Compiling C to Safe Rust, Formalized

Compiling a tiny subset of C, that is. It might be so tiny as to be useless in practice.

I have low hopes for this kind of approach; it’s sure to hit the limits of what’s possible with static analysis of C code. Also, choosing Rust as the target makes the problem unnecessarily hard because Rust’s ownership model is so foreign to how real C programs work.

Rust's ownership model is close enough for translating C. It's just more explicit and strongly typed, so the translation needs to figure out what a more free-form C code is trying to do, and map that to Rust's idioms.

For example, C's buffers obviously have lengths, but in C the length isn't explicitly tied to a pointer, so the translator has to deduce how the C program tracks the length to convert that into a slice. It's non-trivial even if the length is an explicit variable, and even trickier if it's calculated or changes representations (e.g. sometimes used in the form of one-past-the-end pointer).

Other C patterns like `bool should_free_this_pointer` can be translated to Rust's enum of `Owned`/`Borrowed`, but again it requires deducing which allocation is tied to which boolean, and what's the true safe scope of the borrowed variant.

Rust’s ownership model forbids things like doubly linked lists, which C programs use a lot.

That’s just one example of how C code is nowhere near meeting Rust’s requirements. There are lots of others.

> Rust’s ownership model forbids things like doubly linked lists, which C programs use a lot.

It’s literally in the standard library

https://doc.rust-lang.org/std/collections/struct.LinkedList....