jit: resume an aborted walk at the enclosing frame's own opcode boundary - #1238
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WalkthroughThe change validates blackhole resume positions against instruction boundaries, preserves enclosing opcode positions during abort recovery, wires interior-field load opcodes, and adds provenance and boundary diagnostics for single- and multi-frame adoption. ChangesBlackhole resume integrity
Estimated code review effort: 3 (Moderate) | ~20 minutes Merge Risk: ⚪ Minimal · up to The change addresses the targeted runtime crashes, with no actionable merge-blocking risk remaining beyond normal checks and review. Sequence Diagram(s)sequenceDiagram
participant JITDispatch
participant ResidualCall
participant Trace
participant BlackholeInterpreter
JITDispatch->>ResidualCall: latch enclosing opcode_position
ResidualCall->>Trace: provide latched image and origin
Trace->>BlackholeInterpreter: adopt resume coordinates
BlackholeInterpreter-->>Trace: report boundary validity
Trace-->>Trace: log provenance and commit leg
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Suggested reviewers: Poem
🚥 Pre-merge checks | ✅ 5✅ Passed checks (5 passed)
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| // lands `setposition` inside an operand payload. Resume | ||
| // the enclosing frame at the opcode whose step propagated | ||
| // the abort instead. | ||
| let _ = latch_abort_blackhole(ctx, opcode_position, "mod2730"); |
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When a transparent canonical helper makes an unjournaled heap mutation before a later OrthodoxSubWalkTraceUnsupported abort, inline_call.rs:2504-2525 explicitly propagates that abort because the effect cannot be rewound. Latching the enclosing opcode's entry coordinate here then makes the blackhole execute the entire helper again while the first mutation remains, silently applying the effect twice. Preserve and resume the helper's own MIFrame/coordinate instead of collapsing it onto the caller boundary.
AGENTS.md reference: AGENTS.md:L32-L42
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Inline comments:
In `@majit/majit-metainterp/src/blackhole.rs`:
- Around line 1634-1648: Preserve the tri-state startpoint status instead of
collapsing missing metadata to false: update the unwired-opcode panic in
majit/majit-metainterp/src/blackhole.rs:1634-1648 to report Option<bool> or
explicit startpoints presence, and update the single-frame adoption logs in
pyre/pyre-jit-trace/src/trace.rs:2334-2347 and multi-frame adoption logs at
2757-2773 likewise. Keep known-valid and known-invalid positions distinguishable
from unknown startpoint metadata.
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📒 Files selected for processing (4)
majit/majit-metainterp/src/blackhole.rspyre/pyre-jit-trace/src/jitcode_dispatch/mod.rspyre/pyre-jit-trace/src/jitcode_dispatch/residual_call.rspyre/pyre-jit-trace/src/trace.rs
🤖 Codex parity reviewStatic analysis of this diff vs the local RPython/PyPy sources (commit 057f735). Files in the reviewed diff1. Regressions to PyPy parity introduced by this patchNone. 2. Other mismatches introduced by this patchNone. 3. Pre-existing mismatches (already present before this patch)
4. Structural adaptations
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`walk`'s abort latch passed `error.stop_pc()` to `latch_abort_blackhole`. A canonical helper runs through `run_sub_jitcode_walk`, which propagates the helper's `DispatchError` unchanged (`walk(sub_body.code, 0, &mut sub_wc)?`), so `stop_pc` is a byte offset into the helper's JitCode. The helper sets `transparent_helper_subwalk`, so it does not latch its own image and the enclosing Python frame's `walk` does — pairing that offset with this frame's JitCode. `setposition` then lands inside an operand payload. Pass `opcode_position`, the coordinate of the opcode whose step propagated the abort. Measured in the ubuntu24-arm64 container with `MAJIT_STRICT=1`, dynasm: lib-python/3/test/test_numeric_tower.py 5/5 rc=101 -> 5/5 rc=0 lib-python/3/test/test_long.py 3/3 rc=101 -> 3/3 rc=0 Both panics named a byte the frame was resumed in the middle of. test_numeric_tower stopped at `dispatch_step: unwired opcode=0x5 pos=18`, where 5 is the register operand of an `int_copy/i>i` and 18 is the `stop_pc` of an `OrthodoxSubWalkTraceUnsupported` raised inside the helper. test_long stopped in `handler_cast_float_to_int` reading float register 65 out of a bank of length 0. `baseline.json` records `dynasm: PASS` for both modules. Assisted-by: Claude
