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/EndianStream.h"
31 #include "llvm/Support/ErrorHandling.h"
32 #include "llvm/Support/LEB128.h"
33 #include "llvm/Support/StringSaver.h"
34 #include <vector>
35
36 using namespace llvm;
37
38 #define DEBUG_TYPE "mc"
39
40 namespace {
41
42 // Went we ceate the indirect function table we start at 1, so that there is
43 // and emtpy slot at 0 and therefore calling a null function pointer will trap.
44 static const uint32_t InitialTableOffset = 1;
45
46 // For patching purposes, we need to remember where each section starts, both
47 // for patching up the section size field, and for patching up references to
48 // locations within the section.
49 struct SectionBookkeeping {
50 // Where the size of the section is written.
51 uint64_t SizeOffset;
52 // Where the section header ends (without custom section name).
53 uint64_t PayloadOffset;
54 // Where the contents of the section starts.
55 uint64_t ContentsOffset;
56 uint32_t Index;
57 };
58
59 // The signature of a wasm function or event, in a struct capable of being used
60 // as a DenseMap key.
61 // TODO: Consider using wasm::WasmSignature directly instead.
62 struct WasmSignature {
63 // Support empty and tombstone instances, needed by DenseMap.
64 enum { Plain, Empty, Tombstone } State = Plain;
65
66 // The return types of the function.
67 SmallVector<wasm::ValType, 1> Returns;
68
69 // The parameter types of the function.
70 SmallVector<wasm::ValType, 4> Params;
71
operator ==__anoneedd02a30111::WasmSignature72 bool operator==(const WasmSignature &Other) const {
73 return State == Other.State && Returns == Other.Returns &&
74 Params == Other.Params;
75 }
76 };
77
78 // Traits for using WasmSignature in a DenseMap.
79 struct WasmSignatureDenseMapInfo {
getEmptyKey__anoneedd02a30111::WasmSignatureDenseMapInfo80 static WasmSignature getEmptyKey() {
81 WasmSignature Sig;
82 Sig.State = WasmSignature::Empty;
83 return Sig;
84 }
getTombstoneKey__anoneedd02a30111::WasmSignatureDenseMapInfo85 static WasmSignature getTombstoneKey() {
86 WasmSignature Sig;
87 Sig.State = WasmSignature::Tombstone;
88 return Sig;
89 }
getHashValue__anoneedd02a30111::WasmSignatureDenseMapInfo90 static unsigned getHashValue(const WasmSignature &Sig) {
91 uintptr_t Value = Sig.State;
92 for (wasm::ValType Ret : Sig.Returns)
93 Value += DenseMapInfo<uint32_t>::getHashValue(uint32_t(Ret));
94 for (wasm::ValType Param : Sig.Params)
95 Value += DenseMapInfo<uint32_t>::getHashValue(uint32_t(Param));
96 return Value;
97 }
isEqual__anoneedd02a30111::WasmSignatureDenseMapInfo98 static bool isEqual(const WasmSignature &LHS, const WasmSignature &RHS) {
99 return LHS == RHS;
100 }
101 };
102
103 // A wasm data segment. A wasm binary contains only a single data section
104 // but that can contain many segments, each with their own virtual location
105 // in memory. Each MCSection data created by llvm is modeled as its own
106 // wasm data segment.
107 struct WasmDataSegment {
108 MCSectionWasm *Section;
109 StringRef Name;
110 uint32_t InitFlags;
111 uint64_t Offset;
112 uint32_t Alignment;
113 uint32_t LinkerFlags;
114 SmallVector<char, 4> Data;
115 };
116
117 // A wasm function to be written into the function section.
118 struct WasmFunction {
119 uint32_t SigIndex;
120 const MCSymbolWasm *Sym;
121 };
122
123 // A wasm global to be written into the global section.
124 struct WasmGlobal {
125 wasm::WasmGlobalType Type;
126 uint64_t InitialValue;
127 };
128
129 // Information about a single item which is part of a COMDAT. For each data
130 // segment or function which is in the COMDAT, there is a corresponding
131 // WasmComdatEntry.
132 struct WasmComdatEntry {
133 unsigned Kind;
134 uint32_t Index;
135 };
136
137 // Information about a single relocation.
138 struct WasmRelocationEntry {
139 uint64_t Offset; // Where is the relocation.
140 const MCSymbolWasm *Symbol; // The symbol to relocate with.
141 int64_t Addend; // A value to add to the symbol.
142 unsigned Type; // The type of the relocation.
143 const MCSectionWasm *FixupSection; // The section the relocation is targeting.
144
WasmRelocationEntry__anoneedd02a30111::WasmRelocationEntry145 WasmRelocationEntry(uint64_t Offset, const MCSymbolWasm *Symbol,
146 int64_t Addend, unsigned Type,
147 const MCSectionWasm *FixupSection)
148 : Offset(Offset), Symbol(Symbol), Addend(Addend), Type(Type),
149 FixupSection(FixupSection) {}
150
hasAddend__anoneedd02a30111::WasmRelocationEntry151 bool hasAddend() const { return wasm::relocTypeHasAddend(Type); }
152
print__anoneedd02a30111::WasmRelocationEntry153 void print(raw_ostream &Out) const {
154 Out << wasm::relocTypetoString(Type) << " Off=" << Offset
155 << ", Sym=" << *Symbol << ", Addend=" << Addend
156 << ", FixupSection=" << FixupSection->getName();
157 }
158
159 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
dump__anoneedd02a30111::WasmRelocationEntry160 LLVM_DUMP_METHOD void dump() const { print(dbgs()); }
161 #endif
162 };
163
164 static const uint32_t InvalidIndex = -1;
165
166 struct WasmCustomSection {
167
168 StringRef Name;
169 MCSectionWasm *Section;
170
171 uint32_t OutputContentsOffset;
172 uint32_t OutputIndex;
173
WasmCustomSection__anoneedd02a30111::WasmCustomSection174 WasmCustomSection(StringRef Name, MCSectionWasm *Section)
175 : Name(Name), Section(Section), OutputContentsOffset(0),
176 OutputIndex(InvalidIndex) {}
177 };
178
179 #if !defined(NDEBUG)
operator <<(raw_ostream & OS,const WasmRelocationEntry & Rel)180 raw_ostream &operator<<(raw_ostream &OS, const WasmRelocationEntry &Rel) {
181 Rel.print(OS);
182 return OS;
183 }
184 #endif
185
186 // Write X as an (unsigned) LEB value at offset Offset in Stream, padded
187 // to allow patching.
188 template <int W>
writePatchableLEB(raw_pwrite_stream & Stream,uint64_t X,uint64_t Offset)189 void writePatchableLEB(raw_pwrite_stream &Stream, uint64_t X, uint64_t Offset) {
190 uint8_t Buffer[W];
191 unsigned SizeLen = encodeULEB128(X, Buffer, W);
192 assert(SizeLen == W);
193 Stream.pwrite((char *)Buffer, SizeLen, Offset);
194 }
195
196 // Write X as an signed LEB value at offset Offset in Stream, padded
197 // to allow patching.
198 template <int W>
writePatchableSLEB(raw_pwrite_stream & Stream,int64_t X,uint64_t Offset)199 void writePatchableSLEB(raw_pwrite_stream &Stream, int64_t X, uint64_t Offset) {
200 uint8_t Buffer[W];
201 unsigned SizeLen = encodeSLEB128(X, Buffer, W);
202 assert(SizeLen == W);
203 Stream.pwrite((char *)Buffer, SizeLen, Offset);
204 }
205
206 // Write X as a plain integer value at offset Offset in Stream.
patchI32(raw_pwrite_stream & Stream,uint32_t X,uint64_t Offset)207 static void patchI32(raw_pwrite_stream &Stream, uint32_t X, uint64_t Offset) {
208 uint8_t Buffer[4];
209 support::endian::write32le(Buffer, X);
210 Stream.pwrite((char *)Buffer, sizeof(Buffer), Offset);
211 }
212
patchI64(raw_pwrite_stream & Stream,uint64_t X,uint64_t Offset)213 static void patchI64(raw_pwrite_stream &Stream, uint64_t X, uint64_t Offset) {
214 uint8_t Buffer[8];
215 support::endian::write64le(Buffer, X);
216 Stream.pwrite((char *)Buffer, sizeof(Buffer), Offset);
217 }
218
219 class WasmObjectWriter : public MCObjectWriter {
220 support::endian::Writer W;
221
222 /// The target specific Wasm writer instance.
223 std::unique_ptr<MCWasmObjectTargetWriter> TargetObjectWriter;
224
225 // Relocations for fixing up references in the code section.
226 std::vector<WasmRelocationEntry> CodeRelocations;
227 // Relocations for fixing up references in the data section.
228 std::vector<WasmRelocationEntry> DataRelocations;
229
230 // Index values to use for fixing up call_indirect type indices.
231 // Maps function symbols to the index of the type of the function
232 DenseMap<const MCSymbolWasm *, uint32_t> TypeIndices;
233 // Maps function symbols to the table element index space. Used
234 // for TABLE_INDEX relocation types (i.e. address taken functions).
235 DenseMap<const MCSymbolWasm *, uint32_t> TableIndices;
236 // Maps function/global symbols to the function/global/event/section index
237 // space.
238 DenseMap<const MCSymbolWasm *, uint32_t> WasmIndices;
239 DenseMap<const MCSymbolWasm *, uint32_t> GOTIndices;
240 // Maps data symbols to the Wasm segment and offset/size with the segment.
241 DenseMap<const MCSymbolWasm *, wasm::WasmDataReference> DataLocations;
242
243 // Stores output data (index, relocations, content offset) for custom
244 // section.
245 std::vector<WasmCustomSection> CustomSections;
246 std::unique_ptr<WasmCustomSection> ProducersSection;
247 std::unique_ptr<WasmCustomSection> TargetFeaturesSection;
248 // Relocations for fixing up references in the custom sections.
