1  /* Hash table for TLS descriptors.
       2     Copyright (C) 2005-2023 Free Software Foundation, Inc.
       3     This file is part of the GNU C Library.
       4  
       5     The GNU C Library is free software; you can redistribute it and/or
       6     modify it under the terms of the GNU Lesser General Public
       7     License as published by the Free Software Foundation; either
       8     version 2.1 of the License, or (at your option) any later version.
       9  
      10     The GNU C Library is distributed in the hope that it will be useful,
      11     but WITHOUT ANY WARRANTY; without even the implied warranty of
      12     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
      13     Lesser General Public License for more details.
      14  
      15     You should have received a copy of the GNU Lesser General Public
      16     License along with the GNU C Library; if not, see
      17     <https://www.gnu.org/licenses/>.  */
      18  
      19  #ifndef TLSDESCHTAB_H
      20  # define TLSDESCHTAB_H 1
      21  
      22  #include <atomic.h>
      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 size_t
      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].map == map && 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  /* Returns the data pointer for a given map and tls offset that is used
      81     to fill in one of the GOT entries referenced by a TLSDESC relocation
      82     when using dynamic TLS.  This requires allocation, returns NULL on
      83     allocation failure.  */
      84  void *
      85  _dl_make_tlsdesc_dynamic (struct link_map *map, size_t ti_offset)
      86  {
      87    struct hashtab *ht;
      88    void **entry;
      89    struct tlsdesc_dynamic_arg *td, test;
      90  
      91    ht = map->l_mach.tlsdesc_table;
      92    if (! ht)
      93      {
      94        ht = htab_create ();
      95        if (! ht)
      96  	return 0;
      97        map->l_mach.tlsdesc_table = ht;
      98      }
      99  
     100    test.tlsinfo.ti_module = map->l_tls_modid;
     101    test.tlsinfo.ti_offset = ti_offset;
     102    entry = htab_find_slot (ht, &test, 1, hash_tlsdesc, eq_tlsdesc);
     103    if (! entry)
     104      return 0;
     105  
     106    if (*entry)
     107      {
     108        td = *entry;
     109        return td;
     110      }
     111  
     112    *entry = td = malloc (sizeof (struct tlsdesc_dynamic_arg));
     113    if (! td)
     114      return 0;
     115    /* This may be higher than the map's generation, but it doesn't
     116       matter much.  Worst case, we'll have one extra DTV update per
     117       thread.  */
     118    td->gen_count = map_generation (map);
     119    td->tlsinfo = test.tlsinfo;
     120    return td;
     121  }
     122  
     123  # endif /* SHARED */
     124  
     125  #endif