elftools/dwarf/die.py

   1 #-------------------------------------------------------------------------------
   2 # elftools: dwarf/die.py
   3 #
   4 # DWARF Debugging Information Entry
   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.ordereddict import OrderedDict
  12 from ..common.utils import struct_parse, preserve_stream_pos
  13
  14
  15 # AttributeValue - describes an attribute value in the DIE:
  16 #
  17 # form:
  18 #   The DW_FORM_* name of this attribute
  19 #
  20 # value:
  21 #   The value parsed from the section and translated accordingly to the form
  22 #   (e.g. for a DW_FORM_strp it's the actual string taken from the string table)
  23 #
  24 # raw_value:
  25 #   Raw value as parsed from the section - used for debugging and presentation
  26 #   (e.g. for a DW_FORM_strp it's the raw string offset into the table)
  27 #
  28 AttributeValue = namedtuple('AttributeValue', 'form value raw_value')
  29
  30
  31 class DIE(object):
  32     """ A DWARF debugging information entry. On creation, parses itself from
  33         the stream. Each DIE is held by a CU.
  34
  35         Accessible attributes:
  36
  37             tag:
  38                 The DIE tag
  39
  40             size:
  41                 The size this DIE occupies in the section
  42
  43             attributes:
  44                 An ordered dictionary mapping attribute names to values. It's
  45                 ordered to enable both efficient name->value mapping and
  46                 preserve the order of attributes in the section
  47
  48             has_children:
  49                 Specifies whether this DIE has children
  50     """
  51     def __init__(self, cu, stream, offset):
  52         """ cu:
  53                 CompileUnit object this DIE belongs to. Used to obtain context
  54                 information (structs, abbrev table, etc.)
  55
  56             stream, offset:
  57                 The stream and offset into it where this DIE's data is located
  58         """
  59         self.cu = cu
  60         self.dwarfinfo = self.cu.dwarfinfo # get DWARFInfo context
  61         self.stream = stream
  62         self.offset = offset
  63         self.attributes = OrderedDict()
  64         self._parse_DIE()
  65
  66     def _parse_DIE(self):
  67         """ Parses the DIE info from the section, based on the abbreviation
  68             table of the CU
  69         """
  70         structs = self.cu.structs
  71
  72         # A DIE begins with the abbreviation code. Read it and use it to
  73         # obtain the abbrev declaration for this DIE.
  74         # Note: here and elsewhere, preserve_stream_pos is used on operations
  75         # that manipulate the stream by reading data from it.
  76         #
  77         abbrev_code = struct_parse(
  78             structs.Dwarf_uleb128(''), self.stream, self.offset)
  79         with preserve_stream_pos(self.stream):
  80             abbrev_decl = self.cu.get_abbrev_table().get_abbrev(abbrev_code)
  81         self.has_children = abbrev_decl.has_children()
  82
  83         # Guided by the attributes listed in the abbreviation declaration, parse
  84         # values from the stream.
  85         #
  86         for name, form in abbrev_decl.iter_attr_specs():
  87             raw_value = struct_parse(structs.Dwarf_dw_form[form], self.stream)
  88             value = self._translate_attr_value(form, raw_value)
  89             self.attributes[name] = AttributeValue(form, value, raw_value)
  90
  91         self.size = self.stream.tell() - self.offset
  92
  93     def _translate_attr_value(self, form, raw_value):
  94         """ Translate a raw attr value according to the form
  95         """
  96         value = None
  97         if form == 'DW_FORM_strp':
  98             with preserve_stream_pos(self.stream):
  99                 value = self.dwarfinfo.get_string_from_table(raw_value)
 100         elif form == 'DW_FORM_flag':
 101             value = not raw_value == 0
 102         elif form == 'DW_FORM_indirect':
 103             form = raw_value
 104             raw_value = struct_parse(
 105                 structs.Dwarf_dw_form[form], self.stream)
 106             # Let's hope this doesn't get too deep :-)
 107             return self._translate_attr_value(form, raw_value)
 108         else:
 109             value = raw_value
 110         return value
 111
 112