//===- 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/DWARF.h" #include "lld/Common/ErrorHandler.h" #include "lld/Common/Memory.h" #include "lld/Common/Strings.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 "llvm/Support/Parallel.h" #include "llvm/Support/TimeProfiler.h" #include #include 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 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 ". // The returned object is a mergeable string section. MergeInputSection *elf::createCommentSection() { return make(SHF_MERGE | SHF_STRINGS, SHT_PROGBITS, 1, getVersion(), ".comment"); } // .MIPS.abiflags section. template MipsAbiFlagsSection::MipsAbiFlagsSection(Elf_Mips_ABIFlags flags) : SyntheticSection(SHF_ALLOC, SHT_MIPS_ABIFLAGS, 8, ".MIPS.abiflags"), flags(flags) { this->entsize = sizeof(Elf_Mips_ABIFlags); } template void MipsAbiFlagsSection::writeTo(uint8_t *buf) { memcpy(buf, &flags, sizeof(flags)); } template MipsAbiFlagsSection *MipsAbiFlagsSection::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(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>(flags); return nullptr; } // .MIPS.options section. template MipsOptionsSection::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 void MipsOptionsSection::writeTo(uint8_t *buf) { auto *options = reinterpret_cast(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 MipsOptionsSection *MipsOptionsSection::create() { // N64 ABI only. if (!ELFT::Is64Bits) return nullptr; std::vector 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 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(d.data()); if (opt->kind == ODK_REGINFO) { reginfo.ri_gprmask |= opt->getRegInfo().ri_gprmask; sec->getFile()->mipsGp0 = opt->getRegInfo().ri_gp_value; break; } if (!opt->size) fatal(filename + ": zero option descriptor size"); d = d.slice(opt->size); } }; return make>(reginfo); } // MIPS .reginfo section. template MipsReginfoSection::MipsReginfoSection(Elf_Mips_RegInfo reginfo) : SyntheticSection(SHF_ALLOC, SHT_MIPS_REGINFO, 4, ".reginfo"), reginfo(reginfo) { this->entsize = sizeof(Elf_Mips_RegInfo); } template void MipsReginfoSection::writeTo(uint8_t *buf) { if (!config->relocatable) reginfo.ri_gp_value = in.mipsGot->getGp(); memcpy(buf, ®info, sizeof(reginfo)); } template MipsReginfoSection *MipsReginfoSection::create() { // Section should be alive for O32 and N32 ABIs only. if (ELFT::Is64Bits) return nullptr; std::vector 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(sec->data().data()); reginfo.ri_gprmask |= r->ri_gprmask; sec->getFile()->mipsGp0 = r->ri_gp_value; }; return make>(reginfo); } InputSection *elf::createInterpSection() { // StringSaver guarantees that the returned string ends with '\0'. StringRef s = saver.save(config->dynamicLinker); ArrayRef contents = {(const uint8_t *)s.data(), s.size() + 1}; return make(nullptr, SHF_ALLOC, SHT_PROGBITS, 1, contents, ".interp"); } Defined *elf::addSyntheticLocal(StringRef name, uint8_t type, uint64_t value, uint64_t size, InputSectionBase §ion) { auto *s = make(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, config->wordsize, ".note.gnu.property") {} void GnuPropertySection::writeTo(uint8_t *buf) { uint32_t featureAndType = config->emachine == EM_AARCH64 ? GNU_PROPERTY_AARCH64_FEATURE_1_AND : GNU_PROPERTY_X86_FEATURE_1_AND; write32(buf, 4); // Name size write32(buf + 4, config->is64 ? 16 : 12); // Content size write32(buf + 8, NT_GNU_PROPERTY_TYPE_0); // Type memcpy(buf + 12, "GNU", 4); // Name string write32(buf + 16, featureAndType); // Feature type write32(buf + 20, 4); // Feature size write32(buf + 24, config->andFeatures); // Feature flags if (config->is64) write32(buf + 28, 0); // Padding } size_t GnuPropertySection::getSize() const { return config->is64 ? 32 : 28; } BuildIdSection::BuildIdSection() : SyntheticSection(SHF_ALLOC, SHT_NOTE, 4, ".note.gnu.build-id"), hashSize(getHashSize()) {} void BuildIdSection::writeTo(uint8_t *buf) { write32(buf, 4); // Name size write32(buf + 4, hashSize); // Content size write32(buf + 8, NT_GNU_BUILD_ID); // Type memcpy(buf + 12, "GNU", 4); // Name string hashBuf = buf + 16; } void BuildIdSection::writeBuildId(ArrayRef 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 CieRecord *EhFrameSection::addCie(EhSectionPiece &cie, ArrayRef rels) { Symbol *personality = nullptr; unsigned firstRelI = cie.firstRelocation; if (firstRelI != (unsigned)-1) personality = &cie.sec->template getFile()->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(); rec->cie = &cie; cieRecords.push_back(rec); } return rec; } // There is one FDE per function. Returns a non-null pointer to the function // symbol if the given FDE points to a live function. template Defined *EhFrameSection::isFdeLive(EhSectionPiece &fde, ArrayRef rels) { auto *sec = cast(fde.sec); unsigned firstRelI = fde.firstRelocation; // An FDE should point to some function because FDEs are to describe // functions. That's however not always the case due to an issue of // ld.gold with -r. ld.gold may discard only functions and leave their // corresponding FDEs, which results in creating bad .eh_frame sections. // To deal with that, we ignore such FDEs. if (firstRelI == (unsigned)-1) return nullptr; const RelTy &rel = rels[firstRelI]; Symbol &b = sec->template getFile()->getRelocTargetSym(rel); // FDEs for garbage-collected or merged-by-ICF sections, or sections in // another partition, are dead. if (auto *d = dyn_cast(&b)) if (d->section && d->section->partition == partition) return d; return nullptr; } // .eh_frame is a sequence of CIE or FDE records. In general, there // is one CIE record per input object file which is followed by // a list of FDEs. This function searches an existing CIE or create a new // one and associates FDEs to the CIE. template void EhFrameSection::addRecords(EhInputSection *sec, ArrayRef 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(piece, rels); continue; } uint32_t cieOffset = offset + 4 - id; CieRecord *rec = offsetToCie[cieOffset]; if (!rec) fatal(toString(sec) + ": invalid CIE reference"); if (!isFdeLive(piece, rels)) continue; rec->fdes.push_back(&piece); numFdes++; } } template void EhFrameSection::addSectionAux(EhInputSection *sec) { if (!sec->isLive()) return; if (sec->areRelocsRela) addRecords(sec, sec->template relas()); else addRecords(sec, sec->template rels()); } void EhFrameSection::addSection(EhInputSection *sec) { sec->parent = this; alignment = std::max(alignment, sec->alignment); sections.push_back(sec); for (auto *ds : sec->dependentSections) dependentSections.push_back(ds); } // Used by ICF::handleLSDA(). This function is very similar to // EhFrameSection::addRecords(). template void EhFrameSection::iterateFDEWithLSDAAux( EhInputSection &sec, ArrayRef rels, DenseSet &ciesWithLSDA, llvm::function_ref fn) { for (EhSectionPiece &piece : sec.pieces) { // Skip ZERO terminator. if (piece.size == 4) continue; size_t offset = piece.inputOff; uint32_t id = endian::read32(piece.data().data() + 4); if (id == 0) { if (hasLSDA(piece)) ciesWithLSDA.insert(offset); continue; } uint32_t cieOffset = offset + 4 - id; if (ciesWithLSDA.count(cieOffset) == 0) continue; // The CIE has a LSDA argument. Call fn with d's section. if (Defined *d = isFdeLive(piece, rels)) if (auto *s = dyn_cast_or_null(d->section)) fn(*s); } } template void EhFrameSection::iterateFDEWithLSDA( llvm::function_ref fn) { DenseSet ciesWithLSDA; for (EhInputSection *sec : sections) { ciesWithLSDA.clear(); if (sec->areRelocsRela) iterateFDEWithLSDAAux(*sec, sec->template relas(), ciesWithLSDA, fn); else iterateFDEWithLSDAAux(*sec, sec->template rels(), ciesWithLSDA, fn); } } static void writeCieFde(uint8_t *buf, ArrayRef 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. switch (config->ekind) { case ELFNoneKind: llvm_unreachable("invalid ekind"); case ELF32LEKind: for (EhInputSection *sec : sections) addSectionAux(sec); break; case ELF32BEKind: for (EhInputSection *sec : sections) addSectionAux(sec); break; case ELF64LEKind: for (EhInputSection *sec : sections) addSectionAux(sec); break; case ELF64BEKind: for (EhInputSection *sec : sections) addSectionAux(sec); break; } 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::getFdeData() const { uint8_t *buf = Out::bufferStart + getParent()->offset + outSecOff; std::vector 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, target->gotEntrySize, ".got") { 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() { if (config->emachine == EM_PPC64 && numEntries <= target->gotHeaderEntriesNum && !ElfSym::globalOffsetTable) size = 0; else size = numEntries * config->wordsize; } bool GotSection::isNeeded() const { // Needed if the GOT symbol is used or the number of entries is more than just // the header. A GOT with just the header may not be needed. return hasGotOffRel || numEntries > target->gotHeaderEntriesNum; } void GotSection::writeTo(uint8_t *buf) { target->writeGotHeader(buf); relocateAlloc(buf, buf + 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 &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(&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(&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 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 &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 &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 &p : got.pagesMap) { const OutputSection *os = p.first; uint64_t secSize = 0; for (BaseCommand *cmd : os->sectionCommands) { if (auto *isd = dyn_cast(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 subtracting "global" entries in the primary GOT. primGot = &gots.front(); primGot->relocs.remove_if([&](const std::pair &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 &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 &p : got.tls) { Symbol *s = p.first; uint64_t offset = p.second * config->wordsize; // When building a shared library we still need a dynamic relocation // for the TP-relative offset as we don't know how much other data will // be allocated before us in the static TLS block. if (s->isPreemptible || config->shared) mainPart->relaDyn->addReloc({target->tlsGotRel, this, offset, DynamicReloc::AgainstSymbolWithTargetVA, *s, 0, R_ABS}); } for (std::pair &p : got.dynTlsSymbols) { Symbol *s = p.first; uint64_t offset = p.second * config->wordsize; if (s == nullptr) { if (!config->shared) continue; mainPart->relaDyn->addReloc({target->tlsModuleIndexRel, this, offset}); } else { // When building a shared library we still need a dynamic relocation // for the module index. Therefore only checking for // S->isPreemptible is not sufficient (this happens e.g. for // thread-locals that have been marked as local through a linker script) if (!s->isPreemptible && !config->shared) continue; mainPart->relaDyn->addSymbolReloc(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->addSymbolReloc(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 &p : got.global) { uint64_t offset = p.second * config->wordsize; mainPart->relaDyn->addSymbolReloc(target->relativeRel, this, offset, *p.first); } if (!config->isPic) continue; // Dynamic relocations for "local" entries in case of PIC. for (const std::pair &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 &p : got.local16) { uint64_t offset = p.second * config->wordsize; mainPart->relaDyn->addReloc({target->relativeRel, this, offset, DynamicReloc::AddendOnlyWithTargetVA, *p.first.first, p.first.second, R_ABS}); } } } bool MipsGotSection::isNeeded() const { // We add the .got section to the result for dynamic MIPS target because // its address and properties are mentioned in the .dynamic section. return !config->relocatable; } uint64_t MipsGotSection::getGp(const InputFile *f) const { // For files without related GOT or files refer a primary GOT // returns "common" _gp value. For secondary GOTs calculate // individual _gp values. if (!f || !f->mipsGotIndex.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 &l : g.pagesMap) { size_t pageCount = l.second.count; uint64_t firstPageAddr = getMipsPageAddr(l.first->addr); for (size_t pi = 0; pi < pageCount; ++pi) write(l.second.firstIndex + pi, nullptr, firstPageAddr + pi * 0x10000); } // Local, global, TLS, reloc-only entries. // If TLS entry has a corresponding dynamic relocations, leave it // initialized by zero. Write down adjusted TLS symbol's values otherwise. // To calculate the adjustments use offsets for thread-local storage. // http://web.archive.org/web/20190324223224/https://www.linux-mips.org/wiki/NPTL for (const std::pair &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 &p : g.global) write(p.second, p.first, 0); for (const std::pair &p : g.relocs) write(p.second, p.first, 0); for (const std::pair &p : g.tls) write(p.second, p.first, p.first->isPreemptible || config->shared ? 0 : -0x7000); for (const std::pair &p : g.dynTlsSymbols) { if (p.first == nullptr && !config->shared) write(p.second, nullptr, 1); else if (p.first && !p.first->isPreemptible) { // If we are emitting a shared libary with relocations we mustn't write // anything to the GOT here. When using Elf_Rel relocations the value // one will be treated as an addend and will cause crashes at runtime if (!config->shared) write(p.second, nullptr, 1); write(p.second + 1, p.first, -0x8000); } } } } // On PowerPC the .plt section is used to hold the table of function addresses // instead of the .got.plt, and the type is SHT_NOBITS similar to a .bss // section. I don't know why we have a BSS style type for the section but it is // consistent across both 64-bit PowerPC ABIs as well as the 32-bit PowerPC ABI. GotPltSection::GotPltSection() : SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_PROGBITS, config->wordsize, ".got.plt") { if (config->emachine == EM_PPC) { name = ".plt"; } else if (config->emachine == EM_PPC64) { type = SHT_NOBITS; name = ".plt"; } } void GotPltSection::addEntry(Symbol &sym) { assert(sym.pltIndex == entries.size()); entries.push_back(&sym); } size_t GotPltSection::getSize() const { return (target->gotPltHeaderEntriesNum + entries.size()) * target->gotEntrySize; } void GotPltSection::writeTo(uint8_t *buf) { target->writeGotPltHeader(buf); buf += target->gotPltHeaderEntriesNum * target->gotEntrySize; for (const Symbol *b : entries) { target->writeGotPlt(buf, *b); buf += target->gotEntrySize; } } bool GotPltSection::isNeeded() const { // We need to emit GOTPLT even if it's empty if there's a relocation relative // to it. return !entries.empty() || hasGotPltOffRel; } static StringRef getIgotPltName() { // On ARM the IgotPltSection is part of the GotSection. if (config->emachine == EM_ARM) return ".got"; // On PowerPC64 the GotPltSection is renamed to '.plt' so the IgotPltSection // needs to be named the same. if (config->emachine == EM_PPC64) return ".plt"; return ".got.plt"; } // On PowerPC64 the GotPltSection type is SHT_NOBITS so we have to follow suit // with the IgotPltSection. IgotPltSection::IgotPltSection() : SyntheticSection(SHF_ALLOC | SHF_WRITE, config->emachine == EM_PPC64 ? SHT_NOBITS : SHT_PROGBITS, target->gotEntrySize, getIgotPltName()) {} void IgotPltSection::addEntry(Symbol &sym) { assert(sym.pltIndex == entries.size()); entries.push_back(&sym); } size_t IgotPltSection::getSize() const { return entries.size() * target->gotEntrySize; } void IgotPltSection::writeTo(uint8_t *buf) { for (const Symbol *b : entries) { target->writeIgotPlt(buf, *b); buf += target->gotEntrySize; } } StringTableSection::StringTableSection(StringRef name, bool dynamic) : SyntheticSection(dynamic ? (uint64_t)SHF_ALLOC : 0, SHT_STRTAB, 1, name), dynamic(dynamic) { // ELF string tables start with a NUL byte. 