1 //===- Thunks.cpp --------------------------------------------------------===// 2 // 3 // The LLVM Linker 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===---------------------------------------------------------------------===// 9 // 10 // This file contains Thunk subclasses. 11 // 12 // A thunk is a small piece of code written after an input section 13 // which is used to jump between "incompatible" functions 14 // such as MIPS PIC and non-PIC or ARM non-Thumb and Thumb functions. 15 // 16 // If a jump target is too far and its address doesn't fit to a 17 // short jump instruction, we need to create a thunk too, but we 18 // haven't supported it yet. 19 // 20 // i386 and x86-64 don't need thunks. 21 // 22 //===---------------------------------------------------------------------===// 23 24 #include "Thunks.h" 25 #include "Config.h" 26 #include "Error.h" 27 #include "InputSection.h" 28 #include "Memory.h" 29 #include "OutputSections.h" 30 #include "Symbols.h" 31 #include "SyntheticSections.h" 32 #include "Target.h" 33 #include "llvm/Support/Casting.h" 34 #include "llvm/Support/ELF.h" 35 #include "llvm/Support/Endian.h" 36 #include "llvm/Support/ErrorHandling.h" 37 #include "llvm/Support/MathExtras.h" 38 #include <cstdint> 39 #include <cstring> 40 41 using namespace llvm; 42 using namespace llvm::object; 43 using namespace llvm::support::endian; 44 using namespace llvm::ELF; 45 46 namespace lld { 47 namespace elf { 48 49 namespace { 50 51 // Specific ARM Thunk implementations. The naming convention is: 52 // Source State, TargetState, Target Requirement, ABS or PI, Range 53 template <class ELFT> class ARMV7ABSLongThunk final : public Thunk { 54 public: 55 ARMV7ABSLongThunk(const SymbolBody &Dest) : Thunk(Dest) {} 56 57 uint32_t size() const override { return 12; } 58 void writeTo(uint8_t *Buf, ThunkSection &IS) const override; 59 void addSymbols(ThunkSection &IS) override; 60 }; 61 62 template <class ELFT> class ARMV7PILongThunk final : public Thunk { 63 public: 64 ARMV7PILongThunk(const SymbolBody &Dest) : Thunk(Dest) {} 65 66 uint32_t size() const override { return 16; } 67 void writeTo(uint8_t *Buf, ThunkSection &IS) const override; 68 void addSymbols(ThunkSection &IS) override; 69 }; 70 71 template <class ELFT> class ThumbV7ABSLongThunk final : public Thunk { 72 public: 73 ThumbV7ABSLongThunk(const SymbolBody &Dest) : Thunk(Dest) { 74 this->alignment = 2; 75 } 76 77 uint32_t size() const override { return 10; } 78 void writeTo(uint8_t *Buf, ThunkSection &IS) const override; 79 void addSymbols(ThunkSection &IS) override; 80 }; 81 82 template <class ELFT> class ThumbV7PILongThunk final : public Thunk { 83 public: 84 ThumbV7PILongThunk(const SymbolBody &Dest) : Thunk(Dest) { 85 this->alignment = 2; 86 } 87 88 uint32_t size() const override { return 12; } 89 void writeTo(uint8_t *Buf, ThunkSection &IS) const override; 90 void addSymbols(ThunkSection &IS) override; 91 }; 92 93 // MIPS LA25 thunk 94 template <class ELFT> class MipsThunk final : public Thunk { 95 public: 96 MipsThunk(const SymbolBody &Dest) : Thunk(Dest) {} 97 98 uint32_t size() const override { return 16; } 99 void writeTo(uint8_t *Buf, ThunkSection &IS) const override; 100 void addSymbols(ThunkSection &IS) override; 101 