1 //===-- CodeGen/AsmPrinter/DwarfException.cpp - Dwarf Exception Impl ------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file contains support for writing DWARF exception info into asm files.
12 //===----------------------------------------------------------------------===//
14 #include "DwarfException.h"
15 #include "llvm/Module.h"
16 #include "llvm/CodeGen/MachineModuleInfo.h"
17 #include "llvm/CodeGen/MachineFrameInfo.h"
18 #include "llvm/CodeGen/MachineFunction.h"
19 #include "llvm/CodeGen/MachineLocation.h"
20 #include "llvm/MC/MCAsmInfo.h"
21 #include "llvm/MC/MCContext.h"
22 #include "llvm/MC/MCExpr.h"
23 #include "llvm/MC/MCSection.h"
24 #include "llvm/MC/MCStreamer.h"
25 #include "llvm/Target/TargetData.h"
26 #include "llvm/Target/TargetFrameInfo.h"
27 #include "llvm/Target/TargetLoweringObjectFile.h"
28 #include "llvm/Target/TargetOptions.h"
29 #include "llvm/Target/TargetRegisterInfo.h"
30 #include "llvm/Support/Dwarf.h"
31 #include "llvm/Support/Mangler.h"
32 #include "llvm/Support/Timer.h"
33 #include "llvm/Support/raw_ostream.h"
34 #include "llvm/ADT/SmallString.h"
35 #include "llvm/ADT/StringExtras.h"
38 static TimerGroup &getDwarfTimerGroup() {
39 static TimerGroup DwarfTimerGroup("DWARF Exception");
40 return DwarfTimerGroup;
43 DwarfException::DwarfException(raw_ostream &OS, AsmPrinter *A,
45 : Dwarf(OS, A, T, "eh"), shouldEmitTable(false), shouldEmitMoves(false),
46 shouldEmitTableModule(false), shouldEmitMovesModule(false),
48 if (TimePassesIsEnabled)
49 ExceptionTimer = new Timer("DWARF Exception Writer",
50 getDwarfTimerGroup());
53 DwarfException::~DwarfException() {
54 delete ExceptionTimer;
57 /// SizeOfEncodedValue - Return the size of the encoding in bytes.
58 unsigned DwarfException::SizeOfEncodedValue(unsigned Encoding) {
59 if (Encoding == dwarf::DW_EH_PE_omit)
62 switch (Encoding & 0x07) {
63 case dwarf::DW_EH_PE_absptr:
64 return TD->getPointerSize();
65 case dwarf::DW_EH_PE_udata2:
67 case dwarf::DW_EH_PE_udata4:
69 case dwarf::DW_EH_PE_udata8:
73 assert(0 && "Invalid encoded value.");
77 /// EmitCIE - Emit a Common Information Entry (CIE). This holds information that
78 /// is shared among many Frame Description Entries. There is at least one CIE
79 /// in every non-empty .debug_frame section.
80 void DwarfException::EmitCIE(const Function *PersonalityFn, unsigned Index) {
81 // Size and sign of stack growth.
83 Asm->TM.getFrameInfo()->getStackGrowthDirection() ==
84 TargetFrameInfo::StackGrowsUp ?
85 TD->getPointerSize() : -TD->getPointerSize();
87 const TargetLoweringObjectFile &TLOF = Asm->getObjFileLowering();
89 // Begin eh frame section.
90 Asm->OutStreamer.SwitchSection(TLOF.getEHFrameSection());
92 if (MAI->is_EHSymbolPrivate())
93 O << MAI->getPrivateGlobalPrefix();
94 O << "EH_frame" << Index << ":\n";
96 EmitLabel("section_eh_frame", Index);
98 // Define base labels.
99 EmitLabel("eh_frame_common", Index);
101 // Define the eh frame length.
102 EmitDifference("eh_frame_common_end", Index,
103 "eh_frame_common_begin", Index, true);
104 Asm->EOL("Length of Common Information Entry");
107 EmitLabel("eh_frame_common_begin", Index);
108 Asm->EmitInt32((int)0);
109 Asm->EOL("CIE Identifier Tag");
110 Asm->EmitInt8(dwarf::DW_CIE_VERSION);
111 Asm->EOL("CIE Version");
113 // The personality presence indicates that language specific information will
114 // show up in the eh frame. Find out how we are supposed to lower the
115 // personality function reference:
116 const MCExpr *PersonalityRef = 0;
117 bool IsPersonalityIndirect = false, IsPersonalityPCRel = false;
119 // FIXME: HANDLE STATIC CODEGEN MODEL HERE.
121 // In non-static mode, ask the object file how to represent this reference.
123 TLOF.getSymbolForDwarfGlobalReference(PersonalityFn, Asm->Mang,
125 IsPersonalityIndirect,
129 unsigned PerEncoding = dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4;
130 if (IsPersonalityIndirect)
131 PerEncoding |= dwarf::DW_EH_PE_indirect;
132 unsigned LSDAEncoding = dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4;
133 unsigned FDEEncoding = dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4;
135 char Augmentation[5] = { 0 };
136 unsigned AugmentationSize = 0;
137 char *APtr = Augmentation + 1;
139 if (PersonalityRef) {
140 // There is a personality function.