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 entries in .gnu.version_d: the number of // non-VER_NDX_LOCAL-non-VER_NDX_GLOBAL definitions, plus 1. // Note that we don't support vd_cnt > 1 yet. static unsigned getVerDefNum() { return namedVersionDefs().size() + 1; } template DynamicSection::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 void DynamicSection::add(int32_t tag, std::function fn) { entries.push_back({tag, fn}); } template void DynamicSection::addInt(int32_t tag, uint64_t val) { entries.push_back({tag, [=] { return val; }}); } template void DynamicSection::addInSec(int32_t tag, InputSection *sec) { entries.push_back({tag, [=] { return sec->getVA(0); }}); } template void DynamicSection::addInSecRelative(int32_t tag, InputSection *sec) { size_t tagOffset = entries.size() * entsize; entries.push_back( {tag, [=] { return sec->getVA(0) - (getVA() + tagOffset); }}); } template void DynamicSection::addOutSec(int32_t tag, OutputSection *sec) { entries.push_back({tag, [=] { return sec->addr; }}); } template void DynamicSection::addSize(int32_t tag, OutputSection *sec) { entries.push_back({tag, [=] { return sec->size; }}); } template void DynamicSection::addSym(int32_t tag, Symbol *sym) { entries.push_back({tag, [=] { return sym->getVA(); }}); } // The output section .rela.dyn may include these synthetic sections: // // - part.relaDyn // - in.relaIplt: this is included if in.relaIplt is named .rela.dyn // - in.relaPlt: this is included if a linker script places .rela.plt inside // .rela.dyn // // DT_RELASZ is the total size of the included sections. static std::function addRelaSz(RelocationBaseSection *relaDyn) { return [=]() { size_t size = relaDyn->getSize(); if (in.relaIplt->getParent() == relaDyn->getParent()) size += in.relaIplt->getSize(); if (in.relaPlt->getParent() == relaDyn->getParent()) size += in.relaPlt->getSize(); return size; }; } // A Linker script may assign the RELA relocation sections to the same // output section. When this occurs we cannot just use the OutputSection // Size. Moreover the [DT_JMPREL, DT_JMPREL + DT_PLTRELSZ) is permitted to // overlap with the [DT_RELA, DT_RELA + DT_RELASZ). static uint64_t addPltRelSz() { 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 void DynamicSection::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 == BsymbolicKind::All) dtFlags |= DF_SYMBOLIC; if (config->zGlobal) dtFlags1 |= DF_1_GLOBAL; if (config->zInitfirst) dtFlags1 |= DF_1_INITFIRST; if (config->zInterpose) dtFlags1 |= DF_1_INTERPOSE; if (config->zNodefaultlib) dtFlags1 |= DF_1_NODEFLIB; if (config->zNodelete) dtFlags1 |= DF_1_NODELETE; if (config->zNodlopen) dtFlags1 |= DF_1_NOOPEN; if (config->pie) dtFlags1 |= DF_1_PIE; if (config->zNow) { dtFlags |= DF_BIND_NOW; dtFlags1 |= DF_1_NOW; } if (config->zOrigin) { dtFlags |= DF_ORIGIN; dtFlags1 |= DF_1_ORIGIN; } if (!config->zText) dtFlags |= DF_TEXTREL; if (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 information used by debuggers at runtime. We // need it for each process, so we don't write it for DSOs. The loader writes // the pointer into this entry. // // DT_DEBUG is the only .dynamic entry that needs to be written to. Some // systems (currently only Fuchsia OS) provide other means to give the // debugger this information. Such systems may choose make .dynamic read-only. // If the target is such a system (used -z rodynamic) don't write DT_DEBUG. if (!config->shared && !config->relocatable && !config->zRodynamic) addInt(DT_DEBUG, 0); if (OutputSection *sec = part.dynStrTab->getParent()) this->link = sec->sectionIndex; if (part.relaDyn->isNeeded() || (in.relaIplt->isNeeded() && part.relaDyn->getParent() == in.relaIplt->getParent())) { addInSec(part.relaDyn->dynamicTag, part.relaDyn); entries.push_back({part.relaDyn->sizeDynamicTag, addRelaSz(part.relaDyn)}); bool isRela = config->isRela; addInt(isRela ? DT_RELAENT : DT_RELENT, isRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel)); // MIPS dynamic loader does not support RELCOUNT tag. // The problem is in the tight relation between dynamic // relocations and GOT. So do not emit this tag on MIPS. if (config->emachine != EM_MIPS) { size_t numRelativeRels = part.relaDyn->getRelativeRelocCount(); if (config->zCombreloc && numRelativeRels) addInt(isRela ? DT_RELACOUNT : DT_RELCOUNT, numRelativeRels); } } if (part.relrDyn && !part.relrDyn->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 beginning 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; case EM_AARCH64: if (llvm::find_if(in.relaPlt->relocs, [](const DynamicReloc &r) { return r.type == target->pltRel && r.sym->stOther & STO_AARCH64_VARIANT_PCS; }) != in.relaPlt->relocs.end()) addInt(DT_AARCH64_VARIANT_PCS, 0); LLVM_FALLTHROUGH; 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->zPacPlt) 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); } if (part.verSym && part.verSym->isNeeded()) addInSec(DT_VERSYM, part.verSym); if (part.verDef && part.verDef->isLive()) { addInSec(DT_VERDEF, part.verDef); addInt(DT_VERDEFNUM, getVerDefNum()); } if (part.verNeed && part.verNeed->isNeeded()) { addInSec(DT_VERNEED, part.verNeed); unsigned needNum = 0; for (SharedFile *f : 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 void DynamicSection::writeTo(uint8_t *buf) { auto *p = reinterpret_cast(buf); for (std::pair> &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 { switch (kind) { case AddendOnly: assert(sym == nullptr); return addend; case AgainstSymbol: assert(sym != nullptr); return addend; case AddendOnlyWithTargetVA: case AgainstSymbolWithTargetVA: return InputSection::getRelocTargetVA(inputSec->file, type, addend, getOffset(), *sym, expr); case MipsMultiGotPage: assert(sym == nullptr); return getMipsPageAddr(outputSec->addr) + addend; } llvm_unreachable("Unknown DynamicReloc::Kind enum"); } uint32_t DynamicReloc::getSymIndex(SymbolTableBaseSection *symTab) const { if (needsDynSymIndex()) return 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::addSymbolReloc(RelType dynType, InputSectionBase *isec, uint64_t offsetInSec, Symbol &sym, int64_t addend, Optional addendRelType) { addReloc(DynamicReloc::AgainstSymbol, dynType, isec, offsetInSec, sym, addend, R_ADDEND, addendRelType ? *addendRelType : target->noneRel); } void RelocationBaseSection::addRelativeReloc( RelType dynType, InputSectionBase *inputSec, uint64_t offsetInSec, Symbol &sym, int64_t addend, RelType addendRelType, RelExpr expr) { // This function should only be called for non-preemptible symbols or // RelExpr values that refer to an address inside the output file (e.g. the // address of the GOT entry for a potentially preemptible symbol). assert((!sym.isPreemptible || expr == R_GOT) && "cannot add relative relocation against preemptible symbol"); assert(expr != R_ADDEND && "expected non-addend relocation expression"); addReloc(DynamicReloc::AddendOnlyWithTargetVA, dynType, inputSec, offsetInSec, sym, addend, expr, addendRelType); } void RelocationBaseSection::addAddendOnlyRelocIfNonPreemptible( RelType dynType, InputSectionBase *isec, uint64_t offsetInSec, Symbol &sym, RelType addendRelType) { // No need to write an addend to the section for preemptible symbols. if (sym.isPreemptible) addReloc({dynType, isec, offsetInSec, DynamicReloc::AgainstSymbol, sym, 0, R_ABS}); else addReloc(DynamicReloc::AddendOnlyWithTargetVA, dynType, isec, offsetInSec, sym, 0, R_ABS, addendRelType); } void RelocationBaseSection::addReloc(DynamicReloc::Kind kind, RelType dynType, InputSectionBase *inputSec, uint64_t offsetInSec, Symbol &sym, int64_t addend, RelExpr expr, RelType addendRelType) { // 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, addendRelType, offsetInSec, addend, &sym}); addReloc({dynType, inputSec, offsetInSec, kind, sym, addend, expr}); } 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()->flags |= ELF::SHF_INFO_LINK; getParent()->info = in.gotPlt->getParent()->sectionIndex; } if (in.relaIplt == this) { getParent()->flags |= ELF::SHF_INFO_LINK; getParent()->info = in.igotPlt->getParent()->sectionIndex; } } RelrBaseSection::RelrBaseSection() : SyntheticSection(SHF_ALLOC, config->useAndroidRelrTags ? SHT_ANDROID_RELR : SHT_RELR, config->wordsize, ".relr.dyn") {} template 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 RelocationSection::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 void