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

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Message-ID: <20220705154852.GR25951@gate.crashing.org>
Date:   Tue, 5 Jul 2022 10:48:52 -0500
From:   Segher Boessenkool <segher@...nel.crashing.org>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Marc Zyngier <maz@...nel.org>, "aik@...abs.ru" <aik@...abs.ru>,
        Sathvika Vasireddy <sv@...ux.vnet.ibm.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>,
        Chen Zhongjin <chenzhongjin@...wei.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        Sathvika Vasireddy <sv@...ux.ibm.com>,
        "jpoimboe@...hat.com" <jpoimboe@...hat.com>,
        "paulus@...ba.org" <paulus@...ba.org>,
        "naveen.n.rao@...ux.vnet.ibm.com" <naveen.n.rao@...ux.vnet.ibm.com>,
        "mbenes@...e.cz" <mbenes@...e.cz>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC PATCH v3 11/12] powerpc: Remove unreachable() from WARN_ON()

On Mon, Jul 04, 2022 at 12:34:08PM +0000, Christophe Leroy wrote:
> Le 04/07/2022 à 13:45, Peter Zijlstra a écrit :
> > I'm somewhat confused; how is an empty STT_FUNC a valid construct on
> > Power?
> 
> So am I. It is likely not a valid construct, but that's what GCC seems 
> to generate when you call annotate_unreachable().

It is a valid construct on (almost) all targets.  If the user chooses to
have executable code terminate in limbo, that is what the compiler will
do (and this can result in a code symbol with size 0).  Compare this to
data symbols with no size, the situation is quite similar.


Segher