llvm-project/lld/ELF/SyntheticSections.h

1217 lines
40 KiB
C++

//===- SyntheticSection.h ---------------------------------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// Synthetic sections represent chunks of linker-created data. If you
// need to create a chunk of data that to be included in some section
// in the result, you probably want to create that as a synthetic section.
//
// Synthetic sections are designed as input sections as opposed to
// output sections because we want to allow them to be manipulated
// using linker scripts just like other input sections from regular
// files.
//
//===----------------------------------------------------------------------===//
#ifndef LLD_ELF_SYNTHETIC_SECTIONS_H
#define LLD_ELF_SYNTHETIC_SECTIONS_H
#include "DWARF.h"
#include "EhFrame.h"
#include "InputSection.h"
#include "llvm/ADT/MapVector.h"
#include "llvm/MC/StringTableBuilder.h"
#include "llvm/Support/Endian.h"
#include <functional>
namespace lld {
namespace elf {
class Defined;
struct PhdrEntry;
class SymbolTableBaseSection;
class VersionNeedBaseSection;
class SyntheticSection : public InputSection {
public:
SyntheticSection(uint64_t flags, uint32_t type, uint32_t alignment,
StringRef name)
: InputSection(nullptr, flags, type, alignment, {}, name,
InputSectionBase::Synthetic) {
markLive();
}
virtual ~SyntheticSection() = default;
virtual void writeTo(uint8_t *buf) = 0;
virtual size_t getSize() const = 0;
virtual void finalizeContents() {}
// If the section has the SHF_ALLOC flag and the size may be changed if
// thunks are added, update the section size.
virtual bool updateAllocSize() { return false; }
virtual bool isNeeded() const { return true; }
static bool classof(const SectionBase *d) {
return d->kind() == InputSectionBase::Synthetic;
}
};
struct CieRecord {
EhSectionPiece *cie = nullptr;
std::vector<EhSectionPiece *> fdes;
};
// Section for .eh_frame.
class EhFrameSection final : public SyntheticSection {
public:
EhFrameSection();
void writeTo(uint8_t *buf) override;
void finalizeContents() override;
bool isNeeded() const override { return !sections.empty(); }
size_t getSize() const override { return size; }
static bool classof(const SectionBase *d) {
return SyntheticSection::classof(d) && d->name == ".eh_frame";
}
void addSection(EhInputSection *sec);
std::vector<EhInputSection *> sections;
size_t numFdes = 0;
struct FdeData {
uint32_t pcRel;
uint32_t fdeVARel;
};
std::vector<FdeData> getFdeData() const;
ArrayRef<CieRecord *> getCieRecords() const { return cieRecords; }
private:
// This is used only when parsing EhInputSection. We keep it here to avoid
// allocating one for each EhInputSection.
llvm::DenseMap<size_t, CieRecord *> offsetToCie;
uint64_t size = 0;
template <class ELFT, class RelTy>
void addRecords(EhInputSection *s, llvm::ArrayRef<RelTy> rels);
template <class ELFT>
void addSectionAux(EhInputSection *s);
template <class ELFT, class RelTy>
CieRecord *addCie(EhSectionPiece &piece, ArrayRef<RelTy> rels);
template <class ELFT, class RelTy>
bool isFdeLive(EhSectionPiece &piece, ArrayRef<RelTy> rels);
uint64_t getFdePc(uint8_t *buf, size_t off, uint8_t enc) const;
std::vector<CieRecord *> cieRecords;
// CIE records are uniquified by their contents and personality functions.
llvm::DenseMap<std::pair<ArrayRef<uint8_t>, Symbol *>, CieRecord *> cieMap;
};
class GotSection : public SyntheticSection {
public:
GotSection();
size_t getSize() const override { return size; }
void finalizeContents() override;
bool isNeeded() const override;
void writeTo(uint8_t *buf) override;
void addEntry(Symbol &sym);
bool addDynTlsEntry(Symbol &sym);
bool addTlsIndex();
uint64_t getGlobalDynAddr(const Symbol &b) const;
uint64_t getGlobalDynOffset(const Symbol &b) const;
uint64_t getTlsIndexVA() { return this->getVA() + tlsIndexOff; }
uint32_t getTlsIndexOff() const { return tlsIndexOff; }
// Flag to force GOT to be in output if we have relocations
// that relies on its address.
bool hasGotOffRel = false;
protected:
size_t numEntries = 0;
uint32_t tlsIndexOff = -1;
uint64_t size = 0;
};
// .note.GNU-stack section.
class GnuStackSection : public SyntheticSection {
public:
GnuStackSection()
: SyntheticSection(0, llvm::ELF::SHT_PROGBITS, 1, ".note.GNU-stack") {}
void writeTo(uint8_t *buf) override {}
size_t getSize() const override { return 0; }
};
class GnuPropertySection : public SyntheticSection {
public:
GnuPropertySection();
void writeTo(uint8_t *buf) override;
size_t getSize() const override;
};
// .note.gnu.build-id section.
class BuildIdSection : public SyntheticSection {
// First 16 bytes are a header.
static const unsigned headerSize = 16;
public:
const size_t hashSize;
BuildIdSection();
void writeTo(uint8_t *buf) override;
size_t getSize() const override { return headerSize + hashSize; }
void writeBuildId(llvm::ArrayRef<uint8_t> buf);
private:
uint8_t *hashBuf;
};
// BssSection is used to reserve space for copy relocations and common symbols.
