LOG4 (0xa4) - Voltaire

This page is a placeholder. All examples on this page are currently AI-generated and are not correct. This documentation will be completed in the future with accurate, tested examples.

Overview

Opcode: 0xa4 Introduced: Frontier (EVM genesis) LOG4 emits a log entry with four indexed topics, the maximum allowed. This enables filtering events with up to four indexed parameters, supporting complex multi-dimensional queries like buyer-seller-token-amount combinations.

Specification

Stack Input:

offset (top)
length
topic0
topic1
topic2
topic3

Stack Output:

(none)

Gas Cost: 375 + (4 × 375) + (8 × data_length) + memory_expansion_cost Operation:

data = memory[offset : offset + length]
topic0 = stack.pop()
topic1 = stack.pop()
topic2 = stack.pop()
topic3 = stack.pop()
log_entry = { address: msg.sender, topics: [topic0, topic1, topic2, topic3], data: data }
append log_entry to logs

Behavior

LOG4 pops six values from the stack:

Offset: Starting position in memory (256-bit value)
Length: Number of bytes to read from memory (256-bit value)
Topic0: First indexed parameter (256-bit value)
Topic1: Second indexed parameter (256-bit value)
Topic2: Third indexed parameter (256-bit value)
Topic3: Fourth indexed parameter (256-bit value)

This represents the maximum topic capacity, enabling four-dimensional filtering without on-chain computation.

Topic Values

All four topics are preserved as full 256-bit values. For dynamic types, keccak256 hashes are used.

Memory Expansion

Memory expands in 32-byte word increments with proportional gas costs.

Static Call Protection

LOG4 cannot execute in static call context (EIP-214).

Examples

Complex Event with Four Dimensions

import { handler_0xa4_LOG4 } from '@tevm/voltaire/evm/log';

const frame = createFrame({
  address: "0x1234567890123456789012345678901234567890",
  stack: [
    0xdddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddn,  // topic3
    0xccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccn,  // topic2
    0xbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbn,  // topic1
    0xaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaan,  // topic0
    0n,  // length
    0n,  // offset
  ],
  gasRemaining: 1000000n,
});

const err = handler_0xa4_LOG4(frame);
console.log(err); // null (success)
console.log(frame.logs[0].topics.length); // 4
console.log(frame.gasRemaining);
// 999000n - 375 (base) - 1500 (4 topics)

Marketplace Event with Full Metadata

const frame = createFrame({
  address: "0xmarketplace",
  memory: new Map([
    [0, 0x00], [1, 0x00], [2, 0x00], [3, 0x00],  // Price/metadata
  ]),
  stack: [
    0xtoken_id,
    0xcurrency_type,
    0xseller,
    0xbuyer,
    4n,    // length
    0n,    // offset
  ],
  gasRemaining: 1000000n,
});

handler_0xa4_LOG4(frame);

const log = frame.logs[0];
console.log(log.topics.length); // 4
console.log(log.topics);
// [buyer, seller, currency_type, token_id]

Order Book Entry

event OrderCreated(
  address indexed maker,
  address indexed taker,
  address indexed baseToken,
  address indexed quoteToken,
  uint256 amount
);

contract OrderBook {
  function createOrder(
    address taker,
    address baseToken,
    address quoteToken,
    uint256 amount
  ) public {
    uint256 orderId = nextOrderId++;
    orders[orderId] = Order({
      maker: msg.sender,
      taker: taker,
      baseToken: baseToken,
      quoteToken: quoteToken,
      amount: amount
    });

    // Compiler generates LOG4
    emit OrderCreated(msg.sender, taker, baseToken, quoteToken, amount);
  }
}

MultiHop Swap Event

event Swap(
  address indexed user,
  address indexed tokenIn,
  address indexed tokenOut,
  address indexed pool,
  uint256 amountIn
);

contract MultiHopDEX {
  function swapMultiHop(
    address[] calldata path,
    uint256 amountIn
  ) external {
    require(path.length >= 2, "Invalid path");

    address tokenIn = path[0];
    address tokenOut = path[path.length - 1];

    // Swap through each pool
    for (uint i = 0; i < path.length - 1; i++) {
      address pool = getPool(path[i], path[i + 1]);
      amountIn = executeSwap(pool, path[i], path[i + 1], amountIn);

      // LOG4: user, tokenIn, tokenOut, pool, amountIn
      emit Swap(msg.sender, path[i], path[i + 1], pool, amountIn);
    }
  }
}

