[dsymutil] Remove paper trail warnings (llvm#67041)

Remove the paper trail warning from dsymutil and the DWARF linker. The
original purpose of this functionality was to leave a paper trail in the
output artifact about missing object files. The current implementation
however has diverged and is the source of a pretty serious bug:

- In the debug map parser, missing object files are not the only
  warnings we emit. When paper trail warnings are enabled, all of them end
  up in the dSYM which wasn't the goal.

- When warnings are associated with a object file in the debug map, it
  is skipped by the DWARF linker. This only makes sense if the object file
  is missing and is obviously incorrect for any other type of warning
  (such as a missing symbol).

The combination of the two means that we can generate broken DWARF when
the feature is enabled. AFAIK it was only used by Apple and nobody I
spoke to has relied on it, so rather than fixing the broken behavior I
propose we remove it.

(cherry picked from commit 697b34f)

llvm/docs/CommandGuide/dsymutil.rst

@@ -100,13 +100,6 @@ OPTIONS
  Specifies an alternate ``path`` to place the dSYM bundle. The default dSYM
  bundle path is created by appending ``.dSYM`` to the executable name.
 
-.. option:: --papertrail
-
- When running dsymutil as part of your build system, it can be desirable for
- warnings to be part of the end product, rather than just being emitted to the
- output stream. When enabled warnings are embedded in the linked DWARF debug
- information.
-
 .. option:: --remarks-drop-without-debug
 
  Drop remarks without valid debug locations. Without this flags, all remarks are kept.

llvm/include/llvm/DWARFLinker/DWARFLinker.h

@@ -99,9 +99,6 @@ class DwarfEmitter {
 public:
   virtual ~DwarfEmitter();
 
-  /// Emit DIE containing warnings.
-  virtual void emitPaperTrailWarningsDie(DIE &Die) = 0;
-
   /// Emit section named SecName with data SecData.
   virtual void emitSectionContents(StringRef SecData, StringRef SecName) = 0;
 
@@ -267,10 +264,9 @@ using UnitListTy = std::vector<std::unique_ptr<CompileUnit>>;
 class DWARFFile {
 public:
   DWARFFile(StringRef Name, std::unique_ptr<DWARFContext> Dwarf,
-            std::unique_ptr<AddressesMap> Addresses,
-            const std::vector<std::string> &Warnings)
+            std::unique_ptr<AddressesMap> Addresses)
       : FileName(Name), Dwarf(std::move(Dwarf)),
-        Addresses(std::move(Addresses)), Warnings(Warnings) {}
+        Addresses(std::move(Addresses)) {}
 
   /// The object file name.
   StringRef FileName;
@@ -280,9 +276,6 @@ class DWARFFile {
 
   /// Helpful address information(list of valid address ranges, relocations).
   std::unique_ptr<AddressesMap> Addresses;
-
-  /// Warnings for this object file.
-  const std::vector<std::string> &Warnings;
 };
 
 typedef std::map<std::string, std::string> swiftInterfacesMap;
@@ -502,10 +495,6 @@ class DWARFLinker {
       ErrorHandler(Warning, File.FileName, DIE);
   }
 
-  /// Emit warnings as Dwarf compile units to leave a trail after linking.
-  bool emitPaperTrailWarnings(const DWARFFile &File,
-                              OffsetsStringPool &StringPool);
-
   void copyInvariantDebugSection(DWARFContext &Dwarf);
 
   /// Keep information for referenced clang module: already loaded DWARF info

llvm/include/llvm/DWARFLinker/DWARFStreamer.h

@@ -72,9 +72,6 @@ class DwarfStreamer : public DwarfEmitter {
   void emitAbbrevs(const std::vector<std::unique_ptr<DIEAbbrev>> &Abbrevs,
                    unsigned DwarfVersion) override;
 
