Do not copy return data inside JIT

libevmjit-cpp/JitVM.cpp

@@ -50,7 +50,7 @@ bytesConstRef JitVM::go(ExtVMFace& _ext, OnOpFunc const&, uint64_t)
 	}
 
 	m_gas = llvm2eth(m_data.elems[RuntimeData::Gas]);
-	return {m_engine.returnData.data(), m_engine.returnData.size()};  // TODO: This all bytesConstRef is problematic, review.
+	return {std::get<0>(m_engine.returnData), std::get<1>(m_engine.returnData)};
 }
 
 }

libevmjit/Common.h

@@ -12,6 +12,7 @@ namespace jit
 
 using byte = uint8_t;
 using bytes = std::vector<byte>;
+using bytes_ref = std::tuple<byte const*, size_t>;
 using u256 = boost::multiprecision::uint256_t;
 using bigint = boost::multiprecision::cpp_int;
 

libevmjit/ExecutionEngine.cpp

@@ -136,7 +136,10 @@ ReturnCode ExecutionEngine::run(bytes const& _code, RuntimeData* _data, Env* _en
 
 	auto returnCode = runEntryFunc(entryFuncPtr, &runtime);
 	if (returnCode == ReturnCode::Return)
-		this->returnData = runtime.getReturnData();
+	{
+		returnData = runtime.getReturnData();     // Save reference to return data
+		std::swap(m_memory, runtime.getMemory()); // Take ownership of memory
+	}
 
 	auto executionEndTime = std::chrono::high_resolution_clock::now();
 	clog(JIT) << " + " << std::chrono::duration_cast<std::chrono::milliseconds>(executionEndTime - executionStartTime).count() << " ms\n";

libevmjit/ExecutionEngine.h

@@ -18,7 +18,13 @@ public:
 
 	ReturnCode run(bytes const& _code, RuntimeData* _data, Env* _env);
 
-	bytes returnData;
+	/// Reference to returned data (RETURN opcode used)
+	bytes_ref returnData;
+
+private:
+	/// After execution, if RETURN used, memory is moved there
+	/// to allow client copy the returned data
+	bytes m_memory;
 };
 
 }

libevmjit/Runtime.cpp

@@ -18,7 +18,7 @@ Runtime::Runtime(RuntimeData* _data, Env* _env) :
 	m_currJmpBuf(m_jmpBuf)
 {}
 
-bytes Runtime::getReturnData() const	// FIXME: Reconsider returning by copy
+bytes_ref Runtime::getReturnData() const
 {
 	// TODO: Handle large indexes
 	auto offset = static_cast<size_t>(llvm2eth(m_data.elems[RuntimeData::ReturnDataOffset]));
@@ -28,8 +28,8 @@ bytes Runtime::getReturnData() const	// FIXME: Reconsider returning by copy
 	if (offset + size > m_memory.size())
 		return {};
 
-	auto dataBeg = m_memory.begin() + offset;
+	auto dataBeg = m_memory.data() + offset;
-	return {dataBeg, dataBeg + size};
+	return bytes_ref{dataBeg, size};
 }
 
 }

libevmjit/Runtime.h

@@ -2,15 +2,8 @@
 #pragma once
 
 #include <csetjmp>
-#include <vector>
-
-#include "Instruction.h"
-#include "CompilerHelper.h"
-#include "Utils.h"
-#include "Type.h"
 #include "RuntimeData.h"
 
-
 #ifdef _MSC_VER
 	#define EXPORT __declspec(dllexport)
 #else
@@ -40,7 +33,7 @@ public:
 	MemoryImpl& getMemory() { return m_memory; }
 	Env* getEnvPtr() { return &m_env; }
 
-	bytes getReturnData() const;
+	bytes_ref getReturnData() const;
 	jmp_buf_ref getJmpBuf() { return m_jmpBuf; }
 
 private:

libevmjit/interface.cpp

@@ -20,12 +20,12 @@ evmjit_result evmjit_run(void* _data, void* _env)
 
 	auto returnCode = engine.run(bytecode, data, static_cast<Env*>(_env));
 	evmjit_result result = {static_cast<int32_t>(returnCode), 0, nullptr};
-	if (returnCode == ReturnCode::Return && !engine.returnData.empty())
+	if (returnCode == ReturnCode::Return && std::get<0>(engine.returnData))
 	{
 		// TODO: Optimized returning data. Allocating memory on client side by callback function might be a good idea
-		result.returnDataSize = engine.returnData.size();
+		result.returnDataSize = std::get<1>(engine.returnData);
 		result.returnData = std::malloc(result.returnDataSize);
-		std::memcpy(result.returnData, engine.returnData.data(), result.returnDataSize);
+		std::memcpy(result.returnData, std::get<0>(engine.returnData), result.returnDataSize);
 	}
 
 	return result;