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 [63.128.21.124]) by sourceware.org (Postfix) with ESMTP id 74BFC386F027 for ; Thu, 18 Feb 2021 13:28:21 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 74BFC386F027 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-200-6lxBWoYHMFKb46KdUIy_uw-1; Thu, 18 Feb 2021 08:28:19 -0500 X-MC-Unique: 6lxBWoYHMFKb46KdUIy_uw-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 06BBD18501A0; Thu, 18 Feb 2021 13:28:16 +0000 (UTC) Received: from oldenburg.str.redhat.com (ovpn-113-131.ams2.redhat.com [10.36.113.131]) by smtp.corp.redhat.com (Postfix) with ESMTPS id CE1FD60C6B; Thu, 18 Feb 2021 13:28:13 +0000 (UTC) From: Florian Weimer To: Szabolcs Nagy Cc: "H.J. Lu" , "Kirill A. Shutemov" , "Shanbhogue, Vedvyas" , "H.J. Lu via Libc-alpha" , Joseph Myers Subject: Re: [RFC] : An API for tagged address References: <20210211173711.71736-1-hjl.tools@gmail.com> <877dndmxj3.fsf@oldenburg.str.redhat.com> <20210218132419.GD12795@arm.com> Date: Thu, 18 Feb 2021 14:28:47 +0100 In-Reply-To: <20210218132419.GD12795@arm.com> (Szabolcs Nagy's message of "Thu, 18 Feb 2021 13:24:19 +0000") Message-ID: <874ki9mrn4.fsf@oldenburg.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 10.5.11.12 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain X-Spam-Status: No, score=-6.4 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, RCVD_IN_DNSWL_LOW, 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: Thu, 18 Feb 2021 13:28:22 -0000 * Szabolcs Nagy: >> was called in a thread. It won't work when 2 threads have different address >> masks. I think set_tagged_address_mask should be disallowed in child >> threads and in parent thread when there are any active child threads. > > i think this is the wrong api. currently the libc should set > things up early. api for user code is too late. > > user code does not know if it runs single threaded or not > (although we have __libc_single_threaded now, i'm not sure if > we can use that for this purpose) We could, but it's possible to launch threads from ELF constructors (and I think some libraries do that). So you could avoid the call or diagnose a failure if single-threaded, but the tagged address feature wouldn't compose well. Some kernel interfaces have this problem (e.g., unshare), but they are less general-purpose than tagged addresses. Thanks, Florian