linux-kernel - Re: [RFC PATCH glibc 4/8] glibc: Perform rseq(2) registration at C startup and thread creation (v15)

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Date:   Thu, 19 Mar 2020 15:53:48 +0100
From:   Florian Weimer <fw@...eb.enyo.de>
To:     Mathieu Desnoyers via Libc-alpha <libc-alpha@...rceware.org>
Cc:     Carlos O'Donell <carlos@...hat.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Rich Felker <dalias@...c.org>, linux-api@...r.kernel.org,
        Boqun Feng <boqun.feng@...il.com>,
        Will Deacon <will.deacon@....com>,
        linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ben Maurer <bmaurer@...com>, Dave Watson <davejwatson@...com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Paul Turner <pjt@...gle.com>,
        Joseph Myers <joseph@...esourcery.com>
Subject: Re: [RFC PATCH glibc 4/8] glibc: Perform rseq(2) registration at C startup and thread creation (v15)

* Mathieu Desnoyers via Libc-alpha:

> Changes since v14:
> - Update copyright range to include 2020.
> - Introduce __ASSUME_RSEQ defined for --enable-kernel=4.18.0 and higher.
> - Use ifdef __ASSUME_RSEQ rather than ifdef __NR_rseq to discover rseq
>   availability. This is necessary now that the system call numbers are
>   integrated within glibc.

It's not quite clear to me why you need __ASSUME_RSEQ.

Can you use __has_include in <sys/rseq.h>, with a copy of the kernel
definitions if the kernel header is not available?