Propose a 2025H2 goal for comprehensive niche checks

[1c3t3a]

This is a follow-up goal to the previous one that I did in H1. It's continuing the work by making the checks more efficient (broader coverage) and cover all niches.

cc @saethlin, @RalfJung who helped me with the previous goal

Rendered

[RalfJung]

I don't understand this paragraph...

[1c3t3a]

Oke I rephrased it and want to give a bit more background here. Essentially the problem I face when sanitizing for e.g. invalid enum discriminants is that the compiler already performs optimizations that make it impossible for us to check.

E.g. in this example, where we craft a repr(u8) enum that has two members. The compiler already optimizes the backing representation of the discriminant to be an i1, which means when we store a value of 42 here, the compiler truncates the bits and our "check" ends up not firing.

As a solution to this I'd like to propose a "checked load" operation that checks values when they are loaded from memory or something like a "shadow block" at the start of a function that checks validity of the arguments. What is your opinion on this?

[RalfJung]

Ah I see. I don't have a good idea for how to resolve this, but I understand the question now. :) Please extend the text to make that more clear.

[1c3t3a]

Oke I see, happy to hear it is clearer now. I also changed the example to another one that saethlin@ proposed as it is easier to understand the problem. The i1 for enums is already fairly specific.