From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0E276C10F05 for ; Fri, 29 Mar 2019 16:44:28 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id CFDCD21871 for ; Fri, 29 Mar 2019 16:44:27 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="F3kmUQfc"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=armh.onmicrosoft.com header.i=@armh.onmicrosoft.com header.b="OA678YyY" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CFDCD21871 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:Content-ID:In-Reply-To: References:Message-ID:Date:Subject:To:From:Reply-To:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=CIVRU44ASOEfUQMld+IKC8yykSrdkaHbynRa9gFCNF0=; b=F3kmUQfcjz91RV U9GsZcx+1Vs1LdUwJ469z9zpeuS5J5C9p2W+MOtGj06bUhSsj7N8p7yDToGnY46K/1jZw5rvzs9n+ h4BOoTgadLQgJUROIseShIgndVzH6FtWnTDhR0PUj9vALudbXQvzPE0/b0BOnqCCxaVgDp3hwNr+Q 1rlLgq8mOGJhyPvsVfe4yWWQLGBaeVDSoeCgJLeJwb9OxA/RP8KnHurPoXMExppmk2dvsoX//Crx7 s4XRT0gJGnOQxkuJYb91esxyEcodk5xSM16zgT6QMHtZaS9Utb94gRjD+2rk6ueK91iva7n4ss29Z NWe/88sgx0z2eGTXusLw==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1h9uc6-0008Iu-Cs; Fri, 29 Mar 2019 16:44:18 +0000 Received: from mail-eopbgr80058.outbound.protection.outlook.com ([40.107.8.58] helo=EUR04-VI1-obe.outbound.protection.outlook.com) by bombadil.infradead.org with esmtps (Exim 4.90_1 #2 (Red Hat Linux)) id 1h9uc2-0008IK-Ja for linux-arm-kernel@lists.infradead.org; Fri, 29 Mar 2019 16:44:16 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=armh.onmicrosoft.com; s=selector1-arm-com; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=jke8tornkd9KQAJSkBL2emB4wZjIQzKlUbeCtxHnBwQ=; b=OA678YyYiPzRRUOu7oMlzh6Euhh1vxMEG7iTmpE7yPSTEuEhNQTbRuv0fcrmcEg6NCHpRkG90wNZjWHh9eOK80fmFZKW6zfB8dQ+gUdjAAKiAwWLkyfjUS+sLlEfrCMFQ8KREgkN9GsAhN+VTPdXKRXI35DRzW8S3cVGSIMZLHg= Received: from VI1PR08MB4223.eurprd08.prod.outlook.com (20.178.13.96) by VI1PR08MB3214.eurprd08.prod.outlook.com (52.133.15.154) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.1750.17; Fri, 29 Mar 2019 16:44:05 +0000 Received: from VI1PR08MB4223.eurprd08.prod.outlook.com ([fe80::c49b:320c:780b:c8f3]) by VI1PR08MB4223.eurprd08.prod.outlook.com ([fe80::c49b:320c:780b:c8f3%5]) with mapi id 15.20.1750.017; Fri, 29 Mar 2019 16:44:05 +0000 From: Szabolcs Nagy To: Dave P Martin , Andrew Murray Subject: Re: [PATCH v2 2/6] arm64: HWCAP: add support for AT_HWCAP2 Thread-Topic: [PATCH v2 2/6] arm64: HWCAP: add support for AT_HWCAP2 Thread-Index: AQHUyd/t7tbqB8zsQECnf+yB7P6UeaXql1yAgAEJZwCANCepgIAABhqAgAFQNgCAAeq/gA== Date: Fri, 29 Mar 2019 16:44:05 +0000 Message-ID: <83b59b0f-cee7-92d5-2ed2-5300f92d7329@arm.com> References: <1550751657-30252-1-git-send-email-andrew.murray@arm.com> <1550751657-30252-3-git-send-email-andrew.murray@arm.com> <20190221184500.GO16031@e103592.cambridge.arm.com> <20190327150224.GE43527@e119886-lin.cambridge.arm.com> <20190327152414.GF43527@e119886-lin.cambridge.arm.com> <20190328112734.GZ3567@e103592.cambridge.arm.com> In-Reply-To: <20190328112734.GZ3567@e103592.cambridge.arm.com> Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: user-agent: Mozilla/5.0 (X11; Linux aarch64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 x-originating-ip: [217.140.106.51] x-clientproxiedby: LO2P265CA0323.GBRP265.PROD.OUTLOOK.COM (2603:10a6:600:a4::23) To VI1PR08MB4223.eurprd08.prod.outlook.com (2603:10a6:803:b5::32) authentication-results: spf=none (sender IP is ) smtp.mailfrom=Szabolcs.Nagy@arm.com; x-ms-exchange-messagesentrepresentingtype: 1 x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: 03a8a3ba-b05c-4061-a30e-08d6b465c184 x-ms-office365-filtering-ht: Tenant x-microsoft-antispam: BCL:0; PCL:0; RULEID:(2390118)(7020095)(4652040)(8989299)(4534185)(4627221)(201703031133081)(201702281549075)(8990200)(5600127)(711020)(4605104)(4618075)(2017052603328)(7153060)(7193020); SRVR:VI1PR08MB3214; x-ms-traffictypediagnostic: VI1PR08MB3214: x-ms-exchange-purlcount: 2 nodisclaimer: True x-microsoft-antispam-prvs: x-forefront-prvs: 0991CAB7B3 x-forefront-antispam-report: