lib/MC/WasmObjectWriter.cpp

   1 //===- lib/MC/WasmObjectWriter.cpp - Wasm File Writer ---------------------===//
   2 //
   3 //                     The LLVM Compiler Infrastructure
   4 //
   5 // This file is distributed under the University of Illinois Open Source
   6 // License. See LICENSE.TXT for details.
   7 //
   8 //===----------------------------------------------------------------------===//
   9 //
  10 // This file implements Wasm object file writer information.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "llvm/ADT/STLExtras.h"
  15 #include "llvm/ADT/SmallPtrSet.h"
  16 #include "llvm/BinaryFormat/Wasm.h"
  17 #include "llvm/MC/MCAsmBackend.h"
  18 #include "llvm/MC/MCAsmLayout.h"
  19 #include "llvm/MC/MCAssembler.h"
  20 #include "llvm/MC/MCContext.h"
  21 #include "llvm/MC/MCExpr.h"
  22 #include "llvm/MC/MCFixupKindInfo.h"
  23 #include "llvm/MC/MCObjectWriter.h"
  24 #include "llvm/MC/MCSectionWasm.h"
  25 #include "llvm/MC/MCSymbolWasm.h"
  26 #include "llvm/MC/MCValue.h"
  27 #include "llvm/MC/MCWasmObjectWriter.h"
  28 #include "llvm/Support/Casting.h"
  29 #include "llvm/Support/Debug.h"
  30 #include "llvm/Support/ErrorHandling.h"
  31 #include "llvm/Support/LEB128.h"
  32 #include "llvm/Support/StringSaver.h"
  33 #include <vector>
  34
  35 using namespace llvm;
  36
  37 #define DEBUG_TYPE "mc"
  38
  39 namespace {
  40
  41 // Went we ceate the indirect function table we start at 1, so that there is
  42 // and emtpy slot at 0 and therefore calling a null function pointer will trap.
  43 static const uint32_t kInitialTableOffset = 1;
  44
  45 // For patching purposes, we need to remember where each section starts, both
  46 // for patching up the section size field, and for patching up references to
  47 // locations within the section.
  48 struct SectionBookkeeping {
  49   // Where the size of the section is written.
  50   uint64_t SizeOffset;
  51   // Where the section header ends (without custom section name).
  52   uint64_t PayloadOffset;
  53   // Where the contents of the section starts.
  54   uint64_t ContentsOffset;
  55   uint32_t Index;
  56 };
  57
  58 // The signature of a wasm function, in a struct capable of being used as a
  59 // DenseMap key.
  60 struct WasmFunctionType {
  61   // Support empty and tombstone instances, needed by DenseMap.
  62   enum { Plain, Empty, Tombstone } State;
  63
  64   // The return types of the function.
  65   SmallVector<wasm::ValType, 1> Returns;
  66
  67   // The parameter types of the function.
  68   SmallVector<wasm::ValType, 4> Params;
  69
  70   WasmFunctionType() : State(Plain) {}
  71
  72   bool operator==(const WasmFunctionType &Other) const {
  73     return State == Other.State && Returns == Other.Returns &&
  74            Params == Other.Params;
  75   }
  76 };
  77
  78 // Traits for using WasmFunctionType in a DenseMap.
  79 struct WasmFunctionTypeDenseMapInfo {
  80   static WasmFunctionType getEmptyKey() {
  81     WasmFunctionType FuncTy;
  82     FuncTy.State = WasmFunctionType::Empty;
  83     return FuncTy;
  84   }
  85   static WasmFunctionType getTombstoneKey() {
  86     WasmFunctionType FuncTy;
  87     FuncTy.State = WasmFunctionType::Tombstone;
  88     return FuncTy;
  89   }
  90   static unsigned getHashValue(const WasmFunctionType &FuncTy) {
  91     uintptr_t Value = FuncTy.State;
  92     for (wasm::ValType Ret : FuncTy.Returns)
  93       Value += DenseMapInfo<int32_t>::getHashValue(int32_t(Ret));
  94     for (wasm::ValType Param : FuncTy.Params)
  95       Value += DenseMapInfo<int32_t>::getHashValue(int32_t(Param));
  96     return Value;
  97   }
  98   static bool isEqual(const WasmFunctionType &LHS,
  99                       const WasmFunctionType &RHS) {
 100     return LHS == RHS;
 101   }
 102 };
 103
 104 // A wasm data segment.  A wasm binary contains only a single data section
 105 // but that can contain many segments, each with their own virtual location
 106 // in memory.  Each MCSection data created by llvm is modeled as its own
 107 // wasm data segment.
 108 struct WasmDataSegment {
 109   MCSectionWasm *Section;
 110   StringRef Name;
 111   uint32_t Offset;
 112   uint32_t Alignment;
 113   uint32_t Flags;
 114   SmallVector<char, 4> Data;
 115 };
 116
 117 // A wasm function to be written into the function section.
 118 struct WasmFunction {
 119   int32_t Type;
 120   const MCSymbolWasm *Sym;
 121 };
 122
 123 // A wasm global to be written into the global section.
 124 struct WasmGlobal {
 125   wasm::WasmGlobalType Type;
 126   uint64_t InitialValue;
 127 };
 128
 129 // Information about a single item which is part of a COMDAT.  For each data
 130 // segment or function which is in the COMDAT, there is a corresponding
 131 // WasmComdatEntry.
 132 struct WasmComdatEntry {
 133   unsigned Kind;
 134   uint32_t Index;
 135 };
 136
 137 // Information about a single relocation.
 138 struct WasmRelocationEntry {
 139   uint64_t Offset;                  // Where is the relocation.
 140   const MCSymbolWasm *Symbol;       // The symbol to relocate with.
 141   int64_t Addend;                   // A value to add to the symbol.
 142   unsigned Type;                    // The type of the relocation.
 143   const MCSectionWasm *FixupSection;// The section the relocation is targeting.
 144
 145   WasmRelocationEntry(uint64_t Offset, const MCSymbolWasm *Symbol,
 146                       int64_t Addend, unsigned Type,
 147                       const MCSectionWasm *FixupSection)
 148       : Offset(Offset), Symbol(Symbol), Addend(Addend), Type(Type),
 149         FixupSection(FixupSection) {}
 150
 151   bool hasAddend() const {
 152     switch (Type) {
 153     case wasm::R_WEBASSEMBLY_MEMORY_ADDR_LEB:
 154     case wasm::R_WEBASSEMBLY_MEMORY_ADDR_SLEB:
 155     case wasm::R_WEBASSEMBLY_MEMORY_ADDR_I32:
 156     case wasm::R_WEBASSEMBLY_FUNCTION_OFFSET_I32:
 157     case wasm::R_WEBASSEMBLY_SECTION_OFFSET_I32:
 158       return true;
 159     default:
 160       return false;
 161     }
 162   }
 163
 164   void print(raw_ostream &Out) const {
 165     Out << "Off=" << Offset << ", Sym=" << *Symbol << ", Addend=" << Addend
 166         << ", Type=" << Type
 167         << ", FixupSection=" << FixupSection->getSectionName();
 168   }
 169
 170 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
 171   LLVM_DUMP_METHOD void dump() const { print(dbgs()); }
 172 #endif
 173 };
 174
 175 struct WasmCustomSection {
 176   const uint32_t INVALID_INDEX = -1;
 177
 178   StringRef Name;
 179   MCSectionWasm *Section;
 180
 181   uint32_t OutputContentsOffset;
 182   uint32_t OutputIndex;
 183
 184   WasmCustomSection(StringRef Name, MCSectionWasm *Section)
 185       : Name(Name), Section(Section), OutputContentsOffset(0),
 186         OutputIndex(INVALID_INDEX) {}
 187 };
 188
 189 #if !defined(NDEBUG)
 190 raw_ostream &operator<<(raw_ostream &OS, const WasmRelocationEntry &Rel) {
 191   Rel.print(OS);
 192   return OS;
 193 }
 194 #endif
 195
 196 class WasmObjectWriter : public MCObjectWriter {
 197   /// The target specific Wasm writer instance.
 198   std::unique_ptr<MCWasmObjectTargetWriter> TargetObjectWriter;
 199
 200   // Relocations for fixing up references in the code section.
 201   std::vector<WasmRelocationEntry> CodeRelocations;
 202   uint32_t CodeSectionIndex;
 203
 204   // Relocations for fixing up references in the data section.
 205   std::vector<WasmRelocationEntry> DataRelocations;
 206   uint32_t DataSectionIndex;
 207
 208   // Index values to use for fixing up call_indirect type indices.
