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 # 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             length:
  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     def __init__(self, cu, stream, offset):
  49         """ cu:
  50                 CompileUnit object this DIE belongs to. Used to obtain context
  51                 information (structs, abbrev table, etc.)
  52
  53             stream, offset:
  54                 The stream and offset into it where this DIE's data is located
  55         """
  56         self.cu = cu
  57         self.dwarfinfo = self.cu.dwarfinfo # get DWARFInfo context
  58         self.stream = stream
  59         self.offset = offset
  60         self.attributes = OrderedDict()
  61         self._parse_DIE()
  62
  63     def _parse_DIE(self):
  64         """ Parses the DIE info from the section, based on the abbreviation
  65             table of the CU
  66         """
  67         print self.offset, self.cu.structs.dwarf_format
  68         structs = self.cu.structs
  69
  70         # A DIE begins with the abbreviation code. Read it and use it to
  71         # obtain the abbrev declaration for this DIE.
  72         # Note: here and elsewhere, preserve_stream_pos is used on operations
  73         # that manipulate the stream by reading data from it.
  74         #
  75         abbrev_code = struct_parse(
  76             structs.Dwarf_uleb128(''), self.stream, self.offset)
  77         with preserve_stream_pos(self.stream):
  78             abbrev = self.cu.get_abbrev_table().get_abbrev(abbrev_code)
  79
  80         print '**', abbrev_code, abbrev, abbrev.decl
  81
  82         # Guided by the attributes listed in the abbreviation declaration, parse
  83         # values from the stream.
  84         #
  85         for name, form in abbrev.iter_attr_specs():
  86             print '** parsing at stream + ', self.stream.tell()
  87             raw_value = struct_parse(structs.Dwarf_dw_form[form], self.stream)
  88             print '**', name, form, raw_value
  89             #~ print structs.Dwarf_dw_form[form]
  90
  91