From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joe Perches Subject: Re: [PATCH 00/12] treewide: Fix GENMASK misuses Date: Wed, 10 Jul 2019 08:45:53 -0700 Message-ID: References: <5fa1fa6998332642c49e2d5209193ffe2713f333.camel@sipsolutions.net> <20190710094337.wf2lftxzfjq2etro@shell.armlinux.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20190710094337.wf2lftxzfjq2etro@shell.armlinux.org.uk> Sender: netdev-owner@vger.kernel.org To: Russell King - ARM Linux admin , Johannes Berg Cc: Andrew Morton , Patrick Venture , Nancy Yuen , Benjamin Fair , Andrew Jeffery , openbmc@lists.ozlabs.org, linux-kernel@vger.kernel.org, linux-aspeed@lists.ozlabs.org, linux-arm-kernel@lists.infradead.org, linux-amlogic@lists.infradead.org, netdev@vger.kernel.org, linux-mediatek@lists.infradead.org, linux-stm32@st-md-mailman.stormreply.com, linux-wireless@vger.kernel.org, linux-media@vger.kernel.org, linux-iio@vger.kernel.org, devel@driverdev.osuosl.org, alsa-devel@alsa-project.org, linux-mmc@vger.kernel.org, dri-devel@lists.freedesktop.org List-Id: linux-mmc@vger.kernel.org On Wed, 2019-07-10 at 10:43 +0100, Russell King - ARM Linux admin wrote: > On Wed, Jul 10, 2019 at 11:17:31AM +0200, Johannes Berg wrote: > > On Tue, 2019-07-09 at 22:04 -0700, Joe Perches wrote: > > > These GENMASK uses are inverted argument order and the > > > actual masks produced are incorrect. Fix them. > > > > > > Add checkpatch tests to help avoid more misuses too. > > > > > > Joe Perches (12): > > > checkpatch: Add GENMASK tests > > > > IMHO this doesn't make a lot of sense as a checkpatch test - just throw > > in a BUILD_BUG_ON()? I tried that. It'd can't be done as it's used in declarations and included in asm files and it uses the UL() macro. I also tried just making it do the right thing whatever the argument order. Oh well. > My personal take on this is that GENMASK() is really not useful, it's > just pure obfuscation and leads to exactly these kinds of mistakes. > > Yes, I fully understand the argument that you can just specify the > start and end bits, and it _in theory_ makes the code more readable. > > However, the problem is when writing code. GENMASK(a, b). Is a the > starting bit or ending bit? Is b the number of bits? It's confusing > and causes mistakes resulting in incorrect code. A BUILD_BUG_ON() > can catch some of the cases, but not all of them. It's a horrid little macro and I agree with Russell. I also think if it existed at all it should have been GENMASK(low, high) not GENMASK(high, low). I