The Wasm JS string builtin 'substring' does not correctly clamp the 'end' param
Categories
(Core :: JavaScript: WebAssembly, defect, P3)
Tracking
()
People
(Reporter: sjrdoeraene, Unassigned)
References
(Blocks 2 open bugs)
Details
Attachments
(1 file)
|
1.26 KB,
application/x-zip-compressed
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Details |
User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:130.0) Gecko/20100101 Firefox/130.0
Steps to reproduce:
Either unzip the attached bug.zip file to a directory, or recreate the files as follows:
index.html:
<html>
<head>
<title>Bug</title>
</head>
<body>
<script type=module src="./bug.js"></script>
</body>
</html>
bug.js
const options = {
builtins: ["js-string"],
};
const instantiated = await WebAssembly.instantiateStreaming(
fetch("./bug.wasm"), {}, options
);
const instance = instantiated.instance;
console.log(instance);
const { substringBridge } = instance.exports;
console.log(substringBridge("foobar", 1, 4)); // 'oob', OK
console.log(substringBridge("foobar", 1, 6)); // 'oobar', OK
console.log(substringBridge("foobar", 1, 10)); // '', should be 'oobar'
console.log(substringBridge("foobar", 1, -1)); // '', should be 'oobar'
bug.wat
(module
(type $substringType (func (param externref) (param i32) (param i32) (result (ref extern))))
(import "wasm:js-string" "substring" (func $substring (type $substringType)))
(func (export "substringBridge") (param $str externref) (param $start i32) (param $end i32) (result externref)
local.get $str
local.get $start
local.get $end
call $substring))
and compile to bug.wasm.
Then
- In Firefox's
about:configpage, turn on the optionjavascript.options.wasm_js_string_builtins - Start a local web server in the given directory (e.g., with
npx http-server) - Open
http://127.0.0.1:8080/(or another appropriate URL depending on the web server used) - Open the console
- Observe results
Actual results:
The following four strings are logged:
oob
oobar
<empty string>
<empty string>
The last 2 strings are incorrect. They should both be oobar.
Expected results:
oob
oobar
oobar
oobar
Indeed, the spec of the JS string builtin for substring (https://github.com/WebAssembly/js-string-builtins/blob/main/proposals/js-string-builtins/Overview.md#wasmjs-string-substring) says that
- The integer arguments are interpreted as unsigned 32-bit integers (so
-1is interpreted as2**32 - 1 - The
endparameter is clamped to thestring.lengthif it is larger.
Therefore, both for 10 and -1, end should be clamped at 6 and behave like the second call.
(For the record, and as some validation that my interpretation of the spec is accurate, V8 behaves as expected.)
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Comment 1•8 days ago
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The Bugbug bot thinks this bug should belong to the 'Core::JavaScript: WebAssembly' component, and is moving the bug to that component. Please correct in case you think the bot is wrong.
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Updated•3 days ago
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Description
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