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Comment by arghwhat | Hacker News Reader

It significantly simplifies OS development. E.g., syscalls can be modified and improved or entirely deprecated without concern.

If OpenBSD wanted to, they could implement something like io_uring with support for all kernel functionality, port libc to use that and ditch conventional syscalls entirely (simulating blocking where needed), without user-space knowing anything changed.

Under Linux, which is actually rather unusual in providing ABI guarantees, you're stuck maintaining bug-for-bug compatibility for every syscall you've ever written, and cannot change user-space no matter how good that change would be for either or both.

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> you're stuck maintaining bug-for-bug compatibility for every syscall you've ever written

But instead you have to maintain bug-for-bug compability in libc for every API you've ever written. In case of macOS where the kernel and libc/libSystem developments are closed and done by the same entity is makes zero difference (imho).

Also, I understand catiopatio's argument in the sibling comment about doing more in user-space than in kernel in case of a bug, but it breaks down the moment thin wrappers around syscalls exist there. You link to libc/libSystem and use every thin wrapper in existence - now no syscall can be changed (if I understand correctly how macOS works, never used one)

I'd much rather export this complexity to userland code than privileged kernel mode code though. It reduces the potential consequence for a mistake pretty drastically.

> But instead you have to maintain bug-for-bug compability in libc for every API you've ever written.

It is not instead. With syscall ABI you need to maintain both, without it you only need to maintain libc (a majority of which is dictated by POSIX anyway).

> In case of macOS where the kernel and libc/libSystem developments are closed and done by the same entity is makes zero difference (imho).

As above, maintaining two contracts is harder than one.

Proprietary parts aside, most OS's have their kernel and user-space developed together, and that is exactly what allows them to work this way.

This is used to adopt new features, change or deprecate old features with a brutal efficiency that Linux cannot compete with - e.g., when OpenBSD implemented pledge in both kernel and all relevant tools.

This is one of the reasons that these projects can keep up or in some cases surpass Linux (FreeBSD networking is seen as superior, and you used to get better performance from running Linux binaries on FreeBSD through its compatibility layer) despite having much smaller groups of maintainers and users.

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