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From: Segher Boessenkool <segher@kernel.crashing.org>
Subject: Re: Saving to 32 bits of GPRs in signal context
Date: Wed, 30 May 2007 14:01:48 +0200
To: Kumar Gala <galak@kernel.crashing.org>
Cc: Ulrich Weigand <Ulrich.Weigand@de.ibm.com>,
	Paul Mackerras <paulus@samba.org>, Steve Munroe <sjmunroe@us.ibm.com>,
	Anton Blanchard <anton@samba.org>,
	linuxppc-dev list <linuxppc-dev@ozlabs.org>
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>> 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.

It also means every such application has to make sure
it calls the prctl() before running any 64-bit insns.
No one will get this right unless support for this
is put into the ELF loader.


Segher