1 //===-- CodeGen/AsmPrinter/DwarfException.cpp - Dwarf Exception Impl ------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file contains support for writing DWARF exception info into asm files.
12 //===----------------------------------------------------------------------===//
14 #include "DwarfException.h"
15 #include "llvm/Module.h"
16 #include "llvm/CodeGen/MachineModuleInfo.h"
17 #include "llvm/CodeGen/MachineFrameInfo.h"
18 #include "llvm/CodeGen/MachineFunction.h"
19 #include "llvm/CodeGen/MachineLocation.h"
20 #include "llvm/MC/MCAsmInfo.h"
21 #include "llvm/MC/MCContext.h"
22 #include "llvm/MC/MCExpr.h"
23 #include "llvm/MC/MCSection.h"
24 #include "llvm/MC/MCStreamer.h"
25 #include "llvm/MC/MCSymbol.h"
26 #include "llvm/Target/Mangler.h"
27 #include "llvm/Target/TargetData.h"
28 #include "llvm/Target/TargetFrameInfo.h"
29 #include "llvm/Target/TargetLoweringObjectFile.h"
30 #include "llvm/Target/TargetOptions.h"
31 #include "llvm/Target/TargetRegisterInfo.h"
32 #include "llvm/Support/Dwarf.h"
33 #include "llvm/Support/FormattedStream.h"
34 #include "llvm/Support/Timer.h"
35 #include "llvm/ADT/SmallString.h"
36 #include "llvm/ADT/StringExtras.h"
39 DwarfException::DwarfException(raw_ostream &OS, AsmPrinter *A,
41 : DwarfPrinter(OS, A, T, "eh"), shouldEmitTable(false),shouldEmitMoves(false),
42 shouldEmitTableModule(false), shouldEmitMovesModule(false),
44 if (TimePassesIsEnabled)
45 ExceptionTimer = new Timer("DWARF Exception Writer");
48 DwarfException::~DwarfException() {
49 delete ExceptionTimer;
52 /// SizeOfEncodedValue - Return the size of the encoding in bytes.
53 unsigned DwarfException::SizeOfEncodedValue(unsigned Encoding) {
54 if (Encoding == dwarf::DW_EH_PE_omit)
57 switch (Encoding & 0x07) {
58 case dwarf::DW_EH_PE_absptr:
59 return TD->getPointerSize();
60 case dwarf::DW_EH_PE_udata2:
62 case dwarf::DW_EH_PE_udata4:
64 case dwarf::DW_EH_PE_udata8:
68 assert(0 && "Invalid encoded value.");
72 /// CreateLabelDiff - Emit a label and subtract it from the expression we
73 /// already have. This is equivalent to emitting "foo - .", but we have to emit
74 /// the label for "." directly.
75 const MCExpr *DwarfException::CreateLabelDiff(const MCExpr *ExprRef,
76 const char *LabelName,
79 raw_svector_ostream(Name) << MAI->getPrivateGlobalPrefix()
80 << LabelName << Asm->getFunctionNumber()
82 MCSymbol *DotSym = Asm->OutContext.GetOrCreateSymbol(Name.str());
83 Asm->OutStreamer.EmitLabel(DotSym);
85 return MCBinaryExpr::CreateSub(ExprRef,
86 MCSymbolRefExpr::Create(DotSym,
91 /// EmitCIE - Emit a Common Information Entry (CIE). This holds information that
92 /// is shared among many Frame Description Entries. There is at least one CIE
93 /// in every non-empty .debug_frame section.
94 void DwarfException::EmitCIE(const Function *PersonalityFn, unsigned Index) {
95 // Size and sign of stack growth.
97 Asm->TM.getFrameInfo()->getStackGrowthDirection() ==
98 TargetFrameInfo::StackGrowsUp ?
99 TD->getPointerSize() : -TD->getPointerSize();
101 const TargetLoweringObjectFile &TLOF = Asm->getObjFileLowering();
103 // Begin eh frame section.
104 Asm->OutStreamer.SwitchSection(TLOF.getEHFrameSection());
106 if (MAI->is_EHSymbolPrivate())
107 O << MAI->getPrivateGlobalPrefix();
108 O << "EH_frame" << Index << ":\n";
110 EmitLabel("section_eh_frame", Index);
112 // Define base labels.
113 EmitLabel("eh_frame_common", Index);
115 // Define the eh frame length.
116 EmitDifference("eh_frame_common_end", Index,
117 "eh_frame_common_begin", Index, true);
118 Asm->EOL("Length of Common Information Entry");
121 EmitLabel("eh_frame_common_begin", Index);
122 if (Asm->VerboseAsm) Asm->OutStreamer.AddComment("CIE Identifier Tag");
123 Asm->OutStreamer.EmitIntValue(0, 4/*size*/, 0/*addrspace*/);
124 if (Asm->VerboseAsm) Asm->OutStreamer.AddComment("DW_CIE_VERSION");
125 Asm->OutStreamer.EmitIntValue(dwarf::DW_CIE_VERSION, 1/*size*/, 0/*addr*/);
127 // The personality presence indicates that language specific information will
128 // show up in the eh frame. Find out how we are supposed to lower the
129 // personality function reference:
130 const MCExpr *PersonalityRef = 0;
131 bool IsPersonalityIndirect = false, IsPersonalityPCRel = false;
133 // FIXME: HANDLE STATIC CODEGEN MODEL HERE.
