[cDAC]: convert DacDbi GetRcwCachedInterfacePointers to EnumerateRcwCachedInterfacePointers and implement in cDAC (#128341)

* Convert `GetRcwCachedInterfacePointers` to
`EnumerateRcwCachedInterfacePointers`
* Create template for these add-to-list callbacks

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: rcj1 <77995559+rcj1@users.noreply.github.com>
Co-authored-by: Rachel Jarvi <rachel.jarvi@gmail.com>

Author: Copilot

src/coreclr/debug/daccess/dacdbiimpl.cpp

@@ -3593,42 +3593,39 @@ HRESULT STDMETHODCALLTYPE DacDbiInterfaceImpl::IsRcw(VMPTR_Object vmObject, OUT
 #endif // FEATURE_COMINTEROP
 }
 
-HRESULT STDMETHODCALLTYPE DacDbiInterfaceImpl::GetRcwCachedInterfacePointers(VMPTR_Object vmObject, BOOL bIInspectableOnly, OUT DacDbiArrayList<CORDB_ADDRESS> * pDacItfPtrs)
+HRESULT STDMETHODCALLTYPE DacDbiInterfaceImpl::EnumerateRcwCachedInterfacePointers(VMPTR_Object vmObject, FP_RCW_INTERFACE_CALLBACK fpCallback, CALLBACK_DATA pUserData)
 {
 #ifdef FEATURE_COMINTEROP
 
     DD_ENTER_MAY_THROW;
 
+    if (fpCallback == NULL)
+        return E_POINTER;
+
     HRESULT hr = S_OK;
     EX_TRY
     {
-
-        Object* objPtr = vmObject.GetDacPtr();
-
-        InlineSArray<TADDR, INTERFACE_ENTRY_CACHE_SIZE> rgUnks;
-
         PTR_RCW pRCW = GetRcwFromVmptrObject(vmObject);
         if (pRCW != NULL)
         {
-            pRCW->GetCachedInterfacePointers(bIInspectableOnly, &rgUnks);
-
-            pDacItfPtrs->Alloc(rgUnks.GetCount());
-
-            for (COUNT_T i = 0; i < rgUnks.GetCount(); ++i)
+            RCW::CachedInterfaceEntryIterator it = pRCW->IterateCachedInterfacePointers();
+            while (it.Next())
             {
-                (*pDacItfPtrs)[i] = (CORDB_ADDRESS)(rgUnks[i]);
+                PTR_MethodTable pMT = dac_cast<PTR_MethodTable>((TADDR)(it.GetEntry()->m_pMT.Load()));
+                if (pMT != NULL)
+                {
+                    TADDR taUnk = (TADDR)(it.GetEntry()->m_pUnknown.Load());
+                    if (taUnk != NULL)
+                    {
+                        fpCallback((CORDB_ADDRESS)taUnk, pUserData);
+                    }
+                }
             }
-
-        }
-        else
-        {
-            pDacItfPtrs->Alloc(0);
         }
     }
     EX_CATCH_HRESULT(hr);
     return hr;
 #else
-    pDacItfPtrs->Alloc(0);
     return S_OK;
 #endif // FEATURE_COMINTEROP
 }

src/coreclr/debug/daccess/dacdbiimpl.h

@@ -314,7 +314,7 @@ class DacDbiInterfaceImpl :
     // retrieves the list of interfaces pointers implemented by vmObject, as it is known at
     // the time of the call (the list may change as new interface types become available
     // in the runtime)
-    HRESULT STDMETHODCALLTYPE GetRcwCachedInterfacePointers(VMPTR_Object vmObject, BOOL bIInspectableOnly, OUT DacDbiArrayList<CORDB_ADDRESS> * pDacItfPtrs);
+    HRESULT STDMETHODCALLTYPE EnumerateRcwCachedInterfacePointers(VMPTR_Object vmObject, FP_RCW_INTERFACE_CALLBACK fpCallback, CALLBACK_DATA pUserData);
 
 private:
     // Given a pointer to a managed function, obtain the method desc for it.

src/coreclr/debug/di/divalue.cpp

@@ -2802,6 +2802,16 @@ HRESULT CordbObjectValue::GetCachedInterfaceTypes(
 #endif
 }
 
