1 //===-- CodeGen/AsmPrinter/DwarfException.cpp - Dwarf Exception Impl ------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file contains support for writing DWARF exception info into asm files.
12 //===----------------------------------------------------------------------===//
14 #include "DwarfException.h"
15 #include "llvm/Module.h"
16 #include "llvm/CodeGen/MachineModuleInfo.h"
17 #include "llvm/CodeGen/MachineFrameInfo.h"
18 #include "llvm/CodeGen/MachineFunction.h"
19 #include "llvm/CodeGen/MachineLocation.h"
20 #include "llvm/MC/MCAsmInfo.h"
21 #include "llvm/MC/MCContext.h"
22 #include "llvm/MC/MCExpr.h"
23 #include "llvm/MC/MCSection.h"
24 #include "llvm/MC/MCStreamer.h"
25 #include "llvm/MC/MCSymbol.h"
26 #include "llvm/Target/Mangler.h"
27 #include "llvm/Target/TargetData.h"
28 #include "llvm/Target/TargetFrameInfo.h"
29 #include "llvm/Target/TargetLoweringObjectFile.h"
30 #include "llvm/Target/TargetOptions.h"
31 #include "llvm/Target/TargetRegisterInfo.h"
32 #include "llvm/Support/Dwarf.h"
33 #include "llvm/Support/FormattedStream.h"
34 #include "llvm/Support/Timer.h"
35 #include "llvm/ADT/SmallString.h"
36 #include "llvm/ADT/StringExtras.h"
39 DwarfException::DwarfException(raw_ostream &OS, AsmPrinter *A,
41 : DwarfPrinter(OS, A, T, "eh"), shouldEmitTable(false),shouldEmitMoves(false),
42 shouldEmitTableModule(false), shouldEmitMovesModule(false),
44 if (TimePassesIsEnabled)
45 ExceptionTimer = new Timer("DWARF Exception Writer");
48 DwarfException::~DwarfException() {
49 delete ExceptionTimer;
52 /// SizeOfEncodedValue - Return the size of the encoding in bytes.
53 unsigned DwarfException::SizeOfEncodedValue(unsigned Encoding) {
54 if (Encoding == dwarf::DW_EH_PE_omit)
57 switch (Encoding & 0x07) {
58 case dwarf::DW_EH_PE_absptr:
59 return TD->getPointerSize();
60 case dwarf::DW_EH_PE_udata2:
62 case dwarf::DW_EH_PE_udata4:
64 case dwarf::DW_EH_PE_udata8:
68 assert(0 && "Invalid encoded value.");
72 /// CreateLabelDiff - Emit a label and subtract it from the expression we
73 /// already have. This is equivalent to emitting "foo - .", but we have to emit
74 /// the label for "." directly.
75 const MCExpr *DwarfException::CreateLabelDiff(const MCExpr *ExprRef,
76 const char *LabelName,
79 raw_svector_ostream(Name) << MAI->getPrivateGlobalPrefix()
80 << LabelName << Asm->getFunctionNumber()
82 MCSymbol *DotSym = Asm->OutContext.GetOrCreateSymbol(Name.str());
83 Asm->OutStreamer.EmitLabel(DotSym);
85 return MCBinaryExpr::CreateSub(ExprRef,
86 MCSymbolRefExpr::Create(DotSym,
91 /// EmitCIE - Emit a Common Information Entry (CIE). This holds information that
92 /// is shared among many Frame Description Entries. There is at least one CIE
93 /// in every non-empty .debug_frame section.
94 void DwarfException::EmitCIE(const Function *PersonalityFn, unsigned Index) {
95 // Size and sign of stack growth.
97 Asm->TM.getFrameInfo()->getStackGrowthDirection() ==
98 TargetFrameInfo::StackGrowsUp ?
99 TD->getPointerSize() : -TD->getPointerSize();
101 const TargetLoweringObjectFile &TLOF = Asm->getObjFileLowering();
103 // Begin eh frame section.
104 Asm->OutStreamer.SwitchSection(TLOF.getEHFrameSection());
106 if (MAI->is_EHSymbolPrivate())
107 O << MAI->getPrivateGlobalPrefix();
108 O << "EH_frame" << Index << ":\n";
110 EmitLabel("section_eh_frame", Index);
112 // Define base labels.
113 EmitLabel("eh_frame_common", Index);
115 // Define the eh frame length.
116 EmitDifference("eh_frame_common_end", Index,
117 "eh_frame_common_begin", Index, true);
118 EOL("Length of Common Information Entry");
121 EmitLabel("eh_frame_common_begin", Index);
122 if (Asm->VerboseAsm) Asm->OutStreamer.AddComment("CIE Identifier Tag");
123 Asm->OutStreamer.EmitIntValue(0, 4/*size*/, 0/*addrspace*/);
124 if (Asm->VerboseAsm) Asm->OutStreamer.AddComment("DW_CIE_VERSION");
125 Asm->OutStreamer.EmitIntValue(dwarf::DW_CIE_VERSION, 1/*size*/, 0/*addr*/);
127 // The personality presence indicates that language specific information will
128 // show up in the eh frame. Find out how we are supposed to lower the
129 // personality function reference:
130 const MCExpr *PersonalityRef = 0;
131 bool IsPersonalityIndirect = false, IsPersonalityPCRel = false;
133 // FIXME: HANDLE STATIC CODEGEN MODEL HERE.
