solidity/libevmasm/KnownState.cpp

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/*
This file is part of solidity.
solidity is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
solidity is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with solidity. If not, see <http://www.gnu.org/licenses/>.
*/
// SPDX-License-Identifier: GPL-3.0
/**
* @file KnownState.cpp
* @author Christian <c@ethdev.com>
* @date 2015
* Contains knowledge about the state of the virtual machine at a specific instruction.
*/
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#include <libevmasm/KnownState.h>
#include <libevmasm/AssemblyItem.h>
#include <libsolutil/Keccak256.h>
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#include <functional>
using namespace std;
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using namespace solidity;
using namespace solidity::evmasm;
using namespace solidity::langutil;
ostream& KnownState::stream(ostream& _out) const
{
auto streamExpressionClass = [this](ostream& _out, Id _id)
{
auto const& expr = m_expressionClasses->representative(_id);
_out << " " << dec << _id << ": ";
if (!expr.item)
_out << " no item";
else if (expr.item->type() == UndefinedItem)
_out << " unknown " << static_cast<int>(expr.item->data());
else
_out << *expr.item;
if (expr.sequenceNumber)
_out << "@" << dec << expr.sequenceNumber;
_out << "(";
for (Id arg: expr.arguments)
_out << dec << arg << ",";
_out << ")" << endl;
};
_out << "=== State ===" << endl;
_out << "Stack height: " << dec << m_stackHeight << endl;
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_out << "Equivalence classes:" << endl;
for (Id eqClass = 0; eqClass < m_expressionClasses->size(); ++eqClass)
streamExpressionClass(_out, eqClass);
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_out << "Stack:" << endl;
for (auto const& it: m_stackElements)
{
_out << " " << dec << it.first << ": ";
streamExpressionClass(_out, it.second);
}
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_out << "Storage:" << endl;
for (auto const& it: m_storageContent)
{
_out << " ";
streamExpressionClass(_out, it.first);
_out << ": ";
streamExpressionClass(_out, it.second);
}
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_out << "Memory:" << endl;
for (auto const& it: m_memoryContent)
{
_out << " ";
streamExpressionClass(_out, it.first);
_out << ": ";
streamExpressionClass(_out, it.second);
}
return _out;
}
KnownState::StoreOperation KnownState::feedItem(AssemblyItem const& _item, bool _copyItem)
{
StoreOperation op;
if (_item.type() == Tag)
{
// can be ignored
}
else if (_item.type() == AssignImmutable)
{
// Since AssignImmutable breaks blocks, it should be fine to only consider its changes to the stack, which
// is the same as two POPs.
// Note that the StoreOperation for POP is generic and _copyItem is ignored.
feedItem(AssemblyItem(Instruction::POP), _copyItem);
return feedItem(AssemblyItem(Instruction::POP), _copyItem);
}
else if (_item.type() == VerbatimBytecode)
{
m_sequenceNumber += 2;
resetMemory();
resetKnownKeccak256Hashes();
resetStorage();
// Consume all arguments and place unknown return values on the stack.
m_stackElements.erase(
m_stackElements.upper_bound(m_stackHeight - static_cast<int>(_item.arguments())),
m_stackElements.end()
);
m_stackHeight += static_cast<int>(_item.deposit());
for (size_t i = 0; i < _item.returnValues(); ++i)
setStackElement(
m_stackHeight - static_cast<int>(i),
m_expressionClasses->newClass(_item.location())
);
}
else if (_item.type() != Operation)
{
assertThrow(_item.deposit() == 1, InvalidDeposit, "");
if (_item.pushedValue())
// only available after assembly stage, should not be used for optimisation
setStackElement(++m_stackHeight, m_expressionClasses->find(*_item.pushedValue()));
else
setStackElement(++m_stackHeight, m_expressionClasses->find(_item, {}, _copyItem));
}
else
{
Instruction instruction = _item.instruction();
// The latest EVMVersion is used here, since the InstructionInfo is assumed to be
// the same across all EVM versions except for the instruction name.
