lld/MachO/InputSection.h

   1 //===- InputSection.h -------------------------------------------*- C++ -*-===//
   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 #ifndef LLD_MACHO_INPUT_SECTION_H
  10 #define LLD_MACHO_INPUT_SECTION_H
  11
  12 #include "Config.h"
  13 #include "Relocations.h"
  14 #include "Symbols.h"
  15
  16 #include "lld/Common/LLVM.h"
  17 #include "lld/Common/Memory.h"
  18 #include "llvm/ADT/ArrayRef.h"
  19 #include "llvm/ADT/BitVector.h"
  20 #include "llvm/ADT/CachedHashString.h"
  21 #include "llvm/ADT/TinyPtrVector.h"
  22 #include "llvm/BinaryFormat/MachO.h"
  23
  24 namespace lld {
  25 namespace macho {
  26
  27 class InputFile;
  28 class OutputSection;
  29
  30 class InputSection {
  31 public:
  32   enum Kind : uint8_t {
  33     ConcatKind,
  34     CStringLiteralKind,
  35     WordLiteralKind,
  36   };
  37
  38   Kind kind() const { return sectionKind; }
  39   virtual ~InputSection() = default;
  40   virtual uint64_t getSize() const { return data.size(); }
  41   virtual bool empty() const { return data.empty(); }
  42   InputFile *getFile() const { return section.file; }
  43   StringRef getName() const { return section.name; }
  44   StringRef getSegName() const { return section.segname; }
  45   uint32_t getFlags() const { return section.flags; }
  46   uint64_t getFileSize() const;
  47   // Translates \p off -- an offset relative to this InputSection -- into an
  48   // offset from the beginning of its parent OutputSection.
  49   virtual uint64_t getOffset(uint64_t off) const = 0;
  50   // The offset from the beginning of the file.
  51   uint64_t getVA(uint64_t off) const;
  52   // Return a user-friendly string for use in diagnostics.
  53   // Format: /path/to/object.o:(symbol _func+0x123)
  54   std::string getLocation(uint64_t off) const;
  55   // Return the source line corresponding to an address, or the empty string.
  56   // Format: Source.cpp:123 (/path/to/Source.cpp:123)
  57   std::string getSourceLocation(uint64_t off) const;
  58   // Return the relocation at \p off, if it exists. This does a linear search.
  59   const Reloc *getRelocAt(uint32_t off) const;
  60   // Whether the data at \p off in this InputSection is live.
  61   virtual bool isLive(uint64_t off) const = 0;
  62   virtual void markLive(uint64_t off) = 0;
  63   virtual InputSection *canonical() { return this; }
  64   virtual const InputSection *canonical() const { return this; }
  65
  66 protected:
  67   InputSection(Kind kind, const Section &section, ArrayRef<uint8_t> data,
  68                uint32_t align)
  69       : sectionKind(kind), keepUnique(false), hasAltEntry(false), align(align),
  70         data(data), section(section) {}
  71
  72   InputSection(const InputSection &rhs)
  73       : sectionKind(rhs.sectionKind), keepUnique(false), hasAltEntry(false),
  74         align(rhs.align), data(rhs.data), section(rhs.section) {}
  75
  76   Kind sectionKind;
  77
  78 public:
  79   // is address assigned?
  80   bool isFinal = false;
  81   // keep the address of the symbol(s) in this section unique in the final
  82   // binary ?
  83   bool keepUnique : 1;
  84   // Does this section have symbols at offsets other than zero? (NOTE: only
  85   // applies to ConcatInputSections.)
  86   bool hasAltEntry : 1;
  87   uint32_t align = 1;
  88
  89   OutputSection *parent = nullptr;
  90   ArrayRef<uint8_t> data;
  91   std::vector<Reloc> relocs;
  92   // The symbols that belong to this InputSection, sorted by value. With
  93   // .subsections_via_symbols, there is typically only one element here.
  94   llvm::TinyPtrVector<Defined *> symbols;
  95
  96 protected:
  97   const Section &section;
  98
  99   const Defined *getContainingSymbol(uint64_t off) const;
 100 };
 101
 102 // ConcatInputSections are combined into (Concat)OutputSections through simple
 103 // concatenation, in contrast with literal sections which may have their
 104 // contents merged before output.
