[crossgen2][wasm] Shrink Code Section Relocs

src/coreclr/tools/Common/Compiler/DependencyAnalysis/Relocation.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Diagnostics;
+using System.Runtime.Serialization;
 using ILCompiler.ObjectWriter;
 
 namespace ILCompiler.DependencyAnalysis
@@ -696,6 +697,31 @@ public static unsafe void WriteValue(RelocType relocType, void* location, long v
             }
         }
 
+        public static unsafe int WriteVariableLengthValue(RelocType relocType, byte* location, long value)
+        {
+            Debug.Assert(IsVariableLength(relocType));
+            switch (relocType)
+            {
+                case RelocType.WASM_TYPE_INDEX_LEB:
+                case RelocType.WASM_GLOBAL_INDEX_LEB:
+                case RelocType.WASM_FUNCTION_INDEX_LEB:
+                case RelocType.WASM_MEMORY_ADDR_LEB:
+                case RelocType.WASM_MEMORY_ADDR_REL_LEB:
+                case RelocType.WASM_CLR_RESTORE_CONTEXT_EXCEPTION_TAG_LEB:
+                    DwarfHelper.WriteULEB128(new Span<byte>((byte*)location, WASM_PADDED_RELOC_SIZE_32), checked((ulong)value));
+                    return (int)DwarfHelper.SizeOfULEB128((ulong)value);
+
+                case RelocType.WASM_TABLE_INDEX_SLEB:
+                case RelocType.WASM_MEMORY_ADDR_SLEB:
+                case RelocType.WASM_MEMORY_ADDR_REL_SLEB:
+                    DwarfHelper.WriteSLEB128(new Span<byte>((byte*)location, WASM_PADDED_RELOC_SIZE_32), value);
+                    return (int)DwarfHelper.SizeOfSLEB128(value);
+                default:
+                    Debug.Fail("Invalid variable-length RelocType: " + relocType);
+                    return 0;
+            }
+        }
+
         public static readonly int MaxSize = 8;
         // Note: Please update the above field if the max size
         // changes when adding a new case to this method.
@@ -742,6 +768,45 @@ public static int GetSize(RelocType relocType)
             };
         }
 
+        public static bool IsVariableLength(RelocType relocType)
+        {
+            return relocType switch
+            {
+                RelocType.WASM_FUNCTION_INDEX_LEB or
+                RelocType.WASM_TABLE_INDEX_SLEB or
+                RelocType.WASM_TYPE_INDEX_LEB or
+                RelocType.WASM_GLOBAL_INDEX_LEB or
+                RelocType.WASM_MEMORY_ADDR_LEB or
+                RelocType.WASM_MEMORY_ADDR_SLEB or
+                RelocType.WASM_MEMORY_ADDR_REL_LEB or
+                RelocType.WASM_MEMORY_ADDR_REL_SLEB or
+                RelocType.WASM_CLR_RESTORE_CONTEXT_EXCEPTION_TAG_LEB => true,
+                _ => false,
+            };
+        }
+
+        public static int ActualSize(RelocType relocType, long resolvedValue)
+        {
+            Debug.Assert(IsVariableLength(relocType));
+            switch (relocType)
+            {
+                case RelocType.WASM_FUNCTION_INDEX_LEB:
+                case RelocType.WASM_TYPE_INDEX_LEB:
+                case RelocType.WASM_GLOBAL_INDEX_LEB:
+                case RelocType.WASM_MEMORY_ADDR_LEB:
+                case RelocType.WASM_MEMORY_ADDR_REL_LEB:
+                case RelocType.WASM_CLR_RESTORE_CONTEXT_EXCEPTION_TAG_LEB:
+                    return (int)DwarfHelper.SizeOfULEB128((ulong)resolvedValue);
+                case RelocType.WASM_TABLE_INDEX_SLEB:
+                case RelocType.WASM_MEMORY_ADDR_SLEB:
+                case RelocType.WASM_MEMORY_ADDR_REL_SLEB:
+                    return (int)DwarfHelper.SizeOfSLEB128(resolvedValue);
+                default:
+                    Debug.Fail("Invalid reloc type");
+                    return 0;
+            }
+        }
+
         public static unsafe long ReadValue(RelocType relocType, void* location)
         {
             switch (relocType)

src/coreclr/tools/Common/Compiler/ObjectWriter/Dwarf/DwarfHelper.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Buffers;
+using System.IO;
 using System.Numerics;
 
 namespace ILCompiler.ObjectWriter
@@ -122,6 +123,31 @@ public static ulong ReadULEB128(ReadOnlySpan<byte> buffer, out int bytesRead)
             return value;
         }
 
+        public static ulong? ReadULEB128(Stream source, out int bytesRead)
+        {
+            ulong value = 0;
+            byte @byte;
+            int shift = 0;
+            long startPos = source.Position;
+
+            do
+            {
+                int b = source.ReadByte();
+                if (b < 0)
+                {
+                    bytesRead = (int)(source.Position - startPos);
+                    return null;
+                }
+
+                @byte = (byte)b;
+                value |= ((ulong)@byte & 0x7f) << shift;
+                shift += 7;
+            } while ((@byte & 0x80) != 0);
+
+            bytesRead = (int)(source.Position - startPos);
+            return value;
+        }
+
         public static long ReadSLEB128(ReadOnlySpan<byte> buffer) => ReadSLEB128(buffer, out _);
 
         public static long ReadSLEB128(ReadOnlySpan<byte> buffer, out int bytesRead)