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Re: Debugger support for __float128 type?
- From: Joseph Myers <joseph at codesourcery dot com>
- To: Ulrich Weigand <uweigand at de dot ibm dot com>
- Cc: <gcc at gcc dot gnu dot org>, <gdb at sourceware dot org>
- Date: Thu, 1 Oct 2015 20:40:35 +0000
- Subject: Re: Debugger support for __float128 type?
- Authentication-results: sourceware.org; auth=none
- References: <20151001172313 dot 132825FB4 at oc7340732750 dot ibm dot 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