sysdeps/i386/tlsdesc.c

   1 /* Manage TLS descriptors.  i386 version.
   2    Copyright (C) 2005-2014 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    <http://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 <tlsdeschtab.h>
  25
  26 /* The following 4 functions take an entry_check_offset argument.
  27    It's computed by the caller as an offset between its entry point
  28    and the call site, such that by adding the built-in return address
  29    that is implicitly passed to the function with this offset, we can
  30    easily obtain the caller's entry point to compare with the entry
  31    point given in the TLS descriptor.  If it's changed, we want to
  32    return immediately.  */
  33
  34 /* This function is used to lazily resolve TLS_DESC REL relocations
  35    that reference the *ABS* segment in their own link maps.  The
  36    argument is the addend originally stored there.  */
  37
  38 void
  39 __attribute__ ((regparm (3))) attribute_hidden
  40 _dl_tlsdesc_resolve_abs_plus_addend_fixup (struct tlsdesc volatile *td,
  41                                            struct link_map *l,
  42                                            ptrdiff_t entry_check_offset)
  43 {
  44   ptrdiff_t addend = (ptrdiff_t) td->arg;
  45
  46   if (_dl_tlsdesc_resolve_early_return_p (td, __builtin_return_address (0)
  47                                           - entry_check_offset))
  48     return;
  49
  50 #ifndef SHARED
  51   CHECK_STATIC_TLS (l, l);
  52 #else
  53   if (!TRY_STATIC_TLS (l, l))
  54     {
  55       td->arg = _dl_make_tlsdesc_dynamic (l, addend);
  56       td->entry = _dl_tlsdesc_dynamic;
  57     }
  58   else
  59 #endif
  60     {
  61       td->arg = (void*) (addend - l->l_tls_offset);
  62       td->entry = _dl_tlsdesc_return;
  63     }
  64
  65   _dl_tlsdesc_wake_up_held_fixups ();
  66 }
  67
  68 /* This function is used to lazily resolve TLS_DESC REL relocations
  69    that originally had zero addends.  The argument location, that
  70    originally held the addend, is used to hold a pointer to the
  71    relocation, but it has to be restored before we call the function
  72    that applies relocations.  */
  73
  74 void
  75 __attribute__ ((regparm (3))) attribute_hidden
  76 _dl_tlsdesc_resolve_rel_fixup (struct tlsdesc volatile *td,
  77                                struct link_map *l,
  78                                ptrdiff_t entry_check_offset)
  79 {
  80   const ElfW(Rel) *reloc = td->arg;
  81
  82   if (_dl_tlsdesc_resolve_early_return_p (td, __builtin_return_address (0)
  83                                           - entry_check_offset))
  84     return;
  85
  86   /* The code below was borrowed from _dl_fixup(),
  87      except for checking for STB_LOCAL.  */
  88   const ElfW(Sym) *const symtab
  89     = (const void *) D_PTR (l, l_info[DT_SYMTAB]);
  90   const char *strtab = (const void *) D_PTR (l, l_info[DT_STRTAB]);
  91   const ElfW(Sym) *sym = &symtab[ELFW(R_SYM) (reloc->r_info)];
  92   lookup_t result;
  93
  94    /* Look up the target symbol.  If the normal lookup rules are not
  95       used don't look in the global scope.  */
  96   if (ELFW(ST_BIND) (sym->st_info) != STB_LOCAL
  97       && __builtin_expect (ELFW(ST_VISIBILITY) (sym->st_other), 0) == 0)
  98     {
  99       const struct r_found_version *version = NULL;
 100
 101       if (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
 102         {
 103           const ElfW(Half) *vernum =
 104             (const void *) D_PTR (l, l_info[VERSYMIDX (DT_VERSYM)]);
 105           ElfW(Half) ndx = vernum[ELFW(R_SYM) (reloc->r_info)] & 0x7fff;
 106           version = &l->l_versions[ndx];
 107           if (version->hash == 0)
 108             version = NULL;
 109         }
 110
 111       result = _dl_lookup_symbol_x (strtab + sym->st_name, l, &sym,
 112                                     l->l_scope, version, ELF_RTYPE_CLASS_PLT,
 113                                     DL_LOOKUP_ADD_DEPENDENCY, NULL);
 114     }
 115   else
 116     {
 117       /* We already found the symbol.  The module (and therefore its load
 118          address) is also known.  */
 119       result = l;
 120     }
 121
 122   if (!sym)
 123     {
 124       td->arg = 0;
 125       td->entry = _dl_tlsdesc_undefweak;
 126     }
 127   else
 128     {
 129 #  ifndef SHARED
 130       CHECK_STATIC_TLS (l, result);
 131 #  else
 132       if (!TRY_STATIC_TLS (l, result))
 133         {
 134           td->arg = _dl_make_tlsdesc_dynamic (result, sym->st_value);
 135           td->entry = _dl_tlsdesc_dynamic;
 136         }
 137       else
 138 #  endif
 139         {
 140           td->arg = (void*)(sym->st_value - result->l_tls_offset);
 141           td->entry = _dl_tlsdesc_return;
 142         }
 143     }
 144
 145   _dl_tlsdesc_wake_up_held_fixups ();
 146 }
 147
 148 /* This function is used to lazily resolve TLS_DESC RELA relocations.
