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 <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 #define CACHEMAGIC "ld.so-1.7.0"
  31
  32 struct cache_file
  33   {
  34     char magic[sizeof CACHEMAGIC - 1];
  35     unsigned int nlibs;
  36     struct
  37       {
  38         int flags;              /* This is 1 for an ELF library.  */
  39         unsigned int key, value; /* String table indices.  */
  40       } libs[0];
  41   };
  42
  43 /* Look up NAME in ld.so.cache and return the file name stored there,
  44    or null if none is found.  */
  45
  46 const char *
  47 _dl_load_cache_lookup (const char *name)
  48 {
  49   static struct cache_file *cache;
  50   static size_t cachesize;
  51   unsigned int i;
  52
  53   if (cache == (void *) -1)
  54     /* Previously looked for the cache file and didn't find it.  */
  55     return NULL;
  56
  57   if (cache == NULL)
  58     {
  59       /* Read the contents of the file.  */
  60       void *file = _dl_sysdep_read_whole_file ("/etc/ld.so.cache", &cachesize,
  61                                                PROT_READ);
  62       if (file && cachesize > sizeof *cache &&
  63           !memcmp (file, CACHEMAGIC, sizeof CACHEMAGIC - 1))
  64         /* Looks ok.  */
  65         cache = file;
  66       else
  67         {
  68           if (file)
  69             __munmap (file, cachesize);
  70           cache = (void *) -1;
  71           return NULL;
  72         }
  73     }
  74
  75   for (i = 0; i < cache->nlibs; ++i)
  76     if (cache->libs[i].flags == 1 && /* ELF library entry.  */
  77         /* Make sure string table indices are not bogus before using them.  */
  78         cache->libs[i].key < cachesize - sizeof *cache &&
  79         cache->libs[i].value < cachesize - sizeof *cache &&
  80         /* Does the name match?  */
  81         ! strcmp (name, ((const char *) &cache->libs[cache->nlibs] +
  82                          cache->libs[i].key)))
  83       return (const char *) &cache->libs[cache->nlibs] + cache->libs[i].value;
  84
  85   return NULL;
  86 }