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//===- InputSection.h -------------------------------------------*- C++ -*-===//
// The LLVM Linker
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
#include "Config.h"
#include "Relocations.h"
#include "Thunks.h"
#include "lld/Core/LLVM.h"
#include "llvm/ADT/CachedHashString.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/TinyPtrVector.h"
#include "llvm/Object/ELF.h"
#include <mutex>
namespace lld {
namespace elf {
class DefinedCommon;
class SymbolBody;
struct SectionPiece;
class DefinedRegular;
class SyntheticSection;
template <class ELFT> class EhFrameSection;
class MergeSyntheticSection;
template <class ELFT> class ObjectFile;
class OutputSection;
// This is the base class of all sections that lld handles. Some are sections in
// input files, some are sections in the produced output file and some exist
// just as a convenience for implementing special ways of combining some
// sections.
class SectionBase {
enum Kind { Regular, EHFrame, Merge, Synthetic, Output };
Kind kind() const { return (Kind)SectionKind; }
StringRef Name;
unsigned SectionKind : 3;
// The next two bit fields are only used by InputSectionBase, but we
// put them here so the struct packs better.
// The garbage collector sets sections' Live bits.
// If GC is disabled, all sections are considered live by default.
unsigned Live : 1; // for garbage collection
unsigned Assigned : 1; // for linker script
uint32_t Alignment;
// These corresponds to the fields in Elf_Shdr.
uint64_t Flags;
uint64_t Entsize;
uint32_t Type;
uint32_t Link;
uint32_t Info;
OutputSection *getOutputSection();
const OutputSection *getOutputSection() const {
return const_cast<SectionBase *>(this)->getOutputSection();
// Translate an offset in the input section to an offset in the output
// section.
uint64_t getOffset(uint64_t Offset) const;
uint64_t getOffset(const DefinedRegular &Sym) const;
SectionBase(Kind SectionKind, StringRef Name, uint64_t Flags,
uint64_t Entsize, uint64_t Alignment, uint32_t Type,
uint32_t Info, uint32_t Link)
: Name(Name), SectionKind(SectionKind), Alignment(Alignment),
Flags(Flags), Entsize(Entsize), Type(Type), Link(Link), Info(Info) {
Live = false;
Assigned = false;
// This corresponds to a section of an input file.
class InputSectionBase : public SectionBase {
static bool classof(const SectionBase *S);
// The file this section is from.
InputFile *File;
ArrayRef<uint8_t> Data;
uint64_t getOffsetInFile() const;
static InputSectionBase Discarded;
: SectionBase(Regular, "", /*Flags*/ 0, /*Entsize*/ 0, /*Alignment*/ 0,
/*Type*/ 0,
/*Info*/ 0, /*Link*/ 0),
Repl(this) {
Live = false;
Assigned = false;
NumRelocations = 0;
AreRelocsRela = false;
template <class ELFT>
InputSectionBase(ObjectFile<ELFT> *File, const typename ELFT::Shdr *Header,
StringRef Name, Kind SectionKind);
InputSectionBase(InputFile *File, uint64_t Flags, uint32_t Type,
uint64_t Entsize, uint32_t Link, uint32_t Info,
uint32_t Alignment, ArrayRef<uint8_t> Data, StringRef Name,
Kind SectionKind);
OutputSection *OutSec = nullptr;
// Relocations that refer to this section.
const void *FirstRelocation = nullptr;
unsigned NumRelocations : 31;
unsigned AreRelocsRela : 1;
template <class ELFT> ArrayRef<typename ELFT::Rel> rels() const {
return llvm::makeArrayRef(
static_cast<const typename ELFT::Rel *>(FirstRelocation),
template <class ELFT> ArrayRef<typename ELFT::Rela> relas() const {
return llvm::makeArrayRef(
static_cast<const typename ELFT::Rela *>(FirstRelocation),
// This pointer points to the "real" instance of this instance.
// Usually Repl == this. However, if ICF merges two sections,
// Repl pointer of one section points to another section. So,
// if you need to get a pointer to this instance, do not use
// this but instead this->Repl.
InputSectionBase *Repl;
// InputSections that are dependent on us (reverse dependency for GC)
llvm::TinyPtrVector<InputSectionBase *> DependentSections;
// Returns the size of this section (even if this is a common or BSS.)
size_t getSize() const;
template <class ELFT> ObjectFile<ELFT> *getFile() const;
template <class ELFT> llvm::object::ELFFile<ELFT> getObj() const {
return getFile<ELFT>()->getObj();
InputSectionBase *getLinkOrderDep() const;
void uncompress();
// Returns a source location string. Used to construct an error message.
template <class ELFT> std::string getLocation(uint64_t Offset);
template <class ELFT> std::string getSrcMsg(uint64_t Offset);
template <class ELFT> std::string getObjMsg(uint64_t Offset);
template <class ELFT> void relocate(uint8_t *Buf, uint8_t *BufEnd);
std::vector<Relocation> Relocations;
template <typename T> llvm::ArrayRef<T> getDataAs() const {
size_t S = Data.size();
assert(S % sizeof(T) == 0);
return llvm::makeArrayRef<T>((const T *), S / sizeof(T));
// SectionPiece represents a piece of splittable section contents.
