Decoding Storage From trace_call (stateDiff)

Question

I am using Erigon. I am using pendent transactions of swap in goerli, this is an output from trace_call (stateDiff):

{
  "output": "0x",
  "stateDiff": {
    "0x07865c6e87b9f70255377e024ace6630c1eaa37f": {
      "balance": "=",
      "code": "=",
      "nonce": "=",
      "storage": {
        "0x03e5bce0671ceb85a9355530f54e34b1e23f58e03b8a4bb2dac84399d45da206": {
          "*": {
            "from": "0x0000000000000000000000000000000000000000000000000000000000000000",
            "to": "0x0000000000000000000000000000000000000000000000000000000003107bda"
          }
        },
        "0xfb16c5559f3de6ff269cf27b0716d0aae93e66f8a2b0c58671322b7b60443200": {
          "*": {
            "from": "0x000000000000000000000000000000000000000000000000000000029bd018e6",
            "to": "0x0000000000000000000000000000000000000000000000000000000298bf9d0c"
          }
        }
      }
    },...

it is clear that 0x07865c6e87b9f70255377e024ace6630c1eaa37f is the address of USDC token. In the "storage" field, i suppose, are the changes in balances of the trader wallet (0x9a5b87993c80eead6260438149b43eec081483ae) and the pool contract (0xfae941346ac34908b8d7d000f86056a18049146e).

How to decode the values "0x03e5bce0671ceb85a9355530f54e34b1e23f58e03b8a4bb2dac84399d45da206" and "0xfb16c5559f3de6ff269cf27b0716d0aae93e66f8a2b0c58671322b7b60443200", which are fields of "storage"?

OBS: The ABI is publicly available in https://goerli.etherscan.io/address/0x07865c6e87b9f70255377e024ace6630c1eaa37f#code.

score 1 · Accepted Answer · answered Jan 27 '23 at 15:59

1

0x03e5bce0671ceb85a9355530f54e34b1e23f58e03b8a4bb2dac84399d45da206 and 0xfb16c5559f3de6ff269cf27b0716d0aae93e66f8a2b0c58671322b7b60443200 should be the storage slots on the smart contract where the data has been modified so

        "0x03e5bce0671ceb85a9355530f54e34b1e23f58e03b8a4bb2dac84399d45da206": {
          "*": {
            "from": "0x0000000000000000000000000000000000000000000000000000000000000000",
            "to": "0x0000000000000000000000000000000000000000000000000000000003107bda"
          }
        },

would mean that at the storage location 0x03e5bce0671ceb85a9355530f54e34b1e23f58e03b8a4bb2dac84399d45da206 the value has been changed from 0x0000000000000000000000000000000000000000000000000000000000000000 to 0x0000000000000000000000000000000000000000000000000000000003107bda.

That along with the next storage location change (0xfb16c5559f3de6ff269cf27b0716d0aae93e66f8a2b0c58671322b7b60443200) result in the state change of 0x07865c6e87b9f70255377e024ace6630c1eaa37f.

They are hex values and you can write programs in solidity or js that read out the value of a particular storage slot in a contract at a given transaction.

answered Jan 27 '23 at 15:59

shankar

109
3

thanks, it help a bit, but those storages are values in a mapping of balances in a ERC20 contract, i'd like to calculate wich is the storage of address 0xabc... – Rafael Jan 27 '23 at 16:13
do you mean the storage slot for a particular address's token balance? – shankar Jan 27 '23 at 16:19
yes, i suppose those storages are from a balance mapping, so yes – Rafael Jan 27 '23 at 16:20
ok so what you can do is:
```
`bytes32 read_slot_data = keccak256(abi.encode(_addr, slot));`

`assembly {
    result := sload(read_slot_data)
} `
```
where slot is the position of the variable in the code. so if the contract has mapping(address => uint) A; and mapping(address => uint) B;

then A would be at slot0 and B at slot1
– shankar Jan 27 '23 at 16:50
so you would have to find the slot number of the mapping you're interested in reading out – shankar Jan 27 '23 at 16:55
what does means assembly { result := sload(read_slot_data) }? Is this js? I can not translate it to js – Rafael Jan 27 '23 at 17:36
oh its not javascript its solidity assembly code. check https://ethereum.stackexchange.com/questions/133473/how-to-calculate-the-location-index-slot-in-storage-of-a-mapping-key out, I think its what you want – shankar Jan 27 '23 at 17:58

Decoding Storage From trace_call (stateDiff)

1 Answers1