Re: arch/m68k/include/asm/raw_io.h:91:13: warning: array subscript 0 is outside array bounds of 'volatile u16[0]' {aka 'volatile short unsigned int[]'}

[Guenter Roeck]

On 9/19/23 11:37, Rob Herring wrote:
> On Tue, Sep 19, 2023 at 7:09 AM kernel test robot <lkp@xxxxxxxxx> wrote:
> > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> > head:   2cf0f715623872823a72e451243bbf555d10d032
> > commit: f1a43aadb5a690e141a3b6700e2a40c1d4dbe088 watchdog: Enable COMPILE_TEST for more drivers
> > date:   5 weeks ago
> > config: m68k-allyesconfig (https://download.01.org/0day-ci/archive/20230919/202309192013.vI4DKHmw-lkp@xxxxxxxxx/config)
> > compiler: m68k-linux-gcc (GCC) 13.2.0
> > reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20230919/202309192013.vI4DKHmw-lkp@xxxxxxxxx/reproduce)
> >
> > If you fix the issue in a separate patch/commit (i.e. not just a new version of
> > the same patch/commit), kindly add following tags
> > | Reported-by: kernel test robot <lkp@xxxxxxxxx>
> > | Closes: https://lore.kernel.org/oe-kbuild-all/202309192013.vI4DKHmw-lkp@xxxxxxxxx/
> >
> > All warnings (new ones prefixed by >>):
> >
> >     In file included from arch/m68k/include/asm/io_mm.h:25,
> >                      from arch/m68k/include/asm/io.h:8,
> >                      from include/linux/io.h:13,
> >                      from drivers/watchdog/machzwd.c:39:
> >     In function 'zf_set_timer',
> >         inlined from 'zf_timer_on' at drivers/watchdog/machzwd.c:218:2:
> > > > arch/m68k/include/asm/raw_io.h:91:13: warning: array subscript 0 is outside array bounds of 'volatile u16[0]' {aka 'volatile short unsigned int[]'} [-Warray-bounds=]
> >        91 |         __w = ((*(__force volatile u16 *) ((_addr & 0xFFFF0000UL) + ((__v >> 8)<<1)))); \
> >           |         ~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >     arch/m68k/include/asm/io_mm.h:228:20: note: in expansion of macro 'rom_out_le16'
> >       228 |                  : rom_out_le16(isa_itw(port), (val)))
> >           |                    ^~~~~~~~~~~~
> >     arch/m68k/include/asm/io_mm.h:356:42: note: in expansion of macro 'isa_rom_outw'
> >       356 | #define outw(val, port) ((port) < 1024 ? isa_rom_outw((val), (port)) : out_le16((port), (val)))
> >           |                                          ^~~~~~~~~~~~
> >     drivers/watchdog/machzwd.c:74:53: note: in expansion of macro 'outw'
> >        74 | #define zf_writew(port, data)  { outb(port, INDEX); outw(data, DATA_W); }
> >           |                                                     ^~~~
> >     drivers/watchdog/machzwd.c:173:17: note: in expansion of macro 'zf_writew'
> >       173 |                 zf_writew(COUNTER_1, new);
> >           |                 ^~~~~~~~~
> >     In function 'zf_timer_on':
> >     cc1: note: source object is likely at address zero
>
> This seems to be some newish check in gcc which looks for fixed
> pointers below 4KB[1]. The linked issue says more was planned for
> gcc-13, but I haven't found what that is. AFAICT, that shouldn't
> happen with this config because isa_itw() should be variable and the
> compiler shouldn't be able to determine the value of _addr. However, a
> config with CONFIG_Q40=n, CONFIG_AMIGA_PCMCIA=n, and
> CONFIG_ATARI_ROM_ISA=n would have a fixed NULL value and could trigger
> the warning. This should also have warnings everywhere outw() (and
> others) are used with a constant port value.
>
> Rob
>
> [1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99578

A long time ago, when someone submitted a "cleanup: patch for the machzwd
watchdog driver, I approved it but added this comment.

> If anyone is still using the HW supported by this driver, it would
> be a prime target for conversion to use the watchdog subsystem.
> This would reduce code size and improve driver stability.
> _That_ would be useful.

> The only reason for replacing 0 with NULL is to make a static checker
> happy. This kind of change adds zero value to the code. Instead, it
> takes time from those who have to review the patches and apply them.

> If we ignore such patches, we'll get them again and again, taking
> away even more time. If we don't ignore them, we encourage submitters
> and get even more useless patches. If we try to discourage them, we
> risk being accused of being unfriendly. This is a perfect lose-lose
> situation for maintainers.

I do wonder if enabling BUILD_TEST on such drivers is any better.

Guenter