[Bug debug/48229] New: DW_TAG_type_unit has no DW_AT_producer

[Bug debug/48229] New: DW_TAG_type_unit has no DW_AT_producer

[jan.kratochvil at redhat dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48229

           Summary: DW_TAG_type_unit has no DW_AT_producer
           Product: gcc
           Version: 4.5.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: debug
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: jan.kratochvil@redhat.com
            Target: x86_64-unknown-linux-gnu


FAIL g++ (GCC) 4.5.3 20110322 (prerelease)
FAIL g++ (GCC) 4.6.0 20110322 (prerelease)
FAIL g++ (GCC) 4.7.0 20110322 (experimental)

echo 'class C {} c;' | g++ -o 1.o -c -g -Wall -x c++ - -gdwarf-4

Contents of the .debug_info section:
 <0><b>: Abbrev Number: 3 (DW_TAG_compile_unit)
    < c>   DW_AT_producer    : GNU C++ 4.5.3 20110322 (prerelease)      
+
Contents of the .debug_types section:
 <0><17>: Abbrev Number: 1 (DW_TAG_type_unit)
    <18>   DW_AT_language    : 4        (C++)
    <19>   DW_AT_GNU_odr_signature: 0xef4f1478 0xafb836e1       
    <21>   DW_AT_stmt_list   : 0x0      
 - no DW_AT_producer here to check for workaround of PR debug/45124.

[Bug debug/48229] DW_TAG_type_unit has no DW_AT_producer

[dodji at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48229

Dodji Seketeli <dodji at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2011.03.22 20:31:59
                 CC|                            |dodji at gcc dot gnu.org
         AssignedTo|unassigned at gcc dot       |dodji at gcc dot gnu.org
                   |gnu.org                     |
     Ever Confirmed|0                           |1

[Bug debug/48229] DW_TAG_type_unit has no DW_AT_producer

[dodji at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48229

--- Comment #1 from Dodji Seketeli <dodji at gcc dot gnu.org> 2011-03-23 09:31:08 UTC ---
I am not sure to understand why the DW_TAG_type_unit DIE should have a
DW_AT_producer attribute.  From the DWARF-4 specification, I can't see
DW_AT_producer listed as a possible attribute of the DW_TAG_type_unit
DIE. AIUI, the DW_AT_producer attribute is meant to be hung off of
DW_AT_compile_unit and DW_AT_partial_unit.  I guess I am missing
something ...

[Bug debug/48229] DW_TAG_type_unit has no DW_AT_producer

[dodji at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48229

--- Comment #2 from Dodji Seketeli <dodji at gcc dot gnu.org> 2011-03-23 11:28:28 UTC ---
This is a very lightly tested patch to add the DW_AT_producer
attribute to the DW_TAG_type_unit DIE.

diff --git a/gcc/dwarf2out.c b/gcc/dwarf2out.c
index f62bb48..ff1adc3 100644
--- a/gcc/dwarf2out.c
+++ b/gcc/dwarf2out.c
@@ -6498,6 +6498,7 @@ static inline int local_scope_p (dw_die_ref);
 static inline int class_scope_p (dw_die_ref);
 static inline int class_or_namespace_scope_p (dw_die_ref);
 static void add_type_attribute (dw_die_ref, tree, int, int, dw_die_ref);
+static void add_producer_attribute (dw_die_ref);
 static void add_calling_convention_attribute (dw_die_ref, tree);
 static const char *type_tag (const_tree);
 static tree member_declared_type (const_tree);
@@ -10298,6 +10299,13 @@ break_out_comdat_types (dw_die_ref die)
         unit = new_die (DW_TAG_type_unit, NULL, NULL);
         add_AT_unsigned (unit, DW_AT_language,
                          get_AT_unsigned (comp_unit_die (), DW_AT_language));
+
+    /* Add a DW_AT_producer attribute.  This is not mandated by
+       the DWARF-4 specification.  But it appears that GDB needs
+       it for cases where different DW_TAG_type_unit DIEs might
+       be emitted by different compilers.  */
+    add_producer_attribute (unit);
+
         type_node = ggc_alloc_cleared_comdat_type_node ();
         type_node->root_die = unit;
         type_node->next = comdat_type_list;
@@ -18014,6 +18022,28 @@ add_type_attribute (dw_die_ref object_die, tree type,
int decl_const,
     add_AT_die_ref (object_die, DW_AT_type, type_die);
 }

+/* Add an DW_AT_producer attribute to a given DIE.  */
+
+static void
+add_producer_attribute (dw_die_ref die)
+{
+  char producer[250];
+  const char *language_string = lang_hooks.name;
+  
+   sprintf (producer, "%s %s", language_string, version_string);
+#ifdef MIPS_DEBUGGING_INFO
+  /* The MIPS/SGI compilers place the 'cc' command line options in the
producer
+     string.  The SGI debugger looks for -g, -g1, -g2, or -g3; if they do
+     not appear in the producer string, the debugger reaches the conclusion
+     that the object file is stripped and has no debugging information.
+     To get the MIPS/SGI debugger to believe that there is debugging
+     information in the object file, we add a -g to the producer string.  */
+  if (debug_info_level > DINFO_LEVEL_TERSE)
+    strcat (producer, " -g");
+#endif
+  add_AT_string (die, DW_AT_producer, producer);
+}
+
 /* Given an object die, add the calling convention attribute for the
    function call type.  */
 static void
@@ -20101,7 +20131,6 @@ static dw_die_ref
 gen_compile_unit_die (const char *filename)
 {
   dw_die_ref die;
-  char producer[250];
   const char *language_string = lang_hooks.name;
   int language;

