Access violation when backtracing a JS error on the Hololens 2

[KallynGowdy]

Details

With this patch applied, it appears that there is some sort of crash that occurs on Windows ARM64 devices when an exception triggers the js_backtrace build feature. (Hololens 2)

It happens as the result of attempting to get a JS stacktrace via the capture_stack macro.

The actual crash is an access violation due attempting to write to NULL. The code is specified in mozjs here. I believe it is likely that this crash is actually caused by a failed assertion, but there were no debug logs indicating such so I am unaware as to what the assertion may be.

The stack trace indicates that mozjs::js::SavedStacks::insertFrames() is the culprit, and some tracing seems to indicate that this assertion is failing. Maybe some program counter is not getting set or maybe there's some race condition? I'm not sure but it seems like an issue with mozjs.

I tried builds on MacOS, the Hololens 2 emulator, and Hololens 2, but it only crashed on the Hololens 2. This may be an indication of an issue specific to ARM64.

Reproduction steps:

1. Make a build on Windows for the Hololens 2.
   • This is the command I used: C:\Python27\python.exe mach build -d --uwp --win-arm64 --features js_backtrace
2. Open the project in Visual Studio.
3. Change the default URL in DefaultUrl.h to "http://yeticgi.casualos.com/?story=test1&pagePortal=home".
   • Note the lack of HTTPS. There's a separate issue that causes a websocket error. Was trying to debug when I ran into this issue.
   • The same issue occurs if you load from a build of this this repository. Follow the instructions in DEVELOPERS.md if you do.
4. Run on the Hololens 2 via Visual Studio.
   • If the default URL doesn't take effect, you may have to uninstall the app from the Hololens 2 and reinstall.
5. Wait for it to load and stop at a breakpoint for SavedStacks.cpp.
   • It will say the source cannot be found but its actually because the breakpoint doesn't have a related line in the source code.
   • If you continue then it will run into the access violation exception.

Extra details:

Error message:

Unfortunately, this is the extent of the error message that was written to the debug log.

Exception thrown at 0x00007FFBCDD16784 (simpleservo.dll) in ServoApp.exe: 0xC0000005: Access violation writing location 0x0000000000000000.

The full debug log is available below.

Stack Trace:
This is the full stack trace that was available in Visual Studio at the time that the exception was created.

