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"
37 #include "llvm/ADT/Twine.h"
40 DwarfException::DwarfException(raw_ostream &OS, AsmPrinter *A,
42 : DwarfPrinter(OS, A, T, "eh"), shouldEmitTable(false),shouldEmitMoves(false),
43 shouldEmitTableModule(false), shouldEmitMovesModule(false),
45 if (TimePassesIsEnabled)
46 ExceptionTimer = new Timer("DWARF Exception Writer");
49 DwarfException::~DwarfException() {
50 delete ExceptionTimer;
53 /// SizeOfEncodedValue - Return the size of the encoding in bytes.
54 unsigned DwarfException::SizeOfEncodedValue(unsigned Encoding) {
55 if (Encoding == dwarf::DW_EH_PE_omit)
58 switch (Encoding & 0x07) {
59 case dwarf::DW_EH_PE_absptr:
60 return TD->getPointerSize();
61 case dwarf::DW_EH_PE_udata2:
63 case dwarf::DW_EH_PE_udata4:
65 case dwarf::DW_EH_PE_udata8:
69 assert(0 && "Invalid encoded value.");
73 /// CreateLabelDiff - Emit a label and subtract it from the expression we
74 /// already have. This is equivalent to emitting "foo - .", but we have to emit
75 /// the label for "." directly.
76 const MCExpr *DwarfException::CreateLabelDiff(const MCExpr *ExprRef,
77 const char *LabelName,
80 raw_svector_ostream(Name) << MAI->getPrivateGlobalPrefix()
81 << LabelName << Asm->getFunctionNumber()
83 MCSymbol *DotSym = Asm->OutContext.GetOrCreateSymbol(Name.str());
84 Asm->OutStreamer.EmitLabel(DotSym);
86 return MCBinaryExpr::CreateSub(ExprRef,
87 MCSymbolRefExpr::Create(DotSym,
92 /// EmitCIE - Emit a Common Information Entry (CIE). This holds information that
93 /// is shared among many Frame Description Entries. There is at least one CIE
94 /// in every non-empty .debug_frame section.
95 void DwarfException::EmitCIE(const Function *PersonalityFn, unsigned Index) {
96 // Size and sign of stack growth.
98 Asm->TM.getFrameInfo()->getStackGrowthDirection() ==
99 TargetFrameInfo::StackGrowsUp ?
100 TD->getPointerSize() : -TD->getPointerSize();
102 const TargetLoweringObjectFile &TLOF = Asm->getObjFileLowering();
104 // Begin eh frame section.
105 Asm->OutStreamer.SwitchSection(TLOF.getEHFrameSection());
107 if (MAI->is_EHSymbolPrivate())
108 O << MAI->getPrivateGlobalPrefix();
109 O << "EH_frame" << Index << ":\n";
111 EmitLabel("section_eh_frame", Index);
113 // Define base labels.
114 EmitLabel("eh_frame_common", Index);
116 // Define the eh frame length.
117 EmitDifference("eh_frame_common_end", Index,
118 "eh_frame_common_begin", Index, true);
119 EOL("Length of Common Information Entry");
122 EmitLabel("eh_frame_common_begin", Index);
123 if (Asm->VerboseAsm) Asm->OutStreamer.AddComment("CIE Identifier Tag");
124 Asm->OutStreamer.EmitIntValue(0, 4/*size*/, 0/*addrspace*/);
125 if (Asm->VerboseAsm) Asm->OutStreamer.AddComment("DW_CIE_VERSION");
126 Asm->OutStreamer.EmitIntValue(dwarf::DW_CIE_VERSION, 1/*size*/, 0/*addr*/);
128 // The personality presence indicates that language specific information will
129 // show up in the eh frame. Find out how we are supposed to lower the
130 // personality function reference:
131 const MCExpr *PersonalityRef = 0;
132 bool IsPersonalityIndirect = false, IsPersonalityPCRel = false;
134 // FIXME: HANDLE STATIC CODEGEN MODEL HERE.
136 // In non-static mode, ask the object file how to represent this reference.
138 TLOF.getSymbolForDwarfGlobalReference(PersonalityFn, Asm->Mang,
140 IsPersonalityIndirect,
144 unsigned PerEncoding = dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4;
145 if (IsPersonalityIndirect)
146 PerEncoding |= dwarf::DW_EH_PE_indirect;
147 unsigned LSDAEncoding = dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4;
148 unsigned FDEEncoding = dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4;
150 char Augmentation[6] = { 0 };
151 unsigned AugmentationSize = 0;
152 char *APtr = Augmentation + 1;
154 if (PersonalityRef) {
155 // There is a personality function.
157 AugmentationSize += 1 + SizeOfEncodedValue(PerEncoding);
160 if (UsesLSDA[Index]) {
161 // An LSDA pointer is in the FDE augmentation.
