Re: [PATCH 4.4] net/mac80211/debugfs.c: prevent build failure with CONFIG_UBSAN=y

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Tue, Jan 09, 2018 at 12:53:27PM +0100, Daniel Wagner wrote:
> From: Andrey Ryabinin <aryabinin@virtuozzo.com>
> 
> commit 68920c973254c5b71a684645c5f6f82d6732c5d6 upstream.
> 
> With upcoming CONFIG_UBSAN the following BUILD_BUG_ON in
> net/mac80211/debugfs.c starts to trigger:
> 
>   BUILD_BUG_ON(hw_flag_names[NUM_IEEE80211_HW_FLAGS] != (void *)0x1);
> 
> It seems, that compiler instrumentation causes some code
> deoptimizations.  Because of that GCC is not being able to resolve
> condition in BUILD_BUG_ON() at compile time.
> 
> We could make size of hw_flag_names array unspecified and replace the
> condition in BUILD_BUG_ON() with following:
> 
>   ARRAY_SIZE(hw_flag_names) != NUM_IEEE80211_HW_FLAGS
> 
> That will have the same effect as before (adding new flag without
> updating array will trigger build failure) except it doesn't fail with
> CONFIG_UBSAN.  As a bonus this patch slightly decreases size of
> hw_flag_names array.
> 
> Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
> Cc: Johannes Berg <johannes@sipsolutions.net>
> Cc: "David S. Miller" <davem@davemloft.net>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
> [Daniel: backport to 4.4.]
> Signed-off-by: Daniel Wagner <daniel.wagner@siemens.com>
> ---
> 
> Hi,
> 
> The only stable tree which is missing this fix is 4.4. 4.1 doesn't
> have 30686bf7f5b3 ("mac80211: convert HW flags to unsigned long
> bitmap") which makes gcc unhappy with allmodconfig. 4.9 contains the
> fix.

Now queued up, thanks for the backport.

greg k-h