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

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Date:   Sun, 6 Jun 2021 12:13:56 -0500
From:   Segher Boessenkool <segher@...nel.crashing.org>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     Linus Torvalds <torvalds@...ux-foundation.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 06, 2021 at 09:47:49AM -0400, Alan Stern wrote:
> > GCC does not pretend it can understand the asm.  But it can see when
> > two asm statements are identical.
> 
> How similar do two asm strings have to be before they are considered 
> identical?  For instance, do changes to the amount of leading or 
> trailing whitespace matter?

They have to be identical to be considered identical.

> Or what about including an empty assembly statement in one but not the 
> other?

GCC does not parse the assembler template.


Segher