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->OutStreamer.EmitIntValue(0, 4/*size*/, 0/*addrspace*/);
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() << *PersonalityRef;
198 Asm->EOL("Personality");
200 Asm->EmitInt8(LSDAEncoding);
201 Asm->EOL("LSDA Encoding", LSDAEncoding);
203 Asm->EmitInt8(FDEEncoding);
204 Asm->EOL("FDE Encoding", FDEEncoding);
207 // Indicate locations of general callee saved registers in frame.
208 std::vector<MachineMove> Moves;
209 RI->getInitialFrameState(Moves);
210 EmitFrameMoves(NULL, 0, Moves, true);
212 // On Darwin the linker honors the alignment of eh_frame, which means it must
213 // be 8-byte on 64-bit targets to match what gcc does. Otherwise you get
214 // holes which confuse readers of eh_frame.
215 Asm->EmitAlignment(TD->getPointerSize() == 4 ? 2 : 3, 0, 0, false);
216 EmitLabel("eh_frame_common_end", Index);
221 /// EmitFDE - Emit the Frame Description Entry (FDE) for the function.
222 void DwarfException::EmitFDE(const FunctionEHFrameInfo &EHFrameInfo) {
223 assert(!EHFrameInfo.function->hasAvailableExternallyLinkage() &&
224 "Should not emit 'available externally' functions at all");
226 const Function *TheFunc = EHFrameInfo.function;
228 Asm->OutStreamer.SwitchSection(Asm->getObjFileLowering().getEHFrameSection());
230 // Externally visible entry into the functions eh frame info. If the
231 // corresponding function is static, this should not be externally visible.
232 if (!TheFunc->hasLocalLinkage())
233 if (const char *GlobalEHDirective = MAI->getGlobalEHDirective())
234 O << GlobalEHDirective << *EHFrameInfo.FunctionEHSym << '\n';
236 // If corresponding function is weak definition, this should be too.
237 if (TheFunc->isWeakForLinker() && MAI->getWeakDefDirective())
238 O << MAI->getWeakDefDirective() << *EHFrameInfo.FunctionEHSym << '\n';
240 // If corresponding function is hidden, this should be too.
241 if (TheFunc->hasHiddenVisibility())
242 if (const char *HiddenDirective = MAI->getHiddenDirective())
243 O << HiddenDirective << *EHFrameInfo.FunctionEHSym << '\n';
245 // If there are no calls then you can't unwind. This may mean we can omit the
246 // EH Frame, but some environments do not handle weak absolute symbols. If
247 // UnwindTablesMandatory is set we cannot do this optimization; the unwind
248 // info is to be available for non-EH uses.
249 if (!EHFrameInfo.hasCalls && !UnwindTablesMandatory &&
250 (!TheFunc->isWeakForLinker() ||
251 !MAI->getWeakDefDirective() ||
252 MAI->getSupportsWeakOmittedEHFrame())) {
253 O << *EHFrameInfo.FunctionEHSym << " = 0\n";
254 // This name has no connection to the function, so it might get
255 // dead-stripped when the function is not, erroneously. Prohibit
256 // dead-stripping unconditionally.
257 if (const char *UsedDirective = MAI->getUsedDirective())
258 O << UsedDirective << *EHFrameInfo.FunctionEHSym << "\n\n";
260 O << *EHFrameInfo.FunctionEHSym << ":\n";
263 EmitDifference("eh_frame_end", EHFrameInfo.Number,
264 "eh_frame_begin", EHFrameInfo.Number, true);
265 Asm->EOL("Length of Frame Information Entry");
267 EmitLabel("eh_frame_begin", EHFrameInfo.Number);
269 EmitSectionOffset("eh_frame_begin", "eh_frame_common",
270 EHFrameInfo.Number, EHFrameInfo.PersonalityIndex,
273 Asm->EOL("FDE CIE offset");
275 EmitReference("eh_func_begin", EHFrameInfo.Number, true, true);
276 Asm->EOL("FDE initial location");
277 EmitDifference("eh_func_end", EHFrameInfo.Number,
278 "eh_func_begin", EHFrameInfo.Number, true);
279 Asm->EOL("FDE address range");
281 // If there is a personality and landing pads then point to the language
282 // specific data area in the exception table.
