RFR: JDK-8225056 VM support for sealed classes
Harold Seigel
harold.seigel at oracle.com
Tue May 19 16:46:21 UTC 2020
I think that's a good idea.
Thanks, Harold
On 5/19/2020 11:49 AM, serguei.spitsyn at oracle.com wrote:
> Hi Harold and David,
>
> Just one comment.
> We could save on the CSR's for:
> make/data/jdwp/jdwp.spec
> || src/jdk.jdi/share/classes/com/sun/jdi/VirtualMachine.java
> ||
> src/java.instrument/share/classes/java/lang/instrument/Instrumentation.java
>
> As we discussed with David, it could make sense to remove duplication
> in the Serviceability class redefinition and retransformation specs.
> I'd suggest something like this webrev:
> http://cr.openjdk.java.net/~sspitsyn/webrevs/2020/redef-spec-dedup.1/
>
> If the direction looks okay then I could file RFE+CSR (and post an RFR).
>
> Thanks,
> Serguei
>
>
> On 5/18/20 22:26, David Holmes wrote:
>> Hi Harold,
>>
>> Adding serviceability-dev for the serviceability related changes.
>>
>> Nit: "VM support for sealed classes"
>>
>> This RFR covers the VM, core-libs, serviceability and even some
>> langtools tests. AFAICS only the javac changes are not included here
>> so when and where will they be reviewed and under what bug id?
>> Ideally there will be a single JBS issue for "Implementation of JEP
>> 360: Sealed types". It's okay to break up the RFRs across different
>> areas, but it should be done under one bug id.
>>
>> Overall this looks good. I've looked at all files and mainly have
>> some style nits in various places. But there are some more
>> significant items below.
>>
>> On 14/05/2020 7:09 am, Harold Seigel wrote:
>>> Hi,
>>>
>>> Please review this patch for JVM and Core-libs support for the JEP
>>> 360 Sealed Classes preview feature. Code changes include the
>>> following:
>>>
>>> * Processing of the new PermittedSubclasses attribute to enforce that
>>> a class or interface, whose super is a sealed class or interface,
>>> must be listed in the super's PermittedSubclasses attribute.
>>> * Disallow redefinition of a sealed class or interface if its
>>> redefinition would change its PermittedSubclasses attribute.
>>> * Support API's to determine if a class or interface is sealed
>>> and, if
>>> it's sealed, return a list of its permitted subclasses.
>>> * asm support for the PermittedSubclasses attribute
>>
>> I assume Remi is providing the upstream support in ASM? :) But also
>> see below ...
>>
>>>
>>> Open Webrev:
>>> http://cr.openjdk.java.net/~vromero/8225056/webrev.00/index.html
>>
>> make/data/jdwp/jdwp.spec
>>
>> There needs to be a sub-task and associated CSR request for this JDWP
>> spec update. I couldn't see this covered anywhere.
>>
>> ---
>>
>> src/hotspot/share/classfile/classFileParser.cpp
>>
>> 3215 u2
>> ClassFileParser::parse_classfile_permitted_subclasses_attribute(const
>> ClassFileStream* const cfs,
>> 3216 const u1* const permitted_subclasses_attribute_start,
>> 3217 TRAPS) {
>>
>> Indention on L3216/17 needs fixing after the copy'n'edit.
>>
>> 3515 return _major_version == JVM_CLASSFILE_MAJOR_VERSION &&
>> 3516 _minor_version == JAVA_PREVIEW_MINOR_VERSION &&
>> 3517 Arguments::enable_preview();
>>
>> Too much indentation on L3516/17
>>
>> 3790 // Check for PermittedSubclasses tag
>>
>> That comment (copied from my nestmates code :) is in the wrong place.
>> It needs to be before
>>
>> 3788 if (tag == vmSymbols::tag_permitted_subclasses()) {
>>
>>
>> Minor nit: I would suggest checking
>> parsed_permitted_subclasses_attribute before checking ACC_FINAL.
>>
>> 3876 if (parsed_permitted_subclasses_attribute) {
>> 3877 const u2 num_of_subclasses =
>> parse_classfile_permitted_subclasses_attribute(
>> 3878 cfs,
>> 3879 permitted_subclasses_attribute_start,
>> 3880 CHECK);
>>
>> Although it looks odd the preceding, similarly shaped, sections all
>> indent to the same absolute position. Can you make L3878/78/80 match
>> please.
