Embedded JVM - JamVM on MIPS

Documenting some work done to run JVM on a embedded product.

I found this worth noting down due to lack of information (or rather, largely scatter information in forum, blogsphere etc) around this topic. What can be found on internet are usually deployment on the ARMs. The main reference (with detail steps that's also applicable for MIPS) was: Running OpenMUC on ARM systems

This project dealt with:

• Processor: MIPS 24Kc 
• JVM: JamVM 1.5.4
• Classpath 0.98 (Could have been 0.99)

Here are the adapted steps, assuming the cross-compile tools are built and setup beforehand.

1. zlib

Download zlib 1.2.8 from http://www.zlib.net/
Build:

CHOST=mips-example-linux-gnu ./configure

Before make, edit the Makefile to add -fPIC to the SFLAGS that's used to build the static lib. Otherwise will encounter error when building JamVM.

vim Makefile
    SFLAGS=-O3  -fPIC -D_LARGEFILE64_SOURCE=1 -DHAVE_HIDDEN
make

Install the lib and headers to the toolchains directory:

sudo cp libz.a [toolchains_path]/lib
sudo cp zlib.h [toolchains_path]/include
sudo cp zconf.h [toolchains_path]/include

1. JamVM

Download from http://jamvm.sourceforge.net/
Edit the configure to support mips-*-linux compiler:

vim configure   
   mips-*-linux*) host_cpu=mips host_os=linux ;;

Configure and build:

./configure --host=mips-example-linux-gnu --with-classpath-install-dir=/usr/local --prefix=/usr/local --enable-shared --enable-int-threading --enable-int-direct --enable-int-caching --enable-int-prefetch --enable-runtime-reloc-checks --enable-tls --enable-dependency-tracking
make

I think the -install-dir and -prefix is whatever will be like at the target system. Here I just follow convention.
This is what will be printed when running "jamvm -version" on target later on.

Boot Library Path: /usr/local/lib/classpath
Boot Class Path: /usr/local/share/jamvm/classes.zip:/usr/local/share/classpath/glibj.zip

Strip down the binary (I think this step can be skipped if the target build will strip it when making the rootfs):

cd src
mips-example-linux-gnu-strip jamvm

Deploy to target at:

• src/jamvm -> /usr/sbin/jamvm
• lib/classes.zip -> /usr/local/share/jamvm/

1. Classpath

JamVM 1.5.4 requires GNU classpath.
Download 0.98 at http://www.gnu.org/software/classpath/

Configure and build:

./configure --host=mips-example-linux-gnu --without-x --disable-gtk-peer --disable-plugin --disable-dssi --enable-jni --disable-gconf-peer --enable-default-preferences-peer=memory --enable-default-toolkit --disable-examples --disable-tools --disable-Werror --disable-alsa
make

The resulted lib/glibj.zip is ~9MB.
This can be reduced further. Unzip the glibj.zip, remove "unneeded" (for now) class and zip back.
Depends on the apps to run, some cannot be removed. 

For example, these classes can be removed:
- gnu/CORBA
- gnu/java/awt
- gnu/javax/imageio
- gnu/javax/sound
- gnu/javax/swing
- java/sql/
- javax/imageio
- javax/sound
- javax/sql
- javax/swing

Zip the reduced classpath. This is reduced to about 6.5MB.

zip glibj.zip -r *

Deploy to target:

• lib/glibj.zip -> /usr/local/share/classpath/glibj.zip

All the native libraries must also be deployed on target:

find ./native/ -name "*.so" -exec cp {} ${ROOT_PATH}/usr/local/lib/classpath \;

After completed the above step, should be able to just run the java apps by:

jamvm -jar hello.jar