linux-kernel - Re: [PATCH 01/16] powerpc: Replace unreachable() with it's builtin variant in WARN

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Message-ID: <43a23349-3356-3347-f395-ba31db8c6978@csgroup.eu>
Date:   Fri, 26 Aug 2022 10:18:35 +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>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "naveen.n.rao@...ux.vnet.ibm.com" <naveen.n.rao@...ux.vnet.ibm.com>
Subject: Re: [PATCH 01/16] powerpc: Replace unreachable() with it's builtin
 variant in WARN_ON()



Le 08/08/2022 à 13:48, Sathvika Vasireddy a écrit :
> objtool is throwing *unannotated intra-function call*
> warnings with a few instructions that are marked
> unreachable. Replace unreachable() with __builtin_unreachable()
> to fix these warnings, as the codegen remains same
> with unreachable() and __builtin_unreachable().
> 
> Signed-off-by: Sathvika Vasireddy <sv@...ux.ibm.com>
> ---
>   arch/powerpc/include/asm/bug.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/include/asm/bug.h b/arch/powerpc/include/asm/bug.h
> index 61a4736355c2..074be1a78c56 100644
> --- a/arch/powerpc/include/asm/bug.h
> +++ b/arch/powerpc/include/asm/bug.h
> @@ -99,7 +99,7 @@
>   	__label__ __label_warn_on;				\
>   								\
>   	WARN_ENTRY("twi 31, 0, 0", BUGFLAG_WARNING | (flags), __label_warn_on); \
> -	unreachable();						\
> +	__builtin_unreachable();				\

Should you add barrier_before_unreachable() before 
__builtin_unreachable() to avoid stack bombs ?

See commit 173a3efd3edb ("bug.h: work around GCC PR82365 in BUG()")




>   								\
>   __label_warn_on:						\
>   	break;							\