glibc/elf/dl-reloc.c

/* Relocate a shared object and resolve its references to other loaded objects.
Copyright (C) 1995 Free Software Foundation, Inc.
This file is part of the GNU C Library.

The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Library General Public License as
published by the Free Software Foundation; either version 2 of the
License, or (at your option) any later version.

The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
Library General Public License for more details.

You should have received a copy of the GNU Library General Public
License along with the GNU C Library; see the file COPYING.LIB.  If
not, write to the Free Software Foundation, Inc., 675 Mass Ave,
Cambridge, MA 02139, USA.  */

#include <link.h>
#include <sys/types.h>
#include <sys/mman.h>
#include <unistd.h>
#include <errno.h>
#include "dynamic-link.h"


void
_dl_relocate_object (struct link_map *l, int lazy)
{
  const size_t pagesize = getpagesize ();

  if (l->l_relocated)
    return;

  if (l->l_info[DT_TEXTREL])
    {
      /* Bletch.  We must make read-only segments writable
	 long enough to relocate them.  */
      const Elf32_Phdr *ph;
      for (ph = l->l_phdr; ph < &l->l_phdr[l->l_phnum]; ++ph)
	if (ph->p_type == PT_LOAD && (ph->p_flags & PF_W) == 0)
	  {
	    caddr_t mapstart = ((caddr_t) l->l_addr +
				(ph->p_vaddr & ~(pagesize - 1)));
	    caddr_t mapend = ((caddr_t) l->l_addr +
			      ((ph->p_vaddr + ph->p_memsz + pagesize - 1)
			       & ~(pagesize - 1)));
	    if (mprotect (mapstart, mapend - mapstart,
			  PROT_READ|PROT_WRITE) < 0)
	      _dl_signal_error (errno,
				"cannot make segment writable for relocation");
	  }
    }

  {
    struct link_map *real_next, *scope;

    const char *strtab
      = ((void *) l->l_addr + l->l_info[DT_STRTAB]->d_un.d_ptr);


    Elf32_Addr resolve (const Elf32_Sym **ref)
      {
	return _dl_lookup_symbol (strtab + (*ref)->st_name, ref, scope);
      }

    real_next = l->l_next;
    if (l->l_info[DT_SYMBOLIC])
      {
	l->l_prev->l_next = real_next;
	l->l_next = _dl_loaded;
	scope = l;
      }
    else
      scope = _dl_loaded;

    elf_dynamic_relocate (l->l_info, l->l_addr, lazy, resolve);

    /* Restore list frobnication done above for DT_SYMBOLIC.  */
    l->l_next = real_next;
    l->l_prev->l_next = l;
  }

  if (l->l_info[DT_JMPREL] && ! lazy)
    /* Set up the PLT so its unrelocated entries will
       jump to _dl_runtime_resolve, which will relocate them.  */
    elf_machine_runtime_setup (l);

  l->l_relocated = 1;

  if (l->l_info[DT_TEXTREL])
    {
      /* Undo the protection change we made before relocating.  */
      const Elf32_Phdr *ph;
      for (ph = l->l_phdr; ph < &l->l_phdr[l->l_phnum]; ++ph)
	if (ph->p_type == PT_LOAD && (ph->p_flags & PF_W) == 0)
	  {
	    caddr_t mapstart = ((caddr_t) l->l_addr +
				(ph->p_vaddr & ~(pagesize - 1)));
	    caddr_t mapend = ((caddr_t) l->l_addr +
			      ((ph->p_vaddr + ph->p_memsz + pagesize - 1)
			       & ~(pagesize - 1)));
	    int prot = 0;
	    if (ph->p_flags & PF_R)
	      prot |= PROT_READ;
	    if (ph->p_flags & PF_X)
	      prot |= PROT_EXEC;
	    if (mprotect (mapstart, mapend - mapstart, prot) < 0)
	      _dl_signal_error (errno,
				"can't restore segment prot after reloc");
	  }
    }

}