+#if defined(FEATURE_COMINTEROP)
+namespace
+{
+    void RcwInterfacePointerCallback(CORDB_ADDRESS itfPtr, CALLBACK_DATA pUserData)
+    {
+        CallbackAccumulator<CORDB_ADDRESS>::From(pUserData)->Push(itfPtr);
+    }
+}
+#endif // FEATURE_COMINTEROP
+
 HRESULT CordbObjectValue::GetCachedInterfacePointers(
                         BOOL bIInspectableOnly,
                         ULONG32 celt,
@@ -2825,25 +2835,29 @@ HRESULT CordbObjectValue::GetCachedInterfacePointers(
     HRESULT hr = S_OK;
     ULONG32 cItfs = 0;
 
-    // retrieve interface types
-
-    CORDB_ADDRESS objAddr = m_valueHome.GetAddress();
+    CallbackAccumulator<CORDB_ADDRESS> acc;
 
-    DacDbiArrayList<CORDB_ADDRESS> dacItfPtrs;
-    EX_TRY
+    // The RCW interface pointer cache only holds non-IInspectable interfaces, so when the caller
+    // asks for IInspectable-only pointers the result is always empty.
+    if (!bIInspectableOnly)
     {
-        IDacDbiInterface* pDAC = GetProcess()->GetDAC();
-        VMPTR_Object vmObj;
-        IfFailThrow(pDAC->GetObject(objAddr, &vmObj));
+        CORDB_ADDRESS objAddr = m_valueHome.GetAddress();
 
-        // retrieve type info from LS
-        IfFailThrow(pDAC->GetRcwCachedInterfacePointers(vmObj, bIInspectableOnly, &dacItfPtrs));
+        EX_TRY
+        {
+            IDacDbiInterface* pDAC = GetProcess()->GetDAC();
+            VMPTR_Object vmObj;
+            IfFailThrow(pDAC->GetObject(objAddr, &vmObj));
+
+            IfFailThrow(pDAC->EnumerateRcwCachedInterfacePointers(vmObj, &RcwInterfacePointerCallback, &acc));
+        }
+        EX_CATCH_HRESULT(hr);
+        IfFailRet(hr);
+        IfFailRet(acc.hrError);
     }
-    EX_CATCH_HRESULT(hr);
-    IfFailRet(hr);
 
     // synthesize CordbType instances
-    cItfs = (ULONG32)dacItfPtrs.Count();
+    cItfs = (ULONG32)acc.items.Size();
 
     if (pcEltFetched != NULL && ptrs == NULL)
     {
@@ -2859,7 +2873,7 @@ HRESULT CordbObjectValue::GetCachedInterfacePointers(
     if (ptrs != NULL && *pcEltFetched > 0)
     {
         for (ULONG32 i = 0; i < *pcEltFetched; ++i)
-            ptrs[i] = dacItfPtrs[i];
+            ptrs[i] = acc.items[i];
     }
 
     return (*pcEltFetched == celt ? S_OK : S_FALSE);

src/coreclr/debug/di/process.cpp

@@ -2190,38 +2190,19 @@ HRESULT CordbProcess::GetGCHeapInformation(COR_HEAPINFO *pHeapInfo)
 
 namespace
 {
-    struct HeapSegmentAccumulator
-    {
-        CQuickArrayList<COR_SEGMENT> segments;
-        HRESULT                      hrError;
-    };
-
     void HeapSegmentCallback(
         CORDB_ADDRESS rangeStart,
         CORDB_ADDRESS rangeEnd,
         int generation,
         ULONG heap,
         CALLBACK_DATA pUserData)
     {
-        HeapSegmentAccumulator *acc =
-            reinterpret_cast<HeapSegmentAccumulator*>(pUserData);
-
-        if (FAILED(acc->hrError))
-            return;
-
         COR_SEGMENT s;
         s.start = rangeStart;
         s.end = rangeEnd;
         s.type = (CorDebugGenerationTypes)generation;
         s.heap = heap;
-        HRESULT hr = S_OK;
-        EX_TRY
-        {
-            acc->segments.Push(s);
-        }
-        EX_CATCH_HRESULT(hr);
-        if (FAILED(hr))
-            acc->hrError = hr;
+        CallbackAccumulator<COR_SEGMENT>::From(pUserData)->Push(s);
     }
 }
 