166 if (FDEEncoding != dwarf::DW_EH_PE_absptr) {
167 // A non-default pointer encoding for the FDE.
172 if (APtr != Augmentation + 1)
173 Augmentation[0] = 'z';
175 Asm->OutStreamer.EmitBytes(StringRef(Augmentation, strlen(Augmentation)+1),0);
176 EOL("CIE Augmentation");
179 EmitULEB128(1, "CIE Code Alignment Factor");
180 EmitSLEB128(stackGrowth, "CIE Data Alignment Factor");
181 Asm->EmitInt8(RI->getDwarfRegNum(RI->getRARegister(), true));
182 EOL("CIE Return Address Column");
184 EmitULEB128(AugmentationSize, "Augmentation Size");
185 EmitEncodingByte(PerEncoding, "Personality");
187 // If there is a personality, we need to indicate the function's location.
188 if (PersonalityRef) {
189 if (!IsPersonalityPCRel)
190 PersonalityRef = CreateLabelDiff(PersonalityRef, "personalityref_addr",
193 O << MAI->getData32bitsDirective() << *PersonalityRef;
196 EmitEncodingByte(LSDAEncoding, "LSDA");
197 EmitEncodingByte(FDEEncoding, "FDE");
200 // Indicate locations of general callee saved registers in frame.
201 std::vector<MachineMove> Moves;
202 RI->getInitialFrameState(Moves);
203 EmitFrameMoves(NULL, 0, Moves, true);
205 // On Darwin the linker honors the alignment of eh_frame, which means it must
206 // be 8-byte on 64-bit targets to match what gcc does. Otherwise you get
207 // holes which confuse readers of eh_frame.
208 Asm->EmitAlignment(TD->getPointerSize() == 4 ? 2 : 3, 0, 0, false);
209 EmitLabel("eh_frame_common_end", Index);
213 /// EmitFDE - Emit the Frame Description Entry (FDE) for the function.
214 void DwarfException::EmitFDE(const FunctionEHFrameInfo &EHFrameInfo) {
215 assert(!EHFrameInfo.function->hasAvailableExternallyLinkage() &&
216 "Should not emit 'available externally' functions at all");
218 const Function *TheFunc = EHFrameInfo.function;
220 Asm->OutStreamer.SwitchSection(Asm->getObjFileLowering().getEHFrameSection());
222 // Externally visible entry into the functions eh frame info. If the
223 // corresponding function is static, this should not be externally visible.
224 if (!TheFunc->hasLocalLinkage())
225 if (const char *GlobalEHDirective = MAI->getGlobalEHDirective())
226 O << GlobalEHDirective << *EHFrameInfo.FunctionEHSym << '\n';
228 // If corresponding function is weak definition, this should be too.
229 if (TheFunc->isWeakForLinker() && MAI->getWeakDefDirective())
230 O << MAI->getWeakDefDirective() << *EHFrameInfo.FunctionEHSym << '\n';
232 // If corresponding function is hidden, this should be too.
233 if (TheFunc->hasHiddenVisibility())
234 if (MCSymbolAttr HiddenAttr = MAI->getHiddenVisibilityAttr())
235 Asm->OutStreamer.EmitSymbolAttribute(EHFrameInfo.FunctionEHSym,
238 // If there are no calls then you can't unwind. This may mean we can omit the
239 // EH Frame, but some environments do not handle weak absolute symbols. If
240 // UnwindTablesMandatory is set we cannot do this optimization; the unwind
241 // info is to be available for non-EH uses.
242 if (!EHFrameInfo.hasCalls && !UnwindTablesMandatory &&
243 (!TheFunc->isWeakForLinker() ||
244 !MAI->getWeakDefDirective() ||
245 MAI->getSupportsWeakOmittedEHFrame())) {
246 O << *EHFrameInfo.FunctionEHSym << " = 0\n";
247 // This name has no connection to the function, so it might get
248 // dead-stripped when the function is not, erroneously. Prohibit
249 // dead-stripping unconditionally.
250 if (MAI->hasNoDeadStrip())
251 Asm->OutStreamer.EmitSymbolAttribute(EHFrameInfo.FunctionEHSym,
254 O << *EHFrameInfo.FunctionEHSym << ":\n";
257 EmitDifference("eh_frame_end", EHFrameInfo.Number,
258 "eh_frame_begin", EHFrameInfo.Number, true);
259 EOL("Length of Frame Information Entry");
261 EmitLabel("eh_frame_begin", EHFrameInfo.Number);
263 EmitSectionOffset("eh_frame_begin", "eh_frame_common",
264 EHFrameInfo.Number, EHFrameInfo.PersonalityIndex,
267 EOL("FDE CIE offset");
269 EmitReference("eh_func_begin", EHFrameInfo.Number, true, true);
270 EOL("FDE initial location");
271 EmitDifference("eh_func_end", EHFrameInfo.Number,
272 "eh_func_begin", EHFrameInfo.Number, true);
273 EOL("FDE address range");
275 // If there is a personality and landing pads then point to the language
276 // specific data area in the exception table.
