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llvm-project/lld/ELF/SyntheticSections.cpp
Fangrui Song e88b7ff016 [ELF] Move InStruct into Ctx. NFC 
Ctx was introduced in March 2022 as a more suitable place for such
singletons.

llvm/Support/thread.h includes <thread>, which transitively includes
sstream in libc++ and uses ios_base::in, so we cannot use `#define in ctx.sec`.

`symtab, config, ctx` are now the only variables using
LLVM_LIBRARY_VISIBILITY.
2024-09-15 22:15:02 -07:00

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//===- SyntheticSections.cpp ----------------------------------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// 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 "Config.h"
#include "DWARF.h"
#include "EhFrame.h"
#include "InputFiles.h"
#include "LinkerScript.h"
#include "OutputSections.h"
#include "SymbolTable.h"
#include "Symbols.h"
#include "Target.h"
#include "Thunks.h"
#include "Writer.h"
#include "lld/Common/CommonLinkerContext.h"
#include "lld/Common/DWARF.h"
#include "lld/Common/Strings.h"
#include "lld/Common/Version.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/Sequence.h"
#include "llvm/ADT/SetOperations.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/BinaryFormat/Dwarf.h"
#include "llvm/BinaryFormat/ELF.h"
#include "llvm/DebugInfo/DWARF/DWARFAcceleratorTable.h"
#include "llvm/DebugInfo/DWARF/DWARFDebugPubTable.h"
#include "llvm/Support/DJB.h"
#include "llvm/Support/Endian.h"
#include "llvm/Support/LEB128.h"
#include "llvm/Support/Parallel.h"
#include "llvm/Support/TimeProfiler.h"
#include <cinttypes>
#include <cstdlib>
using namespace llvm;
using namespace llvm::dwarf;
using namespace llvm::ELF;
using namespace llvm::object;
using namespace llvm::support;
using namespace lld;
using namespace lld::elf;
using llvm::support::endian::read32le;
using llvm::support::endian::write32le;
using llvm::support::endian::write64le;
constexpr size_t MergeNoTailSection::numShards;
static uint64_t readUint(uint8_t *buf) {
return config->is64 ? read64(buf) : read32(buf);
}
static void writeUint(uint8_t *buf, uint64_t val) {
if (config->is64)
write64(buf, val);
else
write32(buf, val);
}
// Returns an LLD version string.
static ArrayRef<uint8_t> getVersion() {
// Check LLD_VERSION first for ease of testing.
// You can get consistent 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() {
auto *sec = make<MergeInputSection>(SHF_MERGE | SHF_STRINGS, SHT_PROGBITS, 1,
getVersion(), ".comment");
sec->splitIntoPieces();
return sec;
}
// .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>
std::unique_ptr<MipsAbiFlagsSection<ELFT>> MipsAbiFlagsSection<ELFT>::create() {
Elf_Mips_ABIFlags flags = {};
bool create = false;
for (InputSectionBase *sec : ctx.inputSections) {
if (sec->type != SHT_MIPS_ABIFLAGS)
continue;
sec->markDead();
create = true;
std::string filename = toString(sec->file);
const size_t size = sec->content().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->content().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 std::make_unique<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 = ctx.in.mipsGot->getGp();
memcpy(buf + sizeof(Elf_Mips_Options), &reginfo, sizeof(reginfo));
}
template <class ELFT>
std::unique_ptr<MipsOptionsSection<ELFT>> MipsOptionsSection<ELFT>::create() {
// N64 ABI only.
if (!ELFT::Is64Bits)
return nullptr;
SmallVector<InputSectionBase *, 0> sections;
for (InputSectionBase *sec : ctx.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->markDead();
std::string filename = toString(sec->file);
ArrayRef<uint8_t> d = sec->content();
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) {
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 std::make_unique<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 = ctx.in.mipsGot->getGp();
memcpy(buf, &reginfo, sizeof(reginfo));
}
template <class ELFT>
std::unique_ptr<MipsReginfoSection<ELFT>> MipsReginfoSection<ELFT>::create() {
// Section should be alive for O32 and N32 ABIs only.
if (ELFT::Is64Bits)
return nullptr;
SmallVector<InputSectionBase *, 0> sections;
for (InputSectionBase *sec : ctx.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->markDead();
if (sec->content().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->content().data());
reginfo.ri_gprmask |= r->ri_gprmask;
sec->getFile<ELFT>()->mipsGp0 = r->ri_gp_value;
};
return std::make_unique<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};
return make<InputSection>(ctx.internalFile, SHF_ALLOC, SHT_PROGBITS, 1,
contents, ".interp");
}
Defined *elf::addSyntheticLocal(StringRef name, uint8_t type, uint64_t value,
uint64_t size, InputSectionBase &section) {
Defined *s = makeDefined(section.file, name, STB_LOCAL, STV_DEFAULT, type,
value, size, &section);
if (ctx.in.symTab)
ctx.in.symTab->addSymbol(s);
if (config->emachine == EM_ARM && !config->isLE && config->armBe8 &&
(section.flags & SHF_EXECINSTR))
// Adding Linker generated mapping symbols to the arm specific mapping
// symbols list.
addArmSyntheticSectionMappingSymbol(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");
}
}
// This class represents a linker-synthesized .note.gnu.property section.
//
// In x86 and AArch64, object files may contain feature flags indicating the
// features that they have used. The flags are stored in a .note.gnu.property
// section.
//
// lld reads the sections from input files and merges them by computing AND of
// the flags. The result is written as a new .note.gnu.property section.
//
// If the flag is zero (which indicates that the intersection of the feature
// sets is empty, or some input files didn't have .note.gnu.property sections),
// we don't create this section.
GnuPropertySection::GnuPropertySection()
: SyntheticSection(llvm::ELF::SHF_ALLOC, llvm::ELF::SHT_NOTE,
config->wordsize, ".note.gnu.property") {}
void GnuPropertySection::writeTo(uint8_t *buf) {
write32(buf, 4); // Name size
write32(buf + 4, getSize() - 16); // Content size
write32(buf + 8, NT_GNU_PROPERTY_TYPE_0); // Type
memcpy(buf + 12, "GNU", 4); // Name string
uint32_t featureAndType = config->emachine == EM_AARCH64
? GNU_PROPERTY_AARCH64_FEATURE_1_AND
: GNU_PROPERTY_X86_FEATURE_1_AND;
unsigned offset = 16;
if (config->andFeatures != 0) {
write32(buf + offset + 0, featureAndType); // Feature type
write32(buf + offset + 4, 4); // Feature size
write32(buf + offset + 8, config->andFeatures); // Feature flags
if (config->is64)
write32(buf + offset + 12, 0); // Padding
offset += 16;
}
if (!ctx.aarch64PauthAbiCoreInfo.empty()) {
write32(buf + offset + 0, GNU_PROPERTY_AARCH64_FEATURE_PAUTH);
write32(buf + offset + 4, ctx.aarch64PauthAbiCoreInfo.size());
memcpy(buf + offset + 8, ctx.aarch64PauthAbiCoreInfo.data(),
ctx.aarch64PauthAbiCoreInfo.size());
}
}
size_t GnuPropertySection::getSize() const {
uint32_t contentSize = 0;
if (config->andFeatures != 0)
contentSize += config->is64 ? 16 : 12;
if (!ctx.aarch64PauthAbiCoreInfo.empty())
contentSize += 4 + 4 + ctx.aarch64PauthAbiCoreInfo.size();
assert(contentSize != 0);
return contentSize + 16;
}
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;
}
void BuildIdSection::writeBuildId(ArrayRef<uint8_t> buf) {
assert(buf.size() == hashSize);
memcpy(hashBuf, buf.data(), hashSize);
}
BssSection::BssSection(StringRef name, uint64_t size, uint32_t alignment)
: SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_NOBITS, alignment, name) {
this->bss = true;
this->size = size;
}
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) {
Symbol *personality = nullptr;
unsigned firstRelI = cie.firstRelocation;
if (firstRelI != (unsigned)-1)
personality = &cie.sec->file->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 a non-null pointer to the function
// symbol if the given FDE points to a live function.
template <class ELFT, class RelTy>
Defined *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 nullptr;
const RelTy &rel = rels[firstRelI];
Symbol &b = sec->file->getRelocTargetSym(rel);
// FDEs for garbage-collected or merged-by-ICF sections, or sections in
// another partition, are dead.
if (auto *d = dyn_cast<Defined>(&b))
if (!d->folded && d->section && d->section->partition == partition)
return d;
return nullptr;
}
// .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::addRecords(EhInputSection *sec, ArrayRef<RelTy> rels) {
offsetToCie.clear();
for (EhSectionPiece &cie : sec->cies)
offsetToCie[cie.inputOff] = addCie<ELFT>(cie, rels);
for (EhSectionPiece &fde : sec->fdes) {
uint32_t id = endian::read32<ELFT::Endianness>(fde.data().data() + 4);
CieRecord *rec = offsetToCie[fde.inputOff + 4 - id];
if (!rec)
fatal(toString(sec) + ": invalid CIE reference");
if (!isFdeLive<ELFT>(fde, rels))
continue;
rec->fdes.push_back(&fde);
numFdes++;
}
}
template <class ELFT>
void EhFrameSection::addSectionAux(EhInputSection *sec) {
if (!sec->isLive())
return;
const RelsOrRelas<ELFT> rels =
sec->template relsOrRelas<ELFT>(/*supportsCrel=*/false);
if (rels.areRelocsRel())
addRecords<ELFT>(sec, rels.rels);
else
addRecords<ELFT>(sec, rels.relas);
}
// Used by ICF<ELFT>::handleLSDA(). This function is very similar to
// EhFrameSection::addRecords().
template <class ELFT, class RelTy>
void EhFrameSection::iterateFDEWithLSDAAux(
EhInputSection &sec, ArrayRef<RelTy> rels, DenseSet<size_t> &ciesWithLSDA,
llvm::function_ref<void(InputSection &)> fn) {
for (EhSectionPiece &cie : sec.cies)
if (hasLSDA(cie))
ciesWithLSDA.insert(cie.inputOff);
for (EhSectionPiece &fde : sec.fdes) {
uint32_t id = endian::read32<ELFT::Endianness>(fde.data().data() + 4);
if (!ciesWithLSDA.contains(fde.inputOff + 4 - id))
continue;
// The CIE has a LSDA argument. Call fn with d's section.
if (Defined *d = isFdeLive<ELFT>(fde, rels))
if (auto *s = dyn_cast_or_null<InputSection>(d->section))
fn(*s);
}
}
template <class ELFT>
void EhFrameSection::iterateFDEWithLSDA(
llvm::function_ref<void(InputSection &)> fn) {
DenseSet<size_t> ciesWithLSDA;
for (EhInputSection *sec : sections) {
ciesWithLSDA.clear();
const RelsOrRelas<ELFT> rels =
sec->template relsOrRelas<ELFT>(/*supportsCrel=*/false);
if (rels.areRelocsRel())
iterateFDEWithLSDAAux<ELFT>(*sec, rels.rels, ciesWithLSDA, fn);
else
iterateFDEWithLSDAAux<ELFT>(*sec, rels.relas, ciesWithLSDA, fn);
}
}
static void writeCieFde(uint8_t *buf, ArrayRef<uint8_t> d) {
memcpy(buf, d.data(), d.size());
// Fix the size field. -4 since size does not include the size field itself.
write32(buf, d.size() - 4);
}
void EhFrameSection::finalizeContents() {
assert(!this->size); // Not finalized.
switch (config->ekind) {
case ELFNoneKind:
llvm_unreachable("invalid ekind");
case ELF32LEKind:
for (EhInputSection *sec : sections)
addSectionAux<ELF32LE>(sec);
break;
case ELF32BEKind:
for (EhInputSection *sec : sections)
addSectionAux<ELF32BE>(sec);
break;
case ELF64LEKind:
for (EhInputSection *sec : sections)
addSectionAux<ELF64LE>(sec);
break;
case ELF64BEKind:
for (EhInputSection *sec : sections)
addSectionAux<ELF64BE>(sec);
break;
}
size_t off = 0;
for (CieRecord *rec : cieRecords) {
rec->cie->outputOff = off;
off += rec->cie->size;
for (EhSectionPiece *fde : rec->fdes) {
fde->outputOff = off;
off += fde->size;
}
}
// The LSB standard does not allow a .eh_frame section with zero
// Call Frame Information records. glibc unwind-dw2-fde.c
// classify_object_over_fdes expects there is a CIE record length 0 as a
// terminator. Thus we add one unconditionally.
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.
SmallVector<EhFrameSection::FdeData, 0> EhFrameSection::getFdeData() const {
uint8_t *buf = ctx.bufferStart + getParent()->offset + outSecOff;
SmallVector<FdeData, 0> ret;
uint64_t va = getPartition().ehFrameHdr->getVA();
for (CieRecord *rec : cieRecords) {
uint8_t enc = getFdeEncoding(rec->cie);
for (EhSectionPiece *fde : rec->fdes) {
uint64_t pc = getFdePc(buf, fde->outputOff, enc);
uint64_t fdeVA = getParent()->addr + fde->outputOff;
if (!isInt<32>(pc - va)) {
errorOrWarn(toString(fde->sec) + ": PC offset is too large: 0x" +
Twine::utohexstr(pc - va));
continue;
}
ret.push_back({uint32_t(pc - va), uint32_t(fdeVA - va)});
}
}
// 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.pcRel < b.pcRel;
};
llvm::stable_sort(ret, less);
auto eq = [](const FdeData &a, const FdeData &b) {
return a.pcRel == b.pcRel;
};
ret.erase(std::unique(ret.begin(), ret.end(), eq), ret.end());
return ret;
}
static uint64_t readFdeAddr(uint8_t *buf, int size) {
switch (size) {
case DW_EH_PE_udata2:
return read16(buf);
case DW_EH_PE_sdata2:
return (int16_t)read16(buf);
case DW_EH_PE_udata4:
return read32(buf);
case DW_EH_PE_sdata4:
return (int32_t)read32(buf);
case DW_EH_PE_udata8:
case DW_EH_PE_sdata8:
return read64(buf);
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. And this offset is within
// the .eh_frame section.
size_t off = fdeOff + 8;
uint64_t addr = readFdeAddr(buf + off, enc & 0xf);
if ((enc & 0x70) == DW_EH_PE_absptr)
return config->is64 ? addr : uint32_t(addr);
if ((enc & 0x70) == DW_EH_PE_pcrel)
return addr + getParent()->addr + off + outSecOff;
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)
ctx.target->relocateAlloc(*s, buf);
if (getPartition().ehFrameHdr && getPartition().ehFrameHdr->getParent())
getPartition().ehFrameHdr->write();
}
GotSection::GotSection()
: SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_PROGBITS,
ctx.target->gotEntrySize, ".got") {
numEntries = ctx.target->gotHeaderEntriesNum;
}
void GotSection::addConstant(const Relocation &r) { relocations.push_back(r); }
void GotSection::addEntry(const Symbol &sym) {
assert(sym.auxIdx == ctx.symAux.size() - 1);
ctx.symAux.back().gotIdx = numEntries++;
}
bool GotSection::addTlsDescEntry(const Symbol &sym) {
assert(sym.auxIdx == ctx.symAux.size() - 1);
ctx.symAux.back().tlsDescIdx = numEntries;
numEntries += 2;
return true;
}
bool GotSection::addDynTlsEntry(const Symbol &sym) {
assert(sym.auxIdx == ctx.symAux.size() - 1);
ctx.symAux.back().tlsGdIdx = 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;
}
uint32_t GotSection::getTlsDescOffset(const Symbol &sym) const {
return sym.getTlsDescIdx() * config->wordsize;
}
uint64_t GotSection::getTlsDescAddr(const Symbol &sym) const {
return getVA() + getTlsDescOffset(sym);
}
uint64_t GotSection::getGlobalDynAddr(const Symbol &b) const {
return this->getVA() + b.getTlsGdIdx() * config->wordsize;
}
uint64_t GotSection::getGlobalDynOffset(const Symbol &b) const {
return b.getTlsGdIdx() * config->wordsize;
}
void GotSection::finalizeContents() {
if (config->emachine == EM_PPC64 &&
numEntries <= ctx.target->gotHeaderEntriesNum &&
!ctx.sym.globalOffsetTable)
size = 0;
else
size = numEntries * config->wordsize;
}
bool GotSection::isNeeded() const {
// Needed if the GOT symbol is used or the number of entries is more than just
// the header. A GOT with just the header may not be needed.
return hasGotOffRel || numEntries > ctx.target->gotHeaderEntriesNum;
}
void GotSection::writeTo(uint8_t *buf) {
// On PPC64 .got may be needed but empty. Skip the write.
if (size == 0)
return;
ctx.target->writeGotHeader(buf);
ctx.target->relocateAlloc(*this, buf);
}
static uint64_t getMipsPageAddr(uint64_t addr) {
return (addr + 0x8000) & ~0xffff;
}
static uint64_t getMipsPageCount(uint64_t size) {
return (size + 0xfffe) / 0xffff + 1;
}
MipsGotSection::MipsGotSection()
: SyntheticSection(SHF_ALLOC | SHF_WRITE | SHF_MIPS_GPREL, SHT_PROGBITS, 16,
".got") {}
void MipsGotSection::addEntry(InputFile &file, Symbol &sym, int64_t addend,
RelExpr expr) {
FileGot &g = getGot(file);
if (expr == R_MIPS_GOT_LOCAL_PAGE) {
if (const OutputSection *os = sym.getOutputSection())
g.pagesMap.insert({os, {}});
else
g.local16.insert({{nullptr, getMipsPageAddr(sym.getVA(addend))}, 0});
} else if (sym.isTls())
g.tls.insert({&sym, 0});
else if (sym.isPreemptible && expr == R_ABS)
g.relocs.insert({&sym, 0});
else if (sym.isPreemptible)
g.global.insert({&sym, 0});
else if (expr == R_MIPS_GOT_OFF32)
g.local32.insert({{&sym, addend}, 0});
else
g.local16.insert({{&sym, addend}, 0});
}
void MipsGotSection::addDynTlsEntry(InputFile &file, Symbol &sym) {
getGot(file).dynTlsSymbols.insert({&sym, 0});
}
void MipsGotSection::addTlsIndex(InputFile &file) {
getGot(file).dynTlsSymbols.insert({nullptr, 0});
}
size_t MipsGotSection::FileGot::getEntriesNum() const {
return getPageEntriesNum() + local16.size() + global.size() + relocs.size() +
tls.size() + dynTlsSymbols.size() * 2;
}
size_t MipsGotSection::FileGot::getPageEntriesNum() const {
size_t num = 0;
for (const std::pair<const OutputSection *, FileGot::PageBlock> &p : pagesMap)
num += p.second.count;
return num;
}
size_t MipsGotSection::FileGot::getIndexedEntriesNum() const {
size_t count = getPageEntriesNum() + local16.size() + global.size();
// If there are relocation-only entries in the GOT, TLS entries
// are allocated after them. TLS entries should be addressable
// by 16-bit index so count both reloc-only and TLS entries.
if (!tls.empty() || !dynTlsSymbols.empty())
count += relocs.size() + tls.size() + dynTlsSymbols.size() * 2;
return count;
}
MipsGotSection::FileGot &MipsGotSection::getGot(InputFile &f) {
if (f.mipsGotIndex == uint32_t(-1)) {
gots.emplace_back();
gots.back().file = &f;
f.mipsGotIndex = gots.size() - 1;
}
return gots[f.mipsGotIndex];
}
uint64_t MipsGotSection::getPageEntryOffset(const InputFile *f,
const Symbol &sym,
int64_t addend) const {
const FileGot &g = gots[f->mipsGotIndex];
uint64_t index = 0;
if (const OutputSection *outSec = sym.getOutputSection()) {
uint64_t secAddr = getMipsPageAddr(outSec->addr);
uint64_t symAddr = getMipsPageAddr(sym.getVA(addend));
index = g.pagesMap.lookup(outSec).firstIndex + (symAddr - secAddr) / 0xffff;
} else {
index = g.local16.lookup({nullptr, getMipsPageAddr(sym.getVA(addend))});
}
return index * config->wordsize;
}
uint64_t MipsGotSection::getSymEntryOffset(const InputFile *f, const Symbol &s,
int64_t addend) const {
const FileGot &g = gots[f->mipsGotIndex];
Symbol *sym = const_cast<Symbol *>(&s);
if (sym->isTls())
return g.tls.lookup(sym) * config->wordsize;
if (sym->isPreemptible)
return g.global.lookup(sym) * config->wordsize;
return g.local16.lookup({sym, addend}) * config->wordsize;
}
uint64_t MipsGotSection::getTlsIndexOffset(const InputFile *f) const {
const FileGot &g = gots[f->mipsGotIndex];
return g.dynTlsSymbols.lookup(nullptr) * config->wordsize;
}
uint64_t MipsGotSection::getGlobalDynOffset(const InputFile *f,
const Symbol &s) const {
const FileGot &g = gots[f->mipsGotIndex];
Symbol *sym = const_cast<Symbol *>(&s);
return g.dynTlsSymbols.lookup(sym) * config->wordsize;
}
const Symbol *MipsGotSection::getFirstGlobalEntry() const {
if (gots.empty())
return nullptr;
const FileGot &primGot = gots.front();
if (!primGot.global.empty())
return primGot.global.front().first;
if (!primGot.relocs.empty())
return primGot.relocs.front().first;
return nullptr;
}
unsigned MipsGotSection::getLocalEntriesNum() const {
if (gots.empty())
return headerEntriesNum;
return headerEntriesNum + gots.front().getPageEntriesNum() +
gots.front().local16.size();
}
bool MipsGotSection::tryMergeGots(FileGot &dst, FileGot &src, bool isPrimary) {
FileGot tmp = dst;
set_union(tmp.pagesMap, src.pagesMap);
set_union(tmp.local16, src.local16);
set_union(tmp.global, src.global);
set_union(tmp.relocs, src.relocs);
set_union(tmp.tls, src.tls);
set_union(tmp.dynTlsSymbols, src.dynTlsSymbols);
size_t count = isPrimary ? headerEntriesNum : 0;
count += tmp.getIndexedEntriesNum();
if (count * config->wordsize > config->mipsGotSize)
return false;
std::swap(tmp, dst);
return true;
}
void MipsGotSection::finalizeContents() { updateAllocSize(); }
bool MipsGotSection::updateAllocSize() {
size = headerEntriesNum * config->wordsize;
for (const FileGot &g : gots)
size += g.getEntriesNum() * config->wordsize;
return false;
}
void MipsGotSection::build() {
if (gots.empty())
return;
std::vector<FileGot> mergedGots(1);
// For each GOT move non-preemptible symbols from the `Global`
// to `Local16` list. Preemptible symbol might become non-preemptible
// one if, for example, it gets a related copy relocation.
for (FileGot &got : gots) {
for (auto &p: got.global)
if (!p.first->isPreemptible)
got.local16.insert({{p.first, 0}, 0});
got.global.remove_if([&](const std::pair<Symbol *, size_t> &p) {
return !p.first->isPreemptible;
});
}
// For each GOT remove "reloc-only" entry if there is "global"
// entry for the same symbol. And add local entries which indexed
// using 32-bit value at the end of 16-bit entries.
for (FileGot &got : gots) {
got.relocs.remove_if([&](const std::pair<Symbol *, size_t> &p) {
return got.global.count(p.first);
});
set_union(got.local16, got.local32);
got.local32.clear();
}
// Evaluate number of "reloc-only" entries in the resulting GOT.
// To do that put all unique "reloc-only" and "global" entries
// from all GOTs to the future primary GOT.
FileGot *primGot = &mergedGots.front();
for (FileGot &got : gots) {
set_union(primGot->relocs, got.global);
set_union(primGot->relocs, got.relocs);
got.relocs.clear();
}
// Evaluate number of "page" entries in each GOT.
for (FileGot &got : gots) {
for (std::pair<const OutputSection *, FileGot::PageBlock> &p :
got.pagesMap) {
const OutputSection *os = p.first;
uint64_t secSize = 0;
for (SectionCommand *cmd : os->commands) {
if (auto *isd = dyn_cast<InputSectionDescription>(cmd))
for (InputSection *isec : isd->sections) {
uint64_t off = alignToPowerOf2(secSize, isec->addralign);
secSize = off + isec->getSize();
}
}
p.second.count = getMipsPageCount(secSize);
}
}
// Merge GOTs. Try to join as much as possible GOTs but do not exceed
// maximum GOT size. At first, try to fill the primary GOT because
// the primary GOT can be accessed in the most effective way. If it
// is not possible, try to fill the last GOT in the list, and finally
// create a new GOT if both attempts failed.
for (FileGot &srcGot : gots) {
InputFile *file = srcGot.file;
if (tryMergeGots(mergedGots.front(), srcGot, true)) {
file->mipsGotIndex = 0;
} else {
// If this is the first time we failed to merge with the primary GOT,
// MergedGots.back() will also be the primary GOT. We must make sure not
// to try to merge again with isPrimary=false, as otherwise, if the
// inputs are just right, we could allow the primary GOT to become 1 or 2
// words bigger due to ignoring the header size.
if (mergedGots.size() == 1 ||
!tryMergeGots(mergedGots.back(), srcGot, false)) {
mergedGots.emplace_back();
std::swap(mergedGots.back(), srcGot);
}
file->mipsGotIndex = mergedGots.size() - 1;
}
}
std::swap(gots, mergedGots);
// Reduce number of "reloc-only" entries in the primary GOT
// by subtracting "global" entries in the primary GOT.
primGot = &gots.front();
primGot->relocs.remove_if([&](const std::pair<Symbol *, size_t> &p) {
return primGot->global.count(p.first);
});
// Calculate indexes for each GOT entry.
size_t index = headerEntriesNum;
for (FileGot &got : gots) {
got.startIndex = &got == primGot ? 0 : index;
for (std::pair<const OutputSection *, FileGot::PageBlock> &p :
got.pagesMap) {
// For each output section referenced by GOT page relocations calculate
// and save into pagesMap 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.firstIndex = index;
index += p.second.count;
}
for (auto &p: got.local16)
p.second = index++;
for (auto &p: got.global)
p.second = index++;
for (auto &p: got.relocs)
p.second = index++;
for (auto &p: got.tls)
p.second = index++;
for (auto &p: got.dynTlsSymbols) {
p.second = index;
index += 2;
}
}
// Update SymbolAux::gotIdx field to use this
// value later in the `sortMipsSymbols` function.
for (auto &p : primGot->global) {
if (p.first->auxIdx == 0)
p.first->allocateAux();
ctx.symAux.back().gotIdx = p.second;
}
for (auto &p : primGot->relocs) {
if (p.first->auxIdx == 0)
p.first->allocateAux();
ctx.symAux.back().gotIdx = p.second;
}
// Create dynamic relocations.
for (FileGot &got : gots) {
// Create dynamic relocations for TLS entries.
for (std::pair<Symbol *, size_t> &p : got.tls) {
Symbol *s = p.first;
uint64_t offset = p.second * config->wordsize;
// When building a shared library we still need a dynamic relocation
// for the TP-relative offset as we don't know how much other data will
// be allocated before us in the static TLS block.
if (s->isPreemptible || config->shared)
ctx.mainPart->relaDyn->addReloc(
{ctx.target->tlsGotRel, this, offset,
DynamicReloc::AgainstSymbolWithTargetVA, *s, 0, R_ABS});
}
for (std::pair<Symbol *, size_t> &p : got.dynTlsSymbols) {
Symbol *s = p.first;
uint64_t offset = p.second * config->wordsize;
if (s == nullptr) {
if (!config->shared)
continue;
ctx.mainPart->relaDyn->addReloc(
{ctx.target->tlsModuleIndexRel, this, offset});
} else {
// When building a shared library we still need a dynamic relocation
// for the module index. Therefore only checking for
// S->isPreemptible is not sufficient (this happens e.g. for
// thread-locals that have been marked as local through a linker script)
if (!s->isPreemptible && !config->shared)
continue;
ctx.mainPart->relaDyn->addSymbolReloc(ctx.target->tlsModuleIndexRel,
*this, offset, *s);
// However, we can skip writing the TLS offset reloc for non-preemptible
// symbols since it is known even in shared libraries
if (!s->isPreemptible)
continue;
offset += config->wordsize;
ctx.mainPart->relaDyn->addSymbolReloc(ctx.target->tlsOffsetRel, *this,
offset, *s);
}
}
// Do not create dynamic relocations for non-TLS
// entries in the primary GOT.
if (&got == primGot)
continue;
// Dynamic relocations for "global" entries.
for (const std::pair<Symbol *, size_t> &p : got.global) {
uint64_t offset = p.second * config->wordsize;
ctx.mainPart->relaDyn->addSymbolReloc(ctx.target->relativeRel, *this,
offset, *p.first);
}
if (!config->isPic)
continue;
// Dynamic relocations for "local" entries in case of PIC.
for (const std::pair<const OutputSection *, FileGot::PageBlock> &l :
got.pagesMap) {
size_t pageCount = l.second.count;
for (size_t pi = 0; pi < pageCount; ++pi) {
uint64_t offset = (l.second.firstIndex + pi) * config->wordsize;
ctx.mainPart->relaDyn->addReloc({ctx.target->relativeRel, this, offset,
l.first, int64_t(pi * 0x10000)});
}
}
for (const std::pair<GotEntry, size_t> &p : got.local16) {
uint64_t offset = p.second * config->wordsize;
ctx.mainPart->relaDyn->addReloc({ctx.target->relativeRel, this, offset,
DynamicReloc::AddendOnlyWithTargetVA,
*p.first.first, p.first.second, R_ABS});
}
}
}
bool MipsGotSection::isNeeded() 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 InputFile *f) const {
// For files without related GOT or files refer a primary GOT
// returns "common" _gp value. For secondary GOTs calculate
// individual _gp values.
if (!f || f->mipsGotIndex == uint32_t(-1) || f->mipsGotIndex == 0)
return ctx.sym.mipsGp->getVA(0);
return getVA() + gots[f->mipsGotIndex].startIndex * config->wordsize + 0x7ff0;
}
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));
for (const FileGot &g : gots) {
auto write = [&](size_t i, const Symbol *s, int64_t a) {
uint64_t va = a;
if (s)
va = s->getVA(a);
writeUint(buf + i * config->wordsize, va);
};
// Write 'page address' entries to the local part of the GOT.
for (const std::pair<const OutputSection *, FileGot::PageBlock> &l :
g.pagesMap) {
size_t pageCount = l.second.count;
uint64_t firstPageAddr = getMipsPageAddr(l.first->addr);
for (size_t pi = 0; pi < pageCount; ++pi)
write(l.second.firstIndex + pi, nullptr, firstPageAddr + pi * 0x10000);
}
// Local, global, TLS, reloc-only entries.
// If TLS 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.
// http://web.archive.org/web/20190324223224/https://www.linux-mips.org/wiki/NPTL
for (const std::pair<GotEntry, size_t> &p : g.local16)
write(p.second, p.first.first, p.first.second);
// Write VA to the primary GOT only. For secondary GOTs that
// will be done by REL32 dynamic relocations.
if (&g == &gots.front())
for (const std::pair<Symbol *, size_t> &p : g.global)
write(p.second, p.first, 0);
for (const std::pair<Symbol *, size_t> &p : g.relocs)
write(p.second, p.first, 0);
for (const std::pair<Symbol *, size_t> &p : g.tls)
write(p.second, p.first,
p.first->isPreemptible || config->shared ? 0 : -0x7000);
for (const std::pair<Symbol *, size_t> &p : g.dynTlsSymbols) {
if (p.first == nullptr && !config->shared)
write(p.second, nullptr, 1);
else if (p.first && !p.first->isPreemptible) {
// If we are emitting a shared library with relocations we mustn't write
// anything to the GOT here. When using Elf_Rel relocations the value
// one will be treated as an addend and will cause crashes at runtime
if (!config->shared)
write(p.second, nullptr, 1);
write(p.second + 1, p.first, -0x8000);
}
}
}
}
// On PowerPC the .plt section is used to hold the table of function addresses
// instead of the .got.plt, and the type is SHT_NOBITS similar to a .bss
// section. I don't know why we have a BSS style type for the section but it is
// consistent across both 64-bit PowerPC ABIs as well as the 32-bit PowerPC ABI.
GotPltSection::GotPltSection()
: SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_PROGBITS, config->wordsize,
".got.plt") {
if (config->emachine == EM_PPC) {
name = ".plt";
} else if (config->emachine == EM_PPC64) {
type = SHT_NOBITS;
name = ".plt";
}
}
void GotPltSection::addEntry(Symbol &sym) {
assert(sym.auxIdx == ctx.symAux.size() - 1 &&
ctx.symAux.back().pltIdx == entries.size());
entries.push_back(&sym);
}
size_t GotPltSection::getSize() const {
return (ctx.target->gotPltHeaderEntriesNum + entries.size()) *
ctx.target->gotEntrySize;
}
void GotPltSection::writeTo(uint8_t *buf) {
ctx.target->writeGotPltHeader(buf);
buf += ctx.target->gotPltHeaderEntriesNum * ctx.target->gotEntrySize;
for (const Symbol *b : entries) {
ctx.target->writeGotPlt(buf, *b);
buf += ctx.target->gotEntrySize;
}
}
bool GotPltSection::isNeeded() const {
// We need to emit GOTPLT even if it's empty if there's a relocation relative
// to it.
return !entries.empty() || hasGotPltOffRel;
}
static StringRef getIgotPltName() {
// On ARM the IgotPltSection is part of the GotSection.
if (config->emachine == EM_ARM)
return ".got";
// On PowerPC64 the GotPltSection is renamed to '.plt' so the IgotPltSection
// needs to be named the same.
if (config->emachine == EM_PPC64)
return ".plt";
return ".got.plt";
}
// On PowerPC64 the GotPltSection type is SHT_NOBITS so we have to follow suit
// with the IgotPltSection.
IgotPltSection::IgotPltSection()
: SyntheticSection(SHF_ALLOC | SHF_WRITE,
config->emachine == EM_PPC64 ? SHT_NOBITS : SHT_PROGBITS,
ctx.target->gotEntrySize, getIgotPltName()) {}
void IgotPltSection::addEntry(Symbol &sym) {
assert(ctx.symAux.back().pltIdx == entries.size());
entries.push_back(&sym);
}
size_t IgotPltSection::getSize() const {
return entries.size() * ctx.target->gotEntrySize;
}
void IgotPltSection::writeTo(uint8_t *buf) {
for (const Symbol *b : entries) {
ctx.target->writeIgotPlt(buf, *b);
buf += ctx.target->gotEntrySize;
}
}
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.
strings.push_back("");
stringMap.try_emplace(CachedHashStringRef(""), 0);
size = 1;
}
// 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.try_emplace(CachedHashStringRef(s), size);
if (!r.second)
return r.first->second;
}
if (s.empty())
return 0;
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 entries in .gnu.version_d: the number of
// non-VER_NDX_LOCAL-non-VER_NDX_GLOBAL definitions, plus 1.
// Note that we don't support vd_cnt > 1 yet.
static unsigned getVerDefNum() {
return namedVersionDefs().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;
}
// The output section .rela.dyn may include these synthetic sections:
//
// - part.relaDyn
// - ctx.in.relaPlt: this is included if a linker script places .rela.plt inside
// .rela.dyn
//
// DT_RELASZ is the total size of the included sections.
static uint64_t addRelaSz(const RelocationBaseSection &relaDyn) {
size_t size = relaDyn.getSize();
if (ctx.in.relaPlt->getParent() == relaDyn.getParent())
size += ctx.in.relaPlt->getSize();
return size;
}
// A Linker script may assign the RELA relocation sections to the same
// output section. When this occurs we cannot just use the OutputSection
// Size. Moreover the [DT_JMPREL, DT_JMPREL + DT_PLTRELSZ) is permitted to
// overlap with the [DT_RELA, DT_RELA + DT_RELASZ).
static uint64_t addPltRelSz() { return ctx.in.relaPlt->getSize(); }
// Add remaining entries to complete .dynamic contents.
template <class ELFT>
std::vector<std::pair<int32_t, uint64_t>>
DynamicSection<ELFT>::computeContents() {
elf::Partition &part = getPartition();
bool isMain = part.name.empty();
std::vector<std::pair<int32_t, uint64_t>> entries;
auto addInt = [&](int32_t tag, uint64_t val) {
entries.emplace_back(tag, val);
};
auto addInSec = [&](int32_t tag, const InputSection &sec) {
entries.emplace_back(tag, sec.getVA());
};
for (StringRef s : config->filterList)
addInt(DT_FILTER, part.dynStrTab->addString(s));
for (StringRef s : config->auxiliaryList)
addInt(DT_AUXILIARY, part.dynStrTab->addString(s));
if (!config->rpath.empty())
addInt(config->enableNewDtags ? DT_RUNPATH : DT_RPATH,
part.dynStrTab->addString(config->rpath));
for (SharedFile *file : ctx.sharedFiles)
if (file->isNeeded)
addInt(DT_NEEDED, part.dynStrTab->addString(file->soName));
if (isMain) {
if (!config->soName.empty())
addInt(DT_SONAME, part.dynStrTab->addString(config->soName));
} else {
if (!config->soName.empty())
addInt(DT_NEEDED, part.dynStrTab->addString(config->soName));
addInt(DT_SONAME, part.dynStrTab->addString(part.name));
}
// Set DT_FLAGS and DT_FLAGS_1.
