Document memset_s(3). memset_s(3) is defined in
C11 standard (ISO/IEC 9899:2011) K.3.7.4.1 The memset_s function (p: 621-622) Fix memset(3) portion of the man page by replacing the first argument (destination) "b" with "dest", which is more descriptive than "b". This also makes it consistent with the term used in the memset_s() portion of the man page. See also http://en.cppreference.com/w/c/string/byte/memset. Reviewed by: kib MFC after: 1 week Differential Revision: https://reviews.freebsd.org/D13682
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@ -50,6 +50,7 @@ MLINKS+=ffs.3 ffsl.3 \
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ffs.3 flsll.3
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ffs.3 flsll.3
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MLINKS+=index.3 rindex.3
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MLINKS+=index.3 rindex.3
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MLINKS+=memchr.3 memrchr.3
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MLINKS+=memchr.3 memrchr.3
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MLINKS+=memset.3 memset_s.3
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MLINKS+=strcasecmp.3 strncasecmp.3 \
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MLINKS+=strcasecmp.3 strncasecmp.3 \
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strcasecmp.3 strcasecmp_l.3 \
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strcasecmp.3 strcasecmp_l.3 \
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strcasecmp.3 strncasecmp_l.3
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strcasecmp.3 strncasecmp_l.3
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@ -32,7 +32,7 @@
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.\" @(#)memset.3 8.1 (Berkeley) 6/4/93
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.\" @(#)memset.3 8.1 (Berkeley) 6/4/93
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.\" $FreeBSD$
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.\" $FreeBSD$
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.\"
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.\"
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.Dd June 4, 1993
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.Dd February 15, 2018
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.Dt MEMSET 3
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.Dt MEMSET 3
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.Os
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.Os
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.Sh NAME
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.Sh NAME
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@ -43,7 +43,9 @@
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.Sh SYNOPSIS
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.Sh SYNOPSIS
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.In string.h
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.In string.h
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.Ft void *
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.Ft void *
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.Fn memset "void *b" "int c" "size_t len"
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.Fn memset "void *dest" "int c" "size_t len"
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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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.Sh DESCRIPTION
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The
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The
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.Fn memset
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.Fn memset
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@ -55,13 +57,66 @@ bytes of value
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(converted to an
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(converted to an
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.Vt "unsigned char" )
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.Vt "unsigned char" )
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to the string
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to the string
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.Fa b .
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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 the length of buffer
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.Fa dest .
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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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.Sp
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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 sensitve 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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.Sh RETURN VALUES
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The
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The
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.Fn memset
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.Fn memset
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function returns its first argument.
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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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.Sh SEE ALSO
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.Xr bzero 3 ,
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.Xr bzero 3 ,
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.Xr explicit_bzero 3 ,
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.Xr swab 3 ,
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.Xr swab 3 ,
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.Xr wmemset 3
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.Xr wmemset 3
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.Sh STANDARDS
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.Sh STANDARDS
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@ -70,3 +125,7 @@ The
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function
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function
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conforms to
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conforms to
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.St -isoC .
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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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