Question

我在TASM汇编语言上编写DOS命令行参数解析器。这是我的代码：

.model tiny
.386
.code
org 100h
start:


    mov ax, ax  
    mov bp, 80h
    mov si, 81h
    mov ch, 0
    mov cl, ds:[bp]
    push 0
    cmp cx, 0
    je FINISH

    CYCLE_BEGIN:
        lodsb
        cmp al, 2Fh
        je SLASH
        cmp al, 31h
        je ONE
        cmp al, 32h
        je TWO
        cmp al, 33h
        je THREE
        cmp al, 68h
        je HELP
        cmp al, 20h
        je SPACE
        mov bx, 6
        jmp CHANGE_STATE

        SLASH:
            mov bx, 0
            jmp CHANGE_STATE
        ONE:
            mov bx, 1
            jmp CHANGE_STATE
        TWO:
            mov bx, 2
            jmp CHANGE_STATE
        THREE:
            mov bx, 3
            jmp CHANGE_STATE
        HELP:
            mov bx, 4
            jmp CHANGE_STATE
        SPACE:
            mov bx, 5
        CHANGE_STATE:
            mov ax, 7
            mul dx
            add ax, bx
            mov dh, 0
            push si
            mov si, offset AU
            add si, ax
            lodsb
            mov dl, al
            pop si

        cmp dx, 6
        JE ERROR

        cmp dx, 1
        je HAVEONE
        cmp dx, 2
        je HAVETWO
        cmp dx, 3
        je HAVETHREE
        cmp dx, 4
        je HAVEHELP
        jmp CYCLE_END

        HAVEONE:
            mov ax, 0001h
            jmp SETFLAGS
        HAVETWO:
            mov ax, 0010h
            jmp SETFLAGS
        HAVETHREE:
            mov ax, 0100h
            jmp SETFLAGS
        HAVEHELP:
            mov ax, 1000h
        SETFLAGS:
            pop bx
            or bx, ax
            push bx
        CYCLE_END:
            dec cx
            jne CYCLE_BEGIN
    jmp SUCCESS
    ERROR:
        pop bx
        mov dx, offset merror
        mov ah, 09h
        int 21h
        jmp FINISH
    SUCCESS:
    pop bx
    mov dx, bx
    and dx, 1000h
    je MESSAGES_CHECK
    mov dx, offset mhelp
    mov ah, 09h
    int 21h
    jmp FINISH

    MESSAGES_CHECK:
    mov dx, bx
    and dx, 0001h
    je CHECK2
    mov dx, offset m1
    mov ah, 09h
    int 21h
    mov ah, 02h
    mov dl, 0dh
    int 21h
    mov dl, 0ah
    int 21h

    CHECK2:
    mov dx, bx
    and dx, 0010h
    je CHECK3
    mov dx, offset m2
    mov ah, 09h
    int 21h
    mov ah, 02h
    mov dl, 0dh
    int 21h
    mov dl, 0ah
    int 21h
    CHECK3:
    mov dx, bx
    and dx, 0100h
    je FINISH
    mov dx, offset m3
    mov ah, 09h
    int 21h

    FINISH:
        RET

        m1  db  'You have used /1 key$'
        m2  db  'You have used /2 key$'
        m3  db  'You have used /3 key$'
        mhelp   db  'ad.asm [/1 | /2 | /3| /h]$'
        merror  db  'Wrong input$'

        AU:;        / 1 2 3 h   *
        db  5,6,6,6,6,0,6 ;
        db  6,6,6,6,6,0,6 ; /1
        db  6,6,6,6,6,0,6 ; /2
        db  6,6,6,6,6,0,6 ; /3
        db  6,6,6,6,6,0,6 ; /h
        db  6,1,2,3,4,6,6 ; /
        db  6,6,6,6,6,6,6 ; err



end start

如果有m1，/1，如果有m2和/2＆＃，则会打印m3的内容39;如果/3。问题在于此代码部分：

mov dx, offset m1
    mov ah, 09h
    int 21h
----

mov dx, offset m2
    mov ah, 09h
    int 21h
----

mov dx, offset m3
    mov ah, 09h
    int 21h

它不会打印任何东西。即使我在Turbo Debugger中看到代码已到达并且dx中存在正确的偏移量，int 21h之后的stdout中也没有文本。为什么呢？

Answer 1

由于DX未事先初始化，因此CHANGE_STATE的乘法没有任何意义！

CHANGE_STATE:
        mov ax, 7
        mul dx

希望这会有所帮助。

另外，因为您正在使用字符串原语lodsb，所以您可以确保清除方向标记cld。

Answer 2

DOS .com应用程序仅将其所有代码和数据存储在一个段中，DS和ES已经初始化，并且在开始执行时等于CS。

...

为了获得一些命令行参数，建议之前获取PSP的段地址，因为当前PSP不一定是调用者的PSP，如果我们从父应用程序中启动子应用程序例如，使用int 21h的exec函数AX = 4B00h。

RBIL-＆GT; inter61b.zip-＆GT; INTERRUP.H

--------D-2162-------------------------------
INT 21 - DOS 3.0+ - GET CURRENT PSP ADDRESS
AH = 62h
Return: BX = segment of PSP for current process
Notes:  this function does not use any of the DOS-internal stacks and may
thus be called at any time, even during another INT 21h call
the current PSP is not necessarily the caller's PSP
identical to the undocumented AH=51h
SeeAlso: AH=50h,AH=51h

DOS汇编程序：MOV啊，09h和int 21h组合不打印任何东西

2 个答案: