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

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Message-ID: <14399397.44601.1508412942855.JavaMail.zimbra@efficios.com>
Date:   Thu, 19 Oct 2017 11:35:42 +0000 (UTC)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Ben Maurer <bmaurer@...com>, Carlos O'Donell <carlos@...hat.com>,
        Florian Weimer <fw@...eb.enyo.de>
Cc:     "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

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.

Thoughts ?

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com