# Friday, 26 June 2009
IKVM.Reflection.Emit Update

I have done a massive amount of fixes to IKVM.Reflection.Emit to make it full featured (even though it still doesn't implement all Reflection.Emit APIs, the functionality should (almost) all be there, for example via different overloads).

I completed support for generics (I think) and fixed many bugs in that area, ikvmc only uses a very small amount of generics so these fixes are unlikely to affect it.

It's worth explicitly stating the design goals of IKVM.Reflection.Emit:

  • It's a write-only API. Some GetXXX methods or properties may be implemented, but that's mostly for its internal convenience.
  • There is intentionally no error checking. During ikvm development the error checking in System.Reflection.Emit has cost me a huge amount of time, it is generally much easier to diagnose the problem when you have a broken assembly file. PEverify and ILDASM are your friends.
  • Code that uses System.Reflection.Emit in a write-only way is supposed to "just work" (modulo missing APIs, but those changes should be trivial).

I've done some pretty heavy duty testing on it. It should be ready for external (i.e. non-ikvmc) usage now. If you decide to use it (or consider using it), please let me know. As always, feedback is appreciated.


  • Added support for ByRef and Pointer types.
  • Completed support for all literal field constant types and fixed null literal fields.
  • Added ModuleBuilder.DefineInitializedData().
  • Fixed many generics related bugs.
  • Added a (non-standard) API to ModuleBuilder to set the PE image base address.
  • Added TypeBuilder.SetParent().
  • Added TypeBuilder.GetMethod() and TypeBuilder.GetConstructor() to instantiate methods on generic types.
  • Added a (non-standard) API to ILGenerator to disable the "helpful" automatic leave/endfinally instructions in exception blocks.
  • Added support for pinned local variables.
  • Added UIntPtr and TypedReference signature encodings.
  • Fixed handling of TypeBuilder enums in custom attributes.
  • Added MethodBuilder.SetSignature().
  • Added GenericTypeParameterBuilder.SetInterfaceConstraints() and .SetGenericParameterAttributes().
  • Fixed (Method|Type)Builder.SetCustomAttribute() to set HasSecurity flag when SuppressUnmanagedCodeSecurityAttribute is set.
  • Added support for defining events.

Binary available here: ikvm-refemit-0.41.3464.zip

Friday, 26 June 2009 06:42:52 (W. Europe Daylight Time, UTC+02:00)  #    Comments [0]
# Monday, 15 June 2009
IKVM 0.40 Update 1 Release Candidate 0

A minor update.


  • Changed version to
  • Changed build to generate rmi stubs instead of depend on .class files in openjdk6-b12-stripped-IKVM-0.40.zip. Thanks to Jo Shields for helping with this.
  • Fixed verifier bugs. Thanks to Brian Heineman for reporting this.

Binaries available here: ikvmbin-

Sources: ikvm-, classpath-0.95-stripped.zip, openjdk6-b12-stripped-IKVM-0.40.zip

Monday, 15 June 2009 07:40:05 (W. Europe Daylight Time, UTC+02:00)  #    Comments [4]
# Friday, 05 June 2009
IKVM 0.40 Released

I've released IKVM 0.40 to SourceForge. The binaries are identical to the ones in release candidate 1.

Release Notes

This document lists the known issues and incompatibilities.


  • Code unloading (aka class GC) is not supported.
  • In Java static initializers can deadlock, on .NET some threads can see uninitialized state in cases where deadlock would occur on the JVM.
  • JNI
    • Only supported in the default AppDomain.
    • Only the JNICALL calling convention is supported! (On Windows, HotSpot appears to also support the cdecl calling convention).
    • Cannot call string contructors on already existing string instances
    • A few limitations in Invocation API support
      • The Invocation API is only supported when running on .NET.
      • JNI_CreateJavaVM: init options "-verbose[:class|:gc|:jni]", "vfprintf", "exit" and "abort" are not implemented. The JDK 1.1 version of JavaVMInitArgs isn't supported.
      • JNI_GetDefaultJavaVMInitArgs not implemented
      • JNI_GetCreatedJavaVMs only returns the JavaVM if the VM was started through JNI or a JNI call that retrieves the JavaVM has already occurred.
      • DestroyJVM is only partially implemented (it waits until there are no more non-daemon Java threads and then returns JNI_ERR).
      • DetachCurrentThread doesn't release monitors held by the thread.
    • Native libraries are never unloaded (because code unloading is not supported).
  • The JVM allows any reference type to be passed where an interface reference is expected (and to store any reference type in an interface reference type field), on IKVM this results in an IncompatibleClassChangeError.
  • monitorenter / monitorexit cannot be used on unitialized this reference.
  • Floating point is not fully spec compliant.
  • A method returning a boolean that returns an integer other than 0 or 1 behaves differently (this also applies to byte/char/short and for method parameters).
  • Synchronized blocks are not async exception safe.
  • Ghost arrays don't throw ArrayStoreException when you store an object that doesn't implement the ghost interface.
  • Class loading is more eager than on the reference VM.
  • Interface implementation methods are never really final (interface can be reimplemented by .NET subclasses).
  • JSR-133 finalization spec change is not fully implemented. The JSR-133 changes dictate that an object should not be finalized unless the Object constructor has run successfully, but this isn't implemented.

