Taurus Java Virtual Machine v1.06a
The following release notes are applicable to the above version of the Taurus
Java Virtual Machive. The copyright notice is applicable to any version of the
VM unless stated otherwise.
Copyright notice
The Taurus Java Virtual Machine is © Copyright 2003, Taurus Software.
This program is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the Free
Software Foundation; either version 2 of the License, or (at your option) any
later version.
This program is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
The Taurus Java Virtual Machine has been produced, as a "clean room"
implementation, in accordance with Sun Microsystems, Inc's (SUN) licence
agreement for "The Java™ Virtual Machine" specification. Also, in
accordance with this agreement the virtual machine distribution does NOT, to
the author's knowledge, contain ANY material which is copyrighted by SUN.
As such the class files relied upon by the virtual machine must be obtained
separately, directly from SUN. The use of this specifcation does not in any
way imply that the software conforms to it, nor does it imply that it will ever
wholey do so. The Taurus Java Virtual Machine does not, and will not, ever
pretend to be "Java-compliant", it will always remain as closer approximation
as time and money will allow. Users of this software do so at their own risk.
Developers of any Java software should NEVER use this as a reference platform.
Taurus Java Virtual Machine is a trademark of Taurus Software. Sun, Sun
Microsystems, the Sun logo, Java, JavaSoft, Personal Java, Embedded Java, KVM
and Java 2 Micro Edition are all trademarks or registered trademarks of Sun
Microsystems, Inc. All other product names mentioned herein are the trademarks
of their respective owners.
All references to Taurus Software directly refer to the non-profit
freeware/shareware software development unit run from the UK by myself. Any
conflict with names of companies inside or outside of the UK is unintentional
and should be disregarded.
Platform Support
The Taurus Java Virtual Machine version 1.06 alpha is provided as binaries
for the following platforms:
- Win32 - should work with any i386 based Microsoft Windows™ OS
(95/98/ME/NT/2K/XP)
- Linux-i386 - any i386 based Linux™ distribution
- Cygwin - Cygwin running on Win32
- RISC OS - Archimedes or RISC PC running Acorn RISC OS 3.10 or
later
For space reasons is provided without any of the required support libraries
(DLLs, .so or RMs). In order to run this software you must install these
libraries yourself (they are likely to be already installed on most systems).
Binaries for other platforms may follow at some later date.
Java Support
This alpha release provides an incomplete implementation of the SUN Java
Virtual Machine Specification 1.0. The key features of this release are as
follows:
- Loading and execution of Java applications - the VM should be able to load
and begin executing any Java application.
- Dynamic loading - classes are loaded as needed, exceptions or errors are
reported when a class cannot be found
- Can interpret almost all Java virtual instructions - all the common
instructions used by large programs like the
javac
and javadoc
have been implemented.
- Can read and write files on disk.
- Support for exceptions - most exceptions generated by the VM can be caught,
all exceptions generated by user code can be caught. All Java exceptions support
the stack trace facility.
- Runs with standard JDK classes - there are no modified class files used by
the VM. (SIBO and DOS versions do use modified classes).
- Debug at method, instruction and exception level is supported. Any serious
VM problemsc(access violations) should generate a Java stack trace.
- Complete virtual instruction set implementation - 100% of the virtual
instructions have been implemented, though one or two are dummy
implementations.
The main restrictions are as follows:
- Non-conformant arithmetic implementation - the VM uses its own internal
format (that of C) to represent numbers on the stack. In particular
floating-point numbers may not behave quite correctly for NaN, +Inf and
-Inf. Also beware of bitwise logic on large numbers, as shifts etc. may
not be 100% correctly implemented.
- Incomplete native method implementation - only those native methods which
have been encountered in pratice (about 18%) have been implemented. This
leaves a lot of unimplemented native methods, including those native
methods which fall outside the core implementation, namely those found in
the "winawt", "net" and "zip" libraries. No attempt has been made to
support the Java Native Interface (JNI) specification, though the code has
been designed to make support a possibility in the future.
- Single thread of execution - multi-threading may be added in the form of
"green" threads in a later release. Native threads are unlikely to be
supported as the smaller target platforms do not support threading.
- No AWT - the standard Java AWT classes require far too much native
support and are tied too closely to the host platform for implementation in
a truely "portable" VM. Mechanisms to implement the AWT may be provided in
a later release.
- No Networking - as with the AWT, the standard
java.net
classes require a lot of native support. Mechanisms to implement
networking may be provided in a later release.
- No Garbage Collector - due to the complexity of GC, its implementation
has been left until a later release. It is likely to be necessary to adopt
a smarter GC technique in order to allow the Java VM to run on really small
platforms.
- No JIT - a performance enhancing JIT may be added later. The development
of a JIT is difficult and ties the VM to a host platform. JITs are also a
complex technology to develop and even some of the commercial Java vendors
still haven't got it quite right!
- Limited refelection interface - reflection is limited to obtaining handles
of classes, super-classes and fields (for
serialver
) Support
for interrogating class definitions has been omitted.
- No support for CLASSPATH - only a single directory (or on some platforms,
the current directory) is checked for class files.
- No support for Applets or sandbox - at the moment the VM must be run as a
stand-alone application.
Support for "Standard Applications"
Below is a table of the "standard Java applications", which come with most
JVM's. They are all written in Java, so should run on any virtual machine.
