1 //===- lib/MC/WasmObjectWriter.cpp - Wasm File Writer ---------------------===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 // 9 // This file implements Wasm object file writer information. 10 // 11 //===----------------------------------------------------------------------===// 12 13 #include "llvm/ADT/STLExtras.h" 14 #include "llvm/BinaryFormat/Wasm.h" 15 #include "llvm/BinaryFormat/WasmTraits.h" 16 #include "llvm/Config/llvm-config.h" 17 #include "llvm/MC/MCAsmBackend.h" 18 #include "llvm/MC/MCAsmLayout.h" 19 #include "llvm/MC/MCAssembler.h" 20 #include "llvm/MC/MCContext.h" 21 #include "llvm/MC/MCExpr.h" 22 #include "llvm/MC/MCFixupKindInfo.h" 23 #include "llvm/MC/MCObjectWriter.h" 24 #include "llvm/MC/MCSectionWasm.h" 25 #include "llvm/MC/MCSymbolWasm.h" 26 #include "llvm/MC/MCValue.h" 27 #include "llvm/MC/MCWasmObjectWriter.h" 28 #include "llvm/Support/Casting.h" 29 #include "llvm/Support/Debug.h" 30 #include "llvm/Support/EndianStream.h" 31 #include "llvm/Support/ErrorHandling.h" 32 #include "llvm/Support/LEB128.h" 33 #include <vector> 34 35 using namespace llvm; 36 37 #define DEBUG_TYPE "mc" 38 39 namespace { 40 41 // When we create the indirect function table we start at 1, so that there is 42 // and empty slot at 0 and therefore calling a null function pointer will trap. 43 static const uint32_t InitialTableOffset = 1; 44 45 // For patching purposes, we need to remember where each section starts, both 46 // for patching up the section size field, and for patching up references to 47 // locations within the section. 48 struct SectionBookkeeping { 49 // Where the size of the section is written. 50 uint64_t SizeOffset; 51 // Where the section header ends (without custom section name). 52 uint64_t PayloadOffset; 53 // Where the contents of the section starts. 54 uint64_t ContentsOffset; 55 uint32_t Index; 56 }; 57 58 // A wasm data segment. A wasm binary contains only a single data section 59 // but that can contain many segments, each with their own virtual location 60 // in memory. Each MCSection data created by llvm is modeled as its own 61 // wasm data segment. 62 struct WasmDataSegment { 63 MCSectionWasm *Section; 64 StringRef Name; 65 uint32_t InitFlags; 66 uint64_t Offset; 67 uint32_t Alignment; 68 uint32_t LinkingFlags; 69 SmallVector<char, 4> Data; 70 }; 71 72 // A wasm function to be written into the function section. 73 struct WasmFunction { 74 uint32_t SigIndex; 75 MCSection *Section; 76 }; 77 78 // A wasm global to be written into the global section. 79 struct WasmGlobal { 80 wasm::WasmGlobalType Type; 81 uint64_t InitialValue; 82 }; 83 84 // Information about a single item which is part of a COMDAT. For each data 85 // segment or function which is in the COMDAT, there is a corresponding 86 // WasmComdatEntry. 87 struct WasmComdatEntry { 88 unsigned Kind; 89 uint32_t Index; 90 }; 91 92 // Information about a single relocation. 93 struct WasmRelocationEntry { 94 uint64_t Offset; // Where is the relocation. 95 const MCSymbolWasm *Symbol; // The symbol to relocate with. 96 int64_t Addend; // A value to add to the symbol. 97 unsigned Type; // The type of the relocation. 98 const MCSectionWasm *FixupSection; // The section the relocation is targeting. 99 100 WasmRelocationEntry(uint64_t Offset, const MCSymbolWasm *Symbol, 101 int64_t Addend, unsigned Type, 102 const MCSectionWasm *FixupSection) 103 : Offset(Offset), Symbol(Symbol), Addend(Addend), Type(Type), 104 FixupSection(FixupSection) {} 105 106 bool hasAddend() const { return wasm::relocTypeHasAddend(Type); } 107 108 void print(raw_ostream &Out) const { 109 Out << wasm::relocTypetoString(Type) << " Off=" << Offset 110 << ", Sym=" << *Symbol << ", Addend=" << Addend 111 << ", FixupSection=" << FixupSection->getName(); 112 } 113 114 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP) 115 LLVM_DUMP_METHOD void dump() const { print(dbgs()); } 116 #endif 117 }; 118 119 static const uint32_t InvalidIndex = -1; 120 121 struct WasmCustomSection { 122 123 StringRef Name; 124 MCSectionWasm *Section; 125 126 uint32_t OutputContentsOffset = 0; 127 uint32_t OutputIndex = InvalidIndex; 128 129 WasmCustomSection(StringRef Name, MCSectionWasm *Section) 130 : Name(Name), Section(Section) {} 131 }; 132 133 #if !defined(NDEBUG) 134 raw_ostream &operator<<(raw_ostream &OS, const WasmRelocationEntry &Rel) { 135 Rel.print(OS); 136 return OS; 137 } 138 #endif 139 140 // Write Value as an (unsigned) LEB value at offset Offset in Stream, padded 141 // to allow patching. 142 template <typename T, int W> 143 void writePatchableULEB(raw_pwrite_stream &Stream, T Value, uint64_t Offset) { 144 uint8_t Buffer[W]; 145 unsigned SizeLen = encodeULEB128(Value, Buffer, W); 146 assert(SizeLen == W); 147 Stream.pwrite((char *)Buffer, SizeLen, Offset); 148 } 149 150 // Write Value as an signed LEB value at offset Offset in Stream, padded 151 // to allow patching. 152 template <typename T, int W> 153 void writePatchableSLEB(raw_pwrite_stream &Stream, T Value, uint64_t Offset) { 154 uint8_t Buffer[W]; 155 unsigned SizeLen = encodeSLEB128(Value, Buffer, W); 156 assert(SizeLen == W); 157 Stream.pwrite((char *)Buffer, SizeLen, Offset); 158 } 159 160 static void writePatchableU32(raw_pwrite_stream &Stream, uint32_t Value, 161 uint64_t Offset) { 162 writePatchableULEB<uint32_t, 5>(Stream, Value, Offset); 163 } 164 165 static void writePatchableS32(raw_pwrite_stream &Stream, int32_t Value, 166 uint64_t Offset) { 167 writePatchableSLEB<int32_t, 5>(Stream, Value, Offset); 168 } 169 170 static void writePatchableU64(raw_pwrite_stream &Stream, uint64_t Value, 171 uint64_t Offset) { 172 writePatchableSLEB<uint64_t, 10>(Stream, Value, Offset); 173 } 174 175 static void writePatchableS64(raw_pwrite_stream &Stream, int64_t Value, 176 uint64_t Offset) { 177 writePatchableSLEB<int64_t, 10>(Stream, Value, Offset); 178 } 179 180 // Write Value as a plain integer value at offset Offset in Stream. 181 static void patchI32(raw_pwrite_stream &Stream, uint32_t Value, 182 uint64_t Offset) { 183 uint8_t Buffer[4]; 184 support::endian::write32le(Buffer, Value); 185 Stream.pwrite((char *)Buffer, sizeof(Buffer), Offset); 186 } 187 188 static void patchI64(raw_pwrite_stream &Stream, uint64_t Value, 189 uint64_t Offset) { 190 uint8_t Buffer[8]; 191 support::endian::write64le(Buffer, Value); 192 Stream.pwrite((char *)Buffer, sizeof(Buffer), Offset); 193 } 194 195 bool isDwoSection(const MCSection &Sec) { 196 return Sec.getName().endswith(".dwo"); 197 } 198 199 class WasmObjectWriter : public MCObjectWriter { 200 support::endian::Writer *W; 201 202 /// The target specific Wasm writer instance. 203 std::unique_ptr<MCWasmObjectTargetWriter> TargetObjectWriter; 204 205 // Relocations for fixing up references in the code section. 206 std::vector<WasmRelocationEntry> CodeRelocations; 207 // Relocations for fixing up references in the data section. 208 std::vector<WasmRelocationEntry> DataRelocations; 209 210 // Index values to use for fixing up call_indirect type indices. 211 // Maps function symbols to the index of the type of the function 212 DenseMap<const MCSymbolWasm *, uint32_t> TypeIndices; 213 // Maps function symbols to the table element index space. Used 214 // for TABLE_INDEX relocation types (i.e. address taken functions). 215 DenseMap<const MCSymbolWasm *, uint32_t> TableIndices; 216 // Maps function/global/table symbols to the 217 // function/global/table/tag/section index space. 218 DenseMap<const MCSymbolWasm *, uint32_t> WasmIndices; 219 DenseMap<const MCSymbolWasm *, uint32_t> GOTIndices; 220 // Maps data symbols to the Wasm segment and offset/size with the segment. 221 DenseMap<const MCSymbolWasm *, wasm::WasmDataReference> DataLocations; 222 223 // Stores output data (index, relocations, content offset) for custom 224 // section. 225 std::vector<WasmCustomSection> CustomSections; 226 std::unique_ptr<WasmCustomSection> ProducersSection; 227 std::unique_ptr<WasmCustomSection> TargetFeaturesSection; 228 // Relocations for fixing up references in the custom sections. 229 DenseMap<const MCSectionWasm *, std::vector<WasmRelocationEntry>> 230 CustomSectionsRelocations; 231 232 // Map from section to defining function symbol. 233 DenseMap<const MCSection *, const MCSymbol *> SectionFunctions; 234 235 DenseMap<wasm::WasmSignature, uint32_t> SignatureIndices; 236 SmallVector<wasm::WasmSignature, 4> Signatures; 237 SmallVector<WasmDataSegment, 4> DataSegments; 238 unsigned NumFunctionImports = 0; 239 unsigned NumGlobalImports = 0; 240 unsigned NumTableImports = 0; 241 unsigned NumTagImports = 0; 242 uint32_t SectionCount = 0; 243 244 enum class DwoMode { 245 AllSections, 246 NonDwoOnly, 247 DwoOnly, 248 }; 249 bool IsSplitDwarf = false; 250 raw_pwrite_stream *OS = nullptr; 251 raw_pwrite_stream *DwoOS = nullptr; 252 253 // TargetObjectWriter wranppers. 