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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 "Config.h"
#include "Relocations.h"
#include "lld/Core/LLVM.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/MC/StringTableBuilder.h"
#include "llvm/Object/ELF.h"
#include "llvm/Support/MD5.h"
#include "llvm/Support/SHA1.h"
namespace lld {
namespace elf {
class SymbolBody;
struct EhSectionPiece;
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 SharedFile;
template <class ELFT> class SharedSymbol;
template <class ELFT> class DefinedRegular;
// 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 ELFT::uint uintX_t;
typedef typename ELFT::Shdr Elf_Shdr;
enum Kind {
Base,
BuildId,
Dynamic,
EHFrame,
EHFrameHdr,
GnuHashTable,
Got,
GotPlt,
HashTable,
Interp,
Merge,
MipsReginfo,
MipsOptions,
MipsAbiFlags,
Plt,
Regular,
Reloc,
StrTable,
SymTable,
VersDef,
VersNeed,
VersTable
};
OutputSectionBase(StringRef Name, uint32_t Type, uintX_t 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) {}
virtual Kind getKind() const { return Base; }
static bool classof(const OutputSectionBase<ELFT> *B) {
return B->getKind() == Base;
}
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() const { return Header.sh_flags; }
void updateFlags(uintX_t Val) { Header.sh_flags |= Val; }
uint32_t getPhdrFlags() const;
uintX_t getFileOff() const { return Header.sh_offset; }
uintX_t getAlignment() const { return Header.sh_addralign; }
uint32_t getType() const { return Header.sh_type; }
void updateAlignment(uintX_t Alignment) {
if (Alignment > Header.sh_addralign)
Header.sh_addralign = Alignment;
}
// If true, this section will be page aligned on disk.
// Typically the first section of each PT_LOAD segment has this flag.
bool PageAlign = false;
virtual void finalize() {}
virtual void finalizePieces() {}
virtual void assignOffsets() {}
virtual void writeTo(uint8_t *Buf) {}
virtual ~OutputSectionBase() = default;
protected:
StringRef Name;
Elf_Shdr Header;
};
template <class ELFT> class GotSection final : public OutputSectionBase<ELFT> {
typedef OutputSectionBase<ELFT> Base;
typedef typename ELFT::uint uintX_t;
public:
GotSection();
void finalize() override;
void writeTo(uint8_t *Buf) override;
void addEntry(SymbolBody &Sym);
void addMipsEntry(SymbolBody &Sym, uintX_t Addend, RelExpr Expr);
bool addDynTlsEntry(SymbolBody &Sym);
bool addTlsIndex();
bool empty() const { return MipsPageEntries == 0 && Entries.empty(); }
uintX_t getMipsLocalPageOffset(uintX_t Addr);
uintX_t getMipsGotOffset(const SymbolBody &B, uintX_t Addend) const;
uintX_t getGlobalDynAddr(const SymbolBody &B) const;
uintX_t getGlobalDynOffset(const SymbolBody &B) const;
typename Base::Kind getKind() const override { return Base::Got; }
static bool classof(const Base *B) { return B->getKind() == Base::Got; }
// 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;
// Returns offset of TLS part of the MIPS GOT table. This part goes
// after 'local' and 'global' entries.
uintX_t getMipsTlsOffset();
uintX_t getTlsIndexVA() { return Base::getVA() + TlsIndexOff; }
uint32_t getTlsIndexOff() { return TlsIndexOff; }
// Flag to force GOT to be in output if we have relocations
// that relies on its address.
bool HasGotOffRel = false;
private:
std::vector<const SymbolBody *> Entries;
uint32_t TlsIndexOff = -1;
uint32_t MipsPageEntries = 0;
// Output sections referenced by MIPS GOT relocations.
llvm::SmallPtrSet<const OutputSectionBase<ELFT> *, 10> MipsOutSections;
llvm::DenseMap<uintX_t, size_t> MipsLocalGotPos;
// MIPS ABI requires to create unique GOT entry for each Symbol/Addend
// pairs. The `MipsGotMap` maps (S,A) pair to the GOT index in the `MipsLocal`
// or `MipsGlobal` vectors. In general it does not have a sence to take in
// account addend for preemptible symbols because the corresponding
// GOT entries should have one-to-one mapping with dynamic symbols table.
