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/BinaryFormat/WasmTraits.h" 17 #include "llvm/Config/llvm-config.h" 18 #include "llvm/MC/MCAsmBackend.h" 19 #include "llvm/MC/MCAsmLayout.h" 20 #include "llvm/MC/MCAssembler.h" 21 #include "llvm/MC/MCContext.h" 22 #include "llvm/MC/MCExpr.h" 23 #include "llvm/MC/MCFixupKindInfo.h" 24 #include "llvm/MC/MCObjectWriter.h" 25 #include "llvm/MC/MCSectionWasm.h" 26 #include "llvm/MC/MCSymbolWasm.h" 27 #include "llvm/MC/MCValue.h" 28 #include "llvm/MC/MCWasmObjectWriter.h" 29 #include "llvm/Support/Casting.h" 30 #include "llvm/Support/Debug.h" 31 #include "llvm/Support/EndianStream.h" 32 #include "llvm/Support/ErrorHandling.h" 33 #include "llvm/Support/LEB128.h" 34 #include "llvm/Support/StringSaver.h" 35 #include <vector> 36 37 using namespace llvm; 38 39 #define DEBUG_TYPE "mc" 40 41 namespace { 42 43 // When we create the indirect function table we start at 1, so that there is 44 // and empty slot at 0 and therefore calling a null function pointer will trap. 45 static const uint32_t InitialTableOffset = 1; 46 47 // For patching purposes, we need to remember where each section starts, both 48 // for patching up the section size field, and for patching up references to 49 // locations within the section. 50 struct SectionBookkeeping { 51 // Where the size of the section is written. 52 uint64_t SizeOffset; 53 // Where the section header ends (without custom section name). 54 uint64_t PayloadOffset; 55 // Where the contents of the section starts. 56 uint64_t ContentsOffset; 57 uint32_t Index; 58 }; 59 60 // A wasm data segment. A wasm binary contains only a single data section 61 // but that can contain many segments, each with their own virtual location 62 // in memory. Each MCSection data created by llvm is modeled as its own 63 // wasm data segment. 64 struct WasmDataSegment { 65 MCSectionWasm *Section; 66 StringRef Name; 67 uint32_t InitFlags; 68 uint64_t Offset; 69 uint32_t Alignment; 70 uint32_t LinkingFlags; 71 SmallVector<char, 4> Data; 72 }; 73 74 // A wasm function to be written into the function section. 75 struct WasmFunction { 76 uint32_t SigIndex; 77 const MCSymbolWasm *Sym; 78 }; 79 80 // A wasm global to be written into the global section. 81 struct WasmGlobal { 82 wasm::WasmGlobalType Type; 83 uint64_t InitialValue; 84 }; 85 86 // Information about a single item which is part of a COMDAT. For each data 87 // segment or function which is in the COMDAT, there is a corresponding 88 // WasmComdatEntry. 89 struct WasmComdatEntry { 90 unsigned Kind; 91 uint32_t Index; 92 }; 93 94 // Information about a single relocation. 95 struct WasmRelocationEntry { 96 uint64_t Offset; // Where is the relocation. 97 const MCSymbolWasm *Symbol; // The symbol to relocate with. 98 int64_t Addend; // A value to add to the symbol. 99 unsigned Type; // The type of the relocation. 100 const MCSectionWasm *FixupSection; // The section the relocation is targeting. 101 102 WasmRelocationEntry(uint64_t Offset, const MCSymbolWasm *Symbol, 103 int64_t Addend, unsigned Type, 104 const MCSectionWasm *FixupSection) 105 : Offset(Offset), Symbol(Symbol), Addend(Addend), Type(Type), 106 FixupSection(FixupSection) {} 107 108 bool hasAddend() const { return wasm::relocTypeHasAddend(Type); } 109 110 void print(raw_ostream &Out) const { 111 Out << wasm::relocTypetoString(Type) << " Off=" << Offset 112 << ", Sym=" << *Symbol << ", Addend=" << Addend 113 << ", FixupSection=" << FixupSection->getName(); 114 } 115 116 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP) 117 LLVM_DUMP_METHOD void dump() const { print(dbgs()); } 118 #endif 119 }; 120 121 static const uint32_t InvalidIndex = -1; 122 123 struct WasmCustomSection { 124 125 StringRef Name; 126 MCSectionWasm *Section; 127 128 uint32_t OutputContentsOffset; 129 uint32_t OutputIndex; 130 131 WasmCustomSection(StringRef Name, MCSectionWasm *Section) 132 : Name(Name), Section(Section), OutputContentsOffset(0), 133 OutputIndex(InvalidIndex) {} 134 }; 135 136 #if !defined(NDEBUG) 137 raw_ostream &operator<<(raw_ostream &OS, const WasmRelocationEntry &Rel) { 138 Rel.print(OS); 139 return OS; 140 } 141 #endif 142 143 // Write X as an (unsigned) LEB value at offset Offset in Stream, padded 144 // to allow patching. 145 template <int W> 146 void writePatchableLEB(raw_pwrite_stream &Stream, uint64_t X, uint64_t Offset) { 147 uint8_t Buffer[W]; 148 unsigned SizeLen = encodeULEB128(X, Buffer, W); 149 assert(SizeLen == W); 150 Stream.pwrite((char *)Buffer, SizeLen, Offset); 151 } 152 153 // Write X as an signed LEB value at offset Offset in Stream, padded 154 // to allow patching. 155 template <int W> 156 void writePatchableSLEB(raw_pwrite_stream &Stream, int64_t X, uint64_t Offset) { 157 uint8_t Buffer[W]; 158 unsigned SizeLen = encodeSLEB128(X, Buffer, W); 159 assert(SizeLen == W); 160 Stream.pwrite((char *)Buffer, SizeLen, Offset); 161 } 162 163 // Write X as a plain integer value at offset Offset in Stream. 164 static void patchI32(raw_pwrite_stream &Stream, uint32_t X, uint64_t Offset) { 165 uint8_t Buffer[4]; 166 support::endian::write32le(Buffer, X); 167 Stream.pwrite((char *)Buffer, sizeof(Buffer), Offset); 168 } 169 170 static void patchI64(raw_pwrite_stream &Stream, uint64_t X, uint64_t Offset) { 171 uint8_t Buffer[8]; 172 support::endian::write64le(Buffer, X); 173 Stream.pwrite((char *)Buffer, sizeof(Buffer), Offset); 174 } 175 176 bool isDwoSection(const MCSection &Sec) { 177 return Sec.getName().endswith(".dwo"); 178 } 179 180 class WasmObjectWriter : public MCObjectWriter { 181 support::endian::Writer *W; 182 183 /// The target specific Wasm writer instance. 184 std::unique_ptr<MCWasmObjectTargetWriter> TargetObjectWriter; 185 186 // Relocations for fixing up references in the code section. 187 std::vector<WasmRelocationEntry> CodeRelocations; 188 // Relocations for fixing up references in the data section. 189 std::vector<WasmRelocationEntry> DataRelocations; 190 191 // Index values to use for fixing up call_indirect type indices. 192 // Maps function symbols to the index of the type of the function 193 DenseMap<const MCSymbolWasm *, uint32_t> TypeIndices; 194 // Maps function symbols to the table element index space. Used 195 // for TABLE_INDEX relocation types (i.e. address taken functions). 196 DenseMap<const MCSymbolWasm *, uint32_t> TableIndices; 197 // Maps function/global/table symbols to the 198 // function/global/table/tag/section index space. 199 DenseMap<const MCSymbolWasm *, uint32_t> WasmIndices; 200 DenseMap<const MCSymbolWasm *, uint32_t> GOTIndices; 201 // Maps data symbols to the Wasm segment and offset/size with the segment. 202 DenseMap<const MCSymbolWasm *, wasm::WasmDataReference> DataLocations; 203 204 // Stores output data (index, relocations, content offset) for custom 205 // section. 206 std::vector<WasmCustomSection> CustomSections; 207 std::unique_ptr<WasmCustomSection> ProducersSection; 208 std::unique_ptr<WasmCustomSection> TargetFeaturesSection; 209 // Relocations for fixing up references in the custom sections. 210 DenseMap<const MCSectionWasm *, std::vector<WasmRelocationEntry>> 211 CustomSectionsRelocations; 212 213 // Map from section to defining function symbol. 214 DenseMap<const MCSection *, const MCSymbol *> SectionFunctions; 215 216 DenseMap<wasm::WasmSignature, uint32_t> SignatureIndices; 217 SmallVector<wasm::WasmSignature, 4> Signatures; 218 SmallVector<WasmDataSegment, 4> DataSegments; 219 unsigned NumFunctionImports = 0; 220 unsigned NumGlobalImports = 0; 221 unsigned NumTableImports = 0; 222 unsigned NumTagImports = 0; 223 uint32_t SectionCount = 0; 224 225 enum class DwoMode { 226 AllSections, 227 NonDwoOnly, 228 DwoOnly, 229 }; 230 bool IsSplitDwarf = false; 231 raw_pwrite_stream *OS = nullptr; 232 raw_pwrite_stream *DwoOS = nullptr; 233 234 // TargetObjectWriter wranppers. 