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

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Message-ID: <20150114115749.GB6369@krava.redhat.com>
Date:	Wed, 14 Jan 2015 12:57:49 +0100
From:	Jiri Olsa <jolsa@...hat.com>
To:	Wang Nan <wangnan0@...wei.com>
Cc:	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, acme@...nel.org, masami.hiramatsu.pt@...achi.com
Subject: Re: [PATCH v2] perf: fix dwarf unwind using libunwind.

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,
jirka
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