cc.asm

cc.asm

; linux x86 assembly example of a standard calling convention
; tweak the linker flag if not on intel cpu
; assemble:     nasm -felf32 cc.asm
; link:         ld -m elf_i386 cc.o -o cc
; run:          ./cc
; exit code:    echo $?
; exposes the startpoint of the program to the linker
global  _start

; code sits in the text section
section .text
; C equivalent
; int func (int a, int b, int c) {
;     return (a + b) * c;
; }
func:
    push    ebp
    mov     ebp, esp

    mov     eax, [ebp + 8]  ; eax is often used for return value
                            ; get a
    add     eax, [ebp + 12] ; get and add b
    mul     DWORD [ebp + 16] ; get and multiply c
                            ; automatically multiplies into eax

    mov     esp, ebp
    pop     ebp
    ret

_start:
                            ; let's call func(1, 2, 3)
    push    DWORD 3         ; parameters are passed in reverse
    push    DWORD 2
    push    DWORD 1
    call    func            ; eax now should have 9
    mov     ebx, eax        ; set eax as the exit code
    mov     eax, 1          ; sys_exit is syscall 1
    int     0x80