249 DenseMap<const MCSectionWasm *, std::vector<WasmRelocationEntry>>
250 CustomSectionsRelocations;
251
252 // Map from section to defining function symbol.
253 DenseMap<const MCSection *, const MCSymbol *> SectionFunctions;
254
255 DenseMap<WasmSignature, uint32_t, WasmSignatureDenseMapInfo> SignatureIndices;
256 SmallVector<WasmSignature, 4> Signatures;
257 SmallVector<WasmDataSegment, 4> DataSegments;
258 unsigned NumFunctionImports = 0;
259 unsigned NumGlobalImports = 0;
260 unsigned NumEventImports = 0;
261 uint32_t SectionCount = 0;
262
263 // TargetObjectWriter wrappers.
is64Bit() const264 bool is64Bit() const { return TargetObjectWriter->is64Bit(); }
isEmscripten() const265 bool isEmscripten() const { return TargetObjectWriter->isEmscripten(); }
266
267 void startSection(SectionBookkeeping &Section, unsigned SectionId);
268 void startCustomSection(SectionBookkeeping &Section, StringRef Name);
269 void endSection(SectionBookkeeping &Section);
270
271 public:
WasmObjectWriter(std::unique_ptr<MCWasmObjectTargetWriter> MOTW,raw_pwrite_stream & OS)272 WasmObjectWriter(std::unique_ptr<MCWasmObjectTargetWriter> MOTW,
273 raw_pwrite_stream &OS)
274 : W(OS, support::little), TargetObjectWriter(std::move(MOTW)) {}
275
276 private:
reset()277 void reset() override {
278 CodeRelocations.clear();
279 DataRelocations.clear();
280 TypeIndices.clear();
281 WasmIndices.clear();
282 GOTIndices.clear();
283 TableIndices.clear();
284 DataLocations.clear();
285 CustomSections.clear();
286 ProducersSection.reset();
287 TargetFeaturesSection.reset();
288 CustomSectionsRelocations.clear();
289 SignatureIndices.clear();
290 Signatures.clear();
291 DataSegments.clear();
292 SectionFunctions.clear();
293 NumFunctionImports = 0;
294 NumGlobalImports = 0;
295 MCObjectWriter::reset();
296 }
297
298 void writeHeader(const MCAssembler &Asm);
299
300 void recordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
301 const MCFragment *Fragment, const MCFixup &Fixup,
302 MCValue Target, uint64_t &FixedValue) override;
303
304 void executePostLayoutBinding(MCAssembler &Asm,
305 const MCAsmLayout &Layout) override;
306
307 uint64_t writeObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
308
writeString(const StringRef Str)309 void writeString(const StringRef Str) {
310 encodeULEB128(Str.size(), W.OS);
311 W.OS << Str;
312 }
313
writeI32(int32_t val)314 void writeI32(int32_t val) {
315 char Buffer[4];
316 support::endian::write32le(Buffer, val);
317 W.OS.write(Buffer, sizeof(Buffer));
318 }
319
writeI64(int64_t val)320 void writeI64(int64_t val) {
321 char Buffer[8];
322 support::endian::write64le(Buffer, val);
323 W.OS.write(Buffer, sizeof(Buffer));
324 }
325
writeValueType(wasm::ValType Ty)326 void writeValueType(wasm::ValType Ty) { W.OS << static_cast<char>(Ty); }
327
328 void writeTypeSection(ArrayRef<WasmSignature> Signatures);
329 void writeImportSection(ArrayRef<wasm::WasmImport> Imports, uint64_t DataSize,
330 uint32_t NumElements);
331 void writeFunctionSection(ArrayRef<WasmFunction> Functions);
332 void writeExportSection(ArrayRef<wasm::WasmExport> Exports);
333 void writeElemSection(ArrayRef<uint32_t> TableElems);
334 void writeDataCountSection();
335 uint32_t writeCodeSection(const MCAssembler &Asm, const MCAsmLayout &Layout,
336 ArrayRef<WasmFunction> Functions);
337 uint32_t writeDataSection(const MCAsmLayout &Layout);
338 void writeEventSection(ArrayRef<wasm::WasmEventType> Events);
339 void writeGlobalSection(ArrayRef<wasm::WasmGlobal> Globals);
340 void writeRelocSection(uint32_t SectionIndex, StringRef Name,
341 std::vector<WasmRelocationEntry> &Relocations);
342 void writeLinkingMetaDataSection(
343 ArrayRef<wasm::WasmSymbolInfo> SymbolInfos,
344 ArrayRef<std::pair<uint16_t, uint32_t>> InitFuncs,
345 const std::map<StringRef, std::vector<WasmComdatEntry>> &Comdats);
346 void writeCustomSection(WasmCustomSection &CustomSection,
347 const MCAssembler &Asm, const MCAsmLayout &Layout);
348 void writeCustomRelocSections();
349 void
350 updateCustomSectionRelocations(const SmallVector<WasmFunction, 4> &Functions,
351 const MCAsmLayout &Layout);
352
353 uint64_t getProvisionalValue(const WasmRelocationEntry &RelEntry,
354 const MCAsmLayout &Layout);
355 void applyRelocations(ArrayRef<WasmRelocationEntry> Relocations,
356 uint64_t ContentsOffset, const MCAsmLayout &Layout);
357
358 uint32_t getRelocationIndexValue(const WasmRelocationEntry &RelEntry);
359 uint32_t getFunctionType(const MCSymbolWasm &Symbol);
360 uint32_t getEventType(const MCSymbolWasm &Symbol);
361 void registerFunctionType(const MCSymbolWasm &Symbol);
362 void registerEventType(const MCSymbolWasm &Symbol);
363 };
364
365 } // end anonymous namespace
366
367 // Write out a section header and a patchable section size field.
startSection(SectionBookkeeping & Section,unsigned SectionId)368 void WasmObjectWriter::startSection(SectionBookkeeping &Section,
369 unsigned SectionId) {
370 LLVM_DEBUG(dbgs() << "startSection " << SectionId << "\n");
371 W.OS << char(SectionId);
372
373 Section.SizeOffset = W.OS.tell();
374
375 // The section size. We don't know the size yet, so reserve enough space
376 // for any 32-bit value; we'll patch it later.
377 encodeULEB128(0, W.OS, 5);
378
379 // The position where the section starts, for measuring its size.
380 Section.ContentsOffset = W.OS.tell();
381 Section.PayloadOffset = W.OS.tell();
382 Section.Index = SectionCount++;
383 }
384
startCustomSection(SectionBookkeeping & Section,StringRef Name)385 void WasmObjectWriter::startCustomSection(SectionBookkeeping &Section,
386 StringRef Name) {
387 LLVM_DEBUG(dbgs() << "startCustomSection " << Name << "\n");
388 startSection(Section, wasm::WASM_SEC_CUSTOM);
389
390 // The position where the section header ends, for measuring its size.
391 Section.PayloadOffset = W.OS.tell();
392
393 // Custom sections in wasm also have a string identifier.
394 writeString(Name);
395
396 // The position where the custom section starts.
397 Section.ContentsOffset = W.OS.tell();
398 }
399
400 // Now that the section is complete and we know how big it is, patch up the
401 // section size field at the start of the section.
endSection(SectionBookkeeping & Section)402 void WasmObjectWriter::endSection(SectionBookkeeping &Section) {
403 uint64_t Size = W.OS.tell();
404 // /dev/null doesn't support seek/tell and can report offset of 0.
405 // Simply skip this patching in that case.
406 if (!Size)
407 return;
408
409 Size -= Section.PayloadOffset;
410 if (uint32_t(Size) != Size)
411 report_fatal_error("section size does not fit in a uint32_t");
412
413 LLVM_DEBUG(dbgs() << "endSection size=" << Size << "\n");
414
415 // Write the final section size to the payload_len field, which follows
416 // the section id byte.
417 writePatchableLEB<5>(static_cast<raw_pwrite_stream &>(W.OS), Size,
418 Section.SizeOffset);
419 }
420
421 // Emit the Wasm header.
writeHeader(const MCAssembler & Asm)422 void WasmObjectWriter::writeHeader(const MCAssembler &Asm) {
423 W.OS.write(wasm::WasmMagic, sizeof(wasm::WasmMagic));
424 W.write<uint32_t>(wasm::WasmVersion);
425 }
426
executePostLayoutBinding(MCAssembler & Asm,const MCAsmLayout & Layout)427 void WasmObjectWriter::executePostLayoutBinding(MCAssembler &Asm,
428 const MCAsmLayout &Layout) {
429 // Build a map of sections to the function that defines them, for use
430 // in recordRelocation.
431 for (const MCSymbol &S : Asm.symbols()) {
432 const auto &WS = static_cast<const MCSymbolWasm &>(S);
433 if (WS.isDefined() && WS.isFunction() && !WS.isVariable()) {
434 const auto &Sec = static_cast<const MCSectionWasm &>(S.getSection());
435 auto Pair = SectionFunctions.insert(std::make_pair(&Sec, &S));
436 if (!Pair.second)
437 report_fatal_error("section already has a defining function: " +
438 Sec.getName());
439 }
440 }
441 }
442
recordRelocation(MCAssembler & Asm,const MCAsmLayout & Layout,const MCFragment * Fragment,const MCFixup & Fixup,MCValue Target,uint64_t & FixedValue)443 void WasmObjectWriter::recordRelocation(MCAssembler &Asm,
444 const MCAsmLayout &Layout,
445 const MCFragment *Fragment,
446 const MCFixup &Fixup, MCValue Target,
447 uint64_t &FixedValue) {
448 // The WebAssembly backend should never generate FKF_IsPCRel fixups
449 assert(!(Asm.getBackend().getFixupKindInfo(Fixup.getKind()).Flags &
450 MCFixupKindInfo::FKF_IsPCRel));
451
452 const auto &FixupSection = cast<MCSectionWasm>(*Fragment->getParent());
453 uint64_t C = Target.getConstant();
454 uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
455 MCContext &Ctx = Asm.getContext();
456
457 if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
458 // To get here the A - B expression must have failed evaluateAsRelocatable.
