InputSection.cpp revision 319887
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 + A; 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 + A; 267 case R_ARM_THM_CALL: 268 // We don't want an interworking BLX to ARM 269 return P + 5 + A; 270 default: 271 return P + 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 + A; 283 default: 284 return P + 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_HINT: 294 case R_TLSDESC_CALL: 295 llvm_unreachable("cannot relocate hint relocs"); 296 case R_TLSLD: 297 return In<ELFT>::Got->getTlsIndexOff() + A - In<ELFT>::Got->getSize(); 298 case R_TLSLD_PC: 299 return In<ELFT>::Got->getTlsIndexVA() + A - P; 300 case R_THUNK_ABS: 301 return Body.getThunkVA<ELFT>() + A; 302 case R_THUNK_PC: 303 case R_THUNK_PLT_PC: 304 return Body.getThunkVA<ELFT>() + A - P; 305 case R_PPC_TOC: 306 return getPPC64TocBase() + A; 307 case R_TLSGD: 308 return In<ELFT>::Got->getGlobalDynOffset(Body) + A - 309 In<ELFT>::Got->getSize(); 310 case R_TLSGD_PC: 311 return In<ELFT>::Got->getGlobalDynAddr(Body) + A - P; 312 case R_TLSDESC: 313 return In<ELFT>::Got->getGlobalDynAddr(Body) + A; 314 case R_TLSDESC_PAGE: 315 return getAArch64Page(In<ELFT>::Got->getGlobalDynAddr(Body) + A) - 316 getAArch64Page(P); 317 case R_PLT: 318 return Body.getPltVA<ELFT>() + A; 319 case R_PLT_PC: 320 case R_PPC_PLT_OPD: 321 return Body.getPltVA<ELFT>() + A - P; 322 case R_SIZE: 323 return Body.getSize<ELFT>() + A; 324 case R_GOTREL: 325 return Body.getVA<ELFT>(A) - In<ELFT>::Got->getVA(); 326 case R_GOTREL_FROM_END: 327 return Body.getVA<ELFT>(A) - In<ELFT>::Got->getVA() - 328 In<ELFT>::Got->getSize(); 329 case R_RELAX_TLS_GD_TO_IE_END: 330 case R_GOT_FROM_END: 331 return Body.getGotOffset<ELFT>() + A - In<ELFT>::Got->getSize(); 332 case R_RELAX_TLS_GD_TO_IE_ABS: 333 case R_GOT: 334 return Body.getGotVA<ELFT>() + A; 335 case R_RELAX_TLS_GD_TO_IE_PAGE_PC: 336 case R_GOT_PAGE_PC: 337 return getAArch64Page(Body.getGotVA<ELFT>() + A) - getAArch64Page(P); 338 case R_RELAX_TLS_GD_TO_IE: 339 case R_GOT_PC: 340 return Body.getGotVA<ELFT>() + A - P; 341 case R_GOTONLY_PC: 342 return In<ELFT>::Got->getVA() + A - P; 343 case R_GOTONLY_PC_FROM_END: 344 return In<ELFT>::Got->getVA() + A - P + In<ELFT>::Got->getSize(); 345 case R_RELAX_TLS_LD_TO_LE: 346 case R_RELAX_TLS_IE_TO_LE: 347 case R_RELAX_TLS_GD_TO_LE: 348 case R_TLS: 349 // A weak undefined TLS symbol resolves to the base of the TLS 350 // block, i.e. gets a value of zero. If we pass --gc-sections to 351 // lld and .tbss is not referenced, it gets reclaimed and we don't 352 // create a TLS program header. Therefore, we resolve this 353 // statically to zero. 354 if (Body.isTls() && (Body.isLazy() || Body.isUndefined()) && 355 Body.symbol()->isWeak()) 356 return 0; 357 if (Target->TcbSize) 358 return Body.getVA<ELFT>(A) + 359 alignTo(Target->TcbSize, Out<ELFT>::TlsPhdr->p_align); 360 return Body.getVA<ELFT>(A) - Out<ELFT>::TlsPhdr->p_memsz; 361 case R_RELAX_TLS_GD_TO_LE_NEG: 362 case R_NEG_TLS: 363 return Out<ELF32LE>::TlsPhdr->p_memsz - Body.getVA<ELFT>(A); 364 case R_ABS: 365 case R_RELAX_GOT_PC_NOPIC: 366 return Body.getVA<ELFT>(A); 367 case R_GOT_OFF: 368 return Body.getGotOffset<ELFT>() + A; 369 case R_MIPS_GOT_LOCAL_PAGE: 370 // If relocation against MIPS local symbol requires GOT entry, this entry 371 // should be initialized by 'page address'. This address is high 16-bits 372 // of sum the symbol's value and the addend. 