135 // In non-static mode, ask the object file how to represent this reference.
137 TLOF.getSymbolForDwarfGlobalReference(PersonalityFn, Asm->Mang,
139 IsPersonalityIndirect,
143 unsigned PerEncoding = dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4;
144 if (IsPersonalityIndirect)
145 PerEncoding |= dwarf::DW_EH_PE_indirect;
146 unsigned LSDAEncoding = dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4;
147 unsigned FDEEncoding = dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4;
149 char Augmentation[5] = { 0 };
150 unsigned AugmentationSize = 0;
151 char *APtr = Augmentation + 1;
153 if (PersonalityRef) {
154 // There is a personality function.
156 AugmentationSize += 1 + SizeOfEncodedValue(PerEncoding);
159 if (UsesLSDA[Index]) {
160 // An LSDA pointer is in the FDE augmentation.
165 if (FDEEncoding != dwarf::DW_EH_PE_absptr) {
166 // A non-default pointer encoding for the FDE.
171 if (APtr != Augmentation + 1)
172 Augmentation[0] = 'z';
174 Asm->EmitString(Augmentation);
175 Asm->EOL("CIE Augmentation");
178 Asm->EmitULEB128Bytes(1);
179 Asm->EOL("CIE Code Alignment Factor");
180 Asm->EmitSLEB128Bytes(stackGrowth);
181 Asm->EOL("CIE Data Alignment Factor");
182 Asm->EmitInt8(RI->getDwarfRegNum(RI->getRARegister(), true));
183 Asm->EOL("CIE Return Address Column");
185 Asm->EmitULEB128Bytes(AugmentationSize);
186 Asm->EOL("Augmentation Size");
188 EmitEncodingByte(PerEncoding, "Personality");
190 // If there is a personality, we need to indicate the function's location.
191 if (PersonalityRef) {
192 if (!IsPersonalityPCRel)
193 PersonalityRef = CreateLabelDiff(PersonalityRef, "personalityref_addr",
196 O << MAI->getData32bitsDirective() << *PersonalityRef;
197 Asm->EOL("Personality");
199 EmitEncodingByte(LSDAEncoding, "LSDA");
200 EmitEncodingByte(FDEEncoding, "FDE");
203 // Indicate locations of general callee saved registers in frame.
204 std::vector<MachineMove> Moves;
205 RI->getInitialFrameState(Moves);
206 EmitFrameMoves(NULL, 0, Moves, true);
208 // On Darwin the linker honors the alignment of eh_frame, which means it must
209 // be 8-byte on 64-bit targets to match what gcc does. Otherwise you get
210 // holes which confuse readers of eh_frame.
211 Asm->EmitAlignment(TD->getPointerSize() == 4 ? 2 : 3, 0, 0, false);
212 EmitLabel("eh_frame_common_end", Index);
216 /// EmitFDE - Emit the Frame Description Entry (FDE) for the function.
217 void DwarfException::EmitFDE(const FunctionEHFrameInfo &EHFrameInfo) {
218 assert(!EHFrameInfo.function->hasAvailableExternallyLinkage() &&
219 "Should not emit 'available externally' functions at all");
221 const Function *TheFunc = EHFrameInfo.function;
223 Asm->OutStreamer.SwitchSection(Asm->getObjFileLowering().getEHFrameSection());
225 // Externally visible entry into the functions eh frame info. If the
226 // corresponding function is static, this should not be externally visible.
227 if (!TheFunc->hasLocalLinkage())
228 if (const char *GlobalEHDirective = MAI->getGlobalEHDirective())
229 O << GlobalEHDirective << *EHFrameInfo.FunctionEHSym << '\n';
231 // If corresponding function is weak definition, this should be too.
232 if (TheFunc->isWeakForLinker() && MAI->getWeakDefDirective())
233 O << MAI->getWeakDefDirective() << *EHFrameInfo.FunctionEHSym << '\n';
235 // If corresponding function is hidden, this should be too.
236 if (TheFunc->hasHiddenVisibility())
237 if (const char *HiddenDirective = MAI->getHiddenDirective())
238 O << HiddenDirective << *EHFrameInfo.FunctionEHSym << '\n';
240 // If there are no calls then you can't unwind. This may mean we can omit the
241 // EH Frame, but some environments do not handle weak absolute symbols. If
242 // UnwindTablesMandatory is set we cannot do this optimization; the unwind
243 // info is to be available for non-EH uses.
