# Monday, 29 March 2010
New Development Snapshot

It's been a while and enough changes have accumulated to warrant a new development snapshot.


  • Volker implemented dumping a list of threads when Ctrl-Break is pressed (Windows only).
  • Fixed class loader caching in CallerID (thanks to Mainsoft for reporting this).
  • Added workaround to ikvmc for Assembly.Location differing in case when the assembly is loaded from DEVPATH.
  • Added error handling to ikvmc -key: and -keyfile: options.
  • Added code gen optimization to remove some unnecessary explicit class initialization triggers.
  • Several IKVM.Reflection fixes/improvements.
  • Added support to IKVM.Reflection for mcs specific AssemblyBuilderAccess flag (0x800 aka COMPILER_ACCESS) to allow access to members of unbaked TypeBuilders.
  • Added hack to ikvmc to automatically load OpenJDK assemblies from the same location as OpenJDK.Core (when a non-default OpenJDK.Core assembly is specified).
  • Introduced a base class for intrisified AtomitcReferenceFieldUpdaters. This reduces the size of the generates classes somewhat and allows for a public type to represent all intrinsified instances (instead of the HideFromJava nested type).
  • Intrinsified ThreadLocal (under specific circumstances).
  • Fix for bug #2946842.
  • Removed ../../openjdk6-b16 path from response files.
  • Fixed ikvmstub to not export generic type definitions, because the resulting class is final | abstract and that (intentionally) isn't legal.
  • Fixed ClassLoader to not allow unitialized class loader to be used as parent.
  • Replaced incorrect usages of Type.IsArray with ReflectUtil.IsVector().
  • Added workaround for Mono bug #583669.
  • Fixed bug in handling of unrecognized time zones.
  • When running on .NET 3.5 or later, use TimeZoneInfo.Id to identify timezone, because that maps better to the Win32 names that the Java name mapping is based on.
  • Fix for partial trust regression in assembly class loader initialization.
  • Partial trust: File.listRoots() now uses Environment.GetLogicalDrives() instead of Directory.GetLogicalDrives(). Both methods are semantically identical, but the former requires EnvironmentPermission(Unrestricted = true) and the latter SecurityPermission(UnmanagedCode = true). We also now swallow a SecurityException, should it occur.
  • Partial trust: Getting the host name now falls back to "localhost" if we don't have permission to query the name (or if anything else causes GetHostName to fail).

Binaries available here: ikvmbin-0.43.3736.zip

Monday, 29 March 2010 09:00:57 (W. Europe Daylight Time, UTC+02:00)  #    Comments [3]
IE9 Preview disables CLR DEVPATH feature

(This is not related to IKVM.NET, but since I spent several hours tracking this down, I thought I'd write it up here in the hope anyone else struggling with this will find it.)

One of the lesser known (development) features of the CLR is the ability to override the regular Fusion assembly loading rules by setting the DEVPATH environment variable (and adding an entry to the machine.config to enable this).

It turns out that this feature can be disabled by setting HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Image File Execution Options\DevOverrideEnable to 1.

When the IE9 Platform Preview is installed it adds this value to the registry.

To re-enable DEVPATH, set the value to 0 or delete it.

Monday, 29 March 2010 08:20:22 (W. Europe Daylight Time, UTC+02:00)  #    Comments [1]
# Friday, 19 February 2010
0.42 Update 1 RC 1

I fixed a major bug in the automagic .NET serialization support.


  • Updated version to
  • Fix for bug #2946842.

Binaries available here: ikvmbin-

Sources: ikvm-, openjdk6-b16-stripped.zip

Friday, 19 February 2010 09:40:08 (W. Europe Standard Time, UTC+01:00)  #    Comments [0]
# Friday, 29 January 2010
New Development Snapshot

I've modified ikvmc to use IKVM.Reflection and largely rewritten ikvmstub to directly work with the ikvm internals instead of using the java reflection API. Both ikvmc and ikvmstub can now process assemblies independent from the .NET runtime they run on. This opens up the possibility to start investigating the possibility of Silverlight support.


