RFR: 8361725: Do not load Java agent with "-Xshare:dump -XX:+AOTClassLinking"

[Ioi Lam]

On Fri, 18 Jul 2025 16:43:09 GMT, Calvin Cheung <ccheung at openjdk.org> wrote:

>> When `-XX:+AOTClassLinking` is enabled when dumping CDS archives with `java -Xshare:dump`, we have more stringent restriction of what Java code can be executed -- if arbitrary Java code is executed, it may produce side effects that cannot be handled when archiving Java heap objects. This usually leads to cdsHeapVerifier.cpp reporting suspicious references to static fields that are not known to be safe.
>> 
>> We already avoid loading Java agents when dumping AOT caches (which are just enhanced CDS archives with more optimizations), we should do the same thing for `java -Xshare:dump -XX:+AOTClassLinking`.
>> 
>> After this PR, we still allow Java agents for `java -Xshare:dump -XX:-AOTClassLinking`, as that is required by some CDS tests. In a subsequent RFE, we will fix these CDS tests so Java agents are always disabled for `java -Xshare:dump`. See [JDK-8362561](https://bugs.openjdk.org/browse/JDK-8362561)
>
> test/hotspot/jtreg/runtime/cds/appcds/aotCache/JavaAgentTransformer.java line 41:
> 
>> 39:         savedInstrumentation = instrumentation;
>> 40: 
>> 41:         LOGGER.log(Level.WARNING, "JavaAgentTransformer::premain() is finished");
> 
> Just curious why not use `Level.INFO` instead. Is it because the log won't be printed with product build if `Level.INFO` is used?

I copied this code from the original reproducer. If this code was executed inside the assembly phase, then we will get a CDSHeapVerifier error.

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PR Review Comment: https://git.openjdk.org/jdk/pull/26374#discussion_r2216943972