142 AugmentationSize += 1 + SizeOfEncodedValue(PerEncoding);
145 if (UsesLSDA[Index]) {
146 // An LSDA pointer is in the FDE augmentation.
151 if (FDEEncoding != dwarf::DW_EH_PE_absptr) {
152 // A non-default pointer encoding for the FDE.
157 if (APtr != Augmentation + 1)
158 Augmentation[0] = 'z';
160 Asm->EmitString(Augmentation);
161 Asm->EOL("CIE Augmentation");
164 Asm->EmitULEB128Bytes(1);
165 Asm->EOL("CIE Code Alignment Factor");
166 Asm->EmitSLEB128Bytes(stackGrowth);
167 Asm->EOL("CIE Data Alignment Factor");
168 Asm->EmitInt8(RI->getDwarfRegNum(RI->getRARegister(), true));
169 Asm->EOL("CIE Return Address Column");
171 Asm->EmitULEB128Bytes(AugmentationSize);
172 Asm->EOL("Augmentation Size");
174 Asm->EmitInt8(PerEncoding);
175 Asm->EOL("Personality", PerEncoding);
177 // If there is a personality, we need to indicate the function's location.
178 if (PersonalityRef) {
179 // If the reference to the personality function symbol is not already
180 // pc-relative, then we need to subtract our current address from it. Do
181 // this by emitting a label and subtracting it from the expression we
182 // already have. This is equivalent to emitting "foo - .", but we have to
183 // emit the label for "." directly.
184 if (!IsPersonalityPCRel) {
185 SmallString<64> Name;
186 raw_svector_ostream(Name) << MAI->getPrivateGlobalPrefix()
187 << "personalityref_addr" << Asm->getFunctionNumber() << "_" << Index;
188 MCSymbol *DotSym = Asm->OutContext.GetOrCreateSymbol(Name.str());
189 Asm->OutStreamer.EmitLabel(DotSym);
192 MCBinaryExpr::CreateSub(PersonalityRef,
193 MCSymbolRefExpr::Create(DotSym,Asm->OutContext),
197 O << MAI->getData32bitsDirective();
198 PersonalityRef->print(O, MAI);
199 Asm->EOL("Personality");
201 Asm->EmitInt8(LSDAEncoding);
202 Asm->EOL("LSDA Encoding", LSDAEncoding);
204 Asm->EmitInt8(FDEEncoding);
205 Asm->EOL("FDE Encoding", FDEEncoding);
208 // Indicate locations of general callee saved registers in frame.
209 std::vector<MachineMove> Moves;
210 RI->getInitialFrameState(Moves);
211 EmitFrameMoves(NULL, 0, Moves, true);
213 // On Darwin the linker honors the alignment of eh_frame, which means it must
214 // be 8-byte on 64-bit targets to match what gcc does. Otherwise you get
215 // holes which confuse readers of eh_frame.
216 Asm->EmitAlignment(TD->getPointerSize() == 4 ? 2 : 3, 0, 0, false);
217 EmitLabel("eh_frame_common_end", Index);
222 /// EmitFDE - Emit the Frame Description Entry (FDE) for the function.
223 void DwarfException::EmitFDE(const FunctionEHFrameInfo &EHFrameInfo) {
224 assert(!EHFrameInfo.function->hasAvailableExternallyLinkage() &&
225 "Should not emit 'available externally' functions at all");
227 const Function *TheFunc = EHFrameInfo.function;
229 Asm->OutStreamer.SwitchSection(Asm->getObjFileLowering().getEHFrameSection());
231 // Externally visible entry into the functions eh frame info. If the
232 // corresponding function is static, this should not be externally visible.
233 if (!TheFunc->hasLocalLinkage())
234 if (const char *GlobalEHDirective = MAI->getGlobalEHDirective())
235 O << GlobalEHDirective << EHFrameInfo.FnName << "\n";
237 // If corresponding function is weak definition, this should be too.
238 if (TheFunc->isWeakForLinker() && MAI->getWeakDefDirective())
239 O << MAI->getWeakDefDirective() << EHFrameInfo.FnName << "\n";
241 // If there are no calls then you can't unwind. This may mean we can omit the
242 // EH Frame, but some environments do not handle weak absolute symbols. If
243 // UnwindTablesMandatory is set we cannot do this optimization; the unwind
244 // info is to be available for non-EH uses.
245 if (!EHFrameInfo.hasCalls && !UnwindTablesMandatory &&
246 (!TheFunc->isWeakForLinker() ||
247 !MAI->getWeakDefDirective() ||
248 MAI->getSupportsWeakOmittedEHFrame())) {
249 O << EHFrameInfo.FnName << " = 0\n";
250 // This name has no connection to the function, so it might get
251 // dead-stripped when the function is not, erroneously. Prohibit
252 // dead-stripping unconditionally.
