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/Timer.h"
34 #include "llvm/Support/raw_ostream.h"
35 #include "llvm/ADT/SmallString.h"
36 #include "llvm/ADT/StringExtras.h"
39 DwarfException::DwarfException(raw_ostream &OS, AsmPrinter *A,
41 : Dwarf(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 Asm->EOL("Length of Common Information Entry");
121 EmitLabel("eh_frame_common_begin", Index);
122 Asm->EmitInt32((int)0);
123 Asm->EOL("CIE Identifier Tag");
124 Asm->EmitInt8(dwarf::DW_CIE_VERSION);
125 Asm->EOL("CIE Version");
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[5] = { 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->EmitString(Augmentation);
175 Asm->EOL("CIE Augmentation");
178 Asm->EmitULEB128Bytes(1);
179 Asm->EOL("CIE Code Alignment Factor");
180 Asm->EmitSLEB128Bytes(stackGrowth);
181 Asm->EOL("CIE Data Alignment Factor");
182 Asm->EmitInt8(RI->getDwarfRegNum(RI->getRARegister(), true));
183 Asm->EOL("CIE Return Address Column");
185 Asm->EmitULEB128Bytes(AugmentationSize);
186 Asm->EOL("Augmentation Size");
188 Asm->EmitInt8(PerEncoding);
189 Asm->EOL("Personality", PerEncoding);
191 // If there is a personality, we need to indicate the function's location.
192 if (PersonalityRef) {
193 if (!IsPersonalityPCRel)
194 PersonalityRef = CreateLabelDiff(PersonalityRef, "personalityref_addr",
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;
236 EHFrameInfo.FunctionEHSym->print(O, MAI);
240 // If corresponding function is weak definition, this should be too.
241 if (TheFunc->isWeakForLinker() && MAI->getWeakDefDirective()) {
242 O << MAI->getWeakDefDirective();
243 EHFrameInfo.FunctionEHSym->print(O, MAI);
247 // If corresponding function is hidden, this should be too.
248 if (TheFunc->hasHiddenVisibility())
249 if (const char *HiddenDirective = MAI->getHiddenDirective()) {
250 O << HiddenDirective;
251 EHFrameInfo.FunctionEHSym->print(O, MAI);
255 // If there are no calls then you can't unwind. This may mean we can omit the
256 // EH Frame, but some environments do not handle weak absolute symbols. If
257 // UnwindTablesMandatory is set we cannot do this optimization; the unwind
258 // info is to be available for non-EH uses.
259 if (!EHFrameInfo.hasCalls && !UnwindTablesMandatory &&
260 (!TheFunc->isWeakForLinker() ||
261 !MAI->getWeakDefDirective() ||
262 MAI->getSupportsWeakOmittedEHFrame())) {
263 EHFrameInfo.FunctionEHSym->print(O, MAI);
265 // This name has no connection to the function, so it might get
266 // dead-stripped when the function is not, erroneously. Prohibit
267 // dead-stripping unconditionally.
268 if (const char *UsedDirective = MAI->getUsedDirective()) {
270 EHFrameInfo.FunctionEHSym->print(O, MAI);
274 EHFrameInfo.FunctionEHSym->print(O, MAI);
278 EmitDifference("eh_frame_end", EHFrameInfo.Number,
279 "eh_frame_begin", EHFrameInfo.Number, true);
280 Asm->EOL("Length of Frame Information Entry");
282 EmitLabel("eh_frame_begin", EHFrameInfo.Number);
284 EmitSectionOffset("eh_frame_begin", "eh_frame_common",
285 EHFrameInfo.Number, EHFrameInfo.PersonalityIndex,
288 Asm->EOL("FDE CIE offset");
290 EmitReference("eh_func_begin", EHFrameInfo.Number, true, true);
291 Asm->EOL("FDE initial location");
292 EmitDifference("eh_func_end", EHFrameInfo.Number,
293 "eh_func_begin", EHFrameInfo.Number, true);
294 Asm->EOL("FDE address range");
296 // If there is a personality and landing pads then point to the language
297 // specific data area in the exception table.
