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Diffstat (limited to 'contrib/llvm/tools/lld/ELF/InputSection.cpp')
| -rw-r--r-- | contrib/llvm/tools/lld/ELF/InputSection.cpp | 850 |
1 files changed, 850 insertions, 0 deletions
diff --git a/contrib/llvm/tools/lld/ELF/InputSection.cpp b/contrib/llvm/tools/lld/ELF/InputSection.cpp new file mode 100644 index 000000000000..e87d92aa207c --- /dev/null +++ b/contrib/llvm/tools/lld/ELF/InputSection.cpp @@ -0,0 +1,850 @@ +//===- InputSection.cpp ---------------------------------------------------===// +// +// The LLVM Linker +// +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// + +#include "InputSection.h" +#include "Config.h" +#include "EhFrame.h" +#include "Error.h" +#include "InputFiles.h" +#include "LinkerScript.h" +#include "Memory.h" +#include "OutputSections.h" +#include "Relocations.h" +#include "SyntheticSections.h" +#include "Target.h" +#include "Thunks.h" +#include "llvm/Support/Compression.h" +#include "llvm/Support/Endian.h" +#include <mutex> + +using namespace llvm; +using namespace llvm::ELF; +using namespace llvm::object; +using namespace llvm::support; +using namespace llvm::support::endian; + +using namespace lld; +using namespace lld::elf; + +// Returns a string to construct an error message. +template <class ELFT> +std::string lld::toString(const InputSectionBase<ELFT> *Sec) { + return (Sec->getFile()->getName() + ":(" + Sec->Name + ")").str(); +} + +template <class ELFT> +static ArrayRef<uint8_t> getSectionContents(elf::ObjectFile<ELFT> *File, + const typename ELFT::Shdr *Hdr) { + if (!File || Hdr->sh_type == SHT_NOBITS) + return makeArrayRef<uint8_t>(nullptr, Hdr->sh_size); + return check(File->getObj().getSectionContents(Hdr)); +} + +template <class ELFT> +InputSectionBase<ELFT>::InputSectionBase(elf::ObjectFile<ELFT> *File, + uintX_t Flags, uint32_t Type, + uintX_t Entsize, uint32_t Link, + uint32_t Info, uintX_t Addralign, + ArrayRef<uint8_t> Data, StringRef Name, + Kind SectionKind) + : InputSectionData(SectionKind, Name, Data, + !Config->GcSections || !(Flags & SHF_ALLOC)), + File(File), Flags(Flags), Entsize(Entsize), Type(Type), Link(Link), + Info(Info), Repl(this) { + NumRelocations = 0; + AreRelocsRela = false; + + // The ELF spec states that a value of 0 means the section has + // no alignment constraits. + uint64_t V = std::max<uint64_t>(Addralign, 1); + if (!isPowerOf2_64(V)) + fatal(toString(File) + ": section sh_addralign is not a power of 2"); + + // We reject object files having insanely large alignments even though + // they are allowed by the spec. I think 4GB is a reasonable limitation. + // We might want to relax this in the future. + if (V > UINT32_MAX) + fatal(toString(File) + ": section sh_addralign is too large"); + Alignment = V; + + // If it is not a mergeable section, overwrite the flag so that the flag + // is consistent with the class. This inconsistency could occur when + // string merging is disabled using -O0 flag. + if (!Config->Relocatable && !isa<MergeInputSection<ELFT>>(this)) + this->Flags &= ~(SHF_MERGE | SHF_STRINGS); +} + +template <class ELFT> +InputSectionBase<ELFT>::InputSectionBase(elf::ObjectFile<ELFT> *File, + const Elf_Shdr *Hdr, StringRef Name, + Kind SectionKind) + : InputSectionBase(File, Hdr->sh_flags & ~SHF_INFO_LINK, Hdr->sh_type, + Hdr->sh_entsize, Hdr->sh_link, Hdr->sh_info, + Hdr->sh_addralign, getSectionContents(File, Hdr), Name, + SectionKind) { + this->Offset = Hdr->sh_offset; +} + +template <class ELFT> size_t InputSectionBase<ELFT>::getSize() const { + if (auto *S = dyn_cast<SyntheticSection<ELFT>>(this)) + return S->getSize(); + + if (auto *D = dyn_cast<InputSection<ELFT>>(this)) + if (D->getThunksSize() > 