235 bool is64Bit() const { return TargetObjectWriter->is64Bit(); } 236 bool isEmscripten() const { return TargetObjectWriter->isEmscripten(); } 237 238 void startSection(SectionBookkeeping &Section, unsigned SectionId); 239 void startCustomSection(SectionBookkeeping &Section, StringRef Name); 240 void endSection(SectionBookkeeping &Section); 241 242 public: 243 WasmObjectWriter(std::unique_ptr<MCWasmObjectTargetWriter> MOTW, 244 raw_pwrite_stream &OS_) 245 : TargetObjectWriter(std::move(MOTW)), OS(&OS_) {} 246 247 WasmObjectWriter(std::unique_ptr<MCWasmObjectTargetWriter> MOTW, 248 raw_pwrite_stream &OS_, raw_pwrite_stream &DwoOS_) 249 : TargetObjectWriter(std::move(MOTW)), IsSplitDwarf(true), OS(&OS_), 250 DwoOS(&DwoOS_) {} 251 252 private: 253 void reset() override { 254 CodeRelocations.clear(); 255 DataRelocations.clear(); 256 TypeIndices.clear(); 257 WasmIndices.clear(); 258 GOTIndices.clear(); 259 TableIndices.clear(); 260 DataLocations.clear(); 261 CustomSections.clear(); 262 ProducersSection.reset(); 263 TargetFeaturesSection.reset(); 264 CustomSectionsRelocations.clear(); 265 SignatureIndices.clear(); 266 Signatures.clear(); 267 DataSegments.clear(); 268 SectionFunctions.clear(); 269 NumFunctionImports = 0; 270 NumGlobalImports = 0; 271 NumTableImports = 0; 272 MCObjectWriter::reset(); 273 } 274 275 void writeHeader(const MCAssembler &Asm); 276 277 void recordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout, 278 const MCFragment *Fragment, const MCFixup &Fixup, 279 MCValue Target, uint64_t &FixedValue) override; 280 281 void executePostLayoutBinding(MCAssembler &Asm, 282 const MCAsmLayout &Layout) override; 283 void prepareImports(SmallVectorImpl<wasm::WasmImport> &Imports, 284 MCAssembler &Asm, const MCAsmLayout &Layout); 285 uint64_t writeObject(MCAssembler &Asm, const MCAsmLayout &Layout) override; 286 287 uint64_t writeOneObject(MCAssembler &Asm, const MCAsmLayout &Layout, 288 DwoMode Mode); 289 290 void writeString(const StringRef Str) { 291 encodeULEB128(Str.size(), W->OS); 292 W->OS << Str; 293 } 294 295 void writeI32(int32_t val) { 296 char Buffer[4]; 297 support::endian::write32le(Buffer, val); 298 W->OS.write(Buffer, sizeof(Buffer)); 299 } 300 301 void writeI64(int64_t val) { 302 char Buffer[8]; 303 support::endian::write64le(Buffer, val); 304 W->OS.write(Buffer, sizeof(Buffer)); 305 } 306 307 void writeValueType(wasm::ValType Ty) { W->OS << static_cast<char>(Ty); } 308 309 void writeTypeSection(ArrayRef<wasm::WasmSignature> Signatures); 310 void writeImportSection(ArrayRef<wasm::WasmImport> Imports, uint64_t DataSize, 311 uint32_t NumElements); 312 void writeFunctionSection(ArrayRef<WasmFunction> Functions); 313 void writeExportSection(ArrayRef<wasm::WasmExport> Exports); 314 void writeElemSection(const MCSymbolWasm *IndirectFunctionTable, 315 ArrayRef<uint32_t> TableElems); 316 void writeDataCountSection(); 317 uint32_t writeCodeSection(const MCAssembler &Asm, const MCAsmLayout &Layout, 318 ArrayRef<WasmFunction> Functions); 319 uint32_t writeDataSection(const MCAsmLayout &Layout); 320 void writeTagSection(ArrayRef<wasm::WasmTagType> Tags); 321 void writeGlobalSection(ArrayRef<wasm::WasmGlobal> Globals); 322 void writeTableSection(ArrayRef<wasm::WasmTable> Tables); 323 void writeRelocSection(uint32_t SectionIndex, StringRef Name, 324 std::vector<WasmRelocationEntry> &Relocations); 325 void writeLinkingMetaDataSection( 326 ArrayRef<wasm::WasmSymbolInfo> SymbolInfos, 327 ArrayRef<std::pair<uint16_t, uint32_t>> InitFuncs, 328 const std::map<StringRef, std::vector<WasmComdatEntry>> &Comdats); 329 void writeCustomSection(WasmCustomSection &CustomSection, 330 const MCAssembler &Asm, const MCAsmLayout &Layout); 331 void writeCustomRelocSections(); 332 333 uint64_t getProvisionalValue(const WasmRelocationEntry &RelEntry, 334 const MCAsmLayout &Layout); 335 void applyRelocations(ArrayRef<WasmRelocationEntry> Relocations, 336 uint64_t ContentsOffset, const MCAsmLayout &Layout); 337 338 uint32_t getRelocationIndexValue(const WasmRelocationEntry &RelEntry); 339 uint32_t getFunctionType(const MCSymbolWasm &Symbol); 340 uint32_t getTagType(const MCSymbolWasm &Symbol); 341 void registerFunctionType(const MCSymbolWasm &Symbol); 342 void registerTagType(const MCSymbolWasm &Symbol); 343 }; 344 345 } // end anonymous namespace 346 347 // Write out a section header and a patchable section size field. 348 void WasmObjectWriter::startSection(SectionBookkeeping &Section, 349 unsigned SectionId) { 350 LLVM_DEBUG(dbgs() << "startSection " << SectionId << "\n"); 351 W->OS << char(SectionId); 352 353 Section.SizeOffset = W->OS.tell(); 354 355 // The section size. We don't know the size yet, so reserve enough space 356 // for any 32-bit value; we'll patch it later. 357 encodeULEB128(0, W->OS, 5); 358 359 // The position where the section starts, for measuring its size. 360 Section.ContentsOffset = W->OS.tell(); 361 Section.PayloadOffset = W->OS.tell(); 362 Section.Index = SectionCount++; 363 } 364 365 void WasmObjectWriter::startCustomSection(SectionBookkeeping &Section, 366 StringRef Name) { 367 LLVM_DEBUG(dbgs() << "startCustomSection " << Name << "\n"); 368 startSection(Section, wasm::WASM_SEC_CUSTOM); 369 370 // The position where the section header ends, for measuring its size. 371 Section.PayloadOffset = W->OS.tell(); 372 373 // Custom sections in wasm also have a string identifier. 374 writeString(Name); 375 376 // The position where the custom section starts. 377 Section.ContentsOffset = W->OS.tell(); 378 } 379 380 // Now that the section is complete and we know how big it is, patch up the 381 // section size field at the start of the section. 382 void WasmObjectWriter::endSection(SectionBookkeeping &Section) { 383 uint64_t Size = W->OS.tell(); 384 // /dev/null doesn't support seek/tell and can report offset of 0. 385 // Simply skip this patching in that case. 386 if (!Size) 387 return; 388 389 Size -= Section.PayloadOffset; 390 if (uint32_t(Size) != Size) 391 report_fatal_error("section size does not fit in a uint32_t"); 392 393 LLVM_DEBUG(dbgs() << "endSection size=" << Size << "\n"); 394 395 // Write the final section size to the payload_len field, which follows 396 // the section id byte. 397 writePatchableLEB<5>(static_cast<raw_pwrite_stream &>(W->OS), Size, 398 Section.SizeOffset); 399 } 400 401 // Emit the Wasm header. 402 void WasmObjectWriter::writeHeader(const MCAssembler &Asm) { 403 W->OS.write(wasm::WasmMagic, sizeof(wasm::WasmMagic)); 404 W->write<uint32_t>(wasm::WasmVersion); 405 } 406 407 void WasmObjectWriter::executePostLayoutBinding(MCAssembler &Asm, 408 const MCAsmLayout &Layout) { 409 // Some compilation units require the indirect function table to be present 410 // but don't explicitly reference it. This is the case for call_indirect 411 // without the reference-types feature, and also function bitcasts in all 412 // cases. In those cases the __indirect_function_table has the 413 // WASM_SYMBOL_NO_STRIP attribute. Here we make sure this symbol makes it to 414 // the assembler, if needed. 415 if (auto *Sym = Asm.getContext().lookupSymbol("__indirect_function_table")) { 416 const auto *WasmSym = static_cast<const MCSymbolWasm *>(Sym); 417 if (WasmSym->isNoStrip()) 418 Asm.registerSymbol(*Sym); 419 } 420 421 // Build a map of sections to the function that defines them, for use 422 // in recordRelocation. 423 for (const MCSymbol &S : Asm.symbols()) { 424 const auto &WS = static_cast<const MCSymbolWasm &>(S); 425 if (WS.isDefined() && WS.isFunction() && !WS.isVariable()) { 426 const auto &Sec = static_cast<const MCSectionWasm &>(S.getSection()); 427 auto Pair = SectionFunctions.insert(std::make_pair(&Sec, &S)); 428 if (!Pair.second) 429 report_fatal_error("section already has a defining function: " + 430 Sec.getName()); 431 } 432 } 433 } 434 435 void WasmObjectWriter::recordRelocation(MCAssembler &Asm, 436 const MCAsmLayout &Layout, 437 const MCFragment *Fragment, 438 const MCFixup &Fixup, MCValue Target, 439 uint64_t &FixedValue) { 440 // The WebAssembly backend should never generate FKF_IsPCRel fixups 441 assert(!(Asm.getBackend().getFixupKindInfo(Fixup.getKind()).Flags & 442 MCFixupKindInfo::FKF_IsPCRel)); 443 444 const auto &FixupSection = cast<MCSectionWasm>(*Fragment->getParent()); 445 uint64_t C = Target.getConstant(); 446 uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset(); 447 MCContext &Ctx = Asm.getContext(); 448 bool IsLocRel = false; 449 450 if (const MCSymbolRefExpr *RefB = Target.getSymB()) { 451 452 const auto &SymB = cast<MCSymbolWasm>(RefB->getSymbol()); 453 454 if (FixupSection.getKind().isText()) { 455 Ctx.reportError(Fixup.getLoc(), 456 Twine("symbol '") + SymB.getName() + 457 "' unsupported subtraction expression used in " 458 "relocation in code section."); 459 return; 460 } 461 462 if (SymB.isUndefined()) { 463 Ctx.reportError(Fixup.getLoc(), 464 Twine("symbol '") + SymB.getName() + 465 "' can not be undefined in a subtraction expression"); 466 return; 467 } 468 const MCSection &SecB = SymB.getSection(); 469 if (&SecB != &FixupSection) { 470 Ctx.reportError(Fixup.getLoc(), 471 Twine("symbol '") + SymB.getName() + 472 "' can not be placed in a different section"); 473 return; 474 } 475 IsLocRel = true; 476 C += FixupOffset - Layout.getSymbolOffset(SymB); 477 } 478 479 // We either rejected the fixup or folded B into C at this point. 