perf(runtime): an inline address window in front of the registry probes — cc --help −5.16% instructions, −6.30% cycles - #9272
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📝 WalkthroughWalkthroughAdds concurrent process-global address windows for buffer and typed-array registry probes. Registration paths widen the windows before publication. Probes reject out-of-window addresses before registry access. Closure pointer checks validate the magic tag before arena classification. ChangesRegistry probe fast paths
Estimated code review effort: 3 (Moderate) | ~30 minutes Merge Risk: 🟠 High · up to The closure-pointer fast path reads a raw tag before establishing that the candidate address is mapped and live; an in-range stale or invalid pointer could therefore fault the process. This is a concrete runtime-correctness and availability risk, so the PR is not merge-ready until the validation order or an equivalent safety check is fixed. Sequence Diagram(s)sequenceDiagram
participant Registration
participant RegistryAddrWindow
participant BufferProbe
participant TypedArrayProbe
participant Registry
Registration->>RegistryAddrWindow: Admit registered address
BufferProbe->>RegistryAddrWindow: Check buffer address
RegistryAddrWindow-->>BufferProbe: Return window result
TypedArrayProbe->>RegistryAddrWindow: Check typed-array address
RegistryAddrWindow-->>TypedArrayProbe: Return window result
BufferProbe->>Registry: Perform exact lookup when admitted
TypedArrayProbe->>Registry: Perform exact lookup when admitted
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✅ Passed checks (4 passed)
Full details: Description checkExplanation The description gives detailed technical context, measurements, validation results, and test evidence, but it does not follow the repository template. It omits the required section headings and checklist, and it does not state a related issue as required.
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Inline comments:
In `@crates/perry-runtime/src/closure/dynamic_props.rs`:
- Around line 525-526: Move the arena validation using classify_heap_generation
before the unsafe type-tag read in the relevant closure classification flow,
ensuring is_valid_obj_ptr alone never permits dereferencing an unmapped or stale
pointer. Preserve the existing behavior for validated pointers and reject or
return through the current invalid-pointer path before accessing
CLOSURE_TYPE_TAG_OFFSET.
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changelog.d/registry-probe-address-window.mdcrates/perry-runtime/src/buffer/header.rscrates/perry-runtime/src/buffer/mod.rscrates/perry-runtime/src/closure/dynamic_props.rscrates/perry-runtime/src/registry_latch.rscrates/perry-runtime/src/registry_latch_probes.rscrates/perry-runtime/src/shared_sab.rscrates/perry-runtime/src/typedarray/mod.rs
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| let type_tag = | ||
| unsafe { *((ptr as *const u8).add(CLOSURE_TYPE_TAG_OFFSET) as *const u32) }; |
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🩺 Stability & Availability | 🟠 Major | ⚡ Quick win
🔎 Supported by static analysis
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set -euo pipefail
ast-grep outline crates/perry-runtime/src/closure/dynamic_props.rs \
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| sort \
| while read -r f; do
case "$f" in
*/learnings/*|*/architecture/*) ;;
*) printf '\n### %s\n' "$f"; cat "$f" ;;
esac
done
printf '%s\n' '--- dynamic_props.rs target ---'
sed -n '480,555p' crates/perry-runtime/src/closure/dynamic_props.rs
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rg -n -C 18 \
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crates/perry-runtime/src/value crates/perry-runtime/src/arena/page_meta.rs crates/perry-runtime/src/value/addr_class.rs
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Keep arena validation before the raw tag read.
is_valid_obj_ptr checks only a numeric address range. It does not prove allocation membership, liveness, or readable storage. classify_heap_generation runs after the unsafe read at ptr + CLOSURE_TYPE_TAG_OFFSET, so an unmapped or stale accepted pointer can fault before arena validation.
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only still-valid issues, skip the rest with a brief reason, keep changes
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In `@crates/perry-runtime/src/closure/dynamic_props.rs` around lines 525 - 526,
Move the arena validation using classify_heap_generation before the unsafe
type-tag read in the relevant closure classification flow, ensuring
is_valid_obj_ptr alone never permits dereferencing an unmapped or stale pointer.
