I made some research:
GCC 4.4.6 + GDB 7.2 (Both Scientific Linux 6.3 defaults) – doesn’t work
GCC 4.4.6 (from SL 6.3) + GDB 7.5.1 (Manually compiled) – doesn’t work
GCC 4.8 (Manually compiled) + GDB 7.2 (from SL 6.3) – debugging doesn’t work at all 🙁
GCC 4.8 + GDB 7.5.1 (Both manually compiled) – works perfect
I’m a little disappointed. But using newest GCC and GDB has solved my problem.