Learning Assembly

It is time to face the final trial, that of The Whisperer. This figure is one of legend. The master of riddles, secrets, and rumors. Every word they speak is true, but that doesn’t mean everyone has the wit to understand them. To pass their trial, prove that you are able to understand that which so many others cannot…

Inline assembly also enables the precise control of calldata. In this quest, learn how to exploit this ability to achieve hidden functionality like implicit call parameters and custom-encoded data.

What is Calldata?

Reading Hidden Calldata

Custom Encoding

The Whisperer falls silent and nods to you. You feel a sense of contentment from him. It has been long since he has met a stranger with the understanding to follow his speech and answer his riddles. 

The fifth Pillar, the Wanderer is the explorer. One who walks the lands in search of new knowledge and secrets.

Behind you, the door to the balcony opens, and the other three Pillars join you to welcome you to their ranks. By passing their trials, you have proven yourself worthy of joining their number. The remaining Pillars gather around to acknowledge their new Wanderer.

It will take some time to learn your new responsibilities and tasks. However, you can relax that your new mantle will not prevent you from continuing to travel the world and seek out the unknown. 

You are led out onto a balcony, the feel of the wind cool on your face as the hood is removed. Only… you were sure you were underground…

At the edge of the balcony stands the Whisperer. Their face is covered by the cowl of their robe, leaving only their mouth exposed. They say nothing to you as you approach. You’ve heard rumors of the Whisperer. Everyone has, although most people believe them to be little more than a myth. Their realm is one of secrets, rumors, and the half-known, but every word that passes their lips is the truth.

You approach, and without preamble, the Whisperer begins to speak, almost too low to hear.

To pass this final trial, you will have to prove you can hear and understand the cryptic words of the Whisperer.

In this quest, we learned about calldata in the context of inline assembly.

To recap, the calldata related instructions are:

We have explored how to support extraneous calldata parameters. This is typically unnecessary and introduces unwanted complexity in your code. However, this can be used to support informal parameters in default functions like <code class="richtext rt-inlinecode">receive()</code> and <code class="richtext rt-inlinecode">fallback()</code>. The proxy pattern actually uses low-level calldata manipulation extensively.

<a class="richtext rt-link" target="_blank" rel="noopener noreferrer" href="https://github.com/Nodeguardians/ng-quests/blob/develop/campaigns/learning-assembly/calldata-manipulation/description/summary.md#supporting-custom-encoding"></a>Supporting custom encoding

Another interesting use case we have explored is to support non-standard encoded parameters. In our hypothetical example, we passed a uint256 array encoded in a compressed format. We then wrote a function that decompresses the data into a standard <code class="richtext rt-inlinecode">uint256[]</code>.

Calldata Manipulation

Here is an odd puzzle for any self-proclaimed EVM master. See if you can build an "Ouroboros", and prove your mastery over low-level bytecode sorcery.

Finding Ouroboros

Starknet contracts support state variables, but how they live in contract storage is generally abstracted away from the typical developer. In this quest, we will take a peek under the hood and see how state variables are stored exactly.

Starknet Storage Layout

Do you know how low-level calls work in Starknet? Or how calldata is encoded? This knowledge could be useful for on-chain sleuthing and some other advanced use cases. 

Learn about the inner workings of calls and calldata in this fun interface spoofing exercise!

Calldata Spoofing

Starknet contract addresses, like in many other blockchains, can be precomputed too. This allows for the creation of vanity addresses.

In this quest, see if you can deploy your smart contract under a specified address pattern...

Vanity Addresses

Can we build an EVM inside of an EVM? That seems like a strange question, but the answer is yes we can! In this quest, we will build a self-hosted EVM (sEVM), squeezed into a single smart contract. By rebuilding the EVM, develop a deeper appreciation of the machine's inner workings and EVM bytecode.