elf/dl-runtime.c

   1 /* On-demand PLT fixup for shared objects.
   2    Copyright (C) 1995-2002, 2003, 2004 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 #define IN_DL_RUNTIME 1         /* This can be tested in dl-machine.h.  */
  21
  22 #include <alloca.h>
  23 #include <stdlib.h>
  24 #include <unistd.h>
  25 #include <ldsodefs.h>
  26 #include "dynamic-link.h"
  27
  28 #if (!defined ELF_MACHINE_NO_RELA && !defined ELF_MACHINE_PLT_REL) \
  29     || ELF_MACHINE_NO_REL
  30 # define PLTREL  ElfW(Rela)
  31 #else
  32 # define PLTREL  ElfW(Rel)
  33 #endif
  34
  35 #ifndef VERSYMIDX
  36 # define VERSYMIDX(sym) (DT_NUM + DT_THISPROCNUM + DT_VERSIONTAGIDX (sym))
  37 #endif
  38
  39 /* The fixup functions might have need special attributes.  If none
  40    are provided define the macro as empty.  */
  41 #ifndef ARCH_FIXUP_ATTRIBUTE
  42 # define ARCH_FIXUP_ATTRIBUTE
  43 #endif
  44
  45
  46 /* This function is called through a special trampoline from the PLT the
  47    first time each PLT entry is called.  We must perform the relocation
  48    specified in the PLT of the given shared object, and return the resolved
  49    function address to the trampoline, which will restart the original call
  50    to that address.  Future calls will bounce directly from the PLT to the
  51    function.  */
  52
  53 #ifndef ELF_MACHINE_NO_PLT
  54 static ElfW(Addr)
  55 __attribute ((used, noinline)) ARCH_FIXUP_ATTRIBUTE
  56 fixup (
  57 # ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS
  58         ELF_MACHINE_RUNTIME_FIXUP_ARGS,
  59 # endif
  60         /* GKM FIXME: Fix trampoline to pass bounds so we can do
  61            without the `__unbounded' qualifier.  */
  62        struct link_map *__unbounded l, ElfW(Word) reloc_offset)
  63 {
  64   const ElfW(Sym) *const symtab
  65     = (const void *) D_PTR (l, l_info[DT_SYMTAB]);
  66   const char *strtab = (const void *) D_PTR (l, l_info[DT_STRTAB]);
  67
  68   const PLTREL *const reloc
  69     = (const void *) (D_PTR (l, l_info[DT_JMPREL]) + reloc_offset);
  70   const ElfW(Sym) *sym = &symtab[ELFW(R_SYM) (reloc->r_info)];
  71   void *const rel_addr = (void *)(l->l_addr + reloc->r_offset);
  72   lookup_t result;
  73   ElfW(Addr) value;
  74
  75   /* Sanity check that we're really looking at a PLT relocation.  */
  76   assert (ELFW(R_TYPE)(reloc->r_info) == ELF_MACHINE_JMP_SLOT);
  77
  78    /* Look up the target symbol.  If the normal lookup rules are not
  79       used don't look in the global scope.  */
  80   if (__builtin_expect (ELFW(ST_VISIBILITY) (sym->st_other), 0) == 0)
  81     {
  82       const struct r_found_version *version = NULL;
  83       // XXX Why exactly do we have the differentiation of the flags here?
