lld/wasm/InputChunks.cpp

   1 //===- InputChunks.cpp ----------------------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #include "InputChunks.h"
  10 #include "Config.h"
  11 #include "OutputSegment.h"
  12 #include "WriterUtils.h"
  13 #include "lld/Common/ErrorHandler.h"
  14 #include "lld/Common/LLVM.h"
  15 #include "llvm/Support/LEB128.h"
  16 #include "llvm/Support/xxhash.h"
  17
  18 #define DEBUG_TYPE "lld"
  19
  20 using namespace llvm;
  21 using namespace llvm::wasm;
  22 using namespace llvm::support::endian;
  23
  24 namespace lld {
  25 StringRef relocTypeToString(uint8_t relocType) {
  26   switch (relocType) {
  27 #define WASM_RELOC(NAME, REL)                                                  \
  28   case REL:                                                                    \
  29     return #NAME;
  30 #include "llvm/BinaryFormat/WasmRelocs.def"
  31 #undef WASM_RELOC
  32   }
  33   llvm_unreachable("unknown reloc type");
  34 }
  35
  36 bool relocIs64(uint8_t relocType) {
  37   switch (relocType) {
  38   case R_WASM_MEMORY_ADDR_LEB64:
  39   case R_WASM_MEMORY_ADDR_SLEB64:
  40   case R_WASM_MEMORY_ADDR_REL_SLEB64:
  41   case R_WASM_MEMORY_ADDR_I64:
  42   case R_WASM_TABLE_INDEX_SLEB64:
  43   case R_WASM_TABLE_INDEX_I64:
  44   case R_WASM_FUNCTION_OFFSET_I64:
  45   case R_WASM_TABLE_INDEX_REL_SLEB64:
  46   case R_WASM_MEMORY_ADDR_TLS_SLEB64:
  47     return true;
  48   default:
  49     return false;
  50   }
  51 }
  52
  53 std::string toString(const wasm::InputChunk *c) {
  54   return (toString(c->file) + ":(" + c->name + ")").str();
  55 }
  56
  57 namespace wasm {
  58 StringRef InputChunk::getComdatName() const {
  59   uint32_t index = getComdat();
  60   if (index == UINT32_MAX)
  61     return StringRef();
  62   return file->getWasmObj()->linkingData().Comdats[index];
  63 }
  64
  65 uint32_t InputChunk::getSize() const {
  66   if (const auto *ms = dyn_cast<SyntheticMergedChunk>(this))
  67     return ms->builder.getSize();
  68
  69   if (const auto *f = dyn_cast<InputFunction>(this)) {
  70     if (config->compressRelocations && f->file) {
  71       return f->getCompressedSize();
  72     }
  73   }
  74
  75   return data().size();
  76 }
  77
  78 uint32_t InputChunk::getInputSize() const {
  79   if (const auto *f = dyn_cast<InputFunction>(this))
  80     return f->function->Size;
  81   return getSize();
  82 }
  83
  84 // Copy this input chunk to an mmap'ed output file and apply relocations.
  85 void InputChunk::writeTo(uint8_t *buf) const {
  86   if (const auto *f = dyn_cast<InputFunction>(this)) {
  87     if (file && config->compressRelocations)
  88       return f->writeCompressed(buf);
  89   } else if (const auto *ms = dyn_cast<SyntheticMergedChunk>(this)) {
  90     ms->builder.write(buf + outSecOff);
  91     // Apply relocations
  92     ms->relocate(buf + outSecOff);
  93     return;
  94   }
  95
  96   // Copy contents
  97   memcpy(buf + outSecOff, data().data(), data().size());
  98
  99   // Apply relocations
 100   relocate(buf + outSecOff);
 101 }
 102
 103 void InputChunk::relocate(uint8_t *buf) const {
 104   if (relocations.empty())
 105     return;
 106
 107   LLVM_DEBUG(dbgs() << "applying relocations: " << toString(this)
 108                     << " count=" << relocations.size() << "\n");
 109   int32_t inputSectionOffset = getInputSectionOffset();
 110   uint64_t tombstone = getTombstone();
 111
 112   for (const WasmRelocation &rel : relocations) {
 113     uint8_t *loc = buf + rel.Offset - inputSectionOffset;
 114     LLVM_DEBUG(dbgs() << "apply reloc: type=" << relocTypeToString(rel.Type));
 115     if (rel.Type != R_WASM_TYPE_INDEX_LEB)
 116       LLVM_DEBUG(dbgs() << " sym=" << file->getSymbols()[rel.Index]->getName());
 117     LLVM_DEBUG(dbgs() << " addend=" << rel.Addend << " index=" << rel.Index
 118                       << " offset=" << rel.Offset << "\n");
 119     // TODO(sbc): Check that the value is within the range of the
 120     // relocation type below.  Most likely we must error out here
 121     // if its not with range.
