sysdeps/x86_64/tlsdesc.c

   1 /* Manage TLS descriptors.  x86_64 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 2 functions take a caller argument, that contains the
  27    address expected to be in the TLS descriptor.  If it's changed, we
  28    want to return immediately.  */
  29
  30 /* This function is used to lazily resolve TLS_DESC RELA relocations.
  31    The argument location is used to hold a pointer to the relocation.  */
  32
  33 void
  34 attribute_hidden
  35 _dl_tlsdesc_resolve_rela_fixup (struct tlsdesc volatile *td,
  36                                 struct link_map *l)
  37 {
  38   const ElfW(Rela) *reloc = td->arg;
  39
  40   if (_dl_tlsdesc_resolve_early_return_p
  41       (td, (void*)(D_PTR (l, l_info[ADDRIDX (DT_TLSDESC_PLT)]) + l->l_addr)))
  42     return;
  43
  44   /* The code below was borrowed from _dl_fixup().  */
  45   const ElfW(Sym) *const symtab
  46     = (const void *) D_PTR (l, l_info[DT_SYMTAB]);
  47   const char *strtab = (const void *) D_PTR (l, l_info[DT_STRTAB]);
  48   const ElfW(Sym) *sym = &symtab[ELFW(R_SYM) (reloc->r_info)];
  49   lookup_t result;
  50
  51    /* Look up the target symbol.  If the normal lookup rules are not
  52       used don't look in the global scope.  */
  53   if (ELFW(ST_BIND) (sym->st_info) != STB_LOCAL
  54       && __builtin_expect (ELFW(ST_VISIBILITY) (sym->st_other), 0) == 0)
  55     {
  56       const struct r_found_version *version = NULL;
  57
  58       if (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
  59         {
  60           const ElfW(Half) *vernum =
  61             (const void *) D_PTR (l, l_info[VERSYMIDX (DT_VERSYM)]);
  62           ElfW(Half) ndx = vernum[ELFW(R_SYM) (reloc->r_info)] & 0x7fff;
  63           version = &l->l_versions[ndx];
  64           if (version->hash == 0)
  65             version = NULL;
  66         }
  67
  68       result = _dl_lookup_symbol_x (strtab + sym->st_name, l, &sym,
  69                                     l->l_scope, version, ELF_RTYPE_CLASS_PLT,
  70                                     DL_LOOKUP_ADD_DEPENDENCY, NULL);
  71     }
  72   else
  73     {
  74       /* We already found the symbol.  The module (and therefore its load
  75          address) is also known.  */
  76       result = l;
  77     }
  78
  79   if (! sym)
  80     {
  81       td->arg = (void*)reloc->r_addend;
  82       td->entry = _dl_tlsdesc_undefweak;
  83     }
  84   else
  85     {
  86 #  ifndef SHARED
  87       CHECK_STATIC_TLS (l, result);
  88 #  else
  89       if (!TRY_STATIC_TLS (l, result))
  90         {
  91           td->arg = _dl_make_tlsdesc_dynamic (result, sym->st_value
  92                                               + reloc->r_addend);
  93           td->entry = _dl_tlsdesc_dynamic;
  94         }
  95       else
  96 #  endif
  97         {
  98           td->arg = (void*)(sym->st_value - result->l_tls_offset
  99                             + reloc->r_addend);
 100           td->entry = _dl_tlsdesc_return;
 101         }
 102     }
 103
 104   _dl_tlsdesc_wake_up_held_fixups ();
 105 }
 106
 107 /* This function is used to avoid busy waiting for other threads to
 108    complete the lazy relocation.  Once another thread wins the race to
 109    relocate a TLS descriptor, it sets the descriptor up such that this
 110    function is called to wait until the resolver releases the
 111    lock.  */
 112
 113 void
 114 attribute_hidden
 115 _dl_tlsdesc_resolve_hold_fixup (struct tlsdesc volatile *td,
 116                                 void *caller)
 117 {
 118   /* Maybe we're lucky and can return early.  */
 119   if (caller != td->entry)
 120     return;
 121
 122   /* Locking here will stop execution until the running resolver runs
 123      _dl_tlsdesc_wake_up_held_fixups(), releasing the lock.
 124
 125      FIXME: We'd be better off waiting on a condition variable, such
 126      that we didn't have to hold the lock throughout the relocation
 127      processing.  */
 128   __rtld_lock_lock_recursive (GL(dl_load_lock));
 129   __rtld_lock_unlock_recursive (GL(dl_load_lock));
 130 }
 131
 132 /* Unmap the dynamic object, but also release its TLS descriptor table
 133    if there is one.  */
 134
 135 void
 136 internal_function
 137 _dl_unmap (struct link_map *map)
 138 {
 139   __munmap ((void *) (map)->l_map_start,
 140             (map)->l_map_end - (map)->l_map_start);
 141
 142 #if SHARED
 143   /* _dl_unmap is only called for dlopen()ed libraries, for which
 144      calling free() is safe, or before we've completed the initial
 145      relocation, in which case calling free() is probably pointless,
 146      but still safe.  */
 147   if (map->l_mach.tlsdesc_table)
 148     htab_delete (map->l_mach.tlsdesc_table);
 149 #endif
 150 }