lib/MC/MCWin64EH.cpp

   1 //===- lib/MC/MCWin64EH.cpp - MCWin64EH implementation --------------------===//
   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 #include "llvm/MC/MCWin64EH.h"
  10 #include "llvm/ADT/Twine.h"
  11 #include "llvm/MC/MCContext.h"
  12 #include "llvm/MC/MCExpr.h"
  13 #include "llvm/MC/MCObjectFileInfo.h"
  14 #include "llvm/MC/MCObjectStreamer.h"
  15 #include "llvm/MC/MCSectionCOFF.h"
  16 #include "llvm/MC/MCStreamer.h"
  17 #include "llvm/MC/MCSymbol.h"
  18 #include "llvm/Support/Win64EH.h"
  19
  20 using namespace llvm;
  21
  22 // NOTE: All relocations generated here are 4-byte image-relative.
  23
  24 static uint8_t CountOfUnwindCodes(std::vector<WinEH::Instruction> &Insns) {
  25   uint8_t Count = 0;
  26   for (const auto &I : Insns) {
  27     switch (static_cast<Win64EH::UnwindOpcodes>(I.Operation)) {
  28     default:
  29       llvm_unreachable("Unsupported unwind code");
  30     case Win64EH::UOP_PushNonVol:
  31     case Win64EH::UOP_AllocSmall:
  32     case Win64EH::UOP_SetFPReg:
  33     case Win64EH::UOP_PushMachFrame:
  34       Count += 1;
  35       break;
  36     case Win64EH::UOP_SaveNonVol:
  37     case Win64EH::UOP_SaveXMM128:
  38       Count += 2;
  39       break;
  40     case Win64EH::UOP_SaveNonVolBig:
  41     case Win64EH::UOP_SaveXMM128Big:
  42       Count += 3;
  43       break;
  44     case Win64EH::UOP_AllocLarge:
  45       Count += (I.Offset > 512 * 1024 - 8) ? 3 : 2;
  46       break;
  47     }
  48   }
  49   return Count;
  50 }
  51
  52 static void EmitAbsDifference(MCStreamer &Streamer, const MCSymbol *LHS,
  53                               const MCSymbol *RHS) {
  54   MCContext &Context = Streamer.getContext();
  55   const MCExpr *Diff =
  56       MCBinaryExpr::createSub(MCSymbolRefExpr::create(LHS, Context),
  57                               MCSymbolRefExpr::create(RHS, Context), Context);
  58   Streamer.EmitValue(Diff, 1);
  59 }
  60
  61 static void EmitUnwindCode(MCStreamer &streamer, const MCSymbol *begin,
  62                            WinEH::Instruction &inst) {
  63   uint8_t b2;
  64   uint16_t w;
  65   b2 = (inst.Operation & 0x0F);
  66   switch (static_cast<Win64EH::UnwindOpcodes>(inst.Operation)) {
  67   default:
  68     llvm_unreachable("Unsupported unwind code");
  69   case Win64EH::UOP_PushNonVol:
  70     EmitAbsDifference(streamer, inst.Label, begin);
  71     b2 |= (inst.Register & 0x0F) << 4;
  72     streamer.EmitIntValue(b2, 1);
  73     break;
  74   case Win64EH::UOP_AllocLarge:
  75     EmitAbsDifference(streamer, inst.Label, begin);
  76     if (inst.Offset > 512 * 1024 - 8) {
  77       b2 |= 0x10;
  78       streamer.EmitIntValue(b2, 1);
  79       w = inst.Offset & 0xFFF8;
  80       streamer.EmitIntValue(w, 2);
  81       w = inst.Offset >> 16;
  82     } else {
  83       streamer.EmitIntValue(b2, 1);
  84       w = inst.Offset >> 3;
  85     }
  86     streamer.EmitIntValue(w, 2);
  87     break;
  88   case Win64EH::UOP_AllocSmall:
  89     b2 |= (((inst.Offset - 8) >> 3) & 0x0F) << 4;
  90     EmitAbsDifference(streamer, inst.Label, begin);
  91     streamer.EmitIntValue(b2, 1);
  92     break;
  93   case Win64EH::UOP_SetFPReg:
  94     EmitAbsDifference(streamer, inst.Label, begin);
  95     streamer.EmitIntValue(b2, 1);
  96     break;
  97   case Win64EH::UOP_SaveNonVol:
  98   case Win64EH::UOP_SaveXMM128:
  99     b2 |= (inst.Register & 0x0F) << 4;
 100     EmitAbsDifference(streamer, inst.Label, begin);
 101     streamer.EmitIntValue(b2, 1);
 102     w = inst.Offset >> 3;
 103     if (inst.Operation == Win64EH::UOP_SaveXMM128)
 104       w >>= 1;