277 if (MMI->getPersonalities()[0] != NULL) {
279 if (Asm->TM.getLSDAEncoding() != DwarfLSDAEncoding::EightByte) {
280 EmitULEB128(4, "Augmentation size");
282 if (EHFrameInfo.hasLandingPads)
283 EmitReference("exception", EHFrameInfo.Number, true, true);
285 Asm->OutStreamer.EmitIntValue(0, 4/*size*/, 0/*addrspace*/);
287 EmitULEB128(TD->getPointerSize(), "Augmentation size");
289 if (EHFrameInfo.hasLandingPads) {
290 EmitReference("exception", EHFrameInfo.Number, true, false);
292 Asm->OutStreamer.EmitIntValue(0, TD->getPointerSize(),
297 EOL("Language Specific Data Area");
299 EmitULEB128(0, "Augmentation size");
302 // Indicate locations of function specific callee saved registers in frame.
303 EmitFrameMoves("eh_func_begin", EHFrameInfo.Number, EHFrameInfo.Moves,
306 // On Darwin the linker honors the alignment of eh_frame, which means it
307 // must be 8-byte on 64-bit targets to match what gcc does. Otherwise you
308 // get holes which confuse readers of eh_frame.
309 Asm->EmitAlignment(TD->getPointerSize() == sizeof(int32_t) ? 2 : 3,
311 EmitLabel("eh_frame_end", EHFrameInfo.Number);
313 // If the function is marked used, this table should be also. We cannot
314 // make the mark unconditional in this case, since retaining the table also
315 // retains the function in this case, and there is code around that depends
316 // on unused functions (calling undefined externals) being dead-stripped to
317 // link correctly. Yes, there really is.
318 if (MMI->isUsedFunction(EHFrameInfo.function))
319 if (MAI->hasNoDeadStrip())
320 Asm->OutStreamer.EmitSymbolAttribute(EHFrameInfo.FunctionEHSym,
326 /// SharedTypeIds - How many leading type ids two landing pads have in common.
327 unsigned DwarfException::SharedTypeIds(const LandingPadInfo *L,
328 const LandingPadInfo *R) {
329 const std::vector<int> &LIds = L->TypeIds, &RIds = R->TypeIds;
330 unsigned LSize = LIds.size(), RSize = RIds.size();
331 unsigned MinSize = LSize < RSize ? LSize : RSize;
334 for (; Count != MinSize; ++Count)
335 if (LIds[Count] != RIds[Count])
341 /// PadLT - Order landing pads lexicographically by type id.
342 bool DwarfException::PadLT(const LandingPadInfo *L, const LandingPadInfo *R) {
343 const std::vector<int> &LIds = L->TypeIds, &RIds = R->TypeIds;
344 unsigned LSize = LIds.size(), RSize = RIds.size();
345 unsigned MinSize = LSize < RSize ? LSize : RSize;
347 for (unsigned i = 0; i != MinSize; ++i)
348 if (LIds[i] != RIds[i])
349 return LIds[i] < RIds[i];
351 return LSize < RSize;
354 /// ComputeActionsTable - Compute the actions table and gather the first action
355 /// index for each landing pad site.
356 unsigned DwarfException::
357 ComputeActionsTable(const SmallVectorImpl<const LandingPadInfo*> &LandingPads,
358 SmallVectorImpl<ActionEntry> &Actions,
359 SmallVectorImpl<unsigned> &FirstActions) {
361 // The action table follows the call-site table in the LSDA. The individual
362 // records are of two types:
365 // * Exception specification
367 // The two record kinds have the same format, with only small differences.
368 // They are distinguished by the "switch value" field: Catch clauses
369 // (TypeInfos) have strictly positive switch values, and exception
370 // specifications (FilterIds) have strictly negative switch values. Value 0
371 // indicates a catch-all clause.
373 // Negative type IDs index into FilterIds. Positive type IDs index into
374 // TypeInfos. The value written for a positive type ID is just the type ID
375 // itself. For a negative type ID, however, the value written is the
376 // (negative) byte offset of the corresponding FilterIds entry. The byte
377 // offset is usually equal to the type ID (because the FilterIds entries are
378 // written using a variable width encoding, which outputs one byte per entry
379 // as long as the value written is not too large) but can differ. This kind
380 // of complication does not occur for positive type IDs because type infos are
381 // output using a fixed width encoding. FilterOffsets[i] holds the byte
382 // offset corresponding to FilterIds[i].