283 if (MMI->getPersonalities()[0] != NULL) {
285 if (Asm->TM.getLSDAEncoding() != DwarfLSDAEncoding::EightByte) {
286 Asm->EmitULEB128Bytes(4);
287 Asm->EOL("Augmentation size");
289 if (EHFrameInfo.hasLandingPads)
290 EmitReference("exception", EHFrameInfo.Number, true, true);
292 Asm->OutStreamer.EmitIntValue(0, 4/*size*/, 0/*addrspace*/);
294 Asm->EmitULEB128Bytes(TD->getPointerSize());
295 Asm->EOL("Augmentation size");
297 if (EHFrameInfo.hasLandingPads) {
298 EmitReference("exception", EHFrameInfo.Number, true, false);
300 Asm->OutStreamer.EmitIntValue(0, TD->getPointerSize(),
305 Asm->EOL("Language Specific Data Area");
307 Asm->EmitULEB128Bytes(0);
308 Asm->EOL("Augmentation size");
311 // Indicate locations of function specific callee saved registers in frame.
312 EmitFrameMoves("eh_func_begin", EHFrameInfo.Number, EHFrameInfo.Moves,
315 // On Darwin the linker honors the alignment of eh_frame, which means it
316 // must be 8-byte on 64-bit targets to match what gcc does. Otherwise you
317 // get holes which confuse readers of eh_frame.
318 Asm->EmitAlignment(TD->getPointerSize() == sizeof(int32_t) ? 2 : 3,
320 EmitLabel("eh_frame_end", EHFrameInfo.Number);
322 // If the function is marked used, this table should be also. We cannot
323 // make the mark unconditional in this case, since retaining the table also
324 // retains the function in this case, and there is code around that depends
325 // on unused functions (calling undefined externals) being dead-stripped to
326 // link correctly. Yes, there really is.
327 if (MMI->isUsedFunction(EHFrameInfo.function))
328 if (const char *UsedDirective = MAI->getUsedDirective()) {
329 O << UsedDirective << *EHFrameInfo.FunctionEHSym << "\n\n";
336 /// SharedTypeIds - How many leading type ids two landing pads have in common.
337 unsigned DwarfException::SharedTypeIds(const LandingPadInfo *L,
338 const LandingPadInfo *R) {
339 const std::vector<int> &LIds = L->TypeIds, &RIds = R->TypeIds;
340 unsigned LSize = LIds.size(), RSize = RIds.size();
341 unsigned MinSize = LSize < RSize ? LSize : RSize;
344 for (; Count != MinSize; ++Count)
345 if (LIds[Count] != RIds[Count])
351 /// PadLT - Order landing pads lexicographically by type id.
352 bool DwarfException::PadLT(const LandingPadInfo *L, const LandingPadInfo *R) {
353 const std::vector<int> &LIds = L->TypeIds, &RIds = R->TypeIds;
354 unsigned LSize = LIds.size(), RSize = RIds.size();
355 unsigned MinSize = LSize < RSize ? LSize : RSize;
357 for (unsigned i = 0; i != MinSize; ++i)
358 if (LIds[i] != RIds[i])
359 return LIds[i] < RIds[i];
361 return LSize < RSize;
364 /// ComputeActionsTable - Compute the actions table and gather the first action
365 /// index for each landing pad site.
366 unsigned DwarfException::
367 ComputeActionsTable(const SmallVectorImpl<const LandingPadInfo*> &LandingPads,
368 SmallVectorImpl<ActionEntry> &Actions,
369 SmallVectorImpl<unsigned> &FirstActions) {
371 // The action table follows the call-site table in the LSDA. The individual
372 // records are of two types:
375 // * Exception specification
377 // The two record kinds have the same format, with only small differences.
378 // They are distinguished by the "switch value" field: Catch clauses
379 // (TypeInfos) have strictly positive switch values, and exception
380 // specifications (FilterIds) have strictly negative switch values. Value 0
381 // indicates a catch-all clause.