@@ -2236,18 +2217,17 @@ HRESULT CordbProcess::EnumerateHeapRegions(ICorDebugHeapSegmentEnum **ppRegions)
 
     EX_TRY
     {
-        HeapSegmentAccumulator acc;
-        acc.hrError = S_OK;
+        CallbackAccumulator<COR_SEGMENT> acc;
 
         hr = GetDAC()->EnumerateHeapSegments(&HeapSegmentCallback, &acc);
         if (SUCCEEDED(hr) && FAILED(acc.hrError))
             hr = acc.hrError;
 
         if (SUCCEEDED(hr))
         {
-            if (acc.segments.Size() != 0)
+            if (acc.items.Size() != 0)
             {
-                CordbHeapSegmentEnumerator *segEnum = new CordbHeapSegmentEnumerator(this, acc.segments.Ptr(), (DWORD)acc.segments.Size());
+                CordbHeapSegmentEnumerator *segEnum = new CordbHeapSegmentEnumerator(this, acc.items.Ptr(), (DWORD)acc.items.Size());
                 GetContinueNeuterList()->Add(this, segEnum);
                 hr = segEnum->QueryInterface(__uuidof(ICorDebugHeapSegmentEnum), (void**)ppRegions);
             }

src/coreclr/debug/di/rspriv.h

@@ -69,6 +69,45 @@ struct MachineInfo;
 #define WriteProcessMemory DONT_USE_WRITEPROCESS_MEMORY
 
 
+//-----------------------------------------------------------------------------
+// CallbackAccumulator<T>
+//
+// Helper for FP_*_CALLBACK consumers on the DI side that need to collect a
+// list of values produced by the DAC and surface a single HRESULT. The
+// callback can call Push() without worrying about exceptions - the first
+// failure is captured in hrError and subsequent pushes are short-circuited.
+// After the enumeration call returns, the caller should check both the DAC's
+// returned HRESULT and acc.hrError, then consume acc.items.
+//-----------------------------------------------------------------------------
+template <typename T>
+struct CallbackAccumulator
+{
+    CQuickArrayList<T> items;
+    HRESULT            hrError;
+
+    CallbackAccumulator() : hrError(S_OK) { }
+
+    void Push(const T& item)
+    {
+        if (FAILED(hrError))
+            return;
+        HRESULT hr = S_OK;
+        EX_TRY
+        {
+            items.Push(item);
+        }
+        EX_CATCH_HRESULT(hr);
+        if (FAILED(hr))
+            hrError = hr;
+    }
+
+    static CallbackAccumulator* From(CALLBACK_DATA pUserData)
+    {
+        return reinterpret_cast<CallbackAccumulator*>(pUserData);
+    }
+};
+
+
 /* ------------------------------------------------------------------------- *
  * Forward class declarations
  * ------------------------------------------------------------------------- */

src/coreclr/debug/inc/dacdbiinterface.h

@@ -1709,10 +1709,13 @@ IDacDbiInterface : public IUnknown
     // Check whether the argument is a runtime callable wrapper.
     virtual HRESULT STDMETHODCALLTYPE IsRcw(VMPTR_Object vmObject, OUT BOOL * pResult) = 0;
 
-    // retrieves the list of interfaces pointers implemented by vmObject, as it is known at
-    // the time of the call (the list may change as new interface types become available
-    // in the runtime)
-    virtual HRESULT STDMETHODCALLTYPE GetRcwCachedInterfacePointers(VMPTR_Object vmObject, BOOL bIInspectableOnly, OUT DacDbiArrayList<CORDB_ADDRESS> * pDacItfPtrs) = 0;
+    // Callback invoked for each cached interface pointer held by an RCW.
+    typedef void (*FP_RCW_INTERFACE_CALLBACK)(CORDB_ADDRESS itfPtr, CALLBACK_DATA pUserData);
+
+    // Enumerates the interface pointers cached by the RCW associated with vmObject, as known at
+    // the time of the call (the list may change as new interface types become available in the
+    // runtime). If vmObject is not an RCW the enumeration is empty. The callback must not throw.
+    virtual HRESULT STDMETHODCALLTYPE EnumerateRcwCachedInterfacePointers(VMPTR_Object vmObject, FP_RCW_INTERFACE_CALLBACK fpCallback, CALLBACK_DATA pUserData) = 0;
 
