This is the mail archive of the
gdb-patches@sourceware.org
mailing list for the GDB project.
Re: [PATCH] DWARFv5 DW_TAG_aligned_type.
- From: Mark Wielaard <mjw at redhat dot com>
- To: Tom Tromey <tromey at redhat dot com>
- Cc: gdb-patches at sourceware dot org, Joel Brobecker <brobecker at adacore dot com>
- Date: Fri, 18 Jul 2014 00:36:12 +0200
- Subject: Re: [PATCH] DWARFv5 DW_TAG_aligned_type.
- Authentication-results: sourceware.org; auth=none
- References: <1404944457-4500-1-git-send-email-mjw at redhat dot com> <87sim77wce dot fsf at fleche dot redhat dot com>
On Fri, 2014-07-11 at 09:23 -0600, Tom Tromey wrote:
> Mark> + if (TYPE_USER_ALIGN (domain) != 0)
> Mark> + fprintf_filtered (stream, " _Alignas (%u)", TYPE_USER_ALIGN (domain));
>
> I think the preferred spelling in C++ is "alignas", not "_Alignas".
> It would be a bit prettier if this were language-dependent.
> What do you think? It affects a few spots.
Yes, C++ uses a keyword for this with slightly different, but almost
equal, semantics than the C _Alignas qualifier (C11 does define a header
stdalign.h that has #define alignas _Alignas so that you can use alignas
almost like in C++).
How does the c-typeprint.c code determine the current language of the
type?
> Mark> +/* Add the given user alignment to the element type of the array. GCC
> Mark> + outputs DWARF type qualifiers that apply to an array, not the
> Mark> + element type. But GDB relies on the array element type to carry
> Mark> + the cv-qualifiers. This is mimics section 6.7.3, point 9 of the
> Mark> + C11 specification (n1570). */
> Mark> +static struct type *
> Mark> +add_array_cv_aligned_type (struct die_info *die, struct dwarf2_cu *cu,
> Mark> + struct type *base_type, unsigned int user_align)
> Mark> +{
>
> gdb rules put a blank line between the comment and the start of the
> function.
Fixed.
> Mark> + TYPE_TARGET_TYPE (inner_array) =
> Mark> + copy_type (TYPE_TARGET_TYPE (inner_array));
>
> The "=" goes on the start of the next line.
Fixed.
> Mark> +static struct type *
> Mark> +read_tag_aligned_type (struct die_info *die, struct dwarf2_cu *cu)
> Mark> +{
>
> Needs some kind of intro comment.
Added:
/* Handle DW_TAG_aligned_type and DW_AT_alignment. */
> Mark> +/* Make a '_Alignas'-qualified version of TYPE (if user_align is
> Mark> + stricter than the user alignment of TYPE). */
> Mark> +
> Mark> +struct type *
> Mark> +make_aligned_type (struct type *type, unsigned int user_align)
> Mark> +{
> Mark> + if (user_align > TYPE_USER_ALIGN (type))
> Mark> + return make_qualified_aligned_type (type, TYPE_INSTANCE_FLAGS (type),
> Mark> + user_align, NULL);
>
> Like Joel I am curious about the need for this.
>
> I thought maybe it was just following the (C & C++) language standard.
> But would DWARF like this really be emitted by the compiler?
> It wasn't clear to me.
Yeah, it wouldn't actually be emitted by my gcc patch. As I explained to
Joel I just wanted to handle the "nested alignment" case somehow and
assumed C11 semantics. We will define something for this and handle it
properly.
> Mark> + int new_user_align = TYPE_USER_ALIGN (type);
>
> Most spots are using unsigned for this.
>
> Occasionally I'm tempted to adopt the C++ style of ubiquitous typedefs
> to avoid this kind of mismatch. But I've never really brought that up,
> so I suggest just changing this instance.
Changed to unsigned.
Thanks,
Mark