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/BinaryFormat/Wasm.h"
15#include "llvm/BinaryFormat/WasmTraits.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/EndianStream.h"
31#include "llvm/Support/ErrorHandling.h"
32#include "llvm/Support/LEB128.h"
33#include <vector>
34
35using namespace llvm;
36
37#define DEBUG_TYPE "mc"
38
39namespace {
40
41// When we create the indirect function table we start at 1, so that there is
42// and empty slot at 0 and therefore calling a null function pointer will trap.
43static 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.
48struct 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// A wasm data segment.  A wasm binary contains only a single data section
59// but that can contain many segments, each with their own virtual location
60// in memory.  Each MCSection data created by llvm is modeled as its own
61// wasm data segment.
62struct WasmDataSegment {
63  MCSectionWasm *Section;
64  StringRef Name;
65  uint32_t InitFlags;
66  uint64_t Offset;
67  uint32_t Alignment;
68  uint32_t LinkingFlags;
69  SmallVector<char, 4> Data;
70};
71
72// A wasm function to be written into the function section.
73struct WasmFunction {
74  uint32_t SigIndex;
75  MCSection *Section;
76};
77
78// A wasm global to be written into the global section.
79struct WasmGlobal {
80  wasm::WasmGlobalType Type;
81  uint64_t InitialValue;
82};
83
84// Information about a single item which is part of a COMDAT.  For each data
85// segment or function which is in the COMDAT, there is a corresponding
86// WasmComdatEntry.
87struct WasmComdatEntry {
88  unsigned Kind;
89  uint32_t Index;
90};
91
92// Information about a single relocation.
93struct WasmRelocationEntry {
94  uint64_t Offset;                   // Where is the relocation.
95  const MCSymbolWasm *Symbol;        // The symbol to relocate with.
96  int64_t Addend;                    // A value to add to the symbol.
97  unsigned Type;                     // The type of the relocation.
98  const MCSectionWasm *FixupSection; // The section the relocation is targeting.
99
100  WasmRelocationEntry(uint64_t Offset, const MCSymbolWasm *Symbol,
101                      int64_t Addend, unsigned Type,
102                      const MCSectionWasm *FixupSection)
103      : Offset(Offset), Symbol(Symbol), Addend(Addend), Type(Type),
104        FixupSection(FixupSection) {}
105
106  bool hasAddend() const { return wasm::relocTypeHasAddend(Type); }
107
108  void print(raw_ostream &Out) const {
109    Out << wasm::relocTypetoString(Type) << " Off=" << Offset
110        << ", Sym=" << *Symbol << ", Addend=" << Addend
111        << ", FixupSection=" << FixupSection->getName();
112  }
113
114#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
115  LLVM_DUMP_METHOD void dump() const { print(dbgs()); }
116#endif
117};
118
119static const uint32_t InvalidIndex = -1;
120
121struct WasmCustomSection {
122
123  StringRef Name;
124  MCSectionWasm *Section;
125
126  uint32_t OutputContentsOffset = 0;
127  uint32_t OutputIndex = InvalidIndex;
128
129  WasmCustomSection(StringRef Name, MCSectionWasm *Section)
130      : Name(Name), Section(Section) {}
131};
132
133#if !defined(NDEBUG)
134raw_ostream &operator<<(raw_ostream &OS, const WasmRelocationEntry &Rel) {
135  Rel.print(OS);
136  return OS;
137}
138#endif
139
140// Write Value as an (unsigned) LEB value at offset Offset in Stream, padded
141// to allow patching.
142template <typename T, int W>
143void writePatchableULEB(raw_pwrite_stream &Stream, T Value, uint64_t Offset) {
144  uint8_t Buffer[W];
145  unsigned SizeLen = encodeULEB128(Value, Buffer, W);
146  assert(SizeLen == W);
147  Stream.pwrite((char *)Buffer, SizeLen, Offset);
148}
149
150// Write Value as an signed LEB value at offset Offset in Stream, padded
151// to allow patching.
152template <typename T, int W>
153void writePatchableSLEB(raw_pwrite_stream &Stream, T Value, uint64_t Offset) {
154  uint8_t Buffer[W];
155  unsigned SizeLen = encodeSLEB128(Value, Buffer, W);
156  assert(SizeLen == W);
157  Stream.pwrite((char *)Buffer, SizeLen, Offset);
158}
159
160static void writePatchableU32(raw_pwrite_stream &Stream, uint32_t Value,
161                              uint64_t Offset) {
162  writePatchableULEB<uint32_t, 5>(Stream, Value, Offset);
163}
164
165static void writePatchableS32(raw_pwrite_stream &Stream, int32_t Value,
166                              uint64_t Offset) {
167  writePatchableSLEB<int32_t, 5>(Stream, Value, Offset);
168}
169
170static void writePatchableU64(raw_pwrite_stream &Stream, uint64_t Value,
171                              uint64_t Offset) {
172  writePatchableSLEB<uint64_t, 10>(Stream, Value, Offset);
173}
174
175static void writePatchableS64(raw_pwrite_stream &Stream, int64_t Value,
176                              uint64_t Offset) {
177  writePatchableSLEB<int64_t, 10>(Stream, Value, Offset);
178}
179
180// Write Value as a plain integer value at offset Offset in Stream.
181static void patchI32(raw_pwrite_stream &Stream, uint32_t Value,
182                     uint64_t Offset) {
183  uint8_t Buffer[4];
184  support::endian::write32le(Buffer, Value);
185  Stream.pwrite((char *)Buffer, sizeof(Buffer), Offset);
186}
187
188static void patchI64(raw_pwrite_stream &Stream, uint64_t Value,
189                     uint64_t Offset) {
190  uint8_t Buffer[8];
191  support::endian::write64le(Buffer, Value);
192  Stream.pwrite((char *)Buffer, sizeof(Buffer), Offset);
193}
194
195bool isDwoSection(const MCSection &Sec) {
196  return Sec.getName().ends_with(".dwo");
197}
198
199class WasmObjectWriter : public MCObjectWriter {
200  support::endian::Writer *W = nullptr;
201
202  /// The target specific Wasm writer instance.
203  std::unique_ptr<MCWasmObjectTargetWriter> TargetObjectWriter;
204
205  // Relocations for fixing up references in the code section.
206  std::vector<WasmRelocationEntry> CodeRelocations;
207  // Relocations for fixing up references in the data section.
208  std::vector<WasmRelocationEntry> DataRelocations;
209
210  // Index values to use for fixing up call_indirect type indices.
211  // Maps function symbols to the index of the type of the function
212  DenseMap<const MCSymbolWasm *, uint32_t> TypeIndices;
213  // Maps function symbols to the table element index space. Used
214  // for TABLE_INDEX relocation types (i.e. address taken functions).
215  DenseMap<const MCSymbolWasm *, uint32_t> TableIndices;
216  // Maps function/global/table symbols to the
217  // function/global/table/tag/section index space.
218  DenseMap<const MCSymbolWasm *, uint32_t> WasmIndices;
219  DenseMap<const MCSymbolWasm *, uint32_t> GOTIndices;
220  // Maps data symbols to the Wasm segment and offset/size with the segment.
221  DenseMap<const MCSymbolWasm *, wasm::WasmDataReference> DataLocations;
222
223  // Stores output data (index, relocations, content offset) for custom
224  // section.
225  std::vector<WasmCustomSection> CustomSections;
226  std::unique_ptr<WasmCustomSection> ProducersSection;
227  std::unique_ptr<WasmCustomSection> TargetFeaturesSection;
228  // Relocations for fixing up references in the custom sections.
229  DenseMap<const MCSectionWasm *, std::vector<WasmRelocationEntry>>
230      CustomSectionsRelocations;
231
232  // Map from section to defining function symbol.
233  DenseMap<const MCSection *, const MCSymbol *> SectionFunctions;
234
235  DenseMap<wasm::WasmSignature, uint32_t> SignatureIndices;
236  SmallVector<wasm::WasmSignature, 4> Signatures;
237  SmallVector<WasmDataSegment, 4> DataSegments;
238  unsigned NumFunctionImports = 0;
239  unsigned NumGlobalImports = 0;
240  unsigned NumTableImports = 0;
241  unsigned NumTagImports = 0;
242  uint32_t SectionCount = 0;
243
244  enum class DwoMode {
245    AllSections,
246    NonDwoOnly,
247    DwoOnly,
248  };
249  bool IsSplitDwarf = false;
250  raw_pwrite_stream *OS = nullptr;
251  raw_pwrite_stream *DwoOS = nullptr;
252
253  // TargetObjectWriter wranppers.
