c++ so的undefined symbol問題

我有一隻簡單的範例程式如下，我想把它編成so好透過JNA存取:

int test()
{
        return 0;
}

接著透過以下指令把它編成so:

g++ -shared -fPIC -o libtest.so test.c

import com.sun.jna.Library;
import com.sun.jna.Native;

public class Tester {

	public interface Test extends Library {
		Test INSTANCE = (Test)Native.loadLibrary("test", Test.class);

		int test();
	}
	
	public static void main(String[] args) {
		System.out.println(Test.INSTANCE.test());
	}
}

Exception in thread "main" java.lang.UnsatisfiedLinkError: Error looking up function 'test': /opt/test/libtest.so: undefined symbol: test
	at com.sun.jna.Function.<init>(Function.java:208)
	at com.sun.jna.NativeLibrary.getFunction(NativeLibrary.java:536)
	at com.sun.jna.NativeLibrary.getFunction(NativeLibrary.java:513)
	at com.sun.jna.NativeLibrary.getFunction(NativeLibrary.java:499)
	at com.sun.jna.Library$Handler.invoke(Library.java:199)
	at com.sun.proxy.$Proxy0.test(Unknown Source)
	at com.supermicro.ssm.common.jna.Tester.main(Tester.java:15)