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test: cover a failed JSC allocation on Windows and a JSC release assertion in the crash handler - #42821
test: cover a failed JSC allocation on Windows and a JSC release assertion in the crash handler#42821robobun wants to merge 1 commit into
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Status: ready for review. This PR is test-only, and its tests pass on every CI lane that ran them. The WebKit fixes that this PR first pinned (oven-sh/WebKit#316 and oven-sh/WebKit#485) are on main since #42822. The branch is rebased onto main. It keeps only the two tests in How I reproduced it (Windows x64): $env:MIMALLOC_RESERVE_OS_MEMORY="512MiB"; $env:MIMALLOC_DISALLOW_OS_ALLOC="1"; $env:MIMALLOC_RETRY_ON_OOM="0"
bun -e 'const s = "x".repeat(300 * 1024 * 1024); s.toUpperCase()'
The Windows test now also skips debug builds, because the debug WebKit prebuilt does not use mimalloc. The POSIX test passes on Linux x64 builds of main without ASAN. I did not run macOS locally. CI on 4770761 (build 116401):
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Included review availability: Your plan provides up to 10 included reviews per hour; 0 remain after this review. WalkthroughThe crash-handler tests now use sanitizer and macOS detection. They add coverage for a Windows allocation failure and a cross-platform JavaScriptCore release assertion with platform-specific crash signals. ChangesCrash-handler validation
Priority: ➖ Normal Merge Risk: ⚪ Minimal · up to The added crash-handler coverage introduces no identified merge-blocking risk. 🚥 Pre-merge checks | ✅ 4✅ Passed checks (4 passed)
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Inline comments:
In `@test/cli/run/run-crash-handler.test.ts`:
- Line 397: Update the repetitive string fixture in the crash-handler test to
use Buffer.alloc(count, fill).toString() instead of "x".repeat(...). Retune the
allocation size if necessary so toUpperCase() remains the must-succeed
allocation being tested.
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scripts/build/deps/webkit.tstest/cli/run/run-crash-handler.test.ts
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I reviewed this PR and didn't find any bugs. Because it bumps the pinned JavaScriptCore build — pulling in several upstream WebKit changes beyond the two headline fixes and activating ~60 previously-elided RELEASE_BASSERT sites on Windows for the first time — a human sign-off on the pin and the cross-platform CI results is still worthwhile.
What was reviewed:
- The two new crash-handler tests follow the file's existing conventions (
noReportEnvspreadsbunEnv,noCoreCmdwraps the POSIX case, pipes drained concurrently, stderr asserted before exit code, platform gates via harness helpers with reasons in comments). - The
"x".repeat(...)in the Windows OOM test runs in the spawned child and is the deliberate fallible-allocator setup step (per the inline comment), not a test-runner hot path. - Both tests assert positive, specific output (
0xBBADBEEF,Trap instruction/abort() called, signal codes) rather than absence-of-panic.
Extended reasoning...
Overview
The PR changes two files: a one-line bump of WEBKIT_VERSION in scripts/build/deps/webkit.ts from 65513e2… to 16a8ab7…, and two new tests in test/cli/run/run-crash-handler.test.ts. The tests cover behavior fixed by that WebKit range: on Windows, WTF::fastMalloc now crashes at the allocator with the 0xBBADBEEF sentinel when mimalloc returns null (previously clang-cl elided BCRASH() as UB and callers dereferenced null); on POSIX, a real JSC RELEASE_ASSERT failure now produces a catchable crash report on macOS 26 arm64 (previously brk #0xbb08 was delivered as SIGKILL).
Security risks
None identified. The change does not touch auth, crypto, permissions, or input parsing. The WebKit bump alters crash-path codegen (making assertions crash reliably rather than being optimized away), which is a hardening change. The tests are hermetic — no network, no external hosts, subprocess-only.
Level of scrutiny
Moderate-to-high. The diff itself is small and mechanical, but the pinned-hash change swaps the entire JavaScriptCore prebuilt. Per the PR's own notes, the range includes at least four upstream WebKit PRs (#316, #485, #630, #635), and enabling RELEASE_BASSERT on Windows for the first time activates ~60 previously dead assertion sites. The macOS 26 arm64 path was not verified locally by the author and depends on CI. Engine bumps of this kind conventionally get a human look at the full CI matrix before merge, which an automated diff review cannot substitute for.
