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 import posixpath
  16
  17 # If pyelftools is not installed, the example can also run from the root or
  18 # examples/ dir of the source distribution.
  19 sys.path[0:0] = ['.', '..']
  20
  21 from elftools.elf.elffile import ELFFile
  22
  23
  24 def process_file(filename):
  25     print('Processing file:', filename)
  26     with open(filename, 'rb') as f:
  27         elffile = ELFFile(f)
  28
  29         if not elffile.has_dwarf_info():
  30             print('  file has no DWARF info')
  31             return
  32
  33         dwarfinfo = elffile.get_dwarf_info()
  34         for CU in dwarfinfo.iter_CUs():
  35             print('  Found a compile unit at offset %s, length %s' % (
  36                 CU.cu_offset, CU['unit_length']))
  37
  38             # Every compilation unit in the DWARF information may or may not
  39             # have a corresponding line program in .debug_line.
  40             line_program = dwarfinfo.line_program_for_CU(CU)
  41             if line_program is None:
  42                 print('  DWARF info is missing a line program for this CU')
  43                 continue
  44
  45             # Print a reverse mapping of filename -> #entries
  46             line_entry_mapping(line_program)
  47
  48
  49 def line_entry_mapping(line_program):
  50     filename_map = defaultdict(int)
  51
  52     # The line program, when decoded, returns a list of line program
  53     # entries. Each entry contains a state, which we'll use to build
  54     # a reverse mapping of filename -> #entries.
  55     lp_entries = line_program.get_entries()
  56     for lpe in lp_entries:
  57         # We skip LPEs that don't have an associated file.
  58         # This can happen if instructions in the compiled binary
  59         # don't correspond directly to any original source file.
  60         if not lpe.state or lpe.state.file == 0:
  61             continue
  62         filename = lpe_filename(line_program, lpe.state.file)
  63         filename_map[filename] += 1
  64
  65     for filename, lpe_count in filename_map.items():
  66         print("    filename=%s -> %d entries" % (filename, lpe_count))
  67
  68
  69 def lpe_filename(line_program, file_index):
  70     # Retrieving the filename associated with a line program entry
  71     # involves two levels of indirection: we take the file index from
  72     # the LPE to grab the file_entry from the line program header,
  73     # then take the directory index from the file_entry to grab the
  74     # directory name from the line program header. Finally, we
  75     # join the (base) filename from the file_entry to the directory
  76     # name to get the absolute filename.
  77     lp_header = line_program.header
  78     file_entries = lp_header["file_entry"]
  79
  80     # File and directory indices are 1-indexed.
  81     file_entry = file_entries[file_index - 1]
  82     dir_index = file_entry["dir_index"]
  83
  84     # A dir_index of 0 indicates that no absolute directory was recorded during
  85     # compilation; return just the basename.
  86     if dir_index == 0:
  87         return file_entry.name.decode()
  88
  89     directory = lp_header["include_directory"][dir_index - 1]
  90     return posixpath.join(directory, file_entry.name).decode()
  91
  92
  93 if __name__ == '__main__':
  94     if sys.argv[1] == '--test':
  95         for filename in sys.argv[2:]:
  96             process_file(filename)