Re: Super Lint (was: Unexecutable Stack / Buffer Overflow Exploits...)

[Joe Buck]

Undecidability simply means that any correct program that attempts to
do certain kinds of analysis must return a three-valued answer: yes,
no, or "I can't tell".  gcc is already full of code that attempts to
solve undecidable problems: warning about code that will never be
reached, or warning about using variables before they are initialized,
is one obvious example:

	CODE;
	STATEMENT;

STATEMENT is reached iff CODE halts, so we must solve the halting problem
to tell, in general, which statements can be reached.  If STATEMENT uses a
variable that is not set, then we can't write a perfect -Winitialized
without solving the halting problem.

Yet we have a useful -Winitialized anyway; it warns in the "I can't tell"
cases as well as in the "yes" cases.