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), 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 /// EmitCIE - Emit a Common Information Entry (CIE). This holds information that
54 /// is shared among many Frame Description Entries. There is at least one CIE
55 /// in every non-empty .debug_frame section.
56 void DwarfException::EmitCIE(const Function *PersonalityFn, unsigned Index) {
57 // Size and sign of stack growth.
59 Asm->TM.getFrameInfo()->getStackGrowthDirection() ==
60 TargetFrameInfo::StackGrowsUp ?
61 TD->getPointerSize() : -TD->getPointerSize();
63 const TargetLoweringObjectFile &TLOF = Asm->getObjFileLowering();
65 // Begin eh frame section.
66 Asm->OutStreamer.SwitchSection(TLOF.getEHFrameSection());
69 if (TLOF.isFunctionEHFrameSymbolPrivate())
70 EHFrameSym = getDWLabel("EH_frame", Index);
72 EHFrameSym = Asm->OutContext.GetOrCreateSymbol(Twine("EH_frame") +
74 Asm->OutStreamer.EmitLabel(EHFrameSym);
76 Asm->OutStreamer.EmitLabel(getDWLabel("section_eh_frame", Index));
78 // Define base labels.
79 Asm->OutStreamer.EmitLabel(getDWLabel("eh_frame_common", Index));
81 // Define the eh frame length.
82 Asm->OutStreamer.AddComment("Length of Common Information Entry");
83 EmitDifference(getDWLabel("eh_frame_common_end", Index),
84 getDWLabel("eh_frame_common_begin", Index), true);
87 Asm->OutStreamer.EmitLabel(getDWLabel("eh_frame_common_begin", Index));
88 Asm->OutStreamer.AddComment("CIE Identifier Tag");
89 Asm->OutStreamer.EmitIntValue(0, 4/*size*/, 0/*addrspace*/);
90 Asm->OutStreamer.AddComment("DW_CIE_VERSION");
91 Asm->OutStreamer.EmitIntValue(dwarf::DW_CIE_VERSION, 1/*size*/, 0/*addr*/);
93 // The personality presence indicates that language specific information will
94 // show up in the eh frame. Find out how we are supposed to lower the
95 // personality function reference:
97 unsigned LSDAEncoding = TLOF.getLSDAEncoding();
98 unsigned FDEEncoding = TLOF.getFDEEncoding();
99 unsigned PerEncoding = TLOF.getPersonalityEncoding();
101 char Augmentation[6] = { 0 };
102 unsigned AugmentationSize = 0;
103 char *APtr = Augmentation + 1;
106 // There is a personality function.
108 AugmentationSize += 1 + SizeOfEncodedValue(PerEncoding);
111 if (UsesLSDA[Index]) {
112 // An LSDA pointer is in the FDE augmentation.
117 if (FDEEncoding != dwarf::DW_EH_PE_absptr) {
118 // A non-default pointer encoding for the FDE.
123 if (APtr != Augmentation + 1)
124 Augmentation[0] = 'z';
126 Asm->OutStreamer.AddComment("CIE Augmentation");
127 Asm->OutStreamer.EmitBytes(StringRef(Augmentation, strlen(Augmentation)+1),0);
130 EmitULEB128(1, "CIE Code Alignment Factor");
131 EmitSLEB128(stackGrowth, "CIE Data Alignment Factor");
132 Asm->OutStreamer.AddComment("CIE Return Address Column");
133 Asm->EmitInt8(RI->getDwarfRegNum(RI->getRARegister(), true));
135 if (Augmentation[0]) {
136 EmitULEB128(AugmentationSize, "Augmentation Size");
138 // If there is a personality, we need to indicate the function's location.
140 EmitEncodingByte(PerEncoding, "Personality");
141 Asm->OutStreamer.AddComment("Personality");
142 EmitReference(PersonalityFn, PerEncoding);
145 EmitEncodingByte(LSDAEncoding, "LSDA");
146 if (FDEEncoding != dwarf::DW_EH_PE_absptr)
147 EmitEncodingByte(FDEEncoding, "FDE");
150 // Indicate locations of general callee saved registers in frame.
151 std::vector<MachineMove> Moves;
152 RI->getInitialFrameState(Moves);
153 EmitFrameMoves(0, Moves, true);
155 // On Darwin the linker honors the alignment of eh_frame, which means it must
156 // be 8-byte on 64-bit targets to match what gcc does. Otherwise you get
157 // holes which confuse readers of eh_frame.
158 Asm->EmitAlignment(TD->getPointerSize() == 4 ? 2 : 3, 0, 0, false);
159 Asm->OutStreamer.EmitLabel(getDWLabel("eh_frame_common_end", Index));
162 /// EmitFDE - Emit the Frame Description Entry (FDE) for the function.
