Building DLL for Unity with functions with callback fails - unity3d

Question

I want to build DLL for Unity with functions with callback.
When I build with X64, Callback function works.
But when I build with arm64 and deploy it on HoloLens2, it doesnot work.
Here is my code to build DLL
enter image description here
Here is my code to use it.
enter image description here
Accroding to the result shown in HoloLens. It shows "20". So the fuction "Add" runs, But callback doesnot run.
Thanks if someone can help me.

Answer 1

I've had some experience with native->managed callbacks in my day. Yours is simple and should work without a hitch. One thing that raises a bit of a suspicion is the calling convention of the delegate. In general calling conventions are more of a 32bit era thing. In 64bit code there is one convention so it should just be left at the default. I'd suggest you remove the explicit calling convention declarations from the attributes.
Another thing I've noticed is that squiggly green line on your screenshot. Since you already declared the callback type as typedef int (*addP)(int) why not actually use it in the function definition?
int TestAddWithCallBack(addP callback)
{
int result = Add(3,5);
return callback(result);
}
You may also want to test if the TestAddWithCallBack function is even getting called at all. Change it to:
int TestAddWithCallBack(addP callback)
{
int result = Add(3,5);
return result;
}
and see if it returns properly.