libc: Import strlcat from FreeBSD project

From commit: 21571b1d140ae7bb44e94c0afba2ec61456b275b
Made small changes to fit into TF-A project

Change-Id: I07fd7fe1037857f6b299c35367c104fb51fa5cfa
Signed-off-by: Madhukar Pappireddy <madhukar.pappireddy@arm.com>

include/lib/libc/string.h

@@ -4,7 +4,7 @@
  * SPDX-License-Identifier: BSD-3-Clause
  */
 /*
- * Portions copyright (c) 2018-2019, ARM Limited and Contributors.
+ * Portions copyright (c) 2018-2020, ARM Limited and Contributors.
  * All rights reserved.
  */
 
@@ -26,5 +26,6 @@ size_t strlen(const char *s);
 size_t strnlen(const char *s, size_t maxlen);
 char *strrchr(const char *p, int ch);
 size_t strlcpy(char * dst, const char * src, size_t dsize);
+size_t strlcat(char * dst, const char * src, size_t dsize);
 
 #endif /* STRING_H */

lib/libc/strlcat.c

+/*	$OpenBSD: strlcat.c,v 1.15 2015/03/02 21:41:08 millert Exp $	*/
+
+/*
+ * SPDX-License-Identifier: ISC
+ *
+ * Copyright (c) 1998, 2015 Todd C. Miller <Todd.Miller@courtesan.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include <string.h>
+
+/*
+ * Appends src to string dst of size dsize (unlike strncat, dsize is the
+ * full size of dst, not space left).  At most dsize-1 characters
+ * will be copied.  Always NUL terminates (unless dsize <= strlen(dst)).
+ * Returns strlen(src) + MIN(dsize, strlen(initial dst)).
+ * If retval >= dsize, truncation occurred.
+ */
+size_t
+strlcat(char * dst, const char * src, size_t dsize)
+{
+	const char *odst = dst;
+	const char *osrc = src;
+	size_t n = dsize;
+	size_t dlen;
+
+	/* Find the end of dst and adjust bytes left but don't go past end. */
+	while (n-- != 0 && *dst != '\0')
+		dst++;
+	dlen = dst - odst;
+	n = dsize - dlen;
+
+	if (n-- == 0)
+		return(dlen + strlen(src));
+	while (*src != '\0') {
+		if (n != 0) {
+			*dst++ = *src;
+			n--;
+		}
+		src++;
+	}
+	*dst = '\0';
+
+	return(dlen + (src - osrc));	/* count does not include NUL */
+}