//===- 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 "Error.h" #include "InputFiles.h" #include "OutputSections.h" #include "Target.h" #include "llvm/Support/Endian.h" using namespace llvm; using namespace llvm::ELF; using namespace llvm::object; using namespace llvm::support::endian; using namespace lld; using namespace lld::elf; template InputSectionBase::InputSectionBase(elf::ObjectFile *File, const Elf_Shdr *Header, Kind SectionKind) : Header(Header), File(File), SectionKind(SectionKind), Repl(this) { // The garbage collector sets sections' Live bits. // If GC is disabled, all sections are considered live by default. Live = !Config->GcSections; // The ELF spec states that a value of 0 means the section has // no alignment constraits. Align = std::max(Header->sh_addralign, 1); } template size_t InputSectionBase::getSize() const { if (auto *D = dyn_cast>(this)) if (D->getThunksSize() > 0) return D->getThunkOff() + D->getThunksSize(); return Header->sh_size; } template StringRef InputSectionBase::getSectionName() const { return check(File->getObj().getSectionName(this->Header)); } template ArrayRef InputSectionBase::getSectionData() const { return check(this->File->getObj().getSectionContents(this->Header)); } template typename ELFT::uint InputSectionBase::getOffset(uintX_t Offset) { switch (SectionKind) { case Regular: return cast>(this)->OutSecOff + Offset; case EHFrame: return cast>(this)->getOffset(Offset); case Merge: return cast>(this)->getOffset(Offset); case MipsReginfo: case MipsOptions: // MIPS .reginfo and .MIPS.options sections are consumed by the linker, // so they should never be copied to output. llvm_unreachable("MIPS reginfo/options section reached writeTo()."); } llvm_unreachable("invalid section kind"); } template typename ELFT::uint InputSectionBase::getOffset(const DefinedRegular &Sym) { return getOffset(Sym.Value); } template InputSection::InputSection(elf::ObjectFile *F, const Elf_Shdr *Header) : InputSectionBase(F, Header, Base::Regular) {} template bool InputSection::classof(const InputSectionBase *S) { return S->SectionKind == Base::Regular; } template InputSectionBase *InputSection::getRelocatedSection() { assert(this->Header->sh_type == SHT_RELA || this->Header->sh_type == SHT_REL); ArrayRef *> Sections = this->File->getSections(); return Sections[this->Header->sh_info]; } template void InputSection::addThunk(SymbolBody &Body) { Body.ThunkIndex = Thunks.size(); Thunks.push_back(&Body); } template uint64_t InputSection::getThunkOff() const { return this->Header->sh_size; } template uint64_t InputSection::getThunksSize() const { return Thunks.size() * Target->ThunkSize; } // 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 template void InputSection::copyRelocations(uint8_t *Buf, ArrayRef Rels) { InputSectionBase *RelocatedSection = getRelocatedSection(); for (const RelTy &Rel : Rels) { uint32_t Type = Rel.getType(Config->Mips64EL); SymbolBody &Body = this->File->getRelocTargetSym(Rel); RelTy *P = reinterpret_cast(Buf); Buf += sizeof(RelTy); P->r_offset = RelocatedSection->getOffset(Rel.r_offset); P->setSymbolAndType(Body.DynsymIndex, Type, Config->Mips64EL); } } // Page(Expr) is the page address of the expression Expr, defined // as (Expr & ~0xFFF). (This applies even if the machine page size // supported by the platform has a different value.) static uint64_t getAArch64Page(uint64_t Expr) { return Expr & (~static_cast(0xFFF)); } // For computing values, each R_RELAX_TLS_* corresponds to whatever expression // the target uses in the mode this is being relaxed into. For example, anything // that relaxes to LE just needs an R_TLS since that is what is used if we // had a local exec expression to begin with. static RelExpr getRelaxedExpr(RelExpr Expr) { switch (Expr) { default: return Expr; case R_RELAX_TLS_GD_TO_LE: if (Config->EMachine == EM_386) return R_NEG_TLS; return R_TLS; case R_RELAX_TLS_GD_TO_IE: if (Config->EMachine == EM_386) return R_GOT_FROM_END; return R_GOT_PC; case