9.4.2 Casting to void*

If T is void*, the result is a pointer to the complete object. That is, v might point to one of the base classes of some complete object. In that case, the result of dynamic_cast<void*>(v) is the same as if you converted v down the hierarchy to the type of the complete object (whatever that is) and then to void*.

When casting to void*, the hierarchy must be polymorphic (have virtual functions).