 122     uint64_t value = file->calcNewValue(rel, tombstone, this);
 123
 124     switch (rel.Type) {
 125     case R_WASM_TYPE_INDEX_LEB:
 126     case R_WASM_FUNCTION_INDEX_LEB:
 127     case R_WASM_GLOBAL_INDEX_LEB:
 128     case R_WASM_TAG_INDEX_LEB:
 129     case R_WASM_MEMORY_ADDR_LEB:
 130     case R_WASM_TABLE_NUMBER_LEB:
 131       encodeULEB128(static_cast<uint32_t>(value), loc, 5);
 132       break;
 133     case R_WASM_MEMORY_ADDR_LEB64:
 134       encodeULEB128(value, loc, 10);
 135       break;
 136     case R_WASM_TABLE_INDEX_SLEB:
 137     case R_WASM_TABLE_INDEX_REL_SLEB:
 138     case R_WASM_MEMORY_ADDR_SLEB:
 139     case R_WASM_MEMORY_ADDR_REL_SLEB:
 140     case R_WASM_MEMORY_ADDR_TLS_SLEB:
 141       encodeSLEB128(static_cast<int32_t>(value), loc, 5);
 142       break;
 143     case R_WASM_TABLE_INDEX_SLEB64:
 144     case R_WASM_TABLE_INDEX_REL_SLEB64:
 145     case R_WASM_MEMORY_ADDR_SLEB64:
 146     case R_WASM_MEMORY_ADDR_REL_SLEB64:
 147     case R_WASM_MEMORY_ADDR_TLS_SLEB64:
 148       encodeSLEB128(static_cast<int64_t>(value), loc, 10);
 149       break;
 150     case R_WASM_TABLE_INDEX_I32:
 151     case R_WASM_MEMORY_ADDR_I32:
 152     case R_WASM_FUNCTION_OFFSET_I32:
 153     case R_WASM_FUNCTION_INDEX_I32:
 154     case R_WASM_SECTION_OFFSET_I32:
 155     case R_WASM_GLOBAL_INDEX_I32:
 156     case R_WASM_MEMORY_ADDR_LOCREL_I32:
 157       write32le(loc, value);
 158       break;
 159     case R_WASM_TABLE_INDEX_I64:
 160     case R_WASM_MEMORY_ADDR_I64:
 161     case R_WASM_FUNCTION_OFFSET_I64:
 162       write64le(loc, value);
 163       break;
 164     default:
 165       llvm_unreachable("unknown relocation type");
 166     }
 167   }
 168 }
 169
 170 // Copy relocation entries to a given output stream.
 171 // This function is used only when a user passes "-r". For a regular link,
 172 // we consume relocations instead of copying them to an output file.
 173 void InputChunk::writeRelocations(raw_ostream &os) const {
 174   if (relocations.empty())
 175     return;
 176
 177   int32_t off = outSecOff - getInputSectionOffset();
 178   LLVM_DEBUG(dbgs() << "writeRelocations: " << file->getName()
 179                     << " offset=" << Twine(off) << "\n");
 180
 181   for (const WasmRelocation &rel : relocations) {
 182     writeUleb128(os, rel.Type, "reloc type");
 183     writeUleb128(os, rel.Offset + off, "reloc offset");
 184     writeUleb128(os, file->calcNewIndex(rel), "reloc index");
 185
 186     if (relocTypeHasAddend(rel.Type))
 187       writeSleb128(os, file->calcNewAddend(rel), "reloc addend");
 188   }
 189 }
 190
 191 uint64_t InputChunk::getTombstone() const {
 192   if (const auto *s = dyn_cast<InputSection>(this)) {
 193     return s->tombstoneValue;
 194   }
 195
 196   return 0;
 197 }
 198
 199 void InputFunction::setFunctionIndex(uint32_t index) {
 200   LLVM_DEBUG(dbgs() << "InputFunction::setFunctionIndex: " << name << " -> "
 201                     << index << "\n");
 202   assert(!hasFunctionIndex());
 203   functionIndex = index;
 204 }
 205
 206 void InputFunction::setTableIndex(uint32_t index) {
 207   LLVM_DEBUG(dbgs() << "InputFunction::setTableIndex: " << name << " -> "
 208                     << index << "\n");
 209   assert(!hasTableIndex());
 210   tableIndex = index;
 211 }
 212
 213 // Write a relocation value without padding and return the number of bytes
 214 // witten.
