Re: mainline build failure of powerpc allmodconfig for prom_init_check

From: Segher Boessenkool <segher@kernel.crashing.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Kees Cook <keescook@chromium.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Paul Mackerras <paulus@samba.org>,
	linux-hardening@vger.kernel.org,
	linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
	Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Subject: Re: mainline build failure of powerpc allmodconfig for prom_init_check
Date: Sun, 17 Jul 2022 15:56:15 -0500	[thread overview]
Message-ID: <20220717205615.GC25951@gate.crashing.org> (raw)
In-Reply-To: <CAHk-=whjWyoognKy4QUUwf95L6qvPg7MGdp0CxqD2fpvZo7DLw@mail.gmail.com>

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@gmail.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