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llvm / lld / refs/heads/release_60 / . / ELF / SyntheticSections.cpp
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//===- SyntheticSections.cpp ----------------------------------------------===//
//
// The LLVM Linker
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file contains linker-synthesized sections. Currently,
// synthetic sections are created either output sections or input sections,
// but we are rewriting code so that all synthetic sections are created as
// input sections.
//
//===----------------------------------------------------------------------===//
#include "SyntheticSections.h"
#include "Bits.h"
#include "Config.h"
#include "InputFiles.h"
#include "LinkerScript.h"
#include "OutputSections.h"
#include "Strings.h"
#include "SymbolTable.h"
#include "Symbols.h"
#include "Target.h"
#include "Writer.h"
#include "lld/Common/ErrorHandler.h"
#include "lld/Common/Memory.h"
#include "lld/Common/Threads.h"
#include "lld/Common/Version.h"
#include "llvm/BinaryFormat/Dwarf.h"
#include "llvm/DebugInfo/DWARF/DWARFDebugPubTable.h"
#include "llvm/Object/Decompressor.h"
#include "llvm/Object/ELFObjectFile.h"
#include "llvm/Support/Endian.h"
#include "llvm/Support/LEB128.h"
#include "llvm/Support/MD5.h"
#include "llvm/Support/RandomNumberGenerator.h"
#include "llvm/Support/SHA1.h"
#include "llvm/Support/xxhash.h"
#include <cstdlib>
#include <thread>
using namespace llvm;
using namespace llvm::dwarf;
using namespace llvm::ELF;
using namespace llvm::object;
using namespace llvm::support;
using namespace llvm::support::endian;
using namespace lld;
using namespace lld::elf;
constexpr size_t MergeNoTailSection::NumShards;
static void write32(void *Buf, uint32_t Val) {
endian::write32(Buf, Val, Config->Endianness);
}
uint64_t SyntheticSection::getVA() const {
if (OutputSection *Sec = getParent())
return Sec->Addr + OutSecOff;
return 0;
}
// Returns an LLD version string.
static ArrayRef<uint8_t> getVersion() {
// Check LLD_VERSION first for ease of testing.
// You can get consitent output by using the environment variable.
// This is only for testing.
StringRef S = getenv("LLD_VERSION");
if (S.empty())
S = Saver.save(Twine("Linker: ") + getLLDVersion());
// +1 to include the terminating '\0'.
return {(const uint8_t *)S.data(), S.size() + 1};
}
// Creates a .comment section containing LLD version info.
// With this feature, you can identify LLD-generated binaries easily
// by "readelf --string-dump .comment <file>".
// The returned object is a mergeable string section.
MergeInputSection *elf::createCommentSection() {
return make<MergeInputSection>(SHF_MERGE | SHF_STRINGS, SHT_PROGBITS, 1,
getVersion(), ".comment");
}
// .MIPS.abiflags section.
template <class ELFT>
MipsAbiFlagsSection<ELFT>::MipsAbiFlagsSection(Elf_Mips_ABIFlags Flags)
: SyntheticSection(SHF_ALLOC, SHT_MIPS_ABIFLAGS, 8, ".MIPS.abiflags"),
Flags(Flags) {
this->Entsize = sizeof(Elf_Mips_ABIFlags);
}
template <class ELFT> void MipsAbiFlagsSection<ELFT>::writeTo(uint8_t *Buf) {
memcpy(Buf, &Flags, sizeof(Flags));
}
template <class ELFT>
MipsAbiFlagsSection<ELFT> *MipsAbiFlagsSection<ELFT>::create() {
Elf_Mips_ABIFlags Flags = {};
bool Create = false;
for (InputSectionBase *Sec : InputSections) {
if (Sec->Type != SHT_MIPS_ABIFLAGS)
continue;
Sec->Live = false;
Create = true;
std::string Filename = toString(Sec->File);
const size_t Size = Sec->Data.size();
// Older version of BFD (such as the default FreeBSD linker) concatenate
// .MIPS.abiflags instead of merging. To allow for this case (or potential
// zero padding) we ignore everything after the first Elf_Mips_ABIFlags
if (Size < sizeof(Elf_Mips_ABIFlags)) {
error(Filename + ": invalid size of .MIPS.abiflags section: got " +
Twine(Size) + " instead of " + Twine(sizeof(Elf_Mips_ABIFlags)));
return nullptr;
}
auto *S = reinterpret_cast<const Elf_Mips_ABIFlags *>(Sec->Data.data());
if (S->version != 0) {
error(Filename + ": unexpected .MIPS.abiflags version " +
Twine(S->version));
return nullptr;
}
// LLD checks ISA compatibility in calcMipsEFlags(). Here we just
// select the highest number of ISA/Rev/Ext.
Flags.isa_level = std::max(Flags.isa_level, S->isa_level);
Flags.isa_rev = std::max(Flags.isa_rev, S->isa_rev);
Flags.isa_ext = std::max(Flags.isa_ext, S->isa_ext);
Flags.gpr_size = std::max(Flags.gpr_size, S->gpr_size);
Flags.cpr1_size = std::max(Flags.cpr1_size, S->cpr1_size);
Flags.cpr2_size = std::max(Flags.cpr2_size, S->cpr2_size);
Flags.ases |= S->ases;
Flags.flags1 |= S->flags1;
Flags.flags2 |= S->flags2;
Flags.fp_abi = elf::getMipsFpAbiFlag(Flags.fp_abi, S->fp_abi, Filename);
};
if (Create)
return make<MipsAbiFlagsSection<ELFT>>(Flags);
return nullptr;
}
// .MIPS.options section.
template <class ELFT>
MipsOptionsSection<ELFT>::MipsOptionsSection(Elf_Mips_RegInfo Reginfo)
: SyntheticSection(SHF_ALLOC, SHT_MIPS_OPTIONS, 8, ".MIPS.options"),
Reginfo(Reginfo) {
this->Entsize = sizeof(Elf_Mips_Options) + sizeof(Elf_Mips_RegInfo);
}
template <class ELFT> void MipsOptionsSection<ELFT>::writeTo(uint8_t *Buf) {
auto *Options = reinterpret_cast<Elf_Mips_Options *>(Buf);
Options->kind = ODK_REGINFO;
Options->size = getSize();
if (!Config->Relocatable)
Reginfo.ri_gp_value = InX::MipsGot->getGp();
memcpy(Buf + sizeof(Elf_Mips_Options), &Reginfo, sizeof(Reginfo));
}
template <class ELFT>
MipsOptionsSection<ELFT> *MipsOptionsSection<ELFT>::create() {
// N64 ABI only.
if (!ELFT::Is64Bits)
return nullptr;
std::vector<InputSectionBase *> Sections;
for (InputSectionBase *Sec : InputSections)
if (Sec->Type == SHT_MIPS_OPTIONS)
Sections.push_back(Sec);
if (Sections.empty())
return nullptr;
Elf_Mips_RegInfo Reginfo = {};
for (InputSectionBase *Sec : Sections) {
Sec->Live = false;
std::string Filename = toString(Sec->File);
ArrayRef<uint8_t> D = Sec->Data;
while (!D.empty()) {
if (D.size() < sizeof(Elf_Mips_Options)) {
error(Filename + ": invalid size of .MIPS.options section");
break;
}
auto *Opt = reinterpret_cast<const Elf_Mips_Options *>(D.data());
if (Opt->kind == ODK_REGINFO) {
if (Config->Relocatable && Opt->getRegInfo().ri_gp_value)
error(Filename + ": unsupported non-zero ri_gp_value");
Reginfo.ri_gprmask |= Opt->getRegInfo().ri_gprmask;
Sec->getFile<ELFT>()->MipsGp0 = Opt->getRegInfo().ri_gp_value;
break;
}
if (!Opt->size)
fatal(Filename + ": zero option descriptor size");
D = D.slice(Opt->size);
}
};
return make<MipsOptionsSection<ELFT>>(Reginfo);
}
// MIPS .reginfo section.
template <class ELFT>
MipsReginfoSection<ELFT>::MipsReginfoSection(Elf_Mips_RegInfo Reginfo)
: SyntheticSection(SHF_ALLOC, SHT_MIPS_REGINFO, 4, ".reginfo"),
Reginfo(Reginfo) {
this->Entsize = sizeof(Elf_Mips_RegInfo);
}
template <class ELFT> void MipsReginfoSection<ELFT>::writeTo(uint8_t *Buf) {
if (!Config->Relocatable)
Reginfo.ri_gp_value = InX::MipsGot->getGp();
memcpy(Buf, &Reginfo, sizeof(Reginfo));
}
template <class ELFT>
MipsReginfoSection<ELFT> *MipsReginfoSection<ELFT>::create() {
// Section should be alive for O32 and N32 ABIs only.
if (ELFT::Is64Bits)
return nullptr;
std::vector<InputSectionBase *> Sections;
for (InputSectionBase *Sec : InputSections)
if (Sec->Type == SHT_MIPS_REGINFO)
Sections.push_back(Sec);
if (Sections.empty())
return nullptr;
Elf_Mips_RegInfo Reginfo = {};
for (InputSectionBase *Sec : Sections) {
Sec->Live = false;
if (Sec->Data.size() != sizeof(Elf_Mips_RegInfo)) {
error(toString(Sec->File) + ": invalid size of .reginfo section");
return nullptr;
}
auto *R = reinterpret_cast<const Elf_Mips_RegInfo *>(Sec->Data.data());
if (Config->Relocatable && R->ri_gp_value)
error(toString(Sec->File) + ": unsupported non-zero ri_gp_value");
Reginfo.ri_gprmask |= R->ri_gprmask;
Sec->getFile<ELFT>()->MipsGp0 = R->ri_gp_value;
};
return make<MipsReginfoSection<ELFT>>(Reginfo);
}
InputSection *elf::createInterpSection() {
// StringSaver guarantees that the returned string ends with '\0'.
StringRef S = Saver.save(Config->DynamicLinker);
ArrayRef<uint8_t> Contents = {(const uint8_t *)S.data(), S.size() + 1};
auto *Sec = make<InputSection>(nullptr, SHF_ALLOC, SHT_PROGBITS, 1, Contents,
".interp");
Sec->Live = true;
return Sec;
}
Symbol *elf::addSyntheticLocal(StringRef Name, uint8_t Type, uint64_t Value,
uint64_t Size, InputSectionBase &Section) {
auto *S = make<Defined>(Section.File, Name, STB_LOCAL, STV_DEFAULT, Type,
Value, Size, &Section);
if (InX::SymTab)
InX::SymTab->addSymbol(S);
return S;
}
static size_t getHashSize() {
switch (Config->BuildId) {
case BuildIdKind::Fast:
return 8;
case BuildIdKind::Md5:
case BuildIdKind::Uuid:
return 16;
case BuildIdKind::Sha1:
return 20;
case BuildIdKind::Hexstring:
return Config->BuildIdVector.size();
default:
llvm_unreachable("unknown BuildIdKind");
}
}
BuildIdSection::BuildIdSection()
: SyntheticSection(SHF_ALLOC, SHT_NOTE, 4, ".note.gnu.build-id"),
HashSize(getHashSize()) {}
void BuildIdSection::writeTo(uint8_t *Buf) {
write32(Buf, 4); // Name size
write32(Buf + 4, HashSize); // Content size
write32(Buf + 8, NT_GNU_BUILD_ID); // Type
memcpy(Buf + 12, "GNU", 4); // Name string
HashBuf = Buf + 16;
}
// Split one uint8 array into small pieces of uint8 arrays.
static std::vector<ArrayRef<uint8_t>> split(ArrayRef<uint8_t> Arr,
size_t ChunkSize) {
std::vector<ArrayRef<uint8_t>> Ret;
while (Arr.size() > ChunkSize) {
Ret.push_back(Arr.take_front(ChunkSize));
Arr = Arr.drop_front(ChunkSize);
}
if (!Arr.empty())
Ret.push_back(Arr);
return Ret;
}
// Computes a hash value of Data using a given hash function.
// In order to utilize multiple cores, we first split data into 1MB
// chunks, compute a hash for each chunk, and then compute a hash value
// of the hash values.
void BuildIdSection::computeHash(
llvm::ArrayRef<uint8_t> Data,
std::function<void(uint8_t *Dest, ArrayRef<uint8_t> Arr)> HashFn) {
std::vector<ArrayRef<uint8_t>> Chunks = split(Data, 1024 * 1024);
std::vector<uint8_t> Hashes(Chunks.size() * HashSize);
// Compute hash values.
parallelForEachN(0, Chunks.size(), [&](size_t I) {
HashFn(Hashes.data() + I * HashSize, Chunks[I]);
});
// Write to the final output buffer.
