elf/dl-runtime.c

   1 /* On-demand PLT fixup for shared objects.
   2    Copyright (C) 1995, 1996, 1997 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 <link.h>
  21 #include <stddef.h>
  22
  23
  24 /* The global scope we will use for symbol lookups.
  25    This will be modified by _dl_open if RTLD_GLOBAL is used.  */
  26 struct link_map **_dl_global_scope = _dl_default_scope;
  27 struct link_map **_dl_global_scope_end = &_dl_default_scope[3];
  28
  29
  30 /* Hack _dl_global_scope[0] and [1] as necessary, and return a pointer into
  31    _dl_global_scope that should be passed to _dl_lookup_symbol for symbol
  32    references made in the object L's relocations.  */
  33 inline struct link_map **
  34 _dl_object_relocation_scope (struct link_map *l)
  35 {
  36   if (l->l_info[DT_SYMBOLIC])
  37     {
  38       /* This object's global references are to be resolved first
  39          in the object itself, and only secondarily in more global
  40          scopes.  */
  41
  42       if (! l->l_searchlist)
  43         /* We must construct the searchlist for this object.  */
  44         _dl_map_object_deps (l, NULL, 0, 0);
  45
  46       /* The primary scope is this object itself and its
  47          dependencies.  */
  48       _dl_global_scope[0] = l;
  49
  50       /* Secondary is the dependency tree that reached L; the object
  51          requested directly by the user is at the root of that tree.  */
  52       while (l->l_loader)
  53         l = l->l_loader;
  54       _dl_global_scope[1] = l;
  55
  56       /* Finally, the global scope follows.  */
  57
  58       return _dl_global_scope;
  59     }
  60   else
  61     {
  62       /* Use first the global scope, and then the scope of the root of the
  63          dependency tree that first caused this object to be loaded.  */
  64       while (l->l_loader)
  65         l = l->l_loader;
  66       *_dl_global_scope_end = l;
  67       return &_dl_global_scope[2];
  68     }
  69 }
  70 \f
  71 #include "dynamic-link.h"
  72
  73 /* Figure out the right type, Rel or Rela.  */
  74 #define elf_machine_rel 1
  75 #define elf_machine_rela 2
  76 #if elf_machine_relplt == elf_machine_rel
  77 # define PLTREL ElfW(Rel)
  78 #elif elf_machine_relplt == elf_machine_rela
  79 # define PLTREL ElfW(Rela)
  80 #else
  81 # error "dl-machine.h bug: elf_machine_relplt not rel or rela"
  82 #endif
  83 #undef elf_machine_rel
  84 #undef elf_machine_rela
  85
  86 #ifndef VERSYMIDX
  87 # define VERSYMIDX(sym) (DT_NUM + DT_PROCNUM + DT_VERSIONTAGIDX (sym))
  88 #endif
  89
  90 /* We need to define the function as a local symbol so that the reference
  91    in the trampoline code will be a local PC-relative call.  Tell the
  92    compiler not to worry that the function appears not to be called.  */
  93
  94 static ElfW(Addr) fixup (
  95 #ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS
  96                          ELF_MACHINE_RUNTIME_FIXUP_ARGS,
  97 #endif
  98                          struct link_map *l, ElfW(Word) reloc_offset)
  99      __attribute__ ((unused));
 100
 101 /* This function is called through a special trampoline from the PLT the
 102    first time each PLT entry is called.  We must perform the relocation
 103    specified in the PLT of the given shared object, and return the resolved
 104    function address to the trampoline, which will restart the original call
 105    to that address.  Future calls will bounce directly from the PLT to the
 106    function.  */
 107
 108 static ElfW(Addr)
 109 fixup (
 110 #ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS
 111        ELF_MACHINE_RUNTIME_FIXUP_ARGS,
 112 #endif
 113        struct link_map *l, ElfW(Word) reloc_offset)
 114 {
 115   const ElfW(Sym) *const symtab
 116     = (const ElfW(Sym) *) (l->l_addr + l->l_info[DT_SYMTAB]->d_un.d_ptr);
 117   const char *strtab =
 118     (const char *) (l->l_addr + l->l_info[DT_STRTAB]->d_un.d_ptr);
 119
 120   const PLTREL *const reloc
 121     = (const void *) (l->l_addr + l->l_info[DT_JMPREL]->d_un.d_ptr +
 122                       reloc_offset);
 123
 124   /* Set up the scope to find symbols referenced by this object.  */
 125   struct link_map **scope = _dl_object_relocation_scope (l);
 126
 127   {
 128     /* This macro is used as a callback from the elf_machine_relplt code.  */
 129 #define RESOLVE(ref, version, flags) \
 130   ((version) != NULL && (version)->hash != 0                                  \
 131    ? _dl_lookup_versioned_symbol (strtab + (*ref)->st_name, (ref), scope,     \
 132                                   l->l_name, (version), (flags))              \
 133    : _dl_lookup_symbol (strtab + (*ref)->st_name, (ref), scope,               \
 134                         l->l_name, (flags)))
 135 #include "dynamic-link.h"
 136
 137     /* Perform the specified relocation.  */
 138     if (l->l_info[VERSYMIDX (DT_VERNEEDNUM)])
 139       {
 140         const ElfW(Half) * version =
 141           (const ElfW(Half) *) (l->l_addr +
 142                                 l->l_info[VERSYMIDX (DT_VERSYM)]->d_un.d_ptr);
 143         ElfW(Half) ndx = version[ELFW(R_SYM) (reloc->r_info)];
 144
 145         elf_machine_relplt (l, reloc, &symtab[ELFW(R_SYM) (reloc->r_info)],
 146                             &l->l_versions[ndx]);
 147       }
 148     else
 149       elf_machine_relplt (l, reloc, &symtab[ELFW(R_SYM) (reloc->r_info)],
 150                           NULL);
 151   }
 152
 153   *_dl_global_scope_end = NULL;
 154
 155   /* Return the address that was written by the relocation.  */
 156 #ifdef ELF_FIXUP_RETURNS_ADDRESS
 157   return (ElfW(Addr))(l->l_addr + reloc->r_offset);
 158 #else
 159   return *(ElfW(Addr) *) (l->l_addr + reloc->r_offset);
 160 #endif
 161 }
 162
 163
 164 /* This macro is defined in dl-machine.h to define the entry point called
 165    by the PLT.  The `fixup' function above does the real work, but a little
 166    more twiddling is needed to get the stack right and jump to the address
 167    finally resolved.  */
 168
 169 ELF_MACHINE_RUNTIME_TRAMPOLINE