From owner-freebsd-current@FreeBSD.ORG  Mon Nov 13 02:10:47 2006
Return-Path: <owner-freebsd-current@FreeBSD.ORG>
X-Original-To: current@freebsd.org
Delivered-To: freebsd-current@FreeBSD.ORG
Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125])
	by hub.freebsd.org (Postfix) with ESMTP id 7077016A40F;
	Mon, 13 Nov 2006 02:10:47 +0000 (UTC)
	(envelope-from kientzle@freebsd.org)
Received: from kientzle.com (h-66-166-149-50.snvacaid.covad.net
	[66.166.149.50])
	by mx1.FreeBSD.org (Postfix) with ESMTP id 5CED543D67;
	Mon, 13 Nov 2006 02:10:46 +0000 (GMT)
	(envelope-from kientzle@freebsd.org)
Received: from [10.0.0.221] (p54.kientzle.com [66.166.149.54])
	by kientzle.com (8.12.9/8.12.9) with ESMTP id kAD2Ak24079878;
	Sun, 12 Nov 2006 18:10:46 -0800 (PST)
	(envelope-from kientzle@freebsd.org)
Message-ID: <4557D425.40101@freebsd.org>
Date: Sun, 12 Nov 2006 18:10:45 -0800
From: Tim Kientzle <kientzle@freebsd.org>
User-Agent: Mozilla/5.0 (X11; U; FreeBSD i386; en-US; rv:1.7.12) Gecko/20060422
X-Accept-Language: en-us, en
MIME-Version: 1.0
References: <20061112180758.GD4237@kobe.laptop>	<20061112132105.6bac38d6@kan.dnsalias.net>	<20061112192810.GC1173@rambler-co.ru>
	<20061112.154733.-432839119.imp@bsdimp.com>
In-Reply-To: <20061112.154733.-432839119.imp@bsdimp.com>
Content-Type: text/plain; charset=us-ascii; format=flowed
Content-Transfer-Encoding: 7bit
Cc: arm@freebsd.org, current@freebsd.org, keramida@freebsd.org
Subject: Re: [head tinderbox] failure on arm/arm
X-BeenThere: freebsd-current@freebsd.org
X-Mailman-Version: 2.1.5
Precedence: list
List-Id: Discussions about the use of FreeBSD-current
	<freebsd-current.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-current>, 
	<mailto:freebsd-current-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-current>
List-Post: <mailto:freebsd-current@freebsd.org>
List-Help: <mailto:freebsd-current-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-current>,
	<mailto:freebsd-current-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Mon, 13 Nov 2006 02:10:47 -0000

In message: <20061112192810.GC1173@rambler-co.ru>
             Ruslan Ermilov <ru@freebsd.org> writes:
: On the other hand, having GCC align "struct foo { char x[11]; }"
: on a four-byte boundary (other than for backward compatibility)
: doesn't make too much sense to me.

It makes a lot of sense, actually, even on i386, which is
why the standard allows the compiler a lot of leeway to
pad and align such structure.  For example, consider this
structure assignment:

    struct foo a,b;
    a = b;

The structure copy here is a LOT faster if the structures
are always suitably aligned and padded.  If the compiler
pads your sample struct to 12 bytes and 4-aligns, the
structure copy here can be done with 3 aligned 32-bit moves.
Even on i386, aligned operations are a lot faster than
unaligned ones.

The code mentioned in the original post is simply broken;
it does not comply with the ISO C Standard.

Tim Kientzle