Hi, I have reported a bug #975339[¹] to the clinfo package. There was an uninitialized variable that caused that strange result.
The bug is closed so the next version of clinfo will not generate anymore this strange characters.
Anyway I think that piglit must manage these type of errors. Ciao Davide [¹] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=975339
