elf/dl-deps.c

   1 /* Load the dependencies of a mapped object.
   2    Copyright (C) 1996, 1997 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 <link.h>
  21 #include <errno.h>
  22 #include <dlfcn.h>
  23 #include <stdlib.h>
  24 #include <string.h>
  25 #include <assert.h>
  26
  27 /* Whether an shared object references one or more auxiliary objects
  28    is signaled by the AUXTAG entry in l_info.  */
  29 #define AUXTAG  (DT_NUM + DT_PROCNUM + DT_VERSIONTAGNUM \
  30                  + DT_EXTRATAGIDX (DT_AUXILIARY))
  31 /* Whether an shared object references one or more auxiliary objects
  32    is signaled by the AUXTAG entry in l_info.  */
  33 #define FILTERTAG (DT_NUM + DT_PROCNUM + DT_VERSIONTAGNUM \
  34                    + DT_EXTRATAGIDX (DT_FILTER))
  35
  36
  37 /* When loading auxiliary objects we must ignore errors.  It's ok if
  38    an object is missing.  */
  39 struct openaux_args
  40   {
  41     /* The arguments to openaux.  */
  42     struct link_map *map;
  43     int trace_mode;
  44     const char *strtab;
  45     const ElfW(Dyn) *d;
  46
  47     /* The return value of openaux.  */
  48     struct link_map *aux;
  49   };
  50
  51 static void
  52 openaux (void *a)
  53 {
  54   struct openaux_args *args = (struct openaux_args *) a;
  55
  56   args->aux = _dl_map_object (args->map, args->strtab + args->d->d_un.d_val,
  57                               (args->map->l_type == lt_executable
  58                                ? lt_library : args->map->l_type),
  59                               args->trace_mode);
  60 }
  61
  62
  63
  64 /* We use a very special kind of list to track the two kinds paths
  65    through the list of loaded shared objects.  We have to
  66
  67    - produce a flat list with unique members of all involved objects
  68
  69    - produce a flat list of all shared objects.
  70 */
  71 struct list
  72   {
  73     int done;                   /* Nonzero if this map was processed.  */
  74     struct link_map *map;       /* The data.  */
  75
  76     struct list *unique;        /* Elements for normal list.  */
  77     struct list *dup;           /* Elements in complete list.  */
  78   };
  79
  80
  81 void
  82 _dl_map_object_deps (struct link_map *map,
  83                      struct link_map **preloads, unsigned int npreloads,
  84                      int trace_mode)
  85 {
  86   struct list known[1 + npreloads + 1];
  87   struct list *runp, *utail, *dtail;
  88   unsigned int nlist, nduplist, i;
  89
  90   inline void preload (struct link_map *map)
  91     {
  92       known[nlist].done = 0;
  93       known[nlist].map = map;
  94
  95       known[nlist].unique = &known[nlist + 1];
  96       known[nlist].dup = &known[nlist + 1];
  97
  98       ++nlist;
  99       /* We use `l_reserved' as a mark bit to detect objects we have
 100          already put in the search list and avoid adding duplicate
 101          elements later in the list.  */
 102       map->l_reserved = 1;
 103     }
 104
 105   /* No loaded object so far.  */
 106   nlist = 0;
 107
 108   /* First load MAP itself.  */
 109   preload (map);
 110
 111   /* Add the preloaded items after MAP but before any of its dependencies.  */
 112   for (i = 0; i < npreloads; ++i)
 113     preload (preloads[i]);
 114
 115   /* Terminate the lists.  */
 116   known[nlist - 1].unique = NULL;
 117   known[nlist - 1].dup = NULL;
 118
 119   /* Pointer to last unique object.  */
 120   utail = &known[nlist - 1];
 121   /* Pointer to last loaded object.  */
 122   dtail = &known[nlist - 1];
 123
 124   /* Until now we have the same number of libraries in the normal and
 125      the list with duplicates.  */
 126   nduplist = nlist;
 127
 128   /* Process each element of the search list, loading each of its
 129      auxiliary objects and immediate dependencies.  Auxiliary objects
 130      will be added in the list before the object itself and
 131      dependencies will be appended to the list as we step through it.
 132      This produces a flat, ordered list that represents a
 133      breadth-first search of the dependency tree.
