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llvm-project/lld/ELF/OutputSections.h

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//===- OutputSections.h -----------------------------------------*- C++ -*-===//
//
// The LLVM Linker
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#ifndef LLD_ELF_OUTPUT_SECTIONS_H
#define LLD_ELF_OUTPUT_SECTIONS_H
#include "lld/Core/LLVM.h"
#include "llvm/MC/StringTableBuilder.h"
#include "llvm/Object/ELF.h"
#include "Config.h"
#include <type_traits>
namespace lld {
namespace elf2 {
class SymbolBody;
template <class ELFT> class SymbolTable;
template <class ELFT> class SymbolTableSection;
template <class ELFT> class StringTableSection;
template <class ELFT> class EHInputSection;
template <class ELFT> class InputSection;
template <class ELFT> class InputSectionBase;
template <class ELFT> class MergeInputSection;
template <class ELFT> class MipsReginfoInputSection;
template <class ELFT> class OutputSection;
template <class ELFT> class ObjectFile;
template <class ELFT> class DefinedRegular;
template <class ELFT>
static inline typename llvm::object::ELFFile<ELFT>::uintX_t
getAddend(const typename llvm::object::ELFFile<ELFT>::Elf_Rel &Rel) {
return 0;
}
template <class ELFT>
static inline typename llvm::object::ELFFile<ELFT>::uintX_t
getAddend(const typename llvm::object::ELFFile<ELFT>::Elf_Rela &Rel) {
return Rel.r_addend;
}
template <class ELFT, bool IsRela>
typename llvm::object::ELFFile<ELFT>::uintX_t
getLocalRelTarget(const ObjectFile<ELFT> &File,
const llvm::object::Elf_Rel_Impl<ELFT, IsRela> &Rel,
typename llvm::object::ELFFile<ELFT>::uintX_t Addend);
bool canBePreempted(const SymbolBody *Body, bool NeedsGot);
// This represents a section in an output file.
// Different sub classes represent different types of sections. Some contain
// input sections, others are created by the linker.
// The writer creates multiple OutputSections and assign them unique,
// non-overlapping file offsets and VAs.
template <class ELFT> class OutputSectionBase {
public:
typedef typename llvm::object::ELFFile<ELFT>::uintX_t uintX_t;
typedef typename llvm::object::ELFFile<ELFT>::Elf_Shdr Elf_Shdr;
OutputSectionBase(StringRef Name, uint32_t sh_type, uintX_t sh_flags);
void setVA(uintX_t VA) { Header.sh_addr = VA; }
uintX_t getVA() const { return Header.sh_addr; }
void setFileOffset(uintX_t Off) { Header.sh_offset = Off; }
void setSHName(unsigned Val) { Header.sh_name = Val; }
void writeHeaderTo(Elf_Shdr *SHdr);
StringRef getName() { return Name; }
virtual void addSection(InputSectionBase<ELFT> *C) {}
unsigned SectionIndex;
// Returns the size of the section in the output file.
uintX_t getSize() const { return Header.sh_size; }
void setSize(uintX_t Val) { Header.sh_size = Val; }
uintX_t getFlags() { return Header.sh_flags; }
uintX_t getFileOff() { return Header.sh_offset; }
uintX_t getAlign() {
// The ELF spec states that a value of 0 means the section has no alignment
// constraits.
