linux-kernel - Re: [RFC PATCH v9 for 4.15 01/14] Restartable sequences system call

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Message-ID: <87efpz2hrz.fsf@mid.deneb.enyo.de>
Date:   Thu, 19 Oct 2017 19:01:52 +0200
From:   Florian Weimer <fw@...eb.enyo.de>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     Ben Maurer <bmaurer@...com>, Carlos O'Donell <carlos@...hat.com>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Paul Turner <pjt@...gle.com>, Andrew Hunter <ahh@...gle.com>,
        Andy Lutomirski <luto@...capital.net>,
        Dave Watson <davejwatson@...com>,
        Josh Triplett <josh@...htriplett.org>,
        Will Deacon <will.deacon@....com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andi Kleen <andi@...stfloor.org>, Chris Lameter <cl@...ux.com>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, rostedt <rostedt@...dmis.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Russell King <linux@....linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-api <linux-api@...r.kernel.org>
Subject: Re: [RFC PATCH v9 for 4.15 01/14] Restartable sequences system call

* Mathieu Desnoyers:

> Speaking of optimization, I think the rseq.c helper library
> (and eventually glibc) should define the __rseq_abi TLS
> variable with __attribute__((tls_model("initial-exec"))).
> It provides faster, and signal-safe, accesses to the TLS
> variable from libraries.
>
> The idea you were suggesting where the application could
> override the glibc symbol with its own just ends up enforcing
> an initial-exec model, but it looks like we can do this
> directly from the library.

This really depends on how the programming model turns out once
multiple libraries are involved.  I think it's premature to discuss
such details.