elf/dl-runtime.c

   1 /* On-demand PLT fixup for shared objects.
   2    Copyright (C) 1995-1999, 2000, 2001, 2002 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 <alloca.h>
  21 #include <stdlib.h>
  22 #include <unistd.h>
  23 #include <ldsodefs.h>
  24 #include "dynamic-link.h"
  25
  26 #if (!defined ELF_MACHINE_NO_RELA && !defined ELF_MACHINE_PLT_REL) \
  27     || ELF_MACHINE_NO_REL
  28 # define PLTREL  ElfW(Rela)
  29 #else
  30 # define PLTREL  ElfW(Rel)
  31 #endif
  32
  33 #ifndef VERSYMIDX
  34 # define VERSYMIDX(sym) (DT_NUM + DT_THISPROCNUM + DT_VERSIONTAGIDX (sym))
  35 #endif
  36
  37
  38 /* This function is called through a special trampoline from the PLT the
  39    first time each PLT entry is called.  We must perform the relocation
  40    specified in the PLT of the given shared object, and return the resolved
  41    function address to the trampoline, which will restart the original call
  42    to that address.  Future calls will bounce directly from the PLT to the
  43    function.  */
  44
  45 #ifndef ELF_MACHINE_NO_PLT
  46 static ElfW(Addr) __attribute_used__
  47 fixup (
  48 # ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS
  49         ELF_MACHINE_RUNTIME_FIXUP_ARGS,
  50 # endif
  51         /* GKM FIXME: Fix trampoline to pass bounds so we can do
  52            without the `__unbounded' qualifier.  */
  53        struct link_map *__unbounded l, ElfW(Word) reloc_offset)
  54 {
  55   const ElfW(Sym) *const symtab
  56     = (const void *) D_PTR (l, l_info[DT_SYMTAB]);
  57   const char *strtab = (const void *) D_PTR (l, l_info[DT_STRTAB]);
  58
  59   const PLTREL *const reloc
  60     = (const void *) (D_PTR (l, l_info[DT_JMPREL]) + reloc_offset);
  61   const ElfW(Sym) *sym = &symtab[ELFW(R_SYM) (reloc->r_info)];
  62   void *const rel_addr = (void *)(l->l_addr + reloc->r_offset);
  63   lookup_t result;
  64   ElfW(Addr) value;
  65
  66   /* The use of `alloca' here looks ridiculous but it helps.  The goal is
  67      to prevent the function from being inlined and thus optimized out.
  68      There is no official way to do this so we use this trick.  gcc never
  69      inlines functions which use `alloca'.  */
  70   alloca (sizeof (int));
  71
  72   /* Sanity check that we're really looking at a PLT relocation.  */
  73   assert (ELFW(R_TYPE)(reloc->r_info) == ELF_MACHINE_JMP_SLOT);
  74
  75    /* Look up the target symbol.  If the normal lookup rules are not
  76       used don't look in the global scope.  */
  77   if (__builtin_expect (ELFW(ST_VISIBILITY) (sym->st_other), 0) == 0)
  78     {
  79       switch (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
  80         {
  81         default:
  82           {
  83             const ElfW(Half) *vernum =
  84               (const void *) D_PTR (l, l_info[VERSYMIDX (DT_VERSYM)]);
  85             ElfW(Half) ndx = vernum[ELFW(R_SYM) (reloc->r_info)];
  86             const struct r_found_version *version = &l->l_versions[ndx];
  87
  88             if (version->hash != 0)
  89               {
  90                 result = INTUSE(_dl_lookup_versioned_symbol) (strtab
  91                                                               + sym->st_name,
  92                                                               l, &sym, l->l_scope,
  93                                                               version,
  94                                                               ELF_RTYPE_CLASS_PLT,
  95                                                               0);
  96                 break;
  97               }
  98           }
  99         case 0:
 100           result = INTUSE(_dl_lookup_symbol) (strtab + sym->st_name, l, &sym,
 101                                               l->l_scope, ELF_RTYPE_CLASS_PLT,
 102                                               DL_LOOKUP_ADD_DEPENDENCY);
 103         }
 104
 105       /* Currently result contains the base load address (or link map)
 106          of the object that defines sym.  Now add in the symbol
 107          offset.  */
 108       value = (sym ? LOOKUP_VALUE_ADDRESS (result) + sym->st_value : 0);
 109     }
 110   else
 111     {
 112       /* We already found the symbol.  The module (and therefore its load
 113          address) is also known.  */
 114       value = l->l_addr + sym->st_value;
 115 #ifdef DL_LOOKUP_RETURNS_MAP
 116       result = l;
 117 #endif
 118     }
 119
 120   /* And now perhaps the relocation addend.  */
 121   value = elf_machine_plt_value (l, reloc, value);
 122
 123   /* Finally, fix up the plt itself.  */
 124   if (__builtin_expect (GL(dl_bind_not), 0))
 125     return value;
 126
 127   return elf_machine_fixup_plt (l, result, reloc, rel_addr, value);
 128 }
 129 #endif
 130
 131 #if !defined PROF && !defined ELF_MACHINE_NO_PLT && !__BOUNDED_POINTERS__
 132
 133 static ElfW(Addr) __attribute_used__
 134 profile_fixup (
 135 #ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS
 136        ELF_MACHINE_RUNTIME_FIXUP_ARGS,
 137 #endif
 138        struct link_map *l, ElfW(Word) reloc_offset, ElfW(Addr) retaddr)
 139 {
 140   void (*mcount_fct) (ElfW(Addr), ElfW(Addr)) = INTUSE(_dl_mcount);
 141   ElfW(Addr) *resultp;
 142   lookup_t result;
 143   ElfW(Addr) value;
 144
 145   /* The use of `alloca' here looks ridiculous but it helps.  The goal is
 146      to prevent the function from being inlined, and thus optimized out.
