Unable to compile IcedTea with CACAO under Fedora 17

[Andrew Haley]

On 12/18/2012 06:02 PM, Greg Johnson wrote:
>>> No, they're using the same VM.  The problem is that Raspberry Pi
>>> doesn't support the Thumb2 instruction set, and the ARM JIT in OpenJDK
>>> needs it.  I've been hoping that some day a brave soul will come along
>>> and convert the Thumb2 JIT to generate ARM code instead of Thumb2
>>> code, but there haven't been any takers.
> 
> Under Debian, I have this:
> # java -version
> java version "1.6.0_18"
> OpenJDK Runtime Environment (IcedTea6 1.8.13) (6b18-1.8.13-0+squeeze1)
> OpenJDK Zero VM (build 14.0-b16, mixed mode)
> 
> 
> Under Fedora, I have this:
> # java -version
> java version "1.7.0_b147-icedtea"
> OpenJDK Runtime Environment (fedora-2.1.fc17.6-arm)
> OpenJDK Zero VM (build 22.0-b10, interpreted mode)
> 
> 
> Both are using Zero VM, but with different modes. Then I received
> this explanation from the Raspberry Pi forums:
> --------------------------------------

> The main reason why you see a magnitude difference in the Debian vs
> Fedora results really boils down to that there exist two variants of
> Zero.
> 
> In Fedora you have installed OpenJDK Zero VM (build 22.0-b10,
> interpreted mode) This is using the C++ interpreter only.

Ahhh, okay.  All is now clear.  One is Java 7, the other is Java 6.

The problem is that the ARM assembler port isn't working on Java 7.
It's nothing to do with Fedora versus Debian: it's just that Debian
has an old version of OpenJDK.

> In Debian you have installed OpenJDK Zero VM (build 14.0-b16, mixed mode)
> The "mixed mode" version contains two addons, designed by Edward
> Nevill, on top of the generic Zero C++ interpreter, a rewritten
> interpreter main loop in ARM assembly this speeds up the jvm about a
> factor x3 this do benefit the Pi.
> The "mixed mode" also include a Thumb2 JIT that improves speed for
> ARMv7 cores and later, the Pi could benefit from this JIT if it got
> rewritten from Thumb2 to target generic ARM or Thumb1 assembly.

That part is true.

> The Thumb2 info is out of my league. However, the disparity on
> performance was drastic, thus I searched out other avenues. Cacao
> was suggested, so I thought I'd try it out. Since it won't compile
> on 32bit x86, I have no hope of compiling it on ARM. I guess my
> search continues.... :-( Stefan suggested JamVM as a
> possibility. Off I go. :-)

Well, you're talking to the right person: I wrote a lot of this
stuff.  We are working on getting the ARM assembler port working on 7,
and we expect to have it done at the start of next year.

Andrew.