pointer to
> + * prevent potential optimization, which may expand
> + * bsearch and call compare directly from this function,
> + * instead of libc shared object.
> + */
> + void *(*volatile _bsearch)(void *, void *, size_t,
> + size_t, int (*)(void *, void *));
> +
> + _bsearch = fp;
> + _bsearch(array, &thread, 2, sizeof(struct thread **), compare);
> + return global_unwind_retval;
> }

ah, I've got confused with the NO_LIBUNWIND_DEBUG_FRAME name
and got the impression that we could use it in the tests/make
as another compile option test..

but your change is even better ;-) thanks for updating this test

Acked-by: Jiri Olsa <jolsa@kernel.org>

thanks,
jirka