uint32_t dtFlags = 0;
uint32_t dtFlags1 = 0;
if (config->bsymbolic == BsymbolicKind::All)
dtFlags |= DF_SYMBOLIC;
if (config->zGlobal)
dtFlags1 |= DF_1_GLOBAL;
if (config->zInitfirst)
dtFlags1 |= DF_1_INITFIRST;
if (config->zInterpose)
dtFlags1 |= DF_1_INTERPOSE;
if (config->zNodefaultlib)
dtFlags1 |= DF_1_NODEFLIB;
if (config->zNodelete)
dtFlags1 |= DF_1_NODELETE;
if (config->zNodlopen)
dtFlags1 |= DF_1_NOOPEN;
if (config->pie)
dtFlags1 |= DF_1_PIE;
if (config->zNow) {
dtFlags |= DF_BIND_NOW;
dtFlags1 |= DF_1_NOW;
}
if (config->zOrigin) {
dtFlags |= DF_ORIGIN;
dtFlags1 |= DF_1_ORIGIN;
}
if (!config->zText)
dtFlags |= DF_TEXTREL;
if (ctx.hasTlsIe && config->shared)
dtFlags |= DF_STATIC_TLS;
if (dtFlags)
addInt(DT_FLAGS, dtFlags);
if (dtFlags1)
addInt(DT_FLAGS_1, dtFlags1);
// DT_DEBUG is a pointer to debug information 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);
if (part.relaDyn->isNeeded()) {
addInSec(part.relaDyn->dynamicTag, *part.relaDyn);
entries.emplace_back(part.relaDyn->sizeDynamicTag,
addRelaSz(*part.relaDyn));
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 = part.relaDyn->getRelativeRelocCount();
if (config->zCombreloc && numRelativeRels)
addInt(isRela ? DT_RELACOUNT : DT_RELCOUNT, numRelativeRels);
}
}
if (part.relrDyn && part.relrDyn->getParent() &&
!part.relrDyn->relocs.empty()) {
addInSec(config->useAndroidRelrTags ? DT_ANDROID_RELR : DT_RELR,
*part.relrDyn);
addInt(config->useAndroidRelrTags ? DT_ANDROID_RELRSZ : DT_RELRSZ,
part.relrDyn->getParent()->size);
addInt(config->useAndroidRelrTags ? DT_ANDROID_RELRENT : DT_RELRENT,
sizeof(Elf_Relr));
}
if (part.relrAuthDyn && part.relrAuthDyn->getParent() &&
!part.relrAuthDyn->relocs.empty()) {
addInSec(DT_AARCH64_AUTH_RELR, *part.relrAuthDyn);
addInt(DT_AARCH64_AUTH_RELRSZ, part.relrAuthDyn->getParent()->size);
addInt(DT_AARCH64_AUTH_RELRENT, sizeof(Elf_Relr));
}
if (isMain && ctx.in.relaPlt->isNeeded()) {
addInSec(DT_JMPREL, *ctx.in.relaPlt);
entries.emplace_back(DT_PLTRELSZ, addPltRelSz());
switch (config->emachine) {
case EM_MIPS:
addInSec(DT_MIPS_PLTGOT, *ctx.in.gotPlt);
break;
case EM_S390:
addInSec(DT_PLTGOT, *ctx.in.got);
break;
case EM_SPARCV9:
addInSec(DT_PLTGOT, *ctx.in.plt);
break;
case EM_AARCH64:
if (llvm::find_if(ctx.in.relaPlt->relocs, [](const DynamicReloc &r) {
return r.type == ctx.target->pltRel &&
r.sym->stOther & STO_AARCH64_VARIANT_PCS;
}) != ctx.in.relaPlt->relocs.end())
addInt(DT_AARCH64_VARIANT_PCS, 0);
addInSec(DT_PLTGOT, *ctx.in.gotPlt);
break;
case EM_RISCV:
if (llvm::any_of(ctx.in.relaPlt->relocs, [](const DynamicReloc &r) {
return r.type == ctx.target->pltRel &&
(r.sym->stOther & STO_RISCV_VARIANT_CC);
}))
addInt(DT_RISCV_VARIANT_CC, 0);
[[fallthrough]];
default:
addInSec(DT_PLTGOT, *ctx.in.gotPlt);
break;
}
addInt(DT_PLTREL, config->isRela ? DT_RELA : DT_REL);
}
if (config->emachine == EM_AARCH64) {
if (config->andFeatures & GNU_PROPERTY_AARCH64_FEATURE_1_BTI)
addInt(DT_AARCH64_BTI_PLT, 0);
if (config->zPacPlt)
addInt(DT_AARCH64_PAC_PLT, 0);
if (hasMemtag()) {
addInt(DT_AARCH64_MEMTAG_MODE, config->androidMemtagMode == NT_MEMTAG_LEVEL_ASYNC);
addInt(DT_AARCH64_MEMTAG_HEAP, config->androidMemtagHeap);
addInt(DT_AARCH64_MEMTAG_STACK, config->androidMemtagStack);
if (ctx.mainPart->memtagGlobalDescriptors->isNeeded()) {
addInSec(DT_AARCH64_MEMTAG_GLOBALS,
*ctx.mainPart->memtagGlobalDescriptors);
addInt(DT_AARCH64_MEMTAG_GLOBALSSZ,
ctx.mainPart->memtagGlobalDescriptors->getSize());
}
}
}
addInSec(DT_SYMTAB, *part.dynSymTab);
addInt(DT_SYMENT, sizeof(Elf_Sym));
addInSec(DT_STRTAB, *part.dynStrTab);
addInt(DT_STRSZ, part.dynStrTab->getSize());
if (!config->zText)
addInt(DT_TEXTREL, 0);
if (part.gnuHashTab && part.gnuHashTab->getParent())
addInSec(DT_GNU_HASH, *part.gnuHashTab);
if (part.hashTab && part.hashTab->getParent())
addInSec(DT_HASH, *part.hashTab);
if (isMain) {
if (ctx.out.preinitArray) {
addInt(DT_PREINIT_ARRAY, ctx.out.preinitArray->addr);
addInt(DT_PREINIT_ARRAYSZ, ctx.out.preinitArray->size);
}
if (ctx.out.initArray) {
addInt(DT_INIT_ARRAY, ctx.out.initArray->addr);
addInt(DT_INIT_ARRAYSZ, ctx.out.initArray->size);
}
if (ctx.out.finiArray) {
addInt(DT_FINI_ARRAY, ctx.out.finiArray->addr);
addInt(DT_FINI_ARRAYSZ, ctx.out.finiArray->size);
}
if (Symbol *b = symtab.find(config->init))
if (b->isDefined())
addInt(DT_INIT, b->getVA());
if (Symbol *b = symtab.find(config->fini))
if (b->isDefined())
addInt(DT_FINI, b->getVA());
}
if (part.verSym && part.verSym->isNeeded())
addInSec(DT_VERSYM, *part.verSym);
if (part.verDef && part.verDef->isLive()) {
addInSec(DT_VERDEF, *part.verDef);
addInt(DT_VERDEFNUM, getVerDefNum());
}
if (part.verNeed && part.verNeed->isNeeded()) {
addInSec(DT_VERNEED, *part.verNeed);
unsigned needNum = 0;
for (SharedFile *f : ctx.sharedFiles)
if (!f->vernauxs.empty())
++needNum;
addInt(DT_VERNEEDNUM, needNum);
}
if (config->emachine == EM_MIPS) {
addInt(DT_MIPS_RLD_VERSION, 1);
addInt(DT_MIPS_FLAGS, RHF_NOTPOT);
addInt(DT_MIPS_BASE_ADDRESS, ctx.target->getImageBase());
addInt(DT_MIPS_SYMTABNO, part.dynSymTab->getNumSymbols());
addInt(DT_MIPS_LOCAL_GOTNO, ctx.in.mipsGot->getLocalEntriesNum());
if (const Symbol *b = ctx.in.mipsGot->getFirstGlobalEntry())
addInt(DT_MIPS_GOTSYM, b->dynsymIndex);
else
addInt(DT_MIPS_GOTSYM, part.dynSymTab->getNumSymbols());
addInSec(DT_PLTGOT, *ctx.in.mipsGot);
if (ctx.in.mipsRldMap) {
if (!config->pie)
addInSec(DT_MIPS_RLD_MAP, *ctx.in.mipsRldMap);
// Store the offset to the .rld_map section
// relative to the address of the tag.
addInt(DT_MIPS_RLD_MAP_REL,
ctx.in.mipsRldMap->getVA() - (getVA() + entries.size() * entsize));
}
}
// DT_PPC_GOT indicates to glibc Secure PLT is used. If DT_PPC_GOT is absent,
// glibc assumes the old-style BSS PLT layout which we don't support.
if (config->emachine == EM_PPC)
addInSec(DT_PPC_GOT, *ctx.in.got);
// Glink dynamic tag is required by the V2 abi if the plt section isn't empty.
if (config->emachine == EM_PPC64 && ctx.in.plt->isNeeded()) {
// The Glink tag points to 32 bytes before the first lazy symbol resolution
// stub, which starts directly after the header.
addInt(DT_PPC64_GLINK,
ctx.in.plt->getVA() + ctx.target->pltHeaderSize - 32);
}
if (config->emachine == EM_PPC64)
addInt(DT_PPC64_OPT, getPPC64TargetInfo()->ppc64DynamicSectionOpt);
addInt(DT_NULL, 0);
return entries;
}
template <class ELFT> void DynamicSection<ELFT>::finalizeContents() {
if (OutputSection *sec = getPartition().dynStrTab->getParent())
getParent()->link = sec->sectionIndex;
this->size = computeContents().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, uint64_t> kv : computeContents()) {
p->d_tag = kv.first;
p->d_un.d_val = kv.second;
++p;
}
}
uint64_t DynamicReloc::getOffset() const {
return inputSec->getVA(offsetInSec);
}
int64_t DynamicReloc::computeAddend() const {
switch (kind) {
case AddendOnly:
assert(sym == nullptr);
return addend;
case AgainstSymbol:
assert(sym != nullptr);
return addend;
case AddendOnlyWithTargetVA:
case AgainstSymbolWithTargetVA: {
uint64_t ca = InputSection::getRelocTargetVA(inputSec->file, type, addend,
getOffset(), *sym, expr);
return config->is64 ? ca : SignExtend64<32>(ca);
}
case MipsMultiGotPage:
assert(sym == nullptr);
return getMipsPageAddr(outputSec->addr) + addend;
}
llvm_unreachable("Unknown DynamicReloc::Kind enum");
}
uint32_t DynamicReloc::getSymIndex(SymbolTableBaseSection *symTab) const {
if (!needsDynSymIndex())
return 0;
size_t index = symTab->getSymbolIndex(*sym);
assert((index != 0 ||
(type != ctx.target->gotRel && type != ctx.target->pltRel) ||
!ctx.mainPart->dynSymTab->getParent()) &&
"GOT or PLT relocation must refer to symbol in dynamic symbol table");
return index;
}
RelocationBaseSection::RelocationBaseSection(StringRef name, uint32_t type,
int32_t dynamicTag,
int32_t sizeDynamicTag,
bool combreloc,
unsigned concurrency)
: SyntheticSection(SHF_ALLOC, type, config->wordsize, name),
dynamicTag(dynamicTag), sizeDynamicTag(sizeDynamicTag),
relocsVec(concurrency), combreloc(combreloc) {}
void RelocationBaseSection::addSymbolReloc(
RelType dynType, InputSectionBase &isec, uint64_t offsetInSec, Symbol &sym,
int64_t addend, std::optional<RelType> addendRelType) {
addReloc(DynamicReloc::AgainstSymbol, dynType, isec, offsetInSec, sym, addend,
R_ADDEND, addendRelType ? *addendRelType : ctx.target->noneRel);
}
void RelocationBaseSection::addAddendOnlyRelocIfNonPreemptible(
RelType dynType, InputSectionBase &isec, uint64_t offsetInSec, Symbol &sym,
RelType addendRelType) {
// No need to write an addend to the section for preemptible symbols.
if (sym.isPreemptible)
addReloc({dynType, &isec, offsetInSec, DynamicReloc::AgainstSymbol, sym, 0,
R_ABS});
else
addReloc(DynamicReloc::AddendOnlyWithTargetVA, dynType, isec, offsetInSec,
sym, 0, R_ABS, addendRelType);
}
void RelocationBaseSection::mergeRels() {
size_t newSize = relocs.size();
for (const auto &v : relocsVec)
newSize += v.size();
relocs.reserve(newSize);
for (const auto &v : relocsVec)
llvm::append_range(relocs, v);
relocsVec.clear();
}
void RelocationBaseSection::partitionRels() {
if (!combreloc)
return;
const RelType relativeRel = ctx.target->relativeRel;
numRelativeRelocs =
std::stable_partition(relocs.begin(), relocs.end(),
[=](auto &r) { return r.type == relativeRel; }) -
relocs.begin();
}
void RelocationBaseSection::finalizeContents() {
SymbolTableBaseSection *symTab = getPartition().dynSymTab.get();
// When linking glibc statically, .rel{,a}.plt contains R_*_IRELATIVE
// relocations due to IFUNC (e.g. strcpy). sh_link will be set to 0 in that
// case.
if (symTab && symTab->getParent())
getParent()->link = symTab->getParent()->sectionIndex;
else
getParent()->link = 0;
if (ctx.in.relaPlt.get() == this && ctx.in.gotPlt->getParent()) {
getParent()->flags |= ELF::SHF_INFO_LINK;
getParent()->info = ctx.in.gotPlt->getParent()->sectionIndex;
}
}
void DynamicReloc::computeRaw(SymbolTableBaseSection *symtab) {
r_offset = getOffset();
r_sym = getSymIndex(symtab);
addend = computeAddend();
kind = AddendOnly; // Catch errors
}
void RelocationBaseSection::computeRels() {
SymbolTableBaseSection *symTab = getPartition().dynSymTab.get();
parallelForEach(relocs,
[symTab](DynamicReloc &rel) { rel.computeRaw(symTab); });
auto irelative = std::stable_partition(
relocs.begin() + numRelativeRelocs, relocs.end(),
[t = ctx.target->iRelativeRel](auto &r) { return r.type != t; });
// Sort by (!IsRelative,SymIndex,r_offset). DT_REL[A]COUNT requires us to
// place R_*_RELATIVE first. SymIndex is to improve locality, while r_offset
// is to make results easier to read.
if (combreloc) {
auto nonRelative = relocs.begin() + numRelativeRelocs;
parallelSort(relocs.begin(), nonRelative,
[&](auto &a, auto &b) { return a.r_offset < b.r_offset; });
// Non-relative relocations are few, so don't bother with parallelSort.
llvm::sort(nonRelative, irelative, [&](auto &a, auto &b) {
return std::tie(a.r_sym, a.r_offset) < std::tie(b.r_sym, b.r_offset);
});
}
}
template <class ELFT>
RelocationSection<ELFT>::RelocationSection(StringRef name, bool combreloc,
unsigned concurrency)
: RelocationBaseSection(name, config->isRela ? SHT_RELA : SHT_REL,
config->isRela ? DT_RELA : DT_REL,
config->isRela ? DT_RELASZ : DT_RELSZ, combreloc,
concurrency) {
this->entsize = config->isRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel);
}
template <class ELFT> void RelocationSection<ELFT>::writeTo(uint8_t *buf) {
computeRels();
for (const DynamicReloc &rel : relocs) {
auto *p = reinterpret_cast<Elf_Rela *>(buf);
p->r_offset = rel.r_offset;
p->setSymbolAndType(rel.r_sym, rel.type, config->isMips64EL);
if (config->isRela)
p->r_addend = rel.addend;
buf += config->isRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel);
}
}
RelrBaseSection::RelrBaseSection(unsigned concurrency, bool isAArch64Auth)
: SyntheticSection(
SHF_ALLOC,
isAArch64Auth
? SHT_AARCH64_AUTH_RELR
: (config->useAndroidRelrTags ? SHT_ANDROID_RELR : SHT_RELR),
config->wordsize, isAArch64Auth ? ".relr.auth.dyn" : ".relr.dyn"),
relocsVec(concurrency) {}
void RelrBaseSection::mergeRels() {
size_t newSize = relocs.size();
for (const auto &v : relocsVec)
newSize += v.size();
relocs.reserve(newSize);
for (const auto &v : relocsVec)
llvm::append_range(relocs, v);
relocsVec.clear();
}
template <class ELFT>
AndroidPackedRelocationSection<ELFT>::AndroidPackedRelocationSection(
StringRef name, unsigned concurrency)
: 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,
/*combreloc=*/false, concurrency) {
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;
r.r_offset = rel.getOffset();
r.setSymbolAndType(rel.getSymIndex(getPartition().dynSymTab.get()),
rel.type, false);
r.r_addend = config->isRela ? rel.computeAddend() : 0;
if (r.getType(config->isMips64EL) == ctx.target->relativeRel)
relatives.push_back(r);
else
nonRelatives.push_back(r);
}
llvm::sort(relatives, [](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));
}
// For non-relative relocations, we would like to:
// 1. Have relocations with the same symbol offset to be consecutive, so
// that the runtime linker can speed-up symbol lookup by implementing an
// 1-entry cache.
// 2. Group relocations by r_info to reduce the size of the relocation
// section.
// Since the symbol offset is the high bits in r_info, sorting by r_info
// allows us to do both.
//
// For Rela, we also want to sort by r_addend when r_info is the same. This
// enables us to group by r_addend as well.
llvm::sort(nonRelatives, [](const Elf_Rela &a, const Elf_Rela &b) {
if (a.r_info != b.r_info)
return a.r_info < b.r_info;
if (a.r_addend != b.r_addend)
return a.r_addend < b.r_addend;
return a.r_offset < b.r_offset;
});
// Group relocations with the same r_info. Note that each group emits a group
// header and that may make the relocation section larger. It is hard to
// estimate the size of a group header as the encoded size of that varies
// based on r_info. However, we can approximate this trade-off by the number
// of values encoded. Each group header contains 3 values, and each relocation
// in a group encodes one less value, as compared to when it is not grouped.
// Therefore, we only group relocations if there are 3 or more of them with
// the same r_info.
//
// For Rela, the addend for most non-relative relocations is zero, and thus we
// can usually get a smaller relocation section if we group relocations with 0
// addend as well.
std::vector<Elf_Rela> ungroupedNonRelatives;
std::vector<std::vector<Elf_Rela>> nonRelativeGroups;
for (auto i = nonRelatives.begin(), e = nonRelatives.end(); i != e;) {
auto j = i + 1;
while (j != e && i->r_info == j->r_info &&
(!config->isRela || i->r_addend == j->r_addend))
++j;
if (j - i < 3 || (config->isRela && i->r_addend != 0))
ungroupedNonRelatives.insert(ungroupedNonRelatives.end(), i, j);
else
nonRelativeGroups.emplace_back(i, j);
i = j;
}
// Sort ungrouped relocations by offset to minimize the encoded length.
llvm::sort(ungroupedNonRelatives, [](const Elf_Rela &a, const Elf_Rela &b) {
return a.r_offset < b.r_offset;
});
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(ctx.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(ctx.target->relativeRel);
if (config->isRela) {
for (const auto &i : llvm::drop_begin(g)) {
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(ctx.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;
}
}
}
// Grouped non-relatives.
for (ArrayRef<Elf_Rela> g : nonRelativeGroups) {
add(g.size());
add(RELOCATION_GROUPED_BY_INFO_FLAG);
add(g[0].r_info);
for (const Elf_Rela &r : g) {
add(r.r_offset - offset);
offset = r.r_offset;
}
addend = 0;
}
// Finally the ungrouped non-relative relocations.
if (!ungroupedNonRelatives.empty()) {
add(ungroupedNonRelatives.size());
add(hasAddendIfRela);
for (Elf_Rela &r : ungroupedNonRelatives) {
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;
}
}
}
// Don't allow the section to shrink; otherwise the size of the section can
// oscillate infinitely.
if (relocData.size() < oldSize)
relocData.append(oldSize - relocData.size(), 0);
// 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;
}
template <class ELFT>
RelrSection<ELFT>::RelrSection(unsigned concurrency, bool isAArch64Auth)
: RelrBaseSection(concurrency, isAArch64Auth) {
this->entsize = config->wordsize;
}
template <class ELFT> bool RelrSection<ELFT>::updateAllocSize() {
// This function computes the contents of an SHT_RELR packed relocation
// section.
//
// Proposal for adding SHT_RELR sections to generic-abi is here:
// https://groups.google.com/forum/#!topic/generic-abi/bX460iggiKg
//
// The encoded sequence of Elf64_Relr entries in a SHT_RELR section looks
// like [ AAAAAAAA BBBBBBB1 BBBBBBB1 ... AAAAAAAA BBBBBB1 ... ]
//
// i.e. start with an address, followed by any number of bitmaps. The address
// entry encodes 1 relocation. The subsequent bitmap entries encode up to 63
// relocations each, at subsequent offsets following the last address entry.
//
// The bitmap entries must have 1 in the least significant bit. The assumption
// here is that an address cannot have 1 in lsb. Odd addresses are not
// supported.
//
// Excluding the least significant bit in the bitmap, each non-zero bit in
// the bitmap represents a relocation to be applied to a corresponding machine
// word that follows the base address word. The second least significant bit
// represents the machine word immediately following the initial address, and
// each bit that follows represents the next word, in linear order. As such,
// a single bitmap can encode up to 31 relocations in a 32-bit object, and
// 63 relocations in a 64-bit object.
//
// This encoding has a couple of interesting properties:
// 1. Looking at any entry, it is clear whether it's an address or a bitmap:
// even means address, odd means bitmap.
// 2. Just a simple list of addresses is a valid encoding.
size_t oldSize = relrRelocs.size();
relrRelocs.clear();
// Same as Config->Wordsize but faster because this is a compile-time
// constant.
const size_t wordsize = sizeof(typename ELFT::uint);
// Number of bits to use for the relocation offsets bitmap.
// Must be either 63 or 31.
const size_t nBits = wordsize * 8 - 1;
// Get offsets for all relative relocations and sort them.
std::unique_ptr<uint64_t[]> offsets(new uint64_t[relocs.size()]);
for (auto [i, r] : llvm::enumerate(relocs))
offsets[i] = r.getOffset();
llvm::sort(offsets.get(), offsets.get() + relocs.size());
// For each leading relocation, find following ones that can be folded
// as a bitmap and fold them.
for (size_t i = 0, e = relocs.size(); i != e;) {
// Add a leading relocation.
relrRelocs.push_back(Elf_Relr(offsets[i]));
uint64_t base = offsets[i] + wordsize;
++i;
// Find foldable relocations to construct bitmaps.
for (;;) {
uint64_t bitmap = 0;
for (; i != e; ++i) {
uint64_t d = offsets[i] - base;
if (d >= nBits * wordsize || d % wordsize)
break;
bitmap |= uint64_t(1) << (d / wordsize);
}
if (!bitmap)
break;
relrRelocs.push_back(Elf_Relr((bitmap << 1) | 1));
base += nBits * wordsize;
}
}
// Don't allow the section to shrink; otherwise the size of the section can
// oscillate infinitely. Trailing 1s do not decode to more relocations.
if (relrRelocs.size() < oldSize) {
log(".relr.dyn needs " + Twine(oldSize - relrRelocs.size()) +
" padding word(s)");
relrRelocs.resize(oldSize, Elf_Relr(1));
}
return relrRelocs.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 beginning of a dynsym in arbitrary order.
if (l.sym->isInGot() && r.sym->isInGot())
return l.sym->getGotIdx() < r.sym->getGotIdx();
if (!l.sym->isInGot() && !r.sym->isInGot())
return false;
return !l.sym->isInGot();
}
void SymbolTableBaseSection::finalizeContents() {
if (OutputSection *sec = strTabSec.getParent())
getParent()->link = sec->sectionIndex;
if (this->type != SHT_DYNSYM) {
sortSymTabSymbols();
return;
}
// If it is a .dynsym, there should be no local symbols, but we need
// to do a few things for the dynamic linker.
// 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 (getPartition().gnuHashTab) {
// NB: It also sorts Symbols to meet the GNU hash table requirements.
getPartition().gnuHashTab->addSymbols(symbols);
} else if (config->emachine == EM_MIPS) {
llvm::stable_sort(symbols, sortMipsSymbols);
}
// Only the main partition's dynsym indexes are stored in the symbols
// themselves. All other partitions use a lookup table.
if (this == ctx.mainPart->dynSymTab.get()) {
size_t i = 0;
for (const SymbolTableEntry &s : symbols)
s.sym->dynsymIndex = ++i;
}
}
// 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.)
//
// Aside from above, we put local symbols in groups starting with the STT_FILE
// symbol. That is convenient for purpose of identifying where are local symbols
// coming from.
void SymbolTableBaseSection::sortSymTabSymbols() {
// Move all local symbols before global symbols.
auto e = std::stable_partition(
symbols.begin(), symbols.end(),
[](const SymbolTableEntry &s) { return s.sym->isLocal(); });
size_t numLocals = e - symbols.begin();
getParent()->info = numLocals + 1;
// We want to group the local symbols by file. For that we rebuild the local
// part of the symbols vector. We do not need to care about the STT_FILE
// symbols, they are already naturally placed first in each group. That
// happens because STT_FILE is always the first symbol in the object and hence
// precede all other local symbols we add for a file.
MapVector<InputFile *, SmallVector<SymbolTableEntry, 0>> arr;
for (const SymbolTableEntry &s : llvm::make_range(symbols.begin(), e))
arr[s.sym->file].push_back(s);
auto i = symbols.begin();
for (auto &p : arr)
for (SymbolTableEntry &entry : p.second)
*i++ = entry;
}
void SymbolTableBaseSection::addSymbol(Symbol *b) {
// Adding a local symbol to a .dynsym is a bug.
assert(this->type != SHT_DYNSYM || !b->isLocal());
symbols.push_back({b, strTabSec.addString(b->getName(), false)});
}
size_t SymbolTableBaseSection::getSymbolIndex(const Symbol &sym) {
if (this == ctx.mainPart->dynSymTab.get())
return sym.dynsymIndex;
// Initializes symbol lookup tables lazily. This is used only for -r,
// --emit-relocs and dynsyms in partitions other than the main one.
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);
}
static BssSection *getCommonSec(Symbol *sym) {
if (config->relocatable)
if (auto *d = dyn_cast<Defined>(sym))
return dyn_cast_or_null<BssSection>(d->section);
return nullptr;
}
static uint32_t getSymSectionIndex(Symbol *sym) {
assert(!(sym->hasFlag(NEEDS_COPY) && sym->isObject()));
if (!isa<Defined>(sym) || sym->hasFlag(NEEDS_COPY))
return SHN_UNDEF;
if (const OutputSection *os = sym->getOutputSection())
return os->sectionIndex >= SHN_LORESERVE ? (uint32_t)SHN_XINDEX
: os->sectionIndex;
return SHN_ABS;
}
// 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.
buf += sizeof(Elf_Sym);
auto *eSym = reinterpret_cast<Elf_Sym *>(buf);
for (SymbolTableEntry &ent : symbols) {
Symbol *sym = ent.sym;
bool isDefinedHere = type == SHT_SYMTAB || sym->partition == partition;
// Set st_name, st_info and st_other.
eSym->st_name = ent.strTabOffset;
eSym->setBindingAndType(sym->binding, sym->type);
eSym->st_other = sym->stOther;
if (BssSection *commonSec = getCommonSec(sym)) {
// When -r is specified, a COMMON symbol is not allocated. Its st_shndx
// holds SHN_COMMON and st_value holds the alignment.
eSym->st_shndx = SHN_COMMON;
eSym->st_value = commonSec->addralign;
eSym->st_size = cast<Defined>(sym)->size;
} else {
const uint32_t shndx = getSymSectionIndex(sym);
if (isDefinedHere) {
eSym->st_shndx = shndx;
eSym->st_value = sym->getVA();
// 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.
eSym->st_size = shndx != SHN_UNDEF ? cast<Defined>(sym)->size : 0;
} else {
eSym->st_shndx = 0;
eSym->st_value = 0;
eSym->st_size = 0;
}
}
++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->hasFlag(NEEDS_COPY))
eSym->st_other |= STO_MIPS_PLT;
if (isMicroMips()) {
// We already set the less-significant bit for symbols
// marked by the `STO_MIPS_MICROMIPS` flag and for microMIPS PLT
// records. That allows us to distinguish such symbols in
// the `MIPS<ELFT>::relocate()` routine. Now we should
// clear that bit for non-dynamic symbol table, so tools
// like `objdump` will be able to deal with a correct
// symbol position.
if (sym->isDefined() &&
((sym->stOther & STO_MIPS_MICROMIPS) || sym->hasFlag(NEEDS_COPY))) {
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;
}
}
}
SymtabShndxSection::SymtabShndxSection()
: SyntheticSection(0, SHT_SYMTAB_SHNDX, 4, ".symtab_shndx") {
this->entsize = 4;
}
void SymtabShndxSection::writeTo(uint8_t *buf) {
// We write an array of 32 bit values, where each value has 1:1 association
// with an entry in .symtab. If the corresponding entry contains SHN_XINDEX,
// we need to write actual index, otherwise, we must write SHN_UNDEF(0).
buf += 4; // Ignore .symtab[0] entry.
for (const SymbolTableEntry &entry : ctx.in.symTab->getSymbols()) {
if (!getCommonSec(entry.sym) && getSymSectionIndex(entry.sym) == SHN_XINDEX)
write32(buf, entry.sym->getOutputSection()->sectionIndex);
buf += 4;
}
}
bool SymtabShndxSection::isNeeded() const {
// SHT_SYMTAB can hold symbols with section indices values up to
// SHN_LORESERVE. If we need more, we want to use extension SHT_SYMTAB_SHNDX
// section. Problem is that we reveal the final section indices a bit too
// late, and we do not know them here. For simplicity, we just always create
// a .symtab_shndx section when the amount of output sections is huge.
size_t size = 0;
for (SectionCommand *cmd : ctx.script->sectionCommands)
if (isa<OutputDesc>(cmd))
++size;
return size >= SHN_LORESERVE;
}
void SymtabShndxSection::finalizeContents() {
getParent()->link = ctx.in.symTab->getParent()->sectionIndex;
}
size_t SymtabShndxSection::getSize() const {
return ctx.in.symTab->getNumSymbols() * 4;
}
// .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.
//
// 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 substantially
// 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 compatibility.
GnuHashTableSection::GnuHashTableSection()
: SyntheticSection(SHF_ALLOC, SHT_GNU_HASH, config->wordsize, ".gnu.hash") {
}
void GnuHashTableSection::finalizeContents() {
if (OutputSection *sec = getPartition().dynSymTab->getParent())
getParent()->link = sec->sectionIndex;
// Computes bloom filter size in word size. We want to allocate 12
// bits for each symbol. It must be a power of two.
if (symbols.empty()) {
maskWords = 1;
} else {
uint64_t numBits = symbols.size() * 12;
maskWords = NextPowerOf2(numBits / (config->wordsize * 8));
}
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) {
// Write a header.
write32(buf, nBuckets);
write32(buf + 4, getPartition().dynSymTab->getNumSymbols() - symbols.size());
write32(buf + 8, maskWords);
write32(buf + 12, Shift2);
buf += 16;
// Write the 2-bit bloom filter.
const unsigned c = config->is64 ? 64 : 32;
for (const Entry &sym : symbols) {
// When C = 64, we choose a word with bits [6:...] and set 1 to two bits in
// the word using bits [0:5] and [26:31].
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 >> Shift2) % c);
writeUint(buf + i * config->wordsize, val);
}
buf += config->wordsize * maskWords;
// Write the hash table.
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,
getPartition().dynSymTab->getSymbolIndex(*i->sym));
oldBucket = i->bucketIdx;
}
}
// 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(SmallVectorImpl<SymbolTableEntry> &v) {
// We cannot use 'auto' for Mid because GCC 6.1 cannot deduce
// its type correctly.
auto mid =
std::stable_partition(v.begin(), v.end(), [&](const SymbolTableEntry &s) {
return !s.sym->isDefined() || s.sym->partition != partition;
});
// 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.
//
// Note that we don't want to create a zero-sized hash table because
// Android loader as of 2018 doesn't like a .gnu.hash containing such
// table. If that's the case, we create a hash table with one unused
// dummy slot.
nBuckets = std::max<size_t>((v.end() - mid) / 4, 1);
if (mid == v.end())
return;
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});
}
llvm::sort(symbols, [](const Entry &l, const Entry &r) {
return std::tie(l.bucketIdx, l.strTabOffset) <
std::tie(r.bucketIdx, r.strTabOffset);
});
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() {
SymbolTableBaseSection *symTab = getPartition().dynSymTab.get();
if (OutputSection *sec = symTab->getParent())
getParent()->link = sec->sectionIndex;
unsigned numEntries = 2; // nbucket and nchain.
numEntries += symTab->getNumSymbols(); // The chain entries.
// Create as many buckets as there are symbols.
numEntries += symTab->getNumSymbols();
this->size = numEntries * 4;
}
void HashTableSection::writeTo(uint8_t *buf) {
SymbolTableBaseSection *symTab = getPartition().dynSymTab.get();
unsigned numSymbols = symTab->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 : symTab->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()
: SyntheticSection(SHF_ALLOC | SHF_EXECINSTR, SHT_PROGBITS, 16, ".plt"),
headerSize(ctx.target->pltHeaderSize) {
// On PowerPC, this section contains lazy symbol resolvers.
if (config->emachine == EM_PPC64) {
name = ".glink";
addralign = 4;
}
// On x86 when IBT is enabled, this section contains the second PLT (lazy
// symbol resolvers).
if ((config->emachine == EM_386 || config->emachine == EM_X86_64) &&
(config->andFeatures & GNU_PROPERTY_X86_FEATURE_1_IBT))
name = ".plt.sec";
// 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, we have code to call the dynamic
// linker to resolve dynsyms at runtime. Write such code.
ctx.target->writePltHeader(buf);
size_t off = headerSize;
for (const Symbol *sym : entries) {
ctx.target->writePlt(buf + off, *sym, getVA() + off);
off += ctx.target->pltEntrySize;
}
}
void PltSection::addEntry(Symbol &sym) {
assert(sym.auxIdx == ctx.symAux.size() - 1);
ctx.symAux.back().pltIdx = entries.size();
entries.push_back(&sym);
}
size_t PltSection::getSize() const {
return headerSize + entries.size() * ctx.target->pltEntrySize;
}
bool PltSection::isNeeded() const {
// For -z retpolineplt, .iplt needs the .plt header.
return !entries.empty() || (config->zRetpolineplt && ctx.in.iplt->isNeeded());
}
// Used by ARM to add mapping symbols in the PLT section, which aid
// disassembly.
void PltSection::addSymbols() {
ctx.target->addPltHeaderSymbols(*this);
size_t off = headerSize;
for (size_t i = 0; i < entries.size(); ++i) {
ctx.target->addPltSymbols(*this, off);
off += ctx.target->pltEntrySize;
}
}
IpltSection::IpltSection()
: SyntheticSection(SHF_ALLOC | SHF_EXECINSTR, SHT_PROGBITS, 16, ".iplt") {
if (config->emachine == EM_PPC || config->emachine == EM_PPC64) {
name = ".glink";
addralign = 4;
}
}
void IpltSection::writeTo(uint8_t *buf) {
uint32_t off = 0;
for (const Symbol *sym : entries) {
ctx.target->writeIplt(buf + off, *sym, getVA() + off);
off += ctx.target->ipltEntrySize;
}
}
size_t IpltSection::getSize() const {
return entries.size() * ctx.target->ipltEntrySize;
}
void IpltSection::addEntry(Symbol &sym) {
assert(sym.auxIdx == ctx.symAux.size() - 1);
ctx.symAux.back().pltIdx = entries.size();
entries.push_back(&sym);
}
// ARM uses mapping symbols to aid disassembly.
void IpltSection::addSymbols() {
size_t off = 0;
for (size_t i = 0, e = entries.size(); i != e; ++i) {
ctx.target->addPltSymbols(*this, off);
off += ctx.target->pltEntrySize;
}
}
PPC32GlinkSection::PPC32GlinkSection() {
name = ".glink";
addralign = 4;
}
void PPC32GlinkSection::writeTo(uint8_t *buf) {
writePPC32GlinkSection(buf, entries.size());
}
size_t PPC32GlinkSection::getSize() const {
return headerSize + entries.size() * ctx.target->pltEntrySize + footerSize;
}
// This is an x86-only extra PLT section and used only when a security
// enhancement feature called CET is enabled. In this comment, I'll explain what
// the feature is and why we have two PLT sections if CET is enabled.
//
// So, what does CET do? CET introduces a new restriction to indirect jump
// instructions. CET works this way. Assume that CET is enabled. Then, if you
// execute an indirect jump instruction, the processor verifies that a special
// "landing pad" instruction (which is actually a repurposed NOP instruction and
// now called "endbr32" or "endbr64") is at the jump target. If the jump target
// does not start with that instruction, the processor raises an exception
// instead of continuing executing code.
//
// If CET is enabled, the compiler emits endbr to all locations where indirect
// jumps may jump to.
//
// This mechanism makes it extremely hard to transfer the control to a middle of
// a function that is not supporsed to be a indirect jump target, preventing
// certain types of attacks such as ROP or JOP.
//
// Note that the processors in the market as of 2019 don't actually support the
// feature. Only the spec is available at the moment.
//
// Now, I'll explain why we have this extra PLT section for CET.
//
// Since you can indirectly jump to a PLT entry, we have to make PLT entries
// start with endbr. The problem is there's no extra space for endbr (which is 4
// bytes long), as the PLT entry is only 16 bytes long and all bytes are already
// used.
//
// In order to deal with the issue, we split a PLT entry into two PLT entries.
// Remember that each PLT entry contains code to jump to an address read from
// .got.plt AND code to resolve a dynamic symbol lazily. With the 2-PLT scheme,
// the former code is written to .plt.sec, and the latter code is written to
// .plt.
//
// Lazy symbol resolution in the 2-PLT scheme works in the usual way, except
// that the regular .plt is now called .plt.sec and .plt is repurposed to
// contain only code for lazy symbol resolution.
//
// In other words, this is how the 2-PLT scheme works. Application code is
// supposed to jump to .plt.sec to call an external function. Each .plt.sec
// entry contains code to read an address from a corresponding .got.plt entry
// and jump to that address. Addresses in .got.plt initially point to .plt, so
// when an application calls an external function for the first time, the
// control is transferred to a function that resolves a symbol name from
// external shared object files. That function then rewrites a .got.plt entry
// with a resolved address, so that the subsequent function calls directly jump
// to a desired location from .plt.sec.
//
// There is an open question as to whether the 2-PLT scheme was desirable or
// not. We could have simply extended the PLT entry size to 32-bytes to
// accommodate endbr, and that scheme would have been much simpler than the
// 2-PLT scheme. One reason to split PLT was, by doing that, we could keep hot
// code (.plt.sec) from cold code (.plt). But as far as I know no one proved
// that the optimization actually makes a difference.
//
// That said, the 2-PLT scheme is a part of the ABI, debuggers and other tools
// depend on it, so we implement the ABI.
IBTPltSection::IBTPltSection()
: SyntheticSection(SHF_ALLOC | SHF_EXECINSTR, SHT_PROGBITS, 16, ".plt") {}
void IBTPltSection::writeTo(uint8_t *buf) {
ctx.target->writeIBTPlt(buf, ctx.in.plt->getNumEntries());
}
size_t IBTPltSection::getSize() const {
// 16 is the header size of .plt.
return 16 + ctx.in.plt->getNumEntries() * ctx.target->pltEntrySize;
}
bool IBTPltSection::isNeeded() const { return ctx.in.plt->getNumEntries() > 0; }
RelroPaddingSection::RelroPaddingSection()
: SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_NOBITS, 1, ".relro_padding") {
}
// 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;
}
// 4-byte alignment ensures that values in the hash lookup table and the name
// table are aligned.
DebugNamesBaseSection::DebugNamesBaseSection()
: SyntheticSection(0, SHT_PROGBITS, 4, ".debug_names") {}
// Get the size of the .debug_names section header in bytes for DWARF32:
static uint32_t getDebugNamesHeaderSize(uint32_t augmentationStringSize) {
return /* unit length */ 4 +
/* version */ 2 +
/* padding */ 2 +
/* CU count */ 4 +
/* TU count */ 4 +
/* Foreign TU count */ 4 +
/* Bucket Count */ 4 +
/* Name Count */ 4 +
/* Abbrev table size */ 4 +
/* Augmentation string size */ 4 +
/* Augmentation string */ augmentationStringSize;
}
static Expected<DebugNamesBaseSection::IndexEntry *>
readEntry(uint64_t &offset, const DWARFDebugNames::NameIndex &ni,
uint64_t entriesBase, DWARFDataExtractor &namesExtractor,
const LLDDWARFSection &namesSec) {
auto ie = makeThreadLocal<DebugNamesBaseSection::IndexEntry>();
ie->poolOffset = offset;
Error err = Error::success();
uint64_t ulebVal = namesExtractor.getULEB128(&offset, &err);
if (err)
return createStringError(inconvertibleErrorCode(),
"invalid abbrev code: %s",
toString(std::move(err)).c_str());
if (!isUInt<32>(ulebVal))
return createStringError(inconvertibleErrorCode(),
"abbrev code too large for DWARF32: %" PRIu64,
ulebVal);
ie->abbrevCode = static_cast<uint32_t>(ulebVal);
auto it = ni.getAbbrevs().find_as(ie->abbrevCode);
if (it == ni.getAbbrevs().end())
return createStringError(inconvertibleErrorCode(),
"abbrev code not found in abbrev table: %" PRIu32,
ie->abbrevCode);
DebugNamesBaseSection::AttrValue attr, cuAttr = {0, 0};
for (DWARFDebugNames::AttributeEncoding a : it->Attributes) {
if (a.Index == dwarf::DW_IDX_parent) {
if (a.Form == dwarf::DW_FORM_ref4) {
attr.attrValue = namesExtractor.getU32(&offset, &err);
attr.attrSize = 4;
ie->parentOffset = entriesBase + attr.attrValue;
} else if (a.Form != DW_FORM_flag_present)
return createStringError(inconvertibleErrorCode(),
"invalid form for DW_IDX_parent");
} else {
switch (a.Form) {
case DW_FORM_data1:
case DW_FORM_ref1: {
attr.attrValue = namesExtractor.getU8(&offset, &err);
attr.attrSize = 1;
break;
}
case DW_FORM_data2:
case DW_FORM_ref2: {
attr.attrValue = namesExtractor.getU16(&offset, &err);
attr.attrSize = 2;
break;
}
case DW_FORM_data4:
case DW_FORM_ref4: {
attr.attrValue = namesExtractor.getU32(&offset, &err);
attr.attrSize = 4;
break;
}
default:
return createStringError(
inconvertibleErrorCode(),
"unrecognized form encoding %d in abbrev table", a.Form);
}
}
if (err)
return createStringError(inconvertibleErrorCode(),
"error while reading attributes: %s",
toString(std::move(err)).c_str());
if (a.Index == DW_IDX_compile_unit)
cuAttr = attr;
else if (a.Form != DW_FORM_flag_present)
ie->attrValues.push_back(attr);
}
// Canonicalize abbrev by placing the CU/TU index at the end.
ie->attrValues.push_back(cuAttr);
return ie;
}
void DebugNamesBaseSection::parseDebugNames(
InputChunk &inputChunk, OutputChunk &chunk,
DWARFDataExtractor &namesExtractor, DataExtractor &strExtractor,
function_ref<SmallVector<uint32_t, 0>(
uint32_t numCus, const DWARFDebugNames::Header &,
const DWARFDebugNames::DWARFDebugNamesOffsets &)>
readOffsets) {
const LLDDWARFSection &namesSec = inputChunk.section;
DenseMap<uint32_t, IndexEntry *> offsetMap;
// Number of CUs seen in previous NameIndex sections within current chunk.
uint32_t numCus = 0;
for (const DWARFDebugNames::NameIndex &ni : *inputChunk.llvmDebugNames) {
NameData &nd = inputChunk.nameData.emplace_back();
nd.hdr = ni.getHeader();
if (nd.hdr.Format != DwarfFormat::DWARF32) {
errorOrWarn(toString(namesSec.sec) +
Twine(": found DWARF64, which is currently unsupported"));
return;
}
if (nd.hdr.Version != 5) {
errorOrWarn(toString(namesSec.sec) + Twine(": unsupported version: ") +
Twine(nd.hdr.Version));
return;
}
uint32_t dwarfSize = dwarf::getDwarfOffsetByteSize(DwarfFormat::DWARF32);
DWARFDebugNames::DWARFDebugNamesOffsets locs = ni.getOffsets();
if (locs.EntriesBase > namesExtractor.getData().size()) {
errorOrWarn(toString(namesSec.sec) +
Twine(": entry pool start is beyond end of section"));
return;
}
SmallVector<uint32_t, 0> entryOffsets = readOffsets(numCus, nd.hdr, locs);
// Read the entry pool.
offsetMap.clear();
nd.nameEntries.resize(nd.hdr.NameCount);
for (auto i : seq(nd.hdr.NameCount)) {
NameEntry &ne = nd.nameEntries[i];
uint64_t strOffset = locs.StringOffsetsBase + i * dwarfSize;
ne.stringOffset = strOffset;
uint64_t strp = namesExtractor.getRelocatedValue(dwarfSize, &strOffset);
StringRef name = strExtractor.getCStrRef(&strp);
ne.name = name.data();
ne.hashValue = caseFoldingDjbHash(name);
// Read a series of index entries that end with abbreviation code 0.
uint64_t offset = locs.EntriesBase + entryOffsets[i];
while (offset < namesSec.Data.size() && namesSec.Data[offset] != 0) {
// Read & store all entries (for the same string).
Expected<IndexEntry *> ieOrErr =
readEntry(offset, ni, locs.EntriesBase, namesExtractor, namesSec);
if (!ieOrErr) {
errorOrWarn(toString(namesSec.sec) + ": " +
toString(ieOrErr.takeError()));
return;
}
ne.indexEntries.push_back(std::move(*ieOrErr));
}
if (offset >= namesSec.Data.size())
errorOrWarn(toString(namesSec.sec) +
Twine(": index entry is out of bounds"));
for (IndexEntry &ie : ne.entries())
offsetMap[ie.poolOffset] = &ie;
}
// Assign parent pointers, which will be used to update DW_IDX_parent index
// attributes. Note: offsetMap[0] does not exist, so parentOffset == 0 will
// get parentEntry == null as well.
for (NameEntry &ne : nd.nameEntries)
for (IndexEntry &ie : ne.entries())
ie.parentEntry = offsetMap.lookup(ie.parentOffset);
numCus += nd.hdr.CompUnitCount;
}
}
// Compute the form for output DW_IDX_compile_unit attributes, similar to
// DIEInteger::BestForm. The input form (often DW_FORM_data1) may not hold all
// the merged CU indices.
std::pair<uint8_t, dwarf::Form> static getMergedCuCountForm(
uint32_t compUnitCount) {
if (compUnitCount > UINT16_MAX)
return {4, DW_FORM_data4};
if (compUnitCount > UINT8_MAX)
return {2, DW_FORM_data2};
return {1, DW_FORM_data1};
}
void DebugNamesBaseSection::computeHdrAndAbbrevTable(
MutableArrayRef<InputChunk> inputChunks) {
TimeTraceScope timeScope("Merge .debug_names", "hdr and abbrev table");
size_t numCu = 0;
hdr.Format = DwarfFormat::DWARF32;
hdr.Version = 5;
hdr.CompUnitCount = 0;
hdr.LocalTypeUnitCount = 0;
hdr.ForeignTypeUnitCount = 0;
hdr.AugmentationStringSize = 0;
// Compute CU and TU counts.
for (auto i : seq(numChunks)) {
InputChunk &inputChunk = inputChunks[i];
inputChunk.baseCuIdx = numCu;
numCu += chunks[i].compUnits.size();
for (const NameData &nd : inputChunk.nameData) {
hdr.CompUnitCount += nd.hdr.CompUnitCount;
// TODO: We don't handle type units yet, so LocalTypeUnitCount &
// ForeignTypeUnitCount are left as 0.
if (nd.hdr.LocalTypeUnitCount || nd.hdr.ForeignTypeUnitCount)
warn(toString(inputChunk.section.sec) +
Twine(": type units are not implemented"));
// If augmentation strings are not identical, use an empty string.
if (i == 0) {
hdr.AugmentationStringSize = nd.hdr.AugmentationStringSize;
hdr.AugmentationString = nd.hdr.AugmentationString;
} else if (hdr.AugmentationString != nd.hdr.AugmentationString) {
// There are conflicting augmentation strings, so it's best for the
// merged index to not use an augmentation string.
hdr.AugmentationStringSize = 0;
hdr.AugmentationString.clear();
}
}
}
// Create the merged abbrev table, uniquifyinng the input abbrev tables and
// computing mapping from old (per-cu) abbrev codes to new (merged) abbrev
// codes.
FoldingSet<Abbrev> abbrevSet;
// Determine the form for the DW_IDX_compile_unit attributes in the merged
// index. The input form may not be big enough for all CU indices.
dwarf::Form cuAttrForm = getMergedCuCountForm(hdr.CompUnitCount).second;
for (InputChunk &inputChunk : inputChunks) {
for (auto [i, ni] : enumerate(*inputChunk.llvmDebugNames)) {
for (const DWARFDebugNames::Abbrev &oldAbbrev : ni.getAbbrevs()) {
// Canonicalize abbrev by placing the CU/TU index at the end,
// similar to 'parseDebugNames'.
Abbrev abbrev;
DWARFDebugNames::AttributeEncoding cuAttr(DW_IDX_compile_unit,
cuAttrForm);
abbrev.code = oldAbbrev.Code;
abbrev.tag = oldAbbrev.Tag;
for (DWARFDebugNames::AttributeEncoding a : oldAbbrev.Attributes) {
if (a.Index == DW_IDX_compile_unit)
cuAttr.Index = a.Index;
else
abbrev.attributes.push_back({a.Index, a.Form});
}
// Put the CU/TU index at the end of the attributes list.
abbrev.attributes.push_back(cuAttr);
// Profile the abbrev, get or assign a new code, then record the abbrev
// code mapping.
FoldingSetNodeID id;
abbrev.Profile(id);
uint32_t newCode;
void *insertPos;
if (Abbrev *existing = abbrevSet.FindNodeOrInsertPos(id, insertPos)) {
// Found it; we've already seen an identical abbreviation.
newCode = existing->code;
} else {
Abbrev *abbrev2 =
new (abbrevAlloc.Allocate()) Abbrev(std::move(abbrev));
abbrevSet.InsertNode(abbrev2, insertPos);
abbrevTable.push_back(abbrev2);
newCode = abbrevTable.size();
abbrev2->code = newCode;
}
inputChunk.nameData[i].abbrevCodeMap[oldAbbrev.Code] = newCode;
}
}
}
// Compute the merged abbrev table.
raw_svector_ostream os(abbrevTableBuf);
for (Abbrev *abbrev : abbrevTable) {
encodeULEB128(abbrev->code, os);
encodeULEB128(abbrev->tag, os);
for (DWARFDebugNames::AttributeEncoding a : abbrev->attributes) {
encodeULEB128(a.Index, os);
encodeULEB128(a.Form, os);
}
os.write("\0", 2); // attribute specification end
}
os.write(0); // abbrev table end
hdr.AbbrevTableSize = abbrevTableBuf.size();
}
void DebugNamesBaseSection::Abbrev::Profile(FoldingSetNodeID &id) const {
id.AddInteger(tag);
for (const DWARFDebugNames::AttributeEncoding &attr : attributes) {
id.AddInteger(attr.Index);
id.AddInteger(attr.Form);
}
}
std::pair<uint32_t, uint32_t> DebugNamesBaseSection::computeEntryPool(
MutableArrayRef<InputChunk> inputChunks) {
TimeTraceScope timeScope("Merge .debug_names", "entry pool");
// Collect and de-duplicate all the names (preserving all the entries).
// Speed it up using multithreading, as the number of symbols can be in the
// order of millions.
const size_t concurrency =
bit_floor(std::min<size_t>(config->threadCount, numShards));
const size_t shift = 32 - countr_zero(numShards);
const uint8_t cuAttrSize = getMergedCuCountForm(hdr.CompUnitCount).first;
DenseMap<CachedHashStringRef, size_t> maps[numShards];
parallelFor(0, concurrency, [&](size_t threadId) {
for (auto i : seq(numChunks)) {
InputChunk &inputChunk = inputChunks[i];
for (auto j : seq(inputChunk.nameData.size())) {
NameData &nd = inputChunk.nameData[j];
// Deduplicate the NameEntry records (based on the string/name),
// appending all IndexEntries from duplicate NameEntry records to
// the single preserved copy.
for (NameEntry &ne : nd.nameEntries) {
auto shardId = ne.hashValue >> shift;
if ((shardId & (concurrency - 1)) != threadId)
continue;
ne.chunkIdx = i;
for (IndexEntry &ie : ne.entries()) {
// Update the IndexEntry's abbrev code to match the merged
// abbreviations.
ie.abbrevCode = nd.abbrevCodeMap[ie.abbrevCode];
// Update the DW_IDX_compile_unit attribute (the last one after
// canonicalization) to have correct merged offset value and size.
auto &back = ie.attrValues.back();
back.attrValue += inputChunk.baseCuIdx + j;
back.attrSize = cuAttrSize;
}
auto &nameVec = nameVecs[shardId];
auto [it, inserted] = maps[shardId].try_emplace(
CachedHashStringRef(ne.name, ne.hashValue), nameVec.size());
if (inserted)
nameVec.push_back(std::move(ne));
else
nameVec[it->second].indexEntries.append(std::move(ne.indexEntries));
}
}
}
});
// Compute entry offsets in parallel. First, compute offsets relative to the
// current shard.
uint32_t offsets[numShards];
parallelFor(0, numShards, [&](size_t shard) {
uint32_t offset = 0;
for (NameEntry &ne : nameVecs[shard]) {
ne.entryOffset = offset;
for (IndexEntry &ie : ne.entries()) {
ie.poolOffset = offset;
offset += getULEB128Size(ie.abbrevCode);
for (AttrValue value : ie.attrValues)
offset += value.attrSize;
}
++offset; // index entry sentinel
}
offsets[shard] = offset;
});
// Then add shard offsets.
std::partial_sum(offsets, std::end(offsets), offsets);
parallelFor(1, numShards, [&](size_t shard) {
uint32_t offset = offsets[shard - 1];
for (NameEntry &ne : nameVecs[shard]) {
ne.entryOffset += offset;
for (IndexEntry &ie : ne.entries())
ie.poolOffset += offset;
}
});
// Update the DW_IDX_parent entries that refer to real parents (have
// DW_FORM_ref4).
parallelFor(0, numShards, [&](size_t shard) {
for (NameEntry &ne : nameVecs[shard]) {
for (IndexEntry &ie : ne.entries()) {
if (!ie.parentEntry)
continue;
// Abbrevs are indexed starting at 1; vector starts at 0. (abbrevCode
// corresponds to position in the merged table vector).
const Abbrev *abbrev = abbrevTable[ie.abbrevCode - 1];
for (const auto &[a, v] : zip_equal(abbrev->attributes, ie.attrValues))
if (a.Index == DW_IDX_parent && a.Form == DW_FORM_ref4)
v.attrValue = ie.parentEntry->poolOffset;
}
}
});
// Return (entry pool size, number of entries).
uint32_t num = 0;
for (auto &map : maps)
num += map.size();
return {offsets[numShards - 1], num};
}
void DebugNamesBaseSection::init(
function_ref<void(InputFile *, InputChunk &, OutputChunk &)> parseFile) {
TimeTraceScope timeScope("Merge .debug_names");
// Collect and remove input .debug_names sections. Save InputSection pointers
// to relocate string offsets in `writeTo`.
SetVector<InputFile *> files;
for (InputSectionBase *s : ctx.inputSections) {
InputSection *isec = dyn_cast<InputSection>(s);
if (!isec)
continue;
if (!(s->flags & SHF_ALLOC) && s->name == ".debug_names") {
s->markDead();
inputSections.push_back(isec);
files.insert(isec->file);
}
}
// Parse input .debug_names sections and extract InputChunk and OutputChunk
// data. OutputChunk contains CU information, which will be needed by
// `writeTo`.
auto inputChunksPtr = std::make_unique<InputChunk[]>(files.size());
MutableArrayRef<InputChunk> inputChunks(inputChunksPtr.get(), files.size());
numChunks = files.size();
chunks = std::make_unique<OutputChunk[]>(files.size());
{
TimeTraceScope timeScope("Merge .debug_names", "parse");
parallelFor(0, files.size(), [&](size_t i) {
parseFile(files[i], inputChunks[i], chunks[i]);
});
}
// Compute section header (except unit_length), abbrev table, and entry pool.
computeHdrAndAbbrevTable(inputChunks);
uint32_t entryPoolSize;
std::tie(entryPoolSize, hdr.NameCount) = computeEntryPool(inputChunks);
hdr.BucketCount = dwarf::getDebugNamesBucketCount(hdr.NameCount);
// Compute the section size. Subtract 4 to get the unit_length for DWARF32.
uint32_t hdrSize = getDebugNamesHeaderSize(hdr.AugmentationStringSize);
size = findDebugNamesOffsets(hdrSize, hdr).EntriesBase + entryPoolSize;
hdr.UnitLength = size - 4;
}
template <class ELFT> DebugNamesSection<ELFT>::DebugNamesSection() {
init([](InputFile *f, InputChunk &inputChunk, OutputChunk &chunk) {
auto *file = cast<ObjFile<ELFT>>(f);
DWARFContext dwarf(std::make_unique<LLDDwarfObj<ELFT>>(file));
auto &dobj = static_cast<const LLDDwarfObj<ELFT> &>(dwarf.getDWARFObj());
chunk.infoSec = dobj.getInfoSection();
DWARFDataExtractor namesExtractor(dobj, dobj.getNamesSection(),
ELFT::Endianness == endianness::little,
ELFT::Is64Bits ? 8 : 4);
// .debug_str is needed to get symbol names from string offsets.
DataExtractor strExtractor(dobj.getStrSection(),
ELFT::Endianness == endianness::little,
ELFT::Is64Bits ? 8 : 4);
inputChunk.section = dobj.getNamesSection();
inputChunk.llvmDebugNames.emplace(namesExtractor, strExtractor);
if (Error e = inputChunk.llvmDebugNames->extract()) {
errorOrWarn(toString(dobj.getNamesSection().sec) + Twine(": ") +
toString(std::move(e)));
}
parseDebugNames(
inputChunk, chunk, namesExtractor, strExtractor,
[&chunk, namesData = dobj.getNamesSection().Data.data()](
uint32_t numCus, const DWARFDebugNames::Header &hdr,
const DWARFDebugNames::DWARFDebugNamesOffsets &locs) {
// Read CU offsets, which are relocated by .debug_info + X
// relocations. Record the section offset to be relocated by
// `finalizeContents`.
chunk.compUnits.resize_for_overwrite(numCus + hdr.CompUnitCount);
for (auto i : seq(hdr.CompUnitCount))
chunk.compUnits[numCus + i] = locs.CUsBase + i * 4;
// Read entry offsets.
const char *p = namesData + locs.EntryOffsetsBase;
SmallVector<uint32_t, 0> entryOffsets;
entryOffsets.resize_for_overwrite(hdr.NameCount);
for (uint32_t &offset : entryOffsets)
offset = endian::readNext<uint32_t, ELFT::Endianness, unaligned>(p);
return entryOffsets;
});
});
}
template <class ELFT>
template <class RelTy>
void DebugNamesSection<ELFT>::getNameRelocs(
const InputFile &file, DenseMap<uint32_t, uint32_t> &relocs,
Relocs<RelTy> rels) {
for (const RelTy &rel : rels) {
Symbol &sym = file.getRelocTargetSym(rel);
relocs[rel.r_offset] = sym.getVA(getAddend<ELFT>(rel));
}
}
template <class ELFT> void DebugNamesSection<ELFT>::finalizeContents() {
// Get relocations of .debug_names sections.
auto relocs = std::make_unique<DenseMap<uint32_t, uint32_t>[]>(numChunks);
parallelFor(0, numChunks, [&](size_t i) {
InputSection *sec = inputSections[i];
invokeOnRelocs(*sec, getNameRelocs, *sec->file, relocs.get()[i]);
// Relocate CU offsets with .debug_info + X relocations.
OutputChunk &chunk = chunks.get()[i];
for (auto [j, cuOffset] : enumerate(chunk.compUnits))
cuOffset = relocs.get()[i].lookup(cuOffset);
});
// Relocate string offsets in the name table with .debug_str + X relocations.
parallelForEach(nameVecs, [&](auto &nameVec) {
for (NameEntry &ne : nameVec)
ne.stringOffset = relocs.get()[ne.chunkIdx].lookup(ne.stringOffset);
});
}
template <class ELFT> void DebugNamesSection<ELFT>::writeTo(uint8_t *buf) {
[[maybe_unused]] const uint8_t *const beginBuf = buf;
// Write the header.
endian::writeNext<uint32_t, ELFT::Endianness>(buf, hdr.UnitLength);
endian::writeNext<uint16_t, ELFT::Endianness>(buf, hdr.Version);
buf += 2; // padding
endian::writeNext<uint32_t, ELFT::Endianness>(buf, hdr.CompUnitCount);
endian::writeNext<uint32_t, ELFT::Endianness>(buf, hdr.LocalTypeUnitCount);
endian::writeNext<uint32_t, ELFT::Endianness>(buf, hdr.ForeignTypeUnitCount);
endian::writeNext<uint32_t, ELFT::Endianness>(buf, hdr.BucketCount);
endian::writeNext<uint32_t, ELFT::Endianness>(buf, hdr.NameCount);
endian::writeNext<uint32_t, ELFT::Endianness>(buf, hdr.AbbrevTableSize);
endian::writeNext<uint32_t, ELFT::Endianness>(buf,
hdr.AugmentationStringSize);
memcpy(buf, hdr.AugmentationString.c_str(), hdr.AugmentationString.size());
buf += hdr.AugmentationStringSize;
// Write the CU list.
for (auto &chunk : getChunks())
for (uint32_t cuOffset : chunk.compUnits)
endian::writeNext<uint32_t, ELFT::Endianness>(buf, cuOffset);
// TODO: Write the local TU list, then the foreign TU list..
// Write the hash lookup table.
SmallVector<SmallVector<NameEntry *, 0>, 0> buckets(hdr.BucketCount);
// Symbols enter into a bucket whose index is the hash modulo bucket_count.
for (auto &nameVec : nameVecs)
for (NameEntry &ne : nameVec)
buckets[ne.hashValue % hdr.BucketCount].push_back(&ne);
// Write buckets (accumulated bucket counts).
uint32_t bucketIdx = 1;
for (const SmallVector<NameEntry *, 0> &bucket : buckets) {
if (!bucket.empty())
endian::write32<ELFT::Endianness>(buf, bucketIdx);
buf += 4;
bucketIdx += bucket.size();
}
// Write the hashes.
for (const SmallVector<NameEntry *, 0> &bucket : buckets)
for (const NameEntry *e : bucket)
endian::writeNext<uint32_t, ELFT::Endianness>(buf, e->hashValue);
// Write the name table. The name entries are ordered by bucket_idx and
// correspond one-to-one with the hash lookup table.
//
// First, write the relocated string offsets.
for (const SmallVector<NameEntry *, 0> &bucket : buckets)
for (const NameEntry *ne : bucket)
endian::writeNext<uint32_t, ELFT::Endianness>(buf, ne->stringOffset);
// Then write the entry offsets.
for (const SmallVector<NameEntry *, 0> &bucket : buckets)
for (const NameEntry *ne : bucket)
endian::writeNext<uint32_t, ELFT::Endianness>(buf, ne->entryOffset);
// Write the abbrev table.
buf = llvm::copy(abbrevTableBuf, buf);
// Write the entry pool. Unlike the name table, the name entries follow the
// nameVecs order computed by `computeEntryPool`.
for (auto &nameVec : nameVecs) {
for (NameEntry &ne : nameVec) {
// Write all the entries for the string.
for (const IndexEntry &ie : ne.entries()) {
buf += encodeULEB128(ie.abbrevCode, buf);
for (AttrValue value : ie.attrValues) {
switch (value.attrSize) {
case 1:
*buf++ = value.attrValue;
break;
case 2:
endian::writeNext<uint16_t, ELFT::Endianness>(buf, value.attrValue);
break;
case 4:
endian::writeNext<uint32_t, ELFT::Endianness>(buf, value.attrValue);
break;
default:
llvm_unreachable("invalid attrSize");
}
}
}
++buf; // index entry sentinel
}
}
assert(uint64_t(buf - beginBuf) == size);
}
GdbIndexSection::GdbIndexSection()
: SyntheticSection(0, SHT_PROGBITS, 1, ".gdb_index") {}
// Returns the desired size of an on-disk hash table for a .gdb_index section.
// There's a tradeoff between size and collision rate. We aim 75% utilization.
size_t GdbIndexSection::computeSymtabSize() const {
return std::max<size_t>(NextPowerOf2(symbols.size() * 4 / 3), 1024);
}
static SmallVector<GdbIndexSection::CuEntry, 0>
readCuList(DWARFContext &dwarf) {
SmallVector<GdbIndexSection::CuEntry, 0> ret;
for (std::unique_ptr<DWARFUnit> &cu : dwarf.compile_units())
ret.push_back({cu->getOffset(), cu->getLength() + 4});
return ret;
}
static SmallVector<GdbIndexSection::AddressEntry, 0>
readAddressAreas(DWARFContext &dwarf, InputSection *sec) {
SmallVector<GdbIndexSection::AddressEntry, 0> ret;
uint32_t cuIdx = 0;
for (std::unique_ptr<DWARFUnit> &cu : dwarf.compile_units()) {
if (Error e = cu->tryExtractDIEsIfNeeded(false)) {
warn(toString(sec) + ": " + toString(std::move(e)));
return {};
}
Expected<DWARFAddressRangesVector> ranges = cu->collectAddressRanges();
if (!ranges) {
warn(toString(sec) + ": " + toString(ranges.takeError()));
return {};
}
ArrayRef<InputSectionBase *> sections = sec->file->getSections();
for (DWARFAddressRange &r : *ranges) {
if (r.SectionIndex == -1ULL)
continue;
// Range list with zero size has no effect.
InputSectionBase *s = sections[r.SectionIndex];
if (s && s != &InputSection::discarded && s->isLive())
if (r.LowPC != r.HighPC)
ret.push_back({cast<InputSection>(s), r.LowPC, r.HighPC, cuIdx});
}
++cuIdx;
}
return ret;
}
template <class ELFT>
static SmallVector<GdbIndexSection::NameAttrEntry, 0>
readPubNamesAndTypes(const LLDDwarfObj<ELFT> &obj,
const SmallVectorImpl<GdbIndexSection::CuEntry> &cus) {
const LLDDWARFSection &pubNames = obj.getGnuPubnamesSection();
const LLDDWARFSection &pubTypes = obj.getGnuPubtypesSection();
SmallVector<GdbIndexSection::NameAttrEntry, 0> ret;
for (const LLDDWARFSection *pub : {&pubNames, &pubTypes}) {
DWARFDataExtractor data(obj, *pub, ELFT::Endianness == endianness::little,
ELFT::Is64Bits ? 8 : 4);
DWARFDebugPubTable table;
table.extract(data, /*GnuStyle=*/true, [&](Error e) {
warn(toString(pub->sec) + ": " + toString(std::move(e)));
});
for (const DWARFDebugPubTable::Set &set : table.getData()) {
// The value written into the constant pool is kind << 24 | cuIndex. As we
// don't know how many compilation units precede this object to compute
// cuIndex, we compute (kind << 24 | cuIndexInThisObject) instead, and add
// the number of preceding compilation units later.
uint32_t i = llvm::partition_point(cus,
[&](GdbIndexSection::CuEntry cu) {
return cu.cuOffset < set.Offset;
}) -
cus.begin();
for (const DWARFDebugPubTable::Entry &ent : set.Entries)
ret.push_back({{ent.Name, computeGdbHash(ent.Name)},
(ent.Descriptor.toBits() << 24) | i});
}
}
return ret;
}
// Create a list of symbols from a given list of symbol names and types
// by uniquifying them by name.
static std::pair<SmallVector<GdbIndexSection::GdbSymbol, 0>, size_t>
createSymbols(
ArrayRef<SmallVector<GdbIndexSection::NameAttrEntry, 0>> nameAttrs,
const SmallVector<GdbIndexSection::GdbChunk, 0> &chunks) {
using GdbSymbol = GdbIndexSection::GdbSymbol;
using NameAttrEntry = GdbIndexSection::NameAttrEntry;
// For each chunk, compute the number of compilation units preceding it.
uint32_t cuIdx = 0;
std::unique_ptr<uint32_t[]> cuIdxs(new uint32_t[chunks.size()]);
for (uint32_t i = 0, e = chunks.size(); i != e; ++i) {
cuIdxs[i] = cuIdx;
cuIdx += chunks[i].compilationUnits.size();
}
// Collect the compilation unitss for each unique name. Speed it up using
// multi-threading as the number of symbols can be in the order of millions.
// Shard GdbSymbols by hash's high bits.
constexpr size_t numShards = 32;
const size_t concurrency =
llvm::bit_floor(std::min<size_t>(config->threadCount, numShards));
const size_t shift = 32 - llvm::countr_zero(numShards);
auto map =
std::make_unique<DenseMap<CachedHashStringRef, size_t>[]>(numShards);
auto symbols = std::make_unique<SmallVector<GdbSymbol, 0>[]>(numShards);
parallelFor(0, concurrency, [&](size_t threadId) {
uint32_t i = 0;
for (ArrayRef<NameAttrEntry> entries : nameAttrs) {
for (const NameAttrEntry &ent : entries) {
size_t shardId = ent.name.hash() >> shift;
if ((shardId & (concurrency - 1)) != threadId)
continue;
uint32_t v = ent.cuIndexAndAttrs + cuIdxs[i];
auto [it, inserted] =
map[shardId].try_emplace(ent.name, symbols[shardId].size());
if (inserted)
symbols[shardId].push_back({ent.name, {v}, 0, 0});
else
symbols[shardId][it->second].cuVector.push_back(v);
}
++i;
}
});
size_t numSymbols = 0;
for (ArrayRef<GdbSymbol> v : ArrayRef(symbols.get(), numShards))
numSymbols += v.size();
// The return type is a flattened vector, so we'll copy each vector
// contents to Ret.
SmallVector<GdbSymbol, 0> ret;
ret.reserve(numSymbols);
for (SmallVector<GdbSymbol, 0> &vec :
MutableArrayRef(symbols.get(), numShards))
for (GdbSymbol &sym : vec)
ret.push_back(std::move(sym));
// CU vectors and symbol names are adjacent in the output file.
// We can compute their offsets in the output file now.
size_t off = 0;
for (GdbSymbol &sym : ret) {
sym.cuVectorOff = off;
off += (sym.cuVector.size() + 1) * 4;
}
for (GdbSymbol &sym : ret) {
sym.nameOff = off;
off += sym.name.size() + 1;
}
// If off overflows, the last symbol's nameOff likely overflows.
if (!isUInt<32>(off))
errorOrWarn("--gdb-index: constant pool size (" + Twine(off) +
") exceeds UINT32_MAX");
return {ret, off};
}
// Returns a newly-created .gdb_index section.
template <class ELFT>
std::unique_ptr<GdbIndexSection> GdbIndexSection::create() {
llvm::TimeTraceScope timeScope("Create gdb index");
// Collect InputFiles with .debug_info. See the comment in
// LLDDwarfObj<ELFT>::LLDDwarfObj. If we do lightweight parsing in the future,
// note that isec->data() may uncompress the full content, which should be
// parallelized.
SetVector<InputFile *> files;
for (InputSectionBase *s : ctx.inputSections) {
InputSection *isec = dyn_cast<InputSection>(s);
if (!isec)
continue;
// .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 them from the output.
if (s->name == ".debug_gnu_pubnames" || s->name == ".debug_gnu_pubtypes")
s->markDead();
else if (isec->name == ".debug_info")
files.insert(isec->file);
}
// Drop .rel[a].debug_gnu_pub{names,types} for --emit-relocs.
llvm::erase_if(ctx.inputSections, [](InputSectionBase *s) {
if (auto *isec = dyn_cast<InputSection>(s))
if (InputSectionBase *rel = isec->getRelocatedSection())
return !rel->isLive();
return !s->isLive();
});
SmallVector<GdbChunk, 0> chunks(files.size());
SmallVector<SmallVector<NameAttrEntry, 0>, 0> nameAttrs(files.size());
parallelFor(0, files.size(), [&](size_t i) {
// To keep memory usage low, we don't want to keep cached DWARFContext, so
// avoid getDwarf() here.
ObjFile<ELFT> *file = cast<ObjFile<ELFT>>(files[i]);
DWARFContext dwarf(std::make_unique<LLDDwarfObj<ELFT>>(file));
auto &dobj = static_cast<const LLDDwarfObj<ELFT> &>(dwarf.getDWARFObj());
// If the are multiple compile units .debug_info (very rare ld -r --unique),
// this only picks the last one. Other address ranges are lost.
chunks[i].sec = dobj.getInfoSection();
chunks[i].compilationUnits = readCuList(dwarf);
chunks[i].addressAreas = readAddressAreas(dwarf, chunks[i].sec);
nameAttrs[i] = readPubNamesAndTypes<ELFT>(dobj, chunks[i].compilationUnits);
});
auto ret = std::make_unique<GdbIndexSection>();
ret->chunks = std::move(chunks);
std::tie(ret->symbols, ret->size) = createSymbols(nameAttrs, ret->chunks);
// Count the areas other than the constant pool.
ret->size += sizeof(GdbIndexHeader) + ret->computeSymtabSize() * 8;
for (GdbChunk &chunk : ret->chunks)
ret->size +=
chunk.compilationUnits.size() * 16 + chunk.addressAreas.size() * 20;
return ret;
}
void GdbIndexSection::writeTo(uint8_t *buf) {
// Write the header.
auto *hdr = reinterpret_cast<GdbIndexHeader *>(buf);
uint8_t *start = buf;
hdr->version = 7;
buf += sizeof(*hdr);
// Write the CU list.
hdr->cuListOff = buf - start;
for (GdbChunk &chunk : chunks) {
for (CuEntry &cu : chunk.compilationUnits) {
write64le(buf, chunk.sec->outSecOff + cu.cuOffset);
write64le(buf + 8, cu.cuLength);
buf += 16;
}
}
// Write the address area.
hdr->cuTypesOff = buf - start;
hdr->addressAreaOff = buf - start;
uint32_t cuOff = 0;
for (GdbChunk &chunk : chunks) {
for (AddressEntry &e : chunk.addressAreas) {
// In the case of ICF there may be duplicate address range entries.
const uint64_t baseAddr = e.section->repl->getVA(0);
write64le(buf, baseAddr + e.lowAddress);
write64le(buf + 8, baseAddr + e.highAddress);
write32le(buf + 16, e.cuIndex + cuOff);
buf += 20;
}
cuOff += chunk.compilationUnits.size();
}
// Write the on-disk open-addressing hash table containing symbols.
hdr->symtabOff = buf - start;
size_t symtabSize = computeSymtabSize();
uint32_t mask = symtabSize - 1;
for (GdbSymbol &sym : symbols) {
uint32_t h = sym.name.hash();
uint32_t i = h & mask;
uint32_t step = ((h * 17) & mask) | 1;
while (read32le(buf + i * 8))
i = (i + step) & mask;
write32le(buf + i * 8, sym.nameOff);
write32le(buf + i * 8 + 4, sym.cuVectorOff);
}
buf += symtabSize * 8;
// Write the string pool.
hdr->constantPoolOff = buf - start;
parallelForEach(symbols, [&](GdbSymbol &sym) {
memcpy(buf + sym.nameOff, sym.name.data(), sym.name.size());
});
// Write the CU vectors.
for (GdbSymbol &sym : symbols) {
write32le(buf, sym.cuVector.size());
buf += 4;
for (uint32_t val : sym.cuVector) {
write32le(buf, val);
buf += 4;
}
}
}
bool GdbIndexSection::isNeeded() const { return !chunks.empty(); }
EhFrameHeader::EhFrameHeader()
: SyntheticSection(SHF_ALLOC, SHT_PROGBITS, 4, ".eh_frame_hdr") {}
void EhFrameHeader::writeTo(uint8_t *buf) {
// Unlike most sections, the EhFrameHeader section is written while writing
// another section, namely EhFrameSection, which calls the write() function
// below from its writeTo() function. This is necessary because the contents
// of EhFrameHeader depend on the relocated contents of EhFrameSection and we
// don't know which order the sections will be written in.
}
// .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::write() {
uint8_t *buf = ctx.bufferStart + getParent()->offset + outSecOff;
using FdeData = EhFrameSection::FdeData;
SmallVector<FdeData, 0> fdes = getPartition().ehFrame->getFdeData();
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,
getPartition().ehFrame->getParent()->addr - this->getVA() - 4);
write32(buf + 8, fdes.size());
buf += 12;
for (FdeData &fde : fdes) {
write32(buf, fde.pcRel);
write32(buf + 4, fde.fdeVARel);
buf += 8;
}
}
size_t EhFrameHeader::getSize() const {
// .eh_frame_hdr has a 12 bytes header followed by an array of FDEs.
return 12 + getPartition().ehFrame->numFdes * 8;
}
bool EhFrameHeader::isNeeded() const {
return isLive() && getPartition().ehFrame->isNeeded();
}
VersionDefinitionSection::VersionDefinitionSection()
: SyntheticSection(SHF_ALLOC, SHT_GNU_verdef, sizeof(uint32_t),
".gnu.version_d") {}
StringRef VersionDefinitionSection::getFileDefName() {
if (!getPartition().name.empty())
return getPartition().name;
if (!config->soName.empty())
return config->soName;
return config->outputFile;
}
void VersionDefinitionSection::finalizeContents() {
fileDefNameOff = getPartition().dynStrTab->addString(getFileDefName());
for (const VersionDefinition &v : namedVersionDefs())
verDefNameOffs.push_back(getPartition().dynStrTab->addString(v.name));
if (OutputSection *sec = getPartition().dynStrTab->getParent())
getParent()->link = sec->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();
}
void VersionDefinitionSection::writeOne(uint8_t *buf, uint32_t index,
StringRef name, size_t nameOff) {
uint16_t flags = index == 1 ? VER_FLG_BASE : 0;
// Write a verdef.
write16(buf, 1); // vd_version
write16(buf + 2, flags); // vd_flags
write16(buf + 4, index); // vd_ndx
write16(buf + 6, 1); // vd_cnt
write32(buf + 8, hashSysV(name)); // vd_hash
write32(buf + 12, 20); // vd_aux
write32(buf + 16, 28); // vd_next
// Write a veraux.
write32(buf + 20, nameOff); // vda_name
write32(buf + 24, 0); // vda_next
}
void VersionDefinitionSection::writeTo(uint8_t *buf) {
writeOne(buf, 1, getFileDefName(), fileDefNameOff);
auto nameOffIt = verDefNameOffs.begin();
for (const VersionDefinition &v : namedVersionDefs()) {
buf += EntrySize;
writeOne(buf, v.id, v.name, *nameOffIt++);
}
// Need to terminate the last version definition.
write32(buf + 16, 0); // vd_next
}
size_t VersionDefinitionSection::getSize() const {
return EntrySize * getVerDefNum();
}
// .gnu.version is a table where each entry is 2 byte long.
VersionTableSection::VersionTableSection()
: SyntheticSection(SHF_ALLOC, SHT_GNU_versym, sizeof(uint16_t),
".gnu.version") {
this->entsize = 2;
}
void VersionTableSection::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 = getPartition().dynSymTab->getParent()->sectionIndex;
}
size_t VersionTableSection::getSize() const {
return (getPartition().dynSymTab->getSymbols().size() + 1) * 2;
}
void VersionTableSection::writeTo(uint8_t *buf) {
buf += 2;
for (const SymbolTableEntry &s : getPartition().dynSymTab->getSymbols()) {
// For an unextracted lazy symbol (undefined weak), it must have been
// converted to Undefined and have VER_NDX_GLOBAL version here.
assert(!s.sym->isLazy());
write16(buf, s.sym->versionId);
buf += 2;
}
}
bool VersionTableSection::isNeeded() const {
return isLive() &&
(getPartition().verDef || getPartition().verNeed->isNeeded());
}
void elf::addVerneed(Symbol *ss) {
auto &file = cast<SharedFile>(*ss->file);
if (ss->versionId == VER_NDX_GLOBAL)
return;
if (file.vernauxs.empty())
file.vernauxs.resize(file.verdefs.size());
// Select a version identifier for the vernaux data structure, if we haven't
// already allocated one. The verdef identifiers cover the range
// [1..getVerDefNum()]; this causes the vernaux identifiers to start from
// getVerDefNum()+1.
if (file.vernauxs[ss->versionId] == 0)
file.vernauxs[ss->versionId] = ++SharedFile::vernauxNum + getVerDefNum();
ss->versionId = file.vernauxs[ss->versionId];
}
template <class ELFT>
VersionNeedSection<ELFT>::VersionNeedSection()
: SyntheticSection(SHF_ALLOC, SHT_GNU_verneed, sizeof(uint32_t),
".gnu.version_r") {}
template <class ELFT> void VersionNeedSection<ELFT>::finalizeContents() {
for (SharedFile *f : ctx.sharedFiles) {
if (f->vernauxs.empty())
continue;
verneeds.emplace_back();
Verneed &vn = verneeds.back();
vn.nameStrTab = getPartition().dynStrTab->addString(f->soName);
bool isLibc = config->relrGlibc && f->soName.starts_with("libc.so.");
bool isGlibc2 = false;
for (unsigned i = 0; i != f->vernauxs.size(); ++i) {
if (f->vernauxs[i] == 0)
continue;
auto *verdef =
reinterpret_cast<const typename ELFT::Verdef *>(f->verdefs[i]);
StringRef ver(f->getStringTable().data() + verdef->getAux()->vda_name);
if (isLibc && ver.starts_with("GLIBC_2."))
isGlibc2 = true;
vn.vernauxs.push_back({verdef->vd_hash, f->vernauxs[i],
getPartition().dynStrTab->addString(ver)});
}
if (isGlibc2) {
const char *ver = "GLIBC_ABI_DT_RELR";
vn.vernauxs.push_back({hashSysV(ver),
++SharedFile::vernauxNum + getVerDefNum(),
getPartition().dynStrTab->addString(ver)});
}
}
if (OutputSection *sec = getPartition().dynStrTab->getParent())
getParent()->link = sec->sectionIndex;
getParent()->info = verneeds.size();
}
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 + verneeds.size());
for (auto &vn : verneeds) {
// Create an Elf_Verneed for this DSO.
verneed->vn_version = 1;
verneed->vn_cnt = vn.vernauxs.size();
verneed->vn_file = vn.nameStrTab;
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.
