elf/dl-cache.c

   1 /* Support for reading /etc/ld.so.cache files written by Linux ldconfig.
   2    Copyright (C) 1996-2013 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 Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the 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    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 #include <assert.h>
  20 #include <unistd.h>
  21 #include <ldsodefs.h>
  22 #include <sys/mman.h>
  23 #include <dl-cache.h>
  24 #include <dl-procinfo.h>
  25
  26 #include <_itoa.h>
  27
  28 #ifndef _DL_PLATFORMS_COUNT
  29 # define _DL_PLATFORMS_COUNT 0
  30 #endif
  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 < cache_data_size)
  39
  40 #define SEARCH_CACHE(cache) \
  41 /* We use binary search since the table is sorted in the cache file.          \
  42    The first matching entry in the table is returned.                         \
  43    It is important to use the same algorithm as used while generating         \
  44    the cache file.  */                                                        \
  45 do                                                                            \
  46   {                                                                           \
  47     left = 0;                                                                 \
  48     right = cache->nlibs - 1;                                                 \
  49                                                                               \
  50     while (left <= right)                                                     \
  51       {                                                                       \
  52         __typeof__ (cache->libs[0].key) key;                                  \
  53                                                                               \
  54         middle = (left + right) / 2;                                          \
  55                                                                               \
  56         key = cache->libs[middle].key;                                        \
  57                                                                               \
  58         /* Make sure string table indices are not bogus before using          \
  59            them.  */                                                          \
  60         if (! _dl_cache_verify_ptr (key))                                     \
  61           {                                                                   \
  62             cmpres = 1;                                                       \
  63             break;                                                            \
  64           }                                                                   \
  65                                                                               \
  66         /* Actually compare the entry with the key.  */                       \
  67         cmpres = _dl_cache_libcmp (name, cache_data + key);                   \
  68         if (__builtin_expect (cmpres == 0, 0))                                \
  69           {                                                                   \
  70             /* Found it.  LEFT now marks the last entry for which we          \
  71                know the name is correct.  */                                  \
  72             left = middle;                                                    \
  73                                                                               \
  74             /* There might be entries with this name before the one we        \
  75                found.  So we have to find the beginning.  */                  \
  76             while (middle > 0)                                                \
  77               {                                                               \
  78                 __typeof__ (cache->libs[0].key) key;                          \
  79                                                                               \
  80                 key = cache->libs[middle - 1].key;                            \
  81                 /* Make sure string table indices are not bogus before        \
  82                    using them.  */                                            \
  83                 if (! _dl_cache_verify_ptr (key)                              \
  84                     /* Actually compare the entry.  */                        \
  85                     || _dl_cache_libcmp (name, cache_data + key) != 0)        \
  86                   break;                                                      \
  87                 --middle;                                                     \
  88               }                                                               \
  89                                                                               \
  90             do                                                                \
  91               {                                                               \
  92                 int flags;                                                    \
  93                 __typeof__ (cache->libs[0]) *lib = &cache->libs[middle];      \
  94                                                                               \
  95                 /* Only perform the name test if necessary.  */               \
  96                 if (middle > left                                             \
  97                     /* We haven't seen this string so far.  Test whether the  \
  98                        index is ok and whether the name matches.  Otherwise   \
  99                        we are done.  */                                       \
 100                     && (! _dl_cache_verify_ptr (lib->key)                     \
 101                         || (_dl_cache_libcmp (name, cache_data + lib->key)    \
 102                             != 0)))                                           \
 103                   break;                                                      \
 104                                                                               \
 105                 flags = lib->flags;                                           \
 106                 if (_dl_cache_check_flags (flags)                             \
 107                     && _dl_cache_verify_ptr (lib->value))                     \
 108                   {                                                           \
 109                     if (best == NULL || flags == GLRO(dl_correct_cache_id))   \
 110                       {                                                       \
 111                         HWCAP_CHECK;                                          \
 112                         best = cache_data + lib->value;                       \
 113                                                                               \
 114                         if (flags == GLRO(dl_correct_cache_id))               \
 115                           /* We've found an exact match for the shared        \
 116                              object and no general `ELF' release.  Stop       \
 117                              searching.  */                                   \
 118                           break;                                              \