return std::max<uintX_t>(Header.sh_addralign, 1);
}
uint32_t getType() { return Header.sh_type; }
void updateAlign(uintX_t Align) {
if (Align > Header.sh_addralign)
Header.sh_addralign = Align;
}
virtual void finalize() {}
virtual void writeTo(uint8_t *Buf) = 0;
virtual ~OutputSectionBase() = default;
protected:
StringRef Name;
Elf_Shdr Header;
};
template <class ELFT> class GotSection final : public OutputSectionBase<ELFT> {
typedef OutputSectionBase<ELFT> Base;
typedef typename Base::uintX_t uintX_t;
public:
GotSection();
void finalize() override;
void writeTo(uint8_t *Buf) override;
void addEntry(SymbolBody *Sym);
void addMipsLocalEntry();
bool addDynTlsEntry(SymbolBody *Sym);
bool addTlsIndex();
bool empty() const { return MipsLocalEntries == 0 && Entries.empty(); }
uintX_t getMipsLocalFullAddr(const SymbolBody &B);
uintX_t getMipsLocalPageAddr(uintX_t Addr);
uintX_t getGlobalDynAddr(const SymbolBody &B) const;
uintX_t getNumEntries() const { return Entries.size(); }
// Returns the symbol which corresponds to the first entry of the global part
// of GOT on MIPS platform. It is required to fill up MIPS-specific dynamic
// table properties.
// Returns nullptr if the global part is empty.
const SymbolBody *getMipsFirstGlobalEntry() const;
// Returns the number of entries in the local part of GOT including
// the number of reserved entries. This method is MIPS-specific.
unsigned getMipsLocalEntriesNum() const;
uintX_t getTlsIndexVA() { return Base::getVA() + TlsIndexOff; }
private:
std::vector<const SymbolBody *> Entries;
uint32_t TlsIndexOff = -1;
uint32_t MipsLocalEntries = 0;
llvm::DenseMap<uintX_t, size_t> MipsLocalGotPos;
uintX_t getMipsLocalEntryAddr(uintX_t EntryValue);
};
template <class ELFT>
class GotPltSection final : public OutputSectionBase<ELFT> {
typedef typename llvm::object::ELFFile<ELFT>::uintX_t uintX_t;
public:
GotPltSection();
void finalize() override;
void writeTo(uint8_t *Buf) override;
void addEntry(SymbolBody *Sym);
bool empty() const;
private:
std::vector<const SymbolBody *> Entries;
};
template <class ELFT> class PltSection final : public OutputSectionBase<ELFT> {
typedef OutputSectionBase<ELFT> Base;
typedef typename Base::uintX_t uintX_t;
public:
PltSection();
void finalize() override;
void writeTo(uint8_t *Buf) override;
void addEntry(SymbolBody *Sym);
bool empty() const { return Entries.empty(); }
private:
std::vector<std::pair<const SymbolBody *, unsigned>> Entries;
};
template <class ELFT> struct DynamicReloc {
typedef typename llvm::object::ELFFile<ELFT>::uintX_t uintX_t;
uint32_t Type;
// Where the relocation is.
enum OffsetKind {
Off_Got, // The got entry of Sym.
Off_GotPlt, // The got.plt entry of Sym.
Off_Bss, // The bss entry of Sym (copy reloc).
Off_Sec, // The final position of the given input section and offset.
Off_LTlsIndex, // The local tls index.
Off_GTlsIndex, // The global tls index of Sym.
Off_GTlsOffset // The global tls offset of Sym.
