linux-kernel - Re: [RFC] LKMM: Add volatile

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Message-ID: <CAHk-=wis8zq3WrEupCY6wcBeW3bB0WMOzaUkXpb-CsKuxM=6-w@mail.gmail.com>
Date:   Sun, 6 Jun 2021 12:22:44 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Jakub Jelinek <jakub@...hat.com>
Cc:     Alan Stern <stern@...land.harvard.edu>,
        Segher Boessenkool <segher@...nel.crashing.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Will Deacon <will@...nel.org>,
        Andrea Parri <parri.andrea@...il.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Nick Piggin <npiggin@...il.com>,
        David Howells <dhowells@...hat.com>,
        Jade Alglave <j.alglave@....ac.uk>,
        Luc Maranget <luc.maranget@...ia.fr>,
        Akira Yokosawa <akiyks@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-toolchains@...r.kernel.org,
        linux-arch <linux-arch@...r.kernel.org>
Subject: Re: [RFC] LKMM: Add volatile_if()

On Sun, Jun 6, 2021 at 11:59 AM Jakub Jelinek <jakub@...hat.com> wrote:
>
> I think just
> #define barrier() __asm__ __volatile__("" : : "i" (__COUNTER__) : "memory")
> should be enough

Oh, I like that. Much better.

It avoids all the issues with comments etc, and because it's not using
__COUNTER__ as a string, it doesn't need the preprocessor games with
double expansion either.

So yeah, that seems like a nice solution to the issue, and should make
the barriers all unique to the compiler.

             Linus