Subject: Re: Floating Point broken on Alpha 21066?
To: None <port-alpha@netbsd.org, werner@bit-1.de>
From: R.o.s.s H.a.r.v.e.y <ross@ghs.com>
List: port-alpha
Date: 01/03/2002 10:49:43
You did some good research, but that patch was never accepted into
linux or even tested successfully, AFAICT.  (I've read that particular
linux code many times. :-)

The whole point of that fp emul routine is to search backwards
through the trap shadow to find the trapping instruction, so given
the trap shadow rules, it doesn't even matter if it's called with
pc or pc - 4, as any trap barrier present will just be skipped
later. Also, it won't even be called at all on any system unless
the program was compiled with software completion enabled, which
is not the default on any system I'm aware of.

I think there are really two sets of problems here.

One problem has to do with the way the popularity of x86 has worked
to prevent people from discovering errors like divide-by-zero. Most
or all alpha kernels do not run run in full IEEE mode by default,
and so divide-by-zero has the historical behavior of trapping. This
is not precisely a bad thing, but given the x86-problem, I'm
considering building our userland with completion enabled. Fortunately,
in NetBSD we have such a diversity of platforms that we catch almost
all these errors and fix them.

I think the other problem is a hardware issue on your particular
CPU chip -- we can verify that without too much trouble.

Let's start with your current uname -a, and also let me know what
vintage of userland you are running.


> From: Werner Backes <werner@bit-1.de>
>
> Hello,
>
> I had a very hard time getting my Multia up&running. I get 
> lot's of floating point exceptions which prevented (for 
> example) the disk label editor form working. After partioning
> with an old OpenBSD-2.6 (which worked), I could boot the NetBSD
> 1.5.2 boot disks, start a shell, configure network and FTP and
> extract the base-distribution by hand. After installboot the 
> systems works, but I get floating point exceptions for most 
> commands I use (top, ps, ping, cc ....). I searched the net
> and found the following article posted by a LINUX user:
> http://www.bluegum.com/NetNews/default/69.html 
>
> Does anyone else discovered problems like this on *BSD? (I got
> nearly the same effect while trying to install OpenBSD and FreeBSD)
>
> :(
>     Werner
>