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 = _dl_lookup_versioned_symbol (strtab + sym->st_name,
  91                                                       l, &sym, l->l_scope,
  92                                                       version,
  93                                                       ELF_RTYPE_CLASS_PLT, 0);
  94                 break;
  95               }
  96           }
  97         case 0:
  98           result = _dl_lookup_symbol (strtab + sym->st_name, l, &sym,
  99                                       l->l_scope, ELF_RTYPE_CLASS_PLT, 0);
 100         }
 101
 102       /* Currently result contains the base load address (or link map)
 103          of the object that defines sym.  Now add in the symbol
 104          offset.  */
 105       value = (sym ? LOOKUP_VALUE_ADDRESS (result) + sym->st_value : 0);
 106     }
 107   else
 108     {
 109       /* We already found the symbol.  The module (and therefore its load
 110          address) is also known.  */
 111       value = l->l_addr + sym->st_value;
 112 #ifdef DL_LOOKUP_RETURNS_MAP
 113       result = l;
 114 #endif
 115     }
 116
 117   /* And now perhaps the relocation addend.  */
 118   value = elf_machine_plt_value (l, reloc, value);
 119
 120   /* Finally, fix up the plt itself.  */
 121   if (__builtin_expect (GL(dl_bind_not), 0))
 122     return value;
 123
 124   return elf_machine_fixup_plt (l, result, reloc, rel_addr, value);
 125 }
 126 #endif
 127
 128 #if !defined PROF && !defined ELF_MACHINE_NO_PLT && !__BOUNDED_POINTERS__
 129
 130 static ElfW(Addr) __attribute_used__
 131 profile_fixup (
 132 #ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS
 133        ELF_MACHINE_RUNTIME_FIXUP_ARGS,
 134 #endif
 135        struct link_map *l, ElfW(Word) reloc_offset, ElfW(Addr) retaddr)
 136 {
 137   void (*mcount_fct) (ElfW(Addr), ElfW(Addr)) = _dl_mcount;
 138   ElfW(Addr) *resultp;
 139   lookup_t result;
 140   ElfW(Addr) value;
 141
 142   /* The use of `alloca' here looks ridiculous but it helps.  The goal is
 143      to prevent the function from being inlined, and thus optimized out.
 144      There is no official way to do this so we use this trick.  gcc never
 145      inlines functions which use `alloca'.  */
 146   alloca (sizeof (int));
 147
 148   /* This is the address in the array where we store the result of previous
 149      relocations.  */
 150   resultp = &l->l_reloc_result[reloc_offset / sizeof (PLTREL)];
 151
 152   value = *resultp;
 153   if (value == 0)
 154     {
 155       /* This is the first time we have to relocate this object.  */
 156       const ElfW(Sym) *const symtab
 157         = (const void *) D_PTR (l, l_info[DT_SYMTAB]);
 158       const char *strtab = (const void *) D_PTR (l, l_info[DT_STRTAB]);
 159
 160       const PLTREL *const reloc
 161         = (const void *) (D_PTR (l, l_info[DT_JMPREL]) + reloc_offset);
 162       const ElfW(Sym) *sym = &symtab[ELFW(R_SYM) (reloc->r_info)];
 163
 164       /* Sanity check that we're really looking at a PLT relocation.  */
 165       assert (ELFW(R_TYPE)(reloc->r_info) == ELF_MACHINE_JMP_SLOT);
 166
 167       /* Look up the target symbol.  If the symbol is marked STV_PROTECTED
 168          don't look in the global scope.  */
 169       if (__builtin_expect (ELFW(ST_VISIBILITY) (sym->st_other), 0) == 0)
 170         {
 171           switch (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
 172             {
 173             default:
 174               {
 175                 const ElfW(Half) *vernum =
 176                   (const void *) D_PTR (l,l_info[VERSYMIDX (DT_VERSYM)]);
 177                 ElfW(Half) ndx = vernum[ELFW(R_SYM) (reloc->r_info)];
 178                 const struct r_found_version *version = &l->l_versions[ndx];
 179
 180                 if (version->hash != 0)
 181                   {
 182                     result = _dl_lookup_versioned_symbol(strtab + sym->st_name,
 183                                                          l, &sym, l->l_scope,
 184                                                          version,
 185                                                          ELF_RTYPE_CLASS_PLT,
 186                                                          0);
 187                     break;
 188                   }
 189               }
 190             case 0:
 191               result = _dl_lookup_symbol (strtab + sym->st_name, l, &sym,
 192                                           l->l_scope, ELF_RTYPE_CLASS_PLT, 0);
 193             }
 194
 195           /* Currently result contains the base load address (or link map)
 196              of the object that defines sym.  Now add in the symbol
 197              offset.  */
 198           value = (sym ? LOOKUP_VALUE_ADDRESS (result) + sym->st_value : 0);
 199         }
 200       else
 201         {
 202           /* We already found the symbol.  The module (and therefore its load
 203              address) is also known.  */
 204           value = l->l_addr + sym->st_value;
 205 #ifdef DL_LOOKUP_RETURNS_MAP
 206           result = l;
 207 #endif
 208         }
 209       /* And now perhaps the relocation addend.  */
 210       value = elf_machine_plt_value (l, reloc, value);
 211
 212       /* Store the result for later runs.  */
 213       if (__builtin_expect (! GL(dl_bind_not), 1))
 214         *resultp = value;
 215     }
 216
 217   (*mcount_fct) (retaddr, value);
 218
 219   return value;
 220 }
 221
 222 #endif /* PROF && ELF_MACHINE_NO_PLT */
 223
 224
 225 /* This macro is defined in dl-machine.h to define the entry point called
 226    by the PLT.  The `fixup' function above does the real work, but a little
 227    more twiddling is needed to get the stack right and jump to the address
 228    finally resolved.  */
 229
 230 ELF_MACHINE_RUNTIME_TRAMPOLINE