Add a script to unpack boot image

The script prints out the boot image header
contents and extracts the kernel, ramdisk,
second bootloader and recovery DTBO images.

Bug: 74763691
Test: unpack_bootimg --boot_img $OUT/recovery.img

Change-Id: Iadbca81c157d9e4607f808a14468ab5542347507

mkbootimg/Android.mk

@@ -9,3 +9,12 @@ LOCAL_IS_HOST_MODULE := true
 LOCAL_MODULE := mkbootimg
 
 include $(BUILD_PREBUILT)
+
+include $(CLEAR_VARS)
+LOCAL_SRC_FILES := unpack_bootimg
+LOCAL_MODULE_CLASS := EXECUTABLES
+LOCAL_IS_HOST_MODULE := true
+
+LOCAL_MODULE := unpack_bootimg
+
+include $(BUILD_PREBUILT)

mkbootimg/unpack_bootimg

@@ -0,0 +1,137 @@
+#!/usr/bin/env python
+# Copyright 2018, The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""unpacks the bootimage.
+
+Extracts the kernel, ramdisk, second bootloader and recovery dtbo images.
+"""
+
+from __future__ import print_function
+from argparse import ArgumentParser, FileType
+from struct import unpack
+import os
+
+
+def create_out_dir(dir_path):
+    """creates a directory 'dir_path' if it does not exist"""
+    if not os.path.exists(dir_path):
+        os.makedirs(dir_path)
+
+
+def extract_image(offset, size, bootimage, extracted_image_name):
+    """extracts an image from the bootimage"""
+    bootimage.seek(offset)
+    with open(extracted_image_name, 'wb') as file_out:
+        file_out.write(bootimage.read(size))
+
+
+def get_number_of_pages(image_size, page_size):
+    """calculates the number of pages required for the image"""
+    return (image_size + page_size - 1) / page_size
+
+
+def unpack_bootimage(args):
+    """extracts kernel, ramdisk, second bootloader and recovery dtbo"""
+    boot_magic = unpack('8s', args.boot_img.read(8))
+    print('boot_magic: %s' % boot_magic)
+    kernel_ramdisk_second_info = unpack('10I', args.boot_img.read(10 * 4))
+    print('kernel_size: %s' % kernel_ramdisk_second_info[0])
+    print('kernel load address: %s' % kernel_ramdisk_second_info[1])
+    print('ramdisk size: %s' % kernel_ramdisk_second_info[2])
+    print('ramdisk load address: %s' % kernel_ramdisk_second_info[3])
+    print('second bootloader size: %s' % kernel_ramdisk_second_info[4])
+    print('second bootloader load address: %s' % kernel_ramdisk_second_info[5])
+    print('kernel tags load address: %s' % kernel_ramdisk_second_info[6])
+    print('page size: %s' % kernel_ramdisk_second_info[7])
+    print('boot image header version: %s' % kernel_ramdisk_second_info[8])
+    print('os version and patch level: %s' % kernel_ramdisk_second_info[9])
+
+    product_name = unpack('16s', args.boot_img.read(16))
+    print('product name: %s' % product_name)
+    cmdline = unpack('512s', args.boot_img.read(512))
+    print('command line args: %s' % cmdline)
+
+    args.boot_img.read(32)  # ignore SHA
+
+    extra_cmdline = unpack('1024s', args.boot_img.read(1024))
+    print('additional command line args: %s' % extra_cmdline)
+
+    kernel_size = kernel_ramdisk_second_info[0]
+    ramdisk_size = kernel_ramdisk_second_info[2]
+    second_size = kernel_ramdisk_second_info[4]
+    page_size = kernel_ramdisk_second_info[7]
+    version = kernel_ramdisk_second_info[8]
+    if version > 0:
+        recovery_dtbo_size = unpack('I', args.boot_img.read(1 * 4))[0]
+        print('recovery dtbo size: %s' % recovery_dtbo_size)
+        recovery_dtbo_address = unpack('Q', args.boot_img.read(8))[0]
+        print('recovery dtbo load address: %s' % recovery_dtbo_address)
+        boot_header_size = unpack('I', args.boot_img.read(4))[0]
+        print('boot header size: %s' % boot_header_size)
+    else:
+        recovery_dtbo_size = 0
+
+    # The first page contains the boot header
+    num_header_pages = 1
+
+    num_kernel_pages = get_number_of_pages(kernel_size, page_size)
+    kernel_offset = page_size * num_header_pages  # header occupies a page
+    image_info_list = [(kernel_offset, kernel_size, 'kernel')]
+
+    num_ramdisk_pages = get_number_of_pages(ramdisk_size, page_size)
+    ramdisk_offset = page_size * (num_header_pages + num_kernel_pages
+                                 ) # header + kernel
+    image_info_list.append((ramdisk_offset, ramdisk_size, 'ramdisk'))
+
+    num_second_pages = get_number_of_pages(second_size, page_size)
+    second_offset = page_size * (
+        num_header_pages + num_kernel_pages + num_ramdisk_pages
+    )  # header + kernel + ramdisk
+    image_info_list.append((second_offset, second_size, 'second'))
+
+    if recovery_dtbo_size > 0:
+        dtbo_offset = page_size * (num_header_pages + num_kernel_pages +
+                                   num_ramdisk_pages + num_second_pages)
+        image_info_list.append((dtbo_offset, recovery_dtbo_size,
+                                'recovery_dtbo'))
+
+    for image_info in image_info_list:
+        extract_image(image_info[0], image_info[1], args.boot_img,
+                      os.path.join(args.out, image_info[2]))
+
+
+def parse_cmdline():
+    """parse command line arguments"""
+    parser = ArgumentParser(
+        description='Unpacks boot.img/recovery.img, extracts the kernel,'
+        'ramdisk, second bootloader and recovery dtbo')
+    parser.add_argument(
+        '--boot_img',
+        help='path to boot image',
+        type=FileType('rb'),
+        required=True)
+    parser.add_argument('--out', help='path to out binaries', default='out')
+    return parser.parse_args()
+
+
+def main():
+    """parse arguments and unpack boot image"""
+    args = parse_cmdline()
+    create_out_dir(args.out)
+    unpack_bootimage(args)
+
+
+if __name__ == '__main__':
+    main()