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

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Message-Id: <20170117.144254.1482863576417019498.davem@davemloft.net>
Date:   Tue, 17 Jan 2017 14:42:54 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     khalid.aziz@...cle.com
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)

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.