solidity/libyul/AsmAnalysis.cpp

/*
	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/>.
*/
/**
 * Analyzer part of inline assembly.
 */

#include <libyul/AsmAnalysis.h>

#include <libyul/AsmData.h>
#include <libyul/AsmScopeFiller.h>
#include <libyul/AsmScope.h>
#include <libyul/AsmAnalysisInfo.h>

#include <liblangutil/ErrorReporter.h>

#include <boost/range/adaptor/reversed.hpp>
#include <boost/algorithm/string.hpp>

#include <memory>
#include <functional>

using namespace std;
using namespace dev;
using namespace langutil;
using namespace yul;
using namespace dev;
using namespace dev::solidity;

namespace {

set<string> const builtinTypes{"bool", "u8", "s8", "u32", "s32", "u64", "s64", "u128", "s128", "u256", "s256"};

}

bool AsmAnalyzer::analyze(Block const& _block)
{
	if (!(ScopeFiller(m_info, m_errorReporter))(_block))
		return false;

	return (*this)(_block);
}

bool AsmAnalyzer::operator()(Label const& _label)
{
	solAssert(!_label.name.empty(), "");
	checkLooseFeature(
		_label.location,
		"The use of labels is disallowed. Please use \"if\", \"switch\", \"for\" or function calls instead."
	);
	m_info.stackHeightInfo[&_label] = m_stackHeight;
	warnOnInstructions(solidity::Instruction::JUMPDEST, _label.location);
	return true;
}

bool AsmAnalyzer::operator()(yul::Instruction const& _instruction)
{
	checkLooseFeature(
		_instruction.location,
		"The use of non-functional instructions is disallowed. Please use functional notation instead."
	);
	auto const& info = instructionInfo(_instruction.instruction);
	m_stackHeight += info.ret - info.args;
	m_info.stackHeightInfo[&_instruction] = m_stackHeight;
	warnOnInstructions(_instruction.instruction, _instruction.location);
	return true;
}

bool AsmAnalyzer::operator()(Literal const& _literal)
{
	expectValidType(_literal.type.str(), _literal.location);
	++m_stackHeight;
	if (_literal.kind == LiteralKind::String && _literal.value.str().size() > 32)
	{
		m_errorReporter.typeError(
			_literal.location,
			"String literal too long (" + to_string(_literal.value.str().size()) + " > 32)"
		);
		return false;
	}
	else if (_literal.kind == LiteralKind::Number && bigint(_literal.value.str()) > u256(-1))
	{
		m_errorReporter.typeError(
			_literal.location,
			"Number literal too large (> 256 bits)"
		);
		return false;
	}
	else if (_literal.kind == LiteralKind::Boolean)
	{
		solAssert(m_dialect->flavour == AsmFlavour::Yul, "");
		solAssert(_literal.value == "true"_yulstring || _literal.value == "false"_yulstring, "");
	}
	m_info.stackHeightInfo[&_literal] = m_stackHeight;
	return true;
}

bool AsmAnalyzer::operator()(Identifier const& _identifier)
{
	solAssert(!_identifier.name.empty(), "");
	size_t numErrorsBefore = m_errorReporter.errors().size();
	bool success = true;
	if (m_currentScope->lookup(_identifier.name, Scope::Visitor(
		[&](Scope::Variable const& _var)
		{
			if (!m_activeVariables.count(&_var))
			{
				m_errorReporter.declarationError(
					_identifier.location,
					"Variable " + _identifier.name.str() + " used before it was declared."
				);
				success = false;
			}
			++m_stackHeight;
		},
		[&](Scope::Label const&)
		{
			++m_stackHeight;
		},
		[&](Scope::Function const&)
		{
			m_errorReporter.typeError(
				_identifier.location,
				"Function " + _identifier.name.str() + " used without being called."
			);
			success = false;
		}
	)))
	{
	}
	else
	{
		size_t stackSize(-1);
		if (m_resolver)
		{
			bool insideFunction = m_currentScope->insideFunction();
			stackSize = m_resolver(_identifier, yul::IdentifierContext::RValue, insideFunction);
		}
		if (stackSize == size_t(-1))
		{
			// Only add an error message if the callback did not do it.
			if (numErrorsBefore == m_errorReporter.errors().size())
				m_errorReporter.declarationError(_identifier.location, "Identifier not found.");
			success = false;
		}
		m_stackHeight += stackSize == size_t(-1) ? 1 : stackSize;
	}
	m_info.stackHeightInfo[&_identifier] = m_stackHeight;
	return success;
}

