elf/dl-cache.c

   1 /* Support for reading /etc/ld.so.cache files written by Linux ldconfig.
   2    Copyright (C) 1996-2002, 2003, 2004, 2006 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, write to the Free
  17    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  18    02111-1307 USA.  */
  19
  20 #include <assert.h>
  21 #include <unistd.h>
  22 #include <ldsodefs.h>
  23 #include <sys/mman.h>
  24 #include <dl-cache.h>
  25 #include <dl-procinfo.h>
  26
  27 #include <stdio-common/_itoa.h>
  28
  29 #ifndef _DL_PLATFORMS_COUNT
  30 # define _DL_PLATFORMS_COUNT 0
  31 #endif
  32
  33 /* This is the starting address and the size of the mmap()ed file.  */
  34 static struct cache_file *cache;
  35 static struct cache_file_new *cache_new;
  36 static size_t cachesize;
  37
  38 /* 1 if cache_data + PTR points into the cache.  */
  39 #define _dl_cache_verify_ptr(ptr) (ptr < cache_data_size)
  40
  41 #define SEARCH_CACHE(cache) \
  42 /* We use binary search since the table is sorted in the cache file.          \
  43    The first matching entry in the table is returned.                         \
  44    It is important to use the same algorithm as used while generating         \
  45    the cache file.  */                                                        \
  46 do                                                                            \
  47   {                                                                           \
  48     left = 0;                                                                 \
  49     right = cache->nlibs - 1;                                                 \
  50                                                                               \
  51     while (left <= right)                                                     \
  52       {                                                                       \
  53         __typeof__ (cache->libs[0].key) key;                                  \
  54                                                                               \
  55         middle = (left + right) / 2;                                          \
  56                                                                               \
  57         key = cache->libs[middle].key;                                        \
  58                                                                               \
  59         /* Make sure string table indices are not bogus before using          \
  60            them.  */                                                          \
  61         if (! _dl_cache_verify_ptr (key))                                     \
  62           {                                                                   \
  63             cmpres = 1;                                                       \
  64             break;                                                            \
  65           }                                                                   \
  66                                                                               \
  67         /* Actually compare the entry with the key.  */                       \
  68         cmpres = _dl_cache_libcmp (name, cache_data + key);                   \
  69         if (__builtin_expect (cmpres == 0, 0))                                \
  70           {                                                                   \
  71             /* Found it.  LEFT now marks the last entry for which we          \
  72                know the name is correct.  */                                  \
  73             left = middle;                                                    \
  74                                                                               \
  75             /* There might be entries with this name before the one we        \
  76                found.  So we have to find the beginning.  */                  \
  77             while (middle > 0)                                                \
  78               {                                                               \
  79                 __typeof__ (cache->libs[0].key) key;                          \
  80                                                                               \
  81                 key = cache->libs[middle - 1].key;                            \
  82                 /* Make sure string table indices are not bogus before        \
  83                    using them.  */                                            \
  84                 if (! _dl_cache_verify_ptr (key)                              \
  85                     /* Actually compare the entry.  */                        \
  86                     || _dl_cache_libcmp (name, cache_data + key) != 0)        \
  87                   break;                                                      \
  88                 --middle;                                                     \
  89               }                                                               \
  90                                                                               \
  91             do                                                                \
  92               {                                                               \
  93                 int flags;                                                    \
  94                 __typeof__ (cache->libs[0]) *lib = &cache->libs[middle];      \
  95                                                                               \
  96                 /* Only perform the name test if necessary.  */               \
  97                 if (middle > left                                             \
  98                     /* We haven't seen this string so far.  Test whether the  \
  99                        index is ok and whether the name matches.  Otherwise   \
