Re: [PATCH] gnu-v2-abi.c: Add casts

[Simon Marchi <simon dot marchi at polymtl dot ca>]

On 28 October 2015 at 14:46, Pedro Alves <palves@redhat.com> wrote:
> I looked at changing these is_destructor_name/is_constructor_name
> interfaces in order to detangle the boolean result from the ctor/dtor
> kind return, but then realized that this design goes all the way down
> to the libiberty demangler interfaces.  E.g, include/demangle.h:
>
>  ~~~
>  /* Return non-zero iff NAME is the mangled form of a constructor name
>     in the G++ V3 ABI demangling style.  Specifically, return an `enum
>     gnu_v3_ctor_kinds' value indicating what kind of constructor
>     it is.  */
>  extern enum gnu_v3_ctor_kinds
>          is_gnu_v3_mangled_ctor (const char *name);
>
>
>  enum gnu_v3_dtor_kinds {
>    gnu_v3_deleting_dtor = 1,
>    gnu_v3_complete_object_dtor,
>    gnu_v3_base_object_dtor,
>    /* These are not part of the V3 ABI.  Unified destructors are generated
>       as a speed-for-space optimization when the -fdeclone-ctor-dtor option
>       is used, and are always internal symbols.  */
>    gnu_v3_unified_dtor,
>    gnu_v3_object_dtor_group
>  };
>  ~~~
>
> libiberty/cp-demangle.c:
>
>  ~~~
>  enum gnu_v3_ctor_kinds
>  is_gnu_v3_mangled_ctor (const char *name)
>  {
>    enum gnu_v3_ctor_kinds ctor_kind;
>    enum gnu_v3_dtor_kinds dtor_kind;
>
>    if (! is_ctor_or_dtor (name, &ctor_kind, &dtor_kind))
>      return (enum gnu_v3_ctor_kinds) 0;
>    return ctor_kind;
>  }
>  ~~~
>
> etc.
>
> gdb/ChangeLog:
> 2015-10-27  Pedro Alves  <palves@redhat.com>
>
>         * gnu-v2-abi.c (gnuv2_is_destructor_name)
>         (gnuv2_is_constructor_name): Add casts.
> ---
>  gdb/gnu-v2-abi.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/gdb/gnu-v2-abi.c b/gdb/gnu-v2-abi.c
> index c508b55..6c2b92a 100644
> --- a/gdb/gnu-v2-abi.c
> +++ b/gdb/gnu-v2-abi.c
> @@ -40,7 +40,7 @@ gnuv2_is_destructor_name (const char *name)
>        || startswith (name, "__dt__"))
>      return complete_object_dtor;
>    else
> -    return 0;
> +    return (enum dtor_kinds) 0;
>  }
>
>  static enum ctor_kinds
> @@ -51,7 +51,7 @@ gnuv2_is_constructor_name (const char *name)
>        || startswith (name, "__ct__"))
>      return complete_object_ctor;
>    else
> -    return 0;
> +    return (enum ctor_kinds) 0;
>  }
>
>  static int
> --
> 1.9.3
>

I am ok with the cast, but just to note that we could do another way.
I think it would be safe to add a "not_a_ctor = 0" enum value to
ctor_kinds (which is defined in gdb), and return that in
gnuv2_is_constructor_name.  Meanwhile, the function in libiberty for
gnu-abi-v3 (is_gnu_v3_mangled_ctor) will still return a casted 0,
which will map to not_a_ctor.

Of course, the comment

/* Kinds of constructors.  All these values are guaranteed to be
   non-zero.  */

would need to change.  Idem for destructors.