and esp, 0xfffffff0

Question

I don\'t entirely understand the line with comment in it below. I read a few posts on SO and in the gcc manual and learned that it is for stack address alignmen

Answer 1

and esp, 0xfffffff0 does a bitwise AND between the stack pointer and a constant, and stores the result back in the stack pointer.

The constant is chosen so that its low four bits are zero. Therefore the AND operation will set these bits to zero in the result, and leave the other bits of esp intact. This has the effect of rounding the stack pointer down to the nearest multiple of 16.