linux-kernel - Re: [RFC PATCH] LKMM: Add ctrl_dep() macro for control dependency

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Message-ID: <871r54ww2k.fsf@oldenburg.str.redhat.com>
Date:   Fri, 01 Oct 2021 18:26:11 +0200
From:   Florian Weimer <fweimer@...hat.com>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     Segher Boessenkool <segher@...nel.crashing.org>,
        Will Deacon <will@...nel.org>, paulmck <paulmck@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Alan Stern <stern@...land.harvard.edu>,
        Andrea Parri <parri.andrea@...il.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Nicholas Piggin <npiggin@...il.com>,
        David Howells <dhowells@...hat.com>,
        j alglave <j.alglave@....ac.uk>,
        luc maranget <luc.maranget@...ia.fr>,
        akiyks <akiyks@...il.com>,
        linux-toolchains <linux-toolchains@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>
Subject: Re: [RFC PATCH] LKMM: Add ctrl_dep() macro for control dependency

* Mathieu Desnoyers:

> One cheap way to achieve said R->W dependency (as well as R->RW on
> architectures which to not reorder R->R) is to ensure that the
> generated assembly contains a conditional branch.

Will any conditional branch do, or is it necessary that it depends in
some way on the data read?

Thanks,
Florian