linux-kernel - Re: mainline build failure of powerpc allmodconfig for prom_init

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Message-ID: <CADVatmMRC-T3vUfgzya1hYmGOme79kBu2hK2CxBU3+C5h1TAYA@mail.gmail.com>
Date:   Sun, 17 Jul 2022 21:38:17 +0100
From:   Sudip Mukherjee <sudipm.mukherjee@...il.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Kees Cook <keescook@...omium.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-hardening@...r.kernel.org,
        Segher Boessenkool <segher@...nel.crashing.org>
Subject: Re: mainline build failure of powerpc allmodconfig for prom_init_check

On Sun, Jul 17, 2022 at 9:29 PM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> On Sun, Jul 17, 2022 at 1:25 PM Sudip Mukherjee
> <sudipm.mukherjee@...il.com> wrote:
> >
> > And the generated assembly still has the memset for "struct prom_args".
>
> Strange. That smells like a compiler bug to me.

Both gcc-12 and clang gives this error.

>
> But I can't read powerpc assembly code - it's been too many years, and
> even back when I did read it I hated how the register "names" worked.
>
> Maybe it was never the args array, and it was about the other fields.
> Not that that makes any sense either, but it makes more sense than the
> compiler turning a series of volatile accesses into a memset.

I have also tried adding volatile to all the members of that struct.  :(


-- 
Regards
Sudip