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ChangescaptureStackTrace target handling
Suggested reviewers: Priority: ➖ Normal Severity of issue fixed: Medium Merge Risk: ⚪ Minimal · up to No actionable merge-blocking issue is established for this change; it is mergeable after normal checks. 🚥 Pre-merge checks | ✅ 4✅ Passed checks (4 passed)
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Nothing blocking. The comments below are optional suggestions. There is no need to push a fix for them before merging.
LGTM — a one-line widening of the existing argument guard to match V8's rejection of Proxy receivers, with a test; the inline notes are minor and do not change the correctness of the fix.
Extended reasoning...
The diff touches only the argument guard at the top of errorConstructorFuncCaptureStackTrace in src/jsc/bindings/FormatStackTraceForJS.cpp and adds one test in test/js/node/v8/capture-stack-trace.test.js; it touches no security-sensitive surface. The new condition keeps isObject() first so asCell()->type() is only evaluated on a cell, ProxyObjectType is the single JSType JSC uses for callable and non-callable ProxyObject, and the thrown TypeError reuses the same "invalid_argument" message as the pre-existing non-object path, which matches V8's ErrorCaptureStackTrace rejecting non-JSObject receivers. Neither changed file is covered by .github/CODEOWNERS. The inline findings are a test nit (the revocable proxy is never revoked) and a pre-existing GlobalProxyType gap not introduced here, so they do not warrant holding the PR.
…globalThis, revoke the test proxy
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Actionable comments posted: 1
- 🪄 Fix CodeRabbit comments on this PR
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only still-valid issues, skip the rest with a brief reason, keep changes
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Inline comments:
In `@test/js/node/v8/capture-stack-trace.test.js`:
- Line 418: Update the cleanup around Error.captureStackTrace(globalThis) to
preserve shared global state: save the existing own-property descriptor for
globalThis.stack before the call, then in the finally block restore it with
Object.defineProperty when present, deleting the property only when no
descriptor existed.
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src/jsc/bindings/FormatStackTraceForJS.cpptest/js/node/v8/capture-stack-trace.test.js
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Nothing blocking. The comments below are optional suggestions. There is no need to push a fix for them before merging.
Beyond the inline finding, I also checked the new guard's ordering in src/jsc/bindings/FormatStackTraceForJS.cpp:844 (the || short-circuits on isObject() before asCell() runs, so primitives never reach the type read), that a revoked Proxy keeps ProxyObjectType and so is covered by the same check (the test now calls revoke() before the loop), and that the GlobalProxyType unwrap at line 851 mirrors the existing unchecked target() pattern in src/jsc/bindings/JSMockFunction.cpp:1528 and src/jsc/bindings/Weak.cpp:82.
Extended reasoning...
The change is a two-line guard/unwrap in the V8-compat Error.captureStackTrace host function plus two new tests; it touches no auth, crypto, or injection surface. A confirmed finding on the prepareStackTrace receiver identity is posted inline and a further verified finding is unposted, so the change is not approved; this note only records the additional checks that came up clean.
…ly the stack write to the global object
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LGTM — the latest pushes address everything raised earlier (revoked proxy now actually revoked in the test; only the stack writes are redirected to the JSGlobalProxy target while errorObject itself stays the Error.prepareStackTrace argument).
What was reviewed:
stackStorageObjectuses the exactGlobalProxyTypecheck beforeuncheckedDowncast, the same shape as JSMockFunction.cpp:1528, Weak.cpp:82 and JSEventTargetCustom.cpp:69;asCell()is only reached afterisObject()short-circuits.- The two untouched
putDirect(stack)sites (lazy getter at :829, materialized ErrorInstance path at :880) are reachable only with anErrorInstancereceiver, which can never be a Proxy or GlobalProxy cell, so they need no unwrap. - No other caller of
computeErrorInfoToJSValuecan pass a ProxyObject (errorConstructorFuncCaptureStackTraceis the sole non-ErrorInstance entry), and no existing test orsrc/caller relies oncaptureStackTraceaccepting a Proxy. - The globalThis test asserts the precondition, cleans up
globalThis.stackinfinally, andError.prepareStackTraceis restored by the file'safterEach.
Extended reasoning...
