Re: drivers/hwmon/pmbus/ibm-cffps.c:184:60: warning: '%04X' directive output may be truncated writing between 4 and 8 bytes into a region of size 5

[Guenter Roeck]

On 12/20/24 08:30, David Laight wrote:
> On Fri, 20 Dec 2024 07:21:18 -0800
> Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
>
> > On 12/20/24 05:54, kernel test robot wrote:
> > > Hi Eddie,
> > >
> > > FYI, the error/warning still remains.
> > >
> > > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> > > head:   8faabc041a001140564f718dabe37753e88b37fa
> > > commit: 2f8a855efe8a6faf962c53af406e5ea4791b3877 pmbus: (ibm-cffps) Add support for version 2 of the PSU
> > > date:   5 years ago
> > > config: x86_64-randconfig-077-20241209 (https://download.01.org/0day-ci/archive/20241220/202412202139.tZ2VJL2f-lkp@xxxxxxxxx/config)
> > > compiler: gcc-12 (Debian 12.2.0-14) 12.2.0
> > > reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20241220/202412202139.tZ2VJL2f-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/202412202139.tZ2VJL2f-lkp@xxxxxxxxx/
> > >    
> >
> > We could use %2. 2X and %4.4X to make the compiler happy, but those are false positives.
> > rc is known in all cases to not exceed the format size. I don't see the point of changing
> > the code just to make the compiler happy.
>
> I doubt they'd make any difference.
Yes, you are correct.

> > >      drivers/hwmon/pmbus/ibm-cffps.c:171:60: warning: '%02X' directive output may be truncated writing between 2 and 8 bytes into a region of size 3 [-Wformat-truncation=]
> > >        171 |                                 snprintf(&data[i * 2], 3, "%02X", rc);
>
> The only ways I know are to bound check the value or to use
> OPTIMISER_HIDE_VAR() on the length.

-                               snprintf(&data[i * 2], 3, "%02X", rc);
+                               snprintf(&data[i * 2], 3, "%02X", rc & 0xff);

works as well, at least with gcc 11 and 12, but I really dislike that kind of nonsense.

Guenter