Known breaking changes / differences in CoreCLR

[rolfbjarne]

This issue is to list all differences between MonoVM and CoreCLR.

Differences between legacy Xamarin and .NET 6+ (that happen for both MonoVM and CoreCLR) should be listed here: #8900

Assembly.GetType works differently for nested types

Mono accepts both + and / as the character that separates the declaring type and the nested type, while CoreCLR only accepts /.

Test case:

using System;

class Program
{
	class N {}
	static void Main (string[] args)
	{
		Console.WriteLine ($"Program+N: {typeof (Program).Assembly.GetType ("Program+N")}");
		Console.WriteLine ($"Program/N: {typeof (Program).Assembly.GetType ("Program/N")}");
	}
}

Mono prints:

$ mcs Program.cs && mono Program.exe
Program+N: Program+N
Program/N: Program+N

CoreCLR prints:

$ dotnet run
Program+N: Program+N
Program/N: 

It's not possible to pass an Action<T> or a Func<T> to a P/Invoke

Ref: dotnet/runtime#32963

It's not possible to have CoreCLR unwind native frames for managed exceptions.

This means that no entry point into managed code can "leak" exceptions, because CoreCLR will abort the process.

For Objective-C entry points, Xamarin will catch managed exceptions and convert them to Objective-C exceptions, but this won't be done for reverse P/Invokes in user code.

As a result, the UnwindNativeCode and UnwindManagedCode values for exception marshaling are not valid when using CoreCLR.

Ref: #11344

[rolfbjarne]

I've moved this to the wiki: https://github.com/xamarin/xamarin-macios/wiki/Incompatibilities-between-CoreCLR-and-Mono