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 <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 /* System-dependent function to read a file's whole contents
  30    in the most convenient manner available.  */
  31 extern void *_dl_sysdep_read_whole_file (const char *filename,
  32                                          size_t *filesize_ptr,
  33                                          int mmap_prot);
  34
  35 extern const char *_dl_platform;
  36
  37 #ifndef _DL_PLATFORMS_COUNT
  38 # define _DL_PLATFORMS_COUNT 0
  39 #endif
  40
  41 /* This is the starting address and the size of the mmap()ed file.  */
  42 static struct cache_file *cache;
  43 static struct cache_file_new *cache_new;
  44 static size_t cachesize;
  45
  46 /* 1 if cache_data + PTR points into the cache.  */
  47 #define _dl_cache_verify_ptr(ptr) (ptr < cache_data_size)
  48
  49 /* This is the cache ID we expect.  Normally it is 3 for glibc linked
  50    binaries.  */
  51 int _dl_correct_cache_id = _DL_CACHE_DEFAULT_ID;
  52
  53 #define SEARCH_CACHE(cache)                                               \
  54 /* We use binary search since the table is sorted in the cache file.      \
  55    The first matching entry in the table is returned.                     \
  56    It is important to use the same algorithm as used while generating     \
  57    the cache file.  */                                                    \
  58 do                                                                        \
  59   {                                                                       \
  60     left = 0;                                                             \
  61     right = cache->nlibs - 1;                                             \
  62     middle = (left + right) / 2;                                          \
  63     cmpres = 1;                                                           \
  64                                                                           \
  65     while (left <= right)                                                 \
  66       {                                                                   \
  67         /* Make sure string table indices are not bogus before using      \
  68            them.  */                                                      \
  69         if (! _dl_cache_verify_ptr (cache->libs[middle].key))             \
  70           {                                                               \
  71             cmpres = 1;                                                   \
  72             break;                                                        \
  73           }                                                               \
  74                                                                           \
  75         /* Actually compare the entry with the key.  */                   \
  76         cmpres = _dl_cache_libcmp (name,                                  \
  77                                    cache_data + cache->libs[middle].key); \
  78         if (cmpres == 0)                                                  \
  79           /* Found it.  */                                                \
  80           break;                                                          \
  81                                                                           \
  82         if (cmpres < 0)                                                   \
  83           left = middle + 1;                                              \
  84         else                                                              \
  85           right = middle - 1;                                             \
  86                                                                           \
  87         middle = (left + right) / 2;                                      \
  88       }                                                                   \
  89                                                                           \
  90     if (cmpres == 0)                                                      \
  91       {                                                                   \
  92         /* LEFT now marks the last entry for which we know the name is    \
  93            correct.  */                                                   \
  94         left = middle;                                                    \
  95                                                                           \
  96         /* There might be entries with this name before the one we        \
  97            found.  So we have to find the beginning.  */                  \
  98         while (middle > 0                                                 \
  99                /* Make sure string table indices are not bogus before     \
 100                   using them.  */                                         \
 101                && _dl_cache_verify_ptr (cache->libs[middle - 1].key)      \
 102                /* Actually compare the entry.  */                         \
 103                && (_dl_cache_libcmp (name,                                \
 104                                      cache_data                           \
 105                                      + cache->libs[middle - 1].key)       \
 106                    == 0))                                                 \
 107           --middle;                                                       \
 108                                                                           \
 109         do                                                                \
 110           {                                                               \
 111             int flags;                                                    \
 112                                                                           \
 113             /* Only perform the name test if necessary.  */               \
 114             if (middle > left                                             \
 115                 /* We haven't seen this string so far.  Test whether the  \
 116                    index is ok and whether the name matches.  Otherwise   \
 117                    we are done.  */                                       \
 118                 && (! _dl_cache_verify_ptr (cache->libs[middle].key)      \
 119                     || (_dl_cache_libcmp (name,                           \
 120                                           cache_data                      \
 121                                           + cache->libs[middle].key)      \
 122                         != 0)))                                           \
 123               break;                                                      \
