elf/dl-addr.c

   1 /* Locate the shared object symbol nearest a given address.
   2    Copyright (C) 1996-2022 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, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <dlfcn.h>
  20 #include <stddef.h>
  21 #include <ldsodefs.h>
  22
  23
  24 static inline void
  25 __attribute ((always_inline))
  26 determine_info (const ElfW(Addr) addr, struct link_map *match, Dl_info *info,
  27                 struct link_map **mapp, const ElfW(Sym) **symbolp)
  28 {
  29   /* Now we know what object the address lies in.  */
  30   info->dli_fname = match->l_name;
  31   info->dli_fbase = (void *) match->l_map_start;
  32
  33   /* If this is the main program the information is incomplete.  */
  34   if (__builtin_expect (match->l_name[0], 'a') == '\0'
  35       && match->l_type == lt_executable)
  36     info->dli_fname = _dl_argv[0];
  37
  38   const ElfW(Sym) *symtab
  39     = (const ElfW(Sym) *) D_PTR (match, l_info[DT_SYMTAB]);
  40   const char *strtab = (const char *) D_PTR (match, l_info[DT_STRTAB]);
  41
  42   ElfW(Word) strtabsize = match->l_info[DT_STRSZ]->d_un.d_val;
  43
  44   const ElfW(Sym) *matchsym = NULL;
  45   if (match->l_info[ELF_MACHINE_GNU_HASH_ADDRIDX] != NULL)
  46     {
  47       /* We look at all symbol table entries referenced by the hash
  48          table.  */
  49       for (Elf_Symndx bucket = 0; bucket < match->l_nbuckets; ++bucket)
  50         {
  51           Elf32_Word symndx = match->l_gnu_buckets[bucket];
  52           if (symndx != 0)
  53             {
  54               const Elf32_Word *hasharr = &match->l_gnu_chain_zero[symndx];
  55
  56               do
  57                 {
  58                   /* The hash table never references local symbols so
  59                      we can omit that test here.  */
  60                   symndx = ELF_MACHINE_HASH_SYMIDX (match, hasharr);
  61                   if ((symtab[symndx].st_shndx != SHN_UNDEF
  62                        || symtab[symndx].st_value != 0)
  63                       && symtab[symndx].st_shndx != SHN_ABS
  64                       && ELFW(ST_TYPE) (symtab[symndx].st_info) != STT_TLS
  65                       && DL_ADDR_SYM_MATCH (match, &symtab[symndx],
  66                                             matchsym, addr)
  67                       && symtab[symndx].st_name < strtabsize)
  68                     matchsym = (ElfW(Sym) *) &symtab[symndx];
  69                 }
  70               while ((*hasharr++ & 1u) == 0);
  71             }
  72         }
  73     }
  74   else
  75     {
  76       const ElfW(Sym) *symtabend;
  77       if (match->l_info[DT_HASH] != NULL)
  78         symtabend = (symtab
  79                      + ((Elf_Symndx *) D_PTR (match, l_info[DT_HASH]))[1]);
  80       else
  81         /* There is no direct way to determine the number of symbols in the
  82            dynamic symbol table and no hash table is present.  The ELF
  83            binary is ill-formed but what shall we do?  Use the beginning of
  84            the string table which generally follows the symbol table.  */
  85         symtabend = (const ElfW(Sym) *) strtab;
  86
  87       for (; (void *) symtab < (void *) symtabend; ++symtab)
  88         if ((ELFW(ST_BIND) (symtab->st_info) == STB_GLOBAL
  89              || ELFW(ST_BIND) (symtab->st_info) == STB_WEAK)
  90             && __glibc_likely (!dl_symbol_visibility_binds_local_p (symtab))
  91             && ELFW(ST_TYPE) (symtab->st_info) != STT_TLS
  92             && (symtab->st_shndx != SHN_UNDEF
  93                 || symtab->st_value != 0)
  94             && symtab->st_shndx != SHN_ABS
  95             && DL_ADDR_SYM_MATCH (match, symtab, matchsym, addr)
  96             && symtab->st_name < strtabsize)
  97           matchsym = (ElfW(Sym) *) symtab;
  98     }
  99
 100   if (mapp)
 101     *mapp = match;
 102   if (symbolp)
 103     *symbolp = matchsym;
 104
 105   if (matchsym)
 106     {
 107       /* We found a symbol close by.  Fill in its name and exact
 108          address.  */
 109       lookup_t matchl = LOOKUP_VALUE (match);
 110
 111       info->dli_sname = strtab + matchsym->st_name;
 112       info->dli_saddr = DL_SYMBOL_ADDRESS (matchl, matchsym);
 113     }
 114   else
 115     {
 116       /* No symbol matches.  We return only the containing object.  */
 117       info->dli_sname = NULL;
 118       info->dli_saddr = NULL;
 119     }
 120 }
 121
 122
 123 int
 124 _dl_addr (const void *address, Dl_info *info,
 125           struct link_map **mapp, const ElfW(Sym) **symbolp)
 126 {
 127   const ElfW(Addr) addr = DL_LOOKUP_ADDRESS (address);
 128   int result = 0;
 129
 130   /* Protect against concurrent loads and unloads.  */
 131   __rtld_lock_lock_recursive (GL(dl_load_lock));
 132
 133   struct link_map *l = _dl_find_dso_for_object (addr);
 134
 135   if (l)
 136     {
 137       determine_info (addr, l, info, mapp, symbolp);
 138       result = 1;
 139     }
 140
 141   __rtld_lock_unlock_recursive (GL(dl_load_lock));
 142
 143   return result;
 144 }