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Diffstat (limited to 'contrib/llvm-project/lld/ELF/SyntheticSections.cpp')
| -rw-r--r-- | contrib/llvm-project/lld/ELF/SyntheticSections.cpp | 3630 |
1 files changed, 3630 insertions, 0 deletions
diff --git a/contrib/llvm-project/lld/ELF/SyntheticSections.cpp b/contrib/llvm-project/lld/ELF/SyntheticSections.cpp new file mode 100644 index 000000000000..35b9b8928c9f --- /dev/null +++ b/contrib/llvm-project/lld/ELF/SyntheticSections.cpp @@ -0,0 +1,3630 @@ +//===- 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 "InputFiles.h" +#include "LinkerScript.h" +#include "OutputSections.h" +#include "SymbolTable.h" +#include "Symbols.h" +#include "Target.h" +#include "Writer.h" +#include "lld/Common/ErrorHandler.h" +#include "lld/Common/Memory.h" +#include "lld/Common/Strings.h" +#include "lld/Common/Threads.h" +#include "lld/Common/Version.h" +#include "llvm/ADT/SetOperations.h" +#include "llvm/ADT/StringExtras.h" +#include "llvm/BinaryFormat/Dwarf.h" +#include "llvm/DebugInfo/DWARF/DWARFDebugPubTable.h" +#include "llvm/Object/ELFObjectFile.h" +#include "llvm/Support/Compression.h" +#include "llvm/Support/Endian.h" +#include "llvm/Support/LEB128.h" +#include "llvm/Support/MD5.h" +#include <cstdlib> +#include <thread> + +using namespace llvm; +using namespace llvm::dwarf; +using namespace llvm::ELF; +using namespace llvm::object; +using namespace llvm::support; + +using namespace 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() { + return make<MergeInputSection>(SHF_MERGE | SHF_STRINGS, SHT_PROGBITS, 1, + getVersion(), ".comment"); +} + +// .MIPS.abiflags section. +template <class ELFT> +MipsAbiFlagsSection<ELFT>::MipsAbiFlagsSection(Elf_Mips_ABIFlags flags) + : SyntheticSection(SHF_ALLOC, SHT_MIPS_ABIFLAGS, 8, ".MIPS.abiflags"), + flags(flags) { + this->entsize = sizeof(Elf_Mips_ABIFlags); +} + +template <class ELFT> void MipsAbiFlagsSection<ELFT>::writeTo(uint8_t *buf) { + memcpy(buf, &flags, sizeof(flags)); +} + +template <class ELFT> +MipsAbiFlagsSection<ELFT> *MipsAbiFlagsSection<ELFT>::create() { + Elf_Mips_ABIFlags flags = {}; + bool create = false; + + for (InputSectionBase *sec : inputSections) { + if (sec->type != SHT_MIPS_ABIFLAGS) + continue; + sec->markDead(); + create = true; + + std::string filename = toString(sec->file); + const size_t size = sec->data().size(); + // Older version of BFD (such as the default FreeBSD linker) concatenate + // .MIPS.abiflags instead of merging. To allow for this case (or potential + // zero padding) we ignore everything after the first Elf_Mips_ABIFlags + if (size < sizeof(Elf_Mips_ABIFlags)) { + error(filename + ": invalid size of .MIPS.abiflags section: got " + + Twine(size) + " instead of " + Twine(sizeof(Elf_Mips_ABIFlags))); + return nullptr; + } + auto *s = reinterpret_cast<const Elf_Mips_ABIFlags *>(sec->data().data()); + if (s->version != 0) { + error(filename + ": unexpected .MIPS.abiflags version " + + Twine(s->version)); + return nullptr; + } + + // LLD checks ISA compatibility in calcMipsEFlags(). Here we just + // select the highest number of ISA/Rev/Ext. + flags.isa_level = std::max(flags.isa_level, s->isa_level); + flags.isa_rev = std::max(flags.isa_rev, s->isa_rev); + flags.isa_ext = std::max(flags.isa_ext, s->isa_ext); + flags.gpr_size = std::max(flags.gpr_size, s->gpr_size); + flags.cpr1_size = std::max(flags.cpr1_size, s->cpr1_size); + flags.cpr2_size = std::max(flags.cpr2_size, s->cpr2_size); + flags.ases |= s->ases; + flags.flags1 |= s->flags1; + flags.flags2 |= s->flags2; + flags.fp_abi = elf::getMipsFpAbiFlag(flags.fp_abi, s->fp_abi, filename); + }; + + if (create) + return make<MipsAbiFlagsSection<ELFT>>(flags); + return nullptr; +} + +// .MIPS.options section. +template <class ELFT> +MipsOptionsSection<ELFT>::MipsOptionsSection(Elf_Mips_RegInfo reginfo) + : SyntheticSection(SHF_ALLOC, SHT_MIPS_OPTIONS, 8, ".MIPS.options"), + reginfo(reginfo) { + this->entsize = sizeof(Elf_Mips_Options) + sizeof(Elf_Mips_RegInfo); +} + +template <class ELFT> void MipsOptionsSection<ELFT>::writeTo(uint8_t *buf) { + auto *options = reinterpret_cast<Elf_Mips_Options *>(buf); + options->kind = ODK_REGINFO; + options->size = getSize(); + + if (!config->relocatable) + reginfo.ri_gp_value = in.mipsGot->getGp(); + memcpy(buf + sizeof(Elf_Mips_Options), ®info, sizeof(reginfo)); +} + +template <class ELFT> +MipsOptionsSection<ELFT> *MipsOptionsSection<ELFT>::create() { + // N64 ABI only. + if (!ELFT::Is64Bits) + return nullptr; + + std::vector<InputSectionBase *> sections; + for (InputSectionBase *sec : inputSections) + if (sec->type == SHT_MIPS_OPTIONS) + sections.push_back(sec); + + if (sections.empty()) + return nullptr; + + Elf_Mips_RegInfo reginfo = {}; + for (InputSectionBase *sec : sections) { + sec->markDead(); + + std::string filename = toString(sec->file); + ArrayRef<uint8_t> d = sec->data(); + + while (!d.empty()) { + if (d.size() < sizeof(Elf_Mips_Options)) { + error(filename + ": invalid size of .MIPS.options section"); + break; + } + + auto *opt = reinterpret_cast<const Elf_Mips_Options *>(d.data()); + if (opt->kind == ODK_REGINFO) { + reginfo.ri_gprmask |= opt->getRegInfo().ri_gprmask; + sec->getFile<ELFT>()->mipsGp0 = opt->getRegInfo().ri_gp_value; + break; + } + + if (!opt->size) + fatal(filename + ": zero option descriptor size"); + d = d.slice(opt->size); + } + }; + + return make<MipsOptionsSection<ELFT>>(reginfo); +} + +// MIPS .reginfo section. +template <class ELFT> +MipsReginfoSection<ELFT>::MipsReginfoSection(Elf_Mips_RegInfo reginfo) + : SyntheticSection(SHF_ALLOC, SHT_MIPS_REGINFO, 4, ".reginfo"), + reginfo(reginfo) { + this->entsize = sizeof(Elf_Mips_RegInfo); +} + +template <class ELFT> void MipsReginfoSection<ELFT>::writeTo(uint8_t *buf) { + if (!config->relocatable) + reginfo.ri_gp_value = in.mipsGot->getGp(); + memcpy(buf, ®info, sizeof(reginfo)); +} + +template <class ELFT> +MipsReginfoSection<ELFT> *MipsReginfoSection<ELFT>::create() { + // Section should be alive for O32 and N32 ABIs only. + if (ELFT::Is64Bits) + return nullptr; + + std::vector<InputSectionBase *> sections; + for (InputSectionBase *sec : inputSections) + if (sec->type == SHT_MIPS_REGINFO) + sections.push_back(sec); + + if (sections.empty()) + return nullptr; + + Elf_Mips_RegInfo reginfo = {}; + for (InputSectionBase *sec : sections) { + sec->markDead(); + + if (sec->data().size() != sizeof(Elf_Mips_RegInfo)) { + error(toString(sec->file) + ": invalid size of .reginfo section"); + return nullptr; + } + + auto *r = reinterpret_cast<const Elf_Mips_RegInfo *>(sec->data().data()); + reginfo.ri_gprmask |= r->ri_gprmask; + sec->getFile<ELFT>()->mipsGp0 = r->ri_gp_value; + }; + + return make<MipsReginfoSection<ELFT>>(reginfo); +} + +InputSection *elf::createInterpSection() { + // StringSaver guarantees that the returned string ends with '\0'. + StringRef s = saver.save(config->dynamicLinker); + ArrayRef<uint8_t> contents = {(const uint8_t *)s.data(), s.size() + 1}; + + auto *sec = make<InputSection>(nullptr, SHF_ALLOC, SHT_PROGBITS, 1, contents, + ".interp"); + sec->markLive(); + return sec; +} + +Defined *elf::addSyntheticLocal(StringRef name, uint8_t type, uint64_t value, + uint64_t size, InputSectionBase §ion) { + auto *s = make<Defined>(section.file, name, STB_LOCAL, STV_DEFAULT, type, + value, size, §ion); + if (in.symTab) + in.symTab->addSymbol(s); + return s; +} + +static size_t getHashSize() { + switch (config->buildId) { + case BuildIdKind::Fast: + return 8; + case BuildIdKind::Md5: + case BuildIdKind::Uuid: + return 16; + case BuildIdKind::Sha1: + return 20; + case BuildIdKind::Hexstring: + return config->buildIdVector.size(); + default: + llvm_unreachable("unknown BuildIdKind"); + } +} + +// 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, 4, + ".