Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752639AbaBCKGA (ORCPT ); Mon, 3 Feb 2014 05:06:00 -0500 Received: from mx0.aculab.com ([213.249.233.131]:44157 "HELO mx0.aculab.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1751339AbaBCKF5 convert rfc822-to-8bit (ORCPT ); Mon, 3 Feb 2014 05:05:57 -0500 From: David Laight To: "'Dan Carpenter'" , Chen Gang CC: James Hogan , "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: AQHPH1WqrPdkB9hsu0CwpyENM0ZOOpqjPaqAgAARGPA= Date: Mon, 3 Feb 2014 10:05:14 +0000 Message-ID: <063D6719AE5E284EB5DD2968C1650D6D0F6B772B@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> In-Reply-To: <20140203085855.GA26722@mwanda> 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: Dan Carpenter > On Sat, Feb 01, 2014 at 09:57:39PM +0800, Chen Gang wrote: > > It seems, our kernel still stick to treate 'pack' region have effect > > with both 'align' and 'sizeof'. > > It's not about packed regions. It's about unions. It's saying the > sizeof() a union is a multiple of 4 unless it's packed. > > union foo { > short x; > short y; > }; > > The author intended the sizeof(union foo) to be 2 but on metag arch then > it is 4. The same is probably be true of: struct foo { _u16 bar; }; Architectures that define such alignment rules are a right PITA. You either need to get the size to 2 without using 'packed', or just not define such structures. It is worth seeing if adding aligned(2) will change the size - I'm not sure. 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/