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Lu" , Wilco Dijkstra via Libc-alpha , Szabolcs Nagy Subject: Re: [PATCH 2/3] Revert "[AArch64][BZ #17711] Fix extern protected data handling" Thread-Topic: [PATCH 2/3] Revert "[AArch64][BZ #17711] Fix extern protected data handling" Thread-Index: AQHYb3AQ5vf+RU34WECR0bcI7jSh4q0uk9gAgAE6UOaAABuQDoAAJ+oAgAFzTuWAAAkQt4AAA4r8 Date: Thu, 26 May 2022 20:03:02 +0000 Message-ID: References: <87mtf5wk0k.fsf@oldenburg.str.redhat.com> <8735gwhz9i.fsf@oldenburg.str.redhat.com> In-Reply-To: <8735gwhz9i.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-Office365-Filtering-Correlation-Id: 15e3c0b7-07f0-4df0-e42c-08da3f52c83a x-ms-traffictypediagnostic: VI1PR0801MB1728:EE_|VE1EUR03FT044:EE_|VI1PR08MB3328:EE_ X-Microsoft-Antispam-PRVS: 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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}=0A= int main(void) { return f(); }=0A= =0A= compile with -O2 -fPIC -flto -shared:=0A= =0A= 00000000000004f0 :=0A= =A04f0: =A0 b0000090 =A0 =A0 =A0 =A0adrp =A0 =A0x16, 11000 <__cxa_finalize@= GLIBC_2.17>=0A= =A04f4: =A0 f9400611 =A0 =A0 =A0 =A0ldr =A0 =A0 x17, [x16, #8]=0A= =A04f8: =A0 91002210 =A0 =A0 =A0 =A0add =A0 =A0 x16, x16, #0x8=0A= =A04fc: =A0 d61f0220 =A0 =A0 =A0 =A0br =A0 =A0 =A0x17=0A= =0A= 0000000000000510
:=0A= =A0510: =A0 17fffff8 =A0 =A0 =A0 =A0b =A0 =A0 =A0 4f0 =0A= =0A= 0000000000000600 :=0A= =A0600: =A0 90000081 =A0 =A0 =A0 =A0adrp =A0 =A0x1, 10000 <__FRAME_END__+0x= f8f8>=0A= =A0604: =A0 f947e821 =A0 =A0 =A0 =A0ldr =A0 =A0 x1, [x1, #4048]=0A= =A0608: =A0 b9400020 =A0 =A0 =A0 =A0ldr =A0 =A0 w0, [x1]=0A= =A060c: =A0 11000400 =A0 =A0 =A0 =A0add =A0 =A0 w0, w0, #0x1=0A= =A0610: =A0 b9000020 =A0 =A0 =A0 =A0str =A0 =A0 w0, [x1]=0A= =A0614: =A0 d65f03c0 =A0 =A0 =A0 =A0ret=0A= =0A= So f() does not get inlined into main, it is redirected via PLT, and it use= s a GOT=0A= indirection to access the global. The underlying problem is that ELF assume= s by=0A= default that you want interposition/export for all symbols. In reality that= is=0A= almost never needed. LLVM makes -fno-semantic-interposition the default,=0A= which solves the PLT and inlining issue, but not the unnecessary GOT indire= ctions.=0A= =0A= Cheers,=0A= Wilco=