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It's easy enough to grab the data at any storage location of a contract, but we need to know the state variable declarations/storage layout of the contract to know what we're doing and how to interpret the data.

How can I programmatically find out the state variable declarations/storage layout for a contract?

I'd like to make a storage explorer type tool and being able to determine the storage layout of a contract is a game changer.

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5
  • Well, any contact published on the network should have it's code public, and from there (its code) you should be able to understand it's storage layout. Right?
    – Sky
    Commented Jul 16, 2022 at 21:40
  • that is a manual process, not determining the storage layout programmatically. A tool would be even more useful if it could figure out the storage layout for a contract didn't have the contacts source code available
    – sola24
    Commented Jul 17, 2022 at 8:12
  • Hmm, it should be possible (after all , the code published on Blockchain is publicly available). But I had heard of no tool that can do that. Good question.
    – Sky
    Commented Jul 17, 2022 at 8:47
  • It does not satisfy all the requirements (needs the contract source), but it may be helpful nonetheless: github.com/tintinweb/smart-contract-inspector
    – shamisen
    Commented Jul 20, 2022 at 22:30
  • You could also pretty easily write a script to read all the transactions made to a contract and play all the storage events.
    – Patrick Collins
    Commented Jul 24, 2022 at 23:13

1 Answer 1

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If a contract is written in Solidity entirely, then it should follow the storage layout rules. We can implement the logic ourselves, or use the output from solc:

% solc --storage-layout /tmp/A.sol | tail -1 | jq .
{
  "storage": [
    {
      "astId": 4,
      "contract": "/tmp/A.sol:A",
      "label": "x",
      "offset": 0,
      "slot": "0",
      "type": "t_uint64"
    },
    {
      "astId": 7,
      "contract": "/tmp/A.sol:A",
      "label": "y",
      "offset": 8,
      "slot": "0",
      "type": "t_uint128"
    },

A decompiler might be helpful if the source is not available.

If the author uses assembly / inline assembly, then the contract may not follow any layout rules. For example,

PUSH1 42
TIMESTAMP
SSTORE

this code will write 42 to the storage slot pointed by the timestamp.

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  • I tried to run this command and it gives me an error unrecognised option '--storage-layout' . I ran it without the tail command as a I am on windows. Is there any other way you can suggest?? for windows
    – Zartaj Afser
    Commented May 17, 2023 at 17:47

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