253 if (const char *UsedDirective = MAI->getUsedDirective())
254 O << UsedDirective << EHFrameInfo.FnName << "\n\n";
256 O << EHFrameInfo.FnName << ":\n";
259 EmitDifference("eh_frame_end", EHFrameInfo.Number,
260 "eh_frame_begin", EHFrameInfo.Number, true);
261 Asm->EOL("Length of Frame Information Entry");
263 EmitLabel("eh_frame_begin", EHFrameInfo.Number);
265 EmitSectionOffset("eh_frame_begin", "eh_frame_common",
266 EHFrameInfo.Number, EHFrameInfo.PersonalityIndex,
269 Asm->EOL("FDE CIE offset");
271 EmitReference("eh_func_begin", EHFrameInfo.Number, true, true);
272 Asm->EOL("FDE initial location");
273 EmitDifference("eh_func_end", EHFrameInfo.Number,
274 "eh_func_begin", EHFrameInfo.Number, true);
275 Asm->EOL("FDE address range");
277 // If there is a personality and landing pads then point to the language
278 // specific data area in the exception table.
279 if (MMI->getPersonalities()[0] != NULL) {
280 bool is4Byte = TD->getPointerSize() == sizeof(int32_t);
282 Asm->EmitULEB128Bytes(is4Byte ? 4 : 8);
283 Asm->EOL("Augmentation size");
285 if (EHFrameInfo.hasLandingPads)
286 EmitReference("exception", EHFrameInfo.Number, true, false);
289 Asm->EmitInt32((int)0);
291 Asm->EmitInt64((int)0);
293 Asm->EOL("Language Specific Data Area");
295 Asm->EmitULEB128Bytes(0);
296 Asm->EOL("Augmentation size");
299 // Indicate locations of function specific callee saved registers in frame.
300 EmitFrameMoves("eh_func_begin", EHFrameInfo.Number, EHFrameInfo.Moves,
303 // On Darwin the linker honors the alignment of eh_frame, which means it
304 // must be 8-byte on 64-bit targets to match what gcc does. Otherwise you
305 // get holes which confuse readers of eh_frame.
306 Asm->EmitAlignment(TD->getPointerSize() == sizeof(int32_t) ? 2 : 3,
308 EmitLabel("eh_frame_end", EHFrameInfo.Number);
310 // If the function is marked used, this table should be also. We cannot
311 // make the mark unconditional in this case, since retaining the table also
312 // retains the function in this case, and there is code around that depends
313 // on unused functions (calling undefined externals) being dead-stripped to
314 // link correctly. Yes, there really is.
315 if (MMI->isUsedFunction(EHFrameInfo.function))
316 if (const char *UsedDirective = MAI->getUsedDirective())
317 O << UsedDirective << EHFrameInfo.FnName << "\n\n";
323 /// SharedTypeIds - How many leading type ids two landing pads have in common.
324 unsigned DwarfException::SharedTypeIds(const LandingPadInfo *L,
325 const LandingPadInfo *R) {
326 const std::vector<int> &LIds = L->TypeIds, &RIds = R->TypeIds;
327 unsigned LSize = LIds.size(), RSize = RIds.size();
328 unsigned MinSize = LSize < RSize ? LSize : RSize;
331 for (; Count != MinSize; ++Count)
332 if (LIds[Count] != RIds[Count])
338 /// PadLT - Order landing pads lexicographically by type id.
339 bool DwarfException::PadLT(const LandingPadInfo *L, const LandingPadInfo *R) {
340 const std::vector<int> &LIds = L->TypeIds, &RIds = R->TypeIds;
341 unsigned LSize = LIds.size(), RSize = RIds.size();
342 unsigned MinSize = LSize < RSize ? LSize : RSize;
344 for (unsigned i = 0; i != MinSize; ++i)
345 if (LIds[i] != RIds[i])
346 return LIds[i] < RIds[i];
348 return LSize < RSize;
351 /// ComputeActionsTable - Compute the actions table and gather the first action
352 /// index for each landing pad site.
353 unsigned DwarfException::
354 ComputeActionsTable(const SmallVectorImpl<const LandingPadInfo*> &LandingPads,
355 SmallVectorImpl<ActionEntry> &Actions,
356 SmallVectorImpl<unsigned> &FirstActions) {
358 // The action table follows the call-site table in the LSDA. The individual
359 // records are of two types:
362 // * Exception specification
364 // The two record kinds have the same format, with only small differences.
365 // They are distinguished by the "switch value" field: Catch clauses
366 // (TypeInfos) have strictly positive switch values, and exception
367 // specifications (FilterIds) have strictly negative switch values. Value 0
368 // indicates a catch-all clause.