244 if (!EHFrameInfo.hasCalls && !UnwindTablesMandatory &&
245 (!TheFunc->isWeakForLinker() ||
246 !MAI->getWeakDefDirective() ||
247 MAI->getSupportsWeakOmittedEHFrame())) {
248 O << *EHFrameInfo.FunctionEHSym << " = 0\n";
249 // This name has no connection to the function, so it might get
250 // dead-stripped when the function is not, erroneously. Prohibit
251 // dead-stripping unconditionally.
252 if (const char *UsedDirective = MAI->getUsedDirective())
253 O << UsedDirective << *EHFrameInfo.FunctionEHSym << "\n\n";
255 O << *EHFrameInfo.FunctionEHSym << ":\n";
258 EmitDifference("eh_frame_end", EHFrameInfo.Number,
259 "eh_frame_begin", EHFrameInfo.Number, true);
260 Asm->EOL("Length of Frame Information Entry");
262 EmitLabel("eh_frame_begin", EHFrameInfo.Number);
264 EmitSectionOffset("eh_frame_begin", "eh_frame_common",
265 EHFrameInfo.Number, EHFrameInfo.PersonalityIndex,
268 Asm->EOL("FDE CIE offset");
270 EmitReference("eh_func_begin", EHFrameInfo.Number, true, true);
271 Asm->EOL("FDE initial location");
272 EmitDifference("eh_func_end", EHFrameInfo.Number,
273 "eh_func_begin", EHFrameInfo.Number, true);
274 Asm->EOL("FDE address range");
276 // If there is a personality and landing pads then point to the language
277 // specific data area in the exception table.
278 if (MMI->getPersonalities()[0] != NULL) {
280 if (Asm->TM.getLSDAEncoding() != DwarfLSDAEncoding::EightByte) {
281 Asm->EmitULEB128Bytes(4);
282 Asm->EOL("Augmentation size");
284 if (EHFrameInfo.hasLandingPads)
285 EmitReference("exception", EHFrameInfo.Number, true, true);
287 Asm->OutStreamer.EmitIntValue(0, 4/*size*/, 0/*addrspace*/);
289 Asm->EmitULEB128Bytes(TD->getPointerSize());
290 Asm->EOL("Augmentation size");
292 if (EHFrameInfo.hasLandingPads) {
293 EmitReference("exception", EHFrameInfo.Number, true, false);
295 Asm->OutStreamer.EmitIntValue(0, TD->getPointerSize(),
300 Asm->EOL("Language Specific Data Area");
302 Asm->EmitULEB128Bytes(0);
303 Asm->EOL("Augmentation size");
306 // Indicate locations of function specific callee saved registers in frame.
307 EmitFrameMoves("eh_func_begin", EHFrameInfo.Number, EHFrameInfo.Moves,
310 // On Darwin the linker honors the alignment of eh_frame, which means it
311 // must be 8-byte on 64-bit targets to match what gcc does. Otherwise you
312 // get holes which confuse readers of eh_frame.
313 Asm->EmitAlignment(TD->getPointerSize() == sizeof(int32_t) ? 2 : 3,
315 EmitLabel("eh_frame_end", EHFrameInfo.Number);
317 // If the function is marked used, this table should be also. We cannot
318 // make the mark unconditional in this case, since retaining the table also
319 // retains the function in this case, and there is code around that depends
320 // on unused functions (calling undefined externals) being dead-stripped to
321 // link correctly. Yes, there really is.
322 if (MMI->isUsedFunction(EHFrameInfo.function))
323 if (const char *UsedDirective = MAI->getUsedDirective())
324 O << UsedDirective << *EHFrameInfo.FunctionEHSym << "\n\n";
329 /// SharedTypeIds - How many leading type ids two landing pads have in common.
330 unsigned DwarfException::SharedTypeIds(const LandingPadInfo *L,
331 const LandingPadInfo *R) {
332 const std::vector<int> &LIds = L->TypeIds, &RIds = R->TypeIds;
333 unsigned LSize = LIds.size(), RSize = RIds.size();
334 unsigned MinSize = LSize < RSize ? LSize : RSize;
337 for (; Count != MinSize; ++Count)
338 if (LIds[Count] != RIds[Count])
344 /// PadLT - Order landing pads lexicographically by type id.
345 bool DwarfException::PadLT(const LandingPadInfo *L, const LandingPadInfo *R) {
346 const std::vector<int> &LIds = L->TypeIds, &RIds = R->TypeIds;
347 unsigned LSize = LIds.size(), RSize = RIds.size();
348 unsigned MinSize = LSize < RSize ? LSize : RSize;
350 for (unsigned i = 0; i != MinSize; ++i)
351 if (LIds[i] != RIds[i])
352 return LIds[i] < RIds[i];
354 return LSize < RSize;
357 /// ComputeActionsTable - Compute the actions table and gather the first action
358 /// index for each landing pad site.
359 unsigned DwarfException::
360 ComputeActionsTable(const SmallVectorImpl<const LandingPadInfo*> &LandingPads,
361 SmallVectorImpl<ActionEntry> &Actions,
362 SmallVectorImpl<unsigned> &FirstActions) {
364 // The action table follows the call-site table in the LSDA. The individual
365 // records are of two types:
368 // * Exception specification
370 // The two record kinds have the same format, with only small differences.
