Saving to 32 bits of GPRs in signal context

[Benjamin Herrenschmidt]

On Wed, 2007-05-30 at 00:32 -0500, Kumar Gala wrote:
> > I think actually it would be useful to have the saving/restoring of
> > the high 32 bits controlled by a prctl, so that programs have to ask
> > explicitly for the new behaviour (and programs that don't want to
> use
> > the high 32 bits don't incur the extra overhead).
> 
> I like this, it means we can error if HW doesn't support it and  
> requires applications to do something specific to enable the feature.

Yeah well.... I liked the prctl at first.. but then, I though twice :-)

Thing is, a typical usage pattern would be some library having a hand
optimized tigh loop or something like that using 64 bits registers. An
example, would be some memcpy-type thing in glibc.

You don't want those things to do prctl's all over the place on behalf
of the host application.

Ben.