CODECOPY

CODECOPY is an instruction in the Ethereum Virtual Machine (EVM) that copies code from the contract’s own code space into memory. It takes three stack inputs: memOffset, codeOffset, and length. It copies length bytes starting at codeOffset in the contract’s code into memory starting at memOffset. The operation reads only from code and does not modify storage or the code itself. The opcode is 0x39.

Uses and behavior: In contract creation, the initialization code often uses CODECOPY to copy runtime code into memory and then RETURN it, producing the deployed bytecode. It can also be used in code introspection patterns where a contract reads its own code to influence behavior based on its contents. In general, CODECOPY is a low-level primitive used by compilers and tooling to access code dynamically or to implement self-referential logic.

Semantics and costs: The instruction consumes gas, with the cost influenced by the amount of memory touched and the length of data copied, as memory expansion incurs additional gas. If codeOffset plus length extends beyond the actual code length, the remaining bytes are treated as zeros. CODECOPY does not interact with storage or logs, and its effects are limited to writing to memory and enabling subsequent RETURN or other memory-based operations.

Context: CODECOPY is one of several code-access opcodes in the EVM, alongside others like CODECOPY’s related instructions CODECOPY, CODEHASH, and EXTCODECOPY, each serving different aspects of code access and inspection within smart contracts.