 105 class ConcatInputSection final : public InputSection {
 106 public:
 107   ConcatInputSection(const Section &section, ArrayRef<uint8_t> data,
 108                      uint32_t align = 1)
 109       : InputSection(ConcatKind, section, data, align) {}
 110
 111   uint64_t getOffset(uint64_t off) const override { return outSecOff + off; }
 112   uint64_t getVA() const { return InputSection::getVA(0); }
 113   // ConcatInputSections are entirely live or dead, so the offset is irrelevant.
 114   bool isLive(uint64_t off) const override { return live; }
 115   void markLive(uint64_t off) override { live = true; }
 116   bool isCoalescedWeak() const { return wasCoalesced && symbols.empty(); }
 117   bool shouldOmitFromOutput() const { return !live || isCoalescedWeak(); }
 118   void writeTo(uint8_t *buf);
 119
 120   void foldIdentical(ConcatInputSection *redundant);
 121   ConcatInputSection *canonical() override {
 122     return replacement ? replacement : this;
 123   }
 124   const InputSection *canonical() const override {
 125     return replacement ? replacement : this;
 126   }
 127
 128   static bool classof(const InputSection *isec) {
 129     return isec->kind() == ConcatKind;
 130   }
 131
 132   // Points to the surviving section after this one is folded by ICF
 133   ConcatInputSection *replacement = nullptr;
 134   // Equivalence-class ID for ICF
 135   uint32_t icfEqClass[2] = {0, 0};
 136
 137   // With subsections_via_symbols, most symbols have their own InputSection,
 138   // and for weak symbols (e.g. from inline functions), only the
 139   // InputSection from one translation unit will make it to the output,
 140   // while all copies in other translation units are coalesced into the
 141   // first and not copied to the output.
 142   bool wasCoalesced = false;
 143   bool live = !config->deadStrip;
 144   bool hasCallSites = false;
 145   // This variable has two usages. Initially, it represents the input order.
 146   // After assignAddresses is called, it represents the offset from the
 147   // beginning of the output section this section was assigned to.
 148   uint64_t outSecOff = 0;
 149 };
 150
 151 // Initialize a fake InputSection that does not belong to any InputFile.
 152 ConcatInputSection *makeSyntheticInputSection(StringRef segName,
 153                                               StringRef sectName,
 154                                               uint32_t flags = 0,
 155                                               ArrayRef<uint8_t> data = {},
 156                                               uint32_t align = 1);
 157
 158 // Helper functions to make it easy to sprinkle asserts.
 159
 160 inline bool shouldOmitFromOutput(InputSection *isec) {
 161   return isa<ConcatInputSection>(isec) &&
 162          cast<ConcatInputSection>(isec)->shouldOmitFromOutput();
 163 }
 164
 165 inline bool isCoalescedWeak(InputSection *isec) {
 166   return isa<ConcatInputSection>(isec) &&
 167          cast<ConcatInputSection>(isec)->isCoalescedWeak();
 168 }
 169
 170 // We allocate a lot of these and binary search on them, so they should be as
 171 // compact as possible. Hence the use of 31 rather than 64 bits for the hash.
 172 struct StringPiece {
 173   // Offset from the start of the containing input section.
 174   uint32_t inSecOff;
 175   uint32_t live : 1;
 176   // Only set if deduplicating literals
 177   uint32_t hash : 31;
 178   // Offset from the start of the containing output section.
 179   uint64_t outSecOff = 0;
 180
 181   StringPiece(uint64_t off, uint32_t hash)
 182       : inSecOff(off), live(!config->deadStrip), hash(hash) {}
 183 };
 184
 185 static_assert(sizeof(StringPiece) == 16, "StringPiece is too big!");
 186
 187 // CStringInputSections are composed of multiple null-terminated string
 188 // literals, which we represent using StringPieces. These literals can be
 189 // deduplicated and tail-merged, so translating offsets between the input and
 190 // outputs sections is more complicated.
 191 //
 192 // NOTE: One significant difference between LLD and ld64 is that we merge all
 193 // cstring literals, even those referenced directly by non-private symbols.
 194 // ld64 is more conservative and does not do that. This was mostly done for
 195 // implementation simplicity; if we find programs that need the more
 196 // conservative behavior we can certainly implement that.