 105     streamer.EmitIntValue(w, 2);
 106     break;
 107   case Win64EH::UOP_SaveNonVolBig:
 108   case Win64EH::UOP_SaveXMM128Big:
 109     b2 |= (inst.Register & 0x0F) << 4;
 110     EmitAbsDifference(streamer, inst.Label, begin);
 111     streamer.EmitIntValue(b2, 1);
 112     if (inst.Operation == Win64EH::UOP_SaveXMM128Big)
 113       w = inst.Offset & 0xFFF0;
 114     else
 115       w = inst.Offset & 0xFFF8;
 116     streamer.EmitIntValue(w, 2);
 117     w = inst.Offset >> 16;
 118     streamer.EmitIntValue(w, 2);
 119     break;
 120   case Win64EH::UOP_PushMachFrame:
 121     if (inst.Offset == 1)
 122       b2 |= 0x10;
 123     EmitAbsDifference(streamer, inst.Label, begin);
 124     streamer.EmitIntValue(b2, 1);
 125     break;
 126   }
 127 }
 128
 129 static void EmitSymbolRefWithOfs(MCStreamer &streamer,
 130                                  const MCSymbol *Base,
 131                                  const MCSymbol *Other) {
 132   MCContext &Context = streamer.getContext();
 133   const MCSymbolRefExpr *BaseRef = MCSymbolRefExpr::create(Base, Context);
 134   const MCSymbolRefExpr *OtherRef = MCSymbolRefExpr::create(Other, Context);
 135   const MCExpr *Ofs = MCBinaryExpr::createSub(OtherRef, BaseRef, Context);
 136   const MCSymbolRefExpr *BaseRefRel = MCSymbolRefExpr::create(Base,
 137                                               MCSymbolRefExpr::VK_COFF_IMGREL32,
 138                                               Context);
 139   streamer.EmitValue(MCBinaryExpr::createAdd(BaseRefRel, Ofs, Context), 4);
 140 }
 141
 142 static void EmitRuntimeFunction(MCStreamer &streamer,
 143                                 const WinEH::FrameInfo *info) {
 144   MCContext &context = streamer.getContext();
 145
 146   streamer.EmitValueToAlignment(4);
 147   EmitSymbolRefWithOfs(streamer, info->Function, info->Begin);
 148   EmitSymbolRefWithOfs(streamer, info->Function, info->End);
 149   streamer.EmitValue(MCSymbolRefExpr::create(info->Symbol,
 150                                              MCSymbolRefExpr::VK_COFF_IMGREL32,
 151                                              context), 4);
 152 }
 153
 154 static void EmitUnwindInfo(MCStreamer &streamer, WinEH::FrameInfo *info) {
 155   // If this UNWIND_INFO already has a symbol, it's already been emitted.
 156   if (info->Symbol)
 157     return;
 158
 159   MCContext &context = streamer.getContext();
 160   MCSymbol *Label = context.createTempSymbol();
 161
 162   streamer.EmitValueToAlignment(4);
 163   streamer.EmitLabel(Label);
 164   info->Symbol = Label;
 165
 166   // Upper 3 bits are the version number (currently 1).
 167   uint8_t flags = 0x01;
 168   if (info->ChainedParent)
 169     flags |= Win64EH::UNW_ChainInfo << 3;
 170   else {
 171     if (info->HandlesUnwind)
 172       flags |= Win64EH::UNW_TerminateHandler << 3;
 173     if (info->HandlesExceptions)
 174       flags |= Win64EH::UNW_ExceptionHandler << 3;
 175   }
 176   streamer.EmitIntValue(flags, 1);
 177
 178   if (info->PrologEnd)
 179     EmitAbsDifference(streamer, info->PrologEnd, info->Begin);
 180   else
 181     streamer.EmitIntValue(0, 1);
 182
 183   uint8_t numCodes = CountOfUnwindCodes(info->Instructions);
 184   streamer.EmitIntValue(numCodes, 1);
 185
 186   uint8_t frame = 0;
 187   if (info->LastFrameInst >= 0) {
 188     WinEH::Instruction &frameInst = info->Instructions[info->LastFrameInst];
 189     assert(frameInst.Operation == Win64EH::UOP_SetFPReg);
 190     frame = (frameInst.Register & 0x0F) | (frameInst.Offset & 0xF0);
 191   }
 192   streamer.EmitIntValue(frame, 1);
 193
 194   // Emit unwind instructions (in reverse order).
