JSVM

by jawb • 13 years ago

69 16 13 years ago

Javascript virtual machine is one instruction set machine to parse and execute an assembly like code.

jared314• 13 years ago

I love low-level learning projects like this, but I wish more of them would centralize around something like Nand2Tetris[1] to create an expanded, and interconnected, learning ecosystem.

[1] http://www.nand2tetris.org/

chengsun• 13 years ago

Shameless plug: a while back I wrote an assembler-and-VM for a similarly hypothetical assembly language that I was studying in class. Just for kicks, I wondered if I could fit the entire thing into 1KB of JavaScript, whilst including features as step by step execution, a "debugging GUI" (as much as you could expect from 1KB!) featuring the stack, register contents and program counter, plus the assembler on top which performs full syntax/opcode argument checking.

The result (which I'm pretty pleased with) is here: http://chengsun.github.io/ocremutiny.html

angersock3• 13 years ago

If I make make a few suggestions (mostly from a desire to see a more familiar sort of spec):

Add arithmetic shift left/right
Add logical shift left/right
Add exclusive OR (XOR)
Pick a word size so your integer and bit ops have meaning

Questions:

How do I set the program counter from my assembly?
Do I have registers (seems like a stack-based VM, so no)? If not, can I have more stacks?
Can you setup a dedicated block of memory to use as a framebuffer and render it to a <canvas> tag?

Good work so far!

jawb6• 13 years ago

Add arithmetic shift left/right .. I'll add Add logical shift left/right .. I'll add Add exclusive OR (XOR) .. I'll add Pick a word size so your integer and bit ops have meaning .. I think I'll just rely on js types to keep things simple, If you see any reason not to please explain further
How do I set the program counter from my assembly? The only way to set PC is through branching
Do I have registers (seems like a stack-based VM, so no)? If not, can I have more stacks? Like you said it's a stack-based VM, so no registers. Currently it's a single stack since it's enough. I never encountered a machine with multiple stacks, can you enlighten me about this ?
Can you setup a dedicated block of memory to use as a framebuffer and render it to a <canvas> tag I made this machine to be used by students to test compilers, But I think I'll add this feature in case there is any ambitious student who wants to embed a graphics library in his language :)

Thanks,

jawb6• 13 years ago

I think I understand the thing about word size, thank you I'll fix it

tylerkahn• 13 years ago

I had to write one of these (in C) for a class a couple years ago.

https://github.com/tylerkahn/MIPS-Virtual-Machine

angersock3• 13 years ago

Yay MIPS!

Also, let us not forget the Halt and Spontaneously Combust (HSC) instruction: ftp://reports.stanford.edu/pub/cstr/reports/csl/tr/86/289/CSL-TR-86-289.pdf .

gcr• 13 years ago

Whoa dude, this is awesome!

I once wrote a MIPS assembler+VM in Racket. It went OK but I never used it for anything: https://github.com/gcr/mips-simulator Was a great learning experience though.

Xelom• 13 years ago

Better name it VM.js !!

gkya• 13 years ago

I real disappointed when I discovered this was not an amateur JS vm that I could read in a weekend or two, that would be awesome to have :(

jawb6• 13 years ago

Sorry for disappointing you, the name is correct, what you're looking for is called a javascript engine like V8, SpiderMonkey ...

jawb6• 13 years ago

I didn't want to call it VM.js since it sounds like a library, this project is a library (you can find it in js/vm.js) + UI which uses the library and define IO methods and callbacks. It's a webapp, briefly

knome• 13 years ago

Your VM will work much faster if you take the time to do a second pass over the generated "code" and resolve the jumps to LABELs all at once instead of linearly scanning the code for the appropriate target on each jump.

jawb6• 13 years ago

I agree with you, I'll fix these ASAP.

JSVM

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