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
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.
To get rid of the special characters write the strlen function before the start process and create a new register for the newline character
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