459 // This means either A or B must be undefined and in WebAssembly we can't
460 // support either of those cases.
461 const auto &SymB = cast<MCSymbolWasm>(RefB->getSymbol());
462 Ctx.reportError(
463 Fixup.getLoc(),
464 Twine("symbol '") + SymB.getName() +
465 "': unsupported subtraction expression used in relocation.");
466 return;
467 }
468
469 // We either rejected the fixup or folded B into C at this point.
470 const MCSymbolRefExpr *RefA = Target.getSymA();
471 const auto *SymA = cast<MCSymbolWasm>(&RefA->getSymbol());
472
473 // The .init_array isn't translated as data, so don't do relocations in it.
474 if (FixupSection.getName().startswith(".init_array")) {
475 SymA->setUsedInInitArray();
476 return;
477 }
478
479 if (SymA->isVariable()) {
480 const MCExpr *Expr = SymA->getVariableValue();
481 if (const auto *Inner = dyn_cast<MCSymbolRefExpr>(Expr))
482 if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF)
483 llvm_unreachable("weakref used in reloc not yet implemented");
484 }
485
486 // Put any constant offset in an addend. Offsets can be negative, and
487 // LLVM expects wrapping, in contrast to wasm's immediates which can't
488 // be negative and don't wrap.
489 FixedValue = 0;
490
491 unsigned Type = TargetObjectWriter->getRelocType(Target, Fixup);
492
493 // Absolute offset within a section or a function.
494 // Currently only supported for for metadata sections.
495 // See: test/MC/WebAssembly/blockaddress.ll
496 if (Type == wasm::R_WASM_FUNCTION_OFFSET_I32 ||
497 Type == wasm::R_WASM_SECTION_OFFSET_I32) {
498 if (!FixupSection.getKind().isMetadata())
499 report_fatal_error("relocations for function or section offsets are "
500 "only supported in metadata sections");
501
502 const MCSymbol *SectionSymbol = nullptr;
503 const MCSection &SecA = SymA->getSection();
504 if (SecA.getKind().isText())
505 SectionSymbol = SectionFunctions.find(&SecA)->second;
506 else
507 SectionSymbol = SecA.getBeginSymbol();
508 if (!SectionSymbol)
509 report_fatal_error("section symbol is required for relocation");
510
511 C += Layout.getSymbolOffset(*SymA);
512 SymA = cast<MCSymbolWasm>(SectionSymbol);
513 }
514
515 // Relocation other than R_WASM_TYPE_INDEX_LEB are required to be
516 // against a named symbol.
517 if (Type != wasm::R_WASM_TYPE_INDEX_LEB) {
518 if (SymA->getName().empty())
519 report_fatal_error("relocations against un-named temporaries are not yet "
520 "supported by wasm");
521
522 SymA->setUsedInReloc();
523 }
524
525 if (RefA->getKind() == MCSymbolRefExpr::VK_GOT)
526 SymA->setUsedInGOT();
527
528 WasmRelocationEntry Rec(FixupOffset, SymA, C, Type, &FixupSection);
529 LLVM_DEBUG(dbgs() << "WasmReloc: " << Rec << "\n");
530
531 if (FixupSection.isWasmData()) {
532 DataRelocations.push_back(Rec);
533 } else if (FixupSection.getKind().isText()) {
534 CodeRelocations.push_back(Rec);
535 } else if (FixupSection.getKind().isMetadata()) {
536 CustomSectionsRelocations[&FixupSection].push_back(Rec);
537 } else {
538 llvm_unreachable("unexpected section type");
539 }
540 }
541
542 // Compute a value to write into the code at the location covered
543 // by RelEntry. This value isn't used by the static linker; it just serves
544 // to make the object format more readable and more likely to be directly
545 // useable.
546 uint64_t
getProvisionalValue(const WasmRelocationEntry & RelEntry,const MCAsmLayout & Layout)547 WasmObjectWriter::getProvisionalValue(const WasmRelocationEntry &RelEntry,
548 const MCAsmLayout &Layout) {
549 if ((RelEntry.Type == wasm::R_WASM_GLOBAL_INDEX_LEB ||
550 RelEntry.Type == wasm::R_WASM_GLOBAL_INDEX_I32) &&
551 !RelEntry.Symbol->isGlobal()) {
552 assert(GOTIndices.count(RelEntry.Symbol) > 0 && "symbol not found in GOT index space");
553 return GOTIndices[RelEntry.Symbol];
554 }
555
556 switch (RelEntry.Type) {
557 case wasm::R_WASM_TABLE_INDEX_REL_SLEB:
558 case wasm::R_WASM_TABLE_INDEX_SLEB:
559 case wasm::R_WASM_TABLE_INDEX_I32: {
560 // Provisional value is table address of the resolved symbol itself
561 const MCSymbolWasm *Base =
562 cast<MCSymbolWasm>(Layout.getBaseSymbol(*RelEntry.Symbol));
563 assert(Base->isFunction());
564 if (RelEntry.Type == wasm::R_WASM_TABLE_INDEX_REL_SLEB)
565 return TableIndices[Base] - InitialTableOffset;
566 else
567 return TableIndices[Base];
568 }
569 case wasm::R_WASM_TYPE_INDEX_LEB:
570 // Provisional value is same as the index
571 return getRelocationIndexValue(RelEntry);
572 case wasm::R_WASM_FUNCTION_INDEX_LEB:
573 case wasm::R_WASM_GLOBAL_INDEX_LEB:
574 case wasm::R_WASM_GLOBAL_INDEX_I32:
575 case wasm::R_WASM_EVENT_INDEX_LEB:
576 // Provisional value is function/global/event Wasm index
577 assert(WasmIndices.count(RelEntry.Symbol) > 0 && "symbol not found in wasm index space");
578 return WasmIndices[RelEntry.Symbol];
579 case wasm::R_WASM_FUNCTION_OFFSET_I32:
580 case wasm::R_WASM_SECTION_OFFSET_I32: {
581 const auto &Section =
582 static_cast<const MCSectionWasm &>(RelEntry.Symbol->getSection());
583 return Section.getSectionOffset() + RelEntry.Addend;
584 }
585 case wasm::R_WASM_MEMORY_ADDR_LEB:
586 case wasm::R_WASM_MEMORY_ADDR_LEB64:
587 case wasm::R_WASM_MEMORY_ADDR_SLEB:
588 case wasm::R_WASM_MEMORY_ADDR_SLEB64:
589 case wasm::R_WASM_MEMORY_ADDR_REL_SLEB:
590 case wasm::R_WASM_MEMORY_ADDR_REL_SLEB64:
591 case wasm::R_WASM_MEMORY_ADDR_I32:
592 case wasm::R_WASM_MEMORY_ADDR_I64: {
593 // Provisional value is address of the global
594 const MCSymbolWasm *Base =
595 cast<MCSymbolWasm>(Layout.getBaseSymbol(*RelEntry.Symbol));
596 // For undefined symbols, use zero
597 if (!Base->isDefined())
598 return 0;
599 const wasm::WasmDataReference &Ref = DataLocations[Base];
600 const WasmDataSegment &Segment = DataSegments[Ref.Segment];
601 // Ignore overflow. LLVM allows address arithmetic to silently wrap.
602 return Segment.Offset + Ref.Offset + RelEntry.Addend;
603 }
604 default:
605 llvm_unreachable("invalid relocation type");
606 }
607 }
608
addData(SmallVectorImpl<char> & DataBytes,MCSectionWasm & DataSection)609 static void addData(SmallVectorImpl<char> &DataBytes,
610 MCSectionWasm &DataSection) {
611 LLVM_DEBUG(errs() << "addData: " << DataSection.getName() << "\n");
612
613 DataBytes.resize(alignTo(DataBytes.size(), DataSection.getAlignment()));
614
615 for (const MCFragment &Frag : DataSection) {
616 if (Frag.hasInstructions())
617 report_fatal_error("only data supported in data sections");
618
619 if (auto *Align = dyn_cast<MCAlignFragment>(&Frag)) {
620 if (Align->getValueSize() != 1)
621 report_fatal_error("only byte values supported for alignment");
622 // If nops are requested, use zeros, as this is the data section.
623 uint8_t Value = Align->hasEmitNops() ? 0 : Align->getValue();
624 uint64_t Size =
625 std::min<uint64_t>(alignTo(DataBytes.size(), Align->getAlignment()),
626 DataBytes.size() + Align->getMaxBytesToEmit());
627 DataBytes.resize(Size, Value);
628 } else if (auto *Fill = dyn_cast<MCFillFragment>(&Frag)) {
629 int64_t NumValues;
630 if (!Fill->getNumValues().evaluateAsAbsolute(NumValues))
631 llvm_unreachable("The fill should be an assembler constant");
632 DataBytes.insert(DataBytes.end(), Fill->getValueSize() * NumValues,
633 Fill->getValue());
634 } else if (auto *LEB = dyn_cast<MCLEBFragment>(&Frag)) {
635 const SmallVectorImpl<char> &Contents = LEB->getContents();
636 DataBytes.insert(DataBytes.end(), Contents.begin(), Contents.end());
637 } else {
638 const auto &DataFrag = cast<MCDataFragment>(Frag);
639 const SmallVectorImpl<char> &Contents = DataFrag.getContents();
640 DataBytes.insert(DataBytes.end(), Contents.begin(), Contents.end());
641 }
642 }
643
644 LLVM_DEBUG(dbgs() << "addData -> " << DataBytes.size() << "\n");
645 }
646
647 uint32_t
getRelocationIndexValue(const WasmRelocationEntry & RelEntry)648 WasmObjectWriter::getRelocationIndexValue(const WasmRelocationEntry &RelEntry) {
649 if (RelEntry.Type == wasm::R_WASM_TYPE_INDEX_LEB) {
650 if (!TypeIndices.count(RelEntry.Symbol))
651 report_fatal_error("symbol not found in type index space: " +
652 RelEntry.Symbol->getName());
653 return TypeIndices[RelEntry.Symbol];
654 }
655
656 return RelEntry.Symbol->getIndex();
657 }
658
659 // Apply the portions of the relocation records that we can handle ourselves
660 // directly.
