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      1 //===-- CodeGen/AsmPrinter/DwarfException.cpp - Dwarf Exception Impl ------===//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 //
     10 // This file contains support for writing DWARF exception info into asm files.
     11 //
     12 //===----------------------------------------------------------------------===//
     13 
     14 #include "DwarfException.h"
     15 #include "llvm/Module.h"
     16 #include "llvm/CodeGen/AsmPrinter.h"
     17 #include "llvm/CodeGen/MachineModuleInfo.h"
     18 #include "llvm/CodeGen/MachineFrameInfo.h"
     19 #include "llvm/CodeGen/MachineFunction.h"
     20 #include "llvm/MC/MachineLocation.h"
     21 #include "llvm/MC/MCAsmInfo.h"
     22 #include "llvm/MC/MCContext.h"
     23 #include "llvm/MC/MCExpr.h"
     24 #include "llvm/MC/MCSection.h"
     25 #include "llvm/MC/MCStreamer.h"
     26 #include "llvm/MC/MCSymbol.h"
     27 #include "llvm/Target/Mangler.h"
     28 #include "llvm/Target/TargetData.h"
     29 #include "llvm/Target/TargetFrameLowering.h"
     30 #include "llvm/Target/TargetLoweringObjectFile.h"
     31 #include "llvm/Target/TargetMachine.h"
     32 #include "llvm/Target/TargetOptions.h"
     33 #include "llvm/Target/TargetRegisterInfo.h"
     34 #include "llvm/Support/Dwarf.h"
     35 #include "llvm/Support/ErrorHandling.h"
     36 #include "llvm/Support/FormattedStream.h"
     37 #include "llvm/ADT/SmallString.h"
     38 #include "llvm/ADT/StringExtras.h"
     39 #include "llvm/ADT/Twine.h"
     40 using namespace llvm;
     41 
     42 DwarfCFIException::DwarfCFIException(AsmPrinter *A)
     43   : DwarfException(A),
     44     shouldEmitPersonality(false), shouldEmitLSDA(false), shouldEmitMoves(false),
     45     moveTypeModule(AsmPrinter::CFI_M_None) {}
     46 
     47 DwarfCFIException::~DwarfCFIException() {}
     48 
     49 /// EndModule - Emit all exception information that should come after the
     50 /// content.
     51 void DwarfCFIException::EndModule() {
     52   if (moveTypeModule == AsmPrinter::CFI_M_Debug)
     53     Asm->OutStreamer.EmitCFISections(false, true);
     54 
     55   if (!Asm->MAI->isExceptionHandlingDwarf())
     56     return;
     57 
     58   const TargetLoweringObjectFile &TLOF = Asm->getObjFileLowering();
     59 
     60   unsigned PerEncoding = TLOF.getPersonalityEncoding();
     61 
     62   if ((PerEncoding & 0x70) != dwarf::DW_EH_PE_pcrel)
     63     return;
     64 
     65   // Emit references to all used personality functions
     66   bool AtLeastOne = false;
     67   const std::vector<const Function*> &Personalities = MMI->getPersonalities();
     68   for (size_t i = 0, e = Personalities.size(); i != e; ++i) {
     69     if (!Personalities[i])
     70       continue;
     71     MCSymbol *Sym = Asm->Mang->getSymbol(Personalities[i]);
     72     TLOF.emitPersonalityValue(Asm->OutStreamer, Asm->TM, Sym);
     73     AtLeastOne = true;
     74   }
     75 
     76   if (AtLeastOne && !TLOF.isFunctionEHFrameSymbolPrivate()) {
     77     // This is a temporary hack to keep sections in the same order they
     78     // were before. This lets us produce bit identical outputs while
     79     // transitioning to CFI.
     80     Asm->OutStreamer.SwitchSection(
     81                const_cast<TargetLoweringObjectFile&>(TLOF).getEHFrameSection());
     82   }
     83 }
     84 
     85 /// BeginFunction - Gather pre-function exception information. Assumes it's
     86 /// being emitted immediately after the function entry point.
     87 void DwarfCFIException::BeginFunction(const MachineFunction *MF) {
     88   shouldEmitMoves = shouldEmitPersonality = shouldEmitLSDA = false;
     89 
     90   // If any landing pads survive, we need an EH table.
     91   bool hasLandingPads = !MMI->getLandingPads().empty();
     92 
     93   // See if we need frame move info.
     94   AsmPrinter::CFIMoveType MoveType = Asm->needsCFIMoves();
     95   if (MoveType == AsmPrinter::CFI_M_EH ||
     96       (MoveType == AsmPrinter::CFI_M_Debug &&
     97        moveTypeModule == AsmPrinter::CFI_M_None))
     98     moveTypeModule = MoveType;
     99 
    100   shouldEmitMoves = MoveType != AsmPrinter::CFI_M_None;
    101 
    102   const TargetLoweringObjectFile &TLOF = Asm->getObjFileLowering();
    103   unsigned PerEncoding = TLOF.getPersonalityEncoding();
    104   const Function *Per = MMI->getPersonalities()[MMI->getPersonalityIndex()];
    105 
    106   shouldEmitPersonality = hasLandingPads &&
    107     PerEncoding != dwarf::DW_EH_PE_omit && Per;
    108 
    109   unsigned LSDAEncoding = TLOF.getLSDAEncoding();
    110   shouldEmitLSDA = shouldEmitPersonality &&
    111     LSDAEncoding != dwarf::DW_EH_PE_omit;
    112 
    113   if (!shouldEmitPersonality && !shouldEmitMoves)
    114     return;
    115 
    116   Asm->OutStreamer.EmitCFIStartProc();
    117 
    118   // Indicate personality routine, if any.
    119   if (!shouldEmitPersonality)
    120     return;
    121 
    122   const MCSymbol *Sym = TLOF.getCFIPersonalitySymbol(Per, Asm->Mang, MMI);
    123   Asm->OutStreamer.EmitCFIPersonality(Sym, PerEncoding);
    124 
    125   Asm->OutStreamer.EmitLabel(Asm->GetTempSymbol("eh_func_begin",
    126                                                 Asm->getFunctionNumber()));
    127 
    128   // Provide LSDA information.
    129   if (!shouldEmitLSDA)
    130     return;
    131 
    132   Asm->OutStreamer.EmitCFILsda(Asm->GetTempSymbol("exception",
    133                                                   Asm->getFunctionNumber()),
    134                                LSDAEncoding);
    135 }
    136 
    137 /// EndFunction - Gather and emit post-function exception information.
    138 ///
    139 void DwarfCFIException::EndFunction() {
    140   if (!shouldEmitPersonality && !shouldEmitMoves)
    141     return;
    142 
    143   Asm->OutStreamer.EmitCFIEndProc();
    144 
    145   Asm->OutStreamer.EmitLabel(Asm->GetTempSymbol("eh_func_end",
    146                                                 Asm->getFunctionNumber()));
    147 
    148   // Map all labels and get rid of any dead landing pads.
    149   MMI->TidyLandingPads();
    150 
    151   if (shouldEmitPersonality)
    152     EmitExceptionTable();
    153 }
    154