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   mcc (mcc@mastodon.social)'s status on Wednesday, 28-May-2025 08:25:43 JST mcc

   #BabelOfCode 2024
   Week 11 (??)
   Language: Textual Wasm

   Confidence level: Medium high

   PREV WEEK: https://mastodon.social/@mcc/114524697727786286
   RULES: https://mastodon.social/@mcc/113676228091546556

   I'm now doing the puzzles slightly out of order.

   "Wasm" is a bytecode VM that runs in web browsers as an alternative to JavaScript. Oddly for a modern VM, it's designed to be targeted by C.

   A thing I've heard repeatedly claimed, both excitedly and with eye-rolls, is that Wasm's human readable form is "a LISP". I want to know what that means.

   • Embed this notice
     ✧✦Catherine✦✧ (whitequark@mastodon.social)'s status on Wednesday, 28-May-2025 08:25:41 JST ✧✦Catherine✦✧

     in reply to

     @mcc wasmtime generates code that is competitive with C on computation-heavy workloads. wasm-interp is just the reference interpreter

   • Embed this notice
     mcc (mcc@mastodon.social)'s status on Wednesday, 28-May-2025 08:25:42 JST mcc

     in reply to

     I check out Wabt and try to build it, and… oh. There's… no cmake, on this machine. I hadn't needed it until now. Oh! What a peaceful and innocent life I have lead, since first I set up this laptop.

     clacke@libranet.de is my main likes this.
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     mcc (mcc@mastodon.social)'s status on Wednesday, 28-May-2025 08:25:42 JST mcc

     in reply to

     It seems I can assemble³ with:

     wat2wasm source.wast -o exec.wasm

     And execute with either, from wabt:

     wasm-interp simple.wasm -r add -a i32:1 -a i32:2

     Or if I have wasmtime:

     wasmtime --invoke add simple.wasm 1 2

     I don't know why I'd bother with wasmtime if I have wasm-interp. Is wasmtime faster?

     ³ Assume simple.wasm contains, code from MDN:

     (module
     (func $add (param $lhs i32) (param $rhs i32) (result i32)
     local.get $lhs
     local.get $rhs
     i32.add)
     (export "add" (func $add))
     )

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     mcc (mcc@mastodon.social)'s status on Wednesday, 28-May-2025 08:25:43 JST mcc

     in reply to

     On initially cracking open the MDN guide¹, *so far* it kind of seems like it only means "It's structured as an S-expression". That's a bit disappointing. It's an understandable decision, as S-expressions make parsing easy— I've used this shortcut myself— but also, it seems this is preserving *only* the part of LISP people hate most. What do people complain about the most? What do LISP heads complain the most about other people complaining about? *It's the parentheses*.

     ¹ https://developer.mozilla.org/en-US/docs/WebAssembly/Guides/Understanding_the_text_format

     clacke@libranet.de is my main likes this.
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     mcc (mcc@mastodon.social)'s status on Wednesday, 28-May-2025 08:25:43 JST mcc

     in reply to

     It's not actually clear what file extension you're supposed to use for textual wasm files. The Sublime plugin claims this language is called "WAST" and as such suggests .wast. I guess I'll go with that. MDN calls the format "WAT". I wonder if there's subtle commentary there.

     It's also a *little* nonobvious how to assemble and run this stuff. Wasm was originally intended to be loaded from JavaScript. Both MDN and help on mastodon² suggest a toolset named WABT.
     
     ² https://mastodon.social/@mcc/114581638222018210

     clacke@libranet.de is my main likes this.
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     ✧✦Catherine✦✧ (whitequark@mastodon.social)'s status on Wednesday, 28-May-2025 08:26:18 JST ✧✦Catherine✦✧

     in reply to

     @mcc also wasmtime has features like "bindings" and "real multithreading" and "knows how to do various types of I/O", basically everything you need to run a production app (or yowasp.org)

   • Embed this notice
     mcc (mcc@mastodon.social)'s status on Wednesday, 28-May-2025 08:29:50 JST mcc

     in reply to

     • ✧✦Catherine✦✧

     @whitequark Bindings to what?

