push and pop in Assembly

The stack grows down; last in, first out swaps for free.

; The stack grows down; push and pop move rsp for you.
        global _start

        section .text
_start:
        mov rax, 3
        mov rbx, 39

        push rax                ; save 3
        push rbx                ; save 39
        pop rax                 ; rax = 39 (last in, first out)
        pop rbx                 ; rbx = 3

        add rax, rbx            ; 42, values swapped and summed
        mov rdi, rax
        mov rax, 60             ; exit code 42
        syscall

How it works

1. push writes and moves rsp; pop does the reverse.
2. Popping in the same order swaps the two values.
3. rsp bookkeeping is entirely implicit here.

Keywords and builtins used here

• add
• global
• mov
• pop
• push
• rax
• rbx
• rdi
• section
• syscall

The run, in numbers

Lines

17

Characters to type

389

Tokens

41

Three-star pace

60 tpm

At the three-star pace of 60 tokens a minute, this run takes about 41 seconds.

Type this snippet

Step 1 of 3 in The stack, step 19 of 31 in Language basics.

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