 215 static unsigned writeCompressedReloc(uint8_t *buf, const WasmRelocation &rel,
 216                                      uint64_t value) {
 217   switch (rel.Type) {
 218   case R_WASM_TYPE_INDEX_LEB:
 219   case R_WASM_FUNCTION_INDEX_LEB:
 220   case R_WASM_GLOBAL_INDEX_LEB:
 221   case R_WASM_TAG_INDEX_LEB:
 222   case R_WASM_MEMORY_ADDR_LEB:
 223   case R_WASM_MEMORY_ADDR_LEB64:
 224   case R_WASM_TABLE_NUMBER_LEB:
 225     return encodeULEB128(value, buf);
 226   case R_WASM_TABLE_INDEX_SLEB:
 227   case R_WASM_TABLE_INDEX_SLEB64:
 228   case R_WASM_MEMORY_ADDR_SLEB:
 229   case R_WASM_MEMORY_ADDR_SLEB64:
 230     return encodeSLEB128(static_cast<int64_t>(value), buf);
 231   default:
 232     llvm_unreachable("unexpected relocation type");
 233   }
 234 }
 235
 236 static unsigned getRelocWidthPadded(const WasmRelocation &rel) {
 237   switch (rel.Type) {
 238   case R_WASM_TYPE_INDEX_LEB:
 239   case R_WASM_FUNCTION_INDEX_LEB:
 240   case R_WASM_GLOBAL_INDEX_LEB:
 241   case R_WASM_TAG_INDEX_LEB:
 242   case R_WASM_MEMORY_ADDR_LEB:
 243   case R_WASM_TABLE_NUMBER_LEB:
 244   case R_WASM_TABLE_INDEX_SLEB:
 245   case R_WASM_MEMORY_ADDR_SLEB:
 246     return 5;
 247   case R_WASM_TABLE_INDEX_SLEB64:
 248   case R_WASM_MEMORY_ADDR_LEB64:
 249   case R_WASM_MEMORY_ADDR_SLEB64:
 250     return 10;
 251   default:
 252     llvm_unreachable("unexpected relocation type");
 253   }
 254 }
 255
 256 static unsigned getRelocWidth(const WasmRelocation &rel, uint64_t value) {
 257   uint8_t buf[10];
 258   return writeCompressedReloc(buf, rel, value);
 259 }
 260
 261 // Relocations of type LEB and SLEB in the code section are padded to 5 bytes
 262 // so that a fast linker can blindly overwrite them without needing to worry
 263 // about the number of bytes needed to encode the values.
 264 // However, for optimal output the code section can be compressed to remove
 265 // the padding then outputting non-relocatable files.
 266 // In this case we need to perform a size calculation based on the value at each
 267 // relocation.  At best we end up saving 4 bytes for each relocation entry.
 268 //
 269 // This function only computes the final output size.  It must be called
 270 // before getSize() is used to calculate of layout of the code section.
