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/MC/MCSymbol.h"
26 #include "llvm/Target/Mangler.h"
27 #include "llvm/Target/TargetData.h"
28 #include "llvm/Target/TargetFrameInfo.h"
29 #include "llvm/Target/TargetLoweringObjectFile.h"
30 #include "llvm/Target/TargetOptions.h"
31 #include "llvm/Target/TargetRegisterInfo.h"
32 #include "llvm/Support/Dwarf.h"
33 #include "llvm/Support/FormattedStream.h"
34 #include "llvm/Support/Timer.h"
35 #include "llvm/ADT/SmallString.h"
36 #include "llvm/ADT/StringExtras.h"
39 DwarfException::DwarfException(raw_ostream &OS, AsmPrinter *A,
41 : DwarfPrinter(OS, A, T, "eh"), shouldEmitTable(false),shouldEmitMoves(false),
42 shouldEmitTableModule(false), shouldEmitMovesModule(false),
44 if (TimePassesIsEnabled)
45 ExceptionTimer = new Timer("DWARF Exception Writer");
48 DwarfException::~DwarfException() {
49 delete ExceptionTimer;
52 /// SizeOfEncodedValue - Return the size of the encoding in bytes.
53 unsigned DwarfException::SizeOfEncodedValue(unsigned Encoding) {
54 if (Encoding == dwarf::DW_EH_PE_omit)
57 switch (Encoding & 0x07) {
58 case dwarf::DW_EH_PE_absptr:
59 return TD->getPointerSize();
60 case dwarf::DW_EH_PE_udata2:
62 case dwarf::DW_EH_PE_udata4:
64 case dwarf::DW_EH_PE_udata8:
68 assert(0 && "Invalid encoded value.");
72 /// CreateLabelDiff - Emit a label and subtract it from the expression we
73 /// already have. This is equivalent to emitting "foo - .", but we have to emit
74 /// the label for "." directly.
75 const MCExpr *DwarfException::CreateLabelDiff(const MCExpr *ExprRef,
76 const char *LabelName,
79 raw_svector_ostream(Name) << MAI->getPrivateGlobalPrefix()
80 << LabelName << Asm->getFunctionNumber()
82 MCSymbol *DotSym = Asm->OutContext.GetOrCreateSymbol(Name.str());
83 Asm->OutStreamer.EmitLabel(DotSym);
85 return MCBinaryExpr::CreateSub(ExprRef,
86 MCSymbolRefExpr::Create(DotSym,
91 /// EmitCIE - Emit a Common Information Entry (CIE). This holds information that
92 /// is shared among many Frame Description Entries. There is at least one CIE
93 /// in every non-empty .debug_frame section.
94 void DwarfException::EmitCIE(const Function *PersonalityFn, unsigned Index) {
95 // Size and sign of stack growth.
97 Asm->TM.getFrameInfo()->getStackGrowthDirection() ==
98 TargetFrameInfo::StackGrowsUp ?
99 TD->getPointerSize() : -TD->getPointerSize();
101 const TargetLoweringObjectFile &TLOF = Asm->getObjFileLowering();
103 // Begin eh frame section.
104 Asm->OutStreamer.SwitchSection(TLOF.getEHFrameSection());
106 if (MAI->is_EHSymbolPrivate())
107 O << MAI->getPrivateGlobalPrefix();
108 O << "EH_frame" << Index << ":\n";
110 EmitLabel("section_eh_frame", Index);
112 // Define base labels.
113 EmitLabel("eh_frame_common", Index);
115 // Define the eh frame length.
116 EmitDifference("eh_frame_common_end", Index,
117 "eh_frame_common_begin", Index, true);
118 EOL("Length of Common Information Entry");
121 EmitLabel("eh_frame_common_begin", Index);
122 if (Asm->VerboseAsm) Asm->OutStreamer.AddComment("CIE Identifier Tag");
123 Asm->OutStreamer.EmitIntValue(0, 4/*size*/, 0/*addrspace*/);
124 if (Asm->VerboseAsm) Asm->OutStreamer.AddComment("DW_CIE_VERSION");
125 Asm->OutStreamer.EmitIntValue(dwarf::DW_CIE_VERSION, 1/*size*/, 0/*addr*/);
127 // The personality presence indicates that language specific information will
128 // show up in the eh frame. Find out how we are supposed to lower the
129 // personality function reference:
130 const MCExpr *PersonalityRef = 0;
131 bool IsPersonalityIndirect = false, IsPersonalityPCRel = false;
133 // FIXME: HANDLE STATIC CODEGEN MODEL HERE.
135 // In non-static mode, ask the object file how to represent this reference.
