Apply basic patch by David Blaikie to update gold dwp tool to handle
DWARF v5. This is the third of three patches for DWARF v5.

This patch contains a few more efficiency improvements.

This patch created for Chrome OS by Caroline Tice.
Date: 20-Nov-2020
diff --git a/gold/dwp.cc b/gold/dwp.cc
index 60de58bc..4d83948c 100644
--- a/gold/dwp.cc
+++ b/gold/dwp.cc
@@ -817,27 +817,15 @@ get_dwarf_section_name(elfcpp::DW_SECT section_id)
   static const char* dwarf_section_names[] = {
     NULL,		      // unused
     ".debug_info.dwo",	      // DW_SECT_INFO = 1
-    NULL,		      // unused
+    ".debug_types.dwo",	      // LEGACY_DW_SECT_TYPES = 2
     ".debug_abbrev.dwo",      // DW_SECT_ABBREV = 3
     ".debug_line.dwo",	      // DW_SECT_LINE = 4
     ".debug_loclists.dwo",    // DW_SECT_LOCLISTS = 5
     ".debug_str_offsets.dwo", // DW_SECT_STR_OFFSETS = 6
     ".debug_macro.dwo",	      // DW_SECT_MACRO = 7
     ".debug_rnglists.dwo",    // DW_SECT_RNGLISTS = 8
-    NULL,		      // unused
-    NULL,		      // unused
-    NULL,		      // unused
-    NULL,		      // unused
-    NULL,		      // unused
-    NULL,		      // unused
-    NULL,		      // unused
-    NULL,		      // unused
-    NULL,		      // unused
-    NULL,		      // unused
-    NULL,		      // unused
-    ".debug_types.dwo",	      // LEGACY_DW_SECT_TYPES = 20
-    ".debug_loc.dwo",	      // LEGACY_DW_SECT_LOC = 21
-    ".debug_macinfo.dwo",     // LEGACY_DW_SECT_MACINFO = 22
+    ".debug_loc.dwo",	      // LEGACY_DW_SECT_LOC = 9
+    ".debug_macinfo.dwo",     // LEGACY_DW_SECT_MACINFO = 10
   };
 
   gold_assert(section_id > 0 && section_id <= elfcpp::DW_SECT_MAX);
@@ -2183,6 +2171,13 @@ Dwp_output_file::write_index(const char* sect_name, const Dwp_index& index)
   const unsigned int nused = index.hash_table_used_slots();
   const unsigned int nrows = index.section_table_rows();
 
+  // If there is no contribution, don't create .debug_cu_index or
+  // .debug_ty_index. We can't assign a meaningful index version.  Assigning an
+  // arbitrary version is not great because an upper-level dwp may have to deal
+  // with mixed index versions.
+  if (nused == 0)
+    return;
+
   int column_mask = index.section_table_cols();
   unsigned int ncols = 0;
   for (unsigned int c = 1; c <= elfcpp::DW_SECT_MAX; ++c)
diff --git a/elfcpp/dwarf.h b/elfcpp/dwarf.h
index 75769e5b..f23a9bf8 100644
--- a/elfcpp/dwarf.h
+++ b/elfcpp/dwarf.h
@@ -250,16 +250,16 @@ enum DW_LANG
 enum DW_SECT
 {
   DW_SECT_INFO = 1,
-  DW_SECT_TYPES = 2, // removed in v5
+  // DW_SECT_TYPES = 2, // removed in v5
   DW_SECT_ABBREV = 3,
   DW_SECT_LINE = 4,
   DW_SECT_LOCLISTS = 5, // was LOC pre-v5
   DW_SECT_STR_OFFSETS = 6,
   DW_SECT_MACRO = 7, // was MACINFO pre-v5
   DW_SECT_RNGLISTS = 8,  // was MACRO pre-v5
-  LEGACY_DW_SECT_TYPES = 20,
-  LEGACY_DW_SECT_LOC = 21,
-  LEGACY_DW_SECT_MACINFO = 22,
+  LEGACY_DW_SECT_TYPES = 2,
+  LEGACY_DW_SECT_LOC = 9,
+  LEGACY_DW_SECT_MACINFO = 10,
   DW_SECT_MAX = LEGACY_DW_SECT_MACINFO
 };