0) + return D->getThunkOff() + D->getThunksSize(); + + return Data.size(); +} + +// Returns a string for an error message. +template <class SectionT> static std::string getName(SectionT *Sec) { + return (Sec->getFile()->getName() + ":(" + Sec->Name + ")").str(); +} + +template <class ELFT> +typename ELFT::uint InputSectionBase<ELFT>::getOffset(uintX_t Offset) const { + switch (kind()) { + case Regular: + return cast<InputSection<ELFT>>(this)->OutSecOff + Offset; + case Synthetic: + // For synthetic sections we treat offset -1 as the end of the section. + // The same approach is used for synthetic symbols (DefinedSynthetic). + return cast<InputSection<ELFT>>(this)->OutSecOff + + (Offset == uintX_t(-1) ? getSize() : Offset); + case EHFrame: + // The file crtbeginT.o has relocations pointing to the start of an empty + // .eh_frame that is known to be the first in the link. It does that to + // identify the start of the output .eh_frame. + return Offset; + case Merge: + return cast<MergeInputSection<ELFT>>(this)->getOffset(Offset); + } + llvm_unreachable("invalid section kind"); +} + +template <class ELFT> bool InputSectionBase<ELFT>::isCompressed() const { + return (Flags & SHF_COMPRESSED) || Name.startswith(".zdebug"); +} + +// Returns compressed data and its size when uncompressed. +template <class ELFT> +std::pair<ArrayRef<uint8_t>, uint64_t> +InputSectionBase<ELFT>::getElfCompressedData(ArrayRef<uint8_t> Data) { + // Compressed section with Elf_Chdr is the ELF standard. + if (Data.size() < sizeof(Elf_Chdr)) + fatal(toString(this) + ": corrupted compressed section"); + auto *Hdr = reinterpret_cast<const Elf_Chdr *>(Data.data()); + if (Hdr->ch_type != ELFCOMPRESS_ZLIB) + fatal(toString(this) + ": unsupported compression type"); + return {Data.slice(sizeof(*Hdr)), Hdr->ch_size}; +} + +// Returns compressed data and its size when uncompressed. +template <class ELFT> +std::pair<ArrayRef<uint8_t>, uint64_t> +InputSectionBase<ELFT>::getRawCompressedData(ArrayRef<uint8_t> Data) { + // Compressed sections without Elf_Chdr header contain this header + // instead. This is a GNU extension. + struct ZlibHeader { + char Magic[4]; // Should be "ZLIB" + char Size[8]; // Uncompressed size in big-endian + }; + + if (Data.size() < sizeof(ZlibHeader)) + fatal(toString(this) + ": corrupted compressed section"); + auto *Hdr = reinterpret_cast<const ZlibHeader *>(Data.data()); + if (memcmp(Hdr->Magic, "ZLIB", 4)) + fatal(toString(this) + ": broken ZLIB-compressed section"); + return {Data.slice(sizeof(*Hdr)), read64be(Hdr->Size)}; +} + +// Uncompress section contents. Note that this function is called +// from parallel_for_each, so it must be thread-safe. +template <class ELFT> void InputSectionBase<ELFT>::uncompress() { + if (!zlib::isAvailable()) + fatal(toString(this) + + ": build lld with zlib to enable compressed sections support"); + + // This section is compressed. Here we decompress it. Ideally, all + // compressed sections have SHF_COMPRESSED bit and their contents + // start with headers of Elf_Chdr type. However, sections whose + // names start with ".zdebug_" don't have the bit and contains a raw + // ZLIB-compressed data (which is a bad thing because section names + // shouldn't be significant in ELF.) We need to be able to read both. + ArrayRef<uint8_t> Buf; // Compressed data + size_t Size; // Uncompressed size + if (Flags & SHF_COMPRESSED) + std::tie(Buf, Size) = getElfCompressedData(Data); + else + std::tie(Buf, Size) = getRawCompressedData(Data); + + // Uncompress Buf. + char *OutputBuf; + { + static std::mutex Mu; + std::lock_guard<std::mutex> Lock(Mu); + OutputBuf = BAlloc.Allocate<char>(Size); + } + if (zlib::uncompress(toStringRef(Buf), OutputBuf, Size) != zlib::StatusOK) + fatal(toString(this) + ": error while uncompressing section"); + Data = ArrayRef<uint8_t>((uint8_t *)OutputBuf, Size); +} + +template <class ELFT> +typename ELFT::uint +InputSectionBase<ELFT>::getOffset(const DefinedRegular<ELFT> &Sym) const { + return getOffset(Sym.Value); +} + +template <class ELFT> +InputSectionBase<ELFT> *InputSectionBase<ELFT>::getLinkOrderDep() const { + if ((Flags & SHF_LINK_ORDER) && Link != 0) + return getFile()->getSections()[Link]; + return nullptr; +} + +// Returns a source location string. Used to construct an error message. +template <class ELFT> +std::string InputSectionBase<ELFT>::getLocation(typename ELFT::uint Offset) { + // First check if we can get desired values from debugging information. + std::string LineInfo = File->getLineInfo(this, Offset); + if (!LineInfo.empty()) + return LineInfo; + + // File->SourceFile contains STT_FILE symbol that contains a + // source file name. If it's missing, we use an object file name. + std::string SrcFile = File->SourceFile; + if (SrcFile.empty()) + SrcFile = toString(File); + + // Find a function symbol that encloses a given location. + for (SymbolBody *B : File->getSymbols()) + if (auto *D = dyn_cast<DefinedRegular<ELFT>>(B)) + if (D->Section == this && D->Type == STT_FUNC) + if (D->Value <= Offset && Offset < D->Value + D->Size) + return SrcFile + ":(function " + toString(*D) + ")"; + + // If there's no symbol, print out the offset in the section. + return (SrcFile + ":(" + Name + "+0x" + utohexstr(Offset) + ")").str(); +} + +template <class ELFT> +InputSection<ELFT>::InputSection() : InputSectionBase<ELFT>() {} + +template <class ELFT> +InputSection<ELFT>::InputSection(uintX_t Flags, uint32_t Type, + uintX_t Addralign, ArrayRef<uint8_t> Data, + StringRef Name, Kind K) + : InputSectionBase<ELFT>(nullptr, Flags, Type, + /*Entsize*/ 0, /*Link*/ 0, /*Info*/ 0, Addralign, + Data, Name, K) {} + +template <class ELFT> +InputSection<ELFT>::InputSection(elf::ObjectFile<ELFT> *F, + const Elf_Shdr *Header, StringRef Name) + : InputSectionBase<ELFT>(F, Header, Name, Base::Regular) {} + +template <class ELFT> +bool InputSection<ELFT>::classof(const InputSectionData *S) { + return S->kind() == Base::Regular || S->kind() == Base::Synthetic; +} + +template <class ELFT> +InputSectionBase<ELFT> *InputSection<ELFT>::getRelocatedSection() { + assert(this->Type == SHT_RELA || this->Type == SHT_REL); + ArrayRef<InputSectionBase<ELFT> *> Sections = this->File->getSections(); + return Sections[this->Info]; +} + +template <class ELFT> void InputSection<ELFT>::addThunk(const Thunk<ELFT> *T) { + Thunks.push_back(T); +} + +template <class ELFT> uint64_t InputSection<ELFT>::getThunkOff() const { + return this->Data.size(); +} + +template <class ELFT> uint64_t InputSection<ELFT>::getThunksSize() const { + uint64_t Total = 0; + for (const Thunk<ELFT> *T : Thunks) + Total += T->size(); + return Total; +} + +// This is used for -r. We can't use memcpy to copy relocations because we need +// to update symbol table offset and section index for each relocation. So we +// copy relocations one by one. +template <class ELFT> +template <class RelTy> +void InputSection<ELFT>::copyRelocations(uint8_t *Buf, ArrayRef<RelTy> Rels) { + InputSectionBase<ELFT> *RelocatedSection = getRelocatedSection(); + + for (const RelTy &Rel : Rels) { + uint32_t Type = Rel.getType(Config->Mips64EL); + SymbolBody &Body = this->File->getRelocTargetSym(Rel); + + Elf_Rela *P = reinterpret_cast<Elf_Rela *>(Buf); + Buf += sizeof(RelTy); + + if (Config->Rela) + P->r_addend = getAddend<ELFT>(Rel); + P->r_offset = RelocatedSection->getOffset(Rel.r_offset); + P->setSymbolAndType(Body.DynsymIndex, Type, Config->Mips64EL); + } +} + +static