lld/MachO/InputSection.cpp

   1 //===- InputSection.cpp ---------------------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #include "InputSection.h"
  10 #include "ConcatOutputSection.h"
  11 #include "Config.h"
  12 #include "InputFiles.h"
  13 #include "OutputSegment.h"
  14 #include "Symbols.h"
  15 #include "SyntheticSections.h"
  16 #include "Target.h"
  17 #include "UnwindInfoSection.h"
  18 #include "Writer.h"
  19
  20 #include "lld/Common/ErrorHandler.h"
  21 #include "lld/Common/Memory.h"
  22 #include "llvm/Support/Endian.h"
  23 #include "llvm/Support/xxhash.h"
  24
  25 using namespace llvm;
  26 using namespace llvm::MachO;
  27 using namespace llvm::support;
  28 using namespace lld;
  29 using namespace lld::macho;
  30
  31 // Verify ConcatInputSection's size on 64-bit builds. The size of std::vector
  32 // can differ based on STL debug levels (e.g. iterator debugging on MSVC's STL),
  33 // so account for that.
  34 static_assert(sizeof(void *) != 8 ||
  35                   sizeof(ConcatInputSection) == sizeof(std::vector<Reloc>) + 88,
  36               "Try to minimize ConcatInputSection's size, we create many "
  37               "instances of it");
  38
  39 std::vector<ConcatInputSection *> macho::inputSections;
  40 int macho::inputSectionsOrder = 0;
  41
  42 // Call this function to add a new InputSection and have it routed to the
  43 // appropriate container. Depending on its type and current config, it will
  44 // either be added to 'inputSections' vector or to a synthetic section.
  45 void lld::macho::addInputSection(InputSection *inputSection) {
  46   if (auto *isec = dyn_cast<ConcatInputSection>(inputSection)) {
  47     if (isec->isCoalescedWeak())
  48       return;
  49     if (config->emitRelativeMethodLists &&
  50         ObjCMethListSection::isMethodList(isec)) {
  51       if (in.objcMethList->inputOrder == UnspecifiedInputOrder)
  52         in.objcMethList->inputOrder = inputSectionsOrder++;
  53       in.objcMethList->addInput(isec);
  54       isec->parent = in.objcMethList;
  55       return;
  56     }
  57     if (config->emitInitOffsets &&
  58         sectionType(isec->getFlags()) == S_MOD_INIT_FUNC_POINTERS) {
  59       in.initOffsets->addInput(isec);
  60       return;
  61     }
  62     isec->outSecOff = inputSectionsOrder++;
  63     auto *osec = ConcatOutputSection::getOrCreateForInput(isec);
  64     isec->parent = osec;
  65     inputSections.push_back(isec);
  66   } else if (auto *isec = dyn_cast<CStringInputSection>(inputSection)) {
  67     if (isec->getName() == section_names::objcMethname) {
  68       if (in.objcMethnameSection->inputOrder == UnspecifiedInputOrder)
  69         in.objcMethnameSection->inputOrder = inputSectionsOrder++;
  70       in.objcMethnameSection->addInput(isec);
  71     } else {
  72       if (in.cStringSection->inputOrder == UnspecifiedInputOrder)
  73         in.cStringSection->inputOrder = inputSectionsOrder++;
  74       in.cStringSection->addInput(isec);
  75     }
  76   } else if (auto *isec = dyn_cast<WordLiteralInputSection>(inputSection)) {
  77     if (in.wordLiteralSection->inputOrder == UnspecifiedInputOrder)
  78       in.wordLiteralSection->inputOrder = inputSectionsOrder++;
  79     in.wordLiteralSection->addInput(isec);
  80   } else {
  81     llvm_unreachable("unexpected input section kind");
  82   }
  83
  84   assert(inputSectionsOrder <= UnspecifiedInputOrder);
  85 }
  86
  87 uint64_t InputSection::getFileSize() const {
  88   return isZeroFill(getFlags()) ? 0 : getSize();
  89 }
  90
  91 uint64_t InputSection::getVA(uint64_t off) const {
  92   return parent->addr + getOffset(off);
  93 }
  94
  95 static uint64_t resolveSymbolVA(const Symbol *sym, uint8_t type) {
  96   const RelocAttrs &relocAttrs = target->getRelocAttrs(type);
  97   if (relocAttrs.hasAttr(RelocAttrBits::BRANCH))
  98     return sym->resolveBranchVA();
  99   if (relocAttrs.hasAttr(RelocAttrBits::GOT))
 100     return sym->resolveGotVA();
 101   if (relocAttrs.hasAttr(RelocAttrBits::TLV))
 102     return sym->resolveTlvVA();
 103   return sym->getVA();
 104 }
 105
 106 const Defined *InputSection::getContainingSymbol(uint64_t off) const {
 107   auto *nextSym = llvm::upper_bound(
 108       symbols, off, [](uint64_t a, const Defined *b) { return a < b->value; });
 109   if (nextSym == symbols.begin())
 110     return nullptr;
 111   return *std::prev(nextSym);
 112 }
 113
 114 std::string InputSection::getLocation(uint64_t off) const {
 115   // First, try to find a symbol that's near the offset. Use it as a reference
 116   // point.
