ldso/ldso/dl-hash.c

   1 /* vi: set sw=4 ts=4: */
   2 /*
   3  * Program to load an ELF binary on a linux system, and run it
   4  * after resolving ELF shared library symbols
   5  *
   6  * Copyright (C) 2004 by Joakim Tjernlund <joakim.tjernlund@lumentis.se>
   7  * Copyright (C) 2000-2006 by Erik Andersen <andersen@codepoet.org>
   8  * Copyright (c) 1994-2000 Eric Youngdale, Peter MacDonald,
   9  *                              David Engel, Hongjiu Lu and Mitch D'Souza
  10  *
  11  * Redistribution and use in source and binary forms, with or without
  12  * modification, are permitted provided that the following conditions
  13  * are met:
  14  * 1. Redistributions of source code must retain the above copyright
  15  *    notice, this list of conditions and the following disclaimer.
  16  * 2. The name of the above contributors may not be
  17  *    used to endorse or promote products derived from this software
  18  *    without specific prior written permission.
  19  *
  20  * THIS SOFTWARE IS PROVIDED BY THE CONTRIBUTORS ``AS IS'' AND
  21  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  22  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  23  * ARE DISCLAIMED.  IN NO EVENT SHALL THE CONTRIBUTORS BE LIABLE
  24  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  25  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  26  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  27  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  28  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  29  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  30  * SUCH DAMAGE.
  31  */
  32
  33
  34 /* Various symbol table handling functions, including symbol lookup */
  35 /*
  36  * This is the list of modules that are loaded when the image is first
  37  * started.  As we add more via dlopen, they get added into other
  38  * chains.
  39  */
  40 struct dyn_elf *_dl_symbol_tables = NULL;
  41
  42 /*
  43  * This is the list of modules that are loaded via dlopen.  We may need
  44  * to search these for RTLD_GLOBAL files.
  45  */
  46 struct dyn_elf *_dl_handles = NULL;
  47
  48 #ifdef __LDSO_GNU_HASH_SUPPORT__
  49 /* This is the new hash function that is used by the ELF linker to generate the
  50  * GNU hash table that each executable and library will have if --hash-style=[gnu,both]
  51  * is passed to the linker. We need it to decode the GNU hash table.  */
  52 static __inline__ Elf_Symndx _dl_gnu_hash (const unsigned char *name)
  53 {
  54   unsigned long h = 5381;
  55   unsigned char c;
  56   for (c = *name; c != '\0'; c = *++name)
  57     h = h * 33 + c;
  58   return h & 0xffffffff;
  59 }
  60 #endif
  61
  62 /* This is the hash function that is used by the ELF linker to generate the
  63  * hash table that each executable and library is required to have.  We need
  64  * it to decode the hash table.  */
  65 static __inline__ Elf_Symndx _dl_elf_hash(const unsigned char *name)
  66 {
  67         unsigned long hash=0;
  68         unsigned long tmp;
  69
  70         while (*name) {
  71                 hash = (hash << 4) + *name++;
  72                 tmp = hash & 0xf0000000;
  73                 /* The algorithm specified in the ELF ABI is as follows:
  74                    if (tmp != 0)
  75                        hash ^= tmp >> 24;
  76                    hash &= ~tmp;
  77                    But the following is equivalent and a lot
  78                    faster, especially on modern processors. */
  79                 hash ^= tmp;
  80                 hash ^= tmp >> 24;
  81         }
  82         return hash;
  83 }
  84
  85 /*
  86  * We call this function when we have just read an ELF library or executable.
  87  * We add the relevant info to the symbol chain, so that we can resolve all
  88  * externals properly.