163 void DwarfException::EmitFDE(const FunctionEHFrameInfo &EHFrameInfo) {
164 assert(!EHFrameInfo.function->hasAvailableExternallyLinkage() &&
165 "Should not emit 'available externally' functions at all");
167 const Function *TheFunc = EHFrameInfo.function;
168 const TargetLoweringObjectFile &TLOF = Asm->getObjFileLowering();
170 unsigned LSDAEncoding = TLOF.getLSDAEncoding();
171 unsigned FDEEncoding = TLOF.getFDEEncoding();
173 Asm->OutStreamer.SwitchSection(TLOF.getEHFrameSection());
175 // Externally visible entry into the functions eh frame info. If the
176 // corresponding function is static, this should not be externally visible.
177 if (!TheFunc->hasLocalLinkage() && TLOF.isFunctionEHSymbolGlobal())
178 Asm->OutStreamer.EmitSymbolAttribute(EHFrameInfo.FunctionEHSym,MCSA_Global);
180 // If corresponding function is weak definition, this should be too.
181 if (TheFunc->isWeakForLinker() && MAI->getWeakDefDirective())
182 Asm->OutStreamer.EmitSymbolAttribute(EHFrameInfo.FunctionEHSym,
183 MCSA_WeakDefinition);
185 // If corresponding function is hidden, this should be too.
186 if (TheFunc->hasHiddenVisibility())
187 if (MCSymbolAttr HiddenAttr = MAI->getHiddenVisibilityAttr())
188 Asm->OutStreamer.EmitSymbolAttribute(EHFrameInfo.FunctionEHSym,
191 // If there are no calls then you can't unwind. This may mean we can omit the
192 // EH Frame, but some environments do not handle weak absolute symbols. If
193 // UnwindTablesMandatory is set we cannot do this optimization; the unwind
194 // info is to be available for non-EH uses.
195 if (!EHFrameInfo.hasCalls && !UnwindTablesMandatory &&
196 (!TheFunc->isWeakForLinker() ||
197 !MAI->getWeakDefDirective() ||
198 TLOF.getSupportsWeakOmittedEHFrame())) {
199 Asm->OutStreamer.EmitAssignment(EHFrameInfo.FunctionEHSym,
200 MCConstantExpr::Create(0, Asm->OutContext));
201 // This name has no connection to the function, so it might get
202 // dead-stripped when the function is not, erroneously. Prohibit
203 // dead-stripping unconditionally.
204 if (MAI->hasNoDeadStrip())
205 Asm->OutStreamer.EmitSymbolAttribute(EHFrameInfo.FunctionEHSym,
208 Asm->OutStreamer.EmitLabel(EHFrameInfo.FunctionEHSym);
211 Asm->OutStreamer.AddComment("Length of Frame Information Entry");
212 EmitDifference(getDWLabel("eh_frame_end", EHFrameInfo.Number),
213 getDWLabel("eh_frame_begin", EHFrameInfo.Number),
216 Asm->OutStreamer.EmitLabel(getDWLabel("eh_frame_begin",EHFrameInfo.Number));
218 Asm->OutStreamer.AddComment("FDE CIE offset");
219 EmitSectionOffset(getDWLabel("eh_frame_begin", EHFrameInfo.Number),
220 getDWLabel("eh_frame_common",
221 EHFrameInfo.PersonalityIndex),
224 MCSymbol *EHFuncBeginSym = getDWLabel("eh_func_begin", EHFrameInfo.Number);
226 Asm->OutStreamer.AddComment("FDE initial location");
227 EmitReference(EHFuncBeginSym, FDEEncoding);
229 Asm->OutStreamer.AddComment("FDE address range");
230 EmitDifference(getDWLabel("eh_func_end", EHFrameInfo.Number),EHFuncBeginSym,
231 SizeOfEncodedValue(FDEEncoding) == 4);
233 // If there is a personality and landing pads then point to the language
234 // specific data area in the exception table.
235 if (MMI->getPersonalities()[0] != NULL) {
236 unsigned Size = SizeOfEncodedValue(LSDAEncoding);
238 EmitULEB128(Size, "Augmentation size");
239 Asm->OutStreamer.AddComment("Language Specific Data Area");
240 if (EHFrameInfo.hasLandingPads)
241 EmitReference(getDWLabel("exception", EHFrameInfo.Number),LSDAEncoding);
243 Asm->OutStreamer.EmitIntValue(0, Size/*size*/, 0/*addrspace*/);
246 EmitULEB128(0, "Augmentation size");
249 // Indicate locations of function specific callee saved registers in frame.
250 EmitFrameMoves(EHFuncBeginSym, EHFrameInfo.Moves, true);
252 // On Darwin the linker honors the alignment of eh_frame, which means it
253 // must be 8-byte on 64-bit targets to match what gcc does. Otherwise you
254 // get holes which confuse readers of eh_frame.
