Re: drivers/platform/surface/surface3_power.c:243:2: warning: 'snprintf' will always be truncated; specified size is 10, but format string expands to at least 12
From: Andy Shevchenko
Date: Wed Jan 29 2025 - 07:51:32 EST
On Wed, Jan 29, 2025 at 2:45 PM Andy Shevchenko
<andy.shevchenko@xxxxxxxxx> wrote:
> On Wed, Jan 29, 2025 at 10:09 AM kernel test robot <lkp@xxxxxxxxx> wrote:
> > tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> > head: 05dbaf8dd8bf537d4b4eb3115ab42a5fb40ff1f5
> > commit: 85f7582cd484dbf491b6d9bb2af6ef1467a024d2 platform/surface: Move Surface 3 Power OpRegion driver to platform/surface
> > date: 4 years, 3 months ago
> > config: x86_64-randconfig-071-20241231 (https://download.01.org/0day-ci/archive/20250129/202501291646.VtwF98qd-lkp@xxxxxxxxx/config)
> > compiler: clang version 19.1.3 (https://github.com/llvm/llvm-project ab51eccf88f5321e7c60591c5546b254b6afab99)
> > reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250129/202501291646.VtwF98qd-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/202501291646.VtwF98qd-lkp@xxxxxxxxx/
> >
> > All warnings (new ones prefixed by >>):
> >
> > >> drivers/platform/surface/surface3_power.c:243:2: warning: 'snprintf' will always be truncated; specified size is 10, but format string expands to at least 12 [-Wformat-truncation-non-kprintf]
> > 243 | snprintf(bix->serial, ARRAY_SIZE(bix->serial), "%3pE%6pE", buf + 7, buf);
>
> 3 + 'E' + 6 + 'E' + NUL, that's how the compiler thinks about this
> formatting string...
>
> > | ^
> > 1 warning generated.
>
> I do not know how to properly address this because it's false positive
> due to the compiler not being aware of pointer extensions used in
> Linux kernel. The w/a is to increase the buffer if we can, but is it
> practical? OTOH, this warning will be translated to a compilation
> error in case of default WERROR settings on `make W=1` builds which is
> also annoying to people who want to have that clean.
Actually using %pE implies that the buffer should be 4 times bigger
than the input string. So, with the given format string the
ARRAY_SIZE(bix->serial) has to be equal to or greater than 3 * 4 + 6 *
4 + 1, i.e. 37.
--
With Best Regards,
Andy Shevchenko