Wasmtime GitHub notifications bot (Oct 10 2026 at 01:24): Wasmtime GitHub notifications bot (Oct 10 2026 at 01:24):cfallin opened PR #14650 from cfallin:fix-stackslot-align to bytecodealliance:main:
We previously accepted arbitrarily large requested alignments for explicit stackslot entities in CLIF. We even tried to give the user this alignment relative to the start of the frame. But in a given ABI, if the stack is only N-aligned on function entry, unless we pad it out to get greater alignment depending on the low bits of SP, an M-aligned (M > N) offset from that initial SP is still only N-aligned.
We could do the complicated thing and try to pad to a greater alignment, but it turns out that we don't need to, at least in Wasmtime. Most things (including ValRaw!) only need 8-alignment. x64, aarch64 and riscv64 can support 16-alignment because their native-ABI stacks are 16-aligned. s390x's stack is only 8-aligned, however, but per above, that's fine for core Wasmtime uses. Stack-switching still requests 16-alignment for a u128, so we'll either need to not do that, or do something fancier, on s390x if/when we support stack switching there. For now, this aligns the Cranelift checks with what we can support in reality, and cleanly rejects invalid requests.
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Wasmtime GitHub notifications bot (Oct 10 2026 at 01:24):cfallin requested alexcrichton for a review on PR #14650.
Wasmtime GitHub notifications bot (Oct 10 2026 at 01:24):cfallin requested wasmtime-compiler-reviewers for a review on PR #14650.
Wasmtime GitHub notifications bot (Oct 10 2026 at 01:24):cfallin requested wasmtime-core-reviewers for a review on PR #14650.
Wasmtime GitHub notifications bot (Oct 10 2026 at 01:36)::thumbs_up: alexcrichton submitted PR review.
Wasmtime GitHub notifications bot (Oct 10 2026 at 01:36):alexcrichton has enabled auto merge for PR #14650.
Wasmtime GitHub notifications bot (Oct 10 2026 at 01:44):alexcrichton added PR #14650 Cranelift: reject too-large stackslot alignment. to the merge queue
Wasmtime GitHub notifications bot (Oct 10 2026 at 03:53):github-actions[bot] added the label cranelift:area:machinst on PR #14650.
Wasmtime GitHub notifications bot (Oct 10 2026 at 03:53):github-actions[bot] added the label cranelift on PR #14650.
Wasmtime GitHub notifications bot (Oct 10 2026 at 06:14)::check: alexcrichton merged PR #14650.
Wasmtime GitHub notifications bot (Oct 10 2026 at 06:14):alexcrichton removed PR #14650 Cranelift: reject too-large stackslot alignment. from the merge queue
Last updated: Oct 11 2026 at 04:10 UTC