384 const std::vector<unsigned> &FilterIds = MMI->getFilterIds();
385 SmallVector<int, 16> FilterOffsets;
386 FilterOffsets.reserve(FilterIds.size());
389 for (std::vector<unsigned>::const_iterator
390 I = FilterIds.begin(), E = FilterIds.end(); I != E; ++I) {
391 FilterOffsets.push_back(Offset);
392 Offset -= MCAsmInfo::getULEB128Size(*I);
395 FirstActions.reserve(LandingPads.size());
398 unsigned SizeActions = 0;
399 const LandingPadInfo *PrevLPI = 0;
401 for (SmallVectorImpl<const LandingPadInfo *>::const_iterator
402 I = LandingPads.begin(), E = LandingPads.end(); I != E; ++I) {
403 const LandingPadInfo *LPI = *I;
404 const std::vector<int> &TypeIds = LPI->TypeIds;
405 const unsigned NumShared = PrevLPI ? SharedTypeIds(LPI, PrevLPI) : 0;
406 unsigned SizeSiteActions = 0;
408 if (NumShared < TypeIds.size()) {
409 unsigned SizeAction = 0;
410 unsigned PrevAction = (unsigned)-1;
413 const unsigned SizePrevIds = PrevLPI->TypeIds.size();
414 assert(Actions.size());
415 PrevAction = Actions.size() - 1;
417 MCAsmInfo::getSLEB128Size(Actions[PrevAction].NextAction) +
418 MCAsmInfo::getSLEB128Size(Actions[PrevAction].ValueForTypeID);
420 for (unsigned j = NumShared; j != SizePrevIds; ++j) {
421 assert(PrevAction != (unsigned)-1 && "PrevAction is invalid!");
423 MCAsmInfo::getSLEB128Size(Actions[PrevAction].ValueForTypeID);
424 SizeAction += -Actions[PrevAction].NextAction;
425 PrevAction = Actions[PrevAction].Previous;
429 // Compute the actions.
430 for (unsigned J = NumShared, M = TypeIds.size(); J != M; ++J) {
431 int TypeID = TypeIds[J];
432 assert(-1 - TypeID < (int)FilterOffsets.size() && "Unknown filter id!");
433 int ValueForTypeID = TypeID < 0 ? FilterOffsets[-1 - TypeID] : TypeID;
434 unsigned SizeTypeID = MCAsmInfo::getSLEB128Size(ValueForTypeID);
436 int NextAction = SizeAction ? -(SizeAction + SizeTypeID) : 0;
437 SizeAction = SizeTypeID + MCAsmInfo::getSLEB128Size(NextAction);
438 SizeSiteActions += SizeAction;
440 ActionEntry Action = { ValueForTypeID, NextAction, PrevAction };
441 Actions.push_back(Action);
442 PrevAction = Actions.size() - 1;
445 // Record the first action of the landing pad site.
446 FirstAction = SizeActions + SizeSiteActions - SizeAction + 1;
447 } // else identical - re-use previous FirstAction
449 // Information used when created the call-site table. The action record
450 // field of the call site record is the offset of the first associated
451 // action record, relative to the start of the actions table. This value is
452 // biased by 1 (1 indicating the start of the actions table), and 0
453 // indicates that there are no actions.
454 FirstActions.push_back(FirstAction);
456 // Compute this sites contribution to size.
457 SizeActions += SizeSiteActions;
465 /// CallToNoUnwindFunction - Return `true' if this is a call to a function
466 /// marked `nounwind'. Return `false' otherwise.
467 bool DwarfException::CallToNoUnwindFunction(const MachineInstr *MI) {
468 assert(MI->getDesc().isCall() && "This should be a call instruction!");
470 bool MarkedNoUnwind = false;
471 bool SawFunc = false;
473 for (unsigned I = 0, E = MI->getNumOperands(); I != E; ++I) {
474 const MachineOperand &MO = MI->getOperand(I);
477 if (Function *F = dyn_cast<Function>(MO.getGlobal())) {
479 // Be conservative. If we have more than one function operand for this
480 // call, then we can't make the assumption that it's the callee and
481 // not a parameter to the call.
483 // FIXME: Determine if there's a way to say that `F' is the callee or
485 MarkedNoUnwind = false;
489 MarkedNoUnwind = F->doesNotThrow();
495 return MarkedNoUnwind;
498 /// ComputeCallSiteTable - Compute the call-site table. The entry for an invoke
499 /// has a try-range containing the call, a non-zero landing pad, and an
500 /// appropriate action. The entry for an ordinary call has a try-range
501 /// containing the call and zero for the landing pad and the action. Calls
502 /// marked 'nounwind' have no entry and must not be contained in the try-range
503 /// of any entry - they form gaps in the table. Entries must be ordered by
504 /// try-range address.
505 void DwarfException::
506 ComputeCallSiteTable(SmallVectorImpl<CallSiteEntry> &CallSites,
507 const RangeMapType &PadMap,
508 const SmallVectorImpl<const LandingPadInfo *> &LandingPads,
509 const SmallVectorImpl<unsigned> &FirstActions) {
510 // The end label of the previous invoke or nounwind try-range.