383 // Negative type IDs index into FilterIds. Positive type IDs index into
384 // TypeInfos. The value written for a positive type ID is just the type ID
385 // itself. For a negative type ID, however, the value written is the
386 // (negative) byte offset of the corresponding FilterIds entry. The byte
387 // offset is usually equal to the type ID (because the FilterIds entries are
388 // written using a variable width encoding, which outputs one byte per entry
389 // as long as the value written is not too large) but can differ. This kind
390 // of complication does not occur for positive type IDs because type infos are
391 // output using a fixed width encoding. FilterOffsets[i] holds the byte
392 // offset corresponding to FilterIds[i].
394 const std::vector<unsigned> &FilterIds = MMI->getFilterIds();
395 SmallVector<int, 16> FilterOffsets;
396 FilterOffsets.reserve(FilterIds.size());
399 for (std::vector<unsigned>::const_iterator
400 I = FilterIds.begin(), E = FilterIds.end(); I != E; ++I) {
401 FilterOffsets.push_back(Offset);
402 Offset -= MCAsmInfo::getULEB128Size(*I);
405 FirstActions.reserve(LandingPads.size());
408 unsigned SizeActions = 0;
409 const LandingPadInfo *PrevLPI = 0;
411 for (SmallVectorImpl<const LandingPadInfo *>::const_iterator
412 I = LandingPads.begin(), E = LandingPads.end(); I != E; ++I) {
413 const LandingPadInfo *LPI = *I;
414 const std::vector<int> &TypeIds = LPI->TypeIds;
415 const unsigned NumShared = PrevLPI ? SharedTypeIds(LPI, PrevLPI) : 0;
416 unsigned SizeSiteActions = 0;
418 if (NumShared < TypeIds.size()) {
419 unsigned SizeAction = 0;
420 ActionEntry *PrevAction = 0;
423 const unsigned SizePrevIds = PrevLPI->TypeIds.size();
424 assert(Actions.size());
425 PrevAction = &Actions.back();
426 SizeAction = MCAsmInfo::getSLEB128Size(PrevAction->NextAction) +
427 MCAsmInfo::getSLEB128Size(PrevAction->ValueForTypeID);
429 for (unsigned j = NumShared; j != SizePrevIds; ++j) {
431 MCAsmInfo::getSLEB128Size(PrevAction->ValueForTypeID);
432 SizeAction += -PrevAction->NextAction;
433 PrevAction = PrevAction->Previous;
437 // Compute the actions.
438 for (unsigned J = NumShared, M = TypeIds.size(); J != M; ++J) {
439 int TypeID = TypeIds[J];
440 assert(-1 - TypeID < (int)FilterOffsets.size() && "Unknown filter id!");
441 int ValueForTypeID = TypeID < 0 ? FilterOffsets[-1 - TypeID] : TypeID;
442 unsigned SizeTypeID = MCAsmInfo::getSLEB128Size(ValueForTypeID);
444 int NextAction = SizeAction ? -(SizeAction + SizeTypeID) : 0;
445 SizeAction = SizeTypeID + MCAsmInfo::getSLEB128Size(NextAction);
446 SizeSiteActions += SizeAction;
448 ActionEntry Action = { ValueForTypeID, NextAction, PrevAction };
449 Actions.push_back(Action);
450 PrevAction = &Actions.back();
453 // Record the first action of the landing pad site.
454 FirstAction = SizeActions + SizeSiteActions - SizeAction + 1;
455 } // else identical - re-use previous FirstAction
457 // Information used when created the call-site table. The action record
458 // field of the call site record is the offset of the first associated
459 // action record, relative to the start of the actions table. This value is
460 // biased by 1 (1 in dicating the start of the actions table), and 0
461 // indicates that there are no actions.
462 FirstActions.push_back(FirstAction);
464 // Compute this sites contribution to size.
465 SizeActions += SizeSiteActions;
473 /// CallToNoUnwindFunction - Return `true' if this is a call to a function
474 /// marked `nounwind'. Return `false' otherwise.
475 bool DwarfException::CallToNoUnwindFunction(const MachineInstr *MI) {
476 assert(MI->getDesc().isCall() && "This should be a call instruction!");
478 bool MarkedNoUnwind = false;
479 bool SawFunc = false;
481 for (unsigned I = 0, E = MI->getNumOperands(); I != E; ++I) {
482 const MachineOperand &MO = MI->getOperand(I);
485 if (Function *F = dyn_cast<Function>(MO.getGlobal())) {
487 // Be conservative. If we have more than one function operand for this
488 // call, then we can't make the assumption that it's the callee and
489 // not a parameter to the call.