370 // Negative type IDs index into FilterIds. Positive type IDs index into
371 // TypeInfos. The value written for a positive type ID is just the type ID
372 // itself. For a negative type ID, however, the value written is the
373 // (negative) byte offset of the corresponding FilterIds entry. The byte
374 // offset is usually equal to the type ID (because the FilterIds entries are
375 // written using a variable width encoding, which outputs one byte per entry
376 // as long as the value written is not too large) but can differ. This kind
377 // of complication does not occur for positive type IDs because type infos are
378 // output using a fixed width encoding. FilterOffsets[i] holds the byte
379 // offset corresponding to FilterIds[i].
381 const std::vector<unsigned> &FilterIds = MMI->getFilterIds();
382 SmallVector<int, 16> FilterOffsets;
383 FilterOffsets.reserve(FilterIds.size());
386 for (std::vector<unsigned>::const_iterator
387 I = FilterIds.begin(), E = FilterIds.end(); I != E; ++I) {
388 FilterOffsets.push_back(Offset);
389 Offset -= MCAsmInfo::getULEB128Size(*I);
392 FirstActions.reserve(LandingPads.size());
395 unsigned SizeActions = 0;
396 const LandingPadInfo *PrevLPI = 0;
398 for (SmallVectorImpl<const LandingPadInfo *>::const_iterator
399 I = LandingPads.begin(), E = LandingPads.end(); I != E; ++I) {
400 const LandingPadInfo *LPI = *I;
401 const std::vector<int> &TypeIds = LPI->TypeIds;
402 const unsigned NumShared = PrevLPI ? SharedTypeIds(LPI, PrevLPI) : 0;
403 unsigned SizeSiteActions = 0;
405 if (NumShared < TypeIds.size()) {
406 unsigned SizeAction = 0;
407 ActionEntry *PrevAction = 0;
410 const unsigned SizePrevIds = PrevLPI->TypeIds.size();
411 assert(Actions.size());
412 PrevAction = &Actions.back();
413 SizeAction = MCAsmInfo::getSLEB128Size(PrevAction->NextAction) +
414 MCAsmInfo::getSLEB128Size(PrevAction->ValueForTypeID);
416 for (unsigned j = NumShared; j != SizePrevIds; ++j) {
418 MCAsmInfo::getSLEB128Size(PrevAction->ValueForTypeID);
419 SizeAction += -PrevAction->NextAction;
420 PrevAction = PrevAction->Previous;
424 // Compute the actions.
425 for (unsigned J = NumShared, M = TypeIds.size(); J != M; ++J) {
426 int TypeID = TypeIds[J];
427 assert(-1 - TypeID < (int)FilterOffsets.size() && "Unknown filter id!");
428 int ValueForTypeID = TypeID < 0 ? FilterOffsets[-1 - TypeID] : TypeID;
429 unsigned SizeTypeID = MCAsmInfo::getSLEB128Size(ValueForTypeID);
431 int NextAction = SizeAction ? -(SizeAction + SizeTypeID) : 0;
432 SizeAction = SizeTypeID + MCAsmInfo::getSLEB128Size(NextAction);
433 SizeSiteActions += SizeAction;
435 ActionEntry Action = { ValueForTypeID, NextAction, PrevAction };
436 Actions.push_back(Action);
437 PrevAction = &Actions.back();
440 // Record the first action of the landing pad site.
441 FirstAction = SizeActions + SizeSiteActions - SizeAction + 1;
442 } // else identical - re-use previous FirstAction
444 // Information used when created the call-site table. The action record
445 // field of the call site record is the offset of the first associated
446 // action record, relative to the start of the actions table. This value is
447 // biased by 1 (1 in dicating the start of the actions table), and 0
448 // indicates that there are no actions.
449 FirstActions.push_back(FirstAction);
451 // Compute this sites contribution to size.
452 SizeActions += SizeSiteActions;
460 /// ComputeCallSiteTable - Compute the call-site table. The entry for an invoke
461 /// has a try-range containing the call, a non-zero landing pad, and an
462 /// appropriate action. The entry for an ordinary call has a try-range
463 /// containing the call and zero for the landing pad and the action. Calls
464 /// marked 'nounwind' have no entry and must not be contained in the try-range
465 /// of any entry - they form gaps in the table. Entries must be ordered by
466 /// try-range address.
467 void DwarfException::
468 ComputeCallSiteTable(SmallVectorImpl<CallSiteEntry> &CallSites,
469 const RangeMapType &PadMap,
470 const SmallVectorImpl<const LandingPadInfo *> &LandingPads,
471 const SmallVectorImpl<unsigned> &FirstActions) {
472 // The end label of the previous invoke or nounwind try-range.
473 unsigned LastLabel = 0;
475 // Whether there is a potentially throwing instruction (currently this means
476 // an ordinary call) between the end of the previous try-range and now.
477 bool SawPotentiallyThrowing = false;
479 // Whether the last CallSite entry was for an invoke.
480 bool PreviousIsInvoke = false;
482 // Visit all instructions in order of address.