uint32_t getARMUndefinedRelativeWeakVA(uint32_t Type, uint32_t A, + uint32_t P) { + switch (Type) { + case R_ARM_THM_JUMP11: + return P + 2; + case R_ARM_CALL: + case R_ARM_JUMP24: + case R_ARM_PC24: + case R_ARM_PLT32: + case R_ARM_PREL31: + case R_ARM_THM_JUMP19: + case R_ARM_THM_JUMP24: + return P + 4; + case R_ARM_THM_CALL: + // We don't want an interworking BLX to ARM + return P + 5; + default: + return A; + } +} + +static uint64_t getAArch64UndefinedRelativeWeakVA(uint64_t Type, uint64_t A, + uint64_t P) { + switch (Type) { + case R_AARCH64_CALL26: + case R_AARCH64_CONDBR19: + case R_AARCH64_JUMP26: + case R_AARCH64_TSTBR14: + return P + 4; + default: + return A; + } +} + +template <class ELFT> +static typename ELFT::uint +getRelocTargetVA(uint32_t Type, typename ELFT::uint A, typename ELFT::uint P, + const SymbolBody &Body, RelExpr Expr) { + switch (Expr) { + case R_HINT: + case R_TLSDESC_CALL: + llvm_unreachable("cannot relocate hint relocs"); + case R_TLSLD: + return In<ELFT>::Got->getTlsIndexOff() + A - In<ELFT>::Got->getSize(); + case R_TLSLD_PC: + return In<ELFT>::Got->getTlsIndexVA() + A - P; + case R_THUNK_ABS: + return Body.getThunkVA<ELFT>() + A; + case R_THUNK_PC: + case R_THUNK_PLT_PC: + return Body.getThunkVA<ELFT>() + A - P; + case R_PPC_TOC: + return getPPC64TocBase() + A; + case R_TLSGD: + return In<ELFT>::Got->getGlobalDynOffset(Body) + A - + In<ELFT>::Got->getSize(); + case R_TLSGD_PC: + return In<ELFT>::Got->getGlobalDynAddr(Body) + A - P; + case R_TLSDESC: + return In<ELFT>::Got->getGlobalDynAddr(Body) + A; + case R_TLSDESC_PAGE: + return getAArch64Page(In<ELFT>::Got->getGlobalDynAddr(Body) + A) - + getAArch64Page(P); + case R_PLT: + return Body.getPltVA<ELFT>() + A; + case R_PLT_PC: + case R_PPC_PLT_OPD: + return Body.getPltVA<ELFT>() + A - P; + case R_SIZE: + return Body.getSize<ELFT>() + A; + case R_GOTREL: + return Body.getVA<ELFT>(A) - In<ELFT>::Got->getVA(); + case R_GOTREL_FROM_END: + return Body.getVA<ELFT>(A) - In<ELFT>::Got->getVA() - + In<ELFT>::Got->getSize(); + case R_RELAX_TLS_GD_TO_IE_END: + case R_GOT_FROM_END: + return Body.getGotOffset<ELFT>() + A - In<ELFT>::Got->getSize(); + case R_RELAX_TLS_GD_TO_IE_ABS: + case R_GOT: + return Body.getGotVA<ELFT>() + A; + case R_RELAX_TLS_GD_TO_IE_PAGE_PC: + case R_GOT_PAGE_PC: + return getAArch64Page(Body.getGotVA<ELFT>() + A) - getAArch64Page(P); + case R_RELAX_TLS_GD_TO_IE: + case R_GOT_PC: + return Body.getGotVA<ELFT>() + A - P; + case R_GOTONLY_PC: + return In<ELFT>::Got->getVA() + A - P; + case R_GOTONLY_PC_FROM_END: + return In<ELFT>::Got->getVA() + A - P + In<ELFT>::Got->getSize(); + case R_RELAX_TLS_LD_TO_LE: + case R_RELAX_TLS_IE_TO_LE: + case R_RELAX_TLS_GD_TO_LE: + case R_TLS: + // A weak undefined TLS symbol resolves to the base of the TLS + // block, i.e. gets a value of zero. If we pass --gc-sections to + // lld and .tbss is not referenced, it gets reclaimed and we don't + // create a TLS program header. Therefore, we resolve this + // statically to zero. + if (Body.isTls() && (Body.isLazy() || Body.isUndefined()) && + Body.symbol()->isWeak()) + return 0; + if (Target->TcbSize) + return Body.getVA<ELFT>(A) + + alignTo(Target->TcbSize, Out<ELFT>::TlsPhdr->p_align); + return Body.getVA<ELFT>(A) - Out<ELFT>::TlsPhdr->p_memsz; + case R_RELAX_TLS_GD_TO_LE_NEG: + case R_NEG_TLS: + return Out<ELF32LE>::TlsPhdr->p_memsz - Body.getVA<ELFT>(A); + case R_ABS: + case R_RELAX_GOT_PC_NOPIC: + return Body.getVA<ELFT>(A); + case R_GOT_OFF: + return Body.getGotOffset<ELFT>() + A; + case R_MIPS_GOT_LOCAL_PAGE: + // If relocation against MIPS local symbol requires GOT entry, this entry + // should be initialized by 'page