Re: [RFC PATCH glibc 09/13] glibc: Perform rseq(2) registration at C startup and thread creation (v13)

From: Florian Weimer
Date: Tue Jan 07 2020 - 07:24:14 EST

* Mathieu Desnoyers:

> Register rseq(2) TLS for each thread (including main), and unregister
> for each thread (excluding main). "rseq" stands for Restartable
> Sequences.
> See the rseq(2) man page proposed here:
> This patch is based on glibc-2.30. The rseq(2) system call was merged
> into Linux 4.18.

This patch needs to be updated for some be/le abilist splits.
Big-endian ABI lists for arm, microblaze, sh, appear to be missing.
This is something that can be checked with

> diff --git a/manual/threads.texi b/manual/threads.texi
> index 0858ef8f92..059f781120 100644
> --- a/manual/threads.texi
> +++ b/manual/threads.texi
> @@ -881,3 +881,20 @@ Behaves like @code{pthread_timedjoin_np} except that the absolute time in
> @c pthread_spin_unlock
> @c pthread_testcancel
> @c pthread_yield
> +
> +@node Restartable Sequences
> +@section Restartable Sequences
> +@cindex rseq
> +
> +This section describes the @glibcadj{} Restartable Sequences integration.
> +
> +The @glibcadj{} implements a __rseq_abi TLS symbol to interact with the
@Theglibc{} @code{__rseq_abi}

> +Restartable Sequences system call (Linux-specific). The layout of this
> +structure is defined by the Linux kernel rseq.h UAPI. Registration of each
> +thread's __rseq_abi is performed by @glibcadj{} at libc initialization and
> +pthread creation.

> +Each supported architecture provide a RSEQ_SIG signature in sys/rseq.h. That
@code{RSEQ_SIG} @file{sys/rseq.h}

> +signature is expected to be present in the code before each Restartable
> +Sequences abort handler. Failure to provide the expected signature may
> +terminate the process with a Segmentation fault.

Two spaces at the end of setences, please.

The manual should use @deftypevar to create an index entry etc. for
__rseq_abi. See argp_program_version for an example of how to do this.

I think current policy is to have documentation for at least the minimum
functionality in the manual. I understand that it makes it a lot of
work to write patches which add system call wrappers.