[Wasm RyuJit] Zero init gc shadow stack slots in the prolog#129073
Merged
AndyAyersMS merged 3 commits intoJun 7, 2026
Conversation
github-actions
Bot
added
the
area-CodeGen-coreclr
Member
Author
|
@dotnet/wasm-contrib PTAL |
Contributor
|
Tagging subscribers to this area: @JulieLeeMSFT, @jakobbotsch |
Contributor
There was a problem hiding this comment.
Pull request overview
This PR updates the CoreCLR JIT’s WASM backend prolog generation to ensure stack-frame zero-initialization is emitted as a single memory.fill, with the goal of explicitly zeroing GC-ref slots on the WASM shadow stack.
Changes:
- Add a WASM-specific
CodeGen::genZeroInitFrameimplementation that emits a singlememory.fill. - Update
genCheckUseBlockInit()so WASM always uses block-init when there are any init slots. - Adjust
genFnProlog()on WASM to compute the prolog zero-init byte range from memory-residentlvMustInitlocals (skipping certain WASM frame-header locals).
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.
| File | Description |
|---|---|
| src/coreclr/jit/codegenwasm.cpp | Adds WASM-specific prolog frame zero-init via memory.fill and marks the block-init helper as unreachable. |
| src/coreclr/jit/codegencommon.cpp | Forces block-init selection on WASM and changes prolog range computation to WASM-specific logic. |
Member
|
With this applied to my local branch, my spilling test scenario works without GC crashes, so I think you're right! |
kg
reviewed
Jun 6, 2026
kg
approved these changes
Jun 6, 2026
Use a single memory.fill to zero the slots. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
AndyAyersMS
force-pushed
the
fix-wasm-r2r-prolog-zero-init
branch
from
45a9808 to
1f9b88e
Compare
Address PR review feedback: drop the confusing reference to `register-init bookkeeping below`. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Member
Author
|
Seems to be working and showing what we'd expect; memory.fills in the prologs. |
Address PR review feedback: genCheckUseBlockInit now uses block-init on WASM whenever there are any init slots, so fgVarNeedsExplicitZeroInit should mirror that and skip the per-target size threshold for WASM. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
We must explicitly zero GC ref slots on the shadow stack in the prolog. Do this via a single memory.fill.