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#-------------------------------------------------------------------------------
# elftools example: dwarf_location_info.py
#
# Examine DIE entries which have either location list values or location
# expression values and decode that information.
#
# Location information can either be completely contained within a DIE
# (using 'DW_FORM_exprloc' in DWARFv4 or 'DW_FORM_block1' in earlier
# versions) or be a reference to a location list contained within
# the .debug_loc section (using 'DW_FORM_sec_offset' in DWARFv4 or
# 'DW_FORM_data4' / 'DW_FORM_data8' in earlier versions).
#
# The LocationParser object parses the DIE attributes and handles both
# formats.
#
# The directory 'test/testfiles_for_location_info' contains test files with
# location information represented in both DWARFv4 and DWARFv2 forms.
#
# Eli Bendersky (eliben@gmail.com)
# This code is in the public domain
#-------------------------------------------------------------------------------
from __future__ import print_function
import sys
# If pyelftools is not installed, the example can also run from the root or
# examples/ dir of the source distribution.
sys.path[0:0] = ['.', '..']
from elftools.elf.elffile import ELFFile
from elftools.dwarf.descriptions import (
describe_DWARF_expr, set_global_machine_arch)
from elftools.dwarf.locationlists import (
LocationEntry, LocationExpr, LocationParser)
def process_file(filename):
print('Processing file:', filename)
with open(filename, 'rb') as f:
elffile = ELFFile(f)
if not elffile.has_dwarf_info():
print(' file has no DWARF info')
return
# get_dwarf_info returns a DWARFInfo context object, which is the
# starting point for all DWARF-based processing in pyelftools.
dwarfinfo = elffile.get_dwarf_info()
# The location lists are extracted by DWARFInfo from the .debug_loc
# section, and returned here as a LocationLists object.
location_lists = dwarfinfo.location_lists()
# This is required for the descriptions module to correctly decode
# register names contained in DWARF expressions.
set_global_machine_arch(elffile.get_machine_arch())
# Create a LocationParser object that parses the DIE attributes and
# creates objects representing the actual location information.
loc_parser = LocationParser(location_lists)
for CU in dwarfinfo.iter_CUs():
# DWARFInfo allows to iterate over the compile units contained in
# the .debug_info section. CU is a CompileUnit object, with some
# computed attributes (such as its offset in the section) and
# a header which conforms to the DWARF standard. The access to
# header elements is, as usual, via item-lookup.
print(' Found a compile unit at offset %s, length %s' % (
CU.cu_offset, CU['unit_length']))
# A CU provides a simple API to iterate over all the DIEs in it.
for DIE in CU.iter_DIEs():
# Go over all attributes of the DIE. Each attribute is an
# AttributeValue object (from elftools.dwarf.die), which we
# can examine.
for attr in DIE.attributes.values():
# Check if this attribute contains location information
if loc_parser.attribute_has_location(attr, CU['version']):
print(' DIE %s. attr %s.' % (DIE.tag, attr.name))
loc = loc_parser.parse_from_attribute(attr,
CU['version'], DIE)
# We either get a list (in case the attribute is a
# reference to the .debug_loc section) or a LocationExpr
# object (in case the attribute itself contains location
# information).
if isinstance(loc, LocationExpr):
print(' %s' % (
describe_DWARF_expr(loc.loc_expr,
dwarfinfo.structs, CU.cu_offset)))
elif isinstance(loc, list):
print(show_loclist(loc,
dwarfinfo,
' ', CU.cu_offset))
def show_loclist(loclist, dwarfinfo, indent, cu_offset):
""" Display a location list nicely, decoding the DWARF expressions
contained within.
"""
d = []
for loc_entity in loclist:
if isinstance(loc_entity, LocationEntry):
d.append('%s <<%s>>' % (
loc_entity,
describe_DWARF_expr(loc_entity.loc_expr, dwarfinfo.structs, cu_offset)))
else:
d.append(str(loc_entity))
return '\n'.join(indent + s for s in d)
if __name__ == '__main__':
if sys.argv[1] == '--test':
for filename in sys.argv[2:]:
process_file(filename)
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