56 lines
2.0 KiB
C++
56 lines
2.0 KiB
C++
/*
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* This file is part of the Flowee project
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* Copyright (C) 2009-2010 Satoshi Nakamoto
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* Copyright (C) 2009-2015 The Bitcoin Core developers
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include "cleanse.h"
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#include <cstring>
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/**
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* Compilers have a bad habit of removing "superfluous" memset calls that
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* are trying to zero memory. For example, when memset()ing a buffer and
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* then free()ing it, the compiler might decide that the memset is
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* unobservable and thus can be removed.
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*
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* Previously we used OpenSSL which tried to stop this by a) implementing
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* memset in assembly on x86 and b) putting the function in its own file
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* for other platforms.
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*
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* This change removes those tricks in favor of using asm directives to
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* scare the compiler away. As best as our compiler folks can tell, this is
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* sufficient and will continue to be so.
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*
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* Adam Langley <agl@google.com>
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* Commit: ad1907fe73334d6c696c8539646c21b11178f20f
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* BoringSSL (LICENSE: ISC)
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*/
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void memory_cleanse(void *ptr, size_t len)
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{
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std::memset(ptr, 0, len);
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/**
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* As best as we can tell, this is sufficient to break any optimizations
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* that might try to eliminate "superfluous" memsets. If there's an easy way
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* to detect memset_s, it would be better to use that.
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*/
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#if defined(_MSC_VER)
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__asm;
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#else
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__asm__ __volatile__("" : : "r"(ptr) : "memory");
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#endif
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}
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