InputSection.cpp revision 319955
1//===- InputSection.cpp ---------------------------------------------------===// 2// 3// The LLVM Linker 4// 5// This file is distributed under the University of Illinois Open Source 6// License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9 10#include "InputSection.h" 11#include "Config.h" 12#include "EhFrame.h" 13#include "Error.h" 14#include "InputFiles.h" 15#include "LinkerScript.h" 16#include "Memory.h" 17#include "OutputSections.h" 18#include "Relocations.h" 19#include "SyntheticSections.h" 20#include "Target.h" 21#include "Thunks.h" 22#include "llvm/Object/Decompressor.h" 23#include "llvm/Support/Compression.h" 24#include "llvm/Support/Endian.h" 25#include <mutex> 26 27using namespace llvm; 28using namespace llvm::ELF; 29using namespace llvm::object; 30using namespace llvm::support; 31using namespace llvm::support::endian; 32 33using namespace lld; 34using namespace lld::elf; 35 36// Returns a string to construct an error message. 37template <class ELFT> 38std::string lld::toString(const InputSectionBase<ELFT> *Sec) { 39 // File can be absent if section is synthetic. 40 std::string FileName = 41 Sec->getFile() ? Sec->getFile()->getName() : "<internal>"; 42 return (FileName + ":(" + Sec->Name + ")").str(); 43} 44 45template <class ELFT> 46static ArrayRef<uint8_t> getSectionContents(elf::ObjectFile<ELFT> *File, 47 const typename ELFT::Shdr *Hdr) { 48 if (!File || Hdr->sh_type == SHT_NOBITS) 49 return makeArrayRef<uint8_t>(nullptr, Hdr->sh_size); 50 return check(File->getObj().getSectionContents(Hdr)); 51} 52 53template <class ELFT> 54InputSectionBase<ELFT>::InputSectionBase(elf::ObjectFile<ELFT> *File, 55 uintX_t Flags, uint32_t Type, 56 uintX_t Entsize, uint32_t Link, 57 uint32_t Info, uintX_t Addralign, 58 ArrayRef<uint8_t> Data, StringRef Name, 59 Kind SectionKind) 60 : InputSectionData(SectionKind, Name, Data, 61 !Config->GcSections || !(Flags & SHF_ALLOC)), 62 File(File), Flags(Flags), Entsize(Entsize), Type(Type), Link(Link), 63 Info(Info), Repl(this) { 64 NumRelocations = 0; 65 AreRelocsRela = false; 66 67 // The ELF spec states that a value of 0 means the section has 68 // no alignment constraits. 69 uint64_t V = std::max<uint64_t>(Addralign, 1); 70 if (!isPowerOf2_64(V)) 71 fatal(toString(File) + ": section sh_addralign is not a power of 2"); 72 73 // We reject object files having insanely large alignments even though 74 // they are allowed by the spec. I think 4GB is a reasonable limitation. 75 // We might want to relax this in the future. 76 if (V > UINT32_MAX) 77 fatal(toString(File) + ": section sh_addralign is too large"); 78 Alignment = V; 79 80 // If it is not a mergeable section, overwrite the flag so that the flag 81 // is consistent with the class. This inconsistency could occur when 82 // string merging is disabled using -O0 flag. 83 if (!Config->Relocatable && !isa<MergeInputSection<ELFT>>(this)) 84 this->Flags &= ~(SHF_MERGE | SHF_STRINGS); 85} 86 87template <class ELFT> 88InputSectionBase<ELFT>::InputSectionBase(elf::ObjectFile<ELFT> *File, 89 const Elf_Shdr *Hdr, StringRef Name, 90 Kind SectionKind) 91 : InputSectionBase(File, Hdr->sh_flags & ~SHF_INFO_LINK, Hdr->sh_type, 92 Hdr->sh_entsize, Hdr->sh_link, Hdr->sh_info, 93 Hdr->sh_addralign, getSectionContents(File, Hdr), Name, 94 SectionKind) { 95 this->Offset = Hdr->sh_offset; 96} 97 98template <class ELFT> size_t InputSectionBase<ELFT>::getSize() const { 99 if (auto *S = dyn_cast<SyntheticSection<ELFT>>(this)) 100 return S->getSize(); 101 102 if (auto *D = dyn_cast<InputSection<ELFT>>(this)) 103 if (D->getThunksSize() > 0) 104 return D->getThunkOff() + D->getThunksSize(); 105 106 return Data.size(); 107} 108 109template <class ELFT> 110typename ELFT::uint InputSectionBase<ELFT>::getOffset(uintX_t Offset) const { 111 switch (kind()) { 112 case Regular: 113 return cast<InputSection<ELFT>>(this)->OutSecOff + Offset; 114 case Synthetic: 115 // For synthetic sections we treat offset -1 as the end of the section. 