wasm

Since wasm is supported pretty much universally for some time now we can now ask for the next steps after the MVP:

https://wasm-feature-detect.surma.technology/

Supported wasm features as of 2021:

https://github.com/WebAssembly/proposals

HOSTS BROWSERS

Node20	Chrome	Safari	WebKit	Firefox	Feature
✔️	✔️	✔️	✔️	✔️	multiValue
✔️	✔️	✔️	✔️	✔️	bigInt
✔️	✔️	✔️	❌	✔️	bulkMemory
✔️	✔️	✔️	❌	✔️	exceptions
✔️	❌	❌	❌	❌	extendedConst
✔️	❌	❌	❌	❌	memory64
✔️	✔️	✔️	✔️	✔️	mutableGlobals
✔️[1]	✔️	✔️	❌	✔️	referenceTypes (externref)
✔️	✔️	✔️	❌	✔️	saturatedFloatToInt
✔️	✔️	✔️	✔️	✔️	streamingCompilation
✔️	✔️	✔️	✔️	✔️	signExtensions
✔️	✔️	❌	❌	✔️	SIMD ⚠️ ⇨ Flexible Vectors relaxed-simd
✔️	✔️	❌	❌	❌	tailCall
✔️	✔️/❌	❌	❌	❌	threads
✔️	✔️	❌	❌	✔️	GC: reference-types type struct (Chrome 108, FF 111)
?	?	?	?	?	GC: interface types <= webidl ≠ reference-types
?	?	?	?	?	type imports Overview
?	?	?	?	?	function-references
?	?	?	?	?	import/script type=module
?	?	?	?	?	https://github.com/tc39/proposal-import-reflection import module Foo from "foo.wasm";
✔️	?	?	?	?	typeReflection ?
❌	❌	❌	❌	❌	multi-memory
❌	❌	❌	❌	❌	jspi (Java Script Promise Integration: async!)
?	?	?	?	?	stringref GC?

binaryen

binaryen wasm-as --all is always first to implement proposals: ✔️ multi-memory ✔️ GC ✔️ GC non-null locals ✔️ strings ✔️ extended const

wit / wasm world Component Model MVP Canonical ABI webidl strings [SharedArrayBuffer] has lately been DISABLED in all browsers!

TOOLS

Binaryen | Binaryen | Wabt | Feature
wasm-as | wasm-objdump| wat2wasm | ---------|-------------|----------|---------- ✔️ | ✔️ | multiValue ✔️ | ❌ | stringref https://github.com/WebAssembly/wabt/issues/2144

RUNTIMES

Wasmer	Wasmtime	Wasm3	Wasmedge	Feature
✔️	✔️	✔️	✔️
✔️	✔️	✔️	✔️
✔️	✔️	✔️	✔️
❌	✔️	✔️	✔️
❌	❌	❌	✔️
?	❌	❌	✔️
✔️	✔️	✔️	✔️
✔️[1]	✔️	✔️		✔️
✔️	✔️	✔️	✔️
✔️	✔️	✔️	✔️
✔️⚠️	✔️⚠️	❌	⚠️	✔️⚠️
❌	✔️	❌	✔️
✔️	✔️/❌	❌		❌
?	?	?	?	?
?	?	?	?	?
✔️[1]	✔️[2]	?	✔️	?
?	?	?	?	?
?	?	?	?	?
?	?	?	✔️	?

Garbage Collection GC Proposal

GC is working in V8 (d8,deno,node) but not in other runtimes: https://github.com/WasmEdge/WasmEdge/issues/1122 (soon!) https://github.com/bytecodealliance/wasmtime/issues/5032 (baby steps) https://github.com/wasmerio/wasmer/issues/357 (NOT worked on) https://github.com/wasm3/wasm3/issues/432 (Bombed by Russians)

Most importantly multi-value is supported on all platforms

[1] : https://github.com/wasmerio/interface-types see struct [2] :

threads & tailCall are supported by wasmedge, together with interruptible aot instruction-count gas and time metering.

