MachO/InputSection.cpp - llvm-project/lld - Git at Google

 //===- InputSection.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
 //
 //===----------------------------------------------------------------------===//

 #include "InputSection.h"
 #include "ConcatOutputSection.h"
 #include "Config.h"
 #include "InputFiles.h"
 #include "OutputSegment.h"
 #include "Symbols.h"
 #include "SyntheticSections.h"
 #include "Target.h"
 #include "UnwindInfoSection.h"
 #include "Writer.h"

 #include "lld/Common/ErrorHandler.h"
 #include "lld/Common/Memory.h"
 #include "llvm/Support/Endian.h"
 #include "llvm/Support/xxhash.h"

 using namespace llvm;
 using namespace llvm::MachO;
 using namespace llvm::support;
 using namespace lld;
 using namespace lld::macho;

 // Verify ConcatInputSection's size on 64-bit builds. The size of std::vector
 // can differ based on STL debug levels (e.g. iterator debugging on MSVC's STL),
 // so account for that.
 static_assert(sizeof(void *) != 8 ||
                   sizeof(ConcatInputSection) == sizeof(std::vector<Reloc>) + 88,
               "Try to minimize ConcatInputSection's size, we create many "
               "instances of it");

 std::vector<ConcatInputSection *> macho::inputSections;
 int macho::inputSectionsOrder = 0;

 // Call this function to add a new InputSection and have it routed to the
 // appropriate container. Depending on its type and current config, it will
 // either be added to 'inputSections' vector or to a synthetic section.
 void lld::macho::addInputSection(InputSection *inputSection) {
   if (auto *isec = dyn_cast<ConcatInputSection>(inputSection)) {
     if (isec->isCoalescedWeak())
       return;
     if (config->emitRelativeMethodLists &&
         ObjCMethListSection::isMethodList(isec)) {
       if (in.objcMethList->inputOrder == UnspecifiedInputOrder)
         in.objcMethList->inputOrder = inputSectionsOrder++;
       in.objcMethList->addInput(isec);
       isec->parent = in.objcMethList;
       return;
     }
     if (config->emitInitOffsets &&
         sectionType(isec->getFlags()) == S_MOD_INIT_FUNC_POINTERS) {
       in.initOffsets->addInput(isec);
       return;
     }
     isec->outSecOff = inputSectionsOrder++;
     auto *osec = ConcatOutputSection::getOrCreateForInput(isec);
     isec->parent = osec;
     inputSections.push_back(isec);
   } else if (auto *isec = dyn_cast<CStringInputSection>(inputSection)) {
     if (isec->getName() == section_names::objcMethname) {
       if (in.objcMethnameSection->inputOrder == UnspecifiedInputOrder)
         in.objcMethnameSection->inputOrder = inputSectionsOrder++;
       in.objcMethnameSection->addInput(isec);
     } else {
       if (in.cStringSection->inputOrder == UnspecifiedInputOrder)
         in.cStringSection->inputOrder = inputSectionsOrder++;
       in.cStringSection->addInput(isec);
     }
   } else if (auto *isec = dyn_cast<WordLiteralInputSection>(inputSection)) {
     if (in.wordLiteralSection->inputOrder == UnspecifiedInputOrder)
       in.wordLiteralSection->inputOrder = inputSectionsOrder++;
     in.wordLiteralSection->addInput(isec);
   } else {
     llvm_unreachable("unexpected input section kind");
   }

   assert(inputSectionsOrder <= UnspecifiedInputOrder);
 }

 uint64_t InputSection::getFileSize() const {
   return isZeroFill(getFlags()) ? 0 : getSize();
 }

 uint64_t InputSection::getVA(uint64_t off) const {
   return parent->addr + getOffset(off);
 }

