Cheat Engine

[supercharger]

i found different opcodes for the same instruction, such as
mov eax,[xxxxxxxx].
and most of the time CE generates 6 byte code. why is that?

another thing, is it possible that CE generated codes be incompatible with AMD CPU or Win7 / Vista ? i mean, a game originally works with AMD/Vista, after inserting codes generated by CE, the game doesn't work with AMD/Vista, but still works with INTEL / WinXP .

[Recifense]

[Dark Byte]

mov eax,[eax+01235678] = 8b 80 + 32bit address
In that case, 6 bytes

and mov eax,[eax+eax*4] = 8b 04 80
3 bytes

as for incompatible with amd, only if you use instructions that are incompatible with amd yourself

[Psy]

What the guys said ^

And..
[quote="supercharger"
another thing, is it possible that CE generated codes be incompatible with AMD CPU or Win7 / Vista ? i mean, a game originally works with AMD/Vista, after inserting codes generated by CE, the game doesn't work with AMD/Vista[/quote]

I'm not sure this is the issue; it'd be hard for you to do this :/ You'd have to be using some instruction set such as SSE3/4 which a modern Intel CPU would be able to handle but not an AMD; although you'd have to define these yourself (using 'DB' and then the byte array) as the auto-assembler won't parse these.

[supercharger]

sorry i made a mistake. the problem is like this.

the following codes were all generated by CE:
89 05 b8 74 53 00 - mov [005374b8],eax
a3 f8 2f 53 00 - mov [00532ff8],eax
89 05 f8 2f 53 00 - mov [00532ff8],eax
a3 c8 1d 4f 00 - mov [004f1dc8],eax

see the 2nd and 3rd line, i wrote the same instruction and CE generated different codes, one 5 byte , the other 6 byte.
are there any difference of function between these codes?
and i also met other cases that different opcodes are interpreted as the same instruction. such as
03 c1 - add eax,ecx
01 c8 - add eax,ecx
the 1st line was taken from a game, CE generates the 2nd line everytime i type the instruction. i was afraid they have different functions so i rewrote the code to "03 c1" by menu "fill memory" (sometimes i can't confirm whether there are wrong codes only by checking the appearance of the game)

[Recifense]

Hi,

According to "IA-32 Intel® Architecture Software Developer’s Manual" all the instructions you cited are correct. Please take a look:

[supercharger]

thanks.

now, what i don't understand is why would CE generate different codes even if i type-in the same instruction.
if 2 opcodes have the same function, i would always prefer the shorter one.( 5 bytes for mov [00456789],eax )