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 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 75B0BC433FF for ; Thu, 1 Aug 2019 02:51:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4732A205F4 for ; Thu, 1 Aug 2019 02:51:23 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=nifty.com header.i=@nifty.com header.b="Ip3T/FmO" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728168AbfHACvW (ORCPT ); Wed, 31 Jul 2019 22:51:22 -0400 Received: from conssluserg-04.nifty.com ([210.131.2.83]:48880 "EHLO conssluserg-04.nifty.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726125AbfHACvV (ORCPT ); Wed, 31 Jul 2019 22:51:21 -0400 Received: from mail-vs1-f47.google.com (mail-vs1-f47.google.com [209.85.217.47]) (authenticated) by conssluserg-04.nifty.com with ESMTP id x712pDvX024730 for ; Thu, 1 Aug 2019 11:51:14 +0900 DKIM-Filter: OpenDKIM Filter v2.10.3 conssluserg-04.nifty.com x712pDvX024730 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nifty.com; s=dec2015msa; t=1564627874; bh=6TJM9VDYF9EtQNeGWDC4vgS6nHe+nk5JsaYmJiVXyBI=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=Ip3T/FmOcMM0Xe1G9kF0kVoTwbrk8BewSMJnPxRispVgtY50AhB8uFI3rOG3M9/QM XLjmSx3URsrphsgwvgQdUY57MfeEMzr8IKvwp2zJljTdnoCYQ/FTmf/AqqA90Mq5CE Rc/shGko8O6Sozs4Pnx9H0Wd/zCHvt4HvA4Lav7j6IoMWkHTd9w80ZWJqStvYT8nhj TpiwvOOmJy8UalIPDjzobDQqg6bSLmAnMSbMQLF0SY7nAtoXj2AWy0NJXLOGP3jbaU mzSot8oistN5lDod77IzhazhuL2o27wHMpat6HsD6Xb9wHOHYk8H5pZHZ9mZIM+kHS qyumrdtP1ZZDQ== X-Nifty-SrcIP: [209.85.217.47] Received: by mail-vs1-f47.google.com with SMTP id 2so47771454vso.8 for ; Wed, 31 Jul 2019 19:51:13 -0700 (PDT) X-Gm-Message-State: APjAAAXBrmW+T8baILD1sT6AzUDhnorG+VJ4Nr3P9hgvLfqgsobVGKnj C/U9KdjE58CRiRYEHhr8BsydGg9YSrmVXhPcyAY= X-Google-Smtp-Source: APXvYqwHhHB2zdOBNLzdxW0bRxUMu2FfZ44yc107C8w3WGao4L0NcTxQPnTBuBwfLpd397ee2X7kKqxcaDQTatWMN2E= X-Received: by 2002:a67:d46:: with SMTP id 67mr81172763vsn.181.1564627872707; Wed, 31 Jul 2019 19:51:12 -0700 (PDT) MIME-Version: 1.0 References: <0306bec0ec270b01b09441da3200252396abed27.camel@perches.com> <20190731190309.19909-1-rikard.falkeborn@gmail.com> In-Reply-To: <20190731190309.19909-1-rikard.falkeborn@gmail.com> From: Masahiro Yamada Date: Thu, 1 Aug 2019 11:50:36 +0900 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH] linux/bits.h: Add compile time sanity check of GENMASK inputs To: Rikard Falkeborn Cc: Joe Perches , 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 4:04 AM 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... > > include/linux/bits.h | 14 ++++++++++++-- > 1 file changed, 12 insertions(+), 2 deletions(-) > > diff --git a/include/linux/bits.h b/include/linux/bits.h > index 669d69441a62..73489579eef9 100644 > --- 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 > +#endif > + > #define GENMASK(h, l) \ > + (GENMASK_INPUT_CHECK(h, l) + \ > (((~UL(0)) - (UL(1) << (l)) + 1) & \ > - (~UL(0) >> (BITS_PER_LONG - 1 - (h)))) > + (~UL(0) >> (BITS_PER_LONG - 1 - (h))))) > > #define GENMASK_ULL(h, l) \ > + (GENMASK_INPUT_CHECK(h, l) + \ > (((~ULL(0)) - (ULL(1) << (l)) + 1) & \ > - (~ULL(0) >> (BITS_PER_LONG_LONG - 1 - (h)))) > + (~ULL(0) >> (BITS_PER_LONG_LONG - 1 - (h))))) This is getting cluttered with so many parentheses. One way of clean-up is to rename the current macros as follows: GENMASK() -> __GENMASK() GENMASK_UL() -> __GENMASK_ULL() Then, #define GENMASK(h, l) (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l)) #define GENMASK_ULL(h, l) (GENMASK_INPUT_CHECK(h, l) + __GENMASK_ULL(h, l)) -- Best Regards Masahiro Yamada