 static uint64_t resolveSymbolVA(const Symbol *sym, uint8_t type) {
   const RelocAttrs &relocAttrs = target->getRelocAttrs(type);
   if (relocAttrs.hasAttr(RelocAttrBits::BRANCH))
     return sym->resolveBranchVA();
   if (relocAttrs.hasAttr(RelocAttrBits::GOT))
     return sym->resolveGotVA();
   if (relocAttrs.hasAttr(RelocAttrBits::TLV))
     return sym->resolveTlvVA();
   return sym->getVA();
 }

 const Defined *InputSection::getContainingSymbol(uint64_t off) const {
   auto *nextSym = llvm::upper_bound(
       symbols, off, [](uint64_t a, const Defined *b) { return a < b->value; });
   if (nextSym == symbols.begin())
     return nullptr;
   return *std::prev(nextSym);
 }

 std::string InputSection::getLocation(uint64_t off) const {
   // First, try to find a symbol that's near the offset. Use it as a reference
   // point.
   if (auto *sym = getContainingSymbol(off))
     return (toString(getFile()) + ":(symbol " + toString(*sym) + "+0x" +
             Twine::utohexstr(off - sym->value) + ")")
         .str();

   // If that fails, use the section itself as a reference point.
   for (const Subsection &subsec : section.subsections) {
     if (subsec.isec == this) {
       off += subsec.offset;
       break;
     }
   }

   return (toString(getFile()) + ":(" + getName() + "+0x" +
           Twine::utohexstr(off) + ")")
       .str();
 }

 std::string InputSection::getSourceLocation(uint64_t off) const {
   auto *obj = dyn_cast_or_null<ObjFile>(getFile());
   if (!obj)
     return {};

   DWARFCache *dwarf = obj->getDwarf();
   if (!dwarf)
     return std::string();

   for (const Subsection &subsec : section.subsections) {
     if (subsec.isec == this) {
       off += subsec.offset;
       break;
     }
   }

   auto createMsg = [&](StringRef path, unsigned line) {
     std::string filename = sys::path::filename(path).str();
     std::string lineStr = (":" + Twine(line)).str();
     if (filename == path)
       return filename + lineStr;
     return (filename + lineStr + " (" + path + lineStr + ")").str();
   };

   // First, look up a function for a given offset.
   if (std::optional<DILineInfo> li = dwarf->getDILineInfo(
           section.addr + off, object::SectionedAddress::UndefSection))
     return createMsg(li->FileName, li->Line);

   // If it failed, look up again as a variable.
   if (const Defined *sym = getContainingSymbol(off)) {
     // Symbols are generally prefixed with an underscore, which is not included
     // in the debug information.
     StringRef symName = sym->getName();
     if (!symName.empty() && symName[0] == '_')
       symName = symName.substr(1);

     if (std::optional<std::pair<std::string, unsigned>> fileLine =
             dwarf->getVariableLoc(symName))
       return createMsg(fileLine->first, fileLine->second);
   }

   // Try to get the source file's name from the DWARF information.
   if (obj->compileUnit)
     return obj->sourceFile();

   return {};
 }

 const Reloc *InputSection::getRelocAt(uint32_t off) const {
   auto it = llvm::find_if(
       relocs, [=](const macho::Reloc &r) { return r.offset == off; });
   if (it == relocs.end())
     return nullptr;
   return &*it;
 }

 void ConcatInputSection::foldIdentical(ConcatInputSection *copy) {
   align = std::max(align, copy->align);
   copy->live = false;
   copy->wasCoalesced = true;
   copy->replacement = this;
   for (auto &copySym : copy->symbols)
     copySym->wasIdenticalCodeFolded = true;

   symbols.insert(symbols.end(), copy->symbols.begin(), copy->symbols.end());
   copy->symbols.clear();