`build_inline_call_only_bh_builder` left BC_GETINTERIORFIELD_GC_I / _R / _F on the unwired placeholder while `bhimpl_getinteriorfield_gc_*` handlers already existed. Register all three, and add a test asserting their dispatch slots are not the placeholder. Not related to the two blackhole crashes fixed in the preceding commit: those reproduce and clear identically whether or not these three bytes are wired. Assisted-by: Claude
…'s writer blackhole.py:86-91 asserts `position in jitcode._startpoints` on every dispatch iteration. The port sits in `BlackholeInterpBuilder::dispatch_ loop`, whose only callers are `#[cfg(test)]`; the loop production runs is `run_inner`, which had no check. A resume coordinate pointing into an operand payload therefore surfaced as `dispatch_step: unwired opcode=..`, naming the dispatch table rather than the frame's pc. - `run_inner` carries the assertion, gated on `jit_strict_mode()` (debug builds plus `MAJIT_STRICT`) — `debug_assert!` is compiled out of the release builds these appear in. - The `dispatch_step` panic reports the jitcode index and whether the position is a recorded startpoint. The name alone is not an identity: jitcodes 2639, 2648, 2649 and 2650 are all named `__new__`. - `LatchedSingleFrameBlackhole` / `LatchedMultiFrameBlackhole` carry the latch that produced them, and the two adopters print origin, jitcode, pc and startpoint membership per frame under `PYRE_FBW_DEBUG_ABORT` or `MAJIT_BH_DEBUG`. Four latches supply that coordinate from four sources; the panic fires arbitrarily far from whichever one wrote it. Assisted-by: Claude
…loads from the gap snapshot `cargo fmt --check` rejected the `let`-chain in `run_inner`, the `is_valid_startpoint` call in the `dispatch_step` panic, and the one in `try_adopt_single_frame_blackhole`. `production_bh_builder_overlay_only_gap_snapshot` pins the opnames that are in the blackhole's key universe, are absent from `BUILD_EMITTED_INSNS`, and are unregistered. Registering `getinteriorfield_gc_i/_r/_f` in `build_inline_call_only_bh_builder` removed them from that set, so the snapshot no longer matched. Drop the three entries and record why they left: they are registered pre-emptively, not in response to an observed panic naming one of them. Assisted-by: Claude
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A descent that propagates its `DispatchError` hands the coordinate upward and the enclosing frame resumes at its own CALL (`mod2730`, since #1238), which re-enters the descent. Whether that resume can re-apply something the descent already applied is a question about the frame's effect delta, and `PYRE_FBW_DEBUG_ABORT` reported every decline but never a propagate. Print the journal delta and the unjournaled-effect flip at that path in `run_sub_jitcode_walk`. Measured on darwin dynasm: `test.test_long` propagates 168 times with 0 journaled effects and 62 unjournaled-effect flips, `test.test_numeric_tower` 40 times with 0 and 10. Under the #1238 remedy the same run accepts 6 `mod2730` latches, and all 6 follow a propagate whose unjournaled flag flipped. Assisted-by: Claude
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`arith_int_bool` reads `bridges_compiled` 11 and `guard_failures` 2307 where the file recorded 10 and 2211; `short_circuit_value_kept_stack` reads 11 and 2201 where it recorded 12 and 2510. Both are main's, not this branch's: the CI run on `3b403691725` reports the same two fixtures with the same numbers, and they do not move across `#1238`/`#1240` or with the environment byte length varied from 0 to 512. The ratio row on `short_circuit_value_kept_stack` is a separate inherited red and is not addressed here. Assisted-by: Claude
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A descent that propagates its `DispatchError` hands the coordinate upward and the enclosing frame resumes at its own CALL (`mod2730`, since #1238), which re-enters the descent. Whether that resume can re-apply something the descent already applied is a question about the frame's effect delta, and `PYRE_FBW_DEBUG_ABORT` reported every decline but never a propagate. Print the journal delta and the unjournaled-effect flip at that path in `run_sub_jitcode_walk`. Measured on darwin dynasm: `test.test_long` propagates 168 times with 0 journaled effects and 62 unjournaled-effect flips, `test.test_numeric_tower` 40 times with 0 and 10. Under the #1238 remedy the same run accepts 6 `mod2730` latches, and all 6 follow a propagate whose unjournaled flag flipped. Assisted-by: Claude
