[DWARFv5] Emit file 0 to the line table.

[probinson]

Summary

DWARF v5 specifies that the root file (also given in the DW_AT_name attribute
of the compilation unit DIE) should be emitted explicitly to the line table's list of files.
This makes the line table more independent of the .debug_info section.

I am a bit nonplussed that more directory names are appearing in the .file directives now, which required more test changes than I expected, but I can't see that being harmful.

[aprantl]

llvm/lib/MC/MCAsmStreamer.cpp

1119

That looks odd — is that a placeholder for later?

[probinson]

llvm/lib/MC/MCAsmStreamer.cpp

1119

No, it's because asm output doesn't know how to distinguish multiple compile units in the line table. The corresponding MCStreamer (direct-to-object) method can handle different CUIDs.

[aprantl]

llvm/lib/MC/MCAsmStreamer.cpp

1119

Perhaps add a && "not supported by MCAsmStreamer" for clarity?

[dstenb]

With this change, we will emit the .file 0 directive even for -gdwarf-[234]. The directive results in an error when assembling with GAS. Should this be seen as a problem, or is it something that we accept?

In general, when using -gdwarf-[234], to what degree should clang/LLVM be compatible with assemblers and other tools that only partially support DWARFv5?

[probinson]

In D44054#1050311, @dstenb wrote:

With this change, we will emit the .file 0 directive even for -gdwarf-[234]. The directive results in an error when assembling with GAS. Should this be seen as a problem, or is it something that we accept?

In general, when using -gdwarf-[234], to what degree should clang/LLVM be compatible with assemblers and other tools that only partially support DWARFv5?

You are correct, we should emit the '.file 0' directive and 'md5' clause only if we are producing DWARF v5. If we are producing DWARF v5 we require that the assembler be able to handle the extra information correctly.

I have somewhat arbitrarily picked syntax for supporting these v5 features. I don't know how to go about negotiating syntax with other assembler providers, or whether anyone else has started trying to produce standard DWARF v5 line tables. If anyone has advice I'd be pleased to hear it.
Probably llvm-dev would be a better forum than this code review.

[dblaikie]

Yeah, before committing to any new asm syntax, worth a conversation on
llvm-dev with the usual crew & hopefully we can rope in some folks from GCC
or whatnot. It might even be worth discussing on dwarf-discuss, even though
it's not technically a dwarf issue. (& if you're feeling up for it - if
we're having conversations about assembly syntax extensions anyway, there's
a couple of others that might be nice - the ability to specify a CU for
line table entries (LLVM can produce multiple line tables with its
integrated assembler, for use with LTO and ThinLTO, but falls back to
producing a single line table when producing textual assembly) - and maybe
one day the address pool stuff we've talked about)

llvm/include/llvm/MC/MCContext.h

public:
     }
 
     unsigned getDwarfCompileUnitID() { return DwarfCompileUnitID; }
 
     void setDwarfCompileUnitID(unsigned CUIndex) {
       DwarfCompileUnitID = CUIndex;
     }
 
-    void setMCLineTableCompilationDir(unsigned CUID, StringRef CompilationDir) {
-      getMCDwarfLineTable(CUID).setCompilationDir(CompilationDir);
+    /// Specifies the "root" file and directory of the compilation unit.
+    /// These are "file 0" and "directory 0" in DWARF v5.
+    void setMCLineTableRootFile(unsigned CUID, StringRef CompilationDir,
+                                StringRef Filename, MD5::MD5Result *Checksum,
+                                Optional<StringRef> Source) {
+      getMCDwarfLineTable(CUID).setRootFile(CompilationDir, Filename, Checksum,
+                                            Source);
     }
 
     /// Saves the information from the currently parsed dwarf .loc directive
     /// and sets DwarfLocSeen.  When the next instruction is assembled an entry
     /// in the line number table with this information and the address of the
     /// instruction will be created.
     void setCurrentDwarfLoc(unsigned FileNum, unsigned Line, unsigned Column,
                             unsigned Flags, unsigned Isa,

llvm/include/llvm/MC/MCDwarf.h

 };
 
 struct MCDwarfLineTableHeader {
   MCSymbol *Label = nullptr;
   SmallVector<std::string, 3> MCDwarfDirs;
   SmallVector<MCDwarfFile, 3> MCDwarfFiles;
   StringMap<unsigned> SourceIdMap;
   StringRef CompilationDir;
+  MCDwarfFile RootFile;
   bool HasMD5 = false;
   bool HasSource = false;
 
   MCDwarfLineTableHeader() = default;
 
   Expected<unsigned> tryGetFile(StringRef &Directory, StringRef &FileName,
                                 MD5::MD5Result *Checksum,
                                 Optional<StringRef> &Source,
private:
   void emitV5FileDirTables(MCStreamer *MCOS,
                            Optional<MCDwarfLineStr> &LineStr) const;
 };
 
 class MCDwarfDwoLineTable {
   MCDwarfLineTableHeader Header;
 
 public:
-  void setCompilationDir(StringRef CompilationDir) {
-    Header.CompilationDir = CompilationDir;
+  void maybeSetRootFile(StringRef Directory, StringRef FileName,
+                        MD5::MD5Result *Checksum, Optional<StringRef> Source) {
+    if (!Header.RootFile.Name.empty())
+      return;
+    Header.CompilationDir = Directory;
+    Header.RootFile.Name = FileName;
+    Header.RootFile.DirIndex = 0;
+    Header.RootFile.Checksum = Checksum;
+    Header.RootFile.Source = Source;
+    Header.HasMD5 = (Checksum != nullptr);
+    Header.HasSource = Source.hasValue();
   }
 
   unsigned getFile(StringRef Directory, StringRef FileName,
                    MD5::MD5Result *Checksum, Optional<StringRef> Source) {
     return cantFail(Header.tryGetFile(Directory, FileName, Checksum, Source));
   }
 
   void Emit(MCStreamer &MCOS, MCDwarfLineTableParams Params) const;
Expected<unsigned> tryGetFile(StringRef &Directory, StringRef &FileName,
                                 unsigned FileNumber = 0);
   unsigned getFile(StringRef &Directory, StringRef &FileName,
                    MD5::MD5Result *Checksum, Optional<StringRef> &Source,
                    unsigned FileNumber = 0) {
     return cantFail(tryGetFile(Directory, FileName, Checksum, Source,
                                FileNumber));
   }
 
