linux-kernel - Re: [PATCH 5/7] exec: In setup_new_exec cache current in the local variable me

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Message-ID: <202005051351.74B5320@keescook>
Date:   Tue, 5 May 2020 13:51:09 -0700
From:   Kees Cook <keescook@...omium.org>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>, Jann Horn <jannh@...gle.com>,
        Greg Ungerer <gerg@...ux-m68k.org>,
        Rob Landley <rob@...dley.net>,
        Bernd Edlinger <bernd.edlinger@...mail.de>,
        linux-fsdevel@...r.kernel.org, Al Viro <viro@...IV.linux.org.uk>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 5/7] exec: In setup_new_exec cache current in the local
 variable me

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@...ssion.com>

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

-- 
Kees Cook