HashFn(HashBuf, Hashes);
}
BssSection::BssSection(StringRef Name, uint64_t Size, uint32_t Alignment)
: SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_NOBITS, Alignment, Name) {
this->Bss = true;
if (OutputSection *Sec = getParent())
Sec->Alignment = std::max(Sec->Alignment, Alignment);
this->Size = Size;
}
void BuildIdSection::writeBuildId(ArrayRef<uint8_t> Buf) {
switch (Config->BuildId) {
case BuildIdKind::Fast:
computeHash(Buf, [](uint8_t *Dest, ArrayRef<uint8_t> Arr) {
write64le(Dest, xxHash64(toStringRef(Arr)));
});
break;
case BuildIdKind::Md5:
computeHash(Buf, [](uint8_t *Dest, ArrayRef<uint8_t> Arr) {
memcpy(Dest, MD5::hash(Arr).data(), 16);
});
break;
case BuildIdKind::Sha1:
computeHash(Buf, [](uint8_t *Dest, ArrayRef<uint8_t> Arr) {
memcpy(Dest, SHA1::hash(Arr).data(), 20);
});
break;
case BuildIdKind::Uuid:
if (auto EC = getRandomBytes(HashBuf, HashSize))
error("entropy source failure: " + EC.message());
break;
case BuildIdKind::Hexstring:
memcpy(HashBuf, Config->BuildIdVector.data(), Config->BuildIdVector.size());
break;
default:
llvm_unreachable("unknown BuildIdKind");
}
}
EhFrameSection::EhFrameSection()
: SyntheticSection(SHF_ALLOC, SHT_PROGBITS, 1, ".eh_frame") {}
// Search for an existing CIE record or create a new one.
// CIE records from input object files are uniquified by their contents
// and where their relocations point to.
template <class ELFT, class RelTy>
CieRecord *EhFrameSection::addCie(EhSectionPiece &Cie, ArrayRef<RelTy> Rels) {
auto *Sec = cast<EhInputSection>(Cie.Sec);
if (read32(Cie.data().data() + 4, Config->Endianness) != 0)
fatal(toString(Sec) + ": CIE expected at beginning of .eh_frame");
Symbol *Personality = nullptr;
unsigned FirstRelI = Cie.FirstRelocation;
if (FirstRelI != (unsigned)-1)
Personality =
&Sec->template getFile<ELFT>()->getRelocTargetSym(Rels[FirstRelI]);
// Search for an existing CIE by CIE contents/relocation target pair.
CieRecord *&Rec = CieMap[{Cie.data(), Personality}];
// If not found, create a new one.
if (!Rec) {
Rec = make<CieRecord>();
Rec->Cie = &Cie;
CieRecords.push_back(Rec);
}
return Rec;
}
// There is one FDE per function. Returns true if a given FDE
// points to a live function.
template <class ELFT, class RelTy>
bool EhFrameSection::isFdeLive(EhSectionPiece &Fde, ArrayRef<RelTy> Rels) {
auto *Sec = cast<EhInputSection>(Fde.Sec);
unsigned FirstRelI = Fde.FirstRelocation;
// An FDE should point to some function because FDEs are to describe
// functions. That's however not always the case due to an issue of
// ld.gold with -r. ld.gold may discard only functions and leave their
// corresponding FDEs, which results in creating bad .eh_frame sections.
// To deal with that, we ignore such FDEs.
if (FirstRelI == (unsigned)-1)
return false;
const RelTy &Rel = Rels[FirstRelI];
Symbol &B = Sec->template getFile<ELFT>()->getRelocTargetSym(Rel);
// FDEs for garbage-collected or merged-by-ICF sections are dead.
if (auto *D = dyn_cast<Defined>(&B))
if (SectionBase *Sec = D->Section)
return Sec->Live;
return false;
}
// .eh_frame is a sequence of CIE or FDE records. In general, there
// is one CIE record per input object file which is followed by
// a list of FDEs. This function searches an existing CIE or create a new
// one and associates FDEs to the CIE.
template <class ELFT, class RelTy>
void EhFrameSection::addSectionAux(EhInputSection *Sec, ArrayRef<RelTy> Rels) {
DenseMap<size_t, CieRecord *> OffsetToCie;
for (EhSectionPiece &Piece : Sec->Pieces) {
// The empty record is the end marker.
if (Piece.Size == 4)
return;
size_t Offset = Piece.InputOff;
uint32_t ID = read32(Piece.data().data() + 4, Config->Endianness);
if (ID == 0) {
OffsetToCie[Offset] = addCie<ELFT>(Piece, Rels);
continue;
}
uint32_t CieOffset = Offset + 4 - ID;
CieRecord *Rec = OffsetToCie[CieOffset];
if (!Rec)
fatal(toString(Sec) + ": invalid CIE reference");
if (!isFdeLive<ELFT>(Piece, Rels))
continue;
Rec->Fdes.push_back(&Piece);
NumFdes++;
}
}
template <class ELFT> void EhFrameSection::addSection(InputSectionBase *C) {
auto *Sec = cast<EhInputSection>(C);
Sec->Parent = this;
Alignment = std::max(Alignment, Sec->Alignment);
Sections.push_back(Sec);
for (auto *DS : Sec->DependentSections)
DependentSections.push_back(DS);
// .eh_frame is a sequence of CIE or FDE records. This function
// splits it into pieces so that we can call
// SplitInputSection::getSectionPiece on the section.
Sec->split<ELFT>();
if (Sec->Pieces.empty())
return;
if (Sec->AreRelocsRela)
addSectionAux<ELFT>(Sec, Sec->template relas<ELFT>());
else
addSectionAux<ELFT>(Sec, Sec->template rels<ELFT>());
}
static void writeCieFde(uint8_t *Buf, ArrayRef<uint8_t> D) {
memcpy(Buf, D.data(), D.size());
size_t Aligned = alignTo(D.size(), Config->Wordsize);
// Zero-clear trailing padding if it exists.
memset(Buf + D.size(), 0, Aligned - D.size());
// Fix the size field. -4 since size does not include the size field itself.
write32(Buf, Aligned - 4);
}
void EhFrameSection::finalizeContents() {
if (this->Size)
return; // Already finalized.
size_t Off = 0;
for (CieRecord *Rec : CieRecords) {
Rec->Cie->OutputOff = Off;
Off += alignTo(Rec->Cie->Size, Config->Wordsize);
for (EhSectionPiece *Fde : Rec->Fdes) {
Fde->OutputOff = Off;
Off += alignTo(Fde->Size, Config->Wordsize);
}
}
// The LSB standard does not allow a .eh_frame section with zero
// Call Frame Information records. Therefore add a CIE record length
// 0 as a terminator if this .eh_frame section is empty.
if (Off == 0)
Off = 4;
this->Size = Off;
}
// Returns data for .eh_frame_hdr. .eh_frame_hdr is a binary search table
// to get an FDE from an address to which FDE is applied. This function
// returns a list of such pairs.
std::vector<EhFrameSection::FdeData> EhFrameSection::getFdeData() const {
uint8_t *Buf = getParent()->Loc + OutSecOff;
std::vector<FdeData> Ret;
for (CieRecord *Rec : CieRecords) {
uint8_t Enc = getFdeEncoding(Rec->Cie);
for (EhSectionPiece *Fde : Rec->Fdes) {
uint32_t Pc = getFdePc(Buf, Fde->OutputOff, Enc);
uint32_t FdeVA = getParent()->Addr + Fde->OutputOff;
Ret.push_back({Pc, FdeVA});
}
}
return Ret;
}
static uint64_t readFdeAddr(uint8_t *Buf, int Size) {
switch (Size) {
case DW_EH_PE_udata2:
return read16(Buf, Config->Endianness);
case DW_EH_PE_udata4:
return read32(Buf, Config->Endianness);
case DW_EH_PE_udata8:
return read64(Buf, Config->Endianness);
case DW_EH_PE_absptr:
return readUint(Buf);
}
fatal("unknown FDE size encoding");
}
// Returns the VA to which a given FDE (on a mmap'ed buffer) is applied to.
// We need it to create .eh_frame_hdr section.
uint64_t EhFrameSection::getFdePc(uint8_t *Buf, size_t FdeOff,
uint8_t Enc) const {
// The starting address to which this FDE applies is
// stored at FDE + 8 byte.
size_t Off = FdeOff + 8;
uint64_t Addr = readFdeAddr(Buf + Off, Enc & 0x7);
if ((Enc & 0x70) == DW_EH_PE_absptr)
return Addr;
if ((Enc & 0x70) == DW_EH_PE_pcrel)
return Addr + getParent()->Addr + Off;
fatal("unknown FDE size relative encoding");
}
void EhFrameSection::writeTo(uint8_t *Buf) {
// Write CIE and FDE records.
for (CieRecord *Rec : CieRecords) {
size_t CieOffset = Rec->Cie->OutputOff;
writeCieFde(Buf + CieOffset, Rec->Cie->data());
for (EhSectionPiece *Fde : Rec->Fdes) {
size_t Off = Fde->OutputOff;
writeCieFde(Buf + Off, Fde->data());
// FDE's second word should have the offset to an associated CIE.
// Write it.
write32(Buf + Off + 4, Off + 4 - CieOffset);
}
}
// Apply relocations. .eh_frame section contents are not contiguous
// in the output buffer, but relocateAlloc() still works because
// getOffset() takes care of discontiguous section pieces.
for (EhInputSection *S : Sections)
S->relocateAlloc(Buf, nullptr);
}
GotSection::GotSection()
: SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_PROGBITS,
Target->GotEntrySize, ".got") {}
void GotSection::addEntry(Symbol &Sym) {
Sym.GotIndex = NumEntries;
++NumEntries;
}
bool GotSection::addDynTlsEntry(Symbol &Sym) {
if (Sym.GlobalDynIndex != -1U)
return false;
Sym.GlobalDynIndex = NumEntries;
// Global Dynamic TLS entries take two GOT slots.
NumEntries += 2;
return true;
}
// Reserves TLS entries for a TLS module ID and a TLS block offset.
// In total it takes two GOT slots.
bool GotSection::addTlsIndex() {
if (TlsIndexOff != uint32_t(-1))
return false;
TlsIndexOff = NumEntries * Config->Wordsize;
NumEntries += 2;
return true;
}
uint64_t GotSection::getGlobalDynAddr(const Symbol &B) const {
return this->getVA() + B.GlobalDynIndex * Config->Wordsize;
}
uint64_t GotSection::getGlobalDynOffset(const Symbol &B) const {
return B.GlobalDynIndex * Config->Wordsize;
}
void GotSection::finalizeContents() { Size = NumEntries * Config->Wordsize; }
bool GotSection::empty() const {
// We need to emit a GOT even if it's empty if there's a relocation that is
// relative to GOT(such as GOTOFFREL) or there's a symbol that points to a GOT
// (i.e. _GLOBAL_OFFSET_TABLE_).
return NumEntries == 0 && !HasGotOffRel && !ElfSym::GlobalOffsetTable;
}
void GotSection::writeTo(uint8_t *Buf) {
// Buf points to the start of this section's buffer,
// whereas InputSectionBase::relocateAlloc() expects its argument
// to point to the start of the output section.
relocateAlloc(Buf - OutSecOff, Buf - OutSecOff + Size);
}
MipsGotSection::MipsGotSection()
: SyntheticSection(SHF_ALLOC | SHF_WRITE | SHF_MIPS_GPREL, SHT_PROGBITS, 16,
".got") {}
void MipsGotSection::addEntry(Symbol &Sym, int64_t Addend, RelExpr Expr) {
// For "true" local symbols which can be referenced from the same module
// only compiler creates two instructions for address loading:
//
// lw $8, 0($gp) # R_MIPS_GOT16
// addi $8, $8, 0 # R_MIPS_LO16
//
// The first instruction loads high 16 bits of the symbol address while
// the second adds an offset. That allows to reduce number of required
// GOT entries because only one global offset table entry is necessary
// for every 64 KBytes of local data. So for local symbols we need to
// allocate number of GOT entries to hold all required "page" addresses.
//
// All global symbols (hidden and regular) considered by compiler uniformly.
// It always generates a single `lw` instruction and R_MIPS_GOT16 relocation
// to load address of the symbol. So for each such symbol we need to
// allocate dedicated GOT entry to store its address.
//
// If a symbol is preemptible we need help of dynamic linker to get its
// final address. The corresponding GOT entries are allocated in the
// "global" part of GOT. Entries for non preemptible global symbol allocated
// in the "local" part of GOT.
//
// See "Global Offset Table" in Chapter 5:
// ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
if (Expr == R_MIPS_GOT_LOCAL_PAGE) {
// At this point we do not know final symbol value so to reduce number
// of allocated GOT entries do the following trick. Save all output
// sections referenced by GOT relocations. Then later in the `finalize`
// method calculate number of "pages" required to cover all saved output
// section and allocate appropriate number of GOT entries.
PageIndexMap.insert({Sym.getOutputSection(), 0});
return;
}
if (Sym.isTls()) {
// GOT entries created for MIPS TLS relocations behave like
// almost GOT entries from other ABIs. They go to the end
// of the global offset table.