InstructionInfo info = instructionInfo(instruction, EVMVersion());
if (SemanticInformation::isDupInstruction(_item))
setStackElement(
m_stackHeight + 1,
stackElement(
m_stackHeight - static_cast<int>(instruction) + static_cast<int>(Instruction::DUP1),
_item.location()
)
);
else if (SemanticInformation::isSwapInstruction(_item))
swapStackElements(
m_stackHeight,
m_stackHeight - 1 - static_cast<int>(instruction) + static_cast<int>(Instruction::SWAP1),
_item.location()
);
else if (instruction != Instruction::POP)
{
vector<Id> arguments(static_cast<size_t>(info.args));
for (size_t i = 0; i < static_cast<size_t>(info.args); ++i)
arguments[i] = stackElement(m_stackHeight - static_cast<int>(i), _item.location());
switch (_item.instruction())
{
case Instruction::SSTORE:
op = storeInStorage(arguments[0], arguments[1], _item.location());
break;
case Instruction::SLOAD:
setStackElement(
m_stackHeight + static_cast<int>(_item.deposit()),
loadFromStorage(arguments[0], _item.location())
);
break;
case Instruction::MSTORE:
op = storeInMemory(arguments[0], arguments[1], _item.location());
break;
case Instruction::MLOAD:
setStackElement(
m_stackHeight + static_cast<int>(_item.deposit()),
loadFromMemory(arguments[0], _item.location())
);
break;
case Instruction::KECCAK256:
setStackElement(
m_stackHeight + static_cast<int>(_item.deposit()),
applyKeccak256(arguments.at(0), arguments.at(1), _item.location())
);
break;
default:
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bool invMem =
SemanticInformation::memory(_item.instruction()) == SemanticInformation::Write;
bool invStor =
SemanticInformation::storage(_item.instruction()) == SemanticInformation::Write;
// We could be a bit more fine-grained here (CALL only invalidates part of
// memory, etc), but we do not for now.
if (invMem)
{
resetMemory();
resetKnownKeccak256Hashes();
}
if (invStor)
resetStorage();
if (invMem || invStor)
m_sequenceNumber += 2; // Increment by two because it can read and write
assertThrow(info.ret <= 1, InvalidDeposit, "");
if (info.ret == 1)
setStackElement(
m_stackHeight + static_cast<int>(_item.deposit()),
m_expressionClasses->find(_item, arguments, _copyItem)
);
}
}
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m_stackElements.erase(
m_stackElements.upper_bound(m_stackHeight + static_cast<int>(_item.deposit())),
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m_stackElements.end()
);
m_stackHeight += static_cast<int>(_item.deposit());
}
return op;
}
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/// Helper function for KnownState::reduceToCommonKnowledge, removes everything from
/// _this which is not in or not equal to the value in _other.
template <class Mapping> void intersect(Mapping& _this, Mapping const& _other)
{
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for (auto it = _this.begin(); it != _this.end();)
if (_other.count(it->first) && _other.at(it->first) == it->second)
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++it;
else
it = _this.erase(it);
}
void KnownState::reduceToCommonKnowledge(KnownState const& _other, bool _combineSequenceNumbers)
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{
int stackDiff = m_stackHeight - _other.m_stackHeight;
for (auto it = m_stackElements.begin(); it != m_stackElements.end();)
if (_other.m_stackElements.count(it->first - stackDiff))
{
Id other = _other.m_stackElements.at(it->first - stackDiff);
if (it->second == other)
++it;
else
{
set<u256> theseTags = tagsInExpression(it->second);
set<u256> otherTags = tagsInExpression(other);
if (!theseTags.empty() && !otherTags.empty())
{
theseTags.insert(otherTags.begin(), otherTags.end());
it->second = tagUnion(theseTags);
++it;
}
else
it = m_stackElements.erase(it);
}
}
else
it = m_stackElements.erase(it);
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// Use the smaller stack height. Essential to terminate in case of loops.
