Obtain contract storage?

[andrevidela]

Hi there,

I've been using HEVM with concrete execution to run some of the lido contracts, and I am trying to extract the amount of locked steth after calling "lockStETH", as far as I understand, this value is held in this field which itself is a reference to this struct which contains the total amount of locked StETH which is what I'm after.

After loading up the contract and sending my transaction, I lookup the contracts field the env and I get a value of type Contract. This record has multiple storage fields but all of them are empty. Is there a way to access the stETHTotals from a value of type Contract? Is there another way to do it?

[msooseth]

Hi,

Hmmm... I think storage in Contract should contain a ConcreteStore :: (Map W256 W256) -> Expr Storage, i.e. Map, which should contain all the elements you are looking for. The _accounting will be Keccak-hashed as a key and then the value will be the thing you are looking for. My only thought is that maybe you are:

1. Looking at the data at the wrong time. If the call e.g. reverts, then after the call is completed, the values will not be there.
2. Looking at the wrong contract. It may be that Lido creates many contracts on initialization, and the one you are looking for is at another address. Maybe you can check the address of the contract if it matches what you are expecting.

Have you tried dumping the whole env (with show env) and then trying to grep for the field name (Keccak'ed of course)? I think that might just do the trick :)

[andrevidela]

Thanks for the pointers, I'll try dumping env :)

[andrevidela]

I tried dumping env and grepping for the keccak's _accounting but got nothing. I think it's because the show instance for the contracts escape bytes and so we get \155 instead of hex. I also might have done something wrong with the hashing, I just hashed the string _accounting but maybe there is some offset that needs to be computed?
I'm also very confident I'm looking at the right contract. But I'm not quite sure if the transaction reverted or not. I'll double check again tomorrow

[msooseth]

Ah okay, if you give me a little time, I'll look into this in the evening :) I think Format.hs has some much nicer printing, using that with putStrLn $ T.unpack (formatWhatever env) is probably gonna give you sooo much nicer printing. I'll look into what it should look like when it's hashed :)

[andrevidela]

I have to be away until Friday. I think the contract is reverting but I'm not sure why. Is there a way to get the reason why it reverted or a trace of what happened? I'm using exec1 to run the VM step by step until I get a result

[msooseth]

Hmmm.. have you tried loading the contract into Remix and debugging it there? It's actually a pretty good system. I know this sounds kinda insane, but it has quite good debug facilities. Since we removed the interactive debug facility, it has become quite hard to do what you are asking. You can run Remix locally, so it should be possible not to leak information into the wild.

The other option is to run with geth and get a so-called trace. Actually... I think we support traces! Yesss we do :) Here:

  --trace                  Dump trace

That should tell you how/when we revert! I think our traces match the geth trace setup, so you should be able to use them just like the geth traces!

I hope the above helps,

Mate

[andrevidela]

Amazing, I'll try this out! Thanks for the help :)

[andrevidela]

Sorry for the silence, I was taken on other project, just got some time today to look at it.

I've tried using showTraceTree between calls to exec1 the VM but I get an empty string every time. This is the initial VM state I start from:

  pure $
    VM
      { result = Nothing,
        state = blankSt,
        frames = [],
        env = envForContracts contracts,
        block = emptyBlock,
        tx = emptyTransaction,
        logs = [],
        traces = Zipper.fromForest mempty,
        cache = Cache mempty mempty,
        burned = 0,
        iterations = mempty,
        constraints = [],
        config =
          RuntimeConfig
            True
            Nothing
            False
            EmptyBase
      }

THis is how I run the VM

run' :: EVM Concrete s (Maybe (Expr Buf), VM Concrete s)
run' = do
  vm <- get
  trace (unpack $ showTraceTree undefined vm) $ case vm.result of
    Nothing -> exec1 >> run'
    Just (HandleEffect (Query (PleaseAskSMT (Lit c) _ cont))) ->
      error "SMT effects not handled"
    Just (VMFailure y) -> pure (trace (show y) Nothing, vm)
    Just (VMSuccess y) -> pure (trace "finish ok" (Just y), vm)

This code works, and in case of failure I can see that the transaction was indeed reverted although it does not give me any information about why.

I haven't tried debugging my contracts with Remix yet, I'll try that next

EDIT: I'm now stuck in a completely unrelated rabbithole: I cannot pull "@openzeppelin/contracts/token/ERC20/ERC20.sol" because HEVM cannot find it dependencies, I'm sure I can figure this one out though