linux-kernel - Re: x86: Is 'volatile' necessary for readb/writeb and friends?

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Message-Id: <200912041700.39564.arnd@arndb.de>
Date:	Fri, 4 Dec 2009 17:00:39 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Segher Boessenkool <segher@...nel.crashing.org>
Cc:	"Ahmed S. Darwish" <darwish.07@...il.com>, x86@...nel.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org
Subject: Re: x86: Is 'volatile' necessary for readb/writeb and friends?

On Friday 04 December 2009, Segher Boessenkool wrote:
> If you want to get all language-lawyery, if the object pointed to by
> "addr" is volatile, the volatile here is needed: accessing volatile
> objects via a not volatile-qualified lvalue is undefined.  But since
> this is GCC-specific code anyway, do you care?  :-)

I think the real reason for having it is to avoid a warning when
device drivers pass volatile objects. Not sure if that's a good
thing or if we should better actually warn about it.

	Arnd <><
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