371 // They are distinguished by the "switch value" field: Catch clauses
372 // (TypeInfos) have strictly positive switch values, and exception
373 // specifications (FilterIds) have strictly negative switch values. Value 0
374 // indicates a catch-all clause.
376 // Negative type IDs index into FilterIds. Positive type IDs index into
377 // TypeInfos. The value written for a positive type ID is just the type ID
378 // itself. For a negative type ID, however, the value written is the
379 // (negative) byte offset of the corresponding FilterIds entry. The byte
380 // offset is usually equal to the type ID (because the FilterIds entries are
381 // written using a variable width encoding, which outputs one byte per entry
382 // as long as the value written is not too large) but can differ. This kind
383 // of complication does not occur for positive type IDs because type infos are
384 // output using a fixed width encoding. FilterOffsets[i] holds the byte
385 // offset corresponding to FilterIds[i].
387 const std::vector<unsigned> &FilterIds = MMI->getFilterIds();
388 SmallVector<int, 16> FilterOffsets;
389 FilterOffsets.reserve(FilterIds.size());
392 for (std::vector<unsigned>::const_iterator
393 I = FilterIds.begin(), E = FilterIds.end(); I != E; ++I) {
394 FilterOffsets.push_back(Offset);
395 Offset -= MCAsmInfo::getULEB128Size(*I);
398 FirstActions.reserve(LandingPads.size());
401 unsigned SizeActions = 0;
402 const LandingPadInfo *PrevLPI = 0;
404 for (SmallVectorImpl<const LandingPadInfo *>::const_iterator
405 I = LandingPads.begin(), E = LandingPads.end(); I != E; ++I) {
406 const LandingPadInfo *LPI = *I;
407 const std::vector<int> &TypeIds = LPI->TypeIds;
408 const unsigned NumShared = PrevLPI ? SharedTypeIds(LPI, PrevLPI) : 0;
409 unsigned SizeSiteActions = 0;
411 if (NumShared < TypeIds.size()) {
412 unsigned SizeAction = 0;
413 ActionEntry *PrevAction = 0;
416 const unsigned SizePrevIds = PrevLPI->TypeIds.size();
417 assert(Actions.size());
418 PrevAction = &Actions.back();
419 SizeAction = MCAsmInfo::getSLEB128Size(PrevAction->NextAction) +
420 MCAsmInfo::getSLEB128Size(PrevAction->ValueForTypeID);
422 for (unsigned j = NumShared; j != SizePrevIds; ++j) {
424 MCAsmInfo::getSLEB128Size(PrevAction->ValueForTypeID);
425 SizeAction += -PrevAction->NextAction;
426 PrevAction = PrevAction->Previous;
430 // Compute the actions.
431 for (unsigned J = NumShared, M = TypeIds.size(); J != M; ++J) {
432 int TypeID = TypeIds[J];
433 assert(-1 - TypeID < (int)FilterOffsets.size() && "Unknown filter id!");
434 int ValueForTypeID = TypeID < 0 ? FilterOffsets[-1 - TypeID] : TypeID;
435 unsigned SizeTypeID = MCAsmInfo::getSLEB128Size(ValueForTypeID);
437 int NextAction = SizeAction ? -(SizeAction + SizeTypeID) : 0;
438 SizeAction = SizeTypeID + MCAsmInfo::getSLEB128Size(NextAction);
439 SizeSiteActions += SizeAction;
441 ActionEntry Action = { ValueForTypeID, NextAction, PrevAction };
442 Actions.push_back(Action);
443 PrevAction = &Actions.back();
446 // Record the first action of the landing pad site.
447 FirstAction = SizeActions + SizeSiteActions - SizeAction + 1;
448 } // else identical - re-use previous FirstAction
450 // Information used when created the call-site table. The action record
451 // field of the call site record is the offset of the first associated
452 // action record, relative to the start of the actions table. This value is
453 // biased by 1 (1 in dicating the start of the actions table), and 0
454 // indicates that there are no actions.
455 FirstActions.push_back(FirstAction);
457 // Compute this sites contribution to size.
458 SizeActions += SizeSiteActions;
466 /// CallToNoUnwindFunction - Return `true' if this is a call to a function
467 /// marked `nounwind'. Return `false' otherwise.
468 bool DwarfException::CallToNoUnwindFunction(const MachineInstr *MI) {
469 assert(MI->getDesc().isCall() && "This should be a call instruction!");
471 bool MarkedNoUnwind = false;
472 bool SawFunc = false;
474 for (unsigned I = 0, E = MI->getNumOperands(); I != E; ++I) {
475 const MachineOperand &MO = MI->getOperand(I);
478 if (Function *F = dyn_cast<Function>(MO.getGlobal())) {
480 // Be conservative. If we have more than one function operand for this
481 // call, then we can't make the assumption that it's the callee and
482 // not a parameter to the call.
