lib/MC/WasmObjectWriter.cpp

   1 //===- lib/MC/WasmObjectWriter.cpp - Wasm File Writer ---------------------===//
   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 // This file implements Wasm object file writer information.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #include "llvm/ADT/STLExtras.h"
  14 #include "llvm/ADT/SmallPtrSet.h"
  15 #include "llvm/BinaryFormat/Wasm.h"
  16 #include "llvm/Config/llvm-config.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 InitialTableOffset = 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 or event, in a struct capable of being used
  59 // as a DenseMap key.
  60 // TODO: Consider using wasm::WasmSignature directly instead.
  61 struct WasmSignature {
  62   // Support empty and tombstone instances, needed by DenseMap.
  63   enum { Plain, Empty, Tombstone } State = Plain;
  64
  65   // The return types of the function.
  66   SmallVector<wasm::ValType, 1> Returns;
  67
  68   // The parameter types of the function.
  69   SmallVector<wasm::ValType, 4> Params;
  70
  71   bool operator==(const WasmSignature &Other) const {
  72     return State == Other.State && Returns == Other.Returns &&
  73            Params == Other.Params;
  74   }
  75 };
  76
  77 // Traits for using WasmSignature in a DenseMap.
  78 struct WasmSignatureDenseMapInfo {
  79   static WasmSignature getEmptyKey() {
  80     WasmSignature Sig;
  81     Sig.State = WasmSignature::Empty;
  82     return Sig;
  83   }
  84   static WasmSignature getTombstoneKey() {
  85     WasmSignature Sig;
  86     Sig.State = WasmSignature::Tombstone;
  87     return Sig;
  88   }
  89   static unsigned getHashValue(const WasmSignature &Sig) {
  90     uintptr_t Value = Sig.State;
  91     for (wasm::ValType Ret : Sig.Returns)
  92       Value += DenseMapInfo<uint32_t>::getHashValue(uint32_t(Ret));
  93     for (wasm::ValType Param : Sig.Params)
  94       Value += DenseMapInfo<uint32_t>::getHashValue(uint32_t(Param));
  95     return Value;
  96   }
  97   static bool isEqual(const WasmSignature &LHS, const WasmSignature &RHS) {
  98     return LHS == RHS;
  99   }
 100 };
 101
 102 // A wasm data segment.  A wasm binary contains only a single data section
 103 // but that can contain many segments, each with their own virtual location
 104 // in memory.  Each MCSection data created by llvm is modeled as its own
 105 // wasm data segment.
 106 struct WasmDataSegment {
 107   MCSectionWasm *Section;
 108   StringRef Name;
 109   uint32_t InitFlags;
 110   uint32_t Offset;
 111   uint32_t Alignment;
 112   uint32_t LinkerFlags;
 113   SmallVector<char, 4> Data;
 114 };
 115
 116 // A wasm function to be written into the function section.
 117 struct WasmFunction {
 118   uint32_t SigIndex;
 119   const MCSymbolWasm *Sym;
 120 };
 121
 122 // A wasm global to be written into the global section.
 123 struct WasmGlobal {
 124   wasm::WasmGlobalType Type;
 125   uint64_t InitialValue;
 126 };
 127
 128 // Information about a single item which is part of a COMDAT.  For each data
 129 // segment or function which is in the COMDAT, there is a corresponding
 130 // WasmComdatEntry.
 131 struct WasmComdatEntry {
 132   unsigned Kind;
 133   uint32_t Index;
 134 };
 135
 136 // Information about a single relocation.
 137 struct WasmRelocationEntry {
 138   uint64_t Offset;                   // Where is the relocation.
 139   const MCSymbolWasm *Symbol;        // The symbol to relocate with.
 140   int64_t Addend;                    // A value to add to the symbol.
 141   unsigned Type;                     // The type of the relocation.
 142   const MCSectionWasm *FixupSection; // The section the relocation is targeting.
 143
 144   WasmRelocationEntry(uint64_t Offset, const MCSymbolWasm *Symbol,
 145                       int64_t Addend, unsigned Type,
 146                       const MCSectionWasm *FixupSection)
 147       : Offset(Offset), Symbol(Symbol), Addend(Addend), Type(Type),
 148         FixupSection(FixupSection) {}
 149
 150   bool hasAddend() const { return wasm::relocTypeHasAddend(Type); }
 151
 152   void print(raw_ostream &Out) const {
 153     Out << wasm::relocTypetoString(Type) << " Off=" << Offset
 154         << ", Sym=" << *Symbol << ", Addend=" << Addend
 155         << ", FixupSection=" << FixupSection->getSectionName();
 156   }
 157
 158 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
 159   LLVM_DUMP_METHOD void dump() const { print(dbgs()); }
 160 #endif
 161 };
 162
 163 static const uint32_t InvalidIndex = -1;
 164
 165 struct WasmCustomSection {
 166
 167   StringRef Name;
 168   MCSectionWasm *Section;
 169
 170   uint32_t OutputContentsOffset;
 171   uint32_t OutputIndex;
 172
 173   WasmCustomSection(StringRef Name, MCSectionWasm *Section)
 174       : Name(Name), Section(Section), OutputContentsOffset(0),
 175         OutputIndex(InvalidIndex) {}
 176 };
 177
 178 #if !defined(NDEBUG)
 179 raw_ostream &operator<<(raw_ostream &OS, const WasmRelocationEntry &Rel) {
 180   Rel.print(OS);
 181   return OS;
 182 }
 183 #endif
 184
 185 // Write X as an (unsigned) LEB value at offset Offset in Stream, padded
 186 // to allow patching.
 187 static void writePatchableLEB(raw_pwrite_stream &Stream, uint32_t X,
 188                               uint64_t Offset) {
 189   uint8_t Buffer[5];
 190   unsigned SizeLen = encodeULEB128(X, Buffer, 5);
 191   assert(SizeLen == 5);
 192   Stream.pwrite((char *)Buffer, SizeLen, Offset);
 193 }
 194
 195 // Write X as an signed LEB value at offset Offset in Stream, padded
 196 // to allow patching.
 197 static void writePatchableSLEB(raw_pwrite_stream &Stream, int32_t X,
 198                                uint64_t Offset) {
 199   uint8_t Buffer[5];
 200   unsigned SizeLen = encodeSLEB128(X, Buffer, 5);
 201   assert(SizeLen == 5);
 202   Stream.pwrite((char *)Buffer, SizeLen, Offset);
 203 }
 204
 205 // Write X as a plain integer value at offset Offset in Stream.
 206 static void writeI32(raw_pwrite_stream &Stream, uint32_t X, uint64_t Offset) {
 207   uint8_t Buffer[4];
 208   support::endian::write32le(Buffer, X);
 209   Stream.pwrite((char *)Buffer, sizeof(Buffer), Offset);
 210 }
 211
 212 class WasmObjectWriter : public MCObjectWriter {
 213   support::endian::Writer W;
 214
 215   /// The target specific Wasm writer instance.
 216   std::unique_ptr<MCWasmObjectTargetWriter> TargetObjectWriter;
 217
 218   // Relocations for fixing up references in the code section.
 219   std::vector<WasmRelocationEntry> CodeRelocations;
 220   uint32_t CodeSectionIndex;
 221
 222   // Relocations for fixing up references in the data section.
 223   std::vector<WasmRelocationEntry> DataRelocations;
 224   uint32_t DataSectionIndex;
 225
 226   // Index values to use for fixing up call_indirect type indices.
 227   // Maps function symbols to the index of the type of the function
 228   DenseMap<const MCSymbolWasm *, uint32_t> TypeIndices;
 229   // Maps function symbols to the table element index space. Used
 230   // for TABLE_INDEX relocation types (i.e. address taken functions).
 231   DenseMap<const MCSymbolWasm *, uint32_t> TableIndices;
 232   // Maps function/global symbols to the function/global/event/section index
 233   // space.
 234   DenseMap<const MCSymbolWasm *, uint32_t> WasmIndices;
 235   DenseMap<const MCSymbolWasm *, uint32_t> GOTIndices;
 236   // Maps data symbols to the Wasm segment and offset/size with the segment.
 237   DenseMap<const MCSymbolWasm *, wasm::WasmDataReference> DataLocations;
 238
 239   // Stores output data (index, relocations, content offset) for custom
 240   // section.
 241   std::vector<WasmCustomSection> CustomSections;
 242   std::unique_ptr<WasmCustomSection> ProducersSection;
 243   std::unique_ptr<WasmCustomSection> TargetFeaturesSection;
 244   // Relocations for fixing up references in the custom sections.
 245   DenseMap<const MCSectionWasm *, std::vector<WasmRelocationEntry>>
 246       CustomSectionsRelocations;
 247
 248   // Map from section to defining function symbol.
