Re: [PATCH bpf-next v2 2/2] selftests/bpf: Test bpf_strcat,bpf_strncat kfuncs

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/[email protected]/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/[email protected]/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 <[email protected]>
| Closes: https://lore.kernel.org/oe-kbuild-all/[email protected]/

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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