[Nestmates] RFR (S): 8197915: [Nestmates] Implement receiver typecheck for private invokeinterface use

Vladimir Ivanov vladimir.x.ivanov at oracle.com
Fri May 4 07:57:44 UTC 2018

>>> If necessary/desirable I can fix that part in mainline separately. So 
>>> far no tests (including jck/API/java/lang) seem to tickle it.
>> Or file a bug. I have some ideas how to improve relevant code and make 
>> LF construction cleaner.
> I'll either fix in mainline or else just wait for nestmates to integrate 
> in a few weeks. I'd like to avoid any other code disruption in this area 
> until after that. :)

I'm fine with taking care of that after nestmates land in mainline.

No plans to cause you additional headaches with merging code changes :-)

Best regards,
Vladimir Ivanov

>>> On 4/05/2018 11:41 AM, David Holmes wrote:
>>>> Hi Karen,
>>>> On 4/05/2018 6:39 AM, Karen Kinnear wrote:
>>>>> David,
>>>>> Really delighted to see you near the end of the major functional 
>>>>> changes!
>>>> Thanks for taking a look so quickly!
>>>>> A couple minor comments, and then a question please:
>>>>> 1. MethodHandles.java
>>>> DirectMethodHandle.java :)
>>>>>   174 different “to” -> different “from” ?
>>>> Changed. That's my UK upbringing :)
>>>> https://en.oxforddictionaries.com/usage/different-from-than-or-to
>>>>> 2. methodHandles.cpp
>>>>>    300-301
>>>>>    Thank you for the comment.
>>>>>    Might it also be worth adding that direct call is used by:
>>>>>      invoke static, invokespecial, invokeinterface:local private, 
>>>>> invoke virtual:vfinal and private methods
>>>>>    (or are you concerned about getting out of sync if this changes?)
>>>> It is not used by invokestatic. I'm not 100% sure of all the exact 
>>>> cases where an invokeinterface/invokevirtual becomes a direct call, 
>>>> so didn't want to say anything inaccurate. But the comment as it 
>>>> stands is awkward so I've expanded it:
>>>>        // "special" reflects that this is a direct call, not that it
>>>>        // necessarily originates from an invokespecial. We can also do
>>>>        // direct calls for private and/or final non-static methods.
>>>>> 3. DirectMethodHandle.java - this was subtle!
>>>> More than you realise ;-)
>>>>> I believe this is correct assuming that:
>>>>>    CallerClass is always and only set for invokespecial. Is this 
>>>>> accurate? Could you possibly add a comment?
>>>> That's an excellent question and one that should have been asked 
>>>> before 8200167 was finalized. :(  The short answer is "no" - 
>>>> callerClass can be non-null for any of the invocation modes. And yes 
>>>> the current mainline code is broken - seems there is a gap in the 
>>>> existing test coverage as we never call a final method from an 
>>>> interface method. If we do we get:
>>>> Exception in thread "main" java.lang.InternalError: Should only be 
>>>> invoked on a subclass
>>>>          at 
>>>> java.base/java.lang.invoke.DirectMethodHandle.checkReceiver(DirectMethodHandle.java:441) 
>>>> <sigh>
>>>> We only look at callerClass when dealing with LF_INVSPECIAL, which 
>>>> in mainline means we either have an invokespecial or an 
>>>> invokevirtual. For invokespecial this is fine of course. But the 
>>>> invokevirtual case was never encountered and so slipped by in error. 
>>>> With nestmates we also add invokeinterface to the mix - which is 
>>>> fine because if it is an invokeinterface then we want the check 
>>>> regardless. It doesn't matter if the check is enabled because of the 
>>>> (incidental) callerClass.isInterface check, or the explicit 
>>>> m.getDeclaringClass().isInterface(). But the logic is messy and far 
>>>> from clear and not correct by construction. So I will completely 
>>>> redo it in a simpler and more direct/explicit way.
>>>> BTW another red-herring: the !m.isStatic() part of the condition was 
>>>> not needed. I was tracking down two failure modes before finalizing 
>>>> this. The first was a problem with a static interface method - fixed 
>>>> by the !m.isStatic(). The second was caused by missing parentheses 
>>>> in the overall condition - which once fixed precluded the static 
>>>> case, so the first fix was not needed (as we never use LF_INVSPECIAL 
>>>> with statics). If only I'd tackled them in the reverse order.
>>>> I'll post an updated webrev later today once I've re-tested lots of 
>>>> things.
