Access to backtraces from user-space tracepoint callback in perf-script?

Access to backtraces from user-space tracepoint callback in perf-script?

[Milian Wolff]

Hello,

today I played around with perf-script(-python) and custom tracepoints. What I 
could not figure out so far is how to print a backtrace from the python 
callback. Can someone explain me how this is done, or point me to the 
documentation for this?

Bye
-- 
Milian Wolff
mail@milianw.de
http://milianw.de

Re: Access to backtraces from user-space tracepoint callback in perf-script?

[Milian Wolff]

On Tuesday 29 April 2014 17:44:54 Milian Wolff wrote:
> Hello,
> 
> today I played around with perf-script(-python) and custom tracepoints. What
> I could not figure out so far is how to print a backtrace from the python
> callback. Can someone explain me how this is done, or point me to the
> documentation for this?

Ping? Could someone help me here please?
-- 
Milian Wolff
mail@milianw.de
http://milianw.de

Re: Access to backtraces from user-space tracepoint callback in perf-script?

[Namhyung Kim]

Hi Milian,

On Wed, 07 May 2014 14:46:31 +0200, Milian Wolff wrote:
> On Tuesday 29 April 2014 17:44:54 Milian Wolff wrote:
>> Hello,
>> 
>> today I played around with perf-script(-python) and custom tracepoints. What
>> I could not figure out so far is how to print a backtrace from the python
>> callback. Can someone explain me how this is done, or point me to the
>> documentation for this?
>
> Ping? Could someone help me here please?

As far as I know it's not possible currently.. I vaguely recall that
there's a patch to support the feature but unfortunately it didn't get
reviews..

Thanks,
Namhyung

Re: Access to backtraces from user-space tracepoint callback in perf-script?

[Milian Wolff]

On Wednesday 14 May 2014 09:33:35 Namhyung Kim wrote:
> Hi Milian,
> 
> On Wed, 07 May 2014 14:46:31 +0200, Milian Wolff wrote:
> > On Tuesday 29 April 2014 17:44:54 Milian Wolff wrote:
> >> Hello,
> >> 
> >> today I played around with perf-script(-python) and custom tracepoints.
> >> What I could not figure out so far is how to print a backtrace from the
> >> python callback. Can someone explain me how this is done, or point me to
> >> the documentation for this?
> > 
> > Ping? Could someone help me here please?
> 
> As far as I know it's not possible currently.. I vaguely recall that
> there's a patch to support the feature but unfortunately it didn't get
> reviews..

Is it this one: https://lkml.org/lkml/2014/4/3/217 ?

If so, could I kindly ask the perf developers to take a look at that? It would 
be an immensely useful feature for third-party tool developers to have.

Cheers
-- 
Milian Wolff
mail@milianw.de
http://milianw.de

Re: Access to backtraces from user-space tracepoint callback in perf-script?

[Frank Ch. Eigler]

Milian Wolff <mail@milianw.de> writes:

> [...]
>> >> today I played around with perf-script(-python) and custom tracepoints.
>> >> What I could not figure out so far is how to print a backtrace from the
>> >> python callback. [...]

While you wait, you might try systemtap, wherein there exists support
not just for plain C-level backtracing (print_ubacktrace() as for any
other program), but also python source-level backtracing (via a tapset
function).

https://sourceware.org/systemtap/examples/#general/py2example.stp

- FChE

Re: Access to backtraces from user-space tracepoint callback in perf-script?

[Milian Wolff]

On Friday 16 May 2014 11:57:02 Frank Ch. Eigler wrote:
> Milian Wolff <mail@milianw.de> writes:
> > [...]
> > 
> >> >> today I played around with perf-script(-python) and custom
> >> >> tracepoints.
> >> >> What I could not figure out so far is how to print a backtrace from
> >> >> the
> >> >> python callback. [...]
> 
> While you wait, you might try systemtap, wherein there exists support
> not just for plain C-level backtracing (print_ubacktrace() as for any
> other program), but also python source-level backtracing (via a tapset
> function).
> 
> https://sourceware.org/systemtap/examples/#general/py2example.stp

Hey,

thanks for the hint. But I never got SystemTap to work on any of my machines 
:-/

For now I'll stick to manual libunwind + libbacktrace + LD_PRELOAD tracing. 
But I'd love to see this available in perf eventually.

Bye
-- 
Milian Wolff
mail@milianw.de
http://milianw.de

Re: Access to backtraces from user-space tracepoint callback in perf-script?

[David Ahern]

On 5/17/14, 5:24 AM, Milian Wolff wrote:
> On Friday 16 May 2014 11:57:02 Frank Ch. Eigler wrote:
>> Milian Wolff <mail@milianw.de> writes:
>>> [...]
>>>
>>>>>> today I played around with perf-script(-python) and custom
>>>>>> tracepoints.
>>>>>> What I could not figure out so far is how to print a backtrace from
>>>>>> the
>>>>>> python callback. [...]
>>
>> While you wait, you might try systemtap, wherein there exists support
>> not just for plain C-level backtracing (print_ubacktrace() as for any
>> other program), but also python source-level backtracing (via a tapset
>> function).
>>
>> https://sourceware.org/systemtap/examples/#general/py2example.stp
>
> Hey,
>
> thanks for the hint. But I never got SystemTap to work on any of my machines
> :-/
>
> For now I'll stick to manual libunwind + libbacktrace + LD_PRELOAD tracing.
> But I'd love to see this available in perf eventually.
>

Did you try the patch to perf? Does it give you access to the callchain 
in python scripts like you want?

David