glibc/elf/dl-setup_hash.c

/* Cache the location of a link map hash table.
   Copyright (C) 1995-2024 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <https://www.gnu.org/licenses/>.  */

#include <assert.h>
#include <link.h>
#include <ldsodefs.h>

void
_dl_setup_hash (struct link_map *map)
{
  Elf_Symndx *hash;

  if (__glibc_likely (map->l_info[ELF_MACHINE_GNU_HASH_ADDRIDX] != NULL))
    {
      Elf32_Word *hash32
        = (void *) D_PTR (map, l_info[ELF_MACHINE_GNU_HASH_ADDRIDX]);
      map->l_nbuckets = *hash32++;
      Elf32_Word symbias = *hash32++;
      Elf32_Word bitmask_nwords = *hash32++;
      /* Must be a power of two.  */
      assert ((bitmask_nwords & (bitmask_nwords - 1)) == 0);
      map->l_gnu_bitmask_idxbits = bitmask_nwords - 1;
      map->l_gnu_shift = *hash32++;

      map->l_gnu_bitmask = (ElfW(Addr) *) hash32;
      hash32 += __ELF_NATIVE_CLASS / 32 * bitmask_nwords;

      map->l_gnu_buckets = hash32;
      hash32 += map->l_nbuckets;
      map->l_gnu_chain_zero = hash32 - symbias;

      /* Initialize MIPS xhash translation table.  */
      ELF_MACHINE_XHASH_SETUP (hash32, symbias, map);

      return;
    }

  if (!map->l_info[DT_HASH])
    return;
  hash = (void *) D_PTR (map, l_info[DT_HASH]);

  map->l_nbuckets = *hash++;
  /* Skip nchain.  */
  hash++;
  map->l_buckets = hash;
  hash += map->l_nbuckets;
  map->l_chain = hash;
}