116 // The same approach is used for synthetic symbols (DefinedSynthetic). 117 return cast<InputSection<ELFT>>(this)->OutSecOff + 118 (Offset == uintX_t(-1) ? getSize() : Offset); 119 case EHFrame: 120 // The file crtbeginT.o has relocations pointing to the start of an empty 121 // .eh_frame that is known to be the first in the link. It does that to 122 // identify the start of the output .eh_frame. 123 return Offset; 124 case Merge: 125 return cast<MergeInputSection<ELFT>>(this)->getOffset(Offset); 126 } 127 llvm_unreachable("invalid section kind"); 128} 129 130// Uncompress section contents. Note that this function is called 131// from parallel_for_each, so it must be thread-safe. 132template <class ELFT> void InputSectionBase<ELFT>::uncompress() { 133 Decompressor Decompressor = check(Decompressor::create( 134 Name, toStringRef(Data), ELFT::TargetEndianness == llvm::support::little, 135 ELFT::Is64Bits)); 136 137 size_t Size = Decompressor.getDecompressedSize(); 138 char *OutputBuf; 139 { 140 static std::mutex Mu; 141 std::lock_guard<std::mutex> Lock(Mu); 142 OutputBuf = BAlloc.Allocate<char>(Size); 143 } 144 145 if (Error E = Decompressor.decompress({OutputBuf, Size})) 146 fatal(E, toString(this)); 147 Data = ArrayRef<uint8_t>((uint8_t *)OutputBuf, Size); 148} 149 150template <class ELFT> 151typename ELFT::uint 152InputSectionBase<ELFT>::getOffset(const DefinedRegular<ELFT> &Sym) const { 153 return getOffset(Sym.Value); 154} 155 156template <class ELFT> 157InputSectionBase<ELFT> *InputSectionBase<ELFT>::getLinkOrderDep() const { 158 if ((Flags & SHF_LINK_ORDER) && Link != 0) 159 return getFile()->getSections()[Link]; 160 return nullptr; 161} 162 163// Returns a source location string. Used to construct an error message. 164template <class ELFT> 165std::string InputSectionBase<ELFT>::getLocation(typename ELFT::uint Offset) { 166 // First check if we can get desired values from debugging information. 167 std::string LineInfo = File->getLineInfo(this, Offset); 168 if (!LineInfo.empty()) 169 return LineInfo; 170 171 // File->SourceFile contains STT_FILE symbol that contains a 172 // source file name. If it's missing, we use an object file name. 173 std::string SrcFile = File->SourceFile; 174 if (SrcFile.empty()) 175 SrcFile = toString(File); 176 177 // Find a function symbol that encloses a given location. 178 for (SymbolBody *B : File->getSymbols()) 179 if (auto *D = dyn_cast<DefinedRegular<ELFT>>(B)) 180 if (D->Section == this && D->Type == STT_FUNC) 181 if (D->Value <= Offset && Offset < D->Value + D->Size) 182 return SrcFile + ":(function " + toString(*D) + ")"; 183 184 // If there's no symbol, print out the offset in the section. 