This is the mail archive of the
gcc@gcc.gnu.org
mailing list for the GCC project.
Re: GCC/powerpc AltiVec expectations.
- From: Alex Rosenberg <alexr at spies dot com>
- To: Matt Thomas <matt at 3am-software dot com>, Geoff Keating <geoffk at geoffk dot org>
- Cc: egcs <gcc at gcc dot gnu dot org>
- Date: Mon, 01 Jul 2002 15:44:25 -0700
- Subject: Re: GCC/powerpc AltiVec expectations.
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. |