137 TLOF.getSymbolForDwarfGlobalReference(PersonalityFn, Asm->Mang,
139 IsPersonalityIndirect,
143 unsigned PerEncoding = dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4;
144 if (IsPersonalityIndirect)
145 PerEncoding |= dwarf::DW_EH_PE_indirect;
146 unsigned LSDAEncoding = dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4;
147 unsigned FDEEncoding = dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4;
149 char Augmentation[6] = { 0 };
150 unsigned AugmentationSize = 0;
151 char *APtr = Augmentation + 1;
153 if (PersonalityRef) {
154 // There is a personality function.
156 AugmentationSize += 1 + SizeOfEncodedValue(PerEncoding);
159 if (UsesLSDA[Index]) {
160 // An LSDA pointer is in the FDE augmentation.
165 if (FDEEncoding != dwarf::DW_EH_PE_absptr) {
166 // A non-default pointer encoding for the FDE.
171 if (APtr != Augmentation + 1)
172 Augmentation[0] = 'z';
174 Asm->OutStreamer.EmitBytes(StringRef(Augmentation, strlen(Augmentation)+1),0);
175 EOL("CIE Augmentation");
178 EmitULEB128(1, "CIE Code Alignment Factor");
179 EmitSLEB128(stackGrowth, "CIE Data Alignment Factor");
180 Asm->EmitInt8(RI->getDwarfRegNum(RI->getRARegister(), true));
181 EOL("CIE Return Address Column");
183 EmitULEB128(AugmentationSize, "Augmentation Size");
184 EmitEncodingByte(PerEncoding, "Personality");
186 // If there is a personality, we need to indicate the function's location.
187 if (PersonalityRef) {
188 if (!IsPersonalityPCRel)
189 PersonalityRef = CreateLabelDiff(PersonalityRef, "personalityref_addr",
192 O << MAI->getData32bitsDirective() << *PersonalityRef;
195 EmitEncodingByte(LSDAEncoding, "LSDA");
196 EmitEncodingByte(FDEEncoding, "FDE");
199 // Indicate locations of general callee saved registers in frame.
200 std::vector<MachineMove> Moves;
201 RI->getInitialFrameState(Moves);
202 EmitFrameMoves(NULL, 0, Moves, true);
204 // On Darwin the linker honors the alignment of eh_frame, which means it must
205 // be 8-byte on 64-bit targets to match what gcc does. Otherwise you get
206 // holes which confuse readers of eh_frame.
207 Asm->EmitAlignment(TD->getPointerSize() == 4 ? 2 : 3, 0, 0, false);
208 EmitLabel("eh_frame_common_end", Index);
212 /// EmitFDE - Emit the Frame Description Entry (FDE) for the function.
213 void DwarfException::EmitFDE(const FunctionEHFrameInfo &EHFrameInfo) {
214 assert(!EHFrameInfo.function->hasAvailableExternallyLinkage() &&
215 "Should not emit 'available externally' functions at all");
217 const Function *TheFunc = EHFrameInfo.function;
219 Asm->OutStreamer.SwitchSection(Asm->getObjFileLowering().getEHFrameSection());
221 // Externally visible entry into the functions eh frame info. If the
222 // corresponding function is static, this should not be externally visible.
223 if (!TheFunc->hasLocalLinkage())
224 if (const char *GlobalEHDirective = MAI->getGlobalEHDirective())
225 O << GlobalEHDirective << *EHFrameInfo.FunctionEHSym << '\n';
227 // If corresponding function is weak definition, this should be too.
228 if (TheFunc->isWeakForLinker() && MAI->getWeakDefDirective())
229 O << MAI->getWeakDefDirective() << *EHFrameInfo.FunctionEHSym << '\n';
231 // If corresponding function is hidden, this should be too.
232 if (TheFunc->hasHiddenVisibility())
233 if (const char *HiddenDirective = MAI->getHiddenDirective())
234 O << HiddenDirective << *EHFrameInfo.FunctionEHSym << '\n';
236 // If there are no calls then you can't unwind. This may mean we can omit the
237 // EH Frame, but some environments do not handle weak absolute symbols. If
238 // UnwindTablesMandatory is set we cannot do this optimization; the unwind
239 // info is to be available for non-EH uses.
240 if (!EHFrameInfo.hasCalls && !UnwindTablesMandatory &&
241 (!TheFunc->isWeakForLinker() ||
242 !MAI->getWeakDefDirective() ||
243 MAI->getSupportsWeakOmittedEHFrame())) {
244 O << *EHFrameInfo.FunctionEHSym << " = 0\n";
245 // This name has no connection to the function, so it might get
246 // dead-stripped when the function is not, erroneously. Prohibit
247 // dead-stripping unconditionally.
