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Replace function selector jump table by more resilient linear time check.

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Christian 2014-11-10 13:13:40 +01:00
parent d9822190c6
commit 41b26e491b
1 changed files with 18 additions and 19 deletions
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37
Compiler.cpp
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@ -81,35 +81,34 @@ void Compiler::appendFunctionSelector(vector<ASTPointer<FunctionDefinition>> con
if (publicFunctions.size() > 255)
BOOST_THROW_EXCEPTION(CompilerError() << errinfo_comment("More than 255 public functions for contract."));
//@todo check for calldatasize?
// retrieve the first byte of the call data
m_context << u256(0) << eth::Instruction::CALLDATALOAD << u256(0) << eth::Instruction::BYTE;
// check that it is not too large
m_context << eth::Instruction::DUP1 << u256(publicFunctions.size() - 1) << eth::Instruction::LT;
eth::AssemblyItem returnTag = m_context.appendConditionalJump();
// retrieve the first byte of the call data, which determines the called function
// @todo This code had a jump table in a previous version which was more efficient but also
// error prone (due to the optimizer and variable length tag addresses)
m_context << u256(1) << u256(0) // some constants
<< eth::dupInstruction(1) << eth::Instruction::CALLDATALOAD
<< eth::dupInstruction(2) << eth::Instruction::BYTE
<< eth::dupInstruction(2);
// otherwise, jump inside jump table (each entry of the table has size 4)
m_context << u256(4) << eth::Instruction::MUL;
eth::AssemblyItem jumpTableStart = m_context.pushNewTag();
m_context << eth::Instruction::ADD << eth::Instruction::JUMP;
// jump table @todo it could be that the optimizer destroys this
m_context << jumpTableStart;
// stack here: 1 0 <funid> 0, stack top will be counted up until it matches funid
for (pair<string, pair<FunctionDefinition const*, eth::AssemblyItem>> const& f: publicFunctions)
m_context.appendJumpTo(f.second.second) << eth::Instruction::JUMPDEST;
m_context << returnTag << eth::Instruction::STOP;
{
eth::AssemblyItem const& callDataUnpackerEntry = f.second.second;
m_context << eth::dupInstruction(2) << eth::dupInstruction(2) << eth::Instruction::EQ;
m_context.appendConditionalJumpTo(callDataUnpackerEntry);
m_context << eth::dupInstruction(4) << eth::Instruction::ADD;
//@todo avoid the last ADD (or remove it in the optimizer)
}
m_context << eth::Instruction::STOP; // function not found
for (pair<string, pair<FunctionDefinition const*, eth::AssemblyItem>> const& f: publicFunctions)
{
FunctionDefinition const& function = *f.second.first;
m_context << f.second.second;
eth::AssemblyItem const& callDataUnpackerEntry = f.second.second;
m_context << callDataUnpackerEntry;
eth::AssemblyItem returnTag = m_context.pushNewTag();
appendCalldataUnpacker(function);
m_context.appendJumpTo(m_context.getFunctionEntryLabel(function));
m_context << returnTag;
appendReturnValuePacker(function);
}
}