lld/wasm/SyntheticSections.cpp

   1 //===- SyntheticSections.cpp ----------------------------------------------===//
   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 contains linker-synthesized sections.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #include "SyntheticSections.h"
  14
  15 #include "InputChunks.h"
  16 #include "InputElement.h"
  17 #include "OutputSegment.h"
  18 #include "SymbolTable.h"
  19 #include "llvm/Support/Path.h"
  20 #include <optional>
  21
  22 using namespace llvm;
  23 using namespace llvm::wasm;
  24
  25 namespace lld::wasm {
  26
  27 OutStruct out;
  28
  29 namespace {
  30
  31 // Some synthetic sections (e.g. "name" and "linking") have subsections.
  32 // Just like the synthetic sections themselves these need to be created before
  33 // they can be written out (since they are preceded by their length). This
  34 // class is used to create subsections and then write them into the stream
  35 // of the parent section.
  36 class SubSection {
  37 public:
  38   explicit SubSection(uint32_t type) : type(type) {}
  39
  40   void writeTo(raw_ostream &to) {
  41     writeUleb128(to, type, "subsection type");
  42     writeUleb128(to, body.size(), "subsection size");
  43     to.write(body.data(), body.size());
  44   }
  45
  46 private:
  47   uint32_t type;
  48   std::string body;
  49
  50 public:
  51   raw_string_ostream os{body};
  52 };
  53
  54 } // namespace
  55
  56 bool DylinkSection::isNeeded() const {
  57   return ctx.isPic ||
  58          ctx.arg.unresolvedSymbols == UnresolvedPolicy::ImportDynamic ||
  59          !ctx.sharedFiles.empty();
  60 }
  61
  62 void DylinkSection::writeBody() {
  63   raw_ostream &os = bodyOutputStream;
  64
  65   {
  66     SubSection sub(WASM_DYLINK_MEM_INFO);
  67     writeUleb128(sub.os, memSize, "MemSize");
  68     writeUleb128(sub.os, memAlign, "MemAlign");
  69     writeUleb128(sub.os, out.elemSec->numEntries(), "TableSize");
  70     writeUleb128(sub.os, 0, "TableAlign");
  71     sub.writeTo(os);
  72   }
  73
  74   if (ctx.sharedFiles.size()) {
  75     SubSection sub(WASM_DYLINK_NEEDED);
  76     writeUleb128(sub.os, ctx.sharedFiles.size(), "Needed");
  77     for (auto *so : ctx.sharedFiles)
  78       writeStr(sub.os, llvm::sys::path::filename(so->getName()), "so name");
  79     sub.writeTo(os);
  80   }
  81
  82   // Under certain circumstances we need to include extra information about our
  83   // exports and/or imports to the dynamic linker.
  84   // For exports we need to notify the linker when an export is TLS since the
  85   // exported value is relative to __tls_base rather than __memory_base.
  86   // For imports we need to notify the dynamic linker when an import is weak
  87   // so that knows not to report an error for such symbols.
  88   std::vector<const Symbol *> importInfo;
  89   std::vector<const Symbol *> exportInfo;
  90   for (const Symbol *sym : symtab->symbols()) {
  91     if (sym->isLive()) {
  92       if (sym->isExported() && sym->isTLS() && isa<DefinedData>(sym)) {
  93         exportInfo.push_back(sym);
  94       }
  95       if (sym->isUndefWeak()) {
  96         importInfo.push_back(sym);
  97       }
  98     }
  99   }
 100
 101   if (!exportInfo.empty()) {
 102     SubSection sub(WASM_DYLINK_EXPORT_INFO);
 103     writeUleb128(sub.os, exportInfo.size(), "num exports");
 104
 105     for (const Symbol *sym : exportInfo) {
 106       LLVM_DEBUG(llvm::dbgs() << "export info: " << toString(*sym) << "\n");
 107       StringRef name = sym->getName();
 108       if (auto *f = dyn_cast<DefinedFunction>(sym)) {
 109         if (std::optional<StringRef> exportName =
 110                 f->function->getExportName()) {
 111           name = *exportName;
 112         }
 113       }
 114       writeStr(sub.os, name, "sym name");
 115       writeUleb128(sub.os, sym->flags, "sym flags");
 116     }
 117
 118     sub.writeTo(os);
 119   }
 120
 121   if (!importInfo.empty()) {
 122     SubSection sub(WASM_DYLINK_IMPORT_INFO);
 123     writeUleb128(sub.os, importInfo.size(), "num imports");
 124
 125     for (const Symbol *sym : importInfo) {
 126       LLVM_DEBUG(llvm::dbgs() << "imports info: " << toString(*sym) << "\n");
 127       StringRef module = sym->importModule.value_or(defaultModule);
 128       StringRef name = sym->importName.value_or(sym->getName());
 129       writeStr(sub.os, module, "import module");
 130       writeStr(sub.os, name, "import name");
 131       writeUleb128(sub.os, sym->flags, "sym flags");
 132     }
 133
 134     sub.writeTo(os);
 135   }
 136 }
 137
 138 uint32_t TypeSection::registerType(const WasmSignature &sig) {
 139   auto pair = typeIndices.insert(std::make_pair(sig, types.size()));
 140   if (pair.second) {
 141     LLVM_DEBUG(llvm::dbgs() << "registerType " << toString(sig) << "\n");
 142     types.push_back(&sig);
 143   }
 144   return pair.first->second;
 145 }
 146
 147 uint32_t TypeSection::lookupType(const WasmSignature &sig) {
 148   auto it = typeIndices.find(sig);
 149   if (it == typeIndices.end()) {
 150     error("type not found: " + toString(sig));
 151     return 0;
 152   }
 153   return it->second;
 154 }
 155
 156 void TypeSection::writeBody() {
 157   writeUleb128(bodyOutputStream, types.size(), "type count");
 158   for (const WasmSignature *sig : types)
 159     writeSig(bodyOutputStream, *sig);
 160 }
 161
 162 uint32_t ImportSection::getNumImports() const {
 163   assert(isSealed);
 164   uint32_t numImports = importedSymbols.size() + gotSymbols.size();
 165   if (ctx.arg.memoryImport.has_value())
 166     ++numImports;
 167   return numImports;
 168 }
 169
 170 void ImportSection::addGOTEntry(Symbol *sym) {
 171   assert(!isSealed);
 172   if (sym->hasGOTIndex())
 173     return;
 174   LLVM_DEBUG(dbgs() << "addGOTEntry: " << toString(*sym) << "\n");
 175   sym->setGOTIndex(numImportedGlobals++);
 176   if (ctx.isPic) {
 177     // Any symbol that is assigned an normal GOT entry must be exported
 178     // otherwise the dynamic linker won't be able create the entry that contains
 179     // it.