Preserve the existing behavior for validated pointers and reject or return
through the current invalid-pointer path before accessing
CLOSURE_TYPE_TAG_OFFSET.
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…e buffer/typed-array probes Preserved work from an interrupted session. admit() uses fetch_min/fetch_max (the non-atomic read-modify-write race the previous run caught is fixed here); memory orderings still to be tightened and all numbers still to be re-measured.
… writer set admit() is now two unconditional AcqRel fetch_min/fetch_max. The Relaxed 'skip if already covered' pre-check was a second form of the same lost-update bug that fetch_min/fetch_max fixed, moved one level up into the memory model: a thread that SKIPS the RMW performs no acquire, so another thread's widening never joins its happens-before graph, and a reader synchronising with this thread's publish is not guaranteed to see the bound that covers the address -- a false negative for a genuinely registered pointer. Registration runs 52 times in a 6.9G-instruction cc run, so the fast path bought nothing measurable and cost the proof. Both probes now re-derive every window rejection from the authoritative tables under debug_assertions, so a registration route added without admit() panics in the first test that exercises it instead of misclassifying a pointer in release.
…arena Same conjunction, reordered. Measured on claude-code --help (2,240,934 calls): the tag test partitions them 231,704/2,009,230 -- bit for bit the partition the whole function produces -- yet classify_heap_generation and the GC-header read ran on 100% of calls to change none of them. The load is safe where it now sits because the three checks above it are the only guard it has ever had: the Unknown arm performed this same read with nothing else in front of it, and Unknown means 'in no arena this process knows about' -- the least known case, not the most. Arena ownership still runs, below, where it does its actual job of rejecting a coincidental "CLOS"; that is pinned by managed_error_with_closure_magic_in_padding_is_not_a_closure.
…tprobe counts The preserved notes carried bucket-estimated figures (4,651,086 probes, '88% rejected'). Direct uprobe/uretprobe counts on the measured binaries give 4,650,058 probes with 4 'yes', 3,566,956 typed-array probes with zero 'Some', and 98.0%/97.2% of calls removed. Comment-only; no code lines change. Also states the cross-thread visibility argument in terms of admit()'s AcqRel RMWs rather than deferring to the latch's hand-off edges, since that is now the edge the window actually relies on.
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Inline comments:
In `@crates/perry-runtime/src/closure/dynamic_props.rs`:
- Line 525: Restore arena ownership and readability validation before the unsafe
type-tag dereference in the closure pointer-validation flow, using the existing
validation helper or an equivalent check before every raw tag read. Ensure
in-range stale, unmapped, or mis-boxed pointers return false without faulting,
while preserving the existing handle-band, numeric-range, alignment, and
heap-generation checks.
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| // no arena this process knows about" — the LEAST known case, not the most. | ||
| // Arena ownership was never what made the load safe; it is what | ||
| // disambiguates a coincidental "CLOS", which is why it stays below. | ||
| let type_tag = unsafe { *((ptr as *const u8).add(CLOSURE_TYPE_TAG_OFFSET) as *const u32) }; |
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🩺 Stability & Availability | 🟠 Major | ⚡ Quick win
Restore arena validation before the raw tag read.
Line 525 dereferences ptr + CLOSURE_TYPE_TAG_OFFSET after only the handle-band, numeric-range, and alignment checks. is_valid_obj_ptr does not establish that the address is mapped, allocated, live, or readable. An in-range stale or mis-boxed pointer can therefore fault before classify_heap_generation runs.
Restore the previous validation order, or add an equivalent ownership and readability check before every unsafe tag read. Verify that an in-range unmapped pointer returns false without a process fault. Run perry-runtime tests with RUST_TEST_THREADS=1.
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In `@crates/perry-runtime/src/closure/dynamic_props.rs` at line 525, Restore arena
ownership and readability validation before the unsafe type-tag dereference in
the closure pointer-validation flow, using the existing validation helper or an
equivalent check before every raw tag read. Ensure in-range stale, unmapped, or
mis-boxed pointers return false without faulting, while preserving the existing
handle-band, numeric-range, alignment, and heap-generation checks.
