• pushl x subtracts 4 from %esp and inserts the value x at the address now in %esp
• popl y copies the value pointed to by %esp into location y and then adds 4 to %esp.

Using R and M notations:

1. pushl x
        R[%esp] = R[%esp] - 4
        M[R[%esp]] = x

2. popl y
        y = M[R[%esp]]
        R[%esp] = R[%esp] + 4