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hardware2win

Web is eating world

We use it for crossplatform dev.

We use json as data exchange format everywhere

We will run our apps in webassembly based sandboxes

So how about using this mature techstack to talk to OSes too?

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Plenty of people do--it's called Electron. The problem C and friends solve is "how do you write the web or the OS?"

You can't bootstrap an interpreted language like JavaScript or even WebAssembly, the VM has to be written in something.

and in fact the VM pretty much has to be written in C (or C++, or you could get away with unsafe rust) since efficient function dispatch (not to mention JIT) are difficult without wildeyed pointer manipulation (you want to emit instructions to somewhere in memory and then jump to them, something inherently unsafe)

> you want to emit instructions to somewhere in memory and then jump to them, something inherently unsafe

Isn't this only for JIT? My understanding was that non-JIT VMs basically function as emulators of a non-existent CPU, so they interpret each bytecode instruction rather than asking the CPU proper to do a jump.

even a bytecode vm has to emit bytecode and then move an instruction pointer around. You can do it without using C pointer manipulation but it will always be less than ideal. This is a nice little blog post about it: https://pliniker.github.io/post/dispatchers/

Thanks! I'm starting work on a VM right now for a side project and was seriously considering using Rust, so this will be really helpful!

> and in fact the VM pretty much has to be written in C

What makes you think that you need C/C++ for this? Compilers were and still are written in many languages, and you can always come up with a compiler written in an "arbitrary" language which outputs e.g. an executable ELF file containing your VM runtime code.

There are a few examples of this in the wild btw, look at e.g. the GraalVM and its SubstrateVM sub-project.

I'm not familiar with the way GraalVM is implemented but I do know that at some point it has to have access to raw memory and registers in order to do JIT. There's no getting around that (and you can't do that with just java).

A compiler is different from a JIT engine since yeah you can just write whatever binary you want to disk, hell you could write an x86 compiler in javascript. but if you want to emit instructions to memory and send the CPU there to consume them, you need a smidge of native code.

Yes you can, that is what compiler intrisics are for.

https://chrisseaton.com/truffleruby/jokerconf17/

and how, pray tell, are intrinsics implemented?

The JIT compiler reckognizes them and give special meaning, see linked article.

i was being rhetorical, the intrinsics are implemented in native code

From Java code AOT compiled into native code, better learn about compilers instead of being rhetorical.

We're literally saying the same thing. Java compiled into a native code library for each target with intrinsics that give access to things like CPU registers is just another way of implementing intrinsics in native code

And native code is not C or C++? How do you think the very first C compiler were written? Spoiler, it was bootstrapped with assembly which was bootstrapped with machine code.

Someone actually has to implement the web browser / "tech stack". Web assembly, despite it's name, is an interpreted language. It is not magic. Interpreted languages need an interpreter (written in C).

Why written in C?

If C is just wrapper over asm

Then emit it from any other lang

Because, as the article states, the OS interface is C. In order to do anything useful at all in your code, you need to call through the C API of your operating system.

To replace this, you would need another compiled language. It can't be "any other lang" - it needs to be something compiled down to machine code that can be directly executed on your CPU. So you could write a new OS that presents an interface in Rust, or Zig, but never WASM.

IBM and Unisys mainframes and microcomputers beg to differ, with their language environments.

I don't think it has to be C, but it can't be any arbitrary language. It has to compile to machine code, and I wouldn't want to implement a VM in a garbage collected language because you need more fine-grained control over memory then those can provide.

That last requirement rules out most languages with any significant community besides C/C++, Rust, Zig, and a few other even lower profile C replacements.

Because that mature stack is burning a lot of cycles converting binary data into text and back.

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