135 // In non-static mode, ask the object file how to represent this reference.
137 TLOF.getSymbolForDwarfGlobalReference(PersonalityFn, Asm->Mang,
139 IsPersonalityIndirect,
143 unsigned PerEncoding = dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4;
144 if (IsPersonalityIndirect)
145 PerEncoding |= dwarf::DW_EH_PE_indirect;
146 unsigned LSDAEncoding = dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4;
147 unsigned FDEEncoding = dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4;
149 char Augmentation[6] = { 0 };
150 unsigned AugmentationSize = 0;
151 char *APtr = Augmentation + 1;
153 if (PersonalityRef) {
154 // There is a personality function.
156 AugmentationSize += 1 + SizeOfEncodedValue(PerEncoding);
159 if (UsesLSDA[Index]) {
160 // An LSDA pointer is in the FDE augmentation.
165 if (FDEEncoding != dwarf::DW_EH_PE_absptr) {
166 // A non-default pointer encoding for the FDE.
171 if (APtr != Augmentation + 1)
172 Augmentation[0] = 'z';
174 Asm->OutStreamer.EmitBytes(StringRef(Augmentation, strlen(Augmentation)+1),0);
175 EOL("CIE Augmentation");
178 EmitULEB128(1, "CIE Code Alignment Factor");
179 EmitSLEB128(stackGrowth, "CIE Data Alignment Factor");
180 Asm->EmitInt8(RI->getDwarfRegNum(RI->getRARegister(), true));
181 EOL("CIE Return Address Column");
183 EmitULEB128(AugmentationSize, "Augmentation Size");
184 EmitEncodingByte(PerEncoding, "Personality");
186 // If there is a personality, we need to indicate the function's location.
187 if (PersonalityRef) {
188 if (!IsPersonalityPCRel)
189 PersonalityRef = CreateLabelDiff(PersonalityRef, "personalityref_addr",
192 O << MAI->getData32bitsDirective() << *PersonalityRef;
195 EmitEncodingByte(LSDAEncoding, "LSDA");
196 EmitEncodingByte(FDEEncoding, "FDE");
199 // Indicate locations of general callee saved registers in frame.
200 std::vector<MachineMove> Moves;
201 RI->getInitialFrameState(Moves);
202 EmitFrameMoves(NULL, 0, Moves, true);
204 // On Darwin the linker honors the alignment of eh_frame, which means it must
205 // be 8-byte on 64-bit targets to match what gcc does. Otherwise you get
206 // holes which confuse readers of eh_frame.
207 Asm->EmitAlignment(TD->getPointerSize() == 4 ? 2 : 3, 0, 0, false);
208 EmitLabel("eh_frame_common_end", Index);
212 /// EmitFDE - Emit the Frame Description Entry (FDE) for the function.
213 void DwarfException::EmitFDE(const FunctionEHFrameInfo &EHFrameInfo) {
214 assert(!EHFrameInfo.function->hasAvailableExternallyLinkage() &&
215 "Should not emit 'available externally' functions at all");
217 const Function *TheFunc = EHFrameInfo.function;
219 Asm->OutStreamer.SwitchSection(Asm->getObjFileLowering().getEHFrameSection());
221 // Externally visible entry into the functions eh frame info. If the
222 // corresponding function is static, this should not be externally visible.
223 if (!TheFunc->hasLocalLinkage())
224 if (const char *GlobalEHDirective = MAI->getGlobalEHDirective())
225 O << GlobalEHDirective << *EHFrameInfo.FunctionEHSym << '\n';
227 // If corresponding function is weak definition, this should be too.
228 if (TheFunc->isWeakForLinker() && MAI->getWeakDefDirective())
229 O << MAI->getWeakDefDirective() << *EHFrameInfo.FunctionEHSym << '\n';
231 // If corresponding function is hidden, this should be too.
232 if (TheFunc->hasHiddenVisibility())
233 if (MCSymbolAttr HiddenAttr = MAI->getHiddenVisibilityAttr())
234 Asm->OutStreamer.EmitSymbolAttribute(EHFrameInfo.FunctionEHSym,
237 // If there are no calls then you can't unwind. This may mean we can omit the
238 // EH Frame, but some environments do not handle weak absolute symbols. If
239 // UnwindTablesMandatory is set we cannot do this optimization; the unwind
240 // info is to be available for non-EH uses.
