linux-kernel - 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

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Message-ID: <e76a0071-b6dd-4a99-9a78-69f104278c70@roeck-us.net>
Date: Fri, 20 Dec 2024 09:03:51 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: David Laight <david.laight.linux@...il.com>
Cc: kernel test robot <lkp@...el.com>, Eddie James <eajames@...ux.ibm.com>,
 oe-kbuild-all@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: 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

On 12/20/24 08:30, David Laight wrote:
> On Fri, 20 Dec 2024 07:21:18 -0800
> Guenter Roeck <linux@...ck-us.net> 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@intel.com/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@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/202412202139.tZ2VJL2f-lkp@intel.com/
>>>    
>>
>> 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