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/AsmPrinter.h"
17 #include "llvm/CodeGen/MachineModuleInfo.h"
18 #include "llvm/CodeGen/MachineFrameInfo.h"
19 #include "llvm/CodeGen/MachineFunction.h"
20 #include "llvm/CodeGen/MachineLocation.h"
21 #include "llvm/MC/MCAsmInfo.h"
22 #include "llvm/MC/MCContext.h"
23 #include "llvm/MC/MCExpr.h"
24 #include "llvm/MC/MCSection.h"
25 #include "llvm/MC/MCStreamer.h"
26 #include "llvm/MC/MCSymbol.h"
27 #include "llvm/Target/Mangler.h"
28 #include "llvm/Target/TargetData.h"
29 #include "llvm/Target/TargetFrameInfo.h"
30 #include "llvm/Target/TargetLoweringObjectFile.h"
31 #include "llvm/Target/TargetMachine.h"
32 #include "llvm/Target/TargetOptions.h"
33 #include "llvm/Target/TargetRegisterInfo.h"
34 #include "llvm/Support/Dwarf.h"
35 #include "llvm/Support/FormattedStream.h"
36 #include "llvm/Support/Timer.h"
37 #include "llvm/ADT/SmallString.h"
38 #include "llvm/ADT/StringExtras.h"
39 #include "llvm/ADT/Twine.h"
43 const char *DWARFGroupName = "DWARF Emission";
44 const char *EHTimerName = "DWARF Exception Writer";
45 } // end anonymous namespace
47 DwarfException::DwarfException(AsmPrinter *A)
48 : Asm(A), MMI(Asm->MMI), shouldEmitTable(false), shouldEmitMoves(false),
49 shouldEmitTableModule(false), shouldEmitMovesModule(false) {}
51 DwarfException::~DwarfException() {}
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.
58 int stackGrowth = Asm->getTargetData().getPointerSize();
59 if (Asm->TM.getFrameInfo()->getStackGrowthDirection() ==
60 TargetFrameInfo::StackGrowsDown)
63 const TargetLoweringObjectFile &TLOF = Asm->getObjFileLowering();
65 // Begin eh frame section.
66 Asm->OutStreamer.SwitchSection(TLOF.getEHFrameSection());
69 if (TLOF.isFunctionEHFrameSymbolPrivate())
70 EHFrameSym = Asm->GetTempSymbol("EH_frame", Index);
72 EHFrameSym = Asm->OutContext.GetOrCreateSymbol(Twine("EH_frame") +
74 Asm->OutStreamer.EmitLabel(EHFrameSym);
76 Asm->OutStreamer.EmitLabel(Asm->GetTempSymbol("section_eh_frame", Index));
78 // Define base labels.
79 Asm->OutStreamer.EmitLabel(Asm->GetTempSymbol("eh_frame_common", Index));
81 // Define the eh frame length.
82 Asm->OutStreamer.AddComment("Length of Common Information Entry");
83 Asm->EmitLabelDifference(Asm->GetTempSymbol("eh_frame_common_end", Index),
84 Asm->GetTempSymbol("eh_frame_common_begin", Index),
88 Asm->OutStreamer.EmitLabel(Asm->GetTempSymbol("eh_frame_common_begin",Index));
89 Asm->OutStreamer.AddComment("CIE Identifier Tag");
90 Asm->OutStreamer.EmitIntValue(0, 4/*size*/, 0/*addrspace*/);
91 Asm->OutStreamer.AddComment("DW_CIE_VERSION");
92 Asm->OutStreamer.EmitIntValue(dwarf::DW_CIE_VERSION, 1/*size*/, 0/*addr*/);
94 // The personality presence indicates that language specific information will
95 // show up in the eh frame. Find out how we are supposed to lower the
96 // personality function reference:
98 unsigned LSDAEncoding = TLOF.getLSDAEncoding();
99 unsigned FDEEncoding = TLOF.getFDEEncoding();
100 unsigned PerEncoding = TLOF.getPersonalityEncoding();
102 char Augmentation[6] = { 0 };
103 unsigned AugmentationSize = 0;
104 char *APtr = Augmentation + 1;
107 // There is a personality function.
109 AugmentationSize += 1 + Asm->GetSizeOfEncodedValue(PerEncoding);
112 if (UsesLSDA[Index]) {
113 // An LSDA pointer is in the FDE augmentation.
118 if (FDEEncoding != dwarf::DW_EH_PE_absptr) {
119 // A non-default pointer encoding for the FDE.
124 if (APtr != Augmentation + 1)
125 Augmentation[0] = 'z';
127 Asm->OutStreamer.AddComment("CIE Augmentation");
128 Asm->OutStreamer.EmitBytes(StringRef(Augmentation, strlen(Augmentation)+1),0);
131 Asm->EmitULEB128(1, "CIE Code Alignment Factor");
132 Asm->EmitSLEB128(stackGrowth, "CIE Data Alignment Factor");
133 Asm->OutStreamer.AddComment("CIE Return Address Column");
135 const TargetRegisterInfo *RI = Asm->TM.getRegisterInfo();
136 Asm->EmitInt8(RI->getDwarfRegNum(RI->getRARegister(), true));
138 if (Augmentation[0]) {
139 Asm->EmitULEB128(AugmentationSize, "Augmentation Size");
141 // If there is a personality, we need to indicate the function's location.
