elf/tlsdeschtab.h

   1 /* Hash table for TLS descriptors.
   2    Copyright (C) 2005-2021 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    <https://www.gnu.org/licenses/>.  */
  19
  20 #ifndef TLSDESCHTAB_H
  21 # define TLSDESCHTAB_H 1
  22
  23 #include <atomic.h>
  24
  25 # ifdef SHARED
  26
  27 #  include <inline-hashtab.h>
  28
  29 inline static int
  30 hash_tlsdesc (void *p)
  31 {
  32   struct tlsdesc_dynamic_arg *td = p;
  33
  34   /* We know all entries are for the same module, so ti_offset is the
  35      only distinguishing entry.  */
  36   return td->tlsinfo.ti_offset;
  37 }
  38
  39 inline static int
  40 eq_tlsdesc (void *p, void *q)
  41 {
  42   struct tlsdesc_dynamic_arg *tdp = p, *tdq = q;
  43
  44   return tdp->tlsinfo.ti_offset == tdq->tlsinfo.ti_offset;
  45 }
  46
  47 inline static size_t
  48 map_generation (struct link_map *map)
  49 {
  50   size_t idx = map->l_tls_modid;
  51   struct dtv_slotinfo_list *listp = GL(dl_tls_dtv_slotinfo_list);
  52
  53   /* Find the place in the dtv slotinfo list.  */
  54   do
  55     {
  56       /* Does it fit in the array of this list element?  */
  57       if (idx < listp->len)
  58         {
  59           /* We should never get here for a module in static TLS, so
  60              we can assume that, if the generation count is zero, we
  61              still haven't determined the generation count for this
  62              module.  */
  63           if (listp->slotinfo[idx].map == map && listp->slotinfo[idx].gen)
  64             return listp->slotinfo[idx].gen;
  65           else
  66             break;
  67         }
  68       idx -= listp->len;
  69       listp = listp->next;
  70     }
  71   while (listp != NULL);
  72
  73   /* If we get to this point, the module still hasn't been assigned an
  74      entry in the dtv slotinfo data structures, and it will when we're
  75      done with relocations.  At that point, the module will get a
  76      generation number that is one past the current generation, so
  77      return exactly that.  */
  78   return GL(dl_tls_generation) + 1;
  79 }
  80
  81 /* Returns the data pointer for a given map and tls offset that is used
  82    to fill in one of the GOT entries referenced by a TLSDESC relocation
  83    when using dynamic TLS.  This requires allocation, returns NULL on
  84    allocation failure.  */
  85 void *
  86 _dl_make_tlsdesc_dynamic (struct link_map *map, size_t ti_offset)
  87 {
  88   struct hashtab *ht;
  89   void **entry;
  90   struct tlsdesc_dynamic_arg *td, test;
  91
  92   ht = map->l_mach.tlsdesc_table;
  93   if (! ht)
  94     {
  95       ht = htab_create ();
  96       if (! ht)
  97         return 0;
  98       map->l_mach.tlsdesc_table = ht;
  99     }
 100
 101   test.tlsinfo.ti_module = map->l_tls_modid;
 102   test.tlsinfo.ti_offset = ti_offset;
 103   entry = htab_find_slot (ht, &test, 1, hash_tlsdesc, eq_tlsdesc);
 104   if (! entry)
 105     return 0;
 106
 107   if (*entry)
 108     {
 109       td = *entry;
 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   return td;
 120 }
 121
 122 # endif /* SHARED */
 123
 124 #endif