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Diffstat (limited to 'lib/CodeGen/AsmPrinter/DwarfException.cpp')
| -rw-r--r-- | lib/CodeGen/AsmPrinter/DwarfException.cpp | 1021 |
1 files changed, 1021 insertions, 0 deletions
diff --git a/lib/CodeGen/AsmPrinter/DwarfException.cpp b/lib/CodeGen/AsmPrinter/DwarfException.cpp new file mode 100644 index 0000000..b6801dc --- /dev/null +++ b/lib/CodeGen/AsmPrinter/DwarfException.cpp @@ -0,0 +1,1021 @@ +//===-- 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/MC/MCSymbol.h" +#include "llvm/Target/Mangler.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/FormattedStream.h" +#include "llvm/Support/Timer.h" +#include "llvm/ADT/SmallString.h" +#include "llvm/ADT/StringExtras.h" +#include "llvm/ADT/Twine.h" +using namespace llvm; + +DwarfException::DwarfException(raw_ostream &OS, AsmPrinter *A, + const MCAsmInfo *T) + : DwarfPrinter(OS, A, T, "eh"), shouldEmitTable(false),shouldEmitMoves(false), + shouldEmitTableModule(false), shouldEmitMovesModule(false), + ExceptionTimer(0) { + if (TimePassesIsEnabled) + ExceptionTimer = new Timer("DWARF Exception Writer"); +} + +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; +} + +/// CreateLabelDiff - Emit a label and subtract it from the expression we +/// already have. This is equivalent to emitting "foo - .", but we have to emit +/// the label for "." directly. +const MCExpr *DwarfException::CreateLabelDiff(const MCExpr *ExprRef, + const char *LabelName, + unsigned Index) { + SmallString<64> Name; + raw_svector_ostream(Name) << MAI->getPrivateGlobalPrefix() + << LabelName << Asm->getFunctionNumber() + << "_" << Index; + MCSymbol *DotSym = Asm->OutContext.GetOrCreateSymbol(Name.str()); + Asm->OutStreamer.EmitLabel(DotSym); + + return MCBinaryExpr::CreateSub(ExprRef, + MCSymbolRefExpr::Create(DotSym, + Asm->OutContext), + Asm->OutContext); +} + +/// 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); + EOL("Length of Common Information Entry"); + + // EH frame header. + EmitLabel("eh_frame_common_begin", Index); + if (Asm->VerboseAsm) Asm->OutStreamer.AddComment("CIE Identifier Tag"); + Asm->OutStreamer.EmitIntValue(0, 4/*size*/, 0/*addrspace*/); + if (Asm->VerboseAsm) Asm->OutStreamer.AddComment("DW_CIE_VERSION"); + Asm->OutStreamer.EmitIntValue(dwarf::DW_CIE_VERSION, 1/*size*/, 0/*addr*/); + + // 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[6] = { 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->OutStreamer.EmitBytes(StringRef(Augmentation, strlen(Augmentation)+1),0); + EOL("CIE Augmentation"); + + // Round out reader. + EmitULEB128(1, "CIE Code Alignment Factor"); + EmitSLEB128(stackGrowth, "CIE Data Alignment Factor"); + Asm->EmitInt8(RI->getDwarfRegNum(RI->getRARegister(), true)); + EOL("CIE Return Address Column"); + + EmitULEB128(AugmentationSize, "Augmentation Size"); + EmitEncodingByte(PerEncoding, "Personality"); + + // If there is a personality, we need to indicate the function's location. + if (PersonalityRef) { + if (!IsPersonalityPCRel) + PersonalityRef = CreateLabelDiff(PersonalityRef, "personalityref_addr", + Index); + + O << MAI->getData32bitsDirective() << *PersonalityRef; + EOL("Personality"); + + EmitEncodingByte(LSDAEncoding, "LSDA"); + EmitEncodingByte(FDEEncoding, "FDE"); + } + + // Indicate locations of general callee saved registers in frame. + std::vector<MachineMove> 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->O << '\n'; +} + +/// 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.FunctionEHSym << '\n'; + + // If corresponding function is weak definition, this should be too. + if (TheFunc->isWeakForLinker() && MAI->getWeakDefDirective()) + O << MAI->getWeakDefDirective() << *EHFrameInfo.FunctionEHSym << '\n'; + + // If corresponding function is hidden, this should be too. + if (TheFunc->hasHiddenVisibility()) + if (MCSymbolAttr HiddenAttr = MAI->getHiddenVisibilityAttr()) + Asm->OutStreamer.EmitSymbolAttribute(EHFrameInfo.FunctionEHSym, + HiddenAttr); + + // 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.FunctionEHSym << " = 