254  bool is64Bit() const { return TargetObjectWriter->is64Bit(); }
255  bool isEmscripten() const { return TargetObjectWriter->isEmscripten(); }
256
257  void startSection(SectionBookkeeping &Section, unsigned SectionId);
258  void startCustomSection(SectionBookkeeping &Section, StringRef Name);
259  void endSection(SectionBookkeeping &Section);
260
261public:
262  WasmObjectWriter(std::unique_ptr<MCWasmObjectTargetWriter> MOTW,
263                   raw_pwrite_stream &OS_)
264      : TargetObjectWriter(std::move(MOTW)), OS(&OS_) {}
265
266  WasmObjectWriter(std::unique_ptr<MCWasmObjectTargetWriter> MOTW,
267                   raw_pwrite_stream &OS_, raw_pwrite_stream &DwoOS_)
268      : TargetObjectWriter(std::move(MOTW)), IsSplitDwarf(true), OS(&OS_),
269        DwoOS(&DwoOS_) {}
270
271private:
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    NumTableImports = 0;
291    MCObjectWriter::reset();
292  }
293
294  void writeHeader(const MCAssembler &Asm);
295
296  void recordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
297                        const MCFragment *Fragment, const MCFixup &Fixup,
298                        MCValue Target, uint64_t &FixedValue) override;
299
300  void executePostLayoutBinding(MCAssembler &Asm,
301                                const MCAsmLayout &Layout) override;
302  void prepareImports(SmallVectorImpl<wasm::WasmImport> &Imports,
303                      MCAssembler &Asm, const MCAsmLayout &Layout);
304  uint64_t writeObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
305
306  uint64_t writeOneObject(MCAssembler &Asm, const MCAsmLayout &Layout,
307                          DwoMode Mode);
308
309  void writeString(const StringRef Str) {
310    encodeULEB128(Str.size(), W->OS);
311    W->OS << Str;
312  }
313
314  void writeStringWithAlignment(const StringRef Str, unsigned Alignment);
315
316  void writeI32(int32_t val) {
317    char Buffer[4];
318    support::endian::write32le(Buffer, val);
319    W->OS.write(Buffer, sizeof(Buffer));
320  }
321
322  void writeI64(int64_t val) {
323    char Buffer[8];
324    support::endian::write64le(Buffer, val);
325    W->OS.write(Buffer, sizeof(Buffer));
326  }
327
328  void writeValueType(wasm::ValType Ty) { W->OS << static_cast<char>(Ty); }
329
330  void writeTypeSection(ArrayRef<wasm::WasmSignature> Signatures);
331  void writeImportSection(ArrayRef<wasm::WasmImport> Imports, uint64_t DataSize,
332                          uint32_t NumElements);
333  void writeFunctionSection(ArrayRef<WasmFunction> Functions);
334  void writeExportSection(ArrayRef<wasm::WasmExport> Exports);
335  void writeElemSection(const MCSymbolWasm *IndirectFunctionTable,
336                        ArrayRef<uint32_t> TableElems);
337  void writeDataCountSection();
338  uint32_t writeCodeSection(const MCAssembler &Asm, const MCAsmLayout &Layout,
339                            ArrayRef<WasmFunction> Functions);
340  uint32_t writeDataSection(const MCAsmLayout &Layout);
341  void writeTagSection(ArrayRef<uint32_t> TagTypes);
342  void writeGlobalSection(ArrayRef<wasm::WasmGlobal> Globals);
343  void writeTableSection(ArrayRef<wasm::WasmTable> Tables);
344  void writeRelocSection(uint32_t SectionIndex, StringRef Name,
345                         std::vector<WasmRelocationEntry> &Relocations);
346  void writeLinkingMetaDataSection(
347      ArrayRef<wasm::WasmSymbolInfo> SymbolInfos,
348      ArrayRef<std::pair<uint16_t, uint32_t>> InitFuncs,
349      const std::map<StringRef, std::vector<WasmComdatEntry>> &Comdats);
350  void writeCustomSection(WasmCustomSection &CustomSection,
351                          const MCAssembler &Asm, const MCAsmLayout &Layout);
352  void writeCustomRelocSections();
353
354  uint64_t getProvisionalValue(const WasmRelocationEntry &RelEntry,
355                               const MCAsmLayout &Layout);
356  void applyRelocations(ArrayRef<WasmRelocationEntry> Relocations,
357                        uint64_t ContentsOffset, const MCAsmLayout &Layout);
358
359  uint32_t getRelocationIndexValue(const WasmRelocationEntry &RelEntry);
360  uint32_t getFunctionType(const MCSymbolWasm &Symbol);
361  uint32_t getTagType(const MCSymbolWasm &Symbol);
362  void registerFunctionType(const MCSymbolWasm &Symbol);
363  void registerTagType(const MCSymbolWasm &Symbol);
364};
365
366} // end anonymous namespace
367
368// Write out a section header and a patchable section size field.
369void WasmObjectWriter::startSection(SectionBookkeeping &Section,
370                                    unsigned SectionId) {
371  LLVM_DEBUG(dbgs() << "startSection " << SectionId << "\n");
372  W->OS << char(SectionId);
373
374  Section.SizeOffset = W->OS.tell();
375
376  // The section size. We don't know the size yet, so reserve enough space
377  // for any 32-bit value; we'll patch it later.
378  encodeULEB128(0, W->OS, 5);
379
380  // The position where the section starts, for measuring its size.
381  Section.ContentsOffset = W->OS.tell();
382  Section.PayloadOffset = W->OS.tell();
383  Section.Index = SectionCount++;
384}
385
386// Write a string with extra paddings for trailing alignment
387// TODO: support alignment at asm and llvm level?
388void WasmObjectWriter::writeStringWithAlignment(const StringRef Str,
389                                                unsigned Alignment) {
390
391  // Calculate the encoded size of str length and add pads based on it and
392  // alignment.
393  raw_null_ostream NullOS;
394  uint64_t StrSizeLength = encodeULEB128(Str.size(), NullOS);
395  uint64_t Offset = W->OS.tell() + StrSizeLength + Str.size();
396  uint64_t Paddings = offsetToAlignment(Offset, Align(Alignment));
397  Offset += Paddings;
398
399  // LEB128 greater than 5 bytes is invalid
400  assert((StrSizeLength + Paddings) <= 5 && "too long string to align");
401
402  encodeSLEB128(Str.size(), W->OS, StrSizeLength + Paddings);
403  W->OS << Str;
404
405  assert(W->OS.tell() == Offset && "invalid padding");
406}
407
408void WasmObjectWriter::startCustomSection(SectionBookkeeping &Section,
409                                          StringRef Name) {
410  LLVM_DEBUG(dbgs() << "startCustomSection " << Name << "\n");
411  startSection(Section, wasm::WASM_SEC_CUSTOM);
412
413  // The position where the section header ends, for measuring its size.
414  Section.PayloadOffset = W->OS.tell();
415
416  // Custom sections in wasm also have a string identifier.
417  if (Name != "__clangast") {
418    writeString(Name);
419  } else {
420    // The on-disk hashtable in clangast needs to be aligned by 4 bytes.
421    writeStringWithAlignment(Name, 4);
422  }
423
424  // The position where the custom section starts.
425  Section.ContentsOffset = W->OS.tell();
426}
427
428// Now that the section is complete and we know how big it is, patch up the
429// section size field at the start of the section.
430void WasmObjectWriter::endSection(SectionBookkeeping &Section) {
431  uint64_t Size = W->OS.tell();
432  // /dev/null doesn't support seek/tell and can report offset of 0.
433  // Simply skip this patching in that case.
434  if (!Size)
435    return;
436
437  Size -= Section.PayloadOffset;
438  if (uint32_t(Size) != Size)
439    report_fatal_error("section size does not fit in a uint32_t");
440
441  LLVM_DEBUG(dbgs() << "endSection size=" << Size << "\n");
442
443  // Write the final section size to the payload_len field, which follows
444  // the section id byte.
445  writePatchableU32(static_cast<raw_pwrite_stream &>(W->OS), Size,
446                    Section.SizeOffset);
447}
448
449// Emit the Wasm header.
450void WasmObjectWriter::writeHeader(const MCAssembler &Asm) {
451  W->OS.write(wasm::WasmMagic, sizeof(wasm::WasmMagic));
452  W->write<uint32_t>(wasm::WasmVersion);
453}
454
455void WasmObjectWriter::executePostLayoutBinding(MCAssembler &Asm,
456                                                const MCAsmLayout &Layout) {
457  // Some compilation units require the indirect function table to be present
458  // but don't explicitly reference it.  This is the case for call_indirect
459  // without the reference-types feature, and also function bitcasts in all
460  // cases.  In those cases the __indirect_function_table has the
461  // WASM_SYMBOL_NO_STRIP attribute.  Here we make sure this symbol makes it to
462  // the assembler, if needed.
463  if (auto *Sym = Asm.getContext().lookupSymbol("__indirect_function_table")) {
464    const auto *WasmSym = static_cast<const MCSymbolWasm *>(Sym);
465    if (WasmSym->isNoStrip())
466      Asm.registerSymbol(*Sym);
467  }
468
469  // Build a map of sections to the function that defines them, for use
470  // in recordRelocation.
471  for (const MCSymbol &S : Asm.symbols()) {
472    const auto &WS = static_cast<const MCSymbolWasm &>(S);
473    if (WS.isDefined() && WS.isFunction() && !WS.isVariable()) {
474      const auto &Sec = static_cast<const MCSectionWasm &>(S.getSection());
475      auto Pair = SectionFunctions.insert(std::make_pair(&Sec, &S));
476      if (!Pair.second)
477        report_fatal_error("section already has a defining function: " +
478                           Sec.getName());
479    }
480  }
481}
482
483void WasmObjectWriter::recordRelocation(MCAssembler &Asm,
484                                        const MCAsmLayout &Layout,
485                                        const MCFragment *Fragment,
486                                        const MCFixup &Fixup, MCValue Target,
487                                        uint64_t &FixedValue) {
488  // The WebAssembly backend should never generate FKF_IsPCRel fixups
489  assert(!(Asm.getBackend().getFixupKindInfo(Fixup.getKind()).Flags &
490           MCFixupKindInfo::FKF_IsPCRel));
491
492  const auto &FixupSection = cast<MCSectionWasm>(*Fragment->getParent());
493  uint64_t C = Target.getConstant();
494  uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
495  MCContext &Ctx = Asm.getContext();
496  bool IsLocRel = false;
497
498  if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
499
500    const auto &SymB = cast<MCSymbolWasm>(RefB->getSymbol());
501
502    if (FixupSection.getKind().isText()) {
503      Ctx.reportError(Fixup.getLoc(),
504                      Twine("symbol '") + SymB.getName() +
505                          "' unsupported subtraction expression used in "
506                          "relocation in code section.");
507      return;
508    }
509
510    if (SymB.isUndefined()) {
511      Ctx.reportError(Fixup.getLoc(),
512                      Twine("symbol '") + SymB.getName() +
513                          "' can not be undefined in a subtraction expression");
514      return;
515    }
516    const MCSection &SecB = SymB.getSection();
517    if (&SecB != &FixupSection) {
518      Ctx.reportError(Fixup.getLoc(),
519                      Twine("symbol '") + SymB.getName() +
520                          "' can not be placed in a different section");
521      return;
522    }
523    IsLocRel = true;
524    C += FixupOffset - Layout.getSymbolOffset(SymB);
525  }
526
527  // We either rejected the fixup or folded B into C at this point.
528  const MCSymbolRefExpr *RefA = Target.getSymA();
529  const auto *SymA = cast<MCSymbolWasm>(&RefA->getSymbol());
530
531  // The .init_array isn't translated as data, so don't do relocations in it.
532  if (FixupSection.getName().starts_with(".init_array")) {
533    SymA->setUsedInInitArray();
534    return;
535  }
536
537  if (SymA->isVariable()) {
538    const MCExpr *Expr = SymA->getVariableValue();
539    if (const auto *Inner = dyn_cast<MCSymbolRefExpr>(Expr))
540      if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF)
541        llvm_unreachable("weakref used in reloc not yet implemented");
542  }
543
544  // Put any constant offset in an addend. Offsets can be negative, and
545  // LLVM expects wrapping, in contrast to wasm's immediates which can't
546  // be negative and don't wrap.
547  FixedValue = 0;
548
549  unsigned Type =
550      TargetObjectWriter->getRelocType(Target, Fixup, FixupSection, IsLocRel);
551
552  // Absolute offset within a section or a function.
553  // Currently only supported for metadata sections.
554  // See: test/MC/WebAssembly/blockaddress.ll
555  if ((Type == wasm::R_WASM_FUNCTION_OFFSET_I32 ||
556       Type == wasm::R_WASM_FUNCTION_OFFSET_I64 ||
557       Type == wasm::R_WASM_SECTION_OFFSET_I32) &&
558      SymA->isDefined()) {
559    // SymA can be a temp data symbol that represents a function (in which case
560    // it needs to be replaced by the section symbol), [XXX and it apparently
561    // later gets changed again to a func symbol?] or it can be a real
562    // function symbol, in which case it can be left as-is.
