sysdeps/generic/dl-cache.c

   1 /* Support for reading /etc/ld.so.cache files written by Linux ldconfig.
   2    Copyright (C) 1996, 1997, 1998, 1999, 2000 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 <unistd.h>
  21 #include <ldsodefs.h>
  22 #include <sys/mman.h>
  23 #include <dl-cache.h>
  24
  25
  26 /* System-dependent function to read a file's whole contents
  27    in the most convenient manner available.  */
  28 extern void *_dl_sysdep_read_whole_file (const char *filename,
  29                                          size_t *filesize_ptr,
  30                                          int mmap_prot);
  31
  32 /* This is the starting address and the size of the mmap()ed file.  */
  33 static struct cache_file *cache;
  34 static struct cache_file_new *cache_new;
  35 static size_t cachesize;
  36
  37 /* 1 if cache_data + PTR points into the cache.  */
  38 #define _dl_cache_verify_ptr(ptr) (ptr < cachesize - sizeof *cache)
  39
  40 /* This is the cache ID we expect.  Normally it is 3 for glibc linked
  41    binaries.  */
  42 int _dl_correct_cache_id = _DL_CACHE_DEFAULT_ID;
  43
  44 #define SEARCH_CACHE(cache)                                               \
  45 /* We use binary search since the table is sorted in the cache file.      \
  46    The first matching entry in the table is returned.                     \
  47    It is important to use the same algorithm as used while generating     \
  48    the cache file.  */                                                    \
  49 do                                                                        \
  50   {                                                                       \
  51     left = 0;                                                             \
  52     right = cache->nlibs - 1;                                             \
  53     middle = (left + right) / 2;                                          \
  54     cmpres = 1;                                                           \
  55                                                                           \
  56     while (left <= right)                                                 \
  57       {                                                                   \
  58         /* Make sure string table indices are not bogus before using      \
  59            them.  */                                                      \
  60         if (! _dl_cache_verify_ptr (cache->libs[middle].key))             \
  61           {                                                               \
  62             cmpres = 1;                                                   \
  63             break;                                                        \
  64           }                                                               \
  65                                                                           \
  66         /* Actually compare the entry with the key.  */                   \
  67         cmpres = _dl_cache_libcmp (name,                                  \
  68                                    cache_data + cache->libs[middle].key); \
  69         if (cmpres == 0)                                                  \
  70           /* Found it.  */                                                \
  71           break;                                                          \
  72                                                                           \
  73         if (cmpres < 0)                                                   \
  74           left = middle + 1;                                              \
  75         else                                                              \
  76           right = middle - 1;                                             \
  77                                                                           \
  78         middle = (left + right) / 2;                                      \
  79       }                                                                   \
  80                                                                           \
  81     if (cmpres == 0)                                                      \
  82       {                                                                   \
  83         /* LEFT now marks the last entry for which we know the name is    \
  84            correct.  */                                                   \
  85         left = middle;                                                    \
  86                                                                           \
  87         /* There might be entries with this name before the one we        \
  88            found.  So we have to find the beginning.  */                  \
  89         while (middle > 0                                                 \
  90                /* Make sure string table indices are not bogus before     \
  91                   using them.  */                                         \
  92                && _dl_cache_verify_ptr (cache->libs[middle - 1].key)      \
  93                /* Actually compare the entry.  */                         \
  94                && (_dl_cache_libcmp (name,                                \
  95                                      cache_data                           \
  96                                      + cache->libs[middle - 1].key)       \
  97                    == 0))                                                 \
  98           --middle;                                                       \
  99                                                                           \
 100         do                                                                \
 101           {                                                               \
 102             int flags;                                                    \
 103                                                                           \
 104             /* Only perform the name test if necessary.  */               \
 105             if (middle > left                                             \
 106                 /* We haven't seen this string so far.  Test whether the  \
 107                    index is ok and whether the name matches.  Otherwise   \
