blob: 982d1a5cbf1df85cdf17b592d9938f53a4298263 [file] [log] [blame]
#!/usr/bin/env python
#
# Copyright 2010, Google Inc.
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"""
This module provides basic encode and decode functionality to the flashrom
memory map (FMAP) structure.
Usage:
(decode)
obj = fmap_decode(blob)
print obj
(encode)
blob = fmap_encode(obj)
open('output.bin', 'w').write(blob)
The object returned by fmap_decode is a dictionary with names defined in
fmap.h. A special property 'FLAGS' is provided as a readable and read-only
tuple of decoded area flags.
"""
import logging
import struct
import sys
# constants imported from lib/fmap.h
FMAP_SIGNATURE = '__FMAP__'
FMAP_VER_MAJOR = 1
FMAP_VER_MINOR_MIN = 0
FMAP_VER_MINOR_MAX = 1
FMAP_STRLEN = 32
FMAP_SEARCH_STRIDE = 4
FMAP_FLAGS = {
'FMAP_AREA_STATIC': 1 << 0,
'FMAP_AREA_COMPRESSED': 1 << 1,
'FMAP_AREA_RO': 1 << 2,
'FMAP_AREA_PRESERVE': 1 << 3,
}
FMAP_HEADER_NAMES = (
'signature',
'ver_major',
'ver_minor',
'base',
'size',
'name',
'nareas',
)
FMAP_AREA_NAMES = (
'offset',
'size',
'name',
'flags',
)
# format string
FMAP_HEADER_FORMAT = '<8sBBQI%dsH' % (FMAP_STRLEN)
FMAP_AREA_FORMAT = '<II%dsH' % (FMAP_STRLEN)
def _fmap_decode_header(blob, offset):
""" (internal) Decodes a FMAP header from blob by offset"""
header = {}
for (name, value) in zip(FMAP_HEADER_NAMES,
struct.unpack_from(FMAP_HEADER_FORMAT,
blob,
offset)):
header[name] = value
if header['signature'] != FMAP_SIGNATURE:
raise struct.error('Invalid signature')
if (header['ver_major'] != FMAP_VER_MAJOR or
header['ver_minor'] < FMAP_VER_MINOR_MIN or
header['ver_minor'] > FMAP_VER_MINOR_MAX):
raise struct.error('Incompatible version')
# convert null-terminated names
header['name'] = header['name'].strip(chr(0))
return (header, struct.calcsize(FMAP_HEADER_FORMAT))
def _fmap_decode_area(blob, offset):
""" (internal) Decodes a FMAP area record from blob by offset """
area = {}
for (name, value) in zip(FMAP_AREA_NAMES,
struct.unpack_from(FMAP_AREA_FORMAT, blob, offset)):
area[name] = value
# convert null-terminated names
area['name'] = area['name'].strip(chr(0))
# add a (readonly) readable FLAGS
area['FLAGS'] = _fmap_decode_area_flags(area['flags'])
return (area, struct.calcsize(FMAP_AREA_FORMAT))
def _fmap_decode_area_flags(area_flags):
""" (internal) Decodes a FMAP flags property """
return tuple([name for name in FMAP_FLAGS if area_flags & FMAP_FLAGS[name]])
def _fmap_check_name(fmap, name):
"""Checks if the FMAP structure has correct name.
Args:
fmap: A decoded FMAP structure.
name: A string to specify expected FMAP name.
Raises:
struct.error if the name does not match.
"""
if fmap['name'] != name:
raise struct.error('Incorrect FMAP (found: "%s", expected: "%s")' %
(fmap['name'], name))
def _fmap_search_header(blob, fmap_name=None):
"""Searches FMAP headers in given blob.
Uses same logic from vboot_reference/host/lib/fmap.c.
Args:
blob: A string containing FMAP data.
fmap_name: A string to specify target FMAP name.
Returns:
A tuple of (fmap, size, offset).
"""
lim = len(blob) - struct.calcsize(FMAP_HEADER_FORMAT)
align = FMAP_SEARCH_STRIDE
# Search large alignments before small ones to find "right" FMAP.
while align <= lim:
align *= 2
while align >= FMAP_SEARCH_STRIDE:
for offset in xrange(align, lim + 1, align * 2):
if not blob.startswith(FMAP_SIGNATURE, offset):
continue
try:
(fmap, size) = _fmap_decode_header(blob, offset)
if fmap_name is not None:
_fmap_check_name(fmap, fmap_name)
return (fmap, size, offset)
except struct.error as e:
# Search for next FMAP candidate.
logging.debug('Continue searching FMAP due to exception %r', e)
pass
align /= 2
raise struct.error('No valid FMAP signatures.')
def fmap_decode(blob, offset=None, fmap_name=None):
""" Decodes a blob to FMAP dictionary object.
Arguments:
blob: a binary data containing FMAP structure.
offset: starting offset of FMAP. When omitted, fmap_decode will search in
the blob.
"""
fmap = {}
if offset is None:
(fmap, size, offset) = _fmap_search_header(blob, fmap_name)
else:
(fmap, size) = _fmap_decode_header(blob, offset)
if fmap_name is not None:
_fmap_check_name(fmap, fmap_name)
fmap['areas'] = []
offset = offset + size
for _ in range(fmap['nareas']):
(area, size) = _fmap_decode_area(blob, offset)
offset = offset + size
fmap['areas'].append(area)
return fmap
def _fmap_encode_header(obj):
""" (internal) Encodes a FMAP header """
values = [obj[name] for name in FMAP_HEADER_NAMES]
return struct.pack(FMAP_HEADER_FORMAT, *values)
def _fmap_encode_area(obj):
""" (internal) Encodes a FMAP area entry """
values = [obj[name] for name in FMAP_AREA_NAMES]
return struct.pack(FMAP_AREA_FORMAT, *values)
def fmap_encode(obj):
""" Encodes a FMAP dictionary object to blob.
Arguments
obj: a FMAP dictionary object.
"""
# fix up values
obj['nareas'] = len(obj['areas'])
# TODO(hungte) re-assign signature / version?
blob = _fmap_encode_header(obj)
for area in obj['areas']:
blob = blob + _fmap_encode_area(area)
return blob
def main():
"""Decode FMAP from supplied file and print."""
if len(sys.argv) < 2:
print 'Usage: fmap.py <file>'
sys.exit(1)
filename = sys.argv[1]
print 'Decoding FMAP from: %s' % filename
blob = open(filename).read()
obj = fmap_decode(blob)
print obj
if __name__ == '__main__':
main()