241 if (!EHFrameInfo.hasCalls && !UnwindTablesMandatory &&
242 (!TheFunc->isWeakForLinker() ||
243 !MAI->getWeakDefDirective() ||
244 MAI->getSupportsWeakOmittedEHFrame())) {
245 O << *EHFrameInfo.FunctionEHSym << " = 0\n";
246 // This name has no connection to the function, so it might get
247 // dead-stripped when the function is not, erroneously. Prohibit
248 // dead-stripping unconditionally.
249 if (MAI->hasNoDeadStrip())
250 Asm->OutStreamer.EmitSymbolAttribute(EHFrameInfo.FunctionEHSym,
253 O << *EHFrameInfo.FunctionEHSym << ":\n";
256 EmitDifference("eh_frame_end", EHFrameInfo.Number,
257 "eh_frame_begin", EHFrameInfo.Number, true);
258 EOL("Length of Frame Information Entry");
260 EmitLabel("eh_frame_begin", EHFrameInfo.Number);
262 EmitSectionOffset("eh_frame_begin", "eh_frame_common",
263 EHFrameInfo.Number, EHFrameInfo.PersonalityIndex,
266 EOL("FDE CIE offset");
268 EmitReference("eh_func_begin", EHFrameInfo.Number, true, true);
269 EOL("FDE initial location");
270 EmitDifference("eh_func_end", EHFrameInfo.Number,
271 "eh_func_begin", EHFrameInfo.Number, true);
272 EOL("FDE address range");
274 // If there is a personality and landing pads then point to the language
275 // specific data area in the exception table.
276 if (MMI->getPersonalities()[0] != NULL) {
278 if (Asm->TM.getLSDAEncoding() != DwarfLSDAEncoding::EightByte) {
279 EmitULEB128(4, "Augmentation size");
281 if (EHFrameInfo.hasLandingPads)
282 EmitReference("exception", EHFrameInfo.Number, true, true);
284 Asm->OutStreamer.EmitIntValue(0, 4/*size*/, 0/*addrspace*/);
286 EmitULEB128(TD->getPointerSize(), "Augmentation size");
288 if (EHFrameInfo.hasLandingPads) {
289 EmitReference("exception", EHFrameInfo.Number, true, false);
291 Asm->OutStreamer.EmitIntValue(0, TD->getPointerSize(),
296 EOL("Language Specific Data Area");
298 EmitULEB128(0, "Augmentation size");
301 // Indicate locations of function specific callee saved registers in frame.
302 EmitFrameMoves("eh_func_begin", EHFrameInfo.Number, EHFrameInfo.Moves,
305 // On Darwin the linker honors the alignment of eh_frame, which means it
306 // must be 8-byte on 64-bit targets to match what gcc does. Otherwise you
307 // get holes which confuse readers of eh_frame.
308 Asm->EmitAlignment(TD->getPointerSize() == sizeof(int32_t) ? 2 : 3,
310 EmitLabel("eh_frame_end", EHFrameInfo.Number);
312 // If the function is marked used, this table should be also. We cannot
313 // make the mark unconditional in this case, since retaining the table also
314 // retains the function in this case, and there is code around that depends
315 // on unused functions (calling undefined externals) being dead-stripped to
316 // link correctly. Yes, there really is.
317 if (MMI->isUsedFunction(EHFrameInfo.function))
318 if (MAI->hasNoDeadStrip())
319 Asm->OutStreamer.EmitSymbolAttribute(EHFrameInfo.FunctionEHSym,
325 /// SharedTypeIds - How many leading type ids two landing pads have in common.
326 unsigned DwarfException::SharedTypeIds(const LandingPadInfo *L,
327 const LandingPadInfo *R) {
328 const std::vector<int> &LIds = L->TypeIds, &RIds = R->TypeIds;
329 unsigned LSize = LIds.size(), RSize = RIds.size();
330 unsigned MinSize = LSize < RSize ? LSize : RSize;
333 for (; Count != MinSize; ++Count)
334 if (LIds[Count] != RIds[Count])
340 /// PadLT - Order landing pads lexicographically by type id.
341 bool DwarfException::PadLT(const LandingPadInfo *L, const LandingPadInfo *R) {
342 const std::vector<int> &LIds = L->TypeIds, &RIds = R->TypeIds;
343 unsigned LSize = LIds.size(), RSize = RIds.size();
344 unsigned MinSize = LSize < RSize ? LSize : RSize;
346 for (unsigned i = 0; i != MinSize; ++i)
347 if (LIds[i] != RIds[i])
348 return LIds[i] < RIds[i];
350 return LSize < RSize;
353 /// ComputeActionsTable - Compute the actions table and gather the first action
354 /// index for each landing pad site.
355 unsigned DwarfException::
356 ComputeActionsTable(const SmallVectorImpl<const LandingPadInfo*> &LandingPads,
357 SmallVectorImpl<ActionEntry> &Actions,
358 SmallVectorImpl<unsigned> &FirstActions) {
360 // The action table follows the call-site table in the LSDA. The individual
361 // records are of two types:
364 // * Exception specification
366 // The two record kinds have the same format, with only small differences.
