[Dwarf Patch] Create .debug_str section in .o with -gsplit-dwarf

[saugustine, 2013-04-23 21:01:31]

As things stand now when using -gsplit-dwarf, all strings in the main .o file
are emitted in line with DW_FORM_string, resulting in a large amount of
duplication, particularly with the .dwo name attribute.

The enclosed patch fixes that by putting these string in a small .debug_str
section, similar to the way force_direct works for other debug info that we want
to stay in the .o file that would otherwise go in the .dwo.

Google has been using this patch locally for a while now. However, now that
stage-1 is open again, it makes sense to apply it to trunk.

Tested with full bootstrap and not observing new failures.

OK for trunk?

Sterling


2013-04-22  Sterling Augustine  <saugustine@google.com>

	* dwarf2out.c (skeleton_debug_str_hash, comp_dir_string,
	add_skeleton_AT_string. comp_dir_string, debug_str_dwo_section): New.
	(DEBUG_STR_DWO_SECTION): Rename to ...
	(DEBUG_DWO_STR_SECTION): ... this.
	(DEBUG_NORM_STR_SECTION): Delete.
	(DEBUG_STR_SECTION, DEBUG_STR_SECTION_FLAGS): Edit definitions.
	(DEBUG_STR_DWO_SECTION_FLAGS): New.
	(find_AT_string): Move most logic to ...
	(find_AT_string_in_table): ... here.  New.
	(add_top_level_skeleton_die_attrs): Call comp_dir_string and
	add_skeleton_AT_string.  Delete logic.
	(output_skeleton_debug_sections): Remove call to
	add_top_level_skeleton_die_attrs.
	(add_comp_dir_attribute): Move logic to comp_dir_string.
	(dwarf2out_init): Initialize debug_str_dwo_section.
	(output_indirect_string): Call find_string_form.
	(output_indirect_strings): Rewrite.
	(prune_unused_types): Empty skeleton_debug_str_hash.
	Call get_skeleton_type_unit and add_top_level_skeleton_die_attrs.
	(dwarf2out_finish):  Call output_indirect_strings.


Index: gcc/dwarf2out.c
===================================================================
--- gcc/dwarf2out.c	(revision 198161)
+++ gcc/dwarf2out.c	(working copy)
@@ -157,6 +157,7 @@
 static GTY(()) section *debug_pubnames_section;
 static GTY(()) section *debug_pubtypes_section;
 static GTY(()) section *debug_str_section;
+static GTY(()) section *debug_str_dwo_section;
 static GTY(()) section *debug_str_offsets_section;
 static GTY(()) section *debug_ranges_section;
 static GTY(()) section *debug_frame_section;
@@ -206,6 +207,28 @@
 
 static GTY ((param_is (struct indirect_string_node))) htab_t debug_str_hash;
 
+/* With split_debug_info, both the comp_dir and dwo_name go in the
+   main object file, rather than the dwo, similar to the force_direct
+   parameter elsewhere but with additional complications:
+
+   1) The string is needed in both the main object file and the dwo.
+   That is, the comp_dir and dwo_name will appear in both places.
+
+   2) Strings can use three forms: DW_FORM_string, DW_FORM_strp or
+   DW_FORM_GNU_str_index.
+
+   3) GCC chooses the form to use late, depending on the size and
+   reference count.
+
+   Rather than forcing the all debug string handling functions and
+   callers to deal with these complications, simply use a separate,
+   special-cased string table for any attribute that should go in the
+   main object file.  This limits the complexity to just the places
+   that need it.  */
+
+static GTY ((param_is (struct indirect_string_node)))
+  htab_t skeleton_debug_str_hash;
+
 static GTY(()) int dw2_string_counter;
 
 /* True if the compilation unit places functions in more than one section.  */
@@ -3197,6 +3220,8 @@
 static void schedule_generic_params_dies_gen (tree t);
 static void gen_scheduled_generic_parms_dies (void);
 