// We create three instances of this class for .bss, .bss.rel.ro and "COMMON",
// that are used for writable symbols, read-only symbols and common symbols,
// respectively.
class BssSection final : public SyntheticSection {
public:
BssSection(StringRef name, uint64_t size, uint32_t alignment);
void writeTo(uint8_t *) override {
llvm_unreachable("unexpected writeTo() call for SHT_NOBITS section");
}
bool isNeeded() const override { return size != 0; }
size_t getSize() const override { return size; }
static bool classof(const SectionBase *s) { return s->bss; }
uint64_t size;
};
class MipsGotSection final : public SyntheticSection {
public:
MipsGotSection();
void writeTo(uint8_t *buf) override;
size_t getSize() const override { return size; }
bool updateAllocSize() override;
void finalizeContents() override;
bool isNeeded() const override;
// Join separate GOTs built for each input file to generate
// primary and optional multiple secondary GOTs.
void build();
void addEntry(InputFile &file, Symbol &sym, int64_t addend, RelExpr expr);
void addDynTlsEntry(InputFile &file, Symbol &sym);
void addTlsIndex(InputFile &file);
uint64_t getPageEntryOffset(const InputFile *f, const Symbol &s,
int64_t addend) const;
uint64_t getSymEntryOffset(const InputFile *f, const Symbol &s,
int64_t addend) const;
uint64_t getGlobalDynOffset(const InputFile *f, const Symbol &s) const;
uint64_t getTlsIndexOffset(const InputFile *f) const;
// 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 Symbol *getFirstGlobalEntry() const;
// Returns the number of entries in the local part of GOT including
// the number of reserved entries.
unsigned getLocalEntriesNum() const;
// Return _gp value for primary GOT (nullptr) or particular input file.
uint64_t getGp(const InputFile *f = nullptr) const;
private:
// MIPS GOT consists of three parts: local, global and tls. Each part
// contains different types of entries. Here is a layout of GOT:
// - Header entries |
// - Page entries | Local part
// - Local entries (16-bit access) |
// - Local entries (32-bit access) |
// - Normal global entries || Global part
// - Reloc-only global entries ||
// - TLS entries ||| TLS part
//
// Header:
// Two entries hold predefined value 0x0 and 0x80000000.
// Page entries:
// These entries created by R_MIPS_GOT_PAGE relocation and R_MIPS_GOT16
// relocation against local symbols. They are initialized by higher 16-bit
// of the corresponding symbol's value. So each 64kb of address space
// requires a single GOT entry.
// Local entries (16-bit access):
// These entries created by GOT relocations against global non-preemptible
// symbols so dynamic linker is not necessary to resolve the symbol's
// values. "16-bit access" means that corresponding relocations address
// GOT using 16-bit index. Each unique Symbol-Addend pair has its own
// GOT entry.
// Local entries (32-bit access):
// These entries are the same as above but created by relocations which
// address GOT using 32-bit index (R_MIPS_GOT_HI16/LO16 etc).
// Normal global entries:
// These entries created by GOT relocations against preemptible global
// symbols. They need to be initialized by dynamic linker and they ordered
// exactly as the corresponding entries in the dynamic symbols table.
// Reloc-only global entries:
// These entries created for symbols that are referenced by dynamic
// relocations R_MIPS_REL32. These entries are not accessed with gp-relative
// addressing, but MIPS ABI requires that these entries be present in GOT.
// TLS entries:
// Entries created by TLS relocations.
//
// If the sum of local, global and tls entries is less than 64K only single
// got is enough. Otherwise, multi-got is created. Series of primary and
// multiple secondary GOTs have the following layout:
// - Primary GOT
// Header
// Local entries
// Global entries
// Relocation only entries
// TLS entries
//
// - Secondary GOT
// Local entries
// Global entries
// TLS entries
// ...
//
// All GOT entries required by relocations from a single input file entirely
// belong to either primary or one of secondary GOTs. To reference GOT entries
// each GOT has its own _gp value points to the "middle" of the GOT.
// In the code this value loaded to the register which is used for GOT access.
