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 class Symbol; 20 class InputSection; 21 class InputSectionBase; 22 class OutputSection; 23 class SectionBase; 24 25 // Represents a relocation type, such as R_X86_64_PC32 or R_ARM_THM_CALL. 26 using RelType = uint32_t; 27 using JumpModType = uint32_t; 28 29 // List of target-independent relocation types. Relocations read 30 // from files are converted to these types so that the main code 31 // doesn't have to know about architecture-specific details. 32 enum RelExpr { 33 R_ABS, 34 R_ADDEND, 35 R_DTPREL, 36 R_GOT, 37 R_GOT_OFF, 38 R_GOT_PC, 39 R_GOTONLY_PC, 40 R_GOTPLTONLY_PC, 41 R_GOTPLT, 42 R_GOTPLTREL, 43 R_GOTREL, 44 R_GOTPLT_GOTREL, 45 R_GOTPLT_PC, 46 R_NONE, 47 R_PC, 48 R_PLT, 49 R_PLT_PC, 50 R_PLT_GOTPLT, 51 R_PLT_GOTREL, 52 R_RELAX_HINT, 53 R_RELAX_GOT_PC, 54 R_RELAX_GOT_PC_NOPIC, 55 R_RELAX_TLS_GD_TO_IE, 56 R_RELAX_TLS_GD_TO_IE_ABS, 57 R_RELAX_TLS_GD_TO_IE_GOT_OFF, 58 R_RELAX_TLS_GD_TO_IE_GOTPLT, 59 R_RELAX_TLS_GD_TO_LE, 60 R_RELAX_TLS_GD_TO_LE_NEG, 61 R_RELAX_TLS_IE_TO_LE, 62 R_RELAX_TLS_LD_TO_LE, 63 R_RELAX_TLS_LD_TO_LE_ABS, 64 R_SIZE, 65 R_TPREL, 66 R_TPREL_NEG, 67 R_TLSDESC, 68 R_TLSDESC_CALL, 69 R_TLSDESC_PC, 70 R_TLSDESC_GOTPLT, 71 R_TLSGD_GOT, 72 R_TLSGD_GOTPLT, 73 R_TLSGD_PC, 74 R_TLSIE_HINT, 75 R_TLSLD_GOT, 76 R_TLSLD_GOTPLT, 77 R_TLSLD_GOT_OFF, 78 R_TLSLD_HINT, 79 R_TLSLD_PC, 80 81 // The following is abstract relocation types used for only one target. 82 // 83 // Even though RelExpr is intended to be a target-neutral representation 84 // of a relocation type, there are some relocations whose semantics are 85 // unique to a target. Such relocation are marked with R_<TARGET_NAME>. 86 R_AARCH64_GOT_PAGE_PC, 87 R_AARCH64_GOT_PAGE, 88 R_AARCH64_PAGE_PC, 89 R_AARCH64_RELAX_TLS_GD_TO_IE_PAGE_PC, 90 R_AARCH64_TLSDESC_PAGE, 91 R_AARCH64_AUTH, 92 R_ARM_PCA, 93 R_ARM_SBREL, 94 R_MIPS_GOTREL, 95 R_MIPS_GOT_GP, 96 R_MIPS_GOT_GP_PC, 97 R_MIPS_GOT_LOCAL_PAGE, 98 R_MIPS_GOT_OFF, 99 R_MIPS_GOT_OFF32, 100 R_MIPS_TLSGD, 101 R_MIPS_TLSLD, 102 R_PPC32_PLTREL, 103 R_PPC64_CALL, 104 R_PPC64_CALL_PLT, 105 R_PPC64_RELAX_TOC, 106 R_PPC64_TOCBASE, 107 R_PPC64_RELAX_GOT_PC, 108 R_RISCV_ADD, 109 R_RISCV_LEB128, 110 R_RISCV_PC_INDIRECT, 111 // Same as R_PC but with page-aligned semantics. 112 R_LOONGARCH_PAGE_PC, 113 // Same as R_PLT_PC but with page-aligned semantics. 114 R_LOONGARCH_PLT_PAGE_PC, 115 // In addition to having page-aligned semantics, LoongArch GOT relocs are 116 // also reused for TLS, making the semantics differ from other architectures. 117 R_LOONGARCH_GOT, 118 R_LOONGARCH_GOT_PAGE_PC, 119 R_LOONGARCH_TLSGD_PAGE_PC, 120 R_LOONGARCH_TLSDESC_PAGE_PC, 121 }; 122 123 // Architecture-neutral representation of relocation. 124 struct Relocation { 125 RelExpr expr; 126 RelType type; 127 uint64_t offset; 128 int64_t addend; 129 Symbol *sym; 130 }; 131 132 // Manipulate jump instructions with these modifiers. These are used to relax 133 // jump instruction opcodes at basic block boundaries and are particularly 134 // useful when basic block sections are enabled. 135 struct JumpInstrMod { 136 uint64_t offset; 137 JumpModType original; 138 unsigned size; 139 }; 140 141 // This function writes undefined symbol diagnostics to an internal buffer. 142 // Call reportUndefinedSymbols() after calling scanRelocations() to emit 143 // the diagnostics. 