applyRelocations(ArrayRef<WasmRelocationEntry> Relocations,uint64_t ContentsOffset,const MCAsmLayout & Layout)661 void WasmObjectWriter::applyRelocations(
662 ArrayRef<WasmRelocationEntry> Relocations, uint64_t ContentsOffset,
663 const MCAsmLayout &Layout) {
664 auto &Stream = static_cast<raw_pwrite_stream &>(W.OS);
665 for (const WasmRelocationEntry &RelEntry : Relocations) {
666 uint64_t Offset = ContentsOffset +
667 RelEntry.FixupSection->getSectionOffset() +
668 RelEntry.Offset;
669
670 LLVM_DEBUG(dbgs() << "applyRelocation: " << RelEntry << "\n");
671 auto Value = getProvisionalValue(RelEntry, Layout);
672
673 switch (RelEntry.Type) {
674 case wasm::R_WASM_FUNCTION_INDEX_LEB:
675 case wasm::R_WASM_TYPE_INDEX_LEB:
676 case wasm::R_WASM_GLOBAL_INDEX_LEB:
677 case wasm::R_WASM_MEMORY_ADDR_LEB:
678 case wasm::R_WASM_EVENT_INDEX_LEB:
679 writePatchableLEB<5>(Stream, Value, Offset);
680 break;
681 case wasm::R_WASM_MEMORY_ADDR_LEB64:
682 writePatchableLEB<10>(Stream, Value, Offset);
683 break;
684 case wasm::R_WASM_TABLE_INDEX_I32:
685 case wasm::R_WASM_MEMORY_ADDR_I32:
686 case wasm::R_WASM_FUNCTION_OFFSET_I32:
687 case wasm::R_WASM_SECTION_OFFSET_I32:
688 case wasm::R_WASM_GLOBAL_INDEX_I32:
689 patchI32(Stream, Value, Offset);
690 break;
691 case wasm::R_WASM_MEMORY_ADDR_I64:
692 patchI64(Stream, Value, Offset);
693 break;
694 case wasm::R_WASM_TABLE_INDEX_SLEB:
695 case wasm::R_WASM_TABLE_INDEX_REL_SLEB:
696 case wasm::R_WASM_MEMORY_ADDR_SLEB:
697 case wasm::R_WASM_MEMORY_ADDR_REL_SLEB:
698 writePatchableSLEB<5>(Stream, Value, Offset);
699 break;
700 case wasm::R_WASM_MEMORY_ADDR_SLEB64:
701 case wasm::R_WASM_MEMORY_ADDR_REL_SLEB64:
702 writePatchableSLEB<10>(Stream, Value, Offset);
703 break;
704 default:
705 llvm_unreachable("invalid relocation type");
706 }
707 }
708 }
709
writeTypeSection(ArrayRef<WasmSignature> Signatures)710 void WasmObjectWriter::writeTypeSection(ArrayRef<WasmSignature> Signatures) {
711 if (Signatures.empty())
712 return;
713
714 SectionBookkeeping Section;
715 startSection(Section, wasm::WASM_SEC_TYPE);
716
717 encodeULEB128(Signatures.size(), W.OS);
718
719 for (const WasmSignature &Sig : Signatures) {
720 W.OS << char(wasm::WASM_TYPE_FUNC);
721 encodeULEB128(Sig.Params.size(), W.OS);
722 for (wasm::ValType Ty : Sig.Params)
723 writeValueType(Ty);
724 encodeULEB128(Sig.Returns.size(), W.OS);
725 for (wasm::ValType Ty : Sig.Returns)
726 writeValueType(Ty);
727 }
728
729 endSection(Section);
730 }
731
writeImportSection(ArrayRef<wasm::WasmImport> Imports,uint64_t DataSize,uint32_t NumElements)732 void WasmObjectWriter::writeImportSection(ArrayRef<wasm::WasmImport> Imports,
733 uint64_t DataSize,
734 uint32_t NumElements) {
735 if (Imports.empty())
736 return;
737
738 uint64_t NumPages = (DataSize + wasm::WasmPageSize - 1) / wasm::WasmPageSize;
739
740 SectionBookkeeping Section;
741 startSection(Section, wasm::WASM_SEC_IMPORT);
742
743 encodeULEB128(Imports.size(), W.OS);
744 for (const wasm::WasmImport &Import : Imports) {
745 writeString(Import.Module);
746 writeString(Import.Field);
747 W.OS << char(Import.Kind);
748
749 switch (Import.Kind) {
750 case wasm::WASM_EXTERNAL_FUNCTION:
751 encodeULEB128(Import.SigIndex, W.OS);
752 break;
753 case wasm::WASM_EXTERNAL_GLOBAL:
754 W.OS << char(Import.Global.Type);
755 W.OS << char(Import.Global.Mutable ? 1 : 0);
756 break;
757 case wasm::WASM_EXTERNAL_MEMORY:
758 encodeULEB128(Import.Memory.Flags, W.OS);
759 encodeULEB128(NumPages, W.OS); // initial
760 break;
761 case wasm::WASM_EXTERNAL_TABLE:
762 W.OS << char(Import.Table.ElemType);
763 encodeULEB128(0, W.OS); // flags
764 encodeULEB128(NumElements, W.OS); // initial
765 break;
766 case wasm::WASM_EXTERNAL_EVENT:
767 encodeULEB128(Import.Event.Attribute, W.OS);
768 encodeULEB128(Import.Event.SigIndex, W.OS);
769 break;
770 default:
771 llvm_unreachable("unsupported import kind");
772 }
773 }
774
775 endSection(Section);
776 }
777
writeFunctionSection(ArrayRef<WasmFunction> Functions)778 void WasmObjectWriter::writeFunctionSection(ArrayRef<WasmFunction> Functions) {
779 if (Functions.empty())
780 return;
781
782 SectionBookkeeping Section;
783 startSection(Section, wasm::WASM_SEC_FUNCTION);
784
785 encodeULEB128(Functions.size(), W.OS);
786 for (const WasmFunction &Func : Functions)
787 encodeULEB128(Func.SigIndex, W.OS);
788
789 endSection(Section);
790 }
791
writeEventSection(ArrayRef<wasm::WasmEventType> Events)792 void WasmObjectWriter::writeEventSection(ArrayRef<wasm::WasmEventType> Events) {
793 if (Events.empty())
794 return;
795
796 SectionBookkeeping Section;
797 startSection(Section, wasm::WASM_SEC_EVENT);
798
799 encodeULEB128(Events.size(), W.OS);
800 for (const wasm::WasmEventType &Event : Events) {
801 encodeULEB128(Event.Attribute, W.OS);
802 encodeULEB128(Event.SigIndex, W.OS);
803 }
804
805 endSection(Section);
806 }
807
writeGlobalSection(ArrayRef<wasm::WasmGlobal> Globals)808 void WasmObjectWriter::writeGlobalSection(ArrayRef<wasm::WasmGlobal> Globals) {
809 if (Globals.empty())
810 return;
811
812 SectionBookkeeping Section;
813 startSection(Section, wasm::WASM_SEC_GLOBAL);
814
815 encodeULEB128(Globals.size(), W.OS);
816 for (const wasm::WasmGlobal &Global : Globals) {
817 encodeULEB128(Global.Type.Type, W.OS);
818 W.OS << char(Global.Type.Mutable);
819 W.OS << char(Global.InitExpr.Opcode);
820 switch (Global.Type.Type) {
821 case wasm::WASM_TYPE_I32:
822 encodeSLEB128(0, W.OS);
823 break;
824 case wasm::WASM_TYPE_I64:
825 encodeSLEB128(0, W.OS);
826 break;
827 case wasm::WASM_TYPE_F32:
828 writeI32(0);
829 break;
830 case wasm::WASM_TYPE_F64:
831 writeI64(0);
832 break;
833 case wasm::WASM_TYPE_EXTERNREF:
834 writeValueType(wasm::ValType::EXTERNREF);
835 break;
836 default:
837 llvm_unreachable("unexpected type");
838 }
839 W.OS << char(wasm::WASM_OPCODE_END);
840 }
841
842 endSection(Section);
843 }
844
writeExportSection(ArrayRef<wasm::WasmExport> Exports)845 void WasmObjectWriter::writeExportSection(ArrayRef<wasm::WasmExport> Exports) {
846 if (Exports.empty())
847 return;
848
849 SectionBookkeeping Section;
850 startSection(Section, wasm::WASM_SEC_EXPORT);
851
852 encodeULEB128(Exports.size(), W.OS);
853 for (const wasm::WasmExport &Export : Exports) {
854 writeString(Export.Name);
855 W.OS << char(Export.Kind);
856 encodeULEB128(Export.Index, W.OS);
857 }
858
859 endSection(Section);
860 }
861
writeElemSection(ArrayRef<uint32_t> TableElems)862 void WasmObjectWriter::writeElemSection(ArrayRef<uint32_t> TableElems) {
863 if (TableElems.empty())
864 return;
865
866 SectionBookkeeping Section;
867 startSection(Section, wasm::WASM_SEC_ELEM);
868
869 encodeULEB128(1, W.OS); // number of "segments"
870 encodeULEB128(0, W.OS); // the table index
871
872 // init expr for starting offset
873 W.OS << char(wasm::WASM_OPCODE_I32_CONST);
874 encodeSLEB128(InitialTableOffset, W.OS);
875 W.OS << char(wasm::WASM_OPCODE_END);
876
877 encodeULEB128(TableElems.size(), W.OS);
878 for (uint32_t Elem : TableElems)
879 encodeULEB128(Elem, W.OS);
880
881 endSection(Section);
882 }
883
writeDataCountSection()884 void WasmObjectWriter::writeDataCountSection() {
885 if (DataSegments.empty())
886 return;
887
888 SectionBookkeeping Section;
889 startSection(Section, wasm::WASM_SEC_DATACOUNT);
890 encodeULEB128(DataSegments.size(), W.OS);
891 endSection(Section);
892 }
893
writeCodeSection(const MCAssembler & Asm,const MCAsmLayout & Layout,ArrayRef<WasmFunction> Functions)894 uint32_t WasmObjectWriter::writeCodeSection(const MCAssembler &Asm,
895 const MCAsmLayout &Layout,
896 ArrayRef<WasmFunction> Functions) {
897 if (Functions.empty())
898 return 0;
899
900 SectionBookkeeping Section;
901 startSection(Section, wasm::WASM_SEC_CODE);
902
903 encodeULEB128(Functions.size(), W.OS);
904
905 for (const WasmFunction &Func : Functions) {
906 auto &FuncSection = static_cast<MCSectionWasm &>(Func.Sym->getSection());
907
908 int64_t Size = 0;
909 if (!Func.Sym->getSize()->evaluateAsAbsolute(Size, Layout))
910 report_fatal_error(".size expression must be evaluatable");
911
912 encodeULEB128(Size, W.OS);
913 FuncSection.setSectionOffset(W.OS.tell() - Section.ContentsOffset);
914 Asm.writeSectionData(W.OS, &FuncSection, Layout);
915 }
916
917 // Apply fixups.
