Removal of NWFPE in its entirety, and VFP emulation code

[Aaro Koskinen]

On Wed, Apr 10, 2013 at 01:30:35PM -0400, Nicolas Pitre wrote:
> On Wed, 10 Apr 2013, Russell King - ARM Linux wrote:
> 
> > I have just committed a patch to remove the arch/arm/nwfpe code from
> > the kernel, and the VFP code emulating the FP operations.
> > 
> > This I have done after it has been brought to my attention by the OSADL's
> > GPL-violations project that the license for the softfloat library is
> > incompatible with GPLv2.  This is because the FSF have ruled that
> > indemnification clauses consitute an "additional restriction" which is
> > incompatible with the GPLv2 section 6.  NWFPE contains the softfloat
> > library, and VFP's emulation code is a derivative of softfloat.
> > 
> > This will be very disruptive for ARMv4 and ARMv5 CPUs, which will no
> > longer be able to run userspace with NWFPE support removed.  A possible
> > solution there is to resurrect FASTFPE support and merge that into
> > mainline in place of NWFPE.  FASTFPE's hooks are all present in the
> > kernel, and it should just be a case of adding the FASTFPE code.
> > However, FASTFPE is probably lacking GDB and signal stack support.
> > (FastFPE's per-thread workspace is different from NWFPE.)
> 
> A point worth mentioning is the EABI availability since 2006 which moved 
> away from FPA completely. A soft-float library in user space is used in 
> that case.  Major ARM binary producers including all ARM distros moved 
> to EABI with user space soft-float since then as it is order of 
> magnitude faster than FPA emulation.  So 99.99% of ARMv4 and ARMv5 users 
> are unlikely to be affected.

Menuconfig mentions under "Floating point emulation" that "At least one
emulation must be selected". But if I compile my OS with EABI userspace
soft-float I guess I won't actually need to select any emulation,
or have I missed something? (I just checked my configs, and at least
on Kirkwood/openrd I have been already running without any emulation,
so I guess the help text is wrong?)

A.