…lass-prototype probes Round 2 (PerryTS#9272) put an inline [lo, hi] address window in front of the buffer and typed-array probes. Measured against the four probes it named as follow-up, a window is the wrong shape for two of them and the right shape for one: is_registered_symbol 378,163 calls, window rejects 38.3% is_registered_class_prototype_object 26,290 calls, window rejects 54.0% is_uint8array_buffer 537,921 calls, window rejects 100% Symbols and class prototypes are ordinary GC-heap objects, so [lo, hi] grows to cover most of the heap. RegistryAddrFilter is the same monotone contract over a 1024-bit Bloom filter instead of a range; replaying each probe's real argument stream from a cc --help run, it rejects 99.58% and 99.05%. is_uint8array_buffer keeps the cheaper window (100% rejection, 0 true answers). Every rejection is re-derived from the authoritative table under debug_assertions, so a registration route added without admitting panics in the first test that touches it.
|
Merged. The machine-check is the thing worth reviewing here, and I verified it fires rather than trusting that it exists. Context for why I care: this is the fourth PR in this family, and I found real defects in the first two — #9176 armed its latch on one of two insert paths into the external-Uint8Array registry, so a WebCrypto key registered on one thread answered "no" from every other; #9177 didn't widen its range on the collector's re-key, so a symbol evacuated past its allocation's bounds became invisible to Replacing the enumeration with Verified by sabotage, because a clean run only proves the net didn't trip. I removed Address, which tables to look in, which function to call — caught by the first test touching that route. That is #9176's bug class turned from a hand audit into a build failure. One thing worth knowing about its reach. It is The measurement discipline is also right, and I'd single it out: cycles fall more than instructions (−6.30% vs −5.16%) with IPC rising 2.077 → 2.102, contrasted against an earlier change in this campaign that removed 24% of instructions and raised cycles because the work rode free in superscalar slack. That contrast is what separates real removal from bookkeeping, and most perf PRs don't make it. Validation: The one probe divergence is pre-existing and unrelated: |
…lass-prototype probes Round 2 (PerryTS#9272) put an inline [lo, hi] address window in front of the buffer and typed-array probes. Measured against the four probes it named as follow-up, a window is the wrong shape for two of them and the right shape for one: is_registered_symbol 378,163 calls, window rejects 38.3% is_registered_class_prototype_object 26,290 calls, window rejects 54.0% is_uint8array_buffer 537,921 calls, window rejects 100% Symbols and class prototypes are ordinary GC-heap objects, so [lo, hi] grows to cover most of the heap. RegistryAddrFilter is the same monotone contract over a 1024-bit Bloom filter instead of a range; replaying each probe's real argument stream from a cc --help run, it rejects 99.58% and 99.05%. is_uint8array_buffer keeps the cheaper window (100% rejection, 0 true answers). Every rejection is re-derived from the authoritative table under debug_assertions, so a registration route added without admitting panics in the first test that touches it.
…lass-prototype probes Round 2 (PerryTS#9272) put an inline [lo, hi] address window in front of the buffer and typed-array probes. Measured against the four probes it named as follow-up, a window is the wrong shape for two of them and the right shape for one: is_registered_symbol 378,163 calls, window rejects 38.3% is_registered_class_prototype_object 26,290 calls, window rejects 54.0% is_uint8array_buffer 537,921 calls, window rejects 100% Symbols and class prototypes are ordinary GC-heap objects, so [lo, hi] grows to cover most of the heap. RegistryAddrFilter is the same monotone contract over a 1024-bit Bloom filter instead of a range; replaying each probe's real argument stream from a cc --help run, it rejects 99.58% and 99.05%. is_uint8array_buffer keeps the cheaper window (100% rejection, 0 true answers). Every rejection is re-derived from the authoritative table under debug_assertions, so a registration route added without admitting panics in the first test that touches it.
…lass-prototype probes Round 2 (PerryTS#9272) put an inline [lo, hi] address window in front of the buffer and typed-array probes. Measured against the four probes it named as follow-up, a window is the wrong shape for two of them and the right shape for one: is_registered_symbol 378,163 calls, window rejects 38.3% is_registered_class_prototype_object 26,290 calls, window rejects 54.0% is_uint8array_buffer 537,921 calls, window rejects 100% Symbols and class prototypes are ordinary GC-heap objects, so [lo, hi] grows to cover most of the heap. RegistryAddrFilter is the same monotone contract over a 1024-bit Bloom filter instead of a range; replaying each probe's real argument stream from a cc --help run, it rejects 99.58% and 99.05%. is_uint8array_buffer keeps the cheaper window (100% rejection, 0 true answers). Every rejection is re-derived from the authoritative table under debug_assertions, so a registration route added without admitting panics in the first test that touches it.