 195   uint8_t numInst = info->Instructions.size();
 196   for (uint8_t c = 0; c < numInst; ++c) {
 197     WinEH::Instruction inst = info->Instructions.back();
 198     info->Instructions.pop_back();
 199     EmitUnwindCode(streamer, info->Begin, inst);
 200   }
 201
 202   // For alignment purposes, the instruction array will always have an even
 203   // number of entries, with the final entry potentially unused (in which case
 204   // the array will be one longer than indicated by the count of unwind codes
 205   // field).
 206   if (numCodes & 1) {
 207     streamer.EmitIntValue(0, 2);
 208   }
 209
 210   if (flags & (Win64EH::UNW_ChainInfo << 3))
 211     EmitRuntimeFunction(streamer, info->ChainedParent);
 212   else if (flags &
 213            ((Win64EH::UNW_TerminateHandler|Win64EH::UNW_ExceptionHandler) << 3))
 214     streamer.EmitValue(MCSymbolRefExpr::create(info->ExceptionHandler,
 215                                               MCSymbolRefExpr::VK_COFF_IMGREL32,
 216                                               context), 4);
 217   else if (numCodes == 0) {
 218     // The minimum size of an UNWIND_INFO struct is 8 bytes. If we're not
 219     // a chained unwind info, if there is no handler, and if there are fewer
 220     // than 2 slots used in the unwind code array, we have to pad to 8 bytes.
 221     streamer.EmitIntValue(0, 4);
 222   }
 223 }
 224
 225 void llvm::Win64EH::UnwindEmitter::Emit(MCStreamer &Streamer) const {
 226   // Emit the unwind info structs first.
 227   for (const auto &CFI : Streamer.getWinFrameInfos()) {
 228     MCSection *XData = Streamer.getAssociatedXDataSection(CFI->TextSection);
 229     Streamer.SwitchSection(XData);
 230     ::EmitUnwindInfo(Streamer, CFI.get());
 231   }
 232
 233   // Now emit RUNTIME_FUNCTION entries.
 234   for (const auto &CFI : Streamer.getWinFrameInfos()) {
 235     MCSection *PData = Streamer.getAssociatedPDataSection(CFI->TextSection);
 236     Streamer.SwitchSection(PData);
 237     EmitRuntimeFunction(Streamer, CFI.get());
 238   }
 239 }
 240
 241 void llvm::Win64EH::UnwindEmitter::EmitUnwindInfo(
 242     MCStreamer &Streamer, WinEH::FrameInfo *info) const {
 243   // Switch sections (the static function above is meant to be called from
 244   // here and from Emit().
