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 ActionEntry *PrevAction = 0;
413 const unsigned SizePrevIds = PrevLPI->TypeIds.size();
414 assert(Actions.size());
415 PrevAction = &Actions.back();
416 SizeAction = MCAsmInfo::getSLEB128Size(PrevAction->NextAction) +
417 MCAsmInfo::getSLEB128Size(PrevAction->ValueForTypeID);
419 for (unsigned j = NumShared; j != SizePrevIds; ++j) {
421 MCAsmInfo::getSLEB128Size(PrevAction->ValueForTypeID);
422 SizeAction += -PrevAction->NextAction;
423 PrevAction = PrevAction->Previous;
427 // Compute the actions.
428 for (unsigned J = NumShared, M = TypeIds.size(); J != M; ++J) {
429 int TypeID = TypeIds[J];
430 assert(-1 - TypeID < (int)FilterOffsets.size() && "Unknown filter id!");
431 int ValueForTypeID = TypeID < 0 ? FilterOffsets[-1 - TypeID] : TypeID;
432 unsigned SizeTypeID = MCAsmInfo::getSLEB128Size(ValueForTypeID);
434 int NextAction = SizeAction ? -(SizeAction + SizeTypeID) : 0;
435 SizeAction = SizeTypeID + MCAsmInfo::getSLEB128Size(NextAction);
436 SizeSiteActions += SizeAction;
438 ActionEntry Action = { ValueForTypeID, NextAction, PrevAction };
439 Actions.push_back(Action);
440 PrevAction = &Actions.back();
443 // Record the first action of the landing pad site.
444 FirstAction = SizeActions + SizeSiteActions - SizeAction + 1;
445 } // else identical - re-use previous FirstAction
447 // Information used when created the call-site table. The action record
448 // field of the call site record is the offset of the first associated
449 // action record, relative to the start of the actions table. This value is
450 // biased by 1 (1 in dicating the start of the actions table), and 0
451 // indicates that there are no actions.
452 FirstActions.push_back(FirstAction);
454 // Compute this sites contribution to size.
455 SizeActions += SizeSiteActions;
463 /// CallToNoUnwindFunction - Return `true' if this is a call to a function
464 /// marked `nounwind'. Return `false' otherwise.
465 bool DwarfException::CallToNoUnwindFunction(const MachineInstr *MI) {
466 assert(MI->getDesc().isCall() && "This should be a call instruction!");
468 bool MarkedNoUnwind = false;
469 bool SawFunc = false;
471 for (unsigned I = 0, E = MI->getNumOperands(); I != E; ++I) {
472 const MachineOperand &MO = MI->getOperand(I);
475 if (Function *F = dyn_cast<Function>(MO.getGlobal())) {
477 // Be conservative. If we have more than one function operand for this
478 // call, then we can't make the assumption that it's the callee and
479 // not a parameter to the call.
481 // FIXME: Determine if there's a way to say that `F' is the callee or
483 MarkedNoUnwind = false;
487 MarkedNoUnwind = F->doesNotThrow();
493 return MarkedNoUnwind;
496 /// ComputeCallSiteTable - Compute the call-site table. The entry for an invoke
497 /// has a try-range containing the call, a non-zero landing pad, and an
498 /// appropriate action. The entry for an ordinary call has a try-range
499 /// containing the call and zero for the landing pad and the action. Calls
500 /// marked 'nounwind' have no entry and must not be contained in the try-range
501 /// of any entry - they form gaps in the table. Entries must be ordered by
502 /// try-range address.
503 void DwarfException::
504 ComputeCallSiteTable(SmallVectorImpl<CallSiteEntry> &CallSites,
505 const RangeMapType &PadMap,
506 const SmallVectorImpl<const LandingPadInfo *> &LandingPads,
507 const SmallVectorImpl<unsigned> &FirstActions) {
508 // The end label of the previous invoke or nounwind try-range.
509 unsigned LastLabel = 0;
511 // Whether there is a potentially throwing instruction (currently this means
512 // an ordinary call) between the end of the previous try-range and now.
513 bool SawPotentiallyThrowing = false;
515 // Whether the last CallSite entry was for an invoke.
516 bool PreviousIsInvoke = false;
518 // Visit all instructions in order of address.
519 for (MachineFunction::const_iterator I = MF->begin(), E = MF->end();
521 for (MachineBasicBlock::const_iterator MI = I->begin(), E = I->end();
523 if (!MI->isLabel()) {
524 if (MI->getDesc().isCall())
525 SawPotentiallyThrowing |= !CallToNoUnwindFunction(MI);
530 unsigned BeginLabel = MI->getOperand(0).getImm();
531 assert(BeginLabel && "Invalid label!");
533 // End of the previous try-range?
534 if (BeginLabel == LastLabel)
535 SawPotentiallyThrowing = false;
537 // Beginning of a new try-range?
538 RangeMapType::const_iterator L = PadMap.find(BeginLabel);
539 if (L == PadMap.end())
540 // Nope, it was just some random label.
543 const PadRange &P = L->second;
544 const LandingPadInfo *LandingPad = LandingPads[P.PadIndex];
545 assert(BeginLabel == LandingPad->BeginLabels[P.RangeIndex] &&
546 "Inconsistent landing pad map!");
548 // For Dwarf exception handling (SjLj handling doesn't use this). If some
549 // instruction between the previous try-range and this one may throw,
550 // create a call-site entry with no landing pad for the region between the
552 if (SawPotentiallyThrowing &&
553 MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf) {
554 CallSiteEntry Site = { LastLabel, BeginLabel, 0, 0 };
555 CallSites.push_back(Site);
556 PreviousIsInvoke = false;
559 LastLabel = LandingPad->EndLabels[P.RangeIndex];
560 assert(BeginLabel && LastLabel && "Invalid landing pad!");
562 if (LandingPad->LandingPadLabel) {
563 // This try-range is for an invoke.
564 CallSiteEntry Site = {
567 LandingPad->LandingPadLabel,
568 FirstActions[P.PadIndex]
571 // Try to merge with the previous call-site. SJLJ doesn't do this
572 if (PreviousIsInvoke &&
573 MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf) {
574 CallSiteEntry &Prev = CallSites.back();
575 if (Site.PadLabel == Prev.PadLabel && Site.Action == Prev.Action) {
576 // Extend the range of the previous entry.
577 Prev.EndLabel = Site.EndLabel;
582 // Otherwise, create a new call-site.
583 if (MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf)
584 CallSites.push_back(Site);
586 // SjLj EH must maintain the call sites in the order assigned
587 // to them by the SjLjPrepare pass.
588 unsigned SiteNo = MMI->getCallSiteBeginLabel(BeginLabel);
589 if (CallSites.size() < SiteNo)
590 CallSites.resize(SiteNo);
591 CallSites[SiteNo - 1] = Site;
593 PreviousIsInvoke = true;
596 PreviousIsInvoke = false;
601 // If some instruction between the previous try-range and the end of the
602 // function may throw, create a call-site entry with no landing pad for the
603 // region following the try-range.
604 if (SawPotentiallyThrowing &&
605 MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf) {
606 CallSiteEntry Site = { LastLabel, 0, 0, 0 };
607 CallSites.push_back(Site);
611 /// EmitExceptionTable - Emit landing pads and actions.
613 /// The general organization of the table is complex, but the basic concepts are
614 /// easy. First there is a header which describes the location and organization
615 /// of the three components that follow.