563
564    if (!FixupSection.getKind().isMetadata())
565      report_fatal_error("relocations for function or section offsets are "
566                         "only supported in metadata sections");
567
568    const MCSymbol *SectionSymbol = nullptr;
569    const MCSection &SecA = SymA->getSection();
570    if (SecA.getKind().isText()) {
571      auto SecSymIt = SectionFunctions.find(&SecA);
572      if (SecSymIt == SectionFunctions.end())
573        report_fatal_error("section doesn\'t have defining symbol");
574      SectionSymbol = SecSymIt->second;
575    } else {
576      SectionSymbol = SecA.getBeginSymbol();
577    }
578    if (!SectionSymbol)
579      report_fatal_error("section symbol is required for relocation");
580
581    C += Layout.getSymbolOffset(*SymA);
582    SymA = cast<MCSymbolWasm>(SectionSymbol);
583  }
584
585  if (Type == wasm::R_WASM_TABLE_INDEX_REL_SLEB ||
586      Type == wasm::R_WASM_TABLE_INDEX_REL_SLEB64 ||
587      Type == wasm::R_WASM_TABLE_INDEX_SLEB ||
588      Type == wasm::R_WASM_TABLE_INDEX_SLEB64 ||
589      Type == wasm::R_WASM_TABLE_INDEX_I32 ||
590      Type == wasm::R_WASM_TABLE_INDEX_I64) {
591    // TABLE_INDEX relocs implicitly use the default indirect function table.
592    // We require the function table to have already been defined.
593    auto TableName = "__indirect_function_table";
594    MCSymbolWasm *Sym = cast_or_null<MCSymbolWasm>(Ctx.lookupSymbol(TableName));
595    if (!Sym) {
596      report_fatal_error("missing indirect function table symbol");
597    } else {
598      if (!Sym->isFunctionTable())
599        report_fatal_error("__indirect_function_table symbol has wrong type");
600      // Ensure that __indirect_function_table reaches the output.
601      Sym->setNoStrip();
602      Asm.registerSymbol(*Sym);
603    }
604  }
605
606  // Relocation other than R_WASM_TYPE_INDEX_LEB are required to be
607  // against a named symbol.
608  if (Type != wasm::R_WASM_TYPE_INDEX_LEB) {
609    if (SymA->getName().empty())
610      report_fatal_error("relocations against un-named temporaries are not yet "
611                         "supported by wasm");
612
613    SymA->setUsedInReloc();
614  }
615
616  switch (RefA->getKind()) {
617  case MCSymbolRefExpr::VK_GOT:
618  case MCSymbolRefExpr::VK_WASM_GOT_TLS:
619    SymA->setUsedInGOT();
620    break;
621  default:
622    break;
623  }
624
625  WasmRelocationEntry Rec(FixupOffset, SymA, C, Type, &FixupSection);
626  LLVM_DEBUG(dbgs() << "WasmReloc: " << Rec << "\n");
627
628  if (FixupSection.isWasmData()) {
629    DataRelocations.push_back(Rec);
630  } else if (FixupSection.getKind().isText()) {
631    CodeRelocations.push_back(Rec);
632  } else if (FixupSection.getKind().isMetadata()) {
633    CustomSectionsRelocations[&FixupSection].push_back(Rec);
634  } else {
635    llvm_unreachable("unexpected section type");
636  }
637}
638
639// Compute a value to write into the code at the location covered
640// by RelEntry. This value isn't used by the static linker; it just serves
641// to make the object format more readable and more likely to be directly
642// useable.
643uint64_t
644WasmObjectWriter::getProvisionalValue(const WasmRelocationEntry &RelEntry,
645                                      const MCAsmLayout &Layout) {
646  if ((RelEntry.Type == wasm::R_WASM_GLOBAL_INDEX_LEB ||
647       RelEntry.Type == wasm::R_WASM_GLOBAL_INDEX_I32) &&
648      !RelEntry.Symbol->isGlobal()) {
649    assert(GOTIndices.count(RelEntry.Symbol) > 0 && "symbol not found in GOT index space");
650    return GOTIndices[RelEntry.Symbol];
651  }
652
653  switch (RelEntry.Type) {
654  case wasm::R_WASM_TABLE_INDEX_REL_SLEB:
655  case wasm::R_WASM_TABLE_INDEX_REL_SLEB64:
656  case wasm::R_WASM_TABLE_INDEX_SLEB:
657  case wasm::R_WASM_TABLE_INDEX_SLEB64:
658  case wasm::R_WASM_TABLE_INDEX_I32:
659  case wasm::R_WASM_TABLE_INDEX_I64: {
660    // Provisional value is table address of the resolved symbol itself
661    const MCSymbolWasm *Base =
662        cast<MCSymbolWasm>(Layout.getBaseSymbol(*RelEntry.Symbol));
663    assert(Base->isFunction());
664    if (RelEntry.Type == wasm::R_WASM_TABLE_INDEX_REL_SLEB ||
665        RelEntry.Type == wasm::R_WASM_TABLE_INDEX_REL_SLEB64)
666      return TableIndices[Base] - InitialTableOffset;
667    else
668      return TableIndices[Base];
669  }
670  case wasm::R_WASM_TYPE_INDEX_LEB:
671    // Provisional value is same as the index
672    return getRelocationIndexValue(RelEntry);
673  case wasm::R_WASM_FUNCTION_INDEX_LEB:
674  case wasm::R_WASM_FUNCTION_INDEX_I32:
675  case wasm::R_WASM_GLOBAL_INDEX_LEB:
676  case wasm::R_WASM_GLOBAL_INDEX_I32:
677  case wasm::R_WASM_TAG_INDEX_LEB:
678  case wasm::R_WASM_TABLE_NUMBER_LEB:
679    // Provisional value is function/global/tag Wasm index
680    assert(WasmIndices.count(RelEntry.Symbol) > 0 && "symbol not found in wasm index space");
681    return WasmIndices[RelEntry.Symbol];
682  case wasm::R_WASM_FUNCTION_OFFSET_I32:
683  case wasm::R_WASM_FUNCTION_OFFSET_I64:
684  case wasm::R_WASM_SECTION_OFFSET_I32: {
685    if (!RelEntry.Symbol->isDefined())
686      return 0;
687    const auto &Section =
688        static_cast<const MCSectionWasm &>(RelEntry.Symbol->getSection());
689    return Section.getSectionOffset() + RelEntry.Addend;
690  }
691  case wasm::R_WASM_MEMORY_ADDR_LEB:
692  case wasm::R_WASM_MEMORY_ADDR_LEB64:
693  case wasm::R_WASM_MEMORY_ADDR_SLEB:
694  case wasm::R_WASM_MEMORY_ADDR_SLEB64:
695  case wasm::R_WASM_MEMORY_ADDR_REL_SLEB:
696  case wasm::R_WASM_MEMORY_ADDR_REL_SLEB64:
697  case wasm::R_WASM_MEMORY_ADDR_I32:
698  case wasm::R_WASM_MEMORY_ADDR_I64:
699  case wasm::R_WASM_MEMORY_ADDR_TLS_SLEB:
700  case wasm::R_WASM_MEMORY_ADDR_TLS_SLEB64:
701  case wasm::R_WASM_MEMORY_ADDR_LOCREL_I32: {
702    // Provisional value is address of the global plus the offset
703    // For undefined symbols, use zero
704    if (!RelEntry.Symbol->isDefined())
705      return 0;
706    const wasm::WasmDataReference &SymRef = DataLocations[RelEntry.Symbol];
707    const WasmDataSegment &Segment = DataSegments[SymRef.Segment];
708    // Ignore overflow. LLVM allows address arithmetic to silently wrap.
709    return Segment.Offset + SymRef.Offset + RelEntry.Addend;
710  }
711  default:
712    llvm_unreachable("invalid relocation type");
713  }
714}
715
716static void addData(SmallVectorImpl<char> &DataBytes,
717                    MCSectionWasm &DataSection) {
718  LLVM_DEBUG(errs() << "addData: " << DataSection.getName() << "\n");
719
720  DataBytes.resize(alignTo(DataBytes.size(), DataSection.getAlign()));
721
722  for (const MCFragment &Frag : DataSection) {
723    if (Frag.hasInstructions())
724      report_fatal_error("only data supported in data sections");
725
726    if (auto *Align = dyn_cast<MCAlignFragment>(&Frag)) {
727      if (Align->getValueSize() != 1)
728        report_fatal_error("only byte values supported for alignment");
729      // If nops are requested, use zeros, as this is the data section.
730      uint8_t Value = Align->hasEmitNops() ? 0 : Align->getValue();
731      uint64_t Size =
732          std::min<uint64_t>(alignTo(DataBytes.size(), Align->getAlignment()),
733                             DataBytes.size() + Align->getMaxBytesToEmit());
734      DataBytes.resize(Size, Value);
735    } else if (auto *Fill = dyn_cast<MCFillFragment>(&Frag)) {
736      int64_t NumValues;
737      if (!Fill->getNumValues().evaluateAsAbsolute(NumValues))
738        llvm_unreachable("The fill should be an assembler constant");
739      DataBytes.insert(DataBytes.end(), Fill->getValueSize() * NumValues,
740                       Fill->getValue());
741    } else if (auto *LEB = dyn_cast<MCLEBFragment>(&Frag)) {
742      const SmallVectorImpl<char> &Contents = LEB->getContents();
743      llvm::append_range(DataBytes, Contents);
744    } else {
745      const auto &DataFrag = cast<MCDataFragment>(Frag);
746      const SmallVectorImpl<char> &Contents = DataFrag.getContents();
747      llvm::append_range(DataBytes, Contents);
748    }
749  }
750
751  LLVM_DEBUG(dbgs() << "addData -> " << DataBytes.size() << "\n");
752}
753
754uint32_t
755WasmObjectWriter::getRelocationIndexValue(const WasmRelocationEntry &RelEntry) {
756  if (RelEntry.Type == wasm::R_WASM_TYPE_INDEX_LEB) {
757    if (!TypeIndices.count(RelEntry.Symbol))
758      report_fatal_error("symbol not found in type index space: " +
759                         RelEntry.Symbol->getName());
760    return TypeIndices[RelEntry.Symbol];
761  }
762
763  return RelEntry.Symbol->getIndex();
764}
765
766// Apply the portions of the relocation records that we can handle ourselves
767// directly.
