sysdeps/aarch64/tlsdesc.c

   1 /* Manage TLS descriptors.  AArch64 version.
   2
   3    Copyright (C) 2011-2015 Free Software Foundation, Inc.
   4
   5    This file is part of the GNU C Library.
   6
   7    The GNU C Library is free software; you can redistribute it and/or
   8    modify it under the terms of the GNU Lesser General Public
   9    License as published by the Free Software Foundation; either
  10    version 2.1 of the License, or (at your option) any later version.
  11
  12    The GNU C Library is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15    Lesser General Public License for more details.
  16
  17    You should have received a copy of the GNU Lesser General Public
  18    License along with the GNU C Library; if not, see
  19    <http://www.gnu.org/licenses/>.  */
  20
  21 #include <link.h>
  22 #include <ldsodefs.h>
  23 #include <elf/dynamic-link.h>
  24 #include <tls.h>
  25 #include <dl-tlsdesc.h>
  26 #include <dl-unmap-segments.h>
  27 #include <tlsdeschtab.h>
  28
  29 /* The following functions take an entry_check_offset argument.  It's
  30    computed by the caller as an offset between its entry point and the
  31    call site, such that by adding the built-in return address that is
  32    implicitly passed to the function with this offset, we can easily
  33    obtain the caller's entry point to compare with the entry point
  34    given in the TLS descriptor.  If it's changed, we want to return
  35    immediately.  */
  36
  37 /* This function is used to lazily resolve TLS_DESC RELA relocations.
  38    The argument location is used to hold a pointer to the relocation.  */
  39
  40 void
  41 attribute_hidden
  42 _dl_tlsdesc_resolve_rela_fixup (struct tlsdesc volatile *td,
  43                                 struct link_map *l)
  44 {
  45   const ElfW(Rela) *reloc = td->arg;
  46
  47   if (_dl_tlsdesc_resolve_early_return_p
  48       (td, (void*)(D_PTR (l, l_info[ADDRIDX (DT_TLSDESC_PLT)]) + l->l_addr)))
  49     return;
  50
  51   /* The code below was borrowed from _dl_fixup(),
  52      except for checking for STB_LOCAL.  */
  53   const ElfW(Sym) *const symtab
  54     = (const void *) D_PTR (l, l_info[DT_SYMTAB]);
  55   const char *strtab = (const void *) D_PTR (l, l_info[DT_STRTAB]);
  56   const ElfW(Sym) *sym = &symtab[ELFW(R_SYM) (reloc->r_info)];
  57   lookup_t result;
  58
  59    /* Look up the target symbol.  If the normal lookup rules are not
  60       used don't look in the global scope.  */
  61   if (ELFW(ST_BIND) (sym->st_info) != STB_LOCAL
  62       && __builtin_expect (ELFW(ST_VISIBILITY) (sym->st_other), 0) == 0)
  63     {
  64       const struct r_found_version *version = NULL;
  65
  66       if (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
  67         {
  68           const ElfW(Half) *vernum =
  69             (const void *) D_PTR (l, l_info[VERSYMIDX (DT_VERSYM)]);
  70           ElfW(Half) ndx = vernum[ELFW(R_SYM) (reloc->r_info)] & 0x7fff;
  71           version = &l->l_versions[ndx];
  72           if (version->hash == 0)
  73             version = NULL;
  74         }
  75
  76       result = _dl_lookup_symbol_x (strtab + sym->st_name, l, &sym,
  77                                     l->l_scope, version, ELF_RTYPE_CLASS_PLT,
  78                                     DL_LOOKUP_ADD_DEPENDENCY, NULL);
  79     }
  80   else
  81     {
  82       /* We already found the symbol.  The module (and therefore its load
  83          address) is also known.  */
  84       result = l;
  85     }
  86
  87   if (!sym)
  88     {
  89       td->arg = (void*) reloc->r_addend;
  90       td->entry = _dl_tlsdesc_undefweak;
  91     }
  92   else
  93     {
  94 #  ifndef SHARED
  95       CHECK_STATIC_TLS (l, result);
  96 #  else
  97       if (!TRY_STATIC_TLS (l, result))
  98         {
  99           td->arg = _dl_make_tlsdesc_dynamic (result, sym->st_value
 100                                               + reloc->r_addend);
 101           td->entry = _dl_tlsdesc_dynamic;
 102         }
 103       else
 104 #  endif
 105         {
 106           td->arg = (void*) (sym->st_value + result->l_tls_offset
 107                              + reloc->r_addend);
 108           td->entry = _dl_tlsdesc_return;
 109         }
 110     }
 111
 112   _dl_tlsdesc_wake_up_held_fixups ();
 113 }
 114
 115 /* This function is used to avoid busy waiting for other threads to
 116    complete the lazy relocation.  Once another thread wins the race to
 117    relocate a TLS descriptor, it sets the descriptor up such that this
 118    function is called to wait until the resolver releases the
 119    lock.  */
 120
 121 void
 122 attribute_hidden
 123 _dl_tlsdesc_resolve_hold_fixup (struct tlsdesc volatile *td,
 124                                 void *caller)
 125 {
 126   /* Maybe we're lucky and can return early.  */
 127   if (caller != td->entry)
 128     return;
 129
 130   /* Locking here will stop execution until the running resolver runs
 131      _dl_tlsdesc_wake_up_held_fixups(), releasing the lock.
 132
 133      FIXME: We'd be better off waiting on a condition variable, such
 134      that we didn't have to hold the lock throughout the relocation
 135      processing.  */
 136   __rtld_lock_lock_recursive (GL(dl_load_lock));
 137   __rtld_lock_unlock_recursive (GL(dl_load_lock));
 138 }
 139
 140
 141 /* Unmap the dynamic object, but also release its TLS descriptor table
 142    if there is one.  */
 143
 144 void
 145 internal_function
 146 _dl_unmap (struct link_map *map)
 147 {
 148   _dl_unmap_segments (map);
 149
 150 #ifdef SHARED
 151   if (map->l_mach.tlsdesc_table)
 152     htab_delete (map->l_mach.tlsdesc_table);
 153 #endif
 154 }