sysdeps/unix/sysv/linux/dl-vdso.h

   1 /* ELF symbol resolve functions for VDSO objects.
   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 #ifndef _DL_VDSO_H
  20 #define _DL_VDSO_H      1
  21
  22 #include <ldsodefs.h>
  23 #include <dl-hash.h>
  24
  25 /* If the architecture support vDSO it should define which is the expected
  26    kernel version and hash value through both VDSO_NAME and VDSO_HASH
  27    (usually defined at architecture sysdep.h).  */
  28
  29 #ifndef VDSO_NAME
  30 # define VDSO_NAME "LINUX_0.0"
  31 #endif
  32 #ifndef VDSO_HASH
  33 # define VDSO_HASH 0
  34 #endif
  35
  36 /* Functions for resolving symbols in the VDSO link map.  */
  37 static inline void *
  38 dl_vdso_vsym (const char *name)
  39 {
  40   struct link_map *map = GLRO (dl_sysinfo_map);
  41   if (map == NULL)
  42     return NULL;
  43
  44   /* Use a WEAK REF so we don't error out if the symbol is not found.  */
  45   ElfW (Sym) wsym = { 0 };
  46   wsym.st_info = (unsigned char) ELFW (ST_INFO (STB_WEAK, STT_NOTYPE));
  47
  48   const struct r_found_version rfv = { VDSO_NAME, VDSO_HASH, 1, NULL };
  49
  50   /* Search the scope of the vdso map.  */
  51   const ElfW (Sym) *ref = &wsym;
  52   lookup_t result = GLRO (dl_lookup_symbol_x) (name, map, &ref,
  53                                                map->l_local_scope,
  54                                                &rfv, 0, 0, NULL);
  55   return ref != NULL ? DL_SYMBOL_ADDRESS (result, ref) : NULL;
  56 }
  57
  58 #endif /* dl-vdso.h */