The diff adds one 6-line static helper and a widened type check in src/jsc/bindings/FormatStackTraceForJS.cpp plus two tests in test/js/node/v8/capture-stack-trace.test.js (+83/-3 total). It touches Error.captureStackTrace argument validation and property storage, not auth, crypto, or any security-sensitive surface. The unwrap pattern is copied from three existing in-tree sites, the exception-check ordering around the user-visible prepareStackTrace call is unchanged, and neither file is covered by CODEOWNERS. All three of my prior inline findings are addressed in the current code, the only third-party thread was resolved by a non-author, and the bug hunt exited on dry_streak with no findings, which decided approve.
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Update: #42605 no longer stores Three changes of #42605 meet this PR:
The store that #42605 had is in its history: c0c534f (
The commit is there to take if it helps. The TypeError for a |
Fixes #43829
Problem
Error.captureStackTrace(new Proxy({}, {}))returns with no error. Node throwsTypeError: invalid_argumentbecause V8 rejects any receiver that is not a plain object, and a Proxy is not one.objectArg.isObject()(src/jsc/bindings/FormatStackTraceForJS.cpp:843). AProxyObjectpasses it. The laterputDirectofstacklands in the proxy cell's own storage, which no trap and no[[Get]]can reach. So the call is a silent no-op:proxy.stackstaysundefinedandReflect.ownKeys(proxy)is empty.Error.captureStackTrace(globalThis)has the same defect through a different cell:globalThisis aJSGlobalProxythat forwards reads to the global object, andputDirectwrites the proxy cell. Node givestypeof globalThis.stack === "string". Bun gaveundefined.Fix
ProxyObjectTypethrows the sameTypeError("invalid_argument")as a non-object. This matches V8'sErrorCaptureStackTracebuiltin, which throwskInvalidArgumentwhen the argument is not aJSObject(aJSProxyis not). Callable and revoked proxies have the same cell type, so they throw too.GlobalProxyTypeargument, redirect only thestackwrites to the proxy's target (stackStorageObject).stackthen lands on the global object, where the proxy's forwarding[[Get]]finds it. The proxy stays the receiver for everything script can see: theError.prepareStackTraceargument and the name and message reads. JSC never hands the raw global object to script (a strictthisof it isundefined).test/js/node/v8/capture-stack-trace.test.js(two new tests, both fail on stock bun 1.4.3). TheglobalThistest also checks thatError.prepareStackTracereceivesglobalThisitself. Also the rest oftest/js/node/v8/,test/js/bun/test/mock, andtest-process-emitwarning.js.Background
Error.captureStackTraceis a V8 extension that Bun implements in C++ inerrorConstructorFuncCaptureStackTrace. For a non-ErrorInstancetarget it formats the frames to a string and stores it withputDirect, which writes the object's own property storage without running any JS-visible hook.isObject()accepts.ProxyObjectis the ESProxy: every user-visible access goes through the handler and the target.JSGlobalProxyis the cell behindglobalThis: it forwards every access to the real global object. A direct write to either cell is invisible.definePropertytrap instead, so the write reaches the target. V8 does not do that, and Error.captureStackTrace: honor the target's integrity level #33412 (integrity level checks in the same function) leaves the Proxy case out on purpose. The type check keeps Node parity and keeps a trap from running with a half-built stack string.Downsides
captureStackTraceon a Proxy and relied on it not throwing now gets aTypeError. Node has thrown for this call since the builtin exists, so such code already fails there.isObject()load. No allocation, no syscall.node:vmcontext,Error.captureStackTrace(globalThis)still leavesglobalThis.stackasundefined: the write lands on the context's global object and reads go to the sandbox. Node behaves the same there (checked on v26.3.0).[human-review] gate passed · iteration 1 · 2 files touched
fails on main (without fix)
passes on PR (with fix)
diff hotspot
gate history · 2 passed · 0 rejected · iteration 1
evidence per changed file
root cause · written by the author bot
Error.captureStackTracein Bun accepted any object as its target, so a Proxy was passed through and the captured stack was silently written into the Proxy (where it could be intercepted or dropped by traps), whereas V8 refuses Proxy targets outright. The fix inFormatStackTraceForJS.cppchecks the target before capturing and throws aTypeErrorwith the message"invalid_argument"when it is a Proxy, matching Node. It also unwrapsGlobalProxytargets such asglobalThisso the.stackproperty is installed on the underlying global object rather than the proxy wrapper.