RFR: 8342303: Segfault in update_inherited_vtable: AppCDS, old bytecode, and redefineClasses

[Calvin Cheung]

On Tue, 29 Oct 2024 10:00:56 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> A simple fix to avoid referencing invalid vtable and itable entires in `InstanceKlass::restore_unshareable_info` if a class is not linked during CDS dump time.
>> 
>> Passed tiers 1 - 4 testing.
>> 
>> ---------
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>
> test/hotspot/jtreg/runtime/cds/appcds/jvmti/redefineClasses/OldClassAndRedefineClassApp.java line 34:
> 
>> 32:         System.out.println("Main: loading OldSuper");
>> 33:         // Load an old class (version 49), but not linking it.
>> 34:         Thread.currentThread().getContextClassLoader().loadClass("OldSuper");
> 
> Why the context classloader? Has it been set in this test?

In this case, the `getContextClassLoader()` is default to the AppClassLoader.
I added some println in the test:

        System.out.println("    ClassLoader " + Thread.currentThread().getContextClassLoader());
        Class superCls = Thread.currentThread().getContextClassLoader().loadClass("OldSuper");
        System.out.println("OldSuper>> loader = " + superCls.getClassLoader());


below is the output:

    ClassLoader jdk.internal.loader.ClassLoaders$AppClassLoader at 5451c3a8
OldSuper>> loader = jdk.internal.loader.ClassLoaders$AppClassLoader at 5451c3a8

If the class is in the boot class path, then the class should be loaded by the boot class loader.

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PR Review Comment: https://git.openjdk.org/jdk/pull/21667#discussion_r1821536499