RelocationSection::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(symTab, reinterpret_cast(buf), rel); buf += config->isRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel); } } template AndroidPackedRelocationSection::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 bool AndroidPackedRelocationSection::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 relatives, nonRelatives; for (const DynamicReloc &rel : relocs) { Elf_Rela r; encodeDynamicReloc(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 ungroupedRelatives; std::vector> relativeGroups; for (auto i = relatives.begin(), e = relatives.end(); i != e;) { std::vector group; do { group.push_back(*i++); } while (i != e && (i - 1)->r_offset + config->wordsize == i->r_offset); if (group.size() < 8) ungroupedRelatives.insert(ungroupedRelatives.end(), group.begin(), group.end()); else relativeGroups.emplace_back(std::move(group)); } // For non-relative relocations, we would like to: // 1. Have relocations with the same symbol offset to be consecutive, so // that the runtime linker can speed-up symbol lookup by implementing an // 1-entry cache. // 2. Group relocations by r_info to reduce the size of the relocation // section. // Since the symbol offset is the high bits in r_info, sorting by r_info // allows us to do both. // // For Rela, we also want to sort by r_addend when r_info is the same. This // enables us to group by r_addend as well. llvm::stable_sort(nonRelatives, [](const Elf_Rela &a, const Elf_Rela &b) { if (a.r_info != b.r_info) return a.r_info < b.r_info; if (config->isRela) return a.r_addend < b.r_addend; return false; }); // Group relocations with the same r_info. Note that each group emits a group // header and that may make the relocation section larger. It is hard to // estimate the size of a group header as the encoded size of that varies // based on r_info. However, we can approximate this trade-off by the number // of values encoded. Each group header contains 3 values, and each relocation // in a group encodes one less value, as compared to when it is not grouped. // Therefore, we only group relocations if there are 3 or more of them with // the same r_info. // // For Rela, the addend for most non-relative relocations is zero, and thus we // can usually get a smaller relocation section if we group relocations with 0 // addend as well. std::vector ungroupedNonRelatives; std::vector> nonRelativeGroups; for (auto i = nonRelatives.begin(), e = nonRelatives.end(); i != e;) { auto j = i + 1; while (j != e && i->r_info == j->r_info && (!config->isRela || i->r_addend == j->r_addend)) ++j; if (j - i < 3 || (config->isRela && i->r_addend != 0)) ungroupedNonRelatives.insert(ungroupedNonRelatives.end(), i, j); else nonRelativeGroups.emplace_back(i, j); i = j; } // Sort ungrouped relocations by offset to minimize the encoded length. llvm::sort(ungroupedNonRelatives, [](const Elf_Rela &a, const Elf_Rela &b) { return a.r_offset < b.r_offset; }); unsigned hasAddendIfRela = config->isRela ? RELOCATION_GROUP_HAS_ADDEND_FLAG : 0; uint64_t offset = 0; uint64_t addend = 0; // Emit the run-length encoding for the groups of adjacent relative // relocations. Each group is represented using two groups in the packed // format. The first is used to set the current offset to the start of the // group (and also encodes the first relocation), and the second encodes the // remaining relocations. for (std::vector &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; } } } // Grouped non-relatives. for (ArrayRef g : nonRelativeGroups) { add(g.size()); add(RELOCATION_GROUPED_BY_INFO_FLAG); add(g[0].r_info); for (const Elf_Rela &r : g) { add(r.r_offset - offset); offset = r.r_offset; } addend = 0; } // Finally the ungrouped non-relative relocations. if (!ungroupedNonRelatives.empty()) { add(ungroupedNonRelatives.size()); add(hasAddendIfRela); for (Elf_Rela &r : ungroupedNonRelatives) { add(r.r_offset - offset); offset = r.r_offset; add(r.r_info); if (config->isRela) { add(r.r_addend - addend); addend = r.r_addend; } } } // Don't allow the section to shrink; otherwise the size of the section can // oscillate infinitely. if (relocData.size() < oldSize) relocData.append(oldSize - relocData.size(), 0); // Returns whether the section size changed. We need to keep recomputing both // section layout and the contents of this section until the size converges // because changing this section's size can affect section layout, which in // turn can affect the sizes of the LEB-encoded integers stored in this // section. return relocData.size() != oldSize; } template RelrSection::RelrSection() { this->entsize = config->wordsize; } template bool RelrSection::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 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; } } // Don't allow the section to shrink; otherwise the size of the section can // oscillate infinitely. Trailing 1s do not decode to more relocations. if (relrRelocs.size() < oldSize) { log(".relr.dyn needs " + Twine(oldSize - relrRelocs.size()) + " padding word(s)"); relrRelocs.resize(oldSize, Elf_Relr(1)); } return relrRelocs.size() != oldSize; } SymbolTableBaseSection::SymbolTableBaseSection(StringTableSection &strTabSec) : SyntheticSection(strTabSec.isDynamic() ? (uint64_t)SHF_ALLOC : 0, strTabSec.isDynamic() ? SHT_DYNSYM : SHT_SYMTAB, config->wordsize, strTabSec.isDynamic() ? ".dynsym" : ".symtab"), strTabSec(strTabSec) {} // Orders symbols according to their positions in the GOT, // in compliance with MIPS ABI rules. // See "Global Offset Table" in Chapter 5 in the following document // for detailed description: // ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf static bool sortMipsSymbols(const SymbolTableEntry &l, const SymbolTableEntry &r) { // Sort entries related to non-local preemptible symbols by GOT indexes. // All other entries go to the beginning of a dynsym in arbitrary order. if (l.sym->isInGot() && r.sym->isInGot()) return l.sym->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> 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> &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 SymbolTableSection::SymbolTableSection(StringTableSection &strTabSec) : SymbolTableBaseSection(strTabSec) { this->entsize = sizeof(Elf_Sym); } static BssSection *getCommonSec(Symbol *sym) { if (!config->defineCommon) if (auto *d = dyn_cast(sym)) return dyn_cast_or_null(d->section); return nullptr; } static uint32_t getSymSectionIndex(Symbol *sym) { if (getCommonSec(sym)) return SHN_COMMON; if (!isa(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 void SymbolTableSection::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(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; // The most significant bit of st_other is used by AArch64 ABI for the // variant PCS. else if (config->emachine == EM_AARCH64) eSym->st_other |= sym->stOther & STO_AARCH64_VARIANT_PCS; 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 // meaning for uninstantiated common symbols (--no-define-common). 