 271 void InputFunction::calculateSize() {
 272   if (!file || !config->compressRelocations)
 273     return;
 274
 275   LLVM_DEBUG(dbgs() << "calculateSize: " << name << "\n");
 276
 277   const uint8_t *secStart = file->codeSection->Content.data();
 278   const uint8_t *funcStart = secStart + getInputSectionOffset();
 279   uint32_t functionSizeLength;
 280   decodeULEB128(funcStart, &functionSizeLength);
 281
 282   uint32_t start = getInputSectionOffset();
 283   uint32_t end = start + function->Size;
 284
 285   uint64_t tombstone = getTombstone();
 286
 287   uint32_t lastRelocEnd = start + functionSizeLength;
 288   for (const WasmRelocation &rel : relocations) {
 289     LLVM_DEBUG(dbgs() << "  region: " << (rel.Offset - lastRelocEnd) << "\n");
 290     compressedFuncSize += rel.Offset - lastRelocEnd;
 291     compressedFuncSize +=
 292         getRelocWidth(rel, file->calcNewValue(rel, tombstone, this));
 293     lastRelocEnd = rel.Offset + getRelocWidthPadded(rel);
 294   }
 295   LLVM_DEBUG(dbgs() << "  final region: " << (end - lastRelocEnd) << "\n");
 296   compressedFuncSize += end - lastRelocEnd;
 297
 298   // Now we know how long the resulting function is we can add the encoding
 299   // of its length
 300   uint8_t buf[5];
 301   compressedSize = compressedFuncSize + encodeULEB128(compressedFuncSize, buf);
 302
 303   LLVM_DEBUG(dbgs() << "  calculateSize orig: " << function->Size << "\n");
 304   LLVM_DEBUG(dbgs() << "  calculateSize  new: " << compressedSize << "\n");
 305 }
 306
 307 // Override the default writeTo method so that we can (optionally) write the
 308 // compressed version of the function.
 309 void InputFunction::writeCompressed(uint8_t *buf) const {
 310   buf += outSecOff;
 311   uint8_t *orig = buf;
 312   (void)orig;
 313
 314   const uint8_t *secStart = file->codeSection->Content.data();
 315   const uint8_t *funcStart = secStart + getInputSectionOffset();
 316   const uint8_t *end = funcStart + function->Size;
 317   uint64_t tombstone = getTombstone();
 318   uint32_t count;
 319   decodeULEB128(funcStart, &count);
 320   funcStart += count;
 321
 322   LLVM_DEBUG(dbgs() << "write func: " << name << "\n");
 323   buf += encodeULEB128(compressedFuncSize, buf);
 324   const uint8_t *lastRelocEnd = funcStart;
 325   for (const WasmRelocation &rel : relocations) {
 326     unsigned chunkSize = (secStart + rel.Offset) - lastRelocEnd;
 327     LLVM_DEBUG(dbgs() << "  write chunk: " << chunkSize << "\n");
 328     memcpy(buf, lastRelocEnd, chunkSize);
 329     buf += chunkSize;
 330     buf += writeCompressedReloc(buf, rel,
 331                                 file->calcNewValue(rel, tombstone, this));
 332     lastRelocEnd = secStart + rel.Offset + getRelocWidthPadded(rel);
 333   }
 334
 335   unsigned chunkSize = end - lastRelocEnd;
 336   LLVM_DEBUG(dbgs() << "  write final chunk: " << chunkSize << "\n");
 337   memcpy(buf, lastRelocEnd, chunkSize);
 338   LLVM_DEBUG(dbgs() << "  total: " << (buf + chunkSize - orig) << "\n");
 339 }
 340
 341 uint64_t InputChunk::getChunkOffset(uint64_t offset) const {
 342   if (const auto *ms = dyn_cast<MergeInputChunk>(this)) {
 343     LLVM_DEBUG(dbgs() << "getChunkOffset(merged): " << name << "\n");
 344     LLVM_DEBUG(dbgs() << "offset: " << offset << "\n");
 345     LLVM_DEBUG(dbgs() << "parentOffset: " << ms->getParentOffset(offset)
 346                       << "\n");
 347     assert(ms->parent);
 348     return ms->parent->getChunkOffset(ms->getParentOffset(offset));
 349   }
 350   return outputSegmentOffset + offset;
 351 }
 352
 353 uint64_t InputChunk::getOffset(uint64_t offset) const {
 354   return outSecOff + getChunkOffset(offset);
 355 }
 356
 357 uint64_t InputChunk::getVA(uint64_t offset) const {
 358   return (outputSeg ? outputSeg->startVA : 0) + getChunkOffset(offset);
 359 }
 360
 361 // Generate code to apply relocations to the data section at runtime.
 362 // This is only called when generating shared libraries (PIC) where address are
 363 // not known at static link time.
 364 void InputChunk::generateRelocationCode(raw_ostream &os) const {
 365   LLVM_DEBUG(dbgs() << "generating runtime relocations: " << name
 366                     << " count=" << relocations.size() << "\n");
 367
 368   bool is64 = config->is64.value_or(false);
 369   unsigned opcode_ptr_const = is64 ? WASM_OPCODE_I64_CONST
 370                                    : WASM_OPCODE_I32_CONST;
 371   unsigned opcode_ptr_add = is64 ? WASM_OPCODE_I64_ADD
 372                                  : WASM_OPCODE_I32_ADD;
 373
 374   uint64_t tombstone = getTombstone();
 375   // TODO(sbc): Encode the relocations in the data section and write a loop
 376   // here to apply them.
 377   for (const WasmRelocation &rel : relocations) {
 378     uint64_t offset = getVA(rel.Offset) - getInputSectionOffset();
 379
 380     Symbol *sym = file->getSymbol(rel);
 381     if (!config->isPic && sym->isDefined())
 382       continue;
 383
 384     LLVM_DEBUG(dbgs() << "gen reloc: type=" << relocTypeToString(rel.Type)
 385                       << " addend=" << rel.Addend << " index=" << rel.Index
 386                       << " output offset=" << offset << "\n");
 387
 388     // Calculate the address at which to apply the relocation
 389     writeU8(os, opcode_ptr_const, "CONST");
 390     writeSleb128(os, offset, "offset");
 391
 392     // In PIC mode we need to add the __memory_base
 393     if (config->isPic) {
 394       writeU8(os, WASM_OPCODE_GLOBAL_GET, "GLOBAL_GET");
 395       if (isTLS())
 396         writeUleb128(os, WasmSym::tlsBase->getGlobalIndex(), "tls_base");
 397       else
 398         writeUleb128(os, WasmSym::memoryBase->getGlobalIndex(), "memory_base");
 399       writeU8(os, opcode_ptr_add, "ADD");
 400     }
 401
 402     // Now figure out what we want to store at this location
 403     bool is64 = relocIs64(rel.Type);
 404     unsigned opcode_reloc_const =
 405         is64 ? WASM_OPCODE_I64_CONST : WASM_OPCODE_I32_CONST;
 406     unsigned opcode_reloc_add =
 407         is64 ? WASM_OPCODE_I64_ADD : WASM_OPCODE_I32_ADD;
 408     unsigned opcode_reloc_store =
 409         is64 ? WASM_OPCODE_I64_STORE : WASM_OPCODE_I32_STORE;
 410
 411     if (sym->hasGOTIndex()) {
 412       writeU8(os, WASM_OPCODE_GLOBAL_GET, "GLOBAL_GET");
 413       writeUleb128(os, sym->getGOTIndex(), "global index");
 414       if (rel.Addend) {
 415         writeU8(os, opcode_reloc_const, "CONST");
 416         writeSleb128(os, rel.Addend, "addend");
 417         writeU8(os, opcode_reloc_add, "ADD");
 418       }
 419     } else {
 420       assert(config->isPic);
 421       const GlobalSymbol* baseSymbol = WasmSym::memoryBase;
 422       if (rel.Type == R_WASM_TABLE_INDEX_I32 ||
 423           rel.Type == R_WASM_TABLE_INDEX_I64)
 424         baseSymbol = WasmSym::tableBase;
 425       else if (sym->isTLS())
 426         baseSymbol = WasmSym::tlsBase;
 427       writeU8(os, WASM_OPCODE_GLOBAL_GET, "GLOBAL_GET");
 428       writeUleb128(os, baseSymbol->getGlobalIndex(), "base");
 429       writeU8(os, opcode_reloc_const, "CONST");
 430       writeSleb128(os, file->calcNewValue(rel, tombstone, this), "offset");
 431       writeU8(os, opcode_reloc_add, "ADD");
 432     }
 433
 434     // Store that value at the virtual address
 435     writeU8(os, opcode_reloc_store, "I32_STORE");
 436     writeUleb128(os, 2, "align");
 437     writeUleb128(os, 0, "offset");
 438   }
 439 }
 440
 441 // Split WASM_SEG_FLAG_STRINGS section. Such a section is a sequence of
 442 // null-terminated strings.
