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MonoMod

Random C# / Mono / .NET assembly patcher using Mono.Cecil.

Special thanks to my patrons on Patreon:

What does it do?

It patches any C# assembly (PE32 executable (console) Intel 80386 Mono/.Net assembly) with any given assembly patches.

The patches are in form of C# assemblies, making it easy to use for quick and (as long as the input assembly isn't obfuscated) version-independent patching / modding / prototyping.

Finally, MonoMod patches itself into the input assembly entry point. In case the user runs the patched assembly in a shell, the used MonoMod version gets printed.

How to use it?

You drop the MonoMod.exe, Mono.Cecil.dll and your patches into a folder. Then, in your favorite shell (cmd, bash):

MonoMod.exe Assembly.exe

MonoMod then scans the directory the file is in for files named Assembly.*.mm.dll (in case of FEZ.exe: FEZ.Mod.mm.dll). Finally, it produces an Assembly.mm.exe, which is the patched version of the assembly.

How does it exactly work?

Black magic, Mono.Cecil and a lot of luck. Oh, and many, many hacks and workarounds.

For modders: How to create a patch assembly?

You decompile the input assembly to get a tree of all types and methods. Use that tree to create another assembly which contains pieces of that tree with custom code.

To further simplify patching, MonoMod offers following features:

  • For types and methods, to be ignored by MonoMod (because of a superclass that is defined in another assembly and thus shouldn't be patched), use the MonoModIgnore attribute.
  • For types that must have another name than the original type but should still get patched into the input assembly by MonoMod, prefix the type with "patch_".
  • To call the original method, create a stub method of the same signature with the prefix "orig_".

##For gamedevs and others: How can I check my game etc. has been modded? MonoMod creates a type called "WasHere" in the namespace "MonoMod" in your assembly. You can simply call

if (Assembly.GetExecutingAssembly().GetType("MonoMod.WasHere") != null) {
    //We Interrupt This Programme
}

to check if your game has been modded.

Are there limits?

Yes.

  • Any patch that doesn't compile due to any reasons (feel free to add your workaround here).
  • Any patch that crashes MonoMod (feel free to add your fix here).
  • Any patch that causes issues at IL level (feel free to add your black magic here).
  • Any patch that is blacklisted or accessing anything blacklisted (feel free to contact me about adding your field / method / ... to the blacklist).
  • Anyone can compile a "black" (blacklist- and WasHere-free) version of MonoMod, avoiding the one limitation listed above.

Am I allowed to redistibute the patched assembly?

Ask the creator of the input assembly, the patches and your lawyer (actually not your lawyer).

Am I allowed to redistribute MonoMod?

Yes. Do so freely, as long as you don't charge the user any costs for using / downloading MonoMod.

##Is it possible to patch patches? Yes, but the orig_ methods will be ignored by MonoMod.

##Is it possible to patch patched patches? ...

##Is it possible to make my PC burn? Maybe. I've heard AMD CPUs start smoking at 400°C.