address'. This address is high 16-bits + // of sum the symbol's value and the addend. + return In<ELFT>::MipsGot->getVA() + + In<ELFT>::MipsGot->getPageEntryOffset(Body, A) - + In<ELFT>::MipsGot->getGp(); + case R_MIPS_GOT_OFF: + case R_MIPS_GOT_OFF32: + // In case of MIPS if a GOT relocation has non-zero addend this addend + // should be applied to the GOT entry content not to the GOT entry offset. + // That is why we use separate expression type. + return In<ELFT>::MipsGot->getVA() + + In<ELFT>::MipsGot->getBodyEntryOffset(Body, A) - + In<ELFT>::MipsGot->getGp(); + case R_MIPS_GOTREL: + return Body.getVA<ELFT>(A) - In<ELFT>::MipsGot->getGp(); + case R_MIPS_TLSGD: + return In<ELFT>::MipsGot->getVA() + In<ELFT>::MipsGot->getTlsOffset() + + In<ELFT>::MipsGot->getGlobalDynOffset(Body) - + In<ELFT>::MipsGot->getGp(); + case R_MIPS_TLSLD: + return In<ELFT>::MipsGot->getVA() + In<ELFT>::MipsGot->getTlsOffset() + + In<ELFT>::MipsGot->getTlsIndexOff() - In<ELFT>::MipsGot->getGp(); + case R_PPC_OPD: { + uint64_t SymVA = Body.getVA<ELFT>(A); + // If we have an undefined weak symbol, we might get here with a symbol + // address of zero. That could overflow, but the code must be unreachable, + // so don't bother doing anything at all. + if (!SymVA) + return 0; + if (Out<ELF64BE>::Opd) { + // If this is a local call, and we currently have the address of a + // function-descriptor, get the underlying code address instead. + uint64_t OpdStart = Out<ELF64BE>::Opd->Addr; + uint64_t OpdEnd = OpdStart + Out<ELF64BE>::Opd->Size; + bool InOpd = OpdStart <= SymVA && SymVA < OpdEnd; + if (InOpd) + SymVA = read64be(&Out<ELF64BE>::OpdBuf[SymVA - OpdStart]); + } + return SymVA - P; + } + case R_PC: + if (Body.isUndefined() && !Body.isLocal() && Body.symbol()->isWeak()) { + // On ARM and AArch64 a branch to an undefined weak resolves to the + // next instruction, otherwise the place. + if (Config->EMachine == EM_ARM) + return getARMUndefinedRelativeWeakVA(Type, A, P); + if (Config->EMachine == EM_AARCH64) + return getAArch64UndefinedRelativeWeakVA(Type, A, P); + } + case R_RELAX_GOT_PC: + return Body.getVA<ELFT>(A) - P; + case R_PLT_PAGE_PC: + case R_PAGE_PC: + if (Body.isUndefined() && !Body.isLocal() && Body.symbol()->isWeak()) + return getAArch64Page(A); + return getAArch64Page(Body.getVA<ELFT>(A)) - getAArch64Page(P); + } + llvm_unreachable("Invalid expression"); +} + +// This function applies relocations to sections without SHF_ALLOC bit. +// Such sections are never mapped to memory at runtime. Debug sections are +// an example. Relocations in non-alloc sections are much easier to +// handle than in allocated sections because it will never need complex +// treatement such as GOT or PLT (because at runtime no one refers them). +// So, we handle relocations for non-alloc sections directly in this +// function as a performance optimization. +template <class ELFT> +template <class RelTy> +void InputSection<ELFT>::relocateNonAlloc(uint8_t *Buf, ArrayRef<RelTy> Rels) { + for (const RelTy &Rel : Rels) { + uint32_t Type = Rel.getType(Config->Mips64EL); + uintX_t Offset = this->getOffset(Rel.r_offset); + uint8_t *BufLoc = Buf + Offset; + uintX_t Addend = getAddend<ELFT>(Rel); + if (!RelTy::IsRela) + Addend += Target->getImplicitAddend(BufLoc, Type); + + SymbolBody &Sym = this->File->getRelocTargetSym(Rel); + if (Target->getRelExpr(Type, Sym) != R_ABS) { + error(this->getLocation(Offset) + ": has non-ABS reloc"); + return; + } + + uintX_t AddrLoc = this->OutSec->Addr + Offset; + uint64_t SymVA = 0; + if (!Sym.isTls() || Out<ELFT>::TlsPhdr) + SymVA = SignExtend64<sizeof(uintX_t) * 8>( + getRelocTargetVA<ELFT>(Type, Addend, AddrLoc, Sym, R_ABS)); + Target->relocateOne(BufLoc, Type, SymVA); + } +} + +template <class ELFT> +void InputSectionBase<ELFT>::relocate(uint8_t *Buf, uint8_t *BufEnd) { + // scanReloc function in Writer.cpp constructs Relocations + // vector only for SHF_ALLOC'ed sections. For other sections, + // we handle relocations directly here. + auto *IS = dyn_cast<InputSection<ELFT>>(this); + if (IS && !