 245   MCSection *XData = Streamer.getAssociatedXDataSection(info->TextSection);
 246   Streamer.SwitchSection(XData);
 247
 248   ::EmitUnwindInfo(Streamer, info);
 249 }
 250
 251 static int64_t GetAbsDifference(MCStreamer &Streamer, const MCSymbol *LHS,
 252                                 const MCSymbol *RHS) {
 253   MCContext &Context = Streamer.getContext();
 254   const MCExpr *Diff =
 255       MCBinaryExpr::createSub(MCSymbolRefExpr::create(LHS, Context),
 256                               MCSymbolRefExpr::create(RHS, Context), Context);
 257   MCObjectStreamer *OS = (MCObjectStreamer *)(&Streamer);
 258   int64_t value;
 259   Diff->evaluateAsAbsolute(value, OS->getAssembler());
 260   return value;
 261 }
 262
 263 static uint32_t
 264 ARM64CountOfUnwindCodes(const std::vector<WinEH::Instruction> &Insns) {
 265   uint32_t Count = 0;
 266   for (const auto &I : Insns) {
 267     switch (static_cast<Win64EH::UnwindOpcodes>(I.Operation)) {
 268     default:
 269       llvm_unreachable("Unsupported ARM64 unwind code");
 270     case Win64EH::UOP_AllocSmall:
 271       Count += 1;
 272       break;
 273     case Win64EH::UOP_AllocMedium:
 274       Count += 2;
 275       break;
 276     case Win64EH::UOP_AllocLarge:
 277       Count += 4;
 278       break;
 279     case Win64EH::UOP_SaveFPLRX:
 280       Count += 1;
 281       break;
 282     case Win64EH::UOP_SaveFPLR:
 283       Count += 1;
 284       break;
 285     case Win64EH::UOP_SaveReg:
 286       Count += 2;
 287       break;
 288     case Win64EH::UOP_SaveRegP:
 289       Count += 2;
 290       break;
 291     case Win64EH::UOP_SaveRegPX:
 292       Count += 2;
 293       break;
 294     case Win64EH::UOP_SaveRegX:
 295       Count += 2;
 296       break;
 297     case Win64EH::UOP_SaveFReg:
 298       Count += 2;
 299       break;
 300     case Win64EH::UOP_SaveFRegP:
 301       Count += 2;
 302       break;
 303     case Win64EH::UOP_SaveFRegX:
 304       Count += 2;
 305       break;
 306     case Win64EH::UOP_SaveFRegPX:
 307       Count += 2;
 308       break;
 309     case Win64EH::UOP_SetFP:
 310       Count += 1;
 311       break;
 312     case Win64EH::UOP_AddFP:
 313       Count += 2;
 314       break;
 315     case Win64EH::UOP_Nop:
 316       Count += 1;
 317       break;
 318     case Win64EH::UOP_End:
 319       Count += 1;
 320       break;
 321     }
 322   }
 323   return Count;
 324 }
 325
 326 // Unwind opcode encodings and restrictions are documented at
 327 // https://docs.microsoft.com/en-us/cpp/build/arm64-exception-handling
 328 static void ARM64EmitUnwindCode(MCStreamer &streamer, const MCSymbol *begin,
 329                                 WinEH::Instruction &inst) {
 330   uint8_t b, reg;
 331   switch (static_cast<Win64EH::UnwindOpcodes>(inst.Operation)) {
 332   default:
 333     llvm_unreachable("Unsupported ARM64 unwind code");
 334   case Win64EH::UOP_AllocSmall:
 335     b = (inst.Offset >> 4) & 0x1F;
 336     streamer.EmitIntValue(b, 1);
 337     break;
 338   case Win64EH::UOP_AllocMedium: {
 339     uint16_t hw = (inst.Offset >> 4) & 0x7FF;
 340     b = 0xC0;
 341     b |= (hw >> 8);
 342     streamer.EmitIntValue(b, 1);
 343     b = hw & 0xFF;
 344     streamer.EmitIntValue(b, 1);
 345     break;
 346   }
 347   case Win64EH::UOP_AllocLarge: {
 348     uint32_t w;
 349     b = 0xE0;
 350     streamer.EmitIntValue(b, 1);
 351     w = inst.Offset >> 4;
 352     b = (w & 0x00FF0000) >> 16;
 353     streamer.EmitIntValue(b, 1);
 354     b = (w & 0x0000FF00) >> 8;
 355     streamer.EmitIntValue(b, 1);
 356     b = w & 0x000000FF;
 357     streamer.EmitIntValue(b, 1);
 358     break;
 359   }