144 template <class ELFT> void scanRelocations(); 145 template <class ELFT> void checkNoCrossRefs(); 146 void reportUndefinedSymbols(); 147 void postScanRelocations(); 148 void addGotEntry(Symbol &sym); 149 150 void hexagonTLSSymbolUpdate(ArrayRef<OutputSection *> outputSections); 151 bool hexagonNeedsTLSSymbol(ArrayRef<OutputSection *> outputSections); 152 153 class ThunkSection; 154 class Thunk; 155 class InputSectionDescription; 156 157 class ThunkCreator { 158 public: 159 // Return true if Thunks have been added to OutputSections 160 bool createThunks(uint32_t pass, ArrayRef<OutputSection *> outputSections); 161 162 private: 163 void mergeThunks(ArrayRef<OutputSection *> outputSections); 164 165 ThunkSection *getISDThunkSec(OutputSection *os, InputSection *isec, 166 InputSectionDescription *isd, 167 const Relocation &rel, uint64_t src); 168 169 ThunkSection *getISThunkSec(InputSection *isec); 170 171 void createInitialThunkSections(ArrayRef<OutputSection *> outputSections); 172 173 std::pair<Thunk *, bool> getThunk(InputSection *isec, Relocation &rel, 174 uint64_t src); 175 176 ThunkSection *addThunkSection(OutputSection *os, InputSectionDescription *, 177 uint64_t off); 178 179 bool normalizeExistingThunk(Relocation &rel, uint64_t src); 180 181 // Record all the available Thunks for a (Symbol, addend) pair, where Symbol 182 // is represented as a (section, offset) pair. There may be multiple 183 // relocations sharing the same (section, offset + addend) pair. We may revert 184 // a relocation back to its original non-Thunk target, and restore the 185 // original addend, so we cannot fold offset + addend. A nested pair is used 186 // because DenseMapInfo is not specialized for std::tuple. 187 llvm::DenseMap<std::pair<std::pair<SectionBase *, uint64_t>, int64_t>, 188 std::vector<Thunk *>> 189 thunkedSymbolsBySectionAndAddend; 190 llvm::DenseMap<std::pair<Symbol *, int64_t>, std::vector<Thunk *>> 191 thunkedSymbols; 192 193 // Find a Thunk from the Thunks symbol definition, we can use this to find 194 // the Thunk from a relocation to the Thunks symbol definition. 195 llvm::DenseMap<Symbol *, Thunk *> thunks; 196 197 // Track InputSections that have an inline ThunkSection placed in front 198 // an inline ThunkSection may have control fall through to the section below 199 // so we need to make sure that there is only one of them. 200 // The Mips LA25 Thunk is an example of an inline ThunkSection. 201 llvm::DenseMap<InputSection *, ThunkSection *> thunkedSections; 202 203 // The number of completed passes of createThunks this permits us 204 // to do one time initialization on Pass 0 and put a limit on the 205 // number of times it can be called to prevent infinite loops. 206 uint32_t pass = 0; 207 }; 208 209 // Decode LEB128 without error checking. Only used by performance critical code 210 // like RelocsCrel. 211 inline uint64_t readLEB128(const uint8_t *&p, uint64_t leb) { 212 uint64_t acc = 0, shift = 0, byte; 213 do { 214 byte = *p++; 215 acc |= (byte - 128 * (byte >= leb)) << shift; 216 shift += 7; 217 } while (byte >= 128); 218 return acc; 219 } 220 inline uint64_t readULEB128(const uint8_t *&p) { return readLEB128(p, 128); } 221 inline int64_t readSLEB128(const uint8_t *&p) { return readLEB128(p, 64); } 222 223 // This class implements a CREL iterator that does not allocate extra memory. 