367 // They are distinguished by the "switch value" field: Catch clauses
368 // (TypeInfos) have strictly positive switch values, and exception
369 // specifications (FilterIds) have strictly negative switch values. Value 0
370 // indicates a catch-all clause.
372 // Negative type IDs index into FilterIds. Positive type IDs index into
373 // TypeInfos. The value written for a positive type ID is just the type ID
374 // itself. For a negative type ID, however, the value written is the
375 // (negative) byte offset of the corresponding FilterIds entry. The byte
376 // offset is usually equal to the type ID (because the FilterIds entries are
377 // written using a variable width encoding, which outputs one byte per entry
378 // as long as the value written is not too large) but can differ. This kind
379 // of complication does not occur for positive type IDs because type infos are
380 // output using a fixed width encoding. FilterOffsets[i] holds the byte
381 // offset corresponding to FilterIds[i].
383 const std::vector<unsigned> &FilterIds = MMI->getFilterIds();
384 SmallVector<int, 16> FilterOffsets;
385 FilterOffsets.reserve(FilterIds.size());
388 for (std::vector<unsigned>::const_iterator
389 I = FilterIds.begin(), E = FilterIds.end(); I != E; ++I) {
390 FilterOffsets.push_back(Offset);
391 Offset -= MCAsmInfo::getULEB128Size(*I);
394 FirstActions.reserve(LandingPads.size());
397 unsigned SizeActions = 0;
398 const LandingPadInfo *PrevLPI = 0;
400 for (SmallVectorImpl<const LandingPadInfo *>::const_iterator
401 I = LandingPads.begin(), E = LandingPads.end(); I != E; ++I) {
402 const LandingPadInfo *LPI = *I;
403 const std::vector<int> &TypeIds = LPI->TypeIds;
404 const unsigned NumShared = PrevLPI ? SharedTypeIds(LPI, PrevLPI) : 0;
405 unsigned SizeSiteActions = 0;
407 if (NumShared < TypeIds.size()) {
408 unsigned SizeAction = 0;
409 ActionEntry *PrevAction = 0;
412 const unsigned SizePrevIds = PrevLPI->TypeIds.size();
413 assert(Actions.size());
414 PrevAction = &Actions.back();
415 SizeAction = MCAsmInfo::getSLEB128Size(PrevAction->NextAction) +
416 MCAsmInfo::getSLEB128Size(PrevAction->ValueForTypeID);
418 for (unsigned j = NumShared; j != SizePrevIds; ++j) {
420 MCAsmInfo::getSLEB128Size(PrevAction->ValueForTypeID);
421 SizeAction += -PrevAction->NextAction;
422 PrevAction = PrevAction->Previous;
426 // Compute the actions.
427 for (unsigned J = NumShared, M = TypeIds.size(); J != M; ++J) {
428 int TypeID = TypeIds[J];
429 assert(-1 - TypeID < (int)FilterOffsets.size() && "Unknown filter id!");
430 int ValueForTypeID = TypeID < 0 ? FilterOffsets[-1 - TypeID] : TypeID;
431 unsigned SizeTypeID = MCAsmInfo::getSLEB128Size(ValueForTypeID);
433 int NextAction = SizeAction ? -(SizeAction + SizeTypeID) : 0;
434 SizeAction = SizeTypeID + MCAsmInfo::getSLEB128Size(NextAction);
435 SizeSiteActions += SizeAction;
437 ActionEntry Action = { ValueForTypeID, NextAction, PrevAction };
438 Actions.push_back(Action);
439 PrevAction = &Actions.back();
442 // Record the first action of the landing pad site.
443 FirstAction = SizeActions + SizeSiteActions - SizeAction + 1;
444 } // else identical - re-use previous FirstAction
446 // Information used when created the call-site table. The action record
447 // field of the call site record is the offset of the first associated
448 // action record, relative to the start of the actions table. This value is
449 // biased by 1 (1 in dicating the start of the actions table), and 0
450 // indicates that there are no actions.
451 FirstActions.push_back(FirstAction);
453 // Compute this sites contribution to size.
454 SizeActions += SizeSiteActions;
462 /// CallToNoUnwindFunction - Return `true' if this is a call to a function
463 /// marked `nounwind'. Return `false' otherwise.
464 bool DwarfException::CallToNoUnwindFunction(const MachineInstr *MI) {
465 assert(MI->getDesc().isCall() && "This should be a call instruction!");
467 bool MarkedNoUnwind = false;
468 bool SawFunc = false;
470 for (unsigned I = 0, E = MI->getNumOperands(); I != E; ++I) {
471 const MachineOperand &MO = MI->getOperand(I);
474 if (Function *F = dyn_cast<Function>(MO.getGlobal())) {
476 // Be conservative. If we have more than one function operand for this
477 // call, then we can't make the assumption that it's the callee and
478 // not a parameter to the call.