 180     sym->forceExport = true;
 181   }
 182   gotSymbols.push_back(sym);
 183 }
 184
 185 void ImportSection::addImport(Symbol *sym) {
 186   assert(!isSealed);
 187   StringRef module = sym->importModule.value_or(defaultModule);
 188   StringRef name = sym->importName.value_or(sym->getName());
 189   if (auto *f = dyn_cast<FunctionSymbol>(sym)) {
 190     ImportKey<WasmSignature> key(*(f->getSignature()), module, name);
 191     auto entry = importedFunctions.try_emplace(key, numImportedFunctions);
 192     if (entry.second) {
 193       importedSymbols.emplace_back(sym);
 194       f->setFunctionIndex(numImportedFunctions++);
 195     } else {
 196       f->setFunctionIndex(entry.first->second);
 197     }
 198   } else if (auto *g = dyn_cast<GlobalSymbol>(sym)) {
 199     ImportKey<WasmGlobalType> key(*(g->getGlobalType()), module, name);
 200     auto entry = importedGlobals.try_emplace(key, numImportedGlobals);
 201     if (entry.second) {
 202       importedSymbols.emplace_back(sym);
 203       g->setGlobalIndex(numImportedGlobals++);
 204     } else {
 205       g->setGlobalIndex(entry.first->second);
 206     }
 207   } else if (auto *t = dyn_cast<TagSymbol>(sym)) {
 208     ImportKey<WasmSignature> key(*(t->getSignature()), module, name);
 209     auto entry = importedTags.try_emplace(key, numImportedTags);
 210     if (entry.second) {
 211       importedSymbols.emplace_back(sym);
 212       t->setTagIndex(numImportedTags++);
 213     } else {
 214       t->setTagIndex(entry.first->second);
 215     }
 216   } else {
 217     assert(TableSymbol::classof(sym));
 218     auto *table = cast<TableSymbol>(sym);
 219     ImportKey<WasmTableType> key(*(table->getTableType()), module, name);
 220     auto entry = importedTables.try_emplace(key, numImportedTables);
 221     if (entry.second) {
 222       importedSymbols.emplace_back(sym);
 223       table->setTableNumber(numImportedTables++);
 224     } else {
 225       table->setTableNumber(entry.first->second);
 226     }
 227   }
 228 }
 229
 230 void ImportSection::writeBody() {
 231   raw_ostream &os = bodyOutputStream;
 232
 233   writeUleb128(os, getNumImports(), "import count");
 234
 235   bool is64 = ctx.arg.is64.value_or(false);
 236
 237   if (ctx.arg.memoryImport) {
 238     WasmImport import;
 239     import.Module = ctx.arg.memoryImport->first;
 240     import.Field = ctx.arg.memoryImport->second;
 241     import.Kind = WASM_EXTERNAL_MEMORY;
 242     import.Memory.Flags = 0;
 243     import.Memory.Minimum = out.memorySec->numMemoryPages;
 244     if (out.memorySec->maxMemoryPages != 0 || ctx.arg.sharedMemory) {
 245       import.Memory.Flags |= WASM_LIMITS_FLAG_HAS_MAX;
 246       import.Memory.Maximum = out.memorySec->maxMemoryPages;
 247     }
 248     if (ctx.arg.sharedMemory)
 249       import.Memory.Flags |= WASM_LIMITS_FLAG_IS_SHARED;
 250     if (is64)
 251       import.Memory.Flags |= WASM_LIMITS_FLAG_IS_64;
 252     writeImport(os, import);
 253   }
 254
 255   for (const Symbol *sym : importedSymbols) {
 256     WasmImport import;
 257     import.Field = sym->importName.value_or(sym->getName());
 258     import.Module = sym->importModule.value_or(defaultModule);
 259
 260     if (auto *functionSym = dyn_cast<FunctionSymbol>(sym)) {
 261       import.Kind = WASM_EXTERNAL_FUNCTION;
 262       import.SigIndex = out.typeSec->lookupType(*functionSym->signature);
 263     } else if (auto *globalSym = dyn_cast<GlobalSymbol>(sym)) {
 264       import.Kind = WASM_EXTERNAL_GLOBAL;
 265       import.Global = *globalSym->getGlobalType();
 266     } else if (auto *tagSym = dyn_cast<TagSymbol>(sym)) {
 267       import.Kind = WASM_EXTERNAL_TAG;
 268       import.SigIndex = out.typeSec->lookupType(*tagSym->signature);
 269     } else {
 270       auto *tableSym = cast<TableSymbol>(sym);
 271       import.Kind = WASM_EXTERNAL_TABLE;
 272       import.Table = *tableSym->getTableType();