bool AsmAnalyzer::operator()(FunctionalInstruction const& _instr)
{
	solAssert(m_dialect->flavour != AsmFlavour::Yul, "");
	bool success = true;
	for (auto const& arg: _instr.arguments | boost::adaptors::reversed)
		if (!expectExpression(arg))
			success = false;
	// Parser already checks that the number of arguments is correct.
	auto const& info = instructionInfo(_instr.instruction);
	solAssert(info.args == int(_instr.arguments.size()), "");
	m_stackHeight += info.ret - info.args;
	m_info.stackHeightInfo[&_instr] = m_stackHeight;
	warnOnInstructions(_instr.instruction, _instr.location);
	return success;
}

bool AsmAnalyzer::operator()(ExpressionStatement const& _statement)
{
	int initialStackHeight = m_stackHeight;
	bool success = boost::apply_visitor(*this, _statement.expression);
	if (m_stackHeight != initialStackHeight && (m_dialect->flavour != AsmFlavour::Loose || m_errorTypeForLoose))
	{
		Error::Type errorType = m_dialect->flavour == AsmFlavour::Loose ? *m_errorTypeForLoose : Error::Type::TypeError;
		string msg =
			"Top-level expressions are not supposed to return values (this expression returns " +
			to_string(m_stackHeight - initialStackHeight) +
			" value" +
			(m_stackHeight - initialStackHeight == 1 ? "" : "s") +
			"). Use ``pop()`` or assign them.";
		m_errorReporter.error(errorType, _statement.location, msg);
		if (errorType != Error::Type::Warning)
			success = false;
	}
	m_info.stackHeightInfo[&_statement] = m_stackHeight;
	return success;
}

bool AsmAnalyzer::operator()(StackAssignment const& _assignment)
{
	checkLooseFeature(
		_assignment.location,
		"The use of stack assignment is disallowed. Please use assignment in functional notation instead."
	);
	bool success = checkAssignment(_assignment.variableName, size_t(-1));
	m_info.stackHeightInfo[&_assignment] = m_stackHeight;
	return success;
}

bool AsmAnalyzer::operator()(Assignment const& _assignment)
{
	solAssert(_assignment.value, "");
	int const expectedItems = _assignment.variableNames.size();
	solAssert(expectedItems >= 1, "");
	int const stackHeight = m_stackHeight;
	bool success = boost::apply_visitor(*this, *_assignment.value);
	if ((m_stackHeight - stackHeight) != expectedItems)
	{
		m_errorReporter.declarationError(
			_assignment.location,
			"Variable count does not match number of values (" +
			to_string(expectedItems) +
			" vs. " +
			to_string(m_stackHeight - stackHeight) +
			")"
		);
		return false;
	}
	for (auto const& variableName: _assignment.variableNames)
		if (!checkAssignment(variableName, 1))
			success = false;
	m_info.stackHeightInfo[&_assignment] = m_stackHeight;
	return success;
}

bool AsmAnalyzer::operator()(VariableDeclaration const& _varDecl)
{
	bool success = true;
	int const numVariables = _varDecl.variables.size();
	if (_varDecl.value)
	{
		int const stackHeight = m_stackHeight;
		success = boost::apply_visitor(*this, *_varDecl.value);
		int numValues = m_stackHeight - stackHeight;
		if (numValues != numVariables)
		{
			m_errorReporter.declarationError(_varDecl.location,
				"Variable count mismatch: " +
				to_string(numVariables) +
				" variables and " +
				to_string(numValues) +
				" values."
			);
			// Adjust stack height to avoid misleading additional errors.
			m_stackHeight += numVariables - numValues;
			return false;
		}
	}
	else
		m_stackHeight += numVariables;