143 Asm->EmitEncodingByte(PerEncoding, "Personality");
144 Asm->OutStreamer.AddComment("Personality");
145 Asm->EmitReference(PersonalityFn, PerEncoding);
148 Asm->EmitEncodingByte(LSDAEncoding, "LSDA");
149 if (FDEEncoding != dwarf::DW_EH_PE_absptr)
150 Asm->EmitEncodingByte(FDEEncoding, "FDE");
153 // Indicate locations of general callee saved registers in frame.
154 std::vector<MachineMove> Moves;
155 RI->getInitialFrameState(Moves);
156 Asm->EmitFrameMoves(Moves, 0, true);
158 // On Darwin the linker honors the alignment of eh_frame, which means it must
159 // be 8-byte on 64-bit targets to match what gcc does. Otherwise you get
160 // holes which confuse readers of eh_frame.
161 Asm->EmitAlignment(Asm->getTargetData().getPointerSize() == 4 ? 2 : 3,
163 Asm->OutStreamer.EmitLabel(Asm->GetTempSymbol("eh_frame_common_end", Index));
166 /// EmitFDE - Emit the Frame Description Entry (FDE) for the function.
167 void DwarfException::EmitFDE(const FunctionEHFrameInfo &EHFrameInfo) {
168 assert(!EHFrameInfo.function->hasAvailableExternallyLinkage() &&
169 "Should not emit 'available externally' functions at all");
171 const Function *TheFunc = EHFrameInfo.function;
172 const TargetLoweringObjectFile &TLOF = Asm->getObjFileLowering();
174 unsigned LSDAEncoding = TLOF.getLSDAEncoding();
175 unsigned FDEEncoding = TLOF.getFDEEncoding();
177 Asm->OutStreamer.SwitchSection(TLOF.getEHFrameSection());
179 // Externally visible entry into the functions eh frame info. If the
180 // corresponding function is static, this should not be externally visible.
181 if (!TheFunc->hasLocalLinkage() && TLOF.isFunctionEHSymbolGlobal())
182 Asm->OutStreamer.EmitSymbolAttribute(EHFrameInfo.FunctionEHSym,MCSA_Global);
184 // If corresponding function is weak definition, this should be too.
185 if (TheFunc->isWeakForLinker() && Asm->MAI->getWeakDefDirective())
186 Asm->OutStreamer.EmitSymbolAttribute(EHFrameInfo.FunctionEHSym,
187 MCSA_WeakDefinition);
189 // If corresponding function is hidden, this should be too.
190 if (TheFunc->hasHiddenVisibility())
191 if (MCSymbolAttr HiddenAttr = Asm->MAI->getHiddenVisibilityAttr())
192 Asm->OutStreamer.EmitSymbolAttribute(EHFrameInfo.FunctionEHSym,
195 // If there are no calls then you can't unwind. This may mean we can omit the
196 // EH Frame, but some environments do not handle weak absolute symbols. If
197 // UnwindTablesMandatory is set we cannot do this optimization; the unwind
198 // info is to be available for non-EH uses.
199 if (!EHFrameInfo.hasCalls && !UnwindTablesMandatory &&
200 (!TheFunc->isWeakForLinker() ||
201 !Asm->MAI->getWeakDefDirective() ||
202 TLOF.getSupportsWeakOmittedEHFrame())) {
203 Asm->OutStreamer.EmitAssignment(EHFrameInfo.FunctionEHSym,
204 MCConstantExpr::Create(0, Asm->OutContext));
205 // This name has no connection to the function, so it might get
206 // dead-stripped when the function is not, erroneously. Prohibit
207 // dead-stripping unconditionally.
208 if (Asm->MAI->hasNoDeadStrip())
209 Asm->OutStreamer.EmitSymbolAttribute(EHFrameInfo.FunctionEHSym,
212 Asm->OutStreamer.EmitLabel(EHFrameInfo.FunctionEHSym);
215 Asm->OutStreamer.AddComment("Length of Frame Information Entry");
216 Asm->EmitLabelDifference(
217 Asm->GetTempSymbol("eh_frame_end", EHFrameInfo.Number),
218 Asm->GetTempSymbol("eh_frame_begin", EHFrameInfo.Number), 4);
220 Asm->OutStreamer.EmitLabel(Asm->GetTempSymbol("eh_frame_begin",
221 EHFrameInfo.Number));
223 Asm->OutStreamer.AddComment("FDE CIE offset");
224 Asm->EmitLabelDifference(
225 Asm->GetTempSymbol("eh_frame_begin", EHFrameInfo.Number),
226 Asm->GetTempSymbol("eh_frame_common",
227 EHFrameInfo.PersonalityIndex), 4);
229 MCSymbol *EHFuncBeginSym =
230 Asm->GetTempSymbol("eh_func_begin", EHFrameInfo.Number);
232 Asm->OutStreamer.AddComment("FDE initial location");
233 Asm->EmitReference(EHFuncBeginSym, FDEEncoding);
235 Asm->OutStreamer.AddComment("FDE address range");
236 Asm->EmitLabelDifference(Asm->GetTempSymbol("eh_func_end",
239 Asm->GetSizeOfEncodedValue(FDEEncoding));
241 // If there is a personality and landing pads then point to the language
242 // specific data area in the exception table.
243 if (MMI->getPersonalities()[0] != NULL) {
244 unsigned Size = Asm->GetSizeOfEncodedValue(LSDAEncoding);
246 Asm->EmitULEB128(Size, "Augmentation size");
247 Asm->OutStreamer.AddComment("Language Specific Data Area");
248 if (EHFrameInfo.hasLandingPads)
249 Asm->EmitReference(Asm->GetTempSymbol("exception", EHFrameInfo.Number),
252 Asm->OutStreamer.EmitIntValue(0, Size/*size*/, 0/*addrspace*/);
255 Asm->EmitULEB128(0, "Augmentation size");
258 // Indicate locations of function specific callee saved registers in frame.
259 Asm->EmitFrameMoves(EHFrameInfo.Moves, EHFuncBeginSym, true);
261 // On Darwin the linker honors the alignment of eh_frame, which means it
262 // must be 8-byte on 64-bit targets to match what gcc does. Otherwise you
263 // get holes which confuse readers of eh_frame.
264 Asm->EmitAlignment(Asm->getTargetData().getPointerSize() == 4 ? 2 : 3,
266 Asm->OutStreamer.EmitLabel(Asm->GetTempSymbol("eh_frame_end",
267 EHFrameInfo.Number));
269 // If the function is marked used, this table should be also. We cannot
270 // make the mark unconditional in this case, since retaining the table also
271 // retains the function in this case, and there is code around that depends
272 // on unused functions (calling undefined externals) being dead-stripped to
273 // link correctly. Yes, there really is.
274 if (MMI->isUsedFunction(EHFrameInfo.function))
275 if (Asm->MAI->hasNoDeadStrip())
276 Asm->OutStreamer.EmitSymbolAttribute(EHFrameInfo.FunctionEHSym,
279 Asm->OutStreamer.AddBlankLine();
282 /// SharedTypeIds - How many leading type ids two landing pads have in common.
283 unsigned DwarfException::SharedTypeIds(const LandingPadInfo *L,
284 const LandingPadInfo *R) {
285 const std::vector<int> &LIds = L->TypeIds, &RIds = R->TypeIds;
286 unsigned LSize = LIds.size(), RSize = RIds.size();
287 unsigned MinSize = LSize < RSize ? LSize : RSize;
290 for (; Count != MinSize; ++Count)
291 if (LIds[Count] != RIds[Count])
297 /// PadLT - Order landing pads lexicographically by type id.
298 bool DwarfException::PadLT(const LandingPadInfo *L, const LandingPadInfo *R) {
299 const std::vector<int> &LIds = L->TypeIds, &RIds = R->TypeIds;
300 unsigned LSize = LIds.size(), RSize = RIds.size();
301 unsigned MinSize = LSize < RSize ? LSize : RSize;
303 for (unsigned i = 0; i != MinSize; ++i)
304 if (LIds[i] != RIds[i])
305 return LIds[i] < RIds[i];
307 return LSize < RSize;
310 /// ComputeActionsTable - Compute the actions table and gather the first action
311 /// index for each landing pad site.
312 unsigned DwarfException::
313 ComputeActionsTable(const SmallVectorImpl<const LandingPadInfo*> &LandingPads,
314 SmallVectorImpl<ActionEntry> &Actions,
315 SmallVectorImpl<unsigned> &FirstActions) {
317 // The action table follows the call-site table in the LSDA. The individual
318 // records are of two types:
321 // * Exception specification
323 // The two record kinds have the same format, with only small differences.
324 // They are distinguished by the "switch value" field: Catch clauses
325 // (TypeInfos) have strictly positive switch values, and exception
326 // specifications (FilterIds) have strictly negative switch values. Value 0
327 // indicates a catch-all clause.
329 // Negative type IDs index into FilterIds. Positive type IDs index into
330 // TypeInfos. The value written for a positive type ID is just the type ID
331 // itself. For a negative type ID, however, the value written is the
332 // (negative) byte offset of the corresponding FilterIds entry. The byte
333 // offset is usually equal to the type ID (because the FilterIds entries are
334 // written using a variable width encoding, which outputs one byte per entry
335 // as long as the value written is not too large) but can differ. This kind
336 // of complication does not occur for positive type IDs because type infos are
337 // output using a fixed width encoding. FilterOffsets[i] holds the byte
338 // offset corresponding to FilterIds[i].
