From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 120970 invoked by alias); 14 Dec 2015 20:39:18 -0000 Mailing-List: contact gcc-patches-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Id: List-Archive: List-Post: List-Help: Sender: gcc-patches-owner@gcc.gnu.org Received: (qmail 120961 invoked by uid 89); 14 Dec 2015 20:39:17 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-1.6 required=5.0 tests=AWL,BAYES_00,FREEMAIL_FROM,RCVD_IN_DNSWL_LOW,SPF_PASS autolearn=ham version=3.3.2 X-HELO: mail-oi0-f48.google.com Received: from mail-oi0-f48.google.com (HELO mail-oi0-f48.google.com) (209.85.218.48) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with (AES128-GCM-SHA256 encrypted) ESMTPS; Mon, 14 Dec 2015 20:39:16 +0000 Received: by oian133 with SMTP id n133so21766817oia.3 for ; Mon, 14 Dec 2015 12:39:14 -0800 (PST) MIME-Version: 1.0 X-Received: by 10.202.73.209 with SMTP id w200mr25453821oia.85.1450125554511; Mon, 14 Dec 2015 12:39:14 -0800 (PST) Received: by 10.76.77.99 with HTTP; Mon, 14 Dec 2015 12:39:14 -0800 (PST) In-Reply-To: <566F23AE.6070604@redhat.com> References: <20151209213118.GC317@x4> <566C346B.8030601@redhat.com> <20151212152731.GB18720@tucnak.redhat.com> <566F23AE.6070604@redhat.com> Date: Mon, 14 Dec 2015 20:39:00 -0000 Message-ID: Subject: Re: PING^1: [PATCH] Add TYPE_EMPTY_RECORD for C++ empty class From: "H.J. Lu" To: Jason Merrill Cc: GCC Patches , Jakub Jelinek , Richard Biener , Markus Trippelsdorf Content-Type: text/plain; charset=UTF-8 X-IsSubscribed: yes X-SW-Source: 2015-12/txt/msg01438.txt.bz2 On Mon, Dec 14, 2015 at 12:16 PM, Jason Merrill wrote: > On 12/12/2015 01:42 PM, Marc Glisse wrote: >> >> On Sat, 12 Dec 2015, Jakub Jelinek wrote: >> >>> On Sat, Dec 12, 2015 at 09:51:23AM -0500, Jason Merrill wrote: >>>> >>>> On 12/11/2015 06:52 PM, H.J. Lu wrote: >>>>> >>>>> On Thu, Dec 10, 2015 at 3:24 AM, Richard Biener >>>>> wrote: >>>>>> >>>>>> On Wed, Dec 9, 2015 at 10:31 PM, Markus Trippelsdorf >>>>>> wrote: >>>>>>> >>>>>>> On 2015.12.09 at 10:53 -0800, H.J. Lu wrote: >>>>>>>> >>>>>>>> >>>>>>>> Empty C++ class is a corner case which isn't covered in psABI nor >>>>>>>> C++ ABI. >>>>>>>> There is no mention of "empty record" in GCC documentation. But >>>>>>>> there are >>>>>>>> plenty of "empty class" in gcc/cp. This change affects all >>>>>>>> targets. C++ ABI >>>>>>>> should specify how it should be passed. >> >> >> >> About this patch, aren't we supposed to enable new C++ ABIs with >> -fabi-version=42 (or whatever the next number is)? > > > Yes, the patch should definitely make this conditional on > abi_version_at_least. > >>>>>>> There is a C++ ABI mailinglist, where you could discuss this issue: >>>>>>> http://sourcerytools.com/cgi-bin/mailman/listinfo/cxx-abi-dev >>>>>> >>>>>> >>>>>> Yep. As long as the ABI doesn't state how to pass those I'd rather >>>>>> _not_ change GCCs way. >>>>> >>>>> >>>>> It is agreed that GCC is wrong on this: >>>>> >>>>> >>>>> http://sourcerytools.com/pipermail/cxx-abi-dev/2015-December/002876.html >>>>> >>>> >>>> Yes, I think this is just a (nasty) bug on some GCC targets. >>> >>> >>> Well, the argument in that thread is weird, because C and C++ empty >>> structs >>> are different, so it isn't surprising they are passed differently. >>> C++ makes those sizeof == 1, while C has them sizeof == 0. >> >> >> Maybe it isn't surprising, but it isn't particularly helpful either. It >> increases the number of places where the 2 are incompatible. >> (I personally don't care about empty C structs) > > > Yep. The C standard doesn't have empty structs; it's a GNU extension. But > in any case argument passing can be compatible between C and C++, so it > really should be. > > Before I make any changes, I'd like to ask if we should make argument passing can be compatible between C and C++ for all targets GCC support or just x86. -- H.J.