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+.\"	$NetBSD: explicit_memset.3,v 1.3 2024/11/02 02:43:48 riastradh Exp $
+.\"
+.\" Copyright (c) 2013 The NetBSD Foundation, Inc.
+.\" All rights reserved.
+.\"
+.\" This documentation is derived from text contributed to The NetBSD
+.\" Foundation by Taylor R. Campbell.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. 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 NETBSD FOUNDATION, INC. 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 FOUNDATION 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.
+.\"
+.Dd November 1, 2024
+.Dt EXPLICIT_MEMSET 3
+.Os
+.Sh NAME
+.Nm explicit_memset
+.Nm memset_explicit
+.Nd guarantee writing a byte to a byte string
+.Sh LIBRARY
+.Lb libc
+.Sh SYNOPSIS
+.In string.h
+.Ft void *
+.Fn explicit_memset "void *b" "int c" "size_t len"
+.Ft void *
+.Fn memset_explicit "void *b" "int c" "size_t len"
+.Sh DESCRIPTION
+The
+.Fn explicit_memset
+and
+.Fn memset_explicit
+functions write
+.Fa len
+bytes of value
+.Fa c
+(converted to an unsigned char) to the string
+.Fa b .
+They are guaranteed not to be optimized away by the compiler even if
+.Fa b
+is no longer used and is about to be freed or go out of scope.
+.Sh RETURN VALUES
+The
+.Fn explicit_memset
+function returns the original value of
+.Fa b .
+.Sh EXAMPLES
+Create a buffer on the stack for a secret key, use it, and then zero it
+in memory before throwing it away.
+.Bd -literal -offset indent
+void
+f(void)
+{
+	uint8_t key[32];
+
+	crypto_random(key, sizeof(key));
+	do_crypto_stuff(key, sizeof(key));
+	\&...
+
+	explicit_memset(key, 0, sizeof(key));
+}
+.Ed
+.Sh SEE ALSO
+.Xr consttime_memequal 3 ,
+.Xr memset 3
+.Sh STANDARDS
+The
+.Fn memset_explicit
+function conforms to
+.St -isoC-2023 .
+.Sh HISTORY
+The
+.Fn explicit_memset
+function appeared in
+.Nx 7.0 .
+The
+.Fn memset_explicit
+alias was added in
+.Nx 11.0 .