vmbus_msg_create_gpadl_additional
sizeof(vmbus_msg_create_gpadl_additional));
messageLength = sizeof(vmbus_msg_create_gpadl_additional)
vmbus_msg_create_gpadl_additional* additionalMessage
((HYPERCALL_MAX_DATA_SIZE - sizeof(vmbus_msg_create_gpadl_additional)) / sizeof(uint64))
vmbus_msg_create_gpadl_additional create_gpadl_additional;