…lass-prototype probes Round 2 (PerryTS#9272) put an inline [lo, hi] address window in front of the buffer and typed-array probes. Measured against the four probes it named as follow-up, a window is the wrong shape for two of them and the right shape for one: is_registered_symbol 378,163 calls, window rejects 38.3% is_registered_class_prototype_object 26,290 calls, window rejects 54.0% is_uint8array_buffer 537,921 calls, window rejects 100% Symbols and class prototypes are ordinary GC-heap objects, so [lo, hi] grows to cover most of the heap. RegistryAddrFilter is the same monotone contract over a 1024-bit Bloom filter instead of a range; replaying each probe's real argument stream from a cc --help run, it rejects 99.58% and 99.05%. is_uint8array_buffer keeps the cheaper window (100% rejection, 0 true answers). Every rejection is re-derived from the authoritative table under debug_assertions, so a registration route added without admitting panics in the first test that touches it.
…9225's linear scan gated — cc --help −1.25% instructions, −2.37% cycles (#9291) * wip(runtime): address windows for the symbol and Uint8Array probes Hoist #9177's symbol address range out of is_registered_symbol_slow into is_registered_symbol as a RegistryAddrWindow, so the common negative answer costs no call; add the same window to is_uint8array_buffer. Both rejections are re-derived from the authoritative tables under debug_assertions. Not yet measured on cc --help. * perf(runtime): a monotone address FILTER in front of the symbol and class-prototype probes Round 2 (#9272) put an inline [lo, hi] address window in front of the buffer and typed-array probes. Measured against the four probes it named as follow-up, a window is the wrong shape for two of them and the right shape for one: is_registered_symbol 378,163 calls, window rejects 38.3% is_registered_class_prototype_object 26,290 calls, window rejects 54.0% is_uint8array_buffer 537,921 calls, window rejects 100% Symbols and class prototypes are ordinary GC-heap objects, so [lo, hi] grows to cover most of the heap. RegistryAddrFilter is the same monotone contract over a 1024-bit Bloom filter instead of a range; replaying each probe's real argument stream from a cc --help run, it rejects 99.58% and 99.05%. is_uint8array_buffer keeps the cheaper window (100% rejection, 0 true answers). Every rejection is re-derived from the authoritative table under debug_assertions, so a registration route added without admitting panics in the first test that touches it. * changelog: registry-probe address filter (symbol, class prototype) + Uint8Array window * test(runtime): keep TEST_SYMBOL_REGISTRY_PROBES meaning 'entry past the latch' Two sabotage checks in other suites defeat a cheaper upstream screen and require this counter to move; counting filter admissions instead made them fail. Filter admissions get their own counter, mirroring typedarray::TEST_TA_WINDOW_ADMITTED_PROBES. * test(runtime): the unregistered-scratch probe sweep covers the class-prototype probe too * docs(runtime): the descriptor-target scan comment's premise is false for every bundle (#9225) * docs(runtime): name the filter's saturation regime and the knob for it * fix(runtime): the debug audits use try_lock/try_read, not lock/read The rejection path never took either lock, so a blocking audit could hang on a caller the audited code would not have. Sabotage-checked: removing the admit from either registration funnel fails 1 test (symbol) and 3 tests (class prototype), so the audits demonstrably run. * docs(runtime): the symbol side's comments and the funnel's name say 'filter', not 'range' * docs(runtime): bits accrue per admission (the collector re-keys both tables); record the end-of-run false-positive rate * revert: unrelated cargo fmt reformat of two perry-codegen files They are fmt-dirty on pristine main (42d0f45) from #9274/#9279; a stray `cargo fmt --all` picked them up. Reported separately, not fixed here. * test: split the #8067 shape-authority tests out of parent_static.rs parent_static.rs was at 1992 lines on main and this PR adds 52, crossing the 2000-line cap. Extracts the inline shape_authority_tests_8067 module to a sibling under parent_static/; body unchanged. --------- Co-authored-by: Ralph Küpper <ralph@skelpo.com>
1 participant
The registry-probe family was 6.86% of a symbolized
claude --helpprofile after round one (#9176/#9177) cleared part of it. This takes it to 2.65%.11 interleaved reps, both arms built from
b3f14e9cdein one session.--helpoutput byte-identical to node (9,175 bytes, rc=0) in both arms.Cycles fall by more than instructions and IPC rises 2.077 → 2.102. That is the check that matters here: an earlier change in this campaign removed 24% of instructions and moved cycles +1%, because the removed work rode free in superscalar slack. This is the opposite — the removed work was real.