617 /// 1. The landing pad site information describes the range of code covered by
618 /// the try. In our case it's an accumulation of the ranges covered by the
619 /// invokes in the try. There is also a reference to the landing pad that
620 /// handles the exception once processed. Finally an index into the actions
622 /// 2. The action table, in our case, is composed of pairs of type IDs and next
623 /// action offset. Starting with the action index from the landing pad
624 /// site, each type ID is checked for a match to the current exception. If
625 /// it matches then the exception and type id are passed on to the landing
626 /// pad. Otherwise the next action is looked up. This chain is terminated
627 /// with a next action of zero. If no type id is found then the frame is
628 /// unwound and handling continues.
629 /// 3. Type ID table contains references to all the C++ typeinfo for all
630 /// catches in the function. This tables is reverse indexed base 1.
631 void DwarfException::EmitExceptionTable() {
632 const std::vector<GlobalVariable *> &TypeInfos = MMI->getTypeInfos();
633 const std::vector<unsigned> &FilterIds = MMI->getFilterIds();
634 const std::vector<LandingPadInfo> &PadInfos = MMI->getLandingPads();
635 if (PadInfos.empty()) return;
637 // Sort the landing pads in order of their type ids. This is used to fold
638 // duplicate actions.
639 SmallVector<const LandingPadInfo *, 64> LandingPads;
640 LandingPads.reserve(PadInfos.size());
642 for (unsigned i = 0, N = PadInfos.size(); i != N; ++i)
643 LandingPads.push_back(&PadInfos[i]);
645 std::sort(LandingPads.begin(), LandingPads.end(), PadLT);
647 // Compute the actions table and gather the first action index for each
649 SmallVector<ActionEntry, 32> Actions;
650 SmallVector<unsigned, 64> FirstActions;
651 unsigned SizeActions = ComputeActionsTable(LandingPads, Actions,
654 // Invokes and nounwind calls have entries in PadMap (due to being bracketed
655 // by try-range labels when lowered). Ordinary calls do not, so appropriate
656 // try-ranges for them need be deduced when using DWARF exception handling.
658 for (unsigned i = 0, N = LandingPads.size(); i != N; ++i) {
659 const LandingPadInfo *LandingPad = LandingPads[i];
660 for (unsigned j = 0, E = LandingPad->BeginLabels.size(); j != E; ++j) {
661 unsigned BeginLabel = LandingPad->BeginLabels[j];
662 assert(!PadMap.count(BeginLabel) && "Duplicate landing pad labels!");
663 PadRange P = { i, j };
664 PadMap[BeginLabel] = P;
668 // Compute the call-site table.
669 SmallVector<CallSiteEntry, 64> CallSites;
670 ComputeCallSiteTable(CallSites, PadMap, LandingPads, FirstActions);
675 const unsigned SiteStartSize = SizeOfEncodedValue(dwarf::DW_EH_PE_udata4);
676 const unsigned SiteLengthSize = SizeOfEncodedValue(dwarf::DW_EH_PE_udata4);
677 const unsigned LandingPadSize = SizeOfEncodedValue(dwarf::DW_EH_PE_udata4);
678 bool IsSJLJ = MAI->getExceptionHandlingType() == ExceptionHandling::SjLj;
679 bool HaveTTData = IsSJLJ ? (!TypeInfos.empty() || !FilterIds.empty()) : true;
685 SizeSites = CallSites.size() *
686 (SiteStartSize + SiteLengthSize + LandingPadSize);
688 for (unsigned i = 0, e = CallSites.size(); i < e; ++i) {
689 SizeSites += MCAsmInfo::getULEB128Size(CallSites[i].Action);
691 SizeSites += MCAsmInfo::getULEB128Size(i);
695 const MCSection *LSDASection = Asm->getObjFileLowering().getLSDASection();
696 unsigned TTypeFormat;
697 unsigned TypeFormatSize;
700 // For SjLj exceptions, if there is no TypeInfo, then we just explicitly say
701 // that we're omitting that bit.
