llvm-project/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp

//===-- llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp --*- C++ -*--===//
//
//                     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 Microsoft CodeView debug info.
//
//===----------------------------------------------------------------------===//

#include "CodeViewDebug.h"
#include "llvm/DebugInfo/CodeView/CodeView.h"
#include "llvm/DebugInfo/CodeView/Line.h"
#include "llvm/DebugInfo/CodeView/SymbolRecord.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCSymbol.h"
#include "llvm/Support/COFF.h"

using namespace llvm::codeview;

namespace llvm {

StringRef CodeViewDebug::getFullFilepath(const DIFile *File) {
  std::string &Filepath = FileToFilepathMap[File];
  if (!Filepath.empty())
    return Filepath;

  StringRef Dir = File->getDirectory(), Filename = File->getFilename();

  // Clang emits directory and relative filename info into the IR, but CodeView
  // operates on full paths.  We could change Clang to emit full paths too, but
  // that would increase the IR size and probably not needed for other users.
  // For now, just concatenate and canonicalize the path here.
  if (Filename.find(':') == 1)
    Filepath = Filename;
  else
    Filepath = (Dir + "\\" + Filename).str();

  // Canonicalize the path.  We have to do it textually because we may no longer
  // have access the file in the filesystem.
  // First, replace all slashes with backslashes.
  std::replace(Filepath.begin(), Filepath.end(), '/', '\\');

  // Remove all "\.\" with "\".
  size_t Cursor = 0;
  while ((Cursor = Filepath.find("\\.\\", Cursor)) != std::string::npos)
    Filepath.erase(Cursor, 2);

  // Replace all "\XXX\..\" with "\".  Don't try too hard though as the original
  // path should be well-formatted, e.g. start with a drive letter, etc.
  Cursor = 0;
  while ((Cursor = Filepath.find("\\..\\", Cursor)) != std::string::npos) {
    // Something's wrong if the path starts with "\..\", abort.
    if (Cursor == 0)
      break;

    size_t PrevSlash = Filepath.rfind('\\', Cursor - 1);
    if (PrevSlash == std::string::npos)
      // Something's wrong, abort.
      break;

    Filepath.erase(PrevSlash, Cursor + 3 - PrevSlash);
    // The next ".." might be following the one we've just erased.
    Cursor = PrevSlash;
  }

  // Remove all duplicate backslashes.
  Cursor = 0;
  while ((Cursor = Filepath.find("\\\\", Cursor)) != std::string::npos)
    Filepath.erase(Cursor, 1);

  return Filepath;
}

unsigned CodeViewDebug::maybeRecordFile(const DIFile *F) {
  unsigned NextId = FileIdMap.size() + 1;
  auto Insertion = FileIdMap.insert(std::make_pair(F, NextId));
  if (Insertion.second) {
    // We have to compute the full filepath and emit a .cv_file directive.
    StringRef FullPath = getFullFilepath(F);
    NextId = Asm->OutStreamer->EmitCVFileDirective(NextId, FullPath);
    assert(NextId == FileIdMap.size() && ".cv_file directive failed");
  }
  return Insertion.first->second;
}

void CodeViewDebug::maybeRecordLocation(DebugLoc DL,
                                        const MachineFunction *MF) {
  // Skip this instruction if it has the same location as the previous one.
  if (DL == CurFn->LastLoc)
    return;

  const DIScope *Scope = DL.get()->getScope();
  if (!Scope)
    return;

  // Skip this line if it is longer than the maximum we can record.
  LineInfo LI(DL.getLine(), DL.getLine(), /*IsStatement=*/true);
  if (LI.getStartLine() != DL.getLine() || LI.isAlwaysStepInto() ||
      LI.isNeverStepInto())
    return;

  ColumnInfo CI(DL.getCol(), /*EndColumn=*/0);
  if (CI.getStartColumn() != DL.getCol())
    return;

  if (!CurFn->HaveLineInfo)
    CurFn->HaveLineInfo = true;
  unsigned FileId = 0;
  if (CurFn->LastLoc.get() && CurFn->LastLoc->getFile() == DL->getFile())
    FileId = CurFn->LastFileId;
  else
    FileId = CurFn->LastFileId = maybeRecordFile(DL->getFile());
  CurFn->LastLoc = DL;
  Asm->OutStreamer->EmitCVLocDirective(CurFn->FuncId, FileId, DL.getLine(),
                                       DL.getCol(), /*PrologueEnd=*/false,
                                       /*IsStmt=*/false, DL->getFilename());
}