224 template <bool is64> struct RelocsCrel { 225 using uint = std::conditional_t<is64, uint64_t, uint32_t>; 226 struct const_iterator { 227 using iterator_category = std::forward_iterator_tag; 228 using value_type = llvm::object::Elf_Crel_Impl<is64>; 229 using difference_type = ptrdiff_t; 230 using pointer = value_type *; 231 using reference = const value_type &; 232 uint32_t count; 233 uint8_t flagBits, shift; 234 const uint8_t *p; 235 llvm::object::Elf_Crel_Impl<is64> crel{}; 236 const_iterator(size_t hdr, const uint8_t *p) 237 : count(hdr / 8), flagBits(hdr & 4 ? 3 : 2), shift(hdr % 4), p(p) { 238 if (count) 239 step(); 240 } 241 void step() { 242 // See object::decodeCrel. 243 const uint8_t b = *p++; 244 crel.r_offset += b >> flagBits << shift; 245 if (b >= 0x80) 246 crel.r_offset += 247 ((readULEB128(p) << (7 - flagBits)) - (0x80 >> flagBits)) << shift; 248 if (b & 1) 249 crel.r_symidx += readSLEB128(p); 250 if (b & 2) 251 crel.r_type += readSLEB128(p); 252 if (b & 4 && flagBits == 3) 253 crel.r_addend += static_cast<uint>(readSLEB128(p)); 254 } 255 llvm::object::Elf_Crel_Impl<is64> operator*() const { return crel; }; 256 const llvm::object::Elf_Crel_Impl<is64> *operator->() const { 257 return &crel; 258 } 259 // For llvm::enumerate. 260 bool operator==(const const_iterator &r) const { return count == r.count; } 261 bool operator!=(const const_iterator &r) const { return count != r.count; } 262 const_iterator &operator++() { 263 if (--count) 264 step(); 265 return *this; 266 } 267 // For RelocationScanner::scanOne. 268 void operator+=(size_t n) { 269 for (; n; --n) 270 operator++(); 271 } 272 }; 273 274 size_t hdr = 0; 275 const uint8_t *p = nullptr; 276 277 constexpr RelocsCrel() = default; 278 RelocsCrel(const uint8_t *p) : hdr(readULEB128(p)) { this->p = p; } 279 size_t size() const { return hdr / 8; } 280 const_iterator begin() const { return {hdr, p}; } 281 const_iterator end() const { return {0, nullptr}; } 282 }; 283 284 template <class RelTy> struct Relocs : ArrayRef<RelTy> { 285 Relocs() = default; 286 Relocs(ArrayRef<RelTy> a) : ArrayRef<RelTy>(a) {} 287 }; 288 289 template <bool is64> 290 struct Relocs<llvm::object::Elf_Crel_Impl<is64>> : RelocsCrel<is64> { 291 using RelocsCrel<is64>::RelocsCrel; 292 }; 293 294 // Return a int64_t to make sure we get the sign extension out of the way as 295 // early as possible. 296 template <class ELFT> 297 static inline int64_t getAddend(const typename ELFT::Rel &rel) { 298 return 0; 299 } 300 template <class ELFT> 301 static inline int64_t getAddend(const typename ELFT::Rela &rel) { 302 return rel.r_addend; 303 } 304 template <class ELFT> 305 static inline int64_t getAddend(const typename ELFT::Crel &rel) { 306 return rel.r_addend; 307 } 308 309 template <typename RelTy> 310 inline Relocs<RelTy> sortRels(Relocs<RelTy> rels, 311 SmallVector<RelTy, 0> &storage) { 312 auto cmp = [](const RelTy &a, const RelTy &b) { 313 return a.r_offset < b.r_offset; 314 }; 315 if (!llvm::is_sorted(rels, cmp)) { 316 storage.assign(rels.begin(), rels.end()); 317 llvm::stable_sort(storage, cmp); 318 rels = Relocs<RelTy>(storage); 319 } 320 return rels; 321 } 322 323 template <bool is64> 324 inline Relocs<llvm::object::Elf_Crel_Impl<is64>> 325 sortRels(Relocs<llvm::object::Elf_Crel_Impl<is64>> rels, 326 SmallVector<llvm::object::Elf_Crel_Impl<is64>, 0> &storage) { 327 return {}; 328 } 329 330 // Returns true if Expr refers a GOT entry. Note that this function returns 331 // false for TLS variables even though they need GOT, because TLS variables uses 332 // GOT differently than the regular variables. 333 bool needsGot(RelExpr expr); 334 } // namespace lld::elf 335 336 #endif 337