bug(debugger): layout displays the wrong SSTORE and JUMP opcode cost

[alex0207s]

Component

Forge

Have you ensured that all of these are up to date?

• [X] Foundry
• [x] Foundryup

What version of Foundry are you on?

forge 0.2.0 (55dd5de 2023-11-24T00:21:15.586516000Z)

What command(s) is the bug in?

forge debug

Operating System

macOS (Apple Silicon)

Describe the bug

Repro example

Paste the contract setNumber.sol in src folder

// SPDX-License-Identifier: MIT
pragma solidity 0.8.7;

contract SetNumber {
    uint256 num = 1;

    function setNumber(uint256 _num) external payable {
        num = _num;
    }
}

Run:

forge debug src/setNumber.sol --sig "setNumber(uint256)" 0

In the debugger layout, the SSTORE and JUMP opcode are 3969 and 6 gas, respectively.

Issues Identified:

• The reported gas cost for the JUMP opcode is incorrect. It should be 8 gas, but it is currently reported as 6 gas.
• The reported gas cost for the SSTORE opcode is incorrect. It should be 3967 gas (5000 - refund gas calculated in foundry test, see below explanation), but it is currently reported as 3969, leading to the inaccurate display of a 6-gas cost for the JUMP opcode.
• Foundry does not include intrinsic gas, leading to miscalculations in refund gas when the total transaction cost is small.

Additional Info

• The gas cost for the SSTORE opcode is dynamic and depends on various factors such as refund gas, warm access, and cold access.
• Foundry only calculates the sum of opcode cost and does not include the intrinsic gas
• Therefore, Foundry might fail to calculate the correct refund gas when the total transaction cost is low
  • The refund gas formula is min(refund_gas_accmulated_in_refund_counter, tx.gas_consumed // 5)
  • In this case,
    • On-chain: refund_gas_accmulated_in_refund_counter is 4800 and tx.gas_consumed is 26358 (before get refund gas)
    • Foundry: refund_gas_accmulated_in_refund_counter is 4800 and tx.gas_consumed is 5166 (the sum of all opcode cost in this example)
  • According to the refund gas formula:
    • On-chain: get 4800 refund gas (4800 = min(4800, 26358//5))
    • Foundry: get 1033 refund gas (1033 = min(4800, 5166//5))
  • Therefore, in Foundry, the SSTORE opcode costs 3967 (5000-1033) gas

Further Question

Is there a way to include intrinsic gas when calculating the refund gas or even include it in the gas report?

[zerosnacks]

Able to reproduce with given setup, values have remained the same since the report