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   // It should normally be possible to calculate the length of a function
 259   // at this point, but it might not be possible in the presence of certain
 260   // unusual constructs, like an inline asm with an alignment directive.
 261   int64_t value;
 262   if (!Diff->evaluateAsAbsolute(value, OS->getAssembler()))
 263     report_fatal_error("Failed to evaluate function length in SEH unwind info");
 264   return value;
 265 }
 266
 267 static uint32_t
 268 ARM64CountOfUnwindCodes(const std::vector<WinEH::Instruction> &Insns) {
 269   uint32_t Count = 0;
 270   for (const auto &I : Insns) {
 271     switch (static_cast<Win64EH::UnwindOpcodes>(I.Operation)) {
 272     default:
 273       llvm_unreachable("Unsupported ARM64 unwind code");
 274     case Win64EH::UOP_AllocSmall:
 275       Count += 1;
 276       break;
 277     case Win64EH::UOP_AllocMedium:
 278       Count += 2;
 279       break;
 280     case Win64EH::UOP_AllocLarge:
 281       Count += 4;
 282       break;
 283     case Win64EH::UOP_SaveFPLRX:
 284       Count += 1;
 285       break;
 286     case Win64EH::UOP_SaveFPLR:
 287       Count += 1;
 288       break;
 289     case Win64EH::UOP_SaveReg:
 290       Count += 2;
 291       break;
 292     case Win64EH::UOP_SaveRegP:
 293       Count += 2;
 294       break;
 295     case Win64EH::UOP_SaveRegPX:
 296       Count += 2;
 297       break;
 298     case Win64EH::UOP_SaveRegX:
 299       Count += 2;
 300       break;
 301     case Win64EH::UOP_SaveFReg:
 302       Count += 2;
 303       break;
 304     case Win64EH::UOP_SaveFRegP:
 305       Count += 2;
 306       break;
 307     case Win64EH::UOP_SaveFRegX:
 308       Count += 2;
 309       break;
 310     case Win64EH::UOP_SaveFRegPX:
 311       Count += 2;
 312       break;
 313     case Win64EH::UOP_SetFP:
 314       Count += 1;
 315       break;
 316     case Win64EH::UOP_AddFP:
 317       Count += 2;
 318       break;
 319     case Win64EH::UOP_Nop:
 320       Count += 1;
 321       break;
 322     case Win64EH::UOP_End:
 323       Count += 1;
 324       break;
 325     }
 326   }
 327   return Count;
 328 }
 329
 330 // Unwind opcode encodings and restrictions are documented at
 331 // https://docs.microsoft.com/en-us/cpp/build/arm64-exception-handling
 332 static void ARM64EmitUnwindCode(MCStreamer &streamer, const MCSymbol *begin,
 333                                 WinEH::Instruction &inst) {
 334   uint8_t b, reg;
 335   switch (static_cast<Win64EH::UnwindOpcodes>(inst.Operation)) {
 336   default:
 337     llvm_unreachable("Unsupported ARM64 unwind code");
 338   case Win64EH::UOP_AllocSmall:
 339     b = (inst.Offset >> 4) & 0x1F;
 340     streamer.EmitIntValue(b, 1);
 341     break;
 342   case Win64EH::UOP_AllocMedium: {
 343     uint16_t hw = (inst.Offset >> 4) & 0x7FF;
 344     b = 0xC0;
 345     b |= (hw >> 8);
 346     streamer.EmitIntValue(b, 1);
 347     b = hw & 0xFF;
 348     streamer.EmitIntValue(b, 1);
 349     break;
 350   }
 351   case Win64EH::UOP_AllocLarge: {
 352     uint32_t w;
 353     b = 0xE0;
 354     streamer.EmitIntValue(b, 1);
 355     w = inst.Offset >> 4;
 356     b = (w & 0x00FF0000) >> 16;
 357     streamer.EmitIntValue(b, 1);
 358     b = (w & 0x0000FF00) >> 8;
 359     streamer.EmitIntValue(b, 1);
 360     b = w & 0x000000FF;
 361     streamer.EmitIntValue(b, 1);
 362     break;
 363   }
 364   case Win64EH::UOP_SetFP:
 365     b = 0xE1;