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 true if a given FDE +// points to a live function. +template <class ELFT, class RelTy> +bool EhFrameSection::isFdeLive(EhSectionPiece &fde, ArrayRef<RelTy> rels) { + auto *sec = cast<EhInputSection>(fde.sec); + unsigned firstRelI = fde.firstRelocation; + + // An FDE should point to some function because FDEs are to describe + // functions. That's however not always the case due to an issue of + // ld.gold with -r. ld.gold may discard only functions and leave their + // corresponding FDEs, which results in creating bad .eh_frame sections. + // To deal with that, we ignore such FDEs. + if (firstRelI == (unsigned)-1) + return false; + + const RelTy &rel = rels[firstRelI]; + Symbol &b = sec->template getFile<ELFT>()->getRelocTargetSym(rel); + + // FDEs for garbage-collected or merged-by-ICF sections, or sections in + // another partition, are dead. + if (auto *d = dyn_cast<Defined>(&b)) + if (SectionBase *sec = d->section) + return sec->partition == partition; + return false; +} + +// .eh_frame is a sequence of CIE or FDE records. In general, there +// is one CIE record per input object file which is followed by +// a list of FDEs. This function searches an existing CIE or create a new +// one and associates FDEs to the CIE. +template <class ELFT, class RelTy> +void EhFrameSection::addSectionAux(EhInputSection *sec, ArrayRef<RelTy> rels) { + offsetToCie.clear(); + for (EhSectionPiece &piece : sec->pieces) { + // The empty record is the end marker. + if (piece.size == 4) + return; + + size_t offset = piece.inputOff; + uint32_t id = read32(piece.data().data() + 4); + if (id == 0) { + offsetToCie[offset] = addCie<ELFT>(piece, rels); + continue; + } + + uint32_t cieOffset = offset + 4 - id; + CieRecord *rec = offsetToCie[cieOffset]; + if (!rec) + fatal(toString(sec) + ": invalid CIE reference"); + + if (!isFdeLive<ELFT>(piece, rels)) + continue; + rec->fdes.push_back(&piece); + numFdes++; + } +} + +template <class ELFT> void EhFrameSection::addSection(InputSectionBase *c) { + auto *sec = cast<EhInputSection>(c); + sec->parent = this; + + alignment = std::max(alignment, sec->alignment); + sections.push_back(sec); + + for (auto *ds : sec->dependentSections) + dependentSections.push_back(ds); + + if (sec->pieces.empty()) + return; + + if (sec->areRelocsRela) + addSectionAux<ELFT>(sec, sec->template relas<ELFT>()); + else + addSectionAux<ELFT>(sec, sec->template rels<ELFT>()); +} + +static void writeCieFde(uint8_t *buf, ArrayRef<uint8_t> d) { + memcpy(buf, d.data(), d.size()); + + size_t aligned = alignTo(d.size(), config->wordsize); + + // Zero-clear trailing padding if it exists. + memset(buf + d.size(), 0, aligned - d.size()); + + // Fix the size field. -4 since size does not include the size field itself. + write32(buf, aligned - 4); +} + +void EhFrameSection::finalizeContents() { + assert(!this->size); // Not finalized. + size_t off = 0; + for (CieRecord *rec : cieRecords) { + rec->cie->outputOff = off; + off += alignTo(rec->cie->size, config->wordsize); + + for (EhSectionPiece *fde : rec->fdes) { + fde->outputOff = off; + off += alignTo(fde->size, config->wordsize); + } + } + + // The LSB standard does not allow a .eh_frame section with zero + // Call Frame Information records. 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. +std::vector<EhFrameSection::FdeData> EhFrameSection::getFdeData() const { + uint8_t *buf = Out::bufferStart + getParent()->offset + outSecOff; + std::vector<FdeData> 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)) + fatal(toString(fde->sec) + ": PC offset is too large: 0x" + + Twine::utohexstr(pc - va)); + 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. + 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; + fatal("unknown FDE size relative encoding"); +} + +void EhFrameSection::writeTo(uint8_t *buf) { + // Write CIE and FDE records. + for (CieRecord *rec : cieRecords) { + size_t cieOffset = rec->cie->outputOff; + writeCieFde(buf + cieOffset, rec->cie->data()); + + for (EhSectionPiece *fde : rec->fdes) { + size_t off = fde->outputOff; + writeCieFde(buf + off, fde->data()); + + // FDE's second word should have the offset to an associated CIE. + // Write it. + write32(buf + off + 4, off + 4 - cieOffset); + } + } + + // Apply relocations. .eh_frame section contents are not contiguous + // in the output buffer, but relocateAlloc() still works because + // getOffset() takes care of discontiguous section pieces. + for (EhInputSection *s : sections) + s->relocateAlloc(buf, nullptr); + + if (getPartition().ehFrameHdr && getPartition().ehFrameHdr->getParent()) + getPartition().ehFrameHdr->write(); +} + +GotSection::GotSection() + : SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_PROGBITS, config->wordsize, + ".got") { + // If ElfSym::globalOffsetTable is relative to .got and is referenced, + // increase numEntries by the number of entries used to emit + // ElfSym::globalOffsetTable. + if (ElfSym::globalOffsetTable && !target->gotBaseSymInGotPlt) + numEntries += target->gotHeaderEntriesNum; +} + +void GotSection::addEntry(Symbol &sym) { + sym.gotIndex = numEntries; + ++numEntries; +} + +bool GotSection::addDynTlsEntry(Symbol &sym) { + if (sym.globalDynIndex != -1U) + return false; + sym.globalDynIndex = numEntries; + // Global Dynamic TLS entries take two GOT slots. + numEntries += 2; + return true; +} + +// Reserves TLS entries for a TLS module ID and a TLS block offset. +// In total it takes two GOT slots. +bool GotSection::addTlsIndex() { + if (tlsIndexOff != uint32_t(-1)) + return false; + tlsIndexOff = numEntries * config->wordsize; + numEntries += 2; + return true; +} + +uint64_t GotSection::getGlobalDynAddr(const Symbol &b) const { + return this->getVA() + b.globalDynIndex * config->wordsize; +} + +uint64_t GotSection::getGlobalDynOffset(const Symbol &b) const { + return b.globalDynIndex * config->wordsize; +} + +void GotSection::finalizeContents() { + size = numEntries * config->wordsize; +} + +bool GotSection::isNeeded() const { + // We need to emit a GOT even if it's empty if there's a relocation that is + // relative to GOT(such as GOTOFFREL). + return numEntries || hasGotOffRel; +} + +void GotSection::writeTo(uint8_t *buf) { + // Buf points to the start of this section's buffer, + // whereas InputSectionBase::relocateAlloc() expects its argument + // to point to the start of the output section. + target->writeGotHeader(buf); + relocateAlloc(buf - outSecOff, buf - outSecOff + size); +} + +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.hasValue()) { + 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 (BaseCommand *cmd : os->sectionCommands) { + if (auto *isd = dyn_cast<InputSectionDescription>(cmd)) + for (InputSection *isec : isd->sections) { + uint64_t off = alignTo(secSize, isec->alignment); + 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 substracting "global" entries exist 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 Symbol::gotIndex field to use this + // value later in the `sortMipsSymbols` function. + for (auto &p : primGot->global) + p.first->gotIndex = p.second; + for (auto &p : primGot->relocs) + p.first->gotIndex = 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; + if (s->isPreemptible) + mainPart->relaDyn->addReloc(target->tlsGotRel, this, offset, s); + } + 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->isPic) + continue; + mainPart->relaDyn->addReloc(target->tlsModuleIndexRel, this, offset, s); + } 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->isPic) + continue; + mainPart->relaDyn->addReloc(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; + mainPart->relaDyn->addReloc(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; + mainPart->relaDyn->addReloc(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; + mainPart->relaDyn->addReloc({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; + mainPart->relaDyn->addReloc({target->relativeRel, this, offset, true, + p.first.first, p.first.second}); + } + } +} + +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.hasValue() || *f->mipsGotIndex == 0) + return ElfSym::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. + // 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<const 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 ? 0 : -0x7000); + for (const std::pair<Symbol *, size_t> &p : g.dynTlsSymbols) { + if (p.first == nullptr && !config->isPic) + write(p.second, nullptr, 1); + else if (p.first && !p.first->isPreemptible) { + // If we are emitting PIC code 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->isPic) + 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 +// consitent 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.pltIndex == entries.size()); + entries.push_back(&sym); +} + +size_t GotPltSection::getSize() const { + return (target->gotPltHeaderEntriesNum + entries.size()) * config->wordsize; +} + +void GotPltSection::writeTo(uint8_t *buf) { + target->writeGotPltHeader(buf); + buf += target->gotPltHeaderEntriesNum * config->wordsize; + for (const Symbol *b : entries) { + target->writeGotPlt(buf, *b); + buf += config->wordsize; + } +} + +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, + config->wordsize, getIgotPltName()) {} + +void IgotPltSection::addEntry(Symbol &sym) { + assert(sym.pltIndex == entries.size()); + entries.push_back(&sym); +} + +size_t IgotPltSection::getSize() const { + return entries.size() * config->wordsize; +} + +void IgotPltSection::writeTo(uint8_t *buf) { + for (const Symbol *b : entries) { + target->writeIgotPlt(buf, *b); + buf += config->wordsize; + } +} + +StringTableSection::StringTableSection(StringRef name, bool dynamic) + : SyntheticSection(dynamic ? (uint64_t)SHF_ALLOC : 0, SHT_STRTAB, 1, name), + dynamic(dynamic) { + // ELF string tables start with a NUL byte. + addString(""); +} + +// Adds a string to the string table. If `hashIt` is true we hash and check for +// duplicates. It is optional because the name of global symbols are already +// uniqued and hashing them again has a big cost for a small value: uniquing +// them with some other string that happens to be the same. +unsigned StringTableSection::addString(StringRef s, bool hashIt) { + if (hashIt) { + auto r = stringMap.insert(std::make_pair(s, this->size)); + if (!r.second) + return r.first->second; + } + unsigned ret = this->size; + this->size = this->size + s.size() + 1; + strings.push_back(s); + return ret; +} + +void StringTableSection::writeTo(uint8_t *buf) { + for (StringRef s : strings) { + memcpy(buf, s.data(), s.size()); + buf[s.size()] = '\0'; + buf += s.size() + 1; + } +} + +// Returns the number of version definition entries. Because the first entry +// is for the version definition itself, it is the number of versioned symbols +// plus one. Note that we don't support multiple versions yet. +static unsigned getVerDefNum() { return config->versionDefinitions.size() + 1; } + +template <class ELFT> +DynamicSection<ELFT>::DynamicSection() + : SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_DYNAMIC, config->wordsize, + ".dynamic") { + this->entsize = ELFT::Is64Bits ? 