Bbum on obj_msgSend()
In a three part blog post, Bill Bumgarner goes into the details of how obj_msgSend() works on x86-64 under MacOS X 10.6.2. If you know enough assembly language, you can easily take what he’s given and make it apply to the iPhone or any of the other architectures that MacOS X supports.
For those who might be wondering what obj_msgSend() is used for, it is probably the most called method in MacOS X and iPhone OS. It is the method that actually looks up and dispatches Objective C method calls at runtime. If you’ve ever debugged an OS X or iPhone application before, you’ll recognize obj_msgSend() as it is typically where you will see your app crash if you are trying to use a pointer that you have already released.
Dec 18, 2009