511 unsigned LastLabel = 0;
513 // Whether there is a potentially throwing instruction (currently this means
514 // an ordinary call) between the end of the previous try-range and now.
515 bool SawPotentiallyThrowing = false;
517 // Whether the last CallSite entry was for an invoke.
518 bool PreviousIsInvoke = false;
520 // Visit all instructions in order of address.
521 for (MachineFunction::const_iterator I = MF->begin(), E = MF->end();
523 for (MachineBasicBlock::const_iterator MI = I->begin(), E = I->end();
525 if (!MI->isLabel()) {
526 if (MI->getDesc().isCall())
527 SawPotentiallyThrowing |= !CallToNoUnwindFunction(MI);
532 unsigned BeginLabel = MI->getOperand(0).getImm();
533 assert(BeginLabel && "Invalid label!");
535 // End of the previous try-range?
536 if (BeginLabel == LastLabel)
537 SawPotentiallyThrowing = false;
539 // Beginning of a new try-range?
540 RangeMapType::const_iterator L = PadMap.find(BeginLabel);
541 if (L == PadMap.end())
542 // Nope, it was just some random label.
545 const PadRange &P = L->second;
546 const LandingPadInfo *LandingPad = LandingPads[P.PadIndex];
547 assert(BeginLabel == LandingPad->BeginLabels[P.RangeIndex] &&
548 "Inconsistent landing pad map!");
550 // For Dwarf exception handling (SjLj handling doesn't use this). If some
551 // instruction between the previous try-range and this one may throw,
552 // create a call-site entry with no landing pad for the region between the
554 if (SawPotentiallyThrowing &&
555 MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf) {
556 CallSiteEntry Site = { LastLabel, BeginLabel, 0, 0 };
557 CallSites.push_back(Site);
558 PreviousIsInvoke = false;
561 LastLabel = LandingPad->EndLabels[P.RangeIndex];
562 assert(BeginLabel && LastLabel && "Invalid landing pad!");
564 if (LandingPad->LandingPadLabel) {
565 // This try-range is for an invoke.
566 CallSiteEntry Site = {
569 LandingPad->LandingPadLabel,
570 FirstActions[P.PadIndex]
573 // Try to merge with the previous call-site. SJLJ doesn't do this
574 if (PreviousIsInvoke &&
575 MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf) {
576 CallSiteEntry &Prev = CallSites.back();
577 if (Site.PadLabel == Prev.PadLabel && Site.Action == Prev.Action) {
578 // Extend the range of the previous entry.
579 Prev.EndLabel = Site.EndLabel;
584 // Otherwise, create a new call-site.
585 if (MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf)
586 CallSites.push_back(Site);
588 // SjLj EH must maintain the call sites in the order assigned
589 // to them by the SjLjPrepare pass.
590 unsigned SiteNo = MMI->getCallSiteBeginLabel(BeginLabel);
591 if (CallSites.size() < SiteNo)
592 CallSites.resize(SiteNo);
593 CallSites[SiteNo - 1] = Site;
595 PreviousIsInvoke = true;
598 PreviousIsInvoke = false;
603 // If some instruction between the previous try-range and the end of the
604 // function may throw, create a call-site entry with no landing pad for the
605 // region following the try-range.
606 if (SawPotentiallyThrowing &&
607 MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf) {
608 CallSiteEntry Site = { LastLabel, 0, 0, 0 };
609 CallSites.push_back(Site);
613 /// EmitExceptionTable - Emit landing pads and actions.
615 /// The general organization of the table is complex, but the basic concepts are
616 /// easy. First there is a header which describes the location and organization
617 /// of the three components that follow.
619 /// 1. The landing pad site information describes the range of code covered by
620 /// the try. In our case it's an accumulation of the ranges covered by the
621 /// invokes in the try. There is also a reference to the landing pad that
622 /// handles the exception once processed. Finally an index into the actions
624 /// 2. The action table, in our case, is composed of pairs of type IDs and next
625 /// action offset. Starting with the action index from the landing pad
626 /// site, each type ID is checked for a match to the current exception. If
627 /// it matches then the exception and type id are passed on to the landing
628 /// pad. Otherwise the next action is looked up. This chain is terminated
629 /// with a next action of zero. If no type id is found then the frame is
630 /// unwound and handling continues.
631 /// 3. Type ID table contains references to all the C++ typeinfo for all
632 /// catches in the function. This tables is reverse indexed base 1.
633 void DwarfException::EmitExceptionTable() {
634 const std::vector<GlobalVariable *> &TypeInfos = MMI->getTypeInfos();
635 const std::vector<unsigned> &FilterIds = MMI->getFilterIds();
636 const std::vector<LandingPadInfo> &PadInfos = MMI->getLandingPads();
637 if (PadInfos.empty()) return;
639 // Sort the landing pads in order of their type ids. This is used to fold
640 // duplicate actions.