   // Remove duplicate compact unwind info for symbols at the same address.
   if (symbols.empty())
     return;
   for (auto it = symbols.begin() + 1; it != symbols.end(); ++it) {
     assert((*it)->value == 0);
     (*it)->originalUnwindEntry = nullptr;
   }
 }

 void ConcatInputSection::writeTo(uint8_t *buf) {
   assert(!shouldOmitFromOutput());

   if (getFileSize() == 0)
     return;

   memcpy(buf, data.data(), data.size());

   for (size_t i = 0; i < relocs.size(); i++) {
     const Reloc &r = relocs[i];
     uint8_t *loc = buf + r.offset;
     uint64_t referentVA = 0;

     const bool needsFixup = config->emitChainedFixups &&
                             target->hasAttr(r.type, RelocAttrBits::UNSIGNED);
     if (target->hasAttr(r.type, RelocAttrBits::SUBTRAHEND)) {
       const Symbol *fromSym = r.referent.get<Symbol *>();
       const Reloc &minuend = relocs[++i];
       uint64_t minuendVA;
       if (const Symbol *toSym = minuend.referent.dyn_cast<Symbol *>())
         minuendVA = toSym->getVA() + minuend.addend;
       else {
         auto *referentIsec = minuend.referent.get<InputSection *>();
         assert(!::shouldOmitFromOutput(referentIsec));
         minuendVA = referentIsec->getVA(minuend.addend);
       }
       referentVA = minuendVA - fromSym->getVA();
     } else if (auto *referentSym = r.referent.dyn_cast<Symbol *>()) {
       if (target->hasAttr(r.type, RelocAttrBits::LOAD) &&
           !referentSym->isInGot())
         target->relaxGotLoad(loc, r.type);
       // For dtrace symbols, do not handle them as normal undefined symbols
       if (referentSym->getName().starts_with("___dtrace_")) {
         // Change dtrace call site to pre-defined instructions
         target->handleDtraceReloc(referentSym, r, loc);
         continue;
       }
       referentVA = resolveSymbolVA(referentSym, r.type) + r.addend;

       if (isThreadLocalVariables(getFlags()) && isa<Defined>(referentSym)) {
         // References from thread-local variable sections are treated as offsets
         // relative to the start of the thread-local data memory area, which
         // is initialized via copying all the TLV data sections (which are all
         // contiguous).
         referentVA -= firstTLVDataSection->addr;
       } else if (needsFixup) {
         writeChainedFixup(loc, referentSym, r.addend);
         continue;
       }
     } else if (auto *referentIsec = r.referent.dyn_cast<InputSection *>()) {
       assert(!::shouldOmitFromOutput(referentIsec));
       referentVA = referentIsec->getVA(r.addend);

       if (needsFixup) {
         writeChainedRebase(loc, referentVA);
         continue;
       }
     }
     target->relocateOne(loc, r, referentVA, getVA() + r.offset);
   }
 }

 ConcatInputSection *macho::makeSyntheticInputSection(StringRef segName,
                                                      StringRef sectName,
                                                      uint32_t flags,
                                                      ArrayRef<uint8_t> data,
                                                      uint32_t align) {
   Section &section =
       *make<Section>(/*file=*/nullptr, segName, sectName, flags, /*addr=*/0);
   auto isec = make<ConcatInputSection>(section, data, align);
   // Since this is an explicitly created 'fake' input section,
   // it should not be dead stripped.
   isec->live = true;
   section.subsections.push_back({0, isec});
   return isec;
 }

 void CStringInputSection::splitIntoPieces() {
   size_t off = 0;
   StringRef s = toStringRef(data);
   while (!s.empty()) {
     size_t end = s.find(0);
     if (end == StringRef::npos)
       fatal(getLocation(off) + ": string is not null terminated");
     uint32_t hash = deduplicateLiterals ? xxh3_64bits(s.take_front(end)) : 0;
     pieces.emplace_back(off, hash);
     size_t size = end + 1; // include null terminator
     s = s.substr(size);
     off += size;
   }
 }

 StringPiece &CStringInputSection::getStringPiece(uint64_t off) {
   if (off >= data.size())
     fatal(toString(this) + ": offset is outside the section");

   auto it =
       partition_point(pieces, [=](StringPiece p) { return p.inSecOff <= off; });
   return it[-1];
 }

 const StringPiece &CStringInputSection::getStringPiece(uint64_t off) const {
   return const_cast<CStringInputSection *>(this)->getStringPiece(off);
 }

 size_t CStringInputSection::getStringPieceIndex(uint64_t off) const {
   if (off >= data.size())
     fatal(toString(this) + ": offset is outside the section");

   auto it =
       partition_point(pieces, [=](StringPiece p) { return p.inSecOff <= off; });
   return std::distance(pieces.begin(), it) - 1;
 }

 uint64_t CStringInputSection::getOffset(uint64_t off) const {
   const StringPiece &piece = getStringPiece(off);
   uint64_t addend = off - piece.inSecOff;
   return piece.outSecOff + addend;
 }

 WordLiteralInputSection::WordLiteralInputSection(const Section &section,
                                                  ArrayRef<uint8_t> data,
                                                  uint32_t align)
     : InputSection(WordLiteralKind, section, data, align) {
   switch (sectionType(getFlags())) {
   case S_4BYTE_LITERALS:
     power2LiteralSize = 2;
     break;
   case S_8BYTE_LITERALS:
     power2LiteralSize = 3;
     break;
   case S_16BYTE_LITERALS:
     power2LiteralSize = 4;
     break;
   default:
     llvm_unreachable("invalid literal section type");
   }

   live.resize(data.size() >> power2LiteralSize, !config->deadStrip);
 }

 uint64_t WordLiteralInputSection::getOffset(uint64_t off) const {
   auto *osec = cast<WordLiteralSection>(parent);
   const uintptr_t buf = reinterpret_cast<uintptr_t>(data.data());
   switch (sectionType(getFlags())) {
   case S_4BYTE_LITERALS:
     return osec->getLiteral4Offset(buf + (off & ~3LLU)) | (off & 3);
   case S_8BYTE_LITERALS:
     return osec->getLiteral8Offset(buf + (off & ~7LLU)) | (off & 7);
   case S_16BYTE_LITERALS:
     return osec->getLiteral16Offset(buf + (off & ~15LLU)) | (off & 15);
   default:
     llvm_unreachable("invalid literal section type");
   }
 }

 bool macho::isCodeSection(const InputSection *isec) {
   uint32_t type = sectionType(isec->getFlags());
   if (type != S_REGULAR && type != S_COALESCED)
     return false;

   uint32_t attr = isec->getFlags() & SECTION_ATTRIBUTES_USR;
   if (attr == S_ATTR_PURE_INSTRUCTIONS)
     return true;

   if (isec->getSegName() == segment_names::text)
     return StringSwitch<bool>(isec->getName())
         .Cases(section_names::textCoalNt, section_names::staticInit, true)
         .Default(false);

   return false;
 }

 bool macho::isCfStringSection(const InputSection *isec) {
   return isec->getName() == section_names::cfString &&
          isec->getSegName() == segment_names::data;
 }

 bool macho::isClassRefsSection(const InputSection *isec) {
   return isec->getName() == section_names::objcClassRefs &&
          isec->getSegName() == segment_names::data;
 }

 bool macho::isSelRefsSection(const InputSection *isec) {
   return isec->getName() == section_names::objcSelrefs &&
          isec->getSegName() == segment_names::data;
 }

 bool macho::isEhFrameSection(const InputSection *isec) {
   return isec->getName() == section_names::ehFrame &&
          isec->getSegName() == segment_names::text;
 }

 bool macho::isGccExceptTabSection(const InputSection *isec) {
   return isec->getName() == section_names::gccExceptTab &&
          isec->getSegName() == segment_names::text;
 }

 std::string lld::toString(const InputSection *isec) {
   return (toString(isec->getFile()) + ":(" + isec->getName() + ")").str();
 }
	//===- InputSection.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
	//
	//===----------------------------------------------------------------------===//

