Index: lib/libc/string/Makefile.inc
===================================================================
--- lib/libc/string/Makefile.inc
+++ lib/libc/string/Makefile.inc
@@ -50,6 +50,7 @@
 	ffs.3 flsll.3
 MLINKS+=index.3 rindex.3
 MLINKS+=memchr.3 memrchr.3
+MLINKS+=memset.3 memset_s.3
 MLINKS+=strcasecmp.3 strncasecmp.3 \
 	strcasecmp.3 strcasecmp_l.3 \
 	strcasecmp.3 strncasecmp_l.3
Index: lib/libc/string/memset.3
===================================================================
--- lib/libc/string/memset.3
+++ lib/libc/string/memset.3
@@ -44,6 +44,7 @@
 .In string.h
 .Ft void *
 .Fn memset "void *b" "int c" "size_t len"
+.Fn memset_s "void *b" "rsize_t destsz" "int c" "rsize_t len"
 .Sh DESCRIPTION
 The
 .Fn memset
@@ -56,6 +57,21 @@
 .Vt "unsigned char" )
 to the string
 .Fa b .
+The
+.Fn memset_s
+function performs the same as
+.Fn memset
+except that an error is thrown and constraint handler is called if
+.Fa b
+is a null pointer,
+.Fa destsz
+or
+.Fa len
+is greater than RSIZE_MAX, or
+.Fa len
+is greater than
+.Fa destsz
+(buffer overflow would occur).
 .Sh RETURN VALUES
 The
 .Fn memset