16 : 8; + + // .dynamic section is not writable on MIPS and on Fuchsia OS + // which passes -z rodynamic. + // See "Special Section" in Chapter 4 in the following document: + // ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf + if (config->emachine == EM_MIPS || config->zRodynamic) + this->flags = SHF_ALLOC; +} + +template <class ELFT> +void DynamicSection<ELFT>::add(int32_t tag, std::function<uint64_t()> fn) { + entries.push_back({tag, fn}); +} + +template <class ELFT> +void DynamicSection<ELFT>::addInt(int32_t tag, uint64_t val) { + entries.push_back({tag, [=] { return val; }}); +} + +template <class ELFT> +void DynamicSection<ELFT>::addInSec(int32_t tag, InputSection *sec) { + entries.push_back({tag, [=] { return sec->getVA(0); }}); +} + +template <class ELFT> +void DynamicSection<ELFT>::addInSecRelative(int32_t tag, InputSection *sec) { + size_t tagOffset = entries.size() * entsize; + entries.push_back( + {tag, [=] { return sec->getVA(0) - (getVA() + tagOffset); }}); +} + +template <class ELFT> +void DynamicSection<ELFT>::addOutSec(int32_t tag, OutputSection *sec) { + entries.push_back({tag, [=] { return sec->addr; }}); +} + +template <class ELFT> +void DynamicSection<ELFT>::addSize(int32_t tag, OutputSection *sec) { + entries.push_back({tag, [=] { return sec->size; }}); +} + +template <class ELFT> +void DynamicSection<ELFT>::addSym(int32_t tag, Symbol *sym) { + entries.push_back({tag, [=] { return sym->getVA(); }}); +} + +// 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() { + size_t size = in.relaPlt->getSize(); + if (in.relaIplt->getParent() == in.relaPlt->getParent() && + in.relaIplt->name == in.relaPlt->name) + size += in.relaIplt->getSize(); + return size; +} + +// Add remaining entries to complete .dynamic contents. +template <class ELFT> void DynamicSection<ELFT>::finalizeContents() { + elf::Partition &part = getPartition(); + bool isMain = part.name.empty(); + + 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 : 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) + 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->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 (config->hasStaticTlsModel) + dtFlags |= DF_STATIC_TLS; + + if (dtFlags) + addInt(DT_FLAGS, dtFlags); + if (dtFlags1) + addInt(DT_FLAGS_1, dtFlags1); + + // DT_DEBUG is a pointer to debug informaion used by debuggers at runtime. We + // need it for each process, so we don't write it for DSOs. The loader writes + // the pointer into this entry. + // + // DT_DEBUG is the only .dynamic entry that needs to be written to. Some + // systems (currently only Fuchsia OS) provide other means to give the + // debugger this information. Such systems may choose make .dynamic read-only. + // If the target is such a system (used -z rodynamic) don't write DT_DEBUG. + if (!config->shared && !config->relocatable && !config->zRodynamic) + addInt(DT_DEBUG, 0); + + if (OutputSection *sec = part.dynStrTab->getParent()) + this->link = sec->sectionIndex; + + if (part.relaDyn->isNeeded()) { + addInSec(part.relaDyn->dynamicTag, part.relaDyn); + addSize(part.relaDyn->sizeDynamicTag, part.relaDyn->getParent()); + + bool isRela = config->isRela; + addInt(isRela ? DT_RELAENT : DT_RELENT, + isRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel)); + + // MIPS dynamic loader does not support RELCOUNT tag. + // The problem is in the tight relation between dynamic + // relocations and GOT. So do not emit this tag on MIPS. + if (config->emachine != EM_MIPS) { + size_t numRelativeRels = part.relaDyn->getRelativeRelocCount(); + if (config->zCombreloc && numRelativeRels) + addInt(isRela ? DT_RELACOUNT : DT_RELCOUNT, numRelativeRels); + } + } + if (part.relrDyn && !part.relrDyn->relocs.empty()) { + addInSec(config->useAndroidRelrTags ? DT_ANDROID_RELR : DT_RELR, + part.relrDyn); + addSize(config->useAndroidRelrTags ? DT_ANDROID_RELRSZ : DT_RELRSZ, + part.relrDyn->getParent()); + addInt(config->useAndroidRelrTags ? DT_ANDROID_RELRENT : DT_RELRENT, + sizeof(Elf_Relr)); + } + // .rel[a].plt section usually consists of two parts, containing plt and + // iplt relocations. It is possible to have only iplt relocations in the + // output. In that case relaPlt is empty and have zero offset, the same offset + // as relaIplt has. And we still want to emit proper dynamic tags for that + // case, so here we always use relaPlt as marker for the begining of + // .rel[a].plt section. + if (isMain && (in.relaPlt->isNeeded() || in.relaIplt->isNeeded())) { + addInSec(DT_JMPREL, in.relaPlt); + entries.push_back({DT_PLTRELSZ, addPltRelSz}); + switch (config->emachine) { + case EM_MIPS: + addInSec(DT_MIPS_PLTGOT, in.gotPlt); + break; + case EM_SPARCV9: + addInSec(DT_PLTGOT, in.plt); + break; + default: + addInSec(DT_PLTGOT, 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->andFeatures & GNU_PROPERTY_AARCH64_FEATURE_1_PAC) + addInt(DT_AARCH64_PAC_PLT, 0); + } + + 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) + addInSec(DT_GNU_HASH, part.gnuHashTab); + if (part.hashTab) + addInSec(DT_HASH, part.hashTab); + + if (isMain) { + if (Out::preinitArray) { + addOutSec(DT_PREINIT_ARRAY, Out::preinitArray); + addSize(DT_PREINIT_ARRAYSZ, Out::preinitArray); + } + if (Out::initArray) { + addOutSec(DT_INIT_ARRAY, Out::initArray); + addSize(DT_INIT_ARRAYSZ, Out::initArray); + } + if (Out::finiArray) { + addOutSec(DT_FINI_ARRAY, Out::finiArray); + addSize(DT_FINI_ARRAYSZ, Out::finiArray); + } + + if (Symbol *b = symtab->find(config->init)) + if (b->isDefined()) + addSym(DT_INIT, b); + if (Symbol *b = symtab->find(config->fini)) + if (b->isDefined()) + addSym(DT_FINI, b); + } + + bool hasVerNeed = SharedFile::vernauxNum != 0; + if (hasVerNeed || part.verDef) + addInSec(DT_VERSYM, part.verSym); + if (part.verDef) { + addInSec(DT_VERDEF, part.verDef); + addInt(DT_VERDEFNUM, getVerDefNum()); + } + if (hasVerNeed) { + addInSec(DT_VERNEED, part.verNeed); + unsigned needNum = 0; + for (SharedFile *f : 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, target->getImageBase()); + addInt(DT_MIPS_SYMTABNO, part.dynSymTab->getNumSymbols()); + + add(DT_MIPS_LOCAL_GOTNO, [] { return in.mipsGot->getLocalEntriesNum(); }); + + if (const Symbol *b = in.mipsGot->getFirstGlobalEntry()) + addInt(DT_MIPS_GOTSYM, b->dynsymIndex); + else + addInt(DT_MIPS_GOTSYM, part.dynSymTab->getNumSymbols()); + addInSec(DT_PLTGOT, in.mipsGot); + if (in.mipsRldMap) { + if (!config->pie) + addInSec(DT_MIPS_RLD_MAP, in.mipsRldMap); + // Store the offset to the .rld_map section + // relative to the address of the tag. + addInSecRelative(DT_MIPS_RLD_MAP_REL, in.mipsRldMap); + } + } + + // 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) + add(DT_PPC_GOT, [] { return in.got->getVA(); }); + + // Glink dynamic tag is required by the V2 abi if the plt section isn't empty. + if (config->emachine == EM_PPC64 && in.plt->isNeeded()) { + // The Glink tag points to 32 bytes before the first lazy symbol resolution + // stub, which starts directly after the header. + entries.push_back({DT_PPC64_GLINK, [=] { + unsigned offset = target->pltHeaderSize - 32; + return in.plt->getVA(0) + offset; + }}); + } + + addInt(DT_NULL, 0); + + getParent()->link = this->link; + this->size = entries.size() * this->entsize; +} + +template <class ELFT> void DynamicSection<ELFT>::writeTo(uint8_t *buf) { + auto *p = reinterpret_cast<Elf_Dyn *>(buf); + + for (std::pair<int32_t, std::function<uint64_t()>> &kv : entries) { + p->d_tag = kv.first; + p->d_un.d_val = kv.second(); + ++p; + } +} + +uint64_t