 249   DenseMap<const MCSection *, const MCSymbol *> SectionFunctions;
 250
 251   DenseMap<WasmSignature, uint32_t, WasmSignatureDenseMapInfo> SignatureIndices;
 252   SmallVector<WasmSignature, 4> Signatures;
 253   SmallVector<WasmDataSegment, 4> DataSegments;
 254   unsigned NumFunctionImports = 0;
 255   unsigned NumGlobalImports = 0;
 256   unsigned NumEventImports = 0;
 257   uint32_t SectionCount = 0;
 258
 259   // TargetObjectWriter wrappers.
 260   bool is64Bit() const { return TargetObjectWriter->is64Bit(); }
 261
 262   void startSection(SectionBookkeeping &Section, unsigned SectionId);
 263   void startCustomSection(SectionBookkeeping &Section, StringRef Name);
 264   void endSection(SectionBookkeeping &Section);
 265
 266 public:
 267   WasmObjectWriter(std::unique_ptr<MCWasmObjectTargetWriter> MOTW,
 268                    raw_pwrite_stream &OS)
 269       : W(OS, support::little), TargetObjectWriter(std::move(MOTW)) {}
 270
 271 private:
 272   void reset() override {
 273     CodeRelocations.clear();
 274     DataRelocations.clear();
 275     TypeIndices.clear();
 276     WasmIndices.clear();
 277     GOTIndices.clear();
 278     TableIndices.clear();
 279     DataLocations.clear();
 280     CustomSections.clear();
 281     ProducersSection.reset();
 282     TargetFeaturesSection.reset();
 283     CustomSectionsRelocations.clear();
 284     SignatureIndices.clear();
 285     Signatures.clear();
 286     DataSegments.clear();
 287     SectionFunctions.clear();
 288     NumFunctionImports = 0;
 289     NumGlobalImports = 0;
 290     MCObjectWriter::reset();
 291   }
 292
 293   void writeHeader(const MCAssembler &Asm);
 294
 295   void recordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
 296                         const MCFragment *Fragment, const MCFixup &Fixup,
 297                         MCValue Target, uint64_t &FixedValue) override;
 298
 299   void executePostLayoutBinding(MCAssembler &Asm,
 300                                 const MCAsmLayout &Layout) override;
 301
 302   uint64_t writeObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
 303
 304   void writeString(const StringRef Str) {
 305     encodeULEB128(Str.size(), W.OS);
 306     W.OS << Str;
 307   }
 308
 309   void writeValueType(wasm::ValType Ty) { W.OS << static_cast<char>(Ty); }
 310
 311   void writeTypeSection(ArrayRef<WasmSignature> Signatures);
 312   void writeImportSection(ArrayRef<wasm::WasmImport> Imports, uint32_t DataSize,
 313                           uint32_t NumElements);
 314   void writeFunctionSection(ArrayRef<WasmFunction> Functions);
 315   void writeExportSection(ArrayRef<wasm::WasmExport> Exports);
 316   void writeElemSection(ArrayRef<uint32_t> TableElems);
 317   void writeDataCountSection();
 318   void writeCodeSection(const MCAssembler &Asm, const MCAsmLayout &Layout,
 319                         ArrayRef<WasmFunction> Functions);
 320   void writeDataSection();
 321   void writeEventSection(ArrayRef<wasm::WasmEventType> Events);
 322   void writeRelocSection(uint32_t SectionIndex, StringRef Name,
 323                          std::vector<WasmRelocationEntry> &Relocations);
 324   void writeLinkingMetaDataSection(
 325       ArrayRef<wasm::WasmSymbolInfo> SymbolInfos,
 326       ArrayRef<std::pair<uint16_t, uint32_t>> InitFuncs,
 327       const std::map<StringRef, std::vector<WasmComdatEntry>> &Comdats);
 328   void writeCustomSection(WasmCustomSection &CustomSection,
 329                           const MCAssembler &Asm, const MCAsmLayout &Layout);
 330   void writeCustomRelocSections();
 331   void
 332   updateCustomSectionRelocations(const SmallVector<WasmFunction, 4> &Functions,
 333                                  const MCAsmLayout &Layout);
 334
 335   uint32_t getProvisionalValue(const WasmRelocationEntry &RelEntry);
 336   void applyRelocations(ArrayRef<WasmRelocationEntry> Relocations,
 337                         uint64_t ContentsOffset);
 338
 339   uint32_t getRelocationIndexValue(const WasmRelocationEntry &RelEntry);
 340   uint32_t getFunctionType(const MCSymbolWasm &Symbol);
 341   uint32_t getEventType(const MCSymbolWasm &Symbol);
 342   void registerFunctionType(const MCSymbolWasm &Symbol);
 343   void registerEventType(const MCSymbolWasm &Symbol);
 344 };
 345
 346 } // end anonymous namespace
 347
 348 // Write out a section header and a patchable section size field.
 349 void WasmObjectWriter::startSection(SectionBookkeeping &Section,
 350                                     unsigned SectionId) {
 351   LLVM_DEBUG(dbgs() << "startSection " << SectionId << "\n");
 352   W.OS << char(SectionId);
 353
 354   Section.SizeOffset = W.OS.tell();
 355
 356   // The section size. We don't know the size yet, so reserve enough space
 357   // for any 32-bit value; we'll patch it later.
 358   encodeULEB128(0, W.OS, 5);
 359
 360   // The position where the section starts, for measuring its size.
 361   Section.ContentsOffset = W.OS.tell();
 362   Section.PayloadOffset = W.OS.tell();
 363   Section.Index = SectionCount++;
 364 }
 365
 366 void WasmObjectWriter::startCustomSection(SectionBookkeeping &Section,
 367                                           StringRef Name) {
 368   LLVM_DEBUG(dbgs() << "startCustomSection " << Name << "\n");
 369   startSection(Section, wasm::WASM_SEC_CUSTOM);
 370
 371   // The position where the section header ends, for measuring its size.
 372   Section.PayloadOffset = W.OS.tell();
 373
 374   // Custom sections in wasm also have a string identifier.
 375   writeString(Name);
 376
 377   // The position where the custom section starts.
 378   Section.ContentsOffset = W.OS.tell();
 379 }
 380
 381 // Now that the section is complete and we know how big it is, patch up the
 382 // section size field at the start of the section.
 383 void WasmObjectWriter::endSection(SectionBookkeeping &Section) {
 384   uint64_t Size = W.OS.tell();
 385   // /dev/null doesn't support seek/tell and can report offset of 0.
 386   // Simply skip this patching in that case.
 387   if (!Size)
 388     return;
 389
 390   Size -= Section.PayloadOffset;
 391   if (uint32_t(Size) != Size)
 392     report_fatal_error("section size does not fit in a uint32_t");
 393
 394   LLVM_DEBUG(dbgs() << "endSection size=" << Size << "\n");
 395
 396   // Write the final section size to the payload_len field, which follows
 397   // the section id byte.
 398   writePatchableLEB(static_cast<raw_pwrite_stream &>(W.OS), Size,
 399                     Section.SizeOffset);
 400 }
 401
 402 // Emit the Wasm header.
 403 void WasmObjectWriter::writeHeader(const MCAssembler &Asm) {
 404   W.OS.write(wasm::WasmMagic, sizeof(wasm::WasmMagic));
 405   W.write<uint32_t>(wasm::WasmVersion);
 406 }
 407
 408 void WasmObjectWriter::executePostLayoutBinding(MCAssembler &Asm,
 409                                                 const MCAsmLayout &Layout) {
 410   // Build a map of sections to the function that defines them, for use
 411   // in recordRelocation.
 412   for (const MCSymbol &S : Asm.symbols()) {
 413     const auto &WS = static_cast<const MCSymbolWasm &>(S);
 414     if (WS.isDefined() && WS.isFunction() && !WS.isVariable()) {
 415       const auto &Sec = static_cast<const MCSectionWasm &>(S.getSection());
 416       auto Pair = SectionFunctions.insert(std::make_pair(&Sec, &S));
 417       if (!Pair.second)
 418         report_fatal_error("section already has a defining function: " +
 419                            Sec.getSectionName());
 420     }
 421   }
 422 }
 423
 424 void WasmObjectWriter::recordRelocation(MCAssembler &Asm,
 425                                         const MCAsmLayout &Layout,
 426                                         const MCFragment *Fragment,
 427                                         const MCFixup &Fixup, MCValue Target,
 428                                         uint64_t &FixedValue) {
 429   // The WebAssembly backend should never generate FKF_IsPCRel fixups
 430   assert(!(Asm.getBackend().getFixupKindInfo(Fixup.getKind()).Flags &
 431            MCFixupKindInfo::FKF_IsPCRel));
 432
 433   const auto &FixupSection = cast<MCSectionWasm>(*Fragment->getParent());
 434   uint64_t C = Target.getConstant();
 435   uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
 436   MCContext &Ctx = Asm.getContext();
 437
 438   // The .init_array isn't translated as data, so don't do relocations in it.
