elf/dl-cache.c

   1 /* Support for reading /etc/ld.so.cache files written by Linux ldconfig.
   2 Copyright (C) 1996 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 Library General Public License as
   7 published by the Free Software Foundation; either version 2 of the
   8 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 Library General Public License for more details.
  14
  15 You should have received a copy of the GNU Library General Public
  16 License along with the GNU C Library; see the file COPYING.LIB.  If
  17 not, write to the Free Software Foundation, Inc., 675 Mass Ave,
  18 Cambridge, MA 02139, USA.  */
  19
  20 #include <link.h>
  21 #include <sys/mman.h>
  22
  23 /* System-dependent function to read a file's whole contents
  24    in the most convenient manner available.  */
  25 extern void *_dl_sysdep_read_whole_file (const char *filename,
  26                                          size_t *filesize_ptr,
  27                                          int mmap_prot);
  28
  29 #define CACHEMAGIC "ld.so-1.7.0"
  30
  31 struct cache_file
  32   {
  33     char magic[sizeof CACHEMAGIC - 1];
  34     unsigned int nlibs;
  35     struct
  36       {
  37         int flags;              /* This is 1 for an ELF library.  */
  38         unsigned int key, value; /* String table indices.  */
  39       } libs[0];
  40   };
  41
  42 /* Look up NAME in ld.so.cache and return the file name stored there,
  43    or null if none is found.  */
  44
  45 const char *
  46 _dl_load_cache_lookup (const char *name)
  47 {
  48   static struct cache_file *cache;
  49   static size_t cachesize;
  50   unsigned int i;
  51
  52   if (cache == (void *) -1)
  53     /* Previously looked for the cache file and didn't find it.  */
  54     return NULL;
  55
  56   if (cache == NULL)
  57     {
  58       /* Read the contents of the file.  */
  59       void *file = _dl_sysdep_read_whole_file ("/etc/ld.so.cache", &cachesize,
  60                                                PROT_READ);
  61       if (file && cachesize > sizeof *cache &&
  62           !memcmp (file, CACHEMAGIC, sizeof CACHEMAGIC - 1))
  63         /* Looks ok.  */
  64         cache = file;
  65       else
  66         {
  67           if (file)
  68             __munmap (file, cachesize);
  69           cache = (void *) -1;
  70           return NULL;
  71         }
  72     }
  73
  74   for (i = 0; i < cache->nlibs; ++i)
  75     if (cache->libs[i].flags == 1 && /* ELF library entry.  */
  76         /* Make sure string table indices are not bogus before using them.  */
  77         cache->libs[i].key < cachesize - sizeof *cache &&
  78         cache->libs[i].value < cachesize - sizeof *cache &&
  79         /* Does the name match?  */
  80         ! strcmp (name, ((const char *) &cache->libs[cache->nlibs] +
  81                          cache->libs[i].key)))
  82       return (const char *) &cache->libs[cache->nlibs] + cache->libs[i].value;
  83
  84   return NULL;
  85 }