 134
 135      The whole process is complicated by the fact that we better
 136      should use alloca for the temporary list elements.  But using
 137      alloca means we cannot use recursive function calls.  */
 138   for (runp = known; runp; )
 139     {
 140       struct link_map *l = runp->map;
 141
 142       if (l->l_info[AUXTAG] || l->l_info[FILTERTAG] || l->l_info[DT_NEEDED])
 143         {
 144           const char *strtab = ((void *) l->l_addr
 145                                 + l->l_info[DT_STRTAB]->d_un.d_ptr);
 146           struct openaux_args args;
 147           struct list *orig;
 148           const ElfW(Dyn) *d;
 149
 150           /* Mark map as processed.  */
 151           runp->done = 1;
 152
 153           args.strtab = strtab;
 154           args.map = l;
 155           args.trace_mode = trace_mode;
 156           orig = runp;
 157
 158           for (d = l->l_ld; d->d_tag != DT_NULL; ++d)
 159             if (d->d_tag == DT_NEEDED)
 160               {
 161                 /* Map in the needed object.  */
 162                 struct link_map *dep
 163                   = _dl_map_object (l, strtab + d->d_un.d_val,
 164                                     l->l_type == lt_executable ? lt_library :
 165                                     l->l_type, trace_mode);
 166                 /* Allocate new entry.  */
 167                 struct list *newp = alloca (sizeof (struct list));
 168
 169                 /* Add it in any case to the duplicate list.  */
 170                 newp->map = dep;
 171                 newp->dup = NULL;
 172                 dtail->dup = newp;
 173                 dtail = newp;
 174                 ++nduplist;
 175
 176                 if (dep->l_reserved)
 177                   /* This object is already in the search list we are
 178                      building.  Don't add a duplicate pointer.
 179                      Release the reference just added by
 180                      _dl_map_object.  */
 181                   --dep->l_opencount;
 182                 else
 183                   {
 184                     /* Append DEP to the unique list.  */
 185                     newp->done = 0;
 186                     newp->unique = NULL;
 187                     utail->unique = newp;
 188                     utail = newp;
 189                     ++nlist;
 190                     /* Set the mark bit that says it's already in the list.  */
 191                     dep->l_reserved = 1;
 192                   }
 193               }
 194             else if (d->d_tag == DT_AUXILIARY || d->d_tag == DT_FILTER)
 195               {
 196                 char *errstring;
 197                 const char *objname;
 198                 struct list *newp;
 199
 200                 if (d->d_tag == DT_AUXILIARY)
 201                   {
 202                     /* Store the tag in the argument structure.  */
 203                     args.d = d;
 204
 205                     /* We must be prepared that the addressed shared
 206                        object is not available.  */
 207                     if (_dl_catch_error (&errstring, &objname, openaux, &args))
 208                       {
 209                         /* We are not interested in the error message.  */
 210                         assert (errstring != NULL);
 211                         free (errstring);
 212
 213                         /* Simply ignore this error and continue the work.  */
 214                         continue;
 215                       }
 216                   }
 217                 else
 218                   /* For filter objects the dependency must be available.  */
 219                   args.aux = _dl_map_object (l, strtab + d->d_un.d_val,
 220                                              (l->l_type == lt_executable
 221                                               ? lt_library : l->l_type),
 222                                              trace_mode);
 223
 224                 /* The auxiliary object is actually available.
 225                    Incorporate the map in all the lists.  */
 226
 227                 /* Allocate new entry.  This always has to be done.  */
 228                 newp = alloca (sizeof (struct list));
 229
 230                 /* Copy the content of the current entry over.  */
 231                 memcpy (newp, orig, sizeof (*newp));
 232
 233                 /* Initialize new entry.  */
 234                 orig->done = 0;
 235                 orig->map = args.aux;
 236                 orig->dup = newp;
 237
 238                 /* We must handle two situations here: the map is new,
 239                    so we must add it in all three lists.  If the map
 240                    is already known, we have two further possibilities:
 241                    - if the object is before the current map in the
 242                    search list, we do nothing.  It is already found
 243                    early
 244                    - if the object is after the current one, we must
 245                    move it just before the current map to make sure
 246                    the symbols are found early enough
 247                 */
 248                 if (args.aux->l_reserved)
 249                   {
 250                     /* The object is already somewhere in the list.
 251                        Locate it first.  */
 252                     struct list *late;
 253
 254                     /* This object is already in the search list we
 255                        are building.  Don't add a duplicate pointer.
