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

[Robin Murphy]

On 30/05/2024 6:11 pm, Yury Norov wrote:
> On Wed, May 29, 2024 at 04:12:25PM +0100, Robin Murphy wrote:
> > 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.
>
> It's a compiler false-positive. The straightforward fix is to disable the warning
> For gcc9+, and it's in Andrew Morton's tree alrady. but there's some discussion
> ongoing on how it should be mitigated properlu:
>
> https://lore.kernel.org/all/0ab2702f-8245-4f02-beb7-dcc7d79d5416@xxxxxxxxxxxxxxxx/T/

Ah, great! Guess I really should have scrolled further down my lore 
search results - I assumed I was looking for any other reports of a 
recent regression in mainline, not ones from 6 months ago :)

Cheers,
Robin.