From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.org/gmane.linux.lib.musl.general/11656 Path: news.gmane.org!.POSTED!not-for-mail From: Jens Gustedt Newsgroups: gmane.linux.lib.musl.general Subject: Re: more on missing volatile qualifications Date: Wed, 5 Jul 2017 00:03:03 +0200 Organization: inria.fr Message-ID: <20170705000303.6936aefe@inria.fr> References: <20170625104516.17ac9466@inria.fr> <20170625101704.GA2032@port70.net> <20170625130629.03dc67bc@inria.fr> <20170704211909.GR1627@brightrain.aerifal.cx> Reply-To: musl@lists.openwall.com NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; boundary="Sig_/b5uHAgtbPVyJtm6P__R7wPO"; protocol="application/pgp-signature" X-Trace: blaine.gmane.org 1499205863 28109 195.159.176.226 (4 Jul 2017 22:04:23 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Tue, 4 Jul 2017 22:04:23 +0000 (UTC) To: musl@lists.openwall.com Original-X-From: musl-return-11669-gllmg-musl=m.gmane.org@lists.openwall.com Wed Jul 05 00:04:19 2017 Return-path: Envelope-to: gllmg-musl@m.gmane.org Original-Received: from mother.openwall.net ([195.42.179.200]) by blaine.gmane.org with smtp (Exim 4.84_2) (envelope-from ) id 1dSVvS-0006Xi-N3 for gllmg-musl@m.gmane.org; Wed, 05 Jul 2017 00:04:06 +0200 Original-Received: (qmail 9969 invoked by uid 550); 4 Jul 2017 22:04:10 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Original-Received: (qmail 9715 invoked from network); 4 Jul 2017 22:03:16 -0000 X-IronPort-AV: E=Sophos;i="5.40,309,1496095200"; d="scan'208";a="282046970" In-Reply-To: <20170704211909.GR1627@brightrain.aerifal.cx> X-Mailer: Claws Mail 3.14.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) X-Face: iVBORw0KGgoAAAANSUhEUgAAADAAAAAwBAMAAAClLOS0AAAAAXNSR0IArs4c6QAAACRQTFRFERslNjAsLTE9Ok9wUk9TaUs8iWhSrYZkj42Rz6aD3sGZ Xref: news.gmane.org gmane.linux.lib.musl.general:11656 Archived-At: --Sig_/b5uHAgtbPVyJtm6P__R7wPO Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable Hello Rich, On Tue, 4 Jul 2017 17:19:09 -0400 Rich Felker wrote: > On Sun, Jun 25, 2017 at 01:06:29PM +0200, Jens Gustedt wrote: > > There is a reading of the C standard that says that volatile only > > has implications if an object itself is such qualified, having a > > volatile qualified lvalue access isn't enough. I don't think that > > any current compiler does such weird things, but who knows where > > optimisers will go in the future. =20 >=20 > Indeed. GCC seems committed to treating "accesses through volatile > lvalue" as volatile, but I'd rather not depend on it. Perhaps we > should add a primitive to atomic.h for loading the value of atomics so > that we never access them directly; then volatile would not matter. While I agree for the principle, identifying all these places and replace them with a primitive might not be so easy. Luckily most of these variables a called "lock" :) I'll look into it and see what I can do. But I will probably not be able to come up with sensible platform specific choices for an "a_load" primitive and set it to "a_cas(p, 0, 0)" or so, to have a start. > > AFAICS for the third finding in sigaction.c this would not be an > > issue. Since in addition this is something dealing with signal > > stuff, I still think that volatile would be in order, here. =20 >=20 > The line: >=20 > memcpy(set, handler_set, sizeof handler_set); >=20 > is not valid if handler_set is made volatile; Yes, so said the compiler, too. > we'd have to write out > the code to copy it. Not a big deal though, and more correct anyway; > using memcpy to copy something that's semantically atomic is sloppy. Ok, so let's do this properly. > Unfortunately since I don't want to encode knowledge of the naming of > sigset_t internals here, we'd probably need a loop to copy to a > non-volatile array the same as handler_set, then memcpy from there to > set. Yes, unfortunately. To do that we'd also need an "a_load_l" primitive, or we'd have to change handler_set to an array of unsigned, which is far more intrusive. Jens --=20 :: INRIA Nancy Grand Est ::: Camus ::::::: ICube/ICPS ::: :: ::::::::::::::: office Strasbourg : +33 368854536 :: :: :::::::::::::::::::::: gsm France : +33 651400183 :: :: ::::::::::::::: gsm international : +49 15737185122 :: :: http://icube-icps.unistra.fr/index.php/Jens_Gustedt :: --Sig_/b5uHAgtbPVyJtm6P__R7wPO Content-Type: application/pgp-signature Content-Description: Digitale Signatur von OpenPGP -----BEGIN PGP SIGNATURE----- iF0EARECAB0WIQSN9stI2OFN1pLljN0P0+hp2tU34gUCWVwQlwAKCRAP0+hp2tU3 4rHoAJ9idsaQ+1879/3vdi6TmNh+cPZlIwCeLJ11/zlMJ7Fd6in1Oab5DZRpG9E= =QP/I -----END PGP SIGNATURE----- --Sig_/b5uHAgtbPVyJtm6P__R7wPO--