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Re: [RFC PATCH 1/2] glibc: Perform rseq(2) registration at nptl init and thread creation (v3)
- From: Andy Lutomirski <luto at amacapital dot net>
- To: Mathieu Desnoyers <mathieu dot desnoyers at efficios dot com>
- Cc: libc-alpha <libc-alpha at sourceware dot org>, "Carlos O'Donell" <carlos at redhat dot com>, Florian Weimer <fweimer at redhat dot com>, "Joseph S. Myers" <joseph at codesourcery dot com>, szabolcs dot nagy at arm dot com, 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>, LKML <linux-kernel at vger dot kernel dot org>, Linux API <linux-api at vger dot kernel dot org>
- Date: Fri, 2 Nov 2018 08:20:18 -0700
- Subject: Re: [RFC PATCH 1/2] glibc: Perform rseq(2) registration at nptl init and thread creation (v3)
- References: <firstname.lastname@example.org>
On Fri, Nov 2, 2018 at 4:53 AM Mathieu Desnoyers
> Here is a third round of prototype registering rseq(2) TLS for each
> thread (including main), and unregistering for each thread (excluding
> main). "rseq" stands for Restartable Sequences.
> Remaining open questions:
> - How early do we want to register rseq and how late do we want to
> unregister it ? It's important to consider if we expect rseq to
> be used by the memory allocator and within destructor callbacks.
> However, we want to be sure the TLS (__thread) area is properly
> allocated across its entire use by rseq.
> - We do not need an atomic increment/decrement for the refcount per
> se. Just being atomic with respect to the current thread (and nested
> signals) would be enough. What is the proper API to use there ?
> See the rseq(2) man page proposed here:
Merely having rseq registered carries some small but nonzero overhead,
right? Should this perhaps live in a librseq.so or similar (possibly
built as part of libc) to avoid the overhead for programs that don't