simpleservo.dll!MOZ_NoReturn(int aLine) Line 236
	at E:\Projects\Yeti\servo\target\aarch64-uwp-windows-msvc\debug\build\mozjs_sys-aa48eb6c20c205d4\out\build\dist\include\mozilla\Assertions.h(236)
simpleservo.dll!js::SavedStacks::insertFrames(JSContext * cx, JS::MutableHandle<js::SavedFrame *> frame, mozilla::Variant<JS::AllFrames,JS::MaxFrames,JS::FirstSubsumedFrame> && capture) Line 0
	at E:\.cargo\git\checkouts\mozjs-fa11ffc7d4f1cc2d\9a6d8fc\mozjs\js\src\vm\SavedStacks.cpp(0)
simpleservo.dll!js::SavedStacks::saveCurrentStack(JSContext * cx, JS::MutableHandle<js::SavedFrame *> frame, mozilla::Variant<JS::AllFrames,JS::MaxFrames,JS::FirstSubsumedFrame> && capture) Line 1292
	at E:\.cargo\git\checkouts\mozjs-fa11ffc7d4f1cc2d\9a6d8fc\mozjs\js\src\vm\SavedStacks.cpp(1292)
simpleservo.dll!JS::CaptureCurrentStack(JSContext * cx, JS::MutableHandle<JSObject *> stackp, mozilla::Variant<JS::AllFrames,JS::MaxFrames,JS::FirstSubsumedFrame> && capture) Line 5926
	at E:\.cargo\git\checkouts\mozjs-fa11ffc7d4f1cc2d\9a6d8fc\mozjs\js\src\jsapi.cpp(5926)
simpleservo.dll!mozjs::rust::CapturedJSStack::new(mozjs::rust::RootedGuard<mut mozjs_sys::generated::root::JSObject*> cx, core::option::Option<u32> guard) Line 1337
	at E:\.cargo\git\checkouts\rust-mozjs-8611526964119dd6\28248e1\src\rust.rs(1337)
simpleservo.dll!script::dom::bindings::error::throw_dom_exception(script::script_runtime::JSContext cx, script::dom::globalscope::GlobalScope * global, script::dom::bindings::error::Error result) Line 114
	at E:\Projects\Yeti\servo\components\script\dom\bindings\error.rs(114)
simpleservo.dll!script::dom::bindings::codegen::Bindings::URLBinding::URLBinding::_constructor::{{closure}}::{{closure}}(script::dom::bindings::codegen::Bindings::URLBinding::URLBinding::_constructor::{{closure}}::closure-0 *) Line 2079
	at E:\Projects\Yeti\servo\target\aarch64-uwp-windows-msvc\debug\build\script-850361cbc8173e5f\out\Bindings\URLBinding.rs(2079)
simpleservo.dll!script::dom::bindings::codegen::Bindings::URLBinding::URLBinding::_constructor::{{closure}}(script::dom::bindings::codegen::Bindings::URLBinding::URLBinding::_constructor::closure-0 *) Line 2042
	at E:\Projects\Yeti\servo\target\aarch64-uwp-windows-msvc\debug\build\script-850361cbc8173e5f\out\Bindings\URLBinding.rs(2042)
simpleservo.dll!core::ops::function::impls::{{impl}}::call_once<(),FnMut<()>>(core::ops::function::mut FnMut<()>* self) Line 286
	at C:\Users\kally\.rustup\toolchains\nightly-2020-05-15-x86_64-pc-windows-msvc\lib\rustlib\src\rust\src\libcore\ops\function.rs(286)
simpleservo.dll!std::panic::{{impl}}::call_once<(),mut FnMut<()>*>(std::panic::AssertUnwindSafe<mut FnMut<()>*> self) Line 319
	at C:\Users\kally\.rustup\toolchains\nightly-2020-05-15-x86_64-pc-windows-msvc\lib\rustlib\src\rust\src\libstd\panic.rs(319)
simpleservo.dll!std::panicking::try::do_call<std::panic::AssertUnwindSafe<mut FnMut<()>*>,()>(unsigned char * data) Line 299
	at C:\Users\kally\.rustup\toolchains\nightly-2020-05-15-x86_64-pc-windows-msvc\lib\rustlib\src\rust\src\libstd\panicking.rs(299)
[External Code]
simpleservo.dll!std::panicking::try<(),std::panic::AssertUnwindSafe<mut FnMut<()>*>>(std::panic::AssertUnwindSafe<mut FnMut<()>*> f) Line 274
	at C:\Users\kally\.rustup\toolchains\nightly-2020-05-15-x86_64-pc-windows-msvc\lib\rustlib\src\rust\src\libstd\panicking.rs(274)
simpleservo.dll!std::panic::catch_unwind<std::panic::AssertUnwindSafe<mut FnMut<()>*>,()>(std::panic::AssertUnwindSafe<mut FnMut<()>*> f) Line 394
	at C:\Users\kally\.rustup\toolchains\nightly-2020-05-15-x86_64-pc-windows-msvc\lib\rustlib\src\rust\src\libstd\panic.rs(394)
simpleservo.dll!mozjs::panic::wrap_panic(core::ops::function::mut FnMut<()>* function) Line 22
	at E:\.cargo\git\checkouts\rust-mozjs-8611526964119dd6\28248e1\src\panic.rs(22)
simpleservo.dll!script::dom::bindings::codegen::Bindings::URLBinding::URLBinding::_constructor(mozjs_sys::generated::root::JSContext * cx, unsigned int argc, mozjs_sys::generated::root::JS::Value * vp) Line 2087
	at E:\Projects\Yeti\servo\target\aarch64-uwp-windows-msvc\debug\build\script-850361cbc8173e5f\out\Bindings\URLBinding.rs(2087)
[Inline Frame] simpleservo.dll!CallJSNative(JSContext * cx, bool(*)(JSContext *, unsigned int, JS::Value *) native, js::CallReason reason, const JS::CallArgs & args) Line 456
	at E:\.cargo\git\checkouts\mozjs-fa11ffc7d4f1cc2d\9a6d8fc\mozjs\js\src\vm\Interpreter.cpp(456)
[Inline Frame] simpleservo.dll!CallJSNativeConstructor(JSContext * cx, bool(*)(JSContext *, unsigned int, JS::Value *) native, const JS::CallArgs & args) Line 472
	at E:\.cargo\git\checkouts\mozjs-fa11ffc7d4f1cc2d\9a6d8fc\mozjs\js\src\vm\Interpreter.cpp(472)
simpleservo.dll!InternalConstruct(JSContext * cx, const js::AnyConstructArgs & args) Line 680
	at E:\.cargo\git\checkouts\mozjs-fa11ffc7d4f1cc2d\9a6d8fc\mozjs\js\src\vm\Interpreter.cpp(680)
simpleservo.dll!Interpret(JSContext * cx, js::RunState & state) Line 3108
	at E:\.cargo\git\checkouts\mozjs-fa11ffc7d4f1cc2d\9a6d8fc\mozjs\js\src\vm\Interpreter.cpp(3108)
simpleservo.dll!js::RunScript(JSContext * cx, js::RunState & state) Line 424
	at E:\.cargo\git\checkouts\mozjs-fa11ffc7d4f1cc2d\9a6d8fc\mozjs\js\src\vm\Interpreter.cpp(424)
simpleservo.dll!js::InternalCallOrConstruct(JSContext * cx, const JS::CallArgs & args, js::MaybeConstruct construct, js::CallReason reason) Line 593
	at E:\.cargo\git\checkouts\mozjs-fa11ffc7d4f1cc2d\9a6d8fc\mozjs\js\src\vm\Interpreter.cpp(593)
simpleservo.dll!InternalCall(JSContext * cx, const js::AnyInvokeArgs & args, js::CallReason reason) Line 617
	at E:\.cargo\git\checkouts\mozjs-fa11ffc7d4f1cc2d\9a6d8fc\mozjs\js\src\vm\Interpreter.cpp(617)
simpleservo.dll!js::Call(JSContext * cx, JS::Handle<JS::Value> fval, JS::Handle<JS::Value> thisv, const js::AnyInvokeArgs & args, JS::MutableHandle<JS::Value> rval, js::CallReason reason) Line 634
	at E:\.cargo\git\checkouts\mozjs-fa11ffc7d4f1cc2d\9a6d8fc\mozjs\js\src\vm\Interpreter.cpp(634)
simpleservo.dll!js::CallSelfHostedFunction(JSContext * cx, JS::Handle<js::PropertyName *> name, JS::Handle<JS::Value> thisv, const js::AnyInvokeArgs & args, JS::MutableHandle<JS::Value> rval) Line 1693
	at E:\.cargo\git\checkouts\mozjs-fa11ffc7d4f1cc2d\9a6d8fc\mozjs\js\src\vm\SelfHosting.cpp(1693)
simpleservo.dll!js::jit::InterpretResume(JSContext * cx, JS::Handle<JSObject *> obj, JS::Handle<JS::Value> val, JS::Handle<js::PropertyName *> kind, JS::MutableHandle<JS::Value> rval) Line 985
	at E:\.cargo\git\checkouts\mozjs-fa11ffc7d4f1cc2d\9a6d8fc\mozjs\js\src\jit\VMFunctions.cpp(985)

Full log

'ServoApp.exe' (Win32): Loaded 'U:\USERS\DefaultAccount\AppData\Local\DevelopmentFiles\MozillaFoundation.FirefoxRealityVS.Debug_ARM64.kally\ServoApp.exe'. Symbols loaded.
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\ntdll.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\KernelBase.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\combase.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\ucrtbase.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\rpcrt4.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\kernel32legacy.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\oleaut32.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\msvcp_win.dll'. 
'ServoApp.exe' (Win32): Loaded 'U:\USERS\DefaultAccount\AppData\Local\DevelopmentFiles\MozillaFoundation.FirefoxRealityVS.Debug_ARM64.kally\libEGL.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\forwarders\kernel32.dll'. 
'ServoApp.exe' (Win32): Loaded 'U:\USERS\DefaultAccount\AppData\Local\DevelopmentFiles\MozillaFoundation.FirefoxRealityVS.Debug_ARM64.kally\simpleservo.dll'. Symbols loaded.
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\ws2_32.dll'. 
'ServoApp.exe' (Win32): Loaded 'P:\WindowsApps\Microsoft.VCLibs.140.00.Debug_14.0.27810.0_arm64__8wekyb3d8bbwe\msvcp140d_app.dll'. 
'ServoApp.exe' (Win32): Loaded 'P:\WindowsApps\Microsoft.VCLibs.140.00.Debug_14.0.27810.0_arm64__8wekyb3d8bbwe\vcruntime140d_app.dll'. 
'ServoApp.exe' (Win32): Loaded 'U:\USERS\DefaultAccount\AppData\Local\DevelopmentFiles\MozillaFoundation.FirefoxRealityVS.Debug_ARM64.kally\ucrtbased.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\forwarders\ole32.dll'. 
'ServoApp.exe' (Win32): Loaded 'P:\WindowsApps\Microsoft.VCLibs.140.00.Debug_14.0.27810.0_arm64__8wekyb3d8bbwe\msvcp140_app.dll'. 
'ServoApp.exe' (Win32): Loaded 'P:\WindowsApps\Microsoft.VCLibs.140.00.Debug_14.0.27810.0_arm64__8wekyb3d8bbwe\vcruntime140_app.dll'. 
'ServoApp.exe' (Win32): Loaded 'U:\USERS\DefaultAccount\AppData\Local\DevelopmentFiles\MozillaFoundation.FirefoxRealityVS.Debug_ARM64.kally\libcrypto.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\D3DCompiler_47.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\bcrypt.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\dxgi.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\msvcrt.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\win32u.dll'. 
'ServoApp.exe' (Win32): Loaded 'U:\USERS\DefaultAccount\AppData\Local\DevelopmentFiles\MozillaFoundation.FirefoxRealityVS.Debug_ARM64.kally\libssl.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\d3d11.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\cryptsp.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\gdi32.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\gdi32min.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\MinUser.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\msvcp110_win.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\SHCore.dll'. 
The thread 0x1634 has exited with code 0 (0x0).
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\procthreadexthost.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\kernel.appcore.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\bcryptprimitives.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\Windows.UI.Xaml.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\sechost.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\dcomp.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\CoreMessaging.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\iertutil.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\BCP47Langs.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\advapi32legacy.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\advapi32legacy.dll'. 
'ServoApp.exe' (Win32): Unloaded 'C:\Windows\system32\advapi32legacy.dll'
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\XamlPalWp.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\twinapi.appcore.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\WinTypes.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\CoreUIComponents.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\ntmarta.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\Windows.StateRepositoryCore.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\Windows.UI.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\WindowManagementAPI.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\InputHost.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\propsys.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\TextInputFramework.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\OneCoreUAPCommonProxyStub.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\urlmon.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\Microsoft.Composable.Contracts.AppThemeApiStub.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\UserMgrProxy.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\ResourcePolicyClient.dll'. 
'ServoApp.exe' (Win32): Unloaded 'C:\Windows\system32\ResourcePolicyClient.dll'
'ServoApp.exe' (Win32): Loaded 'B:\Windows\System32\DriverStore\FileRepository\qcdx_ffu850.inf_arm64_3f3ec3a0cb26c5d1\qcdx11arm64um850.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\forwarders\advapi32.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\MrmCoreR.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\Windows.StateRepositoryClient.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\usermgrcli.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\DXCore.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\cfgmgr32.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\profapi.dll'. 
'ServoApp.exe' (Win32): Loaded 'B:\Windows\System32\DriverStore\FileRepository\qcdx_ffu850.inf_arm64_3f3ec3a0cb26c5d1\qcdxarm64compiler850.DLL'. 
Exception thrown at 0x00007FFBF7E939EC in ServoApp.exe: Microsoft C++ exception: Cn::XH at memory location 0x0000006988AFE2A0.
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\BCP47mrm.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\cryptbase.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\D3DSCache.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\userenv.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\profext.dll'. 
'ServoApp.exe' (Win32): Loaded 'P:\WindowsApps\Microsoft.UI.Xaml.2.4_2.42005.18002.0_arm64__8wekyb3d8bbwe\Microsoft.UI.Xaml.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\d2d1.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\DWrite.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\TextShaping.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\Windows.Shell.ServiceHostBuilder.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\execmodelproxy.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\rmclient.dll'. 