 366     streamer.EmitIntValue(b, 1);
 367     break;
 368   case Win64EH::UOP_AddFP:
 369     b = 0xE2;
 370     streamer.EmitIntValue(b, 1);
 371     b = (inst.Offset >> 3);
 372     streamer.EmitIntValue(b, 1);
 373     break;
 374   case Win64EH::UOP_Nop:
 375     b = 0xE3;
 376     streamer.EmitIntValue(b, 1);
 377     break;
 378   case Win64EH::UOP_SaveFPLRX:
 379     b = 0x80;
 380     b |= ((inst.Offset - 1) >> 3) & 0x3F;
 381     streamer.EmitIntValue(b, 1);
 382     break;
 383   case Win64EH::UOP_SaveFPLR:
 384     b = 0x40;
 385     b |= (inst.Offset >> 3) & 0x3F;
 386     streamer.EmitIntValue(b, 1);
 387     break;
 388   case Win64EH::UOP_SaveReg:
 389     assert(inst.Register >= 19 && "Saved reg must be >= 19");
 390     reg = inst.Register - 19;
 391     b = 0xD0 | ((reg & 0xC) >> 2);
 392     streamer.EmitIntValue(b, 1);
 393     b = ((reg & 0x3) << 6) | (inst.Offset >> 3);
 394     streamer.EmitIntValue(b, 1);
 395     break;
 396   case Win64EH::UOP_SaveRegX:
 397     assert(inst.Register >= 19 && "Saved reg must be >= 19");
 398     reg = inst.Register - 19;
 399     b = 0xD4 | ((reg & 0x8) >> 3);
 400     streamer.EmitIntValue(b, 1);
 401     b = ((reg & 0x7) << 5) | ((inst.Offset >> 3) - 1);
 402     streamer.EmitIntValue(b, 1);
 403     break;
 404   case Win64EH::UOP_SaveRegP:
 405     assert(inst.Register >= 19 && "Saved registers must be >= 19");
 406     reg = inst.Register - 19;
 407     b = 0xC8 | ((reg & 0xC) >> 2);
 408     streamer.EmitIntValue(b, 1);
 409     b = ((reg & 0x3) << 6) | (inst.Offset >> 3);
 410     streamer.EmitIntValue(b, 1);
 411     break;
 412   case Win64EH::UOP_SaveRegPX:
 413     assert(inst.Register >= 19 && "Saved registers must be >= 19");
 414     reg = inst.Register - 19;
 415     b = 0xCC | ((reg & 0xC) >> 2);
 416     streamer.EmitIntValue(b, 1);
 417     b = ((reg & 0x3) << 6) | ((inst.Offset >> 3) - 1);
 418     streamer.EmitIntValue(b, 1);
 419     break;
 420   case Win64EH::UOP_SaveFReg:
 421     assert(inst.Register >= 8 && "Saved dreg must be >= 8");
 422     reg = inst.Register - 8;
 423     b = 0xDC | ((reg & 0x4) >> 2);
 424     streamer.EmitIntValue(b, 1);
 425     b = ((reg & 0x3) << 6) | (inst.Offset >> 3);
 426     streamer.EmitIntValue(b, 1);
 427     break;
 428   case Win64EH::UOP_SaveFRegX:
 429     assert(inst.Register >= 8 && "Saved dreg must be >= 8");
 430     reg = inst.Register - 8;
 431     b = 0xDE;
 432     streamer.EmitIntValue(b, 1);
 433     b = ((reg & 0x7) << 5) | ((inst.Offset >> 3) - 1);
 434     streamer.EmitIntValue(b, 1);
 435     break;
 436   case Win64EH::UOP_SaveFRegP:
 437     assert(inst.Register >= 8 && "Saved dregs must be >= 8");
 438     reg = inst.Register - 8;
 439     b = 0xD8 | ((reg & 0x4) >> 2);
 440     streamer.EmitIntValue(b, 1);
 441     b = ((reg & 0x3) << 6) | (inst.Offset >> 3);
 442     streamer.EmitIntValue(b, 1);
 443     break;
 444   case Win64EH::UOP_SaveFRegPX:
 445     assert(inst.Register >= 8 && "Saved dregs must be >= 8");
 446     reg = inst.Register - 8;
 447     b = 0xDA | ((reg & 0x4) >> 2);
 448     streamer.EmitIntValue(b, 1);
 449     b = ((reg & 0x3) << 6) | ((inst.Offset >> 3) - 1);
 450     streamer.EmitIntValue(b, 1);
 451     break;
 452   case Win64EH::UOP_End:
 453     b = 0xE4;
 454     streamer.EmitIntValue(b, 1);
 455     break;
 456   }
 457 }
 458
 459 // Returns the epilog symbol of an epilog with the exact same unwind code
 460 // sequence, if it exists.  Otherwise, returns nulltpr.
