linux-kernel - Re: [RFC PATCH v3 11/12] powerpc: Remove unreachable() from WARN

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Date:   Fri, 1 Jul 2022 12:26:49 +0530
From:   Sathvika Vasireddy <sv@...ux.vnet.ibm.com>
To:     Chen Zhongjin <chenzhongjin@...wei.com>,
        "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        Sathvika Vasireddy <sv@...ux.ibm.com>
Cc:     "aik@...abs.ru" <aik@...abs.ru>,
        "benh@...nel.crashing.org" <benh@...nel.crashing.org>,
        "jpoimboe@...hat.com" <jpoimboe@...hat.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Marc Zyngier <maz@...nel.org>,
        "mbenes@...e.cz" <mbenes@...e.cz>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "mpe@...erman.id.au" <mpe@...erman.id.au>,
        "paulus@...ba.org" <paulus@...ba.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>
Subject: Re: [RFC PATCH v3 11/12] powerpc: Remove unreachable() from WARN_ON()

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