lld/ELF/Relocations.h

   1 //===- Relocations.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_ELF_RELOCATIONS_H
  10 #define LLD_ELF_RELOCATIONS_H
  11
  12 #include "lld/Common/LLVM.h"
  13 #include "llvm/ADT/DenseMap.h"
  14 #include "llvm/ADT/STLExtras.h"
  15 #include "llvm/Object/ELFTypes.h"
  16 #include <vector>
  17
  18 namespace lld::elf {
  19 struct Ctx;
  20 class Defined;
  21 class Symbol;
  22 class InputSection;
  23 class InputSectionBase;
  24 class OutputSection;
  25 class RelocationBaseSection;
  26 class SectionBase;
  27
  28 // Represents a relocation type, such as R_X86_64_PC32 or R_ARM_THM_CALL.
  29 struct RelType {
  30   uint32_t v = 0;
  31   /*implicit*/ constexpr RelType(uint32_t v = 0) : v(v) {}
  32   /*implicit*/ operator uint32_t() const { return v; }
  33 };
  34
  35 using JumpModType = uint32_t;
  36
  37 // List of target-independent relocation types. Relocations read
  38 // from files are converted to these types so that the main code
  39 // doesn't have to know about architecture-specific details.
  40 enum RelExpr {
  41   R_ABS,
  42   R_ADDEND,
  43   R_DTPREL,
  44   R_GOT,
  45   R_GOT_OFF,
  46   R_GOT_PC,
  47   R_GOTONLY_PC,
  48   R_GOTPLTONLY_PC,
  49   R_GOTPLT,
  50   R_GOTPLTREL,
  51   R_GOTREL,
  52   R_GOTPLT_GOTREL,
  53   R_GOTPLT_PC,
  54   R_NONE,
  55   R_PC,
  56   R_PLT,
  57   R_PLT_PC,
  58   R_PLT_GOTPLT,
  59   R_PLT_GOTREL,
  60   R_RELAX_HINT,
  61   R_RELAX_GOT_PC,
  62   R_RELAX_GOT_PC_NOPIC,
  63   R_RELAX_TLS_GD_TO_IE,
  64   R_RELAX_TLS_GD_TO_IE_ABS,
  65   R_RELAX_TLS_GD_TO_IE_GOT_OFF,
  66   R_RELAX_TLS_GD_TO_IE_GOTPLT,
  67   R_RELAX_TLS_GD_TO_LE,
  68   R_RELAX_TLS_GD_TO_LE_NEG,
  69   R_RELAX_TLS_IE_TO_LE,
  70   R_RELAX_TLS_LD_TO_LE,
  71   R_RELAX_TLS_LD_TO_LE_ABS,
  72   R_SIZE,
  73   R_TPREL,
  74   R_TPREL_NEG,
  75   R_TLSDESC,
  76   R_TLSDESC_CALL,
  77   R_TLSDESC_PC,
  78   R_TLSDESC_GOTPLT,
  79   R_TLSGD_GOT,
  80   R_TLSGD_GOTPLT,
  81   R_TLSGD_PC,
  82   R_TLSIE_HINT,
  83   R_TLSLD_GOT,
  84   R_TLSLD_GOTPLT,
  85   R_TLSLD_GOT_OFF,
  86   R_TLSLD_HINT,
  87   R_TLSLD_PC,
  88
  89   // The following is abstract relocation types used for only one target.
  90   //
  91   // Even though RelExpr is intended to be a target-neutral representation
  92   // of a relocation type, there are some relocations whose semantics are
  93   // unique to a target. Such relocation are marked with RE_<TARGET_NAME>.
