Re: Debugger support for __float128 type?

[Joseph Myers <joseph@codesourcery.com>]

On Thu, 1 Oct 2015, Ulrich Weigand wrote:

> The _DecimalN types are already supported by DWARF using a base type with
> encoding DW_ATE_decimal_float and the appropriate DW_AT_byte_size.

Which doesn't actually say whether the DPD or BID encoding is used, but as 
long as each architecture uses only one that's not a problem in practice.

> For the interchange type, it seems one could define a new encoding,
> e.g. DW_ATE_interchange_float, and use this together with the
> appropriate DW_AT_byte_size to identify the format.

It's not clear to me that (for example) distinguishing float and _Float32 
(other than by name) is useful in DWARF (and if you change float from 
DW_ATE_float to DW_ATE_interchange_float that would affect old debuggers - 
is the idea to use DW_ATE_interchange_float only for the new types, not 
for old types with the same encodings, so for _Float32 but not float?).  
But it's true that if you say it's an interchange type then together with 
size and endianness that uniquely determines the encoding.

> I'm not sure how to handle an extended decimal format that does not
> match any of the decimal interchange formats.  Does this occur in
> practice at all?

I don't know, but I doubt it.

> Well, complex types have their own encoding (DW_ATE_complex_float), so we'd
> have to define the corresponding variants for those as well, e.g.
> DW_ATE_complex_interchange_float or the like.

And DW_ATE_imaginary_interchange_float, I suppose.

-- 
Joseph S. Myers
joseph@codesourcery.com