Hi Chris,
I looked into this for one of our applications - TCC is reasonably good
for generating VM code but a simple VM interpreter won't be fast to execute.
Instead I have been working on a TCC target that generates architecture,
position and size independent code (with a fixed register/memory model)
that can be converted into native instructions by the target processor.
For a 32-bit processor the byte-codes generally translate to a single
instruction or two for a literal.
The targets we use are all embedded processors, often with less than 64k
of RAM - with this approach the bytecode isn't stored, it gets
translated on the fly as it is downloaded. My main test target is a
Ubicom ip3k and the translator uses less than 4k of code space... less
space than a VM would :-)
The translator is that it is written in c-code but with an additional
custom pre-processor that translates target specific assembler into
binary constants so the author doesn't need to know or enter any binary
numbers.
What is your application?
Nick
Chris wrote:
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I have seen some brief mention of bytecode targets here and there on
this list over the last few years. Has anything come of any of those?
I really would like to see a C to bytecode compiler and an
accompanying lightweight VM to run the bytecode. I imagine the VM
would be extremely simple (relatively speaking at least), lightweight,
and fast if the only functionality was similar to standard ANSI C.
This would allow easy embedding of the VM in applications. Especially
if it allowed direct calling to/from native (binary) system libraries.
This would be very useful as a lightweight cross-platform system that
didn't require recompiling for each target and kept the simplicity of
C. Dynamically loading code off the network and running directly from
memory would be much easier as well.
Targeting TCC bytecode to a new processor would be as easy as porting
the VM to that processor using pre-existing compiler tools for that
hardware; no machine code messiness.
The Quake3 game engine actually has a VM and compiler that is pretty
close to exactly what I speak of but unfortunately it's GPL'd so not
all that useful for commercial embedding.
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