254 bool is64Bit() const { return TargetObjectWriter->is64Bit(); } 255 bool isEmscripten() const { return TargetObjectWriter->isEmscripten(); } 256 257 void startSection(SectionBookkeeping &Section, unsigned SectionId); 258 void startCustomSection(SectionBookkeeping &Section, StringRef Name); 259 void endSection(SectionBookkeeping &Section); 260 261 public: 262 WasmObjectWriter(std::unique_ptr<MCWasmObjectTargetWriter> MOTW, 263 raw_pwrite_stream &OS_) 264 : TargetObjectWriter(std::move(MOTW)), OS(&OS_) {} 265 266 WasmObjectWriter(std::unique_ptr<MCWasmObjectTargetWriter> MOTW, 267 raw_pwrite_stream &OS_, raw_pwrite_stream &DwoOS_) 268 : TargetObjectWriter(std::move(MOTW)), IsSplitDwarf(true), OS(&OS_), 269 DwoOS(&DwoOS_) {} 270 271 private: 272 void reset() override { 273 CodeRelocations.clear(); 274 DataRelocations.clear(); 275 TypeIndices.clear(); 276 WasmIndices.clear(); 277 GOTIndices.clear(); 278 TableIndices.clear(); 279 DataLocations.clear(); 280 CustomSections.clear(); 281 ProducersSection.reset(); 282 TargetFeaturesSection.reset(); 283 CustomSectionsRelocations.clear(); 284 SignatureIndices.clear(); 285 Signatures.clear(); 286 DataSegments.clear(); 287 SectionFunctions.clear(); 288 NumFunctionImports = 0; 289 NumGlobalImports = 0; 290 NumTableImports = 0; 291 MCObjectWriter::reset(); 292 } 293 294 void writeHeader(const MCAssembler &Asm); 295 296 void recordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout, 297 const MCFragment *Fragment, const MCFixup &Fixup, 298 MCValue Target, uint64_t &FixedValue) override; 299 300 void executePostLayoutBinding(MCAssembler &Asm, 301 const MCAsmLayout &Layout) override; 302 void prepareImports(SmallVectorImpl<wasm::WasmImport> &Imports, 303 MCAssembler &Asm, const MCAsmLayout &Layout); 304 uint64_t writeObject(MCAssembler &Asm, const MCAsmLayout &Layout) override; 305 306 uint64_t writeOneObject(MCAssembler &Asm, const MCAsmLayout &Layout, 307 DwoMode Mode); 308 309 void writeString(const StringRef Str) { 310 encodeULEB128(Str.size(), W->OS); 311 W->OS << Str; 312 } 313 314 void writeStringWithAlignment(const StringRef Str, unsigned Alignment); 315 316 void writeI32(int32_t val) { 317 char Buffer[4]; 318 support::endian::write32le(Buffer, val); 319 W->OS.write(Buffer, sizeof(Buffer)); 320 } 321 322 void writeI64(int64_t val) { 323 char Buffer[8]; 324 support::endian::write64le(Buffer, val); 325 W->OS.write(Buffer, sizeof(Buffer)); 326 } 327 328 void writeValueType(wasm::ValType Ty) { W->OS << static_cast<char>(Ty); } 329 330 void writeTypeSection(ArrayRef<wasm::WasmSignature> Signatures); 331 void writeImportSection(ArrayRef<wasm::WasmImport> Imports, uint64_t DataSize, 332 uint32_t NumElements); 333 void writeFunctionSection(ArrayRef<WasmFunction> Functions); 334 void writeExportSection(ArrayRef<wasm::WasmExport> Exports); 335 void writeElemSection(const MCSymbolWasm *IndirectFunctionTable, 336 ArrayRef<uint32_t> TableElems); 337 void writeDataCountSection(); 338 uint32_t writeCodeSection(const MCAssembler &Asm, const MCAsmLayout &Layout, 339 ArrayRef<WasmFunction> Functions); 340 uint32_t writeDataSection(const MCAsmLayout &Layout); 341 void writeTagSection(ArrayRef<uint32_t> TagTypes); 342 void writeGlobalSection(ArrayRef<wasm::WasmGlobal> Globals); 343 void writeTableSection(ArrayRef<wasm::WasmTable> Tables); 344 void writeRelocSection(uint32_t SectionIndex, StringRef Name, 345 std::vector<WasmRelocationEntry> &Relocations); 346 void writeLinkingMetaDataSection( 347 ArrayRef<wasm::WasmSymbolInfo> SymbolInfos, 348 ArrayRef<std::pair<uint16_t, uint32_t>> InitFuncs, 349 const std::map<StringRef, std::vector<WasmComdatEntry>> &Comdats); 350 void writeCustomSection(WasmCustomSection &CustomSection, 351 const MCAssembler &Asm, const MCAsmLayout &Layout); 352 void writeCustomRelocSections(); 353 354 uint64_t getProvisionalValue(const WasmRelocationEntry &RelEntry, 355 const MCAsmLayout &Layout); 356 void applyRelocations(ArrayRef<WasmRelocationEntry> Relocations, 357 uint64_t ContentsOffset, const MCAsmLayout &Layout); 358 359 uint32_t getRelocationIndexValue(const WasmRelocationEntry &RelEntry); 360 uint32_t getFunctionType(const MCSymbolWasm &Symbol); 361 uint32_t getTagType(const MCSymbolWasm &Symbol); 362 void registerFunctionType(const MCSymbolWasm &Symbol); 363 void registerTagType(const MCSymbolWasm &Symbol); 364 }; 365 366 } // end anonymous namespace 367 368 // Write out a section header and a patchable section size field. 369 void WasmObjectWriter::startSection(SectionBookkeeping &Section, 370 unsigned SectionId) { 371 LLVM_DEBUG(dbgs() << "startSection " << SectionId << "\n"); 372 W->OS << char(SectionId); 373 374 Section.SizeOffset = W->OS.tell(); 375 376 // The section size. We don't know the size yet, so reserve enough space 377 // for any 32-bit value; we'll patch it later. 378 encodeULEB128(0, W->OS, 5); 379 380 // The position where the section starts, for measuring its size. 381 Section.ContentsOffset = W->OS.tell(); 382 Section.PayloadOffset = W->OS.tell(); 383 Section.Index = SectionCount++; 384 } 385 386 // Write a string with extra paddings for trailing alignment 387 // TODO: support alignment at asm and llvm level? 388 void WasmObjectWriter::writeStringWithAlignment(const StringRef Str, 389 unsigned Alignment) { 390 391 // Calculate the encoded size of str length and add pads based on it and 392 // alignment. 393 raw_null_ostream NullOS; 394 uint64_t StrSizeLength = encodeULEB128(Str.size(), NullOS); 395 uint64_t Offset = W->OS.tell() + StrSizeLength + Str.size(); 396 uint64_t Paddings = offsetToAlignment(Offset, Align(Alignment)); 397 Offset += Paddings; 398 399 // LEB128 greater than 5 bytes is invalid 400 assert((StrSizeLength + Paddings) <= 5 && "too long string to align"); 401 402 encodeSLEB128(Str.size(), W->OS, StrSizeLength + Paddings); 403 W->OS << Str; 404 405 assert(W->OS.tell() == Offset && "invalid padding"); 406 } 407 408 void WasmObjectWriter::startCustomSection(SectionBookkeeping &Section, 409 StringRef Name) { 410 LLVM_DEBUG(dbgs() << "startCustomSection " << Name << "\n"); 411 startSection(Section, wasm::WASM_SEC_CUSTOM); 412 413 // The position where the section header ends, for measuring its size. 414 Section.PayloadOffset = W->OS.tell(); 415 416 // Custom sections in wasm also have a string identifier. 417 if (Name != "__clangast") { 418 writeString(Name); 419 } else { 420 // The on-disk hashtable in clangast needs to be aligned by 4 bytes. 421 writeStringWithAlignment(Name, 4); 422 } 423 424 // The position where the custom section starts. 425 Section.ContentsOffset = W->OS.tell(); 426 } 427 428 // Now that the section is complete and we know how big it is, patch up the 429 // section size field at the start of the section. 430 void WasmObjectWriter::endSection(SectionBookkeeping &Section) { 431 uint64_t Size = W->OS.tell(); 432 // /dev/null doesn't support seek/tell and can report offset of 0. 433 // Simply skip this patching in that case. 434 if (!Size) 435 return; 436 437 Size -= Section.PayloadOffset; 438 if (uint32_t(Size) != Size) 439 report_fatal_error("section size does not fit in a uint32_t"); 440 441 LLVM_DEBUG(dbgs() << "endSection size=" << Size << "\n"); 442 443 // Write the final section size to the payload_len field, which follows 444 // the section id byte. 445 writePatchableU32(static_cast<raw_pwrite_stream &>(W->OS), Size, 446 Section.SizeOffset); 447 } 448 449 // Emit the Wasm header. 450 void WasmObjectWriter::writeHeader(const MCAssembler &Asm) { 451 W->OS.write(wasm::WasmMagic, sizeof(wasm::WasmMagic)); 452 W->write<uint32_t>(wasm::WasmVersion); 453 } 454 455 void WasmObjectWriter::executePostLayoutBinding(MCAssembler &Asm, 456 const MCAsmLayout &Layout) { 457 // Some compilation units require the indirect function table to be present 458 // but don't explicitly reference it. This is the case for call_indirect 459 // without the reference-types feature, and also function bitcasts in all 460 // cases. In those cases the __indirect_function_table has the 461 // WASM_SYMBOL_NO_STRIP attribute. Here we make sure this symbol makes it to 462 // the assembler, if needed. 463 if (auto *Sym = Asm.getContext().lookupSymbol("__indirect_function_table")) { 464 const auto *WasmSym = static_cast<const MCSymbolWasm *>(Sym); 465 if (WasmSym->isNoStrip()) 466 Asm.registerSymbol(*Sym); 467 } 468 469 // Build a map of sections to the function that defines them, for use 470 // in recordRelocation. 471 for (const MCSymbol &S : Asm.symbols()) { 472 const auto &WS = static_cast<const MCSymbolWasm &>(S); 473 if (WS.isDefined() && WS.isFunction() && !WS.isVariable()) { 474 const auto &Sec = static_cast<const MCSectionWasm &>(S.getSection()); 475 auto Pair = SectionFunctions.insert(std::make_pair(&Sec, &S)); 476 if (!Pair.second) 477 report_fatal_error("section already has a defining function: " + 478 Sec.getName()); 479 } 480 } 481 } 482 483 void WasmObjectWriter::recordRelocation(MCAssembler &Asm, 484 const MCAsmLayout &Layout, 485 const MCFragment *Fragment, 486 const MCFixup &Fixup, MCValue Target, 487 uint64_t &FixedValue) { 488 // The WebAssembly backend should never generate FKF_IsPCRel fixups 489 assert(!