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u-boot/tools/binman/cbfs_util.py
Simon Glass 0d1e95aa18 binman: Tidy up pylint warnings in comp_util 
Tweak some naming and comments to resolve these. Use WriteFile() to write
the file.

Signed-off-by: Simon Glass <sjg@chromium.org>
2022-01-25 12:36:11 -07:00

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# SPDX-License-Identifier: GPL-2.0+
# Copyright 2019 Google LLC
# Written by Simon Glass <sjg@chromium.org>
"""Support for coreboot's CBFS format
CBFS supports a header followed by a number of files, generally targeted at SPI
flash.
The format is somewhat defined by documentation in the coreboot tree although
it is necessary to rely on the C structures and source code (mostly cbfstool)
to fully understand it.
Currently supported: raw and stage types with compression, padding empty areas
with empty files, fixed-offset files
"""
from collections import OrderedDict
import io
import struct
import sys
from binman import comp_util
from binman import elf
from patman import command
from patman import tools
# Set to True to enable printing output while working
DEBUG = False
# Set to True to enable output from running cbfstool for debugging
VERBOSE = False
# The master header, at the start of the CBFS
HEADER_FORMAT = '>IIIIIIII'
HEADER_LEN = 0x20
HEADER_MAGIC = 0x4f524243
HEADER_VERSION1 = 0x31313131
HEADER_VERSION2 = 0x31313132
# The file header, at the start of each file in the CBFS
FILE_HEADER_FORMAT = b'>8sIIII'
FILE_HEADER_LEN = 0x18
FILE_MAGIC = b'LARCHIVE'
FILENAME_ALIGN = 16 # Filename lengths are aligned to this
# A stage header containing information about 'stage' files
# Yes this is correct: this header is in litte-endian format
STAGE_FORMAT = '<IQQII'
STAGE_LEN = 0x1c
# An attribute describring the compression used in a file
ATTR_COMPRESSION_FORMAT = '>IIII'
