Re: [PATCH] PowerPC: fix _Float128 type output string

[Kevin Buettner <kevinb@redhat.com>]

Hi Carl,

On Wed, 05 Apr 2023 13:18:26 -0700
Carl Love via Gdb-patches <gdb-patches@sourceware.org> wrote:

> PowerPC: fix _Float128 type output string
> 
> PowerPC supports two 128-bit floating point formats, the IBM long double
> and IEEE 128-bit float.  The issue is the DWARF information does not
> distinguish between the two.  There have been proposals of how to extend
> the DWARF information as discussed in
> 
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104194
> 
> but has not been fully implemented.
> 
> GCC introduced the _Float128 internal type as a work around for the issue.
> The workaround is not transparent to GDB.  The internal _Float128 type
> name is printed rather then the user specified long double type.  This
> patch adds a new gdbarch method to allow PowerPC to detect the GCC
> workaround.  The workaround checks for "_Float128" name when reading the
> base typedef from the die_info.  If the workaround is detected, the type
> and format fields from the _Float128 typedef are copied to the long
> double typedef.  The same is done for the complex long double typedef.

This approach sounds reasonable to me.

One nit though...

> diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
> index c9208a097bf..fa319e346c0 100644
> --- a/gdb/dwarf2/read.c
> +++ b/gdb/dwarf2/read.c
> @@ -14702,14 +14702,22 @@ static struct type *
>  read_typedef (struct die_info *die, struct dwarf2_cu *cu)
>  {
>    struct objfile *objfile = cu->per_objfile->objfile;
> -  const char *name = NULL;
> -  struct type *this_type, *target_type;
> +  const char *name = dwarf2_full_name (NULL, die, cu);
> +  struct type *this_type;
> +  struct gdbarch *gdbarch = objfile->arch ();
> +  struct type *target_type = die_type (die, cu);
> +
> +  if (gdbarch_dwarf2_omit_typedef_p (gdbarch, target_type, cu->producer, name))
> +    {
> +      this_type = copy_type (target_type);
> +      this_type->set_name (name);
> +      set_die_type (die, this_type, cu);
> +      return this_type;
> +    }

I'd like to see a comment before the if statement that you added above
which explains what's going on. 
>  
> -  name = dwarf2_full_name (NULL, die, cu);
>    this_type = type_allocator (objfile).new_type (TYPE_CODE_TYPEDEF, 0, name);
>    this_type->set_target_is_stub (true);
>    set_die_type (die, this_type, cu);
> -  target_type = die_type (die, cu);
>    if (target_type != this_type)
>      this_type->set_target_type (target_type);
>    else