1  /* Resolve function pointers to VDSO functions.
       2     Copyright (C) 2005-2023 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 */