 360   case Win64EH::UOP_SetFP:
 361     b = 0xE1;
 362     streamer.EmitIntValue(b, 1);
 363     break;
 364   case Win64EH::UOP_AddFP:
 365     b = 0xE2;
 366     streamer.EmitIntValue(b, 1);
 367     b = (inst.Offset >> 3);
 368     streamer.EmitIntValue(b, 1);
 369     break;
 370   case Win64EH::UOP_Nop:
 371     b = 0xE3;
 372     streamer.EmitIntValue(b, 1);
 373     break;
 374   case Win64EH::UOP_SaveFPLRX:
 375     b = 0x80;
 376     b |= ((inst.Offset - 1) >> 3) & 0x3F;
 377     streamer.EmitIntValue(b, 1);
 378     break;
 379   case Win64EH::UOP_SaveFPLR:
 380     b = 0x40;
 381     b |= (inst.Offset >> 3) & 0x3F;
 382     streamer.EmitIntValue(b, 1);
 383     break;
 384   case Win64EH::UOP_SaveReg:
 385     assert(inst.Register >= 19 && "Saved reg must be >= 19");
 386     reg = inst.Register - 19;
 387     b = 0xD0 | ((reg & 0xC) >> 2);
 388     streamer.EmitIntValue(b, 1);
 389     b = ((reg & 0x3) << 6) | (inst.Offset >> 3);
 390     streamer.EmitIntValue(b, 1);
 391     break;
 392   case Win64EH::UOP_SaveRegX:
 393     assert(inst.Register >= 19 && "Saved reg must be >= 19");
 394     reg = inst.Register - 19;
 395     b = 0xD4 | ((reg & 0x8) >> 3);
 396     streamer.EmitIntValue(b, 1);
 397     b = ((reg & 0x7) << 5) | ((inst.Offset >> 3) - 1);
 398     streamer.EmitIntValue(b, 1);
 399     break;
 400   case Win64EH::UOP_SaveRegP:
 401     assert(inst.Register >= 19 && "Saved registers must be >= 19");
 402     reg = inst.Register - 19;
 403     b = 0xC8 | ((reg & 0xC) >> 2);
 404     streamer.EmitIntValue(b, 1);
 405     b = ((reg & 0x3) << 6) | (inst.Offset >> 3);
 406     streamer.EmitIntValue(b, 1);
 407     break;
 408   case Win64EH::UOP_SaveRegPX:
 409     assert(inst.Register >= 19 && "Saved registers must be >= 19");
 410     reg = inst.Register - 19;
 411     b = 0xCC | ((reg & 0xC) >> 2);
 412     streamer.EmitIntValue(b, 1);
 413     b = ((reg & 0x3) << 6) | ((inst.Offset >> 3) - 1);
 414     streamer.EmitIntValue(b, 1);
 415     break;
 416   case Win64EH::UOP_SaveFReg:
 417     assert(inst.Register >= 8 && "Saved dreg must be >= 8");
 418     reg = inst.Register - 8;
 419     b = 0xDC | ((reg & 0x4) >> 2);
 420     streamer.EmitIntValue(b, 1);
 421     b = ((reg & 0x3) << 6) | (inst.Offset >> 3);
 422     streamer.EmitIntValue(b, 1);
 423     break;
 424   case Win64EH::UOP_SaveFRegX:
 425     assert(inst.Register >= 8 && "Saved dreg must be >= 8");
 426     reg = inst.Register - 8;
 427     b = 0xDE;
 428     streamer.EmitIntValue(b, 1);
 429     b = ((reg & 0x7) << 5) | ((inst.Offset >> 3) - 1);
 430     streamer.EmitIntValue(b, 1);
 431     break;
 432   case Win64EH::UOP_SaveFRegP:
 433     assert(inst.Register >= 8 && "Saved dregs must be >= 8");
 434     reg = inst.Register - 8;
 435     b = 0xD8 | ((reg & 0x4) >> 2);
 436     streamer.EmitIntValue(b, 1);
 437     b = ((reg & 0x3) << 6) | (inst.Offset >> 3);
 438     streamer.EmitIntValue(b, 1);
 439     break;
 440   case Win64EH::UOP_SaveFRegPX:
 441     assert(inst.Register >= 8 && "Saved dregs must be >= 8");
 442     reg = inst.Register - 8;
 443     b = 0xDA | ((reg & 0x4) >> 2);
 444     streamer.EmitIntValue(b, 1);
 445     b = ((reg & 0x3) << 6) | ((inst.Offset >> 3) - 1);
 446     streamer.EmitIntValue(b, 1);
 447     break;
 448   case Win64EH::UOP_End:
 449     b = 0xE4;
 450     streamer.EmitIntValue(b, 1);
 451     break;
 452   }
 453 }
 454
 455 // Returns the epilog symbol of an epilog with the exact same unwind code
 456 // sequence, if it exists.  Otherwise, returns nulltpr.
 457 // EpilogInstrs - Unwind codes for the current epilog.
 458 // Epilogs - Epilogs that potentialy match the current epilog.
