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-eB... 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/168301dda58989eca274d5f5c92667554... 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(a)intel.com&gt; 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 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; 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 https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org