 443 void MergeInputChunk::splitStrings(ArrayRef<uint8_t> data) {
 444   LLVM_DEBUG(llvm::dbgs() << "splitStrings\n");
 445   size_t off = 0;
 446   StringRef s = toStringRef(data);
 447
 448   while (!s.empty()) {
 449     size_t end = s.find(0);
 450     if (end == StringRef::npos)
 451       fatal(toString(this) + ": string is not null terminated");
 452     size_t size = end + 1;
 453
 454     pieces.emplace_back(off, xxh3_64bits(s.substr(0, size)), true);
 455     s = s.substr(size);
 456     off += size;
 457   }
 458 }
 459
 460 // This function is called after we obtain a complete list of input sections
 461 // that need to be linked. This is responsible to split section contents
 462 // into small chunks for further processing.
 463 //
 464 // Note that this function is called from parallelForEach. This must be
 465 // thread-safe (i.e. no memory allocation from the pools).
 466 void MergeInputChunk::splitIntoPieces() {
 467   assert(pieces.empty());
 468   // As of now we only support WASM_SEG_FLAG_STRINGS but in the future we
 469   // could add other types of splitting (see ELF's splitIntoPieces).
 470   assert(flags & WASM_SEG_FLAG_STRINGS);
 471   splitStrings(data());
 472 }
 473
 474 SectionPiece *MergeInputChunk::getSectionPiece(uint64_t offset) {
 475   if (this->data().size() <= offset)
 476     fatal(toString(this) + ": offset is outside the section");
 477
 478   // If Offset is not at beginning of a section piece, it is not in the map.
 479   // In that case we need to  do a binary search of the original section piece
 480   // vector.
 481   auto it = partition_point(
 482       pieces, [=](SectionPiece p) { return p.inputOff <= offset; });
 483   return &it[-1];
 484 }
 485
 486 // Returns the offset in an output section for a given input offset.
 487 // Because contents of a mergeable section is not contiguous in output,
 488 // it is not just an addition to a base output offset.
 489 uint64_t MergeInputChunk::getParentOffset(uint64_t offset) const {
 490   // If Offset is not at beginning of a section piece, it is not in the map.
 491   // In that case we need to search from the original section piece vector.
 492   const SectionPiece *piece = getSectionPiece(offset);
 493   uint64_t addend = offset - piece->inputOff;
 494   return piece->outputOff + addend;
 495 }
 496
 497 void SyntheticMergedChunk::finalizeContents() {
 498   // Add all string pieces to the string table builder to create section
 499   // contents.
 500   for (MergeInputChunk *sec : chunks)
 501     for (size_t i = 0, e = sec->pieces.size(); i != e; ++i)
 502       if (sec->pieces[i].live)
 503         builder.add(sec->getData(i));
 504
 505   // Fix the string table content. After this, the contents will never change.
 506   builder.finalize();
 507
 508   // finalize() fixed tail-optimized strings, so we can now get
 509   // offsets of strings. Get an offset for each string and save it
 510   // to a corresponding SectionPiece for easy access.
 511   for (MergeInputChunk *sec : chunks)
 512     for (size_t i = 0, e = sec->pieces.size(); i != e; ++i)
 513       if (sec->pieces[i].live)
 514         sec->pieces[i].outputOff = builder.getOffset(sec->getData(i));
 515 }
 516
 517 uint64_t InputSection::getTombstoneForSection(StringRef name) {
 518   // When a function is not live we need to update relocations referring to it.
 519   // If they occur in DWARF debug symbols, we want to change the pc of the
 520   // function to -1 to avoid overlapping with a valid range. However for the
 521   // debug_ranges and debug_loc sections that would conflict with the existing
 522   // meaning of -1 so we use -2.
 523   if (name.equals(".debug_ranges") || name.equals(".debug_loc"))
 524     return UINT64_C(-2);
 525   if (name.starts_with(".debug_"))
 526     return UINT64_C(-1);
 527   // If the function occurs in an function attribute section change it to -1 since
 528   // 0 is a valid function index.
 529   if (name.starts_with("llvm.func_attr."))
 530     return UINT64_C(-1);
 531   // Returning 0 means there is no tombstone value for this section, and relocation
 532   // will just use the addend.
 533   return 0;
 534 }
 535
 536 } // namespace wasm
 537 } // namespace lld