RFR: 8200559: Java agents doing instrumentation need a means to define auxiliary classes [v2]

[Rafael Winterhalter]

On Fri, 16 Apr 2021 20:30:15 GMT, Rafael Winterhalter <winterhalter at openjdk.org> wrote:

>> To allow agents the definition of auxiliary classes, an API is needed to allow this. Currently, this is often achieved by using `sun.misc.Unsafe` or `jdk.internal.misc.Unsafe` ever since the `defineClass` method was removed from `sun.misc.Unsafe`.
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> Rafael Winterhalter has refreshed the contents of this pull request, and previous commits have been removed. Incremental views are not available. The pull request now contains one commit:
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>   8200559: Java agents doing instrumentation need a means to define auxiliary classes

Requiring such an API opens the module to anybody, though, punching a hole into the module boundary.

BB currently opens the jdk.internal.misc.Unsafe class to a module on a seperate class loader that is not reachable outside an agent, using Instrumentation. This also caters the need to inject utility classes from an agent before any class file transformer is triggered, to maintain a well-defined life-cycle.

Of course I'd prefer if there was a way to resolve a lookup from Instrumentation for a given class loader and for example a package-info class, however rendering the issue that packages might not exist (yet).

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PR Comment: https://git.openjdk.org/jdk/pull/3546#issuecomment-1910087337