DynamicReloc::getOffset() const { + return inputSec->getVA(offsetInSec); +} + +int64_t DynamicReloc::computeAddend() const { + if (useSymVA) + return sym->getVA(addend); + if (!outputSec) + return addend; + // See the comment in the DynamicReloc ctor. + return getMipsPageAddr(outputSec->addr) + addend; +} + +uint32_t DynamicReloc::getSymIndex(SymbolTableBaseSection *symTab) const { + if (sym && !useSymVA) + return symTab->getSymbolIndex(sym); + return 0; +} + +RelocationBaseSection::RelocationBaseSection(StringRef name, uint32_t type, + int32_t dynamicTag, + int32_t sizeDynamicTag) + : SyntheticSection(SHF_ALLOC, type, config->wordsize, name), + dynamicTag(dynamicTag), sizeDynamicTag(sizeDynamicTag) {} + +void RelocationBaseSection::addReloc(RelType dynType, InputSectionBase *isec, + uint64_t offsetInSec, Symbol *sym) { + addReloc({dynType, isec, offsetInSec, false, sym, 0}); +} + +void RelocationBaseSection::addReloc(RelType dynType, + InputSectionBase *inputSec, + uint64_t offsetInSec, Symbol *sym, + int64_t addend, RelExpr expr, + RelType type) { + // Write the addends to the relocated address if required. We skip + // it if the written value would be zero. + if (config->writeAddends && (expr != R_ADDEND || addend != 0)) + inputSec->relocations.push_back({expr, type, offsetInSec, addend, sym}); + addReloc({dynType, inputSec, offsetInSec, expr != R_ADDEND, sym, addend}); +} + +void RelocationBaseSection::addReloc(const DynamicReloc &reloc) { + if (reloc.type == target->relativeRel) + ++numRelativeRelocs; + relocs.push_back(reloc); +} + +void RelocationBaseSection::finalizeContents() { + SymbolTableBaseSection *symTab = getPartition().dynSymTab; + + // 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 (in.relaPlt == this) + getParent()->info = in.gotPlt->getParent()->sectionIndex; + if (in.relaIplt == this) + getParent()->info = in.igotPlt->getParent()->sectionIndex; +} + +RelrBaseSection::RelrBaseSection() + : SyntheticSection(SHF_ALLOC, + config->useAndroidRelrTags ? SHT_ANDROID_RELR : SHT_RELR, + config->wordsize, ".relr.dyn") {} + +template <class ELFT> +static void encodeDynamicReloc(SymbolTableBaseSection *symTab, + typename ELFT::Rela *p, + const DynamicReloc &rel) { + if (config->isRela) + p->r_addend = rel.computeAddend(); + p->r_offset = rel.getOffset(); + p->setSymbolAndType(rel.getSymIndex(symTab), rel.type, config->isMips64EL); +} + +template <class ELFT> +RelocationSection<ELFT>::RelocationSection(StringRef name, bool sort) + : RelocationBaseSection(name, config->isRela ? SHT_RELA : SHT_REL, + config->isRela ? DT_RELA : DT_REL, + config->isRela ? DT_RELASZ : DT_RELSZ), + sort(sort) { + this->entsize = config->isRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel); +} + +template <class ELFT> void RelocationSection<ELFT>::writeTo(uint8_t *buf) { + SymbolTableBaseSection *symTab = getPartition().dynSymTab; + + // 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 (sort) + llvm::stable_sort( + relocs, [&](const DynamicReloc &a, const DynamicReloc &b) { + return std::make_tuple(a.type != target->relativeRel, + a.getSymIndex(symTab), a.getOffset()) < + std::make_tuple(b.type != target->relativeRel, + b.getSymIndex(symTab), b.getOffset()); + }); + + for (const DynamicReloc &rel : relocs) { + encodeDynamicReloc<ELFT>(symTab, reinterpret_cast<Elf_Rela *>(buf), rel); + buf += config->isRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel); + } +} + +template <class ELFT> +AndroidPackedRelocationSection<ELFT>::AndroidPackedRelocationSection( + StringRef name) + : RelocationBaseSection( + name, config->isRela ? SHT_ANDROID_RELA : SHT_ANDROID_REL, + config->isRela ? DT_ANDROID_RELA : DT_ANDROID_REL, + config->isRela ? DT_ANDROID_RELASZ : DT_ANDROID_RELSZ) { + this->entsize = 1; +} + +template <class ELFT> +bool AndroidPackedRelocationSection<ELFT>::updateAllocSize() { + // This function computes the contents of an Android-format packed relocation + // section. + // + // This format compresses relocations by using relocation groups to factor out + // fields that are common between relocations and storing deltas from previous + // relocations in SLEB128 format (which has a short representation for small + // numbers). A good example of a relocation type with common fields is + // R_*_RELATIVE, which is normally used to represent function pointers in + // vtables. In the REL format, each relative relocation has the same r_info + // field, and is only different from other relative relocations in terms of + // the r_offset field. By sorting relocations by offset, grouping them by + // r_info and representing each relocation with only the delta from the + // previous offset, each 8-byte relocation can be compressed to as little as 1 + // byte (or less with run-length encoding). This relocation packer was able to + // reduce the size of the relocation section in an Android Chromium DSO from + // 2,911,184 bytes to 174,693 bytes, or 6% of the original size. + // + // A relocation section consists of a header containing the literal bytes + // 'APS2' followed by a sequence of SLEB128-encoded integers. The first two + // elements are the total number of relocations in the section and an initial + // r_offset value. The remaining elements define a sequence of relocation + // groups. Each relocation group starts with a header consisting of the + // following elements: + // + // - the number of relocations in the relocation group + // - flags for the relocation group + // - (if RELOCATION_GROUPED_BY_OFFSET_DELTA_FLAG is set) the r_offset delta + // for each relocation in the group. + // - (if RELOCATION_GROUPED_BY_INFO_FLAG is set) the value of the r_info + // field for each relocation in the group. + // - (if RELOCATION_GROUP_HAS_ADDEND_FLAG and + // RELOCATION_GROUPED_BY_ADDEND_FLAG are set) the r_addend delta for + // each relocation in the group. + // + // Following the relocation group header are descriptions of each of the + // relocations in the group. They consist of the following elements: + // + // - (if RELOCATION_GROUPED_BY_OFFSET_DELTA_FLAG is not set) the r_offset + // delta for this relocation. + // - (if RELOCATION_GROUPED_BY_INFO_FLAG is not set) the value of the r_info + // field for this relocation. + // - (if RELOCATION_GROUP_HAS_ADDEND_FLAG is set and + // RELOCATION_GROUPED_BY_ADDEND_FLAG is not set) the r_addend delta for + // this relocation. + + size_t oldSize = relocData.size(); + + relocData = {'A', 'P', 'S', '2'}; + raw_svector_ostream os(relocData); + auto add = [&](int64_t v) { encodeSLEB128(v, os); }; + + // The format header includes the number of relocations and the initial + // offset (we set this to zero because the first relocation group will + // perform the initial adjustment). + add(relocs.size()); + add(0); + + std::vector<Elf_Rela> relatives, nonRelatives; + + for (const DynamicReloc &rel : relocs) { + Elf_Rela r; + encodeDynamicReloc<ELFT>(getPartition().dynSymTab, &r, rel); + + if (r.getType(config->isMips64EL) == 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)); + } + + unsigned hasAddendIfRela = + config->isRela ? RELOCATION_GROUP_HAS_ADDEND_FLAG : 0; + + uint64_t offset = 0; + uint64_t addend = 0; + + // Emit the run-length encoding for the groups of adjacent relative + // relocations. Each group is represented using two groups in the packed + // format. The first is used to set the current offset to the start of the + // group (and also encodes the first relocation), and the second encodes the + // remaining relocations. + for (std::vector<Elf_Rela> &g : relativeGroups) { + // The first relocation in the group. + add(1); + add(RELOCATION_GROUPED_BY_OFFSET_DELTA_FLAG | + RELOCATION_GROUPED_BY_INFO_FLAG | hasAddendIfRela); + add(g[0].r_offset - offset); + add(target->relativeRel); + if (config->isRela) { + add(g[0].r_addend - addend); + addend = g[0].r_addend; + } + + // The remaining relocations. + add(g.size() - 1); + add(RELOCATION_GROUPED_BY_OFFSET_DELTA_FLAG | + RELOCATION_GROUPED_BY_INFO_FLAG | hasAddendIfRela); + add(config->wordsize); + add(target->relativeRel); + if (config->isRela) { + for (auto i = g.begin() + 1, e = g.end(); i != e; ++i) { + add(i->r_addend - addend); + addend = i->r_addend; + } + } + + offset = g.back().r_offset; + } + + // Now the ungrouped relatives. + if (!ungroupedRelatives.empty()) { + add(ungroupedRelatives.size()); + add(RELOCATION_GROUPED_BY_INFO_FLAG | hasAddendIfRela); + add(target->relativeRel); + for (Elf_Rela &r : ungroupedRelatives) { + add(r.r_offset - offset); + offset = r.r_offset; + if (config->isRela) { + add(r.r_addend - addend); + addend = r.r_addend; + } + } + } + + // Finally the non-relative relocations. + llvm::sort(nonRelatives, [](const Elf_Rela &a, const Elf_Rela &b) { + return a.r_offset < b.r_offset; + }); + if (!nonRelatives.empty()) { + add(nonRelatives.size()); + add(hasAddendIfRela); + for (Elf_Rela &r : nonRelatives) { + add(r.r_offset - offset); + offset = r.r_offset; + add(r.r_info); + if (config->isRela) { + add(r.r_addend - addend); + addend = r.r_addend; + } + } + } + + // 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() { + 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::vector<uint64_t> offsets; + for (const RelativeReloc &rel : relocs) + offsets.push_back(rel.getOffset()); + llvm::sort(offsets); + + // For each leading relocation, find following ones that can be folded + // as a bitmap and fold them. + for (size_t i = 0, e = offsets.