484 // FIXME: Determine if there's a way to say that `F' is the callee or
486 MarkedNoUnwind = false;
490 MarkedNoUnwind = F->doesNotThrow();
496 return MarkedNoUnwind;
499 /// ComputeCallSiteTable - Compute the call-site table. The entry for an invoke
500 /// has a try-range containing the call, a non-zero landing pad, and an
501 /// appropriate action. The entry for an ordinary call has a try-range
502 /// containing the call and zero for the landing pad and the action. Calls
503 /// marked 'nounwind' have no entry and must not be contained in the try-range
504 /// of any entry - they form gaps in the table. Entries must be ordered by
505 /// try-range address.
506 void DwarfException::
507 ComputeCallSiteTable(SmallVectorImpl<CallSiteEntry> &CallSites,
508 const RangeMapType &PadMap,
509 const SmallVectorImpl<const LandingPadInfo *> &LandingPads,
510 const SmallVectorImpl<unsigned> &FirstActions) {
511 // The end label of the previous invoke or nounwind try-range.
512 unsigned LastLabel = 0;
514 // Whether there is a potentially throwing instruction (currently this means
515 // an ordinary call) between the end of the previous try-range and now.
516 bool SawPotentiallyThrowing = false;
518 // Whether the last CallSite entry was for an invoke.
519 bool PreviousIsInvoke = false;
521 // Visit all instructions in order of address.
522 for (MachineFunction::const_iterator I = MF->begin(), E = MF->end();
524 for (MachineBasicBlock::const_iterator MI = I->begin(), E = I->end();
526 if (!MI->isLabel()) {
527 if (MI->getDesc().isCall())
528 SawPotentiallyThrowing |= !CallToNoUnwindFunction(MI);
533 unsigned BeginLabel = MI->getOperand(0).getImm();
534 assert(BeginLabel && "Invalid label!");
536 // End of the previous try-range?
537 if (BeginLabel == LastLabel)
538 SawPotentiallyThrowing = false;
540 // Beginning of a new try-range?
541 RangeMapType::const_iterator L = PadMap.find(BeginLabel);
542 if (L == PadMap.end())
543 // Nope, it was just some random label.
546 const PadRange &P = L->second;
547 const LandingPadInfo *LandingPad = LandingPads[P.PadIndex];
548 assert(BeginLabel == LandingPad->BeginLabels[P.RangeIndex] &&
549 "Inconsistent landing pad map!");
551 // For Dwarf exception handling (SjLj handling doesn't use this). If some
552 // instruction between the previous try-range and this one may throw,
553 // create a call-site entry with no landing pad for the region between the
555 if (SawPotentiallyThrowing &&
556 MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf) {
557 CallSiteEntry Site = { LastLabel, BeginLabel, 0, 0 };
558 CallSites.push_back(Site);
559 PreviousIsInvoke = false;
562 LastLabel = LandingPad->EndLabels[P.RangeIndex];
563 assert(BeginLabel && LastLabel && "Invalid landing pad!");
565 if (LandingPad->LandingPadLabel) {
566 // This try-range is for an invoke.
567 CallSiteEntry Site = {
570 LandingPad->LandingPadLabel,
571 FirstActions[P.PadIndex]
574 // Try to merge with the previous call-site. SJLJ doesn't do this
575 if (PreviousIsInvoke &&
576 MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf) {
577 CallSiteEntry &Prev = CallSites.back();
578 if (Site.PadLabel == Prev.PadLabel && Site.Action == Prev.Action) {
579 // Extend the range of the previous entry.
580 Prev.EndLabel = Site.EndLabel;
585 // Otherwise, create a new call-site.
586 CallSites.push_back(Site);
587 PreviousIsInvoke = true;
590 PreviousIsInvoke = false;
595 // If some instruction between the previous try-range and the end of the
596 // function may throw, create a call-site entry with no landing pad for the
597 // region following the try-range.
598 if (SawPotentiallyThrowing &&
599 MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf) {
600 CallSiteEntry Site = { LastLabel, 0, 0, 0 };
601 CallSites.push_back(Site);
605 /// EmitExceptionTable - Emit landing pads and actions.
607 /// The general organization of the table is complex, but the basic concepts are
608 /// easy. First there is a header which describes the location and organization
609 /// of the three components that follow.
611 /// 1. The landing pad site information describes the range of code covered by
612 /// the try. In our case it's an accumulation of the ranges covered by the
613 /// invokes in the try. There is also a reference to the landing pad that
614 /// handles the exception once processed. Finally an index into the actions
616 /// 2. The action table, in our case, is composed of pairs of type IDs and next
617 /// action offset. Starting with the action index from the landing pad
618 /// site, each type ID is checked for a match to the current exception. If
619 /// it matches then the exception and type id are passed on to the landing
620 /// pad. Otherwise the next action is looked up. This chain is terminated
621 /// with a next action of zero. If no type id is found then the frame is
622 /// unwound and handling continues.
623 /// 3. Type ID table contains references to all the C++ typeinfo for all
624 /// catches in the function. This tables is reverse indexed base 1.
