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

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Message-ID: <1329439108.43041.1560348962006.JavaMail.zimbra@efficios.com>
Date:   Wed, 12 Jun 2019 10:16:02 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Florian Weimer <fweimer@...hat.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)

----- On Jun 6, 2019, at 1:57 PM, Florian Weimer fweimer@...hat.com wrote:

> * Mathieu Desnoyers:
> 
[...]
> 
>>> The final remaining case is static dlopen.  There is a copy of ld.so on
>>> the dynamic side, but it is completely inactive and has never run.  I do
>>> not think we need to support that because multi-threading does not work
>>> reliably in this scenario, either.  However, we should skip rseq
>>> registration in a nested libc (see the rtld_active function).
>>
>> So for SHARED, if (!rtld_active ()), we should indeed leave the state of
>> __rseq_handled as it is, because we are within a nested inactive ld.so.
> 
> I think we should add __rseq_handled initialization to ld.so, so it will
> only run once, ever.

OK

> 
> It's the registration from libc.so which needs some care.  In
> particular, we must not override an existing registration.

OK, so it could check if __rseq_abi.cpu_id is -1, and only
perform registration if it is the case. Or do you have another
approach in mind ?

For the main thread, "nested" unregistration does not appear to be a
problem, because we rely on program exit() to implicitly unregister.

Thanks,

Mathieu

> 
> Thanks,
> Florian

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