elf/tlsdeschtab.h

   1 /* Hash table for TLS descriptors.
   2    Copyright (C) 2005, 2008 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, write to the Free
  18    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  19    02111-1307 USA.  */
  20
  21 #ifndef TLSDESCHTAB_H
  22 # define TLSDESCHTAB_H 1
  23
  24 # ifdef SHARED
  25
  26 #  include <inline-hashtab.h>
  27
  28 inline static int
  29 hash_tlsdesc (void *p)
  30 {
  31   struct tlsdesc_dynamic_arg *td = p;
  32
  33   /* We know all entries are for the same module, so ti_offset is the
  34      only distinguishing entry.  */
  35   return td->tlsinfo.ti_offset;
  36 }
  37
  38 inline static int
  39 eq_tlsdesc (void *p, void *q)
  40 {
  41   struct tlsdesc_dynamic_arg *tdp = p, *tdq = q;
  42
  43   return tdp->tlsinfo.ti_offset == tdq->tlsinfo.ti_offset;
  44 }
  45
  46 inline static int
  47 map_generation (struct link_map *map)
  48 {
  49   size_t idx = map->l_tls_modid;
  50   struct dtv_slotinfo_list *listp = GL(dl_tls_dtv_slotinfo_list);
  51
  52   /* Find the place in the dtv slotinfo list.  */
  53   do
  54     {
  55       /* Does it fit in the array of this list element?  */
  56       if (idx < listp->len)
  57         {
  58           /* We should never get here for a module in static TLS, so
  59              we can assume that, if the generation count is zero, we
  60              still haven't determined the generation count for this
  61              module.  */
  62           if (listp->slotinfo[idx].gen)
  63             return listp->slotinfo[idx].gen;
  64           else
  65             break;
  66         }
  67       idx -= listp->len;
  68       listp = listp->next;
  69     }
  70   while (listp != NULL);
  71
  72   /* If we get to this point, the module still hasn't been assigned an
  73      entry in the dtv slotinfo data structures, and it will when we're
  74      done with relocations.  At that point, the module will get a
  75      generation number that is one past the current generation, so
  76      return exactly that.  */
  77   return GL(dl_tls_generation) + 1;
  78 }
  79
  80 void *
  81 internal_function
  82 _dl_make_tlsdesc_dynamic (struct link_map *map, size_t ti_offset)
  83 {
  84   struct hashtab *ht;
  85   void **entry;
  86   struct tlsdesc_dynamic_arg *td, test;
  87
  88   /* FIXME: We could use a per-map lock here, but is it worth it?  */
  89   __rtld_lock_lock_recursive (GL(dl_load_lock));
  90
  91   ht = map->l_mach.tlsdesc_table;
  92   if (! ht)
  93     {
  94       ht = htab_create ();
  95       if (! ht)
  96         {
  97           __rtld_lock_unlock_recursive (GL(dl_load_lock));
  98           return 0;
  99         }
 100       map->l_mach.tlsdesc_table = ht;
 101     }
 102
 103   test.tlsinfo.ti_module = map->l_tls_modid;
 104   test.tlsinfo.ti_offset = ti_offset;
 105   entry = htab_find_slot (ht, &test, 1, hash_tlsdesc, eq_tlsdesc);
 106   if (*entry)
 107     {
 108       td = *entry;
 109       __rtld_lock_unlock_recursive (GL(dl_load_lock));
 110       return td;
 111     }
 112
 113   *entry = td = malloc (sizeof (struct tlsdesc_dynamic_arg));
 114   /* This may be higher than the map's generation, but it doesn't
 115      matter much.  Worst case, we'll have one extra DTV update per
 116      thread.  */
 117   td->gen_count = map_generation (map);
 118   td->tlsinfo = test.tlsinfo;
 119
 120   __rtld_lock_unlock_recursive (GL(dl_load_lock));
 121   return td;
 122 }
 123
 124 # endif /* SHARED */
 125
 126 /* The idea of the following two functions is to stop multiple threads
 127    from attempting to resolve the same TLS descriptor without busy
 128    waiting.  Ideally, we should be able to release the lock right
 129    after changing td->entry, and then using say a condition variable
 130    or a futex wake to wake up any waiting threads, but let's try to
 131    avoid introducing such dependencies.  */
 132
 133 inline static int
 134 _dl_tlsdesc_resolve_early_return_p (struct tlsdesc volatile *td, void *caller)
 135 {
 136   if (caller != td->entry)
 137     return 1;
 138
 139   __rtld_lock_lock_recursive (GL(dl_load_lock));
 140   if (caller != td->entry)
 141     {
 142       __rtld_lock_unlock_recursive (GL(dl_load_lock));
 143       return 1;
 144     }
 145
 146   td->entry = _dl_tlsdesc_resolve_hold;
 147
 148   return 0;
 149 }
 150
 151 inline static void
 152 _dl_tlsdesc_wake_up_held_fixups (void)
 153 {
 154   __rtld_lock_unlock_recursive (GL(dl_load_lock));
 155 }
 156
 157 #endif