625 void DwarfException::EmitExceptionTable() {
626 const std::vector<GlobalVariable *> &TypeInfos = MMI->getTypeInfos();
627 const std::vector<unsigned> &FilterIds = MMI->getFilterIds();
628 const std::vector<LandingPadInfo> &PadInfos = MMI->getLandingPads();
629 if (PadInfos.empty()) return;
631 // Sort the landing pads in order of their type ids. This is used to fold
632 // duplicate actions.
633 SmallVector<const LandingPadInfo *, 64> LandingPads;
634 LandingPads.reserve(PadInfos.size());
636 for (unsigned i = 0, N = PadInfos.size(); i != N; ++i)
637 LandingPads.push_back(&PadInfos[i]);
639 std::sort(LandingPads.begin(), LandingPads.end(), PadLT);
641 // Compute the actions table and gather the first action index for each
643 SmallVector<ActionEntry, 32> Actions;
644 SmallVector<unsigned, 64> FirstActions;
645 unsigned SizeActions = ComputeActionsTable(LandingPads, Actions,
648 // Invokes and nounwind calls have entries in PadMap (due to being bracketed
649 // by try-range labels when lowered). Ordinary calls do not, so appropriate
650 // try-ranges for them need be deduced when using DWARF exception handling.
652 for (unsigned i = 0, N = LandingPads.size(); i != N; ++i) {
653 const LandingPadInfo *LandingPad = LandingPads[i];
654 for (unsigned j = 0, E = LandingPad->BeginLabels.size(); j != E; ++j) {
655 unsigned BeginLabel = LandingPad->BeginLabels[j];
656 assert(!PadMap.count(BeginLabel) && "Duplicate landing pad labels!");
657 PadRange P = { i, j };
658 PadMap[BeginLabel] = P;
662 // Compute the call-site table.
663 SmallVector<CallSiteEntry, 64> CallSites;
664 ComputeCallSiteTable(CallSites, PadMap, LandingPads, FirstActions);
669 const unsigned SiteStartSize = SizeOfEncodedValue(dwarf::DW_EH_PE_udata4);
670 const unsigned SiteLengthSize = SizeOfEncodedValue(dwarf::DW_EH_PE_udata4);
671 const unsigned LandingPadSize = SizeOfEncodedValue(dwarf::DW_EH_PE_udata4);
672 bool IsSJLJ = MAI->getExceptionHandlingType() == ExceptionHandling::SjLj;
673 bool HaveTTData = IsSJLJ ? (!TypeInfos.empty() || !FilterIds.empty()) : true;
679 SizeSites = CallSites.size() *
680 (SiteStartSize + SiteLengthSize + LandingPadSize);
682 for (unsigned i = 0, e = CallSites.size(); i < e; ++i) {
683 SizeSites += MCAsmInfo::getULEB128Size(CallSites[i].Action);
685 SizeSites += MCAsmInfo::getULEB128Size(i);
689 const MCSection *LSDASection = Asm->getObjFileLowering().getLSDASection();
690 unsigned TTypeFormat;
691 unsigned TypeFormatSize;
694 // For SjLj exceptions, if there is no TypeInfo, then we just explicitly say
695 // that we're omitting that bit.
696 TTypeFormat = dwarf::DW_EH_PE_omit;
697 TypeFormatSize = SizeOfEncodedValue(dwarf::DW_EH_PE_absptr);
699 // Okay, we have actual filters or typeinfos to emit. As such, we need to
700 // pick a type encoding for them. We're about to emit a list of pointers to
701 // typeinfo objects at the end of the LSDA. However, unless we're in static
702 // mode, this reference will require a relocation by the dynamic linker.
704 // Because of this, we have a couple of options:
706 // 1) If we are in -static mode, we can always use an absolute reference
707 // from the LSDA, because the static linker will resolve it.
709 // 2) Otherwise, if the LSDA section is writable, we can output the direct
710 // reference to the typeinfo and allow the dynamic linker to relocate
711 // it. Since it is in a writable section, the dynamic linker won't
714 // 3) Finally, if we're in PIC mode and the LDSA section isn't writable,
715 // we need to use some form of indirection. For example, on Darwin,
716 // we can output a statically-relocatable reference to a dyld stub. The
717 // offset to the stub is constant, but the contents are in a section
718 // that is updated by the dynamic linker. This is easy enough, but we
719 // need to tell the personality function of the unwinder to indirect
720 // through the dyld stub.
722 // FIXME: When (3) is actually implemented, we'll have to emit the stubs
723 // somewhere. This predicate should be moved to a shared location that is
724 // in target-independent code.
726 if (LSDASection->getKind().isWriteable() ||
727 Asm->TM.getRelocationModel() == Reloc::Static)
728 TTypeFormat = dwarf::DW_EH_PE_absptr;
730 TTypeFormat = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
731 dwarf::DW_EH_PE_sdata4;
733 TypeFormatSize = SizeOfEncodedValue(TTypeFormat);
736 // Begin the exception table.