 209   // Maps function symbols to the index of the type of the function
 210   DenseMap<const MCSymbolWasm *, uint32_t> TypeIndices;
 211   // Maps function symbols to the table element index space. Used
 212   // for TABLE_INDEX relocation types (i.e. address taken functions).
 213   DenseMap<const MCSymbolWasm *, uint32_t> TableIndices;
 214   // Maps function/global symbols to the (shared) Symbol index space.
 215   DenseMap<const MCSymbolWasm *, uint32_t> SymbolIndices;
 216   // Maps function/global symbols to the function/global Wasm index space.
 217   DenseMap<const MCSymbolWasm *, uint32_t> WasmIndices;
 218   // Maps data symbols to the Wasm segment and offset/size with the segment.
 219   DenseMap<const MCSymbolWasm *, wasm::WasmDataReference> DataLocations;
 220   // Maps section symbols to the section.
 221   DenseMap<const MCSymbolWasm *, const MCSectionWasm *> CustomSectionSymbols;
 222
 223   // Stores output data (index, relocations, content offset) for custom
 224   // section.
 225   std::vector<WasmCustomSection> CustomSections;
 226   // Relocations for fixing up references in the custom sections.
 227   DenseMap<const MCSectionWasm *, std::vector<WasmRelocationEntry>>
 228       CustomSectionsRelocations;
 229
 230   DenseMap<WasmFunctionType, int32_t, WasmFunctionTypeDenseMapInfo>
 231       FunctionTypeIndices;
 232   SmallVector<WasmFunctionType, 4> FunctionTypes;
 233   SmallVector<WasmGlobal, 4> Globals;
 234   SmallVector<WasmDataSegment, 4> DataSegments;
 235   unsigned NumFunctionImports = 0;
 236   unsigned NumGlobalImports = 0;
 237   uint32_t SectionCount = 0;
 238
 239   // TargetObjectWriter wrappers.
 240   bool is64Bit() const { return TargetObjectWriter->is64Bit(); }
 241   unsigned getRelocType(const MCValue &Target, const MCFixup &Fixup) const {
 242     return TargetObjectWriter->getRelocType(Target, Fixup);
 243   }
 244
 245   void startSection(SectionBookkeeping &Section, unsigned SectionId);
 246   void startCustomSection(SectionBookkeeping &Section, StringRef Name);
 247   void endSection(SectionBookkeeping &Section);
 248
 249 public:
 250   WasmObjectWriter(std::unique_ptr<MCWasmObjectTargetWriter> MOTW,
 251                    raw_pwrite_stream &OS)
 252       : MCObjectWriter(OS, /*IsLittleEndian=*/true),
 253         TargetObjectWriter(std::move(MOTW)) {}
 254
 255   ~WasmObjectWriter() override;
 256
 257 private:
 258   void reset() override {
 259     CodeRelocations.clear();
 260     DataRelocations.clear();
 261     TypeIndices.clear();
 262     SymbolIndices.clear();
 263     WasmIndices.clear();
 264     TableIndices.clear();
 265     DataLocations.clear();
 266     CustomSectionsRelocations.clear();
 267     FunctionTypeIndices.clear();
 268     FunctionTypes.clear();
 269     Globals.clear();
 270     DataSegments.clear();
 271     CustomSectionSymbols.clear();
 272     MCObjectWriter::reset();
 273     NumFunctionImports = 0;
 274     NumGlobalImports = 0;
 275   }
 276
 277   void writeHeader(const MCAssembler &Asm);
 278
 279   void recordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
 280                         const MCFragment *Fragment, const MCFixup &Fixup,
 281                         MCValue Target, uint64_t &FixedValue) override;
 282
 283   void executePostLayoutBinding(MCAssembler &Asm,
 284                                 const MCAsmLayout &Layout) override;
 285
 286   void writeObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
 287
 288   void writeString(const StringRef Str) {
 289     encodeULEB128(Str.size(), getStream());
 290     writeBytes(Str);
 291   }
 292
 293   void writeValueType(wasm::ValType Ty) {
 294     write8(static_cast<uint8_t>(Ty));
 295   }
 296
 297   void writeTypeSection(ArrayRef<WasmFunctionType> FunctionTypes);
 298   void writeImportSection(ArrayRef<wasm::WasmImport> Imports, uint32_t DataSize,
 299                           uint32_t NumElements);
 300   void writeFunctionSection(ArrayRef<WasmFunction> Functions);
 301   void writeGlobalSection();
 302   void writeExportSection(ArrayRef<wasm::WasmExport> Exports);
 303   void writeElemSection(ArrayRef<uint32_t> TableElems);
 304   void writeCodeSection(const MCAssembler &Asm, const MCAsmLayout &Layout,
 305                         ArrayRef<WasmFunction> Functions);
 306   void writeDataSection();
 307   void writeRelocSection(uint32_t SectionIndex, StringRef Name,
 308                          ArrayRef<WasmRelocationEntry> Relocations);
 309   void writeLinkingMetaDataSection(
 310       ArrayRef<wasm::WasmSymbolInfo> SymbolInfos,
 311       ArrayRef<std::pair<uint16_t, uint32_t>> InitFuncs,
 312       const std::map<StringRef, std::vector<WasmComdatEntry>> &Comdats);
 313   void writeCustomSections(const MCAssembler &Asm, const MCAsmLayout &Layout);
 314   void writeCustomRelocSections();
 315   void
 316   updateCustomSectionRelocations(const SmallVector<WasmFunction, 4> &Functions,
 317                                  const MCAsmLayout &Layout);
 318
 319   uint32_t getProvisionalValue(const WasmRelocationEntry &RelEntry);
 320   void applyRelocations(ArrayRef<WasmRelocationEntry> Relocations,
 321                         uint64_t ContentsOffset);
 322
 323   uint32_t getRelocationIndexValue(const WasmRelocationEntry &RelEntry);
 324   uint32_t getFunctionType(const MCSymbolWasm &Symbol);
 325   uint32_t registerFunctionType(const MCSymbolWasm &Symbol);
 326 };
 327
 328 } // end anonymous namespace
 329
 330 WasmObjectWriter::~WasmObjectWriter() {}
 331
 332 // Write out a section header and a patchable section size field.
 333 void WasmObjectWriter::startSection(SectionBookkeeping &Section,
 334                                     unsigned SectionId) {
 335   DEBUG(dbgs() << "startSection " << SectionId << "\n");
 336   write8(SectionId);
 337
 338   Section.SizeOffset = getStream().tell();
 339
 340   // The section size. We don't know the size yet, so reserve enough space
 341   // for any 32-bit value; we'll patch it later.
 342   encodeULEB128(UINT32_MAX, getStream());
 343
 344   // The position where the section starts, for measuring its size.
 345   Section.ContentsOffset = getStream().tell();
 346   Section.PayloadOffset = getStream().tell();
 347   Section.Index = SectionCount++;
 348 }
 349
 350 void WasmObjectWriter::startCustomSection(SectionBookkeeping &Section,
 351                                           StringRef Name) {
 352   DEBUG(dbgs() << "startCustomSection " << Name << "\n");
 353   startSection(Section, wasm::WASM_SEC_CUSTOM);
 354
 355   // The position where the section header ends, for measuring its size.
 356   Section.PayloadOffset = getStream().tell();
 357
 358   // Custom sections in wasm also have a string identifier.
 359   writeString(Name);
 360
 361   // The position where the custom section starts.
 362   Section.ContentsOffset = getStream().tell();
 363 }
 364
 365 // Now that the section is complete and we know how big it is, patch up the
 366 // section size field at the start of the section.
 367 void WasmObjectWriter::endSection(SectionBookkeeping &Section) {
 368   uint64_t Size = getStream().tell() - Section.PayloadOffset;
 369   if (uint32_t(Size) != Size)
 370     report_fatal_error("section size does not fit in a uint32_t");
 371
 372   DEBUG(dbgs() << "endSection size=" << Size << "\n");
 373
 374   // Write the final section size to the payload_len field, which follows
 375   // the section id byte.
 376   uint8_t Buffer[16];
 377   unsigned SizeLen = encodeULEB128(Size, Buffer, 5);
 378   assert(SizeLen == 5);
 379   getStream().pwrite((char *)Buffer, SizeLen, Section.SizeOffset);
 380 }
 381
 382 // Emit the Wasm header.