+static const char *comp_dir_string (void);
+
 /* enum for tracking thread-local variables whose address is really an offset
    relative to the TLS pointer, which will need link-time relocation, but will
    not need relocation by the DWARF consumer.  */
@@ -3310,11 +3335,11 @@
   (!dwarf_split_debug_info                                              \
    ? (DEBUG_NORM_STR_OFFSETS_SECTION) : (DEBUG_DWO_STR_OFFSETS_SECTION))
 #endif
-#define DEBUG_DWO_STR_SECTION   ".debug_str.dwo"
-#define DEBUG_NORM_STR_SECTION  ".debug_str"
+#ifndef DEBUG_STR_DWO_SECTION
+#define DEBUG_STR_DWO_SECTION   ".debug_str.dwo"
+#endif
 #ifndef DEBUG_STR_SECTION
-#define DEBUG_STR_SECTION                               \
-  (!dwarf_split_debug_info ? (DEBUG_NORM_STR_SECTION) :
(DEBUG_DWO_STR_SECTION))
+#define DEBUG_STR_SECTION  ".debug_str"
 #endif
 #ifndef DEBUG_RANGES_SECTION
 #define DEBUG_RANGES_SECTION	".debug_ranges"
@@ -3326,17 +3351,18 @@
 #endif
 
 /* Section flags for .debug_macinfo/.debug_macro section.  */
-#define DEBUG_MACRO_SECTION_FLAGS \
+#define DEBUG_MACRO_SECTION_FLAGS                                       \
   (dwarf_split_debug_info ? SECTION_DEBUG | SECTION_EXCLUDE : SECTION_DEBUG)
 
 /* Section flags for .debug_str section.  */
-#define DEBUG_STR_SECTION_FLAGS \
-  (dwarf_split_debug_info \
-   ? SECTION_DEBUG | SECTION_EXCLUDE \
-   : (HAVE_GAS_SHF_MERGE && flag_merge_debug_strings \
-      ? SECTION_DEBUG | SECTION_MERGE | SECTION_STRINGS | 1        \
-      : SECTION_DEBUG))
+#define DEBUG_STR_SECTION_FLAGS                                 \
+  (HAVE_GAS_SHF_MERGE && flag_merge_debug_strings               \
+   ? SECTION_DEBUG | SECTION_MERGE | SECTION_STRINGS | 1        \
+   : SECTION_DEBUG)
 
+/* Section flags for .debug_str.dwo section.  */
+#define DEBUG_STR_DWO_SECTION_FLAGS (SECTION_DEBUG | SECTION_EXCLUDE)
+
 /* Labels we insert at beginning sections we can reference instead of
    the section names themselves.  */
 
@@ -3819,19 +3845,15 @@
 		 (const char *)x2) == 0;
 }
 
-/* Add STR to the indirect string hash table.  */
+/* Add STR to the given string hash table.  */
 
 static struct indirect_string_node *
-find_AT_string (const char *str)
+find_AT_string_in_table (const char *str, htab_t table)
 {
   struct indirect_string_node *node;
   void **slot;
 
-  if (! debug_str_hash)
-    debug_str_hash = htab_create_ggc (10, debug_str_do_hash,
-				      debug_str_eq, NULL);
-
-  slot = htab_find_slot_with_hash (debug_str_hash, str,
+  slot = htab_find_slot_with_hash (table, str,
 				   htab_hash_string (str), INSERT);
   if (*slot == NULL)
     {
@@ -3846,6 +3868,18 @@
   return node;
 }
 
+/* Add STR to the indirect string hash table.  */
+
+static struct indirect_string_node *
+find_AT_string (const char *str)
+{
+  if (! debug_str_hash)
+    debug_str_hash = htab_create_ggc (10, debug_str_do_hash,
+				      debug_str_eq, NULL);
+
+  return find_AT_string_in_table (str, debug_str_hash);
+}
+
 /* Add a string attribute value to a DIE.  */
 
 static inline void
@@ -8680,6 +8714,31 @@
     add_AT_flag (die, DW_AT_GNU_pubnames, 1);
 }
 
+/* Add a string attribute value to a skeleton DIE.  */
+
+static inline void
+add_skeleton_AT_string (dw_die_ref die, enum dwarf_attribute attr_kind,
+                        const char *str)
+{
+  dw_attr_node attr;
+  struct indirect_string_node *node;
+
+  if (! skeleton_debug_str_hash)
+    skeleton_debug_str_hash = htab_create_ggc (10, debug_str_do_hash,
+                                               debug_str_eq, NULL);
+
+  node = find_AT_string_in_table (str, skeleton_debug_str_hash);
+  find_string_form (node);
+  if (node->form == DW_FORM_GNU_str_index)
+    node->form = DW_FORM_strp;
+
+  attr.dw_attr = attr_kind;
+  attr.dw_attr_val.val_class = dw_val_class_str;
+  attr.dw_attr_val.val_entry = NULL;
+  attr.dw_attr_val.v.val_str = node;
+  add_dwarf_attr (die, &attr);
+}
+
 /* Helper function to generate top-level dies for skeleton debug_info and
    debug_types.  */
 
