//===-- CodeGen/AsmPrinter/DwarfException.cpp - Dwarf Exception Impl ------===// // // The LLVM Compiler Infrastructure // // This file is distributed under the University of Illinois Open Source // License. See LICENSE.TXT for details. // //===----------------------------------------------------------------------===// // // This file contains support for writing DWARF exception info into asm files. // //===----------------------------------------------------------------------===// #include "DwarfException.h" #include "llvm/Module.h" #include "llvm/CodeGen/MachineModuleInfo.h" #include "llvm/CodeGen/MachineFrameInfo.h" #include "llvm/CodeGen/MachineFunction.h" #include "llvm/CodeGen/MachineLocation.h" #include "llvm/MC/MCAsmInfo.h" #include "llvm/MC/MCContext.h" #include "llvm/MC/MCExpr.h" #include "llvm/MC/MCSection.h" #include "llvm/MC/MCStreamer.h" #include "llvm/Target/TargetData.h" #include "llvm/Target/TargetFrameInfo.h" #include "llvm/Target/TargetLoweringObjectFile.h" #include "llvm/Target/TargetOptions.h" #include "llvm/Target/TargetRegisterInfo.h" #include "llvm/Support/Dwarf.h" #include "llvm/Support/Mangler.h" #include "llvm/Support/Timer.h" #include "llvm/Support/raw_ostream.h" #include "llvm/ADT/SmallString.h" #include "llvm/ADT/StringExtras.h" using namespace llvm; static TimerGroup &getDwarfTimerGroup() { static TimerGroup DwarfTimerGroup("DWARF Exception"); return DwarfTimerGroup; } DwarfException::DwarfException(raw_ostream &OS, AsmPrinter *A, const MCAsmInfo *T) : Dwarf(OS, A, T, "eh"), shouldEmitTable(false), shouldEmitMoves(false), shouldEmitTableModule(false), shouldEmitMovesModule(false), ExceptionTimer(0) { if (TimePassesIsEnabled) ExceptionTimer = new Timer("DWARF Exception Writer", getDwarfTimerGroup()); } DwarfException::~DwarfException() { delete ExceptionTimer; } /// SizeOfEncodedValue - Return the size of the encoding in bytes. unsigned DwarfException::SizeOfEncodedValue(unsigned Encoding) { if (Encoding == dwarf::DW_EH_PE_omit) return 0; switch (Encoding & 0x07) { case dwarf::DW_EH_PE_absptr: return TD->getPointerSize(); case dwarf::DW_EH_PE_udata2: return 2; case dwarf::DW_EH_PE_udata4: return 4; case dwarf::DW_EH_PE_udata8: return 8; } assert(0 && "Invalid encoded value."); return 0; } /// EmitCIE - Emit a Common Information Entry (CIE). This holds information that /// is shared among many Frame Description Entries. There is at least one CIE /// in every non-empty .debug_frame section. void DwarfException::EmitCIE(const Function *PersonalityFn, unsigned Index) { // Size and sign of stack growth. int stackGrowth = Asm->TM.getFrameInfo()->getStackGrowthDirection() == TargetFrameInfo::StackGrowsUp ? TD->getPointerSize() : -TD->getPointerSize(); const TargetLoweringObjectFile &TLOF = Asm->getObjFileLowering(); // Begin eh frame section. Asm->OutStreamer.SwitchSection(TLOF.getEHFrameSection()); if (MAI->is_EHSymbolPrivate()) O << MAI->getPrivateGlobalPrefix(); O << "EH_frame" << Index << ":\n"; EmitLabel("section_eh_frame", Index); // Define base labels. EmitLabel("eh_frame_common", Index); // Define the eh frame length. EmitDifference("eh_frame_common_end", Index, "eh_frame_common_begin", Index, true); Asm->EOL("Length of Common Information Entry"); // EH frame header. EmitLabel("eh_frame_common_begin", Index); Asm->EmitInt32((int)0); Asm->EOL("CIE Identifier Tag"); Asm->EmitInt8(dwarf::DW_CIE_VERSION); Asm->EOL("CIE Version"); // The personality presence indicates that language specific information will // show up in the eh frame. Find out how we are supposed to lower the // personality function reference: const MCExpr *PersonalityRef = 0; bool IsPersonalityIndirect = false, IsPersonalityPCRel = false; if (PersonalityFn) { // FIXME: HANDLE STATIC CODEGEN MODEL HERE. // In non-static mode, ask the object file how to represent this reference. PersonalityRef = TLOF.getSymbolForDwarfGlobalReference(PersonalityFn, Asm->Mang, Asm->MMI, IsPersonalityIndirect, IsPersonalityPCRel); } unsigned PerEncoding = dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4; if (IsPersonalityIndirect) PerEncoding |= dwarf::DW_EH_PE_indirect; unsigned LSDAEncoding = dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4; unsigned FDEEncoding = dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4; char Augmentation[5] = { 0 }; unsigned AugmentationSize = 0; char *APtr = Augmentation + 1; if (PersonalityRef) { // There is a personality function. *APtr++ = 'P'; AugmentationSize += 1 + SizeOfEncodedValue(PerEncoding); } if (UsesLSDA[Index]) { // An LSDA pointer is in the FDE augmentation. *APtr++ = 'L'; ++AugmentationSize; } if (FDEEncoding != dwarf::DW_EH_PE_absptr) { // A non-default pointer encoding for the FDE. *APtr++ = 'R'; ++AugmentationSize; } if (APtr != Augmentation + 1) Augmentation[0] = 'z'; Asm->EmitString(Augmentation); Asm->EOL("CIE Augmentation"); // Round out reader. Asm->EmitULEB128Bytes(1); Asm->EOL("CIE Code Alignment Factor"); Asm->EmitSLEB128Bytes(stackGrowth); Asm->EOL("CIE Data Alignment Factor"); Asm->EmitInt8(RI->getDwarfRegNum(RI->getRARegister(), true)); Asm->EOL("CIE Return Address Column"); Asm->EmitULEB128Bytes(AugmentationSize); Asm->EOL("Augmentation Size"); Asm->EmitInt8(PerEncoding); Asm->EOL("Personality", PerEncoding); // If there is a personality, we need to indicate the function's location. if (PersonalityRef) { // If the reference to the personality function symbol is not already // pc-relative, then we need to subtract our current address from it. Do // this by emitting a label and subtracting it from the expression we // already have. This is equivalent to emitting "foo - .", but we have to // emit the label for "." directly. if (!IsPersonalityPCRel) { SmallString<64> Name; raw_svector_ostream(Name) << MAI->getPrivateGlobalPrefix() << "personalityref_addr" << Asm->getFunctionNumber() << "_" << Index; MCSymbol *DotSym = Asm->OutContext.GetOrCreateSymbol(Name.str()); Asm->OutStreamer.EmitLabel(DotSym); PersonalityRef = MCBinaryExpr::CreateSub(PersonalityRef, MCSymbolRefExpr::Create(DotSym,Asm->OutContext), Asm->OutContext); } O << MAI->getData32bitsDirective(); PersonalityRef->print(O, MAI); Asm->EOL("Personality"); Asm->EmitInt8(LSDAEncoding); Asm->EOL("LSDA Encoding", LSDAEncoding); Asm->EmitInt8(FDEEncoding); Asm->EOL("FDE Encoding", FDEEncoding); } // Indicate locations of general callee saved registers in frame. std::vector Moves; RI->getInitialFrameState(Moves); EmitFrameMoves(NULL, 0, Moves, true); // On Darwin the linker honors the alignment of eh_frame, which means it must // be 8-byte on 64-bit targets to match what gcc does. Otherwise you get // holes which confuse readers of eh_frame. Asm->EmitAlignment(TD->getPointerSize() == 4 ? 2 : 3, 0, 0, false); EmitLabel("eh_frame_common_end", Index); Asm->EOL(); } /// EmitFDE - Emit the Frame Description Entry (FDE) for the function. void DwarfException::EmitFDE(const FunctionEHFrameInfo &EHFrameInfo) { assert(!EHFrameInfo.function->hasAvailableExternallyLinkage() && "Should not emit 'available externally' functions at all"); const Function *TheFunc = EHFrameInfo.function; Asm->OutStreamer.SwitchSection(Asm->getObjFileLowering().getEHFrameSection()); // Externally visible entry into the functions eh frame info. If the // corresponding function is static, this should not be externally visible. if (!TheFunc->hasLocalLinkage()) if (const char *GlobalEHDirective = MAI->getGlobalEHDirective()) O << GlobalEHDirective << EHFrameInfo.FnName << "\n"; // If corresponding function is weak definition, this should be too. if (TheFunc->isWeakForLinker() && MAI->getWeakDefDirective()) O << MAI->getWeakDefDirective() << EHFrameInfo.FnName << "\n"; // If there are no calls then you can't unwind. This may mean we can omit the // EH Frame, but some environments do not handle weak absolute symbols. If // UnwindTablesMandatory is set we cannot do this optimization; the unwind // info is to be available for non-EH uses. if (!EHFrameInfo.hasCalls && !UnwindTablesMandatory && (!TheFunc->isWeakForLinker() || !MAI->getWeakDefDirective() || MAI->getSupportsWeakOmittedEHFrame())) { O << EHFrameInfo.FnName << " = 0\n"; // This name has no connection to the function, so it might get // dead-stripped when the function is not, erroneously. Prohibit // dead-stripping