	#include "InputSection.h"
	#include "ConcatOutputSection.h"
	#include "Config.h"
	#include "InputFiles.h"
	#include "OutputSegment.h"
	#include "Symbols.h"
	#include "SyntheticSections.h"
	#include "Target.h"
	#include "UnwindInfoSection.h"
	#include "Writer.h"

	#include "lld/Common/ErrorHandler.h"
	#include "lld/Common/Memory.h"
	#include "llvm/Support/Endian.h"
	#include "llvm/Support/xxhash.h"

	using namespace llvm;
	using namespace llvm::MachO;
	using namespace llvm::support;
	using namespace lld;
	using namespace lld::macho;

	// Verify ConcatInputSection's size on 64-bit builds. The size of std::vector
	// can differ based on STL debug levels (e.g. iterator debugging on MSVC's STL),
	// so account for that.
	static_assert(sizeof(void *) != 8 \|\|
	sizeof(ConcatInputSection) == sizeof(std::vector<Reloc>) + 88,
	"Try to minimize ConcatInputSection's size, we create many "
	"instances of it");

	std::vector<ConcatInputSection *> macho::inputSections;
	int macho::inputSectionsOrder = 0;

	// Call this function to add a new InputSection and have it routed to the
	// appropriate container. Depending on its type and current config, it will
	// either be added to 'inputSections' vector or to a synthetic section.
	void lld::macho::addInputSection(InputSection *inputSection) {
	if (auto *isec = dyn_cast<ConcatInputSection>(inputSection)) {
	if (isec->isCoalescedWeak())
	return;
	if (config->emitRelativeMethodLists &&
	ObjCMethListSection::isMethodList(isec)) {
	if (in.objcMethList->inputOrder == UnspecifiedInputOrder)
	in.objcMethList->inputOrder = inputSectionsOrder++;
	in.objcMethList->addInput(isec);
	isec->parent = in.objcMethList;
	return;
	}
	if (config->emitInitOffsets &&
	sectionType(isec->getFlags()) == S_MOD_INIT_FUNC_POINTERS) {
	in.initOffsets->addInput(isec);
	return;
	}
	isec->outSecOff = inputSectionsOrder++;
	auto *osec = ConcatOutputSection::getOrCreateForInput(isec);
	isec->parent = osec;
	inputSections.push_back(isec);
	} else if (auto *isec = dyn_cast<CStringInputSection>(inputSection)) {
	if (isec->getName() == section_names::objcMethname) {
	if (in.objcMethnameSection->inputOrder == UnspecifiedInputOrder)
	in.objcMethnameSection->inputOrder = inputSectionsOrder++;
	in.objcMethnameSection->addInput(isec);
	} else {
	if (in.cStringSection->inputOrder == UnspecifiedInputOrder)
	in.cStringSection->inputOrder = inputSectionsOrder++;
	in.cStringSection->addInput(isec);
	}
	} else if (auto *isec = dyn_cast<WordLiteralInputSection>(inputSection)) {
	if (in.wordLiteralSection->inputOrder == UnspecifiedInputOrder)
	in.wordLiteralSection->inputOrder = inputSectionsOrder++;
	in.wordLiteralSection->addInput(isec);
	} else {
	llvm_unreachable("unexpected input section kind");
	}

	assert(inputSectionsOrder <= UnspecifiedInputOrder);
	}

	uint64_t InputSection::getFileSize() const {
	return isZeroFill(getFlags()) ? 0 : getSize();
	}

	uint64_t InputSection::getVA(uint64_t off) const {
	return parent->addr + getOffset(off);
	}

