Some languages, including C and C++, contain an operation that creates a pointer to a data object. That is, p = &x takes the address of object x, whose type is t, and assigns it top, whose type is t*. How is management of the run-time stack complicated if it is possible to create pointers to arbitrary data objects in frames? What restrictions on the creation and copying of pointers to data objects suffice to guarantee the integrity of the run-time stack?