examples/elf_low_high_api.py

   1 #-------------------------------------------------------------------------------
   2 # elftools example: elf_low_high_api.py
   3 #
   4 # A simple example that shows some usage of the low-level API pyelftools
   5 # provides versus the high-level API while inspecting an ELF file's symbol
   6 # table.
   7 #
   8 # Eli Bendersky (eliben@gmail.com)
   9 # This code is in the public domain
  10 #-------------------------------------------------------------------------------
  11 from __future__ import print_function
  12 import sys
  13
  14 # If pyelftools is not installed, the example can also run from the root or
  15 # examples/ dir of the source distribution.
  16 sys.path[0:0] = ['.', '..']
  17
  18 from elftools.common.py3compat import bytes2str
  19 from elftools.elf.elffile import ELFFile
  20 from elftools.elf.sections import SymbolTableSection
  21
  22
  23 def process_file(filename):
  24     print('Processing file:', filename)
  25     with open(filename, 'rb') as f:
  26         section_info_lowlevel(f)
  27         f.seek(0)
  28         section_info_highlevel(f)
  29
  30
  31 def section_info_lowlevel(stream):
  32     print('Low level API...')
  33     # We'll still be using the ELFFile context object. It's just too
  34     # convenient to give up, even in the low-level API demonstation :-)
  35     elffile = ELFFile(stream)
  36
  37     # The e_shnum ELF header field says how many sections there are in a file
  38     print('  %s sections' % elffile['e_shnum'])
  39
  40     # Try to find the symbol table
  41     for i in range(elffile['e_shnum']):
  42         section_offset = elffile['e_shoff'] + i * elffile['e_shentsize']
  43         # Parse the section header using structs.Elf_Shdr
  44         stream.seek(section_offset)
  45         section_header = elffile.structs.Elf_Shdr.parse_stream(stream)
  46         if section_header['sh_type'] == 'SHT_SYMTAB':
  47             # Some details about the section. Note that the section name is a
  48             # pointer to the object's string table, so it's only a number
  49             # here. To get to the actual name one would need to parse the string
  50             # table section and extract the name from there (or use the
  51             # high-level API!)
  52             print('  Section name: %s, type: %s' % (
  53                     section_header['sh_name'], section_header['sh_type']))
  54             break
  55     else:
  56         print('  No symbol table found. Perhaps this ELF has been stripped?')
  57
  58
  59 def section_info_highlevel(stream):
  60     print('High level API...')
  61     elffile = ELFFile(stream)
  62
  63     # Just use the public methods of ELFFile to get what we need
  64     # Note that section names, like everything read from the file, are bytes
  65     # objects.
  66     print('  %s sections' % elffile.num_sections())
  67     section = elffile.get_section_by_name(b'.symtab')
  68
  69     if not section:
  70         print('  No symbol table found. Perhaps this ELF has been stripped?')
  71         return
  72
  73     # A section type is in its header, but the name was decoded and placed in
  74     # a public attribute.
  75     # bytes2str is used to print the name of the section for consistency of
  76     # output between Python 2 and 3. The section name is a bytes object.
  77     print('  Section name: %s, type: %s' %(
  78         bytes2str(section.name), section['sh_type']))
  79
  80     # But there's more... If this section is a symbol table section (which is
  81     # the case in the sample ELF file that comes with the examples), we can
  82     # get some more information about it.
  83     if isinstance(section, SymbolTableSection):
  84         num_symbols = section.num_symbols()
  85         print("  It's a symbol section with %s symbols" % num_symbols)
  86         print("  The name of the last symbol in the section is: %s" % (
  87             bytes2str(section.get_symbol(num_symbols - 1).name)))
  88
  89
  90 if __name__ == '__main__':
  91     for filename in sys.argv[1:]:
  92         process_file(filename)
  93
  94