[kees:dev/v7.0-rc2/strncpy 11/11] drivers/misc/lkdtm/fortify.c:28:9: warning: incompatible implicit declaration of built-in function 'strncpy'

[kernel test robot <lkp@intel.com>]

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git dev/v7.0-rc2/strncpy
head:   da9b6bdc716b766da262998c114c86ebb1b96d43
commit: da9b6bdc716b766da262998c114c86ebb1b96d43 [11/11] string: Remove strncpy() from the kernel
config: x86_64-rhel-9.4-kselftests (https://download.01.org/0day-ci/archive/20260324/202603240259.tUb5PplF-lkp@intel.com/config)
compiler: gcc-14 (Debian 14.2.0-19) 14.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260324/202603240259.tUb5PplF-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@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202603240259.tUb5PplF-lkp@intel.com/

All warnings (new ones prefixed by >>):

   drivers/misc/lkdtm/fortify.c: In function 'lkdtm_FORTIFY_STR_OBJECT':
   drivers/misc/lkdtm/fortify.c:28:9: error: implicit declaration of function 'strncpy' [-Wimplicit-function-declaration]
      28 |         strncpy(target[0].a, target[1].a, size);
         |         ^~~~~~~
   drivers/misc/lkdtm/fortify.c:10:1: note: include '<string.h>' or provide a declaration of 'strncpy'
       9 | #include <linux/slab.h>
     +++ |+#include <string.h>
      10 | 
>> drivers/misc/lkdtm/fortify.c:28:9: warning: incompatible implicit declaration of built-in function 'strncpy' [-Wbuiltin-declaration-mismatch]
      28 |         strncpy(target[0].a, target[1].a, size);
         |         ^~~~~~~
   drivers/misc/lkdtm/fortify.c:28:9: note: include '<string.h>' or provide a declaration of 'strncpy'
   drivers/misc/lkdtm/fortify.c: In function 'lkdtm_FORTIFY_STR_MEMBER':
   drivers/misc/lkdtm/fortify.c:60:9: warning: incompatible implicit declaration of built-in function 'strncpy' [-Wbuiltin-declaration-mismatch]
      60 |         strncpy(target.a, src, size);
         |         ^~~~~~~
   drivers/misc/lkdtm/fortify.c:60:9: note: include '<string.h>' or provide a declaration of 'strncpy'


vim +/strncpy +28 drivers/misc/lkdtm/fortify.c

fe8e353bfda6d6c Kees Cook 2021-08-18  12  
325bf6d84bad3fc Kees Cook 2022-08-31  13  static void lkdtm_FORTIFY_STR_OBJECT(void)
fe8e353bfda6d6c Kees Cook 2021-08-18  14  {
fe8e353bfda6d6c Kees Cook 2021-08-18  15  	struct target {
fe8e353bfda6d6c Kees Cook 2021-08-18  16  		char a[10];
325bf6d84bad3fc Kees Cook 2022-08-31  17  		int foo;
325bf6d84bad3fc Kees Cook 2022-08-31  18  	} target[3] = {};
fe8e353bfda6d6c Kees Cook 2021-08-18  19  	/*
fe8e353bfda6d6c Kees Cook 2021-08-18  20  	 * Using volatile prevents the compiler from determining the value of
fe8e353bfda6d6c Kees Cook 2021-08-18  21  	 * 'size' at compile time. Without that, we would get a compile error
fe8e353bfda6d6c Kees Cook 2021-08-18  22  	 * rather than a runtime error.
fe8e353bfda6d6c Kees Cook 2021-08-18  23  	 */
325bf6d84bad3fc Kees Cook 2022-08-31  24  	volatile int size = 20;
325bf6d84bad3fc Kees Cook 2022-08-31  25  
325bf6d84bad3fc Kees Cook 2022-08-31  26  	pr_info("trying to strcmp() past the end of a struct\n");
fe8e353bfda6d6c Kees Cook 2021-08-18  27  
325bf6d84bad3fc Kees Cook 2022-08-31 @28  	strncpy(target[0].a, target[1].a, size);
fe8e353bfda6d6c Kees Cook 2021-08-18  29  
fe8e353bfda6d6c Kees Cook 2021-08-18  30  	/* Store result to global to prevent the code from being eliminated */
325bf6d84bad3fc Kees Cook 2022-08-31  31  	fortify_scratch_space = target[0].a[3];
fe8e353bfda6d6c Kees Cook 2021-08-18  32  
325bf6d84bad3fc Kees Cook 2022-08-31  33  	pr_err("FAIL: fortify did not block a strncpy() object write overflow!\n");
fe8e353bfda6d6c Kees Cook 2021-08-18  34  	pr_expected_config(CONFIG_FORTIFY_SOURCE);
fe8e353bfda6d6c Kees Cook 2021-08-18  35  }
fe8e353bfda6d6c Kees Cook 2021-08-18  36  

:::::: The code at line 28 was first introduced by commit
:::::: 325bf6d84bad3fc641b94fad6e69c70e960fdf2e lkdtm: Update tests for memcpy() run-time warnings

:::::: TO: Kees Cook <keescook@chromium.org>
:::::: CC: Kees Cook <keescook@chromium.org>

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