1//=--------- MachOLinkGraphBuilder.cpp - MachO LinkGraph builder ----------===// 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// Generic MachO LinkGraph buliding code. 10// 11//===----------------------------------------------------------------------===// 12 13#include "MachOLinkGraphBuilder.h" 14 15#define DEBUG_TYPE "jitlink" 16 17static const char *CommonSectionName = "__common"; 18 19namespace llvm { 20namespace jitlink { 21 22MachOLinkGraphBuilder::~MachOLinkGraphBuilder() {} 23 24Expected<std::unique_ptr<LinkGraph>> MachOLinkGraphBuilder::buildGraph() { 25 26 // Sanity check: we only operate on relocatable objects. 27 if (!Obj.isRelocatableObject()) 28 return make_error<JITLinkError>("Object is not a relocatable MachO"); 29 30 if (auto Err = createNormalizedSections()) 31 return std::move(Err); 32 33 if (auto Err = createNormalizedSymbols()) 34 return std::move(Err); 35 36 if (auto Err = graphifyRegularSymbols()) 37 return std::move(Err); 38 39 if (auto Err = graphifySectionsWithCustomParsers()) 40 return std::move(Err); 41 42 if (auto Err = addRelocations()) 43 return std::move(Err); 44 45 return std::move(G); 46} 47 48MachOLinkGraphBuilder::MachOLinkGraphBuilder( 49 const object::MachOObjectFile &Obj, Triple TT, 50 LinkGraph::GetEdgeKindNameFunction GetEdgeKindName) 51 : Obj(Obj), 52 G(std::make_unique<LinkGraph>( 53 std::string(Obj.getFileName()), std::move(TT), getPointerSize(Obj), 54 getEndianness(Obj), std::move(GetEdgeKindName))) {} 55 56void MachOLinkGraphBuilder::addCustomSectionParser( 57 StringRef SectionName, SectionParserFunction Parser) { 58 assert(!CustomSectionParserFunctions.count(SectionName) && 59 "Custom parser for this section already exists"); 60 CustomSectionParserFunctions[SectionName] = std::move(Parser); 61} 62 63Linkage MachOLinkGraphBuilder::getLinkage(uint16_t Desc) { 64 if ((Desc & MachO::N_WEAK_DEF) || (Desc & MachO::N_WEAK_REF)) 65 return Linkage::Weak; 66 return Linkage::Strong; 67} 68 69Scope MachOLinkGraphBuilder::getScope(StringRef Name, uint8_t Type) { 70 if (Type & MachO::N_EXT) { 71 if ((Type & MachO::N_PEXT) || Name.startswith("l")) 72 return Scope::Hidden; 73 else 74 return Scope::Default; 75 } 76 return Scope::Local; 77} 78 79bool MachOLinkGraphBuilder::isAltEntry(const NormalizedSymbol &NSym) { 80 return NSym.Desc & MachO::N_ALT_ENTRY; 81} 82 83bool MachOLinkGraphBuilder::isDebugSection(const NormalizedSection &NSec) { 84 return (NSec.Flags & MachO::S_ATTR_DEBUG && 85 strcmp(NSec.SegName, "__DWARF") == 0); 86} 87 88unsigned 89MachOLinkGraphBuilder::getPointerSize(const object::MachOObjectFile &Obj) { 90 return Obj.is64Bit() ? 8 : 4; 91} 92 93support::endianness 94MachOLinkGraphBuilder::getEndianness(const object::MachOObjectFile &Obj) { 95 return Obj.isLittleEndian() ? support::little : support::big; 96} 97 98Section &MachOLinkGraphBuilder::getCommonSection() { 99 if (!CommonSection) { 100 auto Prot = static_cast<sys::Memory::ProtectionFlags>( 101 sys::Memory::MF_READ | sys::Memory::MF_WRITE); 102 CommonSection = &G->createSection(CommonSectionName, Prot); 103 } 104 return *CommonSection; 105} 106 107Error MachOLinkGraphBuilder::createNormalizedSections() { 108 // Build normalized sections. Verifies that section data is in-range (for 109 // sections with content) and that address ranges are non-overlapping. 