Re: Re: musl libc for PPC64

[David Edelsohn <dje.gcc@gmail.com>]

On Mon, Feb 8, 2016 at 6:29 PM, Rich Felker <dalias@libc.org> wrote:
> On Mon, Feb 08, 2016 at 06:24:27PM -0500, David Edelsohn wrote:
>> You *can* use v2 ABI for BE, but there is no software to run.  There
>> is no software or ecosystem or operating system that runs v2 ABI BE.
>> It's not a hardware limitation, but there is no environment for the
>> alternate combination.
>
> Indeed. At this point there's no musl ecosystem for ppc64 at all
> though; whatever we add is a fresh start.
>
>> >> IBM has announced that the next generation of the processor will
>> >> support native IEEE128 floating point in hardware.  There will be
>> >> software emulation for the current processors.  Support is included in
>> >> the forthcoming GCC 6.
>> >
>> > OK. Does the existing software emulation properly update the hardware
>> > floating point status (exception flags) and use the rounding mode?
>>
>> I'm not sure what you mean.  The software emulation assumes the
>> hardware support is not present.  It doesn't mirror back the state to
>> the processor in 64 bit mode.  But the emulation is fully IEEE128
>> compliant.
>
> if fesetround(FE_DOWNWARD) succeeds but then long double math still
> rounds to nearest, that's not IEEE compliant.
>
> The big obstacle to having fenv with softfloat on fully-softfloat
> archs is the lack of register state for the rounding mode and
> exception flags, so it should be possible to do this right as long as
> the cpu has status/mode registers for single/double, which the
> soft-quad code can then access/set. If this isn't done right already
> we could either try to get it fixed in libgcc or punt and go with
> ld64.

Who would be interested in working on this?

Thanks, David