sysdeps/generic/dl-cache.c

   1 /* Support for reading /etc/ld.so.cache files written by Linux ldconfig.
   2    Copyright (C) 1996, 1997 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 not,
  17    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  18    Boston, MA 02111-1307, USA.  */
  19
  20 #include <link.h>
  21 #include <stddef.h>
  22 #include <sys/mman.h>
  23
  24 /* System-dependent function to read a file's whole contents
  25    in the most convenient manner available.  */
  26 extern void *_dl_sysdep_read_whole_file (const char *filename,
  27                                          size_t *filesize_ptr,
  28                                          int mmap_prot);
  29
  30 #ifndef LD_SO_CACHE
  31 # define LD_SO_CACHE "/etc/ld.so.cache"
  32 #endif
  33
  34 #define CACHEMAGIC "ld.so-1.7.0"
  35
  36 struct cache_file
  37   {
  38     char magic[sizeof CACHEMAGIC - 1];
  39     unsigned int nlibs;
  40     struct
  41       {
  42         int flags;              /* This is 1 for an ELF library.  */
  43         unsigned int key, value; /* String table indices.  */
  44       } libs[0];
  45   };
  46
  47 /* Look up NAME in ld.so.cache and return the file name stored there,
  48    or null if none is found.  */
  49
  50 const char *
  51 _dl_load_cache_lookup (const char *name)
  52 {
  53   static struct cache_file *cache;
  54   static size_t cachesize;
  55   unsigned int i;
  56
  57   if (cache == (void *) -1)
  58     /* Previously looked for the cache file and didn't find it.  */
  59     return NULL;
  60
  61   if (cache == NULL)
  62     {
  63       /* Read the contents of the file.  */
  64       void *file = _dl_sysdep_read_whole_file (LD_SO_CACHE, &cachesize,
  65                                                PROT_READ);
  66       if (file && cachesize > sizeof *cache &&
  67           !memcmp (file, CACHEMAGIC, sizeof CACHEMAGIC - 1))
  68         /* Looks ok.  */
  69         cache = file;
  70       else
  71         {
  72           if (file)
  73             __munmap (file, cachesize);
  74           cache = (void *) -1;
  75           return NULL;
  76         }
  77     }
  78
  79   for (i = 0; i < cache->nlibs; ++i)
  80     if (cache->libs[i].flags == 1 && /* ELF library entry.  */
  81         /* Make sure string table indices are not bogus before using them.  */
  82         cache->libs[i].key < cachesize - sizeof *cache &&
  83         cache->libs[i].value < cachesize - sizeof *cache &&
  84         /* Does the name match?  */
  85         ! strcmp (name, ((const char *) &cache->libs[cache->nlibs] +
  86                          cache->libs[i].key)))
  87       return (const char *) &cache->libs[cache->nlibs] + cache->libs[i].value;
  88
  89   return NULL;
  90 }