Ideas for improving profil.c

[Brian Ford]

I tracked down my pc sampling (profiling) problems mentioned here:

http://cygwin.com/ml/cygwin/2003-04/msg01781.html

My problem was that the eip returned was almost never in the profiling
range.  It was usually way down in the bowels of Windows that I have yet
to understand.  Something like 0x7ffe0304.

Raising the profiling thread priority helped catch a few more valid
addresses.  I would be glad to submit a one line patch for this if anyone
is interested.

I think most OS's are able to trace processes in the kernel back to the
entering trap, thus finding an in-range pc.  So, my idea was to (and I do
have a rough version working) naively try and walk the stack back some
maximum number of frames until I hit the range.  Better yet, only
walk back if we are below a cygwin entry point and only up to that point.

Is there any way to know this from the pc?  I am probably just a rambling
lunatic, so feel free to shut me up.

-- 
Brian Ford
Senior Realtime Software Engineer
VITAL - Visual Simulation Systems
FlightSafety International
Phone: 314-551-8460
Fax:   314-551-8444