GCC/powerpc AltiVec expectations.

[Alex Rosenberg]

on 7/1/02 2:56 PM, Matt Thomas at matt@3am-software.com wrote:

>>> Does it expect all vector registers to be save on a context-switch
>>> or only those specified in VRSAVE?  What about VSCR?
>> 
>> Only those in VRSAVE, plus VSCR.  However, you might decide that you
>> have to save all of them to ensure process isolation, in which case
>> you don't need VRSAVE at all.  VRSAVE is most useful on a system where
>> all processes trust each other.
> 
> I was planning to use VRSAVE to control which ones to be saved.  On
> loading VRSAVE would control which would be vxor'ed (bit not set) or
> loaded (bit set).

No trust is required in either Mac OS 9 or X.

Instead of clearing dead registers, Mac OS loads up 0x7FFFDEAD in each
element of the dead registers. This value is both easy to recognize in a
debugger and is a NaN.

+------------------------------------------------------------+
| Alexander M. Rosenberg           <mailto:alexr@_spies.com> |
| Nobody cares what I say. Remove the underscore to mail me. |