Joe Damato's Defcon 18 presentation on Function hooking in OSX and Linux.
An excellent talk from track 4 that was both technically competent and entertaining.
Official talk description:
"This talk will cover three different methods of function hooking for Mac OSX and Linux. The talk will begin by describing useful bits of Intel64 assembly followed up with 3 different binary rewriting techniques to hook a range of different functions, including some inlined functions, too. We'll finish up with a demo of two nice things that these techniques make possible (a memory profiler and a function call tracer), and one slightly more evil thing."
You can find the slides at Joe's blog:
and follow him on twitter: @joedamato