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be5f42adea
This patch introduces the concept of shadow bits. For every byte of
memory there is a corresponding shadow byte that contains metadata
about that memory.
Initially, the only metadata is whether the byte has been initialized
or not. That's represented by the least significant shadow bit.
Shadow bits travel together with regular values throughout the entire
CPU and MMU emulation. There are two main helper classes to facilitate
this: ValueWithShadow and ValueAndShadowReference.
ValueWithShadow<T> is basically a struct { T value; T shadow; } whereas
ValueAndShadowReference<T> is struct { T& value; T& shadow; }.
The latter is used as a wrapper around general-purpose registers, since
they can't use the plain ValueWithShadow memory as we need to be able
to address individual 8-bit and 16-bit subregisters (EAX, AX, AL, AH.)
Whenever a computation is made using uninitialized inputs, the result
is tainted and becomes uninitialized as well. This allows us to track
this state as it propagates throughout memory and registers.
This patch doesn't yet keep track of tainted flags, that will be an
important upcoming improvement to this.
I'm sure I've messed up some things here and there, but it seems to
basically work, so we have a place to start! :^)
89 lines
3 KiB
C++
89 lines
3 KiB
C++
/*
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* Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are met:
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*
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* 1. Redistributions of source code must retain the above copyright notice, this
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* list of conditions and the following disclaimer.
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*
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* 2. Redistributions in binary form must reproduce the above copyright notice,
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* this list of conditions and the following disclaimer in the documentation
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* and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#include "SimpleRegion.h"
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namespace UserspaceEmulator {
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SimpleRegion::SimpleRegion(u32 base, u32 size)
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: Region(base, size)
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{
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m_data = (u8*)calloc(1, size);
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m_shadow_data = (u8*)calloc(1, size);
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}
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SimpleRegion::~SimpleRegion()
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{
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free(m_shadow_data);
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free(m_data);
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}
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ValueWithShadow<u8> SimpleRegion::read8(FlatPtr offset)
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{
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ASSERT(offset < size());
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return { *reinterpret_cast<const u8*>(m_data + offset), *reinterpret_cast<const u8*>(m_shadow_data + offset) };
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}
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ValueWithShadow<u16> SimpleRegion::read16(u32 offset)
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{
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ASSERT(offset + 1 < size());
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return { *reinterpret_cast<const u16*>(m_data + offset), *reinterpret_cast<const u16*>(m_shadow_data + offset) };
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}
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ValueWithShadow<u32> SimpleRegion::read32(u32 offset)
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{
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ASSERT(offset + 3 < size());
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return { *reinterpret_cast<const u32*>(m_data + offset), *reinterpret_cast<const u32*>(m_shadow_data + offset) };
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}
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void SimpleRegion::write8(u32 offset, ValueWithShadow<u8> value)
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{
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ASSERT(offset < size());
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*reinterpret_cast<u8*>(m_data + offset) = value.value();
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*reinterpret_cast<u8*>(m_shadow_data + offset) = value.shadow();
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}
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void SimpleRegion::write16(u32 offset, ValueWithShadow<u16> value)
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{
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ASSERT(offset + 1 < size());
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*reinterpret_cast<u16*>(m_data + offset) = value.value();
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*reinterpret_cast<u16*>(m_shadow_data + offset) = value.shadow();
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}
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void SimpleRegion::write32(u32 offset, ValueWithShadow<u32> value)
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{
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ASSERT(offset + 3 < size());
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*reinterpret_cast<u32*>(m_data + offset) = value.value();
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*reinterpret_cast<u32*>(m_shadow_data + offset) = value.shadow();
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}
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u8* SimpleRegion::cacheable_ptr(u32 offset)
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{
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return m_data + offset;
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}
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}
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