298 if (MMI->getPersonalities()[0] != NULL) {
299 bool is4Byte = TD->getPointerSize() == sizeof(int32_t);
301 if (Asm->TM.getLSDAEncoding() == DwarfLSDAEncoding::FourByte) {
302 Asm->EmitULEB128Bytes(4);
303 Asm->EOL("Augmentation size");
305 if (EHFrameInfo.hasLandingPads)
306 EmitReference("exception", EHFrameInfo.Number, true, true);
308 Asm->EmitInt32((int)0);
310 Asm->EmitULEB128Bytes(is4Byte ? 4 : 8);
311 Asm->EOL("Augmentation size");
313 if (EHFrameInfo.hasLandingPads) {
314 EmitReference("exception", EHFrameInfo.Number, true, false);
317 Asm->EmitInt32((int)0);
319 Asm->EmitInt64((int)0);
323 Asm->EOL("Language Specific Data Area");
325 Asm->EmitULEB128Bytes(0);
326 Asm->EOL("Augmentation size");
329 // Indicate locations of function specific callee saved registers in frame.
330 EmitFrameMoves("eh_func_begin", EHFrameInfo.Number, EHFrameInfo.Moves,
333 // On Darwin the linker honors the alignment of eh_frame, which means it
334 // must be 8-byte on 64-bit targets to match what gcc does. Otherwise you
335 // get holes which confuse readers of eh_frame.
336 Asm->EmitAlignment(TD->getPointerSize() == sizeof(int32_t) ? 2 : 3,
338 EmitLabel("eh_frame_end", EHFrameInfo.Number);
340 // If the function is marked used, this table should be also. We cannot
341 // make the mark unconditional in this case, since retaining the table also
342 // retains the function in this case, and there is code around that depends
343 // on unused functions (calling undefined externals) being dead-stripped to
344 // link correctly. Yes, there really is.
345 if (MMI->isUsedFunction(EHFrameInfo.function))
346 if (const char *UsedDirective = MAI->getUsedDirective()) {
348 EHFrameInfo.FunctionEHSym->print(O, MAI);
356 /// SharedTypeIds - How many leading type ids two landing pads have in common.
357 unsigned DwarfException::SharedTypeIds(const LandingPadInfo *L,
358 const LandingPadInfo *R) {
359 const std::vector<int> &LIds = L->TypeIds, &RIds = R->TypeIds;
360 unsigned LSize = LIds.size(), RSize = RIds.size();
361 unsigned MinSize = LSize < RSize ? LSize : RSize;
364 for (; Count != MinSize; ++Count)
365 if (LIds[Count] != RIds[Count])
371 /// PadLT - Order landing pads lexicographically by type id.
372 bool DwarfException::PadLT(const LandingPadInfo *L, const LandingPadInfo *R) {
373 const std::vector<int> &LIds = L->TypeIds, &RIds = R->TypeIds;
374 unsigned LSize = LIds.size(), RSize = RIds.size();
375 unsigned MinSize = LSize < RSize ? LSize : RSize;
377 for (unsigned i = 0; i != MinSize; ++i)
378 if (LIds[i] != RIds[i])
379 return LIds[i] < RIds[i];
381 return LSize < RSize;
384 /// ComputeActionsTable - Compute the actions table and gather the first action
385 /// index for each landing pad site.
386 unsigned DwarfException::
387 ComputeActionsTable(const SmallVectorImpl<const LandingPadInfo*> &LandingPads,
388 SmallVectorImpl<ActionEntry> &Actions,
389 SmallVectorImpl<unsigned> &FirstActions) {
391 // The action table follows the call-site table in the LSDA. The individual
392 // records are of two types:
395 // * Exception specification
397 // The two record kinds have the same format, with only small differences.
398 // They are distinguished by the "switch value" field: Catch clauses
399 // (TypeInfos) have strictly positive switch values, and exception
400 // specifications (FilterIds) have strictly negative switch values. Value 0
401 // indicates a catch-all clause.
