Using A Sun based Javac to compile rt-closed.jar different from using gcj

[Andrew John Hughes]

2009/8/20 Michael Franz <mvfranz at gmail.com>:
> Hi,
>
> It has taken a few days but I have figured out why my rt-closed.jar is
> missing a bunch of classes.
>
> I am building on OS X and using either Apple's JKD or an older version of
> OpenJDK.  It seems that on Fedora the creation of the rt-closed.jar using
> gcj to compile the sources in rt/ .  The class files are created in lib/rt,
> this is then jar'ed to create rt-closed.jar.  It seems that gcj (and ecj)
> will put classes that are reference (directly/indirectly) by the classes it
> compile into the output directory.  This explains why lib/rt has class files
> that are not in rt.  Since Apple's JDK or OpenJDK itself do not do this the
> rt-closed.jar is missing classes that are assumed to be there later causing
> the bootstrap process to fail.
>
> Is this functionality of gcj and ecj an undocumented switch in OpenJDK?
>
> Michael
>

Well, I believe Apple's JDK is a Sun derivative too, so its behaviour
being similar to OpenJDK is not too much of a surprise.  When or how
it was derived is impossible to tell as it's a proprietary product.
Equally, gcj uses ecj so we're only talking about the difference in
two compilers here: ecj and javac.

I believe the purpose of rt-closed.jar is to precompile classes from
OpenJDK that would otherwise be present in a Sun-derived JDK to begin
with (this bit is so old it predates my involvement in IcedTea).  So,
although ecj spits out every class it touches, the loss shouldn't
matter on with Sun-derived boot JDKs -- in theory.

The whole build process is currently based on two presumptions:

  * If you build with the defaults, you do a full bootstrap build: gcj
for stage 1 and the built JDK for stage 2.
  * If you build with --disable-bootstrap (renamed from
--with-icedtea/--with-openjdk et. al. in IcedTea7, but still under
those names in 6) then you are assumed to be doing a build closer to
the OpenJDK default, so less patches are applied, etc.

I'm working on making the stages JDK-independent but this takes time.
The first stage will be getting a full build working with OpenJDK but
as you (and others) have seen, we aren't there yet.  This is
documented in the NEWS for 1.11.

You could try building using --disable-bootstrap for now, or just do a
raw OpenJDK build without IcedTea by checking out the IcedTea forest:
hg fclone http://hg.openjdk.java.net/icedtea/jdk7

Patches are of course welcome, but touching such a hairy build system
is not for the faint-hearted :)
-- 
Andrew :-)

Free Java Software Engineer
Red Hat, Inc. (http://www.redhat.com)

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