lib/Target/RISCV/MCTargetDesc/RISCVMCExpr.cpp

   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 }