1 /* Erase sensitive data from memory.
2 Copyright 2022-2023 Free Software Foundation, Inc.
3
4 This file is free software: you can redistribute it and/or modify
5 it under the terms of the GNU Lesser General Public License as
6 published by the Free Software Foundation; either version 2.1 of the
7 License, or (at your option) any later version.
8
9 This file is distributed in the hope that it will be useful,
10 but WITHOUT ANY WARRANTY; without even the implied warranty of
11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 GNU Lesser General Public License for more details.
13
14 You should have received a copy of the GNU Lesser General Public License
15 along with this program. If not, see <https://www.gnu.org/licenses/>. */
16
17 #include <config.h>
18
19 /* memset_s need this define */
20 #if HAVE_MEMSET_S
21 # define __STDC_WANT_LIB_EXT1__ 1
22 #endif
23
24 #include <string.h>
25
26 /* Set S's bytes to C, where S has LEN bytes. The compiler will not
27 optimize effects away, even if S is dead after the call. */
28 void *
29 memset_explicit (void *s, int c, size_t len)
30 {
31 #if HAVE_EXPLICIT_MEMSET
32 return explicit_memset (s, c, len);
33 #elif HAVE_MEMSET_S
34 (void) memset_s (s, len, c, len);
35 return s;
36 #elif defined __GNUC__ && !defined __clang__
37 memset (s, c, len);
38 /* Compiler barrier. */
39 __asm__ volatile ("" ::: "memory");
40 return s;
41 #elif defined __clang__
42 memset (s, c, len);
43 /* Compiler barrier. */
44 /* With asm ("" ::: "memory") LLVM analyzes uses of 's' and finds that the
45 whole thing is dead and eliminates it. Use 'g' to work around this
46 problem. See <https://bugs.llvm.org/show_bug.cgi?id=15495#c11>. */
47 __asm__ volatile ("" : : "g"(s) : "memory");
48 return s;
49 #else
50 /* Invoke memset through a volatile function pointer. This defeats compiler
51 optimizations. */
52 void * (* const volatile volatile_memset) (void *, int, size_t) = memset;
53 return volatile_memset (s, c, len);
54 #endif
55 }