Hi Florent,

I love your patch! Perhaps something to improve:

[auto build test WARNING on bpf-next/master]

url:    https://github.com/0day-ci/linux/commits/Florent-Revest/Add-a-snprintf-eBPF-helper/20210412-233921
base:   https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git master
config: i386-randconfig-s002-20210412 (attached as .config)
compiler: gcc-9 (Debian 9.3.0-22) 9.3.0
reproduce:
        # apt-get install sparse
        # sparse version: v0.6.3-280-g2cd6d34e-dirty
        # https://github.com/0day-ci/linux/commit/168301dda58989eca274d5f5c926675540010e13
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review Florent-Revest/Add-a-snprintf-eBPF-helper/20210412-233921
        git checkout 168301dda58989eca274d5f5c926675540010e13
        # save the attached .config to linux build tree
        make W=1 C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' ARCH=i386 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>


sparse warnings: (new ones prefixed by >>)
   kernel/bpf/verifier.c:1674:41: sparse: sparse: subtraction of functions? Share your drugs
   kernel/bpf/verifier.c:12051:76: sparse: sparse: subtraction of functions? Share your drugs
   kernel/bpf/verifier.c:12489:81: sparse: sparse: subtraction of functions? Share your drugs
   kernel/bpf/verifier.c:12493:81: sparse: sparse: subtraction of functions? Share your drugs
   kernel/bpf/verifier.c:12497:81: sparse: sparse: subtraction of functions? Share your drugs
   kernel/bpf/verifier.c:12501:79: sparse: sparse: subtraction of functions? Share your drugs
   kernel/bpf/verifier.c:12505:78: sparse: sparse: subtraction of functions? Share your drugs
   kernel/bpf/verifier.c:12509:79: sparse: sparse: subtraction of functions? Share your drugs
   kernel/bpf/verifier.c:12513:78: sparse: sparse: subtraction of functions? Share your drugs
   kernel/bpf/verifier.c:12557:38: sparse: sparse: subtraction of functions? Share your drugs
>> kernel/bpf/verifier.c:5944:23: sparse: sparse: non size-preserving integer to pointer cast

vim +5944 kernel/bpf/verifier.c

  5920	
  5921	static int check_bpf_snprintf_call(struct bpf_verifier_env *env,
  5922					   struct bpf_reg_state *regs)
  5923	{
  5924		struct bpf_reg_state *fmt_reg = &regs[BPF_REG_3];
  5925		struct bpf_reg_state *data_len_reg = &regs[BPF_REG_5];
  5926		struct bpf_map *fmt_map = fmt_reg->map_ptr;
  5927		int err, fmt_map_off, num_args;
  5928		u64 fmt_addr;
  5929		char *fmt;
  5930	
  5931		/* data must be an array of u64 */
  5932		if (data_len_reg->var_off.value % 8)
  5933			return -EINVAL;
  5934		num_args = data_len_reg->var_off.value / 8;
  5935	
  5936		/* fmt being ARG_PTR_TO_CONST_STR guarantees that var_off is const
  5937		 * and map_direct_value_addr is set.
  5938		 */
  5939		fmt_map_off = fmt_reg->off + fmt_reg->var_off.value;
  5940		err = fmt_map->ops->map_direct_value_addr(fmt_map, &fmt_addr,
  5941							  fmt_map_off);
  5942		if (err)
  5943			return err;
> 5944		fmt = (char *)fmt_addr + fmt_map_off;
  5945	
  5946		/* We are also guaranteed that fmt+fmt_map_off is NULL terminated, we
  5947		 * can focus on validating the format specifiers.
  5948		 */
  5949		err = bpf_printf_prepare(fmt, UINT_MAX, NULL, NULL, NULL, num_args);
  5950		if (err < 0)
  5951			verbose(env, "Invalid format string\n");
  5952	
  5953		return err;
  5954	}
  5955	

---
0-DAY CI Kernel Test Service, Intel Corporation
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