netdev - Re: [PATCH wireless-drivers] mt76x0: Remove VLA usage

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Date:   Wed, 8 Aug 2018 11:24:52 +0200
From:   Stanislaw Gruszka <sgruszka@...hat.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Kalle Valo <kvalo@...eaurora.org>,
        "David S. Miller" <davem@...emloft.net>,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH wireless-drivers] mt76x0: Remove VLA usage

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 <keescook@...omium.org>
> ---
> 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.

Thanks
Stanislaw