dotnet · AaronRobinsonMSFT · Feb 15, 2026 · Feb 11, 2026 · Feb 12, 2026 · Feb 12, 2026
diff --git a/src/coreclr/System.Private.CoreLib/src/System/Reflection/LoaderAllocator.cs b/src/coreclr/System.Private.CoreLib/src/System/Reflection/LoaderAllocator.cs
@@ -54,6 +54,19 @@ private LoaderAllocator()
             m_scout = new LoaderAllocatorScout();
         }
 
+        [UnmanagedCallersOnly]
+        private static unsafe void Create(object* pResult, Exception* pException)
+        {
+            try
+            {
+                *pResult = new LoaderAllocator();
+            }
+            catch (Exception ex)
+            {
+                *pException = ex;
+            }
+        }
+
 #pragma warning disable CA1823, 414, 169
         private LoaderAllocatorScout m_scout;
         private object[] m_slots;

diff --git a/src/coreclr/System.Private.CoreLib/src/System/RuntimeHandles.cs b/src/coreclr/System.Private.CoreLib/src/System/RuntimeHandles.cs
@@ -2207,5 +2207,57 @@ internal struct CORINFO_EH_CLAUSE
         internal abstract byte[]? ResolveSignature(int token, int fromMethod);
         //
         internal abstract MethodInfo GetDynamicMethod();
+
+        [UnmanagedCallersOnly]
+        internal static unsafe void GetJitContext(Resolver* pResolver, int* pSecurityControlFlags, RuntimeType* ppResult, Exception* pException)
+        {
+            try
+            {
+                *ppResult = pResolver->GetJitContext(out *pSecurityControlFlags);
+            }
+            catch (Exception ex)
+            {
+                *pException = ex;
+            }
+        }
+
+        [UnmanagedCallersOnly]
+        internal static unsafe void GetCodeInfo(Resolver* pResolver, int* pStackSize, int* pInitLocals, int* pEHCount, byte[]* ppResult, Exception* pException)
+        {
+            try
+            {
+                *ppResult = pResolver->GetCodeInfo(out *pStackSize, out *pInitLocals, out *pEHCount);
+            }
+            catch (Exception ex)
+            {
+                *pException = ex;
+            }
+        }
+
+        [UnmanagedCallersOnly]
+        internal static unsafe void GetLocalsSignature(Resolver* pResolver, byte[]* ppResult, Exception* pException)
+        {
+            try
+            {
+                *ppResult = pResolver->GetLocalsSignature();
+            }
+            catch (Exception ex)
+            {
+                *pException = ex;
+            }
+        }
+
+        [UnmanagedCallersOnly]
+        internal static unsafe void GetStringLiteral(Resolver* pResolver, int token, string* ppResult, Exception* pException)
+        {
+            try
+            {
+                *ppResult = pResolver->GetStringLiteral(token);
+            }
+            catch (Exception ex)
+            {
+                *pException = ex;
+            }
+        }
     }
 }
diff --git a/src/coreclr/System.Private.CoreLib/src/System/StubHelpers.cs b/src/coreclr/System.Private.CoreLib/src/System/StubHelpers.cs
@@ -1628,6 +1628,54 @@ internal static void MulticastDebuggerTraceHelper(object o, int count)
     }  // class StubHelpers
 
 #if FEATURE_COMINTEROP
+    internal static class CultureInfoMarshaler
+    {
+        [UnmanagedCallersOnly]
+        internal static unsafe void GetCurrentCulture(bool bUICulture, object* pResult, Exception* pException)
+        {
+            try
+            {
+                *pResult = bUICulture
+                    ? Globalization.CultureInfo.CurrentUICulture
+                    : Globalization.CultureInfo.CurrentCulture;
+            }
+            catch (Exception ex)
+            {
+                *pException = ex;
+            }
+        }
+
+        [UnmanagedCallersOnly]
+        internal static unsafe void SetCurrentCulture(bool bUICulture, Globalization.CultureInfo* pValue, Exception* pException)
+        {
+            try
+            {
+                if (bUICulture)
+                    Globalization.CultureInfo.CurrentUICulture = *pValue;
+                else
+                    Globalization.CultureInfo.CurrentCulture = *pValue;
+            }
+            catch (Exception ex)
+            {
+                *pException = ex;
+            }
+        }
+
+        [UnmanagedCallersOnly]
+        internal static unsafe void CreateCultureInfo(int culture, object* pResult, Exception* pException)
+        {
+            try
+            {
+                // Consider calling CultureInfo.GetCultureInfo that returns a cached instance to avoid this expensive creation.
+                *pResult = new Globalization.CultureInfo(culture);
+            }
+            catch (Exception ex)
+            {
+                *pException = ex;
+            }
+        }
+    }
+
     internal static class ColorMarshaler
     {
         private static readonly MethodInvoker s_oleColorToDrawingColorMethod;
@@ -1657,6 +1705,32 @@ internal static int ConvertToNative(object? managedColor)
         {
             return (int)s_drawingColorToOleColorMethod.Invoke(null, managedColor)!;
         }
+
+        [UnmanagedCallersOnly]
+        internal static unsafe void ConvertToManaged(int oleColor, object* pResult, Exception* pException)
+        {
+            try
+            {
+                *pResult = ConvertToManaged(oleColor);
+            }
+            catch (Exception ex)
+            {
+                *pException = ex;
+            }
+        }
+
+        [UnmanagedCallersOnly]
+        internal static unsafe void ConvertToNative(object* pSrcObj, int* pResult, Exception* pException)
+        {
+            try
+            {
+                *pResult = ConvertToNative(*pSrcObj);
+            }
+            catch (Exception ex)
+            {
+                *pException = ex;
+            }
+        }
     }
 #endif
 }
diff --git a/src/coreclr/vm/callhelpers.h b/src/coreclr/vm/callhelpers.h
@@ -665,6 +665,10 @@ void CallDefaultConstructor(OBJECTREF ref);
 // from native code.
 //
 
+// Use CLR_BOOL_ARG to convert a BOOL value to a CLR_BOOL for passing to
+// UnmanagedCallersOnlyCaller::InvokeThrowing when the managed parameter is bool.
+#define CLR_BOOL_ARG(x) ((CLR_BOOL)(!!(x)))
+
 // Helper class for calling managed methods marked with [UnmanagedCallersOnly].
 // This provides a more efficient alternative to MethodDescCallSite for methods
 // using the reverse P/Invoke infrastructure.

diff --git a/src/coreclr/vm/corelib.h b/src/coreclr/vm/corelib.h
@@ -659,12 +659,12 @@ DEFINE_METHOD(PROPERTY,             GET_GETTER,             GetGetMethod,
 DEFINE_CLASS(PROPERTY_INFO,         Reflection,             PropertyInfo)
 
 DEFINE_CLASS(RESOLVER,              System,                 Resolver)
-DEFINE_METHOD(RESOLVER,             GET_JIT_CONTEXT,        GetJitContext,              IM_RefInt_RetRuntimeType)
-DEFINE_METHOD(RESOLVER,             GET_CODE_INFO,          GetCodeInfo,                IM_RefInt_RefInt_RefInt_RetArrByte)
-DEFINE_METHOD(RESOLVER,             GET_LOCALS_SIGNATURE,   GetLocalsSignature,         IM_RetArrByte)
+DEFINE_METHOD(RESOLVER,             GET_JIT_CONTEXT,        GetJitContext,              SM_PtrResolver_PtrInt_PtrClass_PtrException_RetVoid)
+DEFINE_METHOD(RESOLVER,             GET_CODE_INFO,          GetCodeInfo,                SM_PtrResolver_PtrInt_PtrInt_PtrInt_PtrArrByte_PtrException_RetVoid)
+DEFINE_METHOD(RESOLVER,             GET_LOCALS_SIGNATURE,   GetLocalsSignature,         SM_PtrResolver_PtrArrByte_PtrException_RetVoid)
 DEFINE_METHOD(RESOLVER,             GET_EH_INFO,            GetEHInfo,                  IM_Int_VoidPtr_RetVoid)
 DEFINE_METHOD(RESOLVER,             GET_RAW_EH_INFO,        GetRawEHInfo,               IM_RetArrByte)
-DEFINE_METHOD(RESOLVER,             GET_STRING_LITERAL,     GetStringLiteral,           IM_Int_RetStr)
+DEFINE_METHOD(RESOLVER,             GET_STRING_LITERAL,     GetStringLiteral,           SM_PtrResolver_Int_PtrStr_PtrException_RetVoid)
 DEFINE_METHOD(RESOLVER,             RESOLVE_TOKEN,          ResolveToken,               IM_Int_RefIntPtr_RefIntPtr_RefIntPtr_RetVoid)
 DEFINE_METHOD(RESOLVER,             RESOLVE_SIGNATURE,      ResolveSignature,           IM_IntInt_RetArrByte)
 
@@ -892,11 +892,11 @@ DEFINE_FIELD_U(rgiLastFrameFromForeignExceptionStackTrace,            StackFrame
 DEFINE_FIELD_U(iFrameCount,                StackFrameHelper,   iFrameCount)
 
 DEFINE_CLASS(EVENT_SOURCE,           Tracing,            EventSource)
-DEFINE_METHOD(EVENT_SOURCE,          INITIALIZE_DEFAULT_EVENT_SOURCES, InitializeDefaultEventSources, SM_RetVoid)
+DEFINE_METHOD(EVENT_SOURCE,          INITIALIZE_DEFAULT_EVENT_SOURCES, InitializeDefaultEventSources, SM_PtrException_RetVoid)
 
 DEFINE_CLASS(STARTUP_HOOK_PROVIDER,  System,                StartupHookProvider)
 DEFINE_METHOD(STARTUP_HOOK_PROVIDER, MANAGED_STARTUP, ManagedStartup, SM_PtrChar_RetVoid)
-DEFINE_METHOD(STARTUP_HOOK_PROVIDER, CALL_STARTUP_HOOK, CallStartupHook, SM_PtrChar_RetVoid)
+DEFINE_METHOD(STARTUP_HOOK_PROVIDER, CALL_STARTUP_HOOK, CallStartupHook, SM_PtrChar_PtrException_RetVoid)
 
 DEFINE_CLASS(STREAM,                IO,                     Stream)
 DEFINE_METHOD(STREAM,               BEGIN_READ,             BeginRead,  IM_ArrByte_Int_Int_AsyncCallback_Object_RetIAsyncResult)
@@ -1124,9 +1124,16 @@ DEFINE_METHOD(MNGD_SAFE_ARRAY_MARSHALER, CONVERT_SPACE_TO_MANAGED,    ConvertSpa
 DEFINE_METHOD(MNGD_SAFE_ARRAY_MARSHALER, CONVERT_CONTENTS_TO_MANAGED, ConvertContentsToManaged,   SM_IntPtr_RefObj_IntPtr_RetVoid)
 DEFINE_METHOD(MNGD_SAFE_ARRAY_MARSHALER, CLEAR_NATIVE,                ClearNative,                SM_IntPtr_RefObj_IntPtr_RetVoid)
 
+DEFINE_CLASS(CULTUREINFOMARSHALER, StubHelpers, CultureInfoMarshaler)
+DEFINE_METHOD(CULTUREINFOMARSHALER, GET_CURRENT_CULTURE,    GetCurrentCulture,          NoSig)
+DEFINE_METHOD(CULTUREINFOMARSHALER, SET_CURRENT_CULTURE,    SetCurrentCulture,          NoSig)
+DEFINE_METHOD(CULTUREINFOMARSHALER, CREATE_CULTURE_INFO,            CreateCultureInfo,          NoSig)
+
 DEFINE_CLASS(COLORMARSHALER, StubHelpers, ColorMarshaler)
-DEFINE_METHOD(COLORMARSHALER, CONVERT_TO_NATIVE,  ConvertToNative,  SM_Obj_RetInt)
-DEFINE_METHOD(COLORMARSHALER, CONVERT_TO_MANAGED, ConvertToManaged, SM_Int_RetObj)
+DEFINE_METHOD(COLORMARSHALER, CONVERT_TO_NATIVE,      ConvertToNative,  SM_Obj_RetInt)
+DEFINE_METHOD(COLORMARSHALER, CONVERT_TO_MANAGED,     ConvertToManaged, SM_Int_RetObj)
+DEFINE_METHOD(COLORMARSHALER, CONVERT_TO_NATIVE_UCO,  ConvertToNative,  SM_PtrObj_PtrInt_PtrException_RetVoid)
+DEFINE_METHOD(COLORMARSHALER, CONVERT_TO_MANAGED_UCO, ConvertToManaged, SM_Int_PtrObj_PtrException_RetVoid)
 DEFINE_FIELD(COLORMARSHALER, COLOR_TYPE, s_colorType)
 #endif // FEATURE_COMINTEROP
 END_ILLINK_FEATURE_SWITCH()
@@ -1223,7 +1230,7 @@ DEFINE_CLASS_U(Reflection,             LoaderAllocator,          LoaderAllocator
 DEFINE_FIELD_U(m_slots,                  LoaderAllocatorObject,      m_pSlots)
 DEFINE_FIELD_U(m_slotsUsed,              LoaderAllocatorObject,      m_slotsUsed)
 DEFINE_CLASS(LOADERALLOCATOR,           Reflection,             LoaderAllocator)
-DEFINE_METHOD(LOADERALLOCATOR,          CTOR,                   .ctor,                    IM_RetVoid)
+DEFINE_METHOD(LOADERALLOCATOR,          CREATE,                 Create,                     NoSig)
 
 DEFINE_CLASS_U(Reflection,             LoaderAllocatorScout,     LoaderAllocatorScoutObject)
 DEFINE_FIELD_U(m_nativeLoaderAllocator,  LoaderAllocatorScoutObject,      m_nativeLoaderAllocator)

diff --git a/src/coreclr/vm/corhost.cpp b/src/coreclr/vm/corhost.cpp
@@ -659,8 +659,8 @@ HRESULT CorHost2::CreateAppDomainWithManager(
     // Initialize default event sources
     {
         GCX_COOP();
-        MethodDescCallSite initEventSources(METHOD__EVENT_SOURCE__INITIALIZE_DEFAULT_EVENT_SOURCES);
-        initEventSources.Call(NULL);
+        UnmanagedCallersOnlyCaller initEventSources(METHOD__EVENT_SOURCE__INITIALIZE_DEFAULT_EVENT_SOURCES);
+        initEventSources.InvokeThrowing();
     }
 #endif // FEATURE_PERFTRACING
 

diff --git a/src/coreclr/vm/dispatchinfo.cpp b/src/coreclr/vm/dispatchinfo.cpp
@@ -1555,8 +1555,8 @@ void DispatchInfo::InvokeMemberWorker(DispatchMemberInfo*   pDispMemberInfo,
         {
             // If the method is culture aware, then set the specified culture on the thread.
             GetCultureInfoForLCID(lcid, &pObjs->CultureInfo);
-            pObjs->OldCultureInfo = Thread::GetCulture(FALSE);
-            Thread::SetCulture(&pObjs->CultureInfo, FALSE);
+            pObjs->OldCultureInfo = GetCurrentCulture(FALSE);
+            SetCurrentCulture(&pObjs->CultureInfo, FALSE);
         }
 
         // If the method has custom marshalers then we will need to call
@@ -2284,7 +2284,7 @@ HRESULT DispatchInfo::InvokeMember(SimpleComCallWrapper *pSimpleWrap, DISPID id,
 
         // If the culture was changed then restore it to the old culture.
         if (Objs.OldCultureInfo != NULL)
-            Thread::SetCulture(&Objs.OldCultureInfo, FALSE);
+            SetCurrentCulture(&Objs.OldCultureInfo, FALSE);
     }
     GCPROTECT_END();
     GCPROTECT_END();

diff --git a/src/coreclr/vm/dllimport.cpp b/src/coreclr/vm/dllimport.cpp
@@ -6168,7 +6168,7 @@ EXTERN_C void STDCALL GenericPInvokeCalliStubWorker(TransitionBlock * pTransitio
     pFrame->Pop(CURRENT_THREAD);
 }
 
-EXTERN_C void LookupMethodByName(const char* fullQualifiedTypeName, const char* methodName, MethodDesc** ppMD)
+EXTERN_C void LookupUnmanagedCallersOnlyMethodByName(const char* fullQualifiedTypeName, const char* methodName, MethodDesc** ppMD)
 {
     CONTRACTL
     {
@@ -6185,7 +6185,24 @@ EXTERN_C void LookupMethodByName(const char* fullQualifiedTypeName, const char*
     TypeHandle type = TypeName::GetTypeFromAsmQualifiedName(fullQualifiedTypeNameUtf8.GetUnicode(), /*bThrowIfNotFound*/ TRUE);
     _ASSERTE(!type.IsTypeDesc());
 
-    *ppMD = MemberLoader::FindMethodByName(type.GetMethodTable(), methodName);
+    // Iterate the type looking for a method with the given name that has the
+    // UnmanagedCallersOnly attribute.
+    MethodTable* pMT = type.GetMethodTable();
+    MethodTable::MethodIterator it(pMT);
+    it.MoveToEnd();
+    for (; it.IsValid(); it.Prev())
+    {
+        MethodDesc* pMD = it.GetMethodDesc();
+        if (strcmp(pMD->GetNameOnNonArrayClass(), methodName) == 0
+            && pMD->HasUnmanagedCallersOnlyAttribute())
+        {
+            *ppMD = pMD;
+            return;
+        }
+    }
+
+    // Fallback if no UCO match found.
+    *ppMD = MemberLoader::FindMethodByName(pMT, methodName);
 }
 
 namespace