	static uint64_t resolveSymbolVA(const Symbol *sym, uint8_t type) {
	const RelocAttrs &relocAttrs = target->getRelocAttrs(type);
	if (relocAttrs.hasAttr(RelocAttrBits::BRANCH))
	return sym->resolveBranchVA();
	if (relocAttrs.hasAttr(RelocAttrBits::GOT))
	return sym->resolveGotVA();
	if (relocAttrs.hasAttr(RelocAttrBits::TLV))
	return sym->resolveTlvVA();
	return sym->getVA();
	}

	const Defined *InputSection::getContainingSymbol(uint64_t off) const {
	auto *nextSym = llvm::upper_bound(
	symbols, off, [](uint64_t a, const Defined *b) { return a < b->value; });
	if (nextSym == symbols.begin())
	return nullptr;
	return *std::prev(nextSym);
	}

	std::string InputSection::getLocation(uint64_t off) const {
	// First, try to find a symbol that's near the offset. Use it as a reference
	// point.
	if (auto *sym = getContainingSymbol(off))
	return (toString(getFile()) + ":(symbol " + toString(*sym) + "+0x" +
	Twine::utohexstr(off - sym->value) + ")")
	.str();

	// If that fails, use the section itself as a reference point.
	for (const Subsection &subsec : section.subsections) {
	if (subsec.isec == this) {
	off += subsec.offset;
	break;
	}
	}

	return (toString(getFile()) + ":(" + getName() + "+0x" +
	Twine::utohexstr(off) + ")")
	.str();
	}

	std::string InputSection::getSourceLocation(uint64_t off) const {
	auto *obj = dyn_cast_or_null<ObjFile>(getFile());
	if (!obj)
	return {};

	DWARFCache *dwarf = obj->getDwarf();
	if (!dwarf)
	return std::string();

	for (const Subsection &subsec : section.subsections) {
	if (subsec.isec == this) {
	off += subsec.offset;
	break;
	}
	}

	auto createMsg = [&](StringRef path, unsigned line) {
	std::string filename = sys::path::filename(path).str();
	std::string lineStr = (":" + Twine(line)).str();
	if (filename == path)
	return filename + lineStr;
	return (filename + lineStr + " (" + path + lineStr + ")").str();
	};

	// First, look up a function for a given offset.
	if (std::optional<DILineInfo> li = dwarf->getDILineInfo(
	section.addr + off, object::SectionedAddress::UndefSection))
	return createMsg(li->FileName, li->Line);

	// If it failed, look up again as a variable.
	if (const Defined *sym = getContainingSymbol(off)) {
	// Symbols are generally prefixed with an underscore, which is not included
	// in the debug information.
	StringRef symName = sym->getName();
	if (!symName.empty() && symName[0] == '_')
	symName = symName.substr(1);

	if (std::optional<std::pair<std::string, unsigned>> fileLine =
	dwarf->getVariableLoc(symName))
	return createMsg(fileLine->first, fileLine->second);
	}

	// Try to get the source file's name from the DWARF information.
	if (obj->compileUnit)
	return obj->sourceFile();

	return {};
	}

	const Reloc *InputSection::getRelocAt(uint32_t off) const {
	auto it = llvm::find_if(
	relocs, [=](const macho::Reloc &r) { return r.offset == off; });
	if (it == relocs.end())
	return nullptr;
	return &*it;
	}

	void ConcatInputSection::foldIdentical(ConcatInputSection *copy) {
	align = std::max(align, copy->align);
	copy->live = false;
	copy->wasCoalesced = true;
	copy->replacement = this;
	for (auto &copySym : copy->symbols)
	copySym->wasIdenticalCodeFolded = true;

	symbols.insert(symbols.end(), copy->symbols.begin(), copy->symbols.end());
	copy->symbols.clear();