youknowone
added a commit
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this pull request
Aug 16, 2026
A descent that propagates its `DispatchError` hands the coordinate upward and the enclosing frame resumes at its own CALL (`mod2730`, since #1238), which re-enters the descent. Whether that resume can re-apply something the descent already applied is a question about the frame's effect delta, and `PYRE_FBW_DEBUG_ABORT` reported every decline but never a propagate. Print the journal delta and the unjournaled-effect flip at that path in `run_sub_jitcode_walk`. Measured on darwin dynasm: `test.test_long` propagates 168 times with 0 journaled effects and 62 unjournaled-effect flips, `test.test_numeric_tower` 40 times with 0 and 10. Under the #1238 remedy the same run accepts 6 `mod2730` latches, and all 6 follow a propagate whose unjournaled flag flipped. Assisted-by: Claude
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… report a propagating descent's effects (#1248) * jit: name the origin and entry of a latched blackhole coordinate Only declines were reported, so a bad blackhole resume coordinate could be seen failing but not traced back to the site that latched it. Report acceptance at the two `residual_call.rs` latch sites under `PYRE_FBW_DEBUG_ABORT`, printing `origin`, the image pc and the jitcode name and index. Print `setposition` under `MAJIT_BH_DEBUG` with the same fields. Add the entry position to the unwired-opcode panic: `entry == pos` means the frame was `setposition`ed straight onto that byte and dispatched with no prior step, which reads apart from a byte a forward walk arrived at. Assisted-by: Claude * jit: report whether a propagating sub-jitcode descent applied an effect A descent that propagates its `DispatchError` hands the coordinate upward and the enclosing frame resumes at its own CALL (`mod2730`, since #1238), which re-enters the descent. Whether that resume can re-apply something the descent already applied is a question about the frame's effect delta, and `PYRE_FBW_DEBUG_ABORT` reported every decline but never a propagate. Print the journal delta and the unjournaled-effect flip at that path in `run_sub_jitcode_walk`. Measured on darwin dynasm: `test.test_long` propagates 168 times with 0 journaled effects and 62 unjournaled-effect flips, `test.test_numeric_tower` 40 times with 0 and 10. Under the #1238 remedy the same run accepts 6 `mod2730` latches, and all 6 follow a propagate whose unjournaled flag flipped. Assisted-by: Claude
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test_numeric_towerandtest_longcrashed under dynasm on linux. Both aredynasm: PASSinbaseline.json, so both were live gate regressions. One rootcause.
Root cause
run_sub_jitcode_walk(inline_call.rs) runs a canonical helper withwalk(sub_body.code, 0, &mut sub_wc)?. The?propagates the helper'sDispatchErrorupward unchanged, soerror.stop_pc()is a byte offset into thehelper's JitCode. The helper sets
transparent_helper_subwalk, so it doesnot latch its own image — the enclosing Python frame's
walk()does, and it waspairing that foreign offset with its own JitCode.
latch_abort_blackhole→MIFrame::new(jitcode, pc)→setpositionthen lands inside an operandpayload, and the blackhole later decodes a payload byte as an opcode.
The fix is one argument: pass
opcode_position— the coordinate of the opcodewhose step propagated the abort — instead of
error.stop_pc().Both panics named something other than the defect
test_numeric_towerdispatch_step: unwired opcode=0x5 pos=18 … jitcode="__new__"int_copy/i>i;pos=18is thestop_pcof anOrthodoxSubWalkTraceUnsupportedraised inside the helpertest_longblackhole.rs:6675 index out of bounds: the len is 0 but the index is 65bhhandler_f_i!(handler_cast_float_to_int, …)— a JitCode with zero float registers handed byte 65 as a float registerThe jitcode's own metadata is what settles it:
startpointscontains 17 and 20but not 18, and
resulttypesagrees.Measurement
ubuntu24-arm64 container, dynasm,
MAJIT_STRICT=1:test_numeric_towertest_longThe third row rules out the diagnostics in this PR as the cause of the green.
