汇编代码自动运行一个终端命令。

Recently, I wrote a bit of assembly code that asks for the password and if the user enters the correct password as stored internally, it prints out "Correct!". Else, it prints out "Incorrect!".

最近，我编写了一段程序集代码，要求输入密码，如果用户输入了内部存储的正确密码，它会打印出“正确!”否则，它会打印出“错误!”

Here is the code:

这是代码:

section .text
    global _start
_start:
    mov edx, len_whatis
    mov ecx, whatis
    mov ebx, 1
    mov eax, 4
    int 80h ; outputs: "What is the password?"

    mov edx, 5 ; expect 5 bytes of input(so 4 numbers)
    mov ecx, pass
    mov ebx, 0
    mov eax, 3
    int 80h ; accepts intput and stores in pass

    mov eax, [pass] ; move the pass variable into eax
    sub eax, '0' ; change the ascii number in eax to a numerical number
    mov ebx, [thepass] ; move the thepass variable into ebx
    sub ebx, '0' ; change the ascii number in ebx to a numerical number

    cmp eax, ebx ; compare the 2 numbers
    je correct ; if they are equal, jump to correct
    jmp incorrect ; if not, jump to incorrect
correct:
    mov edx, len_corr
    mov ecx, corr
    mov ebx, 1
    mov eax, 4
    int 80h ; outputs: "Correct!"

    mov ebx, 0
    mov eax, 1
    int 80h ; exits with status 0
incorrect:
    mov edx, len_incor
    mov ecx, incor
    mov ebx, 1
    mov eax, 4
    int 80h ; outputs: "Incorrect!"

    mov eax, 1
    int 80h ; exits with status: 1
section .data
    whatis db "What is the password?", 0xA
    len_whatis equ $ - whatis

    thepass db "12345"

    corr db "Correct!", 0xA
    len_corr equ $ - corr

    incor db "Incorrect!", 0xA
    len_incor equ $ - incor
section .bss
    pass resb 5

Assemble:nasm -f elf password.s

组装:nasm - f精灵password.s

Link:ld -m elf_i386 -s -o password password.o

链接:ld -m elf_i386 -s -o密码密码密码

(If you did try to assemble link and run this, you may notice that it checks the password incorrectly - ignore this. It is "off topic")

(如果您尝试组装链接并运行此链接，您可能会注意到它检查密码不正确——忽略它。这是“主题”)

Then, I ran a test:

然后，我做了一个测试:

I ran the code with ./password
我用./密码运行代码
When I was prompted for the password, I typed in 123456, one more byte than the code expects
当我被提示输入密码时，我输入了123456，比代码预期的多一个字节
After I hit enter and the code exits, the terminal immediately tries to run a command 6
在我点击enter并退出代码后，终端立即尝试运行命令6

What is causing this behavior? Is it something to do with the assembler, or how my computer is reading the code?

是什么导致了这种行为?这与汇编程序有关吗?或者我的计算机是如何读取代码的?

EDIT:

编辑:

And, when I run the code with 12345, the terminal prompts for a command twice when the program closes, as if someone just hit the enter button without entering a command.

而且，当我用12345运行代码时，当程序关闭时，终端会提示两次命令，就好像有人在没有输入命令的情况下按下了enter键。

1 个解决方案

#1

You're only reading five bytes from standard input, so when you type 123456↵, your application ends up reading 12345 and leaving 6↵ in the buffer. That gets passed on to the shell.

你只是读五个字节从标准输入,所以当你123456型↵,您的应用程序最终阅读12345,留下6↵缓冲区。它传递给壳层。

If you want to read the whole line, use a larger buffer.

如果要读取整行，请使用较大的缓冲区。

#1