EVM/Bytecode Analysis Skill

Expert-level EVM bytecode analysis and decompilation for smart contract security audits, gas optimization, and reverse engineering.

Capabilities

• Bytecode Analysis: Analyze EVM bytecode and opcodes
• Gas Cost Calculation: Calculate gas costs per operation
• Storage Layout Identification: Identify storage slot layouts and packing
• Decompilation: Decompile bytecode to pseudo-Solidity
• Proxy Analysis: Analyze proxy implementation slots (EIP-1967)
• Pattern Detection: Detect bytecode patterns (CREATE2, selfdestruct)
• Bytecode Verification: Verify contract bytecode against source

MCP Server Integration

This skill can leverage the following MCP servers:

Server	Purpose	Install
EVM MCP Tools	Smart contract auditing, security analysis	0xGval/evm-mcp-tools
Solidity Contract Analyzer	Contract code analysis with metadata	Skywork

Opcode Reference

Common EVM opcodes and gas costs:

Category	Opcodes	Base Gas
Arithmetic	ADD, SUB, MUL, DIV	3-5
Comparison	LT, GT, EQ, ISZERO	3
Bitwise	AND, OR, XOR, NOT, SHL, SHR	3
Memory	MLOAD, MSTORE	3 + memory expansion
Storage	SLOAD	100 (warm) / 2100 (cold)
Storage	SSTORE	100-20000 (varies)
Control	JUMP, JUMPI	8-10
Call	CALL, DELEGATECALL, STATICCALL	100 + memory + value

Storage Layout Analysis

Standard Slot Patterns

// Basic types (slot 0, 1, 2...)
uint256 public a;     // slot 0
uint256 public b;     // slot 1

// Packed storage
uint128 public c;     // slot 2, bytes 0-15
uint128 public d;     // slot 2, bytes 16-31

// Mappings: keccak256(key . slot)
mapping(address => uint256) public balances;  // slot 3
// balances[addr] at keccak256(addr . 3)

// Dynamic arrays: length at slot, data at keccak256(slot)
uint256[] public arr; // length at slot 4, arr[i] at keccak256(4) + i

EIP-1967 Proxy Slots

Implementation: 0x360894a13ba1a3210667c828492db98dca3e2076cc3735a920a3ca505d382bbc
Admin:          0xb53127684a568b3173ae13b9f8a6016e243e63b6e8ee1178d6a717850b5d6103
Beacon:         0xa3f0ad74e5423aebfd80d3ef4346578335a9a72aeaee59ff6cb3582b35133d50

Bytecode Patterns

Contract Creation

PUSH1 0x80          // Free memory pointer
PUSH1 0x40
MSTORE
...
CODECOPY            // Copy runtime code
RETURN              // Return runtime code

Selector Dispatch

PUSH4 <selector>    // 4-byte function selector
EQ                  // Compare with calldata[0:4]
PUSH2 <offset>      // Jump destination
JUMPI               // Jump if match

Common Vulnerability Patterns

// Reentrancy indicator: CALL before SSTORE
CALL
...
SSTORE

// Unchecked return: CALL without ISZERO check
CALL
// Missing: ISZERO, JUMPI for error handling

// Self-destruct (deprecated but detectable)
SELFDESTRUCT

Workflow

1. Fetch Contract Bytecode

# Using cast (Foundry)
cast code <address> --rpc-url <rpc>

# Using curl
curl -X POST <rpc> \
  -H "Content-Type: application/json" \
  -d '{"jsonrpc":"2.0","method":"eth_getCode","params":["<address>","latest"],"id":1}'

2. Analyze Opcodes

# Disassemble with cast
cast disassemble <bytecode>

# Or use online tools
# - evm.codes/playground
# - ethervm.io/decompile

3. Storage Slot Analysis

# Read specific storage slot
cast storage <address> <slot> --rpc-url <rpc>

# Read EIP-1967 implementation slot
cast storage <address> 0x360894a13ba1a3210667c828492db98dca3e2076cc3735a920a3ca505d382bbc --rpc-url <rpc>

4. Bytecode Comparison

# Get deployed bytecode
cast code <address> --rpc-url <rpc> > deployed.bin

# Compile source and compare
forge build
diff deployed.bin out/Contract.sol/Contract.bin

Process Integration

This skill integrates with the following processes:

• gas-optimization.js - Identify gas-heavy opcodes
• smart-contract-security-audit.js - Bytecode-level vulnerability detection
• smart-contract-upgrade.js - Proxy slot verification
• formal-verification.js - Bytecode correctness verification

Tools Reference

Tool	Purpose	URL
Foundry Cast	CLI bytecode interaction	foundry-rs/foundry
evm.codes	Opcode reference	evm.codes
Dedaub	Decompiler	dedaub.com
Heimdall	Advanced decompiler	heimdall-rs
panoramix	Python decompiler	eveem.org

Example Analysis

// Analyze proxy contract
const analysis = {
  type: 'proxy',
  pattern: 'EIP-1967 Transparent',
  implementation: '0x...',
  admin: '0x...',

  // Storage layout
  storageSlots: {
    0: { name: '_initialized', type: 'uint8' },
    1: { name: '_initializing', type: 'bool' },
    // ...
  },

  // Function selectors
  selectors: {
    '0xa9059cbb': 'transfer(address,uint256)',
    '0x23b872dd': 'transferFrom(address,address,uint256)',
    // ...
  },

  // Gas hotspots
  gasHotspots: [
    { offset: 0x1a4, opcode: 'SSTORE', context: 'balance update' },
    { offset: 0x2f0, opcode: 'CALL', context: 'external call' }
  ]
};

See Also

• skills/gas-optimization/SKILL.md - Gas optimization techniques
• agents/solidity-auditor/AGENT.md - Security audit agent
• references.md - External resources