ATTR_COMPRESSION_LEN = 0x10
# Attribute tags
# Depending on how the header was initialised, it may be backed with 0x00 or
# 0xff. Support both.
FILE_ATTR_TAG_UNUSED = 0
FILE_ATTR_TAG_UNUSED2 = 0xffffffff
FILE_ATTR_TAG_COMPRESSION = 0x42435a4c
FILE_ATTR_TAG_HASH = 0x68736148
FILE_ATTR_TAG_POSITION = 0x42435350 # PSCB
FILE_ATTR_TAG_ALIGNMENT = 0x42434c41 # ALCB
FILE_ATTR_TAG_PADDING = 0x47444150 # PDNG
# This is 'the size of bootblock reserved in firmware image (cbfs.txt)'
# Not much more info is available, but we set it to 4, due to this comment in
# cbfstool.c:
# This causes 4 bytes to be left out at the end of the image, for two reasons:
# 1. The cbfs master header pointer resides there
# 2. Ssme cbfs implementations assume that an image that resides below 4GB has
# a bootblock and get confused when the end of the image is at 4GB == 0.
MIN_BOOTBLOCK_SIZE = 4
# Files start aligned to this boundary in the CBFS
ENTRY_ALIGN = 0x40
# CBFSs must declare an architecture since much of the logic is designed with
# x86 in mind. The effect of setting this value is not well documented, but in
# general x86 is used and this makes use of a boot block and an image that ends
# at the end of 32-bit address space.
ARCHITECTURE_UNKNOWN = 0xffffffff
ARCHITECTURE_X86 = 0x00000001
ARCHITECTURE_ARM = 0x00000010
ARCHITECTURE_AARCH64 = 0x0000aa64
ARCHITECTURE_MIPS = 0x00000100
ARCHITECTURE_RISCV = 0xc001d0de
ARCHITECTURE_PPC64 = 0x407570ff
ARCH_NAMES = {
ARCHITECTURE_UNKNOWN : 'unknown',
ARCHITECTURE_X86 : 'x86',
ARCHITECTURE_ARM : 'arm',
ARCHITECTURE_AARCH64 : 'arm64',
ARCHITECTURE_MIPS : 'mips',
ARCHITECTURE_RISCV : 'riscv',
ARCHITECTURE_PPC64 : 'ppc64',
}
# File types. Only supported ones are included here
TYPE_CBFSHEADER = 0x02 # Master header, HEADER_FORMAT
TYPE_STAGE = 0x10 # Stage, holding an executable, see STAGE_FORMAT
TYPE_RAW = 0x50 # Raw file, possibly compressed
TYPE_EMPTY = 0xffffffff # Empty data
# Compression types
COMPRESS_NONE, COMPRESS_LZMA, COMPRESS_LZ4 = range(3)
COMPRESS_NAMES = {
COMPRESS_NONE : 'none',
COMPRESS_LZMA : 'lzma',
COMPRESS_LZ4 : 'lz4',
}
def find_arch(find_name):
"""Look up an architecture name
Args:
find_name: Architecture name to find
Returns:
ARCHITECTURE_... value or None if not found
"""
for arch, name in ARCH_NAMES.items():
if name == find_name:
return arch
return None
def find_compress(find_name):
"""Look up a compression algorithm name
Args:
find_name: Compression algorithm name to find
Returns:
COMPRESS_... value or None if not found
"""
for compress, name in COMPRESS_NAMES.items():
if name == find_name:
return compress
return None
def compress_name(compress):
"""Look up the name of a compression algorithm
Args:
compress: Compression algorithm number to find (COMPRESS_...)
Returns:
Compression algorithm name (string)
Raises:
KeyError if the algorithm number is invalid
"""
return COMPRESS_NAMES[compress]
def align_int(val, align):
"""Align a value up to the given alignment
Args:
val: Integer value to align
align: Integer alignment value (e.g. 4 to align to 4-byte boundary)
Returns:
integer value aligned to the required boundary, rounding up if necessary
"""
return int((val + align - 1) / align) * align
def align_int_down(val, align):
"""Align a value down to the given alignment
Args:
val: Integer value to align
align: Integer alignment value (e.g. 4 to align to 4-byte boundary)
Returns:
integer value aligned to the required boundary, rounding down if
necessary
"""
return int(val / align) * align
def _pack_string(instr):
"""Pack a string to the required aligned size by adding padding
Args:
instr: String to process
Returns:
String with required padding (at least one 0x00 byte) at the end
"""
val = tools.ToBytes(instr)
pad_len = align_int(len(val) + 1, FILENAME_ALIGN)
return val + tools.GetBytes(0, pad_len - len(val))
class CbfsFile(object):
"""Class to represent a single CBFS file
This is used to hold the information about a file, including its contents.
Use the get_data_and_offset() method to obtain the raw output for writing to
CBFS.
Properties:
name: Name of file
offset: Offset of file data from start of file header
cbfs_offset: Offset of file data in bytes from start of CBFS, or None to
place this file anyway
data: Contents of file, uncompressed
orig_data: Original data added to the file, possibly compressed
data_len: Length of (possibly compressed) data in bytes
ftype: File type (TYPE_...)
compression: Compression type (COMPRESS_...)