+  void setRootFile(StringRef Directory, StringRef FileName,
+                   MD5::MD5Result *Checksum, Optional<StringRef> Source) {
+    Header.CompilationDir = Directory;
+    Header.RootFile.Name = FileName;
+    Header.RootFile.DirIndex = 0;
+    Header.RootFile.Checksum = Checksum;
+    Header.RootFile.Source = Source;
+    Header.HasMD5 = (Checksum != nullptr);
+    Header.HasSource = Source.hasValue();
+  }
+
   MCSymbol *getLabel() const {
     return Header.Label;
   }
 
   void setLabel(MCSymbol *Label) {
     Header.Label = Label;
   }
 
-  void setCompilationDir(StringRef CompilationDir) {
-    Header.CompilationDir = CompilationDir;
-  }
-
   const SmallVectorImpl<std::string> &getMCDwarfDirs() const {
     return Header.MCDwarfDirs;
   }
 
   SmallVectorImpl<std::string> &getMCDwarfDirs() {
     return Header.MCDwarfDirs;
   }
 

llvm/include/llvm/MC/MCStreamer.h

public:
   /// text with the logical file.  This implements the DWARF2
   /// '.file 4 "dir/foo.c"' assembler directive, and the DWARF5
   /// '.file 4 "dir/foo.c" md5 "..." source "..."' assembler directive.
   virtual Expected<unsigned> tryEmitDwarfFileDirective(
       unsigned FileNo, StringRef Directory, StringRef Filename,
       MD5::MD5Result *Checksum = nullptr, Optional<StringRef> Source = None,
       unsigned CUID = 0);
 
+  /// Specify the "root" file of the compilation, using the ".file 0" extension.
+  virtual void emitDwarfFile0Directive(StringRef Directory, StringRef Filename,
+                                       MD5::MD5Result *Checksum,
+                                       Optional<StringRef> Source,
+                                       unsigned CUID = 0);
+
   /// \brief This implements the DWARF2 '.loc fileno lineno ...' assembler
   /// directive.
   virtual void EmitDwarfLocDirective(unsigned FileNo, unsigned Line,
                                      unsigned Column, unsigned Flags,
                                      unsigned Isa, unsigned Discriminator,
                                      StringRef FileName);
 
   /// Associate a filename with a specified logical file number, and also

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp

DwarfDebug::getOrCreateDwarfCompileUnit(const DICompileUnit *DIUnit) {
   for (auto *IE : DIUnit->getImportedEntities())
     NewCU.addImportedEntity(IE);
 
   // LTO with assembly output shares a single line table amongst multiple CUs.
   // To avoid the compilation directory being ambiguous, let the line table
   // explicitly describe the directory of all files, never relying on the
   // compilation directory.
   if (!Asm->OutStreamer->hasRawTextSupport() || SingleCU)
-    Asm->OutStreamer->getContext().setMCLineTableCompilationDir(
-        NewCU.getUniqueID(), CompilationDir);
+    Asm->OutStreamer->emitDwarfFile0Directive(
+        CompilationDir, FN, NewCU.getMD5AsBytes(DIUnit->getFile()),
+        DIUnit->getSource(), NewCU.getUniqueID());
 
   StringRef Producer = DIUnit->getProducer();
   StringRef Flags = DIUnit->getFlags();
   if (!Flags.empty()) {
     std::string ProducerWithFlags = Producer.str() + " " + Flags.str();
     NewCU.addString(Die, dwarf::DW_AT_producer, ProducerWithFlags);
   } else
     NewCU.addString(Die, dwarf::DW_AT_producer, Producer);
void DwarfDebug::emitDebugStrDWO() {
   MCSection *OffSec = Asm->getObjFileLowering().getDwarfStrOffDWOSection();
   InfoHolder.emitStrings(Asm->getObjFileLowering().getDwarfStrDWOSection(),
                          OffSec, /* UseRelativeOffsets = */ false);
 }
 
 MCDwarfDwoLineTable *DwarfDebug::getDwoLineTable(const DwarfCompileUnit &CU) {
   if (!useSplitDwarf())
     return nullptr;
-  if (SingleCU)
-    SplitTypeUnitFileTable.setCompilationDir(CU.getCUNode()->getDirectory());
+  const DICompileUnit *DIUnit = CU.getCUNode();
+  SplitTypeUnitFileTable.maybeSetRootFile(
+      DIUnit->getDirectory(), DIUnit->getFilename(),
+      CU.getMD5AsBytes(DIUnit->getFile()), DIUnit->getSource());
   return &SplitTypeUnitFileTable;
 }
 
 uint64_t DwarfDebug::makeTypeSignature(StringRef Identifier) {
   MD5 Hash;
   Hash.update(Identifier);
   // ... take the least significant 8 bytes and return those. Our MD5
   // implementation always returns its results in little endian, so we actually

llvm/lib/CodeGen/AsmPrinter/DwarfUnit.h

public:
   DIE::value_iterator addSectionDelta(DIE &Die, dwarf::Attribute Attribute,
                                       const MCSymbol *Hi, const MCSymbol *Lo);
 
   /// Add a Dwarf section label attribute data and value.
   DIE::value_iterator addSectionLabel(DIE &Die, dwarf::Attribute Attribute,
                                       const MCSymbol *Label,
                                       const MCSymbol *Sec);
 
+  /// If the \p File has an MD5 checksum, return it as an MD5Result
+  /// allocated in the MCContext.
+  MD5::MD5Result *getMD5AsBytes(const DIFile *File) const;
+
 protected:
   ~DwarfUnit();
 
   /// Create new static data member DIE.
   DIE *getOrCreateStaticMemberDIE(const DIDerivedType *DT);
 
   /// Look up the source ID for the given file. If none currently exists,
   /// create a new ID and insert it in the line table.
   virtual unsigned getOrCreateSourceID(const DIFile *File) = 0;
 
-  /// If the \p File has an MD5 checksum, return it as an MD5Result
-  /// allocated in the MCContext.
-  MD5::MD5Result *getMD5AsBytes(const DIFile *File);
-
   /// Look in the DwarfDebug map for the MDNode that corresponds to the
   /// reference.
   template <typename T> T *resolve(TypedDINodeRef<T> Ref) const {
     return Ref.resolve();
   }
 
   /// If this is a named finished type then include it in the list of types for
   /// the accelerator tables.

llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp

 void DwarfUnit::addSectionOffset(DIE &Die, dwarf::Attribute Attribute,
                                  uint64_t Integer) {
   if (DD->getDwarfVersion() >= 4)
     addUInt(Die, Attribute, dwarf::DW_FORM_sec_offset, Integer);
   else
     addUInt(Die, Attribute, dwarf::DW_FORM_data4, Integer);
 }
 
-MD5::MD5Result *DwarfUnit::getMD5AsBytes(const DIFile *File) {
+MD5::MD5Result *DwarfUnit::getMD5AsBytes(const DIFile *File) const {
   assert(File);
   Optional<DIFile::ChecksumInfo<StringRef>> Checksum = File->getChecksum();
   if (!Checksum || Checksum->Kind != DIFile::CSK_MD5)
     return nullptr;
 