(Asm.getBackend().getFixupKindInfo(Fixup.getKind()).Flags & 490 MCFixupKindInfo::FKF_IsPCRel)); 491 492 const auto &FixupSection = cast<MCSectionWasm>(*Fragment->getParent()); 493 uint64_t C = Target.getConstant(); 494 uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset(); 495 MCContext &Ctx = Asm.getContext(); 496 bool IsLocRel = false; 497 498 if (const MCSymbolRefExpr *RefB = Target.getSymB()) { 499 500 const auto &SymB = cast<MCSymbolWasm>(RefB->getSymbol()); 501 502 if (FixupSection.getKind().isText()) { 503 Ctx.reportError(Fixup.getLoc(), 504 Twine("symbol '") + SymB.getName() + 505 "' unsupported subtraction expression used in " 506 "relocation in code section."); 507 return; 508 } 509 510 if (SymB.isUndefined()) { 511 Ctx.reportError(Fixup.getLoc(), 512 Twine("symbol '") + SymB.getName() + 513 "' can not be undefined in a subtraction expression"); 514 return; 515 } 516 const MCSection &SecB = SymB.getSection(); 517 if (&SecB != &FixupSection) { 518 Ctx.reportError(Fixup.getLoc(), 519 Twine("symbol '") + SymB.getName() + 520 "' can not be placed in a different section"); 521 return; 522 } 523 IsLocRel = true; 524 C += FixupOffset - Layout.getSymbolOffset(SymB); 525 } 526 527 // We either rejected the fixup or folded B into C at this point. 528 const MCSymbolRefExpr *RefA = Target.getSymA(); 529 const auto *SymA = cast<MCSymbolWasm>(&RefA->getSymbol()); 530 531 // The .init_array isn't translated as data, so don't do relocations in it. 532 if (FixupSection.getName().startswith(".init_array")) { 533 SymA->setUsedInInitArray(); 534 return; 535 } 536 537 if (SymA->isVariable()) { 538 const MCExpr *Expr = SymA->getVariableValue(); 539 if (const auto *Inner = dyn_cast<MCSymbolRefExpr>(Expr)) 540 if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF) 541 llvm_unreachable("weakref used in reloc not yet implemented"); 542 } 543 544 // Put any constant offset in an addend. Offsets can be negative, and 545 // LLVM expects wrapping, in contrast to wasm's immediates which can't 546 // be negative and don't wrap. 547 FixedValue = 0; 548 549 unsigned Type = 550 TargetObjectWriter->getRelocType(Target, Fixup, FixupSection, IsLocRel); 551 552 // Absolute offset within a section or a function. 553 // Currently only supported for for metadata sections. 554 // See: test/MC/WebAssembly/blockaddress.ll 555 if ((Type == wasm::R_WASM_FUNCTION_OFFSET_I32 || 556 Type == wasm::R_WASM_FUNCTION_OFFSET_I64 || 557 Type == wasm::R_WASM_SECTION_OFFSET_I32) && 558 SymA->isDefined()) { 559 // SymA can be a temp data symbol that represents a function (in which case 560 // it needs to be replaced by the section symbol), [XXX and it apparently 561 // later gets changed again to a func symbol?] or it can be a real 562 // function symbol, in which case it can be left as-is. 563 564 if (!FixupSection.getKind().isMetadata()) 565 report_fatal_error("relocations for function or section offsets are " 566 "only supported in metadata sections"); 567 568 const MCSymbol *SectionSymbol = nullptr; 569 const MCSection &SecA = SymA->getSection(); 570 if (SecA.getKind().isText()) { 571 auto SecSymIt = SectionFunctions.find(&SecA); 572 if (SecSymIt == SectionFunctions.end()) 573 report_fatal_error("section doesn\'t have defining symbol"); 574 SectionSymbol = SecSymIt->second; 575 } else { 576 SectionSymbol = SecA.getBeginSymbol(); 577 } 578 if (!SectionSymbol) 579 report_fatal_error("section symbol is required for relocation"); 580 581 C += Layout.getSymbolOffset(*SymA); 582 SymA = cast<MCSymbolWasm>(SectionSymbol); 583 } 584 585 if (Type == wasm::R_WASM_TABLE_INDEX_REL_SLEB || 586 Type == wasm::R_WASM_TABLE_INDEX_REL_SLEB64 || 587 Type == wasm::R_WASM_TABLE_INDEX_SLEB || 588 Type == wasm::R_WASM_TABLE_INDEX_SLEB64 || 589 Type == wasm::R_WASM_TABLE_INDEX_I32 || 590 Type == wasm::R_WASM_TABLE_INDEX_I64) { 591 // TABLE_INDEX relocs implicitly use the default indirect function table. 592 // We require the function table to have already been defined. 593 auto TableName = "__indirect_function_table"; 594 MCSymbolWasm *Sym = cast_or_null<MCSymbolWasm>(Ctx.lookupSymbol(TableName)); 595 if (!Sym) { 596 report_fatal_error("missing indirect function table symbol"); 597 } else { 598 if (!Sym->isFunctionTable()) 599 report_fatal_error("__indirect_function_table symbol has wrong type"); 600 // Ensure that __indirect_function_table reaches the output. 601 Sym->setNoStrip(); 602 Asm.registerSymbol(*Sym); 603 } 604 } 605 606 // Relocation other than R_WASM_TYPE_INDEX_LEB are required to be 607 // against a named symbol. 608 if (Type != wasm::R_WASM_TYPE_INDEX_LEB) { 609 if (SymA->getName().empty()) 610 report_fatal_error("relocations against un-named temporaries are not yet " 611 "supported by wasm"); 612 613 SymA->setUsedInReloc(); 614 } 615 616 switch (RefA->getKind()) { 617 case MCSymbolRefExpr::VK_GOT: 618 case MCSymbolRefExpr::VK_WASM_GOT_TLS: 619 SymA->setUsedInGOT(); 620 break; 621 default: 622 break; 623 } 624 625 WasmRelocationEntry Rec(FixupOffset, SymA, C, Type, &FixupSection); 626 LLVM_DEBUG(dbgs() << "WasmReloc: " << Rec << "\n"); 627 628 if (FixupSection.isWasmData()) { 629 DataRelocations.push_back(Rec); 630 } else if (FixupSection.getKind().isText()) { 631 CodeRelocations.push_back(Rec); 632 } else if (FixupSection.getKind().isMetadata()) { 633 CustomSectionsRelocations[&FixupSection].push_back(Rec); 634 } else { 635 llvm_unreachable("unexpected section type"); 636 } 637 } 638 639 // Compute a value to write into the code at the location covered 640 // by RelEntry. This value isn't used by the static linker; it just serves 641 // to make the object format more readable and more likely to be directly 642 // useable. 643 uint64_t 644 WasmObjectWriter::getProvisionalValue(const WasmRelocationEntry &RelEntry, 645 const MCAsmLayout &Layout) { 646 if ((RelEntry.Type == wasm::R_WASM_GLOBAL_INDEX_LEB || 647 RelEntry.Type == wasm::R_WASM_GLOBAL_INDEX_I32) && 648 !RelEntry.Symbol->isGlobal()) { 649 assert(GOTIndices.count(RelEntry.Symbol) > 0 && "symbol not found in GOT index space"); 650 return GOTIndices[RelEntry.Symbol]; 651 } 652 653 switch (RelEntry.Type) { 654 case wasm::R_WASM_TABLE_INDEX_REL_SLEB: 655 case wasm::R_WASM_TABLE_INDEX_REL_SLEB64: 656 case wasm::R_WASM_TABLE_INDEX_SLEB: 657 case wasm::R_WASM_TABLE_INDEX_SLEB64: 658 case wasm::R_WASM_TABLE_INDEX_I32: 659 case wasm::R_WASM_TABLE_INDEX_I64: { 660 // Provisional value is table address of the resolved symbol itself 661 const MCSymbolWasm *Base = 662 cast<MCSymbolWasm>(Layout.getBaseSymbol(*RelEntry.Symbol)); 663 assert(Base->isFunction()); 664 if (RelEntry.Type == wasm::R_WASM_TABLE_INDEX_REL_SLEB || 665 RelEntry.Type == wasm::R_WASM_TABLE_INDEX_REL_SLEB64) 666 return TableIndices[Base] - InitialTableOffset; 667 else 668 return TableIndices[Base]; 669 } 670 case wasm::R_WASM_TYPE_INDEX_LEB: 671 // Provisional value is same as the index 672 return getRelocationIndexValue(RelEntry); 673 case wasm::R_WASM_FUNCTION_INDEX_LEB: 674 case wasm::R_WASM_GLOBAL_INDEX_LEB: 675 case wasm::R_WASM_GLOBAL_INDEX_I32: 676 case wasm::R_WASM_TAG_INDEX_LEB: 677 case wasm::R_WASM_TABLE_NUMBER_LEB: 678 // Provisional value is function/global/tag Wasm index 679 assert(WasmIndices.count(RelEntry.Symbol) > 0 && "symbol not found in wasm index space"); 680 return WasmIndices[RelEntry.Symbol]; 681 case wasm::R_WASM_FUNCTION_OFFSET_I32: 682 case wasm::R_WASM_FUNCTION_OFFSET_I64: 683 case wasm::R_WASM_SECTION_OFFSET_I32: { 684 if (!RelEntry.Symbol->isDefined()) 685 return 0; 686 const auto &Section = 687 static_cast<const MCSectionWasm &>(RelEntry.Symbol->getSection()); 688 return Section.getSectionOffset() + RelEntry.Addend; 689 } 690 case wasm::R_WASM_MEMORY_ADDR_LEB: 691 case wasm::R_WASM_MEMORY_ADDR_LEB64: 692 case wasm::R_WASM_MEMORY_ADDR_SLEB: 693 case wasm::R_WASM_MEMORY_ADDR_SLEB64: 694 case wasm::R_WASM_MEMORY_ADDR_REL_SLEB: 695 case wasm::R_WASM_MEMORY_ADDR_REL_SLEB64: 696 case wasm::R_WASM_MEMORY_ADDR_I32: 697 case wasm::R_WASM_MEMORY_ADDR_I64: 698 case wasm::R_WASM_MEMORY_ADDR_TLS_SLEB: 699 case wasm::R_WASM_MEMORY_ADDR_TLS_SLEB64: 700 case wasm::R_WASM_MEMORY_ADDR_LOCREL_I32: { 701 // Provisional value is address of the global plus the offset 702 // For undefined symbols, use zero 703 if (!RelEntry.Symbol->isDefined()) 704 return 0; 705 const wasm::WasmDataReference &SymRef = DataLocations[RelEntry.Symbol]; 706 const WasmDataSegment &Segment = DataSegments[SymRef.Segment]; 707 // Ignore overflow. LLVM allows address arithmetic to silently wrap. 708 return Segment.Offset + SymRef.Offset + RelEntry.Addend; 709 } 710 default: 711 llvm_unreachable("invalid relocation type"); 712 } 713 } 714 715 static void addData(SmallVectorImpl<char> &DataBytes, 716 MCSectionWasm &DataSection) { 717 LLVM_DEBUG(errs() << "addData: " << DataSection.getName() << "\n"); 718 719 DataBytes.resize(alignTo(DataBytes.size(), DataSection.getAlign())); 720 721 for (const MCFragment &Frag : DataSection) { 722 if (Frag.hasInstructions()) 723 report_fatal_error("only data supported in data sections"); 724 725 if (auto *Align = dyn_cast<MCAlignFragment>(&Frag)) { 726 if (Align->getValueSize() != 1) 727 report_fatal_error("only byte values supported for alignment"); 728 // If nops are requested, use zeros, as this is the data section. 