  94   RE_AARCH64_GOT_PAGE_PC,
  95   RE_AARCH64_AUTH_GOT_PAGE_PC,
  96   RE_AARCH64_GOT_PAGE,
  97   RE_AARCH64_AUTH_GOT,
  98   RE_AARCH64_AUTH_GOT_PC,
  99   RE_AARCH64_PAGE_PC,
 100   RE_AARCH64_RELAX_TLS_GD_TO_IE_PAGE_PC,
 101   RE_AARCH64_TLSDESC_PAGE,
 102   RE_AARCH64_AUTH_TLSDESC_PAGE,
 103   RE_AARCH64_AUTH_TLSDESC,
 104   RE_AARCH64_AUTH,
 105   RE_ARM_PCA,
 106   RE_ARM_SBREL,
 107   RE_MIPS_GOTREL,
 108   RE_MIPS_GOT_GP,
 109   RE_MIPS_GOT_GP_PC,
 110   RE_MIPS_GOT_LOCAL_PAGE,
 111   RE_MIPS_GOT_OFF,
 112   RE_MIPS_GOT_OFF32,
 113   RE_MIPS_TLSGD,
 114   RE_MIPS_TLSLD,
 115   RE_PPC32_PLTREL,
 116   RE_PPC64_CALL,
 117   RE_PPC64_CALL_PLT,
 118   RE_PPC64_RELAX_TOC,
 119   RE_PPC64_TOCBASE,
 120   RE_PPC64_RELAX_GOT_PC,
 121   RE_RISCV_ADD,
 122   RE_RISCV_LEB128,
 123   RE_RISCV_PC_INDIRECT,
 124   // Same as R_PC but with page-aligned semantics.
 125   RE_LOONGARCH_PAGE_PC,
 126   // Same as R_PLT_PC but with page-aligned semantics.
 127   RE_LOONGARCH_PLT_PAGE_PC,
 128   // In addition to having page-aligned semantics, LoongArch GOT relocs are
 129   // also reused for TLS, making the semantics differ from other architectures.
 130   RE_LOONGARCH_GOT,
 131   RE_LOONGARCH_GOT_PAGE_PC,
 132   RE_LOONGARCH_TLSGD_PAGE_PC,
 133   RE_LOONGARCH_TLSDESC_PAGE_PC,
 134 };
 135
 136 // Architecture-neutral representation of relocation.
 137 struct Relocation {
 138   RelExpr expr;
 139   RelType type;
 140   uint64_t offset;
 141   int64_t addend;
 142   Symbol *sym;
 143 };
 144
 145 // Manipulate jump instructions with these modifiers.  These are used to relax
 146 // jump instruction opcodes at basic block boundaries and are particularly
 147 // useful when basic block sections are enabled.
 148 struct JumpInstrMod {
 149   uint64_t offset;
 150   JumpModType original;
 151   unsigned size;
 152 };
 153
 154 // This function writes undefined symbol diagnostics to an internal buffer.
 155 // Call reportUndefinedSymbols() after calling scanRelocations() to emit
 156 // the diagnostics.
 157 template <class ELFT> void scanRelocations(Ctx &ctx);
 158 template <class ELFT> void checkNoCrossRefs(Ctx &ctx);
 159 void reportUndefinedSymbols(Ctx &);
 160 void postScanRelocations(Ctx &ctx);
 161 void addGotEntry(Ctx &ctx, Symbol &sym);
 162
 163 void hexagonTLSSymbolUpdate(Ctx &ctx);
 164 bool hexagonNeedsTLSSymbol(ArrayRef<OutputSection *> outputSections);
 165
 166 class ThunkSection;
 167 class Thunk;
 168 class InputSectionDescription;
 169
 170 class ThunkCreator {
 171 public:
 172   // Thunk may be incomplete. Avoid inline ctor/dtor.
 173   ThunkCreator(Ctx &ctx);
 174   ~ThunkCreator();
 175   // Return true if Thunks have been added to OutputSections
 176   bool createThunks(uint32_t pass, ArrayRef<OutputSection *> outputSections);
 177
 178 private:
 179   void mergeThunks(ArrayRef<OutputSection *> outputSections);
 180
 181   ThunkSection *getISDThunkSec(OutputSection *os, InputSection *isec,
 182                                InputSectionDescription *isd,
 183                                const Relocation &rel, uint64_t src);
 184
 185   ThunkSection *getISThunkSec(InputSection *isec);
 186
 187   void createInitialThunkSections(ArrayRef<OutputSection *> outputSections);
 188
 189   std::pair<Thunk *, bool> getThunk(InputSection *isec, Relocation &rel,
 190                                     uint64_t src);
 191
 192   std::pair<Thunk *, bool> getSyntheticLandingPad(Defined &d, int64_t a);
 193
 194   ThunkSection *addThunkSection(OutputSection *os, InputSectionDescription *,
 195                                 uint64_t off);
 196
 197   bool normalizeExistingThunk(Relocation &rel, uint64_t src);
 198
 199   bool addSyntheticLandingPads();
 200
 201   Ctx &ctx;
 202
 203   // Record all the available Thunks for a (Symbol, addend) pair, where Symbol
 204   // is represented as a (section, offset) pair. There may be multiple
 205   // relocations sharing the same (section, offset + addend) pair. We may revert
 206   // a relocation back to its original non-Thunk target, and restore the
 207   // original addend, so we cannot fold offset + addend. A nested pair is used
 208   // because DenseMapInfo is not specialized for std::tuple.
