Stream: git-wasmtime

Topic: wasmtime / PR #13949 Configure async task context on `rea...

Wasmtime GitHub notifications bot (Jul 23 2026 at 22:57):

alexcrichton opened PR #13949 from alexcrichton:reset-realloc-context to bytecodealliance:main:

This commit is an implementation of WebAssembly/component-model#680 which is a semantic change for invocations of the realloc canonical ABI option. Previously when this function was invoked the configured context-storage was whatever happened to run last in the store and in general wasn't well-defined. Additionally the context of the thread being run in was whatever happened to run last. The goal of the upstream spec change, and this commit, is to fully define what happens in this situation. Specifically:

• Invocations of realloc always start with context slots set to 0.
• The thread.index intrinsics, part of the component-model-threading proposal, is now no longer exempt from may-leave checks.

These changes combined mean that it's not actually possible for realloc to witness anything about its thread identity. This means that we don't actually have to allocate anything, all that's necessary is to save/restore context around invocation of cabi_realloc.

While this is a breaking change it's not expected to be observable in the ecosystem. This only affects context slots which are primarily only used for the WASIp3 ABI as the stack pointer and TLS base. There is no shipping WASIp3 target anywhere right now, so this breakage should not be observable.

<!--
Please make sure you include the following information:

• If this work has been discussed elsewhere, please include a link to that
  conversation. If it was discussed in an issue, just mention "issue #...".

• Explain why this change is needed. If the details are in an issue already,
  this can be brief.

Our development process is documented in the Wasmtime book:
https://docs.wasmtime.dev/contributing-development-process.html

Please ensure all communication follows the code of conduct:
https://github.com/bytecodealliance/wasmtime/blob/main/CODE_OF_CONDUCT.md
-->

Wasmtime GitHub notifications bot (Jul 23 2026 at 22:57):

alexcrichton requested wasmtime-compiler-reviewers for a review on PR #13949.

Wasmtime GitHub notifications bot (Jul 23 2026 at 22:57):

alexcrichton requested cfallin for a review on PR #13949.

Wasmtime GitHub notifications bot (Jul 23 2026 at 22:57):

alexcrichton requested wasmtime-core-reviewers for a review on PR #13949.

Wasmtime GitHub notifications bot (Jul 23 2026 at 23:06):

:thumbs_up: cfallin submitted PR review.

Wasmtime GitHub notifications bot (Jul 23 2026 at 23:06):

:speech_balloon: cfallin created PR review comment:

Do we need a drop-guard to restore the context if an error is returned (e.g. the bail! above), or are those always trap-cases I guess?

Wasmtime GitHub notifications bot (Jul 23 2026 at 23:08):

alexcrichton updated PR #13949.

Wasmtime GitHub notifications bot (Jul 23 2026 at 23:09):

alexcrichton updated PR #13949.

Wasmtime GitHub notifications bot (Jul 23 2026 at 23:10):

:memo: alexcrichton submitted PR review.

Wasmtime GitHub notifications bot (Jul 23 2026 at 23:10):

:speech_balloon: alexcrichton created PR review comment:

We should be good in this case because once a component traps everything internally is inaccessible and no longer able to be seen by a guest. There's a fair number of locations in concurrent.rs that do this as well (don't restore on trap/panic) as well. I've added a comment now to that effect though for future readers

Wasmtime GitHub notifications bot (Jul 23 2026 at 23:10):

alexcrichton has enabled auto merge for PR #13949.

Wasmtime GitHub notifications bot (Jul 23 2026 at 23:19):

alexcrichton added PR #13949 Configure async task context on realloc calls to the merge queue.

Wasmtime GitHub notifications bot (Jul 23 2026 at 23:44):

github-merge-queue[bot] removed PR #13949 Configure async task context on realloc calls from the merge queue.

Wasmtime GitHub notifications bot (Jul 23 2026 at 23:46):

alexcrichton commented on PR #13949:

Heh well @dicej maybe your Windows-specific failure wasn't Windows-specific after all (failing test on macOS)

Wasmtime GitHub notifications bot (Jul 23 2026 at 23:46):

alexcrichton added PR #13949 Configure async task context on realloc calls to the merge queue.

Wasmtime GitHub notifications bot (Jul 24 2026 at 00:11):

:check: alexcrichton merged PR #13949.

Wasmtime GitHub notifications bot (Jul 24 2026 at 00:11):

alexcrichton removed PR #13949 Configure async task context on realloc calls from the merge queue.

Last updated: Jul 29 2026 at 05:03 UTC