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 [170.10.129.124]) by sourceware.org (Postfix) with ESMTPS id 80C8F385840C for ; Wed, 30 Mar 2022 10:08:03 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 80C8F385840C Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-455-1CcDa8TWOVmE9M4pbEWNXA-1; Wed, 30 Mar 2022 06:07:59 -0400 X-MC-Unique: 1CcDa8TWOVmE9M4pbEWNXA-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 9C8273C021AD; Wed, 30 Mar 2022 10:07:58 +0000 (UTC) Received: from tucnak.zalov.cz (unknown [10.39.192.15]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 54B43C07F48; Wed, 30 Mar 2022 10:07:58 +0000 (UTC) Received: from tucnak.zalov.cz (localhost [127.0.0.1]) by tucnak.zalov.cz (8.16.1/8.16.1) with ESMTPS id 22UA7tLF158511 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NOT); Wed, 30 Mar 2022 12:07:56 +0200 Received: (from jakub@localhost) by tucnak.zalov.cz (8.16.1/8.16.1/Submit) id 22UA7tKW158510; Wed, 30 Mar 2022 12:07:55 +0200 Date: Wed, 30 Mar 2022 12:07:55 +0200 From: Jakub Jelinek To: gcc-patches@gcc.gnu.org Subject: [wwwdocs] Document zero width bit-field passing ABI changes in gcc-12/changes.html [PR104796] Message-ID: Reply-To: Jakub Jelinek MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.85 on 10.11.54.8 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=-10.4 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, KAM_SHORT, RCVD_IN_DNSWL_LOW, RCVD_IN_MSPIKE_H4, RCVD_IN_MSPIKE_WL, SPF_HELO_NONE, SPF_NONE, TXREP, T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on server2.sourceware.org X-BeenThere: gcc-patches@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 30 Mar 2022 10:08:05 -0000 Hi! This patch documents the PR102024 ABI changes. The x86-64, ARM and AArch64 backends refer to this in their -Wpsabi diagnostics. Ok for wwwdocs? diff --git a/htdocs/gcc-12/changes.html b/htdocs/gcc-12/changes.html index 689feeba..dc0e4074 100644 --- a/htdocs/gcc-12/changes.html +++ b/htdocs/gcc-12/changes.html @@ -28,6 +28,31 @@ a work-in-progress.

Caveats

    +
  • + An ABI incompatibility between C and + C++ when passing or returning by value certain aggregates with zero + width bit-fields has been discovered on various targets. + As mentioned in PR102024, + since the PR42217 fix in + GCC 4.5 the C++ front-end has been removing zero width bit-fields + from the internal representation of the aggregates after the layout of those + aggregates, but the C front-end kept them, so passing e.g. + struct S { float a; int : 0; float b; } or + struct T { float c; int : 0; } by value could differ + between C and C++. Starting with GCC 12 the C++ front-end no longer + removes those bit-fields from the internal representation and + per clarified psABI some targets have been changed, so that they + either ignore those bit-fields in the argument passing by value + decisions in both C and C++, or they always take them into account. + x86-64, ARM and AArch64 will always ignore them (so there is + a C ABI incompatibility between GCC 11 and earlier with GCC 12 or + later), PowerPC64 ELFv2 and S/390 always take them into account + (so there is a C++ ABI incompatibility, GCC 4.4 and earlier compatible + with GCC 12 or later, incompatible with GCC 4.5 through GCC 11). + RISC-V has changed the handling of these already starting with GCC 10. + GCC 12 on the above targets will report such incompatibilities as + warnings or other diagnostics unless -Wno-psabi is used. +
  • C: Computed gotos require a pointer type now. Jakub