Unreal Engine Issues and Bug Tracker (UE-70072)

Description

A licensee has reported that Custom Structs can cause a crash when using StompMalloc under certain situations.

Regression?: No
This occurs in 4.20

Steps to Reproduce

Open a new project
Create an Actor Component blueprint named Component_Parent
Create a child class of Component_Parent named Component_Child
Create a new User Defined Struct called My_Custom_Struct
Add a new variable to the struct created in step 4 and change its type to be a class reference to Component_Parent, setting its default value to Component_Parent
Create an Actor blueprint called Actor_To_Place, add a variable and change its class to My_Custom_Struct and change the value of its variable to Component_Child
Save all and close the project.

Open Command Prompt and run the following command (change to the path you're using)

 "D:\Epic Games\UE_4.20\Engine\Binaries\Win64\UE4Editor.exe" "D:\Unreal Projects\4.20\StompTest" -stompmalloc

Drag Actor_To_Place into the level
Result: The editor crashes with the callstack below
Expected: The actor is added to the level properly

Callstack

 Access violation - code c0000005 (first/second chance not available)

UE4Editor_CoreUObject!UObjectProperty::GetObjectPropertyValue() [d:\build\++ue4\sync\engine\source\runtime\coreuobject\private\uobject\propertyobject.cpp:153]
UE4Editor_CoreUObject!FLinkerPlaceholderObjectImpl::ResolvePlaceholderValues() [d:\build\++ue4\sync\engine\source\runtime\coreuobject\private\uobject\linkerplaceholderbase.cpp:82]
UE4Editor_CoreUObject!FLinkerPlaceholderBase::ResolvePlaceholderPropertyValues() [d:\build\++ue4\sync\engine\source\runtime\coreuobject\private\uobject\linkerplaceholderbase.cpp:514]
UE4Editor_CoreUObject!FLinkerPlaceholderBase::ResolveAllPlaceholderReferences() [d:\build\++ue4\sync\engine\source\runtime\coreuobject\private\uobject\linkerplaceholderbase.cpp:434]
UE4Editor_CoreUObject!TLinkerImportPlaceholder<UClass>::ResolveAllPlaceholderReferences() [d:\build\++ue4\sync\engine\source\runtime\coreuobject\private\uobject\linkerplaceholderbase.inl:63]
UE4Editor_CoreUObject!FLinkerLoad::ResolveDependencyPlaceholder() [d:\build\++ue4\sync\engine\source\runtime\coreuobject\private\blueprint\blueprintsupport.cpp:1586]
UE4Editor_CoreUObject!FLinkerLoad::ResolveDeferredDependencies() [d:\build\++ue4\sync\engine\source\runtime\coreuobject\private\blueprint\blueprintsupport.cpp:1360]
UE4Editor_CoreUObject!FLinkerLoad::ResolveDeferredDependencies() [d:\build\++ue4\sync\engine\source\runtime\coreuobject\private\blueprint\blueprintsupport.cpp:1376]
UE4Editor_CoreUObject!FLinkerLoad::Preload() [d:\build\++ue4\sync\engine\source\runtime\coreuobject\private\uobject\linkerload.cpp:3550]
UE4Editor_CoreUObject!FLinkerLoad::CreateExport() [d:\build\++ue4\sync\engine\source\runtime\coreuobject\private\uobject\linkerload.cpp:4244]
UE4Editor_CoreUObject!FLinkerLoad::IndexToObject() [d:\build\++ue4\sync\engine\source\runtime\coreuobject\private\uobject\linkerload.cpp:4467]
UE4Editor_CoreUObject!FLinkerLoad::CreateExport() [d:\build\++ue4\sync\engine\source\runtime\coreuobject\private\uobject\linkerload.cpp:3864]
UE4Editor_CoreUObject!FLinkerLoad::CreateExportAndPreload() [d:\build\++ue4\sync\engine\source\runtime\coreuobject\private\uobject\linkerload.cpp:2925]
UE4Editor_CoreUObject!FLinkerLoad::LoadAllObjects() [d:\build\++ue4\sync\engine\source\runtime\coreuobject\private\uobject\linkerload.cpp:3087]
UE4Editor_CoreUObject!LoadPackageInternal() [d:\build\++ue4\sync\engine\source\runtime\coreuobject\private\uobject\uobjectglobals.cpp:1364]
UE4Editor_CoreUObject!LoadPackage() [d:\build\++ue4\sync\engine\source\runtime\coreuobject\private\uobject\uobjectglobals.cpp:1471]