for (auto &vna : vn.vernauxs) {
vernaux->vna_hash = vna.hash;
vernaux->vna_flags = 0;
vernaux->vna_other = vna.verneedIndex;
vernaux->vna_name = vna.nameStrTab;
vernaux->vna_next = sizeof(Elf_Vernaux);
++vernaux;
}
vernaux[-1].vna_next = 0;
}
verneed[-1].vn_next = 0;
}
template <class ELFT> size_t VersionNeedSection<ELFT>::getSize() const {
return verneeds.size() * sizeof(Elf_Verneed) +
SharedFile::vernauxNum * sizeof(Elf_Vernaux);
}
template <class ELFT> bool VersionNeedSection<ELFT>::isNeeded() const {
return isLive() && SharedFile::vernauxNum != 0;
}
void MergeSyntheticSection::addSection(MergeInputSection *ms) {
ms->parent = this;
sections.push_back(ms);
assert(addralign == ms->addralign || !(ms->flags & SHF_STRINGS));
addralign = std::max(addralign, ms->addralign);
}
MergeTailSection::MergeTailSection(StringRef name, uint32_t type,
uint64_t flags, uint32_t alignment)
: MergeSyntheticSection(name, type, flags, alignment),
builder(StringTableBuilder::RAW, llvm::Align(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 SectionPiece 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) {
parallelFor(0, numShards,
[&](size_t 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, llvm::Align(addralign));
// Concurrency level. Must be a power of 2 to avoid expensive modulo
// operations in the following tight loop.
const size_t concurrency =
llvm::bit_floor(std::min<size_t>(config->threadCount, numShards));
// Add section pieces to the builders.
parallelFor(0, concurrency, [&](size_t threadId) {
for (MergeInputSection *sec : sections) {
for (size_t i = 0, e = sec->pieces.size(); i != e; ++i) {
if (!sec->pieces[i].live)
continue;
size_t shardId = getShardId(sec->pieces[i].hash);
if ((shardId & (concurrency - 1)) == threadId)
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 = alignToPowerOf2(off, addralign);
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)];
});
}
template <class ELFT> void elf::splitSections() {
llvm::TimeTraceScope timeScope("Split sections");
// splitIntoPieces needs to be called on each MergeInputSection
// before calling finalizeContents().
parallelForEach(ctx.objectFiles, [](ELFFileBase *file) {
for (InputSectionBase *sec : file->getSections()) {
if (!sec)
continue;
if (auto *s = dyn_cast<MergeInputSection>(sec))
s->splitIntoPieces();
else if (auto *eh = dyn_cast<EhInputSection>(sec))
eh->split<ELFT>();
}
});
}
void elf::combineEhSections() {
llvm::TimeTraceScope timeScope("Combine EH sections");
for (EhInputSection *sec : ctx.ehInputSections) {
EhFrameSection &eh = *sec->getPartition().ehFrame;
sec->parent = &eh;
eh.addralign = std::max(eh.addralign, sec->addralign);
eh.sections.push_back(sec);
llvm::append_range(eh.dependentSections, sec->dependentSections);
}
if (!ctx.mainPart->armExidx)
return;
llvm::erase_if(ctx.inputSections, [](InputSectionBase *s) {
// Ignore dead sections and the partition end marker (.part.end),
// whose partition number is out of bounds.
if (!s->isLive() || s->partition == 255)
return false;
Partition &part = s->getPartition();
return s->kind() == SectionBase::Regular && part.armExidx &&
part.armExidx->addSection(cast<InputSection>(s));
});
}
MipsRldMapSection::MipsRldMapSection()
: SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_PROGBITS, config->wordsize,
".rld_map") {}
ARMExidxSyntheticSection::ARMExidxSyntheticSection()
: SyntheticSection(SHF_ALLOC | SHF_LINK_ORDER, SHT_ARM_EXIDX,
config->wordsize, ".ARM.exidx") {}
static InputSection *findExidxSection(InputSection *isec) {
for (InputSection *d : isec->dependentSections)
if (d->type == SHT_ARM_EXIDX && d->isLive())
return d;
return nullptr;
}
static bool isValidExidxSectionDep(InputSection *isec) {
return (isec->flags & SHF_ALLOC) && (isec->flags & SHF_EXECINSTR) &&
isec->getSize() > 0;
}
bool ARMExidxSyntheticSection::addSection(InputSection *isec) {
if (isec->type == SHT_ARM_EXIDX) {
if (InputSection *dep = isec->getLinkOrderDep())
if (isValidExidxSectionDep(dep)) {
exidxSections.push_back(isec);
// Every exidxSection is 8 bytes, we need an estimate of
// size before assignAddresses can be called. Final size
// will only be known after finalize is called.
size += 8;
}
return true;
}
if (isValidExidxSectionDep(isec)) {
executableSections.push_back(isec);
return false;
}
// FIXME: we do not output a relocation section when --emit-relocs is used
// as we do not have relocation sections for linker generated table entries
// and we would have to erase at a late stage relocations from merged entries.
// Given that exception tables are already position independent and a binary
// analyzer could derive the relocations we choose to erase the relocations.
if (config->emitRelocs && isec->type == SHT_REL)
if (InputSectionBase *ex = isec->getRelocatedSection())
if (isa<InputSection>(ex) && ex->type == SHT_ARM_EXIDX)
return true;
return false;
}
// References to .ARM.Extab Sections have bit 31 clear and are not the
// special EXIDX_CANTUNWIND bit-pattern.
static bool isExtabRef(uint32_t unwind) {
return (unwind & 0x80000000) == 0 && unwind != 0x1;
}
// Return true if the .ARM.exidx section Cur can be merged into the .ARM.exidx
// section Prev, where Cur follows Prev in the table. This can be done if the
// unwinding instructions in Cur are identical to Prev. Linker generated
// EXIDX_CANTUNWIND entries are represented by nullptr as they do not have an
// InputSection.
static bool isDuplicateArmExidxSec(InputSection *prev, InputSection *cur) {
// Get the last table Entry from the previous .ARM.exidx section. If Prev is
// nullptr then it will be a synthesized EXIDX_CANTUNWIND entry.
uint32_t prevUnwind = 1;
if (prev)
prevUnwind = read32(prev->content().data() + prev->content().size() - 4);
if (isExtabRef(prevUnwind))
return false;
// We consider the unwind instructions of an .ARM.exidx table entry
// a duplicate if the previous unwind instructions if:
// - Both are the special EXIDX_CANTUNWIND.
// - Both are the same inline unwind instructions.
// We do not attempt to follow and check links into .ARM.extab tables as
// consecutive identical entries are rare and the effort to check that they
// are identical is high.
// If Cur is nullptr then this is synthesized EXIDX_CANTUNWIND entry.
if (cur == nullptr)
return prevUnwind == 1;
for (uint32_t offset = 4; offset < (uint32_t)cur->content().size(); offset +=8) {
uint32_t curUnwind = read32(cur->content().data() + offset);
if (isExtabRef(curUnwind) || curUnwind != prevUnwind)
return false;
}
// All table entries in this .ARM.exidx Section can be merged into the
// previous Section.
return true;
}
// The .ARM.exidx table must be sorted in ascending order of the address of the
// functions the table describes. std::optionally duplicate adjacent table
// entries can be removed. At the end of the function the executableSections
// must be sorted in ascending order of address, Sentinel is set to the
// InputSection with the highest address and any InputSections that have
// mergeable .ARM.exidx table entries are removed from it.
void ARMExidxSyntheticSection::finalizeContents() {
// Ensure that any fixed-point iterations after the first see the original set
// of sections.
if (!originalExecutableSections.empty())
executableSections = originalExecutableSections;
else if (config->enableNonContiguousRegions)
originalExecutableSections = executableSections;
// The executableSections and exidxSections that we use to derive the final
// contents of this SyntheticSection are populated before
// processSectionCommands() and ICF. A /DISCARD/ entry in SECTIONS command or
// ICF may remove executable InputSections and their dependent .ARM.exidx
// section that we recorded earlier.
auto isDiscarded = [](const InputSection *isec) { return !isec->isLive(); };
llvm::erase_if(exidxSections, isDiscarded);
// We need to remove discarded InputSections and InputSections without
// .ARM.exidx sections that if we generated the .ARM.exidx it would be out
// of range.
auto isDiscardedOrOutOfRange = [this](InputSection *isec) {
if (!isec->isLive())
return true;
if (findExidxSection(isec))
return false;
int64_t off = static_cast<int64_t>(isec->getVA() - getVA());
return off != llvm::SignExtend64(off, 31);
};
llvm::erase_if(executableSections, isDiscardedOrOutOfRange);
// Sort the executable sections that may or may not have associated
// .ARM.exidx sections by order of ascending address. This requires the
// relative positions of InputSections and OutputSections to be known.
auto compareByFilePosition = [](const InputSection *a,
const InputSection *b) {
OutputSection *aOut = a->getParent();
OutputSection *bOut = b->getParent();
if (aOut != bOut)
return aOut->addr < bOut->addr;
return a->outSecOff < b->outSecOff;
};
llvm::stable_sort(executableSections, compareByFilePosition);
sentinel = executableSections.back();
// std::optionally merge adjacent duplicate entries.
if (config->mergeArmExidx) {
SmallVector<InputSection *, 0> selectedSections;
selectedSections.reserve(executableSections.size());
selectedSections.push_back(executableSections[0]);
size_t prev = 0;
for (size_t i = 1; i < executableSections.size(); ++i) {
InputSection *ex1 = findExidxSection(executableSections[prev]);
InputSection *ex2 = findExidxSection(executableSections[i]);
if (!isDuplicateArmExidxSec(ex1, ex2)) {
selectedSections.push_back(executableSections[i]);
prev = i;
}
}
executableSections = std::move(selectedSections);
}
// offset is within the SyntheticSection.
size_t offset = 0;
size = 0;
for (InputSection *isec : executableSections) {
if (InputSection *d = findExidxSection(isec)) {
d->outSecOff = offset;
d->parent = getParent();
offset += d->getSize();
} else {
offset += 8;
}
}
// Size includes Sentinel.
size = offset + 8;
}
InputSection *ARMExidxSyntheticSection::getLinkOrderDep() const {
return executableSections.front();
}
// To write the .ARM.exidx table from the ExecutableSections we have three cases
// 1.) The InputSection has a .ARM.exidx InputSection in its dependent sections.
// We write the .ARM.exidx section contents and apply its relocations.
// 2.) The InputSection does not have a dependent .ARM.exidx InputSection. We
// must write the contents of an EXIDX_CANTUNWIND directly. We use the
// start of the InputSection as the purpose of the linker generated
// section is to terminate the address range of the previous entry.
// 3.) A trailing EXIDX_CANTUNWIND sentinel section is required at the end of
// the table to terminate the address range of the final entry.
void ARMExidxSyntheticSection::writeTo(uint8_t *buf) {
// A linker generated CANTUNWIND entry is made up of two words:
// 0x0 with R_ARM_PREL31 relocation to target.
// 0x1 with EXIDX_CANTUNWIND.
uint64_t offset = 0;
for (InputSection *isec : executableSections) {
assert(isec->getParent() != nullptr);
if (InputSection *d = findExidxSection(isec)) {
for (int dataOffset = 0; dataOffset != (int)d->content().size();
dataOffset += 4)
write32(buf + offset + dataOffset,
read32(d->content().data() + dataOffset));
// Recalculate outSecOff as finalizeAddressDependentContent()
// may have altered syntheticSection outSecOff.
d->outSecOff = offset + outSecOff;
ctx.target->relocateAlloc(*d, buf + offset);
offset += d->getSize();
} else {
// A Linker generated CANTUNWIND section.
write32(buf + offset + 0, 0x0);
write32(buf + offset + 4, 0x1);
uint64_t s = isec->getVA();
uint64_t p = getVA() + offset;
ctx.target->relocateNoSym(buf + offset, R_ARM_PREL31, s - p);
offset += 8;
}
}
// Write Sentinel CANTUNWIND entry.
write32(buf + offset + 0, 0x0);
write32(buf + offset + 4, 0x1);
uint64_t s = sentinel->getVA(sentinel->getSize());
uint64_t p = getVA() + offset;
ctx.target->relocateNoSym(buf + offset, R_ARM_PREL31, s - p);
assert(size == offset + 8);
}
bool ARMExidxSyntheticSection::isNeeded() const {
return llvm::any_of(exidxSections,
[](InputSection *isec) { return isec->isLive(); });
}
ThunkSection::ThunkSection(OutputSection *os, uint64_t off)
: SyntheticSection(SHF_ALLOC | SHF_EXECINSTR, SHT_PROGBITS,
config->emachine == EM_PPC64 ? 16 : 4, ".text.thunk") {
this->parent = os;
this->outSecOff = off;
}
size_t ThunkSection::getSize() const {
if (roundUpSizeForErrata)
return alignTo(size, 4096);
return size;
}
void ThunkSection::addThunk(Thunk *t) {
thunks.push_back(t);
t->addSymbols(*this);
}
void ThunkSection::writeTo(uint8_t *buf) {
for (Thunk *t : thunks)
t->writeTo(buf + t->offset);
}
InputSection *ThunkSection::getTargetInputSection() const {
if (thunks.empty())
return nullptr;
const Thunk *t = thunks.front();
return t->getTargetInputSection();
}
bool ThunkSection::assignOffsets() {
uint64_t off = 0;
for (Thunk *t : thunks) {
off = alignToPowerOf2(off, t->alignment);
t->setOffset(off);
uint32_t size = t->size();
t->getThunkTargetSym()->size = size;
off += size;
}
bool changed = off != size;
size = off;
return changed;
}
PPC32Got2Section::PPC32Got2Section()
: SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_PROGBITS, 4, ".got2") {}
bool PPC32Got2Section::isNeeded() const {
// See the comment below. This is not needed if there is no other
// InputSection.
for (SectionCommand *cmd : getParent()->commands)
if (auto *isd = dyn_cast<InputSectionDescription>(cmd))
for (InputSection *isec : isd->sections)
if (isec != this)
return true;
return false;
}
void PPC32Got2Section::finalizeContents() {
// PPC32 may create multiple GOT sections for -fPIC/-fPIE, one per file in
// .got2 . This function computes outSecOff of each .got2 to be used in
// PPC32PltCallStub::writeTo(). The purpose of this empty synthetic section is
// to collect input sections named ".got2".
for (SectionCommand *cmd : getParent()->commands)
if (auto *isd = dyn_cast<InputSectionDescription>(cmd)) {
for (InputSection *isec : isd->sections) {
// isec->file may be nullptr for MergeSyntheticSection.
if (isec != this && isec->file)
isec->file->ppc32Got2 = isec;
}
}
}
// If linking position-dependent code then the table will store the addresses
// directly in the binary so the section has type SHT_PROGBITS. If linking
// position-independent code the section has type SHT_NOBITS since it will be
// allocated and filled in by the dynamic linker.
PPC64LongBranchTargetSection::PPC64LongBranchTargetSection()
: SyntheticSection(SHF_ALLOC | SHF_WRITE,
config->isPic ? SHT_NOBITS : SHT_PROGBITS, 8,
".branch_lt") {}
uint64_t PPC64LongBranchTargetSection::getEntryVA(const Symbol *sym,
int64_t addend) {
return getVA() + entry_index.find({sym, addend})->second * 8;
}
std::optional<uint32_t>
PPC64LongBranchTargetSection::addEntry(const Symbol *sym, int64_t addend) {
auto res =
entry_index.try_emplace(std::make_pair(sym, addend), entries.size());
if (!res.second)
return std::nullopt;
entries.emplace_back(sym, addend);
return res.first->second;
}
size_t PPC64LongBranchTargetSection::getSize() const {
return entries.size() * 8;
}
void PPC64LongBranchTargetSection::writeTo(uint8_t *buf) {
// If linking non-pic we have the final addresses of the targets and they get
// written to the table directly. For pic the dynamic linker will allocate
// the section and fill it.
if (config->isPic)
return;
for (auto entry : entries) {
const Symbol *sym = entry.first;
int64_t addend = entry.second;
assert(sym->getVA());
// Need calls to branch to the local entry-point since a long-branch
// must be a local-call.
write64(buf, sym->getVA(addend) +
getPPC64GlobalEntryToLocalEntryOffset(sym->stOther));
buf += 8;
}
}
bool PPC64LongBranchTargetSection::isNeeded() const {
// `removeUnusedSyntheticSections()` is called before thunk allocation which
// is too early to determine if this section will be empty or not. We need
// Finalized to keep the section alive until after thunk creation. Finalized
// only gets set to true once `finalizeSections()` is called after thunk
// creation. Because of this, if we don't create any long-branch thunks we end
// up with an empty .branch_lt section in the binary.
return !finalized || !entries.empty();
}
static uint8_t getAbiVersion() {
// MIPS non-PIC executable gets ABI version 1.
if (config->emachine == EM_MIPS) {
if (!config->isPic && !config->relocatable &&
(config->eflags & (EF_MIPS_PIC | EF_MIPS_CPIC)) == EF_MIPS_CPIC)
return 1;
return 0;
}
if (config->emachine == EM_AMDGPU && !ctx.objectFiles.empty()) {
uint8_t ver = ctx.objectFiles[0]->abiVersion;
for (InputFile *file : ArrayRef(ctx.objectFiles).slice(1))
if (file->abiVersion != ver)
error("incompatible ABI version: " + toString(file));
return ver;
}
return 0;
}
template <typename ELFT> void elf::writeEhdr(uint8_t *buf, Partition &part) {
memcpy(buf, "\177ELF", 4);
auto *eHdr = reinterpret_cast<typename ELFT::Ehdr *>(buf);
eHdr->e_ident[EI_CLASS] = ELFT::Is64Bits ? ELFCLASS64 : ELFCLASS32;
eHdr->e_ident[EI_DATA] =
ELFT::Endianness == endianness::little ? ELFDATA2LSB : ELFDATA2MSB;
eHdr->e_ident[EI_VERSION] = EV_CURRENT;
eHdr->e_ident[EI_OSABI] = config->osabi;
eHdr->e_ident[EI_ABIVERSION] = getAbiVersion();
eHdr->e_machine = config->emachine;
eHdr->e_version = EV_CURRENT;
eHdr->e_flags = config->eflags;
eHdr->e_ehsize = sizeof(typename ELFT::Ehdr);
eHdr->e_phnum = part.phdrs.size();
eHdr->e_shentsize = sizeof(typename ELFT::Shdr);
if (!config->relocatable) {
eHdr->e_phoff = sizeof(typename ELFT::Ehdr);
eHdr->e_phentsize = sizeof(typename ELFT::Phdr);
}
}
template <typename ELFT> void elf::writePhdrs(uint8_t *buf, Partition &part) {
// Write the program header table.
auto *hBuf = reinterpret_cast<typename ELFT::Phdr *>(buf);
for (PhdrEntry *p : part.phdrs) {
hBuf->p_type = p->p_type;
hBuf->p_flags = p->p_flags;
hBuf->p_offset = p->p_offset;
hBuf->p_vaddr = p->p_vaddr;
hBuf->p_paddr = p->p_paddr;
hBuf->p_filesz = p->p_filesz;
hBuf->p_memsz = p->p_memsz;
hBuf->p_align = p->p_align;
++hBuf;
}
}
template <typename ELFT>
PartitionElfHeaderSection<ELFT>::PartitionElfHeaderSection()
: SyntheticSection(SHF_ALLOC, SHT_LLVM_PART_EHDR, 1, "") {}
template <typename ELFT>
size_t PartitionElfHeaderSection<ELFT>::getSize() const {
return sizeof(typename ELFT::Ehdr);
}
template <typename ELFT>
void PartitionElfHeaderSection<ELFT>::writeTo(uint8_t *buf) {
writeEhdr<ELFT>(buf, getPartition());
// Loadable partitions are always ET_DYN.
auto *eHdr = reinterpret_cast<typename ELFT::Ehdr *>(buf);
eHdr->e_type = ET_DYN;
}
template <typename ELFT>
PartitionProgramHeadersSection<ELFT>::PartitionProgramHeadersSection()
: SyntheticSection(SHF_ALLOC, SHT_LLVM_PART_PHDR, 1, ".phdrs") {}
template <typename ELFT>
size_t PartitionProgramHeadersSection<ELFT>::getSize() const {
return sizeof(typename ELFT::Phdr) * getPartition().phdrs.size();
}
template <typename ELFT>
void PartitionProgramHeadersSection<ELFT>::writeTo(uint8_t *buf) {
writePhdrs<ELFT>(buf, getPartition());
}
PartitionIndexSection::PartitionIndexSection()
: SyntheticSection(SHF_ALLOC, SHT_PROGBITS, 4, ".rodata") {}
size_t PartitionIndexSection::getSize() const {
return 12 * (ctx.partitions.size() - 1);
}
void PartitionIndexSection::finalizeContents() {
for (size_t i = 1; i != ctx.partitions.size(); ++i)
ctx.partitions[i].nameStrTab =
ctx.mainPart->dynStrTab->addString(ctx.partitions[i].name);
}
void PartitionIndexSection::writeTo(uint8_t *buf) {
uint64_t va = getVA();
for (size_t i = 1; i != ctx.partitions.size(); ++i) {
write32(buf, ctx.mainPart->dynStrTab->getVA() +
ctx.partitions[i].nameStrTab - va);
write32(buf + 4, ctx.partitions[i].elfHeader->getVA() - (va + 4));
SyntheticSection *next = i == ctx.partitions.size() - 1
? ctx.in.partEnd.get()
: ctx.partitions[i + 1].elfHeader.get();
write32(buf + 8, next->getVA() - ctx.partitions[i].elfHeader->getVA());
va += 12;
buf += 12;
}
}
void InStruct::reset() {
attributes.reset();
riscvAttributes.reset();
bss.reset();
bssRelRo.reset();
got.reset();
gotPlt.reset();
igotPlt.reset();
relroPadding.reset();
armCmseSGSection.reset();
ppc64LongBranchTarget.reset();
mipsAbiFlags.reset();
mipsGot.reset();
mipsOptions.reset();
mipsReginfo.reset();
mipsRldMap.reset();
partEnd.reset();
partIndex.reset();
plt.reset();
iplt.reset();
ppc32Got2.reset();
ibtPlt.reset();
relaPlt.reset();
debugNames.reset();
gdbIndex.reset();
shStrTab.reset();
strTab.reset();
symTab.reset();
symTabShndx.reset();
}
static bool needsInterpSection() {
return !config->relocatable && !config->shared &&
!config->dynamicLinker.empty() && ctx.script->needsInterpSection();
}
bool elf::hasMemtag() {
return config->emachine == EM_AARCH64 &&
config->androidMemtagMode != ELF::NT_MEMTAG_LEVEL_NONE;
}
// Fully static executables don't support MTE globals at this point in time, as
// we currently rely on:
// - A dynamic loader to process relocations, and
// - Dynamic entries.