(IS->Flags & SHF_ALLOC)) { + if (IS->AreRelocsRela) + IS->relocateNonAlloc(Buf, IS->relas()); + else + IS->relocateNonAlloc(Buf, IS->rels()); + return; + } + + const unsigned Bits = sizeof(uintX_t) * 8; + for (const Relocation &Rel : Relocations) { + uintX_t Offset = getOffset(Rel.Offset); + uint8_t *BufLoc = Buf + Offset; + uint32_t Type = Rel.Type; + uintX_t A = Rel.Addend; + + uintX_t AddrLoc = OutSec->Addr + Offset; + RelExpr Expr = Rel.Expr; + uint64_t TargetVA = SignExtend64<Bits>( + getRelocTargetVA<ELFT>(Type, A, AddrLoc, *Rel.Sym, Expr)); + + switch (Expr) { + case R_RELAX_GOT_PC: + case R_RELAX_GOT_PC_NOPIC: + Target->relaxGot(BufLoc, TargetVA); + break; + case R_RELAX_TLS_IE_TO_LE: + Target->relaxTlsIeToLe(BufLoc, Type, TargetVA); + break; + case R_RELAX_TLS_LD_TO_LE: + Target->relaxTlsLdToLe(BufLoc, Type, TargetVA); + break; + case R_RELAX_TLS_GD_TO_LE: + case R_RELAX_TLS_GD_TO_LE_NEG: + Target->relaxTlsGdToLe(BufLoc, Type, TargetVA); + break; + case R_RELAX_TLS_GD_TO_IE: + case R_RELAX_TLS_GD_TO_IE_ABS: + case R_RELAX_TLS_GD_TO_IE_PAGE_PC: + case R_RELAX_TLS_GD_TO_IE_END: + Target->relaxTlsGdToIe(BufLoc, Type, TargetVA); + break; + case R_PPC_PLT_OPD: + // Patch a nop (0x60000000) to a ld. + if (BufLoc + 8 <= BufEnd && read32be(BufLoc + 4) == 0x60000000) + write32be(BufLoc + 4, 0xe8410028); // ld %r2, 40(%r1) + // fallthrough + default: + Target->relocateOne(BufLoc, Type, TargetVA); + break; + } + } +} + +template <class ELFT> void InputSection<ELFT>::writeTo(uint8_t *Buf) { + if (this->Type == SHT_NOBITS) + return; + + if (auto *S = dyn_cast<SyntheticSection<ELFT>>(this)) { + S->writeTo(Buf + OutSecOff); + return; + } + + // If -r is given, then an InputSection may be a relocation section. + if (this->Type == SHT_RELA) { + copyRelocations(Buf + OutSecOff, this->template getDataAs<Elf_Rela>()); + return; + } + if (this->Type == SHT_REL) { + copyRelocations(Buf + OutSecOff, this->template getDataAs<Elf_Rel>()); + return; + } + + // Copy section contents from source object file to output file. + ArrayRef<uint8_t> Data = this->Data; + memcpy(Buf + OutSecOff, Data.data(), Data.size()); + + // Iterate over all relocation sections that apply to this section. + uint8_t *BufEnd = Buf + OutSecOff + Data.size(); + this->relocate(Buf, BufEnd); + + // The section might have a data/code generated by the linker and need + // to be written after the section. Usually these are thunks - small piece + // of code used to jump between "incompatible" functions like PIC and non-PIC + // or if the jump target too far and its address does not fit to the short + // jump istruction. + if (!Thunks.empty()) { + Buf += OutSecOff + getThunkOff(); + for (const Thunk<ELFT> *T : Thunks) { + T->writeTo(Buf); + Buf += T->size(); + } + } +} + +template <class ELFT> +void InputSection<ELFT>::replace(InputSection<ELFT> *Other) { + this->Alignment = std::max(this->Alignment, Other->Alignment); + Other->Repl = this->Repl; + Other->Live = false; +} + +template <class ELFT> +EhInputSection<ELFT>::EhInputSection(elf::ObjectFile<ELFT> *F, + const Elf_Shdr *Header, StringRef Name) + : InputSectionBase<ELFT>(F, Header, Name, InputSectionBase<ELFT>::EHFrame) { + // Mark .eh_frame sections as live by default because there are + // usually no relocations that point to .eh_frames. Otherwise, + // the garbage collector would drop all .eh_frame sections. + this->Live = true; +} + +template <class ELFT> +bool EhInputSection<ELFT>::classof(const InputSectionData *S) { + return S->kind() == InputSectionBase<ELFT>::EHFrame; +} + +// Returns the index of the first relocation that points to a region between +// Begin and Begin+Size. +template <class IntTy, class RelTy> +static unsigned getReloc(IntTy Begin, IntTy Size, const ArrayRef<RelTy> &Rels, + unsigned &RelocI) { + // Start search from RelocI for fast access. That works because the + // relocations are sorted in .eh_frame. + for (unsigned N = Rels.size(); RelocI < N; ++RelocI) { + const RelTy &Rel = Rels[RelocI]; + if (Rel.r_offset < Begin) + continue; + + if (Rel.r_offset < Begin + Size) + return RelocI; + return -1; + } + return -1; +} + +// .eh_frame is a sequence of CIE or FDE records. +// This function splits an input section into records and returns them. +template <class ELFT> void EhInputSection<ELFT>::split() { + // Early exit if already split. + if (!this->Pieces.empty()) + return; + + if (this->NumRelocations) { + if (this->AreRelocsRela) + split(this->relas()); + else + split(this->rels()); + return; + } + split(makeArrayRef<typename ELFT::Rela>(nullptr, nullptr)); +} + +template <class ELFT> +template <class RelTy> +void EhInputSection<ELFT>::split(ArrayRef<RelTy> Rels) { + ArrayRef<uint8_t> Data = this->Data; + unsigned RelI = 0; + for (size_t Off = 0, End = Data.size(); Off != End;) { + size_t Size = readEhRecordSize<ELFT>(this, Off); + this->Pieces.emplace_back(Off, this, Size, getReloc(Off, Size, Rels, RelI)); + // The empty record is the end marker. + if (Size == 4) + break; + Off += Size; + } +} + +static size_t findNull(ArrayRef<uint8_t> A, size_t EntSize) { + // Optimize the common case. + StringRef S((const char *)A.data(), A.size()); + if (EntSize == 1) + return S.find(0); + + for (unsigned I = 0, N = S.size(); I != N; I += EntSize) { + const char *B = S.begin() + I; + if (std::all_of(B, B + EntSize, [](char C) { return C == 0; })) + return I; + } + return StringRef::npos; +} + +// Split SHF_STRINGS section. Such section is a sequence of +// null-terminated strings. +template <class ELFT> +void MergeInputSection<ELFT>::splitStrings(ArrayRef<uint8_t> Data, + size_t EntSize) { + size_t Off = 0; + bool IsAlloc = this->Flags & SHF_ALLOC; + while (!Data.empty()) { + size_t End = findNull(Data, EntSize); + if (End == StringRef::npos) + fatal(toString(this) + ": string is not null terminated"); + size_t Size = End + EntSize; + Pieces.emplace_back(Off, !IsAlloc); + Hashes.push_back(hash_value(toStringRef(Data.slice(0, Size)))); + Data = Data.slice(Size); + Off += Size; + } +} + +// Split non-SHF_STRINGS section. Such section is a sequence of +// fixed size records. +template <class ELFT> +void MergeInputSection<ELFT>::splitNonStrings(ArrayRef<uint8_t> Data, + size_t EntSize) { + size_t Size = Data.size(); + assert((Size % EntSize) == 0); + bool IsAlloc = this->Flags & SHF_ALLOC; + for (unsigned I = 0, N = Size; I != N; I += EntSize) { + Hashes.push_back(hash_value(toStringRef(Data.slice(I, EntSize)))); + Pieces.emplace_back(I, !IsAlloc); + } +} + +template <class ELFT> +MergeInputSection<ELFT>::MergeInputSection(elf::ObjectFile<ELFT> *F, + const Elf_Shdr *Header, + StringRef Name) + : InputSectionBase<ELFT>(F, Header, Name, InputSectionBase<ELFT>::Merge) {} + +// This function is called after we obtain a complete list of input sections +// that need to be linked. This is responsible to split section contents +// into small chunks for further processing. +// +// Note that this function is called from parallel_for_each. This must be +// thread-safe (i.e. no memory allocation from the pools). +template <class