110 111 LLVM_DEBUG(dbgs() << "Creating normalized sections...\n"); 112 113 for (auto &SecRef : Obj.sections()) { 114 NormalizedSection NSec; 115 uint32_t DataOffset = 0; 116 117 auto SecIndex = Obj.getSectionIndex(SecRef.getRawDataRefImpl()); 118 119 if (Obj.is64Bit()) { 120 const MachO::section_64 &Sec64 = 121 Obj.getSection64(SecRef.getRawDataRefImpl()); 122 123 memcpy(&NSec.SectName, &Sec64.sectname, 16); 124 NSec.SectName[16] = '\0'; 125 memcpy(&NSec.SegName, Sec64.segname, 16); 126 NSec.SegName[16] = '\0'; 127 128 NSec.Address = Sec64.addr; 129 NSec.Size = Sec64.size; 130 NSec.Alignment = 1ULL << Sec64.align; 131 NSec.Flags = Sec64.flags; 132 DataOffset = Sec64.offset; 133 } else { 134 const MachO::section &Sec32 = Obj.getSection(SecRef.getRawDataRefImpl()); 135 136 memcpy(&NSec.SectName, &Sec32.sectname, 16); 137 NSec.SectName[16] = '\0'; 138 memcpy(&NSec.SegName, Sec32.segname, 16); 139 NSec.SegName[16] = '\0'; 140 141 NSec.Address = Sec32.addr; 142 NSec.Size = Sec32.size; 143 NSec.Alignment = 1ULL << Sec32.align; 144 NSec.Flags = Sec32.flags; 145 DataOffset = Sec32.offset; 146 } 147 148 LLVM_DEBUG({ 149 dbgs() << " " << NSec.SegName << "," << NSec.SectName << ": " 150 << formatv("{0:x16}", NSec.Address) << " -- " 151 << formatv("{0:x16}", NSec.Address + NSec.Size) 152 << ", align: " << NSec.Alignment << ", index: " << SecIndex 153 << "\n"; 154 }); 155 156 // Get the section data if any. 157 { 158 unsigned SectionType = NSec.Flags & MachO::SECTION_TYPE; 159 if (SectionType != MachO::S_ZEROFILL && 160 SectionType != MachO::S_GB_ZEROFILL) { 161 162 if (DataOffset + NSec.Size > Obj.getData().size()) 163 return make_error<JITLinkError>( 164 "Section data extends past end of file"); 165 166 NSec.Data = Obj.getData().data() + DataOffset; 167 } 168 } 169 170 // Get prot flags. 171 // FIXME: Make sure this test is correct (it's probably missing cases 172 // as-is). 173 sys::Memory::ProtectionFlags Prot; 174 if (NSec.Flags & MachO::S_ATTR_PURE_INSTRUCTIONS) 175 Prot = static_cast<sys::Memory::ProtectionFlags>(sys::Memory::MF_READ | 176 sys::Memory::MF_EXEC); 177 else 178 Prot = static_cast<sys::Memory::ProtectionFlags>(sys::Memory::MF_READ | 179 sys::Memory::MF_WRITE); 180 181 if (!isDebugSection(NSec)) { 182 auto FullyQualifiedName = 183 G->allocateString(StringRef(NSec.SegName) + "," + NSec.SectName); 184 NSec.GraphSection = &G->createSection( 185 StringRef(FullyQualifiedName.data(), FullyQualifiedName.size()), 186 Prot); 187 } else 188 LLVM_DEBUG({ 189 dbgs() << " " << NSec.SegName << "," << NSec.SectName 190 << " is a debug section: No graph section will be created.\n"; 191 }); 192 193 IndexToSection.insert(std::make_pair(SecIndex, std::move(NSec))); 194 } 195 196 std::vector<NormalizedSection *> Sections; 197 Sections.reserve(IndexToSection.size()); 198 for (auto &KV : IndexToSection) 199 Sections.push_back(&KV.second); 200 201 // If we didn't end up creating any sections then bail out. The code below 202 // assumes that we have at least one section. 