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author | Dimitry <winsvega@mail.ru> | 2016-03-21 16:55:45 +0800 |
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committer | Dimitry <winsvega@mail.ru> | 2016-03-21 16:55:45 +0800 |
commit | b50e65437ebad535af29e84156b8b1af71f61c3d (patch) | |
tree | f2594fc7b539e5848f4fc08ebcfafedab90e00b5 /libevmasm/PathGasMeter.cpp | |
parent | 2fe6037b9bc42946dafbf0f870ca59546712d14c (diff) | |
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move libevmasm
Diffstat (limited to 'libevmasm/PathGasMeter.cpp')
-rw-r--r-- | libevmasm/PathGasMeter.cpp | 128 |
1 files changed, 128 insertions, 0 deletions
diff --git a/libevmasm/PathGasMeter.cpp b/libevmasm/PathGasMeter.cpp new file mode 100644 index 00000000..8f7314f8 --- /dev/null +++ b/libevmasm/PathGasMeter.cpp @@ -0,0 +1,128 @@ +/* + This file is part of cpp-ethereum. + + cpp-ethereum 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. + + cpp-ethereum 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 cpp-ethereum. If not, see <http://www.gnu.org/licenses/>. +*/ +/** @file PathGasMeter.cpp + * @author Christian <c@ethdev.com> + * @date 2015 + */ + +#include "PathGasMeter.h" +#include <libevmasm/KnownState.h> +#include <libevmasm/SemanticInformation.h> + +using namespace std; +using namespace dev; +using namespace dev::eth; + +PathGasMeter::PathGasMeter(AssemblyItems const& _items): + m_items(_items) +{ + for (size_t i = 0; i < m_items.size(); ++i) + if (m_items[i].type() == Tag) + m_tagPositions[m_items[i].data()] = i; +} + +GasMeter::GasConsumption PathGasMeter::estimateMax( + size_t _startIndex, + shared_ptr<KnownState> const& _state +) +{ + auto path = unique_ptr<GasPath>(new GasPath()); + path->index = _startIndex; + path->state = _state->copy(); + m_queue.push_back(move(path)); + + GasMeter::GasConsumption gas; + while (!m_queue.empty() && !gas.isInfinite) + gas = max(gas, handleQueueItem()); + return gas; +} + +GasMeter::GasConsumption PathGasMeter::handleQueueItem() +{ + assertThrow(!m_queue.empty(), OptimizerException, ""); + + unique_ptr<GasPath> path = move(m_queue.back()); + m_queue.pop_back(); + + shared_ptr<KnownState> state = path->state; + GasMeter meter(state, path->largestMemoryAccess); + ExpressionClasses& classes = state->expressionClasses(); + GasMeter::GasConsumption gas = path->gas; + size_t index = path->index; + + if (index >= m_items.size() || (index > 0 && m_items.at(index).type() != Tag)) + // Invalid jump usually provokes an out-of-gas exception, but we want to give an upper + // bound on the gas that is needed without changing the behaviour, so it is fine to + // return the current gas value. + return gas; + + set<u256> jumpTags; + for (; index < m_items.size() && !gas.isInfinite; ++index) + { + bool branchStops = false; + jumpTags.clear(); + AssemblyItem const& item = m_items.at(index); + if (item.type() == Tag || item == AssemblyItem(eth::Instruction::JUMPDEST)) + { + // Do not allow any backwards jump. This is quite restrictive but should work for + // the simplest things. + if (path->visitedJumpdests.count(index)) + return GasMeter::GasConsumption::infinite(); + path->visitedJumpdests.insert(index); + } + else if (item == AssemblyItem(eth::Instruction::JUMP)) + { + branchStops = true; + jumpTags = state->tagsInExpression(state->relativeStackElement(0)); + if (jumpTags.empty()) // unknown jump destination + return GasMeter::GasConsumption::infinite(); + } + else if (item == AssemblyItem(eth::Instruction::JUMPI)) + { + ExpressionClasses::Id condition = state->relativeStackElement(-1); + if (classes.knownNonZero(condition) || !classes.knownZero(condition)) + { + jumpTags = state->tagsInExpression(state->relativeStackElement(0)); + if (jumpTags.empty()) // unknown jump destination + return GasMeter::GasConsumption::infinite(); + } + branchStops = classes.knownNonZero(condition); + } + else if (SemanticInformation::altersControlFlow(item)) + branchStops = true; + + gas += meter.estimateMax(item); + + for (u256 const& tag: jumpTags) + { + auto newPath = unique_ptr<GasPath>(new GasPath()); + newPath->index = m_items.size(); + if (m_tagPositions.count(tag)) + newPath->index = m_tagPositions.at(tag); + newPath->gas = gas; + newPath->largestMemoryAccess = meter.largestMemoryAccess(); + newPath->state = state->copy(); + newPath->visitedJumpdests = path->visitedJumpdests; + m_queue.push_back(move(newPath)); + } + + if (branchStops) + break; + } + + return gas; +} |