>>>>>     - agree with the theory that invokevirtual will never find a 
>>>>> private interface method (and ACC_FINAL is illegal for interfaces)
>>>> Yes. More specifically as we're dealing with MH semantics: 
>>>> findVirtual for an interface method yields a MH with invokeInterface 
>>>> "kind", not one with invokeVirtual "kind".
>>>> public MethodHandle findVirtual(Class<?> refc, String name, 
>>>> MethodType type) throws NoSuchMethodException, IllegalAccessException {
>>>> ...
>>>>      byte refKind = (refc.isInterface() ? REF_invokeInterface : 
>>>> REF_invokeVirtual);
>>>> ...
>>>> }
>>>>> 4. Test - I still need to study this
>>>>> I have been writing down test cases to make sure we don’t test 
>>>>> cases we don’t want to, and I
>>>>> need to double-check you have them covered. Will do that tomorrow.
>>>> The testing is all "positive" in the sense that it ensures a 
>>>> receiver subtype check is in place when it "must be". In fact it 
>>>> must always be the case the receiver has a type that has the method 
>>>> being invoked. We were just missing a few cases that verified that 
>>>> (and some stronger conditions: ie receiver <: caller for 
>>>> invokespecial semantics).
>>>> If you want to test that we don't insert the new explicit checks in 
>>>> cases where they are not needed, then I don't know how to do that - 
>>>> other than by adding tracing and running the test case and not 
>>>> seeing checkReceiver being called.
>>>> That said, once I've reworked the logic it will be blindingly 
>>>> obvious when the new explicit check is being added.
>>>> Thanks,
>>>> David
>>>>> thanks,
>>>>> Karen
>>>>>> On May 3, 2018, at 6:21 AM, David Holmes <david.holmes at oracle.com> 
>>>>>> wrote:
>>>>>> bug id: https://bugs.openjdk.java.net/browse/JDK-8197915
>>>>>> webrev: http://cr.openjdk.java.net/~dholmes/8197915/webrev/
>>>>>> JDK-8174962 implemented receiver typechecks for invokeinterface 
>>>>>> within the interpreter (templateTable), compilers and for 
>>>>>> MethodHandles. In nestmates invokeinterface can now be used for 
>>>>>> private interface methods - which result in direct calls. So we 
>>>>>> need to extend the receiver subtype checks to cover the new cases.
>>>>>> Summary of changes:
>>>>>> - src/hotspot/cpu/<cpu>/templateTable_<cpu>.cpp
>>>>>> In the templateTable the 8174962 checks come after the private 
>>>>>> interface method invocation logic ("vfinal") we already had in 
>>>>>> place for the nestmate changes, and they rely on itable 
>>>>>> information that doesn't exist for private methods. So we insert a 
>>>>>> direct subtype check.
>>>>>> I've provided code for all CPU's but only x86 and sparc have been 
>>>>>> tested. I'll be soliciting aid on the other ports before nestmates 
>>>>>> goes to mainline later this month.
>>>>>> -  src/hotspot/share/oops/cpCache.cpp
>>>>>> We have to pass the interface klass* so it's available for the 
>>>>>> typecheck.
>>>>>> -  src/hotspot/share/oops/klassVtable.cpp
>>>>>> Updated a comment that's no longer accurate.
>>>>>> - src/hotspot/share/opto/doCall.cpp
>>>>>> This code was provided by Vladimir Ivanov (thank you!) and expands 
>>>>>> the existing "invokespecial" support for receiver typechecks in 
>>>>>> C2, to "invokeinterface" as well.
>>>>>> Aside: no changes were needed for C1. It's seems all the receiver 
>>>>>> typechecks for C1 are being handled at a higher level (through 
>>>>>> linkResolver and/or cpCache logic).
>>>>>> - src/hotspot/share/prims/methodHandles.cpp
>>>>>> Comment clarifying JVM_REF_invokeSpecial doesn't necessarily mean 
>>>>>> it relates to an actual "invokespecial" - it is used for all 
>>>>>> direct calls.
>>>>>> - 
>>>>>> src/java.base/share/classes/java/lang/invoke/DirectMethodHandle.java
>>>>>> Add clarifying comments regarding how "kind" can vary if a direct 
>>>>>> call is involved.
>>>>>> Expand the condition to switch from LF_INVSPECIAL to 
>>>>>> LF_INVSPECIAL_IFC (which adds the additional receiver typecheck) 
>>>>>> to account for the invokeinterface case.
>>>>>> -  test/jdk/java/lang/invoke/PrivateInterfaceCall.java
>>>>>> New test for invokeinterface semantics that mirrors the existing 
>>>>>> SpecialInterfaceCall test for invokespecial.
>>>>>> This is the last of the significant functional changes for nestmates.
>>>>>> Thanks,
>>>>>> David

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