HV: rewrite strncpy_s to be iso c11 compliant

Per C11 standard (ISO/IEC 9899:2011): K.3.7.1.4

1. Copying shall not take place between objects that overlap;
2. If there is a runtime-constraint violation, the strncpy_s function sets
   s1[0] to '\0\;
3. The strncpy_s function returns zero if there was no runtime-constraint
   violation. Otherwise, a nonzero value is returned.
4. The function is implemented with memcpy_s() because the runtime-constraint
   detection is almost same.

Tracked-On: projectacrn#4885

Signed-off-by: Victor Sun <victor.sun@intel.com>
Reviewed-by: Yonghua Huang <yonghua.huang@intel.com>
Reviewed-by: Yin Fengwei <fengwei.yin@intel.com>
Acked-by: Eddie Dong <eddie.dong@intel.com>

hypervisor/include/lib/rtl.h

@@ -32,7 +32,7 @@ static inline bool is_space(char c)
 /* Function prototypes */
 int32_t strcmp(const char *s1_arg, const char *s2_arg);
 int32_t strncmp(const char *s1_arg, const char *s2_arg, size_t n_arg);
-char *strncpy_s(char *d_arg, size_t dmax, const char *s_arg, size_t slen_arg);
+int32_t strncpy_s(char *d, size_t dmax, const char *s, size_t slen);
 char *strchr(char *s_arg, char ch);
 size_t strnlen_s(const char *str_arg, size_t maxlen_arg);
 void *memset(void *base, uint8_t v, size_t n);

hypervisor/lib/string.c

@@ -98,87 +98,35 @@ char *strchr(char *s_arg, char ch)
  *              string.
  *
  * return value:
- *    dest      pointer to dest string if source string is copied
- *              successfully, or else return null.
+ *    0		if source string is copied successfully;
+ *    -1	if there is a runtime-constraint violation.
  *
  * notes:
- *    1) both dmax and slen should not be 0.
- *    2) both d and s should not be null pointers.
- *    3) will assert() if overlap happens or dest buffer has no
- *       enough space.
+ *    1) dmax shall not be 0.
+ *    2) both d and s shall not be null pointers.
+ *    3) Copying shall not take place between objects that overlap.
+ *    4) If slen is not less than dmax, then dmax shall be more than strnlen_s(s, dmax).
+ *    5) d[0] shall be set to '\0' if there is a runtime-constraint violation.
  */
-char *strncpy_s(char *d_arg, size_t dmax, const char *s_arg, size_t slen_arg)
+int32_t strncpy_s(char *d, size_t dmax, const char *s, size_t slen)
 {
-	const char *s = s_arg;
-	char *d = d_arg;
-	char *pret;
-	size_t dest_avail;
-	uint64_t overlap_guard;
-	size_t slen = slen_arg;
+	char *dest = d;
+	int32_t ret = -1;
+	size_t len = strnlen_s(s, dmax);
 
-	if ((d == NULL) || (s == NULL)) {
-		pr_err("%s: invlaid src or dest buffer", __func__);
-		pret = NULL;
-	} else {
-		pret = d_arg;
-	}
-
-	if (pret != NULL) {
-		if ((dmax == 0U) || (slen == 0U)) {
-			pr_err("%s: invlaid length of src or dest buffer", __func__);
-			pret =  NULL;
-		}
+	if ((slen < dmax) || (dmax > len)) {
+		ret = memcpy_s(d, dmax, s, len);
 	}
 
-	/* if d equal to s, just return d; else execute the below code */
-	if ((pret != NULL) && (d != s)) {
-		overlap_guard = (uint64_t)((d > s) ? (d - s - 1) : (s - d - 1));
-		dest_avail = dmax;
-
-		while (dest_avail > 0U) {
-			bool complete = false;
-
-			if (overlap_guard == 0U) {
-				pr_err("%s: overlap happened.", __func__);
-				d--;
-				*d = '\0';
-				pret = NULL;
-				/* copy complete */
-				complete = true;
-			} else {
-				if (slen == 0U) {
-					*d = '\0';
-					/* copy complete */
-					complete = true;
-				} else {
-					*d = *s;
-					if (*d == '\0') {
-						/* copy complete */
-						complete = true;
-					} else {
-						d++;
-						s++;
-						slen--;
-						dest_avail--;
-						overlap_guard--;
-					}
-				}
-			}
-
-			if (complete) {
-				break;
-			}
-		}
-
-		if (dest_avail == 0U) {
-			pr_err("%s: dest buffer has no enough space.", __func__);
-
-			/* to avoid a string that is not null-terminated in dest buffer */
-			pret[dmax - 1] = '\0';
+	if (ret == 0) {
+		*(dest + len) = '\0';
+	} else {
+		if ((d != NULL) && (dmax > 0U)) {
+			*dest = '\0';
 		}
 	}
 
-	return pret;
+	return ret;
 }
 
 /**