134 lines
3.7 KiB
Groff
134 lines
3.7 KiB
Groff
.\" Copyright (c) 1990, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" This code is derived from software contributed to Berkeley by
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.\" Chris Torek and the American National Standards Committee X3,
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.\" on Information Processing Systems.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)memset.3 8.1 (Berkeley) 6/4/93
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.\" $FreeBSD$
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.\"
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.Dd August 19, 2018
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.Dt MEMSET 3
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.Os
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.Sh NAME
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.Nm memset
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.Nd write a byte to byte string
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In string.h
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.Ft void *
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.Fn memset "void *dest" "int c" "size_t len"
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.Fd #define __STDC_WANT_LIB_EXT1__ 1
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.Ft errno_t
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.Fn memset_s "void *dest" "rsize_t destsz" "int c" "rsize_t len"
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.Sh DESCRIPTION
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The
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.Fn memset
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function
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writes
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.Fa len
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bytes of value
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.Fa c
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(converted to an
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.Vt "unsigned char" )
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to the string
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.Fa dest .
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Undefined behaviour from
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.Fn memset ,
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resulting from storage overflow, will occur if
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.Fa len
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is greater than the length of the
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.Fa dest
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buffer.
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The behaviour is also undefined if
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.Fa dest
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is an invalid pointer.
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.Pp
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The
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.Fn memset_s
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function behaves the same as
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.Fn memset
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except that an error is returned and the currently registered
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runtime-constraint handler is called if
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.Fa dest
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is a null pointer,
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.Fa destsz
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or
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.Fa len
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is greater than
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.Dv RSIZE_MAX ,
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or
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.Fa len
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is greater than
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.Fa destsz
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(buffer overflow would occur).
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The runtime-constraint handler is called first and may not return.
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If it does return, an error is returned to the caller.
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Like
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.Xr explicit_bzero 3 ,
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.Fn memset_s
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is not removed through Dead Store Elimination (DSE), making it useful for
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clearing sensitive data.
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In contrast
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.Fn memset
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function
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may be optimized away if the object modified by the function is not accessed
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again.
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To clear memory that will not subsequently be accessed it is advised to use
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.Fn memset_s
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instead of
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.Fn memset .
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For instance, a buffer containing a password should be cleared with
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.Fn memset_s
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before
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.Xr free 3 .
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.Sh RETURN VALUES
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The
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.Fn memset
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function returns its first argument.
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The
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.Fn memset_s
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function returns zero on success, non-zero on error.
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.Sh SEE ALSO
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.Xr bzero 3 ,
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.Xr explicit_bzero 3 ,
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.Xr set_constraint_handler_s 3 ,
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.Xr swab 3 ,
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.Xr wmemset 3
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.Sh STANDARDS
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The
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.Fn memset
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function
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conforms to
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.St -isoC .
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.Fn memset_s
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conforms to
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.St -isoC-2011
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K.3.7.4.1.
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