 273     }
 274     writeImport(os, import);
 275   }
 276
 277   for (const Symbol *sym : gotSymbols) {
 278     WasmImport import;
 279     import.Kind = WASM_EXTERNAL_GLOBAL;
 280     auto ptrType = is64 ? WASM_TYPE_I64 : WASM_TYPE_I32;
 281     import.Global = {static_cast<uint8_t>(ptrType), true};
 282     if (isa<DataSymbol>(sym))
 283       import.Module = "GOT.mem";
 284     else
 285       import.Module = "GOT.func";
 286     import.Field = sym->getName();
 287     writeImport(os, import);
 288   }
 289 }
 290
 291 void FunctionSection::writeBody() {
 292   raw_ostream &os = bodyOutputStream;
 293
 294   writeUleb128(os, inputFunctions.size(), "function count");
 295   for (const InputFunction *func : inputFunctions)
 296     writeUleb128(os, out.typeSec->lookupType(func->signature), "sig index");
 297 }
 298
 299 void FunctionSection::addFunction(InputFunction *func) {
 300   if (!func->live)
 301     return;
 302   uint32_t functionIndex =
 303       out.importSec->getNumImportedFunctions() + inputFunctions.size();
 304   inputFunctions.emplace_back(func);
 305   func->setFunctionIndex(functionIndex);
 306 }
 307
 308 void TableSection::writeBody() {
 309   raw_ostream &os = bodyOutputStream;
 310
 311   writeUleb128(os, inputTables.size(), "table count");
 312   for (const InputTable *table : inputTables)
 313     writeTableType(os, table->getType());
 314 }
 315
 316 void TableSection::addTable(InputTable *table) {
 317   if (!table->live)
 318     return;
 319   // Some inputs require that the indirect function table be assigned to table
 320   // number 0.
 321   if (ctx.legacyFunctionTable &&
 322       isa<DefinedTable>(WasmSym::indirectFunctionTable) &&
 323       cast<DefinedTable>(WasmSym::indirectFunctionTable)->table == table) {
 324     if (out.importSec->getNumImportedTables()) {
 325       // Alack!  Some other input imported a table, meaning that we are unable
 326       // to assign table number 0 to the indirect function table.
 327       for (const auto *culprit : out.importSec->importedSymbols) {
 328         if (isa<UndefinedTable>(culprit)) {
 329           error("object file not built with 'reference-types' or "
 330                 "'call-indirect-overlong' feature conflicts with import of "
 331                 "table " +
 332                 culprit->getName() + " by file " +
 333                 toString(culprit->getFile()));
 334           return;
 335         }
 336       }
 337       llvm_unreachable("failed to find conflicting table import");
 338     }
 339     inputTables.insert(inputTables.begin(), table);
 340     return;
 341   }
 342   inputTables.push_back(table);
 343 }
 344
 345 void TableSection::assignIndexes() {
 346   uint32_t tableNumber = out.importSec->getNumImportedTables();
 347   for (InputTable *t : inputTables)
 348     t->assignIndex(tableNumber++);
 349 }
 350
 351 void MemorySection::writeBody() {
 352   raw_ostream &os = bodyOutputStream;
 353
 354   bool hasMax = maxMemoryPages != 0 || ctx.arg.sharedMemory;
 355   writeUleb128(os, 1, "memory count");
 356   unsigned flags = 0;
 357   if (hasMax)
 358     flags |= WASM_LIMITS_FLAG_HAS_MAX;
 359   if (ctx.arg.sharedMemory)
 360     flags |= WASM_LIMITS_FLAG_IS_SHARED;
 361   if (ctx.arg.is64.value_or(false))
 362     flags |= WASM_LIMITS_FLAG_IS_64;
 363   writeUleb128(os, flags, "memory limits flags");
 364   writeUleb128(os, numMemoryPages, "initial pages");
 365   if (hasMax)
 366     writeUleb128(os, maxMemoryPages, "max pages");
 367 }
 368
 369 void TagSection::writeBody() {
 370   raw_ostream &os = bodyOutputStream;
 371
 372   writeUleb128(os, inputTags.size(), "tag count");
 373   for (InputTag *t : inputTags) {
 374     writeUleb128(os, 0, "tag attribute"); // Reserved "attribute" field
 375     writeUleb128(os, out.typeSec->lookupType(t->signature), "sig index");
 376   }
 377 }
 378
 379 void TagSection::addTag(InputTag *tag) {
