[wasm][coreCLR] Dispatch R2R-compiled methods from reflection and UnmanagedCallersOnly paths

src/coreclr/vm/method.cpp

@@ -2006,8 +2006,10 @@ PCODE MethodDesc::GetSingleCallableAddrOfCodeForUnmanagedCallersOnly()
     CONTRACTL
     {
         THROWS;
-        GC_NOTRIGGER;
-        MODE_ANY;
+        // On portable entrypoint platforms resolving the entrypoint may need to run the prestub
+        // (e.g. to publish R2R native code for the method), which can trigger a GC.
+        GC_TRIGGERS;
+        MODE_PREEMPTIVE;
         PRECONDITION(HasUnmanagedCallersOnlyAttribute());
     }
     CONTRACTL_END;

src/coreclr/vm/method.hpp

@@ -2298,6 +2298,13 @@ class MethodDesc
     PCODE PrepareInitialCode(CallerGCMode callerGCMode = CallerGCMode::Unknown);
     PCODE PrepareCode(PrepareCodeConfig* pConfig);
 
+#ifdef FEATURE_PORTABLE_ENTRYPOINTS
+    // Probe for precompiled R2R native code for an UnmanagedCallersOnly method and, if present,
+    // publish it into this method's portable entrypoint WITHOUT compiling interpreter byte code.
+    // Returns true if native code was found and published, false otherwise.
+    bool TryPublishR2RCodeForUnmanagedCallersOnly();
+#endif // FEATURE_PORTABLE_ENTRYPOINTS
+
 private:
     PCODE GetPrecompiledCode(PrepareCodeConfig* pConfig, bool shouldTier);
     PCODE GetPrecompiledR2RCode(PrepareCodeConfig* pConfig);

src/coreclr/vm/precode_portable.cpp

@@ -174,7 +174,8 @@ void* GetUnmanagedCallersOnlyThunk(MethodDesc* pMD);
 
 bool PortableEntryPoint::EnsureCodeForUnmanagedCallersOnly()
 {
-    LIMITED_METHOD_CONTRACT;
+    STANDARD_VM_CONTRACT;
+
     _ASSERTE(IsValid());
 
     if (HasFlags(_flags, kUnmanagedCallersOnly_Checked | kUnmanagedCallersOnly_Has))

src/coreclr/vm/prestub.cpp

@@ -502,6 +502,28 @@ PCODE MethodDesc::GetPrecompiledR2RCode(PrepareCodeConfig* pConfig)
     return pCode;
 }
 
+#ifdef FEATURE_PORTABLE_ENTRYPOINTS
+bool MethodDesc::TryPublishR2RCodeForUnmanagedCallersOnly()
+{
+    STANDARD_VM_CONTRACT;
+    _ASSERTE(HasUnmanagedCallersOnlyAttribute());
+
+#ifdef FEATURE_READYTORUN
+    PrepareCodeConfig config(NativeCodeVersion(this), TRUE, TRUE);
+    config.SetCallerGCMode(CallerGCMode::Preemptive);
+
+    // GetPrecompiledR2RCode resolves the R2R entrypoint and, on portable-entrypoint (wasm) targets,
+    // publishes it into this method's portable entrypoint as a side effect (PortableEntryPoint::SetActualCode).
+    // It never compiles interpreter byte code, so purely interpreted methods simply return NULL here and
+    // are left unprepared for lazy byte code generation on first call.
+    PCODE pCode = GetPrecompiledR2RCode(&config);
+    return pCode != (PCODE)NULL;
+#else // !FEATURE_READYTORUN
+    return false;
+#endif // FEATURE_READYTORUN
+}
+#endif // FEATURE_PORTABLE_ENTRYPOINTS
+
 PCODE MethodDesc::GetMulticoreJitCode(PrepareCodeConfig* pConfig, bool* pWasTier0)
 {
     STANDARD_VM_CONTRACT;
@@ -2081,6 +2103,12 @@ extern "C" void* STDCALL ExecuteInterpretedMethod(TransitionBlock* pTransitionBl
 
 void ExecuteInterpretedMethodWithArgs(TADDR targetIp, int8_t* args, size_t argSize, void* retBuff, PCODE callerIp)
 {
+    // targetIp must point to valid interpreter byte code. A NULL here means a caller failed to route a
+    // method that has native (R2R) code but no interpreter code to InvokeManagedMethod. Dispatching a
+    // NULL byte code pointer would be (mis)interpreted as INTOP_INVALID and fail with a cryptic fatal
+    // error, so assert here at the actual point of misuse.
+    _ASSERTE(targetIp != (TADDR)NULL);
+
     // Copy arguments to the stack
     if (argSize > 0)
     {
@@ -2225,10 +2253,14 @@ extern "C" void ExecuteInterpretedMethodFromUnmanaged(MethodDesc* pMD, int8_t* a
     InterpByteCodeStart* targetIp = pMD->GetInterpreterCode();
     if (targetIp == NULL)
     {
-        GCX_PREEMP();
-        (void)pMD->DoPrestub(NULL /* MethodTable */, CallerGCMode::Coop);
+        (void)pMD->DoPrestub(NULL /* MethodTable */, CallerGCMode::Preemptive);
         targetIp = pMD->GetInterpreterCode();
     }
+    // The g_ReverseThunks reverse thunk is only used for UnmanagedCallersOnly methods that are executed
+    // by the interpreter. Methods compiled to native (R2R) code are dispatched directly to their R2R
+    // entrypoint by GetUnmanagedCallersOnlyThunk and never reach this path, so the interpreter byte code
+    // must exist here.
+    _ASSERTE(targetIp != NULL);
     (void)ExecuteInterpretedMethodWithArgs((TADDR)targetIp, args, argSize, ret, callerIp);
 }
 #endif // FEATURE_INTERPRETER

src/coreclr/vm/wasm/calldescrworkerwasm.cpp

@@ -38,5 +38,17 @@ extern "C" void STDCALL CallDescrWorkerInternal(CallDescrData* pCallDescrData)
         retBuff = &pCallDescrData->returnValue;
     }
 
+    if (targetIp == NULL)
+    {
+        // The target method has no interpreter code because it was compiled to native (R2R) code.
+        // Invoke it as a compiled managed method through the interpreter->R2R thunk, mirroring the
+        // fallback already present in ExecuteInterpretedMethodWithArgs_PortableEntryPoint_Complex and
+        // the CALL_INTERP_METHOD path in InterpExecMethod. Without this, the NULL bytecode pointer
+        // would be handed to the interpreter and dispatched as INTOP_INVALID.
+        ManagedMethodParam param = { pMethod, args, (int8_t*)retBuff, (PCODE)NULL, nullptr };
+        InvokeManagedMethod(&param);
+        return;
+    }
+
     ExecuteInterpretedMethodWithArgs((TADDR)targetIp, args, argsSize, retBuff, (PCODE)&CallDescrWorkerInternal);
 }

src/coreclr/vm/wasm/helpers.cpp

@@ -1361,6 +1361,30 @@ void* GetUnmanagedCallersOnlyThunk(MethodDesc* pMD)
     _ASSERTE(pMD != NULL);
     _ASSERTE(pMD->HasUnmanagedCallersOnlyAttribute());
 
+    // Prefer R2R-compiled native code for UnmanagedCallersOnly methods since it is emitted
+    // with the native (unmanaged) calling convention and its R2R code is itself the directly-callable
+    // unmanaged entrypoint. Resolve the method's code first and, if it has native (R2R) code, return that
+    // entrypoint directly. The g_ReverseThunks interpreter fallback below is only required for methods
+    // that are executed by the interpreter (no native code), and is intentionally unused for R2R methods.
+    PCODE entryPoint = pMD->GetPortableEntryPoint();
+    if (!PortableEntryPoint::HasNativeEntryPoint(entryPoint) && pMD->GetInterpreterCode() == NULL)
+    {
+        // The method has not been prepared yet. Probe for precompiled R2R native code and, if present,
+        // publish it into the portable entrypoint WITHOUT compiling interpreter byte code. Purely
+        // interpreted methods are intentionally left unprepared here so that their byte code is generated
+        // lazily on first call through the reverse thunk below (better for startup). For R2R methods we
+        // run the prestub to perform the canonical full preparation; it finds the R2R code first and never
+        // falls back to compiling byte code.
+        if (pMD->TryPublishR2RCodeForUnmanagedCallersOnly())
+        {
+            (void)pMD->DoPrestub(NULL /* MethodTable */, CallerGCMode::Preemptive);
+        }
+    }
+    if (PortableEntryPoint::HasNativeEntryPoint(entryPoint))
+    {
+        return PortableEntryPoint::GetActualCode(entryPoint);
+    }
+
     const ReverseThunkMapValue* value = LookupThunk(pMD);
     if (value == NULL)
     {