linux-kernel - RE: Control Dependencies vs C Compilers

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Date:   Tue, 6 Oct 2020 15:37:24 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Nick Clifton' <nickc@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "stern@...land.harvard.edu" <stern@...land.harvard.edu>
CC:     "linux-toolchains@...r.kernel.org" <linux-toolchains@...r.kernel.org>,
        Will Deacon <will@...nel.org>,
        Paul McKenney <paulmck@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "parri.andrea@...il.com" <parri.andrea@...il.com>,
        "boqun.feng@...il.com" <boqun.feng@...il.com>,
        "npiggin@...il.com" <npiggin@...il.com>,
        "dhowells@...hat.com" <dhowells@...hat.com>,
        "j.alglave@....ac.uk" <j.alglave@....ac.uk>,
        "luc.maranget@...ia.fr" <luc.maranget@...ia.fr>,
        "akiyks@...il.com" <akiyks@...il.com>,
        "dlustig@...dia.com" <dlustig@...dia.com>,
        "joel@...lfernandes.org" <joel@...lfernandes.org>,
        "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>
Subject: RE: Control Dependencies vs C Compilers

>   My suggestion as an alternative is to use assembler instead.
>   That way you can guarantee that you get the instructions you
>   want in the order that you want them.  It should be fairly
>   straightforward to create a macro or inline function that
>   contains the necessary code and this can be done once and
>   then used wherever the functionality is required.

C exists because K&R got fed up of writing pdp-11 assembler.
Compared to some modern ones it is nice and easy to write
(I'm old enough to have used pdp-11.)

You can't put control dependencies inside C asm statements.

	David

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