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. + while (i < e) { + uint64_t bitmap = 0; + + while (i < e) { + uint64_t delta = offsets[i] - base; + + // If it is too far, it cannot be folded. + if (delta >= nBits * wordsize) + break; + + // If it is not a multiple of wordsize away, it cannot be folded. + if (delta % wordsize) + break; + + // Fold it. + bitmap |= 1ULL << (delta / wordsize); + ++i; + } + + if (!bitmap) + break; + + relrRelocs.push_back(Elf_Relr((bitmap << 1) | 1)); + base += nBits * wordsize; + } + } + + 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->gotIndex < r.sym->gotIndex; + 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 == mainPart->dynSymTab) { + 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() || s.sym->computeBinding() == STB_LOCAL; + }); + 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 *, std::vector<SymbolTableEntry>> arr; + for (const SymbolTableEntry &s : llvm::make_range(symbols.begin(), e)) + arr[s.sym->file].push_back(s); + + auto i = symbols.begin(); + for (std::pair<InputFile *, std::vector<SymbolTableEntry>> &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()); + + bool hashIt = b->isLocal(); + symbols.push_back({b, strTabSec.addString(b->getName(), hashIt)}); +} + +size_t SymbolTableBaseSection::getSymbolIndex(Symbol *sym) { + if (this == mainPart->dynSymTab) + 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->defineCommon) + if (auto *d = dyn_cast<Defined>(sym)) + return dyn_cast_or_null<BssSection>(d->section); + return nullptr; +} + +static uint32_t getSymSectionIndex(Symbol *sym) { + if (getCommonSec(sym)) + return SHN_COMMON; + if (!isa<Defined>(sym) || sym->needsPltAddr) + 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. + memset(buf, 0, sizeof(Elf_Sym)); + buf += sizeof(Elf_Sym); + + auto *eSym = reinterpret_cast<Elf_Sym *>(buf); + + for (SymbolTableEntry &ent : symbols) { + Symbol *sym = ent.sym; + bool isDefinedHere = type == SHT_SYMTAB || sym->partition == partition; + + // Set st_info and st_other. + eSym->st_other = 0; + if (sym->isLocal()) { + eSym->setBindingAndType(STB_LOCAL, sym->type); + } else { + eSym->setBindingAndType(sym->computeBinding(), sym->type); + eSym->setVisibility(sym->visibility); + } + + // The 3 most significant bits of st_other are used by OpenPOWER ABI. + // See getPPC64GlobalEntryToLocalEntryOffset() for more details. + if (config->emachine == EM_PPC64) + eSym->st_other |= sym->stOther & 0xe0; + + eSym->st_name = ent.strTabOffset; + if (isDefinedHere) + eSym->st_shndx = getSymSectionIndex(ent.sym); + else + eSym->st_shndx = 0; + + // Copy symbol size if it is a defined symbol. st_size is not significant + // for undefined symbols, so whether copying it or not is up to us if that's + // the case. We'll leave it as zero because by not setting a value, we can + // get the exact same outputs for two sets of input files that differ only + // in undefined symbol size in DSOs. + if (eSym->st_shndx == SHN_UNDEF || !isDefinedHere) + eSym->st_size = 0; + else + eSym->st_size = sym->getSize(); + + // st_value is usually an address of a symbol, but that has a + // special meaining for uninstantiated common symbols (this can + // occur if -r is given). + if (BssSection *commonSec = getCommonSec(ent.sym)) + eSym->st_value = commonSec->alignment; + else if (isDefinedHere) + eSym->st_value = sym->getVA(); + else + eSym->st_value = 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->needsPltAddr) + 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>::relocateOne()` 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->needsPltAddr)) { + if (!strTabSec.isDynamic()) + eSym->st_value &= ~1; + eSym->st_other |= STO_MIPS_MICROMIPS; + } + } + if (config->relocatable) + if (auto *d = dyn_cast<Defined>(sym)) + if (isMipsPIC<ELFT>(d)) + eSym->st_other |= STO_MIPS_PIC; + ++eSym; + } + } +} + +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 : in.symTab->getSymbols()) { + if (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 (BaseCommand *base : script->sectionCommands) + if (isa<OutputSection>(base)) + ++size; + return size >= SHN_LORESERVE; +} + +void SymtabShndxSection::finalizeContents() { + getParent()->link = in.symTab->getParent()->sectionIndex; +} + +size_t SymtabShndxSection::getSize() const { + return 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. A .gnu.hash is added if you +// give the -hash-style=gnu or -hash-style=both option. +// +// The Unix semantics of resolving dynamic symbols is somewhat expensive. +// Each ELF file has a list of DSOs that the ELF file depends on and a +// list of dynamic symbols that need to be resolved from any of the +// DSOs. That means resolving all dynamic symbols takes O(m)*O(n) +// where m is the number of DSOs and n is the number of dynamic +// symbols. For modern large programs, both m and n are large. So +// making each step faster by using hash tables substiantially +// improves time to load programs. +// +// (Note that this is not the only way to design the shared library. +// For instance, the Windows DLL takes a different approach. On +// Windows, each dynamic symbol has a name of DLL from which the symbol +// has to be resolved. That makes the cost of symbol resolution O(n). +// This disables some hacky techniques you can use on Unix such as +// LD_PRELOAD, but this is arguably better semantics than the Unix ones.) +// +// Due to historical reasons, we have two different hash tables, .hash +// and .gnu.hash. They are for the same purpose, and .gnu.hash is a new +// and better version of .hash. .hash is just an on-disk hash table, but +// .gnu.hash has a bloom filter in addition to a hash table to skip +// DSOs very quickly. If you are sure that your dynamic linker knows +// about .gnu.hash, you want to specify -hash-style=gnu. Otherwise, a +// safe bet is to specify -hash-style=both for backward compatibilty. +GnuHashTableSection::GnuHashTableSection() + : SyntheticSection(SHF_ALLOC, SHT_GNU_HASH, config->wordsize, ".gnu.hash") { +} + +void GnuHashTableSection::finalizeContents() { + 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) { + // The output buffer is not guaranteed to be zero-cleared because we pre- + // fill executable sections with trap instructions. This is a precaution + // for that case, which happens only when -no-rosegment is given. + memset(buf, 0, size); + + // Write a header. + write32(buf, nBuckets); + write32(buf + 4, getPartition().dynSymTab->getNumSymbols() - symbols.size()); + write32(buf + 8, maskWords); + write32(buf + 12, Shift2); + buf += 16; + + // Write a bloom filter and a hash table. + writeBloomFilter(buf); + buf += config->wordsize * maskWords; + writeHashTable(buf); +} + +// This function writes a 2-bit bloom filter. This bloom filter alone +// usually filters out 80% or more of all symbol lookups [1]. +// The dynamic linker uses the hash table only when a symbol is not +// filtered out by a bloom filter. +// +// [1] Ulrich Drepper (2011), "How To Write Shared Libraries" (Ver. 4.1.2), +// p.9, https://www.akkadia.org/drepper/dsohowto.pdf +void GnuHashTableSection::writeBloomFilter(uint8_t *buf) { + 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); + } +} + +void GnuHashTableSection::writeHashTable(uint8_t *buf) { + uint32_t *buckets = reinterpret_cast<uint32_t *>(buf); + uint32_t oldBucket = -1; + uint32_t *values = buckets + nBuckets; + for (auto i = symbols.begin(), e = symbols.end(); i != e; ++i) { + // Write a hash value. It represents a sequence of chains that share the + // same hash modulo value. The last element of each chain is terminated by + // LSB 1. + uint32_t hash = i->hash; + bool isLastInChain = (i + 1) == e || i->bucketIdx != (i + 1)->bucketIdx; + hash = isLastInChain ? hash | 1 : hash & ~1; + write32(values++, hash); + + if (i->bucketIdx == oldBucket) + continue; + // Write a hash bucket. Hash buckets contain indices in the following hash + // value table. + write32(buckets + i->bucketIdx, + getPartition().dynSymTab->getSymbolIndex(i->sym)); + oldBucket = i->bucketIdx; + } +} + +static uint32_t hashGnu(StringRef name) { + uint32_t h = 5381; + for (uint8_t c : name) + h = (h << 5) + h + c; + return