unconditionally. if (const char *UsedDirective = MAI->getUsedDirective()) O << UsedDirective << EHFrameInfo.FnName << "\n\n"; } else { O << EHFrameInfo.FnName << ":\n"; // EH frame header. EmitDifference("eh_frame_end", EHFrameInfo.Number, "eh_frame_begin", EHFrameInfo.Number, true); Asm->EOL("Length of Frame Information Entry"); EmitLabel("eh_frame_begin", EHFrameInfo.Number); EmitSectionOffset("eh_frame_begin", "eh_frame_common", EHFrameInfo.Number, EHFrameInfo.PersonalityIndex, true, true, false); Asm->EOL("FDE CIE offset"); EmitReference("eh_func_begin", EHFrameInfo.Number, true, true); Asm->EOL("FDE initial location"); EmitDifference("eh_func_end", EHFrameInfo.Number, "eh_func_begin", EHFrameInfo.Number, true); Asm->EOL("FDE address range"); // If there is a personality and landing pads then point to the language // specific data area in the exception table. if (MMI->getPersonalities()[0] != NULL) { bool is4Byte = TD->getPointerSize() == sizeof(int32_t); Asm->EmitULEB128Bytes(is4Byte ? 4 : 8); Asm->EOL("Augmentation size"); if (EHFrameInfo.hasLandingPads) EmitReference("exception", EHFrameInfo.Number, true, false); else { if (is4Byte) Asm->EmitInt32((int)0); else Asm->EmitInt64((int)0); } Asm->EOL("Language Specific Data Area"); } else { Asm->EmitULEB128Bytes(0); Asm->EOL("Augmentation size"); } // Indicate locations of function specific callee saved registers in frame. EmitFrameMoves("eh_func_begin", EHFrameInfo.Number, EHFrameInfo.Moves, true); // On Darwin the linker honors the alignment of eh_frame, which means it // must be 8-byte on 64-bit targets to match what gcc does. Otherwise you // get holes which confuse readers of eh_frame. Asm->EmitAlignment(TD->getPointerSize() == sizeof(int32_t) ? 2 : 3, 0, 0, false); EmitLabel("eh_frame_end", EHFrameInfo.Number); // If the function is marked used, this table should be also. We cannot // make the mark unconditional in this case, since retaining the table also // retains the function in this case, and there is code around that depends // on unused functions (calling undefined externals) being dead-stripped to // link correctly. Yes, there really is. if (MMI->isUsedFunction(EHFrameInfo.function)) if (const char *UsedDirective = MAI->getUsedDirective()) O << UsedDirective << EHFrameInfo.FnName << "\n\n"; } Asm->EOL(); } /// SharedTypeIds - How many leading type ids two landing pads have in common. unsigned DwarfException::SharedTypeIds(const LandingPadInfo *L, const LandingPadInfo *R) { const std::vector &LIds = L->TypeIds, &RIds = R->TypeIds; unsigned LSize = LIds.size(), RSize = RIds.size(); unsigned MinSize = LSize < RSize ? LSize : RSize; unsigned Count = 0; for (; Count != MinSize; ++Count) if (LIds[Count] != RIds[Count]) return Count; return Count; } /// PadLT - Order landing pads lexicographically by type id. bool DwarfException::PadLT(const LandingPadInfo *L, const LandingPadInfo *R) { const std::vector &LIds = L->TypeIds, &RIds = R->TypeIds; unsigned LSize = LIds.size(), RSize = RIds.size(); unsigned MinSize = LSize < RSize ? LSize : RSize; for (unsigned i = 0; i != MinSize; ++i) if (LIds[i] != RIds[i]) return LIds[i] < RIds[i]; return LSize < RSize; } /// ComputeActionsTable - Compute the actions table and gather the first action /// index for each landing pad site. unsigned DwarfException:: ComputeActionsTable(const SmallVectorImpl &LandingPads, SmallVectorImpl &Actions, SmallVectorImpl &FirstActions) { // The action table follows the call-site table in the LSDA. The individual // records are of two types: // // * Catch clause // * Exception specification // // The two record kinds have the same format, with only small differences. // They are distinguished by the "switch value" field: Catch clauses // (TypeInfos) have strictly positive switch values, and exception // specifications (FilterIds) have strictly negative switch values. Value 0 // indicates a catch-all clause. // // Negative type IDs index into FilterIds. Positive type IDs index into // TypeInfos. The value written for a positive type ID is just the type ID // itself. For a negative type ID, however, the value written is the // (negative) byte offset of the