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/Target/TargetData.h"
26 #include "llvm/Target/TargetFrameInfo.h"
27 #include "llvm/Target/TargetLoweringObjectFile.h"
28 #include "llvm/Target/TargetOptions.h"
29 #include "llvm/Target/TargetRegisterInfo.h"
30 #include "llvm/Support/Dwarf.h"
31 #include "llvm/Support/Mangler.h"
32 #include "llvm/Support/Timer.h"
33 #include "llvm/Support/raw_ostream.h"
34 #include "llvm/ADT/SmallString.h"
35 #include "llvm/ADT/StringExtras.h"
38 static TimerGroup &getDwarfTimerGroup() {
39 static TimerGroup DwarfTimerGroup("DWARF Exception");
40 return DwarfTimerGroup;
43 DwarfException::DwarfException(raw_ostream &OS, AsmPrinter *A,
45 : Dwarf(OS, A, T, "eh"), shouldEmitTable(false), shouldEmitMoves(false),
46 shouldEmitTableModule(false), shouldEmitMovesModule(false),
48 if (TimePassesIsEnabled)
49 ExceptionTimer = new Timer("DWARF Exception Writer",
50 getDwarfTimerGroup());
53 DwarfException::~DwarfException() {
54 delete ExceptionTimer;
57 /// SizeOfEncodedValue - Return the size of the encoding in bytes.
58 unsigned DwarfException::SizeOfEncodedValue(unsigned Encoding) {
59 if (Encoding == dwarf::DW_EH_PE_omit)
62 switch (Encoding & 0x07) {
63 case dwarf::DW_EH_PE_absptr:
64 return TD->getPointerSize();
65 case dwarf::DW_EH_PE_udata2:
67 case dwarf::DW_EH_PE_udata4:
69 case dwarf::DW_EH_PE_udata8:
73 assert(0 && "Invalid encoded value.");
77 /// EmitCIE - Emit a Common Information Entry (CIE). This holds information that
78 /// is shared among many Frame Description Entries. There is at least one CIE
79 /// in every non-empty .debug_frame section.
80 void DwarfException::EmitCIE(const Function *PersonalityFn, unsigned Index) {
81 // Size and sign of stack growth.
83 Asm->TM.getFrameInfo()->getStackGrowthDirection() ==
84 TargetFrameInfo::StackGrowsUp ?
85 TD->getPointerSize() : -TD->getPointerSize();
87 const TargetLoweringObjectFile &TLOF = Asm->getObjFileLowering();
89 // Begin eh frame section.
90 Asm->OutStreamer.SwitchSection(TLOF.getEHFrameSection());
92 if (MAI->is_EHSymbolPrivate())
93 O << MAI->getPrivateGlobalPrefix();
94 O << "EH_frame" << Index << ":\n";
96 EmitLabel("section_eh_frame", Index);
98 // Define base labels.
99 EmitLabel("eh_frame_common", Index);
101 // Define the eh frame length.
102 EmitDifference("eh_frame_common_end", Index,
103 "eh_frame_common_begin", Index, true);
104 Asm->EOL("Length of Common Information Entry");
107 EmitLabel("eh_frame_common_begin", Index);
108 Asm->EmitInt32((int)0);
109 Asm->EOL("CIE Identifier Tag");
110 Asm->EmitInt8(dwarf::DW_CIE_VERSION);
111 Asm->EOL("CIE Version");
113 // The personality presence indicates that language specific information will
114 // show up in the eh frame. Find out how we are supposed to lower the
115 // personality function reference:
116 const MCExpr *PersonalityRef = 0;
117 bool IsPersonalityIndirect = false, IsPersonalityPCRel = false;
119 // FIXME: HANDLE STATIC CODEGEN MODEL HERE.
121 // In non-static mode, ask the object file how to represent this reference.
123 TLOF.getSymbolForDwarfGlobalReference(PersonalityFn, Asm->Mang,
125 IsPersonalityIndirect,
129 unsigned PerEncoding = dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4;
130 if (IsPersonalityIndirect)
131 PerEncoding |= dwarf::DW_EH_PE_indirect;
132 unsigned LSDAEncoding = dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4;
133 unsigned FDEEncoding = dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4;
135 char Augmentation[5] = { 0 };
136 unsigned AugmentationSize = 0;
137 char *APtr = Augmentation + 1;
139 if (PersonalityRef) {
140 // There is a personality function.