491 // FIXME: Determine if there's a way to say that `F' is the callee or
493 MarkedNoUnwind = false;
497 MarkedNoUnwind = F->doesNotThrow();
503 return MarkedNoUnwind;
506 /// ComputeCallSiteTable - Compute the call-site table. The entry for an invoke
507 /// has a try-range containing the call, a non-zero landing pad, and an
508 /// appropriate action. The entry for an ordinary call has a try-range
509 /// containing the call and zero for the landing pad and the action. Calls
510 /// marked 'nounwind' have no entry and must not be contained in the try-range
511 /// of any entry - they form gaps in the table. Entries must be ordered by
512 /// try-range address.
513 void DwarfException::
514 ComputeCallSiteTable(SmallVectorImpl<CallSiteEntry> &CallSites,
515 const RangeMapType &PadMap,
516 const SmallVectorImpl<const LandingPadInfo *> &LandingPads,
517 const SmallVectorImpl<unsigned> &FirstActions) {
518 // The end label of the previous invoke or nounwind try-range.
519 unsigned LastLabel = 0;
521 // Whether there is a potentially throwing instruction (currently this means
522 // an ordinary call) between the end of the previous try-range and now.
523 bool SawPotentiallyThrowing = false;
525 // Whether the last CallSite entry was for an invoke.
526 bool PreviousIsInvoke = false;
528 // Visit all instructions in order of address.
529 for (MachineFunction::const_iterator I = MF->begin(), E = MF->end();
531 for (MachineBasicBlock::const_iterator MI = I->begin(), E = I->end();
533 if (!MI->isLabel()) {
534 if (MI->getDesc().isCall())
535 SawPotentiallyThrowing |= !CallToNoUnwindFunction(MI);
540 unsigned BeginLabel = MI->getOperand(0).getImm();
541 assert(BeginLabel && "Invalid label!");
543 // End of the previous try-range?
544 if (BeginLabel == LastLabel)
545 SawPotentiallyThrowing = false;
547 // Beginning of a new try-range?
548 RangeMapType::const_iterator L = PadMap.find(BeginLabel);
549 if (L == PadMap.end())
550 // Nope, it was just some random label.
553 const PadRange &P = L->second;
554 const LandingPadInfo *LandingPad = LandingPads[P.PadIndex];
555 assert(BeginLabel == LandingPad->BeginLabels[P.RangeIndex] &&
556 "Inconsistent landing pad map!");
558 // For Dwarf exception handling (SjLj handling doesn't use this). If some
559 // instruction between the previous try-range and this one may throw,
560 // create a call-site entry with no landing pad for the region between the
562 if (SawPotentiallyThrowing &&
563 MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf) {
564 CallSiteEntry Site = { LastLabel, BeginLabel, 0, 0 };
565 CallSites.push_back(Site);
566 PreviousIsInvoke = false;
569 LastLabel = LandingPad->EndLabels[P.RangeIndex];
570 assert(BeginLabel && LastLabel && "Invalid landing pad!");
572 if (LandingPad->LandingPadLabel) {
573 // This try-range is for an invoke.
574 CallSiteEntry Site = {
577 LandingPad->LandingPadLabel,
578 FirstActions[P.PadIndex]
581 // Try to merge with the previous call-site. SJLJ doesn't do this
582 if (PreviousIsInvoke &&
583 MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf) {
584 CallSiteEntry &Prev = CallSites.back();
585 if (Site.PadLabel == Prev.PadLabel && Site.Action == Prev.Action) {
586 // Extend the range of the previous entry.
587 Prev.EndLabel = Site.EndLabel;
592 // Otherwise, create a new call-site.
593 if (MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf)
594 CallSites.push_back(Site);
596 // SjLj EH must maintain the call sites in the order assigned
597 // to them by the SjLjPrepare pass.
598 unsigned SiteNo = MMI->getCallSiteBeginLabel(BeginLabel);
599 if (CallSites.size() < SiteNo)
600 CallSites.resize(SiteNo);
601 CallSites[SiteNo - 1] = Site;
603 PreviousIsInvoke = true;
606 PreviousIsInvoke = false;
611 // If some instruction between the previous try-range and the end of the
612 // function may throw, create a call-site entry with no landing pad for the
613 // region following the try-range.