Static Compiler (ikvmc)

  • Some subtle differences with ikvmc compiled code for public members inherited from non-public base classes (so called "access stubs"). Because the access stub lives in a derived class, when accessing a member in a base class, the derived cctor will be run whereas java (and ikvm) only runs the base cctor.
  • Try blocks around base class ctor invocation result in unverifiable code (no known compilers produce this type of code).
  • Try/catch blocks before base class ctor invocation result in unverifiable code (this actually happens with the Eclipse compiler when you pass a class literal to the base class ctor and compile with -target 1.4).
  • Only code compiled in a single assembly fully obeys the JLS binary compatibility rules.
  • An assembly can only contain one resource with a particular name.
  • Passing incorrect command line options to ikvmc may result in an exception rather than a proper error messages.

Class Library

Most class library code is based on OpenJDK 6 build 12. Below is a list of divergences and IKVM specific implementation notes.

com.sun.security.auth.module        Not implemented.
java.applet GNU Classpath implementation. Not implemented.
java.awt GNU Classpath implementation with partial System.Windows.Forms based back-end. Not supported.
java.io.Console Not implemented.
java.lang.instrument Not implemented.
java.lang.management Not implemented.
java.net No IPv6 support implemented.
java.net.ProxySelector Getting the default system proxy for a URL is not implemented.
java.text.Bidi GNU Classpath implementation. Not supported.
java.util.zip Partially based on GNU Classpath implementation.
javax.imageio.plugins.jpeg Partial implementation. JPEGs can be read and written, but there is no metadata support.
javax.management Not implemented.
javax.print Not implemented.
javax.script Not implemented.
javax.smartcardio Not implemented.
javax.sound Not implemented.
javax.swing GNU Classpath implementation. Not supported.
javax.tools Not implemented.
org.ietfs.jgss Not implemented.
sun.jdbc.odbc Implementation based on .NET ODBC managed provider.
sun.net.www.content.audio Audio content handlers not implemented.
sun.net.www.content.image Image content handlers not implemented.

The entire public API is available, so "Not implemented." for javax.print, for example, means that the API is there but there is no back-end to provide the actual printing support. "Not supported." means that the code is there and probably works at least somewhat, but that I'm less likely to fix bugs reported in these areas.

Specific API notes:

  • java.lang.Thread.stop(Throwable t) doesn't support throwing arbitrary exceptions on other threads (only java.lang.ThreadDeath).
  • java.lang.Thread.holdsLock(Object o) causes a spurious notify on the object (this is allowed by the J2SE 5.0 spec).
  • java.lang.String.intern() strings are never garbage collected.
  • Weak/soft references and reference queues are inefficient and do not fully implement the required semantics.
  • java.lang.ref.SoftReference: Soft references are not guaranteed to be cleared before an OutOfMemoryError is thrown.
  • Threads started outside of Java aren't "visible" (e.g. in ThreadGroup.enumerate()) until they first call Thread.currentThread().
  • java.lang.Thread.getState() returns WAITING or TIMED_WAITING instead of BLOCKING when we're inside Object.wait() and blocking to re-acquire the monitor.
  • java.nio.channel.FileChannel.lock() shared locks are only supported on Windows NT derived operating systems.
  • java.lang.SecurityManager: Deprecated methods not implemented: classDepth(String), inClass(String), classLoaderDepth(), currentLoadedClass(), currentClassLoader(), inClassLoader()

Supported Platforms

This release has been tested on the following CLI implementations / platforms:

CLI Implementation       Architecture      Operating System
.NET 2.0 SP2 x86 Windows
.NET 2.0 SP2 x64 Windows

Partial Trust

There is experimental support for running in partial trust.

Friday, 05 June 2009 15:32:45 (W. Europe Daylight Time, UTC+02:00)  #    Comments [2]
# Tuesday, 02 June 2009
New Development Snapshot

Class gc support has now been checked in (but is not available in the attached binaries, because they've been built for .NET 2.0). This is somewhat of a milestone snapshot, because it is the first version that no longer requires GNU Classpath to build*. However, please note that AWT / Swing still needs a lot of work.

*What this means is that there is no longer an external dependency on GNU Classpath. There is still GNU Classpath derived code in ikvm's source tree. For example, small parts of AWT and the pure Java  implementation of java.util.zip.


  • Removed dependency on classpath-0.95-stripped.zip. All AWT / Swing code is now from OpenJDK or in the ikvm codebase.
  • Defined NET_4_0 when building on .NET 4.0 to enable conditional code.
  • Changed IKVM.Reflection.Emit's ModuleBuilder and AssemblyBuilder to extends Module and Assembly respectively when building on .NET 4.0.
  • Added .NET 4.0 fix to IKVM.Reflection.Emit (for the fact that Type now defines == operator).
  • Fixed locking for image based Graphics.
  • Various changes to remove warnings when building on .NET 4.0.
  • Several fixes related to dynamic assemblies.
  • Several improvements to better work in partial trust.
  • More AWT work.
  • Made java.lang.reflect.Field exception messages the same as JDK 6.
  • Implemented class gc (for .NET 4.0 builds).
  • Added -Xnoclassgc option to ikvm (only meaningful in a .NET 4.0 build).

Binaries available here: ikvmbin-0.41.3440.zip.

Tuesday, 02 June 2009 10:49:01 (W. Europe Daylight Time, UTC+02:00)  #    Comments [4]