Cross-Chain Bridge Event

event BridgeTransfer(
  address indexed sender,
  address indexed recipient,
  address indexed token,
  uint256 chainId,
  uint256 amount
);

contract Bridge {
  function bridgeTransfer(
    uint256 destChain,
    address recipient,
    address token,
    uint256 amount
  ) public {
    require(supportedChains[destChain], "Unsupported chain");

    bridges[msg.sender][token][destChain] += amount;
    escrow.lock(token, amount);

    // LOG4: all 4 key parameters are indexed
    emit BridgeTransfer(msg.sender, recipient, token, destChain, amount);
  }
}

Permission Grant Event

event PermissionGrant(
  address indexed grantor,
  address indexed grantee,
  address indexed resource,
  uint256 roleId,
  uint256 permissions
);

contract AccessControl {
  function grantPermission(
    address grantee,
    address resource,
    uint256 roleId,
    uint256 permissions
  ) public {
    require(hasAdmin(msg.sender), "Not admin");

    rolePermissions[grantee][resource][roleId] = permissions;

    // LOG4: all parameters indexed for fine-grained filtering
    emit PermissionGrant(msg.sender, grantee, resource, roleId, permissions);
  }
}

Gas Cost

Base Cost: 375 gas Topic Cost: 375 gas per topic = 1500 gas (for 4 topics) Data Cost: 8 gas per byte Memory Expansion: Proportional to new memory range Examples:

Empty data: 375 + 1500 = 1875 gas
1 byte: 1875 + 8 = 1883 gas
32 bytes: 1875 + 256 = 2131 gas
64 bytes: 1875 + 512 + 3 = 2390 gas
256 bytes: 1875 + 2048 + 6 = 3929 gas
1024 bytes: 1875 + 8192 + 15 = 10082 gas

Edge Cases

All Topics Identical

const topic = 0x1234567890abcdef1234567890abcdef1234567890abcdef1234567890abcdefn;
const frame = createFrame({
  stack: [topic, topic, topic, topic, 0n, 0n],
  gasRemaining: 1000000n,
});
handler_0xa4_LOG4(frame);
const log = frame.logs[0];
console.log(log.topics); // [topic, topic, topic, topic]

Mixed Topic Values

const frame = createFrame({
  stack: [
    (1n << 256n) - 1n,     // Max
    0xaabbccddaabbccddaabbccddaabbccddaabbccddaabbccddaabbccddaabbccddne, // Mixed
    0x1111111111111111111111111111111111111111111111111111111111111111n,   // Custom
    0n,                    // Min
    0n,                    // length
    0n,                    // offset
  ],
  gasRemaining: 1000000n,
});
handler_0xa4_LOG4(frame);
const log = frame.logs[0];
// Topics preserved exactly as provided

Large Data with Maximum Topics

const frame = createFrame({
  stack: [
    0xfff, 0xfff, 0xfff, 0xfff,
    10000n,  // length
    0n,      // offset
  ],
  gasRemaining: 100000n,
});
const err = handler_0xa4_LOG4(frame);
// Gas: 1875 + 80000 (data) + memory expansion
// Result: OutOfGas

Stack Underflow

const frame = createFrame({ stack: [0n, 0n, 0n, 0n, 0n] });  // Only 5 items
const err = handler_0xa4_LOG4(frame);
console.log(err); // { type: "StackUnderflow" }

Out of Gas

const frame = createFrame({
  stack: [0xfff, 0xfff, 0xfff, 0xfff, 0n, 0n],
  gasRemaining: 1874n,  // Not enough for base + all topics
});
const err = handler_0xa4_LOG4(frame);
console.log(err); // { type: "OutOfGas" }

Common Usage

Four-Dimensional Event Filtering

event Transaction(
  address indexed user,
  address indexed from,
  address indexed to,
  bytes32 indexed txId,
  uint256 amount
);

contract Router {
  function route(address from, address to, bytes32 txId, uint256 amount) public {
    // ... routing logic
    emit Transaction(msg.sender, from, to, txId, amount);  // LOG4
  }
}

Off-chain filtering:

// Listen for transactions by a specific user and pair
const logs = await provider.getLogs({
  address: router.address,
  topics: [
    keccak256("Transaction(address,indexed address,indexed address,indexed bytes32,uint256)"),
    "0xuser_address",
    "0xfrom_address",
    "0xto_address",
    // txId can also be filtered here if needed
  ]
});