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 (MAI->hasNoDeadStrip()) + Asm->OutStreamer.EmitSymbolAttribute(EHFrameInfo.FunctionEHSym, + MCSA_NoDeadStrip); + } else { + O << *EHFrameInfo.FunctionEHSym << ":\n"; + + // EH frame header. + EmitDifference("eh_frame_end", EHFrameInfo.Number, + "eh_frame_begin", EHFrameInfo.Number, true); + 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); + + EOL("FDE CIE offset"); + + EmitReference("eh_func_begin", EHFrameInfo.Number, true, true); + EOL("FDE initial location"); + EmitDifference("eh_func_end", EHFrameInfo.Number, + "eh_func_begin", EHFrameInfo.Number, true); + 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) { + + if (Asm->TM.getLSDAEncoding() != DwarfLSDAEncoding::EightByte) { + EmitULEB128(4, "Augmentation size"); + + if (EHFrameInfo.hasLandingPads) + EmitReference("exception", EHFrameInfo.Number, true, true); + else + Asm->OutStreamer.EmitIntValue(0, 4/*size*/, 0/*addrspace*/); + } else { + EmitULEB128(TD->getPointerSize(), "Augmentation size"); + + if (EHFrameInfo.hasLandingPads) { + EmitReference("exception", EHFrameInfo.Number, true, false); + } else { + Asm->OutStreamer.EmitIntValue(0, TD->getPointerSize(), + 0/*addrspace*/); + } + } + + EOL("Language Specific Data Area"); + } else { + EmitULEB128(0, "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 (MAI->hasNoDeadStrip()) + Asm->OutStreamer.EmitSymbolAttribute(EHFrameInfo.FunctionEHSym, + MCSA_NoDeadStrip); + } + Asm->O << '\n'; +} + +/// SharedTypeIds - How many leading type ids two landing pads have in common. +unsigned DwarfException::SharedTypeIds(const LandingPadInfo *L, + const LandingPadInfo *R) { + const std::vector<int> &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<int> &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<const LandingPadInfo*> &LandingPads, + SmallVectorImpl<ActionEntry> &Actions, + SmallVectorImpl<unsigned> &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<unsigned> &FilterIds = MMI->getFilterIds(); + SmallVector<int, 16> FilterOffsets; + FilterOffsets.reserve(FilterIds.size()); + int Offset = -1; + + for (std::vector<unsigned>::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 LandingPadInfo *>::const_iterator + I = LandingPads.begin(), E = LandingPads.end(); I != E; ++I) { + const LandingPadInfo *LPI = *I; + const std::vector<int> &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; +} + +/// CallToNoUnwindFunction - Return `true' if this is a call to a function +/// marked `nounwind'. Return `false' otherwise. +bool DwarfException::CallToNoUnwindFunction(const MachineInstr *MI) { + assert(MI->getDesc().isCall() && "This should be a call instruction!"); + + bool MarkedNoUnwind = false; + bool SawFunc = false; + + for (unsigned I = 0, E = MI->getNumOperands(); I != E; ++I) { + const MachineOperand &MO = MI->getOperand(I); + + if (MO.isGlobal()) { + if (Function *F = dyn_cast<Function>(MO.getGlobal())) { + if (SawFunc) { + // Be conservative. If we have more than one function operand for this + // call, then we can't make the assumption that it's the callee and + // not a parameter to the call. + // + // FIXME: Determine if there's a way to say that `F' is the callee or + // parameter. + MarkedNoUnwind = false; + break; + } + + MarkedNoUnwind = F->doesNotThrow(); + SawFunc = true; + } + } + } + + return MarkedNoUnwind; +} + +/// 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<CallSiteEntry> &CallSites, + const RangeMapType &PadMap, + const SmallVectorImpl<const LandingPadInfo *> &LandingPads, + const SmallVectorImpl<unsigned> &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()) { + if (MI->getDesc().isCall()) + SawPotentiallyThrowing |= !CallToNoUnwindFunction(MI); + + 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::const_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. + if (MAI->getExceptionHandlingType() == ExceptionHandling::Dwarf) + CallSites.push_back(Site); + else { + // SjLj EH must maintain the call sites in the order assigned + // to them by the SjLjPrepare pass. + unsigned SiteNo = MMI->getCallSiteBeginLabel(BeginLabel); + if (CallSites.size() < SiteNo) + CallSites.resize(SiteNo); + CallSites[SiteNo - 1] = 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<GlobalVariable *> &TypeInfos = MMI->getTypeInfos(); + const std::vector<unsigned> &FilterIds = MMI->getFilterIds(); + const std::vector<LandingPadInfo> &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<const LandingPadInfo *, 64> 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<ActionEntry, 32> Actions; + SmallVector<unsigned, 64> 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<CallSiteEntry, 64> 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); + 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. + EmitEncodingByte(dwarf::DW_EH_PE_omit, "@LPStart"); + EmitEncodingByte(TTypeFormat, "@TType"); + + if (HaveTTData) + EmitULEB128(TyOffset, "@TType base offset"); + + // SjLj Exception handling + if (IsSJLJ) { + EmitEncodingByte(dwarf::DW_EH_PE_udata4, "Call site"); + EmitULEB128(SizeSites, "Call site table length"); + + // Emit the landing pad site information. + unsigned idx = 0; + for (SmallVectorImpl<CallSiteEntry>::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. + EmitULEB128(idx, "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. + EmitULEB128(S.Action, "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. + EmitEncodingByte(dwarf::DW_EH_PE_udata4, "Call site"); + EmitULEB128(SizeSites, "Call site table length"); + + for (SmallVectorImpl<CallSiteEntry>::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); + EOL("Region start"); + + if (!S.EndLabel) + EmitDifference("eh_func_end", SubprogramCount, BeginTag, BeginNumber, + true); + else + EmitDifference("label", S.EndLabel, BeginTag, BeginNumber, true); + + EOL("Region length"); + + // Offset of the landing pad, counted in 16-byte bundles relative to the + // @LPStart address. + if (!S.PadLabel) { + Asm->OutStreamer.AddComment("Landing pad"); + Asm->OutStreamer.EmitIntValue(0, 4/*size*/, 0/*addrspace*/); + } else { + EmitSectionOffset("label", "eh_func_begin", S.PadLabel, SubprogramCount, + true, true); + 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. + EmitULEB128(S.Action, "Action"); + } + } + + // Emit the Action Table. + if (Actions.size() != 0) EOL("-- Action Record Table --"); + for (SmallVectorImpl<ActionEntry>::const_iterator + I = Actions.begin(), E = Actions.end(); I != E; ++I) { + const ActionEntry &Action = *I; + EOL("Action Record:"); + + // 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. + EmitSLEB128(Action.ValueForTypeID, " TypeInfo index"); + + // Action Record + // + // Self-relative signed displacement in bytes of the next action record, + // or 0 if there is no next action record. + EmitSLEB128(Action.NextAction, " Next action"); + } + + // Emit the Catch TypeInfos. + if (TypeInfos.size() != 0) EOL("-- Catch TypeInfos --"); + for (std::vector<GlobalVariable *>::const_reverse_iterator + I = TypeInfos.rbegin(), E = TypeInfos.rend(); I != E; ++I) { + const GlobalVariable *GV = *I; + PrintRelDirective(); + + if (GV) { + O << *Asm->GetGlobalValueSymbol(GV); + EOL("TypeInfo"); + } else { + O << "0x0"; + EOL(""); + } + } + + // Emit the Exception Specifications. + if (FilterIds.size() != 0) EOL("-- Filter IDs --"); + for (std::vector<unsigned>::const_iterator + I = FilterIds.begin(), E = FilterIds.end(); I < E; ++I) { + unsigned TypeID = *I; + EmitULEB128(TypeID, TypeID != 0 ? "Exception specification" : 0); + } + + 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<Function *> Personalities = MMI->getPersonalities(); + + for (unsigned I = 0, E = Personalities.size(); I < E; ++I) + EmitCIE(Personalities[I], I); + + for (std::vector<FunctionEHFrameInfo>::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(const 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(); + + MCSymbol *FunctionEHSym = + Asm->GetSymbolWithGlobalValueBase(MF->getFunction(), ".eh", + Asm->MAI->is_EHSymbolPrivate()); + + // Save EH frame information + EHFrames.push_back(FunctionEHFrameInfo(FunctionEHSym, 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(); +} |