480 // FIXME: Determine if there's a way to say that `F' is the callee or
482 MarkedNoUnwind = false;
486 MarkedNoUnwind = F->doesNotThrow();
492 return MarkedNoUnwind;
495 /// ComputeCallSiteTable - Compute the call-site table. The entry for an invoke
496 /// has a try-range containing the call, a non-zero landing pad, and an
497 /// appropriate action. The entry for an ordinary call has a try-range
498 /// containing the call and zero for the landing pad and the action. Calls
499 /// marked 'nounwind' have no entry and must not be contained in the try-range
500 /// of any entry - they form gaps in the table. Entries must be ordered by
501 /// try-range address.
502 void DwarfException::
503 ComputeCallSiteTable(SmallVectorImpl<CallSiteEntry> &CallSites,
504 const RangeMapType &PadMap,
505 const SmallVectorImpl<const LandingPadInfo *> &LandingPads,
506 const SmallVectorImpl<unsigned> &FirstActions) {
507 // The end label of the previous invoke or nounwind try-range.
508 unsigned LastLabel = 0;
510 // Whether there is a potentially throwing instruction (currently this means
511 // an ordinary call) between the end of the previous try-range and now.
512 bool SawPotentiallyThrowing = false;
514 // Whether the last CallSite entry was for an invoke.
515 bool PreviousIsInvoke = false;
517 // Visit all instructions in order of address.
518 for (MachineFunction::const_iterator I = MF->begin(), E = MF->end();
520 for (MachineBasicBlock::const_iterator MI = I->begin(), E = I->end();
522 if (!MI->isLabel()) {
523 if (MI->getDesc().isCall())
524 SawPotentiallyThrowing |= !CallToNoUnwindFunction(MI);
529 unsigned BeginLabel = MI->getOperand(0).getImm();
530 assert(BeginLabel && "Invalid label!");
532 // End of the previous try-range?
533 if (BeginLabel == LastLabel)
534 SawPotentiallyThrowing = false;
536 // Beginning of a new try-range?
537 RangeMapType::const_iterator L = PadMap.find(BeginLabel);
538 if (L == PadMap.end())
539 // Nope, it was just some random label.
542 const PadRange &P = L->second;
543 const LandingPadInfo *LandingPad = LandingPads[P.PadIndex];
544 assert(BeginLabel == LandingPad->BeginLabels[P.RangeIndex] &&
545 "Inconsistent landing pad map!");
547 // For Dwarf exception handling (SjLj handling doesn't use this). If some
548 // instruction between the previous try-range and this one may throw,
549 // create a call-site entry with no landing pad for the region between the
551 if (SawPotentiallyThrowing &&
552 MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf) {
553 CallSiteEntry Site = { LastLabel, BeginLabel, 0, 0 };
554 CallSites.push_back(Site);
555 PreviousIsInvoke = false;
558 LastLabel = LandingPad->EndLabels[P.RangeIndex];
559 assert(BeginLabel && LastLabel && "Invalid landing pad!");
561 if (LandingPad->LandingPadLabel) {
562 // This try-range is for an invoke.
563 CallSiteEntry Site = {
566 LandingPad->LandingPadLabel,
567 FirstActions[P.PadIndex]
570 // Try to merge with the previous call-site. SJLJ doesn't do this
571 if (PreviousIsInvoke &&
572 MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf) {
573 CallSiteEntry &Prev = CallSites.back();
574 if (Site.PadLabel == Prev.PadLabel && Site.Action == Prev.Action) {
575 // Extend the range of the previous entry.
576 Prev.EndLabel = Site.EndLabel;
581 // Otherwise, create a new call-site.
582 if (MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf)
583 CallSites.push_back(Site);
585 // SjLj EH must maintain the call sites in the order assigned
586 // to them by the SjLjPrepare pass.
587 unsigned SiteNo = MMI->getCallSiteBeginLabel(BeginLabel);
588 if (CallSites.size() < SiteNo)
589 CallSites.resize(SiteNo);
590 CallSites[SiteNo - 1] = Site;
592 PreviousIsInvoke = true;
595 PreviousIsInvoke = false;
600 // If some instruction between the previous try-range and the end of the
601 // function may throw, create a call-site entry with no landing pad for the
602 // region following the try-range.
603 if (SawPotentiallyThrowing &&
604 MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf) {
605 CallSiteEntry Site = { LastLabel, 0, 0, 0 };
606 CallSites.push_back(Site);
610 /// EmitExceptionTable - Emit landing pads and actions.
612 /// The general organization of the table is complex, but the basic concepts are
613 /// easy. First there is a header which describes the location and organization
614 /// of the three components that follow.
616 /// 1. The landing pad site information describes the range of code covered by
617 /// the try. In our case it's an accumulation of the ranges covered by the
618 /// invokes in the try. There is also a reference to the landing pad that
619 /// handles the exception once processed. Finally an index into the actions
621 /// 2. The action table, in our case, is composed of pairs of type IDs and next
622 /// action offset. Starting with the action index from the landing pad
623 /// site, each type ID is checked for a match to the current exception. If
624 /// it matches then the exception and type id are passed on to the landing
625 /// pad. Otherwise the next action is looked up. This chain is terminated
626 /// with a next action of zero. If no type id is found then the frame is
627 /// unwound and handling continues.
