After a bit of googling I found this: The caller ensures that the stack is 16-byte aligned at the point of the function call. “At the point of the function ca

After a bit of googling I found this: The caller ensures that the stack is 16-byte aligned at the point of the function call. “At the point of the function call” means just before the CALL instruction is executed, the top of the stack. No further explanation is given, but an inference can be made: the Darwin kernel is using SIMD instructions to quickly move data on the stack, possibly during context switches. http://pages.cs.wisc.edu/~weinrich/papers/method_dispatch.pdf http://pages.cs.wisc.edu/~weinrich/papers/method_dispatch.pd...