彙編語言中的putch函數通過堆棧 (putch function in assembly language through stack)

問題描述

彙編語言中的putch函數通過堆棧 (putch function in assembly language through stack)

我正在用彙編語言製作一個程序，我試圖通過將字符推入堆棧來在控制台上顯示一個字符。我正在使用中斷 21H 的服務號 2 來打印字符。

當我運行程序時，字符顯示在控制台上，但問題是它在控制台上顯示無限次。我沒有使用任何循環，所以不知道為什麼它會在控制台上無限次打印。

需要幫助來解決問題。

我正在使用emu8086。

.model small
.data
st1 db "A",'$' 
.code
main proc
    mov AX,@data
    mov DS, AX

    mov AX, offset st1
    push AX

    call putch

    putch proc near
        mov BP,SP 
        mov DX,[BP+2]
        mov AH,2
        INT 21H
        ret
    putch endp 

    mov AH,4CH
    INT 21H

end main 

參考解法

方法 1:

Next image illustrates the problem :

• When you call putch the program jumps as the red arrow.
• When putch finishes it returns to the call as the green arrow.
• Then the program continues (blue arrow) and executes the next line, which is putch again (that's a loop).

The solution is to move above the block that finishes the program. Another problem is that your program requires a stack. Finally, @MargaretBloom is right (as usual), your code is pushing the address of the string, but you are using int 21h ah=2 to display the char, so there are two options : #1 push the char and display with ah=2, or, #2 push the address and display with ah=9 :

#1

.model small
.stack 100h              ;◄■■ STACK!!!
.data
st1 db "A",'$' 
.code
main proc
    mov AX,@data
    mov DS, AX

    xor ax, ax           ;◄■■ CLEAR AX.
    mov AL, st1          ;◄■■ CHAR IN AX.
    push AX              ;◄■■ PUSH THE CHAR.

    call putch

    mov AH,4CH           ;◄■■ FINISH PROGRAM HERE.
    INT 21H

    putch proc near
        mov BP,SP 
        mov DX,[BP+2]    ;◄■■ THE CHAR.
        mov AH,2         ;◄■■ 2 = DISPLAY ONE CHAR.
        INT 21H
        ret
    putch endp 

end main 

#2

.model small
.stack 100h              ;◄■■ STACK!!!
.data
st1 db "A",'$' 
.code
main proc
    mov AX,@data
    mov DS, AX

    mov AX, offset st1   ;◄■■ GET THE ADDRESS.
    push AX              ;◄■■ PUSH THE ADDRESS.

    call putch

    mov AH,4CH         
    INT 21H

    putch proc near
        mov BP,SP 
        mov DX,[BP+2]    ;◄■■ GET THE ADDRESS.
        mov AH,9         ;◄■■ 9 = DISPLAY STRING '$' TERMINATED.
        INT 21H
        ret
    putch endp 

end main 

(by Yousaf、Jose Manuel Abarca Rodríguez)

參考文件

1. putch function in assembly language through stack (CC BY‑SA 2.5/3.0/4.0)