203 if (Sections.empty()) 204 return Error::success(); 205 206 llvm::sort(Sections, 207 [](const NormalizedSection *LHS, const NormalizedSection *RHS) { 208 assert(LHS && RHS && "Null section?"); 209 if (LHS->Address != RHS->Address) 210 return LHS->Address < RHS->Address; 211 return LHS->Size < RHS->Size; 212 }); 213 214 for (unsigned I = 0, E = Sections.size() - 1; I != E; ++I) { 215 auto &Cur = *Sections[I]; 216 auto &Next = *Sections[I + 1]; 217 if (Next.Address < Cur.Address + Cur.Size) 218 return make_error<JITLinkError>( 219 "Address range for section " + 220 formatv("\"{0}/{1}\" [ {2:x16} -- {3:x16} ] ", Cur.SegName, 221 Cur.SectName, Cur.Address, Cur.Address + Cur.Size) + 222 "overlaps section \"" + Next.SegName + "/" + Next.SectName + "\"" + 223 formatv("\"{0}/{1}\" [ {2:x16} -- {3:x16} ] ", Next.SegName, 224 Next.SectName, Next.Address, Next.Address + Next.Size)); 225 } 226 227 return Error::success(); 228} 229 230Error MachOLinkGraphBuilder::createNormalizedSymbols() { 231 LLVM_DEBUG(dbgs() << "Creating normalized symbols...\n"); 232 233 for (auto &SymRef : Obj.symbols()) { 234 235 unsigned SymbolIndex = Obj.getSymbolIndex(SymRef.getRawDataRefImpl()); 236 uint64_t Value; 237 uint32_t NStrX; 238 uint8_t Type; 239 uint8_t Sect; 240 uint16_t Desc; 241 242 if (Obj.is64Bit()) { 243 const MachO::nlist_64 &NL64 = 244 Obj.getSymbol64TableEntry(SymRef.getRawDataRefImpl()); 245 Value = NL64.n_value; 246 NStrX = NL64.n_strx; 247 Type = NL64.n_type; 248 Sect = NL64.n_sect; 249 Desc = NL64.n_desc; 250 } else { 251 const MachO::nlist &NL32 = 252 Obj.getSymbolTableEntry(SymRef.getRawDataRefImpl()); 253 Value = NL32.n_value; 254 NStrX = NL32.n_strx; 255 Type = NL32.n_type; 256 Sect = NL32.n_sect; 257 Desc = NL32.n_desc; 258 } 259 260 // Skip stabs. 261 // FIXME: Are there other symbols we should be skipping? 262 if (Type & MachO::N_STAB) 263 continue; 264 265 Optional<StringRef> Name; 266 if (NStrX) { 267 if (auto NameOrErr = SymRef.getName()) 268 Name = *NameOrErr; 269 else 270 return NameOrErr.takeError(); 271 } 272 273 LLVM_DEBUG({ 274 dbgs() << " "; 275 if (!Name) 276 dbgs() << "<anonymous symbol>"; 277 else 278 dbgs() << *Name; 279 dbgs() << ": value = " << formatv("{0:x16}", Value) 280 << ", type = " << formatv("{0:x2}", Type) 281 << ", desc = " << formatv("{0:x4}", Desc) << ", sect = "; 282 if (Sect) 283 dbgs() << static_cast<unsigned>(Sect - 1); 284 else 285 dbgs() << "none"; 286 dbgs() << "\n"; 287 }); 288 289 // If this symbol has a section, sanity check that the addresses line up. 290 if (Sect != 0) { 291 auto NSec = findSectionByIndex(Sect - 1); 292 if (!NSec) 293 return NSec.takeError(); 294 295 if (Value < NSec->Address || Value > NSec->Address + NSec->Size) 296 return make_error<JITLinkError>("Symbol address does not fall within " 297 "section"); 298 299 if (!NSec->GraphSection) { 300 LLVM_DEBUG({ 301 dbgs() << " Skipping: Symbol is in section " << NSec->SegName << "/" 302 << NSec->SectName 303 << " which has no associated graph section.