linux-kernel - Re: [PATCH] doc: volatile considered evil

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Message-ID: <20070509212313.7d61f113@the-village.bc.nu>
Date:	Wed, 9 May 2007 21:23:13 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Randy Dunlap <randy.dunlap@...cle.com>,
	Satyam Sharma <satyam.sharma@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Paul Sokolovsky <pmiscml@...il.com>,
	linux-kernel@...r.kernel.org, jeremy@...p.org
Subject: Re: [PATCH] doc: volatile considered evil

On Wed, 9 May 2007 11:41:27 -0700 (PDT)
David Rientjes <rientjes@...gle.com> wrote:

> On Wed, 9 May 2007, Alan Cox wrote:
> 
> > > Thus, any reliance on type-qualifying an object that represents an atomic 
> > > or locking primitive on the keyword 'volatile' is misplaced.
> > 
> > arch/foo is generally implementation specific code.
> > 
> 
> That's true, but what qualifies as an "access" to an object that is 
> type qualified with the 'volatile' keyword is _implementation_ defined, 
> meaning the behavior is defined by the compiler and not this new 
> architecture you're proposing 'volatile' is appropriate for.  That's pure 
> C99.

arch/foo almost always supports a single compiler too - gcc. We simply
don't support anything else. We use gcc inlines and features extensively.

And who cares about such fine detail of C99, did they fix the struct copy
bug in ANSI C even ? [1]

Alan
[1] ANSI C says access to the padding fields of a struct is undefined.
ANSI C also says that struct assignment is a memcpy. Therefore struct
assignment in ANSI C is a violation of ANSI C...

At this point its a lot simpler not to care about other compilers pet
insanities or areas of the spec like volatile that are vaguer and less
credible than the output of the US congress.

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