Other factors
The new tests are well-constructed against the repo's test conventions: they use test.if/test.skipIf with isWindows/isASAN/isMacOS from harness, spread the file-local noReportEnv (which itself spreads bunEnv), wrap the POSIX abort case in noCoreCmd to suppress core dumps, drain pipes with Promise.all, assert stderr content before exit/signal, and carry load-bearing comments explaining the mechanism and citing the upstream fix. The "x".repeat(300 MiB) in the Windows test is inside the child's -e script and is explicitly chosen because repeat() uses the fallible allocator (setup) while toUpperCase() uses the must-succeed path (the trigger) — a justified, documented deviation from the Buffer.alloc convention, which targets test-runner performance rather than child-process allocation semantics. No CODEOWNERS entry covers the changed paths, and there are no outstanding third-party review objections in the timeline.
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Updated 1:11 AM PT - Sep 16th, 2026
❌ @robobun, your commit 4770761 has 2 failures in
🧪 To try this PR locally: bunx bun-pr 42821That installs a local version of the PR into your bun-42821 --bun |
…rtion in the crash handler Add two tests to test/cli/run/run-crash-handler.test.ts for crash paths that the WebKit upgrade in #42822 fixed. Windows: the child gets a fixed 512 MiB mimalloc arena, and String.prototype.toUpperCase asks WTF::fastMalloc for a second 300 MiB block. The report must show the allocator's crash address, 0xBBADBEEF, and not a null pointer in the caller (oven-sh/WebKit#316). The test runs on release builds only: the debug and ASAN WebKit prebuilts do not use mimalloc. POSIX: BUN_JSC_structureHeapSizeInKB=3072 fails a RELEASE_ASSERT in JSC::initialize(). The crash handler must print a report: "Trap instruction" and SIGTRAP on macOS, "abort() called" and SIGABRT elsewhere. On macOS 26 arm64 the process used to die from SIGKILL with no report (oven-sh/WebKit#485).
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I reviewed the rebased version and didn't find any bugs in the two new tests, but a human look is still worthwhile because the diff no longer matches the PR title/description: the WebKit pin in scripts/build/deps/webkit.ts is already d3720d515e14 on the base commit (bumped by earlier commits), so this PR is now test-only and the "Bump WebKit" title, the bundler_bytecode_portable snapshot note, and the pin hashes in the description are stale.
What was reviewed:
- Both new tests in
test/cli/run/run-crash-handler.test.ts:noReportEnvdisables crash upload,noCoreCmdsuppresses cores, pipes are drained viaPromise.all, stdout/stderr are asserted before the exit/signal code, and the expected strings ("Segmentation fault at address", "abort() called", "Trap instruction") matchsrc/crash_handler/lib.rs. - Skip gates: the Windows test gates on
!isDebug && !isASANand the POSIX test on!isASAN, consistent with the sibling SIGABRT/SIGTRAP tests in the same describe block. - Not verified here: the Windows 0xBBADBEEF path and the macOS 26 SIGTRAP path can only be exercised by the Windows and macOS CI lanes; the Linux debug non-ASAN variant of the JSC-assertion test was not run by the author per the description.
Extended reasoning...
Overview
The reviewed range (55c11065..HEAD) is a single commit touching only test/cli/run/run-crash-handler.test.ts. It adds two tests: a Windows-only release test that constrains mimalloc via MIMALLOC_RESERVE_OS_MEMORY/MIMALLOC_DISALLOW_OS_ALLOC/MIMALLOC_RETRY_ON_OOM so toUpperCase() on a 300 MiB string hits a failed must-succeed fastMalloc and expects the 0xBBADBEEF fault in the crash report; and a POSIX concurrent test that sets BUN_JSC_structureHeapSizeInKB=3072 to trip a real JSC RELEASE_ASSERT during JSC::initialize() and expects the crash handler to report SIGTRAP (macOS) or SIGABRT (elsewhere). No native or build-config changes are in the diff; git log -- scripts/build/deps/webkit.ts shows the pin already moved past the hash named in the description in earlier main commits (#42787, #42822, #42823).
Security risks
None. The change is test-only, spawns only the local debug binary, sets BUN_CRASH_REPORT_URL="" and BUN_ENABLE_CRASH_REPORTING=0 through noReportEnv, and contacts no network.
