gdb over Firewire

Hello Current'ers,

I'm trying to get two-machine kernel debugging over Firewire working, 
unfortunately without much luck so far. dconschat over Firewire works 
fine, but gdb won't attach, complaining about get_tty_state failed, 
among other things.
Is kernel gdb over Firewire a -current-only feature?

Cheers,
Gerald