 256                        Release the reference just added by
 257                        _dl_map_object.  */
 258                     --args.aux->l_opencount;
 259
 260                     for (late = orig; late->unique; late = late->unique)
 261                       if (late->unique->map == args.aux)
 262                         break;
 263
 264                     if (late->unique)
 265                       {
 266                         /* The object is somewhere behind the current
 267                            position in the search path.  We have to
 268                            move it to this earlier position.  */
 269                         orig->unique = newp;
 270
 271                         /* Now remove the later entry from the unique list.  */
 272                         late->unique = late->unique->unique;
 273
 274                         /* We must move the earlier in the chain.  */
 275                         if (args.aux->l_prev)
 276                           args.aux->l_prev->l_next = args.aux->l_next;
 277                         if (args.aux->l_next)
 278                           args.aux->l_next->l_prev = args.aux->l_prev;
 279
 280                         args.aux->l_prev = newp->map->l_prev;
 281                         newp->map->l_prev = args.aux;
 282                         if (args.aux->l_prev != NULL)
 283                           args.aux->l_prev->l_next = args.aux;
 284                         args.aux->l_next = newp->map;
 285                       }
 286                     else
 287                       {
 288                         /* The object must be somewhere earlier in the
 289                            list.  That's good, we only have to insert
 290                            an entry for the duplicate list.  */
 291                         orig->unique = NULL;    /* Never used.  */
 292
 293                         /* Now we have a problem.  The element
 294                            pointing to ORIG in the unique list must
 295                            point to NEWP now.  This is the only place
 296                            where we need this backreference and this
 297                            situation is really not that frequent.  So
 298                            we don't use a double-linked list but
 299                            instead search for the preceding element.  */
 300                         late = known;
 301                         while (late->unique != orig)
 302                           late = late->unique;
 303                         late->unique = newp;
 304                       }
 305                   }
 306                 else
 307                   {
 308                     /* This is easy.  We just add the symbol right here.  */
 309                     orig->unique = newp;
 310                     ++nlist;
 311                     /* Set the mark bit that says it's already in the list.  */
 312                     args.aux->l_reserved = 1;
 313
 314                     /* The only problem is that in the double linked
 315                        list of all objects we don't have this new
 316                        object at the correct place.  Correct this here.  */
 317                     if (args.aux->l_prev)
 318                       args.aux->l_prev->l_next = args.aux->l_next;
 319                     if (args.aux->l_next)
 320                       args.aux->l_next->l_prev = args.aux->l_prev;
 321
 322                     args.aux->l_prev = newp->map->l_prev;
 323                     newp->map->l_prev = args.aux;
 324                     if (args.aux->l_prev != NULL)
 325                       args.aux->l_prev->l_next = args.aux;
 326                     args.aux->l_next = newp->map;
 327                   }
 328
 329                 /* Move the tail pointers if necessary.  */
 330                 if (orig == utail)
 331                   utail = newp;
 332                 if (orig == dtail)
 333                   dtail = newp;
 334
 335                 /* Move on the insert point.  */
 336                 orig = newp;
 337
 338                 /* We always add an entry to the duplicate list.  */
 339                 ++nduplist;
 340               }
 341         }
 342       else
 343         /* Mark as processed.  */
 344         runp->done = 1;
 345
 346       /* If we have no auxiliary objects just go on to the next map.  */
 347       if (runp->done)
 348         do
 349           runp = runp->unique;
 350         while (runp && runp->done);
 351     }
 352
 353   /* Store the search list we built in the object.  It will be used for
 354      searches in the scope of this object.  */
 355   map->l_searchlist = malloc (nlist * sizeof (struct link_map *));
 356   if (map->l_searchlist == NULL)
 357     _dl_signal_error (ENOMEM, map->l_name,
 358                       "cannot allocate symbol search list");
 359   map->l_nsearchlist = nlist;
 360
 361   for (nlist = 0, runp = known; runp; runp = runp->unique)
 362     {
 363       map->l_searchlist[nlist++] = runp->map;
 364
 365       /* Now clear all the mark bits we set in the objects on the search list
 366          to avoid duplicates, so the next call starts fresh.  */
 367       runp->map->l_reserved = 0;
 368     }
 369
 370   map->l_ndupsearchlist = nduplist;
 371   if (nlist == nduplist)
 372     map->l_dupsearchlist = map->l_searchlist;
 373   else
 374     {
 375       map->l_dupsearchlist = malloc (nduplist * sizeof (struct link_map *));
 376       if (map->l_dupsearchlist == NULL)
 377         _dl_signal_error (ENOMEM, map->l_name,
 378                           "cannot allocate symbol search list");
 379
 380       for (nlist = 0, runp = known; runp; runp = runp->dup)
 381         map->l_dupsearchlist[nlist++] = runp->map;
 382     }
 383 }