Qualcomm Snapdragon (MSM) bootloader.img format: format specification

A bootloader for Android used on various devices powered by Qualcomm Snapdragon chips:

https://en.wikipedia.org/wiki/Devices_using_Qualcomm_Snapdragon_processors

Although not all of the Snapdragon based Android devices use this particular bootloader format, it is known that devices with the following chips have used it (example devices are given for each chip):

APQ8064 (devices)
- Nexus 4 "mako": sample (other samples), releasetools.py
MSM8974AA (devices)
- Nexus 5 "hammerhead": sample (other samples), releasetools.py
MSM8992 (devices)
- Nexus 5X "bullhead": sample (other samples), releasetools.py
APQ8064-1AA (devices)
- Nexus 7 [2013] (Mobile) "deb" (**): sample (other samples), releasetools.py
- Nexus 7 [2013] (Wi-Fi) "flo" (**): sample (other samples), releasetools.py
MSM8996 Pro-AB (devices)
- Pixel "sailfish" (*): sample (other samples)
- Pixel XL "marlin" (*): sample (other samples)
MSM8998 (devices)
- Pixel 2 "walleye" (*): sample (other samples)
- Pixel 2 XL "taimen": sample (other samples)

(*) bootloader_size is equal to the size of the whole file (not just img_bodies as usual).

(**) There are some data after the end of img_bodies.

On the other hand, devices with these chips do not use this format:

APQ8084 (devices)
- Nexus 6 "shamu": sample (other samples), releasetools.py - uses "Motoboot packed image format" instead
MSM8994 (devices)
- Nexus 6P "angler": sample (other samples), releasetools.py - uses "Huawei Bootloader packed image format" instead

The bootloader-*.img samples referenced above originally come from factory images packed in ZIP archives that can be found on the page Factory Images for Nexus and Pixel Devices on the Google Developers site. Note that the codenames on that page may be different than the ones that are written in the list above. That's because the Google page indicates ROM codenames in headings (e.g. "occam" for Nexus 4) but the above list uses model codenames (e.g. "mako" for Nexus 4) because that is how the original bootloader-*.img files are identified. For most devices, however, these code names are the same.

File extension

img

KS implementation details

License: CC0-1.0

This page hosts a formal specification of Qualcomm Snapdragon (MSM) bootloader.img format using Kaitai Struct. This specification can be automatically translated into a variety of programming languages to get a parsing library.

Block diagram

Format specification in Kaitai Struct YAML

meta:
  id: android_bootldr_qcom
  title: Qualcomm Snapdragon (MSM) bootloader.img format
  file-extension: img
  tags:
    - archive
    - android
  license: CC0-1.0
  # The `releasetools.py` script is written for Python 2, where the default
  # encoding is ASCII.
  encoding: ASCII
  endian: le
doc: |
  A bootloader for Android used on various devices powered by Qualcomm
  Snapdragon chips:

  <https://en.wikipedia.org/wiki/Devices_using_Qualcomm_Snapdragon_processors>

  Although not all of the Snapdragon based Android devices use this particular
  bootloader format, it is known that devices with the following chips have used
  it (example devices are given for each chip):

  * APQ8064 ([devices](https://en.wikipedia.org/wiki/Devices_using_Qualcomm_Snapdragon_processors#Snapdragon_S4_Pro))
    - Nexus 4 "mako": [sample][sample-mako] ([other samples][others-mako]),
      [releasetools.py](https://android.googlesource.com/device/lge/mako/+/33f0114/releasetools.py#98)

  * MSM8974AA ([devices](https://en.wikipedia.org/wiki/Devices_using_Qualcomm_Snapdragon_processors#Snapdragon_800,_801_and_805_(2013/14)))
    - Nexus 5 "hammerhead": [sample][sample-hammerhead] ([other samples][others-hammerhead]),
      [releasetools.py](https://android.googlesource.com/device/lge/hammerhead/+/7618a7d/releasetools.py#116)

  * MSM8992 ([devices](https://en.wikipedia.org/wiki/Devices_using_Qualcomm_Snapdragon_processors#Snapdragon_808_and_810_(2015)))
    - Nexus 5X "bullhead": [sample][sample-bullhead] ([other samples][others-bullhead]),
      [releasetools.py](https://android.googlesource.com/device/lge/bullhead/+/2994b6b/releasetools.py#126)