⚠️ SIMD harmful proposal should be avoided in favour of much cleaner extension:
Flexible Vectors great proposal!

Wasmtime supports Memory64, Multiple memories, Module Linking

https://github.com/WebAssembly/module-linking/ see

https://github.com/WebAssembly/component-model https://github.com/WebAssembly/component-model/blob/main/design/mvp/WIT.md https://github.com/WebAssembly/component-model/blob/main/design/mvp/CanonicalABI.md https://github.com/WebAssembly/component-model/blob/main/design/mvp/canonical-abi/definitions.py

https://github.com/WebAssembly/annotations WasmEdge OK supported by wat2wasm but not wasm-as

(module (@name "Gümüsü")
  (func $lambda (@name "λ") (@js ignore) )
)

https://github.com/WebAssembly/relaxed-simd/issues/ CANCER proposal, please stop it and add abstract vector ops i32.vector_add(a,b,out,length)

assemblyscript : https://www.assemblyscript.org/status.html

Most importantly multi-value is supported on all platforms

Apple is intentionally limiting the mobile web to force your hand to create an app.

wasix and witx

To try out cutting edge or extended functionality try this: https://docs.rs/wasix/latest/wasix/index.html

annotations

https://github.com/WebAssembly/annotations

(module (@name "Gümüsü") (@custom "my-fancy-section" (after func) "contents-bytes") (func $lambda (@name "λ") (param $x (@name "α") i32) (result i32) (get_local $x)) )

shared memory

Shared memory works in many environments even with 'threads' proposal not fully implemented.

(import "env" "memory" (memory (;0;) 1 1 shared))
…
const memory = new WebAssembly.Memory({ initial: 1, maximum: 1, shared:true });

atomics

https://webassembly.github.io/threads/core/syntax/instructions.html#atomic-memory-instructions

struct and array

The GC proposal has types like struct and array, which are a subset of interface types.

interface types are different from reference types

Interface Types

motivations

With the newly-added externref, WebAssembly can import JavaScript functions that create JavaScript values that can be passed to the Web IDL functions via the ECMAScript Binding, but the performance of this approach may be even worse than the JIT-optimized glue code.

(type $Coord (record (field "x" s32) (field "y" s32)))

intertype ::= u8 | s8 | s16 | u16 | s32 | u32 | s64 | u64 | f32 | f64
			|  char
			|  (list <intertype>)
			|  (record (field <name> <id>? <intertype>)*)
			|  (variant (case <name> <id>? <intertype>?)*)

While core wasm's type contains reference values which refer to mutable state, intertype compound values are transitively immutable.

https://github.com/WebAssembly/interface-types/blob/main/proposals/interface-types/Explainer.md

the following abbreviations only exist in the concrete formats:
bool ≡ (variant (case "false") (case "true"))
string ≡ (list char)
( tuple <intertype>*) ≡ (record ("𝒊" <intertype>)*) for 𝒊=0,1,...
(flags <name>*) ≡ (record (field <name> bool)*)
( enum <name>*) ≡ (variant (case <name>)*)
( option <intertype>) ≡ (variant (case "none") (case "some" <intertype>))
( union <intertype>*) ≡ (variant (case "𝒊" <intertype>)*) for 𝒊=0,1,...
(expected <intertype>? (error <intertype>)?) ≡ (variant (case "ok" <intertype>?) (case "error" <intertype>?))