142 AugmentationSize += 1 + SizeOfEncodedValue(PerEncoding);
145 if (UsesLSDA[Index]) {
146 // An LSDA pointer is in the FDE augmentation.
151 if (FDEEncoding != dwarf::DW_EH_PE_absptr) {
152 // A non-default pointer encoding for the FDE.
157 if (APtr != Augmentation + 1)
158 Augmentation[0] = 'z';
160 Asm->EmitString(Augmentation);
161 Asm->EOL("CIE Augmentation");
164 Asm->EmitULEB128Bytes(1);
165 Asm->EOL("CIE Code Alignment Factor");
166 Asm->EmitSLEB128Bytes(stackGrowth);
167 Asm->EOL("CIE Data Alignment Factor");
168 Asm->EmitInt8(RI->getDwarfRegNum(RI->getRARegister(), true));
169 Asm->EOL("CIE Return Address Column");
171 Asm->EmitULEB128Bytes(AugmentationSize);
172 Asm->EOL("Augmentation Size");
174 Asm->EmitInt8(PerEncoding);
175 Asm->EOL("Personality", PerEncoding);
177 // If there is a personality, we need to indicate the function's location.
178 if (PersonalityRef) {
179 // If the reference to the personality function symbol is not already
180 // pc-relative, then we need to subtract our current address from it. Do
181 // this by emitting a label and subtracting it from the expression we
182 // already have. This is equivalent to emitting "foo - .", but we have to
183 // emit the label for "." directly.
184 if (!IsPersonalityPCRel) {
185 SmallString<64> Name;
186 raw_svector_ostream(Name) << MAI->getPrivateGlobalPrefix()
187 << "personalityref_addr" << Asm->getFunctionNumber() << "_" << Index;
188 MCSymbol *DotSym = Asm->OutContext.GetOrCreateSymbol(Name.str());
189 Asm->OutStreamer.EmitLabel(DotSym);
192 MCBinaryExpr::CreateSub(PersonalityRef,
193 MCSymbolRefExpr::Create(DotSym,Asm->OutContext),
197 O << MAI->getData32bitsDirective();
198 PersonalityRef->print(O, MAI);
199 Asm->EOL("Personality");
201 Asm->EmitInt8(LSDAEncoding);
202 Asm->EOL("LSDA Encoding", LSDAEncoding);
204 Asm->EmitInt8(FDEEncoding);
205 Asm->EOL("FDE Encoding", FDEEncoding);
208 // Indicate locations of general callee saved registers in frame.
209 std::vector<MachineMove> Moves;
210 RI->getInitialFrameState(Moves);
211 EmitFrameMoves(NULL, 0, Moves, true);
213 // On Darwin the linker honors the alignment of eh_frame, which means it must
214 // be 8-byte on 64-bit targets to match what gcc does. Otherwise you get
215 // holes which confuse readers of eh_frame.
216 Asm->EmitAlignment(TD->getPointerSize() == 4 ? 2 : 3, 0, 0, false);
217 EmitLabel("eh_frame_common_end", Index);
222 /// EmitFDE - Emit the Frame Description Entry (FDE) for the function.
223 void DwarfException::EmitFDE(const FunctionEHFrameInfo &EHFrameInfo) {
224 assert(!EHFrameInfo.function->hasAvailableExternallyLinkage() &&
225 "Should not emit 'available externally' functions at all");
227 const Function *TheFunc = EHFrameInfo.function;
229 Asm->OutStreamer.SwitchSection(Asm->getObjFileLowering().getEHFrameSection());
231 // Externally visible entry into the functions eh frame info. If the
232 // corresponding function is static, this should not be externally visible.
233 if (!TheFunc->hasLocalLinkage())
234 if (const char *GlobalEHDirective = MAI->getGlobalEHDirective())
235 O << GlobalEHDirective << EHFrameInfo.FnName << '\n';
237 // If corresponding function is weak definition, this should be too.
238 if (TheFunc->isWeakForLinker() && MAI->getWeakDefDirective())
239 O << MAI->getWeakDefDirective() << EHFrameInfo.FnName << '\n';
241 // If corresponding function is hidden, this should be too.
242 if (TheFunc->hasHiddenVisibility())
243 if (const char *HiddenDirective = MAI->getHiddenDirective())
244 O << HiddenDirective << EHFrameInfo.FnName << '\n' ;
246 // If there are no calls then you can't unwind. This may mean we can omit the
247 // EH Frame, but some environments do not handle weak absolute symbols. If
248 // UnwindTablesMandatory is set we cannot do this optimization; the unwind
249 // info is to be available for non-EH uses.