h; +} + +// Add symbols to this symbol hash table. Note that this function +// destructively sort a given vector -- which is needed because +// GNU-style hash table places some sorting requirements. +void GnuHashTableSection::addSymbols(std::vector<SymbolTableEntry> &v) { + // We cannot use 'auto' for Mid because GCC 6.1 cannot deduce + // its type correctly. + std::vector<SymbolTableEntry>::iterator mid = + std::stable_partition(v.begin(), v.end(), [&](const SymbolTableEntry &s) { + 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::stable_sort(symbols, [](const Entry &l, const Entry &r) { + return l.bucketIdx < r.bucketIdx; + }); + + v.erase(mid, v.end()); + for (const Entry &ent : symbols) + v.push_back({ent.sym, ent.strTabOffset}); +} + +HashTableSection::HashTableSection() + : SyntheticSection(SHF_ALLOC, SHT_HASH, 4, ".hash") { + this->entsize = 4; +} + +void HashTableSection::finalizeContents() { + SymbolTableBaseSection *symTab = getPartition().dynSymTab; + + 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; + + // See comment in GnuHashTableSection::writeTo. + memset(buf, 0, size); + + 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); + } +} + +// On PowerPC64 the lazy symbol resolvers go into the `global linkage table` +// in the .glink section, rather then the typical .plt section. +PltSection::PltSection(bool isIplt) + : SyntheticSection( + SHF_ALLOC | SHF_EXECINSTR, SHT_PROGBITS, 16, + (config->emachine == EM_PPC || config->emachine == EM_PPC64) + ? ".glink" + : ".plt"), + headerSize(!isIplt || config->zRetpolineplt ? target->pltHeaderSize : 0), + isIplt(isIplt) { + // 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) { + if (config->emachine == EM_PPC) { + writePPC32GlinkSection(buf, entries.size()); + return; + } + + // At beginning of PLT or retpoline IPLT, we have code to call the dynamic + // linker to resolve dynsyms at runtime. Write such code. + if (headerSize) + target->writePltHeader(buf); + size_t off = headerSize; + + RelocationBaseSection *relSec = isIplt ? in.relaIplt : in.relaPlt; + + // The IPlt is immediately after the Plt, account for this in relOff + size_t pltOff = isIplt ? in.plt->getSize() : 0; + + for (size_t i = 0, e = entries.size(); i != e; ++i) { + const Symbol *b = entries[i]; + unsigned relOff = relSec->entsize * i + pltOff; + uint64_t got = b->getGotPltVA(); + uint64_t plt = this->getVA() + off; + target->writePlt(buf + off, got, plt, b->pltIndex, relOff); + off += target->pltEntrySize; + } +} + +template <class ELFT> void PltSection::addEntry(Symbol &sym) { + sym.pltIndex = entries.size(); + entries.push_back(&sym); +} + +size_t PltSection::getSize() const { + return headerSize + entries.size() * target->pltEntrySize; +} + +// Some architectures such as additional symbols in the PLT section. For +// example ARM uses mapping symbols to aid disassembly +void PltSection::addSymbols() { + // The PLT may have symbols defined for the Header, the IPLT has no header + if (!isIplt) + target->addPltHeaderSymbols(*this); + + size_t off = headerSize; + for (size_t i = 0; i < entries.size(); ++i) { + target->addPltSymbols(*this, off); + off += target->pltEntrySize; + } +} + +// 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; +} + +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); +} + +// Compute the output section size. +void GdbIndexSection::initOutputSize() { + size = sizeof(GdbIndexHeader) + computeSymtabSize() * 8; + + for (GdbChunk &chunk : chunks) + size += chunk.compilationUnits.size() * 16 + chunk.addressAreas.size() * 20; + + // Add the constant pool size if exists. + if (!symbols.empty()) { + GdbSymbol &sym = symbols.back(); + size += sym.nameOff + sym.name.size() + 1; + } +} + +static std::vector<InputSection *> getDebugInfoSections() { + std::vector<InputSection *> ret; + for (InputSectionBase *s : inputSections) + if (InputSection *isec = dyn_cast<InputSection>(s)) + if (isec->name == ".debug_info") + ret.push_back(isec); + return ret; +} + +static std::vector<GdbIndexSection::CuEntry> readCuList(DWARFContext &dwarf) { + std::vector<GdbIndexSection::CuEntry> ret; + for (std::unique_ptr<DWARFUnit> &cu : dwarf.compile_units()) + ret.push_back({cu->getOffset(), cu->getLength() + 4}); + return ret; +} + +static std::vector<GdbIndexSection::AddressEntry> +readAddressAreas(DWARFContext &dwarf, InputSection *sec) { + std::vector<GdbIndexSection::AddressEntry> ret; + + uint32_t cuIdx = 0; + for (std::unique_ptr<DWARFUnit> &cu : dwarf.compile_units()) { + Expected<DWARFAddressRangesVector> ranges = cu->collectAddressRanges(); + if (!ranges) { + error(toString(sec) + ": " + toString(ranges.takeError())); + return {}; + } + + ArrayRef<InputSectionBase *> sections = sec->file->getSections(); + for (DWARFAddressRange &r : *ranges) { + if (r.SectionIndex == -1ULL) + continue; + InputSectionBase *s = sections[r.SectionIndex]; + if (!s || s == &InputSection::discarded || !s->isLive()) + continue; + // Range list with zero size has no effect. + if (r.LowPC == r.HighPC) + continue; + auto *isec = cast<InputSection>(s); + uint64_t offset = isec->getOffsetInFile(); + ret.push_back({isec, r.LowPC - offset, r.HighPC - offset, cuIdx}); + } + ++cuIdx; + } + + return ret; +} + +template <class ELFT> +static std::vector<GdbIndexSection::NameAttrEntry> +readPubNamesAndTypes(const LLDDwarfObj<ELFT> &obj, + const std::vector<GdbIndexSection::CuEntry> &cUs) { + const DWARFSection &pubNames = obj.getGnuPubNamesSection(); + const DWARFSection &pubTypes = obj.getGnuPubTypesSection(); + + std::vector<GdbIndexSection::NameAttrEntry> ret; + for (const DWARFSection *pub : {&pubNames, &pubTypes}) { + DWARFDebugPubTable table(obj, *pub, config->isLE, true); + 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 = + lower_bound(cUs, set.Offset, + [](GdbIndexSection::CuEntry cu, uint32_t offset) { + return cu.cuOffset < 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::vector<GdbIndexSection::GdbSymbol> +createSymbols(ArrayRef<std::vector<GdbIndexSection::NameAttrEntry>> nameAttrs, + const std::vector<GdbIndexSection::GdbChunk> &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::vector<uint32_t> cuIdxs(chunks.size()); + for (uint32_t i = 0, e = chunks.size(); i != e; ++i) { + cuIdxs[i] = cuIdx; + cuIdx += chunks[i].compilationUnits.size(); + } + + // The number of symbols we will handle in this function is of the order + // of millions for very large executables, so we use multi-threading to + // speed it up. + size_t numShards = 32; + size_t concurrency = 1; + if (threadsEnabled) + concurrency = + std::min<size_t>(PowerOf2Floor(hardware_concurrency()), numShards); + + // A sharded map to uniquify symbols by name. + std::vector<DenseMap<CachedHashStringRef, size_t>> map(numShards); + size_t shift = 32 - countTrailingZeros(numShards); + + // Instantiate GdbSymbols while uniqufying them by name. + std::vector<std::vector<GdbSymbol>> symbols(numShards); + parallelForEachN(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]; + size_t &idx = map[shardId][ent.name]; + if (idx) { + symbols[shardId][idx - 1].cuVector.push_back(v); + continue; + } + + idx = symbols[shardId].size() + 1; + symbols[shardId].push_back({ent.name, {v}, 0, 0}); + } + ++i; + } + }); + + size_t numSymbols = 0; + for (ArrayRef<GdbSymbol> v : symbols) + numSymbols += v.size(); + + // The return type is a flattened vector, so we'll copy each vector + // contents to Ret. + std::vector<GdbSymbol> ret; + ret.reserve(numSymbols); + for (std::vector<GdbSymbol> &vec : symbols) + 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; + } + + return ret; +} + +// Returns a newly-created .gdb_index section. +template <class ELFT> GdbIndexSection *GdbIndexSection::create() { + std::vector<InputSection *> sections = getDebugInfoSections(); + + // .