From patchwork Tue Jan 17 16:42:37 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: John Paul Adrian Glaubitz X-Patchwork-Id: 13104868 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 3C646C678D4 for ; Tue, 17 Jan 2023 16:43:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233234AbjAQQnU (ORCPT ); Tue, 17 Jan 2023 11:43:20 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50098 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233880AbjAQQmy (ORCPT ); Tue, 17 Jan 2023 11:42:54 -0500 Received: from outpost1.zedat.fu-berlin.de (outpost1.zedat.fu-berlin.de [130.133.4.66]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id EB85742BF7; Tue, 17 Jan 2023 08:42:40 -0800 (PST) Received: from inpost2.zedat.fu-berlin.de ([130.133.4.69]) by outpost.zedat.fu-berlin.de (Exim 4.95) with esmtps (TLS1.3) tls TLS_AES_256_GCM_SHA384 (envelope-from ) id 1pHp2k-001f9B-4y; Tue, 17 Jan 2023 17:42:38 +0100 Received: from p57bd9464.dip0.t-ipconnect.de ([87.189.148.100] helo=[192.168.178.81]) by inpost2.zedat.fu-berlin.de (Exim 4.95) with esmtpsa (TLS1.3) tls TLS_AES_128_GCM_SHA256 (envelope-from ) id 1pHp2j-002q0C-UX; Tue, 17 Jan 2023 17:42:38 +0100 Message-ID: <3800eaa8-a4da-b2f0-da31-6627176cb92e@physik.fu-berlin.de> Date: Tue, 17 Jan 2023 17:42:37 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.6.1 Subject: Calculating array sizes in C - was: Re: Build regressions/improvements in v6.2-rc1 Content-Language: en-US To: Geert Uytterhoeven Cc: linux-kernel@vger.kernel.org, amd-gfx@lists.freedesktop.org, linux-arm-kernel@lists.infradead.org, linux-media@vger.kernel.org, linux-wireless@vger.kernel.org, linux-mips@vger.kernel.org, linux-sh@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, linuxppc-dev@lists.ozlabs.org, kasan-dev@googlegroups.com, linux-xtensa@linux-xtensa.org, Michael Karcher References: <20221227082932.798359-1-geert@linux-m68k.org> From: John Paul Adrian Glaubitz In-Reply-To: X-Original-Sender: glaubitz@physik.fu-berlin.de X-Originating-IP: 87.189.148.100 Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org Hi Geert! On 1/6/23 16:17, Geert Uytterhoeven wrote: >> I'm not seeing this one, but I am getting this one instead: >> >> In file included from ./arch/sh/include/asm/hw_irq.h:6, >> from ./include/linux/irq.h:596, >> from ./include/asm-generic/hardirq.h:17, >> from ./arch/sh/include/asm/hardirq.h:9, >> from ./include/linux/hardirq.h:11, >> from ./include/linux/interrupt.h:11, >> from ./include/linux/serial_core.h:13, >> from ./include/linux/serial_sci.h:6, >> from arch/sh/kernel/cpu/sh2/setup-sh7619.c:11: >> ./include/linux/sh_intc.h:100:63: error: division 'sizeof (void *) / sizeof (void)' does not compute the number of array elements [-Werror=sizeof-pointer-div] >> 100 | #define _INTC_ARRAY(a) a, __same_type(a, NULL) ? 0 : sizeof(a)/sizeof(*a) >> | ^ >> ./include/linux/sh_intc.h:105:31: note: in expansion of macro '_INTC_ARRAY' >> 105 | _INTC_ARRAY(vectors), _INTC_ARRAY(groups), \ >> | ^~~~~~~~~~~ > > The easiest fix for the latter is to disable CONFIG_WERROR. > Unfortunately I don't know a simple solution to get rid of the warning. I did some research and it seems that what the macro _INT_ARRAY() does with "sizeof(a)/sizeof(*a)" is a commonly used way to calculate array sizes and the kernel has even its own macro for that called ARRAY_SIZE() which Linus asks people to use here [1]. So, I replaced _INTC_ARRAY() with ARRAY_SIZE() (see below), however the kernel's own ARRAY_SIZE() macro triggers the same compiler warning. I'm CC'ing Michael Karcher who has more knowledge on writing proper C code than me and maybe an idea how to fix this warning. Thanks, Adrian > [1] https://lkml.org/lkml/2015/9/3/428 diff --git a/include/linux/sh_intc.h b/include/linux/sh_intc.h index c255273b0281..07a187686a84 100644 --- a/include/linux/sh_intc.h +++ b/include/linux/sh_intc.h @@ -97,14 +97,12 @@ struct intc_hw_desc { unsigned int nr_subgroups; }; -#define _INTC_ARRAY(a) a, __same_type(a, NULL) ? 0 : sizeof(a)/sizeof(*a) - #define INTC_HW_DESC(vectors, groups, mask_regs, \ prio_regs, sense_regs, ack_regs) \ { \ - _INTC_ARRAY(vectors), _INTC_ARRAY(groups), \ - _INTC_ARRAY(mask_regs), _INTC_ARRAY(prio_regs), \ - _INTC_ARRAY(sense_regs), _INTC_ARRAY(ack_regs), \ + ARRAY_SIZE(vectors), ARRAY_SIZE(groups), \ + ARRAY_SIZE(mask_regs), ARRAY_SIZE(prio_regs), \ + ARRAY_SIZE(sense_regs), ARRAY_SIZE(ack_regs), \ } struct intc_desc {