NASM中的变量声明和stx / etx

Question

请考虑以下内容

func session(_ session: MCSession, didFinishReceivingResourceWithName resourceName: String, fromPeer peerID: MCPeerID, at localURL: URL?, withError error: Error?) {
    do {
        let localData = try Data(contentsOf: localURL!)
        let image = UIImage(data: localData)
        DispatchQueue.main.async {
            // DispatchQueue.main.async necessary because modifying UI
            self.imageView.image = image
        }
    }
    catch let error {
        print("error \(error)")
    }
}

我在DosBox中得到的输出是：

根据此网站（https://www.ascii-codes.com/），笑脸和心脏是STX和ETX字符，而不是预期的括号。

如果我按如下所示更改JMP start leftbr DB '(' rightbr DB ')' key DB '' start: MOV AH, 08 INT 21h ; Read keypress MOV [key], AL ; Store the key pressed in variable 'key' output: MOV DL, leftbr ; Move the value from 'leftbr' to DL MOV AH, 02 INT 21h ; Should output ( MOV DL, [key] ; Put the value from 'key' in the DL register INT 21h ; Output 'key' MOV DL, rightbr INT 21h ; Output ) exit: MOV AH, 4Ch MOV AL, 00 INT 21h ; Terminate the program 块，则会得到正确的输出：

start:

谁能解释为什么会这样？我应该能够声明一个具有初始值的变量。