if (m_stackHeight > _other.m_stackHeight)
{
map<int, Id> shiftedStack;
for (auto const& stackElement: m_stackElements)
shiftedStack[stackElement.first - stackDiff] = stackElement.second;
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m_stackElements = std::move(shiftedStack);
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m_stackHeight = _other.m_stackHeight;
}
intersect(m_storageContent, _other.m_storageContent);
intersect(m_memoryContent, _other.m_memoryContent);
if (_combineSequenceNumbers)
m_sequenceNumber = max(m_sequenceNumber, _other.m_sequenceNumber);
}
bool KnownState::operator==(KnownState const& _other) const
{
if (m_storageContent != _other.m_storageContent || m_memoryContent != _other.m_memoryContent)
return false;
int stackDiff = m_stackHeight - _other.m_stackHeight;
auto thisIt = m_stackElements.cbegin();
auto otherIt = _other.m_stackElements.cbegin();
for (; thisIt != m_stackElements.cend() && otherIt != _other.m_stackElements.cend(); ++thisIt, ++otherIt)
if (thisIt->first - stackDiff != otherIt->first || thisIt->second != otherIt->second)
return false;
return (thisIt == m_stackElements.cend() && otherIt == _other.m_stackElements.cend());
}
ExpressionClasses::Id KnownState::stackElement(int _stackHeight, SourceLocation const& _location)
{
if (m_stackElements.count(_stackHeight))
return m_stackElements.at(_stackHeight);
// Stack element not found (not assigned yet), create new unknown equivalence class.
return m_stackElements[_stackHeight] =
m_expressionClasses->find(AssemblyItem(UndefinedItem, _stackHeight, _location));
}
KnownState::Id KnownState::relativeStackElement(int _stackOffset, SourceLocation const& _location)
{
return stackElement(m_stackHeight + _stackOffset, _location);
}
void KnownState::clearTagUnions()
{
for (auto it = m_stackElements.begin(); it != m_stackElements.end();)
if (m_tagUnions.left.count(it->second))
it = m_stackElements.erase(it);
else
++it;
}
void KnownState::setStackElement(int _stackHeight, Id _class)
{
m_stackElements[_stackHeight] = _class;
}
void KnownState::swapStackElements(
int _stackHeightA,
int _stackHeightB,
SourceLocation const& _location
)
{
assertThrow(_stackHeightA != _stackHeightB, OptimizerException, "Swap on same stack elements.");
// ensure they are created
stackElement(_stackHeightA, _location);
stackElement(_stackHeightB, _location);
swap(m_stackElements[_stackHeightA], m_stackElements[_stackHeightB]);
}
KnownState::StoreOperation KnownState::storeInStorage(
Id _slot,
Id _value,
SourceLocation const& _location)
{
if (m_storageContent.count(_slot) && m_storageContent[_slot] == _value)
// do not execute the storage if we know that the value is already there
return StoreOperation();
m_sequenceNumber++;
decltype(m_storageContent) storageContents;
// Copy over all values (i.e. retain knowledge about them) where we know that this store
// operation will not destroy the knowledge. Specifically, we copy storage locations we know
// are different from _slot or locations where we know that the stored value is equal to _value.
