elf/dl-addr.c

   1 /* Locate the shared object symbol nearest a given address.
   2    Copyright (C) 1996-2007, 2009 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 <dlfcn.h>
  21 #include <stddef.h>
  22 #include <ldsodefs.h>
  23
  24
  25 static void
  26 __attribute ((always_inline))
  27 determine_info (const ElfW(Addr) addr, struct link_map *match, Dl_info *info,
  28                 struct link_map **mapp, const ElfW(Sym) **symbolp)
  29 {
  30   /* Now we know what object the address lies in.  */
  31   info->dli_fname = match->l_name;
  32   info->dli_fbase = (void *) match->l_map_start;
  33
  34   /* If this is the main program the information is incomplete.  */
  35   if (__builtin_expect (match->l_name[0], 'a') == '\0'
  36       && match->l_type == lt_executable)
  37     info->dli_fname = _dl_argv[0];
  38
  39   const ElfW(Sym) *symtab
  40     = (const ElfW(Sym) *) D_PTR (match, l_info[DT_SYMTAB]);
  41   const char *strtab = (const char *) D_PTR (match, l_info[DT_STRTAB]);
  42
  43   ElfW(Word) strtabsize = match->l_info[DT_STRSZ]->d_un.d_val;
  44
  45   const ElfW(Sym) *matchsym = NULL;
  46   if (match->l_info[DT_ADDRTAGIDX (DT_GNU_HASH) + DT_NUM + DT_THISPROCNUM
  47                     + DT_VERSIONTAGNUM + DT_EXTRANUM + DT_VALNUM] != NULL)
  48     {
  49       /* We look at all symbol table entries referenced by the hash
  50          table.  */
  51       for (Elf_Symndx bucket = 0; bucket < match->l_nbuckets; ++bucket)
  52         {
  53           Elf32_Word symndx = match->l_gnu_buckets[bucket];
  54           if (symndx != 0)
  55             {
  56               const Elf32_Word *hasharr = &match->l_gnu_chain_zero[symndx];
  57
  58               do
  59                 {
  60                   /* The hash table never references local symbols so
  61                      we can omit that test here.  */
  62                   if ((symtab[symndx].st_shndx != SHN_UNDEF
  63                        || symtab[symndx].st_value != 0)
  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                   ++symndx;
  71                 }
  72               while ((*hasharr++ & 1u) == 0);
  73             }
  74         }
  75     }
  76   else
  77     {
  78       const ElfW(Sym) *symtabend;
  79       if (match->l_info[DT_HASH] != NULL)
  80         symtabend = (symtab
  81                      + ((Elf_Symndx *) D_PTR (match, l_info[DT_HASH]))[1]);
  82       else
  83         /* There is no direct way to determine the number of symbols in the
  84            dynamic symbol table and no hash table is present.  The ELF
  85            binary is ill-formed but what shall we do?  Use the beginning of
  86            the string table which generally follows the symbol table.  */
  87         symtabend = (const ElfW(Sym) *) strtab;
  88
  89       for (; (void *) symtab < (void *) symtabend; ++symtab)
  90         if ((ELFW(ST_BIND) (symtab->st_info) == STB_GLOBAL
  91              || ELFW(ST_BIND) (symtab->st_info) == STB_WEAK)
  92             && ELFW(ST_TYPE) (symtab->st_info) != STT_TLS
  93             && (symtab->st_shndx != SHN_UNDEF
  94                 || symtab->st_value != 0)
  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 internal_function
 125 _dl_addr (const void *address, Dl_info *info,
 126           struct link_map **mapp, const ElfW(Sym) **symbolp)
 127 {
 128   const ElfW(Addr) addr = DL_LOOKUP_ADDRESS (address);
 129   int result = 0;
 130
 131   /* Protect against concurrent loads and unloads.  */
 132   __rtld_lock_lock_recursive (GL(dl_load_lock));
 133
 134   /* Find the highest-addressed object that ADDRESS is not below.  */
 135   for (Lmid_t ns = 0; ns < GL(dl_nns); ++ns)
 136     for (struct link_map *l = GL(dl_ns)[ns]._ns_loaded; l; l = l->l_next)
 137       if (addr >= l->l_map_start && addr < l->l_map_end
 138           && (l->l_contiguous || _dl_addr_inside_object (l, addr)))
 139         {
 140           determine_info (addr, l, info, mapp, symbolp);
 141           result = 1;
 142           goto out;
 143         }
 144
 145  out:
 146   __rtld_lock_unlock_recursive (GL(dl_load_lock));
 147
 148   return result;
 149 }
 150 libc_hidden_def (_dl_addr)
 151
 152 /* Return non-zero if ADDR lies within one of L's segments.  */
 153 int
 154 internal_function
 155 _dl_addr_inside_object (struct link_map *l, const ElfW(Addr) addr)
 156 {
 157   int n = l->l_phnum;
 158   const ElfW(Addr) reladdr = addr - l->l_addr;
 159
 160   while (--n >= 0)
 161     if (l->l_phdr[n].p_type == PT_LOAD
 162         && reladdr - l->l_phdr[n].p_vaddr >= 0
 163         && reladdr - l->l_phdr[n].p_vaddr < l->l_phdr[n].p_memsz)
 164       return 1;
 165   return 0;
 166 }