A complete specification also must include assumptions about external systems and limits. Here the assumptions are infinite stack (or item count < stack size l

A complete specification also must include assumptions about external systems and limits. Here the assumptions are infinite stack (or item count < stack size limit) and a malloc that never fails. Incomplete specs are just as bad as buggy code. I'd even argue that incomplete specs are worse in this scenario, because the "proven correctness" gives a false sense of security.