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 <link.h>
  21 #include <unistd.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 _dl_object_relocation_scope (struct link_map *l)
  35 {
  36   if (l->l_info[DT_SYMBOLIC])
  37     {
  38       /* This object's global references are to be resolved first
  39          in the object itself, and only secondarily in more global
  40          scopes.  */
  41
  42       if (! l->l_searchlist)
  43         /* We must construct the searchlist for this object.  */
  44         _dl_map_object_deps (l, NULL, 0, 0);
  45
  46       /* The primary scope is this object itself and its
  47          dependencies.  */
  48       _dl_global_scope[0] = l;
  49
  50       /* Secondary is the dependency tree that reached L; the object
  51          requested directly by the user is at the root of that tree.  */
  52       while (l->l_loader)
  53         l = l->l_loader;
  54       _dl_global_scope[1] = l;
  55
  56       /* Finally, the global scope follows.  */
  57
  58       return _dl_global_scope;
  59     }
  60   else
  61     {
  62       /* Use first the global scope, and then the scope of the root of the
  63          dependency tree that first caused this object to be loaded.  */
  64       while (l->l_loader)
  65         l = l->l_loader;
  66       *_dl_global_scope_end = l;
  67       return &_dl_global_scope[2];
  68     }
  69 }
  70 \f
  71 #include "dynamic-link.h"
  72
  73 #if !defined ELF_MACHINE_NO_RELA || ELF_MACHINE_NO_REL
  74 # define PLTREL  ElfW(Rela)
  75 #else
  76 # define PLTREL  ElfW(Rel)
  77 #endif
  78
  79 #ifndef VERSYMIDX
  80 # define VERSYMIDX(sym) (DT_NUM + DT_PROCNUM + DT_VERSIONTAGIDX (sym))
  81 #endif
  82
  83
  84 /* This function is called through a special trampoline from the PLT the
  85    first time each PLT entry is called.  We must perform the relocation
  86    specified in the PLT of the given shared object, and return the resolved
  87    function address to the trampoline, which will restart the original call
  88    to that address.  Future calls will bounce directly from the PLT to the
  89    function.  */
  90
  91 static ElfW(Addr) __attribute__ ((unused))
  92 fixup (
  93 #ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS
  94        ELF_MACHINE_RUNTIME_FIXUP_ARGS,
  95 #endif
  96        struct link_map *l, ElfW(Word) reloc_offset)
  97 {
  98   const ElfW(Sym) *const symtab
  99     = (const ElfW(Sym) *) (l->l_addr + l->l_info[DT_SYMTAB]->d_un.d_ptr);
 100   const char *strtab =
 101     (const char *) (l->l_addr + l->l_info[DT_STRTAB]->d_un.d_ptr);
 102
 103   const PLTREL *const reloc
 104     = (const void *) (l->l_addr + l->l_info[DT_JMPREL]->d_un.d_ptr +
 105                       reloc_offset);
 106   const ElfW(Sym) *sym = &symtab[ELFW(R_SYM) (reloc->r_info)];
 107   void *const rel_addr = (void *)(l->l_addr + reloc->r_offset);
 108   ElfW(Addr) value;
 109
 110   /* Set up the scope to find symbols referenced by this object.  */
 111   struct link_map **scope = _dl_object_relocation_scope (l);
 112
 113   /* Sanity check that we're really looking at a PLT relocation.  */
 114   assert (ELFW(R_TYPE)(reloc->r_info) == ELF_MACHINE_JMP_SLOT);
 115
 116    /* Look up the target symbol.  */
 117   switch (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
 118     {
 119     default:
 120       {
 121         const ElfW(Half) *vernum = (const ElfW(Half) *)
 122           (l->l_addr + l->l_info[VERSYMIDX (DT_VERSYM)]->d_un.d_ptr);
 123         ElfW(Half) ndx = vernum[ELFW(R_SYM) (reloc->r_info)];
 124         const struct r_found_version *version = &l->l_versions[ndx];
 125
 126         if (version->hash != 0)
 127           {
 128             value = _dl_lookup_versioned_symbol(strtab + sym->st_name,
 129                                                 &sym, scope, l->l_name,
 130                                                 version, ELF_MACHINE_JMP_SLOT);
 131             break;
 132           }
 133       }
 134     case 0:
 135       value = _dl_lookup_symbol (strtab + sym->st_name, &sym, scope,