Level of scrutiny
Moderate. The tests themselves follow the file's existing conventions (noReportEnv, noCoreCmd, test.concurrent, harness isASAN/isDebug/isMacOS gates, Promise.all pipe draining, output asserted before exit code). The assertions are non-vacuous and the expected strings exist in src/crash_handler/lib.rs. The main reason for a human look is process rather than code: the PR title and description still describe a WebKit bump and a bytecode snapshot update that are not in this diff, and the platform-specific behavior (Windows allocator crash, macOS 26 brk #0 handling) can only be confirmed by the corresponding CI lanes. The "x".repeat(...) usage deviates from the harness guidance but is deliberately chosen because repeat uses the fallible allocator and the test is gated to release builds where it is fast.
Other factors
My earlier review on a previous push covered a larger diff that included the WebKit bump; the PR has since been rebased so the scope shrank to tests only, which is a substantive change worth a fresh note. No build was available in this checkout to run the tests locally, and running the repro directly was not permitted, so I did not independently reproduce the crash output on Linux. No third-party objections are outstanding (the one coderabbit thread was resolved by a non-author).
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On the stale title and description: both were rewritten at 07:50 UTC, after the rebase and before that review was posted. They now describe the test-only diff. The WebKit upgrade itself reached main through #42822. |
Problem
panic(main thread): Segmentation fault at address 0x0. clang-cl compiledBCRASH()(Source/bmalloc/bmalloc/BAssert.h) as undefined behavior, so LLVM deleted everyRELEASE_BASSERT.RELEASE_ASSERTended inKilled: 9with no crash report. macOS 26 kills a process onbrk #0xbb08before it delivers SIGTRAP.Fix
toUpperCase()requests a second 300 MiB block. The report must saySegmentation fault at address 0xBBADBEEF.BUN_JSC_structureHeapSizeInKB=3072fails aRELEASE_ASSERTinJSC::initialize(). The report must sayTrap instruction(SIGTRAP) on macOS andabort() called(SIGABRT) elsewhere.test/cli/run/run-crash-handler.test.tson Windows x64 and Linux x64 builds of main. bun v1.4.2 fails the Windows test withaddress 0x0.Background
WTF::fastMallocis JavaScriptCore's must-succeed allocator: it must crash on failure. In release builds it calls mimalloc, bun's allocator, and checks the result withRELEASE_BASSERT.RELEASE_BASSERT(x)isif (!(x)) BCRASH();. The fixedBCRASH()stores to address0xBBADBEEF, which faults.sigactionhandler on POSIX. It cannot see a SIGKILL.Notes
History of this PR. It first bumped
WEBKIT_VERSIONfrom65513e295c73to16a8ab732f62to pick up oven-sh/WebKit#316 and oven-sh/WebKit#485. #42822 (c775a5dc527d) and #42823 (d3720d515e14) then moved main past both commits:gh api repos/oven-sh/WebKit/compare/16a8ab732f62...d3720d515e14reportsaheadwithbehind_by: 0. The branch is now one commit on top of main. It drops thescripts/build/deps/webkit.tschange and thetest/bundler/bundler_bytecode_portable.test.tssnapshot (main has its own snapshot for the newer WebKit). #35193 and #39978 stay closed: main has their fixes.Sentry issues that oven-sh/WebKit#316 covers. Each fault address is the null buffer plus a fixed offset.
Vector<DFG::AbstractValue>::reserveCapacitymoves the elements into the new buffer0x0in 1055 of 1057 eventsSymbolTable::localToEntry->Vector(FillWith, size, nullptr)->memset0x0in 224 of 224UnlinkedMetadataTable::link->memcpy(table, ...), wheretableisbuffer + valueProfileSize + sizeof(LinkingData)0x1B6A8,0x5EE28,0x60A8, ...HashTable::rehash->setTableSizewrites atm_table - 4, andm_tableis the allocation plus 16 bytes of metadata0xCin 97 of 97BUN-2Z94 (
StringImpl::createUninitializedInternalNonEmpty) and BUN-4RGJ (Encoder::release) have the same cause. All of these are Windows x64 only. Nearly all events come from one large standalone executable. The requests are about 100 KB to 1 MB, and they fail because the machine is out of commit (BUN-3PM1, os error 1455, is the same population).The shipped binary before the fix. In
bun-profile.exefrom bun v1.4.2,WTF::fastMallocis at RVA0x88ab0. It is the inlinedmi_mallocfast path and it ends withjmp _mi_malloc_generic. Nothing tests the result. The linker folded it (ICF) withOPENSSL_system_malloc, which is a plainmi_malloccall.The prebuilt object code.