 100                        we are done.  */                                       \
 101                     && (! _dl_cache_verify_ptr (lib->key)                     \
 102                         || (_dl_cache_libcmp (name, cache_data + lib->key)    \
 103                             != 0)))                                           \
 104                   break;                                                      \
 105                                                                               \
 106                 flags = lib->flags;                                           \
 107                 if (_dl_cache_check_flags (flags)                             \
 108                     && _dl_cache_verify_ptr (lib->value))                     \
 109                   {                                                           \
 110                     if (best == NULL || flags == GLRO(dl_correct_cache_id))   \
 111                       {                                                       \
 112                         HWCAP_CHECK;                                          \
 113                         best = cache_data + lib->value;                       \
 114                                                                               \
 115                         if (flags == GLRO(dl_correct_cache_id))               \
 116                           /* We've found an exact match for the shared        \
 117                              object and no general `ELF' release.  Stop       \
 118                              searching.  */                                   \
 119                           break;                                              \
 120                       }                                                       \
 121                   }                                                           \
 122               }                                                               \
 123             while (++middle <= right);                                        \
 124             break;                                                            \
 125         }                                                                     \
 126                                                                               \
 127         if (cmpres < 0)                                                       \
 128           left = middle + 1;                                                  \
 129         else                                                                  \
 130           right = middle - 1;                                                 \
 131       }                                                                       \
 132   }                                                                           \
 133 while (0)
 134
 135
 136 int
 137 internal_function
 138 _dl_cache_libcmp (const char *p1, const char *p2)
 139 {
 140   while (*p1 != '\0')
 141     {
 142       if (*p1 >= '0' && *p1 <= '9')
 143         {
 144           if (*p2 >= '0' && *p2 <= '9')
 145             {
 146               /* Must compare this numerically.  */
 147               int val1;
 148               int val2;
 149
 150               val1 = *p1++ - '0';
 151               val2 = *p2++ - '0';
 152               while (*p1 >= '0' && *p1 <= '9')
 153                 val1 = val1 * 10 + *p1++ - '0';
 154               while (*p2 >= '0' && *p2 <= '9')
 155                 val2 = val2 * 10 + *p2++ - '0';
 156               if (val1 != val2)
 157                 return val1 - val2;
 158             }
 159           else
 160             return 1;
 161         }
 162       else if (*p2 >= '0' && *p2 <= '9')
 163         return -1;
 164       else if (*p1 != *p2)
 165         return *p1 - *p2;
 166       else
 167         {
 168           ++p1;
 169           ++p2;
 170         }
 171     }
 172   return *p1 - *p2;
 173 }
 174
 175
 176 /* Look up NAME in ld.so.cache and return the file name stored there,
 177    or null if none is found.  */
 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 (__builtin_expect (GLRO(dl_debug_mask) & DL_DEBUG_LIBS, 0))
 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       /* Only accept hwcap if it's for the right platform.  */
 259 #ifdef USE_TLS
 260 # define _DL_HWCAP_TLS_MASK (1LL << 63)
 261 #else
 262 # define _DL_HWCAP_TLS_MASK 0
 263 #endif
 264 #define HWCAP_CHECK \
 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       if (lib->hwcap                                                          \
 272           & ~(GLRO(dl_hwcap) | _DL_HWCAP_PLATFORM | _DL_HWCAP_TLS_MASK))      \
 273         continue
 274       SEARCH_CACHE (cache_new);
 275     }
 276   else
 277     {
 278       /* This is where the strings start.  */
 279       cache_data = (const char *) &cache->libs[cache->nlibs];
 280
 281       /* Now we can compute how large the string table is.  */
 282       cache_data_size = (const char *) cache + cachesize - cache_data;
 283
 284 #undef HWCAP_CHECK
 285 #define HWCAP_CHECK do {} while (0)
 286       SEARCH_CACHE (cache);
 287     }
 288
 289   /* Print our result if wanted.  */
 290   if (__builtin_expect (GLRO(dl_debug_mask) & DL_DEBUG_LIBS, 0)
 291       && best != NULL)
 292     _dl_debug_printf ("  trying file=%s\n", best);
 293
 294   return best;
 295 }
 296
 297 #ifndef MAP_COPY
 298 /* If the system does not support MAP_COPY we cannot leave the file open
 299    all the time since this would create problems when the file is replaced.
 300    Therefore we provide this function to close the file and open it again
 301    once needed.  */
 302 void
 303 _dl_unload_cache (void)
 304 {
 305   if (cache != NULL && cache != (struct cache_file *) -1)
 306     {
 307       __munmap (cache, cachesize);
 308       cache = NULL;
 309     }
 310 }
 311 #endif