Stream: git-wasmtime

Topic: wasmtime / issue #12497 PCC regression notification

Wasmtime GitHub notifications bot (Feb 02 2026 at 20:29):

joell opened issue #12497:

Hi. This is a tragically unhelpful bug report -- in that I do not have a WASM file I am able to share to reproduce it -- but I have narrowed down the exact version of wasmtime in which the regression occurred. I am sharing what I know and can communicate purely in hopes that someone finds it useful in connection with some other issue, without any expectation anyone can act on this limited information.

Test Case

(unable to provide)

Steps to Reproduce

Load a .wasm file as a Component::from_binary with cranelift_pcc(true) in the Engine's Config.

Expected Results

The component loads.

Actual Results

Under wasmtime 37.0.2 the Component loads without any issue.
Under wasmtime 38.0.1 the Component load fails with this error:

Failure loading WASM extracted algorithms.: Compilation error: Proof-carrying-code validation error: UnimplementedInst

Versions and Environment

Wasmtime version or commit: 38.0.1

Operating system: Arch Linux

Architecture: x86-64

Extra Info

Once again, I'm sorry I cannot provide a .wasm file to reproduce this. I just wanted to do the courtesy of reporting what I knew, without any expectation of response to it. My only hope is that this information might be valuable the next time someone looks at the PCC system. Feel free to close and discard this issue at your pleasure.

Wasmtime GitHub notifications bot (Feb 02 2026 at 20:29):

joell added the bug label to Issue #12497.

Wasmtime GitHub notifications bot (Feb 02 2026 at 20:59):

cfallin commented on issue #12497:

Hi @joell -- thanks for the bug report.

It's known that PCC is not currently being tested in CI, so it's likely and in fact even probable that we'll have more cases like this over time, up until the point that we're able to bring it up to date and get it in CI so it stays that way.

This report simply states that there exists some Wasm file for which PCC is incomplete. Since no Wasm file is actually provided, I'll go ahead and close it, as the underlying state is already known. Please do feel free to file another issue (and/or PR to fix!) if you have a concrete example. Thanks!

Wasmtime GitHub notifications bot (Feb 02 2026 at 20:59):

cfallin closed issue #12497:

Hi. This is a tragically unhelpful bug report -- in that I do not have a WASM file I am able to share to reproduce it -- but I have narrowed down the exact version of wasmtime in which the regression occurred. I am sharing what I know and can communicate purely in hopes that someone finds it useful in connection with some other issue, without any expectation anyone can act on this limited information.

Test Case

(unable to provide)

Steps to Reproduce

Load a .wasm file as a Component::from_binary with cranelift_pcc(true) in the Engine's Config.

Expected Results

The component loads.

Actual Results

Under wasmtime 37.0.2 the Component loads without any issue.
Under wasmtime 38.0.1 the Component load fails with this error:

Failure loading WASM extracted algorithms.: Compilation error: Proof-carrying-code validation error: UnimplementedInst

Versions and Environment

Wasmtime version or commit: 38.0.1

Operating system: Arch Linux

Architecture: x86-64

Extra Info

Once again, I'm sorry I cannot provide a .wasm file to reproduce this. I just wanted to do the courtesy of reporting what I knew, without any expectation of response to it. My only hope is that this information might be valuable the next time someone looks at the PCC system. Feel free to close and discard this issue at your pleasure.

Last updated: Feb 24 2026 at 04:36 UTC