Re: failed to add c++ probe

[Masami Hiramatsu]

On Mon, 19 Sep 2016 11:54:02 +0200
Jiri Olsa <jolsa@xxxxxxxxxx> wrote:

> hi,
> Thomas reported failure to add an uprobe on libstdc++.so.6 like:
> 
> [jolsa@krava perf]$ sudo ./perf probe -x /usr/lib64/libstdc++.so.6 'std::ostream::flush'
> Semantic error :There is non-digit char in line number.
>   Error: Command Parse Error.

Ah, I should start adding mangling support on perf probe...


> it does not work also if I use the mangled name like:
> 
> [jolsa@krava perf]$ sudo ./perf probe -x /usr/lib64/libstdc++.so.6 '_ZSt5flushIwSt11char_traitsIwEERSt13basic_ostreamIT_T0_ES6_'
> Probe point '_ZSt5flushIwSt11char_traitsIwEERSt13basic_ostreamIT_T0_ES6_' not found.
>   Error: Failed to add events.

Hmm, could you try to find mangled symbol from the library as below?

./perf probe -x /usr/lib64/libstdc++.so.6 -F \*

And also try to do adding probe with -v option again?

In my case, I could find the mangled symbol, but failed to setup the probe...

$ sudo ./perf probe -x /usr/lib/x86_64-linux-gnu/libstdc++.so.6 -v _ZSt5flushIwSt11char_traitsIwEERSt13basic_ostreamIT_T0_ES6_
probe-definition(0): _ZSt5flushIwSt11char_traitsIwEERSt13basic_ostreamIT_T0_ES6_ 
symbol:_ZSt5flushIwSt11char_traitsIwEERSt13basic_ostreamIT_T0_ES6_ file:(null) line:0 offset:0 return:0 lazy:(null)
0 arguments
symbol:catch file:(null) line:0 offset:0 return:0 lazy:(null)
symbol:throw file:(null) line:0 offset:0 return:0 lazy:(null)
symbol:rethrow file:(null) line:0 offset:0 return:0 lazy:(null)
Could not open debuginfo. Try to use symbols.
Opening /sys/kernel/debug/tracing//uprobe_events write=1
Writing event: p:probe_libstdc++/_ZSt5flushIwSt11char_traitsIwEERSt13basic_ostreamIT_T0_ES6_ /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.21:0x1114c0
Failed to write event: Invalid argument
  Error: Failed to add events. Reason: Invalid argument (Code: -22)

dmsg -k said;

[143725.339609] Failed to allocate trace_uprobe.(-22)
[143725.339612] Failed to parse address or file.

It seems we need to fix trace_uprobe.c at least.

Thank you!

-- 
Masami Hiramatsu <mhiramat@xxxxxxxxxx>