>>
>> 3882 guarantee_property(
>> 3883 permitted_subclasses_attribute_length ==
>> 3884 sizeof(num_of_subclasses) + sizeof(u2) *
>> num_of_subclasses,
>> 3885 "Wrong PermittedSubclasses attribute length in class
>> file %s", CHECK);
>>
>> Nits: please reformat as:
>>
>> 3882 guarantee_property(
>> 3883 permitted_subclasses_attribute_length ==
>> sizeof(num_of_subclasses) + sizeof(u2) * num_of_subclasses,
>> 3885 "Wrong PermittedSubclasses attribute length in class
>> file %s", CHECK);
>>
>> It would also look slightly better if you shortened the name of the
>> num_of_subclasses variable.
>>
>> ---
>>
>> src/hotspot/share/classfile/classFileParser.hpp
>>
>> + u2 parse_classfile_permitted_subclasses_attribute(const
>> ClassFileStream* const cfs,
>> + const u1* const
>> permitted_subclasses_attribute_start,
>> + TRAPS);
>>
>> Please fix indentation after copy'n'edit.
>>
>> ---
>>
>> src/hotspot/share/oops/instanceKlass.cpp
>>
>> 247 if (classloader1 != classloader2) {
>>
>> I'm not clear what rule this is verifying. The same module check
>> follows this one. The rule is that the subclass must be accessible to
>> the superclass implying:
>> 1. same named module (regardless of class access modifiers); or
>> 2. (implicitly in un-named module) same package if subclass not
>> public; or
>> 3. public subclass
>>
>> Having the same classloader implies same package, but that alone
>> doesn't address 2 or 3. So this doesn't conform to proposed JVMS rules.
>>
>>
>> 264 if (_constants->tag_at(cp_index).is_klass()) {
>> 265 Klass* k2 = _constants->klass_at(cp_index, CHECK_false);
>>
>> You've copied this code from the nestmember checks but your changes
>> don't quite make sense to me. If we have already checked is_klass()
>> then klass_at() cannot lead to any exceptions.
>>
>> 272 if (name == k->name()) {
>> 273 log_trace(class, sealed)("- Found it at
>> permitted_subclasses[%d] => cp[%d]", i, cp_index);
>> 274 return true;
>>
>> I was wondering why you don't resolve the cp entry when you find the
>> name matches, as we do for nest members, but realized that unlike the
>> nest membership check, which can happen many times for a given class,
>> this permitted subclass check can only happen once per class. As you
>> don't actually resolve here, and given that the earlier check cannot
>> throw exceptions, it follows that the entire method never results in
>> any exceptions and so callers should not be using the CHECK macro.
>>
>> ---
>>
>> src/hotspot/share/oops/method.cpp
>>
>> I don't understand how knowing the class is sealed allows you to
>> infer that a non-final method is actually final ??
>>
>> ---
>>
>> src/hotspot/share/prims/jvm.cpp
>>
>> It would be simpler (and cheaper) if the Java side of this ensures it
>> doesn't call into the VM with an array or primitive class.
>>
>> ---
>>
>> src/hotspot/share/prims/jvmti.xml
>>
>> The JVM TI spec changes also need to be covered by a CSR request.
>>
>> ---
>>
>> src/hotspot/share/prims/jvmtiRedefineClasses.cpp
>>
>> We should file a RFE to refactor the logic that checks that an
>> attribute consisting of a list of classes has not changed. :)
>>
>> Aside: I spotted a bug in the nest member code (missing NULL check!)
>> thanks to your change :)
>>
>> ---
>>
>> src/java.base/share/classes/java/lang/Class.java
>>
>> There needs to be a CSR request for these changes.
>>
>> + * Returns an array containing {@code ClassDesc} objects
>> representing all the
>> + * permitted subclasses of this {@linkplain Class} if it is
>> sealed. Returns an empty array if this
>> + * {@linkplain Class} is not sealed.
>>
>> should add "or this class represents an array or primitive type"
>> (using the standard wording for such cases).