// But we use the same container's types for both kind of GOT entries
// to handle them uniformly.
typedef std::pair<const SymbolBody*, uintX_t> MipsGotEntry;
typedef std::vector<MipsGotEntry> MipsGotEntries;
llvm::DenseMap<MipsGotEntry, size_t> MipsGotMap;
MipsGotEntries MipsLocal;
MipsGotEntries MipsGlobal;
// Write MIPS-specific parts of the GOT.
void writeMipsGot(uint8_t *Buf);
};
template <class ELFT>
class GotPltSection final : public OutputSectionBase<ELFT> {
typedef typename ELFT::uint uintX_t;
typedef OutputSectionBase<ELFT> Base;
public:
GotPltSection();
void finalize() override;
void writeTo(uint8_t *Buf) override;
void addEntry(SymbolBody &Sym);
bool empty() const;
typename Base::Kind getKind() const override { return Base::GotPlt; }
static bool classof(const Base *B) { return B->getKind() == Base::GotPlt; }
private:
std::vector<const SymbolBody *> Entries;
};
template <class ELFT> class PltSection final : public OutputSectionBase<ELFT> {
typedef OutputSectionBase<ELFT> Base;
typedef typename ELFT::uint uintX_t;
public:
PltSection();
void finalize() override;
void writeTo(uint8_t *Buf) override;
void addEntry(SymbolBody &Sym);
bool empty() const { return Entries.empty(); }
typename Base::Kind getKind() const override { return Base::Plt; }
static bool classof(const Base *B) { return B->getKind() == Base::Plt; }
private:
std::vector<std::pair<const SymbolBody *, unsigned>> Entries;
};
template <class ELFT> class DynamicReloc {
typedef typename ELFT::uint uintX_t;
public:
DynamicReloc(uint32_t Type, const InputSectionBase<ELFT> *InputSec,
uintX_t OffsetInSec, bool UseSymVA, SymbolBody *Sym,
uintX_t Addend)
: Type(Type), Sym(Sym), InputSec(InputSec), OffsetInSec(OffsetInSec),
UseSymVA(UseSymVA), Addend(Addend) {}
DynamicReloc(uint32_t Type, const OutputSectionBase<ELFT> *OutputSec,
uintX_t OffsetInSec, bool UseSymVA, SymbolBody *Sym,
uintX_t Addend)
: Type(Type), Sym(Sym), OutputSec(OutputSec), OffsetInSec(OffsetInSec),
UseSymVA(UseSymVA), Addend(Addend) {}
uintX_t getOffset() const;
uintX_t getAddend() const;
uint32_t getSymIndex() const;
const OutputSectionBase<ELFT> *getOutputSec() const { return OutputSec; }
uint32_t Type;
private:
SymbolBody *Sym;
const InputSectionBase<ELFT> *InputSec = nullptr;
const OutputSectionBase<ELFT> *OutputSec = nullptr;
uintX_t OffsetInSec;
bool UseSymVA;
uintX_t Addend;
};
template <class ELFT>
class SymbolTableSection final : public OutputSectionBase<ELFT> {
typedef OutputSectionBase<ELFT> Base;
public:
typedef typename ELFT::Shdr Elf_Shdr;
typedef typename ELFT::Sym Elf_Sym;
typedef typename ELFT::SymRange Elf_Sym_Range;
typedef typename ELFT::uint uintX_t;
SymbolTableSection(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; }
typename Base::Kind getKind() const override { return Base::SymTable; }
static bool classof(const Base *B) { return B->getKind() == Base::SymTable; }
ArrayRef<std::pair<SymbolBody *, size_t>> getSymbols() const {
return Symbols;
}
unsigned NumLocals = 0;
StringTableSection<ELFT> &StrTabSec;
private:
void writeLocalSymbols(uint8_t *&Buf);
void writeGlobalSymbols(uint8_t *Buf);
const OutputSectionBase<ELFT> *getOutputSection(SymbolBody *Sym);
// A vector of symbols and their string table offsets.
std::vector<std::pair<SymbolBody *, size_t>> Symbols;
};
// For more information about .gnu.version and .gnu.version_r see:
// https://www.akkadia.org/drepper/symbol-versioning
// The .gnu.version_d section which has a section type of SHT_GNU_verdef shall
// contain symbol version definitions. The number of entries in this section
// shall be contained in the DT_VERDEFNUM entry of the .dynamic section.
// The section shall contain an array of Elf_Verdef structures, optionally
// followed by an array of Elf_Verdaux structures.
template <class ELFT>
class VersionDefinitionSection final : public OutputSectionBase<ELFT> {
typedef typename ELFT::Verdef Elf_Verdef;
typedef typename ELFT::Verdaux Elf_Verdaux;
typedef OutputSectionBase<ELFT> Base;
public:
VersionDefinitionSection();
void finalize() override;
void writeTo(uint8_t *Buf) override;
typename Base::Kind getKind() const override { return Base::VersDef; }
static bool classof(const Base *B) { return B->getKind() == Base::VersDef; }
private:
void writeOne(uint8_t *Buf, uint32_t Index, StringRef Name, size_t NameOff);
unsigned FileDefNameOff;
};
// The .gnu.version section specifies the required version of each symbol in the
// dynamic symbol table. It contains one Elf_Versym for each dynamic symbol
// table entry. An Elf_Versym is just a 16-bit integer that refers to a version
// identifier defined in the either .gnu.version_r or .gnu.version_d section.
// The values 0 and 1 are reserved. All other values are used for versions in
// the own object or in any of the dependencies.
template <class ELFT>
class VersionTableSection final : public OutputSectionBase<ELFT> {
typedef OutputSectionBase<ELFT> Base;
typedef typename ELFT::Versym Elf_Versym;
public:
VersionTableSection();
void finalize() override;
void writeTo(uint8_t *Buf) override;
typename Base::Kind getKind() const override { return Base::VersTable; }
static bool classof(const Base *B) { return B->getKind() == Base::VersTable; }
};
// The .gnu.version_r section defines the version identifiers used by
// .gnu.version. It contains a linked list of Elf_Verneed data structures. Each
// Elf_Verneed specifies the version requirements for a single DSO, and contains
// a reference to a linked list of Elf_Vernaux data structures which define the
// mapping from version identifiers to version names.
template <class ELFT>
class VersionNeedSection final : public OutputSectionBase<ELFT> {
typedef OutputSectionBase<ELFT> Base;
typedef typename ELFT::Verneed Elf_Verneed;
typedef typename ELFT::Vernaux Elf_Vernaux;
// A vector of shared files that need Elf_Verneed data structures and the
// string table offsets of their sonames.
std::vector<std::pair<SharedFile<ELFT> *, size_t>> Needed;
// The next available version identifier.
unsigned NextIndex;
public:
VersionNeedSection();
void addSymbol(SharedSymbol<ELFT> *SS);
void finalize() override;
void writeTo(uint8_t *Buf) override;
size_t getNeedNum() const { return Needed.size(); }
typename Base::Kind getKind() const override { return Base::VersNeed; }
static bool classof(const Base *B) { return B->getKind() == Base::VersNeed; }
};
template <class ELFT>
class RelocationSection final : public OutputSectionBase<ELFT> {
typedef typename ELFT::Rel Elf_Rel;
typedef typename ELFT::Rela Elf_Rela;
typedef typename ELFT::uint uintX_t;
typedef OutputSectionBase<ELFT> Base;
public:
RelocationSection(StringRef Name, bool Sort);
void addReloc(const DynamicReloc<ELFT> &Reloc);
unsigned getRelocOffset();
void finalize() override;
void writeTo(uint8_t *Buf) override;
bool hasRelocs() const { return !Relocs.empty(); }
typename Base::Kind getKind() const override { return Base::Reloc; }
size_t getRelativeRelocCount() const { return NumRelativeRelocs; }
static bool classof(const Base *B) { return B->getKind() == Base::Reloc; }
private:
bool Sort;
size_t NumRelativeRelocs = 0;
std::vector<DynamicReloc<ELFT>> Relocs;
};
template <class ELFT>
class OutputSection final : public OutputSectionBase<ELFT> {
typedef OutputSectionBase<ELFT> Base;
public:
typedef typename ELFT::Shdr Elf_Shdr;
typedef typename ELFT::Sym Elf_Sym;
typedef typename ELFT::Rel Elf_Rel;
typedef typename ELFT::Rela Elf_Rela;
typedef typename ELFT::uint uintX_t;
OutputSection(StringRef Name, uint32_t Type, uintX_t Flags);
void addSection(InputSectionBase<ELFT> *C) override;
void sortInitFini();
void sortCtorsDtors();
void writeTo(uint8_t *Buf) override;
void finalize() override;
void assignOffsets() override;
typename Base::Kind getKind() const override { return Base::Regular; }
static bool classof(const Base *B) { return B->getKind() == Base::Regular; }
std::vector<InputSection<ELFT> *> Sections;
};
template <class ELFT>
class MergeOutputSection final : public OutputSectionBase<ELFT> {
typedef typename ELFT::uint uintX_t;
typedef OutputSectionBase<ELFT> Base;
public:
MergeOutputSection(StringRef Name, uint32_t Type, uintX_t Flags,
uintX_t Alignment);
void addSection(InputSectionBase<ELFT> *S) override;
void writeTo(uint8_t *Buf) override;
unsigned getOffset(StringRef Val);
void finalize() override;
void finalizePieces() override;
bool shouldTailMerge() const;
typename Base::Kind getKind() const override { return Base::Merge; }
static bool classof(const Base *B) { return B->getKind() == Base::Merge; }
private:
llvm::StringTableBuilder Builder;
std::vector<MergeInputSection<ELFT> *> Sections;
};
struct CieRecord {
EhSectionPiece *Piece = nullptr;
std::vector<EhSectionPiece *> FdePieces;
};
// Output section for .eh_frame.