Exception thrown at 0x00007FFBF7E939EC in ServoApp.exe: Microsoft C++ exception: Cn::XH at memory location 0x0000006988AFD2D0.
onecoreuap\windows\moderncore\inputv2\inputhost\components\cursor\client\cursorclient.cpp(44)\InputHost.dll!00007FFBE703D5C4: (caller: 00007FFBE703CCCC) ReturnHr(1) tid(f7c) 87B20809 onecoreuap\windows\moderncore\inputv2\inputhost\components\cursor\client\cursorclient.cpp(76)\InputHost.dll!00007FFBE703CCEC: (caller: 00007FFBF73FD37C) ReturnHr(2) tid(f7c) 87B20809 'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\UiaManager.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\Windows.UI.Core.TextInput.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\edgegdi.dll'. 
The thread 0x1bd0 has exited with code 0 (0x0).
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\DataExchange.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\Windows.Graphics.dll'. 
'ServoApp.exe' (Win32): Loaded 'U:\USERS\DefaultAccount\AppData\Local\DevelopmentFiles\VisualStudio\16.6\arm64\Microsoft.VisualStudio.DesignTools.UwpTap.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\xmllite.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\Windows.Globalization.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\msftedit.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\forwarders\user32.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\minglobinputhost.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\WindowsCodecs.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\Windows.UI.Xaml.Controls.dll'. 
OpenGLES::OpenGLES()
'ServoApp.exe' (Win32): Loaded 'U:\USERS\DefaultAccount\AppData\Local\DevelopmentFiles\MozillaFoundation.FirefoxRealityVS.Debug_ARM64.kally\libGLESv2.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\Windows.ApplicationModel.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\Windows.Energy.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\directmanipulation.dll'. 
BrowserPage::StartRenderLoop(). UI thread: 3964
BrowserPage::Loop(). GL thread: 4352
Entering loop
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\Windows.Storage.ApplicationData.dll'. 
onecoreuap\base\appmodel\statemanager\winrt\lib\windows.storage.applicationdatafactory.server.cpp(235)\Windows.Storage.ApplicationData.dll!00007FFBE1BF85F4: (caller: 00007FF6032666A8) ReturnHr(1) tid(1100) 8000000B The operation attempted to access data outside the valid range
    Msg:[User S-1-12-1-570682017-1108323634-2119347075-430557224] 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\logoncli.dll'. 
Exception thrown at 0x00007FFBF7E939EC (KernelBase.dll) in ServoApp.exe: 0x000006D9: There are no more endpoints available from the endpoint mapper.
onecoreuap\base\appmodel\statemanager\roamingrpc\stateroamingrpcclient.cpp(124)\Windows.Storage.ApplicationData.dll!00007FFBE1BF4E60: (caller: 00007FFBE1BFDA70) ReturnHr(2) tid(1100) 800706D9 There are no more endpoints available from the endpoint mapper.
    Msg:[c_SignalRoamingDataChange 2] 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\windows.storage.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\wldp.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\shlwapi_onecore.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\threadpoolwinrt.dll'. 
'ServoApp.exe' (Win32): Loaded 'U:\USERS\DefaultAccount\AppData\Local\DevelopmentFiles\MozillaFoundation.FirefoxRealityVS.Debug_ARM64.kally\openxr_loader.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\MixedRealityRuntime.dll'. 
'ServoApp.exe' (Win32): Loaded 'P:\WindowsApps\Microsoft.WindowsMixedReality.Runtime_102.2006.3006.0_arm64__8wekyb3d8bbwe\arm64\WinXrRuntime.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\D3D12.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\forwarders\version.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\rometadata.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\WinMetadata\Windows.Perception.winmd'. Module was built without symbols.
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\WinMetadata\Windows.UI.winmd'. Module was built without symbols.
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\WinMetadata\Windows.Graphics.winmd'. Module was built without symbols.
'ServoApp.exe' (Win32): Unloaded 'C:\Windows\system32\D3D12.dll'
'ServoApp.exe' (Win32): Unloaded 'C:\Windows\system32\forwarders\version.dll'
'ServoApp.exe' (Win32): Unloaded 'P:\WindowsApps\Microsoft.WindowsMixedReality.Runtime_102.2006.3006.0_arm64__8wekyb3d8bbwe\arm64\WinXrRuntime.dll'
'ServoApp.exe' (Win32): Unloaded 'C:\Windows\system32\MixedRealityRuntime.dll'
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\MixedRealityRuntime.dll'. 
'ServoApp.exe' (Win32): Loaded 'P:\WindowsApps\Microsoft.WindowsMixedReality.Runtime_102.2006.3006.0_arm64__8wekyb3d8bbwe\arm64\WinXrRuntime.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\D3D12.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\forwarders\version.dll'. 
'ServoApp.exe' (Win32): Unloaded 'C:\Windows\system32\D3D12.dll'
'ServoApp.exe' (Win32): Unloaded 'C:\Windows\system32\forwarders\version.dll'
'ServoApp.exe' (Win32): Unloaded 'P:\WindowsApps\Microsoft.WindowsMixedReality.Runtime_102.2006.3006.0_arm64__8wekyb3d8bbwe\arm64\WinXrRuntime.dll'
'ServoApp.exe' (Win32): Unloaded 'C:\Windows\system32\MixedRealityRuntime.dll'
RUST: WARN - webxr::openxr - Available extensions:
ExtensionSet { epic_view_configuration_fov: false, ext_performance_settings: false, ext_thermal_query: false, ext_debug_utils: true, ext_eye_gaze_interaction: true, ext_view_configuration_depth_range: false, ext_conformance_automation: true, ext_win32_appcontainer_compatible: true, extx_overlay: false, khr_composition_layer_cube: false, khr_composition_layer_depth: true, khr_vulkan_swapchain_format_list: false, khr_composition_layer_cylinder: false, khr_composition_layer_equirect: false, khr_opengl_enable: false, khr_opengl_es_enable: false, khr_vulkan_enable: false, khr_d3d11_enable: true, khr_d3d12_enable: true, khr_visibility_mask: false, khr_win32_convert_performance_counter_time: true, khr_convert_timespec_time: false, mnd_headless: false, msft_unbounded_reference_space: true, msft_spatial_anchor: true, msft_hand_interaction: true, msft_spatial_graph_bridge_preview: false, msft_hand_tracking_preview: false, msft_hand_tracking_mesh_preview: false, msft_secondary_view_configuration_preview: false, msft_first_person_observer_preview: false, msft_controller_model_preview: false, varjo_quad_views: false, other: [] }