-  /// Emit DIE containing warnings.
-  void emitPaperTrailWarningsDie(DIE &Die) override;
-
   /// Emit contents of section SecName From Obj.
   void emitSectionContents(StringRef SecData, StringRef SecName) override;
 

llvm/include/llvm/DWARFLinkerParallel/DWARFFile.h

@@ -29,11 +29,9 @@ class DWARFFile {
 
   DWARFFile(StringRef Name, std::unique_ptr<DWARFContext> Dwarf,
             std::unique_ptr<AddressesMap> Addresses,
-            const std::vector<std::string> &Warnings,
             UnloadCallbackTy UnloadFunc = nullptr)
       : FileName(Name), Dwarf(std::move(Dwarf)),
-        Addresses(std::move(Addresses)), Warnings(Warnings),
-        UnloadFunc(UnloadFunc) {
+        Addresses(std::move(Addresses)), UnloadFunc(UnloadFunc) {
     if (this->Dwarf)
       Endianess = this->Dwarf->isLittleEndian() ? support::endianness::little
                                                 : support::endianness::big;
@@ -48,9 +46,6 @@ class DWARFFile {
   /// Helpful address information(list of valid address ranges, relocations).
   std::unique_ptr<AddressesMap> Addresses;
 
-  /// Warnings for object file.
-  const std::vector<std::string> &Warnings;
-
   /// Endiannes of source DWARF information.
   support::endianness Endianess = support::endianness::little;
 

llvm/lib/DWARFLinker/DWARFLinker.cpp

@@ -2561,69 +2561,6 @@ uint64_t DWARFLinker::DIECloner::cloneAllCompileUnits(
   return OutputDebugInfoSize - StartOutputDebugInfoSize;
 }
 
-bool DWARFLinker::emitPaperTrailWarnings(const DWARFFile &File,
-                                         OffsetsStringPool &StringPool) {
-
-  if (File.Warnings.empty())
-    return false;
-
-  DIE *CUDie = DIE::get(DIEAlloc, dwarf::DW_TAG_compile_unit);
-  CUDie->setOffset(11);
-  StringRef Producer;
-  StringRef WarningHeader;
-
-  switch (DwarfLinkerClientID) {
-  case DwarfLinkerClient::Dsymutil:
-    Producer = StringPool.internString("dsymutil");
-    WarningHeader = "dsymutil_warning";
-    break;
-
-  default:
-    Producer = StringPool.internString("dwarfopt");
-    WarningHeader = "dwarfopt_warning";
-    break;
-  }
-
-  StringRef FileName = StringPool.internString(File.FileName);
-  CUDie->addValue(DIEAlloc, dwarf::DW_AT_producer, dwarf::DW_FORM_strp,
-                  DIEInteger(StringPool.getStringOffset(Producer)));
-  DIEBlock *String = new (DIEAlloc) DIEBlock();
-  DIEBlocks.push_back(String);
-  for (auto &C : FileName)
-    String->addValue(DIEAlloc, dwarf::Attribute(0), dwarf::DW_FORM_data1,
-                     DIEInteger(C));
-  String->addValue(DIEAlloc, dwarf::Attribute(0), dwarf::DW_FORM_data1,
-                   DIEInteger(0));
-
-  CUDie->addValue(DIEAlloc, dwarf::DW_AT_name, dwarf::DW_FORM_string, String);
-  for (const auto &Warning : File.Warnings) {
-    DIE &ConstDie = CUDie->addChild(DIE::get(DIEAlloc, dwarf::DW_TAG_constant));
-    ConstDie.addValue(DIEAlloc, dwarf::DW_AT_name, dwarf::DW_FORM_strp,
-                      DIEInteger(StringPool.getStringOffset(WarningHeader)));
-    ConstDie.addValue(DIEAlloc, dwarf::DW_AT_artificial, dwarf::DW_FORM_flag,
-                      DIEInteger(1));
-    ConstDie.addValue(DIEAlloc, dwarf::DW_AT_const_value, dwarf::DW_FORM_strp,
-                      DIEInteger(StringPool.getStringOffset(Warning)));
-  }
-  unsigned Size = 4 /* FORM_strp */ + FileName.size() + 1 +
-                  File.Warnings.size() * (4 + 1 + 4) + 1 /* End of children */;
-  DIEAbbrev Abbrev = CUDie->generateAbbrev();
-  assignAbbrev(Abbrev);
-  CUDie->setAbbrevNumber(Abbrev.getNumber());
-  Size += getULEB128Size(Abbrev.getNumber());
-  // Abbreviation ordering needed for classic compatibility.
-  for (auto &Child : CUDie->children()) {
-    Abbrev = Child.generateAbbrev();
-    assignAbbrev(Abbrev);
-    Child.setAbbrevNumber(Abbrev.getNumber());
-    Size += getULEB128Size(Abbrev.getNumber());
-  }
-  CUDie->setSize(Size);
-  TheDwarfEmitter->emitPaperTrailWarningsDie(*CUDie);
-
-  return true;
-}
-
 void DWARFLinker::copyInvariantDebugSection(DWARFContext &Dwarf) {
   TheDwarfEmitter->emitSectionContents(Dwarf.getDWARFObj().getLocSection().Data,
                                        "debug_loc");
@@ -2687,9 +2624,6 @@ Error DWARFLinker::link() {
         outs() << "OBJECT FILE: " << OptContext.File.FileName << "\n";
     }
 
-    if (emitPaperTrailWarnings(OptContext.File, DebugStrPool))
-      continue;
-
     if (!OptContext.File.Dwarf)
       continue;
 

llvm/lib/DWARFLinker/DWARFStreamer.cpp

@@ -234,18 +234,6 @@ void DwarfStreamer::emitSectionContents(StringRef SecData, StringRef SecName) {
   }
 }
 
-/// Emit DIE containing warnings.
-void DwarfStreamer::emitPaperTrailWarningsDie(DIE &Die) {
-  switchToDebugInfoSection(/* Version */ 2);
-  auto &Asm = getAsmPrinter();
-  Asm.emitInt32(11 + Die.getSize() - 4);
-  Asm.emitInt16(2);
-  Asm.emitInt32(0);
-  Asm.emitInt8(MC->getTargetTriple().isArch64Bit() ? 8 : 4);
-  DebugInfoSectionSize += 11;
-  emitDIE(Die);
-}
-
 /// Emit the debug_str section stored in \p Pool.
 void DwarfStreamer::emitStrings(const NonRelocatableStringpool &Pool) {
   Asm->OutStreamer->switchSection(MOFI->getDwarfStrSection());

llvm/test/tools/dsymutil/cmdline.test

@@ -21,7 +21,6 @@ CHECK: -object-prefix-map <prefix=remapped>
 CHECK: -oso-prepend-path <path>
 CHECK: -out <filename>
 CHECK: {{-o <filename>}}
-CHECK: -papertrail
 CHECK: -remarks-drop-without-debug
 CHECK: -remarks-output-format <format>
 CHECK: -remarks-prepend-path <path>

llvm/tools/dsymutil/DwarfLinkerForBinary.cpp

@@ -234,8 +234,7 @@ DwarfLinkerForBinary::loadObject(const DebugMapObject &Obj,
   if (ErrorOrObj) {
     Res = std::make_unique<OutDWARFFile>(
         Obj.getObjectFilename(), DWARFContext::create(*ErrorOrObj),
-        std::make_unique<AddressesMap>(*this, *ErrorOrObj, Obj),
-        Obj.empty() ? Obj.getWarnings() : EmptyWarnings);
+        std::make_unique<AddressesMap>(*this, *ErrorOrObj, Obj));
 