768void WasmObjectWriter::applyRelocations(
769    ArrayRef<WasmRelocationEntry> Relocations, uint64_t ContentsOffset,
770    const MCAsmLayout &Layout) {
771  auto &Stream = static_cast<raw_pwrite_stream &>(W->OS);
772  for (const WasmRelocationEntry &RelEntry : Relocations) {
773    uint64_t Offset = ContentsOffset +
774                      RelEntry.FixupSection->getSectionOffset() +
775                      RelEntry.Offset;
776
777    LLVM_DEBUG(dbgs() << "applyRelocation: " << RelEntry << "\n");
778    uint64_t Value = getProvisionalValue(RelEntry, Layout);
779
780    switch (RelEntry.Type) {
781    case wasm::R_WASM_FUNCTION_INDEX_LEB:
782    case wasm::R_WASM_TYPE_INDEX_LEB:
783    case wasm::R_WASM_GLOBAL_INDEX_LEB:
784    case wasm::R_WASM_MEMORY_ADDR_LEB:
785    case wasm::R_WASM_TAG_INDEX_LEB:
786    case wasm::R_WASM_TABLE_NUMBER_LEB:
787      writePatchableU32(Stream, Value, Offset);
788      break;
789    case wasm::R_WASM_MEMORY_ADDR_LEB64:
790      writePatchableU64(Stream, Value, Offset);
791      break;
792    case wasm::R_WASM_TABLE_INDEX_I32:
793    case wasm::R_WASM_MEMORY_ADDR_I32:
794    case wasm::R_WASM_FUNCTION_OFFSET_I32:
795    case wasm::R_WASM_FUNCTION_INDEX_I32:
796    case wasm::R_WASM_SECTION_OFFSET_I32:
797    case wasm::R_WASM_GLOBAL_INDEX_I32:
798    case wasm::R_WASM_MEMORY_ADDR_LOCREL_I32:
799      patchI32(Stream, Value, Offset);
800      break;
801    case wasm::R_WASM_TABLE_INDEX_I64:
802    case wasm::R_WASM_MEMORY_ADDR_I64:
803    case wasm::R_WASM_FUNCTION_OFFSET_I64:
804      patchI64(Stream, Value, Offset);
805      break;
806    case wasm::R_WASM_TABLE_INDEX_SLEB:
807    case wasm::R_WASM_TABLE_INDEX_REL_SLEB:
808    case wasm::R_WASM_MEMORY_ADDR_SLEB:
809    case wasm::R_WASM_MEMORY_ADDR_REL_SLEB:
810    case wasm::R_WASM_MEMORY_ADDR_TLS_SLEB:
811      writePatchableS32(Stream, Value, Offset);
812      break;
813    case wasm::R_WASM_TABLE_INDEX_SLEB64:
814    case wasm::R_WASM_TABLE_INDEX_REL_SLEB64:
815    case wasm::R_WASM_MEMORY_ADDR_SLEB64:
816    case wasm::R_WASM_MEMORY_ADDR_REL_SLEB64:
817    case wasm::R_WASM_MEMORY_ADDR_TLS_SLEB64:
818      writePatchableS64(Stream, Value, Offset);
819      break;
820    default:
821      llvm_unreachable("invalid relocation type");
822    }
823  }
824}
825
826void WasmObjectWriter::writeTypeSection(
827    ArrayRef<wasm::WasmSignature> Signatures) {
828  if (Signatures.empty())
829    return;
830
831  SectionBookkeeping Section;
832  startSection(Section, wasm::WASM_SEC_TYPE);
833
834  encodeULEB128(Signatures.size(), W->OS);
835
836  for (const wasm::WasmSignature &Sig : Signatures) {
837    W->OS << char(wasm::WASM_TYPE_FUNC);
838    encodeULEB128(Sig.Params.size(), W->OS);
839    for (wasm::ValType Ty : Sig.Params)
840      writeValueType(Ty);
841    encodeULEB128(Sig.Returns.size(), W->OS);
842    for (wasm::ValType Ty : Sig.Returns)
843      writeValueType(Ty);
844  }
845
846  endSection(Section);
847}
848
849void WasmObjectWriter::writeImportSection(ArrayRef<wasm::WasmImport> Imports,
850                                          uint64_t DataSize,
851                                          uint32_t NumElements) {
852  if (Imports.empty())
853    return;
854
855  uint64_t NumPages = (DataSize + wasm::WasmPageSize - 1) / wasm::WasmPageSize;
856
857  SectionBookkeeping Section;
858  startSection(Section, wasm::WASM_SEC_IMPORT);
859
860  encodeULEB128(Imports.size(), W->OS);
861  for (const wasm::WasmImport &Import : Imports) {
862    writeString(Import.Module);
863    writeString(Import.Field);
864    W->OS << char(Import.Kind);
865
866    switch (Import.Kind) {
867    case wasm::WASM_EXTERNAL_FUNCTION:
868      encodeULEB128(Import.SigIndex, W->OS);
869      break;
870    case wasm::WASM_EXTERNAL_GLOBAL:
871      W->OS << char(Import.Global.Type);
872      W->OS << char(Import.Global.Mutable ? 1 : 0);
873      break;
874    case wasm::WASM_EXTERNAL_MEMORY:
875      encodeULEB128(Import.Memory.Flags, W->OS);
876      encodeULEB128(NumPages, W->OS); // initial
877      break;
878    case wasm::WASM_EXTERNAL_TABLE:
879      W->OS << char(Import.Table.ElemType);
880      encodeULEB128(0, W->OS);           // flags
881      encodeULEB128(NumElements, W->OS); // initial
882      break;
883    case wasm::WASM_EXTERNAL_TAG:
884      W->OS << char(0); // Reserved 'attribute' field
885      encodeULEB128(Import.SigIndex, W->OS);
886      break;
887    default:
888      llvm_unreachable("unsupported import kind");
889    }
890  }
891
892  endSection(Section);
893}
894
895void WasmObjectWriter::writeFunctionSection(ArrayRef<WasmFunction> Functions) {
896  if (Functions.empty())
897    return;
898
899  SectionBookkeeping Section;
900  startSection(Section, wasm::WASM_SEC_FUNCTION);
901
902  encodeULEB128(Functions.size(), W->OS);
903  for (const WasmFunction &Func : Functions)
904    encodeULEB128(Func.SigIndex, W->OS);
905
906  endSection(Section);
907}
908
909void WasmObjectWriter::writeTagSection(ArrayRef<uint32_t> TagTypes) {
910  if (TagTypes.empty())
911    return;
912
913  SectionBookkeeping Section;
914  startSection(Section, wasm::WASM_SEC_TAG);
915
916  encodeULEB128(TagTypes.size(), W->OS);
917  for (uint32_t Index : TagTypes) {
918    W->OS << char(0); // Reserved 'attribute' field
919    encodeULEB128(Index, W->OS);
920  }
921
922  endSection(Section);
923}
924
925void WasmObjectWriter::writeGlobalSection(ArrayRef<wasm::WasmGlobal> Globals) {
926  if (Globals.empty())
927    return;
928
929  SectionBookkeeping Section;
930  startSection(Section, wasm::WASM_SEC_GLOBAL);
931
932  encodeULEB128(Globals.size(), W->OS);
933  for (const wasm::WasmGlobal &Global : Globals) {
934    encodeULEB128(Global.Type.Type, W->OS);
935    W->OS << char(Global.Type.Mutable);
936    if (Global.InitExpr.Extended) {
937      llvm_unreachable("extected init expressions not supported");
938    } else {
939      W->OS << char(Global.InitExpr.Inst.Opcode);
940      switch (Global.Type.Type) {
941      case wasm::WASM_TYPE_I32:
942        encodeSLEB128(0, W->OS);
943        break;
944      case wasm::WASM_TYPE_I64:
945        encodeSLEB128(0, W->OS);
946        break;
947      case wasm::WASM_TYPE_F32:
948        writeI32(0);
949        break;
950      case wasm::WASM_TYPE_F64:
951        writeI64(0);
952        break;
953      case wasm::WASM_TYPE_EXTERNREF:
954        writeValueType(wasm::ValType::EXTERNREF);
955        break;
956      default:
957        llvm_unreachable("unexpected type");
958      }
959    }
960    W->OS << char(wasm::WASM_OPCODE_END);
961  }
962
963  endSection(Section);
964}
965
966void WasmObjectWriter::writeTableSection(ArrayRef<wasm::WasmTable> Tables) {
967  if (Tables.empty())
968    return;
969
970  SectionBookkeeping Section;
971  startSection(Section, wasm::WASM_SEC_TABLE);
972
973  encodeULEB128(Tables.size(), W->OS);
974  for (const wasm::WasmTable &Table : Tables) {
975    encodeULEB128((uint32_t)Table.Type.ElemType, W->OS);
976    encodeULEB128(Table.Type.Limits.Flags, W->OS);
977    encodeULEB128(Table.Type.Limits.Minimum, W->OS);
978    if (Table.Type.Limits.Flags & wasm::WASM_LIMITS_FLAG_HAS_MAX)
979      encodeULEB128(Table.Type.Limits.Maximum, W->OS);
980  }
981  endSection(Section);
982}
983
984void WasmObjectWriter::writeExportSection(ArrayRef<wasm::WasmExport> Exports) {
985  if (Exports.empty())
986    return;
987
988  SectionBookkeeping Section;
989  startSection(Section, wasm::WASM_SEC_EXPORT);
990
991  encodeULEB128(Exports.size(), W->OS);
992  for (const wasm::WasmExport &Export : Exports) {
993    writeString(Export.Name);
994    W->OS << char(Export.Kind);
995    encodeULEB128(Export.Index, W->OS);
996  }
997
998  endSection(Section);
999}
1000
1001void WasmObjectWriter::writeElemSection(
1002    const MCSymbolWasm *IndirectFunctionTable, ArrayRef<uint32_t> TableElems) {
1003  if (TableElems.empty())
1004    return;
1005
1006  assert(IndirectFunctionTable);
1007
1008  SectionBookkeeping Section;
1009  startSection(Section, wasm::WASM_SEC_ELEM);
1010
1011  encodeULEB128(1, W->OS); // number of "segments"
1012
1013  assert(WasmIndices.count(IndirectFunctionTable));
1014  uint32_t TableNumber = WasmIndices.find(IndirectFunctionTable)->second;
1015  uint32_t Flags = 0;
1016  if (TableNumber)
1017    Flags |= wasm::WASM_ELEM_SEGMENT_HAS_TABLE_NUMBER;
1018  encodeULEB128(Flags, W->OS);
1019  if (Flags & wasm::WASM_ELEM_SEGMENT_HAS_TABLE_NUMBER)
1020    encodeULEB128(TableNumber, W->OS); // the table number
1021
1022  // init expr for starting offset
1023  W->OS << char(wasm::WASM_OPCODE_I32_CONST);
1024  encodeSLEB128(InitialTableOffset, W->OS);
1025  W->OS << char(wasm::WASM_OPCODE_END);
1026
1027  if (Flags & wasm::WASM_ELEM_SEGMENT_MASK_HAS_ELEM_KIND) {
1028    // We only write active function table initializers, for which the elem kind
1029    // is specified to be written as 0x00 and interpreted to mean "funcref".
