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 = INT(_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 = INT(_dl_lookup_symbol) (strtab + sym->st_name, l, &sym,
 101                                            l->l_scope, ELF_RTYPE_CLASS_PLT, 0);
 102         }
 103
 104       /* Currently result contains the base load address (or link map)
 105          of the object that defines sym.  Now add in the symbol
 106          offset.  */
 107       value = (sym ? LOOKUP_VALUE_ADDRESS (result) + sym->st_value : 0);
 108     }
 109   else
 110     {
 111       /* We already found the symbol.  The module (and therefore its load
 112          address) is also known.  */
 113       value = l->l_addr + sym->st_value;
 114 #ifdef DL_LOOKUP_RETURNS_MAP
 115       result = l;
 116 #endif
 117     }
 118
 119   /* And now perhaps the relocation addend.  */
 120   value = elf_machine_plt_value (l, reloc, value);
 121
 122   /* Finally, fix up the plt itself.  */
 123   if (__builtin_expect (GL(dl_bind_not), 0))
 124     return value;
 125
 126   return elf_machine_fixup_plt (l, result, reloc, rel_addr, value);
 127 }
 128 #endif
 129
 130 #if !defined PROF && !defined ELF_MACHINE_NO_PLT && !__BOUNDED_POINTERS__
 131
 132 static ElfW(Addr) __attribute_used__
 133 profile_fixup (
 134 #ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS
 135        ELF_MACHINE_RUNTIME_FIXUP_ARGS,
 136 #endif
 137        struct link_map *l, ElfW(Word) reloc_offset, ElfW(Addr) retaddr)
 138 {
 139   void (*mcount_fct) (ElfW(Addr), ElfW(Addr)) = _dl_mcount;
 140   ElfW(Addr) *resultp;
 141   lookup_t result;
 142   ElfW(Addr) value;
 143
 144   /* The use of `alloca' here looks ridiculous but it helps.  The goal is
 145      to prevent the function from being inlined, and thus optimized out.
 146      There is no official way to do this so we use this trick.  gcc never
 147      inlines functions which use `alloca'.  */
 148   alloca (sizeof (int));
 149
 150   /* This is the address in the array where we store the result of previous
 151      relocations.  */
 152   resultp = &l->l_reloc_result[reloc_offset / sizeof (PLTREL)];
 153
 154   value = *resultp;
 155   if (value == 0)
 156     {
 157       /* This is the first time we have to relocate this object.  */
 158       const ElfW(Sym) *const symtab
 159         = (const void *) D_PTR (l, l_info[DT_SYMTAB]);
 160       const char *strtab = (const void *) D_PTR (l, l_info[DT_STRTAB]);
 161
 162       const PLTREL *const reloc
 163         = (const void *) (D_PTR (l, l_info[DT_JMPREL]) + reloc_offset);
 164       const ElfW(Sym) *sym = &symtab[ELFW(R_SYM) (reloc->r_info)];
 165
 166       /* Sanity check that we're really looking at a PLT relocation.  */
 167       assert (ELFW(R_TYPE)(reloc->r_info) == ELF_MACHINE_JMP_SLOT);
 168
 169       /* Look up the target symbol.  If the symbol is marked STV_PROTECTED
 170          don't look in the global scope.  */
 171       if (__builtin_expect (ELFW(ST_VISIBILITY) (sym->st_other), 0) == 0)
 172         {
 173           switch (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
 174             {
 175             default:
 176               {
 177                 const ElfW(Half) *vernum =
 178                   (const void *) D_PTR (l,l_info[VERSYMIDX (DT_VERSYM)]);
 179                 ElfW(Half) ndx = vernum[ELFW(R_SYM) (reloc->r_info)];
 180                 const struct r_found_version *version = &l->l_versions[ndx];
 181
 182                 if (version->hash != 0)
 183                   {
 184                     result = INT(_dl_lookup_versioned_symbol) (strtab
 185                                                                + sym->st_name,
 186                                                                l, &sym,
 187                                                                l->l_scope,
 188                                                                version,
 189                                                                ELF_RTYPE_CLASS_PLT,
 190                                                                0);
 191                     break;
 192                   }
 193               }
 194             case 0:
 195               result = INT(_dl_lookup_symbol) (strtab + sym->st_name, l, &sym,
 196                                                l->l_scope, ELF_RTYPE_CLASS_PLT,
 197                                                0);
 198             }
 199
 200           /* Currently result contains the base load address (or link map)
 201              of the object that defines sym.  Now add in the symbol
 202              offset.  */
 203           value = (sym ? LOOKUP_VALUE_ADDRESS (result) + sym->st_value : 0);
 204         }
 205       else
 206         {
 207           /* We already found the symbol.  The module (and therefore its load
 208              address) is also known.  */
 209           value = l->l_addr + sym->st_value;
 210 #ifdef DL_LOOKUP_RETURNS_MAP
 211           result = l;
 212 #endif
 213         }
 214       /* And now perhaps the relocation addend.  */
 215       value = elf_machine_plt_value (l, reloc, value);
 216
 217       /* Store the result for later runs.  */
 218       if (__builtin_expect (! GL(dl_bind_not), 1))
 219         *resultp = value;
 220     }
 221
 222   (*mcount_fct) (retaddr, value);
 223
 224   return value;
 225 }
 226
 227 #endif /* PROF && ELF_MACHINE_NO_PLT */
 228
 229
 230 /* This macro is defined in dl-machine.h to define the entry point called
 231    by the PLT.  The `fixup' function above does the real work, but a little
 232    more twiddling is needed to get the stack right and jump to the address
 233    finally resolved.  */
 234
 235 ELF_MACHINE_RUNTIME_TRAMPOLINE