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//===- InputSection.h -------------------------------------------*- C++ -*-===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
#include "Config.h"
#include "Relocations.h"
#include "Thunks.h"
#include "lld/Common/LLVM.h"
#include "llvm/ADT/CachedHashString.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/TinyPtrVector.h"
#include "llvm/Object/ELF.h"
namespace lld {
namespace elf {
class Symbol;
struct SectionPiece;
class Defined;
struct Partition;
class SyntheticSection;
class MergeSyntheticSection;
template <class ELFT> class ObjFile;
class OutputSection;
extern std::vector<Partition> partitions;
// Returned by InputSectionBase::relsOrRelas. At least one member is empty.
template <class ELFT> struct RelsOrRelas {
ArrayRef<typename ELFT::Rel> rels;
ArrayRef<typename ELFT::Rela> relas;
bool areRelocsRel() const { return rels.size(); }
// 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;
// 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.
SectionBase *repl;
uint8_t sectionKind : 3;
// The next two bit fields are only used by InputSectionBase, but we
// put them here so the struct packs better.
uint8_t bss : 1;
// Set for sections that should not be folded by ICF.
uint8_t keepUnique : 1;
// The 1-indexed partition that this section is assigned to by the garbage
// collector, or 0 if this section is dead. Normally there is only one
// partition, so this will either be 0 or 1.
uint8_t partition;
elf::Partition &getPartition() const;
// These corresponds to the fields in Elf_Shdr.
uint32_t alignment;
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 getVA(uint64_t offset = 0) const;
bool isLive() const { return partition != 0; }
void markLive() { partition = 1; }
void markDead() { partition = 0; }
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), repl(this), sectionKind(sectionKind), bss(false),
keepUnique(false), partition(0), alignment(alignment), flags(flags),
entsize(entsize), type(type), link(link), info(info) {}
// This corresponds to a section of an input file.
class InputSectionBase : public SectionBase {
template <class ELFT>
InputSectionBase(ObjFile<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);
static bool classof(const SectionBase *s) { return s->kind() != Output; }
// Section index of the relocation section if exists.
uint32_t relSecIdx = 0;
// The file which contains this section. Its dynamic type is always
// ObjFile<ELFT>, but in order to avoid ELFT, we use InputFile as
// its static type.
InputFile *file;
template <class ELFT> ObjFile<ELFT> *getFile() const {
return cast_or_null<ObjFile<ELFT>>(file);
// If basic block sections are enabled, many code sections could end up with
// one or two jump instructions at the end that could be relaxed to a smaller
// instruction. The members below help trimming the trailing jump instruction
// and shrinking a section.
unsigned bytesDropped = 0;
// Whether the section needs to be padded with a NOP filler due to
// deleteFallThruJmpInsn.
bool nopFiller = false;
void drop_back(uint64_t num) { bytesDropped += num; }
void push_back(uint64_t num) {
assert(bytesDropped >= num);
bytesDropped -= num;
void trim() {
if (bytesDropped) {
rawData = rawData.drop_back(bytesDropped);
bytesDropped = 0;
ArrayRef<uint8_t> data() const {
if (uncompressedSize >= 0)
return rawData;
uint64_t getOffsetInFile() const;
// Input sections are part of an output section. Special sections
// like .eh_frame and merge sections are first combined into a
// synthetic section that is then added to an output section. In all
// cases this points one level up.
SectionBase *parent = nullptr;
// The next member in the section group if this section is in a group. This is
// used by --gc-sections.
InputSectionBase *nextInSectionGroup = nullptr;
template <class ELFT> RelsOrRelas<ELFT> relsOrRelas() const;
// InputSections that are dependent on us (reverse dependency for GC)
llvm::TinyPtrVector<InputSection *> dependentSections;
// Returns the size of this section (even if this is a common or BSS.)
size_t getSize() const;
InputSection *getLinkOrderDep() const;
// Get the function symbol that encloses this offset from within the
// section.
template <class ELFT>
Defined *getEnclosingFunction(uint64_t offset);
// Returns a source location string. Used to construct an error message.
template <class ELFT> std::string getLocation(uint64_t offset);
std::string getSrcMsg(const Symbol &sym, uint64_t offset);
std::string getObjMsg(uint64_t offset);
// Each section knows how to relocate itself. These functions apply
// relocations, assuming that Buf points to this section's copy in
// the mmap'ed output buffer.
template <class ELFT> void relocate(uint8_t *buf, uint8_t *bufEnd);
void relocateAlloc(uint8_t *buf, uint8_t *bufEnd);
static uint64_t getRelocTargetVA(const InputFile *File, RelType Type,
int64_t A, uint64_t P, const Symbol &Sym,
RelExpr Expr);
// The native ELF reloc data type is not very convenient to handle.
// So we convert ELF reloc records to our own records in Relocations.cpp.
// This vector contains such "cooked" relocations.
SmallVector<Relocation, 0> relocations;
// These are modifiers to jump instructions that are necessary when basic
// block sections are enabled. Basic block sections creates opportunities to
// relax jump instructions at basic block boundaries after reordering the
// basic blocks.