   // Convert the string checksum to an MD5Result for the streamer.
   // The verifier validates the checksum so we assume it's okay.
   // An MD5 checksum is 16 bytes.

llvm/lib/MC/MCAsmStreamer.cpp

public:
 
   void EmitFileDirective(StringRef Filename) override;
   Expected<unsigned> tryEmitDwarfFileDirective(unsigned FileNo,
                                                StringRef Directory,
                                                StringRef Filename,
                                                MD5::MD5Result *Checksum = 0,
                                                Optional<StringRef> Source = None,
                                                unsigned CUID = 0) override;
+  void emitDwarfFile0Directive(StringRef Directory, StringRef Filename,
+                               MD5::MD5Result *Checksum,
+                               Optional<StringRef> Source,
+                               unsigned CUID = 0) override;
   void EmitDwarfLocDirective(unsigned FileNo, unsigned Line,
                              unsigned Column, unsigned Flags,
                              unsigned Isa, unsigned Discriminator,
                              StringRef FileName) override;
   MCSymbol *getDwarfLineTableSymbol(unsigned CUID) override;
 
   bool EmitCVFileDirective(unsigned FileNo, StringRef Filename,
                            ArrayRef<uint8_t> Checksum,

 
 void MCAsmStreamer::EmitFileDirective(StringRef Filename) {
   assert(MAI->hasSingleParameterDotFile());
   OS << "\t.file\t";
   PrintQuotedString(Filename, OS);
   EmitEOL();
 }
 
-Expected<unsigned> MCAsmStreamer::tryEmitDwarfFileDirective(
-    unsigned FileNo, StringRef Directory, StringRef Filename,
-    MD5::MD5Result *Checksum, Optional<StringRef> Source, unsigned CUID) {
-  assert(CUID == 0);
-
-  MCDwarfLineTable &Table = getContext().getMCDwarfLineTable(CUID);
-  unsigned NumFiles = Table.getMCDwarfFiles().size();
-  Expected<unsigned> FileNoOrErr =
-      Table.tryGetFile(Directory, Filename, Checksum, Source, FileNo);
-  if (!FileNoOrErr)
-    return FileNoOrErr.takeError();
-  FileNo = FileNoOrErr.get();
-  if (NumFiles == Table.getMCDwarfFiles().size())
-    return FileNo;
-
+void printDwarfFileDirective(unsigned FileNo, StringRef Directory,
+                             StringRef Filename, MD5::MD5Result *Checksum,
+                             Optional<StringRef> Source, bool UseDwarfDirectory,
+                             raw_svector_ostream &OS) {
   SmallString<128> FullPathName;
 
   if (!UseDwarfDirectory && !Directory.empty()) {
     if (sys::path::is_absolute(Filename))
       Directory = "";
     else {
       FullPathName = Directory;
       sys::path::append(FullPathName, Filename);
       Directory = "";
       Filename = FullPathName;
     }
   }
 
-  SmallString<128> Str;
-  raw_svector_ostream OS1(Str);
-  OS1 << "\t.file\t" << FileNo << ' ';
+  OS << "\t.file\t" << FileNo << ' ';
   if (!Directory.empty()) {
-    PrintQuotedString(Directory, OS1);
-    OS1 << ' ';
+    PrintQuotedString(Directory, OS);
+    OS << ' ';
   }
-  PrintQuotedString(Filename, OS1);
+  PrintQuotedString(Filename, OS);
   if (Checksum) {
-    OS1 << " md5 ";
-    PrintQuotedString(Checksum->digest(), OS1);
+    OS << " md5 ";
+    PrintQuotedString(Checksum->digest(), OS);
   }
   if (Source) {
-    OS1 << " source ";
-    PrintQuotedString(*Source, OS1);
+    OS << " source ";
+    PrintQuotedString(*Source, OS);
   }
-  if (MCTargetStreamer *TS = getTargetStreamer()) {
+}
+
+Expected<unsigned> MCAsmStreamer::tryEmitDwarfFileDirective(
+    unsigned FileNo, StringRef Directory, StringRef Filename,
+    MD5::MD5Result *Checksum, Optional<StringRef> Source, unsigned CUID) {
+  assert(CUID == 0);
+
+  MCDwarfLineTable &Table = getContext().getMCDwarfLineTable(CUID);
+  unsigned NumFiles = Table.getMCDwarfFiles().size();
+  Expected<unsigned> FileNoOrErr =
+      Table.tryGetFile(Directory, Filename, Checksum, Source, FileNo);
+  if (!FileNoOrErr)
+    return FileNoOrErr.takeError();
+  FileNo = FileNoOrErr.get();
+  if (NumFiles == Table.getMCDwarfFiles().size())
+    return FileNo;
+
+  SmallString<128> Str;
+  raw_svector_ostream OS1(Str);
+  printDwarfFileDirective(FileNo, Directory, Filename, Checksum, Source,
+                          UseDwarfDirectory, OS1);
+
+  if (MCTargetStreamer *TS = getTargetStreamer())
     TS->emitDwarfFileDirective(OS1.str());
-  } else {
+  else
     EmitRawText(OS1.str());
-  }
 
   return FileNo;
 }
 
+void MCAsmStreamer::emitDwarfFile0Directive(StringRef Directory,
+                                            StringRef Filename,
+                                            MD5::MD5Result *Checksum,
+                                            Optional<StringRef> Source,
+                                            unsigned CUID) {
+  assert(CUID == 0);
+
+  SmallString<128> Str;
+  raw_svector_ostream OS1(Str);
+  printDwarfFileDirective(0, Directory, Filename, Checksum, Source,
+                          UseDwarfDirectory, OS1);
+
+  if (MCTargetStreamer *TS = getTargetStreamer())
+    TS->emitDwarfFileDirective(OS1.str());
+  else
+    EmitRawText(OS1.str());
+}
+
 void MCAsmStreamer::EmitDwarfLocDirective(unsigned FileNo, unsigned Line,
                                           unsigned Column, unsigned Flags,
                                           unsigned Isa,
                                           unsigned Discriminator,
                                           StringRef FileName) {
   OS << "\t.loc\t" << FileNo << " " << Line << " " << Column;
   if (Flags & DWARF2_FLAG_BASIC_BLOCK)
     OS << " basic_block";

llvm/lib/MC/MCDwarf.cpp

for (unsigned i = 1; i < MCDwarfFiles.size(); i++) {
     MCOS->EmitBytes(StringRef("\0", 1));   // its null terminator.
     MCOS->EmitULEB128IntValue(MCDwarfFiles[i].DirIndex); // Directory number.
     MCOS->EmitIntValue(0, 1); // Last modification timestamp (always 0).
     MCOS->EmitIntValue(0, 1); // File size (always 0).
   }
   MCOS->EmitIntValue(0, 1); // Terminate the file list.
 }
 