255 Asm->EmitAlignment(TD->getPointerSize() == sizeof(int32_t) ? 2 : 3,
257 Asm->OutStreamer.EmitLabel(getDWLabel("eh_frame_end", EHFrameInfo.Number));
259 // If the function is marked used, this table should be also. We cannot
260 // make the mark unconditional in this case, since retaining the table also
261 // retains the function in this case, and there is code around that depends
262 // on unused functions (calling undefined externals) being dead-stripped to
263 // link correctly. Yes, there really is.
264 if (MMI->isUsedFunction(EHFrameInfo.function))
265 if (MAI->hasNoDeadStrip())
266 Asm->OutStreamer.EmitSymbolAttribute(EHFrameInfo.FunctionEHSym,
269 Asm->OutStreamer.AddBlankLine();
272 /// SharedTypeIds - How many leading type ids two landing pads have in common.
273 unsigned DwarfException::SharedTypeIds(const LandingPadInfo *L,
274 const LandingPadInfo *R) {
275 const std::vector<int> &LIds = L->TypeIds, &RIds = R->TypeIds;
276 unsigned LSize = LIds.size(), RSize = RIds.size();
277 unsigned MinSize = LSize < RSize ? LSize : RSize;
280 for (; Count != MinSize; ++Count)
281 if (LIds[Count] != RIds[Count])
287 /// PadLT - Order landing pads lexicographically by type id.
288 bool DwarfException::PadLT(const LandingPadInfo *L, const LandingPadInfo *R) {
289 const std::vector<int> &LIds = L->TypeIds, &RIds = R->TypeIds;
290 unsigned LSize = LIds.size(), RSize = RIds.size();
291 unsigned MinSize = LSize < RSize ? LSize : RSize;
293 for (unsigned i = 0; i != MinSize; ++i)
294 if (LIds[i] != RIds[i])
295 return LIds[i] < RIds[i];
297 return LSize < RSize;
300 /// ComputeActionsTable - Compute the actions table and gather the first action
301 /// index for each landing pad site.
302 unsigned DwarfException::
303 ComputeActionsTable(const SmallVectorImpl<const LandingPadInfo*> &LandingPads,
304 SmallVectorImpl<ActionEntry> &Actions,
305 SmallVectorImpl<unsigned> &FirstActions) {
307 // The action table follows the call-site table in the LSDA. The individual
308 // records are of two types:
311 // * Exception specification
313 // The two record kinds have the same format, with only small differences.
314 // They are distinguished by the "switch value" field: Catch clauses
315 // (TypeInfos) have strictly positive switch values, and exception
316 // specifications (FilterIds) have strictly negative switch values. Value 0
317 // indicates a catch-all clause.
319 // Negative type IDs index into FilterIds. Positive type IDs index into
320 // TypeInfos. The value written for a positive type ID is just the type ID
321 // itself. For a negative type ID, however, the value written is the
322 // (negative) byte offset of the corresponding FilterIds entry. The byte
323 // offset is usually equal to the type ID (because the FilterIds entries are
324 // written using a variable width encoding, which outputs one byte per entry
325 // as long as the value written is not too large) but can differ. This kind
326 // of complication does not occur for positive type IDs because type infos are
327 // output using a fixed width encoding. FilterOffsets[i] holds the byte
328 // offset corresponding to FilterIds[i].
330 const std::vector<unsigned> &FilterIds = MMI->getFilterIds();
331 SmallVector<int, 16> FilterOffsets;
332 FilterOffsets.reserve(FilterIds.size());
335 for (std::vector<unsigned>::const_iterator
336 I = FilterIds.begin(), E = FilterIds.end(); I != E; ++I) {
337 FilterOffsets.push_back(Offset);
338 Offset -= MCAsmInfo::getULEB128Size(*I);
341 FirstActions.reserve(LandingPads.size());
344 unsigned SizeActions = 0;
345 const LandingPadInfo *PrevLPI = 0;
347 for (SmallVectorImpl<const LandingPadInfo *>::const_iterator
348 I = LandingPads.begin(), E = LandingPads.end(); I != E; ++I) {
349 const LandingPadInfo *LPI = *I;
350 const std::vector<int> &TypeIds = LPI->TypeIds;
351 const unsigned NumShared = PrevLPI ? SharedTypeIds(LPI, PrevLPI) : 0;
352 unsigned SizeSiteActions = 0;
354 if (NumShared < TypeIds.size()) {
355 unsigned SizeAction = 0;
356 unsigned PrevAction = (unsigned)-1;
359 const unsigned SizePrevIds = PrevLPI->TypeIds.size();
360 assert(Actions.size());
361 PrevAction = Actions.size() - 1;
363 MCAsmInfo::getSLEB128Size(Actions[PrevAction].NextAction) +
364 MCAsmInfo::getSLEB128Size(Actions[PrevAction].ValueForTypeID);
366 for (unsigned j = NumShared; j != SizePrevIds; ++j) {
367 assert(PrevAction != (unsigned)-1 && "PrevAction is invalid!");
369 MCAsmInfo::getSLEB128Size(Actions[PrevAction].ValueForTypeID);
370 SizeAction += -Actions[PrevAction].NextAction;
371 PrevAction = Actions[PrevAction].Previous;
375 // Compute the actions.
376 for (unsigned J = NumShared, M = TypeIds.size(); J != M; ++J) {
377 int TypeID = TypeIds[J];
378 assert(-1 - TypeID < (int)FilterOffsets.size() && "Unknown filter id!");
379 int ValueForTypeID = TypeID < 0 ? FilterOffsets[-1 - TypeID] : TypeID;
380 unsigned SizeTypeID = MCAsmInfo::getSLEB128Size(ValueForTypeID);
382 int NextAction = SizeAction ? -(SizeAction + SizeTypeID) : 0;
383 SizeAction = SizeTypeID + MCAsmInfo::getSLEB128Size(NextAction);
384 SizeSiteActions += SizeAction;
386 ActionEntry Action = { ValueForTypeID, NextAction, PrevAction };
387 Actions.push_back(Action);
388 PrevAction = Actions.size() - 1;
391 // Record the first action of the landing pad site.
392 FirstAction = SizeActions + SizeSiteActions - SizeAction + 1;
393 } // else identical - re-use previous FirstAction
395 // Information used when created the call-site table. The action record
396 // field of the call site record is the offset of the first associated
397 // action record, relative to the start of the actions table. This value is
398 // biased by 1 (1 indicating the start of the actions table), and 0
399 // indicates that there are no actions.
400 FirstActions.push_back(FirstAction);
402 // Compute this sites contribution to size.
403 SizeActions += SizeSiteActions;
411 /// CallToNoUnwindFunction - Return `true' if this is a call to a function
412 /// marked `nounwind'. Return `false' otherwise.
413 bool DwarfException::CallToNoUnwindFunction(const MachineInstr *MI) {
414 assert(MI->getDesc().isCall() && "This should be a call instruction!");
416 bool MarkedNoUnwind = false;
417 bool SawFunc = false;
419 for (unsigned I = 0, E = MI->getNumOperands(); I != E; ++I) {
420 const MachineOperand &MO = MI->getOperand(I);
423 if (Function *F = dyn_cast<Function>(MO.getGlobal())) {
425 // Be conservative. If we have more than one function operand for this
426 // call, then we can't make the assumption that it's the callee and
427 // not a parameter to the call.
429 // FIXME: Determine if there's a way to say that `F' is the callee or
431 MarkedNoUnwind = false;
435 MarkedNoUnwind = F->doesNotThrow();
441 return MarkedNoUnwind;
444 /// ComputeCallSiteTable - Compute the call-site table. The entry for an invoke
445 /// has a try-range containing the call, a non-zero landing pad, and an
446 /// appropriate action. The entry for an ordinary call has a try-range
447 /// containing the call and zero for the landing pad and the action. Calls
448 /// marked 'nounwind' have no entry and must not be contained in the try-range
449 /// of any entry - they form gaps in the table. Entries must be ordered by
450 /// try-range address.
451 void DwarfException::
452 ComputeCallSiteTable(SmallVectorImpl<CallSiteEntry> &CallSites,
453 const RangeMapType &PadMap,
454 const SmallVectorImpl<const LandingPadInfo *> &LandingPads,
455 const SmallVectorImpl<unsigned> &FirstActions) {
456 // The end label of the previous invoke or nounwind try-range.
457 MCSymbol *LastLabel = 0;
459 // Whether there is a potentially throwing instruction (currently this means
460 // an ordinary call) between the end of the previous try-range and now.
461 bool SawPotentiallyThrowing = false;
463 // Whether the last CallSite entry was for an invoke.
464 bool PreviousIsInvoke = false;
466 // Visit all instructions in order of address.
467 for (MachineFunction::const_iterator I = MF->begin(), E = MF->end();
469 for (MachineBasicBlock::const_iterator MI = I->begin(), E = I->end();
471 if (!MI->isLabel()) {
472 if (MI->getDesc().isCall())
473 SawPotentiallyThrowing |= !CallToNoUnwindFunction(MI);
477 // End of the previous try-range?
478 MCSymbol *BeginLabel = MI->getOperand(0).getMCSymbol();
479 if (BeginLabel == LastLabel)
480 SawPotentiallyThrowing = false;
482 // Beginning of a new try-range?
483 RangeMapType::const_iterator L = PadMap.find(BeginLabel);
484 if (L == PadMap.end())
485 // Nope, it was just some random label.
