binder_rs

The stub libbinder_ndk.so in ndk's sysroot hides some apis, so that we cannot link our libbiner_rs to it. However, we can rebuild a stub so to make linker happy. The stub source is generated from symbols.txt, whose contents are extracted from prebuilt libbinder_ndk.so from aosp-mainline.

The libbinder_ndk.so is introduced in api-29, you need to compile it with specified target api level. The compilation won't fail if api is lower than 29, because we build the dynamic library ourselves.

Adding Android targets via rustup

For each Android target you wish to build for you must e.g.

rustup target add \
    aarch64-linux-android \
    armv7-linux-androideabi \
    x86_64-linux-android \
    i686-linux-android

Building using the cargo-ndk tooling

cargo-ndk simplifies the process of building libraries and binaries for Android targets.

1. Install Android Studio

2. Install the NDK from within Android Studio

3. Install cargo-ndk with:

cargo install cargo-ndk

We use cargo ndk to build the stub so, ANDROID_NDK_HOME must be set in your env !

Building your own libbinder_ndk.so from the AOSP

If you follow the steps below in Generate Rust code from AIDL from the AOSP you will get a libbinder_ndk.so build 'for free' for your target architecture.

Copy that libbinder_ndk.so from where it's built in the aosp root to where it should belong in the path to your NDK install.

In my case I copied it from:

<aosp-root>/out/target/product/generic_x86_64/system/lib64/libbinder_ndk.so

to

~/Android/Sdk/ndk/<version-of-ndk>/toolchains/llvm/prebuilt/linux-x86_64/sysroot/usr/lib/x86_64-linux-android/29/libbinder_ndk.so

since I was going to compile with platform API level 29 and for x86_64.

Side note on where the sources are from

sys/src/include_* from platform/frameworks/native/libs/binder/ndk

Example

1. Build

   cargo ndk -t arm64-v8a --platform=29 --bindgen build
   

2. Push file to phone

   adb push target/aarch64-linux-android/debug/binder-example /data/local/tmp
   

3. Run 2 adb shell

   Run server:

   adb shell
   su -c /data/local/tmp/binder-example server
   

   Run client:

   adb shell
   su -c /data/local/tmp/binder-example client
   

Test

1. Build

   cargo ndk -t arm64-v8a --platform=29 --bindgen build
   

2. Push files to phone

   adb push target/aarch64-linux-android/debug/binder-tests /data/local/tmp
   

3. Build unittest binary

   cargo ndk -t arm64-v8a --platform=29 --bindgen test --bin binder-tests --no-run
   

4. Push files to phone

   adb push target/aarch64-linux-android/debug/deps/binder_tests-acf830ec15b8864e /data/local/tmp
   

5. Run test

   adb shell
   cd /data/local/tmp/ && su -c ./binder_tests-acf830ec15b8864e
   

   if you see error like this

   CANNOT LINK EXECUTABLE "/data/local/tmp/binder_tests-acf830ec15b8864e": cannot locate symbol "AIBinder_DeathRecipient_setOnUnlinked" referenced by "/data/local/tmp/binder_tests-acf830ec15b8864e"...
   

   This is because your android version is too low, the source is from android-mainline. You can try in avd, with Android U

Using AIDLs with UnstructuredParcelable

Generate Rust code from AIDL from the AOSP

1. Create AIDL + any UnstructuredParcelable you want to use in your AIDL interface
   • Reference unstructured_parcelable_example/aosp_module_to_generate_aidl

Note the structure:

• my_simple_parcelable_service/
  • Android.bp: Soong build file
  • aidl/
    • Android.bp: Soong build file
    • com/example/mysimpleparcelableservice
      • IMySimpleParcelableService.aidl: The service interface, note we are including MySimpleParcelable as a return parameter
      • MySimpleParcelable.aidl: Essentially a bit of a "wrapper" which points to the actual definition of the UnstructuredParcelable in the rust folder, see below
      • rust/
        • my_simple_parcelable.rs: Note that we have to impl the UnstructuredParcelable trait.
  • src/
    • lib.rs: Implementation of the service. We only need to impl it because Soong will not let us make the AIDL directly. Note that this is not actually used at all.

2. Use Soong to build. You need to put the above folder under <aosp-root>/external/rust/<your-aidl-lib-folder>
   • As per normal when building out of the AOSP, you'll need to choose your target architecture, so do the following steps first from the aosp root:
     • source build/envsetup.sh
     • lunch <your-target-choice>
       • Recall you can type lunch by itself to get a listing of available targets

You may then proceed with building:

m libmysimpleparcelableservice

Expected output

============================================
PLATFORM_VERSION_CODENAME=VanillaIceCream
PLATFORM_VERSION=VanillaIceCream
PRODUCT_INCLUDE_TAGS=com.android.mainline mainline_module_prebuilt_nightly
TARGET_PRODUCT=aosp_x86_64
TARGET_BUILD_VARIANT=eng
TARGET_ARCH=x86_64
TARGET_ARCH_VARIANT=x86_64
TARGET_2ND_ARCH=x86
TARGET_2ND_ARCH_VARIANT=x86_64
HOST_OS=linux
HOST_OS_EXTRA=Linux-5.15.0-79-generic-x86_64-Ubuntu-20.04.6-LTS
HOST_CROSS_OS=windows
BUILD_ID=MAIN
OUT_DIR=out
============================================
[ 22% 8/36 1m15s remaining] AIDL Rust external/rust/my_simple_parcelable_service/aidl/com/example/mysimp
Compiling IDL...
GenerateRust: out/soong/.intermediates/external/rust/my_simple_parcelable_service/aidl/com.example.mysim
pleparcelableservice-rust-source/gen/com/example/mysimpleparcelableservice/IMySimpleParcelableService.rs
[100% 36/36 1m14s remaining] Install: out/target/product/generic_x86_64/system/lib64/libmysimpleparcelab

#### build completed successfully (02:19 (mm:ss)) ####

3. Navigate to Soong intermediate build folder and scoop up generated Rust code.

   • In this case it was located at:
     • <aosp-root>/out/soong/.intermediates/external/rust/my_simple_parcelable_service/aidl/com.example.mysimpleparcelableservice-rust-source/gen/com/example/mysimpleparcelableservice/IMySimpleParcelableService.rs

4. Assemble the pieces in your Rust project

   • Copy in your generated Rust source for the interface from step 3
   • Copy in the Rust source of your UnstructuredParcelables from step 1

5. Build

cargo ndk -t x86_64 --platform=29 --bindgen build

6. Remaining steps to copy / run example same as above