Re: [PATCH bpf-next v2 2/2] selftests/bpf: Test bpf_strcat,bpf_strncat kfuncs
From: kernel test robot
Date: Fri Aug 07 2026 - 18:10:44 EST
Hi Rong,
kernel test robot noticed the following build errors:
[auto build test ERROR on bpf-next/master]
url: https://github.com/intel-lab-lkp/linux/commits/Rong-Tao/selftests-bpf-Test-bpf_strcat-bpf_strncat-kfuncs/20260807-065842
base: https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git master
patch link: https://lore.kernel.org/r/tencent_DB0510330C3A8574B3C62E6154165FCB4709%40qq.com
patch subject: [PATCH bpf-next v2 2/2] selftests/bpf: Test bpf_strcat,bpf_strncat kfuncs
config: s390-randconfig-r052-20260807 (https://download.01.org/0day-ci/archive/20260808/202608080502.lI7AVjty-lkp@xxxxxxxxx/config)
compiler: clang version 24.0.0git (https://github.com/llvm/llvm-project 12df34b8469b8095359de8c249cb1b2753fadeea)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260808/202608080502.lI7AVjty-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/202608080502.lI7AVjty-lkp@xxxxxxxxx/
All errors (new ones prefixed by >>):
>> kernel/bpf/helpers.c:4228:3: error: invalid lvalue in asm output
4228 | __put_kernel_nofault(dst + dlen + copied, &cs, char, err_out);
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
include/linux/uaccess.h:612:2: note: expanded from macro '__put_kernel_nofault'
612 | arch_put_kernel_nofault(dst, src, type, local_label); \
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
arch/s390/include/asm/uaccess.h:471:33: note: expanded from macro 'arch_put_kernel_nofault'
471 | #define arch_put_kernel_nofault __mvc_kernel_nofault
| ^
arch/s390/include/asm/uaccess.h:424:19: note: expanded from macro '__mvc_kernel_nofault'
424 | : [_dst] "=Q" (*(type *)dst) \
| ^~~~~~~~~~~~
kernel/bpf/helpers.c:4233:2: error: invalid lvalue in asm output
4233 | __put_kernel_nofault(dst + dlen + copied, &cs, char, err_out);
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
include/linux/uaccess.h:612:2: note: expanded from macro '__put_kernel_nofault'
612 | arch_put_kernel_nofault(dst, src, type, local_label); \
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
arch/s390/include/asm/uaccess.h:471:33: note: expanded from macro 'arch_put_kernel_nofault'
471 | #define arch_put_kernel_nofault __mvc_kernel_nofault
| ^
arch/s390/include/asm/uaccess.h:424:19: note: expanded from macro '__mvc_kernel_nofault'
424 | : [_dst] "=Q" (*(type *)dst) \
| ^~~~~~~~~~~~
2 errors generated.
vim +4228 kernel/bpf/helpers.c
4197
4198 static int __bpf_strncat(char *dst, u32 dsz, const char *src, u32 sz)
4199 {
4200 int dlen, slen, space, copied;
4201 char cs = '?';
4202
4203 if (!copy_from_kernel_nofault_allowed(dst, 1) ||
4204 !copy_from_kernel_nofault_allowed(src, 1)) {
4205 return -ERANGE;
4206 }
4207
4208 dlen = bpf_strnlen(dst, dsz);
4209 if (dlen < 0)
4210 return dlen;
4211 slen = bpf_strnlen(src, sz);
4212 if (slen < 0)
4213 return slen;
4214
4215 if (dlen >= dsz || sz == 0 || dsz == 0)
4216 return -EINVAL;
4217
4218 space = dsz - dlen;
4219 if (space <= 1 || space < min(slen, sz) + 1)
4220 return -E2BIG;
4221
4222 guard(pagefault)();
4223 for (copied = 0; copied < space - 1 && copied < slen; copied++) {
4224 __get_kernel_nofault(&cs, src, char, err_out);
4225 if (cs == '\0')
4226 break;
4227
> 4228 __put_kernel_nofault(dst + dlen + copied, &cs, char, err_out);
4229
4230 src++;
4231 }
4232 cs = '\0';
4233 __put_kernel_nofault(dst + dlen + copied, &cs, char, err_out);
4234
4235 __get_kernel_nofault(&cs, src, char, err_out);
4236 if (cs != '\0' && sz > copied)
4237 return -E2BIG;
4238
4239 return dlen + copied;
4240 err_out:
4241 return -EFAULT;
4242 }
4243
--
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https://github.com/intel/lkp-tests/wiki