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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 EE159C433E0 for ; Sun, 7 Mar 2021 19:14:45 +0000 (UTC) Received: from isis.lip6.fr (isis.lip6.fr [132.227.60.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 2F2ED60230 for ; Sun, 7 Mar 2021 19:14:44 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2F2ED60230 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=inria.fr Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=cocci-bounces@systeme.lip6.fr Received: from systeme.lip6.fr (systeme.lip6.fr [132.227.104.7]) by isis.lip6.fr (8.15.2/8.15.2) with ESMTP id 127JEFYL018938; Sun, 7 Mar 2021 20:14:16 +0100 (CET) Received: from systeme.lip6.fr (systeme.lip6.fr [127.0.0.1]) by systeme.lip6.fr (Postfix) with ESMTP id D4CA777BF; Sun, 7 Mar 2021 20:14:15 +0100 (CET) Received: from isis.lip6.fr (isis.lip6.fr [132.227.60.2]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by systeme.lip6.fr (Postfix) with ESMTPS id 9BDDA571B for ; Sun, 7 Mar 2021 20:14:13 +0100 (CET) Received: from mail3-relais-sop.national.inria.fr (mail3-relais-sop.national.inria.fr [192.134.164.104]) by isis.lip6.fr (8.15.2/8.15.2) with ESMTP id 127JECxv000043 for ; Sun, 7 Mar 2021 20:14:12 +0100 (CET) X-IronPort-AV: E=Sophos;i="5.81,230,1610406000"; d="scan'208";a="375022443" Received: from 173.121.68.85.rev.sfr.net (HELO hadrien) ([85.68.121.173]) by mail3-relais-sop.national.inria.fr with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 07 Mar 2021 20:14:12 +0100 Date: Sun, 7 Mar 2021 20:14:11 +0100 (CET) From: Julia Lawall X-X-Sender: jll@hadrien To: Joe Perches In-Reply-To: Message-ID: References: <053b06c47f08631675c295b5c893b90be4248347.camel@perches.com> User-Agent: Alpine 2.22 (DEB 394 2020-01-19) MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="8323329-1189131414-1615144452=:2930" X-Greylist: Sender IP whitelisted, Sender e-mail whitelisted, not delayed by milter-greylist-4.4.3 (isis.lip6.fr [132.227.60.2]); Sun, 07 Mar 2021 20:14:16 +0100 (CET) X-Greylist: Sender passed SPF test, not delayed by milter-greylist-4.4.3 (isis.lip6.fr [132.227.60.2]); Sun, 07 Mar 2021 20:14:12 +0100 (CET) X-Scanned-By: MIMEDefang 2.78 on 132.227.60.2 X-Scanned-By: MIMEDefang 2.78 on 132.227.60.2 Cc: LKML , kernelnewbies , kernel-janitors , cocci , Rasmus Villemoes Subject: Re: [Cocci] linux-kernel janitorial RFP: Mark static arrays as const X-BeenThere: cocci@systeme.lip6.fr X-Mailman-Version: 2.1.13 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: cocci-bounces@systeme.lip6.fr Errors-To: cocci-bounces@systeme.lip6.fr This message is in MIME format. The first part should be readable text, while the remaining parts are likely unreadable without MIME-aware tools. --8323329-1189131414-1615144452=:2930 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT On Wed, 3 Mar 2021, Joe Perches wrote: > On Wed, 2021-03-03 at 10:41 +0100, Rasmus Villemoes wrote: > > On 02/03/2021 18.42, Joe Perches wrote: > > > Here is a possible opportunity to reduce data usage in the kernel. > > > > > > $ git grep -P -n '^static\s+(?!const|struct)(?:\w+\s+){1,3}\w+\s*\[\s*\]' drivers/ | \ > > >   grep -v __initdata | \ > > >   wc -l > > > 3250 > > > > > > Meaning there are ~3000 declarations of arrays with what appears to be > > > file static const content that are not marked const. > > > > > > So there are many static arrays that could be marked const to move the > > > compiled object code from data to text minimizing the total amount of > > > exposed r/w data. > > > > You can add const if you like, but it will rarely change the generated > > code. gcc is already smart enough to take a static array whose contents > > are provably never modified within the TU and put it in .rodata: > > At least some or perhaps even most of the time, true, but the gcc compiler > from v5 through at least v10 seems inconsistent about when it does the > appropriate conversion. > > See the example I posted: > https://lore.kernel.org/lkml/6b8b250a06a98ce42120a14824531a8641f5e8aa.camel@perches.com/ > > It was a randomly chosen source file conversion btw, I had no prior > knowledge of whether the text/data use would change. > > I'm unsure about clang consistently moving static but provably const arrays > from data to text. I rarely use clang. At least for v11 it seems to be > better though. I didn't try 10.1. I tried the relevnt drivers in drivers/input/joystick. I got only one driver that changed with gcc 9.3, which was drivers/input/joystick/analog.c. It actually got larger: original: text data bss dec hex filename 22607 10560 320 33487 82cf drivers/input/joystick/analog.o after adding const: text data bss dec hex filename 22728 10816 320 33864 8448 drivers/input/joystick/analog.o This was the only case where bss was not 0, but I don't know if there is a connection. julia --8323329-1189131414-1615144452=:2930 Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline _______________________________________________ Cocci mailing list Cocci@systeme.lip6.fr https://systeme.lip6.fr/mailman/listinfo/cocci --8323329-1189131414-1615144452=:2930--