1030    const uint8_t ElemKind = 0;
1031    W->OS << ElemKind;
1032  }
1033
1034  encodeULEB128(TableElems.size(), W->OS);
1035  for (uint32_t Elem : TableElems)
1036    encodeULEB128(Elem, W->OS);
1037
1038  endSection(Section);
1039}
1040
1041void WasmObjectWriter::writeDataCountSection() {
1042  if (DataSegments.empty())
1043    return;
1044
1045  SectionBookkeeping Section;
1046  startSection(Section, wasm::WASM_SEC_DATACOUNT);
1047  encodeULEB128(DataSegments.size(), W->OS);
1048  endSection(Section);
1049}
1050
1051uint32_t WasmObjectWriter::writeCodeSection(const MCAssembler &Asm,
1052                                            const MCAsmLayout &Layout,
1053                                            ArrayRef<WasmFunction> Functions) {
1054  if (Functions.empty())
1055    return 0;
1056
1057  SectionBookkeeping Section;
1058  startSection(Section, wasm::WASM_SEC_CODE);
1059
1060  encodeULEB128(Functions.size(), W->OS);
1061
1062  for (const WasmFunction &Func : Functions) {
1063    auto *FuncSection = static_cast<MCSectionWasm *>(Func.Section);
1064
1065    int64_t Size = Layout.getSectionAddressSize(FuncSection);
1066    encodeULEB128(Size, W->OS);
1067    FuncSection->setSectionOffset(W->OS.tell() - Section.ContentsOffset);
1068    Asm.writeSectionData(W->OS, FuncSection, Layout);
1069  }
1070
1071  // Apply fixups.
1072  applyRelocations(CodeRelocations, Section.ContentsOffset, Layout);
1073
1074  endSection(Section);
1075  return Section.Index;
1076}
1077
1078uint32_t WasmObjectWriter::writeDataSection(const MCAsmLayout &Layout) {
1079  if (DataSegments.empty())
1080    return 0;
1081
1082  SectionBookkeeping Section;
1083  startSection(Section, wasm::WASM_SEC_DATA);
1084
1085  encodeULEB128(DataSegments.size(), W->OS); // count
1086
1087  for (const WasmDataSegment &Segment : DataSegments) {
1088    encodeULEB128(Segment.InitFlags, W->OS); // flags
1089    if (Segment.InitFlags & wasm::WASM_DATA_SEGMENT_HAS_MEMINDEX)
1090      encodeULEB128(0, W->OS); // memory index
1091    if ((Segment.InitFlags & wasm::WASM_DATA_SEGMENT_IS_PASSIVE) == 0) {
1092      W->OS << char(is64Bit() ? wasm::WASM_OPCODE_I64_CONST
1093                              : wasm::WASM_OPCODE_I32_CONST);
1094      encodeSLEB128(Segment.Offset, W->OS); // offset
1095      W->OS << char(wasm::WASM_OPCODE_END);
1096    }
1097    encodeULEB128(Segment.Data.size(), W->OS); // size
1098    Segment.Section->setSectionOffset(W->OS.tell() - Section.ContentsOffset);
1099    W->OS << Segment.Data; // data
1100  }
1101
1102  // Apply fixups.
1103  applyRelocations(DataRelocations, Section.ContentsOffset, Layout);
1104
1105  endSection(Section);
1106  return Section.Index;
1107}
1108
1109void WasmObjectWriter::writeRelocSection(
1110    uint32_t SectionIndex, StringRef Name,
1111    std::vector<WasmRelocationEntry> &Relocs) {
1112  // See: https://github.com/WebAssembly/tool-conventions/blob/main/Linking.md
1113  // for descriptions of the reloc sections.
1114
1115  if (Relocs.empty())
1116    return;
1117
1118  // First, ensure the relocations are sorted in offset order.  In general they
1119  // should already be sorted since `recordRelocation` is called in offset
1120  // order, but for the code section we combine many MC sections into single
1121  // wasm section, and this order is determined by the order of Asm.Symbols()
1122  // not the sections order.
1123  llvm::stable_sort(
1124      Relocs, [](const WasmRelocationEntry &A, const WasmRelocationEntry &B) {
1125        return (A.Offset + A.FixupSection->getSectionOffset()) <
1126               (B.Offset + B.FixupSection->getSectionOffset());
1127      });
1128
1129  SectionBookkeeping Section;
1130  startCustomSection(Section, std::string("reloc.") + Name.str());
1131
1132  encodeULEB128(SectionIndex, W->OS);
1133  encodeULEB128(Relocs.size(), W->OS);
1134  for (const WasmRelocationEntry &RelEntry : Relocs) {
1135    uint64_t Offset =
1136        RelEntry.Offset + RelEntry.FixupSection->getSectionOffset();
1137    uint32_t Index = getRelocationIndexValue(RelEntry);
1138
1139    W->OS << char(RelEntry.Type);
1140    encodeULEB128(Offset, W->OS);
1141    encodeULEB128(Index, W->OS);
1142    if (RelEntry.hasAddend())
1143      encodeSLEB128(RelEntry.Addend, W->OS);
1144  }
1145
1146  endSection(Section);
1147}
1148
1149void WasmObjectWriter::writeCustomRelocSections() {
1150  for (const auto &Sec : CustomSections) {
1151    auto &Relocations = CustomSectionsRelocations[Sec.Section];
1152    writeRelocSection(Sec.OutputIndex, Sec.Name, Relocations);
1153  }
1154}
1155
1156void WasmObjectWriter::writeLinkingMetaDataSection(
1157    ArrayRef<wasm::WasmSymbolInfo> SymbolInfos,
1158    ArrayRef<std::pair<uint16_t, uint32_t>> InitFuncs,
1159    const std::map<StringRef, std::vector<WasmComdatEntry>> &Comdats) {
1160  SectionBookkeeping Section;
1161  startCustomSection(Section, "linking");
1162  encodeULEB128(wasm::WasmMetadataVersion, W->OS);
1163
1164  SectionBookkeeping SubSection;
1165  if (SymbolInfos.size() != 0) {
1166    startSection(SubSection, wasm::WASM_SYMBOL_TABLE);
1167    encodeULEB128(SymbolInfos.size(), W->OS);
1168    for (const wasm::WasmSymbolInfo &Sym : SymbolInfos) {
1169      encodeULEB128(Sym.Kind, W->OS);
1170      encodeULEB128(Sym.Flags, W->OS);
1171      switch (Sym.Kind) {
1172      case wasm::WASM_SYMBOL_TYPE_FUNCTION:
1173      case wasm::WASM_SYMBOL_TYPE_GLOBAL:
1174      case wasm::WASM_SYMBOL_TYPE_TAG:
1175      case wasm::WASM_SYMBOL_TYPE_TABLE:
1176        encodeULEB128(Sym.ElementIndex, W->OS);
1177        if ((Sym.Flags & wasm::WASM_SYMBOL_UNDEFINED) == 0 ||
1178            (Sym.Flags & wasm::WASM_SYMBOL_EXPLICIT_NAME) != 0)
1179          writeString(Sym.Name);
1180        break;
1181      case wasm::WASM_SYMBOL_TYPE_DATA:
1182        writeString(Sym.Name);
1183        if ((Sym.Flags & wasm::WASM_SYMBOL_UNDEFINED) == 0) {
1184          encodeULEB128(Sym.DataRef.Segment, W->OS);
1185          encodeULEB128(Sym.DataRef.Offset, W->OS);
1186          encodeULEB128(Sym.DataRef.Size, W->OS);
1187        }
1188        break;
1189      case wasm::WASM_SYMBOL_TYPE_SECTION: {
1190        const uint32_t SectionIndex =
1191            CustomSections[Sym.ElementIndex].OutputIndex;
1192        encodeULEB128(SectionIndex, W->OS);
1193        break;
1194      }
1195      default:
1196        llvm_unreachable("unexpected kind");
1197      }
1198    }
1199    endSection(SubSection);
1200  }
1201
1202  if (DataSegments.size()) {
1203    startSection(SubSection, wasm::WASM_SEGMENT_INFO);
1204    encodeULEB128(DataSegments.size(), W->OS);
1205    for (const WasmDataSegment &Segment : DataSegments) {
1206      writeString(Segment.Name);
1207      encodeULEB128(Segment.Alignment, W->OS);
1208      encodeULEB128(Segment.LinkingFlags, W->OS);
1209    }
1210    endSection(SubSection);
1211  }
1212
1213  if (!InitFuncs.empty()) {
1214    startSection(SubSection, wasm::WASM_INIT_FUNCS);
1215    encodeULEB128(InitFuncs.size(), W->OS);
1216    for (auto &StartFunc : InitFuncs) {
1217      encodeULEB128(StartFunc.first, W->OS);  // priority
1218      encodeULEB128(StartFunc.second, W->OS); // function index
1219    }
1220    endSection(SubSection);
1221  }
1222
1223  if (Comdats.size()) {
1224    startSection(SubSection, wasm::WASM_COMDAT_INFO);
1225    encodeULEB128(Comdats.size(), W->OS);
1226    for (const auto &C : Comdats) {
1227      writeString(C.first);
1228      encodeULEB128(0, W->OS); // flags for future use
1229      encodeULEB128(C.second.size(), W->OS);
1230      for (const WasmComdatEntry &Entry : C.second) {
1231        encodeULEB128(Entry.Kind, W->OS);
1232        encodeULEB128(Entry.Index, W->OS);
1233      }
1234    }
1235    endSection(SubSection);
1236  }
1237
1238  endSection(Section);
1239}
1240
1241void WasmObjectWriter::writeCustomSection(WasmCustomSection &CustomSection,
1242                                          const MCAssembler &Asm,
1243                                          const MCAsmLayout &Layout) {
1244  SectionBookkeeping Section;
1245  auto *Sec = CustomSection.Section;
1246  startCustomSection(Section, CustomSection.Name);
1247
1248  Sec->setSectionOffset(W->OS.tell() - Section.ContentsOffset);
1249  Asm.writeSectionData(W->OS, Sec, Layout);
1250
1251  CustomSection.OutputContentsOffset = Section.ContentsOffset;
1252  CustomSection.OutputIndex = Section.Index;
1253
1254  endSection(Section);
1255
1256  // Apply fixups.