template <class ELFT>
class EhOutputSection final : public OutputSectionBase<ELFT> {
typedef typename ELFT::uint uintX_t;
typedef typename ELFT::Shdr Elf_Shdr;
typedef typename ELFT::Rel Elf_Rel;
typedef typename ELFT::Rela Elf_Rela;
typedef OutputSectionBase<ELFT> Base;
public:
EhOutputSection();
void writeTo(uint8_t *Buf) override;
void finalize() override;
bool empty() const { return Sections.empty(); }
void addSection(InputSectionBase<ELFT> *S) override;
typename Base::Kind getKind() const override { return Base::EHFrame; }
static bool classof(const Base *B) { return B->getKind() == Base::EHFrame; }
size_t NumFdes = 0;
private:
template <class RelTy>
void addSectionAux(EhInputSection<ELFT> *S, llvm::ArrayRef<RelTy> Rels);
template <class RelTy>
CieRecord *addCie(EhSectionPiece &Piece, EhInputSection<ELFT> *Sec,
ArrayRef<RelTy> Rels);
template <class RelTy>
bool isFdeLive(EhSectionPiece &Piece, EhInputSection<ELFT> *Sec,
ArrayRef<RelTy> Rels);
uintX_t getFdePc(uint8_t *Buf, size_t Off, uint8_t Enc);
std::vector<EhInputSection<ELFT> *> Sections;
std::vector<CieRecord *> Cies;
// CIE records are uniquified by their contents and personality functions.
llvm::DenseMap<std::pair<ArrayRef<uint8_t>, SymbolBody *>, CieRecord> CieMap;
};
template <class ELFT>
class InterpSection final : public OutputSectionBase<ELFT> {
typedef OutputSectionBase<ELFT> Base;
public:
InterpSection();
void writeTo(uint8_t *Buf) override;
typename Base::Kind getKind() const override { return Base::Interp; }
static bool classof(const Base *B) { return B->getKind() == Base::Interp; }
};
template <class ELFT>
class StringTableSection final : public OutputSectionBase<ELFT> {
typedef OutputSectionBase<ELFT> Base;
public:
typedef typename ELFT::uint 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; }
typename Base::Kind getKind() const override { return Base::StrTable; }
static bool classof(const Base *B) { return B->getKind() == Base::StrTable; }
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 ELFT::Word Elf_Word;
typedef OutputSectionBase<ELFT> Base;
public:
HashTableSection();
void finalize() override;
void writeTo(uint8_t *Buf) override;
typename Base::Kind getKind() const override { return Base::HashTable; }
static bool classof(const Base *B) { return B->getKind() == Base::HashTable; }
};
// 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 ELFT::Off Elf_Off;
typedef typename ELFT::Word Elf_Word;
typedef typename ELFT::uint uintX_t;
typedef OutputSectionBase<ELFT> Base;
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 *, size_t>> &Symbols);
typename Base::Kind getKind() const override { return Base::GnuHashTable; }
static bool classof(const Base *B) {
return B->getKind() == Base::GnuHashTable;
}
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 SymbolData {
SymbolBody *Body;
size_t STName;
uint32_t Hash;
};
std::vector<SymbolData> Symbols;
unsigned MaskWords;
unsigned NBuckets;
unsigned Shift2;
};
template <class ELFT>
class DynamicSection final : public OutputSectionBase<ELFT> {
typedef OutputSectionBase<ELFT> Base;
typedef typename ELFT::Dyn Elf_Dyn;
typedef typename ELFT::Rel Elf_Rel;
typedef typename ELFT::Rela Elf_Rela;
typedef typename ELFT::Shdr Elf_Shdr;
typedef typename ELFT::Sym Elf_Sym;
typedef typename ELFT::uint 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, SecSize, SymAddr, PlainInt } Kind;
Entry(int32_t Tag, OutputSectionBase<ELFT> *OutSec, KindT Kind = SecAddr)