 383 void WasmObjectWriter::writeHeader(const MCAssembler &Asm) {
 384   writeBytes(StringRef(wasm::WasmMagic, sizeof(wasm::WasmMagic)));
 385   writeLE32(wasm::WasmVersion);
 386 }
 387
 388 void WasmObjectWriter::executePostLayoutBinding(MCAssembler &Asm,
 389                                                 const MCAsmLayout &Layout) {
 390 }
 391
 392 void WasmObjectWriter::recordRelocation(MCAssembler &Asm,
 393                                         const MCAsmLayout &Layout,
 394                                         const MCFragment *Fragment,
 395                                         const MCFixup &Fixup, MCValue Target,
 396                                         uint64_t &FixedValue) {
 397   MCAsmBackend &Backend = Asm.getBackend();
 398   bool IsPCRel = Backend.getFixupKindInfo(Fixup.getKind()).Flags &
 399                  MCFixupKindInfo::FKF_IsPCRel;
 400   const auto &FixupSection = cast<MCSectionWasm>(*Fragment->getParent());
 401   uint64_t C = Target.getConstant();
 402   uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
 403   MCContext &Ctx = Asm.getContext();
 404
 405   // The .init_array isn't translated as data, so don't do relocations in it.
 406   if (FixupSection.getSectionName().startswith(".init_array"))
 407     return;
 408
 409   // TODO: Add support for non-debug metadata sections?
 410   if (FixupSection.getKind().isMetadata() &&
 411       !FixupSection.getSectionName().startswith(".debug_"))
 412     return;
 413
 414   if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
 415     assert(RefB->getKind() == MCSymbolRefExpr::VK_None &&
 416            "Should not have constructed this");
 417
 418     // Let A, B and C being the components of Target and R be the location of
 419     // the fixup. If the fixup is not pcrel, we want to compute (A - B + C).
 420     // If it is pcrel, we want to compute (A - B + C - R).
 421
 422     // In general, Wasm has no relocations for -B. It can only represent (A + C)
 423     // or (A + C - R). If B = R + K and the relocation is not pcrel, we can
 424     // replace B to implement it: (A - R - K + C)
 425     if (IsPCRel) {
 426       Ctx.reportError(
 427           Fixup.getLoc(),
 428           "No relocation available to represent this relative expression");
 429       return;
 430     }
 431
 432     const auto &SymB = cast<MCSymbolWasm>(RefB->getSymbol());
 433
 434     if (SymB.isUndefined()) {
 435       Ctx.reportError(Fixup.getLoc(),
 436                       Twine("symbol '") + SymB.getName() +
 437                           "' can not be undefined in a subtraction expression");
 438       return;
 439     }
 440
 441     assert(!SymB.isAbsolute() && "Should have been folded");
 442     const MCSection &SecB = SymB.getSection();
 443     if (&SecB != &FixupSection) {
 444       Ctx.reportError(Fixup.getLoc(),
 445                       "Cannot represent a difference across sections");
 446       return;
 447     }
 448
 449     uint64_t SymBOffset = Layout.getSymbolOffset(SymB);
 450     uint64_t K = SymBOffset - FixupOffset;
 451     IsPCRel = true;
 452     C -= K;
 453   }
 454
 455   // We either rejected the fixup or folded B into C at this point.
 456   const MCSymbolRefExpr *RefA = Target.getSymA();
 457   const auto *SymA = RefA ? cast<MCSymbolWasm>(&RefA->getSymbol()) : nullptr;
 458
 459   if (SymA && SymA->isVariable()) {
 460     const MCExpr *Expr = SymA->getVariableValue();
 461     const auto *Inner = cast<MCSymbolRefExpr>(Expr);
 462     if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF)
 463       llvm_unreachable("weakref used in reloc not yet implemented");
 464   }
 465
 466   // Put any constant offset in an addend. Offsets can be negative, and
 467   // LLVM expects wrapping, in contrast to wasm's immediates which can't
 468   // be negative and don't wrap.
 469   FixedValue = 0;
 470
 471   if (SymA)
 472     SymA->setUsedInReloc();
 473
 474   assert(!IsPCRel);
 475   assert(SymA);
 476
 477   unsigned Type = getRelocType(Target, Fixup);
 478
 479   WasmRelocationEntry Rec(FixupOffset, SymA, C, Type, &FixupSection);
 480   DEBUG(dbgs() << "WasmReloc: " << Rec << "\n");
 481
 482   // Relocation other than R_WEBASSEMBLY_TYPE_INDEX_LEB,
 483   // R_WEBASSEMBLY_SECTION_OFFSET_I32 or R_WEBASSEMBLY_FUNCTION_OFFSET_I32
 484   // are currently required to be against a named symbol.
 485   // TODO(sbc): Add support for relocations against unnamed temporaries such
 486   // as those generated by llvm's `blockaddress`.
 487   // See: test/MC/WebAssembly/blockaddress.ll
 488   if (SymA->getName().empty() &&
 489       !(Type == wasm::R_WEBASSEMBLY_TYPE_INDEX_LEB ||
 490         Type == wasm::R_WEBASSEMBLY_FUNCTION_OFFSET_I32 ||
 491         Type == wasm::R_WEBASSEMBLY_SECTION_OFFSET_I32))
 492     report_fatal_error("relocations against un-named temporaries are not yet "
 493                        "supported by wasm");
 494
 495   if (FixupSection.isWasmData()) {
 496     DataRelocations.push_back(Rec);
 497   } else if (FixupSection.getKind().isText()) {
 498     CodeRelocations.push_back(Rec);
 499   } else if (FixupSection.getKind().isMetadata()) {
 500     assert(FixupSection.getSectionName().startswith(".debug_"));
 501     CustomSectionsRelocations[&FixupSection].push_back(Rec);
 502   } else {
 503     llvm_unreachable("unexpected section type");
 504   }
 505 }
 506
 507 // Write X as an (unsigned) LEB value at offset Offset in Stream, padded
 508 // to allow patching.
 509 static void
 510 WritePatchableLEB(raw_pwrite_stream &Stream, uint32_t X, uint64_t Offset) {
 511   uint8_t Buffer[5];
 512   unsigned SizeLen = encodeULEB128(X, Buffer, 5);
 513   assert(SizeLen == 5);
 514   Stream.pwrite((char *)Buffer, SizeLen, Offset);
 515 }
 516
 517 // Write X as an signed LEB value at offset Offset in Stream, padded
 518 // to allow patching.
 519 static void
 520 WritePatchableSLEB(raw_pwrite_stream &Stream, int32_t X, uint64_t Offset) {
 521   uint8_t Buffer[5];
 522   unsigned SizeLen = encodeSLEB128(X, Buffer, 5);
 523   assert(SizeLen == 5);
 524   Stream.pwrite((char *)Buffer, SizeLen, Offset);
 525 }
 526
 527 // Write X as a plain integer value at offset Offset in Stream.
 528 static void WriteI32(raw_pwrite_stream &Stream, uint32_t X, uint64_t Offset) {
 529   uint8_t Buffer[4];
 530   support::endian::write32le(Buffer, X);
 531   Stream.pwrite((char *)Buffer, sizeof(Buffer), Offset);
 532 }
 533
 534 static const MCSymbolWasm* ResolveSymbol(const MCSymbolWasm& Symbol) {
 535   if (Symbol.isVariable()) {
 536     const MCExpr *Expr = Symbol.getVariableValue();
 537     auto *Inner = cast<MCSymbolRefExpr>(Expr);
 538     return cast<MCSymbolWasm>(&Inner->getSymbol());
 539   }
 540   return &Symbol;
 541 }
 542
 543 // Compute a value to write into the code at the location covered
 544 // by RelEntry. This value isn't used by the static linker; it just serves
 545 // to make the object format more readable and more likely to be directly
 546 // useable.
