text: #-------------------------------------------------------------------------------
  # elftools: elf/relocation.py
  #
  # ELF relocations
  #
  # Eli Bendersky (eliben@gmail.com)
  # This code is in the public domain
  #-------------------------------------------------------------------------------
  from collections import namedtuple
  
  from ..common.exceptions import ELFRelocationError
  from ..common.utils import elf_assert, struct_parse
  from .sections import Section
  from .enums import (
      ENUM_RELOC_TYPE_i386, ENUM_RELOC_TYPE_x64, ENUM_RELOC_TYPE_MIPS,
      ENUM_RELOC_TYPE_ARM, ENUM_RELOC_TYPE_AARCH64, ENUM_RELOC_TYPE_PPC64,
      ENUM_D_TAG)
  from ..construct import Container
  
  
  class Relocation(object):
      """ Relocation object - representing a single relocation entry. Allows
          dictionary-like access to the entry's fields.
  
          Can be either a REL or RELA relocation.
      """
      def __init__(self, entry, elffile):
          self.entry = entry
          self.elffile = elffile
  
      def is_RELA(self):
          """ Is this a RELA relocation? If not, it's REL.
          """
          return 'r_addend' in self.entry
  
      def __getitem__(self, name):
          """ Dict-like access to entries
          """
          return self.entry[name]
  
      def __repr__(self):
          return '<Relocation (%s): %s>' % (
                  'RELA' if self.is_RELA() else 'REL',
                  self.entry)
  
      def __str__(self):
          return self.__repr__()
  
  
  class RelocationTable(object):
      """ Shared functionality between relocation sections and relocation tables
      """
  
      def __init__(self, elffile, offset, size, is_rela):
          self._stream = elffile.stream
          self._elffile = elffile
          self._elfstructs = elffile.structs
          self._size = size
          self._offset = offset
          self._is_rela = is_rela
  
          if is_rela:
              self.entry_struct = self._elfstructs.Elf_Rela
          else:
              self.entry_struct = self._elfstructs.Elf_Rel
  
          self.entry_size = self.entry_struct.sizeof()
  
      def is_RELA(self):
          """ Is this a RELA relocation section? If not, it's REL.
          """
          return self._is_rela
  
      def num_relocations(self):
          """ Number of relocations in the section
          """
          return self._size // self.entry_size
  
      def get_relocation(self, n):
          """ Get the relocation at index #n from the section (Relocation object)
          """
          entry_offset = self._offset + n * self.entry_size
          entry = struct_parse(
              self.entry_struct,
              self._stream,
              stream_pos=entry_offset)
          return Relocation(entry, self._elffile)
  
      def iter_relocations(self):
          """ Yield all the relocations in the section
          """
          for i in range(self.num_relocations()):
              yield self.get_relocation(i)
  
  
  class RelocationSection(Section, RelocationTable):
      """ ELF relocation section. Serves as a collection of Relocation entries.
      """
      def __init__(self, header, name, elffile):
          Section.__init__(self, header, name, elffile)
          RelocationTable.__init__(self, self.elffile,
              self['sh_offset'], self['sh_size'], header['sh_type'] == 'SHT_RELA')
  
          elf_assert(header['sh_type'] in ('SHT_REL', 'SHT_RELA'),
              'Unknown relocation type section')
          elf_assert(header['sh_entsize'] == self.entry_size,
              'Expected sh_entsize of %s section to be %s' % (
                  header['sh_type'], self.entry_size))
  
  class RelrRelocationSection(Section):
      """ RELR compressed relocation section. This stores relative relocations
          in a compressed format. An entry with an even value serves as an
          'anchor' that defines a base address. Following this entry are one or
          more bitmaps for consecutive addresses after the anchor which determine
          if the corresponding relocation exists (if the bit is 1) or if it is
          skipped. Addends are stored at the respective addresses (as in REL
          relocations).
      """
      def __init__(self, header, name, elffile):
          Section.__init__(self, header, name, elffile)
          self._offset = self['sh_offset']
          self._size = self['sh_size']
          self._relr_struct = self.elffile.structs.Elf_Relr
          self._entrysize = self._relr_struct.sizeof()
          self._cached_relocations = None
  
