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/* Erasure of sensitive data, generic implementation.
Copyright (C) 2016-2021 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public
License as published by the Free Software Foundation; either
version 3 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details.
You should have received a copy of the GNU General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
/* An assembler implementation of explicit_bzero can be created as an
assembler alias of an optimized bzero implementation.
Architecture-specific implementations also need to define
__explicit_bzero_chk. */
#if !_LIBC
# include <config.h>
#endif
/* memset_s need this define */
#if HAVE_MEMSET_S
# define __STDC_WANT_LIB_EXT1__ 1
#endif
#include <string.h>
#if defined _WIN32 && !defined __CYGWIN__
# define WIN32_LEAN_AND_MEAN
# include <windows.h>
#endif
#if _LIBC
/* glibc-internal users use __explicit_bzero_chk, and explicit_bzero
redirects to that. */
# undef explicit_bzero
#endif
/* Set LEN bytes of S to 0. The compiler will not delete a call to
this function, even if S is dead after the call. */
void
explicit_bzero (void *s, size_t len)
{
#if defined _WIN32 && !defined __CYGWIN__
(void) SecureZeroMemory (s, len);
#elif HAVE_EXPLICIT_MEMSET
explicit_memset (s, '\0', len);
#elif HAVE_MEMSET_S
(void) memset_s (s, len, '\0', len);
#elif defined __GNUC__ && !defined __clang__
memset (s, '\0', len);
/* Compiler barrier. */
asm volatile ("" ::: "memory");
#elif defined __clang__
memset (s, '\0', len);
/* Compiler barrier. */
/* With asm ("" ::: "memory") LLVM analyzes uses of 's' and finds that the
whole thing is dead and eliminates it. Use 'g' to work around this
problem. See <https://bugs.llvm.org/show_bug.cgi?id=15495#c11>. */
__asm__ volatile ("" : : "g"(s) : "memory");
#else
/* Invoke memset through a volatile function pointer. This defeats compiler
optimizations. */
void * (* const volatile volatile_memset) (void *, int, size_t) = memset;
(void) volatile_memset (s, '\0', len);
#endif
}
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