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

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Date:   Thu, 3 Nov 2022 09:48:52 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     Sathvika Vasireddy <sv@...ux.ibm.com>,
        "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>
Subject: Re: [PATCH v5 02/16] powerpc: Override __ALIGN and __ALIGN_STR macros

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