 459 static MCSymbol*
 460 FindMatchingEpilog(const std::vector<WinEH::Instruction>& EpilogInstrs,
 461                    const std::vector<MCSymbol *>& Epilogs,
 462                    const WinEH::FrameInfo *info) {
 463   for (auto *EpilogStart : Epilogs) {
 464     auto InstrsIter = info->EpilogMap.find(EpilogStart);
 465     assert(InstrsIter != info->EpilogMap.end() &&
 466            "Epilog not found in EpilogMap");
 467     const auto &Instrs = InstrsIter->second;
 468
 469     if (Instrs.size() != EpilogInstrs.size())
 470       continue;
 471
 472     bool Match = true;
 473     for (unsigned i = 0; i < Instrs.size(); ++i)
 474       if (Instrs[i].Operation != EpilogInstrs[i].Operation ||
 475           Instrs[i].Offset != EpilogInstrs[i].Offset ||
 476           Instrs[i].Register != EpilogInstrs[i].Register) {
 477          Match = false;
 478          break;
 479       }
 480
 481     if (Match)
 482       return EpilogStart;
 483   }
 484   return nullptr;
 485 }
 486
 487 // Populate the .xdata section.  The format of .xdata on ARM64 is documented at
 488 // https://docs.microsoft.com/en-us/cpp/build/arm64-exception-handling
 489 static void ARM64EmitUnwindInfo(MCStreamer &streamer, WinEH::FrameInfo *info) {
 490   // If this UNWIND_INFO already has a symbol, it's already been emitted.
 491   if (info->Symbol)
 492     return;
 493
 494   MCContext &context = streamer.getContext();
 495   MCSymbol *Label = context.createTempSymbol();
 496
 497   streamer.EmitValueToAlignment(4);
 498   streamer.EmitLabel(Label);
 499   info->Symbol = Label;
 500
 501   uint32_t FuncLength = 0x0;
 502   if (info->FuncletOrFuncEnd)
 503     FuncLength = (uint32_t)GetAbsDifference(streamer, info->FuncletOrFuncEnd,
 504                                             info->Begin);
 505   FuncLength /= 4;
 506   uint32_t PrologCodeBytes = ARM64CountOfUnwindCodes(info->Instructions);
 507   uint32_t TotalCodeBytes = PrologCodeBytes;
 508
 509   // Process epilogs.
 510   MapVector<MCSymbol *, uint32_t> EpilogInfo;
 511   // Epilogs processed so far.
 512   std::vector<MCSymbol *> AddedEpilogs;
 513
 514   for (auto &I : info->EpilogMap) {
 515     MCSymbol *EpilogStart = I.first;
 516     auto &EpilogInstrs = I.second;
 517     uint32_t CodeBytes = ARM64CountOfUnwindCodes(EpilogInstrs);
 518
 519     MCSymbol* MatchingEpilog =
 520       FindMatchingEpilog(EpilogInstrs, AddedEpilogs, info);
 521     if (MatchingEpilog) {
 522       assert(EpilogInfo.find(MatchingEpilog) != EpilogInfo.end() &&
 523              "Duplicate epilog not found");
 524       EpilogInfo[EpilogStart] = EpilogInfo.lookup(MatchingEpilog);
 525       // Clear the unwind codes in the EpilogMap, so that they don't get output
 526       // in the logic below.
 527       EpilogInstrs.clear();
 528     } else {
 529       EpilogInfo[EpilogStart] = TotalCodeBytes;
 530       TotalCodeBytes += CodeBytes;
 531       AddedEpilogs.push_back(EpilogStart);
 532     }
 533   }
 534
 535   // Code Words, Epilog count, E, X, Vers, Function Length
 536   uint32_t row1 = 0x0;
 537   uint32_t CodeWords = TotalCodeBytes / 4;
 538   uint32_t CodeWordsMod = TotalCodeBytes % 4;
 539   if (CodeWordsMod)
 540     CodeWords++;
 541   uint32_t EpilogCount = info->EpilogMap.size();
 542   bool ExtensionWord = EpilogCount > 31 || TotalCodeBytes > 124;
 543   if (!ExtensionWord) {
 544     row1 |= (EpilogCount & 0x1F) << 22;
 545     row1 |= (CodeWords & 0x1F) << 27;
 546   }
 547   // E is always 0 right now, TODO: packed epilog setup
 548   if (info->HandlesExceptions) // X
 549     row1 |= 1 << 20;
 550   row1 |= FuncLength & 0x3FFFF;
 551   streamer.EmitIntValue(row1, 4);
 552
 553   // Extended Code Words, Extended Epilog Count
 554   if (ExtensionWord) {
 555     // FIXME: We should be able to split unwind info into multiple sections.
