Integrated: 8317269: Store old classes in linked state in AOT cache

[Ioi Lam]

On Tue, 12 Aug 2025 23:55:19 GMT, Ioi Lam <iklam at openjdk.org> wrote:

> During the assembly phase of the AOT cache, we link and verify all classes that were loaded during the training run. When verifying a class like this:
> 
> 
> class X {
>     A getA() { return new B(); } // Verifier requires B to be a subtype of A.
> }
> 
> 
> We remember `A` and `B` as the "verification dependencies" of `X`. A class will be excluded from the AOT cache if any of its verification dependencies are excluded. For example, `X` will be excluded if
> 
> - `A` fails verification
> - `B` is a signed class, which is always excluded from the AOT cache
> 
> Conversely, if both `A` and `B`  are included in the AOT cache, in the production run, they will be unconditionally loaded during VM bootstrap. Therefore, we can guarantee that the verification result computed for `X` will remain valid during the production run.
> 
> Notes for reviewers:
> 
> - The checks for verification dependencies are done inside `SystemDictionaryShared::check_exclusion_for_self_and_dependencies()`. These checks are done for both old and new classes. Since the dependencies can form a cyclic graph, the checks cannot be implemented with a simple recursion. See "Algorithm notes" in this function for details. 
> - The verification dependencies for "new" classes are already stored in `DumpTimeClassInfo::_verifier_constraints`.
> - This PR adds code to record the verification dependencies for "old" classes into `DumpTimeClassInfo::_old_verifier_dependencies`, by intercepting `JVM_FindClassFromCaller()`.
> - This new functionality (store old classes in linked state) is available only when using the AOT cache. For simplicity, this functionality is not available with the old CDS workflows. See comments in `CDSConfig::is_preserving_verification_dependencies()`.

This pull request has now been integrated.

Changeset: 85715e10
Author:    Ioi Lam <iklam at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/85715e1050fa774c3267dbbe2f749717aeeec8ff
Stats:     1405 lines in 35 files changed: 1311 ins; 22 del; 72 mod

8317269: Store old classes in linked state in AOT cache

Reviewed-by: coleenp, matsaave

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PR: https://git.openjdk.org/jdk/pull/26754