Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S940863AbXHJULz (ORCPT ); Fri, 10 Aug 2007 16:11:55 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S937760AbXHJULX (ORCPT ); Fri, 10 Aug 2007 16:11:23 -0400 Received: from gate.crashing.org ([63.228.1.57]:51136 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932648AbXHJULV (ORCPT ); Fri, 10 Aug 2007 16:11:21 -0400 In-Reply-To: References: Mime-Version: 1.0 (Apple Message framework v623) Content-Type: text/plain; charset=US-ASCII; format=flowed Message-Id: <442f95ba19f8622ce04cf0334f34be11@kernel.crashing.org> Content-Transfer-Encoding: 7bit Cc: paulmck@linux.vnet.ibm.com, heiko.carstens@de.ibm.com, horms@verge.net.au, linux-kernel@vger.kernel.org, csnook@redhat.com, rpjday@mindspring.com, netdev@vger.kernel.org, ak@suse.de, cfriesen@nortel.com, akpm@linux-foundation.org, torvalds@linux-foundation.org, jesper.juhl@gmail.com, linux-arch@vger.kernel.org, zlynx@acm.org, schwidefsky@de.ibm.com, davem@davemloft.net, wensong@linux-vs.org, wjiang@resilience.com From: Segher Boessenkool Subject: Re: [PATCH 1/24] make atomic_read() behave consistently on alpha Date: Fri, 10 Aug 2007 22:07:27 +0200 To: Herbert Xu X-Mailer: Apple Mail (2.623) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 866 Lines: 23 >> The compiler is within its rights to read a 32-bit quantity 16 bits at >> at time, even on a 32-bit machine. I would be glad to help pummel any >> compiler writer that pulls such a dirty trick, but the C standard >> really >> does permit this. > > Code all over the kernel assumes that 32-bit reads/writes > are atomic so while such a compiler might be legal it certainly > can't compile Linux. 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. Segher - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/