memlen: Length of data in memory, i.e. the uncompressed length, None if
no compression algortihm is selected
load: Load address in memory if known, else None
entry: Entry address in memory if known, else None. This is where
execution starts after the file is loaded
base_address: Base address to use for 'stage' files
erase_byte: Erase byte to use for padding between the file header and
contents (used for empty files)
size: Size of the file in bytes (used for empty files)
"""
def __init__(self, name, ftype, data, cbfs_offset, compress=COMPRESS_NONE):
self.name = name
self.offset = None
self.cbfs_offset = cbfs_offset
self.data = data
self.orig_data = data
self.ftype = ftype
self.compress = compress
self.memlen = None
self.load = None
self.entry = None
self.base_address = None
self.data_len = len(data)
self.erase_byte = None
self.size = None
def decompress(self):
"""Handle decompressing data if necessary"""
indata = self.data
if self.compress == COMPRESS_LZ4:
data = comp_util.decompress(indata, 'lz4', with_header=False)
elif self.compress == COMPRESS_LZMA:
data = comp_util.decompress(indata, 'lzma', with_header=False)
else:
data = indata
self.memlen = len(data)
self.data = data
self.data_len = len(indata)
@classmethod
def stage(cls, base_address, name, data, cbfs_offset):
"""Create a new stage file
Args:
base_address: Int base address for memory-mapping of ELF file
name: String file name to put in CBFS (does not need to correspond
to the name that the file originally came from)
data: Contents of file
cbfs_offset: Offset of file data in bytes from start of CBFS, or
None to place this file anyway
Returns:
CbfsFile object containing the file information
"""
cfile = CbfsFile(name, TYPE_STAGE, data, cbfs_offset)
cfile.base_address = base_address
return cfile
@classmethod
def raw(cls, name, data, cbfs_offset, compress):
"""Create a new raw file
Args:
name: String file name to put in CBFS (does not need to correspond
to the name that the file originally came from)
data: Contents of file
cbfs_offset: Offset of file data in bytes from start of CBFS, or
None to place this file anyway
compress: Compression algorithm to use (COMPRESS_...)
Returns:
CbfsFile object containing the file information
"""
return CbfsFile(name, TYPE_RAW, data, cbfs_offset, compress)
@classmethod
def empty(cls, space_to_use, erase_byte):
"""Create a new empty file of a given size
Args:
space_to_use:: Size of available space, which must be at least as
large as the alignment size for this CBFS
erase_byte: Byte to use for contents of file (repeated through the
whole file)
Returns:
CbfsFile object containing the file information
"""
cfile = CbfsFile('', TYPE_EMPTY, b'', None)
cfile.size = space_to_use - FILE_HEADER_LEN - FILENAME_ALIGN
cfile.erase_byte = erase_byte
return cfile
def calc_start_offset(self):
"""Check if this file needs to start at a particular offset in CBFS
Returns:
None if the file can be placed anywhere, or
the largest offset where the file could start (integer)
"""
if self.cbfs_offset is None:
return None
return self.cbfs_offset - self.get_header_len()
def get_header_len(self):
"""Get the length of headers required for a file
This is the minimum length required before the actual data for this file
could start. It might start later if there is padding.
Returns:
Total length of all non-data fields, in bytes
"""
name = _pack_string(self.name)
hdr_len = len(name) + FILE_HEADER_LEN
if self.ftype == TYPE_STAGE:
pass
elif self.ftype == TYPE_RAW:
hdr_len += ATTR_COMPRESSION_LEN
elif self.ftype == TYPE_EMPTY:
pass
else:
raise ValueError('Unknown file type %#x\n' % self.ftype)
return hdr_len
def get_data_and_offset(self, offset=None, pad_byte=None):
"""Obtain the contents of the file, in CBFS format and the offset of
the data within the file
Returns:
tuple:
bytes representing the contents of this file, packed and aligned
for directly inserting into the final CBFS output
offset to the file data from the start of the returned data.
"""
name = _pack_string(self.name)
hdr_len = len(name) + FILE_HEADER_LEN
attr_pos = 0
content = b''
attr = b''
pad = b''
data = self.data
if self.ftype == TYPE_STAGE:
elf_data = elf.DecodeElf(data, self.base_address)
content = struct.pack(STAGE_FORMAT, self.compress,
elf_data.entry, elf_data.load,
len(elf_data.data), elf_data.memsize)
data = elf_data.data
elif self.ftype == TYPE_RAW:
orig_data = data
if self.compress == COMPRESS_LZ4:
data = comp_util.compress(orig_data, 'lz4', with_header=False)
elif self.compress == COMPRESS_LZMA:
data = comp_util.compress(orig_data, 'lzma', with_header=False)
self.memlen = len(orig_data)
self.data_len = len(data)
attr = struct.pack(ATTR_COMPRESSION_FORMAT,
FILE_ATTR_TAG_COMPRESSION, ATTR_COMPRESSION_LEN,
self.compress, self.memlen)
elif self.ftype == TYPE_EMPTY:
data = tools.GetBytes(self.erase_byte, self.size)
else:
raise ValueError('Unknown type %#x when writing\n' % self.ftype)
if attr:
attr_pos = hdr_len
hdr_len += len(attr)
if self.cbfs_offset is not None:
