[WebAssembly] Provide WasmFunction content offset information.

WasmObjectWriter mostly operates with function segments offsets that do
not include their size fields. WasmObjectFile needs to have and provide
this information to the lld to maintain proper
R_WEBASSEMBLY_FUNCTION_OFFSET_I32 relocations entries.

Patch by Yury Delendik

Differential Revision: https://reviews.llvm.org/D46763

llvm-svn: 332406

llvm/include/llvm/BinaryFormat/Wasm.h

@@ -102,6 +102,7 @@ struct WasmFunction {
   ArrayRef<uint8_t> Body;
   uint32_t CodeSectionOffset;
   uint32_t Size;
+  uint32_t CodeOffset;  // start of Locals and Body
   StringRef SymbolName; // from the "linking" section
   StringRef DebugName; // from the "name" section
   uint32_t Comdat; // from the "comdat info" section

llvm/lib/Object/WasmObjectFile.cpp

@@ -875,6 +875,7 @@ Error WasmObjectFile::parseCodeSection(const uint8_t *Ptr, const uint8_t *End) {
     uint32_t Size = readVaruint32(Ptr);
     const uint8_t *FunctionEnd = Ptr + Size;
 
+    Function.CodeOffset = Ptr - FunctionStart;
     Function.Index = NumImportedFunctions + Functions.size();
     Function.CodeSectionOffset = FunctionStart - CodeSectionStart;
     Function.Size = FunctionEnd - FunctionStart;