From mboxrd@z Thu Jan  1 00:00:00 1970
X-Msuck: nntp://news.gmane.org/gmane.linux.lib.musl.general/3289
Path: news.gmane.org!not-for-mail
From: Szabolcs Nagy <nsz@port70.net>
Newsgroups: gmane.linux.lib.musl.general
Subject: Re: [patch] add ether_(aton, ntoa)
Date: Sun, 5 May 2013 18:24:19 +0200
Message-ID: <20130505162419.GW12689@port70.net>
References: <CAL3m8eCcZkn2YDAHyf1Ns4a4Zcz0Mk3ENrdby8tarCoKEc+qkw@mail.gmail.com>
 <20130415014005.GR20323@brightrain.aerifal.cx>
 <CAL3m8eCdz_eUGptYsn5NDPho0PQ_=wH+F4aY9eSmgsPj+vS00w@mail.gmail.com>
 <20130420014945.GI20323@brightrain.aerifal.cx>
 <CAL3m8eCHiS2ypw0a0enPJvGtTu-C5-45a7XG74UCNLWHFRR-iw@mail.gmail.com>
Reply-To: musl@lists.openwall.com
NNTP-Posting-Host: plane.gmane.org
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
X-Trace: ger.gmane.org 1367771074 8434 80.91.229.3 (5 May 2013 16:24:34 GMT)
X-Complaints-To: usenet@ger.gmane.org
NNTP-Posting-Date: Sun, 5 May 2013 16:24:34 +0000 (UTC)
To: musl@lists.openwall.com
Original-X-From: musl-return-3293-gllmg-musl=m.gmane.org@lists.openwall.com Sun May 05 18:24:34 2013
Return-path: <musl-return-3293-gllmg-musl=m.gmane.org@lists.openwall.com>
Envelope-to: gllmg-musl@plane.gmane.org
Original-Received: from mother.openwall.net ([195.42.179.200])
	by plane.gmane.org with smtp (Exim 4.69)
	(envelope-from <musl-return-3293-gllmg-musl=m.gmane.org@lists.openwall.com>)
	id 1UZ1jl-0002JY-4Y
	for gllmg-musl@plane.gmane.org; Sun, 05 May 2013 18:24:33 +0200
Original-Received: (qmail 24105 invoked by uid 550); 5 May 2013 16:24:31 -0000
Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm
Precedence: bulk
List-Post: <mailto:musl@lists.openwall.com>
List-Help: <mailto:musl-help@lists.openwall.com>
List-Unsubscribe: <mailto:musl-unsubscribe@lists.openwall.com>
List-Subscribe: <mailto:musl-subscribe@lists.openwall.com>
Original-Received: (qmail 24097 invoked from network); 5 May 2013 16:24:31 -0000
Content-Disposition: inline
In-Reply-To: <CAL3m8eCHiS2ypw0a0enPJvGtTu-C5-45a7XG74UCNLWHFRR-iw@mail.gmail.com>
User-Agent: Mutt/1.5.21 (2010-09-15)
Xref: news.gmane.org gmane.linux.lib.musl.general:3289
Archived-At: <http://permalink.gmane.org/gmane.linux.lib.musl.general/3289>

* Strake <strake888@gmail.com> [2013-05-05 09:02:04 -0500]:
> On 19/04/2013, Rich Felker <dalias@aerifal.cx> wrote:
> > &x has the wrong type; strtoul requires char **, not const char **.
> > A separate temp var is required for the output, as in.
> >
> > 	char *y;
> > 	n = strtoul (x, &y, 16);
> > 	x = y;
> >
> > or similar. As far as I know the naive cast one could make to "fix"
> > the type mismatch is not valid; it would be an aliasing violation.
> 
> What bad could happen?


the naive cast is strtoul(x, (char**)&x, 16)

(const char **) and (char **) are not compatible types
and they are not required to have the same representation
and alignment

so the conversion itself may invoke undefined behaviour

but even if the representation and alignment is the same
an object with effective type (const char*) cannot be
accessed through a (char*) lvalue expression within strtoul

so the aliasing rules are violated as well
(a compiler may reorder the loads from x and the stores
to *(char**)&x arbitarily)