483 for (MachineFunction::const_iterator I = MF->begin(), E = MF->end();
485 for (MachineBasicBlock::const_iterator MI = I->begin(), E = I->end();
487 if (!MI->isLabel()) {
488 SawPotentiallyThrowing |= MI->getDesc().isCall();
492 unsigned BeginLabel = MI->getOperand(0).getImm();
493 assert(BeginLabel && "Invalid label!");
495 // End of the previous try-range?
496 if (BeginLabel == LastLabel)
497 SawPotentiallyThrowing = false;
499 // Beginning of a new try-range?
500 RangeMapType::iterator L = PadMap.find(BeginLabel);
501 if (L == PadMap.end())
502 // Nope, it was just some random label.
505 const PadRange &P = L->second;
506 const LandingPadInfo *LandingPad = LandingPads[P.PadIndex];
507 assert(BeginLabel == LandingPad->BeginLabels[P.RangeIndex] &&
508 "Inconsistent landing pad map!");
510 // For Dwarf exception handling (SjLj handling doesn't use this). If some
511 // instruction between the previous try-range and this one may throw,
512 // create a call-site entry with no landing pad for the region between the
514 if (SawPotentiallyThrowing &&
515 MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf) {
516 CallSiteEntry Site = { LastLabel, BeginLabel, 0, 0 };
517 CallSites.push_back(Site);
518 PreviousIsInvoke = false;
521 LastLabel = LandingPad->EndLabels[P.RangeIndex];
522 assert(BeginLabel && LastLabel && "Invalid landing pad!");
524 if (LandingPad->LandingPadLabel) {
525 // This try-range is for an invoke.
526 CallSiteEntry Site = {
529 LandingPad->LandingPadLabel,
530 FirstActions[P.PadIndex]
533 // Try to merge with the previous call-site. SJLJ doesn't do this
534 if (PreviousIsInvoke &&
535 MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf) {
536 CallSiteEntry &Prev = CallSites.back();
537 if (Site.PadLabel == Prev.PadLabel && Site.Action == Prev.Action) {
538 // Extend the range of the previous entry.
539 Prev.EndLabel = Site.EndLabel;
544 // Otherwise, create a new call-site.
545 CallSites.push_back(Site);
546 PreviousIsInvoke = true;
549 PreviousIsInvoke = false;
554 // If some instruction between the previous try-range and the end of the
555 // function may throw, create a call-site entry with no landing pad for the
556 // region following the try-range.
557 if (SawPotentiallyThrowing &&
558 MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf) {
559 CallSiteEntry Site = { LastLabel, 0, 0, 0 };
560 CallSites.push_back(Site);
564 /// EmitExceptionTable - Emit landing pads and actions.
566 /// The general organization of the table is complex, but the basic concepts are
567 /// easy. First there is a header which describes the location and organization
568 /// of the three components that follow.
570 /// 1. The landing pad site information describes the range of code covered by
571 /// the try. In our case it's an accumulation of the ranges covered by the
572 /// invokes in the try. There is also a reference to the landing pad that
573 /// handles the exception once processed. Finally an index into the actions
575 /// 2. The action table, in our case, is composed of pairs of type IDs and next
576 /// action offset. Starting with the action index from the landing pad
577 /// site, each type ID is checked for a match to the current exception. If
578 /// it matches then the exception and type id are passed on to the landing
579 /// pad. Otherwise the next action is looked up. This chain is terminated
580 /// with a next action of zero. If no type id is found then the frame is
581 /// unwound and handling continues.
582 /// 3. Type ID table contains references to all the C++ typeinfo for all
583 /// catches in the function. This tables is reverse indexed base 1.
584 void DwarfException::EmitExceptionTable() {
585 const std::vector<GlobalVariable *> &TypeInfos = MMI->getTypeInfos();
586 const std::vector<unsigned> &FilterIds = MMI->getFilterIds();
587 const std::vector<LandingPadInfo> &PadInfos = MMI->getLandingPads();
588 if (PadInfos.empty()) return;
590 // Sort the landing pads in order of their type ids. This is used to fold
591 // duplicate actions.
592 SmallVector<const LandingPadInfo *, 64> LandingPads;
593 LandingPads.reserve(PadInfos.size());
595 for (unsigned i = 0, N = PadInfos.size(); i != N; ++i)
596 LandingPads.push_back(&PadInfos[i]);
598 std::sort(LandingPads.begin(), LandingPads.end(), PadLT);
600 // Compute the actions table and gather the first action index for each
602 SmallVector<ActionEntry, 32> Actions;
603 SmallVector<unsigned, 64> FirstActions;
604 unsigned SizeActions = ComputeActionsTable(LandingPads, Actions,
607 // Invokes and nounwind calls have entries in PadMap (due to being bracketed
608 // by try-range labels when lowered). Ordinary calls do not, so appropriate
609 // try-ranges for them need be deduced when using DWARF exception handling.