     Error E = RL.link(*ErrorOrObj);
     if (Error NewE = handleErrors(
@@ -768,8 +767,7 @@ bool DwarfLinkerForBinary::linkImpl(
                                    OnCUDieLoaded);
     } else {
       ObjectsForLinking.push_back(std::make_unique<OutDwarfFile>(
-          Obj->getObjectFilename(), nullptr, nullptr,
-          Obj->empty() ? Obj->getWarnings() : EmptyWarnings));
+          Obj->getObjectFilename(), nullptr, nullptr));
       GeneralLinker->addObjectFile(*ObjectsForLinking.back());
     }
   }

llvm/tools/dsymutil/MachODebugMapParser.cpp

@@ -28,11 +28,9 @@ class MachODebugMapParser {
 public:
   MachODebugMapParser(llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> VFS,
                       StringRef BinaryPath, ArrayRef<std::string> Archs,
-                      StringRef PathPrefix = "",
-                      bool PaperTrailWarnings = false, bool Verbose = false)
+                      StringRef PathPrefix = "", bool Verbose = false)
       : BinaryPath(std::string(BinaryPath)), Archs(Archs.begin(), Archs.end()),
-        PathPrefix(std::string(PathPrefix)),
-        PaperTrailWarnings(PaperTrailWarnings), BinHolder(VFS, Verbose),
+        PathPrefix(std::string(PathPrefix)), BinHolder(VFS, Verbose),
         CurrentDebugMapObject(nullptr), SkipDebugMapObject(false) {}
 
   /// Parses and returns the DebugMaps of the input binary. The binary contains
@@ -50,7 +48,6 @@ class MachODebugMapParser {
   std::string BinaryPath;
   SmallVector<StringRef, 1> Archs;
   std::string PathPrefix;
-  bool PaperTrailWarnings;
 
   /// Owns the MemoryBuffer for the main binary.
   BinaryHolder BinHolder;
@@ -137,13 +134,6 @@ class MachODebugMapParser {
                          << MachOUtils::getArchName(
                                 Result->getTriple().getArchName())
                          << ") " << File << " " << Msg << "\n";
-
-    if (PaperTrailWarnings) {
-      if (!File.empty())
-        Result->addDebugMapObject(File, sys::TimePoint<std::chrono::seconds>());
-      if (Result->end() != Result->begin())
-        (*--Result->end())->addWarning(Msg.str());
-    }
   }
 };
 
@@ -704,13 +694,11 @@ namespace dsymutil {
 llvm::ErrorOr<std::vector<std::unique_ptr<DebugMap>>>
 parseDebugMap(llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> VFS,
               StringRef InputFile, ArrayRef<std::string> Archs,
-              StringRef PrependPath, bool PaperTrailWarnings, bool Verbose,
-              bool InputIsYAML) {
+              StringRef PrependPath, bool Verbose, bool InputIsYAML) {
   if (InputIsYAML)
     return DebugMap::parseYAMLDebugMap(InputFile, PrependPath, Verbose);
 
-  MachODebugMapParser Parser(VFS, InputFile, Archs, PrependPath,
-                             PaperTrailWarnings, Verbose);
+  MachODebugMapParser Parser(VFS, InputFile, Archs, PrependPath, Verbose);
   return Parser.parse();
 }
 

llvm/tools/dsymutil/Options.td

@@ -69,10 +69,6 @@ def yaml_input: Flag<["-", "--"], "y">,
   HelpText<"Treat the input file is a YAML debug map rather than a binary.">,
   Group<grp_general>;
 
-def papertrail: F<"papertrail">,
-  HelpText<"Embed warnings in the linked DWARF debug info.">,
-  Group<grp_general>;
-
 def assembly: Flag<["-", "--"], "S">,
   HelpText<"Output textual assembly instead of a binary dSYM companion file.">,
   Group<grp_general>;

llvm/tools/dsymutil/dsymutil.cpp

@@ -106,7 +106,6 @@ struct DsymutilOptions {
   bool DumpStab = false;
   bool Flat = false;
   bool InputIsYAMLDebugMap = false;
-  bool PaperTrailWarnings = false;
   bool ForceKeepFunctionForStatic = false;
   std::string SymbolMap;
   std::string OutputFile;
@@ -197,11 +196,6 @@ static Error verifyOptions(const DsymutilOptions &Options) {
         "cannot use -o with multiple inputs in flat mode.",
         errc::invalid_argument);
 
