elf-get-entry

#!/usr/bin/env python2

# Copyright (c) 2015, NVIDIA CORPORATION. All rights reserved.
#
# Permission is hereby granted, free of charge, to any person obtaining a
# copy of this software and associated documentation files (the "Software"),
# to deal in the Software without restriction, including without limitation
# the rights to use, copy, modify, merge, publish, distribute, sublicense,
# and/or sell copies of the Software, and to permit persons to whom the
# Software is furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
# THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
# FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
# DEALINGS IN THE SOFTWARE.

import sys
import struct

if len(sys.argv) != 2:
    print >>sys.stderr, "usage: %s filename.elf" % sys.argv[0]
    sys.exit(-1)

f = file(sys.argv[1], 'rb')
data = f.read(0x20)
f.close()

if data[0:4] != '\x7fELF':
    print >>sys.stderr, "ELF magic mismatch"
    sys.exit(-1)

ei_class = ord(data[4])
if ei_class == 1:
    elf_bytes = 4
    struct_type = 'I'
elif ei_class == 2:
    elf_bytes = 8
    struct_type = 'Q'
else:
    print >>sys.stderr, "Bad EI_CLASS value"
    sys.exit(-1)

ei_data = ord(data[5])
if ei_data == 1:
    struct_endian = '<'
elif ei_data == 2:
    struct_endian = '>'
else:
    print >>sys.stderr, "Bad EI_DATA value"
    sys.exit(-1)

ei_version = ord(data[6])
if ei_version != 1:
    print >>sys.stderr, "Bad EI_VERSION value"
    sys.exit(-1)

e_entry = data[0x18:0x18 + elf_bytes]
ep = struct.unpack(struct_endian + struct_type, e_entry)
print '0x%x' % ep