[UncleMeat]

Hard. Apple actually has a RFC for this where functions taking buffer-like parameters are adjusted to take an additional length parameter and then the compiler edits the code to plumb lengths through all of these things to insert a bounds check at use. This can work in many cases, but not all.

Rolling out this sort of change across a large codebase is hard as shit. While it sounds like it is mostly transparent, as soon as you run into a sufficiently large codebase all sorts of things start blowing up that you need to fix by hand before such a feature can be rolled out.

You can also do this with pointer tagging and some other techniques, but without hardware support this is amazingly slow. You can see just how much slower an asan build is, for example.

[pjmlp]

Apple is basically catching up with the Windows XP SP2 effort, which lead to the introduction of SAL annotations on Windows, and yes it was the reason for its delay.