250 if (!EHFrameInfo.hasCalls && !UnwindTablesMandatory &&
251 (!TheFunc->isWeakForLinker() ||
252 !MAI->getWeakDefDirective() ||
253 MAI->getSupportsWeakOmittedEHFrame())) {
254 O << EHFrameInfo.FnName << " = 0\n";
255 // This name has no connection to the function, so it might get
256 // dead-stripped when the function is not, erroneously. Prohibit
257 // dead-stripping unconditionally.
258 if (const char *UsedDirective = MAI->getUsedDirective())
259 O << UsedDirective << EHFrameInfo.FnName << "\n\n";
261 O << EHFrameInfo.FnName << ":\n";
264 EmitDifference("eh_frame_end", EHFrameInfo.Number,
265 "eh_frame_begin", EHFrameInfo.Number, true);
266 Asm->EOL("Length of Frame Information Entry");
268 EmitLabel("eh_frame_begin", EHFrameInfo.Number);
270 EmitSectionOffset("eh_frame_begin", "eh_frame_common",
271 EHFrameInfo.Number, EHFrameInfo.PersonalityIndex,
274 Asm->EOL("FDE CIE offset");
276 EmitReference("eh_func_begin", EHFrameInfo.Number, true, true);
277 Asm->EOL("FDE initial location");
278 EmitDifference("eh_func_end", EHFrameInfo.Number,
279 "eh_func_begin", EHFrameInfo.Number, true);
280 Asm->EOL("FDE address range");
282 // If there is a personality and landing pads then point to the language
283 // specific data area in the exception table.
284 if (MMI->getPersonalities()[0] != NULL) {
285 bool is4Byte = TD->getPointerSize() == sizeof(int32_t);
287 Asm->EmitULEB128Bytes(is4Byte ? 4 : 8);
288 Asm->EOL("Augmentation size");
290 if (EHFrameInfo.hasLandingPads)
291 EmitReference("exception", EHFrameInfo.Number, true, false);
294 Asm->EmitInt32((int)0);
296 Asm->EmitInt64((int)0);
298 Asm->EOL("Language Specific Data Area");
300 Asm->EmitULEB128Bytes(0);
301 Asm->EOL("Augmentation size");
304 // Indicate locations of function specific callee saved registers in frame.
305 EmitFrameMoves("eh_func_begin", EHFrameInfo.Number, EHFrameInfo.Moves,
308 // On Darwin the linker honors the alignment of eh_frame, which means it
309 // must be 8-byte on 64-bit targets to match what gcc does. Otherwise you
310 // get holes which confuse readers of eh_frame.
311 Asm->EmitAlignment(TD->getPointerSize() == sizeof(int32_t) ? 2 : 3,
313 EmitLabel("eh_frame_end", EHFrameInfo.Number);
315 // If the function is marked used, this table should be also. We cannot
316 // make the mark unconditional in this case, since retaining the table also
317 // retains the function in this case, and there is code around that depends
318 // on unused functions (calling undefined externals) being dead-stripped to
319 // link correctly. Yes, there really is.
320 if (MMI->isUsedFunction(EHFrameInfo.function))
321 if (const char *UsedDirective = MAI->getUsedDirective())
322 O << UsedDirective << EHFrameInfo.FnName << "\n\n";
328 /// SharedTypeIds - How many leading type ids two landing pads have in common.
329 unsigned DwarfException::SharedTypeIds(const LandingPadInfo *L,
330 const LandingPadInfo *R) {
331 const std::vector<int> &LIds = L->TypeIds, &RIds = R->TypeIds;
332 unsigned LSize = LIds.size(), RSize = RIds.size();
333 unsigned MinSize = LSize < RSize ? LSize : RSize;
336 for (; Count != MinSize; ++Count)
337 if (LIds[Count] != RIds[Count])
343 /// PadLT - Order landing pads lexicographically by type id.
344 bool DwarfException::PadLT(const LandingPadInfo *L, const LandingPadInfo *R) {
345 const std::vector<int> &LIds = L->TypeIds, &RIds = R->TypeIds;
346 unsigned LSize = LIds.size(), RSize = RIds.size();
347 unsigned MinSize = LSize < RSize ? LSize : RSize;
349 for (unsigned i = 0; i != MinSize; ++i)
350 if (LIds[i] != RIds[i])
351 return LIds[i] < RIds[i];
353 return LSize < RSize;
356 /// ComputeActionsTable - Compute the actions table and gather the first action
357 /// index for each landing pad site.
