| #!/usr/bin/env python |
| # Copyright (c) 2010 The Chromium OS Authors. All rights reserved. |
| # Use of this source code is governed by a BSD-style license that can be |
| # found in the LICENSE file. |
| """Basic encode and decode function for 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_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(): |
| """Unit test.""" |
| if len(sys.argv) > 1: |
| filename = sys.argv[1] |
| else: |
| filename = 'bin/example.bin' |
| logging.basicConfig(level=logging.DEBUG) |
| print 'Decoding FMAP from: %s' % filename |
| blob = open(filename).read() |
| obj = fmap_decode(blob) |
| print obj |
| blob2 = fmap_encode(obj) |
| obj2 = fmap_decode(blob2, 0) |
| print obj2 |
| assert obj == obj2 |
| |
| |
| if __name__ == '__main__': |
| main() |