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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 "lld/Common/LLVM.h"
#include "lld/Common/Memory.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/BitVector.h"
#include "llvm/ADT/CachedHashString.h"
#include "llvm/BinaryFormat/MachO.h"
namespace lld {
namespace macho {
class InputFile;
class OutputSection;
class Defined;
class InputSection {
enum Kind {
Kind kind() const { return shared->sectionKind; }
virtual ~InputSection() = default;
virtual uint64_t getSize() const { return data.size(); }
InputFile *getFile() const { return shared->file; }
StringRef getName() const { return shared->name; }
StringRef getSegName() const { return shared->segname; }
uint32_t getFlags() const { return shared->flags; }
uint64_t getFileSize() const;
// Translates \p off -- an offset relative to this InputSection -- into an
// offset from the beginning of its parent OutputSection.
virtual uint64_t getOffset(uint64_t off) const = 0;
// The offset from the beginning of the file.
uint64_t getVA(uint64_t off) const;
// Whether the data at \p off in this InputSection is live.
virtual bool isLive(uint64_t off) const = 0;
virtual void markLive(uint64_t off) = 0;
virtual InputSection *canonical() { return this; }
OutputSection *parent = nullptr;
uint32_t align = 1;
uint32_t callSiteCount : 31;
// is address assigned?
uint32_t isFinal : 1;
ArrayRef<uint8_t> data;
std::vector<Reloc> relocs;
// The fields in this struct are immutable. Since we create a lot of
// InputSections with identical values for them (due to
// .subsections_via_symbols), factoring them out into a shared struct reduces
// memory consumption and makes copying cheaper.
struct Shared {
InputFile *file;
StringRef name;
StringRef segname;
uint32_t flags;
Kind sectionKind;
Shared(InputFile *file, StringRef name, StringRef segname, uint32_t flags,
Kind kind)
: file(file), name(name), segname(segname), flags(flags),
sectionKind(kind) {}
InputSection(Kind kind, StringRef segname, StringRef name, InputFile *file,
ArrayRef<uint8_t> data, uint32_t align, uint32_t flags)
: align(align), callSiteCount(0), isFinal(false), data(data),
shared(make<Shared>(file, name, segname, flags, kind)) {}
const Shared *const shared;
// ConcatInputSections are combined into (Concat)OutputSections through simple
// concatenation, in contrast with literal sections which may have their
// contents merged before output.
class ConcatInputSection final : public InputSection {
ConcatInputSection(StringRef segname, StringRef name, InputFile *file,
ArrayRef<uint8_t> data, uint32_t align = 1,
uint32_t flags = 0)
: InputSection(ConcatKind, segname, name, file, data, align, flags) {}
ConcatInputSection(StringRef segname, StringRef name)
: ConcatInputSection(segname, name, /*file=*/nullptr,
/*align=*/1, /*flags=*/0) {}
uint64_t getOffset(uint64_t off) const override { return outSecOff + off; }
uint64_t getVA() const { return InputSection::getVA(0); }
// ConcatInputSections are entirely live or dead, so the offset is irrelevant.
bool isLive(uint64_t off) const override { return live; }
void markLive(uint64_t off) override { live = true; }
bool isCoalescedWeak() const { return wasCoalesced && numRefs == 0; }
bool shouldOmitFromOutput() const { return !live || isCoalescedWeak(); }
bool isHashableForICF() const;
void hashForICF();
void writeTo(uint8_t *buf);
void foldIdentical(ConcatInputSection *redundant);
InputSection *canonical() override {
return replacement ? replacement : this;
static bool classof(const InputSection *isec) {
return isec->kind() == ConcatKind;
// Points to the surviving section after this one is folded by ICF
InputSection *replacement = nullptr;
// Equivalence-class ID for ICF
uint64_t icfEqClass[2] = {0, 0};
// With subsections_via_symbols, most symbols have their own InputSection,
// and for weak symbols (e.g. from inline functions), only the
// InputSection from one translation unit will make it to the output,
// while all copies in other translation units are coalesced into the
// first and not copied to the output.
bool wasCoalesced = false;
bool live = !config->deadStrip;
// How many symbols refer to this InputSection.
uint32_t numRefs = 0;
// This variable has two usages. Initially, it represents the input order.
