RFR: 8256640: assert(!m->is_old() || ik()->is_being_redefined()) failed: old methods should not be in vtable

[Daniel D.Daugherty]

On Thu, 19 Nov 2020 19:30:58 GMT, Lois Foltan <lfoltan at openjdk.org> wrote:

>> I added an assert with https://bugs.openjdk.java.net/browse/JDK-8256365 to catch adding redefined methods into the vtable where they don't belong (except while redefining that class).  The assert found that CDS was restoring classes with methods in the default_methods array which can be from a redefined class.  So these methods need to be adjusted before recreating the vtable.
>> Also fixed is a potential bug where a Method in a methodHandle in the default_methods array can be redefined in the safepoint caused by loader constraint checking, then added to the vtable.  The window for this bug is very small so I couldn't write a test for it. This change was in my v1 patch for JDK-8256365, so reintroduced here.
>> 
>> The test java/lang/instrument/IsModifiableClassAgent.java now passes with this patch.  Rerunning tier1-6 tests in progress.  Built with minimal VM to verify #if INCLUDE_JVMTIs were in the right places.
>
> src/hotspot/share/oops/klassVtable.cpp line 507:
> 
>> 505:         // Set the vtable index before the constraint check safepoint potentially
>> 506:         // redefines this method, which is possible if it is a default method belonging
>> 507:         // to a super class or interface.
> 
> Minor nit, wording is awkward.  Maybe:
> Set the vtable index before the constraint check safepoint, which potentially redefines this method if this method is a default method belonging to a super class or interface.

The suggested rewrite reads better.

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PR: https://git.openjdk.java.net/jdk/pull/1323