358 unsigned DwarfException::
359 ComputeActionsTable(const SmallVectorImpl<const LandingPadInfo*> &LandingPads,
360 SmallVectorImpl<ActionEntry> &Actions,
361 SmallVectorImpl<unsigned> &FirstActions) {
363 // The action table follows the call-site table in the LSDA. The individual
364 // records are of two types:
367 // * Exception specification
369 // The two record kinds have the same format, with only small differences.
370 // They are distinguished by the "switch value" field: Catch clauses
371 // (TypeInfos) have strictly positive switch values, and exception
372 // specifications (FilterIds) have strictly negative switch values. Value 0
373 // indicates a catch-all clause.
375 // Negative type IDs index into FilterIds. Positive type IDs index into
376 // TypeInfos. The value written for a positive type ID is just the type ID
377 // itself. For a negative type ID, however, the value written is the
378 // (negative) byte offset of the corresponding FilterIds entry. The byte
379 // offset is usually equal to the type ID (because the FilterIds entries are
380 // written using a variable width encoding, which outputs one byte per entry
381 // as long as the value written is not too large) but can differ. This kind
382 // of complication does not occur for positive type IDs because type infos are
383 // output using a fixed width encoding. FilterOffsets[i] holds the byte
384 // offset corresponding to FilterIds[i].
386 const std::vector<unsigned> &FilterIds = MMI->getFilterIds();
387 SmallVector<int, 16> FilterOffsets;
388 FilterOffsets.reserve(FilterIds.size());
391 for (std::vector<unsigned>::const_iterator
392 I = FilterIds.begin(), E = FilterIds.end(); I != E; ++I) {
393 FilterOffsets.push_back(Offset);
394 Offset -= MCAsmInfo::getULEB128Size(*I);
397 FirstActions.reserve(LandingPads.size());
400 unsigned SizeActions = 0;
401 const LandingPadInfo *PrevLPI = 0;
403 for (SmallVectorImpl<const LandingPadInfo *>::const_iterator
404 I = LandingPads.begin(), E = LandingPads.end(); I != E; ++I) {
405 const LandingPadInfo *LPI = *I;
406 const std::vector<int> &TypeIds = LPI->TypeIds;
407 const unsigned NumShared = PrevLPI ? SharedTypeIds(LPI, PrevLPI) : 0;
408 unsigned SizeSiteActions = 0;
410 if (NumShared < TypeIds.size()) {
411 unsigned SizeAction = 0;
412 ActionEntry *PrevAction = 0;
415 const unsigned SizePrevIds = PrevLPI->TypeIds.size();
416 assert(Actions.size());
417 PrevAction = &Actions.back();
418 SizeAction = MCAsmInfo::getSLEB128Size(PrevAction->NextAction) +
419 MCAsmInfo::getSLEB128Size(PrevAction->ValueForTypeID);
421 for (unsigned j = NumShared; j != SizePrevIds; ++j) {
423 MCAsmInfo::getSLEB128Size(PrevAction->ValueForTypeID);
424 SizeAction += -PrevAction->NextAction;
425 PrevAction = PrevAction->Previous;
429 // Compute the actions.
430 for (unsigned J = NumShared, M = TypeIds.size(); J != M; ++J) {
431 int TypeID = TypeIds[J];
432 assert(-1 - TypeID < (int)FilterOffsets.size() && "Unknown filter id!");
433 int ValueForTypeID = TypeID < 0 ? FilterOffsets[-1 - TypeID] : TypeID;
434 unsigned SizeTypeID = MCAsmInfo::getSLEB128Size(ValueForTypeID);
436 int NextAction = SizeAction ? -(SizeAction + SizeTypeID) : 0;
437 SizeAction = SizeTypeID + MCAsmInfo::getSLEB128Size(NextAction);
438 SizeSiteActions += SizeAction;
440 ActionEntry Action = { ValueForTypeID, NextAction, PrevAction };
441 Actions.push_back(Action);
442 PrevAction = &Actions.back();
445 // Record the first action of the landing pad site.
446 FirstAction = SizeActions + SizeSiteActions - SizeAction + 1;
447 } // else identical - re-use previous FirstAction
449 // Information used when created the call-site table. The action record
450 // field of the call site record is the offset of the first associated
451 // action record, relative to the start of the actions table. This value is
452 // biased by 1 (1 in dicating the start of the actions table), and 0
453 // indicates that there are no actions.
