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Date: Fri, 11 Jun 2010 06:07:52 -0700
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Subject: Re: [Qemu-devel] [PATCH 15/35] tcg-s390: Query instruction extensions
	that are installed.
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To: Aurelien Jarno <aurelien@aurel32.net>
Cc: qemu-devel@nongnu.org, agraf@suse.de

On 06/11/2010 01:06 AM, Aurelien Jarno wrote:
> What's the difference between FACILITY_ZARCH and FACILITY_ZARCH_ACTIVE,
> as both are actually flagged together. My guess is that
> FACILITY_ZARCH_ACTIVE is needed in 64-bit mode, why FACILITY_ZARCH is
> only needed for a possible future 32-bit mode. Is it correct?

Loosely,

ZARCH is set when the system is 64-bit capable, whether or not it is active.
The OS would check this bit at startup if it wanted to change modes.  This
bit isn't really interesting to us in userspace.

ZARCH_ACTIVE is set when the system is in 64-bit mode, i.e. you've booted
with a 64-bit kernel.  Note that this says nothing about the address 
decoding mode -- this bit can be set while the PSW is set for 31-bit
address translation, e.g. running a 32-bit program on a 64-bit kernel.


r~