@@ -8687,18 +8746,11 @@
 add_top_level_skeleton_die_attrs (dw_die_ref die)
 {
   const char *dwo_file_name = concat (aux_base_name, ".dwo", NULL);
-  dw_attr_ref attr;
+  const char *comp_dir = comp_dir_string ();
 
-  add_comp_dir_attribute (die);
-  add_AT_string (die, DW_AT_GNU_dwo_name, dwo_file_name);
-  /* The specification suggests that these attributes be inline to avoid
-     having a .debug_str section.  We know that they exist in the die because
-     we just added them.  */
-  attr = get_AT (die, DW_AT_GNU_dwo_name);
-  attr->dw_attr_val.v.val_str->form = DW_FORM_string;
-  attr = get_AT (die, DW_AT_comp_dir);
-  attr->dw_attr_val.v.val_str->form = DW_FORM_string;
-
+  add_skeleton_AT_string (die, DW_AT_GNU_dwo_name, dwo_file_name);
+  if (comp_dir != NULL)
+    add_skeleton_AT_string (die, DW_AT_comp_dir, comp_dir);
   add_AT_pubnames (die);
   add_AT_lineptr (die, DW_AT_GNU_addr_base, debug_addr_section_label);
 }
@@ -8732,9 +8784,6 @@
   remove_AT (comp_unit, DW_AT_producer);
   remove_AT (comp_unit, DW_AT_language);
 
-  /* Add attributes common to skeleton compile_units and type_units.  */
-  add_top_level_skeleton_die_attrs (comp_unit);
-
   switch_to_section (debug_skeleton_info_section);
   ASM_OUTPUT_LABEL (asm_out_file, debug_skeleton_info_section_label);
 
@@ -15787,16 +15836,16 @@
   add_AT_die_ref (die, DW_AT_GNAT_descriptive_type, dtype_die);
 }
 
-/* Generate a DW_AT_comp_dir attribute for DIE.  */
+/* Retrieve the comp_dir string suitable for use with DW_AT_comp_dir.  */
 
-static void
-add_comp_dir_attribute (dw_die_ref die)
+static const char *
+comp_dir_string (void)
 {
   const char *wd = get_src_pwd ();
   char *wd1;
 
   if (wd == NULL)
-    return;
+    return NULL;
 
   if (DWARF2_DIR_SHOULD_END_WITH_SEPARATOR)
     {
@@ -15809,8 +15858,17 @@
       wd1 [wdlen + 1] = 0;
       wd = wd1;
     }
+  return remap_debug_filename (wd);
+}
 
-    add_AT_string (die, DW_AT_comp_dir, remap_debug_filename (wd));
+/* Generate a DW_AT_comp_dir attribute for DIE.  */
+
+static void
+add_comp_dir_attribute (dw_die_ref die)
+{
+  const char * wd = comp_dir_string ();
+  if (wd != NULL)
+    add_AT_string (die, DW_AT_comp_dir, wd);
 }
 
 /* Return the default for DW_AT_lower_bound, or -1 if there is not any
@@ -21718,6 +21776,8 @@
                                    DEBUG_SKELETON_INFO_SECTION_LABEL, 0);
       debug_loc_section = get_section (DEBUG_DWO_LOC_SECTION,
                                        SECTION_DEBUG | SECTION_EXCLUDE, NULL);
+      debug_str_dwo_section = get_section (DEBUG_STR_DWO_SECTION,
+                                           DEBUG_STR_DWO_SECTION_FLAGS, NULL);
     }
   debug_aranges_section = get_section (DEBUG_ARANGES_SECTION,
 				       SECTION_DEBUG, NULL);
@@ -21842,7 +21902,6 @@
       /* Assert that the strings are output in the same order as their
          indexes were assigned.  */
       gcc_assert (*cur_idx == node->index);
-      ASM_OUTPUT_LABEL (asm_out_file, node->label);
       assemble_string (node->str, strlen (node->str) + 1);
       *cur_idx += 1;
     }
@@ -21857,6 +21916,7 @@
 {
   struct indirect_string_node *node = (struct indirect_string_node *) *h;
 