373 return In<ELFT>::MipsGot->getVA() + 374 In<ELFT>::MipsGot->getPageEntryOffset(Body, A) - 375 In<ELFT>::MipsGot->getGp(); 376 case R_MIPS_GOT_OFF: 377 case R_MIPS_GOT_OFF32: 378 // In case of MIPS if a GOT relocation has non-zero addend this addend 379 // should be applied to the GOT entry content not to the GOT entry offset. 380 // That is why we use separate expression type. 381 return In<ELFT>::MipsGot->getVA() + 382 In<ELFT>::MipsGot->getBodyEntryOffset(Body, A) - 383 In<ELFT>::MipsGot->getGp(); 384 case R_MIPS_GOTREL: 385 return Body.getVA<ELFT>(A) - In<ELFT>::MipsGot->getGp(); 386 case R_MIPS_TLSGD: 387 return In<ELFT>::MipsGot->getVA() + In<ELFT>::MipsGot->getTlsOffset() + 388 In<ELFT>::MipsGot->getGlobalDynOffset(Body) - 389 In<ELFT>::MipsGot->getGp(); 390 case R_MIPS_TLSLD: 391 return In<ELFT>::MipsGot->getVA() + In<ELFT>::MipsGot->getTlsOffset() + 392 In<ELFT>::MipsGot->getTlsIndexOff() - In<ELFT>::MipsGot->getGp(); 393 case R_PPC_OPD: { 394 uint64_t SymVA = Body.getVA<ELFT>(A); 395 // If we have an undefined weak symbol, we might get here with a symbol 396 // address of zero. That could overflow, but the code must be unreachable, 397 // so don't bother doing anything at all. 398 if (!SymVA) 399 return 0; 400 if (Out<ELF64BE>::Opd) { 401 // If this is a local call, and we currently have the address of a 402 // function-descriptor, get the underlying code address instead. 403 uint64_t OpdStart = Out<ELF64BE>::Opd->Addr; 404 uint64_t OpdEnd = OpdStart + Out<ELF64BE>::Opd->Size; 405 bool InOpd = OpdStart <= SymVA && SymVA < OpdEnd; 406 if (InOpd) 407 SymVA = read64be(&Out<ELF64BE>::OpdBuf[SymVA - OpdStart]); 408 } 409 return SymVA - P; 410 } 411 case R_PC: 412 if (Body.isUndefined() && !Body.isLocal() && Body.symbol()->isWeak()) { 413 // On ARM and AArch64 a branch to an undefined weak resolves to the 414 // next instruction, otherwise the place. 415 if (Config->EMachine == EM_ARM) 416 return getARMUndefinedRelativeWeakVA(Type, A, P); 417 if (Config->EMachine == EM_AARCH64) 418 return getAArch64UndefinedRelativeWeakVA(Type, A, P); 419 } 420 case R_RELAX_GOT_PC: 421 return Body.getVA<ELFT>(A) - P; 422 case R_PLT_PAGE_PC: 423 case R_PAGE_PC: 424 if (Body.isUndefined() && !Body.isLocal() && Body.symbol()->isWeak()) 425 return getAArch64Page(A); 426 return getAArch64Page(Body.getVA<ELFT>(A)) - getAArch64Page(P); 427 } 428 llvm_unreachable("Invalid expression"); 429} 430 431// This function applies relocations to sections without SHF_ALLOC bit. 432// Such sections are never mapped to memory at runtime. Debug sections are 433// an example. Relocations in non-alloc sections are much easier to 434// handle than in allocated sections because it will never need complex 435// treatement such as GOT or PLT (because at runtime no one refers them). 436// So, we handle relocations for non-alloc sections directly in this 437// function as a performance optimization. 