Using STANDALONE_WASM with emmalloc the second call to malloc fails if free was never called on allocation with size > 48

[peterhirn]

Building with -sMALLOC=emmalloc and -o argon2.wasm.

import { readFile } from "node:fs/promises";

const wasm = await readFile("./argon2.wasm");

const emscripten_notify_memory_growth = (memoryIndex) =>
  console.log("emscripten_notify_memory_growth", memoryIndex);

const imports = { env: { emscripten_notify_memory_growth } };
const { instance } = await WebAssembly.instantiate(wasm, imports);

// Uncomment this to make emmalloc work
// Note that this allocation needs to be > 48
/*
const ptr1 = instance.exports.malloc(49);
instance.exports.free(ptr1);
*/

console.log(instance.exports.malloc(10));
console.log(instance.exports.malloc(10));
console.log(instance.exports.malloc(10));

Output

70264
wasm://wasm/0001c5ce:1

RuntimeError: memory access out of bounds
    at wasm://wasm/0001c5ce:wasm-function[6]:0x529
    at wasm://wasm/0001c5ce:wasm-function[7]:0x74d

After uncommenting the marked section or removing -sMALLOC=emmalloc

70264
70288
70312

[peterhirn]

While investigating this problem trying to use emmalloc-debug I had to add proper WASI imports (https://nodejs.org/api/wasi.html). Turns out the problem is not reproducible with these imports:

import { readFile } from "node:fs/promises";
import { WASI } from "node:wasi";

const binary = await readFile("./src/argon2.wasm");

const wasi = new WASI({
  version: "preview1"
});

const emscripten_notify_memory_growth = (memoryIndex) =>
  console.log("emscripten_notify_memory_growth", memoryIndex);

const imports = { emscripten_notify_memory_growth };
const $imports = { env: imports, ...wasi.getImportObject() };
const { instance } = await WebAssembly.instantiate(binary, $imports);

wasi.initialize(instance);

console.log(instance.exports.malloc(10));
console.log(instance.exports.malloc(10));
console.log(instance.exports.malloc(10));

Output

(node:145241) ExperimentalWarning: WASI is an experimental feature and might change at any time
(Use `node --trace-warnings ...` to show where the warning was created)
69064
69088
69112

Now I'm even more confused 😅

Edit It's actually wasi.initialize(instance); that fixes the issue.

[peterhirn]

Figured it out. I have to call instance.exports._initialize() to make this work.

import { readFile } from "node:fs/promises";

const binary = await readFile("./src/argon2.wasm");

const emscripten_notify_memory_growth = (memoryIndex) =>
  console.log("emscripten_notify_memory_growth", memoryIndex);

const imports = { emscripten_notify_memory_growth };
const $imports = { env: imports, wasi_snapshot_preview1: imports };
const { instance } = await WebAssembly.instantiate(binary, $imports);

instance.exports._initialize();

console.log(instance.exports.malloc(10));
console.log(instance.exports.malloc(10));
console.log(instance.exports.malloc(10));

69064
69088
69112