Remove functional cDAC fallbacks

src/coreclr/debug/daccess/cdac.cpp

@@ -163,18 +163,38 @@ CDAC::~CDAC()
     }
 }
 
-void CDAC::CreateSosInterface(IUnknown** sos)
+HRESULT CDAC::CreateSosInterface(IUnknown** sos)
 {
+    if (sos == nullptr)
+    {
+        return E_INVALIDARG;
+    }
+
+    *sos = nullptr;
+
     decltype(&cdac_reader_create_sos_interface) createSosInterface = reinterpret_cast<decltype(&cdac_reader_create_sos_interface)>(::GetProcAddress(m_module, "cdac_reader_create_sos_interface"));
-    _ASSERTE(createSosInterface != nullptr);
-    int ret = createSosInterface(m_cdac_handle, m_legacyImpl, sos);
-    _ASSERTE(ret == 0);
+    if (createSosInterface == nullptr)
+    {
+        return E_FAIL;
+    }
+
+    return createSosInterface(m_cdac_handle, m_legacyImpl, sos);
 }
 
-void CDAC::CreateDacDbiInterface(IUnknown** dbi)
+HRESULT CDAC::CreateDacDbiInterface(IUnknown** dbi)
 {
+    if (dbi == nullptr)
+    {
+        return E_INVALIDARG;
+    }
+
+    *dbi = nullptr;
+
     decltype(&cdac_reader_create_dacdbi_interface) createDacDbiInterface = reinterpret_cast<decltype(&cdac_reader_create_dacdbi_interface)>(::GetProcAddress(m_module, "cdac_reader_create_dacdbi_interface"));
-    _ASSERTE(createDacDbiInterface != nullptr);
-    int ret = createDacDbiInterface(m_cdac_handle, m_legacyImpl, dbi);
-    _ASSERTE(ret == 0);
+    if (createDacDbiInterface == nullptr)
+    {
+        return E_FAIL;
+    }
+
+    return createDacDbiInterface(m_cdac_handle, m_legacyImpl, dbi);
 }

src/coreclr/debug/daccess/cdac.h

@@ -49,8 +49,8 @@ class CDAC final
         return m_module != NULL && m_cdac_handle != 0;
     }
 
-    void CreateSosInterface(IUnknown** sos);
-    void CreateDacDbiInterface(IUnknown** dbi);
+    HRESULT CreateSosInterface(IUnknown** sos);
+    HRESULT CreateDacDbiInterface(IUnknown** dbi);
 
 private:
     CDAC(HMODULE module, intptr_t handle, ICorDebugDataTarget* target, IUnknown* legacyImpl);

src/coreclr/debug/daccess/daccess.cpp

@@ -6558,7 +6558,9 @@ CLRDataCreateInstance(REFIID iid,
     if (enable.IsSet())
     {
         DWORD val;
-        if (enable.TryAsInteger(10, val) && val == 1)
+        // cDAC does not yet support the memory enumeration used to create debugger dumps.
+        if (enable.TryAsInteger(10, val) && val == 1 &&
+            !(IsEqualIID(iid, __uuidof(ICLRDataEnumMemoryRegions))))
         {
             // TODO: [cdac] TryGetSymbol is only implemented for Linux, OSX, and Windows.
             uint64_t contractDescriptorAddr = 0;
@@ -6572,11 +6574,11 @@ CLRDataCreateInstance(REFIID iid,
                 if (cdac.IsValid())
                 {
                     // Get SOS interfaces from the cDAC if available.
-                    cdac.CreateSosInterface(&cdacInterface);
-                    _ASSERTE(cdacInterface != nullptr);
-
-                    // Lifetime is now managed by cDAC implementation of SOS interfaces
-                    pClrDataAccess->Release();
+                    if (cdac.CreateSosInterface(&cdacInterface) == S_OK && cdacInterface != nullptr)
+                    {
+                        // Lifetime is now managed by cDAC implementation of SOS interfaces.
+                        pClrDataAccess->Release();
+                    }
                 }
 
                 // Release the AddRef from the QI.

src/coreclr/debug/daccess/dacdbiimpl.cpp

@@ -320,8 +320,7 @@ DacDbiInterfaceInstance(
                 if (cdac.IsValid())
                 {
                     ReleaseHolder<IUnknown> cdacInterface;
-                    cdac.CreateDacDbiInterface(&cdacInterface);
-                    if (cdacInterface != nullptr)
+                    if (cdac.CreateDacDbiInterface(&cdacInterface) == S_OK && cdacInterface != nullptr)
                     {
                         IDacDbiInterface* pCDacDbi = nullptr;
                         HRESULT hr = cdacInterface->QueryInterface(__uuidof(IDacDbiInterface), (void**)&pCDacDbi);

src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Legacy/ClrDataExceptionState.cs

@@ -128,7 +128,7 @@ int IXCLRDataExceptionState.GetManagedObject(DacComNullableByRef<IXCLRDataValue>
         int hr = HResults.S_OK, hrLocal = HResults.S_OK;
         IXCLRDataValue? legacyValue = null;
 
-        if (_legacyImpl is not null && LegacyFallbackHelper.CanFallback())
+        if (_legacyImpl is not null)
         {
             DacComNullableByRef<IXCLRDataValue> legacyValueOut = new(value.IsNullRef);
             hrLocal = _legacyImpl.GetManagedObject(legacyValueOut);

src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Legacy/ClrDataFrame.cs

@@ -376,7 +376,7 @@ int IXCLRDataFrame.GetCodeName(
     {
         using Lock.Scope scope = _apiLock.EnterScope();
 