628 /// 3. Type ID table contains references to all the C++ typeinfo for all
629 /// catches in the function. This tables is reverse indexed base 1.
630 void DwarfException::EmitExceptionTable() {
631 const std::vector<GlobalVariable *> &TypeInfos = MMI->getTypeInfos();
632 const std::vector<unsigned> &FilterIds = MMI->getFilterIds();
633 const std::vector<LandingPadInfo> &PadInfos = MMI->getLandingPads();
634 if (PadInfos.empty()) return;
636 // Sort the landing pads in order of their type ids. This is used to fold
637 // duplicate actions.
638 SmallVector<const LandingPadInfo *, 64> LandingPads;
639 LandingPads.reserve(PadInfos.size());
641 for (unsigned i = 0, N = PadInfos.size(); i != N; ++i)
642 LandingPads.push_back(&PadInfos[i]);
644 std::sort(LandingPads.begin(), LandingPads.end(), PadLT);
646 // Compute the actions table and gather the first action index for each
648 SmallVector<ActionEntry, 32> Actions;
649 SmallVector<unsigned, 64> FirstActions;
650 unsigned SizeActions = ComputeActionsTable(LandingPads, Actions,
653 // Invokes and nounwind calls have entries in PadMap (due to being bracketed
654 // by try-range labels when lowered). Ordinary calls do not, so appropriate
655 // try-ranges for them need be deduced when using DWARF exception handling.
657 for (unsigned i = 0, N = LandingPads.size(); i != N; ++i) {
658 const LandingPadInfo *LandingPad = LandingPads[i];
659 for (unsigned j = 0, E = LandingPad->BeginLabels.size(); j != E; ++j) {
660 unsigned BeginLabel = LandingPad->BeginLabels[j];
661 assert(!PadMap.count(BeginLabel) && "Duplicate landing pad labels!");
662 PadRange P = { i, j };
663 PadMap[BeginLabel] = P;
667 // Compute the call-site table.
668 SmallVector<CallSiteEntry, 64> CallSites;
669 ComputeCallSiteTable(CallSites, PadMap, LandingPads, FirstActions);
674 const unsigned SiteStartSize = SizeOfEncodedValue(dwarf::DW_EH_PE_udata4);
675 const unsigned SiteLengthSize = SizeOfEncodedValue(dwarf::DW_EH_PE_udata4);
676 const unsigned LandingPadSize = SizeOfEncodedValue(dwarf::DW_EH_PE_udata4);
677 bool IsSJLJ = MAI->getExceptionHandlingType() == ExceptionHandling::SjLj;
678 bool HaveTTData = IsSJLJ ? (!TypeInfos.empty() || !FilterIds.empty()) : true;
684 SizeSites = CallSites.size() *
685 (SiteStartSize + SiteLengthSize + LandingPadSize);
687 for (unsigned i = 0, e = CallSites.size(); i < e; ++i) {
688 SizeSites += MCAsmInfo::getULEB128Size(CallSites[i].Action);
690 SizeSites += MCAsmInfo::getULEB128Size(i);
694 const MCSection *LSDASection = Asm->getObjFileLowering().getLSDASection();
695 unsigned TTypeFormat;
696 unsigned TypeFormatSize;
699 // For SjLj exceptions, if there is no TypeInfo, then we just explicitly say
700 // that we're omitting that bit.
701 TTypeFormat = dwarf::DW_EH_PE_omit;
702 TypeFormatSize = SizeOfEncodedValue(dwarf::DW_EH_PE_absptr);
704 // Okay, we have actual filters or typeinfos to emit. As such, we need to
705 // pick a type encoding for them. We're about to emit a list of pointers to
706 // typeinfo objects at the end of the LSDA. However, unless we're in static
707 // mode, this reference will require a relocation by the dynamic linker.
709 // Because of this, we have a couple of options:
711 // 1) If we are in -static mode, we can always use an absolute reference
712 // from the LSDA, because the static linker will resolve it.
714 // 2) Otherwise, if the LSDA section is writable, we can output the direct
715 // reference to the typeinfo and allow the dynamic linker to relocate
716 // it. Since it is in a writable section, the dynamic linker won't
719 // 3) Finally, if we're in PIC mode and the LDSA section isn't writable,
720 // we need to use some form of indirection. For example, on Darwin,
721 // we can output a statically-relocatable reference to a dyld stub. The
722 // offset to the stub is constant, but the contents are in a section
723 // that is updated by the dynamic linker. This is easy enough, but we
724 // need to tell the personality function of the unwinder to indirect
725 // through the dyld stub.
727 // FIXME: When (3) is actually implemented, we'll have to emit the stubs
728 // somewhere. This predicate should be moved to a shared location that is
729 // in target-independent code.