  • Drag-n-drop fix by Nat.
  • Fixed regression introduced in previous development snapshot, related to field accessors.
  • Removed caching of inner classes.
  • Fix for bug #2908683.
  • Various AWT fixes by Volker.
  • Changed JNI to use standard caller ID mechanism.
  • Various JNI optimizations.
  • Fixed http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41696
  • Fixed exception sorter bug exposed by recent Mono sorting change.
  • Fixed Thread.getAllStackTraces() to resume threads that it suspends.
  • Integrated new IKVM.Reflection implementation.
  • Added AllowMultiple = true to RemappedClassAttribute.
  • Fixed atomic update helper nested types to be invisible from Java.
  • Removed support for "ikvm.stubgen.serialver" property that is no longer needed now that ikvmstub doesn't use the runtime to generate stubs.
  • Removed pre-generated stub jars from cvs and modified build process to generate them during the build.
  • Removed "constant" instance field support (which was only used by ikvmstub and doesn't make any sense anyway).
  • Removed ReflectionOnly support from runtime. Now that ikvmstub no longer requires it, there's no good reason to allow Java code to see ReflectionOnly types.

Binaries available here: ikvmbin-0.43.3681.zip

Friday, 29 January 2010 09:35:13 (W. Europe Standard Time, UTC+01:00)  #    Comments [1]
# Monday, 25 January 2010
Introducing IKVM.Reflection

In November 2008 I introduced IKVM.Reflection.Emit, today I'm introducing IKVM.Reflection. It superseded IKVM.Reflection.Emit and also includes the ability to read managed assemblies. In addition, I've also added many other features that aren't directly needed for ikvmc, but are useful for other applications. Almost the complete reflection API has now been implemented and there are several API extensions to support managed PE features that reflection doesn't support (well).


When I started on IKVM.Reflection.Emit, it wasn't at all clear to me that it would be possible to re-implement the System.Reflection.Emit namespace without also re-implementing the System.Reflection namespace, but it turned out it was. I did run into a few snags, such as the inability to subclass Module and Assembly (this was fixed in .NET 4.0) and a couple of Mono bugs, but on the whole IKVM.Reflection.Emit was very successful. So why then re-implement the System.Reflection namespace as well? The main reasons are Silverlight and .NET 4.0. For ikvmc to be able to target versions of the runtime different from the one it is currently running on, it is necessary to avoid using System.Reflection, because System.Reflection can only ever work with the mscorlib version of the current runtime.

ikvmc & ikvmstub

In the coming time, I plan on integrating IKVM.Reflection into ikvmc (most of the work for this has already been done, if you've been following the ikvm-commit list, you may have seen some changes go in and wondered why they are necessary) and ikvmstub (I haven't started on this yet). Currently, ikvmstub uses java reflection to expose members of the .NET types in an assembly. I chose this because it was the easiest way to make sure that what ikvmstub generated matched the ikvm runtime behavior (because it simply used the ikvm runtime to do the mapping). There are two downsides to this approach. The first is the same as mentioned above with ikvmc, you can only generate mscorlib stubs for the runtime you're currently running on. The second is more philosophical, it introduces a cycle in the build process. To build the IKVM.OpenJDK.*.dll assemblies, you need mscorlib.jar and System.jar, but to generate these stubs you need a compiled class library. To solve both these issues, I plan to rewrite ikvmstub to work directly on the internal ikvm runtime representations (with conditional compilation, like ikvmc does).


