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test_worst_modexp()

Documentation for tests/zkevm/test_worst_compute.py::test_worst_modexp@v4.5.0.

Generate fixtures for these test cases for Prague with:

fill -v tests/zkevm/test_worst_compute.py::test_worst_modexp --fork Prague

Test running a block with as many MODEXP calls as possible.

Source code in tests/zkevm/test_worst_compute.py 
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@pytest.mark.zkevm
@pytest.mark.valid_from("Cancun")
@pytest.mark.parametrize(
    "gas_limit",
    [
        Environment().gas_limit,
    ],
)
def test_worst_modexp(
    blockchain_test: BlockchainTestFiller,
    pre: Alloc,
    fork: Fork,
    gas_limit: int,
):
    """Test running a block with as many MODEXP calls as possible."""
    env = Environment(gas_limit=gas_limit)

    base_mod_length = 32
    exp_length = 32

    base = 2 ** (8 * base_mod_length) - 1
    mod = 2 ** (8 * base_mod_length) - 2  # Prevents base == mod
    exp = 2 ** (8 * exp_length) - 1

    # MODEXP calldata
    calldata = (
        Op.MSTORE(0 * 32, base_mod_length)
        + Op.MSTORE(1 * 32, exp_length)
        + Op.MSTORE(2 * 32, base_mod_length)
        + Op.MSTORE(3 * 32, base)
        + Op.MSTORE(4 * 32, exp)
        + Op.MSTORE(5 * 32, mod)
    )

    # EIP-2565
    mul_complexity = math.ceil(base_mod_length / 8) ** 2
    iter_complexity = exp.bit_length() - 1
    gas_cost = math.floor((mul_complexity * iter_complexity) / 3)
    attack_block = Op.POP(Op.STATICCALL(gas_cost, 0x5, 0, 32 * 6, 0, 0))

    # The attack contract is: JUMPDEST + [attack_block]* + PUSH0 + JUMP
    jumpdest = Op.JUMPDEST
    jump_back = Op.JUMP(len(calldata))
    max_iters_loop = (MAX_CODE_SIZE - len(calldata) - len(jumpdest) - len(jump_back)) // len(
        attack_block
    )
    code = calldata + jumpdest + sum([attack_block] * max_iters_loop) + jump_back
    if len(code) > MAX_CODE_SIZE:
        # Must never happen, but keep it as a sanity check.
        raise ValueError(f"Code size {len(code)} exceeds maximum code size {MAX_CODE_SIZE}")

    code_address = pre.deploy_contract(code=code)

    tx = Transaction(
        to=code_address,
        gas_limit=gas_limit,
        sender=pre.fund_eoa(),
    )

    blockchain_test(
        env=env,
        pre=pre,
        post={},
        blocks=[Block(txs=[tx])],
    )

Parametrized Test Cases

This test case is only parametrized by fork.

Test ID (Abbreviated) gas_limit
...fork_Cancun-blockchain_test-gas_limit_0x044aa200 0x044aa200
...fork_Prague-blockchain_test-gas_limit_0x044aa200 0x044aa200
...fork_Osaka-blockchain_test-gas_limit_0x044aa200 0x044aa200