linux-kernel - Re: [PATCH 1/5] glibc: Perform rseq(2) registration at C startup and thread creation (v10)

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Message-ID: <802638054.3032.1560506584705.JavaMail.zimbra@efficios.com>
Date:   Fri, 14 Jun 2019 06:03:04 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     carlos <carlos@...hat.com>, Florian Weimer <fweimer@...hat.com>
Cc:     Joseph Myers <joseph@...esourcery.com>,
        Szabolcs Nagy <szabolcs.nagy@....com>,
        libc-alpha <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 <linux-kernel@...r.kernel.org>,
        linux-api <linux-api@...r.kernel.org>
Subject: Re: [PATCH 1/5] glibc: Perform rseq(2) registration at C startup
 and thread creation (v10)

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

> ----- On Jun 10, 2019, at 4:43 PM, carlos carlos@...hat.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