Add `m3_LinkRawFunctionEx` support

[johannesvollmer]

If I am not mistaken, this function will be necessary for linking non-static C# functions, such as closures, correct? I have experimented a little bit, but could not make it work. This would be necessary to later add a function that automatically marshals all the arguments and return types between c# and wasm3.

My plan is as follows:

• assume that m3_LinkRawFunctionEx(..., void* userdata) can be used to call functions with extra data
• add public static extern string m3_LinkRawFunctionEx(...) function mapping
• add IM3ImportContext type mapping
• use IM3ImportContext type mapping everywhere instead of IntPtr
• call m3_LinkRawFunctionEx with a pointer to a data structure that contains a closure object
• inside of the registered M3RawCall callback, when called, retrieve closure object from the ctx->userdata pointer in IM3ImportContext
• call the C# closure with the data

Will this work? Is this a clean approach? I would like to contribute.

[johannesvollmer]

Actually, to pass an instance method or a closure, nothing needs to be changed. The C# marshaller knows how to create a working function pointer from a C# closure. But of course you need to keep alive a delegate of the correct type, which is M3RawCall. For example, like this:

            m3Module.LinkRawFunction(
                "externals", "print_add", "i(ii)", 
                this.keepAliveM3FunctionPointer = new M3RawCall(MyClosureDelegate)
            );

where MyClosureDelegate can by a closure with state or a non-static method reference.

[tana]

I apologize for not responding for more than one year.

Today I fixed the problem using approach you suggested (keep a delegate above by storing it) in commit 55c8ab0.

[johannesvollmer]

Excellent! I have had a workaround monkey-patched, but I'm glad that you are back :) because I have a few more fixes in my fork that I would be glad to discuss with you, and maybe feed back to your repo :)

[johannesvollmer]

I'll close this issue for now, as C# will manage the closures in my use case, which means I don't need LinkRawFunctionEx anymore.