185 return (SrcFile + ":(" + Name + "+0x" + utohexstr(Offset) + ")").str(); 186} 187 188template <class ELFT> 189InputSection<ELFT>::InputSection() : InputSectionBase<ELFT>() {} 190 191template <class ELFT> 192InputSection<ELFT>::InputSection(uintX_t Flags, uint32_t Type, 193 uintX_t Addralign, ArrayRef<uint8_t> Data, 194 StringRef Name, Kind K) 195 : InputSectionBase<ELFT>(nullptr, Flags, Type, 196 /*Entsize*/ 0, /*Link*/ 0, /*Info*/ 0, Addralign, 197 Data, Name, K) {} 198 199template <class ELFT> 200InputSection<ELFT>::InputSection(elf::ObjectFile<ELFT> *F, 201 const Elf_Shdr *Header, StringRef Name) 202 : InputSectionBase<ELFT>(F, Header, Name, Base::Regular) {} 203 204template <class ELFT> 205bool InputSection<ELFT>::classof(const InputSectionData *S) { 206 return S->kind() == Base::Regular || S->kind() == Base::Synthetic; 207} 208 209template <class ELFT> 210InputSectionBase<ELFT> *InputSection<ELFT>::getRelocatedSection() { 211 assert(this->Type == SHT_RELA || this->Type == SHT_REL); 212 ArrayRef<InputSectionBase<ELFT> *> Sections = this->File->getSections(); 213 return Sections[this->Info]; 214} 215 216template <class ELFT> void InputSection<ELFT>::addThunk(const Thunk<ELFT> *T) { 217 Thunks.push_back(T); 218} 219 220template <class ELFT> uint64_t InputSection<ELFT>::getThunkOff() const { 221 return this->Data.size(); 222} 223 224template <class ELFT> uint64_t InputSection<ELFT>::getThunksSize() const { 225 uint64_t Total = 0; 226 for (const Thunk<ELFT> *T : Thunks) 227 Total += T->size(); 228 return Total; 229} 230 231// This is used for -r. We can't use memcpy to copy relocations because we need 232// to update symbol table offset and section index for each relocation. So we 233// copy relocations one by one. 234template <class ELFT> 235template <class RelTy> 236void InputSection<ELFT>::copyRelocations(uint8_t *Buf, ArrayRef<RelTy> Rels) { 237 InputSectionBase<ELFT> *RelocatedSection = getRelocatedSection(); 238 239 for (const RelTy &Rel : Rels) { 240 uint32_t Type = Rel.getType(Config->Mips64EL); 241 SymbolBody &Body = this->File->getRelocTargetSym(Rel); 242 243 Elf_Rela *P = reinterpret_cast<Elf_Rela *>(Buf); 244 Buf += sizeof(RelTy); 245 246 if (Config->Rela) 247 P->r_addend = getAddend<ELFT>(Rel); 248 P->r_offset = RelocatedSection->getOffset(Rel.r_offset); 249 P->setSymbolAndType(In<ELFT>::SymTab->getSymbolIndex(&Body), Type, 250 Config->Mips64EL); 251 } 252} 253 254static uint32_t getARMUndefinedRelativeWeakVA(uint32_t Type, uint32_t A, 255 uint32_t P) { 256 switch (Type) { 257 case R_ARM_THM_JUMP11: 258 return P + 2; 259 case R_ARM_CALL: 260 case R_ARM_JUMP24: 261 case R_ARM_PC24: 262 case R_ARM_PLT32: 263 case R_ARM_PREL31: 264 case R_ARM_THM_JUMP19: 265 case R_ARM_THM_JUMP24: 266 return P + 4; 267 case R_ARM_THM_CALL: 268 // We don't want an interworking BLX to ARM 269 return P + 5; 270 default: 271 return A; 272 } 273} 274 275static uint64_t getAArch64UndefinedRelativeWeakVA(uint64_t Type, uint64_t A, 276 uint64_t P) { 277 switch (Type) { 278 case R_AARCH64_CALL26: 279 case R_AARCH64_CONDBR19: 280 case R_AARCH64_JUMP26: 281 case R_AARCH64_TSTBR14: 282 return P + 4; 283 default: 284 return A; 285 } 286} 287 288template <class ELFT> 289static typename ELFT::uint 290getRelocTargetVA(uint32_t Type, typename ELFT::uint A, typename ELFT::uint P, 291 const SymbolBody &Body, RelExpr Expr) { 292 switch (Expr) { 293 case R_ABS: 294 case R_RELAX_GOT_PC_NOPIC: 295 return Body.getVA<ELFT>(A); 296 case R_GOT: 297 case R_RELAX_TLS_GD_TO_IE_ABS: 298 return Body.getGotVA<ELFT>() + A; 299 case R_GOTONLY_PC: 300 return In<ELFT>::Got->getVA() + A - P; 301 case R_GOTONLY_PC_FROM_END: 302 return In<ELFT>::Got->getVA() + A - P + In<ELFT>::Got->getSize(); 303 case R_GOTREL: 304 return Body.getVA<ELFT>(A) - In<ELFT>::Got->getVA(); 305 case R_GOTREL_FROM_END: 306 return Body.getVA<ELFT>(A) - In<ELFT>::Got->getVA() - 307 In<ELFT>::Got->getSize(); 308 case R_GOT_FROM_END: 309 case R_RELAX_TLS_GD_TO_IE_END: 310 return Body.getGotOffset<ELFT>() + A - In<ELFT>::Got->getSize(); 311 case R_GOT_OFF: 312 return Body.getGotOffset<ELFT>() + A; 