+static void emitOneV5FileEntry(MCStreamer *MCOS, const MCDwarfFile &DwarfFile,
+                               bool HasMD5, bool HasSource,
+                               Optional<MCDwarfLineStr> &LineStr) {
+  assert(!DwarfFile.Name.empty());
+  if (LineStr)
+    LineStr->emitRef(MCOS, DwarfFile.Name);
+  else {
+    MCOS->EmitBytes(DwarfFile.Name);     // FileName and...
+    MCOS->EmitBytes(StringRef("\0", 1)); // its null terminator.
+  }
+  MCOS->EmitULEB128IntValue(DwarfFile.DirIndex); // Directory number.
+  if (HasMD5) {
+    MD5::MD5Result *Cksum = DwarfFile.Checksum;
+    MCOS->EmitBinaryData(
+        StringRef(reinterpret_cast<const char *>(Cksum->Bytes.data()),
+                  Cksum->Bytes.size()));
+  }
+  if (HasSource) {
+    if (LineStr)
+      LineStr->emitRef(MCOS, DwarfFile.Source.getValueOr(StringRef()));
+    else {
+      MCOS->EmitBytes(
+          DwarfFile.Source.getValueOr(StringRef())); // Source and...
+      MCOS->EmitBytes(StringRef("\0", 1));           // its null terminator.
+    }
+  }
+}
+
 void MCDwarfLineTableHeader::emitV5FileDirTables(
     MCStreamer *MCOS, Optional<MCDwarfLineStr> &LineStr) const {
   // The directory format, which is just a list of the directory paths.  In a
   // non-split object, these are references to .debug_line_str; in a split
   // object, they are inline strings.
   MCOS->EmitIntValue(1, 1);
   MCOS->EmitULEB128IntValue(dwarf::DW_LNCT_path);
   MCOS->EmitULEB128IntValue(LineStr ? dwarf::DW_FORM_line_strp
if (HasMD5) {
     MCOS->EmitULEB128IntValue(dwarf::DW_LNCT_MD5);
     MCOS->EmitULEB128IntValue(dwarf::DW_FORM_data16);
   }
   if (HasSource) {
     MCOS->EmitULEB128IntValue(dwarf::DW_LNCT_LLVM_source);
     MCOS->EmitULEB128IntValue(LineStr ? dwarf::DW_FORM_line_strp
                                       : dwarf::DW_FORM_string);
   }
-  // Then the list of file names. These start at 1.
-  MCOS->EmitULEB128IntValue(MCDwarfFiles.size() - 1);
-  for (unsigned i = 1; i < MCDwarfFiles.size(); ++i) {
-    assert(!MCDwarfFiles[i].Name.empty());
-    if (LineStr)
-      LineStr->emitRef(MCOS, MCDwarfFiles[i].Name);
-    else {
-      MCOS->EmitBytes(MCDwarfFiles[i].Name); // FileName and...
-      MCOS->EmitBytes(StringRef("\0", 1));   // its null terminator.
-    }
-    MCOS->EmitULEB128IntValue(MCDwarfFiles[i].DirIndex); // Directory number.
-    if (HasMD5) {
-      MD5::MD5Result *Cksum = MCDwarfFiles[i].Checksum;
-      MCOS->EmitBinaryData(
-          StringRef(reinterpret_cast<const char *>(Cksum->Bytes.data()),
-                    Cksum->Bytes.size()));
-    }
-    if (HasSource) {
-      if (LineStr)
-        LineStr->emitRef(MCOS, MCDwarfFiles[i].Source.getValueOr(StringRef()));
-      else {
-        MCOS->EmitBytes(
-            MCDwarfFiles[i].Source.getValueOr(StringRef())); // Source and...
-        MCOS->EmitBytes(StringRef("\0", 1)); // its null terminator.
-      }
-    }
-  }
+  // Then the counted list of files. The root file is file #0, then emit the
+  // files as provide by .file directives.
+  MCOS->EmitULEB128IntValue(MCDwarfFiles.size());
+  emitOneV5FileEntry(MCOS, RootFile, HasMD5, HasSource, LineStr);
+  for (unsigned i = 1; i < MCDwarfFiles.size(); ++i)
+    emitOneV5FileEntry(MCOS, MCDwarfFiles[i], HasMD5, HasSource, LineStr);
 }
 
 std::pair<MCSymbol *, MCSymbol *>
 MCDwarfLineTableHeader::Emit(MCStreamer *MCOS, MCDwarfLineTableParams Params,
                              ArrayRef<char> StandardOpcodeLengths,
                              Optional<MCDwarfLineStr> &LineStr) const {
   MCContext &context = MCOS->getContext();
 

llvm/lib/MC/MCParser/AsmParser.cpp

 /// ::= .file number [directory] filename [md5 checksum] [source source-text]
 bool AsmParser::parseDirectiveFile(SMLoc DirectiveLoc) {
   // FIXME: I'm not sure what this is.
   int64_t FileNumber = -1;
   if (getLexer().is(AsmToken::Integer)) {
     FileNumber = getTok().getIntVal();
     Lex();
 
-    if (FileNumber < 1)
-      return TokError("file number less than one");
+    if (FileNumber < 0)
+      return TokError("negative file number");
   }
 
   std::string Path = getTok().getString();
 
   // Usually the directory and filename together, otherwise just the directory.
   // Allow the strings to have escaped octal character sequence.
   if (check(getTok().isNot(AsmToken::String),
             "unexpected token in '.file' directive") ||
if (HasSource) {
       char *SourceBuf = static_cast<char *>(Ctx.allocate(SourceString.size()));
       memcpy(SourceBuf, SourceString.data(), SourceString.size());
       Source = StringRef(SourceBuf, SourceString.size());
     }
     // If there is -g option as well as debug info from directive file,
     // we turn off -g option, directly use the existing debug info instead.
     if (getContext().getGenDwarfForAssembly())
       getContext().setGenDwarfForAssembly(false);
+    else if (FileNumber == 0)
+      getStreamer().emitDwarfFile0Directive(Directory, Filename, CKMem, Source);
     else {
       Expected<unsigned> FileNumOrErr = getStreamer().tryEmitDwarfFileDirective(
           FileNumber, Directory, Filename, CKMem, Source);
       if (!FileNumOrErr)
         return Error(DirectiveLoc, toString(FileNumOrErr.takeError()));
       FileNumber = FileNumOrErr.get();
     }
   }

llvm/lib/MC/MCStreamer.cpp

MCStreamer::tryEmitDwarfFileDirective(unsigned FileNo, StringRef Directory,
                                       StringRef Filename,
                                       MD5::MD5Result *Checksum,
                                       Optional<StringRef> Source,
                                       unsigned CUID) {
   return getContext().getDwarfFile(Directory, Filename, FileNo, Checksum,
                                    Source, CUID);
 }
 
