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Lu" Cc: Richard Earnshaw , GNU C Library , Richard Earnshaw Subject: Re: [PATCH v3 2/8] elf: Add a tunable to control use of tagged memory Message-ID: <20201126180612.GR20578@arm.com> References: <87e8b15f-8c86-4b2c-a5e4-3e70631ea505@gotplt.org> <23a8ad00-a376-48ae-cc6a-2684261146a1@foss.arm.com> <6173c59d-ee67-9499-ac61-c2dd37b56c67@foss.arm.com> <3b69bc46-df40-f9ad-b76b-b69483b0934c@foss.arm.com> <20201126172056.GQ20578@arm.com> Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) X-Originating-IP: [217.140.106.54] X-ClientProxiedBy: SA9PR13CA0118.namprd13.prod.outlook.com (2603:10b6:806:24::33) To PR3PR08MB5564.eurprd08.prod.outlook.com (2603:10a6:102:87::18) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from arm.com (217.140.106.54) by SA9PR13CA0118.namprd13.prod.outlook.com (2603:10b6:806:24::33) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3632.9 via Frontend Transport; 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DIR:OUT; SFP:1101; X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 26 Nov 2020 18:06:28.2019 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 1f32215f-e81c-4d72-8f35-08d89235ff13 X-MS-Exchange-CrossTenant-Id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=f34e5979-57d9-4aaa-ad4d-b122a662184d; Ip=[63.35.35.123]; Helo=[64aa7808-outbound-1.mta.getcheckrecipient.com] X-MS-Exchange-CrossTenant-AuthSource: VE1EUR03FT061.eop-EUR03.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: AM9PR08MB5922 X-Spam-Status: No, score=-8.1 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, MSGID_FROM_MTA_HEADER, RCVD_IN_DNSWL_NONE, RCVD_IN_MSPIKE_H2, SPF_HELO_PASS, SPF_PASS, TXREP, UNPARSEABLE_RELAY 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, 26 Nov 2020 18:06:33 -0000 The 11/26/2020 09:31, H.J. Lu wrote: > I don't disagree with it. If the new libc will be installed as the > system glibc, it needs to support binary marker even if there > are currently no binaries with marker. i don't yet see how things break if the marking support comes in a later glibc. for unmarked binaries the env var behaviour is fixed and backward compatible. marked binaries will depend on a new glibc, we currently don't have a way to do an abi bump on a binary such that old glibc rejects it (other than using symbol references or new dyn relc type), so we may end up with silent breakage if a new marked binary is used with old glibc. this is not too bad, but if this is a concern then e.g. we can do an e_flags check in aarch64 so new flags there are always rejected which will allow us to bump the mte abi.