elf/dl-reloc.c

   1 /* Relocate a shared object and resolve its references to other loaded 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 <sys/types.h>
  22 #include <sys/mman.h>
  23 #include <unistd.h>
  24 #include <errno.h>
  25 #include "dynamic-link.h"
  26
  27 void
  28 _dl_relocate_object (struct link_map *l, struct link_map *scope[], int lazy)
  29 {
  30   if (l->l_relocated)
  31     return;
  32
  33   if (l->l_info[DT_TEXTREL])
  34     {
  35       /* Bletch.  We must make read-only segments writable
  36          long enough to relocate them.  */
  37       const ElfW(Phdr) *ph;
  38       for (ph = l->l_phdr; ph < &l->l_phdr[l->l_phnum]; ++ph)
  39         if (ph->p_type == PT_LOAD && (ph->p_flags & PF_W) == 0)
  40           {
  41             caddr_t mapstart = ((caddr_t) l->l_addr +
  42                                 (ph->p_vaddr & ~(_dl_pagesize - 1)));
  43             caddr_t mapend = ((caddr_t) l->l_addr +
  44                               ((ph->p_vaddr + ph->p_memsz + _dl_pagesize - 1)
  45                                & ~(_dl_pagesize - 1)));
  46             if (__mprotect (mapstart, mapend - mapstart,
  47                             PROT_READ|PROT_WRITE) < 0)
  48               _dl_signal_error (errno, l->l_name,
  49                                 "cannot make segment writable for relocation");
  50           }
  51     }
  52
  53   {
  54     /* Do the actual relocation of the object's GOT and other data.  */
  55
  56     const char *strtab          /* String table object symbols.  */
  57       = ((void *) l->l_addr + l->l_info[DT_STRTAB]->d_un.d_ptr);
  58
  59     /* This macro is used as a callback from the ELF_DYNAMIC_RELOCATE code.  */
  60 #define RESOLVE(ref, flags) \
  61     (((*ref)->st_shndx != SHN_UNDEF &&                                        \
  62       ELFW(ST_BIND) ((*ref)->st_info) == STB_LOCAL)                           \
  63      ? l->l_addr                                                              \
  64      : _dl_lookup_symbol (strtab + (*ref)->st_name, ref, scope,               \
  65                           l->l_name, flags))
  66
  67 #include "dynamic-link.h"
  68     ELF_DYNAMIC_RELOCATE (l, lazy);
  69   }
  70
  71   /* Mark the object so we know ths work has been done.  */
  72   l->l_relocated = 1;
  73
  74   if (l->l_info[DT_TEXTREL])
  75     {
  76       /* Undo the protection change we made before relocating.  */
  77       const ElfW(Phdr) *ph;
  78       for (ph = l->l_phdr; ph < &l->l_phdr[l->l_phnum]; ++ph)
  79         if (ph->p_type == PT_LOAD && (ph->p_flags & PF_W) == 0)
  80           {
  81             caddr_t mapstart = ((caddr_t) l->l_addr +
  82                                 (ph->p_vaddr & ~(_dl_pagesize - 1)));
  83             caddr_t mapend = ((caddr_t) l->l_addr +
  84                               ((ph->p_vaddr + ph->p_memsz + _dl_pagesize - 1)
  85                                & ~(_dl_pagesize - 1)));
  86             int prot = 0;
  87             if (ph->p_flags & PF_R)
  88               prot |= PROT_READ;
  89             if (ph->p_flags & PF_X)
  90               prot |= PROT_EXEC;
  91             if (__mprotect (mapstart, mapend - mapstart, prot) < 0)
  92               _dl_signal_error (errno, l->l_name,
  93                                 "can't restore segment prot after reloc");
  94           }
  95     }
  96 }