> IMO an OS provided dynamically linked library is a great abstraction boundary. In theory, yes that's true. In practice it's a question of whether it actuall

> IMO an OS provided dynamically linked library is a great abstraction boundary. In theory, yes that's true. In practice it's a question of whether it actually reduces anybodies work load. If everybody respected the boundary I sure it would reduce Microsofts work load. But as has been reported repeatedly here, that's isn't how it's worked out in practice. Not only do applications not respect it, Microsoft finds itself in the position of having to ensure some of those applications keep working on newer kernel versions despite the fact they've wilfully violated the rules. So we end up the Windows GUI having to expose with "compatibility levels", and users having to deal with it. That doesn't sound like a win to me. There are other ways of doing it that wouldn't suffer from that fate. Trampolines (a page the kernel creates in user space that intercepts some syscalls) is one way that Linux uses. I don't think Linux does, but it wouldn't be hard to insist that any syscall come from those pages. Do that and you have your cake (low overhead user space mediating some calls), and get to eat it to (you can safely assume every one uses it).