Merge pull request #963 from gurukamath/eips/prague/eip-2935-1

Update EIP-2935 to the latest spec

src/ethereum/prague/fork.py

@@ -112,7 +112,7 @@ class BlockChain:
     chain_id: U64
 
 
-def apply_fork(old: BlockChain, block: Block) -> BlockChain:
+def apply_fork(old: BlockChain) -> BlockChain:
     """
     Transforms the state from the previous hard fork (`old`) into the block
     chain object for this hard fork and returns it.
@@ -125,34 +125,55 @@ def apply_fork(old: BlockChain, block: Block) -> BlockChain:
     ----------
     old :
         Previous block chain object.
-    block :
-        Block to apply to `old`.
 
     Returns
     -------
     new : `BlockChain`
         Upgraded block chain object for this hard fork.
     """
-    # At fork block, store the hashes for earlier blocks.
-    current_block = block
-    for i in range(HISTORY_SERVE_WINDOW - 1):
-        if current_block.header.number == 0:
-            break
-
-        set_storage(
-            old.state,
-            HISTORY_STORAGE_ADDRESS,
-            (
-                (current_block.header.number - 1) % HISTORY_SERVE_WINDOW
-            ).to_be_bytes32(),
-            U256.from_be_bytes(current_block.header.parent_hash),
-        )
-        # Set the earlier block as the current block
-        current_block = old.blocks[-1 - i]
-
     return old
 
 
+def get_last_256_block_hashes(chain: BlockChain) -> List[Hash32]:
+    """
+    Obtain the list of hashes of the previous 256 blocks in order of
+    increasing block number.
+
+    This function will return less hashes for the first 256 blocks.
+
+    The ``BLOCKHASH`` opcode needs to access the latest hashes on the chain,
+    therefore this function retrieves them.
+
+    Parameters
+    ----------
+    chain :
+        History and current state.
+
+    Returns
+    -------
+    recent_block_hashes : `List[Hash32]`
+        Hashes of the recent 256 blocks in order of increasing block number.
+    """
+    recent_blocks = chain.blocks[-255:]
+    # TODO: This function has not been tested rigorously
+    if len(recent_blocks) == 0:
+        return []
+
+    recent_block_hashes = []
+
+    for block in recent_blocks:
+        prev_block_hash = block.header.parent_hash
+        recent_block_hashes.append(prev_block_hash)
+
+    # We are computing the hash only for the most recent block and not for
+    # the rest of the blocks as they have successors which have the hash of
+    # the current block as parent hash.
+    most_recent_block_hash = keccak256(rlp.encode(recent_blocks[-1].header))
+    recent_block_hashes.append(most_recent_block_hash)
+
+    return recent_block_hashes
+
+
 def state_transition(chain: BlockChain, block: Block) -> None:
     """
     Attempts to apply a block to an existing block chain.
@@ -193,6 +214,7 @@ def state_transition(chain: BlockChain, block: Block) -> None:
 
     apply_body_output = apply_body(
         chain.state,
+        get_last_256_block_hashes(chain),
         block.header.coinbase,
         block.header.number,
         block.header.base_fee_per_gas,
@@ -511,6 +533,7 @@ class ApplyBodyOutput:
 def process_system_transaction(
     target_address: Address,
     data: Bytes,
+    block_hashes: List[Hash32],
     coinbase: Address,
     block_number: Uint,
     base_fee_per_gas: Uint,
@@ -530,6 +553,8 @@ def process_system_transaction(
         Address of the contract to call.
     data :
         Data to pass to the contract.
+    block_hashes :
+        List of hashes of the previous 256 blocks.
     coinbase :
         Address of the block's coinbase.
     block_number :
@@ -575,6 +600,7 @@ def process_system_transaction(
 
     system_tx_env = vm.Environment(
         caller=SYSTEM_ADDRESS,
+        block_hashes=block_hashes,
         origin=SYSTEM_ADDRESS,
         coinbase=coinbase,
         number=block_number,
@@ -607,6 +633,7 @@ def process_system_transaction(
 
