Messages in this thread | | | Subject | Re: Official Linux system wrapper library? | From | Andy Lutomirski <> | Date | Wed, 14 Nov 2018 06:46:47 -0800 |
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> On Nov 14, 2018, at 3:58 AM, Szabolcs Nagy <Szabolcs.Nagy@arm.com> wrote: > >> On 13/11/18 19:39, Dave Martin wrote: >>> On Mon, Nov 12, 2018 at 05:19:14AM -0800, Daniel Colascione wrote: >>> We should adopt a similar approach. Shipping a lower-level >>> "liblinux.so" tightly bound to the kernel would not only let the >>> kernel bypass glibc's "editorial discretion" in exposing new >>> facilities to userspace, but would also allow for tighter user-kernel >>> integration that one can achieve with a simplistic syscall(2)-style >>> escape hatch. (For example, for a long time now, I've wanted to go >>> beyond POSIX and improve the system's signal handling API, and this >>> improvement requires userspace cooperation.) The vdso is probably too >>> small and simplistic to serve in this role; I'd want a real library. >> >> Can you expand on your reasoning here? > > such lib creates a useless abi+api layer that > somebody has to maintain and document (with or > without vdso).
I’m not so sure it’s useless. Historically, POSIX systems have, in practice and almost by definition, been very C focused, but the world is changing. A less crufty library could be useful for newer languages:
> > it obviously cannot work together with a posix > conform libc implementation for which it would > require knowledge about > > thread cancellation internals,
Thread cancellation is a big mess, and we only really need to support it because on legacy code. The whole mechanism should IMO be considered extremely deprecated.
> potentially TLS > for errno,
errno is IMO a libc thing, full stop. A lower level library should *not* support errno.
> know libc types even ones that are > based on compile time feature macros (and expose > them in headers in a way that does not collide > with libc headers),
This one is tricky. I wonder if we could instead get a C compiler extension to set libc declare that a given struct is a layout-compatible variant of another.
> abi variants the libc supports > (e.g. softfp, security hardened abi),
Hmm.
> libc > internal signals (for anything that's changing > signal masks),
This is nasty, but see my cancellation comment above.
> thread internals for syscalls that > require coordination between all user created > threads (setxid),
We should just deal with this in the kernel. The current state of affairs is nuts.
> libc internal state for syscalls > that create/destroy threads.
I disagree. If you make or destroy threads behind libc’s back, I think you get to keep both pieces.
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