731 if (LSDASection->getKind().isWriteable() ||
732 Asm->TM.getRelocationModel() == Reloc::Static)
733 TTypeFormat = dwarf::DW_EH_PE_absptr;
735 TTypeFormat = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
736 dwarf::DW_EH_PE_sdata4;
738 TypeFormatSize = SizeOfEncodedValue(TTypeFormat);
741 // Begin the exception table.
742 Asm->OutStreamer.SwitchSection(LSDASection);
743 Asm->EmitAlignment(2, 0, 0, false);
745 O << "GCC_except_table" << SubprogramCount << ":\n";
747 // The type infos need to be aligned. GCC does this by inserting padding just
748 // before the type infos. However, this changes the size of the exception
749 // table, so you need to take this into account when you output the exception
750 // table size. However, the size is output using a variable length encoding.
751 // So by increasing the size by inserting padding, you may increase the number
752 // of bytes used for writing the size. If it increases, say by one byte, then
753 // you now need to output one less byte of padding to get the type infos
754 // aligned. However this decreases the size of the exception table. This
755 // changes the value you have to output for the exception table size. Due to
756 // the variable length encoding, the number of bytes used for writing the
757 // length may decrease. If so, you then have to increase the amount of
758 // padding. And so on. If you look carefully at the GCC code you will see that
759 // it indeed does this in a loop, going on and on until the values stabilize.
760 // We chose another solution: don't output padding inside the table like GCC
761 // does, instead output it before the table.
762 unsigned SizeTypes = TypeInfos.size() * TypeFormatSize;
763 unsigned TyOffset = sizeof(int8_t) + // Call site format
764 MCAsmInfo::getULEB128Size(SizeSites) + // Call-site table length
765 SizeSites + SizeActions + SizeTypes;
766 unsigned TotalSize = sizeof(int8_t) + // LPStart format
767 sizeof(int8_t) + // TType format
769 MCAsmInfo::getULEB128Size(TyOffset) : 0) + // TType base offset
771 unsigned SizeAlign = (4 - TotalSize) & 3;
773 for (unsigned i = 0; i != SizeAlign; ++i) {
778 EmitLabel("exception", SubprogramCount);
781 SmallString<16> LSDAName;
782 raw_svector_ostream(LSDAName) << MAI->getPrivateGlobalPrefix() <<
783 "_LSDA_" << Asm->getFunctionNumber();
784 O << LSDAName.str() << ":\n";
788 EmitEncodingByte(dwarf::DW_EH_PE_omit, "@LPStart");
789 EmitEncodingByte(TTypeFormat, "@TType");
792 EmitULEB128(TyOffset, "@TType base offset");
794 // SjLj Exception handling
796 EmitEncodingByte(dwarf::DW_EH_PE_udata4, "Call site");
797 EmitULEB128(SizeSites, "Call site table length");
799 // Emit the landing pad site information.
801 for (SmallVectorImpl<CallSiteEntry>::const_iterator
802 I = CallSites.begin(), E = CallSites.end(); I != E; ++I, ++idx) {
803 const CallSiteEntry &S = *I;
805 // Offset of the landing pad, counted in 16-byte bundles relative to the
807 EmitULEB128(idx, "Landing pad");
809 // Offset of the first associated action record, relative to the start of
810 // the action table. This value is biased by 1 (1 indicates the start of
811 // the action table), and 0 indicates that there are no actions.
812 EmitULEB128(S.Action, "Action");
815 // DWARF Exception handling
816 assert(MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf);
818 // The call-site table is a list of all call sites that may throw an
819 // exception (including C++ 'throw' statements) in the procedure
820 // fragment. It immediately follows the LSDA header. Each entry indicates,
821 // for a given call, the first corresponding action record and corresponding
824 // The table begins with the number of bytes, stored as an LEB128
825 // compressed, unsigned integer. The records immediately follow the record
826 // count. They are sorted in increasing call-site address. Each record
829 // * The position of the call-site.
830 // * The position of the landing pad.
831 // * The first action record for that call site.
833 // A missing entry in the call-site table indicates that a call is not
834 // supposed to throw.
836 // Emit the landing pad call site table.
837 EmitEncodingByte(dwarf::DW_EH_PE_udata4, "Call site");
838 EmitULEB128(SizeSites, "Call site table size");
840 for (SmallVectorImpl<CallSiteEntry>::const_iterator
841 I = CallSites.begin(), E = CallSites.end(); I != E; ++I) {
842 const CallSiteEntry &S = *I;
843 const char *BeginTag;
844 unsigned BeginNumber;
847 BeginTag = "eh_func_begin";
848 BeginNumber = SubprogramCount;
851 BeginNumber = S.BeginLabel;
854 // Offset of the call site relative to the previous call site, counted in
855 // number of 16-byte bundles. The first call site is counted relative to
856 // the start of the procedure fragment.