	// Remove duplicate compact unwind info for symbols at the same address.
	if (symbols.empty())
	return;
	for (auto it = symbols.begin() + 1; it != symbols.end(); ++it) {
	assert((*it)->value == 0);
	(*it)->originalUnwindEntry = nullptr;
	}
	}

	void ConcatInputSection::writeTo(uint8_t *buf) {
	assert(!shouldOmitFromOutput());

	if (getFileSize() == 0)
	return;

	memcpy(buf, data.data(), data.size());

	for (size_t i = 0; i < relocs.size(); i++) {
	const Reloc &r = relocs[i];
	uint8_t *loc = buf + r.offset;
	uint64_t referentVA = 0;

	const bool needsFixup = config->emitChainedFixups &&
	target->hasAttr(r.type, RelocAttrBits::UNSIGNED);
	if (target->hasAttr(r.type, RelocAttrBits::SUBTRAHEND)) {
	const Symbol fromSym = r.referent.get<Symbol >();
	const Reloc &minuend = relocs[++i];
	uint64_t minuendVA;
	if (const Symbol toSym = minuend.referent.dyn_cast<Symbol >())
	minuendVA = toSym->getVA() + minuend.addend;
	else {
	auto referentIsec = minuend.referent.get<InputSection >();
	assert(!::shouldOmitFromOutput(referentIsec));
	minuendVA = referentIsec->getVA(minuend.addend);
	}
	referentVA = minuendVA - fromSym->getVA();
	} else if (auto referentSym = r.referent.dyn_cast<Symbol >()) {
	if (target->hasAttr(r.type, RelocAttrBits::LOAD) &&
	!referentSym->isInGot())
	target->relaxGotLoad(loc, r.type);
	// For dtrace symbols, do not handle them as normal undefined symbols
	if (referentSym->getName().starts_with("___dtrace_")) {
	// Change dtrace call site to pre-defined instructions
	target->handleDtraceReloc(referentSym, r, loc);
	continue;
	}
	referentVA = resolveSymbolVA(referentSym, r.type) + r.addend;

	if (isThreadLocalVariables(getFlags()) && isa<Defined>(referentSym)) {
	// References from thread-local variable sections are treated as offsets
	// relative to the start of the thread-local data memory area, which
	// is initialized via copying all the TLV data sections (which are all
	// contiguous).
	referentVA -= firstTLVDataSection->addr;
	} else if (needsFixup) {
	writeChainedFixup(loc, referentSym, r.addend);
	continue;
	}
	} else if (auto referentIsec = r.referent.dyn_cast<InputSection >()) {
	assert(!::shouldOmitFromOutput(referentIsec));
	referentVA = referentIsec->getVA(r.addend);

	if (needsFixup) {
	writeChainedRebase(loc, referentVA);
	continue;
	}
	}
	target->relocateOne(loc, r, referentVA, getVA() + r.offset);
	}
	}

	ConcatInputSection *macho::makeSyntheticInputSection(StringRef segName,
	StringRef sectName,
	uint32_t flags,
	ArrayRef<uint8_t> data,
	uint32_t align) {
	Section &section =
	make<Section>(/file=/nullptr, segName, sectName, flags, /addr=*/0);
	auto isec = make<ConcatInputSection>(section, data, align);
	// Since this is an explicitly created 'fake' input section,
	// it should not be dead stripped.
	isec->live = true;
	section.subsections.push_back({0, isec});
	return isec;
	}

	void CStringInputSection::splitIntoPieces() {
	size_t off = 0;
	StringRef s = toStringRef(data);
	while (!s.empty()) {
	size_t end = s.find(0);
	if (end == StringRef::npos)
	fatal(getLocation(off) + ": string is not null terminated");
	uint32_t hash = deduplicateLiterals ? xxh3_64bits(s.take_front(end)) : 0;
	pieces.emplace_back(off, hash);
	size_t size = end + 1; // include null terminator
	s = s.substr(size);
	off += size;
	}
	}