340 const std::vector<unsigned> &FilterIds = MMI->getFilterIds();
341 SmallVector<int, 16> FilterOffsets;
342 FilterOffsets.reserve(FilterIds.size());
345 for (std::vector<unsigned>::const_iterator
346 I = FilterIds.begin(), E = FilterIds.end(); I != E; ++I) {
347 FilterOffsets.push_back(Offset);
348 Offset -= MCAsmInfo::getULEB128Size(*I);
351 FirstActions.reserve(LandingPads.size());
354 unsigned SizeActions = 0;
355 const LandingPadInfo *PrevLPI = 0;
357 for (SmallVectorImpl<const LandingPadInfo *>::const_iterator
358 I = LandingPads.begin(), E = LandingPads.end(); I != E; ++I) {
359 const LandingPadInfo *LPI = *I;
360 const std::vector<int> &TypeIds = LPI->TypeIds;
361 unsigned NumShared = PrevLPI ? SharedTypeIds(LPI, PrevLPI) : 0;
362 unsigned SizeSiteActions = 0;
364 if (NumShared < TypeIds.size()) {
365 unsigned SizeAction = 0;
366 unsigned PrevAction = (unsigned)-1;
369 unsigned SizePrevIds = PrevLPI->TypeIds.size();
370 assert(Actions.size());
371 PrevAction = Actions.size() - 1;
373 MCAsmInfo::getSLEB128Size(Actions[PrevAction].NextAction) +
374 MCAsmInfo::getSLEB128Size(Actions[PrevAction].ValueForTypeID);
376 for (unsigned j = NumShared; j != SizePrevIds; ++j) {
377 assert(PrevAction != (unsigned)-1 && "PrevAction is invalid!");
379 MCAsmInfo::getSLEB128Size(Actions[PrevAction].ValueForTypeID);
380 SizeAction += -Actions[PrevAction].NextAction;
381 PrevAction = Actions[PrevAction].Previous;
385 // Compute the actions.
386 for (unsigned J = NumShared, M = TypeIds.size(); J != M; ++J) {
387 int TypeID = TypeIds[J];
388 assert(-1 - TypeID < (int)FilterOffsets.size() && "Unknown filter id!");
389 int ValueForTypeID = TypeID < 0 ? FilterOffsets[-1 - TypeID] : TypeID;
390 unsigned SizeTypeID = MCAsmInfo::getSLEB128Size(ValueForTypeID);
392 int NextAction = SizeAction ? -(SizeAction + SizeTypeID) : 0;
393 SizeAction = SizeTypeID + MCAsmInfo::getSLEB128Size(NextAction);
394 SizeSiteActions += SizeAction;
396 ActionEntry Action = { ValueForTypeID, NextAction, PrevAction };
397 Actions.push_back(Action);
398 PrevAction = Actions.size() - 1;
401 // Record the first action of the landing pad site.
402 FirstAction = SizeActions + SizeSiteActions - SizeAction + 1;
403 } // else identical - re-use previous FirstAction
405 // Information used when created the call-site table. The action record
406 // field of the call site record is the offset of the first associated
407 // action record, relative to the start of the actions table. This value is
408 // biased by 1 (1 indicating the start of the actions table), and 0
409 // indicates that there are no actions.
410 FirstActions.push_back(FirstAction);
412 // Compute this sites contribution to size.
413 SizeActions += SizeSiteActions;
421 /// CallToNoUnwindFunction - Return `true' if this is a call to a function
422 /// marked `nounwind'. Return `false' otherwise.
423 bool DwarfException::CallToNoUnwindFunction(const MachineInstr *MI) {
424 assert(MI->getDesc().isCall() && "This should be a call instruction!");
426 bool MarkedNoUnwind = false;
427 bool SawFunc = false;
429 for (unsigned I = 0, E = MI->getNumOperands(); I != E; ++I) {
430 const MachineOperand &MO = MI->getOperand(I);
432 if (!MO.isGlobal()) continue;
434 Function *F = dyn_cast<Function>(MO.getGlobal());
435 if (F == 0) continue;
438 // Be conservative. If we have more than one function operand for this
439 // call, then we can't make the assumption that it's the callee and
440 // not a parameter to the call.
442 // FIXME: Determine if there's a way to say that `F' is the callee or
444 MarkedNoUnwind = false;
448 MarkedNoUnwind = F->doesNotThrow();
452 return MarkedNoUnwind;
455 /// ComputeCallSiteTable - Compute the call-site table. The entry for an invoke
456 /// has a try-range containing the call, a non-zero landing pad, and an
457 /// appropriate action. The entry for an ordinary call has a try-range
458 /// containing the call and zero for the landing pad and the action. Calls
459 /// marked 'nounwind' have no entry and must not be contained in the try-range
460 /// of any entry - they form gaps in the table. Entries must be ordered by
461 /// try-range address.
462 void DwarfException::
463 ComputeCallSiteTable(SmallVectorImpl<CallSiteEntry> &CallSites,
464 const RangeMapType &PadMap,
465 const SmallVectorImpl<const LandingPadInfo *> &LandingPads,
466 const SmallVectorImpl<unsigned> &FirstActions) {
467 // The end label of the previous invoke or nounwind try-range.
468 MCSymbol *LastLabel = 0;
470 // Whether there is a potentially throwing instruction (currently this means
471 // an ordinary call) between the end of the previous try-range and now.
472 bool SawPotentiallyThrowing = false;
474 // Whether the last CallSite entry was for an invoke.
475 bool PreviousIsInvoke = false;
477 // Visit all instructions in order of address.
478 for (MachineFunction::const_iterator I = Asm->MF->begin(), E = Asm->MF->end();
480 for (MachineBasicBlock::const_iterator MI = I->begin(), E = I->end();
482 if (!MI->isLabel()) {
483 if (MI->getDesc().isCall())
484 SawPotentiallyThrowing |= !CallToNoUnwindFunction(MI);
488 // End of the previous try-range?
489 MCSymbol *BeginLabel = MI->getOperand(0).getMCSymbol();
490 if (BeginLabel == LastLabel)
491 SawPotentiallyThrowing = false;
493 // Beginning of a new try-range?
494 RangeMapType::const_iterator L = PadMap.find(BeginLabel);
495 if (L == PadMap.end())
496 // Nope, it was just some random label.
499 const PadRange &P = L->second;
500 const LandingPadInfo *LandingPad = LandingPads[P.PadIndex];
501 assert(BeginLabel == LandingPad->BeginLabels[P.RangeIndex] &&
502 "Inconsistent landing pad map!");
504 // For Dwarf exception handling (SjLj handling doesn't use this). If some
505 // instruction between the previous try-range and this one may throw,
506 // create a call-site entry with no landing pad for the region between the
508 if (SawPotentiallyThrowing &&
509 Asm->MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf) {
510 CallSiteEntry Site = { LastLabel, BeginLabel, 0, 0 };
511 CallSites.push_back(Site);
512 PreviousIsInvoke = false;
515 LastLabel = LandingPad->EndLabels[P.RangeIndex];
516 assert(BeginLabel && LastLabel && "Invalid landing pad!");
518 if (!LandingPad->LandingPadLabel) {
520 PreviousIsInvoke = false;
522 // This try-range is for an invoke.
523 CallSiteEntry Site = {
526 LandingPad->LandingPadLabel,
527 FirstActions[P.PadIndex]
530 // Try to merge with the previous call-site. SJLJ doesn't do this
531 if (PreviousIsInvoke &&
532 Asm->MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf) {
533 CallSiteEntry &Prev = CallSites.back();
534 if (Site.PadLabel == Prev.PadLabel && Site.Action == Prev.Action) {
535 // Extend the range of the previous entry.
536 Prev.EndLabel = Site.EndLabel;
541 // Otherwise, create a new call-site.
542 if (Asm->MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf)
543 CallSites.push_back(Site);
545 // SjLj EH must maintain the call sites in the order assigned
546 // to them by the SjLjPrepare pass.
547 unsigned SiteNo = MMI->getCallSiteBeginLabel(BeginLabel);
548 if (CallSites.size() < SiteNo)
549 CallSites.resize(SiteNo);
550 CallSites[SiteNo - 1] = Site;
552 PreviousIsInvoke = true;
557 // If some instruction between the previous try-range and the end of the
558 // function may throw, create a call-site entry with no landing pad for the
559 // region following the try-range.
560 if (SawPotentiallyThrowing &&
561 Asm->MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf) {
562 CallSiteEntry Site = { LastLabel, 0, 0, 0 };
563 CallSites.push_back(Site);
567 /// EmitExceptionTable - Emit landing pads and actions.
569 /// The general organization of the table is complex, but the basic concepts are
570 /// easy. First there is a header which describes the location and organization
571 /// of the three components that follow.
573 /// 1. The landing pad site information describes the range of code covered by
574 /// the try. In our case it's an accumulation of the ranges covered by the
575 /// invokes in the try. There is also a reference to the landing pad that
576 /// handles the exception once processed. Finally an index into the actions
578 /// 2. The action table, in our case, is composed of pairs of type IDs and next
579 /// action offset. Starting with the action index from the landing pad
580 /// site, each type ID is checked for a match to the current exception. If
581 /// it matches then the exception and type id are passed on to the landing
582 /// pad. Otherwise the next action is looked up. This chain is terminated
583 /// with a next action of zero. If no type id is found then the frame is
584 /// unwound and handling continues.
585 /// 3. Type ID table contains references to all the C++ typeinfo for all
586 /// catches in the function. This tables is reverse indexed base 1.
587 void DwarfException::EmitExceptionTable() {
588 const std::vector<GlobalVariable *> &TypeInfos = MMI->getTypeInfos();
589 const std::vector<unsigned> &FilterIds = MMI->getFilterIds();
590 const std::vector<LandingPadInfo> &PadInfos = MMI->getLandingPads();
592 // Sort the landing pads in order of their type ids. This is used to fold
593 // duplicate actions.
594 SmallVector<const LandingPadInfo *, 64> LandingPads;
595 LandingPads.reserve(PadInfos.size());
597 for (unsigned i = 0, N = PadInfos.size(); i != N; ++i)
598 LandingPads.push_back(&PadInfos[i]);
600 std::sort(LandingPads.begin(), LandingPads.end(), PadLT);
602 // Compute the actions table and gather the first action index for each
604 SmallVector<ActionEntry, 32> Actions;
605 SmallVector<unsigned, 64> FirstActions;
606 unsigned SizeActions=ComputeActionsTable(LandingPads, Actions, FirstActions);
608 // Invokes and nounwind calls have entries in PadMap (due to being bracketed
609 // by try-range labels when lowered). Ordinary calls do not, so appropriate
610 // try-ranges for them need be deduced when using DWARF exception handling.