 556     // FIXME: We should share epilog codes across epilogs, where possible,
 557     // which would make this issue show up less frequently.
 558     if (CodeWords > 0xFF || EpilogCount > 0xFFFF)
 559       report_fatal_error("SEH unwind data splitting not yet implemented");
 560     uint32_t row2 = 0x0;
 561     row2 |= (CodeWords & 0xFF) << 16;
 562     row2 |= (EpilogCount & 0xFFFF);
 563     streamer.EmitIntValue(row2, 4);
 564   }
 565
 566   // Epilog Start Index, Epilog Start Offset
 567   for (auto &I : EpilogInfo) {
 568     MCSymbol *EpilogStart = I.first;
 569     uint32_t EpilogIndex = I.second;
 570     uint32_t EpilogOffset =
 571         (uint32_t)GetAbsDifference(streamer, EpilogStart, info->Begin);
 572     if (EpilogOffset)
 573       EpilogOffset /= 4;
 574     uint32_t row3 = EpilogOffset;
 575     row3 |= (EpilogIndex & 0x3FF) << 22;
 576     streamer.EmitIntValue(row3, 4);
 577   }
 578
 579   // Emit prolog unwind instructions (in reverse order).
 580   uint8_t numInst = info->Instructions.size();
 581   for (uint8_t c = 0; c < numInst; ++c) {
 582     WinEH::Instruction inst = info->Instructions.back();
 583     info->Instructions.pop_back();
 584     ARM64EmitUnwindCode(streamer, info->Begin, inst);
 585   }
 586
 587   // Emit epilog unwind instructions
 588   for (auto &I : info->EpilogMap) {
 589     auto &EpilogInstrs = I.second;
 590     for (uint32_t i = 0; i < EpilogInstrs.size(); i++) {
 591       WinEH::Instruction inst = EpilogInstrs[i];
 592       ARM64EmitUnwindCode(streamer, info->Begin, inst);
 593     }
 594   }
 595
 596   int32_t BytesMod = CodeWords * 4 - TotalCodeBytes;
 597   assert(BytesMod >= 0);
 598   for (int i = 0; i < BytesMod; i++)
 599     streamer.EmitIntValue(0xE3, 1);
 600
 601   if (info->HandlesExceptions)
 602     streamer.EmitValue(
 603         MCSymbolRefExpr::create(info->ExceptionHandler,
 604                                 MCSymbolRefExpr::VK_COFF_IMGREL32, context),
 605         4);
 606 }
 607
 608 static void ARM64EmitRuntimeFunction(MCStreamer &streamer,
 609                                      const WinEH::FrameInfo *info) {
 610   MCContext &context = streamer.getContext();
 611
 612   streamer.EmitValueToAlignment(4);
 613   EmitSymbolRefWithOfs(streamer, info->Function, info->Begin);
 614   streamer.EmitValue(MCSymbolRefExpr::create(info->Symbol,
 615                                              MCSymbolRefExpr::VK_COFF_IMGREL32,
 616                                              context),
 617                      4);
 618 }
 619
 620 void llvm::Win64EH::ARM64UnwindEmitter::Emit(MCStreamer &Streamer) const {
 621   // Emit the unwind info structs first.
 622   for (const auto &CFI : Streamer.getWinFrameInfos()) {
 623     MCSection *XData = Streamer.getAssociatedXDataSection(CFI->TextSection);
 624     Streamer.SwitchSection(XData);
 625     ARM64EmitUnwindInfo(Streamer, CFI.get());
 626   }
 627
 628   // Now emit RUNTIME_FUNCTION entries.
 629   for (const auto &CFI : Streamer.getWinFrameInfos()) {
 630     MCSection *PData = Streamer.getAssociatedPDataSection(CFI->TextSection);
 631     Streamer.SwitchSection(PData);
 632     ARM64EmitRuntimeFunction(Streamer, CFI.get());
 633   }
 634 }
 635
 636 void llvm::Win64EH::ARM64UnwindEmitter::EmitUnwindInfo(
 637     MCStreamer &Streamer, WinEH::FrameInfo *info) const {
 638   // Switch sections (the static function above is meant to be called from
 639   // here and from Emit().
 640   MCSection *XData = Streamer.getAssociatedXDataSection(info->TextSection);
 641   Streamer.SwitchSection(XData);
 642   ARM64EmitUnwindInfo(Streamer, info);
 643 }