Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: Restartable Sequences system call merged into Linux
To:     Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Pavel Machek <pavel@ucw.cz>
Cc:     carlos <carlos@redhat.com>, Peter Zijlstra <peterz@infradead.org>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Boqun Feng <boqun.feng@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        libc-alpha <libc-alpha@sourceware.org>
References: <1084280721.10859.1528746558696.JavaMail.zimbra@efficios.com>
 <31fc101a-295b-067b-1a82-7e9e509fc92f@redhat.com>
 <305409897.10888.1528747473727.JavaMail.zimbra@efficios.com>
 <091061df-3482-8762-30e4-feaf3417be11@redhat.com>
 <417742741.11550.1528821084084.JavaMail.zimbra@efficios.com>
 <20180614122759.GB8798@amd>
 <894222691.12973.1528981314012.JavaMail.zimbra@efficios.com>
From:   Florian Weimer <fweimer@redhat.com>
Message-ID: <b5c0a91b-b428-7807-0f16-97f15e632bdb@redhat.com>
Date:   Fri, 15 Jun 2018 07:09:42 +0200
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101
 Thunderbird/52.8.0
MIME-Version: 1.0
In-Reply-To: <894222691.12973.1528981314012.JavaMail.zimbra@efficios.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 06/14/2018 03:01 PM, Mathieu Desnoyers wrote:
> Another alternative would be to somehow let glibc handle the registration,
> perhaps only doing it for applications expressing their interest for rseq.

That's not really possible.  We can't rely on the visibility of symbol 
bindings due to lazy binding and hidden visibility.  Registration of 
intent by other means will not work because if it is done from user 
code, some other library may have already launched a thread at this point.

(It's also a moot point if we want to use restartable sequences in glibc 
itself.)

Thanks,
Florian