611 for (unsigned i = 0, N = LandingPads.size(); i != N; ++i) {
612 const LandingPadInfo *LandingPad = LandingPads[i];
613 for (unsigned j = 0, E = LandingPad->BeginLabels.size(); j != E; ++j) {
614 unsigned BeginLabel = LandingPad->BeginLabels[j];
615 assert(!PadMap.count(BeginLabel) && "Duplicate landing pad labels!");
616 PadRange P = { i, j };
617 PadMap[BeginLabel] = P;
621 // Compute the call-site table.
622 SmallVector<CallSiteEntry, 64> CallSites;
623 ComputeCallSiteTable(CallSites, PadMap, LandingPads, FirstActions);
628 const unsigned SiteStartSize = SizeOfEncodedValue(dwarf::DW_EH_PE_udata4);
629 const unsigned SiteLengthSize = SizeOfEncodedValue(dwarf::DW_EH_PE_udata4);
630 const unsigned LandingPadSize = SizeOfEncodedValue(dwarf::DW_EH_PE_udata4);
631 bool IsSJLJ = MAI->getExceptionHandlingType() == ExceptionHandling::SjLj;
632 bool HaveTTData = IsSJLJ ? (!TypeInfos.empty() || !FilterIds.empty()) : true;
638 SizeSites = CallSites.size() *
639 (SiteStartSize + SiteLengthSize + LandingPadSize);
641 for (unsigned i = 0, e = CallSites.size(); i < e; ++i) {
642 SizeSites += MCAsmInfo::getULEB128Size(CallSites[i].Action);
644 SizeSites += MCAsmInfo::getULEB128Size(i);
648 const MCSection *LSDASection = Asm->getObjFileLowering().getLSDASection();
649 unsigned TTypeFormat;
650 unsigned TypeFormatSize;
653 // For SjLj exceptions, if there is no TypeInfo, then we just explicitly say
654 // that we're omitting that bit.
655 TTypeFormat = dwarf::DW_EH_PE_omit;
656 TypeFormatSize = SizeOfEncodedValue(dwarf::DW_EH_PE_absptr);
658 // Okay, we have actual filters or typeinfos to emit. As such, we need to
659 // pick a type encoding for them. We're about to emit a list of pointers to
660 // typeinfo objects at the end of the LSDA. However, unless we're in static
661 // mode, this reference will require a relocation by the dynamic linker.
663 // Because of this, we have a couple of options:
665 // 1) If we are in -static mode, we can always use an absolute reference
666 // from the LSDA, because the static linker will resolve it.
668 // 2) Otherwise, if the LSDA section is writable, we can output the direct
669 // reference to the typeinfo and allow the dynamic linker to relocate
670 // it. Since it is in a writable section, the dynamic linker won't
673 // 3) Finally, if we're in PIC mode and the LDSA section isn't writable,
674 // we need to use some form of indirection. For example, on Darwin,
675 // we can output a statically-relocatable reference to a dyld stub. The
676 // offset to the stub is constant, but the contents are in a section
677 // that is updated by the dynamic linker. This is easy enough, but we
678 // need to tell the personality function of the unwinder to indirect
679 // through the dyld stub.
681 // FIXME: When (3) is actually implemented, we'll have to emit the stubs
682 // somewhere. This predicate should be moved to a shared location that is
683 // in target-independent code.
685 if (LSDASection->getKind().isWriteable() ||
686 Asm->TM.getRelocationModel() == Reloc::Static)
687 TTypeFormat = dwarf::DW_EH_PE_absptr;
689 TTypeFormat = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
690 dwarf::DW_EH_PE_sdata4;
692 TypeFormatSize = SizeOfEncodedValue(TTypeFormat);
695 // Begin the exception table.
696 Asm->OutStreamer.SwitchSection(LSDASection);
697 Asm->EmitAlignment(2, 0, 0, false);
699 O << "GCC_except_table" << SubprogramCount << ":\n";
701 // The type infos need to be aligned. GCC does this by inserting padding just
702 // before the type infos. However, this changes the size of the exception
703 // table, so you need to take this into account when you output the exception
704 // table size. However, the size is output using a variable length encoding.
705 // So by increasing the size by inserting padding, you may increase the number
706 // of bytes used for writing the size. If it increases, say by one byte, then
707 // you now need to output one less byte of padding to get the type infos
708 // aligned. However this decreases the size of the exception table. This
709 // changes the value you have to output for the exception table size. Due to
710 // the variable length encoding, the number of bytes used for writing the
711 // length may decrease. If so, you then have to increase the amount of
712 // padding. And so on. If you look carefully at the GCC code you will see that
713 // it indeed does this in a loop, going on and on until the values stabilize.
714 // We chose another solution: don't output padding inside the table like GCC
715 // does, instead output it before the table.
