linux-kernel - Re: [PATCH] powerpc/xmon: avoid warnings about variables that might be clobbered by ‘longjmp’

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Message-ID: <CA+7wUsx4wpiP+q7NusNgFYfAM3gbnvOOPgrjq4QV7iA510noCg@mail.gmail.com>
Date:   Tue, 26 Jun 2018 08:27:06 +0200
From:   Mathieu Malaterre <malat@...ian.org>
To:     Segher Boessenkool <segher@...nel.crashing.org>
Cc:     Christophe LEROY <christophe.leroy@....fr>,
        Michael Ellerman <mpe@...erman.id.au>,
        Yisheng Xie <xieyisheng1@...wei.com>,
        Vaibhav Jain <vaibhav@...ux.vnet.ibm.com>,
        Nicholas Piggin <npiggin@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Paul Mackerras <paulus@...ba.org>,
        Breno Leitao <leitao@...ian.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH] powerpc/xmon: avoid warnings about variables that might be clobbered by ‘longjmp’

On Sat, Jun 23, 2018 at 9:47 PM Segher Boessenkool
<segher@...nel.crashing.org> wrote:
>
> On Sat, Jun 23, 2018 at 06:59:27PM +0200, christophe leroy wrote:
> >
> >
> > Le 22/06/2018 à 21:27, Mathieu Malaterre a écrit :
> > >Move initialization of variables after data definitions. This silence
> > >warnings treated as error with W=1:
> > >
> > >   arch/powerpc/xmon/xmon.c:3389:14: error: variable ‘name’ might be
> > >   clobbered by ‘longjmp’ or ‘vfork’ [-Werror=clobbered]
> > >   arch/powerpc/xmon/xmon.c:3100:22: error: variable ‘tsk’ might be
> > >   clobbered by ‘longjmp’ or ‘vfork’ [-Werror=clobbered]
> >
> > Is that an invalid warning ?
>
> No, both are correct warnings.  GCC can not see which functions it only
> has a declaration of can call longjmp.

I assumed those were false positive warnings, given how easy it was to
defeat them. Let give it another try.

> > Otherwise, I'd expect one to fix the warning, not just cheat on GCC.
>
> Yes, the patch seems to change the code in such a way that some versions
> of GCC will no longer warn.  Which does not make to code any more correct.
>
> Either restructure the code, or make the var non-automatic, or make it
> volatile.
>
>
> Segher