//
// MIPS 32 function's prologue:
// lui v0,0x0
// 0: R_MIPS_HI16 _gp_disp
// addiu v0,v0,0
// 4: R_MIPS_LO16 _gp_disp
//
// MIPS 64:
// lui at,0x0
// 14: R_MIPS_GPREL16 main
//
// Dynamic linker does not know anything about secondary GOTs and cannot
// use a regular MIPS mechanism for GOT entries initialization. So we have
// to use an approach accepted by other architectures and create dynamic
// relocations R_MIPS_REL32 to initialize global entries (and local in case
// of PIC code) in secondary GOTs. But ironically MIPS dynamic linker
// requires GOT entries and correspondingly ordered dynamic symbol table
// entries to deal with dynamic relocations. To handle this problem
// relocation-only section in the primary GOT contains entries for all
// symbols referenced in global parts of secondary GOTs. Although the sum
// of local and normal global entries of the primary got should be less
// than 64K, the size of the primary got (including relocation-only entries
// can be greater than 64K, because parts of the primary got that overflow
// the 64K limit are used only by the dynamic linker at dynamic link-time
// and not by 16-bit gp-relative addressing at run-time.
//
// For complete multi-GOT description see the following link
// https://dmz-portal.mips.com/wiki/MIPS_Multi_GOT
// Number of "Header" entries.
static const unsigned headerEntriesNum = 2;
uint64_t size = 0;
// Symbol and addend.
using GotEntry = std::pair<Symbol *, int64_t>;
struct FileGot {
InputFile *file = nullptr;
size_t startIndex = 0;
struct PageBlock {
size_t firstIndex;
size_t count;
PageBlock() : firstIndex(0), count(0) {}
};
// Map output sections referenced by MIPS GOT relocations
// to the description (index/count) "page" entries allocated
// for this section.
llvm::SmallMapVector<const OutputSection *, PageBlock, 16> pagesMap;
// Maps from Symbol+Addend pair or just Symbol to the GOT entry index.
llvm::MapVector<GotEntry, size_t> local16;
llvm::MapVector<GotEntry, size_t> local32;
llvm::MapVector<Symbol *, size_t> global;
llvm::MapVector<Symbol *, size_t> relocs;
llvm::MapVector<Symbol *, size_t> tls;
// Set of symbols referenced by dynamic TLS relocations.
llvm::MapVector<Symbol *, size_t> dynTlsSymbols;
// Total number of all entries.
size_t getEntriesNum() const;
// Number of "page" entries.
size_t getPageEntriesNum() const;
// Number of entries require 16-bit index to access.
size_t getIndexedEntriesNum() const;
};
// Container of GOT created for each input file.
// After building a final series of GOTs this container
// holds primary and secondary GOT's.
std::vector<FileGot> gots;
// Return (and create if necessary) `FileGot`.
FileGot &getGot(InputFile &f);
// Try to merge two GOTs. In case of success the `Dst` contains
// result of merging and the function returns true. In case of
// ovwerflow the `Dst` is unchanged and the function returns false.
bool tryMergeGots(FileGot & dst, FileGot & src, bool isPrimary);
};
class GotPltSection final : public SyntheticSection {
public:
GotPltSection();
void addEntry(Symbol &sym);
size_t getSize() const override;
void writeTo(uint8_t *buf) override;
bool isNeeded() const override;
// Flag to force GotPlt to be in output if we have relocations
// that relies on its address.
bool hasGotPltOffRel = false;
private:
std::vector<const Symbol *> entries;
};
// The IgotPltSection is a Got associated with the PltSection for GNU Ifunc
// Symbols that will be relocated by Target->IRelativeRel.
// On most Targets the IgotPltSection will immediately follow the GotPltSection
// on ARM the IgotPltSection will immediately follow the GotSection.
class IgotPltSection final : public SyntheticSection {
public:
IgotPltSection();
void addEntry(Symbol &sym);
size_t getSize() const override;
void writeTo(uint8_t *buf) override;
bool isNeeded() const override { return !entries.empty(); }
private:
std::vector<const Symbol *> entries;
};
class StringTableSection final : public SyntheticSection {
public:
StringTableSection(StringRef name, bool dynamic);
unsigned addString(StringRef s, bool hashIt = true);
void writeTo(uint8_t *buf) override;
size_t getSize() const override { return size; }
bool isDynamic() const { return dynamic; }
private:
const bool dynamic;
uint64_t size = 0;
llvm::DenseMap<StringRef, unsigned> stringMap;
std::vector<StringRef> strings;
};
class DynamicReloc {
public:
DynamicReloc(RelType type, const InputSectionBase *inputSec,
uint64_t offsetInSec, bool useSymVA, Symbol *sym, int64_t addend)
: type(type), sym(sym), inputSec(inputSec), offsetInSec(offsetInSec),
useSymVA(useSymVA), addend(addend), outputSec(nullptr) {}
// This constructor records dynamic relocation settings used by MIPS
// multi-GOT implementation. It's to relocate addresses of 64kb pages
// lie inside the output section.