641 SmallVector<const LandingPadInfo *, 64> LandingPads;
642 LandingPads.reserve(PadInfos.size());
644 for (unsigned i = 0, N = PadInfos.size(); i != N; ++i)
645 LandingPads.push_back(&PadInfos[i]);
647 std::sort(LandingPads.begin(), LandingPads.end(), PadLT);
649 // Compute the actions table and gather the first action index for each
651 SmallVector<ActionEntry, 32> Actions;
652 SmallVector<unsigned, 64> FirstActions;
653 unsigned SizeActions=ComputeActionsTable(LandingPads, Actions, FirstActions);
655 // Invokes and nounwind calls have entries in PadMap (due to being bracketed
656 // by try-range labels when lowered). Ordinary calls do not, so appropriate
657 // try-ranges for them need be deduced when using DWARF exception handling.
659 for (unsigned i = 0, N = LandingPads.size(); i != N; ++i) {
660 const LandingPadInfo *LandingPad = LandingPads[i];
661 for (unsigned j = 0, E = LandingPad->BeginLabels.size(); j != E; ++j) {
662 unsigned BeginLabel = LandingPad->BeginLabels[j];
663 assert(!PadMap.count(BeginLabel) && "Duplicate landing pad labels!");
664 PadRange P = { i, j };
665 PadMap[BeginLabel] = P;
669 // Compute the call-site table.
670 SmallVector<CallSiteEntry, 64> CallSites;
671 ComputeCallSiteTable(CallSites, PadMap, LandingPads, FirstActions);
676 const unsigned SiteStartSize = SizeOfEncodedValue(dwarf::DW_EH_PE_udata4);
677 const unsigned SiteLengthSize = SizeOfEncodedValue(dwarf::DW_EH_PE_udata4);
678 const unsigned LandingPadSize = SizeOfEncodedValue(dwarf::DW_EH_PE_udata4);
679 bool IsSJLJ = MAI->getExceptionHandlingType() == ExceptionHandling::SjLj;
680 bool HaveTTData = IsSJLJ ? (!TypeInfos.empty() || !FilterIds.empty()) : true;
686 SizeSites = CallSites.size() *
687 (SiteStartSize + SiteLengthSize + LandingPadSize);
689 for (unsigned i = 0, e = CallSites.size(); i < e; ++i) {
690 SizeSites += MCAsmInfo::getULEB128Size(CallSites[i].Action);
692 SizeSites += MCAsmInfo::getULEB128Size(i);
696 const MCSection *LSDASection = Asm->getObjFileLowering().getLSDASection();
697 unsigned TTypeFormat;
698 unsigned TypeFormatSize;
701 // For SjLj exceptions, if there is no TypeInfo, then we just explicitly say
702 // that we're omitting that bit.
703 TTypeFormat = dwarf::DW_EH_PE_omit;
704 TypeFormatSize = SizeOfEncodedValue(dwarf::DW_EH_PE_absptr);
706 // Okay, we have actual filters or typeinfos to emit. As such, we need to
707 // pick a type encoding for them. We're about to emit a list of pointers to
708 // typeinfo objects at the end of the LSDA. However, unless we're in static
709 // mode, this reference will require a relocation by the dynamic linker.
711 // Because of this, we have a couple of options:
713 // 1) If we are in -static mode, we can always use an absolute reference
714 // from the LSDA, because the static linker will resolve it.
716 // 2) Otherwise, if the LSDA section is writable, we can output the direct
717 // reference to the typeinfo and allow the dynamic linker to relocate
718 // it. Since it is in a writable section, the dynamic linker won't
721 // 3) Finally, if we're in PIC mode and the LDSA section isn't writable,
722 // we need to use some form of indirection. For example, on Darwin,
723 // we can output a statically-relocatable reference to a dyld stub. The
724 // offset to the stub is constant, but the contents are in a section
725 // that is updated by the dynamic linker. This is easy enough, but we
726 // need to tell the personality function of the unwinder to indirect
727 // through the dyld stub.
729 // FIXME: When (3) is actually implemented, we'll have to emit the stubs
730 // somewhere. This predicate should be moved to a shared location that is
731 // in target-independent code.
733 if (LSDASection->getKind().isWriteable() ||
734 Asm->TM.getRelocationModel() == Reloc::Static)
735 TTypeFormat = dwarf::DW_EH_PE_absptr;
737 TTypeFormat = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
738 dwarf::DW_EH_PE_sdata4;
740 TypeFormatSize = SizeOfEncodedValue(TTypeFormat);
743 // Begin the exception table.
744 Asm->OutStreamer.SwitchSection(LSDASection);
745 Asm->EmitAlignment(2, 0, 0, false);
747 O << "GCC_except_table" << SubprogramCount << ":\n";
749 // The type infos need to be aligned. GCC does this by inserting padding just
750 // before the type infos. However, this changes the size of the exception
751 // table, so you need to take this into account when you output the exception
752 // table size. However, the size is output using a variable length encoding.