 380   if (!tag->live)
 381     return;
 382   uint32_t tagIndex = out.importSec->getNumImportedTags() + inputTags.size();
 383   LLVM_DEBUG(dbgs() << "addTag: " << tagIndex << "\n");
 384   tag->assignIndex(tagIndex);
 385   inputTags.push_back(tag);
 386 }
 387
 388 void GlobalSection::assignIndexes() {
 389   uint32_t globalIndex = out.importSec->getNumImportedGlobals();
 390   for (InputGlobal *g : inputGlobals)
 391     g->assignIndex(globalIndex++);
 392   for (Symbol *sym : internalGotSymbols)
 393     sym->setGOTIndex(globalIndex++);
 394   isSealed = true;
 395 }
 396
 397 static void ensureIndirectFunctionTable() {
 398   if (!WasmSym::indirectFunctionTable)
 399     WasmSym::indirectFunctionTable =
 400         symtab->resolveIndirectFunctionTable(/*required =*/true);
 401 }
 402
 403 void GlobalSection::addInternalGOTEntry(Symbol *sym) {
 404   assert(!isSealed);
 405   if (sym->requiresGOT)
 406     return;
 407   LLVM_DEBUG(dbgs() << "addInternalGOTEntry: " << sym->getName() << " "
 408                     << toString(sym->kind()) << "\n");
 409   sym->requiresGOT = true;
 410   if (auto *F = dyn_cast<FunctionSymbol>(sym)) {
 411     ensureIndirectFunctionTable();
 412     out.elemSec->addEntry(F);
 413   }
 414   internalGotSymbols.push_back(sym);
 415 }
 416
 417 void GlobalSection::generateRelocationCode(raw_ostream &os, bool TLS) const {
 418   assert(!ctx.arg.extendedConst);
 419   bool is64 = ctx.arg.is64.value_or(false);
 420   unsigned opcode_ptr_const = is64 ? WASM_OPCODE_I64_CONST
 421                                    : WASM_OPCODE_I32_CONST;
 422   unsigned opcode_ptr_add = is64 ? WASM_OPCODE_I64_ADD
 423                                  : WASM_OPCODE_I32_ADD;
 424
 425   for (const Symbol *sym : internalGotSymbols) {
 426     if (TLS != sym->isTLS())
 427       continue;
 428
 429     if (auto *d = dyn_cast<DefinedData>(sym)) {
 430       // Get __memory_base
 431       writeU8(os, WASM_OPCODE_GLOBAL_GET, "GLOBAL_GET");
 432       if (sym->isTLS())
 433         writeUleb128(os, WasmSym::tlsBase->getGlobalIndex(), "__tls_base");
 434       else
 435         writeUleb128(os, WasmSym::memoryBase->getGlobalIndex(),
 436                      "__memory_base");
 437
 438       // Add the virtual address of the data symbol
 439       writeU8(os, opcode_ptr_const, "CONST");
 440       writeSleb128(os, d->getVA(), "offset");
 441     } else if (auto *f = dyn_cast<FunctionSymbol>(sym)) {
 442       if (f->isStub)
 443         continue;
 444       // Get __table_base
 445       writeU8(os, WASM_OPCODE_GLOBAL_GET, "GLOBAL_GET");
 446       writeUleb128(os, WasmSym::tableBase->getGlobalIndex(), "__table_base");
 447
 448       // Add the table index to __table_base
 449       writeU8(os, opcode_ptr_const, "CONST");
 450       writeSleb128(os, f->getTableIndex(), "offset");
 451     } else {
 452       assert(isa<UndefinedData>(sym) || isa<SharedData>(sym));
 453       continue;
 454     }
 455     writeU8(os, opcode_ptr_add, "ADD");
 456     writeU8(os, WASM_OPCODE_GLOBAL_SET, "GLOBAL_SET");
 457     writeUleb128(os, sym->getGOTIndex(), "got_entry");
 458   }
 459 }
 460
 461 void GlobalSection::writeBody() {
 462   raw_ostream &os = bodyOutputStream;
 463
 464   writeUleb128(os, numGlobals(), "global count");
 465   for (InputGlobal *g : inputGlobals) {
 466     writeGlobalType(os, g->getType());
 467     writeInitExpr(os, g->getInitExpr());
 468   }
 469   bool is64 = ctx.arg.is64.value_or(false);
 470   uint8_t itype = is64 ? WASM_TYPE_I64 : WASM_TYPE_I32;
 471   for (const Symbol *sym : internalGotSymbols) {
 472     bool mutable_ = false;
 473     if (!sym->isStub) {
 474       // In the case of dynamic linking, unless we have 'extended-const'
 475       // available, these global must to be mutable since they get updated to
 476       // the correct runtime value during `__wasm_apply_global_relocs`.
