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

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Date:   Tue, 07 Jan 2020 13:23:59 +0100
From:   Florian Weimer <fweimer@...hat.com>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     Carlos O'Donell <carlos@...hat.com>,
        Joseph Myers <joseph@...esourcery.com>,
        Szabolcs Nagy <szabolcs.nagy@....com>,
        libc-alpha@...rceware.org, Thomas Gleixner <tglx@...utronix.de>,
        Ben Maurer <bmaurer@...com>,
        Peter Zijlstra <peterz@...radead.org>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Will Deacon <will.deacon@....com>,
        Dave Watson <davejwatson@...com>, Paul Turner <pjt@...gle.com>,
        Rich Felker <dalias@...c.org>, linux-kernel@...r.kernel.org,
        linux-api@...r.kernel.org
Subject: Re: [RFC PATCH glibc 09/13] glibc: Perform rseq(2) registration at C startup and thread creation (v13)

* 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:
>   https://lkml.org/lkml/2018/9/19/647
>
> 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 build-many-glibcs.py.

> 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
> +
> +@...e Restartable Sequences
> +@...tion Restartable Sequences
> +@...dex 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
                                       @theglibc{}
           @code{__rseq_abi}
> +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.

Thanks,
Florian