 439   if (FixupSection.getSectionName().startswith(".init_array"))
 440     return;
 441
 442   if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
 443     // To get here the A - B expression must have failed evaluateAsRelocatable.
 444     // This means either A or B must be undefined and in WebAssembly we can't
 445     // support either of those cases.
 446     const auto &SymB = cast<MCSymbolWasm>(RefB->getSymbol());
 447     Ctx.reportError(
 448         Fixup.getLoc(),
 449         Twine("symbol '") + SymB.getName() +
 450             "': unsupported subtraction expression used in relocation.");
 451     return;
 452   }
 453
 454   // We either rejected the fixup or folded B into C at this point.
 455   const MCSymbolRefExpr *RefA = Target.getSymA();
 456   const auto *SymA = cast<MCSymbolWasm>(&RefA->getSymbol());
 457
 458   if (SymA->isVariable()) {
 459     const MCExpr *Expr = SymA->getVariableValue();
 460     const auto *Inner = cast<MCSymbolRefExpr>(Expr);
 461     if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF)
 462       llvm_unreachable("weakref used in reloc not yet implemented");
 463   }
 464
 465   // Put any constant offset in an addend. Offsets can be negative, and
 466   // LLVM expects wrapping, in contrast to wasm's immediates which can't
 467   // be negative and don't wrap.
 468   FixedValue = 0;
 469
 470   unsigned Type = TargetObjectWriter->getRelocType(Target, Fixup);
 471
 472   // Absolute offset within a section or a function.
 473   // Currently only supported for for metadata sections.
 474   // See: test/MC/WebAssembly/blockaddress.ll
 475   if (Type == wasm::R_WASM_FUNCTION_OFFSET_I32 ||
 476       Type == wasm::R_WASM_SECTION_OFFSET_I32) {
 477     if (!FixupSection.getKind().isMetadata())
 478       report_fatal_error("relocations for function or section offsets are "
 479                          "only supported in metadata sections");
 480
 481     const MCSymbol *SectionSymbol = nullptr;
 482     const MCSection &SecA = SymA->getSection();
 483     if (SecA.getKind().isText())
 484       SectionSymbol = SectionFunctions.find(&SecA)->second;
 485     else
 486       SectionSymbol = SecA.getBeginSymbol();
 487     if (!SectionSymbol)
 488       report_fatal_error("section symbol is required for relocation");
 489
 490     C += Layout.getSymbolOffset(*SymA);
 491     SymA = cast<MCSymbolWasm>(SectionSymbol);
 492   }
 493
 494   // Relocation other than R_WASM_TYPE_INDEX_LEB are required to be
 495   // against a named symbol.
 496   if (Type != wasm::R_WASM_TYPE_INDEX_LEB) {
 497     if (SymA->getName().empty())
 498       report_fatal_error("relocations against un-named temporaries are not yet "
 499                          "supported by wasm");
 500
 501     SymA->setUsedInReloc();
 502   }
 503
 504   if (RefA->getKind() == MCSymbolRefExpr::VK_GOT)
 505     SymA->setUsedInGOT();
 506
 507   WasmRelocationEntry Rec(FixupOffset, SymA, C, Type, &FixupSection);
 508   LLVM_DEBUG(dbgs() << "WasmReloc: " << Rec << "\n");
 509
 510   if (FixupSection.isWasmData()) {
 511     DataRelocations.push_back(Rec);
 512   } else if (FixupSection.getKind().isText()) {
 513     CodeRelocations.push_back(Rec);
 514   } else if (FixupSection.getKind().isMetadata()) {
 515     CustomSectionsRelocations[&FixupSection].push_back(Rec);
 516   } else {
 517     llvm_unreachable("unexpected section type");
 518   }
 519 }
 520
 521 static const MCSymbolWasm *resolveSymbol(const MCSymbolWasm &Symbol) {
 522   const MCSymbolWasm* Ret = &Symbol;
 523   while (Ret->isVariable()) {
 524     const MCExpr *Expr = Ret->getVariableValue();
 525     auto *Inner = cast<MCSymbolRefExpr>(Expr);
 526     Ret = cast<MCSymbolWasm>(&Inner->getSymbol());
 527   }
 528   return Ret;
 529 }
 530
 531 // Compute a value to write into the code at the location covered
 532 // by RelEntry. This value isn't used by the static linker; it just serves
 533 // to make the object format more readable and more likely to be directly
 534 // useable.
 535 uint32_t
 536 WasmObjectWriter::getProvisionalValue(const WasmRelocationEntry &RelEntry) {
 537   if (RelEntry.Type == wasm::R_WASM_GLOBAL_INDEX_LEB && !RelEntry.Symbol->isGlobal()) {
 538     assert(GOTIndices.count(RelEntry.Symbol) > 0 && "symbol not found in GOT index space");
 539     return GOTIndices[RelEntry.Symbol];
 540   }
 541
 542   switch (RelEntry.Type) {
 543   case wasm::R_WASM_TABLE_INDEX_REL_SLEB:
 544   case wasm::R_WASM_TABLE_INDEX_SLEB:
 545   case wasm::R_WASM_TABLE_INDEX_I32: {
 546     // Provisional value is table address of the resolved symbol itself
 547     const MCSymbolWasm *Sym = resolveSymbol(*RelEntry.Symbol);
 548     assert(Sym->isFunction());
 549     return TableIndices[Sym];
 550   }
 551   case wasm::R_WASM_TYPE_INDEX_LEB:
 552     // Provisional value is same as the index
 553     return getRelocationIndexValue(RelEntry);
 554   case wasm::R_WASM_FUNCTION_INDEX_LEB:
 555   case wasm::R_WASM_GLOBAL_INDEX_LEB:
 556   case wasm::R_WASM_EVENT_INDEX_LEB:
 557     // Provisional value is function/global/event Wasm index
 558     assert(WasmIndices.count(RelEntry.Symbol) > 0 && "symbol not found in wasm index space");
 559     return WasmIndices[RelEntry.Symbol];
 560   case wasm::R_WASM_FUNCTION_OFFSET_I32:
 561   case wasm::R_WASM_SECTION_OFFSET_I32: {
 562     const auto &Section =
 563         static_cast<const MCSectionWasm &>(RelEntry.Symbol->getSection());
 564     return Section.getSectionOffset() + RelEntry.Addend;
 565   }
 566   case wasm::R_WASM_MEMORY_ADDR_LEB:
 567   case wasm::R_WASM_MEMORY_ADDR_I32:
 568   case wasm::R_WASM_MEMORY_ADDR_REL_SLEB:
 569   case wasm::R_WASM_MEMORY_ADDR_SLEB: {
 570     // Provisional value is address of the global
 571     const MCSymbolWasm *Sym = resolveSymbol(*RelEntry.Symbol);
 572     // For undefined symbols, use zero
 573     if (!Sym->isDefined())
 574       return 0;
 575     const wasm::WasmDataReference &Ref = DataLocations[Sym];
 576     const WasmDataSegment &Segment = DataSegments[Ref.Segment];
 577     // Ignore overflow. LLVM allows address arithmetic to silently wrap.
 578     return Segment.Offset + Ref.Offset + RelEntry.Addend;
 579   }
 580   default:
 581     llvm_unreachable("invalid relocation type");
 582   }
 583 }
 584
 585 static void addData(SmallVectorImpl<char> &DataBytes,
 586                     MCSectionWasm &DataSection) {
 587   LLVM_DEBUG(errs() << "addData: " << DataSection.getSectionName() << "\n");
 588
 589   DataBytes.resize(alignTo(DataBytes.size(), DataSection.getAlignment()));
 590
 591   for (const MCFragment &Frag : DataSection) {
 592     if (Frag.hasInstructions())
 593       report_fatal_error("only data supported in data sections");
 594
 595     if (auto *Align = dyn_cast<MCAlignFragment>(&Frag)) {
 596       if (Align->getValueSize() != 1)
 597         report_fatal_error("only byte values supported for alignment");
 598       // If nops are requested, use zeros, as this is the data section.
