linux-kernel - 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

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Message-ID: <CAMuHMdVsCt=x_3KdHKHFmr9xgqcMvFNjKGjd4WNHx+LEwiEDOA@mail.gmail.com>
Date: Thu, 30 Jan 2025 09:56:48 +0100
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Andy Shevchenko <andy.shevchenko@...il.com>
Cc: kernel test robot <lkp@...el.com>, Maximilian Luz <luzmaximilian@...il.com>, llvm@...ts.linux.dev, 
	oe-kbuild-all@...ts.linux.dev, linux-kernel@...r.kernel.org, 
	Hans de Goede <hdegoede@...hat.com>
Subject: 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

On Wed, 29 Jan 2025 at 13:51, Andy Shevchenko <andy.shevchenko@...il.com> wrote:
> On Wed, Jan 29, 2025 at 2:45 PM Andy Shevchenko
> <andy.shevchenko@...il.com> wrote:
> > On Wed, Jan 29, 2025 at 10:09 AM kernel test robot <lkp@...el.com> 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@intel.com/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@intel.com/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@...el.com>
> > > | Closes: https://lore.kernel.org/oe-kbuild-all/202501291646.VtwF98qd-lkp@intel.com/
> > >
> > > 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.

    #define SURFACE_3_STRLEN                10

    struct bix {
            ...
            char    serial[SURFACE_3_STRLEN];

Oops...

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds