Accessing module internals from bytecode rewriting agent

[Kirk Pepperdine]

Hi Alan,

One of the techniques that I’ve used in the past for troubleshooting is to prepend modified classes to the bootstrap class path. I fear all this mucking about with modularization is going to leave the road to diagnostics littered with a ton of tools that will not longer work. As it is, 8 broke all the techniques and tooling used to diagnose class loader leaks… without fixing the fundamental problems that caused them to leak in the first place..and added a new sources for performance regressions for which there is little in the way of tooling and certainly much less of an understanding of the fundamental issues out in the general developer population. The availability of high quality tooling is a huge bonus in the Java eco structure…. Please, don’t send us back to the Stone Age.

Kind regards,
Kirk Pepperdine

> On May 2, 2017, at 9:48 AM, Alan Bateman <Alan.Bateman at oracle.com> wrote:
> 
> On 02/05/2017 07:50, Jeremy Manson wrote:
>> :
>> 
>> If we follow this path, before we migrate to Java 9, we would need to make sure all of our code builds and the tests pass with Java 9 and Java 8.  We can't make all of the code build and the tests pass with Java 9 as-is, because many of them use options like Xbootclasspath, which have been dropped.  We can't migrate those tests to use the new command line flags before we migrate to Java 9, because if we do, they will stop working with Java 8.  Due to the size of our code base, it's pretty much impossible to migrate all of the users to a new set of command line flags at the same time as we migrate to Java 9.
> So I'm curious about -Xbootclasspath as that completely overrides the runtime classes. Is this static instrumentation or combining the VM/launcher from one build with the classes from a different JDK build? In any case, and as you have found, -Xbootclasspath  and -Xbootclasspath/p are meaningless now, a consequence of moving all the core APIs to modules. The -Xbootclasspath/a option works as before with the caveat that not all platform classes are visible to the boot class loader now (a consequence of ongoing security work to move non-core components away from the fully privileged boot loader).
> 
> It might be that you mean the `javac -bootclasspath,  this works as before when you target 8 or older.
> 
> -Alan
>