@@ -20114,21 +20143,8 @@ gen_compile_unit_die (const char *filename)
       if (!IS_ABSOLUTE_PATH (filename) && filename[0] != '<')
     add_comp_dir_attribute (die);
     }
-
-  sprintf (producer, "%s %s", language_string, version_string);
-
-#ifdef MIPS_DEBUGGING_INFO
-  /* The MIPS/SGI compilers place the 'cc' command line options in the
producer
-     string.  The SGI debugger looks for -g, -g1, -g2, or -g3; if they do
-     not appear in the producer string, the debugger reaches the conclusion
-     that the object file is stripped and has no debugging information.
-     To get the MIPS/SGI debugger to believe that there is debugging
-     information in the object file, we add a -g to the producer string.  */
-  if (debug_info_level > DINFO_LEVEL_TERSE)
-    strcat (producer, " -g");
-#endif
-
-  add_AT_string (die, DW_AT_producer, producer);
+  
+  add_producer_attribute (die);

   /* If our producer is LTO try to figure out a common language to use
      from the global list of translation units.  */

[Bug debug/48229] DW_TAG_type_unit has no DW_AT_producer

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48229

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-03-23 11:56:05 UTC ---
I think it is a bad idea to add DW_AT_producer to .debug_type units.  Making
each .debug_types addition 4 bytes longer is bad for debug info size, we might
have many thousands DW_TAG_type_units for each source.
I think you can safely use referring DW_TAG_compile_unit's DW_AT_producer for
your purposes.  While it is true that .debug_types sections in the end comes
from different *.o file and be produced by different compiler, it will be
referenced by the current CU only if it hashes the same, thus has the same
content (disregarding hash collisions, in which case you are in very bad
trouble, but you are in that very bad trouble no matter whether you just
want to make sure it was produced by the same or compatible producer - when
hash collision happens, it might refer to completely unrelated type).

[Bug debug/48229] DW_TAG_type_unit has no DW_AT_producer

[jan.kratochvil at redhat dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48229

--- Comment #4 from Jan Kratochvil <jan.kratochvil at redhat dot com> 2011-03-23 13:07:02 UTC ---
(In reply to comment #3)
> I think it is a bad idea to add DW_AT_producer to .debug_type units.  Making
> each .debug_types addition 4 bytes longer is bad for debug info size, we might
> have many thousands DW_TAG_type_units for each source.
> I think you can safely use referring DW_TAG_compile_unit's DW_AT_producer for
> your purposes.  While it is true that .debug_types sections in the end comes
> from different *.o file and be produced by different compiler, it will be
> referenced by the current CU only if it hashes the same, thus has the same
> content (disregarding hash collisions, in which case you are in very bad
> trouble, but you are in that very bad trouble no matter whether you just
> want to make sure it was produced by the same or compatible producer - when
> hash collision happens, it might refer to completely unrelated type).

I guess there cannot be two struct/class definitions with different fields
accessibility accidentally matching each other due to ODR.

Still I believe DW_TAG_type_unit should have DW_AT_producer as it is a
standalone entity - but currently it is not.  I guess I have to implement your
described althorithm into GDB instead.  Dodji, thanks and sorry for the patch.

[Bug debug/48229] DW_TAG_type_unit has no DW_AT_producer

[dodji at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48229

Dodji Seketeli <dodji at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |NEW
         AssignedTo|dodji at gcc dot gnu.org    |unassigned at gcc dot
                   |                            |gnu.org

[Bug debug/48229] DW_TAG_type_unit has no DW_AT_producer

[jan.kratochvil at redhat dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48229

--- Comment #5 from Jan Kratochvil <jan.kratochvil at redhat dot com> 2011-03-28 09:12:20 UTC ---
Created attachment 23788
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=23788
GDB patch attempt with ptype regressions.

(In reply to comment #4)
> Still I believe DW_TAG_type_unit should have DW_AT_producer as it is a
> standalone entity - but currently it is not.  I guess I have to implement your
> described althorithm into GDB instead.

It cannot work as GDB often looks up the type without any referrer from
DW_TAG_compile_unit, such as during the `ptype' GDB command.  A draft patch
thus has many regressions such as:
-PASS: gdb.base/nofield.exp: ptype struct not_empty
+FAIL: gdb.base/nofield.exp: ptype struct not_empty (GDB internal error)

This means GDB will have to start full read (like -readnow) of CUs till it
finds some CU referencing the specific type to find its DW_AT_producer.  During
scan of .debug_info for GDB partial symbols GDB currently skips over subtrees
of DIEs which reference the type signature for performance reasons, it no
longer can.

With .gdb_index there is no GDB partial symbols scan but .gdb_index also
indexes types by their name and there is no referrer ever seen during the
`ptype' GDB command.

So it means performance regression for non-.gdb_index case and a possible new
extension/version of .gdb_index to handle it.

[Bug debug/48229] DW_TAG_type_unit has no DW_AT_producer

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48229

--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-03-28 09:22:57 UTC ---
.debug_types only appears with -gdwarf-4, I don't think any gcc defaulted to
that yet, so if you are talking about DW_AT_accessibility default, IMHO just
assume the DWARF3+ semantics in .debug_types.

[Bug debug/48229] 4.5.x should produce unambiguous DW_AT_accessibility

[jan.kratochvil at redhat dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48229

Jan Kratochvil <jan.kratochvil at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|DW_TAG_type_unit has no     |4.5.x should produce
                   |DW_AT_producer              |unambiguous
                   |                            |DW_AT_accessibility

--- Comment #7 from Jan Kratochvil <jan.kratochvil at redhat dot com> 2011-03-28 11:21:41 UTC ---
In such case only the gcc-4.5.x branch should start to produce
DW_AT_accessibility unambiguously (explicitly) at least in the -gdwarf-4 mode.
This way it will not remain a long term regression testsuite problem.