  84       int flags = DL_LOOKUP_ADD_DEPENDENCY;
  85
  86       if (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
  87         {
  88           const ElfW(Half) *vernum =
  89             (const void *) D_PTR (l, l_info[VERSYMIDX (DT_VERSYM)]);
  90           ElfW(Half) ndx = vernum[ELFW(R_SYM) (reloc->r_info)] & 0x7fff;
  91           version = &l->l_versions[ndx];
  92           if (version->hash == 0)
  93             version = NULL;
  94           else
  95             flags = 0;
  96         }
  97
  98       result = _dl_lookup_symbol_x (strtab + sym->st_name, l, &sym,
  99                                     l->l_scope, version, ELF_RTYPE_CLASS_PLT,
 100                                     DL_LOOKUP_ADD_DEPENDENCY, NULL);
 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 (GLRO(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)
 131 __attribute ((used, noinline)) ARCH_FIXUP_ATTRIBUTE
 132 profile_fixup (
 133 #ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS
 134        ELF_MACHINE_RUNTIME_FIXUP_ARGS,
 135 #endif
 136        struct link_map *l, ElfW(Word) reloc_offset, ElfW(Addr) retaddr)
 137 {
 138   void (*mcount_fct) (ElfW(Addr), ElfW(Addr)) = INTUSE(_dl_mcount);
 139   ElfW(Addr) *resultp;
 140   lookup_t result;
 141   ElfW(Addr) value;
 142
 143   /* This is the address in the array where we store the result of previous
 144      relocations.  */
 145   resultp = &l->l_reloc_result[reloc_offset / sizeof (PLTREL)];
 146
 147   value = *resultp;
 148   if (value == 0)
 149     {
 150       /* This is the first time we have to relocate this object.  */
 151       const ElfW(Sym) *const symtab
 152         = (const void *) D_PTR (l, l_info[DT_SYMTAB]);
 153       const char *strtab = (const void *) D_PTR (l, l_info[DT_STRTAB]);
 154
 155       const PLTREL *const reloc
 156         = (const void *) (D_PTR (l, l_info[DT_JMPREL]) + reloc_offset);
 157       const ElfW(Sym) *sym = &symtab[ELFW(R_SYM) (reloc->r_info)];
 158
 159       /* Sanity check that we're really looking at a PLT relocation.  */
 160       assert (ELFW(R_TYPE)(reloc->r_info) == ELF_MACHINE_JMP_SLOT);
 161
 162       /* Look up the target symbol.  If the symbol is marked STV_PROTECTED
 163          don't look in the global scope.  */
 164       if (__builtin_expect (ELFW(ST_VISIBILITY) (sym->st_other), 0) == 0)
 165         {
 166           const struct r_found_version *version = NULL;
 167           // XXX Why exactly do we have the differentiation of the flags here?
 168           int flags = DL_LOOKUP_ADD_DEPENDENCY;
 169
 170           if (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
 171             {
 172               const ElfW(Half) *vernum =
 173                 (const void *) D_PTR (l, l_info[VERSYMIDX (DT_VERSYM)]);
 174               ElfW(Half) ndx = vernum[ELFW(R_SYM) (reloc->r_info)] & 0x7fff;
 175               version = &l->l_versions[ndx];
 176               if (version->hash == 0)
 177                 version = NULL;
 178               else
 179                 flags = 0;
 180             }
 181
 182           result = _dl_lookup_symbol_x (strtab + sym->st_name, l, &sym,
 183                                         l->l_scope, version,
 184                                         ELF_RTYPE_CLASS_PLT,
 185                                         DL_LOOKUP_ADD_DEPENDENCY, NULL);
 186
 187           /* Currently result contains the base load address (or link map)
 188              of the object that defines sym.  Now add in the symbol
 189              offset.  */
 190           value = (sym ? LOOKUP_VALUE_ADDRESS (result) + sym->st_value : 0);
 191         }
 192       else
 193         {
 194           /* We already found the symbol.  The module (and therefore its load
 195              address) is also known.  */
 196           value = l->l_addr + sym->st_value;
 197 #ifdef DL_LOOKUP_RETURNS_MAP
 198           result = l;
 199 #endif
 200         }
 201       /* And now perhaps the relocation addend.  */
 202       value = elf_machine_plt_value (l, reloc, value);
 203
 204       /* Store the result for later runs.  */
 205       if (__builtin_expect (! GLRO(dl_bind_not), 1))
 206         *resultp = value;
 207     }
 208
 209   (*mcount_fct) (retaddr, value);
 210
 211   return value;
 212 }
 213
 214 #endif /* PROF && ELF_MACHINE_NO_PLT */
 215
 216
 217 /* This macro is defined in dl-machine.h to define the entry point called
 218    by the PLT.  The `fixup' function above does the real work, but a little
 219    more twiddling is needed to get the stack right and jump to the address
 220    finally resolved.  */
 221
 222 ELF_MACHINE_RUNTIME_TRAMPOLINE