248 if (const char *UsedDirective = MAI->getUsedDirective())
249 O << UsedDirective << *EHFrameInfo.FunctionEHSym << "\n\n";
251 O << *EHFrameInfo.FunctionEHSym << ":\n";
254 EmitDifference("eh_frame_end", EHFrameInfo.Number,
255 "eh_frame_begin", EHFrameInfo.Number, true);
256 EOL("Length of Frame Information Entry");
258 EmitLabel("eh_frame_begin", EHFrameInfo.Number);
260 EmitSectionOffset("eh_frame_begin", "eh_frame_common",
261 EHFrameInfo.Number, EHFrameInfo.PersonalityIndex,
264 EOL("FDE CIE offset");
266 EmitReference("eh_func_begin", EHFrameInfo.Number, true, true);
267 EOL("FDE initial location");
268 EmitDifference("eh_func_end", EHFrameInfo.Number,
269 "eh_func_begin", EHFrameInfo.Number, true);
270 EOL("FDE address range");
272 // If there is a personality and landing pads then point to the language
273 // specific data area in the exception table.
274 if (MMI->getPersonalities()[0] != NULL) {
276 if (Asm->TM.getLSDAEncoding() != DwarfLSDAEncoding::EightByte) {
277 EmitULEB128(4, "Augmentation size");
279 if (EHFrameInfo.hasLandingPads)
280 EmitReference("exception", EHFrameInfo.Number, true, true);
282 Asm->OutStreamer.EmitIntValue(0, 4/*size*/, 0/*addrspace*/);
284 EmitULEB128(TD->getPointerSize(), "Augmentation size");
286 if (EHFrameInfo.hasLandingPads) {
287 EmitReference("exception", EHFrameInfo.Number, true, false);
289 Asm->OutStreamer.EmitIntValue(0, TD->getPointerSize(),
294 EOL("Language Specific Data Area");
296 EmitULEB128(0, "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.FunctionEHSym << "\n\n";
322 /// SharedTypeIds - How many leading type ids two landing pads have in common.
323 unsigned DwarfException::SharedTypeIds(const LandingPadInfo *L,
324 const LandingPadInfo *R) {
325 const std::vector<int> &LIds = L->TypeIds, &RIds = R->TypeIds;
326 unsigned LSize = LIds.size(), RSize = RIds.size();
327 unsigned MinSize = LSize < RSize ? LSize : RSize;
330 for (; Count != MinSize; ++Count)
331 if (LIds[Count] != RIds[Count])
337 /// PadLT - Order landing pads lexicographically by type id.
338 bool DwarfException::PadLT(const LandingPadInfo *L, const LandingPadInfo *R) {
339 const std::vector<int> &LIds = L->TypeIds, &RIds = R->TypeIds;
340 unsigned LSize = LIds.size(), RSize = RIds.size();
341 unsigned MinSize = LSize < RSize ? LSize : RSize;
343 for (unsigned i = 0; i != MinSize; ++i)
344 if (LIds[i] != RIds[i])
345 return LIds[i] < RIds[i];
347 return LSize < RSize;
350 /// ComputeActionsTable - Compute the actions table and gather the first action
351 /// index for each landing pad site.
352 unsigned DwarfException::
353 ComputeActionsTable(const SmallVectorImpl<const LandingPadInfo*> &LandingPads,
354 SmallVectorImpl<ActionEntry> &Actions,
355 SmallVectorImpl<unsigned> &FirstActions) {
357 // The action table follows the call-site table in the LSDA. The individual
358 // records are of two types:
361 // * Exception specification
363 // The two record kinds have the same format, with only small differences.
364 // They are distinguished by the "switch value" field: Catch clauses
365 // (TypeInfos) have strictly positive switch values, and exception
366 // specifications (FilterIds) have strictly negative switch values. Value 0
367 // indicates a catch-all clause.
369 // Negative type IDs index into FilterIds. Positive type IDs index into
370 // TypeInfos. The value written for a positive type ID is just the type ID
371 // itself. For a negative type ID, however, the value written is the
372 // (negative) byte offset of the corresponding FilterIds entry. The byte
373 // offset is usually equal to the type ID (because the FilterIds entries are
374 // written using a variable width encoding, which outputs one byte per entry
375 // as long as the value written is not too large) but can differ. This kind
376 // of complication does not occur for positive type IDs because type infos are
377 // output using a fixed width encoding. FilterOffsets[i] holds the byte
378 // offset corresponding to FilterIds[i].
