* The Mono runtime
The Mono runtime will implement the JIT engine (and a byte
code interpreter for quickly porting to new systems), the
class loader, the garbage collector, threading system and
metadata access libraries.
Currently the runtime has an image loader and metadata access
entry points. The runtime comes with a simple interpreter
that can execute very simple programs.
** Executing MSIL/CIL images
The code will load an executable and map the references to
external assemblies to our own version of the assemblies on
GNU/Linux.
Our roadmap looks like this, this has been updated as of
Jul 15, 2001:
* Milestone 1: Done Fully read and parse all CIL byte-codes
and metadata tokens (ie, a disassembler).
* Milestone 2: Complete an interpreter for CIL byte
codes. This interpreter can be used temporarly to
run CIL byte code on a system where no JIT is
available.
* Milestone 3: Define an lburg-like instruction
selector for the JITer for Intel. Although slower
at JITing than a streaming JITer, it generates
better code. The same grammar can later be used for
the stream jitter.
* Milestone 4: Implement JITer.
* Milestone 5: Port of the JITer to non IA32 systems.
A setup similar to the Kaffe JIT engine can be used to
layout the code to support non-IA32 architectures. Our work
will be focused on getting a IA32 version running first.
The JIT engine should work on Linux and Win32, although you
will need to install the CygWin32 development tools to get a
Unix-like compilation environment.
** JIT Engine (updated, Jul 14th, 2001)
We will be using a code-generator generator approach for our
JITer. Given the properties of CIL byte codes, we can take
full advantage of a real instruction selector for our code
generator.
There are a couple of books that deal with this technique: "A
Retargetable C Compiler" and "Advanced Compiler Design and
Implementation" are good references. You can also get a
technical description of lbrug
Previously we had looked at a number of JIT engines and tools,
but they would not take full advantage of the CIL properties:
** Garbage Collection
We have decided to implement a generational tracing garbage
collector, which is very similar to the one being used by
.NET. For an introduction to the garbage collection system
used by Microsoft's CLR implementation, you can read this book
on Garbage
Collection.
Another consideration is to use the same interface that ORP
uses to its Garbage Collection system and reuse that GC system
instead of rolling our own, as the ORP system is pretty advanced
and is independent of the rest of ORP.
Although using a conservative garbage collector like Bohem's
would work, all the type information is available at runtime,
so we can actually implement a better collector than a
conservative collector.
** Useful links
Paolo Molaro found a few interesting links:
** PInvoke
PInvoke is the mechanism we are using to wrap Unix API calls
as well as talking to system libraries.
We hvae implemented PInvoke through libffi, but we are likely
going to roll our own system as the runtime matures, specially
as the interpreter is approaching completion, and we move into
the JITer.