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(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::relocate()` routine. Now we should // clear that bit for non-dynamic symbol table, so tools // like `objdump` will be able to deal with a correct // symbol position. if (sym->isDefined() && ((sym->stOther & STO_MIPS_MICROMIPS) || sym->needsPltAddr)) { if (!strTabSec.isDynamic()) eSym->st_value &= ~1; eSym->st_other |= STO_MIPS_MICROMIPS; } } if (config->relocatable) if (auto *d = dyn_cast(sym)) if (isMipsPIC(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(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 substantially // improves time to load programs. // // (Note that this is not the only way to design the shared library. // For instance, the Windows DLL takes a different approach. On // Windows, each dynamic symbol has a name of DLL from which the symbol // has to be resolved. That makes the cost of symbol resolution O(n). // This disables some hacky techniques you can use on Unix such as // LD_PRELOAD, but this is arguably better semantics than the Unix ones.) // // Due to historical reasons, we have two different hash tables, .hash // and .gnu.hash. They are for the same purpose, and .gnu.hash is a new // and better version of .hash. .hash is just an on-disk hash table, but // .gnu.hash has a bloom filter in addition to a hash table to skip // DSOs very quickly. If you are sure that your dynamic linker knows // about .gnu.hash, you want to specify -hash-style=gnu. Otherwise, a // safe bet is to specify -hash-style=both for backward compatibility. GnuHashTableSection::GnuHashTableSection() : SyntheticSection(SHF_ALLOC, SHT_GNU_HASH, config->wordsize, ".gnu.hash") { } void GnuHashTableSection::finalizeContents() { if (OutputSection *sec = getPartition().dynSymTab->getParent()) getParent()->link = sec->sectionIndex; // Computes bloom filter size in word size. We want to allocate 12 // bits for each symbol. It must be a power of two. if (symbols.empty()) { maskWords = 1; } else { uint64_t numBits = symbols.size() * 12; maskWords = NextPowerOf2(numBits / (config->wordsize * 8)); } size = 16; // Header size += config->wordsize * maskWords; // Bloom filter size += nBuckets * 4; // Hash buckets size += symbols.size() * 4; // Hash values } void GnuHashTableSection::writeTo(uint8_t *buf) { // 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(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 &v) { // We cannot use 'auto' for Mid because GCC 6.1 cannot deduce // its type correctly. std::vector::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((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(buf); write32(p++, numSymbols); // nbucket write32(p++, numSymbols); // nchain uint32_t *buckets = p; uint32_t *chains = p + numSymbols; for (const SymbolTableEntry &s : symTab->getSymbols()) { Symbol *sym = s.sym; StringRef name = sym->getName(); unsigned i = sym->dynsymIndex; uint32_t hash = hashSysV(name) % numSymbols; chains[i] = buckets[hash]; write32(buckets + hash, i); } } PltSection::PltSection() : SyntheticSection(SHF_ALLOC | SHF_EXECINSTR, SHT_PROGBITS, 16, ".plt"), headerSize(target->pltHeaderSize) { // On PowerPC, this section contains lazy symbol resolvers. if (config->emachine == EM_PPC64) { name = ".glink"; alignment = 4; } // On x86 when IBT is enabled, this section contains the second PLT (lazy // symbol resolvers). if ((config->emachine == EM_386 || config->emachine == EM_X86_64) && (config->andFeatures & GNU_PROPERTY_X86_FEATURE_1_IBT)) name = ".plt.sec"; // The PLT needs to be writable on SPARC as the dynamic linker will // modify the instructions in the PLT entries. if (config->emachine == EM_SPARCV9) this->flags |= SHF_WRITE; } void PltSection::writeTo(uint8_t *buf) { // At beginning of PLT, we have code to call the dynamic // linker to resolve dynsyms at runtime. Write such code. target->writePltHeader(buf); size_t off = headerSize; for (const Symbol *sym : entries) { target->writePlt(buf + off, *sym, getVA() + off); off += target->pltEntrySize; } } void PltSection::addEntry(Symbol &sym) { sym.pltIndex = entries.size(); entries.push_back(&sym); } size_t PltSection::getSize() const { return headerSize + entries.size() * target->pltEntrySize; } bool PltSection::isNeeded() const { // For -z retpolineplt, .iplt needs the .plt header. return !entries.empty() || (config->zRetpolineplt && in.iplt->isNeeded()); } // Used by ARM to add mapping symbols in the PLT section, which aid // disassembly. void PltSection::addSymbols() { target->addPltHeaderSymbols(*this); size_t off = headerSize; for (size_t i = 0; i < entries.size(); ++i) { target->addPltSymbols(*this, off); off += target->pltEntrySize; } } IpltSection::IpltSection() : SyntheticSection(SHF_ALLOC | SHF_EXECINSTR, SHT_PROGBITS, 16, ".iplt") { if (config->emachine == EM_PPC || config->emachine == EM_PPC64) { name = ".glink"; alignment = 4; } } void IpltSection::writeTo(uint8_t *buf) { uint32_t off = 0; for (const Symbol *sym : entries) { target->writeIplt(buf + off, *sym, getVA() + off); off += target->ipltEntrySize; } } size_t IpltSection::getSize() const { return entries.size() * target->ipltEntrySize; } void IpltSection::addEntry(Symbol &sym) { sym.pltIndex = entries.size(); entries.push_back(&sym); } // ARM uses mapping symbols to aid disassembly. void IpltSection::addSymbols() { size_t off = 0; for (size_t i = 0, e = entries.size(); i != e; ++i) { target->addPltSymbols(*this, off); off += target->pltEntrySize; } } PPC32GlinkSection::PPC32GlinkSection() { name = ".glink"; alignment = 4; } void PPC32GlinkSection::writeTo(uint8_t *buf) { writePPC32GlinkSection(buf, entries.size()); } size_t PPC32GlinkSection::getSize() const { return headerSize + entries.size() * target->pltEntrySize + footerSize; } // This is an x86-only extra PLT section and used only when a security // enhancement feature called CET is enabled. In this comment, I'll explain what // the feature is and why we have two PLT sections if CET is enabled. // // So, what does CET do? CET introduces a new restriction to indirect jump // instructions. CET works this way. Assume that CET is enabled. Then, if you // execute an indirect jump instruction, the processor verifies that a special // "landing pad" instruction (which is actually a repurposed NOP instruction and // now called "endbr32" or "endbr64") is at the jump target. If the jump target // does not start with that instruction, the processor raises an exception // instead of continuing executing code. // // If CET is enabled, the compiler emits endbr to all locations where indirect // jumps may jump to. // // This mechanism makes it extremely hard to transfer the control to a middle of // a function that is not supporsed to be a indirect jump target, preventing // certain types of attacks such as ROP or JOP. // // Note that the processors in the market as of 2019 don't actually support the // feature. Only the spec is available at the moment. // // Now, I'll explain why we have this extra PLT section for CET. // // Since you can indirectly jump to a PLT entry, we have to make PLT entries // start with endbr. The problem is there's no extra space for endbr (which is 4 // bytes long), as the PLT entry is only 16 bytes long and all bytes are already // used. // // In order to deal with the issue, we split a PLT entry into two PLT entries. // Remember that each PLT entry contains code to jump to an address read from // .got.plt AND code to resolve a dynamic symbol lazily. With the 2-PLT scheme, // the former code is written to .plt.sec, and the latter code is written to // .plt. // // Lazy symbol resolution in the 2-PLT scheme works in the usual way, except // that the regular .plt is now called .plt.sec and .plt is repurposed to // contain only code for lazy symbol resolution. // // In other words, this is how the 2-PLT scheme works. Application code is // supposed to jump to .plt.sec to call an external function. Each .plt.sec // entry contains code to read an address from a corresponding .got.plt entry // and jump to that address. Addresses in .got.plt initially point to .plt, so // when an application calls an external function for the first time, the // control is transferred to a function that resolves a symbol name from // external shared object files. That function then rewrites a .got.plt entry // with a resolved address, so that the subsequent function calls directly jump // to a desired location from .plt.sec. // // There is an open question as to whether the 2-PLT scheme was desirable or // not. We could have simply extended the PLT entry size to 32-bytes to // accommodate endbr, and that scheme would have been much simpler than the // 2-PLT scheme. One reason to split PLT was, by doing that, we could keep hot // code (.plt.sec) from cold code (.plt). But as far as I know no one proved // that the optimization actually makes a difference. // // That said, the 2-PLT scheme is a part of the ABI, debuggers and other