Factorial of 3 in Assembly

;This program calculates and displays the factorial of the number 3, using a recursive procedure
;Fact (n) = n * fact (n-1) for n > 0


section	.text
	global _start			;must be declared for using gcc

_start:						;tell linker entry point

	mov bx, 3				;for calculating factorial 3
	call  proc_fact
	add   ax, 30h
	mov  [fact], ax
    
	mov	  edx,len        ;message length
	mov	  ecx,msg        ;message to write
	mov	  ebx,1          ;file descriptor (stdout)
	mov	  eax,4          ;system call number (sys_write)
	int	  0x80           ;call kernel

	mov   edx,1            ;message length
	mov	  ecx,fact       ;message to write
	mov	  ebx,1          ;file descriptor (stdout)
	mov	  eax,4          ;system call number (sys_write)
	int	  0x80           ;call kernel
    
	mov	  eax,1          ;system call number (sys_exit)
	int	  0x80           ;call kernel
	
proc_fact:
	cmp   bl, 1
	jg    do_calculation
	mov   ax, 1
	ret
	
do_calculation:
	dec   bl
	call  proc_fact
	inc   bl
	mul   bl        ;ax = al * bl
	ret

section	.data
msg db 'Factorial 3 is:',0xa ; or 0	
len equ $ - msg			

section .bss
fact resb 1