.wit file format

The intention of the wit format is that it maps down to interface types, so the goal of name resolution is to effectively create the type section of a wasm module using interface types. Definitions of named types such as record foo { ... } are intended to map roughly to declarations in the type section of new types.

record person {
  name: string,
  age: u32,
}
hello: function(who: person) -> string

interface type adapter module with adapter functions

(adapter_module
  (module $CORE
	;; …
  )
  (instance $core (instantiate $CORE))
  (import "duplicate" (adapter_func $dup (param string) (result string string)))
  (import "print" (adapter_func $print (param string)))
  (adapter_func (export "print_twice") (param string)
	call_adapter $dup
	call_adapter $print
	call_adapter $print
  )
  (adapter_func $return_one_of (param string string i32) (result string)
	i32.eqz
	(if (param string string) (result string)
		( then return)
		( else drop return))
  )
)

adapter instructions

rotate $n : [ Tn+1 ... T0 ] -> [ Tn ... T0 Tn+1 ]
call_adapter $f : [ P* ] -> [ R* ]
<it>.lift_<ct> : [ ct ] -> [ it ]
<ct>.lower_<it> : [ it ] -> [ ct ]
char.lift : [ i32 ] -> [ char ]
char.lower : [ char ] -> [ i32 ]
list.lift $List $done $liftElem $destructor? : [ T:<type>* ] -> [ $List ]
list.lift_count $List $liftElem $destructor? : [ T*, count:i32 ] -> [ $List ]
list.has_count : [ (list T) ] -> [ (list T), maybe_count:i32, condition:i32 ]
list.is_canon : [ (list E) ] -> [ (list E), maybe_byte_length:i32, condition:i32 ]
list.lift_canon $List <memidx>? $destructor? : [ T*, offset:i32, byte_length:i32 ] -> [ $List ]
list.lower_canon <memidx>? : [ offset:i32, (list E) ] -> []
record.lift $Record $liftFields $destructor? : [ T:<type>* ] -> [ $Record ]
record.lower $Record $lowerFields : [ T:<type>*, $Record ] -> [ U:<type>* ]
variant.lift $Variant $case $liftCase? $destructor? : [ T:<type>* ] -> [ $Variant ]
variant.lower $Variant $lowerCase* : [ T:<type>*, $Variant ] -> [ U:<type>* ]

(module
  (func $foo (param i32 f32))

  (@interface func $adapter_foo (export "foo") (param s32) (param f32)
	arg.get 0
	s32-to-i32
	arg.get 1
	call-core $foo)
  (@interface func (export "bar") (param s32) (param f32)
	arg.get 0
	arg.get 1
	call-adapter $adapter_foo)
  (type $tf (func (result funcref)))
  (type $tg (func (result (ref $proc))))
	)

Typed Function References

https://github.com/WebAssembly/function-references

Unlike funcref and the existing call_indirect instruction, typed function references need not be stored into a table to be called (though they can)

Heap types

part of Typed Function References

https://github.com/WebAssembly/function-references/blob/master/proposals/function-references/Overview.md#types

heaptype ::= | func | extern reftype ::= ref null?

ref.func creates a function reference from a function index call_ref calls a function through a reference func.bind creates or extends a closure by binding one or several parameters let … locally binds operands to variables

ref.func $f : [] -> [(ref $t)] 0x14 call_ref : [t1* (ref null $t)] -> [t2*] 0x15 return_call_ref : [t1* (ref null $t)] -> [t2*] 0x16 func.bind $t' : [t0* (ref null $t)] -> [(ref $t')] 0x17 let (local t)* instr* end : [t1* t*] -> [t2*] ref.null ht: [] -> [(ref null ht)] ref.is_null 0xd3 ref.as_non_null : [(ref null ht)] -> [(ref ht)] 0xd4 br_on_null $l checks for null and branches if present 0xd6 br_on_non_null $l : [t* (ref null ht)] -> [t*]

Type Imports

https://github.com/WebAssembly/proposal-type-imports/blob/master/proposals/type-imports/Overview.md

(import "..." "..." (type $t))
(export "..." (type <heaptype>))
(type $t (private <type>*))