 def apply_body(
     state: State,
+    block_hashes: List[Hash32],
     coinbase: Address,
     block_number: Uint,
     base_fee_per_gas: Uint,
@@ -634,6 +661,9 @@ def apply_body(
     ----------
     state :
         Current account state.
+    block_hashes :
+        List of hashes of the previous 256 blocks in the order of
+        increasing block number.
     coinbase :
         Address of account which receives block reward and transaction fees.
     block_number :
@@ -687,6 +717,7 @@ def apply_body(
     process_system_transaction(
         BEACON_ROOTS_ADDRESS,
         parent_beacon_block_root,
+        block_hashes,
         coinbase,
         block_number,
         base_fee_per_gas,
@@ -718,6 +749,7 @@ def apply_body(
 
         env = vm.Environment(
             caller=sender_address,
+            block_hashes=block_hashes,
             origin=sender_address,
             coinbase=coinbase,
             number=block_number,
@@ -771,6 +803,7 @@ def apply_body(
     system_withdrawal_tx_output = process_system_transaction(
         WITHDRAWAL_REQUEST_PREDEPLOY_ADDRESS,
         b"",
+        block_hashes,
         coinbase,
         block_number,
         base_fee_per_gas,

src/ethereum/prague/vm/__init__.py

@@ -17,6 +17,7 @@
 from typing import List, Optional, Set, Tuple, Union
 
 from ethereum.base_types import U64, U256, Bytes, Bytes0, Bytes32, Uint
+from ethereum.crypto.hash import Hash32
 
 from ..blocks import Log
 from ..fork_types import Address, VersionedHash
@@ -33,6 +34,7 @@ class Environment:
     """
 
     caller: Address
+    block_hashes: List[Hash32]
     origin: Address
     coinbase: Address
     number: Uint

src/ethereum/prague/vm/gas.py

@@ -38,6 +38,7 @@
 GAS_KECCAK256 = Uint(30)
 GAS_KECCAK256_WORD = Uint(6)
 GAS_COPY = Uint(3)
+GAS_BLOCK_HASH = Uint(20)
 GAS_LOG = Uint(375)
 GAS_LOG_DATA = Uint(8)
 GAS_LOG_TOPIC = Uint(375)

src/ethereum/prague/vm/instructions/block.py

@@ -14,9 +14,8 @@
 
 from ethereum.base_types import U256
 
-from ...state import get_storage
 from .. import Evm
-from ..gas import GAS_BASE, GAS_COLD_SLOAD, GAS_WARM_ACCESS, charge_gas
+from ..gas import GAS_BASE, GAS_BLOCK_HASH, charge_gas
 from ..stack import pop, push
 
 
@@ -37,34 +36,20 @@ def block_hash(evm: Evm) -> None:
     :py:class:`~ethereum.prague.vm.exceptions.OutOfGasError`
         If `evm.gas_left` is less than `20`.
     """
-    from ...fork import HISTORY_SERVE_WINDOW, HISTORY_STORAGE_ADDRESS
-
     # STACK
     block_number = pop(evm.stack)
 
     # GAS
-    key = (block_number % HISTORY_SERVE_WINDOW).to_be_bytes32()
-    if (HISTORY_STORAGE_ADDRESS, key) in evm.accessed_storage_keys:
-        charge_gas(evm, GAS_WARM_ACCESS)
-    else:
-        evm.accessed_storage_keys.add((HISTORY_STORAGE_ADDRESS, key))
-        charge_gas(evm, GAS_COLD_SLOAD)
+    charge_gas(evm, GAS_BLOCK_HASH)
 
     # OPERATION
-    if (
-        evm.env.number <= block_number
-        or evm.env.number > block_number + HISTORY_SERVE_WINDOW
-    ):
+    if evm.env.number <= block_number or evm.env.number > block_number + 256:
         # Default hash to 0, if the block of interest is not yet on the chain
         # (including the block which has the current executing transaction),
-        # or if the block's age is more than HISTORY_SERVE_WINDOW.
+        # or if the block's age is more than 256.
         hash = b"\x00"
     else:
-        hash = get_storage(
-            evm.env.state,
-            HISTORY_STORAGE_ADDRESS,
-            key,
-        ).to_be_bytes32()
+        hash = evm.env.block_hashes[-(evm.env.number - block_number)]
 
     push(evm.stack, U256.from_be_bytes(hash))