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;
Date:   Fri, 14 Jun 2019 06:03:04 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
To:     carlos <carlos@redhat.com>, Florian Weimer <fweimer@redhat.com>
Cc:     Joseph Myers <joseph@codesourcery.com>,
        Szabolcs Nagy <szabolcs.nagy@arm.com>,
        libc-alpha <libc-alpha@sourceware.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ben Maurer <bmaurer@fb.com>,
        Peter Zijlstra <peterz@infradead.org>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Boqun Feng <boqun.feng@gmail.com>,
        Will Deacon <will.deacon@arm.com>,
        Dave Watson <davejwatson@fb.com>, Paul Turner <pjt@google.com>,
        Rich Felker <dalias@libc.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        linux-api <linux-api@vger.kernel.org>
Message-ID: <802638054.3032.1560506584705.JavaMail.zimbra@efficios.com>
In-Reply-To: <914051741.43025.1560348011775.JavaMail.zimbra@efficios.com>
References: <20190503184219.19266-1-mathieu.desnoyers@efficios.com> <87muj2k4ov.fsf@oldenburg2.str.redhat.com> <1528929896.22217.1559326257155.JavaMail.zimbra@efficios.com> <87o93d4lqb.fsf@oldenburg2.str.redhat.com> <117220011.27079.1559663870037.JavaMail.zimbra@efficios.com> <87wohzorj0.fsf@oldenburg2.str.redhat.com> <c16c9785-7f8c-430b-a4df-a53e47bf1600@redhat.com> <914051741.43025.1560348011775.JavaMail.zimbra@efficios.com>
Subject: Re: [PATCH 1/5] glibc: Perform rseq(2) registration at C startup
 and thread creation (v10)
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 7bit
Thread-Topic: glibc: Perform rseq(2) registration at C startup and thread creation (v10)
Thread-Index: 6rG93gdkMSoHS5ZP168diTIrRPG9C+LZilEL
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

----- On Jun 12, 2019, at 4:00 PM, Mathieu Desnoyers mathieu.desnoyers@efficios.com wrote:

> ----- On Jun 10, 2019, at 4:43 PM, carlos carlos@redhat.com wrote:
> 
>> On 6/6/19 7:57 AM, Florian Weimer wrote:
>>> Let me ask the key question again: Does it matter if code observes the
>>> rseq area first without kernel support, and then with kernel support?
>>> If we don't expect any problems immediately, we do not need to worry
>>> much about the constructor ordering right now.  I expect that over time,
>>> fixing this properly will become easier.
>> 
>> I just wanted to chime in and say that splitting this into:
>> 
>> * Ownership (__rseq_handled)
>> 
>> * Initialization (__rseq_abi)
>> 
>> Makes sense to me.
>> 
>> I agree we need an answer to this question of ownership but not yet
>> initialized, to owned and initialized.
>> 
>> I like the idea of having __rseq_handled in ld.so.
> 
> Very good, so I'll implement this approach. Sorry for the delayed
> feedback, I am traveling this week.

I had issues with cases where application or LD_PRELOAD library also
define the __rseq_handled symbol. They appear not to see the same
address as the one initialized by ld.so.

I tried using the GL() macro in ld.so to set __rseq_handled, but it's
the wrong address compared to what the preload lib and application observe.

Any thoughts on how to solve this ?

Thanks,

Mathieu

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