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Floating point questions

To: Linux SGI <linux@cthulhu.engr.sgi.com>
Subject: Floating point questions
From: "Andrew R. Baker" <andrewb@uab.edu>
Date: Mon, 17 Jan 2000 20:55:58 -0600 (CST)
Cc: Ralf Baechle <ralf@oss.sgi.com>
Sender: owner-linuxmips@oss.sgi.com
Whilst playing with floating point support I have noticed that the
"Division By Zero" and "Overflow" Enable bits are set by default on Linux
where they are not in IRIX.  Is there a reason we do this?  Or is this
behaviour unintended?  

Also, when we enter the floating point handler, the floating point
registers have not been saved to the thread structure.  Currently, I get
around this by querying the registers directly.  Unfortunately this won't
work when we support SMP.  What would the drawbacks be of a save and
restore and the start and finish of the exception handler (well the
unimplemented handler)?  Or is there some other way?  I'm really only
concerned about the case where we would run the soft-fp code on a
processor other than the one that triggered the exception.

-Andrew


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