     // ----------------------------------------------------------------------------
     // functions to get information about reference/handle referents for ICDValue

src/coreclr/inc/dacdbi.idl

@@ -144,6 +144,7 @@ typedef void (*FP_MODULE_ENUMERATION_CALLBACK)(VMPTR_Assembly vmAssembly, CALLBA
 typedef void (*FP_THREAD_ENUMERATION_CALLBACK)(VMPTR_Thread vmThread, CALLBACK_DATA pUserData);
 typedef BOOL (*FP_INTERNAL_FRAME_ENUMERATION_CALLBACK)(FramePointer fpFrame, CALLBACK_DATA pUserData);
 typedef void (*FP_HEAPSEGMENT_CALLBACK)(CORDB_ADDRESS rangeStart, CORDB_ADDRESS rangeEnd, int generation, ULONG heap, CALLBACK_DATA pUserData);
+typedef void (*FP_RCW_INTERFACE_CALLBACK)(CORDB_ADDRESS itfPtr, CALLBACK_DATA pUserData);
 
 
 //
@@ -335,7 +336,7 @@ interface IDacDbiInterface : IUnknown
     HRESULT IsExceptionObject([in] VMPTR_Object vmObject, [out] BOOL * pResult);
     HRESULT GetStackFramesFromException([in] VMPTR_Object vmObject, [out] DacDbiArrayList_DacExceptionCallStackData * pDacStackFrames);
     HRESULT IsRcw([in] VMPTR_Object vmObject, [out] BOOL * pResult);
-    HRESULT GetRcwCachedInterfacePointers([in] VMPTR_Object vmObject, [in] BOOL bIInspectableOnly, [out] DacDbiArrayList_CORDB_ADDRESS * pDacItfPtrs);
+    HRESULT EnumerateRcwCachedInterfacePointers([in] VMPTR_Object vmObject, [in] FP_RCW_INTERFACE_CALLBACK fpCallback, [in] CALLBACK_DATA pUserData);
 
     // Object Data
     HRESULT GetTypedByRefInfo([in] CORDB_ADDRESS pTypedByRef, [out] struct DebuggerIPCE_ObjectData * pObjectData);

src/coreclr/vm/runtimecallablewrapper.h

@@ -272,27 +272,6 @@ struct RCW
         return m_cbRefCount;
     }
 
-    void GetCachedInterfacePointers(BOOL bIInspectableOnly,
-                        SArray<TADDR> * rgItfPtrs)
-    {
-        LIMITED_METHOD_DAC_CONTRACT;
-
-        CachedInterfaceEntryIterator it = IterateCachedInterfacePointers();
-        while (it.Next())
-        {
-            PTR_MethodTable pMT = dac_cast<PTR_MethodTable>((TADDR)(it.GetEntry()->m_pMT.Load()));
-            if (pMT != NULL &&
-                (!bIInspectableOnly))
-            {
-                TADDR taUnk = (TADDR)(it.GetEntry()->m_pUnknown.Load());
-                if (taUnk != NULL)
-                {
-                    rgItfPtrs->Append(taUnk);
-                }
-            }
-        }
-    }
-
     LPVOID     GetVTablePtr() { LIMITED_METHOD_CONTRACT; return m_vtablePtr; }
 
     // Remoting aware QI that will attempt to re-unmarshal on object disconnect.

src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Legacy/Dbi/DacDbiImpl.cs

@@ -1934,8 +1934,68 @@ public int IsRcw(ulong vmObject, Interop.BOOL* pResult)
         return hr;
     }
 
