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 [216.205.24.124]) by sourceware.org (Postfix) with ESMTP id E81F33857C4E for ; Tue, 6 Oct 2020 08:21:55 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org E81F33857C4E 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-363-D2NybGmPMhGPUG5nWDaAkQ-1; Tue, 06 Oct 2020 04:21:54 -0400 X-MC-Unique: D2NybGmPMhGPUG5nWDaAkQ-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id F406F1019624; Tue, 6 Oct 2020 08:21:52 +0000 (UTC) Received: from oldenburg2.str.redhat.com (ovpn-113-154.ams2.redhat.com [10.36.113.154]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 4120C5C1BD; Tue, 6 Oct 2020 08:21:52 +0000 (UTC) From: Florian Weimer To: Adhemerval Zanella via Libc-alpha Subject: Re: [PATCH] posix: Fix -Warray-bounds instances building timer_create [BZ #26687] References: <20201005211234.2240007-1-adhemerval.zanella@linaro.org> <87362rvkky.fsf@oldenburg2.str.redhat.com> Date: Tue, 06 Oct 2020 10:21:50 +0200 In-Reply-To: <87362rvkky.fsf@oldenburg2.str.redhat.com> (Florian Weimer's message of "Tue, 06 Oct 2020 10:13:01 +0200") Message-ID: <87v9fnu5lt.fsf@oldenburg2.str.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain X-Spam-Status: No, score=-6.8 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, 06 Oct 2020 08:21:57 -0000 * Florian Weimer: > * Adhemerval Zanella via Libc-alpha: > >> This patch fixes both issues by embedding the information whether >> the timer if a SIGEV_THREAD in the returned 'timer_t'. For >> !SIGEV_THREAD, the resulting 'timer_t' is the returned kernel timer >> identifer (kernel_timer_t), while for SIGEV_THREAD it uses the fact >> malloc returns at least _Alignof (max_align_t) pointers plus that >> valid kernel_timer_t are always positive to set MSB bit of the returned >> 'timer_t' to indicate the timer handles a SIGEV_THREAD. > > LSB, not MSB, right? Ah, no, it is the MSB. I think using the LSB is generally more efficient for this because it is easier to manipulate. In this scenario, pointers would be unencoded, and a kernel_timer_t value ktid would be encoded as 2 * kdid + 1. But I guess the difference does not matter much. Thanks, Florian -- Red Hat GmbH, https://de.redhat.com/ , Registered seat: Grasbrunn, Commercial register: Amtsgericht Muenchen, HRB 153243, Managing Directors: Charles Cachera, Brian Klemm, Laurie Krebs, Michael O'Neill