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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];
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 .
