Re: [Jamvm-general] Proof Of Concept : an alternative to OpenJDK

[Xerxes R. <xe...@za...>]

2013-06-03 23:41, johann Sorel skrev:
> Hello

Hi Johann!

> 
> I would like some advices from some peoples working on JamVM :
> 
> I have been working for several months now on a public domain general purpose library (think of it as a replacement to the ClassPath lib). The projet is going pretty well and is starting to be self sufficient. (for those interested : https://bitbucket.org/Eclesia/un/wiki/Home)
> 
> Now I would like to make a Proof Of Concept that my project can live on it's own without the JVM APIs and classes. Basicly I would like to obtain a draft of VM using JamVM as "kernel" and my project as the main library.

You can use the jamvm libjvm.so standalone in combination with your own projects class library

> 
> - Can JamVM be used without ClassPath/OpenJDK ?
yes create your own jvm launcher using the "JNI Invocation Interface"
I recommend you to take a look at Chapter 7 (page 83) of the "The Java™ Native Interface Programmer’s Guide and Specification" book
http://web.archive.org/web/20120905183616/http://java.sun.com/docs/books/jni/download/jni.pdf

> - Will I need to code some JNI for low level operations ? 
> or are they provided ? (Streams,Sockets,...)
You need to implement all classes you need like a ClassLoader, String, Object and Class class. And you need to use JNI to do low level operations.


> 
> If you think it is possible : where should I start ?
> 
> Thanks
> 
> Johann Sorel


jamvm libjvm finds the JRE classes relative to the libjvm.so thus the folder layout is important.
You may setup a project structure like this:

jamvmMini$ find .
.
./compile.sh
./jre
./jre/classes/java/lang/Object.java <-- you will have to provide your own implementation of all java/lang classes
./jre/classes/java/lang/String.java
./jre/classes/java/lang/Class.java
./jre/classes/java/lang/ClassLoader.java
./jre/classes/java/lang/...
./jre/lib/jvm/jamvm/libjvm.so <- jamvm built using instructions from: http://draenog.blogspot.se/2011/02/openjdkjamvm-git-repository.html
./Prog.java <- the main application to run
./myJVM.c <- example code from "Chapter 7 (page 83) of the "The Java™ Native Interface Programmer’s Guide and Specification" book"
./run.sh

jamvmMini$ cat compile.sh
#compile launcher
gcc myJVM.c -ljvm -L./jre/lib/jvm/jamvm/
#compile java.lang classes
cd jre/classes
javac java/lang/*.java
cd ../../
#compile application
javac Prog.java
#compile jamvm launcher
gcc myJVM.c -o jamvm-launcher -ljvm -L./jre/lib/jvm/jamvm/

jamvmMini$ cat run.sh
#run launcher
LD_LIBRARY_PATH=./jre/lib/jvm/jamvm/ ./jamvm-launcher

Cheers
Xerxes