elf/dl-runtime.c

   1 /* On-demand PLT fixup for shared objects.
   2    Copyright (C) 1995, 1996, 1997, 1998 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 <unistd.h>
  21 #include <elf/ldsodefs.h>
  22
  23
  24 /* The global scope we will use for symbol lookups.
  25    This will be modified by _dl_open if RTLD_GLOBAL is used.  */
  26 struct link_map **_dl_global_scope = _dl_default_scope;
  27 struct link_map **_dl_global_scope_end = &_dl_default_scope[3];
  28
  29
  30 /* Hack _dl_global_scope[0] and [1] as necessary, and return a pointer into
  31    _dl_global_scope that should be passed to _dl_lookup_symbol for symbol
  32    references made in the object L's relocations.  */
  33 inline struct link_map **
  34 internal_function
  35 _dl_object_relocation_scope (struct link_map *l)
  36 {
  37   if (l->l_info[DT_SYMBOLIC])
  38     {
  39       /* This object's global references are to be resolved first
  40          in the object itself, and only secondarily in more global
  41          scopes.  */
  42
  43       if (! l->l_searchlist)
  44         /* We must construct the searchlist for this object.  */
  45         _dl_map_object_deps (l, NULL, 0, 0);
  46
  47       /* The primary scope is this object itself and its
  48          dependencies.  */
  49       _dl_global_scope[0] = l;
  50
  51       /* Secondary is the dependency tree that reached L; the object
  52          requested directly by the user is at the root of that tree.  */
  53       while (l->l_loader)
  54         l = l->l_loader;
  55       _dl_global_scope[1] = l;
  56
  57       /* Finally, the global scope follows.  */
  58
  59       return _dl_global_scope;
  60     }
  61   else
  62     {
  63       /* Use first the global scope, and then the scope of the root of the
  64          dependency tree that first caused this object to be loaded.  */
  65       while (l->l_loader)
  66         l = l->l_loader;
  67       /* There is no point in searching the same list twice.  This isn't
  68          guaranteed to always find all duplicates if new objects are added
  69          to the global scope, but is good enough most of the time.  */
  70       if (_dl_global_scope[2] != l)
  71         *_dl_global_scope_end = l;
  72       return &_dl_global_scope[2];
  73     }
  74 }
  75 \f
  76 #include "dynamic-link.h"
  77
  78 #if !defined ELF_MACHINE_NO_RELA || ELF_MACHINE_NO_REL
  79 # define PLTREL  ElfW(Rela)
  80 #else
  81 # define PLTREL  ElfW(Rel)
  82 #endif
  83
  84 #ifndef VERSYMIDX
  85 # define VERSYMIDX(sym) (DT_NUM + DT_PROCNUM + DT_VERSIONTAGIDX (sym))
  86 #endif
  87
  88
  89 /* This function is called through a special trampoline from the PLT the
  90    first time each PLT entry is called.  We must perform the relocation
  91    specified in the PLT of the given shared object, and return the resolved
  92    function address to the trampoline, which will restart the original call
  93    to that address.  Future calls will bounce directly from the PLT to the
  94    function.  */
  95
  96 static ElfW(Addr) __attribute__ ((unused))
  97 fixup (
  98 #ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS
  99        ELF_MACHINE_RUNTIME_FIXUP_ARGS,
 100 #endif
 101        struct link_map *l, ElfW(Word) reloc_offset)
 102 {
 103   const ElfW(Sym) *const symtab
 104     = (const ElfW(Sym) *) (l->l_addr + l->l_info[DT_SYMTAB]->d_un.d_ptr);
 105   const char *strtab =
 106     (const char *) (l->l_addr + l->l_info[DT_STRTAB]->d_un.d_ptr);
 107
 108   const PLTREL *const reloc
 109     = (const void *) (l->l_addr + l->l_info[DT_JMPREL]->d_un.d_ptr +
 110                       reloc_offset);
 111   const ElfW(Sym) *sym = &symtab[ELFW(R_SYM) (reloc->r_info)];
 112   void *const rel_addr = (void *)(l->l_addr + reloc->r_offset);
 113   ElfW(Addr) value;
 114
 115   /* Set up the scope to find symbols referenced by this object.  */
 116   struct link_map **scope = _dl_object_relocation_scope (l);
 117
 118   /* Sanity check that we're really looking at a PLT relocation.  */
 119   assert (ELFW(R_TYPE)(reloc->r_info) == ELF_MACHINE_JMP_SLOT);
 120
 121    /* Look up the target symbol.  */
 122   switch (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
 123     {
 124     default:
 125       {
 126         const ElfW(Half) *vernum = (const ElfW(Half) *)
 127           (l->l_addr + l->l_info[VERSYMIDX (DT_VERSYM)]->d_un.d_ptr);
 128         ElfW(Half) ndx = vernum[ELFW(R_SYM) (reloc->r_info)];
 129         const struct r_found_version *version = &l->l_versions[ndx];
