From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on dcvr.yhbt.net X-Spam-Level: X-Spam-Status: No, score=-4.2 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,MAILING_LIST_MULTI, SPF_HELO_PASS,SPF_PASS shortcircuit=no autolearn=ham autolearn_force=no version=3.4.2 Received: from sourceware.org (server2.sourceware.org [IPv6:2620:52:3:1:0:246e:9693:128c]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by dcvr.yhbt.net (Postfix) with ESMTPS id 85E391F55B for ; Tue, 26 May 2020 15:22:09 +0000 (UTC) Received: from server2.sourceware.org (localhost [IPv6:::1]) by sourceware.org (Postfix) with ESMTP id 89A213894400; Tue, 26 May 2020 15:22:08 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 89A213894400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sourceware.org; s=default; t=1590506528; bh=SKrOEP5pGa9ajAYrExv6tmSsQLUAXbFOGSG0aVKLqZc=; h=Date:To:In-Reply-To:References:Subject:List-Id:List-Unsubscribe: List-Archive:List-Post:List-Help:List-Subscribe:From:Reply-To:Cc: From; b=ftV/jv/izkqObM4r54zz9OIn0b7ChP3LKZLvfzm0+CB31qZGdJp5RovuQqOLlntMp 3JQ0jbaqNLp5r2DY9bv0VjqWfpH3QhyCD80t7IOKqMb3VrEzUwLeJPlicWWgoWtl0s qW2/STjFjdefAfyhBvSsI/PafS4xSejP4raJdve4= Received: from mail.efficios.com (mail.efficios.com [167.114.26.124]) by sourceware.org (Postfix) with ESMTPS id 66C16388B01D for ; Tue, 26 May 2020 15:22:06 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 66C16388B01D Received: from localhost (localhost [127.0.0.1]) by mail.efficios.com (Postfix) with ESMTP id 2A2B32539DC; Tue, 26 May 2020 11:22:06 -0400 (EDT) Received: from mail.efficios.com ([127.0.0.1]) by localhost (mail03.efficios.com [127.0.0.1]) (amavisd-new, port 10032) with ESMTP id r5CHuBHdRu9w; Tue, 26 May 2020 11:22:05 -0400 (EDT) Received: from localhost (localhost [127.0.0.1]) by mail.efficios.com (Postfix) with ESMTP id CCA652539D9; Tue, 26 May 2020 11:22:05 -0400 (EDT) DKIM-Filter: OpenDKIM Filter v2.10.3 mail.efficios.com CCA652539D9 X-Virus-Scanned: amavisd-new at efficios.com Received: from mail.efficios.com ([127.0.0.1]) by localhost (mail03.efficios.com [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id 15NWPF5usT5q; Tue, 26 May 2020 11:22:05 -0400 (EDT) Received: from mail03.efficios.com (mail03.efficios.com [167.114.26.124]) by mail.efficios.com (Postfix) with ESMTP id BC77C253D8A; Tue, 26 May 2020 11:22:05 -0400 (EDT) Date: Tue, 26 May 2020 11:22:05 -0400 (EDT) To: Florian Weimer Message-ID: <1940294182.34562.1590506525684.JavaMail.zimbra@efficios.com> In-Reply-To: <877dwypwuj.fsf@oldenburg2.str.redhat.com> References: <20200501021439.2456-1-mathieu.desnoyers@efficios.com> <87367ovy6k.fsf@oldenburg2.str.redhat.com> <108939265.33525.1590428184533.JavaMail.zimbra@efficios.com> <87lflerhqt.fsf@oldenburg2.str.redhat.com> <1701081361.34159.1590503556923.JavaMail.zimbra@efficios.com> <87ftbmpxqi.fsf@oldenburg2.str.redhat.com> <1931644690.34207.1590504804638.JavaMail.zimbra@efficios.com> <877dwypwuj.fsf@oldenburg2.str.redhat.com> Subject: Re: [PATCH glibc 1/3] glibc: Perform rseq registration at C startup and thread creation (v19) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Originating-IP: [167.114.26.124] X-Mailer: Zimbra 8.8.15_GA_3928 (ZimbraWebClient - FF76 (Linux)/8.8.15_GA_3928) Thread-Topic: glibc: Perform rseq registration at C startup and thread creation (v19) Thread-Index: fw53pKjM0pFKmGwjq/cBVSRtxzONcQ== 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: , From: Mathieu Desnoyers via Libc-alpha Reply-To: Mathieu Desnoyers Cc: Rich Felker , libc-alpha , Peter Zijlstra , linux-api , Boqun Feng , Will Deacon , linux-kernel , Ben Maurer , Dave Watson , Thomas Gleixner , Paul , Paul Turner , Joseph Myers Errors-To: libc-alpha-bounces@sourceware.org Sender: "Libc-alpha" ----- On May 26, 2020, at 10:57 AM, Florian Weimer fweimer@redhat.com wrote= : > * Mathieu Desnoyers: >=20 >>> Like the attribute, it needs to come right after the struct keyword, I >>> think. (Trailing attributes can be ambiguous, but not in this case.) >> >> Nope. _Alignas really _is_ special :-( >> >> struct _Alignas (16) blah { >> int a; >> }; >> >> p.c:1:8: error: expected =E2=80=98{=E2=80=99 before =E2=80=98_Alignas=E2= =80=99 >> struct _Alignas (16) blah { >=20 > Meh, yet another unnecessary C++ incompatibility. C does not support > empty structs, so I assume they didn't see the field requirement as a > burden. Indeed, it's weird. >=20 >> One last thing I'm planning to add in sys/rseq.h to cover acessing the >> rseq_cs pointers with both the UAPI headers and the glibc struct rseq >> declarations: >> >> /* The rseq_cs_ptr macro can be used to access the pointer to the curren= t >> rseq critical section descriptor. */ >> #ifdef __LP64__ >> # define rseq_cs_ptr(rseq) \ >> ((const struct rseq_cs *) (rseq)->rseq_cs.ptr) >> #else /* __LP64__ */ >> # define rseq_cs_ptr(rseq) \ >> ((const struct rseq_cs *) (rseq)->rseq_cs.ptr.ptr32) >> #endif /* __LP64__ */ >> >> Does it make sense ? >=20 > Written this way, it's an aliasing violation. I don't think it's very > useful. OK, I'll just remove it. Thanks, Mathieu --=20 Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com