438template <class ELFT> 439template <class RelTy> 440void InputSection<ELFT>::relocateNonAlloc(uint8_t *Buf, ArrayRef<RelTy> Rels) { 441 for (const RelTy &Rel : Rels) { 442 uint32_t Type = Rel.getType(Config->Mips64EL); 443 uintX_t Offset = this->getOffset(Rel.r_offset); 444 uint8_t *BufLoc = Buf + Offset; 445 uintX_t Addend = getAddend<ELFT>(Rel); 446 if (!RelTy::IsRela) 447 Addend += Target->getImplicitAddend(BufLoc, Type); 448 449 SymbolBody &Sym = this->File->getRelocTargetSym(Rel); 450 if (Target->getRelExpr(Type, Sym) != R_ABS) { 451 error(this->getLocation(Offset) + ": has non-ABS reloc"); 452 return; 453 } 454 455 uintX_t AddrLoc = this->OutSec->Addr + Offset; 456 uint64_t SymVA = 0; 457 if (!Sym.isTls() || Out<ELFT>::TlsPhdr) 458 SymVA = SignExtend64<sizeof(uintX_t) * 8>( 459 getRelocTargetVA<ELFT>(Type, Addend, AddrLoc, Sym, R_ABS)); 460 Target->relocateOne(BufLoc, Type, SymVA); 461 } 462} 463 464template <class ELFT> 465void InputSectionBase<ELFT>::relocate(uint8_t *Buf, uint8_t *BufEnd) { 466 // scanReloc function in Writer.cpp constructs Relocations 467 // vector only for SHF_ALLOC'ed sections. For other sections, 468 // we handle relocations directly here. 469 auto *IS = dyn_cast<InputSection<ELFT>>(this); 470 if (IS && !(IS->Flags & SHF_ALLOC)) { 471 if (IS->AreRelocsRela) 472 IS->relocateNonAlloc(Buf, IS->relas()); 473 else 474 IS->relocateNonAlloc(Buf, IS->rels()); 475 return; 476 } 477 478 const unsigned Bits = sizeof(uintX_t) * 8; 479 for (const Relocation &Rel : Relocations) { 480 uintX_t Offset = getOffset(Rel.Offset); 481 uint8_t *BufLoc = Buf + Offset; 482 uint32_t Type = Rel.Type; 483 uintX_t A = Rel.Addend; 484 485 uintX_t AddrLoc = OutSec->Addr + Offset; 486 RelExpr Expr = Rel.Expr; 487 uint64_t TargetVA = SignExtend64<Bits>( 488 getRelocTargetVA<ELFT>(Type, A, AddrLoc, *Rel.Sym, Expr)); 489 490 switch (Expr) { 491 case R_RELAX_GOT_PC: 492 case R_RELAX_GOT_PC_NOPIC: 493 Target->relaxGot(BufLoc, TargetVA); 494 break; 495 case R_RELAX_TLS_IE_TO_LE: 496 Target->relaxTlsIeToLe(BufLoc, Type, TargetVA); 497 break; 498 case R_RELAX_TLS_LD_TO_LE: 499 Target->relaxTlsLdToLe(BufLoc, Type, TargetVA); 500 break; 501 case R_RELAX_TLS_GD_TO_LE: 502 case R_RELAX_TLS_GD_TO_LE_NEG: 503 Target->relaxTlsGdToLe(BufLoc, Type, TargetVA); 504 break; 505 case R_RELAX_TLS_GD_TO_IE: 506 case R_RELAX_TLS_GD_TO_IE_ABS: 507 case R_RELAX_TLS_GD_TO_IE_PAGE_PC: 508 case R_RELAX_TLS_GD_TO_IE_END: 509 Target->relaxTlsGdToIe(BufLoc, Type, TargetVA); 510 break; 511 case R_PPC_PLT_OPD: 512 // Patch a nop (0x60000000) to a ld. 513 if (BufLoc + 8 <= BufEnd && read32be(BufLoc + 4) == 0x60000000) 514 write32be(BufLoc + 4, 0xe8410028); // ld %r2, 40(%r1) 515 // fallthrough 516 default: 517 Target->relocateOne(BufLoc, Type, TargetVA); 518 break; 519 } 520 } 521} 522 523template <class ELFT> void InputSection<ELFT>::writeTo(uint8_t *Buf) { 524 if (this->Type == SHT_NOBITS) 525 return; 526 527 if (auto *S = dyn_cast<SyntheticSection<ELFT>>(this)) { 528 S->writeTo(Buf + OutSecOff); 529 return; 530 } 531 532 // If -r is given, then an InputSection may be a relocation section. 