xref: /freebsd/contrib/llvm-project/llvm/lib/MC/MCWin64EH.cpp (revision 7877fdebeeb35fad1cbbafce22598b1bdf97c786) 
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.emitInt8(b2);
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.emitInt8(b2);
79       w = inst.Offset & 0xFFF8;
80       streamer.emitInt16(w);
81       w = inst.Offset >> 16;
82     } else {
83       streamer.emitInt8(b2);
84       w = inst.Offset >> 3;
85     }
86     streamer.emitInt16(w);
87     break;
88   case Win64EH::UOP_AllocSmall:
89     b2 |= (((inst.Offset - 8) >> 3) & 0x0F) << 4;
90     EmitAbsDifference(streamer, inst.Label, begin);
91     streamer.emitInt8(b2);
92     break;
93   case Win64EH::UOP_SetFPReg:
94     EmitAbsDifference(streamer, inst.Label, begin);
95     streamer.emitInt8(b2);
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.emitInt8(b2);
102     w = inst.Offset >> 3;
103     if (inst.Operation == Win64EH::UOP_SaveXMM128)
104       w >>= 1;
105     streamer.emitInt16(w);
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.emitInt8(b2);
112     if (inst.Operation == Win64EH::UOP_SaveXMM128Big)
113       w = inst.Offset & 0xFFF0;
114     else
115       w = inst.Offset & 0xFFF8;
116     streamer.emitInt16(w);
117     w = inst.Offset >> 16;
118     streamer.emitInt16(w);
119     break;
120   case Win64EH::UOP_PushMachFrame:
121     if (inst.Offset == 1)
122       b2 |= 0x10;
123     EmitAbsDifference(streamer, inst.Label, begin);
124     streamer.emitInt8(b2);
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.emitInt8(flags);
177 
178   if (info->PrologEnd)
179     EmitAbsDifference(streamer, info->PrologEnd, info->Begin);
180   else
181     streamer.emitInt8(0);
182 
183   uint8_t numCodes = CountOfUnwindCodes(info->Instructions);
184   streamer.emitInt8(numCodes);
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.emitInt8(frame);
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.emitInt16(0);
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.emitInt32(0);
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.emitInt8(b);
341     break;
342   case Win64EH::UOP_AllocMedium: {
343     uint16_t hw = (inst.Offset >> 4) & 0x7FF;
344     b = 0xC0;
345     b |= (hw >> 8);
346     streamer.emitInt8(b);
347     b = hw & 0xFF;
348     streamer.emitInt8(b);
349     break;
350   }
351   case Win64EH::UOP_AllocLarge: {
352     uint32_t w;
353     b = 0xE0;
354     streamer.emitInt8(b);
355     w = inst.Offset >> 4;
356     b = (w & 0x00FF0000) >> 16;
357     streamer.emitInt8(b);
358     b = (w & 0x0000FF00) >> 8;
359     streamer.emitInt8(b);
360     b = w & 0x000000FF;
361     streamer.emitInt8(b);
362     break;
363   }
364   case Win64EH::UOP_SetFP:
365     b = 0xE1;
366     streamer.emitInt8(b);
367     break;
368   case Win64EH::UOP_AddFP:
369     b = 0xE2;
370     streamer.emitInt8(b);
371     b = (inst.Offset >> 3);
372     streamer.emitInt8(b);
373     break;
374   case Win64EH::UOP_Nop:
375     b = 0xE3;
376     streamer.emitInt8(b);
377     break;
378   case Win64EH::UOP_SaveFPLRX:
379     b = 0x80;
380     b |= ((inst.Offset - 1) >> 3) & 0x3F;
381     streamer.emitInt8(b);
382     break;
383   case Win64EH::UOP_SaveFPLR:
384     b = 0x40;
385     b |= (inst.Offset >> 3) & 0x3F;
386     streamer.emitInt8(b);
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.emitInt8(b);
393     b = ((reg & 0x3) << 6) | (inst.Offset >> 3);
394     streamer.emitInt8(b);
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.emitInt8(b);
401     b = ((reg & 0x7) << 5) | ((inst.Offset >> 3) - 1);
402     streamer.emitInt8(b);
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.emitInt8(b);
409     b = ((reg & 0x3) << 6) | (inst.Offset >> 3);
410     streamer.emitInt8(b);
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.emitInt8(b);
417     b = ((reg & 0x3) << 6) | ((inst.Offset >> 3) - 1);
418     streamer.emitInt8(b);
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.emitInt8(b);
425     b = ((reg & 0x3) << 6) | (inst.Offset >> 3);
426     streamer.emitInt8(b);
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.emitInt8(b);
433     b = ((reg & 0x7) << 5) | ((inst.Offset >> 3) - 1);
434     streamer.emitInt8(b);
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.emitInt8(b);
441     b = ((reg & 0x3) << 6) | (inst.Offset >> 3);
442     streamer.emitInt8(b);
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.emitInt8(b);
449     b = ((reg & 0x3) << 6) | ((inst.Offset >> 3) - 1);
450     streamer.emitInt8(b);
451     break;
452   case Win64EH::UOP_End:
453     b = 0xE4;
454     streamer.emitInt8(b);
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.emitInt32(row1);
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.emitInt32(row2);
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.emitInt32(row3);
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.emitInt8(0xE3);
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 }
681