      def iter_relocations(self):
          """ Yield all the relocations in the section
          """
          limit = self._offset + self._size
          relr = self._offset
          # The addresses of relocations in a bitmap are calculated from a base
          # value provided in an initial 'anchor' relocation.
          base = None
          while relr < limit:
              entry = struct_parse(self._relr_struct,
                                   self.elffile.stream,
                                   stream_pos=relr)
              entry_offset = entry['r_offset']
              if (entry_offset & 1) == 0:
                  # We found an anchor, take the current value as the base address
                  # for the following bitmaps and move the 'where' pointer to the
                  # beginning of the first bitmap.
                  base = entry_offset
                  base += self._entrysize
                  yield Relocation(entry, self.elffile)
              else:
                  # We're processing a bitmap.
                  elf_assert(base is not None, 'RELR bitmap without base address')
                  i = 0
                  while True:
                      # Iterate over all bits except the least significant one.
                      entry_offset = (entry_offset >> 1)
                      if entry_offset == 0:
                          break
                      # if the current LSB is set, we have a relocation at the
                      # corresponding address so generate a Relocation with the
                      # matching offset
                      if (entry_offset & 1) != 0:
                          calc_offset = base + i * self._entrysize
                          yield Relocation(Container(r_offset = calc_offset),
                                           self.elffile)
                      i += 1
                  # Advance 'base' past the current bitmap (8 == CHAR_BIT). There
                  # are 63 (or 31 for 32-bit ELFs) entries in each bitmap, and
                  # every bit corresponds to an ELF_addr-sized relocation.
                  base += (8 * self._entrysize - 1) * self.elffile.structs.Elf_addr('').sizeof()
              # Advance to the next entry
              relr += self._entrysize
  
      def num_relocations(self):
          """ Number of relocations in the section
          """
          if self._cached_relocations is None:
              self._cached_relocations = list(self.iter_relocations())
          return len(self._cached_relocations)
  
      def get_relocation(self, n):
          """ Get the relocation at index #n from the section (Relocation object)
          """
          if self._cached_relocations is None:
              self._cached_relocations = list(self.iter_relocations())
          return self._cached_relocations[n]
  
  class RelocationHandler(object):
      """ Handles the logic of relocations in ELF files.
      """
      def __init__(self, elffile):
          self.elffile = elffile
  
      def find_relocations_for_section(self, section):
          """ Given a section, find the relocation section for it in the ELF
              file. Return a RelocationSection object, or None if none was
              found.
          """
          reloc_section_names = (
                  '.rel' + section.name,
                  '.rela' + section.name)
          # Find the relocation section aimed at this one. Currently assume
          # that either .rel or .rela section exists for this section, but
          # not both.
          for relsection in self.elffile.iter_sections():
              if (    isinstance(relsection, RelocationSection) and
                      relsection.name in reloc_section_names):
                  return relsection
          return None
  
      def apply_section_relocations(self, stream, reloc_section):
          """ Apply all relocations in reloc_section (a RelocationSection object)
              to the given stream, that contains the data of the section that is
              being relocated. The stream is modified as a result.
          """
          # The symbol table associated with this relocation section
          symtab = self.elffile.get_section(reloc_section['sh_link'])
          for reloc in reloc_section.iter_relocations():
              self._do_apply_relocation(stream, reloc, symtab)
  
      def _do_apply_relocation(self, stream, reloc, symtab):
          # Preparations for performing the relocation: obtain the value of
          # the symbol mentioned in the relocation, as well as the relocation
          # recipe which tells us how to actually perform it.
          # All peppered with some sanity checking.
          if reloc['r_info_sym'] >= symtab.num_symbols():
              raise ELFRelocationError(
                  'Invalid symbol reference in relocation: index %s' % (
                      reloc['r_info_sym']))
          sym_value = symtab.get_symbol(reloc['r_info_sym'])['st_value']
  