 477       if (!ctx.arg.extendedConst && ctx.isPic && !sym->isTLS())
 478         mutable_ = true;
 479       // With multi-theadeding any TLS globals must be mutable since they get
 480       // set during `__wasm_apply_global_tls_relocs`
 481       if (ctx.arg.sharedMemory && sym->isTLS())
 482         mutable_ = true;
 483     }
 484     WasmGlobalType type{itype, mutable_};
 485     writeGlobalType(os, type);
 486
 487     bool useExtendedConst = false;
 488     uint32_t globalIdx;
 489     int64_t offset;
 490     if (ctx.arg.extendedConst && ctx.isPic) {
 491       if (auto *d = dyn_cast<DefinedData>(sym)) {
 492         if (!sym->isTLS()) {
 493           globalIdx = WasmSym::memoryBase->getGlobalIndex();
 494           offset = d->getVA();
 495           useExtendedConst = true;
 496         }
 497       } else if (auto *f = dyn_cast<FunctionSymbol>(sym)) {
 498         if (!sym->isStub) {
 499           globalIdx = WasmSym::tableBase->getGlobalIndex();
 500           offset = f->getTableIndex();
 501           useExtendedConst = true;
 502         }
 503       }
 504     }
 505     if (useExtendedConst) {
 506       // We can use an extended init expression to add a constant
 507       // offset of __memory_base/__table_base.
 508       writeU8(os, WASM_OPCODE_GLOBAL_GET, "global get");
 509       writeUleb128(os, globalIdx, "literal (global index)");
 510       if (offset) {
 511         writePtrConst(os, offset, is64, "offset");
 512         writeU8(os, is64 ? WASM_OPCODE_I64_ADD : WASM_OPCODE_I32_ADD, "add");
 513       }
 514       writeU8(os, WASM_OPCODE_END, "opcode:end");
 515     } else {
 516       WasmInitExpr initExpr;
 517       if (auto *d = dyn_cast<DefinedData>(sym))
 518         // In the sharedMemory case TLS globals are set during
 519         // `__wasm_apply_global_tls_relocs`, but in the non-shared case
 520         // we know the absolute value at link time.
 521         initExpr = intConst(d->getVA(/*absolute=*/!ctx.arg.sharedMemory), is64);
 522       else if (auto *f = dyn_cast<FunctionSymbol>(sym))
 523         initExpr = intConst(f->isStub ? 0 : f->getTableIndex(), is64);
 524       else {
 525         assert(isa<UndefinedData>(sym) || isa<SharedData>(sym));
 526         initExpr = intConst(0, is64);
 527       }
 528       writeInitExpr(os, initExpr);
 529     }
 530   }
 531   for (const DefinedData *sym : dataAddressGlobals) {
 532     WasmGlobalType type{itype, false};
 533     writeGlobalType(os, type);
 534     writeInitExpr(os, intConst(sym->getVA(), is64));
 535   }
 536 }
 537
 538 void GlobalSection::addGlobal(InputGlobal *global) {
 539   assert(!isSealed);
 540   if (!global->live)
 541     return;
 542   inputGlobals.push_back(global);
 543 }
 544
 545 void ExportSection::writeBody() {
 546   raw_ostream &os = bodyOutputStream;
 547
 548   writeUleb128(os, exports.size(), "export count");
 549   for (const WasmExport &export_ : exports)
 550     writeExport(os, export_);
 551 }
 552
 553 bool StartSection::isNeeded() const {
 554   return WasmSym::startFunction != nullptr;
 555 }
 556
 557 void StartSection::writeBody() {
 558   raw_ostream &os = bodyOutputStream;
 559   writeUleb128(os, WasmSym::startFunction->getFunctionIndex(),
 560                "function index");
 561 }
 562
 563 void ElemSection::addEntry(FunctionSymbol *sym) {
 564   // Don't add stub functions to the wasm table.  The address of all stub
 565   // functions should be zero and they should they don't appear in the table.
 566   // They only exist so that the calls to missing functions can validate.
 567   if (sym->hasTableIndex() || sym->isStub)
 568     return;
 569   sym->setTableIndex(ctx.arg.tableBase + indirectFunctions.size());
 570   indirectFunctions.emplace_back(sym);
 571 }
 572
 573 void ElemSection::writeBody() {
 574   raw_ostream &os = bodyOutputStream;
 575
 576   assert(WasmSym::indirectFunctionTable);
 577   writeUleb128(os, 1, "segment count");
 578   uint32_t tableNumber = WasmSym::indirectFunctionTable->getTableNumber();
 579   uint32_t flags = 0;
 580   if (tableNumber)
 581     flags |= WASM_ELEM_SEGMENT_HAS_TABLE_NUMBER;
 582   writeUleb128(os, flags, "elem segment flags");
 583   if (flags & WASM_ELEM_SEGMENT_HAS_TABLE_NUMBER)
 584     writeUleb128(os, tableNumber, "table number");
 585
 586   WasmInitExpr initExpr;
 587   initExpr.Extended = false;
 588   if (ctx.isPic) {
 589     initExpr.Inst.Opcode = WASM_OPCODE_GLOBAL_GET;
 590     initExpr.Inst.Value.Global = WasmSym::tableBase->getGlobalIndex();
 591   } else {
 592     bool is64 = ctx.arg.is64.value_or(false);
 593     initExpr = intConst(ctx.arg.tableBase, is64);
 594   }
 595   writeInitExpr(os, initExpr);
 596
 597   if (flags & WASM_ELEM_SEGMENT_MASK_HAS_ELEM_DESC) {
 598     // We only write active function table initializers, for which the elem kind
 599     // is specified to be written as 0x00 and interpreted to mean "funcref".