CodeViewDebug::CodeViewDebug(AsmPrinter *AP)
    : Asm(nullptr), CurFn(nullptr) {
  MachineModuleInfo *MMI = AP->MMI;

  // If module doesn't have named metadata anchors or COFF debug section
  // is not available, skip any debug info related stuff.
  if (!MMI->getModule()->getNamedMetadata("llvm.dbg.cu") ||
      !AP->getObjFileLowering().getCOFFDebugSymbolsSection())
    return;

  // Tell MMI that we have debug info.
  MMI->setDebugInfoAvailability(true);
  Asm = AP;
}

void CodeViewDebug::endModule() {
  if (FnDebugInfo.empty())
    return;

  // FIXME: For functions that are comdat, we should emit separate .debug$S
  // sections that are comdat associative with the main function instead of
  // having one big .debug$S section.
  assert(Asm != nullptr);
  Asm->OutStreamer->SwitchSection(
      Asm->getObjFileLowering().getCOFFDebugSymbolsSection());
  Asm->EmitInt32(COFF::DEBUG_SECTION_MAGIC);

  // The COFF .debug$S section consists of several subsections, each starting
  // with a 4-byte control code (e.g. 0xF1, 0xF2, etc) and then a 4-byte length
  // of the payload followed by the payload itself.  The subsections are 4-byte
  // aligned.

  // Emit per-function debug information.
  for (auto &P : FnDebugInfo)
    emitDebugInfoForFunction(P.first, P.second);

  // This subsection holds a file index to offset in string table table.
  Asm->OutStreamer->AddComment("File index to string table offset subsection");
  Asm->OutStreamer->EmitCVFileChecksumsDirective();

  // This subsection holds the string table.
  Asm->OutStreamer->AddComment("String table");
  Asm->OutStreamer->EmitCVStringTableDirective();

  clear();
}

static void EmitLabelDiff(MCStreamer &Streamer,
                          const MCSymbol *From, const MCSymbol *To,
                          unsigned int Size = 4) {
  MCSymbolRefExpr::VariantKind Variant = MCSymbolRefExpr::VK_None;
  MCContext &Context = Streamer.getContext();
  const MCExpr *FromRef = MCSymbolRefExpr::create(From, Variant, Context),
               *ToRef   = MCSymbolRefExpr::create(To, Variant, Context);
  const MCExpr *AddrDelta =
      MCBinaryExpr::create(MCBinaryExpr::Sub, ToRef, FromRef, Context);
  Streamer.EmitValue(AddrDelta, Size);
}

void CodeViewDebug::emitDebugInfoForFunction(const Function *GV,
                                             FunctionInfo &FI) {
  // For each function there is a separate subsection
  // which holds the PC to file:line table.
  const MCSymbol *Fn = Asm->getSymbol(GV);
  assert(Fn);

  StringRef FuncName;
  if (auto *SP = getDISubprogram(GV))
    FuncName = SP->getDisplayName();

  // If our DISubprogram name is empty, use the mangled name.
  if (FuncName.empty())
    FuncName = GlobalValue::getRealLinkageName(GV->getName());

  // Emit a symbol subsection, required by VS2012+ to find function boundaries.
  MCSymbol *SymbolsBegin = Asm->MMI->getContext().createTempSymbol(),
           *SymbolsEnd = Asm->MMI->getContext().createTempSymbol();
  Asm->OutStreamer->AddComment("Symbol subsection for " + Twine(FuncName));
  Asm->EmitInt32(unsigned(ModuleSubstreamKind::Symbols));
  EmitLabelDiff(*Asm->OutStreamer, SymbolsBegin, SymbolsEnd);
  Asm->OutStreamer->EmitLabel(SymbolsBegin);
  {
    MCSymbol *ProcSegmentBegin = Asm->MMI->getContext().createTempSymbol(),
             *ProcSegmentEnd = Asm->MMI->getContext().createTempSymbol();
    EmitLabelDiff(*Asm->OutStreamer, ProcSegmentBegin, ProcSegmentEnd, 2);
    Asm->OutStreamer->EmitLabel(ProcSegmentBegin);