454 FirstActions.push_back(FirstAction);
456 // Compute this sites contribution to size.
457 SizeActions += SizeSiteActions;
465 /// ComputeCallSiteTable - Compute the call-site table. The entry for an invoke
466 /// has a try-range containing the call, a non-zero landing pad, and an
467 /// appropriate action. The entry for an ordinary call has a try-range
468 /// containing the call and zero for the landing pad and the action. Calls
469 /// marked 'nounwind' have no entry and must not be contained in the try-range
470 /// of any entry - they form gaps in the table. Entries must be ordered by
471 /// try-range address.
472 void DwarfException::
473 ComputeCallSiteTable(SmallVectorImpl<CallSiteEntry> &CallSites,
474 const RangeMapType &PadMap,
475 const SmallVectorImpl<const LandingPadInfo *> &LandingPads,
476 const SmallVectorImpl<unsigned> &FirstActions) {
477 // The end label of the previous invoke or nounwind try-range.
478 unsigned LastLabel = 0;
480 // Whether there is a potentially throwing instruction (currently this means
481 // an ordinary call) between the end of the previous try-range and now.
482 bool SawPotentiallyThrowing = false;
484 // Whether the last CallSite entry was for an invoke.
485 bool PreviousIsInvoke = false;
487 // Visit all instructions in order of address.
488 for (MachineFunction::const_iterator I = MF->begin(), E = MF->end();
490 for (MachineBasicBlock::const_iterator MI = I->begin(), E = I->end();
492 if (!MI->isLabel()) {
493 if (MI->getDesc().isCall()) {
494 // Don't mark a call as potentially throwing if the function it's
495 // calling is marked "nounwind".
496 bool DoesNotThrow = false;
497 for (unsigned OI = 0, OE = MI->getNumOperands(); OI != OE; ++OI) {
498 const MachineOperand &MO = MI->getOperand(OI);
501 if (Function *F = dyn_cast<Function>(MO.getGlobal())) {
502 if (F->doesNotThrow()) {
511 SawPotentiallyThrowing = true;
517 unsigned BeginLabel = MI->getOperand(0).getImm();
518 assert(BeginLabel && "Invalid label!");
520 // End of the previous try-range?
521 if (BeginLabel == LastLabel)
522 SawPotentiallyThrowing = false;
524 // Beginning of a new try-range?
525 RangeMapType::const_iterator L = PadMap.find(BeginLabel);
526 if (L == PadMap.end())
527 // Nope, it was just some random label.
530 const PadRange &P = L->second;
531 const LandingPadInfo *LandingPad = LandingPads[P.PadIndex];
532 assert(BeginLabel == LandingPad->BeginLabels[P.RangeIndex] &&
533 "Inconsistent landing pad map!");
535 // For Dwarf exception handling (SjLj handling doesn't use this). If some
536 // instruction between the previous try-range and this one may throw,
537 // create a call-site entry with no landing pad for the region between the
539 if (SawPotentiallyThrowing &&
540 MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf) {
541 CallSiteEntry Site = { LastLabel, BeginLabel, 0, 0 };
542 CallSites.push_back(Site);
543 PreviousIsInvoke = false;
546 LastLabel = LandingPad->EndLabels[P.RangeIndex];
547 assert(BeginLabel && LastLabel && "Invalid landing pad!");
549 if (LandingPad->LandingPadLabel) {
550 // This try-range is for an invoke.
551 CallSiteEntry Site = {
554 LandingPad->LandingPadLabel,
555 FirstActions[P.PadIndex]
558 // Try to merge with the previous call-site. SJLJ doesn't do this
559 if (PreviousIsInvoke &&
560 MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf) {
561 CallSiteEntry &Prev = CallSites.back();
562 if (Site.PadLabel == Prev.PadLabel && Site.Action == Prev.Action) {
563 // Extend the range of the previous entry.
564 Prev.EndLabel = Site.EndLabel;
569 // Otherwise, create a new call-site.
570 CallSites.push_back(Site);
571 PreviousIsInvoke = true;
574 PreviousIsInvoke = false;
579 // If some instruction between the previous try-range and the end of the
580 // function may throw, create a call-site entry with no landing pad for the
581 // region following the try-range.
582 if (SawPotentiallyThrowing &&
583 MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf) {
584 CallSiteEntry Site = { LastLabel, 0, 0, 0 };
585 CallSites.push_back(Site);
589 /// EmitExceptionTable - Emit landing pads and actions.
