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

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Date:   Fri, 14 Jun 2019 12:06:45 +0200
From:   Florian Weimer <fweimer@...hat.com>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     carlos <carlos@...hat.com>, 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)

* Mathieu Desnoyers:

> ----- 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.

What exactly did you do?  How did you determine the addresses?  How is
__rseq_handled defined in ld.so?

Thanks,
Florian