313 case R_GOT_PAGE_PC: 314 case R_RELAX_TLS_GD_TO_IE_PAGE_PC: 315 return getAArch64Page(Body.getGotVA<ELFT>() + A) - getAArch64Page(P); 316 case R_GOT_PC: 317 case R_RELAX_TLS_GD_TO_IE: 318 return Body.getGotVA<ELFT>() + A - P; 319 case R_HINT: 320 case R_TLSDESC_CALL: 321 llvm_unreachable("cannot relocate hint relocs"); 322 case R_MIPS_GOTREL: 323 return Body.getVA<ELFT>(A) - In<ELFT>::MipsGot->getGp(); 324 case R_MIPS_GOT_LOCAL_PAGE: 325 // If relocation against MIPS local symbol requires GOT entry, this entry 326 // should be initialized by 'page address'. This address is high 16-bits 327 // of sum the symbol's value and the addend. 328 return In<ELFT>::MipsGot->getVA() + 329 In<ELFT>::MipsGot->getPageEntryOffset(Body, A) - 330 In<ELFT>::MipsGot->getGp(); 331 case R_MIPS_GOT_OFF: 332 case R_MIPS_GOT_OFF32: 333 // In case of MIPS if a GOT relocation has non-zero addend this addend 334 // should be applied to the GOT entry content not to the GOT entry offset. 335 // That is why we use separate expression type. 336 return In<ELFT>::MipsGot->getVA() + 337 In<ELFT>::MipsGot->getBodyEntryOffset(Body, A) - 338 In<ELFT>::MipsGot->getGp(); 339 case R_MIPS_TLSGD: 340 return In<ELFT>::MipsGot->getVA() + In<ELFT>::MipsGot->getTlsOffset() + 341 In<ELFT>::MipsGot->getGlobalDynOffset(Body) - 342 In<ELFT>::MipsGot->getGp(); 343 case R_MIPS_TLSLD: 344 return In<ELFT>::MipsGot->getVA() + In<ELFT>::MipsGot->getTlsOffset() + 345 In<ELFT>::MipsGot->getTlsIndexOff() - In<ELFT>::MipsGot->getGp(); 346 case R_PAGE_PC: 347 case R_PLT_PAGE_PC: 348 if (Body.isUndefined() && !Body.isLocal() && Body.symbol()->isWeak()) 349 return getAArch64Page(A); 350 return getAArch64Page(Body.getVA<ELFT>(A)) - getAArch64Page(P); 351 case R_PC: 352 if (Body.isUndefined() && !Body.isLocal() && Body.symbol()->isWeak()) { 353 // On ARM and AArch64 a branch to an undefined weak resolves to the 354 // next instruction, otherwise the place. 355 if (Config->EMachine == EM_ARM) 356 return getARMUndefinedRelativeWeakVA(Type, A, P); 357 if (Config->EMachine == EM_AARCH64) 358 return getAArch64UndefinedRelativeWeakVA(Type, A, P); 359 } 360 return Body.getVA<ELFT>(A) - P; 361 case R_PLT: 362 return Body.getPltVA<ELFT>() + A; 363 case R_PLT_PC: 364 case R_PPC_PLT_OPD: 365 return Body.getPltVA<ELFT>() + A - P; 366 case R_PPC_OPD: { 367 uint64_t SymVA = Body.getVA<ELFT>(A); 368 // If we have an undefined weak symbol, we might get here with a symbol 369 // address of zero. That could overflow, but the code must be unreachable, 370 // so don't bother doing anything at all. 371 if (!SymVA) 372 return 0; 373 if (Out<ELF64BE>::Opd) { 374 // If this is a local call, and we currently have the address of a 375 // function-descriptor, get the underlying code address instead. 376 uint64_t OpdStart = Out<ELF64BE>::Opd->Addr; 377 uint64_t OpdEnd = OpdStart + Out<ELF64BE>::Opd->Size; 378 bool InOpd = OpdStart <= SymVA && SymVA < OpdEnd; 379 if (InOpd) 380 SymVA = read64be(&Out<ELF64BE>::OpdBuf[SymVA - OpdStart]); 381 } 382 return SymVA - P; 383 } 384 case R_PPC_TOC: 385 return getPPC64TocBase() + A; 386 case R_RELAX_GOT_PC: 387 return Body.getVA<ELFT>(A) - P; 388 case R_RELAX_TLS_GD_TO_LE: 389 case R_RELAX_TLS_IE_TO_LE: 390 case R_RELAX_TLS_LD_TO_LE: 391 case R_TLS: 392 // A weak undefined TLS symbol resolves to the base of the TLS 393 // block, i.e. gets a value of zero. If we pass --gc-sections to 394 // lld and .tbss is not referenced, it gets reclaimed and we don't 395 // create a TLS program header. Therefore, we resolve this 396 // statically to zero. 397 if (Body.isTls() && (Body.isLazy() || Body.isUndefined()) && 398 Body.symbol()->isWeak()) 399 return 0; 400 if (Target->TcbSize) 401 return Body.getVA<ELFT>(A) + 402 alignTo(Target->TcbSize, Out<ELFT>::TlsPhdr->p_align); 403 return Body.getVA<ELFT>(A) - Out<ELFT>::TlsPhdr->p_memsz; 404 case R_RELAX_TLS_GD_TO_LE_NEG: 405 case R_NEG_TLS: 406 return Out<ELF32LE>::TlsPhdr->p_memsz - Body.getVA<ELFT>(A); 407 case R_SIZE: 408 return Body.getSize<ELFT>() + A; 409 case R_THUNK_ABS: 410 return Body.getThunkVA<ELFT>() + A; 411 case R_THUNK_PC: 412 case R_THUNK_PLT_PC: 413 return Body.getThunkVA<ELFT>() + A - P; 414 case R_TLSDESC: 415 return In<ELFT>::Got->getGlobalDynAddr(Body) + A; 416 case R_TLSDESC_PAGE: 417 return getAArch64Page(In<ELFT>::Got->getGlobalDynAddr(Body) + A) - 418 getAArch64Page(P); 419 case R_TLSGD: 420 return In<ELFT>::Got->getGlobalDynOffset(Body) + A - 421 In<ELFT>::Got->getSize(); 422 case R_TLSGD_PC: 423 return In<ELFT>::Got->getGlobalDynAddr(Body) + A - P; 424 case R_TLSLD: 425 return In<ELFT>::Got->getTlsIndexOff() + A - In<ELFT>::Got->getSize(); 426 case R_TLSLD_PC: 427 return In<ELFT>::Got->getTlsIndexVA() + A - P; 428 } 429 llvm_unreachable("Invalid expression"); 430} 431 432// This function applies relocations to sections without SHF_ALLOC bit. 433// Such sections are never mapped to memory at runtime. Debug sections are 434// an example. Relocations in non-alloc sections are much easier to 435// handle than in allocated sections because it will never need complex 436// treatement such as GOT or PLT (because at runtime no one refers them). 437// So, we handle relocations for non-alloc sections directly in this 438// function as a performance optimization. 439template <class ELFT> 440template <class RelTy> 441void InputSection<ELFT>::relocateNonAlloc(uint8_t *Buf, ArrayRef<RelTy> Rels) { 442 for (const RelTy &Rel : Rels) { 443 uint32_t Type = Rel.getType(Config->Mips64EL); 444 uintX_t Offset = this->getOffset(Rel.r_offset); 445 uint8_t *BufLoc = Buf + Offset; 446 uintX_t Addend = getAddend<ELFT>(Rel); 447 if (!RelTy::IsRela) 448 Addend += Target->getImplicitAddend(BufLoc, Type); 449 450 SymbolBody &Sym = this->File->getRelocTargetSym(Rel); 451 if (Target->getRelExpr(Type, Sym) != R_ABS) { 452 error(this->getLocation(Offset) + ": has non-ABS reloc"); 453 return; 454 } 455 456 uintX_t AddrLoc = this->OutSec->Addr + Offset; 457 uint64_t SymVA = 0; 458 if (!Sym.isTls() || Out<ELFT>::TlsPhdr) 459 SymVA = SignExtend64<sizeof(uintX_t) * 8>( 460 getRelocTargetVA<ELFT>(Type, Addend, AddrLoc, Sym, R_ABS)); 461 Target->relocateOne(BufLoc, Type, SymVA); 462 } 463} 464 465template <class ELFT> 466void InputSectionBase<ELFT>::relocate(uint8_t *Buf, uint8_t *BufEnd) { 467 // scanReloc function in Writer.cpp constructs Relocations 468 // vector only for SHF_ALLOC'ed sections. For other sections, 469 // we handle relocations directly here. 470 auto *IS = dyn_cast<InputSection<ELFT>>(this); 471 if (IS && !(IS->Flags & SHF_ALLOC)) { 472 if (IS->AreRelocsRela) 473 IS->relocateNonAlloc(Buf, IS->relas()); 474 else 475 IS->relocateNonAlloc(Buf, IS->rels()); 476 return; 477 } 478 479 const unsigned Bits = sizeof(uintX_t) * 8; 480 for (const Relocation &Rel : Relocations) { 481 uintX_t Offset = getOffset(Rel.Offset); 482 uint8_t *BufLoc = Buf + Offset; 483 uint32_t Type = Rel.Type; 484 uintX_t A = Rel.Addend; 485 486 uintX_t AddrLoc = OutSec->Addr + Offset; 487 RelExpr Expr = Rel.Expr; 488 uint64_t TargetVA = SignExtend64<Bits>( 489 getRelocTargetVA<ELFT>(Type, A, AddrLoc, *Rel.Sym, Expr)); 490 491 switch (Expr) { 492 case R_RELAX_GOT_PC: 493 case R_RELAX_GOT_PC_NOPIC: 