 209   llvm::DenseMap<std::pair<std::pair<SectionBase *, uint64_t>, int64_t>,
 210                  SmallVector<std::unique_ptr<Thunk>, 0>>
 211       thunkedSymbolsBySectionAndAddend;
 212   llvm::DenseMap<std::pair<Symbol *, int64_t>,
 213                  SmallVector<std::unique_ptr<Thunk>, 0>>
 214       thunkedSymbols;
 215
 216   // Find a Thunk from the Thunks symbol definition, we can use this to find
 217   // the Thunk from a relocation to the Thunks symbol definition.
 218   llvm::DenseMap<Symbol *, Thunk *> thunks;
 219
 220   // Track InputSections that have an inline ThunkSection placed in front
 221   // an inline ThunkSection may have control fall through to the section below
 222   // so we need to make sure that there is only one of them.
 223   // The Mips LA25 Thunk is an example of an inline ThunkSection, as is
 224   // the AArch64BTLandingPadThunk.
 225   llvm::DenseMap<InputSection *, ThunkSection *> thunkedSections;
 226
 227   // Record landing pads, generated for a section + offset destination.
 228   // Landling pads are alternative entry points for destinations that need
 229   // to be reached via thunks that use indirect branches. A destination
 230   // needs at most one landing pad as that can be reused by all callers.
 231   llvm::DenseMap<std::pair<std::pair<SectionBase *, uint64_t>, int64_t>,
 232                  std::unique_ptr<Thunk>>
 233       landingPadsBySectionAndAddend;
 234
 235   // All the nonLandingPad thunks that have been created, in order of creation.
 236   std::vector<Thunk *> allThunks;
 237
 238   // The number of completed passes of createThunks this permits us
 239   // to do one time initialization on Pass 0 and put a limit on the
 240   // number of times it can be called to prevent infinite loops.
 241   uint32_t pass = 0;
 242 };
 243
 244 // Decode LEB128 without error checking. Only used by performance critical code
 245 // like RelocsCrel.
 246 inline uint64_t readLEB128(const uint8_t *&p, uint64_t leb) {
 247   uint64_t acc = 0, shift = 0, byte;
 248   do {
 249     byte = *p++;
 250     acc |= (byte - 128 * (byte >= leb)) << shift;
 251     shift += 7;
 252   } while (byte >= 128);
 253   return acc;
 254 }
 255 inline uint64_t readULEB128(const uint8_t *&p) { return readLEB128(p, 128); }
 256 inline int64_t readSLEB128(const uint8_t *&p) { return readLEB128(p, 64); }
 257
 258 // This class implements a CREL iterator that does not allocate extra memory.
 259 template <bool is64> struct RelocsCrel {
 260   using uint = std::conditional_t<is64, uint64_t, uint32_t>;
 261   struct const_iterator {
 262     using iterator_category = std::forward_iterator_tag;
 263     using value_type = llvm::object::Elf_Crel_Impl<is64>;
 264     using difference_type = ptrdiff_t;
 265     using pointer = value_type *;
 266     using reference = const value_type &;
 267     uint32_t count;
 268     uint8_t flagBits, shift;
 269     const uint8_t *p;
 270     llvm::object::Elf_Crel_Impl<is64> crel{};
 271     const_iterator(size_t hdr, const uint8_t *p)
 272         : count(hdr / 8), flagBits(hdr & 4 ? 3 : 2), shift(hdr % 4), p(p) {
 273       if (count)
 274         step();
 275     }
 276     void step() {
 277       // See object::decodeCrel.
