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Re: [RFC PATCH glibc 1/4] glibc: Perform rseq(2) registration at nptl init and thread creation (v4)
- From: Florian Weimer <fweimer at redhat dot com>
- To: Mathieu Desnoyers <mathieu dot desnoyers at efficios dot com>
- Cc: carlos <carlos at redhat dot com>, Joseph Myers <joseph at codesourcery dot com>, Szabolcs Nagy <szabolcs dot nagy at arm dot com>, libc-alpha <libc-alpha at sourceware dot org>, Thomas Gleixner <tglx at linutronix dot de>, Ben Maurer <bmaurer at fb dot com>, Peter Zijlstra <peterz at infradead dot org>, "Paul E. McKenney" <paulmck at linux dot vnet dot ibm dot com>, Boqun Feng <boqun dot feng at gmail dot com>, Will Deacon <will dot deacon at arm dot com>, Dave Watson <davejwatson at fb dot com>, Paul Turner <pjt at google dot com>, Rich Felker <dalias at libc dot org>, linux-kernel <linux-kernel at vger dot kernel dot org>, linux-api <linux-api at vger dot kernel dot org>
- Date: Mon, 14 Jan 2019 19:55:07 +0100
- Subject: Re: [RFC PATCH glibc 1/4] glibc: Perform rseq(2) registration at nptl init and thread creation (v4)
- References: <20181204192141.4684-1-mathieu.desnoyers@efficios.com> <87h8fkz6qx.fsf@oldenburg2.str.redhat.com> <1681283664.1380.1547152315426.JavaMail.zimbra@efficios.com>
* Mathieu Desnoyers:
> Therefore, both symbols will end up in
> sysdeps/unix/sysv/linux/Versions.
I'm not sure what you mean by that. The physical location in the
directory tree has little effect on which shared object the symbol is
placed in; that will need other changes.
>> By the way, you could avoid the need for unregistration if you allocated
>> the rseq areas persistently, index by TID. They are quite small, so
>> with the typical PID range, maybe the wasted memory due to changing TIDs
>> would be acceptable?
>
> Would we be able to access those __rseq_abi as normal TLS IE model
> variables ? The overhead of indexing an array matters for a
> fast-path.
No, that wouldn't be possible in this case. You would need another
indirection.
Thanks,
Florian