linux-kernel - Re: drivers/vdpa/pds/debugfs.c:269:49: warning: '%02d' directive output may be truncated writing between 2 and 11 bytes into a region of size 6

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Date:   Sun, 5 Nov 2023 07:57:44 -0500
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     kernel test robot <lkp@...el.com>
Cc:     Shannon Nelson <shannon.nelson@....com>,
        oe-kbuild-all@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: drivers/vdpa/pds/debugfs.c:269:49: warning: '%02d' directive
 output may be truncated writing between 2 and 11 bytes into a region of size
 6

On Sat, Nov 04, 2023 at 01:36:05AM +0800, kernel test robot wrote:
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head:   8f6f76a6a29f36d2f3e4510d0bde5046672f6924
> commit: 9a8864d2a8dc5c49acd66284fd382871d99b5db8 pds_vdpa: pds_vdps.rst and Kconfig
> date:   4 months ago
> config: alpha-allyesconfig (https://download.01.org/0day-ci/archive/20231104/202311040109.RfgJoE7L-lkp@intel.com/config)
> compiler: alpha-linux-gcc (GCC) 13.2.0
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20231104/202311040109.RfgJoE7L-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/202311040109.RfgJoE7L-lkp@intel.com/
> 
> All warnings (new ones prefixed by >>):
> 
>    drivers/vdpa/pds/debugfs.c: In function 'pds_vdpa_debugfs_add_vdpadev':
> >> drivers/vdpa/pds/debugfs.c:269:49: warning: '%02d' directive output may be truncated writing between 2 and 11 bytes into a region of size 6 [-Wformat-truncation=]
>      269 |                 snprintf(name, sizeof(name), "vq%02d", i);
>          |                                                 ^~~~
>    drivers/vdpa/pds/debugfs.c:269:46: note: directive argument in the range [-2147483641, 254]
>      269 |                 snprintf(name, sizeof(name), "vq%02d", i);
>          |                                              ^~~~~~~~
>    drivers/vdpa/pds/debugfs.c:269:17: note: 'snprintf' output between 5 and 14 bytes into a destination of size 8
>      269 |                 snprintf(name, sizeof(name), "vq%02d", i);
>          |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> 
> vim +269 drivers/vdpa/pds/debugfs.c

> 151cc834f3ddafe Shannon Nelson 2023-05-19  259  
> 151cc834f3ddafe Shannon Nelson 2023-05-19  260  void pds_vdpa_debugfs_add_vdpadev(struct pds_vdpa_aux *vdpa_aux)
> 151cc834f3ddafe Shannon Nelson 2023-05-19  261  {
> 151cc834f3ddafe Shannon Nelson 2023-05-19  262  	int i;
> 151cc834f3ddafe Shannon Nelson 2023-05-19  263  
> 151cc834f3ddafe Shannon Nelson 2023-05-19  264  	debugfs_create_file("config", 0400, vdpa_aux->dentry, vdpa_aux->pdsv, &config_fops);
> 151cc834f3ddafe Shannon Nelson 2023-05-19  265  
> 151cc834f3ddafe Shannon Nelson 2023-05-19  266  	for (i = 0; i < vdpa_aux->pdsv->num_vqs; i++) {
> 151cc834f3ddafe Shannon Nelson 2023-05-19  267  		char name[8];
> 151cc834f3ddafe Shannon Nelson 2023-05-19  268  
> 151cc834f3ddafe Shannon Nelson 2023-05-19 @269  		snprintf(name, sizeof(name), "vq%02d", i);
> 151cc834f3ddafe Shannon Nelson 2023-05-19  270  		debugfs_create_file(name, 0400, vdpa_aux->dentry,
> 151cc834f3ddafe Shannon Nelson 2023-05-19  271  				    &vdpa_aux->pdsv->vqs[i], &vq_fops);
> 151cc834f3ddafe Shannon Nelson 2023-05-19  272  	}
> 151cc834f3ddafe Shannon Nelson 2023-05-19  273  }
> 151cc834f3ddafe Shannon Nelson 2023-05-19  274  


So gcc can't figure out that i is positive in this loop :(

Let's make it unsigned I guess? Should calm it down.

Shannon could you send a patch please?

> 
> :::::: The code at line 269 was first introduced by commit
> :::::: 151cc834f3ddafec869269fe48036460d920d08a pds_vdpa: add support for vdpa and vdpamgmt interfaces
> 
> :::::: TO: Shannon Nelson <shannon.nelson@....com>
> :::::: CC: Michael S. Tsirkin <mst@...hat.com>
> 
> -- 
> 0-DAY CI Kernel Test Service
> https://github.com/intel/lkp-tests/wiki