702 TTypeFormat = dwarf::DW_EH_PE_omit;
703 TypeFormatSize = SizeOfEncodedValue(dwarf::DW_EH_PE_absptr);
705 // Okay, we have actual filters or typeinfos to emit. As such, we need to
706 // pick a type encoding for them. We're about to emit a list of pointers to
707 // typeinfo objects at the end of the LSDA. However, unless we're in static
708 // mode, this reference will require a relocation by the dynamic linker.
710 // Because of this, we have a couple of options:
712 // 1) If we are in -static mode, we can always use an absolute reference
713 // from the LSDA, because the static linker will resolve it.
715 // 2) Otherwise, if the LSDA section is writable, we can output the direct
716 // reference to the typeinfo and allow the dynamic linker to relocate
717 // it. Since it is in a writable section, the dynamic linker won't
720 // 3) Finally, if we're in PIC mode and the LDSA section isn't writable,
721 // we need to use some form of indirection. For example, on Darwin,
722 // we can output a statically-relocatable reference to a dyld stub. The
723 // offset to the stub is constant, but the contents are in a section
724 // that is updated by the dynamic linker. This is easy enough, but we
725 // need to tell the personality function of the unwinder to indirect
726 // through the dyld stub.
728 // FIXME: When (3) is actually implemented, we'll have to emit the stubs
729 // somewhere. This predicate should be moved to a shared location that is
730 // in target-independent code.
732 if (LSDASection->getKind().isWriteable() ||
733 Asm->TM.getRelocationModel() == Reloc::Static)
734 TTypeFormat = dwarf::DW_EH_PE_absptr;
736 TTypeFormat = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
737 dwarf::DW_EH_PE_sdata4;
739 TypeFormatSize = SizeOfEncodedValue(TTypeFormat);
742 // Begin the exception table.
743 Asm->OutStreamer.SwitchSection(LSDASection);
744 Asm->EmitAlignment(2, 0, 0, false);
746 O << "GCC_except_table" << SubprogramCount << ":\n";
748 // The type infos need to be aligned. GCC does this by inserting padding just
749 // before the type infos. However, this changes the size of the exception
750 // table, so you need to take this into account when you output the exception
751 // table size. However, the size is output using a variable length encoding.
752 // So by increasing the size by inserting padding, you may increase the number
753 // of bytes used for writing the size. If it increases, say by one byte, then
754 // you now need to output one less byte of padding to get the type infos
755 // aligned. However this decreases the size of the exception table. This
756 // changes the value you have to output for the exception table size. Due to
757 // the variable length encoding, the number of bytes used for writing the
758 // length may decrease. If so, you then have to increase the amount of
759 // padding. And so on. If you look carefully at the GCC code you will see that
760 // it indeed does this in a loop, going on and on until the values stabilize.
761 // We chose another solution: don't output padding inside the table like GCC
762 // does, instead output it before the table.
763 unsigned SizeTypes = TypeInfos.size() * TypeFormatSize;
764 unsigned TyOffset = sizeof(int8_t) + // Call site format
765 MCAsmInfo::getULEB128Size(SizeSites) + // Call site table length
766 SizeSites + SizeActions + SizeTypes;
767 unsigned TotalSize = sizeof(int8_t) + // LPStart format
768 sizeof(int8_t) + // TType format
770 MCAsmInfo::getULEB128Size(TyOffset) : 0) + // TType base offset
772 unsigned SizeAlign = (4 - TotalSize) & 3;
774 for (unsigned i = 0; i != SizeAlign; ++i) {
779 EmitLabel("exception", SubprogramCount);
782 SmallString<16> LSDAName;
783 raw_svector_ostream(LSDAName) << MAI->getPrivateGlobalPrefix() <<
784 "_LSDA_" << Asm->getFunctionNumber();
785 O << LSDAName.str() << ":\n";
789 EmitEncodingByte(dwarf::DW_EH_PE_omit, "@LPStart");
790 EmitEncodingByte(TTypeFormat, "@TType");
793 EmitULEB128(TyOffset, "@TType base offset");
795 // SjLj Exception handling
797 EmitEncodingByte(dwarf::DW_EH_PE_udata4, "Call site");
798 EmitULEB128(SizeSites, "Call site table length");
800 // Emit the landing pad site information.