tools // depend on it, so we implement the ABI. IBTPltSection::IBTPltSection() : SyntheticSection(SHF_ALLOC | SHF_EXECINSTR, SHT_PROGBITS, 16, ".plt") {} void IBTPltSection::writeTo(uint8_t *buf) { target->writeIBTPlt(buf, in.plt->getNumEntries()); } size_t IBTPltSection::getSize() const { // 16 is the header size of .plt. return 16 + in.plt->getNumEntries() * 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(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 readCuList(DWARFContext &dwarf) { std::vector ret; for (std::unique_ptr &cu : dwarf.compile_units()) ret.push_back({cu->getOffset(), cu->getLength() + 4}); return ret; } static std::vector readAddressAreas(DWARFContext &dwarf, InputSection *sec) { std::vector ret; uint32_t cuIdx = 0; for (std::unique_ptr &cu : dwarf.compile_units()) { if (Error e = cu->tryExtractDIEsIfNeeded(false)) { warn(toString(sec) + ": " + toString(std::move(e))); return {}; } Expected ranges = cu->collectAddressRanges(); if (!ranges) { warn(toString(sec) + ": " + toString(ranges.takeError())); return {}; } ArrayRef sections = sec->file->getSections(); for (DWARFAddressRange &r : *ranges) { if (r.SectionIndex == -1ULL) continue; // Range list with zero size has no effect. InputSectionBase *s = sections[r.SectionIndex]; if (s && s != &InputSection::discarded && s->isLive()) if (r.LowPC != r.HighPC) ret.push_back({cast(s), r.LowPC, r.HighPC, cuIdx}); } ++cuIdx; } return ret; } template static std::vector readPubNamesAndTypes(const LLDDwarfObj &obj, const std::vector &cus) { const LLDDWARFSection &pubNames = obj.getGnuPubnamesSection(); const LLDDWARFSection &pubTypes = obj.getGnuPubtypesSection(); std::vector ret; for (const LLDDWARFSection *pub : {&pubNames, &pubTypes}) { DWARFDataExtractor data(obj, *pub, config->isLE, config->wordsize); DWARFDebugPubTable table; table.extract(data, /*GnuStyle=*/true, [&](Error e) { warn(toString(pub->sec) + ": " + toString(std::move(e))); }); for (const DWARFDebugPubTable::Set &set : table.getData()) { // The value written into the constant pool is kind << 24 | cuIndex. As we // don't know how many compilation units precede this object to compute // cuIndex, we compute (kind << 24 | cuIndexInThisObject) instead, and add // the number of preceding compilation units later. uint32_t i = llvm::partition_point(cus, [&](GdbIndexSection::CuEntry cu) { return cu.cuOffset < set.Offset; }) - cus.begin(); for (const DWARFDebugPubTable::Entry &ent : set.Entries) ret.push_back({{ent.Name, computeGdbHash(ent.Name)}, (ent.Descriptor.toBits() << 24) | i}); } } return ret; } // Create a list of symbols from a given list of symbol names and types // by uniquifying them by name. static std::vector createSymbols(ArrayRef> nameAttrs, const std::vector &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 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. constexpr size_t numShards = 32; size_t concurrency = PowerOf2Floor( std::min(hardware_concurrency(parallel::strategy.ThreadsRequested) .compute_thread_count(), numShards)); // A sharded map to uniquify symbols by name. std::vector> map(numShards); size_t shift = 32 - countTrailingZeros(numShards); // Instantiate GdbSymbols while uniqufying them by name. std::vector> symbols(numShards); parallelForEachN(0, concurrency, [&](size_t threadId) { uint32_t i = 0; for (ArrayRef 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 v : symbols) numSymbols += v.size(); // The return type is a flattened vector, so we'll copy each vector // contents to Ret. std::vector ret; ret.reserve(numSymbols); for (std::vector &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 GdbIndexSection *GdbIndexSection::create() { // Collect InputFiles with .debug_info. See the comment in // LLDDwarfObj::LLDDwarfObj. If we do lightweight parsing in the future, // note that isec->data() may uncompress the full content, which should be // parallelized. SetVector files; for (InputSectionBase *s : inputSections) { InputSection *isec = dyn_cast(s); if (!isec) continue; // .debug_gnu_pub{names,types} are useless in executables. // They are present in input object files solely for creating // a .gdb_index. So we can remove them from the output. if (s->name == ".debug_gnu_pubnames" || s->name == ".debug_gnu_pubtypes") s->markDead(); else if (isec->name == ".debug_info") files.insert(isec->file); } // Drop .rel[a].debug_gnu_pub{names,types} for --emit-relocs. llvm::erase_if(inputSections, [](InputSectionBase *s) { if (auto *isec = dyn_cast(s)) if (InputSectionBase *rel = isec->getRelocatedSection()) return !rel->isLive(); return !s->isLive(); }); std::vector chunks(files.size()); std::vector> nameAttrs(files.size()); parallelForEachN(0, files.size(), [&](size_t i) { // To keep memory usage low, we don't want to keep cached DWARFContext, so // avoid getDwarf() here. ObjFile *file = cast>(files[i]); DWARFContext dwarf(std::make_unique>(file)); auto &dobj = static_cast &>(dwarf.getDWARFObj()); // If the are multiple compile units .debug_info (very rare ld -r --unique), // this only picks the last one. Other address ranges are lost. chunks[i].sec = dobj.getInfoSection(); chunks[i].compilationUnits = readCuList(dwarf); chunks[i].addressAreas = readAddressAreas(dwarf, chunks[i].sec); nameAttrs[i] = readPubNamesAndTypes(dobj, chunks[i].compilationUnits); }); auto *ret = make(); 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(buf); uint8_t *start = buf; hdr->version = 7; buf += sizeof(*hdr); // Write the CU list. hdr->cuListOff = buf - start; for (GdbChunk &chunk : chunks) { for (CuEntry &cu : chunk.compilationUnits) { write64le(buf, chunk.sec->outSecOff + cu.cuOffset); write64le(buf + 8, cu.cuLength); buf += 16; } } // Write the address area. hdr->cuTypesOff = buf - start; hdr->addressAreaOff = buf - start; uint32_t cuOff = 0; for (GdbChunk &chunk : chunks) { for (AddressEntry &e : chunk.addressAreas) { // In the case of ICF there may be duplicate address range entries. const uint64_t baseAddr = e.section->repl->getVA(0); write64le(buf, baseAddr + e.lowAddress); write64le(buf + 8, baseAddr + e.highAddress); write32le(buf + 16, e.cuIndex + cuOff); buf += 20; } cuOff += chunk.compilationUnits.size(); } // Write the on-disk open-addressing hash table containing symbols. hdr->symtabOff = buf - start; size_t symtabSize = computeSymtabSize(); uint32_t mask = symtabSize - 1; for (GdbSymbol &sym : symbols) { uint32_t h = sym.name.hash(); uint32_t i = h & mask; uint32_t step = ((h * 17) & mask) | 1; while (read32le(buf + i * 8)) i = (i + step) & mask; write32le(buf + i * 8, sym.nameOff); write32le(buf + i * 8 + 4, sym.cuVectorOff); } buf += symtabSize * 8; // Write the string pool. hdr->constantPoolOff = buf - start; parallelForEach(symbols, [&](GdbSymbol &sym) { memcpy(buf + sym.nameOff, sym.name.data(), sym.name.size()); }); // Write the CU vectors. for (GdbSymbol &sym : symbols) { write32le(buf, sym.cuVector.size()); buf += 4; for (uint32_t val : sym.cuVector) { write32le(buf, val); buf += 4; } } } bool GdbIndexSection::isNeeded() const { return !chunks.empty(); } EhFrameHeader::EhFrameHeader() : SyntheticSection(SHF_ALLOC, SHT_PROGBITS, 4, ".eh_frame_hdr") {} void EhFrameHeader::writeTo(uint8_t *buf) { // Unlike most sections, the EhFrameHeader section is written while writing // another section, namely EhFrameSection, which calls the write() function // below from its writeTo() function. This is necessary because the contents // of EhFrameHeader depend on the relocated contents of EhFrameSection and we // don't know which order the sections will be written in. } // .eh_frame_hdr contains a binary search table of pointers to FDEs. // Each entry of the search table consists of two values, // the starting PC from where FDEs covers, and the FDE's address. // It is sorted by PC. void EhFrameHeader::write() { uint8_t *buf = Out::bufferStart + getParent()->offset + outSecOff; using FdeData = EhFrameSection::FdeData; std::vector fdes = getPartition().ehFrame->getFdeData(); buf[0] = 1; buf[1] = DW_EH_PE_pcrel | DW_EH_PE_sdata4; buf[2] = DW_EH_PE_udata4; buf[3] = DW_EH_PE_datarel | DW_EH_PE_sdata4; write32(buf + 4, getPartition().ehFrame->getParent()->addr - this->getVA() - 4); write32(buf + 8, fdes.size()); buf += 12; for (FdeData &fde : fdes) { write32(buf, fde.pcRel); write32(buf + 4, fde.fdeVARel); buf += 8; } } size_t EhFrameHeader::getSize() const { // .eh_frame_hdr has a 12 bytes header followed by an array of FDEs. return 12 + getPartition().ehFrame->numFdes * 8; } bool EhFrameHeader::isNeeded() const { return isLive() && getPartition().ehFrame->isNeeded(); } VersionDefinitionSection::VersionDefinitionSection() : SyntheticSection(SHF_ALLOC, SHT_GNU_verdef, sizeof(uint32_t), ".gnu.version_d") {} StringRef VersionDefinitionSection::getFileDefName() { if (!getPartition().name.empty()) return getPartition().name; if (!config->soName.empty()) return config->soName; return config->outputFile; } void VersionDefinitionSection::finalizeContents() { fileDefNameOff = getPartition().dynStrTab->addString(getFileDefName()); for (const VersionDefinition &v : namedVersionDefs()) verDefNameOffs.push_back(getPartition().dynStrTab->addString(v.name)); if (OutputSection *sec = getPartition().dynStrTab->getParent()) getParent()->link = sec->sectionIndex; // sh_info should be set to the number of definitions. This fact is missed in // documentation, but confirmed by binutils community: // https://sourceware.org/ml/binutils/2014-11/msg00355.html getParent()->info = getVerDefNum(); } void VersionDefinitionSection::writeOne(uint8_t *buf, uint32_t index, StringRef name, size_t nameOff) { uint16_t flags = index == 1 ? VER_FLG_BASE : 0; // Write a verdef. write16(buf, 1); // vd_version write16(buf + 2, flags); // vd_flags write16(buf + 4, index); // vd_ndx write16(buf + 6, 1); // vd_cnt write32(buf + 8, hashSysV(name)); // vd_hash write32(buf + 12, 20); // vd_aux write32(buf + 16, 28); // vd_next // Write a veraux. write32(buf + 20, nameOff); // vda_name write32(buf + 24, 0); // vda_next } void VersionDefinitionSection::writeTo(uint8_t *buf) { writeOne(buf, 1, getFileDefName(), fileDefNameOff); auto nameOffIt = verDefNameOffs.begin(); for (const VersionDefinition &v : namedVersionDefs()) { buf += EntrySize; writeOne(buf, v.id, v.name, *nameOffIt++); } // Need to terminate the last version definition. write32(buf + 16, 0); // vd_next } size_t VersionDefinitionSection::getSize() const { return EntrySize * getVerDefNum(); } // .gnu.version is a table where each entry is 2 byte long. VersionTableSection::VersionTableSection() : SyntheticSection(SHF_ALLOC, SHT_GNU_versym, sizeof(uint16_t), ".gnu.version") { this->entsize = 2; } void VersionTableSection::finalizeContents() { // At the moment of june 2016 GNU docs does not mention that sh_link field // should be set, but Sun docs do. Also readelf relies on this field. getParent()->link = getPartition().dynSymTab->getParent()->sectionIndex; } size_t VersionTableSection::getSize() const { return (getPartition().dynSymTab->getSymbols().size() + 1) * 2; } void VersionTableSection::writeTo(uint8_t *buf) { buf += 2; for (const SymbolTableEntry &s : getPartition().dynSymTab->getSymbols()) { // Use the original versionId for an unfetched lazy symbol (undefined weak), // which must be VER_NDX_GLOBAL (an undefined versioned symbol is an error). write16(buf, s.sym->isLazy() ? static_cast(VER_NDX_GLOBAL) : s.sym->versionId); buf += 2; } } bool VersionTableSection::isNeeded() const { return isLive() && (getPartition().verDef || getPartition().verNeed->isNeeded()); } void elf::addVerneed(Symbol *ss) { auto &file = cast(*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 VersionNeedSection::VersionNeedSection() : SyntheticSection(SHF_ALLOC, SHT_GNU_verneed, sizeof(uint32_t), ".gnu.version_r") {} template void VersionNeedSection::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(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 void VersionNeedSection::writeTo(uint8_t *buf) { // The Elf_Verneeds need to appear first, followed by the Elf_Vernauxs. auto *verneed = reinterpret_cast(buf); auto *vernaux = reinterpret_cast(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(vernaux) - reinterpret_cast(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 size_t VersionNeedSection::getSize() const { return verneeds.size() * sizeof(Elf_Verneed) + SharedFile::vernauxNum * sizeof(Elf_Vernaux); } template bool VersionNeedSection::isNeeded() const { return isLive() && 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 = PowerOf2Floor( std::min(hardware_concurrency(parallel::strategy.ThreadsRequested) .compute_thread_count(), 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)]; }); } MergeSyntheticSection *elf::createMergeSynthetic(StringRef name, uint32_t type, uint64_t flags, uint32_t alignment) { bool shouldTailMerge = (flags & SHF_STRINGS) && config->optimize >= 2; if (shouldTailMerge) return make(name, type, flags, alignment); return make(name, type, flags, alignment); } template void elf::splitSections() { llvm::TimeTraceScope timeScope("Split sections"); // splitIntoPieces needs to be called on each MergeInputSection // before calling finalizeContents(). parallelForEach(inputSections, [](InputSectionBase *sec) { if (auto *s = dyn_cast(sec)) s->splitIntoPieces(); else if (auto *eh = dyn_cast(sec)) eh->split(); }); } MipsRldMapSection::MipsRldMapSection() : SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_PROGBITS, config->wordsize, ".rld_map") {} ARMExidxSyntheticSection::ARMExidxSyntheticSection() : SyntheticSection(SHF_ALLOC | SHF_LINK_ORDER, SHT_ARM_EXIDX, config->wordsize, ".ARM.exidx") {} static InputSection *findExidxSection(InputSection *isec) { for (InputSection *d : isec->dependentSections) if (d->type == SHT_ARM_EXIDX && d->isLive()) return d; return nullptr; } static bool isValidExidxSectionDep(InputSection *isec) { return (isec->flags & SHF_ALLOC) && (isec->flags & SHF_EXECINSTR) && isec->getSize() > 0; } bool ARMExidxSyntheticSection::addSection(InputSection *isec) { if (isec->type == SHT_ARM_EXIDX) { if (InputSection *dep = isec->getLinkOrderDep()) if (isValidExidxSectionDep(dep)) { exidxSections.push_back(isec); // Every exidxSection is 8 bytes, we need an estimate of // size before assignAddresses can be called. Final size // will only be known after finalize is called. size += 8; } return true; } if (isValidExidxSectionDep(isec)) { executableSections.push_back(isec); return false; } // FIXME: we do not output a relocation section when --emit-relocs is used // as we do not have relocation sections for linker generated table entries // and we would have to erase at a late stage relocations from merged entries. // Given that exception tables are already position independent and a binary // analyzer could derive the relocations we choose to erase the relocations. if (config->emitRelocs && isec->type == SHT_REL) if (InputSectionBase *ex = isec->getRelocatedSection()) if (isa(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().