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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0226DC433EF for ; Sat, 20 Nov 2021 15:22:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237645AbhKTPZr (ORCPT ); Sat, 20 Nov 2021 10:25:47 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50924 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230038AbhKTPZq (ORCPT ); Sat, 20 Nov 2021 10:25:46 -0500 Received: from mail-wm1-x330.google.com (mail-wm1-x330.google.com [IPv6:2a00:1450:4864:20::330]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AB6F6C061574 for ; Sat, 20 Nov 2021 07:22:42 -0800 (PST) Received: by mail-wm1-x330.google.com with SMTP id r9-20020a7bc089000000b00332f4abf43fso9398201wmh.0 for ; Sat, 20 Nov 2021 07:22:42 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=message-id:date:mime-version:user-agent:subject:content-language:to :cc:references:from:in-reply-to:content-transfer-encoding; bh=9h+PyJVI+J/jk7CrfScjFwP4ghuFS8I41cpzNkNVExo=; b=Cq8FDxnYcS05vCM3l13gztARsKs7aMg/b1mLOZFttmI8NmRM1pXVL6My7zn/EnMpQ8 wc74HALnkKl1Rhfq5QdpQCziUJI4FJrHJuL7nPZBH19AVAADNZG12mrSledEkZSRPcae IaUDavJcn3bu0sPulhQUn1YBXi8xqsfPcoOHOr0Hr58ZCPJ2qH4c08z6m8ldhYSYxXLs sweFRIDk0ePuKHWfOqozPdCgLr8dap4wlvG+iDyfqJGTQdhwPwGyV/txnN/TlQ6u9873 unPxGmeZt3AP8VNkZ1WpbO+NR4NhjhFkU8JzwFuulaSnBPvRv6wIrg2bIqhlYBWbUoqi lGjg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:message-id:date:mime-version:user-agent:subject :content-language:to:cc:references:from:in-reply-to :content-transfer-encoding; bh=9h+PyJVI+J/jk7CrfScjFwP4ghuFS8I41cpzNkNVExo=; b=2zjQjCF7e9p+iBw/k6DNmEeK2mE4NCU1TGfpe/GueqgptU/1xoYSkZlntK6rBun4OQ a9ytv4aWGvxJLpuquRwiWWtIQYRR8WCzXHoTLoNzaDrCrE/HDfBPDNF4r7JEjGRT/Geq XpErFoatmbKSxXUs9TC3OyvL3eyjVZDdEyt3nqQ077wlf8/eUzQb5d+W7ix2IbelPXCV Fb6Cq/u3/pEPejtde71P6amIoxarRz2dYCyCT2INPxCV3vKnUk7KWU/qECrW2Si9dPF0 4vwTWtPqRawOV4rHJGe6+lfFcJqW1m7psV1QcpzAueIO/CTzZ4UvNjp7lItaa6kGKb3R te/A== X-Gm-Message-State: AOAM530O4Cdse4kQTRBWA8hG8W+ZMAOd46DOu5foDVrpzWJ20SizC7Ta Sg7mHuhlDiS7QiuwpvaGOgZRAFffOzp+sg== X-Google-Smtp-Source: ABdhPJx3h0kft0+qGWkzsSDM50AiSPsmATzRdJB+5KoqHJAPLmHGCItofRzH1QfDCLUgyvOOQS98Ng== X-Received: by 2002:a7b:cc96:: with SMTP id p22mr10878629wma.69.1637421761321; Sat, 20 Nov 2021 07:22:41 -0800 (PST) Received: from [192.168.0.160] ([170.253.36.171]) by smtp.gmail.com with ESMTPSA id c4sm3069597wrr.37.2021.11.20.07.22.40 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 20 Nov 2021 07:22:41 -0800 (PST) Message-ID: <43a9a694-c58d-e4e1-04e4-585ad9a8fc97@gmail.com> Date: Sat, 20 Nov 2021 16:22:39 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.3.0 Subject: Re: [PATCH v2 12/20] linux/must_be.h: Add must_be() to improve readability of BUILD_BUG_ON_ZERO() Content-Language: en-US To: Alexey Dobriyan Cc: LKML , Andy Shevchenko , Arnd Bergmann , Jani Nikula , Rasmus Villemoes , Kees Cook , Joe Perches References: <20211119113644.1600-1-alx.manpages@gmail.com> <20211120130104.185699-1-alx.manpages@gmail.com> <20211120130104.185699-13-alx.manpages@gmail.com> From: "Alejandro Colomar (man-pages)" In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Alexey, On 11/20/21 16:05, Alexey Dobriyan wrote: > On Sat, Nov 20, 2021 at 02:00:55PM +0100, Alejandro Colomar wrote: >> Historically, BUILD_BUG_ON_ZERO() has been hard to read. >> __must_be_array() is based on BUILD_BUG_ON_ZERO(), >> and unlike BUILD_BUG_ON_*(), >> it has a pretty readable name. > > The best name is assert() which userspace uses and is standartised. Yes, assert() is almost the same thing. In this case, it would be better named static_assert(), since it's a compile-time assert(). However, there's still one slight difference between static_assert() and must_be(): static_assert() is limited; it cannot be used in some places, such as in the implementation of ARRAY_SIZE(). The following doesn't compile: #define __arraycount(a) (sizeof((arr)) / sizeof((arr)[0]) #define ARRAY_SIZE(a) (__arraycount(a) + static_assert(is_array(a))) And if you change it to be: #define ARRAY_SIZE(a) ( \ { \ static_assert(is_array(a)); \ __arraycount(a); \ } \ ) then the macro can't be used at file scope (since ({}) can't be used at file scope). The good thing about __must_be() is that it evaluates to 0, which allows you to use it everywhere a 0 can be used. My own implementation of __must_be() is more standards compliant, and is: #define must_be(e) ( \ 0 * (int)sizeof( \ struct { \ static_assert(e); \ char ISO_C_forbids_a_struct_with_no_members__; \ } \ ) \ ) I would like this to superseed the kernel's BUILD_BUG_ON_ZERO(), but it makes use of C2X static_assert(). I don't know how much that can be a problem. But please consider this proposal. Thanks, Alex -- Alejandro Colomar Linux man-pages comaintainer; https://www.kernel.org/doc/man-pages/ http://www.alejandro-colomar.es/