	for (auto const& variable: _varDecl.variables)
	{
		expectValidType(variable.type.str(), variable.location);
		m_activeVariables.insert(&boost::get<Scope::Variable>(m_currentScope->identifiers.at(variable.name)));
	}
	m_info.stackHeightInfo[&_varDecl] = m_stackHeight;
	return success;
}

bool AsmAnalyzer::operator()(FunctionDefinition const& _funDef)
{
	solAssert(!_funDef.name.empty(), "");
	Block const* virtualBlock = m_info.virtualBlocks.at(&_funDef).get();
	solAssert(virtualBlock, "");
	Scope& varScope = scope(virtualBlock);
	for (auto const& var: _funDef.parameters + _funDef.returnVariables)
	{
		expectValidType(var.type.str(), var.location);
		m_activeVariables.insert(&boost::get<Scope::Variable>(varScope.identifiers.at(var.name)));
	}

	int const stackHeight = m_stackHeight;
	m_stackHeight = _funDef.parameters.size() + _funDef.returnVariables.size();

	bool success = (*this)(_funDef.body);

	m_stackHeight = stackHeight;
	m_info.stackHeightInfo[&_funDef] = m_stackHeight;
	return success;
}

bool AsmAnalyzer::operator()(FunctionCall const& _funCall)
{
	solAssert(!_funCall.functionName.name.empty(), "");
	bool success = true;
	size_t parameters = 0;
	size_t returns = 0;
	if (BuiltinFunction const* f = m_dialect->builtin(_funCall.functionName.name))
	{
		// TODO: compare types, too
		parameters = f->parameters.size();
		returns = f->returns.size();
	}
	else if (!m_currentScope->lookup(_funCall.functionName.name, Scope::Visitor(
		[&](Scope::Variable const&)
		{
			m_errorReporter.typeError(
				_funCall.functionName.location,
				"Attempt to call variable instead of function."
			);
			success = false;
		},
		[&](Scope::Label const&)
		{
			m_errorReporter.typeError(
				_funCall.functionName.location,
				"Attempt to call label instead of function."
			);
			success = false;
		},
		[&](Scope::Function const& _fun)
		{
			/// TODO: compare types too
			parameters = _fun.arguments.size();
			returns = _fun.returns.size();
		}
	)))
	{
		m_errorReporter.declarationError(_funCall.functionName.location, "Function not found.");
		success = false;
	}
	if (success)
		if (_funCall.arguments.size() != parameters)
		{
			m_errorReporter.typeError(
				_funCall.functionName.location,
				"Function expects " +
				to_string(parameters) +
				" arguments but got " +
				to_string(_funCall.arguments.size()) + "."
			);
			success = false;
		}

	for (auto const& arg: _funCall.arguments | boost::adaptors::reversed)
		if (!expectExpression(arg))
			success = false;
	// Use argument size instead of parameter count to avoid misleading errors.
	m_stackHeight += int(returns) - int(_funCall.arguments.size());
	m_info.stackHeightInfo[&_funCall] = m_stackHeight;
	return success;
}

bool AsmAnalyzer::operator()(If const& _if)
{
	bool success = true;

	if (!expectExpression(*_if.condition))
		success = false;
	m_stackHeight--;

	if (!(*this)(_if.body))
		success = false;

	m_info.stackHeightInfo[&_if] = m_stackHeight;

	return success;
}

bool AsmAnalyzer::operator()(Switch const& _switch)
{
	solAssert(_switch.expression, "");

	bool success = true;

	if (!expectExpression(*_switch.expression))
		success = false;

	set<tuple<LiteralKind, YulString>> cases;
	for (auto const& _case: _switch.cases)
	{
		if (_case.value)
		{
			int const initialStackHeight = m_stackHeight;
			// We cannot use "expectExpression" here because *_case.value is not a
			// Statement and would be converted to a Statement otherwise.
			if (!(*this)(*_case.value))
				success = false;
			expectDeposit(1, initialStackHeight, _case.value->location);
			m_stackHeight--;