716 unsigned SizeTypes = TypeInfos.size() * TypeFormatSize;
717 unsigned TyOffset = sizeof(int8_t) + // Call site format
718 MCAsmInfo::getULEB128Size(SizeSites) + // Call-site table length
719 SizeSites + SizeActions + SizeTypes;
720 unsigned TotalSize = sizeof(int8_t) + // LPStart format
721 sizeof(int8_t) + // TType format
723 MCAsmInfo::getULEB128Size(TyOffset) : 0) + // TType base offset
725 unsigned SizeAlign = (4 - TotalSize) & 3;
727 for (unsigned i = 0; i != SizeAlign; ++i) {
732 EmitLabel("exception", SubprogramCount);
735 SmallString<16> LSDAName;
736 raw_svector_ostream(LSDAName) << MAI->getPrivateGlobalPrefix() <<
737 "_LSDA_" << Asm->getFunctionNumber();
738 O << LSDAName.str() << ":\n";
742 Asm->EmitInt8(dwarf::DW_EH_PE_omit);
743 Asm->EOL("@LPStart format", dwarf::DW_EH_PE_omit);
745 Asm->EmitInt8(TTypeFormat);
746 Asm->EOL("@TType format", TTypeFormat);
749 Asm->EmitULEB128Bytes(TyOffset);
750 Asm->EOL("@TType base offset");
753 // SjLj Exception handling
755 Asm->EmitInt8(dwarf::DW_EH_PE_udata4);
756 Asm->EOL("Call site format", dwarf::DW_EH_PE_udata4);
757 Asm->EmitULEB128Bytes(SizeSites);
758 Asm->EOL("Call site table length");
760 // Emit the landing pad site information.
762 for (SmallVectorImpl<CallSiteEntry>::const_iterator
763 I = CallSites.begin(), E = CallSites.end(); I != E; ++I, ++idx) {
764 const CallSiteEntry &S = *I;
766 // Offset of the landing pad, counted in 16-byte bundles relative to the
768 Asm->EmitULEB128Bytes(idx);
769 Asm->EOL("Landing pad");
771 // Offset of the first associated action record, relative to the start of
772 // the action table. This value is biased by 1 (1 indicates the start of
773 // the action table), and 0 indicates that there are no actions.
774 Asm->EmitULEB128Bytes(S.Action);
778 // DWARF Exception handling
779 assert(MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf);
781 // The call-site table is a list of all call sites that may throw an
782 // exception (including C++ 'throw' statements) in the procedure
783 // fragment. It immediately follows the LSDA header. Each entry indicates,
784 // for a given call, the first corresponding action record and corresponding
787 // The table begins with the number of bytes, stored as an LEB128
788 // compressed, unsigned integer. The records immediately follow the record
789 // count. They are sorted in increasing call-site address. Each record
792 // * The position of the call-site.
793 // * The position of the landing pad.
794 // * The first action record for that call site.
796 // A missing entry in the call-site table indicates that a call is not
797 // supposed to throw.
799 // Emit the landing pad call site table.
800 Asm->EmitInt8(dwarf::DW_EH_PE_udata4);
801 Asm->EOL("Call site format", dwarf::DW_EH_PE_udata4);
802 Asm->EmitULEB128Bytes(SizeSites);
803 Asm->EOL("Call site table size");
805 for (SmallVectorImpl<CallSiteEntry>::const_iterator
806 I = CallSites.begin(), E = CallSites.end(); I != E; ++I) {
807 const CallSiteEntry &S = *I;
808 const char *BeginTag;
809 unsigned BeginNumber;
812 BeginTag = "eh_func_begin";
813 BeginNumber = SubprogramCount;
816 BeginNumber = S.BeginLabel;
819 // Offset of the call site relative to the previous call site, counted in
820 // number of 16-byte bundles. The first call site is counted relative to
821 // the start of the procedure fragment.
822 EmitSectionOffset(BeginTag, "eh_func_begin", BeginNumber, SubprogramCount,
824 Asm->EOL("Region start");
827 EmitDifference("eh_func_end", SubprogramCount, BeginTag, BeginNumber,
830 EmitDifference("label", S.EndLabel, BeginTag, BeginNumber, true);
832 Asm->EOL("Region length");
834 // Offset of the landing pad, counted in 16-byte bundles relative to the
839 EmitSectionOffset("label", "eh_func_begin", S.PadLabel, SubprogramCount,
842 Asm->EOL("Landing pad");
844 // Offset of the first associated action record, relative to the start of
845 // the action table. This value is biased by 1 (1 indicates the start of
846 // the action table), and 0 indicates that there are no actions.
847 Asm->EmitULEB128Bytes(S.Action);
852 // Emit the Action Table.
853 for (SmallVectorImpl<ActionEntry>::const_iterator
854 I = Actions.begin(), E = Actions.end(); I != E; ++I) {
855 const ActionEntry &Action = *I;
859 // Used by the runtime to match the type of the thrown exception to the
860 // type of the catch clauses or the types in the exception specification.
