Thanks Darius,
I tried several versions including lldb, the gdb with macports and a *-elf gdb I built myself with no luck.
I then built a *-linux-elf gdb and it works !! It seems that the packet layout is slightly different or something. What's more I have been able to fix the deadlock I had in my kernel which was the real point of the exercise.
thanks very much for taking the time to reply.
regards
Gerry