To illustrate the popl instruction suppose the current stack frame is as we left it:

R[%esp] = 0x08002ffc
R[%ebp] = 0x080030a4
R[%eax] = 20
     

0x08002ffc	10
0x08003000	5
	Rest of Stack Frame
0x080030a4

Now execute: popl %eax   The change to registers and the stack:

R[%esp] = 0x08003000
R[%ebp] = 0x080030a4
R[%eax] = 10
     

0x08003000	5
	Rest of Stack Frame
0x080030a4