From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43)
	id 1HU1Fq-0006cW-Ty
	for qemu-devel@nongnu.org; Wed, 21 Mar 2007 09:53:31 -0400
Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43)
	id 1HU1Fq-0006aq-92
	for qemu-devel@nongnu.org; Wed, 21 Mar 2007 09:53:30 -0400
Received: from [199.232.76.173] (helo=monty-python.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.43) id 1HU1Fq-0006aI-1O
	for qemu-devel@nongnu.org; Wed, 21 Mar 2007 08:53:30 -0500
Received: from grayson.netsweng.com ([207.235.77.11])
	by monty-python.gnu.org with esmtp (Exim 4.60)
	(envelope-from <anderson@netsweng.com>) id 1HU1E9-00087j-1C
	for qemu-devel@nongnu.org; Wed, 21 Mar 2007 09:51:45 -0400
Date: Wed, 21 Mar 2007 09:50:43 -0400 (EDT)
From: Stuart Anderson <anderson@netsweng.com>
Subject: Re: [Qemu-devel] [PATCH] fcntl64 fix
In-Reply-To: <200703202343.36216.paul@codesourcery.com>
Message-ID: <Pine.LNX.4.64.0703210918120.12505@trantor.stuart.netsweng.com>
References: <20070319171303.GE28895@networkno.de>
	<20070320214749.GE2311@networkno.de>
	<Pine.LNX.4.64.0703201852120.12505@trantor.stuart.netsweng.com>
	<200703202343.36216.paul@codesourcery.com>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed
Reply-To: qemu-devel@nongnu.org
List-Id: qemu-devel.nongnu.org
List-Unsubscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.gnu.org/pipermail/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Paul Brook <paul@codesourcery.com>
Cc: qemu-devel@nongnu.org

On Tue, 20 Mar 2007, Paul Brook wrote:

>> Now that the dust has settled, I see where the change is probably a
>> no-op anyway. A quick little test program indicates that on x86_64,
>> l_start will have an offset of 8 wether the structure is packed or not,
>> and wether the __pad member is present or not. The unsigned long long is
>> always going to be aligned to a 8 byte boundary.
>
> The __pad member is essential. Your logic is wrong is two ways:
>
> a) The struct is packed. This overrides normal alignment and ensures the
> structure contains no padding.

And in this case, it does remove some tail padding at the end of the
structure.

> b) long long has whatever alignment the host feels like giving it. There's no
> guarantee it's going to be 8 byte aligned.

No there isn't. This was just an observation of what occurs when
building a simple test case on x86_64.


                                  Stuart

Stuart R. Anderson                               anderson@netsweng.com
Network & Software Engineering                   http://www.netsweng.com/
1024D/37A79149:                                  0791 D3B8 9A4C 2CDC A31F
                                                   BD03 0A62 E534 37A7 9149