533 if (this->Type == SHT_RELA) { 534 copyRelocations(Buf + OutSecOff, this->template getDataAs<Elf_Rela>()); 535 return; 536 } 537 if (this->Type == SHT_REL) { 538 copyRelocations(Buf + OutSecOff, this->template getDataAs<Elf_Rel>()); 539 return; 540 } 541 542 // Copy section contents from source object file to output file. 543 ArrayRef<uint8_t> Data = this->Data; 544 memcpy(Buf + OutSecOff, Data.data(), Data.size()); 545 546 // Iterate over all relocation sections that apply to this section. 547 uint8_t *BufEnd = Buf + OutSecOff + Data.size(); 548 this->relocate(Buf, BufEnd); 549 550 // The section might have a data/code generated by the linker and need 551 // to be written after the section. Usually these are thunks - small piece 552 // of code used to jump between "incompatible" functions like PIC and non-PIC 553 // or if the jump target too far and its address does not fit to the short 554 // jump istruction. 555 if (!Thunks.empty()) { 556 Buf += OutSecOff + getThunkOff(); 557 for (const Thunk<ELFT> *T : Thunks) { 558 T->writeTo(Buf); 559 Buf += T->size(); 560 } 561 } 562} 563 564template <class ELFT> 565void InputSection<ELFT>::replace(InputSection<ELFT> *Other) { 566 this->Alignment = std::max(this->Alignment, Other->Alignment); 567 Other->Repl = this->Repl; 568 Other->Live = false; 569} 570 571template <class ELFT> 572EhInputSection<ELFT>::EhInputSection(elf::ObjectFile<ELFT> *F, 573 const Elf_Shdr *Header, StringRef Name) 574 : InputSectionBase<ELFT>(F, Header, Name, InputSectionBase<ELFT>::EHFrame) { 575 // Mark .eh_frame sections as live by default because there are 576 // usually no relocations that point to .eh_frames. Otherwise, 577 // the garbage collector would drop all .eh_frame sections. 578 this->Live = true; 579} 580 581template <class ELFT> 582bool EhInputSection<ELFT>::classof(const InputSectionData *S) { 583 return S->kind() == InputSectionBase<ELFT>::EHFrame; 584} 585 586// Returns the index of the first relocation that points to a region between 587// Begin and Begin+Size. 588template <class IntTy, class RelTy> 589static unsigned getReloc(IntTy Begin, IntTy Size, const ArrayRef<RelTy> &Rels, 590 unsigned &RelocI) { 591 // Start search from RelocI for fast access. That works because the 592 // relocations are sorted in .eh_frame. 593 for (unsigned N = Rels.size(); RelocI < N; ++RelocI) { 594 const RelTy &Rel = Rels[RelocI]; 595 if (Rel.r_offset < Begin) 596 continue; 597 598 if (Rel.r_offset < Begin + Size) 599 return RelocI; 600 return -1; 601 } 602 return -1; 603} 604 605// .eh_frame is a sequence of CIE or FDE records. 606// This function splits an input section into records and returns them. 607template <class ELFT> void EhInputSection<ELFT>::split() { 608 // Early exit if already split. 609 if (!this->Pieces.empty()) 610 return; 611 612 if (this->NumRelocations) { 613 if (this->AreRelocsRela) 614 split(this->relas()); 615 else 616 split(this->rels()); 617 return; 618 } 619 split(makeArrayRef<typename ELFT::Rela>(nullptr, nullptr)); 620} 621 622template <class ELFT> 623template <class RelTy> 624void EhInputSection<ELFT>::split(ArrayRef<RelTy> Rels) { 625 ArrayRef<uint8_t> Data = this->Data; 626 unsigned RelI = 0; 627 for (size_t Off = 0, End = Data.size(); Off != End;) { 628 size_t Size = readEhRecordSize<ELFT>(this, Off); 629 this->Pieces.emplace_back(Off, this, Size, getReloc(Off, Size, Rels, RelI)); 630 // The empty record is the end marker. 