+void MCStreamer::emitDwarfFile0Directive(StringRef Directory,
+                                         StringRef Filename,
+                                         MD5::MD5Result *Checksum,
+                                         Optional<StringRef> Source,
+                                         unsigned CUID) {
+  getContext().setMCLineTableRootFile(CUID, Directory, Filename, Checksum,
+                                      Source);
+}
+
 void MCStreamer::EmitDwarfLocDirective(unsigned FileNo, unsigned Line,
                                        unsigned Column, unsigned Flags,
                                        unsigned Isa,
                                        unsigned Discriminator,
                                        StringRef FileName) {
   getContext().setCurrentDwarfLoc(FileNo, Line, Column, Flags, Isa,
                                   Discriminator);
 }

llvm/test/CodeGen/Generic/dwarf-md5.ll

 ; MD5 checksums provided by IR should be passed through to asm.
 ; They'll be emitted to an object file only for DWARF 5 or later.
 
 ; Darwin clamps the line table at DWARF v2 so XFAIL this test.
 ; XFAIL: darwin
 
 ; REQUIRES: object-emission
 ; RUN: %llc_dwarf -dwarf-version 4 -filetype=asm -o - %s | FileCheck %s --check-prefix=ASM
 ; RUN: %llc_dwarf -dwarf-version 5 -filetype=asm -o - %s | FileCheck %s --check-prefix=ASM
 ; RUN: %llc_dwarf -dwarf-version 4 -filetype=obj -o %t4.o %s
-; RUN: llvm-dwarfdump -debug-line %t4.o | FileCheck %s --check-prefix=OBJ-4
+; RUN: llvm-dwarfdump -debug-line %t4.o | FileCheck %s --check-prefix=OBJ
 ; RUN: %llc_dwarf -dwarf-version 5 -filetype=obj -o %t5.o %s
-; RUN: llvm-dwarfdump -debug-line %t5.o | FileCheck %s --check-prefix=OBJ-5
+; RUN: llvm-dwarfdump -debug-line %t5.o | FileCheck %s --check-prefixes=OBJ,OBJ-5
 
-; FIXME: Need to convey the MD5 for the primary source file.
-; ASM: .file 1 ".{{/|\\\\}}t1.h" md5 "11111111111111111111111111111111"
-; ASM: .file 2 ".{{/|\\\\}}t2.h" md5 "22222222222222222222222222222222"
-
-; OBJ-4: file_names[ 1]:
-; OBJ-4-NEXT: name: "t1.h"
-; OBJ-4-NEXT: dir_index: 1
-; OBJ-4: file_names[ 2]:
-; OBJ-4-NEXT: name: "t2.h"
-; OBJ-4-NEXT: dir_index: 1
+; ASM: .file 0 "[[COMPDIR:.*]]{{[/\\]}}t.c" md5 "00000000000000000000000000000000"
+; ASM: .file 1 "[[COMPDIR]]{{[/\\]}}t1.h" md5 "11111111111111111111111111111111"
+; ASM: .file 2 "[[COMPDIR]]{{[/\\]}}t2.h" md5 "22222222222222222222222222222222"
 
 ; OBJ-5: file_names[ 0]:
-; OBJ-5-NEXT: name: "t1.h"
-; OBJ-5-NEXT: dir_index: 1
+; OBJ-5-NEXT: name: "t.c"
+; OBJ-5-NEXT: dir_index: 0
+; OBJ-5-NEXT: md5_checksum: 00000000000000000000000000000000
+; OBJ: file_names[ 1]:
+; OBJ-NEXT: name: "t1.h"
+; OBJ-NEXT: dir_index: 0
 ; OBJ-5-NEXT: md5_checksum: 11111111111111111111111111111111
-; OBJ-5: file_names[ 1]:
-; OBJ-5-NEXT: name: "t2.h"
-; OBJ-5-NEXT: dir_index: 1
+; OBJ: file_names[ 2]:
+; OBJ-NEXT: name: "t2.h"
+; OBJ-NEXT: dir_index: 0
 ; OBJ-5-NEXT: md5_checksum: 22222222222222222222222222222222
 
 ; ModuleID = 't.c'
 source_filename = "t.c"
 
 @t1 = global i32 1, align 4, !dbg !0
 @t2 = global i32 0, align 4, !dbg !6
 
 !llvm.dbg.cu = !{!2}
 !llvm.module.flags = !{!11, !12, !13}
 !llvm.ident = !{!14}
 
 !0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
 !1 = distinct !DIGlobalVariable(name: "t1", scope: !2, file: !10, line: 1, type: !9, isLocal: false, isDefinition: true)
 !2 = distinct !DICompileUnit(language: DW_LANG_C99, file: !3, producer: "clang version 7.0.0 (trunk 322159)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !4, globals: !5)
 !3 = !DIFile(filename: "t.c", directory: "/home/probinson/projects/scratch", checksumkind: CSK_MD5, checksum: "00000000000000000000000000000000")
 !4 = !{}
 !5 = !{!0, !6}
 !6 = !DIGlobalVariableExpression(var: !7, expr: !DIExpression())
 !7 = distinct !DIGlobalVariable(name: "t2", scope: !2, file: !8, line: 1, type: !9, isLocal: false, isDefinition: true)
-!8 = !DIFile(filename: "./t2.h", directory: "/home/probinson/projects/scratch", checksumkind: CSK_MD5, checksum: "22222222222222222222222222222222")
+!8 = !DIFile(filename: "t2.h", directory: "/home/probinson/projects/scratch", checksumkind: CSK_MD5, checksum: "22222222222222222222222222222222")
 !9 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
-!10 = !DIFile(filename: "./t1.h", directory: "/home/probinson/projects/scratch", checksumkind: CSK_MD5, checksum: "11111111111111111111111111111111")
+!10 = !DIFile(filename: "t1.h", directory: "/home/probinson/projects/scratch", checksumkind: CSK_MD5, checksum: "11111111111111111111111111111111")
 !11 = !{i32 2, !"Dwarf Version", i32 4}
 !12 = !{i32 2, !"Debug Info Version", i32 3}
 !13 = !{i32 1, !"wchar_size", i32 4}
 !14 = !{!"clang version 7.0.0 (trunk 322159)"}

llvm/test/CodeGen/Generic/dwarf-source.ll

 ; Source text provided by IR should be passed through to asm.
 ; It is emitted to an object file only for DWARF 5 or later.
 
