From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by sourceware.org (Postfix) with ESMTPS id 856503858D38 for ; Wed, 14 Jun 2023 06:49:38 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org 856503858D38 Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=redhat.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1686725378; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:in-reply-to:in-reply-to: references:references; bh=UKEzemCet7uyfr7+lQvpO9ZrWyF4QYr93ez/wMc8O9U=; b=Vh9FYGnUxFEFf9yiavY+PQADiQntBh5L3kcOfKlhUIyc6Vj6tnpkIYdKIkjy1m/MsswYYe LdCUbfpH0StjqINqrWVdu+cCjeKYN+asLbjbdUUpze3VeG97jZUjvcDT+xMfn7rIc75Kmr 3kSSNFOZRURUcfxFCUpZ6sAjKvLSL8g= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-270-JG-6CaR5OQalKTM_zG36Aw-1; Wed, 14 Jun 2023 02:49:36 -0400 X-MC-Unique: JG-6CaR5OQalKTM_zG36Aw-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.rdu2.redhat.com [10.11.54.4]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 6502D101A54E; Wed, 14 Jun 2023 06:49:36 +0000 (UTC) Received: from tucnak.zalov.cz (unknown [10.39.194.30]) by smtp.corp.redhat.com (Postfix) with ESMTPS id DE5692026D49; Wed, 14 Jun 2023 06:49:35 +0000 (UTC) Received: from tucnak.zalov.cz (localhost [127.0.0.1]) by tucnak.zalov.cz (8.17.1/8.17.1) with ESMTPS id 35E6nWMc1135681 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NOT); Wed, 14 Jun 2023 08:49:33 +0200 Received: (from jakub@localhost) by tucnak.zalov.cz (8.17.1/8.17.1/Submit) id 35E6nVAa1135680; Wed, 14 Jun 2023 08:49:31 +0200 Date: Wed, 14 Jun 2023 08:49:30 +0200 From: Jakub Jelinek To: Paul Eggert Cc: Joseph Myers , Marek Polacek , gcc-patches@gcc.gnu.org, libc-alpha@sourceware.org Subject: Re: [RFC] Add stdckdint.h header for C23 Message-ID: Reply-To: Jakub Jelinek References: <68578b43-939-1879-9676-2ea55249a2c5@codesourcery.com> MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 3.1 on 10.11.54.4 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Spam-Status: No, score=-3.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,KAM_NUMSUBJECT,RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H5,RCVD_IN_MSPIKE_WL,SPF_HELO_NONE,SPF_NONE,TXREP,T_SCC_BODY_TEXT_LINE autolearn=no autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: On Tue, Jun 13, 2023 at 07:54:25PM -0700, Paul Eggert wrote: > I don't see how you could implement __has_include_next() for > arbitrary non-GCC compilers, which is what we'd need for glibc users. For > glibc internals we can use "#include_next" more readily, since we assume a > new-enough GCC. I.e. we could do something like this: Indeed, limits.h uses #if defined __GNUC__ && !defined _GCC_LIMITS_H_ /* `_GCC_LIMITS_H_' is what GCC's file defines. */ # include_next #endif I'd just do: #if defined (__has_include_next) && !defined (ckd_add) # if __has_include_next () # include_next # endif #endif and then deal with the fallback (if the C library really needs one, does it need to support a C23 feature in arbitrary compiler which doesn't support C23?). A fallback should start with using __builtin_{add,sub,mul}_overflow without extra checking if compiler supports it, with or without use of __has_builtin. GCC 6 and later has __builtin_{add,sub,mul}_overflow, only GCC 10 has __has_builtin, I think clang has added those shortly after they were added in GCC 6 (though, __builtin_{add,sub,mul}_overflow_p which has been added in GCC 7 wasn't added to clang). Jakub