631 if (Size == 4) 632 break; 633 Off += Size; 634 } 635} 636 637static size_t findNull(ArrayRef<uint8_t> A, size_t EntSize) { 638 // Optimize the common case. 639 StringRef S((const char *)A.data(), A.size()); 640 if (EntSize == 1) 641 return S.find(0); 642 643 for (unsigned I = 0, N = S.size(); I != N; I += EntSize) { 644 const char *B = S.begin() + I; 645 if (std::all_of(B, B + EntSize, [](char C) { return C == 0; })) 646 return I; 647 } 648 return StringRef::npos; 649} 650 651// Split SHF_STRINGS section. Such section is a sequence of 652// null-terminated strings. 653template <class ELFT> 654void MergeInputSection<ELFT>::splitStrings(ArrayRef<uint8_t> Data, 655 size_t EntSize) { 656 size_t Off = 0; 657 bool IsAlloc = this->Flags & SHF_ALLOC; 658 while (!Data.empty()) { 659 size_t End = findNull(Data, EntSize); 660 if (End == StringRef::npos) 661 fatal(toString(this) + ": string is not null terminated"); 662 size_t Size = End + EntSize; 663 Pieces.emplace_back(Off, !IsAlloc); 664 Hashes.push_back(hash_value(toStringRef(Data.slice(0, Size)))); 665 Data = Data.slice(Size); 666 Off += Size; 667 } 668} 669 670// Split non-SHF_STRINGS section. Such section is a sequence of 671// fixed size records. 672template <class ELFT> 673void MergeInputSection<ELFT>::splitNonStrings(ArrayRef<uint8_t> Data, 674 size_t EntSize) { 675 size_t Size = Data.size(); 676 assert((Size % EntSize) == 0); 677 bool IsAlloc = this->Flags & SHF_ALLOC; 678 for (unsigned I = 0, N = Size; I != N; I += EntSize) { 679 Hashes.push_back(hash_value(toStringRef(Data.slice(I, EntSize)))); 680 Pieces.emplace_back(I, !IsAlloc); 681 } 682} 683 684template <class ELFT> 685MergeInputSection<ELFT>::MergeInputSection(elf::ObjectFile<ELFT> *F, 686 const Elf_Shdr *Header, 687 StringRef Name) 688 : InputSectionBase<ELFT>(F, Header, Name, InputSectionBase<ELFT>::Merge) {} 689 690// This function is called after we obtain a complete list of input sections 691// that need to be linked. This is responsible to split section contents 692// into small chunks for further processing. 693// 694// Note that this function is called from parallel_for_each. This must be 695// thread-safe (i.e. no memory allocation from the pools). 696template <class ELFT> void MergeInputSection<ELFT>::splitIntoPieces() { 697 ArrayRef<uint8_t> Data = this->Data; 698 uintX_t EntSize = this->Entsize; 699 if (this->Flags & SHF_STRINGS) 700 splitStrings(Data, EntSize); 701 else 702 splitNonStrings(Data, EntSize); 703 704 if (Config->GcSections && (this->Flags & SHF_ALLOC)) 705 for (uintX_t Off : LiveOffsets) 706 this->getSectionPiece(Off)->Live = true; 707} 708 709template <class ELFT> 710bool MergeInputSection<ELFT>::classof(const InputSectionData *S) { 711 return S->kind() == InputSectionBase<ELFT>::Merge; 712} 713 714// Do binary search to get a section piece at a given input offset. 