612 for (unsigned i = 0, N = LandingPads.size(); i != N; ++i) {
613 const LandingPadInfo *LandingPad = LandingPads[i];
614 for (unsigned j = 0, E = LandingPad->BeginLabels.size(); j != E; ++j) {
615 MCSymbol *BeginLabel = LandingPad->BeginLabels[j];
616 assert(!PadMap.count(BeginLabel) && "Duplicate landing pad labels!");
617 PadRange P = { i, j };
618 PadMap[BeginLabel] = P;
622 // Compute the call-site table.
623 SmallVector<CallSiteEntry, 64> CallSites;
624 ComputeCallSiteTable(CallSites, PadMap, LandingPads, FirstActions);
629 bool IsSJLJ = Asm->MAI->getExceptionHandlingType() == ExceptionHandling::SjLj;
630 bool HaveTTData = IsSJLJ ? (!TypeInfos.empty() || !FilterIds.empty()) : true;
632 unsigned CallSiteTableLength;
634 CallSiteTableLength = 0;
636 unsigned SiteStartSize = 4; // dwarf::DW_EH_PE_udata4
637 unsigned SiteLengthSize = 4; // dwarf::DW_EH_PE_udata4
638 unsigned LandingPadSize = 4; // dwarf::DW_EH_PE_udata4
639 CallSiteTableLength =
640 CallSites.size() * (SiteStartSize + SiteLengthSize + LandingPadSize);
643 for (unsigned i = 0, e = CallSites.size(); i < e; ++i) {
644 CallSiteTableLength += MCAsmInfo::getULEB128Size(CallSites[i].Action);
646 CallSiteTableLength += MCAsmInfo::getULEB128Size(i);
650 const MCSection *LSDASection = Asm->getObjFileLowering().getLSDASection();
651 unsigned TTypeEncoding;
652 unsigned TypeFormatSize;
655 // For SjLj exceptions, if there is no TypeInfo, then we just explicitly say
656 // that we're omitting that bit.
657 TTypeEncoding = dwarf::DW_EH_PE_omit;
658 // dwarf::DW_EH_PE_absptr
659 TypeFormatSize = Asm->getTargetData().getPointerSize();
661 // Okay, we have actual filters or typeinfos to emit. As such, we need to
662 // pick a type encoding for them. We're about to emit a list of pointers to
663 // typeinfo objects at the end of the LSDA. However, unless we're in static
664 // mode, this reference will require a relocation by the dynamic linker.
666 // Because of this, we have a couple of options:
668 // 1) If we are in -static mode, we can always use an absolute reference
669 // from the LSDA, because the static linker will resolve it.
671 // 2) Otherwise, if the LSDA section is writable, we can output the direct
672 // reference to the typeinfo and allow the dynamic linker to relocate
673 // it. Since it is in a writable section, the dynamic linker won't
676 // 3) Finally, if we're in PIC mode and the LDSA section isn't writable,
677 // we need to use some form of indirection. For example, on Darwin,
678 // we can output a statically-relocatable reference to a dyld stub. The
679 // offset to the stub is constant, but the contents are in a section
680 // that is updated by the dynamic linker. This is easy enough, but we
681 // need to tell the personality function of the unwinder to indirect
682 // through the dyld stub.
684 // FIXME: When (3) is actually implemented, we'll have to emit the stubs
685 // somewhere. This predicate should be moved to a shared location that is
686 // in target-independent code.
688 TTypeEncoding = Asm->getObjFileLowering().getTTypeEncoding();
689 TypeFormatSize = Asm->GetSizeOfEncodedValue(TTypeEncoding);
692 // Begin the exception table.
693 Asm->OutStreamer.SwitchSection(LSDASection);
694 Asm->EmitAlignment(2, 0, 0, false);
698 Asm->OutContext.GetOrCreateSymbol(Twine("GCC_except_table")+
699 Twine(Asm->getFunctionNumber()));
700 Asm->OutStreamer.EmitLabel(GCCETSym);
701 Asm->OutStreamer.EmitLabel(Asm->GetTempSymbol("exception",
702 Asm->getFunctionNumber()));
705 Asm->OutStreamer.EmitLabel(Asm->GetTempSymbol("_LSDA_",
706 Asm->getFunctionNumber()));
708 // Emit the LSDA header.
709 Asm->EmitEncodingByte(dwarf::DW_EH_PE_omit, "@LPStart");
710 Asm->EmitEncodingByte(TTypeEncoding, "@TType");
712 // The type infos need to be aligned. GCC does this by inserting padding just
713 // before the type infos. However, this changes the size of the exception
714 // table, so you need to take this into account when you output the exception
715 // table size. However, the size is output using a variable length encoding.
