examples/dwarf_lineprogram_filenames.py

   1 #-------------------------------------------------------------------------------
   2 # elftools example: dwarf_lineprogram_filenames.py
   3 #
   4 # In the .debug_line section, the Dwarf line program generates a matrix
   5 # of address-source references. This example demonstrates accessing the state
   6 # of each line program entry to retrieve the underlying filenames.
   7 #
   8 # William Woodruff (william@yossarian.net)
   9 # This code is in the public domain
  10 #-------------------------------------------------------------------------------
  11 from __future__ import print_function
  12 from collections import defaultdict
  13 import os
  14 import sys
  15
  16 # If pyelftools is not installed, the example can also run from the root or
  17 # examples/ dir of the source distribution.
  18 sys.path[0:0] = ['.', '..']
  19
  20 from elftools.elf.elffile import ELFFile
  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         dwarfinfo = elffile.get_dwarf_info()
  33         for CU in dwarfinfo.iter_CUs():
  34             print('  Found a compile unit at offset %s, length %s' % (
  35                 CU.cu_offset, CU['unit_length']))
  36
  37             # Every compilation unit in the DWARF information may or may not
  38             # have a corresponding line program in .debug_line.
  39             line_program = dwarfinfo.line_program_for_CU(CU)
  40             if line_program is None:
  41                 print('  DWARF info is missing a line program for this CU')
  42                 continue
  43
  44             # Print a reverse mapping of filename -> #entries
  45             line_entry_mapping(line_program)
  46
  47
  48 def line_entry_mapping(line_program):
  49     filename_map = defaultdict(int)
  50
  51     # The line program, when decoded, returns a list of line program
  52     # entries. Each entry contains a state, which we'll use to build
  53     # a reverse mapping of filename -> #entries.
  54     lp_entries = line_program.get_entries()
  55     for lpe in lp_entries:
  56         # We skip LPEs that don't have an associated file.
  57         # This can happen if instructions in the compiled binary
  58         # don't correspond directly to any original source file.
  59         if not lpe.state or lpe.state.file == 0:
  60             continue
  61         filename = lpe_filename(line_program, lpe.state.file)
  62         filename_map[filename] += 1
  63
  64     for filename, lpe_count in filename_map.items():
  65         print("    filename=%s -> %d entries" % (filename, lpe_count))
  66
  67
  68 def lpe_filename(line_program, file_index):
  69     # Retrieving the filename associated with a line program entry
  70     # involves two levels of indirection: we take the file index from
  71     # the LPE to grab the file_entry from the line program header,
  72     # then take the directory index from the file_entry to grab the
  73     # directory name from the line program header. Finally, we
  74     # join the (base) filename from the file_entry to the directory
  75     # name to get the absolute filename.
  76     lp_header = line_program.header
  77     file_entries = lp_header["file_entry"]
  78
  79     # File and directory indices are 1-indexed.
  80     file_entry = file_entries[file_index - 1]
  81     dir_index = file_entry["dir_index"]
  82
  83     # A dir_index of 0 indicates that no absolute directory was recorded during
  84     # compilation; return just the basename.
  85     if dir_index == 0:
  86         return file_entry.name.decode()
  87
  88     directory = lp_header["include_directory"][dir_index - 1]
  89     return os.path.join(directory, file_entry.name).decode()
  90
  91
  92 if __name__ == '__main__':
  93     if sys.argv[1] == '--test':
  94         for filename in sys.argv[2:]:
  95             process_file(filename)