403 // Negative type IDs index into FilterIds. Positive type IDs index into
404 // TypeInfos. The value written for a positive type ID is just the type ID
405 // itself. For a negative type ID, however, the value written is the
406 // (negative) byte offset of the corresponding FilterIds entry. The byte
407 // offset is usually equal to the type ID (because the FilterIds entries are
408 // written using a variable width encoding, which outputs one byte per entry
409 // as long as the value written is not too large) but can differ. This kind
410 // of complication does not occur for positive type IDs because type infos are
411 // output using a fixed width encoding. FilterOffsets[i] holds the byte
412 // offset corresponding to FilterIds[i].
414 const std::vector<unsigned> &FilterIds = MMI->getFilterIds();
415 SmallVector<int, 16> FilterOffsets;
416 FilterOffsets.reserve(FilterIds.size());
419 for (std::vector<unsigned>::const_iterator
420 I = FilterIds.begin(), E = FilterIds.end(); I != E; ++I) {
421 FilterOffsets.push_back(Offset);
422 Offset -= MCAsmInfo::getULEB128Size(*I);
425 FirstActions.reserve(LandingPads.size());
428 unsigned SizeActions = 0;
429 const LandingPadInfo *PrevLPI = 0;
431 for (SmallVectorImpl<const LandingPadInfo *>::const_iterator
432 I = LandingPads.begin(), E = LandingPads.end(); I != E; ++I) {
433 const LandingPadInfo *LPI = *I;
434 const std::vector<int> &TypeIds = LPI->TypeIds;
435 const unsigned NumShared = PrevLPI ? SharedTypeIds(LPI, PrevLPI) : 0;
436 unsigned SizeSiteActions = 0;
438 if (NumShared < TypeIds.size()) {
439 unsigned SizeAction = 0;
440 ActionEntry *PrevAction = 0;
443 const unsigned SizePrevIds = PrevLPI->TypeIds.size();
444 assert(Actions.size());
445 PrevAction = &Actions.back();
446 SizeAction = MCAsmInfo::getSLEB128Size(PrevAction->NextAction) +
447 MCAsmInfo::getSLEB128Size(PrevAction->ValueForTypeID);
449 for (unsigned j = NumShared; j != SizePrevIds; ++j) {
451 MCAsmInfo::getSLEB128Size(PrevAction->ValueForTypeID);
452 SizeAction += -PrevAction->NextAction;
453 PrevAction = PrevAction->Previous;
457 // Compute the actions.
458 for (unsigned J = NumShared, M = TypeIds.size(); J != M; ++J) {
459 int TypeID = TypeIds[J];
460 assert(-1 - TypeID < (int)FilterOffsets.size() && "Unknown filter id!");
461 int ValueForTypeID = TypeID < 0 ? FilterOffsets[-1 - TypeID] : TypeID;
462 unsigned SizeTypeID = MCAsmInfo::getSLEB128Size(ValueForTypeID);
464 int NextAction = SizeAction ? -(SizeAction + SizeTypeID) : 0;
465 SizeAction = SizeTypeID + MCAsmInfo::getSLEB128Size(NextAction);
466 SizeSiteActions += SizeAction;
468 ActionEntry Action = { ValueForTypeID, NextAction, PrevAction };
469 Actions.push_back(Action);
470 PrevAction = &Actions.back();
473 // Record the first action of the landing pad site.
474 FirstAction = SizeActions + SizeSiteActions - SizeAction + 1;
475 } // else identical - re-use previous FirstAction
477 // Information used when created the call-site table. The action record
478 // field of the call site record is the offset of the first associated
479 // action record, relative to the start of the actions table. This value is
480 // biased by 1 (1 in dicating the start of the actions table), and 0
481 // indicates that there are no actions.
482 FirstActions.push_back(FirstAction);
484 // Compute this sites contribution to size.
485 SizeActions += SizeSiteActions;
493 /// CallToNoUnwindFunction - Return `true' if this is a call to a function
494 /// marked `nounwind'. Return `false' otherwise.
495 bool DwarfException::CallToNoUnwindFunction(const MachineInstr *MI) {
496 assert(MI->getDesc().isCall() && "This should be a call instruction!");
498 bool MarkedNoUnwind = false;
499 bool SawFunc = false;
501 for (unsigned I = 0, E = MI->getNumOperands(); I != E; ++I) {
502 const MachineOperand &MO = MI->getOperand(I);
505 if (Function *F = dyn_cast<Function>(MO.getGlobal())) {
507 // Be conservative. If we have more than one function operand for this
508 // call, then we can't make the assumption that it's the callee and
509 // not a parameter to the call.
