RFR: 8200559: Java agents doing instrumentation need a means to define auxilary classes

[forax at univ-mlv.fr]

> De: "Rafael Winterhalter" <rafael.wth at gmail.com>
> À: "Remi Forax" <forax at univ-mlv.fr>
> Cc: "Rafael Winterhalter" <winterhalter at openjdk.java.net>, "core-libs-dev"
> <core-libs-dev at openjdk.java.net>, "serviceability-dev"
> <serviceability-dev at openjdk.java.net>
> Envoyé: Vendredi 16 Avril 2021 18:27:46
> Objet: Re: RFR: 8200559: Java agents doing instrumentation need a means to
> define auxilary classes

> Not by my understanding. A suitable lookup requires a loaded class for the
> package. A Java agent might however not provide a handle for a class that is
> not yet loaded. Or how would you suggest to approach this ?

yes, you need a witness class in the package you want to define a new class. 
Apart if you load classes in the unamed module, you can not load a class in a non existing package anyway (apart if you generate your own module-info), 
so you need at least a dummy class to define a package, so you can use it to get a Lookup. 

Rémi 

> Am Fr., 16. Apr. 2021 um 16:21 Uhr schrieb Remi Forax < [
> mailto:forax at univ-mlv.fr | forax at univ-mlv.fr ] >:

>> ----- Mail original -----
>>> De: "Rafael Winterhalter" < [ mailto:winterhalter at openjdk.java.net |
>> > winterhalter at openjdk.java.net ] >
>>> À: "core-libs-dev" < [ mailto:core-libs-dev at openjdk.java.net |
>>> core-libs-dev at openjdk.java.net ] >, "serviceability-dev" < [
>>> mailto:serviceability-dev at openjdk.java.net |
>> > serviceability-dev at openjdk.java.net ] >
>> > Envoyé: Vendredi 16 Avril 2021 15:52:07
>>> Objet: RFR: 8200559: Java agents doing instrumentation need a means to define
>> > auxilary classes

>> > 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`.

>> You can already use Lookup.defineClass() + privateLookupIn() +
>> Instrumentation.redefineModule() for that ?

>> Rémi


>> > -------------

>> > Commit messages:
>> > - 8200559: Java agents doing instrumentation need a means to define auxiliary
>> > classes

>>> Changes: [ https://git.openjdk.java.net/jdk/pull/3546/files |
>> > https://git.openjdk.java.net/jdk/pull/3546/files ]
>>> Webrev: [ https://webrevs.openjdk.java.net/?repo=jdk&pr=3546&range=00 |
>> > https://webrevs.openjdk.java.net/?repo=jdk&pr=3546&range=00 ]
>>> Issue: [ https://bugs.openjdk.java.net/browse/JDK-8200559 |
>> > https://bugs.openjdk.java.net/browse/JDK-8200559 ]
>> > Stats: 185 lines in 4 files changed: 185 ins; 0 del; 0 mod
>>> Patch: [ https://git.openjdk.java.net/jdk/pull/3546.diff |
>> > https://git.openjdk.java.net/jdk/pull/3546.diff ]
>>> Fetch: git fetch [ https://git.openjdk.java.net/jdk |
>> > https://git.openjdk.java.net/jdk ] pull/3546/head:pull/3546

>>> PR: [ https://git.openjdk.java.net/jdk/pull/3546 |
>> > https://git.openjdk.java.net/jdk/pull/3546 ]
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