Comment by steveklabnik

  >  it can't be safe at that low level without a performance penalty.

Many of Rust's safety guarantees come from compile-time checks that then do not have any runtime penalty.

Yes, sometimes you still need unsafe, but even then, it's a superset, not a subset: a lot of safety checks still happen inside an unsafe block.

That said, I do think that building a libc in Rust would take a significant investment and I'm not sure who's going to even attempt it, if anyone.