591 /// The general organization of the table is complex, but the basic concepts are
592 /// easy. First there is a header which describes the location and organization
593 /// of the three components that follow.
595 /// 1. The landing pad site information describes the range of code covered by
596 /// the try. In our case it's an accumulation of the ranges covered by the
597 /// invokes in the try. There is also a reference to the landing pad that
598 /// handles the exception once processed. Finally an index into the actions
600 /// 2. The action table, in our case, is composed of pairs of type IDs and next
601 /// action offset. Starting with the action index from the landing pad
602 /// site, each type ID is checked for a match to the current exception. If
603 /// it matches then the exception and type id are passed on to the landing
604 /// pad. Otherwise the next action is looked up. This chain is terminated
605 /// with a next action of zero. If no type id is found then the frame is
606 /// unwound and handling continues.
607 /// 3. Type ID table contains references to all the C++ typeinfo for all
608 /// catches in the function. This tables is reverse indexed base 1.
609 void DwarfException::EmitExceptionTable() {
610 const std::vector<GlobalVariable *> &TypeInfos = MMI->getTypeInfos();
611 const std::vector<unsigned> &FilterIds = MMI->getFilterIds();
612 const std::vector<LandingPadInfo> &PadInfos = MMI->getLandingPads();
613 if (PadInfos.empty()) return;
615 // Sort the landing pads in order of their type ids. This is used to fold
616 // duplicate actions.
617 SmallVector<const LandingPadInfo *, 64> LandingPads;
618 LandingPads.reserve(PadInfos.size());
620 for (unsigned i = 0, N = PadInfos.size(); i != N; ++i)
621 LandingPads.push_back(&PadInfos[i]);
623 std::sort(LandingPads.begin(), LandingPads.end(), PadLT);
625 // Compute the actions table and gather the first action index for each
627 SmallVector<ActionEntry, 32> Actions;
628 SmallVector<unsigned, 64> FirstActions;
629 unsigned SizeActions = ComputeActionsTable(LandingPads, Actions,
632 // Invokes and nounwind calls have entries in PadMap (due to being bracketed
633 // by try-range labels when lowered). Ordinary calls do not, so appropriate
634 // try-ranges for them need be deduced when using DWARF exception handling.
636 for (unsigned i = 0, N = LandingPads.size(); i != N; ++i) {
637 const LandingPadInfo *LandingPad = LandingPads[i];
638 for (unsigned j = 0, E = LandingPad->BeginLabels.size(); j != E; ++j) {
639 unsigned BeginLabel = LandingPad->BeginLabels[j];
640 assert(!PadMap.count(BeginLabel) && "Duplicate landing pad labels!");
641 PadRange P = { i, j };
642 PadMap[BeginLabel] = P;
646 // Compute the call-site table.
647 SmallVector<CallSiteEntry, 64> CallSites;
648 ComputeCallSiteTable(CallSites, PadMap, LandingPads, FirstActions);
653 const unsigned SiteStartSize = SizeOfEncodedValue(dwarf::DW_EH_PE_udata4);
654 const unsigned SiteLengthSize = SizeOfEncodedValue(dwarf::DW_EH_PE_udata4);
655 const unsigned LandingPadSize = SizeOfEncodedValue(dwarf::DW_EH_PE_udata4);
656 bool IsSJLJ = MAI->getExceptionHandlingType() == ExceptionHandling::SjLj;
657 bool HaveTTData = IsSJLJ ? (!TypeInfos.empty() || !FilterIds.empty()) : true;
663 SizeSites = CallSites.size() *
664 (SiteStartSize + SiteLengthSize + LandingPadSize);
666 for (unsigned i = 0, e = CallSites.size(); i < e; ++i) {
667 SizeSites += MCAsmInfo::getULEB128Size(CallSites[i].Action);
669 SizeSites += MCAsmInfo::getULEB128Size(i);
673 const MCSection *LSDASection = Asm->getObjFileLowering().getLSDASection();
674 unsigned TTypeFormat;
675 unsigned TypeFormatSize;
678 // For SjLj exceptions, if there is no TypeInfo, then we just explicitly say
679 // that we're omitting that bit.
680 TTypeFormat = dwarf::DW_EH_PE_omit;
681 TypeFormatSize = SizeOfEncodedValue(dwarf::DW_EH_PE_absptr);
683 // Okay, we have actual filters or typeinfos to emit. As such, we need to
684 // pick a type encoding for them. We're about to emit a list of pointers to
685 // typeinfo objects at the end of the LSDA. However, unless we're in static
686 // mode, this reference will require a relocation by the dynamic linker.
