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Tue, 20 Sep 2022 16:00:34 +0000 From: Wilco Dijkstra To: Florian Weimer CC: Fangrui Song , "H.J. Lu" , Wilco Dijkstra via Libc-alpha Subject: Re: [RESEND PATCH] Makeconfig: Set pie-ccflag to -fPIE by default Thread-Topic: [RESEND PATCH] Makeconfig: Set pie-ccflag to -fPIE by default Thread-Index: AQHYuXiUB+0tpuwABE6GkvDoDcBwdK3BifSAgAAL3YCAAAdrAIAEJe3/gAAbcZ2AACL8OoAASrgAgAADxICACRsdn4ARur6AgAdAZC+AABz0nYAAE1TZ Date: Tue, 20 Sep 2022 16:00:34 +0000 Message-ID: References: <10cbed26-dc3c-3a55-8e39-95916c614dbb@linaro.org> <87pmgj2o1d.fsf@oldenburg.str.redhat.com> <20220829195703.tvrqhe7ggnaks3oo@google.com> <20220915214513.s6uzsy2zvcnevolx@google.com> <87a66um8wz.fsf@oldenburg.str.redhat.com> In-Reply-To: <87a66um8wz.fsf@oldenburg.str.redhat.com> Accept-Language: en-GB, en-US Content-Language: en-GB X-MS-Has-Attach: X-MS-TNEF-Correlator: msip_labels: Authentication-Results-Original: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=arm.com; x-ms-traffictypediagnostic: AS4PR08MB7901:EE_|PAVPR08MB8920:EE_|DBAEUR03FT051:EE_|AS8PR08MB9600:EE_ X-MS-Office365-Filtering-Correlation-Id: 9a313a1c-adf9-4839-2b11-08da9b2145ad x-checkrecipientrouted: true nodisclaimer: true X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam-Untrusted: BCL:0; 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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 20 Sep 2022 16:00:43.1392 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 9a313a1c-adf9-4839-2b11-08da9b2145ad 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: DBAEUR03FT051.eop-EUR03.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: AS8PR08MB9600 X-Spam-Status: No, score=-5.2 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,FORGED_SPF_HELO,KAM_DMARC_NONE,RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H2,SPF_HELO_PASS,SPF_NONE,TXREP,UNPARSEABLE_RELAY autolearn=no autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: Hi Florian,=0A= =0A= >> Well if changing the default of fPIC is unacceptable in GCC, adding a=0A= >> new option should help LLVM too since it could imply more than=0A= >> -fno-semantic-interposition.=A0 A key question is whether we could=0A= >> require that exported symbols are marked explicitly so that we only=0A= >> emit GOT and PLT indirections on such exported symbols.=0A= >=0A= > -flto with a linker plugin already covers this.=A0 I don't think we need= =0A= > anything else.=A0 Maybe an LTO mode that only deals with visibility, but= =0A= > otherwise does little cross-TU optimization?=0A= =0A= Well it would be great if LTO solved this problem, but unfortunately it can= 't...=0A= LTO tells you which symbols are locally defined, but this doesn't help PIC.= =0A= Local definitions with default visibility must still indirect via the GOT/P= LT,=0A= similarly interprocedural optimizations are still blocked.=0A= =0A= A LTO-lite option that just deals with visibility and global variable optim= ization=0A= (eg. better use of anchors) and other cheap optimizations seems useful inde= ed.=0A= =0A= Cheers,=0A= Wilco=