Review Request: 8238358: Implementation of JEP 371: Hidden Classes

Mon Mar 30 15:02:02 UTC 2020

Hi,  This is great work!  I did a prereview and all of my comments were 
addressed.  These are a few minor things I noticed.

http://cr.openjdk.java.net/~mchung/valhalla/webrevs/hidden-classes/webrev.03/src/hotspot/share/ci/ciInstanceKlass.hpp.udiff.html

Nit. Can you add 'const' to the is_hidden accessor?

http://cr.openjdk.java.net/~mchung/valhalla/webrevs/hidden-classes/webrev.03/src/hotspot/share/classfile/classFileParser.cpp.udiff.html

+ ID annotation_index(const ClassLoaderData* loader_data, const Symbol* 
name, const bool can_access_vm_annotations);

'const' bool is weird and unnecessary.  Can you remove const here?

+ if (is_hidden()) { // Mark methods in hidden classes as 'hidden'.
+ m->set_hidden(true);
+ }
+

Could be:

+ // Mark methods in hidden classes as 'hidden'.
+ m->set_hidden(is_hidden());
+

http://cr.openjdk.java.net/~mchung/valhalla/webrevs/hidden-classes/webrev.03/src/hotspot/share/classfile/javaClasses.cpp.udiff.html

+ macro(_classData_offset, k, "classData", object_signature, false); \

Probably should remove trailing backslash here.

http://cr.openjdk.java.net/~mchung/valhalla/webrevs/hidden-classes/webrev.03/src/hotspot/share/classfile/systemDictionary.cpp.udiff.html

I think in a future RFE, we should add a default parameter to 
register_loader to make the code in the beginning of parse_stream() 
cleaner and remove has_class_mirror_holder_cld().

http://cr.openjdk.java.net/~mchung/valhalla/webrevs/hidden-classes/webrev.03/src/hotspot/share/prims/jvm.cpp.udiff.html

+ jboolean is_nestmate = (flags & NESTMATE) == NESTMATE;
+ jboolean is_hidden = (flags & HIDDEN_CLASS) == HIDDEN_CLASS;
+ jboolean is_strong = (flags & STRONG_LOADER_LINK) == STRONG_LOADER_LINK;
+ jboolean vm_annotations = (flags & ACCESS_VM_ANNOTATIONS) == 
ACCESS_VM_ANNOTATION

Instead of jboolean, please use C++ bool here.

+ oop loader = lookup_k->class_loader();
+ Handle class_loader (THREAD, loader);

Can you rewrite as this to prevent potential unhandled oop for oop loader.

+ Handle class_loader (THREAD, lookup_k->class_loader());

Here:

+ InstanceKlass::cast(defined_k)->class_loader_data()->dec_keep_alive();

Don't have to cast defined_k to get class_loader_data(), but you 
probably just want to move this up to remove the rest of the 
InstanceKlass::cast().

+ InstanceKlass* ik = InstanceKlass::cast(defined_k);

http://cr.openjdk.java.net/~mchung/valhalla/webrevs/hidden-classes/webrev.03/src/hotspot/share/runtime/vmStructs.cpp.udiff.html 
http://cr.openjdk.java.net/~mchung/valhalla/webrevs/hidden-classes/webrev.03/src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/classfile/ClassLoaderData.java.udiff.html

We agreed already that these changes aren't needed by the SA.  You can 
revert these.

These are minor changes.  I don't need to see another webrev.

Thanks,
Coleen

On 3/26/20 7:57 PM, Mandy Chung wrote:
> Please review the implementation of JEP 371: Hidden Classes. The main 
> changes are in core-libs and hotspot runtime area. Small changes are 
> made in javac, VM compiler (intrinsification of Class::isHiddenClass), 
> JFR, JDI, and jcmd.  CSR [1]has been reviewed and is in the finalized 
> state (see specdiff and javadoc below for reference).
>
> Webrev:
> http://cr.openjdk.java.net/~mchung/valhalla/webrevs/hidden-classes/webrev.03
>
> Hidden class is created via `Lookup::defineHiddenClass`. From JVM's point
> of view, a hidden class is a normal class except the following:
>
> - A hidden class has no initiating class loader and is not registered 
> in any dictionary.
> - A hidden class has a name containing an illegal character 
> `Class::getName` returns `p.Foo/0x1234` whereas `GetClassSignature` 
> returns "Lp/Foo.0x1234;".
> - A hidden class is not modifiable, i.e. cannot be redefined or 
> retransformed. JVM TI IsModifableClass returns false on a hidden.
> - Final fields in a hidden class is "final".  The value of final 
> fields cannot be overriden via reflection.  setAccessible(true) can 
> still be called on reflected objects representing final fields in a 
> hidden class and its access check will be suppressed but only have 
> read-access (i.e. can do Field::getXXX but not setXXX).
>
> Brief summary of this patch:
>
> 1. A new Lookup::defineHiddenClass method is the API to create a 
> hidden class.
> 2. A new Lookup.ClassOption enum class defines NESTMATE and STRONG 
> option that
>    can be specified when creating a hidden class.
> 3. A new Class::isHiddenClass method tests if a class is a hidden class.
> 4. Field::setXXX method will throw IAE on a final field of a hidden class
>    regardless of the value of the accessible flag.
> 5. JVM_LookupDefineClass is the new JVM entry point for 
> Lookup::defineClass
>    and defineHiddenClass to create a class from the given bytes.
> 6. ClassLoaderData implementation is not changed.  There is one 
> primary CLD
>    that holds the classes strongly referenced by its defining loader.  
> There
>    can be zero or more additional CLDs - one per weak class.
> 7. Nest host determination is updated per revised JVMS 5.4.4. Access 
> control
>    check no longer throws LinkageError but instead it will throw IAE with
>    a clear message if a class fails to resolve/validate the nest host 
> declared
>    in NestHost/NestMembers attribute.
> 8. JFR, jcmd, JDI are updated to support hidden classes.
> 9. update javac LambdaToMethod as lambda proxy starts using nestmates
>    and generate a bridge method to desuger a method reference to a 
> protected
>    method in its supertype in a different package
>
> This patch also updates StringConcatFactory, LambdaMetaFactory, and 
> LambdaForms
> to use hidden classes.  The webrev includes changes in nashorn to 
> hidden class
> and I will update the webrev if JEP 372 removes it any time soon.
>
> We uncovered a bug in Lookup::defineClass spec throws LinkageError and 
> intends
> to have the newly created class linked.  However, the implementation in 14
> does not link the class.  A separate CSR [2] proposes to update the
> implementation to match the spec.  This patch fixes the implementation.
>
> The spec update on JVM TI, JDI and Instrumentation will be done as
> a separate RFE [3].  This patch includes new tests for JVM TI and
> java.instrument that validates how the existing APIs work for hidden 
> classes.
>
> javadoc/specdiff
> http://cr.openjdk.java.net/~mchung/valhalla/webrevs/hidden-classes/api/
> http://cr.openjdk.java.net/~mchung/valhalla/webrevs/hidden-classes/specdiff/
>
> JVMS 5.4.4 change:
> http://cr.openjdk.java.net/~mchung/valhalla/webrevs/hidden-classes/Draft-JVMS-HiddenClasses.pdf
>
> CSR:
> https://bugs.openjdk.java.net/browse/JDK-8238359
>
> Thanks
> Mandy
> [1] https://bugs.openjdk.java.net/browse/JDK-8238359
> [2] https://bugs.openjdk.java.net/browse/JDK-8240338
> [3] https://bugs.openjdk.java.net/browse/JDK-8230502

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