Re: [Dwarf Patch] Generate -ggnu-pubnames

[Sterling Augustine <saugustine at google dot com>]

On Thu, Oct 17, 2013 at 12:09 PM, Sterling Augustine
<saugustine@google.com> wrote:
> The enclosed patch (which depends on
> http://gcc.gnu.org/ml/gcc-patches/2013-10/msg01395.html), ports the
> new -ggnu-pubnames option from google 4.8 to trunk.
>
> -gnu-pubnames enable the gold linker to to generate a better
> .gdb_index section by including various bits of data about the symbol.
>
> OK for trunk?
>
> Sterling
>
> 2013-10-17    <saugustine@google.com>
>
>     * doc/invoke.texi: Document -ggnu-pubnames.
>     * common.opt: Add new option -ggnu-pubnames and modify -gpubnames
>     logic.
>     * dwarf2out.c: Include gdb/gdb-index.h.
>     (DEBUG_PUBNAMES_SECTION, DEBUG_PUBTYPES_SECTION): Handle
>     debug_generate_pub_sections.
>     (is_java, output_pubtables, output_pubname): New functions.
>     (include_pubname_in_output): Handle debug_generate_pub_sections at
>     level 2.
>     (size_of_pubnames): Use new local space_for_flags based on
>     debug_generate_pub_sections.
>     (output_pubnames): Unify pubnames and pubtypes output logic.
>     Genericize comments.  Call output_pubname.
>     (dwarf2out_finish): Move logic to output_pubnames and call it.

Checked in as below, which has a minor change to not ICE when
encountering unknown DW_TAGs.

Index: dwarf2out.c
===================================================================
--- dwarf2out.c	(revision 203930)
+++ dwarf2out.c	(working copy)
@@ -93,6 +93,7 @@
 #include "dumpfile.h"
 #include "opts.h"
 #include "tree-dfa.h"
+#include "gdb/gdb-index.h"
 
 static void dwarf2out_source_line (unsigned int, const char *, int, bool);
 static rtx last_var_location_insn;
@@ -3323,10 +3324,14 @@
 #define DEBUG_DWO_LOC_SECTION  ".debug_loc.dwo"
 #endif
 #ifndef DEBUG_PUBNAMES_SECTION
-#define DEBUG_PUBNAMES_SECTION	".debug_pubnames"
+#define DEBUG_PUBNAMES_SECTION	\
+  ((debug_generate_pub_sections == 2) \
+   ? ".debug_gnu_pubnames" : ".debug_pubnames")
 #endif
 #ifndef DEBUG_PUBTYPES_SECTION
-#define DEBUG_PUBTYPES_SECTION	".debug_pubtypes"
+#define DEBUG_PUBTYPES_SECTION	\
+  ((debug_generate_pub_sections == 2) \
+   ? ".debug_gnu_pubtypes" : ".debug_pubtypes")
 #endif
 #define DEBUG_NORM_STR_OFFSETS_SECTION ".debug_str_offsets"
 #define DEBUG_DWO_STR_OFFSETS_SECTION ".debug_str_offsets.dwo"
@@ -4569,6 +4574,16 @@
   return lang == DW_LANG_C_plus_plus || lang == DW_LANG_ObjC_plus_plus;
 }
 
+/* Return TRUE if the language is Java.  */
+
+static inline bool
+is_java (void)
+{
+  unsigned int lang = get_AT_unsigned (comp_unit_die (), DW_AT_language);
+
+  return lang == DW_LANG_Java;
+}
+
 /* Return TRUE if the language is Fortran.  */
 
 static inline bool
@@ -7960,6 +7975,12 @@
 static bool
 include_pubname_in_output (vec<pubname_entry, va_gc> *table, pubname_entry *p)
 {
+  /* By limiting gnu pubnames to definitions only, gold can generate a
+     gdb index without entries for declarations, which don't include
+     enough information to be useful.  */
+  if (debug_generate_pub_sections == 2 && is_declaration_die (p->die))
+    return false;
+
   if (table == pubname_table)
     {
       /* Enumerator names are part of the pubname table, but the
@@ -7989,11 +8010,12 @@
   unsigned long size;
   unsigned i;
   pubname_ref p;
+  int space_for_flags = (debug_generate_pub_sections == 2) ? 1 : 0;
 