511 // FIXME: Determine if there's a way to say that `F' is the callee or
513 MarkedNoUnwind = false;
517 MarkedNoUnwind = F->doesNotThrow();
523 return MarkedNoUnwind;
526 /// ComputeCallSiteTable - Compute the call-site table. The entry for an invoke
527 /// has a try-range containing the call, a non-zero landing pad, and an
528 /// appropriate action. The entry for an ordinary call has a try-range
529 /// containing the call and zero for the landing pad and the action. Calls
530 /// marked 'nounwind' have no entry and must not be contained in the try-range
531 /// of any entry - they form gaps in the table. Entries must be ordered by
532 /// try-range address.
533 void DwarfException::
534 ComputeCallSiteTable(SmallVectorImpl<CallSiteEntry> &CallSites,
535 const RangeMapType &PadMap,
536 const SmallVectorImpl<const LandingPadInfo *> &LandingPads,
537 const SmallVectorImpl<unsigned> &FirstActions) {
538 // The end label of the previous invoke or nounwind try-range.
539 unsigned LastLabel = 0;
541 // Whether there is a potentially throwing instruction (currently this means
542 // an ordinary call) between the end of the previous try-range and now.
543 bool SawPotentiallyThrowing = false;
545 // Whether the last CallSite entry was for an invoke.
546 bool PreviousIsInvoke = false;
548 // Visit all instructions in order of address.
549 for (MachineFunction::const_iterator I = MF->begin(), E = MF->end();
551 for (MachineBasicBlock::const_iterator MI = I->begin(), E = I->end();
553 if (!MI->isLabel()) {
554 if (MI->getDesc().isCall())
555 SawPotentiallyThrowing |= !CallToNoUnwindFunction(MI);
560 unsigned BeginLabel = MI->getOperand(0).getImm();
561 assert(BeginLabel && "Invalid label!");
563 // End of the previous try-range?
564 if (BeginLabel == LastLabel)
565 SawPotentiallyThrowing = false;
567 // Beginning of a new try-range?
568 RangeMapType::const_iterator L = PadMap.find(BeginLabel);
569 if (L == PadMap.end())
570 // Nope, it was just some random label.
573 const PadRange &P = L->second;
574 const LandingPadInfo *LandingPad = LandingPads[P.PadIndex];
575 assert(BeginLabel == LandingPad->BeginLabels[P.RangeIndex] &&
576 "Inconsistent landing pad map!");
578 // For Dwarf exception handling (SjLj handling doesn't use this). If some
579 // instruction between the previous try-range and this one may throw,
580 // create a call-site entry with no landing pad for the region between the
582 if (SawPotentiallyThrowing &&
583 MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf) {
584 CallSiteEntry Site = { LastLabel, BeginLabel, 0, 0 };
585 CallSites.push_back(Site);
586 PreviousIsInvoke = false;
589 LastLabel = LandingPad->EndLabels[P.RangeIndex];
590 assert(BeginLabel && LastLabel && "Invalid landing pad!");
592 if (LandingPad->LandingPadLabel) {
593 // This try-range is for an invoke.
594 CallSiteEntry Site = {
597 LandingPad->LandingPadLabel,
598 FirstActions[P.PadIndex]
601 // Try to merge with the previous call-site. SJLJ doesn't do this
602 if (PreviousIsInvoke &&
603 MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf) {
604 CallSiteEntry &Prev = CallSites.back();
605 if (Site.PadLabel == Prev.PadLabel && Site.Action == Prev.Action) {
606 // Extend the range of the previous entry.
607 Prev.EndLabel = Site.EndLabel;
612 // Otherwise, create a new call-site.
613 CallSites.push_back(Site);
614 PreviousIsInvoke = true;
617 PreviousIsInvoke = false;
622 // If some instruction between the previous try-range and the end of the
623 // function may throw, create a call-site entry with no landing pad for the
624 // region following the try-range.
