Fix issue #114504 by not emitting empty gcrefmaps in R2R

src/coreclr/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/GCRefMapNode.cs

@@ -34,6 +34,8 @@ public GCRefMapNode(ImportSectionNode importSection)
 
         public int Offset => 0;
 
+        public bool IsEmpty => _methods.Count == 0;
+
         public void AddImport(Import import)
         {
             lock (_methods)
@@ -50,20 +52,22 @@ public void AppendMangledName(NameMangler nameMangler, Utf8StringBuilder sb)
 
         public override ObjectData GetData(NodeFactory factory, bool relocsOnly = false)
         {
-            if (_methods.Count == 0 || relocsOnly)
-            {
-                return new ObjectData(
-                    data: Array.Empty<byte>(), 
-                    relocs: Array.Empty<Relocation>(), 
-                    alignment: 1, 
-                    definedSymbols: new ISymbolDefinitionNode[] { this });
-            }
+            if (relocsOnly)
+                return new ObjectData(Array.Empty<byte>(), Array.Empty<Relocation>(), 1, new ISymbolDefinitionNode[] { this });
 
             _methods.MergeSort(CompilerComparer.Instance);
             GCRefMapBuilder builder = new GCRefMapBuilder(factory.Target, relocsOnly);
+
             builder.Builder.RequireInitialAlignment(4);
             builder.Builder.AddSymbol(this);
 
+            if (_methods.Count == 0)
+            {
+                // Always generate a size header
+                builder.Builder.EmitInt(0);
+                return builder.Builder.ToObjectData();
+            }
+
             // First, emit the initial ref map offset and reserve the offset map entries
             int offsetCount = _methods.Count / GCREFMAP_LOOKUP_STRIDE;
             builder.Builder.EmitInt((offsetCount + 1) * sizeof(int));

src/coreclr/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/ImportSectionNode.cs

@@ -135,8 +135,9 @@ public override void EncodeData(ref ObjectDataBuilder dataBuilder, NodeFactory f
                 dataBuilder.EmitUInt(0);
             }
 
-            if (_emitGCRefMap)
+            if (_emitGCRefMap && !_gcRefMap.IsEmpty)
             {
+                // This indirectly generates the AuxiliaryDataRva by emitting a placeholder 0 which will be replaced later
                 dataBuilder.EmitReloc(_gcRefMap, RelocType.IMAGE_REL_BASED_ADDR32NB, 0);
             }
             else

src/tests/Common/CLRTest.CrossGen.targets

@@ -110,8 +110,7 @@ if [ ! -z ${RunCrossGen2+x} ]%3B then
         done
 
         echo -o:"$__OutputFile" >> "$__ResponseFile"
-        ## Enable once #114504 is fixed
-        ## echo -O >> "$__ResponseFile"
+        echo -O >> "$__ResponseFile"
         echo --targetarch:$(TargetArchitecture) >> "$__ResponseFile"
         echo --targetos:$(TargetOS) >> "$__ResponseFile"
         echo --verify-type-and-field-layout >> "$__ResponseFile"