At the moment, it is impossible to debug with gdb due to SIGILL, Illegal instruction errors. Details can be found here https://github.com/raspberrypi/linux/issues/766. Take a look to the end of this thread, someone has submitted a patch to gdb and some other users write that after rpi-update the problem is gone now in raspbian.
It would be very nice to see this update for ARCH Linux ARM, too!