sysdeps/i386/tlsdesc.c

   1 /* Manage TLS descriptors.  i386 version.
   2    Copyright (C) 2005-2020 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 #include <link.h>
  20 #include <ldsodefs.h>
  21 #include <elf/dynamic-link.h>
  22 #include <tls.h>
  23 #include <dl-tlsdesc.h>
  24 #include <dl-unmap-segments.h>
  25 #include <tlsdeschtab.h>
  26
  27 /* The following 4 functions take an entry_check_offset argument.
  28    It's computed by the caller as an offset between its entry point
  29    and the call site, such that by adding the built-in return address
  30    that is implicitly passed to the function with this offset, we can
  31    easily obtain the caller's entry point to compare with the entry
  32    point given in the TLS descriptor.  If it's changed, we want to
  33    return immediately.  */
  34
  35 /* This function is used to lazily resolve TLS_DESC REL relocations
  36    that reference the *ABS* segment in their own link maps.  The
  37    argument is the addend originally stored there.  */
  38
  39 void
  40 __attribute__ ((regparm (3))) attribute_hidden
  41 _dl_tlsdesc_resolve_abs_plus_addend_fixup (struct tlsdesc volatile *td,
  42                                            struct link_map *l,
  43                                            ptrdiff_t entry_check_offset)
  44 {
  45   ptrdiff_t addend = (ptrdiff_t) td->arg;
  46
  47   if (_dl_tlsdesc_resolve_early_return_p (td, __builtin_return_address (0)
  48                                           - entry_check_offset))
  49     return;
  50
  51 #ifndef SHARED
  52   CHECK_STATIC_TLS (l, l);
  53 #else
  54   if (!TRY_STATIC_TLS (l, l))
  55     {
  56       td->arg = _dl_make_tlsdesc_dynamic (l, addend);
  57       td->entry = _dl_tlsdesc_dynamic;
  58     }
  59   else
  60 #endif
  61     {
  62       td->arg = (void*) (addend - l->l_tls_offset);
  63       td->entry = _dl_tlsdesc_return;
  64     }
  65
  66   _dl_tlsdesc_wake_up_held_fixups ();
  67 }
  68
  69 /* This function is used to lazily resolve TLS_DESC REL relocations
  70    that originally had zero addends.  The argument location, that
  71    originally held the addend, is used to hold a pointer to the
  72    relocation, but it has to be restored before we call the function
  73    that applies relocations.  */
  74
  75 void
  76 __attribute__ ((regparm (3))) attribute_hidden
  77 _dl_tlsdesc_resolve_rel_fixup (struct tlsdesc volatile *td,
  78                                struct link_map *l,
  79                                ptrdiff_t entry_check_offset)
  80 {
  81   const ElfW(Rel) *reloc = td->arg;
  82
  83   if (_dl_tlsdesc_resolve_early_return_p (td, __builtin_return_address (0)
  84                                           - entry_check_offset))
  85     return;
  86
  87   /* The code below was borrowed from _dl_fixup(),
  88      except for checking for STB_LOCAL.  */
  89   const ElfW(Sym) *const symtab
  90     = (const void *) D_PTR (l, l_info[DT_SYMTAB]);
  91   const char *strtab = (const void *) D_PTR (l, l_info[DT_STRTAB]);
  92   const ElfW(Sym) *sym = &symtab[ELFW(R_SYM) (reloc->r_info)];
  93   lookup_t result;
  94
  95    /* Look up the target symbol.  If the normal lookup rules are not
  96       used don't look in the global scope.  */
  97   if (ELFW(ST_BIND) (sym->st_info) != STB_LOCAL
  98       && __builtin_expect (ELFW(ST_VISIBILITY) (sym->st_other), 0) == 0)
  99     {
 100       const struct r_found_version *version = NULL;
 101
 102       if (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
 103         {
 104           const ElfW(Half) *vernum =
 105             (const void *) D_PTR (l, l_info[VERSYMIDX (DT_VERSYM)]);
 106           ElfW(Half) ndx = vernum[ELFW(R_SYM) (reloc->r_info)] & 0x7fff;
 107           version = &l->l_versions[ndx];
 108           if (version->hash == 0)
 109             version = NULL;
 110         }
 111
 112       result = _dl_lookup_symbol_x (strtab + sym->st_name, l, &sym,
 113                                     l->l_scope, version, ELF_RTYPE_CLASS_PLT,
 114                                     DL_LOOKUP_ADD_DEPENDENCY, NULL);
 115     }
 116   else
 117     {
 118       /* We already found the symbol.  The module (and therefore its load
 119          address) is also known.  */
 120       result = l;
 121     }
 122
 123   if (!sym)
 124     {
 125       td->arg = 0;
 126       td->entry = _dl_tlsdesc_undefweak;
 127     }
 128   else
 129     {
 130 #  ifndef SHARED
 131       CHECK_STATIC_TLS (l, result);
 132 #  else
 133       if (!TRY_STATIC_TLS (l, result))
 134         {
 135           td->arg = _dl_make_tlsdesc_dynamic (result, sym->st_value);
 136           td->entry = _dl_tlsdesc_dynamic;
 137         }
 138       else
 139 #  endif
 140         {
 141           td->arg = (void*)(sym->st_value - result->l_tls_offset);
 142           td->entry = _dl_tlsdesc_return;
 143         }
 144     }
 145
 146   _dl_tlsdesc_wake_up_held_fixups ();
 147 }
 148
 149 /* This function is used to lazily resolve TLS_DESC RELA relocations.