UE4Editor_CoreUObject!ResolveName() [d:\build\++ue4\sync\engine\source\runtime\coreuobject\private\uobject\uobjectglobals.cpp:828]
UE4Editor_CoreUObject!StaticLoadObjectInternal() [d:\build\++ue4\sync\engine\source\runtime\coreuobject\private\uobject\uobjectglobals.cpp:916]
UE4Editor_CoreUObject!StaticLoadObject() [d:\build\++ue4\sync\engine\source\runtime\coreuobject\private\uobject\uobjectglobals.cpp:983]
UE4Editor_UnrealEd!FAssetDragDropOp::Init() [d:\build\++ue4\sync\engine\source\editor\unrealed\private\draganddrop\assetdragdropop.cpp:215]
UE4Editor_UnrealEd!FAssetDragDropOp::New() [d:\build\++ue4\sync\engine\source\editor\unrealed\private\draganddrop\assetdragdropop.cpp:49]
UE4Editor_ContentBrowser!SAssetView::OnDraggingAssetItem() [d:\build\++ue4\sync\engine\source\editor\contentbrowser\private\sassetview.cpp:4088]
UE4Editor_ContentBrowser!TBaseSPMethodDelegateInstance<0,SAssetView,0,FReply __cdecl(FGeometry const & __ptr64,FPointerEvent const & __ptr64)>::Execute() [d:\build\++ue4\sync\engine\source\runtime\core\public\delegates\delegateinstancesimpl.h:269]
UE4Editor_ContentBrowser!STableRow<TSharedPtr<FAssetViewItem,0> >::OnDragDetected() [d:\build\++ue4\sync\engine\source\runtime\slate\public\widgets\views\stablerow.h:562]
UE4Editor_Slate!FEventRouter::Route<FReply,FEventRouter::FDirectPolicy,FPointerEvent,<lambda_3d2f0c0de9bfb1f26dd3fbfeef226ad5> >() [d:\build\++ue4\sync\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:268]
UE4Editor_Slate!FSlateApplication::RoutePointerMoveEvent() [d:\build\++ue4\sync\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:5628]
UE4Editor_Slate!FSlateApplication::ProcessMouseMoveEvent() [d:\build\++ue4\sync\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:6194]
UE4Editor_Slate!FSlateApplication::OnMouseMove() [d:\build\++ue4\sync\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:6128]
UE4Editor_ApplicationCore!FWindowsApplication::ProcessDeferredMessage() [d:\build\++ue4\sync\engine\source\runtime\applicationcore\private\windows\windowsapplication.cpp:1774]
UE4Editor_ApplicationCore!FWindowsApplication::DeferMessage() [d:\build\++ue4\sync\engine\source\runtime\applicationcore\private\windows\windowsapplication.cpp:2182]
UE4Editor_ApplicationCore!FWindowsApplication::ProcessMessage() [d:\build\++ue4\sync\engine\source\runtime\applicationcore\private\windows\windowsapplication.cpp:895]
UE4Editor_ApplicationCore!FWindowsApplication::AppWndProc() [d:\build\++ue4\sync\engine\source\runtime\applicationcore\private\windows\windowsapplication.cpp:732]
user32
user32
UE4Editor_ApplicationCore!FWindowsPlatformApplicationMisc::PumpMessages() [d:\build\++ue4\sync\engine\source\runtime\applicationcore\private\windows\windowsplatformapplicationmisc.cpp:129]
UE4Editor!FEngineLoop::Tick() [d:\build\++ue4\sync\engine\source\runtime\launch\private\launchengineloop.cpp:3417]
UE4Editor!GuardedMain() [d:\build\++ue4\sync\engine\source\runtime\launch\private\launch.cpp:166]
UE4Editor!GuardedMainWrapper() [d:\build\++ue4\sync\engine\source\runtime\launch\private\windows\launchwindows.cpp:144]
UE4Editor!WinMain() [d:\build\++ue4\sync\engine\source\runtime\launch\private\windows\launchwindows.cpp:223]
UE4Editor!__scrt_common_main_seh() [f:\dd\vctools\crt\vcstartup\src\startup\exe_common.inl:283]
kernel32
ntdll

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Fixed

Component	UE - Gameplay
Affects Versions	4.20, 4.21, 4.22, 4.23
Target Fix	4.22

Fix Commit	5241461
Main Commit	5241466
Release Commit	5241461

Created	Feb 14, 2019
Resolved	Feb 28, 2019
Updated	Mar 23, 2019

UE-70072

User Defined Struct causing crash due to accessing freed memory when using Stompmalloc

User Defined Struct causing crash due to accessing freed memory when using Stompmalloc

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