This document serves as a reference on how to unpack Android builds to extract its DEX, APK, and JAR files which contain the source code of Android's application framework and the system apps that would be installed on the target device. It is not meant for explaining the logic underlying the packing/unpacking techniques.

I'm aware of the following sources where you can retrieve Android builds. Please, feel free to suggest more.

• Google AOSP (master builds): https://ci.android.com/
• Google Factory Images: https://developers.google.com/android/images
• Samsung: https://www.sammobile.com/firmwares/

Please note that not all requirments are needed. Use them as you go through out the instructions.

• simg2img to convert sparse images to raw images that can be mounted
• Vdex Extractor to decompile and extract Android dex bytecode from vdex files
• Compact Dex Converter to convert cdex files to standard dex
• unlz4 to decompress lz4 files

Please note that some of the following steps is optional. Read the details to know when to execute each step.

First thing to do after downloading the Android build, is to decompress the downloaded file(s) and locate the system.img or super.img file. For ease of discussion, we will call this file system.img from here on. In SAMSUNG builds, this file can be compressed using lz4. You can use lz4 utility or any other compatable tool to decompress the file.

unlz4 system.img.lz4

Some system.img files are sparse and require one extract step. According to this post, the image is sparse if the output of the following command is < 1.

find system.img -type f ! -size 0 -printf '%S\n'

If the image is sparse, use the simg2img utility to convert it into a raw image, execute the following command.

simg2img ./system.img system.img.raw

Create a directory to mount the the system image and mount it

mkdir ./system
mount -o loop -t ext4 ./system.img.raw ./system

If this step fails to due to:

 mount: {...}system: wrong fs type, bad option, bad superblock on /dev/loop, missing codepage or helper program, or other error.

Then head to the following step.

Change the extension of the system image to .zip and extract it manually.

Depending on the Android version of the build, the DEX files might be packed inside VDEX files. To extract the DEX file from a file named services.vdex, execute the following command and make sure that the corresponding binaries are in the PATH.

vdexExtractor -i services.vdex -o ./output_dir --deps -f

In case the output files are in the CDEX format, execute the following command to convert them to standard DEX format.

compact_dex_converter services.cdex

If any of the above didn't work for you, feel free to create a ticket and share the build image you are trying to unpack and let's figure it out together.