linux-kernel - Re: [PATCH v11 4/9] arm64: add conditional instruction simulation support

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Message-ID: <56EFB241.80909@linaro.org>
Date:	Mon, 21 Mar 2016 04:35:13 -0400
From:	David Long <dave.long@...aro.org>
To:	Marc Zyngier <marc.zyngier@....com>,
	Pratyush Anand <panand@...hat.com>
Cc:	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Sandeepa Prabhu <sandeepa.s.prabhu@...il.com>,
	William Cohen <wcohen@...hat.com>,
	Steve Capper <steve.capper@...aro.org>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Dave P Martin <Dave.Martin@....com>,
	Mark Rutland <mark.rutland@....com>,
	Robin Murphy <Robin.Murphy@....com>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	Jens Wiklander <jens.wiklander@...aro.org>,
	Christoffer Dall <christoffer.dall@...aro.org>,
	Alex Bennée <alex.bennee@...aro.org>,
	Yang Shi <yang.shi@...aro.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	"Suzuki K. Poulose" <suzuki.poulose@....com>,
	Kees Cook <keescook@...omium.org>,
	Zi Shen Lim <zlim.lnx@...il.com>,
	John Blackwood <john.blackwood@...r.com>,
	Feng Kan <fkan@....com>,
	Balamurugan Shanmugam <bshanmugam@....com>,
	James Morse <james.morse@....com>,
	Vladimir Murzin <Vladimir.Murzin@....com>,
	Mark Salyzyn <salyzyn@...roid.com>,
	Petr Mladek <pmladek@...e.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH v11 4/9] arm64: add conditional instruction simulation
 support

On 03/14/2016 03:38 AM, Marc Zyngier wrote:
> On Mon, 14 Mar 2016 09:34:55 +0530
> Pratyush Anand <panand@...hat.com> wrote:
>
> Hi Pratyush,
>
>> On 13/03/2016:12:09:03 PM, Marc Zyngier wrote:
>>> On Wed,  9 Mar 2016 00:32:18 -0500
>>> David Long <dave.long@...aro.org> wrote:
>>>
>>>> +pstate_check_t * const opcode_condition_checks[16] = {
>>>> +	__check_eq, __check_ne, __check_cs, __check_cc,
>>>> +	__check_mi, __check_pl, __check_vs, __check_vc,
>>>> +	__check_hi, __check_ls, __check_ge, __check_lt,
>>>> +	__check_gt, __check_le, __check_al, __check_al
>>>
>>> The very last entry seems wrong, or is at least the opposite of what
>>> the current code has. It should be something called __check_nv(), and
>>> always return false (condition code NEVER).
>>
>> May be __check_nv() name is more appropriate as per definition, but shouldn't it
>> still return true, because TRM says:
>> "The condition code NV exists only to provide a valid disassembly of the 0b1111
>> encoding, otherwise its behavior is identical to AL"
>
> Indeed, I missed that. But this interpretation is for the A64
> instruction set, and this array is also used by the new
> arm32_check_condition. The condition code table for A32 seems to
> completely ignore the 0b1111 code (there is simply no entry for it), and
> it is only in the ConditionHolds pseudocode that you can see how this
> is actually special-cased.
>
> So I'm fine leaving the code as it is, but a comment and a pointer to
> the ARMv8 ARM wouldn't go amiss.
>
> Thanks,
>
> 	M.
>

OK.

-dl