TracEVM

This tool is used to track the values and addresses of slots (storage variables in Solidity) inside the Ethereum contract, as well as tracking logs (Solidity events).

• Partial symbolic execution provides the complete data on how a specific variable or slot address was calculated
• Suitable for learning about Solidity internals
• Written in Go and Python

Building

Python and Flask are required to run the web view.

pip3 install Flask

Additionally, Geth prerequisites are required to compile Geth.

Finally, it is possible to build TracEVM.

./build.py

Running

To open webview on address 127.0.0.1:4334 run the following command.

./run.py conf.json

TracEVM will be running!

Connecting with Remix

It is expected to have Remix installed.

Choose External HTTP Provider

Connect by default address.

Usage example

Let's imagine we have such contract.

Let's deploy the contract and see the output.

We see that:

• event type is final_slot, which means that this slot was written at the end of transaction (not reverted).
• further we see slot offsets (constant - initial slot, mapping - solidity keccak mapping magic, offset - offset from last value)
• short slot formula, which shows all cryptographic operations which were performed with slot

Also there is a full formula, which computes all needed data from initial initcode (or calldata).

Found bug?

Please open an issue and supply solidity code that produced unexpected behaviour.