Function pointers are possible to deal with, with varying levels of automation. You can detect when pointers to functions are taken, and tie them to call sides

Function pointers are possible to deal with, with varying levels of automation. You can detect when pointers to functions are taken, and tie them to call sides with type information or some manual work (I have a static analysis tool which allows function pointers for callbacks by linking functions passed into one function to the list of possible destinations for a given callsite). Recursion is harder but it's still possible in principle to prove a bound in a lot of cases, given a proof framework. Not something I'd encourage, though.