Hello,

The attached patch modifies infrun.c so that, for the non-legacy case, 
the test:
	frame_type == SIGTRAMP frame
	&& step_frame_id != stop_frame_id
is used to determine if a single-step caused the inferior to stumble 
into a signal trampoline (either via a signal, or by returning from the 
handler).  This replaces two pc_in_sigtramp calls and a stack-pointer 
heuristic -- not the most robust of tests.

The new test:

- eliminates the call pc_in_sigtramp(step_pc)
(i.e., on the PC from before the single step) (this was an unexpected 
bonus :-)

- uses the caching call get_frame_type call
pc_in_sigtramp has to re-do all the computation each time it is called 
(typically duplicating the effort of get_frame_type)

- uses !frame_id_eq
Which is a 100% robust frame-changed test.  The old test couldn't detect 
a signal trampoline calling (via a signal) a singnal trampoline.

thoughts?

I'll look to commit this in a few days (already committed to my 
trad-frame branch).

Andrew