Sym.GotIndex = TlsEntries.size();
TlsEntries.push_back(&Sym);
return;
}
auto AddEntry = [&](Symbol &S, uint64_t A, GotEntries &Items) {
if (S.isInGot() && !A)
return;
size_t NewIndex = Items.size();
if (!EntryIndexMap.insert({{&S, A}, NewIndex}).second)
return;
Items.emplace_back(&S, A);
if (!A)
S.GotIndex = NewIndex;
};
if (Sym.IsPreemptible) {
// Ignore addends for preemptible symbols. They got single GOT entry anyway.
AddEntry(Sym, 0, GlobalEntries);
Sym.IsInGlobalMipsGot = true;
} else if (Expr == R_MIPS_GOT_OFF32) {
AddEntry(Sym, Addend, LocalEntries32);
Sym.Is32BitMipsGot = true;
} else {
// Hold local GOT entries accessed via a 16-bit index separately.
// That allows to write them in the beginning of the GOT and keep
// their indexes as less as possible to escape relocation's overflow.
AddEntry(Sym, Addend, LocalEntries);
}
}
bool MipsGotSection::addDynTlsEntry(Symbol &Sym) {
if (Sym.GlobalDynIndex != -1U)
return false;
Sym.GlobalDynIndex = TlsEntries.size();
// Global Dynamic TLS entries take two GOT slots.
TlsEntries.push_back(nullptr);
TlsEntries.push_back(&Sym);
return true;
}
// Reserves TLS entries for a TLS module ID and a TLS block offset.
// In total it takes two GOT slots.
bool MipsGotSection::addTlsIndex() {
if (TlsIndexOff != uint32_t(-1))
return false;
TlsIndexOff = TlsEntries.size() * Config->Wordsize;
TlsEntries.push_back(nullptr);
TlsEntries.push_back(nullptr);
return true;
}
static uint64_t getMipsPageAddr(uint64_t Addr) {
return (Addr + 0x8000) & ~0xffff;
}
static uint64_t getMipsPageCount(uint64_t Size) {
return (Size + 0xfffe) / 0xffff + 1;
}
uint64_t MipsGotSection::getPageEntryOffset(const Symbol &B,
int64_t Addend) const {
const OutputSection *OutSec = B.getOutputSection();
uint64_t SecAddr = getMipsPageAddr(OutSec->Addr);
uint64_t SymAddr = getMipsPageAddr(B.getVA(Addend));
uint64_t Index = PageIndexMap.lookup(OutSec) + (SymAddr - SecAddr) / 0xffff;
assert(Index < PageEntriesNum);
return (HeaderEntriesNum + Index) * Config->Wordsize;
}
uint64_t MipsGotSection::getSymEntryOffset(const Symbol &B,
int64_t Addend) const {
// Calculate offset of the GOT entries block: TLS, global, local.
uint64_t Index = HeaderEntriesNum + PageEntriesNum;
if (B.isTls())
Index += LocalEntries.size() + LocalEntries32.size() + GlobalEntries.size();
else if (B.IsInGlobalMipsGot)
Index += LocalEntries.size() + LocalEntries32.size();
else if (B.Is32BitMipsGot)
Index += LocalEntries.size();
// Calculate offset of the GOT entry in the block.
if (B.isInGot())
Index += B.GotIndex;
else {
auto It = EntryIndexMap.find({&B, Addend});
assert(It != EntryIndexMap.end());
Index += It->second;
}
return Index * Config->Wordsize;
}
uint64_t MipsGotSection::getTlsOffset() const {
return (getLocalEntriesNum() + GlobalEntries.size()) * Config->Wordsize;
}
uint64_t MipsGotSection::getGlobalDynOffset(const Symbol &B) const {
return B.GlobalDynIndex * Config->Wordsize;
}
const Symbol *MipsGotSection::getFirstGlobalEntry() const {
return GlobalEntries.empty() ? nullptr : GlobalEntries.front().first;
}
unsigned MipsGotSection::getLocalEntriesNum() const {
return HeaderEntriesNum + PageEntriesNum + LocalEntries.size() +
LocalEntries32.size();
}
void MipsGotSection::finalizeContents() { updateAllocSize(); }
bool MipsGotSection::updateAllocSize() {
PageEntriesNum = 0;
for (std::pair<const OutputSection *, size_t> &P : PageIndexMap) {
// For each output section referenced by GOT page relocations calculate
// and save into PageIndexMap an upper bound of MIPS GOT entries required
// to store page addresses of local symbols. We assume the worst case -
// each 64kb page of the output section has at least one GOT relocation
// against it. And take in account the case when the section intersects
// page boundaries.
P.second = PageEntriesNum;
PageEntriesNum += getMipsPageCount(P.first->Size);
}
Size = (getLocalEntriesNum() + GlobalEntries.size() + TlsEntries.size()) *
Config->Wordsize;
return false;
}
bool MipsGotSection::empty() const {
// We add the .got section to the result for dynamic MIPS target because
// its address and properties are mentioned in the .dynamic section.
return Config->Relocatable;
}
uint64_t MipsGotSection::getGp() const { return ElfSym::MipsGp->getVA(0); }
void MipsGotSection::writeTo(uint8_t *Buf) {
// Set the MSB of the second GOT slot. This is not required by any
// MIPS ABI documentation, though.
//
// There is a comment in glibc saying that "The MSB of got[1] of a
// gnu object is set to identify gnu objects," and in GNU gold it
// says "the second entry will be used by some runtime loaders".
// But how this field is being used is unclear.
//
// We are not really willing to mimic other linkers behaviors
// without understanding why they do that, but because all files
// generated by GNU tools have this special GOT value, and because
// we've been doing this for years, it is probably a safe bet to
// keep doing this for now. We really need to revisit this to see
// if we had to do this.
writeUint(Buf + Config->Wordsize, (uint64_t)1 << (Config->Wordsize * 8 - 1));
Buf += HeaderEntriesNum * Config->Wordsize;
// Write 'page address' entries to the local part of the GOT.
for (std::pair<const OutputSection *, size_t> &L : PageIndexMap) {
size_t PageCount = getMipsPageCount(L.first->Size);
uint64_t FirstPageAddr = getMipsPageAddr(L.first->Addr);
for (size_t PI = 0; PI < PageCount; ++PI) {
uint8_t *Entry = Buf + (L.second + PI) * Config->Wordsize;
writeUint(Entry, FirstPageAddr + PI * 0x10000);
}
}
Buf += PageEntriesNum * Config->Wordsize;
auto AddEntry = [&](const GotEntry &SA) {
uint8_t *Entry = Buf;
Buf += Config->Wordsize;
const Symbol *Sym = SA.first;
uint64_t VA = Sym->getVA(SA.second);
if (Sym->StOther & STO_MIPS_MICROMIPS)
VA |= 1;
writeUint(Entry, VA);
};
std::for_each(std::begin(LocalEntries), std::end(LocalEntries), AddEntry);
std::for_each(std::begin(LocalEntries32), std::end(LocalEntries32), AddEntry);
std::for_each(std::begin(GlobalEntries), std::end(GlobalEntries), AddEntry);
// Initialize TLS-related GOT entries. If the entry has a corresponding
// dynamic relocations, leave it initialized by zero. Write down adjusted
// TLS symbol's values otherwise. To calculate the adjustments use offsets
// for thread-local storage.
// https://www.linux-mips.org/wiki/NPTL
if (TlsIndexOff != -1U && !Config->Pic)
writeUint(Buf + TlsIndexOff, 1);
for (const Symbol *B : TlsEntries) {
if (!B || B->IsPreemptible)
continue;
uint64_t VA = B->getVA();
if (B->GotIndex != -1U) {
uint8_t *Entry = Buf + B->GotIndex * Config->Wordsize;
writeUint(Entry, VA - 0x7000);
}
if (B->GlobalDynIndex != -1U) {
uint8_t *Entry = Buf + B->GlobalDynIndex * Config->Wordsize;
writeUint(Entry, 1);
Entry += Config->Wordsize;
writeUint(Entry, VA - 0x8000);
}
}
}
GotPltSection::GotPltSection()
: SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_PROGBITS,
Target->GotPltEntrySize, ".got.plt") {}
void GotPltSection::addEntry(Symbol &Sym) {
Sym.GotPltIndex = Target->GotPltHeaderEntriesNum + Entries.size();
Entries.push_back(&Sym);
}
size_t GotPltSection::getSize() const {
return (Target->GotPltHeaderEntriesNum + Entries.size()) *
Target->GotPltEntrySize;
}
void GotPltSection::writeTo(uint8_t *Buf) {
Target->writeGotPltHeader(Buf);
Buf += Target->GotPltHeaderEntriesNum * Target->GotPltEntrySize;
for (const Symbol *B : Entries) {
Target->writeGotPlt(Buf, *B);
Buf += Config->Wordsize;
}
}
// On ARM the IgotPltSection is part of the GotSection, on other Targets it is
// part of the .got.plt
IgotPltSection::IgotPltSection()
: SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_PROGBITS,
Target->GotPltEntrySize,
Config->EMachine == EM_ARM ? ".got" : ".got.plt") {}
void IgotPltSection::addEntry(Symbol &Sym) {
Sym.IsInIgot = true;
Sym.GotPltIndex = Entries.size();
Entries.push_back(&Sym);
}
size_t IgotPltSection::getSize() const {
return Entries.size() * Target->GotPltEntrySize;
}
void IgotPltSection::writeTo(uint8_t *Buf) {
for (const Symbol *B : Entries) {
Target->writeIgotPlt(Buf, *B);
Buf += Config->Wordsize;
}
}
StringTableSection::StringTableSection(StringRef Name, bool Dynamic)
: SyntheticSection(Dynamic ? (uint64_t)SHF_ALLOC : 0, SHT_STRTAB, 1, Name),
Dynamic(Dynamic) {
// ELF string tables start with a NUL byte.
addString("");
}
// Adds a string to the string table. If HashIt is true we hash and check for
// duplicates. It is optional because the name of global symbols are already
// uniqued and hashing them again has a big cost for a small value: uniquing
// them with some other string that happens to be the same.
unsigned StringTableSection::addString(StringRef S, bool HashIt) {
if (HashIt) {
auto R = StringMap.insert(std::make_pair(S, this->Size));
if (!R.second)
return R.first->second;
}
unsigned Ret = this->Size;
this->Size = this->Size + S.size() + 1;
Strings.push_back(S);
return Ret;
}
void StringTableSection::writeTo(uint8_t *Buf) {
for (StringRef S : Strings) {
memcpy(Buf, S.data(), S.size());
Buf[S.size()] = '\0';
Buf += S.size() + 1;
}
}
// Returns the number of version definition entries. Because the first entry
// is for the version definition itself, it is the number of versioned symbols
// plus one. Note that we don't support multiple versions yet.
static unsigned getVerDefNum() { return Config->VersionDefinitions.size() + 1; }
template <class ELFT>
DynamicSection<ELFT>::DynamicSection()
: SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_DYNAMIC, Config->Wordsize,
".dynamic") {
this->Entsize = ELFT::Is64Bits ? 16 : 8;
// .dynamic section is not writable on MIPS and on Fuchsia OS
// which passes -z rodynamic.
// See "Special Section" in Chapter 4 in the following document:
// ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
if (Config->EMachine == EM_MIPS || Config->ZRodynamic)
this->Flags = SHF_ALLOC;
// Add strings to .dynstr early so that .dynstr's size will be
// fixed early.
for (StringRef S : Config->FilterList)
addInt(DT_FILTER, InX::DynStrTab->addString(S));
for (StringRef S : Config->AuxiliaryList)
addInt(DT_AUXILIARY, InX::DynStrTab->addString(S));
if (!Config->Rpath.empty())
addInt(Config->EnableNewDtags ? DT_RUNPATH : DT_RPATH,
InX::DynStrTab->addString(Config->Rpath));
for (InputFile *File : SharedFiles) {
SharedFile<ELFT> *F = cast<SharedFile<ELFT>>(File);
if (F->IsNeeded)
addInt(DT_NEEDED, InX::DynStrTab->addString(F->SoName));
}
if (!Config->SoName.empty())
addInt(DT_SONAME, InX::DynStrTab->addString(Config->SoName));
}
template <class ELFT>
void DynamicSection<ELFT>::add(int32_t Tag, std::function<uint64_t()> Fn) {
Entries.push_back({Tag, Fn});
}
template <class ELFT>
void DynamicSection<ELFT>::addInt(int32_t Tag, uint64_t Val) {
Entries.push_back({Tag, [=] { return Val; }});
}
template <class ELFT>
void DynamicSection<ELFT>::addInSec(int32_t Tag, InputSection *Sec) {
Entries.push_back(
{Tag, [=] { return Sec->getParent()->Addr + Sec->OutSecOff; }});
}
template <class ELFT>
void DynamicSection<ELFT>::addOutSec(int32_t Tag, OutputSection *Sec) {
Entries.push_back({Tag, [=] { return Sec->Addr; }});
}
template <class ELFT>
void DynamicSection<ELFT>::addSize(int32_t Tag, OutputSection *Sec) {
Entries.push_back({Tag, [=] { return Sec->Size; }});
}
template <class ELFT>
void DynamicSection<ELFT>::addSym(int32_t Tag, Symbol *Sym) {
Entries.push_back({Tag, [=] { return Sym->getVA(); }});
}
// Add remaining entries to complete .dynamic contents.
template <class ELFT> void DynamicSection<ELFT>::finalizeContents() {
if (this->Size)
return; // Already finalized.
// Set DT_FLAGS and DT_FLAGS_1.
uint32_t DtFlags = 0;
uint32_t DtFlags1 = 0;
if (Config->Bsymbolic)
DtFlags |= DF_SYMBOLIC;
if (Config->ZNodelete)
DtFlags1 |= DF_1_NODELETE;
if (Config->ZNodlopen)
DtFlags1 |= DF_1_NOOPEN;
if (Config->ZNow) {
DtFlags |= DF_BIND_NOW;
DtFlags1 |= DF_1_NOW;
}
if (Config->ZOrigin) {
DtFlags |= DF_ORIGIN;
DtFlags1 |= DF_1_ORIGIN;
}
if (DtFlags)
addInt(DT_FLAGS, DtFlags);
if (DtFlags1)
addInt(DT_FLAGS_1, DtFlags1);
// DT_DEBUG is a pointer to debug informaion used by debuggers at runtime. We
// need it for each process, so we don't write it for DSOs. The loader writes
// the pointer into this entry.
//
// DT_DEBUG is the only .dynamic entry that needs to be written to. Some
// systems (currently only Fuchsia OS) provide other means to give the
// debugger this information. Such systems may choose make .dynamic read-only.
// If the target is such a system (used -z rodynamic) don't write DT_DEBUG.
if (!Config->Shared && !Config->Relocatable && !Config->ZRodynamic)
addInt(DT_DEBUG, 0);
this->Link = InX::DynStrTab->getParent()->SectionIndex;
if (!InX::RelaDyn->empty()) {
addInSec(InX::RelaDyn->DynamicTag, InX::RelaDyn);
addSize(InX::RelaDyn->SizeDynamicTag, InX::RelaDyn->getParent());
bool IsRela = Config->IsRela;
addInt(IsRela ? DT_RELAENT : DT_RELENT,
IsRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel));
// MIPS dynamic loader does not support RELCOUNT tag.
// The problem is in the tight relation between dynamic
// relocations and GOT. So do not emit this tag on MIPS.
if (Config->EMachine != EM_MIPS) {
size_t NumRelativeRels = InX::RelaDyn->getRelativeRelocCount();
if (Config->ZCombreloc && NumRelativeRels)
addInt(IsRela ? DT_RELACOUNT : DT_RELCOUNT, NumRelativeRels);
}
}
// .rel[a].plt section usually consists of two parts, containing plt and
// iplt relocations. It is possible to have only iplt relocations in the
// output. In that case RelaPlt is empty and have zero offset, the same offset
// as RelaIplt have. And we still want to emit proper dynamic tags for that
// case, so here we always use RelaPlt as marker for the begining of
// .rel[a].plt section.
if (InX::RelaPlt->getParent()->Live) {
addInSec(DT_JMPREL, InX::RelaPlt);
addSize(DT_PLTRELSZ, InX::RelaPlt->getParent());
switch (Config->EMachine) {
case EM_MIPS:
addInSec(DT_MIPS_PLTGOT, InX::GotPlt);
break;
case EM_SPARCV9:
addInSec(DT_PLTGOT, InX::Plt);
break;
default:
addInSec(DT_PLTGOT, InX::GotPlt);
break;
}
addInt(DT_PLTREL, Config->IsRela ? DT_RELA : DT_REL);
}
addInSec(DT_SYMTAB, InX::DynSymTab);
addInt(DT_SYMENT, sizeof(Elf_Sym));
addInSec(DT_STRTAB, InX::DynStrTab);
addInt(DT_STRSZ, InX::DynStrTab->getSize());
if (!Config->ZText)
addInt(DT_TEXTREL, 0);
if (InX::GnuHashTab)
addInSec(DT_GNU_HASH, InX::GnuHashTab);
if (InX::HashTab)
addInSec(DT_HASH, InX::HashTab);
if (Out::PreinitArray) {
addOutSec(DT_PREINIT_ARRAY, Out::PreinitArray);
addSize(DT_PREINIT_ARRAYSZ, Out::PreinitArray);
}
if (Out::InitArray) {
addOutSec(DT_INIT_ARRAY, Out::InitArray);
addSize(DT_INIT_ARRAYSZ, Out::InitArray);
}
if (Out::FiniArray) {
addOutSec(DT_FINI_ARRAY, Out::FiniArray);
addSize(DT_FINI_ARRAYSZ, Out::FiniArray);
}
if (Symbol *B = Symtab->find(Config->Init))
if (B->isDefined())
addSym(DT_INIT, B);
if (Symbol *B = Symtab->find(Config->Fini))
if (B->isDefined())
addSym(DT_FINI, B);
bool HasVerNeed = In<ELFT>::VerNeed->getNeedNum() != 0;
if (HasVerNeed || In<ELFT>::VerDef)
addInSec(DT_VERSYM, In<ELFT>::VerSym);
if (In<ELFT>::VerDef) {
addInSec(DT_VERDEF, In<ELFT>::VerDef);
addInt(DT_VERDEFNUM, getVerDefNum());
}
if (HasVerNeed) {
addInSec(DT_VERNEED, In<ELFT>::VerNeed);
addInt(DT_VERNEEDNUM, In<ELFT>::VerNeed->getNeedNum());
}
if (Config->EMachine == EM_MIPS) {
addInt(DT_MIPS_RLD_VERSION, 1);
addInt(DT_MIPS_FLAGS, RHF_NOTPOT);
addInt(DT_MIPS_BASE_ADDRESS, Target->getImageBase());
addInt(DT_MIPS_SYMTABNO, InX::DynSymTab->getNumSymbols());
add(DT_MIPS_LOCAL_GOTNO, [] { return InX::MipsGot->getLocalEntriesNum(); });
if (const Symbol *B = InX::MipsGot->getFirstGlobalEntry())
addInt(DT_MIPS_GOTSYM, B->DynsymIndex);
else
addInt(DT_MIPS_GOTSYM, InX::DynSymTab->getNumSymbols());
addInSec(DT_PLTGOT, InX::MipsGot);
if (InX::MipsRldMap)
addInSec(DT_MIPS_RLD_MAP, InX::MipsRldMap);
}
addInt(DT_NULL, 0);
getParent()->Link = this->Link;
this->Size = Entries.size() * this->Entsize;
}
template <class ELFT> void DynamicSection<ELFT>::writeTo(uint8_t *Buf) {
auto *P = reinterpret_cast<Elf_Dyn *>(Buf);
for (std::pair<int32_t, std::function<uint64_t()>> &KV : Entries) {
P->d_tag = KV.first;
P->d_un.d_val = KV.second();
++P;
}
}
uint64_t DynamicReloc::getOffset() const {
return InputSec->getOutputSection()->Addr + InputSec->getOffset(OffsetInSec);
}
int64_t DynamicReloc::getAddend() const {
if (UseSymVA)
return Sym->getVA(Addend);
return Addend;
}
uint32_t DynamicReloc::getSymIndex() const {
if (Sym && !UseSymVA)
return Sym->DynsymIndex;
return 0;
}
RelocationBaseSection::RelocationBaseSection(StringRef Name, uint32_t Type,
int32_t DynamicTag,
int32_t SizeDynamicTag)
: SyntheticSection(SHF_ALLOC, Type, Config->Wordsize, Name),
DynamicTag(DynamicTag), SizeDynamicTag(SizeDynamicTag) {}
void RelocationBaseSection::addReloc(const DynamicReloc &Reloc) {
if (Reloc.Type == Target->RelativeRel)
++NumRelativeRelocs;
Relocs.push_back(Reloc);
}
void RelocationBaseSection::finalizeContents() {
// If all relocations are R_*_RELATIVE they don't refer to any
// dynamic symbol and we don't need a dynamic symbol table. If that
// is the case, just use 0 as the link.
Link = InX::DynSymTab ? InX::DynSymTab->getParent()->SectionIndex : 0;
// Set required output section properties.
getParent()->Link = Link;
}
template <class ELFT>
static void encodeDynamicReloc(typename ELFT::Rela *P,
const DynamicReloc &Rel) {
if (Config->IsRela)
P->r_addend = Rel.getAddend();
P->r_offset = Rel.getOffset();
if (Config->EMachine == EM_MIPS && Rel.getInputSec() == InX::MipsGot)
// The MIPS GOT section contains dynamic relocations that correspond to TLS
// entries. These entries are placed after the global and local sections of
// the GOT. At the point when we create these relocations, the size of the
// global and local sections is unknown, so the offset that we store in the
// TLS entry's DynamicReloc is relative to the start of the TLS section of
// the GOT, rather than being relative to the start of the GOT. This line of
// code adds the size of the global and local sections to the virtual
// address computed by getOffset() in order to adjust it into the TLS
// section.
P->r_offset += InX::MipsGot->getTlsOffset();
P->setSymbolAndType(Rel.getSymIndex(), Rel.Type, Config->IsMips64EL);
}
template <class ELFT>
RelocationSection<ELFT>::RelocationSection(StringRef Name, bool Sort)
: RelocationBaseSection(Name, Config->IsRela ? SHT_RELA : SHT_REL,
Config->IsRela ? DT_RELA : DT_REL,
Config->IsRela ? DT_RELASZ : DT_RELSZ),
Sort(Sort) {
this->Entsize = Config->IsRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel);
}
template <class ELFT, class RelTy>
static bool compRelocations(const RelTy &A, const RelTy &B) {
bool AIsRel = A.getType(Config->IsMips64EL) == Target->RelativeRel;
bool BIsRel = B.getType(Config->IsMips64EL) == Target->RelativeRel;
if (AIsRel != BIsRel)
return AIsRel;
return A.getSymbol(Config->IsMips64EL) < B.getSymbol(Config->IsMips64EL);
}
template <class ELFT> void RelocationSection<ELFT>::writeTo(uint8_t *Buf) {
uint8_t *BufBegin = Buf;
for (const DynamicReloc &Rel : Relocs) {
encodeDynamicReloc<ELFT>(reinterpret_cast<Elf_Rela *>(Buf), Rel);
Buf += Config->IsRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel);
}
if (Sort) {
if (Config->IsRela)
std::stable_sort((Elf_Rela *)BufBegin,
(Elf_Rela *)BufBegin + Relocs.size(),
compRelocations<ELFT, Elf_Rela>);
else
std::stable_sort((Elf_Rel *)BufBegin, (Elf_Rel *)BufBegin + Relocs.size(),
compRelocations<ELFT, Elf_Rel>);
}
}
template <class ELFT> unsigned RelocationSection<ELFT>::getRelocOffset() {
return this->Entsize * Relocs.size();
}
template <class ELFT>
AndroidPackedRelocationSection<ELFT>::AndroidPackedRelocationSection(
StringRef Name)
: RelocationBaseSection(
Name, Config->IsRela ? SHT_ANDROID_RELA : SHT_ANDROID_REL,
Config->IsRela ? DT_ANDROID_RELA : DT_ANDROID_REL,
Config->IsRela ? DT_ANDROID_RELASZ : DT_ANDROID_RELSZ) {
this->Entsize = 1;
}
template <class ELFT>
bool AndroidPackedRelocationSection<ELFT>::updateAllocSize() {
// This function computes the contents of an Android-format packed relocation
// section.
//
// This format compresses relocations by using relocation groups to factor out
// fields that are common between relocations and storing deltas from previous
// relocations in SLEB128 format (which has a short representation for small
// numbers). A good example of a relocation type with common fields is
// R_*_RELATIVE, which is normally used to represent function pointers in
// vtables. In the REL format, each relative relocation has the same r_info
// field, and is only different from other relative relocations in terms of
// the r_offset field. By sorting relocations by offset, grouping them by
// r_info and representing each relocation with only the delta from the
// previous offset, each 8-byte relocation can be compressed to as little as 1
// byte (or less with run-length encoding). This relocation packer was able to
// reduce the size of the relocation section in an Android Chromium DSO from
// 2,911,184 bytes to 174,693 bytes, or 6% of the original size.
//
// A relocation section consists of a header containing the literal bytes
// 'APS2' followed by a sequence of SLEB128-encoded integers. The first two
// elements are the total number of relocations in the section and an initial
// r_offset value. The remaining elements define a sequence of relocation
// groups. Each relocation group starts with a header consisting of the
// following elements:
//
// - the number of relocations in the relocation group
// - flags for the relocation group
// - (if RELOCATION_GROUPED_BY_OFFSET_DELTA_FLAG is set) the r_offset delta
// for each relocation in the group.
