Ethereum EVM Explained: A Comprehensive Guide to Ethereum Virtual Machine

Ethereum Virtual Machine (EVM) is the runtime environment for executing smart contracts on the Ethereum blockchain. This guide dives deep into how EVM processes transactions, manages gas fees, and executes contract operations.

How EVM Processes Transactions

When a transaction is submitted to Ethereum, it undergoes the following steps:

1. Transaction Conversion: The transaction is converted into a Message object and passed to the EVM for execution.

2. Execution Types:

   • For simple transfers: Directly updates account balances in the StateDB.
   • For smart contracts: EVM's interpreter loads and executes bytecode, potentially querying or modifying the StateDB.

1. Intrinsic Gas: Fixed Transaction Costs

Every transaction incurs a base gas fee:

• Standard transfers: 21,000 gas (no payload data).

• Smart contracts: Additional fees apply for payload data:

  • Zero-byte: 4 gas per byte.
  • Non-zero byte: 68 gas per byte.

Optimization Tip: Minimize non-zero bytes in contract data to reduce gas costs.

2. Contract Object Creation

The EVM generates a Contract object from the Message:

• Loads contract code from StateDB using the contract address.
• Sets execution gas limits based on the block's GasLimit configuration.

3. Interpreter Execution Workflow

EVM operates as a stack-based virtual machine with four core components:

• PC (Program Counter): Tracks the current instruction.
• Stack: 256-bit width, max depth of 1,024.
• Memory: Temporary data storage.
• Gas Pool: Tracks remaining execution budget.

Execution Flow:

1. Fetch OpCode (1-byte instruction) from contract code.
2. Retrieve corresponding operation from a JumpTable.
3. Deduct gas cost; fail if insufficient.
4. Execute instruction (modifies stack, memory, or StateDB).

Example: PUSH1 (0x60) pushes data to the stack; MSTORE (0x52) writes to memory.

4. Calling Contract Functions

Function calls are identified by 4-byte signatures in transaction input:

• First 4 bytes: Keccak-256 hash of the function signature (e.g., 0x87db03b7 for add(uint256)).
• Remaining bytes: Function arguments.

Function Selection Logic:

• Compiler prepends bytecode with a dispatcher.
• Uses CALLDATALOAD to compare signatures and jump to matched functions.

5. Data Loading Instructions

Four key instructions for data handling:

• CALLDATALOAD: Loads input to stack.
• CALLDATACOPY: Copies input to memory.
• CODECOPY: Copies current contract code to memory.
• EXTCODECOPY (rare): Copies external contract code (for audits).

6. Contract-to-Contract Calls

Four call methods with distinct behaviors:

• CALL: Creates new execution context (default).
• CALLCODE: Shares caller’s storage.
• DELEGATECALL: Preserves original msg.sender.
• STATICALL: Prevents state modifications.

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7. Contract Creation

Deploying a contract involves:

1. Address Generation: Keccak256(RLP(sender_address, nonce))[12:] (20-byte address).
2. State Object Creation: Stores code and initializes storage trie.
3. Immutable Code: Once deployed, code cannot be modified (though storage can via SSTORE).

8. Gas Calculation Rules

Gas costs follow Ethereum Yellow Paper specifications (see core/vm/gas.go). Key factors:

• Base fees per opcode.
• Memory expansion costs.
• Storage operation fees.

FAQs

Q1: Why does EVM use gas fees?

Gas prevents infinite loops and spam, ensuring network stability by pricing computational resources.

Q2: How can I reduce contract gas costs?

• Optimize bytecode (minimize non-zero bytes).
• Use cheaper opcodes (e.g., SSTORE over MSTORE).
• Batch transactions.

Q3: What happens if a transaction runs out of gas?

Execution reverts, but the sender still pays the gas consumed up to the failure point.

Q4: Can EVM execute non-Ethereum contracts?

No—EVM is Ethereum-specific, though compatible chains (e.g., Polygon) reuse its design.

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Next Chapter: Ethereum Address Generation Algorithm
Learn how Ethereum addresses derive from public keys and Keccak-256 hashing.

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