729 uint8_t Value = Align->hasEmitNops() ? 0 : Align->getValue(); 730 uint64_t Size = 731 std::min<uint64_t>(alignTo(DataBytes.size(), Align->getAlignment()), 732 DataBytes.size() + Align->getMaxBytesToEmit()); 733 DataBytes.resize(Size, Value); 734 } else if (auto *Fill = dyn_cast<MCFillFragment>(&Frag)) { 735 int64_t NumValues; 736 if (!Fill->getNumValues().evaluateAsAbsolute(NumValues)) 737 llvm_unreachable("The fill should be an assembler constant"); 738 DataBytes.insert(DataBytes.end(), Fill->getValueSize() * NumValues, 739 Fill->getValue()); 740 } else if (auto *LEB = dyn_cast<MCLEBFragment>(&Frag)) { 741 const SmallVectorImpl<char> &Contents = LEB->getContents(); 742 llvm::append_range(DataBytes, Contents); 743 } else { 744 const auto &DataFrag = cast<MCDataFragment>(Frag); 745 const SmallVectorImpl<char> &Contents = DataFrag.getContents(); 746 llvm::append_range(DataBytes, Contents); 747 } 748 } 749 750 LLVM_DEBUG(dbgs() << "addData -> " << DataBytes.size() << "\n"); 751 } 752 753 uint32_t 754 WasmObjectWriter::getRelocationIndexValue(const WasmRelocationEntry &RelEntry) { 755 if (RelEntry.Type == wasm::R_WASM_TYPE_INDEX_LEB) { 756 if (!TypeIndices.count(RelEntry.Symbol)) 757 report_fatal_error("symbol not found in type index space: " + 758 RelEntry.Symbol->getName()); 759 return TypeIndices[RelEntry.Symbol]; 760 } 761 762 return RelEntry.Symbol->getIndex(); 763 } 764 765 // Apply the portions of the relocation records that we can handle ourselves 766 // directly. 767 void WasmObjectWriter::applyRelocations( 768 ArrayRef<WasmRelocationEntry> Relocations, uint64_t ContentsOffset, 769 const MCAsmLayout &Layout) { 770 auto &Stream = static_cast<raw_pwrite_stream &>(W->OS); 771 for (const WasmRelocationEntry &RelEntry : Relocations) { 772 uint64_t Offset = ContentsOffset + 773 RelEntry.FixupSection->getSectionOffset() + 774 RelEntry.Offset; 775 776 LLVM_DEBUG(dbgs() << "applyRelocation: " << RelEntry << "\n"); 777 uint64_t Value = getProvisionalValue(RelEntry, Layout); 778 779 switch (RelEntry.Type) { 780 case wasm::R_WASM_FUNCTION_INDEX_LEB: 781 case wasm::R_WASM_TYPE_INDEX_LEB: 782 case wasm::R_WASM_GLOBAL_INDEX_LEB: 783 case wasm::R_WASM_MEMORY_ADDR_LEB: 784 case wasm::R_WASM_TAG_INDEX_LEB: 785 case wasm::R_WASM_TABLE_NUMBER_LEB: 786 writePatchableU32(Stream, Value, Offset); 787 break; 788 case wasm::R_WASM_MEMORY_ADDR_LEB64: 789 writePatchableU64(Stream, Value, Offset); 790 break; 791 case wasm::R_WASM_TABLE_INDEX_I32: 792 case wasm::R_WASM_MEMORY_ADDR_I32: 793 case wasm::R_WASM_FUNCTION_OFFSET_I32: 794 case wasm::R_WASM_SECTION_OFFSET_I32: 795 case wasm::R_WASM_GLOBAL_INDEX_I32: 796 case wasm::R_WASM_MEMORY_ADDR_LOCREL_I32: 797 patchI32(Stream, Value, Offset); 798 break; 799 case wasm::R_WASM_TABLE_INDEX_I64: 800 case wasm::R_WASM_MEMORY_ADDR_I64: 801 case wasm::R_WASM_FUNCTION_OFFSET_I64: 802 patchI64(Stream, Value, Offset); 803 break; 804 case wasm::R_WASM_TABLE_INDEX_SLEB: 805 case wasm::R_WASM_TABLE_INDEX_REL_SLEB: 806 case wasm::R_WASM_MEMORY_ADDR_SLEB: 807 case wasm::R_WASM_MEMORY_ADDR_REL_SLEB: 808 case wasm::R_WASM_MEMORY_ADDR_TLS_SLEB: 809 writePatchableS32(Stream, Value, Offset); 810 break; 811 case wasm::R_WASM_TABLE_INDEX_SLEB64: 812 case wasm::R_WASM_TABLE_INDEX_REL_SLEB64: 813 case wasm::R_WASM_MEMORY_ADDR_SLEB64: 814 case wasm::R_WASM_MEMORY_ADDR_REL_SLEB64: 815 case wasm::R_WASM_MEMORY_ADDR_TLS_SLEB64: 816 writePatchableS64(Stream, Value, Offset); 817 break; 818 default: 819 llvm_unreachable("invalid relocation type"); 820 } 821 } 822 } 823 824 void WasmObjectWriter::writeTypeSection( 825 ArrayRef<wasm::WasmSignature> Signatures) { 826 if (Signatures.empty()) 827 return; 828 829 SectionBookkeeping Section; 830 startSection(Section, wasm::WASM_SEC_TYPE); 831 832 encodeULEB128(Signatures.size(), W->OS); 833 834 for (const wasm::WasmSignature &Sig : Signatures) { 835 W->OS << char(wasm::WASM_TYPE_FUNC); 836 encodeULEB128(Sig.Params.size(), W->OS); 837 for (wasm::ValType Ty : Sig.Params) 838 writeValueType(Ty); 839 encodeULEB128(Sig.Returns.size(), W->OS); 840 for (wasm::ValType Ty : Sig.Returns) 841 writeValueType(Ty); 842 } 843 844 endSection(Section); 845 } 846 847 void WasmObjectWriter::writeImportSection(ArrayRef<wasm::WasmImport> Imports, 848 uint64_t DataSize, 849 uint32_t NumElements) { 850 if (Imports.empty()) 851 return; 852 853 uint64_t NumPages = (DataSize + wasm::WasmPageSize - 1) / wasm::WasmPageSize; 854 855 SectionBookkeeping Section; 856 startSection(Section, wasm::WASM_SEC_IMPORT); 857 858 encodeULEB128(Imports.size(), W->OS); 859 for (const wasm::WasmImport &Import : Imports) { 860 writeString(Import.Module); 861 writeString(Import.Field); 862 W->OS << char(Import.Kind); 863 864 switch (Import.Kind) { 865 case wasm::WASM_EXTERNAL_FUNCTION: 866 encodeULEB128(Import.SigIndex, W->OS); 867 break; 868 case wasm::WASM_EXTERNAL_GLOBAL: 869 W->OS << char(Import.Global.Type); 870 W->OS << char(Import.Global.Mutable ? 1 : 0); 871 break; 872 case wasm::WASM_EXTERNAL_MEMORY: 873 encodeULEB128(Import.Memory.Flags, W->OS); 874 encodeULEB128(NumPages, W->OS); // initial 875 break; 876 case wasm::WASM_EXTERNAL_TABLE: 877 W->OS << char(Import.Table.ElemType); 878 encodeULEB128(0, W->OS); // flags 879 encodeULEB128(NumElements, W->OS); // initial 880 break; 881 case wasm::WASM_EXTERNAL_TAG: 882 W->OS << char(0); // Reserved 'attribute' field 883 encodeULEB128(Import.SigIndex, W->OS); 884 break; 885 default: 886 llvm_unreachable("unsupported import kind"); 887 } 888 } 889 890 endSection(Section); 891 } 892 893 void WasmObjectWriter::writeFunctionSection(ArrayRef<WasmFunction> Functions) { 894 if (Functions.empty()) 895 return; 896 897 SectionBookkeeping Section; 898 startSection(Section, wasm::WASM_SEC_FUNCTION); 899 900 encodeULEB128(Functions.size(), W->OS); 901 for (const WasmFunction &Func : Functions) 902 encodeULEB128(Func.SigIndex, W->OS); 903 904 endSection(Section); 905 } 906 907 void WasmObjectWriter::writeTagSection(ArrayRef<uint32_t> TagTypes) { 908 if (TagTypes.empty()) 909 return; 910 911 SectionBookkeeping Section; 912 startSection(Section, wasm::WASM_SEC_TAG); 913 914 encodeULEB128(TagTypes.size(), W->OS); 915 for (uint32_t Index : TagTypes) { 916 W->OS << char(0); // Reserved 'attribute' field 917 encodeULEB128(Index, W->OS); 918 } 919 920 endSection(Section); 921 } 922 923 void WasmObjectWriter::writeGlobalSection(ArrayRef<wasm::WasmGlobal> Globals) { 924 if (Globals.empty()) 925 return; 926 927 SectionBookkeeping Section; 928 startSection(Section, wasm::WASM_SEC_GLOBAL); 929 930 encodeULEB128(Globals.size(), W->OS); 931 for (const wasm::WasmGlobal &Global : Globals) { 932 encodeULEB128(Global.Type.Type, W->OS); 933 W->OS << char(Global.Type.Mutable); 934 if (Global.InitExpr.Extended) { 935 llvm_unreachable("extected init expressions not supported"); 936 } else { 937 W->OS << char(Global.InitExpr.Inst.Opcode); 938 switch (Global.Type.Type) { 939 case wasm::WASM_TYPE_I32: 940 encodeSLEB128(0, W->OS); 941 break; 942 case wasm::WASM_TYPE_I64: 943 encodeSLEB128(0, W->OS); 944 break; 945 case wasm::WASM_TYPE_F32: 946 writeI32(0); 947 break; 948 case wasm::WASM_TYPE_F64: 949 writeI64(0); 950 break; 951 case wasm::WASM_TYPE_EXTERNREF: 952 writeValueType(wasm::ValType::EXTERNREF); 953 break; 954 default: 955 llvm_unreachable("unexpected type"); 956 } 957 } 958 W->OS << char(wasm::WASM_OPCODE_END); 959 } 960 961 endSection(Section); 962 } 963 964 void WasmObjectWriter::writeTableSection(ArrayRef<wasm::WasmTable> Tables) { 965 if (Tables.empty()) 966 return; 967 968 SectionBookkeeping Section; 969 startSection(Section, wasm::WASM_SEC_TABLE); 970 971 encodeULEB128(Tables.size(), W->OS); 972 for (const wasm::WasmTable &Table : Tables) { 973 encodeULEB128(Table.Type.ElemType, W->OS); 974 encodeULEB128(Table.Type.Limits.Flags, W->OS); 975 encodeULEB128(Table.Type.Limits.Minimum, W->OS); 976 if (Table.Type.Limits.Flags & wasm::WASM_LIMITS_FLAG_HAS_MAX) 977 encodeULEB128(Table.Type.Limits.Maximum, W->OS); 978 } 979 endSection(Section); 980 } 981 982 void WasmObjectWriter::writeExportSection(ArrayRef<wasm::WasmExport> Exports) { 983 if (Exports.empty()) 984 return; 985 986 SectionBookkeeping Section; 987 startSection(Section, wasm::WASM_SEC_EXPORT); 