SECTION .data
msg     db      'A cat!', 0Ah

SECTION .text
global  _start

_start:
mov     edx, msg
call    strlen

mov     ecx, msg
mov     ebx, 1
mov     eax, 4
int     80h

mov     ebx, 0
mov     eax, 1
int     80h

strlen:
push    ebx
mov     ebx, edx

nextchar:
cmp     byte [edx], 0
jz      finished
inc     edx
jmp     nextchar

finished:
sub     edx, ebx
pop     ebx
ret