380 const std::vector<unsigned> &FilterIds = MMI->getFilterIds();
381 SmallVector<int, 16> FilterOffsets;
382 FilterOffsets.reserve(FilterIds.size());
385 for (std::vector<unsigned>::const_iterator
386 I = FilterIds.begin(), E = FilterIds.end(); I != E; ++I) {
387 FilterOffsets.push_back(Offset);
388 Offset -= MCAsmInfo::getULEB128Size(*I);
391 FirstActions.reserve(LandingPads.size());
394 unsigned SizeActions = 0;
395 const LandingPadInfo *PrevLPI = 0;
397 for (SmallVectorImpl<const LandingPadInfo *>::const_iterator
398 I = LandingPads.begin(), E = LandingPads.end(); I != E; ++I) {
399 const LandingPadInfo *LPI = *I;
400 const std::vector<int> &TypeIds = LPI->TypeIds;
401 const unsigned NumShared = PrevLPI ? SharedTypeIds(LPI, PrevLPI) : 0;
402 unsigned SizeSiteActions = 0;
404 if (NumShared < TypeIds.size()) {
405 unsigned SizeAction = 0;
406 ActionEntry *PrevAction = 0;
409 const unsigned SizePrevIds = PrevLPI->TypeIds.size();
410 assert(Actions.size());
411 PrevAction = &Actions.back();
412 SizeAction = MCAsmInfo::getSLEB128Size(PrevAction->NextAction) +
413 MCAsmInfo::getSLEB128Size(PrevAction->ValueForTypeID);
415 for (unsigned j = NumShared; j != SizePrevIds; ++j) {
417 MCAsmInfo::getSLEB128Size(PrevAction->ValueForTypeID);
418 SizeAction += -PrevAction->NextAction;
419 PrevAction = PrevAction->Previous;
423 // Compute the actions.
424 for (unsigned J = NumShared, M = TypeIds.size(); J != M; ++J) {
425 int TypeID = TypeIds[J];
426 assert(-1 - TypeID < (int)FilterOffsets.size() && "Unknown filter id!");
427 int ValueForTypeID = TypeID < 0 ? FilterOffsets[-1 - TypeID] : TypeID;
428 unsigned SizeTypeID = MCAsmInfo::getSLEB128Size(ValueForTypeID);
430 int NextAction = SizeAction ? -(SizeAction + SizeTypeID) : 0;
431 SizeAction = SizeTypeID + MCAsmInfo::getSLEB128Size(NextAction);
432 SizeSiteActions += SizeAction;
434 ActionEntry Action = { ValueForTypeID, NextAction, PrevAction };
435 Actions.push_back(Action);
436 PrevAction = &Actions.back();
439 // Record the first action of the landing pad site.
440 FirstAction = SizeActions + SizeSiteActions - SizeAction + 1;
441 } // else identical - re-use previous FirstAction
443 // Information used when created the call-site table. The action record
444 // field of the call site record is the offset of the first associated
445 // action record, relative to the start of the actions table. This value is
446 // biased by 1 (1 in dicating the start of the actions table), and 0
447 // indicates that there are no actions.
448 FirstActions.push_back(FirstAction);
450 // Compute this sites contribution to size.
451 SizeActions += SizeSiteActions;
459 /// CallToNoUnwindFunction - Return `true' if this is a call to a function
460 /// marked `nounwind'. Return `false' otherwise.
461 bool DwarfException::CallToNoUnwindFunction(const MachineInstr *MI) {
462 assert(MI->getDesc().isCall() && "This should be a call instruction!");
464 bool MarkedNoUnwind = false;
465 bool SawFunc = false;
467 for (unsigned I = 0, E = MI->getNumOperands(); I != E; ++I) {
468 const MachineOperand &MO = MI->getOperand(I);
471 if (Function *F = dyn_cast<Function>(MO.getGlobal())) {
473 // Be conservative. If we have more than one function operand for this
474 // call, then we can't make the assumption that it's the callee and
475 // not a parameter to the call.
477 // FIXME: Determine if there's a way to say that `F' is the callee or
479 MarkedNoUnwind = false;
483 MarkedNoUnwind = F->doesNotThrow();
489 return MarkedNoUnwind;
492 /// ComputeCallSiteTable - Compute the call-site table. The entry for an invoke
493 /// has a try-range containing the call, a non-zero landing pad, and an
494 /// appropriate action. The entry for an ordinary call has a try-range
495 /// containing the call and zero for the landing pad and the action. Calls
496 /// marked 'nounwind' have no entry and must not be contained in the try-range
497 /// of any entry - they form gaps in the table. Entries must be ordered by
498 /// try-range address.
499 void DwarfException::
500 ComputeCallSiteTable(SmallVectorImpl<CallSiteEntry> &CallSites,
501 const RangeMapType &PadMap,
502 const SmallVectorImpl<const LandingPadInfo *> &LandingPads,
503 const SmallVectorImpl<unsigned> &FirstActions) {
504 // The end label of the previous invoke or nounwind try-range.