DynamicReloc(RelType type, const InputSectionBase *inputSec,
uint64_t offsetInSec, const OutputSection *outputSec,
int64_t addend)
: type(type), sym(nullptr), inputSec(inputSec), offsetInSec(offsetInSec),
useSymVA(false), addend(addend), outputSec(outputSec) {}
uint64_t getOffset() const;
uint32_t getSymIndex(SymbolTableBaseSection *symTab) const;
// Computes the addend of the dynamic relocation. Note that this is not the
// same as the addend member variable as it also includes the symbol address
// if useSymVA is true.
int64_t computeAddend() const;
RelType type;
Symbol *sym;
const InputSectionBase *inputSec = nullptr;
uint64_t offsetInSec;
// If this member is true, the dynamic relocation will not be against the
// symbol but will instead be a relative relocation that simply adds the
// load address. This means we need to write the symbol virtual address
// plus the original addend as the final relocation addend.
bool useSymVA;
int64_t addend;
const OutputSection *outputSec;
};
template <class ELFT> class DynamicSection final : public SyntheticSection {
using Elf_Dyn = typename ELFT::Dyn;
using Elf_Rel = typename ELFT::Rel;
using Elf_Rela = typename ELFT::Rela;
using Elf_Relr = typename ELFT::Relr;
using Elf_Shdr = typename ELFT::Shdr;
using Elf_Sym = typename ELFT::Sym;
// finalizeContents() fills this vector with the section contents.
std::vector<std::pair<int32_t, std::function<uint64_t()>>> entries;
public:
DynamicSection();
void finalizeContents() override;
void writeTo(uint8_t *buf) override;
size_t getSize() const override { return size; }
private:
void add(int32_t tag, std::function<uint64_t()> fn);
void addInt(int32_t tag, uint64_t val);
void addInSec(int32_t tag, InputSection *sec);
void addInSecRelative(int32_t tag, InputSection *sec);
void addOutSec(int32_t tag, OutputSection *sec);
void addSize(int32_t tag, OutputSection *sec);
void addSym(int32_t tag, Symbol *sym);
uint64_t size = 0;
};
class RelocationBaseSection : public SyntheticSection {
public:
RelocationBaseSection(StringRef name, uint32_t type, int32_t dynamicTag,
int32_t sizeDynamicTag);
void addReloc(RelType dynType, InputSectionBase *isec, uint64_t offsetInSec,
Symbol *sym);
// Add a dynamic relocation that might need an addend. This takes care of
// writing the addend to the output section if needed.
void addReloc(RelType dynType, InputSectionBase *inputSec,
uint64_t offsetInSec, Symbol *sym, int64_t addend, RelExpr expr,
RelType type);
void addReloc(const DynamicReloc &reloc);
bool isNeeded() const override { return !relocs.empty(); }
size_t getSize() const override { return relocs.size() * this->entsize; }
size_t getRelativeRelocCount() const { return numRelativeRelocs; }
void finalizeContents() override;
int32_t dynamicTag, sizeDynamicTag;
std::vector<DynamicReloc> relocs;
protected:
size_t numRelativeRelocs = 0;
};
template <class ELFT>
class RelocationSection final : public RelocationBaseSection {
using Elf_Rel = typename ELFT::Rel;
using Elf_Rela = typename ELFT::Rela;
public:
RelocationSection(StringRef name, bool sort);
void writeTo(uint8_t *buf) override;
private:
bool sort;
};
template <class ELFT>
class AndroidPackedRelocationSection final : public RelocationBaseSection {
using Elf_Rel = typename ELFT::Rel;
using Elf_Rela = typename ELFT::Rela;
public:
AndroidPackedRelocationSection(StringRef name);
bool updateAllocSize() override;
size_t getSize() const override { return relocData.size(); }
void writeTo(uint8_t *buf) override {
memcpy(buf, relocData.data(), relocData.size());
}
private:
SmallVector<char, 0> relocData;
};
struct RelativeReloc {
uint64_t getOffset() const { return inputSec->getVA(offsetInSec); }
const InputSectionBase *inputSec;
uint64_t offsetInSec;
};
class RelrBaseSection : public SyntheticSection {
public:
RelrBaseSection();
bool isNeeded() const override { return !relocs.empty(); }
std::vector<RelativeReloc> relocs;
};
// RelrSection is used to encode offsets for relative relocations.
