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=-6.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 CD0AAC19759 for ; Fri, 2 Aug 2019 01:41:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 53536206A3 for ; Fri, 2 Aug 2019 01:41:23 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=nifty.com header.i=@nifty.com header.b="CXijuyKL" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731394AbfHBBlW (ORCPT ); Thu, 1 Aug 2019 21:41:22 -0400 Received: from conssluserg-05.nifty.com ([210.131.2.90]:30781 "EHLO conssluserg-05.nifty.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731302AbfHBBlV (ORCPT ); Thu, 1 Aug 2019 21:41:21 -0400 Received: from mail-vs1-f54.google.com (mail-vs1-f54.google.com [209.85.217.54]) (authenticated) by conssluserg-05.nifty.com with ESMTP id x721fF1U029735 for ; Fri, 2 Aug 2019 10:41:16 +0900 DKIM-Filter: OpenDKIM Filter v2.10.3 conssluserg-05.nifty.com x721fF1U029735 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nifty.com; s=dec2015msa; t=1564710076; bh=aKdLE8wx2u+7odpbXwBHXRxWu+Y7lWABFR3kwATccXQ=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=CXijuyKLs8ctwH3VGs+HPUQvGdo8SZCX7MREYXCiDRGwPYdRta04qxr0gEly7ImUi 9bXe5B7ZwkmRHB2xxI6PbFfJDX2zpV3lg15jyvQ5y4zqW9aTv3ctINUh9Gjl7fF6/9 a8BDMM3X1JFvYCdy6M8hjoj4RLK0egrkk7QKMiV4W2NMDCrRZxkipYhsROmJwjYVae q98YSwaT6OvtVX4VxWN6TjpPy/JewnMbICRSQJ0CkypW4PNZLv3KDQ4qAmzI9YhlZh YSlC0dL027hPAP3e8Mxcp0ECjyfjFgpUYUoh2cV3Vio2EiNg2bKNYGG1Q7SwcOeDBk VKq7/WLr4ODrQ== X-Nifty-SrcIP: [209.85.217.54] Received: by mail-vs1-f54.google.com with SMTP id j26so50295098vsn.10 for ; Thu, 01 Aug 2019 18:41:15 -0700 (PDT) X-Gm-Message-State: APjAAAW3YmZ1IXyw0nv0D8FHDYeImqhsXyClASLopCcae9AuKPSdPllx yopgxHsIBkKv0Pvxsm5hxpk/aZ5zFVC47MaYo+s= X-Google-Smtp-Source: APXvYqyf3mlA1z4uJLvTfK/fP3la3aeojoOD6X0fqAy+/dt1FXcmPLHdoIx0GBxxus9X5oO/Uji+SVjFlSOggdXM0Tg= X-Received: by 2002:a67:fc45:: with SMTP id p5mr22842997vsq.179.1564710074722; Thu, 01 Aug 2019 18:41:14 -0700 (PDT) MIME-Version: 1.0 References: <0306bec0ec270b01b09441da3200252396abed27.camel@perches.com> <20190731190309.19909-1-rikard.falkeborn@gmail.com> <47d29791addc075431737aff4b64531a668d4c1b.camel@perches.com> In-Reply-To: <47d29791addc075431737aff4b64531a668d4c1b.camel@perches.com> From: Masahiro Yamada Date: Fri, 2 Aug 2019 10:40:38 +0900 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH] linux/bits.h: Add compile time sanity check of GENMASK inputs To: Joe Perches Cc: Rikard Falkeborn , Andrew Morton , Johannes Berg , Linux Kernel Mailing List Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 1, 2019 at 4:27 AM Joe Perches wrote: > > On Wed, 2019-07-31 at 21:03 +0200, Rikard Falkeborn wrote: > > GENMASK() and GENMASK_ULL() are supposed to be called with the high bit > > as the first argument and the low bit as the second argument. Mixing > > them will return a mask with zero bits set. > > > > Recent commits show getting this wrong is not uncommon, see e.g. > > commit aa4c0c9091b0 ("net: stmmac: Fix misuses of GENMASK macro") and > > commit 9bdd7bb3a844 ("clocksource/drivers/npcm: Fix misuse of GENMASK > > macro"). > > > > To prevent such mistakes from appearing again, add compile time sanity > > checking to the arguments of GENMASK() and GENMASK_ULL(). If both the > > arguments are known at compile time, and the low bit is higher than the > > high bit, break the build to detect the mistake immediately. > > > > Since GENMASK() is used in declarations, BUILD_BUG_OR_ZERO() must be > > used instead of BUILD_BUG_ON(), and __is_constexpr() must be used instead > > of __builtin_constant_p(). > > > > Commit 95b980d62d52 ("linux/bits.h: make BIT(), GENMASK(), and friends > > available in assembly") made the macros in linux/bits.h available in > > assembly. Since neither BUILD_BUG_OR_ZERO() or __is_constexpr() are asm > > compatible, disable the checks if the file is included in an asm file. > > > > Signed-off-by: Rikard Falkeborn > > --- > > Joe Perches sent a series to fix the existing misuses of GENMASK() that > > needs to be merged before this to avoid build failures. Currently, 7 of > > the patches were not in Linus tree, and 2 were not in linux-next. > > > > Also, there's currently no asm users of bits.h, but since it was made > > asm-compatible just two weeks ago it would be a shame to break it right > > away... > [] > > diff --git a/include/linux/bits.h b/include/linux/bits.h > [] > > @@ -18,12 +18,22 @@ > > * position @h. For example > > * GENMASK_ULL(39, 21) gives us the 64bit vector 0x000000ffffe00000. > > */ > > +#ifndef __ASSEMBLY__ > > +#include > > +#define GENMASK_INPUT_CHECK(h, l) BUILD_BUG_ON_ZERO(__builtin_choose_expr( \ > > + __is_constexpr(h) && __is_constexpr(l), (l) > (h), 0)) > > +#else > > +#define GENMASK_INPUT_CHECK(h, l) 0 > > A few things: > > o Reading the final code is a bit confusing. > Perhaps add a comment description saying it's not checked > in asm .h uses. > > o Maybe use: > #define GENMASK_INPUT_CHECK(h, l) UL(0) Why? > o The compiler error message when the arguments are in the > wrong order isn't obvious. Is there some way to improve > the compiler error output, maybe by using BUILD_BUG_ON_MSG > or some other mechanism? > > -- Best Regards Masahiro Yamada