 147      There is no official way to do this so we use this trick.  gcc never
 148      inlines functions which use `alloca'.  */
 149   alloca (sizeof (int));
 150
 151   /* This is the address in the array where we store the result of previous
 152      relocations.  */
 153   resultp = &l->l_reloc_result[reloc_offset / sizeof (PLTREL)];
 154
 155   value = *resultp;
 156   if (value == 0)
 157     {
 158       /* This is the first time we have to relocate this object.  */
 159       const ElfW(Sym) *const symtab
 160         = (const void *) D_PTR (l, l_info[DT_SYMTAB]);
 161       const char *strtab = (const void *) D_PTR (l, l_info[DT_STRTAB]);
 162
 163       const PLTREL *const reloc
 164         = (const void *) (D_PTR (l, l_info[DT_JMPREL]) + reloc_offset);
 165       const ElfW(Sym) *sym = &symtab[ELFW(R_SYM) (reloc->r_info)];
 166
 167       /* Sanity check that we're really looking at a PLT relocation.  */
 168       assert (ELFW(R_TYPE)(reloc->r_info) == ELF_MACHINE_JMP_SLOT);
 169
 170       /* Look up the target symbol.  If the symbol is marked STV_PROTECTED
 171          don't look in the global scope.  */
 172       if (__builtin_expect (ELFW(ST_VISIBILITY) (sym->st_other), 0) == 0)
 173         {
 174           switch (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
 175             {
 176             default:
 177               {
 178                 const ElfW(Half) *vernum =
 179                   (const void *) D_PTR (l,l_info[VERSYMIDX (DT_VERSYM)]);
 180                 ElfW(Half) ndx = vernum[ELFW(R_SYM) (reloc->r_info)];
 181                 const struct r_found_version *version = &l->l_versions[ndx];
 182
 183                 if (version->hash != 0)
 184                   {
 185                     result = INTUSE(_dl_lookup_versioned_symbol) (strtab
 186                                                                   + sym->st_name,
 187                                                                   l, &sym,
 188                                                                   l->l_scope,
 189                                                                   version,
 190                                                                   ELF_RTYPE_CLASS_PLT,
 191                                                                   0);
 192                     break;
 193                   }
 194               }
 195             case 0:
 196               result = INTUSE(_dl_lookup_symbol) (strtab + sym->st_name, l,
 197                                                   &sym, l->l_scope,
 198                                                   ELF_RTYPE_CLASS_PLT,
 199                                                   DL_LOOKUP_ADD_DEPENDENCY);
 200             }
 201
 202           /* Currently result contains the base load address (or link map)
 203              of the object that defines sym.  Now add in the symbol
 204              offset.  */
 205           value = (sym ? LOOKUP_VALUE_ADDRESS (result) + sym->st_value : 0);
 206         }
 207       else
 208         {
 209           /* We already found the symbol.  The module (and therefore its load
 210              address) is also known.  */
 211           value = l->l_addr + sym->st_value;
 212 #ifdef DL_LOOKUP_RETURNS_MAP
 213           result = l;
 214 #endif
 215         }
 216       /* And now perhaps the relocation addend.  */
 217       value = elf_machine_plt_value (l, reloc, value);
 218
 219       /* Store the result for later runs.  */
 220       if (__builtin_expect (! GL(dl_bind_not), 1))
 221         *resultp = value;
 222     }
 223
 224   (*mcount_fct) (retaddr, value);
 225
 226   return value;
 227 }
 228
 229 #endif /* PROF && ELF_MACHINE_NO_PLT */
 230
 231
 232 /* This macro is defined in dl-machine.h to define the entry point called
 233    by the PLT.  The `fixup' function above does the real work, but a little
 234    more twiddling is needed to get the stack right and jump to the address
 235    finally resolved.  */
 236
 237 ELF_MACHINE_RUNTIME_TRAMPOLINE