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1 //===----- JITDwarfEmitter.cpp - Write dwarf tables into memory -----------===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file defines a JITDwarfEmitter object that is used by the JIT to
11 // write dwarf tables to memory.
12 //
13 //===----------------------------------------------------------------------===//
14 
15 #include "JIT.h"
16 #include "JITDwarfEmitter.h"
17 #include "llvm/Function.h"
18 #include "llvm/ADT/DenseMap.h"
19 #include "llvm/CodeGen/JITCodeEmitter.h"
20 #include "llvm/CodeGen/MachineFunction.h"
21 #include "llvm/CodeGen/MachineModuleInfo.h"
22 #include "llvm/ExecutionEngine/JITMemoryManager.h"
23 #include "llvm/MC/MachineLocation.h"
24 #include "llvm/MC/MCAsmInfo.h"
25 #include "llvm/MC/MCSymbol.h"
26 #include "llvm/Support/ErrorHandling.h"
27 #include "llvm/Target/TargetData.h"
28 #include "llvm/Target/TargetInstrInfo.h"
29 #include "llvm/Target/TargetFrameLowering.h"
30 #include "llvm/Target/TargetMachine.h"
31 #include "llvm/Target/TargetRegisterInfo.h"
32 using namespace llvm;
33 
JITDwarfEmitter(JIT & theJit)34 JITDwarfEmitter::JITDwarfEmitter(JIT& theJit) : MMI(0), Jit(theJit) {}
35 
36 
EmitDwarfTable(MachineFunction & F,JITCodeEmitter & jce,unsigned char * StartFunction,unsigned char * EndFunction,unsigned char * & EHFramePtr)37 unsigned char* JITDwarfEmitter::EmitDwarfTable(MachineFunction& F,
38                                                JITCodeEmitter& jce,
39                                                unsigned char* StartFunction,
40                                                unsigned char* EndFunction,
41                                                unsigned char* &EHFramePtr) {
42   assert(MMI && "MachineModuleInfo not registered!");
43 
44   const TargetMachine& TM = F.getTarget();
45   TD = TM.getTargetData();
46   stackGrowthDirection = TM.getFrameLowering()->getStackGrowthDirection();
47   RI = TM.getRegisterInfo();
48   MAI = TM.getMCAsmInfo();
49   JCE = &jce;
50 
51   unsigned char* ExceptionTable = EmitExceptionTable(&F, StartFunction,
52                                                      EndFunction);
53 
54   unsigned char* Result = 0;
55 
56   const std::vector<const Function *> Personalities = MMI->getPersonalities();
57   EHFramePtr = EmitCommonEHFrame(Personalities[MMI->getPersonalityIndex()]);
58 
59   Result = EmitEHFrame(Personalities[MMI->getPersonalityIndex()], EHFramePtr,
60                        StartFunction, EndFunction, ExceptionTable);
61 
62   return Result;
63 }
64 
65 
66 void
EmitFrameMoves(intptr_t BaseLabelPtr,const std::vector<MachineMove> & Moves) const67 JITDwarfEmitter::EmitFrameMoves(intptr_t BaseLabelPtr,
68                                 const std::vector<MachineMove> &Moves) const {
69   unsigned PointerSize = TD->getPointerSize();
70   int stackGrowth = stackGrowthDirection == TargetFrameLowering::StackGrowsUp ?
71           PointerSize : -PointerSize;
72   MCSymbol *BaseLabel = 0;
73 
74   for (unsigned i = 0, N = Moves.size(); i < N; ++i) {
75     const MachineMove &Move = Moves[i];
76     MCSymbol *Label = Move.getLabel();
77 
78     // Throw out move if the label is invalid.
79     if (Label && (*JCE->getLabelLocations())[Label] == 0)
80       continue;
81 
82     intptr_t LabelPtr = 0;
83     if (Label) LabelPtr = JCE->getLabelAddress(Label);
84 
85     const MachineLocation &Dst = Move.getDestination();
86     const MachineLocation &Src = Move.getSource();
87 
88     // Advance row if new location.