716 // So by increasing the size by inserting padding, you may increase the number
717 // of bytes used for writing the size. If it increases, say by one byte, then
718 // you now need to output one less byte of padding to get the type infos
719 // aligned. However this decreases the size of the exception table. This
720 // changes the value you have to output for the exception table size. Due to
721 // the variable length encoding, the number of bytes used for writing the
722 // length may decrease. If so, you then have to increase the amount of
723 // padding. And so on. If you look carefully at the GCC code you will see that
724 // it indeed does this in a loop, going on and on until the values stabilize.
725 // We chose another solution: don't output padding inside the table like GCC
726 // does, instead output it before the table.
727 unsigned SizeTypes = TypeInfos.size() * TypeFormatSize;
728 unsigned CallSiteTableLengthSize =
729 MCAsmInfo::getULEB128Size(CallSiteTableLength);
730 unsigned TTypeBaseOffset =
731 sizeof(int8_t) + // Call site format
732 CallSiteTableLengthSize + // Call site table length size
733 CallSiteTableLength + // Call site table length
734 SizeActions + // Actions size
736 unsigned TTypeBaseOffsetSize = MCAsmInfo::getULEB128Size(TTypeBaseOffset);
738 sizeof(int8_t) + // LPStart format
739 sizeof(int8_t) + // TType format
740 (HaveTTData ? TTypeBaseOffsetSize : 0) + // TType base offset size
741 TTypeBaseOffset; // TType base offset
742 unsigned SizeAlign = (4 - TotalSize) & 3;
745 // Account for any extra padding that will be added to the call site table
747 Asm->EmitULEB128(TTypeBaseOffset, "@TType base offset", SizeAlign);
751 // SjLj Exception handling
753 Asm->EmitEncodingByte(dwarf::DW_EH_PE_udata4, "Call site");
755 // Add extra padding if it wasn't added to the TType base offset.
756 Asm->EmitULEB128(CallSiteTableLength, "Call site table length", SizeAlign);
758 // Emit the landing pad site information.
760 for (SmallVectorImpl<CallSiteEntry>::const_iterator
761 I = CallSites.begin(), E = CallSites.end(); I != E; ++I, ++idx) {
762 const CallSiteEntry &S = *I;
764 // Offset of the landing pad, counted in 16-byte bundles relative to the
766 Asm->EmitULEB128(idx, "Landing pad");
768 // Offset of the first associated action record, relative to the start of
769 // the action table. This value is biased by 1 (1 indicates the start of
770 // the action table), and 0 indicates that there are no actions.
771 Asm->EmitULEB128(S.Action, "Action");
774 // DWARF Exception handling
775 assert(Asm->MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf);
777 // The call-site table is a list of all call sites that may throw an
778 // exception (including C++ 'throw' statements) in the procedure
779 // fragment. It immediately follows the LSDA header. Each entry indicates,
780 // for a given call, the first corresponding action record and corresponding
783 // The table begins with the number of bytes, stored as an LEB128
784 // compressed, unsigned integer. The records immediately follow the record
785 // count. They are sorted in increasing call-site address. Each record
788 // * The position of the call-site.
789 // * The position of the landing pad.
790 // * The first action record for that call site.
792 // A missing entry in the call-site table indicates that a call is not
793 // supposed to throw.
795 // Emit the landing pad call site table.
796 Asm->EmitEncodingByte(dwarf::DW_EH_PE_udata4, "Call site");
798 // Add extra padding if it wasn't added to the TType base offset.
799 Asm->EmitULEB128(CallSiteTableLength, "Call site table length", SizeAlign);
801 for (SmallVectorImpl<CallSiteEntry>::const_iterator
802 I = CallSites.begin(), E = CallSites.end(); I != E; ++I) {
803 const CallSiteEntry &S = *I;
805 MCSymbol *EHFuncBeginSym =
806 Asm->GetTempSymbol("eh_func_begin", Asm->getFunctionNumber());
808 MCSymbol *BeginLabel = S.BeginLabel;
810 BeginLabel = EHFuncBeginSym;
811 MCSymbol *EndLabel = S.EndLabel;
813 EndLabel = Asm->GetTempSymbol("eh_func_end", Asm->getFunctionNumber());
815 // Offset of the call site relative to the previous call site, counted in
816 // number of 16-byte bundles. The first call site is counted relative to
817 // the start of the procedure fragment.
818 Asm->OutStreamer.AddComment("Region start");
819 Asm->EmitLabelDifference(BeginLabel, EHFuncBeginSym, 4);
821 Asm->OutStreamer.AddComment("Region length");
822 Asm->EmitLabelDifference(EndLabel, BeginLabel, 4);
825 // Offset of the landing pad, counted in 16-byte bundles relative to the
827 Asm->OutStreamer.AddComment("Landing pad");
829 Asm->OutStreamer.EmitIntValue(0, 4/*size*/, 0/*addrspace*/);
831 Asm->EmitLabelDifference(S.PadLabel, EHFuncBeginSym, 4);
833 // Offset of the first associated action record, relative to the start of
834 // the action table. This value is biased by 1 (1 indicates the start of
835 // the action table), and 0 indicates that there are no actions.
836 Asm->EmitULEB128(S.Action, "Action");
840 // Emit the Action Table.