614 if (SawPotentiallyThrowing &&
615 MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf) {
616 CallSiteEntry Site = { LastLabel, 0, 0, 0 };
617 CallSites.push_back(Site);
621 /// EmitExceptionTable - Emit landing pads and actions.
623 /// The general organization of the table is complex, but the basic concepts are
624 /// easy. First there is a header which describes the location and organization
625 /// of the three components that follow.
627 /// 1. The landing pad site information describes the range of code covered by
628 /// the try. In our case it's an accumulation of the ranges covered by the
629 /// invokes in the try. There is also a reference to the landing pad that
630 /// handles the exception once processed. Finally an index into the actions
632 /// 2. The action table, in our case, is composed of pairs of type IDs and next
633 /// action offset. Starting with the action index from the landing pad
634 /// site, each type ID is checked for a match to the current exception. If
635 /// it matches then the exception and type id are passed on to the landing
636 /// pad. Otherwise the next action is looked up. This chain is terminated
637 /// with a next action of zero. If no type id is found then the frame is
638 /// unwound and handling continues.
639 /// 3. Type ID table contains references to all the C++ typeinfo for all
640 /// catches in the function. This tables is reverse indexed base 1.
641 void DwarfException::EmitExceptionTable() {
642 const std::vector<GlobalVariable *> &TypeInfos = MMI->getTypeInfos();
643 const std::vector<unsigned> &FilterIds = MMI->getFilterIds();
644 const std::vector<LandingPadInfo> &PadInfos = MMI->getLandingPads();
645 if (PadInfos.empty()) return;
647 // Sort the landing pads in order of their type ids. This is used to fold
648 // duplicate actions.
649 SmallVector<const LandingPadInfo *, 64> LandingPads;
650 LandingPads.reserve(PadInfos.size());
652 for (unsigned i = 0, N = PadInfos.size(); i != N; ++i)
653 LandingPads.push_back(&PadInfos[i]);
655 std::sort(LandingPads.begin(), LandingPads.end(), PadLT);
657 // Compute the actions table and gather the first action index for each
659 SmallVector<ActionEntry, 32> Actions;
660 SmallVector<unsigned, 64> FirstActions;
661 unsigned SizeActions = ComputeActionsTable(LandingPads, Actions,
664 // Invokes and nounwind calls have entries in PadMap (due to being bracketed
665 // by try-range labels when lowered). Ordinary calls do not, so appropriate
666 // try-ranges for them need be deduced when using DWARF exception handling.
668 for (unsigned i = 0, N = LandingPads.size(); i != N; ++i) {
669 const LandingPadInfo *LandingPad = LandingPads[i];
670 for (unsigned j = 0, E = LandingPad->BeginLabels.size(); j != E; ++j) {
671 unsigned BeginLabel = LandingPad->BeginLabels[j];
672 assert(!PadMap.count(BeginLabel) && "Duplicate landing pad labels!");
673 PadRange P = { i, j };
674 PadMap[BeginLabel] = P;
678 // Compute the call-site table.
679 SmallVector<CallSiteEntry, 64> CallSites;
680 ComputeCallSiteTable(CallSites, PadMap, LandingPads, FirstActions);
685 const unsigned SiteStartSize = SizeOfEncodedValue(dwarf::DW_EH_PE_udata4);
686 const unsigned SiteLengthSize = SizeOfEncodedValue(dwarf::DW_EH_PE_udata4);
687 const unsigned LandingPadSize = SizeOfEncodedValue(dwarf::DW_EH_PE_udata4);
688 bool IsSJLJ = MAI->getExceptionHandlingType() == ExceptionHandling::SjLj;
689 bool HaveTTData = IsSJLJ ? (!TypeInfos.empty() || !FilterIds.empty()) : true;
695 SizeSites = CallSites.size() *
696 (SiteStartSize + SiteLengthSize + LandingPadSize);
698 for (unsigned i = 0, e = CallSites.size(); i < e; ++i) {
699 SizeSites += MCAsmInfo::getULEB128Size(CallSites[i].Action);
701 SizeSites += MCAsmInfo::getULEB128Size(i);
705 const MCSection *LSDASection = Asm->getObjFileLowering().getLSDASection();
706 unsigned TTypeFormat;
707 unsigned TypeFormatSize;
710 // For SjLj exceptions, if there is no TypeInfo, then we just explicitly say
711 // that we're omitting that bit.