 ; Darwin clamps the line table at DWARF v2 so XFAIL this test.
 ; XFAIL: darwin
 
 ; REQUIRES: object-emission
 ; RUN: %llc_dwarf -dwarf-version 4 -filetype=asm -o - %s | FileCheck %s --check-prefix=ASM
 ; RUN: %llc_dwarf -dwarf-version 5 -filetype=asm -o - %s | FileCheck %s --check-prefix=ASM
 ; RUN: %llc_dwarf -dwarf-version 4 -filetype=obj -o %t4.o %s
-; RUN: llvm-dwarfdump -debug-line %t4.o | FileCheck %s --check-prefix=OBJ-4
+; RUN: llvm-dwarfdump -debug-line %t4.o | FileCheck %s --check-prefixes=OBJ,OBJ-4
 ; RUN: %llc_dwarf -dwarf-version 5 -filetype=obj -o %t5.o %s
-; RUN: llvm-dwarfdump -debug-line %t5.o | FileCheck %s --check-prefix=OBJ-5
+; RUN: llvm-dwarfdump -debug-line %t5.o | FileCheck %s --check-prefixes=OBJ,OBJ-5
 
-; FIXME: Need to convey the source for the primary source file.
-; ASM: .file 1 ".{{/|\\\\}}t1.h" source "11111111111111111111111111111111"
-; ASM: .file 2 ".{{/|\\\\}}t2.h" source "22222222222222222222222222222222"
-
-; OBJ-4: file_names[ 1]:
-; OBJ-4-NEXT: name: "t1.h"
-; OBJ-4-NEXT: dir_index: 1
-; OBJ-4-NOT: 11111111111111111111111111111111
-; OBJ-4: file_names[ 2]:
-; OBJ-4-NEXT: name: "t2.h"
-; OBJ-4-NEXT: dir_index: 1
-; OBJ-4-NOT: 22222222222222222222222222222222
+; ASM: .file 0 "[[COMPDIR:.*]]{{[/\\]}}t.c" source "00000000000000000000000000000000"
+; ASM: .file 1 "[[COMPDIR]]{{[/\\]}}t1.h" source "11111111111111111111111111111111"
+; ASM: .file 2 "[[COMPDIR]]{{[/\\]}}t2.h" source "22222222222222222222222222222222"
 
 ; OBJ-5: file_names[ 0]:
-; OBJ-5-NEXT: name: "t1.h"
-; OBJ-5-NEXT: dir_index: 1
+; OBJ-5-NEXT: name: "t.c"
+; OBJ-5-NEXT: dir_index: 0
+; OBJ-5-NEXT: source: "00000000000000000000000000000000"
+; OBJ: file_names[ 1]:
+; OBJ-NEXT: name: "t1.h"
+; OBJ-NEXT: dir_index: 0
+; OBJ-4-NOT: 11111111111111111111111111111111
 ; OBJ-5-NEXT: source: "11111111111111111111111111111111"
-; OBJ-5: file_names[ 1]:
-; OBJ-5-NEXT: name: "t2.h"
-; OBJ-5-NEXT: dir_index: 1
+; OBJ: file_names[ 2]:
+; OBJ-NEXT: name: "t2.h"
+; OBJ-NEXT: dir_index: 0
+; OBJ-4-NOT: 22222222222222222222222222222222
 ; OBJ-5-NEXT: source: "22222222222222222222222222222222"
 
 ; ModuleID = 't.c'
 source_filename = "t.c"
 
 @t1 = global i32 1, align 4, !dbg !0
 @t2 = global i32 0, align 4, !dbg !6
 
 !llvm.dbg.cu = !{!2}
 !llvm.module.flags = !{!11, !12, !13}
 !llvm.ident = !{!14}
 
 !0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
 !1 = distinct !DIGlobalVariable(name: "t1", scope: !2, file: !10, line: 1, type: !9, isLocal: false, isDefinition: true)
 !2 = distinct !DICompileUnit(language: DW_LANG_C99, file: !3, producer: "clang version 7.0.0 (trunk 322159)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !4, globals: !5)
 !3 = !DIFile(filename: "t.c", directory: "/test", source: "00000000000000000000000000000000")
 !4 = !{}
 !5 = !{!0, !6}
 !6 = !DIGlobalVariableExpression(var: !7, expr: !DIExpression())
 !7 = distinct !DIGlobalVariable(name: "t2", scope: !2, file: !8, line: 1, type: !9, isLocal: false, isDefinition: true)
-!8 = !DIFile(filename: "./t2.h", directory: "/test", source: "22222222222222222222222222222222")
+!8 = !DIFile(filename: "t2.h", directory: "/test", source: "22222222222222222222222222222222")
 !9 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
-!10 = !DIFile(filename: "./t1.h", directory: "/test", source: "11111111111111111111111111111111")
+!10 = !DIFile(filename: "t1.h", directory: "/test", source: "11111111111111111111111111111111")
 !11 = !{i32 2, !"Dwarf Version", i32 4}
 !12 = !{i32 2, !"Debug Info Version", i32 3}
 !13 = !{i32 1, !"wchar_size", i32 4}
 !14 = !{!"clang version 7.0.0 (trunk 322159)"}

llvm/test/DebugInfo/X86/dbg-file-name.ll

 ; RUN: llc -enable-dwarf-directory -mtriple x86_64-apple-darwin10.0.0  < %s | FileCheck %s
 
 ; Verify that the file name is relative to the directory.
 ; rdar://problem/8884898
-; CHECK: file 1 "simple.c"
+; CHECK: file 1 "/Users/manav/one/two" "simple.c"
 
 declare i32 @printf(i8*, ...) nounwind
 
 define i32 @main() nounwind !dbg !6 {
   ret i32 0
 }
 
 !llvm.dbg.cu = !{!2}

llvm/test/DebugInfo/X86/inline-asm-locs.ll

 ; void foo() {
 ;   bar();
 ; }
 
 ; CHECK: .file 1 "A.asm"
 ; CHECK: .file 2 "B.asm"
 ; CHECK: .loc  1 111
 ; CHECK: .loc  2 222
-; CHECK: .file 3 "test.c"
+; CHECK: .file 3 "/{{.*}}/test.c"
 ; CHECK: .loc  3 14 0  
 
 target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-apple-macosx"
 
 module asm ".file 1 \22A.asm\22"
 module asm ".file 2 \22B.asm\22"
 module asm ".loc  1 111"

llvm/test/MC/ARM/dwarf-asm-multiple-sections.s

 // DWARF-NEXT: Address Range Header: length = 0x00000024, version = 0x0002, cu_offset = 0x00000000, addr_size = 0x04, seg_size = 0x00
 // DWARF-NEXT: [0x00000000, 0x00000004)
 // DWARF-NEXT: [0x00000000, 0x00000004)
 
