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

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Date:	Wed, 14 Jan 2015 09:50:25 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	Wang Nan <wangnan0@...wei.com>, jolsa@...nel.org,
	linux-kernel@...r.kernel.org, lizefan@...wei.com,
	namhyung@...nel.org, a.p.zijlstra@...llo.nl, paulus@...ba.org,
	mingo@...hat.com, masami.hiramatsu.pt@...achi.com
Subject: Re: [PATCH v2] perf: fix dwarf unwind using libunwind.

Em Wed, Jan 14, 2015 at 12:57:49PM +0100, Jiri Olsa escreveu:
> 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@...nel.org>

Thanks, applied to perf/urgent.

- Arnaldo
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