Clear ghost-refs from old stack area

Author: ShortDevelopment

bin/NativeTests/JsRTApiTest.cpp

@@ -128,6 +128,7 @@ namespace JsRTApiTest
         valueRef = JS_INVALID_REFERENCE;
         valueRefFromWeakRef = JS_INVALID_REFERENCE;
 
+        CHECK(JsPrivateClearStack() == JsNoError);
         CHECK(JsCollectGarbage(runtime) == JsNoError);
 
         // JsGetWeakReferenceValue should return an invalid reference after the value was GC'd.

lib/Jsrt/ChakraCore.h

@@ -2017,6 +2017,16 @@ JsGetEmbedderData(_In_ JsValueRef instance, _Out_ JsValueRef* embedderData);
 CHAKRA_API
 JsSetEmbedderData(_In_ JsValueRef instance, _In_ JsValueRef embedderData);
 
+/// <summary>
+///     Clear some of the inaccessible part of the stack.
+/// </summary>
+/// <returns>
+///     The code <c>JsNoError</c> if the operation succeeded, a failure code
+///     otherwise.
+/// </returns>
+CHAKRA_API
+JsPrivateClearStack();
+
 #ifdef _WIN32
 #include "ChakraCoreWindows.h"
 #endif // _WIN32

lib/Jsrt/Jsrt.cpp

@@ -475,6 +475,16 @@ CHAKRA_API JsCollectGarbage(_In_ JsRuntimeHandle runtimeHandle)
 }
 
 #ifdef ENABLE_DEBUG_CONFIG_OPTIONS
+CHAKRA_API JsPrivateClearStack()
+{
+    // https://github.com/bdwgc/bdwgc/blob/e1042aa86d9403f433a2ab38ee2aab081984fca8/misc.c#L260-L285
+
+    const int SMALL_CLEAR_SIZE = 256;
+    volatile void* dummy[SMALL_CLEAR_SIZE];
+    std::memset((void*)dummy, 0, sizeof(dummy));
+    return JsNoError;
+}
+
 CHAKRA_API JsPrivateCollectGarbageSkipStack(_In_ JsRuntimeHandle runtimeHandle)
 {
     return JsCollectGarbageCommon<CollectNowExhaustiveSkipStack>(runtimeHandle);

lib/Jsrt/JsrtCommonExports.inc

@@ -1,6 +1,7 @@
     JsSetObjectBeforeCollectCallback
     JsCreateRuntime
     JsCollectGarbage
+    JsPrivateClearStack
     JsDisposeRuntime
     JsAddRef
     JsRelease