C compatibility is marked the same way, but it's not idiomatically used the same way in C++ and Rust. In C++, being C compatible means essentially writing C and for everything else you're expected to rely on the "not really stable" C++ ABI whereas Rust does not even try to give you a stable ABI between stuff that's not part of pretty much the same build. Despite that, you're free to mix C-like and Rustic code in the same crate because the crate is literally the translation unit in Rust.
ABI stability doesn't matter for the kernel since it doesn't have a stable ABI either. You can write a C++ core and C wrappers for C++ classes just fine, the same as what you do in Rust.
