sysdeps/generic/dl-cache.c

   1 /* Support for reading /etc/ld.so.cache files written by Linux ldconfig.
   2    Copyright (C) 1996,1997,1998,1999,2000,2001,2002 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 == GL(dl_correct_cache_id))     \
 111                       {                                                       \
 112                         HWCAP_CHECK;                                          \
 113                         best = cache_data + lib->value;                       \
 114                                                                               \
 115                         if (flags == GL(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
 137 /* Look up NAME in ld.so.cache and return the file name stored there,
 138    or null if none is found.  */
 139
 140 const char *
 141 internal_function
 142 _dl_load_cache_lookup (const char *name)
 143 {
 144   int left, right, middle;
 145   int cmpres;
 146   const char *cache_data;
 147   uint32_t cache_data_size;
 148   const char *best;
 149
 150   /* Print a message if the loading of libs is traced.  */
 151   if (__builtin_expect (GL(dl_debug_mask) & DL_DEBUG_LIBS, 0))
 152     INTUSE(_dl_debug_printf) (" search cache=%s\n", LD_SO_CACHE);
 153
 154   if (cache == NULL)
 155     {
 156       /* Read the contents of the file.  */
 157       void *file = _dl_sysdep_read_whole_file (LD_SO_CACHE, &cachesize,
 158                                                PROT_READ);
 159
 160       /* We can handle three different cache file formats here:
 161          - the old libc5/glibc2.0/2.1 format
 162          - the old format with the new format in it
 163          - only the new format
 164          The following checks if the cache contains any of these formats.  */
 165       if (file != MAP_FAILED && cachesize > sizeof *cache
 166           && memcmp (file, CACHEMAGIC, sizeof CACHEMAGIC - 1) == 0)
 167         {
 168           size_t offset;
 169           /* Looks ok.  */
 170           cache = file;
 171
 172           /* Check for new version.  */
 173           offset = ALIGN_CACHE (sizeof (struct cache_file)
 174                                 + cache->nlibs * sizeof (struct file_entry));
 175
 176           cache_new = (struct cache_file_new *) ((void *) cache + offset);
 177           if (cachesize < (offset + sizeof (struct cache_file_new))
 178               || memcmp (cache_new->magic, CACHEMAGIC_VERSION_NEW,
 179                          sizeof CACHEMAGIC_VERSION_NEW - 1) != 0)
 180             cache_new = (void *) -1;
 181         }
 182       else if (file != MAP_FAILED && cachesize > sizeof *cache_new
 183                && memcmp (file, CACHEMAGIC_VERSION_NEW,
 184                           sizeof CACHEMAGIC_VERSION_NEW - 1) == 0)
 185         {
 186           cache_new = file;
 187           cache = file;
 188         }
 189       else
 190         {
 191           if (file != MAP_FAILED)
 192             __munmap (file, cachesize);
 193           cache = (void *) -1;
 194         }
 195
 196       assert (cache != NULL);
 197     }
 198
 199   if (cache == (void *) -1)
 200     /* Previously looked for the cache file and didn't find it.  */
 201     return NULL;
 202
 203   best = NULL;
 204
 205   if (cache_new != (void *) -1)
 206     {
 207       /* This file ends in static libraries where we don't have a hwcap.  */
 208       unsigned long int *hwcap;
 209       uint64_t platform;
 210 #ifndef SHARED
 211       weak_extern (_dl_hwcap);
 212 #endif
 213
 214       /* This is where the strings start.  */
 215       cache_data = (const char *) cache_new;
 216
 217       /* Now we can compute how large the string table is.  */
 218       cache_data_size = (const char *) cache + cachesize - cache_data;
 219
 220       hwcap = &GL(dl_hwcap);
 221       platform = _dl_string_platform (GL(dl_platform));
 222       if (platform != -1)
 223         platform = 1ULL << platform;
 224
 225       /* Only accept hwcap if it's for the right platform.  */
 226 #define HWCAP_CHECK \
 227       if (GL(dl_osversion)                                                    \
 228           && cache_new->libs[middle].osversion > GL(dl_osversion))            \
 229         continue;                                                             \
 230       if (_DL_PLATFORMS_COUNT && platform != -1                               \
 231           && (lib->hwcap & _DL_HWCAP_PLATFORM) != 0                           \
 232           && (lib->hwcap & _DL_HWCAP_PLATFORM) != platform)                   \
 233         continue;                                                             \
 234       if (hwcap                                                               \
 235           && ((lib->hwcap & *hwcap & ~_DL_HWCAP_PLATFORM) > *hwcap))          \
 236         continue
 237       SEARCH_CACHE (cache_new);
 238     }
 239   else
 240     {
 241       /* This is where the strings start.  */
 242       cache_data = (const char *) &cache->libs[cache->nlibs];
 243
 244       /* Now we can compute how large the string table is.  */
 245       cache_data_size = (const char *) cache + cachesize - cache_data;
 246
 247 #undef HWCAP_CHECK
 248 #define HWCAP_CHECK do {} while (0)
 249       SEARCH_CACHE (cache);
 250     }
 251
 252   /* Print our result if wanted.  */
 253   if (__builtin_expect (GL(dl_debug_mask) & DL_DEBUG_LIBS, 0) && best != NULL)
 254     INTUSE(_dl_debug_printf) ("  trying file=%s\n", best);
 255
 256   return best;
 257 }
 258
 259 #ifndef MAP_COPY
 260 /* If the system does not support MAP_COPY we cannot leave the file open
 261    all the time since this would create problems when the file is replaced.
 262    Therefore we provide this function to close the file and open it again
 263    once needed.  */
 264 void
 265 _dl_unload_cache (void)
 266 {
 267   if (cache != NULL && cache != (struct cache_file *) -1)
 268     {
 269       __munmap (cache, cachesize);
 270       cache = NULL;
 271     }
 272 }
 273 INTDEF (_dl_unload_cache)
 274 #endif