Write Your Own Virtual Machine • Hacker News Board

Re: Write Your Own Virtual Machine

#21

Post by Kwantuum » Sat, Aug 15, 2020, 1:38 PM UTC

p4bl0 wrote: post #10

ghj wrote: post #7

I was tricked into writing a VM while doing Advent of Code last year and it really deepened my understanding of programming (e.g., on how to implement simple coroutines). Advent of Code is supposed to be 25 daily programming puzzles leading up to christmas. I went in thinking they were going to be algo/datastructure tasks but half of them were actually about implementing and using a VM for a made up assembly language…

Funny that VM related days are all prime numbers :). EDIT: No they're not, I wasn't fully awake, sorry.

they're the odd days except for 2.

Re: Write Your Own Virtual Machine

#22

Post by retrac » Sat, Aug 15, 2020, 3:42 PM UTC

Slight tangent. To learn a bit of Zig, I've been doing the usual PDP-8 simulator task I do for systems languages. Zig allows arbitrary fixed width integers, from 1 to 2^16 bits long, signed and unsigned. It is /delightful/ to have those data types when doing an emulator. I'm convinced more languages should have them.

Re: Write Your Own Virtual Machine

#23

Post by cecilpl2 » Sat, Aug 15, 2020, 3:45 PM UTC

I have written a virtual CPU from very simple building blocks and highly recommend doing it.

I started with class Wire (which just wraps a bool) and class Transistor (which accepts two input Wire& and has an output Wire). It has an Update() function which sets the output state.

From those I built up gates, then flipflops, registers, mux/demuxes, counters, an ALU, and memory banks. Then I wrote a machine language, connected the cpu together, wrote a loader to load machine language files into ROM, then an assembler to allow me to write assembly code.

I then added VRAM, async buses, and wrote a working implementation of Game of Life.

It has 32bit instructions and runs about 10kHz with 8KB of RAM.

Re: Write Your Own Virtual Machine

#24

Post by Const-me » Sat, Aug 15, 2020, 4:06 PM UTC

Never wrote virtual machines, because I know why Sun (now Oracle) and Microsoft both spent a billion each to create theirs. You can write something that works over a weekend, but the performance won’t be good without JIT, generational GC, and many other extremely complicated optimizations.

If you think you need to develop a VM, I recommend to reconsider, and think how you can reuse something that’s already there. For instance, modern .NET VM is open source with MIT license, the code quality is more or less OK, and it’s relatively easy to generate .NET bytecode from something else, Reflection.Emit from the inside, or Mono.Cecil from outside.

Re: Write Your Own Virtual Machine

#25

Post by nurettin » Sat, Aug 15, 2020, 4:09 PM UTC

cecilpl2 wrote: post #23

I have written a virtual CPU from very simple building blocks and highly recommend doing it. I started with class Wire (which just wraps a bool) and class Transistor (which accepts two input Wire& and has an output Wire). It has an Update() function which sets the output state. From those I built up gates, then flipflops, registers, mux/demuxes, counters, an ALU, and memory banks. Then I wrote a machine language, con…

I did something similar, but with a LogicGate and a Wire class. I would recommend Morris Mano for those who would like to try.

Re: Write Your Own Virtual Machine

#26

Post by codr7 » Sat, Aug 15, 2020, 4:14 PM UTC

Const-me wrote: post #24

Never wrote virtual machines, because I know why Sun (now Oracle) and Microsoft both spent a billion each to create theirs. You can write something that works over a weekend, but the performance won’t be good without JIT, generational GC, and many other extremely complicated optimizations. If you think you need to develop a VM, I recommend to reconsider, and think how you can reuse something that’s already there. For…

It's a learning experience, it doesn't have to be production quality.

It will teach you skills that are applicable in other contexts and give a deeper understanding of what makes a VM tick.

And sometimes, a tiny VM is just what you need.

Re: Write Your Own Virtual Machine

#27

Post by teacpde » Sat, Aug 15, 2020, 4:16 PM UTC

Const-me wrote: post #24

Never wrote virtual machines, because I know why Sun (now Oracle) and Microsoft both spent a billion each to create theirs. You can write something that works over a weekend, but the performance won’t be good without JIT, generational GC, and many other extremely complicated optimizations. If you think you need to develop a VM, I recommend to reconsider, and think how you can reuse something that’s already there. For…

The point of writing your own vm isn’t to come up something that is on par with Sun’s or Microsoft’s vm, but rather have a hands on learning experience of the inner workings of a vm.

Re: Write Your Own Virtual Machine

#28

Post by nailuj » Sat, Aug 15, 2020, 4:21 PM UTC

If you want a really in-depth intro into the topic (with video lectures and guest appearances from legendary VM implementers!), check out CS294 from UC Berkeley that has been made available under a Creative Commons license: http://www.wolczko.com/CS294/

It‘s great for following along self-paced and has hands-on exercises for each topic. You should be a bit familiar with compilers already though.

Re: Write Your Own Virtual Machine

#29

Post by Const-me » Sat, Aug 15, 2020, 4:23 PM UTC

codr7 wrote: post #26

Const-me wrote: post #24

Never wrote virtual machines, because I know why Sun (now Oracle) and Microsoft both spent a billion each to create theirs. You can write something that works over a weekend, but the performance won’t be good without JIT, generational GC, and many other extremely complicated optimizations. If you think you need to develop a VM, I recommend to reconsider, and think how you can reuse something that’s already there. For…

It's a learning experience, it doesn't have to be production quality. It will teach you skills that are applicable in other contexts and give a deeper understanding of what makes a VM tick. And sometimes, a tiny VM is just what you need.

I agree about learning experience. But when I need a tiny language, I usually implement them so they compile into something already implemented and supported. Not necessarily .NET bytecode, here’s an example where I compiled a tiny language into HLSL source for the Microsoft’s shader compiler: https://github.com/Const-me/vis_avs_dx/tree/master/avs_dx/Dx...

Re: Write Your Own Virtual Machine

#30

Post by dbrueck » Sat, Aug 15, 2020, 4:36 PM UTC

jon-wood wrote: post #17

If you want to go really deep on this I highly recommend NAND To Tetris, a book which starts from the basics of combining NAND gates to build basic logic. You’ll gradually work through building a CPU from those components, building an assembler to program it, and finally putting a virtual machine on top of that.

Haha, I came here just to encourage people to check out www.nand2tetris.org too. It's extremely educational.

It's also realllllly satisfying to play Tetris on something you "built" all the way up from basic logic gates.

It's a great (and free) course during a pandemic lockdown or a fun project over a holiday break.