480 const MCSymbolRefExpr *RefA = Target.getSymA(); 481 const auto *SymA = cast<MCSymbolWasm>(&RefA->getSymbol()); 482 483 // The .init_array isn't translated as data, so don't do relocations in it. 484 if (FixupSection.getName().startswith(".init_array")) { 485 SymA->setUsedInInitArray(); 486 return; 487 } 488 489 if (SymA->isVariable()) { 490 const MCExpr *Expr = SymA->getVariableValue(); 491 if (const auto *Inner = dyn_cast<MCSymbolRefExpr>(Expr)) 492 if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF) 493 llvm_unreachable("weakref used in reloc not yet implemented"); 494 } 495 496 // Put any constant offset in an addend. Offsets can be negative, and 497 // LLVM expects wrapping, in contrast to wasm's immediates which can't 498 // be negative and don't wrap. 499 FixedValue = 0; 500 501 unsigned Type = 502 TargetObjectWriter->getRelocType(Target, Fixup, FixupSection, IsLocRel); 503 504 // Absolute offset within a section or a function. 505 // Currently only supported for for metadata sections. 506 // See: test/MC/WebAssembly/blockaddress.ll 507 if ((Type == wasm::R_WASM_FUNCTION_OFFSET_I32 || 508 Type == wasm::R_WASM_FUNCTION_OFFSET_I64 || 509 Type == wasm::R_WASM_SECTION_OFFSET_I32) && 510 SymA->isDefined()) { 511 // SymA can be a temp data symbol that represents a function (in which case 512 // it needs to be replaced by the section symbol), [XXX and it apparently 513 // later gets changed again to a func symbol?] or it can be a real 514 // function symbol, in which case it can be left as-is. 515 516 if (!FixupSection.getKind().isMetadata()) 517 report_fatal_error("relocations for function or section offsets are " 518 "only supported in metadata sections"); 519 520 const MCSymbol *SectionSymbol = nullptr; 521 const MCSection &SecA = SymA->getSection(); 522 if (SecA.getKind().isText()) { 523 auto SecSymIt = SectionFunctions.find(&SecA); 524 if (SecSymIt == SectionFunctions.end()) 525 report_fatal_error("section doesn\'t have defining symbol"); 526 SectionSymbol = SecSymIt->second; 527 } else { 528 SectionSymbol = SecA.getBeginSymbol(); 529 } 530 if (!SectionSymbol) 531 report_fatal_error("section symbol is required for relocation"); 532 533 C += Layout.getSymbolOffset(*SymA); 534 SymA = cast<MCSymbolWasm>(SectionSymbol); 535 } 536 537 if (Type == wasm::R_WASM_TABLE_INDEX_REL_SLEB || 538 Type == wasm::R_WASM_TABLE_INDEX_REL_SLEB64 || 539 Type == wasm::R_WASM_TABLE_INDEX_SLEB || 540 Type == wasm::R_WASM_TABLE_INDEX_SLEB64 || 541 Type == wasm::R_WASM_TABLE_INDEX_I32 || 542 Type == wasm::R_WASM_TABLE_INDEX_I64) { 543 // TABLE_INDEX relocs implicitly use the default indirect function table. 544 // We require the function table to have already been defined. 545 auto TableName = "__indirect_function_table"; 546 MCSymbolWasm *Sym = cast_or_null<MCSymbolWasm>(Ctx.lookupSymbol(TableName)); 547 if (!Sym) { 548 report_fatal_error("missing indirect function table symbol"); 549 } else { 550 if (!Sym->isFunctionTable()) 551 report_fatal_error("__indirect_function_table symbol has wrong type"); 552 // Ensure that __indirect_function_table reaches the output. 553 Sym->setNoStrip(); 554 Asm.registerSymbol(*Sym); 555 } 556 } 557 558 // Relocation other than R_WASM_TYPE_INDEX_LEB are required to be 559 // against a named symbol. 560 if (Type != wasm::R_WASM_TYPE_INDEX_LEB) { 561 if (SymA->getName().empty()) 562 report_fatal_error("relocations against un-named temporaries are not yet " 563 "supported by wasm"); 564 565 SymA->setUsedInReloc(); 566 } 567 568 if (RefA->getKind() == MCSymbolRefExpr::VK_GOT) 569 SymA->setUsedInGOT(); 570 571 WasmRelocationEntry Rec(FixupOffset, SymA, C, Type, &FixupSection); 572 LLVM_DEBUG(dbgs() << "WasmReloc: " << Rec << "\n"); 573 574 if (FixupSection.isWasmData()) { 575 DataRelocations.push_back(Rec); 576 } else if (FixupSection.getKind().isText()) { 577 CodeRelocations.push_back(Rec); 578 } else if (FixupSection.getKind().isMetadata()) { 579 CustomSectionsRelocations[&FixupSection].push_back(Rec); 580 } else { 581 llvm_unreachable("unexpected section type"); 582 } 583 } 584 585 // Compute a value to write into the code at the location covered 586 // by RelEntry. This value isn't used by the static linker; it just serves 587 // to make the object format more readable and more likely to be directly 588 // useable. 589 uint64_t 590 WasmObjectWriter::getProvisionalValue(const WasmRelocationEntry &RelEntry, 591 const MCAsmLayout &Layout) { 592 if ((RelEntry.Type == wasm::R_WASM_GLOBAL_INDEX_LEB || 593 RelEntry.Type == wasm::R_WASM_GLOBAL_INDEX_I32) && 594 !RelEntry.Symbol->isGlobal()) { 595 assert(GOTIndices.count(RelEntry.Symbol) > 0 && "symbol not found in GOT index space"); 596 return GOTIndices[RelEntry.Symbol]; 597 } 598 599 switch (RelEntry.Type) { 600 case wasm::R_WASM_TABLE_INDEX_REL_SLEB: 601 case wasm::R_WASM_TABLE_INDEX_REL_SLEB64: 602 case wasm::R_WASM_TABLE_INDEX_SLEB: 603 case wasm::R_WASM_TABLE_INDEX_SLEB64: 604 case wasm::R_WASM_TABLE_INDEX_I32: 605 case wasm::R_WASM_TABLE_INDEX_I64: { 606 // Provisional value is table address of the resolved symbol itself 607 const MCSymbolWasm *Base = 608 cast<MCSymbolWasm>(Layout.getBaseSymbol(*RelEntry.Symbol)); 609 assert(Base->isFunction()); 610 if (RelEntry.Type == wasm::R_WASM_TABLE_INDEX_REL_SLEB || 611 RelEntry.Type == wasm::R_WASM_TABLE_INDEX_REL_SLEB64) 612 return TableIndices[Base] - InitialTableOffset; 613 else 614 return TableIndices[Base]; 615 } 616 case wasm::R_WASM_TYPE_INDEX_LEB: 617 // Provisional value is same as the index 618 return getRelocationIndexValue(RelEntry); 619 case wasm::R_WASM_FUNCTION_INDEX_LEB: 620 case wasm::R_WASM_GLOBAL_INDEX_LEB: 621 case wasm::R_WASM_GLOBAL_INDEX_I32: 622 case wasm::R_WASM_TAG_INDEX_LEB: 623 case wasm::R_WASM_TABLE_NUMBER_LEB: 624 // Provisional value is function/global/tag Wasm index 625 assert(WasmIndices.count(RelEntry.Symbol) > 0 && "symbol not found in wasm index space"); 626 return WasmIndices[RelEntry.Symbol]; 627 case wasm::R_WASM_FUNCTION_OFFSET_I32: 628 case wasm::R_WASM_FUNCTION_OFFSET_I64: 629 case wasm::R_WASM_SECTION_OFFSET_I32: { 630 if (!RelEntry.Symbol->isDefined()) 631 return 0; 632 const auto &Section = 633 static_cast<const MCSectionWasm &>(RelEntry.Symbol->getSection()); 634 return Section.getSectionOffset() + RelEntry.Addend; 635 } 636 case wasm::R_WASM_MEMORY_ADDR_LEB: 637 case wasm::R_WASM_MEMORY_ADDR_LEB64: 638 case wasm::R_WASM_MEMORY_ADDR_SLEB: 639 case wasm::R_WASM_MEMORY_ADDR_SLEB64: 640 case wasm::R_WASM_MEMORY_ADDR_REL_SLEB: 641 case wasm::R_WASM_MEMORY_ADDR_REL_SLEB64: 642 case wasm::R_WASM_MEMORY_ADDR_I32: 643 case wasm::R_WASM_MEMORY_ADDR_I64: 644 case wasm::R_WASM_MEMORY_ADDR_TLS_SLEB: 645 case wasm::R_WASM_MEMORY_ADDR_TLS_SLEB64: 646 case wasm::R_WASM_MEMORY_ADDR_LOCREL_I32: { 647 // Provisional value is address of the global plus the offset 648 // For undefined symbols, use zero 649 if (!RelEntry.Symbol->isDefined()) 650 return 0; 651 const wasm::WasmDataReference &SymRef = DataLocations[RelEntry.Symbol]; 652 const WasmDataSegment &Segment = DataSegments[SymRef.Segment]; 653 // Ignore overflow. LLVM allows address arithmetic to silently wrap. 654 return Segment.Offset + SymRef.Offset + RelEntry.Addend; 655 } 656 default: 657 llvm_unreachable("invalid relocation type"); 658 } 659 } 660 661 static void addData(SmallVectorImpl<char> &DataBytes, 662 MCSectionWasm &DataSection) { 663 LLVM_DEBUG(errs() << "addData: " << DataSection.getName() << "\n"); 664 665 DataBytes.resize(alignTo(DataBytes.size(), DataSection.getAlignment())); 666 667 for (const MCFragment &Frag : DataSection) { 668 if (Frag.hasInstructions()) 669 report_fatal_error("only data supported in data sections"); 670 671 if (auto *Align = dyn_cast<MCAlignFragment>(&Frag)) { 672 if (Align->getValueSize() != 1) 673 report_fatal_error("only byte values supported for alignment"); 674 // If nops are requested, use zeros, as this is the data section. 675 uint8_t Value = Align->hasEmitNops() ? 