linux-kernel - Re: [PATCH 09/10] treewide: Remove uninitialized

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Message-ID: <202006040757.0DFC3F28E@keescook>
Date:   Thu, 4 Jun 2020 07:59:40 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Jason Gunthorpe <jgg@...pe.ca>
Cc:     linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        Alexander Potapenko <glider@...gle.com>,
        Joe Perches <joe@...ches.com>,
        Andy Whitcroft <apw@...onical.com>, x86@...nel.org,
        drbd-dev@...ts.linbit.com, linux-block@...r.kernel.org,
        b43-dev@...ts.infradead.org, netdev@...r.kernel.org,
        linux-wireless@...r.kernel.org, linux-ide@...r.kernel.org,
        linux-clk@...r.kernel.org, linux-spi@...r.kernel.org,
        linux-mm@...ck.org, clang-built-linux@...glegroups.com
Subject: Re: [PATCH 09/10] treewide: Remove uninitialized_var() usage

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. ;)

> Otherwise the IB bits look ok to me
> 
> Acked-by: Jason Gunthorpe <jgg@...lanox.com>

Thanks!

-- 
Kees Cook