Convert pointers in a couple tables to relative (#78801)

`EmbeddedPointerIndirection` is used in:

* Array of pointers to dispatch maps
* Array of pointers to GC static infos
* Array of pointers to eager constructors

I'm also updating array of module initializers emission since the code to interpret this table at runtime is the same as eager constructors.

Author: MichalStrehovsky

src/coreclr/nativeaot/Common/src/Internal/Runtime/CompilerHelpers/StartupCodeHelpers.cs

@@ -132,7 +132,7 @@ private static unsafe void InitializeGlobalTablesForModule(TypeManagerHandle typ
             IntPtr staticsSection = RuntimeImports.RhGetModuleSection(typeManager, ReadyToRunSectionType.GCStaticRegion, out length);
             if (staticsSection != IntPtr.Zero)
             {
-                Debug.Assert(length % IntPtr.Size == 0);
+                Debug.Assert(length % (MethodTable.SupportsRelativePointers ? sizeof(int) : sizeof(nint)) == 0);
 
                 object[] spine = InitializeStatics(staticsSection, length);
 
@@ -170,31 +170,39 @@ internal static void RunModuleInitializers()
 
         private static unsafe void RunInitializers(TypeManagerHandle typeManager, ReadyToRunSectionType section)
         {
-            var initializers = (delegate*<void>*)RuntimeImports.RhGetModuleSection(typeManager, section, out int length);
-            Debug.Assert(length % IntPtr.Size == 0);
-            int count = length / IntPtr.Size;
-            for (int i = 0; i < count; i++)
+            var pInitializers = (byte*)RuntimeImports.RhGetModuleSection(typeManager, section, out int length);
+            Debug.Assert(length % (MethodTable.SupportsRelativePointers ? sizeof(int) : sizeof(nint)) == 0);
+
+            for (byte* pCurrent = pInitializers;
+                pCurrent < (pInitializers + length);
+                pCurrent += MethodTable.SupportsRelativePointers ? sizeof(int) : sizeof(nint))
             {
-                initializers[i]();
+                var initializer = MethodTable.SupportsRelativePointers ? (delegate*<void>)ReadRelPtr32(pCurrent) : (delegate*<void>)pCurrent;
+                initializer();
             }
+
+            static void* ReadRelPtr32(void* address)
+                => (byte*)address + *(int*)address;
         }
 
         private static unsafe object[] InitializeStatics(IntPtr gcStaticRegionStart, int length)
         {
-            IntPtr gcStaticRegionEnd = (IntPtr)((byte*)gcStaticRegionStart + length);
+            byte* gcStaticRegionEnd = (byte*)gcStaticRegionStart + length;
 
-            object[] spine = new object[length / IntPtr.Size];
+            object[] spine = new object[length / (MethodTable.SupportsRelativePointers ? sizeof(int) : sizeof(nint))];
 
             ref object rawSpineData = ref Unsafe.As<byte, object>(ref Unsafe.As<RawArrayData>(spine).Data);
 
             int currentBase = 0;
-            for (IntPtr** block = (IntPtr**)gcStaticRegionStart; block < (IntPtr**)gcStaticRegionEnd; block++)
+            for (byte* block = (byte*)gcStaticRegionStart;
+                block < gcStaticRegionEnd;
+                block += MethodTable.SupportsRelativePointers ? sizeof(int) : sizeof(nint))
             {
                 // Gc Static regions can be shared by modules linked together during compilation. To ensure each
                 // is initialized once, the static region pointer is stored with lowest bit set in the image.
                 // The first time we initialize the static region its pointer is replaced with an object reference
                 // whose lowest bit is no longer set.
-                IntPtr* pBlock = *block;
+                IntPtr* pBlock = MethodTable.SupportsRelativePointers ? (IntPtr*)ReadRelPtr32(block) : *(IntPtr**)block;
                 nint blockAddr = MethodTable.SupportsRelativePointers ? (nint)ReadRelPtr32(pBlock) : *pBlock;
                 if ((blockAddr & GCStaticRegionConstants.Uninitialized) == GCStaticRegionConstants.Uninitialized)
                 {

src/coreclr/nativeaot/Common/src/Internal/Runtime/MethodTable.cs

@@ -902,7 +902,10 @@ internal DispatchMap* DispatchMap
                         return DynamicTemplateType->DispatchMap;
                 }
 
-                return ((DispatchMap**)TypeManager.DispatchMap)[idxDispatchMap];
+                if (SupportsRelativePointers)
+                    return (DispatchMap*)FollowRelativePointer((int*)TypeManager.DispatchMap + idxDispatchMap);
+                else
+                    return ((DispatchMap**)TypeManager.DispatchMap)[idxDispatchMap];
             }
         }
 

src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/DependencyAnalysis/EmbeddedPointerIndirectionNode.cs

@@ -30,8 +30,16 @@ protected internal EmbeddedPointerIndirectionNode(TTarget target)
 
         public override void EncodeData(ref ObjectDataBuilder dataBuilder, NodeFactory factory, bool relocsOnly)
         {
-            dataBuilder.RequireInitialPointerAlignment();
-            dataBuilder.EmitPointerReloc(Target);
+            if (factory.Target.SupportsRelativePointers)
+            {
+                dataBuilder.RequireInitialAlignment(sizeof(int));
+                dataBuilder.EmitReloc(Target, RelocType.IMAGE_REL_BASED_RELPTR32);
+            }
+            else
+            {
+                dataBuilder.RequireInitialPointerAlignment();
+                dataBuilder.EmitPointerReloc(Target);
+            }
         }
 
         // At minimum, Target needs to be reported as a static dependency by inheritors.

src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/DependencyAnalysis/ModuleInitializerListNode.cs

@@ -141,7 +141,11 @@ public override ObjectData GetData(NodeFactory factory, bool relocsOnly = false)
 
             foreach (var module in sortedModules)
             {
-                builder.EmitPointerReloc(factory.MethodEntrypoint(module.GetGlobalModuleType().GetStaticConstructor()));
+                IMethodNode entrypoint = factory.MethodEntrypoint(module.GetGlobalModuleType().GetStaticConstructor());
+                if (factory.Target.SupportsRelativePointers)
+                    builder.EmitReloc(entrypoint, RelocType.IMAGE_REL_BASED_RELPTR32);
+                else
+                    builder.EmitPointerReloc(entrypoint);
             }
 
             var result = builder.ToObjectData();