1#!/usr/bin/env python
2#
3# Copyright (C) 2018 The Android Open Source Project
4#
5# Licensed under the Apache License, Version 2.0 (the "License");
6# you may not use this file except in compliance with the License.
7# You may obtain a copy of the License at
8#
9#      http://www.apache.org/licenses/LICENSE-2.0
10#
11# Unless required by applicable law or agreed to in writing, software
12# distributed under the License is distributed on an "AS IS" BASIS,
13# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14# See the License for the specific language governing permissions and
15# limitations under the License.
16
17"""
18A tool to extract kernel information from a kernel image.
19"""
20
21import argparse
22import subprocess
23import sys
24import re
25
26CONFIG_PREFIX = b'IKCFG_ST'
27GZIP_HEADER = b'\037\213\010'
28COMPRESSION_ALGO = (
29    (["gzip", "-d"], GZIP_HEADER),
30    (["xz", "-d"], b'\3757zXZ\000'),
31    (["bzip2", "-d"], b'BZh'),
32    (["lz4", "-d", "-l"], b'\002\041\114\030'),
33
34    # These are not supported in the build system yet.
35    # (["unlzma"], b'\135\0\0\0'),
36    # (["lzop", "-d"], b'\211\114\132'),
37)
38
39# "Linux version " UTS_RELEASE " (" LINUX_COMPILE_BY "@"
40# LINUX_COMPILE_HOST ") (" LINUX_COMPILER ") " UTS_VERSION "\n";
41LINUX_BANNER_PREFIX = b'Linux version '
42LINUX_BANNER_REGEX = LINUX_BANNER_PREFIX + \
43    r'(?P<release>(?P<version>[0-9]+[.][0-9]+[.][0-9]+).*) \(.*@.*\) \(.*\) .*\n'
44
45
46def get_from_release(input_bytes, start_idx, key):
47  null_idx = input_bytes.find('\x00', start_idx)
48  if null_idx < 0:
49    return None
50  try:
51    linux_banner = input_bytes[start_idx:null_idx].decode()
52  except UnicodeDecodeError:
53    return None
54  mo = re.match(LINUX_BANNER_REGEX, linux_banner)
55  if mo:
56    return mo.group(key)
57  return None
58
59
60def dump_from_release(input_bytes, key):
61  """
62  Helper of dump_version and dump_release
63  """
64  idx = 0
65  while True:
66    idx = input_bytes.find(LINUX_BANNER_PREFIX, idx)
67    if idx < 0:
68      return None
69
70    value = get_from_release(input_bytes, idx, key)
71    if value:
72      return value
73
74    idx += len(LINUX_BANNER_PREFIX)
75
76
77def dump_version(input_bytes):
78  """
79  Dump kernel version, w.x.y, from input_bytes. Search for the string
80  "Linux version " and do pattern matching after it. See LINUX_BANNER_REGEX.
81  """
82  return dump_from_release(input_bytes, "version")
83
84
85def dump_release(input_bytes):
86  """
87  Dump kernel release, w.x.y-..., from input_bytes. Search for the string
88  "Linux version " and do pattern matching after it. See LINUX_BANNER_REGEX.
89  """
90  return dump_from_release(input_bytes, "release")
91
92
93def dump_configs(input_bytes):
94  """
95  Dump kernel configuration from input_bytes. This can be done when
96  CONFIG_IKCONFIG is enabled, which is a requirement on Treble devices.
97
98  The kernel configuration is archived in GZip format right after the magic
99  string 'IKCFG_ST' in the built kernel.