 
 // DWARF-DL: .debug_line contents:
 // DWARF-DL: version: [[DWVER]]
 // DWARF-DL-5:    address_size: 4
-// DWARF-DL-5:    include_directories[  0] = ""
+// DWARF-DL-5:    include_directories[  0] = "/tmp"
 // DWARF-DL:      file_names[  [[DWFILE]]]:
-// DWARF-DL:      name: "<stdin>"
+// DWARF-DL:      name: "{{(<stdin>|-)}}"
 // DWARF-DL:      0x0000000000000000     17      0      1   0   0  is_stmt
 // DWARF-DL-NEXT: 0x0000000000000004     17      0      1   0   0  is_stmt end_sequence
 // DWARF-DL-NEXT: 0x0000000000000000     21      0      1   0   0  is_stmt
 // DWARF-DL-NEXT: 0x0000000000000004     21      0      1   0   0  is_stmt end_sequence
 
 
 // DWARF: .debug_ranges contents:
 // DWARF: 00000000 ffffffff 00000000

llvm/test/MC/ELF/debug-file-options.s

-// RUN: llvm-mc -triple x86_64-unknown-unknown -dwarf-version 5 -filetype=obj %s -o -| llvm-dwarfdump --debug-line --debug-line-str -v - | FileCheck %s
+// RUN: llvm-mc -triple x86_64-unknown-unknown -dwarf-version 5 -filetype=obj %s -o -| llvm-dwarfdump --debug-line --debug-line-str -v - | FileCheck %s -DFILE0NAME=%s
 
 // Test combinations of options to the .file directive.
 
         .file 1 "dir1/foo" md5 "ee87e05688663173cd6043a3a15bba6e" source "void foo() {}"
         .file 2 "dir2/bar" source "void bar() {}" md5 "816225a0c90ca8948b70eb58be4d522f"
         .loc 1 1 0
         nop
         .loc 2 1 0
         nop
 
 # CHECK: debug_line[0x00000000]
 # CHECK: version: 5
-# CHECK: include_directories[ 0] = .debug_line_str[0x[[DIR0:[0-9a-f]+]]] = ""
+# CHECK: include_directories[ 0] = .debug_line_str[0x[[DIR0:[0-9a-f]+]]] = "{{.*}}"
 # CHECK: include_directories[ 1] = .debug_line_str[0x[[DIR1:[0-9a-f]+]]] = "dir1"
 # CHECK: include_directories[ 2] = .debug_line_str[0x[[DIR2:[0-9a-f]+]]] = "dir2"
 # CHECK-NOT: include_directories
 # CHECK: file_names[ 0]:
+# CHECK-NEXT: name: .debug_line_str[0x[[FILE0:[0-9a-f]+]]] = "[[FILE0NAME]]"
+# CHECK-NEXT: dir_index: 0
+# CHECK-NEXT: md5_checksum:
+# CHECK-NEXT: source: .debug_line_str[0x[[FILE0SRC:[0-9a-f]+]]] = ""
+# CHECK: file_names[ 1]:
 # CHECK-NEXT: name: .debug_line_str[0x[[FILE1:[0-9a-f]+]]] = "foo"
 # CHECK-NEXT: dir_index: 1
 # CHECK-NEXT: md5_checksum: ee87e05688663173cd6043a3a15bba6e
 # CHECK-NEXT: source: .debug_line_str[0x[[FILE1SRC:[0-9a-f]+]]] = "void foo() {}"
-# CHECK: file_names[ 1]:
+# CHECK: file_names[ 2]:
 # CHECK-NEXT: name: .debug_line_str[0x[[FILE2:[0-9a-f]+]]] = "bar"
 # CHECK-NEXT: dir_index: 2
 # CHECK-NEXT: md5_checksum: 816225a0c90ca8948b70eb58be4d522f
 # CHECK-NEXT: source: .debug_line_str[0x[[FILE2SRC:[0-9a-f]+]]] = "void bar() {}"
 
 # CHECK: .debug_line_str contents:
-# CHECK-NEXT: 0x[[DIR0]]: ""
+# CHECK-NEXT: 0x[[DIR0]]: "{{.*}}"
 # CHECK-NEXT: 0x[[DIR1]]: "dir1"
 # CHECK-NEXT: 0x[[DIR2]]: "dir2"
+# CHECK-NEXT: 0x[[FILE0]]: "[[FILE0NAME]]"
+# CHECK-NEXT: 0x[[FILE0SRC]]: ""
 # CHECK-NEXT: 0x[[FILE1]]: "foo"
 # CHECK-NEXT: 0x[[FILE1SRC]]: "void foo() {}"
 # CHECK-NEXT: 0x[[FILE2]]: "bar"
 # CHECK-NEXT: 0x[[FILE2SRC]]: "void bar() {}"

llvm/test/MC/ELF/debug-md5.s

-// RUN: llvm-mc -triple x86_64-unknown-unknown -dwarf-version 5 -filetype=obj %s -o - | llvm-dwarfdump --debug-line --debug-line-str -v - | FileCheck %s
+// RUN: llvm-mc -triple x86_64-unknown-unknown -dwarf-version 5 -fdebug-compilation-dir=/tmp -filetype=obj %s -o - | llvm-dwarfdump --debug-line --debug-line-str -v - | FileCheck %s -DROOTFILE=%s
 
         .file 1 "dir1/foo"   md5 "00112233445566778899aabbccddeeff"
         .file 2 "dir2" "bar" md5 "ffeeddccbbaa99887766554433221100"
         .loc 1 1 0
         nop
         .loc 2 1 0
         nop
 
 # CHECK: debug_line[0x00000000]
 # CHECK: version: 5
-# CHECK: include_directories[ 0] = .debug_line_str[0x[[DIR0:[0-9a-f]+]]] = ""
+# CHECK: include_directories[ 0] = .debug_line_str[0x[[DIR0:[0-9a-f]+]]] = "/tmp"
 # CHECK: include_directories[ 1] = .debug_line_str[0x[[DIR1:[0-9a-f]+]]] = "dir1"
 # CHECK: include_directories[ 2] = .debug_line_str[0x[[DIR2:[0-9a-f]+]]] = "dir2"
 # CHECK-NOT: include_directories
 # CHECK: file_names[ 0]:
+# CHECK-NEXT: name: .debug_line_str[0x[[FILE0:[0-9a-f]+]]] = "[[ROOTFILE]]"
+# CHECK-NEXT: dir_index: 0
+# CHECK: file_names[ 1]:
 # CHECK-NEXT: name: .debug_line_str[0x[[FILE1:[0-9a-f]+]]] = "foo"
 # CHECK-NEXT: dir_index: 1
 # CHECK-NEXT: md5_checksum: 00112233445566778899aabbccddeeff
-# CHECK: file_names[ 1]:
+# CHECK: file_names[ 2]:
 # CHECK-NEXT: name: .debug_line_str[0x[[FILE2:[0-9a-f]+]]] = "bar"
 # CHECK-NEXT: dir_index: 2
 # CHECK-NEXT: md5_checksum: ffeeddccbbaa99887766554433221100
 
