Binary Format

[Horcrux7]

Are there any ideas for a binary format? After a year this look all there vague.

[lars-t-hansen]

I think the binary format depends on what the spec will be, and it's premature to commit to anything. There will be new kinds of data in the types section, and new opcodes, at a minimum; the POC that I'm implementing in Firefox has those. There may be new import and export entries.

[rossberg]

The basic outcome of more recent discussion is embodied in PR #34 (@lukewagner, still blocked on your thumbs up ;) ). Still in flux is how exactly we want to model runtime types (i.e., downcasts). I agree with @lars-t-hansen that the details of the binary format are probably best decided last.

[kripken]

What's the status here? I'm looking to implement binary format support in binaryen, and I'm not sure if the overview is intended to be fully specified at this point?

If it is, then I'm a little unclear on what to do with "defined types" as mentioned there. Is the idea that a "defined type" is, like a function type, defined in the type section, and those all go in the index of types (so anything providing a type index can refer to them)? If so, are the only things in the type section now going to be function types, struct types, and array types?

[skuzmich]

There is a full temporary binary format described in this document. In was discussed in #81

It is supported in V8 engine, Kotlin compiler prototype, and partially in WABT. Last time I saw Firefox was adjusting its binary encoding to be compatible with the document.

@kripken you are correct about a single type index space. According to the document, types can be:

name	+code	-code	immediate	feature	sm	v8	wabt
func	0x60	-0x20	vec(valtype), vec(valtype)
structtype	0x5f	-0x21	vec(fieldtype)	gc		✔
arraytype	0x5e	-0x22	fieldtype	gc		✔

[kripken]

Great, thanks for all the information @skuzmich !

Sounds like this issue can be closed then.

[rossberg]

@kripken, obviously, nothing is set in stone yet, but yes, the binary format section of the overview should be up to date and in sync with the V8 prototype (probably modulo a couple of recent changes). Also yes to your questions about "defined types" in the type section.