// Proposal for adding SHT_RELR sections to generic-abi is here:
// https://groups.google.com/forum/#!topic/generic-abi/bX460iggiKg
// For more details, see the comment in RelrSection::updateAllocSize().
template <class ELFT> class RelrSection final : public RelrBaseSection {
using Elf_Relr = typename ELFT::Relr;
public:
RelrSection();
bool updateAllocSize() override;
size_t getSize() const override { return relrRelocs.size() * this->entsize; }
void writeTo(uint8_t *buf) override {
memcpy(buf, relrRelocs.data(), getSize());
}
private:
std::vector<Elf_Relr> relrRelocs;
};
struct SymbolTableEntry {
Symbol *sym;
size_t strTabOffset;
};
class SymbolTableBaseSection : public SyntheticSection {
public:
SymbolTableBaseSection(StringTableSection &strTabSec);
void finalizeContents() override;
size_t getSize() const override { return getNumSymbols() * entsize; }
void addSymbol(Symbol *sym);
unsigned getNumSymbols() const { return symbols.size() + 1; }
size_t getSymbolIndex(Symbol *sym);
ArrayRef<SymbolTableEntry> getSymbols() const { return symbols; }
protected:
void sortSymTabSymbols();
// A vector of symbols and their string table offsets.
std::vector<SymbolTableEntry> symbols;
StringTableSection &strTabSec;
llvm::once_flag onceFlag;
llvm::DenseMap<Symbol *, size_t> symbolIndexMap;
llvm::DenseMap<OutputSection *, size_t> sectionIndexMap;
};
template <class ELFT>
class SymbolTableSection final : public SymbolTableBaseSection {
using Elf_Sym = typename ELFT::Sym;
public:
SymbolTableSection(StringTableSection &strTabSec);
void writeTo(uint8_t *buf) override;
};
class SymtabShndxSection final : public SyntheticSection {
public:
SymtabShndxSection();
void writeTo(uint8_t *buf) override;
size_t getSize() const override;
bool isNeeded() const override;
void finalizeContents() override;
};
// Outputs GNU Hash section. For detailed explanation see:
// https://blogs.oracle.com/ali/entry/gnu_hash_elf_sections
class GnuHashTableSection final : public SyntheticSection {
public:
GnuHashTableSection();
void finalizeContents() override;
void writeTo(uint8_t *buf) override;
size_t getSize() const override { return size; }
// Adds symbols to the hash table.
// Sorts the input to satisfy GNU hash section requirements.
void addSymbols(std::vector<SymbolTableEntry> &symbols);
private:
// See the comment in writeBloomFilter.
enum { Shift2 = 26 };
void writeBloomFilter(uint8_t *buf);
void writeHashTable(uint8_t *buf);
struct Entry {
Symbol *sym;
size_t strTabOffset;
uint32_t hash;
uint32_t bucketIdx;
};
std::vector<Entry> symbols;
size_t maskWords;
size_t nBuckets = 0;
size_t size = 0;
};
class HashTableSection final : public SyntheticSection {
public:
HashTableSection();
void finalizeContents() override;
void writeTo(uint8_t *buf) override;
size_t getSize() const override { return size; }
private:
size_t size = 0;
};
// Used for PLT entries. It usually has a PLT header for lazy binding. Each PLT
// entry is associated with a JUMP_SLOT relocation, which may be resolved lazily
// at runtime.
//
// On PowerPC, this section contains lazy symbol resolvers. A branch instruction
// jumps to a PLT call stub, which will then jump to the target (BIND_NOW) or a
// lazy symbol resolver.
//
// On x86 when IBT is enabled, this section (.plt.sec) contains PLT call stubs.
// A call instruction jumps to a .plt.sec entry, which will then jump to the
// target (BIND_NOW) or a .plt entry.
class PltSection : public SyntheticSection {
public:
PltSection();
void writeTo(uint8_t *buf) override;
size_t getSize() const override;
bool isNeeded() const override;
void addSymbols();
void addEntry(Symbol &sym);
size_t getNumEntries() const { return entries.size(); }
size_t headerSize;
size_t footerSize = 0;
std::vector<const Symbol *> entries;
};
// Used for non-preemptible ifuncs. It does not have a header. Each entry is
// associated with an IRELATIVE relocation, which will be resolved eagerly at
// runtime. PltSection can only contain entries associated with JUMP_SLOT
// relocations, so IPLT entries are in a separate section.
class IpltSection final : public SyntheticSection {
std::vector<const Symbol *> entries;
public:
IpltSection();
void writeTo(uint8_t *buf) override;
size_t getSize() const override;
bool isNeeded() const override { return !entries.empty(); }
void addSymbols();
void addEntry(Symbol &sym);
};
// This is x86-only.
