Ethereum Virtual Machine (EVM) Interpreter
Table of Contents
Introduction
A straightforward interpreter that executes EVM code.
Module Contents
Classes
Output of a particular message call |
Functions
If message.current is empty then it creates a smart contract |
|
Executes a call to create a smart contract. |
|
Executes a call to create a smart contract. |
|
Executes bytecode present in the message. |
Attributes
Module Details
STACK_DEPTH_LIMIT
- STACK_DEPTH_LIMIT
STACK_DEPTH_LIMIT = U256(1024)
MAX_CODE_SIZE
- MAX_CODE_SIZE
MAX_CODE_SIZE = 0x6000
MessageCallOutput
Output of a particular message call
Contains the following:
gas_left: remaining gas after execution.
refund_counter: gas to refund after execution.
logs: list of Log generated during execution.
accounts_to_delete: Contracts which have self-destructed.
touched_accounts: Accounts that have been touched.
has_erred: True if execution has caused an error.
- class MessageCallOutput
- gas_left :ethereum.base_types.U256
- refund_counter :ethereum.base_types.U256
- logs :Tuple[ethereum.spurious_dragon.fork_types.Log,:Tuple[ethereum.byzantium.fork_types.Log, Ellipsis]
- accounts_to_delete :Set[ethereum.spurious_dragon.fork_types.Address]:Set[ethereum.byzantium.fork_types.Address]
- touched_accounts :Iterable[ethereum.spurious_dragon.fork_types.Address]:Iterable[ethereum.byzantium.fork_types.Address]
- has_erred :bool
process_message_call
- process_message_call(message, env)
If message.current is empty then it creates a smart contract else it executes a call from the message.caller to the message.target.
- Parameters
message – Transaction specific items.
env – External items required for EVM execution.
- Returns
output – Output of the message call
- Return type
MessageCallOutput
def process_message_call(
message: Message, env: Environment
) -> MessageCallOutput:
if message.target == Bytes0(b""):
is_collision = account_has_code_or_nonce(
env.state, message.current_target
)
if is_collision:
return MessageCallOutput(
U256(0), U256(0), tuple(), set(), set(), True
)
else:
evm = process_create_message(message, env)
else:
evm = process_message(message, env)
if account_exists_and_is_empty(env.state, Address(message.target)):
evm.touched_accounts.add(Address(message.target))
if evm.has_erred:
logs: Tuple[Log, ...] = ()
accounts_to_delete = set()
touched_accounts = set()
refund_counter = U256(0)
else:
logs = evm.logs
accounts_to_delete = evm.accounts_to_delete
touched_accounts = evm.touched_accounts
refund_counter = evm.refund_counter + REFUND_SELF_DESTRUCT * len(
evm.accounts_to_delete
)
return MessageCallOutput(
gas_left=evm.gas_left,
refund_counter=refund_counter,
logs=logs,
accounts_to_delete=accounts_to_delete,
touched_accounts=touched_accounts,
has_erred=evm.has_erred,
)
process_create_message
- process_create_message(message, env)
Executes a call to create a smart contract.
- Parameters
message – Transaction specific items.
env – External items required for EVM execution.
- Returns
evm – Items containing execution specific objects.
- Return type
def process_create_message(message: Message, env: Environment) -> Evm:
# take snapshot of state before processing the message
begin_transaction(env.state)
increment_nonce(env.state, message.current_target)
evm = process_message(message, env)
if not evm.has_erred:
contract_code = evm.output
contract_code_gas = len(contract_code) * GAS_CODE_DEPOSIT
try:
charge_gas(evm, contract_code_gas)
ensure(len(contract_code) <= MAX_CODE_SIZE, OutOfGasError)
except ExceptionalHalt:
rollback_transaction(env.state)
evm.gas_left = U256(0)
evm.output = b""
evm.has_erred = True
else:
set_code(env.state, message.current_target, contract_code)
commit_transaction(env.state)
else:
rollback_transaction(env.state)
return evm
process_message
- process_message(message, env)
Executes a call to create a smart contract.
- Parameters
message – Transaction specific items.
env – External items required for EVM execution.
- Returns
evm – Items containing execution specific objects
- Return type
def process_message(message: Message, env: Environment) -> Evm:
if message.depth > STACK_DEPTH_LIMIT:
raise StackDepthLimitError("Stack depth limit reached")
# take snapshot of state before processing the message
begin_transaction(env.state)
touch_account(env.state, message.current_target)
if message.should_transfer_value and message.value != 0:
move_ether(
env.state, message.caller, message.current_target, message.value
)
evm = execute_code(message, env)
if evm.has_erred:
# revert state to the last saved checkpoint
# since the message call resulted in an error
rollback_transaction(env.state)
else:
commit_transaction(env.state)
return evm
execute_code
- execute_code(message, env)
Executes bytecode present in the message.
- Parameters
message – Transaction specific items.
env – External items required for EVM execution.
- Returns
evm – Items containing execution specific objects
- Return type
ethereum.vm.EVM
def execute_code(message: Message, env: Environment) -> Evm:
code = message.code
valid_jump_destinations = get_valid_jump_destinations(code)
evm = Evm(
pc=Uint(0),
stack=[],
memory=bytearray(),
code=code,
gas_left=message.gas,
env=env,
valid_jump_destinations=valid_jump_destinations,
logs=(),
refund_counter=U256(0),
running=True,
message=message,
output=b"",
accounts_to_delete=set(),
touched_accounts=set(),
has_erred=False,
return_data=b"",
error=None,
)
try:
if evm.message.code_address in PRE_COMPILED_CONTRACTS:
evm_trace(evm, evm.message.code_address)
PRE_COMPILED_CONTRACTS[evm.message.code_address](evm)
return evm
while evm.running and evm.pc < len(evm.code):
try:
op = Ops(evm.code[evm.pc])
except ValueError:
raise InvalidOpcode(evm.code[evm.pc])
evm_trace(evm, op)
op_implementation[op](evm)
except ExceptionalHalt:
evm.gas_left = U256(0)
evm.output = b""
evm.has_erred = True
except Revert as e:
evm.error = e
evm.has_erred = True
return evm