-        return LegacyFallbackHelper.CanFallback() && _legacyImpl is not null ? _legacyImpl.GetCodeName(flags, bufLen, nameLen, nameBuf) : HResults.E_NOTIMPL;
+        return HResults.E_NOTIMPL;
     }
 
     int IXCLRDataFrame.GetMethodInstance(DacComNullableByRef<IXCLRDataMethodInstance> method)
@@ -425,7 +425,7 @@ int IXCLRDataFrame.Request(
     {
         using Lock.Scope scope = _apiLock.EnterScope();
 
-        return LegacyFallbackHelper.CanFallback() && _legacyImpl is not null ? _legacyImpl.Request(reqCode, inBufferSize, inBuffer, outBufferSize, outBuffer) : HResults.E_NOTIMPL;
+        return HResults.E_NOTIMPL;
     }
 
     int IXCLRDataFrame.GetNumTypeArguments(uint* numTypeArgs)

src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Legacy/ClrDataMethodDefinition.cs

@@ -160,9 +160,7 @@ int IXCLRDataMethodDefinition.StartEnumInstances(IXCLRDataAppDomain? appDomain,
         int hr = HResults.S_FALSE;
         *handle = 0;
 
-        // Start the legacy enumeration to keep it in sync with the cDAC enumeration.
-        // EnumInstance passes the legacy method instance to ClrDataMethodInstance,
-        // which delegates some operations to it.
+        // Start the legacy enumeration to keep it in sync for validation.
         ulong legacyHandle = default;
         int hrLocal = default;
         if (_legacyImpl is not null)
@@ -226,8 +224,7 @@ int IXCLRDataMethodDefinition.EnumInstance(ulong* handle, DacComNullableByRef<IX
         if (gcHandle.Target is not SOSDacImpl.EnumMethodInstances emi)
             return HResults.E_INVALIDARG;
 
-        // Advance the legacy enumeration to keep it in sync with the cDAC enumeration.
-        // The legacy method instance is passed to ClrDataMethodInstance for delegation.
+        // Advance the legacy enumeration to keep it in sync for validation.
         IXCLRDataMethodInstance? legacyMethod = null;
         int hrLocal = default;
         if (_legacyImpl is not null)
@@ -253,16 +250,7 @@ int IXCLRDataMethodDefinition.EnumInstance(ulong* handle, DacComNullableByRef<IX
         }
         catch (System.Exception ex)
         {
-            // Fall back to the legacy DAC result when available, otherwise propagate the error.
-            if (_legacyImpl is not null)
-            {
-                hr = hrLocal;
-                instance.Interface = legacyMethod;
-            }
-            else
-            {
-                hr = ex.HResult;
-            }
+            hr = ex.HResult;
         }
 
 #if DEBUG
@@ -295,8 +283,9 @@ int IXCLRDataMethodDefinition.EndEnumInstances(ulong handle)
             if (_legacyImpl is not null && emi.LegacyHandle != 0)
             {
                 int hrLocal = _legacyImpl.EndEnumInstances(emi.LegacyHandle);
-                if (hrLocal < 0)
-                    hr = hrLocal;
+#if DEBUG
+                Debug.ValidateHResult(hr, hrLocal);
+#endif
             }
         }
         catch (System.Exception ex)
@@ -397,9 +386,8 @@ int IXCLRDataMethodDefinition.GetTokenAndScope(uint* token, DacComNullableByRef<
                 {
                     DacComNullableByRef<IXCLRDataModule> legacyModOut = new(isNullRef: false);
                     int hrLegacy = _legacyImpl.GetTokenAndScope(null, legacyModOut);
-                    if (hrLegacy < 0)
-                        return hrLegacy;
-                    legacyMod = legacyModOut.Interface;
+                    if (hrLegacy >= 0)
+                        legacyMod = legacyModOut.Interface;
                 }
 
                 mod.Interface = new ClrDataModule(_module, _target, legacyMod, _apiLock);
@@ -709,7 +697,7 @@ int IXCLRDataMethodDefinition.GetRepresentativeEntryAddress(ClrDataAddress* addr
         }
 
 #if DEBUG
-        if (LegacyFallbackHelper.CanFallback() && _legacyImpl is not null)
+        if (_legacyImpl is not null)
         {
             ClrDataAddress addrLocal = 0;
             int hrLocal = _legacyImpl.GetRepresentativeEntryAddress(addr is null ? null : &addrLocal);

src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Legacy/ClrDataMethodInstance.cs

@@ -63,7 +63,7 @@ int IXCLRDataMethodInstance.GetDefinition(DacComNullableByRef<IXCLRDataMethodDef
 
         try
         {
-            if (LegacyFallbackHelper.CanFallback() && _legacyImpl is not null)
+            if (_legacyImpl is not null)
             {
                 DacComNullableByRef<IXCLRDataMethodDefinition> legacyMethodDefinitionOut = new(isNullRef: methodDefinition.IsNullRef);
                 hrLocal = _legacyImpl.GetDefinition(legacyMethodDefinitionOut);
@@ -110,9 +110,8 @@ int IXCLRDataMethodInstance.GetTokenAndScope(uint* token, DacComNullableByRef<IX
                 {
                     DacComNullableByRef<IXCLRDataModule> legacyModOut = new(isNullRef: false);
                     int hrLegacy = _legacyImpl.GetTokenAndScope(token, legacyModOut);
-                    if (hrLegacy < 0)
-                        return hrLegacy;
-                    legacyMod = legacyModOut.Interface;
+                    if (hrLegacy >= 0)
+                        legacyMod = legacyModOut.Interface;
                 }
 
                 TargetPointer mtAddr = rts.GetMethodTable(_methodDesc);