corresponding FilterIds entry. The byte // offset is usually equal to the type ID (because the FilterIds entries are // written using a variable width encoding, which outputs one byte per entry // as long as the value written is not too large) but can differ. This kind // of complication does not occur for positive type IDs because type infos are // output using a fixed width encoding. FilterOffsets[i] holds the byte // offset corresponding to FilterIds[i]. const std::vector &FilterIds = MMI->getFilterIds(); SmallVector FilterOffsets; FilterOffsets.reserve(FilterIds.size()); int Offset = -1; for (std::vector::const_iterator I = FilterIds.begin(), E = FilterIds.end(); I != E; ++I) { FilterOffsets.push_back(Offset); Offset -= MCAsmInfo::getULEB128Size(*I); } FirstActions.reserve(LandingPads.size()); int FirstAction = 0; unsigned SizeActions = 0; const LandingPadInfo *PrevLPI = 0; for (SmallVectorImpl::const_iterator I = LandingPads.begin(), E = LandingPads.end(); I != E; ++I) { const LandingPadInfo *LPI = *I; const std::vector &TypeIds = LPI->TypeIds; const unsigned NumShared = PrevLPI ? SharedTypeIds(LPI, PrevLPI) : 0; unsigned SizeSiteActions = 0; if (NumShared < TypeIds.size()) { unsigned SizeAction = 0; ActionEntry *PrevAction = 0; if (NumShared) { const unsigned SizePrevIds = PrevLPI->TypeIds.size(); assert(Actions.size()); PrevAction = &Actions.back(); SizeAction = MCAsmInfo::getSLEB128Size(PrevAction->NextAction) + MCAsmInfo::getSLEB128Size(PrevAction->ValueForTypeID); for (unsigned j = NumShared; j != SizePrevIds; ++j) { SizeAction -= MCAsmInfo::getSLEB128Size(PrevAction->ValueForTypeID); SizeAction += -PrevAction->NextAction; PrevAction = PrevAction->Previous; } } // Compute the actions. for (unsigned J = NumShared, M = TypeIds.size(); J != M; ++J) { int TypeID = TypeIds[J]; assert(-1 - TypeID < (int)FilterOffsets.size() && "Unknown filter id!"); int ValueForTypeID = TypeID < 0 ? FilterOffsets[-1 - TypeID] : TypeID; unsigned SizeTypeID = MCAsmInfo::getSLEB128Size(ValueForTypeID); int NextAction = SizeAction ? -(SizeAction + SizeTypeID) : 0; SizeAction = SizeTypeID + MCAsmInfo::getSLEB128Size(NextAction); SizeSiteActions += SizeAction; ActionEntry Action = { ValueForTypeID, NextAction, PrevAction }; Actions.push_back(Action); PrevAction = &Actions.back(); } // Record the first action of the landing pad site. FirstAction = SizeActions + SizeSiteActions - SizeAction + 1; } // else identical - re-use previous FirstAction // Information used when created the call-site table. The action record // field of the call site record is the offset of the first associated // action record, relative to the start of the actions table. This value is // biased by 1 (1 in dicating the start of the actions table), and 0 // indicates that there are no actions. FirstActions.push_back(FirstAction); // Compute this sites contribution to size. SizeActions += SizeSiteActions; PrevLPI = LPI; } return SizeActions; } /// ComputeCallSiteTable - Compute the call-site table. The entry for an invoke /// has a try-range containing the call, a non-zero landing pad, and an /// appropriate action. The entry for an ordinary call has a try-range /// containing the call and zero for the landing pad and the action. Calls /// marked 'nounwind' have no entry and must not be contained in the try-range /// of any entry - they form gaps in the table. Entries must be ordered by /// try-range address. void DwarfException:: ComputeCallSiteTable(SmallVectorImpl &CallSites, const RangeMapType &PadMap, const SmallVectorImpl &LandingPads, const SmallVectorImpl &FirstActions) { // The end label of the previous invoke or nounwind try-range. unsigned LastLabel = 0; // Whether there is a potentially throwing instruction (currently this means // an ordinary call) between the end of the previous try-range and now. bool SawPotentiallyThrowing = false; // Whether the last CallSite entry was for an invoke. bool PreviousIsInvoke = false; // Visit all instructions in order of address. for (MachineFunction::const_iterator I = MF->begin(), E = MF->end(); I != E; ++I) { for (MachineBasicBlock::const_iterator MI = I->begin(), E = I->end(); MI != E; ++MI) { if (!MI->isLabel()) { SawPotentiallyThrowing |= MI->getDesc().isCall(); continue; } unsigned BeginLabel = MI->getOperand(0).getImm(); assert(BeginLabel && "Invalid label!"); // End of the previous try-range? if (BeginLabel == LastLabel) SawPotentiallyThrowing = false; // Beginning of a new try-range? RangeMapType::iterator L = PadMap.find(BeginLabel); if (L == PadMap.end()) // Nope, it was just some random label. continue; const PadRange &P = L->second; const LandingPadInfo *LandingPad = LandingPads[P.PadIndex]; assert(BeginLabel == LandingPad->BeginLabels[P.RangeIndex] && "Inconsistent landing pad map!"); // For Dwarf exception handling (SjLj handling doesn't use this). If some // instruction between the previous try-range and this one may throw, // create a call-site entry with no landing pad for the region between the // try-ranges. if (SawPotentiallyThrowing && MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf) { CallSiteEntry Site = { LastLabel, BeginLabel, 0, 0 }; CallSites.push_back(Site); PreviousIsInvoke = false; } LastLabel = LandingPad->EndLabels[P.RangeIndex]; assert(BeginLabel && LastLabel && "Invalid landing pad!"); if (LandingPad->LandingPadLabel) { // This try-range is for an invoke. CallSiteEntry Site = { BeginLabel, LastLabel, LandingPad->LandingPadLabel, FirstActions[P.PadIndex] }; // Try to merge with the previous call-site. SJLJ doesn't do this if (PreviousIsInvoke && MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf) { CallSiteEntry &Prev = CallSites.back(); if (Site.PadLabel == Prev.PadLabel && Site.Action == Prev.Action) { // Extend the range of the previous entry. Prev.EndLabel = Site.EndLabel; continue; } } // Otherwise, create a new call-site. CallSites.push_back(Site); PreviousIsInvoke = true; } else { // Create a gap. PreviousIsInvoke = false; } } } // If some instruction between the previous try-range and the end of the // function may throw, create a call-site entry with no landing pad for the // region following the try-range. if (SawPotentiallyThrowing && MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf) { CallSiteEntry Site = { LastLabel, 0, 0, 0 }; CallSites.push_back(Site); } } /// EmitExceptionTable - Emit landing pads and actions. /// /// The general organization of the table is complex, but the basic concepts are /// easy. First there is a header which describes the location and organization /// of the three components that follow. /// /// 1. The landing pad site information describes the range of code covered by /// the try. In our case it's an accumulation of the ranges covered by the /// invokes in the try. There is also a reference to the landing pad that /// handles the exception once processed. Finally an index into the actions /// table. /// 2. The action table, in our case, is composed of pairs of type IDs and next /// action offset. Starting with the action index from the landing pad /// site, each type ID is checked for a match to the current exception. If /// it matches then the exception and type id are passed on to the landing /// pad. Otherwise the next action is looked up. This chain is terminated /// with a next action of zero. If no type id is found then the frame is /// unwound and handling continues. /// 3. Type ID table contains references to all the C++ typeinfo for all /// catches in the function. This tables is reverse indexed base 1. void DwarfException::EmitExceptionTable() { const std::vector &TypeInfos = MMI->getTypeInfos(); const std::vector &FilterIds = MMI->getFilterIds(); const std::vector &PadInfos = MMI->getLandingPads(); if (PadInfos.empty()) return; // Sort the landing pads in order of their type ids. This is used to fold // duplicate actions. SmallVector LandingPads; LandingPads.reserve(PadInfos.size()); for (unsigned i = 0, N = PadInfos.size(); i != N; ++i) LandingPads.push_back(&PadInfos[i]); std::sort(LandingPads.begin(), LandingPads.end(), PadLT); // Compute the actions table and gather the first action index for each // landing pad site. SmallVector Actions; SmallVector FirstActions; unsigned SizeActions = ComputeActionsTable(LandingPads, Actions, FirstActions); // Invokes