712 TTypeFormat = dwarf::DW_EH_PE_omit;
713 TypeFormatSize = SizeOfEncodedValue(dwarf::DW_EH_PE_absptr);
715 // Okay, we have actual filters or typeinfos to emit. As such, we need to
716 // pick a type encoding for them. We're about to emit a list of pointers to
717 // typeinfo objects at the end of the LSDA. However, unless we're in static
718 // mode, this reference will require a relocation by the dynamic linker.
720 // Because of this, we have a couple of options:
722 // 1) If we are in -static mode, we can always use an absolute reference
723 // from the LSDA, because the static linker will resolve it.
725 // 2) Otherwise, if the LSDA section is writable, we can output the direct
726 // reference to the typeinfo and allow the dynamic linker to relocate
727 // it. Since it is in a writable section, the dynamic linker won't
730 // 3) Finally, if we're in PIC mode and the LDSA section isn't writable,
731 // we need to use some form of indirection. For example, on Darwin,
732 // we can output a statically-relocatable reference to a dyld stub. The
733 // offset to the stub is constant, but the contents are in a section
734 // that is updated by the dynamic linker. This is easy enough, but we
735 // need to tell the personality function of the unwinder to indirect
736 // through the dyld stub.
738 // FIXME: When (3) is actually implemented, we'll have to emit the stubs
739 // somewhere. This predicate should be moved to a shared location that is
740 // in target-independent code.
742 if (LSDASection->getKind().isWriteable() ||
743 Asm->TM.getRelocationModel() == Reloc::Static)
744 TTypeFormat = dwarf::DW_EH_PE_absptr;
746 TTypeFormat = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
747 dwarf::DW_EH_PE_sdata4;
749 TypeFormatSize = SizeOfEncodedValue(TTypeFormat);
752 // Begin the exception table.
753 Asm->OutStreamer.SwitchSection(LSDASection);
754 Asm->EmitAlignment(2, 0, 0, false);
756 O << "GCC_except_table" << SubprogramCount << ":\n";
758 // The type infos need to be aligned. GCC does this by inserting padding just
759 // before the type infos. However, this changes the size of the exception
760 // table, so you need to take this into account when you output the exception
761 // table size. However, the size is output using a variable length encoding.
762 // So by increasing the size by inserting padding, you may increase the number
763 // of bytes used for writing the size. If it increases, say by one byte, then
764 // you now need to output one less byte of padding to get the type infos
765 // aligned. However this decreases the size of the exception table. This
766 // changes the value you have to output for the exception table size. Due to
767 // the variable length encoding, the number of bytes used for writing the
768 // length may decrease. If so, you then have to increase the amount of
769 // padding. And so on. If you look carefully at the GCC code you will see that
770 // it indeed does this in a loop, going on and on until the values stabilize.
771 // We chose another solution: don't output padding inside the table like GCC
772 // does, instead output it before the table.
773 unsigned SizeTypes = TypeInfos.size() * TypeFormatSize;
774 unsigned TyOffset = sizeof(int8_t) + // Call site format
775 MCAsmInfo::getULEB128Size(SizeSites) + // Call-site table length
776 SizeSites + SizeActions + SizeTypes;
777 unsigned TotalSize = sizeof(int8_t) + // LPStart format
778 sizeof(int8_t) + // TType format
780 MCAsmInfo::getULEB128Size(TyOffset) : 0) + // TType base offset
782 unsigned SizeAlign = (4 - TotalSize) & 3;
784 for (unsigned i = 0; i != SizeAlign; ++i) {
789 EmitLabel("exception", SubprogramCount);
792 SmallString<16> LSDAName;
793 raw_svector_ostream(LSDAName) << MAI->getPrivateGlobalPrefix() <<
794 "_LSDA_" << Asm->getFunctionNumber();
795 O << LSDAName.str() << ":\n";
799 Asm->EmitInt8(dwarf::DW_EH_PE_omit);
800 Asm->EOL("@LPStart format", dwarf::DW_EH_PE_omit);
802 Asm->EmitInt8(TTypeFormat);
803 Asm->EOL("@TType format", TTypeFormat);
806 Asm->EmitULEB128Bytes(TyOffset);
807 Asm->EOL("@TType base offset");
810 // SjLj Exception handling
812 Asm->EmitInt8(dwarf::DW_EH_PE_udata4);
813 Asm->EOL("Call site format", dwarf::DW_EH_PE_udata4);
814 Asm->EmitULEB128Bytes(SizeSites);
815 Asm->EOL("Call site table length");
817 // Emit the landing pad site information.
