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      1 //===-- llvm/lib/CodeGen/AsmPrinter/WinCodeViewLineTables.cpp --*- C++ -*--===//
      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 line tables info into COFF files.
     11 //
     12 //===----------------------------------------------------------------------===//
     13 
     14 #include "WinCodeViewLineTables.h"
     15 #include "llvm/MC/MCExpr.h"
     16 #include "llvm/MC/MCSymbol.h"
     17 #include "llvm/Support/COFF.h"
     18 
     19 namespace llvm {
     20 
     21 StringRef WinCodeViewLineTables::getFullFilepath(const MDNode *S) {
     22   assert(S);
     23   DIDescriptor D(S);
     24   assert((D.isCompileUnit() || D.isFile() || D.isSubprogram() ||
     25           D.isLexicalBlockFile() || D.isLexicalBlock()) &&
     26          "Unexpected scope info");
     27 
     28   DIScope Scope(S);
     29   StringRef Dir = Scope.getDirectory(),
     30             Filename = Scope.getFilename();
     31   char *&Result = DirAndFilenameToFilepathMap[std::make_pair(Dir, Filename)];
     32   if (Result)
     33     return Result;
     34 
     35   // Clang emits directory and relative filename info into the IR, but CodeView
     36   // operates on full paths.  We could change Clang to emit full paths too, but
     37   // that would increase the IR size and probably not needed for other users.
     38   // For now, just concatenate and canonicalize the path here.
     39   std::string Filepath;
     40   if (Filename.find(':') == 1)
     41     Filepath = Filename;
     42   else
     43     Filepath = (Dir + Twine("\\") + Filename).str();
     44 
     45   // Canonicalize the path.  We have to do it textually because we may no longer
     46   // have access the file in the filesystem.
     47   // First, replace all slashes with backslashes.
     48   std::replace(Filepath.begin(), Filepath.end(), '/', '\\');
     49 
     50   // Remove all "\.\" with "\".
     51   size_t Cursor = 0;
     52   while ((Cursor = Filepath.find("\\.\\", Cursor)) != std::string::npos)
     53     Filepath.erase(Cursor, 2);
     54 
     55   // Replace all "\XXX\..\" with "\".  Don't try too hard though as the original
     56   // path should be well-formatted, e.g. start with a drive letter, etc.
     57   Cursor = 0;
     58   while ((Cursor = Filepath.find("\\..\\", Cursor)) != std::string::npos) {
     59     // Something's wrong if the path starts with "\..\", abort.
     60     if (Cursor == 0)
     61       break;
     62 
     63     size_t PrevSlash = Filepath.rfind('\\', Cursor - 1);
     64     if (PrevSlash == std::string::npos)
     65       // Something's wrong, abort.
     66       break;
     67 
     68     Filepath.erase(PrevSlash, Cursor + 3 - PrevSlash);
     69     // The next ".." might be following the one we've just erased.
     70     Cursor = PrevSlash;
     71   }
     72 
     73   // Remove all duplicate backslashes.
     74   Cursor = 0;
     75   while ((Cursor = Filepath.find("\\\\", Cursor)) != std::string::npos)
     76     Filepath.erase(Cursor, 1);
     77 
     78   Result = strdup(Filepath.c_str());
     79   return StringRef(Result);
     80 }
     81 
     82 void WinCodeViewLineTables::maybeRecordLocation(DebugLoc DL,
     83                                                 const MachineFunction *MF) {
     84   const MDNode *Scope = DL.getScope(MF->getFunction()->getContext());
     85   if (!Scope)
     86     return;
     87   StringRef Filename = getFullFilepath(Scope);
     88 
     89   // Skip this instruction if it has the same file:line as the previous one.
