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From: Jani Nikula <jani.nikula@linux.intel.com>
To: Edwin Zimmerman <edwin@211mainstreet.net>,
	'Greg KH' <gregkh@linuxfoundation.org>,
	'Kees Cook' <keescook@chromium.org>
Cc: dev@openvswitch.org, 'Ard Biesheuvel' <ard.biesheuvel@linaro.org>,
	netdev@vger.kernel.org, intel-gfx@lists.freedesktop.org,
	linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
	dri-devel@lists.freedesktop.org, linux-mm@kvack.org,
	linux-security-module@vger.kernel.org,
	kernel-hardening@lists.openwall.com,
	intel-wired-lan@lists.osuosl.org, linux-fsdevel@vger.kernel.org,
	xen-devel@lists.xenproject.org,
	'Laura Abbott' <labbott@redhat.com>,
	linux-kbuild@vger.kernel.org,
	'Alexander Popov' <alex.popov@linux.com>
Subject: RE: [Intel-gfx] [PATCH 1/3] treewide: Lift switch variables out of switches
Date: Wed, 23 Jan 2019 17:46:14 +0200	[thread overview]
Message-ID: <87va2f1int.fsf@intel.com> (raw)
In-Reply-To: <000001d4b32a$845e06e0$8d1a14a0$@211mainstreet.net>

On Wed, 23 Jan 2019, Edwin Zimmerman <edwin@211mainstreet.net> wrote:
> On Wed, 23 Jan 2019, Jani Nikula <jani.nikula@linux.intel.com> wrote:
>> On Wed, 23 Jan 2019, Greg KH <gregkh@linuxfoundation.org> wrote:
>> > On Wed, Jan 23, 2019 at 03:03:47AM -0800, Kees Cook wrote:
>> >> Variables declared in a switch statement before any case statements
>> >> cannot be initialized, so move all instances out of the switches.
>> >> After this, future always-initialized stack variables will work
>> >> and not throw warnings like this:
>> >>
>> >> fs/fcntl.c: In function ‘send_sigio_to_task’:
>> >> fs/fcntl.c:738:13: warning: statement will never be executed [-Wswitch-unreachable]
>> >>    siginfo_t si;
>> >>              ^~
>> >
>> > That's a pain, so this means we can't have any new variables in { }
>> > scope except for at the top of a function?
>> >
>> > That's going to be a hard thing to keep from happening over time, as
>> > this is valid C :(
>> 
>> Not all valid C is meant to be used! ;)
>
> Very true.  The other thing to keep in mind is the burden of enforcing
> a prohibition on a valid C construct like this.  It seems to me that
> patch reviewers and maintainers have enough to do without forcing them
> to watch for variable declarations in switch statements.  Automating
> this prohibition, should it be accepted, seems like a good idea to me.

Considering that the treewide diffstat to fix this is:

 18 files changed, 45 insertions(+), 46 deletions(-)

and using the gcc plugin in question will trigger the switch-unreachable
warning, I think we're good. There'll probably be the occasional
declarations that pass through, and will get fixed afterwards.

BR,
Jani.

-- 
Jani Nikula, Intel Open Source Graphics Center

  reply	other threads:[~2019-01-23 15:44 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-01-23 11:03 [PATCH 0/3] gcc-plugins: Introduce stackinit plugin Kees Cook
2019-01-23 11:03 ` [PATCH 1/3] treewide: Lift switch variables out of switches Kees Cook
2019-01-23 11:58   ` Greg KH
2019-01-23 12:09     ` Jann Horn
2019-01-23 12:12       ` Ard Biesheuvel
2019-01-23 13:21       ` William Kucharski
2019-01-23 14:17     ` [Intel-gfx] " Jani Nikula
2019-01-23 14:23       ` Jani Nikula
2019-01-23 14:47       ` Edwin Zimmerman
2019-01-23 15:46         ` Jani Nikula [this message]
2019-01-23 18:55           ` Kees Cook
2019-01-24  8:10             ` Greg KH
2019-01-23 19:18       ` Matthew Wilcox
2019-01-23 20:36         ` Kees Cook
2019-01-23 16:51   ` [Intel-wired-lan] " Jeff Kirsher
2019-01-24 12:58   ` Edwin Zimmerman
2019-01-23 11:03 ` [PATCH 2/3] gcc-plugins: Introduce stackinit plugin Kees Cook
2019-01-23 11:03 ` [PATCH 3/3] lib: Introduce test_stackinit module Kees Cook
2019-01-29  0:12 ` [PATCH 0/3] gcc-plugins: Introduce stackinit plugin Alexander Popov
2019-02-12 17:54   ` Kees Cook

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