Re: hf/sf [Was Re: CVS commit: pkgsrc/misc/raspberrypi-userland]

[Justin Cormack <justin%specialbusservice.com@localhost>]

On Tue, Nov 12, 2013 at 6:08 AM, Michael van Elst 
<mlelstv%serpens.de@localhost> wrote:
> The "slowdown" is already enormous due to lack of floating point
> hardware. That's why emulating the FP hardware is a very common
> way to handle this situation, just look at the other platforms.
>
> The rationale behind this is, that people who use FP operations
> in any significant way will use hardware that supports it. And
> others will hardly notice the extra slowdown cause by emulation.
>
> The questions are: does ARM support this and is there a usuable
> implementation. Linux dropped NWFPE due to licensing issues.

In principle, but the people who have floating point that is not VFP,
so need emulation of registers but can actually do fp might complain.
And people who want to run existing softfloat binaries, probably a
larger group.

Generally people seem happy with a smallish number of userspaces, of Matts list:
earm{v[4567],}{hf,}{eb}  except earmv4hf isn’t valid.

The most useful are an old earmv4{eb} and a new earmv6hfe (6 could be
7 here). Thats fewer userspaces than eg are useful on MIPS. The soft
and hard ones can be built and tested on newer hardware as they are
backwards compatible. Almost no software needs fixing to know about
this (just compilers, linkers etc). I don't think this is too terrible
for the best selling CPU platform there is.

Justin