 600     const uint8_t elemKind = 0;
 601     writeU8(os, elemKind, "elem kind");
 602   }
 603
 604   writeUleb128(os, indirectFunctions.size(), "elem count");
 605   uint32_t tableIndex = ctx.arg.tableBase;
 606   for (const FunctionSymbol *sym : indirectFunctions) {
 607     assert(sym->getTableIndex() == tableIndex);
 608     (void) tableIndex;
 609     writeUleb128(os, sym->getFunctionIndex(), "function index");
 610     ++tableIndex;
 611   }
 612 }
 613
 614 DataCountSection::DataCountSection(ArrayRef<OutputSegment *> segments)
 615     : SyntheticSection(llvm::wasm::WASM_SEC_DATACOUNT),
 616       numSegments(llvm::count_if(segments, [](OutputSegment *const segment) {
 617         return segment->requiredInBinary();
 618       })) {}
 619
 620 void DataCountSection::writeBody() {
 621   writeUleb128(bodyOutputStream, numSegments, "data count");
 622 }
 623
 624 bool DataCountSection::isNeeded() const {
 625   return numSegments && ctx.arg.sharedMemory;
 626 }
 627
 628 void LinkingSection::writeBody() {
 629   raw_ostream &os = bodyOutputStream;
 630
 631   writeUleb128(os, WasmMetadataVersion, "Version");
 632
 633   if (!symtabEntries.empty()) {
 634     SubSection sub(WASM_SYMBOL_TABLE);
 635     writeUleb128(sub.os, symtabEntries.size(), "num symbols");
 636
 637     for (const Symbol *sym : symtabEntries) {
 638       assert(sym->isDefined() || sym->isUndefined());
 639       WasmSymbolType kind = sym->getWasmType();
 640       uint32_t flags = sym->flags;
 641
 642       writeU8(sub.os, kind, "sym kind");
 643       writeUleb128(sub.os, flags, "sym flags");
 644
 645       if (auto *f = dyn_cast<FunctionSymbol>(sym)) {
 646         if (auto *d = dyn_cast<DefinedFunction>(sym)) {
 647           writeUleb128(sub.os, d->getExportedFunctionIndex(), "index");
 648         } else {
 649           writeUleb128(sub.os, f->getFunctionIndex(), "index");
 650         }
 651         if (sym->isDefined() || (flags & WASM_SYMBOL_EXPLICIT_NAME) != 0)
 652           writeStr(sub.os, sym->getName(), "sym name");
 653       } else if (auto *g = dyn_cast<GlobalSymbol>(sym)) {
 654         writeUleb128(sub.os, g->getGlobalIndex(), "index");
 655         if (sym->isDefined() || (flags & WASM_SYMBOL_EXPLICIT_NAME) != 0)
 656           writeStr(sub.os, sym->getName(), "sym name");
 657       } else if (auto *t = dyn_cast<TagSymbol>(sym)) {
 658         writeUleb128(sub.os, t->getTagIndex(), "index");
 659         if (sym->isDefined() || (flags & WASM_SYMBOL_EXPLICIT_NAME) != 0)
 660           writeStr(sub.os, sym->getName(), "sym name");
 661       } else if (auto *t = dyn_cast<TableSymbol>(sym)) {
 662         writeUleb128(sub.os, t->getTableNumber(), "table number");
 663         if (sym->isDefined() || (flags & WASM_SYMBOL_EXPLICIT_NAME) != 0)
 664           writeStr(sub.os, sym->getName(), "sym name");
 665       } else if (isa<DataSymbol>(sym)) {
 666         writeStr(sub.os, sym->getName(), "sym name");
 667         if (auto *dataSym = dyn_cast<DefinedData>(sym)) {
 668           if (dataSym->segment) {
 669             writeUleb128(sub.os, dataSym->getOutputSegmentIndex(), "index");
 670             writeUleb128(sub.os, dataSym->getOutputSegmentOffset(),
 671                          "data offset");
 672           } else {
 673             writeUleb128(sub.os, 0, "index");
 674             writeUleb128(sub.os, dataSym->getVA(), "data offset");
 675           }
 676           writeUleb128(sub.os, dataSym->getSize(), "data size");
 677         }
 678       } else {
 679         auto *s = cast<OutputSectionSymbol>(sym);
 680         writeUleb128(sub.os, s->section->sectionIndex, "sym section index");
 681       }
 682     }
 683
 684     sub.writeTo(os);
 685   }
 686
 687   if (dataSegments.size()) {
 688     SubSection sub(WASM_SEGMENT_INFO);
 689     writeUleb128(sub.os, dataSegments.size(), "num data segments");
 690     for (const OutputSegment *s : dataSegments) {
 691       writeStr(sub.os, s->name, "segment name");