     90   assert(CurFn);
     91   if (!CurFn->Instrs.empty()) {
     92     const InstrInfoTy &LastInstr = InstrInfo[CurFn->Instrs.back()];
     93     if (LastInstr.Filename == Filename && LastInstr.LineNumber == DL.getLine())
     94       return;
     95   }
     96   FileNameRegistry.add(Filename);
     97 
     98   MCSymbol *MCL = Asm->MMI->getContext().CreateTempSymbol();
     99   Asm->OutStreamer.EmitLabel(MCL);
    100   CurFn->Instrs.push_back(MCL);
    101   InstrInfo[MCL] = InstrInfoTy(Filename, DL.getLine());
    102 }
    103 
    104 WinCodeViewLineTables::WinCodeViewLineTables(AsmPrinter *AP)
    105     : Asm(nullptr), CurFn(nullptr) {
    106   MachineModuleInfo *MMI = AP->MMI;
    107 
    108   // If module doesn't have named metadata anchors or COFF debug section
    109   // is not available, skip any debug info related stuff.
    110   if (!MMI->getModule()->getNamedMetadata("llvm.dbg.cu") ||
    111       !AP->getObjFileLowering().getCOFFDebugSymbolsSection())
    112     return;
    113 
    114   // Tell MMI that we have debug info.
    115   MMI->setDebugInfoAvailability(true);
    116   Asm = AP;
    117 }
    118 
    119 static void EmitLabelDiff(MCStreamer &Streamer,
    120                           const MCSymbol *From, const MCSymbol *To) {
    121   MCSymbolRefExpr::VariantKind Variant = MCSymbolRefExpr::VK_None;
    122   MCContext &Context = Streamer.getContext();
    123   const MCExpr *FromRef = MCSymbolRefExpr::Create(From, Variant, Context),
    124                *ToRef   = MCSymbolRefExpr::Create(To, Variant, Context);
    125   const MCExpr *AddrDelta =
    126       MCBinaryExpr::Create(MCBinaryExpr::Sub, ToRef, FromRef, Context);
    127   Streamer.EmitValue(AddrDelta, 4);
    128 }
    129 
    130 void WinCodeViewLineTables::emitDebugInfoForFunction(const Function *GV) {
    131   // For each function there is a separate subsection
    132   // which holds the PC to file:line table.
    133   const MCSymbol *Fn = Asm->getSymbol(GV);
    134   assert(Fn);
    135 
    136   const FunctionInfo &FI = FnDebugInfo[GV];
    137   if (FI.Instrs.empty())
    138     return;
    139   assert(FI.End && "Don't know where the function ends?");
    140 
    141   // PCs/Instructions are grouped into segments sharing the same filename.
    142   // Pre-calculate the lengths (in instructions) of these segments and store
    143   // them in a map for convenience.  Each index in the map is the sequential
    144   // number of the respective instruction that starts a new segment.
    145   DenseMap<size_t, size_t> FilenameSegmentLengths;
    146   size_t LastSegmentEnd = 0;
    147   StringRef PrevFilename = InstrInfo[FI.Instrs[0]].Filename;
    148   for (size_t J = 1, F = FI.Instrs.size(); J != F; ++J) {
    149     if (PrevFilename == InstrInfo[FI.Instrs[J]].Filename)
    150       continue;
    151     FilenameSegmentLengths[LastSegmentEnd] = J - LastSegmentEnd;
    152     LastSegmentEnd = J;
    153     PrevFilename = InstrInfo[FI.Instrs[J]].Filename;
    154   }
    155   FilenameSegmentLengths[LastSegmentEnd] = FI.Instrs.size() - LastSegmentEnd;
    156 
    157   // Emit the control code of the subsection followed by the payload size.
    158   Asm->OutStreamer.AddComment(
    159       "Linetable subsection for " + Twine(Fn->getName()));
    160   Asm->EmitInt32(COFF::DEBUG_LINE_TABLE_SUBSECTION);
    161   MCSymbol *SubsectionBegin = Asm->MMI->getContext().CreateTempSymbol(),
    162            *SubsectionEnd = Asm->MMI->getContext().CreateTempSymbol();
    163   EmitLabelDiff(Asm->OutStreamer, SubsectionBegin, SubsectionEnd);
    164   Asm->OutStreamer.EmitLabel(SubsectionBegin);
    165 
    166   // Identify the function this subsection is for.
    167   Asm->OutStreamer.EmitCOFFSecRel32(Fn);
    168   Asm->OutStreamer.EmitCOFFSectionIndex(Fn);
    169 
    170   // Length of the function's code, in bytes.