  89  */
  90 struct elf_resolve *_dl_add_elf_hash_table(const char *libname,
  91         DL_LOADADDR_TYPE loadaddr, unsigned long *dynamic_info, unsigned long dynamic_addr,
  92         attribute_unused unsigned long dynamic_size)
  93 {
  94         Elf_Symndx *hash_addr;
  95         struct elf_resolve *tpnt;
  96         int i;
  97
  98         tpnt = _dl_malloc(sizeof(struct elf_resolve));
  99         _dl_memset(tpnt, 0, sizeof(struct elf_resolve));
 100
 101         if (!_dl_loaded_modules)
 102                 _dl_loaded_modules = tpnt;
 103         else {
 104                 struct elf_resolve *t = _dl_loaded_modules;
 105                 while (t->next)
 106                         t = t->next;
 107                 t->next = tpnt;
 108                 t->next->prev = t;
 109                 tpnt = t->next;
 110         }
 111
 112         tpnt->next = NULL;
 113         tpnt->init_flag = 0;
 114         tpnt->libname = _dl_strdup(libname);
 115         tpnt->dynamic_addr = (ElfW(Dyn) *)dynamic_addr;
 116         tpnt->libtype = loaded_file;
 117
 118 #ifdef __DSBT__
 119         if (dynamic_info[DT_DSBT_BASE_IDX] != 0)
 120                 tpnt->dsbt_table = (void *)dynamic_info[DT_DSBT_BASE_IDX];
 121         if (dynamic_info[DT_DSBT_SIZE_IDX] != 0)
 122                 tpnt->dsbt_size = dynamic_info[DT_DSBT_SIZE_IDX];
 123         if (dynamic_info[DT_DSBT_INDEX_IDX] != 0)
 124                 tpnt->dsbt_index = dynamic_info[DT_DSBT_INDEX_IDX];
 125 #endif /* __DSBT__ */
 126
 127 #ifdef __LDSO_GNU_HASH_SUPPORT__
 128         if (dynamic_info[DT_GNU_HASH_IDX] != 0) {
 129                 Elf32_Word *hash32 = (Elf_Symndx*)dynamic_info[DT_GNU_HASH_IDX];
 130
 131                 tpnt->nbucket = *hash32++;
 132                 Elf32_Word symbias = *hash32++;
 133                 Elf32_Word bitmask_nwords = *hash32++;
 134                 /* Must be a power of two.  */
 135                 _dl_assert ((bitmask_nwords & (bitmask_nwords - 1)) == 0);
 136                 tpnt->l_gnu_bitmask_idxbits = bitmask_nwords - 1;
 137                 tpnt->l_gnu_shift = *hash32++;
 138
 139                 tpnt->l_gnu_bitmask = (ElfW(Addr) *) hash32;
 140                 hash32 += __ELF_NATIVE_CLASS / 32 * bitmask_nwords;
 141
 142                 tpnt->l_gnu_buckets = hash32;
 143                 hash32 += tpnt->nbucket;
 144                 tpnt->l_gnu_chain_zero = hash32 - symbias;
 145         } else
 146         /* Fall using old SysV hash table if GNU hash is not present */
 147 #endif
 148
 149         if (dynamic_info[DT_HASH] != 0) {
 150                 hash_addr = (Elf_Symndx*)dynamic_info[DT_HASH];
 151                 tpnt->nbucket = *hash_addr++;
 152                 tpnt->nchain = *hash_addr++;
 153                 tpnt->elf_buckets = hash_addr;
 154                 hash_addr += tpnt->nbucket;
 155                 tpnt->chains = hash_addr;
 156         }
 157         tpnt->loadaddr = loadaddr;
 158         for (i = 0; i < DYNAMIC_SIZE; i++)
 159                 tpnt->dynamic_info[i] = dynamic_info[i];
 160         return tpnt;
 161 }
 162
 163
 164 /* Routine to check whether the symbol matches.  */
 165 static __attribute_noinline__ const ElfW(Sym) *
 166 check_match (const ElfW(Sym) *sym, char *strtab, const char* undef_name, int type_class)
 167 {
 168
 169 #if defined(USE_TLS) && USE_TLS
 170         if ((sym->st_value == 0 && (ELF_ST_TYPE(sym->st_info) != STT_TLS))
 171                       || (type_class & (sym->st_shndx == SHN_UNDEF)))
 172                 /* No value or undefined symbol itself */
 173                 return NULL;
 174
 175         if (ELF_ST_TYPE(sym->st_info) > STT_FUNC
 176                 && ELF_ST_TYPE(sym->st_info) != STT_COMMON
 177                 && ELF_ST_TYPE(sym->st_info) != STT_TLS)
 178                 /* Ignore all but STT_NOTYPE, STT_OBJECT, STT_FUNC and STT_COMMON
 179                  * entries (and STT_TLS if TLS is supported) since these
 180                  * are no code/data definitions.
