IcedTea Bootstrap Process

[Andrew John Hughes]

2009/1/14 Michael Franz <mvfranz at gmail.com>:
> Hi,
>
> I have been trying to find documentation on how the bootstrap build works on
> IcedTea, but have not found it.  I have tried to read the Makefile, but I
> must admit I am not that proficient with makefiles.
>

That would be a little difficult, given most of the makefiles are part
of the OpenJDK build which is downloaded by IcedTea i.e. if you're
looking at just what comes from a Mercurial checkout or a tarball,
it'll not make a lot of sense...

> If there is no documentation, perhaps answers to these question will help
> me.

If you couldn't find any, what there is is too well hidden...

>
> 1. How many passes (full compilations) are there done on the source before
> the final jdk is complete?

By default, 2.  OpenJDK is built once with the system JDK.  This is
assumed to be gcj/ecj or some other GNU Classpath variant as these are
the only Free options other than IcedTea/OpenJDK itself (saying that,
I suppose there is Harmony but I don't know of anyone trying to build
with that and whether that also needs a JDK to build too).  This
applies some additional patches (located in patches/ecj) which disable
a few things, remove some Sun-specific assumptions, etc.  Sorry to be
a bit vague, but we probably do need to go through the patch to see
what's in there and what's still needed.

The built JDK is then tested by being used to build OpenJDK.  If you
already have IcedTea (say from your distro), you can skip straight to
this stage using --with-icedtea and --with-icedtea-home to specify a
path to your existing IcedTea installation if the default is no good
(these two options should be combined IMO).  The system IcedTea needs
to be fairly new as some IcedTea plugin stuff is assumed to be
presented AFAIR.

The alternate builds (zero assembler, shark, cacao) follow the same
process; their alterations primarily affect HotSpot.

> 2. How much (if any) of the source that is being built is compiled and put
> into the rt-closed.jar?

An ecj step before the OpenJDK build compiles enough of the OpenJDK
sources separately to satisfy the OpenJDK build.  The OpenJDK build is
designed only for Sun JDKs it seems, and so relies on a lot of
Sun-specific classes being present in the build JDK (far over and
above what's in the spec.).  These are added to rt-closed.jar (the
naming is from the OpenJDK build assuming this is an existing
proprietary JDK IIRC).  What is included has been found by trial and
error.  For instance, javax/script was recently added to the list as
it's needed by newer versions of HotSpot.  The list can be found as
ICEDTEA_COPY_DIRS in Makefile.am:

# Sources copied from OpenJDK.
ICEDTEA_COPY_DIRS = \
        com/sun/jdi \
        com/sun/jdi/connect \
        com/sun/jdi/connect/spi \
        com/sun/jdi/event \
        com/sun/jdi/request \
        com/sun/jmx/snmp/agent \
        com/sun/tools/jdi \
        java/io \
	java/util \
	java/rmi \
        sun/awt/ \
        javax/net/ssl

if WITH_ALT_HSBUILD
ICEDTEA_COPY_DIRS += \
        javax/script
endif

This is from IcedTea6.  Note that the SNMP stuff is stubbed, and
should probably just be removed and IMPORT_BINARY_PLUGS=false set on
the OpenJDK build.

> 3. Is rt-closed.jar all that should be needed to compile the JDK the first
> time?

Yes, as explained above.

> 4. What is the expected results of a successful bootstrap?

A fully-compliant 1.6 JDK? :)
You should get:

IcedTea is served.

when you reach the end.  The results are in
openjdk/control/build/${OS}-${ARCH}/j2sdk-image (omit the 'control'
segment on IcedTea7).

The easiest way to try a pain-free build is to try it on Fedora where
it should just ./configure and make.

>
> Thanks
>
> Michael
>
>

Thanks,
-- 
Andrew :-)

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