Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Tue, 5 May 2020 13:51:09 -0700
From:   Kees Cook <keescook@chromium.org>
To:     "Eric W. Biederman" <ebiederm@xmission.com>
Cc:     linux-kernel@vger.kernel.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Oleg Nesterov <oleg@redhat.com>, Jann Horn <jannh@google.com>,
        Greg Ungerer <gerg@linux-m68k.org>,
        Rob Landley <rob@landley.net>,
        Bernd Edlinger <bernd.edlinger@hotmail.de>,
        linux-fsdevel@vger.kernel.org, Al Viro <viro@ZenIV.linux.org.uk>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH 5/7] exec: In setup_new_exec cache current in the local
 variable me
Message-ID: <202005051351.74B5320@keescook>
References: <87h7wujhmz.fsf@x220.int.ebiederm.org>
 <87o8r2i2ub.fsf@x220.int.ebiederm.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <87o8r2i2ub.fsf@x220.int.ebiederm.org>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Tue, May 05, 2020 at 02:44:28PM -0500, Eric W. Biederman wrote:
> 
> At least gcc 8.3 when generating code for x86_64 has a hard time
> consolidating multiple calls to current aka get_current(), and winds
> up unnecessarily rereading %gs:current_task several times in
> setup_new_exec.
> 
> Caching the value of current in the local variable of me generates
> slightly better and shorter assembly.
> 
> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

Reviewed-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook