Re: [Qemu-devel] Future of SoftFloat use in QEMU

[Eric Blake]

On 05/08/2017 09:58 AM, Alex Bennée wrote:
> Hi,
> 
> We've got a task coming up to implement half-precision floating point
> (FP16) for ARMv8.2. As you know pretty much all our floating point in
> QEMU is handled by our internal fork of John R. Hauser's BSD SoftFloat
> library. Our current implementation is based on version 2a which doesn't
> support FP16.

Our fork is stuck at 2a because the license of 2b had compatibility
problems (it had legal restrictions that prevent interaction with GPL).

> 
> As it happens there has been a new release of SoftFloat recently.
> Version 3 is a complete re-write which made a number of changes, some
> notable ones being:
> 
>   - Complete rewrite, different use license than earlier releases.

And this different license is what?

> See: http://www.jhauser.us/arithmetic/SoftFloat-3c/doc/SoftFloat-history.html

which says merely "Replaced the license text supplied by the University
of California, Berkeley." but not WHAT the actual license text is.  Are
we lucky enough that it might have a 2-clause BSD license?

/me goes digging...

http://www.jhauser.us/arithmetic/SoftFloat-3c/doc/SoftFloat.html

>  The following applies to the whole of SoftFloat Release 3c as well as to 
> each source file individually.
> 
> Copyright 2011, 2012, 2013, 2014, 2015, 2016, 2017 The Regents of the 
> University of California. All rights reserved.
> 
> Redistribution and use in source and binary forms, with or without 
> modification, are permitted provided that the following conditions are met:
> 
>     Redistributions of source code must retain the above copyright notice, 
> this list of conditions, and the following disclaimer.
> 
>     Redistributions in binary form must reproduce the above copyright notice, 
> this list of conditions, and the following disclaimer in the documentation 
> and/or other materials provided with the distribution.
> 
>     Neither the name of the University nor the names of its contributors may 
> be used to endorse or promote products derived from this software without 
> specific prior written permission.
> 
> THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS “AS IS”, AND ANY 
> EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED 
> WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, ARE 
> DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE FOR ANY 
> DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES 
> (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 
> LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND 
> ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 
> (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS 
> SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 

Not a 2-clause BSD, but sure looks exactly like the stock 3-clause BSD
license.  Yay - https://www.gnu.org/licenses/license-list.en.html says
it is compatible with GPL, and thus we can use it in qemu!

> So any thoughts about what would make the best approach?

No quick thoughts on the best way to proceed, but at least (from my
non-lawyer perspective) it looks like we CAN quit maintaining our fork.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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