\n"; 304 }); 305 continue; 306 } 307 } 308 309 IndexToSymbol[SymbolIndex] = 310 &createNormalizedSymbol(*Name, Value, Type, Sect, Desc, 311 getLinkage(Desc), getScope(*Name, Type)); 312 } 313 314 return Error::success(); 315} 316 317void MachOLinkGraphBuilder::addSectionStartSymAndBlock( 318 Section &GraphSec, uint64_t Address, const char *Data, uint64_t Size, 319 uint32_t Alignment, bool IsLive) { 320 Block &B = 321 Data ? G->createContentBlock(GraphSec, ArrayRef<char>(Data, Size), 322 Address, Alignment, 0) 323 : G->createZeroFillBlock(GraphSec, Size, Address, Alignment, 0); 324 auto &Sym = G->addAnonymousSymbol(B, 0, Size, false, IsLive); 325 assert(!AddrToCanonicalSymbol.count(Sym.getAddress()) && 326 "Anonymous block start symbol clashes with existing symbol address"); 327 AddrToCanonicalSymbol[Sym.getAddress()] = &Sym; 328} 329 330Error MachOLinkGraphBuilder::graphifyRegularSymbols() { 331 332 LLVM_DEBUG(dbgs() << "Creating graph symbols...\n"); 333 334 /// We only have 256 section indexes: Use a vector rather than a map. 335 std::vector<std::vector<NormalizedSymbol *>> SecIndexToSymbols; 336 SecIndexToSymbols.resize(256); 337 338 // Create commons, externs, and absolutes, and partition all other symbols by 339 // section. 340 for (auto &KV : IndexToSymbol) { 341 auto &NSym = *KV.second; 342 343 switch (NSym.Type & MachO::N_TYPE) { 344 case MachO::N_UNDF: 345 if (NSym.Value) { 346 if (!NSym.Name) 347 return make_error<JITLinkError>("Anonymous common symbol at index " + 348 Twine(KV.first)); 349 NSym.GraphSymbol = &G->addCommonSymbol( 350 *NSym.Name, NSym.S, getCommonSection(), 0, NSym.Value, 351 1ull << MachO::GET_COMM_ALIGN(NSym.Desc), 352 NSym.Desc & MachO::N_NO_DEAD_STRIP); 353 } else { 354 if (!NSym.Name) 355 return make_error<JITLinkError>("Anonymous external symbol at " 356 "index " + 357 Twine(KV.first)); 358 NSym.GraphSymbol = &G->addExternalSymbol( 359 *NSym.Name, 0, 360 NSym.Desc & MachO::N_WEAK_REF ? Linkage::Weak : Linkage::Strong); 361 } 362 break; 363 case MachO::N_ABS: 364 if (!NSym.Name) 365 return make_error<JITLinkError>("Anonymous absolute symbol at index " + 366 Twine(KV.first)); 367 NSym.GraphSymbol = &G->addAbsoluteSymbol( 368 *NSym.Name, NSym.Value, 0, Linkage::Strong, Scope::Default, 369 NSym.Desc & MachO::N_NO_DEAD_STRIP); 370 break; 371 case MachO::N_SECT: 372 SecIndexToSymbols[NSym.Sect - 1].push_back(&NSym); 373 break; 374 case MachO::N_PBUD: 375 return make_error<JITLinkError>( 376 "Unupported N_PBUD symbol " + 377 (NSym.Name ? ("\"" + *NSym.Name + "\"") : Twine("<anon>")) + 378 " at index " + Twine(KV.first)); 379 case MachO::N_INDR: 380 return make_error<JITLinkError>( 381 "Unupported N_INDR symbol " + 382 (NSym.Name ? ("\"" + *NSym.Name + "\"") : Twine("<anon>")) + 383 " at index " + Twine(KV.first)); 384 default: 385 return make_error<JITLinkError>( 386 "Unrecognized symbol type " + Twine(NSym.Type & MachO::N_TYPE) + 387 " for symbol " + 388 (NSym.Name ? ("\"" + *NSym.Name + "\"") : Twine("<anon>")) + 389 " at index " + Twine(KV.first)); 390 } 391 } 392 393 // Loop over sections performing regular graphification for those that 394 // don't have custom parsers. 