Qualcomm Snapdragon (MSM) bootloader.img format: Nim parsing library

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):

(*) 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:


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.

Nim source code to parse Qualcomm Snapdragon (MSM) bootloader.img format

android_bootldr_qcom.nim

import kaitai_struct_nim_runtime
import options

type
  AndroidBootldrQcom* = ref object of KaitaiStruct
    `magic`*: seq[byte]
    `numImages`*: uint32
    `ofsImgBodies`*: uint32
    `bootloaderSize`*: uint32
    `imgHeaders`*: seq[AndroidBootldrQcom_ImgHeader]
    `parent`*: KaitaiStruct
    `imgBodiesInst`*: seq[AndroidBootldrQcom_ImgBody]
  AndroidBootldrQcom_ImgHeader* = ref object of KaitaiStruct
    `name`*: string
    `lenBody`*: uint32
    `parent`*: AndroidBootldrQcom
  AndroidBootldrQcom_ImgBody* = ref object of KaitaiStruct
    `body`*: seq[byte]
    `idx`*: int32
    `parent`*: AndroidBootldrQcom
    `imgHeaderInst`*: AndroidBootldrQcom_ImgHeader

proc read*(_: typedesc[AndroidBootldrQcom], io: KaitaiStream, root: KaitaiStruct, parent: KaitaiStruct): AndroidBootldrQcom
proc read*(_: typedesc[AndroidBootldrQcom_ImgHeader], io: KaitaiStream, root: KaitaiStruct, parent: AndroidBootldrQcom): AndroidBootldrQcom_ImgHeader
proc read*(_: typedesc[AndroidBootldrQcom_ImgBody], io: KaitaiStream, root: KaitaiStruct, parent: AndroidBootldrQcom, idx: any): AndroidBootldrQcom_ImgBody

proc imgBodies*(this: AndroidBootldrQcom): seq[AndroidBootldrQcom_ImgBody]
proc imgHeader*(this: AndroidBootldrQcom_ImgBody): AndroidBootldrQcom_ImgHeader


##[
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.

@see <a href="https://android.googlesource.com/device/lge/hammerhead/+/7618a7d/releasetools.py">Source</a>
]##
proc read*(_: typedesc[AndroidBootldrQcom], io: KaitaiStream, root: KaitaiStruct, parent: KaitaiStruct): AndroidBootldrQcom =
  template this: untyped = result
  this = new(AndroidBootldrQcom)
  let root = if root == nil: cast[AndroidBootldrQcom](this) else: cast[AndroidBootldrQcom](root)
  this.io = io
  this.root = root
  this.parent = parent

  let magicExpr = this.io.readBytes(int(8))
  this.magic = magicExpr
  let numImagesExpr = this.io.readU4le()
  this.numImages = numImagesExpr
  let ofsImgBodiesExpr = this.io.readU4le()
  this.ofsImgBodies = ofsImgBodiesExpr

  ##[
  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.

  ]##
  let bootloaderSizeExpr = this.io.readU4le()
  this.bootloaderSize = bootloaderSizeExpr
  for i in 0 ..< int(this.numImages):
    let it = AndroidBootldrQcom_ImgHeader.read(this.io, this.root, this)
    this.imgHeaders.add(it)

proc imgBodies(this: AndroidBootldrQcom): seq[AndroidBootldrQcom_ImgBody] = 
  if this.imgBodiesInst.len != 0:
    return this.imgBodiesInst
  let pos = this.io.pos()
  this.io.seek(int(this.ofsImgBodies))
  for i in 0 ..< int(this.numImages):
    let it = AndroidBootldrQcom_ImgBody.read(this.io, this.root, this, i)
    this.imgBodiesInst.add(it)
  this.io.seek(pos)
  if this.imgBodiesInst.len != 0:
    return this.imgBodiesInst

proc fromFile*(_: typedesc[AndroidBootldrQcom], filename: string): AndroidBootldrQcom =
  AndroidBootldrQcom.read(newKaitaiFileStream(filename), nil, nil)

proc read*(_: typedesc[AndroidBootldrQcom_ImgHeader], io: KaitaiStream, root: KaitaiStruct, parent: AndroidBootldrQcom): AndroidBootldrQcom_ImgHeader =
  template this: untyped = result
  this = new(AndroidBootldrQcom_ImgHeader)
  let root = if root == nil: cast[AndroidBootldrQcom](this) else: cast[AndroidBootldrQcom](root)
  this.io = io
  this.root = root
  this.parent = parent

  let nameExpr = encode(this.io.readBytes(int(64)).bytesTerminate(0, false), "ASCII")
  this.name = nameExpr
  let lenBodyExpr = this.io.readU4le()
  this.lenBody = lenBodyExpr

proc fromFile*(_: typedesc[AndroidBootldrQcom_ImgHeader], filename: string): AndroidBootldrQcom_ImgHeader =
  AndroidBootldrQcom_ImgHeader.read(newKaitaiFileStream(filename), nil, nil)

proc read*(_: typedesc[AndroidBootldrQcom_ImgBody], io: KaitaiStream, root: KaitaiStruct, parent: AndroidBootldrQcom, idx: any): AndroidBootldrQcom_ImgBody =
  template this: untyped = result
  this = new(AndroidBootldrQcom_ImgBody)
  let root = if root == nil: cast[AndroidBootldrQcom](this) else: cast[AndroidBootldrQcom](root)
  this.io = io
  this.root = root
  this.parent = parent
  let idxExpr = int32(idx)
  this.idx = idxExpr

  let bodyExpr = this.io.readBytes(int(this.imgHeader.lenBody))
  this.body = bodyExpr

proc imgHeader(this: AndroidBootldrQcom_ImgBody): AndroidBootldrQcom_ImgHeader = 
  if this.imgHeaderInst != nil:
    return this.imgHeaderInst
  let imgHeaderInstExpr = AndroidBootldrQcom_ImgHeader(AndroidBootldrQcom(this.root).imgHeaders[this.idx])
  this.imgHeaderInst = imgHeaderInstExpr
  if this.imgHeaderInst != nil:
    return this.imgHeaderInst

proc fromFile*(_: typedesc[AndroidBootldrQcom_ImgBody], filename: string): AndroidBootldrQcom_ImgBody =
  AndroidBootldrQcom_ImgBody.read(newKaitaiFileStream(filename), nil, nil)