  * APQ8064-1AA ([devices](https://en.wikipedia.org/wiki/Devices_using_Qualcomm_Snapdragon_processors#Snapdragon_600_(2013)))
    - Nexus 7 \[2013] (Mobile) "deb" <a href="#doc-note-data-after-img-bodies">(\**)</a>: [sample][sample-deb] ([other samples][others-deb]),
      [releasetools.py](https://android.googlesource.com/device/asus/deb/+/14c1638/releasetools.py#105)
    - Nexus 7 \[2013] (Wi-Fi) "flo" <a href="#doc-note-data-after-img-bodies">(\**)</a>: [sample][sample-flo] ([other samples][others-flo]),
      [releasetools.py](https://android.googlesource.com/device/asus/flo/+/9d9fee9/releasetools.py#130)

  * MSM8996 Pro-AB ([devices](https://en.wikipedia.org/wiki/Devices_using_Qualcomm_Snapdragon_processors#Snapdragon_820_and_821_(2016)))
    - Pixel "sailfish" <a href="#doc-note-bootloader-size">(\*)</a>:
      [sample][sample-sailfish] ([other samples][others-sailfish])
    - Pixel XL "marlin" <a href="#doc-note-bootloader-size">(\*)</a>:
      [sample][sample-marlin] ([other samples][others-marlin])

  * MSM8998 ([devices](https://en.wikipedia.org/wiki/Devices_using_Qualcomm_Snapdragon_processors#Snapdragon_835_(2017)))
    - Pixel 2 "walleye" <a href="#doc-note-bootloader-size">(\*)</a>: [sample][sample-walleye] ([other samples][others-walleye])
    - Pixel 2 XL "taimen": [sample][sample-taimen] ([other samples][others-taimen])

  <small id="doc-note-bootloader-size">(\*)
  `bootloader_size` is equal to the size of the whole file (not just `img_bodies` as usual).
  </small>

  <small id="doc-note-data-after-img-bodies">(\**)
  There are some data after the end of `img_bodies`.
  </small>

  ---

  On the other hand, devices with these chips **do not** use this format:

  * <del>APQ8084</del> ([devices](https://en.wikipedia.org/wiki/Devices_using_Qualcomm_Snapdragon_processors#Snapdragon_800,_801_and_805_(2013/14)))
    - Nexus 6 "shamu": [sample][foreign-sample-shamu] ([other samples][foreign-others-shamu]),
      [releasetools.py](https://android.googlesource.com/device/moto/shamu/+/df9354d/releasetools.py#12) -
      uses "Motoboot packed image format" instead

  * <del>MSM8994</del> ([devices](https://en.wikipedia.org/wiki/Devices_using_Qualcomm_Snapdragon_processors#Snapdragon_808_and_810_(2015)))
    - Nexus 6P "angler": [sample][foreign-sample-angler] ([other samples][foreign-others-angler]),
      [releasetools.py](https://android.googlesource.com/device/huawei/angler/+/cf92cd8/releasetools.py#29) -
      uses "Huawei Bootloader packed image format" instead

  [sample-mako]: https://androidfilehost.com/?fid=96039337900113996 "bootloader-mako-makoz30f.img"
  [others-mako]: https://androidfilehost.com/?w=search&s=bootloader-mako&type=files

  [sample-hammerhead]: https://androidfilehost.com/?fid=385035244224410247 "bootloader-hammerhead-hhz20h.img"
  [others-hammerhead]: https://androidfilehost.com/?w=search&s=bootloader-hammerhead&type=files

  [sample-bullhead]: https://androidfilehost.com/?fid=11410963190603870177 "bootloader-bullhead-bhz32c.img"
  [others-bullhead]: https://androidfilehost.com/?w=search&s=bootloader-bullhead&type=files

  [sample-deb]: https://androidfilehost.com/?fid=23501681358552487 "bootloader-deb-flo-04.02.img"
  [others-deb]: https://androidfilehost.com/?w=search&s=bootloader-deb-flo&type=files