 599       uint8_t Value = Align->hasEmitNops() ? 0 : Align->getValue();
 600       uint64_t Size =
 601           std::min<uint64_t>(alignTo(DataBytes.size(), Align->getAlignment()),
 602                              DataBytes.size() + Align->getMaxBytesToEmit());
 603       DataBytes.resize(Size, Value);
 604     } else if (auto *Fill = dyn_cast<MCFillFragment>(&Frag)) {
 605       int64_t NumValues;
 606       if (!Fill->getNumValues().evaluateAsAbsolute(NumValues))
 607         llvm_unreachable("The fill should be an assembler constant");
 608       DataBytes.insert(DataBytes.end(), Fill->getValueSize() * NumValues,
 609                        Fill->getValue());
 610     } else if (auto *LEB = dyn_cast<MCLEBFragment>(&Frag)) {
 611       const SmallVectorImpl<char> &Contents = LEB->getContents();
 612       DataBytes.insert(DataBytes.end(), Contents.begin(), Contents.end());
 613     } else {
 614       const auto &DataFrag = cast<MCDataFragment>(Frag);
 615       const SmallVectorImpl<char> &Contents = DataFrag.getContents();
 616       DataBytes.insert(DataBytes.end(), Contents.begin(), Contents.end());
 617     }
 618   }
 619
 620   LLVM_DEBUG(dbgs() << "addData -> " << DataBytes.size() << "\n");
 621 }
 622
 623 uint32_t
 624 WasmObjectWriter::getRelocationIndexValue(const WasmRelocationEntry &RelEntry) {
 625   if (RelEntry.Type == wasm::R_WASM_TYPE_INDEX_LEB) {
 626     if (!TypeIndices.count(RelEntry.Symbol))
 627       report_fatal_error("symbol not found in type index space: " +
 628                          RelEntry.Symbol->getName());
 629     return TypeIndices[RelEntry.Symbol];
 630   }
 631
 632   return RelEntry.Symbol->getIndex();
 633 }
 634
 635 // Apply the portions of the relocation records that we can handle ourselves
 636 // directly.
 637 void WasmObjectWriter::applyRelocations(
 638     ArrayRef<WasmRelocationEntry> Relocations, uint64_t ContentsOffset) {
 639   auto &Stream = static_cast<raw_pwrite_stream &>(W.OS);
 640   for (const WasmRelocationEntry &RelEntry : Relocations) {
 641     uint64_t Offset = ContentsOffset +
 642                       RelEntry.FixupSection->getSectionOffset() +
 643                       RelEntry.Offset;
 644
 645     LLVM_DEBUG(dbgs() << "applyRelocation: " << RelEntry << "\n");
 646     uint32_t Value = getProvisionalValue(RelEntry);
 647
 648     switch (RelEntry.Type) {
 649     case wasm::R_WASM_FUNCTION_INDEX_LEB:
 650     case wasm::R_WASM_TYPE_INDEX_LEB:
 651     case wasm::R_WASM_GLOBAL_INDEX_LEB:
 652     case wasm::R_WASM_MEMORY_ADDR_LEB:
 653     case wasm::R_WASM_EVENT_INDEX_LEB:
 654       writePatchableLEB(Stream, Value, Offset);
 655       break;
 656     case wasm::R_WASM_TABLE_INDEX_I32:
 657     case wasm::R_WASM_MEMORY_ADDR_I32:
 658     case wasm::R_WASM_FUNCTION_OFFSET_I32:
 659     case wasm::R_WASM_SECTION_OFFSET_I32:
 660       writeI32(Stream, Value, Offset);
 661       break;
 662     case wasm::R_WASM_TABLE_INDEX_SLEB:
 663     case wasm::R_WASM_TABLE_INDEX_REL_SLEB:
 664     case wasm::R_WASM_MEMORY_ADDR_SLEB:
 665     case wasm::R_WASM_MEMORY_ADDR_REL_SLEB:
 666       writePatchableSLEB(Stream, Value, Offset);
 667       break;
 668     default:
 669       llvm_unreachable("invalid relocation type");
 670     }
 671   }
 672 }
 673
 674 void WasmObjectWriter::writeTypeSection(ArrayRef<WasmSignature> Signatures) {
 675   if (Signatures.empty())
 676     return;
 677
 678   SectionBookkeeping Section;
 679   startSection(Section, wasm::WASM_SEC_TYPE);
 680
 681   encodeULEB128(Signatures.size(), W.OS);
 682
 683   for (const WasmSignature &Sig : Signatures) {
 684     W.OS << char(wasm::WASM_TYPE_FUNC);
 685     encodeULEB128(Sig.Params.size(), W.OS);
 686     for (wasm::ValType Ty : Sig.Params)
 687       writeValueType(Ty);
 688     encodeULEB128(Sig.Returns.size(), W.OS);
 689     for (wasm::ValType Ty : Sig.Returns)
 690       writeValueType(Ty);
 691   }
 692
 693   endSection(Section);
 694 }
 695
 696 void WasmObjectWriter::writeImportSection(ArrayRef<wasm::WasmImport> Imports,
 697                                           uint32_t DataSize,
 698                                           uint32_t NumElements) {
 699   if (Imports.empty())
 700     return;
 701
 702   uint32_t NumPages = (DataSize + wasm::WasmPageSize - 1) / wasm::WasmPageSize;
 703
 704   SectionBookkeeping Section;
 705   startSection(Section, wasm::WASM_SEC_IMPORT);
 706
 707   encodeULEB128(Imports.size(), W.OS);
 708   for (const wasm::WasmImport &Import : Imports) {
 709     writeString(Import.Module);
 710     writeString(Import.Field);
 711     W.OS << char(Import.Kind);
 712
 713     switch (Import.Kind) {
 714     case wasm::WASM_EXTERNAL_FUNCTION:
 715       encodeULEB128(Import.SigIndex, W.OS);
 716       break;
 717     case wasm::WASM_EXTERNAL_GLOBAL:
 718       W.OS << char(Import.Global.Type);
 719       W.OS << char(Import.Global.Mutable ? 1 : 0);
 720       break;
 721     case wasm::WASM_EXTERNAL_MEMORY:
 722       encodeULEB128(0, W.OS);        // flags
 723       encodeULEB128(NumPages, W.OS); // initial
 724       break;
 725     case wasm::WASM_EXTERNAL_TABLE:
 726       W.OS << char(Import.Table.ElemType);
 727       encodeULEB128(0, W.OS);           // flags
 728       encodeULEB128(NumElements, W.OS); // initial
 729       break;
 730     case wasm::WASM_EXTERNAL_EVENT:
 731       encodeULEB128(Import.Event.Attribute, W.OS);
 732       encodeULEB128(Import.Event.SigIndex, W.OS);
 733       break;
 734     default:
 735       llvm_unreachable("unsupported import kind");
 736     }
 737   }
 738
 739   endSection(Section);
 740 }
 741
 742 void WasmObjectWriter::writeFunctionSection(ArrayRef<WasmFunction> Functions) {
 743   if (Functions.empty())
 744     return;
 745
 746   SectionBookkeeping Section;
 747   startSection(Section, wasm::WASM_SEC_FUNCTION);
 748
 749   encodeULEB128(Functions.size(), W.OS);
 750   for (const WasmFunction &Func : Functions)
 751     encodeULEB128(Func.SigIndex, W.OS);
 752
 753   endSection(Section);
 754 }
 755
 756 void WasmObjectWriter::writeEventSection(ArrayRef<wasm::WasmEventType> Events) {
 757   if (Events.empty())
 758     return;
 759
 760   SectionBookkeeping Section;
 761   startSection(Section, wasm::WASM_SEC_EVENT);
 762
 763   encodeULEB128(Events.size(), W.OS);
 764   for (const wasm::WasmEventType &Event : Events) {
 765     encodeULEB128(Event.Attribute, W.OS);
 766     encodeULEB128(Event.SigIndex, W.OS);
 767   }
 768
 769   endSection(Section);
 770 }
 771
 772 void WasmObjectWriter::writeExportSection(ArrayRef<wasm::WasmExport> Exports) {
 773   if (Exports.empty())
 774     return;
 775
 776   SectionBookkeeping Section;
 777   startSection(Section, wasm::WASM_SEC_EXPORT);
 778
 779   encodeULEB128(Exports.size(), W.OS);
 780   for (const wasm::WasmExport &Export : Exports) {
 781     writeString(Export.Name);
 782     W.OS << char(Export.Kind);
 783     encodeULEB128(Export.Index, W.OS);
 784   }
 785
 786   endSection(Section);
 787 }
 788
 789 void WasmObjectWriter::writeElemSection(ArrayRef<uint32_t> TableElems) {
 790   if (TableElems.empty())
 791     return;
 792
 793   SectionBookkeeping Section;
 794   startSection(Section, wasm::WASM_SEC_ELEM);
 795
 796   encodeULEB128(1, W.OS); // number of "segments"
 797   encodeULEB128(0, W.OS); // the table index
 798
 799   // init expr for starting offset
 800   W.OS << char(wasm::WASM_OPCODE_I32_CONST);
 801   encodeSLEB128(InitialTableOffset, W.OS);
 802   W.OS << char(wasm::WASM_OPCODE_END);
 803
 804   encodeULEB128(TableElems.size(), W.OS);
 805   for (uint32_t Elem : TableElems)
 806     encodeULEB128(Elem, W.OS);
 807
 808   endSection(Section);
 809 }
 810
 811 void WasmObjectWriter::writeDataCountSection() {
 812   if (DataSegments.empty())
 813     return;
 814
 815   SectionBookkeeping Section;
 816   startSection(Section, wasm::WASM_SEC_DATACOUNT);
 817   encodeULEB128(DataSegments.size(), W.OS);
 818   endSection(Section);
 819 }
 820
 821 void WasmObjectWriter::writeCodeSection(const MCAssembler &Asm,
 822                                         const MCAsmLayout &Layout,
 823                                         ArrayRef<WasmFunction> Functions) {
 824   if (Functions.empty())
 825     return;
 826
 827   SectionBookkeeping Section;
 828   startSection(Section, wasm::WASM_SEC_CODE);
 829   CodeSectionIndex = Section.Index;
 830
 831   encodeULEB128(Functions.size(), W.OS);
 832
 833   for (const WasmFunction &Func : Functions) {
 834     auto &FuncSection = static_cast<MCSectionWasm &>(Func.Sym->getSection());
 835
 836     int64_t Size = 0;
 837     if (!Func.Sym->getSize()->evaluateAsAbsolute(Size, Layout))
 838       report_fatal_error(".size expression must be evaluatable");
 839
 840     encodeULEB128(Size, W.OS);
 841     FuncSection.setSectionOffset(W.OS.tell() - Section.ContentsOffset);
 842     Asm.writeSectionData(W.OS, &FuncSection, Layout);
 843   }
 844
 845   // Apply fixups.