862 Asm->EmitSLEB128Bytes(Action.ValueForTypeID);
863 Asm->EOL("TypeInfo index");
867 // Self-relative signed displacement in bytes of the next action record,
868 // or 0 if there is no next action record.
870 Asm->EmitSLEB128Bytes(Action.NextAction);
871 Asm->EOL("Next action");
874 // Emit the Catch Clauses. The code for the catch clauses following the same
875 // try is similar to a switch statement. The catch clause action record
876 // informs the runtime about the type of a catch clause and about the
877 // associated switch value.
879 // Action Record Fields:
882 // Positive value, starting at 1. Index in the types table of the
883 // __typeinfo for the catch-clause type. 1 is the first word preceding
884 // TTBase, 2 is the second word, and so on. Used by the runtime to check
885 // if the thrown exception type matches the catch-clause type. Back-end
886 // generated switch statements check against this value.
889 // Signed offset, in bytes from the start of this field, to the next
890 // chained action record, or zero if none.
892 // The order of the action records determined by the next field is the order
893 // of the catch clauses as they appear in the source code, and must be kept in
894 // the same order. As a result, changing the order of the catch clause would
895 // change the semantics of the program.
896 for (std::vector<GlobalVariable *>::const_reverse_iterator
897 I = TypeInfos.rbegin(), E = TypeInfos.rend(); I != E; ++I) {
898 const GlobalVariable *GV = *I;
902 O << Asm->Mang->getMangledName(GV);
907 Asm->EOL("TypeInfo");
910 // Emit the Type Table.
911 for (std::vector<unsigned>::const_iterator
912 I = FilterIds.begin(), E = FilterIds.end(); I < E; ++I) {
913 unsigned TypeID = *I;
914 Asm->EmitULEB128Bytes(TypeID);
915 Asm->EOL("Filter TypeInfo index");
918 Asm->EmitAlignment(2, 0, 0, false);
921 /// EndModule - Emit all exception information that should come after the
923 void DwarfException::EndModule() {
924 if (MAI->getExceptionHandlingType() != ExceptionHandling::Dwarf)
927 if (!shouldEmitMovesModule && !shouldEmitTableModule)
930 if (TimePassesIsEnabled)
931 ExceptionTimer->startTimer();
933 const std::vector<Function *> Personalities = MMI->getPersonalities();
935 for (unsigned I = 0, E = Personalities.size(); I < E; ++I)
936 EmitCIE(Personalities[I], I);
938 for (std::vector<FunctionEHFrameInfo>::iterator
939 I = EHFrames.begin(), E = EHFrames.end(); I != E; ++I)
942 if (TimePassesIsEnabled)
943 ExceptionTimer->stopTimer();
946 /// BeginFunction - Gather pre-function exception information. Assumes it's
947 /// being emitted immediately after the function entry point.
948 void DwarfException::BeginFunction(MachineFunction *MF) {
949 if (!MMI || !MAI->doesSupportExceptionHandling()) return;
951 if (TimePassesIsEnabled)
952 ExceptionTimer->startTimer();
955 shouldEmitTable = shouldEmitMoves = false;
957 // Map all labels and get rid of any dead landing pads.
958 MMI->TidyLandingPads();
960 // If any landing pads survive, we need an EH table.
961 if (!MMI->getLandingPads().empty())
962 shouldEmitTable = true;
964 // See if we need frame move info.
965 if (!MF->getFunction()->doesNotThrow() || UnwindTablesMandatory)
966 shouldEmitMoves = true;
968 if (shouldEmitMoves || shouldEmitTable)
969 // Assumes in correct section after the entry point.
970 EmitLabel("eh_func_begin", ++SubprogramCount);
972 shouldEmitTableModule |= shouldEmitTable;
973 shouldEmitMovesModule |= shouldEmitMoves;
975 if (TimePassesIsEnabled)
976 ExceptionTimer->stopTimer();
979 /// EndFunction - Gather and emit post-function exception information.
981 void DwarfException::EndFunction() {
982 if (!shouldEmitMoves && !shouldEmitTable) return;
984 if (TimePassesIsEnabled)
985 ExceptionTimer->startTimer();
987 EmitLabel("eh_func_end", SubprogramCount);
988 EmitExceptionTable();
990 std::string FunctionEHName =
991 Asm->Mang->getMangledName(MF->getFunction(), ".eh",
992 Asm->MAI->is_EHSymbolPrivate());
994 // Save EH frame information
995 EHFrames.push_back(FunctionEHFrameInfo(FunctionEHName, SubprogramCount,
996 MMI->getPersonalityIndex(),
997 MF->getFrameInfo()->hasCalls(),
998 !MMI->getLandingPads().empty(),
999 MMI->getFrameMoves(),
1000 MF->getFunction()));
1002 // Record if this personality index uses a landing pad.
1003 UsesLSDA[MMI->getPersonalityIndex()] |= !MMI->getLandingPads().empty();
1005 if (TimePassesIsEnabled)
1006 ExceptionTimer->stopTimer();