[lldb] Don't put compile unit name into the support file list and support DWARF5 line tables

Summary:
Lldb's "format-independent" debug info made use of the fact that DWARF
(<=4) did not use the file index zero, and reused the support file index
zero for storing the compile unit name.

While this provided some convenience for DWARF<=4, it meant that the PDB
plugin needed to artificially remap file indices in order to free up
index 0. Furthermore, DWARF v5 make file index 0 legal, which meant that
similar remapping would be needed in the dwarf plugin too.

What this patch does instead is remove the requirement of having the
compile unit name in the index 0. It is not that useful since the name
can always be fetched from the CompileUnit object. Remapping code in the
pdb plugin(s) has been removed or simplified.

DWARF plugin has started inserting an empty FileSpec at index 0 to
ensure the indices keep matching up (in case of DWARF<=4). For DWARF5,
we insert the file 0 from the line table.

I add a test to ensure we can correctly lookup line table entries
referencing file 0, and in particular the case where the file 0 is also
duplicated in another file entry, as this is how clang produces line
tables in some circumstances (see pr44170). Though this is probably a
bug in clang, this is not forbidden by DWARF, and lldb already has
support for that in some (but not all) cases -- this adds a test for the
code path which was not fixed in this patch.

Reviewers: clayborg, JDevlieghere, jdoerfert

Subscribers: aprantl, lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D70954

3 files changed, 17 insertions, 26 deletions

diff --git a/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp b/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
index b8575d13d45..fc8fe30101c 100644
--- a/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
+++ b/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
@@ -198,15 +198,23 @@ GetFileByIndex(const llvm::DWARFDebugLine::Prologue &prologue, size_t idx,
   return std::move(rel_path);
 }
 
-static FileSpecList ParseSupportFilesFromPrologue(
-    const lldb::ModuleSP &module,
-    const llvm::DWARFDebugLine::Prologue &prologue, FileSpec::Style style,
-    llvm::StringRef compile_dir = {}, FileSpec first_file = {}) {
+static FileSpecList
+ParseSupportFilesFromPrologue(const lldb::ModuleSP &module,
+                              const llvm::DWARFDebugLine::Prologue &prologue,
+                              FileSpec::Style style,
+                              llvm::StringRef compile_dir = {}) {
   FileSpecList support_files;
-  support_files.Append(first_file);
+  size_t first_file = 0;
+  if (prologue.getVersion() <= 4) {
+    // File index 0 is not valid before DWARF v5. Add a dummy entry to ensure
+    // support file list indices match those we get from the debug info and line
+    // tables.
+    support_files.Append(FileSpec());
+    first_file = 1;
+  }
 
   const size_t number_of_files = prologue.FileNames.size();
-  for (size_t idx = 1; idx <= number_of_files; ++idx) {
+  for (size_t idx = first_file; idx <= number_of_files; ++idx) {
     std::string remapped_file;
     if (auto file_path = GetFileByIndex(prologue, idx, compile_dir, style))
       if (!module->RemapSourceFile(llvm::StringRef(*file_path), remapped_file))
@@ -1046,8 +1054,7 @@ bool SymbolFileDWARF::ParseLineTable(CompileUnit &comp_unit) {
 
   comp_unit.SetSupportFiles(ParseSupportFilesFromPrologue(
       comp_unit.GetModule(), line_table->Prologue, dwarf_cu->GetPathStyle(),
-      dwarf_cu->GetCompilationDirectory().GetCString(),
-      comp_unit.GetPrimaryFile()));
+      dwarf_cu->GetCompilationDirectory().GetCString()));
 
   return true;
 }
diff --git a/lldb/source/Plugins/SymbolFile/NativePDB/SymbolFileNativePDB.cpp b/lldb/source/Plugins/SymbolFile/NativePDB/SymbolFileNativePDB.cpp
index f0308e23c9d..22d1b08ea9e 100644
--- a/lldb/source/Plugins/SymbolFile/NativePDB/SymbolFileNativePDB.cpp
+++ b/lldb/source/Plugins/SymbolFile/NativePDB/SymbolFileNativePDB.cpp
@@ -1110,9 +1110,7 @@ bool SymbolFileNativePDB::ParseLineTable(CompileUnit &comp_unit) {
       // LLDB wants the index of the file in the list of support files.
       auto fn_iter = llvm::find(cci->m_file_list, *efn);
       lldbassert(fn_iter != cci->m_file_list.end());
-      // LLDB support file indices are 1-based.
-      uint32_t file_index =
-          1 + std::distance(cci->m_file_list.begin(), fn_iter);
+      uint32_t file_index = std::distance(cci->m_file_list.begin(), fn_iter);
 
       std::unique_ptr<LineSequence> sequence(
           line_table->CreateLineSequenceContainer());
@@ -1155,14 +1153,6 @@ bool SymbolFileNativePDB::ParseSupportFiles(CompileUnit &comp_unit,
     FileSpec spec(f, style);
     support_files.Append(spec);
   }
-
-  llvm::SmallString<64> main_source_file =
-      m_index->compilands().GetMainSourceFile(*cci);
-  FileSpec::Style style = main_source_file.startswith("/")
-                              ? FileSpec::Style::posix
-                              : FileSpec::Style::windows;
-  FileSpec spec(main_source_file, style);
-  support_files.Insert(0, spec);
   return true;
 }
 
diff --git a/lldb/source/Plugins/SymbolFile/PDB/SymbolFilePDB.cpp b/lldb/source/Plugins/SymbolFile/PDB/SymbolFilePDB.cpp
index dcbefdcbb6f..b3e06fdd1a5 100644
--- a/lldb/source/Plugins/SymbolFile/PDB/SymbolFilePDB.cpp
+++ b/lldb/source/Plugins/SymbolFile/PDB/SymbolFilePDB.cpp
@@ -371,10 +371,6 @@ bool SymbolFilePDB::ParseSupportFiles(
     support_files.AppendIfUnique(spec);
   }
 
-  // LLDB uses the DWARF-like file numeration (one based),
-  // the zeroth file is the compile unit itself
-  support_files.Insert(0, comp_unit.GetPrimaryFile());
-
   return true;
 }
 
@@ -1881,9 +1877,7 @@ void SymbolFilePDB::BuildSupportFileIdToSupportFileIndexMap(
   if (!source_files)
     return;
 
-  // LLDB uses the DWARF-like file numeration (one based)
-  int index = 1;
-
+  int index = 0;
   while (auto file = source_files->getNext()) {
     uint32_t source_id = file->getUniqueId();
     index_map[source_id] = index++;