819 for (SmallVectorImpl<CallSiteEntry>::const_iterator
820 I = CallSites.begin(), E = CallSites.end(); I != E; ++I, ++idx) {
821 const CallSiteEntry &S = *I;
823 // Offset of the landing pad, counted in 16-byte bundles relative to the
825 Asm->EmitULEB128Bytes(idx);
826 Asm->EOL("Landing pad");
828 // Offset of the first associated action record, relative to the start of
829 // the action table. This value is biased by 1 (1 indicates the start of
830 // the action table), and 0 indicates that there are no actions.
831 Asm->EmitULEB128Bytes(S.Action);
835 // DWARF Exception handling
836 assert(MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf);
838 // The call-site table is a list of all call sites that may throw an
839 // exception (including C++ 'throw' statements) in the procedure
840 // fragment. It immediately follows the LSDA header. Each entry indicates,
841 // for a given call, the first corresponding action record and corresponding
844 // The table begins with the number of bytes, stored as an LEB128
845 // compressed, unsigned integer. The records immediately follow the record
846 // count. They are sorted in increasing call-site address. Each record
849 // * The position of the call-site.
850 // * The position of the landing pad.
851 // * The first action record for that call site.
853 // A missing entry in the call-site table indicates that a call is not
854 // supposed to throw.
856 // Emit the landing pad call site table.
857 Asm->EmitInt8(dwarf::DW_EH_PE_udata4);
858 Asm->EOL("Call site format", dwarf::DW_EH_PE_udata4);
859 Asm->EmitULEB128Bytes(SizeSites);
860 Asm->EOL("Call site table size");
862 for (SmallVectorImpl<CallSiteEntry>::const_iterator
863 I = CallSites.begin(), E = CallSites.end(); I != E; ++I) {
864 const CallSiteEntry &S = *I;
865 const char *BeginTag;
866 unsigned BeginNumber;
869 BeginTag = "eh_func_begin";
870 BeginNumber = SubprogramCount;
873 BeginNumber = S.BeginLabel;
876 // Offset of the call site relative to the previous call site, counted in
877 // number of 16-byte bundles. The first call site is counted relative to
878 // the start of the procedure fragment.
879 EmitSectionOffset(BeginTag, "eh_func_begin", BeginNumber, SubprogramCount,
881 Asm->EOL("Region start");
884 EmitDifference("eh_func_end", SubprogramCount, BeginTag, BeginNumber,
887 EmitDifference("label", S.EndLabel, BeginTag, BeginNumber, true);
889 Asm->EOL("Region length");
891 // Offset of the landing pad, counted in 16-byte bundles relative to the
894 Asm->OutStreamer.EmitIntValue(0, 4/*size*/, 0/*addrspace*/);
896 EmitSectionOffset("label", "eh_func_begin", S.PadLabel, SubprogramCount,
899 Asm->EOL("Landing pad");
901 // Offset of the first associated action record, relative to the start of
902 // the action table. This value is biased by 1 (1 indicates the start of
903 // the action table), and 0 indicates that there are no actions.
904 Asm->EmitULEB128Bytes(S.Action);
909 // Emit the Action Table.
910 for (SmallVectorImpl<ActionEntry>::const_iterator
911 I = Actions.begin(), E = Actions.end(); I != E; ++I) {
912 const ActionEntry &Action = *I;
916 // Used by the runtime to match the type of the thrown exception to the
917 // type of the catch clauses or the types in the exception specification.