This list is not exhaustive, but here are some interesting features of IKVM.Reflection (that are not in System.Reflection):

  • There is no AppDomain global state. Everything is contained in an instance of the IKVM.Reflection.Universe class.
  • No thread safety. If you want thread safety, you'll have to lock the universe object during every operation.
  • You can choose what version of mscorlib to load in the universe (using Universe.LoadMscorlib()) and by implementing a Universe.AssemblyResolve handler you can decide the framework assembly unification policy.
  • Support for querying and emitting .NET 2.0 style declarative security.
  • Support for defining unmanaged resources from a byte array (in .NET, AssemblyBuilder.DefineUnmanagedResources(byte[]) is broken, only the overload that accepts a filename works).
  • The ability to read and emit .NET 1.1, .NET 2.0 and .NET 4.0 assemblies (while running on, for example, .NET 2.0).
  • Full support for vararg calling convention.
  • Support for reading field RVA data (e.g. for the fields that are used by the C# compiler to initialize arrays).
  • The ability to enable/disable "exception block assistance", or get "clever" assistance.
  • Support for querying methodimpl mappings.
  • Support for reference, pointer and array types with custom modifiers (this CLR feature is used by C++/CLI).

Missing Features

Some things are still missing. The most notable being the Emit differences. The emit code was based on the IKVM.Reflection.Emit code and likewise still lacks some of the querying support (for baked types), although the new code is much better than the code in IKVM.Reflection.Emit.dll in this respect.

Here's a list of methods that can still throw a NotImplementedException:

  • FieldBuilder.__GetDataFromRVA()
  • ModuleBuilder.ResolveType()
  • ModuleBuilder.ResolveMethod()
  • ModuleBuilder.ResolveField()
  • ModuleBuilder.ResolveMember()
  • ModuleBuilder.ResolveString()
  • ModuleBuilder.__ResolveOptionalParameterTypes()
  • ModuleBuilder.GetArrayMethod()
  • GenericTypeParameterBuilder.BaseType
  • GenericTypeParameterBuilder.__GetDeclaredInterfaces()
  • GenericTypeParameterBuilder.GetGenericParameterConstraints()
  • GenericTypeParameterBuilder.GenericParameterAttributes
  • TypeBuilder.CreateType() (when invoked a second time)
  • TypeBuilder.__GetDeclaredFields()
  • TypeBuilder.__GetDeclaredEvents()
  • TypeBuilder.__GetDeclaredProperties()
  • ISymbolDocumentWriter.SetCheckSum()
  • ISymbolDocumentWriter.SetSource()
  • Most methods in ISymbolWriter
  • ManifestResourceInfo.ResourceLocation (for resources located in another assembly)
  • ManifestResourceInfo.ReferencedAssembly
  • ManifestResourceInfo.FileName
  • MethodBase.GetMethodBody() (if the method data contains unexpected sections)
  • Type.IsAssignableFrom()

Missing members:

  • Module.GetSignerCertificate()
  • Type.GUID
  • ParameterBuilder.GetToken()
  • PropertyBuilder.PropertyToken
  • MethodBuilder.Signature
  • ConstructorBuilder.Signature
  • MethodBuilder.SetSymCustomAttribute()
  • ModuleBuilder.SetSymCustomAttribute()
  • ConstructorBuilder.SetSymCustomAttribute()
  • ModuleBuilder.DefineResource()
  • AssemblyBuilder.ModuleResolve
  • Assembly.GetManifestResourceStream()
  • Assembly.GetSatelliteAssembly()
  • Assembly.GetFile()
  • Assembly.GetFiles()
  • MethodBuilder.SetMarshal() (obsolete, use MarshalAsAttribute instead)
  • ParameterBuilder.SetMarshal() (obsolete, use MarshalAsAttribute instead)
  • FieldBuilder.SetMarshal() (obsolete, use MarshalAsAttribute instead)
  • ModuleBuilder.DefineUnmanagedResource(byte[]) (because it is broken)
  • AssemblyBuilder.DefineUnmanagedResource(byte[]) (because it is broken)
  • MethodBuilder.CreateMethodBody()
  • Everything that doesn't make sense in a ReflectionOnly context.