: Tag(Tag), OutSec(OutSec), Kind(Kind) {}
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:
explicit DynamicSection();
void finalize() override;
void writeTo(uint8_t *Buf) override;
typename Base::Kind getKind() const override { return Base::Dynamic; }
static bool classof(const Base *B) { return B->getKind() == Base::Dynamic; }
};
template <class ELFT>
class MipsReginfoOutputSection final : public OutputSectionBase<ELFT> {
typedef llvm::object::Elf_Mips_RegInfo<ELFT> Elf_Mips_RegInfo;
typedef OutputSectionBase<ELFT> Base;
public:
MipsReginfoOutputSection();
void writeTo(uint8_t *Buf) override;
void addSection(InputSectionBase<ELFT> *S) override;
typename Base::Kind getKind() const override { return Base::MipsReginfo; }
static bool classof(const Base *B) {
return B->getKind() == Base::MipsReginfo;
}
private:
uint32_t GprMask = 0;
};
template <class ELFT>
class MipsOptionsOutputSection final : public OutputSectionBase<ELFT> {
typedef llvm::object::Elf_Mips_Options<ELFT> Elf_Mips_Options;
typedef llvm::object::Elf_Mips_RegInfo<ELFT> Elf_Mips_RegInfo;
typedef OutputSectionBase<ELFT> Base;
public:
MipsOptionsOutputSection();
void writeTo(uint8_t *Buf) override;
void addSection(InputSectionBase<ELFT> *S) override;
typename Base::Kind getKind() const override { return Base::MipsOptions; }
static bool classof(const Base *B) {
return B->getKind() == Base::MipsOptions;
}
private:
uint32_t GprMask = 0;
};
template <class ELFT>
class MipsAbiFlagsOutputSection final : public OutputSectionBase<ELFT> {
typedef llvm::object::Elf_Mips_ABIFlags<ELFT> Elf_Mips_ABIFlags;
typedef OutputSectionBase<ELFT> Base;
public:
MipsAbiFlagsOutputSection();
void writeTo(uint8_t *Buf) override;
void addSection(InputSectionBase<ELFT> *S) override;
typename Base::Kind getKind() const override { return Base::MipsAbiFlags; }
static bool classof(const Base *B) {
return B->getKind() == Base::MipsAbiFlags;
}
private:
Elf_Mips_ABIFlags Flags;
};
// --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 ELFT::uint uintX_t;
typedef OutputSectionBase<ELFT> Base;
public:
EhFrameHeader();
void finalize() override;
void writeTo(uint8_t *Buf) override;
void addFde(uint32_t Pc, uint32_t FdeVA);
typename Base::Kind getKind() const override { return Base::EHFrameHdr; }
static bool classof(const Base *B) {
return B->getKind() == Base::EHFrameHdr;
}
private:
struct FdeData {
uint32_t Pc;
uint32_t FdeVA;
};
std::vector<FdeData> Fdes;
};
template <class ELFT> class BuildIdSection : public OutputSectionBase<ELFT> {
typedef OutputSectionBase<ELFT> Base;
public:
void writeTo(uint8_t *Buf) override;
virtual void writeBuildId(ArrayRef<uint8_t> Buf) = 0;
typename Base::Kind getKind() const override { return Base::BuildId; }
static bool classof(const Base *B) { return B->getKind() == Base::BuildId; }
protected:
BuildIdSection(size_t HashSize);
size_t HashSize;
uint8_t *HashBuf = nullptr;
};
template <class ELFT>
class BuildIdFastHash final : public BuildIdSection<ELFT> {
public:
BuildIdFastHash() : BuildIdSection<ELFT>(8) {}
void writeBuildId(ArrayRef<uint8_t> Buf) override;
};
template <class ELFT> class BuildIdMd5 final : public BuildIdSection<ELFT> {
public:
BuildIdMd5() : BuildIdSection<ELFT>(16) {}
void writeBuildId(ArrayRef<uint8_t> Buf) override;
};
template <class ELFT> class BuildIdSha1 final : public BuildIdSection<ELFT> {
public:
BuildIdSha1() : BuildIdSection<ELFT>(20) {}
void writeBuildId(ArrayRef<uint8_t> Buf) override;
};