988 989 encodeULEB128(Exports.size(), W->OS); 990 for (const wasm::WasmExport &Export : Exports) { 991 writeString(Export.Name); 992 W->OS << char(Export.Kind); 993 encodeULEB128(Export.Index, W->OS); 994 } 995 996 endSection(Section); 997 } 998 999 void WasmObjectWriter::writeElemSection( 1000 const MCSymbolWasm *IndirectFunctionTable, ArrayRef<uint32_t> TableElems) { 1001 if (TableElems.empty()) 1002 return; 1003 1004 assert(IndirectFunctionTable); 1005 1006 SectionBookkeeping Section; 1007 startSection(Section, wasm::WASM_SEC_ELEM); 1008 1009 encodeULEB128(1, W->OS); // number of "segments" 1010 1011 assert(WasmIndices.count(IndirectFunctionTable)); 1012 uint32_t TableNumber = WasmIndices.find(IndirectFunctionTable)->second; 1013 uint32_t Flags = 0; 1014 if (TableNumber) 1015 Flags |= wasm::WASM_ELEM_SEGMENT_HAS_TABLE_NUMBER; 1016 encodeULEB128(Flags, W->OS); 1017 if (Flags & wasm::WASM_ELEM_SEGMENT_HAS_TABLE_NUMBER) 1018 encodeULEB128(TableNumber, W->OS); // the table number 1019 1020 // init expr for starting offset 1021 W->OS << char(wasm::WASM_OPCODE_I32_CONST); 1022 encodeSLEB128(InitialTableOffset, W->OS); 1023 W->OS << char(wasm::WASM_OPCODE_END); 1024 1025 if (Flags & wasm::WASM_ELEM_SEGMENT_MASK_HAS_ELEM_KIND) { 1026 // We only write active function table initializers, for which the elem kind 1027 // is specified to be written as 0x00 and interpreted to mean "funcref". 1028 const uint8_t ElemKind = 0; 1029 W->OS << ElemKind; 1030 } 1031 1032 encodeULEB128(TableElems.size(), W->OS); 1033 for (uint32_t Elem : TableElems) 1034 encodeULEB128(Elem, W->OS); 1035 1036 endSection(Section); 1037 } 1038 1039 void WasmObjectWriter::writeDataCountSection() { 1040 if (DataSegments.empty()) 1041 return; 1042 1043 SectionBookkeeping Section; 1044 startSection(Section, wasm::WASM_SEC_DATACOUNT); 1045 encodeULEB128(DataSegments.size(), W->OS); 1046 endSection(Section); 1047 } 1048 1049 uint32_t WasmObjectWriter::writeCodeSection(const MCAssembler &Asm, 1050 const MCAsmLayout &Layout, 1051 ArrayRef<WasmFunction> Functions) { 1052 if (Functions.empty()) 1053 return 0; 1054 1055 SectionBookkeeping Section; 1056 startSection(Section, wasm::WASM_SEC_CODE); 1057 1058 encodeULEB128(Functions.size(), W->OS); 1059 1060 for (const WasmFunction &Func : Functions) { 1061 auto *FuncSection = static_cast<MCSectionWasm *>(Func.Section); 1062 1063 int64_t Size = Layout.getSectionAddressSize(FuncSection); 1064 encodeULEB128(Size, W->OS); 1065 FuncSection->setSectionOffset(W->OS.tell() - Section.ContentsOffset); 1066 Asm.writeSectionData(W->OS, FuncSection, Layout); 1067 } 1068 1069 // Apply fixups. 1070 applyRelocations(CodeRelocations, Section.ContentsOffset, Layout); 1071 1072 endSection(Section); 1073 return Section.Index; 1074 } 1075 1076 uint32_t WasmObjectWriter::writeDataSection(const MCAsmLayout &Layout) { 1077 if (DataSegments.empty()) 1078 return 0; 1079 1080 SectionBookkeeping Section; 1081 startSection(Section, wasm::WASM_SEC_DATA); 1082 1083 encodeULEB128(DataSegments.size(), W->OS); // count 1084 1085 for (const WasmDataSegment &Segment : DataSegments) { 1086 encodeULEB128(Segment.InitFlags, W->OS); // flags 1087 if (Segment.InitFlags & wasm::WASM_DATA_SEGMENT_HAS_MEMINDEX) 1088 encodeULEB128(0, W->OS); // memory index 1089 if ((Segment.InitFlags & wasm::WASM_DATA_SEGMENT_IS_PASSIVE) == 0) { 1090 W->OS << char(is64Bit() ? wasm::WASM_OPCODE_I64_CONST 1091 : wasm::WASM_OPCODE_I32_CONST); 1092 encodeSLEB128(Segment.Offset, W->OS); // offset 1093 W->OS << char(wasm::WASM_OPCODE_END); 1094 } 1095 encodeULEB128(Segment.Data.size(), W->OS); // size 1096 Segment.Section->setSectionOffset(W->OS.tell() - Section.ContentsOffset); 1097 W->OS << Segment.Data; // data 1098 } 1099 1100 // Apply fixups. 1101 applyRelocations(DataRelocations, Section.ContentsOffset, Layout); 1102 1103 endSection(Section); 1104 return Section.Index; 1105 } 1106 1107 void WasmObjectWriter::writeRelocSection( 1108 uint32_t SectionIndex, StringRef Name, 1109 std::vector<WasmRelocationEntry> &Relocs) { 1110 // See: https://github.com/WebAssembly/tool-conventions/blob/main/Linking.md 1111 // for descriptions of the reloc sections. 1112 1113 if (Relocs.empty()) 1114 return; 1115 1116 // First, ensure the relocations are sorted in offset order. In general they 1117 // should already be sorted since `recordRelocation` is called in offset 1118 // order, but for the code section we combine many MC sections into single 1119 // wasm section, and this order is determined by the order of Asm.Symbols() 1120 // not the sections order. 1121 llvm::stable_sort( 1122 Relocs, [](const WasmRelocationEntry &A, const WasmRelocationEntry &B) { 1123 return (A.Offset + A.FixupSection->getSectionOffset()) < 1124 (B.Offset + B.FixupSection->getSectionOffset()); 1125 }); 1126 1127 SectionBookkeeping Section; 1128 startCustomSection(Section, std::string("reloc.") + Name.str()); 1129 1130 encodeULEB128(SectionIndex, W->OS); 1131 encodeULEB128(Relocs.size(), W->OS); 1132 for (const WasmRelocationEntry &RelEntry : Relocs) { 1133 uint64_t Offset = 1134 RelEntry.Offset + RelEntry.FixupSection->getSectionOffset(); 1135 uint32_t Index = getRelocationIndexValue(RelEntry); 1136 1137 W->OS << char(RelEntry.Type); 1138 encodeULEB128(Offset, W->OS); 1139 encodeULEB128(Index, W->OS); 1140 if (RelEntry.hasAddend()) 1141 encodeSLEB128(RelEntry.Addend, W->OS); 1142 } 1143 1144 endSection(Section); 1145 } 1146 1147 void WasmObjectWriter::writeCustomRelocSections() { 1148 for (const auto &Sec : CustomSections) { 1149 auto &Relocations = CustomSectionsRelocations[Sec.Section]; 1150 writeRelocSection(Sec.OutputIndex, Sec.Name, Relocations); 1151 } 1152 } 1153 1154 void WasmObjectWriter::writeLinkingMetaDataSection( 1155 ArrayRef<wasm::WasmSymbolInfo> SymbolInfos, 1156 ArrayRef<std::pair<uint16_t, uint32_t>> InitFuncs, 1157 const std::map<StringRef, std::vector<WasmComdatEntry>> &Comdats) { 1158 SectionBookkeeping Section; 1159 startCustomSection(Section, "linking"); 1160 encodeULEB128(wasm::WasmMetadataVersion, W->OS); 1161 1162 SectionBookkeeping SubSection; 1163 if (SymbolInfos.size() != 0) { 1164 startSection(SubSection, wasm::WASM_SYMBOL_TABLE); 1165 encodeULEB128(SymbolInfos.size(), W->OS); 1166 for (const wasm::WasmSymbolInfo &Sym : SymbolInfos) { 1167 encodeULEB128(Sym.Kind, W->OS); 1168 encodeULEB128(Sym.Flags, W->OS); 1169 switch (Sym.Kind) { 1170 case wasm::WASM_SYMBOL_TYPE_FUNCTION: 1171 case wasm::WASM_SYMBOL_TYPE_GLOBAL: 1172 case wasm::WASM_SYMBOL_TYPE_TAG: 1173 case wasm::WASM_SYMBOL_TYPE_TABLE: 1174 encodeULEB128(Sym.ElementIndex, W->OS); 1175 if ((Sym.Flags & wasm::WASM_SYMBOL_UNDEFINED) == 0 || 1176 (Sym.Flags & wasm::WASM_SYMBOL_EXPLICIT_NAME) != 0) 1177 writeString(Sym.Name); 1178 break; 1179 case wasm::WASM_SYMBOL_TYPE_DATA: 1180 writeString(Sym.Name); 1181 if ((Sym.Flags & wasm::WASM_SYMBOL_UNDEFINED) == 0) { 1182 encodeULEB128(Sym.DataRef.Segment, W->OS); 1183 encodeULEB128(Sym.DataRef.Offset, W->OS); 1184 encodeULEB128(Sym.DataRef.Size, W->OS); 1185 } 1186 break; 1187 case wasm::WASM_SYMBOL_TYPE_SECTION: { 1188 const uint32_t SectionIndex = 1189 CustomSections[Sym.ElementIndex].OutputIndex; 1190 encodeULEB128(SectionIndex, W->OS); 1191 break; 1192 } 1193 default: 1194 llvm_unreachable("unexpected kind"); 1195 } 1196 } 1197 endSection(SubSection); 1198 } 1199 1200 if (DataSegments.size()) { 1201 startSection(SubSection, wasm::WASM_SEGMENT_INFO); 1202 encodeULEB128(DataSegments.size(), W->OS); 1203 for (const WasmDataSegment &Segment : DataSegments) { 1204 writeString(Segment.Name); 1205 encodeULEB128(Segment.Alignment, W->OS); 1206 encodeULEB128(Segment.LinkingFlags, W->OS); 1207 } 1208 endSection(SubSection); 1209 } 1210 1211 if (!InitFuncs.empty()) { 1212 startSection(SubSection, wasm::WASM_INIT_FUNCS); 1213 encodeULEB128(InitFuncs.size(), W->OS); 1214 for (auto &StartFunc : InitFuncs) { 1215 encodeULEB128(StartFunc.first, W->OS); // priority 1216 encodeULEB128(StartFunc.second, W->OS); // function index 1217 } 1218 endSection(SubSection); 1219 } 1220 1221 if (Comdats.size()) { 1222 startSection(SubSection, wasm::WASM_COMDAT_INFO); 1223 encodeULEB128(Comdats.size(), W->OS); 1224 for (const auto &C : Comdats) { 1225 writeString(C.first); 1226 encodeULEB128(0, W->OS); // flags for future use 1227 encodeULEB128(C.second.size(), W->OS); 1228 for (const WasmComdatEntry &Entry : C.second) { 1229 encodeULEB128(Entry.Kind, W->OS); 1230 encodeULEB128(Entry.Index, W->OS); 1231 } 1232 } 1233 endSection(SubSection); 1234 } 1235 1236 endSection(Section); 1237 } 1238 1239 void WasmObjectWriter::writeCustomSection(WasmCustomSection &CustomSection, 1240 const MCAssembler &Asm, 1241 const MCAsmLayout &Layout) { 1242 SectionBookkeeping Section; 1243 auto *Sec = CustomSection.Section; 1244 startCustomSection(Section, CustomSection.Name); 1245 1246 Sec->setSectionOffset(W->OS.tell() - Section.ContentsOffset); 1247 Asm.writeSectionData(W->OS, Sec, Layout); 1248 1249 CustomSection.OutputContentsOffset = Section.ContentsOffset; 1250 CustomSection.OutputIndex = Section.Index; 1251 1252 endSection(Section); 1253 1254 // Apply fixups. 