} OKind;
SymbolBody *Sym = nullptr;
InputSectionBase<ELFT> *OffsetSec = nullptr;
uintX_t OffsetInSec = 0;
bool UseSymVA = false;
InputSectionBase<ELFT> *TargetSec = nullptr;
uintX_t OffsetInTargetSec = 0;
uintX_t Addend = 0;
DynamicReloc(uint32_t Type, OffsetKind OKind, SymbolBody *Sym)
: Type(Type), OKind(OKind), Sym(Sym) {}
DynamicReloc(uint32_t Type, OffsetKind OKind, bool UseSymVA, SymbolBody *Sym)
: Type(Type), OKind(OKind), Sym(Sym), UseSymVA(UseSymVA) {}
DynamicReloc(uint32_t Type, InputSectionBase<ELFT> *OffsetSec,
uintX_t OffsetInSec, bool UseSymVA, SymbolBody *Sym,
uintX_t Addend)
: Type(Type), OKind(Off_Sec), Sym(Sym), OffsetSec(OffsetSec),
OffsetInSec(OffsetInSec), UseSymVA(UseSymVA), Addend(Addend) {}
DynamicReloc(uint32_t Type, InputSectionBase<ELFT> *OffsetSec,
uintX_t OffsetInSec, InputSectionBase<ELFT> *TargetSec,
uintX_t OffsetInTargetSec, uintX_t Addend)
: Type(Type), OKind(Off_Sec), OffsetSec(OffsetSec),
OffsetInSec(OffsetInSec), TargetSec(TargetSec),
OffsetInTargetSec(OffsetInTargetSec), Addend(Addend) {}
};
template <class ELFT>
class SymbolTableSection final : public OutputSectionBase<ELFT> {
public:
typedef typename llvm::object::ELFFile<ELFT>::Elf_Shdr Elf_Shdr;
typedef typename llvm::object::ELFFile<ELFT>::Elf_Sym Elf_Sym;
typedef typename llvm::object::ELFFile<ELFT>::Elf_Sym_Range Elf_Sym_Range;
typedef typename llvm::object::ELFFile<ELFT>::uintX_t uintX_t;
SymbolTableSection(SymbolTable<ELFT> &Table,
StringTableSection<ELFT> &StrTabSec);
void finalize() override;
void writeTo(uint8_t *Buf) override;
void addSymbol(SymbolBody *Body);
StringTableSection<ELFT> &getStrTabSec() const { return StrTabSec; }
unsigned getNumSymbols() const { return NumLocals + Symbols.size() + 1; }
ArrayRef<std::pair<SymbolBody *, unsigned>> getSymbols() const {
return Symbols;
}
unsigned NumLocals = 0;
StringTableSection<ELFT> &StrTabSec;
private:
void writeLocalSymbols(uint8_t *&Buf);
void writeGlobalSymbols(uint8_t *Buf);
static uint8_t getSymbolBinding(SymbolBody *Body);
SymbolTable<ELFT> &Table;
std::vector<std::pair<SymbolBody *, unsigned>> Symbols;
};
template <class ELFT>
class RelocationSection final : public OutputSectionBase<ELFT> {
typedef typename llvm::object::ELFFile<ELFT>::Elf_Rel Elf_Rel;
typedef typename llvm::object::ELFFile<ELFT>::Elf_Rela Elf_Rela;
typedef typename llvm::object::ELFFile<ELFT>::uintX_t uintX_t;
public:
RelocationSection(StringRef Name, bool IsRela);
void addReloc(const DynamicReloc<ELFT> &Reloc) { Relocs.push_back(Reloc); }
unsigned getRelocOffset();
void finalize() override;
void writeTo(uint8_t *Buf) override;
bool hasRelocs() const { return !Relocs.empty(); }
bool isRela() const { return IsRela; }
bool Static = false;
private:
std::vector<DynamicReloc<ELFT>> Relocs;
const bool IsRela;
};
template <class ELFT>
class OutputSection final : public OutputSectionBase<ELFT> {
public:
typedef typename llvm::object::ELFFile<ELFT>::Elf_Shdr Elf_Shdr;
typedef typename llvm::object::ELFFile<ELFT>::Elf_Sym Elf_Sym;
typedef typename llvm::object::ELFFile<ELFT>::Elf_Rel Elf_Rel;
typedef typename llvm::object::ELFFile<ELFT>::Elf_Rela Elf_Rela;
typedef typename llvm::object::ELFFile<ELFT>::uintX_t uintX_t;
OutputSection(StringRef Name, uint32_t sh_type, uintX_t sh_flags);
void addSection(InputSectionBase<ELFT> *C) override;
void writeTo(uint8_t *Buf) override;
private:
std::vector<InputSection<ELFT> *> Sections;
