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/BinaryFormat/ELF.h" 34 #include "llvm/Support/Casting.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 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 bool isCompatibleWith(uint32_t RelocType) const override; 61 }; 62 63 class ARMV7PILongThunk final : public Thunk { 64 public: 65 ARMV7PILongThunk(const SymbolBody &Dest) : Thunk(Dest) {} 66 67 uint32_t size() const override { return 16; } 68 void writeTo(uint8_t *Buf, ThunkSection &IS) const override; 69 void addSymbols(ThunkSection &IS) override; 70 bool isCompatibleWith(uint32_t RelocType) const override; 71 }; 72 73 class ThumbV7ABSLongThunk final : public Thunk { 74 public: 75 ThumbV7ABSLongThunk(const SymbolBody &Dest) : Thunk(Dest) { Alignment = 2; } 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 bool isCompatibleWith(uint32_t RelocType) const override; 81 }; 82 83 class ThumbV7PILongThunk final : public Thunk { 84 public: 85 ThumbV7PILongThunk(const SymbolBody &Dest) : Thunk(Dest) { Alignment = 2; } 86 87 uint32_t size() const override { return 12; } 88 void writeTo(uint8_t *Buf, ThunkSection &IS) const override; 89 void addSymbols(ThunkSection &IS) override; 90 bool isCompatibleWith(uint32_t RelocType) const override; 91 }; 92 93 // MIPS LA25 thunk 94 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 void ARMV7ABSLongThunk::writeTo(uint8_t *Buf, ThunkSection &IS) const { 113 const uint8_t Data[] = { 114 0x00, 0xc0, 0x00, 0xe3, // movw ip,:lower16:S 115 0x00, 0xc0, 0x40, 0xe3, // movt ip,:upper16:S 116 0x1c, 0xff, 0x2f, 0xe1, // bx ip 117 }; 118 uint64_t S = getARMThunkDestVA(Destination); 119 memcpy(Buf, Data, sizeof(Data)); 120 Target->relocateOne(Buf, R_ARM_MOVW_ABS_NC, S); 121 Target->relocateOne(Buf + 4, R_ARM_MOVT_ABS, S); 122 } 123 124 void ARMV7ABSLongThunk::addSymbols(ThunkSection &IS) { 125 ThunkSym = addSyntheticLocal( 126 Saver.save("__ARMv7ABSLongThunk_" + Destination.getName()), STT_FUNC, 127 Offset, size(), &IS); 128 addSyntheticLocal("$a", STT_NOTYPE, Offset, 0, &IS); 129 } 130 131 bool ARMV7ABSLongThunk::isCompatibleWith(uint32_t RelocType) const { 132 // Thumb branch relocations can't use BLX 133 return RelocType != R_ARM_THM_JUMP19 && RelocType != R_ARM_THM_JUMP24; 134 } 135 136 void ThumbV7ABSLongThunk::writeTo(uint8_t *Buf, ThunkSection &IS) const { 137 const uint8_t Data[] = { 138 0x40, 0xf2, 0x00, 0x0c, // movw ip, :lower16:S 139 0xc0, 0xf2, 0x00, 0x0c, // movt ip, :upper16:S 140 0x60, 0x47, // bx ip 141 }; 142 uint64_t S = getARMThunkDestVA(Destination); 143 memcpy(Buf, Data, sizeof(Data)); 144 Target->relocateOne(Buf, R_ARM_THM_MOVW_ABS_NC, S); 145 Target->relocateOne(Buf + 4, R_ARM_THM_MOVT_ABS, S); 146 } 147 148 void ThumbV7ABSLongThunk::addSymbols(ThunkSection &IS) { 149 ThunkSym = addSyntheticLocal( 150 Saver.save("__Thumbv7ABSLongThunk_" + Destination.getName()), STT_FUNC, 151 Offset | 0x1, size(), &IS); 152 addSyntheticLocal("$t", STT_NOTYPE, Offset, 0, &IS); 153 } 154 155 bool ThumbV7ABSLongThunk::isCompatibleWith(uint32_t RelocType) const { 156 // ARM branch relocations can't use BLX 157 return RelocType != R_ARM_JUMP24 && RelocType != R_ARM_PC24 && 158 RelocType != R_ARM_PLT32; 159 } 160 161 void ARMV7PILongThunk::writeTo(uint8_t *Buf, ThunkSection &IS) const { 162 const uint8_t Data[] = { 163 0xf0, 0xcf, 0x0f, 0xe3, // P: movw ip,:lower16:S - (P + (L1-P) + 8) 164 0x00, 0xc0, 0x40, 0xe3, // movt ip,:upper16:S - (P + (L1-P) + 8) 165 0x0f, 0xc0, 0x8c, 0xe0, // L1: add ip, ip, pc 166 0x1c, 0xff, 0x2f, 0xe1, // bx r12 167 }; 168 uint64_t S = getARMThunkDestVA(Destination); 169 uint64_t P = ThunkSym->getVA(); 170 uint64_t Offset = S - P - 16; 171 memcpy(Buf, Data, sizeof(Data)); 172 Target->relocateOne(Buf, R_ARM_MOVW_PREL_NC, Offset); 173 Target->relocateOne(Buf + 