Dynamic methods use freelisted MethodDescriptors, so we need to

null out m_GcCover when a freelisted entry is reused.

Now we can assert in SetupGcCoverage that m_GcCover is NULL.

Author: AndyAyersMS

src/vm/dynamicmethod.cpp

@@ -280,6 +280,11 @@ DynamicMethodDesc* DynamicMethodTable::GetDynamicMethod(BYTE *psig, DWORD sigSiz
     pNewMD->m_pszDebugClassName  = (LPUTF8)"dynamicclass";
     pNewMD->m_pszDebugMethodSignature = "DynamicMethod Signature not available";
 #endif // _DEBUG
+
+#ifdef HAVE_GCCOVER
+    pNewMD->m_GcCover = NULL;
+#endif
+
     pNewMD->SetNotInline(TRUE);
     pNewMD->GetLCGMethodResolver()->Reset();
 

src/vm/gccover.cpp

@@ -144,13 +144,9 @@ void SetupGcCoverage(MethodDesc* pMD, BYTE* methodStartPtr) {
     }
 #endif
 
-    // We may have lost out to another thread instrumenting this method.
-    // If so, we'll also lose the publishing race. So just return.
-    if (pMD->m_GcCover)
-    {
-        return;
-    }
-
+    // We should be the first and only thread to instrument this
+    // method for gc coverage.
+    _ASSERTE(!pMD->m_GcCover);
     PCODE codeStart = (PCODE) methodStartPtr;
     SetupAndSprinkleBreakpointsForJittedMethod(pMD, codeStart);
 }