svn commit: r314210 - in stable/11/sys: conf i386/conf i386/i386 i386/include i386/isa i386/linux x86/acpica x86/x86

[John Baldwin]

On Friday, February 24, 2017 07:14:05 PM Konstantin Belousov wrote:
> On Fri, Feb 24, 2017 at 08:53:27AM -0800, Rodney W. Grimes wrote:
> > > Author: kib
> > > Date: Fri Feb 24 16:02:01 2017
> > > New Revision: 314210
> > > URL: https://svnweb.freebsd.org/changeset/base/314210
> > > 
> > > Log:
> > >   MFC r313154:
> > >   For i386, remove config options CPU_DISABLE_CMPXCHG, CPU_DISABLE_SSE
> > >   and device npx.
> > 
> > Um, why?????   Makes it much easier to test soft float if we can remove
> > the npx device.   Or has soft float support died yet again?
> Soft float was removed very long time ago.

I think it was gone in 5.0.

> > Yes, an i386 without an FPU is anchient by why are we removing working
> > functionality?
> This question makes an impression that you think that kernel would not
> boot on a machine without FPU.  The code to tolerate such configuration
> is there, but it is not tested for obvious reasons.
> 
> Completely different issue is that userspace requires FPU and e.g. /bin/sh
> traps on the next setjmp(3) call.
> 
> Also, we do not run on real 386, only on 486+, and there was probably only
> Intel 486SX CPU model which has all 486 features but no FPU.

Yes, we effectively require an FPU on i386.  I'd be tempted to start requiring
a built-in FPU (so INT 16 vs IRQ 13) so we could further reduce diffs with
amd64 and eventually have an "x86" fpu.c.  That would only drop support for
systems using a 486sx with an external FPU.  Those systems are probably happier
running FreeBSD 4.x than 12 anyway.

-- 
John Baldwin