Re: [RFA/dwarf-2] Fix for the null record problem

[Joel Brobecker <brobecker@gnat.com>]

>  > This is a followup on the thread that started with:
>  > 
>  >    http://sources.redhat.com/ml/gdb-patches/2004-02/msg00058.html
>  > 
>  > The test proposed under that thread was dropped because an empty
>  > struct is not legal C. However, it is legal in Ada, and I've seen
>  > a message saying that it is also legal in C++.
> 
> Seriously, I'd like to see a testcase that FAIL->PASS with this patch.
> Can somebody get a C++ testcase, at least?
> 
> the patch looks sensible, but I would like to see the testcase go in
> at the same time, or we'll forget.

I tried to update one of the C++ testcase to include an empty struct,
but my C++ is completely rusty. 

In class2.cc, I tried adding

        struct empty_struct {};

Is that a struct type definition or a class definition. In any case,
GDB has no trouble at all printing the description of this type:

        (gdb) ptype empty_struct 
        type = class empty_struct {
        }

Does anybody know of a way to produce the "<incomplete type>" bug
with C++? Otherwise, there is my upcoming null_record.exp test,
but I need a bit more time before the first Ada testcase can be
committed.

>  > I have found the source of the problem, and suggest the attached patch.
>  > The problem was that GDB was mistakenly deducing that the empry record
>  > was only a stub because of the lack of fields, and was therefore tagging
>  > it with TYPE_FLAG_STUB. This is not correct. Instead, the right
>  > approach, I believe, is to check for the DW_AT_declaration attribute.
>  > 
>  > 2004-02-19  J. Brobecker  <brobecker@gnat.com>
>  > 
>  >         * dwarf2read.c (read_structure_scope): Identify stub types
>  >         using the DW_AT_declaration attribute.
>  > 
>  > tested on x86-linux. No regression. Fixes the testcase that was
>  > proposed by Andrew (even though it is not legal C) and the Ada
>  > case.
>  > 
>  > OK to apply?
>  > 
>  > Thanks,
>  > -- 
>  > Joel
>  > 
>  > PS: BTW, my past 3 months of traveling will soon be over. The past
>  > couple of weeks have been very hectic. I have noticed that there were
>  > some messages directed at me to which I haven't answered yet. I am
>  > really sorry. I have kept these messages and will try to answer them
>  > soon.
>  > Index: dwarf2read.c
>  > ===================================================================
>  > RCS file: /cvs/src/src/gdb/dwarf2read.c,v
>  > retrieving revision 1.130
>  > diff -u -p -r1.130 dwarf2read.c
>  > --- dwarf2read.c	28 Jan 2004 18:43:06 -0000	1.130
>  > +++ dwarf2read.c	19 Feb 2004 13:58:42 -0000
>  > @@ -3077,6 +3077,9 @@ read_structure_scope (struct die_info *d
>  >        TYPE_LENGTH (type) = 0;
>  >      }
>  >  
>  > +  if (dwarf2_attr (die, DW_AT_declaration, cu) != NULL)
>  > +    TYPE_FLAGS (type) |= TYPE_FLAG_STUB;
>  > +
>  >    /* We need to add the type field to the die immediately so we don't
>  >       infinitely recurse when dealing with pointers to the structure
>  >       type within the structure itself. */
>  > @@ -3213,11 +3216,6 @@ read_structure_scope (struct die_info *d
>  >        new_symbol (die, type, cu);
>  >  
>  >        do_cleanups (back_to);
>  > -    }
>  > -  else
>  > -    {
>  > -      /* No children, must be stub. */
>  > -      TYPE_FLAGS (type) |= TYPE_FLAG_STUB;
>  >      }
>  >  
>  >    processing_current_prefix = previous_prefix;

-- 
Joel