>>
>> + * @throws IllegalArgumentException if a class descriptor is
>> not in the correct format
>>
>> IllegalArgumentException is not an appropriate exception to use as
>> this method takes no arguments. If the class descriptor is not valid
>> and it comes from the VM then I think we have a problem with how the
>> VM validates class descriptors. Any IAE from ClassDesc.of should be
>> caught and converted to a more suitable exception type - preferably
>> InternalError if the VM should always return valid strings.
>>
>> + public ClassDesc[] getPermittedSubclasses() {
>>
>> As mentioned for jvm.cpp this Java code should do the isArray() and
>> isPrimitive() check before calling the VM.
>>
>> + String[] descriptors = getPermittedSubclasses0();
>>
>> Nit: what you get from the VM are not descriptors, just name strings
>> in internal form. This wouldn't really matter except it then looks
>> strange to call ClassDesc.of(...) instead of
>> ClassDesc.ofDescriptor(...).
>>
>> + if (descriptors == null
>>
>> The VM never returns null.
>>
>> + return getPermittedSubclasses().length != 0;
>>
>> It's grossly inefficient to create the ClassDesc array and then throw
>> it away IMO. The result should be cached either in a field of Class
>> or in the ReflectionData of the class.
>>
>> ---
>>
>> src/java.base/share/classes/jdk/internal/org/objectweb/asm/ClassReader.java
>>
>>
>> ! // - The offset of the PermittedSubclasses attribute, or 0
>> int permittedSubtypesOffset = 0;
>>
>> Obviously ASM already has some prelim support for sealed classes, but
>> now that the attribute has been renamed that should also flow through
>> to the ASM code ie the variable, not just the comment.
>>
>> Ditto for ClassWriter.java and its fields.
>>
>> ---
>>
>> src/java.base/share/native/libjava/Class.c
>>
>> {"isRecord0", "()Z", (void *)&JVM_IsRecord},
>> + {"getPermittedSubclasses0", "()[" STR, (void
>> *)&JVM_GetPermittedSubclasses},
>>
>> please align (void
>>
>> ---
>>
>> src/java.instrument/share/classes/java/lang/instrument/Instrumentation.java
>>
>> src/jdk.jdi/share/classes/com/sun/jdi/VirtualMachine.java
>>
>> There needs to be a CSR for these changes too.
>>
>> ---
>>
>> test/langtools/tools/javac/processing/model/TestSourceVersion.java
>>
>> ! // Assume "record" and "sealed" will be
>> restricted keywords.
>> ! "record", "sealed");
>>
>> What about the non-sealed keyword defined in the JEP?
>>
>> ---
>>
>> In the tests you don't need to explicitly include
>> sun.hotspot.WhiteBox$WhiteBoxPermission on the ClassFileInstaller
>> invocation. (previous RFE's have been removing existing occurrences
>> after the CFI was fixed to handle it internally).
>>
>> Please ensure all new tests have an @bug 8225056 (or whatever the
>> actual JBS issue will be)
>>
>> All test classes (and thus files) should be named in camel-case i.e.
>> C1 not c1, C2 not c2, SuperClass not superClass etc.
>>
>>
>> test/hotspot/jtreg/runtime/modules/sealedP1/superClass.jcod
>> test/hotspot/jtreg/runtime/sealedClasses/Pkg/sealedInterface.jcod
>>
>> Please add comments clarifying why these must be jcod files.
>>
>> ---
>>
>> That's it from me.
>>
>> Thanks,
>> David
>> -----
>>
>>
>>
>>> JBS bug: https://bugs.openjdk.java.net/browse/JDK-8225056
>>>
>>> Java Language Spec changes:
>>> http://cr.openjdk.java.net/~gbierman/jep360/jep360-20200513/specs/sealed-classes-jls.html
>>>
>>>
>>> JVM Spec changes:
>>> http://cr.openjdk.java.net/~gbierman/jep360/jep360-20200513/specs/sealed-classes-jvms.html
>>>
>>>
>>> JEP 360: https://bugs.openjdk.java.net/browse/JDK-8227043
>>>
>>> JVM CSR: https://bugs.openjdk.java.net/browse/JDK-8242578
>>>
>>> Changes to javac and other language tools will be reviewed separately.
>>>
>>> Thanks, Harold
>>>
>>>
>
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