 197 class CStringInputSection final : public InputSection {
 198 public:
 199   CStringInputSection(const Section &section, ArrayRef<uint8_t> data,
 200                       uint32_t align, bool dedupLiterals)
 201       : InputSection(CStringLiteralKind, section, data, align),
 202         deduplicateLiterals(dedupLiterals) {}
 203
 204   uint64_t getOffset(uint64_t off) const override;
 205   bool isLive(uint64_t off) const override { return getStringPiece(off).live; }
 206   void markLive(uint64_t off) override { getStringPiece(off).live = true; }
 207   // Find the StringPiece that contains this offset.
 208   StringPiece &getStringPiece(uint64_t off);
 209   const StringPiece &getStringPiece(uint64_t off) const;
 210   // Split at each null byte.
 211   void splitIntoPieces();
 212
 213   LLVM_ATTRIBUTE_ALWAYS_INLINE
 214   StringRef getStringRef(size_t i) const {
 215     size_t begin = pieces[i].inSecOff;
 216     // The endpoint should be *at* the null terminator, not after. This matches
 217     // the behavior of StringRef(const char *Str).
 218     size_t end =
 219         ((pieces.size() - 1 == i) ? data.size() : pieces[i + 1].inSecOff) - 1;
 220     return toStringRef(data.slice(begin, end - begin));
 221   }
 222
 223   StringRef getStringRefAtOffset(uint64_t off) const {
 224     return getStringRef(getStringPieceIndex(off));
 225   }
 226
 227   // Returns i'th piece as a CachedHashStringRef. This function is very hot when
 228   // string merging is enabled, so we want to inline.
 229   LLVM_ATTRIBUTE_ALWAYS_INLINE
 230   llvm::CachedHashStringRef getCachedHashStringRef(size_t i) const {
 231     assert(deduplicateLiterals);
 232     return {getStringRef(i), pieces[i].hash};
 233   }
 234
 235   static bool classof(const InputSection *isec) {
 236     return isec->kind() == CStringLiteralKind;
 237   }
 238
 239   bool deduplicateLiterals = false;
 240   std::vector<StringPiece> pieces;
 241
 242 private:
 243   size_t getStringPieceIndex(uint64_t off) const;
 244 };
 245
 246 class WordLiteralInputSection final : public InputSection {
 247 public:
 248   WordLiteralInputSection(const Section &section, ArrayRef<uint8_t> data,
 249                           uint32_t align);
 250   uint64_t getOffset(uint64_t off) const override;
 251   bool isLive(uint64_t off) const override {
 252     return live[off >> power2LiteralSize];
 253   }
 254   void markLive(uint64_t off) override {
 255     live[off >> power2LiteralSize] = true;
 256   }
 257
 258   static bool classof(const InputSection *isec) {
 259     return isec->kind() == WordLiteralKind;
 260   }
 261
 262 private:
 263   unsigned power2LiteralSize;
 264   // The liveness of data[off] is tracked by live[off >> power2LiteralSize].
 265   llvm::BitVector live;
 266 };
 267
 268 inline uint8_t sectionType(uint32_t flags) {
 269   return flags & llvm::MachO::SECTION_TYPE;
 270 }
 271
 272 inline bool isZeroFill(uint32_t flags) {
 273   return llvm::MachO::isVirtualSection(sectionType(flags));
 274 }
 275
 276 inline bool isThreadLocalVariables(uint32_t flags) {
 277   return sectionType(flags) == llvm::MachO::S_THREAD_LOCAL_VARIABLES;
 278 }
 279
 280 // These sections contain the data for initializing thread-local variables.