// - (if RELOCATION_GROUPED_BY_INFO_FLAG is set) the value of the r_info
// field for each relocation in the group.
// - (if RELOCATION_GROUP_HAS_ADDEND_FLAG and
// RELOCATION_GROUPED_BY_ADDEND_FLAG are set) the r_addend delta for
// each relocation in the group.
//
// Following the relocation group header are descriptions of each of the
// relocations in the group. They consist of the following elements:
//
// - (if RELOCATION_GROUPED_BY_OFFSET_DELTA_FLAG is not set) the r_offset
// delta for this relocation.
// - (if RELOCATION_GROUPED_BY_INFO_FLAG is not set) the value of the r_info
// field for this relocation.
// - (if RELOCATION_GROUP_HAS_ADDEND_FLAG is set and
// RELOCATION_GROUPED_BY_ADDEND_FLAG is not set) the r_addend delta for
// this relocation.
size_t OldSize = RelocData.size();
RelocData = {'A', 'P', 'S', '2'};
raw_svector_ostream OS(RelocData);
auto Add = [&](int64_t V) { encodeSLEB128(V, OS); };
// The format header includes the number of relocations and the initial
// offset (we set this to zero because the first relocation group will
// perform the initial adjustment).
Add(Relocs.size());
Add(0);
std::vector<Elf_Rela> Relatives, NonRelatives;
for (const DynamicReloc &Rel : Relocs) {
Elf_Rela R;
encodeDynamicReloc<ELFT>(&R, Rel);
if (R.getType(Config->IsMips64EL) == Target->RelativeRel)
Relatives.push_back(R);
else
NonRelatives.push_back(R);
}
std::sort(Relatives.begin(), Relatives.end(),
[](const Elf_Rel &A, const Elf_Rel &B) {
return A.r_offset < B.r_offset;
});
// Try to find groups of relative relocations which are spaced one word
// apart from one another. These generally correspond to vtable entries. The
// format allows these groups to be encoded using a sort of run-length
// encoding, but each group will cost 7 bytes in addition to the offset from
// the previous group, so it is only profitable to do this for groups of
// size 8 or larger.
std::vector<Elf_Rela> UngroupedRelatives;
std::vector<std::vector<Elf_Rela>> RelativeGroups;
for (auto I = Relatives.begin(), E = Relatives.end(); I != E;) {
std::vector<Elf_Rela> Group;
do {
Group.push_back(*I++);
} while (I != E && (I - 1)->r_offset + Config->Wordsize == I->r_offset);
if (Group.size() < 8)
UngroupedRelatives.insert(UngroupedRelatives.end(), Group.begin(),
Group.end());
else
RelativeGroups.emplace_back(std::move(Group));
}
unsigned HasAddendIfRela =
Config->IsRela ? RELOCATION_GROUP_HAS_ADDEND_FLAG : 0;
uint64_t Offset = 0;
uint64_t Addend = 0;
// Emit the run-length encoding for the groups of adjacent relative
// relocations. Each group is represented using two groups in the packed
// format. The first is used to set the current offset to the start of the
// group (and also encodes the first relocation), and the second encodes the
// remaining relocations.
for (std::vector<Elf_Rela> &G : RelativeGroups) {
// The first relocation in the group.
Add(1);
Add(RELOCATION_GROUPED_BY_OFFSET_DELTA_FLAG |
RELOCATION_GROUPED_BY_INFO_FLAG | HasAddendIfRela);
Add(G[0].r_offset - Offset);
Add(Target->RelativeRel);
if (Config->IsRela) {
Add(G[0].r_addend - Addend);
Addend = G[0].r_addend;
}
// The remaining relocations.
Add(G.size() - 1);
Add(RELOCATION_GROUPED_BY_OFFSET_DELTA_FLAG |
RELOCATION_GROUPED_BY_INFO_FLAG | HasAddendIfRela);
Add(Config->Wordsize);
Add(Target->RelativeRel);
if (Config->IsRela) {
for (auto I = G.begin() + 1, E = G.end(); I != E; ++I) {
Add(I->r_addend - Addend);
Addend = I->r_addend;
}
}
Offset = G.back().r_offset;
}
// Now the ungrouped relatives.
if (!UngroupedRelatives.empty()) {
Add(UngroupedRelatives.size());
Add(RELOCATION_GROUPED_BY_INFO_FLAG | HasAddendIfRela);
Add(Target->RelativeRel);
for (Elf_Rela &R : UngroupedRelatives) {
Add(R.r_offset - Offset);
Offset = R.r_offset;
if (Config->IsRela) {
Add(R.r_addend - Addend);
Addend = R.r_addend;
}
}
}
// Finally the non-relative relocations.
std::sort(NonRelatives.begin(), NonRelatives.end(),
[](const Elf_Rela &A, const Elf_Rela &B) {
return A.r_offset < B.r_offset;
});
if (!NonRelatives.empty()) {
Add(NonRelatives.size());
Add(HasAddendIfRela);
for (Elf_Rela &R : NonRelatives) {
Add(R.r_offset - Offset);
Offset = R.r_offset;
Add(R.r_info);
if (Config->IsRela) {
Add(R.r_addend - Addend);
Addend = R.r_addend;
}
}
}
// Returns whether the section size changed. We need to keep recomputing both
// section layout and the contents of this section until the size converges
// because changing this section's size can affect section layout, which in
// turn can affect the sizes of the LEB-encoded integers stored in this
// section.
return RelocData.size() != OldSize;
}
SymbolTableBaseSection::SymbolTableBaseSection(StringTableSection &StrTabSec)
: SyntheticSection(StrTabSec.isDynamic() ? (uint64_t)SHF_ALLOC : 0,
StrTabSec.isDynamic() ? SHT_DYNSYM : SHT_SYMTAB,
Config->Wordsize,
StrTabSec.isDynamic() ? ".dynsym" : ".symtab"),
StrTabSec(StrTabSec) {}
// Orders symbols according to their positions in the GOT,
// in compliance with MIPS ABI rules.
// See "Global Offset Table" in Chapter 5 in the following document
// for detailed description:
// ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
static bool sortMipsSymbols(const SymbolTableEntry &L,
const SymbolTableEntry &R) {
// Sort entries related to non-local preemptible symbols by GOT indexes.
// All other entries go to the first part of GOT in arbitrary order.
bool LIsInLocalGot = !L.Sym->IsInGlobalMipsGot;
bool RIsInLocalGot = !R.Sym->IsInGlobalMipsGot;
if (LIsInLocalGot || RIsInLocalGot)
return !RIsInLocalGot;
return L.Sym->GotIndex < R.Sym->GotIndex;
}
void SymbolTableBaseSection::finalizeContents() {
getParent()->Link = StrTabSec.getParent()->SectionIndex;
// If it is a .dynsym, there should be no local symbols, but we need
// to do a few things for the dynamic linker.
if (this->Type == SHT_DYNSYM) {
// Section's Info field has the index of the first non-local symbol.
// Because the first symbol entry is a null entry, 1 is the first.
getParent()->Info = 1;
if (InX::GnuHashTab) {
// NB: It also sorts Symbols to meet the GNU hash table requirements.
InX::GnuHashTab->addSymbols(Symbols);
} else if (Config->EMachine == EM_MIPS) {
std::stable_sort(Symbols.begin(), Symbols.end(), sortMipsSymbols);
}
size_t I = 0;
for (const SymbolTableEntry &S : Symbols) S.Sym->DynsymIndex = ++I;
return;
}
}
// The ELF spec requires that all local symbols precede global symbols, so we
// sort symbol entries in this function. (For .dynsym, we don't do that because
// symbols for dynamic linking are inherently all globals.)
void SymbolTableBaseSection::postThunkContents() {
if (this->Type == SHT_DYNSYM)
return;
// move all local symbols before global symbols.
auto It = std::stable_partition(
Symbols.begin(), Symbols.end(), [](const SymbolTableEntry &S) {
return S.Sym->isLocal() || S.Sym->computeBinding() == STB_LOCAL;
});
size_t NumLocals = It - Symbols.begin();
getParent()->Info = NumLocals + 1;
}
void SymbolTableBaseSection::addSymbol(Symbol *B) {
// Adding a local symbol to a .dynsym is a bug.
assert(this->Type != SHT_DYNSYM || !B->isLocal());
bool HashIt = B->isLocal();
Symbols.push_back({B, StrTabSec.addString(B->getName(), HashIt)});
}
size_t SymbolTableBaseSection::getSymbolIndex(Symbol *Sym) {
// Initializes symbol lookup tables lazily. This is used only
// for -r or -emit-relocs.
llvm::call_once(OnceFlag, [&] {
SymbolIndexMap.reserve(Symbols.size());
size_t I = 0;
for (const SymbolTableEntry &E : Symbols) {
if (E.Sym->Type == STT_SECTION)
SectionIndexMap[E.Sym->getOutputSection()] = ++I;
else
SymbolIndexMap[E.Sym] = ++I;
}
});
// Section symbols are mapped based on their output sections
// to maintain their semantics.
if (Sym->Type == STT_SECTION)
return SectionIndexMap.lookup(Sym->getOutputSection());
return SymbolIndexMap.lookup(Sym);
}
template <class ELFT>
SymbolTableSection<ELFT>::SymbolTableSection(StringTableSection &StrTabSec)
: SymbolTableBaseSection(StrTabSec) {
this->Entsize = sizeof(Elf_Sym);
}
// Write the internal symbol table contents to the output symbol table.
template <class ELFT> void SymbolTableSection<ELFT>::writeTo(uint8_t *Buf) {
// The first entry is a null entry as per the ELF spec.
memset(Buf, 0, sizeof(Elf_Sym));
Buf += sizeof(Elf_Sym);
auto *ESym = reinterpret_cast<Elf_Sym *>(Buf);
for (SymbolTableEntry &Ent : Symbols) {
Symbol *Sym = Ent.Sym;
// Set st_info and st_other.
ESym->st_other = 0;
if (Sym->isLocal()) {
ESym->setBindingAndType(STB_LOCAL, Sym->Type);
} else {
ESym->setBindingAndType(Sym->computeBinding(), Sym->Type);
ESym->setVisibility(Sym->Visibility);
}
ESym->st_name = Ent.StrTabOffset;
// Set a section index.
BssSection *CommonSec = nullptr;
if (!Config->DefineCommon)
if (auto *D = dyn_cast<Defined>(Sym))
CommonSec = dyn_cast_or_null<BssSection>(D->Section);
if (CommonSec)
ESym->st_shndx = SHN_COMMON;
else if (const OutputSection *OutSec = Sym->getOutputSection())
ESym->st_shndx = OutSec->SectionIndex;
else if (isa<Defined>(Sym))
ESym->st_shndx = SHN_ABS;
else
ESym->st_shndx = SHN_UNDEF;
// Copy symbol size if it is a defined symbol. st_size is not significant
// for undefined symbols, so whether copying it or not is up to us if that's
// the case. We'll leave it as zero because by not setting a value, we can
// get the exact same outputs for two sets of input files that differ only
// in undefined symbol size in DSOs.
if (ESym->st_shndx == SHN_UNDEF)
ESym->st_size = 0;
else
ESym->st_size = Sym->getSize();
// st_value is usually an address of a symbol, but that has a
// special meaining for uninstantiated common symbols (this can
// occur if -r is given).
if (CommonSec)
ESym->st_value = CommonSec->Alignment;
else
ESym->st_value = Sym->getVA();
++ESym;
}
// On MIPS we need to mark symbol which has a PLT entry and requires
// pointer equality by STO_MIPS_PLT flag. That is necessary to help
// dynamic linker distinguish such symbols and MIPS lazy-binding stubs.
// https://sourceware.org/ml/binutils/2008-07/txt00000.txt
if (Config->EMachine == EM_MIPS) {
auto *ESym = reinterpret_cast<Elf_Sym *>(Buf);
for (SymbolTableEntry &Ent : Symbols) {
Symbol *Sym = Ent.Sym;
if (Sym->isInPlt() && Sym->NeedsPltAddr)
ESym->st_other |= STO_MIPS_PLT;
if (isMicroMips()) {
// Set STO_MIPS_MICROMIPS flag and less-significant bit for
// defined microMIPS symbols and shared symbols with PLT record.
if ((Sym->isDefined() && (Sym->StOther & STO_MIPS_MICROMIPS)) ||
(Sym->isShared() && Sym->NeedsPltAddr)) {
if (StrTabSec.isDynamic())
ESym->st_value |= 1;
ESym->st_other |= STO_MIPS_MICROMIPS;
}
}
if (Config->Relocatable)
if (auto *D = dyn_cast<Defined>(Sym))
if (isMipsPIC<ELFT>(D))
ESym->st_other |= STO_MIPS_PIC;
++ESym;
}
}
}
// .hash and .gnu.hash sections contain on-disk hash tables that map
// symbol names to their dynamic symbol table indices. Their purpose
// is to help the dynamic linker resolve symbols quickly. If ELF files
// don't have them, the dynamic linker has to do linear search on all
// dynamic symbols, which makes programs slower. Therefore, a .hash
// section is added to a DSO by default. A .gnu.hash is added if you
// give the -hash-style=gnu or -hash-style=both option.
//
// The Unix semantics of resolving dynamic symbols is somewhat expensive.
// Each ELF file has a list of DSOs that the ELF file depends on and a
// list of dynamic symbols that need to be resolved from any of the
// DSOs. That means resolving all dynamic symbols takes O(m)*O(n)
// where m is the number of DSOs and n is the number of dynamic
// symbols. For modern large programs, both m and n are large. So
// making each step faster by using hash tables substiantially
// improves time to load programs.
//
// (Note that this is not the only way to design the shared library.
// For instance, the Windows DLL takes a different approach. On
// Windows, each dynamic symbol has a name of DLL from which the symbol
// has to be resolved. That makes the cost of symbol resolution O(n).
// This disables some hacky techniques you can use on Unix such as
// LD_PRELOAD, but this is arguably better semantics than the Unix ones.)
//
// Due to historical reasons, we have two different hash tables, .hash
// and .gnu.hash. They are for the same purpose, and .gnu.hash is a new
// and better version of .hash. .hash is just an on-disk hash table, but
// .gnu.hash has a bloom filter in addition to a hash table to skip
// DSOs very quickly. If you are sure that your dynamic linker knows
// about .gnu.hash, you want to specify -hash-style=gnu. Otherwise, a
// safe bet is to specify -hash-style=both for backward compatibilty.
GnuHashTableSection::GnuHashTableSection()
: SyntheticSection(SHF_ALLOC, SHT_GNU_HASH, Config->Wordsize, ".gnu.hash") {
}
void GnuHashTableSection::finalizeContents() {
getParent()->Link = InX::DynSymTab->getParent()->SectionIndex;
// Computes bloom filter size in word size. We want to allocate 8
// bits for each symbol. It must be a power of two.
if (Symbols.empty())
MaskWords = 1;
else
MaskWords = NextPowerOf2((Symbols.size() - 1) / Config->Wordsize);
Size = 16; // Header
Size += Config->Wordsize * MaskWords; // Bloom filter
Size += NBuckets * 4; // Hash buckets
Size += Symbols.size() * 4; // Hash values
}
void GnuHashTableSection::writeTo(uint8_t *Buf) {
// The output buffer is not guaranteed to be zero-cleared because we pre-
// fill executable sections with trap instructions. This is a precaution
// for that case, which happens only when -no-rosegment is given.
memset(Buf, 0, Size);
// Write a header.
write32(Buf, NBuckets);
write32(Buf + 4, InX::DynSymTab->getNumSymbols() - Symbols.size());
write32(Buf + 8, MaskWords);
write32(Buf + 12, getShift2());
Buf += 16;
// Write a bloom filter and a hash table.
writeBloomFilter(Buf);
Buf += Config->Wordsize * MaskWords;
writeHashTable(Buf);
}
// This function writes a 2-bit bloom filter. This bloom filter alone
// usually filters out 80% or more of all symbol lookups [1].
// The dynamic linker uses the hash table only when a symbol is not
// filtered out by a bloom filter.
//
// [1] Ulrich Drepper (2011), "How To Write Shared Libraries" (Ver. 4.1.2),
// p.9, https://www.akkadia.org/drepper/dsohowto.pdf
void GnuHashTableSection::writeBloomFilter(uint8_t *Buf) {
const unsigned C = Config->Wordsize * 8;
for (const Entry &Sym : Symbols) {
size_t I = (Sym.Hash / C) & (MaskWords - 1);
uint64_t Val = readUint(Buf + I * Config->Wordsize);
Val |= uint64_t(1) << (Sym.Hash % C);
Val |= uint64_t(1) << ((Sym.Hash >> getShift2()) % C);
writeUint(Buf + I * Config->Wordsize, Val);
}
}
void GnuHashTableSection::writeHashTable(uint8_t *Buf) {
uint32_t *Buckets = reinterpret_cast<uint32_t *>(Buf);
uint32_t OldBucket = -1;
uint32_t *Values = Buckets + NBuckets;
for (auto I = Symbols.begin(), E = Symbols.end(); I != E; ++I) {
// Write a hash value. It represents a sequence of chains that share the
// same hash modulo value. The last element of each chain is terminated by
// LSB 1.
uint32_t Hash = I->Hash;
bool IsLastInChain = (I + 1) == E || I->BucketIdx != (I + 1)->BucketIdx;
Hash = IsLastInChain ? Hash | 1 : Hash & ~1;
write32(Values++, Hash);
if (I->BucketIdx == OldBucket)
continue;
// Write a hash bucket. Hash buckets contain indices in the following hash
// value table.
write32(Buckets + I->BucketIdx, I->Sym->DynsymIndex);
OldBucket = I->BucketIdx;
}
}
static uint32_t hashGnu(StringRef Name) {
uint32_t H = 5381;
for (uint8_t C : Name)
H = (H << 5) + H + C;
return H;
}
// Add symbols to this symbol hash table. Note that this function
// destructively sort a given vector -- which is needed because
// GNU-style hash table places some sorting requirements.
void GnuHashTableSection::addSymbols(std::vector<SymbolTableEntry> &V) {
// We cannot use 'auto' for Mid because GCC 6.1 cannot deduce
// its type correctly.
std::vector<SymbolTableEntry>::iterator Mid =
std::stable_partition(V.begin(), V.end(), [](const SymbolTableEntry &S) {
// Shared symbols that this executable preempts are special. The dynamic
// linker has to look them up, so they have to be in the hash table.
if (auto *SS = dyn_cast<SharedSymbol>(S.Sym))
return SS->CopyRelSec == nullptr && !SS->NeedsPltAddr;
return !S.Sym->isDefined();
});
if (Mid == V.end())
return;
// We chose load factor 4 for the on-disk hash table. For each hash
// collision, the dynamic linker will compare a uint32_t hash value.
// Since the integer comparison is quite fast, we believe we can make
// the load factor even larger. 4 is just a conservative choice.
NBuckets = std::max<size_t>((V.end() - Mid) / 4, 1);
for (SymbolTableEntry &Ent : llvm::make_range(Mid, V.end())) {
Symbol *B = Ent.Sym;
uint32_t Hash = hashGnu(B->getName());
uint32_t BucketIdx = Hash % NBuckets;
Symbols.push_back({B, Ent.StrTabOffset, Hash, BucketIdx});
}
std::stable_sort(
Symbols.begin(), Symbols.end(),
[](const Entry &L, const Entry &R) { return L.BucketIdx < R.BucketIdx; });
V.erase(Mid, V.end());
for (const Entry &Ent : Symbols)
V.push_back({Ent.Sym, Ent.StrTabOffset});
}
HashTableSection::HashTableSection()
: SyntheticSection(SHF_ALLOC, SHT_HASH, 4, ".hash") {
this->Entsize = 4;
}
void HashTableSection::finalizeContents() {
getParent()->Link = InX::DynSymTab->getParent()->SectionIndex;
unsigned NumEntries = 2; // nbucket and nchain.
NumEntries += InX::DynSymTab->getNumSymbols(); // The chain entries.
// Create as many buckets as there are symbols.
NumEntries += InX::DynSymTab->getNumSymbols();
this->Size = NumEntries * 4;
}
void HashTableSection::writeTo(uint8_t *Buf) {
// See comment in GnuHashTableSection::writeTo.
memset(Buf, 0, Size);
unsigned NumSymbols = InX::DynSymTab->getNumSymbols();
uint32_t *P = reinterpret_cast<uint32_t *>(Buf);
write32(P++, NumSymbols); // nbucket
write32(P++, NumSymbols); // nchain
uint32_t *Buckets = P;
uint32_t *Chains = P + NumSymbols;
for (const SymbolTableEntry &S : InX::DynSymTab->getSymbols()) {
Symbol *Sym = S.Sym;
StringRef Name = Sym->getName();
unsigned I = Sym->DynsymIndex;
uint32_t Hash = hashSysV(Name) % NumSymbols;
Chains[I] = Buckets[Hash];
write32(Buckets + Hash, I);
}
}
PltSection::PltSection(size_t S)
: SyntheticSection(SHF_ALLOC | SHF_EXECINSTR, SHT_PROGBITS, 16, ".plt"),
HeaderSize(S) {
// The PLT needs to be writable on SPARC as the dynamic linker will
// modify the instructions in the PLT entries.
if (Config->EMachine == EM_SPARCV9)
this->Flags |= SHF_WRITE;
}
void PltSection::writeTo(uint8_t *Buf) {
// At beginning of PLT but not the IPLT, we have code to call the dynamic
// linker to resolve dynsyms at runtime. Write such code.
if (HeaderSize != 0)
Target->writePltHeader(Buf);
size_t Off = HeaderSize;
// The IPlt is immediately after the Plt, account for this in RelOff
unsigned PltOff = getPltRelocOff();
for (auto &I : Entries) {
const Symbol *B = I.first;
unsigned RelOff = I.second + PltOff;
uint64_t Got = B->getGotPltVA();
uint64_t Plt = this->getVA() + Off;
Target->writePlt(Buf + Off, Got, Plt, B->PltIndex, RelOff);
Off += Target->PltEntrySize;
}
}
template <class ELFT> void PltSection::addEntry(Symbol &Sym) {
Sym.PltIndex = Entries.size();
RelocationBaseSection *PltRelocSection = InX::RelaPlt;
if (HeaderSize == 0) {
PltRelocSection = InX::RelaIplt;
Sym.IsInIplt = true;
}
unsigned RelOff =
static_cast<RelocationSection<ELFT> *>(PltRelocSection)->getRelocOffset();
Entries.push_back(std::make_pair(&Sym, RelOff));
}
size_t PltSection::getSize() const {
return HeaderSize + Entries.size() * Target->PltEntrySize;
}
// Some architectures such as additional symbols in the PLT section. For
// example ARM uses mapping symbols to aid disassembly
void PltSection::addSymbols() {
// The PLT may have symbols defined for the Header, the IPLT has no header
if (HeaderSize != 0)
Target->addPltHeaderSymbols(*this);
size_t Off = HeaderSize;
for (size_t I = 0; I < Entries.size(); ++I) {
Target->addPltSymbols(*this, Off);
Off += Target->PltEntrySize;
}
}
unsigned PltSection::getPltRelocOff() const {
return (HeaderSize == 0) ? InX::Plt->getSize() : 0;
}
// The string hash function for .gdb_index.
static uint32_t computeGdbHash(StringRef S) {
uint32_t H = 0;
for (uint8_t C : S)
H = H * 67 + tolower(C) - 113;
return H;
}
static std::vector<GdbIndexChunk::CuEntry> readCuList(DWARFContext &Dwarf) {
std::vector<GdbIndexChunk::CuEntry> Ret;
for (std::unique_ptr<DWARFCompileUnit> &Cu : Dwarf.compile_units())
Ret.push_back({Cu->getOffset(), Cu->getLength() + 4});
return Ret;
}
static std::vector<GdbIndexChunk::AddressEntry>
readAddressAreas(DWARFContext &Dwarf, InputSection *Sec) {
std::vector<GdbIndexChunk::AddressEntry> Ret;
uint32_t CuIdx = 0;
for (std::unique_ptr<DWARFCompileUnit> &Cu : Dwarf.compile_units()) {
DWARFAddressRangesVector Ranges;
Cu->collectAddressRanges(Ranges);
ArrayRef<InputSectionBase *> Sections = Sec->File->getSections();
for (DWARFAddressRange &R : Ranges) {
InputSectionBase *S = Sections[R.SectionIndex];
if (!S || S == &InputSection::Discarded || !S->Live)
continue;
// Range list with zero size has no effect.
