~clay

The holidays have given me a chance to relax and geek around with Mac OS X, and I’ve finally gotten around to installing the Developer Tools package, which includes the GNU C compiler (gcc) and the GNU debugger (gdb). Over the years I’ve gotten pretty comfortable using gdb to troubleshoot programs on SPARC and Intel platforms. Debugging requires that you know a bit about assembly language, and I had learned x86 assembly back in the day when I was coding fun little graphics toys for DOS, and had learned some SPARC assembly trying to, uhm, correct an annoying license issue in a piece of commercial software.

During the holiday break I figured I’d learn some PowerPC (PPC) assembly while I still had the chance, given Apple’s decision to move to x86 early next year. Debugging simple programs isn’t much fun, though, so I figured I’d start poking around with a big application. An annoying thing kept happening everytime I fired up the app under the debugger, though; it exited immediately with a strange error code:

% gdb /Applications/blah.app/Contents/MacOS/blah
(gdb) run
Program exited with code 055.


Bummer. I remembered the same problem happening with that commercial Solaris app years before, but I never paid much attention to it back then, because it was possible to work around the problem by attaching to the program after it was already up and running. Apple seems to be a bit smarter than that, though, because whenever I attached to a running copy of the application, GDB seg faulted:

(gdb) attach 17813
Attaching to program: `/Applications/blah.app/Contents/MacOS/blah', process 17813.
Segmentation fault


Since I wanted to know why the application was exiting, I figured I’d step through it one instruction at a time until I found the culprit.
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