 124                                                                           \
 125             flags = cache->libs[middle].flags;                            \
 126             if (_dl_cache_check_flags (flags)                             \
 127                 && _dl_cache_verify_ptr (cache->libs[middle].value))      \
 128               {                                                           \
 129                 if (best == NULL || flags == _dl_correct_cache_id)        \
 130                   {                                                       \
 131                     HWCAP_CHECK;                                          \
 132                     best = cache_data + cache->libs[middle].value;        \
 133                                                                           \
 134                     if (flags == _dl_correct_cache_id)                    \
 135                       /* We've found an exact match for the shared        \
 136                          object and no general `ELF' release.  Stop       \
 137                          searching.  */                                   \
 138                       break;                                              \
 139                   }                                                       \
 140               }                                                           \
 141           }                                                               \
 142         while (++middle <= right);                                        \
 143       }                                                                   \
 144   }                                                                       \
 145 while (0)
 146
 147
 148
 149 /* Look up NAME in ld.so.cache and return the file name stored there,
 150    or null if none is found.  */
 151
 152 const char *
 153 _dl_load_cache_lookup (const char *name)
 154 {
 155   int left, right, middle;
 156   int cmpres;
 157   const char *cache_data;
 158   uint32_t cache_data_size;
 159   const char *best;
 160
 161   /* Print a message if the loading of libs is traced.  */
 162   if (_dl_debug_libs)
 163     _dl_debug_message (1, " search cache=", LD_SO_CACHE, "\n", NULL);
 164
 165   if (cache == NULL)
 166     {
 167       /* Read the contents of the file.  */
 168       void *file = _dl_sysdep_read_whole_file (LD_SO_CACHE, &cachesize,
 169                                                PROT_READ);
 170
 171       /* We can handle three different cache file formats here:
 172          - the old libc5/glibc2.0/2.1 format
 173          - the old format with the new format in it
 174          - only the new format
 175          The following checks if the cache contains any of these formats.  */
 176       if (file != NULL && cachesize > sizeof *cache
 177           && memcmp (file, CACHEMAGIC, sizeof CACHEMAGIC - 1) == 0)
 178         {
 179           size_t offset;
 180           /* Looks ok.  */
 181           cache = file;
 182
 183           /* Check for new version.  */
 184           offset = ALIGN_CACHE (sizeof (struct cache_file)
 185                                 + cache->nlibs * sizeof (struct file_entry));
 186
 187           cache_new = (struct cache_file_new *) ((void *) cache + offset);
 188           if (cachesize < (offset + sizeof (struct cache_file_new))
 189               || memcmp (cache_new->magic, CACHEMAGIC_VERSION_NEW,
 190                          sizeof CACHEMAGIC_VERSION_NEW - 1) != 0)
 191             cache_new = (void *) -1;
 192         }
 193       else if (file != NULL && cachesize > sizeof *cache_new
 194                && memcmp (file, CACHEMAGIC_VERSION_NEW,
 195                           sizeof CACHEMAGIC_VERSION_NEW - 1) == 0)
 196         {
 197           cache_new = file;
 198           cache = file;
 199         }
 200       else
 201         {
 202           if (file != NULL)
 203             __munmap (file, cachesize);
 204           cache = (void *) -1;
 205         }
 206
 207       assert (cache != NULL);
 208     }
 209
 210   if (cache == (void *) -1)
 211     /* Previously looked for the cache file and didn't find it.  */
 212     return NULL;
 213
 214   best = NULL;
 215
 216   if (cache_new != (void *) -1)
 217     {
 218       /* This file ends in static libraries where we don't have a hwcap.  */
 219       unsigned long int *hwcap;
 220       uint64_t platform;
 221       weak_extern (_dl_hwcap);
 222
 223       /* This is where the strings start.  */
 224       cache_data = (const char *) cache_new;
 225
 226       /* Now we can compute how large the string table is.  */
 227       cache_data_size = (const char *) cache + cachesize - cache_data;
 228
 229       hwcap = &_dl_hwcap;
 230       platform = _dl_string_platform (_dl_platform);
 231       if (platform != -1)
 232         platform = 1ULL << platform;
 233
 234       /* Only accept hwcap if it's for the right platform.  */
 235 #define HWCAP_CHECK                                                            \
 236       if (_DL_PLATFORMS_COUNT && platform != -1                                \
 237           && (cache_new->libs[middle].hwcap & _DL_HWCAP_PLATFORM) != 0         \
 238           && (cache_new->libs[middle].hwcap & _DL_HWCAP_PLATFORM) != platform) \
 239         continue;                                                              \
 240       if (hwcap                                                                \
 241           && ((cache_new->libs[middle].hwcap & *hwcap & ~_DL_HWCAP_PLATFORM)   \
 242               > *hwcap))                                                       \
 243         continue
 244       SEARCH_CACHE (cache_new);
 245     }
 246   else
 247     {
 248       /* This is where the strings start.  */
 249       cache_data = (const char *) &cache->libs[cache->nlibs];
 250
 251       /* Now we can compute how large the string table is.  */
 252       cache_data_size = (const char *) cache + cachesize - cache_data;
 253
 254 #undef HWCAP_CHECK
 255 #define HWCAP_CHECK do {} while (0)
 256       SEARCH_CACHE (cache);
 257     }
 258
 259   /* Print our result if wanted.  */
 260   if (_dl_debug_libs && best != NULL)
 261     _dl_debug_message (1, "  trying file=", best, "\n", NULL);
 262
 263   return best;
 264 }
 265
 266 #ifndef MAP_COPY
 267 /* If the system does not support MAP_COPY we cannot leave the file open
 268    all the time since this would create problems when the file is replaced.
 269    Therefore we provide this function to close the file and open it again
 270    once needed.  */
 271 void
 272 _dl_unload_cache (void)
 273 {
 274   if (cache != NULL && cache != (struct cache_file *) -1)
 275     {
 276       __munmap (cache, cachesize);
 277       cache = NULL;
 278     }
 279 }
 280 #endif