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\MixedRealityRuntime.dll'. 
'ServoApp.exe' (Win32): Loaded 'P:\WindowsApps\Microsoft.WindowsMixedReality.Runtime_102.2006.3006.0_arm64__8wekyb3d8bbwe\arm64\WinXrRuntime.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\D3D12.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\forwarders\version.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\Windows.Perception.Stub.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\Windows.Mirage.dll'. 
'ServoApp.exe' (Win32): Unloaded 'C:\Windows\system32\forwarders\version.dll'
'ServoApp.exe' (Win32): Unloaded 'P:\WindowsApps\Microsoft.WindowsMixedReality.Runtime_102.2006.3006.0_arm64__8wekyb3d8bbwe\arm64\WinXrRuntime.dll'
'ServoApp.exe' (Win32): Unloaded 'C:\Windows\system32\MixedRealityRuntime.dll'
'ServoApp.exe' (Win32): Unloaded 'U:\USERS\DefaultAccount\AppData\Local\DevelopmentFiles\MozillaFoundation.FirefoxRealityVS.Debug_ARM64.kally\openxr_loader.dll'
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\mswsock.dll'. 
'ServoApp.exe' (Win32): Loaded 'U:\USERS\DefaultAccount\AppData\Local\DevelopmentFiles\MozillaFoundation.FirefoxRealityVS.Debug_ARM64.kally\openxr_loader.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\MixedRealityRuntime.dll'. 
'ServoApp.exe' (Win32): Loaded 'P:\WindowsApps\Microsoft.WindowsMixedReality.Runtime_102.2006.3006.0_arm64__8wekyb3d8bbwe\arm64\WinXrRuntime.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\forwarders\version.dll'. 
'ServoApp.exe' (Win32): Unloaded 'C:\Windows\system32\forwarders\version.dll'
'ServoApp.exe' (Win32): Unloaded 'P:\WindowsApps\Microsoft.WindowsMixedReality.Runtime_102.2006.3006.0_arm64__8wekyb3d8bbwe\arm64\WinXrRuntime.dll'
'ServoApp.exe' (Win32): Unloaded 'C:\Windows\system32\MixedRealityRuntime.dll'
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\MixedRealityRuntime.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\UIAutomationCore.dll'. 
'ServoApp.exe' (Win32): Loaded 'P:\WindowsApps\Microsoft.WindowsMixedReality.Runtime_102.2006.3006.0_arm64__8wekyb3d8bbwe\arm64\WinXrRuntime.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\forwarders\version.dll'. 
'ServoApp.exe' (Win32): Unloaded 'C:\Windows\system32\forwarders\version.dll'
'ServoApp.exe' (Win32): Unloaded 'P:\WindowsApps\Microsoft.WindowsMixedReality.Runtime_102.2006.3006.0_arm64__8wekyb3d8bbwe\arm64\WinXrRuntime.dll'
'ServoApp.exe' (Win32): Unloaded 'C:\Windows\system32\MixedRealityRuntime.dll'
RUST: WARN - webxr::openxr - Available extensions:
ExtensionSet { epic_view_configuration_fov: false, ext_performance_settings: false, ext_thermal_query: false, ext_debug_utils: true, ext_eye_gaze_interaction: true, ext_view_configuration_depth_range: false, ext_conformance_automation: true, ext_win32_appcontainer_compatible: true, extx_overlay: false, khr_composition_layer_cube: false, khr_composition_layer_depth: true, khr_vulkan_swapchain_format_list: false, khr_composition_layer_cylinder: false, khr_composition_layer_equirect: false, khr_opengl_enable: false, khr_opengl_es_enable: false, khr_vulkan_enable: false, khr_d3d11_enable: true, khr_d3d12_enable: true, khr_visibility_mask: false, khr_win32_convert_performance_counter_time: true, khr_convert_timespec_time: false, mnd_headless: false, msft_unbounded_reference_space: true, msft_spatial_anchor: true, msft_hand_interaction: true, msft_spatial_graph_bridge_preview: false, msft_hand_tracking_preview: false, msft_hand_tracking_mesh_preview: false, msft_secondary_view_configuration_preview: false, msft_first_person_observer_preview: false, msft_controller_model_preview: false, varjo_quad_views: false, other: [] }
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\MixedRealityRuntime.dll'. 
'ServoApp.exe' (Win32): Loaded 'P:\WindowsApps\Microsoft.WindowsMixedReality.Runtime_102.2006.3006.0_arm64__8wekyb3d8bbwe\arm64\WinXrRuntime.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\forwarders\version.dll'. 
'ServoApp.exe' (Win32): Unloaded 'C:\Windows\system32\forwarders\version.dll'
'ServoApp.exe' (Win32): Unloaded 'P:\WindowsApps\Microsoft.WindowsMixedReality.Runtime_102.2006.3006.0_arm64__8wekyb3d8bbwe\arm64\WinXrRuntime.dll'
'ServoApp.exe' (Win32): Unloaded 'C:\Windows\system32\MixedRealityRuntime.dll'
'ServoApp.exe' (Win32): Unloaded 'U:\USERS\DefaultAccount\AppData\Local\DevelopmentFiles\MozillaFoundation.FirefoxRealityVS.Debug_ARM64.kally\openxr_loader.dll'
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\OneCoreCommonProxyStub.dll'. 
RUST: WARN - constellation::constellation - Trying to get an event-loop from an unknown BC group
RUST: WARN - constellation::constellation - Visibility change for closed browsing context PipelineId { namespace_id: PipelineNamespaceId(1), index: PipelineIndex(1) }.
Exception thrown at 0x00007FFBF7E939EC in ServoApp.exe: Microsoft C++ exception: Cn::XH at memory location 0x0000006988AFD830.
Exception thrown at 0x00007FFBF7E939EC in ServoApp.exe: Microsoft C++ exception: Cn::XH at memory location 0x0000006988AFDA80.
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\dnsapi.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\IPHLPAPI.DLL'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\nsi.dll'. 
'ServoApp.exe' (Win32): Loaded 'C:\Windows\system32\FWPUCLNT.DLL'. 
RUST: WARN - net::http_loader - Failed to receive confirmation request was streamed without error.
RUST: WARN - script::timers - Resuming an already resumed timer.
RUST: WARN - net::http_loader - Failed to receive confirmation request was streamed without error.
RUST: WARN - net::http_loader - Failed to receive confirmation request was streamed without error.
RUST: WARN - net::http_loader - Failed to receive confirmation request was streamed without error.
RUST: WARN - net::http_loader - Failed to receive confirmation request was streamed without error.
RUST: WARN - net::http_loader - Failed to receive confirmation request was streamed without error.
RUST: WARN - net::http_loader - Failed to receive confirmation request was streamed without error.
RUST: WARN - net::http_loader - Failed to receive confirmation request was streamed without error.
RUST: WARN - net::http_loader - Failed to receive confirmation request was streamed without error.
RUST: WARN - net::http_loader - Failed to receive confirmation request was streamed without error.
RUST: WARN - net::http_loader - Failed to receive confirmation request was streamed without error.
RUST: WARN - net::http_loader - Failed to receive confirmation request was streamed without error.
RUST: WARN - mozjs::rust - Warning at https://yeticgi.casualos.com/vendors.8e14baa88946c15832fc.js:0:0: asm.js type error: Disabled by lack of compiler support

