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CTRY:IE; LANG:en; SCL:1; SRV:; IPV:CAL; SFV:NSPM; H:64aa7808-outbound-1.mta.getcheckrecipient.com; PTR:ec2-63-35-35-123.eu-west-1.compute.amazonaws.com; CAT:NONE; SFS:(4636009)(396003)(376002)(346002)(39860400002)(136003)(46966006)(36840700001)(356005)(186003)(82310400003)(33656002)(966005)(86362001)(8676002)(70206006)(478600001)(55016002)(8886007)(70586007)(81166007)(44832011)(16526019)(1076003)(316002)(36756003)(6666004)(26005)(7696005)(82740400003)(36860700001)(956004)(4326008)(6862004)(336012)(47076005)(2616005)(5660300002)(83380400001)(8936002)(2906002); DIR:OUT; SFP:1101; X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 19 Mar 2021 16:43:51.9705 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 669a6ee4-2fd4-4344-6897-08d8eaf62d90 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: DB5EUR03FT052.eop-EUR03.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: AS8PR08MB6791 X-Spam-Status: No, score=-8.2 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, MSGID_FROM_MTA_HEADER, RCVD_IN_DNSWL_LOW, 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: Fri, 19 Mar 2021 16:43:55 -0000 The 03/18/2021 13:18, DJ Delorie via Libc-alpha wrote: > > In response to this customer bug... > > https://bugzilla.redhat.com/show_bug.cgi?id=1937515 > > I spent some time digging into this code, and was able to reproduce it > using criu (checkpoint/restore in userspace). In a nutshell: if you > create a task on a machine WITH xsave (or xsavec), and migrate it > (somehow) to a machine WITHOUT xsave (or xsavec), any further DSO > calls will fail because we've already chosen an xsave/xsavec resolver. > > This, of course, is guaranteed to fail, and cannot be fixed. With > criu I had to override the checks with a command line option just to > prove my point. > > However, if you *know* you might do this, there should be a way to use > tunables to avoid xsave/xsavec - with the usual caveats about "YMMV" - > so that a process could be migrated across such CPUs without fault. > > Our tunables almost provide this. so are we supposed to handle migrations to machines with different arch extensions? cpu_features based decisions can break across different machines and there is no reliable (future proof) way to request baseline arch features. on aarch64 the closest is glibc.cpu.name=generic tunable but it only affects the cpuid (which fixes most libc ifunc selection logic, but e.g. not if the cpu has bti or not, there is glibc.cpu.hwcap_mask but not hacap2 mask so bti cannot be turned off in glibc if the hw has it)