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

While I cannot really answer your question of WHY, you may find the manuals at the following site useful:

http://www.agner.org/optimize/

Regarding the ABI, have a look especially at:

http://www.agner.org/optimize/calling_conventions.pdf

Hope that's useful.