 846   applyRelocations(CodeRelocations, Section.ContentsOffset);
 847
 848   endSection(Section);
 849 }
 850
 851 void WasmObjectWriter::writeDataSection() {
 852   if (DataSegments.empty())
 853     return;
 854
 855   SectionBookkeeping Section;
 856   startSection(Section, wasm::WASM_SEC_DATA);
 857   DataSectionIndex = Section.Index;
 858
 859   encodeULEB128(DataSegments.size(), W.OS); // count
 860
 861   for (const WasmDataSegment &Segment : DataSegments) {
 862     encodeULEB128(Segment.InitFlags, W.OS); // flags
 863     if (Segment.InitFlags & wasm::WASM_SEGMENT_HAS_MEMINDEX)
 864       encodeULEB128(0, W.OS); // memory index
 865     if ((Segment.InitFlags & wasm::WASM_SEGMENT_IS_PASSIVE) == 0) {
 866       W.OS << char(wasm::WASM_OPCODE_I32_CONST);
 867       encodeSLEB128(Segment.Offset, W.OS); // offset
 868       W.OS << char(wasm::WASM_OPCODE_END);
 869     }
 870     encodeULEB128(Segment.Data.size(), W.OS); // size
 871     Segment.Section->setSectionOffset(W.OS.tell() - Section.ContentsOffset);
 872     W.OS << Segment.Data; // data
 873   }
 874
 875   // Apply fixups.
 876   applyRelocations(DataRelocations, Section.ContentsOffset);
 877
 878   endSection(Section);
 879 }
 880
 881 void WasmObjectWriter::writeRelocSection(
 882     uint32_t SectionIndex, StringRef Name,
 883     std::vector<WasmRelocationEntry> &Relocs) {
 884   // See: https://github.com/WebAssembly/tool-conventions/blob/master/Linking.md
 885   // for descriptions of the reloc sections.
 886
 887   if (Relocs.empty())
 888     return;
 889
 890   // First, ensure the relocations are sorted in offset order.  In general they
 891   // should already be sorted since `recordRelocation` is called in offset
 892   // order, but for the code section we combine many MC sections into single
 893   // wasm section, and this order is determined by the order of Asm.Symbols()
 894   // not the sections order.
 895   llvm::stable_sort(
 896       Relocs, [](const WasmRelocationEntry &A, const WasmRelocationEntry &B) {
 897         return (A.Offset + A.FixupSection->getSectionOffset()) <
 898                (B.Offset + B.FixupSection->getSectionOffset());
 899       });
 900
 901   SectionBookkeeping Section;
 902   startCustomSection(Section, std::string("reloc.") + Name.str());
 903
 904   encodeULEB128(SectionIndex, W.OS);
 905   encodeULEB128(Relocs.size(), W.OS);
 906   for (const WasmRelocationEntry &RelEntry : Relocs) {
 907     uint64_t Offset =
 908         RelEntry.Offset + RelEntry.FixupSection->getSectionOffset();
 909     uint32_t Index = getRelocationIndexValue(RelEntry);
 910
 911     W.OS << char(RelEntry.Type);
 912     encodeULEB128(Offset, W.OS);
 913     encodeULEB128(Index, W.OS);
 914     if (RelEntry.hasAddend())
 915       encodeSLEB128(RelEntry.Addend, W.OS);
 916   }
 917
 918   endSection(Section);
 919 }
 920
 921 void WasmObjectWriter::writeCustomRelocSections() {
 922   for (const auto &Sec : CustomSections) {
 923     auto &Relocations = CustomSectionsRelocations[Sec.Section];
 924     writeRelocSection(Sec.OutputIndex, Sec.Name, Relocations);
 925   }
 926 }
 927
 928 void WasmObjectWriter::writeLinkingMetaDataSection(
 929     ArrayRef<wasm::WasmSymbolInfo> SymbolInfos,
 930     ArrayRef<std::pair<uint16_t, uint32_t>> InitFuncs,
 931     const std::map<StringRef, std::vector<WasmComdatEntry>> &Comdats) {
 932   SectionBookkeeping Section;
 933   startCustomSection(Section, "linking");
 934   encodeULEB128(wasm::WasmMetadataVersion, W.OS);
 935
 936   SectionBookkeeping SubSection;
 937   if (SymbolInfos.size() != 0) {
 938     startSection(SubSection, wasm::WASM_SYMBOL_TABLE);
 939     encodeULEB128(SymbolInfos.size(), W.OS);
 940     for (const wasm::WasmSymbolInfo &Sym : SymbolInfos) {
 941       encodeULEB128(Sym.Kind, W.OS);
 942       encodeULEB128(Sym.Flags, W.OS);
 943       switch (Sym.Kind) {
 944       case wasm::WASM_SYMBOL_TYPE_FUNCTION:
 945       case wasm::WASM_SYMBOL_TYPE_GLOBAL:
 946       case wasm::WASM_SYMBOL_TYPE_EVENT:
 947         encodeULEB128(Sym.ElementIndex, W.OS);
 948         if ((Sym.Flags & wasm::WASM_SYMBOL_UNDEFINED) == 0 ||
 949             (Sym.Flags & wasm::WASM_SYMBOL_EXPLICIT_NAME) != 0)
 950           writeString(Sym.Name);
 951         break;
 952       case wasm::WASM_SYMBOL_TYPE_DATA:
 953         writeString(Sym.Name);
 954         if ((Sym.Flags & wasm::WASM_SYMBOL_UNDEFINED) == 0) {
 955           encodeULEB128(Sym.DataRef.Segment, W.OS);
 956           encodeULEB128(Sym.DataRef.Offset, W.OS);
 957           encodeULEB128(Sym.DataRef.Size, W.OS);
 958         }
 959         break;
 960       case wasm::WASM_SYMBOL_TYPE_SECTION: {
 961         const uint32_t SectionIndex =
 962             CustomSections[Sym.ElementIndex].OutputIndex;
 963         encodeULEB128(SectionIndex, W.OS);
 964         break;
 965       }
 966       default:
 967         llvm_unreachable("unexpected kind");
 968       }
 969     }
 970     endSection(SubSection);
 971   }
 972
 973   if (DataSegments.size()) {
 974     startSection(SubSection, wasm::WASM_SEGMENT_INFO);
 975     encodeULEB128(DataSegments.size(), W.OS);
 976     for (const WasmDataSegment &Segment : DataSegments) {
 977       writeString(Segment.Name);
 978       encodeULEB128(Segment.Alignment, W.OS);
 979       encodeULEB128(Segment.LinkerFlags, W.OS);
 980     }
 981     endSection(SubSection);
 982   }
 983
 984   if (!InitFuncs.empty()) {
 985     startSection(SubSection, wasm::WASM_INIT_FUNCS);
 986     encodeULEB128(InitFuncs.size(), W.OS);
 987     for (auto &StartFunc : InitFuncs) {
 988       encodeULEB128(StartFunc.first, W.OS);  // priority
 989       encodeULEB128(StartFunc.second, W.OS); // function index
 990     }
 991     endSection(SubSection);
 992   }
 993
 994   if (Comdats.size()) {
 995     startSection(SubSection, wasm::WASM_COMDAT_INFO);
 996     encodeULEB128(Comdats.size(), W.OS);
 997     for (const auto &C : Comdats) {
 998       writeString(C.first);
 999       encodeULEB128(0, W.OS); // flags for future use
1000       encodeULEB128(C.second.size(), W.OS);
1001       for (const WasmComdatEntry &Entry : C.second) {
1002         encodeULEB128(Entry.Kind, W.OS);
1003         encodeULEB128(Entry.Index, W.OS);
1004       }
1005     }
1006     endSection(SubSection);
1007   }
1008
1009   endSection(Section);
1010 }
1011
1012 void WasmObjectWriter::writeCustomSection(WasmCustomSection &CustomSection,
1013                                           const MCAssembler &Asm,
1014                                           const MCAsmLayout &Layout) {
1015   SectionBookkeeping Section;
1016   auto *Sec = CustomSection.Section;
1017   startCustomSection(Section, CustomSection.Name);
1018
1019   Sec->setSectionOffset(W.OS.tell() - Section.ContentsOffset);
1020   Asm.writeSectionData(W.OS, Sec, Layout);
1021
1022   CustomSection.OutputContentsOffset = Section.ContentsOffset;
1023   CustomSection.OutputIndex = Section.Index;
1024
1025   endSection(Section);
1026
1027   // Apply fixups.