494 Target->relaxGot(BufLoc, TargetVA); 495 break; 496 case R_RELAX_TLS_IE_TO_LE: 497 Target->relaxTlsIeToLe(BufLoc, Type, TargetVA); 498 break; 499 case R_RELAX_TLS_LD_TO_LE: 500 Target->relaxTlsLdToLe(BufLoc, Type, TargetVA); 501 break; 502 case R_RELAX_TLS_GD_TO_LE: 503 case R_RELAX_TLS_GD_TO_LE_NEG: 504 Target->relaxTlsGdToLe(BufLoc, Type, TargetVA); 505 break; 506 case R_RELAX_TLS_GD_TO_IE: 507 case R_RELAX_TLS_GD_TO_IE_ABS: 508 case R_RELAX_TLS_GD_TO_IE_PAGE_PC: 509 case R_RELAX_TLS_GD_TO_IE_END: 510 Target->relaxTlsGdToIe(BufLoc, Type, TargetVA); 511 break; 512 case R_PPC_PLT_OPD: 513 // Patch a nop (0x60000000) to a ld. 514 if (BufLoc + 8 <= BufEnd && read32be(BufLoc + 4) == 0x60000000) 515 write32be(BufLoc + 4, 0xe8410028); // ld %r2, 40(%r1) 516 // fallthrough 517 default: 518 Target->relocateOne(BufLoc, Type, TargetVA); 519 break; 520 } 521 } 522} 523 524template <class ELFT> void InputSection<ELFT>::writeTo(uint8_t *Buf) { 525 if (this->Type == SHT_NOBITS) 526 return; 527 528 if (auto *S = dyn_cast<SyntheticSection<ELFT>>(this)) { 529 S->writeTo(Buf + OutSecOff); 530 return; 531 } 532 533 // If -r is given, then an InputSection may be a relocation section. 534 if (this->Type == SHT_RELA) { 535 copyRelocations(Buf + OutSecOff, this->template getDataAs<Elf_Rela>()); 536 return; 537 } 538 if (this->Type == SHT_REL) { 539 copyRelocations(Buf + OutSecOff, this->template getDataAs<Elf_Rel>()); 540 return; 541 } 542 543 // Copy section contents from source object file to output file. 544 ArrayRef<uint8_t> Data = this->Data; 545 memcpy(Buf + OutSecOff, Data.data(), Data.size()); 546 547 // Iterate over all relocation sections that apply to this section. 548 uint8_t *BufEnd = Buf + OutSecOff + Data.size(); 549 this->relocate(Buf, BufEnd); 550 551 // The section might have a data/code generated by the linker and need 552 // to be written after the section. Usually these are thunks - small piece 553 // of code used to jump between "incompatible" functions like PIC and non-PIC 554 // or if the jump target too far and its address does not fit to the short 555 // jump istruction. 556 if (!Thunks.empty()) { 557 Buf += OutSecOff + getThunkOff(); 558 for (const Thunk<ELFT> *T : Thunks) { 559 T->writeTo(Buf); 560 Buf += T->size(); 561 } 562 } 563} 564 565template <class ELFT> 566void InputSection<ELFT>::replace(InputSection<ELFT> *Other) { 567 this->Alignment = std::max(this->Alignment, Other->Alignment); 568 Other->Repl = this->Repl; 569 Other->Live = false; 570} 571 572template <class ELFT> 573EhInputSection<ELFT>::EhInputSection(elf::ObjectFile<ELFT> *F, 574 const Elf_Shdr *Header, StringRef Name) 575 : InputSectionBase<ELFT>(F, Header, Name, InputSectionBase<ELFT>::EHFrame) { 576 // Mark .eh_frame sections as live by default because there are 577 // usually no relocations that point to .eh_frames. Otherwise, 578 // the garbage collector would drop all .eh_frame sections. 579 this->Live = true; 580} 581 582template <class ELFT> 583bool EhInputSection<ELFT>::classof(const InputSectionData *S) { 584 return S->kind() == InputSectionBase<ELFT>::EHFrame; 585} 586 587// Returns the index of the first relocation that points to a region between 588// Begin and Begin+Size. 589template <class IntTy, class RelTy> 590static unsigned getReloc(IntTy Begin, IntTy Size, const ArrayRef<RelTy> &Rels, 591 unsigned &RelocI) { 592 // Start search from RelocI for fast access. That works because the 593 // relocations are sorted in .eh_frame. 