+  node->form = find_string_form (node);
   if (node->form == DW_FORM_strp && node->refcount > 0)
     {
       ASM_OUTPUT_LABEL (asm_out_file, node->label);
@@ -21871,21 +21931,21 @@
 static void
 output_indirect_strings (void)
 {
+  switch_to_section (debug_str_section);
   if (!dwarf_split_debug_info)
-    {
-      switch_to_section (debug_str_section);
-      htab_traverse (debug_str_hash, output_indirect_string, NULL);
-    }
+    htab_traverse (debug_str_hash, output_indirect_string, NULL);
   else
     {
       unsigned int offset = 0;
       unsigned int cur_idx = 0;
 
+      htab_traverse (skeleton_debug_str_hash, output_indirect_string, NULL);
+
       switch_to_section (debug_str_offsets_section);
       htab_traverse_noresize (debug_str_hash,
                               output_index_string_offset,
                               &offset);
-      switch_to_section (debug_str_section);
+      switch_to_section (debug_str_dwo_section);
       htab_traverse_noresize (debug_str_hash,
                               output_index_string,
                               &cur_idx);
@@ -22300,6 +22360,8 @@
 
   if (debug_str_hash)
     htab_empty (debug_str_hash);
+  if (skeleton_debug_str_hash)
+    htab_empty (skeleton_debug_str_hash);
   prune_unused_types_prune (comp_unit_die ());
   for (node = limbo_die_list; node; node = node->next)
     prune_unused_types_prune (node->die);
@@ -23769,9 +23831,18 @@
     optimize_location_lists (comp_unit_die ());
 
   save_macinfo_strings ();
+
   if (dwarf_split_debug_info)
     {
       unsigned int index = 0;
+
+      /* Add attributes common to skeleton compile_units and
+         type_units.  Because these attributes include strings, it
+         must be done before freezing the string table.  Top-level
+         skeleton die attrs are added when the skeleton type unit is
+         created, so ensure it is created by this point.  */
+      add_top_level_skeleton_die_attrs (main_comp_unit_die);
+      (void) get_skeleton_type_unit ();
       htab_traverse_noresize (debug_str_hash, index_string, &index);
     }
 
@@ -23919,7 +23990,7 @@
     }
 
   /* If we emitted any indirect strings, output the string table too.  */
-  if (debug_str_hash)
+  if (debug_str_hash || skeleton_debug_str_hash)
     output_indirect_strings ();
 }
 

--
This patch is available for review at http://codereview.appspot.com/8540048

[Cary, 2013-04-23 21:45:23]

> 2013-04-22  Sterling Augustine  <saugustine@google.com>
>
>         * dwarf2out.c (skeleton_debug_str_hash, comp_dir_string,
>         add_skeleton_AT_string. comp_dir_string, debug_str_dwo_section): New.

s/./,/

I think comp_dir_string only needs to be mentioned once.

>         (DEBUG_STR_DWO_SECTION): Rename to ...
>         (DEBUG_DWO_STR_SECTION): ... this.
>         (DEBUG_NORM_STR_SECTION): Delete.
>         (DEBUG_STR_SECTION, DEBUG_STR_SECTION_FLAGS): Edit definitions.
>         (DEBUG_STR_DWO_SECTION_FLAGS): New.
>         (find_AT_string): Move most logic to ...
>         (find_AT_string_in_table): ... here.  New.
>         (add_top_level_skeleton_die_attrs): Call comp_dir_string and
>         add_skeleton_AT_string.  Delete logic.
>         (output_skeleton_debug_sections): Remove call to
>         add_top_level_skeleton_die_attrs.
>         (add_comp_dir_attribute): Move logic to comp_dir_string.
>         (dwarf2out_init): Initialize debug_str_dwo_section.
>         (output_indirect_string): Call find_string_form.
>         (output_indirect_strings): Rewrite.
>         (prune_unused_types): Empty skeleton_debug_str_hash.
>         Call get_skeleton_type_unit and add_top_level_skeleton_die_attrs.
>         (dwarf2out_finish):  Call output_indirect_strings.

You'll be calling comp_dir_string twice, so I think you should cache
its return value.

-cary