if (R.LowPC == R.HighPC)
continue;
auto *IS = cast<InputSection>(S);
uint64_t Offset = IS->getOffsetInFile();
Ret.push_back({IS, R.LowPC - Offset, R.HighPC - Offset, CuIdx});
}
++CuIdx;
}
return Ret;
}
static std::vector<GdbIndexChunk::NameTypeEntry>
readPubNamesAndTypes(DWARFContext &Dwarf) {
StringRef Sec1 = Dwarf.getDWARFObj().getGnuPubNamesSection();
StringRef Sec2 = Dwarf.getDWARFObj().getGnuPubTypesSection();
std::vector<GdbIndexChunk::NameTypeEntry> Ret;
for (StringRef Sec : {Sec1, Sec2}) {
DWARFDebugPubTable Table(Sec, Config->IsLE, true);
for (const DWARFDebugPubTable::Set &Set : Table.getData()) {
for (const DWARFDebugPubTable::Entry &Ent : Set.Entries) {
CachedHashStringRef S(Ent.Name, computeGdbHash(Ent.Name));
Ret.push_back({S, Ent.Descriptor.toBits()});
}
}
}
return Ret;
}
static std::vector<InputSection *> getDebugInfoSections() {
std::vector<InputSection *> Ret;
for (InputSectionBase *S : InputSections)
if (InputSection *IS = dyn_cast<InputSection>(S))
if (IS->Name == ".debug_info")
Ret.push_back(IS);
return Ret;
}
void GdbIndexSection::fixCuIndex() {
uint32_t Idx = 0;
for (GdbIndexChunk &Chunk : Chunks) {
for (GdbIndexChunk::AddressEntry &Ent : Chunk.AddressAreas)
Ent.CuIndex += Idx;
Idx += Chunk.CompilationUnits.size();
}
}
std::vector<std::vector<uint32_t>> GdbIndexSection::createCuVectors() {
std::vector<std::vector<uint32_t>> Ret;
uint32_t Idx = 0;
uint32_t Off = 0;
for (GdbIndexChunk &Chunk : Chunks) {
for (GdbIndexChunk::NameTypeEntry &Ent : Chunk.NamesAndTypes) {
GdbSymbol *&Sym = Symbols[Ent.Name];
if (!Sym) {
Sym = make<GdbSymbol>(GdbSymbol{Ent.Name.hash(), Off, Ret.size()});
Off += Ent.Name.size() + 1;
Ret.push_back({});
}
// gcc 5.4.1 produces a buggy .debug_gnu_pubnames that contains
// duplicate entries, so we want to dedup them.
std::vector<uint32_t> &Vec = Ret[Sym->CuVectorIndex];
uint32_t Val = (Ent.Type << 24) | Idx;
if (Vec.empty() || Vec.back() != Val)
Vec.push_back(Val);
}
Idx += Chunk.CompilationUnits.size();
}
StringPoolSize = Off;
return Ret;
}
template <class ELFT> GdbIndexSection *elf::createGdbIndex() {
// Gather debug info to create a .gdb_index section.
std::vector<InputSection *> Sections = getDebugInfoSections();
std::vector<GdbIndexChunk> Chunks(Sections.size());
parallelForEachN(0, Chunks.size(), [&](size_t I) {
ObjFile<ELFT> *File = Sections[I]->getFile<ELFT>();
DWARFContext Dwarf(make_unique<LLDDwarfObj<ELFT>>(File));
Chunks[I].DebugInfoSec = Sections[I];
Chunks[I].CompilationUnits = readCuList(Dwarf);
Chunks[I].AddressAreas = readAddressAreas(Dwarf, Sections[I]);
Chunks[I].NamesAndTypes = readPubNamesAndTypes(Dwarf);
});
// .debug_gnu_pub{names,types} are useless in executables.
// They are present in input object files solely for creating
// a .gdb_index. So we can remove it from the output.
for (InputSectionBase *S : InputSections)
if (S->Name == ".debug_gnu_pubnames" || S->Name == ".debug_gnu_pubtypes")
S->Live = false;
// Create a .gdb_index and returns it.
return make<GdbIndexSection>(std::move(Chunks));
}
static size_t getCuSize(ArrayRef<GdbIndexChunk> Arr) {
size_t Ret = 0;
for (const GdbIndexChunk &D : Arr)
Ret += D.CompilationUnits.size();
return Ret;
}
static size_t getAddressAreaSize(ArrayRef<GdbIndexChunk> Arr) {
size_t Ret = 0;
for (const GdbIndexChunk &D : Arr)
Ret += D.AddressAreas.size();
return Ret;
}
std::vector<GdbSymbol *> GdbIndexSection::createGdbSymtab() {
uint32_t Size = NextPowerOf2(Symbols.size() * 4 / 3);
if (Size < 1024)
Size = 1024;
uint32_t Mask = Size - 1;
std::vector<GdbSymbol *> Ret(Size);
for (auto &KV : Symbols) {
GdbSymbol *Sym = KV.second;
uint32_t I = Sym->NameHash & Mask;
uint32_t Step = ((Sym->NameHash * 17) & Mask) | 1;
while (Ret[I])
I = (I + Step) & Mask;
Ret[I] = Sym;
}
return Ret;
}
GdbIndexSection::GdbIndexSection(std::vector<GdbIndexChunk> &&C)
: SyntheticSection(0, SHT_PROGBITS, 1, ".gdb_index"), Chunks(std::move(C)) {
fixCuIndex();
CuVectors = createCuVectors();
GdbSymtab = createGdbSymtab();
// Compute offsets early to know the section size.
// Each chunk size needs to be in sync with what we write in writeTo.
CuTypesOffset = CuListOffset + getCuSize(Chunks) * 16;
SymtabOffset = CuTypesOffset + getAddressAreaSize(Chunks) * 20;
ConstantPoolOffset = SymtabOffset + GdbSymtab.size() * 8;
size_t Off = 0;
for (ArrayRef<uint32_t> Vec : CuVectors) {
CuVectorOffsets.push_back(Off);
Off += (Vec.size() + 1) * 4;
}
StringPoolOffset = ConstantPoolOffset + Off;
}
size_t GdbIndexSection::getSize() const {
return StringPoolOffset + StringPoolSize;
}
void GdbIndexSection::writeTo(uint8_t *Buf) {
// Write the section header.
write32le(Buf, 7);
write32le(Buf + 4, CuListOffset);
write32le(Buf + 8, CuTypesOffset);
write32le(Buf + 12, CuTypesOffset);
write32le(Buf + 16, SymtabOffset);
write32le(Buf + 20, ConstantPoolOffset);
Buf += 24;
// Write the CU list.
for (GdbIndexChunk &D : Chunks) {
for (GdbIndexChunk::CuEntry &Cu : D.CompilationUnits) {
write64le(Buf, D.DebugInfoSec->OutSecOff + Cu.CuOffset);
write64le(Buf + 8, Cu.CuLength);
Buf += 16;
}
}
// Write the address area.
for (GdbIndexChunk &D : Chunks) {
for (GdbIndexChunk::AddressEntry &E : D.AddressAreas) {
uint64_t BaseAddr =
E.Section->getParent()->Addr + E.Section->getOffset(0);
write64le(Buf, BaseAddr + E.LowAddress);
write64le(Buf + 8, BaseAddr + E.HighAddress);
write32le(Buf + 16, E.CuIndex);
Buf += 20;
}
}
// Write the symbol table.
for (GdbSymbol *Sym : GdbSymtab) {
if (Sym) {
write32le(Buf, Sym->NameOffset + StringPoolOffset - ConstantPoolOffset);
write32le(Buf + 4, CuVectorOffsets[Sym->CuVectorIndex]);
}
Buf += 8;
}
// Write the CU vectors.
for (ArrayRef<uint32_t> Vec : CuVectors) {
write32le(Buf, Vec.size());
Buf += 4;
for (uint32_t Val : Vec) {
write32le(Buf, Val);
Buf += 4;
}
}
// Write the string pool.
for (auto &KV : Symbols) {
CachedHashStringRef S = KV.first;
GdbSymbol *Sym = KV.second;
size_t Off = Sym->NameOffset;
memcpy(Buf + Off, S.val().data(), S.size());
Buf[Off + S.size()] = '\0';
}
}
bool GdbIndexSection::empty() const { return !Out::DebugInfo; }
EhFrameHeader::EhFrameHeader()
: SyntheticSection(SHF_ALLOC, SHT_PROGBITS, 1, ".eh_frame_hdr") {}
// .eh_frame_hdr contains a binary search table of pointers to FDEs.
// Each entry of the search table consists of two values,
// the starting PC from where FDEs covers, and the FDE's address.
// It is sorted by PC.
void EhFrameHeader::writeTo(uint8_t *Buf) {
typedef EhFrameSection::FdeData FdeData;
std::vector<FdeData> Fdes = InX::EhFrame->getFdeData();
// Sort the FDE list by their PC and uniqueify. Usually there is only
// one FDE for a PC (i.e. function), but if ICF merges two functions
// into one, there can be more than one FDEs pointing to the address.
auto Less = [](const FdeData &A, const FdeData &B) { return A.Pc < B.Pc; };
std::stable_sort(Fdes.begin(), Fdes.end(), Less);
auto Eq = [](const FdeData &A, const FdeData &B) { return A.Pc == B.Pc; };
Fdes.erase(std::unique(Fdes.begin(), Fdes.end(), Eq), Fdes.end());
Buf[0] = 1;
Buf[1] = DW_EH_PE_pcrel | DW_EH_PE_sdata4;
Buf[2] = DW_EH_PE_udata4;
Buf[3] = DW_EH_PE_datarel | DW_EH_PE_sdata4;
write32(Buf + 4, InX::EhFrame->getParent()->Addr - this->getVA() - 4);
write32(Buf + 8, Fdes.size());
Buf += 12;
uint64_t VA = this->getVA();
for (FdeData &Fde : Fdes) {
write32(Buf, Fde.Pc - VA);
write32(Buf + 4, Fde.FdeVA - VA);
Buf += 8;
}
}
size_t EhFrameHeader::getSize() const {
// .eh_frame_hdr has a 12 bytes header followed by an array of FDEs.
return 12 + InX::EhFrame->NumFdes * 8;
}
bool EhFrameHeader::empty() const { return InX::EhFrame->empty(); }
template <class ELFT>
VersionDefinitionSection<ELFT>::VersionDefinitionSection()
: SyntheticSection(SHF_ALLOC, SHT_GNU_verdef, sizeof(uint32_t),
".gnu.version_d") {}
static StringRef getFileDefName() {
if (!Config->SoName.empty())
return Config->SoName;
return Config->OutputFile;
}
template <class ELFT> void VersionDefinitionSection<ELFT>::finalizeContents() {
FileDefNameOff = InX::DynStrTab->addString(getFileDefName());
for (VersionDefinition &V : Config->VersionDefinitions)
V.NameOff = InX::DynStrTab->addString(V.Name);
getParent()->Link = InX::DynStrTab->getParent()->SectionIndex;
// sh_info should be set to the number of definitions. This fact is missed in
// documentation, but confirmed by binutils community:
// https://sourceware.org/ml/binutils/2014-11/msg00355.html
getParent()->Info = getVerDefNum();
}
template <class ELFT>
void VersionDefinitionSection<ELFT>::writeOne(uint8_t *Buf, uint32_t Index,
StringRef Name, size_t NameOff) {
auto *Verdef = reinterpret_cast<Elf_Verdef *>(Buf);
Verdef->vd_version = 1;
Verdef->vd_cnt = 1;
Verdef->vd_aux = sizeof(Elf_Verdef);
Verdef->vd_next = sizeof(Elf_Verdef) + sizeof(Elf_Verdaux);
Verdef->vd_flags = (Index == 1 ? VER_FLG_BASE : 0);
Verdef->vd_ndx = Index;
Verdef->vd_hash = hashSysV(Name);
auto *Verdaux = reinterpret_cast<Elf_Verdaux *>(Buf + sizeof(Elf_Verdef));
Verdaux->vda_name = NameOff;
Verdaux->vda_next = 0;
}
template <class ELFT>
void VersionDefinitionSection<ELFT>::writeTo(uint8_t *Buf) {
writeOne(Buf, 1, getFileDefName(), FileDefNameOff);
for (VersionDefinition &V : Config->VersionDefinitions) {
Buf += sizeof(Elf_Verdef) + sizeof(Elf_Verdaux);
writeOne(Buf, V.Id, V.Name, V.NameOff);
}
// Need to terminate the last version definition.
Elf_Verdef *Verdef = reinterpret_cast<Elf_Verdef *>(Buf);
Verdef->vd_next = 0;
}
template <class ELFT> size_t VersionDefinitionSection<ELFT>::getSize() const {
return (sizeof(Elf_Verdef) + sizeof(Elf_Verdaux)) * getVerDefNum();
}
template <class ELFT>
VersionTableSection<ELFT>::VersionTableSection()
: SyntheticSection(SHF_ALLOC, SHT_GNU_versym, sizeof(uint16_t),
".gnu.version") {
this->Entsize = sizeof(Elf_Versym);
}
template <class ELFT> void VersionTableSection<ELFT>::finalizeContents() {
// At the moment of june 2016 GNU docs does not mention that sh_link field
// should be set, but Sun docs do. Also readelf relies on this field.
getParent()->Link = InX::DynSymTab->getParent()->SectionIndex;
}
template <class ELFT> size_t VersionTableSection<ELFT>::getSize() const {
return sizeof(Elf_Versym) * (InX::DynSymTab->getSymbols().size() + 1);
}
template <class ELFT> void VersionTableSection<ELFT>::writeTo(uint8_t *Buf) {
auto *OutVersym = reinterpret_cast<Elf_Versym *>(Buf) + 1;
for (const SymbolTableEntry &S : InX::DynSymTab->getSymbols()) {
OutVersym->vs_index = S.Sym->VersionId;
++OutVersym;
}
}
template <class ELFT> bool VersionTableSection<ELFT>::empty() const {
return !In<ELFT>::VerDef && In<ELFT>::VerNeed->empty();
}
template <class ELFT>
VersionNeedSection<ELFT>::VersionNeedSection()
: SyntheticSection(SHF_ALLOC, SHT_GNU_verneed, sizeof(uint32_t),
".gnu.version_r") {
// Identifiers in verneed section start at 2 because 0 and 1 are reserved
// for VER_NDX_LOCAL and VER_NDX_GLOBAL.