 117   if (auto *sym = getContainingSymbol(off))
 118     return (toString(getFile()) + ":(symbol " + toString(*sym) + "+0x" +
 119             Twine::utohexstr(off - sym->value) + ")")
 120         .str();
 121
 122   // If that fails, use the section itself as a reference point.
 123   for (const Subsection &subsec : section.subsections) {
 124     if (subsec.isec == this) {
 125       off += subsec.offset;
 126       break;
 127     }
 128   }
 129
 130   return (toString(getFile()) + ":(" + getName() + "+0x" +
 131           Twine::utohexstr(off) + ")")
 132       .str();
 133 }
 134
 135 std::string InputSection::getSourceLocation(uint64_t off) const {
 136   auto *obj = dyn_cast_or_null<ObjFile>(getFile());
 137   if (!obj)
 138     return {};
 139
 140   DWARFCache *dwarf = obj->getDwarf();
 141   if (!dwarf)
 142     return std::string();
 143
 144   for (const Subsection &subsec : section.subsections) {
 145     if (subsec.isec == this) {
 146       off += subsec.offset;
 147       break;
 148     }
 149   }
 150
 151   auto createMsg = [&](StringRef path, unsigned line) {
 152     std::string filename = sys::path::filename(path).str();
 153     std::string lineStr = (":" + Twine(line)).str();
 154     if (filename == path)
 155       return filename + lineStr;
 156     return (filename + lineStr + " (" + path + lineStr + ")").str();
 157   };
 158
 159   // First, look up a function for a given offset.
 160   if (std::optional<DILineInfo> li = dwarf->getDILineInfo(
 161           section.addr + off, object::SectionedAddress::UndefSection))
 162     return createMsg(li->FileName, li->Line);
 163
 164   // If it failed, look up again as a variable.
 165   if (const Defined *sym = getContainingSymbol(off)) {
 166     // Symbols are generally prefixed with an underscore, which is not included
 167     // in the debug information.
 168     StringRef symName = sym->getName();
 169     if (!symName.empty() && symName[0] == '_')
 170       symName = symName.substr(1);
 171
 172     if (std::optional<std::pair<std::string, unsigned>> fileLine =
 173             dwarf->getVariableLoc(symName))
 174       return createMsg(fileLine->first, fileLine->second);
 175   }
 176
 177   // Try to get the source file's name from the DWARF information.
 178   if (obj->compileUnit)
 179     return obj->sourceFile();
 180
 181   return {};
 182 }
 183
 184 const Reloc *InputSection::getRelocAt(uint32_t off) const {
 185   auto it = llvm::find_if(
 186       relocs, [=](const macho::Reloc &r) { return r.offset == off; });
 187   if (it == relocs.end())
 188     return nullptr;
 189   return &*it;
 190 }
 191
 192 void ConcatInputSection::foldIdentical(ConcatInputSection *copy) {
 193   align = std::max(align, copy->align);
 194   copy->live = false;
 195   copy->wasCoalesced = true;
 196   copy->replacement = this;
 197   for (auto &copySym : copy->symbols)
 198     copySym->wasIdenticalCodeFolded = true;
 199
 200   symbols.insert(symbols.end(), copy->symbols.begin(), copy->symbols.end());
 201   copy->symbols.clear();
 202
 203   // Remove duplicate compact unwind info for symbols at the same address.