    171   EmitLabelDiff(Asm->OutStreamer, Fn, FI.End);
    172 
    173   // PC-to-linenumber lookup table:
    174   MCSymbol *FileSegmentEnd = nullptr;
    175   for (size_t J = 0, F = FI.Instrs.size(); J != F; ++J) {
    176     MCSymbol *Instr = FI.Instrs[J];
    177     assert(InstrInfo.count(Instr));
    178 
    179     if (FilenameSegmentLengths.count(J)) {
    180       // We came to a beginning of a new filename segment.
    181       if (FileSegmentEnd)
    182         Asm->OutStreamer.EmitLabel(FileSegmentEnd);
    183       StringRef CurFilename = InstrInfo[FI.Instrs[J]].Filename;
    184       assert(FileNameRegistry.Infos.count(CurFilename));
    185       size_t IndexInStringTable =
    186           FileNameRegistry.Infos[CurFilename].FilenameID;
    187       // Each segment starts with the offset of the filename
    188       // in the string table.
    189       Asm->OutStreamer.AddComment(
    190           "Segment for file '" + Twine(CurFilename) + "' begins");
    191       MCSymbol *FileSegmentBegin = Asm->MMI->getContext().CreateTempSymbol();
    192       Asm->OutStreamer.EmitLabel(FileSegmentBegin);
    193       Asm->EmitInt32(8 * IndexInStringTable);
    194 
    195       // Number of PC records in the lookup table.
    196       size_t SegmentLength = FilenameSegmentLengths[J];
    197       Asm->EmitInt32(SegmentLength);
    198 
    199       // Full size of the segment for this filename, including the prev two
    200       // records.
    201       FileSegmentEnd = Asm->MMI->getContext().CreateTempSymbol();
    202       EmitLabelDiff(Asm->OutStreamer, FileSegmentBegin, FileSegmentEnd);
    203     }
    204 
    205     // The first PC with the given linenumber and the linenumber itself.
    206     EmitLabelDiff(Asm->OutStreamer, Fn, Instr);
    207     Asm->EmitInt32(InstrInfo[Instr].LineNumber);
    208   }
    209 
    210   if (FileSegmentEnd)
    211     Asm->OutStreamer.EmitLabel(FileSegmentEnd);
    212   Asm->OutStreamer.EmitLabel(SubsectionEnd);
    213 }
    214 
    215 void WinCodeViewLineTables::endModule() {
    216   if (FnDebugInfo.empty())
    217     return;
    218 
    219   assert(Asm != nullptr);
    220   Asm->OutStreamer.SwitchSection(
    221       Asm->getObjFileLowering().getCOFFDebugSymbolsSection());
    222   Asm->EmitInt32(COFF::DEBUG_SECTION_MAGIC);
    223 
    224   // The COFF .debug$S section consists of several subsections, each starting
    225   // with a 4-byte control code (e.g. 0xF1, 0xF2, etc) and then a 4-byte length
    226   // of the payload followed by the payload itself.  The subsections are 4-byte
    227   // aligned.
    228 
    229   for (size_t I = 0, E = VisitedFunctions.size(); I != E; ++I)
    230     emitDebugInfoForFunction(VisitedFunctions[I]);
    231 
    232   // This subsection holds a file index to offset in string table table.
    233   Asm->OutStreamer.AddComment("File index to string table offset subsection");
    234   Asm->EmitInt32(COFF::DEBUG_INDEX_SUBSECTION);
    235   size_t NumFilenames = FileNameRegistry.Infos.size();
    236   Asm->EmitInt32(8 * NumFilenames);
    237   for (size_t I = 0, E = FileNameRegistry.Filenames.size(); I != E; ++I) {
    238     StringRef Filename = FileNameRegistry.Filenames[I];
    239     // For each unique filename, just write it's offset in the string table.
    240     Asm->EmitInt32(FileNameRegistry.Infos[Filename].StartOffset);
    241     // The function name offset is not followed by any additional data.
    242     Asm->EmitInt32(0);
    243   }
    244 
    245   // This subsection holds the string table.
