linux-kernel - Re: [PATCH 1/24] make atomic_read() behave consistently on alpha

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Message-ID: <20070811004322.GA13178@gondor.apana.org.au>
Date:	Sat, 11 Aug 2007 08:43:22 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Segher Boessenkool <segher@...nel.crashing.org>
Cc:	paulmck@...ux.vnet.ibm.com, heiko.carstens@...ibm.com,
	horms@...ge.net.au, linux-kernel@...r.kernel.org,
	csnook@...hat.com, rpjday@...dspring.com, netdev@...r.kernel.org,
	ak@...e.de, cfriesen@...tel.com, akpm@...ux-foundation.org,
	torvalds@...ux-foundation.org, jesper.juhl@...il.com,
	linux-arch@...r.kernel.org, zlynx@....org, schwidefsky@...ibm.com,
	davem@...emloft.net, wensong@...ux-vs.org, wjiang@...ilience.com
Subject: Re: [PATCH 1/24] make atomic_read() behave consistently on alpha

On Sat, Aug 11, 2007 at 02:38:40AM +0200, Segher Boessenkool wrote:
> >>That means GCC cannot compile Linux; it already optimises
> >>some accesses to scalars to smaller accesses when it knows
> >>it is allowed to.  Not often though, since it hardly ever
> >>helps in the cost model it employs.
> >
> >Please give an example code snippet + gcc version + arch
> >to back this up.
> 
> 	unsigned char f(unsigned long *p)
> 	{
> 	        return *p & 1;
> 	}

This doesn't really matter since we only care about the LSB.
Do you have an example where gcc reads it non-atmoically and
we care about all parts?

Cheers,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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