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 SectionBase;
  26
  27 // Represents a relocation type, such as R_X86_64_PC32 or R_ARM_THM_CALL.
  28 struct RelType {
  29   uint32_t v = 0;
  30   /*implicit*/ constexpr RelType(uint32_t v = 0) : v(v) {}
  31   /*implicit*/ operator uint32_t() const { return v; }
  32 };
  33
  34 using JumpModType = uint32_t;
  35
  36 // List of target-independent relocation types. Relocations read
  37 // from files are converted to these types so that the main code
  38 // doesn't have to know about architecture-specific details.
  39 enum RelExpr {
  40   R_ABS,
  41   R_ADDEND,
  42   R_DTPREL,
  43   R_GOT,
  44   R_GOT_OFF,
  45   R_GOT_PC,
  46   R_GOTONLY_PC,
  47   R_GOTPLTONLY_PC,
  48   R_GOTPLT,
  49   R_GOTPLTREL,
  50   R_GOTREL,
  51   R_GOTPLT_GOTREL,
  52   R_GOTPLT_PC,
  53   R_NONE,
  54   R_PC,
  55   R_PLT,
  56   R_PLT_PC,
  57   R_PLT_GOTPLT,
  58   R_PLT_GOTREL,
  59   R_RELAX_HINT,
  60   R_RELAX_GOT_PC,
  61   R_RELAX_GOT_PC_NOPIC,
  62   R_RELAX_TLS_GD_TO_IE,
  63   R_RELAX_TLS_GD_TO_IE_ABS,
  64   R_RELAX_TLS_GD_TO_IE_GOT_OFF,
  65   R_RELAX_TLS_GD_TO_IE_GOTPLT,
  66   R_RELAX_TLS_GD_TO_LE,
  67   R_RELAX_TLS_GD_TO_LE_NEG,
  68   R_RELAX_TLS_IE_TO_LE,
  69   R_RELAX_TLS_LD_TO_LE,
  70   R_RELAX_TLS_LD_TO_LE_ABS,
  71   R_SIZE,
  72   R_TPREL,
  73   R_TPREL_NEG,
  74   R_TLSDESC,
  75   R_TLSDESC_CALL,
  76   R_TLSDESC_PC,
  77   R_TLSDESC_GOTPLT,
  78   R_TLSGD_GOT,
  79   R_TLSGD_GOTPLT,
  80   R_TLSGD_PC,
  81   R_TLSIE_HINT,
  82   R_TLSLD_GOT,
  83   R_TLSLD_GOTPLT,
  84   R_TLSLD_GOT_OFF,
  85   R_TLSLD_HINT,
  86   R_TLSLD_PC,
  87
  88   // The following is abstract relocation types used for only one target.
  89   //
  90   // Even though RelExpr is intended to be a target-neutral representation
  91   // of a relocation type, there are some relocations whose semantics are
  92   // unique to a target. Such relocation are marked with R_<TARGET_NAME>.
  93   R_AARCH64_GOT_PAGE_PC,
  94   R_AARCH64_GOT_PAGE,
  95   R_AARCH64_PAGE_PC,
  96   R_AARCH64_RELAX_TLS_GD_TO_IE_PAGE_PC,
  97   R_AARCH64_TLSDESC_PAGE,
  98   R_AARCH64_AUTH,
  99   R_ARM_PCA,
 100   R_ARM_SBREL,
 101   R_MIPS_GOTREL,
 102   R_MIPS_GOT_GP,
 103   R_MIPS_GOT_GP_PC,
 104   R_MIPS_GOT_LOCAL_PAGE,
 105   R_MIPS_GOT_OFF,
 106   R_MIPS_GOT_OFF32,
 107   R_MIPS_TLSGD,
 108   R_MIPS_TLSLD,
 109   R_PPC32_PLTREL,
 110   R_PPC64_CALL,
 111   R_PPC64_CALL_PLT,
 112   R_PPC64_RELAX_TOC,
 113   R_PPC64_TOCBASE,
 114   R_PPC64_RELAX_GOT_PC,
 115   R_RISCV_ADD,
 116   R_RISCV_LEB128,
 117   R_RISCV_PC_INDIRECT,
 118   // Same as R_PC but with page-aligned semantics.