class IBTPltSection : public SyntheticSection {
public:
IBTPltSection();
void writeTo(uint8_t *Buf) override;
size_t getSize() const override;
};
class GdbIndexSection final : public SyntheticSection {
public:
struct AddressEntry {
InputSection *section;
uint64_t lowAddress;
uint64_t highAddress;
uint32_t cuIndex;
};
struct CuEntry {
uint64_t cuOffset;
uint64_t cuLength;
};
struct NameAttrEntry {
llvm::CachedHashStringRef name;
uint32_t cuIndexAndAttrs;
};
struct GdbChunk {
InputSection *sec;
std::vector<AddressEntry> addressAreas;
std::vector<CuEntry> compilationUnits;
};
struct GdbSymbol {
llvm::CachedHashStringRef name;
std::vector<uint32_t> cuVector;
uint32_t nameOff;
uint32_t cuVectorOff;
};
GdbIndexSection();
template <typename ELFT> static GdbIndexSection *create();
void writeTo(uint8_t *buf) override;
size_t getSize() const override { return size; }
bool isNeeded() const override;
private:
struct GdbIndexHeader {
llvm::support::ulittle32_t version;
llvm::support::ulittle32_t cuListOff;
llvm::support::ulittle32_t cuTypesOff;
llvm::support::ulittle32_t addressAreaOff;
llvm::support::ulittle32_t symtabOff;
llvm::support::ulittle32_t constantPoolOff;
};
void initOutputSize();
size_t computeSymtabSize() const;
// Each chunk contains information gathered from debug sections of a
// single object file.
std::vector<GdbChunk> chunks;
// A symbol table for this .gdb_index section.
std::vector<GdbSymbol> symbols;
size_t size;
};
// --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")
class EhFrameHeader final : public SyntheticSection {
public:
EhFrameHeader();
void write();
void writeTo(uint8_t *buf) override;
size_t getSize() const override;
bool isNeeded() const override;
};
// 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.
class VersionDefinitionSection final : public SyntheticSection {
public:
VersionDefinitionSection();
void finalizeContents() override;
size_t getSize() const override;
void writeTo(uint8_t *buf) override;
private:
enum { EntrySize = 28 };
void writeOne(uint8_t *buf, uint32_t index, StringRef name, size_t nameOff);
StringRef getFileDefName();
unsigned fileDefNameOff;
std::vector<unsigned> verDefNameOffs;
};
// 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.
class VersionTableSection final : public SyntheticSection {
public:
VersionTableSection();
void finalizeContents() override;
size_t getSize() const override;
void writeTo(uint8_t *buf) override;
bool isNeeded() const override;
};
// 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 SyntheticSection {
using Elf_Verneed = typename ELFT::Verneed;
using Elf_Vernaux = typename ELFT::Vernaux;
struct Vernaux {
uint64_t hash;
uint32_t verneedIndex;
uint64_t nameStrTab;
};
struct Verneed {
uint64_t nameStrTab;
std::vector<Vernaux> vernauxs;
};
std::vector<Verneed> verneeds;
public:
VersionNeedSection();
void finalizeContents() override;
void writeTo(uint8_t *buf) override;
size_t getSize() const override;
bool isNeeded() const override;
};
// MergeSyntheticSection is a class that allows us to put mergeable sections
// with different attributes in a single output sections. To do that
// we put them into MergeSyntheticSection synthetic input sections which are
// attached to regular output sections.
class MergeSyntheticSection : public SyntheticSection {
public:
void addSection(MergeInputSection *ms);
std::vector<MergeInputSection *> sections;
protected:
MergeSyntheticSection(StringRef name, uint32_t type, uint64_t flags,
uint32_t alignment)
: SyntheticSection(flags, type, alignment, name) {}
};
class MergeTailSection final : public MergeSyntheticSection {
public:
MergeTailSection(StringRef name, uint32_t type, uint64_t flags,
uint32_t alignment);
size_t getSize() const override;
void writeTo(uint8_t *buf) override;
void finalizeContents() override;
private:
llvm::StringTableBuilder builder;
};
class MergeNoTailSection final : public MergeSyntheticSection {
public:
MergeNoTailSection(StringRef name, uint32_t type, uint64_t flags,
uint32_t alignment)
: MergeSyntheticSection(name, type, flags, alignment) {}
size_t getSize() const override { return size; }
void writeTo(uint8_t *buf) override;
void finalizeContents() override;
private:
// We use the most significant bits of a hash as a shard ID.
// The reason why we don't want to use the least significant bits is
// because DenseMap also uses lower bits to determine a bucket ID.
// If we use lower bits, it significantly increases the probability of
// hash collisons.
size_t getShardId(uint32_t hash) {
assert((hash >> 31) == 0);
return hash >> (31 - llvm::countTrailingZeros(numShards));
}
// Section size
size_t size;
// String table contents
constexpr static size_t numShards = 32;
std::vector<llvm::StringTableBuilder> shards;
size_t shardOffsets[numShards];
};
// .MIPS.abiflags section.
template <class ELFT>
class MipsAbiFlagsSection final : public SyntheticSection {
using Elf_Mips_ABIFlags = llvm::object::Elf_Mips_ABIFlags<ELFT>;
public:
static MipsAbiFlagsSection *create();
MipsAbiFlagsSection(Elf_Mips_ABIFlags flags);
size_t getSize() const override { return sizeof(Elf_Mips_ABIFlags); }
void writeTo(uint8_t *buf) override;
private:
Elf_Mips_ABIFlags flags;
};
// .MIPS.options section.
