linux-kernel - Re: [PATCH v2 02/16] powerpc: override __ALIGN() and __ALIGN

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Date:   Mon, 29 Aug 2022 13:26:56 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     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>,
        "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 v2 02/16] powerpc: override __ALIGN() and __ALIGN_STR()
 macros



Le 29/08/2022 à 07:52, Sathvika Vasireddy a écrit :
> Powerpc instructions must be word-aligned. Currently,
> there is an alignment of 16 bytes (by default), and it is
> much more than what is required for powerpc (4 bytes).
> 
> The default expansion of __ALIGN() macro is:
> #define __ALIGN       .align 4,0x90
> 
> Since Powerpc Linux does not require a 16 byte alignment,
> override __ALIGN() and __ALIGN_STR() macros to use required
> 4 byte alignment.
> 
> Signed-off-by: Sathvika Vasireddy <sv@...ux.ibm.com>
> ---
>   arch/powerpc/include/asm/linkage.h | 4 ++++
>   1 file changed, 4 insertions(+)
> 
> diff --git a/arch/powerpc/include/asm/linkage.h b/arch/powerpc/include/asm/linkage.h
> index b71b9582e754..8df88fe61438 100644
> --- a/arch/powerpc/include/asm/linkage.h
> +++ b/arch/powerpc/include/asm/linkage.h
> @@ -2,8 +2,12 @@
>   #ifndef _ASM_POWERPC_LINKAGE_H
>   #define _ASM_POWERPC_LINKAGE_H
>   
> +#include <linux/stringify.h>
>   #include <asm/types.h>
>   
> +#define __ALIGN			.align 2
> +#define __ALIGN_STR		__stringify(__ALIGN)
> +

I still can't see the added value of using __stringify() macro here. In 
order to use that macro you have to include linux/stringify.h . Usually 
we try to minimise the amount of headers required by other headers.

>   #ifdef CONFIG_PPC64_ELF_ABI_V1
>   #define cond_syscall(x) \
>   	asm ("\t.weak " #x "\n\t.set " #x ", sys_ni_syscall\n"		\