Accessing module internals from bytecode rewriting agent

[Alan Bateman]

On 14/06/2017 00:57, Jeremy Manson wrote:
> Hey folks,
>
> As a followup to this, given everything else that has happened in the mean
> time: I wonder if the same logic Mark put in his proposal to allow illegal
> access to internal APIs (
> http://mail.openjdk.java.net/pipermail/jigsaw-dev/2017-June/012841.html) in
> JDK 9 also applies to Xbootclasspath/p.
>
> Mark's stated goal in his revised proposal is to address concerns that code
> that works on JDK 8 today will not work on JDK 9 tomorrow, yet no advance
> warning of this change was given at run time in JDK 8.  No advance warning
> was given for the removal of -Xbootclasspath/p, and, without it, there will
> need to be a lot of fiddly logic in a lot of scripting languages to allow
> for testing to switch between Java 8 and Java 9.
>
> Dalibor's previous response of "-X options are subject to change" is
> probably not relevant, given the fact that everything that is being done
> via access to internal APIs is subject to change, and Mark's proposal is
> probably the way Java 9 will be rolled out.
>
> There are plenty of XX flags that aren't removed without warning, too:
> -XX:+UseConcMarkSweepGC is going to spend an entire release cycle
> deprecated.
>
> Would it make sense to make -Xbootclasspath/p available again, possibly
> only if the kill switch is enabled?
>
There is no proposal to bring back the unsupported -Xbootclasspath/p. 
That option was for overriding classes defined to the boot loader, 
something that doesn't make sense with JDK 9 where the boot class path 
is mostly gone and where many of the APIs that could potentially be 
patched via -Xbootclasspath/p are not defined to the boot loader 
anymore. As Remi note, the option to look at is -patch-module option, 
the details are in JEP 261 [1].

As regards --illegal-access then there is no connection. That proposal 
just opens the packages that existed in JDK 8 to allow code that hacks 
JDK internals (with core reflection mostly) to continue to work for a 
bit longer. It doesn't change anything else.

-Alan.

[1] http://openjdk.java.net/jeps/261