SmallVector<JumpInstrMod, 0> jumpInstrMods;
// A function compiled with -fsplit-stack calling a function
// compiled without -fsplit-stack needs its prologue adjusted. Find
// such functions and adjust their prologues. This is very similar
// to relocation. See for more
// information.
template <typename ELFT>
void adjustSplitStackFunctionPrologues(uint8_t *buf, uint8_t *end);
template <typename T> llvm::ArrayRef<T> getDataAs() const {
size_t s = data().size();
assert(s % sizeof(T) == 0);
return llvm::makeArrayRef<T>((const T *)data().data(), s / sizeof(T));
template <typename ELFT>
void parseCompressedHeader();
void uncompress() const;
mutable ArrayRef<uint8_t> rawData;
// This field stores the uncompressed size of the compressed data in rawData,
// or -1 if rawData is not compressed (either because the section wasn't
// compressed in the first place, or because we ended up uncompressing it).
// Since the feature is not used often, this is usually -1.
mutable int64_t uncompressedSize = -1;
// 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).
struct SectionPiece {
SectionPiece(size_t off, uint32_t hash, bool live)
: inputOff(off), live(live || !config->gcSections), hash(hash >> 1) {}
uint32_t inputOff;
uint32_t live : 1;
uint32_t hash : 31;
uint64_t outputOff = 0;
static_assert(sizeof(SectionPiece) == 16, "SectionPiece is too big");
// This corresponds to a SHF_MERGE section of an input file.
class MergeInputSection : public InputSectionBase {
template <class ELFT>
MergeInputSection(ObjFile<ELFT> &f, const typename ELFT::Shdr &header,
StringRef name);
MergeInputSection(uint64_t flags, uint32_t type, uint64_t entsize,
ArrayRef<uint8_t> data, StringRef name);
static bool classof(const SectionBase *s) { return s->kind() == Merge; }
void splitIntoPieces();
// Translate an offset in the input section to an offset in the parent
// MergeSyntheticSection.
uint64_t getParentOffset(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 =
(pieces.size() - 1 == i) ? data().size() : pieces[i + 1].inputOff;
return {toStringRef(data().slice(begin, end - begin)), pieces[i].hash};
// Returns the SectionPiece at a given input section offset.
SectionPiece *getSectionPiece(uint64_t offset);
const SectionPiece *getSectionPiece(uint64_t offset) const {
return const_cast<MergeInputSection *>(this)->getSectionPiece(offset);
SyntheticSection *getParent() const;
void splitStrings(ArrayRef<uint8_t> a, size_t size);
void splitNonStrings(ArrayRef<uint8_t> a, size_t size);
struct EhSectionPiece {
EhSectionPiece(size_t off, InputSectionBase *sec, uint32_t size,
unsigned firstRelocation)
: inputOff(off), sec(sec), size(size), firstRelocation(firstRelocation) {}
ArrayRef<uint8_t> data() const {
return {sec->data().data() + this->inputOff, size};
size_t inputOff;
ssize_t outputOff = -1;
InputSectionBase *sec;
uint32_t size;
unsigned firstRelocation;
// This corresponds to a .eh_frame section of an input file.
class EhInputSection : public InputSectionBase {
template <class ELFT>
EhInputSection(ObjFile<ELFT> &f, const typename ELFT::Shdr &header,
StringRef name);
static bool classof(const SectionBase *s) { return s->kind() == EHFrame; }
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 *getParent() const;
// 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(InputFile *f, uint64_t flags, uint32_t type, uint32_t alignment,
ArrayRef<uint8_t> data, StringRef name, Kind k = Regular);
template <class ELFT>
InputSection(ObjFile<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);
uint64_t getOffset(uint64_t offset) const { return outSecOff + offset; }
OutputSection *getParent() const;
// This variable has two usages. Initially, it represents an index in the
// OutputSection's InputSection list, and is used when ordering SHF_LINK_ORDER
// sections. After assignAddresses is called, it represents the offset from
// the beginning of the output section this section was assigned to.
uint64_t outSecOff = 0;
static bool classof(const SectionBase *s);
InputSectionBase *getRelocatedSection() const;
template <class ELFT, class RelTy>
void relocateNonAlloc(uint8_t *buf, llvm::ArrayRef<RelTy> rels);
// Used by ICF.
uint32_t eqClass[2] = {0, 0};
// Called by ICF to merge two input sections.
void replace(InputSection *other);
static InputSection discarded;
template <class ELFT, class RelTy>
void copyRelocations(uint8_t *buf, llvm::ArrayRef<RelTy> rels);
template <class ELFT> void copyShtGroup(uint8_t *buf);
#ifdef _WIN32
static_assert(sizeof(InputSection) <= 184, "InputSection is too big");
static_assert(sizeof(InputSection) <= 176, "InputSection is too big");
inline bool isDebugSection(const InputSectionBase &sec) {
return (sec.flags & llvm::ELF::SHF_ALLOC) == 0 &&
(".debug") ||".zdebug"));
// The list of all input sections.
extern std::vector<InputSectionBase *> inputSections;
// The set of TOC entries (.toc + addend) for which we should not apply
// toc-indirect to toc-relative relaxation. const Symbol * refers to the
// STT_SECTION symbol associated to the .toc input section.
extern llvm::DenseSet<std::pair<const Symbol *, uint64_t>> ppc64noTocRelax;
} // namespace elf
std::string toString(const elf::InputSectionBase *);
} // namespace lld