Dimensional Data Warehouse

event DataPoint(
  uint256 indexed dimension1,
  uint256 indexed dimension2,
  uint256 indexed dimension3,
  uint256 indexed dimension4,
  bytes value
);

contract DataWarehouse {
  function logDataPoint(
    uint256 d1,
    uint256 d2,
    uint256 d3,
    uint256 d4,
    bytes memory value
  ) public {
    emit DataPoint(d1, d2, d3, d4, value);  // LOG4
  }
}

Maximum Filtering Capability

// When all 4 topics are indexed, off-chain systems can efficiently:
// 1. Filter by any subset of topics
// 2. Combine filters with AND logic
// 3. Query without parsing event data

event MultiFilter(
  address indexed a,
  address indexed b,
  address indexed c,
  bytes32 indexed d
);

Security

Topic Visibility and Privacy

All topics are visible off-chain. Maximum topics = maximum visibility:

// All 4 parameters are filterable, searchable, and visible
event BadPractice(
  address indexed user,
  address indexed password,        // DO NOT: hashed passwords in topics
  address indexed privateKey,      // DO NOT: sensitive keys
  address indexed secret           // DO NOT: confidential data
);

// BETTER: Hash sensitive values
event GoodPractice(
  address indexed user,
  bytes32 passwordHash,            // Hash sensitive data
  bytes32 keyHash,
  bytes32 secretHash
);

Filtering Logic

Ensure consistent topic interpretation:

// Standard pattern: indexed parameters in function signature order
event Action(
  address indexed user,
  address indexed resource,
  address indexed operator,
  uint256 timestamp
);

// Off-chain filtering uses topics in same order:
// topics[0] = event signature hash
// topics[1] = user
// topics[2] = resource
// topics[3] = operator
// topics[4] = timestamp

Static Call Context

LOG4 reverts in view/pure functions:

// WRONG: Reverts in static context
function badView(address a, address b, address c, bytes32 d) external view {
  emit Event(a, b, c, d);
}

// CORRECT: State-changing function
function goodNonView(address a, address b, address c, bytes32 d) external {
  emit Event(a, b, c, d);
}

Implementation

TypeScript

/**
 * LOG4 opcode (0xa4) - Emit log with 4 indexed topics (maximum)
 */
export function handler_0xa4_LOG4(frame: FrameType): EvmError | null {
  if (frame.isStatic) {
    return { type: "WriteProtection" };
  }

  if (frame.stack.length < 6) {
    return { type: "StackUnderflow" };
  }

  const offset = frame.stack.pop();
  const length = frame.stack.pop();
  const topic0 = frame.stack.pop();
  const topic1 = frame.stack.pop();
  const topic2 = frame.stack.pop();
  const topic3 = frame.stack.pop();

  if (offset > Number.MAX_SAFE_INTEGER || length > Number.MAX_SAFE_INTEGER) {
    return { type: "OutOfBounds" };
  }

  const offsetNum = Number(offset);
  const lengthNum = Number(length);

  // Gas: 375 base + 1500 topics + 8 per byte data
  const logGas = 375n + 1500n;
  const dataGas = BigInt(lengthNum) * 8n;
  const totalGas = logGas + dataGas;

  // Memory expansion
  if (lengthNum > 0) {
    const endByte = offsetNum + lengthNum;
    const newMemWords = Math.ceil(endByte / 32);
    const newMemSize = newMemWords * 32;
    const memExpansion = calculateMemoryExpansion(frame.memorySize, newMemSize);
    frame.memorySize = newMemSize;
    frame.gasRemaining -= BigInt(memExpansion);
  }

  frame.gasRemaining -= totalGas;
  if (frame.gasRemaining < 0n) {
    return { type: "OutOfGas" };
  }

  // Read data
  const data = new Uint8Array(lengthNum);
  for (let i = 0; i < lengthNum; i++) {
    data[i] = frame.memory.get(offsetNum + i) ?? 0;
  }

