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From: Kees Cook <keescook@chromium.org>
To: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Edwin Zimmerman <edwin@211mainstreet.net>,
	Greg KH <gregkh@linuxfoundation.org>,
	dev@openvswitch.org, Ard Biesheuvel <ard.biesheuvel@linaro.org>,
	Network Development <netdev@vger.kernel.org>,
	intel-gfx@lists.freedesktop.org, linux-usb@vger.kernel.org,
	LKML <linux-kernel@vger.kernel.org>,
	Maling list - DRI developers  <dri-devel@lists.freedesktop.org>,
	Linux-MM <linux-mm@kvack.org>,
	linux-security-module <linux-security-module@vger.kernel.org>,
	Kernel Hardening <kernel-hardening@lists.openwall.com>,
	intel-wired-lan@lists.osuosl.org,
	"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
	xen-devel <xen-devel@lists.xenproject.org>,
	Laura Abbott <labbott@redhat.com>,
	linux-kbuild <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: Thu, 24 Jan 2019 07:55:51 +1300	[thread overview]
Message-ID: <CAGXu5jJUxHtFq0rBJ9FwzMcZDWnusPUauC_=MaOz7H0_PF25jQ@mail.gmail.com> (raw)
In-Reply-To: <87va2f1int.fsf@intel.com>

On Thu, Jan 24, 2019 at 4:44 AM Jani Nikula <jani.nikula@linux.intel.com> wrote:
>
> 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?

Just in case this wasn't clear: no, it's just the switch statement
before the first "case". I cannot imagine how bad it would be if we
couldn't have block-scoped variables! Heh. :)

> >> >
> >> > 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.

Yeah, that was my thinking as well: it's a rare use, and we get a
warning when it comes up.

Thanks!

-- 
Kees Cook

  reply	other threads:[~2019-01-23 19:04 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
2019-01-23 18:55           ` Kees Cook [this message]
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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