89     if (BaseLabelPtr && Label && BaseLabel != Label) {
90       JCE->emitByte(dwarf::DW_CFA_advance_loc4);
91       JCE->emitInt32(LabelPtr - BaseLabelPtr);
92 
93       BaseLabel = Label;
94       BaseLabelPtr = LabelPtr;
95     }
96 
97     // If advancing cfa.
98     if (Dst.isReg() && Dst.getReg() == MachineLocation::VirtualFP) {
99       if (!Src.isReg()) {
100         if (Src.getReg() == MachineLocation::VirtualFP) {
101           JCE->emitByte(dwarf::DW_CFA_def_cfa_offset);
102         } else {
103           JCE->emitByte(dwarf::DW_CFA_def_cfa);
104           JCE->emitULEB128Bytes(RI->getDwarfRegNum(Src.getReg(), true));
105         }
106 
107         JCE->emitULEB128Bytes(-Src.getOffset());
108       } else {
109         llvm_unreachable("Machine move not supported yet.");
110       }
111     } else if (Src.isReg() &&
112       Src.getReg() == MachineLocation::VirtualFP) {
113       if (Dst.isReg()) {
114         JCE->emitByte(dwarf::DW_CFA_def_cfa_register);
115         JCE->emitULEB128Bytes(RI->getDwarfRegNum(Dst.getReg(), true));
116       } else {
117         llvm_unreachable("Machine move not supported yet.");
118       }
119     } else {
120       unsigned Reg = RI->getDwarfRegNum(Src.getReg(), true);
121       int Offset = Dst.getOffset() / stackGrowth;
122 
123       if (Offset < 0) {
124         JCE->emitByte(dwarf::DW_CFA_offset_extended_sf);
125         JCE->emitULEB128Bytes(Reg);
126         JCE->emitSLEB128Bytes(Offset);
127       } else if (Reg < 64) {
128         JCE->emitByte(dwarf::DW_CFA_offset + Reg);
129         JCE->emitULEB128Bytes(Offset);
130       } else {
131         JCE->emitByte(dwarf::DW_CFA_offset_extended);
132         JCE->emitULEB128Bytes(Reg);
133         JCE->emitULEB128Bytes(Offset);
134       }
135     }
136   }
137 }
138 
139 /// SharedTypeIds - How many leading type ids two landing pads have in common.
SharedTypeIds(const LandingPadInfo * L,const LandingPadInfo * R)140 static unsigned SharedTypeIds(const LandingPadInfo *L,
141                               const LandingPadInfo *R) {
142   const std::vector<int> &LIds = L->TypeIds, &RIds = R->TypeIds;
143   unsigned LSize = LIds.size(), RSize = RIds.size();
144   unsigned MinSize = LSize < RSize ? LSize : RSize;
145   unsigned Count = 0;
146 
147   for (; Count != MinSize; ++Count)
148     if (LIds[Count] != RIds[Count])
149       return Count;
150 
151   return Count;
152 }
153 
154 
155 /// PadLT - Order landing pads lexicographically by type id.
PadLT(const LandingPadInfo * L,const LandingPadInfo * R)156 static bool PadLT(const LandingPadInfo *L, const LandingPadInfo *R) {
157   const std::vector<int> &LIds = L->TypeIds, &RIds = R->TypeIds;
158   unsigned LSize = LIds.size(), RSize = RIds.size();
159   unsigned MinSize = LSize < RSize ? LSize : RSize;
160 
161   for (unsigned i = 0; i != MinSize; ++i)
162     if (LIds[i] != RIds[i])
163       return LIds[i] < RIds[i];
164 
165   return LSize < RSize;
166 }
167 
168 namespace {
169 
170 /// ActionEntry - Structure describing an entry in the actions table.
171 struct ActionEntry {
172   int ValueForTypeID; // The value to write - may not be equal to the type id.
173   int NextAction;
174   struct ActionEntry *Previous;
175 };
176 
177 /// PadRange - Structure holding a try-range and the associated landing pad.
178 struct PadRange {
179   // The index of the landing pad.
180   unsigned PadIndex;
181   // The index of the begin and end labels in the landing pad's label lists.
182   unsigned RangeIndex;
183 };
184 
185 typedef DenseMap<MCSymbol*, PadRange> RangeMapType;
186 
187 /// CallSiteEntry - Structure describing an entry in the call-site table.
188 struct CallSiteEntry {
189   MCSymbol *BeginLabel; // zero indicates the start of the function.
190   MCSymbol *EndLabel;   // zero indicates the end of the function.
191   MCSymbol *PadLabel;   // zero indicates that there is no landing pad.
192   unsigned Action;
193 };
194 
195 }
196 
EmitExceptionTable(MachineFunction * MF,unsigned char * StartFunction,unsigned char * EndFunction) const197 unsigned char* JITDwarfEmitter::EmitExceptionTable(MachineFunction* MF,
198                                          unsigned char* StartFunction,
199                                          unsigned char* EndFunction) const {
200   assert(MMI && "MachineModuleInfo not registered!");
201 
202   // Map all labels and get rid of any dead landing pads.
203   MMI->TidyLandingPads(JCE->getLabelLocations());
204 
205   const std::vector<const GlobalVariable *> &TypeInfos = MMI->getTypeInfos();
206   const std::vector<unsigned> &FilterIds = MMI->getFilterIds();
207   const std::vector<LandingPadInfo> &PadInfos = MMI->getLandingPads();
208   if (PadInfos.empty()) return 0;
209 
210   // Sort the landing pads in order of their type ids.  This is used to fold
211   // duplicate actions.
212   SmallVector<const LandingPadInfo *, 64> LandingPads;
213   LandingPads.reserve(PadInfos.size());
214   for (unsigned i = 0, N = PadInfos.size(); i != N; ++i)
215     LandingPads.push_back(&PadInfos[i]);
216   std::sort(LandingPads.begin(), LandingPads.end(), PadLT);
217 
218   // Negative type ids index into FilterIds, positive type ids index into
219   // TypeInfos.  The value written for a positive type id is just the type
220   // id itself.  For a negative type id, however, the value written is the
221   // (negative) byte offset of the corresponding FilterIds entry.  The byte
222   // offset is usually equal to the type id, because the FilterIds entries
223   // are written using a variable width encoding which outputs one byte per
224   // entry as long as the value written is not too large, but can differ.
225   // This kind of complication does not occur for positive type ids because
226   // type infos are output using a fixed width encoding.
227   // FilterOffsets[i] holds the byte offset corresponding to FilterIds[i].
228   SmallVector<int, 16> FilterOffsets;
229   FilterOffsets.reserve(FilterIds.size());
230   int Offset = -1;
231   for(std::vector<unsigned>::const_iterator I = FilterIds.begin(),
232     E = FilterIds.end(); I != E; ++I) {
233     FilterOffsets.push_back(Offset);
234     Offset -= MCAsmInfo::getULEB128Size(*I);
235   }
236 
237   // Compute the actions table and gather the first action index for each
238   // landing pad site.