Re-verified after rebasing onto
04498478b2b, on a binary rebuilt from therebased tree (markers confirmed present in it, so this is not a stale artefact):
3/3 rc=0 for each target module, and the full suite reports
CRASH 0.cargo test -p majit-metainterp --features dynasmis green, which exercises thenew assertion under
debug_assertions.Measurement
Evidence that the defect is real and this PR removes it
Taken at the earlier merge-base
04498478b2b, where both sides ran the sameCPython suite (gate)job on the same runner — main run 31860244817, branch run31862581203:
Main reproduced both panics with the exact messages this PR opens with
(
blackhole.rs:6675 index out of bounds: the len is 0 but the index is 65anddispatch_step: unwired opcode=0x5 pos=18 jitcode="__new__"); on the branch bothrows were gone. Fixed:
test_long,test_numeric_tower. Introduced: none —PASS+2 andCRASH−2 are accounted for entirely by those two rows.After rebasing onto current main
The branch has since been rebased onto a main that includes #1237, which fixed
the exception-state leak behind
test_pickle. Re-verified on a binary rebuiltfrom the rebased tree (LLBC re-extracted first):
test_numeric_tower3/3 rc=0,test_long3/3 rc=0, underMAJIT_STRICT=1PASS 212 FAIL 1 **CRASH 0** IMPORTERROR 1cargo test --all --no-default-features --features dynasm: 130 test binaries,7958 passed, 0 failed
cargo fmt --check: cleanThe three remaining rows are not this PR's:
test_strtest_raiseMemErrorasserts exactsys.getsizeofarithmetic, a per-platform quantity, and it is compared against the darwinbaseline.jsontest_interpreterstest_urllib2--no-jit, and neither CI run has itbaseline.linux-aarch64.jsoncarries only two module entries, so nearly everyrow on this host is really a row compared against the darwin baseline. Note also
that the local runner and CI run different populations (
215 to runlocally vs217 to runon CI, which does not apply the host overlay).One thing I have not measured
#1237 also changed sub-walk code paths. Its
mod.rschanges are elsewhere — theresidual call's
null_or_selfslot, the rewind guards' odometer read, and therange
FOR_ITERdemotion key — so by inspection it does not touch the resumecoordinate this PR fixes. I have not built current main without these commits
to confirm the two crashes still reproduce on it, so "this PR is still
necessary" rests on that inspection rather than on a control run. Main's own
gate at this base settles it if it runs.
Commits
jit: resume an aborted walk at the enclosing frame's own opcode boundary— the fix.
majit: wire the interior-field loads in the production blackhole builder—
BC_GETINTERIORFIELD_GC_I/_R/_Fsat on the unwired placeholder whilebhimpl_getinteriorfield_gc_*handlers already existed. Kept separatedeliberately: the A/B above shows both crashes reproduce and clear
identically whether or not these three bytes are wired, so this is not part
of the fix even though
BC_GETINTERIORFIELD_GC_Fhappens to be byte 5.majit, jit: fail a mid-instruction blackhole resume at the coordinate's writer—
blackhole.py:86-91assertsposition in jitcode._startpointseverydispatch iteration. The port sits in
BlackholeInterpBuilder::dispatch_loop,whose only callers are
#[cfg(test)]; the loop production runs isrun_inner, which had no check. So a bad resume coordinate failed far fromits writer, as a bogus opcode byte that accused the dispatch table.
run_innernow carries the assertion underjit_strict_mode()(debugbuilds plus
MAJIT_STRICT).debug_assert!would be compiled out of therelease builds these appear in.
dispatch_steppanic reports the jitcode index and startpointmembership. The name is not an identity — jitcodes 2639, 2648, 2649 and
2650 are all named
__new__, which is why the original panic could not beresolved to a jitcode.
adopters print origin / jitcode / pc / startpoint per frame under
PYRE_FBW_DEBUG_ABORTorMAJIT_BH_DEBUG. Four latches supply thatcoordinate from four different sources.
Note for review
bridge_subwalk.rs's"bridge1361"latch still passeserror.stop_pc()raw,and unlike the site fixed here it carries no
!abort_blackhole_latched()guard,so it can overwrite a correct image. It is the same class. I did not change it:
there is no repro for it, and its own doc argues a decline there is unsound
because the sub-walk is the callee's one real execution. The assert added in
commit 3 is live across the whole CPython suite gate (
run.pysetsMAJIT_STRICT=1), so that run is a standing probe for this and every othersite that writes a resume coordinate.
— authored by Claude