 547 uint32_t
 548 WasmObjectWriter::getProvisionalValue(const WasmRelocationEntry &RelEntry) {
 549   switch (RelEntry.Type) {
 550   case wasm::R_WEBASSEMBLY_TABLE_INDEX_SLEB:
 551   case wasm::R_WEBASSEMBLY_TABLE_INDEX_I32: {
 552     // Provisional value is table address of the resolved symbol itself
 553     const MCSymbolWasm *Sym = ResolveSymbol(*RelEntry.Symbol);
 554     assert(Sym->isFunction());
 555     return TableIndices[Sym];
 556   }
 557   case wasm::R_WEBASSEMBLY_TYPE_INDEX_LEB:
 558     // Provisional value is same as the index
 559     return getRelocationIndexValue(RelEntry);
 560   case wasm::R_WEBASSEMBLY_FUNCTION_INDEX_LEB:
 561   case wasm::R_WEBASSEMBLY_GLOBAL_INDEX_LEB:
 562     // Provisional value is function/global Wasm index
 563     if (!WasmIndices.count(RelEntry.Symbol))
 564       report_fatal_error("symbol not found in wasm index space: " +
 565                          RelEntry.Symbol->getName());
 566     return WasmIndices[RelEntry.Symbol];
 567   case wasm::R_WEBASSEMBLY_FUNCTION_OFFSET_I32: {
 568     const auto &Section =
 569         static_cast<const MCSectionWasm &>(RelEntry.Symbol->getSection());
 570     return Section.getSectionOffset() + RelEntry.Addend;
 571   }
 572   case wasm::R_WEBASSEMBLY_SECTION_OFFSET_I32: {
 573     const auto &Section = *CustomSectionSymbols.find(RelEntry.Symbol)->second;
 574     return Section.getSectionOffset() + RelEntry.Addend;
 575   }
 576   case wasm::R_WEBASSEMBLY_MEMORY_ADDR_LEB:
 577   case wasm::R_WEBASSEMBLY_MEMORY_ADDR_I32:
 578   case wasm::R_WEBASSEMBLY_MEMORY_ADDR_SLEB: {
 579     // Provisional value is address of the global
 580     const MCSymbolWasm *Sym = ResolveSymbol(*RelEntry.Symbol);
 581     // For undefined symbols, use zero
 582     if (!Sym->isDefined())
 583       return 0;
 584     const wasm::WasmDataReference &Ref = DataLocations[Sym];
 585     const WasmDataSegment &Segment = DataSegments[Ref.Segment];
 586     // Ignore overflow. LLVM allows address arithmetic to silently wrap.
 587     return Segment.Offset + Ref.Offset + RelEntry.Addend;
 588   }
 589   default:
 590     llvm_unreachable("invalid relocation type");
 591   }
 592 }
 593
 594 static void addData(SmallVectorImpl<char> &DataBytes,
 595                     MCSectionWasm &DataSection) {
 596   DEBUG(errs() << "addData: " << DataSection.getSectionName() << "\n");
 597
 598   DataBytes.resize(alignTo(DataBytes.size(), DataSection.getAlignment()));
 599
 600   for (const MCFragment &Frag : DataSection) {
 601     if (Frag.hasInstructions())
 602       report_fatal_error("only data supported in data sections");
 603
 604     if (auto *Align = dyn_cast<MCAlignFragment>(&Frag)) {
 605       if (Align->getValueSize() != 1)
 606         report_fatal_error("only byte values supported for alignment");
 607       // If nops are requested, use zeros, as this is the data section.
 608       uint8_t Value = Align->hasEmitNops() ? 0 : Align->getValue();
 609       uint64_t Size = std::min<uint64_t>(alignTo(DataBytes.size(),
 610                                                  Align->getAlignment()),
 611                                          DataBytes.size() +
 612                                              Align->getMaxBytesToEmit());
 613       DataBytes.resize(Size, Value);
 614     } else if (auto *Fill = dyn_cast<MCFillFragment>(&Frag)) {
 615       int64_t Size;
 616       if (!Fill->getSize().evaluateAsAbsolute(Size))
 617         llvm_unreachable("The fill should be an assembler constant");
 618       DataBytes.insert(DataBytes.end(), Size, Fill->getValue());
 619     } else {
 620       const auto &DataFrag = cast<MCDataFragment>(Frag);
 621       const SmallVectorImpl<char> &Contents = DataFrag.getContents();
 622
 623       DataBytes.insert(DataBytes.end(), Contents.begin(), Contents.end());
 624     }
 625   }
 626
 627   DEBUG(dbgs() << "addData -> " << DataBytes.size() << "\n");
 628 }
 629
 630 uint32_t
 631 WasmObjectWriter::getRelocationIndexValue(const WasmRelocationEntry &RelEntry) {
 632   if (RelEntry.Type == wasm::R_WEBASSEMBLY_TYPE_INDEX_LEB) {
 633     if (!TypeIndices.count(RelEntry.Symbol))
 634       report_fatal_error("symbol not found in type index space: " +
 635                          RelEntry.Symbol->getName());
 636     return TypeIndices[RelEntry.Symbol];
 637   }
 638
 639   if (!SymbolIndices.count(RelEntry.Symbol))
 640     report_fatal_error("symbol not found in symbol index space: " +
 641                        RelEntry.Symbol->getName());
 642   return SymbolIndices[RelEntry.Symbol];
 643 }
 644
 645 // Apply the portions of the relocation records that we can handle ourselves
 646 // directly.
 647 void WasmObjectWriter::applyRelocations(
 648     ArrayRef<WasmRelocationEntry> Relocations, uint64_t ContentsOffset) {
 649   raw_pwrite_stream &Stream = getStream();
 650   for (const WasmRelocationEntry &RelEntry : Relocations) {
 651     uint64_t Offset = ContentsOffset +
 652                       RelEntry.FixupSection->getSectionOffset() +
 653                       RelEntry.Offset;
 654
 655     DEBUG(dbgs() << "applyRelocation: " << RelEntry << "\n");
 656     uint32_t Value = getProvisionalValue(RelEntry);
 657
 658     switch (RelEntry.Type) {
 659     case wasm::R_WEBASSEMBLY_FUNCTION_INDEX_LEB:
 660     case wasm::R_WEBASSEMBLY_TYPE_INDEX_LEB:
 661     case wasm::R_WEBASSEMBLY_GLOBAL_INDEX_LEB:
 662     case wasm::R_WEBASSEMBLY_MEMORY_ADDR_LEB:
 663       WritePatchableLEB(Stream, Value, Offset);
 664       break;
 665     case wasm::R_WEBASSEMBLY_TABLE_INDEX_I32:
 666     case wasm::R_WEBASSEMBLY_MEMORY_ADDR_I32:
 667     case wasm::R_WEBASSEMBLY_FUNCTION_OFFSET_I32:
 668     case wasm::R_WEBASSEMBLY_SECTION_OFFSET_I32:
 669       WriteI32(Stream, Value, Offset);
 670       break;
 671     case wasm::R_WEBASSEMBLY_TABLE_INDEX_SLEB:
 672     case wasm::R_WEBASSEMBLY_MEMORY_ADDR_SLEB:
 673       WritePatchableSLEB(Stream, Value, Offset);
 674       break;
 675     default:
 676       llvm_unreachable("invalid relocation type");
 677     }
 678   }
 679 }
 680
 681 void WasmObjectWriter::writeTypeSection(
 682     ArrayRef<WasmFunctionType> FunctionTypes) {
 683   if (FunctionTypes.empty())
 684     return;
 685
 686   SectionBookkeeping Section;
 687   startSection(Section, wasm::WASM_SEC_TYPE);
 688
 689   encodeULEB128(FunctionTypes.size(), getStream());
 690
 691   for (const WasmFunctionType &FuncTy : FunctionTypes) {
 692     write8(wasm::WASM_TYPE_FUNC);
 693     encodeULEB128(FuncTy.Params.size(), getStream());
 694     for (wasm::ValType Ty : FuncTy.Params)
 695       writeValueType(Ty);
 696     encodeULEB128(FuncTy.Returns.size(), getStream());
 697     for (wasm::ValType Ty : FuncTy.Returns)
 698       writeValueType(Ty);
 699   }
 700
 701   endSection(Section);
 702 }
 703
 704 void WasmObjectWriter::writeImportSection(ArrayRef<wasm::WasmImport> Imports,
 705                                           uint32_t DataSize,
 706                                           uint32_t NumElements) {
 707   if (Imports.empty())
 708     return;
 709
 710   uint32_t NumPages = (DataSize + wasm::WasmPageSize - 1) / wasm::WasmPageSize;
 711
 712   SectionBookkeeping Section;
 713   startSection(Section, wasm::WASM_SEC_IMPORT);
 714
 715   encodeULEB128(Imports.size(), getStream());
 716   for (const wasm::WasmImport &Import : Imports) {
 717     writeString(Import.Module);
 718     writeString(Import.Field);
 719     write8(Import.Kind);
 720
 721     switch (Import.Kind) {
 722     case wasm::WASM_EXTERNAL_FUNCTION:
 723       encodeULEB128(Import.SigIndex, getStream());
 724       break;
 725     case wasm::WASM_EXTERNAL_GLOBAL:
 726       write8(Import.Global.Type);
 727       write8(Import.Global.Mutable ? 1 : 0);
 728       break;
 729     case wasm::WASM_EXTERNAL_MEMORY:
 730       encodeULEB128(0, getStream()); // flags
 731       encodeULEB128(NumPages, getStream()); // initial
 732       break;
 733     case wasm::WASM_EXTERNAL_TABLE:
 734       write8(Import.Table.ElemType);
 735       encodeULEB128(0, getStream()); // flags
 736       encodeULEB128(NumElements, getStream()); // initial
 737       break;
 738     default:
 739       llvm_unreachable("unsupported import kind");
 740     }
 741   }
 742
 743   endSection(Section);
 744 }
 745
 746 void WasmObjectWriter::writeFunctionSection(ArrayRef<WasmFunction> Functions) {
 747   if (Functions.empty())
 748     return;
 749
 750   SectionBookkeeping Section;
 751   startSection(Section, wasm::WASM_SEC_FUNCTION);
 752
 753   encodeULEB128(Functions.size(), getStream());
 754   for (const WasmFunction &Func : Functions)
 755     encodeULEB128(Func.Type, getStream());
 756
 757   endSection(Section);
 758 }
 759
 760 void WasmObjectWriter::writeGlobalSection() {
 761   if (Globals.empty())
 762     return;
 763
 764   SectionBookkeeping Section;
 765   startSection(Section, wasm::WASM_SEC_GLOBAL);
 766
 767   encodeULEB128(Globals.size(), getStream());
 768   for (const WasmGlobal &Global : Globals) {
 769     writeValueType(static_cast<wasm::ValType>(Global.Type.Type));
 770     write8(Global.Type.Mutable);
 771
 772     write8(wasm::WASM_OPCODE_I32_CONST);
 773     encodeSLEB128(Global.InitialValue, getStream());
 774     write8(wasm::WASM_OPCODE_END);
 775   }
 776
 777   endSection(Section);
 778 }
 779
 780 void WasmObjectWriter::writeExportSection(ArrayRef<wasm::WasmExport> Exports) {
 781   if (Exports.empty())
 782     return;
 783
 784   SectionBookkeeping Section;
 785   startSection(Section, wasm::WASM_SEC_EXPORT);
 786
 787   encodeULEB128(Exports.size(), getStream());
 788   for (const wasm::WasmExport &Export : Exports) {
 789     writeString(Export.Name);
 790     write8(Export.Kind);
 791     encodeULEB128(Export.Index, getStream());
 792   }
 793
 794   endSection(Section);
 795 }
 796
 797 void WasmObjectWriter::writeElemSection(ArrayRef<uint32_t> TableElems) {
 798   if (TableElems.empty())
 799     return;
 800
 801   SectionBookkeeping Section;
 802   startSection(Section, wasm::WASM_SEC_ELEM);
 803
 804   encodeULEB128(1, getStream()); // number of "segments"
 805   encodeULEB128(0, getStream()); // the table index
 806
 807   // init expr for starting offset
 808   write8(wasm::WASM_OPCODE_I32_CONST);
 809   encodeSLEB128(kInitialTableOffset, getStream());
 810   write8(wasm::WASM_OPCODE_END);
 811
 812   encodeULEB128(TableElems.size(), getStream());
 813   for (uint32_t Elem : TableElems)
 814     encodeULEB128(Elem, getStream());
 815
 816   endSection(Section);
 817 }
 818
 819 void WasmObjectWriter::writeCodeSection(const MCAssembler &Asm,
 820                                         const MCAsmLayout &Layout,
 821                                         ArrayRef<WasmFunction> Functions) {
 822   if (Functions.empty())
 823     return;
 824
 825   SectionBookkeeping Section;
 826   startSection(Section, wasm::WASM_SEC_CODE);
 827   CodeSectionIndex = Section.Index;
 828
 829   encodeULEB128(Functions.size(), getStream());
 830
 831   for (const WasmFunction &Func : Functions) {
 832     auto &FuncSection = static_cast<MCSectionWasm &>(Func.Sym->getSection());
 833
 834     int64_t Size = 0;
 835     if (!Func.Sym->getSize()->evaluateAsAbsolute(Size, Layout))
 836       report_fatal_error(".size expression must be evaluatable");
 837
 838     encodeULEB128(Size, getStream());
 839     FuncSection.setSectionOffset(getStream().tell() - Section.ContentsOffset);
 840     Asm.writeSectionData(&FuncSection, Layout);
 841   }
 842
 843   // Apply fixups.
 844   applyRelocations(CodeRelocations, Section.ContentsOffset);
 845
 846   endSection(Section);
 847 }
 848
 849 void WasmObjectWriter::writeDataSection() {
 850   if (DataSegments.empty())
 851     return;
 852
 853   SectionBookkeeping Section;
 854   startSection(Section, wasm::WASM_SEC_DATA);
 855   DataSectionIndex = Section.Index;
 856
 857   encodeULEB128(DataSegments.size(), getStream()); // count
 858
 859   for (const WasmDataSegment &Segment : DataSegments) {
 860     encodeULEB128(0, getStream()); // memory index
 861     write8(wasm::WASM_OPCODE_I32_CONST);
 862     encodeSLEB128(Segment.Offset, getStream()); // offset
 863     write8(wasm::WASM_OPCODE_END);
 864     encodeULEB128(Segment.Data.size(), getStream()); // size
 865     Segment.Section->setSectionOffset(getStream().tell() - Section.ContentsOffset);
 866     writeBytes(Segment.Data); // data
 867   }
 868
 869   // Apply fixups.
 870   applyRelocations(DataRelocations, Section.ContentsOffset);
 871
 872   endSection(Section);
 873 }
 874
 875 void WasmObjectWriter::writeRelocSection(
 876     uint32_t SectionIndex, StringRef Name,
 877     ArrayRef<WasmRelocationEntry> Relocations) {
 878   // See: https://github.com/WebAssembly/tool-conventions/blob/master/Linking.md
 879   // for descriptions of the reloc sections.
 880
 881   if (Relocations.empty())
 882     return;
 883
 884   SectionBookkeeping Section;
 885   startCustomSection(Section, std::string("reloc.") + Name.str());
 886
 887   raw_pwrite_stream &Stream = getStream();
 888
 889   encodeULEB128(SectionIndex, Stream);
 890   encodeULEB128(Relocations.size(), Stream);
 891   for (const WasmRelocationEntry& RelEntry : Relocations) {
 892     uint64_t Offset = RelEntry.Offset +
 893                       RelEntry.FixupSection->getSectionOffset();
 894     uint32_t Index = getRelocationIndexValue(RelEntry);
 895
 896     write8(RelEntry.Type);
 897     encodeULEB128(Offset, Stream);
 898     encodeULEB128(Index, Stream);
 899     if (RelEntry.hasAddend())
 900       encodeSLEB128(RelEntry.Addend, Stream);
 901   }
 902
 903   endSection(Section);
 904 }
 905
 906 void WasmObjectWriter::writeCustomRelocSections() {
 907   for (const auto &Sec : CustomSections) {
 908     auto &Relocations = CustomSectionsRelocations[Sec.Section];
 909     writeRelocSection(Sec.OutputIndex, Sec.Name, Relocations);
 910   }
 911 }
 912
 913 void WasmObjectWriter::writeLinkingMetaDataSection(
 914     ArrayRef<wasm::WasmSymbolInfo> SymbolInfos,
 915     ArrayRef<std::pair<uint16_t, uint32_t>> InitFuncs,
 916     const std::map<StringRef, std::vector<WasmComdatEntry>> &Comdats) {
 917   SectionBookkeeping Section;
 918   startCustomSection(Section, "linking");
 919   encodeULEB128(wasm::WasmMetadataVersion, getStream());
 920
 921   SectionBookkeeping SubSection;
 922   if (SymbolInfos.size() != 0) {
 923     startSection(SubSection, wasm::WASM_SYMBOL_TABLE);
 924     encodeULEB128(SymbolInfos.size(), getStream());
 925     for (const wasm::WasmSymbolInfo &Sym : SymbolInfos) {
 926       encodeULEB128(Sym.Kind, getStream());
 927       encodeULEB128(Sym.Flags, getStream());
 928       switch (Sym.Kind) {
 929       case wasm::WASM_SYMBOL_TYPE_FUNCTION:
 930       case wasm::WASM_SYMBOL_TYPE_GLOBAL:
 931         encodeULEB128(Sym.ElementIndex, getStream());
 932         if ((Sym.Flags & wasm::WASM_SYMBOL_UNDEFINED) == 0)
 933           writeString(Sym.Name);
 934         break;
 935       case wasm::WASM_SYMBOL_TYPE_DATA:
 936         writeString(Sym.Name);
 937         if ((Sym.Flags & wasm::WASM_SYMBOL_UNDEFINED) == 0) {
 938           encodeULEB128(Sym.DataRef.Segment, getStream());
 939           encodeULEB128(Sym.DataRef.Offset, getStream());
 940           encodeULEB128(Sym.DataRef.Size, getStream());
 941         }