753 // So by increasing the size by inserting padding, you may increase the number
754 // of bytes used for writing the size. If it increases, say by one byte, then
755 // you now need to output one less byte of padding to get the type infos
756 // aligned. However this decreases the size of the exception table. This
757 // changes the value you have to output for the exception table size. Due to
758 // the variable length encoding, the number of bytes used for writing the
759 // length may decrease. If so, you then have to increase the amount of
760 // padding. And so on. If you look carefully at the GCC code you will see that
761 // it indeed does this in a loop, going on and on until the values stabilize.
762 // We chose another solution: don't output padding inside the table like GCC
763 // does, instead output it before the table.
764 unsigned SizeTypes = TypeInfos.size() * TypeFormatSize;
765 unsigned TyOffset = sizeof(int8_t) + // Call site format
766 MCAsmInfo::getULEB128Size(SizeSites) + // Call site table length
767 SizeSites + SizeActions + SizeTypes;
768 unsigned TotalSize = sizeof(int8_t) + // LPStart format
769 sizeof(int8_t) + // TType format
771 MCAsmInfo::getULEB128Size(TyOffset) : 0) + // TType base offset
773 unsigned SizeAlign = (4 - TotalSize) & 3;
775 for (unsigned i = 0; i != SizeAlign; ++i) {
780 EmitLabel("exception", SubprogramCount);
783 SmallString<16> LSDAName;
784 raw_svector_ostream(LSDAName) << MAI->getPrivateGlobalPrefix() <<
785 "_LSDA_" << Asm->getFunctionNumber();
786 O << LSDAName.str() << ":\n";
790 EmitEncodingByte(dwarf::DW_EH_PE_omit, "@LPStart");
791 EmitEncodingByte(TTypeFormat, "@TType");
794 EmitULEB128(TyOffset, "@TType base offset");
796 // SjLj Exception handling
798 EmitEncodingByte(dwarf::DW_EH_PE_udata4, "Call site");
799 EmitULEB128(SizeSites, "Call site table length");
801 // Emit the landing pad site information.
803 for (SmallVectorImpl<CallSiteEntry>::const_iterator
804 I = CallSites.begin(), E = CallSites.end(); I != E; ++I, ++idx) {
805 const CallSiteEntry &S = *I;
807 // Offset of the landing pad, counted in 16-byte bundles relative to the
809 EmitULEB128(idx, "Landing pad");
811 // Offset of the first associated action record, relative to the start of
812 // the action table. This value is biased by 1 (1 indicates the start of
813 // the action table), and 0 indicates that there are no actions.
814 EmitULEB128(S.Action, "Action");
817 // DWARF Exception handling
818 assert(MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf);
820 // The call-site table is a list of all call sites that may throw an
821 // exception (including C++ 'throw' statements) in the procedure
822 // fragment. It immediately follows the LSDA header. Each entry indicates,
823 // for a given call, the first corresponding action record and corresponding
826 // The table begins with the number of bytes, stored as an LEB128
827 // compressed, unsigned integer. The records immediately follow the record
828 // count. They are sorted in increasing call-site address. Each record
831 // * The position of the call-site.
832 // * The position of the landing pad.
833 // * The first action record for that call site.
835 // A missing entry in the call-site table indicates that a call is not
836 // supposed to throw.
838 // Emit the landing pad call site table.
839 EmitEncodingByte(dwarf::DW_EH_PE_udata4, "Call site");
840 EmitULEB128(SizeSites, "Call site table length");
842 for (SmallVectorImpl<CallSiteEntry>::const_iterator
843 I = CallSites.begin(), E = CallSites.end(); I != E; ++I) {
844 const CallSiteEntry &S = *I;
845 const char *BeginTag;
846 unsigned BeginNumber;
849 BeginTag = "eh_func_begin";
850 BeginNumber = SubprogramCount;
853 BeginNumber = S.BeginLabel;
856 // Offset of the call site relative to the previous call site, counted in
857 // number of 16-byte bundles. The first call site is counted relative to
858 // the start of the procedure fragment.
859 EmitSectionOffset(BeginTag, "eh_func_begin", BeginNumber, SubprogramCount,
864 EmitDifference("eh_func_end", SubprogramCount, BeginTag, BeginNumber,
867 EmitDifference("label", S.EndLabel, BeginTag, BeginNumber, true);
869 EOL("Region length");
871 // Offset of the landing pad, counted in 16-byte bundles relative to the
874 Asm->OutStreamer.AddComment("Landing pad");
875 Asm->OutStreamer.EmitIntValue(0, 4/*size*/, 0/*addrspace*/);
877 EmitSectionOffset("label", "eh_func_begin", S.PadLabel, SubprogramCount,
882 // Offset of the first associated action record, relative to the start of
883 // the action table. This value is biased by 1 (1 indicates the start of
884 // the action table), and 0 indicates that there are no actions.