239   SmallVector<ActionEntry, 32> Actions;
240   SmallVector<unsigned, 64> FirstActions;
241   FirstActions.reserve(LandingPads.size());
242 
243   int FirstAction = 0;
244   unsigned SizeActions = 0;
245   for (unsigned i = 0, N = LandingPads.size(); i != N; ++i) {
246     const LandingPadInfo *LP = LandingPads[i];
247     const std::vector<int> &TypeIds = LP->TypeIds;
248     const unsigned NumShared = i ? SharedTypeIds(LP, LandingPads[i-1]) : 0;
249     unsigned SizeSiteActions = 0;
250 
251     if (NumShared < TypeIds.size()) {
252       unsigned SizeAction = 0;
253       ActionEntry *PrevAction = 0;
254 
255       if (NumShared) {
256         const unsigned SizePrevIds = LandingPads[i-1]->TypeIds.size();
257         assert(Actions.size());
258         PrevAction = &Actions.back();
259         SizeAction = MCAsmInfo::getSLEB128Size(PrevAction->NextAction) +
260           MCAsmInfo::getSLEB128Size(PrevAction->ValueForTypeID);
261         for (unsigned j = NumShared; j != SizePrevIds; ++j) {
262           SizeAction -= MCAsmInfo::getSLEB128Size(PrevAction->ValueForTypeID);
263           SizeAction += -PrevAction->NextAction;
264           PrevAction = PrevAction->Previous;
265         }
266       }
267 
268       // Compute the actions.
269       for (unsigned I = NumShared, M = TypeIds.size(); I != M; ++I) {
270         int TypeID = TypeIds[I];
271         assert(-1-TypeID < (int)FilterOffsets.size() && "Unknown filter id!");
272         int ValueForTypeID = TypeID < 0 ? FilterOffsets[-1 - TypeID] : TypeID;
273         unsigned SizeTypeID = MCAsmInfo::getSLEB128Size(ValueForTypeID);
274 
275         int NextAction = SizeAction ? -(SizeAction + SizeTypeID) : 0;
276         SizeAction = SizeTypeID + MCAsmInfo::getSLEB128Size(NextAction);
277         SizeSiteActions += SizeAction;
278 
279         ActionEntry Action = {ValueForTypeID, NextAction, PrevAction};
280         Actions.push_back(Action);
281 
282         PrevAction = &Actions.back();
283       }
284 
285       // Record the first action of the landing pad site.
286       FirstAction = SizeActions + SizeSiteActions - SizeAction + 1;
287     } // else identical - re-use previous FirstAction
288 
289     FirstActions.push_back(FirstAction);
290 
291     // Compute this sites contribution to size.
292     SizeActions += SizeSiteActions;
293   }
294 
295   // Compute the call-site table.  Entries must be ordered by address.
296   SmallVector<CallSiteEntry, 64> CallSites;
297 
298   RangeMapType PadMap;
299   for (unsigned i = 0, N = LandingPads.size(); i != N; ++i) {
300     const LandingPadInfo *LandingPad = LandingPads[i];
301     for (unsigned j=0, E = LandingPad->BeginLabels.size(); j != E; ++j) {
302       MCSymbol *BeginLabel = LandingPad->BeginLabels[j];
303       assert(!PadMap.count(BeginLabel) && "Duplicate landing pad labels!");
304       PadRange P = { i, j };
305       PadMap[BeginLabel] = P;
306     }
307   }
308 
309   bool MayThrow = false;
310   MCSymbol *LastLabel = 0;
311   for (MachineFunction::const_iterator I = MF->begin(), E = MF->end();
312         I != E; ++I) {
313     for (MachineBasicBlock::const_iterator MI = I->begin(), E = I->end();
314           MI != E; ++MI) {
315       if (!MI->isLabel()) {
316         MayThrow |= MI->getDesc().isCall();
317         continue;
318       }
319 
320       MCSymbol *BeginLabel = MI->getOperand(0).getMCSymbol();
321       assert(BeginLabel && "Invalid label!");
322 
323       if (BeginLabel == LastLabel)
324         MayThrow = false;
325 
326       RangeMapType::iterator L = PadMap.find(BeginLabel);
327 
328       if (L == PadMap.end())
329         continue;
330 
331       PadRange P = L->second;
332       const LandingPadInfo *LandingPad = LandingPads[P.PadIndex];
333 
334       assert(BeginLabel == LandingPad->BeginLabels[P.RangeIndex] &&
335               "Inconsistent landing pad map!");
336 
337       // If some instruction between the previous try-range and this one may
338       // throw, create a call-site entry with no landing pad for the region
339       // between the try-ranges.