802 for (SmallVectorImpl<CallSiteEntry>::const_iterator
803 I = CallSites.begin(), E = CallSites.end(); I != E; ++I, ++idx) {
804 const CallSiteEntry &S = *I;
806 // Offset of the landing pad, counted in 16-byte bundles relative to the
808 EmitULEB128(idx, "Landing pad");
810 // Offset of the first associated action record, relative to the start of
811 // the action table. This value is biased by 1 (1 indicates the start of
812 // the action table), and 0 indicates that there are no actions.
813 EmitULEB128(S.Action, "Action");
816 // DWARF Exception handling
817 assert(MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf);
819 // The call-site table is a list of all call sites that may throw an
820 // exception (including C++ 'throw' statements) in the procedure
821 // fragment. It immediately follows the LSDA header. Each entry indicates,
822 // for a given call, the first corresponding action record and corresponding
825 // The table begins with the number of bytes, stored as an LEB128
826 // compressed, unsigned integer. The records immediately follow the record
827 // count. They are sorted in increasing call-site address. Each record
830 // * The position of the call-site.
831 // * The position of the landing pad.
832 // * The first action record for that call site.
834 // A missing entry in the call-site table indicates that a call is not
835 // supposed to throw.
837 // Emit the landing pad call site table.
838 EmitEncodingByte(dwarf::DW_EH_PE_udata4, "Call site");
839 EmitULEB128(SizeSites, "Call site table length");
841 for (SmallVectorImpl<CallSiteEntry>::const_iterator
842 I = CallSites.begin(), E = CallSites.end(); I != E; ++I) {
843 const CallSiteEntry &S = *I;
844 const char *BeginTag;
845 unsigned BeginNumber;
848 BeginTag = "eh_func_begin";
849 BeginNumber = SubprogramCount;
852 BeginNumber = S.BeginLabel;
855 // Offset of the call site relative to the previous call site, counted in
856 // number of 16-byte bundles. The first call site is counted relative to
857 // the start of the procedure fragment.
858 EmitSectionOffset(BeginTag, "eh_func_begin", BeginNumber, SubprogramCount,
863 EmitDifference("eh_func_end", SubprogramCount, BeginTag, BeginNumber,
866 EmitDifference("label", S.EndLabel, BeginTag, BeginNumber, true);
868 EOL("Region length");
870 // Offset of the landing pad, counted in 16-byte bundles relative to the
873 Asm->OutStreamer.AddComment("Landing pad");
874 Asm->OutStreamer.EmitIntValue(0, 4/*size*/, 0/*addrspace*/);
876 EmitSectionOffset("label", "eh_func_begin", S.PadLabel, SubprogramCount,
881 // Offset of the first associated action record, relative to the start of
882 // the action table. This value is biased by 1 (1 indicates the start of
883 // the action table), and 0 indicates that there are no actions.
884 EmitULEB128(S.Action, "Action");
888 // Emit the Action Table.
889 if (Actions.size() != 0) EOL("-- Action Record Table --");
890 for (SmallVectorImpl<ActionEntry>::const_iterator
891 I = Actions.begin(), E = Actions.end(); I != E; ++I) {
892 const ActionEntry &Action = *I;
893 EOL("Action Record:");
897 // Used by the runtime to match the type of the thrown exception to the
898 // type of the catch clauses or the types in the exception specification.
899 EmitSLEB128(Action.ValueForTypeID, " TypeInfo index");
903 // Self-relative signed displacement in bytes of the next action record,
904 // or 0 if there is no next action record.
905 EmitSLEB128(Action.NextAction, " Next action");
908 // Emit the Catch TypeInfos.
