rebind key in a single major mode

[Glen Coates]

Hi,

I've currently got the enter key bound to C-j in all modes because it
makes indenting so much easier, however, in gdb-mode this means I have to
hit C-m instead of enter because gdb-mode doesn't recognise C-j as the
newline character (I think).

What do I need to put in my .emacs in order to rebind enter to C-m for
gdb-mode only?

--
Cheers,
Glen