As a simple test of the Taurus Java VM, here is what happens when they are run
with the scripts provided:
Application |
Status |
Comments |
appletviewer |
Will not run |
Needs Threads and native AWT support. |
jar |
Will not run |
Needs native Zip support. |
javac |
Runs |
Compiles Java code correctly. |
javadoc |
Runs |
Successfully documents my Hello.java example |
javakey |
Runs buggily |
Always prints the message "could not initialize scope". |
javap |
Don't know |
I don't have all the class files for javap to test it. |
jdb |
Will not run |
Needs native network support. |
native2ascii |
Runs |
But I don't know what it does! |
rmic |
Runs |
Generates and compiles RMI stubs and skeletons correctly. |
rmiregistry |
Will not run |
Needs native network support. |
serialver |
Runs |
Produces correct UID as Sun's implementation. |
Installation
The Taurus JavaVM is shipped as an archive (usually ZIP) without the standard
class files. If you haven't done so already, you need to download a copy
of JDK 1.1 from java.sun.com. Pick the
latest 1.1 release.
Win32, Linux and Cygwin
Create a suitable directory (e.g. C:\JavaVM
or
/home/robert/javavm
), and unpack the downloaded ZIP file
containing the VM into this directory.
Next install the class files from the JDK 1.1.x - these come packed as a
zero compression Zip file called classes.zip
, approx 8Mb in size.
You need to unpack this directly into your JavaVM lib
directory
(You may need to create this, if there isn't one already).
RISCOS
Unpack the downloaded ZIP file using !ZipEE or similar into a suitable
directory e.g. $.Apps
. This will create an !JavaVM
application directory containing the necessary files.
Next install the class files from the JDK 1.1.x - these come packed as a
zero compression Zip file called classes.zip
, approx 8Mb in size.
You need to unpack this into $.Classes
(unlike !JavaVM, this
cannot be moved anywhere else). You then need to rename all the files to
remove the .class
file extensions.
Running
Running JavaVM is very simple, and it is designed to be run in a similar way to
other virtual machine implementations.
Win32, Linux and Cygwin
To run the VM you must either add JavaVM's bin
directory
to your path, or if you have other VM's installed, you must cd
to this directory and type, for example, .\java
(Win32) or
./java
(Cygwin and Linux).
To run your own programs, you must place your .class
files in
the lib
directory along with the standard Java classes.
RISC OS
Before you can run the VM under RISC OS, you must first double-click the
!JavaVM
application. This doesn't actually launch an
application, it just sets up various environment variables, adds the VM's
bin
directory to you path and loads the appropriate modules.
To actually run the VM, open a Task Window (Ctrl+F12). As with most large
programs, you need to increase the wimpslot of the task with
wimpslot -min 3000k
for example. Larger programs will need a
bigger wimpslot. The VM is then run by typing, for example, java
,
in the same manner as other platforms.
To run your own programs, you must place your .class
files in
the $.Classes
directory along with the standard Java classes.
Testing the VM
To make sure that the VM is setup properly and that you are running the
right VM (if you have more than one installed), run the VM with the
-version
switch. This should result in something similar to the
following:
|
robert@odie$ ./java -version
java version "1.1"
Taurus Java Virtual Machine CYGWIN32 v1.0.6a DBG
(C) Copyright 2001, Taurus Software
|
If you don't get this, or you get a similar message which does not
contain the word "Taurus", then check your path, or make sure you are using
.\java -version
(Windows) or ./java -version
. On
RISC OS make sure you have double-clicked !JavaVM
.
Minimum requirements
The VM can function in a much smaller environment than provided by the JDK
classes. If you wist to implement your own "standard" classes, then the VM
really only needs the following classes and methods to function:
Class | Usage |
java.lang.Object |
All classes derive from it, either directly or indirectly. |
java.lang.System |
Loaded at system startup.
|
|
Called at system startup. |
java.lang.Thread |
For the "main" thread object. |
java.lang.ThreadGroup |
For the "system" thread group. |
java.lang.String |
For strings (Note: this can be cut down a lot). |
java.lang.Throwable |
For all exceptions and errors. |
java.lang.Error |
For all errors. |
java.lang.Exception |
For all exceptions. |
java.lang.InternalError |
Can be generated by any field or method access. |
java.lang.NullPointerException |
Can be generated by any field or method access. |
java.lang.ArrayIndexOutOfBoundsException |
Can be generated by any array access |
java.lang.ArithmeticException |
Can be generated by maths ops (e.g divide by zero) |
java.lang.ClassCastException |
Can be generated by any explicit or implicit cast. |
java.lang.ClassNotFoundException |
Generated by dynamic loading. |
It is also advisable to include the following error/exception classes, as
they can be raised directly by the VM (either in response to class-loading or
by being thrown by native method implementations):
Class | Usage |
java.lang.VerifyError |
Can be raised by the verifier. |
java.lang.NoClassDefFoundError |
Can be raised by the linker. |
java.lang.IllegalAccessError |
Will be used in future releases. |
java.lang.ClassFormatError |
Raised by the loader when it encounters a corrupt class file. |
java.lang.NoSuchFieldError |
Will be used in future releases (1.06a erroniously raises
NoSuchMethodError's instead). |
java.lang.NoSuchMethodError |
Raised by the VM in response to incompatible class changes. |
java.lang.UnsatisfiedLinkError |
Raised by the VM when linking fails. |
java.lang.IOException |
Can be raised by native I/O methods. |
java.lang.NegativeArraySizeException |
Can be raised by the VM when dereferencing arrays. |
To make your own environment, you need to implement a set of Java classes
similar to those provided by Sun. The main reason for doing this on a small
platform is the amount of crap that gets loaded before any of your classes. I
am currently looking at the Personal Java and Embedded Java specifications for
some ideas on how to shrink the VM - Just using System.out loads an awful lot
of classes!
Last updated 28th January 2003
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