linux-kernel - Re: [RFC PATCH glibc 1/4] glibc: Perform rseq(2) registration at nptl init and thread creation (v4)

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Message-ID: <1488546469.1564.1547169116539.JavaMail.zimbra@efficios.com>
Date:   Thu, 10 Jan 2019 20:11:56 -0500 (EST)
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: [RFC PATCH glibc 1/4] glibc: Perform rseq(2) registration at
 nptl init and thread creation (v4)

----- On Jan 10, 2019, at 12:31 PM, Mathieu Desnoyers mathieu.desnoyers@...icios.com wrote:

> ----- On Dec 11, 2018, at 2:40 AM, Florian Weimer fweimer@...hat.com wrote:
[...]
>> 
>>> diff --git a/nptl/Versions b/nptl/Versions
>>> index e7f691da7a..f7890f73fc 100644
>>> --- a/nptl/Versions
>>> +++ b/nptl/Versions
>>> @@ -277,6 +277,10 @@ libpthread {
>>>      cnd_timedwait; cnd_wait; tss_create; tss_delete; tss_get; tss_set;
>>>    }
>>>  
>>> +  GLIBC_2.29 {
>>> +    __rseq_refcount;
>>> +  }
>> 
>> Why put this into libpthread, and __rseq_abi into libc?
> 
> The __rseq_abi symbol should be available to the glibc memory allocator.
> I plan to move the __rseq_abi to sysdeps/unix/sysv/linux/Versions instead
> so it becomes Linux-specific.
> 
> The __rseq_refcount symbol only needs to be made available to applications
> and libraries linking against libpthread, because only libpthread actually
> handles the rseq registration/unregistration at thread start/exit and
> library initialization.
> 
> However, considering that we want this to be Linux-specific as well,
> I could move it to sysdeps/unix/sysv/linux/Versions too.
> 
> Then it would make sense to move the __rseq_refcount symbol defined in
> nptl/rseq.c to sysdeps/unix/sysv/linux/rseq.c as well and group
> everything together.
> 
> Therefore, both symbols will end up in sysdeps/unix/sysv/linux/Versions.

Now that I think about it, it's important to move the rseq registration
done at nptl init (in my current code) to some lower-level csu initialiation,
so applications that happen _not_ to link against libpthread also get
registered rseq for the main thread.

Does it make sense ?

Thanks,

Mathieu

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