[PATCH] openjdk/zero: only use FPU opcodes if FPU is available

[Gary Benson]

Sebastian Andrzej Siewior wrote:
> * Gary Benson | 2010-06-22 09:47:51 [+0100]:
> > I'm happy with this patch if it allows Zero to build where it
> > otherwise wouldn't, but be aware that without this code or
> > some equivalent it will not be possible to pass the TCK with
> > the build.
> 
> I've built the code with this patch and I saw no further
> problems. Can you please describe what you mean by " it will not be
> possible to pass the TCK with the build" ?  It looks to me that it
> is just an optimization on s390 and powerpc (with FPU). Other
> Architectures like arm or mips are treated the same way.

The TCK is the set of tests that checks whether or not a JVM is
compatible with a specific version of Java.

This little piece of assembler is there because the Java Language
Specification [1] states that reads and writes of volatile long and
volatile double fields must be atomic.  If you remove that bit of
code then what you build does not conform to the spec.  It will
work without it, but it's not certifyable.  The reason ARM and
32-bit MIPS don't have that piece of assembler is that nobody has
tried to certify them yet so nobody has written that piece of
assembler for those platforms.

Basically, if you just want to run stuff then it's ok to bypass
that piece of assembler, but if you want to certify the builds
for whatever reason then you will need to figure out some other
way to do a 64-bit atomic copy.

> > Have you signed the SCA?  If so I can (or you can) make a webrev
> > for this and submit it for inclusion.
> 
> I haven't.

Are you able to sign it?

Or (for the Oracle guys) is it necessary to have an SCA on file for
such a small change, or is it acceptable without?

Cheers,
Gary

-- 
http://gbenson.net/

[1] http://java.sun.com/docs/books/jls/third_edition/html/memory.html#17.7

PS I'm away on vacation from 1130 UTC, 23/06/2010, back Tuesday.