elftools/dwarf/locationlists.py

   1 #-------------------------------------------------------------------------------
   2 # elftools: dwarf/locationlists.py
   3 #
   4 # DWARF location lists section decoding (.debug_loc)
   5 #
   6 # Eli Bendersky (eliben@gmail.com)
   7 # This code is in the public domain
   8 #-------------------------------------------------------------------------------
   9 import os
  10 from collections import namedtuple
  11
  12 from ..common.utils import struct_parse
  13
  14
  15 LocationEntry = namedtuple('LocationEntry', 'begin_offset end_offset loc_expr')
  16 BaseAddressEntry = namedtuple('BaseAddressEntry', 'base_address')
  17
  18
  19 class LocationLists(object):
  20     """ A single location list is a Python list consisting of LocationEntry or
  21         BaseAddressEntry objects.
  22     """
  23     def __init__(self, stream, structs):
  24         self.stream = stream
  25         self.structs = structs
  26         self._max_addr = 2 ** (self.structs.address_size * 8) - 1
  27
  28     def get_location_list_at_offset(self, offset):
  29         """ Get a location list at the given offset in the section.
  30         """
  31         self.stream.seek(offset, os.SEEK_SET)
  32         return self._parse_location_list_from_stream()
  33
  34     def iter_location_lists(self):
  35         """ Yield all location lists found in the section.
  36         """
  37         # Just call _parse_location_list_from_stream until the stream ends
  38         self.stream.seek(0, os.SEEK_END)
  39         endpos = self.stream.tell()
  40
  41         self.stream.seek(0, os.SEEK_SET)
  42         while self.stream.tell() < endpos:
  43             yield self._parse_location_list_from_stream()
  44
  45     #------ PRIVATE ------#
  46
  47     def _parse_location_list_from_stream(self):
  48         lst = []
  49         while True:
  50             begin_offset = struct_parse(
  51                 self.structs.Dwarf_target_addr(''), self.stream)
  52             end_offset = struct_parse(
  53                 self.structs.Dwarf_target_addr(''), self.stream)
  54             if begin_offset == 0 and end_offset == 0:
  55                 # End of list - we're done.
  56                 break
  57             elif begin_offset == self._max_addr:
  58                 # Base address selection entry
  59                 lst.append(BaseAddressEntry(base_address=end_offset))
  60             else:
  61                 # Location list entry
  62                 expr_len = struct_parse(
  63                     self.structs.Dwarf_uint16(''), self.stream)
  64                 loc_expr = [struct_parse(self.structs.Dwarf_uint8(''),
  65                                          self.stream)
  66                                 for i in range(expr_len)]
  67                 lst.append(LocationEntry(
  68                     begin_offset=begin_offset,
  69                     end_offset=end_offset,
  70                     loc_expr=loc_expr))
  71         return lst
  72