In hindsight, it would have been easier to have built IcedTea (RedHat’s OpenJDK hybrid) rather than Sun’s raw OpenJDK. However since I spent quite a bit of time setting up the environment I was determined to get it to build.

At a high level I did the following:

• Downloaded the source (~ 85Mb): http://download.java.net/openjdk/jdk7/.
• Downloaded the binary plugins (the bits of the OpenJDK that are yet to be open sourced).
• Downloaded the dependencies.
• Modified some environment variables.
• Checked the environment is ok via the sanity script.
• Made 1 change to the source code.
• Made 1 change to the make compiler flags.
• Ran the build.

The README file did not cover all of the dependencies needed to build the OpenJDK on Ubuntu, here is what worked for me:

• sudo apt-get install build-essential
• sudo apt-get install gawk
• sudo apt-get install m4
• sudo apt-get install libasound2-dev
• sudo apt-get install libcupsys2-dev
• sudo apt-get install sun-java6-jdk
• sudo apt-get install x11proto-print-dev
• sudo apt-get install libxp-dev
• sudo apt-get install libfreetype6-dev
• sudo apt-get install libxt-dev
• sudo apt-get install libxtst-dev

The OpenJDK comes with a script (jdk/make/jdk_generic_profile.sh) to help set up your environment. The main updates I needed to make were:

• The bootjdk variable which holds the folder name of your Java 6 install.
• The jdk_instances variable which holds the parent directory of your bootjdk.
• The binplugs variable which holds the location of the non open source bits of the OpenJDK.
• Ensure ANT_HOME was exported.
• Ensusre ANT_HOME/bin was on the PATH.

You can see my full environment here: jdk_generic_profile.

The environment was then verified using the sanity make target:

 
$ . jdk/make/jdk_generic_profile.sh
$ make sanity

Once this passed I tried building but got a couple of errors.

The first error was:

 
/openjdk/hotspot/src/share/vm/libadt/port.hpp:
In function 'void bcopy(const void*, void*, size_t)':
/openjdk/hotspot/src/share/vm/libadt/port.hpp:40:
error: 'void bcopy(const void*, void*, size_t)' redeclared inline
without 'gnu_inline' attribute
/usr/include/bits/string3.h:90:
error: 'void bcopy(const void*, void*, size_t)' previously defined here
make[6]: *** [incls/_precompiled.incl.gch] Error 1

I understand what the error means but I could not work out why the error occurs because after looking through /usr/include/string.h, the include of /usr/include/bits/string3.h is only done if the user specifies _FORTIFY_SOURCE which as far as I can tell is not done in the OpenJDK. My workaround is quite simple, I commented out the redeclaration of inline void bcopy(const void*, void*, size_t) since it appears to already be inlined somehow.

The second error was:

 
/openjdk/hotspot/src/share/vm/runtime/arguments.cpp:
In static member function 'static void Arguments::set_aggressive_opts_flags()':
/openjdk/hotspot/src/share/vm/runtime/arguments.cpp:1359:
error: format '%d' expects type 'int', but argument 3 has type 'intx'

This occurs because of a flag that treats WARNINGS as ERRORS. The correct approach would have been to go and fix the warnings, instead I disabled the flag WARNINGS_ARE_ERRORS = -Werror which can be found in hotspot/make/linux/makefiles/gcc.make.

After making these changes I was able to run the build (just typed make) and saw the following output in the end:

 
Control linux amd64 1.7.0-internal build_product_image build finished:
Control linux amd64 1.7.0-internal all_product_build build finished:
Control linux amd64 1.7.0-internal all build finished:

I had a working JDK which could be found in build/linux-amd64/j2sdk-image/bin.

 
$ ./java -version
openjdk version "1.7.0-internal"
OpenJDK Runtime Environment (build 1.7.0-internal-jeffsinc_2009_01_03_10_52-b00)
OpenJDK 64-Bit Server VM (build 14.0-b09, mixed mode)