1 //===-- RISCVMCExpr.cpp - RISCV specific MC expression classes ------------===// 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 // This file contains the implementation of the assembly expression modifiers 10 // accepted by the RISCV architecture (e.g. ":lo12:", ":gottprel_g1:", ...). 11 // 12 //===----------------------------------------------------------------------===// 13 14 #include "RISCVMCExpr.h" 15 #include "MCTargetDesc/RISCVAsmBackend.h" 16 #include "RISCV.h" 17 #include "RISCVFixupKinds.h" 18 #include "llvm/BinaryFormat/ELF.h" 19 #include "llvm/MC/MCAsmLayout.h" 20 #include "llvm/MC/MCAssembler.h" 21 #include "llvm/MC/MCContext.h" 22 #include "llvm/MC/MCStreamer.h" 23 #include "llvm/MC/MCSymbolELF.h" 24 #include "llvm/MC/MCValue.h" 25 #include "llvm/Support/ErrorHandling.h" 26 27 using namespace llvm; 28 29 #define DEBUG_TYPE "riscvmcexpr" 30 31 const RISCVMCExpr *RISCVMCExpr::create(const MCExpr *Expr, VariantKind Kind, 32 MCContext &Ctx) { 33 return new (Ctx) RISCVMCExpr(Expr, Kind); 34 } 35 36 void RISCVMCExpr::printImpl(raw_ostream &OS, const MCAsmInfo *MAI) const { 37 VariantKind Kind = getKind(); 38 bool HasVariant = ((Kind != VK_RISCV_None) && (Kind != VK_RISCV_CALL) && 39 (Kind != VK_RISCV_CALL_PLT)); 40 41 if (HasVariant) 42 OS << '%' << getVariantKindName(getKind()) << '('; 43 Expr->print(OS, MAI); 44 if (Kind == VK_RISCV_CALL_PLT) 45 OS << "@plt"; 46 if (HasVariant) 47 OS << ')'; 48 } 49 50 const MCFixup *RISCVMCExpr::getPCRelHiFixup() const { 51 MCValue AUIPCLoc; 52 if (!getSubExpr()->evaluateAsRelocatable(AUIPCLoc, nullptr, nullptr)) 53 return nullptr; 54 55 const MCSymbolRefExpr *AUIPCSRE = AUIPCLoc.getSymA(); 56 if (!AUIPCSRE) 57 return nullptr; 58 59 const MCSymbol *AUIPCSymbol = &AUIPCSRE->getSymbol(); 60 const auto *DF = dyn_cast_or_null<MCDataFragment>(AUIPCSymbol->getFragment()); 61 62 if (!DF) 63 return nullptr; 64 65 uint64_t Offset = AUIPCSymbol->getOffset(); 66 if (DF->getContents().size() == Offset) { 67 DF = dyn_cast_or_null<MCDataFragment>(DF->getNextNode()); 68 if (!DF) 69 return nullptr; 70 Offset = 0; 71 } 72 73 for (const MCFixup &F : DF->getFixups()) { 74 if (F.getOffset() != Offset) 75 continue; 76 77 switch ((unsigned)F.getKind()) { 78 default: 79 continue; 80 case RISCV::fixup_riscv_got_hi20: 81 case RISCV::fixup_riscv_tls_got_hi20: 82 case RISCV::fixup_riscv_tls_gd_hi20: 83 case RISCV::fixup_riscv_pcrel_hi20: 84 return &F; 85 } 86 } 87 88 return nullptr; 89 } 90 91 bool RISCVMCExpr::evaluatePCRelLo(MCValue &Res, const MCAsmLayout *Layout, 92 const MCFixup *Fixup) const { 93 // VK_RISCV_PCREL_LO has to be handled specially. The MCExpr inside is 94 // actually the location of a auipc instruction with a VK_RISCV_PCREL_HI fixup 95 // pointing to the real target. We need to generate an MCValue in the form of 96 // (<real target> + <offset from this fixup to the auipc fixup>). The Fixup 97 // is pcrel relative to the VK_RISCV_PCREL_LO fixup, so we need to add the 98 // offset to the VK_RISCV_PCREL_HI Fixup from VK_RISCV_PCREL_LO to correct. 