 # CHECK: .debug_line_str contents:
-# CHECK-NEXT: 0x[[DIR0]]: ""
+# CHECK-NEXT: 0x[[DIR0]]: "/tmp"
 # CHECK-NEXT: 0x[[DIR1]]: "dir1"
 # CHECK-NEXT: 0x[[DIR2]]: "dir2"
+# CHECK-NEXT: 0x[[FILE0]]: "[[ROOTFILE]]"
 # CHECK-NEXT: 0x[[FILE1]]: "foo"
 # CHECK-NEXT: 0x[[FILE2]]: "bar"

llvm/test/MC/ELF/debug-source.s

-// RUN: llvm-mc -triple x86_64-unknown-unknown -dwarf-version 5 -filetype=obj %s -o -| llvm-dwarfdump --debug-line --debug-line-str -v - | FileCheck %s
+// RUN: llvm-mc -triple x86_64-unknown-unknown -dwarf-version 5 -filetype=obj %s -o -| llvm-dwarfdump --debug-line --debug-line-str -v - | FileCheck %s -DFILE0NAME=%s
 
         .file 1 "dir1/foo"   source "void foo() {}"
         .file 2 "dir2" "bar" source "void bar()\n{\n}"
         .loc 1 1 0
         nop
         .loc 2 1 0
         nop
 
 # CHECK: debug_line[0x00000000]
 # CHECK: version: 5
-# CHECK: include_directories[ 0] = .debug_line_str[0x[[DIR0:[0-9a-f]+]]] = ""
+# CHECK: include_directories[ 0] = .debug_line_str[0x[[DIR0:[0-9a-f]+]]] = "{{.*}}"
 # CHECK: include_directories[ 1] = .debug_line_str[0x[[DIR1:[0-9a-f]+]]] = "dir1"
 # CHECK: include_directories[ 2] = .debug_line_str[0x[[DIR2:[0-9a-f]+]]] = "dir2"
 # CHECK-NOT: include_directories
 # CHECK: file_names[ 0]:
+# CHECK-NEXT: name: .debug_line_str[0x[[FILE0:[0-9a-f]+]]] = "[[FILE0NAME]]"
+# CHECK-NEXT: dir_index: 0
+# CHECK-NEXT: source: .debug_line_str[0x[[FILE0SRC:[0-9a-f]+]]] = ""
+# CHECK: file_names[ 1]:
 # CHECK-NEXT: name: .debug_line_str[0x[[FILE1:[0-9a-f]+]]] = "foo"
 # CHECK-NEXT: dir_index: 1
 # CHECK-NEXT: source: .debug_line_str[0x[[FILE1SRC:[0-9a-f]+]]] = "void foo() {}"
-# CHECK: file_names[ 1]:
+# CHECK: file_names[ 2]:
 # CHECK-NEXT: name: .debug_line_str[0x[[FILE2:[0-9a-f]+]]] = "bar"
 # CHECK-NEXT: dir_index: 2
 # CHECK-NEXT: source: .debug_line_str[0x[[FILE2SRC:[0-9a-f]+]]] = "void bar()\n{\n}"
 
 # CHECK: .debug_line_str contents:
-# CHECK-NEXT: 0x[[DIR0]]: ""
+# CHECK-NEXT: 0x[[DIR0]]: "{{.*}}"
 # CHECK-NEXT: 0x[[DIR1]]: "dir1"
 # CHECK-NEXT: 0x[[DIR2]]: "dir2"
+# CHECK-NEXT: 0x[[FILE0]]: "[[FILE0NAME]]"
+# CHECK-NEXT: 0x[[FILE0SRC]]: ""
 # CHECK-NEXT: 0x[[FILE1]]: "foo"
 # CHECK-NEXT: 0x[[FILE1SRC]]: "void foo() {}"
 # CHECK-NEXT: 0x[[FILE2]]: "bar"
 # CHECK-NEXT: 0x[[FILE2SRC]]: "void bar()\n{\n}"

llvm/test/MC/ELF/dwarf-file0.s

+# RUN: llvm-mc -dwarf-version 4 %s -filetype=obj -o - | llvm-dwarfdump -debug-line - | FileCheck %s --check-prefixes=CHECK,CHECK-4
+# RUN: llvm-mc -dwarf-version 5 %s -filetype=obj -o - | llvm-dwarfdump -debug-line - | FileCheck %s --check-prefixes=CHECK,CHECK-5
+        .file 0 "root.cpp"
+        .file 1 "header.h"
+        .file 2 "root.cpp"
+# CHECK-5:     include_directories[ 0] = ""
+# CHECK-4-NOT: include_directories
+# CHECK-4-NOT: file_names[ 0]
+# CHECK-5:     file_names[ 0]:
+# CHECK-5-NEXT: name: "root.cpp"
+# CHECK-5-NEXT: dir_index: 0
+# CHECK:       file_names[ 1]:
+# CHECK-NEXT:  name: "header.h"
+# CHECK-NEXT:  dir_index: 0
+# CHECK:       file_names[ 2]:
+# CHECK-NEXT:  name: "root.cpp"
+# CHECK-NEXT:  dir_index: 0

llvm/tools/llvm-mc/llvm-mc.cpp

int main(int argc, char **argv) {
   else {
     // If no compilation dir is set, try to use the current directory.
     SmallString<128> CWD;
     if (!sys::fs::current_path(CWD))
       Ctx.setCompilationDir(CWD);
   }
   if (!MainFileName.empty())
     Ctx.setMainFileName(MainFileName);
+  if (DwarfVersion >= 5) {
+    // DWARF v5 needs the root file as well as the compilation directory.
+    // If we find a '.file 0' directive that will supersede these values.
+    MD5 Hash;
+    MD5::MD5Result Cksum;
+    Hash.update(Buffer->getBuffer());
+    Hash.final(Cksum);
+    Ctx.setMCLineTableRootFile(
+        /*CUID=*/0, Ctx.getCompilationDir(),
+        !MainFileName.empty() ? MainFileName : InputFilename, &Cksum, None);
+  }
 
   // Package up features to be passed to target/subtarget
   std::string FeaturesStr;
   if (MAttrs.size()) {
     SubtargetFeatures Features;
     for (unsigned i = 0; i != MAttrs.size(); ++i)
       Features.AddFeature(MAttrs[i]);
     FeaturesStr = Features.getString();