Re: [RFC] DW_AT_type missing from DW_TAG_subrange_type

[Daniel Jacobowitz <drow at false dot org>]

On Tue, Apr 03, 2007 at 03:23:56PM +0200, Denis PILAT wrote:
> For the global variable declared like that
>  int array[] = {1, 2, 3, 4};
> the dwarf information generated by our specific compiler is missing DW_AT_type 
> missing from DW_TAG_subrange_type.
> 
> Usually in dwarf2 information (ie like the bellow example for gcc4 under 
> linux), the DW_AT_type exists for subranges :
> 
>   < 175 (0xaf) > DW_TAG_array_type
>   | DW_AT_sibling : < 191 (0xbf) >
>   | DW_AT_type : < 168 (0xa8) >
>   `--------------------------
>      < 184 (0xb8) > DW_TAG_subrange_type
>    * | DW_AT_type : < 191 (0xbf) >*          <<<<<-------- missing from my elf 
> file
>      | DW_AT_upper_bound : DW_AT_upper_bound(DW_FORM_data1) : 3
>      `--------------------------

Conveniently, the DWARF 3 standard specifies what this means (DWARF 2
may also; I didn't check).  From the standard:

> If the subrange entry has no type attribute describing the basis type,
> the basis type is assumed to be the same as the object described by
> the lower bound attribute (if it references an object). If there is no
> lower bound attribute, or that attribute does not reference an object,
> the basis type is the type of the upper bound or count attribute (if
> either of them references an object). If there is no upper bound or
> count attribute, or neither references an object, the type is assumed
> to be the same type, in the source language of the compilation unit
> containing the subrange entry, as a signed integer with the same size
> as an address on the target machine.

Since we do not handle objects for bounds yet, we're only interested
in that last case.  So, we should use an integer type the size of an
address.  Try using dwarf_base_type (DW_ATE_signed, TARGET_ADDR_BIT /
8, cu)?

That function is, in fact, very buggy.  We should fix it.  It has
hardcoded sizes of 1, 2, 4 for char, short, int and doesn't support
long long at all.

> I'm also wondering about  the code:
>  base_type = die_type (die, cu);
>  if (base_type == NULL)
>    {
>      complaint (&symfile_complaints,
>                _("DW_AT_type missing from DW_TAG_subrange_type"));
>      return;
>    }
> It seems we'll never have (base_type == NULL). Am I right ?
> May be it's time to remove that as well. The complaints seems to be in a better 
> place in my patch.

You're right; please do.

-- 
Daniel Jacobowitz
CodeSourcery