};
template <class ELFT>
class MergeOutputSection final : public OutputSectionBase<ELFT> {
typedef typename OutputSectionBase<ELFT>::uintX_t uintX_t;
bool shouldTailMerge() const;
public:
MergeOutputSection(StringRef Name, uint32_t sh_type, uintX_t sh_flags);
void addSection(InputSectionBase<ELFT> *S) override;
void writeTo(uint8_t *Buf) override;
unsigned getOffset(StringRef Val);
void finalize() override;
private:
llvm::StringTableBuilder Builder{llvm::StringTableBuilder::RAW};
};
// FDE or CIE
template <class ELFT> struct EHRegion {
typedef typename llvm::object::ELFFile<ELFT>::uintX_t uintX_t;
EHRegion(EHInputSection<ELFT> *S, unsigned Index);
StringRef data() const;
EHInputSection<ELFT> *S;
unsigned Index;
};
template <class ELFT> struct Cie : public EHRegion<ELFT> {
Cie(EHInputSection<ELFT> *S, unsigned Index);
std::vector<EHRegion<ELFT>> Fdes;
uint8_t FdeEncoding;
};
template <class ELFT>
class EHOutputSection final : public OutputSectionBase<ELFT> {
public:
typedef typename llvm::object::ELFFile<ELFT>::uintX_t uintX_t;
typedef typename llvm::object::ELFFile<ELFT>::Elf_Shdr Elf_Shdr;
typedef typename llvm::object::ELFFile<ELFT>::Elf_Rel Elf_Rel;
typedef typename llvm::object::ELFFile<ELFT>::Elf_Rela Elf_Rela;
EHOutputSection(StringRef Name, uint32_t sh_type, uintX_t sh_flags);
void writeTo(uint8_t *Buf) override;
template <bool IsRela>
void addSectionAux(
EHInputSection<ELFT> *S,
llvm::iterator_range<const llvm::object::Elf_Rel_Impl<ELFT, IsRela> *>
Rels);
void addSection(InputSectionBase<ELFT> *S) override;
private:
uint8_t getFdeEncoding(ArrayRef<uint8_t> D);
uintX_t readEntryLength(ArrayRef<uint8_t> D);
std::vector<EHInputSection<ELFT> *> Sections;
std::vector<Cie<ELFT>> Cies;
// Maps CIE content + personality to a index in Cies.
llvm::DenseMap<std::pair<StringRef, StringRef>, unsigned> CieMap;
};
template <class ELFT>
class InterpSection final : public OutputSectionBase<ELFT> {
public:
InterpSection();
void writeTo(uint8_t *Buf) override;
};
template <class ELFT>
class StringTableSection final : public OutputSectionBase<ELFT> {
public:
typedef typename llvm::object::ELFFile<ELFT>::uintX_t uintX_t;
StringTableSection(StringRef Name, bool Dynamic);
unsigned addString(StringRef S, bool HashIt = true);
void writeTo(uint8_t *Buf) override;
unsigned getSize() const { return Size; }
void finalize() override { this->Header.sh_size = getSize(); }
bool isDynamic() const { return Dynamic; }
private:
const bool Dynamic;
llvm::DenseMap<StringRef, unsigned> StringMap;
std::vector<StringRef> Strings;
unsigned Size = 1; // ELF string tables start with a NUL byte, so 1.
};
template <class ELFT>
class HashTableSection final : public OutputSectionBase<ELFT> {
typedef typename llvm::object::ELFFile<ELFT>::Elf_Word Elf_Word;
public:
HashTableSection();
void finalize() override;
void writeTo(uint8_t *Buf) override;
};
// Outputs GNU Hash section. For detailed explanation see:
// https://blogs.oracle.com/ali/entry/gnu_hash_elf_sections
template <class ELFT>
class GnuHashTableSection final : public OutputSectionBase<ELFT> {
typedef typename llvm::object::ELFFile<ELFT>::Elf_Off Elf_Off;
typedef typename llvm::object::ELFFile<ELFT>::Elf_Word Elf_Word;
typedef typename llvm::object::ELFFile<ELFT>::uintX_t uintX_t;
public:
GnuHashTableSection();
void finalize() override;
void writeTo(uint8_t *Buf) override;
// Adds symbols to the hash table.