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()) 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() { // The executableSections and exidxSections that we use to derive the final // contents of this SyntheticSection are populated before // processSectionCommands() and ICF. A /DISCARD/ entry in SECTIONS command or // ICF may remove executable InputSections and their dependent .ARM.exidx // section that we recorded earlier. auto isDiscarded = [](const InputSection *isec) { return !isec->isLive(); }; llvm::erase_if(exidxSections, isDiscarded); // We need to remove discarded InputSections and InputSections without // .ARM.exidx sections that if we generated the .ARM.exidx it would be out // of range. auto isDiscardedOrOutOfRange = [this](InputSection *isec) { if (!isec->isLive()) return true; if (findExidxSection(isec)) return false; int64_t off = static_cast(isec->getVA() - getVA()); return off != llvm::SignExtend64(off, 31); }; llvm::erase_if(executableSections, isDiscardedOrOutOfRange); // Sort the executable sections that may or may not have associated // .ARM.exidx sections by order of ascending address. This requires the // relative positions of InputSections and OutputSections to be known. auto compareByFilePosition = [](const InputSection *a, const InputSection *b) { OutputSection *aOut = a->getParent(); OutputSection *bOut = b->getParent(); if (aOut != bOut) return aOut->addr < bOut->addr; return a->outSecOff < b->outSecOff; }; llvm::stable_sort(executableSections, compareByFilePosition); sentinel = executableSections.back(); // Optionally merge adjacent duplicate entries. if (config->mergeArmExidx) { std::vector 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 + d->outSecOff, buf + d->outSecOff + 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->relocateNoSym(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->relocateNoSym(buf + offset, R_ARM_PREL31, s - p); assert(size == offset + 8); } bool ARMExidxSyntheticSection::isNeeded() const { return llvm::find_if(exidxSections, [](InputSection *isec) { return isec->isLive(); }) != exidxSections.end(); } 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->emachine == EM_PPC64 ? 16 : 4, ".text.thunk") { this->parent = os; this->outSecOff = off; } size_t ThunkSection::getSize() const { if (roundUpSizeForErrata) return alignTo(size, 4096); return size; } void ThunkSection::addThunk(Thunk *t) { thunks.push_back(t); t->addSymbols(*this); } void ThunkSection::writeTo(uint8_t *buf) { for (Thunk *t : thunks) t->writeTo(buf + t->offset); } InputSection *ThunkSection::getTargetInputSection() const { if (thunks.empty()) return nullptr; const Thunk *t = thunks.front(); return t->getTargetInputSection(); } bool ThunkSection::assignOffsets() { uint64_t off = 0; for (Thunk *t : thunks) { off = 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(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(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") {} uint64_t PPC64LongBranchTargetSection::getEntryVA(const Symbol *sym, int64_t addend) { return getVA() + entry_index.find({sym, addend})->second * 8; } Optional PPC64LongBranchTargetSection::addEntry(const Symbol *sym, int64_t addend) { auto res = entry_index.try_emplace(std::make_pair(sym, addend), entries.size()); if (!res.second) return None; entries.emplace_back(sym, addend); return res.first->second; } size_t PPC64LongBranchTargetSection::getSize() const { return entries.size() * 8; } void PPC64LongBranchTargetSection::writeTo(uint8_t *buf) { // If linking non-pic we have the final addresses of the targets and they get // written to the table directly. For pic the dynamic linker will allocate // the section and fill it it. if (config->isPic) return; for (auto entry : entries) { const Symbol *sym = entry.first; int64_t addend = entry.second; assert(sym->getVA()); // Need calls to branch to the local entry-point since a long-branch // must be a local-call. write64(buf, sym->getVA(addend) + getPPC64GlobalEntryToLocalEntryOffset(sym->stOther)); buf += 8; } } bool PPC64LongBranchTargetSection::isNeeded() const { // `removeUnusedSyntheticSections()` is called before thunk allocation which // is too early to determine if this section will be empty or not. We need // Finalized to keep the section alive until after thunk creation. Finalized // only gets set to true once `finalizeSections()` is called after thunk // creation. Because of this, if we don't create any long-branch thunks we end // up with an empty .branch_lt section in the binary. return !finalized || !entries.empty(); } static uint8_t getAbiVersion() { // MIPS non-PIC executable gets ABI version 1. if (config->emachine == EM_MIPS) { if (!config->isPic && !config->relocatable && (config->eflags & (EF_MIPS_PIC | EF_MIPS_CPIC)) == EF_MIPS_CPIC) return 1; return 0; } if (config->emachine == EM_AMDGPU) { 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 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(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 void elf::writePhdrs(uint8_t *buf, Partition &part) { // Write the program header table. auto *hBuf = reinterpret_cast(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 PartitionElfHeaderSection::PartitionElfHeaderSection() : SyntheticSection(SHF_ALLOC, SHT_LLVM_PART_EHDR, 1, "") {} template size_t PartitionElfHeaderSection::getSize() const { return sizeof(typename ELFT::Ehdr); } template void PartitionElfHeaderSection::writeTo(uint8_t *buf) { writeEhdr(buf, getPartition()); // Loadable partitions are always ET_DYN. auto *eHdr = reinterpret_cast(buf); eHdr->e_type = ET_DYN; } template PartitionProgramHeadersSection::PartitionProgramHeadersSection() : SyntheticSection(SHF_ALLOC, SHT_LLVM_PART_PHDR, 1, ".phdrs") {} template size_t PartitionProgramHeadersSection::getSize() const { return sizeof(typename ELFT::Phdr) * getPartition().phdrs.size(); } template void PartitionProgramHeadersSection::writeTo(uint8_t *buf) { writePhdrs(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 elf::partitions; Partition *elf::mainPart; template GdbIndexSection *GdbIndexSection::create(); template GdbIndexSection *GdbIndexSection::create(); template GdbIndexSection *GdbIndexSection::create(); template GdbIndexSection *GdbIndexSection::create(); template void elf::splitSections(); template void elf::splitSections(); template void elf::splitSections(); template void elf::splitSections(); template class elf::MipsAbiFlagsSection; template class elf::MipsAbiFlagsSection; template class elf::MipsAbiFlagsSection; template class elf::MipsAbiFlagsSection; template class elf::MipsOptionsSection; template class elf::MipsOptionsSection; template class elf::MipsOptionsSection; template class elf::MipsOptionsSection; template void EhFrameSection::iterateFDEWithLSDA( function_ref); template void EhFrameSection::iterateFDEWithLSDA( function_ref); template void EhFrameSection::iterateFDEWithLSDA( function_ref); template void EhFrameSection::iterateFDEWithLSDA( function_ref); template class elf::MipsReginfoSection; template class elf::MipsReginfoSection; template class elf::MipsReginfoSection; template class elf::MipsReginfoSection; template class elf::DynamicSection; template class elf::DynamicSection; template class elf::DynamicSection; template class elf::DynamicSection; template class elf::RelocationSection; template class elf::RelocationSection; template class elf::RelocationSection; template class elf::RelocationSection; template class elf::AndroidPackedRelocationSection; template class elf::AndroidPackedRelocationSection; template class elf::AndroidPackedRelocationSection; template class elf::AndroidPackedRelocationSection; template class elf::RelrSection; template class elf::RelrSection; template class elf::RelrSection; template class elf::RelrSection; template class elf::SymbolTableSection; template class elf::SymbolTableSection; template class elf::SymbolTableSection; template class elf::SymbolTableSection; template class elf::VersionNeedSection; template class elf::VersionNeedSection; template class elf::VersionNeedSection; template class elf::VersionNeedSection; template void elf::writeEhdr(uint8_t *Buf, Partition &Part); template void elf::writeEhdr(uint8_t *Buf, Partition &Part); template void elf::writeEhdr(uint8_t *Buf, Partition &Part); template void elf::writeEhdr(uint8_t *Buf, Partition &Part); template void elf::writePhdrs(uint8_t *Buf, Partition &Part); template void elf::writePhdrs(uint8_t *Buf, Partition &Part); template void elf::writePhdrs(uint8_t *Buf, Partition &Part); template void elf::writePhdrs(uint8_t *Buf, Partition &Part); template class elf::PartitionElfHeaderSection; template class elf::PartitionElfHeaderSection; template class elf::PartitionElfHeaderSection; template class elf::PartitionElfHeaderSection; template class elf::PartitionProgramHeadersSection; template class elf::PartitionProgramHeadersSection; template class elf::PartitionProgramHeadersSection; template class elf::PartitionProgramHeadersSection;