Converting DOS code into Windows

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me239

Joined: 06 Jan 2011
Posts: 200

me239 29 Sep 2011, 04:33

Hey everyone, I just ran into a bit of a dilemma with my TXT parser I have. The problem is it can't take any files larger that 64kb (obviously) so I would love to convert it to a Windows cmdline driven PE. It's a very simple program, I just don't know too much about Windows file editing. Basically the point of the program is to find multiple occurrences of hex 0x0D and replace them with 0x00.

Code:

org 100h
start:
        mov     ax, 3d02h
        mov     dx, filen
        int     21h
        jc      error
        xchg    ax, bx
        mov     ah, 3fh
        mov     cx, 9ah
        push    cx
        mov     dx, buff
        int     21h
        mov     si, buff
        pop     cx
        mov     word[size], cx
loop1:
        lodsb
        cmp     al, 0dh
        jz      @f
        loop    loop1
        jmp     done
@@:
        lodsb
        cmp     al, 0dh
        jz      @f
        dec     si
        jmp     loop1
@@:
        sub     si, 2
        mov     byte[si], 0
        add     si, 2
        jmp     loop1
done:
        mov     ax, 4200h
        xor     cx, cx
        cwd
        int     21h
        mov     ah, 40h
        mov     dx, buff
        mov     cx, [size]
        int     21h
error:
        int     20h
size    dw      0
filen   db      'enc.txt', 0
buff:

29 Sep 2011, 04:33

typedef

Joined: 25 Jul 2010
Posts: 2909
Location: 0x77760000

typedef 29 Sep 2011, 09:04

CreateFile()
ReadFile()
cld
mov esi,buff
mov ecx,file_size_or_bytes_read_
@@:
mov ah,0x00
lodsb
cmp al,0dh
jne k
xchg ah,[esi]
k:
dec ecx
jnz @B
WriteFile --- If needed.
CloseHandle()

look up those APIs, i'm posting from my psp so i can't type much

29 Sep 2011, 09:04

AsmGuru62

Joined: 28 Jan 2004
Posts: 1619
Location: Toronto, Canada

AsmGuru62 29 Sep 2011, 14:17

Good, but LODSB will increment ESI, so "XCHG AH, [ESI-1]" would be better. Also, why not just "MOV [ESI-1], AH"?

29 Sep 2011, 14:17

typedef

Joined: 25 Jul 2010
Posts: 2909
Location: 0x77760000

typedef 29 Sep 2011, 16:37

^^You are right I wasn't thinking there. Very Happy

thanks

29 Sep 2011, 16:37

me239

Joined: 06 Jan 2011
Posts: 200

me239 29 Sep 2011, 17:25

I tried writing a simple program to write "Hello!" to a file with no luck Sad

Code:

format PE GUI 4.0
entry start
include 'win32a.inc'
start:
        invoke  CreateFile, filen, GENERIC_WRITE, 2, NULL, 3, 80h, NULL, NULL
        invoke  WriteFile, buff, 6
        invoke  ExitProcess
filen   db      'test.txt', 0
rights  db      2
buff    db      'Hello!', 0
section '.idata' import data readable writeable
        library  kernel32, 'KERNEL32.DLL'
        import   kernel32,\
                 CreateFile, 'CreateFileA',\
                 WriteFile, 'WriteFile',\
                 ExitProcess, 'ExitProcess'

29 Sep 2011, 17:25

typedef

Joined: 25 Jul 2010
Posts: 2909
Location: 0x77760000

typedef 29 Sep 2011, 17:42

lol lmao.......you are really a noob at win32 API (no offense)
hold on let me get on my computer so i can type fast and help you

29 Sep 2011, 17:42

me239

Joined: 06 Jan 2011
Posts: 200

me239 29 Sep 2011, 18:31

typedef wrote:

lol lmao.......you are really a noob at win32 API (no offense)
hold on let me get on my computer so i can type fast and help you

I got it working

Code:

format PE GUI 4.0
entry start
include 'win32a.inc'
start:
        invoke  CreateFile, filen, GENERIC_WRITE, 0, 0, CREATE_NEW, FILE_ATTRIBUTE_NORMAL, 0
        mov     [hFile], eax
        invoke  WriteFile, [hFile], buff, 6, bwrt, 0
        invoke  ExitProcess
filen   db      'test.txt', 0
rights  db      2
buff    db      'Hello!', 0
hFile   dd      0
bwrt    db      0
section '.idata' import data readable writeable
        library  kernel32, 'KERNEL32.DLL'
        import   kernel32,\
                 CreateFile, 'CreateFileA',\
                 WriteFile, 'WriteFile',\
                 ExitProcess, 'ExitProcess'

29 Sep 2011, 18:31

typedef

Joined: 25 Jul 2010
Posts: 2909
Location: 0x77760000

typedef 30 Sep 2011, 02:04

Yea, sorry.. My friend came over and I was playing MK vs DC & God Of War 3 ... Very Happy

30 Sep 2011, 02:04

me239

Joined: 06 Jan 2011
Posts: 200

me239 30 Sep 2011, 04:29

nice, I played L4D2

30 Sep 2011, 04:29

typedef

Joined: 25 Jul 2010
Posts: 2909
Location: 0x77760000

typedef 30 Sep 2011, 13:25

haven't played that yet. is it online too?

30 Sep 2011, 13:25

me239

Joined: 06 Jan 2011
Posts: 200

me239 01 Oct 2011, 03:22

typedef wrote:

haven't played that yet. is it online too?

Look up Left 4 Dead 2

01 Oct 2011, 03:22

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