AOT-Compatlyzer

Transforms .NET DLLs for use in AOT (for use on iOS platforms, including Unity3D.) Fixes Unity's .NET 3.5 event add/remove code and a workaround for generic virtual methods.

STATUS

My status: This tool only addresses some of the issues in AOT compatibility. Unfortunately, despite putting in a lot of time, I have not been able to successfully port all of my own codebase to Unity3D's Mono. There are issues with generic interface dispatch, including calls to foreach(IEnumerable<T>). I like generic interfaces and foreach and have a lot of both, so I appear to be somewhat doomed until I can make a comprehensive sweep of my codebase (and hope I have covered all the issues, which is still a gamble.)

So, I have put my iOS project on hold and am instead targeting PC (a non-Unity3D project), Mac, and Android first. Perhaps by then Unity3D will have a newer version of mono that is less broken, or perhaps another viable cross platform C# engine will exist by then.

PREREQUISITES

Mono.Cecil.dll (DLL version 0.9.4.0, from package Cecil 2.10.9)

What it does

Bringing a .NET codebase onto iOS via Mono? (Perhaps via Unity3D?) This tool can help ease the pain!

The Events CompareExchange problem

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Unity 3.5 (and I believe 4) ships with a modified version of Mono 2.6.5 that spits out Interlocked.CompareExchange<>() virtual methods inside of auto-generated add_/remove_ properties for C# events. This is a problem in AOT code. AOT-Compatlyzer replaces this autogenerated code with a version that uses an alternate implementation.

WARNING: Currently, I do not add the Synchronized attribute to the new add_/remove_ methods, which should be present, according to the example code I was working from.

UPDATE: There is a better fix that preserves thread safety, using the version of CompareExchange/Exchange that accepts parameters of objects instead of value types. For details see Issue 1

The Virtual Methods problem

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AOT does not support virtual methods.

AOTCompatlyzer introduces some workarounds for some scenarios:

#define AOT   // Comment this to hide code only needed for AOT-only mode

class Abc 
{
    // Compiles, but throws ExecutionEngineException in AOT-only mode if invoked!
    T MyMethod<T>(int p1, int p2) { …  }

#if AOT // AOTCompatlyzer will detect and use this instead!
    object MyMethod(int p1, int p2, Type T) { …  }
#endif

    void Run()
    {
        ...
        T myObj = MyMethod<T>(1, 2);
        ...
    }
}

AOTCopatlyzer will replace Run's MyMethod invocation with:

void Run() //
{
    ...
    T myObj = (T) MyMethod(1, 2, typeof(T));
    ...
}

These cases are also supported:

• both methods return void
• both method return same type (in this case, casting to T is not necessary).

LIMITATIONS:

• Only one generic parameter is supported: i.e. MyMethod<T> and not MyMethod<T1,T2>. (TODO: This could be easily supported.)

Other problems

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I am not finished porting my codebase to an AOT-only environment yet. As I run into more problems I will either adapt my codebase, or extend this utility to morph my DLL to something that works in AOT-only mode.

• I believe Action<T1,T2> events fail.