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java – Linking thirdparty libs (libs.a) with NDK

Posted by: admin June 15, 2020 Leave a comment

Questions:

I’m building an Android apk who uses some native libraries of a third party, these libs are in Static Object Code Library (.a files) and I need to write a JNI wrapper to access in Java these functions.

Those libs are already compiled with a cross-compiler and are natively to Android.

How do I compile my JNI sources linking to the functions in the .a libs files?

This is my Android.mk

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)

LOCAL_LDLIBS := -llog

LOCAL_MODULE    := ndk1
LOCAL_SRC_FILES := native.c

include $(BUILD_SHARED_LIBRARY)

When I compile, I get only the native.c file compiled.

How to&Answers:

To do that.

I have to declare these libs as modules. Like the following.

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)

LOCAL_MODULE    := curl
LOCAL_SRC_FILES := libcurl.a
LOCAL_EXPORT_C_INCLUDES := $(LOCAL_PATH)/include

include $(PREBUILT_STATIC_LIBRARY)

With a libcurl.a file in the same folder as this Android.mk file, and a /include fodler with the headers.

Now in the main module just declare the lib and the Android NDK will take care of the rest.

LOCAL_PATH := $(call my-dir)

include $(call all-subdir-makefiles)
include $(CLEAR_VARS)

LOCAL_LDLIBS := -llog -ldl
LOCAL_MODULE    := rmsdk
LOCAL_SRC_FILES := curlnetprovider.cpp native.c
LOCAL_STATIC_LIBRARIES := curl

include $(BUILD_SHARED_LIBRARY)

Note.. you should include the Android.mk file of the module before using it. I do that with the call all-subdir-makefiles.

Answer:

Your libs have to be compiled for your specific target (Arm), to do that I think you have to use the toolchain as described in docs/STANDALONE-TOOLCHAIN.html (in your ndk-r5 folder).