   size = DWARF_PUBNAMES_HEADER_SIZE;
   FOR_EACH_VEC_ELT (*names, i, p)
     if (include_pubname_in_output (names, p))
-      size += strlen (p->name) + DWARF_OFFSET_SIZE + 1;
+      size += strlen (p->name) + DWARF_OFFSET_SIZE + 1 + space_for_flags;
 
   size += DWARF_OFFSET_SIZE;
   return size;
@@ -9146,6 +9168,76 @@
     }
 }
 
+/* Output a single entry in the pubnames table.  */
+
+static void
+output_pubname (dw_offset die_offset, pubname_entry *entry)
+{
+  dw_die_ref die = entry->die;
+  int is_static = get_AT_flag (die, DW_AT_external) ? 0 : 1;
+
+  dw2_asm_output_data (DWARF_OFFSET_SIZE, die_offset, "DIE offset");
+
+  if (debug_generate_pub_sections == 2)
+    {
+      /* This logic follows gdb's method for determining the value of the flag
+         byte.  */
+      uint32_t flags = GDB_INDEX_SYMBOL_KIND_NONE;
+      switch (die->die_tag)
+      {
+        case DW_TAG_typedef:
+        case DW_TAG_base_type:
+        case DW_TAG_subrange_type:
+          GDB_INDEX_SYMBOL_KIND_SET_VALUE(flags, GDB_INDEX_SYMBOL_KIND_TYPE);
+          GDB_INDEX_SYMBOL_STATIC_SET_VALUE(flags, 1);
+          break;
+        case DW_TAG_enumerator:
+          GDB_INDEX_SYMBOL_KIND_SET_VALUE(flags,
+                                          GDB_INDEX_SYMBOL_KIND_VARIABLE);
+          if (!is_cxx () && !is_java ())
+            GDB_INDEX_SYMBOL_STATIC_SET_VALUE(flags, 1);
+          break;
+        case DW_TAG_subprogram:
+          GDB_INDEX_SYMBOL_KIND_SET_VALUE(flags,
+                                          GDB_INDEX_SYMBOL_KIND_FUNCTION);
+          if (!is_ada ())
+            GDB_INDEX_SYMBOL_STATIC_SET_VALUE(flags, is_static);
+          break;
+        case DW_TAG_constant:
+          GDB_INDEX_SYMBOL_KIND_SET_VALUE(flags,
+                                          GDB_INDEX_SYMBOL_KIND_VARIABLE);
+          GDB_INDEX_SYMBOL_STATIC_SET_VALUE(flags, is_static);
+          break;
+        case DW_TAG_variable:
+          GDB_INDEX_SYMBOL_KIND_SET_VALUE(flags,
+                                          GDB_INDEX_SYMBOL_KIND_VARIABLE);
+          GDB_INDEX_SYMBOL_STATIC_SET_VALUE(flags, is_static);
+          break;
+        case DW_TAG_namespace:
+        case DW_TAG_imported_declaration:
+          GDB_INDEX_SYMBOL_KIND_SET_VALUE(flags, GDB_INDEX_SYMBOL_KIND_TYPE);
+          break;
+        case DW_TAG_class_type:
+        case DW_TAG_interface_type:
+        case DW_TAG_structure_type:
+        case DW_TAG_union_type:
+        case DW_TAG_enumeration_type:
+          GDB_INDEX_SYMBOL_KIND_SET_VALUE(flags, GDB_INDEX_SYMBOL_KIND_TYPE);
+          if (!is_cxx () && !is_java ())
+	    GDB_INDEX_SYMBOL_STATIC_SET_VALUE(flags, 1);
+          break;
+        default:
+          /* An unusual tag.  Leave the flag-byte empty.  */
+          break;
+      }
+      dw2_asm_output_data (1, flags >> GDB_INDEX_CU_BITSIZE,
+                           "GDB-index flags");
+    }
+
+  dw2_asm_output_nstring (entry->name, -1, "external name");
+}
+
+
 /* Output the public names table used to speed up access to externally
    visible names; or the public types table used to find type definitions.  */
 
@@ -9156,23 +9248,14 @@
   unsigned long pubnames_length = size_of_pubnames (names);
   pubname_ref pub;
 