			/// Note: the parser ensures there is only one default case
			auto val = make_tuple(_case.value->kind, _case.value->value);
			if (!cases.insert(val).second)
			{
				m_errorReporter.declarationError(
					_case.location,
					"Duplicate case defined"
				);
				success = false;
			}
		}

		if (!(*this)(_case.body))
			success = false;
	}

	m_stackHeight--;
	m_info.stackHeightInfo[&_switch] = m_stackHeight;

	return success;
}

bool AsmAnalyzer::operator()(ForLoop const& _for)
{
	solAssert(_for.condition, "");

	Scope* originalScope = m_currentScope;

	bool success = true;
	if (!(*this)(_for.pre))
		success = false;
	// The block was closed already, but we re-open it again and stuff the
	// condition, the body and the post part inside.
	m_stackHeight += scope(&_for.pre).numberOfVariables();
	m_currentScope = &scope(&_for.pre);

	if (!expectExpression(*_for.condition))
		success = false;
	m_stackHeight--;
	if (!(*this)(_for.body))
		success = false;
	if (!(*this)(_for.post))
		success = false;

	m_stackHeight -= scope(&_for.pre).numberOfVariables();
	m_info.stackHeightInfo[&_for] = m_stackHeight;
	m_currentScope = originalScope;

	return success;
}

bool AsmAnalyzer::operator()(Block const& _block)
{
	bool success = true;
	auto previousScope = m_currentScope;
	m_currentScope = &scope(&_block);

	int const initialStackHeight = m_stackHeight;

	for (auto const& s: _block.statements)
		if (!boost::apply_visitor(*this, s))
			success = false;

	m_stackHeight -= scope(&_block).numberOfVariables();

	int const stackDiff = m_stackHeight - initialStackHeight;
	if (stackDiff != 0)
	{
		m_errorReporter.declarationError(
			_block.location,
			"Unbalanced stack at the end of a block: " +
			(
				stackDiff > 0 ?
				to_string(stackDiff) + string(" surplus item(s).") :
				to_string(-stackDiff) + string(" missing item(s).")
			)
		);
		success = false;
	}

	m_info.stackHeightInfo[&_block] = m_stackHeight;
	m_currentScope = previousScope;
	return success;
}

bool AsmAnalyzer::expectExpression(Expression const& _expr)
{
	bool success = true;
	int const initialHeight = m_stackHeight;
	if (!boost::apply_visitor(*this, _expr))
		success = false;
	if (!expectDeposit(1, initialHeight, locationOf(_expr)))
		success = false;
	return success;
}

bool AsmAnalyzer::expectDeposit(int _deposit, int _oldHeight, SourceLocation const& _location)
{
	if (m_stackHeight - _oldHeight != _deposit)
	{
		m_errorReporter.typeError(
			_location,
			"Expected expression to return one item to the stack, but did return " +
			to_string(m_stackHeight - _oldHeight) +
			" items."
		);
		return false;
	}
	return true;
}

bool AsmAnalyzer::checkAssignment(Identifier const& _variable, size_t _valueSize)
{
	solAssert(!_variable.name.empty(), "");
	bool success = true;
	size_t numErrorsBefore = m_errorReporter.errors().size();
	size_t variableSize(-1);
	if (Scope::Identifier const* var = m_currentScope->lookup(_variable.name))
	{
		// Check that it is a variable
		if (var->type() != typeid(Scope::Variable))
		{
			m_errorReporter.typeError(_variable.location, "Assignment requires variable.");
			success = false;
		}
		else if (!m_activeVariables.count(&boost::get<Scope::Variable>(*var)))
		{
			m_errorReporter.declarationError(
				_variable.location,
				"Variable " + _variable.name.str() + " used before it was declared."
			);
			success = false;
		}
		variableSize = 1;
	}
	else if (m_resolver)
	{
		bool insideFunction = m_currentScope->insideFunction();
		variableSize = m_resolver(_variable, yul::IdentifierContext::LValue, insideFunction);
	}
	if (variableSize == size_t(-1))
	{
		// Only add message if the callback did not.
		if (numErrorsBefore == m_errorReporter.errors().size())
			m_errorReporter.declarationError(_variable.location, "Variable not found or variable not lvalue.");
		success = false;
	}
	if (_valueSize == size_t(-1))
		_valueSize = variableSize == size_t(-1) ? 1 : variableSize;

	m_stackHeight -= _valueSize;

	if (_valueSize != variableSize && variableSize != size_t(-1))
	{
		m_errorReporter.typeError(
			_variable.location,
			"Variable size (" +
			to_string(variableSize) +
			") and value size (" +
			to_string(_valueSize) +
			") do not match."
		);
		success = false;
	}
	return success;
}

