This one liner isn't obvious.

The various ABIs have a requrement that the SP be decremented before 
writing anything to the stack (ignoring the red zone).  This is to stop 
signal handlers and the like trashing the callers stack.  The two PPC 
push_dummy_call (nee push_arguments) methods are already carefully 
complying to this requirement (setting SP before using the stack) and 
hence [deprecated] write_sp method which also sets the SP before a call 
is entirely redundant.

Thing is, I don't see any reason to exactly matching the ABI behavior 
(that thread is stopped so it won't get anything writing to its stack) 
and further, I think exactly matching the behavior makes the code harder 
to understand (I'm having trouble convincing my self that it does what I 
think it does :-).

So, in addition to eliminating deprecated write_sp, would it be ok to 
move the write SP code to the end of the push_dummy_call methods?

Andrew