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 16:17:30 +0200 [thread overview]
Message-ID: <874l9z31c5.fsf@intel.com> (raw)
In-Reply-To: <20190123115829.GA31385@kroah.com>
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.
BR,
Jani.
--
Jani Nikula, Intel Open Source Graphics Center
next prev parent reply other threads:[~2019-01-23 14:16 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 ` Jani Nikula [this message]
2019-01-23 14:23 ` [Intel-gfx] " Jani Nikula
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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