; File: twopass.asm
;
; Demonstrating a two-pass assembler

        section .data
x:      db      87h
y:      dw      1492h
zalias  equ $
z:      dd      17762001h

calc equ (x-y)*2
x4 equ x+1

        section .text
        global _start

_start: mov     eax, [zalias]
        mov     bx, [y]
        mov     cx, [x4]
        cmp     bx, cx
        jne     error

OK:     add     ax, bx
        mov     [x], al
        mov     ebx, 0          ; 0=normal exit

done:   mov     eax, 1          ; syscall number for exit
        int     080h

error:  mov     ebx, 17         ; abnormal exit
        jmp     done