-  if (Options.PaperTrailWarnings && Options.InputIsYAMLDebugMap)
-    return make_error<StringError>(
-        "paper trail warnings are not supported for YAML input.",
-        errc::invalid_argument);
-
   if (!Options.ReproducerPath.empty() &&
       Options.ReproMode != ReproducerMode::Use)
     return make_error<StringError>(
@@ -303,7 +297,6 @@ static Expected<DsymutilOptions> getOptions(opt::InputArgList &Args) {
   Options.DumpStab = Args.hasArg(OPT_symtab);
   Options.Flat = Args.hasArg(OPT_flat);
   Options.InputIsYAMLDebugMap = Args.hasArg(OPT_yaml_input);
-  Options.PaperTrailWarnings = Args.hasArg(OPT_papertrail);
 
   if (Expected<DWARFVerify> Verify = getVerifyKind(Args)) {
     Options.Verify = *Verify;
@@ -389,9 +382,6 @@ static Expected<DsymutilOptions> getOptions(opt::InputArgList &Args) {
   if (Options.DumpDebugMap || Options.LinkOpts.Verbose)
     Options.LinkOpts.Threads = 1;
 
-  if (getenv("RC_DEBUG_OPTIONS"))
-    Options.PaperTrailWarnings = true;
-
   if (opt::Arg *RemarksPrependPath = Args.getLastArg(OPT_remarks_prepend_path))
     Options.LinkOpts.RemarksPrependPath = RemarksPrependPath->getValue();
 
@@ -671,8 +661,8 @@ int main(int argc, char **argv) {
 
     auto DebugMapPtrsOrErr =
         parseDebugMap(Options.LinkOpts.VFS, InputFile, Options.Archs,
-                      Options.LinkOpts.PrependPath, Options.PaperTrailWarnings,
-                      Options.LinkOpts.Verbose, Options.InputIsYAMLDebugMap);
+                      Options.LinkOpts.PrependPath, Options.LinkOpts.Verbose,
+                      Options.InputIsYAMLDebugMap);
 
     if (auto EC = DebugMapPtrsOrErr.getError()) {
       WithColor::error() << "cannot parse the debug map for '" << InputFile

llvm/tools/dsymutil/dsymutil.h

@@ -37,8 +37,7 @@ class BinaryHolder;
 ErrorOr<std::vector<std::unique_ptr<DebugMap>>>
 parseDebugMap(llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> VFS,
               StringRef InputFile, ArrayRef<std::string> Archs,
-              StringRef PrependPath, bool PaperTrailWarnings, bool Verbose,
-              bool InputIsYAML);
+              StringRef PrependPath, bool Verbose, bool InputIsYAML);
 
 /// Dump the symbol table.
 bool dumpStab(llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> VFS,

llvm/tools/llvm-dwarfutil/DebugInfoLinker.cpp

@@ -322,17 +322,15 @@ Error linkDebugInfoImpl(object::ObjectFile &File, const Options &Options,
   DebugInfoLinker->setUpdateIndexTablesOnly(!Options.DoGarbageCollection);
 
   std::vector<std::unique_ptr<OutDwarfFile>> ObjectsForLinking(1);
-  std::vector<std::string> EmptyWarnings;
 
   // Add object files to the DWARFLinker.
   std::unique_ptr<DWARFContext> Context = DWARFContext::create(File);
   std::unique_ptr<ObjFileAddressMap<AddressMapBase>> AddressesMap(
       std::make_unique<ObjFileAddressMap<AddressMapBase>>(*Context, Options,
                                                           File));
 
-  ObjectsForLinking[0] =
-      std::make_unique<OutDwarfFile>(File.getFileName(), std::move(Context),
-                                     std::move(AddressesMap), EmptyWarnings);
+  ObjectsForLinking[0] = std::make_unique<OutDwarfFile>(
+      File.getFileName(), std::move(Context), std::move(AddressesMap));
 
   uint16_t MaxDWARFVersion = 0;
   std::function<void(const DWARFUnit &Unit)> OnCUDieLoaded =