ELFT> void MergeInputSection<ELFT>::splitIntoPieces() { + ArrayRef<uint8_t> Data = this->Data; + uintX_t EntSize = this->Entsize; + if (this->Flags & SHF_STRINGS) + splitStrings(Data, EntSize); + else + splitNonStrings(Data, EntSize); + + if (Config->GcSections && (this->Flags & SHF_ALLOC)) + for (uintX_t Off : LiveOffsets) + this->getSectionPiece(Off)->Live = true; +} + +template <class ELFT> +bool MergeInputSection<ELFT>::classof(const InputSectionData *S) { + return S->kind() == InputSectionBase<ELFT>::Merge; +} + +// Do binary search to get a section piece at a given input offset. +template <class ELFT> +SectionPiece *MergeInputSection<ELFT>::getSectionPiece(uintX_t Offset) { + auto *This = static_cast<const MergeInputSection<ELFT> *>(this); + return const_cast<SectionPiece *>(This->getSectionPiece(Offset)); +} + +template <class It, class T, class Compare> +static It fastUpperBound(It First, It Last, const T &Value, Compare Comp) { + size_t Size = std::distance(First, Last); + assert(Size != 0); + while (Size != 1) { + size_t H = Size / 2; + const It MI = First + H; + Size -= H; + First = Comp(Value, *MI) ? First : First + H; + } + return Comp(Value, *First) ? First : First + 1; +} + +template <class ELFT> +const SectionPiece * +MergeInputSection<ELFT>::getSectionPiece(uintX_t Offset) const { + uintX_t Size = this->Data.size(); + if (Offset >= Size) + fatal(toString(this) + ": entry is past the end of the section"); + + // Find the element this offset points to. + auto I = fastUpperBound( + Pieces.begin(), Pieces.end(), Offset, + [](const uintX_t &A, const SectionPiece &B) { return A < B.InputOff; }); + --I; + return &*I; +} + +// Returns the offset in an output section for a given input offset. +// Because contents of a mergeable section is not contiguous in output, +// it is not just an addition to a base output offset. +template <class ELFT> +typename ELFT::uint MergeInputSection<ELFT>::getOffset(uintX_t Offset) const { + // Initialize OffsetMap lazily. + std::call_once(InitOffsetMap, [&] { + OffsetMap.reserve(Pieces.size()); + for (const SectionPiece &Piece : Pieces) + OffsetMap[Piece.InputOff] = Piece.OutputOff; + }); + + // Find a string starting at a given offset. + auto It = OffsetMap.find(Offset); + if (It != OffsetMap.end()) + return It->second; + + if (!this->Live) + return 0; + + // If Offset is not at beginning of a section piece, it is not in the map. + // In that case we need to search from the original section piece vector. + const SectionPiece &Piece = *this->getSectionPiece(Offset); + if (!Piece.Live) + return 0; + + uintX_t Addend = Offset - Piece.InputOff; + return Piece.OutputOff + Addend; +} + +template class elf::InputSectionBase<ELF32LE>; +template class elf::InputSectionBase<ELF32BE>; +template class elf::InputSectionBase<ELF64LE>; +template class elf::InputSectionBase<ELF64BE>; + +template class elf::InputSection<ELF32LE>; +template class elf::InputSection<ELF32BE>; +template class elf::InputSection<ELF64LE>; +template class elf::InputSection<ELF64BE>; + +template class elf::EhInputSection<ELF32LE>; +template class elf::EhInputSection<ELF32BE>; +template class elf::EhInputSection<ELF64LE>; +template class elf::EhInputSection<ELF64BE>; + +template class elf::MergeInputSection<ELF32LE>; +template class elf::MergeInputSection<ELF32BE>; +template class elf::MergeInputSection<ELF64LE>; +template class elf::MergeInputSection<ELF64BE>; + +template std::string lld::toString(const InputSectionBase<ELF32LE> *); +template std::string lld::toString(const InputSectionBase<ELF32BE> *); +template std::string lld::toString(const InputSectionBase<ELF64LE> *); +template std::string lld::toString(const InputSectionBase<ELF64BE> *); |