Re: newbie question: tracing userspace call/return sequences

[Milian Wolff <milian.wolff@kdab.com>]

[-- Attachment #1: Type: text/plain, Size: 2027 bytes --]

On Thursday, January 5, 2017 10:49:13 PM CET Christian Convey wrote:
> Hi guys,
> 
> Any suggestions for the best way to achieve something with perf tools?
> 
> Systemtap has an example script, "para-callgraph.stp", that reports
> the *sequence* of userspace function calls and returns made by an
> application.
> 
> I'd like to perform that kind of analysis using perf tools rather than
> Systemtap, because I recently learned that Canonical considers
> Systemtap to be unsupported.  (E.g., it's pretty broken on Ubuntu
> 14.04.)
> 
> I think I've gotten fairly close with these steps:
> 
>   perf probe --exec=./fib -f --add='*'
>   perf probe --exec=./fib -f --add='*:%return'
>   perf record -e 'probe_fib:*' -aR ./fib
>   perf script -g py
>   perf script -s ./perf_script.py
> 
> The generated Python script contains two Python functions for each
> userspace function that's called during the execution of "fib".  This
> seems to work, at least on a small, toy program.
> 
> But AFAICT, this has two major downsides relative to the
> Systemtap-based approach, in cases where the target program has
> thousands of functions:
> 
> (1) The generated Python script will be huge, and
> 
> (2) It will require some non-trivial Python coding for me to tweak
> what that script does for every call/return event.
> 
> Any suggestions for a good/better way to pull this off?

There is a catch-all handler:

*trace_unhandled*, if defined, is called after for any event that
 doesn't have a handler explicitly defined for it.  The standard set
 of common arguments are passed into it:

----
def trace_unhandled(event_name, context, common_cpu, common_secs,
        common_nsecs, common_pid, common_comm):
    pass
----

Maybe you can use that one instead? I'd still be interested to know whether 
you can get all required information. If not, extending the API is doable.

Bye
-- 
Milian Wolff | milian.wolff@kdab.com | Software Engineer
KDAB (Deutschland) GmbH&Co KG, a KDAB Group company
Tel: +49-30-521325470
KDAB - The Qt Experts

[-- Attachment #2: smime.p7s --]
[-- Type: application/pkcs7-signature, Size: 5903 bytes --]