netdev - Re: [PATCH net-next v6 13/21] bitmap: make bitmap_{get,set}_value8() use bitmap

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Date: Wed, 29 May 2024 16:12:25 +0100
From: Robin Murphy <robin.murphy@....com>
To: Alexander Lobakin <aleksander.lobakin@...el.com>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>
Cc: Yury Norov <yury.norov@...il.com>, Alexander Potapenko
 <glider@...gle.com>, nex.sw.ncis.osdt.itp.upstreaming@...el.com,
 intel-wired-lan@...ts.osuosl.org, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v6 13/21] bitmap: make bitmap_{get,set}_value8()
 use bitmap_{read,write}()

Hi Alexander,

On 27/03/2024 3:23 pm, Alexander Lobakin wrote:
> Now that we have generic bitmap_read() and bitmap_write(), which are
> inline and try to take care of non-bound-crossing and aligned cases
> to keep them optimized, collapse bitmap_{get,set}_value8() into
> simple wrappers around the former ones.
> bloat-o-meter shows no difference in vmlinux and -2 bytes for
> gpio-pca953x.ko, which says the optimization didn't suffer due to
> that change. The converted helpers have the value width embedded
> and always compile-time constant and that helps a lot.

This change appears to have introduced a build failure for me on arm64
(with GCC 9.4.0 from Ubuntu 20.04.02) - reverting b44759705f7d makes
these errors go away again:

In file included from drivers/gpio/gpio-pca953x.c:12:
drivers/gpio/gpio-pca953x.c: In function ‘pca953x_probe’:
./include/linux/bitmap.h:799:17: error: array subscript [1, 1024] is outside array bounds of ‘long unsigned int[1]’ [-Werror=array-bounds]
   799 |  map[index + 1] &= BITMAP_FIRST_WORD_MASK(start + nbits);
       |                 ^~
In file included from ./include/linux/atomic.h:5,
                  from drivers/gpio/gpio-pca953x.c:11:
drivers/gpio/gpio-pca953x.c:1015:17: note: while referencing ‘val’
  1015 |  DECLARE_BITMAP(val, MAX_LINE);
       |                 ^~~
./include/linux/types.h:11:16: note: in definition of macro ‘DECLARE_BITMAP’
    11 |  unsigned long name[BITS_TO_LONGS(bits)]
       |                ^~~~
In file included from drivers/gpio/gpio-pca953x.c:12:
./include/linux/bitmap.h:800:17: error: array subscript [1, 1024] is outside array bounds of ‘long unsigned int[1]’ [-Werror=array-bounds]
   800 |  map[index + 1] |= (value >> space);
       |  ~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~
In file included from ./include/linux/atomic.h:5,
                  from drivers/gpio/gpio-pca953x.c:11:
drivers/gpio/gpio-pca953x.c:1015:17: note: while referencing ‘val’
  1015 |  DECLARE_BITMAP(val, MAX_LINE);
       |                 ^~~
./include/linux/types.h:11:16: note: in definition of macro ‘DECLARE_BITMAP’
    11 |  unsigned long name[BITS_TO_LONGS(bits)]
       |                ^~~~

I've not dug further since I don't have any interest in the pca953x
driver - it just happened to be enabled in my config, so for now I've
turned it off. However I couldn't obviously see any other reports of
this, so here it is.

Thanks,
Robin.