RUST: WARN - net::http_loader - Failed to receive confirmation request was streamed without error.
[globalThis-polyfill] load
THREE.WebGLRenderer: WEBGL_depth_texture extension not supported.
[AppManager] Starting init...
[AppManager] Fetching config...
TypeError: e.style is undefined
RUST: WARN - net::http_loader - Failed to receive confirmation request was streamed without error.
The thread 0xf4c has exited with code 0 (0x0).
Unable to save config: 
MissingAPIError: indexedDB API not found. If using IE10+, make sure to run your code on a server URL (not locally). If using old Safari versions, make sure to include indexedDB polyfill.
Skipping Sentry Initialization
[AppManager] Setting primary simulation:
test1
Unable to get Username
MissingAPIError: indexedDB API not found. If using IE10+, make sure to run your code on a server URL (not locally). If using old Safari versions, make sure to include indexedDB polyfill.
[AppManager] Generating new login key...
Unable to save user to DB
MissingAPIError: indexedDB API not found. If using IE10+, make sure to run your code on a server URL (not locally). If using old Safari versions, make sure to include indexedDB polyfill.
Unable to save username
MissingAPIError: indexedDB API not found. If using IE10+, make sure to run your code on a server URL (not locally). If using old Safari versions, make sure to include indexedDB polyfill.
ServoApp.exe has triggered a breakpoint.