 461 // EpilogInstrs - Unwind codes for the current epilog.
 462 // Epilogs - Epilogs that potentialy match the current epilog.
 463 static MCSymbol*
 464 FindMatchingEpilog(const std::vector<WinEH::Instruction>& EpilogInstrs,
 465                    const std::vector<MCSymbol *>& Epilogs,
 466                    const WinEH::FrameInfo *info) {
 467   for (auto *EpilogStart : Epilogs) {
 468     auto InstrsIter = info->EpilogMap.find(EpilogStart);
 469     assert(InstrsIter != info->EpilogMap.end() &&
 470            "Epilog not found in EpilogMap");
 471     const auto &Instrs = InstrsIter->second;
 472
 473     if (Instrs.size() != EpilogInstrs.size())
 474       continue;
 475
 476     bool Match = true;
 477     for (unsigned i = 0; i < Instrs.size(); ++i)
 478       if (Instrs[i].Operation != EpilogInstrs[i].Operation ||
 479           Instrs[i].Offset != EpilogInstrs[i].Offset ||
 480           Instrs[i].Register != EpilogInstrs[i].Register) {
 481          Match = false;
 482          break;
 483       }
 484
 485     if (Match)
 486       return EpilogStart;
 487   }
 488   return nullptr;
 489 }
 490
 491 // Populate the .xdata section.  The format of .xdata on ARM64 is documented at
 492 // https://docs.microsoft.com/en-us/cpp/build/arm64-exception-handling
 493 static void ARM64EmitUnwindInfo(MCStreamer &streamer, WinEH::FrameInfo *info) {
 494   // If this UNWIND_INFO already has a symbol, it's already been emitted.
 495   if (info->Symbol)
 496     return;
 497
 498   MCContext &context = streamer.getContext();
 499   MCSymbol *Label = context.createTempSymbol();
 500
 501   streamer.EmitValueToAlignment(4);
 502   streamer.EmitLabel(Label);
 503   info->Symbol = Label;
 504
 505   int64_t RawFuncLength;
 506   if (!info->FuncletOrFuncEnd) {
 507     // FIXME: This is very wrong; we emit SEH data which covers zero bytes
 508     // of code. But otherwise test/MC/AArch64/seh.s crashes.
 509     RawFuncLength = 0;
 510   } else {
 511     // FIXME: GetAbsDifference tries to compute the length of the function
 512     // immediately, before the whole file is emitted, but in general
 513     // that's impossible: the size in bytes of certain assembler directives
 514     // like .align and .fill is not known until the whole file is parsed and
 515     // relaxations are applied. Currently, GetAbsDifference fails with a fatal
 516     // error in that case. (We mostly don't hit this because inline assembly
 517     // specifying those directives is rare, and we don't normally try to
 518     // align loops on AArch64.)
 519     //
 520     // There are two potential approaches to delaying the computation. One,
 521     // we could emit something like ".word (endfunc-beginfunc)/4+0x10800000",
 522     // as long as we have some conservative estimate we could use to prove
 523     // that we don't need to split the unwind data. Emitting the constant
 524     // is straightforward, but there's no existing code for estimating the
 525     // size of the function.