488 const PadRange &P = L->second;
489 const LandingPadInfo *LandingPad = LandingPads[P.PadIndex];
490 assert(BeginLabel == LandingPad->BeginLabels[P.RangeIndex] &&
491 "Inconsistent landing pad map!");
493 // For Dwarf exception handling (SjLj handling doesn't use this). If some
494 // instruction between the previous try-range and this one may throw,
495 // create a call-site entry with no landing pad for the region between the
497 if (SawPotentiallyThrowing &&
498 MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf) {
499 CallSiteEntry Site = { LastLabel, BeginLabel, 0, 0 };
500 CallSites.push_back(Site);
501 PreviousIsInvoke = false;
504 LastLabel = LandingPad->EndLabels[P.RangeIndex];
505 assert(BeginLabel && LastLabel && "Invalid landing pad!");
507 if (LandingPad->LandingPadLabel) {
508 // This try-range is for an invoke.
509 CallSiteEntry Site = {
512 LandingPad->LandingPadLabel,
513 FirstActions[P.PadIndex]
516 // Try to merge with the previous call-site. SJLJ doesn't do this
517 if (PreviousIsInvoke &&
518 MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf) {
519 CallSiteEntry &Prev = CallSites.back();
520 if (Site.PadLabel == Prev.PadLabel && Site.Action == Prev.Action) {
521 // Extend the range of the previous entry.
522 Prev.EndLabel = Site.EndLabel;
527 // Otherwise, create a new call-site.
528 if (MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf)
529 CallSites.push_back(Site);
531 // SjLj EH must maintain the call sites in the order assigned
532 // to them by the SjLjPrepare pass.
533 unsigned SiteNo = MMI->getCallSiteBeginLabel(BeginLabel);
534 if (CallSites.size() < SiteNo)
535 CallSites.resize(SiteNo);
536 CallSites[SiteNo - 1] = Site;
538 PreviousIsInvoke = true;
541 PreviousIsInvoke = false;
546 // If some instruction between the previous try-range and the end of the
547 // function may throw, create a call-site entry with no landing pad for the
548 // region following the try-range.
549 if (SawPotentiallyThrowing &&
550 MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf) {
551 CallSiteEntry Site = { LastLabel, 0, 0, 0 };
552 CallSites.push_back(Site);
556 /// EmitExceptionTable - Emit landing pads and actions.
558 /// The general organization of the table is complex, but the basic concepts are
559 /// easy. First there is a header which describes the location and organization
560 /// of the three components that follow.
562 /// 1. The landing pad site information describes the range of code covered by
563 /// the try. In our case it's an accumulation of the ranges covered by the
564 /// invokes in the try. There is also a reference to the landing pad that
565 /// handles the exception once processed. Finally an index into the actions
567 /// 2. The action table, in our case, is composed of pairs of type IDs and next
568 /// action offset. Starting with the action index from the landing pad
569 /// site, each type ID is checked for a match to the current exception. If
570 /// it matches then the exception and type id are passed on to the landing
571 /// pad. Otherwise the next action is looked up. This chain is terminated
572 /// with a next action of zero. If no type id is found then the frame is
573 /// unwound and handling continues.
574 /// 3. Type ID table contains references to all the C++ typeinfo for all
575 /// catches in the function. This tables is reverse indexed base 1.
576 void DwarfException::EmitExceptionTable() {
577 const std::vector<GlobalVariable *> &TypeInfos = MMI->getTypeInfos();
578 const std::vector<unsigned> &FilterIds = MMI->getFilterIds();
579 const std::vector<LandingPadInfo> &PadInfos = MMI->getLandingPads();
581 // Sort the landing pads in order of their type ids. This is used to fold
582 // duplicate actions.
583 SmallVector<const LandingPadInfo *, 64> LandingPads;
584 LandingPads.reserve(PadInfos.size());
586 for (unsigned i = 0, N = PadInfos.size(); i != N; ++i)
587 LandingPads.push_back(&PadInfos[i]);
589 std::sort(LandingPads.begin(), LandingPads.end(), PadLT);
591 // Compute the actions table and gather the first action index for each
593 SmallVector<ActionEntry, 32> Actions;
594 SmallVector<unsigned, 64> FirstActions;
595 unsigned SizeActions=ComputeActionsTable(LandingPads, Actions, FirstActions);
597 // Invokes and nounwind calls have entries in PadMap (due to being bracketed
598 // by try-range labels when lowered). Ordinary calls do not, so appropriate
599 // try-ranges for them need be deduced when using DWARF exception handling.
601 for (unsigned i = 0, N = LandingPads.size(); i != N; ++i) {
602 const LandingPadInfo *LandingPad = LandingPads[i];
603 for (unsigned j = 0, E = LandingPad->BeginLabels.size(); j != E; ++j) {
604 MCSymbol *BeginLabel = LandingPad->BeginLabels[j];
605 assert(!PadMap.count(BeginLabel) && "Duplicate landing pad labels!");
606 PadRange P = { i, j };
607 PadMap[BeginLabel] = P;
611 // Compute the call-site table.