	StringPiece &CStringInputSection::getStringPiece(uint64_t off) {
	if (off >= data.size())
	fatal(toString(this) + ": offset is outside the section");

	auto it =
	partition_point(pieces, [=](StringPiece p) { return p.inSecOff <= off; });
	return it[-1];
	}

	const StringPiece &CStringInputSection::getStringPiece(uint64_t off) const {
	return const_cast<CStringInputSection *>(this)->getStringPiece(off);
	}

	size_t CStringInputSection::getStringPieceIndex(uint64_t off) const {
	if (off >= data.size())
	fatal(toString(this) + ": offset is outside the section");

	auto it =
	partition_point(pieces, [=](StringPiece p) { return p.inSecOff <= off; });
	return std::distance(pieces.begin(), it) - 1;
	}

	uint64_t CStringInputSection::getOffset(uint64_t off) const {
	const StringPiece &piece = getStringPiece(off);
	uint64_t addend = off - piece.inSecOff;
	return piece.outSecOff + addend;
	}

	WordLiteralInputSection::WordLiteralInputSection(const Section &section,
	ArrayRef<uint8_t> data,
	uint32_t align)
	: InputSection(WordLiteralKind, section, data, align) {
	switch (sectionType(getFlags())) {
	case S_4BYTE_LITERALS:
	power2LiteralSize = 2;
	break;
	case S_8BYTE_LITERALS:
	power2LiteralSize = 3;
	break;
	case S_16BYTE_LITERALS:
	power2LiteralSize = 4;
	break;
	default:
	llvm_unreachable("invalid literal section type");
	}

	live.resize(data.size() >> power2LiteralSize, !config->deadStrip);
	}

	uint64_t WordLiteralInputSection::getOffset(uint64_t off) const {
	auto *osec = cast<WordLiteralSection>(parent);
	const uintptr_t buf = reinterpret_cast<uintptr_t>(data.data());
	switch (sectionType(getFlags())) {
	case S_4BYTE_LITERALS:
	return osec->getLiteral4Offset(buf + (off & ~3LLU)) \| (off & 3);
	case S_8BYTE_LITERALS:
	return osec->getLiteral8Offset(buf + (off & ~7LLU)) \| (off & 7);
	case S_16BYTE_LITERALS:
	return osec->getLiteral16Offset(buf + (off & ~15LLU)) \| (off & 15);
	default:
	llvm_unreachable("invalid literal section type");
	}
	}

	bool macho::isCodeSection(const InputSection *isec) {
	uint32_t type = sectionType(isec->getFlags());
	if (type != S_REGULAR && type != S_COALESCED)
	return false;

	uint32_t attr = isec->getFlags() & SECTION_ATTRIBUTES_USR;
	if (attr == S_ATTR_PURE_INSTRUCTIONS)
	return true;

	if (isec->getSegName() == segment_names::text)
	return StringSwitch<bool>(isec->getName())
	.Cases(section_names::textCoalNt, section_names::staticInit, true)
	.Default(false);

	return false;
	}

	bool macho::isCfStringSection(const InputSection *isec) {
	return isec->getName() == section_names::cfString &&
	isec->getSegName() == segment_names::data;
	}

	bool macho::isClassRefsSection(const InputSection *isec) {
	return isec->getName() == section_names::objcClassRefs &&
	isec->getSegName() == segment_names::data;
	}

	bool macho::isSelRefsSection(const InputSection *isec) {
	return isec->getName() == section_names::objcSelrefs &&
	isec->getSegName() == segment_names::data;
	}

	bool macho::isEhFrameSection(const InputSection *isec) {
	return isec->getName() == section_names::ehFrame &&
	isec->getSegName() == segment_names::text;
	}

	bool macho::isGccExceptTabSection(const InputSection *isec) {
	return isec->getName() == section_names::gccExceptTab &&
	isec->getSegName() == segment_names::text;
	}

	std::string lld::toString(const InputSection *isec) {
	return (toString(isec->getFile()) + ":(" + isec->getName() + ")").str();
	}