From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7D4DEC47254 for ; Tue, 5 May 2020 20:51:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 58150206B8 for ; Tue, 5 May 2020 20:51:13 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=chromium.org header.i=@chromium.org header.b="WgX/BZxH" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729354AbgEEUvM (ORCPT ); Tue, 5 May 2020 16:51:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54664 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1728660AbgEEUvL (ORCPT ); Tue, 5 May 2020 16:51:11 -0400 Received: from mail-pj1-x1041.google.com (mail-pj1-x1041.google.com [IPv6:2607:f8b0:4864:20::1041]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 240DBC061A0F for ; Tue, 5 May 2020 13:51:11 -0700 (PDT) Received: by mail-pj1-x1041.google.com with SMTP id h12so1581986pjz.1 for ; Tue, 05 May 2020 13:51:11 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=3hao9Rbd2DOkgWQuq9i9E+Ng3Pr6zL+wsaZllNiP784=; b=WgX/BZxHr++sd2IPiEB/unUtdMnEP1tXqVSjjQPQ7/lC6eDNdAE1MDzdb6OFx5jM6n iPGWeclUB9c9273Ekhi4XWJet840MqRqm8KbgQEQ2SIRTuL6i9FqK716EuoCCJSDNzvj jZlhOgsztO8LVHZZJLNeJsVSyIPERfb1DQfqE= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=3hao9Rbd2DOkgWQuq9i9E+Ng3Pr6zL+wsaZllNiP784=; b=prJBVXS8DtXN5SitN1KN3y5ziXlbTnlj1OCF7CTLjvYbnHYL4H8xlqJeCD2hCtFmkP xXhM9z5cdAhWxN2vk87C6TJ5yn/TdtprC3JZyMp5WyYAqBl+MwLoB84hSEGFklh1Mi2G //zFA1cHrKgyPGBSeY/BrIK7QsNO/ApxNMWjvMpZdEbdimqkBGcl3XM07iZVQ5ZYldwu c6s2rO4PUS36N4Gj8uJWJdzUkEeHFwnc4DqM6UN1X+5KrV1NJuYFww+yVlllYrqISft7 QsHyqYmzKGMkJC8Cn4vvDkKLMH96ugNiXcF57ZSfGE1VSG5vVFnNMOdr1nWyHUGLA4Xu PBuQ== X-Gm-Message-State: AGi0PuYiTjiD6HjVKyPlU+QU4hbL78rTsD4pslo0KycjIP4jCS38aLt2 pGZ+5IYfe5WC9UsBmY8+7B7fcu7LWEA= X-Google-Smtp-Source: APiQypJ6njqoyd6pae1zIPv2aNYbmoo179h4Ms13R64/sNOWb9cOrMDgTpfu6+4Az4zWRwzmrRVS5A== X-Received: by 2002:a17:902:728e:: with SMTP id d14mr4880686pll.107.1588711870715; Tue, 05 May 2020 13:51:10 -0700 (PDT) Received: from www.outflux.net (smtp.outflux.net. [198.145.64.163]) by smtp.gmail.com with ESMTPSA id g16sm2739074pfq.203.2020.05.05.13.51.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 05 May 2020 13:51:09 -0700 (PDT) Date: Tue, 5 May 2020 13:51:09 -0700 From: Kees Cook To: "Eric W. Biederman" Cc: linux-kernel@vger.kernel.org, Linus Torvalds , Oleg Nesterov , Jann Horn , Greg Ungerer , Rob Landley , Bernd Edlinger , linux-fsdevel@vger.kernel.org, Al Viro , Alexey Dobriyan , Andrew Morton 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 List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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" Reviewed-by: Kees Cook -- Kees Cook