 130
 131         if (version->hash != 0)
 132           {
 133             value = _dl_lookup_versioned_symbol(strtab + sym->st_name,
 134                                                 &sym, scope, l->l_name,
 135                                                 version, ELF_MACHINE_JMP_SLOT);
 136             break;
 137           }
 138       }
 139     case 0:
 140       value = _dl_lookup_symbol (strtab + sym->st_name, &sym, scope,
 141                                  l->l_name, ELF_MACHINE_JMP_SLOT);
 142     }
 143
 144   /* Currently value contains the base load address of the object
 145      that defines sym.  Now add in the symbol offset.  */
 146   value = (sym ? value + sym->st_value : 0);
 147
 148   /* And now perhaps the relocation addend.  */
 149   value = elf_machine_plt_value (l, reloc, value);
 150
 151   /* Finally, fix up the plt itself.  */
 152   elf_machine_fixup_plt (l, reloc, rel_addr, value);
 153
 154   *_dl_global_scope_end = NULL;
 155
 156   return value;
 157 }
 158
 159
 160 #ifndef PROF
 161
 162 static ElfW(Addr) __attribute__ ((unused))
 163 profile_fixup (
 164 #ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS
 165        ELF_MACHINE_RUNTIME_FIXUP_ARGS,
 166 #endif
 167        struct link_map *l, ElfW(Word) reloc_offset, ElfW(Addr) retaddr)
 168 {
 169   void (*mcount_fct) (ElfW(Addr), ElfW(Addr)) = _dl_mcount;
 170   ElfW(Addr) *resultp;
 171   ElfW(Addr) value;
 172
 173   /* This is the address in the array where we store the result of previous
 174      relocations.  */
 175   resultp = &l->l_reloc_result[reloc_offset / sizeof (PLTREL)];
 176
 177   value = *resultp;
 178   if (value == 0)
 179     {
 180       /* This is the first time we have to relocate this object.  */
 181       const ElfW(Sym) *const symtab
 182         = (const ElfW(Sym) *) (l->l_addr + l->l_info[DT_SYMTAB]->d_un.d_ptr);
 183       const char *strtab =
 184         (const char *) (l->l_addr + l->l_info[DT_STRTAB]->d_un.d_ptr);
 185
 186       const PLTREL *const reloc
 187         = (const void *) (l->l_addr + l->l_info[DT_JMPREL]->d_un.d_ptr +
 188                           reloc_offset);
 189       const ElfW(Sym) *sym = &symtab[ELFW(R_SYM) (reloc->r_info)];
 190
 191       /* Set up the scope to find symbols referenced by this object.  */
 192       struct link_map **scope = _dl_object_relocation_scope (l);
 193
 194       /* Sanity check that we're really looking at a PLT relocation.  */
 195       assert (ELFW(R_TYPE)(reloc->r_info) == ELF_MACHINE_JMP_SLOT);
 196
 197       /* Look up the target symbol.  */
 198       switch (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
 199         {
 200         default:
 201           {
 202             const ElfW(Half) *vernum = (const ElfW(Half) *)
 203               (l->l_addr + l->l_info[VERSYMIDX (DT_VERSYM)]->d_un.d_ptr);
 204             ElfW(Half) ndx = vernum[ELFW(R_SYM) (reloc->r_info)];
 205             const struct r_found_version *version = &l->l_versions[ndx];
 206
 207             if (version->hash != 0)
 208               {
 209                 value = _dl_lookup_versioned_symbol(strtab + sym->st_name,
 210                                                     &sym, scope, l->l_name,
 211                                                     version,
 212                                                     ELF_MACHINE_JMP_SLOT);
 213                 break;
 214               }
 215           }
 216         case 0:
 217           value = _dl_lookup_symbol (strtab + sym->st_name, &sym, scope,
 218                                      l->l_name, ELF_MACHINE_JMP_SLOT);
 219         }
 220
 221       /* Currently value contains the base load address of the object
 222          that defines sym.  Now add in the symbol offset.  */
 223       value = (sym ? value + sym->st_value : 0);
 224
 225       /* And now perhaps the relocation addend.  */
 226       value = elf_machine_plt_value (l, reloc, value);
 227
 228       *_dl_global_scope_end = NULL;
 229
 230       /* Store the result for later runs.  */
 231       *resultp = value;
 232     }
 233
 234   (*mcount_fct) (retaddr, value);
 235
 236   return value;
 237 }
 238
 239 #endif /* PROF */
 240
 241
 242 /* This macro is defined in dl-machine.h to define the entry point called
 243    by the PLT.  The `fixup' function above does the real work, but a little
 244    more twiddling is needed to get the stack right and jump to the address
 245    finally resolved.  */
 246
 247 ELF_MACHINE_RUNTIME_TRAMPOLINE