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

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Message-ID: <87tu3gsy6l.fsf@mpe.ellerman.id.au>
Date:   Thu, 03 Nov 2022 11:01:54 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Christophe Leroy <christophe.leroy@...roup.eu>,
        Sathvika Vasireddy <sv@...ux.ibm.com>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>
Cc:     "jpoimboe@...hat.com" <jpoimboe@...hat.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "aik@...abs.ru" <aik@...abs.ru>,
        "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>
Subject: Re: [PATCH v5 02/16] powerpc: Override __ALIGN and __ALIGN_STR macros

Christophe Leroy <christophe.leroy@...roup.eu> writes:
> 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 ?

According to objdump it's:

stw     r4,-28528(r16)

cheers