linux-kernel - Re: [PATCH v2 3/4] perf annotate: configure objdump path at compile time

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Date:	Mon, 1 Oct 2012 02:37:21 +0300
From:	Irina Tirdea <irina.tirdea@...il.com>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Ingo Molnar <mingo@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	LKML <linux-kernel@...r.kernel.org>,
	Paul Mackerras <paulus@...ba.org>,
	David Ahern <dsahern@...il.com>,
	Pekka Enberg <penberg@...nel.org>,
	Jiri Olsa <jolsa@...hat.com>,
	Irina Tirdea <irina.tirdea@...el.com>
Subject: Re: [PATCH v2 3/4] perf annotate: configure objdump path at compile time

On Thu, Sep 27, 2012 at 4:16 PM, Namhyung Kim <namhyung@...nel.org> wrote:
> On Thu, 27 Sep 2012 14:25:10 +0300, Irina Tirdea wrote:
>>>> The perf built to run on the host needs to use arm-eabi-objdump from
>>>> the toolchain so that it can analyse data recorded on Android. This
>>>> patch is targeting this scenario, not the previous one. In this case,
>>>> the CROSS_COMPILE option would be different than arm-eabi- so using
>>>> $(CROSS_COMPILE)objdump would be wrong. objdump should be overridden
>>>> when running make since there is no connection between the toolchain
>>>> used here and the path for objdump. I am always overriding objdump
>>>> when calling make, so I did not catch this.
>>>>
>>>> I think that I should change DEFAULT_OBJDUMP_PATH=objdump in the
>>>> Makefile to handle the first scenario. I'll also explain this in the
>>>> commit message so that it is more clear and make the same change for
>>>> the addr2line patch.
>>>>
>>>> What do you think?
>>>
>>> I think the right thing to do is finding a correct objdump at runtime in
>>> some way.  Why do you want to make it compile-time configurable?
>>>
>>
>> The correct objdump path can be detected at runtime by setting the
>> toolchain path. But since the name is arm-eabi-objdump and not
>> objdump, it does not know to use it instead.
>>
>> The only way (I can think of) to change objdump at runtime would be to
>> use the --objdump option for perf annotate (and provide a similar
>> option for addr2line). The problem with this approach is that the user
>> has to be aware that perf annotate uses the objdump tool and that he
>> has to use the cross-compiler version instead. Since the user will
>> have perf compiled for host as part of his Android tree, he will
>> expect it to work without these further changes from his part. The
>> path for objdump can be set in the Android Makefile at compile time so
>> that the user doesn't need to be aware of it.
>
> What I'm thinking is that perf can try to find cross-built binutils when
> it detects perf.data file is came from other machine/architecture.
> Fortunately perf_session_env was added recently and it has the arch
> information from the file so we can use it to find the path.
>
> Following patch is a proof-of-concept patch and only build tested.
> What do you think?  Could you play with it for some time? :)
>

Thanks, this looks like the right approach. :)
I'm going to test it for Android cross-compiling and submit an update if needed.

Thanks,
Irina
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