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 }; 61 62 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 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 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 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("$a", STT_NOTYPE, Offset, 0, &IS); 129 } 130 131 void ThumbV7ABSLongThunk::writeTo(uint8_t *Buf, ThunkSection &IS) const { 132 const uint8_t Data[] = { 133 0x40, 0xf2, 0x00, 0x0c, // movw ip, :lower16:S 134 0xc0, 0xf2, 0x00, 0x0c, // movt ip, :upper16:S 135 0x60, 0x47, // bx ip 136 }; 137 uint64_t S = getARMThunkDestVA(Destination); 138 memcpy(Buf, Data, sizeof(Data)); 139 Target->relocateOne(Buf, R_ARM_THM_MOVW_ABS_NC, S); 140 Target->relocateOne(Buf + 4, R_ARM_THM_MOVT_ABS, S); 141 } 142 143 void ThumbV7ABSLongThunk::addSymbols(ThunkSection &IS) { 144 ThunkSym = addSyntheticLocal( 145 Saver.save("__Thumbv7ABSLongThunk_" + Destination.getName()), STT_FUNC, 146 Offset | 0x1, size(), &IS); 147 addSyntheticLocal("$t", STT_NOTYPE, Offset, 0, &IS); 148 } 149 150 void ARMV7PILongThunk::writeTo(uint8_t *Buf, ThunkSection &IS) const { 151 const uint8_t Data[] = { 152 0xf0, 0xcf, 0x0f, 0xe3, // P: movw ip,:lower16:S - (P + (L1-P) +8) 153 0x00, 0xc0, 0x40, 0xe3, // movt ip,:upper16:S - (P + (L1-P+4) +8) 154 0x0f, 0xc0, 0x8c, 0xe0, // L1: add ip, ip, pc 155 0x1c, 0xff, 0x2f, 0xe1, // bx r12 156 }; 157 uint64_t S = getARMThunkDestVA(Destination); 158 uint64_t P = ThunkSym->getVA(); 159 memcpy(Buf, Data, sizeof(Data)); 160 Target->relocateOne(Buf, R_ARM_MOVW_PREL_NC, S - P - 16); 161 Target->relocateOne(Buf + 4, R_ARM_MOVT_PREL, S - P - 12); 162 } 163 164 void ARMV7PILongThunk::addSymbols(ThunkSection &IS) { 165 ThunkSym = addSyntheticLocal( 166 Saver.save("__ARMV7PILongThunk_" + Destination.getName()), STT_FUNC, 167 Offset, size(), &IS); 168 addSyntheticLocal("$a", STT_NOTYPE, Offset, 0, &IS); 169 } 170 171 void ThumbV7PILongThunk::writeTo(uint8_t *Buf, ThunkSection &IS) const { 172 const uint8_t Data[] = { 173 0x4f, 0xf6, 0xf4, 0x7c, // P: movw ip,:lower16:S - (P + (L1-P) + 4) 174 0xc0, 0xf2, 0x00, 0x0c, // movt ip,:upper16:S - (P + (L1-P+4) + 4) 175 0xfc, 0x44, // L1: add r12, pc 176 0x60, 0x47, // bx r12 177 }; 178 uint64_t S = getARMThunkDestVA(Destination); 179 uint64_t P = ThunkSym->getVA() & ~0x1; 180 memcpy(Buf, Data, sizeof(Data)); 181 Target->relocateOne(Buf, R_ARM_THM_MOVW_PREL_NC, S - P - 12); 182 Target->relocateOne(Buf + 4, R_ARM_THM_MOVT_PREL, S - P - 8); 183 } 184 185 void ThumbV7PILongThunk::addSymbols(ThunkSection &IS) { 186 ThunkSym = addSyntheticLocal( 187 Saver.save("__ThumbV7PILongThunk_" + Destination.getName()), STT_FUNC, 188 Offset | 0x1, size(), &IS); 189 addSyntheticLocal("$t", STT_NOTYPE, Offset, 0, &IS); 190 } 191 192 // Write MIPS LA25 thunk code to call PIC function from the non-PIC one. 193 void MipsThunk::writeTo(uint8_t *Buf, ThunkSection &) const { 194 uint64_t S = this->Destination.getVA(); 195 write32(Buf, 0x3c190000, Config->Endianness); // lui $25, %hi(func) 196 write32(Buf + 4, 0x08000000 | (S >> 2), Config->Endianness); // j func 197 write32(Buf + 8, 0x27390000, Config->Endianness); // addiu $25, $25, %lo(func) 198 write32(Buf + 12, 0x00000000, Config->Endianness); // nop 199 Target->relocateOne(Buf, R_MIPS_HI16, S); 200 Target->relocateOne(Buf + 8, R_MIPS_LO16, S); 201 } 202 203 void MipsThunk::addSymbols(ThunkSection &IS) { 204 ThunkSym = 205 addSyntheticLocal(Saver.save("__LA25Thunk_" + Destination.getName()), 206 STT_FUNC, Offset, size(), &IS); 207 } 208 209 InputSection *MipsThunk::getTargetInputSection() const { 210 auto *DR = dyn_cast<DefinedRegular>(&Destination); 211 return dyn_cast<InputSection>(DR->Section); 212 } 213 214 Thunk::Thunk(const SymbolBody &D) : Destination(D), Offset(0) {} 215 216 Thunk::~Thunk() = default; 217 218 // Creates a thunk for Thumb-ARM interworking. 219 static Thunk *addThunkArm(uint32_t Reloc, SymbolBody &S) { 220 // ARM relocations need ARM to Thumb interworking Thunks. 221 // Thumb relocations need Thumb to ARM relocations. 222 // Use position independent Thunks if we require position independent code. 223 switch (Reloc) { 224 case R_ARM_PC24: 225 case R_ARM_PLT32: 226 case R_ARM_JUMP24: 227 if (Config->Pic) 228 return make<ARMV7PILongThunk>(S); 229 return make<ARMV7ABSLongThunk>(S); 230 case R_ARM_THM_JUMP19: 231 case R_ARM_THM_JUMP24: 232 if (Config->Pic) 233 return make<ThumbV7PILongThunk>(S); 234 return make<ThumbV7ABSLongThunk>(S); 235 } 236 fatal("unrecognized relocation type"); 237 } 238 239 static Thunk *addThunkMips(SymbolBody &S) { 240 return make<MipsThunk>(S); 241 } 242 243 Thunk *addThunk(uint32_t RelocType, SymbolBody &S) { 244 if (Config->EMachine == EM_ARM) 245 return addThunkArm(RelocType, S); 246 else if (Config->EMachine == EM_MIPS) 247 return addThunkMips(S); 248 llvm_unreachable("add Thunk only supported for ARM and Mips"); 249 return nullptr; 250 } 251 252 } // end namespace elf 253 } // end namespace lld 254