; CFG example
bits 64

    SECTION .data
; empty

    SECTION .text

add_two_numbers:
    push    rbp
    mov     rbp, rsp
    mov     rax, rdi
    add     rax, rsi
    leave
    ret

global _start
_start:
    mov     rdi, 20     ; first parameter
    mov     rsi, 30     ; second parameter

    test    rdi, rdi
    js      negative
    
    test    rsi, rsi
    js      negative

    call    add_two_numbers
    jmp     return

negative:
    mov     rax, -1

return:
    ; sys_exit(42)
    mov     rax,60  ; system call number (sys_exit)
    mov     rdi,42  ; system call return value
    syscall