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. + for (InputSectionBase *s : inputSections) + if (s->name == ".debug_gnu_pubnames" || s->name == ".debug_gnu_pubtypes") + s->markDead(); + + std::vector<GdbChunk> chunks(sections.size()); + std::vector<std::vector<NameAttrEntry>> nameAttrs(sections.size()); + + parallelForEachN(0, sections.size(), [&](size_t i) { + ObjFile<ELFT> *file = sections[i]->getFile<ELFT>(); + DWARFContext dwarf(make_unique<LLDDwarfObj<ELFT>>(file)); + + chunks[i].sec = sections[i]; + chunks[i].compilationUnits = readCuList(dwarf); + chunks[i].addressAreas = readAddressAreas(dwarf, sections[i]); + nameAttrs[i] = readPubNamesAndTypes<ELFT>( + static_cast<const LLDDwarfObj<ELFT> &>(dwarf.getDWARFObj()), + chunks[i].compilationUnits); + }); + + auto *ret = make<GdbIndexSection>(); + ret->chunks = std::move(chunks); + ret->symbols = createSymbols(nameAttrs, ret->chunks); + ret->initOutputSize(); + 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) { + uint64_t baseAddr = e.section->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 = Out::bufferStart + getParent()->offset + outSecOff; + using FdeData = EhFrameSection::FdeData; + + std::vector<FdeData> 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 (VersionDefinition &v : config->versionDefinitions) + 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 (VersionDefinition &v : config->versionDefinitions) { + 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()) { + write16(buf, s.sym->versionId); + buf += 2; + } +} + +bool VersionTableSection::isNeeded() const { + return getPartition().verDef || getPartition().verNeed->isNeeded(); +} + +void elf::addVerneed(Symbol *ss) { + auto &file = cast<SharedFile>(*ss->file); + if (ss->verdefIndex == VER_NDX_GLOBAL) { + 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->verdefIndex] == 0) + file.vernauxs[ss->verdefIndex] = ++SharedFile::vernauxNum + getVerDefNum(); + + ss->versionId = file.vernauxs[ss->verdefIndex]; +} + +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 : sharedFiles) { + if (f->vernauxs.empty()) + continue; + verneeds.emplace_back(); + Verneed &vn = verneeds.back(); + vn.nameStrTab = getPartition().dynStrTab->addString(f->soName); + 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]); + vn.vernauxs.push_back( + {verdef->vd_hash, f->vernauxs[i], + getPartition().dynStrTab->addString(f->getStringTable().data() + + verdef->getAux()->vda_name)}); + } + } + + 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 SharedFile::vernauxNum != 0; +} + +void MergeSyntheticSection::addSection(MergeInputSection *ms) { + ms->parent = this; + sections.push_back(ms); + assert(alignment == ms->alignment || !(ms->flags & SHF_STRINGS)); + alignment = std::max(alignment, ms->alignment); +} + +MergeTailSection::MergeTailSection(StringRef name, uint32_t type, + uint64_t flags, uint32_t alignment) + : MergeSyntheticSection(name, type, flags, alignment), + builder(StringTableBuilder::RAW, alignment) {} + +size_t MergeTailSection::getSize() const { return builder.getSize(); } + +void MergeTailSection::writeTo(uint8_t *buf) { builder.write(buf); } + +void MergeTailSection::finalizeContents() { + // Add all string pieces to the string table builder to create section + // contents. + for (MergeInputSection *sec : sections) + for (size_t i = 0, e = sec->pieces.size(); i != e; ++i) + if (sec->pieces[i].live) + builder.add(sec->getData(i)); + + // Fix the string table content. After this, the contents will never change. + builder.finalize(); + + // finalize() fixed tail-optimized strings, so we can now get + // offsets of strings. Get an offset for each string and save it + // to a corresponding 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) { + for (size_t i = 0; i < numShards; ++i) + shards[i].write(buf + shardOffsets[i]); +} + +// This function is very hot (i.e. it can take several seconds to finish) +// because sometimes the number of inputs is in an order of magnitude of +// millions. So, we use multi-threading. +// +// For any strings S and T, we know S is not mergeable with T if S's hash +// value is different from T's. If that's the case, we can safely put S and +// T into different string builders without worrying about merge misses. +// We do it in parallel. +void MergeNoTailSection::finalizeContents() { + // Initializes string table builders. + for (size_t i = 0; i < numShards; ++i) + shards.emplace_back(StringTableBuilder::RAW, alignment); + + // Concurrency level. Must be a power of 2 to avoid expensive modulo + // operations in the following tight loop. + size_t concurrency = 1; + if (threadsEnabled) + concurrency = + std::min<size_t>(PowerOf2Floor(hardware_concurrency()), numShards); + + // Add section pieces to the builders. + parallelForEachN(0, concurrency, [&](size_t threadId) { + for (MergeInputSection *sec : sections) { + for (size_t i = 0, e = sec->pieces.size(); i != e; ++i) { + 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 = alignTo(off, alignment); + shardOffsets[i] = off; + off += shards[i].getSize(); + } + size = off; + + // So far, section pieces have offsets from beginning of shards, but + // we want offsets from beginning of the whole section. Fix them. + parallelForEach(sections, [&](MergeInputSection *sec) { + for (size_t i = 0, e = sec->pieces.size(); i != e; ++i) + if (sec->pieces[i].live) + sec->pieces[i].outputOff += + shardOffsets[getShardId(sec->pieces[i].hash)]; + }); +} + +static MergeSyntheticSection *createMergeSynthetic(StringRef name, + uint32_t type, + uint64_t flags, + uint32_t alignment) { + bool shouldTailMerge = (flags & SHF_STRINGS) && config->optimize >= 2; + if (shouldTailMerge) + return make<MergeTailSection>(name, type, flags, alignment); + return make<MergeNoTailSection>(name, type, flags, alignment); +} + +template <class ELFT> void elf::splitSections() { + // splitIntoPieces needs to be called on each MergeInputSection + // before calling finalizeContents(). + parallelForEach(inputSections, [](InputSectionBase *sec) { + if (auto *s = dyn_cast<MergeInputSection>(sec)) + s->splitIntoPieces(); + else if (auto *eh = dyn_cast<EhInputSection>(sec)) + eh->split<ELFT>(); + }); +} + +// This function scans over the inputsections to create mergeable +// synthetic sections. +// +// It removes MergeInputSections from the input section array and adds +// new synthetic sections at the location of the first input section +// that it replaces. It then finalizes each synthetic section in order +// to compute an output offset for each piece of each input section. +void elf::mergeSections() { + std::vector<MergeSyntheticSection *> mergeSections; + for (InputSectionBase *&s : inputSections) { + MergeInputSection *ms = dyn_cast<MergeInputSection>(s); + if (!ms) + continue; + + // We do not want to handle sections that are not alive, so just remove + // them instead of trying to merge. + if (!ms->isLive()) { + s = nullptr; + continue; + } + + StringRef outsecName = getOutputSectionName(ms); + + auto i = llvm::find_if(mergeSections, [=](MergeSyntheticSection *sec) { + // While we could create a single synthetic section for two different + // values of Entsize, it is better to take Entsize into consideration. + // + // With a single synthetic section no two pieces with different Entsize + // could be equal, so we may as well have two sections. + // + // Using Entsize in here also allows us to propagate it to the synthetic + // section. + // + // SHF_STRINGS section with different alignments should not be merged. + return sec->name == outsecName && sec->flags == ms->flags && + sec->entsize == ms->entsize && + (sec->alignment == ms->alignment || !(sec->flags & SHF_STRINGS)); + }); + if (i == mergeSections.end()) { + MergeSyntheticSection *syn = + createMergeSynthetic(outsecName, ms->type, ms->flags, ms->alignment); + mergeSections.push_back(syn); + i = std::prev(mergeSections.end()); + s = syn; + syn->entsize = ms->entsize; + } else { + s = nullptr; + } + (*i)->addSection(ms); + } + for (auto *ms : mergeSections) + ms->finalizeContents(); + + std::vector<InputSectionBase *> &v = inputSections; + v.erase(std::remove(v.begin(), v.end(), nullptr), v.end()); +} + +MipsRldMapSection::MipsRldMapSection() + : SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_PROGBITS, config->wordsize, + ".rld_map") {} + +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) + return d; + return nullptr; +} + +bool ARMExidxSyntheticSection::addSection(InputSection *isec) { + if (isec->type == SHT_ARM_EXIDX) { + exidxSections.push_back(isec); + return true; + } + + if ((isec->flags & SHF_ALLOC) && (isec->flags & SHF_EXECINSTR) && + isec->getSize() > 0) { + executableSections.push_back(isec); + if (empty && findExidxSection(isec)) + empty = false; + 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) { + + struct ExidxEntry { + ulittle32_t fn; + ulittle32_t unwind; + }; + // Get the last table Entry from the previous .ARM.exidx section. If Prev is + // nullptr then it will be a synthesized EXIDX_CANTUNWIND entry. + ExidxEntry prevEntry = {ulittle32_t(0), ulittle32_t(1)}; + if (prev) + prevEntry = prev->getDataAs<ExidxEntry>().back(); + if (isExtabRef(prevEntry.unwind)) + 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 prevEntry.unwind == 1; + + for (const ExidxEntry entry : cur->getDataAs<ExidxEntry>()) + if (isExtabRef(entry.unwind) || entry.unwind != prevEntry.unwind) + 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. 