On Jan 28, 2009, at 10:33 AM, Karan, Cem (Civ, ARL/CISD) wrote:
First off, I know this question is going to the wrong list, but I
have NO idea which list would be best. If anyone wants to jump in
and tell me a better list, I'll gladly move there.
Background:
I have an application that is working very, very hard to drive me
insane. It is multithreaded, lazy, and has my broken attempt at
trampoline code. Now, it crashes once in a while, but I'm not sure
what the trail of broken bits are that causes the crash. If only I
had a way of instrumenting every single entry and exit of each
function, I could log it all… which is exactly what -finstrument-
functions does.
You'll likely get better results from dtrace than -finstrument-
functions. DTrace can be programmed to act on function entry or exit
for all functions in a specified file. (DTrace experts: this is your
cue to chime in.)
Be warned that any instrumentation tool is likely to perturb your bug
away, if it is in fact a problem with multithreading or code generation.
For those of you that don't know about it, when you compile your
code using -finstrument-functions, just after the entry point of
each instrumented function the function __cyg_profile_func_enter()
will be called, and __cyg_profile_func_exit() will be called just
before function exit. You define those functions as you wish.
The tricky part is that there are certain functions that must not be
instrumented like that, so you need to set the attribute
no_instrument_function on those functions. In my case, I want to
run some startup code before either of those methods ever get
called. I put my code into main(), but, IIRC, there is some
function that gets called before main() does. If that is a library
function, I'm OK since __cyg*() won't get compiled into anything I
don't have the source for, but if gcc is generating some code that
calls __cyg*() before I get the chance to do the setup, I'm going to
have another crash. So, is there anything called before main()?
What about just before main() returns?
+load methods and static C++ constructors are obvious examples of code
run before main().
For testing purposes, you could add a flag that's set after your prep
work is complete, and check it in __cyg_profile_func_enter. You could
even do the prep work inside __cyg_profile_func_enter if the flag
isn't set yet.
--
Greg Parker gpar...@apple.com Runtime Wrangler
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