Trying to figure out MASM syntax

Question

I've done some assembly programming on Linux and am now trying to do it on Windows using MASM. I am running into a couple issues though.

(Here I am trying to implement the strlen() function. I know the function logic/instructions aren't optimal, but I'm just trying to rig something dirty up so I can get going on implementing other C library functions.)

.386
.model flat, stdcall
option casemap:none

include \masm32\include\kernel32.inc
includelib \masm32\lib\kernel32.lib

include \masm32\include\masm32.inc
includelib \masm32\lib\masm32.lib

.data
       testString db "test string", 0   ; 0 -> terminator

.code
my_strlen proc
        mov ebp, esp                    ; function prologue
        push esp
        push ebx
        push ecx

        xor ecx, ecx                    ; set count to 0
        mov bl, byte ptr [ebp + 8]      ; set low of b to 1st character

    repeat:
        cmp bl, 0                           ; if null terminator, return
        jz done
        inc ecx                             ; increase count
        mov bl, byte ptr [ebp + 8 + ecx]    ; increase *ebx
        jmp repeat                          ; repeat

    done:

        mov eax, ecx                    ; return count

        pop ecx                         ; function epilogue
        pop ebx
        pop esp
        ret

my_strlen endp


main:
       push offset testString                       ; result = my_strlen(testString)
       call my_strlen

       push eax                                     ; StdOut(result)
       call StdOut

       push 0                                       ; ExitProcess(0)
       call ExitProcess                              
end main

When I try to compile, it doesn't appear to like my jmp labels, throwing unmatched macro nesting, etc. Whats the proper way to do this? p.s. I am trying to avoid using MASM macros where possible, preferring to code the instructions myself.

Can someone please make this program compile? Once I see how it is done correctly I will be on my merry way, I will be able to. Yes I looked for resources and still am as this question is up.

Answer 1

Can someone please make this program compile?

Voilà (explanation in the comments):

.386
.model flat, stdcall
option casemap:none

include \masm32\include\kernel32.inc
includelib \masm32\lib\kernel32.lib

include \masm32\include\masm32.inc
includelib \masm32\lib\masm32.lib

.data
    testString db "test string", 0

.code
my_strlen proc

;   mov ebp, esp                        ; function prologue
;   push esp

    push ebp                            ; this is a correct prologue
    mov ebp, esp

    push ebx
    push ecx
    push esi

    mov esi, [ebp+8]                    ; in [EBP+8] is a pointer

    xor ecx, ecx
    mov bl, byte ptr [esi]

    repea:                              ; "repeat" is a keyword
        cmp bl, 0
        jz done
        inc ecx
        mov bl, byte ptr [esi + ecx]    ; increase *esi
        jmp repea                       ; repeat

    done:
        mov eax, ecx

        pop esi
        pop ecx
        pop ebx

        leave                           ; this is a correct epilogue
        ret

my_strlen endp


main proc                               ; this is better
       push offset testString
       call my_strlen

;      push eax                         ; StdOut(result)
       push offset testString           ; The MASM32-function StdOut needs only an ASCIZ-string
       call StdOut

       push 0                
       call ExitProcess
main endp

end main

I suspect you want to output the result of my_strlen. This is not possible with StdOut because StdOut needs a pointer to a string. You have to create a function to convert EAX to a string.