Concepts that are not implemented:

  • Most metadata tokens returned by Emit objects are not properly typed (and can't be used for anything, other than comparing them against other metadata tokens).
  • When defining debugging symbols, a single method can only point to a single source document.
  • All type/member lookup operations are case sensitive.
  • Implementing a custom System.Reflection.Binder is not supported.
  • Modules with unsorted metadata tables are not supported.
  • When Type.GetMethods() (or __GetDeclaredMethods) is called on Array types it throws a NotImplementedException, instead of returning the special array accessor methods.
  • Managed function pointer types are not supported. Like System.Reflection, they are returned as System.IntPtr instead.

Linker Prototype

To see if I did miss any important CLR features, I wrote a prototype assembly linker. It is pretty capable, but should not be confused for something that is usable for anything other than exploring. I've used it with C++/CLI (compiled with /clr:pure) to test the more esoteric CLR features. The source for the linker prototype is in the zip linked to below.

The IKVM.Reflection source code is available in cvs. If you just want the binary, the LinkerPrototype.zip contains it.

Monday, 25 January 2010 08:28:20 (W. Europe Standard Time, UTC+01:00)  #    Comments [1]
# Tuesday, 12 January 2010
0.42 Update 1 RC 0

Yesterday, I released 0.42 and as seemingly always happens a bug was reported right after that. So with that we're now on the road to the 0.42 Update 1 release. This is release candidate 0.


Binaries available here: ikvmbin-

Sources: ikvm-, openjdk6-b16-stripped.zip

Tuesday, 12 January 2010 18:11:43 (W. Europe Standard Time, UTC+01:00)  #    Comments [0]
# Monday, 11 January 2010
IKVM 0.42 Released
I've released IKVM 0.42 to SourceForge. The binaries are identical to the ones in release candidate 3.

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 16. 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 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 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.

Monday, 11 January 2010 06:36:26 (W. Europe Standard Time, UTC+01:00)  #    Comments [0]
# Monday, 07 December 2009
New Development Snapshot

The 0.42 release still isn't done, but in the mean time, development of 0.43 continues.


  • Fixed interface method resolution (via JNI) and various other minor JNI method resolution compatibility tweaks.
  • When there is no Java code on the stack JNIEnv->FindClass() should use the system class loader instead of the boot class loader.
  • Removed micro optimization that requires full trust on .NET 4.0.
  • Removed .NET 4.0 workaround.
  • Renamed ILGenerator.__GetILOffset() to ILGenerator.ILOffset to match with .NET 4.0.
  • More AWT fixes by Volker
  • Added support for adding "new-style" declarative security (i.e. .NET 2.0 compatible) to IKVM.Reflection.Emit.
  • Various minor optimizations
  • Added a couple of missing classes (that tools.jar depends on).
  • Removed classes that aren't supposed to be in the boot class path (they're from tools.jar). This includes the entire IKVM.OpenJDK.XML.RelaxNG assembly.
  • Created IKVM.OpenJDK.Tools.dll (which is going to be the equivalent of tools.jar).
  • Fixed IsPackageAccessibleFrom to consider class loaders, instead of InternalsVisibleToAttribute
  • Added automatic access to internal accessibility members across assemblies in multi target compilation (previously this was only done for -sharedclassloader scenarios)
  • Cleaned up existing field access stubs (now known as "type 1") and added type 2 access stubs to make public fields that have a non-public field type accessible.
  • Moved FindMainMethod from ikvm.exe into runtime, to avoid the need for hacks (to avoid NoClassDefFoundErrors).
  • Deleting of an non existing Preferences Key should not throw an exception.
  • Type export map performance bug fix by Eyal Alaluf. AssemblyName doesn't implement Equals/GetHashCode and this caused the map to contain an assembly entry for every type.
  • Added IKVM_EXPERIMENTAL_JDK_7 environment variable to enable loading Java 7 class files. Note that no JDK 7 functionality has been implemented yet.
  • Mangle all artificial type names if they clash with Java type names in the same assembly.
  • Added two constructors to ThowsAttribute that take a Type and a Type[] for greater convenience when applying the attribute to user code and for compatibility with Grasshopper's ThrowsAttribute.
  • Various minor reflection optimizations.
  • Don't automatically hide Java "op_Implicit" methods (marked with SpecialName). Instead mark the ones we automatically generate with HideFromJavaAttribute.

