RFR: 8374639: Static archive with AOTClassLinking breaks dynamic archive

[Coleen Phillimore]

On Wed, 7 Jan 2026 06:10:58 GMT, Ioi Lam <iklam at openjdk.org> wrote:

> **Bug fix**
> 
> The assert happens because [JDK-8309240](https://bugs.openjdk.org/browse/JDK-8309240) (Array classes should be stored in dynamic CDS archive) is not compatible with `AOTClassLinking` since JDK 26.
> 
> Since the benefit of [JDK-8309240](https://bugs.openjdk.org/browse/JDK-8309240) is small (obj array classes can be quickly created at run time), we should remove [JDK-8309240](https://bugs.openjdk.org/browse/JDK-8309240).
> 
> **Background**
> 
> The incompatibility is caused by [JDK-8350550](https://bugs.openjdk.org/browse/JDK-8350550) (Preload classes from AOT cache during VM bootstrap) added in JDK 26.
> 
> [JDK-8309240](https://bugs.openjdk.org/browse/JDK-8309240) adds support for scenarios like this:
> 
> - class `Foo` is in the static archive, but `Foo[]` is not in the static archive
> - class `Foo[]` is in the dynamic archive
> 
> There's a pointer from the InstanceKlass of `Foo` to its array class `Foo[]` (`InstanceKlass::_array_klasses`). With [JDK-8309240](https://bugs.openjdk.org/browse/JDK-8309240), we update this pointer to point to `Foo[]` right after the CDS archives are mapped. This happens before `vmClasses::resolve_all()`:
> 
> https://github.com/openjdk/jdk/blob/dd20e9150666f247af61dfa524a170ef7dd96c03/src/hotspot/share/cds/aotMetaspace.cpp#L2162
> 
> With [JDK-8350550](https://bugs.openjdk.org/browse/JDK-8350550), if the static archive has AOT-linked classes, we will restore all of its classes inside `vmClasses::resolve_all()` -- see the callstack in the Description of [JDK-8374639](https://bugs.openjdk.org/browse/JDK-8374639).
> 
> The class restoration requires that all the classes (both instance classes and their array classes) must have a Java mirror. In this example, `Foo` is from the static archive and has an archived Java mirror, so we are OK. However, `Foo[]` is from the dynamic archive and doesn't have an archived mirror. Also, we are too early in the bootstrap process so we are unable to allocate a Java mirror from the heap yet. Hence the assert.

So for the static archive, there will still be InstanceKlass::_array_klasses saved, just not for dynamic archive?
This looks really good.  It is easy to recreate array classes on demand as they're needed.

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Marked as reviewed by coleenp (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/29078#pullrequestreview-3636683248