From mboxrd@z Thu Jan 1 00:00:00 1970 From: Chen Gang Subject: Re: [PATCH] drivers: staging: lustre: lustre: include: add "__attribute__((packed))" for the related union Date: Mon, 03 Feb 2014 18:25:41 +0800 Message-ID: <52EF6EA5.1050701@gmail.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> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=message-id:date:from:user-agent:mime-version:to:cc:subject :references:in-reply-to:content-type:content-transfer-encoding; bh=Zodi3txzmxlD0nv6hiedtkl3FIvl0f8dp5SCQqima18=; b=hec8faFUn77o2LJuQ8kdJ9487gL1/ZE4EZGvg//0YzQOPC9+oV/SM8v6Dsd5i6UT0b DH1U0AaeVx7l/3Ox5ZepQ/sZ0GPK3QR8uZIiCHHb2pQR4i0Y24FSSIHj6/uRH8OLG+BE wZ+zQ+NT6nBL58y8xuoa5esuejodB514OKwT9R3hrD3IAw3zQWEp+Ohf2aBKlljh4K8x DUbNcbIuLk3XsWOpyn1sOCzdwhb4Zy0OfaXjUdk5Q9EPKG2C5JOi2xpmD8iQ9RqwT0oc ODGhuorOZOwAQMoiyghjoMer3wYtCYuTWcfgs1f8RzI8DHFhbKL15l7SjsxTeyHxVHUs kNfw== In-Reply-To: <063D6719AE5E284EB5DD2968C1650D6D0F6B772B-VkEWCZq2GCInGFn1LkZF6NBPR1lH4CV8@public.gmane.org> Sender: linux-metag-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii" To: David Laight Cc: 'Dan Carpenter' , James Hogan , "devel-gWbeCf7V1WCQmaza687I9mD2FQJk+8+b@public.gmane.org" , "andreas.dilger-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org" , Antonio Quartulli , Greg KH , "bergwolf-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org" , "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , David Miller , "oleg.drokin-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org" , "jacques-charles.lafoucriere-KCE40YydGKI@public.gmane.org" , "jinshan.xiong-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org" , netdev , "linux-metag-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" On 02/03/2014 06:05 PM, David Laight wrote: > 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; }; > I guess so. > Architectures that define such alignment rules are a right PITA. Sorry, I do not know about PITA (after google or wiki, I can not get more related information). Could you provide more information about PITA, thanks? > You either need to get the size to 2 without using 'packed', or > just not define such structures. Excuse me, I don't quite understand your meaning. I guess your meaning is: "normally, we should not use a struct/union like that, no matter what it is (2 or 4)". Is it correct. > It is worth seeing if adding aligned(2) will change the size - I'm > not sure. > Yes, it will/should make sure that it must be 2. Thanks. -- Chen Gang Open, share and attitude like air, water and life which God blessed -- To unsubscribe from this list: send the line "unsubscribe linux-metag" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html