 149    The argument location is used to hold a pointer to the relocation.  */
 150
 151 void
 152 __attribute__ ((regparm (3))) attribute_hidden
 153 _dl_tlsdesc_resolve_rela_fixup (struct tlsdesc volatile *td,
 154                                 struct link_map *l,
 155                                 ptrdiff_t entry_check_offset)
 156 {
 157   const ElfW(Rela) *reloc = td->arg;
 158
 159   if (_dl_tlsdesc_resolve_early_return_p (td, __builtin_return_address (0)
 160                                           - entry_check_offset))
 161     return;
 162
 163   /* The code below was borrowed from _dl_fixup(),
 164      except for checking for STB_LOCAL.  */
 165   const ElfW(Sym) *const symtab
 166     = (const void *) D_PTR (l, l_info[DT_SYMTAB]);
 167   const char *strtab = (const void *) D_PTR (l, l_info[DT_STRTAB]);
 168   const ElfW(Sym) *sym = &symtab[ELFW(R_SYM) (reloc->r_info)];
 169   lookup_t result;
 170
 171    /* Look up the target symbol.  If the normal lookup rules are not
 172       used don't look in the global scope.  */
 173   if (ELFW(ST_BIND) (sym->st_info) != STB_LOCAL
 174       && __builtin_expect (ELFW(ST_VISIBILITY) (sym->st_other), 0) == 0)
 175     {
 176       const struct r_found_version *version = NULL;
 177
 178       if (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
 179         {
 180           const ElfW(Half) *vernum =
 181             (const void *) D_PTR (l, l_info[VERSYMIDX (DT_VERSYM)]);
 182           ElfW(Half) ndx = vernum[ELFW(R_SYM) (reloc->r_info)] & 0x7fff;
 183           version = &l->l_versions[ndx];
 184           if (version->hash == 0)
 185             version = NULL;
 186         }
 187
 188       result = _dl_lookup_symbol_x (strtab + sym->st_name, l, &sym,
 189                                     l->l_scope, version, ELF_RTYPE_CLASS_PLT,
 190                                     DL_LOOKUP_ADD_DEPENDENCY, NULL);
 191     }
 192   else
 193     {
 194       /* We already found the symbol.  The module (and therefore its load
 195          address) is also known.  */
 196       result = l;
 197     }
 198
 199   if (!sym)
 200     {
 201       td->arg = (void*) reloc->r_addend;
 202       td->entry = _dl_tlsdesc_undefweak;
 203     }
 204   else
 205     {
 206 #  ifndef SHARED
 207       CHECK_STATIC_TLS (l, result);
 208 #  else
 209       if (!TRY_STATIC_TLS (l, result))
 210         {
 211           td->arg = _dl_make_tlsdesc_dynamic (result, sym->st_value
 212                                               + reloc->r_addend);
 213           td->entry = _dl_tlsdesc_dynamic;
 214         }
 215       else
 216 #  endif
 217         {
 218           td->arg = (void*) (sym->st_value - result->l_tls_offset
 219                              + reloc->r_addend);
 220           td->entry = _dl_tlsdesc_return;
 221         }
 222     }
 223
 224   _dl_tlsdesc_wake_up_held_fixups ();
 225 }
 226
 227 /* This function is used to avoid busy waiting for other threads to
 228    complete the lazy relocation.  Once another thread wins the race to
 229    relocate a TLS descriptor, it sets the descriptor up such that this
 230    function is called to wait until the resolver releases the
 231    lock.  */
 232
 233 void
 234 __attribute__ ((regparm (3))) attribute_hidden
 235 _dl_tlsdesc_resolve_hold_fixup (struct tlsdesc volatile *td,
 236                                 struct link_map *l __attribute__((__unused__)),
 237                                 ptrdiff_t entry_check_offset)
 238 {
 239   /* Maybe we're lucky and can return early.  */
 240   if (__builtin_return_address (0) - entry_check_offset != td->entry)
 241     return;
 242
 243   /* Locking here will stop execution until the running resolver runs
 244      _dl_tlsdesc_wake_up_held_fixups(), releasing the lock.
 245
 246      FIXME: We'd be better off waiting on a condition variable, such
 247      that we didn't have to hold the lock throughout the relocation
 248      processing.  */
 249   __rtld_lock_lock_recursive (GL(dl_load_lock));
 250   __rtld_lock_unlock_recursive (GL(dl_load_lock));
 251 }
 252
 253
 254 /* Unmap the dynamic object, but also release its TLS descriptor table
 255    if there is one.  */
 256
 257 void
 258 internal_function
 259 _dl_unmap (struct link_map *map)
 260 {
 261   __munmap ((void *) (map)->l_map_start,
 262             (map)->l_map_end - (map)->l_map_start);
 263
 264 #if SHARED
 265   if (map->l_mach.tlsdesc_table)
 266     htab_delete (map->l_mach.tlsdesc_table);
 267 #endif
 268 }