918 applyRelocations(CodeRelocations, Section.ContentsOffset, Layout);
919
920 endSection(Section);
921 return Section.Index;
922 }
923
writeDataSection(const MCAsmLayout & Layout)924 uint32_t WasmObjectWriter::writeDataSection(const MCAsmLayout &Layout) {
925 if (DataSegments.empty())
926 return 0;
927
928 SectionBookkeeping Section;
929 startSection(Section, wasm::WASM_SEC_DATA);
930
931 encodeULEB128(DataSegments.size(), W.OS); // count
932
933 for (const WasmDataSegment &Segment : DataSegments) {
934 encodeULEB128(Segment.InitFlags, W.OS); // flags
935 if (Segment.InitFlags & wasm::WASM_SEGMENT_HAS_MEMINDEX)
936 encodeULEB128(0, W.OS); // memory index
937 if ((Segment.InitFlags & wasm::WASM_SEGMENT_IS_PASSIVE) == 0) {
938 W.OS << char(Segment.Offset > std::numeric_limits<int32_t>().max()
939 ? wasm::WASM_OPCODE_I64_CONST
940 : wasm::WASM_OPCODE_I32_CONST);
941 encodeSLEB128(Segment.Offset, W.OS); // offset
942 W.OS << char(wasm::WASM_OPCODE_END);
943 }
944 encodeULEB128(Segment.Data.size(), W.OS); // size
945 Segment.Section->setSectionOffset(W.OS.tell() - Section.ContentsOffset);
946 W.OS << Segment.Data; // data
947 }
948
949 // Apply fixups.
950 applyRelocations(DataRelocations, Section.ContentsOffset, Layout);
951
952 endSection(Section);
953 return Section.Index;
954 }
955
writeRelocSection(uint32_t SectionIndex,StringRef Name,std::vector<WasmRelocationEntry> & Relocs)956 void WasmObjectWriter::writeRelocSection(
957 uint32_t SectionIndex, StringRef Name,
958 std::vector<WasmRelocationEntry> &Relocs) {
959 // See: https://github.com/WebAssembly/tool-conventions/blob/master/Linking.md
960 // for descriptions of the reloc sections.
961
962 if (Relocs.empty())
963 return;
964
965 // First, ensure the relocations are sorted in offset order. In general they
966 // should already be sorted since `recordRelocation` is called in offset
967 // order, but for the code section we combine many MC sections into single
968 // wasm section, and this order is determined by the order of Asm.Symbols()
969 // not the sections order.
970 llvm::stable_sort(
971 Relocs, [](const WasmRelocationEntry &A, const WasmRelocationEntry &B) {
972 return (A.Offset + A.FixupSection->getSectionOffset()) <
973 (B.Offset + B.FixupSection->getSectionOffset());
974 });
975
976 SectionBookkeeping Section;
977 startCustomSection(Section, std::string("reloc.") + Name.str());
978
979 encodeULEB128(SectionIndex, W.OS);
980 encodeULEB128(Relocs.size(), W.OS);
981 for (const WasmRelocationEntry &RelEntry : Relocs) {
982 uint64_t Offset =
983 RelEntry.Offset + RelEntry.FixupSection->getSectionOffset();
984 uint32_t Index = getRelocationIndexValue(RelEntry);
985
986 W.OS << char(RelEntry.Type);
987 encodeULEB128(Offset, W.OS);
988 encodeULEB128(Index, W.OS);
989 if (RelEntry.hasAddend())
990 encodeSLEB128(RelEntry.Addend, W.OS);
991 }
992
993 endSection(Section);
994 }
995
writeCustomRelocSections()996 void WasmObjectWriter::writeCustomRelocSections() {
997 for (const auto &Sec : CustomSections) {
998 auto &Relocations = CustomSectionsRelocations[Sec.Section];
999 writeRelocSection(Sec.OutputIndex, Sec.Name, Relocations);
1000 }
1001 }
1002
writeLinkingMetaDataSection(ArrayRef<wasm::WasmSymbolInfo> SymbolInfos,ArrayRef<std::pair<uint16_t,uint32_t>> InitFuncs,const std::map<StringRef,std::vector<WasmComdatEntry>> & Comdats)1003 void WasmObjectWriter::writeLinkingMetaDataSection(
1004 ArrayRef<wasm::WasmSymbolInfo> SymbolInfos,
1005 ArrayRef<std::pair<uint16_t, uint32_t>> InitFuncs,
1006 const std::map<StringRef, std::vector<WasmComdatEntry>> &Comdats) {
1007 SectionBookkeeping Section;
1008 startCustomSection(Section, "linking");
1009 encodeULEB128(wasm::WasmMetadataVersion, W.OS);
1010
1011 SectionBookkeeping SubSection;
1012 if (SymbolInfos.size() != 0) {
1013 startSection(SubSection, wasm::WASM_SYMBOL_TABLE);
1014 encodeULEB128(SymbolInfos.size(), W.OS);
1015 for (const wasm::WasmSymbolInfo &Sym : SymbolInfos) {
1016 encodeULEB128(Sym.Kind, W.OS);
1017 encodeULEB128(Sym.Flags, W.OS);
1018 switch (Sym.Kind) {
1019 case wasm::WASM_SYMBOL_TYPE_FUNCTION:
1020 case wasm::WASM_SYMBOL_TYPE_GLOBAL:
1021 case wasm::WASM_SYMBOL_TYPE_EVENT:
1022 encodeULEB128(Sym.ElementIndex, W.OS);
1023 if ((Sym.Flags & wasm::WASM_SYMBOL_UNDEFINED) == 0 ||
1024 (Sym.Flags & wasm::WASM_SYMBOL_EXPLICIT_NAME) != 0)
1025 writeString(Sym.Name);
1026 break;
1027 case wasm::WASM_SYMBOL_TYPE_DATA:
1028 writeString(Sym.Name);
1029 if ((Sym.Flags & wasm::WASM_SYMBOL_UNDEFINED) == 0) {
1030 encodeULEB128(Sym.DataRef.Segment, W.OS);
1031 encodeULEB128(Sym.DataRef.Offset, W.OS);
1032 encodeULEB128(Sym.DataRef.Size, W.OS);
1033 }
1034 break;
1035 case wasm::WASM_SYMBOL_TYPE_SECTION: {
1036 const uint32_t SectionIndex =
1037 CustomSections[Sym.ElementIndex].OutputIndex;
1038 encodeULEB128(SectionIndex, W.OS);
1039 break;
1040 }
1041 default:
1042 llvm_unreachable("unexpected kind");
1043 }
1044 }
1045 endSection(SubSection);
1046 }
1047
1048 if (DataSegments.size()) {
1049 startSection(SubSection, wasm::WASM_SEGMENT_INFO);
1050 encodeULEB128(DataSegments.size(), W.OS);
1051 for (const WasmDataSegment &Segment : DataSegments) {
1052 writeString(Segment.Name);
1053 encodeULEB128(Segment.Alignment, W.OS);
1054 encodeULEB128(Segment.LinkerFlags, W.OS);
1055 }
1056 endSection(SubSection);
1057 }
1058
1059 if (!InitFuncs.empty()) {
1060 startSection(SubSection, wasm::WASM_INIT_FUNCS);
1061 encodeULEB128(InitFuncs.size(), W.OS);
1062 for (auto &StartFunc : InitFuncs) {
1063 encodeULEB128(StartFunc.first, W.OS); // priority
1064 encodeULEB128(StartFunc.second, W.OS); // function index
1065 }
1066 endSection(SubSection);
1067 }
1068
1069 if (Comdats.size()) {
1070 startSection(SubSection, wasm::WASM_COMDAT_INFO);
1071 encodeULEB128(Comdats.size(), W.OS);
1072 for (const auto &C : Comdats) {
1073 writeString(C.first);
1074 encodeULEB128(0, W.OS); // flags for future use
1075 encodeULEB128(C.second.size(), W.OS);
1076 for (const WasmComdatEntry &Entry : C.second) {
1077 encodeULEB128(Entry.Kind, W.OS);
1078 encodeULEB128(Entry.Index, W.OS);
1079 }
1080 }
1081 endSection(SubSection);
1082 }
1083
1084 endSection(Section);
1085 }
1086
writeCustomSection(WasmCustomSection & CustomSection,const MCAssembler & Asm,const MCAsmLayout & Layout)1087 void WasmObjectWriter::writeCustomSection(WasmCustomSection &CustomSection,
1088 const MCAssembler &Asm,
1089 const MCAsmLayout &Layout) {
1090 SectionBookkeeping Section;
1091 auto *Sec = CustomSection.Section;
1092 startCustomSection(Section, CustomSection.Name);
1093
1094 Sec->setSectionOffset(W.OS.tell() - Section.ContentsOffset);
1095 Asm.writeSectionData(W.OS, Sec, Layout);
1096
1097 CustomSection.OutputContentsOffset = Section.ContentsOffset;
1098 CustomSection.OutputIndex = Section.Index;
1099
1100 endSection(Section);
1101
1102 // Apply fixups.
