16位汇编字符串比较功能失效，疑似存在Bug？

你的代码存在两个关键问题，导致输入cupcake后无法正确触发correct逻辑并显示成功信息：

1. correct标签后的执行流程错误 #

在correct分支中，你设置了si指向correctkey但没有调用printText函数，而是直接进入了printText的函数体代码。这会导致：

• 执行完printText的ret指令时，栈顶的返回地址是之前调用printText（打印correctnewline）时压入的地址，会跳回mov si, correctkey这一行，形成死循环。
• 最终程序可能崩溃，无法正常显示成功提示。

修复方法：在mov si, correctkey后添加call printText，并在最后加入无限循环防止执行后续数据区代码：

correct:
    mov si, correctnewline
    call printText
    mov si, correctkey
    call printText
    jmp $ ; 无限循环，避免执行后续数据

2. inputString缓冲区定义错误 #

你的inputString times 8 db " ", 0写法会重复8次db " ", 0，生成16字节的缓冲区（8个空格+8个null），这不符合输入存储的预期（我们只需要8字节存储7个字符+1个终止符）。正确的定义应该是：

inputString times 8 db ' '

修复后的完整代码 #

ORG 0x7C00
BITS 16


jmp getUserInput                 ; Call function 'getUserInput'

incorrect:
        mov si, invalidKey       ; Set text to SI register
        call printText           ; Call print text function

getUserInput:
        mov si, msg              ; Set greeting text to SI register
        call printText           ; Call print text function
        mov di, inputString      ; set up the string to be read in into di

getKeyLoop:
        mov ah, 0x00             ; Set function 'Reading' for interrupt 16h
        int 0x16                 ; Use 16h interrupt to read next char from keyboard

        mov ah, 0x0e             ; Set char types and colors
        cmp al, 0xD              ; when enter button is pressed...
        je getCheckKey           ; compare the string entered

        int 0x10                 ; otherwise use 10h interrupt to display character
        mov [di], al             ; Move AL to memory of DI address
        inc di                   ; DI += 1; increments the address of DI to store the next character
        jmp getKeyLoop           ; Loop | jump to function 'getKeyLoop'

getCheckKey:                       
        mov byte [di], 0         ; add null terminator to the end of inputString
        mov di, inputString      ; move input string into di
        mov si, password         ; copy password to si for comparison
        CheckKeyLoop:
                mov al, [di]     ; move 1st character or inputString into al
                mov cl, [si]     ; move 1st character of key into cl
                cmp cl, al       ; compare 1st character of both strings
                jne incorrect    ; if they don't match, jump back to getUserInput but print incorrect message first

                cmp al, 0        ; otherwise compare to null terminator
                je correct       ; password match

                inc di           ; otherwise check next char
                inc si           ; check next char
                jmp CheckKeyLoop ; resume the loop

correct:
    mov si, correctnewline
    call printText
    mov si, correctkey
    call printText
    jmp $ ; 无限循环，防止执行后续数据

printText:                       ; Function 'printText'
        mov ah, 0x0e             ; Set the text print mode
        mov bh, 0x00             ; Set screen and text parameters
        mov bl, 0x07             ; Set screen and text parameters
printChar:
        mov al, [si]             ; Move character from si (dereferenced) to al

        cmp al, 0                ; If AL = 0...
        je endPrinting           ; Call function 'endPrinting'
                                 ; Else...
        int 0x10                 ; Use 10h interrupt
        add si, 1                ; Move +1 to SI register (inc si)
        jmp printChar            ; Loop back up to 'printChar' function.

endPrinting:                     ; Function 'endPrinting'
        ret                      ; Return



password db "cupcake", 0
msg db " Enter the password: ", 0
invalidKey db " <= Incorrect. Try again..", 13, 10, 0
inputString times 8 db ' '
correctnewline db " ", 13, 10, 0
correctkey db " Congratulations!", 13, 10, 0
times 510 - ($-$$) db 0 
dw 0xAA55

验证修复 #

重新编译运行：

nasm -f bin -o cmp-input.bin cmp-input.asm
qemu-system-x86_64 cmp-input.bin

输入cupcake并回车，就能看到成功提示了。

内容的提问来源于stack exchange，提问作者unixpipe