594 for (unsigned N = Rels.size(); RelocI < N; ++RelocI) { 595 const RelTy &Rel = Rels[RelocI]; 596 if (Rel.r_offset < Begin) 597 continue; 598 599 if (Rel.r_offset < Begin + Size) 600 return RelocI; 601 return -1; 602 } 603 return -1; 604} 605 606// .eh_frame is a sequence of CIE or FDE records. 607// This function splits an input section into records and returns them. 608template <class ELFT> void EhInputSection<ELFT>::split() { 609 // Early exit if already split. 610 if (!this->Pieces.empty()) 611 return; 612 613 if (this->NumRelocations) { 614 if (this->AreRelocsRela) 615 split(this->relas()); 616 else 617 split(this->rels()); 618 return; 619 } 620 split(makeArrayRef<typename ELFT::Rela>(nullptr, nullptr)); 621} 622 623template <class ELFT> 624template <class RelTy> 625void EhInputSection<ELFT>::split(ArrayRef<RelTy> Rels) { 626 ArrayRef<uint8_t> Data = this->Data; 627 unsigned RelI = 0; 628 for (size_t Off = 0, End = Data.size(); Off != End;) { 629 size_t Size = readEhRecordSize<ELFT>(this, Off); 630 this->Pieces.emplace_back(Off, this, Size, getReloc(Off, Size, Rels, RelI)); 631 // The empty record is the end marker. 632 if (Size == 4) 633 break; 634 Off += Size; 635 } 636} 637 638static size_t findNull(ArrayRef<uint8_t> A, size_t EntSize) { 639 // Optimize the common case. 640 StringRef S((const char *)A.data(), A.size()); 641 if (EntSize == 1) 642 return S.find(0); 643 644 for (unsigned I = 0, N = S.size(); I != N; I += EntSize) { 645 const char *B = S.begin() + I; 646 if (std::all_of(B, B + EntSize, [](char C) { return C == 0; })) 647 return I; 648 } 649 return StringRef::npos; 650} 651 652// Split SHF_STRINGS section. Such section is a sequence of 653// null-terminated strings. 654template <class ELFT> 655void MergeInputSection<ELFT>::splitStrings(ArrayRef<uint8_t> Data, 656 size_t EntSize) { 657 size_t Off = 0; 658 bool IsAlloc = this->Flags & SHF_ALLOC; 659 while (!Data.empty()) { 660 size_t End = findNull(Data, EntSize); 661 if (End == StringRef::npos) 662 fatal(toString(this) + ": string is not null terminated"); 663 size_t Size = End + EntSize; 664 Pieces.emplace_back(Off, !IsAlloc); 665 Hashes.push_back(hash_value(toStringRef(Data.slice(0, Size)))); 666 Data = Data.slice(Size); 667 Off += Size; 668 } 669} 670 671// Split non-SHF_STRINGS section. Such section is a sequence of 672// fixed size records. 673template <class ELFT> 674void MergeInputSection<ELFT>::splitNonStrings(ArrayRef<uint8_t> Data, 675 size_t EntSize) { 676 size_t Size = Data.size(); 677 assert((Size % EntSize) == 0); 678 bool IsAlloc = this->Flags & SHF_ALLOC; 679 for (unsigned I = 0, N = Size; I != N; I += EntSize) { 680 Hashes.push_back(hash_value(toStringRef(Data.slice(I, EntSize)))); 681 Pieces.emplace_back(I, !IsAlloc); 682 } 683} 684 685template <class ELFT> 686MergeInputSection<ELFT>::MergeInputSection(elf::ObjectFile<ELFT> *F, 687 const Elf_Shdr *Header, 688 StringRef Name) 689 : InputSectionBase<ELFT>(F, Header, Name, InputSectionBase<ELFT>::Merge) {} 690 691// This function is called after we obtain a complete list of input sections 692// that need to be linked. This is responsible to split section contents 693// into small chunks for further processing. 694// 695// Note that this function is called from parallel_for_each. This must be 696// thread-safe (i.e. no memory allocation from the pools). 697template <class ELFT> void MergeInputSection<ELFT>::splitIntoPieces() { 698 ArrayRef<uint8_t> Data = this->Data; 699 uintX_t EntSize = this->Entsize; 700 if (this->Flags & SHF_STRINGS) 701 splitStrings(Data, EntSize); 702 else 703 splitNonStrings(Data, EntSize); 704 705 if (Config->GcSections && (this->Flags & SHF_ALLOC)) 706 for (uintX_t Off : LiveOffsets) 707 this->getSectionPiece(Off)->Live = true; 708} 709 710template <class ELFT> 711bool MergeInputSection<ELFT>::classof(const InputSectionData *S) { 712 return S->kind() == InputSectionBase<ELFT>::Merge; 713} 714 715// Do binary search to get a section piece at a given input offset. 