[reflection] Return n2m wrapper from RuntimeMethodHandle.GetFunctionPointer

for functions marked with UnmanagedCallersOnlyAttribute, return a pointer to
the n2m wrapper for calls to GetFunctionPointer

Contributes to #59815

Author: lambdageek

src/mono/mono/metadata/icall.c

@@ -6293,6 +6293,11 @@ ves_icall_System_Environment_get_TickCount64 (void)
 gpointer
 ves_icall_RuntimeMethodHandle_GetFunctionPointer (MonoMethod *method, MonoError *error)
 {
+	/* WISH: we should do this in managed */
+	if (G_UNLIKELY (mono_method_has_unmanaged_callers_only_attribute (method))) {
+		method = mono_marshal_get_managed_wrapper  (method, NULL, (MonoGCHandle)0, error);
+		return_val_if_nok (error, NULL);
+	}
 	return mono_get_runtime_callbacks ()->get_ftnptr (method, error);
 }
 

src/mono/mono/mini/interp/interp.c

@@ -6537,9 +6537,16 @@ MINT_IN_CASE(MINT_BRTRUE_I8_SP) ZEROP_SP(gint64, !=); MINT_IN_BREAK;
 
 			MonoMethod *cmethod = LOCAL_VAR (ip [2], MonoMethod*);
 
-			InterpMethod *m = mono_interp_get_imethod (cmethod, error);
-			mono_error_assert_ok (error);
-			LOCAL_VAR (ip [1], gpointer) = imethod_to_ftnptr (m, FALSE);
+			if (G_UNLIKELY (mono_method_has_unmanaged_callers_only_attribute (cmethod))) {
+				cmethod = mono_marshal_get_managed_wrapper  (cmethod, NULL, (MonoGCHandle)0, error);
+				mono_error_assert_ok (error);
+				gpointer addr = mini_get_interp_callbacks ()->create_method_pointer (cmethod, TRUE, error);
+				LOCAL_VAR (ip [1], gpointer) = addr;
+			} else {
+				InterpMethod *m = mono_interp_get_imethod (cmethod, error);
+				mono_error_assert_ok (error);
+				LOCAL_VAR (ip [1], gpointer) = imethod_to_ftnptr (m, FALSE);
+			}
 			ip += 3;
 			MINT_IN_BREAK;
 		}