Scope& AsmAnalyzer::scope(Block const* _block)
{
	solAssert(m_info.scopes.count(_block) == 1, "Scope requested but not present.");
	auto scopePtr = m_info.scopes.at(_block);
	solAssert(scopePtr, "Scope requested but not present.");
	return *scopePtr;
}
void AsmAnalyzer::expectValidType(string const& type, SourceLocation const& _location)
{
	if (m_dialect->flavour != AsmFlavour::Yul)
		return;

	if (!builtinTypes.count(type))
		m_errorReporter.typeError(
			_location,
			"\"" + type + "\" is not a valid type (user defined types are not yet supported)."
		);
}

void AsmAnalyzer::warnOnInstructions(solidity::Instruction _instr, SourceLocation const& _location)
{
	// We assume that returndatacopy, returndatasize and staticcall are either all available
	// or all not available.
	solAssert(m_evmVersion.supportsReturndata() == m_evmVersion.hasStaticCall(), "");
	// Similarly we assume bitwise shifting and create2 go together.
	solAssert(m_evmVersion.hasBitwiseShifting() == m_evmVersion.hasCreate2(), "");

	if (_instr == solidity::Instruction::EXTCODEHASH)
		m_errorReporter.warning(
			_location,
			"The \"" +
			boost::to_lower_copy(instructionInfo(_instr).name)
			+ "\" instruction is not supported by the VM version \"" +
			"" + m_evmVersion.name() +
			"\" you are currently compiling for. " +
			"It will be interpreted as an invalid instruction on this VM."
		);
	else if ((
		_instr == solidity::Instruction::RETURNDATACOPY ||
		_instr == solidity::Instruction::RETURNDATASIZE ||
		_instr == solidity::Instruction::STATICCALL
	) && !m_evmVersion.supportsReturndata())
		m_errorReporter.warning(
			_location,
			"The \"" +
			boost::to_lower_copy(instructionInfo(_instr).name)
			+ "\" instruction is only available for Byzantium-compatible VMs. " +
			"You are currently compiling for \"" +
			m_evmVersion.name() +
			"\", where it will be interpreted as an invalid instruction."
		);
	else if ((
		_instr == solidity::Instruction::SHL ||
		_instr == solidity::Instruction::SHR ||
		_instr == solidity::Instruction::SAR ||
		_instr == solidity::Instruction::CREATE2
	) && !m_evmVersion.hasBitwiseShifting())
		m_errorReporter.warning(
			_location,
			"The \"" +
			boost::to_lower_copy(instructionInfo(_instr).name)
			+ "\" instruction is only available for Constantinople-compatible VMs. " +
			"You are currently compiling for \"" +
			m_evmVersion.name() +
			"\", where it will be interpreted as an invalid instruction."
		);

	if (_instr == solidity::Instruction::JUMP || _instr == solidity::Instruction::JUMPI || _instr == solidity::Instruction::JUMPDEST)
	{
		if (m_dialect->flavour != AsmFlavour::Loose)
			solAssert(m_errorTypeForLoose && *m_errorTypeForLoose != Error::Type::Warning, "");

		m_errorReporter.error(
			m_errorTypeForLoose ? *m_errorTypeForLoose : Error::Type::Warning,
			_location,
			"Jump instructions and labels are low-level EVM features that can lead to "
			"incorrect stack access. Because of that they are discouraged. "
			"Please consider using \"switch\", \"if\" or \"for\" statements instead."
		);
	}
}

void AsmAnalyzer::checkLooseFeature(SourceLocation const& _location, string const& _description)
{
	if (m_dialect->flavour != AsmFlavour::Loose)
		solAssert(false, _description);
	else if (m_errorTypeForLoose)
		m_errorReporter.error(*m_errorTypeForLoose, _location, _description);
}