100  """
101
102  # Search for magic string + GZip header
103  idx = input_bytes.find(CONFIG_PREFIX + GZIP_HEADER)
104  if idx < 0:
105    return None
106
107  # Seek to the start of the archive
108  idx += len(CONFIG_PREFIX)
109
110  sp = subprocess.Popen(["gzip", "-d", "-c"], stdin=subprocess.PIPE,
111                        stdout=subprocess.PIPE, stderr=subprocess.PIPE)
112  o, _ = sp.communicate(input=input_bytes[idx:])
113  if sp.returncode == 1: # error
114    return None
115
116  # success or trailing garbage warning
117  assert sp.returncode in (0, 2), sp.returncode
118
119  return o
120
121
122def try_decompress_bytes(cmd, input_bytes):
123  sp = subprocess.Popen(cmd, stdin=subprocess.PIPE, stdout=subprocess.PIPE,
124                        stderr=subprocess.PIPE)
125  o, _ = sp.communicate(input=input_bytes)
126  # ignore errors
127  return o
128
129
130def try_decompress(cmd, search_bytes, input_bytes):
131  idx = 0
132  while True:
133    idx = input_bytes.find(search_bytes, idx)
134    if idx < 0:
135      raise StopIteration()
136
137    yield try_decompress_bytes(cmd, input_bytes[idx:])
138    idx += 1
139
140
141def decompress_dump(func, input_bytes):
142  """
143  Run func(input_bytes) first; and if that fails (returns value evaluates to
144  False), then try different decompression algorithm before running func.
145  """
146  o = func(input_bytes)
147  if o:
148    return o
149  for cmd, search_bytes in COMPRESSION_ALGO:
150    for decompressed in try_decompress(cmd, search_bytes, input_bytes):
151      if decompressed:
152        o = decompress_dump(func, decompressed)
153        if o:
154          return o
155    # Force decompress the whole file even if header doesn't match
156    decompressed = try_decompress_bytes(cmd, input_bytes)
157    if decompressed:
158      o = decompress_dump(func, decompressed)
159      if o:
160        return o
161
162
163def dump_to_file(f, dump_fn, input_bytes, desc):
164  """
165  Call decompress_dump(dump_fn, input_bytes) and write to f. If it fails, return
166  False; otherwise return True.
167  """
168  if f is not None:
169    o = decompress_dump(dump_fn, input_bytes)
170    if o:
171      f.write(o)
172    else:
173      sys.stderr.write(
174          "Cannot extract kernel {}".format(desc))
175      return False
176  return True
177
178
179def main():
180  parser = argparse.ArgumentParser(
181      formatter_class=argparse.RawTextHelpFormatter,
182      description=__doc__ +
183      "\nThese algorithms are tried when decompressing the image:\n    " +
184      " ".join(tup[0][0] for tup in COMPRESSION_ALGO))
185  parser.add_argument('--input',
186                      help='Input kernel image. If not specified, use stdin',
187                      metavar='FILE',
188                      type=argparse.FileType('rb'),
189                      default=sys.stdin)
190  parser.add_argument('--output-configs',
191                      help='If specified, write configs. Use stdout if no file '
192                           'is specified.',
193                      metavar='FILE',
194                      nargs='?',
195                      type=argparse.FileType('wb'),
196                      const=sys.stdout)
197  parser.add_argument('--output-version',
198                      help='If specified, write version. Use stdout if no file '
199                           'is specified.',
200                      metavar='FILE',
201                      nargs='?',
202                      type=argparse.FileType('wb'),
203                      const=sys.stdout)
204  parser.add_argument('--output-release',
205                      help='If specified, write kernel release. Use stdout if '
206                           'no file is specified.',
207                      metavar='FILE',
208                      nargs='?',
209                      type=argparse.FileType('wb'),
210                      const=sys.stdout)
211  parser.add_argument('--tools',
212                      help='Decompression tools to use. If not specified, PATH '
213                           'is searched.',
214                      metavar='ALGORITHM:EXECUTABLE',
215                      nargs='*')
216  args = parser.parse_args()
217
218  tools = {pair[0]: pair[1]
219           for pair in (token.split(':') for token in args.tools or [])}
220  for cmd, _ in COMPRESSION_ALGO:
221    if cmd[0] in tools:
222      cmd[0] = tools[cmd[0]]
223
224  input_bytes = args.input.read()
225
226  ret = 0
227  if not dump_to_file(args.output_configs, dump_configs, input_bytes,
228                      "configs in {}".format(args.input.name)):
229    ret = 1
230  if not dump_to_file(args.output_version, dump_version, input_bytes,
231                      "version in {}".format(args.input.name)):
232    ret = 1
233  if not dump_to_file(args.output_release, dump_release, input_bytes,
234                      "kernel release in {}".format(args.input.name)):
235    ret = 1
236
237  return ret
238
239
240if __name__ == '__main__':
241  sys.exit(main())
242