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SubjectRe: [PATCH 2/3] perf tools: Add callchain order support for libunwind DWARF unwinder
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On November 18, 2015 5:25:25 PM GMT+09:00, Jiri Olsa <jolsa@redhat.com> wrote:
>On Wed, Nov 18, 2015 at 02:41:14PM +0900, Namhyung Kim wrote:
>
>SNIP
>
>> > I'm not sure whether we can regard this behavior changing as a
>bugfix? I
>> > think
>> > there may be some reason the original code explicitly avoid
>creating an '0'
>> > entry.
>>
>> I think callchain value being 0 is an error or marker for the end of
>> callchain. So it'd be better avoiding 0 entry.
>>
>> But unfortunately, we have many 0 entries (and broken callchain after
>> them) with fp recording on optimized binaries. I think we should
>omit
>> those callchains.
>>
>> Maybe something like this?
>>
>>
>>
>> diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
>> index 5ef90be2a249..22642c5719ab 100644
>> --- a/tools/perf/util/machine.c
>> +++ b/tools/perf/util/machine.c
>> @@ -1850,6 +1850,15 @@ static int
>thread__resolve_callchain_sample(struct thread *thread,
>> #endif
>> ip = chain->ips[j];
>>
>> + /* callchain value inside zero page means it's broken, stop */
>> + if (ip < 4096) {
>> + if (callchain_param.order == ORDER_CALLER) {
>> + callchain_cursor_reset(&callchain_cursor);
>
>hum, do we want to throw away whatever we have till now?

For caller order, yes.

For callee order, everything after 0 value is garbage. So we need to discard any chains before the 0 for caller IMHO.

Thanks
Namhyung


--
Sent from my Android device with K-9 Mail. Please excuse my brevity.


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