[crng-random:master 2/2] arch/x86/coco/core.c:189:2: error: call to undeclared function 'memzero_explicit'; ISO C99 and later do not support implicit function declarations

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

tree:   git://git.kernel.org/pub/scm/linux/kernel/git/crng/random.git master
head:   6fba9af4a847c5ee67715bc6f7959e9ab6394275
commit: 6fba9af4a847c5ee67715bc6f7959e9ab6394275 [2/2] x86/coco: Require seeding RNG with RDRAND on CoCo systems
config: x86_64-rhel-8.3-bpf (https://download.01.org/0day-ci/archive/20240324/202403240934.Nf4UUK5L-lkp@intel.com/config)
compiler: clang version 17.0.6 (https://github.com/llvm/llvm-project 6009708b4367171ccdbf4b5905cb6a803753fe18)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240324/202403240934.Nf4UUK5L-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/202403240934.Nf4UUK5L-lkp@intel.com/

All errors (new ones prefixed by >>):

>> arch/x86/coco/core.c:189:2: error: call to undeclared function 'memzero_explicit'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
     189 |         memzero_explicit(rng_seed, sizeof(rng_seed));
         |         ^
   1 error generated.


vim +/memzero_explicit +189 arch/x86/coco/core.c

   154	
   155	__init void cc_random_init(void)
   156	{
   157		/*
   158		 * The seed is 32 bytes (in units of longs), which is 256 bits, which
   159		 * is the security level that the RNG is targeting.
   160		 */
   161		unsigned long rng_seed[32 / sizeof(long)];
   162		size_t i, longs;
   163	
   164		if (!cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT))
   165			return;
   166	
   167		/*
   168		 * Since the CoCo threat model includes the host, the only reliable
   169		 * source of entropy that can be neither observed nor manipulated is
   170		 * RDRAND. Usually, RDRAND failure is considered tolerable, but since
   171		 * CoCo guests have no other unobservable source of entropy, it's
   172		 * important to at least ensure the RNG gets some initial random seeds.
   173		 */
   174		for (i = 0; i < ARRAY_SIZE(rng_seed); i += longs) {
   175			longs = arch_get_random_longs(&rng_seed[i], ARRAY_SIZE(rng_seed) - i);
   176	
   177			/*
   178			 * A zero return value means that the guest doesn't have RDRAND
   179			 * or the CPU is physically broken, and in both cases that
   180			 * means most crypto inside of the CoCo instance will be
   181			 * broken, defeating the purpose of CoCo in the first place. So
   182			 * just panic here because it's absolutely unsafe to continue
   183			 * executing.
   184			 */
   185			if (longs == 0)
   186				panic("RDRAND is defective.");
   187		}
   188		add_device_randomness(rng_seed, sizeof(rng_seed));
 > 189		memzero_explicit(rng_seed, sizeof(rng_seed));

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