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 <unistd.h>
  21 #include <elf/ldsodefs.h>
  22 #include "dynamic-link.h"
  23
  24 #if !defined ELF_MACHINE_NO_RELA || ELF_MACHINE_NO_REL
  25 # define PLTREL  ElfW(Rela)
  26 #else
  27 # define PLTREL  ElfW(Rel)
  28 #endif
  29
  30 #ifndef VERSYMIDX
  31 # define VERSYMIDX(sym) (DT_NUM + DT_PROCNUM + DT_VERSIONTAGIDX (sym))
  32 #endif
  33
  34
  35 /* This function is called through a special trampoline from the PLT the
  36    first time each PLT entry is called.  We must perform the relocation
  37    specified in the PLT of the given shared object, and return the resolved
  38    function address to the trampoline, which will restart the original call
  39    to that address.  Future calls will bounce directly from the PLT to the
  40    function.  */
  41
  42 static ElfW(Addr) __attribute__ ((unused))
  43 fixup (
  44 #ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS
  45        ELF_MACHINE_RUNTIME_FIXUP_ARGS,
  46 #endif
  47        struct link_map *l, ElfW(Word) reloc_offset)
  48 {
  49   const ElfW(Sym) *const symtab
  50     = (const ElfW(Sym) *) (l->l_addr + l->l_info[DT_SYMTAB]->d_un.d_ptr);
  51   const char *strtab =
  52     (const char *) (l->l_addr + l->l_info[DT_STRTAB]->d_un.d_ptr);
  53
  54   const PLTREL *const reloc
  55     = (const void *) (l->l_addr + l->l_info[DT_JMPREL]->d_un.d_ptr +
  56                       reloc_offset);
  57   const ElfW(Sym) *sym = &symtab[ELFW(R_SYM) (reloc->r_info)];
  58   void *const rel_addr = (void *)(l->l_addr + reloc->r_offset);
  59   ElfW(Addr) value;
  60
  61   /* Sanity check that we're really looking at a PLT relocation.  */
  62   assert (ELFW(R_TYPE)(reloc->r_info) == ELF_MACHINE_JMP_SLOT);
  63
  64    /* Look up the target symbol.  */
  65   switch (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
  66     {
  67     default:
  68       {
  69         const ElfW(Half) *vernum = (const ElfW(Half) *)
  70           (l->l_addr + l->l_info[VERSYMIDX (DT_VERSYM)]->d_un.d_ptr);
  71         ElfW(Half) ndx = vernum[ELFW(R_SYM) (reloc->r_info)];
  72         const struct r_found_version *version = &l->l_versions[ndx];
  73
  74         if (version->hash != 0)
  75           {
  76             value = _dl_lookup_versioned_symbol(strtab + sym->st_name,
  77                                                 &sym, l->l_scope, l->l_name,
  78                                                 version, ELF_MACHINE_JMP_SLOT);
  79             break;
  80           }
  81       }
  82     case 0:
  83       value = _dl_lookup_symbol (strtab + sym->st_name, &sym, l->l_scope,
  84                                  l->l_name, ELF_MACHINE_JMP_SLOT);
  85     }
  86
  87   /* Currently value contains the base load address of the object
  88      that defines sym.  Now add in the symbol offset.  */
  89   value = (sym ? value + sym->st_value : 0);
  90
  91   /* And now perhaps the relocation addend.  */
  92   value = elf_machine_plt_value (l, reloc, value);
  93
  94   /* Finally, fix up the plt itself.  */
  95   elf_machine_fixup_plt (l, reloc, rel_addr, value);
  96
  97   return value;
  98 }
  99
 100
 101 #ifndef PROF
 102
 103 static ElfW(Addr) __attribute__ ((unused))
 104 profile_fixup (
 105 #ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS
 106        ELF_MACHINE_RUNTIME_FIXUP_ARGS,
 107 #endif
 108        struct link_map *l, ElfW(Word) reloc_offset, ElfW(Addr) retaddr)
 109 {
 110   void (*mcount_fct) (ElfW(Addr), ElfW(Addr)) = _dl_mcount;
 111   ElfW(Addr) *resultp;
 112   ElfW(Addr) value;
 113
 114   /* This is the address in the array where we store the result of previous
 115      relocations.  */
 116   resultp = &l->l_reloc_result[reloc_offset / sizeof (PLTREL)];
 117
 118   value = *resultp;
 119   if (value == 0)
 120     {
 121       /* This is the first time we have to relocate this object.  */
 122       const ElfW(Sym) *const symtab
 123         = (const ElfW(Sym) *) (l->l_addr + l->l_info[DT_SYMTAB]->d_un.d_ptr);
 124       const char *strtab =
 125         (const char *) (l->l_addr + l->l_info[DT_STRTAB]->d_un.d_ptr);
 126
 127       const PLTREL *const reloc
 128         = (const void *) (l->l_addr + l->l_info[DT_JMPREL]->d_un.d_ptr +
 129                           reloc_offset);
 130       const ElfW(Sym) *sym = &symtab[ELFW(R_SYM) (reloc->r_info)];
 131
 132       /* Sanity check that we're really looking at a PLT relocation.  */
 133       assert (ELFW(R_TYPE)(reloc->r_info) == ELF_MACHINE_JMP_SLOT);
 134
 135       /* Look up the target symbol.  */
 136       switch (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
 137         {
 138         default:
 139           {
 140             const ElfW(Half) *vernum = (const ElfW(Half) *)
 141               (l->l_addr + l->l_info[VERSYMIDX (DT_VERSYM)]->d_un.d_ptr);
 142             ElfW(Half) ndx = vernum[ELFW(R_SYM) (reloc->r_info)];
 143             const struct r_found_version *version = &l->l_versions[ndx];
 144
 145             if (version->hash != 0)
 146               {
 147                 value = _dl_lookup_versioned_symbol(strtab + sym->st_name,
 148                                                     &sym, l->l_scope,
 149                                                     l->l_name, version,
 150                                                     ELF_MACHINE_JMP_SLOT);
 151                 break;
 152               }
 153           }
 154         case 0:
 155           value = _dl_lookup_symbol (strtab + sym->st_name, &sym, l->l_scope,
 156                                      l->l_name, ELF_MACHINE_JMP_SLOT);
 157         }
 158
 159       /* Currently value contains the base load address of the object
 160          that defines sym.  Now add in the symbol offset.  */
 161       value = (sym ? value + sym->st_value : 0);
 162
 163       /* And now perhaps the relocation addend.  */
 164       value = elf_machine_plt_value (l, reloc, value);
 165
 166       /* Store the result for later runs.  */
 167       *resultp = value;
 168     }
 169
 170   (*mcount_fct) (retaddr, value);
 171
 172   return value;
 173 }
 174
 175 #endif /* PROF */
 176
 177
 178 /* This macro is defined in dl-machine.h to define the entry point called
 179    by the PLT.  The `fixup' function above does the real work, but a little
 180    more twiddling is needed to get the stack right and jump to the address
 181    finally resolved.  */
 182
 183 ELF_MACHINE_RUNTIME_TRAMPOLINE