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=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,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 E06CDC433DB for ; Mon, 8 Mar 2021 06:55:19 +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 DFFB364E56 for ; Mon, 8 Mar 2021 06:55:18 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DFFB364E56 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 1286srjF017010; Mon, 8 Mar 2021 07:54:53 +0100 (CET) Received: from systeme.lip6.fr (systeme.lip6.fr [127.0.0.1]) by systeme.lip6.fr (Postfix) with ESMTP id C3F1377BF; Mon, 8 Mar 2021 07:54:53 +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 A77AA5DC3 for ; Mon, 8 Mar 2021 07:54:52 +0100 (CET) Received: from mail2-relais-roc.national.inria.fr (mail2-relais-roc.national.inria.fr [192.134.164.83]) by isis.lip6.fr (8.15.2/8.15.2) with ESMTP id 1286spQq011577 for ; Mon, 8 Mar 2021 07:54:51 +0100 (CET) X-IronPort-AV: E=Sophos;i="5.81,231,1610406000"; d="scan'208";a="496617192" Received: from 173.121.68.85.rev.sfr.net (HELO hadrien) ([85.68.121.173]) by mail2-relais-roc.national.inria.fr with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 08 Mar 2021 07:54:51 +0100 Date: Mon, 8 Mar 2021 07:54:51 +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="8323329-899039469-1615186491=:3383" X-Greylist: Sender IP whitelisted, Sender e-mail whitelisted, not delayed by milter-greylist-4.4.3 (isis.lip6.fr [132.227.60.2]); Mon, 08 Mar 2021 07:54:54 +0100 (CET) X-Greylist: Sender passed SPF test, not delayed by milter-greylist-4.4.3 (isis.lip6.fr [132.227.60.2]); Mon, 08 Mar 2021 07:54:51 +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. --8323329-899039469-1615186491=:3383 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT On Sun, 7 Mar 2021, Joe Perches wrote: > On Sun, 2021-03-07 at 20:14 +0100, Julia Lawall wrote: > > > > 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. > > You really need consider using defconfig so whatever object code > does not have tracing/debugging support. > > For instance, this code with defconfig and analog joystick: > > Original: > > $ size drivers/input/joystick/analog.o > text data bss dec hex filename > 8115 261 224 8600 2198 drivers/input/joystick/analog.o > > with const: > > $ size drivers/input/joystick/analog.o > text data bss dec hex filename > 8179 201 224 8604 219c drivers/input/joystick/analog.o Thanks for the suggestion. It occurred to me that in one case my transformation was wrong, because the array was multi-level, and a sub array was being stored in a structure field that was not declared as const. So the argument that the compiler would figure out to put the array in .rodata didn't make sense. But I still go the same sizes for that file. So I'll try the whole thing again. thanks, julia --8323329-899039469-1615186491=:3383 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 --8323329-899039469-1615186491=:3383--