737 Asm->OutStreamer.SwitchSection(LSDASection);
738 Asm->EmitAlignment(2, 0, 0, false);
740 O << "GCC_except_table" << SubprogramCount << ":\n";
742 // The type infos need to be aligned. GCC does this by inserting padding just
743 // before the type infos. However, this changes the size of the exception
744 // table, so you need to take this into account when you output the exception
745 // table size. However, the size is output using a variable length encoding.
746 // So by increasing the size by inserting padding, you may increase the number
747 // of bytes used for writing the size. If it increases, say by one byte, then
748 // you now need to output one less byte of padding to get the type infos
749 // aligned. However this decreases the size of the exception table. This
750 // changes the value you have to output for the exception table size. Due to
751 // the variable length encoding, the number of bytes used for writing the
752 // length may decrease. If so, you then have to increase the amount of
753 // padding. And so on. If you look carefully at the GCC code you will see that
754 // it indeed does this in a loop, going on and on until the values stabilize.
755 // We chose another solution: don't output padding inside the table like GCC
756 // does, instead output it before the table.
757 unsigned SizeTypes = TypeInfos.size() * TypeFormatSize;
758 unsigned TyOffset = sizeof(int8_t) + // Call site format
759 MCAsmInfo::getULEB128Size(SizeSites) + // Call-site table length
760 SizeSites + SizeActions + SizeTypes;
761 unsigned TotalSize = sizeof(int8_t) + // LPStart format
762 sizeof(int8_t) + // TType format
764 MCAsmInfo::getULEB128Size(TyOffset) : 0) + // TType base offset
766 unsigned SizeAlign = (4 - TotalSize) & 3;
768 for (unsigned i = 0; i != SizeAlign; ++i) {
773 EmitLabel("exception", SubprogramCount);
776 SmallString<16> LSDAName;
777 raw_svector_ostream(LSDAName) << MAI->getPrivateGlobalPrefix() <<
778 "_LSDA_" << Asm->getFunctionNumber();
779 O << LSDAName.str() << ":\n";
783 EmitEncodingByte(dwarf::DW_EH_PE_omit, "@LPStart");
784 EmitEncodingByte(TTypeFormat, "@TType");
787 Asm->EmitULEB128Bytes(TyOffset);
788 Asm->EOL("@TType base offset");
791 // SjLj Exception handling
793 EmitEncodingByte(dwarf::DW_EH_PE_udata4, "Call site");
794 Asm->EmitULEB128Bytes(SizeSites);
795 Asm->EOL("Call site table length");
797 // Emit the landing pad site information.
799 for (SmallVectorImpl<CallSiteEntry>::const_iterator
800 I = CallSites.begin(), E = CallSites.end(); I != E; ++I, ++idx) {
801 const CallSiteEntry &S = *I;
803 // Offset of the landing pad, counted in 16-byte bundles relative to the
805 Asm->EmitULEB128Bytes(idx);
806 Asm->EOL("Landing pad");
808 // Offset of the first associated action record, relative to the start of
809 // the action table. This value is biased by 1 (1 indicates the start of
810 // the action table), and 0 indicates that there are no actions.
811 Asm->EmitULEB128Bytes(S.Action);
815 // DWARF Exception handling
816 assert(MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf);
818 // The call-site table is a list of all call sites that may throw an
819 // exception (including C++ 'throw' statements) in the procedure
820 // fragment. It immediately follows the LSDA header. Each entry indicates,
821 // for a given call, the first corresponding action record and corresponding
824 // The table begins with the number of bytes, stored as an LEB128
825 // compressed, unsigned integer. The records immediately follow the record
826 // count. They are sorted in increasing call-site address. Each record
829 // * The position of the call-site.
830 // * The position of the landing pad.
831 // * The first action record for that call site.
833 // A missing entry in the call-site table indicates that a call is not
834 // supposed to throw.
836 // Emit the landing pad call site table.
837 EmitEncodingByte(dwarf::DW_EH_PE_udata4, "Call site");
838 Asm->EmitULEB128Bytes(SizeSites);
839 Asm->EOL("Call site table size");
841 for (SmallVectorImpl<CallSiteEntry>::const_iterator
842 I = CallSites.begin(), E = CallSites.end(); I != E; ++I) {
843 const CallSiteEntry &S = *I;
844 const char *BeginTag;
845 unsigned BeginNumber;
848 BeginTag = "eh_func_begin";
849 BeginNumber = SubprogramCount;
852 BeginNumber = S.BeginLabel;
855 // Offset of the call site relative to the previous call site, counted in
856 // number of 16-byte bundles. The first call site is counted relative to
857 // the start of the procedure fragment.
858 EmitSectionOffset(BeginTag, "eh_func_begin", BeginNumber, SubprogramCount,
860 Asm->EOL("Region start");
863 EmitDifference("eh_func_end", SubprogramCount, BeginTag, BeginNumber,
866 EmitDifference("label", S.EndLabel, BeginTag, BeginNumber, true);
868 Asm->EOL("Region length");
870 // Offset of the landing pad, counted in 16-byte bundles relative to the
873 Asm->OutStreamer.EmitIntValue(0, 4/*size*/, 0/*addrspace*/);
875 EmitSectionOffset("label", "eh_func_begin", S.PadLabel, SubprogramCount,
878 Asm->EOL("Landing pad");
880 // Offset of the first associated action record, relative to the start of
881 // the action table. This value is biased by 1 (1 indicates the start of
882 // the action table), and 0 indicates that there are no actions.