template <class ELFT> class MipsOptionsSection final : public SyntheticSection {
using Elf_Mips_Options = llvm::object::Elf_Mips_Options<ELFT>;
using Elf_Mips_RegInfo = llvm::object::Elf_Mips_RegInfo<ELFT>;
public:
static MipsOptionsSection *create();
MipsOptionsSection(Elf_Mips_RegInfo reginfo);
void writeTo(uint8_t *buf) override;
size_t getSize() const override {
return sizeof(Elf_Mips_Options) + sizeof(Elf_Mips_RegInfo);
}
private:
Elf_Mips_RegInfo reginfo;
};
// MIPS .reginfo section.
template <class ELFT> class MipsReginfoSection final : public SyntheticSection {
using Elf_Mips_RegInfo = llvm::object::Elf_Mips_RegInfo<ELFT>;
public:
static MipsReginfoSection *create();
MipsReginfoSection(Elf_Mips_RegInfo reginfo);
size_t getSize() const override { return sizeof(Elf_Mips_RegInfo); }
void writeTo(uint8_t *buf) override;
private:
Elf_Mips_RegInfo reginfo;
};
// This is a MIPS specific section to hold a space within the data segment
// of executable file which is pointed to by the DT_MIPS_RLD_MAP entry.
// See "Dynamic section" in Chapter 5 in the following document:
// ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
class MipsRldMapSection : public SyntheticSection {
public:
MipsRldMapSection();
size_t getSize() const override { return config->wordsize; }
void writeTo(uint8_t *buf) override {}
};
// Representation of the combined .ARM.Exidx input sections. We process these
// as a SyntheticSection like .eh_frame as we need to merge duplicate entries
// and add terminating sentinel entries.
//
// The .ARM.exidx input sections after SHF_LINK_ORDER processing is done form
// a table that the unwinder can derive (Addresses are encoded as offsets from
// table):
// | Address of function | Unwind instructions for function |
// where the unwind instructions are either a small number of unwind or the
// special EXIDX_CANTUNWIND entry representing no unwinding information.
// When an exception is thrown from an address A, the unwinder searches the
// table for the closest table entry with Address of function <= A. This means
// that for two consecutive table entries:
// | A1 | U1 |
// | A2 | U2 |
// The range of addresses described by U1 is [A1, A2)
//
// There are two cases where we need a linker generated table entry to fixup
// the address ranges in the table
// Case 1:
// - A sentinel entry added with an address higher than all
// executable sections. This was needed to work around libunwind bug pr31091.
// - After address assignment we need to find the highest addressed executable
// section and use the limit of that section so that the unwinder never
// matches it.
// Case 2:
// - InputSections without a .ARM.exidx section (usually from Assembly)
// need a table entry so that they terminate the range of the previously
// function. This is pr40277.
//
// Instead of storing pointers to the .ARM.exidx InputSections from
// InputObjects, we store pointers to the executable sections that need
// .ARM.exidx sections. We can then use the dependentSections of these to
// either find the .ARM.exidx section or know that we need to generate one.
class ARMExidxSyntheticSection : public SyntheticSection {
public:
ARMExidxSyntheticSection();
// Add an input section to the ARMExidxSyntheticSection. Returns whether the
// section needs to be removed from the main input section list.
bool addSection(InputSection *isec);
size_t getSize() const override { return size; }
void writeTo(uint8_t *buf) override;
bool isNeeded() const override;
// Sort and remove duplicate entries.
void finalizeContents() override;
InputSection *getLinkOrderDep() const;
static bool classof(const SectionBase *d);
// Links to the ARMExidxSections so we can transfer the relocations once the
// layout is known.
std::vector<InputSection *> exidxSections;
private:
size_t size;
// Instead of storing pointers to the .ARM.exidx InputSections from
// InputObjects, we store pointers to the executable sections that need
// .ARM.exidx sections. We can then use the dependentSections of these to
// either find the .ARM.exidx section or know that we need to generate one.
std::vector<InputSection *> executableSections;
// The executable InputSection with the highest address to use for the
// sentinel. We store separately from ExecutableSections as merging of
// duplicate entries may mean this InputSection is removed from
// ExecutableSections.