// We allocate a lot of these and binary search on them. This means that they
// have to be as compact as possible, which is why we don't store the size (can
// be found by looking at the next one) and put the hash in a side table.
struct SectionPiece {
SectionPiece(size_t Off, bool Live = false)
: InputOff(Off), OutputOff(-1), Live(Live || !Config->GcSections) {}
size_t InputOff;
ssize_t OutputOff : 8 * sizeof(ssize_t) - 1;
size_t Live : 1;
static_assert(sizeof(SectionPiece) == 2 * sizeof(size_t),
"SectionPiece is too big");
// This corresponds to a SHF_MERGE section of an input file.
class MergeInputSection : public InputSectionBase {
template <class ELFT>
MergeInputSection(ObjectFile<ELFT> *F, const typename ELFT::Shdr *Header,
StringRef Name);
static bool classof(const SectionBase *S);
void splitIntoPieces();
// Mark the piece at a given offset live. Used by GC.
void markLiveAt(uint64_t Offset) {
assert(this->Flags & llvm::ELF::SHF_ALLOC);
// Translate an offset in the input section to an offset
// in the output section.
uint64_t getOffset(uint64_t Offset) const;
// Splittable sections are handled as a sequence of data
// rather than a single large blob of data.
std::vector<SectionPiece> Pieces;
// Returns I'th piece's data. This function is very hot when
// string merging is enabled, so we want to inline.
llvm::CachedHashStringRef getData(size_t I) const {
size_t Begin = Pieces[I].InputOff;
size_t End;
if (Pieces.size() - 1 == I)
End = this->Data.size();
End = Pieces[I + 1].InputOff;
StringRef S = {(const char *)(this-> + Begin), End - Begin};
return {S, Hashes[I]};
// Returns the SectionPiece at a given input section offset.
SectionPiece *getSectionPiece(uint64_t Offset);
const SectionPiece *getSectionPiece(uint64_t Offset) const;
// MergeInputSections are aggregated to a synthetic input sections,
// and then added to an OutputSection. This pointer points to a
// synthetic MergeSyntheticSection which this section belongs to.
MergeSyntheticSection *MergeSec = nullptr;
void splitStrings(ArrayRef<uint8_t> A, size_t Size);
void splitNonStrings(ArrayRef<uint8_t> A, size_t Size);
std::vector<uint32_t> Hashes;
mutable llvm::DenseMap<uint64_t, uint64_t> OffsetMap;
mutable std::once_flag InitOffsetMap;
llvm::DenseSet<uint64_t> LiveOffsets;
struct EhSectionPiece : public SectionPiece {
EhSectionPiece(size_t Off, InputSectionBase *ID, uint32_t Size,
unsigned FirstRelocation)
: SectionPiece(Off, false), ID(ID), Size(Size),
FirstRelocation(FirstRelocation) {}
InputSectionBase *ID;
uint32_t Size;
uint32_t size() const { return Size; }
ArrayRef<uint8_t> data() { return {ID-> + this->InputOff, Size}; }
unsigned FirstRelocation;
// This corresponds to a .eh_frame section of an input file.
class EhInputSection : public InputSectionBase {
template <class ELFT>
EhInputSection(ObjectFile<ELFT> *F, const typename ELFT::Shdr *Header,
StringRef Name);
static bool classof(const SectionBase *S);
template <class ELFT> void split();
template <class ELFT, class RelTy> void split(ArrayRef<RelTy> Rels);
// Splittable sections are handled as a sequence of data
// rather than a single large blob of data.
std::vector<EhSectionPiece> Pieces;
SyntheticSection *EHSec = nullptr;
// This is a section that is added directly to an output section
// instead of needing special combination via a synthetic section. This
// includes all input sections with the exceptions of SHF_MERGE and
// .eh_frame. It also includes the synthetic sections themselves.
class InputSection : public InputSectionBase {
InputSection(uint64_t Flags, uint32_t Type, uint32_t Alignment,
ArrayRef<uint8_t> Data, StringRef Name, Kind K = Regular);
template <class ELFT>
InputSection(ObjectFile<ELFT> *F, const typename ELFT::Shdr *Header,
StringRef Name);
// Write this section to a mmap'ed file, assuming Buf is pointing to
// beginning of the output section.
template <class ELFT> void writeTo(uint8_t *Buf);
// The offset from beginning of the output sections this section was assigned
// to. The writer sets a value.
uint64_t OutSecOff = 0;
static bool classof(const SectionBase *S);
InputSectionBase *getRelocatedSection();
template <class ELFT, class RelTy>
void relocateNonAlloc(uint8_t *Buf, llvm::ArrayRef<RelTy> Rels);
// Used by ICF.
uint32_t Class[2] = {0, 0};
// Called by ICF to merge two input sections.
void replace(InputSection *Other);
template <class ELFT, class RelTy>
void copyRelocations(uint8_t *Buf, llvm::ArrayRef<RelTy> Rels);
// The list of all input sections.
extern std::vector<InputSectionBase *> InputSections;
} // namespace elf
std::string toString(const elf::InputSectionBase *);
} // namespace lld