 526     //
 527     // The other approach would be to use a dedicated, relaxable fragment,
 528     // which could grow to accommodate splitting the unwind data if
 529     // necessary. This is more straightforward, since it automatically works
 530     // without any new infrastructure, and it's consistent with how we handle
 531     // relaxation in other contexts.  But it would require some refactoring
 532     // to move parts of the pdata/xdata emission into the implementation of
 533     // a fragment. We could probably continue to encode the unwind codes
 534     // here, but we'd have to emit the pdata, the xdata header, and the
 535     // epilogue scopes later, since they depend on whether the we need to
 536     // split the unwind data.
 537     RawFuncLength = GetAbsDifference(streamer, info->FuncletOrFuncEnd,
 538                                      info->Begin);
 539   }
 540   if (RawFuncLength > 0xFFFFF)
 541     report_fatal_error("SEH unwind data splitting not yet implemented");
 542   uint32_t FuncLength = (uint32_t)RawFuncLength / 4;
 543   uint32_t PrologCodeBytes = ARM64CountOfUnwindCodes(info->Instructions);
 544   uint32_t TotalCodeBytes = PrologCodeBytes;
 545
 546   // Process epilogs.
 547   MapVector<MCSymbol *, uint32_t> EpilogInfo;
 548   // Epilogs processed so far.
 549   std::vector<MCSymbol *> AddedEpilogs;
 550
 551   for (auto &I : info->EpilogMap) {
 552     MCSymbol *EpilogStart = I.first;
 553     auto &EpilogInstrs = I.second;
 554     uint32_t CodeBytes = ARM64CountOfUnwindCodes(EpilogInstrs);
 555
 556     MCSymbol* MatchingEpilog =
 557       FindMatchingEpilog(EpilogInstrs, AddedEpilogs, info);
 558     if (MatchingEpilog) {
 559       assert(EpilogInfo.find(MatchingEpilog) != EpilogInfo.end() &&
 560              "Duplicate epilog not found");
 561       EpilogInfo[EpilogStart] = EpilogInfo.lookup(MatchingEpilog);
 562       // Clear the unwind codes in the EpilogMap, so that they don't get output
 563       // in the logic below.
 564       EpilogInstrs.clear();
 565     } else {
 566       EpilogInfo[EpilogStart] = TotalCodeBytes;
 567       TotalCodeBytes += CodeBytes;
 568       AddedEpilogs.push_back(EpilogStart);
 569     }
 570   }
 571
 572   // Code Words, Epilog count, E, X, Vers, Function Length
 573   uint32_t row1 = 0x0;
 574   uint32_t CodeWords = TotalCodeBytes / 4;
 575   uint32_t CodeWordsMod = TotalCodeBytes % 4;
 576   if (CodeWordsMod)
 577     CodeWords++;
 578   uint32_t EpilogCount = info->EpilogMap.size();
 579   bool ExtensionWord = EpilogCount > 31 || TotalCodeBytes > 124;
 580   if (!ExtensionWord) {
 581     row1 |= (EpilogCount & 0x1F) << 22;
 582     row1 |= (CodeWords & 0x1F) << 27;
 583   }
 584   // E is always 0 right now, TODO: packed epilog setup
 585   if (info->HandlesExceptions) // X
 586     row1 |= 1 << 20;
 587   row1 |= FuncLength & 0x3FFFF;
 588   streamer.EmitIntValue(row1, 4);
 589
 590   // Extended Code Words, Extended Epilog Count
 591   if (ExtensionWord) {
 592     // FIXME: We should be able to split unwind info into multiple sections.
 593     // FIXME: We should share epilog codes across epilogs, where possible,
 594     // which would make this issue show up less frequently.
