Hi Mandy,

A couple of very minor nits in the jvmtiRedefineClasses.cpp comments:

 153     // classes for primitives, arrays, hidden and vm unsafe anonymous classes  154     // cannot be redefined.  Check here so following code can assume these classes
 155     // are InstanceKlass.
 156     if (!is_modifiable_class(mirror)) {
 157       _res = JVMTI_ERROR_UNMODIFIABLE_CLASS;
 158       return false;
 159     }

I think this code and comment predate anonymous classes. Probably before anonymous classes the check was not for !is_modifiable_class() but instead was just a check for primitive or array class types since they are not an InstanceKlass, and would cause issues when cast to one in the code that lies below this section. When anonymous classes were added, the code got changed to use !is_modifiable_class() and the comment was not correctly updated (anonymous classes are an InstanceKlass). Then with this webrev the mention of hidden classes was added, also incorrectly implying they are not an InstanceKlass. I think you should just leave off the last sentence of the comment.

There's some ambiguity in the application of adjectives in the following:

 297   // Cannot redefine or retransform a hidden or an unsafe anonymous class.

I'd suggest:

 297   // Cannot redefine or retransform a hidden class or an unsafe anonymous class.

There are some places in libjdwp that need to be fixed. I spoke to Serguei about those this afternoon. Basically the convertSignatureToClassname() function needs to be fixed to handle hidden classes. Without the fix classname filtering will have problems if the filter contains a pattern with a '/' to filter on hidden classes. Also CLASS_UNLOAD events will not properly convert hidden class names. We also need tests for these cases. I think these are all things that can be addressed later.

I still need to look over the JVMTI tests.

thanks,

Chris

On 3/26/20 4:57 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


Reply via email to