[binji]

JVM is a great choice! You might also want to check out WebAssembly too (full disclosure: I used to work on wasm). There aren't too many opcodes, and a lot of them are relatively simple math operations.

Once you get it working, you could run things like JSLinux! https://bellard.org/jslinux/vm.html?url=win2k.cfg&mem=192&gr...

[javajosh]

Given your experience at this level of abstraction, do you have any thoughts on what an ideal set of opcodes look like? E.g. something like Knuth's MMIX. Do you prefer RISC or CISC? What about RISC-V? How much do the designers of real-world micro-architectures talk to folks like you?

A bit of a tangent, I know, but it feels important.

[binji]

I'm probably the wrong person to ask, to be honest. I was around for a lot of the design of Wasm, but wasn't really involved at that level.

That said, in my opinion the ideal set of opcodes really depends on your goal. There were many goals For Wasm, but I think there was a focus on keeping it small and simple. Originally it was AST-based, but it was changed to a stack machine to reduce size. It was also designed to be AoT or JIT compiled, so the opcode layout is not particularly friendly to hardware decoding or interpreters (although people have made some very high quality Wasm interpreters).

And of course there were a lot of discussions and disagreements about the best way forward: AST vs. register VM vs. stack machine. Structured control flow vs. goto. How to handle unreachable code. How to store integer literals (LEB vs. prefix byte). What the text format should look like (sexprs vs. ...?) etc.

[ywei3410]

Are there any meeting notes/chat logs for those discussions? It would be fascinating to get some insight into the design process for a modern VM.

[binji]

Yes, you can find all the meeting notes here: https://github.com/webassembly/meetings

However there were a lot of discussions that were not in those meetings and were in smaller groups or held in GitHub issues or PRs. Most of these were in https://github.com/webassembly/design.

[tiddles]

That’s a great idea, I’m not that familiar with wasm and the best way to learn is of course to implement a VM :)

Cheers for the link to the meeting notes in the other comment chain, sounds like a great rabbit hole

[kfrane]

You're right about wasm not being too complicated, I've learned this when watching David Beazley coding a WebAssembly interpreter in under an hour. And it doesn't require any knowledge about it beforehand.

https://www.youtube.com/watch?v=r-A78RgMhZU