0 : Align->getValue(); 676 uint64_t Size = 677 std::min<uint64_t>(alignTo(DataBytes.size(), Align->getAlignment()), 678 DataBytes.size() + Align->getMaxBytesToEmit()); 679 DataBytes.resize(Size, Value); 680 } else if (auto *Fill = dyn_cast<MCFillFragment>(&Frag)) { 681 int64_t NumValues; 682 if (!Fill->getNumValues().evaluateAsAbsolute(NumValues)) 683 llvm_unreachable("The fill should be an assembler constant"); 684 DataBytes.insert(DataBytes.end(), Fill->getValueSize() * NumValues, 685 Fill->getValue()); 686 } else if (auto *LEB = dyn_cast<MCLEBFragment>(&Frag)) { 687 const SmallVectorImpl<char> &Contents = LEB->getContents(); 688 llvm::append_range(DataBytes, Contents); 689 } else { 690 const auto &DataFrag = cast<MCDataFragment>(Frag); 691 const SmallVectorImpl<char> &Contents = DataFrag.getContents(); 692 llvm::append_range(DataBytes, Contents); 693 } 694 } 695 696 LLVM_DEBUG(dbgs() << "addData -> " << DataBytes.size() << "\n"); 697 } 698 699 uint32_t 700 WasmObjectWriter::getRelocationIndexValue(const WasmRelocationEntry &RelEntry) { 701 if (RelEntry.Type == wasm::R_WASM_TYPE_INDEX_LEB) { 702 if (!TypeIndices.count(RelEntry.Symbol)) 703 report_fatal_error("symbol not found in type index space: " + 704 RelEntry.Symbol->getName()); 705 return TypeIndices[RelEntry.Symbol]; 706 } 707 708 return RelEntry.Symbol->getIndex(); 709 } 710 711 // Apply the portions of the relocation records that we can handle ourselves 712 // directly. 713 void WasmObjectWriter::applyRelocations( 714 ArrayRef<WasmRelocationEntry> Relocations, uint64_t ContentsOffset, 715 const MCAsmLayout &Layout) { 716 auto &Stream = static_cast<raw_pwrite_stream &>(W->OS); 717 for (const WasmRelocationEntry &RelEntry : Relocations) { 718 uint64_t Offset = ContentsOffset + 719 RelEntry.FixupSection->getSectionOffset() + 720 RelEntry.Offset; 721 722 LLVM_DEBUG(dbgs() << "applyRelocation: " << RelEntry << "\n"); 723 auto Value = getProvisionalValue(RelEntry, Layout); 724 725 switch (RelEntry.Type) { 726 case wasm::R_WASM_FUNCTION_INDEX_LEB: 727 case wasm::R_WASM_TYPE_INDEX_LEB: 728 case wasm::R_WASM_GLOBAL_INDEX_LEB: 729 case wasm::R_WASM_MEMORY_ADDR_LEB: 730 case wasm::R_WASM_TAG_INDEX_LEB: 731 case wasm::R_WASM_TABLE_NUMBER_LEB: 732 writePatchableLEB<5>(Stream, Value, Offset); 733 break; 734 case wasm::R_WASM_MEMORY_ADDR_LEB64: 735 writePatchableLEB<10>(Stream, Value, Offset); 736 break; 737 case wasm::R_WASM_TABLE_INDEX_I32: 738 case wasm::R_WASM_MEMORY_ADDR_I32: 739 case wasm::R_WASM_FUNCTION_OFFSET_I32: 740 case wasm::R_WASM_SECTION_OFFSET_I32: 741 case wasm::R_WASM_GLOBAL_INDEX_I32: 742 case wasm::R_WASM_MEMORY_ADDR_LOCREL_I32: 743 patchI32(Stream, Value, Offset); 744 break; 745 case wasm::R_WASM_TABLE_INDEX_I64: 746 case wasm::R_WASM_MEMORY_ADDR_I64: 747 case wasm::R_WASM_FUNCTION_OFFSET_I64: 748 patchI64(Stream, Value, Offset); 749 break; 750 case wasm::R_WASM_TABLE_INDEX_SLEB: 751 case wasm::R_WASM_TABLE_INDEX_REL_SLEB: 752 case wasm::R_WASM_MEMORY_ADDR_SLEB: 753 case wasm::R_WASM_MEMORY_ADDR_REL_SLEB: 754 case wasm::R_WASM_MEMORY_ADDR_TLS_SLEB: 755 writePatchableSLEB<5>(Stream, Value, Offset); 756 break; 757 case wasm::R_WASM_TABLE_INDEX_SLEB64: 758 case wasm::R_WASM_TABLE_INDEX_REL_SLEB64: 759 case wasm::R_WASM_MEMORY_ADDR_SLEB64: 760 case wasm::R_WASM_MEMORY_ADDR_REL_SLEB64: 761 case wasm::R_WASM_MEMORY_ADDR_TLS_SLEB64: 762 writePatchableSLEB<10>(Stream, Value, Offset); 763 break; 764 default: 765 llvm_unreachable("invalid relocation type"); 766 } 767 } 768 } 769 770 void WasmObjectWriter::writeTypeSection( 771 ArrayRef<wasm::WasmSignature> Signatures) { 772 if (Signatures.empty()) 773 return; 774 775 SectionBookkeeping Section; 776 startSection(Section, wasm::WASM_SEC_TYPE); 777 778 encodeULEB128(Signatures.size(), W->OS); 779 780 for (const wasm::WasmSignature &Sig : Signatures) { 781 W->OS << char(wasm::WASM_TYPE_FUNC); 782 encodeULEB128(Sig.Params.size(), W->OS); 783 for (wasm::ValType Ty : Sig.Params) 784 writeValueType(Ty); 785 encodeULEB128(Sig.Returns.size(), W->OS); 786 for (wasm::ValType Ty : Sig.Returns) 787 writeValueType(Ty); 788 } 789 790 endSection(Section); 791 } 792 793 void WasmObjectWriter::writeImportSection(ArrayRef<wasm::WasmImport> Imports, 794 uint64_t DataSize, 795 uint32_t NumElements) { 796 if (Imports.empty()) 797 return; 798 799 uint64_t NumPages = (DataSize + wasm::WasmPageSize - 1) / wasm::WasmPageSize; 800 801 SectionBookkeeping Section; 802 startSection(Section, wasm::WASM_SEC_IMPORT); 803 804 encodeULEB128(Imports.size(), W->OS); 805 for (const wasm::WasmImport &Import : Imports) { 806 writeString(Import.Module); 807 writeString(Import.Field); 808 W->OS << char(Import.Kind); 809 810 switch (Import.Kind) { 811 case wasm::WASM_EXTERNAL_FUNCTION: 812 encodeULEB128(Import.SigIndex, W->OS); 813 break; 814 case wasm::WASM_EXTERNAL_GLOBAL: 815 W->OS << char(Import.Global.Type); 816 W->OS << char(Import.Global.Mutable ? 1 : 0); 817 break; 818 case wasm::WASM_EXTERNAL_MEMORY: 819 encodeULEB128(Import.Memory.Flags, W->OS); 820 encodeULEB128(NumPages, W->OS); // initial 821 break; 822 case wasm::WASM_EXTERNAL_TABLE: 823 W->OS << char(Import.Table.ElemType); 824 encodeULEB128(0, W->OS); // flags 825 encodeULEB128(NumElements, W->OS); // initial 826 break; 827 case wasm::WASM_EXTERNAL_TAG: 828 W->OS << char(Import.Tag.Attribute); 829 encodeULEB128(Import.Tag.SigIndex, W->OS); 830 break; 831 default: 832 llvm_unreachable("unsupported import kind"); 833 } 834 } 835 836 endSection(Section); 837 } 838 839 void WasmObjectWriter::writeFunctionSection(ArrayRef<WasmFunction> Functions) { 840 if (Functions.empty()) 841 return; 842 843 SectionBookkeeping Section; 844 startSection(Section, wasm::WASM_SEC_FUNCTION); 845 846 encodeULEB128(Functions.size(), W->OS); 847 for (const WasmFunction &Func : Functions) 848 encodeULEB128(Func.SigIndex, W->OS); 849 850 endSection(Section); 851 } 852 853 void WasmObjectWriter::writeTagSection(ArrayRef<wasm::WasmTagType> Tags) { 854 if (Tags.empty()) 855 return; 856 857 SectionBookkeeping Section; 858 startSection(Section, wasm::WASM_SEC_TAG); 859 860 encodeULEB128(Tags.size(), W->OS); 861 for (const wasm::WasmTagType &Tag : Tags) { 862 W->OS << char(Tag.Attribute); 863 encodeULEB128(Tag.SigIndex, W->OS); 864 } 865 866 endSection(Section); 867 } 868 869 void WasmObjectWriter::writeGlobalSection(ArrayRef<wasm::WasmGlobal> Globals) { 870 if (Globals.empty()) 871 return; 872 873 SectionBookkeeping Section; 874 startSection(Section, wasm::WASM_SEC_GLOBAL); 875 876 encodeULEB128(Globals.size(), W->OS); 877 for (const wasm::WasmGlobal &Global : Globals) { 878 encodeULEB128(Global.Type.Type, W->OS); 879 W->OS << char(Global.Type.Mutable); 880 W->OS << char(Global.InitExpr.Opcode); 881 switch (Global.Type.Type) { 882 case wasm::WASM_TYPE_I32: 883 encodeSLEB128(0, W->OS); 884 break; 885 case wasm::WASM_TYPE_I64: 886 encodeSLEB128(0, W->OS); 887 break; 888 case wasm::WASM_TYPE_F32: 889 writeI32(0); 890 break; 891 case wasm::WASM_TYPE_F64: 892 writeI64(0); 893 break; 894 case wasm::WASM_TYPE_EXTERNREF: 895 writeValueType(wasm::ValType::EXTERNREF); 896 break; 897 default: 898 llvm_unreachable("unexpected type"); 899 } 900 W->OS << char(wasm::WASM_OPCODE_END); 901 } 902 903 endSection(Section); 904 } 905 906 void WasmObjectWriter::writeTableSection(ArrayRef<wasm::WasmTable> Tables) { 907 if (Tables.empty()) 908 return; 909 910 SectionBookkeeping Section; 911 startSection(Section, wasm::WASM_SEC_TABLE); 912 913 encodeULEB128(Tables.size(), W->OS); 914 for (const wasm::WasmTable &Table : Tables) { 915 encodeULEB128(Table.Type.ElemType, W->OS); 916 encodeULEB128(Table.Type.Limits.Flags, W->OS); 917 encodeULEB128(Table.Type.Limits.Minimum, W->OS); 918 if (Table.Type.Limits.Flags & wasm::WASM_LIMITS_FLAG_HAS_MAX) 919 encodeULEB128(Table.Type.Limits.Maximum, W->OS); 920 } 921 endSection(Section); 922 } 923 924 void WasmObjectWriter::writeExportSection(ArrayRef<wasm::WasmExport> Exports) { 925 if (Exports.empty()) 926 return; 927 928 SectionBookkeeping Section; 929 startSection(Section, wasm::WASM_SEC_EXPORT); 930 931 encodeULEB128(Exports.size(), W->OS); 932 for (const wasm::WasmExport &Export : Exports) { 933 writeString(Export.Name); 934 W->OS << char(Export.Kind); 935 encodeULEB128(Export.Index, W->OS); 936 } 937 938 endSection(Section); 939 } 940 941 void WasmObjectWriter::writeElemSection( 942 const MCSymbolWasm *IndirectFunctionTable, ArrayRef<uint32_t> TableElems) { 943 if (TableElems.empty()) 944 return; 945 946 assert(IndirectFunctionTable); 947 948 SectionBookkeeping Section; 949 startSection(Section, wasm::WASM_SEC_ELEM); 950 951 encodeULEB128(1, W->OS); // number of "segments" 952 953 assert(WasmIndices.count(IndirectFunctionTable)); 954 uint32_t TableNumber = WasmIndices.find(IndirectFunctionTable)->second; 955 uint32_t Flags = 0; 956 if (TableNumber) 957 Flags |= wasm::WASM_ELEM_SEGMENT_HAS_TABLE_NUMBER; 958 encodeULEB128(Flags, W->OS); 959 if (Flags & wasm::WASM_ELEM_SEGMENT_HAS_TABLE_NUMBER) 960 encodeULEB128(TableNumber, W->OS); // the table number 961 962 // init expr for starting offset 963 W->OS << char(wasm::WASM_OPCODE_I32_CONST); 964 encodeSLEB128(InitialTableOffset, W->OS); 965 W->OS << char(wasm::WASM_OPCODE_END); 966 967 if (Flags & wasm::WASM_ELEM_SEGMENT_MASK_HAS_ELEM_KIND) { 968 // We only write active function table initializers, for which the elem kind 969 // is specified to be written as 0x00 and interpreted to mean "funcref". 