 119                       }                                                       \
 120                   }                                                           \
 121               }                                                               \
 122             while (++middle <= right);                                        \
 123             break;                                                            \
 124         }                                                                     \
 125                                                                               \
 126         if (cmpres < 0)                                                       \
 127           left = middle + 1;                                                  \
 128         else                                                                  \
 129           right = middle - 1;                                                 \
 130       }                                                                       \
 131   }                                                                           \
 132 while (0)
 133
 134
 135 int
 136 internal_function
 137 _dl_cache_libcmp (const char *p1, const char *p2)
 138 {
 139   while (*p1 != '\0')
 140     {
 141       if (*p1 >= '0' && *p1 <= '9')
 142         {
 143           if (*p2 >= '0' && *p2 <= '9')
 144             {
 145               /* Must compare this numerically.  */
 146               int val1;
 147               int val2;
 148
 149               val1 = *p1++ - '0';
 150               val2 = *p2++ - '0';
 151               while (*p1 >= '0' && *p1 <= '9')
 152                 val1 = val1 * 10 + *p1++ - '0';
 153               while (*p2 >= '0' && *p2 <= '9')
 154                 val2 = val2 * 10 + *p2++ - '0';
 155               if (val1 != val2)
 156                 return val1 - val2;
 157             }
 158           else
 159             return 1;
 160         }
 161       else if (*p2 >= '0' && *p2 <= '9')
 162         return -1;
 163       else if (*p1 != *p2)
 164         return *p1 - *p2;
 165       else
 166         {
 167           ++p1;
 168           ++p2;
 169         }
 170     }
 171   return *p1 - *p2;
 172 }
 173
 174
 175 /* Look up NAME in ld.so.cache and return the file name stored there,
 176    or null if none is found.  */
 177
 178 const char *
 179 internal_function
 180 _dl_load_cache_lookup (const char *name)
 181 {
 182   int left, right, middle;
 183   int cmpres;
 184   const char *cache_data;
 185   uint32_t cache_data_size;
 186   const char *best;
 187
 188   /* Print a message if the loading of libs is traced.  */
 189   if (__builtin_expect (GLRO(dl_debug_mask) & DL_DEBUG_LIBS, 0))
 190     _dl_debug_printf (" search cache=%s\n", LD_SO_CACHE);
 191
 192   if (cache == NULL)
 193     {
 194       /* Read the contents of the file.  */
 195       void *file = _dl_sysdep_read_whole_file (LD_SO_CACHE, &cachesize,
 196                                                PROT_READ);
 197
 198       /* We can handle three different cache file formats here:
 199          - the old libc5/glibc2.0/2.1 format
 200          - the old format with the new format in it
 201          - only the new format
 202          The following checks if the cache contains any of these formats.  */
 203       if (file != MAP_FAILED && cachesize > sizeof *cache
 204           && memcmp (file, CACHEMAGIC, sizeof CACHEMAGIC - 1) == 0)
 205         {
 206           size_t offset;
 207           /* Looks ok.  */
 208           cache = file;
 209
 210           /* Check for new version.  */
 211           offset = ALIGN_CACHE (sizeof (struct cache_file)
 212                                 + cache->nlibs * sizeof (struct file_entry));
 213
 214           cache_new = (struct cache_file_new *) ((void *) cache + offset);
 215           if (cachesize < (offset + sizeof (struct cache_file_new))
 216               || memcmp (cache_new->magic, CACHEMAGIC_VERSION_NEW,
 217                          sizeof CACHEMAGIC_VERSION_NEW - 1) != 0)
 218             cache_new = (void *) -1;
 219         }
 220       else if (file != MAP_FAILED && cachesize > sizeof *cache_new
 221                && memcmp (file, CACHEMAGIC_VERSION_NEW,
 222                           sizeof CACHEMAGIC_VERSION_NEW - 1) == 0)
 223         {
 224           cache_new = file;
 225           cache = file;
 226         }
 227       else
 228         {
 229           if (file != MAP_FAILED)
 230             __munmap (file, cachesize);
 231           cache = (void *) -1;
 232         }
 233
 234       assert (cache != NULL);
 235     }
 236
 237   if (cache == (void *) -1)
 238     /* Previously looked for the cache file and didn't find it.  */
 239     return NULL;
 240
 241   best = NULL;
 242
 243   if (cache_new != (void *) -1)
 244     {
 245       uint64_t platform;
 246
 247       /* This is where the strings start.  */
 248       cache_data = (const char *) cache_new;
 249
 250       /* Now we can compute how large the string table is.  */
 251       cache_data_size = (const char *) cache + cachesize - cache_data;
 252
 253       platform = _dl_string_platform (GLRO(dl_platform));
 254       if (platform != (uint64_t) -1)
 255         platform = 1ULL << platform;
 256
 257 #define _DL_HWCAP_TLS_MASK (1LL << 63)
 258       uint64_t hwcap_exclude = ~((GLRO(dl_hwcap) & GLRO(dl_hwcap_mask))
 259                                  | _DL_HWCAP_PLATFORM | _DL_HWCAP_TLS_MASK);
 260
 261       /* Only accept hwcap if it's for the right platform.  */
 262 #define HWCAP_CHECK \
 263       if (lib->hwcap & hwcap_exclude)                                         \
 264         continue;                                                             \
 265       if (GLRO(dl_osversion) && lib->osversion > GLRO(dl_osversion))          \
 266         continue;                                                             \
 267       if (_DL_PLATFORMS_COUNT                                                 \
 268           && (lib->hwcap & _DL_HWCAP_PLATFORM) != 0                           \
 269           && (lib->hwcap & _DL_HWCAP_PLATFORM) != platform)                   \
 270         continue
 271       SEARCH_CACHE (cache_new);
 272     }
 273   else
 274     {
 275       /* This is where the strings start.  */
 276       cache_data = (const char *) &cache->libs[cache->nlibs];
 277
 278       /* Now we can compute how large the string table is.  */
 279       cache_data_size = (const char *) cache + cachesize - cache_data;
 280
 281 #undef HWCAP_CHECK
 282 #define HWCAP_CHECK do {} while (0)
 283       SEARCH_CACHE (cache);
 284     }
 285
 286   /* Print our result if wanted.  */
 287   if (__builtin_expect (GLRO(dl_debug_mask) & DL_DEBUG_LIBS, 0)
 288       && best != NULL)
 289     _dl_debug_printf ("  trying file=%s\n", best);
 290
 291   return best;
 292 }
 293
 294 #ifndef MAP_COPY
 295 /* If the system does not support MAP_COPY we cannot leave the file open
 296    all the time since this would create problems when the file is replaced.
 297    Therefore we provide this function to close the file and open it again
 298    once needed.  */
 299 void
 300 _dl_unload_cache (void)
 301 {
 302   if (cache != NULL && cache != (struct cache_file *) -1)
 303     {
 304       __munmap (cache, cachesize);
 305       cache = NULL;
 306     }
 307 }
 308 #endif