688 // Because of this, we have a couple of options:
690 // 1) If we are in -static mode, we can always use an absolute reference
691 // from the LSDA, because the static linker will resolve it.
693 // 2) Otherwise, if the LSDA section is writable, we can output the direct
694 // reference to the typeinfo and allow the dynamic linker to relocate
695 // it. Since it is in a writable section, the dynamic linker won't
698 // 3) Finally, if we're in PIC mode and the LDSA section isn't writable,
699 // we need to use some form of indirection. For example, on Darwin,
700 // we can output a statically-relocatable reference to a dyld stub. The
701 // offset to the stub is constant, but the contents are in a section
702 // that is updated by the dynamic linker. This is easy enough, but we
703 // need to tell the personality function of the unwinder to indirect
704 // through the dyld stub.
706 // FIXME: When (3) is actually implemented, we'll have to emit the stubs
707 // somewhere. This predicate should be moved to a shared location that is
708 // in target-independent code.
710 if (LSDASection->getKind().isWriteable() ||
711 Asm->TM.getRelocationModel() == Reloc::Static)
712 TTypeFormat = dwarf::DW_EH_PE_absptr;
714 TTypeFormat = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
715 dwarf::DW_EH_PE_sdata4;
717 TypeFormatSize = SizeOfEncodedValue(TTypeFormat);
720 // Begin the exception table.
721 Asm->OutStreamer.SwitchSection(LSDASection);
722 Asm->EmitAlignment(2, 0, 0, false);
724 O << "GCC_except_table" << SubprogramCount << ":\n";
726 // The type infos need to be aligned. GCC does this by inserting padding just
727 // before the type infos. However, this changes the size of the exception
728 // table, so you need to take this into account when you output the exception
729 // table size. However, the size is output using a variable length encoding.
730 // So by increasing the size by inserting padding, you may increase the number
731 // of bytes used for writing the size. If it increases, say by one byte, then
732 // you now need to output one less byte of padding to get the type infos
733 // aligned. However this decreases the size of the exception table. This
734 // changes the value you have to output for the exception table size. Due to
735 // the variable length encoding, the number of bytes used for writing the
736 // length may decrease. If so, you then have to increase the amount of
737 // padding. And so on. If you look carefully at the GCC code you will see that
738 // it indeed does this in a loop, going on and on until the values stabilize.
739 // We chose another solution: don't output padding inside the table like GCC
740 // does, instead output it before the table.
741 unsigned SizeTypes = TypeInfos.size() * TypeFormatSize;
742 unsigned TyOffset = sizeof(int8_t) + // Call site format
743 MCAsmInfo::getULEB128Size(SizeSites) + // Call-site table length
744 SizeSites + SizeActions + SizeTypes;
745 unsigned TotalSize = sizeof(int8_t) + // LPStart format
746 sizeof(int8_t) + // TType format
748 MCAsmInfo::getULEB128Size(TyOffset) : 0) + // TType base offset
750 unsigned SizeAlign = (4 - TotalSize) & 3;
752 for (unsigned i = 0; i != SizeAlign; ++i) {
757 EmitLabel("exception", SubprogramCount);
760 SmallString<16> LSDAName;
761 raw_svector_ostream(LSDAName) << MAI->getPrivateGlobalPrefix() <<
762 "_LSDA_" << Asm->getFunctionNumber();
763 O << LSDAName.str() << ":\n";
767 Asm->EmitInt8(dwarf::DW_EH_PE_omit);
768 Asm->EOL("@LPStart format", dwarf::DW_EH_PE_omit);
770 Asm->EmitInt8(TTypeFormat);
771 Asm->EOL("@TType format", TTypeFormat);
774 Asm->EmitULEB128Bytes(TyOffset);
775 Asm->EOL("@TType base offset");
778 // SjLj Exception handling
780 Asm->EmitInt8(dwarf::DW_EH_PE_udata4);
781 Asm->EOL("Call site format", dwarf::DW_EH_PE_udata4);
782 Asm->EmitULEB128Bytes(SizeSites);
783 Asm->EOL("Call site table length");
785 // Emit the landing pad site information.
