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Date: Sun, 13 Jun 2010 09:02:40 -0700
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Subject: Re: [Qemu-devel] [PATCH 15/35] tcg-s390: Query instruction extensions
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To: Aurelien Jarno <aurelien@aurel32.net>
Cc: qemu-devel@nongnu.org, agraf@suse.de

On 06/13/2010 03:49 AM, Aurelien Jarno wrote:
>> Also, what era is that second machine without highgprs?  Is it running an
>> old kernel, or a 32-bit kernel?
> 
> I have very few infos about it, it's an IBM System z10 machine running a
> 64-bit 2.6.26 kernel.

Ah, I see it now: ea2a4d3a3a929ef494952bba57a0ef1a8a877881

    [S390] 64-bit register support for 31-bit processes

which adds a mechanism to pass the high parts of the gprs
in the ucontext to the 31-bit signal handler, and adds a
spot for them in the 31-bit core dump.

It doesn't change the actual saving of registers within
the kernel.  Since we take asynchronous signals and return
from them (as opposed to always longjmping out), we cannot
use the full 64-bit register within a 31-bit process without
having that bit set in HWCAP.

Something to remember if we ever implement TCG for 31-bit mode.
At the moment we only allow KVM in 31-bit mode.


r~