1103 auto &Relocations = CustomSectionsRelocations[CustomSection.Section];
1104 applyRelocations(Relocations, CustomSection.OutputContentsOffset, Layout);
1105 }
1106
getFunctionType(const MCSymbolWasm & Symbol)1107 uint32_t WasmObjectWriter::getFunctionType(const MCSymbolWasm &Symbol) {
1108 assert(Symbol.isFunction());
1109 assert(TypeIndices.count(&Symbol));
1110 return TypeIndices[&Symbol];
1111 }
1112
getEventType(const MCSymbolWasm & Symbol)1113 uint32_t WasmObjectWriter::getEventType(const MCSymbolWasm &Symbol) {
1114 assert(Symbol.isEvent());
1115 assert(TypeIndices.count(&Symbol));
1116 return TypeIndices[&Symbol];
1117 }
1118
registerFunctionType(const MCSymbolWasm & Symbol)1119 void WasmObjectWriter::registerFunctionType(const MCSymbolWasm &Symbol) {
1120 assert(Symbol.isFunction());
1121
1122 WasmSignature S;
1123
1124 if (auto *Sig = Symbol.getSignature()) {
1125 S.Returns = Sig->Returns;
1126 S.Params = Sig->Params;
1127 }
1128
1129 auto Pair = SignatureIndices.insert(std::make_pair(S, Signatures.size()));
1130 if (Pair.second)
1131 Signatures.push_back(S);
1132 TypeIndices[&Symbol] = Pair.first->second;
1133
1134 LLVM_DEBUG(dbgs() << "registerFunctionType: " << Symbol
1135 << " new:" << Pair.second << "\n");
1136 LLVM_DEBUG(dbgs() << " -> type index: " << Pair.first->second << "\n");
1137 }
1138
registerEventType(const MCSymbolWasm & Symbol)1139 void WasmObjectWriter::registerEventType(const MCSymbolWasm &Symbol) {
1140 assert(Symbol.isEvent());
1141
1142 // TODO Currently we don't generate imported exceptions, but if we do, we
1143 // should have a way of infering types of imported exceptions.
1144 WasmSignature S;
1145 if (auto *Sig = Symbol.getSignature()) {
1146 S.Returns = Sig->Returns;
1147 S.Params = Sig->Params;
1148 }
1149
1150 auto Pair = SignatureIndices.insert(std::make_pair(S, Signatures.size()));
1151 if (Pair.second)
1152 Signatures.push_back(S);
1153 TypeIndices[&Symbol] = Pair.first->second;
1154
1155 LLVM_DEBUG(dbgs() << "registerEventType: " << Symbol << " new:" << Pair.second
1156 << "\n");
1157 LLVM_DEBUG(dbgs() << " -> type index: " << Pair.first->second << "\n");
1158 }
1159
isInSymtab(const MCSymbolWasm & Sym)1160 static bool isInSymtab(const MCSymbolWasm &Sym) {
1161 if (Sym.isUsedInReloc() || Sym.isUsedInInitArray())
1162 return true;
1163
1164 if (Sym.isComdat() && !Sym.isDefined())
1165 return false;
1166
1167 if (Sym.isTemporary())
1168 return false;
1169
1170 if (Sym.isSection())
1171 return false;
1172
1173 return true;
1174 }
1175
writeObject(MCAssembler & Asm,const MCAsmLayout & Layout)1176 uint64_t WasmObjectWriter::writeObject(MCAssembler &Asm,
1177 const MCAsmLayout &Layout) {
1178 uint64_t StartOffset = W.OS.tell();
1179
1180 LLVM_DEBUG(dbgs() << "WasmObjectWriter::writeObject\n");
1181
1182 // Collect information from the available symbols.
1183 SmallVector<WasmFunction, 4> Functions;
1184 SmallVector<uint32_t, 4> TableElems;
1185 SmallVector<wasm::WasmImport, 4> Imports;
1186 SmallVector<wasm::WasmExport, 4> Exports;
1187 SmallVector<wasm::WasmEventType, 1> Events;
1188 SmallVector<wasm::WasmGlobal, 1> Globals;
1189 SmallVector<wasm::WasmSymbolInfo, 4> SymbolInfos;
1190 SmallVector<std::pair<uint16_t, uint32_t>, 2> InitFuncs;
1191 std::map<StringRef, std::vector<WasmComdatEntry>> Comdats;
1192 uint64_t DataSize = 0;
1193
1194 // For now, always emit the memory import, since loads and stores are not
1195 // valid without it. In the future, we could perhaps be more clever and omit
1196 // it if there are no loads or stores.
1197 wasm::WasmImport MemImport;
1198 MemImport.Module = "env";
1199 MemImport.Field = "__linear_memory";
1200 MemImport.Kind = wasm::WASM_EXTERNAL_MEMORY;
1201 MemImport.Memory.Flags = is64Bit() ? wasm::WASM_LIMITS_FLAG_IS_64
1202 : wasm::WASM_LIMITS_FLAG_NONE;
1203 Imports.push_back(MemImport);
1204
1205 // For now, always emit the table section, since indirect calls are not
1206 // valid without it. In the future, we could perhaps be more clever and omit
1207 // it if there are no indirect calls.
1208 wasm::WasmImport TableImport;
1209 TableImport.Module = "env";
1210 TableImport.Field = "__indirect_function_table";
1211 TableImport.Kind = wasm::WASM_EXTERNAL_TABLE;
1212 TableImport.Table.ElemType = wasm::WASM_TYPE_FUNCREF;
1213 Imports.push_back(TableImport);
1214
1215 // Populate SignatureIndices, and Imports and WasmIndices for undefined
1216 // symbols. This must be done before populating WasmIndices for defined
1217 // symbols.
1218 for (const MCSymbol &S : Asm.symbols()) {
1219 const auto &WS = static_cast<const MCSymbolWasm &>(S);
1220
1221 // Register types for all functions, including those with private linkage
1222 // (because wasm always needs a type signature).
1223 if (WS.isFunction()) {
1224 const MCSymbolWasm *Base = cast<MCSymbolWasm>(Layout.getBaseSymbol(S));
1225 registerFunctionType(*Base);
1226 }
1227
1228 if (WS.isEvent())
1229 registerEventType(WS);
1230
1231 if (WS.isTemporary())
1232 continue;
1233
1234 // If the symbol is not defined in this translation unit, import it.
1235 if (!WS.isDefined() && !WS.isComdat()) {
1236 if (WS.isFunction()) {
1237 wasm::WasmImport Import;
1238 Import.Module = WS.getImportModule();
1239 Import.Field = WS.getImportName();
1240 Import.Kind = wasm::WASM_EXTERNAL_FUNCTION;
1241 Import.SigIndex = getFunctionType(WS);
1242 Imports.push_back(Import);
1243 assert(WasmIndices.count(&WS) == 0);
1244 WasmIndices[&WS] = NumFunctionImports++;
1245 } else if (WS.isGlobal()) {
1246 if (WS.isWeak())
1247 report_fatal_error("undefined global symbol cannot be weak");
1248
1249 wasm::WasmImport Import;
1250 Import.Field = WS.getImportName();
1251 Import.Kind = wasm::WASM_EXTERNAL_GLOBAL;
1252 Import.Module = WS.getImportModule();
1253 Import.Global = WS.getGlobalType();
1254 Imports.push_back(Import);
1255 assert(WasmIndices.count(&WS) == 0);
1256 WasmIndices[&WS] = NumGlobalImports++;
1257 } else if (WS.isEvent()) {
1258 if (WS.isWeak())
1259 report_fatal_error("undefined event symbol cannot be weak");
1260
1261 wasm::WasmImport Import;
1262 Import.Module = WS.getImportModule();
1263 Import.Field = WS.getImportName();
1264 Import.Kind = wasm::WASM_EXTERNAL_EVENT;
1265 Import.Event.Attribute = wasm::WASM_EVENT_ATTRIBUTE_EXCEPTION;
1266 Import.Event.SigIndex = getEventType(WS);
1267 Imports.push_back(Import);
1268 assert(WasmIndices.count(&WS) == 0);
1269 WasmIndices[&WS] = NumEventImports++;
1270 }
1271 }
1272 }
1273
1274 // Add imports for GOT globals
1275 for (const MCSymbol &S : Asm.symbols()) {
1276 const auto &WS = static_cast<const MCSymbolWasm &>(S);
1277 if (WS.isUsedInGOT()) {
1278 wasm::WasmImport Import;
1279 if (WS.isFunction())
1280 Import.Module = "GOT.func";
1281 else
1282 Import.Module = "GOT.mem";
1283 Import.Field = WS.getName();
1284 Import.Kind = wasm::WASM_EXTERNAL_GLOBAL;
1285 Import.Global = {wasm::WASM_TYPE_I32, true};
1286 Imports.push_back(Import);
1287 assert(GOTIndices.count(&WS) == 0);
1288 GOTIndices[&WS] = NumGlobalImports++;
1289 }
1290 }
1291
1292 // Populate DataSegments and CustomSections, which must be done before
1293 // populating DataLocations.
1294 for (MCSection &Sec : Asm) {
1295 auto &Section = static_cast<MCSectionWasm &>(Sec);
1296 StringRef SectionName = Section.getName();
1297
1298 // .init_array sections are handled specially elsewhere.
