roken: Add memset_s implementation

Add an implementation of memset_s to roken.

Some optimising compilers may remove the memset() instruction when it
is used immediately before a free, which defeats its purpose if the
intention is to zero memory before returning it to the heap or stack.

C11 added memset_s, provide a fallback in roken so that memset_s can
be used on all platforms.

lib/roken/memset_s.c

@@ -0,0 +1,51 @@
+/***********************************************************************
+ * Copyright (c) 2015, Your File System Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above copyright
+ *   notice, this list of conditions and the following disclaimer in
+ *   the documentation and/or other materials provided with the
+ *   distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
+ * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ **********************************************************************/
+
+#include <config.h>
+#include "roken.h"
+
+int ROKEN_LIB_FUNCTION
+memset_s(void *s, size_t smax, int c, size_t n)
+{
+    volatile unsigned char *p = s;
+
+#ifdef _WIN32
+    if (c == 0) {
+	SecureZeroMemory(s, n);
+	return 0;
+    }
+#endif
+
+    while (n--) 
+    	*p++ = c; 
+
+    return 0;
+}