 181                  */
 182                 return NULL;
 183 #else
 184         if (type_class & (sym->st_shndx == SHN_UNDEF))
 185                 /* undefined symbol itself */
 186                 return NULL;
 187
 188         if (sym->st_value == 0)
 189                 /* No value */
 190                 return NULL;
 191
 192         if (ELF_ST_TYPE(sym->st_info) > STT_FUNC
 193                 && ELF_ST_TYPE(sym->st_info) != STT_COMMON)
 194                 /* Ignore all but STT_NOTYPE, STT_OBJECT, STT_FUNC
 195                  * and STT_COMMON entries since these are no
 196                  * code/data definitions
 197                  */
 198                 return NULL;
 199 #endif
 200 #ifdef ARCH_SKIP_RELOC
 201         if (ARCH_SKIP_RELOC(type_class, sym))
 202                 return NULL;
 203 #endif
 204         if (_dl_strcmp(strtab + sym->st_name, undef_name) != 0)
 205                 return NULL;
 206
 207         /* This is the matching symbol */
 208         return sym;
 209 }
 210
 211
 212 #ifdef __LDSO_GNU_HASH_SUPPORT__
 213
 214 static __always_inline const ElfW(Sym) *
 215 _dl_lookup_gnu_hash(struct elf_resolve *tpnt, ElfW(Sym) *symtab, unsigned long hash,
 216                                         const char* undef_name, int type_class)
 217 {
 218         Elf_Symndx symidx;
 219         const ElfW(Sym) *sym;
 220         char *strtab;
 221
 222         const ElfW(Addr) *bitmask = tpnt->l_gnu_bitmask;
 223
 224         ElfW(Addr) bitmask_word = bitmask[(hash / __ELF_NATIVE_CLASS) & tpnt->l_gnu_bitmask_idxbits];
 225
 226         unsigned int hashbit1 = hash & (__ELF_NATIVE_CLASS - 1);
 227         unsigned int hashbit2 = ((hash >> tpnt->l_gnu_shift) & (__ELF_NATIVE_CLASS - 1));
 228         _dl_assert (bitmask != NULL);
 229
 230         if (unlikely((bitmask_word >> hashbit1) & (bitmask_word >> hashbit2) & 1)) {
 231                 unsigned long rem;
 232                 Elf32_Word bucket;
 233
 234                 do_rem (rem, hash, tpnt->nbucket);
 235                 bucket = tpnt->l_gnu_buckets[rem];
 236
 237                 if (bucket != 0) {
 238                         const Elf32_Word *hasharr = &tpnt->l_gnu_chain_zero[bucket];
 239                         do {
 240                                 if (((*hasharr ^ hash) >> 1) == 0) {
 241                                         symidx = hasharr - tpnt->l_gnu_chain_zero;
 242                                         strtab = (char *) (tpnt->dynamic_info[DT_STRTAB]);
 243                                         sym = check_match (&symtab[symidx], strtab, undef_name, type_class);
 244                                         if (sym != NULL)
 245                                                 return sym;
 246                                 }
 247                         } while ((*hasharr++ & 1u) == 0);
 248                 }
 249         }
 250         /* No symbol found.  */
 251         return NULL;
 252 }
 253 #endif
 254
 255 static __always_inline const ElfW(Sym) *
 256 _dl_lookup_sysv_hash(struct elf_resolve *tpnt, ElfW(Sym) *symtab, unsigned long hash,  const char* undef_name, int type_class)
 257 {
 258         unsigned long hn;
 259         char *strtab;
 260         const ElfW(Sym) *sym;
 261         Elf_Symndx symidx;
 262
 263         /* Avoid calling .urem here. */
 264         do_rem(hn, hash, tpnt->nbucket);
 265         strtab = (char *) (tpnt->dynamic_info[DT_STRTAB]);
 266
 267         _dl_assert(tpnt->elf_buckets != NULL);
 268
 269         for (symidx = tpnt->elf_buckets[hn]; symidx != STN_UNDEF; symidx = tpnt->chains[symidx]) {
 270                 sym = check_match (&symtab[symidx], strtab, undef_name, type_class);
 271                 if (sym != NULL)
 272                         /* At this point the symbol is that we are looking for */
 273                         return sym;
 274         }
 275         /* No symbol found into the current module*/
 276         return NULL;
 277 }
 278
 279 /*
 280  * This function resolves externals, and this is either called when we process
 281  * relocations or when we call an entry in the PLT table for the first time.
