elf/dl-runtime.c

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