 204   if (symbols.empty())
 205     return;
 206   for (auto it = symbols.begin() + 1; it != symbols.end(); ++it) {
 207     assert((*it)->value == 0);
 208     (*it)->originalUnwindEntry = nullptr;
 209   }
 210 }
 211
 212 void ConcatInputSection::writeTo(uint8_t *buf) {
 213   assert(!shouldOmitFromOutput());
 214
 215   if (getFileSize() == 0)
 216     return;
 217
 218   memcpy(buf, data.data(), data.size());
 219
 220   for (size_t i = 0; i < relocs.size(); i++) {
 221     const Reloc &r = relocs[i];
 222     uint8_t *loc = buf + r.offset;
 223     uint64_t referentVA = 0;
 224
 225     const bool needsFixup = config->emitChainedFixups &&
 226                             target->hasAttr(r.type, RelocAttrBits::UNSIGNED);
 227     if (target->hasAttr(r.type, RelocAttrBits::SUBTRAHEND)) {
 228       const Symbol *fromSym = r.referent.get<Symbol *>();
 229       const Reloc &minuend = relocs[++i];
 230       uint64_t minuendVA;
 231       if (const Symbol *toSym = minuend.referent.dyn_cast<Symbol *>())
 232         minuendVA = toSym->getVA() + minuend.addend;
 233       else {
 234         auto *referentIsec = minuend.referent.get<InputSection *>();
 235         assert(!::shouldOmitFromOutput(referentIsec));
 236         minuendVA = referentIsec->getVA(minuend.addend);
 237       }
 238       referentVA = minuendVA - fromSym->getVA();
 239     } else if (auto *referentSym = r.referent.dyn_cast<Symbol *>()) {
 240       if (target->hasAttr(r.type, RelocAttrBits::LOAD) &&
 241           !referentSym->isInGot())
 242         target->relaxGotLoad(loc, r.type);
 243       // For dtrace symbols, do not handle them as normal undefined symbols
 244       if (referentSym->getName().starts_with("___dtrace_")) {
 245         // Change dtrace call site to pre-defined instructions
 246         target->handleDtraceReloc(referentSym, r, loc);
 247         continue;
 248       }
 249       referentVA = resolveSymbolVA(referentSym, r.type) + r.addend;
 250
 251       if (isThreadLocalVariables(getFlags()) && isa<Defined>(referentSym)) {
 252         // References from thread-local variable sections are treated as offsets
 253         // relative to the start of the thread-local data memory area, which
 254         // is initialized via copying all the TLV data sections (which are all
 255         // contiguous).
 256         referentVA -= firstTLVDataSection->addr;
 257       } else if (needsFixup) {
 258         writeChainedFixup(loc, referentSym, r.addend);
 259         continue;
 260       }
 261     } else if (auto *referentIsec = r.referent.dyn_cast<InputSection *>()) {
 262       assert(!::shouldOmitFromOutput(referentIsec));
 263       referentVA = referentIsec->getVA(r.addend);
 264
 265       if (needsFixup) {
 266         writeChainedRebase(loc, referentVA);
 267         continue;
 268       }
 269     }
 270     target->relocateOne(loc, r, referentVA, getVA() + r.offset);
 271   }
 272 }
 273
 274 ConcatInputSection *macho::makeSyntheticInputSection(StringRef segName,
 275                                                      StringRef sectName,
 276                                                      uint32_t flags,
 277                                                      ArrayRef<uint8_t> data,
 278                                                      uint32_t align) {
 279   Section &section =
 280       *make<Section>(/*file=*/nullptr, segName, sectName, flags, /*addr=*/0);
 281   auto isec = make<ConcatInputSection>(section, data, align);
 282   // Since this is an explicitly created 'fake' input section,
 283   // it should not be dead stripped.