970 const uint8_t ElemKind = 0; 971 W->OS << ElemKind; 972 } 973 974 encodeULEB128(TableElems.size(), W->OS); 975 for (uint32_t Elem : TableElems) 976 encodeULEB128(Elem, W->OS); 977 978 endSection(Section); 979 } 980 981 void WasmObjectWriter::writeDataCountSection() { 982 if (DataSegments.empty()) 983 return; 984 985 SectionBookkeeping Section; 986 startSection(Section, wasm::WASM_SEC_DATACOUNT); 987 encodeULEB128(DataSegments.size(), W->OS); 988 endSection(Section); 989 } 990 991 uint32_t WasmObjectWriter::writeCodeSection(const MCAssembler &Asm, 992 const MCAsmLayout &Layout, 993 ArrayRef<WasmFunction> Functions) { 994 if (Functions.empty()) 995 return 0; 996 997 SectionBookkeeping Section; 998 startSection(Section, wasm::WASM_SEC_CODE); 999 1000 encodeULEB128(Functions.size(), W->OS); 1001 1002 for (const WasmFunction &Func : Functions) { 1003 auto &FuncSection = static_cast<MCSectionWasm &>(Func.Sym->getSection()); 1004 1005 int64_t Size = 0; 1006 if (!Func.Sym->getSize()->evaluateAsAbsolute(Size, Layout)) 1007 report_fatal_error(".size expression must be evaluatable"); 1008 1009 encodeULEB128(Size, W->OS); 1010 FuncSection.setSectionOffset(W->OS.tell() - Section.ContentsOffset); 1011 Asm.writeSectionData(W->OS, &FuncSection, Layout); 1012 } 1013 1014 // Apply fixups. 1015 applyRelocations(CodeRelocations, Section.ContentsOffset, Layout); 1016 1017 endSection(Section); 1018 return Section.Index; 1019 } 1020 1021 uint32_t WasmObjectWriter::writeDataSection(const MCAsmLayout &Layout) { 1022 if (DataSegments.empty()) 1023 return 0; 1024 1025 SectionBookkeeping Section; 1026 startSection(Section, wasm::WASM_SEC_DATA); 1027 1028 encodeULEB128(DataSegments.size(), W->OS); // count 1029 1030 for (const WasmDataSegment &Segment : DataSegments) { 1031 encodeULEB128(Segment.InitFlags, W->OS); // flags 1032 if (Segment.InitFlags & wasm::WASM_DATA_SEGMENT_HAS_MEMINDEX) 1033 encodeULEB128(0, W->OS); // memory index 1034 if ((Segment.InitFlags & wasm::WASM_DATA_SEGMENT_IS_PASSIVE) == 0) { 1035 W->OS << char(is64Bit() ? wasm::WASM_OPCODE_I64_CONST 1036 : wasm::WASM_OPCODE_I32_CONST); 1037 encodeSLEB128(Segment.Offset, W->OS); // offset 1038 W->OS << char(wasm::WASM_OPCODE_END); 1039 } 1040 encodeULEB128(Segment.Data.size(), W->OS); // size 1041 Segment.Section->setSectionOffset(W->OS.tell() - Section.ContentsOffset); 1042 W->OS << Segment.Data; // data 1043 } 1044 1045 // Apply fixups. 1046 applyRelocations(DataRelocations, Section.ContentsOffset, Layout); 1047 1048 endSection(Section); 1049 return Section.Index; 1050 } 1051 1052 void WasmObjectWriter::writeRelocSection( 1053 uint32_t SectionIndex, StringRef Name, 1054 std::vector<WasmRelocationEntry> &Relocs) { 1055 // See: https://github.com/WebAssembly/tool-conventions/blob/master/Linking.md 1056 // for descriptions of the reloc sections. 1057 1058 if (Relocs.empty()) 1059 return; 1060 1061 // First, ensure the relocations are sorted in offset order. In general they 1062 // should already be sorted since `recordRelocation` is called in offset 1063 // order, but for the code section we combine many MC sections into single 1064 // wasm section, and this order is determined by the order of Asm.Symbols() 1065 // not the sections order. 1066 llvm::stable_sort( 1067 Relocs, [](const WasmRelocationEntry &A, const WasmRelocationEntry &B) { 1068 return (A.Offset + A.FixupSection->getSectionOffset()) < 1069 (B.Offset + B.FixupSection->getSectionOffset()); 1070 }); 1071 1072 SectionBookkeeping Section; 1073 startCustomSection(Section, std::string("reloc.") + Name.str()); 1074 1075 encodeULEB128(SectionIndex, W->OS); 1076 encodeULEB128(Relocs.size(), W->OS); 1077 for (const WasmRelocationEntry &RelEntry : Relocs) { 1078 uint64_t Offset = 1079 RelEntry.Offset + RelEntry.FixupSection->getSectionOffset(); 1080 uint32_t Index = getRelocationIndexValue(RelEntry); 1081 1082 W->OS << char(RelEntry.Type); 1083 encodeULEB128(Offset, W->OS); 1084 encodeULEB128(Index, W->OS); 1085 if (RelEntry.hasAddend()) 1086 encodeSLEB128(RelEntry.Addend, W->OS); 1087 } 1088 1089 endSection(Section); 1090 } 1091 1092 void WasmObjectWriter::writeCustomRelocSections() { 1093 for (const auto &Sec : CustomSections) { 1094 auto &Relocations = CustomSectionsRelocations[Sec.Section]; 1095 writeRelocSection(Sec.OutputIndex, Sec.Name, Relocations); 1096 } 1097 } 1098 1099 void WasmObjectWriter::writeLinkingMetaDataSection( 1100 ArrayRef<wasm::WasmSymbolInfo> SymbolInfos, 1101 ArrayRef<std::pair<uint16_t, uint32_t>> InitFuncs, 1102 const std::map<StringRef, std::vector<WasmComdatEntry>> &Comdats) { 1103 SectionBookkeeping Section; 1104 startCustomSection(Section, "linking"); 1105 encodeULEB128(wasm::WasmMetadataVersion, W->OS); 1106 1107 SectionBookkeeping SubSection; 1108 if (SymbolInfos.size() != 0) { 1109 startSection(SubSection, wasm::WASM_SYMBOL_TABLE); 1110 encodeULEB128(SymbolInfos.size(), W->OS); 1111 for (const wasm::WasmSymbolInfo &Sym : SymbolInfos) { 1112 encodeULEB128(Sym.Kind, W->OS); 1113 encodeULEB128(Sym.Flags, W->OS); 1114 switch (Sym.Kind) { 1115 case wasm::WASM_SYMBOL_TYPE_FUNCTION: 1116 case wasm::WASM_SYMBOL_TYPE_GLOBAL: 1117 case wasm::WASM_SYMBOL_TYPE_TAG: 1118 case wasm::WASM_SYMBOL_TYPE_TABLE: 1119 encodeULEB128(Sym.ElementIndex, W->OS); 1120 if ((Sym.Flags & wasm::WASM_SYMBOL_UNDEFINED) == 0 || 1121 (Sym.Flags & wasm::WASM_SYMBOL_EXPLICIT_NAME) != 0) 1122 writeString(Sym.Name); 1123 break; 1124 case wasm::WASM_SYMBOL_TYPE_DATA: 1125 writeString(Sym.Name); 1126 if ((Sym.Flags & wasm::WASM_SYMBOL_UNDEFINED) == 0) { 1127 encodeULEB128(Sym.DataRef.Segment, W->OS); 1128 encodeULEB128(Sym.DataRef.Offset, W->OS); 1129 encodeULEB128(Sym.DataRef.Size, W->OS); 1130 } 1131 break; 1132 case wasm::WASM_SYMBOL_TYPE_SECTION: { 1133 const uint32_t SectionIndex = 1134 CustomSections[Sym.ElementIndex].OutputIndex; 1135 encodeULEB128(SectionIndex, W->OS); 1136 break; 1137 } 1138 default: 1139 llvm_unreachable("unexpected kind"); 1140 } 1141 } 1142 endSection(SubSection); 1143 } 1144 1145 if (DataSegments.size()) { 1146 startSection(SubSection, wasm::WASM_SEGMENT_INFO); 1147 encodeULEB128(DataSegments.size(), W->OS); 1148 for (const WasmDataSegment &Segment : DataSegments) { 1149 writeString(Segment.Name); 1150 encodeULEB128(Segment.Alignment, W->OS); 1151 encodeULEB128(Segment.LinkingFlags, W->OS); 1152 } 1153 endSection(SubSection); 1154 } 1155 1156 if (!InitFuncs.empty()) { 1157 startSection(SubSection, wasm::WASM_INIT_FUNCS); 1158 encodeULEB128(InitFuncs.size(), W->OS); 1159 for (auto &StartFunc : InitFuncs) { 1160 encodeULEB128(StartFunc.first, W->OS); // priority 1161 encodeULEB128(StartFunc.second, W->OS); // function index 1162 } 1163 endSection(SubSection); 1164 } 1165 1166 if (Comdats.size()) { 1167 startSection(SubSection, wasm::WASM_COMDAT_INFO); 1168 encodeULEB128(Comdats.size(), W->OS); 1169 for (const auto &C : Comdats) { 1170 writeString(C.first); 1171 encodeULEB128(0, W->OS); // flags for future use 1172 encodeULEB128(C.second.size(), W->OS); 1173 for (const WasmComdatEntry &Entry : C.second) { 1174 encodeULEB128(Entry.Kind, W->OS); 1175 encodeULEB128(Entry.Index, W->OS); 1176 } 1177 } 1178 endSection(SubSection); 1179 } 1180 1181 endSection(Section); 1182 } 1183 1184 void WasmObjectWriter::writeCustomSection(WasmCustomSection &CustomSection, 1185 const MCAssembler &Asm, 1186 const MCAsmLayout &Layout) { 1187 SectionBookkeeping Section; 1188 auto *Sec = CustomSection.Section; 1189 startCustomSection(Section, CustomSection.Name); 1190 1191 Sec->setSectionOffset(W->OS.tell() - Section.ContentsOffset); 1192 Asm.writeSectionData(W->OS, Sec, Layout); 1193 1194 CustomSection.OutputContentsOffset = Section.ContentsOffset; 1195 CustomSection.OutputIndex = Section.Index; 1196 1197 endSection(Section); 1198 1199 // Apply fixups. 