505 unsigned LastLabel = 0;
507 // Whether there is a potentially throwing instruction (currently this means
508 // an ordinary call) between the end of the previous try-range and now.
509 bool SawPotentiallyThrowing = false;
511 // Whether the last CallSite entry was for an invoke.
512 bool PreviousIsInvoke = false;
514 // Visit all instructions in order of address.
515 for (MachineFunction::const_iterator I = MF->begin(), E = MF->end();
517 for (MachineBasicBlock::const_iterator MI = I->begin(), E = I->end();
519 if (!MI->isLabel()) {
520 if (MI->getDesc().isCall())
521 SawPotentiallyThrowing |= !CallToNoUnwindFunction(MI);
526 unsigned BeginLabel = MI->getOperand(0).getImm();
527 assert(BeginLabel && "Invalid label!");
529 // End of the previous try-range?
530 if (BeginLabel == LastLabel)
531 SawPotentiallyThrowing = false;
533 // Beginning of a new try-range?
534 RangeMapType::const_iterator L = PadMap.find(BeginLabel);
535 if (L == PadMap.end())
536 // Nope, it was just some random label.
539 const PadRange &P = L->second;
540 const LandingPadInfo *LandingPad = LandingPads[P.PadIndex];
541 assert(BeginLabel == LandingPad->BeginLabels[P.RangeIndex] &&
542 "Inconsistent landing pad map!");
544 // For Dwarf exception handling (SjLj handling doesn't use this). If some
545 // instruction between the previous try-range and this one may throw,
546 // create a call-site entry with no landing pad for the region between the
548 if (SawPotentiallyThrowing &&
549 MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf) {
550 CallSiteEntry Site = { LastLabel, BeginLabel, 0, 0 };
551 CallSites.push_back(Site);
552 PreviousIsInvoke = false;
555 LastLabel = LandingPad->EndLabels[P.RangeIndex];
556 assert(BeginLabel && LastLabel && "Invalid landing pad!");
558 if (LandingPad->LandingPadLabel) {
559 // This try-range is for an invoke.
560 CallSiteEntry Site = {
563 LandingPad->LandingPadLabel,
564 FirstActions[P.PadIndex]
567 // Try to merge with the previous call-site. SJLJ doesn't do this
568 if (PreviousIsInvoke &&
569 MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf) {
570 CallSiteEntry &Prev = CallSites.back();
571 if (Site.PadLabel == Prev.PadLabel && Site.Action == Prev.Action) {
572 // Extend the range of the previous entry.
573 Prev.EndLabel = Site.EndLabel;
578 // Otherwise, create a new call-site.
579 CallSites.push_back(Site);
580 PreviousIsInvoke = true;
583 PreviousIsInvoke = false;
588 // If some instruction between the previous try-range and the end of the
589 // function may throw, create a call-site entry with no landing pad for the
590 // region following the try-range.
591 if (SawPotentiallyThrowing &&
592 MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf) {
593 CallSiteEntry Site = { LastLabel, 0, 0, 0 };
594 CallSites.push_back(Site);
598 /// EmitExceptionTable - Emit landing pads and actions.
600 /// The general organization of the table is complex, but the basic concepts are
601 /// easy. First there is a header which describes the location and organization
602 /// of the three components that follow.
604 /// 1. The landing pad site information describes the range of code covered by
605 /// the try. In our case it's an accumulation of the ranges covered by the
606 /// invokes in the try. There is also a reference to the landing pad that
607 /// handles the exception once processed. Finally an index into the actions
609 /// 2. The action table, in our case, is composed of pairs of type IDs and next
610 /// action offset. Starting with the action index from the landing pad
611 /// site, each type ID is checked for a match to the current exception. If
612 /// it matches then the exception and type id are passed on to the landing
613 /// pad. Otherwise the next action is looked up. This chain is terminated
614 /// with a next action of zero. If no type id is found then the frame is
615 /// unwound and handling continues.
616 /// 3. Type ID table contains references to all the C++ typeinfo for all
617 /// catches in the function. This tables is reverse indexed base 1.
618 void DwarfException::EmitExceptionTable() {
619 const std::vector<GlobalVariable *> &TypeInfos = MMI->getTypeInfos();
620 const std::vector<unsigned> &FilterIds = MMI->getFilterIds();
621 const std::vector<LandingPadInfo> &PadInfos = MMI->getLandingPads();
622 if (PadInfos.empty()) return;
624 // Sort the landing pads in order of their type ids. This is used to fold
625 // duplicate actions.
