# Wednesday, 16 July 2014
Java Method Overriding Is FUBAR Part 10 of ∞

Yesterday's JDK 7u65 and 8u11 updates changed method overriding yet again and, of course, it is still broken.

Take this example:

package pkg1;

public class A {
  { foo(); }
  void foo() { System.out.println("A.foo"); }
}

package pkg2;

public class B extends pkg1.A {
  { foo(); }
  void foo() { System.out.println("B.foo"); }
}

package pkg1;

public class C extends pkg2.B {
  { foo(); }
  void foo() { System.out.println("C.foo"); }
}

package pkg2;

public class D extends pkg1.C {
  { foo(); }
  void foo() { System.out.println("D.foo"); }
}

public class test {
  public static void main(String[] args) {
    new pkg2.D();
  }
}

Running this with JDK 8u5 yields:

D.foo
D.foo
D.foo
D.foo

Which is, of course, wrong. In yesterday's updates they tried to fix this, but only partially succeeded:

D.foo
D.foo
C.foo
D.foo

The sensible output would be:

C.foo
D.foo
C.foo
D.foo

Wednesday, 16 July 2014 13:27:41 (W. Europe Daylight Time, UTC+02:00)  #    Comments [2]
Java Security Fixes

In Februari I reported two Java vulnerabilities to Oracle. Yesterday they released the update that fixed them, so here are the descriptions of the two issues.

@java.lang.invoke.LambdaForm.Compiled

Internally, the JDK uses the LambdaForm.Compiled annotation to mark methods that should be skipped in a security stack walk. In JDK 7 it was possible to apply this annotation to untrusted code. Here's an example:

import java.lang.annotation.*;

@Retention(RetentionPolicy.RUNTIME)
@interface java_lang_invoke_LambdaForm$Compiled { }

class test {
  @java_lang_invoke_LambdaForm$Compiled
  public static void main(String[] args) throws Throwable {
    System.out.println(Class.forName("sun.misc.Unsafe"));
  }
}

If you compile and run this with JDK 1.7.0_60 with a security manager, you get the appropriate AccessControlException. However, if you edit test.class to replace java_lang_invoke_LambdaForm with java/lang/invoke/LambdaForm and run it again, you see that the main method is now skipped in the security check and hence is allowed to access a privileged class.

The fix can be seen here.

MaxArityBug

This example demonstrates that the JDK 1.7.0_60 LambdaForm method handle implementation has a type safety bug when dealing with method signatures with the maximum number of parameters.

Wednesday, 16 July 2014 08:53:16 (W. Europe Daylight Time, UTC+02:00)  #    Comments [2]
# Sunday, 13 July 2014
Blog Update

I updated my ancient version of dasBlog. Please let me know if something isn't working properly.

Sunday, 13 July 2014 10:18:00 (W. Europe Daylight Time, UTC+02:00)  #    Comments [0]
# Friday, 11 July 2014
New Development Snapshot

Completed LambdaMetafactory intrinsification.

Changes:

  • Fixed several LambdaMetafactory.metafactory() intrinsic bug.
  • Implemented LambdaMetafactory.altMetafactory() intrinsic.
  • Include full class name of anonymous classes in stack trace.
  • Added method and field reflection support for lambda classes.

Binaries available here: ikvmbin-8.0.5305.zip

Friday, 11 July 2014 10:08:05 (W. Europe Daylight Time, UTC+02:00)  #    Comments [0]
# Wednesday, 02 July 2014
New Development Snapshot

I fixed a whole bunch of weird edge case behaviors and finally did the first part of the lambda performance work.

Here are some rough performance results (times in milliseconds) for this crude microbenchmark:

iteration IKVM 8.0.5274 IKVM 8.0.5296 JDK 1.8.0_05                     ikvmc ngen
1 1040.2 87.6 71.8   1.3 0.4
2 0.9 0.3 0.3   0.3 0.4
3 0.9 0.3 0.3   0.3 0.4

Only LambdaMetafactory.metafactory() is supported at the moment. LambdaMetafactory.altMetafactory() will follow in a future snapshot.

Changes:

  • Removed sun.misc.Unsafe usage from java.util.concurrent.atomic.Striped64.
  • Bug fix. Handle malformed UTF-16 (invalid surrogates) in type/member names and annotations.
  • Added ikvm.exe.manifest file to enable Windows 8.1 behavior (including getting the right version number).
  • Bug fix. Invokedynamic bootstrap method can also be a constructor.
  • Bug fix. Improved handling of incorrect invokedynamic bootstrap methods.
  • Bug fix. Non-canonical modified UTF-8 encodings should throw ClassFormatError.
  • Changed ClassFormatError message for invalid UTF-8 to match JDK.
  • Bug fix. Array classes get the system protection domain, not the element type's.
  • Bug fix. Interfaces can't "override" final methods in Object.
  • Bug fix. Only the bootstrap class loader is allowed to define classes in the java package.
  • Bug fix. Since Java 1.7 class names aren't allowed to have [ and ] characters.
  • Updated ldc error behavior to match Java 8.
  • Bug fix. Calling BasicFileAttributes.size() on a directory didn't work. Thanks to Lucius Junevicus for reporting this.
  • Bug fix. If an invokedynamic bootstrap argument conversion fails, the exception should not be wrapped in BootstrapMethodError.
  • Added intrinsic for invokedynamic using LambdaMetafactory.metafactory().

Binaries available here: ikvmbin-8.0.5296.zip

Wednesday, 02 July 2014 13:43:42 (W. Europe Daylight Time, UTC+02:00)  #    Comments [0]