// Sorts the input to satisfy GNU hash section requirements.
void addSymbols(std::vector<std::pair<SymbolBody *, unsigned>> &Symbols);
private:
static unsigned calcNBuckets(unsigned NumHashed);
static unsigned calcMaskWords(unsigned NumHashed);
void writeHeader(uint8_t *&Buf);
void writeBloomFilter(uint8_t *&Buf);
void writeHashTable(uint8_t *Buf);
struct HashedSymbolData {
SymbolBody *Body;
unsigned STName;
uint32_t Hash;
};
std::vector<HashedSymbolData> HashedSymbols;
unsigned MaskWords;
unsigned NBuckets;
unsigned Shift2;
};
template <class ELFT>
class DynamicSection final : public OutputSectionBase<ELFT> {
typedef OutputSectionBase<ELFT> Base;
typedef typename llvm::object::ELFFile<ELFT>::Elf_Dyn Elf_Dyn;
typedef typename llvm::object::ELFFile<ELFT>::Elf_Rel Elf_Rel;
typedef typename llvm::object::ELFFile<ELFT>::Elf_Rela Elf_Rela;
typedef typename llvm::object::ELFFile<ELFT>::Elf_Shdr Elf_Shdr;
typedef typename llvm::object::ELFFile<ELFT>::Elf_Sym Elf_Sym;
typedef typename llvm::object::ELFFile<ELFT>::uintX_t uintX_t;
// The .dynamic section contains information for the dynamic linker.
// The section consists of fixed size entries, which consist of
// type and value fields. Value are one of plain integers, symbol
// addresses, or section addresses. This struct represents the entry.
struct Entry {
int32_t Tag;
union {
OutputSectionBase<ELFT> *OutSec;
uint64_t Val;
const SymbolBody *Sym;
};
enum KindT { SecAddr, SymAddr, PlainInt } Kind;
Entry(int32_t Tag, OutputSectionBase<ELFT> *OutSec)
: Tag(Tag), OutSec(OutSec), Kind(SecAddr) {}
Entry(int32_t Tag, uint64_t Val) : Tag(Tag), Val(Val), Kind(PlainInt) {}
Entry(int32_t Tag, const SymbolBody *Sym)
: Tag(Tag), Sym(Sym), Kind(SymAddr) {}
};
// finalize() fills this vector with the section contents. finalize()
// cannot directly create final section contents because when the
// function is called, symbol or section addresses are not fixed yet.
std::vector<Entry> Entries;
public:
DynamicSection(SymbolTable<ELFT> &SymTab);
void finalize() override;
void writeTo(uint8_t *Buf) override;
OutputSectionBase<ELFT> *PreInitArraySec = nullptr;
OutputSectionBase<ELFT> *InitArraySec = nullptr;
OutputSectionBase<ELFT> *FiniArraySec = nullptr;
private:
SymbolTable<ELFT> &SymTab;
};
template <class ELFT>
class MipsReginfoOutputSection final : public OutputSectionBase<ELFT> {
typedef llvm::object::Elf_Mips_RegInfo<ELFT> Elf_Mips_RegInfo;
public:
MipsReginfoOutputSection();
void writeTo(uint8_t *Buf) override;
void addSection(InputSectionBase<ELFT> *S) override;
private:
uint32_t GprMask = 0;
};
// --eh-frame-hdr option tells linker to construct a header for all the
// .eh_frame sections. This header is placed to a section named .eh_frame_hdr
// and also to a PT_GNU_EH_FRAME segment.
// At runtime the unwinder then can find all the PT_GNU_EH_FRAME segments by
// calling dl_iterate_phdr.
// This section contains a lookup table for quick binary search of FDEs.
