Question

I have an Apache module on Mac OS X that produces random crashes. I can reproduce these crashes with certain sequence of actions, and these crashes produce Crash Reporter dialog “httpd quit unexpectedly”. Is there a way to cause Crash Reporter launch debugger (xcode, gdb, anything) instead of just displaying the backtrace?

I’ve tried running httpd under gdb with httpd -X but the crash doesn’t happen then – it happens only if many httpd’s are running at once, and I found no way to attach gdb to all of them at once. So I was hoping maybe I can cause CrashReporter to attach the debugger when specific process crashes – is there a way to do it?

Answer 1

Unfortunately, the type of bug you describe has a tendency to disappear when perturbed by examination.

That said, an option to try is launching a GDB session from inside your module. QA1573 has an example using DTrace, which would seem a bit cleaner, but after some experimentation this doesn’t seem to work terribly well with multiple processes. (I could not see a way to get DTrace to attach gdb at the time the process crashes; you only get a proc::postsig:signal-handle probe triggered after the process has already crashed.)

You could do something like this from your module:

% echo 'c' > continue.txt
% osascript -e 'tell app "Terminal" to do script "gdb -x continue.txt attach <pid>"'

which would open a separate Terminal window for each httpd process.

You could also start gdb from outside instead, with a script (DTrace or otherwise) watching for httpd processes, and use the SIGSTOP method from QA1573 in your module’s code to wait until the script noticed the new httpd.