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           size_t offset;
 170           /* Looks ok.  */
 171           cache = file;
 172
 173           /* Check for new version.  */
 174           offset = ALIGN_CACHE (sizeof (struct cache_file)
 175                                 + cache->nlibs * sizeof (struct file_entry));
 176
 177           cache_new = (struct cache_file_new *) ((void *)cache + offset);
 178           if (cachesize < (offset + sizeof (struct cache_file_new))
 179               || memcmp (cache_new->magic, CACHEMAGIC_NEW,
 180                           sizeof CACHEMAGIC_NEW - 1)
 181               || memcmp (cache_new->version, CACHE_VERSION,
 182                          sizeof CACHE_VERSION - 1))
 183             cache_new = (void *) -1;
 184         }
 185       else if (file && cachesize > sizeof *cache_new)
 186         {
 187           cache_new = (struct cache_file_new *) file;
 188           if (memcmp (cache_new->magic, CACHEMAGIC_NEW,
 189                       sizeof CACHEMAGIC_NEW - 1)
 190               || memcmp (cache_new->version, CACHE_VERSION,
 191                          sizeof CACHE_VERSION - 1))
 192             cache_new = (void *) -1;
 193         }
 194       else
 195         {
 196           if (file)
 197             __munmap (file, cachesize);
 198           cache = (void *) -1;
 199           return NULL;
 200         }
 201     }
 202
 203   if (cache == (void *) -1)
 204     /* Previously looked for the cache file and didn't find it.  */
 205     return NULL;
 206
 207   best = NULL;
 208
 209   if (cache_new != (void *) -1)
 210     {
 211       /* This file ends in static libraries where we don't have a hwcap.  */
 212       unsigned long int *hwcap;
 213       weak_extern (_dl_hwcap);
 214
 215       /* This is where the strings start.  */
 216       cache_data = (const char *) cache_new;
 217
 218       hwcap = &_dl_hwcap;
 219
 220 #define HWCAP_CHECK                                                          \
 221       if (hwcap && (cache_new->libs[middle].hwcap & *hwcap) > _dl_hwcap)     \
 222         continue
 223       SEARCH_CACHE (cache_new);
 224     }
 225   else
 226     {
 227       /* This is where the strings start.  */
 228       cache_data = (const char *) &cache->libs[cache->nlibs];
 229 #undef HWCAP_CHECK
 230 #define HWCAP_CHECK do {} while (0)
 231       SEARCH_CACHE (cache);
 232     }
 233
 234   /* Print our result if wanted.  */
 235   if (_dl_debug_libs && best != NULL)
 236     _dl_debug_message (1, "  trying file=", best, "\n", NULL);
 237
 238   return best;
 239 }
 240
 241 #ifndef MAP_COPY
 242 /* If the system does not support MAP_COPY we cannot leave the file open
 243    all the time since this would create problems when the file is replaced.
 244    Therefore we provide this function to close the file and open it again
 245    once needed.  */
 246 void
 247 _dl_unload_cache (void)
 248 {
 249   if (cache != NULL && cache != (struct cache_file *) -1)
 250     {
 251       __munmap (cache, cachesize);
 252       cache = NULL;
 253     }
 254 }
 255 #endif