787 for (SmallVectorImpl<CallSiteEntry>::const_iterator
788 I = CallSites.begin(), E = CallSites.end(); I != E; ++I, ++idx) {
789 const CallSiteEntry &S = *I;
791 // Offset of the landing pad, counted in 16-byte bundles relative to the
793 Asm->EmitULEB128Bytes(idx);
794 Asm->EOL("Landing pad");
796 // Offset of the first associated action record, relative to the start of
797 // the action table. This value is biased by 1 (1 indicates the start of
798 // the action table), and 0 indicates that there are no actions.
799 Asm->EmitULEB128Bytes(S.Action);
803 // DWARF Exception handling
804 assert(MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf);
806 // The call-site table is a list of all call sites that may throw an
807 // exception (including C++ 'throw' statements) in the procedure
808 // fragment. It immediately follows the LSDA header. Each entry indicates,
809 // for a given call, the first corresponding action record and corresponding
812 // The table begins with the number of bytes, stored as an LEB128
813 // compressed, unsigned integer. The records immediately follow the record
814 // count. They are sorted in increasing call-site address. Each record
817 // * The position of the call-site.
818 // * The position of the landing pad.
819 // * The first action record for that call site.
821 // A missing entry in the call-site table indicates that a call is not
822 // supposed to throw.
824 // Emit the landing pad call site table.
825 Asm->EmitInt8(dwarf::DW_EH_PE_udata4);
826 Asm->EOL("Call site format", dwarf::DW_EH_PE_udata4);
827 Asm->EmitULEB128Bytes(SizeSites);
828 Asm->EOL("Call site table size");
830 for (SmallVectorImpl<CallSiteEntry>::const_iterator
831 I = CallSites.begin(), E = CallSites.end(); I != E; ++I) {
832 const CallSiteEntry &S = *I;
833 const char *BeginTag;
834 unsigned BeginNumber;
837 BeginTag = "eh_func_begin";
838 BeginNumber = SubprogramCount;
841 BeginNumber = S.BeginLabel;
844 // Offset of the call site relative to the previous call site, counted in
845 // number of 16-byte bundles. The first call site is counted relative to
846 // the start of the procedure fragment.
847 EmitSectionOffset(BeginTag, "eh_func_begin", BeginNumber, SubprogramCount,
849 Asm->EOL("Region start");
852 EmitDifference("eh_func_end", SubprogramCount, BeginTag, BeginNumber,
855 EmitDifference("label", S.EndLabel, BeginTag, BeginNumber, true);
857 Asm->EOL("Region length");
859 // Offset of the landing pad, counted in 16-byte bundles relative to the
864 EmitSectionOffset("label", "eh_func_begin", S.PadLabel, SubprogramCount,
867 Asm->EOL("Landing pad");
869 // Offset of the first associated action record, relative to the start of
870 // the action table. This value is biased by 1 (1 indicates the start of
871 // the action table), and 0 indicates that there are no actions.
872 Asm->EmitULEB128Bytes(S.Action);
877 // Emit the Action Table.
878 for (SmallVectorImpl<ActionEntry>::const_iterator
879 I = Actions.begin(), E = Actions.end(); I != E; ++I) {
880 const ActionEntry &Action = *I;
884 // Used by the runtime to match the type of the thrown exception to the
885 // type of the catch clauses or the types in the exception specification.
887 Asm->EmitSLEB128Bytes(Action.ValueForTypeID);
888 Asm->EOL("TypeInfo index");
892 // Self-relative signed displacement in bytes of the next action record,
893 // or 0 if there is no next action record.
895 Asm->EmitSLEB128Bytes(Action.NextAction);
896 Asm->EOL("Next action");
899 // Emit the Catch TypeInfos.
900 for (std::vector<GlobalVariable *>::const_reverse_iterator
901 I = TypeInfos.rbegin(), E = TypeInfos.rend(); I != E; ++I) {
902 const GlobalVariable *GV = *I;
906 O << Asm->Mang->getMangledName(GV);
911 Asm->EOL("TypeInfo");
914 // Emit the Exception Specifications.
915 for (std::vector<unsigned>::const_iterator
916 I = FilterIds.begin(), E = FilterIds.end(); I < E; ++I) {
917 unsigned TypeID = *I;
918 Asm->EmitULEB128Bytes(TypeID);
920 Asm->EOL("Exception specification");
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(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 std::string FunctionEHName =
998 Asm->Mang->getMangledName(MF->getFunction(), ".eh",
999 Asm->MAI->is_EHSymbolPrivate());
1001 // Save EH frame information
1002 EHFrames.push_back(FunctionEHFrameInfo(FunctionEHName, 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();