    Asm->EmitInt16(unsigned(SymbolRecordKind::S_GPROC32_ID));

    // Some bytes of this segment don't seem to be required for basic debugging,
    // so just fill them with zeroes.
    Asm->OutStreamer->EmitFill(12, 0);
    // This is the important bit that tells the debugger where the function
    // code is located and what's its size:
    EmitLabelDiff(*Asm->OutStreamer, Fn, FI.End);
    Asm->OutStreamer->EmitFill(12, 0);
    Asm->OutStreamer->EmitCOFFSecRel32(Fn);
    Asm->OutStreamer->EmitCOFFSectionIndex(Fn);
    Asm->EmitInt8(0);
    // Emit the function display name as a null-terminated string.
    Asm->OutStreamer->EmitBytes(FuncName);
    Asm->EmitInt8(0);
    Asm->OutStreamer->EmitLabel(ProcSegmentEnd);

    // We're done with this function.
    Asm->EmitInt16(0x0002);
    Asm->EmitInt16(unsigned(SymbolRecordKind::S_PROC_ID_END));
  }
  Asm->OutStreamer->EmitLabel(SymbolsEnd);
  // Every subsection must be aligned to a 4-byte boundary.
  Asm->OutStreamer->EmitFill((-FuncName.size()) % 4, 0);

  // We have an assembler directive that takes care of the whole line table.
  Asm->OutStreamer->EmitCVLinetableDirective(FI.FuncId, Fn, FI.End);
}

void CodeViewDebug::beginFunction(const MachineFunction *MF) {
  assert(!CurFn && "Can't process two functions at once!");

  if (!Asm || !Asm->MMI->hasDebugInfo())
    return;

  const Function *GV = MF->getFunction();
  assert(FnDebugInfo.count(GV) == false);
  CurFn = &FnDebugInfo[GV];
  CurFn->FuncId = NextFuncId++;

  // Find the end of the function prolog.
  // FIXME: is there a simpler a way to do this? Can we just search
  // for the first instruction of the function, not the last of the prolog?
  DebugLoc PrologEndLoc;
  bool EmptyPrologue = true;
  for (const auto &MBB : *MF) {
    if (PrologEndLoc)
      break;
    for (const auto &MI : MBB) {
      if (MI.isDebugValue())
        continue;

      // First known non-DBG_VALUE and non-frame setup location marks
      // the beginning of the function body.
      // FIXME: do we need the first subcondition?
      if (!MI.getFlag(MachineInstr::FrameSetup) && MI.getDebugLoc()) {
        PrologEndLoc = MI.getDebugLoc();
        break;
      }
      EmptyPrologue = false;
    }
  }
  // Record beginning of function if we have a non-empty prologue.
  if (PrologEndLoc && !EmptyPrologue) {
    DebugLoc FnStartDL = PrologEndLoc.getFnDebugLoc();
    maybeRecordLocation(FnStartDL, MF);
  }
}

void CodeViewDebug::endFunction(const MachineFunction *MF) {
  if (!Asm || !CurFn)  // We haven't created any debug info for this function.
    return;

  const Function *GV = MF->getFunction();
  assert(FnDebugInfo.count(GV));
  assert(CurFn == &FnDebugInfo[GV]);

  // Don't emit anything if we don't have any line tables.
  if (!CurFn->HaveLineInfo) {
    FnDebugInfo.erase(GV);
  } else {
    CurFn->End = Asm->getFunctionEnd();
  }
  CurFn = nullptr;
}

void CodeViewDebug::beginInstruction(const MachineInstr *MI) {
  // Ignore DBG_VALUE locations and function prologue.
  if (!Asm || MI->isDebugValue() || MI->getFlag(MachineInstr::FrameSetup))
    return;
  DebugLoc DL = MI->getDebugLoc();
  if (DL == PrevInstLoc || !DL)
    return;
  maybeRecordLocation(DL, Asm->MF);
}
}