1200 auto &Relocations = CustomSectionsRelocations[CustomSection.Section]; 1201 applyRelocations(Relocations, CustomSection.OutputContentsOffset, Layout); 1202 } 1203 1204 uint32_t WasmObjectWriter::getFunctionType(const MCSymbolWasm &Symbol) { 1205 assert(Symbol.isFunction()); 1206 assert(TypeIndices.count(&Symbol)); 1207 return TypeIndices[&Symbol]; 1208 } 1209 1210 uint32_t WasmObjectWriter::getTagType(const MCSymbolWasm &Symbol) { 1211 assert(Symbol.isTag()); 1212 assert(TypeIndices.count(&Symbol)); 1213 return TypeIndices[&Symbol]; 1214 } 1215 1216 void WasmObjectWriter::registerFunctionType(const MCSymbolWasm &Symbol) { 1217 assert(Symbol.isFunction()); 1218 1219 wasm::WasmSignature S; 1220 1221 if (auto *Sig = Symbol.getSignature()) { 1222 S.Returns = Sig->Returns; 1223 S.Params = Sig->Params; 1224 } 1225 1226 auto Pair = SignatureIndices.insert(std::make_pair(S, Signatures.size())); 1227 if (Pair.second) 1228 Signatures.push_back(S); 1229 TypeIndices[&Symbol] = Pair.first->second; 1230 1231 LLVM_DEBUG(dbgs() << "registerFunctionType: " << Symbol 1232 << " new:" << Pair.second << "\n"); 1233 LLVM_DEBUG(dbgs() << " -> type index: " << Pair.first->second << "\n"); 1234 } 1235 1236 void WasmObjectWriter::registerTagType(const MCSymbolWasm &Symbol) { 1237 assert(Symbol.isTag()); 1238 1239 // TODO Currently we don't generate imported exceptions, but if we do, we 1240 // should have a way of infering types of imported exceptions. 1241 wasm::WasmSignature S; 1242 if (auto *Sig = Symbol.getSignature()) { 1243 S.Returns = Sig->Returns; 1244 S.Params = Sig->Params; 1245 } 1246 1247 auto Pair = SignatureIndices.insert(std::make_pair(S, Signatures.size())); 1248 if (Pair.second) 1249 Signatures.push_back(S); 1250 TypeIndices[&Symbol] = Pair.first->second; 1251 1252 LLVM_DEBUG(dbgs() << "registerTagType: " << Symbol << " new:" << Pair.second 1253 << "\n"); 1254 LLVM_DEBUG(dbgs() << " -> type index: " << Pair.first->second << "\n"); 1255 } 1256 1257 static bool isInSymtab(const MCSymbolWasm &Sym) { 1258 if (Sym.isUsedInReloc() || Sym.isUsedInInitArray()) 1259 return true; 1260 1261 if (Sym.isComdat() && !Sym.isDefined()) 1262 return false; 1263 1264 if (Sym.isTemporary()) 1265 return false; 1266 1267 if (Sym.isSection()) 1268 return false; 1269 1270 if (Sym.omitFromLinkingSection()) 1271 return false; 1272 1273 return true; 1274 } 1275 1276 void WasmObjectWriter::prepareImports( 1277 SmallVectorImpl<wasm::WasmImport> &Imports, MCAssembler &Asm, 1278 const MCAsmLayout &Layout) { 1279 // For now, always emit the memory import, since loads and stores are not 1280 // valid without it. In the future, we could perhaps be more clever and omit 1281 // it if there are no loads or stores. 1282 wasm::WasmImport MemImport; 1283 MemImport.Module = "env"; 1284 MemImport.Field = "__linear_memory"; 1285 MemImport.Kind = wasm::WASM_EXTERNAL_MEMORY; 1286 MemImport.Memory.Flags = is64Bit() ? wasm::WASM_LIMITS_FLAG_IS_64 1287 : wasm::WASM_LIMITS_FLAG_NONE; 1288 Imports.push_back(MemImport); 1289 1290 // Populate SignatureIndices, and Imports and WasmIndices for undefined 1291 // symbols. This must be done before populating WasmIndices for defined 1292 // symbols. 1293 for (const MCSymbol &S : Asm.symbols()) { 1294 const auto &WS = static_cast<const MCSymbolWasm &>(S); 1295 1296 // Register types for all functions, including those with private linkage 1297 // (because wasm always needs a type signature). 1298 if (WS.isFunction()) { 1299 const auto *BS = Layout.getBaseSymbol(S); 1300 if (!BS) 1301 report_fatal_error(Twine(S.getName()) + 1302 ": absolute addressing not supported!"); 1303 registerFunctionType(*cast<MCSymbolWasm>(BS)); 1304 } 1305 1306 if (WS.isTag()) 1307 registerTagType(WS); 1308 1309 if (WS.isTemporary()) 1310 continue; 1311 1312 // If the symbol is not defined in this translation unit, import it. 1313 if (!WS.isDefined() && !WS.isComdat()) { 1314 if (WS.isFunction()) { 1315 wasm::WasmImport Import; 1316 Import.Module = WS.getImportModule(); 1317 Import.Field = WS.getImportName(); 1318 Import.Kind = wasm::WASM_EXTERNAL_FUNCTION; 1319 Import.SigIndex = getFunctionType(WS); 1320 Imports.push_back(Import); 1321 assert(WasmIndices.count(&WS) == 0); 1322 WasmIndices[&WS] = NumFunctionImports++; 1323 } else if (WS.isGlobal()) { 1324 if (WS.isWeak()) 1325 report_fatal_error("undefined global symbol cannot be weak"); 1326 1327 wasm::WasmImport Import; 1328 Import.Field = WS.getImportName(); 1329 Import.Kind = wasm::WASM_EXTERNAL_GLOBAL; 1330 Import.Module = WS.getImportModule(); 1331 Import.Global = WS.getGlobalType(); 1332 Imports.push_back(Import); 1333 assert(WasmIndices.count(&WS) == 0); 1334 WasmIndices[&WS] = NumGlobalImports++; 1335 } else if (WS.isTag()) { 1336 if (WS.isWeak()) 1337 report_fatal_error("undefined tag symbol cannot be weak"); 1338 1339 wasm::WasmImport Import; 1340 Import.Module = WS.getImportModule(); 1341 Import.Field = WS.getImportName(); 1342 Import.Kind = wasm::WASM_EXTERNAL_TAG; 1343 Import.Tag.Attribute = wasm::WASM_TAG_ATTRIBUTE_EXCEPTION; 1344 Import.Tag.SigIndex = getTagType(WS); 1345 Imports.push_back(Import); 1346 assert(WasmIndices.count(&WS) == 0); 1347 WasmIndices[&WS] = NumTagImports++; 1348 } else if (WS.isTable()) { 1349 if (WS.isWeak()) 1350 report_fatal_error("undefined table symbol cannot be weak"); 1351 1352 wasm::WasmImport Import; 1353 Import.Module = WS.getImportModule(); 1354 Import.Field = WS.getImportName(); 1355 Import.Kind = wasm::WASM_EXTERNAL_TABLE; 1356 Import.Table = WS.getTableType(); 1357 Imports.push_back(Import); 1358 assert(WasmIndices.count(&WS) == 0); 1359 WasmIndices[&WS] = NumTableImports++; 1360 } 1361 } 1362 } 1363 1364 // Add imports for GOT globals 1365 for (const MCSymbol &S : Asm.symbols()) { 1366 const auto &WS = static_cast<const MCSymbolWasm &>(S); 1367 if (WS.isUsedInGOT()) { 1368 wasm::WasmImport Import; 1369 if (WS.isFunction()) 1370 Import.Module = "GOT.func"; 1371 else 1372 Import.Module = "GOT.mem"; 1373 Import.Field = WS.getName(); 1374 Import.Kind = wasm::WASM_EXTERNAL_GLOBAL; 1375 Import.Global = {wasm::WASM_TYPE_I32, true}; 1376 Imports.push_back(Import); 1377 assert(GOTIndices.count(&WS) == 0); 1378 GOTIndices[&WS] = NumGlobalImports++; 1379 } 1380 } 1381 } 1382 1383 uint64_t WasmObjectWriter::writeObject(MCAssembler &Asm, 1384 const MCAsmLayout &Layout) { 1385 support::endian::Writer MainWriter(*OS, support::little); 1386 W = &MainWriter; 1387 if (IsSplitDwarf) { 1388 uint64_t TotalSize = writeOneObject(Asm, Layout, DwoMode::NonDwoOnly); 1389 assert(DwoOS); 1390 support::endian::Writer DwoWriter(*DwoOS, support::little); 1391 W = &DwoWriter; 1392 return TotalSize + writeOneObject(Asm, Layout, DwoMode::DwoOnly); 1393 } else { 1394 return writeOneObject(Asm, Layout, DwoMode::AllSections); 1395 } 1396 } 1397 1398 uint64_t WasmObjectWriter::writeOneObject(MCAssembler &Asm, 1399 const MCAsmLayout &Layout, 1400 DwoMode Mode) { 1401 uint64_t StartOffset = W->OS.tell(); 1402 SectionCount = 0; 1403 CustomSections.clear(); 1404 1405 LLVM_DEBUG(dbgs() << "WasmObjectWriter::writeObject\n"); 1406 1407 // Collect information from the available symbols. 1408 SmallVector<WasmFunction, 4> Functions; 1409 SmallVector<uint32_t, 4> TableElems; 1410 SmallVector<wasm::WasmImport, 4> Imports; 1411 SmallVector<wasm::WasmExport, 4> Exports; 1412 SmallVector<wasm::WasmTagType, 1> Tags; 1413 SmallVector<wasm::WasmGlobal, 1> Globals; 1414 SmallVector<wasm::WasmTable, 1> Tables; 1415 SmallVector<wasm::WasmSymbolInfo, 4> SymbolInfos; 1416 SmallVector<std::pair<uint16_t, uint32_t>, 2> InitFuncs; 1417 std::map<StringRef, std::vector<WasmComdatEntry>> Comdats; 1418 uint64_t DataSize = 0; 1419 if (Mode != DwoMode::DwoOnly) { 1420 prepareImports(Imports, Asm, Layout); 1421 } 1422 1423 // Populate DataSegments and CustomSections, which must be done before 1424 // populating DataLocations. 1425 for (MCSection &Sec : Asm) { 1426 auto &Section = static_cast<MCSectionWasm &>(Sec); 1427 StringRef SectionName = Section.getName(); 1428 1429 if (Mode == DwoMode::NonDwoOnly && isDwoSection(Sec)) 1430 continue; 1431 if (Mode == DwoMode::DwoOnly && !isDwoSection(Sec)) 1432 continue; 1433 1434 LLVM_DEBUG(dbgs() << "Processing Section " << SectionName << " group " 1435 << Section.getGroup() << "\n";); 1436 1437 // .init_array sections are handled specially elsewhere. 1438 if (SectionName.startswith(".init_array")) 1439 continue; 1440 1441 // Code is handled separately 1442 if (Section.getKind().isText()) 1443 continue; 1444 1445 if (Section.isWasmData()) { 1446 uint32_t SegmentIndex = DataSegments.size(); 1447 DataSize = alignTo(DataSize, Section.getAlignment()); 1448 DataSegments.emplace_back(); 1449 WasmDataSegment &Segment = DataSegments.back(); 1450 Segment.Name = SectionName; 1451 Segment.InitFlags = Section.getPassive() 1452 ? (uint32_t)wasm::WASM_DATA_SEGMENT_IS_PASSIVE 1453 : 0; 1454 Segment.Offset = DataSize; 1455 Segment.Section = &Section; 1456 addData(Segment.Data, Section); 1457 Segment.Alignment = Log2_32(Section.getAlignment()); 1458 Segment.LinkingFlags = Section.getSegmentFlags(); 1459 DataSize += Segment.Data.size(); 1460 Section.setSegmentIndex(SegmentIndex); 1461 1462 if (const MCSymbolWasm *C = Section.getGroup()) { 1463 Comdats[C->getName()].emplace_back( 1464 WasmComdatEntry{wasm::WASM_COMDAT_DATA, SegmentIndex}); 1465 } 1466 } else { 1467 // Create custom sections 1468 assert(Sec.getKind().isMetadata()); 1469 1470 StringRef Name = SectionName; 1471 1472 // For user-defined custom sections, strip the prefix 1473 if (Name.startswith(".custom_section.")) 