 282  */
 283 char *_dl_find_hash(const char *name, struct r_scope_elem *scope, struct elf_resolve *mytpnt,
 284         int type_class, struct symbol_ref *sym_ref)
 285 {
 286         struct elf_resolve *tpnt = NULL;
 287         ElfW(Sym) *symtab;
 288         int i = 0;
 289
 290         unsigned long elf_hash_number = 0xffffffff;
 291         const ElfW(Sym) *sym = NULL;
 292
 293         char *weak_result = NULL;
 294         struct r_scope_elem *loop_scope;
 295
 296 #ifdef __LDSO_GNU_HASH_SUPPORT__
 297         unsigned long gnu_hash_number = _dl_gnu_hash((const unsigned char *)name);
 298 #endif
 299
 300         if ((sym_ref) && (sym_ref->sym) && (ELF32_ST_VISIBILITY(sym_ref->sym->st_other) == STV_PROTECTED)) {
 301                         sym = sym_ref->sym;
 302                 if (mytpnt)
 303                         tpnt = mytpnt;
 304         } else
 305         for (loop_scope = scope; loop_scope && !sym; loop_scope = loop_scope->next) {
 306                 for (i = 0; i < loop_scope->r_nlist; i++) {
 307                         tpnt = loop_scope->r_list[i];
 308
 309                         if (!(tpnt->rtld_flags & RTLD_GLOBAL) && mytpnt) {
 310                                 if (mytpnt == tpnt)
 311                                         ;
 312                                 else {
 313                                         struct init_fini_list *tmp;
 314
 315                                         for (tmp = mytpnt->rtld_local; tmp; tmp = tmp->next) {
 316                                                 if (tmp->tpnt == tpnt)
 317                                                         break;
 318                                         }
 319                                         if (!tmp)
 320                                                 continue;
 321                                 }
 322                         }
 323                         /* Don't search the executable when resolving a copy reloc. */
 324                         if ((type_class &  ELF_RTYPE_CLASS_COPY) && tpnt->libtype == elf_executable)
 325                                 continue;
 326
 327                         /* If the hash table is empty there is nothing to do here.  */
 328                         if (tpnt->nbucket == 0)
 329                                 continue;
 330
 331                         symtab = (ElfW(Sym) *) (intptr_t) (tpnt->dynamic_info[DT_SYMTAB]);
 332
 333 #ifdef __LDSO_GNU_HASH_SUPPORT__
 334                         /* Prefer GNU hash style, if any */
 335                         if (tpnt->l_gnu_bitmask) {
 336                                 sym = _dl_lookup_gnu_hash(tpnt, symtab, gnu_hash_number, name, type_class);
 337                                 if (sym != NULL)
 338                                         /* If sym has been found, do not search further */
 339                                         break;
 340                         } else {
 341 #endif
 342                                 /* Use the old SysV-style hash table */
 343
 344                                 /* Calculate the old sysv hash number only once */
 345                                 if (elf_hash_number == 0xffffffff)
 346                                         elf_hash_number = _dl_elf_hash((const unsigned char *)name);
 347
 348                                 sym = _dl_lookup_sysv_hash(tpnt, symtab, elf_hash_number, name, type_class);
 349                                 if (sym != NULL)
 350                                         /* If sym has been found, do not search further */
 351                                         break;
 352 #ifdef __LDSO_GNU_HASH_SUPPORT__
 353                         }
 354 #endif
 355                 } /* End of inner for */
 356         }
 357
 358         if (sym) {
 359                 if (sym_ref) {
 360                         sym_ref->sym = sym;
 361                         sym_ref->tpnt = tpnt;
 362                 }
 363                 /* At this point we have found the requested symbol, do binding */
 364 #if defined(USE_TLS) && USE_TLS
 365                 if (ELF_ST_TYPE(sym->st_info) == STT_TLS) {
 366                         _dl_assert(sym_ref != NULL);
 367                         return (char *)sym->st_value;
 368                 }
 369 #endif
 370
 371                 switch (ELF_ST_BIND(sym->st_info)) {
 372                         case STB_WEAK:
 373 #if 0
 374         /* Perhaps we should support old style weak symbol handling
 375         * per what glibc does when you export LD_DYNAMIC_WEAK */
 376                                 if (!weak_result)
 377                                         weak_result = (char *)DL_FIND_HASH_VALUE(tpnt, type_class, sym);
 378                                 break;
 379 #endif
 380                         case STB_GLOBAL:
 381 #ifdef __FDPIC__
 382                         if (sym_ref)
 383                                 sym_ref->tpnt = tpnt;
 384 #endif
 385                                 return (char *)DL_FIND_HASH_VALUE(tpnt, type_class, sym);
 386                         default:        /* Local symbols not handled here */
 387                                 break;
 388                 }
 389         }
 390 #ifdef __FDPIC__
 391         if (sym_ref)
 392                 sym_ref->tpnt = tpnt;
 393 #endif
 394         return weak_result;
 395 }