pad_len = self.cbfs_offset - offset - hdr_len
if pad_len < 0: # pragma: no cover
# Test coverage of this is not available since this should never
# happen. It indicates that get_header_len() provided an
# incorrect value (too small) so that we decided that we could
# put this file at the requested place, but in fact a previous
# file extends far enough into the CBFS that this is not
# possible.
raise ValueError("Internal error: CBFS file '%s': Requested offset %#x but current output position is %#x" %
(self.name, self.cbfs_offset, offset))
pad = tools.GetBytes(pad_byte, pad_len)
hdr_len += pad_len
# This is the offset of the start of the file's data,
size = len(content) + len(data)
hdr = struct.pack(FILE_HEADER_FORMAT, FILE_MAGIC, size,
self.ftype, attr_pos, hdr_len)
# Do a sanity check of the get_header_len() function, to ensure that it
# stays in lockstep with this function
expected_len = self.get_header_len()
actual_len = len(hdr + name + attr)
if expected_len != actual_len: # pragma: no cover
# Test coverage of this is not available since this should never
# happen. It probably indicates that get_header_len() is broken.
raise ValueError("Internal error: CBFS file '%s': Expected headers of %#x bytes, got %#d" %
(self.name, expected_len, actual_len))
return hdr + name + attr + pad + content + data, hdr_len
class CbfsWriter(object):
"""Class to handle writing a Coreboot File System (CBFS)
Usage is something like:
cbw = CbfsWriter(size)
cbw.add_file_raw('u-boot', tools.ReadFile('u-boot.bin'))
...
data, cbfs_offset = cbw.get_data_and_offset()
Attributes:
_master_name: Name of the file containing the master header
_size: Size of the filesystem, in bytes
_files: Ordered list of files in the CBFS, each a CbfsFile
_arch: Architecture of the CBFS (ARCHITECTURE_...)
_bootblock_size: Size of the bootblock, typically at the end of the CBFS
_erase_byte: Byte to use for empty space in the CBFS
_align: Alignment to use for files, typically ENTRY_ALIGN
_base_address: Boot block offset in bytes from the start of CBFS.
Typically this is located at top of the CBFS. It is 0 when there is
no boot block
_header_offset: Offset of master header in bytes from start of CBFS
_contents_offset: Offset of first file header
_hdr_at_start: True if the master header is at the start of the CBFS,
instead of the end as normal for x86
_add_fileheader: True to add a fileheader around the master header
"""
def __init__(self, size, arch=ARCHITECTURE_X86):
"""Set up a new CBFS
This sets up all properties to default values. Files can be added using
add_file_raw(), etc.