// Detailed info about internals can be found in Ian Lance Taylor's blog:
// http://www.airs.com/blog/archives/460 (".eh_frame")
// http://www.airs.com/blog/archives/462 (".eh_frame_hdr")
template <class ELFT>
class EhFrameHeader final : public OutputSectionBase<ELFT> {
typedef typename llvm::object::ELFFile<ELFT>::uintX_t uintX_t;
public:
EhFrameHeader();
void writeTo(uint8_t *Buf) override;
void addFde(uint8_t Enc, size_t Off, uint8_t *PCRel);
void assignEhFrame(EHOutputSection<ELFT> *Sec);
void reserveFde();
bool Live = false;
private:
struct FdeData {
uint8_t Enc;
size_t Off;
uint8_t *PCRel;
};
uintX_t getFdePc(uintX_t EhVA, const FdeData &F);
EHOutputSection<ELFT> *Sec = nullptr;
std::vector<FdeData> FdeList;
};
// All output sections that are hadnled by the linker specially are
// globally accessible. Writer initializes them, so don't use them
// until Writer is initialized.
template <class ELFT> struct Out {
typedef typename llvm::object::ELFFile<ELFT>::uintX_t uintX_t;
typedef typename llvm::object::ELFFile<ELFT>::Elf_Phdr Elf_Phdr;
static DynamicSection<ELFT> *Dynamic;
static EhFrameHeader<ELFT> *EhFrameHdr;
static GnuHashTableSection<ELFT> *GnuHashTab;
static GotPltSection<ELFT> *GotPlt;
static GotSection<ELFT> *Got;
static HashTableSection<ELFT> *HashTab;
static InterpSection<ELFT> *Interp;
static OutputSection<ELFT> *Bss;
static OutputSection<ELFT> *MipsRldMap;
static OutputSectionBase<ELFT> *Opd;
static uint8_t *OpdBuf;
static PltSection<ELFT> *Plt;
static RelocationSection<ELFT> *RelaDyn;
static RelocationSection<ELFT> *RelaPlt;
static StringTableSection<ELFT> *DynStrTab;
static StringTableSection<ELFT> *ShStrTab;
static StringTableSection<ELFT> *StrTab;
static SymbolTableSection<ELFT> *DynSymTab;
static SymbolTableSection<ELFT> *SymTab;
static Elf_Phdr *TlsPhdr;
};
template <class ELFT> DynamicSection<ELFT> *Out<ELFT>::Dynamic;
template <class ELFT> EhFrameHeader<ELFT> *Out<ELFT>::EhFrameHdr;
template <class ELFT> GnuHashTableSection<ELFT> *Out<ELFT>::GnuHashTab;
template <class ELFT> GotPltSection<ELFT> *Out<ELFT>::GotPlt;
template <class ELFT> GotSection<ELFT> *Out<ELFT>::Got;
template <class ELFT> HashTableSection<ELFT> *Out<ELFT>::HashTab;
template <class ELFT> InterpSection<ELFT> *Out<ELFT>::Interp;
template <class ELFT> OutputSection<ELFT> *Out<ELFT>::Bss;
template <class ELFT> OutputSection<ELFT> *Out<ELFT>::MipsRldMap;
template <class ELFT> OutputSectionBase<ELFT> *Out<ELFT>::Opd;
template <class ELFT> uint8_t *Out<ELFT>::OpdBuf;
template <class ELFT> PltSection<ELFT> *Out<ELFT>::Plt;
template <class ELFT> RelocationSection<ELFT> *Out<ELFT>::RelaDyn;
template <class ELFT> RelocationSection<ELFT> *Out<ELFT>::RelaPlt;
template <class ELFT> StringTableSection<ELFT> *Out<ELFT>::DynStrTab;
template <class ELFT> StringTableSection<ELFT> *Out<ELFT>::ShStrTab;
template <class ELFT> StringTableSection<ELFT> *Out<ELFT>::StrTab;
template <class ELFT> SymbolTableSection<ELFT> *Out<ELFT>::DynSymTab;
template <class ELFT> SymbolTableSection<ELFT> *Out<ELFT>::SymTab;
template <class ELFT> typename Out<ELFT>::Elf_Phdr *Out<ELFT>::TlsPhdr;
} // namespace elf2
} // namespace lld
#endif // LLD_ELF_OUTPUT_SECTIONS_H
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