ports/sysdeps/arm/tlsdesc.c

   1 /* Manage TLS descriptors.  ARM 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 /* This function is used to lazily resolve TLS_DESC REL relocations
  27    Besides the TLS descriptor itself, we get the module's got address
  28    as the second parameter. */
  29
  30 void
  31 attribute_hidden
  32 _dl_tlsdesc_lazy_resolver_fixup (struct tlsdesc volatile *td,
  33                                  Elf32_Addr *got)
  34 {
  35   struct link_map *l = (struct link_map *)got[1];
  36   lookup_t result;
  37   unsigned long value;
  38
  39   if (_dl_tlsdesc_resolve_early_return_p
  40       (td, (void*)(D_PTR (l, l_info[ADDRIDX (DT_TLSDESC_PLT)]) + l->l_addr)))
  41     return;
  42
  43   if (td->argument.value & 0x80000000)
  44     {
  45       /* A global symbol, this is the symbol index.  */
  46       /* The code below was borrowed from _dl_fixup().  */
  47       const Elf_Symndx symndx = td->argument.value ^ 0x80000000;
  48       const ElfW(Sym) *const symtab
  49         = (const void *) D_PTR (l, l_info[DT_SYMTAB]);
  50       const char *strtab = (const void *) D_PTR (l, l_info[DT_STRTAB]);
  51       const ElfW(Sym) *sym = &symtab[symndx];
  52
  53       /* Look up the target symbol.  If the normal lookup rules are not
  54          used don't look in the global scope.  */
  55       if (ELFW(ST_BIND) (sym->st_info) != STB_LOCAL
  56           && __builtin_expect (ELFW(ST_VISIBILITY) (sym->st_other), 0) == 0)
  57         {
  58           const struct r_found_version *version = NULL;
  59
  60           if (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
  61             {
  62               const ElfW(Half) *vernum =
  63                 (const void *) D_PTR (l, l_info[VERSYMIDX (DT_VERSYM)]);
  64               ElfW(Half) ndx = vernum[symndx] & 0x7fff;
  65               version = &l->l_versions[ndx];
  66               if (version->hash == 0)
  67                 version = NULL;
  68             }
  69
  70           result = _dl_lookup_symbol_x
  71             (strtab + sym->st_name, l, &sym,
  72              l->l_scope, version, ELF_RTYPE_CLASS_PLT,
  73              DL_LOOKUP_ADD_DEPENDENCY, NULL);
  74           if (sym)
  75             value = sym->st_value;
  76           else
  77             {
  78               td->entry = _dl_tlsdesc_undefweak;
  79               goto done;
  80             }
  81         }
  82       else
  83         {
  84           /* We already found the symbol.  The module (and therefore its load
  85              address) is also known.  */
  86           result = l;
  87           value = sym->st_value;
  88         }
  89     }
  90   else
  91     {
  92       /* A local symbol, this is the offset within our tls section.
  93          */
  94       value = td->argument.value;
  95       result = l;
  96     }
  97
  98 #ifndef SHARED
  99   CHECK_STATIC_TLS (l, result);
 100 #else
 101   if (!TRY_STATIC_TLS (l, result))
 102     {
 103       td->argument.pointer = _dl_make_tlsdesc_dynamic (result, value);
 104       td->entry = _dl_tlsdesc_dynamic;
 105     }
 106   else
 107 #endif
 108     {
 109       td->argument.value = value + result->l_tls_offset;
 110       td->entry = _dl_tlsdesc_return;
 111     }
 112
 113  done:
 114   _dl_tlsdesc_wake_up_held_fixups ();
 115 }
 116
 117 /* This function is used to avoid busy waiting for other threads to
 118    complete the lazy relocation.  Once another thread wins the race to
 119    relocate a TLS descriptor, it sets the descriptor up such that this
 120    function is called to wait until the resolver releases the
 121    lock.  */
 122
 123 void
 124 attribute_hidden
 125 _dl_tlsdesc_resolve_hold_fixup (struct tlsdesc volatile *td,
 126                                 void *caller)
 127 {
 128   /* Maybe we're lucky and can return early.  */
 129   if (caller != td->entry)
 130     return;
 131
 132   /* Locking here will stop execution until the running resolver runs
 133      _dl_tlsdesc_wake_up_held_fixups(), releasing the lock.
 134
 135      FIXME: We'd be better off waiting on a condition variable, such
 136      that we didn't have to hold the lock throughout the relocation
 137      processing.  */
 138   __rtld_lock_lock_recursive (GL(dl_load_lock));
 139   __rtld_lock_unlock_recursive (GL(dl_load_lock));
 140 }
 141
 142 /* Unmap the dynamic object, but also release its TLS descriptor table
 143    if there is one.  */
 144
 145 void
 146 internal_function
 147 _dl_unmap (struct link_map *map)
 148 {
 149   __munmap ((void *) (map)->l_map_start,
 150             (map)->l_map_end - (map)->l_map_start);
 151
 152 #if SHARED
 153   /* _dl_unmap is only called for dlopen()ed libraries, for which
 154      calling free() is safe, or before we've completed the initial
 155      relocation, in which case calling free() is probably pointless,
 156      but still safe.  */
 157   if (map->l_mach.tlsdesc_table)
 158     htab_delete (map->l_mach.tlsdesc_table);
 159 #endif
 160 }