919 Asm->EmitSLEB128Bytes(Action.ValueForTypeID);
920 Asm->EOL("TypeInfo index");
924 // Self-relative signed displacement in bytes of the next action record,
925 // or 0 if there is no next action record.
927 Asm->EmitSLEB128Bytes(Action.NextAction);
928 Asm->EOL("Next action");
931 // Emit the Catch TypeInfos.
932 for (std::vector<GlobalVariable *>::const_reverse_iterator
933 I = TypeInfos.rbegin(), E = TypeInfos.rend(); I != E; ++I) {
934 const GlobalVariable *GV = *I;
938 O << *Asm->GetGlobalValueSymbol(GV);
943 Asm->EOL("TypeInfo");
946 // Emit the Exception Specifications.
947 for (std::vector<unsigned>::const_iterator
948 I = FilterIds.begin(), E = FilterIds.end(); I < E; ++I) {
949 unsigned TypeID = *I;
950 Asm->EmitULEB128Bytes(TypeID);
952 Asm->EOL("Exception specification");
957 Asm->EmitAlignment(2, 0, 0, false);
960 /// EndModule - Emit all exception information that should come after the
962 void DwarfException::EndModule() {
963 if (MAI->getExceptionHandlingType() != ExceptionHandling::Dwarf)
966 if (!shouldEmitMovesModule && !shouldEmitTableModule)
969 if (TimePassesIsEnabled)
970 ExceptionTimer->startTimer();
972 const std::vector<Function *> Personalities = MMI->getPersonalities();
974 for (unsigned I = 0, E = Personalities.size(); I < E; ++I)
975 EmitCIE(Personalities[I], I);
977 for (std::vector<FunctionEHFrameInfo>::iterator
978 I = EHFrames.begin(), E = EHFrames.end(); I != E; ++I)
981 if (TimePassesIsEnabled)
982 ExceptionTimer->stopTimer();
985 /// BeginFunction - Gather pre-function exception information. Assumes it's
986 /// being emitted immediately after the function entry point.
987 void DwarfException::BeginFunction(MachineFunction *MF) {
988 if (!MMI || !MAI->doesSupportExceptionHandling()) return;
990 if (TimePassesIsEnabled)
991 ExceptionTimer->startTimer();
994 shouldEmitTable = shouldEmitMoves = false;
996 // Map all labels and get rid of any dead landing pads.
997 MMI->TidyLandingPads();
999 // If any landing pads survive, we need an EH table.
1000 if (!MMI->getLandingPads().empty())
1001 shouldEmitTable = true;
1003 // See if we need frame move info.
1004 if (!MF->getFunction()->doesNotThrow() || UnwindTablesMandatory)
1005 shouldEmitMoves = true;
1007 if (shouldEmitMoves || shouldEmitTable)
1008 // Assumes in correct section after the entry point.
1009 EmitLabel("eh_func_begin", ++SubprogramCount);
1011 shouldEmitTableModule |= shouldEmitTable;
1012 shouldEmitMovesModule |= shouldEmitMoves;
1014 if (TimePassesIsEnabled)
1015 ExceptionTimer->stopTimer();
1018 /// EndFunction - Gather and emit post-function exception information.
1020 void DwarfException::EndFunction() {
1021 if (!shouldEmitMoves && !shouldEmitTable) return;
1023 if (TimePassesIsEnabled)
1024 ExceptionTimer->startTimer();
1026 EmitLabel("eh_func_end", SubprogramCount);
1027 EmitExceptionTable();
1029 const MCSymbol *FunctionEHSym =
1030 Asm->GetSymbolWithGlobalValueBase(MF->getFunction(), ".eh",
1031 Asm->MAI->is_EHSymbolPrivate());
1033 // Save EH frame information
1034 EHFrames.push_back(FunctionEHFrameInfo(FunctionEHSym, SubprogramCount,
1035 MMI->getPersonalityIndex(),
1036 MF->getFrameInfo()->hasCalls(),
1037 !MMI->getLandingPads().empty(),
1038 MMI->getFrameMoves(),
1039 MF->getFunction()));
1041 // Record if this personality index uses a landing pad.
1042 UsesLSDA[MMI->getPersonalityIndex()] |= !MMI->getLandingPads().empty();
1044 if (TimePassesIsEnabled)
1045 ExceptionTimer->stopTimer();