Re: [RFC PATCH 03/13] usb: remove the usage of the list iterator after the loop

From: Segher Boessenkool <segher@kernel.crashing.org>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	Jakob <jakobkoschel@gmail.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	linux-arch <linux-arch@vger.kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Kees Cook <keescook@chromium.org>,
	Mike Rapoport <rppt@kernel.org>,
	"Gustavo A. R. Silva" <gustavo@embeddedor.com>,
	Brian Johannesmeyer <bjohannesmeyer@gmail.com>,
	Cristiano Giuffrida <c.giuffrida@vu.nl>,
	"Bos, H.J." <h.j.bos@vu.nl>
Subject: Re: [RFC PATCH 03/13] usb: remove the usage of the list iterator after the loop
Date: Sun, 27 Feb 2022 16:43:52 -0600	[thread overview]
Message-ID: <20220227224352.GA614@gate.crashing.org> (raw)
In-Reply-To: <CAK8P3a2bocgetbPQzy5xWhnW=mOdGynp_pWrPt6KeVTkEfEwKg@mail.gmail.com>

On Sun, Feb 27, 2022 at 10:28:41PM +0100, Arnd Bergmann wrote:
> On Sun, Feb 27, 2022 at 2:09 AM Segher Boessenkool
> <segher@kernel.crashing.org> wrote:
> >
> > So imo we should just never do this by default, not just if the nasty
> > -fwrapv or nastier -fno-strict-overflow is used, just like we suggest
> > in our own documentation.  The only valid reason -Wshift-negative-value
> > is in -Wextra is it warns for situations that always are undefined
> > behaviour (even if not in GCC).
> 
> Ok, I just realized that this is specific to the i915 driver because
> that, unlike
> most of the kernel builds with -Wextra by default. -Wextra is enabled when
> users ask for a 'make W=1' build in linux, and i915 is one of just three
> drivers that enable an equivalent set of warnings, the other ones
> being greybus and btrfs.
> 
> This means to work around the extra warnings, we also just need to disable
> it in the W=1 part of scripts/Makefile.extrawarn, as well as the three drivers
> that copy those options, but not the default warnings that don't include them.

Ah good, all of the workaround in one simple place, neat.

> > Could you open a GCC PR for this?  The current situation is quite
> > suboptimal, and what we document as our implementation choice is much
> > more useful!
> 
> I hope I managed to capture the issue in
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104711

That looks fine.  Thank you!

(I attached the testcase to the bug itself, we prefer it that way, maybe
godbolt will go away some day, who knows.)

Segher