and nounwind calls have entries in PadMap (due to being bracketed // by try-range labels when lowered). Ordinary calls do not, so appropriate // try-ranges for them need be deduced when using DWARF exception handling. RangeMapType PadMap; for (unsigned i = 0, N = LandingPads.size(); i != N; ++i) { const LandingPadInfo *LandingPad = LandingPads[i]; for (unsigned j = 0, E = LandingPad->BeginLabels.size(); j != E; ++j) { unsigned BeginLabel = LandingPad->BeginLabels[j]; assert(!PadMap.count(BeginLabel) && "Duplicate landing pad labels!"); PadRange P = { i, j }; PadMap[BeginLabel] = P; } } // Compute the call-site table. SmallVector CallSites; ComputeCallSiteTable(CallSites, PadMap, LandingPads, FirstActions); // Final tallies. // Call sites. const unsigned SiteStartSize = SizeOfEncodedValue(dwarf::DW_EH_PE_udata4); const unsigned SiteLengthSize = SizeOfEncodedValue(dwarf::DW_EH_PE_udata4); const unsigned LandingPadSize = SizeOfEncodedValue(dwarf::DW_EH_PE_udata4); bool IsSJLJ = MAI->getExceptionHandlingType() == ExceptionHandling::SjLj; bool HaveTTData = IsSJLJ ? (!TypeInfos.empty() || !FilterIds.empty()) : true; unsigned SizeSites; if (IsSJLJ) SizeSites = 0; else SizeSites = CallSites.size() * (SiteStartSize + SiteLengthSize + LandingPadSize); for (unsigned i = 0, e = CallSites.size(); i < e; ++i) { SizeSites += MCAsmInfo::getULEB128Size(CallSites[i].Action); if (IsSJLJ) SizeSites += MCAsmInfo::getULEB128Size(i); } // Type infos. const MCSection *LSDASection = Asm->getObjFileLowering().getLSDASection(); unsigned TTypeFormat; unsigned TypeFormatSize; if (!HaveTTData) { // For SjLj exceptions, if there is no TypeInfo, then we just explicitly say // that we're omitting that bit. TTypeFormat = dwarf::DW_EH_PE_omit; TypeFormatSize = SizeOfEncodedValue(dwarf::DW_EH_PE_absptr); } else { // Okay, we have actual filters or typeinfos to emit. As such, we need to // pick a type encoding for them. We're about to emit a list of pointers to // typeinfo objects at the end of the LSDA. However, unless we're in static // mode, this reference will require a relocation by the dynamic linker. // // Because of this, we have a couple of options: // // 1) If we are in -static mode, we can always use an absolute reference // from the LSDA, because the static linker will resolve it. // // 2) Otherwise, if the LSDA section is writable, we can output the direct // reference to the typeinfo and allow the dynamic linker to relocate // it. Since it is in a writable section, the dynamic linker won't // have a problem. // // 3) Finally, if we're in PIC mode and the LDSA section isn't writable, // we need to use some form of indirection. For example, on Darwin, // we can output a statically-relocatable reference to a dyld stub. The // offset to the stub is constant, but the contents are in a section // that is updated by the dynamic linker. This is easy enough, but we // need to tell the personality function of the unwinder to indirect // through the dyld stub. // // FIXME: When (3) is actually implemented, we'll have to emit the stubs // somewhere. This predicate should be moved to a shared location that is // in target-independent code. // if (LSDASection->getKind().isWriteable() || Asm->TM.getRelocationModel() == Reloc::Static) TTypeFormat = dwarf::DW_EH_PE_absptr; else TTypeFormat = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4; TypeFormatSize = SizeOfEncodedValue(TTypeFormat); } // Begin the exception table. Asm->OutStreamer.SwitchSection(LSDASection); Asm->EmitAlignment(2, 0, 0, false); O << "GCC_except_table" << SubprogramCount << ":\n"; // The type infos need to be aligned. GCC does this by inserting padding just // before the type infos. However, this changes the size of the exception // table, so you need to take this into account when you output the exception // table size. However, the size is output using a variable length encoding. // So by increasing the size by inserting padding, you may increase the number // of bytes used for writing the size. If it increases, say by one byte, then // you now need to output one less byte of padding to get the type infos // aligned. However this decreases the size of the exception table. This // changes the value you have to output for the exception table size. Due to // the variable length encoding, the number of bytes used for writing the // length may decrease. If so, you then have to increase the amount of // padding. And so on. If you look carefully at the GCC code you will see that // it indeed does this in a loop, going on and on until the values stabilize. // We chose another solution: don't output padding inside the table like GCC // does, instead output it before the table. unsigned SizeTypes = TypeInfos.size() * TypeFormatSize; unsigned TyOffset = sizeof(int8_t) + // Call site format MCAsmInfo::getULEB128Size(SizeSites) + // Call-site table length SizeSites + SizeActions + SizeTypes; unsigned TotalSize = sizeof(int8_t) + // LPStart format sizeof(int8_t) + // TType format (HaveTTData ? MCAsmInfo::getULEB128Size(TyOffset) : 0) + // TType base offset TyOffset; unsigned SizeAlign = (4 - TotalSize) & 3; for (unsigned i = 0; i != SizeAlign; ++i) { Asm->EmitInt8(0); Asm->EOL("Padding"); } EmitLabel("exception", SubprogramCount); if (IsSJLJ) { SmallString<16> LSDAName; raw_svector_ostream(LSDAName) << MAI->getPrivateGlobalPrefix() << "_LSDA_" << Asm->getFunctionNumber(); O << LSDAName.str() << ":\n"; } // Emit the header. Asm->EmitInt8(dwarf::DW_EH_PE_omit); Asm->EOL("@LPStart format", dwarf::DW_EH_PE_omit); Asm->EmitInt8(TTypeFormat); Asm->EOL("@TType format", TTypeFormat); if (HaveTTData) { Asm->EmitULEB128Bytes(TyOffset); Asm->EOL("@TType base offset"); } // SjLj Exception handling if (IsSJLJ) { Asm->EmitInt8(dwarf::DW_EH_PE_udata4); Asm->EOL("Call site format", dwarf::DW_EH_PE_udata4); Asm->EmitULEB128Bytes(SizeSites); Asm->EOL("Call site table length"); // Emit the landing pad site information. unsigned idx = 0; for (SmallVectorImpl::const_iterator I = CallSites.begin(), E = CallSites.end(); I != E; ++I, ++idx) { const CallSiteEntry &S = *I; // Offset of the landing pad, counted in 16-byte bundles relative to the // @LPStart address. Asm->EmitULEB128Bytes(idx); Asm->EOL("Landing pad"); // Offset of the first associated action record, relative to the start of // the action table. This value is biased by 1 (1 indicates the start of // the action table), and 0 indicates that there are no actions. Asm->EmitULEB128Bytes(S.Action); Asm->EOL("Action"); } } else { // DWARF Exception handling assert(MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf); // The call-site table is a list of all call sites that may throw an // exception (including C++ 'throw' statements) in the procedure // fragment. It immediately follows the LSDA header. Each entry indicates, // for a given call, the first corresponding action record and corresponding // landing pad. // // The table begins with the number of bytes, stored as an LEB128 // compressed, unsigned integer. The records immediately follow the record // count. They are sorted in increasing call-site address. Each record // indicates: // // * The position of the call-site. // * The position of the landing pad. // * The first action record for that call site. // // A missing entry in the call-site table indicates that a call is not // supposed to throw. // Emit the landing pad call site table. Asm->EmitInt8(dwarf::DW_EH_PE_udata4); Asm->EOL("Call site format", dwarf::DW_EH_PE_udata4); Asm->EmitULEB128Bytes(SizeSites); Asm->EOL("Call site table size"); for (SmallVectorImpl::const_iterator I = CallSites.begin(), E = CallSites.end(); I != E; ++I) { const CallSiteEntry &S = *I; const char *BeginTag; unsigned BeginNumber; if (!S.BeginLabel) { BeginTag = "eh_func_begin"; BeginNumber = SubprogramCount; } else { BeginTag = "label"; BeginNumber = S.BeginLabel; } // Offset of the call site relative to the previous call site, counted in // number of 16-byte bundles. The first call site is counted relative to // the start of the procedure fragment. EmitSectionOffset(BeginTag, "eh_func_begin", BeginNumber, SubprogramCount, true, true); Asm->EOL("Region start"); if (!S.EndLabel) EmitDifference("eh_func_end", SubprogramCount, BeginTag, BeginNumber, true); else