From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from smtp.codeaurora.org ([198.145.29.96]:40250 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726998AbeHHMFy (ORCPT ); Wed, 8 Aug 2018 08:05:54 -0400 From: Kalle Valo To: Stanislaw Gruszka Cc: Kees Cook , "David S. Miller" , linux-wireless@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH wireless-drivers] mt76x0: Remove VLA usage References: <20180807225040.GA2164@beast> <20180808092450.GA25772@redhat.com> Date: Wed, 08 Aug 2018 12:46:54 +0300 In-Reply-To: <20180808092450.GA25772@redhat.com> (Stanislaw Gruszka's message of "Wed, 8 Aug 2018 11:24:52 +0200") Message-ID: <871sb942cx.fsf@kamboji.qca.qualcomm.com> (sfid-20180808_114708_043657_573C3E69) MIME-Version: 1.0 Content-Type: text/plain Sender: linux-wireless-owner@vger.kernel.org List-ID: Stanislaw Gruszka writes: > On Tue, Aug 07, 2018 at 03:50:40PM -0700, Kees Cook wrote: >> Even with "const" variables, the compiler will generate warnings about >> VLA usage. In the quest to remove all VLAs from the kernel[1], this uses >> a #define instead of a const to do the array sizing. >> >> [1] >> https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com >> >> Fixes: e87b5039511a ("mt76x0: eeprom files") >> Signed-off-by: Kees Cook >> --- >> Please include this for the v4.19 merge window. The VLA was introduced >> with the new source file (which I also note is missing a SPDX line), so > > I thought SPDX line is needed only if file has no license and eeprom.c > file and other mt76x0 files have specified the license. Is SPDX still > needed in that case ? > >> +#define MT_MAP_READS DIV_ROUND_UP(MT_EFUSE_USAGE_MAP_SIZE, 16) >> static int >> mt76x0_efuse_physical_size_check(struct mt76x0_dev *dev) >> { >> - const int map_reads = DIV_ROUND_UP(MT_EFUSE_USAGE_MAP_SIZE, 16); >> - u8 data[map_reads * 16]; > > Why this is variable length array? DIV_ROUND_UP can not be calculated > at compile time? But if so, macro do not change the situation either. The commit log mentioned: "Even with "const" variables, the compiler will generate warnings about VLA usage." So I guess the compiler (gcc?) is just not smart enough in this case? -- Kalle Valo