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

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Message-ID: <20220717205615.GC25951@gate.crashing.org>
Date:   Sun, 17 Jul 2022 15:56:15 -0500
From:   Segher Boessenkool <segher@...nel.crashing.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Sudip Mukherjee <sudipm.mukherjee@...il.com>,
        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
Subject: Re: mainline build failure of powerpc allmodconfig for prom_init_check

On Sun, Jul 17, 2022 at 01:29:07PM -0700, Linus Torvalds 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.
> 
> 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.

Calling mem* on a volatile object (or a struct containing one) is not
valid.  I opened gcc.gnu.org/PR106335.  Thanks for bringing this up!


Segher