Re: [PATCH 09/10] treewide: Remove uninitialized_var() usage

From: Geert Uytterhoeven <geert@linux-m68k.org>
To: Kees Cook <keescook@chromium.org>
Cc: Jason Gunthorpe <jgg@ziepe.ca>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>,
	Alexander Potapenko <glider@google.com>,
	Joe Perches <joe@perches.com>, Andy Whitcroft <apw@canonical.com>,
	"the arch/x86 maintainers" <x86@kernel.org>,
	Lars Ellenberg <drbd-dev@lists.linbit.com>,
	linux-block@vger.kernel.org, b43-dev@lists.infradead.org,
	netdev <netdev@vger.kernel.org>,
	linux-wireless <linux-wireless@vger.kernel.org>,
	linux-ide@vger.kernel.org, linux-clk <linux-clk@vger.kernel.org>,
	linux-spi <linux-spi@vger.kernel.org>,
	Linux MM <linux-mm@kvack.org>,
	clang-built-linux <clang-built-linux@googlegroups.com>
Subject: Re: [PATCH 09/10] treewide: Remove uninitialized_var() usage
Date: Thu, 4 Jun 2020 21:09:32 +0200	[thread overview]
Message-ID: <CAMuHMdVuzvvHt3j+L+_BSPFs5RgaP3rkknEUmRvTAs5nZ9SGPA@mail.gmail.com> (raw)
In-Reply-To: <202006040757.0DFC3F28E@keescook>

Hi Kees,

On Thu, Jun 4, 2020 at 5:01 PM Kees Cook <keescook@chromium.org> wrote:
> On Thu, Jun 04, 2020 at 10:23:06AM -0300, Jason Gunthorpe wrote:
> > On Wed, Jun 03, 2020 at 04:32:02PM -0700, Kees Cook wrote:
> > > Using uninitialized_var() is dangerous as it papers over real bugs[1]
> > > (or can in the future), and suppresses unrelated compiler warnings
> > > (e.g. "unused variable"). If the compiler thinks it is uninitialized,
> > > either simply initialize the variable or make compiler changes.
> > >
> > > I preparation for removing[2] the[3] macro[4], remove all remaining
> > > needless uses with the following script:
> > >
> > > git grep '\buninitialized_var\b' | cut -d: -f1 | sort -u | \
> > >     xargs perl -pi -e \
> > >             's/\buninitialized_var\(([^\)]+)\)/\1/g;
> > >              s:\s*/\* (GCC be quiet|to make compiler happy) \*/$::g;'
> > >
> > > drivers/video/fbdev/riva/riva_hw.c was manually tweaked to avoid
> > > pathological white-space.
> > >
> > > No outstanding warnings were found building allmodconfig with GCC 9.3.0
> > > for x86_64, i386, arm64, arm, powerpc, powerpc64le, s390x, mips, sparc64,
> > > alpha, and m68k.
> >
> > At least in the infiniband part I'm confident that old gcc versions
> > will print warnings after this patch.
> >
> > As the warnings are wrong, do we care? Should old gcc maybe just -Wno-
> > the warning?
>
> I *think* a lot of those are from -Wmaybe-uninitialized, but Linus just
> turned that off unconditionally in v5.7:
> 78a5255ffb6a ("Stop the ad-hoc games with -Wno-maybe-initialized")
>
> I'll try to double-check with some older gcc versions. My compiler
> collection is mostly single-axis: lots of arches, not lots of versions. ;)

Nope, support for the good old gcc 4.1 was removed a while ago.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds