ethereum.istanbul.vm.instructions.storage

Ethereum Virtual Machine (EVM) Storage Instructions ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

.. contents:: Table of Contents :backlinks: none :local:

Introduction

Implementations of the EVM storage related instructions.

sload

Loads to the stack, the value corresponding to a certain key from the storage of the current account.

Parameters

evm : The current EVM frame.

def sload(​evm: Evm​) -> None:
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    """
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    Loads to the stack, the value corresponding to a certain key from the
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    storage of the current account.
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    Parameters
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    ----------
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    evm :
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        The current EVM frame.
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    """
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    # STACK
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    key = pop(evm.stack).to_be_bytes32()
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    # GAS
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    charge_gas(evm, GAS_SLOAD)
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    # OPERATION
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    value = get_storage(evm.env.state, evm.message.current_target, key)
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    push(evm.stack, value)
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    # PROGRAM COUNTER
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    evm.pc += Uint(1)

sstore

Stores a value at a certain key in the current context's storage.

Parameters

evm : The current EVM frame.

def sstore(​evm: Evm​) -> None:
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    """
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    Stores a value at a certain key in the current context's storage.
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    Parameters
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    ----------
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    evm :
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        The current EVM frame.
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    """
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    # STACK
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    key = pop(evm.stack).to_be_bytes32()
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    new_value = pop(evm.stack)
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    if evm.gas_left <= GAS_CALL_STIPEND:
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        raise OutOfGasError
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    original_value = get_storage_original(
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        evm.env.state, evm.message.current_target, key
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    )
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    current_value = get_storage(evm.env.state, evm.message.current_target, key)
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    if original_value == current_value and current_value != new_value:
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        if original_value == 0:
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            gas_cost = GAS_STORAGE_SET
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        else:
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            gas_cost = GAS_STORAGE_UPDATE
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    else:
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        gas_cost = GAS_SLOAD
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    # Refund Counter Calculation
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    if current_value != new_value:
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        if original_value != 0 and current_value != 0 and new_value == 0:
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            # Storage is cleared for the first time in the transaction
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            evm.refund_counter += int(GAS_STORAGE_CLEAR_REFUND)
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        if original_value != 0 and current_value == 0:
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            # Gas refund issued earlier to be reversed
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            evm.refund_counter -= int(GAS_STORAGE_CLEAR_REFUND)
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        if original_value == new_value:
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            # Storage slot being restored to its original value
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            if original_value == 0:
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                # Slot was originally empty and was SET earlier
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                evm.refund_counter += int(GAS_STORAGE_SET - GAS_SLOAD)
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            else:
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                # Slot was originally non-empty and was UPDATED earlier
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                evm.refund_counter += int(GAS_STORAGE_UPDATE - GAS_SLOAD)
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    charge_gas(evm, gas_cost)
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    if evm.message.is_static:
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        raise WriteInStaticContext
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    set_storage(evm.env.state, evm.message.current_target, key, new_value)
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    # PROGRAM COUNTER
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    evm.pc += Uint(1)