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Message-ID: <874l9z31c5.fsf@intel.com>
Date: Wed, 23 Jan 2019 16:17:30 +0200
From: Jani Nikula <jani.nikula@...ux.intel.com>
To: Greg KH <gregkh@...uxfoundation.org>, Kees Cook <keescook@...omium.org>
Cc: dev@...nvswitch.org, Ard Biesheuvel <ard.biesheuvel@...aro.org>, netdev@...r.kernel.org, intel-gfx@...ts.freedesktop.org, linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org, linux-mm@...ck.org, linux-security-module@...r.kernel.org, kernel-hardening@...ts.openwall.com, intel-wired-lan@...ts.osuosl.org, linux-fsdevel@...r.kernel.org, xen-devel@...ts.xenproject.org, Laura Abbott <labbott@...hat.com>, linux-kbuild@...r.kernel.org, Alexander Popov <alex.popov@...ux.com>
Subject: Re: [Intel-gfx] [PATCH 1/3] treewide: Lift switch variables out of switches
On Wed, 23 Jan 2019, Greg KH <gregkh@...uxfoundation.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
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