626 SmallVector<const LandingPadInfo *, 64> LandingPads;
627 LandingPads.reserve(PadInfos.size());
629 for (unsigned i = 0, N = PadInfos.size(); i != N; ++i)
630 LandingPads.push_back(&PadInfos[i]);
632 std::sort(LandingPads.begin(), LandingPads.end(), PadLT);
634 // Compute the actions table and gather the first action index for each
636 SmallVector<ActionEntry, 32> Actions;
637 SmallVector<unsigned, 64> FirstActions;
638 unsigned SizeActions = ComputeActionsTable(LandingPads, Actions,
641 // Invokes and nounwind calls have entries in PadMap (due to being bracketed
642 // by try-range labels when lowered). Ordinary calls do not, so appropriate
643 // try-ranges for them need be deduced when using DWARF exception handling.
645 for (unsigned i = 0, N = LandingPads.size(); i != N; ++i) {
646 const LandingPadInfo *LandingPad = LandingPads[i];
647 for (unsigned j = 0, E = LandingPad->BeginLabels.size(); j != E; ++j) {
648 unsigned BeginLabel = LandingPad->BeginLabels[j];
649 assert(!PadMap.count(BeginLabel) && "Duplicate landing pad labels!");
650 PadRange P = { i, j };
651 PadMap[BeginLabel] = P;
655 // Compute the call-site table.
656 SmallVector<CallSiteEntry, 64> CallSites;
657 ComputeCallSiteTable(CallSites, PadMap, LandingPads, FirstActions);
662 const unsigned SiteStartSize = SizeOfEncodedValue(dwarf::DW_EH_PE_udata4);
663 const unsigned SiteLengthSize = SizeOfEncodedValue(dwarf::DW_EH_PE_udata4);
664 const unsigned LandingPadSize = SizeOfEncodedValue(dwarf::DW_EH_PE_udata4);
665 bool IsSJLJ = MAI->getExceptionHandlingType() == ExceptionHandling::SjLj;
666 bool HaveTTData = IsSJLJ ? (!TypeInfos.empty() || !FilterIds.empty()) : true;
672 SizeSites = CallSites.size() *
673 (SiteStartSize + SiteLengthSize + LandingPadSize);
675 for (unsigned i = 0, e = CallSites.size(); i < e; ++i) {
676 SizeSites += MCAsmInfo::getULEB128Size(CallSites[i].Action);
678 SizeSites += MCAsmInfo::getULEB128Size(i);
682 const MCSection *LSDASection = Asm->getObjFileLowering().getLSDASection();
683 unsigned TTypeFormat;
684 unsigned TypeFormatSize;
687 // For SjLj exceptions, if there is no TypeInfo, then we just explicitly say
688 // that we're omitting that bit.
689 TTypeFormat = dwarf::DW_EH_PE_omit;
690 TypeFormatSize = SizeOfEncodedValue(dwarf::DW_EH_PE_absptr);
692 // Okay, we have actual filters or typeinfos to emit. As such, we need to
693 // pick a type encoding for them. We're about to emit a list of pointers to
694 // typeinfo objects at the end of the LSDA. However, unless we're in static
695 // mode, this reference will require a relocation by the dynamic linker.
697 // Because of this, we have a couple of options:
699 // 1) If we are in -static mode, we can always use an absolute reference
700 // from the LSDA, because the static linker will resolve it.
702 // 2) Otherwise, if the LSDA section is writable, we can output the direct
703 // reference to the typeinfo and allow the dynamic linker to relocate
704 // it. Since it is in a writable section, the dynamic linker won't
707 // 3) Finally, if we're in PIC mode and the LDSA section isn't writable,
708 // we need to use some form of indirection. For example, on Darwin,
709 // we can output a statically-relocatable reference to a dyld stub. The
710 // offset to the stub is constant, but the contents are in a section
711 // that is updated by the dynamic linker. This is easy enough, but we
712 // need to tell the personality function of the unwinder to indirect
713 // through the dyld stub.
715 // FIXME: When (3) is actually implemented, we'll have to emit the stubs
716 // somewhere. This predicate should be moved to a shared location that is
717 // in target-independent code.
719 if (LSDASection->getKind().isWriteable() ||
720 Asm->TM.getRelocationModel() == Reloc::Static)
721 TTypeFormat = dwarf::DW_EH_PE_absptr;
723 TTypeFormat = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
724 dwarf::DW_EH_PE_sdata4;
726 TypeFormatSize = SizeOfEncodedValue(TTypeFormat);
729 // Begin the exception table.
730 Asm->OutStreamer.SwitchSection(LSDASection);
731 Asm->EmitAlignment(2, 0, 0, false);
733 O << "GCC_except_table" << SubprogramCount << ":\n";
735 // The type infos need to be aligned. GCC does this by inserting padding just
736 // before the type infos. However, this changes the size of the exception
737 // table, so you need to take this into account when you output the exception
738 // table size. However, the size is output using a variable length encoding.