SFV:NSPM; SFS:(10009020)(366004)(346002)(39860400002)(136003)(396003)(376002)(199004)(189003)(6506007)(4326008)(68736007)(476003)(105586002)(446003)(2616005)(11346002)(8936002)(6116002)(6306002)(3846002)(486006)(6512007)(31686004)(81166006)(6636002)(93886005)(229853002)(26005)(81156014)(6246003)(53936002)(64126003)(316002)(966005)(85306007)(65956001)(8676002)(2906002)(97736004)(478600001)(72206003)(6486002)(5660300002)(65806001)(6436002)(66066001)(102836004)(36756003)(71190400001)(52116002)(71200400001)(86362001)(25786009)(44832011)(99286004)(106356001)(65826007)(76176011)(14454004)(305945005)(31696002)(186003)(58126008)(54906003)(110136005)(7736002)(386003)(256004)(53546011)(60764002); DIR:OUT; SFP:1101; SCL:1; SRVR:VI1PR08MB3214; H:VI1PR08MB4223.eurprd08.prod.outlook.com; FPR:; SPF:None; LANG:en; PTR:InfoNoRecords; A:1; MX:1; received-spf: None (protection.outlook.com: arm.com does not designate permitted sender hosts) x-ms-exchange-senderadcheck: 1 x-microsoft-antispam-message-info: K3BhgxbpsxfbBASjk2bnmSGLihzT7OyHsik4VY632evnipGRROvPDPE41TjxnAVAXDyNDV4byndlFCgIl/aV26SMFWHZ4F+tx93svqppPGkpu0aUdk1w7vWeW3IHziaFEpIF0MOgLcIEj+1hLXD96leoW07fk+Y+9zOWAVXhEBmls4V8KQ1ncLNSGPLOiqdDzXiYiFVC6fwjVzFhnOhJ+X9kIOE0fM2BDSXRCP6N7hOkyeD/Z/HaKQ1mcx4rIBvs9swV9kfLrL0DLVeog7rb5Qr5DuvUB9QSnFUxxBhh2zGCXAyNBGbYkD5LVGZ+GeN7EYm+d7y45FO2zm7ukiox1yYSqDphF5yO6acpSCFvd7irwHROELQxJ1LKZzFOXC+G9MAS6G9jBmcdI7nYFEHBt6lbytda3p3W4gtcCkrx59A= Content-ID: <2E86A70E2B83544B8B40EB0E895F0539@eurprd08.prod.outlook.com> MIME-Version: 1.0 X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-Network-Message-Id: 03a8a3ba-b05c-4061-a30e-08d6b465c184 X-MS-Exchange-CrossTenant-originalarrivaltime: 29 Mar 2019 16:44:05.3657 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-Transport-CrossTenantHeadersStamped: VI1PR08MB3214 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190329_094414_646920_8E4CAEA3 X-CRM114-Status: GOOD ( 17.65 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Catalin Marinas , nd , Will Deacon , GNU C Library , "linux-arm-kernel@lists.infradead.org" Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 28/03/2019 11:27, Dave Martin wrote: > On Wed, Mar 27, 2019 at 03:24:15PM +0000, Andrew Murray wrote: >> On Wed, Mar 27, 2019 at 03:02:25PM +0000, Andrew Murray wrote: >>> I'll add documentation to Documentation/arm64 to indicate that the upper 32bits >>> of AT_HWCAP will always be 0. Is this correct? >> >> How about this (in Documentation/arm64/elf_hwcaps.txt)? >> + >> + >> +4. Unused AT_HWCAP bits >> +----------------------- >> + >> +Each AT_HWCAP and AT_HWCAP2 entry provides for up to 32 hwcaps contained >> +in bits [31:0]. For interoperation with userspace we guarantee that the >> +top bits [63:32] of AT_HWCAP will always be returned as 0. > > Since the main reason for reserving bits [63:32] is ILP32, and it's > still unclear when (or if) that will be merged, it feels a bit excessive > to promise that we will never use these bits. > > It sounds like glibc has a use for at most one bit in here. > > So maybe we can reserve bit 63 (or 32, whatever) and promise that is > zero, but leave the rest uncommitted for now. > > Szabolcs, does that sound sensible? i think hwcap bit 63 is already reserved by glibc internally for tls support, it is not clear to me if that's still relevant (aarch64 post-dates tls support, so this might be historical cruft that can be cleaned up), i only see one comment about it: 1288 /* The last entry in hwcap_extra is reserved for the "tls" pseudo-hwcap which 1289 indicates support for TLS. This pseudo-hwcap is only used by old versions 1290 under which TLS support was optional. The entry is no longer needed, but 1291 must remain for compatibility. */ 1292 hwcap_extra[63 - _DL_FIRST_EXTRA] = "tls"; https://sourceware.org/git/?p=glibc.git;a=blob;f=elf/ldconfig.c;h=3bc9e618916ebb2fee29ffe3d114525a08390b43;hb=HEAD#l1288 and generic ld.so.cache handling code uses it: https://sourceware.org/git/?p=glibc.git;a=blob;f=elf/dl-cache.c;h=d8d1e2344e612d98689cf7d7ad965822d0ab6ed1;hb=HEAD#l265 since i don't understand how this tls bit was used exactly i think it's better to use a different bit for aarch64 ifunc abi hacks (e.g. 1ULL << 62) cc += libc-alpha in case somebody knows more about this bit. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel