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Tue, 20 Sep 2022 13:59:45 +0000 From: Wilco Dijkstra To: Fangrui Song CC: "H.J. Lu" , Florian Weimer , 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/gAAbcZ2AACL8OoAASrgAgAADxICACRsdn4ARur6AgAdAZC8= Date: Tue, 20 Sep 2022 13:59:45 +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> In-Reply-To: <20220915214513.s6uzsy2zvcnevolx@google.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_|AS8PR08MB8467:EE_|VE1EUR03FT060:EE_|DB9PR08MB9491:EE_ X-MS-Office365-Filtering-Correlation-Id: 60cc713b-cc05-44c1-a89d-08da9b106656 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 13:59:56.3980 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 60cc713b-cc05-44c1-a89d-08da9b106656 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: VE1EUR03FT060.eop-EUR03.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DB9PR08MB9491 X-Spam-Status: No, score=-2.3 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,FORGED_SPF_HELO,KAM_DMARC_NONE,KAM_INFOUSMEBIZ,KAM_SHORT,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 Fangrui,=0A= =0A= > In Clang, -fpic/-fPIC without -fno-semantic-interposition still allows= =0A= > interprocedural optimizations of default visibility external linkage defi= nitions.=0A= >=0A= > It is unfortunate that GCC doesn't allow it and=0A= > --enable-default-semantic-interposition is rejected (https://gcc.gnu.org/= bugzilla/show_bug.cgi?id=3D100937)=0A= =0A= I think it now does it with -Ofast, so that's a start at least...=0A= =0A= > So if such an option -ffast-PIC is made, it will only benefit GCC.=0A= > I have a long write-up in https://maskray.me/blog/2021-05-09-fno-semantic= -interposition#in-action=0A= =0A= Well if changing the default of fPIC is unacceptable in GCC, adding a new o= ption=0A= should help LLVM too since it could imply more than -fno-semantic-interposi= tion.=0A= A key question is whether we could require that exported symbols are marked= =0A= explicitly so that we only emit GOT and PLT indirections on such exported s= ymbols.=0A= =0A= Cheers,=0A= Wilco=