For some time I've been meaning to collect together notes about stuff I've come across that's useful when debugging problems on Mac OS. Stuff that isn't obvious and well-known to a developer from a different Unix. Now I don't have to, because Apple have published TN2124: Mac OS X Debugging Magic which contains just about everything I'd found, plus more.
The only thing I can think of that isn't mentioned there is giving -Wl,-Y -Wl,n options to GCC so Apple's ld(1) shows more information about the first n undefined symbols. Mac OS' linker isn't nearly as loquacious as Linux's, and won't by default tell you which files the symbol appears in; something I often find useful.
Although it sounds useful, I don't understand the INIT_Processes=1 hint, and Google doesn't seem to know anything about it either.