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| 1 | /* Resolve function pointers to VDSO functions. |
|---|---|
| 2 | Copyright (C) 2005-2024 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 |
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