          reloc_type = reloc['r_info_type']
          recipe = None
  
          if self.elffile.get_machine_arch() == 'x86':
              if reloc.is_RELA():
                  raise ELFRelocationError(
                      'Unexpected RELA relocation for x86: %s' % reloc)
              recipe = self._RELOCATION_RECIPES_X86.get(reloc_type, None)
          elif self.elffile.get_machine_arch() == 'x64':
              if not reloc.is_RELA():
                  raise ELFRelocationError(
                      'Unexpected REL relocation for x64: %s' % reloc)
              recipe = self._RELOCATION_RECIPES_X64.get(reloc_type, None)
          elif self.elffile.get_machine_arch() == 'MIPS':
              if reloc.is_RELA():
                  raise ELFRelocationError(
                      'Unexpected RELA relocation for MIPS: %s' % reloc)
              recipe = self._RELOCATION_RECIPES_MIPS.get(reloc_type, None)
          elif self.elffile.get_machine_arch() == 'ARM':
              if reloc.is_RELA():
                  raise ELFRelocationError(
                      'Unexpected RELA relocation for ARM: %s' % reloc)
              recipe = self._RELOCATION_RECIPES_ARM.get(reloc_type, None)
          elif self.elffile.get_machine_arch() == 'AArch64':
              recipe = self._RELOCATION_RECIPES_AARCH64.get(reloc_type, None)
          elif self.elffile.get_machine_arch() == '64-bit PowerPC':
              recipe = self._RELOCATION_RECIPES_PPC64.get(reloc_type, None)
  
          if recipe is None:
              raise ELFRelocationError(
                      'Unsupported relocation type: %s' % reloc_type)
  
          # So now we have everything we need to actually perform the relocation.
          # Let's get to it:
  
          # 0. Find out which struct we're going to be using to read this value
          #    from the stream and write it back.
          if recipe.bytesize == 4:
              value_struct = self.elffile.structs.Elf_word('')
          elif recipe.bytesize == 8:
              value_struct = self.elffile.structs.Elf_word64('')
          else:
              raise ELFRelocationError('Invalid bytesize %s for relocation' %
                      recipe.bytesize)
  
          # 1. Read the value from the stream (with correct size and endianness)
          original_value = struct_parse(
              value_struct,
              stream,
              stream_pos=reloc['r_offset'])
          # 2. Apply the relocation to the value, acting according to the recipe
          relocated_value = recipe.calc_func(
              value=original_value,
              sym_value=sym_value,
              offset=reloc['r_offset'],
              addend=reloc['r_addend'] if recipe.has_addend else 0)
          # 3. Write the relocated value back into the stream
          stream.seek(reloc['r_offset'])
  
          # Make sure the relocated value fits back by wrapping it around. This
          # looks like a problem, but it seems to be the way this is done in
          # binutils too.
          relocated_value = relocated_value % (2 ** (recipe.bytesize * 8))
          value_struct.build_stream(relocated_value, stream)
  
      # Relocations are represented by "recipes". Each recipe specifies:
      #  bytesize: The number of bytes to read (and write back) to the section.
      #            This is the unit of data on which relocation is performed.
      #  has_addend: Does this relocation have an extra addend?
      #  calc_func: A function that performs the relocation on an extracted
      #             value, and returns the updated value.
      #
      _RELOCATION_RECIPE_TYPE = namedtuple('_RELOCATION_RECIPE_TYPE',
          'bytesize has_addend calc_func')
  
      def _reloc_calc_identity(value, sym_value, offset, addend=0):
          return value
  
      def _reloc_calc_sym_plus_value(value, sym_value, offset, addend=0):
          return sym_value + value
  
      def _reloc_calc_sym_plus_value_pcrel(value, sym_value, offset, addend=0):
          return sym_value + value - offset
  
      def _reloc_calc_sym_plus_addend(value, sym_value, offset, addend=0):
          return sym_value + addend
  
      def _reloc_calc_sym_plus_addend_pcrel(value, sym_value, offset, addend=0):
          return sym_value + addend - offset
  
      def _arm_reloc_calc_sym_plus_value_pcrel(value, sym_value, offset, addend=0):
          return sym_value // 4 + value - offset // 4
  
      _RELOCATION_RECIPES_ARM = {
          ENUM_RELOC_TYPE_ARM['R_ARM_ABS32']: _RELOCATION_RECIPE_TYPE(
              bytesize=4, has_addend=False,
              calc_func=_reloc_calc_sym_plus_value),
          ENUM_RELOC_TYPE_ARM['R_ARM_CALL']: _RELOCATION_RECIPE_TYPE(
              bytesize=4, has_addend=False,
              calc_func=_arm_reloc_calc_sym_plus_value_pcrel),
      }
  
