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

[Namhyung Kim]

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,
Namhyung