linux-kernel - Re: [RFC PATCH glibc 1/4] glibc: Perform rseq(2) registration at C startup and thread creation (v6)

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Message-ID: <alpine.DEB.2.21.1901302104360.16754@digraph.polyomino.org.uk>
Date:   Wed, 30 Jan 2019 21:10:07 +0000
From:   Joseph Myers <joseph@...esourcery.com>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
CC:     carlos <carlos@...hat.com>, Florian Weimer <fweimer@...hat.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 C
 startup and thread creation (v6)

On Wed, 30 Jan 2019, Mathieu Desnoyers wrote:

> #if defined (__NR_rseq) && !defined (RSEQ_SIG)
> # error "UAPI headers support rseq system call, but glibc does not define RSEQ_SIG."
> #endif
> 
> Would that take care of your concerns ?

That would of course need appropriate conditionals based on the most 
recent kernel version for which a given glibc version has been updated, so 
that using new kernel headers with an existing glibc release does not make 
the build fail (cf. the test of syscall-names.list).  And being able to 
write such a test only solves one half of the problem - it needs to be 
easy to determine what value to put in that header in glibc for an 
architecture that's newly gained support in the kernel, *without* needing 
any architecture expertise.

-- 
Joseph S. Myers
joseph@...esourcery.com