text: // Copyright (c) 2009-2010 Satoshi Nakamoto
  // Copyright (c) 2009-2015 The Bitcoin Core developers
  // Distributed under the MIT software license, see the accompanying
  // file COPYING or http://www.opensource.org/licenses/mit-license.php.
  
  #include <support/cleanse.h>
  
  #include <cstring>
  
  /* Compilers have a bad habit of removing "superfluous" memset calls that
   * are trying to zero memory. For example, when memset()ing a buffer and
   * then free()ing it, the compiler might decide that the memset is
   * unobservable and thus can be removed.
   *
   * Previously we used OpenSSL which tried to stop this by a) implementing
   * memset in assembly on x86 and b) putting the function in its own file
   * for other platforms.
   *
   * This change removes those tricks in favour of using asm directives to
   * scare the compiler away. As best as our compiler folks can tell, this is
   * sufficient and will continue to be so.
   *
   * Adam Langley <agl@google.com>
   * Commit: ad1907fe73334d6c696c8539646c21b11178f20f
   * BoringSSL (LICENSE: ISC)
   */
  void memory_cleanse(void *ptr, size_t len)
  {
      std::memset(ptr, 0, len);
  
      /* As best as we can tell, this is sufficient to break any optimisations that
         might try to eliminate "superfluous" memsets. If there's an easy way to
         detect memset_s, it would be better to use that. */
  #if defined(_MSC_VER)
      __asm;
  #else
      __asm__ __volatile__("" : : "r"(ptr) : "memory");
  #endif
  }
  