 595     if (CodeWords > 0xFF || EpilogCount > 0xFFFF)
 596       report_fatal_error("SEH unwind data splitting not yet implemented");
 597     uint32_t row2 = 0x0;
 598     row2 |= (CodeWords & 0xFF) << 16;
 599     row2 |= (EpilogCount & 0xFFFF);
 600     streamer.EmitIntValue(row2, 4);
 601   }
 602
 603   // Epilog Start Index, Epilog Start Offset
 604   for (auto &I : EpilogInfo) {
 605     MCSymbol *EpilogStart = I.first;
 606     uint32_t EpilogIndex = I.second;
 607     uint32_t EpilogOffset =
 608         (uint32_t)GetAbsDifference(streamer, EpilogStart, info->Begin);
 609     if (EpilogOffset)
 610       EpilogOffset /= 4;
 611     uint32_t row3 = EpilogOffset;
 612     row3 |= (EpilogIndex & 0x3FF) << 22;
 613     streamer.EmitIntValue(row3, 4);
 614   }
 615
 616   // Emit prolog unwind instructions (in reverse order).
 617   uint8_t numInst = info->Instructions.size();
 618   for (uint8_t c = 0; c < numInst; ++c) {
 619     WinEH::Instruction inst = info->Instructions.back();
 620     info->Instructions.pop_back();
 621     ARM64EmitUnwindCode(streamer, info->Begin, inst);
 622   }
 623
 624   // Emit epilog unwind instructions
 625   for (auto &I : info->EpilogMap) {
 626     auto &EpilogInstrs = I.second;
 627     for (uint32_t i = 0; i < EpilogInstrs.size(); i++) {
 628       WinEH::Instruction inst = EpilogInstrs[i];
 629       ARM64EmitUnwindCode(streamer, info->Begin, inst);
 630     }
 631   }
 632
 633   int32_t BytesMod = CodeWords * 4 - TotalCodeBytes;
 634   assert(BytesMod >= 0);
 635   for (int i = 0; i < BytesMod; i++)
 636     streamer.EmitIntValue(0xE3, 1);
 637
 638   if (info->HandlesExceptions)
 639     streamer.EmitValue(
 640         MCSymbolRefExpr::create(info->ExceptionHandler,
 641                                 MCSymbolRefExpr::VK_COFF_IMGREL32, context),
 642         4);
 643 }
 644
 645 static void ARM64EmitRuntimeFunction(MCStreamer &streamer,
 646                                      const WinEH::FrameInfo *info) {
 647   MCContext &context = streamer.getContext();
 648
 649   streamer.EmitValueToAlignment(4);
 650   EmitSymbolRefWithOfs(streamer, info->Function, info->Begin);
 651   streamer.EmitValue(MCSymbolRefExpr::create(info->Symbol,
 652                                              MCSymbolRefExpr::VK_COFF_IMGREL32,
 653                                              context),
 654                      4);
 655 }
 656
 657 void llvm::Win64EH::ARM64UnwindEmitter::Emit(MCStreamer &Streamer) const {
 658   // Emit the unwind info structs first.
 659   for (const auto &CFI : Streamer.getWinFrameInfos()) {
 660     MCSection *XData = Streamer.getAssociatedXDataSection(CFI->TextSection);
 661     Streamer.SwitchSection(XData);
 662     ARM64EmitUnwindInfo(Streamer, CFI.get());
 663   }
 664
 665   // Now emit RUNTIME_FUNCTION entries.
 666   for (const auto &CFI : Streamer.getWinFrameInfos()) {
 667     MCSection *PData = Streamer.getAssociatedPDataSection(CFI->TextSection);
 668     Streamer.SwitchSection(PData);
 669     ARM64EmitRuntimeFunction(Streamer, CFI.get());
 670   }
 671 }
 672
 673 void llvm::Win64EH::ARM64UnwindEmitter::EmitUnwindInfo(
 674     MCStreamer &Streamer, WinEH::FrameInfo *info) const {
 675   // Switch sections (the static function above is meant to be called from
 676   // here and from Emit().
 677   MCSection *XData = Streamer.getAssociatedXDataSection(info->TextSection);
 678   Streamer.SwitchSection(XData);
 679   ARM64EmitUnwindInfo(Streamer, info);
 680 }