  [sample-flo]: https://androidfilehost.com/?fid=23991606952593542 "bootloader-flo-flo-04.05.img"
  [others-flo]: https://androidfilehost.com/?w=search&s=bootloader-flo-flo&type=files

  [sample-sailfish]: https://androidfilehost.com/?fid=6006931924117907154 "bootloader-sailfish-8996-012001-1904111134.img"
  [others-sailfish]: https://androidfilehost.com/?w=search&s=bootloader-sailfish&type=files

  [sample-marlin]: https://androidfilehost.com/?fid=6006931924117907131 "bootloader-marlin-8996-012001-1904111134.img"
  [others-marlin]: https://androidfilehost.com/?w=search&s=bootloader-marlin&type=files

  [sample-walleye]: https://androidfilehost.com/?fid=14943124697586348540 "bootloader-walleye-mw8998-003.0085.00.img"
  [others-walleye]: https://androidfilehost.com/?w=search&s=bootloader-walleye&type=files

  [sample-taimen]: https://androidfilehost.com/?fid=14943124697586348536 "bootloader-taimen-tmz30m.img"
  [others-taimen]: https://androidfilehost.com/?w=search&s=bootloader-taimen&type=files

  [foreign-sample-shamu]: https://androidfilehost.com/?fid=745849072291678307 "bootloader-shamu-moto-apq8084-72.04.img"
  [foreign-others-shamu]: https://androidfilehost.com/?w=search&s=bootloader-shamu&type=files

  [foreign-sample-angler]: https://androidfilehost.com/?fid=11410963190603870158 "bootloader-angler-angler-03.84.img"
  [foreign-others-angler]: https://androidfilehost.com/?w=search&s=bootloader-angler&type=files

  ---

  The `bootloader-*.img` samples referenced above originally come from factory
  images packed in ZIP archives that can be found on the page [Factory Images
  for Nexus and Pixel Devices](https://developers.google.com/android/images) on
  the Google Developers site. Note that the codenames on that page may be
  different than the ones that are written in the list above. That's because the
  Google page indicates **ROM codenames** in headings (e.g. "occam" for Nexus 4)
  but the above list uses **model codenames** (e.g. "mako" for Nexus 4) because
  that is how the original `bootloader-*.img` files are identified. For most
  devices, however, these code names are the same.

doc-ref: https://android.googlesource.com/device/lge/hammerhead/+/7618a7d/releasetools.py
seq:
  - id: magic
    contents: BOOTLDR!
  - id: num_images
    type: u4
  - id: ofs_img_bodies
    -orig-id: start_offset
    type: u4
  - id: bootloader_size
    -orig-id: bootldr_size
    type: u4
    doc: |
      According to all available `releasetools.py` versions from AOSP (links are
      in the top-level `/doc`), this should determine only the size of
      `img_bodies` - there is [an assertion](
      https://android.googlesource.com/device/lge/hammerhead/+/7618a7d/releasetools.py#167)
      for it.

      However, files for certain Pixel devices (see `/doc`) apparently declare
      the entire file size here (i.e. including also fields from `magic` to
      `img_headers`). So if you interpreted `bootloader_size` as the size of
      `img_bodies` substream in these files, you would exceed the end of file.
      Although you could check that it fits in the file before attempting to
      create a substream of that size, you wouldn't know if it's meant to
      specify the size of just `img_bodies` or the size of the entire bootloader
      payload (whereas there may be additional data after the end of payload)
      until parsing `img_bodies` (or at least summing sizes from `img_headers`,
      but that's stupid).

      So this field isn't reliable enough to be used as the size of any
      substream. If you want to check if it has a reasonable value, do so in
      your application code.
  - id: img_headers
    -orig-id: img_info
    type: img_header
    repeat: expr
    repeat-expr: num_images
instances:
  img_bodies:
    pos: ofs_img_bodies
    type: img_body(_index)
    repeat: expr
    repeat-expr: num_images
types:
  img_header:
    -webide-representation: '{name}'
    seq:
      - id: name
        size: 64
        type: strz
      - id: len_body
        type: u4
  img_body:
    -webide-representation: '{img_header.name}: {img_header.len_body:dec} bytes'
    params:
      - id: idx
        type: s4
    seq:
      - id: body
        size: img_header.len_body
    instances:
      img_header:
        value: _root.img_headers[idx]