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
@@ -43,7 +43,9 @@
 .Sh SYNOPSIS
 .In string.h
 .Ft void *
-.Fn memset "void *b" "int c" "size_t len"
+.Fn memset "void *dest" "int c" "size_t len"
+.Ft errno_t
+.Fn memset_s "void *dest" "rsize_t destsz" "int c" "rsize_t len"
 .Sh DESCRIPTION
 The
 .Fn memset
@@ -55,13 +57,63 @@
 (converted to an
 .Vt "unsigned char" )
 to the string
-.Fa b .
+.Fa dest .
+Undefined behaviour from
+.Fn memset ,
+resulting from storage overflow, will occur if
+.Fa len
+is greater than the the length of buffer
+.Fa dest .
+The behaviour is also undefined if
+.Fa dest
+is an invalid pointer.
+.Pp
+The
+.Fn memset_s
+function behaves the same as
+.Fn memset
+except that an error is thrown and constraint handler is called if
+.Fa dest
+is a null pointer,
+.Fa destsz
+or
+.Fa len
+is greater than
+.Dv RSIZE_MAX ,
+or
+.Sp
+.Fa len
+is greater than
+.Fa destsz
+(buffer overflow would occur).
+Like
+.Xr explicit_bzero 3 ,
+.Fn memset_s
+is not removed through Dead Store Elimination (DSE), making it useful for
+clearing sensitve data.
+In contrast
+.Fn memset
+function 
+may be optimized away if the object modified by the function is not accessed
+again.
+To clear memory that will not subsequently be accessed it is advised to use
+.Fn memset_s
+instead of
+.Fn memset .
+For instance, a buffer containing a password should be cleared with
+.Fn memset_s
+before
+.Xr free 3 .
 .Sh RETURN VALUES
 The
 .Fn memset
 function returns its first argument.
+The
+.Fn memset_s
+function returns zero on success, non-zero on error.
 .Sh SEE ALSO
 .Xr bzero 3 ,
+.Xr explicit_bzero 3 ,
 .Xr swab 3 ,
 .Xr wmemset 3
 .Sh STANDARDS
@@ -70,3 +122,7 @@
 function
 conforms to
 .St -isoC .
+.Fn memset_s
+conforms to:
+.St -isoC-2011
+K.3.7.4.1.