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Date:	Mon, 03 Feb 2014 18:03:17 +0800
From:	Chen Gang <gang.chen.5i5j@...il.com>
To:	Dan Carpenter <dan.carpenter@...cle.com>
CC:	James Hogan <james.hogan@...tec.com>, devel@...verdev.osuosl.org,
	andreas.dilger@...el.com,
	Antonio Quartulli <antonio@...hcoding.com>,
	Greg KH <gregkh@...uxfoundation.org>, bergwolf@...il.com,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	David Miller <davem@...emloft.net>, oleg.drokin@...el.com,
	jacques-charles.lafoucriere@....fr, jinshan.xiong@...el.com,
	netdev <netdev@...r.kernel.org>, linux-metag@...r.kernel.org
Subject: Re: [PATCH] drivers: staging: lustre: lustre: include: add "__attribute__((packed))"
 for the related union

On 02/03/2014 04:58 PM, Dan Carpenter wrote:
> 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.
> 

Yeah, just like your original discussion.  :-)


Hmm... can we say: "for metag compiler, in a pack region, it considers
variables alignment, but does not consider about struct/union alignment
(except append packed to each related struct/union)".

For compatible (consider about its ABI), it has to keep this features,
but for kernel, it needs be changed.

So, I suggest to add one parameter to compiler to switch this feature,
and append this parameter to KBUILD_CFLAGS in "arch/metag/Makefile"
which can satisfy both ABI and kernel.


Thanks.
-- 
Chen Gang

Open, share and attitude like air, water and life which God blessed
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