InputSection *sentinel = nullptr;
};
// A container for one or more linker generated thunks. Instances of these
// thunks including ARM interworking and Mips LA25 PI to non-PI thunks.
class ThunkSection : public SyntheticSection {
public:
// ThunkSection in OS, with desired outSecOff of Off
ThunkSection(OutputSection *os, uint64_t off);
// Add a newly created Thunk to this container:
// Thunk is given offset from start of this InputSection
// Thunk defines a symbol in this InputSection that can be used as target
// of a relocation
void addThunk(Thunk *t);
size_t getSize() const override;
void writeTo(uint8_t *buf) override;
InputSection *getTargetInputSection() const;
bool assignOffsets();
// When true, round up reported size of section to 4 KiB. See comment
// in addThunkSection() for more details.
bool roundUpSizeForErrata = false;
private:
std::vector<Thunk *> thunks;
size_t size = 0;
};
// Used to compute outSecOff of .got2 in each object file. This is needed to
// synthesize PLT entries for PPC32 Secure PLT ABI.
class PPC32Got2Section final : public SyntheticSection {
public:
PPC32Got2Section();
size_t getSize() const override { return 0; }
bool isNeeded() const override;
void finalizeContents() override;
void writeTo(uint8_t *buf) override {}
};
// This section is used to store the addresses of functions that are called
// in range-extending thunks on PowerPC64. When producing position dependent
// code the addresses are link-time constants and the table is written out to
// the binary. When producing position-dependent code the table is allocated and
// filled in by the dynamic linker.
class PPC64LongBranchTargetSection final : public SyntheticSection {
public:
PPC64LongBranchTargetSection();
uint64_t getEntryVA(const Symbol *sym, int64_t addend);
llvm::Optional<uint32_t> addEntry(const Symbol *sym, int64_t addend);
size_t getSize() const override;
void writeTo(uint8_t *buf) override;
bool isNeeded() const override;
void finalizeContents() override { finalized = true; }
private:
std::vector<std::pair<const Symbol *, int64_t>> entries;
llvm::DenseMap<std::pair<const Symbol *, int64_t>, uint32_t> entry_index;
bool finalized = false;
};
template <typename ELFT>
class PartitionElfHeaderSection : public SyntheticSection {
public:
PartitionElfHeaderSection();
size_t getSize() const override;
void writeTo(uint8_t *buf) override;
};
template <typename ELFT>
class PartitionProgramHeadersSection : public SyntheticSection {
public:
PartitionProgramHeadersSection();
size_t getSize() const override;
void writeTo(uint8_t *buf) override;
};
class PartitionIndexSection : public SyntheticSection {
public:
PartitionIndexSection();
size_t getSize() const override;
void finalizeContents() override;
void writeTo(uint8_t *buf) override;
};
InputSection *createInterpSection();
MergeInputSection *createCommentSection();
MergeSyntheticSection *createMergeSynthetic(StringRef name, uint32_t type,
uint64_t flags, uint32_t alignment);
template <class ELFT> void splitSections();
template <typename ELFT> void writeEhdr(uint8_t *buf, Partition &part);
template <typename ELFT> void writePhdrs(uint8_t *buf, Partition &part);
Defined *addSyntheticLocal(StringRef name, uint8_t type, uint64_t value,
uint64_t size, InputSectionBase &section);
void addVerneed(Symbol *ss);
// Linker generated per-partition sections.
struct Partition {
StringRef name;
uint64_t nameStrTab;
SyntheticSection *elfHeader;
SyntheticSection *programHeaders;
std::vector<PhdrEntry *> phdrs;
ARMExidxSyntheticSection *armExidx;
BuildIdSection *buildId;
SyntheticSection *dynamic;
StringTableSection *dynStrTab;
SymbolTableBaseSection *dynSymTab;
EhFrameHeader *ehFrameHdr;
EhFrameSection *ehFrame;
GnuHashTableSection *gnuHashTab;
HashTableSection *hashTab;
RelocationBaseSection *relaDyn;
RelrBaseSection *relrDyn;
VersionDefinitionSection *verDef;
SyntheticSection *verNeed;
VersionTableSection *verSym;
unsigned getNumber() const { return this - &partitions[0] + 1; }
};
extern Partition *mainPart;
inline Partition &SectionBase::getPartition() const {
assert(isLive());
return partitions[partition - 1];
}
// Linker generated sections which can be used as inputs and are not specific to
// a partition.
struct InStruct {
InputSection *armAttributes;
BssSection *bss;
BssSection *bssRelRo;
GotSection *got;
GotPltSection *gotPlt;
IgotPltSection *igotPlt;
PPC64LongBranchTargetSection *ppc64LongBranchTarget;
MipsGotSection *mipsGot;
MipsRldMapSection *mipsRldMap;
SyntheticSection *partEnd;
SyntheticSection *partIndex;
PltSection *plt;
IpltSection *iplt;
PPC32Got2Section *ppc32Got2;
IBTPltSection *ibtPlt;
RelocationBaseSection *relaPlt;
RelocationBaseSection *relaIplt;
StringTableSection *shStrTab;
StringTableSection *strTab;
SymbolTableBaseSection *symTab;
SymtabShndxSection *symTabShndx;
};
extern InStruct in;
} // namespace elf
} // namespace lld
#endif