IcedTea Bootstrap Process
gbenson at redhat.com
Tue Jan 20 02:57:27 PST 2009
Greg Lewis wrote:
> On Mon, Jan 19, 2009 at 09:17:45AM +0000, Gary Benson wrote:
> > Kurt Miller wrote:
> > > True. At some point we will get to OpenJDK6 too. For now I'm
> > > following the standard practice of following current/HEAD/tip to
> > > increase the likelihood of our work making it in the main
> > > tree. If it turns out that Sun isn't interested in merging BSD
> > > support into the main tree I would expect that we will change
> > > our focus to OpenJDK6.
> > How are the BSD changes split between HotSpot and the class
> > library?
> The HotSpot changes are more extensive since we need to create a
> whole BSD hierarchy to mirror the Linux and Solaris ones. However,
> the code itself is often very similar if not identical to Linux or
That's pretty much how it is for Zero too.
> The big sticking point here, as Kurt has already mentioned, is time.
> I think it would be great to get BSD support into IcedTea, but I'm
> not sure that I have time to commit to making it happen. For me,
> the main focus will probably continue to be OpenJDK7 and keeping the
> BSD port of that up to date. That is the minimum bar we need to
> meet to be able to get our changes merged into mainline.
> Having said that, IcedTea has some benefits, the primary one being
> the Zero port which will give us support for extra architectures
> (all? of which are supported by at least one BSD variant I
> believe). So what I'd really like to evaluate is how hard that
> would be to port to BSD. Where do I need to look at in the IcedTea
> tree to get a handle on this? Should I just look at the ppc
> specific directories in HotSpot? Presumably there is also some
> shared code between the different architectures that Zero supports
Some shared code? Zero is *all* shared code :D There is a bit in
os_linux_zero.cpp  to handle ia64's wacky stack, a bit in
os_linux_zero.hpp  to provide 64-bit atomic copy on 32-bit pcc,
and some bits in atomic_linux_zero.inline.hpp  to provide atomic
operations on m68k and arm, but the remaining 6000 lines or so are
plain old C++, with the odd conditional here and there to cope with
differences in endianness and word size.
Zero is basically a CPU port; to the makefiles, when you build with
Zero your $ARCH is "zero" rather than "x86" or "sparc" or whatever.
If you check out a copy of IcedTea (6 or 7) you'll see a ports
directory, the contents of which are symlinked into the OpenJDK tree
at the start of the build. Aside from a couple of patches, the vast
majority of zero is here:
To port Zero to BSD, what you basically need to create is this:
There's something like 1300 lines of code in there, but pretty much
all of it can just be copied straight from the Linux directory.
You could get a nice starting point with something like:
for i in ports/hotspot/src/os_cpu/linux_zero/vm/*; do
j=`echo $i | sed 's/linux_zero/bsd_zero/'`
sed 's/linux_zero\.cpp/bsd_zero.cpp/' < $i > $j
os_linux_zero.cpp may need a little more work but hopefully not much.
> Also, what progress has been made getting Zero into the main
> OpenJDK7 sources (which is an approved project as I understand it)?
It's an approved project, but I haven't started using its repo yet.
There are two reasons why. One is that there are a bunch of cpu-
specific patches in IcedTea that Zero needs, and I need to take a
week to sit down, check they're necessary, file bugs, and submit
patches and make testcases for them all. (This is a lot easier
now that IcedTea6 is using the latest HotSpot.) The other reason
is that Zero is a bit too slow for me to want to develop it without
the ecj-bootstrap stuff in IcedTea; once Shark is good enough to
develop with (and it so very nearly is) I'll get to switching over.
It's taken much longer than I anticipated because I've taken some
time out of Shark development to work on getting a Zero build to
pass the TCK.
 http://tinyurl.com/os-linux-zero-cpp, from line 307
 http://tinyurl.com/os-linux-zero-hpp, from line 37
 http://tinyurl.com/atomic-linux-zero-inline-hpp, from lines 28 and 103
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