strlen 模拟

; Prototype:
;    ax strlen(char *str)
; Param:
;    str: The address of a null terminated string.
; Return:
;    eax: The length of string, excluding null character.; Function own the stack and  response for pop stack.
strlen    PROC NEAR32
    push    ebp
    mov    ebp, esp
    pushf
    push    ebx

    ; Initialize
    mov    eax, 0
    mov    ebx, [ebp + 8]

    ; Count
while_strlen:
    cmp    BYTE PTR [ebx], 0
    jz    exit_strlen
    inc    ebx
    inc    eax
    jmp    while_strlen

    ; Exit
exit_strlen:
    pop    ebx
    popf
    pop    ebp
    ret    4
strlen    ENDP