1 /* Resolve function pointers to VDSO functions. 2 Copyright (C) 2005-2021 Free Software Foundation, Inc. 3 This file is part of the GNU C Library. 4 5 The GNU C Library is free software; you can redistribute it and/or 6 modify it under the terms of the GNU Lesser General Public 7 License as published by the Free Software Foundation; either 8 version 2.1 of the License, or (at your option) any later version. 9 10 The GNU C Library is distributed in the hope that it will be useful, 11 but WITHOUT ANY WARRANTY; without even the implied warranty of 12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 13 Lesser General Public License for more details. 14 15 You should have received a copy of the GNU Lesser General Public 16 License along with the GNU C Library; if not, see 17 <https://www.gnu.org/licenses/>. */ 18 19 20 #ifndef _LIBC_POWERPC_VDSO_H 21 #define _LIBC_POWERPC_VDSO_H 22 23 #include <sysdep.h> 24 #include <sysdep-vdso.h> 25 26 #if (defined(__PPC64__) || defined(__powerpc64__)) && _CALL_ELF != 2 27 # include <dl-funcdesc.h> 28 /* The correct solution is for _dl_vdso_vsym to return the address of the OPD 29 for the kernel VDSO function. That address would then be stored in the 30 __vdso_* variables and returned as the result of the IFUNC resolver function. 31 Yet, the kernel does not contain any OPD entries for the VDSO functions 32 (incomplete implementation). However, PLT relocations for IFUNCs still expect 33 the address of an OPD to be returned from the IFUNC resolver function (since 34 PLT entries on PPC64 are just copies of OPDs). The solution for now is to 35 create an artificial static OPD for each VDSO function returned by a resolver 36 function. The TOC value is set to a non-zero value to avoid triggering lazy 37 symbol resolution via .glink0/.plt0 for a zero TOC (requires thread-safe PLT 38 sequences) when the dynamic linker isn't prepared for it e.g. RTLD_NOW. None 39 of the kernel VDSO routines use the TOC or AUX values so any non-zero value 40 will work. Note that function pointer comparisons will not use this artificial 41 static OPD since those are resolved via ADDR64 relocations and will point at 42 the non-IFUNC default OPD for the symbol. Lastly, because the IFUNC relocations 43 are processed immediately at startup the resolver functions and this code need 44 not be thread-safe, but if the caller writes to a PLT slot it must do so in a 45 thread-safe manner with all the required barriers. */ 46 # define VDSO_IFUNC_RET(value) \ 47 ({ \ 48 static Elf64_FuncDesc vdso_opd = { .fd_toc = ~0x0 }; \ 49 vdso_opd.fd_func = (Elf64_Addr)value; \ 50 &vdso_opd; \ 51 }) 52 53 #else 54 # define VDSO_IFUNC_RET(value) ((void *) (value)) 55 #endif 56 57 #endif /* _LIBC_VDSO_H */ 58