// After assignAddresses is called, it represents the offset from the
// beginning of the output section this section was assigned to.
uint64_t outSecOff = 0;
// Verify ConcatInputSection's size on 64-bit builds.
static_assert(sizeof(int) != 8 || sizeof(ConcatInputSection) == 112,
"Try to minimize ConcatInputSection's size, we create many "
"instances of it");
// Helper functions to make it easy to sprinkle asserts.
inline bool shouldOmitFromOutput(InputSection *isec) {
return isa<ConcatInputSection>(isec) &&
inline bool isCoalescedWeak(InputSection *isec) {
return isa<ConcatInputSection>(isec) &&
// We allocate a lot of these and binary search on them, so they should be as
// compact as possible. Hence the use of 31 rather than 64 bits for the hash.
struct StringPiece {
// Offset from the start of the containing input section.
uint32_t inSecOff;
uint32_t live : 1;
// Only set if deduplicating literals
uint32_t hash : 31;
// Offset from the start of the containing output section.
uint64_t outSecOff = 0;
StringPiece(uint64_t off, uint32_t hash)
: inSecOff(off), live(!config->deadStrip), hash(hash) {}
static_assert(sizeof(StringPiece) == 16, "StringPiece is too big!");
// CStringInputSections are composed of multiple null-terminated string
// literals, which we represent using StringPieces. These literals can be
// deduplicated and tail-merged, so translating offsets between the input and
// outputs sections is more complicated.
// NOTE: One significant difference between LLD and ld64 is that we merge all
// cstring literals, even those referenced directly by non-private symbols.
// ld64 is more conservative and does not do that. This was mostly done for
// implementation simplicity; if we find programs that need the more
// conservative behavior we can certainly implement that.
class CStringInputSection final : public InputSection {
CStringInputSection(StringRef segname, StringRef name, InputFile *file,
ArrayRef<uint8_t> data, uint32_t align, uint32_t flags)
: InputSection(CStringLiteralKind, segname, name, file, data, align,
flags) {}
uint64_t getOffset(uint64_t off) const override;
bool isLive(uint64_t off) const override { return getStringPiece(off).live; }
void markLive(uint64_t off) override { getStringPiece(off).live = true; }
// Find the StringPiece that contains this offset.
StringPiece &getStringPiece(uint64_t off);
const StringPiece &getStringPiece(uint64_t off) const;
// Split at each null byte.
void splitIntoPieces();
StringRef getStringRef(size_t i) const {
size_t begin = pieces[i].inSecOff;
size_t end =
(pieces.size() - 1 == i) ? data.size() : pieces[i + 1].inSecOff;
return toStringRef(data.slice(begin, end - begin));
// Returns i'th piece as a CachedHashStringRef. This function is very hot when
// string merging is enabled, so we want to inline.
llvm::CachedHashStringRef getCachedHashStringRef(size_t i) const {
return {getStringRef(i), pieces[i].hash};
static bool classof(const InputSection *isec) {
return isec->kind() == CStringLiteralKind;
std::vector<StringPiece> pieces;
class WordLiteralInputSection final : public InputSection {
WordLiteralInputSection(StringRef segname, StringRef name, InputFile *file,
ArrayRef<uint8_t> data, uint32_t align,
uint32_t flags);
uint64_t getOffset(uint64_t off) const override;
bool isLive(uint64_t off) const override {
return live[off >> power2LiteralSize];
void markLive(uint64_t off) override { live[off >> power2LiteralSize] = 1; }
static bool classof(const InputSection *isec) {
return isec->kind() == WordLiteralKind;
unsigned power2LiteralSize;
// The liveness of data[off] is tracked by live[off >> power2LiteralSize].
