(WIP) Parse Threaded Modules

[data-pup]

Parse Threaded Modules

🚧 WIP 🚧

Fixes #326.

This continues the work from #365.

First, a reduced test fixture based on the repro posted in the original issue here:

;; `threads.wat` fixture
;;
;; Built with `wat2wasm --enable-bulk-memory --enable-threads`
(module
 (memory $0 1 1)
 (data (i32.const 0) "")
 (func $f (data.drop 0))
)

After building the .wasm file with wat2wasm --enable-bulk-memory --enable-threads, we have a 44 byte file, with the following header sizes:

; exa -l --header twiggy/tests/all/fixtures/threads.wasm

Permissions Size User    Date Modified Name
.rw-rw-r--    44 katelyn 21 Jun 23:07  twiggy/tests/all/fixtures/threads.wasm


; wasm-objdump --headers twiggy/tests/all/fixtures/threads.wasm

threads.wasm:	file format wasm 0x1

Sections:

     Type start=0x0000000a end=0x0000000e (size=0x00000004) count: 1
 Function start=0x00000010 end=0x00000012 (size=0x00000002) count: 1
   Memory start=0x00000014 end=0x00000018 (size=0x00000004) count: 1
DataCount start=0x0000001a end=0x0000001b (size=0x00000001) count: 1
     Code start=0x0000001d end=0x00000024 (size=0x00000007) count: 1
     Data start=0x00000026 end=0x0000002c (size=0x00000006) count: 1

And we can print sizes without a should not parse the same key into multiple items panic!

; target/debug/twiggy top twiggy/tests/all/fixtures/threads.wasm

 Shallow Bytes │ Shallow % │ Item
───────────────┼───────────┼───────────────────────
             8 ┊    18.18% ┊ wasm magic bytes
             7 ┊    15.91% ┊ code[0]
             6 ┊    13.64% ┊ code section headers
             5 ┊    11.36% ┊ data[0]
             3 ┊     6.82% ┊ type[0]: () -> nil
             3 ┊     6.82% ┊ type section headers
             3 ┊     6.82% ┊ memory[0]
             3 ┊     6.82% ┊ memory section headers
             3 ┊     6.82% ┊ "data count" section
             3 ┊     6.82% ┊ data section headers
            44 ┊   100.00% ┊ Σ [10 Total Rows]

Question: Note that twiggy says the data count section is 3 bytes, but wasm-objdump says 1 byte. When I print the full contents like so:

; wasm-objdump --full-contents twiggy/tests/all/fixtures/threads.wasm

threads.wasm:	file format wasm 0x1

Contents of section Type:
000000a: 0160 0000                                .`..

Contents of section Function:
0000010: 0100                                     ..

Contents of section Memory:
0000014: 0101 0101                                ....

Contents of section DataCount:
000001a: 01                                       .

Contents of section Code:
000001d: 0105 00fc 0900 0b                        .......

Contents of section Data:
0000026: 0100 4100 0b00                           ..A...

It does seem to be a size of 1, so I'm inclined to think this isn't a complete fix yet. That said, the code section starts at 1d, so I'm curious if this is just an alignment issue of some sort.

[data-pup]

I'll clean up the history on this branch later of course, pardon! Very much a WIP that I wanted to get online while I figure out the questions above.

[turbolent]

What is needed to get this fix in?