Why does the Mac ABI require 16-byte stack alignment for x86-32?

Question

I can understand this requirement for the old PPC RISC systems and even for x86-64, but for the old tried-and-true x86? In this case, the stack needs to be aligned on 4 byte

Answer 1

In order to maintain consistency in kernel. This allows the same kernel to be booted on multiple architectures without modicfication.