#!/usr/bin/python
'''analyze and create ELF executables

   see /usr/include/linux/elf.h'''
import sys, os, struct
MAGIC = '\x7f' + 'ELF' + ('\1' * 3) + ('\0' * 9)  # ELF "magic" header
EHSIZE = 52  # kinda must be known before even attempting to parse
class reducible(str):
 def __sub__(self, other):
  start = self.find(other)
  if start == -1:
   return self
  else:
   return reducible(self[0:start] + self[start + len(other):])
class elf:
 pass
def main():
 'run the program'
 elffile = reducible(readall('minimal.exe'))
 e = elf()
 (e.magic, e.type, e.machine, e.version, e.entry, e.phoff, e.shoff,
  e.flags, e.ehsize, e.phentsize, e.phnum, e.shentsize, e.shnum,
  e.shstrndx, remainder) = elfheader(elffile)
 print dir(e)
 if e.magic != MAGIC:
  raise Exception, 'not an ELF file'
 dump(e)
 #print 'remainder: ', repr(remainder)
 pheaders = elffile[e.phoff:e.phoff + (e.phnum * e.phentsize)]
 sheaders = elffile[e.shoff:e.shoff + (e.shnum * e.shentsize)]
 shstrhdr = sheaders[e.shstrndx * e.shentsize:(e.shstrndx + 1) * e.shentsize]
 shstrtab = elfdata(elffile, elf_shdr(shstrhdr)[4:6])
 print 'section string table', repr(shstrtab)
 remainder = remainder - pheaders - sheaders
 for i in range(e.phnum):
  pheader = pheaders[i * e.phentsize:(i + 1) * e.phentsize]
  print 'pheader', hex(elf_phdr(pheader))
 for i in range(e.shnum):
  sheader = sheaders[i * e.shentsize:(i + 1) * e.shentsize]
  sheader_values = elf_shdr(sheader)
  print 'sheader', hex(elf_shdr(sheader))
  section_data = elffile[sheader_values[4]:sheader_values[4] + \
   sheader_values[5]]
  print 'section data', repr(section_data)
  if sheader_values[1] == 2:  # symbol table
   for j in range(0, len(section_data), 16):
    print 'symbol', hex(sym(section_data[j:j + 16]))
  remainder -= section_data
 print 'remainder: ', repr(remainder)
def elfdata(elffile, whatpart):
 start, size = whatpart
 return elffile[start:start + size]
def elfheader(elffile):
 'return parsed header and remainder of file'
 format = '<16s 2H 5L 6H'
 return struct.unpack(format, elffile[:EHSIZE]) + (reducible(elffile[EHSIZE:]),)
def elf_phdr(data):
 'return parsed program header'
 format = '<8L'
 return struct.unpack(format, data)
def hex(data):
 return map(lambda n: '0x%x' % n, data)
def elf_shdr(data):
 format = '<10L'
 return struct.unpack(format, data)
def sym(data):
 format = '<3L 2B H'
 return struct.unpack(format, data)
def readall(filename):
 'get contents of a file, closing it properly'
 input = open(filename)
 data = input.read()
 input.close()
 return data
def debug(message):
 'print debugging message to stderr'
 if True:  # change to False when done debugging
  print >>sys.stderr, message
def dump(object):
 for attribute in dir(object):
  if not attribute.startswith('_'):
   value = getattr(object, attribute)
   if isinstance(value, int):
    print attribute, '0x%x' % value
   else:
    print attribute, repr(value)
if __name__ == '__main__':
 main()