 281 inline bool isThreadLocalData(uint32_t flags) {
 282   return sectionType(flags) == llvm::MachO::S_THREAD_LOCAL_REGULAR ||
 283          sectionType(flags) == llvm::MachO::S_THREAD_LOCAL_ZEROFILL;
 284 }
 285
 286 inline bool isDebugSection(uint32_t flags) {
 287   return (flags & llvm::MachO::SECTION_ATTRIBUTES_USR) ==
 288          llvm::MachO::S_ATTR_DEBUG;
 289 }
 290
 291 inline bool isWordLiteralSection(uint32_t flags) {
 292   return sectionType(flags) == llvm::MachO::S_4BYTE_LITERALS ||
 293          sectionType(flags) == llvm::MachO::S_8BYTE_LITERALS ||
 294          sectionType(flags) == llvm::MachO::S_16BYTE_LITERALS;
 295 }
 296
 297 bool isCodeSection(const InputSection *);
 298 bool isCfStringSection(const InputSection *);
 299 bool isClassRefsSection(const InputSection *);
 300 bool isSelRefsSection(const InputSection *);
 301 bool isEhFrameSection(const InputSection *);
 302 bool isGccExceptTabSection(const InputSection *);
 303
 304 extern std::vector<ConcatInputSection *> inputSections;
 305
 306 namespace section_names {
 307
 308 constexpr const char authGot[] = "__auth_got";
 309 constexpr const char authPtr[] = "__auth_ptr";
 310 constexpr const char binding[] = "__binding";
 311 constexpr const char bitcodeBundle[] = "__bundle";
 312 constexpr const char cString[] = "__cstring";
 313 constexpr const char cfString[] = "__cfstring";
 314 constexpr const char cgProfile[] = "__cg_profile";
 315 constexpr const char chainFixups[] = "__chainfixups";
 316 constexpr const char codeSignature[] = "__code_signature";
 317 constexpr const char common[] = "__common";
 318 constexpr const char compactUnwind[] = "__compact_unwind";
 319 constexpr const char data[] = "__data";
 320 constexpr const char debugAbbrev[] = "__debug_abbrev";
 321 constexpr const char debugInfo[] = "__debug_info";
 322 constexpr const char debugLine[] = "__debug_line";
 323 constexpr const char debugStr[] = "__debug_str";
 324 constexpr const char debugStrOffs[] = "__debug_str_offs";
 325 constexpr const char ehFrame[] = "__eh_frame";
 326 constexpr const char gccExceptTab[] = "__gcc_except_tab";
 327 constexpr const char export_[] = "__export";
 328 constexpr const char dataInCode[] = "__data_in_code";
 329 constexpr const char functionStarts[] = "__func_starts";
 330 constexpr const char got[] = "__got";
 331 constexpr const char header[] = "__mach_header";
 332 constexpr const char indirectSymbolTable[] = "__ind_sym_tab";
 333 constexpr const char initOffsets[] = "__init_offsets";
 334 constexpr const char const_[] = "__const";
 335 constexpr const char lazySymbolPtr[] = "__la_symbol_ptr";
 336 constexpr const char lazyBinding[] = "__lazy_binding";
 337 constexpr const char literals[] = "__literals";
 338 constexpr const char moduleInitFunc[] = "__mod_init_func";
 339 constexpr const char moduleTermFunc[] = "__mod_term_func";
 340 constexpr const char nonLazySymbolPtr[] = "__nl_symbol_ptr";
 341 constexpr const char objcCatList[] = "__objc_catlist";
 342 constexpr const char objcClassList[] = "__objc_classlist";
 343 constexpr const char objcClassRefs[] = "__objc_classrefs";
 344 constexpr const char objcConst[] = "__objc_const";
 345 constexpr const char objCImageInfo[] = "__objc_imageinfo";
 346 constexpr const char objcStubs[] = "__objc_stubs";
 347 constexpr const char objcSelrefs[] = "__objc_selrefs";
 348 constexpr const char objcMethname[] = "__objc_methname";
 349 constexpr const char objcNonLazyCatList[] = "__objc_nlcatlist";
 350 constexpr const char objcNonLazyClassList[] = "__objc_nlclslist";
 351 constexpr const char objcProtoList[] = "__objc_protolist";
 352 constexpr const char pageZero[] = "__pagezero";
 353 constexpr const char pointers[] = "__pointers";
 354 constexpr const char rebase[] = "__rebase";
 355 constexpr const char staticInit[] = "__StaticInit";
 356 constexpr const char stringTable[] = "__string_table";
 357 constexpr const char stubHelper[] = "__stub_helper";
 358 constexpr const char stubs[] = "__stubs";
 359 constexpr const char swift[] = "__swift";
 360 constexpr const char symbolTable[] = "__symbol_table";
 361 constexpr const char textCoalNt[] = "__textcoal_nt";
 362 constexpr const char text[] = "__text";
 363 constexpr const char threadPtrs[] = "__thread_ptrs";
 364 constexpr const char threadVars[] = "__thread_vars";
 365 constexpr const char unwindInfo[] = "__unwind_info";
 366 constexpr const char weakBinding[] = "__weak_binding";
 367 constexpr const char zeroFill[] = "__zerofill";
 368 constexpr const char addrSig[] = "__llvm_addrsig";
 369
 370 } // namespace section_names
 371
 372 } // namespace macho
 373
 374 std::string toString(const macho::InputSection *);
 375
 376 } // namespace lld
 377
 378 #endif