-    public int GetRcwCachedInterfacePointers(ulong vmObject, Interop.BOOL bIInspectableOnly, nint pDacItfPtrs)
-        => LegacyFallbackHelper.CanFallback() && _legacy is not null ? _legacy.GetRcwCachedInterfacePointers(vmObject, bIInspectableOnly, pDacItfPtrs) : HResults.E_NOTIMPL;
+#if DEBUG
+    [ThreadStatic]
+    private static List<ulong>? _debugEnumerateRcwCachedInterfacePointers;
+
+    private static List<ulong> DebugEnumerateRcwCachedInterfacePointers
+        => _debugEnumerateRcwCachedInterfacePointers ??= new();
+
+    [UnmanagedCallersOnly]
+    private static void EnumerateRcwCachedInterfacePointersDebugCallback(ulong itfPtr, nint _)
+    {
+        DebugEnumerateRcwCachedInterfacePointers.Add(itfPtr);
+    }
+#endif
+
+    public int EnumerateRcwCachedInterfacePointers(ulong vmObject, delegate* unmanaged<ulong, nint, void> fpCallback, nint pUserData)
+    {
+        int hr = HResults.S_OK;
+        List<ulong> itfPtrs = new();
+        try
+        {
+            if (fpCallback is null)
+                throw new ArgumentNullException(nameof(fpCallback));
+
+            IObject obj = _target.Contracts.Object;
+            _ = obj.GetBuiltInComData(new TargetPointer(vmObject), out TargetPointer rcw, out _, out _);
+            if (rcw != TargetPointer.Null)
+            {
+                IBuiltInCOM builtInCom = _target.Contracts.BuiltInCOM;
+                foreach ((TargetPointer methodTable, TargetPointer unknown) in builtInCom.GetRCWInterfaces(rcw))
+                {
+                    if (methodTable != TargetPointer.Null && unknown != TargetPointer.Null)
+                        itfPtrs.Add(unknown.Value);
+                }
+            }
+
+            foreach (ulong itfPtr in itfPtrs)
+                fpCallback(itfPtr, pUserData);
+        }
+        catch (System.Exception ex)
+        {
+            hr = ex.HResult;
+        }
+
+#if DEBUG
+        if (_legacy is not null)
+        {
+            DebugEnumerateRcwCachedInterfacePointers.Clear();
+            delegate* unmanaged<ulong, nint, void> debugCallbackPtr = &EnumerateRcwCachedInterfacePointersDebugCallback;
+            int hrLocal = _legacy.EnumerateRcwCachedInterfacePointers(vmObject, debugCallbackPtr, 0);
+            Debug.ValidateHResult(hr, hrLocal);
+
+            if (hr == HResults.S_OK)
+            {
+                List<ulong> legacyItfPtrs = DebugEnumerateRcwCachedInterfacePointers;
+                Debug.Assert(itfPtrs.SequenceEqual(legacyItfPtrs),
+                    $"cDAC: [{string.Join(",", itfPtrs.Select(p => $"0x{p:x}"))}], DAC: [{string.Join(",", legacyItfPtrs.Select(p => $"0x{p:x}"))}]");
+            }
+            DebugEnumerateRcwCachedInterfacePointers.Clear();
+        }
+#endif
+        return hr;
+    }
 
     public int GetTypedByRefInfo(ulong pTypedByRef, nint pObjectData)
         => LegacyFallbackHelper.CanFallback() && _legacy is not null ? _legacy.GetTypedByRefInfo(pTypedByRef, pObjectData) : HResults.E_NOTIMPL;

src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Legacy/Dbi/IDacDbiInterface.cs

@@ -580,7 +580,7 @@ public unsafe partial interface IDacDbiInterface
     int IsRcw(ulong vmObject, Interop.BOOL* pResult);
 
     [PreserveSig]
-    int GetRcwCachedInterfacePointers(ulong vmObject, Interop.BOOL bIInspectableOnly, nint pDacItfPtrs);
+    int EnumerateRcwCachedInterfacePointers(ulong vmObject, /*FP_RCW_INTERFACE_CALLBACK*/ delegate* unmanaged<ulong, nint, void> fpCallback, nint pUserData);
 
     [PreserveSig]
     int GetTypedByRefInfo(ulong pTypedByRef, nint pObjectData);