Re: MKSOFTFLOAT for evbppc

Eduardo Horvath <[email protected]> Tue, 18 Sep 2012 22:48:21 +0000 (UTC)

Newsgroups	gmane.os.netbsd.ports.powerpc
Message-ID	<[email protected]>

On Tue, 18 Sep 2012, Greg Troxel wrote:

> Apologies if I've asked about this before and forgotten the reason why
> it's a bad idea.  I don't see anything at
>   http://www.netbsd.org/ports/evbppc/
> 
> We have some evbppc machines based on a P2020.   That needs softfloat,
> and we have the following local change.  Is this something that should
> be on by default, or are there lots of processors in the evbppc that
> have hw floating point?   Or are there few, and those people should set
> MKSOFTFLOAT to no?

If you enable softfloat you essentially change the ABI.  It's better to 
use FPU emulation in the kernel.  There are only a few (but important) 
binaries like mkfs and fsck that use floating point.  If you have 
something that has heavy floating point usage, you can compile it with 
softfloat for better performance, but I recommend against doing this 
globally.  For IBM4xx CPUs we used kernel floating point emulation without 
any problems.

Eduardo