RFR: 8369742 link aot linked classes at vm bootstrap

[Vladimir Kozlov]

On Tue, 14 Oct 2025 04:13:40 GMT, Ioi Lam <iklam at openjdk.org> wrote:

> **PROBLEM**
> 
> If we have an AOT-initialized class like this in java.base
> 
> 
> @AOTSafeClassInitializer
> class Foo {
>     static Bar b = new Bar(); // AOT-cached
>     static void doit() {
>         b.toString(); /// invokevirtual Bar::toString()Ljava/lang/String;
>     }
> }
> 
> 
> If `Foo.doit()` is called before `AOTLinkedClassBulkLoader::link_or_init_javabase_classe()`, it's possible for the `Bar` class to be not yet linked. The `invokevirtual` bytecode will crash because the vtable of the object `b` is not yet initialized.
> 
> **FIX**
> 
> Before we execute the first Java bytecode, unconditionally link all AOT-linked classes. This will ensure that the `Bar` class will have an initialized vtable for the above example.
> 
> **NOTES**
> 
> - The scenario in the  above example does not affect JDK 24, 25 or the current JDK mainline (26). We are lucky that in all the bytecode execution up to `AOTLinkedClassBulkLoader::link_or_init_javabase_classe()`, whenever we do a vtable/itable dispatch on an AOT-cached heap object, we happen to have already linked its class (either by explicit calls from the JVM, or as side effect of invokestatic/getstatic/putstatic/new). However, this is a potential problem that should be fixed. I have run into this problem when implementing [JDK-8368199](https://bugs.openjdk.org/browse/JDK-8368199), which changes the bytecodes that are executed in early VM bootstrap.
> - I had to enable `CDSConfig::is_preserving_verification_constraints()` to for the static CDS archive. The reason is to avoid class loading. Please see the new comments in `AOTLinkedClassBulkLoader::link_classes_in_table()`.
> - The change in `AdapterHandlerLibrary::create_native_wrapper` is for supporting JVMTI. The offending methods are `jdk.internal.vm.Continuation::enterSpecial` and `jdk.internal.vm.Continuation::doYield`. These are "continuation native intrinsic" methods that are usually linked much later after the ServiceThread have been started.

This assumes that `Foo.doit()` can be called before `Foo.<clinit>` class initialization when `static Bar b = new Bar();` is executed and `Bar` class is initialized. Which should not happened (call `doit()` before `<clinit>`) AFAIU. Do I miss something?

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PR Comment: https://git.openjdk.org/jdk/pull/27783#issuecomment-3402567420