trace.py result is full unknown

Hi!
I tried to trace my header, and the result is full unknown.
My code :
[Ember.txt](https://github.com/iovisor/bcc/files/3475703/Ember.txt)
[main.txt](https://github.com/iovisor/bcc/files/3475704/main.txt)

My command, what i used: sudo python trace.py 'p:/home/balazs/Desktop/probalkozas/a.out:_ZN5Ember6getNevB5cxx11Ev "print"' -T -U -K

result:
TIME PID TID COMM FUNC -
09:11:07 13570 13570 a.out _ZN5Ember6getNevB5cxx11Ev print
-14
[unknown]
[unknown]
[unknown]

What did I wrong? Thanks for every answer.
p.s. Sorry for my english, I don't speak very well.

Start with trace.py and reproduce the reported command using the attached Ember.txt and main.txt inputs. Check why the traced C++ symbol produces unknown stack entries, then document the cause or identify the required fix and a way to verify the result.

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