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Date: Fri, 1 Jul 2022 12:26:49 +0530
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Subject: Re: [RFC PATCH v3 11/12] powerpc: Remove unreachable() from WARN_ON()
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To: Chen Zhongjin <chenzhongjin@huawei.com>,
        "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>,
        Christophe Leroy <christophe.leroy@csgroup.eu>,
        "linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
        Sathvika Vasireddy <sv@linux.ibm.com>
References: <20220624183238.388144-1-sv@linux.ibm.com>
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 <1656572413.pbaqjnrrcl.naveen@linux.ibm.com>
 <dcbc25df-ce0c-45bf-35af-4d694e09ad37@huawei.com>
From: Sathvika Vasireddy <sv@linux.vnet.ibm.com>
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Cc: "aik@ozlabs.ru" <aik@ozlabs.ru>, "jpoimboe@redhat.com" <jpoimboe@redhat.com>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, "rostedt@goodmis.org" <rostedt@goodmis.org>, "peterz@infradead.org" <peterz@infradead.org>, "mingo@redhat.com" <mingo@redhat.com>, "paulus@samba.org" <paulus@samba.org>, Marc Zyngier <maz@kernel.org>, "mbenes@suse.cz" <mbenes@suse.cz>, Linux ARM <linux-arm-kernel@lists.infradead.org>
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Sender: "Linuxppc-dev" <linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org>

Hi Chen,

Thanks for pitching in and providing your inputs :-)

On 01/07/22 07:43, Chen Zhongjin wrote:
> Hi everyone,
>
> Hope I'm not too late for this discussion.
>
> I'm not familiar with ppc so it spent me some time to reproduce this. 
> But at last I didn't make it.
>
> What I did:
>
> 1 checkout to tip/objtool/core
>
> 2 apply this patch
>
> 3 recover the unreachable() after WARN_ENTRY(..
>
> 4 compile on defconfig/allyesconfig
>
> If anyone can point out which file will generate this problem it will 
> be perfect.

To reproduce this problem, you may want to apply this patch series on 
top of objtool/core branch of the tip tree, and compile on 
ppc64le_defconfig.

There are a couple of C files that are generating these warnings. One 
such file is: arch/powerpc/kvm/../../../virt/kvm/kvm_main.o which gives
*arch/powerpc/kvm/../../../virt/kvm/kvm_main.o: warning: objtool: 
kvm_mmu_notifier_release+0x6c: unannotated intra-function call* warning.

With unreachable() in __WARN_FLAGS(), we get unannotated intra-function 
call warnings, but without unreachable() like in patch 11/12 or with 
just the builtin variant of unreachable (__builtin_unreachable()) 
instead of unreachable(), we do not get those warnings.


- Sathvika