Modify llvm-gsymutil to ignore invalid file indexes

DWARF produced by LTO and BOLT can sometimes be broken where file indexes are beyond the end of the line table's file list in the prologue. This patch allows llvm-gsymutil to convert this DWARF without crashing, and emits errors when:

line table contains entries with an invalid file index (line entry will be removed)
inline functions that have invalid DW_AT_call_file file indexes
when there are no line table entries for a function and we fall back to making a single line table entry from the functions DW_AT_decl_file/DW_AT_decl_line attributes, we make sure the DW_AT_decl_file attribute is valid before emitting it.

llvm/lib/DebugInfo/GSYM/DwarfTransformer.cpp

@@ -65,10 +65,10 @@ struct llvm::gsym::CUInfo {
   /// the first client that asks for a compile unit file index will end up
   /// doing the conversion, and subsequent clients will get the cached GSYM
   /// index.
-  uint32_t DWARFToGSYMFileIndex(GsymCreator &Gsym, uint32_t DwarfFileIdx) {
-    if (!LineTable)
-      return 0;
-    assert(DwarfFileIdx < FileCache.size());
+  std::optional<uint32_t> DWARFToGSYMFileIndex(GsymCreator &Gsym,
+                                               uint32_t DwarfFileIdx) {
+    if (!LineTable || DwarfFileIdx >= FileCache.size())
+      return std::nullopt;
     uint32_t &GsymFileIdx = FileCache[DwarfFileIdx];
     if (GsymFileIdx != UINT32_MAX)
       return GsymFileIdx;
@@ -272,14 +272,24 @@ static void parseInlineInfo(GsymCreator &Gsym, raw_ostream *Log, CUInfo &CUI,
 
     if (auto NameIndex = getQualifiedNameIndex(Die, CUI.Language, Gsym))
       II.Name = *NameIndex;
-    II.CallFile = CUI.DWARFToGSYMFileIndex(
-        Gsym, dwarf::toUnsigned(Die.find(dwarf::DW_AT_call_file), 0));
-    II.CallLine = dwarf::toUnsigned(Die.find(dwarf::DW_AT_call_line), 0);
-    // parse all children and append to parent
-    for (DWARFDie ChildDie : Die.children())
-      parseInlineInfo(Gsym, Log, CUI, ChildDie, Depth + 1, FI, II,
-                      AllInlineRanges, WarnIfEmpty);
-    Parent.Children.emplace_back(std::move(II));
+    const uint64_t DwarfFileIdx = dwarf::toUnsigned(
+        Die.findRecursively(dwarf::DW_AT_call_file), UINT32_MAX);
+    std::optional<uint32_t> OptGSymFileIdx =
+        CUI.DWARFToGSYMFileIndex(Gsym, DwarfFileIdx);
+    if (OptGSymFileIdx) {
+      II.CallFile = OptGSymFileIdx.value();
+      II.CallLine = dwarf::toUnsigned(Die.find(dwarf::DW_AT_call_line), 0);
+      // parse all children and append to parent
+      for (DWARFDie ChildDie : Die.children())
+        parseInlineInfo(Gsym, Log, CUI, ChildDie, Depth + 1, FI, II,
+                        AllInlineRanges, WarnIfEmpty);
+      Parent.Children.emplace_back(std::move(II));
+    } else if (Log) {
+      *Log << "error: inlined function DIE at " << HEX32(Die.getOffset())
+           << " has an invalid file index " << DwarfFileIdx
+           << " in its DW_AT_call_file attribute, this inline entry and all "
+           << "children will be removed.\n";
+    }
     return;
   }
   if (Tag == dwarf::DW_TAG_subprogram || Tag == dwarf::DW_TAG_lexical_block) {
@@ -306,8 +316,20 @@ static void convertFunctionLineTable(raw_ostream *Log, CUInfo &CUI,
     // the DW_AT_decl_file an d DW_AT_decl_line if we have both attributes.
     std::string FilePath = Die.getDeclFile(
         DILineInfoSpecifier::FileLineInfoKind::AbsoluteFilePath);
-    if (FilePath.empty())
+    if (FilePath.empty()) {
+      // If we had a DW_AT_decl_file, but got no file then we need to emit a
+      // warning.
+      if (Log) {
+        const uint64_t DwarfFileIdx = dwarf::toUnsigned(
+            Die.findRecursively(dwarf::DW_AT_decl_file), UINT32_MAX);
+        *Log << "error: function DIE at " << HEX32(Die.getOffset())
+             << " has an invalid file index " << DwarfFileIdx
+             << " in its DW_AT_decl_file attribute, unable to create a single "
+             << "line entry from the DW_AT_decl_file/DW_AT_decl_line "
+             << "attributes.\n";
+      }
       return;
+    }
     if (auto Line =
             dwarf::toUnsigned(Die.findRecursively({dwarf::DW_AT_decl_line}))) {
       LineEntry LE(StartAddress, Gsym.insertFile(FilePath), *Line);
@@ -322,7 +344,20 @@ static void convertFunctionLineTable(raw_ostream *Log, CUInfo &CUI,
   for (uint32_t RowIndex : RowVector) {
     // Take file number and line/column from the row.
     const DWARFDebugLine::Row &Row = CUI.LineTable->Rows[RowIndex];
-    const uint32_t FileIdx = CUI.DWARFToGSYMFileIndex(Gsym, Row.File);
+    std::optional<uint32_t> OptFileIdx =
+        CUI.DWARFToGSYMFileIndex(Gsym, Row.File);
+    if (!OptFileIdx) {
+      if (Log) {
+        *Log << "error: function DIE at " << HEX32(Die.getOffset()) << " has "
+             << "a line entry with invalid DWARF file index, this entry will "
+             << "be removed:\n";
+        Row.dumpTableHeader(*Log, /*Indent=*/0);
+        Row.dump(*Log);
+        *Log << "\n";
+      }
+      continue;
+    }
+    const uint32_t FileIdx = OptFileIdx.value();
     uint64_t RowAddress = Row.Address.Address;
     // Watch out for a RowAddress that is in the middle of a line table entry
     // in the DWARF. If we pass an address in between two line table entries