 284   isec->live = true;
 285   section.subsections.push_back({0, isec});
 286   return isec;
 287 }
 288
 289 void CStringInputSection::splitIntoPieces() {
 290   size_t off = 0;
 291   StringRef s = toStringRef(data);
 292   while (!s.empty()) {
 293     size_t end = s.find(0);
 294     if (end == StringRef::npos)
 295       fatal(getLocation(off) + ": string is not null terminated");
 296     uint32_t hash = deduplicateLiterals ? xxh3_64bits(s.take_front(end)) : 0;
 297     pieces.emplace_back(off, hash);
 298     size_t size = end + 1; // include null terminator
 299     s = s.substr(size);
 300     off += size;
 301   }
 302 }
 303
 304 StringPiece &CStringInputSection::getStringPiece(uint64_t off) {
 305   if (off >= data.size())
 306     fatal(toString(this) + ": offset is outside the section");
 307
 308   auto it =
 309       partition_point(pieces, [=](StringPiece p) { return p.inSecOff <= off; });
 310   return it[-1];
 311 }
 312
 313 const StringPiece &CStringInputSection::getStringPiece(uint64_t off) const {
 314   return const_cast<CStringInputSection *>(this)->getStringPiece(off);
 315 }
 316
 317 size_t CStringInputSection::getStringPieceIndex(uint64_t off) const {
 318   if (off >= data.size())
 319     fatal(toString(this) + ": offset is outside the section");
 320
 321   auto it =
 322       partition_point(pieces, [=](StringPiece p) { return p.inSecOff <= off; });
 323   return std::distance(pieces.begin(), it) - 1;
 324 }
 325
 326 uint64_t CStringInputSection::getOffset(uint64_t off) const {
 327   const StringPiece &piece = getStringPiece(off);
 328   uint64_t addend = off - piece.inSecOff;
 329   return piece.outSecOff + addend;
 330 }
 331
 332 WordLiteralInputSection::WordLiteralInputSection(const Section &section,
 333                                                  ArrayRef<uint8_t> data,
 334                                                  uint32_t align)
 335     : InputSection(WordLiteralKind, section, data, align) {
 336   switch (sectionType(getFlags())) {
 337   case S_4BYTE_LITERALS:
 338     power2LiteralSize = 2;
 339     break;
 340   case S_8BYTE_LITERALS:
 341     power2LiteralSize = 3;
 342     break;
 343   case S_16BYTE_LITERALS:
 344     power2LiteralSize = 4;
 345     break;
 346   default:
 347     llvm_unreachable("invalid literal section type");
 348   }
 349
 350   live.resize(data.size() >> power2LiteralSize, !config->deadStrip);
 351 }
 352
 353 uint64_t WordLiteralInputSection::getOffset(uint64_t off) const {
 354   auto *osec = cast<WordLiteralSection>(parent);
 355   const uintptr_t buf = reinterpret_cast<uintptr_t>(data.data());
 356   switch (sectionType(getFlags())) {
 357   case S_4BYTE_LITERALS:
 358     return osec->getLiteral4Offset(buf + (off & ~3LLU)) | (off & 3);
 359   case S_8BYTE_LITERALS:
 360     return osec->getLiteral8Offset(buf + (off & ~7LLU)) | (off & 7);
 361   case S_16BYTE_LITERALS:
 362     return osec->getLiteral16Offset(buf + (off & ~15LLU)) | (off & 15);
 363   default:
 364     llvm_unreachable("invalid literal section type");
 365   }
 366 }
 367
 368 bool macho::isCodeSection(const InputSection *isec) {
 369   uint32_t type = sectionType(isec->getFlags());
 370   if (type != S_REGULAR && type != S_COALESCED)
 371     return false;
 372
 373   uint32_t attr = isec->getFlags() & SECTION_ATTRIBUTES_USR;
 374   if (attr == S_ATTR_PURE_INSTRUCTIONS)
 375     return true;
 376
 377   if (isec->getSegName() == segment_names::text)
 378     return StringSwitch<bool>(isec->getName())
 379         .Cases(section_names::textCoalNt, section_names::staticInit, true)
 380         .Default(false);
 381
 382   return false;
 383 }
 384
 385 bool macho::isCfStringSection(const InputSection *isec) {
 386   return isec->getName() == section_names::cfString &&
 387          isec->getSegName() == segment_names::data;
 388 }
 389
 390 bool macho::isClassRefsSection(const InputSection *isec) {
 391   return isec->getName() == section_names::objcClassRefs &&
 392          isec->getSegName() == segment_names::data;
 393 }
 394
 395 bool macho::isSelRefsSection(const InputSection *isec) {
 396   return isec->getName() == section_names::objcSelrefs &&
 397          isec->getSegName() == segment_names::data;
 398 }
 399
 400 bool macho::isEhFrameSection(const InputSection *isec) {
 401   return isec->getName() == section_names::ehFrame &&
 402          isec->getSegName() == segment_names::text;
 403 }
 404
 405 bool macho::isGccExceptTabSection(const InputSection *isec) {
 406   return isec->getName() == section_names::gccExceptTab &&
 407          isec->getSegName() == segment_names::text;
 408 }
 409
 410 std::string lld::toString(const InputSection *isec) {
 411   return (toString(isec->getFile()) + ":(" + isec->getName() + ")").str();
 412 }