assembly x86: simple string comparison routine

Question

What's the problem with this routine? it won't work for the given values below. I'm using this in a shell for a simple kernel but I have no idea why it doesn't work.

mov si, buffer                 ; buffer value from user input: 'help'
mov di, shell_command_help     ; shell_command_help db 'help',0
call os_compare_string 

; ----------------------------------------------------------
; Routine: Compare equality of two strings
; Waits for a complete string of user input and puts it in buffer.
; Sensitive for backspace and Enter buttons
; Input    1. String1 in SI    2. String2 in DI
; Output   1. result in carry flag
; ----------------------------------------------------------
os_compare_string:

  .compare_next_character:      ; a loop that goes character by character
    mov al, [si]      ; focus on next byte in si

    mov bl, [di]      ; focus on next byte in di
    cmp al, bl
    jne .conclude_not_equal       ; if not equal, conclude and exit

                      ; at this point we know the two bytes are equal
    cmp bl, 0         ; did we just compare two zeros?
    je .conclude_equal         ; if yes, we've reached the end of the strings. They are equal.

                      ; increment counters for next loop
    inc di
    inc si
    jmp .compare_next_character

  .conclude_equal:
    stc              ; sets the carry flag (meaning that they ARE equal)
    jmp .done

  .conclude_not_equal:
    clc              ; clears the carry flag (meaning that they ARE NOT equal)
    jmp .done

  .done:
    xor cl, cl
    ret

Answer 1

You are xor'ing cl after setting carry flag. This is a bad idea.