IL2CPP Compatibility

On a Unity IL2CPP build the managed Assembly-CSharp.dll is not shipped: il2cpp.exe consumes it and converts it to C++ (GameAssembly.dll). BitMono obfuscates the assembly before that conversion, so pure managed/metadata protections (renaming, string encryption, …) carry through into global-metadata.dat. Protections that emit native code, calli, pack the PE, or otherwise produce output il2cpp.exe can’t handle would break the build (or only affect the managed PE that IL2CPP throws away), so they must be skipped on IL2CPP builds.

You mark such a protection with [IL2CPPIncompatible]. When BitMono runs in IL2CPP mode (the Unity integration sets it automatically when the scripting backend is IL2CPP, or you pass --il2cpp / "IL2CPP": true), every protection marked this way is skipped and the reason is logged.

[IL2CPPIncompatible("Emits calli, which IL2CPP's AOT compiler does not support")]
public class CallToCalli : Protection

The reason you pass is shown to the user so they understand why the protection was skipped:

[IL2CPP] CallToCalli - Emits calli, which IL2CPP's AOT compiler does not support

Under the hood a protection is treated as IL2CPP-incompatible when it is marked with [IL2CPPIncompatible] or with Native Code ([ConfigureForNativeCode]) - native method bodies can never be converted to C++, so they are always excluded even without an explicit attribute.

[AttributeUsage(AttributeTargets.Class, Inherited = false)]
public class IL2CPPIncompatibleAttribute : Attribute
{
    public IL2CPPIncompatibleAttribute(string reason = "")
    {
        Reason = reason;
    }

    public string Reason { get; }

    public string GetMessage()
    {
        return string.IsNullOrWhiteSpace(Reason)
            ? "Not supported on IL2CPP builds"
            : Reason;
    }
}

Note

The attribute is read automatically by reflection, the same way as Protection Runtime Moniker - you don’t register anything. Add it on top of the protection (a built-in one or a plugin) and BitMono skips it on IL2CPP builds while still running it normally on Mono / standalone .NET builds.

If a protection only does pure managed metadata/IL edits that il2cpp.exe can parse (renaming, clearing namespaces, replacing ldstr with a managed decryptor call, …), don’t mark it - it should keep running on IL2CPP so its effect lands in global-metadata.dat.