bits 64

    SECTION .data
; empty

    SECTION .text
global _start
_start:
    %include "header.asm.inc"
    
    mov     ax, -1      ; initialize with negative value (-1)

    mov     ebx, eax    ; ---> ebx = 0x0000ffff, i.e., positive!
    movsx   ebx, ax     ; ---> ebx = 0xffffffff, i.e., negative (-1)
    
    %include "sysexit.asm.inc"