883 Asm->EmitULEB128Bytes(S.Action);
888 // Emit the Action Table.
889 for (SmallVectorImpl<ActionEntry>::const_iterator
890 I = Actions.begin(), E = Actions.end(); I != E; ++I) {
891 const ActionEntry &Action = *I;
895 // Used by the runtime to match the type of the thrown exception to the
896 // type of the catch clauses or the types in the exception specification.
898 Asm->EmitSLEB128Bytes(Action.ValueForTypeID);
899 Asm->EOL("TypeInfo index");
903 // Self-relative signed displacement in bytes of the next action record,
904 // or 0 if there is no next action record.
906 Asm->EmitSLEB128Bytes(Action.NextAction);
907 Asm->EOL("Next action");
910 // Emit the Catch TypeInfos.
911 for (std::vector<GlobalVariable *>::const_reverse_iterator
912 I = TypeInfos.rbegin(), E = TypeInfos.rend(); I != E; ++I) {
913 const GlobalVariable *GV = *I;
917 O << *Asm->GetGlobalValueSymbol(GV);
922 Asm->EOL("TypeInfo");
925 // Emit the Exception Specifications.
926 for (std::vector<unsigned>::const_iterator
927 I = FilterIds.begin(), E = FilterIds.end(); I < E; ++I) {
928 unsigned TypeID = *I;
929 Asm->EmitULEB128Bytes(TypeID);
931 Asm->EOL("Exception specification");
936 Asm->EmitAlignment(2, 0, 0, false);
939 /// EndModule - Emit all exception information that should come after the
941 void DwarfException::EndModule() {
942 if (MAI->getExceptionHandlingType() != ExceptionHandling::Dwarf)
945 if (!shouldEmitMovesModule && !shouldEmitTableModule)
948 if (TimePassesIsEnabled)
949 ExceptionTimer->startTimer();
951 const std::vector<Function *> Personalities = MMI->getPersonalities();
953 for (unsigned I = 0, E = Personalities.size(); I < E; ++I)
954 EmitCIE(Personalities[I], I);
956 for (std::vector<FunctionEHFrameInfo>::iterator
957 I = EHFrames.begin(), E = EHFrames.end(); I != E; ++I)
960 if (TimePassesIsEnabled)
961 ExceptionTimer->stopTimer();
964 /// BeginFunction - Gather pre-function exception information. Assumes it's
965 /// being emitted immediately after the function entry point.
966 void DwarfException::BeginFunction(MachineFunction *MF) {
967 if (!MMI || !MAI->doesSupportExceptionHandling()) return;
969 if (TimePassesIsEnabled)
970 ExceptionTimer->startTimer();
973 shouldEmitTable = shouldEmitMoves = false;
975 // Map all labels and get rid of any dead landing pads.
976 MMI->TidyLandingPads();
978 // If any landing pads survive, we need an EH table.
979 if (!MMI->getLandingPads().empty())
980 shouldEmitTable = true;
982 // See if we need frame move info.
983 if (!MF->getFunction()->doesNotThrow() || UnwindTablesMandatory)
984 shouldEmitMoves = true;
986 if (shouldEmitMoves || shouldEmitTable)
987 // Assumes in correct section after the entry point.
988 EmitLabel("eh_func_begin", ++SubprogramCount);
990 shouldEmitTableModule |= shouldEmitTable;
991 shouldEmitMovesModule |= shouldEmitMoves;
993 if (TimePassesIsEnabled)
994 ExceptionTimer->stopTimer();
997 /// EndFunction - Gather and emit post-function exception information.
999 void DwarfException::EndFunction() {
1000 if (!shouldEmitMoves && !shouldEmitTable) return;
1002 if (TimePassesIsEnabled)
1003 ExceptionTimer->startTimer();
1005 EmitLabel("eh_func_end", SubprogramCount);
1006 EmitExceptionTable();
1008 const MCSymbol *FunctionEHSym =
1009 Asm->GetSymbolWithGlobalValueBase(MF->getFunction(), ".eh",
1010 Asm->MAI->is_EHSymbolPrivate());
1012 // Save EH frame information
1013 EHFrames.push_back(FunctionEHFrameInfo(FunctionEHSym, SubprogramCount,
1014 MMI->getPersonalityIndex(),
1015 MF->getFrameInfo()->hasCalls(),
1016 !MMI->getLandingPads().empty(),
1017 MMI->getFrameMoves(),
1018 MF->getFunction()));
1020 // Record if this personality index uses a landing pad.
1021 UsesLSDA[MMI->getPersonalityIndex()] |= !MMI->getLandingPads().empty();
1023 if (TimePassesIsEnabled)
1024 ExceptionTimer->stopTimer();