1257  auto &Relocations = CustomSectionsRelocations[CustomSection.Section];
1258  applyRelocations(Relocations, CustomSection.OutputContentsOffset, Layout);
1259}
1260
1261uint32_t WasmObjectWriter::getFunctionType(const MCSymbolWasm &Symbol) {
1262  assert(Symbol.isFunction());
1263  assert(TypeIndices.count(&Symbol));
1264  return TypeIndices[&Symbol];
1265}
1266
1267uint32_t WasmObjectWriter::getTagType(const MCSymbolWasm &Symbol) {
1268  assert(Symbol.isTag());
1269  assert(TypeIndices.count(&Symbol));
1270  return TypeIndices[&Symbol];
1271}
1272
1273void WasmObjectWriter::registerFunctionType(const MCSymbolWasm &Symbol) {
1274  assert(Symbol.isFunction());
1275
1276  wasm::WasmSignature S;
1277
1278  if (auto *Sig = Symbol.getSignature()) {
1279    S.Returns = Sig->Returns;
1280    S.Params = Sig->Params;
1281  }
1282
1283  auto Pair = SignatureIndices.insert(std::make_pair(S, Signatures.size()));
1284  if (Pair.second)
1285    Signatures.push_back(S);
1286  TypeIndices[&Symbol] = Pair.first->second;
1287
1288  LLVM_DEBUG(dbgs() << "registerFunctionType: " << Symbol
1289                    << " new:" << Pair.second << "\n");
1290  LLVM_DEBUG(dbgs() << "  -> type index: " << Pair.first->second << "\n");
1291}
1292
1293void WasmObjectWriter::registerTagType(const MCSymbolWasm &Symbol) {
1294  assert(Symbol.isTag());
1295
1296  // TODO Currently we don't generate imported exceptions, but if we do, we
1297  // should have a way of infering types of imported exceptions.
1298  wasm::WasmSignature S;
1299  if (auto *Sig = Symbol.getSignature()) {
1300    S.Returns = Sig->Returns;
1301    S.Params = Sig->Params;
1302  }
1303
1304  auto Pair = SignatureIndices.insert(std::make_pair(S, Signatures.size()));
1305  if (Pair.second)
1306    Signatures.push_back(S);
1307  TypeIndices[&Symbol] = Pair.first->second;
1308
1309  LLVM_DEBUG(dbgs() << "registerTagType: " << Symbol << " new:" << Pair.second
1310                    << "\n");
1311  LLVM_DEBUG(dbgs() << "  -> type index: " << Pair.first->second << "\n");
1312}
1313
1314static bool isInSymtab(const MCSymbolWasm &Sym) {
1315  if (Sym.isUsedInReloc() || Sym.isUsedInInitArray())
1316    return true;
1317
1318  if (Sym.isComdat() && !Sym.isDefined())
1319    return false;
1320
1321  if (Sym.isTemporary())
1322    return false;
1323
1324  if (Sym.isSection())
1325    return false;
1326
1327  if (Sym.omitFromLinkingSection())
1328    return false;
1329
1330  return true;
1331}
1332
1333void WasmObjectWriter::prepareImports(
1334    SmallVectorImpl<wasm::WasmImport> &Imports, MCAssembler &Asm,
1335    const MCAsmLayout &Layout) {
1336  // For now, always emit the memory import, since loads and stores are not
1337  // valid without it. In the future, we could perhaps be more clever and omit
1338  // it if there are no loads or stores.
1339  wasm::WasmImport MemImport;
1340  MemImport.Module = "env";
1341  MemImport.Field = "__linear_memory";
1342  MemImport.Kind = wasm::WASM_EXTERNAL_MEMORY;
1343  MemImport.Memory.Flags = is64Bit() ? wasm::WASM_LIMITS_FLAG_IS_64
1344                                     : wasm::WASM_LIMITS_FLAG_NONE;
1345  Imports.push_back(MemImport);
1346
1347  // Populate SignatureIndices, and Imports and WasmIndices for undefined
1348  // symbols.  This must be done before populating WasmIndices for defined
1349  // symbols.
1350  for (const MCSymbol &S : Asm.symbols()) {
1351    const auto &WS = static_cast<const MCSymbolWasm &>(S);
1352
1353    // Register types for all functions, including those with private linkage
1354    // (because wasm always needs a type signature).
1355    if (WS.isFunction()) {
1356      const auto *BS = Layout.getBaseSymbol(S);
1357      if (!BS)
1358        report_fatal_error(Twine(S.getName()) +
1359                           ": absolute addressing not supported!");
1360      registerFunctionType(*cast<MCSymbolWasm>(BS));
1361    }
1362
1363    if (WS.isTag())
1364      registerTagType(WS);
1365
1366    if (WS.isTemporary())
1367      continue;
1368
1369    // If the symbol is not defined in this translation unit, import it.
1370    if (!WS.isDefined() && !WS.isComdat()) {
1371      if (WS.isFunction()) {
1372        wasm::WasmImport Import;
1373        Import.Module = WS.getImportModule();
1374        Import.Field = WS.getImportName();
1375        Import.Kind = wasm::WASM_EXTERNAL_FUNCTION;
1376        Import.SigIndex = getFunctionType(WS);
1377        Imports.push_back(Import);
1378        assert(WasmIndices.count(&WS) == 0);
1379        WasmIndices[&WS] = NumFunctionImports++;
1380      } else if (WS.isGlobal()) {
1381        if (WS.isWeak())
1382          report_fatal_error("undefined global symbol cannot be weak");
1383
1384        wasm::WasmImport Import;
1385        Import.Field = WS.getImportName();
1386        Import.Kind = wasm::WASM_EXTERNAL_GLOBAL;
1387        Import.Module = WS.getImportModule();
1388        Import.Global = WS.getGlobalType();
1389        Imports.push_back(Import);
1390        assert(WasmIndices.count(&WS) == 0);
1391        WasmIndices[&WS] = NumGlobalImports++;
1392      } else if (WS.isTag()) {
1393        if (WS.isWeak())
1394          report_fatal_error("undefined tag symbol cannot be weak");
1395
1396        wasm::WasmImport Import;
1397        Import.Module = WS.getImportModule();
1398        Import.Field = WS.getImportName();
1399        Import.Kind = wasm::WASM_EXTERNAL_TAG;
1400        Import.SigIndex = getTagType(WS);
1401        Imports.push_back(Import);
1402        assert(WasmIndices.count(&WS) == 0);
1403        WasmIndices[&WS] = NumTagImports++;
1404      } else if (WS.isTable()) {
1405        if (WS.isWeak())
1406          report_fatal_error("undefined table symbol cannot be weak");
1407
1408        wasm::WasmImport Import;
1409        Import.Module = WS.getImportModule();
1410        Import.Field = WS.getImportName();
1411        Import.Kind = wasm::WASM_EXTERNAL_TABLE;
1412        Import.Table = WS.getTableType();
1413        Imports.push_back(Import);
1414        assert(WasmIndices.count(&WS) == 0);
1415        WasmIndices[&WS] = NumTableImports++;
1416      }
1417    }
1418  }
1419
1420  // Add imports for GOT globals
1421  for (const MCSymbol &S : Asm.symbols()) {
1422    const auto &WS = static_cast<const MCSymbolWasm &>(S);
1423    if (WS.isUsedInGOT()) {
1424      wasm::WasmImport Import;
1425      if (WS.isFunction())
1426        Import.Module = "GOT.func";
1427      else
1428        Import.Module = "GOT.mem";
1429      Import.Field = WS.getName();
1430      Import.Kind = wasm::WASM_EXTERNAL_GLOBAL;
1431      Import.Global = {wasm::WASM_TYPE_I32, true};
1432      Imports.push_back(Import);
1433      assert(GOTIndices.count(&WS) == 0);
1434      GOTIndices[&WS] = NumGlobalImports++;
1435    }
1436  }
1437}
1438
1439uint64_t WasmObjectWriter::writeObject(MCAssembler &Asm,
1440                                       const MCAsmLayout &Layout) {
1441  support::endian::Writer MainWriter(*OS, llvm::endianness::little);
1442  W = &MainWriter;
1443  if (IsSplitDwarf) {
1444    uint64_t TotalSize = writeOneObject(Asm, Layout, DwoMode::NonDwoOnly);
1445    assert(DwoOS);
1446    support::endian::Writer DwoWriter(*DwoOS, llvm::endianness::little);
1447    W = &DwoWriter;
1448    return TotalSize + writeOneObject(Asm, Layout, DwoMode::DwoOnly);
1449  } else {
1450    return writeOneObject(Asm, Layout, DwoMode::AllSections);
1451  }
1452}
1453
1454uint64_t WasmObjectWriter::writeOneObject(MCAssembler &Asm,
1455                                          const MCAsmLayout &Layout,
1456                                          DwoMode Mode) {
1457  uint64_t StartOffset = W->OS.tell();
1458  SectionCount = 0;
1459  CustomSections.clear();
1460
1461  LLVM_DEBUG(dbgs() << "WasmObjectWriter::writeObject\n");
1462
1463  // Collect information from the available symbols.
1464  SmallVector<WasmFunction, 4> Functions;
1465  SmallVector<uint32_t, 4> TableElems;
1466  SmallVector<wasm::WasmImport, 4> Imports;
1467  SmallVector<wasm::WasmExport, 4> Exports;
1468  SmallVector<uint32_t, 2> TagTypes;
1469  SmallVector<wasm::WasmGlobal, 1> Globals;
1470  SmallVector<wasm::WasmTable, 1> Tables;
1471  SmallVector<wasm::WasmSymbolInfo, 4> SymbolInfos;
1472  SmallVector<std::pair<uint16_t, uint32_t>, 2> InitFuncs;
1473  std::map<StringRef, std::vector<WasmComdatEntry>> Comdats;
1474  uint64_t DataSize = 0;
1475  if (Mode != DwoMode::DwoOnly) {
1476    prepareImports(Imports, Asm, Layout);
1477  }
1478
1479  // Populate DataSegments and CustomSections, which must be done before
1480  // populating DataLocations.
1481  for (MCSection &Sec : Asm) {
1482    auto &Section = static_cast<MCSectionWasm &>(Sec);
1483    StringRef SectionName = Section.getName();
1484
1485    if (Mode == DwoMode::NonDwoOnly && isDwoSection(Sec))
1486      continue;
1487    if (Mode == DwoMode::DwoOnly && !isDwoSection(Sec))
1488      continue;
1489
1490    LLVM_DEBUG(dbgs() << "Processing Section " << SectionName << "  group "
1491                      << Section.getGroup() << "\n";);
1492
1493    // .init_array sections are handled specially elsewhere.
