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.2.21.1901292153190.24454@digraph.polyomino.org.uk>
Date:   Tue, 29 Jan 2019 21:56:18 +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 Tue, 29 Jan 2019, Mathieu Desnoyers wrote:

> I recalled that aarch64 defines RSEQ_SIG to a different value which maps to
> a valid trap instruction. So I plan to move the RSEQ_SIG define to per-arch
> headers like this:
> 
>  sysdeps/unix/sysv/linux/aarch64/bits/rseq.h                  |   24 ++
>  sysdeps/unix/sysv/linux/arm/bits/rseq.h                      |   24 ++
>  sysdeps/unix/sysv/linux/bits/rseq.h                          |   23 ++
>  sysdeps/unix/sysv/linux/mips/bits/rseq.h                     |   24 ++
>  sysdeps/unix/sysv/linux/powerpc/bits/rseq.h                  |   24 ++
>  sysdeps/unix/sysv/linux/s390/bits/rseq.h                     |   24 ++
>  sysdeps/unix/sysv/linux/x86/bits/rseq.h                      |   24 ++
> 
> where "bits/rseq.h" contains a #error:
> 
> # error "Architecture does not define RSEQ_SIG.
> 
> sys/rseq.h will now include <bits/rseq.h>.

We're trying to reduce the number of cases where most or all new glibc 
architecture ports need to provide a bits/ header, by making the generic 
headers handle the common case.  So a generic header with a #error, and 
lots of architecture-specific headers mostly with the same value for 
RSEQ_SIG, seems unfortunate.  I'd hope the generic header could use a 
generic value, with architecture-specific variants only for architectures 
with some reason for a different value.

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