-  if (!want_pubnames () || !info_section_emitted)
-    return;
-  if (names == pubname_table)
-    switch_to_section (debug_pubnames_section);
-  else
-    switch_to_section (debug_pubtypes_section);
   if (DWARF_INITIAL_LENGTH_SIZE - DWARF_OFFSET_SIZE == 4)
     dw2_asm_output_data (4, 0xffffffff,
       "Initial length escape value indicating 64-bit DWARF extension");
-  if (names == pubname_table)
-    dw2_asm_output_data (DWARF_OFFSET_SIZE, pubnames_length,
-			 "Length of Public Names Info");
-  else
-    dw2_asm_output_data (DWARF_OFFSET_SIZE, pubnames_length,
-			 "Length of Public Type Names Info");
-  /* Version number for pubnames/pubtypes is still 2, even in DWARF3.  */
+  dw2_asm_output_data (DWARF_OFFSET_SIZE, pubnames_length, "Pub Info Length");
+
+  /* Version number for pubnames/pubtypes is independent of dwarf version.  */
   dw2_asm_output_data (2, 2, "DWARF Version");
+
   if (dwarf_split_debug_info)
     dw2_asm_output_offset (DWARF_OFFSET_SIZE, debug_skeleton_info_section_label,
                            debug_skeleton_info_section,
@@ -9208,15 +9291,31 @@
 			      : 0);
 	    }
 
-	  dw2_asm_output_data (DWARF_OFFSET_SIZE, die_offset, "DIE offset");
-
-	  dw2_asm_output_nstring (pub->name, -1, "external name");
+          output_pubname (die_offset, pub);
 	}
     }
 
   dw2_asm_output_data (DWARF_OFFSET_SIZE, 0, NULL);
 }
 
+/* Output public names and types tables if necessary.  */
+
+static void
+output_pubtables (void)
+{
+  if (!want_pubnames () || !info_section_emitted)
+    return;
+
+  switch_to_section (debug_pubnames_section);
+  output_pubnames (pubname_table);
+  /* ??? Only defined by DWARF3, but emitted by Darwin for DWARF2.
+     It shouldn't hurt to emit it always, since pure DWARF2 consumers
+     simply won't look for the section.  */
+  switch_to_section (debug_pubtypes_section);
+  output_pubnames (pubtype_table);
+}
+
+
 /* Output the information that goes into the .debug_aranges table.
    Namely, define the beginning and ending address range of the
    text section generated for this compilation unit.  */
@@ -24092,12 +24191,7 @@
       output_location_lists (comp_unit_die ());
     }
 
-  /* Output public names and types tables if necessary.  */
-  output_pubnames (pubname_table);
-  /* ??? Only defined by DWARF3, but emitted by Darwin for DWARF2.
-     It shouldn't hurt to emit it always, since pure DWARF2 consumers
-     simply won't look for the section.  */
-  output_pubnames (pubtype_table);
+  output_pubtables ();
 
   /* Output the address range information if a CU (.debug_info section)
      was emitted.  We output an empty table even if we had no functions
Index: doc/invoke.texi
===================================================================
--- doc/invoke.texi	(revision 203930)
+++ doc/invoke.texi	(working copy)
@@ -5087,6 +5087,12 @@
 @opindex gpubnames
 Generate dwarf .debug_pubnames and .debug_pubtypes sections.
 
+@item -ggnu-pubnames
+@opindex ggnu-pubnames
+Generate .debug_pubnames and .debug_pubtypes sections in a format
+suitable for conversion into a GDB@ index.  This option is only useful
+with a linker that can produce GDB@ index version 7.
+
 @item -gstabs
 @opindex gstabs
 Produce debugging information in stabs format (if that is supported),
Index: common.opt
===================================================================
--- common.opt	(revision 203930)
+++ common.opt	(working copy)
@@ -2412,13 +2412,17 @@
 Generate debug information in default extended format
 
 gno-pubnames
-Common RejectNegative Var(debug_generate_pub_sections, 0) Init(-1)
+Common Negative(gpubnames) Var(debug_generate_pub_sections, 0) Init(-1)
 Don't generate DWARF pubnames and pubtypes sections.
 
 gpubnames
-Common RejectNegative Var(debug_generate_pub_sections, 1)
+Common Negative(ggnu-pubnames) Var(debug_generate_pub_sections, 1)
 Generate DWARF pubnames and pubtypes sections.
 
+ggnu-pubnames
+Common Negative(gno-pubnames) Var(debug_generate_pub_sections, 2)
+Generate DWARF pubnames and pubtypes sections with GNU extensions.
+
 gno-record-gcc-switches
 Common RejectNegative Var(dwarf_record_gcc_switches,0) Init(1)
 Don't record gcc command line switches in DWARF DW_AT_producer.