Re: elfutils/libdw ARM compilation (native and cross compile)

[Jean Pihet <jean dot pihet at linaro dot org>]

While at it, I have a concern about the compat mode: profiling an
ARMv7 binary on an ARMv8 system.
Is this supported by libdw? I know you can do it with libunwind by
linking multiple libraries, cf. [1]. However this is utterly complex
to implement.

[1] http://www.nongnu.org/libunwind/man/libunwind%283%29.html#section_4
, cf. 'Cross-platform and Multi-platform Unwinding'.

Regards,
Jean

On 26 February 2014 09:15, Jean Pihet <jean.pihet@linaro.org> wrote:
> Hi Mark,
>
> On 26 February 2014 00:26, Mark Wielaard <mjw@redhat.com> wrote:
>> Hi Jean,
>>
>> Seems you already got your answer to the build question solved.
> Yes! There is quite a huge improvement in performance: >500% for dwarf
> unwinding ;-p
>
>>
>> On Tue, 2014-02-25 at 18:17 +0100, Jean Pihet wrote:
>>> The goal is to add the libdw support for perf on ARM (and later AARCH64).
>>
>> Note that there is some code in elfutils git that handles .debug_frame
>> for ARM, but not yet code for handling EXIDX tables. For non-debug
>> unwinding ARM uses EXIDX tables, not .eh_frames. Handling EXIDX tables
>> is probably easiest done by translating them to CFI. In case you want to
>> do unwinding using libdw without .debug_frame available.
> That is good to know. Our use cases suppose we have the .debug_frame
> section in the binaries by default and otherwise the frame pointer can
> be used.
>
>> For AARCH64 there is some code available on my branch:
>> https://git.fedorahosted.org/cgit/elfutils.git/log/?h=mjw/aarch64-unwind
>> Which might or might not work. I need to get access again to a aarch64
>> setup to do some more testing before moving this to master.
> Great! AARCH64 is next on my plate, I surely will let you know the status.
>
> Thx for you replies!
> Jean
>
>>
>> Cheers,
>>
>> Mark
>>