elf/tlsdeschtab.h

   1 /* Hash table for TLS descriptors.
   2    Copyright (C) 2005-2015 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contributed by Alexandre Oliva  <aoliva@redhat.com>
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; if not, see
  18    <http://www.gnu.org/licenses/>.  */
  19
  20 #ifndef TLSDESCHTAB_H
  21 # define TLSDESCHTAB_H 1
  22
  23 # ifdef SHARED
  24
  25 #  include <inline-hashtab.h>
  26
  27 inline static int
  28 hash_tlsdesc (void *p)
  29 {
  30   struct tlsdesc_dynamic_arg *td = p;
  31
  32   /* We know all entries are for the same module, so ti_offset is the
  33      only distinguishing entry.  */
  34   return td->tlsinfo.ti_offset;
  35 }
  36
  37 inline static int
  38 eq_tlsdesc (void *p, void *q)
  39 {
  40   struct tlsdesc_dynamic_arg *tdp = p, *tdq = q;
  41
  42   return tdp->tlsinfo.ti_offset == tdq->tlsinfo.ti_offset;
  43 }
  44
  45 inline static int
  46 map_generation (struct link_map *map)
  47 {
  48   size_t idx = map->l_tls_modid;
  49   struct dtv_slotinfo_list *listp = GL(dl_tls_dtv_slotinfo_list);
  50
  51   /* Find the place in the dtv slotinfo list.  */
  52   do
  53     {
  54       /* Does it fit in the array of this list element?  */
  55       if (idx < listp->len)
  56         {
  57           /* We should never get here for a module in static TLS, so
  58              we can assume that, if the generation count is zero, we
  59              still haven't determined the generation count for this
  60              module.  */
  61           if (listp->slotinfo[idx].gen)
  62             return listp->slotinfo[idx].gen;
  63           else
  64             break;
  65         }
  66       idx -= listp->len;
  67       listp = listp->next;
  68     }
  69   while (listp != NULL);
  70
  71   /* If we get to this point, the module still hasn't been assigned an
  72      entry in the dtv slotinfo data structures, and it will when we're
  73      done with relocations.  At that point, the module will get a
  74      generation number that is one past the current generation, so
  75      return exactly that.  */
  76   return GL(dl_tls_generation) + 1;
  77 }
  78
  79 void *
  80 internal_function
  81 _dl_make_tlsdesc_dynamic (struct link_map *map, size_t ti_offset)
  82 {
  83   struct hashtab *ht;
  84   void **entry;
  85   struct tlsdesc_dynamic_arg *td, test;
  86
  87   /* FIXME: We could use a per-map lock here, but is it worth it?  */
  88   __rtld_lock_lock_recursive (GL(dl_load_lock));
  89
  90   ht = map->l_mach.tlsdesc_table;
  91   if (! ht)
  92     {
  93       ht = htab_create ();
  94       if (! ht)
  95         {
  96           __rtld_lock_unlock_recursive (GL(dl_load_lock));
  97           return 0;
  98         }
  99       map->l_mach.tlsdesc_table = ht;
 100     }
 101
 102   test.tlsinfo.ti_module = map->l_tls_modid;
 103   test.tlsinfo.ti_offset = ti_offset;
 104   entry = htab_find_slot (ht, &test, 1, hash_tlsdesc, eq_tlsdesc);
 105   if (! entry)
 106     {
 107       __rtld_lock_unlock_recursive (GL(dl_load_lock));
 108       return 0;
 109     }
 110
 111   if (*entry)
 112     {
 113       td = *entry;
 114       __rtld_lock_unlock_recursive (GL(dl_load_lock));
 115       return td;
 116     }
 117
 118   *entry = td = malloc (sizeof (struct tlsdesc_dynamic_arg));
 119   /* This may be higher than the map's generation, but it doesn't
 120      matter much.  Worst case, we'll have one extra DTV update per
 121      thread.  */
 122   td->gen_count = map_generation (map);
 123   td->tlsinfo = test.tlsinfo;
 124
 125   __rtld_lock_unlock_recursive (GL(dl_load_lock));
 126   return td;
 127 }
 128
 129 # endif /* SHARED */
 130
 131 /* The idea of the following two functions is to stop multiple threads
 132    from attempting to resolve the same TLS descriptor without busy
 133    waiting.  Ideally, we should be able to release the lock right
 134    after changing td->entry, and then using say a condition variable
 135    or a futex wake to wake up any waiting threads, but let's try to
 136    avoid introducing such dependencies.  */
 137
 138 static int
 139 _dl_tlsdesc_resolve_early_return_p (struct tlsdesc volatile *td, void *caller)
 140 {
 141   if (caller != td->entry)
 142     return 1;
 143
 144   __rtld_lock_lock_recursive (GL(dl_load_lock));
 145   if (caller != td->entry)
 146     {
 147       __rtld_lock_unlock_recursive (GL(dl_load_lock));
 148       return 1;
 149     }
 150
 151   td->entry = _dl_tlsdesc_resolve_hold;
 152
 153   return 0;
 154 }
 155
 156 static void
 157 _dl_tlsdesc_wake_up_held_fixups (void)
 158 {
 159   __rtld_lock_unlock_recursive (GL(dl_load_lock));
 160 }
 161
 162 #endif