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=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 EFB61C433FF for ; Fri, 2 Aug 2019 03:13:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AC1A1206A3 for ; Fri, 2 Aug 2019 03:13:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728888AbfHBDN6 (ORCPT ); Thu, 1 Aug 2019 23:13:58 -0400 Received: from smtprelay0184.hostedemail.com ([216.40.44.184]:35957 "EHLO smtprelay.hostedemail.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725872AbfHBDN5 (ORCPT ); Thu, 1 Aug 2019 23:13:57 -0400 Received: from filter.hostedemail.com (clb03-v110.bra.tucows.net [216.40.38.60]) by smtprelay06.hostedemail.com (Postfix) with ESMTP id 99FA518224D6C; Fri, 2 Aug 2019 03:13:53 +0000 (UTC) X-Session-Marker: 6A6F6540706572636865732E636F6D X-HE-Tag: tent09_5c08077be4850 X-Filterd-Recvd-Size: 4014 Received: from XPS-9350.home (cpe-23-242-196-136.socal.res.rr.com [23.242.196.136]) (Authenticated sender: joe@perches.com) by omf04.hostedemail.com (Postfix) with ESMTPA; Fri, 2 Aug 2019 03:13:52 +0000 (UTC) Message-ID: <2b782cf609330f53b6ecc5b75a8a4b49898483eb.camel@perches.com> Subject: Re: [PATCH] linux/bits.h: Add compile time sanity check of GENMASK inputs From: Joe Perches To: Masahiro Yamada Cc: Rikard Falkeborn , Andrew Morton , Johannes Berg , Linux Kernel Mailing List Date: Thu, 01 Aug 2019 20:13:51 -0700 In-Reply-To: References: <0306bec0ec270b01b09441da3200252396abed27.camel@perches.com> <20190731190309.19909-1-rikard.falkeborn@gmail.com> <47d29791addc075431737aff4b64531a668d4c1b.camel@perches.com> Content-Type: text/plain; charset="ISO-8859-1" User-Agent: Evolution 3.30.5-0ubuntu0.18.10.1 MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2019-08-02 at 10:40 +0900, Masahiro Yamada wrote: > 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? Consistency with the uses in what's now called __GENMASK