612 SmallVector<CallSiteEntry, 64> CallSites;
613 ComputeCallSiteTable(CallSites, PadMap, LandingPads, FirstActions);
618 const unsigned SiteStartSize = SizeOfEncodedValue(dwarf::DW_EH_PE_udata4);
619 const unsigned SiteLengthSize = SizeOfEncodedValue(dwarf::DW_EH_PE_udata4);
620 const unsigned LandingPadSize = SizeOfEncodedValue(dwarf::DW_EH_PE_udata4);
621 bool IsSJLJ = MAI->getExceptionHandlingType() == ExceptionHandling::SjLj;
622 bool HaveTTData = IsSJLJ ? (!TypeInfos.empty() || !FilterIds.empty()) : true;
623 unsigned CallSiteTableLength;
626 CallSiteTableLength = 0;
628 CallSiteTableLength = CallSites.size() *
629 (SiteStartSize + SiteLengthSize + LandingPadSize);
631 for (unsigned i = 0, e = CallSites.size(); i < e; ++i) {
632 CallSiteTableLength += MCAsmInfo::getULEB128Size(CallSites[i].Action);
634 CallSiteTableLength += MCAsmInfo::getULEB128Size(i);
638 const MCSection *LSDASection = Asm->getObjFileLowering().getLSDASection();
639 unsigned TTypeEncoding;
640 unsigned TypeFormatSize;
643 // For SjLj exceptions, if there is no TypeInfo, then we just explicitly say
644 // that we're omitting that bit.
645 TTypeEncoding = dwarf::DW_EH_PE_omit;
646 TypeFormatSize = SizeOfEncodedValue(dwarf::DW_EH_PE_absptr);
648 // Okay, we have actual filters or typeinfos to emit. As such, we need to
649 // pick a type encoding for them. We're about to emit a list of pointers to
650 // typeinfo objects at the end of the LSDA. However, unless we're in static
651 // mode, this reference will require a relocation by the dynamic linker.
653 // Because of this, we have a couple of options:
655 // 1) If we are in -static mode, we can always use an absolute reference
656 // from the LSDA, because the static linker will resolve it.
658 // 2) Otherwise, if the LSDA section is writable, we can output the direct
659 // reference to the typeinfo and allow the dynamic linker to relocate
660 // it. Since it is in a writable section, the dynamic linker won't
663 // 3) Finally, if we're in PIC mode and the LDSA section isn't writable,
664 // we need to use some form of indirection. For example, on Darwin,
665 // we can output a statically-relocatable reference to a dyld stub. The
666 // offset to the stub is constant, but the contents are in a section
667 // that is updated by the dynamic linker. This is easy enough, but we
668 // need to tell the personality function of the unwinder to indirect
669 // through the dyld stub.
671 // FIXME: When (3) is actually implemented, we'll have to emit the stubs
672 // somewhere. This predicate should be moved to a shared location that is
673 // in target-independent code.
675 TTypeEncoding = Asm->getObjFileLowering().getTTypeEncoding();
676 TypeFormatSize = SizeOfEncodedValue(TTypeEncoding);
679 // Begin the exception table.
680 Asm->OutStreamer.SwitchSection(LSDASection);
681 Asm->EmitAlignment(2, 0, 0, false);
685 Asm->OutContext.GetOrCreateSymbol(Twine("GCC_except_table")+
686 Twine(SubprogramCount));
687 Asm->OutStreamer.EmitLabel(GCCETSym);
688 Asm->OutStreamer.EmitLabel(getDWLabel("exception", SubprogramCount));
691 Asm->OutStreamer.EmitLabel(getDWLabel("_LSDA_", Asm->getFunctionNumber()));
693 // Emit the LSDA header.
694 EmitEncodingByte(dwarf::DW_EH_PE_omit, "@LPStart");
695 EmitEncodingByte(TTypeEncoding, "@TType");
697 // The type infos need to be aligned. GCC does this by inserting padding just
698 // before the type infos. However, this changes the size of the exception
699 // table, so you need to take this into account when you output the exception
700 // table size. However, the size is output using a variable length encoding.
701 // So by increasing the size by inserting padding, you may increase the number
702 // of bytes used for writing the size. If it increases, say by one byte, then
703 // you now need to output one less byte of padding to get the type infos
704 // aligned. However this decreases the size of the exception table. This
705 // changes the value you have to output for the exception table size. Due to
706 // the variable length encoding, the number of bytes used for writing the
707 // length may decrease. If so, you then have to increase the amount of
708 // padding. And so on. If you look carefully at the GCC code you will see that
709 // it indeed does this in a loop, going on and on until the values stabilize.
