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.elf.elffile import ELFFile
  19 from elftools.elf.sections import SymbolTableSection
  20
  21
  22 def process_file(filename):
  23     print('Processing file:', filename)
  24     with open(filename, 'rb') as f:
  25         section_info_lowlevel(f)
  26         f.seek(0)
  27         section_info_highlevel(f)
  28
  29
  30 def section_info_lowlevel(stream):
  31     print('Low level API...')
  32     # We'll still be using the ELFFile context object. It's just too
  33     # convenient to give up, even in the low-level API demonstation :-)
  34     elffile = ELFFile(stream)
  35
  36     # The e_shnum ELF header field says how many sections there are in a file
  37     print('  %s sections' % elffile['e_shnum'])
  38
  39     # Try to find the symbol table
  40     for i in range(elffile['e_shnum']):
  41         section_offset = elffile['e_shoff'] + i * elffile['e_shentsize']
  42         # Parse the section header using structs.Elf_Shdr
  43         stream.seek(section_offset)
  44         section_header = elffile.structs.Elf_Shdr.parse_stream(stream)
  45         if section_header['sh_type'] == 'SHT_SYMTAB':
  46             # Some details about the section. Note that the section name is a
  47             # pointer to the object's string table, so it's only a number
  48             # here. To get to the actual name one would need to parse the string
  49             # table section and extract the name from there (or use the
  50             # high-level API!)
  51             print('  Section name: %s, type: %s' % (
  52                     section_header['sh_name'], section_header['sh_type']))
  53             break
  54     else:
  55         print('  No symbol table found. Perhaps this ELF has been stripped?')
  56
  57
  58 def section_info_highlevel(stream):
  59     print('High level API...')
  60     elffile = ELFFile(stream)
  61
  62     # Just use the public methods of ELFFile to get what we need
  63     # Note that section names are strings.
  64     print('  %s sections' % elffile.num_sections())
  65     section = elffile.get_section_by_name('.symtab')
  66
  67     if not section:
  68         print('  No symbol table found. Perhaps this ELF has been stripped?')
  69         return
  70
  71     # A section type is in its header, but the name was decoded and placed in
  72     # a public attribute.
  73     print('  Section name: %s, type: %s' %(
  74         section.name, section['sh_type']))
  75
  76     # But there's more... If this section is a symbol table section (which is
  77     # the case in the sample ELF file that comes with the examples), we can
  78     # get some more information about it.
  79     if isinstance(section, SymbolTableSection):
  80         num_symbols = section.num_symbols()
  81         print("  It's a symbol section with %s symbols" % num_symbols)
  82         print("  The name of the last symbol in the section is: %s" % (
  83             section.get_symbol(num_symbols - 1).name))
  84
  85
  86 if __name__ == '__main__':
  87     if sys.argv[1] == '--test':
  88         for filename in sys.argv[2:]:
  89             process_file(filename)