Uncertainty of point and pop operands on processors

Question

Why do we have commands like push and pop?

From what I understand popand pushbasically the same as for ( movthen add) and ( subthen mov) respectively esp.

For example, there would be:

pushl %eax

is equivalent to:

subl $4, %esp
movl %eax, (%esp-4)

please correct me, if access to the stack is not (%esp-4), I'm still studying the assembly

The only true advantage that I see is that if both operations simultaneously give some advantage; however, I do not understand how this is possible.

+5

Hawken Apr 14 '12 at 17:23

3 answers

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+2

dbrank0 14 . '12 21:50

1 opcode> 2 opcode, at least when you are trying to reduce CPU usage.

+1

tomByrer Apr 14 '12 at 17:26

Jim Mischel · Accepted Answer · 2012-04-14T20:09:53+0000

CALL. , :

sub esp,4
mov [esp-4], offset return_address
jmp myproc

RET, :

mov eax,[esp]
add esp,4
jmp [eax]

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push eax
push ebx
call proc    ; pushes the return address and jumps to proc
...

proc:
  ; at this point, [esp] contains the return address

RET .

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