857 EmitSectionOffset(BeginTag, "eh_func_begin", BeginNumber, SubprogramCount,
862 EmitDifference("eh_func_end", SubprogramCount, BeginTag, BeginNumber,
865 EmitDifference("label", S.EndLabel, BeginTag, BeginNumber, true);
867 EOL("Region length");
869 // Offset of the landing pad, counted in 16-byte bundles relative to the
872 Asm->OutStreamer.EmitIntValue(0, 4/*size*/, 0/*addrspace*/);
874 EmitSectionOffset("label", "eh_func_begin", S.PadLabel, SubprogramCount,
879 // Offset of the first associated action record, relative to the start of
880 // the action table. This value is biased by 1 (1 indicates the start of
881 // the action table), and 0 indicates that there are no actions.
882 EmitULEB128(S.Action, "Action");
886 // Emit the Action Table.
887 for (SmallVectorImpl<ActionEntry>::const_iterator
888 I = Actions.begin(), E = Actions.end(); I != E; ++I) {
889 const ActionEntry &Action = *I;
893 // Used by the runtime to match the type of the thrown exception to the
894 // type of the catch clauses or the types in the exception specification.
895 EmitSLEB128(Action.ValueForTypeID, "TypeInfo index");
899 // Self-relative signed displacement in bytes of the next action record,
900 // or 0 if there is no next action record.
901 EmitSLEB128(Action.NextAction, "Next action");
904 // Emit the Catch TypeInfos.
905 for (std::vector<GlobalVariable *>::const_reverse_iterator
906 I = TypeInfos.rbegin(), E = TypeInfos.rend(); I != E; ++I) {
907 const GlobalVariable *GV = *I;
911 O << *Asm->GetGlobalValueSymbol(GV);
918 // Emit the Exception Specifications.
919 for (std::vector<unsigned>::const_iterator
920 I = FilterIds.begin(), E = FilterIds.end(); I < E; ++I) {
921 unsigned TypeID = *I;
922 EmitULEB128(TypeID, TypeID != 0 ? "Exception specification" : 0);
925 Asm->EmitAlignment(2, 0, 0, false);
928 /// EndModule - Emit all exception information that should come after the
930 void DwarfException::EndModule() {
931 if (MAI->getExceptionHandlingType() != ExceptionHandling::Dwarf)
934 if (!shouldEmitMovesModule && !shouldEmitTableModule)
937 if (TimePassesIsEnabled)
938 ExceptionTimer->startTimer();
940 const std::vector<Function *> Personalities = MMI->getPersonalities();
942 for (unsigned I = 0, E = Personalities.size(); I < E; ++I)
943 EmitCIE(Personalities[I], I);
945 for (std::vector<FunctionEHFrameInfo>::iterator
946 I = EHFrames.begin(), E = EHFrames.end(); I != E; ++I)
949 if (TimePassesIsEnabled)
950 ExceptionTimer->stopTimer();
953 /// BeginFunction - Gather pre-function exception information. Assumes it's
954 /// being emitted immediately after the function entry point.
955 void DwarfException::BeginFunction(const MachineFunction *MF) {
956 if (!MMI || !MAI->doesSupportExceptionHandling()) return;
958 if (TimePassesIsEnabled)
959 ExceptionTimer->startTimer();
962 shouldEmitTable = shouldEmitMoves = false;
964 // Map all labels and get rid of any dead landing pads.
965 MMI->TidyLandingPads();
967 // If any landing pads survive, we need an EH table.
968 if (!MMI->getLandingPads().empty())
969 shouldEmitTable = true;
971 // See if we need frame move info.
972 if (!MF->getFunction()->doesNotThrow() || UnwindTablesMandatory)
973 shouldEmitMoves = true;
975 if (shouldEmitMoves || shouldEmitTable)
976 // Assumes in correct section after the entry point.
977 EmitLabel("eh_func_begin", ++SubprogramCount);
979 shouldEmitTableModule |= shouldEmitTable;
980 shouldEmitMovesModule |= shouldEmitMoves;
982 if (TimePassesIsEnabled)
983 ExceptionTimer->stopTimer();
986 /// EndFunction - Gather and emit post-function exception information.
988 void DwarfException::EndFunction() {
989 if (!shouldEmitMoves && !shouldEmitTable) return;
991 if (TimePassesIsEnabled)
992 ExceptionTimer->startTimer();
994 EmitLabel("eh_func_end", SubprogramCount);
995 EmitExceptionTable();
997 MCSymbol *FunctionEHSym =
998 Asm->GetSymbolWithGlobalValueBase(MF->getFunction(), ".eh",
999 Asm->MAI->is_EHSymbolPrivate());
1001 // Save EH frame information
1002 EHFrames.push_back(FunctionEHFrameInfo(FunctionEHSym, SubprogramCount,
1003 MMI->getPersonalityIndex(),
1004 MF->getFrameInfo()->hasCalls(),
1005 !MMI->getLandingPads().empty(),
1006 MMI->getFrameMoves(),
1007 MF->getFunction()));
1009 // Record if this personality index uses a landing pad.
1010 UsesLSDA[MMI->getPersonalityIndex()] |= !MMI->getLandingPads().empty();
1012 if (TimePassesIsEnabled)
1013 ExceptionTimer->stopTimer();