 692       writeUleb128(sub.os, s->alignment, "alignment");
 693       writeUleb128(sub.os, s->linkingFlags, "flags");
 694     }
 695     sub.writeTo(os);
 696   }
 697
 698   if (!initFunctions.empty()) {
 699     SubSection sub(WASM_INIT_FUNCS);
 700     writeUleb128(sub.os, initFunctions.size(), "num init functions");
 701     for (const WasmInitEntry &f : initFunctions) {
 702       writeUleb128(sub.os, f.priority, "priority");
 703       writeUleb128(sub.os, f.sym->getOutputSymbolIndex(), "function index");
 704     }
 705     sub.writeTo(os);
 706   }
 707
 708   struct ComdatEntry {
 709     unsigned kind;
 710     uint32_t index;
 711   };
 712   std::map<StringRef, std::vector<ComdatEntry>> comdats;
 713
 714   for (const InputFunction *f : out.functionSec->inputFunctions) {
 715     StringRef comdat = f->getComdatName();
 716     if (!comdat.empty())
 717       comdats[comdat].emplace_back(
 718           ComdatEntry{WASM_COMDAT_FUNCTION, f->getFunctionIndex()});
 719   }
 720   for (uint32_t i = 0; i < dataSegments.size(); ++i) {
 721     const auto &inputSegments = dataSegments[i]->inputSegments;
 722     if (inputSegments.empty())
 723       continue;
 724     StringRef comdat = inputSegments[0]->getComdatName();
 725 #ifndef NDEBUG
 726     for (const InputChunk *isec : inputSegments)
 727       assert(isec->getComdatName() == comdat);
 728 #endif
 729     if (!comdat.empty())
 730       comdats[comdat].emplace_back(ComdatEntry{WASM_COMDAT_DATA, i});
 731   }
 732
 733   if (!comdats.empty()) {
 734     SubSection sub(WASM_COMDAT_INFO);
 735     writeUleb128(sub.os, comdats.size(), "num comdats");
 736     for (const auto &c : comdats) {
 737       writeStr(sub.os, c.first, "comdat name");
 738       writeUleb128(sub.os, 0, "comdat flags"); // flags for future use
 739       writeUleb128(sub.os, c.second.size(), "num entries");
 740       for (const ComdatEntry &entry : c.second) {
 741         writeU8(sub.os, entry.kind, "entry kind");
 742         writeUleb128(sub.os, entry.index, "entry index");
 743       }
 744     }
 745     sub.writeTo(os);
 746   }
 747 }
 748
 749 void LinkingSection::addToSymtab(Symbol *sym) {
 750   sym->setOutputSymbolIndex(symtabEntries.size());
 751   symtabEntries.emplace_back(sym);
 752 }
 753
 754 unsigned NameSection::numNamedFunctions() const {
 755   unsigned numNames = out.importSec->getNumImportedFunctions();
 756
 757   for (const InputFunction *f : out.functionSec->inputFunctions)
 758     if (!f->name.empty() || !f->debugName.empty())
 759       ++numNames;
 760
 761   return numNames;
 762 }
 763
 764 unsigned NameSection::numNamedGlobals() const {
 765   unsigned numNames = out.importSec->getNumImportedGlobals();
 766
 767   for (const InputGlobal *g : out.globalSec->inputGlobals)
 768     if (!g->getName().empty())
 769       ++numNames;
 770
 771   numNames += out.globalSec->internalGotSymbols.size();
 772   return numNames;
 773 }
 774
 775 unsigned NameSection::numNamedDataSegments() const {
 776   unsigned numNames = 0;
 777
 778   for (const OutputSegment *s : segments)
 779     if (!s->name.empty() && s->requiredInBinary())
 780       ++numNames;
 781
 782   return numNames;
 783 }
 784
 785 // Create the custom "name" section containing debug symbol names.
 786 void NameSection::writeBody() {
 787   {
 788     SubSection sub(WASM_NAMES_MODULE);
 789     StringRef moduleName = ctx.arg.soName;
 790     if (ctx.arg.soName.empty())
 791       moduleName = llvm::sys::path::filename(ctx.arg.outputFile);
 792     writeStr(sub.os, moduleName, "module name");
 793     sub.writeTo(bodyOutputStream);
 794   }
 795
 796   unsigned count = numNamedFunctions();
 797   if (count) {
 798     SubSection sub(WASM_NAMES_FUNCTION);
 799     writeUleb128(sub.os, count, "name count");
 800
 801     // Function names appear in function index order.  As it happens
 802     // importedSymbols and inputFunctions are numbered in order with imported
 803     // functions coming first.