1299 if (SectionName.startswith(".init_array"))
1300 continue;
1301
1302 // Code is handled separately
1303 if (Section.getKind().isText())
1304 continue;
1305
1306 if (Section.isWasmData()) {
1307 uint32_t SegmentIndex = DataSegments.size();
1308 DataSize = alignTo(DataSize, Section.getAlignment());
1309 DataSegments.emplace_back();
1310 WasmDataSegment &Segment = DataSegments.back();
1311 Segment.Name = SectionName;
1312 Segment.InitFlags =
1313 Section.getPassive() ? (uint32_t)wasm::WASM_SEGMENT_IS_PASSIVE : 0;
1314 Segment.Offset = DataSize;
1315 Segment.Section = &Section;
1316 addData(Segment.Data, Section);
1317 Segment.Alignment = Log2_32(Section.getAlignment());
1318 Segment.LinkerFlags = 0;
1319 DataSize += Segment.Data.size();
1320 Section.setSegmentIndex(SegmentIndex);
1321
1322 if (const MCSymbolWasm *C = Section.getGroup()) {
1323 Comdats[C->getName()].emplace_back(
1324 WasmComdatEntry{wasm::WASM_COMDAT_DATA, SegmentIndex});
1325 }
1326 } else {
1327 // Create custom sections
1328 assert(Sec.getKind().isMetadata());
1329
1330 StringRef Name = SectionName;
1331
1332 // For user-defined custom sections, strip the prefix
1333 if (Name.startswith(".custom_section."))
1334 Name = Name.substr(strlen(".custom_section."));
1335
1336 MCSymbol *Begin = Sec.getBeginSymbol();
1337 if (Begin) {
1338 WasmIndices[cast<MCSymbolWasm>(Begin)] = CustomSections.size();
1339 if (SectionName != Begin->getName())
1340 report_fatal_error("section name and begin symbol should match: " +
1341 Twine(SectionName));
1342 }
1343
1344 // Separate out the producers and target features sections
1345 if (Name == "producers") {
1346 ProducersSection = std::make_unique<WasmCustomSection>(Name, &Section);
1347 continue;
1348 }
1349 if (Name == "target_features") {
1350 TargetFeaturesSection =
1351 std::make_unique<WasmCustomSection>(Name, &Section);
1352 continue;
1353 }
1354
1355 CustomSections.emplace_back(Name, &Section);
1356 }
1357 }
1358
1359 // Populate WasmIndices and DataLocations for defined symbols.
1360 for (const MCSymbol &S : Asm.symbols()) {
1361 // Ignore unnamed temporary symbols, which aren't ever exported, imported,
1362 // or used in relocations.
1363 if (S.isTemporary() && S.getName().empty())
1364 continue;
1365
1366 const auto &WS = static_cast<const MCSymbolWasm &>(S);
1367 LLVM_DEBUG(
1368 dbgs() << "MCSymbol: " << toString(WS.getType()) << " '" << S << "'"
1369 << " isDefined=" << S.isDefined() << " isExternal="
1370 << S.isExternal() << " isTemporary=" << S.isTemporary()
1371 << " isWeak=" << WS.isWeak() << " isHidden=" << WS.isHidden()
1372 << " isVariable=" << WS.isVariable() << "\n");
1373
1374 if (WS.isVariable())
1375 continue;
1376 if (WS.isComdat() && !WS.isDefined())
1377 continue;
1378
1379 if (WS.isFunction()) {
1380 unsigned Index;
1381 if (WS.isDefined()) {
1382 if (WS.getOffset() != 0)
1383 report_fatal_error(
1384 "function sections must contain one function each");
1385
1386 if (WS.getSize() == nullptr)
1387 report_fatal_error(
1388 "function symbols must have a size set with .size");
1389
1390 // A definition. Write out the function body.
1391 Index = NumFunctionImports + Functions.size();
1392 WasmFunction Func;
1393 Func.SigIndex = getFunctionType(WS);
1394 Func.Sym = &WS;
1395 WasmIndices[&WS] = Index;
1396 Functions.push_back(Func);
1397
1398 auto &Section = static_cast<MCSectionWasm &>(WS.getSection());
1399 if (const MCSymbolWasm *C = Section.getGroup()) {
1400 Comdats[C->getName()].emplace_back(
1401 WasmComdatEntry{wasm::WASM_COMDAT_FUNCTION, Index});
1402 }
1403
1404 if (WS.hasExportName()) {
1405 wasm::WasmExport Export;
1406 Export.Name = WS.getExportName();
1407 Export.Kind = wasm::WASM_EXTERNAL_FUNCTION;
1408 Export.Index = Index;
1409 Exports.push_back(Export);
1410 }
1411 } else {
1412 // An import; the index was assigned above.
1413 Index = WasmIndices.find(&WS)->second;
1414 }
1415
1416 LLVM_DEBUG(dbgs() << " -> function index: " << Index << "\n");
1417
1418 } else if (WS.isData()) {
1419 if (!isInSymtab(WS))
1420 continue;
1421
1422 if (!WS.isDefined()) {
1423 LLVM_DEBUG(dbgs() << " -> segment index: -1"
1424 << "\n");
1425 continue;
1426 }
1427
1428 if (!WS.getSize())
1429 report_fatal_error("data symbols must have a size set with .size: " +
1430 WS.getName());
1431
1432 int64_t Size = 0;
1433 if (!WS.getSize()->evaluateAsAbsolute(Size, Layout))
1434 report_fatal_error(".size expression must be evaluatable");
1435
1436 auto &DataSection = static_cast<MCSectionWasm &>(WS.getSection());
1437 if (!DataSection.isWasmData())
1438 report_fatal_error("data symbols must live in a data section: " +
1439 WS.getName());
1440
1441 // For each data symbol, export it in the symtab as a reference to the
1442 // corresponding Wasm data segment.
1443 wasm::WasmDataReference Ref = wasm::WasmDataReference{
1444 DataSection.getSegmentIndex(), Layout.getSymbolOffset(WS),
1445 static_cast<uint64_t>(Size)};
1446 DataLocations[&WS] = Ref;
1447 LLVM_DEBUG(dbgs() << " -> segment index: " << Ref.Segment << "\n");
1448
1449 } else if (WS.isGlobal()) {
1450 // A "true" Wasm global (currently just __stack_pointer)
1451 if (WS.isDefined()) {
1452 assert(WasmIndices.count(&WS) == 0);
1453 wasm::WasmGlobal Global;
1454 Global.Type = WS.getGlobalType();
1455 Global.Index = NumGlobalImports + Globals.size();
1456 switch (Global.Type.Type) {
1457 case wasm::WASM_TYPE_I32:
1458 Global.InitExpr.Opcode = wasm::WASM_OPCODE_I32_CONST;
1459 break;
1460 case wasm::WASM_TYPE_I64:
1461 Global.InitExpr.Opcode = wasm::WASM_OPCODE_I64_CONST;
1462 break;
1463 case wasm::WASM_TYPE_F32:
1464 Global.InitExpr.Opcode = wasm::WASM_OPCODE_F32_CONST;
1465 break;
1466 case wasm::WASM_TYPE_F64:
1467 Global.InitExpr.Opcode = wasm::WASM_OPCODE_F64_CONST;
1468 break;
1469 case wasm::WASM_TYPE_EXTERNREF:
1470 Global.InitExpr.Opcode = wasm::WASM_OPCODE_REF_NULL;
1471 break;
1472 default:
1473 llvm_unreachable("unexpected type");
1474 }
1475 WasmIndices[&WS] = Global.Index;
1476 Globals.push_back(Global);
1477 } else {
1478 // An import; the index was assigned above
1479 LLVM_DEBUG(dbgs() << " -> global index: "
1480 << WasmIndices.find(&WS)->second << "\n");
1481 }
1482 } else if (WS.isEvent()) {
1483 // C++ exception symbol (__cpp_exception)
1484 unsigned Index;
1485 if (WS.isDefined()) {
1486 assert(WasmIndices.count(&WS) == 0);
1487 Index = NumEventImports + Events.size();
1488 wasm::WasmEventType Event;
1489 Event.SigIndex = getEventType(WS);
1490 Event.Attribute = wasm::WASM_EVENT_ATTRIBUTE_EXCEPTION;
1491 WasmIndices[&WS] = Index;
1492 Events.push_back(Event);
1493 } else {
1494 // An import; the index was assigned above.
1495 assert(WasmIndices.count(&WS) > 0);
1496 }
1497 LLVM_DEBUG(dbgs() << " -> event index: " << WasmIndices.find(&WS)->second
1498 << "\n");
1499
1500 } else {
1501 assert(WS.isSection());
1502 }
1503 }
1504
1505 // Populate WasmIndices and DataLocations for aliased symbols. We need to
1506 // process these in a separate pass because we need to have processed the
1507 // target of the alias before the alias itself and the symbols are not
1508 // necessarily ordered in this way.
1509 for (const MCSymbol &S : Asm.symbols()) {
1510 if (!S.isVariable())
1511 continue;
1512
1513 assert(S.isDefined());
1514
1515 const MCSymbolWasm *Base = cast<MCSymbolWasm>(Layout.getBaseSymbol(S));
1516
1517 // Find the target symbol of this weak alias and export that index
1518 const auto &WS = static_cast<const MCSymbolWasm &>(S);
1519 LLVM_DEBUG(dbgs() << WS.getName() << ": weak alias of '" << *Base << "'\n");
1520
1521 if (Base->isFunction()) {
1522 assert(WasmIndices.count(Base) > 0);
1523 uint32_t WasmIndex = WasmIndices.find(Base)->second;
1524 assert(WasmIndices.count(&WS) == 0);
1525 WasmIndices[&WS] = WasmIndex;
1526 LLVM_DEBUG(dbgs() << " -> index:" << WasmIndex << "\n");
1527 } else if (Base->isData()) {
1528 auto &DataSection = static_cast<MCSectionWasm &>(WS.getSection());
1529 uint64_t Offset = Layout.getSymbolOffset(S);
1530 int64_t Size = 0;
1531 // For data symbol alias we use the size of the base symbol as the
1532 // size of the alias. When an offset from the base is involved this
1533 // can result in a offset + size goes past the end of the data section
1534 // which out object format doesn't support. So we must clamp it.