625 if (SawPotentiallyThrowing &&
626 MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf) {
627 CallSiteEntry Site = { LastLabel, 0, 0, 0 };
628 CallSites.push_back(Site);
632 /// EmitExceptionTable - Emit landing pads and actions.
634 /// The general organization of the table is complex, but the basic concepts are
635 /// easy. First there is a header which describes the location and organization
636 /// of the three components that follow.
638 /// 1. The landing pad site information describes the range of code covered by
639 /// the try. In our case it's an accumulation of the ranges covered by the
640 /// invokes in the try. There is also a reference to the landing pad that
641 /// handles the exception once processed. Finally an index into the actions
643 /// 2. The action table, in our case, is composed of pairs of type IDs and next
644 /// action offset. Starting with the action index from the landing pad
645 /// site, each type ID is checked for a match to the current exception. If
646 /// it matches then the exception and type id are passed on to the landing
647 /// pad. Otherwise the next action is looked up. This chain is terminated
648 /// with a next action of zero. If no type id is found then the frame is
649 /// unwound and handling continues.
650 /// 3. Type ID table contains references to all the C++ typeinfo for all
651 /// catches in the function. This tables is reverse indexed base 1.
652 void DwarfException::EmitExceptionTable() {
653 const std::vector<GlobalVariable *> &TypeInfos = MMI->getTypeInfos();
654 const std::vector<unsigned> &FilterIds = MMI->getFilterIds();
655 const std::vector<LandingPadInfo> &PadInfos = MMI->getLandingPads();
656 if (PadInfos.empty()) return;
658 // Sort the landing pads in order of their type ids. This is used to fold
659 // duplicate actions.
660 SmallVector<const LandingPadInfo *, 64> LandingPads;
661 LandingPads.reserve(PadInfos.size());
663 for (unsigned i = 0, N = PadInfos.size(); i != N; ++i)
664 LandingPads.push_back(&PadInfos[i]);
666 std::sort(LandingPads.begin(), LandingPads.end(), PadLT);
668 // Compute the actions table and gather the first action index for each
670 SmallVector<ActionEntry, 32> Actions;
671 SmallVector<unsigned, 64> FirstActions;
672 unsigned SizeActions = ComputeActionsTable(LandingPads, Actions,
675 // Invokes and nounwind calls have entries in PadMap (due to being bracketed
676 // by try-range labels when lowered). Ordinary calls do not, so appropriate
677 // try-ranges for them need be deduced when using DWARF exception handling.
679 for (unsigned i = 0, N = LandingPads.size(); i != N; ++i) {
680 const LandingPadInfo *LandingPad = LandingPads[i];
681 for (unsigned j = 0, E = LandingPad->BeginLabels.size(); j != E; ++j) {
682 unsigned BeginLabel = LandingPad->BeginLabels[j];
683 assert(!PadMap.count(BeginLabel) && "Duplicate landing pad labels!");
684 PadRange P = { i, j };
685 PadMap[BeginLabel] = P;
689 // Compute the call-site table.
690 SmallVector<CallSiteEntry, 64> CallSites;
691 ComputeCallSiteTable(CallSites, PadMap, LandingPads, FirstActions);
696 const unsigned SiteStartSize = SizeOfEncodedValue(dwarf::DW_EH_PE_udata4);
697 const unsigned SiteLengthSize = SizeOfEncodedValue(dwarf::DW_EH_PE_udata4);
698 const unsigned LandingPadSize = SizeOfEncodedValue(dwarf::DW_EH_PE_udata4);
699 bool IsSJLJ = MAI->getExceptionHandlingType() == ExceptionHandling::SjLj;
700 bool HaveTTData = IsSJLJ ? (!TypeInfos.empty() || !FilterIds.empty()) : true;
706 SizeSites = CallSites.size() *
707 (SiteStartSize + SiteLengthSize + LandingPadSize);
709 for (unsigned i = 0, e = CallSites.size(); i < e; ++i) {
710 SizeSites += MCAsmInfo::getULEB128Size(CallSites[i].Action);
712 SizeSites += MCAsmInfo::getULEB128Size(i);
716 const MCSection *LSDASection = Asm->getObjFileLowering().getLSDASection();
717 unsigned TTypeFormat;
718 unsigned TypeFormatSize;
721 // For SjLj exceptions, if there is no TypeInfo, then we just explicitly say
722 // that we're omitting that bit.
