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WalkthroughThe change updates the WebKit preview identifier and adds explicit oversized heap snapshot errors across serialization and worker paths. A release-only stress test validates large snapshot generation. ChangesHeap snapshot serialization
WebKit preview update
Suggested reviewers: Merge Risk: 🟡 Moderate · up to The dependency pin currently cannot be resolved in a normal checkout, which can prevent developers and build systems from fetching the required WebKit revision. Correct the pin before merging. 🚥 Pre-merge checks | ✅ 4✅ Passed checks (4 passed)
Full details: Description checkExplanation The description explains the problem, fix, verification steps, regression test, known limitations, and merge prerequisite. It does not use the exact template headings, but it provides the required change summary and verification information. Comment |
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Updated 7:29 AM PT - Aug 28th, 2026
✅ @robobun, your commit f373c287d33ec28d779889e4daeb9bbd523017b6 passed in 🧪 To try this PR locally: bunx bun-pr 40749That installs a local version of the PR into your bun-40749 --bun |
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Beyond the inline findings, I also checked that the inlined resolve/reject path in JSWorker.cpp preserves the takeCrossVMRequest + isJSExecutionForbidden() guards from the original resolveCrossVMRequest helper — it does, so the null-handle and stopped-parent-VM cases still short-circuit correctly. The --heap-prof empty-string branch in BunHeapProfiler.rs now printing an overflow message on the text-format path too was looked at and judged acceptable.
Extended reasoning...
Two inline findings are being posted (the preview-PR WebKit pin and the discarded stderr in the new regression test), and additional verified findings were pruned from the posted set, so approval is off the table. I confirmed the JSWorker.cpp inlining is a faithful expansion of resolveCrossVMRequest with an added reject branch — same takeCrossVMRequest(reqId) draw, same isJSExecutionForbidden() bail, and the .isolatedCopy() still happens at capture time before the cross-thread hop. The PR description itself flags that the WebKit pin must be swapped to a merged sha before landing, which aligns with the inline finding.
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Actionable comments posted: 1
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Inline comments:
In `@scripts/build/deps/webkit.ts`:
- Line 6: Update WEBKIT_VERSION to the full preview release tag
autobuild-preview-pr-529-6373bfc9 so direct resolution by sync-webkit-source.ts
succeeds; leave prebuiltUrl() and process.versions.webkit handling unchanged.
🪄 Autofix
Fix all unresolved CodeRabbit comments on this PR:
- Push a commit to this branch (recommended)
- Create a new PR with the fixes
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scripts/build/deps/webkit.tssrc/jsc/BunHeapProfiler.rssrc/jsc/bindings/BunObject.cppsrc/jsc/bindings/webcore/JSWorker.cpptest/js/bun/util/v8-heap-snapshot.test.ts
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CI status for the current head (4245901): the red lanes are unrelated. Every failing test except one passed on retry or when run alone. The one repeat failure, test/js/web/url/url.test.ts on macOS x64, also fails on main and is reported to triage. The new large-heap test passes on all release lanes. This PR stays blocked on oven-sh/WebKit#529. After that merges, I will swap WEBKIT_VERSION to the merged sha, which reruns CI. |
A heap with more than about 15M live cells aborted the process: the V8 snapshot builder stored one 96-byte Node per cell in a contiguous WTF::Vector, and vector growth past the ~2GiB single-allocation cap is a CRASH(). WebKit#529 shrinks the node record to 40 bytes, moves node storage to a SegmentedVector, and turns the remaining container limits into a recorded overflow instead of an abort. On the bun side, consume that overflow signal: Bun.generateHeapSnapshot and worker.getHeapSnapshot() now throw or reject a catchable error when a snapshot is too large to serialize, and the --heap-prof writer prints an error instead of silently writing nothing. Fixes #40686
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Problem
Bun.generateHeapSnapshot("v8")andnode:v8.writeHeapSnapshot()abort the process (SIGABRT,EXC_BREAKPOINTon macOS) once the heap passes about 15M live cells. The crash is inBunV8HeapSnapshotBuilder::Nodevector growth. Issue Bun.generateHeapSnapshot("v8") crashes on large heaps #40686, reproduced with 16M small objects.Nodeper heap cell in a contiguousWTF::Vector. AWTF::Vectorcaps one allocation at about 2GiB andCRASH()es past it. The 16M-object heap needs a 23M-node growth step, which is 2.2GiB.Fix
Nodeto 40 bytes (the removed fields were written but never read), store nodes in aSegmentedVector(no contiguous allocation, so no cap), and record overflow from the still-contiguous containers (edges, strings, serialized output) instead of crashing.Bun.generateHeapSnapshot("v8")throws,worker.getHeapSnapshot()rejects, and the--heap-profwriter prints an error instead of silently writing nothing.test/js/bun/util/v8-heap-snapshot.test.tsruns the repro on release lanes. It is skipped under debug/ASAN, where the heap walk takes over an hour. Existing v8 snapshot, worker snapshot, and node:v8 suites pass.Background
BunV8HeapSnapshotBuilderis a JSCHeapAnalyzerin the oven-sh/WebKit fork. A full GC walks the heap and calls it back for every live cell and edge. The builder records them, then serializes the V8.heapsnapshotJSON.WEBKIT_VERSIONmust then be swapped from the preview tag to the merged sha.Notes
Reproduction (bun 1.4.1, linux x64 and the reporter's macOS arm64):
bun repro.tsexits 134 (SIGABRT) after ~14s at ~3.9GB peak RSS. The trap fires inVector::allocateBufferviaisValidCapacityForVector<Node>: capacity growth 15,354,379 -> 23,031,568 at 96 bytes per node exceeds(UINT_MAX >> 1)bytes, matching the registers in the report.Fail-before note for the mechanical gate: the fix lives in prebuilt WebKit, which
git stash push -- src/ packages/does not revert, and the crash threshold (about 15M live cells) makes the walk take over an hour under a debug ASAN build. The new test therefore proves the fix on release builds only: withUSE_SYSTEM_BUN=1(1.4.1) it fails in ~10s, with this branch it passes.Local verification against WebKit#529 (debug ASAN, local WebKit build):
16000000 825993840(an 826M-char snapshot) and exits cleanly.test/js/bun/util/v8-heap-snapshot.test.ts: 7 pass.test/js/node/worker_threads/worker_heap_snapshot_gc.test.ts: pass.test/js/node/test/parallel/test-v8-getheapsnapshot-twice.js,test-worker-heap-snapshot.js: pass.writeHeapSnapshotoutputs agree on node/edge counts at 200k objects.test/js/bun/util/heap-snapshot.test.tshas two pre-existing 5s timeouts on debug builds (URL, Headers), identical on an unmodified build; tracked by test: keep the URL and Headers heap-snapshot tests under the default timeout on debug builds #37835.The removed
Nodefields (edges,traceLocation,parentNodeId,childrenVectorIndex) were write-only.trace_function_infosis always serialized empty, so droppingtraceLocationchanges no output.[decide:webkit] gate passed · iteration 2 · 5 files touched
fails on main (without fix)
passes on PR (with fix)
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gate history · 3 passed · 0 rejected · iteration 2
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