4, R_ARM_MOVT_PREL, Offset); 174 } 175 176 void ARMV7PILongThunk::addSymbols(ThunkSection &IS) { 177 ThunkSym = addSyntheticLocal( 178 Saver.save("__ARMV7PILongThunk_" + Destination.getName()), STT_FUNC, 179 Offset, size(), &IS); 180 addSyntheticLocal("$a", STT_NOTYPE, Offset, 0, &IS); 181 } 182 183 bool ARMV7PILongThunk::isCompatibleWith(uint32_t RelocType) const { 184 // Thumb branch relocations can't use BLX 185 return RelocType != R_ARM_THM_JUMP19 && RelocType != R_ARM_THM_JUMP24; 186 } 187 188 void ThumbV7PILongThunk::writeTo(uint8_t *Buf, ThunkSection &IS) const { 189 const uint8_t Data[] = { 190 0x4f, 0xf6, 0xf4, 0x7c, // P: movw ip,:lower16:S - (P + (L1-P) + 4) 191 0xc0, 0xf2, 0x00, 0x0c, // movt ip,:upper16:S - (P + (L1-P) + 4) 192 0xfc, 0x44, // L1: add r12, pc 193 0x60, 0x47, // bx r12 194 }; 195 uint64_t S = getARMThunkDestVA(Destination); 196 uint64_t P = ThunkSym->getVA() & ~0x1; 197 uint64_t Offset = S - P - 12; 198 memcpy(Buf, Data, sizeof(Data)); 199 Target->relocateOne(Buf, R_ARM_THM_MOVW_PREL_NC, Offset); 200 Target->relocateOne(Buf + 4, R_ARM_THM_MOVT_PREL, Offset); 201 } 202 203 void ThumbV7PILongThunk::addSymbols(ThunkSection &IS) { 204 ThunkSym = addSyntheticLocal( 205 Saver.save("__ThumbV7PILongThunk_" + Destination.getName()), STT_FUNC, 206 Offset | 0x1, size(), &IS); 207 addSyntheticLocal("$t", STT_NOTYPE, Offset, 0, &IS); 208 } 209 210 bool ThumbV7PILongThunk::isCompatibleWith(uint32_t RelocType) const { 211 // ARM branch relocations can't use BLX 212 return RelocType != R_ARM_JUMP24 && RelocType != R_ARM_PC24 && 213 RelocType != R_ARM_PLT32; 214 } 215 216 // Write MIPS LA25 thunk code to call PIC function from the non-PIC one. 217 void MipsThunk::writeTo(uint8_t *Buf, ThunkSection &) const { 218 uint64_t S = Destination.getVA(); 219 write32(Buf, 0x3c190000, Config->Endianness); // lui $25, %hi(func) 220 write32(Buf + 4, 0x08000000 | (S >> 2), Config->Endianness); // j func 221 write32(Buf + 8, 0x27390000, Config->Endianness); // addiu $25, $25, %lo(func) 222 write32(Buf + 12, 0x00000000, Config->Endianness); // nop 223 Target->relocateOne(Buf, R_MIPS_HI16, S); 224 Target->relocateOne(Buf + 8, R_MIPS_LO16, S); 225 } 226 227 void MipsThunk::addSymbols(ThunkSection &IS) { 228 ThunkSym = 229 addSyntheticLocal(Saver.save("__LA25Thunk_" + Destination.getName()), 230 STT_FUNC, Offset, size(), &IS); 231 } 232 233 InputSection *MipsThunk::getTargetInputSection() const { 234 auto *DR = dyn_cast<DefinedRegular>(&Destination); 235 return dyn_cast<InputSection>(DR->Section); 236 } 237 238 Thunk::Thunk(const SymbolBody &D) : Destination(D), Offset(0) {} 239 240 Thunk::~Thunk() = default; 241 242 // Creates a thunk for Thumb-ARM interworking. 243 static Thunk *addThunkArm(uint32_t Reloc, SymbolBody &S) { 244 // ARM relocations need ARM to Thumb interworking Thunks. 245 // Thumb relocations need Thumb to ARM relocations. 246 // Use position independent Thunks if we require position independent code. 247 switch (Reloc) { 248 case R_ARM_PC24: 249 case R_ARM_PLT32: 250 case R_ARM_JUMP24: 251 if (Config->Pic) 252 return make<ARMV7PILongThunk>(S); 253 return make<ARMV7ABSLongThunk>(S); 254 case R_ARM_THM_JUMP19: 255 case R_ARM_THM_JUMP24: 256 if (Config->Pic) 257 return make<ThumbV7PILongThunk>(S); 258 return make<ThumbV7ABSLongThunk>(S); 259 } 260 fatal("unrecognized relocation type"); 261 } 262 263 static Thunk *addThunkMips(SymbolBody &S) { return make<MipsThunk>(S); } 264 265 Thunk *addThunk(uint32_t RelocType, SymbolBody &S) { 266 if (Config->EMachine == EM_ARM) 267 return addThunkArm(RelocType, S); 268 else if (Config->EMachine == EM_MIPS) 269 return addThunkMips(S); 270 llvm_unreachable("add Thunk only supported for ARM and Mips"); 271 return nullptr; 272 } 273 274 } // end namespace elf 275 } // end namespace lld 276