 119   R_LOONGARCH_PAGE_PC,
 120   // Same as R_PLT_PC but with page-aligned semantics.
 121   R_LOONGARCH_PLT_PAGE_PC,
 122   // In addition to having page-aligned semantics, LoongArch GOT relocs are
 123   // also reused for TLS, making the semantics differ from other architectures.
 124   R_LOONGARCH_GOT,
 125   R_LOONGARCH_GOT_PAGE_PC,
 126   R_LOONGARCH_TLSGD_PAGE_PC,
 127   R_LOONGARCH_TLSDESC_PAGE_PC,
 128 };
 129
 130 // Architecture-neutral representation of relocation.
 131 struct Relocation {
 132   RelExpr expr;
 133   RelType type;
 134   uint64_t offset;
 135   int64_t addend;
 136   Symbol *sym;
 137 };
 138
 139 // Manipulate jump instructions with these modifiers.  These are used to relax
 140 // jump instruction opcodes at basic block boundaries and are particularly
 141 // useful when basic block sections are enabled.
 142 struct JumpInstrMod {
 143   uint64_t offset;
 144   JumpModType original;
 145   unsigned size;
 146 };
 147
 148 // This function writes undefined symbol diagnostics to an internal buffer.
 149 // Call reportUndefinedSymbols() after calling scanRelocations() to emit
 150 // the diagnostics.
 151 template <class ELFT> void scanRelocations(Ctx &ctx);
 152 template <class ELFT> void checkNoCrossRefs(Ctx &ctx);
 153 void reportUndefinedSymbols(Ctx &);
 154 void postScanRelocations(Ctx &ctx);
 155 void addGotEntry(Ctx &ctx, Symbol &sym);
 156
 157 void hexagonTLSSymbolUpdate(Ctx &ctx);
 158 bool hexagonNeedsTLSSymbol(ArrayRef<OutputSection *> outputSections);
 159
 160 class ThunkSection;
 161 class Thunk;
 162 class InputSectionDescription;
 163
 164 class ThunkCreator {
 165 public:
 166   // Thunk may be incomplete. Avoid inline ctor/dtor.
 167   ThunkCreator(Ctx &ctx);
 168   ~ThunkCreator();
 169   // Return true if Thunks have been added to OutputSections
 170   bool createThunks(uint32_t pass, ArrayRef<OutputSection *> outputSections);
 171
 172 private:
 173   void mergeThunks(ArrayRef<OutputSection *> outputSections);
 174
 175   ThunkSection *getISDThunkSec(OutputSection *os, InputSection *isec,
 176                                InputSectionDescription *isd,
 177                                const Relocation &rel, uint64_t src);
 178
 179   ThunkSection *getISThunkSec(InputSection *isec);
 180
 181   void createInitialThunkSections(ArrayRef<OutputSection *> outputSections);
 182
 183   std::pair<Thunk *, bool> getThunk(InputSection *isec, Relocation &rel,
 184                                     uint64_t src);
 185
 186   std::pair<Thunk *, bool> getSyntheticLandingPad(Defined &d, int64_t a);
 187
 188   ThunkSection *addThunkSection(OutputSection *os, InputSectionDescription *,
 189                                 uint64_t off);
 190
 191   bool normalizeExistingThunk(Relocation &rel, uint64_t src);
 192
 193   bool addSyntheticLandingPads();
 194
 195   Ctx &ctx;
 196
 197   // Record all the available Thunks for a (Symbol, addend) pair, where Symbol
 198   // is represented as a (section, offset) pair. There may be multiple
 199   // relocations sharing the same (section, offset + addend) pair. We may revert
 200   // a relocation back to its original non-Thunk target, and restore the
 201   // original addend, so we cannot fold offset + addend. A nested pair is used
 202   // because DenseMapInfo is not specialized for std::tuple.