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     ✧✦Catherine✦✧ (whitequark@mastodon.social)'s status on Wednesday, 28-May-2025 08:50:47 JST ✧✦Catherine✦✧

     in reply to

     @mcc to whatever code you want; you can add host functions written in Rust that your Wasm code can call. i don't think wasm-interp offers anything like this (I believe it just exists to validate the spec)

   • Embed this notice
     mcc (mcc@mastodon.social)'s status on Wednesday, 28-May-2025 08:50:47 JST mcc

     in reply to

     • ✧✦Catherine✦✧

     @whitequark Can I run wasmtime in a mode where only things that would be legal in a browser are legal?

   • Embed this notice
     mcc (mcc@mastodon.social)'s status on Wednesday, 04-Jun-2025 08:46:00 JST mcc

     in reply to

     So. Creeping along with this. I am posting tihs from a bus.

     Learned some more about "textual WASM". Two things I learned. One. It is LISP but also it is Forth. You write it as structurally an S-expression but the commands you write in that S-expression are, as it happens, instructions to a stack machine. This surprised me, but apparently Hotspot was a stack machine, as was the C# CLR as it was based on Hotspot, as is wasm because it was based on… Hotspot. Apparently this works well for JIT.

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     ✧✦Catherine✦✧ (whitequark@mastodon.social)'s status on Wednesday, 04-Jun-2025 08:46:00 JST ✧✦Catherine✦✧

     in reply to

     @mcc Hotspot isn't really a stack machine. *Java bytecode* is written for a stack machine, as is Wasm machine code, which works out well because it's compact: you don't encode (almost) any temporary indices, like you would have in LLVM

     the moment you load it, you transform it into a register representation in memory. not literally every implementation does it, but most do not actually execute it with a data stack

   • Embed this notice
     mcc (mcc@mastodon.social)'s status on Wednesday, 04-Jun-2025 08:46:01 JST mcc

     in reply to

     Been reading the docs and I have a LOT to say but

     I've been using this lovely, friendly guide to figure out how to write WASM assembly

     https://developer.mozilla.org/en-US/docs/WebAssembly/Guides/Understanding_the_text_format

     (The spec https://webassembly.github.io/spec/core/_download/WebAssembly.pdf is a little hard to work with)

     And saw this really alarming note implying the guide hadn't been updated since 2020 (is that when Mozilla fired everyone?)

     Can anyone recommend how I'd find out what has changed in Wasm between 2020 and 2025? Assume I'm targeting wasmtime and can be cutting edge.

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     ✧✦Catherine✦✧ (whitequark@mastodon.social)'s status on Wednesday, 04-Jun-2025 10:54:58 JST ✧✦Catherine✦✧

     in reply to

     • mega

     @mega @mcc there is the caveat that both wasm and java have the separate concept of locals, which is why i said "temporaries"; you still have to do liveness analysis for locals-locals if you want high quality codegen

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     mega (mega@chaos.social)'s status on Wednesday, 04-Jun-2025 10:55:00 JST mega

     in reply to

     • ✧✦Catherine✦✧

     @whitequark @mcc Also (maybe relevant for the JIT comment): the stack at any given point *is* the set of live variables.

     If you calculate a kind of "virtual stack" for a given basic block you will end up with the amount of elements that it pops from the stack (phi nodes/basic block arguments/whatever you want to call them) and the amount of elements it adds to the stack at the end of its execution (values that will be consumed by another block).

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     mcc (mcc@mastodon.social)'s status on Wednesday, 04-Jun-2025 10:56:20 JST mcc

     in reply to

     • ✧✦Catherine✦✧
     • mega

     @whitequark @mega if i am writing/generating code why would i use the stack for live variables instead of the locals, or vice versa?

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     ✧✦Catherine✦✧ (whitequark@mastodon.social)'s status on Wednesday, 04-Jun-2025 10:58:34 JST ✧✦Catherine✦✧

     in reply to

     • mega

     @mcc @mega the stack machine that JVM and Wasm have, and the SSA form that LLVM has, are literally equivalent (they are different ways to serialize the same IR, essentially; with the caveat that Wasm forbids irreducible control flow)

     if you have your code in SSA/CPS form you would find it easy to emit stack bytecode, if you do not, it is most convenient to use locals (and the runtimes are aware of this and optimize for it)