710 // We chose another solution: don't output padding inside the table like GCC
711 // does, instead output it before the table.
712 unsigned SizeTypes = TypeInfos.size() * TypeFormatSize;
713 unsigned CallSiteTableLengthSize =
714 MCAsmInfo::getULEB128Size(CallSiteTableLength);
715 unsigned TTypeBaseOffset =
716 sizeof(int8_t) + // Call site format
717 CallSiteTableLengthSize + // Call site table length size
718 CallSiteTableLength + // Call site table length
719 SizeActions + // Actions size
721 unsigned TTypeBaseOffsetSize = MCAsmInfo::getULEB128Size(TTypeBaseOffset);
723 sizeof(int8_t) + // LPStart format
724 sizeof(int8_t) + // TType format
725 (HaveTTData ? TTypeBaseOffsetSize : 0) + // TType base offset size
726 TTypeBaseOffset; // TType base offset
727 unsigned SizeAlign = (4 - TotalSize) & 3;
730 // Account for any extra padding that will be added to the call site table
732 EmitULEB128(TTypeBaseOffset, "@TType base offset", SizeAlign);
736 // SjLj Exception handling
738 EmitEncodingByte(dwarf::DW_EH_PE_udata4, "Call site");
740 // Add extra padding if it wasn't added to the TType base offset.
741 EmitULEB128(CallSiteTableLength, "Call site table length", SizeAlign);
743 // Emit the landing pad site information.
745 for (SmallVectorImpl<CallSiteEntry>::const_iterator
746 I = CallSites.begin(), E = CallSites.end(); I != E; ++I, ++idx) {
747 const CallSiteEntry &S = *I;
749 // Offset of the landing pad, counted in 16-byte bundles relative to the
751 EmitULEB128(idx, "Landing pad");
753 // Offset of the first associated action record, relative to the start of
754 // the action table. This value is biased by 1 (1 indicates the start of
755 // the action table), and 0 indicates that there are no actions.
756 EmitULEB128(S.Action, "Action");
759 // DWARF Exception handling
760 assert(MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf);
762 // The call-site table is a list of all call sites that may throw an
763 // exception (including C++ 'throw' statements) in the procedure
764 // fragment. It immediately follows the LSDA header. Each entry indicates,
765 // for a given call, the first corresponding action record and corresponding
768 // The table begins with the number of bytes, stored as an LEB128
769 // compressed, unsigned integer. The records immediately follow the record
770 // count. They are sorted in increasing call-site address. Each record
773 // * The position of the call-site.
774 // * The position of the landing pad.
775 // * The first action record for that call site.
777 // A missing entry in the call-site table indicates that a call is not
778 // supposed to throw.
780 // Emit the landing pad call site table.
781 EmitEncodingByte(dwarf::DW_EH_PE_udata4, "Call site");
783 // Add extra padding if it wasn't added to the TType base offset.
784 EmitULEB128(CallSiteTableLength, "Call site table length", SizeAlign);
786 for (SmallVectorImpl<CallSiteEntry>::const_iterator
787 I = CallSites.begin(), E = CallSites.end(); I != E; ++I) {
788 const CallSiteEntry &S = *I;
790 MCSymbol *EHFuncBeginSym = getDWLabel("eh_func_begin", SubprogramCount);
792 MCSymbol *BeginLabel = S.BeginLabel;
794 BeginLabel = EHFuncBeginSym;
795 MCSymbol *EndLabel = S.EndLabel;
797 EndLabel = getDWLabel("eh_func_end", SubprogramCount);
799 // Offset of the call site relative to the previous call site, counted in
800 // number of 16-byte bundles. The first call site is counted relative to
801 // the start of the procedure fragment.
802 Asm->OutStreamer.AddComment("Region start");
803 EmitSectionOffset(BeginLabel, EHFuncBeginSym, true, true);
805 Asm->OutStreamer.AddComment("Region length");
806 EmitDifference(EndLabel, BeginLabel, true);
809 // Offset of the landing pad, counted in 16-byte bundles relative to the
811 Asm->OutStreamer.AddComment("Landing pad");
813 Asm->OutStreamer.EmitIntValue(0, 4/*size*/, 0/*addrspace*/);
815 EmitSectionOffset(S.PadLabel, EHFuncBeginSym, true, true);
817 // Offset of the first associated action record, relative to the start of
818 // the action table. This value is biased by 1 (1 indicates the start of
819 // the action table), and 0 indicates that there are no actions.
820 EmitULEB128(S.Action, "Action");
824 // Emit the Action Table.