885 EmitULEB128(S.Action, "Action");
889 // Emit the Action Table.
890 if (Actions.size() != 0) EOL("-- Action Record Table --");
891 for (SmallVectorImpl<ActionEntry>::const_iterator
892 I = Actions.begin(), E = Actions.end(); I != E; ++I) {
893 const ActionEntry &Action = *I;
894 EOL("Action Record:");
898 // Used by the runtime to match the type of the thrown exception to the
899 // type of the catch clauses or the types in the exception specification.
900 EmitSLEB128(Action.ValueForTypeID, " TypeInfo index");
904 // Self-relative signed displacement in bytes of the next action record,
905 // or 0 if there is no next action record.
906 EmitSLEB128(Action.NextAction, " Next action");
909 // Emit the Catch TypeInfos.
910 if (!TypeInfos.empty()) EOL("-- Catch TypeInfos --");
911 for (std::vector<GlobalVariable *>::const_reverse_iterator
912 I = TypeInfos.rbegin(), E = TypeInfos.rend(); I != E; ++I) {
913 const GlobalVariable *GV = *I;
917 O << *Asm->GetGlobalValueSymbol(GV);
925 // Emit the Exception Specifications.
926 if (!FilterIds.empty()) EOL("-- Filter IDs --");
927 for (std::vector<unsigned>::const_iterator
928 I = FilterIds.begin(), E = FilterIds.end(); I < E; ++I) {
929 unsigned TypeID = *I;
930 EmitULEB128(TypeID, TypeID != 0 ? "Exception specification" : 0);
933 Asm->EmitAlignment(2, 0, 0, false);
936 /// EndModule - Emit all exception information that should come after the
938 void DwarfException::EndModule() {
939 if (MAI->getExceptionHandlingType() != ExceptionHandling::Dwarf)
942 if (!shouldEmitMovesModule && !shouldEmitTableModule)
945 if (TimePassesIsEnabled)
946 ExceptionTimer->startTimer();
948 const std::vector<Function *> Personalities = MMI->getPersonalities();
950 for (unsigned I = 0, E = Personalities.size(); I < E; ++I)
951 EmitCIE(Personalities[I], I);
953 for (std::vector<FunctionEHFrameInfo>::iterator
954 I = EHFrames.begin(), E = EHFrames.end(); I != E; ++I)
957 if (TimePassesIsEnabled)
958 ExceptionTimer->stopTimer();
961 /// BeginFunction - Gather pre-function exception information. Assumes it's
962 /// being emitted immediately after the function entry point.
963 void DwarfException::BeginFunction(const MachineFunction *MF) {
964 if (!MMI || !MAI->doesSupportExceptionHandling()) return;
966 if (TimePassesIsEnabled)
967 ExceptionTimer->startTimer();
970 shouldEmitTable = shouldEmitMoves = false;
972 // Map all labels and get rid of any dead landing pads.
973 MMI->TidyLandingPads();
975 // If any landing pads survive, we need an EH table.
976 if (!MMI->getLandingPads().empty())
977 shouldEmitTable = true;
979 // See if we need frame move info.
980 if (!MF->getFunction()->doesNotThrow() || UnwindTablesMandatory)
981 shouldEmitMoves = true;
983 if (shouldEmitMoves || shouldEmitTable)
984 // Assumes in correct section after the entry point.
985 EmitLabel("eh_func_begin", ++SubprogramCount);
987 shouldEmitTableModule |= shouldEmitTable;
988 shouldEmitMovesModule |= shouldEmitMoves;
990 if (TimePassesIsEnabled)
991 ExceptionTimer->stopTimer();
994 /// EndFunction - Gather and emit post-function exception information.
996 void DwarfException::EndFunction() {
997 if (!shouldEmitMoves && !shouldEmitTable) return;
999 if (TimePassesIsEnabled)
1000 ExceptionTimer->startTimer();
1002 EmitLabel("eh_func_end", SubprogramCount);
1003 EmitExceptionTable();
1005 MCSymbol *FunctionEHSym =
1006 Asm->GetSymbolWithGlobalValueBase(MF->getFunction(), ".eh",
1007 Asm->MAI->is_EHSymbolPrivate());
1009 // Save EH frame information
1010 EHFrames.push_back(FunctionEHFrameInfo(FunctionEHSym, SubprogramCount,
1011 MMI->getPersonalityIndex(),
1012 MF->getFrameInfo()->hasCalls(),
1013 !MMI->getLandingPads().empty(),
1014 MMI->getFrameMoves(),
1015 MF->getFunction()));
1017 // Record if this personality index uses a landing pad.
1018 UsesLSDA[MMI->getPersonalityIndex()] |= !MMI->getLandingPads().empty();
1020 if (TimePassesIsEnabled)
1021 ExceptionTimer->stopTimer();