WTF::fastMallocinFastMalloc.cpp.objfrombun-webkit-windows-amd64.tar.gz:Repro (Windows x64).
JSON.parseof large strings now throwsRangeError: Out of memory, so the repro of #35193 no longer reaches the bug.repeat()uses the fallible allocator.toUpperCase()still allocates with the must-succeedStringImpl::createUninitialized:panic(main thread): Segmentation fault at address 0x0.panic(main thread): Segmentation fault at address 0xBBADBEEF, 3 of 3 runs.unable to allocate memory (314572820 bytes)first.Why the Windows test skips debug builds. On a Windows x64 debug build of main, the child prints
SHOULD NOT REACHand exits 0. mimalloc honors the three options there (MIMALLOC_VERBOSE=1shows them), but JavaScriptCore does not allocate through it.include/cmakeconfig.hof the-debugWebKit prebuilt hasUSE_MIMALLOC 0. The-ltoprebuilt hasUSE_MIMALLOC 1. The Linux prebuilts agree: the plain and-ltovariants have 1, and the-debug,-asanand-debug-asanvariants have 0. The first version of this test skipped only ASAN builds, so it failed on a local Windowsbun bd. CI has no Windows debug lane, so CI did not show it.Who owns the signals. On Linux x64, a script read back
sigaction()for each fatal signal after JavaScriptCore was initialized (plus one WebAssembly instance). SIGTRAP, SIGILL, SIGFPE and SIGABRT point atbun_crash_handler::handle_segfault_posix. SIGSEGV and SIGBUS point atWTF::jscSignalHandler(VM traps and Wasm faults), which calls the previous handler when it does not handle the fault. JavaScriptCore registers handlers forSignal::AccessFaultonly. On macOS it owns a Mach port forEXC_BAD_ACCESSonly, soEXC_BREAKPOINTbecomes SIGTRAP. On Windows the vectored exception handler claims access violations, illegal instructions, stack overflows and misalignment. The fixedBCRASH()faults on the store to0xBBADBEEF, which is an access violation.Why the POSIX expectation differs by platform.
RELEASE_ASSERTends in WTF'sCRASH(). On Darwin that is an inline trap instruction (int3on x64,brk #0on arm64 since oven-sh/WebKit#485), so the signal is SIGTRAP. On the other POSIX platforms it isstd::abort(), so the signal is SIGABRT. The assertion site isRELEASE_ASSERT(hasOneBitSet(preferredStructureHeapSize))inStructureMemoryManager(Source/JavaScriptCore/heap/StructureAlignedMemoryAllocator.cpp), and it is still present atd3720d515e14. The existingtrap produces a crash reporttest uses bun's own trap instruction, so it did not see the macOS 26 problem.Test results for
test/cli/run/run-crash-handler.test.tsat this commit.Segmentation fault at address 0xBBADBEEFand receives a report withaddress 0x0.bun bd(debug, ASAN) of main: 28 pass, 9 skip, 0 fail. ASAN skips the new POSIX test.--profile=debug-no-asan) of main: 29 pass, 8 skip, 0 fail. The new POSIX test passes withabort() calledand SIGABRT.16a8ab732f62. The darwin x64 and aarch64 lanes, the Windows x64 and aarch64 lanes, and the Linux glibc and musl lanes all passed. Bump WebKit (oven-sh/WebKit#485 preview): JSC and WTF crashes on macOS 26 arm64 reach the crash handler again #39978 ran the POSIX test on the macOS 26 CI shard against preview builds of Use brk #0 as the fatal crash instruction on arm64 (macOS 26 kills brk #0xbb08 before a SIGTRAP handler runs) WebKit#485, and it passed there.What the WebKit fix does not change. The allocation still fails, and the process still ends. The report now names the allocator, and all of these Sentry issues become one.
no test proof · iteration 1 · platform-specific test(s) that do not run on this machine, deferring to CI, which covers all platforms: test/cli/run/run-crash-handler.test.ts, test/bundler/bundler_bytecode_portable.test.ts