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Date: Wed, 15 Aug 2007 23:37:21 -0400
From: Bill Fink <billfink@mindspring.com>
To: Satyam Sharma <satyam@infradead.org>
Cc: Stefan Richter <stefanr@s5r6.in-berlin.de>,
       Christoph Lameter <clameter@sgi.com>, Chris Snook <csnook@redhat.com>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       linux-arch@vger.kernel.org,
       Linus Torvalds <torvalds@linux-foundation.org>, netdev@vger.kernel.org,
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       jesper.juhl@gmail.com, segher@kernel.crashing.org,
       Herbert Xu <herbert@gondor.apana.org.au>,
       "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: Re: [PATCH 0/24] make atomic_read() behave consistently across all
 architectures
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On Wed, 15 Aug 2007, Satyam Sharma wrote:

> (C)
> $ cat tp3.c
> int a;
> 
> void func(void)
> {
> 	*(volatile int *)&a = 10;
> 	*(volatile int *)&a = 20;
> }
> $ gcc -Os -S tp3.c
> $ cat tp3.s
> ...
> movl    $10, a
> movl    $20, a
> ...

I'm curious about one minor tangential point.  Why, instead of:

	b = *(volatile int *)&a;

why can't this just be expressed as:

	b = (volatile int)a;

Isn't it the contents of a that's volatile, i.e. it's value can change
invisibly to the compiler, and that's why you want to force a read from
memory?  Why do you need the "*(volatile int *)&" construct?

						-Bill
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