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// Copyright (c) 2009-2010 Satoshi Nakamoto
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// Copyright (c) 2009-2019 The Bitcoin Core developers
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// Distributed under the MIT software license, see the accompanying
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// file COPYING or http://www.opensource.org/licenses/mit-license.php.
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#include <support/cleanse.h>
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#include <cstring>
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#if defined(_MSC_VER)
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#include <Windows.h> // For SecureZeroMemory.
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#endif
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void memory_cleanse(void *ptr, size_t len)
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{
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#if defined(_MSC_VER)
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    /* SecureZeroMemory is guaranteed not to be optimized out by MSVC. */
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    SecureZeroMemory(ptr, len);
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#else
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    std::memset(ptr, 0, len);
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    /* Memory barrier that scares the compiler away from optimizing out the memset.
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     *
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     * Quoting Adam Langley <agl@google.com> in commit ad1907fe73334d6c696c8539646c21b11178f20f
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     * in BoringSSL (ISC License):
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     *    As best as we can tell, this is sufficient to break any optimisations that
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     *    might try to eliminate "superfluous" memsets.
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     * This method is used in memzero_explicit() the Linux kernel, too. Its advantage is that it
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     * is pretty efficient because the compiler can still implement the memset() efficiently,
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     * just not remove it entirely. See "Dead Store Elimination (Still) Considered Harmful" by
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     * Yang et al. (USENIX Security 2017) for more background.
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     */
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    __asm__ __volatile__("" : : "r"(ptr) : "memory");
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#endif
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}