Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752573AbaBCLzp (ORCPT ); Mon, 3 Feb 2014 06:55:45 -0500 Received: from mx0.aculab.com ([213.249.233.131]:46362 "HELO mx0.aculab.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1751039AbaBCLzn convert rfc822-to-8bit (ORCPT ); Mon, 3 Feb 2014 06:55:43 -0500 From: David Laight To: "'James Hogan'" CC: "'Dan Carpenter'" , Chen Gang , "devel@driverdev.osuosl.org" , "andreas.dilger@intel.com" , Antonio Quartulli , "Greg KH" , "bergwolf@gmail.com" , "linux-kernel@vger.kernel.org" , David Miller , "oleg.drokin@intel.com" , "jacques-charles.lafoucriere@cea.fr" , "jinshan.xiong@intel.com" , netdev , "linux-metag@vger.kernel.org" Subject: RE: [PATCH] drivers: staging: lustre: lustre: include: add "__attribute__((packed))" for the related union Thread-Topic: [PATCH] drivers: staging: lustre: lustre: include: add "__attribute__((packed))" for the related union Thread-Index: AQHPH1WqrPdkB9hsu0CwpyENM0ZOOpqjPaqAgAARGPCAAAYjAIAAApBAgAAI3QCAAAzEgA== Date: Mon, 3 Feb 2014 11:54:59 +0000 Message-ID: <063D6719AE5E284EB5DD2968C1650D6D0F6B77F1@AcuExch.aculab.com> References: <20140118142404.GT7444@mwanda> <52DBA3D4.3090308@gmail.com> <52DD0EFF.2010305@imgtec.com> <20140120123045.GV7444@mwanda> <52DD18A5.1090308@imgtec.com> <20140120125603.GD4815@mwanda> <20140120211356.GG4815@mwanda> <52DE4DA3.7090301@imgtec.com> <52E3A642.7010307@gmail.com> <52ECFD53.7010401@gmail.com> <20140203085855.GA26722@mwanda> <063D6719AE5E284EB5DD2968C1650D6D0F6B772B@AcuExch.aculab.com> <52EF6DCC.6040807@imgtec.com> <063D6719AE5E284EB5DD2968C1650D6D0F6B777A@AcuExch.aculab.com> <52EF7762.2060809@imgtec.com> In-Reply-To: <52EF7762.2060809@imgtec.com> Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.202.99.200] Content-Type: text/plain; charset="Windows-1252" Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: James Hogan > On 03/02/14 10:35, David Laight wrote: > > From: James Hogan > >> Combining __packed with __aligned(2) does the trick though (__packed > >> alone sets __aligned(1) which is obviously going to be suboptimal). ... > > Meta is also one of those arches, and according to my quick tests, > __packed alone does correctly make it fall back to byte loads/stores, > but with __packed __aligned(2) it uses 16bit loads/stores. I've also > confirmed that with an ARM toolchain (see below for example). I would either: 1a) Add explicit padding to the relevant structures so that they are multiple of 4 bytes. or: 1b) #define some token to "__packed __aligned(2)" before all the structures that require changing, and use that in there definitions. This lets you comment on WHY you are doing it. and: 2) Add a compile-time assert that the structures are the correct size. Clearly you don't want to mark anything that contains a 32bit value with __packed __aligned(2). I'm not at all clear whether you are sometimes using a different compiler. David -- 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/