909 if (TypeInfos.size() != 0) EOL("-- Catch TypeInfos --");
910 for (std::vector<GlobalVariable *>::const_reverse_iterator
911 I = TypeInfos.rbegin(), E = TypeInfos.rend(); I != E; ++I) {
912 const GlobalVariable *GV = *I;
916 O << *Asm->GetGlobalValueSymbol(GV);
924 // Emit the Exception Specifications.
925 if (FilterIds.size() != 0) EOL("-- Filter IDs --");
926 for (std::vector<unsigned>::const_iterator
927 I = FilterIds.begin(), E = FilterIds.end(); I < E; ++I) {
928 unsigned TypeID = *I;
929 EmitULEB128(TypeID, TypeID != 0 ? "Exception specification" : 0);
932 Asm->EmitAlignment(2, 0, 0, false);
935 /// EndModule - Emit all exception information that should come after the
937 void DwarfException::EndModule() {
938 if (MAI->getExceptionHandlingType() != ExceptionHandling::Dwarf)
941 if (!shouldEmitMovesModule && !shouldEmitTableModule)
944 if (TimePassesIsEnabled)
945 ExceptionTimer->startTimer();
947 const std::vector<Function *> Personalities = MMI->getPersonalities();
949 for (unsigned I = 0, E = Personalities.size(); I < E; ++I)
950 EmitCIE(Personalities[I], I);
952 for (std::vector<FunctionEHFrameInfo>::iterator
953 I = EHFrames.begin(), E = EHFrames.end(); I != E; ++I)
956 if (TimePassesIsEnabled)
957 ExceptionTimer->stopTimer();
960 /// BeginFunction - Gather pre-function exception information. Assumes it's
961 /// being emitted immediately after the function entry point.
962 void DwarfException::BeginFunction(const MachineFunction *MF) {
963 if (!MMI || !MAI->doesSupportExceptionHandling()) return;
965 if (TimePassesIsEnabled)
966 ExceptionTimer->startTimer();
969 shouldEmitTable = shouldEmitMoves = false;
971 // Map all labels and get rid of any dead landing pads.
972 MMI->TidyLandingPads();
974 // If any landing pads survive, we need an EH table.
975 if (!MMI->getLandingPads().empty())
976 shouldEmitTable = true;
978 // See if we need frame move info.
979 if (!MF->getFunction()->doesNotThrow() || UnwindTablesMandatory)
980 shouldEmitMoves = true;
982 if (shouldEmitMoves || shouldEmitTable)
983 // Assumes in correct section after the entry point.
984 EmitLabel("eh_func_begin", ++SubprogramCount);
986 shouldEmitTableModule |= shouldEmitTable;
987 shouldEmitMovesModule |= shouldEmitMoves;
989 if (TimePassesIsEnabled)
990 ExceptionTimer->stopTimer();
993 /// EndFunction - Gather and emit post-function exception information.
995 void DwarfException::EndFunction() {
996 if (!shouldEmitMoves && !shouldEmitTable) return;
998 if (TimePassesIsEnabled)
999 ExceptionTimer->startTimer();
1001 EmitLabel("eh_func_end", SubprogramCount);
1002 EmitExceptionTable();
1004 MCSymbol *FunctionEHSym =
1005 Asm->GetSymbolWithGlobalValueBase(MF->getFunction(), ".eh",
1006 Asm->MAI->is_EHSymbolPrivate());
1008 // Save EH frame information
1009 EHFrames.push_back(FunctionEHFrameInfo(FunctionEHSym, SubprogramCount,
1010 MMI->getPersonalityIndex(),
1011 MF->getFrameInfo()->hasCalls(),
1012 !MMI->getLandingPads().empty(),
1013 MMI->getFrameMoves(),
1014 MF->getFunction()));
1016 // Record if this personality index uses a landing pad.
1017 UsesLSDA[MMI->getPersonalityIndex()] |= !MMI->getLandingPads().empty();
1019 if (TimePassesIsEnabled)
1020 ExceptionTimer->stopTimer();