841 if (Actions.size() != 0) {
842 Asm->OutStreamer.AddComment("-- Action Record Table --");
843 Asm->OutStreamer.AddBlankLine();
846 for (SmallVectorImpl<ActionEntry>::const_iterator
847 I = Actions.begin(), E = Actions.end(); I != E; ++I) {
848 const ActionEntry &Action = *I;
849 Asm->OutStreamer.AddComment("Action Record");
850 Asm->OutStreamer.AddBlankLine();
854 // Used by the runtime to match the type of the thrown exception to the
855 // type of the catch clauses or the types in the exception specification.
856 Asm->EmitSLEB128(Action.ValueForTypeID, " TypeInfo index");
860 // Self-relative signed displacement in bytes of the next action record,
861 // or 0 if there is no next action record.
862 Asm->EmitSLEB128(Action.NextAction, " Next action");
865 // Emit the Catch TypeInfos.
866 if (!TypeInfos.empty()) {
867 Asm->OutStreamer.AddComment("-- Catch TypeInfos --");
868 Asm->OutStreamer.AddBlankLine();
870 for (std::vector<GlobalVariable *>::const_reverse_iterator
871 I = TypeInfos.rbegin(), E = TypeInfos.rend(); I != E; ++I) {
872 const GlobalVariable *GV = *I;
874 Asm->OutStreamer.AddComment("TypeInfo");
876 Asm->EmitReference(GV, TTypeEncoding);
878 Asm->OutStreamer.EmitIntValue(0,Asm->GetSizeOfEncodedValue(TTypeEncoding),
882 // Emit the Exception Specifications.
883 if (!FilterIds.empty()) {
884 Asm->OutStreamer.AddComment("-- Filter IDs --");
885 Asm->OutStreamer.AddBlankLine();
887 for (std::vector<unsigned>::const_iterator
888 I = FilterIds.begin(), E = FilterIds.end(); I < E; ++I) {
889 unsigned TypeID = *I;
890 Asm->EmitULEB128(TypeID, TypeID != 0 ? "Exception specification" : 0);
893 Asm->EmitAlignment(2, 0, 0, false);
896 /// EndModule - Emit all exception information that should come after the
898 void DwarfException::EndModule() {
899 NamedRegionTimer T(EHTimerName, DWARFGroupName);
901 if (Asm->MAI->getExceptionHandlingType() != ExceptionHandling::Dwarf)
904 if (!shouldEmitMovesModule && !shouldEmitTableModule)
907 const std::vector<Function *> Personalities = MMI->getPersonalities();
909 for (unsigned I = 0, E = Personalities.size(); I < E; ++I)
910 EmitCIE(Personalities[I], I);
912 for (std::vector<FunctionEHFrameInfo>::iterator
913 I = EHFrames.begin(), E = EHFrames.end(); I != E; ++I)
917 /// BeginFunction - Gather pre-function exception information. Assumes it's
918 /// being emitted immediately after the function entry point.
919 void DwarfException::BeginFunction(const MachineFunction *MF) {
920 NamedRegionTimer T(EHTimerName, DWARFGroupName);
921 shouldEmitTable = shouldEmitMoves = false;
923 // If any landing pads survive, we need an EH table.
924 shouldEmitTable = !MMI->getLandingPads().empty();
926 // See if we need frame move info.
928 !Asm->MF->getFunction()->doesNotThrow() || UnwindTablesMandatory;
930 if (shouldEmitMoves || shouldEmitTable)
931 // Assumes in correct section after the entry point.
932 Asm->OutStreamer.EmitLabel(Asm->GetTempSymbol("eh_func_begin",
933 Asm->getFunctionNumber()));
935 shouldEmitTableModule |= shouldEmitTable;
936 shouldEmitMovesModule |= shouldEmitMoves;
939 /// EndFunction - Gather and emit post-function exception information.
941 void DwarfException::EndFunction() {
942 NamedRegionTimer T(EHTimerName, DWARFGroupName);
943 if (!shouldEmitMoves && !shouldEmitTable) return;
945 Asm->OutStreamer.EmitLabel(Asm->GetTempSymbol("eh_func_end",
946 Asm->getFunctionNumber()));
948 // Record if this personality index uses a landing pad.
949 bool HasLandingPad = !MMI->getLandingPads().empty();
950 UsesLSDA[MMI->getPersonalityIndex()] |= HasLandingPad;
952 // Map all labels and get rid of any dead landing pads.
953 MMI->TidyLandingPads();
956 EmitExceptionTable();
958 const TargetLoweringObjectFile &TLOF = Asm->getObjFileLowering();
959 MCSymbol *FunctionEHSym =
960 Asm->GetSymbolWithGlobalValueBase(Asm->MF->getFunction(), ".eh",
961 TLOF.isFunctionEHFrameSymbolPrivate());
963 // Save EH frame information
964 EHFrames.push_back(FunctionEHFrameInfo(FunctionEHSym,
965 Asm->getFunctionNumber(),
966 MMI->getPersonalityIndex(),
967 Asm->MF->getFrameInfo()->hasCalls(),
968 !MMI->getLandingPads().empty(),
969 MMI->getFrameMoves(),
970 Asm->MF->getFunction()));