bits 64

    SECTION .data
; empty

    SECTION .text
global _start
_start:
    %include "header.asm.inc"

    mov     rax, 0xFFFFFFFFFFFFFFFF ; maxint

    ; moving data into sub-registers
    mov     al, 0x11        ; rax -> 0xFFFFFFFFFFFFFF11
    mov     ah, 0x22        ; rax -> 0xFFFFFFFFFFFF2211
    mov     ax, 0x3333      ; rax -> 0xFFFFFFFFFFFF3333
   
    ; There is one exception, though:
    ; Intel's reference tells us that "32-bit operands generate
    ; a 32-bit result, zero-extended to a 64-bit result in the
    ; destination general-purpose register.", thus:
    mov     eax, 0x44444444 ; rax -> 0x0000000044444444

    ; moving with zero-extension (movzx)
    mov     rax, 0xFFFFFFFFFFFFFFFF ; maxint
    mov     bx, 0x55      
    mov     al, bl        ; rax -> 0xFFFFFFFFFFFFFF55
    movzx   rax, bx       ; rax -> 0x0000000000000055
    
    %include "sysexit.asm.inc"