1255 auto &Relocations = CustomSectionsRelocations[CustomSection.Section]; 1256 applyRelocations(Relocations, CustomSection.OutputContentsOffset, Layout); 1257 } 1258 1259 uint32_t WasmObjectWriter::getFunctionType(const MCSymbolWasm &Symbol) { 1260 assert(Symbol.isFunction()); 1261 assert(TypeIndices.count(&Symbol)); 1262 return TypeIndices[&Symbol]; 1263 } 1264 1265 uint32_t WasmObjectWriter::getTagType(const MCSymbolWasm &Symbol) { 1266 assert(Symbol.isTag()); 1267 assert(TypeIndices.count(&Symbol)); 1268 return TypeIndices[&Symbol]; 1269 } 1270 1271 void WasmObjectWriter::registerFunctionType(const MCSymbolWasm &Symbol) { 1272 assert(Symbol.isFunction()); 1273 1274 wasm::WasmSignature S; 1275 1276 if (auto *Sig = Symbol.getSignature()) { 1277 S.Returns = Sig->Returns; 1278 S.Params = Sig->Params; 1279 } 1280 1281 auto Pair = SignatureIndices.insert(std::make_pair(S, Signatures.size())); 1282 if (Pair.second) 1283 Signatures.push_back(S); 1284 TypeIndices[&Symbol] = Pair.first->second; 1285 1286 LLVM_DEBUG(dbgs() << "registerFunctionType: " << Symbol 1287 << " new:" << Pair.second << "\n"); 1288 LLVM_DEBUG(dbgs() << " -> type index: " << Pair.first->second << "\n"); 1289 } 1290 1291 void WasmObjectWriter::registerTagType(const MCSymbolWasm &Symbol) { 1292 assert(Symbol.isTag()); 1293 1294 // TODO Currently we don't generate imported exceptions, but if we do, we 1295 // should have a way of infering types of imported exceptions. 1296 wasm::WasmSignature S; 1297 if (auto *Sig = Symbol.getSignature()) { 1298 S.Returns = Sig->Returns; 1299 S.Params = Sig->Params; 1300 } 1301 1302 auto Pair = SignatureIndices.insert(std::make_pair(S, Signatures.size())); 1303 if (Pair.second) 1304 Signatures.push_back(S); 1305 TypeIndices[&Symbol] = Pair.first->second; 1306 1307 LLVM_DEBUG(dbgs() << "registerTagType: " << Symbol << " new:" << Pair.second 1308 << "\n"); 1309 LLVM_DEBUG(dbgs() << " -> type index: " << Pair.first->second << "\n"); 1310 } 1311 1312 static bool isInSymtab(const MCSymbolWasm &Sym) { 1313 if (Sym.isUsedInReloc() || Sym.isUsedInInitArray()) 1314 return true; 1315 1316 if (Sym.isComdat() && !Sym.isDefined()) 1317 return false; 1318 1319 if (Sym.isTemporary()) 1320 return false; 1321 1322 if (Sym.isSection()) 1323 return false; 1324 1325 if (Sym.omitFromLinkingSection()) 1326 return false; 1327 1328 return true; 1329 } 1330 1331 void WasmObjectWriter::prepareImports( 1332 SmallVectorImpl<wasm::WasmImport> &Imports, MCAssembler &Asm, 1333 const MCAsmLayout &Layout) { 1334 // For now, always emit the memory import, since loads and stores are not 1335 // valid without it. In the future, we could perhaps be more clever and omit 1336 // it if there are no loads or stores. 1337 wasm::WasmImport MemImport; 1338 MemImport.Module = "env"; 1339 MemImport.Field = "__linear_memory"; 1340 MemImport.Kind = wasm::WASM_EXTERNAL_MEMORY; 1341 MemImport.Memory.Flags = is64Bit() ? wasm::WASM_LIMITS_FLAG_IS_64 1342 : wasm::WASM_LIMITS_FLAG_NONE; 1343 Imports.push_back(MemImport); 1344 1345 // Populate SignatureIndices, and Imports and WasmIndices for undefined 1346 // symbols. This must be done before populating WasmIndices for defined 1347 // symbols. 1348 for (const MCSymbol &S : Asm.symbols()) { 1349 const auto &WS = static_cast<const MCSymbolWasm &>(S); 1350 1351 // Register types for all functions, including those with private linkage 1352 // (because wasm always needs a type signature). 1353 if (WS.isFunction()) { 1354 const auto *BS = Layout.getBaseSymbol(S); 1355 if (!BS) 1356 report_fatal_error(Twine(S.getName()) + 1357 ": absolute addressing not supported!"); 1358 registerFunctionType(*cast<MCSymbolWasm>(BS)); 1359 } 1360 1361 if (WS.isTag()) 1362 registerTagType(WS); 1363 1364 if (WS.isTemporary()) 1365 continue; 1366 1367 // If the symbol is not defined in this translation unit, import it. 1368 if (!WS.isDefined() && !WS.isComdat()) { 1369 if (WS.isFunction()) { 1370 wasm::WasmImport Import; 1371 Import.Module = WS.getImportModule(); 1372 Import.Field = WS.getImportName(); 1373 Import.Kind = wasm::WASM_EXTERNAL_FUNCTION; 1374 Import.SigIndex = getFunctionType(WS); 1375 Imports.push_back(Import); 1376 assert(WasmIndices.count(&WS) == 0); 1377 WasmIndices[&WS] = NumFunctionImports++; 1378 } else if (WS.isGlobal()) { 1379 if (WS.isWeak()) 1380 report_fatal_error("undefined global symbol cannot be weak"); 1381 1382 wasm::WasmImport Import; 1383 Import.Field = WS.getImportName(); 1384 Import.Kind = wasm::WASM_EXTERNAL_GLOBAL; 1385 Import.Module = WS.getImportModule(); 1386 Import.Global = WS.getGlobalType(); 1387 Imports.push_back(Import); 1388 assert(WasmIndices.count(&WS) == 0); 1389 WasmIndices[&WS] = NumGlobalImports++; 1390 } else if (WS.isTag()) { 1391 if (WS.isWeak()) 1392 report_fatal_error("undefined tag symbol cannot be weak"); 1393 1394 wasm::WasmImport Import; 1395 Import.Module = WS.getImportModule(); 1396 Import.Field = WS.getImportName(); 1397 Import.Kind = wasm::WASM_EXTERNAL_TAG; 1398 Import.SigIndex = getTagType(WS); 1399 Imports.push_back(Import); 1400 assert(WasmIndices.count(&WS) == 0); 1401 WasmIndices[&WS] = NumTagImports++; 1402 } else if (WS.isTable()) { 1403 if (WS.isWeak()) 1404 report_fatal_error("undefined table symbol cannot be weak"); 1405 1406 wasm::WasmImport Import; 1407 Import.Module = WS.getImportModule(); 1408 Import.Field = WS.getImportName(); 1409 Import.Kind = wasm::WASM_EXTERNAL_TABLE; 1410 Import.Table = WS.getTableType(); 1411 Imports.push_back(Import); 1412 assert(WasmIndices.count(&WS) == 0); 1413 WasmIndices[&WS] = NumTableImports++; 1414 } 1415 } 1416 } 1417 1418 // Add imports for GOT globals 1419 for (const MCSymbol &S : Asm.symbols()) { 1420 const auto &WS = static_cast<const MCSymbolWasm &>(S); 1421 if (WS.isUsedInGOT()) { 1422 wasm::WasmImport Import; 1423 if (WS.isFunction()) 1424 Import.Module = "GOT.func"; 1425 else 1426 Import.Module = "GOT.mem"; 1427 Import.Field = WS.getName(); 1428 Import.Kind = wasm::WASM_EXTERNAL_GLOBAL; 1429 Import.Global = {wasm::WASM_TYPE_I32, true}; 1430 Imports.push_back(Import); 1431 assert(GOTIndices.count(&WS) == 0); 1432 GOTIndices[&WS] = NumGlobalImports++; 1433 } 1434 } 1435 } 1436 1437 uint64_t WasmObjectWriter::writeObject(MCAssembler &Asm, 1438 const MCAsmLayout &Layout) { 1439 support::endian::Writer MainWriter(*OS, support::little); 1440 W = &MainWriter; 1441 if (IsSplitDwarf) { 1442 uint64_t TotalSize = writeOneObject(Asm, Layout, DwoMode::NonDwoOnly); 1443 assert(DwoOS); 1444 support::endian::Writer DwoWriter(*DwoOS, support::little); 1445 W = &DwoWriter; 1446 return TotalSize + writeOneObject(Asm, Layout, DwoMode::DwoOnly); 1447 } else { 1448 return writeOneObject(Asm, Layout, DwoMode::AllSections); 1449 } 1450 } 1451 1452 uint64_t WasmObjectWriter::writeOneObject(MCAssembler &Asm, 1453 const MCAsmLayout &Layout, 1454 DwoMode Mode) { 1455 uint64_t StartOffset = W->OS.tell(); 1456 SectionCount = 0; 1457 CustomSections.clear(); 1458 1459 LLVM_DEBUG(dbgs() << "WasmObjectWriter::writeObject\n"); 1460 1461 // Collect information from the available symbols. 1462 SmallVector<WasmFunction, 4> Functions; 1463 SmallVector<uint32_t, 4> TableElems; 1464 SmallVector<wasm::WasmImport, 4> Imports; 1465 SmallVector<wasm::WasmExport, 4> Exports; 1466 SmallVector<uint32_t, 2> TagTypes; 1467 SmallVector<wasm::WasmGlobal, 1> Globals; 1468 SmallVector<wasm::WasmTable, 1> Tables; 1469 SmallVector<wasm::WasmSymbolInfo, 4> SymbolInfos; 1470 SmallVector<std::pair<uint16_t, uint32_t>, 2> InitFuncs; 1471 std::map<StringRef, std::vector<WasmComdatEntry>> Comdats; 1472 uint64_t DataSize = 0; 1473 if (Mode != DwoMode::DwoOnly) { 1474 prepareImports(Imports, Asm, Layout); 1475 } 1476 1477 // Populate DataSegments and CustomSections, which must be done before 1478 // populating DataLocations. 1479 for (MCSection &Sec : Asm) { 1480 auto &Section = static_cast<MCSectionWasm &>(Sec); 1481 StringRef SectionName = Section.getName(); 1482 1483 if (Mode == DwoMode::NonDwoOnly && isDwoSection(Sec)) 1484 continue; 1485 if (Mode == DwoMode::DwoOnly && !isDwoSection(Sec)) 1486 continue; 1487 1488 LLVM_DEBUG(dbgs() << "Processing Section " << SectionName << " group " 1489 << Section.getGroup() << "\n";); 1490 1491 // .init_array sections are handled specially elsewhere. 