Re: [Sablevm-user] bug report -- cannot run 'HelloWorld' test

[John L. <je...@pi...>]

> There's also John Leuner <je...@pi...> who talked to me about
> porting his JIT to SableVM.  You might want to talk with him about
> that.  Maybe you two could help each other.

Hello Etienne, Andrew

Andrew, I've been developing a JVM for the past while
(kissme.sourceforge.net), it's implemented in C and targeted at (free)
UNIX. 

My current project is a JIT written in Java that doesn't conform to the
traditional SUN JIT spec. It comprises of an i386 Assembler written in
Java (although I wish I had a 64-bit architecture :-)) that is used to
translate bytecodes into machine code.

A typical excerpt from the code:

   case op.iconst_5:
            qc("mov eax,0x5 ; iconst_5");
            qc("push eax");
          break;
            /* Load instructions 

               These generally get the pointer to optop by calculating ebp
+ 0x8 and storing it in eax
               Then we add 0,4,8,12 to eax and push [eax]
             */

        case op.fload_0:
        case op.iload_0:
        case op.aload_0:
            qc("mov eax,[ebp + 0x8]");
            qc("push [eax]");
        break;


You can see I use an intel-style assembler syntax. I've basically
replaced the java stack with the native C stack, and all the translated
instructions operate on this native stack. Because of the nature of the
translation the resulting code could probably be optimised a lot. Future
work would be a second stage optimising version of this translator which
uses conventional optimisation techniques to produce faster code.

The translation gets more complicated when the VM wants to invoke a method
or put a value into an array etc, currently I handle these cases by having
the optimised code call back into a special C routine that does what is
necessary.

My next endeavor is to teach the "assembler" to understand some C structs
and thus have easy access to the fields of necessary structures. 

If that can be done the only real special-cases will be method-invocation. 


My JIT is selective, it only compiles certain methods and I intend to
insert some kind of profiling ability at a later stage. 

Unfortunately I had to stop working on this project for two months due to
a sports injury but I've recovered enough to carry on working now.

If you're interested in the code or just discussing jits or whatever, just
let me know.

John Leuner