E.g. a file API might look like

(import "file" "File" (type $File any))
(import "file" "open" (func $open (param $name i32) (result (ref $File))))
(import "file" "read_byte" (func $read (param (ref $File)) (result i32)))

with private implementation

  (type $File (export "File") (private i32))  ;; file handle

Instructions type is an import description with a type constraint sub describes the type of a type import, with an upper bound

private * is a new form of type definition private.new creates a value of private type private.get reads a field from a private value

wasm binary format

deftype is a new category of defined types that generalises the contents of the type section
 	eftype ::= <functype> | <privatetype>
 	odule ::= {..., types vec(<deftype>)}

module-linking

https://github.com/WebAssembly/module-linking/blob/main/design/proposals/module-linking/Explainer.md

esm-integration

https://github.com/WebAssembly/esm-integration/tree/main/proposals/esm-integration

import {foo} from "./myModule.wasm";
<script type=wasm src="myModule.wasm"> 

`import {foo} from "./myModule.wasm";`
` (import "./counter.js" "getCount" (func $getCount (func (result i32)))) `
` (import "./counter.wasm" "count" (global i32))`

wasm-check code

wasm-ld --shared-memory if compiled with 'atomics' or 'bulk-memory'

bulk-memory

table.value: copy a region from an element segment

memory.value: copy a region from a data segment
top-2: destination address
top-1: offset into the source segment
top-0: size of memory region in bytes

memory.copy
top-2: destination address
top-1: source address
top-0: size of memory region in bytes

memory.fill
top-2: destination address
top-1: byte value to set
top-0: size of memory region in bytes

table.copy
data.drop: discard the data in an data segment
elem.drop: discard the data in an element segment

memcpy => memory.copy

replace any exported function called memcpy or memmove with a new function with the following contents: (func (param $dst i32) (param $src i32) (param $size i32) (result i32) local.get $dst local.get $src local.get $size memory.copy local.get $dst) Alternatively connect directly to v8's MemMove function

example data to memory

(import "a" "global" (global i32))  ;; global 0
(memory 1)
(data (i32.const 0) "hello")   ;; data segment 0, is active so always copied
(data "goodbye")               ;; data segment 1, is passive

(func $start
  (if (global.get 0)

    ;; copy data segment 1 into memory 0 (the 0 is implicit)
    (memory.value 1
      (i32.const 16)    ;; target offset
      (i32.const 0)     ;; source offset
      (i32.const 7))    ;; length

    ;; The memory used by this segment is no longer needed, so this segment can
    ;; be dropped.
    (data.drop 1))
)

Combining two wasm files

Combining two wasm files is still absurdly hard, tools regularily get removed and renamed https://github.com/bytecodealliance/wit-bindgen/issues/298 Also they never work on basic standard wasm but need custom sections (wasm-ld) or non-standard binaries (wasm-tools compose). Wasp tries to fill this gap by allowing arbitrary arguments: wasp main.wasm lib.wasm generates out.wasm without preconditions.

Administrative Instructions

https://webassembly.github.io/spec/core/exec/runtime.html#syntax-instr-admin

trap
ref funcaddr
ref.extern funcaddr
invoke funcaddr
label … end
frame … end

Tool conventions

https://github.com/WebAssembly/tool-conventions

see debug

SharedArrayBuffer

SharedArrayBuffer has been turned off by default after Spectre: https://developer.chrome.com/blog/enabling-shared-array-buffer/ https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer only available to pages that are cross-origin isolated. WebAssembly.Memory can still be used to get an instance of SharedArrayBuffer!

package registries

wasmer is now able to run WAPM packages directly via wasmer run

wast vs wat

https://webassembly.github.io/wabt/demo/wat2wasm/

The .wast extension is now used for the scripting language used by the WebAssembly test suite.

Binaryen wasm-as is ahead with implementing features like reference types, struct, array, stringref, i8, i16 wabt wat2wasm has better more forgiving syntax (no brackets needed) but understands no wasm 2.0

wabt wat2wasm --version 1.0.32 (mozilla …) binaryen wasm-as --version 111