 942         break;
 943       case wasm::WASM_SYMBOL_TYPE_SECTION: {
 944         const uint32_t SectionIndex =
 945             CustomSections[Sym.ElementIndex].OutputIndex;
 946         encodeULEB128(SectionIndex, getStream());
 947         break;
 948       }
 949       default:
 950         llvm_unreachable("unexpected kind");
 951       }
 952     }
 953     endSection(SubSection);
 954   }
 955
 956   if (DataSegments.size()) {
 957     startSection(SubSection, wasm::WASM_SEGMENT_INFO);
 958     encodeULEB128(DataSegments.size(), getStream());
 959     for (const WasmDataSegment &Segment : DataSegments) {
 960       writeString(Segment.Name);
 961       encodeULEB128(Segment.Alignment, getStream());
 962       encodeULEB128(Segment.Flags, getStream());
 963     }
 964     endSection(SubSection);
 965   }
 966
 967   if (!InitFuncs.empty()) {
 968     startSection(SubSection, wasm::WASM_INIT_FUNCS);
 969     encodeULEB128(InitFuncs.size(), getStream());
 970     for (auto &StartFunc : InitFuncs) {
 971       encodeULEB128(StartFunc.first, getStream()); // priority
 972       encodeULEB128(StartFunc.second, getStream()); // function index
 973     }
 974     endSection(SubSection);
 975   }
 976
 977   if (Comdats.size()) {
 978     startSection(SubSection, wasm::WASM_COMDAT_INFO);
 979     encodeULEB128(Comdats.size(), getStream());
 980     for (const auto &C : Comdats) {
 981       writeString(C.first);
 982       encodeULEB128(0, getStream()); // flags for future use
 983       encodeULEB128(C.second.size(), getStream());
 984       for (const WasmComdatEntry &Entry : C.second) {
 985         encodeULEB128(Entry.Kind, getStream());
 986         encodeULEB128(Entry.Index, getStream());
 987       }
 988     }
 989     endSection(SubSection);
 990   }
 991
 992   endSection(Section);
 993 }
 994
 995 void WasmObjectWriter::writeCustomSections(const MCAssembler &Asm,
 996                                            const MCAsmLayout &Layout) {
 997   for (auto &CustomSection : CustomSections) {
 998     SectionBookkeeping Section;
 999     auto *Sec = CustomSection.Section;
1000     startCustomSection(Section, CustomSection.Name);
1001
1002     Sec->setSectionOffset(getStream().tell() - Section.ContentsOffset);
1003     Asm.writeSectionData(Sec, Layout);
1004
1005     CustomSection.OutputContentsOffset = Section.ContentsOffset;
1006     CustomSection.OutputIndex = Section.Index;
1007
1008     endSection(Section);
1009   }
1010 }
1011
1012 void WasmObjectWriter::updateCustomSectionRelocations(
1013     const SmallVector<WasmFunction, 4> &Functions, const MCAsmLayout &Layout) {
1014   std::map<const MCSection *, const MCSymbolWasm *> SectionSymbols;
1015   for (const auto &P : CustomSectionSymbols)
1016     SectionSymbols[P.second] = P.first;
1017   std::map<const MCSection *, const MCSymbolWasm *> FuncSymbols;
1018   for (const auto &FuncInfo : Functions)
1019     FuncSymbols[&FuncInfo.Sym->getSection()] = FuncInfo.Sym;
1020
1021   // Patch relocation records for R_WEBASSEMBLY_FUNCTION_OFFSET_I32 and
1022   // R_WEBASSEMBLY_SECTION_OFFSET_I32. The Addend is stuffed the offset from
1023   // the beginning of the function or custom section -- all such relocations
1024   // target the function or custom section starts.
1025   for (auto &Section : CustomSections) {
1026     auto &Relocations = CustomSectionsRelocations[Section.Section];
1027     for (WasmRelocationEntry &RelEntry : Relocations) {
1028       switch (RelEntry.Type) {
1029       case wasm::R_WEBASSEMBLY_FUNCTION_OFFSET_I32: {
1030         assert(RelEntry.hasAddend());
1031         auto &Section =
1032             static_cast<MCSectionWasm &>(RelEntry.Symbol->getSection());
1033         RelEntry.Addend += Layout.getSymbolOffset(*RelEntry.Symbol);
1034         RelEntry.Symbol = FuncSymbols[&Section];
1035         break;
1036       }
1037       case wasm::R_WEBASSEMBLY_SECTION_OFFSET_I32: {
1038         assert(RelEntry.hasAddend());
1039         auto &Section =
1040             static_cast<MCSectionWasm &>(RelEntry.Symbol->getSection());
1041         RelEntry.Addend += Layout.getSymbolOffset(*RelEntry.Symbol);
1042         RelEntry.Symbol = SectionSymbols[&Section];
1043         break;
1044       }
1045       default:
1046         break;
1047       }
1048     }
1049
1050     // Apply fixups.
1051     applyRelocations(Relocations, Section.OutputContentsOffset);
1052   }
1053 }
1054
1055 uint32_t WasmObjectWriter::getFunctionType(const MCSymbolWasm& Symbol) {
1056   assert(Symbol.isFunction());
1057   assert(TypeIndices.count(&Symbol));
1058   return TypeIndices[&Symbol];
1059 }
1060
1061 uint32_t WasmObjectWriter::registerFunctionType(const MCSymbolWasm& Symbol) {
1062   assert(Symbol.isFunction());
1063
1064   WasmFunctionType F;
1065   const MCSymbolWasm* ResolvedSym = ResolveSymbol(Symbol);
1066   F.Returns = ResolvedSym->getReturns();
1067   F.Params = ResolvedSym->getParams();
1068
1069   auto Pair =
1070       FunctionTypeIndices.insert(std::make_pair(F, FunctionTypes.size()));
1071   if (Pair.second)
1072     FunctionTypes.push_back(F);
1073   TypeIndices[&Symbol] = Pair.first->second;
1074
1075   DEBUG(dbgs() << "registerFunctionType: " << Symbol << " new:" << Pair.second << "\n");
1076   DEBUG(dbgs() << "  -> type index: " << Pair.first->second << "\n");
1077   return Pair.first->second;
1078 }
1079
1080 void WasmObjectWriter::writeObject(MCAssembler &Asm,
1081                                    const MCAsmLayout &Layout) {
1082   DEBUG(dbgs() << "WasmObjectWriter::writeObject\n");
1083   MCContext &Ctx = Asm.getContext();
1084
1085   // Collect information from the available symbols.
1086   SmallVector<WasmFunction, 4> Functions;
1087   SmallVector<uint32_t, 4> TableElems;
1088   SmallVector<wasm::WasmImport, 4> Imports;
1089   SmallVector<wasm::WasmExport, 4> Exports;
1090   SmallVector<wasm::WasmSymbolInfo, 4> SymbolInfos;
1091   SmallVector<std::pair<uint16_t, uint32_t>, 2> InitFuncs;
1092   std::map<StringRef, std::vector<WasmComdatEntry>> Comdats;
1093   uint32_t DataSize = 0;
1094
1095   // For now, always emit the memory import, since loads and stores are not
1096   // valid without it. In the future, we could perhaps be more clever and omit
1097   // it if there are no loads or stores.
1098   MCSymbolWasm *MemorySym =
1099       cast<MCSymbolWasm>(Ctx.getOrCreateSymbol("__linear_memory"));
1100   wasm::WasmImport MemImport;
1101   MemImport.Module = MemorySym->getModuleName();
1102   MemImport.Field = MemorySym->getName();
1103   MemImport.Kind = wasm::WASM_EXTERNAL_MEMORY;
1104   Imports.push_back(MemImport);
1105
1106   // For now, always emit the table section, since indirect calls are not
1107   // valid without it. In the future, we could perhaps be more clever and omit
1108   // it if there are no indirect calls.
1109   MCSymbolWasm *TableSym =
1110       cast<MCSymbolWasm>(Ctx.getOrCreateSymbol("__indirect_function_table"));
1111   wasm::WasmImport TableImport;
1112   TableImport.Module = TableSym->getModuleName();
1113   TableImport.Field = TableSym->getName();
1114   TableImport.Kind = wasm::WASM_EXTERNAL_TABLE;
1115   TableImport.Table.ElemType = wasm::WASM_TYPE_ANYFUNC;
1116   Imports.push_back(TableImport);
1117
1118   // Populate FunctionTypeIndices, and Imports and WasmIndices for undefined
1119   // symbols.  This must be done before populating WasmIndices for defined
1120   // symbols.
1121   for (const MCSymbol &S : Asm.symbols()) {
1122     const auto &WS = static_cast<const MCSymbolWasm &>(S);
1123
1124     // Register types for all functions, including those with private linkage
1125     // (because wasm always needs a type signature).
