Android NDK - Android studio gradle undefined reference to __android_log_write

Question

I am trying to debug a JNI C function by inserting log messages, but I can't get it to work. To start with I am just trying to modify the hello-jni example that comes with Android Studio. This is the modified code:

#include <string.h>
#include <jni.h>
#include <android/log.h>

jstring
Java_com_example_hellojni_HelloJni_stringFromJNI( JNIEnv* env,
                                              jobject thiz )
{
#if defined(__arm__)
    #if defined(__ARM_ARCH_7A__)
    #if defined(__ARM_NEON__)
      #if defined(__ARM_PCS_VFP)
        #define ABI "armeabi-v7a/NEON (hard-float)"
      #else
        #define ABI "armeabi-v7a/NEON"
      #endif
    #else
      #if defined(__ARM_PCS_VFP)
        #define ABI "armeabi-v7a (hard-float)"
      #else
        #define ABI "armeabi-v7a"
      #endif
    #endif
  #else
   #define ABI "armeabi"
  #endif
#elif defined(__i386__)
   #define ABI "x86"
#elif defined(__x86_64__)
   #define ABI "x86_64"
#elif defined(__mips64)  /* mips64el-* toolchain defines __mips__ too */
   #define ABI "mips64"
#elif defined(__mips__)
   #define ABI "mips"
#elif defined(__aarch64__)
   #define ABI "arm64-v8a"
#else
   #define ABI "unknown"
#endif

    __android_log_write(ANDROID_LOG_ERROR, "TEST_TAG", "Error here");

    return (*env)->NewStringUTF(env, "Hello from JNI !  Compiled with ABI " ABI ".");
}

And this is my Android.mk file:

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)

LOCAL_MODULE    := hello-jni
LOCAL_SRC_FILES := hello-jni.c
LOCAL_LDFLAGS := -llog

include $(BUILD_SHARED_LIBRARY)

When I use the ndk-build script the libhello-jni.so files get built no problem. When I try to build the project in Android Studio I get the following gradle error message

Information:Gradle tasks [:app:assembleDebug]
:app:preBuild
:app:compileDebugNdk
C:\Android\projects\hello-jni\app\build\intermediates\ndk\debug\obj/local/arm64-v8a/objs/hello-jni/C_\Android\projects\hello-jni\app\src\main\jni\hello-jni.o: In function `Java_com_example_hellojni_HelloJni_stringFromJNI':
hello-jni.c:(.text.Java_com_example_hellojni_HelloJni_stringFromJNI+0x24): undefined reference to `__android_log_write'
Error:error: ld returned 1 exit status
make.exe: *** [C:\Android\projects\hello-jni\app\build\intermediates\ndk\debug\obj/local/arm64-v8a/libhello-jni.so] Error 1
Error:Execution failed for task ':app:compileDebugNdk'.
> com.android.ide.common.internal.LoggedErrorException: Failed to run command:
C:\Android\android-ndk-r10c\ndk-build.cmd NDK_PROJECT_PATH=null APP_BUILD_SCRIPT=C:\Android\projects\hello-jni\app\build\intermediates\ndk\debug\Android.mk APP_PLATFORM=android-19 NDK_OUT=C:\Android\projects\hello-jni\app\build\intermediates\ndk\debug\obj NDK_LIBS_OUT=C:\Android\projects\hello-jni\app\build\intermediates\ndk\debug\lib APP_ABI=all
Error Code:
2
Output:
C:\Android\projects\hello-jni\app\build\intermediates\ndk\debug\obj/local/arm64-v8a/objs/hello-jni/C_\Android\projects\hello-jni\app\src\main\jni\hello-jni.o: In function `Java_com_example_hellojni_HelloJni_stringFromJNI':
hello-jni.c:(.text.Java_com_example_hellojni_HelloJni_stringFromJNI+0x24): undefined reference to `__android_log_write'
collect2.exe: error: ld returned 1 exit status
make.exe: *** [C:\Android\projects\hello-jni\app\build\intermediates\ndk\debug\obj/local/arm64-v8a/libhello-jni.so] Error 1
Information:BUILD FAILED
Information:Total time: 3.297 secs
Information:2 errors
Information:0 warnings
Information:See complete output in console

I've tried the suggestions given in this question, but I still get the same error: What is the Log API to call from an Android JNI program?

What am I doing wrong?

I'm using Android Studio 0.8.9 and NDK r10c.

Answer 1

I found an answer after a bit more searching.

If I build the .so files using the ndk-build script on the command line and add

sourceSets.main {
    jni.srcDirs = []
    jniLibs.srcDir 'src/main/libs'
}

into my build.gradle file so gradle doesn't try to build the .so files it all then works. Looks like a problem with Android Studio-Gradle-NDK integration?

I found the answer here https://stackoverflow.com/a/21111458/4182796