template <class ELFT> class BuildIdUuid final : public BuildIdSection<ELFT> {
public:
BuildIdUuid() : BuildIdSection<ELFT>(16) {}
void writeBuildId(ArrayRef<uint8_t> Buf) override;
};
template <class ELFT>
class BuildIdHexstring final : public BuildIdSection<ELFT> {
public:
BuildIdHexstring();
void writeBuildId(ArrayRef<uint8_t>) override;
};
// 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 ELFT::uint uintX_t;
typedef typename ELFT::Phdr Elf_Phdr;
static BuildIdSection<ELFT> *BuildId;
static DynamicSection<ELFT> *Dynamic;
static EhFrameHeader<ELFT> *EhFrameHdr;
static EhOutputSection<ELFT> *EhFrame;
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 VersionDefinitionSection<ELFT> *VerDef;
static VersionTableSection<ELFT> *VerSym;
static VersionNeedSection<ELFT> *VerNeed;
static Elf_Phdr *TlsPhdr;
static OutputSectionBase<ELFT> *ElfHeader;
static OutputSectionBase<ELFT> *ProgramHeaders;
static OutputSectionBase<ELFT> *PreinitArray;
static OutputSectionBase<ELFT> *InitArray;
static OutputSectionBase<ELFT> *FiniArray;
// This pool owns dynamically-allocated output sections.
static std::vector<std::unique_ptr<OutputSectionBase<ELFT>>> Pool;
};
template <bool Is64Bits> struct SectionKey {
typedef typename std::conditional<Is64Bits, uint64_t, uint32_t>::type uintX_t;
StringRef Name;
uint32_t Type;
uintX_t Flags;
uintX_t Alignment;
};
// This class knows how to create an output section for a given
// input section. Output section type is determined by various
// factors, including input section's sh_flags, sh_type and
// linker scripts.
template <class ELFT> class OutputSectionFactory {
typedef typename ELFT::Shdr Elf_Shdr;
typedef typename ELFT::uint uintX_t;
typedef typename elf::SectionKey<ELFT::Is64Bits> Key;
public:
std::pair<OutputSectionBase<ELFT> *, bool> create(InputSectionBase<ELFT> *C,
StringRef OutsecName);
std::pair<OutputSectionBase<ELFT> *, bool>
create(const SectionKey<ELFT::Is64Bits> &Key, InputSectionBase<ELFT> *C);
private:
llvm::SmallDenseMap<Key, OutputSectionBase<ELFT> *> Map;
};
template <class ELFT> BuildIdSection<ELFT> *Out<ELFT>::BuildId;
template <class ELFT> DynamicSection<ELFT> *Out<ELFT>::Dynamic;
template <class ELFT> EhFrameHeader<ELFT> *Out<ELFT>::EhFrameHdr;
template <class ELFT> EhOutputSection<ELFT> *Out<ELFT>::EhFrame;
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> VersionDefinitionSection<ELFT> *Out<ELFT>::VerDef;
template <class ELFT> VersionTableSection<ELFT> *Out<ELFT>::VerSym;
template <class ELFT> VersionNeedSection<ELFT> *Out<ELFT>::VerNeed;
template <class ELFT> typename ELFT::Phdr *Out<ELFT>::TlsPhdr;
template <class ELFT> OutputSectionBase<ELFT> *Out<ELFT>::ElfHeader;
template <class ELFT> OutputSectionBase<ELFT> *Out<ELFT>::ProgramHeaders;
template <class ELFT> OutputSectionBase<ELFT> *Out<ELFT>::PreinitArray;
template <class ELFT> OutputSectionBase<ELFT> *Out<ELFT>::InitArray;
template <class ELFT> OutputSectionBase<ELFT> *Out<ELFT>::FiniArray;
template <class ELFT>
std::vector<std::unique_ptr<OutputSectionBase<ELFT>>> Out<ELFT>::Pool;
} // namespace elf
} // namespace lld
namespace llvm {
template <bool Is64Bits> struct DenseMapInfo<lld::elf::SectionKey<Is64Bits>> {
typedef typename lld::elf::SectionKey<Is64Bits> Key;
static Key getEmptyKey();
static Key getTombstoneKey();
static unsigned getHashValue(const Key &Val);
static bool isEqual(const Key &LHS, const Key &RHS);
};
}
#endif
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