Binaries available here: ikvmbin-0.43.3628.zip

Monday, 07 December 2009 09:06:05 (W. Europe Standard Time, UTC+01:00)  #    Comments [1]
# Monday, 30 November 2009
IKVM 0.42 Release Candidate 3

A new release candidate is available.

Changes since previous release candidate:

  • Changed version to
  • Fix for bug #2887316.
  • Eyal Alaluf fixed a massive performance bug that caused IKVM.OpenJDK.Core.dll to be 1.4 MB too big and allocate a couple of MB of unnecessary strings on initialization.
  • Fixed JNI to use system class loader instead of bootstrap class loader when no Java code is on the stack.
  • Fixed JNI method lookup algorithm.

Binaries available here: ikvmbin-

Sources: ikvm-, openjdk6-b16-stripped.zip

Monday, 30 November 2009 07:00:02 (W. Europe Standard Time, UTC+01:00)  #    Comments [4]
# Wednesday, 25 November 2009
Running Eclipse with NGEN

In the weeks before PDC I've been working on compiling Eclipse with ikvmc. This works was triggered by Mainsoft's Eyal Alaluf who asked me to work on this and also provided a desperately needed starting point. I had wanted to do this for ages, but didn't feel like struggling with the Eclipse build system to figure out how to get started.

A couple of the changes in the most recent development snapshot are specifically related to this. In particular the ability for custom assembly class loaders to be called when the module initializer is run. This enables the statically compiled Eclipse OSGi bundles to be lazily activated on first use.


Here are the steps needed to compile Eclipse 3.4.2 x86 on Windows:

  1. Download eclipse-SDK-3.4.2-win32.zip
  2. Download ikvmbin-0.43.3595.zip
  3. Download ikvm-eclipse-0.1.zip
  4. Unzip eclipse-SDK-3.4.2-win32.zip
  5. Open a Command Prompt in the just unzipped eclipse directory
  6. Unzip ikvmbin-0.43.3595.zip in that directory
  7. Unzip ikvm-eclipse-0.1.zip in that directory
  8. Create a directory for the compiled plugins:
    md plugins-compiled
  9. Run ikvmc to compile the eclipse plugins:
    ikvm\bin\ikvmc @response0.txt
    ikvm\bin\ikvmc @response1.txt
    (Ignore the warnings and note that this takes a while and requires a lot of memory. I haven't tested this on a 32 bit machine, it may well run out of address space there.)
  10. You can now run "eclipse-clr.exe" to start Eclipse. Note that if you compare startup times, the first time that Eclipse starts it does some initial configuration, so don't compare the first startup with the subsequent ones.
  11. Optionally you can run ngen-all.bat to compile all assemblies to native code. Make sure that you have the x86 version of ngen.exe in your path. Note that this also takes a while.

Source Code

The sources for eclipse-clr.exe are in this Visual Studio 2008 solution. It's pretty small and most of what it does is configure and hook OSGi to change the bundle loading and initialization. If you want to build eclipse-clr.exe, you first have to run ikvmc on response0.txt, then build eclipse-clr.exe (it depends on the OSGi assembly built with response0.txt) and after that you can run ikvmc on response1.txt (it depends on eclipse-clr.exe, because that contains the custom assembly class loader used for the bundles).

The response0.txt and response1.txt files were generated from the OSGi manifests and if there is interest I can publish the source to that as well, but is pretty hacky.


When compiled to native with ngen, Eclipse starts up faster than with JDK 1.6 on my systems. In theory the private working set should also be significantly less, allowing multiple Eclipse instances to use far less memory.


This is just a technology demonstration, not production code and has not been extensively tested.

Wednesday, 25 November 2009 06:32:30 (W. Europe Standard Time, UTC+01:00)  #    Comments [20]