1535 if (!Base->getSize()->evaluateAsAbsolute(Size, Layout))
1536 report_fatal_error(".size expression must be evaluatable");
1537 const WasmDataSegment &Segment =
1538 DataSegments[DataSection.getSegmentIndex()];
1539 Size =
1540 std::min(static_cast<uint64_t>(Size), Segment.Data.size() - Offset);
1541 wasm::WasmDataReference Ref = wasm::WasmDataReference{
1542 DataSection.getSegmentIndex(),
1543 static_cast<uint32_t>(Layout.getSymbolOffset(S)),
1544 static_cast<uint32_t>(Size)};
1545 DataLocations[&WS] = Ref;
1546 LLVM_DEBUG(dbgs() << " -> index:" << Ref.Segment << "\n");
1547 } else {
1548 report_fatal_error("don't yet support global/event aliases");
1549 }
1550 }
1551
1552 // Finally, populate the symbol table itself, in its "natural" order.
1553 for (const MCSymbol &S : Asm.symbols()) {
1554 const auto &WS = static_cast<const MCSymbolWasm &>(S);
1555 if (!isInSymtab(WS)) {
1556 WS.setIndex(InvalidIndex);
1557 continue;
1558 }
1559 LLVM_DEBUG(dbgs() << "adding to symtab: " << WS << "\n");
1560
1561 uint32_t Flags = 0;
1562 if (WS.isWeak())
1563 Flags |= wasm::WASM_SYMBOL_BINDING_WEAK;
1564 if (WS.isHidden())
1565 Flags |= wasm::WASM_SYMBOL_VISIBILITY_HIDDEN;
1566 if (!WS.isExternal() && WS.isDefined())
1567 Flags |= wasm::WASM_SYMBOL_BINDING_LOCAL;
1568 if (WS.isUndefined())
1569 Flags |= wasm::WASM_SYMBOL_UNDEFINED;
1570 if (WS.isNoStrip()) {
1571 Flags |= wasm::WASM_SYMBOL_NO_STRIP;
1572 if (isEmscripten()) {
1573 Flags |= wasm::WASM_SYMBOL_EXPORTED;
1574 }
1575 }
1576 if (WS.hasImportName())
1577 Flags |= wasm::WASM_SYMBOL_EXPLICIT_NAME;
1578 if (WS.hasExportName())
1579 Flags |= wasm::WASM_SYMBOL_EXPORTED;
1580
1581 wasm::WasmSymbolInfo Info;
1582 Info.Name = WS.getName();
1583 Info.Kind = WS.getType();
1584 Info.Flags = Flags;
1585 if (!WS.isData()) {
1586 assert(WasmIndices.count(&WS) > 0);
1587 Info.ElementIndex = WasmIndices.find(&WS)->second;
1588 } else if (WS.isDefined()) {
1589 assert(DataLocations.count(&WS) > 0);
1590 Info.DataRef = DataLocations.find(&WS)->second;
1591 }
1592 WS.setIndex(SymbolInfos.size());
1593 SymbolInfos.emplace_back(Info);
1594 }
1595
1596 {
1597 auto HandleReloc = [&](const WasmRelocationEntry &Rel) {
1598 // Functions referenced by a relocation need to put in the table. This is
1599 // purely to make the object file's provisional values readable, and is
1600 // ignored by the linker, which re-calculates the relocations itself.
1601 if (Rel.Type != wasm::R_WASM_TABLE_INDEX_I32 &&
1602 Rel.Type != wasm::R_WASM_TABLE_INDEX_SLEB &&
1603 Rel.Type != wasm::R_WASM_TABLE_INDEX_REL_SLEB)
1604 return;
1605 assert(Rel.Symbol->isFunction());
1606 const MCSymbolWasm *Base =
1607 cast<MCSymbolWasm>(Layout.getBaseSymbol(*Rel.Symbol));
1608 uint32_t FunctionIndex = WasmIndices.find(Base)->second;
1609 uint32_t TableIndex = TableElems.size() + InitialTableOffset;
1610 if (TableIndices.try_emplace(Base, TableIndex).second) {
1611 LLVM_DEBUG(dbgs() << " -> adding " << Base->getName()
1612 << " to table: " << TableIndex << "\n");
1613 TableElems.push_back(FunctionIndex);
1614 registerFunctionType(*Base);
1615 }
1616 };
1617
1618 for (const WasmRelocationEntry &RelEntry : CodeRelocations)
1619 HandleReloc(RelEntry);
1620 for (const WasmRelocationEntry &RelEntry : DataRelocations)
1621 HandleReloc(RelEntry);
1622 }
1623
1624 // Translate .init_array section contents into start functions.
1625 for (const MCSection &S : Asm) {
1626 const auto &WS = static_cast<const MCSectionWasm &>(S);
1627 if (WS.getName().startswith(".fini_array"))
1628 report_fatal_error(".fini_array sections are unsupported");
1629 if (!WS.getName().startswith(".init_array"))
1630 continue;
1631 if (WS.getFragmentList().empty())
1632 continue;
1633
1634 // init_array is expected to contain a single non-empty data fragment
1635 if (WS.getFragmentList().size() != 3)
1636 report_fatal_error("only one .init_array section fragment supported");
1637
1638 auto IT = WS.begin();
1639 const MCFragment &EmptyFrag = *IT;
1640 if (EmptyFrag.getKind() != MCFragment::FT_Data)
1641 report_fatal_error(".init_array section should be aligned");
1642
1643 IT = std::next(IT);
1644 const MCFragment &AlignFrag = *IT;
1645 if (AlignFrag.getKind() != MCFragment::FT_Align)
1646 report_fatal_error(".init_array section should be aligned");
1647 if (cast<MCAlignFragment>(AlignFrag).getAlignment() != (is64Bit() ? 8 : 4))
1648 report_fatal_error(".init_array section should be aligned for pointers");
1649
1650 const MCFragment &Frag = *std::next(IT);
1651 if (Frag.hasInstructions() || Frag.getKind() != MCFragment::FT_Data)
1652 report_fatal_error("only data supported in .init_array section");
1653
1654 uint16_t Priority = UINT16_MAX;
1655 unsigned PrefixLength = strlen(".init_array");
1656 if (WS.getName().size() > PrefixLength) {
1657 if (WS.getName()[PrefixLength] != '.')
1658 report_fatal_error(
1659 ".init_array section priority should start with '.'");
1660 if (WS.getName().substr(PrefixLength + 1).getAsInteger(10, Priority))
1661 report_fatal_error("invalid .init_array section priority");
1662 }
1663 const auto &DataFrag = cast<MCDataFragment>(Frag);
1664 const SmallVectorImpl<char> &Contents = DataFrag.getContents();
1665 for (const uint8_t *
1666 P = (const uint8_t *)Contents.data(),
1667 *End = (const uint8_t *)Contents.data() + Contents.size();
1668 P != End; ++P) {
1669 if (*P != 0)
1670 report_fatal_error("non-symbolic data in .init_array section");
1671 }
1672 for (const MCFixup &Fixup : DataFrag.getFixups()) {
1673 assert(Fixup.getKind() ==
1674 MCFixup::getKindForSize(is64Bit() ? 8 : 4, false));
1675 const MCExpr *Expr = Fixup.getValue();
1676 auto *SymRef = dyn_cast<MCSymbolRefExpr>(Expr);
1677 if (!SymRef)
1678 report_fatal_error("fixups in .init_array should be symbol references");
1679 const auto &TargetSym = cast<const MCSymbolWasm>(SymRef->getSymbol());
1680 if (TargetSym.getIndex() == InvalidIndex)
1681 report_fatal_error("symbols in .init_array should exist in symtab");
1682 if (!TargetSym.isFunction())
1683 report_fatal_error("symbols in .init_array should be for functions");
1684 InitFuncs.push_back(
1685 std::make_pair(Priority, TargetSym.getIndex()));
1686 }
1687 }
1688
1689 // Write out the Wasm header.
1690 writeHeader(Asm);
1691
1692 writeTypeSection(Signatures);
1693 writeImportSection(Imports, DataSize, TableElems.size());
1694 writeFunctionSection(Functions);
1695 // Skip the "table" section; we import the table instead.
1696 // Skip the "memory" section; we import the memory instead.
1697 writeEventSection(Events);
1698 writeGlobalSection(Globals);
1699 writeExportSection(Exports);
1700 writeElemSection(TableElems);
1701 writeDataCountSection();
1702 uint32_t CodeSectionIndex = writeCodeSection(Asm, Layout, Functions);
1703 uint32_t DataSectionIndex = writeDataSection(Layout);
1704 for (auto &CustomSection : CustomSections)
1705 writeCustomSection(CustomSection, Asm, Layout);
1706 writeLinkingMetaDataSection(SymbolInfos, InitFuncs, Comdats);
1707 writeRelocSection(CodeSectionIndex, "CODE", CodeRelocations);
1708 writeRelocSection(DataSectionIndex, "DATA", DataRelocations);
1709 writeCustomRelocSections();
1710 if (ProducersSection)
1711 writeCustomSection(*ProducersSection, Asm, Layout);
1712 if (TargetFeaturesSection)
1713 writeCustomSection(*TargetFeaturesSection, Asm, Layout);
1714
1715 // TODO: Translate the .comment section to the output.
1716 return W.OS.tell() - StartOffset;
1717 }
1718
1719 std::unique_ptr<MCObjectWriter>
createWasmObjectWriter(std::unique_ptr<MCWasmObjectTargetWriter> MOTW,raw_pwrite_stream & OS)1720 llvm::createWasmObjectWriter(std::unique_ptr<MCWasmObjectTargetWriter> MOTW,
1721 raw_pwrite_stream &OS) {
1722 return std::make_unique<WasmObjectWriter>(std::move(MOTW), OS);
1723 }
1724