examples/dwarf_range_lists.py

   1 #-------------------------------------------------------------------------------
   2 # elftools example: dwarf_range_lists.py
   3 #
   4 # Examine DIE entries which have range list values, and decode these range
   5 # lists.
   6 #
   7 # Eli Bendersky (eliben@gmail.com)
   8 # This code is in the public domain
   9 #-------------------------------------------------------------------------------
  10 from __future__ import print_function
  11 import sys
  12
  13 # If pyelftools is not installed, the example can also run from the root or
  14 # examples/ dir of the source distribution.
  15 sys.path[0:0] = ['.', '..']
  16
  17 from elftools.elf.elffile import ELFFile
  18 from elftools.dwarf.descriptions import (
  19     describe_DWARF_expr, set_global_machine_arch)
  20 from elftools.dwarf.ranges import RangeEntry
  21
  22
  23 def process_file(filename):
  24     print('Processing file:', filename)
  25     with open(filename, 'rb') as f:
  26         elffile = ELFFile(f)
  27
  28         if not elffile.has_dwarf_info():
  29             print('  file has no DWARF info')
  30             return
  31
  32         # get_dwarf_info returns a DWARFInfo context object, which is the
  33         # starting point for all DWARF-based processing in pyelftools.
  34         dwarfinfo = elffile.get_dwarf_info()
  35
  36         # The range lists are extracted by DWARFInfo from the .debug_ranges
  37         # section, and returned here as a RangeLists object.
  38         range_lists = dwarfinfo.range_lists()
  39         if range_lists is None:
  40             print('  file has no .debug_ranges section')
  41             return
  42
  43         for CU in dwarfinfo.iter_CUs():
  44             # DWARFInfo allows to iterate over the compile units contained in
  45             # the .debug_info section. CU is a CompileUnit object, with some
  46             # computed attributes (such as its offset in the section) and
  47             # a header which conforms to the DWARF standard. The access to
  48             # header elements is, as usual, via item-lookup.
  49             print('  Found a compile unit at offset %s, length %s' % (
  50                 CU.cu_offset, CU['unit_length']))
  51
  52             # A CU provides a simple API to iterate over all the DIEs in it.
  53             for DIE in CU.iter_DIEs():
  54                 # Go over all attributes of the DIE. Each attribute is an
  55                 # AttributeValue object (from elftools.dwarf.die), which we
  56                 # can examine.
  57                 for attr in DIE.attributes.values():
  58                     if attribute_has_range_list(attr):
  59                         # This is a range list. Its value is an offset into
  60                         # the .debug_ranges section, so we can use the range
  61                         # lists object to decode it.
  62                         rangelist = range_lists.get_range_list_at_offset(
  63                             attr.value)
  64
  65                         print('   DIE %s. attr %s.\n%s' % (
  66                             DIE.tag,
  67                             attr.name,
  68                             rangelist))
  69
  70
  71 def attribute_has_range_list(attr):
  72     """ Only some attributes can have range list values, if they have the
  73         required DW_FORM (rangelistptr "class" in DWARF spec v3)
  74     """
  75     if attr.name == 'DW_AT_ranges':
  76         if attr.form in ('DW_FORM_data4', 'DW_FORM_data8'):
  77             return True
  78     return False
  79
  80
  81 if __name__ == '__main__':
  82     if sys.argv[1] == '--test':
  83         for filename in sys.argv[2:]:
  84             process_file(filename)