for (auto const& storageItem: m_storageContent)
if (m_expressionClasses->knownToBeDifferent(storageItem.first, _slot) || storageItem.second == _value)
storageContents.insert(storageItem);
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m_storageContent = std::move(storageContents);
AssemblyItem item(Instruction::SSTORE, _location);
Id id = m_expressionClasses->find(item, {_slot, _value}, true, m_sequenceNumber);
StoreOperation operation{StoreOperation::Storage, _slot, m_sequenceNumber, id};
m_storageContent[_slot] = _value;
// increment a second time so that we get unique sequence numbers for writes
m_sequenceNumber++;
return operation;
}
ExpressionClasses::Id KnownState::loadFromStorage(Id _slot, SourceLocation const& _location)
{
if (m_storageContent.count(_slot))
return m_storageContent.at(_slot);
AssemblyItem item(Instruction::SLOAD, _location);
return m_storageContent[_slot] = m_expressionClasses->find(item, {_slot}, true, m_sequenceNumber);
}
KnownState::StoreOperation KnownState::storeInMemory(Id _slot, Id _value, SourceLocation const& _location)
{
if (m_memoryContent.count(_slot) && m_memoryContent[_slot] == _value)
// do not execute the store if we know that the value is already there
return StoreOperation();
m_sequenceNumber++;
decltype(m_memoryContent) memoryContents;
// copy over values at points where we know that they are different from _slot by at least 32
for (auto const& memoryItem: m_memoryContent)
if (m_expressionClasses->knownToBeDifferentBy32(memoryItem.first, _slot))
memoryContents.insert(memoryItem);
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m_memoryContent = std::move(memoryContents);
AssemblyItem item(Instruction::MSTORE, _location);
Id id = m_expressionClasses->find(item, {_slot, _value}, true, m_sequenceNumber);
StoreOperation operation{StoreOperation::Memory, _slot, m_sequenceNumber, id};
m_memoryContent[_slot] = _value;
// increment a second time so that we get unique sequence numbers for writes
m_sequenceNumber++;
return operation;
}
ExpressionClasses::Id KnownState::loadFromMemory(Id _slot, SourceLocation const& _location)
{
if (m_memoryContent.count(_slot))
return m_memoryContent.at(_slot);
AssemblyItem item(Instruction::MLOAD, _location);
return m_memoryContent[_slot] = m_expressionClasses->find(item, {_slot}, true, m_sequenceNumber);
}
KnownState::Id KnownState::applyKeccak256(
Id _start,
Id _length,
SourceLocation const& _location
)
{
AssemblyItem keccak256Item(Instruction::KECCAK256, _location);
// Special logic if length is a short constant, otherwise we cannot tell.
u256 const* l = m_expressionClasses->knownConstant(_length);
// unknown or too large length
if (!l || *l > 128)
return m_expressionClasses->find(keccak256Item, {_start, _length}, true, m_sequenceNumber);
unsigned length = unsigned(*l);
vector<Id> arguments;
for (unsigned i = 0; i < length; i += 32)
{
Id slot = m_expressionClasses->find(
AssemblyItem(Instruction::ADD, _location),
{_start, m_expressionClasses->find(u256(i))}
);
arguments.push_back(loadFromMemory(slot, _location));
}
if (m_knownKeccak256Hashes.count({arguments, length}))
return m_knownKeccak256Hashes.at({arguments, length});
Id v;
// If all arguments are known constants, compute the Keccak-256 here
if (all_of(arguments.begin(), arguments.end(), [this](Id _a) { return !!m_expressionClasses->knownConstant(_a); }))
{
bytes data;
for (Id a: arguments)
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data += toBigEndian(*m_expressionClasses->knownConstant(a));
data.resize(length);
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v = m_expressionClasses->find(AssemblyItem(u256(util::keccak256(data)), _location));
}
else
v = m_expressionClasses->find(keccak256Item, {_start, _length}, true, m_sequenceNumber);
return m_knownKeccak256Hashes[{arguments, length}] = v;
}
set<u256> KnownState::tagsInExpression(KnownState::Id _expressionId)
{
if (m_tagUnions.left.count(_expressionId))
return m_tagUnions.left.at(_expressionId);
// Might be a tag, then return the set of itself.
ExpressionClasses::Expression expr = m_expressionClasses->representative(_expressionId);
if (expr.item && expr.item->type() == PushTag)
return set<u256>({expr.item->data()});
else
return set<u256>();
}
KnownState::Id KnownState::tagUnion(set<u256> _tags)
{
if (m_tagUnions.right.count(_tags))
return m_tagUnions.right.at(_tags);
else
{
Id id = m_expressionClasses->newClass(SourceLocation());
m_tagUnions.right.insert(make_pair(_tags, id));
return id;
}
}