elf/dl-reloc.c

   1 /* Relocate a shared object and resolve its references to other loaded objects.
   2 Copyright (C) 1995, 1996 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
  17 not, write to the Free Software Foundation, Inc., 675 Mass Ave,
  18 Cambridge, MA 02139, 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
  28 void
  29 _dl_relocate_object (struct link_map *l, struct link_map *scope[], int lazy)
  30 {
  31   if (l->l_relocated)
  32     return;
  33
  34   if (l->l_info[DT_TEXTREL])
  35     {
  36       /* Bletch.  We must make read-only segments writable
  37          long enough to relocate them.  */
  38       const ElfW(Phdr) *ph;
  39       for (ph = l->l_phdr; ph < &l->l_phdr[l->l_phnum]; ++ph)
  40         if (ph->p_type == PT_LOAD && (ph->p_flags & PF_W) == 0)
  41           {
  42             caddr_t mapstart = ((caddr_t) l->l_addr +
  43                                 (ph->p_vaddr & ~(_dl_pagesize - 1)));
  44             caddr_t mapend = ((caddr_t) l->l_addr +
  45                               ((ph->p_vaddr + ph->p_memsz + _dl_pagesize - 1)
  46                                & ~(_dl_pagesize - 1)));
  47             if (__mprotect (mapstart, mapend - mapstart,
  48                             PROT_READ|PROT_WRITE) < 0)
  49               _dl_signal_error (errno, l->l_name,
  50                                 "cannot make segment writable for relocation");
  51           }
  52     }
  53
  54   {
  55     /* Do the actual relocation of the object's GOT and other data.  */
  56
  57     const char *strtab          /* String table object symbols.  */
  58       = ((void *) l->l_addr + l->l_info[DT_STRTAB]->d_un.d_ptr);
  59     ElfW(Addr) resolve (const ElfW(Sym) **ref,
  60                         ElfW(Addr) reloc_addr, int noplt)
  61       {
  62         /* Look up the referenced symbol in the specified scope.  */
  63         return _dl_lookup_symbol (strtab + (*ref)->st_name, ref, scope,
  64                                   l->l_name, reloc_addr, noplt);
  65       }
  66
  67     ELF_DYNAMIC_RELOCATE (l, lazy, resolve);
  68   }
  69
  70   /* Set up the PLT so its unrelocated entries will jump to
  71      _dl_runtime_resolve (dl-runtime.c), which will relocate them.  */
  72   elf_machine_runtime_setup (l, lazy);
  73
  74   /* Mark the object so we know ths work has been done.  */
  75   l->l_relocated = 1;
  76
  77   if (l->l_info[DT_TEXTREL])
  78     {
  79       /* Undo the protection change we made before relocating.  */
  80       const ElfW(Phdr) *ph;
  81       for (ph = l->l_phdr; ph < &l->l_phdr[l->l_phnum]; ++ph)
  82         if (ph->p_type == PT_LOAD && (ph->p_flags & PF_W) == 0)
  83           {
  84             caddr_t mapstart = ((caddr_t) l->l_addr +
  85                                 (ph->p_vaddr & ~(_dl_pagesize - 1)));
  86             caddr_t mapend = ((caddr_t) l->l_addr +
  87                               ((ph->p_vaddr + ph->p_memsz + _dl_pagesize - 1)
  88                                & ~(_dl_pagesize - 1)));
  89             int prot = 0;
  90             if (ph->p_flags & PF_R)
  91               prot |= PROT_READ;
  92             if (ph->p_flags & PF_X)
  93               prot |= PROT_EXEC;
  94             if (__mprotect (mapstart, mapend - mapstart, prot) < 0)
  95               _dl_signal_error (errno, l->l_name,
  96                                 "can't restore segment prot after reloc");
  97           }
  98     }
  99 }