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

Vladimir Ivanov vladimir.x.ivanov at oracle.com
Fri May 4 07:01:49 UTC 2018

> http://cr.openjdk.java.net/~dholmes/8197915/webrev.v2/
> Changes:
> - DirectMethodHandles.java: new simple and direct approach to dealing 

I like how java.lang.invoke part shapes out!

Maybe rename adaptToSpecialIfc to needsReceiverCheck? That's what 
confused me in the first version: though it's an interface call (which 
always require receiver check against REFC), new checks only referred to 
  LF_INVSPECIAL (since invocation mode is a direct call).

> - New regression test for the final virtual call from an interface bug 
> introduced by 8200167.
> 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.

Best regards,
Vladimir Ivanov

> Thanks,
> David
> 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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