[dsymutil] Remove paper trail warnings (#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.

2 files changed, 0 insertions, 78 deletions

diff --git a/llvm/lib/DWARFLinker/DWARFLinker.cpp b/llvm/lib/DWARFLinker/DWARFLinker.cpp
index 35e5cef..5ed4923 100644
--- a/llvm/lib/DWARFLinker/DWARFLinker.cpp
+++ b/llvm/lib/DWARFLinker/DWARFLinker.cpp
@@ -2584,69 +2584,6 @@ 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");
@@ -2711,9 +2648,6 @@ Error DWARFLinker::link() {
         outs() << "OBJECT FILE: " << OptContext.File.FileName << "\n";
     }
 
-    if (emitPaperTrailWarnings(OptContext.File, DebugStrPool))
-      continue;
-
     if (!OptContext.File.Dwarf)
       continue;
 
diff --git a/llvm/lib/DWARFLinker/DWARFStreamer.cpp b/llvm/lib/DWARFLinker/DWARFStreamer.cpp
index 4d5eef5..3bcc5a0 100644
--- a/llvm/lib/DWARFLinker/DWARFStreamer.cpp
+++ b/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());