bug: cfg graph starts from offset 0x01 instead of 0x00

[alessandromazza98]

Component

Heimdall (Core)

Have you ensured that you are up to date?

• Bifrost
• Heimdall

What version of Heimdall are you on?

heimdall 0.8.4

Operating System

macOS (Apple Silicon)

Describe the bug

I'm generating the cfg of a very simple contract to try heimdall.

everything works fine but I don't understand why heimdall uses offset in the bytecode starting from 0x01 instead of 0x00.

This creates some confusion because, take the example I have in the image, the first block has a jumpi that should point to 0x20. But heimdall shows the jumpdest at offset 0x21 (because of the shifts of the offset). While at offset 0x20 heimdall shows a different opcode (JUMP in this example).

The contract:

// SPDX-License-Identifier: GPL-3.0
pragma solidity 0.8.27;
contract Faucet {
  // Give out ether to anyone who asks
  function withdraw(uint256 _withdrawAmount, address payable _to) public {
    // Limit withdrawal amount
    require(_withdrawAmount <= 1000000000000);
    // Send the amount to the address that requested it
    _to.transfer(_withdrawAmount);
  }
  fallback() external payable {}
}

I took the runtime bytecode through solc and gave it to heimdall cfg

The graph:

tg discussion here: https://t.me/heimdallsupport/388