715template <class ELFT> 716SectionPiece *MergeInputSection<ELFT>::getSectionPiece(uintX_t Offset) { 717 auto *This = static_cast<const MergeInputSection<ELFT> *>(this); 718 return const_cast<SectionPiece *>(This->getSectionPiece(Offset)); 719} 720 721template <class It, class T, class Compare> 722static It fastUpperBound(It First, It Last, const T &Value, Compare Comp) { 723 size_t Size = std::distance(First, Last); 724 assert(Size != 0); 725 while (Size != 1) { 726 size_t H = Size / 2; 727 const It MI = First + H; 728 Size -= H; 729 First = Comp(Value, *MI) ? First : First + H; 730 } 731 return Comp(Value, *First) ? First : First + 1; 732} 733 734template <class ELFT> 735const SectionPiece * 736MergeInputSection<ELFT>::getSectionPiece(uintX_t Offset) const { 737 uintX_t Size = this->Data.size(); 738 if (Offset >= Size) 739 fatal(toString(this) + ": entry is past the end of the section"); 740 741 // Find the element this offset points to. 742 auto I = fastUpperBound( 743 Pieces.begin(), Pieces.end(), Offset, 744 [](const uintX_t &A, const SectionPiece &B) { return A < B.InputOff; }); 745 --I; 746 return &*I; 747} 748 749// Returns the offset in an output section for a given input offset. 750// Because contents of a mergeable section is not contiguous in output, 751// it is not just an addition to a base output offset. 752template <class ELFT> 753typename ELFT::uint MergeInputSection<ELFT>::getOffset(uintX_t Offset) const { 754 // Initialize OffsetMap lazily. 755 std::call_once(InitOffsetMap, [&] { 756 OffsetMap.reserve(Pieces.size()); 757 for (const SectionPiece &Piece : Pieces) 758 OffsetMap[Piece.InputOff] = Piece.OutputOff; 759 }); 760 761 // Find a string starting at a given offset. 762 auto It = OffsetMap.find(Offset); 763 if (It != OffsetMap.end()) 764 return It->second; 765 766 if (!this->Live) 767 return 0; 768 769 // If Offset is not at beginning of a section piece, it is not in the map. 770 // In that case we need to search from the original section piece vector. 771 const SectionPiece &Piece = *this->getSectionPiece(Offset); 772 if (!Piece.Live) 773 return 0; 774 775 uintX_t Addend = Offset - Piece.InputOff; 776 return Piece.OutputOff + Addend; 777} 778 779template class elf::InputSectionBase<ELF32LE>; 780template class elf::InputSectionBase<ELF32BE>; 781template class elf::InputSectionBase<ELF64LE>; 782template class elf::InputSectionBase<ELF64BE>; 783 784template class elf::InputSection<ELF32LE>; 785template class elf::InputSection<ELF32BE>; 786template class elf::InputSection<ELF64LE>; 787template class elf::InputSection<ELF64BE>; 788 789template class elf::EhInputSection<ELF32LE>; 790template class elf::EhInputSection<ELF32BE>; 791template class elf::EhInputSection<ELF64LE>; 792template class elf::EhInputSection<ELF64BE>; 793 794template class elf::MergeInputSection<ELF32LE>; 795template class elf::MergeInputSection<ELF32BE>; 796template class elf::MergeInputSection<ELF64LE>; 797template class elf::MergeInputSection<ELF64BE>; 798 799template std::string lld::toString(const InputSectionBase<ELF32LE> *); 800template std::string lld::toString(const InputSectionBase<ELF32BE> *); 801template std::string lld::toString(const InputSectionBase<ELF64LE> *); 802template std::string lld::toString(const InputSectionBase<ELF64BE> *); 803