[kaffe] Kaffe and MIPS CPUs

[Jim Pick]

On Mon, 2002-07-08 at 01:14, Kevin D. Kissell wrote:
> Hi Jim,
> 
> Now that the "official" Kaffe 1.0.7 release is out, I've been trying
> to get it running on MIPS platforms, specifically a MIPS Technologies
> "Malta" development board with a contemporary 64-bit 5Kc core
> running Linux 2.4.18, and a Sony Playstation 2 running the Sony
> variant of Linux 2.2.1.  Neither of them will build or run using the
> current distribution, so I'm working on that.  There are those who
> claim to have gotten 1.0.6 working on various MIPS/Linux platforms,
> but I've yet to find one that is functional and compatible with current
> shared libraries, etc.  So I'm rolling up my sleeves and attacking
> 1.0.7.

Cool.  I haven't really attacked MIPS yet - I tested it with 1.0.7, but
there were still some issues.  I've still got the PS2 patches in my
queue - they aren't forgotten.  I'm glad that a few people are
interested.

FWIW, MIPS is quite important to me, since a lot of the activity in the
settop box space seems to be MIPS-based (my new employer, Berkeley
Signal, is doing settop stuff).  I see Kaffe as being really useful as a
prototyping tool for embedded applications (although the fact that it is
GPL'd probably rules it out for most production uses - but then it's
easy to switch to a proprietary JVM).

> I'm not a JVM hacker as such - mostly an OS kernel
> hacker type of 20 or so years experience (BSD, System V,
> Mach, Linux) who has done a moderate amount of Java programming
> and who has a pretty fair, if not expert, idea of how a JVM
> functions.  You won't find me on anyones maintainer lists,
> but you will find my name on some of the Linux/MIPS kernel
> sources.

Cool.  I did some MIPS kernel work too (ported Linux to the VTech
Helio).  That didn't involve too much assembly level work though - it
was mostly driver stuff.

> Kaffe has seemed largely abandoned for the past couple of years,
> and I'm pleased that you have stepped up to bat to maintain it
> for a while.  I would assume that you'd be at least vaguely interested
> in whatever patches I come up with to get things working on MIPS.
> Is that correct?  Are there other people doing the same thing with
> whom I should be in contact?  In general, how should I proceed?

The best place to send patches is just the mailing list at
kaffe@kaffe.org.  By sending them there, you'll get some good comments,
and several developers have CVS commit access, so the patches might go
in quicker if they aren't controversial.

> The current state of play at my end is that I've got kaffe building
> on the 2.4.18/"Red Hat 7.1" MIPS platform, with a couple of
> pretty simple changes in the config/mips stuff (some stuff there
> was fixed since 1.0.6, but not everything).  However, in both
> purely interpretive and JIT configurations, it fails almost all
> tests, mostly due to "stack overflow" errors, and sometimes
> due to System.arraycopy throwing an arithmetic exception
> (which it should never do!).  I'm working on hunting down
> the causes of those things - if you have a clue, I'd be greatful.

Sorry, I don't have a clue (I haven't played with it much yet - so many
ports, so little time).

I do know that Transvirtual proprietary version of Kaffe (which was
released under the GPL as part of PocketLinux) had some pretty solid
MIPS support (at least little-endian) - when I worked there, we had our
software running on quite a few MIPS devices.  I definitely want to see
the good stuff from the PocketLinux release merged into Kaffe.org's
version of Kaffe.  It might be worth taking a look at those sources if
you are running into some problems.  I've got a copy at:

  http://www.kaffe.org/ftp/pub/packages/pocketlinux/

> The Playstation 2 is problematic.  The R5900 CPU in the PS2
> supports single-precision, but not double-precision, floating point
> in hardware, and Sony hacked gcc accordingly.  It will probably
> be necessary to tweak the JIT implementation and configuration
> to take that into account. I know that there are others who were working 
> on getting a "stock" MIPS kaffe 1.0.6 running on it, and another
> of my "spare time" projects has been to get the kernel FPU
> emulation on the PS2 up to the same level that I managed to
> get it for 2.4.x and later 2.2.x MIPS kernels, so that the JIT
> code that emits double-precision FPU instructions could run.

Yeah, Dylan mentioned that.  Really, it's a toolchain/kernel problem,
but I don't see the harm in adding a few hacks into kaffe to workaround
the problem.

> But for the moment, getting Kaffe 1.0.7 running on a non-PS2
> "standard" MIPS platform is my priority.

Cool.  Welcome aboard.  :-)

Cheers,

 - Jim