739 // So by increasing the size by inserting padding, you may increase the number
740 // of bytes used for writing the size. If it increases, say by one byte, then
741 // you now need to output one less byte of padding to get the type infos
742 // aligned. However this decreases the size of the exception table. This
743 // changes the value you have to output for the exception table size. Due to
744 // the variable length encoding, the number of bytes used for writing the
745 // length may decrease. If so, you then have to increase the amount of
746 // padding. And so on. If you look carefully at the GCC code you will see that
747 // it indeed does this in a loop, going on and on until the values stabilize.
748 // We chose another solution: don't output padding inside the table like GCC
749 // does, instead output it before the table.
750 unsigned SizeTypes = TypeInfos.size() * TypeFormatSize;
751 unsigned TyOffset = sizeof(int8_t) + // Call site format
752 MCAsmInfo::getULEB128Size(SizeSites) + // Call-site table length
753 SizeSites + SizeActions + SizeTypes;
754 unsigned TotalSize = sizeof(int8_t) + // LPStart format
755 sizeof(int8_t) + // TType format
757 MCAsmInfo::getULEB128Size(TyOffset) : 0) + // TType base offset
759 unsigned SizeAlign = (4 - TotalSize) & 3;
761 for (unsigned i = 0; i != SizeAlign; ++i) {
766 EmitLabel("exception", SubprogramCount);
769 SmallString<16> LSDAName;
770 raw_svector_ostream(LSDAName) << MAI->getPrivateGlobalPrefix() <<
771 "_LSDA_" << Asm->getFunctionNumber();
772 O << LSDAName.str() << ":\n";
776 EmitEncodingByte(dwarf::DW_EH_PE_omit, "@LPStart");
777 EmitEncodingByte(TTypeFormat, "@TType");
780 EmitULEB128(TyOffset, "@TType base offset");
782 // SjLj Exception handling
784 EmitEncodingByte(dwarf::DW_EH_PE_udata4, "Call site");
785 EmitULEB128(SizeSites, "Call site table length");
787 // Emit the landing pad site information.
789 for (SmallVectorImpl<CallSiteEntry>::const_iterator
790 I = CallSites.begin(), E = CallSites.end(); I != E; ++I, ++idx) {
791 const CallSiteEntry &S = *I;
793 // Offset of the landing pad, counted in 16-byte bundles relative to the
795 EmitULEB128(idx, "Landing pad");
797 // Offset of the first associated action record, relative to the start of
798 // the action table. This value is biased by 1 (1 indicates the start of
799 // the action table), and 0 indicates that there are no actions.
800 EmitULEB128(S.Action, "Action");
803 // DWARF Exception handling
804 assert(MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf);
806 // The call-site table is a list of all call sites that may throw an
807 // exception (including C++ 'throw' statements) in the procedure
808 // fragment. It immediately follows the LSDA header. Each entry indicates,
809 // for a given call, the first corresponding action record and corresponding
812 // The table begins with the number of bytes, stored as an LEB128
813 // compressed, unsigned integer. The records immediately follow the record
814 // count. They are sorted in increasing call-site address. Each record
817 // * The position of the call-site.
818 // * The position of the landing pad.
819 // * The first action record for that call site.
821 // A missing entry in the call-site table indicates that a call is not
822 // supposed to throw.
824 // Emit the landing pad call site table.
825 EmitEncodingByte(dwarf::DW_EH_PE_udata4, "Call site");
826 EmitULEB128(SizeSites, "Call site table size");
828 for (SmallVectorImpl<CallSiteEntry>::const_iterator
829 I = CallSites.begin(), E = CallSites.end(); I != E; ++I) {
830 const CallSiteEntry &S = *I;
831 const char *BeginTag;
832 unsigned BeginNumber;
835 BeginTag = "eh_func_begin";
836 BeginNumber = SubprogramCount;
839 BeginNumber = S.BeginLabel;
842 // Offset of the call site relative to the previous call site, counted in
843 // number of 16-byte bundles. The first call site is counted relative to
844 // the start of the procedure fragment.
845 EmitSectionOffset(BeginTag, "eh_func_begin", BeginNumber, SubprogramCount,
850 EmitDifference("eh_func_end", SubprogramCount, BeginTag, BeginNumber,
853 EmitDifference("label", S.EndLabel, BeginTag, BeginNumber, true);
855 EOL("Region length");
857 // Offset of the landing pad, counted in 16-byte bundles relative to the
860 Asm->OutStreamer.EmitIntValue(0, 4/*size*/, 0/*addrspace*/);
862 EmitSectionOffset("label", "eh_func_begin", S.PadLabel, SubprogramCount,
867 // Offset of the first associated action record, relative to the start of
868 // the action table. This value is biased by 1 (1 indicates the start of
869 // the action table), and 0 indicates that there are no actions.
