IllegalAccessError when executing Java 9 modules after offline instrumentation

$ mkdir -p src/org/example

$ cat <<END > src/module-info.java
module org.example {
}
END

$ cat <<END > src/org/example/HelloWorld.java
package org.example;

class HelloWorld {
  public static void main(String[] args) {
    System.out.println("Hello, World");
  }
}
END

$ javac -d mods/org.example \
        src/module-info.java \
        src/org/example/HelloWorld.java

$ java -jar jacococli.jar \
       instrument mods/org.example/org \
       --dest mods-instrumented/org.example/org

$ java \
       -cp mods-instrumented/org.example:jacocoagent.jar \
       org.example.HelloWorld
Hello, World!

$ cp mods/org.example/module-info.class mods-instrumented/org.example

$ java --version
java 9-ea
Java(TM) SE Runtime Environment (build 9-ea+171)
Java HotSpot(TM) 64-Bit Server VM (build 9-ea+171, mixed mode)

$ java \
       --module-path mods-instrumented \
       -cp jacocoagent.jar \
       --module org.example/org.example.HelloWorld

leads to

Exception in thread "main" java.lang.IllegalAccessError: class org.example.HelloWorld (in module org.example) cannot access class org.jacoco.agent.rt.internal_c42d03f.Offline (in unnamed module @0x15975490) because module org.example does not read unnamed module @0x15975490
	at org.example/org.example.HelloWorld.$jacocoInit(HelloWorld.java)
	at org.example/org.example.HelloWorld.main(HelloWorld.java)

as well as

$ java \
       --module-path mods-instrumented \
       -javaagent:jacocoagent.jar=excludes=org.example.HelloWorld \
       --module org.example/org.example.HelloWorld

According to http://openjdk.java.net/projects/jigsaw/

The module system was merged into JDK 9 build 111 in March 2016

and this error is reproducible with all builds down to 111.

Workaround

Use --add-reads:

$ java \
       --module-path mods-instrumented \
       -cp jacocoagent.jar \
       --add-reads org.example=ALL-UNNAMED \
       --module org.example/org.example.HelloWorld

$ java \
       --module-path mods-instrumented:jacocoagent.jar \
       --add-modules jacocoagent \
       --add-reads org.example=jacocoagent \
       --module org.example/org.example.HelloWorld

Start with the module-info.java and HelloWorld.java reproduction, then run the jacococli.jar offline instrumentation and modular java commands shown in the issue. Compare the failing offline and javaagent paths, including the --add-reads workaround. Done means the instrumented Java 9 module runs without IllegalAccessError or requiring that workaround.