      _RELOCATION_RECIPES_AARCH64 = {
          ENUM_RELOC_TYPE_AARCH64['R_AARCH64_ABS64']: _RELOCATION_RECIPE_TYPE(
              bytesize=8, has_addend=True, calc_func=_reloc_calc_sym_plus_addend),
          ENUM_RELOC_TYPE_AARCH64['R_AARCH64_ABS32']: _RELOCATION_RECIPE_TYPE(
              bytesize=4, has_addend=True, calc_func=_reloc_calc_sym_plus_addend),
          ENUM_RELOC_TYPE_AARCH64['R_AARCH64_PREL32']: _RELOCATION_RECIPE_TYPE(
              bytesize=4, has_addend=True,
              calc_func=_reloc_calc_sym_plus_addend_pcrel),
      }
  
      # https://dmz-portal.mips.com/wiki/MIPS_relocation_types
      _RELOCATION_RECIPES_MIPS = {
          ENUM_RELOC_TYPE_MIPS['R_MIPS_NONE']: _RELOCATION_RECIPE_TYPE(
              bytesize=4, has_addend=False, calc_func=_reloc_calc_identity),
          ENUM_RELOC_TYPE_MIPS['R_MIPS_32']: _RELOCATION_RECIPE_TYPE(
              bytesize=4, has_addend=False,
              calc_func=_reloc_calc_sym_plus_value),
      }
  
      _RELOCATION_RECIPES_PPC64 = {
          ENUM_RELOC_TYPE_PPC64['R_PPC64_ADDR32']: _RELOCATION_RECIPE_TYPE(
              bytesize=4, has_addend=True, calc_func=_reloc_calc_sym_plus_addend),
          ENUM_RELOC_TYPE_PPC64['R_PPC64_REL32']: _RELOCATION_RECIPE_TYPE(
              bytesize=4, has_addend=True, calc_func=_reloc_calc_sym_plus_addend_pcrel),
          ENUM_RELOC_TYPE_PPC64['R_PPC64_ADDR64']: _RELOCATION_RECIPE_TYPE(
              bytesize=8, has_addend=True, calc_func=_reloc_calc_sym_plus_addend),
      }
  
      _RELOCATION_RECIPES_X86 = {
          ENUM_RELOC_TYPE_i386['R_386_NONE']: _RELOCATION_RECIPE_TYPE(
              bytesize=4, has_addend=False, calc_func=_reloc_calc_identity),
          ENUM_RELOC_TYPE_i386['R_386_32']: _RELOCATION_RECIPE_TYPE(
              bytesize=4, has_addend=False,
              calc_func=_reloc_calc_sym_plus_value),
          ENUM_RELOC_TYPE_i386['R_386_PC32']: _RELOCATION_RECIPE_TYPE(
              bytesize=4, has_addend=False,
              calc_func=_reloc_calc_sym_plus_value_pcrel),
      }
  
      _RELOCATION_RECIPES_X64 = {
          ENUM_RELOC_TYPE_x64['R_X86_64_NONE']: _RELOCATION_RECIPE_TYPE(
              bytesize=8, has_addend=True, calc_func=_reloc_calc_identity),
          ENUM_RELOC_TYPE_x64['R_X86_64_64']: _RELOCATION_RECIPE_TYPE(
              bytesize=8, has_addend=True, calc_func=_reloc_calc_sym_plus_addend),
          ENUM_RELOC_TYPE_x64['R_X86_64_PC32']: _RELOCATION_RECIPE_TYPE(
              bytesize=4, has_addend=True,
              calc_func=_reloc_calc_sym_plus_addend_pcrel),
          ENUM_RELOC_TYPE_x64['R_X86_64_32']: _RELOCATION_RECIPE_TYPE(
              bytesize=4, has_addend=True, calc_func=_reloc_calc_sym_plus_addend),
          ENUM_RELOC_TYPE_x64['R_X86_64_32S']: _RELOCATION_RECIPE_TYPE(
              bytesize=4, has_addend=True, calc_func=_reloc_calc_sym_plus_addend),
      }
  
  
  