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SyntheticSections.cpp
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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/SetOperations.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/BinaryFormat/Dwarf.h"
#include "llvm/BinaryFormat/ELF.h"
#include "llvm/DebugInfo/DWARF/DWARFDebugPubTable.h"
#include "llvm/Support/Endian.h"
#include "llvm/Support/LEB128.h"
#include "llvm/Support/Parallel.h"
#include "llvm/Support/TimeProfiler.h"
#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 = in.mipsGot->getGp();
memcpy(buf + sizeof(Elf_Mips_Options), ®info, 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 = in.mipsGot->getGp();
memcpy(buf, ®info, 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 §ion) {
Defined *s = makeDefined(section.file, name, STB_LOCAL, STV_DEFAULT, type,
value, size, §ion);
if (in.symTab)
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) {
uint32_t featureAndType = config->emachine == EM_AARCH64
? GNU_PROPERTY_AARCH64_FEATURE_1_AND
: GNU_PROPERTY_X86_FEATURE_1_AND;
write32(buf, 4); // Name size
write32(buf + 4, config->is64 ? 16 : 12); // Content size
write32(buf + 8, NT_GNU_PROPERTY_TYPE_0); // Type
memcpy(buf + 12, "GNU", 4); // Name string
write32(buf + 16, featureAndType); // Feature type
write32(buf + 20, 4); // Feature size
write32(buf + 24, config->andFeatures); // Feature flags
if (config->is64)
write32(buf + 28, 0); // Padding
}
size_t GnuPropertySection::getSize() const { return config->is64 ? 32 : 28; }
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->template getFile<ELFT>()->getRelocTargetSym(rels[firstRelI]);
// Search for an existing CIE by CIE contents/relocation target pair.
CieRecord *&rec = cieMap[{cie.data(), personality}];
// If not found, create a new one.
if (!rec) {
rec = make<CieRecord>();
rec->cie = &cie;
cieRecords.push_back(rec);
}
return rec;
}
// There is one FDE per function. Returns 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->template getFile<ELFT>()->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::TargetEndianness>(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>();
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::TargetEndianness>(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>();
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 = Out::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 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)
target->relocateAlloc(*s, buf);
if (getPartition().ehFrameHdr && getPartition().ehFrameHdr->getParent())
getPartition().ehFrameHdr->write();
}
GotSection::GotSection()
: SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_PROGBITS,
target->gotEntrySize, ".got") {
numEntries = target->gotHeaderEntriesNum;
}
void GotSection::addConstant(const Relocation &r) { relocations.push_back(r); }
void GotSection::addEntry(Symbol &sym) {
assert(sym.auxIdx == symAux.size() - 1);
symAux.back().gotIdx = numEntries++;
}
bool GotSection::addTlsDescEntry(Symbol &sym) {
assert(sym.auxIdx == symAux.size() - 1);
symAux.back().tlsDescIdx = numEntries;
numEntries += 2;
return true;
}
bool GotSection::addDynTlsEntry(Symbol &sym) {
assert(sym.auxIdx == symAux.size() - 1);
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 <= target->gotHeaderEntriesNum && !ElfSym::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 > target->gotHeaderEntriesNum;
}
void GotSection::writeTo(uint8_t *buf) {
// On PPC64 .got may be needed but empty. Skip the write.
if (size == 0)
return;
target->writeGotHeader(buf);
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();
symAux.back().gotIdx = p.second;
}
for (auto &p : primGot->relocs) {
if (p.first->auxIdx == 0)
p.first->allocateAux();
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)
mainPart->relaDyn->addReloc({target->tlsGotRel, this, offset,
DynamicReloc::AgainstSymbolWithTargetVA,
*s, 0, R_ABS});
}
for (std::pair<Symbol *, size_t> &p : got.dynTlsSymbols) {
Symbol *s = p.first;