 203   llvm::DenseMap<std::pair<std::pair<SectionBase *, uint64_t>, int64_t>,
 204                  SmallVector<std::unique_ptr<Thunk>, 0>>
 205       thunkedSymbolsBySectionAndAddend;
 206   llvm::DenseMap<std::pair<Symbol *, int64_t>,
 207                  SmallVector<std::unique_ptr<Thunk>, 0>>
 208       thunkedSymbols;
 209
 210   // Find a Thunk from the Thunks symbol definition, we can use this to find
 211   // the Thunk from a relocation to the Thunks symbol definition.
 212   llvm::DenseMap<Symbol *, Thunk *> thunks;
 213
 214   // Track InputSections that have an inline ThunkSection placed in front
 215   // an inline ThunkSection may have control fall through to the section below
 216   // so we need to make sure that there is only one of them.
 217   // The Mips LA25 Thunk is an example of an inline ThunkSection, as is
 218   // the AArch64BTLandingPadThunk.
 219   llvm::DenseMap<InputSection *, ThunkSection *> thunkedSections;
 220
 221   // Record landing pads, generated for a section + offset destination.
 222   // Landling pads are alternative entry points for destinations that need
 223   // to be reached via thunks that use indirect branches. A destination
 224   // needs at most one landing pad as that can be reused by all callers.
 225   llvm::DenseMap<std::pair<std::pair<SectionBase *, uint64_t>, int64_t>,
 226                  std::unique_ptr<Thunk>>
 227       landingPadsBySectionAndAddend;
 228
 229   // All the nonLandingPad thunks that have been created, in order of creation.
 230   std::vector<Thunk *> allThunks;
 231
 232   // The number of completed passes of createThunks this permits us
 233   // to do one time initialization on Pass 0 and put a limit on the
 234   // number of times it can be called to prevent infinite loops.
 235   uint32_t pass = 0;
 236 };
 237
 238 // Decode LEB128 without error checking. Only used by performance critical code
 239 // like RelocsCrel.
 240 inline uint64_t readLEB128(const uint8_t *&p, uint64_t leb) {
 241   uint64_t acc = 0, shift = 0, byte;
 242   do {
 243     byte = *p++;
 244     acc |= (byte - 128 * (byte >= leb)) << shift;
 245     shift += 7;
 246   } while (byte >= 128);
 247   return acc;
 248 }
 249 inline uint64_t readULEB128(const uint8_t *&p) { return readLEB128(p, 128); }
 250 inline int64_t readSLEB128(const uint8_t *&p) { return readLEB128(p, 64); }
 251
 252 // This class implements a CREL iterator that does not allocate extra memory.
 253 template <bool is64> struct RelocsCrel {
 254   using uint = std::conditional_t<is64, uint64_t, uint32_t>;
 255   struct const_iterator {
 256     using iterator_category = std::forward_iterator_tag;
 257     using value_type = llvm::object::Elf_Crel_Impl<is64>;
 258     using difference_type = ptrdiff_t;
 259     using pointer = value_type *;
 260     using reference = const value_type &;
 261     uint32_t count;
 262     uint8_t flagBits, shift;
 263     const uint8_t *p;
 264     llvm::object::Elf_Crel_Impl<is64> crel{};
 265     const_iterator(size_t hdr, const uint8_t *p)
 266         : count(hdr / 8), flagBits(hdr & 4 ? 3 : 2), shift(hdr % 4), p(p) {
 267       if (count)
 268         step();
 269     }
 270     void step() {
 271       // See object::decodeCrel.
