From owner-freebsd-current@FreeBSD.ORG  Sun Jul 27 18:35:26 2003
Return-Path: <owner-freebsd-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 7AA5E37B401
	for <freebsd-current@FreeBSD.org>;
	Sun, 27 Jul 2003 18:35:26 -0700 (PDT)
Received: from white.imgsrc.co.jp (ns.imgsrc.co.jp [210.226.20.2])
	by mx1.FreeBSD.org (Postfix) with ESMTP id 3B74343F85
	for <freebsd-current@FreeBSD.org>;
	Sun, 27 Jul 2003 18:35:25 -0700 (PDT)
	(envelope-from kuriyama@imgsrc.co.jp)
Received: from localhost (localhost [127.0.0.1])
	by white.imgsrc.co.jp (Postfix) with ESMTP id BC359413F
	for <freebsd-current@FreeBSD.org>;
	Mon, 28 Jul 2003 10:35:23 +0900 (JST)
Received: from black.imgsrc.co.jp (black.imgsrc.co.jp [2001:218:422:2::130])
	by white.imgsrc.co.jp (Postfix) with ESMTP id 04A4C410C
	for <freebsd-current@FreeBSD.org>;
	Mon, 28 Jul 2003 10:35:23 +0900 (JST)
Received: from black.imgsrc.co.jp (black.imgsrc.co.jp [2001:218:422:2::130])
	by black.imgsrc.co.jp (Postfix) with ESMTP id C62B41E460E
	for <freebsd-current@FreeBSD.org>;
	Mon, 28 Jul 2003 10:35:22 +0900 (JST)
Date: Mon, 28 Jul 2003 10:35:22 +0900
Message-ID: <7mvftnv3fp.wl@black.imgsrc.co.jp>
From: Jun Kuriyama <kuriyama@imgsrc.co.jp>
To: Current <freebsd-current@FreeBSD.org>
In-Reply-To: <7mwue3v6gf.wl@black.imgsrc.co.jp>
References: <7mwue3v6gf.wl@black.imgsrc.co.jp>
User-Agent: Wanderlust/2.10.0 (Venus) SEMI/1.14.5 (Awara-Onsen) FLIM/1.14.5
	(Demachiyanagi) APEL/10.4 Emacs/21.2 (i386--freebsd) MULE/5.0 (SAKAKI)
MIME-Version: 1.0 (generated by SEMI 1.14.5 - "Awara-Onsen")
Content-Type: text/plain; charset=US-ASCII
X-Virus-Scanned: by AMaViS snapshot-20020531
Subject: Re: dereferencing type-punned pointer will break strict-aliasing
	rules
X-BeenThere: freebsd-current@freebsd.org
X-Mailman-Version: 2.1.1
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, 28 Jul 2003 01:35:26 -0000

At Mon, 28 Jul 2003 00:30:35 +0000 (UTC),
kuriyama wrote:
> Is this caused by -oS option?

Grrr, of course this should be s/-oS/-Os/.

These warnings are caused from DROP_GIANT() macro.  By tracking this
down, actual source is __PCPU_GET() macro (line: 115) in
sys/i386/include/pcpu.h.

		__result = *(__pcpu_type(name) *)&__i;

To test this with simplified code:

-----
% cat test.c
struct T {
  int a;
};

void
test()
{
  struct T* c;
  int __i = 0;
  c = *(struct T* *)&__i;
}
% cc -c -Os -Wall test.c
test.c: In function `test':
test.c:11: warning: dereferencing type-punned pointer will break strict-aliasing rules
-----

__PCPU_GET() macro seems to be harmless if -Os is not used or
__pcpu_type() returns actual type rather than pointer.

What should we do?


-- 
Jun Kuriyama <kuriyama@imgsrc.co.jp> // IMG SRC, Inc.
             <kuriyama@FreeBSD.org> // FreeBSD Project