Args:
size: Size of CBFS in bytes
arch: Architecture to declare for CBFS
"""
self._master_name = 'cbfs master header'
self._size = size
self._files = OrderedDict()
self._arch = arch
self._bootblock_size = 0
self._erase_byte = 0xff
self._align = ENTRY_ALIGN
self._add_fileheader = False
if self._arch == ARCHITECTURE_X86:
# Allow 4 bytes for the header pointer. That holds the
# twos-compliment negative offset of the master header in bytes
# measured from one byte past the end of the CBFS
self._base_address = self._size - max(self._bootblock_size,
MIN_BOOTBLOCK_SIZE)
self._header_offset = self._base_address - HEADER_LEN
self._contents_offset = 0
self._hdr_at_start = False
else:
# For non-x86, different rules apply
self._base_address = 0
self._header_offset = align_int(self._base_address +
self._bootblock_size, 4)
self._contents_offset = align_int(self._header_offset +
FILE_HEADER_LEN +
self._bootblock_size, self._align)
self._hdr_at_start = True
def _skip_to(self, fd, offset):
"""Write out pad bytes until a given offset
Args:
fd: File objext to write to
offset: Offset to write to
"""
if fd.tell() > offset:
raise ValueError('No space for data before offset %#x (current offset %#x)' %
(offset, fd.tell()))
fd.write(tools.GetBytes(self._erase_byte, offset - fd.tell()))
def _pad_to(self, fd, offset):
"""Write out pad bytes and/or an empty file until a given offset
Args:
fd: File objext to write to
offset: Offset to write to
"""
self._align_to(fd, self._align)
upto = fd.tell()
if upto > offset:
raise ValueError('No space for data before pad offset %#x (current offset %#x)' %
(offset, upto))
todo = align_int_down(offset - upto, self._align)
if todo:
cbf = CbfsFile.empty(todo, self._erase_byte)
fd.write(cbf.get_data_and_offset()[0])
self._skip_to(fd, offset)
def _align_to(self, fd, align):
"""Write out pad bytes until a given alignment is reached
This only aligns if the resulting output would not reach the end of the
CBFS, since we want to leave the last 4 bytes for the master-header
pointer.
Args:
fd: File objext to write to
align: Alignment to require (e.g. 4 means pad to next 4-byte
boundary)
"""
offset = align_int(fd.tell(), align)
if offset < self._size:
self._skip_to(fd, offset)
def add_file_stage(self, name, data, cbfs_offset=None):
"""Add a new stage file to the CBFS
Args:
name: String file name to put in CBFS (does not need to correspond
to the name that the file originally came from)
data: Contents of file
cbfs_offset: Offset of this file's data within the CBFS, in bytes,
or None to place this file anywhere
Returns:
CbfsFile object created
"""
cfile = CbfsFile.stage(self._base_address, name, data, cbfs_offset)
self._files[name] = cfile
return cfile
def add_file_raw(self, name, data, cbfs_offset=None,
compress=COMPRESS_NONE):
"""Create a new raw file
Args:
name: String file name to put in CBFS (does not need to correspond
to the name that the file originally came from)
data: Contents of file
cbfs_offset: Offset of this file's data within the CBFS, in bytes,
or None to place this file anywhere
compress: Compression algorithm to use (COMPRESS_...)
Returns:
CbfsFile object created
"""
cfile = CbfsFile.raw(name, data, cbfs_offset, compress)
self._files[name] = cfile
return cfile
def _write_header(self, fd, add_fileheader):
"""Write out the master header to a CBFS
Args:
fd: File object
add_fileheader: True to place the master header in a file header
record
"""
if fd.tell() > self._header_offset:
raise ValueError('No space for header at offset %#x (current offset %#x)' %
(self._header_offset, fd.tell()))
if not add_fileheader:
self._pad_to(fd, self._header_offset)
hdr = struct.pack(HEADER_FORMAT, HEADER_MAGIC, HEADER_VERSION2,
self._size, self._bootblock_size, self._align,
self._contents_offset, self._arch, 0xffffffff)
if add_fileheader:
name = _pack_string(self._master_name)
fd.write(struct.pack(FILE_HEADER_FORMAT, FILE_MAGIC, len(hdr),
TYPE_CBFSHEADER, 0,
FILE_HEADER_LEN + len(name)))
fd.write(name)
self._header_offset = fd.tell()
fd.write(hdr)
self._align_to(fd, self._align)
else:
fd.write(hdr)
def get_data(self):
"""Obtain the full contents of the CBFS
Thhis builds the CBFS with headers and all required files.