1494    if (SectionName.starts_with(".init_array"))
1495      continue;
1496
1497    // Code is handled separately
1498    if (Section.getKind().isText())
1499      continue;
1500
1501    if (Section.isWasmData()) {
1502      uint32_t SegmentIndex = DataSegments.size();
1503      DataSize = alignTo(DataSize, Section.getAlign());
1504      DataSegments.emplace_back();
1505      WasmDataSegment &Segment = DataSegments.back();
1506      Segment.Name = SectionName;
1507      Segment.InitFlags = Section.getPassive()
1508                              ? (uint32_t)wasm::WASM_DATA_SEGMENT_IS_PASSIVE
1509                              : 0;
1510      Segment.Offset = DataSize;
1511      Segment.Section = &Section;
1512      addData(Segment.Data, Section);
1513      Segment.Alignment = Log2(Section.getAlign());
1514      Segment.LinkingFlags = Section.getSegmentFlags();
1515      DataSize += Segment.Data.size();
1516      Section.setSegmentIndex(SegmentIndex);
1517
1518      if (const MCSymbolWasm *C = Section.getGroup()) {
1519        Comdats[C->getName()].emplace_back(
1520            WasmComdatEntry{wasm::WASM_COMDAT_DATA, SegmentIndex});
1521      }
1522    } else {
1523      // Create custom sections
1524      assert(Sec.getKind().isMetadata());
1525
1526      StringRef Name = SectionName;
1527
1528      // For user-defined custom sections, strip the prefix
1529      Name.consume_front(".custom_section.");
1530
1531      MCSymbol *Begin = Sec.getBeginSymbol();
1532      if (Begin) {
1533        assert(WasmIndices.count(cast<MCSymbolWasm>(Begin)) == 0);
1534        WasmIndices[cast<MCSymbolWasm>(Begin)] = CustomSections.size();
1535      }
1536
1537      // Separate out the producers and target features sections
1538      if (Name == "producers") {
1539        ProducersSection = std::make_unique<WasmCustomSection>(Name, &Section);
1540        continue;
1541      }
1542      if (Name == "target_features") {
1543        TargetFeaturesSection =
1544            std::make_unique<WasmCustomSection>(Name, &Section);
1545        continue;
1546      }
1547
1548      // Custom sections can also belong to COMDAT groups. In this case the
1549      // decriptor's "index" field is the section index (in the final object
1550      // file), but that is not known until after layout, so it must be fixed up
1551      // later
1552      if (const MCSymbolWasm *C = Section.getGroup()) {
1553        Comdats[C->getName()].emplace_back(
1554            WasmComdatEntry{wasm::WASM_COMDAT_SECTION,
1555                            static_cast<uint32_t>(CustomSections.size())});
1556      }
1557
1558      CustomSections.emplace_back(Name, &Section);
1559    }
1560  }
1561
1562  if (Mode != DwoMode::DwoOnly) {
1563    // Populate WasmIndices and DataLocations for defined symbols.
1564    for (const MCSymbol &S : Asm.symbols()) {
1565      // Ignore unnamed temporary symbols, which aren't ever exported, imported,
1566      // or used in relocations.
1567      if (S.isTemporary() && S.getName().empty())
1568        continue;
1569
1570      const auto &WS = static_cast<const MCSymbolWasm &>(S);
1571      LLVM_DEBUG(
1572          dbgs() << "MCSymbol: "
1573                 << toString(WS.getType().value_or(wasm::WASM_SYMBOL_TYPE_DATA))
1574                 << " '" << S << "'"
1575                 << " isDefined=" << S.isDefined() << " isExternal="
1576                 << S.isExternal() << " isTemporary=" << S.isTemporary()
1577                 << " isWeak=" << WS.isWeak() << " isHidden=" << WS.isHidden()
1578                 << " isVariable=" << WS.isVariable() << "\n");
1579
1580      if (WS.isVariable())
1581        continue;
1582      if (WS.isComdat() && !WS.isDefined())
1583        continue;
1584
1585      if (WS.isFunction()) {
1586        unsigned Index;
1587        if (WS.isDefined()) {
1588          if (WS.getOffset() != 0)
1589            report_fatal_error(
1590                "function sections must contain one function each");
1591
1592          // A definition. Write out the function body.
1593          Index = NumFunctionImports + Functions.size();
1594          WasmFunction Func;
1595          Func.SigIndex = getFunctionType(WS);
1596          Func.Section = &WS.getSection();
1597          assert(WasmIndices.count(&WS) == 0);
1598          WasmIndices[&WS] = Index;
1599          Functions.push_back(Func);
1600
1601          auto &Section = static_cast<MCSectionWasm &>(WS.getSection());
1602          if (const MCSymbolWasm *C = Section.getGroup()) {
1603            Comdats[C->getName()].emplace_back(
1604                WasmComdatEntry{wasm::WASM_COMDAT_FUNCTION, Index});
1605          }
1606
1607          if (WS.hasExportName()) {
1608            wasm::WasmExport Export;
1609            Export.Name = WS.getExportName();
1610            Export.Kind = wasm::WASM_EXTERNAL_FUNCTION;
1611            Export.Index = Index;
1612            Exports.push_back(Export);
1613          }
1614        } else {
1615          // An import; the index was assigned above.
1616          Index = WasmIndices.find(&WS)->second;
1617        }
1618
1619        LLVM_DEBUG(dbgs() << "  -> function index: " << Index << "\n");
1620
1621      } else if (WS.isData()) {
1622        if (!isInSymtab(WS))
1623          continue;
1624
1625        if (!WS.isDefined()) {
1626          LLVM_DEBUG(dbgs() << "  -> segment index: -1"
1627                            << "\n");
1628          continue;
1629        }
1630
1631        if (!WS.getSize())
1632          report_fatal_error("data symbols must have a size set with .size: " +
1633                             WS.getName());
1634
1635        int64_t Size = 0;
1636        if (!WS.getSize()->evaluateAsAbsolute(Size, Layout))
1637          report_fatal_error(".size expression must be evaluatable");
1638
1639        auto &DataSection = static_cast<MCSectionWasm &>(WS.getSection());
1640        if (!DataSection.isWasmData())
1641          report_fatal_error("data symbols must live in a data section: " +
1642                             WS.getName());
1643
1644        // For each data symbol, export it in the symtab as a reference to the
1645        // corresponding Wasm data segment.
1646        wasm::WasmDataReference Ref = wasm::WasmDataReference{
1647            DataSection.getSegmentIndex(), Layout.getSymbolOffset(WS),
1648            static_cast<uint64_t>(Size)};
1649        assert(DataLocations.count(&WS) == 0);
1650        DataLocations[&WS] = Ref;
1651        LLVM_DEBUG(dbgs() << "  -> segment index: " << Ref.Segment << "\n");
1652
1653      } else if (WS.isGlobal()) {
1654        // A "true" Wasm global (currently just __stack_pointer)
1655        if (WS.isDefined()) {
1656          wasm::WasmGlobal Global;
1657          Global.Type = WS.getGlobalType();
1658          Global.Index = NumGlobalImports + Globals.size();
1659          Global.InitExpr.Extended = false;
1660          switch (Global.Type.Type) {
1661          case wasm::WASM_TYPE_I32:
1662            Global.InitExpr.Inst.Opcode = wasm::WASM_OPCODE_I32_CONST;
1663            break;
1664          case wasm::WASM_TYPE_I64:
1665            Global.InitExpr.Inst.Opcode = wasm::WASM_OPCODE_I64_CONST;
1666            break;
1667          case wasm::WASM_TYPE_F32:
1668            Global.InitExpr.Inst.Opcode = wasm::WASM_OPCODE_F32_CONST;
1669            break;
1670          case wasm::WASM_TYPE_F64:
1671            Global.InitExpr.Inst.Opcode = wasm::WASM_OPCODE_F64_CONST;
1672            break;
1673          case wasm::WASM_TYPE_EXTERNREF:
1674            Global.InitExpr.Inst.Opcode = wasm::WASM_OPCODE_REF_NULL;
1675            break;
1676          default:
1677            llvm_unreachable("unexpected type");
1678          }
1679          assert(WasmIndices.count(&WS) == 0);
1680          WasmIndices[&WS] = Global.Index;
1681          Globals.push_back(Global);
1682        } else {
1683          // An import; the index was assigned above
1684          LLVM_DEBUG(dbgs() << "  -> global index: "
1685                            << WasmIndices.find(&WS)->second << "\n");
1686        }
1687      } else if (WS.isTable()) {
1688        if (WS.isDefined()) {
1689          wasm::WasmTable Table;
1690          Table.Index = NumTableImports + Tables.size();
1691          Table.Type = WS.getTableType();
1692          assert(WasmIndices.count(&WS) == 0);
1693          WasmIndices[&WS] = Table.Index;
1694          Tables.push_back(Table);
1695        }
1696        LLVM_DEBUG(dbgs() << " -> table index: "
1697                          << WasmIndices.find(&WS)->second << "\n");
1698      } else if (WS.isTag()) {
1699        // C++ exception symbol (__cpp_exception) or longjmp symbol
1700        // (__c_longjmp)
1701        unsigned Index;
1702        if (WS.isDefined()) {
1703          Index = NumTagImports + TagTypes.size();
1704          uint32_t SigIndex = getTagType(WS);
1705          assert(WasmIndices.count(&WS) == 0);
1706          WasmIndices[&WS] = Index;
1707          TagTypes.push_back(SigIndex);
1708        } else {
1709          // An import; the index was assigned above.
1710          assert(WasmIndices.count(&WS) > 0);
1711        }
1712        LLVM_DEBUG(dbgs() << "  -> tag index: " << WasmIndices.find(&WS)->second
1713                          << "\n");
1714
1715      } else {
1716        assert(WS.isSection());
1717      }
1718    }
1719
1720    // Populate WasmIndices and DataLocations for aliased symbols.  We need to
1721    // process these in a separate pass because we need to have processed the
1722    // target of the alias before the alias itself and the symbols are not
1723    // necessarily ordered in this way.
1724    for (const MCSymbol &S : Asm.symbols()) {
1725      if (!S.isVariable())
1726        continue;
1727
1728      assert(S.isDefined());
1729
1730      const auto *BS = Layout.getBaseSymbol(S);
1731      if (!BS)
1732        report_fatal_error(Twine(S.getName()) +
1733                           ": absolute addressing not supported!");
1734      const MCSymbolWasm *Base = cast<MCSymbolWasm>(BS);
1735
1736      // Find the target symbol of this weak alias and export that index
1737      const auto &WS = static_cast<const MCSymbolWasm &>(S);
1738      LLVM_DEBUG(dbgs() << WS.getName() << ": weak alias of '" << *Base
1739                        << "'\n");
1740
1741      if (Base->isFunction()) {
1742        assert(WasmIndices.count(Base) > 0);
1743        uint32_t WasmIndex = WasmIndices.find(Base)->second;
1744        assert(WasmIndices.count(&WS) == 0);
1745        WasmIndices[&WS] = WasmIndex;
1746        LLVM_DEBUG(dbgs() << "  -> index:" << WasmIndex << "\n");
1747      } else if (Base->isData()) {
1748        auto &DataSection = static_cast<MCSectionWasm &>(WS.getSection());
1749        uint64_t Offset = Layout.getSymbolOffset(S);
1750        int64_t Size = 0;
1751        // For data symbol alias we use the size of the base symbol as the
1752        // size of the alias.  When an offset from the base is involved this
1753        // can result in a offset + size goes past the end of the data section
1754        // which out object format doesn't support.  So we must clamp it.