R_RELAX_TLS_IE_TO_LE: case R_RELAX_TLS_LD_TO_LE: return R_TLS; } } template static typename ELFT::uint getSymVA(uint32_t Type, typename ELFT::uint A, typename ELFT::uint P, const SymbolBody &Body, uint8_t *BufLoc, const elf::ObjectFile &File, RelExpr Expr) { typedef typename ELFT::uint uintX_t; Expr = getRelaxedExpr(Expr); switch (Expr) { case R_HINT: llvm_unreachable("cannot relocate hint relocs"); case R_RELAX_TLS_GD_TO_LE: case R_RELAX_TLS_GD_TO_IE: case R_RELAX_TLS_IE_TO_LE: case R_RELAX_TLS_LD_TO_LE: llvm_unreachable("Should have been mapped"); case R_TLSLD: return Out::Got->getTlsIndexOff() + A - Out::Got->getNumEntries() * sizeof(uintX_t); case R_TLSLD_PC: return Out::Got->getTlsIndexVA() + A - P; case R_THUNK: return Body.getThunkVA(); case R_PPC_TOC: return getPPC64TocBase() + A; case R_TLSGD: return Out::Got->getGlobalDynOffset(Body) + A - Out::Got->getNumEntries() * sizeof(uintX_t); case R_TLSGD_PC: return Out::Got->getGlobalDynAddr(Body) + A - P; case R_PLT: return Body.getPltVA() + A; case R_PLT_PC: case R_PPC_PLT_OPD: return Body.getPltVA() + A - P; case R_SIZE: return Body.getSize() + A; case R_GOTREL: return Body.getVA(A) - Out::Got->getVA(); case R_GOT_FROM_END: return Body.getGotOffset() + A - Out::Got->getNumEntries() * sizeof(uintX_t); case R_GOT: return Body.getGotVA() + A; case R_GOT_PAGE_PC: return getAArch64Page(Body.getGotVA() + A) - getAArch64Page(P); case R_GOT_PC: return Body.getGotVA() + A - P; case R_GOTONLY_PC: return Out::Got->getVA() + A - P; case R_TLS: if (Target->TcbSize) return Body.getVA(A) + alignTo(Target->TcbSize, Out::TlsPhdr->p_align); return Body.getVA(A) - Out::TlsPhdr->p_memsz; case R_NEG_TLS: return Out::TlsPhdr->p_memsz - Body.getVA(A); case R_ABS: return Body.getVA(A); case R_GOT_OFF: return Body.getGotOffset() + 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 Out::Got->getMipsLocalPageOffset(Body.getVA(A)); case R_MIPS_GOT_LOCAL: // For non-local symbols GOT entries should contain their full // addresses. But if such symbol cannot be preempted, we do not // have to put them into the "global" part of GOT and use dynamic // linker to determine their actual addresses. That is why we // create GOT entries for them in the "local" part of GOT. return Out::Got->getMipsLocalEntryOffset(Body.getVA(A)); case R_PPC_OPD: { uint64_t SymVA = Body.getVA(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::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::Opd->getVA(); uint64_t OpdEnd = OpdStart + Out::Opd->getSize(); bool InOpd = OpdStart <= SymVA && SymVA < OpdEnd; if (InOpd) SymVA = read64be(&Out::OpdBuf[SymVA - OpdStart]); } return SymVA - P; } case R_PC: return Body.getVA(A) - P; case R_PAGE_PC: return getAArch64Page(Body.getVA(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 template void InputSection::relocateNonAlloc(uint8_t *Buf, ArrayRef Rels) { const unsigned Bits = sizeof(uintX_t) * 8; 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(Rel); if (!RelTy::IsRela) Addend += Target->getImplicitAddend(BufLoc, Type); SymbolBody &Sym = this->File->getRelocTargetSym(Rel); if (Target->getRelExpr(Type, Sym) != R_ABS) { error(this->getSectionName() + " has non-ABS reloc"); return; } uintX_t AddrLoc = this->OutSec->getVA() + Offset; uint64_t SymVA = SignExtend64(getSymVA( Type, Addend, AddrLoc, Sym, BufLoc, *this->File, R_ABS)); Target->relocateOne(BufLoc, Type, SymVA); } } template void InputSectionBase::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>(this); if (IS && !