395 for (auto &KV : IndexToSection) { 396 auto SecIndex = KV.first; 397 auto &NSec = KV.second; 398 399 if (!NSec.GraphSection) { 400 LLVM_DEBUG({ 401 dbgs() << " " << NSec.SegName << "/" << NSec.SectName 402 << " has no graph section. Skipping.\n"; 403 }); 404 continue; 405 } 406 407 // Skip sections with custom parsers. 408 if (CustomSectionParserFunctions.count(NSec.GraphSection->getName())) { 409 LLVM_DEBUG({ 410 dbgs() << " Skipping section " << NSec.GraphSection->getName() 411 << " as it has a custom parser.\n"; 412 }); 413 continue; 414 } else 415 LLVM_DEBUG({ 416 dbgs() << " Processing section " << NSec.GraphSection->getName() 417 << "...\n"; 418 }); 419 420 bool SectionIsNoDeadStrip = NSec.Flags & MachO::S_ATTR_NO_DEAD_STRIP; 421 bool SectionIsText = NSec.Flags & MachO::S_ATTR_PURE_INSTRUCTIONS; 422 423 auto &SecNSymStack = SecIndexToSymbols[SecIndex]; 424 425 // If this section is non-empty but there are no symbols covering it then 426 // create one block and anonymous symbol to cover the entire section. 427 if (SecNSymStack.empty()) { 428 if (NSec.Size > 0) { 429 LLVM_DEBUG({ 430 dbgs() << " Section non-empty, but contains no symbols. " 431 "Creating anonymous block to cover " 432 << formatv("{0:x16}", NSec.Address) << " -- " 433 << formatv("{0:x16}", NSec.Address + NSec.Size) << "\n"; 434 }); 435 addSectionStartSymAndBlock(*NSec.GraphSection, NSec.Address, NSec.Data, 436 NSec.Size, NSec.Alignment, 437 SectionIsNoDeadStrip); 438 } else 439 LLVM_DEBUG({ 440 dbgs() << " Section empty and contains no symbols. Skipping.\n"; 441 }); 442 continue; 443 } 444 445 // Sort the symbol stack in by address, alt-entry status, scope, and name. 446 // We sort in reverse order so that symbols will be visited in the right 447 // order when we pop off the stack below. 448 llvm::sort(SecNSymStack, [](const NormalizedSymbol *LHS, 449 const NormalizedSymbol *RHS) { 450 if (LHS->Value != RHS->Value) 451 return LHS->Value > RHS->Value; 452 if (isAltEntry(*LHS) != isAltEntry(*RHS)) 453 return isAltEntry(*RHS); 454 if (LHS->S != RHS->S) 455 return static_cast<uint8_t>(LHS->S) < static_cast<uint8_t>(RHS->S); 456 return LHS->Name < RHS->Name; 457 }); 458 459 // The first symbol in a section can not be an alt-entry symbol. 460 if (!SecNSymStack.empty() && isAltEntry(*SecNSymStack.back())) 461 return make_error<JITLinkError>( 462 "First symbol in " + NSec.GraphSection->getName() + " is alt-entry"); 463 464 // If the section is non-empty but there is no symbol covering the start 465 // address then add an anonymous one. 466 if (SecNSymStack.back()->Value != NSec.Address) { 467 auto AnonBlockSize = SecNSymStack.back()->Value - NSec.Address; 468 LLVM_DEBUG({ 469 dbgs() << " Section start not covered by symbol. " 470 << "Creating anonymous block to cover [ " 471 << formatv("{0:x16}", NSec.Address) << " -- " 472 << formatv("{0:x16}", NSec.Address + AnonBlockSize) << " ]\n"; 473 }); 474 addSectionStartSymAndBlock(*NSec.GraphSection, NSec.Address, NSec.Data, 475 AnonBlockSize, NSec.Alignment, 476 SectionIsNoDeadStrip); 477 } 478 479 // Visit section symbols in order by popping off the reverse-sorted stack, 480 // building blocks for each alt-entry chain and creating symbols as we go. 481 while (!SecNSymStack.empty()) { 482 SmallVector<NormalizedSymbol *, 8> BlockSyms; 483 484 BlockSyms.push_back(SecNSymStack.back()); 485 SecNSymStack.pop_back(); 486 while (!SecNSymStack.empty() && 487 (isAltEntry(*SecNSymStack.back()) || 488 SecNSymStack.back()->Value == BlockSyms.back()->Value)) { 489 BlockSyms.push_back(SecNSymStack.back()); 490 SecNSymStack.pop_back(); 491 } 492 493 // BlockNSyms now contains the block symbols in reverse canonical order. 