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From: James Hogan <james@albanarts.com>
Date: Thu, 22 May 2014 01:03:55 +0100
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Subject: Re: [Qemu-devel] [PATCH 2/2] target-mips: implement UserLocal
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To: qemu-devel@nongnu.org
Cc: Petar Jovanovic <petar.jovanovic@rt-rk.com>, aurelien@aurel32.net, petar.jovanovic@imgtec.com

Hi Petar,

On Friday 16 May 2014 20:13:34 Petar Jovanovic wrote:
> From: Petar Jovanovic <petar.jovanovic@imgtec.com>
> 
> From MIPS documentation (Volume III):
> 
> UserLocal Register (CP0 Register 4, Select 2)
> Compliance Level: Recommended.
> 
> The UserLocal register is a read-write register that is not interpreted by
> the hardware and conditionally readable via the RDHWR instruction.
> 
> This register only exists if the Config3-ULRI register field is set.
> 
> Privileged software may write this register with arbitrary information and
> make it accessable to unprivileged software via register 29 (ULR) of the
> RDHWR instruction. To do so, bit 29 of the HWREna register must be set to a
> 1 to enable unprivileged access to the register.
> 
> Signed-off-by: Petar Jovanovic <petar.jovanovic@imgtec.com>
> ---
>  target-mips/cpu.h       |    2 ++
>  target-mips/helper.h    |    1 +
>  target-mips/op_helper.c |   20 +++++++++++++++++++-
>  target-mips/translate.c |   43 +++++++++++++++++++++++++++++++++++++++++--
>  4 files changed, 63 insertions(+), 3 deletions(-)

I think you need to add it to cpu_save/cpu_load in target-mips/machine.c too, 
otherwise snapshotting and live migration may break.

Cheers
James