716template <class ELFT> 717SectionPiece *MergeInputSection<ELFT>::getSectionPiece(uintX_t Offset) { 718 auto *This = static_cast<const MergeInputSection<ELFT> *>(this); 719 return const_cast<SectionPiece *>(This->getSectionPiece(Offset)); 720} 721 722template <class It, class T, class Compare> 723static It fastUpperBound(It First, It Last, const T &Value, Compare Comp) { 724 size_t Size = std::distance(First, Last); 725 assert(Size != 0); 726 while (Size != 1) { 727 size_t H = Size / 2; 728 const It MI = First + H; 729 Size -= H; 730 First = Comp(Value, *MI) ? First : First + H; 731 } 732 return Comp(Value, *First) ? First : First + 1; 733} 734 735template <class ELFT> 736const SectionPiece * 737MergeInputSection<ELFT>::getSectionPiece(uintX_t Offset) const { 738 uintX_t Size = this->Data.size(); 739 if (Offset >= Size) 740 fatal(toString(this) + ": entry is past the end of the section"); 741 742 // Find the element this offset points to. 743 auto I = fastUpperBound( 744 Pieces.begin(), Pieces.end(), Offset, 745 [](const uintX_t &A, const SectionPiece &B) { return A < B.InputOff; }); 746 --I; 747 return &*I; 748} 749 750// Returns the offset in an output section for a given input offset. 751// Because contents of a mergeable section is not contiguous in output, 752// it is not just an addition to a base output offset. 753template <class ELFT> 754typename ELFT::uint MergeInputSection<ELFT>::getOffset(uintX_t Offset) const { 755 // Initialize OffsetMap lazily. 756 std::call_once(InitOffsetMap, [&] { 757 OffsetMap.reserve(Pieces.size()); 758 for (const SectionPiece &Piece : Pieces) 759 OffsetMap[Piece.InputOff] = Piece.OutputOff; 760 }); 761 762 // Find a string starting at a given offset. 763 auto It = OffsetMap.find(Offset); 764 if (It != OffsetMap.end()) 765 return It->second; 766 767 if (!this->Live) 768 return 0; 769 770 // If Offset is not at beginning of a section piece, it is not in the map. 771 // In that case we need to search from the original section piece vector. 772 const SectionPiece &Piece = *this->getSectionPiece(Offset); 773 if (!Piece.Live) 774 return 0; 775 776 uintX_t Addend = Offset - Piece.InputOff; 777 return Piece.OutputOff + Addend; 778} 779 780template class elf::InputSectionBase<ELF32LE>; 781template class elf::InputSectionBase<ELF32BE>; 782template class elf::InputSectionBase<ELF64LE>; 783template class elf::InputSectionBase<ELF64BE>; 784 785template class elf::InputSection<ELF32LE>; 786template class elf::InputSection<ELF32BE>; 787template class elf::InputSection<ELF64LE>; 788template class elf::InputSection<ELF64BE>; 789 790template class elf::EhInputSection<ELF32LE>; 791template class elf::EhInputSection<ELF32BE>; 792template class elf::EhInputSection<ELF64LE>; 793template class elf::EhInputSection<ELF64BE>; 794 795template class elf::MergeInputSection<ELF32LE>; 796template class elf::MergeInputSection<ELF32BE>; 797template class elf::MergeInputSection<ELF64LE>; 798template class elf::MergeInputSection<ELF64BE>; 799 800template std::string lld::toString(const InputSectionBase<ELF32LE> *); 801template std::string lld::toString(const InputSectionBase<ELF32BE> *); 802template std::string lld::toString(const InputSectionBase<ELF64LE> *); 803template std::string lld::toString(const InputSectionBase<ELF64BE> *); 804