Strange Characters when printing a string in x86 assembly language?

Question

My code is required to have a string that will be printed to the console, alongside a string length counting program that will count it instead of manually putting length of string in edx register. But i am getting strange characters printed right after the string is printed.

global          _start

section         .text

_start:

  mov           edi, message
  call          _strlen
  mov           edx, eax

  mov           eax, 4
  mov           ebx, 1
  mov           ecx, message
  int 80h

  mov           eax, 1
  mov           ebx, 5
  int 80h

 section         .data
message: db     "My name is Stanley Hudson", 0Ah
_strlen:

  push          ebx
  push          ecx

  mov           ebx, edi
  xor           al, al
  mov           ecx, 0xffffffff

  repne         scasb               ; REPeat while Not Equal [edi] != al

  sub           edi, ebx            ; length = offset of (edi – ebx)
  mov           eax, edi

  pop           ebx
  pop           ecx
  ret

Here is the output

Answer 1

strlen searches for a 0 byte terminating the string, but your string doesn't have one, so it goes until it does find a zero byte and returns a value that's too large.

You want to write

message: db     "My name is Stanley Hudson", 0Ah, 0
                                               ; ^^^

Another bug is that your _strlen function is apparently in the .data section, because you didn't go back to section .text after your string. x86-32 doesn't have the NX bit so the .data section is executable and everything still works, but it's surely not what you intend.

Answer 2

要摆脱特殊字符，请在启动过程之前编写 strlen 函数并为换行符创建一个新寄存器