Building Android source: error when executing mm?

Troubleshooting 'mm' Command Errors During Android Source Compilation

Encountering issues when executing the mm command during Android source compilation can be frustrating. This guide provides common causes and solutions to help you successfully build your Android ROM.

Building the Android Open Source Project (AOSP) from scratch is a complex process, and it's common to run into various errors. One frequent stumbling block for developers is when the mm command, used to build specific modules, fails. This article will delve into the typical reasons behind mm command failures and provide actionable steps to resolve them, ensuring a smoother compilation experience for your custom Android ROM.

Understanding the 'mm' Command and its Role

The mm command is a convenient wrapper around the make build system, specifically designed for building individual Android modules or subdirectories within the AOSP tree. Unlike make or m (which builds the entire tree or a specific product), mm focuses on a smaller scope, making it ideal for iterative development and testing of specific components. When mm fails, it usually indicates a problem with the build environment, missing dependencies, or issues within the module's Android.mk or Android.bp build files.

flowchart TD
    A[Start Android Build Process] --> B{Source Code Cloned?}
    B -- Yes --> C{Build Environment Setup?}
    B -- No --> D[Clone AOSP Source]
    C -- Yes --> E{Initialize Build Env (source build/envsetup.sh)?}
    C -- No --> F[Install Dependencies & Setup Env]
    E -- Yes --> G{Choose Target (lunch)?}
    E -- No --> H[Run 'source build/envsetup.sh']
    G -- Yes --> I{Execute 'mm' in Module Directory?}
    G -- No --> J[Run 'lunch' command]
    I -- Success --> K[Module Built Successfully]
    I -- Failure --> L[Troubleshoot 'mm' Error]

Simplified Android Build Workflow with 'mm' Command Integration

Common Causes of 'mm' Command Failures

Several factors can lead to mm command errors. Identifying the root cause is crucial for effective troubleshooting. Here are the most common culprits:

1. Incorrect Environment Setup: The Android build environment requires specific variables and paths to be set. If envsetup.sh hasn't been sourced correctly, or if lunch hasn't been run, mm won't know how to find necessary tools and libraries.
2. Missing Dependencies: The module you're trying to build might depend on other modules or external libraries that haven't been built yet or are missing from your system.
3. Wrong Directory: The mm command must be executed from within the root directory of the module you intend to build, or a subdirectory thereof. Executing it from an unrelated location will result in an error.
4. Build System Changes: If you've recently synced your AOSP tree, there might be changes to the build system (Android.mk, Android.bp files) that introduce new requirements or incompatibilities.
5. Outdated Build Tools: Your host machine's Java Development Kit (JDK) version, Python version, or other build tools might not meet the requirements for the specific Android version you are compiling.
6. Disk Space Issues: Android source compilation requires a significant amount of disk space. Running out of space during the build process can cause mm to fail.

Step-by-Step Troubleshooting and Solutions

When mm fails, don't panic. Follow these steps to diagnose and resolve the issue.

1. Verify Environment Setup

Ensure your build environment is correctly initialized. Navigate to the root of your AOSP directory and run:

source build/envsetup.sh
lunch <product_name>-<build_variant>

Replace <product_name> and <build_variant> with your desired target (e.g., aosp_arm64-userdebug). If you're unsure, run lunch without arguments to see a list of available targets. After running lunch, try mm again.

2. Check Current Directory

Confirm that you are in the correct directory. The mm command should be run from the root of the module you want to build. For example, to build frameworks/base, you would cd frameworks/base and then run mm.

3. Examine the Error Output

The error messages provided by mm are your best clue. Look for keywords like 'No rule to make target', 'command not found', 'undefined reference', or specific file paths. These often point directly to missing files, incorrect paths, or build script issues. If the output is too verbose, try redirecting it to a file for easier analysis:

mm 2>&1 | tee mm_error.log

4. Clean and Rebuild

Sometimes, stale build artifacts can cause issues. Try cleaning the module's build output before attempting to rebuild. Navigate to the module's directory and run:

mm clean

Then, try mm again. For a more aggressive clean, you might need to use make clean from the AOSP root, but this will remove all build artifacts and force a full rebuild.

5. Check Dependencies

If the error indicates missing headers or libraries, you might need to build their respective modules first. For example, if you're building an app that depends on a custom framework library, ensure that library is built before the app. You can often find dependency information in the module's Android.mk or Android.bp file.

6. Update Build Tools and Sync Source

Ensure your host machine's build tools (JDK, Python, etc.) meet the AOSP requirements. If you're working with a frequently updated branch, it's good practice to periodically sync your source tree:

repo sync -j<number_of_jobs>

After syncing, re-initialize your environment (source build/envsetup.sh and lunch).

7. Check Disk Space

Verify that you have sufficient free disk space. A full Android build can consume hundreds of gigabytes. Use df -h to check your disk usage.

# Example of a typical 'mm' error message for a missing target
make: *** No rule to make target 'out/target/product/generic_arm64/obj/PACKAGING/target_files_intermediates/android-target_files-userdebug.zip', needed by 'dist'.  Stop.

# Example of a common environment setup error
build/envsetup.sh: No such file or directory

Common error messages encountered during Android source compilation