From: Matthew Wilcox <willy@infradead.org>
To: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Greg KH <gregkh@linuxfoundation.org>,
Kees Cook <keescook@chromium.org>,
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 11:18:02 -0800 [thread overview]
Message-ID: <20190123191802.GB15311@bombadil.infradead.org> (raw)
In-Reply-To: <874l9z31c5.fsf@intel.com>
On Wed, Jan 23, 2019 at 04:17:30PM +0200, Jani Nikula wrote:
> 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.
Another nesting level would be bad, but I think this is OK:
switch (i) {
case 0: {
int j = 0;
/* ... */
}
case 1: {
void *p = q;
/* ... */
}
}
I can imagine Kees' patch might have a bad effect on stack consumption,
unless GCC can be relied on to be smart enough to notice the
non-overlapping liveness of the vriables and use the same stack slots
for both.
next prev parent reply other threads:[~2019-01-23 19:18 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
2019-01-24 8:10 ` Greg KH
2019-01-23 19:18 ` Matthew Wilcox [this message]
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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