Block diagram
This page hosts a formal specification of Android Boot Image using Kaitai Struct. This specification can be automatically translated into a variety of programming languages to get a parsing library.
meta:
id: android_img
title: Android Boot Image
file-extension: img
tags:
- archive
- android
license: CC0-1.0
endian: le
doc-ref: https://source.android.com/docs/core/architecture/bootloader/boot-image-header
seq:
- id: magic
contents: ANDROID!
- id: kernel
type: load
- id: ramdisk
type: load
- id: second
type: load
- id: tags_load
type: u4
- id: page_size
type: u4
- id: header_version
type: u4
- id: os_version
type: os_version
- id: name
type: strz
size: 16
encoding: ASCII
- id: cmdline
type: strz
size: 512
encoding: ASCII
- id: sha
size: 32
- id: extra_cmdline
type: strz
size: 1024
encoding: ASCII
- id: recovery_dtbo
type: size_offset
if: header_version > 0
- id: boot_header_size
type: u4
if: header_version > 0
- id: dtb
type: load_long
if: header_version > 1
instances:
base:
value: kernel.addr - 0x00008000
doc: base loading address
kernel_offset:
value: kernel.addr - base
doc: kernel offset from base
ramdisk_offset:
value: 'ramdisk.addr > 0 ? ramdisk.addr - base : 0'
doc: ramdisk offset from base
second_offset:
value: 'second.addr > 0 ? second.addr - base : 0'
doc: 2nd bootloader offset from base
tags_offset:
value: tags_load - base
doc: tags offset from base
dtb_offset:
value: 'dtb.addr > 0 ? dtb.addr - base : 0'
if: header_version > 1
doc: dtb offset from base
kernel_img:
pos: page_size
size: kernel.size
ramdisk_img:
pos: ((page_size + kernel.size + page_size - 1) / page_size) * page_size
size: ramdisk.size
if: ramdisk.size > 0
second_img:
pos: ((page_size + kernel.size + ramdisk.size + page_size - 1) / page_size) * page_size
size: second.size
if: second.size > 0
recovery_dtbo_img:
pos: recovery_dtbo.offset
size: recovery_dtbo.size
if: header_version > 0 and recovery_dtbo.size > 0
dtb_img:
pos: ((page_size + kernel.size + ramdisk.size + second.size + recovery_dtbo.size + page_size - 1) / page_size) * page_size
size: dtb.size
if: header_version > 1 and dtb.size > 0
types:
load:
seq:
- id: size
type: u4
- id: addr
type: u4
load_long:
seq:
- id: size
type: u4
- id: addr
type: u8
size_offset:
seq:
- id: size
type: u4
- id: offset
type: u8
os_version:
seq:
- id: version
type: u4
instances:
major:
value: (version >> 25) & 0x7f
minor:
value: (version >> 18) & 0x7f
patch:
value: (version >> 11) & 0x7f
year:
value: ((version >> 4) & 0x7f) + 2000
month:
value: version & 0xf