elf/dl-cache.c

   1 /* Support for reading /etc/ld.so.cache files written by Linux ldconfig.
   2    Copyright (C) 1996-2014 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 #include <stdint.h>
  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 (__glibc_unlikely (cmpres == 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, or null
 176    if none is found.  The cache is loaded if it was not already.  If loading
 177    the cache previously failed there will be no more attempts to load it.  */
 178
 179 const char *
 180 internal_function
 181 _dl_load_cache_lookup (const char *name)
 182 {
 183   int left, right, middle;
 184   int cmpres;
 185   const char *cache_data;
 186   uint32_t cache_data_size;
 187   const char *best;
 188
 189   /* Print a message if the loading of libs is traced.  */
 190   if (__glibc_unlikely (GLRO(dl_debug_mask) & DL_DEBUG_LIBS))
 191     _dl_debug_printf (" search cache=%s\n", LD_SO_CACHE);
 192
 193   if (cache == NULL)
 194     {
 195       /* Read the contents of the file.  */
 196       void *file = _dl_sysdep_read_whole_file (LD_SO_CACHE, &cachesize,
 197                                                PROT_READ);
 198
 199       /* We can handle three different cache file formats here:
 200          - the old libc5/glibc2.0/2.1 format
 201          - the old format with the new format in it
 202          - only the new format
 203          The following checks if the cache contains any of these formats.  */
 204       if (file != MAP_FAILED && cachesize > sizeof *cache
 205           && memcmp (file, CACHEMAGIC, sizeof CACHEMAGIC - 1) == 0)
 206         {
 207           size_t offset;
 208           /* Looks ok.  */
 209           cache = file;
 210
 211           /* Check for new version.  */
 212           offset = ALIGN_CACHE (sizeof (struct cache_file)
 213                                 + cache->nlibs * sizeof (struct file_entry));
 214
 215           cache_new = (struct cache_file_new *) ((void *) cache + offset);
 216           if (cachesize < (offset + sizeof (struct cache_file_new))
 217               || memcmp (cache_new->magic, CACHEMAGIC_VERSION_NEW,
 218                          sizeof CACHEMAGIC_VERSION_NEW - 1) != 0)
 219             cache_new = (void *) -1;
 220         }
 221       else if (file != MAP_FAILED && cachesize > sizeof *cache_new
 222                && memcmp (file, CACHEMAGIC_VERSION_NEW,
 223                           sizeof CACHEMAGIC_VERSION_NEW - 1) == 0)
 224         {
 225           cache_new = file;
 226           cache = file;
 227         }
 228       else
 229         {
 230           if (file != MAP_FAILED)
 231             __munmap (file, cachesize);
 232           cache = (void *) -1;
 233         }
 234
 235       assert (cache != NULL);
 236     }
 237
 238   if (cache == (void *) -1)
 239     /* Previously looked for the cache file and didn't find it.  */
 240     return NULL;
 241
 242   best = NULL;
 243
 244   if (cache_new != (void *) -1)
 245     {
 246       uint64_t platform;
 247
 248       /* This is where the strings start.  */
 249       cache_data = (const char *) cache_new;
 250
 251       /* Now we can compute how large the string table is.  */
 252       cache_data_size = (const char *) cache + cachesize - cache_data;
 253
 254       platform = _dl_string_platform (GLRO(dl_platform));
 255       if (platform != (uint64_t) -1)
 256         platform = 1ULL << platform;
 257
 258 #define _DL_HWCAP_TLS_MASK (1LL << 63)
 259       uint64_t hwcap_exclude = ~((GLRO(dl_hwcap) & GLRO(dl_hwcap_mask))
 260                                  | _DL_HWCAP_PLATFORM | _DL_HWCAP_TLS_MASK);
 261
 262       /* Only accept hwcap if it's for the right platform.  */
 263 #define HWCAP_CHECK \
 264       if (lib->hwcap & hwcap_exclude)                                         \
 265         continue;                                                             \
 266       if (GLRO(dl_osversion) && lib->osversion > GLRO(dl_osversion))          \
 267         continue;                                                             \
 268       if (_DL_PLATFORMS_COUNT                                                 \
 269           && (lib->hwcap & _DL_HWCAP_PLATFORM) != 0                           \
 270           && (lib->hwcap & _DL_HWCAP_PLATFORM) != platform)                   \
 271         continue
 272       SEARCH_CACHE (cache_new);
 273     }
 274   else
 275     {
 276       /* This is where the strings start.  */
 277       cache_data = (const char *) &cache->libs[cache->nlibs];
 278
 279       /* Now we can compute how large the string table is.  */
 280       cache_data_size = (const char *) cache + cachesize - cache_data;
 281
 282 #undef HWCAP_CHECK
 283 #define HWCAP_CHECK do {} while (0)
 284       SEARCH_CACHE (cache);
 285     }
 286
 287   /* Print our result if wanted.  */
 288   if (__builtin_expect (GLRO(dl_debug_mask) & DL_DEBUG_LIBS, 0)
 289       && best != NULL)
 290     _dl_debug_printf ("  trying file=%s\n", best);
 291
 292   return best;
 293 }
 294
 295 #ifndef MAP_COPY
 296 /* If the system does not support MAP_COPY we cannot leave the file open
 297    all the time since this would create problems when the file is replaced.
 298    Therefore we provide this function to close the file and open it again
 299    once needed.  */
 300 void
 301 _dl_unload_cache (void)
 302 {
 303   if (cache != NULL && cache != (struct cache_file *) -1)
 304     {
 305       __munmap (cache, cachesize);
 306       cache = NULL;
 307     }
 308 }
 309 #endif