723 TTypeFormat = dwarf::DW_EH_PE_omit;
724 TypeFormatSize = SizeOfEncodedValue(dwarf::DW_EH_PE_absptr);
726 // Okay, we have actual filters or typeinfos to emit. As such, we need to
727 // pick a type encoding for them. We're about to emit a list of pointers to
728 // typeinfo objects at the end of the LSDA. However, unless we're in static
729 // mode, this reference will require a relocation by the dynamic linker.
731 // Because of this, we have a couple of options:
733 // 1) If we are in -static mode, we can always use an absolute reference
734 // from the LSDA, because the static linker will resolve it.
736 // 2) Otherwise, if the LSDA section is writable, we can output the direct
737 // reference to the typeinfo and allow the dynamic linker to relocate
738 // it. Since it is in a writable section, the dynamic linker won't
741 // 3) Finally, if we're in PIC mode and the LDSA section isn't writable,
742 // we need to use some form of indirection. For example, on Darwin,
743 // we can output a statically-relocatable reference to a dyld stub. The
744 // offset to the stub is constant, but the contents are in a section
745 // that is updated by the dynamic linker. This is easy enough, but we
746 // need to tell the personality function of the unwinder to indirect
747 // through the dyld stub.
749 // FIXME: When (3) is actually implemented, we'll have to emit the stubs
750 // somewhere. This predicate should be moved to a shared location that is
751 // in target-independent code.
753 if (LSDASection->getKind().isWriteable() ||
754 Asm->TM.getRelocationModel() == Reloc::Static)
755 TTypeFormat = dwarf::DW_EH_PE_absptr;
757 TTypeFormat = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
758 dwarf::DW_EH_PE_sdata4;
760 TypeFormatSize = SizeOfEncodedValue(TTypeFormat);
763 // Begin the exception table.
764 Asm->OutStreamer.SwitchSection(LSDASection);
765 Asm->EmitAlignment(2, 0, 0, false);
767 O << "GCC_except_table" << SubprogramCount << ":\n";
769 // The type infos need to be aligned. GCC does this by inserting padding just
770 // before the type infos. However, this changes the size of the exception
771 // table, so you need to take this into account when you output the exception
772 // table size. However, the size is output using a variable length encoding.
773 // So by increasing the size by inserting padding, you may increase the number
774 // of bytes used for writing the size. If it increases, say by one byte, then
775 // you now need to output one less byte of padding to get the type infos
776 // aligned. However this decreases the size of the exception table. This
777 // changes the value you have to output for the exception table size. Due to
778 // the variable length encoding, the number of bytes used for writing the
779 // length may decrease. If so, you then have to increase the amount of
780 // padding. And so on. If you look carefully at the GCC code you will see that
781 // it indeed does this in a loop, going on and on until the values stabilize.
782 // We chose another solution: don't output padding inside the table like GCC
783 // does, instead output it before the table.
784 unsigned SizeTypes = TypeInfos.size() * TypeFormatSize;
785 unsigned TyOffset = sizeof(int8_t) + // Call site format
786 MCAsmInfo::getULEB128Size(SizeSites) + // Call-site table length
787 SizeSites + SizeActions + SizeTypes;
788 unsigned TotalSize = sizeof(int8_t) + // LPStart format
789 sizeof(int8_t) + // TType format
791 MCAsmInfo::getULEB128Size(TyOffset) : 0) + // TType base offset
793 unsigned SizeAlign = (4 - TotalSize) & 3;
795 for (unsigned i = 0; i != SizeAlign; ++i) {
800 EmitLabel("exception", SubprogramCount);
803 SmallString<16> LSDAName;
804 raw_svector_ostream(LSDAName) << MAI->getPrivateGlobalPrefix() <<
805 "_LSDA_" << Asm->getFunctionNumber();
806 O << LSDAName.str() << ":\n";
810 Asm->EmitInt8(dwarf::DW_EH_PE_omit);
811 Asm->EOL("@LPStart format", dwarf::DW_EH_PE_omit);
813 Asm->EmitInt8(TTypeFormat);
814 Asm->EOL("@TType format", TTypeFormat);
817 Asm->EmitULEB128Bytes(TyOffset);
818 Asm->EOL("@TType base offset");
821 // SjLj Exception handling
823 Asm->EmitInt8(dwarf::DW_EH_PE_udata4);
824 Asm->EOL("Call site format", dwarf::DW_EH_PE_udata4);
825 Asm->EmitULEB128Bytes(SizeSites);
826 Asm->EOL("Call site table length");
828 // Emit the landing pad site information.