 150    The argument location is used to hold a pointer to the relocation.  */
 151
 152 void
 153 __attribute__ ((regparm (3))) attribute_hidden
 154 _dl_tlsdesc_resolve_rela_fixup (struct tlsdesc volatile *td,
 155                                 struct link_map *l,
 156                                 ptrdiff_t entry_check_offset)
 157 {
 158   const ElfW(Rela) *reloc = td->arg;
 159
 160   if (_dl_tlsdesc_resolve_early_return_p (td, __builtin_return_address (0)
 161                                           - entry_check_offset))
 162     return;
 163
 164   /* The code below was borrowed from _dl_fixup(),
 165      except for checking for STB_LOCAL.  */
 166   const ElfW(Sym) *const symtab
 167     = (const void *) D_PTR (l, l_info[DT_SYMTAB]);
 168   const char *strtab = (const void *) D_PTR (l, l_info[DT_STRTAB]);
 169   const ElfW(Sym) *sym = &symtab[ELFW(R_SYM) (reloc->r_info)];
 170   lookup_t result;
 171
 172    /* Look up the target symbol.  If the normal lookup rules are not
 173       used don't look in the global scope.  */
 174   if (ELFW(ST_BIND) (sym->st_info) != STB_LOCAL
 175       && __builtin_expect (ELFW(ST_VISIBILITY) (sym->st_other), 0) == 0)
 176     {
 177       const struct r_found_version *version = NULL;
 178
 179       if (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
 180         {
 181           const ElfW(Half) *vernum =
 182             (const void *) D_PTR (l, l_info[VERSYMIDX (DT_VERSYM)]);
 183           ElfW(Half) ndx = vernum[ELFW(R_SYM) (reloc->r_info)] & 0x7fff;
 184           version = &l->l_versions[ndx];
 185           if (version->hash == 0)
 186             version = NULL;
 187         }
 188
 189       result = _dl_lookup_symbol_x (strtab + sym->st_name, l, &sym,
 190                                     l->l_scope, version, ELF_RTYPE_CLASS_PLT,
 191                                     DL_LOOKUP_ADD_DEPENDENCY, NULL);
 192     }
 193   else
 194     {
 195       /* We already found the symbol.  The module (and therefore its load
 196          address) is also known.  */
 197       result = l;
 198     }
 199
 200   if (!sym)
 201     {
 202       td->arg = (void*) reloc->r_addend;
 203       td->entry = _dl_tlsdesc_undefweak;
 204     }
 205   else
 206     {
 207 #  ifndef SHARED
 208       CHECK_STATIC_TLS (l, result);
 209 #  else
 210       if (!TRY_STATIC_TLS (l, result))
 211         {
 212           td->arg = _dl_make_tlsdesc_dynamic (result, sym->st_value
 213                                               + reloc->r_addend);
 214           td->entry = _dl_tlsdesc_dynamic;
 215         }
 216       else
 217 #  endif
 218         {
 219           td->arg = (void*) (sym->st_value - result->l_tls_offset
 220                              + reloc->r_addend);
 221           td->entry = _dl_tlsdesc_return;
 222         }
 223     }
 224
 225   _dl_tlsdesc_wake_up_held_fixups ();
 226 }
 227
 228 /* This function is used to avoid busy waiting for other threads to
 229    complete the lazy relocation.  Once another thread wins the race to
 230    relocate a TLS descriptor, it sets the descriptor up such that this
 231    function is called to wait until the resolver releases the
 232    lock.  */
 233
 234 void
 235 __attribute__ ((regparm (3))) attribute_hidden
 236 _dl_tlsdesc_resolve_hold_fixup (struct tlsdesc volatile *td,
 237                                 struct link_map *l __attribute__((__unused__)),
 238                                 ptrdiff_t entry_check_offset)
 239 {
 240   /* Maybe we're lucky and can return early.  */
 241   if (__builtin_return_address (0) - entry_check_offset != td->entry)
 242     return;
 243
 244   /* Locking here will stop execution until the running resolver runs
 245      _dl_tlsdesc_wake_up_held_fixups(), releasing the lock.
 246
 247      FIXME: We'd be better off waiting on a condition variable, such
 248      that we didn't have to hold the lock throughout the relocation
 249      processing.  */
 250   __rtld_lock_lock_recursive (GL(dl_load_lock));
 251   __rtld_lock_unlock_recursive (GL(dl_load_lock));
 252 }
 253
 254
 255 /* Unmap the dynamic object, but also release its TLS descriptor table
 256    if there is one.  */
 257
 258 void
 259 _dl_unmap (struct link_map *map)
 260 {
 261   _dl_unmap_segments (map);
 262
 263 #ifdef SHARED
 264   if (map->l_mach.tlsdesc_table)
 265     htab_delete (map->l_mach.tlsdesc_table);
 266 #endif
 267 }