Modifying the operating system Android opens up unlimited possibilities for the user to customize the device. You can remove pre-installed software, change system fonts, add support for new codecs, or even implement features only available in flagship models. However, this process is complex and requires a deep understanding of the structure of file systems and image formats. To get started, you will need not only root access, but also specialized software tools on your computer.
Before you start editing, you need to be clearly aware of the risks. Any incorrect action when assembling the image can lead to a “brick” of the device, which will have to be restored via Fastboot or recovery mode. The main purpose of modding is to change the contents of sections system, vendor or boot. Each of these sections has its own specifics: the system section contains applications and frameworks, and the boot image is responsible for initializing the kernel and starting the system.
In this article we will analyze professional methods of working with firmware images. We will not consider simplified methods of replacing files through file managers with root access, since they do not provide complete control over the structure of the system. We will talk about complete decompilation and reverse assembly of images on a PC using standard Android development tools. This is the only way to make profound changes to the operating logic of the OS.
Preparing the working environment and the necessary drivers
The foundation for successful firmware editing is a properly configured development environment. You will need a computer running Windows, Linux or macOS with sufficient RAM, as decompilation processes can be resource intensive. The first step will be installation Java Development Kit (JDK). Most tools for working with APKs and system frameworks are written in Java, so they will not start without correctly set environment variables.
Next you need to install the ADB and Fastboot drivers. These utilities allow your computer to communicate with your smartphone in debug and bootloader mode. Without them, you will not be able to download current images from the device for analysis. It is also recommended to install specific drivers for your processor (MediaTek, Qualcomm, Samsung) if you plan to reflash the device with modified images in the future.
⚠️ Attention: Make sure that the drivers specifically for your processor model are installed on your computer. An incorrect driver may result in the device not being detected in Download or EDL mode, which will block the ability to recover after unsuccessful firmware.
To work with the image file system, emulation of the Linux environment is often required, even on Windows. Using the WSL2 (Windows Subsystem for Linux) subsystem greatly simplifies the work with permissions and bash scripts that are often found in modding tool repositories. This eliminates problems with encoding paths and executable files.
☑️ Preparing the workplace
Toolkit for unpacking and analyzing images
Android firmware is a set binary images of partitions packaged in specific formats depending on the manufacturer. To edit the contents, these images must first be extracted from the general firmware file (for example, .zip, .tar.md5 or .payload), and then unpack the file system itself. For these purposes, a set of utilities is used, often combined into projects like Android Image Kitchen or SuperR's Kitchen.
The key tool for working with the system partition is APKTool. It allows you to decompile application APK files and system libraries into human-readable code (Smali) and resources (XML). This is necessary if your goal is to translate the interface, change the operating logic of a system application, or remove advertising from system services. Direct editing of compiled files is not possible.
To work with partition images (system.img, boot.img), utilities simg2img i img2simgare used. They convert images from the Android Sparse Image format (used to save space when flashing) into a standard RAW image, which can be mounted as a virtual disk or unpacked using the utility ext4_utils. Only after gaining access to the file structure can you make changes.
| Tool | Purpose | Complexity | Interface type |
|---|---|---|---|
APKTool |
Decompilation of APKs and resources | Medium | Command line |
simg2img |
Sparse image conversion | Low | Command line |
| Android Image Kitchen | Full unpacking of firmware | Low | Graphical (GUI) |
MagiskBoot |
Modification of the boot image | High | Scripts |
Use graphical shells like Android Image Kitchen for the first experiments - they automate the process of converting image formats, reducing the risk of errors when entering commands.
Editing system applications and frameworks
The most common task when modding is changing the behavior of system applications. After unpacking system.img you get access to the folder /system/app i /system/priv-app. To change, for example, the power menu or the settings panel, you need to decompile the corresponding APK file using apktool d file_name.apk. As a result, you will receive a folder with resources and Smali code.
Smali code is an assembler-like representation of Dalvik/ART bytecode. Editing it is difficult, but possible. Most often, edits concern XML files in the res/valuesfolder, where interface strings, colors and styles are stored. For global changes to the interface, they often modify the file framework-res.apk or services.jar, which are responsible for system themes and services.
After making the changes, you need to perform a reverse assembly with the command apktool b project_folder. It is critical to sign the resulting APK file before replacing it in the firmware image. The Android system partition is protected by a signature verification mechanism (Verified Boot), and files that are unsigned or signed with the wrong key simply will not run, causing a cyclic reboot (bootloop).
- 🛠️ Decompilation: Extracting code and resources from APK for analysis.
- ✏️ Editing Smali/XML: Making changes to logic or appearance.
- 📦 Assembling and signing: Compiling back to APK and cryptographic proof of authorship.
- 🔄 Replacement in the image: Integration of the modified file back into
system.img.
Why does Bootloop occur after replacing a system application?
Most often the reason is a mismatch of permissions or lack of a correct signature. The Android system checks the integrity of critical components when booting. If the file hash does not match the expected one or the signature does not match the system key, the bootloader blocks the OS from starting to prevent the device from being compromised.
Modification of the boot image (Boot Image)
The boot image boot.img contains the Linux kernel (kernel) and ramdisk (ramdisk). Editing this section is required to implement superuser rights (Root), install custom drivers, or change kernel startup parameters. To work with boot.img the de facto standard has become the tool MagiskBoot, which is part of the Magisk project.
The process begins with unpacking the image: magiskboot unpack boot.img. You will receive the kernel files and a compressed ramdisk archive. The ramdisk contains initialization scripts (init.rc), which determine which services start first. This is where the Magisk script is injected to obtain root access. After modifying the contents of the ramdisk, the image is assembled back with the command magiskboot repack.
