Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753469AbXJVUNn (ORCPT ); Mon, 22 Oct 2007 16:13:43 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752304AbXJVUNf (ORCPT ); Mon, 22 Oct 2007 16:13:35 -0400 Received: from outpipe-village-512-1.bc.nu ([81.2.110.250]:51550 "EHLO the-village.bc.nu" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1751834AbXJVUNe (ORCPT ); Mon, 22 Oct 2007 16:13:34 -0400 Date: Mon, 22 Oct 2007 21:16:17 +0100 From: Alan Cox To: Linus Torvalds Cc: Geert Uytterhoeven , Jens Axboe , Linux Kernel Development , mingo@elte.hu, Linux/m68k Subject: Re: [PATCH 09/10] Change table chaining layout Message-ID: <20071022211617.31f5c63d@the-village.bc.nu> In-Reply-To: References: <1193076664-13652-1-git-send-email-jens.axboe@oracle.com> <1193076664-13652-10-git-send-email-jens.axboe@oracle.com> X-Mailer: Claws Mail 2.10.0 (GTK+ 2.10.14; i386-redhat-linux-gnu) Organization: Red Hat UK Cyf., Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SL4 1TE, Y Deyrnas Gyfunol. Cofrestrwyd yng Nghymru a Lloegr o'r rhif cofrestru 3798903 Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1354 Lines: 34 On Mon, 22 Oct 2007 12:49:40 -0700 (PDT) Linus Torvalds wrote: > > > On Mon, 22 Oct 2007, Geert Uytterhoeven wrote: > > > > Better safe than sorry... > > > > Is it possible that a chain entry pointer has bit 1 set on architectures > > (e.g. m68k) where the natural alignment of 32-bit quantities is _2_ bytes, > > not 4? > > Better make sure that such alignment never happens... But no, I don't > think it will, since these things would generally always have to be > allocated with an allocator, and the *allocator* won't return 2-byte > aligned data structures. No - but a structure which has other objects in it before the object being written out may well be 2 byte aligned on M68K and some of the other externally 16bit platforms - ditto local dynamic objects. Why can't we just make the list one item longer than the entry count and stick a NULL on the end of it like normal people ? Then you need one bit which ought to be safe for everyone (and if the bit is a macro any CPU warped enough to have byte alignment is surely going to have top bits spare...) Alan - 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/