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fake-jni

Cloning

git clone --depth 1 --recursive https://github.com/meme/fake-jni.git

Requirements

fake-jni has no runtime dependencies :)

Build Requirements

  • CMake >= 3.8
  • libdl
  • make or ninja

Usage

To include fake-jni in your CMake project, clone it into your project's root directory and add the following lines to your CMakeLists.txt:

project(my_project)

#define any desired fake-jni build variables BEFORE including fake-jni
add_subdirectory(fake-jni)

target_link_libraries(my_project fake-jni)

Building

Build Flags

Flag Usage Default Description
BUILD_FAKE_JNI_TESTS =[ON OFF] ON Builds and runs the test suite
BUILD_FAKE_JNI_EXAMPLES =[ON OFF] ON Builds and runs the examples
BUILD_FAKE_JNI_DEBUG =[ON OFF] OFF Builds a debug release
BUILD_FAKE_JNI_ASAN =[ON OFF] OFF Builds with ASAN
FFI_CC ={DESIRED_C_COMPILER} ${CMAKE_C_COMPILER} Set the C compiler for libffi
FFI_CXX ={DESIRED_CXX_COMPILER} ${CMAKE_CXX_COMPILER} Set the C++ compiler for libffi
FFI_CONFIGURE_FLAGS ={CONFIGURE_FLAGS} `` Set the configure flags for libffi
UNWIND_CC ={DESIRED_C_COMPILER} ${CMAKE_C_COMPILER} Set the C compiler for libunwind
UNWIND_CXX ={DESIRED_CXX_COMPILER} ${CMAKE_CXX_COMPILER} Set the C++ compiler for libunwind
UNWIND_CONFIGURE_FLAGS ={CONFIGURE_FLAGS} `` Set the configure flags for libunwind

Simply build as usual:

mkdir build
cd build
env CC=clang CXX=clang++ cmake ..
make -j

or optionally build with ninja:

mkdir build
cd build
env CC=clang CXX=clang++ cmake -GNinja ..
ninja -j0

Cross Compiling

To compile for another host you must set the following environment variables:

  • CMAKE_CXX_COMPILER_TARGET - The target architecture
  • CC - The C cross-compiler
  • CXX - The C++ cross-compiler

Optionally, you may also set the following variables:

  • FFI_CC
  • FFI_CXX
  • UNWIND_CC
  • UNWIND_CXX

Note: When compiling for Android you must set both FFI_CC and FFI_CXX to their respective toolchains, otherwise libffi will fail to compile. The compilers will be located inside of your distribution's NDK installation, under $ANDROID_NDK/toolchains/llvm/prebuilt/linux-x86_64/bin.

For example, to compile fake-jni for Android API level 21 and the AArch64 architecture, your CMakeLists.txt would look like the following:

project(my_project)

#these build variables must be set BEFORE including fake-jni
set(FFI_CC aarch64-linux-android21-clang)
set(FFI_CXX aarch64-linux-android21-clang++)

add_subdirectory(fake-jni)

target_link_libraries(my_project fake-jni)

Then to build, run the following:

export PATH=$ANDROID_NDK/toolchains/llvm/prebuilt/linux-x86_64/bin:$PATH
mkdir build
cd build
cmake -GNinja -DCMAKE_TOOLCHAIN_FILE=$ANDROID_NDK/build/cmake/android.toolchain.cmake -DANDROID_ABI=arm64-v8a -DANDROID_PLATFORM=android-21 ..
ninja -j0

Goals

  • Binary compatability with JNI 1.8
  • Drop-in replacement for an actual JVM, allowing users to compile against fake-jni while retaining full functionality
  • The definition and linking of C++ classes through fake-jni to act as proxies for Java classes, that would otherwise be running on an actual JVM
  • Portability to other platforms and architectures

Licensing

The JNI headers are licensed under the GPL, with the "classpath" exception, meaning that we are free to use and implement the JNI headers in fake-jni, however, any changes made to include/jni.h or include/jni_md.h will be made under the GPL, in complete compliance with the licensing. The rest of fake-jni, including implementations of other GPL licensed headers, are licensed under the GPLv3 license.