The answer distribution is the whole argument
Measured with uretprobes on a real
cc --helprun, not inferred:is_registered_buffer_slow: 4 "yes" out of 4,650,058 — one per 1.16 millionlookup_registered_typed_array_kind: 0 "Some" out of 3,566,956is_closure_ptr: theCLOSURE_MAGICtag test alone partitions 2,240,934 calls 231,704 / 2,009,230 — bit for bit the partition the whole function produces — yet it ran last, afterclassify_heap_generationand a GC-header read that changed no answer.So the fix is an inline address window in front of the buffer/typed-array probes, and a test reorder for the closure probe. 98.03% of calls now end at the window, and re-running the answer census on the shipped binary confirms all 4 genuine "yes" answers survive.
Attribution says the fix does not belong in the caller
Exact uprobe counts, ~100% coverage:
is_registered_buffer_slowget_accessor_descriptor19.2%,js_array_get_f6416.6%,js_object_get_field_by_name12.3%,object_static_prototype11.7% … 119 callerslookup_registered_typed_array_kindjs_array_get_f6421.2%,js_object_get_field_by_name15.2% … 99 callersis_closure_ptrclosure_get_dynamic_prop26.2%,closure_dynamic_prop_by_key19.8% … 81 callersIt takes ~10 callers to reach 90%. There is no caller-side fix; it is the generic property path, and one structural change covers all of it.
Why it cannot misclassify
These probes classify pointers — a wrong answer is type confusion, not a slow path.
The window never dereferences the candidate. Each probe consults a closed set of tables, and each table has a single module-private insert funnel that
admits the address first. That is an enumeration, and enumerations of writer sets have produced silent wrong answers in this codebase twice recently — so it is not left as one: underdebug_assertionsevery window rejection is re-derived from the authoritative tables, so a registration route added withoutadmitpanics in the first test that touches it. 2,858 unit tests ran with that armed; none fired.The
admitrace, and a second form of itA previous iteration had a non-atomic load+store in
admitthat could drop a concurrent registration; that was already fixed tofetch_min/fetch_max. It left a subtler second form behind, removed here: aRelaxed"skip if already covered" pre-check in front of the RMWs. A thread that skips the RMW performs no acquire, so another thread's widening never joins its happens-before graph, and a reader synchronising only with this thread's publish is not guaranteed to see the bound covering the address — a false negative for a registered pointer.admitis now two unconditionalAcqRelRMWs with no pre-check. It runs 52 times in a 6.9-billion-instruction run; the fast path bought nothing and cost the proof.Three precise negatives
type_probes_skip_offheap_typed_array_with_unmapped_preceding_page(a header read segfaults on aPROT_NONEpreceding page) andnative_memory_copy_rejects_buffer_registry_forged_to_old_non_buffer(a registered buffer whose header claimsGC_TYPE_OBJECT).meta_capable_object'sis_registered_buffercall is redundant with a laterobj_type == GC_TYPE_OBJECTcheck. The comment on that line says the opposite, and the forged-buffer test is exactly the case the registry check catches. Removing it would have been type confusion.Follow-up
Four more probes fit the same shape and are now the largest remaining members of the family:
is_registered_symbol_slow(0.60%),is_registered_class_prototype_object(0.47%),is_registered_box_ptr(0.33%),is_uint8array_buffer_slow(0.21%).Summary by CodeRabbit