1126     if (WS.isFunction())
1127       registerFunctionType(WS);
1128
1129     if (WS.isTemporary())
1130       continue;
1131
1132     // If the symbol is not defined in this translation unit, import it.
1133     if (!WS.isDefined() && !WS.isComdat()) {
1134       if (WS.isFunction()) {
1135         wasm::WasmImport Import;
1136         Import.Module = WS.getModuleName();
1137         Import.Field = WS.getName();
1138         Import.Kind = wasm::WASM_EXTERNAL_FUNCTION;
1139         Import.SigIndex = getFunctionType(WS);
1140         Imports.push_back(Import);
1141         WasmIndices[&WS] = NumFunctionImports++;
1142       } else if (WS.isGlobal()) {
1143         if (WS.isWeak())
1144           report_fatal_error("undefined global symbol cannot be weak");
1145
1146         wasm::WasmImport Import;
1147         Import.Module = WS.getModuleName();
1148         Import.Field = WS.getName();
1149         Import.Kind = wasm::WASM_EXTERNAL_GLOBAL;
1150         Import.Global = WS.getGlobalType();
1151         Imports.push_back(Import);
1152         WasmIndices[&WS] = NumGlobalImports++;
1153       }
1154     }
1155   }
1156
1157   // Populate DataSegments, which must be done before populating DataLocations.
1158   for (MCSection &Sec : Asm) {
1159     auto &Section = static_cast<MCSectionWasm &>(Sec);
1160
1161     if (Section.getSectionName().startswith(".custom_section.")) {
1162       if (Section.getFragmentList().empty())
1163         continue;
1164       if (Section.getFragmentList().size() != 1)
1165         report_fatal_error(
1166             "only one .custom_section section fragment supported");
1167       const MCFragment &Frag = *Section.begin();
1168       if (Frag.hasInstructions() || Frag.getKind() != MCFragment::FT_Data)
1169         report_fatal_error("only data supported in .custom_section section");
1170       const auto &DataFrag = cast<MCDataFragment>(Frag);
1171       if (!DataFrag.getFixups().empty())
1172         report_fatal_error("fixups not supported in .custom_section section");
1173       StringRef UserName = Section.getSectionName().substr(16);
1174       CustomSections.emplace_back(UserName, &Section);
1175       continue;
1176     }
1177
1178     if (!Section.isWasmData())
1179       continue;
1180
1181     // .init_array sections are handled specially elsewhere.
1182     if (cast<MCSectionWasm>(Sec).getSectionName().startswith(".init_array"))
1183       continue;
1184
1185     uint32_t SegmentIndex = DataSegments.size();
1186     DataSize = alignTo(DataSize, Section.getAlignment());
1187     DataSegments.emplace_back();
1188     WasmDataSegment &Segment = DataSegments.back();
1189     Segment.Name = Section.getSectionName();
1190     Segment.Offset = DataSize;
1191     Segment.Section = &Section;
1192     addData(Segment.Data, Section);
1193     Segment.Alignment = Section.getAlignment();
1194     Segment.Flags = 0;
1195     DataSize += Segment.Data.size();
1196     Section.setSegmentIndex(SegmentIndex);
1197
1198     if (const MCSymbolWasm *C = Section.getGroup()) {
1199       Comdats[C->getName()].emplace_back(
1200           WasmComdatEntry{wasm::WASM_COMDAT_DATA, SegmentIndex});
1201     }
1202   }
1203
1204   // Create symbols for debug/custom sections.
1205   for (MCSection &Sec : Asm) {
1206     auto &DebugSection = static_cast<MCSectionWasm &>(Sec);
1207     StringRef SectionName = DebugSection.getSectionName();
1208
1209     // TODO: Add support for non-debug metadata sections?
1210     if (!Sec.getKind().isMetadata() || !SectionName.startswith(".debug_"))
1211       continue;
1212
1213     uint32_t ElementIndex = CustomSections.size();
1214     CustomSections.emplace_back(SectionName, &DebugSection);
1215
1216     MCSymbolWasm *SectionSym =
1217         cast<MCSymbolWasm>(Ctx.getOrCreateSymbol(SectionName));
1218     CustomSectionSymbols[SectionSym] = &DebugSection;
1219
1220     wasm::WasmSymbolInfo Info;
1221     Info.Name = SectionSym->getName();
1222     Info.Kind = wasm::WASM_SYMBOL_TYPE_SECTION;
1223     Info.Flags = wasm::WASM_SYMBOL_BINDING_LOCAL;
1224     Info.ElementIndex = ElementIndex;
1225     SymbolIndices[SectionSym] = SymbolInfos.size();
1226     SymbolInfos.emplace_back(Info);
1227   }
1228
1229   // Populate WasmIndices and DataLocations for defined symbols.
1230   for (const MCSymbol &S : Asm.symbols()) {
1231     // Ignore unnamed temporary symbols, which aren't ever exported, imported,
1232     // or used in relocations.
1233     if (S.isTemporary() && S.getName().empty())
1234       continue;
1235
1236     const auto &WS = static_cast<const MCSymbolWasm &>(S);
1237     DEBUG(dbgs() << "MCSymbol: '" << S << "'"
1238                  << " isDefined=" << S.isDefined()
1239                  << " isExternal=" << S.isExternal()
1240                  << " isTemporary=" << S.isTemporary()
1241                  << " isFunction=" << WS.isFunction()
1242                  << " isWeak=" << WS.isWeak()
1243                  << " isHidden=" << WS.isHidden()
1244                  << " isVariable=" << WS.isVariable() << "\n");
1245
1246     if (WS.isVariable())
1247       continue;
1248     if (WS.isComdat() && !WS.isDefined())
1249       continue;
1250
1251     if (WS.isFunction()) {
1252       unsigned Index;
1253       if (WS.isDefined()) {
1254         if (WS.getOffset() != 0)
1255           report_fatal_error(
1256               "function sections must contain one function each");
1257
1258         if (WS.getSize() == 0)
1259           report_fatal_error(
1260               "function symbols must have a size set with .size");
1261
1262         // A definition. Write out the function body.
1263         Index = NumFunctionImports + Functions.size();
1264         WasmFunction Func;
1265         Func.Type = getFunctionType(WS);
1266         Func.Sym = &WS;
1267         WasmIndices[&WS] = Index;
1268         Functions.push_back(Func);
1269
1270         auto &Section = static_cast<MCSectionWasm &>(WS.getSection());
1271         if (const MCSymbolWasm *C = Section.getGroup()) {
1272           Comdats[C->getName()].emplace_back(
1273               WasmComdatEntry{wasm::WASM_COMDAT_FUNCTION, Index});
1274         }
1275       } else {
1276         // An import; the index was assigned above.
1277         Index = WasmIndices.find(&WS)->second;
1278       }
1279
1280       DEBUG(dbgs() << "  -> function index: " << Index << "\n");
1281     } else if (WS.isData()) {
1282       if (WS.isTemporary() && !WS.getSize())
1283         continue;
1284
1285       if (!WS.isDefined()) {
1286         DEBUG(dbgs() << "  -> segment index: -1");
1287         continue;
1288       }
1289
1290       if (!WS.getSize())
1291         report_fatal_error("data symbols must have a size set with .size: " +
1292                            WS.getName());
1293
1294       int64_t Size = 0;
1295       if (!WS.getSize()->evaluateAsAbsolute(Size, Layout))
1296         report_fatal_error(".size expression must be evaluatable");
1297
1298       auto &DataSection = static_cast<MCSectionWasm &>(WS.getSection());
1299       assert(DataSection.isWasmData());
1300
1301       // For each data symbol, export it in the symtab as a reference to the
1302       // corresponding Wasm data segment.
1303       wasm::WasmDataReference Ref = wasm::WasmDataReference{
1304           DataSection.getSegmentIndex(),
1305           static_cast<uint32_t>(Layout.getSymbolOffset(WS)),
1306           static_cast<uint32_t>(Size)};
1307       DataLocations[&WS] = Ref;
1308       DEBUG(dbgs() << "  -> segment index: " << Ref.Segment);
1309     } else {
1310       // A "true" Wasm global (currently just __stack_pointer)
1311       if (WS.isDefined())
1312         report_fatal_error("don't yet support defined globals");
1313
1314       // An import; the index was assigned above
1315       DEBUG(dbgs() << "  -> global index: " << WasmIndices.find(&WS)->second
1316                    << "\n");
1317     }
1318   }
1319
1320   // Populate WasmIndices and DataLocations for aliased symbols.  We need to
1321   // process these in a separate pass because we need to have processed the
1322   // target of the alias before the alias itself and the symbols are not
1323   // necessarily ordered in this way.