1474 Name = Name.substr(strlen(".custom_section.")); 1475 1476 MCSymbol *Begin = Sec.getBeginSymbol(); 1477 if (Begin) { 1478 assert(WasmIndices.count(cast<MCSymbolWasm>(Begin)) == 0); 1479 WasmIndices[cast<MCSymbolWasm>(Begin)] = CustomSections.size(); 1480 } 1481 1482 // Separate out the producers and target features sections 1483 if (Name == "producers") { 1484 ProducersSection = std::make_unique<WasmCustomSection>(Name, &Section); 1485 continue; 1486 } 1487 if (Name == "target_features") { 1488 TargetFeaturesSection = 1489 std::make_unique<WasmCustomSection>(Name, &Section); 1490 continue; 1491 } 1492 1493 // Custom sections can also belong to COMDAT groups. In this case the 1494 // decriptor's "index" field is the section index (in the final object 1495 // file), but that is not known until after layout, so it must be fixed up 1496 // later 1497 if (const MCSymbolWasm *C = Section.getGroup()) { 1498 Comdats[C->getName()].emplace_back( 1499 WasmComdatEntry{wasm::WASM_COMDAT_SECTION, 1500 static_cast<uint32_t>(CustomSections.size())}); 1501 } 1502 1503 CustomSections.emplace_back(Name, &Section); 1504 } 1505 } 1506 1507 if (Mode != DwoMode::DwoOnly) { 1508 // Populate WasmIndices and DataLocations for defined symbols. 1509 for (const MCSymbol &S : Asm.symbols()) { 1510 // Ignore unnamed temporary symbols, which aren't ever exported, imported, 1511 // or used in relocations. 1512 if (S.isTemporary() && S.getName().empty()) 1513 continue; 1514 1515 const auto &WS = static_cast<const MCSymbolWasm &>(S); 1516 LLVM_DEBUG(dbgs() 1517 << "MCSymbol: " 1518 << toString(WS.getType().getValueOr(wasm::WASM_SYMBOL_TYPE_DATA)) 1519 << " '" << S << "'" 1520 << " isDefined=" << S.isDefined() << " isExternal=" 1521 << S.isExternal() << " isTemporary=" << S.isTemporary() 1522 << " isWeak=" << WS.isWeak() << " isHidden=" << WS.isHidden() 1523 << " isVariable=" << WS.isVariable() << "\n"); 1524 1525 if (WS.isVariable()) 1526 continue; 1527 if (WS.isComdat() && !WS.isDefined()) 1528 continue; 1529 1530 if (WS.isFunction()) { 1531 unsigned Index; 1532 if (WS.isDefined()) { 1533 if (WS.getOffset() != 0) 1534 report_fatal_error( 1535 "function sections must contain one function each"); 1536 1537 if (WS.getSize() == nullptr) 1538 report_fatal_error( 1539 "function symbols must have a size set with .size"); 1540 1541 // A definition. Write out the function body. 1542 Index = NumFunctionImports + Functions.size(); 1543 WasmFunction Func; 1544 Func.SigIndex = getFunctionType(WS); 1545 Func.Sym = &WS; 1546 assert(WasmIndices.count(&WS) == 0); 1547 WasmIndices[&WS] = Index; 1548 Functions.push_back(Func); 1549 1550 auto &Section = static_cast<MCSectionWasm &>(WS.getSection()); 1551 if (const MCSymbolWasm *C = Section.getGroup()) { 1552 Comdats[C->getName()].emplace_back( 1553 WasmComdatEntry{wasm::WASM_COMDAT_FUNCTION, Index}); 1554 } 1555 1556 if (WS.hasExportName()) { 1557 wasm::WasmExport Export; 1558 Export.Name = WS.getExportName(); 1559 Export.Kind = wasm::WASM_EXTERNAL_FUNCTION; 1560 Export.Index = Index; 1561 Exports.push_back(Export); 1562 } 1563 } else { 1564 // An import; the index was assigned above. 1565 Index = WasmIndices.find(&WS)->second; 1566 } 1567 1568 LLVM_DEBUG(dbgs() << " -> function index: " << Index << "\n"); 1569 1570 } else if (WS.isData()) { 1571 if (!isInSymtab(WS)) 1572 continue; 1573 1574 if (!WS.isDefined()) { 1575 LLVM_DEBUG(dbgs() << " -> segment index: -1" 1576 << "\n"); 1577 continue; 1578 } 1579 1580 if (!WS.getSize()) 1581 report_fatal_error("data symbols must have a size set with .size: " + 1582 WS.getName()); 1583 1584 int64_t Size = 0; 1585 if (!WS.getSize()->evaluateAsAbsolute(Size, Layout)) 1586 report_fatal_error(".size expression must be evaluatable"); 1587 1588 auto &DataSection = static_cast<MCSectionWasm &>(WS.getSection()); 1589 if (!DataSection.isWasmData()) 1590 report_fatal_error("data symbols must live in a data section: " + 1591 WS.getName()); 1592 1593 // For each data symbol, export it in the symtab as a reference to the 1594 // corresponding Wasm data segment. 1595 wasm::WasmDataReference Ref = wasm::WasmDataReference{ 1596 DataSection.getSegmentIndex(), Layout.getSymbolOffset(WS), 1597 static_cast<uint64_t>(Size)}; 1598 assert(DataLocations.count(&WS) == 0); 1599 DataLocations[&WS] = Ref; 1600 LLVM_DEBUG(dbgs() << " -> segment index: " << Ref.Segment << "\n"); 1601 1602 } else if (WS.isGlobal()) { 1603 // A "true" Wasm global (currently just __stack_pointer) 1604 if (WS.isDefined()) { 1605 wasm::WasmGlobal Global; 1606 Global.Type = WS.getGlobalType(); 1607 Global.Index = NumGlobalImports + Globals.size(); 1608 switch (Global.Type.Type) { 1609 case wasm::WASM_TYPE_I32: 1610 Global.InitExpr.Opcode = wasm::WASM_OPCODE_I32_CONST; 1611 break; 1612 case wasm::WASM_TYPE_I64: 1613 Global.InitExpr.Opcode = wasm::WASM_OPCODE_I64_CONST; 1614 break; 1615 case wasm::WASM_TYPE_F32: 1616 Global.InitExpr.Opcode = wasm::WASM_OPCODE_F32_CONST; 1617 break; 1618 case wasm::WASM_TYPE_F64: 1619 Global.InitExpr.Opcode = wasm::WASM_OPCODE_F64_CONST; 1620 break; 1621 case wasm::WASM_TYPE_EXTERNREF: 1622 Global.InitExpr.Opcode = wasm::WASM_OPCODE_REF_NULL; 1623 break; 1624 default: 1625 llvm_unreachable("unexpected type"); 1626 } 1627 assert(WasmIndices.count(&WS) == 0); 1628 WasmIndices[&WS] = Global.Index; 1629 Globals.push_back(Global); 1630 } else { 1631 // An import; the index was assigned above 1632 LLVM_DEBUG(dbgs() << " -> global index: " 1633 << WasmIndices.find(&WS)->second << "\n"); 1634 } 1635 } else if (WS.isTable()) { 1636 if (WS.isDefined()) { 1637 wasm::WasmTable Table; 1638 Table.Index = NumTableImports + Tables.size(); 1639 Table.Type = WS.getTableType(); 1640 assert(WasmIndices.count(&WS) == 0); 1641 WasmIndices[&WS] = Table.Index; 1642 Tables.push_back(Table); 1643 } 1644 LLVM_DEBUG(dbgs() << " -> table index: " 1645 << WasmIndices.find(&WS)->second << "\n"); 1646 } else if (WS.isTag()) { 1647 // C++ exception symbol (__cpp_exception) 1648 unsigned Index; 1649 if (WS.isDefined()) { 1650 Index = NumTagImports + Tags.size(); 1651 wasm::WasmTagType Tag; 1652 Tag.SigIndex = getTagType(WS); 1653 Tag.Attribute = wasm::WASM_TAG_ATTRIBUTE_EXCEPTION; 1654 assert(WasmIndices.count(&WS) == 0); 1655 WasmIndices[&WS] = Index; 1656 Tags.push_back(Tag); 1657 } else { 1658 // An import; the index was assigned above. 1659 assert(WasmIndices.count(&WS) > 0); 1660 } 1661 LLVM_DEBUG(dbgs() << " -> tag index: " << WasmIndices.find(&WS)->second 1662 << "\n"); 1663 1664 } else { 1665 assert(WS.isSection()); 1666 } 1667 } 1668 1669 // Populate WasmIndices and DataLocations for aliased symbols. We need to 1670 // process these in a separate pass because we need to have processed the 1671 // target of the alias before the alias itself and the symbols are not 1672 // necessarily ordered in this way. 1673 for (const MCSymbol &S : Asm.symbols()) { 1674 if (!S.isVariable()) 1675 continue; 1676 1677 assert(S.isDefined()); 1678 1679 const auto *BS = Layout.getBaseSymbol(S); 1680 if (!BS) 1681 report_fatal_error(Twine(S.getName()) + 1682 ": absolute addressing not supported!"); 1683 const MCSymbolWasm *Base = cast<MCSymbolWasm>(BS); 1684 1685 // Find the target symbol of this weak alias and export that index 1686 const auto &WS = static_cast<const MCSymbolWasm &>(S); 1687 LLVM_DEBUG(dbgs() << WS.getName() << ": weak alias of '" << *Base 1688 << "'\n"); 1689 1690 if (Base->isFunction()) { 1691 assert(WasmIndices.count(Base) > 0); 1692 uint32_t WasmIndex = WasmIndices.find(Base)->second; 1693 assert(WasmIndices.count(&WS) == 0); 1694 WasmIndices[&WS] = WasmIndex; 1695 LLVM_DEBUG(dbgs() << " -> index:" << WasmIndex << "\n"); 1696 } else if (Base->isData()) { 1697 auto &DataSection = static_cast<MCSectionWasm &>(WS.getSection()); 1698 uint64_t Offset = Layout.getSymbolOffset(S); 1699 int64_t Size = 0; 1700 // For data symbol alias we use the size of the base symbol as the 1701 // size of the alias. When an offset from the base is involved this 1702 // can result in a offset + size goes past the end of the data section 1703 // which out object format doesn't support. So we must clamp it. 1704 if (!Base->getSize()->evaluateAsAbsolute(Size, Layout)) 1705 report_fatal_error(".size expression must be evaluatable"); 1706 const WasmDataSegment &Segment = 1707 DataSegments[DataSection.getSegmentIndex()]; 1708 Size = 1709 std::min(static_cast<uint64_t>(Size), Segment.Data.size() - Offset); 1710 wasm::WasmDataReference Ref = wasm::WasmDataReference{ 1711 DataSection.getSegmentIndex(), 1712 static_cast<uint32_t>(Layout.getSymbolOffset(S)), 1713 static_cast<uint32_t>(Size)}; 1714 DataLocations[&WS] = Ref; 1715 LLVM_DEBUG(dbgs() << " -> index:" << Ref.Segment << "\n"); 1716 } else { 1717 report_fatal_error("don't yet support global/tag aliases"); 1718 } 1719 } 1720 } 1721 1722 // Finally, populate the symbol table itself, in its "natural" order. 