From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!.POSTED!not-for-mail From: Stefan Monnier Newsgroups: gmane.emacs.devel Subject: Re: emacs-26 9e59de9: Use GCALIGNED properly for GCC Date: Fri, 10 Nov 2017 13:02:57 -0500 Message-ID: References: <20171109031206.7056.28312@vcs0.savannah.gnu.org> <20171109031208.D2CAF2033E@vcs0.savannah.gnu.org> <5A0550FE.2030703@gmx.at> <83zi7upnfo.fsf@gnu.org> <4ee60712-789e-f160-52a9-4e24a9733a11@cs.ucla.edu> <83shdmpiah.fsf@gnu.org> <8d9c169a-5f58-6958-9fca-4c68fa547ba3@cs.ucla.edu> NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain X-Trace: blaine.gmane.org 1510337038 6083 195.159.176.226 (10 Nov 2017 18:03:58 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Fri, 10 Nov 2017 18:03:58 +0000 (UTC) User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.0.50 (gnu/linux) To: emacs-devel@gnu.org Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Fri Nov 10 19:03:54 2017 Return-path: Envelope-to: ged-emacs-devel@m.gmane.org Original-Received: from lists.gnu.org ([208.118.235.17]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1eDDei-0001Nh-Mb for ged-emacs-devel@m.gmane.org; Fri, 10 Nov 2017 19:03:52 +0100 Original-Received: from localhost ([::1]:42920 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1eDDeq-00056Z-2Y for ged-emacs-devel@m.gmane.org; Fri, 10 Nov 2017 13:04:00 -0500 Original-Received: from eggs.gnu.org ([2001:4830:134:3::10]:55915) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1eDDeE-00056C-Az for emacs-devel@gnu.org; Fri, 10 Nov 2017 13:03:23 -0500 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1eDDe9-00035q-F8 for emacs-devel@gnu.org; Fri, 10 Nov 2017 13:03:21 -0500 Original-Received: from [195.159.176.226] (port=48646 helo=blaine.gmane.org) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1eDDe9-000351-8o for emacs-devel@gnu.org; Fri, 10 Nov 2017 13:03:17 -0500 Original-Received: from list by blaine.gmane.org with local (Exim 4.84_2) (envelope-from ) id 1eDDdu-0007jR-AV for emacs-devel@gnu.org; Fri, 10 Nov 2017 19:03:02 +0100 X-Injected-Via-Gmane: http://gmane.org/ Original-Lines: 17 Original-X-Complaints-To: usenet@blaine.gmane.org Cancel-Lock: sha1:zQl/EkNaWnLezrUm/9nMzMrl53A= X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 195.159.176.226 X-BeenThere: emacs-devel@gnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: "Emacs development discussions." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Original-Sender: "Emacs-devel" Xref: news.gmane.org gmane.emacs.devel:220032 Archived-At: >>> union gcaligned_foo { struct foo s; int64_t gcaligned; }; >> Are int64_t necessarily aligned on multiples of 8 on 32bit platforms? > No, unfortunately. That was my impression as well. > That does not work either, alas, as C11 says 'alignas (8)' is an error when > the natural alignment of the object is less than 8. This is one of the > problems that we have encountered in earlier attempts to fix this bug. 'char > alignas (8)' avoids this problem. I don't follow: the natural alignment for `char` is definitely less than 8, so if "'alignas (8)' is an error when the natural alignment of the object is less than 8", how can "char alignas (8)" avoid the problem? Stefan