// This restriction could be removed in future by re-using some of the ideas
// that ifuncs use in fully static executables.
bool elf::canHaveMemtagGlobals() {
return hasMemtag() &&
(config->relocatable || config->shared || needsInterpSection());
}
constexpr char kMemtagAndroidNoteName[] = "Android";
void MemtagAndroidNote::writeTo(uint8_t *buf) {
static_assert(
sizeof(kMemtagAndroidNoteName) == 8,
"Android 11 & 12 have an ABI that the note name is 8 bytes long. Keep it "
"that way for backwards compatibility.");
write32(buf, sizeof(kMemtagAndroidNoteName));
write32(buf + 4, sizeof(uint32_t));
write32(buf + 8, ELF::NT_ANDROID_TYPE_MEMTAG);
memcpy(buf + 12, kMemtagAndroidNoteName, sizeof(kMemtagAndroidNoteName));
buf += 12 + alignTo(sizeof(kMemtagAndroidNoteName), 4);
uint32_t value = 0;
value |= config->androidMemtagMode;
if (config->androidMemtagHeap)
value |= ELF::NT_MEMTAG_HEAP;
// Note, MTE stack is an ABI break. Attempting to run an MTE stack-enabled
// binary on Android 11 or 12 will result in a checkfail in the loader.
if (config->androidMemtagStack)
value |= ELF::NT_MEMTAG_STACK;
write32(buf, value); // note value
}
size_t MemtagAndroidNote::getSize() const {
return sizeof(llvm::ELF::Elf64_Nhdr) +
/*namesz=*/alignTo(sizeof(kMemtagAndroidNoteName), 4) +
/*descsz=*/sizeof(uint32_t);
}
void PackageMetadataNote::writeTo(uint8_t *buf) {
write32(buf, 4);
write32(buf + 4, config->packageMetadata.size() + 1);
write32(buf + 8, FDO_PACKAGING_METADATA);
memcpy(buf + 12, "FDO", 4);
memcpy(buf + 16, config->packageMetadata.data(),
config->packageMetadata.size());
}
size_t PackageMetadataNote::getSize() const {
return sizeof(llvm::ELF::Elf64_Nhdr) + 4 +
alignTo(config->packageMetadata.size() + 1, 4);
}
// Helper function, return the size of the ULEB128 for 'v', optionally writing
// it to `*(buf + offset)` if `buf` is non-null.
static size_t computeOrWriteULEB128(uint64_t v, uint8_t *buf, size_t offset) {
if (buf)
return encodeULEB128(v, buf + offset);
return getULEB128Size(v);
}
// https://github.com/ARM-software/abi-aa/blob/main/memtagabielf64/memtagabielf64.rst#83encoding-of-sht_aarch64_memtag_globals_dynamic
constexpr uint64_t kMemtagStepSizeBits = 3;
constexpr uint64_t kMemtagGranuleSize = 16;
static size_t
createMemtagGlobalDescriptors(const SmallVector<const Symbol *, 0> &symbols,
uint8_t *buf = nullptr) {
size_t sectionSize = 0;
uint64_t lastGlobalEnd = 0;
for (const Symbol *sym : symbols) {
if (!includeInSymtab(*sym))
continue;
const uint64_t addr = sym->getVA();
const uint64_t size = sym->getSize();
if (addr <= kMemtagGranuleSize && buf != nullptr)
errorOrWarn("address of the tagged symbol \"" + sym->getName() +
"\" falls in the ELF header. This is indicative of a "
"compiler/linker bug");
if (addr % kMemtagGranuleSize != 0)
errorOrWarn("address of the tagged symbol \"" + sym->getName() +
"\" at 0x" + Twine::utohexstr(addr) +
"\" is not granule (16-byte) aligned");
if (size == 0)
errorOrWarn("size of the tagged symbol \"" + sym->getName() +
"\" is not allowed to be zero");
if (size % kMemtagGranuleSize != 0)
errorOrWarn("size of the tagged symbol \"" + sym->getName() +
"\" (size 0x" + Twine::utohexstr(size) +
") is not granule (16-byte) aligned");
const uint64_t sizeToEncode = size / kMemtagGranuleSize;
const uint64_t stepToEncode = ((addr - lastGlobalEnd) / kMemtagGranuleSize)
<< kMemtagStepSizeBits;
if (sizeToEncode < (1 << kMemtagStepSizeBits)) {
sectionSize += computeOrWriteULEB128(stepToEncode | sizeToEncode, buf, sectionSize);
} else {
sectionSize += computeOrWriteULEB128(stepToEncode, buf, sectionSize);
sectionSize += computeOrWriteULEB128(sizeToEncode - 1, buf, sectionSize);
}
lastGlobalEnd = addr + size;
}
return sectionSize;
}
bool MemtagGlobalDescriptors::updateAllocSize() {
size_t oldSize = getSize();
std::stable_sort(symbols.begin(), symbols.end(),
[](const Symbol *s1, const Symbol *s2) {
return s1->getVA() < s2->getVA();
});
return oldSize != getSize();
}
void MemtagGlobalDescriptors::writeTo(uint8_t *buf) {
createMemtagGlobalDescriptors(symbols, buf);
}
size_t MemtagGlobalDescriptors::getSize() const {
return createMemtagGlobalDescriptors(symbols);
}
static OutputSection *findSection(StringRef name) {
for (SectionCommand *cmd : ctx.script->sectionCommands)
if (auto *osd = dyn_cast<OutputDesc>(cmd))
if (osd->osec.name == name)
return &osd->osec;
return nullptr;
}
static Defined *addOptionalRegular(StringRef name, SectionBase *sec,
uint64_t val, uint8_t stOther = STV_HIDDEN) {
Symbol *s = symtab.find(name);
if (!s || s->isDefined() || s->isCommon())
return nullptr;
s->resolve(Defined{ctx.internalFile, StringRef(), STB_GLOBAL, stOther,
STT_NOTYPE, val,
/*size=*/0, sec});
s->isUsedInRegularObj = true;
return cast<Defined>(s);
}
template <class ELFT> void elf::createSyntheticSections() {
// Add the .interp section first because it is not a SyntheticSection.
// The removeUnusedSyntheticSections() function relies on the
// SyntheticSections coming last.
if (needsInterpSection()) {
for (size_t i = 1; i <= ctx.partitions.size(); ++i) {
InputSection *sec = createInterpSection();
sec->partition = i;
ctx.inputSections.push_back(sec);
}
}
auto add = [](SyntheticSection &sec) { ctx.inputSections.push_back(&sec); };
if (config->zSectionHeader)
ctx.in.shStrTab = std::make_unique<StringTableSection>(".shstrtab", false);
ctx.out.programHeaders = make<OutputSection>("", 0, SHF_ALLOC);
ctx.out.programHeaders->addralign = config->wordsize;
if (config->strip != StripPolicy::All) {
ctx.in.strTab = std::make_unique<StringTableSection>(".strtab", false);
ctx.in.symTab = std::make_unique<SymbolTableSection<ELFT>>(*ctx.in.strTab);
ctx.in.symTabShndx = std::make_unique<SymtabShndxSection>();
}
ctx.in.bss = std::make_unique<BssSection>(".bss", 0, 1);
add(*ctx.in.bss);
// If there is a SECTIONS command and a .data.rel.ro section name use name
// .data.rel.ro.bss so that we match in the .data.rel.ro output section.
// This makes sure our relro is contiguous.
bool hasDataRelRo =
ctx.script->hasSectionsCommand && findSection(".data.rel.ro");
ctx.in.bssRelRo = std::make_unique<BssSection>(
hasDataRelRo ? ".data.rel.ro.bss" : ".bss.rel.ro", 0, 1);
add(*ctx.in.bssRelRo);
// Add MIPS-specific sections.
if (config->emachine == EM_MIPS) {
if (!config->shared && config->hasDynSymTab) {
ctx.in.mipsRldMap = std::make_unique<MipsRldMapSection>();
add(*ctx.in.mipsRldMap);
}
if ((ctx.in.mipsAbiFlags = MipsAbiFlagsSection<ELFT>::create()))
add(*ctx.in.mipsAbiFlags);
if ((ctx.in.mipsOptions = MipsOptionsSection<ELFT>::create()))
add(*ctx.in.mipsOptions);
if ((ctx.in.mipsReginfo = MipsReginfoSection<ELFT>::create()))
add(*ctx.in.mipsReginfo);
}
StringRef relaDynName = config->isRela ? ".rela.dyn" : ".rel.dyn";
const unsigned threadCount = config->threadCount;
for (Partition &part : ctx.partitions) {
auto add = [&](SyntheticSection &sec) {
sec.partition = part.getNumber();
ctx.inputSections.push_back(&sec);
};
if (!part.name.empty()) {
part.elfHeader = std::make_unique<PartitionElfHeaderSection<ELFT>>();
part.elfHeader->name = part.name;
add(*part.elfHeader);
part.programHeaders =
std::make_unique<PartitionProgramHeadersSection<ELFT>>();
add(*part.programHeaders);
}
if (config->buildId != BuildIdKind::None) {
part.buildId = std::make_unique<BuildIdSection>();
add(*part.buildId);
}
// dynSymTab is always present to simplify sym->includeInDynsym() in
// finalizeSections.
part.dynStrTab = std::make_unique<StringTableSection>(".dynstr", true);
part.dynSymTab =
std::make_unique<SymbolTableSection<ELFT>>(*part.dynStrTab);
if (config->relocatable)
continue;
part.dynamic = std::make_unique<DynamicSection<ELFT>>();
if (hasMemtag()) {
part.memtagAndroidNote = std::make_unique<MemtagAndroidNote>();
add(*part.memtagAndroidNote);
if (canHaveMemtagGlobals()) {
part.memtagGlobalDescriptors =
std::make_unique<MemtagGlobalDescriptors>();
add(*part.memtagGlobalDescriptors);
}
}
if (config->androidPackDynRelocs)
part.relaDyn = std::make_unique<AndroidPackedRelocationSection<ELFT>>(
relaDynName, threadCount);
else
part.relaDyn = std::make_unique<RelocationSection<ELFT>>(
relaDynName, config->zCombreloc, threadCount);
if (config->hasDynSymTab) {
add(*part.dynSymTab);
part.verSym = std::make_unique<VersionTableSection>();
add(*part.verSym);
if (!namedVersionDefs().empty()) {
part.verDef = std::make_unique<VersionDefinitionSection>();
add(*part.verDef);
}
part.verNeed = std::make_unique<VersionNeedSection<ELFT>>();
add(*part.verNeed);
if (config->gnuHash) {
part.gnuHashTab = std::make_unique<GnuHashTableSection>();
add(*part.gnuHashTab);
}
if (config->sysvHash) {
part.hashTab = std::make_unique<HashTableSection>();
add(*part.hashTab);
}
add(*part.dynamic);
add(*part.dynStrTab);
}
add(*part.relaDyn);
if (config->relrPackDynRelocs) {
part.relrDyn = std::make_unique<RelrSection<ELFT>>(threadCount);
add(*part.relrDyn);
part.relrAuthDyn = std::make_unique<RelrSection<ELFT>>(
threadCount, /*isAArch64Auth=*/true);
add(*part.relrAuthDyn);
}
if (config->ehFrameHdr) {
part.ehFrameHdr = std::make_unique<EhFrameHeader>();
add(*part.ehFrameHdr);
}
part.ehFrame = std::make_unique<EhFrameSection>();
add(*part.ehFrame);
if (config->emachine == EM_ARM) {
// This section replaces all the individual .ARM.exidx InputSections.
part.armExidx = std::make_unique<ARMExidxSyntheticSection>();
add(*part.armExidx);
}
if (!config->packageMetadata.empty()) {
part.packageMetadataNote = std::make_unique<PackageMetadataNote>();
add(*part.packageMetadataNote);
}
}
if (ctx.partitions.size() != 1) {
// Create the partition end marker. This needs to be in partition number 255
// so that it is sorted after all other partitions. It also has other
// special handling (see createPhdrs() and combineEhSections()).
ctx.in.partEnd =
std::make_unique<BssSection>(".part.end", config->maxPageSize, 1);
ctx.in.partEnd->partition = 255;
add(*ctx.in.partEnd);
ctx.in.partIndex = std::make_unique<PartitionIndexSection>();
addOptionalRegular("__part_index_begin", ctx.in.partIndex.get(), 0);
addOptionalRegular("__part_index_end", ctx.in.partIndex.get(),
ctx.in.partIndex->getSize());
add(*ctx.in.partIndex);
}
// Add .got. MIPS' .got is so different from the other archs,
// it has its own class.
if (config->emachine == EM_MIPS) {
ctx.in.mipsGot = std::make_unique<MipsGotSection>();
add(*ctx.in.mipsGot);
} else {
ctx.in.got = std::make_unique<GotSection>();
add(*ctx.in.got);
}
if (config->emachine == EM_PPC) {
ctx.in.ppc32Got2 = std::make_unique<PPC32Got2Section>();
add(*ctx.in.ppc32Got2);
}
if (config->emachine == EM_PPC64) {
ctx.in.ppc64LongBranchTarget =
std::make_unique<PPC64LongBranchTargetSection>();
add(*ctx.in.ppc64LongBranchTarget);
}
ctx.in.gotPlt = std::make_unique<GotPltSection>();
add(*ctx.in.gotPlt);
ctx.in.igotPlt = std::make_unique<IgotPltSection>();
add(*ctx.in.igotPlt);
// Add .relro_padding if DATA_SEGMENT_RELRO_END is used; otherwise, add the
// section in the absence of PHDRS/SECTIONS commands.
if (config->zRelro &&
((ctx.script->phdrsCommands.empty() && !ctx.script->hasSectionsCommand) ||
ctx.script->seenRelroEnd)) {
ctx.in.relroPadding = std::make_unique<RelroPaddingSection>();
add(*ctx.in.relroPadding);
}
if (config->emachine == EM_ARM) {
ctx.in.armCmseSGSection = std::make_unique<ArmCmseSGSection>();
add(*ctx.in.armCmseSGSection);
}
// _GLOBAL_OFFSET_TABLE_ is defined relative to either .got.plt or .got. Treat
// it as a relocation and ensure the referenced section is created.
if (ctx.sym.globalOffsetTable && config->emachine != EM_MIPS) {
if (ctx.target->gotBaseSymInGotPlt)
ctx.in.gotPlt->hasGotPltOffRel = true;
else
ctx.in.got->hasGotOffRel = true;
}
// We always need to add rel[a].plt to output if it has entries.
// Even for static linking it can contain R_[*]_IRELATIVE relocations.
ctx.in.relaPlt = std::make_unique<RelocationSection<ELFT>>(
config->isRela ? ".rela.plt" : ".rel.plt", /*sort=*/false,
/*threadCount=*/1);
add(*ctx.in.relaPlt);
if ((config->emachine == EM_386 || config->emachine == EM_X86_64) &&
(config->andFeatures & GNU_PROPERTY_X86_FEATURE_1_IBT)) {
ctx.in.ibtPlt = std::make_unique<IBTPltSection>();
add(*ctx.in.ibtPlt);
}
if (config->emachine == EM_PPC)
ctx.in.plt = std::make_unique<PPC32GlinkSection>();
else
ctx.in.plt = std::make_unique<PltSection>();
add(*ctx.in.plt);
ctx.in.iplt = std::make_unique<IpltSection>();
add(*ctx.in.iplt);
if (config->andFeatures || !ctx.aarch64PauthAbiCoreInfo.empty())
add(*make<GnuPropertySection>());
if (config->debugNames) {
ctx.in.debugNames = std::make_unique<DebugNamesSection<ELFT>>();
add(*ctx.in.debugNames);
}
if (config->gdbIndex) {
ctx.in.gdbIndex = GdbIndexSection::create<ELFT>();
add(*ctx.in.gdbIndex);
}
// .note.GNU-stack is always added when we are creating a re-linkable
// object file. Other linkers are using the presence of this marker
// section to control the executable-ness of the stack area, but that
// is irrelevant these days. Stack area should always be non-executable
// by default. So we emit this section unconditionally.
if (config->relocatable)
add(*make<GnuStackSection>());
if (ctx.in.symTab)
add(*ctx.in.symTab);
if (ctx.in.symTabShndx)
add(*ctx.in.symTabShndx);
if (ctx.in.shStrTab)
add(*ctx.in.shStrTab);
if (ctx.in.strTab)
add(*ctx.in.strTab);
}
template void elf::splitSections<ELF32LE>();
template void elf::splitSections<ELF32BE>();
template void elf::splitSections<ELF64LE>();
template void elf::splitSections<ELF64BE>();
template void EhFrameSection::iterateFDEWithLSDA<ELF32LE>(
function_ref<void(InputSection &)>);
template void EhFrameSection::iterateFDEWithLSDA<ELF32BE>(
function_ref<void(InputSection &)>);
template void EhFrameSection::iterateFDEWithLSDA<ELF64LE>(
function_ref<void(InputSection &)>);
template void EhFrameSection::iterateFDEWithLSDA<ELF64BE>(
function_ref<void(InputSection &)>);
template class elf::SymbolTableSection<ELF32LE>;
template class elf::SymbolTableSection<ELF32BE>;
template class elf::SymbolTableSection<ELF64LE>;
template class elf::SymbolTableSection<ELF64BE>;
template void elf::writeEhdr<ELF32LE>(uint8_t *Buf, Partition &Part);
template void elf::writeEhdr<ELF32BE>(uint8_t *Buf, Partition &Part);
template void elf::writeEhdr<ELF64LE>(uint8_t *Buf, Partition &Part);
template void elf::writeEhdr<ELF64BE>(uint8_t *Buf, Partition &Part);
template void elf::writePhdrs<ELF32LE>(uint8_t *Buf, Partition &Part);
template void elf::writePhdrs<ELF32BE>(uint8_t *Buf, Partition &Part);
template void elf::writePhdrs<ELF64LE>(uint8_t *Buf, Partition &Part);
template void elf::writePhdrs<ELF64BE>(uint8_t *Buf, Partition &Part);
template void elf::createSyntheticSections<ELF32LE>();
template void elf::createSyntheticSections<ELF32BE>();
template void elf::createSyntheticSections<ELF64LE>();
template void elf::createSyntheticSections<ELF64BE>();
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