1028   auto &Relocations = CustomSectionsRelocations[CustomSection.Section];
1029   applyRelocations(Relocations, CustomSection.OutputContentsOffset);
1030 }
1031
1032 uint32_t WasmObjectWriter::getFunctionType(const MCSymbolWasm &Symbol) {
1033   assert(Symbol.isFunction());
1034   assert(TypeIndices.count(&Symbol));
1035   return TypeIndices[&Symbol];
1036 }
1037
1038 uint32_t WasmObjectWriter::getEventType(const MCSymbolWasm &Symbol) {
1039   assert(Symbol.isEvent());
1040   assert(TypeIndices.count(&Symbol));
1041   return TypeIndices[&Symbol];
1042 }
1043
1044 void WasmObjectWriter::registerFunctionType(const MCSymbolWasm &Symbol) {
1045   assert(Symbol.isFunction());
1046
1047   WasmSignature S;
1048   const MCSymbolWasm *ResolvedSym = resolveSymbol(Symbol);
1049   if (auto *Sig = ResolvedSym->getSignature()) {
1050     S.Returns = Sig->Returns;
1051     S.Params = Sig->Params;
1052   }
1053
1054   auto Pair = SignatureIndices.insert(std::make_pair(S, Signatures.size()));
1055   if (Pair.second)
1056     Signatures.push_back(S);
1057   TypeIndices[&Symbol] = Pair.first->second;
1058
1059   LLVM_DEBUG(dbgs() << "registerFunctionType: " << Symbol
1060                     << " new:" << Pair.second << "\n");
1061   LLVM_DEBUG(dbgs() << "  -> type index: " << Pair.first->second << "\n");
1062 }
1063
1064 void WasmObjectWriter::registerEventType(const MCSymbolWasm &Symbol) {
1065   assert(Symbol.isEvent());
1066
1067   // TODO Currently we don't generate imported exceptions, but if we do, we
1068   // should have a way of infering types of imported exceptions.
1069   WasmSignature S;
1070   if (auto *Sig = Symbol.getSignature()) {
1071     S.Returns = Sig->Returns;
1072     S.Params = Sig->Params;
1073   }
1074
1075   auto Pair = SignatureIndices.insert(std::make_pair(S, Signatures.size()));
1076   if (Pair.second)
1077     Signatures.push_back(S);
1078   TypeIndices[&Symbol] = Pair.first->second;
1079
1080   LLVM_DEBUG(dbgs() << "registerEventType: " << Symbol << " new:" << Pair.second
1081                     << "\n");
1082   LLVM_DEBUG(dbgs() << "  -> type index: " << Pair.first->second << "\n");
1083 }
1084
1085 static bool isInSymtab(const MCSymbolWasm &Sym) {
1086   if (Sym.isUsedInReloc())
1087     return true;
1088
1089   if (Sym.isComdat() && !Sym.isDefined())
1090     return false;
1091
1092   if (Sym.isTemporary() && Sym.getName().empty())
1093     return false;
1094
1095   if (Sym.isTemporary() && Sym.isData() && !Sym.getSize())
1096     return false;
1097
1098   if (Sym.isSection())
1099     return false;
1100
1101   return true;
1102 }
1103
1104 uint64_t WasmObjectWriter::writeObject(MCAssembler &Asm,
1105                                        const MCAsmLayout &Layout) {
1106   uint64_t StartOffset = W.OS.tell();
1107
1108   LLVM_DEBUG(dbgs() << "WasmObjectWriter::writeObject\n");
1109
1110   // Collect information from the available symbols.
1111   SmallVector<WasmFunction, 4> Functions;
1112   SmallVector<uint32_t, 4> TableElems;
1113   SmallVector<wasm::WasmImport, 4> Imports;
1114   SmallVector<wasm::WasmExport, 4> Exports;
1115   SmallVector<wasm::WasmEventType, 1> Events;
1116   SmallVector<wasm::WasmSymbolInfo, 4> SymbolInfos;
1117   SmallVector<std::pair<uint16_t, uint32_t>, 2> InitFuncs;
1118   std::map<StringRef, std::vector<WasmComdatEntry>> Comdats;
1119   uint32_t DataSize = 0;
1120
1121   // For now, always emit the memory import, since loads and stores are not
1122   // valid without it. In the future, we could perhaps be more clever and omit
1123   // it if there are no loads or stores.
1124   wasm::WasmImport MemImport;
1125   MemImport.Module = "env";
1126   MemImport.Field = "__linear_memory";
1127   MemImport.Kind = wasm::WASM_EXTERNAL_MEMORY;
1128   Imports.push_back(MemImport);
1129
1130   // For now, always emit the table section, since indirect calls are not
1131   // valid without it. In the future, we could perhaps be more clever and omit
1132   // it if there are no indirect calls.
1133   wasm::WasmImport TableImport;
1134   TableImport.Module = "env";
1135   TableImport.Field = "__indirect_function_table";
1136   TableImport.Kind = wasm::WASM_EXTERNAL_TABLE;
1137   TableImport.Table.ElemType = wasm::WASM_TYPE_FUNCREF;
1138   Imports.push_back(TableImport);
1139
1140   // Populate SignatureIndices, and Imports and WasmIndices for undefined
1141   // symbols.  This must be done before populating WasmIndices for defined
1142   // symbols.
1143   for (const MCSymbol &S : Asm.symbols()) {
1144     const auto &WS = static_cast<const MCSymbolWasm &>(S);
1145
1146     // Register types for all functions, including those with private linkage
1147     // (because wasm always needs a type signature).
1148     if (WS.isFunction())
1149       registerFunctionType(WS);
1150
1151     if (WS.isEvent())
1152       registerEventType(WS);
1153
1154     if (WS.isTemporary())
1155       continue;
1156
1157     // If the symbol is not defined in this translation unit, import it.
1158     if (!WS.isDefined() && !WS.isComdat()) {
1159       if (WS.isFunction()) {
1160         wasm::WasmImport Import;
1161         Import.Module = WS.getImportModule();
1162         Import.Field = WS.getImportName();
1163         Import.Kind = wasm::WASM_EXTERNAL_FUNCTION;
1164         Import.SigIndex = getFunctionType(WS);
1165         Imports.push_back(Import);
1166         assert(WasmIndices.count(&WS) == 0);
1167         WasmIndices[&WS] = NumFunctionImports++;
1168       } else if (WS.isGlobal()) {
1169         if (WS.isWeak())
1170           report_fatal_error("undefined global symbol cannot be weak");
1171
1172         wasm::WasmImport Import;
1173         Import.Field = WS.getImportName();
1174         Import.Kind = wasm::WASM_EXTERNAL_GLOBAL;
1175         Import.Module = WS.getImportModule();
1176         Import.Global = WS.getGlobalType();
1177         Imports.push_back(Import);
1178         assert(WasmIndices.count(&WS) == 0);
1179         WasmIndices[&WS] = NumGlobalImports++;
1180       } else if (WS.isEvent()) {
1181         if (WS.isWeak())
1182           report_fatal_error("undefined event symbol cannot be weak");
1183
1184         wasm::WasmImport Import;
1185         Import.Module = WS.getImportModule();
1186         Import.Field = WS.getImportName();
1187         Import.Kind = wasm::WASM_EXTERNAL_EVENT;
1188         Import.Event.Attribute = wasm::WASM_EVENT_ATTRIBUTE_EXCEPTION;
1189         Import.Event.SigIndex = getEventType(WS);
1190         Imports.push_back(Import);
1191         assert(WasmIndices.count(&WS) == 0);
1192         WasmIndices[&WS] = NumEventImports++;
1193       }
1194     }
1195   }
1196
1197   // Add imports for GOT globals
1198   for (const MCSymbol &S : Asm.symbols()) {
1199     const auto &WS = static_cast<const MCSymbolWasm &>(S);
1200     if (WS.isUsedInGOT()) {
1201       wasm::WasmImport Import;
1202       if (WS.isFunction())
1203         Import.Module = "GOT.func";
1204       else
1205         Import.Module = "GOT.mem";
1206       Import.Field = WS.getName();
1207       Import.Kind = wasm::WASM_EXTERNAL_GLOBAL;
1208       Import.Global = {wasm::WASM_TYPE_I32, true};
1209       Imports.push_back(Import);
1210       assert(GOTIndices.count(&WS) == 0);
1211       GOTIndices[&WS] = NumGlobalImports++;
1212     }
1213   }
1214
1215   // Populate DataSegments and CustomSections, which must be done before
1216   // populating DataLocations.