 108                    we are done.  */                                       \
 109                 && (! _dl_cache_verify_ptr (cache->libs[middle].key)      \
 110                     || (_dl_cache_libcmp (name,                           \
 111                                           cache_data                      \
 112                                           + cache->libs[middle].key)      \
 113                         != 0)))                                           \
 114               break;                                                      \
 115                                                                           \
 116             flags = cache->libs[middle].flags;                            \
 117             if (_dl_cache_check_flags (flags)                             \
 118                 && _dl_cache_verify_ptr (cache->libs[middle].value))      \
 119               {                                                           \
 120                 if (best == NULL || flags == _dl_correct_cache_id)        \
 121                   {                                                       \
 122                     HWCAP_CHECK;                                          \
 123                     best = cache_data + cache->libs[middle].value;        \
 124                                                                           \
 125                     if (flags == _dl_correct_cache_id)                    \
 126                       /* We've found an exact match for the shared        \
 127                          object and no general `ELF' release.  Stop       \
 128                          searching.  */                                   \
 129                       break;                                              \
 130                   }                                                       \
 131               }                                                           \
 132           }                                                               \
 133         while (++middle <= right);                                        \
 134       }                                                                   \
 135   }                                                                       \
 136 while (0)
 137
 138
 139
 140 /* Look up NAME in ld.so.cache and return the file name stored there,
 141    or null if none is found.  */
 142
 143 const char *
 144 _dl_load_cache_lookup (const char *name)
 145 {
 146   int left, right, middle;
 147   int cmpres;
 148   const char *cache_data;
 149   const char *best;
 150
 151   /* Print a message if the loading of libs is traced.  */
 152   if (_dl_debug_libs)
 153     _dl_debug_message (1, " search cache=", LD_SO_CACHE, "\n", NULL);
 154
 155   if (cache == NULL)
 156     {
 157       /* Read the contents of the file.  */
 158       void *file = _dl_sysdep_read_whole_file (LD_SO_CACHE, &cachesize,
 159                                                PROT_READ);
 160
 161       /* We can handle three different cache file formats here:
 162          - the old libc5/glibc2.0/2.1 format
 163          - the old format with the new format in it
 164          - only the new format
 165          The following checks if the cache contains any of these formats.  */
 166       if (file && cachesize > sizeof *cache &&
 167           !memcmp (file, CACHEMAGIC, sizeof CACHEMAGIC - 1))
 168         {
 169           /* Looks ok.  */
 170           cache = file;
 171
 172           /* Check for new version.  */
 173           cache_new = (struct cache_file_new *) &cache->libs[cache->nlibs];
 174           if (cachesize <
 175               (sizeof (struct cache_file) + cache->nlibs * sizeof (struct file_entry)
 176                + sizeof (struct cache_file_new))
 177               || memcmp (cache_new->magic, CACHEMAGIC_NEW,
 178                           sizeof CACHEMAGIC_NEW - 1)
 179               || memcmp (cache_new->version, CACHE_VERSION,
 180                          sizeof CACHE_VERSION - 1))
 181             cache_new = (void *) -1;
 182         }
 183       else if (file && cachesize > sizeof *cache_new)
 184         {
 185           cache_new = (struct cache_file_new *) file;
 186           if (memcmp (cache_new->magic, CACHEMAGIC_NEW,
 187                       sizeof CACHEMAGIC_NEW - 1)
 188               || memcmp (cache_new->version, CACHE_VERSION,
 189                          sizeof CACHE_VERSION - 1))
 190             cache_new = (void *) -1;
 191         }
 192       else
 193         {
 194           if (file)
 195             __munmap (file, cachesize);
 196           cache = (void *) -1;
 197           return NULL;
 198         }
 199     }
 200
 201   if (cache == (void *) -1)
 202     /* Previously looked for the cache file and didn't find it.  */
 203     return NULL;
 204
 205   /* This is where the strings start.  */
 206   cache_data = (const char *) &cache->libs[cache->nlibs];
 207
 208   best = NULL;
 209
 210   if (cache_new != (void *) -1)
 211     {
 212       /* This file ends in static libraries where we don't have a hwcap.  */
 213       unsigned long int *hwcap;
 214       weak_extern (_dl_hwcap);
 215
 216       hwcap = &_dl_hwcap;
 217
 218 #define HWCAP_CHECK                                                          \
 219       if (hwcap && (cache_new->libs[middle].hwcap & *hwcap) > _dl_hwcap)     \
 220         continue
 221       SEARCH_CACHE (cache_new);
 222     }
 223   else
 224 #undef HWCAP_CHECK
 225 #define HWCAP_CHECK do {} while (0)
 226     SEARCH_CACHE (cache);
 227
 228   /* Print our result if wanted.  */
 229   if (_dl_debug_libs && best != NULL)
 230     _dl_debug_message (1, "  trying file=", best, "\n", NULL);
 231
 232   return best;
 233 }
 234
 235 #ifndef MAP_COPY
 236 /* If the system does not support MAP_COPY we cannot leave the file open
 237    all the time since this would create problems when the file is replaced.
 238    Therefore we provide this function to close the file and open it again
 239    once needed.  */
 240 void
 241 _dl_unload_cache (void)
 242 {
 243   if (cache != NULL && cache != (struct cache_file *) -1)
 244     {
 245       __munmap (cache, cachesize);
 246       cache = NULL;
 247     }
 248 }
 249 #endif