 272       const uint8_t b = *p++;
 273       crel.r_offset += b >> flagBits << shift;
 274       if (b >= 0x80)
 275         crel.r_offset +=
 276             ((readULEB128(p) << (7 - flagBits)) - (0x80 >> flagBits)) << shift;
 277       if (b & 1)
 278         crel.r_symidx += readSLEB128(p);
 279       if (b & 2)
 280         crel.r_type += readSLEB128(p);
 281       if (b & 4 && flagBits == 3)
 282         crel.r_addend += static_cast<uint>(readSLEB128(p));
 283     }
 284     llvm::object::Elf_Crel_Impl<is64> operator*() const { return crel; };
 285     const llvm::object::Elf_Crel_Impl<is64> *operator->() const {
 286       return &crel;
 287     }
 288     // For llvm::enumerate.
 289     bool operator==(const const_iterator &r) const { return count == r.count; }
 290     bool operator!=(const const_iterator &r) const { return count != r.count; }
 291     const_iterator &operator++() {
 292       if (--count)
 293         step();
 294       return *this;
 295     }
 296     // For RelocationScanner::scanOne.
 297     void operator+=(size_t n) {
 298       for (; n; --n)
 299         operator++();
 300     }
 301   };
 302
 303   size_t hdr = 0;
 304   const uint8_t *p = nullptr;
 305
 306   constexpr RelocsCrel() = default;
 307   RelocsCrel(const uint8_t *p) : hdr(readULEB128(p)) { this->p = p; }
 308   size_t size() const { return hdr / 8; }
 309   const_iterator begin() const { return {hdr, p}; }
 310   const_iterator end() const { return {0, nullptr}; }
 311 };
 312
 313 template <class RelTy> struct Relocs : ArrayRef<RelTy> {
 314   Relocs() = default;
 315   Relocs(ArrayRef<RelTy> a) : ArrayRef<RelTy>(a) {}
 316 };
 317
 318 template <bool is64>
 319 struct Relocs<llvm::object::Elf_Crel_Impl<is64>> : RelocsCrel<is64> {
 320   using RelocsCrel<is64>::RelocsCrel;
 321 };
 322
 323 // Return a int64_t to make sure we get the sign extension out of the way as
 324 // early as possible.
 325 template <class ELFT>
 326 static inline int64_t getAddend(const typename ELFT::Rel &rel) {
 327   return 0;
 328 }
 329 template <class ELFT>
 330 static inline int64_t getAddend(const typename ELFT::Rela &rel) {
 331   return rel.r_addend;
 332 }
 333 template <class ELFT>
 334 static inline int64_t getAddend(const typename ELFT::Crel &rel) {
 335   return rel.r_addend;
 336 }
 337
 338 template <typename RelTy>
 339 inline Relocs<RelTy> sortRels(Relocs<RelTy> rels,
 340                               SmallVector<RelTy, 0> &storage) {
 341   auto cmp = [](const RelTy &a, const RelTy &b) {
 342     return a.r_offset < b.r_offset;
 343   };
 344   if (!llvm::is_sorted(rels, cmp)) {
 345     storage.assign(rels.begin(), rels.end());
 346     llvm::stable_sort(storage, cmp);
 347     rels = Relocs<RelTy>(storage);
 348   }
 349   return rels;
 350 }
 351
 352 template <bool is64>
 353 inline Relocs<llvm::object::Elf_Crel_Impl<is64>>
 354 sortRels(Relocs<llvm::object::Elf_Crel_Impl<is64>> rels,
 355          SmallVector<llvm::object::Elf_Crel_Impl<is64>, 0> &storage) {
 356   return {};
 357 }
 358
 359 // Returns true if Expr refers a GOT entry. Note that this function returns
 360 // false for TLS variables even though they need GOT, because TLS variables uses
 361 // GOT differently than the regular variables.
 362 bool needsGot(RelExpr expr);
 363 } // namespace lld::elf
 364
 365 #endif