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SubjectRe: [PATCH wireless-drivers] mt76x0: Remove VLA usage
On Wed, Aug 8, 2018 at 2:46 AM, Kalle Valo <> wrote:
> 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]
>>> 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 ?

I thought all source files needed SPDX:

>>> 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?

Correct. This is technically a false positive, but with the goal of
adding -Wvla to the build globally, we have to get rid of these as
well. It's a little frustrating, I agree, but with all others fixed
now, these stand out. :)


Kees Cook
Pixel Security

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