elftools/dwarf/dwarfinfo.py

   1 #-------------------------------------------------------------------------------
   2 # elftools: dwarf/dwarfinfo.py
   3 #
   4 # DWARFInfo - Main class for accessing DWARF debug information
   5 #
   6 # Eli Bendersky (eliben@gmail.com)
   7 # This code is in the public domain
   8 #-------------------------------------------------------------------------------
   9 from collections import namedtuple
  10
  11 from ..common.exceptions import DWARFError
  12 from ..common.utils import struct_parse, dwarf_assert
  13 from .structs import DWARFStructs
  14 from .compileunit import CompileUnit
  15
  16
  17 # Describes a debug section in a stream: offset and size
  18 #
  19 DebugSectionLocator = namedtuple('DebugSectionLocator', 'offset size')
  20
  21
  22 class DWARFInfo(object):
  23     """ Creation: the constructor accepts a stream (file-like object) that
  24         contains debug sections, along with locators (DebugSectionLocator)
  25         of the required sections. In addition, little_endian is a boolean
  26         parameter specifying endianity.
  27     """
  28     def __init__(self,
  29             stream,
  30             little_endian,
  31             debug_info_loc,
  32             debug_abbrev_loc,
  33             debug_str_loc,
  34             debug_line_loc):
  35         self.stream = stream
  36         self.debug_info_loc = debug_info_loc
  37         self.debug_abbrev_loc = debug_abbrev_loc
  38         self.debug_str_loc = debug_str_loc
  39         self.debug_line_loc = debug_line_loc
  40
  41         self.little_endian = little_endian
  42         self.dwarf_format = 32
  43         self.structs = DWARFStructs(
  44             little_endian=self.little_endian,
  45             dwarf_format=self.dwarf_format)
  46
  47         # Populate the list with CUs found in debug_info
  48         self._CU = self._parse_CUs()
  49
  50     def _parse_CUs(self):
  51         """ Parse CU entries from debug_info.
  52         """
  53         offset = self.debug_info_loc.offset
  54         section_boundary = self.debug_info_loc.offset + self.debug_info_loc.size
  55         CUlist = []
  56         while offset < section_boundary:
  57             # Section 7.4 (32-bit and 64-bit DWARF Formats) of the DWARF spec v3
  58             # states that the first 32-bit word of the CU header determines
  59             # whether the CU is represented with 32-bit or 64-bit DWARF format.
  60             #
  61             # So we peek at the first byte in the CU header to determine its
  62             # dwarf format. Based on it, we then create a new DWARFStructs
  63             # instance suitable for this CU and use it to parse the rest.
  64             #
  65             initial_length = struct_parse(
  66                 self.structs.Dwarf_uint32(''), self.stream, offset)
  67             if initial_length == 0xFFFFFFFF:
  68                 self.dwarf_format = 64
  69             cu_structs = DWARFStructs(
  70                 little_endian=self.little_endian,
  71                 dwarf_format=self.dwarf_format)
  72
  73             cu_header = struct_parse(
  74                 self.structs.Dwarf_CU_header, self.stream, offset)
  75             dwarf_assert(
  76                 self._is_supported_version(cu_header['version']),
  77                 "Expected supported DWARF version. Got '%s'" % cu_header['version'])
  78             CUlist.append(CompileUnit(cu_header, cu_structs, None))
  79             # Compute the offset of the next CU in the section. The unit_length
  80             # field of the CU header contains its size not including the length
  81             # field itself.
  82             offset = (  offset +
  83                         cu_header['unit_length'] +
  84                         cu_structs.initial_lenght_field_size())
  85         return CUlist
  86
  87     def _is_supported_version(self, version):
  88         """ DWARF version supported by this parser
  89         """
  90         return 2 <= version <= 3
  91