StackTrace outputs a garbage prefix because WTF::StackTrace::m_prefix is filled with the stack content r278474 (Bug 226390) added a new member m_prefix to StackTrace at the bottom of the structure. However, StackTrace isn't a normal structure. the members are filled with the stack content.
In WinCairo, it outputs the garbage prefix like the following: PS C:\home\webkit\gc> .\WebKitBuild\Debug\bin64\WebKitTestRunner.exe LayoutTests/js/dom/transform-stream.html ERROR: 000001F52DC4CE10 - ResourceLoadStatisticsDatabaseStore::turnOnIncrementalAutoVacuum failed, error message: not an error C:\home\webkit\gc\Source\WebKit\NetworkProcess/Classifier/ResourceLoadStatisticsDatabaseStore.cpp(315) : WebKit::ResourceLoadStatisticsDatabaseStore::ResourceLoadStatisticsDatabaseStore ERROR: Unchecked JS exception: This scope can throw a JS exception: JSC::JSObject::get @ C:\home\webkit\gc\WebKitBuild\Debug\JavaScriptCore\PrivateHeaders\JavaScriptCore\JSObject.h:1504 (ExceptionScope::m_recursionDepth was 13) But the exception was unchecked as of this scope: WebCore::invokeWritableStreamFunction @ C:\home\webkit\gc\Source\WebCore\bindings/js/InternalWritableStream.cpp:42 (ExceptionScope::m_recursionDepth was 13) Unchecked exception detected at: H<D$pHĀX_^AIIIIIIIIIIIIIIIIH%LWHēPH<D$`H< 1 00007FFC1110464F JSC::VM::verifyExceptionCheckNeedIsSatisfied H<D$pHĀX_^AIIIIIIIIIIIIIIIIH%LWHēPH<D$`H< 2 00007FFC110D8924 JSC::ThrowScope::ThrowScope H<D$pHĀX_^AIIIIIIIIIIIIIIIIH%LWHēPH<D$`H< 3 00007FFBEE14D4EB WebCore::invokeWritableStreamFunction H<D$pHĀX_^AIIIIIIIIIIIIIIIIH%LWHēPH<D$`H< 4 00007FFBEE14C6E1 WebCore::InternalWritableStream::create H<D$pHĀX_^AIIIIIIIIIIIIIIIIH%LWHēPH<D$`H< 5 00007FFBEDF0733C WebCore::WritableStream::create H<D$pHĀX_^AIIIIIIIIIIIIIIIIH%LWHēPH<D$`H< 6 00007FFBEDF07207 WebCore::WritableStream::create H<D$pHĀX_^AIIIIIIIIIIIIIIIIH%LWHēPH<D$`H< 7 00007FFBEDAF98B6 WebCore::JSDOMConstructor<WebCore::JSWritableStream>::construct H<D$pHĀX_^AIIIIIIIIIIIIIIIIH%LWHēPH<D$`H< 8 00007FFC108BBB6F JSC::NativeFunction::operator() H<D$pHĀX_^AIIIIIIIIIIIIIIIIH%LWHēPH<D$`H< 9 00007FFC108BBBBC JSC::TaggedNativeFunction::operator() H<D$pHĀX_^AIIIIIIIIIIIIIIIIH%LWHēPH<D$`H< 10 00007FFC1095567B JSC::LLInt::handleHostCall H<D$pHĀX_^AIIIIIIIIIIIIIIIIH%LWHēPH<D$`H< 11 00007FFC1096BC4A JSC::LLInt::setUpCall H<D$pHĀX_^AIIIIIIIIIIIIIIIIH%LWHēPH<D$`H< 12 00007FFC109616D6 JSC::LLInt::genericCall<JSC::OpConstruct> H<D$pHĀX_^AIIIIIIIIIIIIIIIIH%LWHēPH<D$`H< 13 00007FFC1094DBAF llint_slow_path_construct H<D$pHĀX_^AIIIIIIIIIIIIIIIIH%LWHēPH<D$`H< 14 00007FFC0F88C4C6 llint_entry ASSERTION FAILED: !m_needExceptionCheck C:\home\webkit\gc\Source\JavaScriptCore\runtime/VM.cpp(1490) : JSC::VM::verifyExceptionCheckNeedIsSatisfied 1 00007FFC3CCA1DEB WTFCrash 2 00007FFC0F88FFBE WTFCrashWithInfo 3 00007FFC11104790 JSC::VM::verifyExceptionCheckNeedIsSatisfied 4 00007FFC110D8924 JSC::ThrowScope::ThrowScope 5 00007FFBEE14D4EB WebCore::invokeWritableStreamFunction 6 00007FFBEE14C6E1 WebCore::InternalWritableStream::create 7 00007FFBEDF0733C WebCore::WritableStream::create 8 00007FFBEDF07207 WebCore::WritableStream::create 9 00007FFBEDAF98B6 WebCore::JSDOMConstructor<WebCore::JSWritableStream>::construct 10 00007FFC108BBB6F JSC::NativeFunction::operator() 11 00007FFC108BBBBC JSC::TaggedNativeFunction::operator() 12 00007FFC1095567B JSC::LLInt::handleHostCall 13 00007FFC1096BC4A JSC::LLInt::setUpCall 14 00007FFC109616D6 JSC::LLInt::genericCall<JSC::OpConstruct> 15 00007FFC1094DBAF llint_slow_path_construct 16 00007FFC0F88C4C6 llint_entry ERROR: 000001D9626D94D0 - [PID=17864] WebProcessProxy::didClose (web process crash) C:\home\webkit\gc\Source\WebKit\UIProcess/WebProcessProxy.cpp(910) : WebKit::WebProcessProxy::didClose ERROR: 000001D9626D94D0 - [PID=17864] WebProcessProxy::processDidTerminateOrFailedToLaunch: reason=4 C:\home\webkit\gc\Source\WebKit\UIProcess/WebProcessProxy.cpp(918) : WebKit::WebProcessProxy::processDidTerminateOrFailedToLaunch ERROR: 000001D9626A6D60 - [pageProxyID=9, webPageID=10, PID=17864] WebPageProxy::processDidTerminate: (pid 17864), reason 4 C:\home\webkit\gc\Source\WebKit\UIProcess/WebPageProxy.cpp(7705) : WebKit::WebPageProxy::resetStateAfterProcessTermination ERROR: 000001D9626A6D60 - [pageProxyID=9, webPageID=10, PID=17864] WebPageProxy::dispatchProcessDidTerminate: reason=4 C:\home\webkit\gc\Source\WebKit\UIProcess/WebPageProxy.cpp(7760) : WebKit::WebPageProxy::dispatchProcessDidTerminate WebProcess terminated (pid 17864) because the process crashed #CRASHED - WebProcess (pid 17864) LEAK: 1 WebProcessPool LEAK: 1 WebPageProxy PS C:\home\webkit\gc>
Created attachment 438008 [details] Patch
Created attachment 438011 [details] Patch
Mac EWS failed. Fixing this bug reveals Bug 230208 for Mac port.
Created attachment 438099 [details] Patch
r282351 fixed Bug 230208. I resubmitted the patch to EWS. It reports all green now.
Comment on attachment 438099 [details] Patch r=me
Comment on attachment 438099 [details] Patch Nice catch.
Comment on attachment 438099 [details] Patch Clearing flags on attachment: 438099 Committed r282405 (241666@main): <https://commits.webkit.org/241666@main>
All reviewed patches have been landed. Closing bug.
<rdar://problem/83113555>