1723 for (const MCSymbol &S : Asm.symbols()) { 1724 const auto &WS = static_cast<const MCSymbolWasm &>(S); 1725 if (!isInSymtab(WS)) { 1726 WS.setIndex(InvalidIndex); 1727 continue; 1728 } 1729 LLVM_DEBUG(dbgs() << "adding to symtab: " << WS << "\n"); 1730 1731 uint32_t Flags = 0; 1732 if (WS.isWeak()) 1733 Flags |= wasm::WASM_SYMBOL_BINDING_WEAK; 1734 if (WS.isHidden()) 1735 Flags |= wasm::WASM_SYMBOL_VISIBILITY_HIDDEN; 1736 if (!WS.isExternal() && WS.isDefined()) 1737 Flags |= wasm::WASM_SYMBOL_BINDING_LOCAL; 1738 if (WS.isUndefined()) 1739 Flags |= wasm::WASM_SYMBOL_UNDEFINED; 1740 if (WS.isNoStrip()) { 1741 Flags |= wasm::WASM_SYMBOL_NO_STRIP; 1742 if (isEmscripten()) { 1743 Flags |= wasm::WASM_SYMBOL_EXPORTED; 1744 } 1745 } 1746 if (WS.hasImportName()) 1747 Flags |= wasm::WASM_SYMBOL_EXPLICIT_NAME; 1748 if (WS.hasExportName()) 1749 Flags |= wasm::WASM_SYMBOL_EXPORTED; 1750 1751 wasm::WasmSymbolInfo Info; 1752 Info.Name = WS.getName(); 1753 Info.Kind = WS.getType().getValueOr(wasm::WASM_SYMBOL_TYPE_DATA); 1754 Info.Flags = Flags; 1755 if (!WS.isData()) { 1756 assert(WasmIndices.count(&WS) > 0); 1757 Info.ElementIndex = WasmIndices.find(&WS)->second; 1758 } else if (WS.isDefined()) { 1759 assert(DataLocations.count(&WS) > 0); 1760 Info.DataRef = DataLocations.find(&WS)->second; 1761 } 1762 WS.setIndex(SymbolInfos.size()); 1763 SymbolInfos.emplace_back(Info); 1764 } 1765 1766 { 1767 auto HandleReloc = [&](const WasmRelocationEntry &Rel) { 1768 // Functions referenced by a relocation need to put in the table. This is 1769 // purely to make the object file's provisional values readable, and is 1770 // ignored by the linker, which re-calculates the relocations itself. 1771 if (Rel.Type != wasm::R_WASM_TABLE_INDEX_I32 && 1772 Rel.Type != wasm::R_WASM_TABLE_INDEX_I64 && 1773 Rel.Type != wasm::R_WASM_TABLE_INDEX_SLEB && 1774 Rel.Type != wasm::R_WASM_TABLE_INDEX_SLEB64 && 1775 Rel.Type != wasm::R_WASM_TABLE_INDEX_REL_SLEB && 1776 Rel.Type != wasm::R_WASM_TABLE_INDEX_REL_SLEB64) 1777 return; 1778 assert(Rel.Symbol->isFunction()); 1779 const MCSymbolWasm *Base = 1780 cast<MCSymbolWasm>(Layout.getBaseSymbol(*Rel.Symbol)); 1781 uint32_t FunctionIndex = WasmIndices.find(Base)->second; 1782 uint32_t TableIndex = TableElems.size() + InitialTableOffset; 1783 if (TableIndices.try_emplace(Base, TableIndex).second) { 1784 LLVM_DEBUG(dbgs() << " -> adding " << Base->getName() 1785 << " to table: " << TableIndex << "\n"); 1786 TableElems.push_back(FunctionIndex); 1787 registerFunctionType(*Base); 1788 } 1789 }; 1790 1791 for (const WasmRelocationEntry &RelEntry : CodeRelocations) 1792 HandleReloc(RelEntry); 1793 for (const WasmRelocationEntry &RelEntry : DataRelocations) 1794 HandleReloc(RelEntry); 1795 } 1796 1797 // Translate .init_array section contents into start functions. 1798 for (const MCSection &S : Asm) { 1799 const auto &WS = static_cast<const MCSectionWasm &>(S); 1800 if (WS.getName().startswith(".fini_array")) 1801 report_fatal_error(".fini_array sections are unsupported"); 1802 if (!WS.getName().startswith(".init_array")) 1803 continue; 1804 if (WS.getFragmentList().empty()) 1805 continue; 1806 1807 // init_array is expected to contain a single non-empty data fragment 1808 if (WS.getFragmentList().size() != 3) 1809 report_fatal_error("only one .init_array section fragment supported"); 1810 1811 auto IT = WS.begin(); 1812 const MCFragment &EmptyFrag = *IT; 1813 if (EmptyFrag.getKind() != MCFragment::FT_Data) 1814 report_fatal_error(".init_array section should be aligned"); 1815 1816 IT = std::next(IT); 1817 const MCFragment &AlignFrag = *IT; 1818 if (AlignFrag.getKind() != MCFragment::FT_Align) 1819 report_fatal_error(".init_array section should be aligned"); 1820 if (cast<MCAlignFragment>(AlignFrag).getAlignment() != (is64Bit() ? 8 : 4)) 1821 report_fatal_error(".init_array section should be aligned for pointers"); 1822 1823 const MCFragment &Frag = *std::next(IT); 1824 if (Frag.hasInstructions() || Frag.getKind() != MCFragment::FT_Data) 1825 report_fatal_error("only data supported in .init_array section"); 1826 1827 uint16_t Priority = UINT16_MAX; 1828 unsigned PrefixLength = strlen(".init_array"); 1829 if (WS.getName().size() > PrefixLength) { 1830 if (WS.getName()[PrefixLength] != '.') 1831 report_fatal_error( 1832 ".init_array section priority should start with '.'"); 1833 if (WS.getName().substr(PrefixLength + 1).getAsInteger(10, Priority)) 1834 report_fatal_error("invalid .init_array section priority"); 1835 } 1836 const auto &DataFrag = cast<MCDataFragment>(Frag); 1837 const SmallVectorImpl<char> &Contents = DataFrag.getContents(); 1838 for (const uint8_t * 1839 P = (const uint8_t *)Contents.data(), 1840 *End = (const uint8_t *)Contents.data() + Contents.size(); 1841 P != End; ++P) { 1842 if (*P != 0) 1843 report_fatal_error("non-symbolic data in .init_array section"); 1844 } 1845 for (const MCFixup &Fixup : DataFrag.getFixups()) { 1846 assert(Fixup.getKind() == 1847 MCFixup::getKindForSize(is64Bit() ? 8 : 4, false)); 1848 const MCExpr *Expr = Fixup.getValue(); 1849 auto *SymRef = dyn_cast<MCSymbolRefExpr>(Expr); 1850 if (!SymRef) 1851 report_fatal_error("fixups in .init_array should be symbol references"); 1852 const auto &TargetSym = cast<const MCSymbolWasm>(SymRef->getSymbol()); 1853 if (TargetSym.getIndex() == InvalidIndex) 1854 report_fatal_error("symbols in .init_array should exist in symtab"); 1855 if (!TargetSym.isFunction()) 1856 report_fatal_error("symbols in .init_array should be for functions"); 1857 InitFuncs.push_back( 1858 std::make_pair(Priority, TargetSym.getIndex())); 1859 } 1860 } 1861 1862 // Write out the Wasm header. 1863 writeHeader(Asm); 1864 1865 uint32_t CodeSectionIndex, DataSectionIndex; 1866 if (Mode != DwoMode::DwoOnly) { 1867 writeTypeSection(Signatures); 1868 writeImportSection(Imports, DataSize, TableElems.size()); 1869 writeFunctionSection(Functions); 1870 writeTableSection(Tables); 1871 // Skip the "memory" section; we import the memory instead. 1872 writeTagSection(Tags); 1873 writeGlobalSection(Globals); 1874 writeExportSection(Exports); 1875 const MCSymbol *IndirectFunctionTable = 1876 Asm.getContext().lookupSymbol("__indirect_function_table"); 1877 writeElemSection(cast_or_null<const MCSymbolWasm>(IndirectFunctionTable), 1878 TableElems); 1879 writeDataCountSection(); 1880 1881 CodeSectionIndex = writeCodeSection(Asm, Layout, Functions); 1882 DataSectionIndex = writeDataSection(Layout); 1883 } 1884 1885 // The Sections in the COMDAT list have placeholder indices (their index among 1886 // custom sections, rather than among all sections). Fix them up here. 1887 for (auto &Group : Comdats) { 1888 for (auto &Entry : Group.second) { 1889 if (Entry.Kind == wasm::WASM_COMDAT_SECTION) { 1890 Entry.Index += SectionCount; 1891 } 1892 } 1893 } 1894 for (auto &CustomSection : CustomSections) 1895 writeCustomSection(CustomSection, Asm, Layout); 1896 1897 if (Mode != DwoMode::DwoOnly) { 1898 writeLinkingMetaDataSection(SymbolInfos, InitFuncs, Comdats); 1899 1900 writeRelocSection(CodeSectionIndex, "CODE", CodeRelocations); 1901 writeRelocSection(DataSectionIndex, "DATA", DataRelocations); 1902 } 1903 writeCustomRelocSections(); 1904 if (ProducersSection) 1905 writeCustomSection(*ProducersSection, Asm, Layout); 1906 if (TargetFeaturesSection) 1907 writeCustomSection(*TargetFeaturesSection, Asm, Layout); 1908 1909 // TODO: Translate the .comment section to the output. 1910 return W->OS.tell() - StartOffset; 1911 } 1912 1913 std::unique_ptr<MCObjectWriter> 1914 llvm::createWasmObjectWriter(std::unique_ptr<MCWasmObjectTargetWriter> MOTW, 1915 raw_pwrite_stream &OS) { 1916 return std::make_unique<WasmObjectWriter>(std::move(MOTW), OS); 1917 } 1918 1919 std::unique_ptr<MCObjectWriter> 1920 llvm::createWasmDwoObjectWriter(std::unique_ptr<MCWasmObjectTargetWriter> MOTW, 1921 raw_pwrite_stream &OS, 1922 raw_pwrite_stream &DwoOS) { 1923 return std::make_unique<WasmObjectWriter>(std::move(MOTW), OS, DwoOS); 1924 } 1925