From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.org/gmane.linux.lib.musl.general/11652 Path: news.gmane.org!.POSTED!not-for-mail From: Rich Felker Newsgroups: gmane.linux.lib.musl.general Subject: Re: more on missing volatile qualifications Date: Tue, 4 Jul 2017 17:19:09 -0400 Message-ID: <20170704211909.GR1627@brightrain.aerifal.cx> References: <20170625104516.17ac9466@inria.fr> <20170625101704.GA2032@port70.net> <20170625130629.03dc67bc@inria.fr> Reply-To: musl@lists.openwall.com NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Trace: blaine.gmane.org 1499203165 14028 195.159.176.226 (4 Jul 2017 21:19:25 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Tue, 4 Jul 2017 21:19:25 +0000 (UTC) User-Agent: Mutt/1.5.21 (2010-09-15) To: musl@lists.openwall.com Original-X-From: musl-return-11665-gllmg-musl=m.gmane.org@lists.openwall.com Tue Jul 04 23:19:21 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 1dSVE6-0003GT-5e for gllmg-musl@m.gmane.org; Tue, 04 Jul 2017 23:19:18 +0200 Original-Received: (qmail 1801 invoked by uid 550); 4 Jul 2017 21:19:21 -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 1780 invoked from network); 4 Jul 2017 21:19:21 -0000 Content-Disposition: inline In-Reply-To: <20170625130629.03dc67bc@inria.fr> Original-Sender: Rich Felker Xref: news.gmane.org gmane.linux.lib.musl.general:11652 Archived-At: On Sun, Jun 25, 2017 at 01:06:29PM +0200, Jens Gustedt wrote: > Hello Szabolcs, > > On Sun, 25 Jun 2017 12:17:04 +0200 Szabolcs Nagy wrote: > > > pthread_once_t and pthread_spinlock_t qualifiers are > > visible in the c++ name mangling if a c++ function takes > > pointer to them as arguments so the change is an abi break. > > too bad, so we can't change these two > > 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. 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. > 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. The line: memcpy(set, handler_set, sizeof handler_set); is not valid if handler_set is made volatile; 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. 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. Rich