340       if (MayThrow) {
341         CallSiteEntry Site = {LastLabel, BeginLabel, 0, 0};
342         CallSites.push_back(Site);
343       }
344 
345       LastLabel = LandingPad->EndLabels[P.RangeIndex];
346       CallSiteEntry Site = {BeginLabel, LastLabel,
347         LandingPad->LandingPadLabel, FirstActions[P.PadIndex]};
348 
349       assert(Site.BeginLabel && Site.EndLabel && Site.PadLabel &&
350               "Invalid landing pad!");
351 
352       // Try to merge with the previous call-site.
353       if (CallSites.size()) {
354         CallSiteEntry &Prev = CallSites.back();
355         if (Site.PadLabel == Prev.PadLabel && Site.Action == Prev.Action) {
356           // Extend the range of the previous entry.
357           Prev.EndLabel = Site.EndLabel;
358           continue;
359         }
360       }
361 
362       // Otherwise, create a new call-site.
363       CallSites.push_back(Site);
364     }
365   }
366   // If some instruction between the previous try-range and the end of the
367   // function may throw, create a call-site entry with no landing pad for the
368   // region following the try-range.
369   if (MayThrow) {
370     CallSiteEntry Site = {LastLabel, 0, 0, 0};
371     CallSites.push_back(Site);
372   }
373 
374   // Final tallies.
375   unsigned SizeSites = CallSites.size() * (sizeof(int32_t) + // Site start.
376                                             sizeof(int32_t) + // Site length.
377                                             sizeof(int32_t)); // Landing pad.
378   for (unsigned i = 0, e = CallSites.size(); i < e; ++i)
379     SizeSites += MCAsmInfo::getULEB128Size(CallSites[i].Action);
380 
381   unsigned SizeTypes = TypeInfos.size() * TD->getPointerSize();
382 
383   unsigned TypeOffset = sizeof(int8_t) + // Call site format
384                         // Call-site table length
385                         MCAsmInfo::getULEB128Size(SizeSites) +
386                         SizeSites + SizeActions + SizeTypes;
387 
388   // Begin the exception table.
389   JCE->emitAlignmentWithFill(4, 0);
390   // Asm->EOL("Padding");
391 
392   unsigned char* DwarfExceptionTable = (unsigned char*)JCE->getCurrentPCValue();
393 
394   // Emit the header.
395   JCE->emitByte(dwarf::DW_EH_PE_omit);
396   // Asm->EOL("LPStart format (DW_EH_PE_omit)");
397   JCE->emitByte(dwarf::DW_EH_PE_absptr);
398   // Asm->EOL("TType format (DW_EH_PE_absptr)");
399   JCE->emitULEB128Bytes(TypeOffset);
400   // Asm->EOL("TType base offset");
401   JCE->emitByte(dwarf::DW_EH_PE_udata4);
402   // Asm->EOL("Call site format (DW_EH_PE_udata4)");
403   JCE->emitULEB128Bytes(SizeSites);
404   // Asm->EOL("Call-site table length");
405 
406   // Emit the landing pad site information.