 278       const uint8_t b = *p++;
 279       crel.r_offset += b >> flagBits << shift;
 280       if (b >= 0x80)
 281         crel.r_offset +=
 282             ((readULEB128(p) << (7 - flagBits)) - (0x80 >> flagBits)) << shift;
 283       if (b & 1)
 284         crel.r_symidx += readSLEB128(p);
 285       if (b & 2)
 286         crel.r_type += readSLEB128(p);
 287       if (b & 4 && flagBits == 3)
 288         crel.r_addend += static_cast<uint>(readSLEB128(p));
 289     }
 290     llvm::object::Elf_Crel_Impl<is64> operator*() const { return crel; };
 291     const llvm::object::Elf_Crel_Impl<is64> *operator->() const {
 292       return &crel;
 293     }
 294     // For llvm::enumerate.
 295     bool operator==(const const_iterator &r) const { return count == r.count; }
 296     bool operator!=(const const_iterator &r) const { return count != r.count; }
 297     const_iterator &operator++() {
 298       if (--count)
 299         step();
 300       return *this;
 301     }
 302     // For RelocationScanner::scanOne.
 303     void operator+=(size_t n) {
 304       for (; n; --n)
 305         operator++();
 306     }
 307   };
 308
 309   size_t hdr = 0;
 310   const uint8_t *p = nullptr;
 311
 312   constexpr RelocsCrel() = default;
 313   RelocsCrel(const uint8_t *p) : hdr(readULEB128(p)) { this->p = p; }
 314   size_t size() const { return hdr / 8; }
 315   const_iterator begin() const { return {hdr, p}; }
 316   const_iterator end() const { return {0, nullptr}; }
 317 };
 318
 319 template <class RelTy> struct Relocs : ArrayRef<RelTy> {
 320   Relocs() = default;
 321   Relocs(ArrayRef<RelTy> a) : ArrayRef<RelTy>(a) {}
 322 };
 323
 324 template <bool is64>
 325 struct Relocs<llvm::object::Elf_Crel_Impl<is64>> : RelocsCrel<is64> {
 326   using RelocsCrel<is64>::RelocsCrel;
 327 };
 328
 329 // Return a int64_t to make sure we get the sign extension out of the way as
 330 // early as possible.
 331 template <class ELFT>
 332 static inline int64_t getAddend(const typename ELFT::Rel &rel) {
 333   return 0;
 334 }
 335 template <class ELFT>
 336 static inline int64_t getAddend(const typename ELFT::Rela &rel) {
 337   return rel.r_addend;
 338 }
 339 template <class ELFT>
 340 static inline int64_t getAddend(const typename ELFT::Crel &rel) {
 341   return rel.r_addend;
 342 }
 343
 344 template <typename RelTy>
 345 inline Relocs<RelTy> sortRels(Relocs<RelTy> rels,
 346                               SmallVector<RelTy, 0> &storage) {
 347   auto cmp = [](const RelTy &a, const RelTy &b) {
 348     return a.r_offset < b.r_offset;
 349   };
 350   if (!llvm::is_sorted(rels, cmp)) {
 351     storage.assign(rels.begin(), rels.end());
 352     llvm::stable_sort(storage, cmp);
 353     rels = Relocs<RelTy>(storage);
 354   }
 355   return rels;
 356 }
 357
 358 template <bool is64>
 359 inline Relocs<llvm::object::Elf_Crel_Impl<is64>>
 360 sortRels(Relocs<llvm::object::Elf_Crel_Impl<is64>> rels,
 361          SmallVector<llvm::object::Elf_Crel_Impl<is64>, 0> &storage) {
 362   return {};
 363 }
 364
 365 RelocationBaseSection &getIRelativeSection(Ctx &ctx);
 366
 367 // Returns true if Expr refers a GOT entry. Note that this function returns
 368 // false for TLS variables even though they need GOT, because TLS variables uses
 369 // GOT differently than the regular variables.
 370 bool needsGot(RelExpr expr);
 371 } // namespace lld::elf
 372
 373 #endif