linux-kernel - Re: [PATCH 3/4] perf tools: Check libunwind for availability of dwarf parsing feature

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Date:	Tue, 24 Sep 2013 14:03:47 +0200
From:	Jean Pihet <jean.pihet@...aro.org>
To:	Will Deacon <will.deacon@....com>, Jiri Olsa <jolsa@...hat.com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"patches@...aro.org" <patches@...aro.org>
Subject: Re: [PATCH 3/4] perf tools: Check libunwind for availability of dwarf
 parsing feature

Hi Jiri, Will,

On 24 September 2013 12:06, Will Deacon <will.deacon@....com> wrote:
> On Tue, Sep 24, 2013 at 10:34:50AM +0100, Jiri Olsa wrote:
>> On Tue, Sep 24, 2013 at 10:55:32AM +0200, Jean Pihet wrote:
>> > Ping on the series. The two patches above (3/4 and 4/4) are generic
>> > while the two others are impacting ARM only.
>> > Is it possible to get an Ack for the generic ones?
>>
>> I'm fine with those changes.. still I'm sort of worried about
>> current DWARF unwind users (but not sure if there're any),
>> who depends on packaged libunwind compiled without
>> --enable-debug-frame option.
>
> Since x86 is the only architecture using libunwind with perf at the moment,
> and I'd expect it to use .eh_frame for unwinding, I'm also not sure there
> are any existing users to worry about.
Right

>
>> I've seen your libunwind patch to make it default, but
>> not sure if it was accepted.. if not, maybe we should
>> detect this and build that code conditionaly.
>
> It certainly defaults to "on" for ARM, but other architectures have to
> enable it explicitly afaict.
Yes that is correct.
This patch (3/4) detects if the debug frame code is enabled in
libunwind and uses the lib only if it is the case.
Users that want the feature have to enable it explicitly; the commit
description documents how to do that.

So I think we are safe here.

>
> Will

Thanks,
Jean
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