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Re: [Qemu-devel] [v2 PATCH] target-mips: implement UserLocal Register

From: Richard Henderson
Subject: Re: [Qemu-devel] [v2 PATCH] target-mips: implement UserLocal Register
Date: Tue, 27 May 2014 09:34:46 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.5.0

On 05/27/2014 02:47 AM, James Hogan wrote:
> I agree for the Config3 bit that it shouldn't change during execution of
> the guest so can be done at translation time, but I'm not convinced it's
> worth wasting tb->flags bits for CP0_HWREna state which the guest OS is
> free to change at any time, just to save a single branch each time it's
> used (which could be done in tcg easily enough to avoid the helper).
> Only a minority of code uses RDHWR, although admittedly UserLocal is the
> most widespread of the RDHWR registers due to it's use for thread local
> storage.

This patch set has used a bit for exactly this.

If there are in fact two bits that control this feature, then we should make
the hflag bit a function of the two.  We shouldn't add the one hflag bit for
Config0 to be checked at translate time, but then go off and check Config3 at


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