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From: Jani Nikula <jani.nikula@linux.intel.com>
To: 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 16:23:39 +0200	[thread overview]
Message-ID: <871s53311w.fsf@intel.com> (raw)
In-Reply-To: <874l9z31c5.fsf@intel.com>

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! ;)
>
> Anyway, I think you're mistaking the limitation to arbitrary blocks
> while it's only about the switch block IIUC.
>
> Can't have:
>
> 	switch (i) {
> 		int j;
> 	case 0:
>         	/* ... */
> 	}
>
> because it can't be turned into:
>
> 	switch (i) {
> 		int j = 0; /* not valid C */
> 	case 0:
>         	/* ... */
> 	}
>
> but can have e.g.:
>
> 	switch (i) {
> 	case 0:
> 		{
> 			int j = 0;
> 	        	/* ... */
> 		}
> 	}
>
> I think Kees' approach of moving such variable declarations to the
> enclosing block scope is better than adding another nesting block.

PS. The patch is

Reviewed-by: Jani Nikula <jani.nikula@intel.com>

and the drivers/gpu/drm/i915/* parts are

Acked-by: Jani Nikula <jani.nikula@intel.com>

for merging via whichever tree is appropriate. (There'll be minor
conflicts with in-flight work in our -next tree, but no biggie.)


-- 
Jani Nikula, Intel Open Source Graphics Center

  reply	other threads:[~2019-01-23 14:22 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 [this message]
2019-01-23 14:47       ` Edwin Zimmerman
2019-01-23 15:46         ` Jani Nikula
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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