Returns:
'bytes' type containing the data
"""
fd = io.BytesIO()
# THe header can go at the start in some cases
if self._hdr_at_start:
self._write_header(fd, add_fileheader=self._add_fileheader)
self._skip_to(fd, self._contents_offset)
# Write out each file
for cbf in self._files.values():
# Place the file at its requested place, if any
offset = cbf.calc_start_offset()
if offset is not None:
self._pad_to(fd, align_int_down(offset, self._align))
pos = fd.tell()
data, data_offset = cbf.get_data_and_offset(pos, self._erase_byte)
fd.write(data)
self._align_to(fd, self._align)
cbf.calced_cbfs_offset = pos + data_offset
if not self._hdr_at_start:
self._write_header(fd, add_fileheader=self._add_fileheader)
# Pad to the end and write a pointer to the CBFS master header
self._pad_to(fd, self._base_address or self._size - 4)
rel_offset = self._header_offset - self._size
fd.write(struct.pack('<I', rel_offset & 0xffffffff))
return fd.getvalue()
class CbfsReader(object):
"""Class to handle reading a Coreboot File System (CBFS)
Usage is something like:
cbfs = cbfs_util.CbfsReader(data)
cfile = cbfs.files['u-boot']
self.WriteFile('u-boot.bin', cfile.data)
Attributes:
files: Ordered list of CbfsFile objects
align: Alignment to use for files, typically ENTRT_ALIGN
stage_base_address: Base address to use when mapping ELF files into the
CBFS for TYPE_STAGE files. If this is larger than the code address
of the ELF file, then data at the start of the ELF file will not
appear in the CBFS. Currently there are no tests for behaviour as
documentation is sparse
magic: Integer magic number from master header (HEADER_MAGIC)
version: Version number of CBFS (HEADER_VERSION2)
rom_size: Size of CBFS
boot_block_size: Size of boot block
cbfs_offset: Offset of the first file in bytes from start of CBFS
arch: Architecture of CBFS file (ARCHITECTURE_...)
"""
def __init__(self, data, read=True):
self.align = ENTRY_ALIGN
self.arch = None
self.boot_block_size = None
self.cbfs_offset = None
self.files = OrderedDict()
self.magic = None
self.rom_size = None
self.stage_base_address = 0
self.version = None
self.data = data
if read:
self.read()
def read(self):
"""Read all the files in the CBFS and add them to self.files"""
with io.BytesIO(self.data) as fd:
# First, get the master header
if not self._find_and_read_header(fd, len(self.data)):
raise ValueError('Cannot find master header')
fd.seek(self.cbfs_offset)
# Now read in the files one at a time
while True:
cfile = self._read_next_file(fd)
if cfile:
self.files[cfile.name] = cfile
elif cfile is False:
break
def _find_and_read_header(self, fd, size):
"""Find and read the master header in the CBFS
This looks at the pointer word at the very end of the CBFS. This is an
offset to the header relative to the size of the CBFS, which is assumed
to be known. Note that the offset is in *little endian* format.
Args:
fd: File to read from
size: Size of file
Returns:
True if header was found, False if not
"""
orig_pos = fd.tell()
fd.seek(size - 4)
rel_offset, = struct.unpack('<I', fd.read(4))
pos = (size + rel_offset) & 0xffffffff
fd.seek(pos)
found = self._read_header(fd)
if not found:
print('Relative offset seems wrong, scanning whole image')
for pos in range(0, size - HEADER_LEN, 4):
fd.seek(pos)
found = self._read_header(fd)
if found:
break
fd.seek(orig_pos)
return found
def _read_next_file(self, fd):
"""Read the next file from a CBFS
Args:
fd: File to read from
Returns:
CbfsFile object, if found
None if no object found, but data was parsed (e.g. TYPE_CBFSHEADER)
False if at end of CBFS and reading should stop
"""
file_pos = fd.tell()
data = fd.read(FILE_HEADER_LEN)
if len(data) < FILE_HEADER_LEN:
print('File header at %#x ran out of data' % file_pos)
return False
magic, size, ftype, attr, offset = struct.unpack(FILE_HEADER_FORMAT,
data)
if magic != FILE_MAGIC:
return False
pos = fd.tell()
name = self._read_string(fd)
if name is None:
print('String at %#x ran out of data' % pos)
return False
if DEBUG:
print('name', name)
# If there are attribute headers present, read those
compress = self._read_attr(fd, file_pos, attr, offset)
if compress is None:
return False
# Create the correct CbfsFile object depending on the type
cfile = None
cbfs_offset = file_pos + offset
fd.seek(cbfs_offset, io.SEEK_SET)
if ftype == TYPE_CBFSHEADER:
self._read_header(fd)
elif ftype == TYPE_STAGE:
data = fd.read(STAGE_LEN)
cfile = CbfsFile.stage(self.stage_base_address, name, b'',
cbfs_offset)
(cfile.compress, cfile.entry, cfile.load, cfile.data_len,
cfile.memlen) = struct.unpack(STAGE_FORMAT, data)
cfile.data = fd.read(cfile.data_len)
elif ftype == TYPE_RAW:
data = fd.read(size)
cfile = CbfsFile.raw(name, data, cbfs_offset, compress)
cfile.decompress()
if DEBUG:
print('data', data)
elif ftype == TYPE_EMPTY:
# Just read the data and discard it, since it is only padding
fd.read(size)
cfile = CbfsFile('', TYPE_EMPTY, b'', cbfs_offset)
else:
raise ValueError('Unknown type %#x when reading\n' % ftype)
if cfile:
cfile.offset = offset
# Move past the padding to the start of a possible next file. If we are
# already at an alignment boundary, then there is no padding.
pad = (self.align - fd.tell() % self.align) % self.align
fd.seek(pad, io.SEEK_CUR)
return cfile
@classmethod
def _read_attr(cls, fd, file_pos, attr, offset):
"""Read attributes from the file
CBFS files can have attributes which are things that cannot fit into the
header. The only attributes currently supported are compression and the
unused tag.
Args:
fd: File to read from
file_pos: Position of file in fd
attr: Offset of attributes, 0 if none
offset: Offset of file data (used to indicate the end of the
attributes)
Returns:
Compression to use for the file (COMPRESS_...)
"""
compress = COMPRESS_NONE
if not attr:
return compress
attr_size = offset - attr
fd.seek(file_pos + attr, io.SEEK_SET)
while attr_size:
pos = fd.tell()
hdr = fd.read(8)
if len(hdr) < 8:
print('Attribute tag at %x ran out of data' % pos)
return None
atag, alen = struct.unpack(">II", hdr)
data = hdr + fd.read(alen - 8)
if atag == FILE_ATTR_TAG_COMPRESSION:
# We don't currently use this information
atag, alen, compress, _decomp_size = struct.unpack(
ATTR_COMPRESSION_FORMAT, data)
elif atag == FILE_ATTR_TAG_UNUSED2:
break
else:
print('Unknown attribute tag %x' % atag)
attr_size -= len(data)
return compress
def _read_header(self, fd):
"""Read the master header
Reads the header and stores the information obtained into the member
variables.
Args:
fd: File to read from
Returns:
True if header was read OK, False if it is truncated or has the
wrong magic or version
"""
pos = fd.tell()
data = fd.read(HEADER_LEN)
if len(data) < HEADER_LEN:
print('Header at %x ran out of data' % pos)
return False
(self.magic, self.version, self.rom_size, self.boot_block_size,
self.align, self.cbfs_offset, self.arch, _) = struct.unpack(
HEADER_FORMAT, data)
return self.magic == HEADER_MAGIC and (
self.version == HEADER_VERSION1 or
self.version == HEADER_VERSION2)
@classmethod
def _read_string(cls, fd):
"""Read a string from a file
This reads a string and aligns the data to the next alignment boundary
Args:
fd: File to read from
Returns:
string read ('str' type) encoded to UTF-8, or None if we ran out of
data
"""
val = b''
while True:
data = fd.read(FILENAME_ALIGN)
if len(data) < FILENAME_ALIGN:
return None
pos = data.find(b'\0')
if pos == -1:
val += data
else:
val += data[:pos]
break
return val.decode('utf-8')
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