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

[Jean Pihet]

Hi Jiri, Will,

I just sent the reworked series as '[PATCH v3 0/4] perf: parse the
dwarf backtrace info from .debug_frame section'.
Tested on x86 and ARMv7.

Regards,
Jean


On 25 September 2013 09:31, Jiri Olsa <jolsa at redhat.com> wrote:
> On Wed, Sep 25, 2013 at 08:53:44AM +0200, Jean Pihet wrote:
>> Hi Jiri,
>>
>> On 24 September 2013 19:43, Jiri Olsa <jolsa at redhat.com> wrote:
>> > On Tue, Sep 24, 2013 at 02:03:47PM +0200, Jean Pihet wrote:
>> >> Hi Jiri, Will,
>> >>
>> >> On 24 September 2013 12:06, Will Deacon <will.deacon at arm.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.
>> >
>> > My concern is about users (again, not sure if there are any ;-) )
>> > that use this with packaged libunwind compiled without
>> > --enable-debug-frame option.
>> >
>> > For them perf will consider libunwind as 'not available' with
>> > your changes:
>> >
>> >       ...
>> >       CHK libunwind
>> >   config/Makefile:223: No libunwind found, disabling post unwind support.  Please install libunwind-dev[el] >= 1.1
>> >       ...
>> >
>> > and they'll need to compile their own libunwind
>> > (thats the case on Fedora).
>> >
>> > This could be solved by detecting this and make your
>> > code conditional as attached below (not much tested).
>> Ok that makes sense.
>> Let me integrate this in the patch series, test it (on ARM and x86)
>> and re-submit. Is that OK?
>
> that'd be great
>
> thanks,
> jirka