Looking at wireguard-rs, in its current form it makes a lot of use of `alloc` (namely `Vec` and `HashMap`) and `std` features (`fs`, `net`, `sync`).

Getting it working on a Cortex-M would involve extracting a core protocol implementation which doesn't make use of any of those features as a library/crate which has no dependencies (or only optional dependencies which can be switched off with Cargo features) on `alloc` and `std`.