494 JITTargetAddress BlockStart = BlockSyms.front()->Value; 495 JITTargetAddress BlockEnd = SecNSymStack.empty() 496 ? NSec.Address + NSec.Size 497 : SecNSymStack.back()->Value; 498 JITTargetAddress BlockOffset = BlockStart - NSec.Address; 499 JITTargetAddress BlockSize = BlockEnd - BlockStart; 500 501 LLVM_DEBUG({ 502 dbgs() << " Creating block for " << formatv("{0:x16}", BlockStart) 503 << " -- " << formatv("{0:x16}", BlockEnd) << ": " 504 << NSec.GraphSection->getName() << " + " 505 << formatv("{0:x16}", BlockOffset) << " with " 506 << BlockSyms.size() << " symbol(s)...\n"; 507 }); 508 509 Block &B = 510 NSec.Data 511 ? G->createContentBlock( 512 *NSec.GraphSection, 513 ArrayRef<char>(NSec.Data + BlockOffset, BlockSize), 514 BlockStart, NSec.Alignment, BlockStart % NSec.Alignment) 515 : G->createZeroFillBlock(*NSec.GraphSection, BlockSize, 516 BlockStart, NSec.Alignment, 517 BlockStart % NSec.Alignment); 518 519 Optional<JITTargetAddress> LastCanonicalAddr; 520 JITTargetAddress SymEnd = BlockEnd; 521 while (!BlockSyms.empty()) { 522 auto &NSym = *BlockSyms.back(); 523 BlockSyms.pop_back(); 524 525 bool SymLive = 526 (NSym.Desc & MachO::N_NO_DEAD_STRIP) || SectionIsNoDeadStrip; 527 528 LLVM_DEBUG({ 529 dbgs() << " " << formatv("{0:x16}", NSym.Value) << " -- " 530 << formatv("{0:x16}", SymEnd) << ": "; 531 if (!NSym.Name) 532 dbgs() << "<anonymous symbol>"; 533 else 534 dbgs() << NSym.Name; 535 if (SymLive) 536 dbgs() << " [no-dead-strip]"; 537 if (LastCanonicalAddr == NSym.Value) 538 dbgs() << " [non-canonical]"; 539 dbgs() << "\n"; 540 }); 541 542 auto &Sym = 543 NSym.Name 544 ? G->addDefinedSymbol(B, NSym.Value - BlockStart, *NSym.Name, 545 SymEnd - NSym.Value, NSym.L, NSym.S, 546 SectionIsText, SymLive) 547 : G->addAnonymousSymbol(B, NSym.Value - BlockStart, 548 SymEnd - NSym.Value, SectionIsText, 549 SymLive); 550 NSym.GraphSymbol = &Sym; 551 if (LastCanonicalAddr != Sym.getAddress()) { 552 if (LastCanonicalAddr) 553 SymEnd = *LastCanonicalAddr; 554 LastCanonicalAddr = Sym.getAddress(); 555 setCanonicalSymbol(Sym); 556 } 557 } 558 } 559 } 560 561 return Error::success(); 562} 563 564Error MachOLinkGraphBuilder::graphifySectionsWithCustomParsers() { 565 // Graphify special sections. 566 for (auto &KV : IndexToSection) { 567 auto &NSec = KV.second; 568 569 // Skip non-graph sections. 570 if (!NSec.GraphSection) 571 continue; 572 573 auto HI = CustomSectionParserFunctions.find(NSec.GraphSection->getName()); 574 if (HI != CustomSectionParserFunctions.end()) { 575 auto &Parse = HI->second; 576 if (auto Err = Parse(NSec)) 577 return Err; 578 } 579 } 580 581 return Error::success(); 582} 583 584} // end namespace jitlink 585} // end namespace llvm 586