$Header$

The machine-dependant part of the ACK debugger support requires three
routines:
___Get_PC takes a frame pointer (local base) argument and returns the
	  return address from this frame.
___Set_PC takes a frame pointer (local base) argument plus a return
	  address and sets the return address of this frame to the
	  return address supplied.
???	  a third routine which is called at every line (see for
	  instance mach/m68020/ncg/mach.c for an example of how to
	  do this). This routine must save the scratch registers
	  and then call (or jump to) ___uX_LiB. If this is a call,
	  ___Get_PC and ___Set_PC are complicated by the existance
	  of a procedure frame that we do not want the "grind" user
	  to know about. See for instance the mach/m68020/libdb version
	  for how to solve this problem.