Inline from C libraries won't -- as far as I'm aware -- inline into a Rust function. Inline is a compile-time hint, not a link-time behavior. In theory this could be changed in LLVM, but it seems really unlikely to me. The function exposed from C (with the inline asm) can be naked, though, assuming you are hygienic.

Yeah, but that is a consequence of not having a Rust aware linker and relying on one that basically uses C semantics.

Languages that use their own linkers tend to have better opportunities for code optimization during linking.