Dive into the instruction set of powerful, general-purpose virtual machines like WebAssembly (WASM) or RISC-V, and you'll find commands for arithmetic, logic, and memory operations â the building blocks of computation. 1 But search for specific opcodes designed to directly read from or write to a blockchain's state, like the EVM's famous SLOAD or SSTORE, and you'll come up empty. This presents a fascinating paradox: if the VMs running smart contracts on many innovative blockchains lack these native state-handling instructions, how do these platforms actually manage the crucial tasks of reading account balances or writing data to contract storage? This post unravels the essential mechanism that bridges the gap between general-purpose computation and blockchain-specific state management.
This VM is not the blockchain, but rather a component of the blockchain
The VM is a powerful component of the blockchain, tasked with state transition function of the blockchain among other features. It is important to note that this VM does not run in Isolation. This engine, be it powered by WASM or RISC-V, doesn't operate in a vacuum. Instead, it thrives within a "host environment," the very blockchain node software itself. This environment provides a set of specialized tools, the Host Functions or APIs, that the VM can utilize. Think of them as bridges, allowing the code within the VM to interact with the broader blockchain ecosystem. These host functions are crucial, as they connect the general-purpose computational capabilities of the VM to the blockchain's unique functionalities, enabling smart contracts to read and write ledger data, interact with other accounts, and ultimately, drive the blockchain's logic.
When a smart contract, compiled into bytecode for a virtual machine (VM) like WASM or RISC-V, needs to interact with the blockchainâwhether to transfer tokens, modify storage, call another contract, or read block informationâit doesnât rely on native VM instructions tailored for those specific actions. Instead, the contract invokes predefined host functions provided by the blockchainâs runtime environment. For example, a function like env.transfer_balance(recipient_address, amount) might be called to send tokens to a recipient, or env.storage_write(key, value) to update the contractâs persistent storage. The VM identifies these as external calls, passing them to the host environment, which securely executes the requested blockchain operation and updates the system state. This design keeps the VM focused on computation while delegating blockchain-specific tasks to the runtime, ensuring both flexibility and security.
When a smart contract executes within a virtual machine (VM), such as WASM or RISC-V, and invokes a blockchain-specific operation, the VMâs execution pauses temporarily. At this point, control shifts to the host environmentâthe blockchain node running the networkâs software. The node takes over, natively executing the requested operation by interpreting the call and interacting with the blockchainâs infrastructure. This process involves accessing the blockchainâs state (e.g., the state trie or database), performing necessary checks (such as verifying an account has sufficient balance for a transaction), and updating relevant data structures like account balances or contract storage tries. All actions adhere strictly to the blockchainâs consensus rules, ensuring consistency and security. Though this execution occurs outside the VMâs core instruction processing, it is seamlessly triggered by the VMâs code, bridging the contractâs logic with the blockchainâs state management.
Returning Control & Results