830 for (SmallVectorImpl<CallSiteEntry>::const_iterator
831 I = CallSites.begin(), E = CallSites.end(); I != E; ++I, ++idx) {
832 const CallSiteEntry &S = *I;
834 // Offset of the landing pad, counted in 16-byte bundles relative to the
836 Asm->EmitULEB128Bytes(idx);
837 Asm->EOL("Landing pad");
839 // Offset of the first associated action record, relative to the start of
840 // the action table. This value is biased by 1 (1 indicates the start of
841 // the action table), and 0 indicates that there are no actions.
842 Asm->EmitULEB128Bytes(S.Action);
846 // DWARF Exception handling
847 assert(MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf);
849 // The call-site table is a list of all call sites that may throw an
850 // exception (including C++ 'throw' statements) in the procedure
851 // fragment. It immediately follows the LSDA header. Each entry indicates,
852 // for a given call, the first corresponding action record and corresponding
855 // The table begins with the number of bytes, stored as an LEB128
856 // compressed, unsigned integer. The records immediately follow the record
857 // count. They are sorted in increasing call-site address. Each record
860 // * The position of the call-site.
861 // * The position of the landing pad.
862 // * The first action record for that call site.
864 // A missing entry in the call-site table indicates that a call is not
865 // supposed to throw.
867 // Emit the landing pad call site table.
868 Asm->EmitInt8(dwarf::DW_EH_PE_udata4);
869 Asm->EOL("Call site format", dwarf::DW_EH_PE_udata4);
870 Asm->EmitULEB128Bytes(SizeSites);
871 Asm->EOL("Call site table size");
873 for (SmallVectorImpl<CallSiteEntry>::const_iterator
874 I = CallSites.begin(), E = CallSites.end(); I != E; ++I) {
875 const CallSiteEntry &S = *I;
876 const char *BeginTag;
877 unsigned BeginNumber;
880 BeginTag = "eh_func_begin";
881 BeginNumber = SubprogramCount;
884 BeginNumber = S.BeginLabel;
887 // Offset of the call site relative to the previous call site, counted in
888 // number of 16-byte bundles. The first call site is counted relative to
889 // the start of the procedure fragment.
890 EmitSectionOffset(BeginTag, "eh_func_begin", BeginNumber, SubprogramCount,
892 Asm->EOL("Region start");
895 EmitDifference("eh_func_end", SubprogramCount, BeginTag, BeginNumber,
898 EmitDifference("label", S.EndLabel, BeginTag, BeginNumber, true);
900 Asm->EOL("Region length");
902 // Offset of the landing pad, counted in 16-byte bundles relative to the
907 EmitSectionOffset("label", "eh_func_begin", S.PadLabel, SubprogramCount,
910 Asm->EOL("Landing pad");
912 // Offset of the first associated action record, relative to the start of
913 // the action table. This value is biased by 1 (1 indicates the start of
914 // the action table), and 0 indicates that there are no actions.
915 Asm->EmitULEB128Bytes(S.Action);
920 // Emit the Action Table.
921 for (SmallVectorImpl<ActionEntry>::const_iterator
922 I = Actions.begin(), E = Actions.end(); I != E; ++I) {
923 const ActionEntry &Action = *I;
927 // Used by the runtime to match the type of the thrown exception to the
928 // type of the catch clauses or the types in the exception specification.
930 Asm->EmitSLEB128Bytes(Action.ValueForTypeID);
931 Asm->EOL("TypeInfo index");
935 // Self-relative signed displacement in bytes of the next action record,
936 // or 0 if there is no next action record.
