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

From: Stanislaw Gruszka <[email-masked]>
Date: Wed, 8 Aug 2018 11:24:52 +0200

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=[email-masked]
> 
> Fixes: e87b5039511a ("mt76x0: eeprom files")
> Signed-off-by: Kees Cook <[email-masked]>
> ---
> 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