1217   for (MCSection &Sec : Asm) {
1218     auto &Section = static_cast<MCSectionWasm &>(Sec);
1219     StringRef SectionName = Section.getSectionName();
1220
1221     // .init_array sections are handled specially elsewhere.
1222     if (SectionName.startswith(".init_array"))
1223       continue;
1224
1225     // Code is handled separately
1226     if (Section.getKind().isText())
1227       continue;
1228
1229     if (Section.isWasmData()) {
1230       uint32_t SegmentIndex = DataSegments.size();
1231       DataSize = alignTo(DataSize, Section.getAlignment());
1232       DataSegments.emplace_back();
1233       WasmDataSegment &Segment = DataSegments.back();
1234       Segment.Name = SectionName;
1235       Segment.InitFlags =
1236           Section.getPassive() ? (uint32_t)wasm::WASM_SEGMENT_IS_PASSIVE : 0;
1237       Segment.Offset = DataSize;
1238       Segment.Section = &Section;
1239       addData(Segment.Data, Section);
1240       Segment.Alignment = Log2_32(Section.getAlignment());
1241       Segment.LinkerFlags = 0;
1242       DataSize += Segment.Data.size();
1243       Section.setSegmentIndex(SegmentIndex);
1244
1245       if (const MCSymbolWasm *C = Section.getGroup()) {
1246         Comdats[C->getName()].emplace_back(
1247             WasmComdatEntry{wasm::WASM_COMDAT_DATA, SegmentIndex});
1248       }
1249     } else {
1250       // Create custom sections
1251       assert(Sec.getKind().isMetadata());
1252
1253       StringRef Name = SectionName;
1254
1255       // For user-defined custom sections, strip the prefix
1256       if (Name.startswith(".custom_section."))
1257         Name = Name.substr(strlen(".custom_section."));
1258
1259       MCSymbol *Begin = Sec.getBeginSymbol();
1260       if (Begin) {
1261         WasmIndices[cast<MCSymbolWasm>(Begin)] = CustomSections.size();
1262         if (SectionName != Begin->getName())
1263           report_fatal_error("section name and begin symbol should match: " +
1264                              Twine(SectionName));
1265       }
1266
1267       // Separate out the producers and target features sections
1268       if (Name == "producers") {
1269         ProducersSection = std::make_unique<WasmCustomSection>(Name, &Section);
1270         continue;
1271       }
1272       if (Name == "target_features") {
1273         TargetFeaturesSection =
1274             std::make_unique<WasmCustomSection>(Name, &Section);
1275         continue;
1276       }
1277
1278       CustomSections.emplace_back(Name, &Section);
1279     }
1280   }
1281
1282   // Populate WasmIndices and DataLocations for defined symbols.
1283   for (const MCSymbol &S : Asm.symbols()) {
1284     // Ignore unnamed temporary symbols, which aren't ever exported, imported,
1285     // or used in relocations.
1286     if (S.isTemporary() && S.getName().empty())
1287       continue;
1288
1289     const auto &WS = static_cast<const MCSymbolWasm &>(S);
1290     LLVM_DEBUG(
1291         dbgs() << "MCSymbol: " << toString(WS.getType()) << " '" << S << "'"
1292                << " isDefined=" << S.isDefined() << " isExternal="
1293                << S.isExternal() << " isTemporary=" << S.isTemporary()
1294                << " isWeak=" << WS.isWeak() << " isHidden=" << WS.isHidden()
1295                << " isVariable=" << WS.isVariable() << "\n");
1296
1297     if (WS.isVariable())
1298       continue;
1299     if (WS.isComdat() && !WS.isDefined())
1300       continue;
1301
1302     if (WS.isFunction()) {
1303       unsigned Index;
1304       if (WS.isDefined()) {
1305         if (WS.getOffset() != 0)
1306           report_fatal_error(
1307               "function sections must contain one function each");
1308
1309         if (WS.getSize() == nullptr)
1310           report_fatal_error(
1311               "function symbols must have a size set with .size");
1312
1313         // A definition. Write out the function body.
1314         Index = NumFunctionImports + Functions.size();
1315         WasmFunction Func;
1316         Func.SigIndex = getFunctionType(WS);
1317         Func.Sym = &WS;
1318         WasmIndices[&WS] = Index;
1319         Functions.push_back(Func);
1320
1321         auto &Section = static_cast<MCSectionWasm &>(WS.getSection());
1322         if (const MCSymbolWasm *C = Section.getGroup()) {
1323           Comdats[C->getName()].emplace_back(
1324               WasmComdatEntry{wasm::WASM_COMDAT_FUNCTION, Index});
1325         }
1326       } else {
1327         // An import; the index was assigned above.
1328         Index = WasmIndices.find(&WS)->second;
1329       }
1330
1331       LLVM_DEBUG(dbgs() << "  -> function index: " << Index << "\n");
1332
1333     } else if (WS.isData()) {
1334       if (!isInSymtab(WS))
1335         continue;
1336
1337       if (!WS.isDefined()) {
1338         LLVM_DEBUG(dbgs() << "  -> segment index: -1"
1339                           << "\n");
1340         continue;
1341       }
1342
1343       if (!WS.getSize())
1344         report_fatal_error("data symbols must have a size set with .size: " +
1345                            WS.getName());
1346
1347       int64_t Size = 0;
1348       if (!WS.getSize()->evaluateAsAbsolute(Size, Layout))
1349         report_fatal_error(".size expression must be evaluatable");
1350
1351       auto &DataSection = static_cast<MCSectionWasm &>(WS.getSection());
1352       assert(DataSection.isWasmData());
1353
1354       // For each data symbol, export it in the symtab as a reference to the
1355       // corresponding Wasm data segment.
1356       wasm::WasmDataReference Ref = wasm::WasmDataReference{
1357           DataSection.getSegmentIndex(),
1358           static_cast<uint32_t>(Layout.getSymbolOffset(WS)),
1359           static_cast<uint32_t>(Size)};
1360       DataLocations[&WS] = Ref;
1361       LLVM_DEBUG(dbgs() << "  -> segment index: " << Ref.Segment << "\n");
1362
1363     } else if (WS.isGlobal()) {
1364       // A "true" Wasm global (currently just __stack_pointer)
1365       if (WS.isDefined())
1366         report_fatal_error("don't yet support defined globals");
1367
1368       // An import; the index was assigned above
1369       LLVM_DEBUG(dbgs() << "  -> global index: "
1370                         << WasmIndices.find(&WS)->second << "\n");
1371
1372     } else if (WS.isEvent()) {
1373       // C++ exception symbol (__cpp_exception)
1374       unsigned Index;
1375       if (WS.isDefined()) {
1376         Index = NumEventImports + Events.size();
1377         wasm::WasmEventType Event;
1378         Event.SigIndex = getEventType(WS);
1379         Event.Attribute = wasm::WASM_EVENT_ATTRIBUTE_EXCEPTION;
1380         assert(WasmIndices.count(&WS) == 0);
1381         WasmIndices[&WS] = Index;
1382         Events.push_back(Event);
1383       } else {
1384         // An import; the index was assigned above.
1385         assert(WasmIndices.count(&WS) > 0);
1386       }
1387       LLVM_DEBUG(dbgs() << "  -> event index: " << WasmIndices.find(&WS)->second
1388                         << "\n");
1389
1390     } else {
1391       assert(WS.isSection());
1392     }
1393   }
1394
1395   // Populate WasmIndices and DataLocations for aliased symbols.  We need to
1396   // process these in a separate pass because we need to have processed the
1397   // target of the alias before the alias itself and the symbols are not
1398   // necessarily ordered in this way.
1399   for (const MCSymbol &S : Asm.symbols()) {
1400     if (!S.isVariable())
1401       continue;
1402
1403     assert(S.isDefined());
1404
1405     // Find the target symbol of this weak alias and export that index
1406     const auto &WS = static_cast<const MCSymbolWasm &>(S);
1407     const MCSymbolWasm *ResolvedSym = resolveSymbol(WS);
1408     LLVM_DEBUG(dbgs() << WS.getName() << ": weak alias of '" << *ResolvedSym
1409                       << "'\n");
1410
1411     if (ResolvedSym->isFunction()) {
1412       assert(WasmIndices.count(ResolvedSym) > 0);
1413       uint32_t WasmIndex = WasmIndices.find(ResolvedSym)->second;
1414       assert(WasmIndices.count(&WS) == 0);
1415       WasmIndices[&WS] = WasmIndex;
1416       LLVM_DEBUG(dbgs() << "  -> index:" << WasmIndex << "\n");
1417     } else if (ResolvedSym->isData()) {
1418       assert(DataLocations.count(ResolvedSym) > 0);
1419       const wasm::WasmDataReference &Ref =
1420           DataLocations.find(ResolvedSym)->second;
1421       DataLocations[&WS] = Ref;
1422       LLVM_DEBUG(dbgs() << "  -> index:" << Ref.Segment << "\n");
1423     } else {
1424       report_fatal_error("don't yet support global/event aliases");
1425     }
1426   }
1427
1428   // Finally, populate the symbol table itself, in its "natural" order.
