Linux 2.6.30 exploit posted

Yes that's the usual response. But the compiler can apply the same logic in userspace and there are ways to make NULL dereferences not crash (installation of a SEGV signal handler, mapping something to page zero).

In any case, it's not like this would be a good idea for userspace code. If you care enough to check if a pointer is NULL, it should really be done before dereferencing it, otherwise it is too late to stop any undefined behavior. Even if you can be sure an implementation will just crash the program, what's the point of adding code afterwards which isn't reachable?