InputSection *getTargetInputSection() const override; 102 }; 103 104 } // end anonymous namespace 105 106 // ARM Target Thunks 107 static uint64_t getARMThunkDestVA(const SymbolBody &S) { 108 uint64_t V = S.isInPlt() ? S.getPltVA() : S.getVA(); 109 return SignExtend64<32>(V); 110 } 111 112 template <class ELFT> 113 void ARMV7ABSLongThunk<ELFT>::writeTo(uint8_t *Buf, ThunkSection &IS) const { 114 const uint8_t Data[] = { 115 0x00, 0xc0, 0x00, 0xe3, // movw ip,:lower16:S 116 0x00, 0xc0, 0x40, 0xe3, // movt ip,:upper16:S 117 0x1c, 0xff, 0x2f, 0xe1, // bx ip 118 }; 119 uint64_t S = getARMThunkDestVA(this->Destination); 120 memcpy(Buf, Data, sizeof(Data)); 121 Target->relocateOne(Buf, R_ARM_MOVW_ABS_NC, S); 122 Target->relocateOne(Buf + 4, R_ARM_MOVT_ABS, S); 123 } 124 125 template <class ELFT> 126 void ARMV7ABSLongThunk<ELFT>::addSymbols(ThunkSection &IS) { 127 this->ThunkSym = addSyntheticLocal<ELFT>( 128 Saver.save("__ARMv7ABSLongThunk_" + this->Destination.getName()), 129 STT_FUNC, this->Offset, size(), &IS); 130 addSyntheticLocal<ELFT>("$a", STT_NOTYPE, this->Offset, 0, &IS); 131 } 132 133 template <class ELFT> 134 void ThumbV7ABSLongThunk<ELFT>::writeTo(uint8_t *Buf, ThunkSection &IS) const { 135 const uint8_t Data[] = { 136 0x40, 0xf2, 0x00, 0x0c, // movw ip, :lower16:S 137 0xc0, 0xf2, 0x00, 0x0c, // movt ip, :upper16:S 138 0x60, 0x47, // bx ip 139 }; 140 uint64_t S = getARMThunkDestVA(this->Destination); 141 memcpy(Buf, Data, sizeof(Data)); 142 Target->relocateOne(Buf, R_ARM_THM_MOVW_ABS_NC, S); 143 Target->relocateOne(Buf + 4, R_ARM_THM_MOVT_ABS, S); 144 } 145 146 template <class ELFT> 147 void ThumbV7ABSLongThunk<ELFT>::addSymbols(ThunkSection &IS) { 148 this->ThunkSym = addSyntheticLocal<ELFT>( 149 Saver.save("__Thumbv7ABSLongThunk_" + this->Destination.getName()), 150 STT_FUNC, this->Offset, size(), &IS); 151 addSyntheticLocal<ELFT>("$t", STT_NOTYPE, this->Offset, 0, &IS); 152 } 153 154 template <class ELFT> 155 void ARMV7PILongThunk<ELFT>::writeTo(uint8_t *Buf, ThunkSection &IS) const { 156 const uint8_t Data[] = { 157 0xf0, 0xcf, 0x0f, 0xe3, // P: movw ip,:lower16:S - (P + (L1-P) +8) 158 0x00, 0xc0, 0x40, 0xe3, // movt ip,:upper16:S - (P + (L1-P+4) +8) 159 0x0f, 0xc0, 0x8c, 0xe0, // L1: add ip, ip, pc 160 0x1c, 0xff, 0x2f, 0xe1, // bx r12 161 }; 162 uint64_t S = getARMThunkDestVA(this->Destination); 163 uint64_t P = this->ThunkSym->getVA(); 164 memcpy(Buf, Data, sizeof(Data)); 165 Target->relocateOne(Buf, R_ARM_MOVW_PREL_NC, S - P - 16); 166 Target->relocateOne(Buf + 4, R_ARM_MOVT_PREL, S - P - 12); 167 } 168 169 template <class ELFT> 170 void ARMV7PILongThunk<ELFT>::addSymbols(ThunkSection &IS) { 171 this->ThunkSym = addSyntheticLocal<ELFT>( 172 Saver.save("__ARMV7PILongThunk_" + this->Destination.getName()), STT_FUNC, 173 this->Offset, size(), &IS); 174 addSyntheticLocal<ELFT>("$a", STT_NOTYPE, this->Offset, 0, &IS); 175 } 176 177 template <class ELFT> 178 void ThumbV7PILongThunk<ELFT>::writeTo(uint8_t *Buf, ThunkSection &IS) const { 179 const uint8_t Data[] = { 180 0x4f, 0xf6, 0xf4, 0x7c, // P: movw ip,:lower16:S - (P + (L1-P) + 4) 181 0xc0, 0xf2, 0x00, 0x0c, // movt ip,:upper16:S - (P + (L1-P+4) + 4) 182 0xfc, 0x44, // L1: add r12, pc 183 0x60, 0x47, // bx r12 184 }; 185 uint64_t S = getARMThunkDestVA(this->Destination); 186 uint64_t P = this->ThunkSym->getVA(); 187 memcpy(Buf, Data, sizeof(Data)); 188 Target->relocateOne(Buf, R_ARM_THM_MOVW_PREL_NC, S - P - 12); 189 Target->relocateOne(Buf + 4, R_ARM_THM_MOVT_PREL, S - P - 8); 190 } 191 192 template <class ELFT> 193 void ThumbV7PILongThunk<ELFT>::addSymbols(ThunkSection &IS) { 194 this->ThunkSym = addSyntheticLocal<ELFT>( 195 Saver.save("__ThumbV7PILongThunk_" + this->Destination.getName()), 196 STT_FUNC, this->Offset, size(), &IS); 197 addSyntheticLocal<ELFT>("$t", STT_NOTYPE, this->Offset, 0, &IS); 198 } 199 200 // Write MIPS LA25 thunk code to call PIC function from the non-PIC one. 201 template <class ELFT> 202 void MipsThunk<ELFT>::writeTo(uint8_t *Buf, ThunkSection &) const { 203 const endianness E = ELFT::TargetEndianness; 204 205 uint64_t S = this->Destination.getVA(); 206 write32<E>(Buf, 0x3c190000); // lui $25, %hi(func) 207 write32<E>(Buf + 4, 0x08000000 | (S >> 2)); // j func 208 write32<E>(Buf + 8, 0x27390000); // addiu $25, $25, %lo(func) 209 write32<E>(Buf + 12, 0x00000000); // nop 210 Target->relocateOne(Buf, R_MIPS_HI16, S); 211 Target->relocateOne(Buf + 8, R_MIPS_LO16, S); 212 } 213 214 template <class ELFT> void MipsThunk<ELFT>::addSymbols(ThunkSection &IS) { 215 this->ThunkSym = addSyntheticLocal<ELFT>( 216 Saver.save("__LA25Thunk_" + this->Destination.getName()), STT_FUNC, 217 this->Offset, size(), &IS); 218 } 219 220 template <class ELFT> 221 InputSection *MipsThunk<ELFT>::getTargetInputSection() const { 222 auto *DR = dyn_cast<DefinedRegular>(&this->Destination); 223 return dyn_cast<InputSection>(DR->Section); 224 } 225 226 Thunk::Thunk(const SymbolBody &D) : Destination(D), Offset(0) {} 227 228 Thunk::~Thunk() = default; 229 230 // Creates a thunk for Thumb-ARM interworking. 231 template <class ELFT> static Thunk *addThunkArm(uint32_t Reloc, SymbolBody &S) { 232 // ARM relocations need ARM to Thumb interworking Thunks. 233 // Thumb relocations need Thumb to ARM relocations. 234 // Use position independent Thunks if we require position independent code. 235 switch (Reloc) { 236 case R_ARM_PC24: 237 case R_ARM_PLT32: 238 case R_ARM_JUMP24: 239 if (Config->Pic) 240 return make<ARMV7PILongThunk<ELFT>>(S); 241 return make<ARMV7ABSLongThunk<ELFT>>(S); 242 case R_ARM_THM_JUMP19: 243 case R_ARM_THM_JUMP24: 244 if (Config->Pic) 245 return make<ThumbV7PILongThunk<ELFT>>(S); 246 return make<ThumbV7ABSLongThunk<ELFT>>(S); 247 } 248 fatal("unrecognized relocation type"); 249 } 250 251 template <class ELFT> static Thunk *addThunkMips(SymbolBody &S) { 252 return make<MipsThunk<ELFT>>(S); 253 } 254 255 template <class ELFT> Thunk *addThunk(uint32_t RelocType, SymbolBody &S) { 256 if (Config->EMachine == EM_ARM) 257 return addThunkArm<ELFT>(RelocType, S); 258 else if (Config->EMachine == EM_MIPS) 259 return addThunkMips<ELFT>(S); 260 llvm_unreachable("add Thunk only supported for ARM and Mips"); 261 return nullptr; 262 } 263 264 template Thunk *addThunk<ELF32LE>(uint32_t, SymbolBody &); 265 template Thunk *addThunk<ELF32BE>(uint32_t, SymbolBody &); 266 template Thunk *addThunk<ELF64LE>(uint32_t, SymbolBody &); 267 template Thunk *addThunk<ELF64BE>(uint32_t, SymbolBody &); 268 } // end namespace elf 269 } // end namespace lld 270