1492 if (SectionName.startswith(".init_array")) 1493 continue; 1494 1495 // Code is handled separately 1496 if (Section.getKind().isText()) 1497 continue; 1498 1499 if (Section.isWasmData()) { 1500 uint32_t SegmentIndex = DataSegments.size(); 1501 DataSize = alignTo(DataSize, Section.getAlign()); 1502 DataSegments.emplace_back(); 1503 WasmDataSegment &Segment = DataSegments.back(); 1504 Segment.Name = SectionName; 1505 Segment.InitFlags = Section.getPassive() 1506 ? (uint32_t)wasm::WASM_DATA_SEGMENT_IS_PASSIVE 1507 : 0; 1508 Segment.Offset = DataSize; 1509 Segment.Section = &Section; 1510 addData(Segment.Data, Section); 1511 Segment.Alignment = Log2(Section.getAlign()); 1512 Segment.LinkingFlags = Section.getSegmentFlags(); 1513 DataSize += Segment.Data.size(); 1514 Section.setSegmentIndex(SegmentIndex); 1515 1516 if (const MCSymbolWasm *C = Section.getGroup()) { 1517 Comdats[C->getName()].emplace_back( 1518 WasmComdatEntry{wasm::WASM_COMDAT_DATA, SegmentIndex}); 1519 } 1520 } else { 1521 // Create custom sections 1522 assert(Sec.getKind().isMetadata()); 1523 1524 StringRef Name = SectionName; 1525 1526 // For user-defined custom sections, strip the prefix 1527 if (Name.startswith(".custom_section.")) 1528 Name = Name.substr(strlen(".custom_section.")); 1529 1530 MCSymbol *Begin = Sec.getBeginSymbol(); 1531 if (Begin) { 1532 assert(WasmIndices.count(cast<MCSymbolWasm>(Begin)) == 0); 1533 WasmIndices[cast<MCSymbolWasm>(Begin)] = CustomSections.size(); 1534 } 1535 1536 // Separate out the producers and target features sections 1537 if (Name == "producers") { 1538 ProducersSection = std::make_unique<WasmCustomSection>(Name, &Section); 1539 continue; 1540 } 1541 if (Name == "target_features") { 1542 TargetFeaturesSection = 1543 std::make_unique<WasmCustomSection>(Name, &Section); 1544 continue; 1545 } 1546 1547 // Custom sections can also belong to COMDAT groups. In this case the 1548 // decriptor's "index" field is the section index (in the final object 1549 // file), but that is not known until after layout, so it must be fixed up 1550 // later 1551 if (const MCSymbolWasm *C = Section.getGroup()) { 1552 Comdats[C->getName()].emplace_back( 1553 WasmComdatEntry{wasm::WASM_COMDAT_SECTION, 1554 static_cast<uint32_t>(CustomSections.size())}); 1555 } 1556 1557 CustomSections.emplace_back(Name, &Section); 1558 } 1559 } 1560 1561 if (Mode != DwoMode::DwoOnly) { 1562 // Populate WasmIndices and DataLocations for defined symbols. 1563 for (const MCSymbol &S : Asm.symbols()) { 1564 // Ignore unnamed temporary symbols, which aren't ever exported, imported, 1565 // or used in relocations. 1566 if (S.isTemporary() && S.getName().empty()) 1567 continue; 1568 1569 const auto &WS = static_cast<const MCSymbolWasm &>(S); 1570 LLVM_DEBUG( 1571 dbgs() << "MCSymbol: " 1572 << toString(WS.getType().value_or(wasm::WASM_SYMBOL_TYPE_DATA)) 1573 << " '" << S << "'" 1574 << " isDefined=" << S.isDefined() << " isExternal=" 1575 << S.isExternal() << " isTemporary=" << S.isTemporary() 1576 << " isWeak=" << WS.isWeak() << " isHidden=" << WS.isHidden() 1577 << " isVariable=" << WS.isVariable() << "\n"); 1578 1579 if (WS.isVariable()) 1580 continue; 1581 if (WS.isComdat() && !WS.isDefined()) 1582 continue; 1583 1584 if (WS.isFunction()) { 1585 unsigned Index; 1586 if (WS.isDefined()) { 1587 if (WS.getOffset() != 0) 1588 report_fatal_error( 1589 "function sections must contain one function each"); 1590 1591 // A definition. Write out the function body. 1592 Index = NumFunctionImports + Functions.size(); 1593 WasmFunction Func; 1594 Func.SigIndex = getFunctionType(WS); 1595 Func.Section = &WS.getSection(); 1596 assert(WasmIndices.count(&WS) == 0); 1597 WasmIndices[&WS] = Index; 1598 Functions.push_back(Func); 1599 1600 auto &Section = static_cast<MCSectionWasm &>(WS.getSection()); 1601 if (const MCSymbolWasm *C = Section.getGroup()) { 1602 Comdats[C->getName()].emplace_back( 1603 WasmComdatEntry{wasm::WASM_COMDAT_FUNCTION, Index}); 1604 } 1605 1606 if (WS.hasExportName()) { 1607 wasm::WasmExport Export; 1608 Export.Name = WS.getExportName(); 1609 Export.Kind = wasm::WASM_EXTERNAL_FUNCTION; 1610 Export.Index = Index; 1611 Exports.push_back(Export); 1612 } 1613 } else { 1614 // An import; the index was assigned above. 1615 Index = WasmIndices.find(&WS)->second; 1616 } 1617 1618 LLVM_DEBUG(dbgs() << " -> function index: " << Index << "\n"); 1619 1620 } else if (WS.isData()) { 1621 if (!isInSymtab(WS)) 1622 continue; 1623 1624 if (!WS.isDefined()) { 1625 LLVM_DEBUG(dbgs() << " -> segment index: -1" 1626 << "\n"); 1627 continue; 1628 } 1629 1630 if (!WS.getSize()) 1631 report_fatal_error("data symbols must have a size set with .size: " + 1632 WS.getName()); 1633 1634 int64_t Size = 0; 1635 if (!WS.getSize()->evaluateAsAbsolute(Size, Layout)) 1636 report_fatal_error(".size expression must be evaluatable"); 1637 1638 auto &DataSection = static_cast<MCSectionWasm &>(WS.getSection()); 1639 if (!DataSection.isWasmData()) 1640 report_fatal_error("data symbols must live in a data section: " + 1641 WS.getName()); 1642 1643 // For each data symbol, export it in the symtab as a reference to the 1644 // corresponding Wasm data segment. 1645 wasm::WasmDataReference Ref = wasm::WasmDataReference{ 1646 DataSection.getSegmentIndex(), Layout.getSymbolOffset(WS), 1647 static_cast<uint64_t>(Size)}; 1648 assert(DataLocations.count(&WS) == 0); 1649 DataLocations[&WS] = Ref; 1650 LLVM_DEBUG(dbgs() << " -> segment index: " << Ref.Segment << "\n"); 1651 1652 } else if (WS.isGlobal()) { 1653 // A "true" Wasm global (currently just __stack_pointer) 1654 if (WS.isDefined()) { 1655 wasm::WasmGlobal Global; 1656 Global.Type = WS.getGlobalType(); 1657 Global.Index = NumGlobalImports + Globals.size(); 1658 Global.InitExpr.Extended = false; 1659 switch (Global.Type.Type) { 1660 case wasm::WASM_TYPE_I32: 1661 Global.InitExpr.Inst.Opcode = wasm::WASM_OPCODE_I32_CONST; 1662 break; 1663 case wasm::WASM_TYPE_I64: 1664 Global.InitExpr.Inst.Opcode = wasm::WASM_OPCODE_I64_CONST; 1665 break; 1666 case wasm::WASM_TYPE_F32: 1667 Global.InitExpr.Inst.Opcode = wasm::WASM_OPCODE_F32_CONST; 1668 break; 1669 case wasm::WASM_TYPE_F64: 1670 Global.InitExpr.Inst.Opcode = wasm::WASM_OPCODE_F64_CONST; 1671 break; 1672 case wasm::WASM_TYPE_EXTERNREF: 1673 Global.InitExpr.Inst.Opcode = wasm::WASM_OPCODE_REF_NULL; 1674 break; 1675 default: 1676 llvm_unreachable("unexpected type"); 1677 } 1678 assert(WasmIndices.count(&WS) == 0); 1679 WasmIndices[&WS] = Global.Index; 1680 Globals.push_back(Global); 1681 } else { 1682 // An import; the index was assigned above 1683 LLVM_DEBUG(dbgs() << " -> global index: " 1684 << WasmIndices.find(&WS)->second << "\n"); 1685 } 1686 } else if (WS.isTable()) { 1687 if (WS.isDefined()) { 1688 wasm::WasmTable Table; 1689 Table.Index = NumTableImports + Tables.size(); 1690 Table.Type = WS.getTableType(); 1691 assert(WasmIndices.count(&WS) == 0); 1692 WasmIndices[&WS] = Table.Index; 1693 Tables.push_back(Table); 1694 } 1695 LLVM_DEBUG(dbgs() << " -> table index: " 1696 << WasmIndices.find(&WS)->second << "\n"); 1697 } else if (WS.isTag()) { 1698 // C++ exception symbol (__cpp_exception) or longjmp symbol 1699 // (__c_longjmp) 1700 unsigned Index; 1701 if (WS.isDefined()) { 1702 Index = NumTagImports + TagTypes.size(); 1703 uint32_t SigIndex = getTagType(WS); 1704 assert(WasmIndices.count(&WS) == 0); 1705 WasmIndices[&WS] = Index; 1706 TagTypes.push_back(SigIndex); 1707 } else { 1708 // An import; the index was assigned above. 1709 assert(WasmIndices.count(&WS) > 0); 1710 } 1711 LLVM_DEBUG(dbgs() << " -> tag index: " << WasmIndices.find(&WS)->second 1712 << "\n"); 1713 1714 } else { 1715 assert(WS.isSection()); 1716 } 1717 } 1718 1719 // Populate WasmIndices and DataLocations for aliased symbols. We need to 1720 // process these in a separate pass because we need to have processed the 1721 // target of the alias before the alias itself and the symbols are not 1722 // necessarily ordered in this way. 1723 for (const MCSymbol &S : Asm.symbols()) { 1724 if (!S.isVariable()) 1725 continue; 1726 1727 assert(S.isDefined()); 1728 1729 const auto *BS = Layout.getBaseSymbol(S); 1730 if (!BS) 1731 report_fatal_error(Twine(S.getName()) + 1732 ": absolute addressing not supported!"); 1733 const MCSymbolWasm *Base = cast<MCSymbolWasm>(BS); 1734 1735 // Find the target symbol of this weak alias and export that index 1736 const auto &WS = static_cast<const MCSymbolWasm &>(S); 1737 LLVM_DEBUG(dbgs() << WS.getName() << ": weak alias of '" << *Base 1738 << "'\n"); 1739 1740 if (Base->isFunction()) { 1741 assert(WasmIndices.count(Base) > 0); 1742 uint32_t WasmIndex = WasmIndices.find(Base)->second; 1743 assert(WasmIndices.count(&WS) == 0); 1744 WasmIndices[&WS] = WasmIndex; 1745 LLVM_DEBUG(dbgs() << " -> index:" << WasmIndex << "\n"); 1746 } else if (Base->isData()) { 1747 auto &DataSection = static_cast<MCSectionWasm &>(WS.getSection()); 1748 uint64_t Offset = Layout.getSymbolOffset(S); 1749 int64_t Size = 0; 1750 // For data symbol alias we use the size of the base symbol as the 1751 // size of the alias. When an offset from the base is involved this 1752 // can result in a offset + size goes past the end of the data section 1753 // which out object format doesn't support. So we must clamp it. 1754 if (!Base->getSize()->evaluateAsAbsolute(Size, Layout)) 1755 report_fatal_error(".size expression must be evaluatable"); 1756 const WasmDataSegment &Segment = 1757 DataSegments[DataSection.getSegmentIndex()]; 1758 Size = 1759 std::min(static_cast<uint64_t>(Size), Segment.Data.size() - Offset); 1760 wasm::WasmDataReference Ref = wasm::WasmDataReference{ 1761 DataSection.getSegmentIndex(), 1762 static_cast<uint32_t>(Layout.getSymbolOffset(S)), 1763 static_cast<uint32_t>(Size)}; 1764 DataLocations[&WS] = Ref; 1765 LLVM_DEBUG(dbgs() << " -> index:" << Ref.Segment << "\n"); 1766 } else { 1767 report_fatal_error("don't yet support global/tag aliases"); 1768 } 1769 } 1770 } 1771 1772 // Finally, populate the symbol table itself, in its "natural" order. 