1755        if (!Base->getSize()->evaluateAsAbsolute(Size, Layout))
1756          report_fatal_error(".size expression must be evaluatable");
1757        const WasmDataSegment &Segment =
1758            DataSegments[DataSection.getSegmentIndex()];
1759        Size =
1760            std::min(static_cast<uint64_t>(Size), Segment.Data.size() - Offset);
1761        wasm::WasmDataReference Ref = wasm::WasmDataReference{
1762            DataSection.getSegmentIndex(),
1763            static_cast<uint32_t>(Layout.getSymbolOffset(S)),
1764            static_cast<uint32_t>(Size)};
1765        DataLocations[&WS] = Ref;
1766        LLVM_DEBUG(dbgs() << "  -> index:" << Ref.Segment << "\n");
1767      } else {
1768        report_fatal_error("don't yet support global/tag aliases");
1769      }
1770    }
1771  }
1772
1773  // Finally, populate the symbol table itself, in its "natural" order.
1774  for (const MCSymbol &S : Asm.symbols()) {
1775    const auto &WS = static_cast<const MCSymbolWasm &>(S);
1776    if (!isInSymtab(WS)) {
1777      WS.setIndex(InvalidIndex);
1778      continue;
1779    }
1780    LLVM_DEBUG(dbgs() << "adding to symtab: " << WS << "\n");
1781
1782    uint32_t Flags = 0;
1783    if (WS.isWeak())
1784      Flags |= wasm::WASM_SYMBOL_BINDING_WEAK;
1785    if (WS.isHidden())
1786      Flags |= wasm::WASM_SYMBOL_VISIBILITY_HIDDEN;
1787    if (!WS.isExternal() && WS.isDefined())
1788      Flags |= wasm::WASM_SYMBOL_BINDING_LOCAL;
1789    if (WS.isUndefined())
1790      Flags |= wasm::WASM_SYMBOL_UNDEFINED;
1791    if (WS.isNoStrip()) {
1792      Flags |= wasm::WASM_SYMBOL_NO_STRIP;
1793      if (isEmscripten()) {
1794        Flags |= wasm::WASM_SYMBOL_EXPORTED;
1795      }
1796    }
1797    if (WS.hasImportName())
1798      Flags |= wasm::WASM_SYMBOL_EXPLICIT_NAME;
1799    if (WS.hasExportName())
1800      Flags |= wasm::WASM_SYMBOL_EXPORTED;
1801    if (WS.isTLS())
1802      Flags |= wasm::WASM_SYMBOL_TLS;
1803
1804    wasm::WasmSymbolInfo Info;
1805    Info.Name = WS.getName();
1806    Info.Kind = WS.getType().value_or(wasm::WASM_SYMBOL_TYPE_DATA);
1807    Info.Flags = Flags;
1808    if (!WS.isData()) {
1809      assert(WasmIndices.count(&WS) > 0);
1810      Info.ElementIndex = WasmIndices.find(&WS)->second;
1811    } else if (WS.isDefined()) {
1812      assert(DataLocations.count(&WS) > 0);
1813      Info.DataRef = DataLocations.find(&WS)->second;
1814    }
1815    WS.setIndex(SymbolInfos.size());
1816    SymbolInfos.emplace_back(Info);
1817  }
1818
1819  {
1820    auto HandleReloc = [&](const WasmRelocationEntry &Rel) {
1821      // Functions referenced by a relocation need to put in the table.  This is
1822      // purely to make the object file's provisional values readable, and is
1823      // ignored by the linker, which re-calculates the relocations itself.
1824      if (Rel.Type != wasm::R_WASM_TABLE_INDEX_I32 &&
1825          Rel.Type != wasm::R_WASM_TABLE_INDEX_I64 &&
1826          Rel.Type != wasm::R_WASM_TABLE_INDEX_SLEB &&
1827          Rel.Type != wasm::R_WASM_TABLE_INDEX_SLEB64 &&
1828          Rel.Type != wasm::R_WASM_TABLE_INDEX_REL_SLEB &&
1829          Rel.Type != wasm::R_WASM_TABLE_INDEX_REL_SLEB64)
1830        return;
1831      assert(Rel.Symbol->isFunction());
1832      const MCSymbolWasm *Base =
1833          cast<MCSymbolWasm>(Layout.getBaseSymbol(*Rel.Symbol));
1834      uint32_t FunctionIndex = WasmIndices.find(Base)->second;
1835      uint32_t TableIndex = TableElems.size() + InitialTableOffset;
1836      if (TableIndices.try_emplace(Base, TableIndex).second) {
1837        LLVM_DEBUG(dbgs() << "  -> adding " << Base->getName()
1838                          << " to table: " << TableIndex << "\n");
1839        TableElems.push_back(FunctionIndex);
1840        registerFunctionType(*Base);
1841      }
1842    };
1843
1844    for (const WasmRelocationEntry &RelEntry : CodeRelocations)
1845      HandleReloc(RelEntry);
1846    for (const WasmRelocationEntry &RelEntry : DataRelocations)
1847      HandleReloc(RelEntry);
1848  }
1849
1850  // Translate .init_array section contents into start functions.
1851  for (const MCSection &S : Asm) {
1852    const auto &WS = static_cast<const MCSectionWasm &>(S);
1853    if (WS.getName().starts_with(".fini_array"))
1854      report_fatal_error(".fini_array sections are unsupported");
1855    if (!WS.getName().starts_with(".init_array"))
1856      continue;
1857    if (WS.getFragmentList().empty())
1858      continue;
1859
1860    // init_array is expected to contain a single non-empty data fragment
1861    if (WS.getFragmentList().size() != 3)
1862      report_fatal_error("only one .init_array section fragment supported");
1863
1864    auto IT = WS.begin();
1865    const MCFragment &EmptyFrag = *IT;
1866    if (EmptyFrag.getKind() != MCFragment::FT_Data)
1867      report_fatal_error(".init_array section should be aligned");
1868
1869    IT = std::next(IT);
1870    const MCFragment &AlignFrag = *IT;
1871    if (AlignFrag.getKind() != MCFragment::FT_Align)
1872      report_fatal_error(".init_array section should be aligned");
1873    if (cast<MCAlignFragment>(AlignFrag).getAlignment() !=
1874        Align(is64Bit() ? 8 : 4))
1875      report_fatal_error(".init_array section should be aligned for pointers");
1876
1877    const MCFragment &Frag = *std::next(IT);
1878    if (Frag.hasInstructions() || Frag.getKind() != MCFragment::FT_Data)
1879      report_fatal_error("only data supported in .init_array section");
1880
1881    uint16_t Priority = UINT16_MAX;
1882    unsigned PrefixLength = strlen(".init_array");
1883    if (WS.getName().size() > PrefixLength) {
1884      if (WS.getName()[PrefixLength] != '.')
1885        report_fatal_error(
1886            ".init_array section priority should start with '.'");
1887      if (WS.getName().substr(PrefixLength + 1).getAsInteger(10, Priority))
1888        report_fatal_error("invalid .init_array section priority");
1889    }
1890    const auto &DataFrag = cast<MCDataFragment>(Frag);
1891    const SmallVectorImpl<char> &Contents = DataFrag.getContents();
1892    for (const uint8_t *
1893             P = (const uint8_t *)Contents.data(),
1894            *End = (const uint8_t *)Contents.data() + Contents.size();
1895         P != End; ++P) {
1896      if (*P != 0)
1897        report_fatal_error("non-symbolic data in .init_array section");
1898    }
1899    for (const MCFixup &Fixup : DataFrag.getFixups()) {
1900      assert(Fixup.getKind() ==
1901             MCFixup::getKindForSize(is64Bit() ? 8 : 4, false));
1902      const MCExpr *Expr = Fixup.getValue();
1903      auto *SymRef = dyn_cast<MCSymbolRefExpr>(Expr);
1904      if (!SymRef)
1905        report_fatal_error("fixups in .init_array should be symbol references");
1906      const auto &TargetSym = cast<const MCSymbolWasm>(SymRef->getSymbol());
1907      if (TargetSym.getIndex() == InvalidIndex)
1908        report_fatal_error("symbols in .init_array should exist in symtab");
1909      if (!TargetSym.isFunction())
1910        report_fatal_error("symbols in .init_array should be for functions");
1911      InitFuncs.push_back(
1912          std::make_pair(Priority, TargetSym.getIndex()));
1913    }
1914  }
1915
1916  // Write out the Wasm header.
1917  writeHeader(Asm);
1918
1919  uint32_t CodeSectionIndex, DataSectionIndex;
1920  if (Mode != DwoMode::DwoOnly) {
1921    writeTypeSection(Signatures);
1922    writeImportSection(Imports, DataSize, TableElems.size());
1923    writeFunctionSection(Functions);
1924    writeTableSection(Tables);
1925    // Skip the "memory" section; we import the memory instead.
1926    writeTagSection(TagTypes);
1927    writeGlobalSection(Globals);
1928    writeExportSection(Exports);
1929    const MCSymbol *IndirectFunctionTable =
1930        Asm.getContext().lookupSymbol("__indirect_function_table");
1931    writeElemSection(cast_or_null<const MCSymbolWasm>(IndirectFunctionTable),
1932                     TableElems);
1933    writeDataCountSection();
1934
1935    CodeSectionIndex = writeCodeSection(Asm, Layout, Functions);
1936    DataSectionIndex = writeDataSection(Layout);
1937  }
1938
1939  // The Sections in the COMDAT list have placeholder indices (their index among
1940  // custom sections, rather than among all sections). Fix them up here.
1941  for (auto &Group : Comdats) {
1942    for (auto &Entry : Group.second) {
1943      if (Entry.Kind == wasm::WASM_COMDAT_SECTION) {
1944        Entry.Index += SectionCount;
1945      }
1946    }
1947  }
1948  for (auto &CustomSection : CustomSections)
1949    writeCustomSection(CustomSection, Asm, Layout);
1950
1951  if (Mode != DwoMode::DwoOnly) {
1952    writeLinkingMetaDataSection(SymbolInfos, InitFuncs, Comdats);
1953
1954    writeRelocSection(CodeSectionIndex, "CODE", CodeRelocations);
1955    writeRelocSection(DataSectionIndex, "DATA", DataRelocations);
1956  }
1957  writeCustomRelocSections();
1958  if (ProducersSection)
1959    writeCustomSection(*ProducersSection, Asm, Layout);
1960  if (TargetFeaturesSection)
1961    writeCustomSection(*TargetFeaturesSection, Asm, Layout);
1962
1963  // TODO: Translate the .comment section to the output.
1964  return W->OS.tell() - StartOffset;
1965}
1966
1967std::unique_ptr<MCObjectWriter>
1968llvm::createWasmObjectWriter(std::unique_ptr<MCWasmObjectTargetWriter> MOTW,
1969                             raw_pwrite_stream &OS) {
1970  return std::make_unique<WasmObjectWriter>(std::move(MOTW), OS);
1971}
1972
1973std::unique_ptr<MCObjectWriter>
1974llvm::createWasmDwoObjectWriter(std::unique_ptr<MCWasmObjectTargetWriter> MOTW,
1975                                raw_pwrite_stream &OS,
1976                                raw_pwrite_stream &DwoOS) {
1977  return std::make_unique<WasmObjectWriter>(std::move(MOTW), OS, DwoOS);
1978}
1979