938 Asm->EmitSLEB128Bytes(Action.NextAction);
939 Asm->EOL("Next action");
942 // Emit the Catch TypeInfos.
943 for (std::vector<GlobalVariable *>::const_reverse_iterator
944 I = TypeInfos.rbegin(), E = TypeInfos.rend(); I != E; ++I) {
945 const GlobalVariable *GV = *I;
949 Asm->GetGlobalValueSymbol(GV)->print(O, MAI);
954 Asm->EOL("TypeInfo");
957 // Emit the Exception Specifications.
958 for (std::vector<unsigned>::const_iterator
959 I = FilterIds.begin(), E = FilterIds.end(); I < E; ++I) {
960 unsigned TypeID = *I;
961 Asm->EmitULEB128Bytes(TypeID);
963 Asm->EOL("Exception specification");
968 Asm->EmitAlignment(2, 0, 0, false);
971 /// EndModule - Emit all exception information that should come after the
973 void DwarfException::EndModule() {
974 if (MAI->getExceptionHandlingType() != ExceptionHandling::Dwarf)
977 if (!shouldEmitMovesModule && !shouldEmitTableModule)
980 if (TimePassesIsEnabled)
981 ExceptionTimer->startTimer();
983 const std::vector<Function *> Personalities = MMI->getPersonalities();
985 for (unsigned I = 0, E = Personalities.size(); I < E; ++I)
986 EmitCIE(Personalities[I], I);
988 for (std::vector<FunctionEHFrameInfo>::iterator
989 I = EHFrames.begin(), E = EHFrames.end(); I != E; ++I)
992 if (TimePassesIsEnabled)
993 ExceptionTimer->stopTimer();
996 /// BeginFunction - Gather pre-function exception information. Assumes it's
997 /// being emitted immediately after the function entry point.
998 void DwarfException::BeginFunction(MachineFunction *MF) {
999 if (!MMI || !MAI->doesSupportExceptionHandling()) return;
1001 if (TimePassesIsEnabled)
1002 ExceptionTimer->startTimer();
1005 shouldEmitTable = shouldEmitMoves = false;
1007 // Map all labels and get rid of any dead landing pads.
1008 MMI->TidyLandingPads();
1010 // If any landing pads survive, we need an EH table.
1011 if (!MMI->getLandingPads().empty())
1012 shouldEmitTable = true;
1014 // See if we need frame move info.
1015 if (!MF->getFunction()->doesNotThrow() || UnwindTablesMandatory)
1016 shouldEmitMoves = true;
1018 if (shouldEmitMoves || shouldEmitTable)
1019 // Assumes in correct section after the entry point.
1020 EmitLabel("eh_func_begin", ++SubprogramCount);
1022 shouldEmitTableModule |= shouldEmitTable;
1023 shouldEmitMovesModule |= shouldEmitMoves;
1025 if (TimePassesIsEnabled)
1026 ExceptionTimer->stopTimer();
1029 /// EndFunction - Gather and emit post-function exception information.
1031 void DwarfException::EndFunction() {
1032 if (!shouldEmitMoves && !shouldEmitTable) return;
1034 if (TimePassesIsEnabled)
1035 ExceptionTimer->startTimer();
1037 EmitLabel("eh_func_end", SubprogramCount);
1038 EmitExceptionTable();
1040 const MCSymbol *FunctionEHSym =
1041 Asm->GetSymbolWithGlobalValueBase(MF->getFunction(), ".eh",
1042 Asm->MAI->is_EHSymbolPrivate());
1044 // Save EH frame information
1045 EHFrames.push_back(FunctionEHFrameInfo(FunctionEHSym, SubprogramCount,
1046 MMI->getPersonalityIndex(),
1047 MF->getFrameInfo()->hasCalls(),
1048 !MMI->getLandingPads().empty(),
1049 MMI->getFrameMoves(),
1050 MF->getFunction()));
1052 // Record if this personality index uses a landing pad.
1053 UsesLSDA[MMI->getPersonalityIndex()] |= !MMI->getLandingPads().empty();
1055 if (TimePassesIsEnabled)
1056 ExceptionTimer->stopTimer();