 136                                  l->l_name, ELF_MACHINE_JMP_SLOT);
 137     }
 138
 139   /* Currently value contains the base load address of the object
 140      that defines sym.  Now add in the symbol offset.  */
 141   value = (sym ? value + sym->st_value : 0);
 142
 143   /* And now perhaps the relocation addend.  */
 144   value = elf_machine_plt_value (l, reloc, value);
 145
 146   /* Finally, fix up the plt itself.  */
 147   elf_machine_fixup_plt (l, reloc, rel_addr, value);
 148
 149   *_dl_global_scope_end = NULL;
 150
 151   return value;
 152 }
 153
 154
 155 #ifndef PROF
 156
 157 static ElfW(Addr) __attribute__ ((unused))
 158 profile_fixup (
 159 #ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS
 160        ELF_MACHINE_RUNTIME_FIXUP_ARGS,
 161 #endif
 162        struct link_map *l, ElfW(Word) reloc_offset, ElfW(Addr) retaddr)
 163 {
 164   void (*mcount_fct) (ElfW(Addr), ElfW(Addr)) = _dl_mcount;
 165   ElfW(Addr) *resultp;
 166   ElfW(Addr) value;
 167
 168   /* This is the address in the array where we store the result of previous
 169      relocations.  */
 170   resultp = &l->l_reloc_result[reloc_offset / sizeof (PLTREL)];
 171
 172   value = *resultp;
 173   if (value == 0)
 174     {
 175       /* This is the first time we have to relocate this object.  */
 176       const ElfW(Sym) *const symtab
 177         = (const ElfW(Sym) *) (l->l_addr + l->l_info[DT_SYMTAB]->d_un.d_ptr);
 178       const char *strtab =
 179         (const char *) (l->l_addr + l->l_info[DT_STRTAB]->d_un.d_ptr);
 180
 181       const PLTREL *const reloc
 182         = (const void *) (l->l_addr + l->l_info[DT_JMPREL]->d_un.d_ptr +
 183                           reloc_offset);
 184       const ElfW(Sym) *sym = &symtab[ELFW(R_SYM) (reloc->r_info)];
 185
 186       /* Set up the scope to find symbols referenced by this object.  */
 187       struct link_map **scope = _dl_object_relocation_scope (l);
 188
 189       /* Sanity check that we're really looking at a PLT relocation.  */
 190       assert (ELFW(R_TYPE)(reloc->r_info) == ELF_MACHINE_JMP_SLOT);
 191
 192       /* Look up the target symbol.  */
 193       switch (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
 194         {
 195         default:
 196           {
 197             const ElfW(Half) *vernum = (const ElfW(Half) *)
 198               (l->l_addr + l->l_info[VERSYMIDX (DT_VERSYM)]->d_un.d_ptr);
 199             ElfW(Half) ndx = vernum[ELFW(R_SYM) (reloc->r_info)];
 200             const struct r_found_version *version = &l->l_versions[ndx];
 201
 202             if (version->hash != 0)
 203               {
 204                 value = _dl_lookup_versioned_symbol(strtab + sym->st_name,
 205                                                     &sym, scope, l->l_name,
 206                                                     version,
 207                                                     ELF_MACHINE_JMP_SLOT);
 208                 break;
 209               }
 210           }
 211         case 0:
 212           value = _dl_lookup_symbol (strtab + sym->st_name, &sym, scope,
 213                                      l->l_name, ELF_MACHINE_JMP_SLOT);
 214         }
 215
 216       /* Currently value contains the base load address of the object
 217          that defines sym.  Now add in the symbol offset.  */
 218       value = (sym ? value + sym->st_value : 0);
 219
 220       /* And now perhaps the relocation addend.  */
 221       value = elf_machine_plt_value (l, reloc, value);
 222
 223       *_dl_global_scope_end = NULL;
 224
 225       /* Store the result for later runs.  */
 226       *resultp = value;
 227     }
 228
 229   (*mcount_fct) (retaddr, value);
 230
 231   return value;
 232 }
 233
 234 #endif /* PROF */
 235
 236
 237 /* This macro is defined in dl-machine.h to define the entry point called
 238    by the PLT.  The `fixup' function above does the real work, but a little
 239    more twiddling is needed to get the stack right and jump to the address
 240    finally resolved.  */
 241
 242 ELF_MACHINE_RUNTIME_TRAMPOLINE