Android NDK无法加载libc ++ _ shared.so，获取“无法定位符号'rand'引用

Question

In my java class I have this:

static
{
    System.loadLibrary("c++_shared");

    System.loadLibrary("com.testandroid.LibAndroidBridge");
}

And my Application.mk has this:

NDK_TOOLCHAIN_VERSION:=4.8
APP_STL := c++_shared
APP_ABI := x86

Things build fine, but when I run the app (on emulator or device, so x85 and arm) I get this in LogCat:

02-13 12:00:32.174: D/dalvikvm(2142): Trying to load lib /data/app-lib/com.testandroid-1/libc++_shared.so 0xb0fcfc60
02-13 12:00:32.174: D/dalvikvm(2142): Added shared lib /data/app-lib/com.testandroid-1/libc++_shared.so 0xb0fcfc60
02-13 12:00:32.174: D/dalvikvm(2142): No JNI_OnLoad found in /data/app-lib/com.testandroid-1/libc++_shared.so 0xb0fcfc60, skipping init
02-13 12:00:32.174: D/dalvikvm(2142): Trying to load lib /data/app-lib/com.testandroid-1/libcom.testandroid.LibAndroidBridge.so 0xb0fcfc60
02-13 12:00:32.174: E/dalvikvm(2142): dlopen("/data/app-lib/com.testandroid-1/libcom.testandroid.LibAndroidBridge.so") failed: dlopen failed: cannot locate symbol "rand" referenced by "libcom.testandroid.LibAndroidBridge.so"...
02-13 12:00:32.174: W/dalvikvm(2142): Exception Ljava/lang/UnsatisfiedLinkError; thrown while initializing Lcom/testandroid/AriesLib;
02-13 12:00:32.174: D/AndroidRuntime(2142): Shutting down VM
02-13 12:00:32.174: W/dalvikvm(2142): threadid=1: thread exiting with uncaught exception (group=0xb0cb0b20)
02-13 12:00:32.174: E/AndroidRuntime(2142): FATAL EXCEPTION: main
02-13 12:00:32.174: E/AndroidRuntime(2142): Process: com.testandroid, PID: 2142
02-13 12:00:32.174: E/AndroidRuntime(2142): java.lang.UnsatisfiedLinkError: dlopen failed: cannot locate symbol "rand" referenced by "libcom.testandroid.LibAndroidBridge.so"...
02-13 12:00:32.174: E/AndroidRuntime(2142):     at java.lang.Runtime.loadLibrary(Runtime.java:364)

Would anyone know why this is failing to import the c++_shared.so library?

Answer 1

The real error is something else: rand() is not present, because of Android-21 incompatibilities.

java.lang.UnsatisfiedLinkError: dlopen failed: cannot locate symbol "rand" referenced by

See this thread for more info.

The recommended fix is to downgrade your API in jni/Application.mk and set it to something lower than Android-21 . If you need Android-21 then Google actually recommends shipping multiple APK files. Ugh.

Answer 2

Problem is entirely on native side. Java has no any clue on what's happening past the JNI boundary. You cannot make two native libraries go along this way. Especially, C++ standard library (it has no any symbols easily and reliably accessible by JNI).

You should resolve all the symbols on the native side, ie you should correctly link C++ Standard Library to your libcom.testandroid.LibAndroidBridge.so .

I'd advised against mixing { gcc toolchain (4.8 in your case) + libc++ ("c++_shared") } or { clang + libstdc++ } on Android. It should work theoretically on desktop Linux or OSX, but there are still portability issues and some quirks persist on Android, depending on NDK version, target, and some "random" factors. So it doesn't always work.

Unfortunately you did not provide the code where you are using rand (maybe it's even non Standard Library rand , but some custom code?), but you can still try:

• to use GCC's GNU Standard Library, leaving GCC 4.8 as toolchain

OR

• to use Clang compiler, leaving libc++ as Standard library

AND/OR

• to use static linking for "debugging purposes" (it won't link until something is missing, allowing you to find the cause without messing with Java and JNI)

Answer 3

You don't have to write

System.loadLibrary("c++_shared");

just include :-

APP_STL := c++_shared 

in your Application.mk That should make it work and now libc++_shared.so will be bundled