  // Create log entry
  const logEntry = {
    address: frame.address,
    topics: [topic0, topic1, topic2, topic3],
    data,
  };

  if (!frame.logs) frame.logs = [];
  frame.logs.push(logEntry);

  frame.pc += 1;
  return null;
}

Testing

import { describe, it, expect } from 'vitest';
import { handler_0xa4_LOG4 } from './0xa4_LOG4.js';

describe('LOG4 (0xa4)', () => {
  it('emits log with 4 topics and empty data', () => {
    const topic0 = 0xaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaan;
    const topic1 = 0xbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbn;
    const topic2 = 0xccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccn;
    const topic3 = 0xdddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddn;
    const frame = createFrame({
      stack: [topic3, topic2, topic1, topic0, 0n, 0n],
      gasRemaining: 1000000n,
    });
    const err = handler_0xa4_LOG4(frame);
    expect(err).toBeNull();
    expect(frame.logs).toHaveLength(1);
    expect(frame.logs[0].topics).toEqual([topic0, topic1, topic2, topic3]);
    expect(frame.gasRemaining).toBe(998125n);
  });

  it('emits log with 4 topics and data', () => {
    const frame = createFrame({
      memory: new Map([[0, 0xde], [1, 0xad], [2, 0xbe], [3, 0xef]]),
      stack: [0x4444n, 0x3333n, 0x2222n, 0x1111n, 4n, 0n],
      gasRemaining: 1000000n,
    });
    handler_0xa4_LOG4(frame);
    const log = frame.logs[0];
    expect(log.topics).toEqual([0x1111n, 0x2222n, 0x3333n, 0x4444n]);
    expect(log.data).toEqual(new Uint8Array([0xde, 0xad, 0xbe, 0xef]));
  });

  it('returns WriteProtection in static context', () => {
    const frame = createFrame({ isStatic: true, stack: [0n, 0n, 0n, 0n, 0n, 0n] });
    const err = handler_0xa4_LOG4(frame);
    expect(err).toEqual({ type: "WriteProtection" });
  });

  it('returns StackUnderflow with 5 items', () => {
    const frame = createFrame({ stack: [0n, 0n, 0n, 0n, 0n] });
    const err = handler_0xa4_LOG4(frame);
    expect(err).toEqual({ type: "StackUnderflow" });
  });

  it('handles boundary topic values', () => {
    const max = (1n << 256n) - 1n;
    const frame = createFrame({
      stack: [max, 0n, max, 0n, 0n, 0n],
      gasRemaining: 1000000n,
    });
    handler_0xa4_LOG4(frame);
    expect(frame.logs[0].topics).toEqual([0n, max, 0n, max]);
  });

  it('expands memory correctly with large data', () => {
    const frame = createFrame({
      stack: [0xffff, 0xffff, 0xffff, 0xffff, 1000n, 0n],
      gasRemaining: 100000n,
    });
    handler_0xa4_LOG4(frame);
    // Memory expands to cover offset 0 + length 1000 = 1000 bytes
    // Word-aligned to 1024 bytes (32 words * 32)
    expect(frame.memorySize).toBe(1024);
  });
});

References

LOG4 Instruction (evm.codes)
EIP-214: New opcode STATICCALL
Solidity Events with Four Indexed Parameters
Yellow Paper - Section 9.4.1 (Logging)
Event Indexing Best Practices

​Overview

​Specification

​Behavior

​Topic Values

​Memory Expansion

​Static Call Protection

​Examples

​Complex Event with Four Dimensions

​Marketplace Event with Full Metadata

​Order Book Entry

​MultiHop Swap Event

​Cross-Chain Bridge Event

​Permission Grant Event

​Gas Cost

​Edge Cases

​All Topics Identical

​Mixed Topic Values

​Large Data with Maximum Topics

​Stack Underflow

​Out of Gas

​Common Usage

​Four-Dimensional Event Filtering

​Dimensional Data Warehouse

​Maximum Filtering Capability

​Security

​Topic Visibility and Privacy

​Filtering Logic

​Static Call Context

​Implementation

​Testing

​References

Overview

Specification

Behavior

Topic Values

Memory Expansion

Static Call Protection

Examples

Complex Event with Four Dimensions

Marketplace Event with Full Metadata

Order Book Entry

MultiHop Swap Event

Cross-Chain Bridge Event

Permission Grant Event

Gas Cost

Edge Cases

All Topics Identical

Mixed Topic Values

Large Data with Maximum Topics

Stack Underflow

Out of Gas

Common Usage

Four-Dimensional Event Filtering

Dimensional Data Warehouse

Maximum Filtering Capability

Security

Topic Visibility and Privacy

Filtering Logic

Static Call Context

Implementation

Testing

References