Wasmtime GitHub notifications bot (Dec 03 2025 at 20:49): Wasmtime GitHub notifications bot (Dec 03 2025 at 20:49):alexcrichton requested dicej for a review on PR #12119.
Wasmtime GitHub notifications bot (Dec 03 2025 at 20:49):alexcrichton opened PR #12119 from alexcrichton:more-async-fuzz to bytecodealliance:main:
This commit adds a new fuzzer mode to the
miscfuzzer of Wasmtime which is focused on async events and interleavings of components using the component-model-async proposal. This fuzzer works by having a precompiled guest program which serves as the component to run. This precompiled component has a customfuzz.witwhich is used to interface with the fuzzer itself. The fuzzer is then a fuzz-generated sequence of commands to send to the component which verifies that everything executes correctly, has no panics, etc.This fuzzer intends to stress async communication and task infrastructure with component-model-async. Notably this does not stress lifting/lowering or arbitrary type signatures. This does, however, permute all of the following:
- Guest/host interactions (also guest/guest, host/host, etc).
- Async functions, both ready and pending.
- Future operations: reads, writes, cancellation, transfers, etc.
- Stream operations: reads, writes, cancellation, transfers, etc.
This is all throwing into a large "soup" and then asserted to work correctly. There's a few gotchas here and there for how this fuzzer is designed, such as some events requiring "yield N times to await this event happening". This is required because Wasmtime is allowed to non-deterministically select between a number of "ready events" and what to dispatch.
This is not intended to be a one-size-fits-all fuzzer for component-model-async. The recent enhancements to the
component_apifuzzer are intended to complement this fuzzer in terms of what's stressed where internally.<!--
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Wasmtime GitHub notifications bot (Dec 03 2025 at 20:50):alexcrichton commented on PR #12119:
Currently leaving this in draft form while https://github.com/bytecodealliance/wit-bindgen/pull/1446 is pending.
Wasmtime GitHub notifications bot (Dec 03 2025 at 20:51):alexcrichton commented on PR #12119:
I'll also note that I understand this is a pretty meat and pretty dense fuzzer, so I'm happy to walk through it if @dicej you or anyone else is interested. I'm also happy to write up more docs anywhere as necessary. Current docs are primarily located at crates/test-programs/src/bin/fuzz_async.rs
Wasmtime GitHub notifications bot (Dec 03 2025 at 23:12):alexcrichton updated PR #12119.
Wasmtime GitHub notifications bot (Dec 03 2025 at 23:25):alexcrichton updated PR #12119.
Wasmtime GitHub notifications bot (Dec 03 2025 at 23:45):github-actions[bot] commented on PR #12119:
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Wasmtime GitHub notifications bot (Dec 04 2025 at 15:35):alexcrichton updated PR #12119.
Wasmtime GitHub notifications bot (Dec 04 2025 at 15:35):alexcrichton has marked PR #12119 as ready for review.
Wasmtime GitHub notifications bot (Dec 04 2025 at 15:35):alexcrichton requested wasmtime-fuzz-reviewers for a review on PR #12119.
Wasmtime GitHub notifications bot (Dec 04 2025 at 15:35):alexcrichton requested fitzgen for a review on PR #12119.
Wasmtime GitHub notifications bot (Dec 04 2025 at 15:35):alexcrichton requested wasmtime-core-reviewers for a review on PR #12119.
Wasmtime GitHub notifications bot (Dec 04 2025 at 15:35):alexcrichton requested wasmtime-default-reviewers for a review on PR #12119.
Wasmtime GitHub notifications bot (Dec 09 2025 at 16:32):dicej submitted PR review:
Awesome work; thanks for doing this!
Wasmtime GitHub notifications bot (Dec 09 2025 at 16:32):dicej created PR review comment:
//! hasn't quite happened yet but it's queued up to happen. To handle these
Wasmtime GitHub notifications bot (Dec 09 2025 at 16:32):dicej created PR review comment:
A comment here explaining why the command list is being reversed would be helpful.
Wasmtime GitHub notifications bot (Dec 09 2025 at 16:32):dicej created PR review comment:
/// All known handles of this type, where they're located, etc.
Wasmtime GitHub notifications bot (Dec 09 2025 at 16:32):dicej created PR review comment:
// Writers can't actually be dropped prior to writing so "fake" a write by
Wasmtime GitHub notifications bot (Dec 09 2025 at 16:32):dicej created PR review comment:
//! The purpose of this fuzzer is to stress the management of async stacks, the
Wasmtime GitHub notifications bot (Dec 09 2025 at 16:32):dicej created PR review comment:
Let's remember to revisit this once e.g. intra-component
stream<u8>reads/writes are allowed.
Wasmtime GitHub notifications bot (Dec 09 2025 at 16:32):dicej created PR review comment:
// Two zero-length operations rendezvousing will leave
Wasmtime GitHub notifications bot (Dec 09 2025 at 18:26):alexcrichton updated PR #12119.
Wasmtime GitHub notifications bot (Dec 09 2025 at 18:27):alexcrichton created PR review comment:
Agreed yeah, there's a lot of parallels in restrictions/limitations of the component model which are baked into this generator and as we relax things we're going to want to make sure to relax the generator here and/or adjust it.
Wasmtime GitHub notifications bot (Dec 09 2025 at 18:27):alexcrichton submitted PR review.
Wasmtime GitHub notifications bot (Dec 09 2025 at 18:28):alexcrichton updated PR #12119.
Wasmtime GitHub notifications bot (Dec 09 2025 at 18:28):alexcrichton has enabled auto merge for PR #12119.
Wasmtime GitHub notifications bot (Dec 09 2025 at 20:11):alexcrichton merged PR #12119.
Last updated: Jan 09 2026 at 13:15 UTC