libreactnativejni.so is built as elf32-i386 on 64bit android ndk (linux)

Issue

EDIT: I managed to built x86_64 version of libreactnativejni.so (see my answer). However it didn't resolved my problem.

To sum up what I learned here is:

You cannot test android components, which are using native libraries on Linux, because "libandroid.so" (core android lib), doesn't exists for Linux.

Original question:

My goal is to run tests on my Linux box using PowerMockito similar to RootViewTest.java. Not sure how react-native team managed to run this test, but from my experience mocking Arguments.createArray is not possible, without loading jni library reactnativejni. Reason is that Arguments.createArray() calls WritableNativeArray which in static initializer ReactBridge.staticInit() calls SoLoader.loadLibrary("reactnativejni").

So I thought I've no other option, but compile this reactnativejni shared library for linux, using 64bit android-ndk-r10e

I managed to load this jni lib and test my code using:

ndkDir=$(pwd)/react-ndk/all/x86 \
  JAVA_OPTS="-Djava.library.path=\".:$ndkDir\"" \
  LD_LIBRARY_PATH="$ndkDir:$LD_LIBRARY_PATH" ./gradlew app:test

But test failed with:

libreactnativejni.so: wrong ELF class: ELFCLASS32 (Possible cause: architecture word width mismatch)

Checked platform with objdump:

objdump -s --section .comment libreactnativejni.so

libreactnativejni.so:     file format elf32-i386

My question how is possible that 64 bit ndk produced 32 bit library and how to force to produce 64 bit.

Library build script is written as gradle script:

https://github.com/facebook/react-native/blob/26684cf3adf4094eb6c405d345a75bf8c7c0bf88/ReactAndroid/build.gradle#L199

Solution

I'm going to answer my own question (thank Alex for good APP_ABI lead). To compile x86_64 variant of reactnativejni follow this steps:

1. Update APP_ABI to APP_ABI := armeabi-v7a x86_64 x86 in file ReactAndroid/src/main/jni/Application.ml

The next problem is dependency jsc-android, which is not build for X86_64 target. There is alternative jsc-android-buildscripts which is also built for X86_64.

2. Extract folder X86_64 directly from aar and put it in ReactAndroid/build/third-party-ndk/jsc/jni/x86_64

However compilation will be failing on X86_64 with errors: lambda capture initializers only available with -std=c++1y or -std=gnu++1y

3. Fix that error, by replacing all occurrences of -std=c++1y with -std=c++11 in all Android.mk files.

4. Now you can start build with: ./gradlew buildReactNdkLib

5. Optionally you might need to clean build folder with ./gradlew cleanReactNdkLib

Built reactnativejni - libreactnativejni.so will be present in ReactAndroid/build/react-ndk/all/x86_64.

But unfortunately libreactnativejni.so will not work on Linux, as it has dependency on libandroid.so, which doesn't exists for Linux.

Answered By - mauron85