99 100 // Don't try to evaluate if the fixup will be forced as a relocation (e.g. 101 // as linker relaxation is enabled). If we evaluated pcrel_lo in this case, 102 // the modified fixup will be converted into a relocation that no longer 103 // points to the pcrel_hi as the linker requires. 104 auto &RAB = 105 static_cast<RISCVAsmBackend &>(Layout->getAssembler().getBackend()); 106 if (RAB.willForceRelocations()) 107 return false; 108 109 MCValue AUIPCLoc; 110 if (!getSubExpr()->evaluateAsValue(AUIPCLoc, *Layout)) 111 return false; 112 113 const MCSymbolRefExpr *AUIPCSRE = AUIPCLoc.getSymA(); 114 // Don't try to evaluate %pcrel_hi/%pcrel_lo pairs that cross fragment 115 // boundries. 116 if (!AUIPCSRE || 117 findAssociatedFragment() != AUIPCSRE->findAssociatedFragment()) 118 return false; 119 120 const MCSymbol *AUIPCSymbol = &AUIPCSRE->getSymbol(); 121 if (!AUIPCSymbol) 122 return false; 123 124 const MCFixup *TargetFixup = getPCRelHiFixup(); 125 if (!TargetFixup) 126 return false; 127 128 if ((unsigned)TargetFixup->getKind() != RISCV::fixup_riscv_pcrel_hi20) 129 return false; 130 131 MCValue Target; 132 if (!TargetFixup->getValue()->evaluateAsValue(Target, *Layout)) 133 return false; 134 135 if (!Target.getSymA() || !Target.getSymA()->getSymbol().isInSection()) 136 return false; 137 138 if (&Target.getSymA()->getSymbol().getSection() != 139 findAssociatedFragment()->getParent()) 140 return false; 141 142 uint64_t AUIPCOffset = AUIPCSymbol->getOffset(); 143 144 Res = MCValue::get(Target.getSymA(), nullptr, 145 Target.getConstant() + (Fixup->getOffset() - AUIPCOffset)); 146 return true; 147 } 148 149 bool RISCVMCExpr::evaluateAsRelocatableImpl(MCValue &Res, 150 const MCAsmLayout *Layout, 151 const MCFixup *Fixup) const { 152 if (Kind == VK_RISCV_PCREL_LO && evaluatePCRelLo(Res, Layout, Fixup)) 153 return true; 154 155 if (!getSubExpr()->evaluateAsRelocatable(Res, Layout, Fixup)) 156 return false; 157 158 // Some custom fixup types are not valid with symbol difference expressions 159 if (Res.getSymA() && Res.getSymB()) { 160 switch (getKind()) { 161 default: 162 return true; 163 case VK_RISCV_LO: 164 case VK_RISCV_HI: 165 case VK_RISCV_PCREL_LO: 166 case VK_RISCV_PCREL_HI: 167 case VK_RISCV_GOT_HI: 168 case VK_RISCV_TPREL_LO: 169 case VK_RISCV_TPREL_HI: 170 case VK_RISCV_TPREL_ADD: 171 case VK_RISCV_TLS_GOT_HI: 172 case VK_RISCV_TLS_GD_HI: 173 return false; 174 } 175 } 176 177 return true; 178 } 179 180 void RISCVMCExpr::visitUsedExpr(MCStreamer &Streamer) const { 181 Streamer.visitUsedExpr(*getSubExpr()); 182 } 183 184 RISCVMCExpr::VariantKind RISCVMCExpr::getVariantKindForName(StringRef name) { 185 return StringSwitch<RISCVMCExpr::VariantKind>(name) 186 .Case("lo", VK_RISCV_LO) 187 .Case("hi", VK_RISCV_HI) 188 .Case("pcrel_lo", VK_RISCV_PCREL_LO) 189 .Case("pcrel_hi", VK_RISCV_PCREL_HI) 190 .Case("got_pcrel_hi", VK_RISCV_GOT_HI) 191 .Case("tprel_lo", VK_RISCV_TPREL_LO) 192 .Case("tprel_hi", VK_RISCV_TPREL_HI) 193 .Case("tprel_add", VK_RISCV_TPREL_ADD) 194 .Case("tls_ie_pcrel_hi", VK_RISCV_TLS_GOT_HI) 195 .Case("tls_gd_pcrel_hi", VK_RISCV_TLS_GD_HI) 196 .Default(VK_RISCV_Invalid); 197 } 198 199 StringRef RISCVMCExpr::getVariantKindName(VariantKind Kind) { 200 switch (Kind) { 201 default: 202 llvm_unreachable("Invalid ELF symbol kind"); 203 case VK_RISCV_LO: 204 return "lo"; 205 case VK_RISCV_HI: 206 return "hi"; 207 case VK_RISCV_PCREL_LO: 208 return "pcrel_lo"; 209 case VK_RISCV_PCREL_HI: 210 return "pcrel_hi"; 211 case VK_RISCV_GOT_HI: 212 return "got_pcrel_hi"; 213 case VK_RISCV_TPREL_LO: 214 return "tprel_lo"; 215 case VK_RISCV_TPREL_HI: 216 return "tprel_hi"; 217 case VK_RISCV_TPREL_ADD: 218 return "tprel_add"; 219 case VK_RISCV_TLS_GOT_HI: 220 return "tls_ie_pcrel_hi"; 221 case VK_RISCV_TLS_GD_HI: 222 return "tls_gd_pcrel_hi"; 223 } 224 } 225 226 static void fixELFSymbolsInTLSFixupsImpl(const MCExpr *Expr, MCAssembler &Asm) { 227 switch (Expr->getKind()) { 228 case MCExpr::Target: 229 llvm_unreachable("Can't handle nested target expression"); 230 break; 231 case MCExpr::Constant: 232 break; 233 234 case MCExpr::Binary: { 235 const MCBinaryExpr *BE = cast<MCBinaryExpr>(Expr); 236 fixELFSymbolsInTLSFixupsImpl(BE->getLHS(), Asm); 237 fixELFSymbolsInTLSFixupsImpl(BE->getRHS(), Asm); 238 break; 239 } 240 241 case MCExpr::SymbolRef: { 242 // We're known to be under a TLS fixup, so any symbol should be 243 // modified. There should be only one. 244 const MCSymbolRefExpr &SymRef = *cast<MCSymbolRefExpr>(Expr); 245 cast<MCSymbolELF>(SymRef.getSymbol()).setType(ELF::STT_TLS); 246 break; 247 } 248 249 case MCExpr::Unary: 250 fixELFSymbolsInTLSFixupsImpl(cast<MCUnaryExpr>(Expr)->getSubExpr(), Asm); 251 break; 252 } 253 } 254 255 void RISCVMCExpr::fixELFSymbolsInTLSFixups(MCAssembler &Asm) const { 256 switch (getKind()) { 257 default: 258 return; 259 case VK_RISCV_TPREL_HI: 260 case VK_RISCV_TLS_GOT_HI: 261 case VK_RISCV_TLS_GD_HI: 262 break; 263 } 264 265 fixELFSymbolsInTLSFixupsImpl(getSubExpr(), Asm); 266 } 267 268 bool RISCVMCExpr::evaluateAsConstant(int64_t &Res) const { 269 MCValue Value; 270 271 if (Kind == VK_RISCV_PCREL_HI || Kind == VK_RISCV_PCREL_LO || 272 Kind == VK_RISCV_GOT_HI || Kind == VK_RISCV_TPREL_HI || 273 Kind == VK_RISCV_TPREL_LO || Kind == VK_RISCV_TPREL_ADD || 274 Kind == VK_RISCV_TLS_GOT_HI || Kind == VK_RISCV_TLS_GD_HI || 275 Kind == VK_RISCV_CALL || Kind == VK_RISCV_CALL_PLT) 276 return false; 277 278 if (!getSubExpr()->evaluateAsRelocatable(Value, nullptr, nullptr)) 279 return false; 280 281 if (!Value.isAbsolute()) 282 return false; 283 284 Res = evaluateAsInt64(Value.getConstant()); 285 return true; 286 } 287 288 int64_t RISCVMCExpr::evaluateAsInt64(int64_t Value) const { 289 switch (Kind) { 290 default: 291 llvm_unreachable("Invalid kind"); 292 case VK_RISCV_LO: 293 return SignExtend64<12>(Value); 294 case VK_RISCV_HI: 295 // Add 1 if bit 11 is 1, to compensate for low 12 bits being negative. 296 return ((Value + 0x800) >> 12) & 0xfffff; 297 } 298 } 299