870 EmitULEB128(S.Action, "Action");
874 // Emit the Action Table.
875 for (SmallVectorImpl<ActionEntry>::const_iterator
876 I = Actions.begin(), E = Actions.end(); I != E; ++I) {
877 const ActionEntry &Action = *I;
881 // Used by the runtime to match the type of the thrown exception to the
882 // type of the catch clauses or the types in the exception specification.
883 EmitSLEB128(Action.ValueForTypeID, "TypeInfo index");
887 // Self-relative signed displacement in bytes of the next action record,
888 // or 0 if there is no next action record.
889 EmitSLEB128(Action.NextAction, "Next action");
892 // Emit the Catch TypeInfos.
893 for (std::vector<GlobalVariable *>::const_reverse_iterator
894 I = TypeInfos.rbegin(), E = TypeInfos.rend(); I != E; ++I) {
895 const GlobalVariable *GV = *I;
899 O << *Asm->GetGlobalValueSymbol(GV);
906 // Emit the Exception Specifications.
907 for (std::vector<unsigned>::const_iterator
908 I = FilterIds.begin(), E = FilterIds.end(); I < E; ++I) {
909 unsigned TypeID = *I;
910 EmitULEB128(TypeID, TypeID != 0 ? "Exception specification" : 0);
913 Asm->EmitAlignment(2, 0, 0, false);
916 /// EndModule - Emit all exception information that should come after the
918 void DwarfException::EndModule() {
919 if (MAI->getExceptionHandlingType() != ExceptionHandling::Dwarf)
922 if (!shouldEmitMovesModule && !shouldEmitTableModule)
925 if (TimePassesIsEnabled)
926 ExceptionTimer->startTimer();
928 const std::vector<Function *> Personalities = MMI->getPersonalities();
930 for (unsigned I = 0, E = Personalities.size(); I < E; ++I)
931 EmitCIE(Personalities[I], I);
933 for (std::vector<FunctionEHFrameInfo>::iterator
934 I = EHFrames.begin(), E = EHFrames.end(); I != E; ++I)
937 if (TimePassesIsEnabled)
938 ExceptionTimer->stopTimer();
941 /// BeginFunction - Gather pre-function exception information. Assumes it's
942 /// being emitted immediately after the function entry point.
943 void DwarfException::BeginFunction(MachineFunction *MF) {
944 if (!MMI || !MAI->doesSupportExceptionHandling()) return;
946 if (TimePassesIsEnabled)
947 ExceptionTimer->startTimer();
950 shouldEmitTable = shouldEmitMoves = false;
952 // Map all labels and get rid of any dead landing pads.
953 MMI->TidyLandingPads();
955 // If any landing pads survive, we need an EH table.
956 if (!MMI->getLandingPads().empty())
957 shouldEmitTable = true;
959 // See if we need frame move info.
960 if (!MF->getFunction()->doesNotThrow() || UnwindTablesMandatory)
961 shouldEmitMoves = true;
963 if (shouldEmitMoves || shouldEmitTable)
964 // Assumes in correct section after the entry point.
965 EmitLabel("eh_func_begin", ++SubprogramCount);
967 shouldEmitTableModule |= shouldEmitTable;
968 shouldEmitMovesModule |= shouldEmitMoves;
970 if (TimePassesIsEnabled)
971 ExceptionTimer->stopTimer();
974 /// EndFunction - Gather and emit post-function exception information.
976 void DwarfException::EndFunction() {
977 if (!shouldEmitMoves && !shouldEmitTable) return;
979 if (TimePassesIsEnabled)
980 ExceptionTimer->startTimer();
982 EmitLabel("eh_func_end", SubprogramCount);
983 EmitExceptionTable();
985 const MCSymbol *FunctionEHSym =
986 Asm->GetSymbolWithGlobalValueBase(MF->getFunction(), ".eh",
987 Asm->MAI->is_EHSymbolPrivate());
989 // Save EH frame information
990 EHFrames.push_back(FunctionEHFrameInfo(FunctionEHSym, SubprogramCount,
991 MMI->getPersonalityIndex(),
992 MF->getFrameInfo()->hasCalls(),
993 !MMI->getLandingPads().empty(),
994 MMI->getFrameMoves(),
997 // Record if this personality index uses a landing pad.
998 UsesLSDA[MMI->getPersonalityIndex()] |= !MMI->getLandingPads().empty();
1000 if (TimePassesIsEnabled)
1001 ExceptionTimer->stopTimer();