Exception thrown at 0x00007FFBCDD16784 (simpleservo.dll) in ServoApp.exe: 0xC0000005: Access violation writing location 0x0000000000000000.
Unhandled exception at 0x00007FFBCDD16784 (simpleservo.dll) in ServoApp.exe: 0xC0000005: Access violation writing location 0x0000000000000000.

[jdm]

I have not been able to reproduce this in a desktop UWP build yet. I realize this was mentioned, but I like to verify that the easiest setup doesn't work.

[jdm]

The next useful step here is probably to do a build with --features debugmozjs to get a non-optimized spidermonkey build.

[jdm]

I have reproduced this on device with a debugmozjs build.

[jdm]

The backtrace I see ends up in the guts of the mozilla::Variant type, which is the underlying type of JS::StackCapture which is passed to JS::CaptureCurrentStack (called from https://github.com/servo/rust-mozjs/blob/28248e1d6658e92dd5ecb0866e53a97f043b9b38/src/rust.rs#L1337). Since the C++ API uses rvalue references, I suspect there's some surprising FFI miscompilation for arm64 going on.

[jdm]

Confirmed - when I move the call to JS::CaptureCurrentStack into the C++ glue so we don't need to pass an rvalue reference from Rust code, the crash disappears.

[jdm]

Disassembly calling from c++:

00007FF86A77B768  mov         x0,x9  
    return JS::CaptureCurrentStack(cx, obj);
00007FF86A77B76C  mov         x1,x10  
00007FF86A77B770  str         x2,[sp,#0x20]  
00007FF86A77B774  str         x8,[sp,#0x18]  
00007FF86A77B778  str         x9,[sp,#0x10]  
00007FF86A77B77C  str         x11,[sp,#8]  
00007FF86A77B780  bl          mozilla::Variant<JS::AllFrames,JS::MaxFrames,JS::FirstSubsumedFrame>::Variant<JS::AllFrames,JS::AllFrames> (07FF86A77DE54h)  
00007FF86A77B784  ldr         x8,[sp,#8]  
00007FF86A77B788  mov         x0,x8  
00007FF86A77B78C  ldr         x1,[sp,#0x18]  
00007FF86A77B790  ldr         x2,[sp,#0x20]  
00007FF86A77B794  bl          memcpy (07FF8709BFEE8h)  
00007FF86A77B798  ldr         x0,[sp,#0x30]  
00007FF86A77B79C  ldr         x1,[sp,#0x28]  
00007FF86A77B7A0  ldr         x2,[sp,#0x10]  
00007FF86A77B7A4  bl          JS::CaptureCurrentStack (07FF86A30A72Ch)  
00007FF86A77B7A8  ldr         x8,[sp,#0x10]  
00007FF86A77B7AC  str         w0,[sp,#4]  
00007FF86A77B7B0  mov         x0,x8  
00007FF86A77B7B4  bl          mozilla::Variant<JS::AllFrames,JS::MaxFrames,JS::FirstSubsumedFrame>::~Variant (07FF86A77DEC8h)  
00007FF86A77B7B8  ldr         x0,[sp,#0x68]  
00007FF86A77B7BC  bl          __security_check_cookie (07FF86E44DE80h)  
00007FF86A77B7C0  mov         w12,#1  
00007FF86A77B7C4  ldr         w3,[sp,#4]  
00007FF86A77B7C8  and         w0,w3,w12  
00007FF86A77B7CC  ldr         lr,[sp,#0x70]  
00007FF86A77B7D0  add         sp,sp,#0x80  
00007FF86A77B7D4  ret  

disassembly calling from rust:

  1333:             None => JS_StackCapture_AllFrames(),
00007FF86A9F28C4  ldur        w8,[fp,#-0x80]  
  1333:             None => JS_StackCapture_AllFrames(),
00007FF86A9F28C8  mov         w1,w8  
00007FF86A9F28CC  stur        x0,[fp,#-0x90]  
00007FF86A9F28D0  cbz         w1,mozjs::rust::CapturedJSStack::new+6Ch (07FF86A9F28FCh)  
00007FF86A9F28D4  b           mozjs::rust::CapturedJSStack::new+48h (07FF86A9F28D8h)  
  1334:             Some(count) => JS_StackCapture_MaxFrames(count),
00007FF86A9F28D8  ldur        w8,[fp,#-0x7C]  
00007FF86A9F28DC  stur        w8,[fp,#-0x14]  
00007FF86A9F28E0  sub         x9,fp,#0x68  
00007FF86A9F28E4  stur        w8,[fp,#-0x94]  
00007FF86A9F28E8  mov         x8,x9  
00007FF86A9F28EC  ldur        w0,[fp,#-0x94]  
00007FF86A9F28F0  bl          glue::JS_StackCapture_MaxFrames (07FF86ECA1D5Ch)  
  1330:                       mut guard: RootedGuard<'a, *mut JSObject>,
  1331:                       max_frame_count: Option<u32>) -> Option<Self> {
  1332:         let ref mut stack_capture = match max_frame_count {
00007FF86A9F28F4  b           mozjs::rust::CapturedJSStack::new+78h (07FF86A9F2908h)  
00007FF86A9F28F8  brk         #1  
  1333:             None => JS_StackCapture_AllFrames(),
00007FF86A9F28FC  sub         x8,fp,#0x68  
00007FF86A9F2900  bl          glue::JS_StackCapture_AllFrames (07FF86ECA1D24h)  
00007FF86A9F2904  b           mozjs::rust::CapturedJSStack::new+78h (07FF86A9F2908h)  
  1330:                       mut guard: RootedGuard<'a, *mut JSObject>,
  1331:                       max_frame_count: Option<u32>) -> Option<Self> {
  1332:         let ref mut stack_capture = match max_frame_count {
00007FF86A9F2908  sub         x8,fp,#0x68  
00007FF86A9F290C  stur        x8,[fp,#-0x10]  
  1335:         };
  1336: 
  1337:         if !jsapi::CaptureCurrentStack(cx, guard.handle_mut().raw(), stack_capture) {
00007FF86A9F2910  sub         x0,fp,#0x88  
00007FF86A9F2914  bl          mozjs::rust::RootedGuard<mut mozjs_sys::generated::root::JSObject*>::handle_mut<mut mozjs_sys::generated::root::JSObject*> (07FF86A4D0088h)  
00007FF86A9F2918  stur        x0,[fp,#-0xA0]  
00007FF86A9F291C  b           mozjs::rust::CapturedJSStack::new+90h (07FF86A9F2920h)  
00007FF86A9F2920  ldur        x8,[fp,#-0xA0]  
00007FF86A9F2924  stur        x8,[fp,#-0x40]  
00007FF86A9F2928  sub         x0,fp,#0x40  
00007FF86A9F292C  bl          mozjs::rust::MutableHandle<mut mozjs_sys::generated::root::JSObject*>::raw<mut mozjs_sys::generated::root::JSObject*> (07FF86A4D03D4h)  
00007FF86A9F2930  stur        x0,[fp,#-0xA8]  
00007FF86A9F2934  b           mozjs::rust::CapturedJSStack::new+0A8h (07FF86A9F2938h)  
00007FF86A9F2938  ldur        x8,[fp,#-0xA8] 

[jdm]

Oh, JS_CaptureStack_AllFrames is already a C++ glue function, so here's that disassembly as well. That means that we're returning a mozilla::Variant by value to Rust code right now, then passing it by rvalue reference to C++:

    39: JS::StackCapture JS_StackCapture_AllFrames() {
00007FF86ECA1D24  sub         sp,sp,#0x30  
    37: }
    38: 
    39: JS::StackCapture JS_StackCapture_AllFrames() {
00007FF86ECA1D28  str         lr,[sp,#0x20]  
00007FF86ECA1D2C  adrp        x8,__rust_panic_type_info (07FF873AD9000h)  
00007FF86ECA1D30  ldr         x8,[x8,#0xE50]  
00007FF86ECA1D34  str         x8,[sp,#0x18]  
00007FF86ECA1D38  add         x1,sp,#0x17  
00007FF86ECA1D3C  str         x0,[sp,#8]  
    40:     return JS::StackCapture(JS::AllFrames());
00007FF86ECA1D40  bl          mozilla::Variant<JS::AllFrames,JS::MaxFrames,JS::FirstSubsumedFrame>::Variant<JS::AllFrames,JS::AllFrames> (07FF86A9BDE54h)  
00007FF86ECA1D44  ldr         x8,[sp,#0x18]  
00007FF86ECA1D48  mov         x0,x8  
00007FF86ECA1D4C  bl          __security_check_cookie (07FF86E68DEC0h)  
00007FF86ECA1D50  ldr         lr,[sp,#0x20]  
00007FF86ECA1D54  add         sp,sp,#0x30  
00007FF86ECA1D58  ret  
    41: }