(IS->Header->sh_flags & SHF_ALLOC)) { for (const Elf_Shdr *RelSec : IS->RelocSections) { if (RelSec->sh_type == SHT_RELA) IS->relocateNonAlloc(Buf, IS->File->getObj().relas(RelSec)); else IS->relocateNonAlloc(Buf, IS->File->getObj().rels(RelSec)); } return; } const unsigned Bits = sizeof(uintX_t) * 8; for (const Relocation &Rel : Relocations) { uintX_t Offset = Rel.Offset; uint8_t *BufLoc = Buf + Offset; uint32_t Type = Rel.Type; uintX_t A = Rel.Addend; uintX_t AddrLoc = OutSec->getVA() + Offset; RelExpr Expr = Rel.Expr; uint64_t SymVA = SignExtend64( getSymVA(Type, A, AddrLoc, *Rel.Sym, BufLoc, *File, Expr)); if (Expr == R_PPC_PLT_OPD) { uint32_t Nop = 0x60000000; if (BufLoc + 8 <= BufEnd && read32be(BufLoc + 4) == Nop) write32be(BufLoc + 4, 0xe8410028); // ld %r2, 40(%r1) } switch (Expr) { case R_RELAX_TLS_IE_TO_LE: Target->relaxTlsIeToLe(BufLoc, Type, SymVA); break; case R_RELAX_TLS_LD_TO_LE: Target->relaxTlsLdToLe(BufLoc, Type, SymVA); break; case R_RELAX_TLS_GD_TO_LE: Target->relaxTlsGdToLe(BufLoc, Type, SymVA); break; case R_RELAX_TLS_GD_TO_IE: Target->relaxTlsGdToIe(BufLoc, Type, SymVA); break; default: Target->relocateOne(BufLoc, Type, SymVA); break; } } } template void InputSection::writeTo(uint8_t *Buf) { if (this->Header->sh_type == SHT_NOBITS) return; ELFFile &EObj = this->File->getObj(); // If -r is given, then an InputSection may be a relocation section. if (this->Header->sh_type == SHT_RELA) { copyRelocations(Buf + OutSecOff, EObj.relas(this->Header)); return; } if (this->Header->sh_type == SHT_REL) { copyRelocations(Buf + OutSecOff, EObj.rels(this->Header)); return; } // Copy section contents from source object file to output file. ArrayRef Data = this->getSectionData(); 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 SymbolBody *S : Thunks) { Target->writeThunk(Buf, S->getVA()); Buf += Target->ThunkSize; } } } template void InputSection::replace(InputSection *Other) { this->Align = std::max(this->Align, Other->Align); Other->Repl = this->Repl; Other->Live = false; } template SplitInputSection::SplitInputSection( elf::ObjectFile *File, const Elf_Shdr *Header, typename InputSectionBase::Kind SectionKind) : InputSectionBase(File, Header, SectionKind) {} template EHInputSection::EHInputSection(elf::ObjectFile *F, const Elf_Shdr *Header) : SplitInputSection(F, Header, InputSectionBase::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 bool EHInputSection::classof(const InputSectionBase *S) { return S->SectionKind == InputSectionBase::EHFrame; } template static size_t readRecordSize(ArrayRef D) { const endianness E = ELFT::TargetEndianness; if (D.size() < 4) fatal("CIE/FDE too small"); // First 4 bytes of CIE/FDE is the size of the record. // If it is 0xFFFFFFFF, the next 8 bytes contain the size instead, // but we do not support that format yet. uint64_t V = read32(D.data()); if (V == UINT32_MAX) fatal("CIE/FDE too large"); uint64_t Size = V + 4; if (Size > D.size()) fatal("CIE/FIE ends past the end of the section"); return Size; } // .eh_frame is a sequence of CIE or FDE records. // This function splits an input section into records and returns them. template void EHInputSection::split() { ArrayRef Data = this->getSectionData(); for (size_t Off = 0, End = Data.size(); Off != End;) { size_t Size = readRecordSize(Data.slice(Off)); // The empty record is the end marker. if (Size == 4) break; this->Pieces.emplace_back(Off, Data.slice(Off, Size)); Off += Size; } } template typename ELFT::uint EHInputSection::getOffset(uintX_t Offset) { // 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. Handle this special case. if (this->getSectionHdr()->sh_size == 0) return Offset; SectionPiece *Piece = this->getSectionPiece(Offset); if (Piece->OutputOff == size_t(-1)) return -1; // Not in the output uintX_t Addend = Offset - Piece->InputOff; return Piece->OutputOff + Addend; } static size_t findNull(ArrayRef 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. std::vector splitStrings(ArrayRef Data, size_t EntSize) { std::vector V; size_t Off = 0; while (!Data.empty()) { size_t End = findNull(Data, EntSize); if (End == StringRef::npos) fatal("string is not null terminated"); size_t Size = End + EntSize; V.emplace_back(Off, Data.slice(0, Size)); Data = Data.slice(Size); Off += Size; } return V; } // Split non-SHF_STRINGS section. Such section is a sequence of // fixed size records. std::vector splitNonStrings(ArrayRef Data, size_t EntSize) { std::vector V; size_t Size = Data.size(); assert((Size % EntSize) == 0); for (unsigned I = 0, N = Size; I != N; I += EntSize) V.emplace_back(I, Data.slice(I, EntSize)); return V; } template MergeInputSection::MergeInputSection(elf::ObjectFile *F, const Elf_Shdr *Header) : SplitInputSection(F, Header, InputSectionBase::Merge) { ArrayRef Data = this->getSectionData(); uintX_t EntSize = this->Header->sh_entsize; if (this->Header->sh_flags & SHF_STRINGS) this->Pieces = splitStrings(Data, EntSize); else this->Pieces = splitNonStrings(Data, EntSize); } template bool MergeInputSection::classof(const InputSectionBase *S) { return S->SectionKind == InputSectionBase::Merge; } template SectionPiece *SplitInputSection::getSectionPiece(uintX_t Offset) { ArrayRef D = this->getSectionData(); StringRef Data((const char *)D.data(), D.size()); uintX_t Size = Data.size(); if (Offset >= Size) fatal("entry is past the end of the section"); // Find the element this offset points to. auto I = std::upper_bound( Pieces.begin(), Pieces.end(), Offset, [](const uintX_t &A, const SectionPiece &B) { return A < B.InputOff; }); --I; return &*I; } template typename ELFT::uint MergeInputSection::getOffset(uintX_t Offset) { SectionPiece &Piece = *this->getSectionPiece(Offset); assert(Piece.Live); // Compute the Addend and if the Base is cached, return. uintX_t Addend = Offset - Piece.InputOff; if (Piece.OutputOff != size_t(-1)) return Piece.OutputOff + Addend; // Map the base to the offset in the output section and cache it. ArrayRef D = this->getSectionData(); StringRef Data((const char *)D.data(), D.size()); StringRef Entry = Data.substr(Piece.InputOff, Piece.size()); auto *MOS = static_cast *>(this->OutSec); Piece.OutputOff = MOS->getOffset(Entry); return Piece.OutputOff + Addend; } template MipsReginfoInputSection::MipsReginfoInputSection(elf::ObjectFile *F, const Elf_Shdr *Hdr) : InputSectionBase(F, Hdr, InputSectionBase::MipsReginfo) { // Initialize this->Reginfo. ArrayRef D = this->getSectionData(); if (D.size() != sizeof(Elf_Mips_RegInfo)) { error("invalid size of .reginfo section"); return; } Reginfo = reinterpret_cast *>(D.data()); } template bool MipsReginfoInputSection::classof(const InputSectionBase *S) { return S->SectionKind == InputSectionBase::MipsReginfo; } template MipsOptionsInputSection::MipsOptionsInputSection(elf::ObjectFile *F, const Elf_Shdr *Hdr) : InputSectionBase(F, Hdr, InputSectionBase::MipsOptions) { // Find ODK_REGINFO option in the section's content. ArrayRef D = this->getSectionData(); while (!D.empty()) { if (D.size() < sizeof(Elf_Mips_Options)) { error("invalid size of .MIPS.options section"); break; } auto *O = reinterpret_cast *>(D.data()); if (O->kind == ODK_REGINFO) { Reginfo = &O->getRegInfo(); break; } D = D.slice(O->size); } } template bool MipsOptionsInputSection::classof(const InputSectionBase *S) { return S->SectionKind == InputSectionBase::MipsOptions; } template class elf::InputSectionBase; template class elf::InputSectionBase; template class elf::InputSectionBase; template class elf::InputSectionBase; template class elf::InputSection; template class elf::InputSection; template class elf::InputSection; template class elf::InputSection; template class elf::SplitInputSection; template class elf::SplitInputSection; template class elf::SplitInputSection; template class elf::SplitInputSection; template class elf::EHInputSection; template class elf::EHInputSection; template class elf::EHInputSection; template class elf::EHInputSection; template class elf::MergeInputSection; template class elf::MergeInputSection; template class elf::MergeInputSection; template class elf::MergeInputSection; template class elf::MipsReginfoInputSection; template class elf::MipsReginfoInputSection; template class elf::MipsReginfoInputSection; template class elf::MipsReginfoInputSection; template class elf::MipsOptionsInputSection; template class elf::MipsOptionsInputSection; template class elf::MipsOptionsInputSection; template class elf::MipsOptionsInputSection;