llvm::BitVector live;
inline uint8_t sectionType(uint32_t flags) {
return flags & llvm::MachO::SECTION_TYPE;
inline bool isZeroFill(uint32_t flags) {
return llvm::MachO::isVirtualSection(sectionType(flags));
inline bool isThreadLocalVariables(uint32_t flags) {
return sectionType(flags) == llvm::MachO::S_THREAD_LOCAL_VARIABLES;
// These sections contain the data for initializing thread-local variables.
inline bool isThreadLocalData(uint32_t flags) {
return sectionType(flags) == llvm::MachO::S_THREAD_LOCAL_REGULAR ||
sectionType(flags) == llvm::MachO::S_THREAD_LOCAL_ZEROFILL;
inline bool isDebugSection(uint32_t flags) {
return (flags & llvm::MachO::SECTION_ATTRIBUTES_USR) ==
inline bool isWordLiteralSection(uint32_t flags) {
return sectionType(flags) == llvm::MachO::S_4BYTE_LITERALS ||
sectionType(flags) == llvm::MachO::S_8BYTE_LITERALS ||
sectionType(flags) == llvm::MachO::S_16BYTE_LITERALS;
bool isCodeSection(const InputSection *);
bool isCfStringSection(const InputSection *);
extern std::vector<ConcatInputSection *> inputSections;
namespace section_names {
constexpr const char authGot[] = "__auth_got";
constexpr const char authPtr[] = "__auth_ptr";
constexpr const char binding[] = "__binding";
constexpr const char bitcodeBundle[] = "__bundle";
constexpr const char cString[] = "__cstring";
constexpr const char cfString[] = "__cfstring";
constexpr const char codeSignature[] = "__code_signature";
constexpr const char common[] = "__common";
constexpr const char compactUnwind[] = "__compact_unwind";
constexpr const char data[] = "__data";
constexpr const char debugAbbrev[] = "__debug_abbrev";
constexpr const char debugInfo[] = "__debug_info";
constexpr const char debugStr[] = "__debug_str";
constexpr const char ehFrame[] = "__eh_frame";
constexpr const char export_[] = "__export";
constexpr const char dataInCode[] = "__data_in_code";
constexpr const char functionStarts[] = "__func_starts";
constexpr const char got[] = "__got";
constexpr const char header[] = "__mach_header";
constexpr const char indirectSymbolTable[] = "__ind_sym_tab";
constexpr const char const_[] = "__const";
constexpr const char lazySymbolPtr[] = "__la_symbol_ptr";
constexpr const char lazyBinding[] = "__lazy_binding";
constexpr const char literals[] = "__literals";
constexpr const char moduleInitFunc[] = "__mod_init_func";
constexpr const char moduleTermFunc[] = "__mod_term_func";
constexpr const char nonLazySymbolPtr[] = "__nl_symbol_ptr";
constexpr const char objcCatList[] = "__objc_catlist";
constexpr const char objcClassList[] = "__objc_classlist";
constexpr const char objcConst[] = "__objc_const";
constexpr const char objcImageInfo[] = "__objc_imageinfo";
constexpr const char objcNonLazyCatList[] = "__objc_nlcatlist";
constexpr const char objcNonLazyClassList[] = "__objc_nlclslist";
constexpr const char objcProtoList[] = "__objc_protolist";
constexpr const char pageZero[] = "__pagezero";
constexpr const char pointers[] = "__pointers";
constexpr const char rebase[] = "__rebase";
constexpr const char staticInit[] = "__StaticInit";
constexpr const char stringTable[] = "__string_table";
constexpr const char stubHelper[] = "__stub_helper";
constexpr const char stubs[] = "__stubs";
constexpr const char swift[] = "__swift";
constexpr const char symbolTable[] = "__symbol_table";
constexpr const char textCoalNt[] = "__textcoal_nt";
constexpr const char text[] = "__text";
constexpr const char threadPtrs[] = "__thread_ptrs";
constexpr const char threadVars[] = "__thread_vars";
constexpr const char unwindInfo[] = "__unwind_info";
constexpr const char weakBinding[] = "__weak_binding";
constexpr const char zeroFill[] = "__zerofill";
} // namespace section_names
} // namespace macho
std::string toString(const macho::InputSection *);
} // namespace lld