[mono][interp] Don't do sign extension when called from gsharedvt_in_sig

Those wrappers use the real type as the return, so sign extension shouldn't be needed and it wouldn't be safe, because the wrapper passes the address of the return var of the actual type. Attemptying to sign extend could overflow the storage of this var.

Author: BrzVlad

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

@@ -2395,8 +2395,17 @@ interp_entry (InterpEntryData *data)
 
 	// The return value is at the bottom of the stack, after the locals space
 	type = rmethod->rtype;
-	if (type->type != MONO_TYPE_VOID)
-		stackval_to_data_sign_ext (type, frame.stack, data->res, FALSE);
+	if (type->type != MONO_TYPE_VOID) {
+		// interp entry is called either from a interp_in wrapper or a gsharedvt_in_sig wrapper
+		// interp_in wrappers always return intptr (they are more aggresively shared) while the
+		// gsharedvt_in_sig wrapper returns the actual type. This check follows the logic in
+		// interp_create_method_pointer_llvmonly and interp_create_method_pointer so we do the
+		// return sign extension only when called from the interp_in wrapper.
+		if (!mono_llvm_only || sig->param_count > MAX_INTERP_ENTRY_ARGS)
+			stackval_to_data_sign_ext (type, frame.stack, data->res, FALSE);
+		else
+			stackval_to_data (type, frame.stack, data->res, FALSE);
+	}
 }
 
 static void