ports/sysdeps/aarch64/tlsdesc.c

   1 /* Manage TLS descriptors.  AArch64 version.
   2
   3    Copyright (C) 2011-2012 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 <tlsdeschtab.h>
  27
  28 /* The following functions take an entry_check_offset argument.  It's
  29    computed by the caller as an offset between its entry point and the
  30    call site, such that by adding the built-in return address that is
  31    implicitly passed to the function with this offset, we can easily
  32    obtain the caller's entry point to compare with the entry point
  33    given in the TLS descriptor.  If it's changed, we want to return
  34    immediately.  */
  35
  36 /* This function is used to lazily resolve TLS_DESC RELA relocations.
  37    The argument location is used to hold a pointer to the relocation.  */
  38
  39 void
  40 attribute_hidden
  41 _dl_tlsdesc_resolve_rela_fixup (struct tlsdesc volatile *td,
  42                                 struct link_map *l)
  43 {
  44   const ElfW(Rela) *reloc = td->arg;
  45
  46   if (_dl_tlsdesc_resolve_early_return_p
  47       (td, (void*)(D_PTR (l, l_info[ADDRIDX (DT_TLSDESC_PLT)]) + l->l_addr)))
  48     return;
  49
  50   /* The code below was borrowed from _dl_fixup(),
  51      except for checking for STB_LOCAL.  */
  52   const ElfW(Sym) *const symtab
  53     = (const void *) D_PTR (l, l_info[DT_SYMTAB]);
  54   const char *strtab = (const void *) D_PTR (l, l_info[DT_STRTAB]);
  55   const ElfW(Sym) *sym = &symtab[ELFW(R_SYM) (reloc->r_info)];
  56   lookup_t result;
  57
  58    /* Look up the target symbol.  If the normal lookup rules are not
  59       used don't look in the global scope.  */
  60   if (ELFW(ST_BIND) (sym->st_info) != STB_LOCAL
  61       && __builtin_expect (ELFW(ST_VISIBILITY) (sym->st_other), 0) == 0)
  62     {
  63       const struct r_found_version *version = NULL;
  64
  65       if (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
  66         {
  67           const ElfW(Half) *vernum =
  68             (const void *) D_PTR (l, l_info[VERSYMIDX (DT_VERSYM)]);
  69           ElfW(Half) ndx = vernum[ELFW(R_SYM) (reloc->r_info)] & 0x7fff;
  70           version = &l->l_versions[ndx];
  71           if (version->hash == 0)
  72             version = NULL;
  73         }
  74
  75       result = _dl_lookup_symbol_x (strtab + sym->st_name, l, &sym,
  76                                     l->l_scope, version, ELF_RTYPE_CLASS_PLT,
  77                                     DL_LOOKUP_ADD_DEPENDENCY, NULL);
  78     }
  79   else
  80     {
  81       /* We already found the symbol.  The module (and therefore its load
  82          address) is also known.  */
  83       result = l;
  84     }
  85
  86   if (!sym)
  87     {
  88       td->arg = (void*) reloc->r_addend;
  89       td->entry = _dl_tlsdesc_undefweak;
  90     }
  91   else
  92     {
  93 #  ifndef SHARED
  94       CHECK_STATIC_TLS (l, result);
  95 #  else
  96       if (!TRY_STATIC_TLS (l, result))
  97         {
  98           td->arg = _dl_make_tlsdesc_dynamic (result, sym->st_value
  99                                               + reloc->r_addend);
 100           td->entry = _dl_tlsdesc_dynamic;
 101         }
 102       else
 103 #  endif
 104         {
 105           td->arg = (void*) (sym->st_value + result->l_tls_offset
 106                              + reloc->r_addend);
 107           td->entry = _dl_tlsdesc_return;
 108         }
 109     }
 110
 111   _dl_tlsdesc_wake_up_held_fixups ();
 112 }
 113
 114 /* This function is used to avoid busy waiting for other threads to
 115    complete the lazy relocation.  Once another thread wins the race to
 116    relocate a TLS descriptor, it sets the descriptor up such that this
 117    function is called to wait until the resolver releases the
 118    lock.  */
 119
 120 void
 121 attribute_hidden
 122 _dl_tlsdesc_resolve_hold_fixup (struct tlsdesc volatile *td,
 123                                 void *caller)
 124 {
 125   /* Maybe we're lucky and can return early.  */
 126   if (caller != td->entry)
 127     return;
 128
 129   /* Locking here will stop execution until the running resolver runs
 130      _dl_tlsdesc_wake_up_held_fixups(), releasing the lock.
 131
 132      FIXME: We'd be better off waiting on a condition variable, such
 133      that we didn't have to hold the lock throughout the relocation
 134      processing.  */
 135   __rtld_lock_lock_recursive (GL(dl_load_lock));
 136   __rtld_lock_unlock_recursive (GL(dl_load_lock));
 137 }
 138
 139
 140 /* Unmap the dynamic object, but also release its TLS descriptor table
 141    if there is one.  */
 142
 143 void
 144 internal_function
 145 _dl_unmap (struct link_map *map)
 146 {
 147   __munmap ((void *) (map)->l_map_start,
 148             (map)->l_map_end - (map)->l_map_start);
 149
 150 #if SHARED
 151   if (map->l_mach.tlsdesc_table)
 152     htab_delete (map->l_mach.tlsdesc_table);
 153 #endif
 154 }