407   for (unsigned i = 0; i < CallSites.size(); ++i) {
408     CallSiteEntry &S = CallSites[i];
409     intptr_t BeginLabelPtr = 0;
410     intptr_t EndLabelPtr = 0;
411 
412     if (!S.BeginLabel) {
413       BeginLabelPtr = (intptr_t)StartFunction;
414       JCE->emitInt32(0);
415     } else {
416       BeginLabelPtr = JCE->getLabelAddress(S.BeginLabel);
417       JCE->emitInt32(BeginLabelPtr - (intptr_t)StartFunction);
418     }
419 
420     // Asm->EOL("Region start");
421 
422     if (!S.EndLabel)
423       EndLabelPtr = (intptr_t)EndFunction;
424     else
425       EndLabelPtr = JCE->getLabelAddress(S.EndLabel);
426 
427     JCE->emitInt32(EndLabelPtr - BeginLabelPtr);
428     //Asm->EOL("Region length");
429 
430     if (!S.PadLabel) {
431       JCE->emitInt32(0);
432     } else {
433       unsigned PadLabelPtr = JCE->getLabelAddress(S.PadLabel);
434       JCE->emitInt32(PadLabelPtr - (intptr_t)StartFunction);
435     }
436     // Asm->EOL("Landing pad");
437 
438     JCE->emitULEB128Bytes(S.Action);
439     // Asm->EOL("Action");
440   }
441 
442   // Emit the actions.
443   for (unsigned I = 0, N = Actions.size(); I != N; ++I) {
444     ActionEntry &Action = Actions[I];
445 
446     JCE->emitSLEB128Bytes(Action.ValueForTypeID);
447     //Asm->EOL("TypeInfo index");
448     JCE->emitSLEB128Bytes(Action.NextAction);
449     //Asm->EOL("Next action");
450   }
451 
452   // Emit the type ids.
453   for (unsigned M = TypeInfos.size(); M; --M) {
454     const GlobalVariable *GV = TypeInfos[M - 1];
455 
456     if (GV) {
457       if (TD->getPointerSize() == sizeof(int32_t))
458         JCE->emitInt32((intptr_t)Jit.getOrEmitGlobalVariable(GV));
459       else
460         JCE->emitInt64((intptr_t)Jit.getOrEmitGlobalVariable(GV));
461     } else {
462       if (TD->getPointerSize() == sizeof(int32_t))
463         JCE->emitInt32(0);
464       else
465         JCE->emitInt64(0);
466     }
467     // Asm->EOL("TypeInfo");
468   }
469 
470   // Emit the filter typeids.
471   for (unsigned j = 0, M = FilterIds.size(); j < M; ++j) {
472     unsigned TypeID = FilterIds[j];
473     JCE->emitULEB128Bytes(TypeID);
474     //Asm->EOL("Filter TypeInfo index");
475   }
476 
477   JCE->emitAlignmentWithFill(4, 0);
478 
479   return DwarfExceptionTable;
480 }
481 
482 unsigned char*
EmitCommonEHFrame(const Function * Personality) const483 JITDwarfEmitter::EmitCommonEHFrame(const Function* Personality) const {
484   unsigned PointerSize = TD->getPointerSize();
485   int stackGrowth = stackGrowthDirection == TargetFrameLowering::StackGrowsUp ?
486           PointerSize : -PointerSize;
487 
488   unsigned char* StartCommonPtr = (unsigned char*)JCE->getCurrentPCValue();
489   // EH Common Frame header
490   JCE->allocateSpace(4, 0);
491   unsigned char* FrameCommonBeginPtr = (unsigned char*)JCE->getCurrentPCValue();
492   JCE->emitInt32((int)0);
493   JCE->emitByte(dwarf::DW_CIE_VERSION);
494   JCE->emitString(Personality ? "zPLR" : "zR");
495   JCE->emitULEB128Bytes(1);
496   JCE->emitSLEB128Bytes(stackGrowth);
497   JCE->emitByte(RI->getDwarfRegNum(RI->getRARegister(), true));
498 
499   if (Personality) {
500     // Augmentation Size: 3 small ULEBs of one byte each, and the personality
501     // function which size is PointerSize.
502     JCE->emitULEB128Bytes(3 + PointerSize);
503 
504     // We set the encoding of the personality as direct encoding because we use
505     // the function pointer. The encoding is not relative because the current
506     // PC value may be bigger than the personality function pointer.