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() { + if (script->hasSectionsCommand) { + // The executableSections and exidxSections that we use to derive the + // final contents of this SyntheticSection are populated before the + // linker script assigns InputSections to OutputSections. The linker script + // SECTIONS command may have a /DISCARD/ entry that removes executable + // InputSections and their dependent .ARM.exidx section that we recorded + // earlier. + auto isDiscarded = [](const InputSection *isec) { return !isec->isLive(); }; + llvm::erase_if(executableSections, isDiscarded); + llvm::erase_if(exidxSections, isDiscarded); + } + + // 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 to be known. + auto compareByFilePosition = [](const InputSection *a, + const InputSection *b) { + OutputSection *aOut = a->getParent(); + OutputSection *bOut = b->getParent(); + + if (aOut != bOut) + return aOut->sectionIndex < bOut->sectionIndex; + return a->outSecOff < b->outSecOff; + }; + llvm::stable_sort(executableSections, compareByFilePosition); + sentinel = executableSections.back(); + // Optionally merge adjacent duplicate entries. + if (config->mergeArmExidx) { + std::vector<InputSection *> 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); + } + + 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) { + + const uint8_t cantUnwindData[8] = {0, 0, 0, 0, // PREL31 to target + 1, 0, 0, 0}; // EXIDX_CANTUNWIND + + uint64_t offset = 0; + for (InputSection *isec : executableSections) { + assert(isec->getParent() != nullptr); + if (InputSection *d = findExidxSection(isec)) { + memcpy(buf + offset, d->data().data(), d->data().size()); + d->relocateAlloc(buf, buf + d->getSize()); + offset += d->getSize(); + } else { + // A Linker generated CANTUNWIND section. + memcpy(buf + offset, cantUnwindData, sizeof(cantUnwindData)); + uint64_t s = isec->getVA(); + uint64_t p = getVA() + offset; + target->relocateOne(buf + offset, R_ARM_PREL31, s - p); + offset += 8; + } + } + // Write Sentinel. + memcpy(buf + offset, cantUnwindData, sizeof(cantUnwindData)); + uint64_t s = sentinel->getVA(sentinel->getSize()); + uint64_t p = getVA() + offset; + target->relocateOne(buf + offset, R_ARM_PREL31, s - p); + assert(size == offset + 8); +} + +bool ARMExidxSyntheticSection::classof(const SectionBase *d) { + return d->kind() == InputSectionBase::Synthetic && d->type == SHT_ARM_EXIDX; +} + +ThunkSection::ThunkSection(OutputSection *os, uint64_t off) + : SyntheticSection(SHF_ALLOC | SHF_EXECINSTR, SHT_PROGBITS, + config->wordsize, ".text.thunk") { + this->parent = os; + this->outSecOff = off; +} + +void ThunkSection::addThunk(Thunk *t) { + 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 = alignTo(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 (BaseCommand *base : getParent()->sectionCommands) + if (auto *isd = dyn_cast<InputSectionDescription>(base)) + 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". + uint32_t offset = 0; + for (BaseCommand *base : getParent()->sectionCommands) + if (auto *isd = dyn_cast<InputSectionDescription>(base)) { + for (InputSection *isec : isd->sections) { + if (isec == this) + continue; + isec->file->ppc32Got2OutSecOff = offset; + offset += (uint32_t)isec->getSize(); + } + } +} + +// 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") {} + +void PPC64LongBranchTargetSection::addEntry(Symbol &sym) { + assert(sym.ppc64BranchltIndex == 0xffff); + sym.ppc64BranchltIndex = entries.size(); + entries.push_back(&sym); +} + +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 it. + if (config->isPic) + return; + + for (const Symbol *sym : entries) { + 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() + 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. Becuase 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(); +} + +RISCVSdataSection::RISCVSdataSection() + : SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_PROGBITS, 1, ".sdata") {} + +bool RISCVSdataSection::isNeeded() const { + if (!ElfSym::riscvGlobalPointer) + return false; + + // __global_pointer$ is defined relative to .sdata . If the section does not + // exist, create a dummy one. + for (BaseCommand *base : getParent()->sectionCommands) + if (auto *isd = dyn_cast<InputSectionDescription>(base)) + for (InputSection *isec : isd->sections) + if (isec != this) + return false; + return true; +} + +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) { + uint8_t ver = objectFiles[0]->abiVersion; + for (InputFile *file : makeArrayRef(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) { + // For executable segments, the trap instructions are written before writing + // the header. Setting Elf header bytes to zero ensures that any unused bytes + // in header are zero-cleared, instead of having trap instructions. + memset(buf, 0, sizeof(typename ELFT::Ehdr)); + memcpy(buf, "\177ELF", 4); + + auto *eHdr = reinterpret_cast<typename ELFT::Ehdr *>(buf); + eHdr->e_ident[EI_CLASS] = config->is64 ? ELFCLASS64 : ELFCLASS32; + eHdr->e_ident[EI_DATA] = config->isLE ? 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 * (partitions.size() - 1); +} + +void PartitionIndexSection::finalizeContents() { + for (size_t i = 1; i != partitions.size(); ++i) + partitions[i].nameStrTab = mainPart->dynStrTab->addString(partitions[i].name); +} + +void PartitionIndexSection::writeTo(uint8_t *buf) { + uint64_t va = getVA(); + for (size_t i = 1; i != partitions.size(); ++i) { + write32(buf, mainPart->dynStrTab->getVA() + partitions[i].nameStrTab - va); + write32(buf + 4, partitions[i].elfHeader->getVA() - (va + 4)); + + SyntheticSection *next = + i == partitions.size() - 1 ? in.partEnd : partitions[i + 1].elfHeader; + write32(buf + 8, next->getVA() - partitions[i].elfHeader->getVA()); + + va += 12; + buf += 12; + } +} + +InStruct elf::in; + +std::vector<Partition> elf::partitions; +Partition *elf::mainPart; + +template GdbIndexSection *GdbIndexSection::create<ELF32LE>(); +template GdbIndexSection *GdbIndexSection::create<ELF32BE>(); +template GdbIndexSection *GdbIndexSection::create<ELF64LE>(); +template GdbIndexSection *GdbIndexSection::create<ELF64BE>(); + +template void elf::splitSections<ELF32LE>(); +template void elf::splitSections<ELF32BE>(); +template void elf::splitSections<ELF64LE>(); +template void elf::splitSections<ELF64BE>(); + +template void EhFrameSection::addSection<ELF32LE>(InputSectionBase *); +template void EhFrameSection::addSection<ELF32BE>(InputSectionBase *); +template void EhFrameSection::addSection<ELF64LE>(InputSectionBase *); +template void EhFrameSection::addSection<ELF64BE>(InputSectionBase *); + +template void PltSection::addEntry<ELF32LE>(Symbol &Sym); +template void PltSection::addEntry<ELF32BE>(Symbol &Sym); +template void PltSection::addEntry<ELF64LE>(Symbol &Sym); +template void PltSection::addEntry<ELF64BE>(Symbol &Sym); + +template class elf::MipsAbiFlagsSection<ELF32LE>; +template class elf::MipsAbiFlagsSection<ELF32BE>; +template class elf::MipsAbiFlagsSection<ELF64LE>; +template class elf::MipsAbiFlagsSection<ELF64BE>; + +template class elf::MipsOptionsSection<ELF32LE>; +template class elf::MipsOptionsSection<ELF32BE>; +template class elf::MipsOptionsSection<ELF64LE>; +template class elf::MipsOptionsSection<ELF64BE>; + +template class elf::MipsReginfoSection<ELF32LE>; +template class elf::MipsReginfoSection<ELF32BE>; +template class elf::MipsReginfoSection<ELF64LE>; +template class elf::MipsReginfoSection<ELF64BE>; + +template class elf::DynamicSection<ELF32LE>; +template class elf::DynamicSection<ELF32BE>; +template class elf::DynamicSection<ELF64LE>; +template class elf::DynamicSection<ELF64BE>; + +template class elf::RelocationSection<ELF32LE>; +template class elf::RelocationSection<ELF32BE>; +template class elf::RelocationSection<ELF64LE>; +template class elf::RelocationSection<ELF64BE>; + +template class elf::AndroidPackedRelocationSection<ELF32LE>; +template class elf::AndroidPackedRelocationSection<ELF32BE>; +template class elf::AndroidPackedRelocationSection<ELF64LE>; +template class elf::AndroidPackedRelocationSection<ELF64BE>; + +template class elf::RelrSection<ELF32LE>; +template class elf::RelrSection<ELF32BE>; +template class elf::RelrSection<ELF64LE>; +template class elf::RelrSection<ELF64BE>; + +template class elf::SymbolTableSection<ELF32LE>; +template class elf::SymbolTableSection<ELF32BE>; +template class elf::SymbolTableSection<ELF64LE>; +template class elf::SymbolTableSection<ELF64BE>; + +template class elf::VersionNeedSection<ELF32LE>; +template class elf::VersionNeedSection<ELF32BE>; +template class elf::VersionNeedSection<ELF64LE>; +template class elf::VersionNeedSection<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 class elf::PartitionElfHeaderSection<ELF32LE>; +template class elf::PartitionElfHeaderSection<ELF32BE>; +template class elf::PartitionElfHeaderSection<ELF64LE>; +template class elf::PartitionElfHeaderSection<ELF64BE>; + +template class elf::PartitionProgramHeadersSection<ELF32LE>; +template class elf::PartitionProgramHeadersSection<ELF32BE>; +template class elf::PartitionProgramHeadersSection<ELF64LE>; +template class elf::PartitionProgramHeadersSection<ELF64BE>; |