linux-kernel - Re: [PATCH v4 4/4] sparc64: Add support for ADI (Application Data Integrity)

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Date:   Tue, 17 Jan 2017 13:12:32 -0700
From:   Khalid Aziz <khalid.aziz@...cle.com>
To:     David Miller <davem@...emloft.net>
Cc:     corbet@....net, viro@...iv.linux.org.uk, nitin.m.gupta@...cle.com,
        mike.kravetz@...cle.com, akpm@...ux-foundation.org,
        mingo@...nel.org, kirill.shutemov@...ux.intel.com,
        adam.buchbinder@...il.com, hughd@...gle.com, minchan@...nel.org,
        keescook@...omium.org, chris.hyser@...cle.com,
        atish.patra@...cle.com, cmetcalf@...lanox.com, atomlin@...hat.com,
        jslaby@...e.cz, joe@...ches.com, paul.gortmaker@...driver.com,
        mhocko@...e.com, lstoakes@...il.com, jack@...e.cz,
        dave.hansen@...ux.intel.com, vbabka@...e.cz,
        dan.j.williams@...el.com, iamjoonsoo.kim@....com,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        sparclinux@...r.kernel.org, linux-mm@...ck.org,
        khalid@...ehiking.org
Subject: Re: [PATCH v4 4/4] sparc64: Add support for ADI (Application Data
 Integrity)

On 01/17/2017 12:42 PM, David Miller wrote:
> From: Khalid Aziz <khalid.aziz@...cle.com>
> Date: Tue, 17 Jan 2017 12:32:46 -0700
>
>> On 01/16/2017 09:39 PM, David Miller wrote:
>>> From: Khalid Aziz <khalid.aziz@...cle.com>
>>> Date: Wed, 11 Jan 2017 09:12:54 -0700
>>>
>>>> +		__asm__ __volatile__(
>>>> +			".word 0xa1438000\n\t"	/* rd  %mcdper, %l0 */
>>>
>>> Just use "rd %%asr14, %0" this way you don't have to play all of these
>>> fixed register games which kill the code generated by gcc.  If you
>>> forcefully clobber a windowed register like %l0 it means the function
>>> being emitted can never be a leaf function, tail calls are no longer
>>> allowed, etc.
>>
>> Hi David,
>>
>> "rd %%asr14, %0" should work but does not due to bugs in assembler -
>> <https://sourceware.org/ml/binutils/2016-03/msg00302.html>, and
>> <https://sourceware.org/ml/binutils/2016-03/msg00303.html>. These bugs
>> were fixed in binutils 2.27 but older assemblers will cause kernel
>> build to fail. Using byte coded equivalent is the safest option.
>
> Fair enough.
>
> Then please at least use %g1 or another usable global register to
> avoid at least some of the problems I mentioned.
>

Sure, I will do that. Thanks for the review and feedback.

--
Khalid