CALLDATACOPY (0x37)

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: 0x37 Introduced: Frontier (EVM genesis) CALLDATACOPY copies a specified range of call data bytes to memory. Out-of-bounds bytes are zero-padded.

Specification

Stack Input:

destOffset (memory offset)
offset (calldata offset)
length (bytes to copy)

Stack Output:

[]

Gas Cost: 3 + memory expansion + (length / 32) * 3 (rounded up) Operation:

destOffset = stack.pop()
offset = stack.pop()
length = stack.pop()
memory[destOffset:destOffset+length] = calldata[offset:offset+length]

Behavior

Copies length bytes from calldata starting at offset to memory starting at destOffset. Zero-pads if calldata bounds exceeded.

Examples

Basic Copy

function copyCalldata() public pure {
    assembly {
        // Copy entire calldata to memory at 0
        calldatacopy(0, 0, calldatasize())
    }
}

Proxy Pattern

fallback() external payable {
    assembly {
        calldatacopy(0, 0, calldatasize())
        let result := delegatecall(gas(), impl, 0, calldatasize(), 0, 0)
        returndatacopy(0, 0, returndatasize())
        switch result
        case 0 { revert(0, returndatasize()) }
        default { return(0, returndatasize()) }
    }
}

Gas Cost

Base: 3 gas Memory expansion: Variable Copy cost: 3 gas per 32-byte word (rounded up)

Common Usage

Forwarding Calls

function forward(address target) public {
    assembly {
        let size := calldatasize()
        calldatacopy(0, 0, size)
        call(gas(), target, 0, 0, size, 0, 0)
    }
}

Security

Bounds Validation

Check offsets don’t overflow when adding length.

Implementation

TypeScript

export function calldatacopy(frame: FrameType): EvmError | null {
  const destOffsetResult = popStack(frame);
  if (destOffsetResult.error) return destOffsetResult.error;

  const offsetResult = popStack(frame);
  if (offsetResult.error) return offsetResult.error;

  const lengthResult = popStack(frame);
  if (lengthResult.error) return lengthResult.error;

  // Gas calculation + copying logic
  // See full implementation in codebase

  frame.pc += 1;
  return null;
}

References

Yellow Paper - Section 9.1
EVM Codes - CALLDATACOPY

CALLDATASIZE (0x36)CODESIZE (0x38)

​Overview

​Specification

​Behavior

​Examples

​Basic Copy

​Proxy Pattern

​Gas Cost

​Common Usage

​Forwarding Calls

​Security

​Bounds Validation

​Implementation

​References

Overview

Specification

Behavior

Examples

Basic Copy

Proxy Pattern

Gas Cost

Common Usage

Forwarding Calls

Security

Bounds Validation

Implementation

References