507     if (PointerSize == 4) {
508       JCE->emitByte(dwarf::DW_EH_PE_sdata4);
509       JCE->emitInt32(((intptr_t)Jit.getPointerToGlobal(Personality)));
510     } else {
511       JCE->emitByte(dwarf::DW_EH_PE_sdata8);
512       JCE->emitInt64(((intptr_t)Jit.getPointerToGlobal(Personality)));
513     }
514 
515     // LSDA encoding: This must match the encoding used in EmitEHFrame ()
516     if (PointerSize == 4)
517       JCE->emitULEB128Bytes(dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4);
518     else
519       JCE->emitULEB128Bytes(dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata8);
520     JCE->emitULEB128Bytes(dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4);
521   } else {
522     JCE->emitULEB128Bytes(1);
523     JCE->emitULEB128Bytes(dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4);
524   }
525 
526   EmitFrameMoves(0, MAI->getInitialFrameState());
527 
528   JCE->emitAlignmentWithFill(PointerSize, dwarf::DW_CFA_nop);
529 
530   JCE->emitInt32At((uintptr_t*)StartCommonPtr,
531                    (uintptr_t)((unsigned char*)JCE->getCurrentPCValue() -
532                                FrameCommonBeginPtr));
533 
534   return StartCommonPtr;
535 }
536 
537 
538 unsigned char*
EmitEHFrame(const Function * Personality,unsigned char * StartCommonPtr,unsigned char * StartFunction,unsigned char * EndFunction,unsigned char * ExceptionTable) const539 JITDwarfEmitter::EmitEHFrame(const Function* Personality,
540                              unsigned char* StartCommonPtr,
541                              unsigned char* StartFunction,
542                              unsigned char* EndFunction,
543                              unsigned char* ExceptionTable) const {
544   unsigned PointerSize = TD->getPointerSize();
545 
546   // EH frame header.
547   unsigned char* StartEHPtr = (unsigned char*)JCE->getCurrentPCValue();
548   JCE->allocateSpace(4, 0);
549   unsigned char* FrameBeginPtr = (unsigned char*)JCE->getCurrentPCValue();
550   // FDE CIE Offset
551   JCE->emitInt32(FrameBeginPtr - StartCommonPtr);
552   JCE->emitInt32(StartFunction - (unsigned char*)JCE->getCurrentPCValue());
553   JCE->emitInt32(EndFunction - StartFunction);
554 
555   // If there is a personality and landing pads then point to the language
556   // specific data area in the exception table.
557   if (Personality) {
558     JCE->emitULEB128Bytes(PointerSize == 4 ? 4 : 8);
559 
560     if (PointerSize == 4) {
561       if (!MMI->getLandingPads().empty())
562         JCE->emitInt32(ExceptionTable-(unsigned char*)JCE->getCurrentPCValue());
563       else
564         JCE->emitInt32((int)0);
565     } else {
566       if (!MMI->getLandingPads().empty())
567         JCE->emitInt64(ExceptionTable-(unsigned char*)JCE->getCurrentPCValue());
568       else
569         JCE->emitInt64((int)0);
570     }
571   } else {
572     JCE->emitULEB128Bytes(0);
573   }
574 
575   // Indicate locations of function specific  callee saved registers in
576   // frame.
577   EmitFrameMoves((intptr_t)StartFunction, MMI->getFrameMoves());
578 
579   JCE->emitAlignmentWithFill(PointerSize, dwarf::DW_CFA_nop);
580 
581   // Indicate the size of the table
582   JCE->emitInt32At((uintptr_t*)StartEHPtr,
583                    (uintptr_t)((unsigned char*)JCE->getCurrentPCValue() -
584                                StartEHPtr));
585 
586   // Double zeroes for the unwind runtime
587   if (PointerSize == 8) {
588     JCE->emitInt64(0);
589     JCE->emitInt64(0);
590   } else {
591     JCE->emitInt32(0);
592     JCE->emitInt32(0);
593   }
594 
595   return StartEHPtr;
596 }
597