 804     for (const Symbol *s : out.importSec->importedSymbols) {
 805       if (auto *f = dyn_cast<FunctionSymbol>(s)) {
 806         writeUleb128(sub.os, f->getFunctionIndex(), "func index");
 807         writeStr(sub.os, toString(*s), "symbol name");
 808       }
 809     }
 810     for (const InputFunction *f : out.functionSec->inputFunctions) {
 811       if (!f->name.empty()) {
 812         writeUleb128(sub.os, f->getFunctionIndex(), "func index");
 813         if (!f->debugName.empty()) {
 814           writeStr(sub.os, f->debugName, "symbol name");
 815         } else {
 816           writeStr(sub.os, maybeDemangleSymbol(f->name), "symbol name");
 817         }
 818       }
 819     }
 820     sub.writeTo(bodyOutputStream);
 821   }
 822
 823   count = numNamedGlobals();
 824   if (count) {
 825     SubSection sub(WASM_NAMES_GLOBAL);
 826     writeUleb128(sub.os, count, "name count");
 827
 828     for (const Symbol *s : out.importSec->importedSymbols) {
 829       if (auto *g = dyn_cast<GlobalSymbol>(s)) {
 830         writeUleb128(sub.os, g->getGlobalIndex(), "global index");
 831         writeStr(sub.os, toString(*s), "symbol name");
 832       }
 833     }
 834     for (const Symbol *s : out.importSec->gotSymbols) {
 835       writeUleb128(sub.os, s->getGOTIndex(), "global index");
 836       writeStr(sub.os, toString(*s), "symbol name");
 837     }
 838     for (const InputGlobal *g : out.globalSec->inputGlobals) {
 839       if (!g->getName().empty()) {
 840         writeUleb128(sub.os, g->getAssignedIndex(), "global index");
 841         writeStr(sub.os, maybeDemangleSymbol(g->getName()), "symbol name");
 842       }
 843     }
 844     for (Symbol *s : out.globalSec->internalGotSymbols) {
 845       writeUleb128(sub.os, s->getGOTIndex(), "global index");
 846       if (isa<FunctionSymbol>(s))
 847         writeStr(sub.os, "GOT.func.internal." + toString(*s), "symbol name");
 848       else
 849         writeStr(sub.os, "GOT.data.internal." + toString(*s), "symbol name");
 850     }
 851
 852     sub.writeTo(bodyOutputStream);
 853   }
 854
 855   count = numNamedDataSegments();
 856   if (count) {
 857     SubSection sub(WASM_NAMES_DATA_SEGMENT);
 858     writeUleb128(sub.os, count, "name count");
 859
 860     for (OutputSegment *s : segments) {
 861       if (!s->name.empty() && s->requiredInBinary()) {
 862         writeUleb128(sub.os, s->index, "global index");
 863         writeStr(sub.os, s->name, "segment name");
 864       }
 865     }
 866
 867     sub.writeTo(bodyOutputStream);
 868   }
 869 }
 870
 871 void ProducersSection::addInfo(const WasmProducerInfo &info) {
 872   for (auto &producers :
 873        {std::make_pair(&info.Languages, &languages),
 874         std::make_pair(&info.Tools, &tools), std::make_pair(&info.SDKs, &sDKs)})
 875     for (auto &producer : *producers.first)
 876       if (llvm::none_of(*producers.second,
 877                         [&](std::pair<std::string, std::string> seen) {
 878                           return seen.first == producer.first;
 879                         }))
 880         producers.second->push_back(producer);
 881 }
 882
 883 void ProducersSection::writeBody() {
 884   auto &os = bodyOutputStream;
 885   writeUleb128(os, fieldCount(), "field count");
 886   for (auto &field :
 887        {std::make_pair("language", languages),
 888         std::make_pair("processed-by", tools), std::make_pair("sdk", sDKs)}) {
 889     if (field.second.empty())
 890       continue;
 891     writeStr(os, field.first, "field name");
 892     writeUleb128(os, field.second.size(), "number of entries");
 893     for (auto &entry : field.second) {
 894       writeStr(os, entry.first, "producer name");
 895       writeStr(os, entry.second, "producer version");
 896     }
 897   }
 898 }
 899
 900 void TargetFeaturesSection::writeBody() {
 901   SmallVector<std::string, 8> emitted(features.begin(), features.end());
 902   llvm::sort(emitted);
 903   auto &os = bodyOutputStream;
 904   writeUleb128(os, emitted.size(), "feature count");
 905   for (auto &feature : emitted) {
 906     writeU8(os, WASM_FEATURE_PREFIX_USED, "feature used prefix");
 907     writeStr(os, feature, "feature name");
 908   }
 909 }
 910
 911 void RelocSection::writeBody() {
 912   uint32_t count = sec->getNumRelocations();
 913   assert(sec->sectionIndex != UINT32_MAX);
 914   writeUleb128(bodyOutputStream, sec->sectionIndex, "reloc section");
 915   writeUleb128(bodyOutputStream, count, "reloc count");
 916   sec->writeRelocations(bodyOutputStream);
 917 }
 918
 919 static size_t getHashSize() {
 920   switch (ctx.arg.buildId) {
 921   case BuildIdKind::Fast:
 922   case BuildIdKind::Uuid:
 923     return 16;
 924   case BuildIdKind::Sha1:
 925     return 20;
 926   case BuildIdKind::Hexstring:
 927     return ctx.arg.buildIdVector.size();
 928   case BuildIdKind::None:
 929     return 0;
 930   }
 931   llvm_unreachable("build id kind not implemented");
 932 }
 933
 934 BuildIdSection::BuildIdSection()
 935     : SyntheticSection(llvm::wasm::WASM_SEC_CUSTOM, buildIdSectionName),
 936       hashSize(getHashSize()) {}
 937
 938 void BuildIdSection::writeBody() {
 939   LLVM_DEBUG(llvm::dbgs() << "BuildId writebody\n");
 940   // Write hash size
 941   auto &os = bodyOutputStream;
 942   writeUleb128(os, hashSize, "build id size");
 943   writeBytes(os, std::vector<char>(hashSize, ' ').data(), hashSize,
 944              "placeholder");
 945 }
 946
 947 void BuildIdSection::writeBuildId(llvm::ArrayRef<uint8_t> buf) {
 948   assert(buf.size() == hashSize);
 949   LLVM_DEBUG(dbgs() << "buildid write " << buf.size() << " "
 950                     << hashPlaceholderPtr << '\n');
 951   memcpy(hashPlaceholderPtr, buf.data(), hashSize);
 952 }
 953
 954 } // namespace wasm::lld