Messages in this thread | | | Subject | Re: [PATCH] drivers: net: wireless: ath: ath9: dfs: remove VLA usage | From | "Gustavo A. R. Silva" <> | Date | Sat, 10 Mar 2018 17:26:46 -0600 |
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On 03/10/2018 05:12 PM, Kees Cook wrote: > On Sat, Mar 10, 2018 at 3:06 PM, Arend van Spriel > <arend.vanspriel@broadcom.com> wrote: >> On 3/9/2018 1:30 PM, Andreas Christoforou wrote: >>> >>> The kernel would like to have all stack VLA usage removed. >> >> >> I think there was a remark made earlier to give more explanation here. It >> should explain why we want "VLA on stack" removed. >> >>> Signed-off-by: Andreas Christoforou <andreaschristofo@gmail.com> >>> --- >>> drivers/net/wireless/ath/ath9k/dfs.c | 3 +-- >>> 1 file changed, 1 insertion(+), 2 deletions(-) >>> >>> diff --git a/drivers/net/wireless/ath/ath9k/dfs.c >>> b/drivers/net/wireless/ath/ath9k/dfs.c >>> index 6fee9a4..cfb0f84 100644 >>> --- a/drivers/net/wireless/ath/ath9k/dfs.c >>> +++ b/drivers/net/wireless/ath/ath9k/dfs.c >>> @@ -41,7 +41,6 @@ static const int BIN_DELTA_MAX = 10; >>> >>> /* we need at least 3 deltas / 4 samples for a reliable chirp detection >>> */ >>> #define NUM_DIFFS 3 >>> -static const int FFT_NUM_SAMPLES = (NUM_DIFFS + 1); >>>
What about this instead?
#define FFT_NUM_SAMPLES (NUM_DIFFS + 1)
>>> /* Threshold for difference of delta peaks */ >>> static const int MAX_DIFF = 2; >>> @@ -101,7 +100,7 @@ static bool ath9k_check_chirping(struct ath_softc *sc, >>> u8 *data, >>> int datalen, bool is_ctl, bool is_ext) >>> { >>> int i; >>> - int max_bin[FFT_NUM_SAMPLES]; >>> + int max_bin[NUM_DIFFS + 1]; >> >> >> Just wondering. Is this actually a VLA. FFT_NUM_SAMPLES was static const so >> not really going to show a lot of variation. This array will always have the >> same size on the stack. > > The problem is that it's not a "constant expression", so the compiler > frontend still yells about it under -Wvla. I would characterize this > mainly as a fix for "accidental VLA" or "misdetected VLA" or something > like that. AIUI, there really isn't a functional change here. > > -Kees >
-- Gustavo
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