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Date:   Mon, 29 Aug 2022 11:16:37 +0530
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Subject: Re: [PATCH 01/16] powerpc: Replace unreachable() with it's builtin
 variant in WARN_ON()
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To:     Christophe Leroy <christophe.leroy@csgroup.eu>,
        Sathvika Vasireddy <sv@linux.ibm.com>,
        "linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>
Cc:     "jpoimboe@redhat.com" <jpoimboe@redhat.com>,
        "peterz@infradead.org" <peterz@infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "aik@ozlabs.ru" <aik@ozlabs.ru>,
        "mpe@ellerman.id.au" <mpe@ellerman.id.au>,
        "mingo@redhat.com" <mingo@redhat.com>,
        "rostedt@goodmis.org" <rostedt@goodmis.org>,
        "mbenes@suse.cz" <mbenes@suse.cz>,
        "npiggin@gmail.com" <npiggin@gmail.com>,
        "chenzhongjin@huawei.com" <chenzhongjin@huawei.com>,
        "linux-arm-kernel@lists.infradead.org" 
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References: <20220808114908.240813-1-sv@linux.ibm.com>
 <20220808114908.240813-2-sv@linux.ibm.com>
 <43a23349-3356-3347-f395-ba31db8c6978@csgroup.eu>
From:   Sathvika Vasireddy <sv@linux.vnet.ibm.com>
In-Reply-To: <43a23349-3356-3347-f395-ba31db8c6978@csgroup.eu>
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Hi Christophe,

On 26/08/22 15:48, Christophe Leroy wrote:
>
> 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@linux.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()")

Yes, adding barrier_before_unreachable() before __builtin_unreachable()

works around the build issues reported at 
https://lkml.org/lkml/2022/8/25/418.

I'll post a v2 with this change.

Thanks for the suggestion!

- Sathvika