Test source T.java:

public class T {
  public static void main(String args[]) {}
}


This works:
$ javac -J-showversion --add-exports jdk.unsupported/sun.misc=ALL-UNNAMED T.java
java version "9-ea"
Java(TM) SE Runtime Environment (build 9-ea+139)
Java HotSpot(TM) 64-Bit Server VM (build 9-ea+139, mixed mode)

But this gives a misleading error message:
$ javac -J-showversion --add-exports foobar/sun.misc=ALL-UNNAMED T.java
java version "9-ea"
Java(TM) SE Runtime Environment (build 9-ea+139)
Java HotSpot(TM) 64-Bit Server VM (build 9-ea+139, mixed mode)

error: module reads package sun.misc from both jdk.unsupported and foobar
1 error

In comparison, the "java" tool gives an error message that's more meaningful:

$ java -showversion --add-exports jdk.unsupported/sun.misc=ALL-UNNAMED T
java version "9-ea"
Java(TM) SE Runtime Environment (build 9-ea+139)
Java HotSpot(TM) 64-Bit Server VM (build 9-ea+139, mixed mode)


$ java -showversion --add-exports foobar/sun.misc=ALL-UNNAMED T
Error occurred during initialization of VM
java.lang.RuntimeException: Unknown module: foobar
at jdk.internal.module.ModuleBootstrap.fail(java.base@9-ea/ModuleBootstrap.java:566)
at jdk.internal.module.ModuleBootstrap.addExtraExports(java.base@9-ea/ModuleBootstrap.java:480)
at jdk.internal.module.ModuleBootstrap.boot(java.base@9-ea/ModuleBootstrap.java:319)
at java.lang.System.initPhase2(java.base@9-ea/System.java:1927)