Fix MSan use-of-uninitialized-value in SimSIMD SVE functions by alexey-milovidov · Pull Request #101239 · ClickHouse/ClickHouse

alexey-milovidov · 2026-03-30T16:01:16Z

Update SimSIMD submodule to include fix for svmla_*_x / svmls_*_x in SVE accumulator operations. The _x (don't-care) variant left inactive lanes undefined, but svaddv(svptrue, ...) summed all lanes including those undefined ones. Changed to _m (merge) which preserves the accumulator value for inactive lanes.

Fixes #101232

Contrib PR: ClickHouse/SimSIMD#18
Upstream PR: ashvardanian/NumKong#331

https://s3.amazonaws.com/clickhouse-test-reports/json.html?PR=100177&sha=a7031a78dd031fc0e90fbeebc0c95df386c5c1a7&name_0=PR&name_1=Stress%20test%20%28arm_msan%29

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Update SimSIMD submodule to include fix for `svmla_*_x` / `svmls_*_x` in SVE accumulator operations. The `_x` (don't-care) variant left inactive lanes undefined, but `svaddv(svptrue, ...)` summed all lanes including those undefined ones. Changed to `_m` (merge) which preserves the accumulator value for inactive lanes. Fixes #101232 https://s3.amazonaws.com/clickhouse-test-reports/json.html?PR=100177&sha=a7031a78dd031fc0e90fbeebc0c95df386c5c1a7&name_0=PR&name_1=Stress%20test%20%28arm_msan%29 Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

clickhouse-gh · 2026-03-30T16:01:59Z

Workflow [PR], commit [792e196]

Summary: ❌

job_name	test_name	status	info
Build (arm_tidy)		failure
	Checkout Submodules	failure	cidb
Build (amd_debug)		dropped
Build (amd_asan_ubsan)		dropped
Build (amd_tsan)		dropped
Build (amd_msan)		dropped
Build (amd_binary)		dropped
Build (arm_debug)		dropped
Build (arm_asan_ubsan)		dropped
Build (arm_tsan)		dropped
Build (arm_msan)		dropped

AI Review

Summary

This PR updates the contrib/SimSIMD submodule from e37149571aba... to 324864d39356... to pull an upstream SVE/MSan fix for inactive-lane handling in accumulator operations. The change is narrowly scoped to a single submodule pointer update, and I did not find correctness, safety, performance, or rollout issues in the ClickHouse tree itself.

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Item	Status	Notes
Deletion logging	➖
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Core-area scrutiny	➖
No test removal	✅
Experimental gate	➖
No magic constants	➖
Backward compatibility	✅
`SettingsChangesHistory.cpp`	➖
PR metadata quality	✅
Safe rollout	✅
Compilation time	✅

Final Verdict

Status: ✅ Approve

nikitamikhaylov · 2026-03-30T17:29:51Z

@groeneai It was right to update the submodule rather than disabling the MSAN in the SimSIMD like you did here #100862

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

groeneai · 2026-03-30T19:16:01Z

Thanks @nikitamikhaylov — agreed, the submodule update fixing the _x → _m SVE accumulator variants is the proper approach since it addresses the root cause in SimSIMD directly. Our #100862 was a workaround (disable SVE under MSAN) that we already closed in favor of this.

nikitamikhaylov · 2026-04-01T12:54:05Z

@groeneai The issue still reproduces. Do you know what's wrong here?

The previous approach (unpoisoning `*result` after the dispatch wrapper returns in lib.c) did not help because MSan reports the error inside the SVE function body before it returns to the dispatch layer. Add `SIMSIMD_UNPOISON` calls after every `svaddv` scalar reduction inside SVE function implementations. This prevents MSan-tainted values from propagating to normalize functions and result stores. https://s3.amazonaws.com/clickhouse-test-reports/json.html?PR=101239&sha=a43cadd697dc5f4dbe13fd8481164dfac8be525e&name_0=PR&name_1=Stress%20test%20%28arm_msan%29 Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

groeneai · 2026-04-01T23:20:28Z

@nikitamikhaylov The PR has never actually built — every CI run fails at Checkout Submodules because the SimSIMD submodule pointer (324864d39356) references a commit that no longer exists on ClickHouse/SimSIMD:

gh api repos/ClickHouse/SimSIMD/commits/324864d393566df939e845a78a81902a25ee2a11
→ 422: "No commit found for SHA: 324864d393566df939e845a78a81902a25ee2a11"

The fix commit exists at a different hash — it was likely force-pushed. The correct commit is 5a0677af82f7e77afae43045ae7c01debf21625a on the ClickHouse/v6.5.15 branch:

gh api repos/ClickHouse/SimSIMD/commits/5a0677af
→ "Fix use-of-uninitialized-value in SVE accumulator operations (#18)"

That commit has the right fix: changes svmla_f32_x → svmla_f32_m (and similarly for f64, f16, bf16) in all SVE accumulator operations in spatial.h and dot.h. The _x (don't-care) suffix leaves inactive lanes undefined; the subsequent svaddv(svptrue, ...) sums all lanes including undefined ones, triggering MSan. The _m (merge) variant preserves the accumulator's initialized-zero value for inactive lanes, so the reduction is clean.

To fix: update the submodule pointer to 5a0677af82f7e77afae43045ae7c01debf21625a. That alone should resolve all the STID 1003-358c/326e/2410-543a/47e0 family (574 hits across 346 PRs in the last 30 days). The SIMSIMD_UNPOISON calls in the latest commit would then be unnecessary since the root cause is addressed.

clickhouse-gh bot added pr-ci submodule changed At least one submodule changed in this PR. labels Mar 30, 2026

Update SimSIMD submodule to merged commit on ClickHouse/v6.5.15

d948394

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Merge branch 'master' into fix-simsimd-sve-msan

a43cadd

This was referenced Apr 1, 2026

Fix endianness in QBit binary serialization #101378

Merged

Regression test for dictGet with unqualified dictionary name over Distributed tables #100878

Merged

This was referenced Apr 2, 2026

Reduce mutex contention in PipelineExecutor::allocateCPU to mitigate TSan crash in 02124_buffer_with_type_map_long #101060

Closed

Fix incorrect ORDER BY elision when read-in-order-through-join meets shard join #101456

Closed

rschu1ze mentioned this pull request Apr 2, 2026

Bump contrib/SimSIMD #101594

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Fix MSan use-of-uninitialized-value in SimSIMD SVE functions#101239

Fix MSan use-of-uninitialized-value in SimSIMD SVE functions#101239
alexey-milovidov wants to merge 4 commits intomasterfrom
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