When editing the kernel, knowledge of Linux compilation is required. You will need the kernel source code corresponding to the version of your device, and a toolchain for cross-compilation for the processor architecture (arm64-v8a, armeabi-v7a). Changing the kernel configuration (.config) allows you to enable support for additional file systems, network modules or unlock processor frequencies.
⚠️ Attention: Incorrect assembly boot.img is guaranteed to prevent the phone from turning on. Always have an original, working boot image on hand for quick recovery via Fastboot.
Working with the Vendor section and drivers
In modern versions of Android (starting with Project Treble), hardware-dependent code is placed in a separate section vendor. Proprietary drivers, libraries for the camera, modem and sensors are stored here. Editing this section is necessary if you want to transfer the camera from one smartphone to another (porting) or correct software errors in the operation of the equipment.
The structure of the section vendor is similar to the system one, but changes here are more risky. Removing a critical library, such as one associated with the display (hwcomposer), will result in a black screen on boot. To analyze file dependencies, this section uses utilities like ldd (in the emulation environment) or specialized library scanners.
If you are porting firmware (GSI or custom assemblies), you will often have to edit the file fstab.qcom (or an analogue for your processor) in the ramdisk. This file describes the file system table and partition mount points. An error in the partition UUID or mount point will make the system unable to find user data.
The Vendor partition contains proprietary vendor drivers. Its modification is required mainly when creating custom firmware or porting camera and sound functions between devices.
Assembling the final image and flashing the firmware onto the device
After making all the necessary changes to the files, they must be packed back into the image. If you worked with unpacked system, use the utility make_ext4fs or mke2fs to create a new one system.img. It is important to observe the partition sizes: the new image should not be larger than the original partition on the device’s flash memory, otherwise the firmware will be interrupted with an error.
For devices with Dynamic Partitions, which appeared in Android 10 and newer, the process becomes more complicated. The format used here is super.img, which combines several logical sections. To work with it, you need a utility lpunpack for extraction and lpmake for reassembly. An error in calculating the size of partition groups will make the image invalid.
The final stage is writing images to the device. This is done through Fastboot mode using commands like fastboot flash system system.img or fastboot flash boot boot.img. Some manufacturers (Samsung, Xiaomi) use their own firmware protocols (Odin, MiFlash), which require packaging images in specific containers (.tar, .mbn). After flashing, be sure to run fastboot reboot.
- 📏 Size control: Make sure that the final image fits into the partition size.
- 🔒 Locking the bootloader: On some devices you need to unlock the bootloader before flashing.
- 🧹 Wipe Data: After changing the Android version or deep modification, a complete data reset is often required.
Frequent errors and debugging methods
The process of editing firmware rarely goes smoothly the first time. The most common error is Bootloop (cyclic reboot). To diagnose, you need to connect the phone to the PC and use the command adb logcat (if the system manages to boot before failure) or fastboot boot recovery.img to view the kernel logs. Analysis of the logs will show which process or service caused the crash.
Another problem is a “black screen” when loading. This usually indicates an error in the display drivers or graphics accelerator in the vendorsection. In this case, it helps to temporarily disable hardware acceleration in the kernel parameters or replace the problematic library with a stock one. It is also worth checking the access rights (chmod/chown) to the modified files; they must match the originals.
If the device is not detected in Fastboot mode after flashing, the bootloader or partition table may have been damaged. In this case, only the emergency recovery mode will help (EDL for Qualcomm, Download Mode for Samsung), which allows you to upload a full dump of the factory firmware, ignoring the bootloader.
⚠️ Attention: Technical characteristics of devices and firmware methods may vary depending on the model and year of manufacture. Always check the documentation for your specific chipset and the developer forum (XDA) before starting work, as the partition structure varies between vendors.
What is Verified Boot and how to bypass it?
Verified Boot (AVB) is a mechanism for checking the integrity of the boot chain. It will not allow you to load a modified kernel or system. The workaround is done by unlocking the bootloader (which erases the data) or introducing a patch into the boot image that disables signature verification (for example, using Magisk or the vbmeta patch).
Is it possible to edit the firmware directly on the phone without a computer?
Technically, this is possible using terminal emulators and root access using utilities like mtk-su or special Magisk modules. However, this method is extremely inconvenient for large-scale changes, since it is difficult to decompile large APKs on the phone, edit the code and control the size of the images. A computer is necessary for reliable operation.
Is it necessary to unlock the bootloader to edit the firmware?
Yes, in 99% of cases, unlocking the bootloader is mandatory. Without this, you will not be able to write modified images to the boot i systempartitions. The exception is temporary root methods through exploit vulnerabilities, but they do not allow you to save changes after a reboot.
What to do if the phone does not turn on after flashing the firmware?
Don’t panic. Try entering Recovery mode and doing Wipe Data/Cache. If it doesn’t help, boot into Fastboot/Download mode and flash the original (stock) firmware image downloaded from the manufacturer’s official website. This will return the device to its factory state.
Which tool is best for a beginner?
For starters, we recommend a bundle Android Image Kitchen (for unpacking/building images) and APKTool (for working with applications). They have a relatively simple interface and a wide documentation base. Avoid manually editing binary files using Hex editors until you gain experience.
Does editing the firmware affect the operation of banking applications?
Yes, it does. Changing the system partition or having root access often triggers security mechanisms (SafetyNet/Play Integrity). Banking applications may refuse to work. To solve this problem, hiding the root through Magisk Hide or Zygisk, as well as modules that mask system changes, are used.