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

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Message-ID: <327c371a-a8f4-1676-3da8-f454612b5c58@csgroup.eu>
Date:   Wed, 2 Nov 2022 12:35:07 +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 v5 02/16] powerpc: Override __ALIGN and __ALIGN_STR macros



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 ?

> 
> Tested-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>
> Reviewed-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>
> Reviewed-by: Christophe Leroy <christophe.leroy@...roup.eu>
> Acked-by: Josh Poimboeuf <jpoimboe@...nel.org>
> Signed-off-by: Sathvika Vasireddy <sv@...ux.ibm.com>
> ---
>   arch/powerpc/include/asm/linkage.h | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/arch/powerpc/include/asm/linkage.h b/arch/powerpc/include/asm/linkage.h
> index b71b9582e754..b88d1d2cf304 100644
> --- a/arch/powerpc/include/asm/linkage.h
> +++ b/arch/powerpc/include/asm/linkage.h
> @@ -4,6 +4,9 @@
>   
>   #include <asm/types.h>
>   
> +#define __ALIGN		.align 2
> +#define __ALIGN_STR	".align 2"
> +
>   #ifdef CONFIG_PPC64_ELF_ABI_V1
>   #define cond_syscall(x) \
>   	asm ("\t.weak " #x "\n\t.set " #x ", sys_ni_syscall\n"		\