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 9/20/23 05:44, Rob Herring wrote:
> On Tue, Sep 19, 2023 at 6:14 PM Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
> > 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.
>
> Agreed. I keep getting one to fix "of of" in a comment. The fix is
> always to drop an "of", but that's actually wrong because it's
> supposed to be "OF". I keep pointing this out and *never* get the
> right fix. I don't fix it myself because at this point, I find
> continuing to get "fixes" entertaining.
>
> > I do wonder if enabling BUILD_TEST on such drivers is any better.
>
> I think that and trivial fixes on a specific driver are completely
> different. If you want to test build one driver, that's not too hard.
> Find its kconfig value, turn it on and build the right arch. For tree
> wide stuff, it's a real pain to ensure you built everything. For
> example, the only way to build many Cavium Octeon drivers is with the
> Octeon defconfig which is just one of dozens configs for MIPS (which
> is still a bigger mess than arm32 ever was).

Sure, but I still argue that this isn't worth it for drivers like this one.
Are you going to submit a fix ? Because otherwise I'll submit a patch
to drop COMPILE_TEST from MACHZ_WDT.

Thanks,
Guenter