1429   for (const MCSymbol &S : Asm.symbols()) {
1430     const auto &WS = static_cast<const MCSymbolWasm &>(S);
1431     if (!isInSymtab(WS)) {
1432       WS.setIndex(InvalidIndex);
1433       continue;
1434     }
1435     LLVM_DEBUG(dbgs() << "adding to symtab: " << WS << "\n");
1436
1437     uint32_t Flags = 0;
1438     if (WS.isWeak())
1439       Flags |= wasm::WASM_SYMBOL_BINDING_WEAK;
1440     if (WS.isHidden())
1441       Flags |= wasm::WASM_SYMBOL_VISIBILITY_HIDDEN;
1442     if (!WS.isExternal() && WS.isDefined())
1443       Flags |= wasm::WASM_SYMBOL_BINDING_LOCAL;
1444     if (WS.isUndefined())
1445       Flags |= wasm::WASM_SYMBOL_UNDEFINED;
1446     if (WS.isExported())
1447       Flags |= wasm::WASM_SYMBOL_EXPORTED;
1448     if (WS.getName() != WS.getImportName())
1449       Flags |= wasm::WASM_SYMBOL_EXPLICIT_NAME;
1450
1451     wasm::WasmSymbolInfo Info;
1452     Info.Name = WS.getName();
1453     Info.Kind = WS.getType();
1454     Info.Flags = Flags;
1455     if (!WS.isData()) {
1456       assert(WasmIndices.count(&WS) > 0);
1457       Info.ElementIndex = WasmIndices.find(&WS)->second;
1458     } else if (WS.isDefined()) {
1459       assert(DataLocations.count(&WS) > 0);
1460       Info.DataRef = DataLocations.find(&WS)->second;
1461     }
1462     WS.setIndex(SymbolInfos.size());
1463     SymbolInfos.emplace_back(Info);
1464   }
1465
1466   {
1467     auto HandleReloc = [&](const WasmRelocationEntry &Rel) {
1468       // Functions referenced by a relocation need to put in the table.  This is
1469       // purely to make the object file's provisional values readable, and is
1470       // ignored by the linker, which re-calculates the relocations itself.
1471       if (Rel.Type != wasm::R_WASM_TABLE_INDEX_I32 &&
1472           Rel.Type != wasm::R_WASM_TABLE_INDEX_SLEB)
1473         return;
1474       assert(Rel.Symbol->isFunction());
1475       const MCSymbolWasm &WS = *resolveSymbol(*Rel.Symbol);
1476       uint32_t FunctionIndex = WasmIndices.find(&WS)->second;
1477       uint32_t TableIndex = TableElems.size() + InitialTableOffset;
1478       if (TableIndices.try_emplace(&WS, TableIndex).second) {
1479         LLVM_DEBUG(dbgs() << "  -> adding " << WS.getName()
1480                           << " to table: " << TableIndex << "\n");
1481         TableElems.push_back(FunctionIndex);
1482         registerFunctionType(WS);
1483       }
1484     };
1485
1486     for (const WasmRelocationEntry &RelEntry : CodeRelocations)
1487       HandleReloc(RelEntry);
1488     for (const WasmRelocationEntry &RelEntry : DataRelocations)
1489       HandleReloc(RelEntry);
1490   }
1491
1492   // Translate .init_array section contents into start functions.
1493   for (const MCSection &S : Asm) {
1494     const auto &WS = static_cast<const MCSectionWasm &>(S);
1495     if (WS.getSectionName().startswith(".fini_array"))
1496       report_fatal_error(".fini_array sections are unsupported");
1497     if (!WS.getSectionName().startswith(".init_array"))
1498       continue;
1499     if (WS.getFragmentList().empty())
1500       continue;
1501
1502     // init_array is expected to contain a single non-empty data fragment
1503     if (WS.getFragmentList().size() != 3)
1504       report_fatal_error("only one .init_array section fragment supported");
1505
1506     auto IT = WS.begin();
1507     const MCFragment &EmptyFrag = *IT;
1508     if (EmptyFrag.getKind() != MCFragment::FT_Data)
1509       report_fatal_error(".init_array section should be aligned");
1510
1511     IT = std::next(IT);
1512     const MCFragment &AlignFrag = *IT;
1513     if (AlignFrag.getKind() != MCFragment::FT_Align)
1514       report_fatal_error(".init_array section should be aligned");
1515     if (cast<MCAlignFragment>(AlignFrag).getAlignment() != (is64Bit() ? 8 : 4))
1516       report_fatal_error(".init_array section should be aligned for pointers");
1517
1518     const MCFragment &Frag = *std::next(IT);
1519     if (Frag.hasInstructions() || Frag.getKind() != MCFragment::FT_Data)
1520       report_fatal_error("only data supported in .init_array section");
1521
1522     uint16_t Priority = UINT16_MAX;
1523     unsigned PrefixLength = strlen(".init_array");
1524     if (WS.getSectionName().size() > PrefixLength) {
1525       if (WS.getSectionName()[PrefixLength] != '.')
1526         report_fatal_error(
1527             ".init_array section priority should start with '.'");
1528       if (WS.getSectionName()
1529               .substr(PrefixLength + 1)
1530               .getAsInteger(10, Priority))
1531         report_fatal_error("invalid .init_array section priority");
1532     }
1533     const auto &DataFrag = cast<MCDataFragment>(Frag);
1534     const SmallVectorImpl<char> &Contents = DataFrag.getContents();
1535     for (const uint8_t *
1536              P = (const uint8_t *)Contents.data(),
1537             *End = (const uint8_t *)Contents.data() + Contents.size();
1538          P != End; ++P) {
1539       if (*P != 0)
1540         report_fatal_error("non-symbolic data in .init_array section");
1541     }
1542     for (const MCFixup &Fixup : DataFrag.getFixups()) {
1543       assert(Fixup.getKind() ==
1544              MCFixup::getKindForSize(is64Bit() ? 8 : 4, false));
1545       const MCExpr *Expr = Fixup.getValue();
1546       auto *SymRef = dyn_cast<MCSymbolRefExpr>(Expr);
1547       if (!SymRef)
1548         report_fatal_error("fixups in .init_array should be symbol references");
1549       const auto &TargetSym = cast<const MCSymbolWasm>(SymRef->getSymbol());
1550       if (TargetSym.getIndex() == InvalidIndex)
1551         report_fatal_error("symbols in .init_array should exist in symbtab");
1552       if (!TargetSym.isFunction())
1553         report_fatal_error("symbols in .init_array should be for functions");
1554       InitFuncs.push_back(
1555           std::make_pair(Priority, TargetSym.getIndex()));
1556     }
1557   }
1558
1559   // Write out the Wasm header.
1560   writeHeader(Asm);
1561
1562   writeTypeSection(Signatures);
1563   writeImportSection(Imports, DataSize, TableElems.size());
1564   writeFunctionSection(Functions);
1565   // Skip the "table" section; we import the table instead.
1566   // Skip the "memory" section; we import the memory instead.
1567   writeEventSection(Events);
1568   writeExportSection(Exports);
1569   writeElemSection(TableElems);
1570   writeDataCountSection();
1571   writeCodeSection(Asm, Layout, Functions);
1572   writeDataSection();
1573   for (auto &CustomSection : CustomSections)
1574     writeCustomSection(CustomSection, Asm, Layout);
1575   writeLinkingMetaDataSection(SymbolInfos, InitFuncs, Comdats);
1576   writeRelocSection(CodeSectionIndex, "CODE", CodeRelocations);
1577   writeRelocSection(DataSectionIndex, "DATA", DataRelocations);
1578   writeCustomRelocSections();
1579   if (ProducersSection)
1580     writeCustomSection(*ProducersSection, Asm, Layout);
1581   if (TargetFeaturesSection)
1582     writeCustomSection(*TargetFeaturesSection, Asm, Layout);
1583
1584   // TODO: Translate the .comment section to the output.
1585   return W.OS.tell() - StartOffset;
1586 }
1587
1588 std::unique_ptr<MCObjectWriter>
1589 llvm::createWasmObjectWriter(std::unique_ptr<MCWasmObjectTargetWriter> MOTW,
1590                              raw_pwrite_stream &OS) {
1591   return std::make_unique<WasmObjectWriter>(std::move(MOTW), OS);
1592 }