    246   Asm->OutStreamer.AddComment("String table");
    247   Asm->EmitInt32(COFF::DEBUG_STRING_TABLE_SUBSECTION);
    248   Asm->EmitInt32(FileNameRegistry.LastOffset);
    249   // The payload starts with a null character.
    250   Asm->EmitInt8(0);
    251 
    252   for (size_t I = 0, E = FileNameRegistry.Filenames.size(); I != E; ++I) {
    253     // Just emit unique filenames one by one, separated by a null character.
    254     Asm->OutStreamer.EmitBytes(FileNameRegistry.Filenames[I]);
    255     Asm->EmitInt8(0);
    256   }
    257 
    258   // No more subsections. Fill with zeros to align the end of the section by 4.
    259   Asm->OutStreamer.EmitFill((-FileNameRegistry.LastOffset) % 4, 0);
    260 
    261   clear();
    262 }
    263 
    264 void WinCodeViewLineTables::beginFunction(const MachineFunction *MF) {
    265   assert(!CurFn && "Can't process two functions at once!");
    266 
    267   if (!Asm || !Asm->MMI->hasDebugInfo())
    268     return;
    269 
    270   const Function *GV = MF->getFunction();
    271   assert(FnDebugInfo.count(GV) == false);
    272   VisitedFunctions.push_back(GV);
    273   CurFn = &FnDebugInfo[GV];
    274 
    275   // Find the end of the function prolog.
    276   // FIXME: is there a simpler a way to do this? Can we just search
    277   // for the first instruction of the function, not the last of the prolog?
    278   DebugLoc PrologEndLoc;
    279   bool EmptyPrologue = true;
    280   for (const auto &MBB : *MF) {
    281     if (!PrologEndLoc.isUnknown())
    282       break;
    283     for (const auto &MI : MBB) {
    284       if (MI.isDebugValue())
    285         continue;
    286 
    287       // First known non-DBG_VALUE and non-frame setup location marks
    288       // the beginning of the function body.
    289       // FIXME: do we need the first subcondition?
    290       if (!MI.getFlag(MachineInstr::FrameSetup) &&
    291           (!MI.getDebugLoc().isUnknown())) {
    292         PrologEndLoc = MI.getDebugLoc();
    293         break;
    294       }
    295       EmptyPrologue = false;
    296     }
    297   }
    298   // Record beginning of function if we have a non-empty prologue.
    299   if (!PrologEndLoc.isUnknown() && !EmptyPrologue) {
    300     DebugLoc FnStartDL =
    301         PrologEndLoc.getFnDebugLoc(MF->getFunction()->getContext());
    302     maybeRecordLocation(FnStartDL, MF);
    303   }
    304 }
    305 
    306 void WinCodeViewLineTables::endFunction(const MachineFunction *MF) {
    307   if (!Asm || !CurFn)  // We haven't created any debug info for this function.
    308     return;
    309 
    310   const Function *GV = MF->getFunction();
    311   assert(FnDebugInfo.count(GV));
    312   assert(CurFn == &FnDebugInfo[GV]);
    313 
    314   if (CurFn->Instrs.empty()) {
    315     FnDebugInfo.erase(GV);
    316     VisitedFunctions.pop_back();
    317   } else {
    318     // Define end label for subprogram.
    319     MCSymbol *FunctionEndSym = Asm->OutStreamer.getContext().CreateTempSymbol();
    320     Asm->OutStreamer.EmitLabel(FunctionEndSym);
    321     CurFn->End = FunctionEndSym;
    322   }
    323   CurFn = nullptr;
    324 }
    325 
    326 void WinCodeViewLineTables::beginInstruction(const MachineInstr *MI) {
    327   // Ignore DBG_VALUE locations and function prologue.
    328   if (!Asm || MI->isDebugValue() || MI->getFlag(MachineInstr::FrameSetup))
    329     return;
    330   DebugLoc DL = MI->getDebugLoc();
    331   if (DL == PrevInstLoc || DL.isUnknown())
    332     return;
    333   maybeRecordLocation(DL, Asm->MF);
    334 }
    335 }
    336