[win xp, olly] Problem assembling this line in olly.

[tukki_2020]

Hey guys, i am new to assembly language and i can't seem to assemble the line in olly:

xor byte ptr ds:[eax], byte ptr ds:[ecx]

what am i doing wrong?

thanks

[LCF-AT]

Hi,

do not use double brackets. [],[]

xor byte ptr ds:[eax], byte ptr ds:[ecx]

PUSHAD
------
MOV EAX,DWORD PTR DS:[1001000]
MOV ECX,DWORD PTR DS:[1014000]
XOR AL,CL
MOV BYTE PTR DS:[1001000],ALNOP		;or
MOV ECX,DWORD PTR DS:[ECX]
XOR BYTE PTR DS:[EAX],CL
-------
POPAD

Try this.

greetz

Edited June 21, 2011 by LCF-AT

[evlncrn8]

Erm nope...

Cant xor mem 2 mem..you need to use a register..

[tukki_2020]

Hey thanks for the quickie. I will try that.

What is the difference between these statements:

MOV EAX, BYTE PTR DS:[1001000]

MOV EAX, DWORD PTR DS:[1001000]

Thanks

[LCF-AT]

MOV EAX, BYTE PTR DS:[1001000] <-- Does not work
MOV EAX, DWORD PTR DS:[1001000]
Byte = 1 byte | 00
DWORD = 4 bytes | 00 00 00 00
Word = 2 bytes | 00 00MOV AL,BYTE PTR DS:[1001000] | byte
MOV AX,WORD PTR DS:[1001000] | word
MOV EAX, DWORD PTR DS:[1001000] | DWORD

greetz

[tukki_2020]

@LCF-AT: thanks

ok i got it to work as:

mov eax, 00404c05
mov ecx, 004129f3mov bh,bype ptr ds:[ecx]
xor byte ptr ds:[eax],bhinc eax
inc ecx

Then i guess that

xor byte ptr ds:[eax],byte ptr ds:[ecx]

is not a valid instruction.

thanks

Edited June 22, 2011 by tukki_2020