I found this article very interesting with regards direct WASM interpretation: https://arxiv.org/abs/2205.01183
I produced https://github.com/peterseymour/winter on the back of it and learnt WASM is not as simple as it should be.
I Wrote a WebAssembly VM in C
11–20 of 104 posts
Re: I Wrote a WebAssembly VM in C
#12One tip for the author from another one, the spec-test contains various weird forms of textual wasm that isn't obvious how to compile but the wast2json converter can produce a simpler JSON desc accompanies by regular binary wasm files.
Re: I Wrote a WebAssembly VM in C
#13One tip for the author from another one, the spec-test contains various weird forms of textual wasm that isn't obvious how to compile but the wast2json converter can produce a simpler JSON desc accompanies by regular binary wasm files.
Same tip here. We did this with Chicory: https://github.com/dylibso/chicory
I'd follow on that, the earlier you can get this test-suite running the better for the iteration speed and correctness of your project.
It took a bit of time to make everything work, but once we did, we very quickly got to the point of running anything. The test-suite is certainly incomplete but gets you 95% there: https://github.com/WebAssembly/testsuite
Re: I Wrote a WebAssembly VM in C
#14Earlier 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…
Yes, interpretation on the fly was never its intention. The intention was to provide interpreted languages with a way to implement fast compiled functions.
Re: I Wrote a WebAssembly VM in C
#15This 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 ado…
> Wasmer
> Installed-Size: 266 MB
What the hell
Re: I Wrote a WebAssembly VM in C
#16Earlier 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…
> 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
That's not correct, when you embed Lua you can choose which APIs are available, to make the full stdlib available you must explicitly call `luaL_openlibs` [1].
[1] https://www.lua.org/manual/5.3/manual.html#luaL_openlibs
Re: I Wrote a WebAssembly VM in C
#17Earlier quoted context omitted.
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.
The embedder could hand the module functions for manipulating external buffers via externrefs. (I'm not sure if that's a good idea, or not, just that it could.)
But if the module wants to compute on the values in the buffer, at some level it would have to copy the data in/out.
Re: I Wrote a WebAssembly VM in C
#18This 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 ado…
> Wasmer > Installed-Size: 266 MB What the hell
Indeed, we need to improve further the base binary size!
Most of the size comes from the LLVM backend, which is a bit heavy. Wasmer ships many backends by default, and if you were to use Wasmer headless that would be just a bit less than a Mb.
If you want, you can always customize the build with only the backends that you are interested in using.
Note: I've seen some builds of LLVM under 5-10Mb, but those require heavy customization. Is clear that we have still some work to do to reduce size on the general build!
Re: I Wrote a WebAssembly VM in C
#19This 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)
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Re: I Wrote a WebAssembly VM in C
#20This 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 think it's much better to just learn how to read inference rules. They're actually quite simple, and are used ubiquitously to define PL semantics definitions.
Constraining this on "that's not an option" is a big waste of time - learning this will open up all of the literature written on the subject.