825 if (Actions.size() != 0) {
826 Asm->OutStreamer.AddComment("-- Action Record Table --");
827 Asm->OutStreamer.AddBlankLine();
830 for (SmallVectorImpl<ActionEntry>::const_iterator
831 I = Actions.begin(), E = Actions.end(); I != E; ++I) {
832 const ActionEntry &Action = *I;
833 Asm->OutStreamer.AddComment("Action Record");
834 Asm->OutStreamer.AddBlankLine();
838 // Used by the runtime to match the type of the thrown exception to the
839 // type of the catch clauses or the types in the exception specification.
840 EmitSLEB128(Action.ValueForTypeID, " TypeInfo index");
844 // Self-relative signed displacement in bytes of the next action record,
845 // or 0 if there is no next action record.
846 EmitSLEB128(Action.NextAction, " Next action");
849 // Emit the Catch TypeInfos.
850 if (!TypeInfos.empty()) {
851 Asm->OutStreamer.AddComment("-- Catch TypeInfos --");
852 Asm->OutStreamer.AddBlankLine();
854 for (std::vector<GlobalVariable *>::const_reverse_iterator
855 I = TypeInfos.rbegin(), E = TypeInfos.rend(); I != E; ++I) {
856 const GlobalVariable *GV = *I;
858 Asm->OutStreamer.AddComment("TypeInfo");
860 EmitReference(GV, TTypeEncoding);
862 Asm->OutStreamer.EmitIntValue(0, SizeOfEncodedValue(TTypeEncoding), 0);
865 // Emit the Exception Specifications.
866 if (!FilterIds.empty()) {
867 Asm->OutStreamer.AddComment("-- Filter IDs --");
868 Asm->OutStreamer.AddBlankLine();
870 for (std::vector<unsigned>::const_iterator
871 I = FilterIds.begin(), E = FilterIds.end(); I < E; ++I) {
872 unsigned TypeID = *I;
873 EmitULEB128(TypeID, TypeID != 0 ? "Exception specification" : 0);
876 Asm->EmitAlignment(2, 0, 0, false);
879 /// EndModule - Emit all exception information that should come after the
881 void DwarfException::EndModule() {
882 if (MAI->getExceptionHandlingType() != ExceptionHandling::Dwarf)
885 if (!shouldEmitMovesModule && !shouldEmitTableModule)
888 TimeRegion Timer(ExceptionTimer);
890 const std::vector<Function *> Personalities = MMI->getPersonalities();
892 for (unsigned I = 0, E = Personalities.size(); I < E; ++I)
893 EmitCIE(Personalities[I], I);
895 for (std::vector<FunctionEHFrameInfo>::iterator
896 I = EHFrames.begin(), E = EHFrames.end(); I != E; ++I)
900 /// BeginFunction - Gather pre-function exception information. Assumes it's
901 /// being emitted immediately after the function entry point.
902 void DwarfException::BeginFunction(const MachineFunction *MF) {
903 if (!MMI || !MAI->doesSupportExceptionHandling()) return;
905 TimeRegion Timer(ExceptionTimer);
907 shouldEmitTable = shouldEmitMoves = false;
909 // If any landing pads survive, we need an EH table.
910 shouldEmitTable = !MMI->getLandingPads().empty();
912 // See if we need frame move info.
913 shouldEmitMoves = !MF->getFunction()->doesNotThrow() || UnwindTablesMandatory;
915 if (shouldEmitMoves || shouldEmitTable)
916 // Assumes in correct section after the entry point.
917 Asm->OutStreamer.EmitLabel(getDWLabel("eh_func_begin", ++SubprogramCount));
919 shouldEmitTableModule |= shouldEmitTable;
920 shouldEmitMovesModule |= shouldEmitMoves;
923 /// EndFunction - Gather and emit post-function exception information.
925 void DwarfException::EndFunction() {
926 if (!shouldEmitMoves && !shouldEmitTable) return;
928 TimeRegion Timer(ExceptionTimer);
929 Asm->OutStreamer.EmitLabel(getDWLabel("eh_func_end", SubprogramCount));
931 // Record if this personality index uses a landing pad.
932 bool HasLandingPad = !MMI->getLandingPads().empty();
933 UsesLSDA[MMI->getPersonalityIndex()] |= HasLandingPad;
935 // Map all labels and get rid of any dead landing pads.
936 MMI->TidyLandingPads();
939 EmitExceptionTable();
941 const TargetLoweringObjectFile &TLOF = Asm->getObjFileLowering();
942 MCSymbol *FunctionEHSym =
943 Asm->GetSymbolWithGlobalValueBase(MF->getFunction(), ".eh",
944 TLOF.isFunctionEHFrameSymbolPrivate());
946 // Save EH frame information
947 EHFrames.push_back(FunctionEHFrameInfo(FunctionEHSym, SubprogramCount,
948 MMI->getPersonalityIndex(),
949 MF->getFrameInfo()->hasCalls(),
950 !MMI->getLandingPads().empty(),
951 MMI->getFrameMoves(),