// First identifiers are reserved by verdef section if it exist.
NextIndex = getVerDefNum() + 1;
}
template <class ELFT>
void VersionNeedSection<ELFT>::addSymbol(SharedSymbol *SS) {
SharedFile<ELFT> &File = SS->getFile<ELFT>();
const typename ELFT::Verdef *Ver = File.Verdefs[SS->VerdefIndex];
if (!Ver) {
SS->VersionId = VER_NDX_GLOBAL;
return;
}
// If we don't already know that we need an Elf_Verneed for this DSO, prepare
// to create one by adding it to our needed list and creating a dynstr entry
// for the soname.
if (File.VerdefMap.empty())
Needed.push_back({&File, InX::DynStrTab->addString(File.SoName)});
typename SharedFile<ELFT>::NeededVer &NV = File.VerdefMap[Ver];
// If we don't already know that we need an Elf_Vernaux for this Elf_Verdef,
// prepare to create one by allocating a version identifier and creating a
// dynstr entry for the version name.
if (NV.Index == 0) {
NV.StrTab = InX::DynStrTab->addString(File.getStringTable().data() +
Ver->getAux()->vda_name);
NV.Index = NextIndex++;
}
SS->VersionId = NV.Index;
}
template <class ELFT> void VersionNeedSection<ELFT>::writeTo(uint8_t *Buf) {
// The Elf_Verneeds need to appear first, followed by the Elf_Vernauxs.
auto *Verneed = reinterpret_cast<Elf_Verneed *>(Buf);
auto *Vernaux = reinterpret_cast<Elf_Vernaux *>(Verneed + Needed.size());
for (std::pair<SharedFile<ELFT> *, size_t> &P : Needed) {
// Create an Elf_Verneed for this DSO.
Verneed->vn_version = 1;
Verneed->vn_cnt = P.first->VerdefMap.size();
Verneed->vn_file = P.second;
Verneed->vn_aux =
reinterpret_cast<char *>(Vernaux) - reinterpret_cast<char *>(Verneed);
Verneed->vn_next = sizeof(Elf_Verneed);
++Verneed;
// Create the Elf_Vernauxs for this Elf_Verneed. The loop iterates over
// VerdefMap, which will only contain references to needed version
// definitions. Each Elf_Vernaux is based on the information contained in
// the Elf_Verdef in the source DSO. This loop iterates over a std::map of
// pointers, but is deterministic because the pointers refer to Elf_Verdef
// data structures within a single input file.
for (auto &NV : P.first->VerdefMap) {
Vernaux->vna_hash = NV.first->vd_hash;
Vernaux->vna_flags = 0;
Vernaux->vna_other = NV.second.Index;
Vernaux->vna_name = NV.second.StrTab;
Vernaux->vna_next = sizeof(Elf_Vernaux);
++Vernaux;
}
Vernaux[-1].vna_next = 0;
}
Verneed[-1].vn_next = 0;
}
template <class ELFT> void VersionNeedSection<ELFT>::finalizeContents() {
getParent()->Link = InX::DynStrTab->getParent()->SectionIndex;
getParent()->Info = Needed.size();
}
template <class ELFT> size_t VersionNeedSection<ELFT>::getSize() const {
unsigned Size = Needed.size() * sizeof(Elf_Verneed);
for (const std::pair<SharedFile<ELFT> *, size_t> &P : Needed)
Size += P.first->VerdefMap.size() * sizeof(Elf_Vernaux);
return Size;
}
template <class ELFT> bool VersionNeedSection<ELFT>::empty() const {
return getNeedNum() == 0;
}
void MergeSyntheticSection::addSection(MergeInputSection *MS) {
MS->Parent = this;
Sections.push_back(MS);
}
MergeTailSection::MergeTailSection(StringRef Name, uint32_t Type,
uint64_t Flags, uint32_t Alignment)
: MergeSyntheticSection(Name, Type, Flags, Alignment),
Builder(StringTableBuilder::RAW, Alignment) {}
size_t MergeTailSection::getSize() const { return Builder.getSize(); }
void MergeTailSection::writeTo(uint8_t *Buf) { Builder.write(Buf); }
void MergeTailSection::finalizeContents() {
// Add all string pieces to the string table builder to create section
// contents.
for (MergeInputSection *Sec : Sections)
for (size_t I = 0, E = Sec->Pieces.size(); I != E; ++I)
if (Sec->Pieces[I].Live)
Builder.add(Sec->getData(I));
// Fix the string table content. After this, the contents will never change.
Builder.finalize();
// finalize() fixed tail-optimized strings, so we can now get
// offsets of strings. Get an offset for each string and save it
// to a corresponding StringPiece for easy access.
for (MergeInputSection *Sec : Sections)
for (size_t I = 0, E = Sec->Pieces.size(); I != E; ++I)
if (Sec->Pieces[I].Live)
Sec->Pieces[I].OutputOff = Builder.getOffset(Sec->getData(I));
}
void MergeNoTailSection::writeTo(uint8_t *Buf) {
for (size_t I = 0; I < NumShards; ++I)
Shards[I].write(Buf + ShardOffsets[I]);
}
// This function is very hot (i.e. it can take several seconds to finish)
// because sometimes the number of inputs is in an order of magnitude of
// millions. So, we use multi-threading.
//
// For any strings S and T, we know S is not mergeable with T if S's hash
// value is different from T's. If that's the case, we can safely put S and
// T into different string builders without worrying about merge misses.
// We do it in parallel.
void MergeNoTailSection::finalizeContents() {
// Initializes string table builders.
for (size_t I = 0; I < NumShards; ++I)
Shards.emplace_back(StringTableBuilder::RAW, Alignment);
// Concurrency level. Must be a power of 2 to avoid expensive modulo
// operations in the following tight loop.
size_t Concurrency = 1;
if (ThreadsEnabled)
Concurrency =
std::min<size_t>(PowerOf2Floor(hardware_concurrency()), NumShards);
// Add section pieces to the builders.
parallelForEachN(0, Concurrency, [&](size_t ThreadId) {
for (MergeInputSection *Sec : Sections) {
for (size_t I = 0, E = Sec->Pieces.size(); I != E; ++I) {
size_t ShardId = getShardId(Sec->Pieces[I].Hash);
if ((ShardId & (Concurrency - 1)) == ThreadId && Sec->Pieces[I].Live)
Sec->Pieces[I].OutputOff = Shards[ShardId].add(Sec->getData(I));
}
}
});
// Compute an in-section offset for each shard.
size_t Off = 0;
for (size_t I = 0; I < NumShards; ++I) {
Shards[I].finalizeInOrder();
if (Shards[I].getSize() > 0)
Off = alignTo(Off, Alignment);
ShardOffsets[I] = Off;
Off += Shards[I].getSize();
}
Size = Off;
// So far, section pieces have offsets from beginning of shards, but
// we want offsets from beginning of the whole section. Fix them.
parallelForEach(Sections, [&](MergeInputSection *Sec) {
for (size_t I = 0, E = Sec->Pieces.size(); I != E; ++I)
if (Sec->Pieces[I].Live)
Sec->Pieces[I].OutputOff +=
ShardOffsets[getShardId(Sec->Pieces[I].Hash)];
});
}
static MergeSyntheticSection *createMergeSynthetic(StringRef Name,
uint32_t Type,
uint64_t Flags,
uint32_t Alignment) {
bool ShouldTailMerge = (Flags & SHF_STRINGS) && Config->Optimize >= 2;
if (ShouldTailMerge)
return make<MergeTailSection>(Name, Type, Flags, Alignment);
return make<MergeNoTailSection>(Name, Type, Flags, Alignment);
}
// Debug sections may be compressed by zlib. Uncompress if exists.
void elf::decompressSections() {
parallelForEach(InputSections, [](InputSectionBase *Sec) {
if (Sec->Live)
Sec->maybeUncompress();
});
}
// This function scans over the inputsections to create mergeable
// synthetic sections.
//
// It removes MergeInputSections from the input section array and adds
// new synthetic sections at the location of the first input section
// that it replaces. It then finalizes each synthetic section in order
// to compute an output offset for each piece of each input section.
void elf::mergeSections() {
// splitIntoPieces needs to be called on each MergeInputSection
// before calling finalizeContents(). Do that first.
parallelForEach(InputSections, [](InputSectionBase *Sec) {
if (Sec->Live)
if (auto *S = dyn_cast<MergeInputSection>(Sec))
S->splitIntoPieces();
});
std::vector<MergeSyntheticSection *> MergeSections;
for (InputSectionBase *&S : InputSections) {
MergeInputSection *MS = dyn_cast<MergeInputSection>(S);
if (!MS)
continue;
// We do not want to handle sections that are not alive, so just remove
// them instead of trying to merge.
if (!MS->Live)
continue;
StringRef OutsecName = getOutputSectionName(MS);
uint32_t Alignment = std::max<uint32_t>(MS->Alignment, MS->Entsize);
auto I = llvm::find_if(MergeSections, [=](MergeSyntheticSection *Sec) {
// While we could create a single synthetic section for two different
// values of Entsize, it is better to take Entsize into consideration.
//
// With a single synthetic section no two pieces with different Entsize
// could be equal, so we may as well have two sections.
//
// Using Entsize in here also allows us to propagate it to the synthetic
// section.
return Sec->Name == OutsecName && Sec->Flags == MS->Flags &&
Sec->Entsize == MS->Entsize && Sec->Alignment == Alignment;
});
if (I == MergeSections.end()) {
MergeSyntheticSection *Syn =
createMergeSynthetic(OutsecName, MS->Type, MS->Flags, Alignment);
MergeSections.push_back(Syn);
I = std::prev(MergeSections.end());
S = Syn;
Syn->Entsize = MS->Entsize;
} else {
S = nullptr;
}
(*I)->addSection(MS);
}
for (auto *MS : MergeSections)
MS->finalizeContents();
std::vector<InputSectionBase *> &V = InputSections;
V.erase(std::remove(V.begin(), V.end(), nullptr), V.end());
}
MipsRldMapSection::MipsRldMapSection()
: SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_PROGBITS, Config->Wordsize,
".rld_map") {}
ARMExidxSentinelSection::ARMExidxSentinelSection()
: SyntheticSection(SHF_ALLOC | SHF_LINK_ORDER, SHT_ARM_EXIDX,
Config->Wordsize, ".ARM.exidx") {}
// Write a terminating sentinel entry to the end of the .ARM.exidx table.
// This section will have been sorted last in the .ARM.exidx table.
// This table entry will have the form:
// | PREL31 upper bound of code that has exception tables | EXIDX_CANTUNWIND |
// The sentinel must have the PREL31 value of an address higher than any
// address described by any other table entry.
void ARMExidxSentinelSection::writeTo(uint8_t *Buf) {
assert(Highest);
uint64_t S =
Highest->getParent()->Addr + Highest->getOffset(Highest->getSize());
uint64_t P = getVA();
Target->relocateOne(Buf, R_ARM_PREL31, S - P);
write32le(Buf + 4, 1);
}
// The sentinel has to be removed if there are no other .ARM.exidx entries.
bool ARMExidxSentinelSection::empty() const {
OutputSection *OS = getParent();
for (auto *B : OS->SectionCommands)
if (auto *ISD = dyn_cast<InputSectionDescription>(B))
for (auto *S : ISD->Sections)
if (!isa<ARMExidxSentinelSection>(S))
return false;
return true;
}
ThunkSection::ThunkSection(OutputSection *OS, uint64_t Off)
: SyntheticSection(SHF_ALLOC | SHF_EXECINSTR, SHT_PROGBITS,
Config->Wordsize, ".text.thunk") {
this->Parent = OS;
this->OutSecOff = Off;
}
void ThunkSection::addThunk(Thunk *T) {
uint64_t Off = alignTo(Size, T->Alignment);
T->Offset = Off;
Thunks.push_back(T);
T->addSymbols(*this);
Size = Off + T->size();
}
void ThunkSection::writeTo(uint8_t *Buf) {
for (const Thunk *T : Thunks)
T->writeTo(Buf + T->Offset, *this);
}
InputSection *ThunkSection::getTargetInputSection() const {