Cheat Engine

thethiny

Hi,
I'm building a MOD Loader for MKX, and I need to check for a file that exists, I'll tell you what I'm doing and correct me if I'm wrong.

I have a string @ Location [rdx-80], let's assume it is Asset\File1.
Now the game will load Asset\File1 as Player1. What I want to do is write a script that loads Asset\File1 from the memory, and then change it to Loadr\File1 and check if the file exists or not, if it exists then I will copy the new string (Loadr\File1) into [rdx-80], if it doesn't exist then I'm gonna jmp to end.

Is there a way to do this using the Auto Assembler? (Note that I actually can do this manually by manually writing the value byte by byte, so I know for sure that I can load Loadr\File1).

Thanks in advance, Hitler.

akumakuja28 · Posted: Sat Jul 16, 2016 1:07 pm Post subject:

IM a little confused at what your asking but this how you check if a file exists in LUA.

thethiny · Posted: Sat Jul 16, 2016 1:22 pm Post subject:

Thanks for the reply,
What I want exactly is how to load the file name from memory. Is there a way to do that? through ASM.

ParkourPenguin · Posted: Sat Jul 16, 2016 1:44 pm Post subject:

Load it into what? A 32-bit register can only hold 32 bits (i.e. 4 chars). If you want to copy it to another memory region, you can do it 4 bytes at a time through registers, use rep stos, or some library function (e.g. msvcrt.strcpy).

To check if a file exists or not, you can use PathFileExists.

thethiny · Posted: Sat Jul 16, 2016 2:32 pm Post subject:

Apparently I'm not explaining it well.

Okay listen guys.

Currently the memory has this @ Address 500 for example: Asset\File1
I want to check if file Loadr\File1 exists.

if the memory has Asset\File7 @ Address 500, then I want to check if Loadr\File7 exists. This is what I'm asking for. Asset\File1 exists in the memory and I know where, but Loadr\File1 may or may not exist.

ParkourPenguin · Posted: Sat Jul 16, 2016 2:43 pm Post subject:

thethiny · Posted: Sat Jul 16, 2016 2:54 pm Post subject:

ParkourPenguin · Posted: Sat Jul 16, 2016 3:16 pm Post subject:

So get the string of the file to be loaded from that address (I'd recommend simply mov instructions), append it to the string "Loadr\" (don't forget to zero terminate it), and call PathFileExists to check if it exists. If it returns true (1), replace "Asset" with "Loadr" in the address of the file to be loaded via mov instructions (recommended), rep stos, or strcpy.

akumakuja28 · Posted: Sat Jul 16, 2016 3:17 pm Post subject:

I remember a question like this for this game before.

Is it a string load?

Meaning if you change the Asset string(File Location) in memory it loads a different asset?

thethiny · Posted: Sat Jul 16, 2016 4:02 pm Post subject:

ParkourPenguin · Posted: Sat Jul 16, 2016 4:27 pm Post subject:

You can move and compare 4 bytes at a time, as well as reference characters directly (CE will convert them to ASCII hex).

thethiny · Posted: Sat Jul 16, 2016 4:48 pm Post subject:

Thank you very much for the help, now this is my final code, but I'm getting an "offset too big" error. Do you think you can tell where the issue resides?

ParkourPenguin · Posted: Sat Jul 16, 2016 5:21 pm Post subject:

When do you get that error? Does it tell you a line number? Does the game crash?

It might be because you're not backing up a register that's being modified by the call (see x64 calling conventions register usage). You probably don't have to worry about the xmm or FPU registers, but RAX, RCX, RDX, and R8-R11 should be backed up if you don't know if the game is using them or not.

I didn't expect you to just copy and paste it. At least remove the createthread. Unless you plan on calling that from some other script, it would be best to put it inline with everything else.

Also make sure the file path string is zero-terminated.

thethiny · Posted: Sat Jul 16, 2016 5:30 pm Post subject:

I'm sorry but I don't know what the createthread does, I'm fairly new to Cheat Engine modding.

Anyways, It just tells me that error with no line whatsoever, I noticed that commenting the BOOL: DD 0 line will get rid of that error but instead gives me another error which is BOOL was not declared. I did some googling and they told me that the distance between the FileCreateA and the Game must not be greater than 2GB, maybe that's it?
About the registers, well if I don't backup them all up, then the game simply crashes.

Edit:
Okay I moved BOOL to DATA+7C and I no longer have the offset issue. But the game now freezes.

Edit2:
Okay so the FileCreate sets XMM0 to 0, I had to backup that too. This fixed the crash, but there's a new issue. The function call ALWAYS returns 0! Why is that?

ParkourPenguin · Posted: Sat Jul 16, 2016 6:23 pm Post subject:

https://en.wikipedia.org/wiki/Thread_%28computing%29 (there's also a simple wiki page if you don't care for the details)

Now that you mention it, file+100 is probably more than 2GB away from newmem which causes the instruction cmp [BOOL],1 to fail (it's not encodable). Pass it back via a register (i.e. eax) instead, or just put it inline like I suggested.

I also just now noticed you're swapping rax and rcx by popping them in the wrong order. Elements are accessed from the stack on a last-in-first-out basis.

If PathFileExists always returns 0, then it's always failing to find the file specified. Try executing my example script in the game but instead of CE's path use '..\Loadr\FileName.txt',0 (replace FileName.txt with a file you know is there). Add the address "derp+100" (4-byte) to your cheat table manually to see the result. Fiddle around with it until it returns 1.