汇编语言>>>请问程序中有错误的么？如何修改？

datarea segment
buffer db 80 dup(?)
flag db ?
datarea ends
prognam segment
main proc far

assume cs:prognam,ds:datarea

start:
push ds
sub ax,ax
push ax
mov ax,datarea
mov ds,ax
lea bx,buffer
mov flag,0
next: mov ah,01
int 21h
test flag,01h
jnz follow
cmp al,20h
jnz exit
mov flag,1
jmp next
follow: cmp al,20h
jz exit
mov [bx],al
inc bx
jmp next
exit: ret
main endp
prognam ends

end start

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