From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-1.mimecast.com (us-smtp-delivery-1.mimecast.com [205.139.110.120]) by sourceware.org (Postfix) with ESMTP id 8F2DA3858D34 for ; Tue, 26 May 2020 12:41:25 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 8F2DA3858D34 Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-220-J_sAvGetPgm4HTtpzu6Dxw-1; Tue, 26 May 2020 08:41:21 -0400 X-MC-Unique: J_sAvGetPgm4HTtpzu6Dxw-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 4BAAE1800D42; Tue, 26 May 2020 12:41:19 +0000 (UTC) Received: from oldenburg2.str.redhat.com (ovpn-112-180.ams2.redhat.com [10.36.112.180]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 5DB661CA; Tue, 26 May 2020 12:41:16 +0000 (UTC) From: Florian Weimer To: Mathieu Desnoyers Cc: libc-alpha , Rich Felker , linux-api , Boqun Feng , Will Deacon , linux-kernel , Peter Zijlstra , Ben Maurer , Dave Watson , Thomas Gleixner , Paul , Paul Turner , Joseph Myers Subject: Re: [PATCH glibc 1/3] glibc: Perform rseq registration at C startup and thread creation (v19) References: <20200501021439.2456-1-mathieu.desnoyers@efficios.com> <20200501021439.2456-2-mathieu.desnoyers@efficios.com> <87v9kqbzse.fsf@oldenburg2.str.redhat.com> <941087675.33347.1590418305398.JavaMail.zimbra@efficios.com> <87367ovy6k.fsf@oldenburg2.str.redhat.com> <108939265.33525.1590428184533.JavaMail.zimbra@efficios.com> Date: Tue, 26 May 2020 14:41:14 +0200 In-Reply-To: <108939265.33525.1590428184533.JavaMail.zimbra@efficios.com> (Mathieu Desnoyers's message of "Mon, 25 May 2020 13:36:24 -0400 (EDT)") Message-ID: <87lflerhqt.fsf@oldenburg2.str.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Spam-Status: No, score=-8.6 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, RCVD_IN_DNSWL_NONE, RCVD_IN_MSPIKE_H4, RCVD_IN_MSPIKE_WL, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.2 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 26 May 2020 12:41:31 -0000 * Mathieu Desnoyers: > Something like this ? > > #ifdef __cplusplus > # if __cplusplus >= 201103L > # define rseq_static_assert (expr, diagnostic) static_assert (expr, diagnostic) > # define rseq_alignof alignof > # endif > #elif __STDC_VERSION__ >= 201112L > # define rseq_static_assert (expr, diagnostic) _Static_assert (expr, diagnostic) > # define rseq_alignof _Alignof > #endif > > #ifndef rseq_static_assert > # define rseq_static_assert (expr, diagnostic) /* nothing */ > #endif You can't have a space in #defines like that, no matter what GNU style says. 8-) > /* Ensure the compiler supports __attribute__ ((aligned)). */ > rseq_static_assert ((rseq_alignof (struct rseq_cs) >= 32, "alignment")); > rseq_static_assert ((rseq_alignof (struct rseq) >= 32, "alignment")); You need to move the ; into rseq_static_assert. And if you use explicit arguments, you can't use double parentheses. >> And something similar for _Alignas/attribute aligned, > > I don't see where _Alignas is needed here ? > > For attribute aligned, what would be the oldest supported C and C++ > standards ? There are no standardized attributes for C, there is only _Alignas. C++11 has an alignas specifier; it's not an attribute either. I think these are syntactically similar. >> with an error for >> older standards and !__GNUC__ compilers (because neither the type nor >> __thread can be represented there). > > By "type" you mean "struct rseq" here ? What does it contain that requires > a __GNUC__ compiler ? __attribute__ and __thread support. > About __thread, I recall other compilers have other means to declare it. > In liburcu, I end up with the following: > > #if defined (__cplusplus) && (__cplusplus >= 201103L) > # define URCU_TLS_STORAGE_CLASS thread_local > #elif defined (__STDC_VERSION__) && (__STDC_VERSION__ >= 201112L) > # define URCU_TLS_STORAGE_CLASS _Thread_local > #elif defined (_MSC_VER) > # define URCU_TLS_STORAGE_CLASS __declspec(thread) > #else > # define URCU_TLS_STORAGE_CLASS __thread > #endif > > Would something along those lines be OK for libc ? Yes, it would be okay (minus the Visual C++ part). This part does not have to go into UAPI headers first. A fallback definition of __thread should be okay. Outside glibc, the TLS model declaration is optional, I think. The glibc *definition* ensures that the variable is initial-exec. Thanks, Florian