I Wrote a WebAssembly VM in C
irreducible.io
I Wrote a WebAssembly VM in C
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Re: I Wrote a WebAssembly VM in C
#2This is great! The WebAssembly Core Specification is actually quite readable, although some of the language can be a bit intimidating if you're not used to reading programming language papers.
If anyone is looking for a slightly more accessible way to learn WebAssembly, you might enjoy WebAssembly from the Ground Up: https://wasmgroundup.com
(Disclaimer: I'm one of the authors)
Re: I Wrote a WebAssembly VM in C
#3This is great! The WebAssembly Core Specification is actually quite readable, although some of the language can be a bit intimidating if you're not used to reading programming language papers. If anyone is looking for a slightly more accessible way to learn WebAssembly, you might enjoy WebAssembly from the Ground Up: https://wasmgroundup.com (Disclaimer: I'm one of the authors)
I know one of WebAssembly's biggest features by design is security / "sandbox".
But I've always gotten confused with... it is secure because by default it can't do much.
I don't quite understand how to view WebAssembly. You write in one language, it compiles things like basic math (nothing with network or filesystem) to another and it runs in an interpreter.
I feel like I have a severe lack/misunderstanding. There's a ton of hype for years, lots of investment... but it isn't like any case where you want to add Lua to an app you can add WebAssembly/vice versa?
Re: I Wrote a WebAssembly VM in C
#4This is a really nice write up! It's giving me motivation to go back to my WASM implementation
Re: I Wrote a WebAssembly VM in C
#5This is great! The WebAssembly Core Specification is actually quite readable, although some of the language can be a bit intimidating if you're not used to reading programming language papers. If anyone is looking for a slightly more accessible way to learn WebAssembly, you might enjoy WebAssembly from the Ground Up: https://wasmgroundup.com (Disclaimer: I'm one of the authors)
I know one of WebAssembly's biggest features by design is security / "sandbox". But I've always gotten confused with... it is secure because by default it can't do much. I don't quite understand how to view WebAssembly. You write in one language, it compiles things like basic math (nothing with network or filesystem) to another and it runs in an interpreter. I feel like I have a severe lack/misunderstanding. There's…
WebAssembly can communicate through buffers. WebAssembly can also import foreign functions (Javascript functions in the browser).
You can get output by reading the buffer at the end of execution/when receiving callbacks. So, for instance, you pass a few frames worth of buffers to WASM, WASM renders pixels into the buffers, calls a callback, and the Javascript reads data from the buffer (sending it to a or similar).
The benefit of WASM is that it can't be very malicious by itself. It requires the runtime to provide it with exported functions and callbacks to do any file I/O, network I/O, or spawning new tasks. Lua and similar tools can go deep into the runtime they exist in, altering system state and messing with system memory if they want to, while WASM can only interact with the specific API surface you provide it.
That makes WASM less powerful, but more predictable, and in my opinion better for building integrations with as there is no risk of internal APIs being accessed (that you will be blamed for if they break in an update).
Re: I Wrote a WebAssembly VM in C
#6This is an interesting approach, great work!
For anyone that wants to check where the meat is at, is mostly in this file: https://github.com/irrio/semblance/blob/main/src/wrun.c
Thinking out loud, I think it would have been a great idea to conform with the Wasm-C-API (https://github.com/WebAssembly/wasm-c-api) as a standard interface for the project (which most of the Wasm runtimes: Wasmer, V8, wasmi, etc. have adopted), as the API is already in C and it would make it easier to try for developers familiar with that API.
Note for the author: if you feel familiar enough with Wasm and you would like to contribute into Wasmer, we would also welcome any patches or improvements. Keep up the work work!
Re: I Wrote a WebAssembly VM in C
#7Earlier quoted context omitted.
I know one of WebAssembly's biggest features by design is security / "sandbox". But I've always gotten confused with... it is secure because by default it can't do much. I don't quite understand how to view WebAssembly. You write in one language, it compiles things like basic math (nothing with network or filesystem) to another and it runs in an interpreter. I feel like I have a severe lack/misunderstanding. There's…
WebAssembly can communicate through buffers. WebAssembly can also import foreign functions (Javascript functions in the browser). You can get output by reading the buffer at the end of execution/when receiving callbacks. So, for instance, you pass a few frames worth of buffers to WASM, WASM renders pixels into the buffers, calls a callback, and the Javascript reads data from the buffer (sending it to a or similar). T…
I don’t believe it is currently possible for a WebAssembly instance to access any buffer other than its own memory. You have to copy data in and out.
Re: I Wrote a WebAssembly VM in C
#8This is great! The WebAssembly Core Specification is actually quite readable, although some of the language can be a bit intimidating if you're not used to reading programming language papers. If anyone is looking for a slightly more accessible way to learn WebAssembly, you might enjoy WebAssembly from the Ground Up: https://wasmgroundup.com (Disclaimer: I'm one of the authors)
I know one of WebAssembly's biggest features by design is security / "sandbox". But I've always gotten confused with... it is secure because by default it can't do much. I don't quite understand how to view WebAssembly. You write in one language, it compiles things like basic math (nothing with network or filesystem) to another and it runs in an interpreter. I feel like I have a severe lack/misunderstanding. There's…
> You write in one language
Not quite. Web assembly isn't a source language, it's a compiler target. So you should be able to write in C, Rust, Fortran, or Lua and compile any of those to WebAssembly.
Except that WebAssembly is a cross-platform assembly language/machine code which is very similar to the native machine code of many/most contemporary CPUs. This means a WebAssembly interpreter can be very straightforward, and could often translate one WebAssembly instruction to one native CPU instruction. Or rather, it can compile a stream of WebAssembly instructions almost one-to-one to native CPU instructions, which it can then execute directly.
Re: I Wrote a WebAssembly VM in C
#9Earlier quoted context omitted.
I know one of WebAssembly's biggest features by design is security / "sandbox". But I've always gotten confused with... it is secure because by default it can't do much. I don't quite understand how to view WebAssembly. You write in one language, it compiles things like basic math (nothing with network or filesystem) to another and it runs in an interpreter. I feel like I have a severe lack/misunderstanding. There's…
> You write in one language Not quite. Web assembly isn't a source language, it's a compiler target. So you should be able to write in C, Rust, Fortran, or Lua and compile any of those to WebAssembly. Except that WebAssembly is a cross-platform assembly language/machine code which is very similar to the native machine code of many/most contemporary CPUs. This means a WebAssembly interpreter can be very straightforwar…
A JIT should be able to translate most arithmetic and binary instructions to single-opcodes, however anything involving memory and functions calls needs safety checks that becomes multi-instruction. branches could mostly be direct _unless_ the runtime has any kind of metering (it should) to stop eternal loops (if it also wants to be crash-safe even if it's exploit safe).
Re: I Wrote a WebAssembly VM in C
#10This is great! The WebAssembly Core Specification is actually quite readable, although some of the language can be a bit intimidating if you're not used to reading programming language papers. If anyone is looking for a slightly more accessible way to learn WebAssembly, you might enjoy WebAssembly from the Ground Up: https://wasmgroundup.com (Disclaimer: I'm one of the authors)
> actually quite readable, although some of the language can be a bit intimidating if you're not used to reading programming language papers
You're more generous than me, I think it's rubbish.
Would have been easier to read if they had written it more like an ISA manual.