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Date:   Wed, 19 Sep 2018 12:53:14 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
To:     Joseph Myers <joseph@codesourcery.com>
Cc:     carlos <carlos@redhat.com>, Florian Weimer <fweimer@redhat.com>,
        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>,
        libc-alpha <libc-alpha@sourceware.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        linux-api <linux-api@vger.kernel.org>
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References: <20180919144438.1066-1-mathieu.desnoyers@efficios.com> <alpine.DEB.2.21.1809191630260.26757@digraph.polyomino.org.uk>
Subject: Re: [RFC PATCH] glibc: Perform rseq(2) registration at nptl init
 and thread creation
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Thread-Topic: glibc: Perform rseq(2) registration at nptl init and thread creation
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----- On Sep 19, 2018, at 12:37 PM, Joseph Myers joseph@codesourcery.com wrote:

> On Wed, 19 Sep 2018, Mathieu Desnoyers wrote:
> 
>> Here is a rough prototype registering rseq(2) TLS for each thread
>> (including main), and unregistering for each thread (excluding
>> main). "rseq" stands for Restartable Sequences.
> 
> A final patch would need to add documentation and tests and a NEWS entry
> and fix various coding style issues.
> 
>> diff --git a/nptl/Versions b/nptl/Versions
>> index e7f691da7a..7316c2815d 100644
>> --- a/nptl/Versions
>> +++ b/nptl/Versions
>> @@ -275,6 +275,7 @@ libpthread {
>>      mtx_init; mtx_lock; mtx_timedlock; mtx_trylock; mtx_unlock; mtx_destroy;
>>      call_once; cnd_broadcast; cnd_destroy; cnd_init; cnd_signal;
>>      cnd_timedwait; cnd_wait; tss_create; tss_delete; tss_get; tss_set;
>> +    __rseq_abi; __rseq_refcount;
> 
> That's the GLIBC_2.28 section, but 2.28 is already out.  New symbols would
> need to go in GLIBC_2.29 or later (and the ABI test baselines would all
> need updating).

Certainly. I'm just not sure where I need to poke to update the ABI version
from 2.28 to 2.29 in my dev branch.

> 
>> diff --git a/sysdeps/unix/sysv/linux/rseq.h b/sysdeps/unix/sysv/linux/rseq.h
> 
> This looks like it's coming from the Linux kernel.  Can't the relevant
> uapi header just be used directly without copying into glibc (with due
> care to ensure that glibc still builds if the kernel headers used for the
> build are too old - you need such conditionals anyway if they don't define
> the relevant syscall number)?

This is indeed in the list of "things to consider" I've put in the patch
commit message. If the usual practice is to build against uapi kernel headers
outside of the glibc tree, I'm fine with that.

Thanks,

Mathieu


> 
> --
> Joseph S. Myers
> joseph@codesourcery.com

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