linux-kernel - Re: [PATCH v5 02/16] powerpc: Override __ALIGN and __ALIGN

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Date:   Mon, 14 Nov 2022 09:18:48 +0530
From:   Sathvika Vasireddy <sv@...ux.ibm.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "jpoimboe@...hat.com" <jpoimboe@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "aik@...abs.ru" <aik@...abs.ru>,
        "mpe@...erman.id.au" <mpe@...erman.id.au>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>,
        "mbenes@...e.cz" <mbenes@...e.cz>,
        "npiggin@...il.com" <npiggin@...il.com>,
        "chenzhongjin@...wei.com" <chenzhongjin@...wei.com>,
        "naveen.n.rao@...ux.vnet.ibm.com" <naveen.n.rao@...ux.vnet.ibm.com>,
        Sathvika Vasireddy <sv@...ux.ibm.com>
Subject: Re: [PATCH v5 02/16] powerpc: Override __ALIGN and __ALIGN_STR macros

Hi Peter,

On 03/11/22 14:18, Peter Zijlstra wrote:
> On Wed, Nov 02, 2022 at 12:35:07PM +0000, Christophe Leroy wrote:
>>
>> Le 28/10/2022 à 16:33, Sathvika Vasireddy a écrit :
>>> In a subsequent patch, we would want to annotate powerpc assembly functions
>>> with SYM_FUNC_START_LOCAL macro. This macro depends on __ALIGN macro.
>>>
>>> The default expansion of __ALIGN macro is:
>>>           #define __ALIGN      .align 4,0x90
>>>
>>> So, override __ALIGN and __ALIGN_STR macros to use the same alignment as
>>> that of the existing _GLOBAL macro. Also, do not pad with 0x90, because
>>> repeated 0x90s are not a nop or trap on powerpc.
>> By the way, do we know what the instruction 0x90909090 is on powerpc ?
>> Is that something valid or not ?
> Please also look at the version that's in tip/x86/core (and next). This
> stuff should be gone now.
>
> include/linux/linkage.h now reads like:
>
> #ifndef __ALIGN
> #define __ALIGN                 .balign CONFIG_FUNCTION_ALIGNMENT
> #define __ALIGN_STR             __stringify(__ALIGN)
> #endif

Since the above mentioned changes are not a part of powerpc/merge branch 
yet, I am retaining this patch for this merge cycle and will post a 
cleanup patch (to move to using FUNCTION_ALIGNMENT_4B) after the next -rc1.

Thanks,
Sathvika