1773 for (const MCSymbol &S : Asm.symbols()) { 1774 const auto &WS = static_cast<const MCSymbolWasm &>(S); 1775 if (!isInSymtab(WS)) { 1776 WS.setIndex(InvalidIndex); 1777 continue; 1778 } 1779 LLVM_DEBUG(dbgs() << "adding to symtab: " << WS << "\n"); 1780 1781 uint32_t Flags = 0; 1782 if (WS.isWeak()) 1783 Flags |= wasm::WASM_SYMBOL_BINDING_WEAK; 1784 if (WS.isHidden()) 1785 Flags |= wasm::WASM_SYMBOL_VISIBILITY_HIDDEN; 1786 if (!WS.isExternal() && WS.isDefined()) 1787 Flags |= wasm::WASM_SYMBOL_BINDING_LOCAL; 1788 if (WS.isUndefined()) 1789 Flags |= wasm::WASM_SYMBOL_UNDEFINED; 1790 if (WS.isNoStrip()) { 1791 Flags |= wasm::WASM_SYMBOL_NO_STRIP; 1792 if (isEmscripten()) { 1793 Flags |= wasm::WASM_SYMBOL_EXPORTED; 1794 } 1795 } 1796 if (WS.hasImportName()) 1797 Flags |= wasm::WASM_SYMBOL_EXPLICIT_NAME; 1798 if (WS.hasExportName()) 1799 Flags |= wasm::WASM_SYMBOL_EXPORTED; 1800 if (WS.isTLS()) 1801 Flags |= wasm::WASM_SYMBOL_TLS; 1802 1803 wasm::WasmSymbolInfo Info; 1804 Info.Name = WS.getName(); 1805 Info.Kind = WS.getType().value_or(wasm::WASM_SYMBOL_TYPE_DATA); 1806 Info.Flags = Flags; 1807 if (!WS.isData()) { 1808 assert(WasmIndices.count(&WS) > 0); 1809 Info.ElementIndex = WasmIndices.find(&WS)->second; 1810 } else if (WS.isDefined()) { 1811 assert(DataLocations.count(&WS) > 0); 1812 Info.DataRef = DataLocations.find(&WS)->second; 1813 } 1814 WS.setIndex(SymbolInfos.size()); 1815 SymbolInfos.emplace_back(Info); 1816 } 1817 1818 { 1819 auto HandleReloc = [&](const WasmRelocationEntry &Rel) { 1820 // Functions referenced by a relocation need to put in the table. This is 1821 // purely to make the object file's provisional values readable, and is 1822 // ignored by the linker, which re-calculates the relocations itself. 1823 if (Rel.Type != wasm::R_WASM_TABLE_INDEX_I32 && 1824 Rel.Type != wasm::R_WASM_TABLE_INDEX_I64 && 1825 Rel.Type != wasm::R_WASM_TABLE_INDEX_SLEB && 1826 Rel.Type != wasm::R_WASM_TABLE_INDEX_SLEB64 && 1827 Rel.Type != wasm::R_WASM_TABLE_INDEX_REL_SLEB && 1828 Rel.Type != wasm::R_WASM_TABLE_INDEX_REL_SLEB64) 1829 return; 1830 assert(Rel.Symbol->isFunction()); 1831 const MCSymbolWasm *Base = 1832 cast<MCSymbolWasm>(Layout.getBaseSymbol(*Rel.Symbol)); 1833 uint32_t FunctionIndex = WasmIndices.find(Base)->second; 1834 uint32_t TableIndex = TableElems.size() + InitialTableOffset; 1835 if (TableIndices.try_emplace(Base, TableIndex).second) { 1836 LLVM_DEBUG(dbgs() << " -> adding " << Base->getName() 1837 << " to table: " << TableIndex << "\n"); 1838 TableElems.push_back(FunctionIndex); 1839 registerFunctionType(*Base); 1840 } 1841 }; 1842 1843 for (const WasmRelocationEntry &RelEntry : CodeRelocations) 1844 HandleReloc(RelEntry); 1845 for (const WasmRelocationEntry &RelEntry : DataRelocations) 1846 HandleReloc(RelEntry); 1847 } 1848 1849 // Translate .init_array section contents into start functions. 1850 for (const MCSection &S : Asm) { 1851 const auto &WS = static_cast<const MCSectionWasm &>(S); 1852 if (WS.getName().startswith(".fini_array")) 1853 report_fatal_error(".fini_array sections are unsupported"); 1854 if (!WS.getName().startswith(".init_array")) 1855 continue; 1856 if (WS.getFragmentList().empty()) 1857 continue; 1858 1859 // init_array is expected to contain a single non-empty data fragment 1860 if (WS.getFragmentList().size() != 3) 1861 report_fatal_error("only one .init_array section fragment supported"); 1862 1863 auto IT = WS.begin(); 1864 const MCFragment &EmptyFrag = *IT; 1865 if (EmptyFrag.getKind() != MCFragment::FT_Data) 1866 report_fatal_error(".init_array section should be aligned"); 1867 1868 IT = std::next(IT); 1869 const MCFragment &AlignFrag = *IT; 1870 if (AlignFrag.getKind() != MCFragment::FT_Align) 1871 report_fatal_error(".init_array section should be aligned"); 1872 if (cast<MCAlignFragment>(AlignFrag).getAlignment() != 1873 Align(is64Bit() ? 8 : 4)) 1874 report_fatal_error(".init_array section should be aligned for pointers"); 1875 1876 const MCFragment &Frag = *std::next(IT); 1877 if (Frag.hasInstructions() || Frag.getKind() != MCFragment::FT_Data) 1878 report_fatal_error("only data supported in .init_array section"); 1879 1880 uint16_t Priority = UINT16_MAX; 1881 unsigned PrefixLength = strlen(".init_array"); 1882 if (WS.getName().size() > PrefixLength) { 1883 if (WS.getName()[PrefixLength] != '.') 1884 report_fatal_error( 1885 ".init_array section priority should start with '.'"); 1886 if (WS.getName().substr(PrefixLength + 1).getAsInteger(10, Priority)) 1887 report_fatal_error("invalid .init_array section priority"); 1888 } 1889 const auto &DataFrag = cast<MCDataFragment>(Frag); 1890 const SmallVectorImpl<char> &Contents = DataFrag.getContents(); 1891 for (const uint8_t * 1892 P = (const uint8_t *)Contents.data(), 1893 *End = (const uint8_t *)Contents.data() + Contents.size(); 1894 P != End; ++P) { 1895 if (*P != 0) 1896 report_fatal_error("non-symbolic data in .init_array section"); 1897 } 1898 for (const MCFixup &Fixup : DataFrag.getFixups()) { 1899 assert(Fixup.getKind() == 1900 MCFixup::getKindForSize(is64Bit() ? 8 : 4, false)); 1901 const MCExpr *Expr = Fixup.getValue(); 1902 auto *SymRef = dyn_cast<MCSymbolRefExpr>(Expr); 1903 if (!SymRef) 1904 report_fatal_error("fixups in .init_array should be symbol references"); 1905 const auto &TargetSym = cast<const MCSymbolWasm>(SymRef->getSymbol()); 1906 if (TargetSym.getIndex() == InvalidIndex) 1907 report_fatal_error("symbols in .init_array should exist in symtab"); 1908 if (!TargetSym.isFunction()) 1909 report_fatal_error("symbols in .init_array should be for functions"); 1910 InitFuncs.push_back( 1911 std::make_pair(Priority, TargetSym.getIndex())); 1912 } 1913 } 1914 1915 // Write out the Wasm header. 1916 writeHeader(Asm); 1917 1918 uint32_t CodeSectionIndex, DataSectionIndex; 1919 if (Mode != DwoMode::DwoOnly) { 1920 writeTypeSection(Signatures); 1921 writeImportSection(Imports, DataSize, TableElems.size()); 1922 writeFunctionSection(Functions); 1923 writeTableSection(Tables); 1924 // Skip the "memory" section; we import the memory instead. 1925 writeTagSection(TagTypes); 1926 writeGlobalSection(Globals); 1927 writeExportSection(Exports); 1928 const MCSymbol *IndirectFunctionTable = 1929 Asm.getContext().lookupSymbol("__indirect_function_table"); 1930 writeElemSection(cast_or_null<const MCSymbolWasm>(IndirectFunctionTable), 1931 TableElems); 1932 writeDataCountSection(); 1933 1934 CodeSectionIndex = writeCodeSection(Asm, Layout, Functions); 1935 DataSectionIndex = writeDataSection(Layout); 1936 } 1937 1938 // The Sections in the COMDAT list have placeholder indices (their index among 1939 // custom sections, rather than among all sections). Fix them up here. 1940 for (auto &Group : Comdats) { 1941 for (auto &Entry : Group.second) { 1942 if (Entry.Kind == wasm::WASM_COMDAT_SECTION) { 1943 Entry.Index += SectionCount; 1944 } 1945 } 1946 } 1947 for (auto &CustomSection : CustomSections) 1948 writeCustomSection(CustomSection, Asm, Layout); 1949 1950 if (Mode != DwoMode::DwoOnly) { 1951 writeLinkingMetaDataSection(SymbolInfos, InitFuncs, Comdats); 1952 1953 writeRelocSection(CodeSectionIndex, "CODE", CodeRelocations); 1954 writeRelocSection(DataSectionIndex, "DATA", DataRelocations); 1955 } 1956 writeCustomRelocSections(); 1957 if (ProducersSection) 1958 writeCustomSection(*ProducersSection, Asm, Layout); 1959 if (TargetFeaturesSection) 1960 writeCustomSection(*TargetFeaturesSection, Asm, Layout); 1961 1962 // TODO: Translate the .comment section to the output. 1963 return W->OS.tell() - StartOffset; 1964 } 1965 1966 std::unique_ptr<MCObjectWriter> 1967 llvm::createWasmObjectWriter(std::unique_ptr<MCWasmObjectTargetWriter> MOTW, 1968 raw_pwrite_stream &OS) { 1969 return std::make_unique<WasmObjectWriter>(std::move(MOTW), OS); 1970 } 1971 1972 std::unique_ptr<MCObjectWriter> 1973 llvm::createWasmDwoObjectWriter(std::unique_ptr<MCWasmObjectTargetWriter> MOTW, 1974 raw_pwrite_stream &OS, 1975 raw_pwrite_stream &DwoOS) { 1976 return std::make_unique<WasmObjectWriter>(std::move(MOTW), OS, DwoOS); 1977 } 1978