root/maint/gnulib/lib/explicit_bzero.c

/* */

DEFINITIONS

1. explicit_bzero

   1 /* Erasure of sensitive data, generic implementation.
   2    Copyright (C) 2016-2021 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4 
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9 
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14 
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18 
  19 /* An assembler implementation of explicit_bzero can be created as an
  20    assembler alias of an optimized bzero implementation.
  21    Architecture-specific implementations also need to define
  22    __explicit_bzero_chk.  */
  23 
  24 #if !_LIBC
  25 # include <config.h>
  26 #endif
  27 
  28 /* memset_s need this define */
  29 #if HAVE_MEMSET_S
  30 # define __STDC_WANT_LIB_EXT1__ 1
  31 #endif
  32 
  33 #include <string.h>
  34 
  35 #if defined _WIN32 && !defined __CYGWIN__
  36 # define  WIN32_LEAN_AND_MEAN
  37 # include <windows.h>
  38 #endif
  39 
  40 #if _LIBC
  41 /* glibc-internal users use __explicit_bzero_chk, and explicit_bzero
  42    redirects to that.  */
  43 # undef explicit_bzero
  44 #endif
  45 
  46 /* Set LEN bytes of S to 0.  The compiler will not delete a call to
  47    this function, even if S is dead after the call.  */
  48 void
  49 explicit_bzero (void *s, size_t len)
     /*  */
  50 {
  51 #if defined _WIN32 && !defined __CYGWIN__
  52   (void) SecureZeroMemory (s, len);
  53 #elif HAVE_EXPLICIT_MEMSET
  54   explicit_memset (s, '\0', len);
  55 #elif HAVE_MEMSET_S
  56   (void) memset_s (s, len, '\0', len);
  57 #elif defined __GNUC__ && !defined __clang__
  58   memset (s, '\0', len);
  59   /* Compiler barrier.  */
  60   asm volatile ("" ::: "memory");
  61 #elif defined __clang__
  62   memset (s, '\0', len);
  63   /* Compiler barrier.  */
  64   /* With asm ("" ::: "memory") LLVM analyzes uses of 's' and finds that the
  65      whole thing is dead and eliminates it.  Use 'g' to work around this
  66      problem.  See <https://bugs.llvm.org/show_bug.cgi?id=15495#c11>.  */
  67   __asm__ volatile ("" : : "g"(s) : "memory");
  68 #else
  69   /* Invoke memset through a volatile function pointer.  This defeats compiler
  70      optimizations.  */
  71   void * (* const volatile volatile_memset) (void *, int, size_t) = memset;
  72   (void) volatile_memset (s, '\0', len);
  73 #endif
  74 }

/* */