[WebAssembly] Fix expected contents of relocations with addends

[sbc100]

Summary

This fixes issues found on the wasm waterfall related to relocations
with addends. Undefined symbols, even those with addends should
always have a provisional value of zero. At least this is what llvm
emits for wasm today (and I believe this is true for ELF too).

[sbc100]

• add test

[dschuff]

LGTM, and confirmed that it makes libcxx configure successfully.

[ncw]

Looks good, well caught

[ruiu]

LGTM

wasm/InputChunks.cpp

 void InputChunk::writeTo(uint8_t *Buf) const {
   // Copy contents
   memcpy(Buf + OutputOffset, data().data(), data().size());
 
   // Apply relocations
   if (Relocations.empty())
     return;
 
-  DEBUG(dbgs() << "applying relocations: count=" << Relocations.size() << "\n");
+  DEBUG(dbgs() << "applying relocations: " << getName()
+               << " count=" << Relocations.size() << "\n");
   int32_t Off = OutputOffset - getInputSectionOffset();
 
   for (const WasmRelocation &Rel : Relocations) {
     uint8_t *Loc = Buf + Rel.Offset + Off;
     uint32_t Value = File->calcNewValue(Rel);
     uint32_t ExistingValue;
     DEBUG(dbgs() << "apply reloc: type=" << ReloctTypeToString(Rel.Type)
                  << " addend=" << Rel.Addend << " index=" << Rel.Index

wasm/InputFiles.cpp

uint32_t ObjFile::calcExpectedValue(const WasmRelocation &Reloc) const {
   }
   case R_WEBASSEMBLY_MEMORY_ADDR_SLEB:
   case R_WEBASSEMBLY_MEMORY_ADDR_I32:
   case R_WEBASSEMBLY_MEMORY_ADDR_LEB: {
     const WasmSymbol& Sym = WasmObj->syms()[Reloc.Index];
     if (Sym.isUndefined())
       return 0;
     const WasmSegment& Segment = WasmObj->dataSegments()[Sym.Info.DataRef.Segment];
-    return Segment.Data.Offset.Value.Int32 + Sym.Info.DataRef.Offset;
+    return Segment.Data.Offset.Value.Int32 + Sym.Info.DataRef.Offset +
+           Reloc.Addend;
   }
   case R_WEBASSEMBLY_TYPE_INDEX_LEB:
     return Reloc.Index;
   case R_WEBASSEMBLY_FUNCTION_INDEX_LEB:
   case R_WEBASSEMBLY_GLOBAL_INDEX_LEB: {
     const WasmSymbol& Sym = WasmObj->syms()[Reloc.Index];
     return Sym.Info.ElementIndex;
   }
   default:
     llvm_unreachable("unknown relocation type");
   }
 }
 
 // Translate from the relocation's index into the final linked output value.
 uint32_t ObjFile::calcNewValue(const WasmRelocation &Reloc) const {
   switch (Reloc.Type) {
   case R_WEBASSEMBLY_TABLE_INDEX_I32:
   case R_WEBASSEMBLY_TABLE_INDEX_SLEB:
     return getFunctionSymbol(Reloc.Index)->getTableIndex();
   case R_WEBASSEMBLY_MEMORY_ADDR_SLEB:
   case R_WEBASSEMBLY_MEMORY_ADDR_I32:
   case R_WEBASSEMBLY_MEMORY_ADDR_LEB:
     if (auto *Sym = dyn_cast<DefinedData>(getDataSymbol(Reloc.Index)))
       return Sym->getVirtualAddress() + Reloc.Addend;
-    return Reloc.Addend;
+    return 0;
   case R_WEBASSEMBLY_TYPE_INDEX_LEB:
     return TypeMap[Reloc.Index];
   case R_WEBASSEMBLY_FUNCTION_INDEX_LEB:
     return getFunctionSymbol(Reloc.Index)->getFunctionIndex();
   case R_WEBASSEMBLY_GLOBAL_INDEX_LEB:
     return getGlobalSymbol(Reloc.Index)->getGlobalIndex();
   default:
     llvm_unreachable("unknown relocation type");