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

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Date:   Sun, 6 Jun 2021 11:53:51 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Segher Boessenkool <segher@...nel.crashing.org>
Cc:     Alan Stern <stern@...land.harvard.edu>,
        "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 11:48 AM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> And to work well, it needs "asm goto", which is so recent that a lot
> of compilers don't support it (thank God for clang dragging gcc
> kicking and screaming to implement it at all - I'd asked for it over a
> decade ago).

Oh, actually, I'm wrong on this.

We don't need an output from the asm (the output ends up being in the
targets), so we can use the old-style asm goto that we've been relying
on for a long time.

So the main code generation problem is just (a) all the architectures
and (b) we'd have to use a fixed conditional against zero.

                Linus