1324   for (const MCSymbol &S : Asm.symbols()) {
1325     if (!S.isVariable())
1326       continue;
1327
1328     assert(S.isDefined());
1329
1330     // Find the target symbol of this weak alias and export that index
1331     const auto &WS = static_cast<const MCSymbolWasm &>(S);
1332     const MCSymbolWasm *ResolvedSym = ResolveSymbol(WS);
1333     DEBUG(dbgs() << WS.getName() << ": weak alias of '" << *ResolvedSym << "'\n");
1334
1335     if (WS.isFunction()) {
1336       assert(WasmIndices.count(ResolvedSym) > 0);
1337       uint32_t WasmIndex = WasmIndices.find(ResolvedSym)->second;
1338       WasmIndices[&WS] = WasmIndex;
1339       DEBUG(dbgs() << "  -> index:" << WasmIndex << "\n");
1340     } else if (WS.isData()) {
1341       assert(DataLocations.count(ResolvedSym) > 0);
1342       const wasm::WasmDataReference &Ref =
1343           DataLocations.find(ResolvedSym)->second;
1344       DataLocations[&WS] = Ref;
1345       DEBUG(dbgs() << "  -> index:" << Ref.Segment << "\n");
1346     } else {
1347       report_fatal_error("don't yet support global aliases");
1348     }
1349   }
1350
1351   // Finally, populate the symbol table itself, in its "natural" order.
1352   for (const MCSymbol &S : Asm.symbols()) {
1353     const auto &WS = static_cast<const MCSymbolWasm &>(S);
1354     if (WS.isTemporary() && WS.getName().empty())
1355       continue;
1356     if (WS.isComdat() && !WS.isDefined())
1357       continue;
1358     if (WS.isTemporary() && WS.isData() && !WS.getSize())
1359       continue;
1360
1361     uint32_t Flags = 0;
1362     if (WS.isWeak())
1363       Flags |= wasm::WASM_SYMBOL_BINDING_WEAK;
1364     if (WS.isHidden())
1365       Flags |= wasm::WASM_SYMBOL_VISIBILITY_HIDDEN;
1366     if (!WS.isExternal() && WS.isDefined())
1367       Flags |= wasm::WASM_SYMBOL_BINDING_LOCAL;
1368     if (WS.isUndefined())
1369       Flags |= wasm::WASM_SYMBOL_UNDEFINED;
1370
1371     wasm::WasmSymbolInfo Info;
1372     Info.Name = WS.getName();
1373     Info.Kind = WS.getType();
1374     Info.Flags = Flags;
1375     if (!WS.isData())
1376       Info.ElementIndex = WasmIndices.find(&WS)->second;
1377     else if (WS.isDefined())
1378       Info.DataRef = DataLocations.find(&WS)->second;
1379     SymbolIndices[&WS] = SymbolInfos.size();
1380     SymbolInfos.emplace_back(Info);
1381   }
1382
1383   {
1384     auto HandleReloc = [&](const WasmRelocationEntry &Rel) {
1385       // Functions referenced by a relocation need to put in the table.  This is
1386       // purely to make the object file's provisional values readable, and is
1387       // ignored by the linker, which re-calculates the relocations itself.
1388       if (Rel.Type != wasm::R_WEBASSEMBLY_TABLE_INDEX_I32 &&
1389           Rel.Type != wasm::R_WEBASSEMBLY_TABLE_INDEX_SLEB)
1390         return;
1391       assert(Rel.Symbol->isFunction());
1392       const MCSymbolWasm &WS = *ResolveSymbol(*Rel.Symbol);
1393       uint32_t FunctionIndex = WasmIndices.find(&WS)->second;
1394       uint32_t TableIndex = TableElems.size() + kInitialTableOffset;
1395       if (TableIndices.try_emplace(&WS, TableIndex).second) {
1396         DEBUG(dbgs() << "  -> adding " << WS.getName()
1397                      << " to table: " << TableIndex << "\n");
1398         TableElems.push_back(FunctionIndex);
1399         registerFunctionType(WS);
1400       }
1401     };
1402
1403     for (const WasmRelocationEntry &RelEntry : CodeRelocations)
1404       HandleReloc(RelEntry);
1405     for (const WasmRelocationEntry &RelEntry : DataRelocations)
1406       HandleReloc(RelEntry);
1407   }
1408
1409   // Translate .init_array section contents into start functions.
1410   for (const MCSection &S : Asm) {
1411     const auto &WS = static_cast<const MCSectionWasm &>(S);
1412     if (WS.getSectionName().startswith(".fini_array"))
1413       report_fatal_error(".fini_array sections are unsupported");
1414     if (!WS.getSectionName().startswith(".init_array"))
1415       continue;
1416     if (WS.getFragmentList().empty())
1417       continue;
1418     if (WS.getFragmentList().size() != 2)
1419       report_fatal_error("only one .init_array section fragment supported");
1420     const MCFragment &AlignFrag = *WS.begin();
1421     if (AlignFrag.getKind() != MCFragment::FT_Align)
1422       report_fatal_error(".init_array section should be aligned");
1423     if (cast<MCAlignFragment>(AlignFrag).getAlignment() != (is64Bit() ? 8 : 4))
1424       report_fatal_error(".init_array section should be aligned for pointers");
1425     const MCFragment &Frag = *std::next(WS.begin());
1426     if (Frag.hasInstructions() || Frag.getKind() != MCFragment::FT_Data)
1427       report_fatal_error("only data supported in .init_array section");
1428     uint16_t Priority = UINT16_MAX;
1429     if (WS.getSectionName().size() != 11) {
1430       if (WS.getSectionName()[11] != '.')
1431         report_fatal_error(".init_array section priority should start with '.'");
1432       if (WS.getSectionName().substr(12).getAsInteger(10, Priority))
1433         report_fatal_error("invalid .init_array section priority");
1434     }
1435     const auto &DataFrag = cast<MCDataFragment>(Frag);
1436     const SmallVectorImpl<char> &Contents = DataFrag.getContents();
1437     for (const uint8_t *p = (const uint8_t *)Contents.data(),
1438                      *end = (const uint8_t *)Contents.data() + Contents.size();
1439          p != end; ++p) {
1440       if (*p != 0)
1441         report_fatal_error("non-symbolic data in .init_array section");
1442     }
1443     for (const MCFixup &Fixup : DataFrag.getFixups()) {
1444       assert(Fixup.getKind() == MCFixup::getKindForSize(is64Bit() ? 8 : 4, false));
1445       const MCExpr *Expr = Fixup.getValue();
1446       auto *Sym = dyn_cast<MCSymbolRefExpr>(Expr);
1447       if (!Sym)
1448         report_fatal_error("fixups in .init_array should be symbol references");
1449       if (Sym->getKind() != MCSymbolRefExpr::VK_WebAssembly_FUNCTION)
1450         report_fatal_error("symbols in .init_array should be for functions");
1451       auto I = SymbolIndices.find(cast<MCSymbolWasm>(&Sym->getSymbol()));
1452       if (I == SymbolIndices.end())
1453         report_fatal_error("symbols in .init_array should be defined");
1454       uint32_t Index = I->second;
1455       InitFuncs.push_back(std::make_pair(Priority, Index));
1456     }
1457   }
1458
1459   // Write out the Wasm header.
1460   writeHeader(Asm);
1461
1462   writeTypeSection(FunctionTypes);
1463   writeImportSection(Imports, DataSize, TableElems.size());
1464   writeFunctionSection(Functions);
1465   // Skip the "table" section; we import the table instead.
1466   // Skip the "memory" section; we import the memory instead.
1467   writeGlobalSection();
1468   writeExportSection(Exports);
1469   writeElemSection(TableElems);
1470   writeCodeSection(Asm, Layout, Functions);
1471   writeDataSection();
1472   writeCustomSections(Asm, Layout);
1473   updateCustomSectionRelocations(Functions, Layout);
1474   writeLinkingMetaDataSection(SymbolInfos, InitFuncs, Comdats);
1475   writeRelocSection(CodeSectionIndex, "CODE", CodeRelocations);
1476   writeRelocSection(DataSectionIndex, "DATA", DataRelocations);
1477   writeCustomRelocSections();
1478
1479   // TODO: Translate the .comment section to the output.
1480 }
1481
1482 std::unique_ptr<MCObjectWriter>
1483 llvm::createWasmObjectWriter(std::unique_ptr<MCWasmObjectTargetWriter> MOTW,
1484                              raw_pwrite_stream &OS) {
1485   return llvm::make_unique<WasmObjectWriter>(std::move(MOTW), OS);
1486 }