EmitDifference("label", S.EndLabel, BeginTag, BeginNumber, true); Asm->EOL("Region length"); // Offset of the landing pad, counted in 16-byte bundles relative to the // @LPStart address. if (!S.PadLabel) Asm->EmitInt32(0); else EmitSectionOffset("label", "eh_func_begin", S.PadLabel, SubprogramCount, true, true); Asm->EOL("Landing pad"); // Offset of the first associated action record, relative to the start of // the action table. This value is biased by 1 (1 indicates the start of // the action table), and 0 indicates that there are no actions. Asm->EmitULEB128Bytes(S.Action); Asm->EOL("Action"); } } // Emit the Action Table. for (SmallVectorImpl::const_iterator I = Actions.begin(), E = Actions.end(); I != E; ++I) { const ActionEntry &Action = *I; // Type Filter // // Used by the runtime to match the type of the thrown exception to the // type of the catch clauses or the types in the exception specification. Asm->EmitSLEB128Bytes(Action.ValueForTypeID); Asm->EOL("TypeInfo index"); // Action Record // // Self-relative signed displacement in bytes of the next action record, // or 0 if there is no next action record. Asm->EmitSLEB128Bytes(Action.NextAction); Asm->EOL("Next action"); } // Emit the Catch TypeInfos. for (std::vector::const_reverse_iterator I = TypeInfos.rbegin(), E = TypeInfos.rend(); I != E; ++I) { const GlobalVariable *GV = *I; PrintRelDirective(); if (GV) { O << Asm->Mang->getMangledName(GV); } else { O << "0x0"; } Asm->EOL("TypeInfo"); } // Emit the Exception Specifications. for (std::vector::const_iterator I = FilterIds.begin(), E = FilterIds.end(); I < E; ++I) { unsigned TypeID = *I; Asm->EmitULEB128Bytes(TypeID); if (TypeID != 0) Asm->EOL("Exception specification"); else Asm->EOL(); } Asm->EmitAlignment(2, 0, 0, false); } /// EndModule - Emit all exception information that should come after the /// content. void DwarfException::EndModule() { if (MAI->getExceptionHandlingType() != ExceptionHandling::Dwarf) return; if (!shouldEmitMovesModule && !shouldEmitTableModule) return; if (TimePassesIsEnabled) ExceptionTimer->startTimer(); const std::vector Personalities = MMI->getPersonalities(); for (unsigned I = 0, E = Personalities.size(); I < E; ++I) EmitCIE(Personalities[I], I); for (std::vector::iterator I = EHFrames.begin(), E = EHFrames.end(); I != E; ++I) EmitFDE(*I); if (TimePassesIsEnabled) ExceptionTimer->stopTimer(); } /// BeginFunction - Gather pre-function exception information. Assumes it's /// being emitted immediately after the function entry point. void DwarfException::BeginFunction(MachineFunction *MF) { if (!MMI || !MAI->doesSupportExceptionHandling()) return; if (TimePassesIsEnabled) ExceptionTimer->startTimer(); this->MF = MF; shouldEmitTable = shouldEmitMoves = false; // Map all labels and get rid of any dead landing pads. MMI->TidyLandingPads(); // If any landing pads survive, we need an EH table. if (!MMI->getLandingPads().empty()) shouldEmitTable = true; // See if we need frame move info. if (!MF->getFunction()->doesNotThrow() || UnwindTablesMandatory) shouldEmitMoves = true; if (shouldEmitMoves || shouldEmitTable) // Assumes in correct section after the entry point. EmitLabel("eh_func_begin", ++SubprogramCount); shouldEmitTableModule |= shouldEmitTable; shouldEmitMovesModule |= shouldEmitMoves; if (TimePassesIsEnabled) ExceptionTimer->stopTimer(); } /// EndFunction - Gather and emit post-function exception information. /// void DwarfException::EndFunction() { if (!shouldEmitMoves && !shouldEmitTable) return; if (TimePassesIsEnabled) ExceptionTimer->startTimer(); EmitLabel("eh_func_end", SubprogramCount); EmitExceptionTable(); std::string FunctionEHName = Asm->Mang->getMangledName(MF->getFunction(), ".eh", Asm->MAI->is_EHSymbolPrivate()); // Save EH frame information EHFrames.push_back(FunctionEHFrameInfo(FunctionEHName, SubprogramCount, MMI->getPersonalityIndex(), MF->getFrameInfo()->hasCalls(), !MMI->getLandingPads().empty(), MMI->getFrameMoves(), MF->getFunction())); // Record if this personality index uses a landing pad. UsesLSDA[MMI->getPersonalityIndex()] |= !MMI->getLandingPads().empty(); if (TimePassesIsEnabled) ExceptionTimer->stopTimer(); }